The disclosure of Japanese Patent Application No. 2002-365609 filed on Dec. 17, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a pressure/temperature calculation apparatus of an internal combustion engine.
2. Description of Related Art
For example, Japanese Laid-open Patent Publication No. 2002-147279 (JP-A-2002-147279) discloses a method of calculating the pressure in an intake pipe of an internal combustion engine, based on the law of conservation of mass or the law of conservation of energy established between air flowing from the atmosphere into the intake pipe, and gas (e.g., exhaust gas) other than the air, which flows into the intake pipe.
As is understood from the whole description of JP-A-2002-147279, the method as disclosed in this publication has been developed on the assumption that the gas (other than the air) flowing into the intake pipe diffuses throughout the intake pipe. In fact, the gas (other than the air) flowing into the intake pipe does not diffuse uniformly throughout the intake pipe, but diffuses with a certain degree of distribution. Thus, the method as disclosed in JP-A-2002-147279 is still desired to be improved so that the pressure in the intake pipe can be calculated with higher accuracy.
It is therefore an object of the invention to accurately calculate the pressure and/or temperature in an intake pipe of an internal combustion engine.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention a pressure/temperature calculation apparatus of an internal combustion engine in which an exhaust passage is connected to an intake passage downstream of a throttle valve via an exhaust gas recirculation passage, and an exhaust gas flow control valve adapted to control a flow rate of exhaust gas flowing in the exhaust gas recirculation passage is disposed in the exhaust gas recirculation passage, which apparatus includes a controller that calculates at least one of a pressure and a temperature in the intake passage downstream of the throttle valve, according to numerical calculations using an expression of a relationship established based on the law of conservation of mass among an amount of air passing the throttle valve and flowing into the intake passage downstream of the throttle valve, an amount of exhaust gas passing the exhaust gas flow control valve and flowing into the intake passage downstream of the throttle valve, and an amount of gas flowing from the intake passage downstream of the throttle valve into a cylinder of the engine, and an expression of a relationship established based on the law of conservation of energy among an amount of energy of the air passing the throttle valve and flowing into the intake passage downstream of the throttle valve, an amount of energy of the exhaust gas passing the exhaust gas flow control valve and flowing into the intake passage downstream of the throttle valve, and an amount of energy of the gas flowing from the intake passage downstream of the throttle valve into the cylinder of the engine.
According to the above aspect of the invention, at least one of the pressure and temperature in the intake passage is calculated by numerical calculations using an expression of a relationship established based on the law of conservation of mass and an expression of a relationship established based on the law of conservation of energy. Thus, the pressure and temperature in the intake passage are determined by simple numerical calculations, without using a large number of sensors and/or maps.
Since there is no need to use a large number of sensors as described above, the number of sensors can be reduced, and the manufacturing cost can be accordingly reduced. Furthermore, since there is no need to use a large number of maps, an effort in preparing maps can be reduced.
The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of exemplary embodiments with reference to the accompanying drawings, in which like numerals are used to represent like elements and wherein:
FIG. 16A and
FIG. 17A and
FIG. 20A and
FIG. 22A through
FIG. 24A and
FIG. 27A and
FIG. 32A through
FIG. 35A through
FIG. 37A and
An exemplary embodiment of the invention will be described with reference to the drawings.
In
The intake port 7 is connected to a surge tank 14 via an intake branch pipe 13 provided for each cylinder 5, and the surge tank 14 is connected to an air cleaner 16 via an upstream-side intake pipe 15. A throttle valve 18 adapted to be driven by a step motor 17 is disposed in the upstream-side intake pipe 15.
On the other hand, the exhaust port 9 is connected to an exhaust pipe 19, which is in turn connected to an emission control device 20. The exhaust pipe 19 is also connected to the intake branch pipe 13 via an exhaust gas recirculation passage (which will be called “EGR passage”) 21. An EGR control valve 22 for controlling the flow rate of exhaust gas flowing in the EGR passage 21 is disposed in the EGR passage 21. With this arrangement, exhaust gas discharged from the cylinder 5 of the engine is inducted or drawn into the cylinder 5 again via the EGR passage 21. In the present specification, the exhaust gas recirculated into the cylinder 5 via the EGR passage 21 will be called “EGR gas” when appropriate.
An electronic control unit (ECU) 31 consists of a digital computer, and includes RAM (random access memory) 33, ROM (read-only memory) 34, CPU (microprocessor) 35, an input port 36 and an output port 37, which are connected to each other by a bi-directional bus 32.
To the intake branch pipe 13 is attached an intake pipe pressure sensor 40 for detecting the pressure in the intake branch pipe 13 (which will be called “intake pipe pressure”). The intake pipe pressure sensor 40 generates an output voltage that is proportional to the intake pipe pressure, and the input port 36 receives the output voltage via a corresponding A/D converter 38.
The engine also includes a throttle opening sensor 43 for detecting the opening angle of the throttle valve 18, an atmospheric pressure sensor 44 for detecting the pressure of the atmosphere around the engine or the pressure (intake pressure) of air drawn into the upstream-side intake pipe 15, and an atmospheric temperature sensor 45 for detecting the temperature of the atmosphere around the engine or the temperature (intake temperature) of air drawn into the upstream-side intake pipe 15. These sensors 44, 45 generate output voltages proportional to the pressure and temperature of the atmosphere, respectively, and the input port 36 receives these output voltages via corresponding A/D converters 38.
A load sensor 47, which is connected to an accelerator pedal 46, is operable to generate an output voltage proportional to an amount of depression of the accelerator pedal 46. The input port 36 receives the output voltage of the load sensor 47 via a corresponding A/D converter 38.
The engine also includes a crank angle sensor 48. For example, the crank angle sensor 48 generates an output pulse each time the crankshaft rotates 30 degrees, and the input port 36 receives the output pulse. The CPU 35 calculates the engine speed from the output pulses of the crank angle sensor 48.
On the other hand, the output port 37 is connected to the ignition plug 10, fuel injector 11, step motor 17 and the EGR control valve 22, via corresponding drive circuits 39. The ECU 31 calculates the opening angle of the EGR control valve 22, based on a step signal transmitted from the output port 37 to the EGR control valve 22.
In the meantime, the amount of fuel to be injected from the fuel injector 10 into the cylinder 5 (which will be simply called “fuel injection amount”) is determined based on the amount of air charged in the cylinder 5, so that the air/fuel ratio of an air-fuel mixture in the cylinder 4 becomes equal to a target air/fuel ratio. To accurately control the air/fuel ratio of the mixture in the cylinder 5 to the target air/fuel ratio, therefore, it is necessary to accurately determine the amount of the air charged in the cylinder 5 (which will be called “in-cylinder charged air amount”).
Here, an example of a method of estimating the in-cylinder charged air amount will be described. Initially, an air flow meter for detecting the mass flow of air passing the throttle valve 18 and other sensor are mounted in the engine, and a map or maps for calculating the in-cylinder charged air amount based on output values of these sensors as variables is/are prepared in advance. In the method, the in-cylinder charged air amount is estimated from the output values of the sensors and the map(s).
When the in-cylinder charged air amount is estimated by using the maps, the number of the maps and their arguments must be large enough to ensure high accuracy in estimating the in-cylinder charged air amount. If the number of the maps is increased, however, the storage capacity of the ROM 34 that stores these maps needs to be increased, resulting in an increase in the cost of the engine.
Also, when the in-cylinder charged air amount is estimated by using the maps, the maps must be prepared for each type of engine, or for each of individual engines of the same type, resulting in increased effort in preparing the maps. If the number of arguments of the maps is increased in an attempt to accurately estimate the in-cylinder charged air amount, on the other hand, the effort in preparing the maps is greatly increased.
In view of the above problems, a method of calculating the in-cylinder charged air amount through numerical computations utilizing mathematical expressions or equations derived from models, rather than maps, has been studied and proposed by the assignee of the present application. This method is disclosed in, for example, WO 03/033897.
The proposed method is applied to an internal combustion engine having no EGR system for recirculating exhaust gas into cylinders, and thus cannot be applied as it is to the engine of the present embodiment equipped with the EGR system. However, this method will be useful in understanding of a method (as described later) that is applicable to the present embodiment, and thus will be described herein.
The method proposed by the assignee of the present application is derived from a model (which will be called “in-cylinder gas amount model”) as shown in FIG. 2. The in-cylinder gas amount model M20 as shown in
The throttle model M21 receives the opening angle (throttle opening) θt of the throttle valve 18 detected by the throttle opening sensor 43, pressure (atmospheric pressure) Pa detected by the atmospheric pressure sensor 45, atmospheric temperature Ta detected by the atmospheric temperature sensor 44, and the pressure Pm in the intake branch pipe 13 which is calculated by the intake pipe model M22. The pressure in the intake branch pipe 13 will be hereinafter called “intake pipe pressure”. The throttle model M21 calculates the amount mt of air passing the throttle valve 18 per unit time (which will be called “throttle passing air flow rate mt”), based on these input parameters.
The intake pipe model M22 receives the throttle passing air flow rate mt calculated by the above-described throttle model M21, the amount mc of gas that flows into the cylinder 5 per unit time, which is calculated by the intake valve model M23 and will be called “cylinder incoming gas flow rate”), and the atmospheric temperature Ta. The intake pipe model M22 calculates the intake pipe pressure Pm and the temperature Tm in the intake branch pipe 13 (which will be called “intake pipe temperature”), from these input parameters.
The intake valve model M23 receives the intake pipe pressure Pm calculated by the above-described intake pipe model M22, intake pipe temperature Tm and the atmospheric temperature Ta, and calculates the cylinder incoming gas flow rate mc from these input parameters.
According to this method, the in-cylinder gas amount model M20 calculates the amount Mc of gas that has entered the cylinder 5 at the cylinder incoming gas flow rate mc, as described later. The gas amount Mc thus calculated will be called “in-cylinder charged gas amount”.
As is understood from
Next, each of the models M21 to M23 will be described in detail. The throttle model M21 calculates the throttle passing air flow rate mt by substituting the atmospheric pressure Pa, atmospheric temperature Ta, intake pipe pressure Pm and the throttle opening θt into the following equation (1), and solving this equation (1).
In the above equation (1), μt is flow coefficient at the throttle valve 18, which is a function of the throttle opening θt and is determined from a map as shown in
In the same equation (1), Φ(Pm/Pa) is a function using Pm/Pa as a variable, and is expressed by the following equation (2):
where κ is ratio of specific heat, and is a fixed or constant value in this method.
