Patent Grant
7316228
This application is based on Japanese Patent Application No. 2006-51176 filed on Feb. 27, 2006, the disclosure of which is incorporated herein by reference.
The present invention relates to an evaporated fuel treatment system for an internal combustion engine.
An evaporated fuel treatment system prevents the dissipation of evaporated fuel produced in a fuel tank to the atmosphere. The evaporated fuel in the fuel tank is introduced into a canister having an adsorbing material and is temporarily adsorbed by the adsorbing material. The evaporated fuel adsorbed by the adsorbing material is desorbed by a negative pressure developed in an intake pipe when an internal combustion engine is operated and is purged to the intake pipe of the internal combustion engine through a purge passage. When the evaporated fuel is desorbed from the adsorbing material in this manner, the adsorption capacity of the adsorbing material is recovered.
When the evaporated fuel is purged, the flow rate of an air-fuel mixture containing the evaporated fuel is controlled by a purge control valve disposed in the purge passage. However, in order to control the quantity of evaporated fuel actually purged to the intake pipe to an appropriate air-fuel ratio by the purge control valve, it is important to measure the concentration of the evaporated fuel in the air-fuel mixture flowing in the purge passage with high accuracy.
JP-5-18326A shows a system in which mass flow meters are disposed in a purge passage and an atmosphere passage branched from the purge passage. The concentration of evaporated fuel in an air-fuel mixture supplied to an intake pipe of an internal combustion engine from the purge passage is detected on the basis of the output values of the two mass flow meters.
However, the flowmeter is disposed in the purge passage in this system, so the concentration of the evaporated fuel cannot be detected unless the air-fuel mixture containing the evaporated fuel is purged and flows in the purge passage. In order to reflect the detected concentration of the evaporated fuel in the control of an air-fuel ratio, it is necessary to measure the concentration of evaporated fuel before the purged evaporated fuel reaches the injector position. It is necessary to correct the amount of fuel to be injected from the injector based on the measured concentration of evaporated fuel.
However, in the case of an engine having a small intake pipe volume or in an operation range of a high flow velocity of intake air, the time required for purged evaporated fuel to reach the injection position is shorter than the time required for completing the measurement of an evaporated fuel concentration. Thus, it may be impossible to reflect a measured evaporated fuel concentration. Therefore, an engine structure including the layout of pipes and the operation range of starting purge may be restricted.
It can be thought as means for solving the above problems that an air-fuel mixture containing air and evaporated fuel is flowed through a restriction to detect the amount of change in the pressure of air caused by the restriction and the amount of change in the pressure of the air-fuel mixture caused by the restriction. The flow rate of the air-fuel mixture introduced into an intake pipe of an internal combustion engine from a canister is controlled on the basis of the amounts of change in the two amounts of change in pressure.
The amount of change in the pressure caused by the restriction is changed by the density of fluid flowing through the restriction, as is known as Bernoulli's theorem. The amount of change in the pressure when gas containing 0% evaporated fuel (that is air) of a reference gas is flowed through a restriction is compared with the amount of change in the pressure when an air-fuel mixture containing evaporated fuel is flowed through the restriction. A difference in density between both gases can be detected. This difference in density corresponds to the evaporated fuel concentration of the air-fuel mixture. Thus, the evaporated fuel concentration of the air-fuel mixture can be known on the basis of the two amounts of change in pressure (refer to U.S. Pat. No. 6,971,375B2).
When an evaporated fuel concentration is computed on the basis of the amount of change in pressure caused by a restriction, it is preferable that the amount of change in pressure caused by the restriction is changed only by the evaporated fuel concentration of the air-fuel mixture and is not changed by other conditions.
