JP3776389B2 - Evaporative fuel processing system leak determination device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a leak determination device that temporarily stores evaporative fuel generated in a fuel tank in a canister and determines whether or not there is a leak in an evaporative fuel processing system of an internal combustion engine that supplies an intake system according to operating conditions.
[0002]
[Prior art]
Conventionally, as this type of leak determination device, for example, a device described in Japanese Patent Application Laid-Open No. 6-159157 is known. The evaporative fuel processing system includes a canister, a fuel tank, a charge path and a purge path. The canister is connected to the fuel tank via the vapor path, and is connected to the intake pipe of the internal combustion engine via the purge path. A pressure sensor is provided in the charge path, and detects the pressure in the space formed by the charge path and the fuel tank (tank internal pressure).
[0003]
The leak determination device determines whether or not there is a leak in the evaporated fuel processing system. At this time, if a fuel shake (SLOSH) that causes a large amount of fuel to evaporate occurs, the presence or absence of slosh is determined. In the slosh determination, when the tank internal pressure is detected every predetermined time and the difference between the current value and the previous value of the detected value is less than the predetermined value, it is determined that no slosh has occurred and the difference is greater than or equal to the predetermined value. It is determined that a slosh has occurred. When the slosh has not occurred, the leak determination for determining the presence or absence of the leak is performed as it is. When the slosh is generated, the leak determination is stopped until the difference between the detected values of the tank internal pressure becomes less than a predetermined value, that is, until the slosh is settled.
[0004]
[Problems to be solved by the invention]
This prior art has a drawback that when a slosh occurs, it takes a long time to obtain a leak determination result. As a technique for solving this drawback, the applicant of the present application performs leak judgment of an evaporated fuel system even in the case of fuel fluctuation in Patent Application No. 2001-072892 (filed on March 14, 2001). A device that can do this is proposed. This method compares the current value of the pressure fluctuation amount during a predetermined time with the previous value as a correction for tank internal pressure fluctuation due to slosh. Is. The tank internal pressure used for the leak determination is corrected by subtracting the pressure fluctuation due to the slosh from the pressure fluctuation from the start to the end of the pressure monitoring mode.
[0005]
It is an object of the present invention to further advance this method, eliminate the excessive correction due to the slosh fluctuation, and improve the accuracy of leak determination.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a leak determination apparatus according to the present invention is a leak determination apparatus in an evaporative fuel processing system in which evaporated fuel generated in a fuel tank is temporarily adsorbed to a canister and supplied to an intake system of an internal combustion engine. The fuel swaying occurred in the fuel tank in accordance with the detecting means for detecting the pressure in the processing system and the change state of the pressure in the processing system detected during the leak determination period. And a shaking determination means for determining whether or not. Further, the leak determination device includes a means for obtaining a maximum value of a pressure change generated in the processing system due to the fluctuation when the fluctuation determination means determines that the fuel fluctuation has occurred, and during a predetermined leak determination period. Leak determination means for determining the presence or absence of a leak in the processing system according to a value obtained by correcting the detected variation amount of the detected pressure in the processing system based on the maximum value of the pressure change.
[0007]
According to the present invention, when a fluctuation occurs in the fuel, the pressure fluctuation amount detected during the leak determination period is corrected based on the maximum value of the pressure change generated in the processing system due to the fluctuation. By doing so, the leak determination can be performed without excessively correcting the pressure fluctuation amount during the leak determination period.
[0008]
In one embodiment of the present invention (Claim 2), the leak determination apparatus includes sampling means for sampling the detection pressure by the detection means at a predetermined cycle during a leak determination period, and the shake determination means is the sampling means. The occurrence of the shaking is determined based on the difference between the sample values generated by the above.
[0009]
In one embodiment of the present invention (claim 3), the means for obtaining the maximum value is a difference between a difference in a predetermined interval of the sample values generated by the sampling means and a difference in a predetermined interval following the predetermined interval. Find the maximum value of.
[0010]
Further, in an embodiment of the present invention (Claim 4), the means for obtaining the maximum value includes an integration means for integrating the maximum value of the difference difference obtained each time fuel swaying, and the leak determination means comprises Then, the fluctuation amount of the detected pressure is corrected based on the value integrated by the integrating means.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a leak determination apparatus for an evaporated fuel processing system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an evaporative fuel processing system to which the leak determination device of the present embodiment is applied, and an internal combustion engine equipped with the same. The leak determination device 1 determines whether or not there is a leak in the evaporated fuel processing system 20 of an internal combustion engine (hereinafter referred to as “engine”) 3 and includes an ECU 2.