The above-indicated function Φ(Pm/Pa) and Pm/Pa has a relationship as shown in FIG. 5. It is thus possible to store in advance a map for calculating the function ((Pm/Pa) using Pm/Pa as a variable in the ROM 34, instead of the above equation (2), and calculate the value of the function Φ(Pm/Pa) from Pm/Pa and this map.
The above-indicated equations (1) and (2) are derived on the basis of a model as shown in
Next, the intake pipe model M22 will be described. The intake pipe model M22 calculates the intake pipe pressure Pm and the intake pipe temperature Tm by substituting the throttle passing air flow rate mt, cylinder incoming gas flow rate mc and the atmospheric temperature Ta into the following equations (3) and (4), and solving these equations.
In the above equations (3) and (4), V is a total volume of the intake pipe 15, surge tank 14, intake branch pipe 13 and the intake port 7 (which will be called “intake pipe portion” that extends from the throttle valve 18 to the intake valve 6), and is usually a fixed value.
The above-indicated equations (3) and (4) are derived on the basis of a model as shown in
More specifically, the amount of change of the total air amount M in the intake pipe portion with time is expressed by the following equation (5) based on the law of conservation of mass. This equation (5) indicates that the rate of change of the total air amount M is equal to a difference between the flow rate mt of the air flowing into the intake pipe portion (i.e., throttle passing air flow rate) and the flow rate mc of the air flowing from the intake pipe portion into the cylinder (i.e., cylinder incoming gas flow rate).
The above-indicated equation (3) is derived from the above equation (5) and the equation of state of gas (Pm·V=M·R*·Tm).
Also, where the atmospheric temperature Ta represents the temperature of the air flowing into the intake pipe portion, and the intake pipe temperature Tm represents the temperature of the air flowing from the intake pipe portion into the cylinder, the amount of change of the energy M·Cv·Tm of the air in the intake pipe portion with time is expressed by the following equation (6) based on the law of conservation of energy. This equation (6) indicates that the rate of change of the energy M·Cv·Tm is equal to a difference between the amount of energy of the air flowing into the intake pipe portion and the amount of energy of the air flowing from the intake pipe portion into the cylinder.
The above-indicated equation (4) is derived from the above equation (6) and the above-described equation of state of gas.
Next, the intake valve model M23 will be described. The intake valve model M23 calculates the cylinder incoming gas flow rate mc by substituting the intake pipe pressure Pm, intake pipe pressure Tm and the atmospheric temperature Ta into the following expression (7), and solving this equation.
In the above expression (7), “a” and “b” are values determined by using the engine speed NE as a variable. In the case where at least one of the valve timing corresponding to the valve closing time or valve opening time of the intake valve 6 and the working or operation angle corresponding to the opening duration of the intake valve 6 can be changed in the engine, “a” and “b” are determined by using the engine speed NE, the valve timing and/or phase angle of the intake valve 6 as variables. In other words, “a” is proportional coefficient, and “b” represents the amount of gas remaining in the cylinder 5 at the time of closing of the exhaust valve 8.
In the expression (7), since the intake pipe temperature Tm may greatly change while the engine is in varying operating conditions (i.e., during transient engine operation), Ta/Tm derived from the theoretical and empirical rules is used as a correction factor for compensating for changes in the intake pipe temperature Tm.
The above-indicated expression (7) is derived from the theoretical and empirical rules, on the basis of a model as shown in
The in-cylinder charged gas amount Mc is established at the time of closing of the intake valve 6, and is proportional to the pressure in the cylinder 5 at the time of closing of the intake valve 6. Since the pressure in the cylinder 5 at the time of closing of the intake valve 6 is regarded as being equal to the pressure Pm of the air upstream of the intake valve 6 (i.e., the intake pipe pressure), the in-cylinder charged gas amount Mc may be approximated to be proportional to the intake pipe pressure Pm.
On the other hand, the in-cylinder charged gas amount Mc is determined by integrating the flow rate (cylinder incoming flow rate) mc of the air flowing into the cylinder 5 with respect to time, over the opening duration of the intake pipe 6. Namely, the in-cylinder charged gas amount Mc and the cylinder incoming gas flow rate mc has a relationship that the in-cylinder charged gas amount Mc is a time integral value of the cylinder incoming gas flow rate mc.
Thus, since the in-cylinder charged gas amount Mc is proportional to the intake pipe pressure Pm, and is also a time integral value of the cylinder incoming gas flow rate mc, the cylinder incoming gas flow rate mc may also be regarded as being proportional to the intake pipe pressure Pm.
In this method, therefore, the above-indicated equation (7) is derived from the theoretical and empirical rules, on the assumption that the cylinder incoming gas flow rate mc is proportional to the intake pipe pressure Pm.
It is to be noted that the cylinder incoming gas flow rate mc calculated according to the equation (7) is the average value of the amount of the air flowing out of the intake pipe portion per unit time. Thus, the in-cylinder charged gas amount Mc for each cylinder 5 is calculated by multiplying the cylinder incoming gas flow rate mc by time obtained by dividing the time required for one cycle of the engine by the number of cylinders in the engine.
The above-described calculation of the in-cylinder charged gas amount Mc will be described with reference to
The average value of the flow rate of air flowing out of the intake pipe portion (which is indicated by the solid line in
Next, a method of calculating the in-cylinder charged gas amount Mc when the above-described in-cylinder gas amount model M20 is actually installed in the engine will be described.
While the in-cylinder charged gas amount Mc is calculated according to the above equations (1)-(4) and (7) of the respective models of the in-cylinder gas amount model M20, these five equations are discretely expressed so as to permit processing by the ECU 31 when the model M20 is actually installed in the engine. Namely, where t represents time and Δt represents calculation interval (calculation period), these five equations (1)-(4) and (7) are discretely expressed by the following equations (8)-(12).
The in-cylinder gas amount model M20 thus discretely expressed and actually installed in the engine calculates the intake pipe pressure Pm(t+Δt) and intake pipe temperature Tm(t+Δt) at time (t+Δt), by substituting the throttle passing air flow rate mt(t) at time t, which is calculated by the throttle model M21, the cylinder incoming gas flow rate mc(t) at time t, which is calculated by the intake valve model M23, and the intake pipe temperature Tm(t) at time t into the expressions (10) and (11) of the intake pipe model M22, and solving these equations (10) and (11).
Then, the intake pipe pressure Pm(t+Δt) calculated by the intake pipe model M22 and the throttle opening θt(t) at time t are substituted into the equations (8) and (9) of the throttle model M21. By solving these equations, the throttle passing air flow rate mt(t+Δt) at time (t+Δt) is calculated.
Furthermore, the intake pipe pressure Pm(t+Δt) and the intake pipe temperature Tm(t+Δt) calculated by the intake pipe model M22 are substituted into the equation (12) of the intake valve model M23, and the cylinder incoming gas flow rate mc(t+Δt) at time (t+Δt) is calculated by solving this equation.
By repeating the above calculations, the cylinder incoming gas flow rate mc at a certain point of time is calculated. Then, the in-cylinder charged gas amount Mc for each cylinder at a certain point of time is calculated by multiplying the thus calculated cylinder incoming gas flow rate mc by time obtained by dividing the time required for one cycle by the number of cylinders, as described above.
Upon a start of the engine, namely, at time t=0, the calculations by the models M21-M23 are started on the assumptions that the intake pipe pressure Pm is equal to the atmospheric pressure Pa(Pm(0)=Pa) and that the intake pipe temperature Tm is equal to the atmospheric temperature Ta(Tm(0)=Ta).
As the atmospheric pressure Pa and the atmospheric temperature Ta used by the above-described in-cylinder gas amount model M20 may be always used the atmospheric pressure and atmospheric temperature detected at the time when the calculation of the model M20 is started, or may be used the atmospheric pressure Pa(t) and atmospheric temperature Ta(t) detected at time t.
Next, an in-cylinder gas amount model, which is applicable to the engine equipped with the EGR system as shown in
Where the flow rate of air (fresh air) contained in the gas flowing into the cylinder is called “cylinder incoming fresh air flow rate mc-air”, the cylinder incoming fresh air flow rate mc-air is calculated according to the following equation (13).
mc-air=mc−mc-egr (13)
In the above equation (13), mc is cylinder incoming gas flow rate as the flow rate of gas flowing into the cylinder, and mc-egr is cylinder incoming EGR gas flow rate as the flow rate of exhaust gas contained in the gas flowing into the cylinder.
When the engine is in a steady-state operation (for example, when the throttle opening, EGR opening and the engine speed are kept substantially constant), the flow rate megr of exhaust gas passing the EGR control valve 22 (which will be called “EGR valve passing gas flow rate”) is equal to the cylinder incoming EGR gas flow rate mc-egr (mc-egr=megr). In this case, therefore, the above equation (13) is rewritten into the following equation (14).
mc-air=mc−megr (14)
If the cylinder incoming gas flow rate mc and the EGR valve passing gas flow rate megr are determined, therefore, the cylinder incoming fresh air flow rate mc-air is determined. Accordingly, an in-cylinder charged fresh air amount Mc-air as the amount of air (fresh air) contained in the cylinder 5 at the time of closing of the intake valve 6 is determined.
In the first embodiment, a model M10 as shown in
The throttle model M11 is the same model as the throttle model M21 shown in
The intake pipe model M12 receives the throttle passing air flow rate mt calculated by the throttle model M11, cylinder incoming gas flow rate mc calculated by the intake valve model M13, atmospheric temperature Ta, and the amount megr of exhaust gas passing the EGR control valve 22 per unit time (which will be called “EGR valve passing gas flow rate megr), which is calculated by the EGR control valve model M14. The intake pipe model M12 then calculates the intake pipe pressure Pm and the intake pipe temperature Tm based on the input parameters.
The EGR control valve model M14 receives the EGR opening θe, atmospheric pressure Pa, atmospheric temperature Ta, intake pipe pressure Pm calculated by the intake pipe model M12 and the exhaust temperature Te, and calculates the EGR valve passing gas flow rate megr based on these input parameters.
As is understood from
Next, the intake pipe model M12 and the EGR control valve model M14 will be described in detail.
The intake pipe model M12 calculates the intake pipe pressure Pm and the intake pipe temperature Tm by substituting the throttle passing air flow rate mt, cylinder incoming gas flow rate mc, atmospheric temperature Ta, EGR valve passing gas flow rate megr and the exhaust temperature Te into the following equations (15) and (16), and solving these equations. In the equations (15) and (16), V is volume of the intake pipe portion extending from the throttle valve 18 to the intake valve 6, and is usually a fixed value.