However, the fuel tank always communicates with the canister and hence the canister communicates with the restriction in a state in which the amount of change in pressure caused by the restriction is measured. Thus, when pressure in the fuel tank is changed due to a swing of fuel in the fuel tank, the variation in pressure propagates to the restriction. This variation in pressure is detected by a pressure sensor. For this reason, there is a possibility that when fuel swings, the amount of change in pressure caused by the restriction is changed. Moreover, when the fuel tank communicates with the restriction also in a state in which the amount of change in pressure of air, caused by the restriction, is measured, there is a possibility that the amount of change in the pressure of air, caused by the restriction, is changed by the swing of fuel. When the amount of change in the pressure of the air-fuel mixture or air, caused by the restriction, is changed by the swing of fuel, the accuracy of controlling the flow rate of the air-fuel mixture is lowered to increase the amount of deviation of the air-fuel ratio from the stoichiometric air-fuel ratio.
The present invention has been accomplished in view of these circumstances. An object of the present invention is to provide an evaporated fuel treatment system that can control the flow rate of an air-fuel mixture introduced into an intake pipe with higher accuracy.
The evaporated fuel treatment system for an internal combustion engine according to the present invention includes a first pressure detection means for detecting an amount of change in pressure of an air-fuel mixture caused by a specified restriction in a first measurement state. In the first measurement state, the fuel tank, the canister, and the restriction communicate with each other and the air-fuel mixture flows through the restriction. The system includes a flow rate control means for controlling a flow rate of the air-fuel mixture introduced into the intake pipe from the canister on a basis of an amount of change in pressure detected by the first pressure detection means and an amount of change in pressure of air flowing through the specified restriction. The system includes a fuel swing determination means for determining whether fuel in the fuel tank swings. When the fuel swing determination means determines that the fuel swings, the flow rate control means stops the control of a flow rate of the air-fuel mixture based on an amount of change in pressure of the air-fuel mixture.
When the fuel swing determination means determines that fuel swings, the flow rate control means does not control the flow rate of the air-fuel mixture on the basis of the amount of change in the pressure of the air-fuel mixture which is caused by the restriction and detected by the first pressure detection means. For this reason, it is possible to prevent the flow rate of the air-fuel mixture from being controlled on the basis of the amount of change in the pressure of the air-fuel mixture which is of insufficient accuracy due to the swings of fuel. As a result, it is possible to control the flow rate of the air-fuel mixture introduced into the intake pipe with higher accuracy.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:
The preferred embodiments of the present invention will be described below.
The canister 13 is packed with an adsorbing material 14 and evaporated fuel produced in the fuel tank 11 is temporarily adsorbed by the adsorbing material 14. The canister 13 is connected to an intake pipe 2 of the engine 1 via a purge line 15 of a purge pipe. The purge line 15 is provided with a purge valve 16 of a purge control valve and when the purge valve 16 is opened, the canister 13 communicates with the intake pipe 2.
Partition plates 14a and 14b are disposed in the canister 13. The partition plate 14a is disposed between the connection position of the evaporation line 12 and the connection position of the purge line 15 and prevents evaporated fuel introduced from the evaporation line 12 from being purged from the purge line 15 without being adsorbed by the adsorbing material 14.
An atmosphere line 17 is also connected to the canister 13. The other partition plate 14b is disposed between the connection position of the atmosphere line 17 and the connection position of the purge line 15 in the substantially same depth as the packing depth of the adsorbing material 14. This prevents the combustion vapor introduced from the evaporation line 12 from being purged from the atmosphere line 17.
The purge valve 16 is a solenoid valve and has its opening controlled by an electronic control unit (ECU) 30 for controlling the respective parts of the engine 1. The flow rate of an air-fuel mixture containing evaporated fuel flowing in the purge line 15 is controlled by the purge valve 16. The air-fuel mixture having its flow rate controlled is purged into the intake pipe 2 by a negative pressure developed in the intake pipe 2 by a throttle valve 3 and is combusted together with fuel injected from an injector 4 (hereinafter, an air-fuel mixture containing the purged evaporated fuel is referred to as purge gas).
The atmosphere line 17 is open to the atmosphere via a filter 50 is connected to the canister 13. The atmosphere line 17 is provided with a selector valve 18. The selector valve 18 switches between two positions. In one position, the canister 13 communicates with the atmosphere line 17. In the other position, the canister communicates with the suction of a pump 26. Here, when the selector valve 18 is not operated by the ECU 30, the selector valve 18 is set at a first position in which the canister 13 communicates with the atmosphere line 17. When the selector valve 18 is operated by the ECU 30, the selector valve 18 is switched to a second position in which the canister 13 communicates with the suction side of the pump 26.
