The present invention relates to a fuel supply method for allowing an internal-combustion engine including an exhaust emission purifier to efficiently perform the activation processing and the regenerating processing of the exhaust emission purifier.
In recent years, for complying with strict exhaust gas regulations applied to an internal combustion engine, it is necessary to activate an oxidation catalytic converter which comprises an exhaust emission purifier at the time of starting up the engine, or to maintain an activated status of the converter in an actuation of the engine. Therefore, Patent Literature 1 has proposed an internal combustion engine in which an exhaust gas heating system is incorporated in an exhaust passage upstream of the exhaust emission purifier. The exhaust gas heating system generates a burning gas in an exhaust gas, and supplies the generated burning gas to the exhaust emission purifier at the downstream thereof, thereby activating the purifier and maintaining the activated status thereof. Therefore, the exhaust gas heating system is generally provided with a fuel supplying valve for supplying fuel to the exhaust passage and an igniting unit such as a glow plug for heating the fuel to be ignited, thereby generating a burning gas.
When controlling the fuel supplied from a fuel supply valve to an exhaust passage, the hunting of the control is preferably avoided by minimizing a change in the exhaust temperature or a change in the air/fuel ratio caused by the fuel supplied from the fuel supply valve to the exhaust passage.
On the other hand, the fuel supply valve for supplying fuel to the exhaust passage in the conventional exhaust heating unit disclosed in PTL 1 for example basically has the same configuration as that of a fuel injection valve for injecting fuel pressurized at a predetermined driving cycle. Thus, the hunting of the control can be effectively avoided by minimizing the driving cycle to the fuel supply valve, by minimizing the energized time per one shot, and by minimizing the amount of fuel supplied to the exhaust passage during the energized time per one shot.
However, in the case of the conventional fuel supply valve, it has been known that the reduction of the energized time per one shot causes a sudden increase of the variation of the amount of the fuel supplied to the exhaust passage. This is caused by the structure of the fuel supply valve itself and an influence by the viscosity of the fuel itself, meaning that different amounts of fuel are supplied to the exhaust passage depending on the manufacturing tolerances of the individual fuel supply valves. Due to the technical background of the fuel supply valve as described above, blindedly minimizing the energized time per one shot is essentially impossible. Thus, the energized time per one shot has been conventionally determined so that the maximum variation error of the fuel supply caused by the manufacturing tolerances of the individual fuel supply valves for example is equal to or lower than the maximum tolerance of the amount of the fuel supplied to the exhaust passage during the energized time per one shot to the fuel supply valve.
Thus, the conventional exhaust heating unit has a disadvantage as described below. That is, when the amount of fuel supplied to the exhaust passage is not so high, the driving cycle of the fuel supply valve is increased to thereby deteriorate the fuel ignitability. Furthermore, a change in the exhaust temperature or the air/fuel ratio is increased depending on when fuel is supplied and when no fuel is supplied, thus causing the hunting phenomenon of the control.
It is an objective of the present invention to provide a method for supplying fuel that can reduce the energized time per one shot to the fuel supply valve than in the case of the conventional structure.
The present invention is in a method for supplying fuel from a fuel supply valve to an exhaust passage at an upstream side of an exhaust emission purifier, the method comprises the steps of calculating, based on the status of the exhaust emission purifier, a required supply of fuel to be supplied from the fuel supply valve to the exhaust passage; reading a unit fuel supply LU to be supplied to the exhaust passage in accordance with a energized time tU to the fuel supply valve per one shot; intermittently supplying, with a driving cycle depending on the required supply, fuel of the unit fuel supply LU from the fuel supply valve to the exhaust passage; reading the maximum tolerance EA corresponding to the unit supply LU; reading the maximum variation error EDU of the fuel supply valve corresponding to the unit supply LU; calculating, regard to the fuel the unit supply LU, an actual fuel supply g actual supplied to the exhaust passage; setting a target fuel supply LUT that is less than the unit supply LU by a certain amount; reading the maximum variation error EDT of the fuel supply valve corresponding to the target fuel supply LUT; judging whether EDT−EDU<EA−(LU−g) is established or not; interpolating, when it is judged that EDT−EDU<EA−(LU−g) is established, a energized time TUT to the fuel supply valve corresponding to the target fuel supply LUT as a function of (LU/g); and updating the target fuel supply LUT as a new unit fuel supply LU and using the function of (LU/g) as a new energized time tU to drive the fuel supply valve to supply fuel to the exhaust passage.
In the method for supplying fuel according to the present invention, the step of reading a unit fuel supply LU to be supplied to the exhaust passage in accordance with a energized time tU to the fuel supply valve per one shot may read the latest updated unit supply LU.
When fuel to be supplied from the fuel supply valve in accordance with the required supply at every driving cycle of the fuel supply valve is in an amount exceeding the double of the unit fuel supply, a half of the to-be-supplied amount may be supplied.
The state of the exhaust emission purifier for calculating the required supply is a temperature of the exhaust emission purifier or an air/fuel ratio of exhaust flowing therein, and the method may further comprise a step of judging, by carrying-out of the step of intermittently supplying fuel from the fuel supply valve to the exhaust passage for the energized time tU, whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not. In this instance, only when it is judged that the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent, the step of judging whether EDT−EDU<EA−(LU−g) is established or not may be carried out. In this case, the step of judging whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not may include a step of judging whether at least one of the temperature of the exhaust emission purifier and the change rate thereof is within a predetermined range or not, or whether at least one of the air/fuel ratio of the exhaust flowing in the exhaust emission purifier and the change rate thereof is within a predetermined range or not.