As explained above with respect to the intake pipe model M22, the equations (15) and (16) are derived on the basis of a model as shown in
The EGR control valve model M14 calculates the EGR valve passing gas flow rate megr by substituting the EGR opening θe, intake pipe pressure Pm, exhaust pressure Pe and the exhaust temperature Te into the following expression (17).
In the above equation (17), μe is flow coefficient at the EGR control valve 22, which is a function of the EGR opening θe, and Ae is opening cross-sectional area of the EGR control valve 22, which is a function of the EGR opening θe. Also, R is a constant related to a gas constant, namely, a value obtained by dividing the gas constant R* by the mass Me of exhaust gas per mole (R=R*/Me). Pe is pressure of exhaust gas upstream of the EGR control valve 22, and Te is temperature of the exhaust gas upstream of the EGR control valve 22.
In the same equation (17), Φ(Pm/Pe) is a function using Pm/Pe as a variable, and is expressed by the following equation (18).
The above equation (18) is obtained by replacing variable Pm/Pa of the above-indicated equation (2) by variable Pm/Pe. In the equation (18), κ is ratio of specific heat, and is a fixed value in this embodiment.
The above-indicated function Φ(Pm/Pe) and Pm/Pe have a relationship similar to that as shown in FIG. 5. Thus, a map for calculating the function Φ(Pm/Pe) using Pm/Pe as a variable may be stored in advance in the ROM 34, in place of the above equation (18), and the value of the function ((Pm/Pe) may be calculated from Pm/Pe and this map.
The above-indicated equations (17) and (18) are derived on the basis of a model as shown in
In the present embodiment as described above, the EGR valve passing gas flow rate is calculated by substituting the exhaust pressure Pe, exhaust temperature Te, intake pipe pressure Pm and the EGR opening θe into the mathematical equations, and performing numerical computations. Accordingly, the number of maps used for the computations is reduced, and the effort in preparing the maps can be significantly reduced.
Next, a method of calculating an in-cylinder charged fresh air amount Mc-air when the in-cylinder gas amount model M10 is actually installed in the engine will be described.
While the in-cylinder charged gas amount Mc-air is calculated according to the above-indicated equations (1), (2), (7) and (15)-(18) of the respective models of the in-cylinder gas amount model M10, these seven equations are discretely expressed so as to permit processing by the ECU 31 when the model M10 is actually installed in the engine. Namely, where t represents time and Δt represents calculation interval (calculation period), the equations (1), (2) and (7) are discretely expressed by the above-indicated equations (8), (9) and (12), respectively, and the equations (15)-(18) are discretely expressed by the following equations (19)-(22).
Also, the equations for calculating the exhaust pressure Pe and the exhaust temperature Te are discretely expressed by the following equations (23) and (24). These equations will be described in detail later.
Pe(t)=ƒ1(KL(t), NE(t)) (23)
Te(t)=ƒ2(megr(t−Δt), NE(t)) (24)
The in-cylinder gas amount model M10 thus discretely expressed and actually installed in the engine calculates the intake pipe pressure Pm(t+Δt) and intake pipe temperature Tm(t+Δt) at time (t+Δt), by substituting the throttle passing air flow rate mt(t) at time t, which is calculated by the throttle model M11, EGR valve passing gas flow rate megr(t) at time t, which is calculated by the EGR control valve model M14, cylinder incoming gas flow rate mc(t) at time t, which is calculated by the intake valve model M13, and the exhaust temperature Te(t) at time t into the equations (19) and (20) of the intake pipe model M12, and solving these equations (19) and (20).
The throttle passing air flow rate mt(t+Δt) at time (t+Δt) is calculated by substituting the intake pipe pressure Pm(t+Δt) at time (t+Δt), which is calculated by the intake pipe model M12, and the throttle opening θt(t+Δt) at time (t+Δt) into the above equations (8) and (9) of the throttle model M11, and solving these equations.
The cylinder incoming gas flow rate mc(t+Δt) at time (t+Δt) is calculated by substituting the intake pipe pressure Pm(t+Δt) and intake pipe temperature Tm(t+Δt) at time (t+Δt), which are calculated by the intake pipe model M12, into the equation (12) of the intake valve model M13, and solving this equation.
The cylinder incoming fresh air flow rate mc-air(t+Δt) at time (t+Δt) is calculated by substituting the cylinder incoming gas flow rate mc(t+Δt) at time (t+Δt), which is calculated by the intake pipe model M12, and the EGR valve passing gas flow rate megr(t) at time t, which was calculated by the EGR control valve model M14 in the last control cycle, into the equation (14), and solving this equation.
The EGR valve passing gas flow rate megr(t+Δt) at time (t+Δt) is calculated by substituting the intake pipe pressure Pm(t+Δt) at time (t+Δt), which is calculated by the intake pipe model M12, exhaust pressure Pe(t+Δt) at time (t+Δt) and the EGR opening θe(t+Δt) at time (t+Δt) into the equations (21) and (22) of the EGR control valve model M14, and solving these equations.
The exhaust pressure Pe(t+Δt) at time (t+Δt) is calculated by substituting the engine load factor KL(t+Δt) at time (t+Δt) and the engine speed NE at time (t+Δt) into the equation (23), and solving this equation. Also, the exhaust temperature Te(t+Δt) at time (t+Δt) is calculated by substituting the EGR valve passing gas flow rate megr(t) at time t and the engine speed NE(t+Δt) at time (t+Δt) into the equation (24), and solving this equation.
The mc(t+Δt), megr(t+Δt) and mt(t+Δt) calculated as described above are substituted again into the equations (19) and (20) of the intake pipe model M12.
By repeating the above calculations, the cylinder incoming fresh air flow rate mc-air at a certain point of time is calculated. Then, the in-cylinder charged fresh air amount Mc-air for each cylinder at a certain point of time is calculated by multiplying the thus calculated cylinder incoming fresh air flow rate mc-air by time obtained by dividing the time required for one cycle by the number of cylinders, as described above.
Upon a start of the engine, namely, at time t=0, the calculations by the models M11-M13 are started on the assumptions that the intake pipe pressure Pm is equal to the atmospheric pressure Pa(Pm(0)=Pa), and that the intake pipe temperature Tm and the exhaust temperature Te are equal to the atmospheric temperature Ta(Tm(0)=Ta, Te(0)=Ta).
As the atmospheric pressure Pa and the atmospheric temperature Ta used by the above-described in-cylinder gas amount model M10 may be usually used the atmospheric pressure and the atmospheric temperature detected at the time when the calculation of the model M10 is started, or may be used the atmospheric pressure Pa(t) and the atmospheric temperature Ta(t) detected at time t.
In the present embodiment, the EGR valve passing gas flow rate megr is calculated from the equation (17) using four parameters, i.e., the exhaust pressure Pe, exhaust temperature Te, intake pipe pressure Pm and the EGR opening θe. However, the EGR valve passing gas flow rate megr may be determined from an equation that uses these four parameters but is different from the equation (17), or may be determined from a map using these four parameters as arguments.
Since the EGR valve passing gas flow rate is calculated with high accuracy according to the present embodiment, the in-cylinder charged fresh air amount is also calculated with high accuracy based on the EGR valve passing gas flow rate, and therefore the fuel injection amount for making the air/fuel ratio equal to the target air/fuel ratio is calculated with high accuracy.
Furthermore, the opening angle of the EGR control valve 22 may be feedback-controlled by using the EGR valve passing gas flow rate calculated according to the present embodiment, so that the EGR valve passing gas flow rate becomes equal to a target value thereof.
Next, a method of deriving the above-indicated equation (23) for calculating the exhaust pressure will be described.
The engine load factor (%) is the ratio of the amount (g) of air actually contained in the cylinder to the amount (g) of gas that fills the maximum volume of the cylinder under standard conditions. The engine load factor (%) is determined from the following equation (25).
In the above equation (25), Mc-air is in-cylinder charged fresh air amount (g) as the amount of fresh air charged in each cylinder at the time when the intake valve is closed, and DSP is displacement (liter) of the engine. In the same equation, NCYL is the number of cylinders, and ρastd is density (about 1.2 g/liter) of air under standard conditions (i.e., at 1 atmospheric pressure, 25° C.).
Referring to
Accordingly, the exhaust pressure Pe may be expressed by function f1(KL, NE) using the engine load factor KL and the engine speed NE as variables, as indicated in the equation (23). In the first embodiment, the function f1(KL, NE) is stored in advance in the ROM 34 in the form of a map having the engine load factor KL and the engine speed NE as variables, and the exhaust pressure Pe is calculated from the engine load factor KL, engine speed NE and this map.
The above arrangement eliminates a need to provide the engine with a sensor for detecting the exhaust pressure, and thus permits accurate detection of the exhaust pressure without increasing the cost of the engine. With the exhaust pressure thus accurately determined, the EGR valve passing gas flow rate megr can be calculated with high accuracy.
In this connection, a conventional method of determining the exhaust pressure by using a map, without using a sensor, in the engine equipped with the EGR system employs a map having, as arguments, a large number of parameters, such as the engine speed, fuel injection amount, fuel ignition timing, and the EGR rate (the ratio of the amount (g) of exhaust gas to the amount (g) of gas contained in the cylinder). In the present embodiment, on the other hand, the engine load factor is employed as a parameter, and the map having only the engine load factor and the engine speed as arguments is used, which leads to a reduction in the effort in preparing the map. Needless to say, the exhaust pressure may be detected by using a sensor if the resulting increase in the cost of the engine does not matter.
When the exhaust pressure is calculated from the above-described function f1, the in-cylinder charged fresh air flow rate mc-air may be used as a variable, in place of the engine speed NE.
Next, a method of deriving the equation (24) for calculating the exhaust temperature Te will be described.
The quantity of heat produced by exhaust gas that newly flows into the EGR passage 21 will be called “input heat quantity”, and the quantity of heat dissipated from the EGR passage 21 to the atmosphere will be called “dissipated heat quantity”. If the EGR valve passing gas flow rate megr increases, namely, if the amount of exhaust gas flowing into the EGR passage 21 increases, the input heat quantity becomes larger than the dissipated heat quantity. Accordingly, if the EGR valve passing gas flow rate megr increases, the exhaust temperature rises. Meanwhile, if the engine speed increases, the temperature of exhaust gas discharged from the cylinders rises. Thus, the EGR valve passing gas flow rate megr, engine speed NE and the exhaust temperature Te have relationships as shown in FIG. 14.