A branch line 19 branched from the purge line 15 is connected to one input port of a three-position valve 21. Moreover, an air supply line 20 branched from a discharge line 27 of the pump 26 is connected to the other input port of the three-position valve 21. The discharge line 27 is opened to the atmosphere via a filter 51. A measurement line 22 of a measurement passage is connected to an output port of the three-position valve 21.
The three-position valve 21 is switched by the ECU 30 between a first position in which the air supply line 20 is connected to the measurement line 22, a second position in which both connections of the air supply line 20 and the branch line 19 to the measurement line 22 are interrupted, and a third position in which the branch line 19 is connected to the measurement line 22. Here, when the three-position valve 21 is not operated, the three-position valve 21 is set at the first position.
The measurement line 22 is provided with a restriction 23 constructed of an orifice and the pump 26. The pump 26 is an electrically operated pump and introduces gas into the measurement line 22 when it is operated. The pump 26 is turned ON or OFF and has the number of revolutions controlled by the ECU 30. When the ECU 30 operates the pump 26, the ECU 30 controls the pump 26 so as to hold the number of revolutions constant at a previously set specified value.
Thus, when the ECU 30 operates the pump 26 in a state where the three-position valve 21 is set at the third position, there is brought about “a first measurement state” where an air-fuel mixture containing evaporated fuel supplied via the atmosphere line 17, the canister 13, a portion of the purge line 15 to the branch line 19, and the branch line 19 flows in the measurement line 22. Moreover, when the ECU 30 operates the pump 26 in a state where the three-position valve 21 is set at the first position with the selector valve 18 held set at the first position, there is brought about “a second measurement state” where air flows in the measurement line 22.
Moreover, in the measurement line 22, one end of a pressure sensor 24 of pressure measuring means is connected on the downstream side of the restriction 23, that is, between the restriction 23 and the pump 26. The other end of the pressure sensor 24 is open to the atmosphere, and a differential pressure ΔP between the atmospheric pressure and a pressure downstream of the restriction 23 in the measurement line 22 is detected by the pressure sensor 24. The differential pressure ΔP measured by the pressure sensor 24 is outputted to the ECU 30.
The ECU 30 controls the position of a throttle valve 3, the amount of fuel injected from the injector 4, and the opening of the purge valve 16 on the basis of detection values detected by various sensors. For example, the ECU 30 controls theses on the basis of an intake air volume detected by an air flow sensor (not shown) disposed in the intake pipe 2, an intake air pressure detected by an intake air pressure sensor (not shown), an air-fuel ratio detected by an air-fuel ratio sensor 6 disposed in an exhaust pipe, an ignition signal, an engine speed, an engine cooling water temperature, an accelerator position, and the like.
The purging condition is established, for example, when the engine cooling water temperature becomes a specified value Temp1 or more so that the warming-up of the engine is completed. The concentration detection conditions are satisfied while the engine is being warmed up but, for example, the cooling water temperature needs to be a specified value Temp2 lower than the specified temperature Temp1. Moreover, the concentration detection conditions are satisfied also in a period (mainly in the period of deceleration) during which purging of evaporated fuel is stopped with the engine operated. Here, when this evaporation fuel treatment system is applied to a hybrid vehicle, the concentration detection conditions are satisfied also in a period during which the vehicle is run by the motor with the engine stopped.
If determination in step S101 is affirmative, the routine proceeds to step S102 where a concentration detection routine is executed. If determination in step S101 is negative, the routine proceeds to step S106. In step S106, it is determined whether an ignition key is turned off. If determination is negative, the routine returns to step S101. If the ignition key is turned off, this flow is finished.