When the sum of a detection error of the air/fuel ratio and a detection error of an air-intake amount is less than the maximum tolerance, the step of judging whether EDT−EDU<EA−(LU−g) is established or not may be carried out.
The method may further comprise a step of judging whether an amount of EC passing through the exhaust emission purifier has a value equal to or less than a predetermined value. In this instance, when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether EDT−EDU<EA−(LU−g) is established or not may be carried out.
The method may further comprise a step of judging whether a value ET/ΔTC obtained by dividing a detection temperature error ET of the exhaust emission purifier by the rate ΔTC of temperature increase of the exhaust emission purifier per unit time smaller than the maximum tolerance EA or not. In this instance, when it is judged that ET/ΔTC<EA is established, the step of judging whether EDT−EDU<EA−(LU−g) is established or not may be carried out. In this case, the method may further comprise a step of judging whether an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value. In this instance, only when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether ET/ΔTC<EA is established or not may be carried out.
According to the method for supplying fuel of the present invention, a unit supply of fuel can be reduced without exceeding the maximum tolerance. This can consequently reduce the driving cycle of the fuel supply valve, thus suppressing the hunting phenomenon of the control than in the case of the conventional structure.
In order to read the unit supply LU of fuel supplied to the exhaust passage, the updated latest unit supply LU can be read to thereby improve the initial accuracy when the fuel supply is reduced.
when the fuel amount to be supplied from the fuel supply valve at every driving cycle of the fuel supply valve in accordance with a required supply exceeds the double of the unit fuel supply, a half of the to-be-supplied amount can be supplied to thereby suppress a sudden change in the fuel supply per one shot. This can consequently further suppress the hunting phenomenon of the control due to a change in the fuel supply. Furthermore, the main effect of the invention can be continuously obtained by continuously supplying the unit supply of fuel as long as possible.
Only when the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent, a step is performed to determine whether EDT−EDU<EA−(LU−g) is established or not. By doing this, a control under a transitional control can be avoided. This can consequently further suppress the hunting phenomenon of the control. In particular, a control under a transitional control can be securely avoided by judging whether at least one of the temperature of the exhaust emission purifier and the change rate thereof is within a predetermined range or whether at least one of the air/fuel ratio of the exhaust flowing in the exhaust emission purifier and the change rate thereof is within a predetermined range or not.
When the sum of the detection error of the air/fuel ratio and the detection error of the air-intake amount is lower than the maximum tolerance, whether EDT−EDU<EA−(LU−g) is established or not can be judged to thereby securely maintain a reliable control.
When the HC amount passing through the exhaust emission purifier is judged to be equal to or less than a predetermined value, whether EDT−EDU<EA−(LU−g) is established or not can be judged to thereby securely maintain a reliable control.
When it is judged that the value ET/ΔTC obtained by dividing the detection temperature error ET of the exhaust emission purifier by the rate ΔTC of temperature increase of the exhaust emission purifier per unit time is lower than the maximum tolerance EA, whether EDT−EDU<EA−(LU−g) is established or not can be judged to thereby obtain a similar effect. In particular, only when the HC amount passing through the exhaust emission purifier is judged to be equal to or less than the predetermined value, whether ET/ΔTC<EA or not can be judged to thereby further maintain a reliable control.
An embodiment in which the present invention is applied to a compression ignition type internal combustion engine will be in detail explained with reference to
The engine 10 in this embodiment is a multicylinder internal-combustion engine in which fuel of light oil is directly injected from a fuel injection valve 11 to a combustion chamber 10a in a compressed state to thereby cause spontaneous ignition. However, according to the characteristic of the present invention, the engine 10 also may be a single-cylinder internal-combustion engine.
A cylinder head 12 includes an intake port 12a and an exhaust port 12b opposed to the combustion chamber 10a. The cylinder head 12 includes a valve actuating mechanism (not shown) including an intake valve 13a for opening and closing the intake port 12a and an exhaust valve 13b for opening and closing the exhaust port 12b. The fuel injection valve 11 opposed to the center of the upper end of the combustion chamber 10a is also mounted on the cylinder head 12 so as to be positioned between the intake valve 13a and the exhaust valve 13b.
The amount and the injection timing of the fuel injected from the fuel injection valve 11 into the combustion chamber 10a is controlled by the Electronic Control Unit (ECU) 15 based on the vehicle operating condition including the depression amount of the accelerator pedal 14 by the driver. The depression amount of the accelerator pedal 14 is detected by an accelerator opening sensor 16. The detection information is outputted to the ECU 15.
The ECUI 15 includes: an operating status determining section 15a for determining the vehicle operating condition based on the information from this accelerator opening sensor 16 and various sensors for example (which will be described later); a fuel injection setting unit 15b; and a fuel injection valve driving unit 15c. The fuel injection setting unit 15b sets, based on the determination result by the operating status determining section 15a, the injection amount and the injection timing of fuel from the fuel injection valve 11. The fuel injection valve driving unit 15c controls the operation of fuel injection valve 11 so that the fuel in an amount set by the fuel injection setting unit 15b is injected from the fuel injection valve 11 at the set timing.