Since the exhaust temperature Te mainly and greatly depends upon the EGR valve passing gas flow rate megr and the engine speed NE, the exhaust temperature determined based on the EGR valve passing gas flow rate megr and the engine speed NE has a relatively high degree of accuracy.
Accordingly, the exhaust temperature Te can be expressed by function f2(megr, NE) having the EGR valve passing gas flow rate megr and the engine speed NE as variables, as indicated above in the equation (24). In the first embodiment, the function f2(megr, NE) is stored in advance in the ROM 34 in the form of a map having the EGR valve passing gas flow rate megr and the engine speed NE as variables, and the exhaust temperature Te is calculated from the EGR valve passing gas flow rate megr, engine speed NE and this map.
The above arrangement eliminates a need to provide the engine with a sensor for detecting the exhaust temperature, and thus permits accurate detection of the exhaust temperature without increasing the cost of the engine. With the exhaust temperature thus accurately determined, the EGR valve passing gas flow rate megr can be calculated with high accuracy. Needless to say, the exhaust temperature may be detected by using a sensor if the resulting increase in the cost of the engine does not matter.
Since the temperature of the exhaust gas discharged from the cylinder varies depending upon the engine speed NE, the exhaust gas temperature may be determined from a one-dimensional map having the engine speed NE as an argument. However, the EGR control valve model M14 is able to calculate the EGR valve passing gas flow rate megr with higher accuracy by using the temperature of exhaust gas upstream of the EGR control valve 22 as the exhaust temperature Te, rather than using the temperature of exhaust gas discharged from the cylinder as the exhaust temperature Te.
In the present embodiment, the temperature of the exhaust gas upstream of the EGR control valve 22 is used as the exhaust temperature Te for use in calculation of the EGR valve passing gas flow rate megr, and therefore the EGR valve passing gas flow rate megr can be calculated with high accuracy.
When the exhaust temperature is calculated from the above-indicated function f2, the in-cylinder charged fresh air flow rate mc-air may be used as a variable, instead of the engine speed NE.
In the above-described embodiment, various calculations or computations are performed on the assumption that the engine is in a steady-state operation, in which the flow rate of exhaust gas flowing into the intake pipe portion (which will be called “pipe incoming exhaust gas flow rate”) is supposed to be equal to the EGR valve passing gas flow rate, and the flow rate of exhaust gas flowing into the cylinder (which will be called “cylinder incoming exhaust gas flow rate”) is also supposed to be equal to the EGR valve passing gas flow rate.
However, if the EGR opening and the EGR valve passing gas flow rate change during transient operation of the engine, for example, the pipe incoming exhaust gas flow rate and the cylinder incoming exhaust gas flow rate temporarily become different from the EGR valve passing gas flow rate. Namely, the pipe incoming exhaust gas flow rate and the cylinder incoming exhaust gas flow rate follow changes in the EGR valve passing gas flow rate, but change with certain delay.
To maintain high accuracy of the parameter values calculated in the above-described embodiment during transient engine operation, therefore, it needs to be taken into consideration that the pipe incoming exhaust gas flow rate and the cylinder incoming exhaust gas flow rate change with delay in response to changes in the EGR valve passing gas flow rate.
The variation in the pipe incoming exhaust gas flow rate in response to a change in the EGR valve passing gas flow rate will be now discussed. As shown in
The above-indicated time Td is a period of time required for the exhaust gas passing the EGR control valve 22 to reach the intake pipe portion. The time period Td becomes shorter as the flow rate or speed of the exhaust gas passing the EGR control valve 22 is greater, or the intake pipe pressure is lower, or the engine speed is higher. Namely, the time Td (which will be called “waste time”) is a function of the engine speed, as shown in FIG. 16A.
Meanwhile, the time constant τ of the first lag represents the likelihood of diffusion of the exhaust gas that has passed the EGR control valve 22. Thus, the time constant τ is reduced as the flow rate or speed of the exhaust gas passing the EGR control valve 22 is greater, or the intake pipe pressure is lower, or the engine speed is higher. Namely, the time constant τ is also a function of the engine speed, as shown in FIG. 16B.
In the present embodiment, the waste time Td1 is stored in advance in the ROM 34 in the form of a map as shown in FIG. 16A. When the EGR valve passing gas flow rate changes, the waste time Td1 is calculated based on the engine speed NE, and the pipe incoming exhaust gas flow rate is calculated on the assumption that the pipe incoming exhaust gas flow rate starts changing toward the EGR valve passing gas flow rate upon a lapse of the waste time Td1.
In the present embodiment, the time constant τ1 is stored in advance in the ROM 34 in the form of a map as shown in FIG. 16B. When the EGR valve passing gas flow rate changes, the time constant τ1 is calculated based on the engine speed NE, and the pipe incoming exhaust gas flow rate is calculated on the assumption that the pipe incoming exhaust gas flow rate changes toward the EGR valve passing gas flow rate with the time constant τ1 after the waste time Td1.
The above concepts of the waste time and the first lag regarding the pipe incoming exhaust gas flow rate are equally applied to those regarding the cylinder incoming gas flow rate.
In the present embodiment, the waste time Td2 associated with the cylinder incoming exhaust gas flow rate is stored in advance in the ROM 34 in the form of a map as shown in FIG. 17A. When the EGR valve passing gas flow rate changes, the waste time Td2 is calculated based on the engine speed NE, and the cylinder incoming exhaust gas flow rate is calculated on the assumption that the cylinder incoming exhaust gas flow rate starts changing toward the EGR valve passing gas flow rate upon a lapse of the waste time Td2.
Also, the time constant τ2 is stored in advance in the ROM 34 in the form of a map as shown in FIG. 17B. When the EGR valve passing gas flow rate changes, the time constant τ2 is calculated based on the engine speed NE, and the cylinder incoming exhaust gas flow rate is calculated on the assumption that the cylinder incoming exhaust gas flow rate changes toward the EGR valve passing gas flow rate with the time constant τ2 after the waste time Td2.
Since the distance from the EGR control valve 22 to the cylinder is longer than the distance from the EGR control valve 22 to the intake pipe portion, the waste time Td2 associated with the cylinder incoming exhaust gas flow rate is likely to be longer than the waste time Td1 associated with the pipe incoming exhaust gas flow rate, and the time constant τ2 associated with the cylinder incoming exhaust gas flow rate is likely to be larger than the time constant τ1 associated with the pipe incoming exhaust gas flow rate.
While the EGR valve passing gas flow rate megr is calculated according to mathematical equations, i.e., the above-indicated equations (17) and (18) in the first embodiment, the inventors developed a method of relatively easily calculating the EGR valve passing gas flow rate megr, without using these equations. Thus, the EGR valve passing gas flow rate may be calculated by using the method as described below, instead of using the equations (17) and (18).
It is known that the in-cylinder charged gas amount Mc is represented by a linear function of the intake pipe pressure Pm detected at the time of closing of the intake valve 6. Namely, according to the theoretical and empirical rules, the in-cylinder charged gas amount Mc is proportional to the in-cylinder pressure detected at the time of closing of the intake valve 6, and the in-cylinder pressure is substantially equal to the pressure of the mixed gas present upstream of the intake valve 6, i.e., the intake pipe pressure Pm.
When no EGR gas is supplied to the intake system, only fresh air is drawn into the cylinder, and therefore the in-cylinder charged fresh air amount Mc-air at this time, or the engine load factor KL, can be represented by a linear function of the intake pipe pressure Pm. Thus, the engine load factor KL can be easily and accurately determined.
In the situation where EGR gas is supplied to the intake system, which is totally different from the above situation, EGR gas as well as fresh air is drawn or charged into the cylinder. Therefore, it was conventionally considered impossible to represent the in-cylinder charged fresh air amount Mc-air, or the engine load factor KL, by a linear function of the intake pipe pressure Pm.
If the in-cylinder charged EGR gas amount Mc-egr can be represented by a linear function of the intake pipe pressure Pm, the in-cylinder charged fresh air amount Mc-air, or the engine load factor KL, during supply of EGR gas, can be represented by a linear function of the intake pipe pressure Pm because the in-cylinder charged gas amount Mc can be represented by a linear function of the intake pipe pressure Pm, and the in-cylinder charged gas amount Mc is the sum of the in-cylinder charged fresh air amount Mc-air and the in-cylinder charged EGR gas amount Mc-egr.
However, it was also conventionally considered impossible to represent the in-cylinder charged EGR gas amount Mc-air by a linear function of the intake pipe pressure Pm. This will be explained with reference to FIG. 12 and FIG. 18.
As described above, the EGR valve passing gas flow rate megr(g/sec) is represented by the equation (17), and the function Φ(Pm/Pe) is expressed by the equation (18). Here, if the exhaust pressure Pe is regarded as being equivalent to the atmospheric pressure Pa for simplification of the calculations, the EGR valve passing gas flow rate megr calculated according to the equation (17) is plotted as shown in FIG. 18. Specifically, the EGR valve passing gas flow rate megr is kept substantially constant while the intake pipe pressure Pm is relatively small, and decreases nonlinearly with respect to the intake pipe pressure Pm (as indicated by NR in
As is understood from the above description, it was considered impossible to represent the EGR valve passing gas flow rate megr, in particular, the non-linear portion NR, by a linear function of the intake pipe pressure Pm. In this connection, if numerous expressions of linear functions are used, the EGR valve passing gas flow rate megr may be expressed by the linear functions of the intake pipe pressure Pm. In this case, however, it cannot be said that the engine load factor KL is calculated in a simple manner.
However, the inventors of the present application found that the EGR valve passing gas flow rate megr can be expressed by two linear functions of the intake pipe pressure Pm, and therefore the in-cylinder charged fresh air amount Mc-air, or the engine load factor KL, can be expressed by two linear functions of the intake pipe pressure Pm.
Referring first to
Also, function Φ(Pm/Pe) can be expressed by a linear function of the intake pipe pressure Pm. This will be explained with reference to FIG. 20A and FIG. 20B. Considering that the exhaust pressure Pe is not kept equal to a given atmospheric pressure Pa but varies depending upon the intake pipe pressure Pm, the value of the function Φ(Pm/Pe) obtained when the intake pipe pressure Pm is equal to Pm1 does not lie on curve Ca that reaches zero at the atmospheric pressure Pa, but lies on curve C1 that reaches zero at the exhaust pressure Pe1, as shown in
The plots (O) obtained in the above manner can be connected by straight line L2 as shown in FIG. 20B. Accordingly, the function Φ(Pm/Pe) can be expressed by a linear function of the intake pipe pressure Pm as represented by straight line L1 when the intake pipe pressure Pm is relatively small, and expressed by a linear function of the intake pipe pressure Pm as represented by straight line L2 when the intake pipe pressure Pm is relatively large. Thus, the function Φ(Pm/Pe) can be expressed by two linear functions of the intake pipe pressure Pm. It follows that the EGR valve passing gas flow rate megr can be expressed by two linear functions of the intake pipe pressure Pm.