In the execution of the concentration detection routine, in the initial state, the purge valve 16 is “closed”, the three-position valve 21 is set at “the first position”, the selector valve 18 is “closed”, and the pump 26 is “stopped” (denoted by [A] in
In step S201, the pump 26 is operated from this state. With this, the state denoted by [B] in
When air flows through the restriction 23, a pressure loss is caused by the restriction 23, so the differential pressure ΔP is transiently changed after timing t0 and is decreased by the pressure loss caused by the restriction 23.
In step S202, the differential pressure ΔP is detected after the measurement line 22 is switched to the second measurement state, that is, at timing t1 when a specified time T1 elapses after the execution of step S201 (this differential pressure ΔP is referred to as ΔP0). This differential pressure ΔP0 shows the amount of pressure drop of air caused by the restriction 23.
In step S203, the three-position valve 21 is set at the third position. This operation starts to detect the differential pressure of an air-fuel mixture and brings about a state denoted by [C] in
In step S204, a fuel swing determination routine shown in
In
If the determination in step S701 is negative, the routine proceeds to step S702. In step S702, a fuel swing flag xFDELT is cleared (changed to 0). After the execution of step S702, this routine is finished.
Since determination in step S701 becomes affirmative after timing t2 when the stabilization time T2 passes, the routine proceeds to step S703. In step S703, it is further determined whether it is already determined that fuel swings, that is, whether the fuel swing flag xFDELT is 1. If this determination is affirmative, this routine is finished without executing any operation. If determination in step S703 is negative, the routine proceeds to step S704 in which the detection value ΔP of the pressure sensor 24 is read. In step S705, a differential pressure variation ΔPd is computed by subtracting the differential pressure ΔP read in the last execution of the routine from the differential pressure ΔP read in the last step S704.
In the subsequent step S706, it is determined whether the differential pressure variation ΔPd computed in step S705 is a predetermined fuel swing determination value KFDELT or more. This determination is to determine whether fuel in the fuel tank 11 swings. The reason why whether fuel swings in the fuel tank 11 can be determined on the basis of the magnitude of the variation ΔPd of the differential pressure ΔP caused by the restriction 23 is as follows: this fuel swing determination routine is executed in the first measurement state, and in the first measurement state, the fuel tank 11 communicates with the restriction 23. Hence, when the fuel swings in the fuel tank 11 to vary pressure in the tank, pressure variation is caused also at the restriction 23 communicating with the fuel tank 11.
If determination in step S706 is negative, this routine is finished without executing any operation. On the other hand, if determination in step S706 is affirmative, it is determined that the fuel in the fuel tank 11 swings and the routine proceeds to step S707 in which the fuel swing flag xFDELT is set to 1 and then this routine is finished.
Returning to description of
When the differential pressure ΔP1 is detected in step S205, the detection of the differential pressure of the air-fuel mixture is finished. While the fuel swing determination routine is executed repeatedly until the differential pressure ΔP1 is detected, when the detection of the differential pressure of the air-fuel mixture is finished, the fuel swing determination routine is finished in step S206.
In the next step S207, it is determined whether it is determined that fuel swings, that is, whether the fuel swing flag xFDELT is 1. As shown by a broken line in
If determination in step S207 is negative, the routine proceeds to step S209. Steps 209, 210 are processing as evaporated fuel concentration computation means and compute a differential pressure ratio P by an equation (1) on the basis of two differential pressures ΔP0, ΔP1 obtained in steps S202, 205.
P=ΔP1/ΔP0 (1)
In step S210, an evaporated fuel concentration C is computed by an equation (2) on the basis of the differential pressure ratio P. In the equation (2), k1 is a constant and is stored previously in the ROM of the ECU 30 together with the control program and the like.
C=k1×(P−1)(=(ΔP1−ΔP0)/ΔP0) (2)
Because evaporated fuel is heavier than air, purge gas containing evaporated fuel has a larger density. If the number of revolutions of the pump 26 is the same and the flow velocity (flow rate) in the measurement line 22 is the same, as the density becomes larger, a differential pressure caused by the restriction 23 becomes larger by the energy conservation law. As the evaporated fuel concentration C becomes higher, the density becomes large, so that as the evaporated fuel concentration C becomes larger, the differential pressure ratio P becomes larger. As a result, a characteristic curve followed by the evaporated fuel concentration C and the differential pressure ratio P becomes a straight line. The equation (2) expresses this characteristic line and the constant k1 is determined previously by experiment or the like.