The cylinder block in which the piston 17a reciprocates is mounted on a crank angle sensor 18. The crank angle sensor 18 detects the rotation phase of the crankshaft 17c connected via a connecting rod 17b to the piston 17a (i.e., a crank angle) to output this to the ECU 15. The operating status determining section 15a of the ECU 15 determines, based on the information from this crank angle sensor 18, the rotation phase of the crankshaft 17c and the engine rotational speed as well as the vehicle speed for example on a real-time basis.
An air-intake pipe 19 connected to the cylinder head 12 so as to communicate with the intake port 12a defines the air-intake passage 19a together with the intake port 12a. The exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12b defines the exhaust passage 20a together with the exhaust port 12b.
An exhaust turbo-supercharger (hereinafter simply referred to as a supercharger) 21 is provided so as to connect the air-intake pipe 19 and the exhaust pipe 20. This supercharger 21 uses the kinetic energy of the exhaust flowing in the exhaust passage 20a to supercharge the combustion chamber 11a to increase the intake filling efficiency. The supercharger 21 in this embodiment is a turbocharger in which the main part is composed of a compressor 21a and an exhaust turbine 21b rotating with this compressor 21a in an integrated manner. The compressor 21a is provided on the midway of the air-intake pipe 19 positioned at the upstream of the surge tank 19b provided on the midway of the air-intake pipe 20. The exhaust turbine 21b is provided on the midway of the exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12b. In order to reduce the intake temperature heated via the compressor 21a by the heat transfer from the exhaust turbine 21b subjected to a high-temperature exhaust, an intercooler 21c is provided. This intercooler 21c is provided on the midway of the air-intake passage 19a between the compressor 21a and the surge tank 19b provided on the midway of the air-intake pipe 19.
The air-intake pipe 19 provided at the upstream of the compressor 21a of the supercharger 21 includes an airflow meter 22 that detects the flow rate VA of the intake flowing in the air-intake passage 19a (which will be hereinafter referred to as an air-intake amount) to output this to the ECU 15.
An exhaust emission purifier 23 is provided on the midway of the exhaust pipe 20 between the exhaust turbine 21b of the supercharger 21 and a silencer (not shown). The exhaust emission purifier 23 functions to detoxify the toxic substance generated by the combustion of mixed air in the combustion chamber 10a. The exhaust emission purifier 23 in this embodiment includes, in an order from the upstream side, generally well-known Nitrogen Oxides (NOX) storage catalytic converter 23a, Diesel Particulate Filter (DPF) 23b, and an oxidation catalytic converter 23c.
An exhaust heating unit 24 is provided on the midway of the exhaust passage 20a between the exhaust port 12b and the exhaust turbine 21b of the supercharger 21. This exhaust heating unit 24 functions to heat the exhaust from the engine 10 to the exhaust emission purifier 23 to activate the oxidation catalytic converter 23c of the exhaust emission purifier 23 and to maintain the active condition or functions to subject the DPF 23b to a regenerating processing or the NOX storage catalytic converter 23a to a deoxidation processing. The exhaust heating unit 24 in this embodiment includes a fuel supply valve 24a and a glow plug 24.
The amount of the fuel supplied from the fuel supply valve 24a mounted on the exhaust pipe 20 to the exhaust passage 20a is set, based on the determination result by a fuel supply requirement determining section 15d of the ECU 15 (which will be described later), by the fuel supply setting section 15e of the ECU 15. The fuel supply valve driving section 15f of the ECU 15 controls the operation of the fuel supply valve 24a so that the fuel in an amount set by fuel supply setting section 15e is supplied from the fuel supply valve 24a to the exhaust passage 20a.
The glow plug 24b for igniting the fuel supplied from the fuel supply valve 24a to the exhaust passage 20a is fixed to the exhaust pipe 20 so that the heat-generating portion thereof protrudes to the exhaust passage 20a to be opposed to an injection region of the fuel injected from the fuel supply valve 24a. This glow plug 24b is connected to an in-vehicle power source (not shown) via the glow plug driving section 15g of the ECU 15. The glow plug driving section 15g switches ON/OFF of the conduction of the glow plug 24b based on the determination result by the fuel supply requirement determining section 15d of the ECU 15.
The exhaust passage 20a at the upstream side of the fuel supply valve 24a includes a first exhaust temperature sensor 25. This first exhaust temperature sensor 25 detects the exhaust temperature TI flowing in the DPF 23b to output this to the ECU 15.
The exhaust passage 20a between the NOX storage catalytic converter 23a and the DPF 23b has an air/fuel ratio sensor 26. This air/fuel ratio sensor 26 detects the air/fuel ratio RN of the exhaust flowing therein to output this to the ECU 15. The DPF 23b and the oxidation catalytic converter 23d have therebetween a catalyst temperature sensor 27 that detects the temperature TC of the oxidation catalytic converter 23c to output this to the ECU 15. The exhaust passage 20a at the downstream side of the oxidation catalytic converter 23c has the second exhaust temperature sensor 28 that detects the exhaust temperature TO having passed through the oxidation catalytic converter 23c to output this to the ECU 15.