While the engine is in a steady-state operation, the EGR valve passing gas flow rate megr (g/sec) and the cylinder incoming gas flow rate mc-egr (g/sec) are equal to each other. Also, the in-cylinder charged EGR gas amount Mc-egr is obtained by multiplying the cylinder incoming EGR gas flow rate mc-egr by time required for one suction stroke of each cylinder, namely, time ΔT(sec) as the ratio of the time required for one cycle of the engine to the number of cylinders (Mc-egr=mc-egr·ΔT). It follows that the in-cylinder charged EGR gas amount Mc-egr during steady-state engine operation can be expressed by linear functions of the intake pipe pressure Pm.
Accordingly, while the engine is in a steady-state operation and the EGR gas is supplied to the intake system, the in-cylinder charged fresh air amount Mc-air, or the engine load factor KL, can be expressed by two linear functions of the intake pipe pressure Pm.
In
Here, these two linear functions can be expressed by the following equations where e1, e2 denote the respective slopes of the two linear functions, and d, r denote intake pipe pressure and engine load factor at the connection point CP, respectively.
KLon=e1·(Pm−d)+r . . . Pm≦d
KLon=e2·(Pm−d)+r . . . Pm>d
These two equations may be expressed by the following equation (26).
KLon=e·(Pm−d)+r (26)
e=e1 . . . Pm≦d
e=e2 . . . Pm>d
In the present embodiment, the two linear functions of the intake pipe pressure Pm, which represent the engine load factor KLon during steady-state engine operation are stored in advance in the ROM 34 in the form of the equation (26) as indicated above. In this case, the two linear functions can be expressed by three parameters e, d and r. Namely, the number of parameters required for expressing the two linear functions can be reduced.
Each of the parameters e, d, r in the equation (26) is calculated according to the following equations:
e1=e1*·ktha
e2=e2*·ktha
d=d*·ktha·kpa
r=r*·ktha·kpa
where e1*, e2*, d* and r* are slopes, intake pipe pressure and engine load factor at the connection point when the ambient conditions of the engine are predetermined reference ambient conditions. While any conditions may be employed as the reference ambient conditions, standard conditions (1 atmospheric pressure, 25° C.) are used as the reference ambient conditions in the present embodiment.
In the above-indicated equations regarding the parameters e, d and r, ktha represents atmospheric temperature correction factor, and kpa represents atmospheric pressure correction factor. The atmospheric temperature correction factor ktha varies with the actual atmospheric temperature detected by the atmospheric temperature sensor 44, and is used for correcting each of the parameters e1*, e2*, d* and r* under the reference ambient conditions. This factor ktha is made equal to 1.0 when no correction is needed. The atmospheric pressure correction factor kpa varies with the actual atmospheric pressure detected by the atmospheric pressure sensor 45, and is used for correcting each of the parameters d*, r* under the reference ambient conditions. This factor kpa is made equal to 1.0 when no correction is needed.
Considering that the atmospheric temperature correction factor ktha and the atmospheric pressure correction factor kpa are representative values that represent the actual ambient conditions of the engine, it can be said that each of the parameters e1*, e2*, d* and r* under reference ambient conditions is corrected based on the values representative of the actual ambient conditions of the engine. It can also be said that the engine load factor KLon under the reference ambient conditions is corrected based on the values representative of the actual ambient conditions of the engine.
In the meantime, considering that the opening cross-sectional area Ae of the EGR control valve 22 in the equation (17) depends upon the EGR opening θe, and the engine charging efficiency depends upon the engine speed NE, the parameters e* (e1*, e2*), d* and r* are set depending upon the EGR opening θe or the engine speed NE.
More specifically described with reference to
The intake pipe pressure d* at the connection point CP decreases as the engine speed NE increases, as shown in FIG. 23. The intake pipe pressure d* at the connection point CP is also determined in advance through experiments, and is stored in advance in the ROM 34 in the form of a map as shown in
As shown in
Accordingly, it may be generally said that two linear functions of the intake pipe pressure Pm representing the in-cylinder charged fresh air amount Mc-air, or the engine load factor KLon, during steady-state engine operation are respectively determined and stored in advance, with respect to each of a plurality of different EGR openings θe. Also, two linear functions of the intake pipe pressure Pm representing the in-cylinder charged fresh air amount Mc-air, or the engine load factor KLon, during steady-state engine operation are respectively determined and stored in advance, with respect to each of a plurality of different engine speeds NE.
As described above, the engine load factor KLoff when no EGR gas is supplied to the intake system can be expressed by linear functions of the intake pipe pressure Pm.
Here, these two linear functions can be expressed by the following equations where a1, a2 denote the respective slopes of the two linear functions, and “d” and “c” denote intake pipe pressure and engine load factor at the connection point CP, respectively.
KLoff=a1·(Pm−d)+c . . . Pm≦d
KLoff=a2·(Pm−d)+c . . . Pm>d
These two equations may be expressed by the following equation (27).
KLoff=a·(Pm−d)+c (27)
a=a1 . . . Pm≦d
a=a2 . . . Pm>d
In the present embodiment, the two linear functions of the intake pipe pressure Pm, which represent the engine load factor KLoff during steady-state engine operation, are stored in advance in the ROM 34 in the form of the equation (27) as indicated above. In this case, the intake pipe pressure d at the connection point CP is identical with the intake pipe pressure d at the connection point CP associated with the engine load factor KLon as described above. Accordingly, the number of parameters can be further reduced. Needless to say, the intake pipe pressure at the connection point CP associated with the engine load factor KLoff may be difference from that associated with the engine load factor KLon.
The parameters a, c in the above equation (27) are respectively calculated according to the following equations:
a1=a1*·ktha
a2=a2*·ktha
c=c·ktha·kpa
where a1*, a2* and c* are slopes and engine load factor at the connection point when the ambient conditions of the engine are the above-described reference ambient conditions, namely, the standard conditions.
Considering that the atmospheric temperature correction factor ktha and the atmospheric pressure correction factor kpa are representative values that represent the actual ambient conditions of the engine, it can be said that each of the parameters a1*, a2* and c* under the reference ambient conditions is corrected based on the values representative of the actual ambient conditions of the engine. In other words, the engine load factor KLoff under the reference ambient conditions is corrected based on the values representative of the actual ambient conditions of the engine.
In the meantime, since the engine charging efficiency depends upon the engine speed NE, the parameters a* (a1*, a2*) and c* are set depending upon the engine speed NE in this embodiment.
More specifically described with reference to
As shown in
Accordingly, it may be generally said that two linear functions of the intake pipe pressure Pm representing the in-cylinder charged fresh air amount Mc-air, or the engine load factor KLoff, during steady-state engine operation are determined and stored in advance, with respect to each of a plurality of different engine speeds NE.
As is understood from the above description, if the intake pipe pressure Pm is detected by, for example, the pressure sensor 39, the engine load factor KLon or KLoff can be accurately and easily determined by using the above-indicated equation (26) or (27), based on the detected intake pipe pressure Pm. Consequently, the air/fuel ratio can be accurately and easily made equal to the target air/fuel ratio.
Since the engine load factor KLon, KLoff can be expressed by linear functions of the intake pipe pressure Pm as described above, there is no need to prepare a map representing the relationship between the engine load factor KLon, KLoff and the intake pipe pressure Pm, thus eliminating any effort in preparing the map. Also, there is no need to solve complicated equations, such as differential equations, and therefore the computing load of the CPU 34 can be reduced.
As is understood from the above equation (25), the engine load factor KL represents the in-cylinder charged fresh air amount Mc-air. Since the cylinder is charged solely with fresh air when no EGR gas is supplied to the intake system, the engine load factor KLoff obtained when no EGR gas is supplied may be considered to represent the total amount of gas that fills the cylinder, or the in-cylinder charged gas amount Mc.
Considering that the in-cylinder charged gas amount Mc does not change depending upon whether the EGR gas is supplied or not supplied, the engine load factor KLoff obtained when no EGR gas is supplied not only represents the in-cylinder charged gas amount Mc when no EGR gas is supplied, but also represents the in-cylinder charged gas amount Mc when EGR gas is supplied.
On the other hand, the in-cylinder charged fresh air amount Mc-air during steady-state engine operation with no EGR gas supplied is represented by the engine load factor KLon, as described above. Accordingly, a result ΔKL(=KLoff−KLon) obtained by subtracting the engine load factor KLon when the EGR gas is supplied from the engine load factor KLoff when no EGR gas is supplied is supposed to represent the in-cylinder charged EGR gas amount Mc-egr during steady-state engine operation.
More specifically, where KLoff is equal to KLoff1 and KLon is equal to KLon1 when Pm is equal to Pm1, as shown in
Accordingly, the in-cylinder charged EGR amount Mc-egr during steady-state engine operation can be calculated according to the following equation (28):
Mc-egr=kegr1·ΔKL (28)
where kegr1 is conversion factor at which the engine load factor KL is converted into the in-cylinder charged EGR gas amount Mc-egr, and KLoff and KLon represent engine load factors calculated according to the above-indicated equations (26), (27), respectively.
If the intake pipe pressure Pm is calculated according to the above-indicated mathematical equation, or is detected by the pressure sensor, therefore, the in-cylinder charged EGR gas amount Mc-egr during steady-state engine operation can be accurately and easily determined based on the intake pipe pressure Pm, by using the above-indicated equation (28).
In the meantime, the EGR valve passing gas flow rate megr and the cylinder incoming EGR gas flow rate mc-egr are equal to each other during steady-state engine operation, as described above, and the in-cylinder charged EGR gas amount Mc-egr is represented by the product of the cylinder incoming EGR gas flow rate mc-egr and ΔT(sec) (Mc-egr=megr·ΔT). Accordingly, the EGR valve passing flow rate megr during steady-state engine operation can also be expressed by using the above-described difference ΔKL.
In the present embodiment, the EGR valve passing gas flow rate megr during steady-state operation is calculated according to the following equation (29):
megr=kegr2·ΔKL (29)
where kegr2 is conversion factor at which the engine load factor KL is converted into the EGR valve passing gas flow rate megr, and KLoff and KLon represent engine load factors calculated according to the above-indicated equations (26), (27), respectively.