In the next step 211, the obtained evaporated fuel concentration C is temporarily stored. In step S212, the three-position valve 21 is returned to the first position and in step S213, the pump 26 is stopped. This state is the same as [A] in
Returning to
If determination in step S103 is affirmative, purging routine is executed in step S104. In the purging routine, the operating state of the engine is detected and the flow rate of purge gas introduced into the intake pipe 2 is computed on the basis of the detected operating state of the engine. Thus, this step S104 corresponds to flow rate control.
Specifically, this flow rate of purge gas is computed on the basis of a fuel injection amount required in the operating state of the engine such as a present throttle opening, a lower limit value of the fuel injection amount to be controlled by the injector 4, and the pressure of the intake pipe 2. The opening of the purge valve 16 for realizing this flow rate of purge gas is computed on the basis of the evaporated fuel concentration C stored in
Moreover, the three-position valve 21 is switched to the first position in the period during which purging is performed by this purging routine. With this, evaporated fuel is desorbed from the canister 13 and the air-fuel mixture containing the evaporated fuel is purged from the purge line 15 to the intake pipe 2.
When the purging routine is finished, the routine proceeds to step S105. Moreover, if determination in step S103 is negative, the routine directly proceeds to step S105. In step S105, it is determined whether a specified time has passed from the time when the concentration detection routine in
According to this embodiment described above, it is determined in the fuel swing determination routine (
Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment only in that a concentration detection routine shown in
In the concentration detection routine shown in
On the other hand, if it is determined in step S207 that fuel swings, step S208-1 is executed. In step S208-1, the fuel swing flag xFDELT is cleared to 0 and the differential pressure ΔP1 is cleared to 0. Then, the routine returns to step s205 after this processing is executed.
In step S205 after the execution of step S208-1, the differential pressure ΔP1 is again detected and the differential pressure ΔP1 to be used in the following processing is updated by the newly detected differential pressure ΔP1. In the next step S207, it is again determined whether the fuel swing flag xFDELT is 1. Since the fuel swing flag xFDELT is cleared to 0 in the last step S208-1, if it is not again determined by the fuel swing determination routine executed in parallel (
As a result, steps S205, S207, and S208-1 are repeatedly executed until fuel stops to swing and when the fuel stops to swing, the routine proceeds to step S206 and its subsequent steps.
In this second embodiment, steps S203, S205, S207, S208-1, and S212 correspond to first pressure detection. After the differential pressure ΔP1 is detected in step S205, step S207 is executed to determine whether fuel swings. If it is determined that fuel swings, step S205 is executed again to immediately detect a differential pressure ΔP1 again and the differential pressure ΔP1 detected at the time when fuel swung is updated by the new detected differential pressure ΔP1.
Thus, it is possible to prevent the flow rate of purge gas introduced into the intake pipe 2 from being controlled on the basis of the differential pressure ΔP which is of insufficient accuracy because fuel swings. As a result, it is possible to control the flow rate of purge gas with higher accuracy. Moreover, the differential pressure ΔP1 is again detected immediately, so a new differential pressure ΔP1 can quickly be acquired. Thus, it is possible to quickly perform the computation of the evaporated fuel concentration C and the control of the flow rate of purge gas based on the evaporated fuel concentration C.
Next, a third embodiment of the present invention will be described.
In fuel swing determination processing in step S107, if the variation of the output value of the remaining fuel amount level sensor 40 for a relatively short specified swing determination time exceeds a predetermined reference value, it is determined that fuel swings and the fuel swing flag xFDELT is set to 1. On the other hand, if the variation is the reference value or less, it is determined that fuel does not swing and the fuel swing flag xFDELT is set to 0.
Thus, if it is determined in step S101 that the concentration detection conditions are satisfied, the fuel swing determination processing in step S107 is executed. Then, it is determined whether fuel in the fuel tank 11 swings and then the concentration detection routine in step S102-1 is executed.