The fuel supply requirement determining section 15d of the ECU 15 determines, based on the determination result of the operation condition by the operating status determining section 15a, the necessity of the activation of the oxidation catalytic converter 23c and the necessities of the regenerating processing in the DPF 23b and the NOX deoxidation processing in the NOX storage catalytic converter 23a. When this fuel supply requirement determining section 15d determines that the activation of the oxidation catalytic converter 23c as well as the regenerating processing in the DPF 23b and the NOX deoxidation processing in the NOX storage catalytic converter 23a are required, then the addition of fuel through the fuel supply valve 24a will be performed. The determination result by this fuel supply requirement determining section 15d is outputted to the glow plug driving section 15g of the ECU 15, the fuel supply setting section 15e, and a unit fuel supply updating section 15h (which will be described later).
The fuel supply requirement determining section 15d of the ECU 15 determines that there is a fuel supply requirement (i.e., the exhaust heating unit 24 must be operated) when any of the following cases “a” to “d” occurs.
a: a case where the oxidation catalytic converter 23c is inactive or is expected to be inactive.
b: a case where the DPF 23b is clogged by the deposition of HC.
a case where the storage of NOX by the NOX storage catalytic converter 23a is in a saturated condition.
d. a case where the regenerating processing of the DPF 23b is required even when the DPF 23b is not clogged.
The case “a” can be judged based on the temperature information TI, TO, and TC from the first exhaust temperature sensor 25 and the second exhaust temperature sensor 26 as well as the catalyst temperature sensor 27. The case “b” can be judged based on the accumulated operating time of the engine 10 or the accumulated fuel injection amount from the fuel injection valve 11 for example and also can be judged by an exhaust pressure sensor. The case “c” can be similarly judged based on the accumulated operating time of the engine 10 or the accumulated fuel injection amount from the fuel injection valve 11 for example.
In order to maintain the correct performance of the exhaust emission purifier 23, the fuel supply setting section 15e of the ECU 15 sets the fuel amount to be supplied to the exhaust passage 20a (hereinafter referred to as a required supply) to LTA and LTR.
More specifically, based on the exhaust temperature TI and the air suction amount VA per a predetermined time (e.g., 1 second), the activation required fuel supply LTA to be supplied to the exhaust passage 20a in order to maintain the active condition of the oxidation catalytic converter 23c is set based on the following formula (1). The exhaust temperature TI is the exhaust temperature that flows at the upstream side of the oxidation catalytic converter 23c and that flows in the exhaust passage 20a proximal to the oxidation catalytic converter 23c. The exhaust temperature TI will be hereinafter referred to as a catalyst upstream exhaust temperature. The air suction amount VA per a predetermined time (which will be hereinafter referred to as an air-intake amount) is acquired from the airflow meter 22.
L
TA={(TL−TI)VA·C}/J (1)
In the formula, TL means the lowest temperature at which the oxidation catalytic converter 23c is in an active condition and is stored in the fuel supply setting section 15e in advance. C shows the air specific heat. J shows the heat generation amount of the fuel supplied to the exhaust passage 20a and is also stored in the fuel supply setting section 15e in advance. The catalyst upstream exhaust temperature TI is acquired from the first exhaust temperature sensor 25.
When the fuel supply requirement determining section 15d determines that the regenerating processing by the DPF 23b constituting the exhaust emission purifier or the NOX deoxidation processing by the NOX storage catalystic converter is required, then the regenerating required fuel supply LTR to be supplied to the exhaust passage 20a is set based on the following formula (2).
L
TR
=V
A
/R
T)−q (2)
In this formula, RT shows the air/fuel ratio as a command of the exhaust flowing through the exhaust passage 20a to the exhaust emission purifier 23 (hereinafter referred to as a target air/fuel ratio) and is stored in the fuel supply setting section 15e in advance. In this formula, q shows the injection amount of the fuel injected from the fuel injection valve 11 to the combustion chamber 10a of the engine 10 and is acquired from the fuel injection valve driving unit 15c.
The information regarding the required fuel supplies LTA and LTR set by the fuel supply setting section 15e (which will be hereinafter collectively referred to as a required fuel supply LT for convenience) is outputted to the fuel supply valve driving section 15f and the unit fuel supply updating section 15h of the ECU 15.
The fuel supply valve driving section 15f performs, at every calculation cycle tP, a processing to multiply the required fuel supply LT set by the fuel supply setting section 15e with the calculation cycle tP (e.g., 20 milliseconds) to totalize the resultant values. When the fuel totalized value obtained at every calculation cycle tP reaches the unit fuel supply LU updated by the unit fuel supply updating section 15h, the energized time tU corresponding to this unit fuel supply LU is given to the fuel supply valve 24a. At the same time, the fuel totalized value is updated to a value obtained by (totalized value−unit supply LU). Then, the fuel totalization processing is repeated to drive the fuel supply valve 24 intermittently. Therefore, the higher the required fuel supply LT per a predetermined time is, the shorter the driving interval of the fuel supply valve 24a is. The lower the required supply LT per a predetermined time is, the longer the driving interval of the fuel supply valve 24a is. The driving information from the fuel supply valve driving 15f to the fuel supply valve 24a is outputted to the surplus tolerance calculating section 15i of the ECU 15.
When the engine 10 is in a transitional operating condition (e.g., in a sudden acceleration requiring the supply of a large amount of fuel within a short time), the driving cycle tC of the fuel supply valve 24a must be synchronized with the fuel burst interval of the respective cylinders of the engine 10. As a result, there may be a case where, even when the unit fuel supply LU is supplied to the exhaust passage 20a at every driving cycle tC matching the fuel burst interval of the respective cylinders of the engine 10, the fuel supply ratio is insufficient to thereby fail to provide an appropriate control. In this embodiment, only when the required supply ΔLT to be supplied at every driving cycle tC of the fuel supply valve 24a (=ΔLA·tC, ΔLTR·tC) exceeds the double of the unit fuel supply LU, a half of the required fuel supply LT multiplied with the driving cycle tC is supplied from the fuel supply valve 24a to the exhaust passage 20a.