As explained above, the EGR valve passing gas flow rate megr during steady-state engine operation is calculated by using the above equation (29). However, the EGR valve passing gas flow rate megr during transient operation may also be calculated by using this equation (29).
The EGR valve passing gas flow rate megr greatly depends upon a pressure difference between the upstream and downstream sides of the EGR control valve 22, namely, a difference between the exhaust pressure Pe and the intake pipe pressure Pm. Assuming that the exhaust pressure Pe and exhaust temperature Te detected upstream of the EGR control valve 22 during transient operation are not so different from the exhaust pressure Pe and exhaust temperature Te detected during steady-state operation, the EGR valve passing gas flow rate megr is determined once the intake pipe pressure Pm is determined, no matter whether the engine is in a steady-state operation or in a transient operation.
Thus, the EGR valve passing gas flow rate megr during steady-state operation and transient operation can be accurately and easily determined based on the intake pipe pressure Pm by using the above-indicated equation (29). In this case, the in-cylinder charged EGR gas amount Mc-egr during steady-state operation may be calculated from the EGR valve passing gas flow rate megr during steady-state operation, or may be calculated from the difference ΔKL by using the above-indicated equation (28).
Referring to
In step S109, parameters a, e are calculated by correcting a*, e* with ktha, kpa. In step S110, the engine load factor KLoff is calculated according to the equation (27) (KLoff=a·(Pm−d)+c). In step S111, the engine load factor KLon is calculated according to the equation (26) (KLon=e·(Pm−d)+r). In step S112, the difference ΔKL is calculated (ΔKL=KLoff−KLon). In step S113, the EGR valve passing gas flow rate megr is calculated according to the equation (28) (megr=kegr2·ΔKL).
In the illustrated embodiment, each of the engine load factors KLoff, KLon is expressed by two linear functions. However, the engine load factor KLoff, KLon may be expressed by a certain number (n) of m-order functions (n, m=1, 2 . . . ).
In the illustrated embodiment, the in-cylinder charged fresh air amount during steady-state engine operation with no EGR gas supplied, or the engine load factor KLoff, is represented by a first function (or a first set of functions) as a function of the intake pipe pressure Pm, and the first function is stored in advance. Also, the in-cylinder charged fresh air amount during steady-state engine operation with EGR gas supplied, or the engine load factor KLon, is represented by a second function (or a second set of functions) as a function of the intake pipe pressure Pm, and the second function is stored in advance. In this condition, the in-cylinder charged fresh air amounts, or the engine load factors KLoff, KLon, are calculated based on the determined intake pipe pressure Pm, by using the first and second functions, respectively, and the difference ΔKL between the in-cylinder charged fresh air amounts, or the engine load factors KLoff, KLon, is calculated. Finally, the EGR valve passing gas flow rate megr is calculated based on the difference ΔKL.
More generally speaking, the difference ΔKL between the in-cylinder charged fresh air amount during steady-state operation with no EGR gas supplied, or the engine load factor KLoff, and the in-cylinder charged fresh air amount during steady-state operation with EGR gas supplied, or the engine load factor KLon, is represented by a function of the intake pipe pressure Pm, which is determined and stored in advance. Upon determination of the intake pipe pressure Pm, the difference ΔKL is calculated from the determined intake pipe pressure Pm by using the above function, and the EGR valve passing gas flow rate megr during steady-state operation and transient operation and the in-cylinder charged EGR gas amount Mc egr during steady-state operation are calculated based on the difference ΔKL.
Next, another embodiment of the invention will be described.
By using the above equations (27), (26) representing KLoff and KLon, respectively, the above-described difference ΔKL may be expressed by the following equation (30).
Here, if (a−e) and (c−r) are replaced by h and i, respectively, namely, if (a−e)=h and (c−r)=i, the above equation (30) is rewritten into the following equation (31).
ΔKL=h·(Pm−d)+i (31)
h=h1 . . . Pm≦d
h=h2 . . . Pm>d
Accordingly, the difference ΔKL is represented by two linear functions of the intake pipe pressure Pm, namely, two straight lines that have different slopes and meet at a connection point CP, as shown in FIG. 31. Namely, the difference ΔKL is represented by one of the linear functions having slope h1 when the intake pipe pressure Pm is relatively small, and is represented by the other linear function having slope h2 when the intake pipe pressure Pm is relatively large.
In the present embodiment, the two linear functions of the intake pipe pressure Pm, which represent the difference ΔKL, are stored in advance in the ROM 34 in the form of the equation (31). In this case, the number of parameters can be further reduced.
Parameters h, d, i used in the above equation (31) are calculated according to the following equations:
h1=h1*·ktha
h2=h2*·ktha
i=i*·ktha·kpa
where h1*, h2* and i* are slopes and difference at the connection point CP when the ambient conditions of the engine are the reference ambient conditions. The h1*, h2* and i* are determined in advance through experiments, and are stored in advance in the ROM 34 in the form of maps as shown in
It may be generally said from the above description that two linear functions of the intake pipe pressure Pm representing the difference ΔKL are determined and stored in advance with respect to each of a plurality of different EGR openings θe. Also, two linear functions of the intake pipe pressure Pm representing the difference ΔKL are determined and stored in advance with respect to each of a plurality of different engine speeds NE.
Referring to
In step S129, the parameter h is calculated by correcting h* with ktha, kpa. In step S130, the difference ΔKL is calculated according to the equation (31) (ΔKL=h·(Pm−d)+i). In step S131, the EGR valve passing gas flow rate megr is calculated according to the equation (29) (megr=kegr2·ΔKL).
Here, the EGR opening θe will be briefly described. As described above, the EGR opening is represented by the number of steps STP of the step motor of the EGR control valve 22. Namely, the EGR control valve 22 is closed when the number of steps STP becomes equal to zero, and the EGR opening increases as the number of steps STP increases.
In fact, the EGR control valve 22 is not immediately opened even if the number of steps STP becomes larger than zero, as shown in FIG. 34. Namely, the EGR control valve 22 is opened when the number of steps STP exceeds step STP1. Thus, the EGR opening θe needs to be expressed by using a result (STP−STP1) obtained by subtracting STP1 from STP.
Also, since the EGR control valve 22 usually involves manufacturing errors, the actual EGR opening θe may deviate from a normal opening determined based on the number of steps STP. In the engine as shown in
Accordingly, the EGR opening θe is expressed by the following equation:
θe=STP−STP0+kg
where STP0 is the number of steps with which the EGR control valve 22 starts being opened in a drawing tolerance middle product. In this embodiment, the EGR opening θe thus calculated is used as an argument of the relevant maps.
In the meantime, the EGR valve passing gas flow rate megr calculated as described above or the in-cylinder charged EGR gas amount Mc-egr during steady-state engine operation may be further corrected in view of the exhaust temperature Te.
In the case where the EGR valve passing gas flow rate megr is corrected, for example, the flow rate megr is expressed, for example, by the following equation:
megr=megr·kwu·krtd·kinc
where kwu is a correction factor used during warm-up of the engine, and krtd is a correction factor used during retarding correction of the ignition timing, while kinc is a correction factor used during increasing correction of the fuel injection amount.
The warm-up correction factor kwu is employed for correcting the EGR valve passing gas flow rate megr during a warm-up operation of the engine. During the warm-up operation, the exhaust temperature Te is lower than that detected after completion of the warm-up operation, and the EGR valve passing gas flow rate megr (g/sec) is increased by an amount corresponding to the difference in the exhaust temperature Te. The EGR valve passing gas flow rate megr calculated by using the above-indicated equation (26), (27) or (31) is established after completion of the warm-up operation, and therefore this flow rate megr needs to be corrected during warm-up of the engine.
As shown in
The correction factor krtd is employed for correcting the EGR valve passing gas flow rate megr when the ignition timing is corrected to be retarded. During the retarding correction of the ignition timing, the exhaust temperature Te is higher than that detected when no retarding correction is effected, and the EGR valve passing gas flow rate megr is reduced by an amount corresponding to the difference in the exhaust temperature Te.
As shown in
The correction factor kinc is employed for correcting the EGR valve passing gas flow rate megr when the fuel injection amount is corrected to be increased. During the increasing correction of the fuel injection amount, the exhaust temperature Te is lower than that detected when no increasing correction is effected, and the EGR valve passing gas flow rate megr is increased by an amount corresponding to the difference in the exhaust temperature Te.
As shown in
In the above-described manner, the EGR valve passing gas flow rate megr can be determined with further improved accuracy.
The EGR valve passing gas flow rate megr may be corrected by another method. For example, the exhaust temperature Te for the time of no retarding correction of the ignition timing or no fuel increasing correction is determined in advance as a function of the engine operating conditions (e.g., the engine speed NE and the required load L) while the actual exhaust temperature Te is detected or estimated, and the EGR valve passing gas flow rate megr is corrected based on a difference between the temperature Te for the time of no retarding correction or no fuel increasing correction, and the actual exhaust temperature Te. The in-cylinder charged EGR gas amount Mc-egr during steady-state engine operation may also be corrected in a similar manner to the EGR valve passing gas flow rate megr.
In the engine as shown in
In this case, when the engine is in a steady-state operation, the restrictor passing gas flow rate mchk (g/sec) as the flow rate of EGR gas passing the flow restrictor 23 is equal to the EGR valve passing gas flow rate megr. Accordingly, the restrictor passing gas flow rate mchk during steady-state operation can be calculated based on the difference ΔKL, as is understood from the above description. It is to be noted that the restrictor passing gas flow rate mchk represents the flow rate of EGR gas flowing into the intake pipe portion.
During transient engine operation, on the other hand, the restrictor passing gas flow rate mchk is not necessarily equal to the EGR valve passing gas flow rate megr. However, if the volume of a portion of the EGR passage 21 that extends from the EGR control valve 22 to the flow restrictor 23 is relatively small, the restrictor passing gas flow rate mchk is substantially equal to the EGR valve passing gas flow rate megr. Accordingly, when the volume of the EGR passage 21 extending from the EGR control valve 22 to the flow restrictor 23 is relatively small, the restrictor passing gas flow rate mchk can be calculated based on the difference ΔKL no matter whether the engine is in a steady-state operation or in a transient operation.