[0012]
The engine 3 is a gasoline engine and is mounted on a vehicle. An engine speed sensor 12 is attached to the main body of the engine 3, and the engine speed sensor 12 detects the engine speed NE and sends a detection signal to the ECU 2.
[0013]
Further, a throttle valve 6 is provided in the intake pipe 5 (intake system) of the engine 3, and an intake pipe absolute pressure sensor 13 is attached downstream thereof. The intake pipe absolute pressure sensor 13 detects the intake pipe absolute pressure PBA in the intake pipe 5 and sends the detection signal to the ECU 2.
[0014]
Further, an injector 7 is attached to a portion of the intake pipe 5 on the downstream side of the intake pipe absolute pressure sensor 13 so as to face an intake port (not shown). The fuel injection time TOUT, which is the valve opening time of the injector 7, is controlled by the ECU 2. The injector 7 is connected to the fuel tank 21 via the fuel supply pipe 8. A fuel pump 9 for sending fuel to the injector 7 is provided in the middle of the fuel supply pipe 8.
[0015]
On the other hand, an O2 sensor 14 is attached to a portion of the exhaust pipe 10 of the engine 3 upstream of the catalyst device 11. The O2 sensor 14 detects the oxygen concentration in the exhaust gas upstream of the catalyst device 11, and outputs a detection signal corresponding to the oxygen concentration to the ECU 2. The ECU 2 obtains the air-fuel ratio correction coefficient KO2 used for calculating the fuel injection time TOUT described above based on the detection signal of the O2 sensor 14. Furthermore, a detection signal indicating the vehicle speed (vehicle speed) VP is input from the vehicle speed sensor 15 to the ECU 2.
[0016]
Further, the above-described evaporated fuel processing system 20 temporarily stores the evaporated fuel generated in the fuel tank 21 in the canister 24, and appropriately discharges it into the intake pipe 5. The charge passage 22, bypass passage 23, a canister 24, a purge passage 25, and the like.
[0017]
The canister 24 is connected to the fuel tank 21 through the charge passage 22, and the evaporated fuel generated in the fuel tank 21 is sent to the canister 24 through the charge passage 22. A pressure sensor 26 is disposed in a portion of the charge passage 22 near the fuel tank 21. The pressure sensor 26 is composed of, for example, a piezoelectric element, detects the pressure in the charge passage 22, and outputs a detection signal to the ECU 2. Since the pressure in the charge passage 22 is usually substantially equal to the pressure in the fuel tank 21, it is hereinafter referred to as tank internal pressure PTANK (pressure in the evaporated fuel processing system).
[0018]
A two-way valve 27 is provided between the pressure sensor 26 in the charge passage 22 and the canister 24. The two-way valve 27 is a mechanical valve that combines a diaphragm positive pressure valve and a negative pressure valve. The positive pressure valve is configured to open when the tank internal pressure PTANK becomes higher than the atmospheric pressure by a predetermined pressure, and the evaporated fuel in the fuel tank 21 is sent to the canister 24 by opening the valve. Further, the negative pressure valve is configured to open when the tank internal pressure PTANK is lower than the pressure on the canister 24 side by a predetermined pressure, and the evaporated fuel stored in the canister 24 is fueled by the valve opening. Returned to tank 21.
[0019]
Further, the bypass passage 23 bypasses the two-way valve 27 and is connected to a portion on the canister 24 side and a portion on the pressure sensor 26 side of the charge passage 22 with respect to the two-way valve 27. A bypass valve 30 is provided in the middle of the bypass passage 23. This bypass valve 30 is configured by a normally closed type electromagnetic valve, and normally closes the bypass passage 23 and opens it when excited by control of the ECU 2 to open the bypass passage 23.
[0020]
The fuel tank 21 is provided with a float valve 21a. This float valve 21a opens and closes the port on the fuel tank 21 side of the charge passage 22, and normally opens the port, while the fuel tank 21 is full or the fuel in the tank shakes, etc. Further, by closing the port, the fuel is prevented from flowing into the charge passage 22 side.
[0021]
On the other hand, the canister 24 incorporates activated carbon, and the evaporated fuel is adsorbed by the activated carbon. The canister 24 is connected to an atmosphere passage 29 that opens to the atmosphere side. The atmosphere passage 29 is provided with a vent shut valve 31 that opens and closes the atmosphere passage 29. The vent shut valve 31 is constituted by a solenoid valve of a type that is always open, and normally holds the atmospheric passage 29 in an open state and closes the atmospheric passage 29 when excited by control of the ECU 2.