The ECU 15 includes a convergence determining section 15j in addition to the above-described operating status determining section 15a and fuel supply valve driving section 15f for example.
The convergence determining section 15j determines, based on the determination result of the operating condition from the operating status determining section 15a, whether the oxidation catalytic converter 23c reaches, by the supply of fuel from the fuel supply valve 24a, to the target activation temperature TT and is in a stable condition or not. The convergence determining section 15j also determines whether the air/fuel ratio RN reaches, by the supply of fuel from the fuel supply valve 24a, to the target air/fuel ratio RT and is in a stable condition or not.
The convergence determining section 15j determines that the temperature of the oxidation catalytic converter 23c is convergent in the vicinity of the target activation temperature TT and is in a stable condition when the following two conditions are satisfied. The first condition is that that the absolute value of the value obtained by deducting from the target activation temperature TT the temperature of the exhaust flowing in the exhaust passage 20a proximal to the oxidation catalytic converter 23c at the downstream side of the oxidation catalytic converter 23c (which will be hereinafter referred to as a catalyst downstream exhaust temperature) is lower than a positive threshold value TR set in advance. The second condition is that the absolute value of a rate dTO of change in the exhaust temperature TO is smaller than the threshold value dTR set in advance (which is generally has a positive value close to 0). As a result, it can be securely judged that the engine 10 does not have a transitional operating condition. However, another configuration also may be used where the oxidation catalytic converter 23c has a temperature convergent to the neighborhood of the target activation temperature TT only when any of the conditions is satisfied.
Similarly, the convergence determining section 15j determines that the exhaust flowing in the exhaust passage 20a has the air/fuel ratio RN that is convergent ant stable at the neighborhood of the target air/fuel ratio RT when the following two conditions are satisfied. The first condition is that the absolute value of the value obtained by deducting, from the target air/fuel ratio RT, the air/fuel ratio RN acquired by the air/fuel ratio sensor 26 is smaller than the positive threshold value dRR set in advance. The second condition is that the rate dRN of change of the air/fuel ratio RN has an absolute value smaller than the positive threshold value dRR set in advance (which is generally has a positive value close to 0). As a result, it can be securely judged that the engine 10 does not have a transitional operating condition. However, another configuration also may be used where the exhaust flowing in the exhaust passage 20a has the air/fuel ratio RN that is convergent in the vicinity of the target air/fuel ratio RT only when any of the conditions is satisfied.
By the determination processing by the convergence determining section 15j as described above, it is possible to confirm that the engine 10 is not in a transitional operating condition. Thus, the exhaust heating unit 24 can be subjected to a smooth control. This determination result is outputted to the surplus tolerance calculating section 15j.
The surplus tolerance calculating section 15i stores therein the map as show in
g=(ΔTI·VA·C) (3)
In the formula, ΔTI shows a difference between TI detected by the first exhaust temperature sensor 25 and the exhaust temperature TO detected by the second exhaust temperature sensor 28 and is represented by ΔTI=TO−TI. Thus, the amount ΔEA of the surplus tolerance is represented as shown by the following formula (4).
ΔEA=EA−ΣLU+(ΔTI·VA·C/J) (4)
The amount ΔEA of the surplus tolerance calculated by the surplus tolerance calculating section 15i is outputted to the unit fuel supply updating section 15h.
The unit fuel supply updating section 15h in this embodiment updates the fuel supply per one energized time tU supplied from the fuel supply valve 24a to the exhaust passage 20a (i.e., the unit fuel supply LU) and outputs the updated unit fuel supply LU to the fuel supply valve driving section 15f. In this embodiment, the initial value LUS of the unit fuel supply LU is stored in advance in the unit fuel supply updating section 15h. Thus, such a control is carried out that stepwisedly reduces the unit fuel supply LU from this initial value LUS by a certain amount of the target unit fuel supply LUT. Basically, the unit fuel supply LU is updated to have a smaller value so that, with regard to the required fuel supply LT set by the fuel supply setting section 15e, the unit fuel supply LU is supplied with the shortest addition interval (the driving cycle tC of the fuel supply valve 24a) as possible. In this case, the initial value LUS of the unit fuel supply is set to a value sufficiently higher than the reference unit fuel supply LUC. The target unit fuel supply LUT is set to a value smaller than the current unit fuel supply LU by a predetermined amount and is updated to have a smaller value, when possible, by the update processing.
More particularly, fuel of the target unit fuel supply LUT smaller than the current unit fuel supply LU by a certain amount is set. A different processing is performed depending on the case where the target unit fuel supply LUT is higher than the reference unit fuel supply LUC and the case where the target unit fuel supply LUT is lower than the reference unit fuel supply LUC. Specifically, when the target unit fuel supply LUT is higher than the reference unit fuel supply LUC, there is no need to consider the maximum variation error ED. Thus, when the supply error EU calculated by the surplus tolerance calculating section 15i is lower than the maximum tolerance EA, the target unit fuel supply LUT is updates as a new unit fuel supply LU.