In the illustrated embodiments, the engine load factor KLon, KLoff or the difference ΔKL is calculated based on the intake pipe pressure Pm estimated by using a calculation model, or the intake pipe pressure Pm detected by the pressure sensor 39. However, the intake pipe pressure Pm may be estimated based on the throttle opening or an output signal of the air flow meter disposed in the intake duct 14 upstream of the throttle valve 17, and the engine load factor KL may be calculated from the thus estimated intake pipe pressure Pm.
When the intake pipe pressure Pm is estimated based on the throttle opening, the intake pipe pressure Pm is determined in advance as a function of the throttle opening θt, engine speed NE and the EGR opening θe, and this function is stored in the form of a map.
When the intake pipe pressure Pm is estimated based on the output signal of the air flow meter, the estimated intake pipe pressure Pm may exceed the maximum pressure Pmmax that can be reached or taken by intake pipe pressure Pm, because of the detection accuracy of the air flow meter. In a region where Pm is larger than Pmmax, however, the engine load factor KLon expressed by the above-indicated equation (26) may exceed the engine load factor KLoff expressed by the above-indicated equation (27), as shown in FIG. 37B. In this case, the difference ΔKL becomes a negative value. Namely, the difference ΔKL cannot be accurately calculated if the estimated intake pipe pressure Pm exceeds the maximum pressure Pmmax.
If the difference ΔKL is kept at a constant value ΔKLC in the region where Pm>Pmmax, as shown in
When the EGR control valve 22 is in a closed position, the EGR passage 21 downstream of the EGR control valve 22 is filled with air (fresh air). Immediately after the EGR control valve 22 is opened, therefore, fresh air, rather than exhaust gas, flows from the EGR passage 21 into the intake pipe portion. After introduction of the fresh air, a mixture of fresh air and exhaust gas flows from the EGR passage 21 into the intake pipe portion for a while.
Since fresh air and exhaust gas have different temperatures, the flow of fresh air from the EGR passage 21 into the intake pipe portion has a particular influence on the relationship established based on the law of conservation of energy. In the illustrated embodiments, however, the flow of fresh air from the EGR passage 21 into the intake pipe portion is not taken into consideration.
In the illustrated embodiments, therefore, the following equation (32) may be employed, in view of the above fact, as an equation of a relationship established based on the law of conservation of energy between air and exhaust gas flowing into the intake pipe portion, and air and exhaust gas flowing from the intake pipe portion into the cylinder.
In the above equation (32), where the EGR valve passing gas flow rate megr is equal to the flow rate of gas flowing from the EGR passage 21 into the intake pipe portion, megr-egr is flow rate of exhaust gas as a part of the gas flowing from the EGR passage 21 into the intake pipe portion, and megr-air is flow rate of air (fresh air) as a part of the gas flowing from the EGR passage 21 into the intake pipe portion. The flow rate megr-egr will be called “pipe incoming exhaust gas flow rate”, and the flow rate megr-air will be called “pipe incoming fresh air flow rate”.
Also, in the above equation (32), mc-egr is flow rate of exhaust gas flowing into the cylinder, and mc-air is flow rate of air (fresh air) flowing into the cylinder. The flow rate mc-egr will be called “cylinder incoming exhaust gas flow rate”, and the flow rate mc-air will be called “cylinder incoming fresh air flow rate”.
Here, a method of calculating the pipe incoming exhaust gas flow rate megr-egr and the pipe incoming fresh air flow rate megr-air will be described.
When the EGR control valve 22 is opened, the flow rate of gas flowing from the EGR passage 21 into the intake pipe portion is equal to the EGR valve passing gas flow rate. Then, the pipe incoming exhaust gas flow rate megr-egr starts increasing after a certain time (waste time) elapses, and then gradually increases with a first-order lag. Thus, the pipe incoming fresh air flow rate megr-air is calculated according to the following equation (33).
megr-air=megr−megr-egr (33)
Here, the EGR valve passing gas flow rate megr is determined in the manner as explained above. Accordingly, once the pipe incoming exhaust gas flow rate megr-egr is determined, the pipe incoming fresh air flow rate megr-air will be determined.
The pipe incoming exhaust gas flow rate megr-egr is calculated in the following manner: the waste time Td1 and the time constant τ1 are calculated from the functions as shown in FIG. 16A and
On the other hand, the cylinder incoming exhaust gas flow rate mc-egr and the cylinder incoming fresh air flow rate mc-air are determined in a similar manner. Namely, the cylinder incoming exhaust gas flow rate mc-egr starts increasing upon a lapse of a certain time (waste time), and then gradually increases with a first-order lag. Thus, the cylinder incoming exhaust gas flow rate mc-air is calculated according to the following equation (34).
mc-air=mc−mc-egr (34)
As is understood from the above equation (34), once the cylinder incoming exhaust gas flow rate mc-egr is determined, the cylinder incoming fresh air flow rate mc-air will be determined.
The cylinder incoming exhaust gas flow rate mc-egr is calculated in the following manner: the waste time Td2 and the time constant τ2 are calculated from the functions as shown in FIG. 17A and
In this embodiment, the accuracy of the calculated values is improved because the fresh air flowing from the EGR passage 21 into the intake pipe portion is taken into consideration.
In the meantime, when the distance from the location at which the EGR passage 21 is connected to the intake pipe portion to the intake valve is considerably shorter than the distance from the EGR control valve 22 to the above location, the following equation (35) is satisfied.
megr-egr≅mc-egr (35)
Namely, the flow rate mc-egr of exhaust gas flowing into the cylinder is substantially equal to the flow rate megr-egr of exhaust gas (as a part of gas) flowing from the EGR passage 21 into the intake pipe portion.
In this case, the above equation (32) can be rewritten into the following equation (36).
In the illustrated embodiments, the above equation (36) may be employed as an equation of relationship established based on the law of conservation of energy between air and exhaust gas flowing into the intake pipe portion, and air and exhaust gas flowing from the intake pipe portion into the cylinder.
Here, the flow rate megr-air of fresh air flowing from the EGR passage 21 into the intake pipe portion (pipe incoming fresh air flow rate) is determined according to the above equation (33) once the pipe incoming exhaust gas flow rate megr-egr is determined.
Also, the flow rate mc-air of fresh air flowing into the cylinder (cylinder incoming fresh air flow rate) is determined according to the above equation (34) once the cylinder incoming exhaust gas flow rate mc-egr is determined.
Needless to say, where the pipe incoming exhaust gas flow rate megr-egr and the cylinder incoming exhaust gas flow rate mc-egr are calculated when the EGR valve passing gas flow rate megr changes, the waste time and the first-order lag are taken into consideration, as described above.
In addition, the exhaust temperature Te is not included in the parameters used in the above-indicated equation (36), and therefore the exhaust temperature Te need not be determined when the above equation (36) is employed.
The above-indicated equation (36) may be rewritten into the following equation (37).
From the relationship of the above-indicated equation (33), the above equation (37) may be further rewritten into the following equation (38).
The above equation (38) may be further rewritten into the following equation (39).
When the engine is in a steady-state operation, the intake pipe pressure Tm is substantially equal to the atmospheric temperature Ta(Tm≈Ta), and the last term of the right side of the equation (39) as indicated below becomes equal to zero.
When the engine is in a transient operation, on the other hand, the intake pipe temperature Tm is different from the atmospheric temperature Ta, and the difference between these temperatures becomes larger as the intake pipe pressure Pm changes by a larger degree. However, if the EGR valve passing gas flow rate megr is large, the intake pipe pressure Pm is kept high so as to promote combustion in the cylinder. On the contrary, if the EGR valve passing gas flow rate megr is small, only a small influence arises from the difference between the intake pipe temperature Tm and the atmospheric temperature Ta even if this difference is large.
Accordingly, even when the engine is in a transient operation, the last term of the right side of the equation (39) as indicated below can be approximated to zero.
With all of the above descriptions integrated, the equation (39) can be approximated to the following equation (40).
In the illustrated embodiments, the above equation (40) may be employed as an equation of relationship established based on the law of conservation of energy between air and exhaust gas flowing into the intake pipe portion and air and exhaust gas flowing from the intake pipe portion into the cylinder. The use of the above equation (40) eliminates a need to take account of the pipe incoming exhaust gas flow rate megr-egr, cylinder incoming exhaust gas flow rate mc-egr, pipe incoming fresh air flow rate megr-air, and the cylinder incoming fresh air flow rate mc-air.
If the flow rate of the exhaust gas flowing into the intake pipe portion (pipe incoming exhaust gas flow rate) is equal to the EGR valve passing gas flow rate, and the flow rate of the exhaust gas flowing into the cylinder (cylinder incoming exhaust gas flow rate) is equal to the pipe incoming exhaust gas flow rate, the above-indicated equation (15) is rewritten into the following equation (41), and the above-indicated equation (16) is rewritten into the following equation (42):
where Tk is temperature of exhaust gas or air or a mixture thereof flowing from the EGR passage 21 into the intake pipe portion.
Furthermore, the equation (42) is rewritten into the following equation (43).
If the above-described conditions that the pipe incoming exhaust gas flow rate is equal to the EGR valve passing gas flow rate and that the cylinder incoming exhaust gas flow rate is equal to the pipe incoming exhaust gas flow rate are satisfied or permitted, the above equations (41) and (43) may be employed as equations of relationships established based on the law of conservation of mass and the law of conservation of energy between air and exhaust gas flowing into the intake pipe portion and air and exhaust gas flowing from the intake pipe portion into the cylinder. The use of the equations (41) and (43) eliminates a need to determine the EGR valve passing gas flow rate megr.
In the equations (41) and (43), the cylinder incoming fresh air flow rate mc-air is calculated from the engine load factor KL calculated according to the above-indicated equation (26) or (27). More specifically, the engine load factor KL is calculated according to the equation (26) or (27), and the in-cylinder charged fresh air amount Mc-air is calculated by substituting the engine load factor KL into the equation (25) and solving this equation. Finally, the cylinder incoming fresh air flow rate mc-air is calculated by dividing the in-cylinder charged fresh air amount Mc-air by time obtained by dividing the time required for one cycle of the engine by the number of cylinders.
In the illustrated embodiments, the throttle passing air flow rate mt is calculated according to the above-indicated equation (1). While the function Φ(Pm/Pa) is used in this equation (1), the accuracy in calculating the function Φ may deteriorate if the shape of the throttle valve 18 is complicated or if pulsation of air passing the throttle valve 18 takes place. Accordingly, the accuracy in calculating the throttle passing air flow rate mt that is calculated by using the function Φ may also deteriorate.