The concentration detection routine in step S102-1 is shown in detail in
On the other hand, if determination in step S207 is affirmative, step S214 is executed. In this step S214, it is determined whether a swing convergence time (SCT) has passed after it is determined in step S107 in
In the third embodiment, it can be thought at the time of executing step S203 that fuel does not swing. Thus, after the operation of detecting the differential pressure of the air-fuel mixture in step S203, a differential pressure ΔP1 is detected in step S205 without determining whether fuel swings, and in step S209, a differential pressure ratio P is computed by the use of the differential pressure ΔP1. The processing after executing step S209 is the same as in
According to the third embodiment, the fuel swing determination processing (in step S107 in
Moreover, according to the third embodiment, it is determined whether the fuel swings before starting the operation of detecting the differential pressure of the air-fuel mixture. Thus, the operation of detecting the differential pressure of the air-fuel mixture is not started uselessly in the period during which the fuel swings, either.
Moreover, it is determined that the fuel stops swinging from the fact that a specified swing convergence time passes from the time when it is determined that the fuel swings. Thus, it is possible to reduce the number of executions of the fuel swing determination processing.
Next, a fourth embodiment of the present invention will be described. The fourth embodiment is different from the third embodiment in that the concentration detection routine in
The concentration detection routine in
If determination in step S207 is affirmative, the fuel swing determination processing is executed in step S215. The processing in this step S215 is the same as step S107 in
In the fourth embodiment, it is repeatedly determined whether fuel swings (step S215) and the operation of detecting the differential pressure of the air-fuel mixture is not performed until it is determined that fuel does not swing. Thus, it is possible to perform the operation of detecting the differential pressure of the air-fuel mixture after fuel surely stops swinging.
While the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments but the following embodiments are also included within the technical scope of the present invention. Further, various modifications other than the embodiments described below may be made without departing from the spirit and scope of the present invention.
For example, in the above embodiments, the fuel tank 11 does not communicate with the restriction 23 in the state in which the differential pressure ΔP0 is detected. However, air may be flowed through a specified restriction in the state in which the fuel tank 11 communicates with the restriction to form a second measurement state and the amount of change in the pressure of air caused by the restriction (that is, differential pressure ΔP0) may be detected in this second measurement state.
When the differential pressure ΔP0 is detected in the state in which the fuel tank 11 communicates with the specified restriction, if it is determined that fuel swings in a period during which the differential pressure ΔP0 is detected, it is preferable that the detected differential pressure ΔP0 is abandoned and that the differential pressure is immediately re-detected.
In
In
Moreover, if the differential pressure ΔP0 is detected in the state in which the fuel tank 11 communicates with the specified restriction and it is determined whether fuel swings on the basis of the output value of the fuel level sensor 40, it may also be determined that fuel swings before detecting the differential pressure ΔP0. If it is determined that fuel swings, the operation of detecting the differential pressure ΔP0 may be not performed until a specified swing convergence time passes. Alternatively, it may be repeatedly determined whether fuel swings and the operation of detecting the differential pressure ΔP0 may be not performed until it is determined that fuel does not swing. In the former case, for example, in
Moreover, in the third and fourth embodiments, it is determined whether fuel swings on the basis of the amount of change in the output value of the remaining fuel amount level sensor 40. If the vehicle is provided with an acceleration sensor, however, it may be determined whether fuel swings on the basis of the output value of the acceleration sensor. This is because it can be thought that since the acceleration sensor can detect the vehicle swinging, when the acceleration sensor can detect the vehicle swinging, fuel is also swinging.
Moreover, in the above embodiments, the differential pressure ΔP1 of the air-fuel mixture and the differential pressure ΔP0 of the air are detected by the common restriction 23, but these differential pressures ΔP1, ΔP0 may be detected by the use of different restrictions. Further, since the variation of the differential pressure ΔP0 is not so large, a previously stored value may be used as the differential pressure ΔP0. Alternatively, the differential pressure ΔP0 may be also determined from a specified computation equation on the basis of the atmospheric temperature and the atmospheric pressure.
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