When the target unit fuel supply LUT is lower than the reference unit fuel supply LUC, then the target unit fuel supply LUT is set to have a value smaller than the current unit fuel supply LU by a certain amount. The maximum variation error EDT of the target unit fuel supply LUT and the maximum variation error EDU of the current unit fuel supply LU are read out from the map of
In any of the cases, the energized time tU corresponding to the updated unit fuel supply LU is interpolated as shown in the following formula (5).
t
U
=t
UT
>k(ΣLU/g) (5)
The energized time tU corresponding to the updated unit fuel supply LU also can be interpolated by any appropriate function formula other than the formula (5) including (ΣLU/g) as a variable. For example, the following formula (6) also can be used.
t
U
=t
UT+(ΣLU/g) (6)
Furthermore, it is also effective to multiply (ΣLU/a) in order to suppress a sudden change of the right sides of the formulae (5) and (6), with such an interpolation coefficient that is higher than 0 and that is equal to 0 and that is equal to or lower than 1. By including such an interpolation coefficient in the formulae (5) and (6), it is possible to avoid an adverse influence by an error of sensors for example used to calculate the unit fuel supply LU and the actual fuel supply g or the calculation of the energized time tU during a transitional operating condition of the vehicle. This interpolation coefficient can be set in advance based on the magnitude of the error based on the resolution of the sensors for example or the vehicle transitional operating condition for example.
As described above, based on the actual fuel supply g corresponding to the unit fuel supply LU, the energized time tUT corresponding to the target unit fuel supply LUT is interpolated. By doing this, even when the current unit fuel supply LU is reduced to the target unit fuel supply LUT, the resultant error can be equal to or lower than the maximum tolerance EA. Thus, when the amount ΔEA of the surplus tolerance exceeds the amount ΔED of the surplus variation error and the current unit fuel supply LU is reduced to the target unit fuel supply LUT this exceeds the maximum tolerance EA. Thus, no update of the unit fuel supply LU is performed.
As described above, the smaller the unit fuel supply LU is when compared with the required fuel supply LT, fuel is supplied from the fuel supply valve 24a to the exhaust passage 20a with a shorter driving cycle tC. As a result, fuel supplied to the exhaust passage 20a shows a smaller temporal fluctuation range, thus providing a smaller fluctuation range of the air/fuel ratio RN in the exhaust in particular.
The unit fuel supply updating section 15h in this embodiment includes an update availability determining section 151 to determine the availability of the above-described update processing of the unit fuel supply LU and the energized time tU. When this update availability determining section 151 determines that the following conditions (A) (C) (E), and (B) or (D) are satisfied, this update availability determining section 151 allows the update of the unit fuel supply LU and the energized time tU by the unit fuel supply updating section 15h. When this update availability determining section 151 determines that the following conditions (A), (C), (E), and (B) or (D) are not satisfied on the other hand, this update availability determining section 151 does not allow the update of the unit fuel supply LU and the energized time tU by the unit fuel supply updating section 15h. Then, unit fuel supply updating section 15h stores the current unit fuel supply LU and energized time tU as the latest unit fuel supply LU and energized time tU.
ΔEA>ΔED (A)
E
A
>E
VA
+E
RT (B)
E
A>(ET/ETC) (C)
E
A
>E
U (E)
With regard to (A), when the amount ΔEA of the surplus tolerance exceeds the amount ΔED of the surplus variation error as described above, the unit fuel supply LU is not updated because the current unit fuel supply LU reduced to the target unit fuel supply LUT in this case exceeds the maximum tolerance EAT.
With regard to (B), it has been well-known that the airflow meter 22 and the air/fuel ratio sensor 26 have a unique measurement error due to the detection system thereof.
With regard to (C), it has been known that the detection value RN of the air/fuel ratio sensor 26 is dislocated to the lean side in proportion to the HC amount included in the exhaust (so-called lean shift). Thus, the error of the detection value RN by the air/fuel ratio sensor due to this lean shift amount ΔES must be lower than the maximum tolerance EA of the unit fuel supply LU. Thus, when the lean shift amount ΔES is too large, the above target unit fuel supply LUT is not updated as a new unit fuel supply LU. Similarly, the calculation of the above formula (5) also must not be performed. In this embodiment, when the value ω·g obtained by multiplying the HC purification rate ω by the exhaust emission purifier 23 with the actual fuel supply g is lower than the lean shift amount ΔES, then the above target unit fuel supply LUT is updated as a new unit fuel supply LU and the above formula (5) is calculated. When the value ω·g obtained by multiplying the HC purification rate ω by the exhaust emission purifier 23 with the actual fuel supply g is equal to or larger than the lean shift amount ΔES on the other hand, the above target unit fuel supply LUT is not updated as a new unit fuel supply LU and the above formula (5) is not performed.
With regard to (D), when a control is carried out based on the activation required fuel supply LTA, an influence by the detection error of the catalyst temperature sensor 27 must be avoided. Thus, it is judged whether the value (ET/ΔTC) obtained by dividing the detection temperature error of the exhaust emission purifier 23 (i.e., the detection error ET of the catalyst temperature TC detected by the catalyst temperature sensor 27) by the rate ΔTC of temperature increase of the exhaust emission purifier 23 per unit time is smaller than the maximum tolerance EA or not. When EA>(ET/ΔTC) is established. Then, the unit supply LU and the energized time tU are updated.