In view of the above possibility, a method of calculating the throttle passing air flow rate mt by using the following equation (44) may be employed as a method of calculating the throttle passing air flow rate while eliminating calculation errors in the function Φ(Pm/Pa):
where Pm-egr is intake pipe pressure that is finally reached or achieved, and is determined based on the engine speed NE, throttle opening θt and the EGR opening θe(Pm-egr=f1(NE, θt, θe)).
In the above equation (44), e, d and r are adapted parameters. These adapted parameters will be described later in detail.
In the same equation (44), Φ(Pm/Pa) is the function of the equation (2), and Φ(Pm-egr/Pa) is a function obtained by substituting variable Pm/Pa in the function Φ(Pm/Pa) by Pm-egr/Pa.
Next, the process of deriving the above-indicated equation (44) will be explained.
Where mt-TA represents throttle passing air flow rate during steady-state engine operation, the throttle passing air flow rate mt-TA is expressed by the following equation (45).
Then, the following equation (46) is derived by dividing each side of the equation (1) by the corresponding side of the equation (45) and simplifying the result of the division.
As described above, the cylinder incoming air flow rate mc-air is proportional to the in-cylinder charged air amount Mc-air, and the in-cylinder charged air amount Mc-air is proportional to the engine load factor KL, which is calculated from the above-indicated equation (26). Therefore, the cylinder incoming air flow rate mc-air during steady-state engine operation with EGR gas supplied is expressed by the following expression (47):
mc-air=f·(Pm−d)+g (47)
f=f1 . . . Pm≦d
f=f2 . . . Pm>d
where f is adapted parameter (f=f2(NE, θe)) determined based on the engine speed NE and the EGR opening θe, and d is adapted parameter (d=f3(NE)) determined based on the engine speed NE, while g is adapted parameter (g=f4(NE, θe) determined based on the engine speed NE and the EGR opening θe. In other words, f, d and g are coefficients determined by using parameters representing the engine operating conditions as variables.
Here, the cylinder incoming air flow rate mc-air is equal to the throttle passing air flow rate mt-TA during steady-state engine operation, and the intake pipe pressure Pm is equal to the intake pipe pressure Pm-egr that would be finally achieved or reached during transient engine operation. Accordingly, the following equation (48) is derived from the above equation (47).
mt-TA=f·(Pm-egr−d)+g (48)
f=f1 . . . Pm-egr≦d
f=f2 . . . Pm-egr>d
By substituting this equation (48) into the above equation (46), the above equation (44) is derived.
The intake pipe pressure Pm-egr is determined in advance through experiments, or the like, and is stored in the ROM 34 in the form of a map, as a function (Pm-egr=f1(NE, θt, θe)) of the engine speed NE, throttle opening θt and the EGR opening θe.
The adapted parameter f is determined in advance through experiments, or the like, and is stored in the ROM 34 in the form of a map, as a function (f=f2(NE, θe)) of the engine speed NE and the EGR opening θe.
The adapted parameter d is determined in advance through experiments, or the like, and is stored in the ROM 34 in the form of a map, as a function (d=f3(NE)) of the engine speed NE.
The adapted parameter g is determined in advance through experiments, or the like, and is stored in the ROM 34 in the form of a map, as a function (g=f4(NE, θe)) of the engine speed NE and the EGR opening θe.
Thus, in the present embodiment, the intake pipe pressure Pm-egr that would be finally reached during transient engine operation and the adapted parameters f, d, g are calculated from the above-described maps, based on the engine speed NE, throttle opening θt, EGR opening θe, and the like, while the intake pipe pressure Pm is calculated based on the detection value of the intake pipe pressure sensor 40. Then, the throttle passing air flow rate mt is calculated by substituting the obtained intake pipe pressures and parameters into the above equation (44) and solving this equation.
The intake pipe pressure Pm may be estimated or calculated by another method, for example, based on the throttle opening θt. If the engine is equipped with an air flow meter, the intake pipe pressure Pm may be estimated or calculated based on the detection value of the air flow meter.
During steady-state engine operation, since the intake pipe pressure Pm and the intake pipe pressure Pm-egr are equal to each other (Pm=Pm-egr), the term Φ(Pm/Pa)/Φ(Pm-egr/Pa) in the equation (44) is equal to 1, and the function Φ is eliminated. Thus, even if the accuracy in calculating the value of the function Φ is low, the throttle passing air flow rate mt can be calculated with high accuracy by using the equation (44) at least during steady-state operation.
In the meantime, the EGR gas is supplied into the cylinders mainly while the engine is operating at a low load. During such low-load engine operation, the exhaust pressure Pe is assumed to be substantially equal to the atmospheric pressure Pa. Accordingly, when the EGR gas is supplied into the cylinders, the pressure upstream of the EGR control valve 22 is equal to the pressure upstream of the throttle valve 18. Also, the pressure downstream of the EGR control valve 22 and the pressure downstream of the throttle valve 18, which are equivalent to the intake pipe pressure Pm, are originally equal to each other.
Namely, when the EGR gas is supplied into the cylinders, the pressures upstream and downstream of the EGR control valve 22 are equal to the pressures upstream and downstream of the throttle valve 18, respectively. In this case, the EGR opening can be relatively easily converted into an equivalent throttle opening. In the following, a method of converting the EGR opening will be described.
If the pressures upstream and downstream of the EGR control valve 22 are made equal to the pressures upstream and downstream of the throttle valve 18, and the engine speed NE is kept constant, the relationship as shown in
As is understood from
Since the intake pipe pressure Pm-egr tends to be lowered as the engine speed NE increases, the curve indicating the relationship between the throttle opening and the intake pipe pressure at each EGR opening moves as a whole downwards as the engine speed NE increases in the example as shown in FIG. 38.
As is understood from
Namely, when the intake pipe pressure is equal to the same value Pm-egre1 the EGR opening is equal to θe1 if the throttle opening is equal to zero, and the throttle opening is equal to θt1 if the EGR opening is equal to zero.
Accordingly, in the example of
The equivalent throttle opening may be determined in advance through experiments, or the like, and may be stored in the form of a map in the ROM 34. When the above-described condition that the pressures upstream and downstream of the EGR control valve 22 are equal to the pressures upstream and downstream of the throttle valve 18 is satisfied or permitted, the equivalent throttle opening may be calculated from this map, by using the EGR opening as an argument, and the equivalent throttle opening may be added to the actual throttle opening so that a total throttle opening is utilized. With this arrangement, the EGR opening need not be used as a parameter in the illustrated embodiments, resulting in a reduction in the effort in preparing maps or the burden of calculation using maps or mathematical equations.
In the above case, the EGR opening itself is not used as a parameter, and, for example, the number of arguments of a certain map may be reduced by one. Generally, if the number of arguments of a map is reduced by one, the accuracy of the value calculated from this map is reduced. According to the above-described method, however, the total throttle opening involves or includes the EGR opening, and therefore the value calculated from the map or mathematical equation is highly accurate.
As the engine speed NE increases, the curve representing the relationship between the throttle opening and the intake pipe pressure at each EGR opening merely moves downwards over the entire range of the throttle opening, as described above. Thus, the relationship between the EGR opening and the throttle opening at the same intake pipe pressure does not change so much.
Accordingly, the function as shown in
To improve the accuracy in conversion of the EGR opening into the equivalent throttle opening, a correction factor for correcting the calculated equivalent throttle opening may be determined based on the engine speed NE as a variable, and the thus determined correction factor may be, for example, multiplied by the equivalent throttle opening so as to compensate for an influence of the engine speed on the equivalent throttle opening.
While the relationship as shown in
When the above-described method is employed, the intake pipe pressure Pm-egr is determined through experiments, or the like, and is stored in the ROM 34 in the form of a map, as a function (Pm-egr=f5(NE, θt)) of the engine speed NE and the throttle opening θt. This map is similar to a map for calculating the intake pipe pressure Pm-TA during steady-state engine operation from the engine speed NE and the throttle opening θt, with respect to the engine that is not equipped with the EGR system. Therefore, the map for calculating the intake pipe pressure Pm-TA may be used as a map for calculating the intake pipe pressure Pm-egr.
In the meantime, the throttle opening θt and the opening cross-sectional area At of the throttle valve 18 has a non-linear relationship as shown in FIG. 40.
In the above-described method of converting the EGR opening into the equivalent throttle opening, the equivalent throttle opening is calculated from the EGR opening by using the relationship as shown in
It, however, will be understood from
Namely, even if the same equivalent throttle opening is added to the actual throttle opening, the degree of an influence of the equivalent throttle opening differs depending upon the actual throttle opening, i.e., the original throttle opening.
Meanwhile, if slope Sb at the throttle opening (which is equal to zero or the throttle opening during idling of the engine in the above example) with reference to which the map of
The value Sb/S obtained by dividing slope Sb by S is a correction factor for correcting the equivalent throttle opening in terms of the actual throttle opening. When the actual throttle opening is equal to θt1, for example, the equivalent throttle opening is multiplied by a correction factor K1 corresponding to the throttle opening θt1, and the total throttle opening is calculated by adding the corrected equivalent throttle opening resulting from the multiplication by the correction factor K1 to the actual throttle opening. The total throttle opening is thus determined in view of the non-linear relationship between the throttle opening θt and the opening cross-sectional area At of the throttle valve 18.
Since the equivalent throttle opening is calculated in view of the non-linear relationship between the throttle opening θt and the opening cross-sectional area At of the throttle valve 18, the value calculated by using the total throttle opening resulting from addition of the corrected equivalent throttle opening has an improved degree of accuracy.
As shown in
It is naturally understood that the intake pipe pressure Pm-egr hardly changes even if the throttle opening θt changes or the EGR opening θe changes in the region where the throttle opening θt is extremely large. Thus, the equivalent throttle opening may be considered as being extremely small or substantially equal to zero.
In the region where the throttle opening θt is extremely large, therefore, the correction factor K may be adapted to gradually decrease toward zero, as indicated by the broke line in FIG. 41. This arrangement makes it possible to avoid problems in terms of control, and permit control conforming to the actual phenomena or situation with a high degree of continuity.
Number | Date | Country | Kind |
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2002-365609 | Dec 2002 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4843553 | Ohata | Jun 1989 | A |
4860707 | Ohata | Aug 1989 | A |
5010866 | Ohata | Apr 1991 | A |
Number | Date | Country |
---|---|---|
A 2001-41095 | Feb 2001 | JP |
A 2002-147279 | May 2002 | JP |
A 2002-201998 | Jul 2002 | JP |
WO 03033897 | Apr 2003 | WO |
Number | Date | Country | |
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20040122584 A1 | Jun 2004 | US |