With regard to (E), when the target unit fuel supply LUT is more than the reference unit fuel supply LUC and the supply error EU is larger than the maximum tolerance EA, the target unit fuel supply LUT cannot be updated as a new unit fuel supply LU.
On the other hand, when the step S141 determines that the required fuel supply ΔLTA per unit time exceeds the double of the unit fuel supply LU (i.e., when it is judged that the continued supply of fuel in the unit fuel supply LU causes an insufficient fuel supply), the processing proceeds to the step S146. Then, fuel in the amount of a half of the required fuel supply ΔLTA per unit time is supplied through the fuel supply valve 24a to the exhaust passage 20a. Then, steps after the above step S143 are carried out.
The step S15 determines whether the new target unit fuel supply LUT set to the current unit fuel supply LU is less than the reference unit fuel supply LUC or not. At an initial stage, the newly-set target unit fuel supply LUT is equal to or more than the reference unit fuel supply LUC. Thus, the processing proceeds to the step S16 to allow the surplus tolerance calculating section 15i to calculate the supply error EU. Next, the step S17 determines whether the supply error EU is smaller than the maximum tolerance EA or not. When it is judged that the supply error EU is smaller than the maximum tolerance EA (i.e., when it is judged that the unit fuel supply LU can be updated), the processing proceeds to the step S18. Then, the set target unit fuel supply LUT is updated as a new unit fuel supply LU and the energized time tU to the corresponding fuel supply valve 24a is interpolated as shown in the formula (5). Then, the processing again returns to the step S11. When the step S17 determines that the supply error EU is equal to or larger than the maximum tolerance EA (i.e., it is judged that the unit fuel supply LU cannot be updated), the current unit fuel supply LU and the energized time tU are directly maintained. Then, the processing again returns to the step S11.
When the above step S15 determines that the target unit fuel supply LUT newly set to the current unit fuel supply LU is less than the reference unit fuel supply LUC, (i.e., when it is judged that the maximum variation error ED must be considered), then the processing proceeds to the step S19. Then, it is judged whether the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature TO from the target activation temperature TT of the oxidation catalytic converter 23c is smaller than the threshold value TR or not. When it is judged that the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature TO from the target activation temperature TT of the oxidation catalytic converter 23c is less than the threshold value TR (i.e., when it is judged that the oxidation catalytic converter 23C reaches the activation temperature), then the processing proceeds to the step S20. Then, it is judged whether the rate dTO of exhaust temperature change in downstream of the catalyst is less than the threshold value dTR or not. When the rate dTO of exhaust temperature change in downstream of the catalyst is smaller than the threshold value dTR (i.e., when the oxidation catalytic converter 23C has a temperature that is converged and stable at the activation temperature), then the processing proceeds to the step S21. Then, the supply error EU is calculated. The step S22 calculates the amount ΔEA of the surplus tolerance. The step S23 calculates the amount ΔED of the surplus variation error.
When the above step S19 determines that the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature TO from the target activation temperature TT is equal to or larger than the threshold value TR (i.e., when it is judged that the oxidation catalytic converter 23c is converged at the activation temperature), then the processing returns to the step S11. in this case, it is noted that the current unit fuel supply LU and energized time tU are maintained continuously. Similarly, when the step S20 determines that the exhaust temperature change rate dTCO is equal to or more than the threshold value dTR (i.e., when the oxidation catalytic converter 23c is not converged at the activation temperature), the processing returns to the step S11 while maintaining the current unit fuel supply LU and energized time tU.
After the step S23, the step S24 determines whether the amount ΔEA of the surplus tolerance is more than the amount ΔED of the surplus variation error or not. When it is judged that the amount ΔEA of the surplus tolerance is larger than the amount ΔED of the surplus variation error (i.e., it is judged that the unit fuel supply LU can be updated to a reduced amount), the processing proceeds to the step S29. Then, it is judged whether the value (ET/ΔTU) obtained by dividing the detection error ET of the catalyst temperature TC by the rate ΔTC of temperature increase of the exhaust emission purifier 23 per unit time is less than the maximum tolerance EA or not. When it is judged that the value of (ET/ΔTC) is smaller than the maximum tolerance EA (i.e., when it is judged that the unit fuel supply LU can be updated to a reduced amount), the processing proceeds to the step S18. When it is judged that the value of (ET/TC) is equal to or larger than the maximum tolerance EA (i.e., when it is judged that the unit fuel supply LU cannot be updated to a reduced amount), the current unit fuel supply LU and energized time tU are directly maintained and the processing returns to the step S11. Similarly, when the step S24 determines that amount ΔEA of the surplus tolerance is equal to or less than the amount ΔED of the surplus variation error (i.e., when it is judged that an updated unit fuel supply LU deviates from the maximum tolerance EA), then the current unit fuel supply LU and energized time tU are maintained. Then, the processing returns to the step S11.
On the other hand, when the above step S11 determines that there is no fuel supply request (i.e., it is judged that there is no need to activate the oxidation catalytic converter 23 in the exhaust emission purifier 23), then the processing proceeds to the step S30 to determine whether a fuel supply flag is set or not. When it is judged that the fuel supply flag is set, (i.e., when it is judged that the fuel supply from the fuel supply valve 24a to the exhaust passage 20a continued), then the processing proceeds to the step S31 to stop the fuel supply processing. Then, the step S32 resets the fuel supply flag to thereby complete a series of controls. When the above step S30 determines that no fuel supply flag is set (i.e., when it is judged that the processing to supply fuel from the fuel supply valve 24a to the exhaust passage 20a is not performed), the processing is completed without doing anything.
As described above, when the amount ΔE of the surplus tolerance is less than the amount ΔED of the surplus variation error, the unit fuel supply LU is updated to a smaller target unit fuel supply LUT. As a result, the oxidation catalytic converter 23c can have a narrower temperature amplitude to reduce the wasteful fuel supply, thus improving fuel consumption. At the same time, even the reduced unit fuel supply LU can be always less than the maximum tolerance, thus securely maintaining a desired control accuracy.
In the above-described embodiment, the temperature of the oxidation catalytic converter 23c was controlled. However, a similar control configuration also can be used when the air/fuel ratio of the exhaust is controlled.
When the step S45 determines that the target unit fuel supply LUT newly set to the current unit fuel supply LU is less than the reference unit supply LUC (i.e., when it is judged that the maximum variation error ED must be considered), the processing proceeds to the step S49. Then, it is judged whether the absolute value of the value obtained by deducting the air/fuel ratio value RN from the target air/fuel ratio value RT is smaller than the positive threshold value RR set in advance or not. When it is judged that the absolute value of the value obtained by deducting the air/fuel ratio value RN from the target air/fuel ratio value RT is less than the positive threshold value RR set in advance (i.e., when it is judged that the current air/fuel ratio RN substantially reaches the target air/fuel ratio RT). Then, the processing proceeds to the step S50. Then, it is judged whether the rate dRN of change of air/fuel ratio detected by the air/fuel ratio sensor 26 has an absolute value that is less than the threshold value dRR or not. When it is judged that the rate dRN of change of the air/fuel ratio RN has an absolute value smaller than the threshold value dRR (i.e., when it is judged that the exhaust flowing in the exhaust passage 20a has the air/fuel ratio RN that is converged and stable at the target air/fuel ratio RT), the processing proceeds to the step S51 to calculate the amount ΔEA of the surplus tolerance.
When the step S49 determines that the absolute value of the value obtained by deducting the current air/fuel ratio value RN from the target air/fuel ratio value RT is equal to or larger than the threshold value RR(i.e., when it is judged that the current air/fuel ratio RN is not converged at the target air/fuel ratio RT), then the processing returns to the step S41. In this case, it is noted that the current unit fuel supply LU and the energized time tU are maintained. When the step S50 determines that the absolute value of the rate dRN of change of the air/fuel ratio is equal to or more than the threshold value RR (i.e., when it is judged that the exhaust flowing in the exhaust passage 20a has the air/fuel ratio RN that does not reach the target air/fuel ratio RT and is unstable), the processing also returns to the step S41. In this case, the current unit fuel supply LU and the energized time tU are similarly maintained.
After the step S53, the step S54 determines whether amount ΔEA of the surplus tolerance is more than the amount ΔED of the surplus variation error or not. When the amount ΔEA of the surplus tolerance is larger than the amount ΔED of the surplus variation error, (i.e., when it is judged that the unit fuel supply LU can be updated and reduced), then the processing proceeds to the step S55. Then, it is judged whether the sum of the measurement errors EVA and ERT of the airflow meter 22 and the air/fuel ratio sensor 26 is less than the maximum tolerance EA or not. When it is judged that the sum of the measurement errors EVA and ERT of the airflow meter 22 and the air/fuel ratio sensor 26 is smaller than the maximum tolerance EA, (i.e., when it is judged that the unit fuel supply LU can be updated and reduced), the processing proceeds to the step S56. Then, the HC amount in the exhaust is calculated. The step S57 calculates the lean shift amount ΔES in the air/fuel ratio sensor 26. The step S58 calculates the catalyst purification rate ω. When the step S55 determines that the sum of the measurement errors EVA and ERT is less than the maximum tolerance EA, (i.e., when it is judged that the unit fuel supply LU cannot be updated and reduced), then the processing returns to the step S41 while maintaining the current unit fuel supply LU and energized time tU.
After the step S58, the step S59 determines whether the above lean shift amount ΔES is less than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g or not. When it is judged that the above lean shift amount ΔES is less than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g, the processing proceeds to the step S48. When it is judged that the above lean shift amount ΔES is equal to or larger than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g (i.e., when it is judged that the unit fuel supply LU cannot be updated and reduced), then the processing returns to the step S41 while maintaining the current unit fuel supply LU and energized time tU.
As described above, similarly in this embodiment, when the amount ΔE of the surplus tolerance is less than the amount ΔED of the surplus variation error, the unit fuel supply LU is updated to a smaller target unit fuel supply LUT. As a result, the oxidation catalytic converter 23c can have a narrower temperature amplitude to reduce the wasteful fuel supply, thus improving fuel consumption. At the same time, even the reduced unit fuel supply LU can be always less than the maximum tolerance, thus securely maintaining a desired control accuracy.
It should be noted that, the present invention should be interpreted based only upon the matters described in claims, and in the aforementioned embodiments, all changes and modifications included within the spirit of the present invention can be made other than the described matters. That is, all the matters in the described embodiments are made not to limit the present invention, but can be arbitrarily changed according to the application, the object and the like, including every construction having no direct relation to the present invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/004843 | 8/30/2011 | WO | 00 | 3/18/2013 |