[0022]
A purge control valve 32 for opening and closing the purge passage 25 is provided in the middle of the purge passage 25 described above. The purge control valve 32 is composed of an electromagnetic valve whose opening degree changes continuously according to the duty ratio of the drive signal from the ECU 2. When the vent shut valve 31 is in the open state, the purge control valve 32 is opened, so that the evaporated fuel adsorbed by the canister 24 is fed into the intake pipe 5 by the negative pressure in the intake pipe 5. The ECU 2 controls the flow rate of the evaporated fuel sent from the canister 24 to the intake pipe 5, that is, the purge flow rate, by duty-controlling the opening degree of the purge control valve 32.
[0023]
On the other hand, the ECU 2 (leak determination means, fuel fluctuation determination means, correction means) is composed of a microcomputer comprising an I / O interface, CPU, RAM, ROM and the like. The detection signals of the various sensors 12 to 15 described above are input to the CPU after A / D conversion and shaping by the I / O interface. The CPU determines the operating state of the engine 3 according to these input signals, and drives the various valves 30 to 32 described above according to the control program stored in advance in the ROM, the data stored in the RAM, and the like. Then, the leak determination process of the evaporated fuel processing system 20 described below is executed.
[0024]
Hereinafter, this leak determination processing will be described with reference to FIG. This process determines whether or not there is a leak in a portion upstream of the two-way valve 27 and the bypass valve 30 in the evaporated fuel processing system 20 including the fuel tank 21. FIG. 2 shows the main routine of this process. This process is executed every predetermined time (for example, 80 msec) according to the timer setting, and the leak determination in this process is executed only once from the start to the end of the operation of the engine 3.
[0025]
First, in step S1, it is determined whether or not a monitor execution condition is satisfied. This monitor execution condition is for determining whether or not the execution condition of the leak determination process is satisfied. For example, when all of the following conditions (1) to (4) are satisfied, It is determined that the execution condition is satisfied.
[0026]
(1) The purge control by the purge control valve 32 is being executed.
[0027]
(2) The engine 3 is in a predetermined steady operation state (determined by, for example, the absolute pressure PBA in the intake pipe and the engine speed NE).
[0028]
(3) The vehicle is in cruising operation with a small change in vehicle speed VP.
[0029]
(4) The air-fuel ratio correction coefficient KO2 is not less than a predetermined value and the influence of the purge fuel on the air-fuel ratio A / F is small.
[0030]
If the determination result in step 1 is YES and all of the above conditions (1) to (4) are satisfied, it is determined that the leak determination can be performed, and the atmospheric release mode process in steps S2 to S6 is performed. After executing the mode process, the leak check mode process, the pressure return mode process, and the correction check mode process in this order, this process ends.
[0031]
On the other hand, if the determination result in step 1 is NO and the monitor execution condition is not satisfied, the process proceeds to step S7, the initialization process is executed, and the process is terminated. In this initialization process, although not shown, both the timer value T of the leak determination timer and the timer value TPHEN of the slosh determination timer are set to the value 0. Both the leak determination timer and the slosh determination timer are constituted by up-count timers.
[0032]
On the other hand, in the atmospheric release mode process of step 2, the tank internal pressure PTANK is substantially equal to the atmospheric pressure by holding the bypass valve 30 and the vent shut valve 31 in the open state and the purge control valve 32 in the closed state. Is done.
[0033]
Further, in the pressure reduction mode processing of step 2 subsequent to step 2, the bypass valve 30 is kept open, the vent shut valve 31 is kept closed, and the purge control valve 32 is duty controlled for a predetermined pressure reduction time exactly 1. Thus, the inside of the evaporated fuel processing system 20 is depressurized. After this decompression, the timer value T of the leak determination timer is set to the value O, and the leak check mode execution permission flag F_EVAP2 is set to “1” to indicate that the leak check mode process can be executed. To do.
[0034]
Next, a process for calculating the gradient of the amount of fluctuation in internal pressure when fuel sway (slosh) occurs will be described with reference to FIG. This inclination of the internal pressure fluctuation amount is used for leak determination. This calculation process is repeated at regular intervals, such as 80 millisecond intervals. The SLOSH processing flag shown in step S101 is set to 1 when the evaporative fuel system monitoring process ends the pressure reduction mode and enters the leak check mode. If this flag is not 1, various parameters are set or cleared, and the process is terminated (S105).
[0035]
The slosh timer (S103) is for setting a sampling period for sampling the output of the pressure sensor. This timer is composed of a down counter, and sampling is performed every time it becomes zero. In this embodiment, the ECU 2 has 11 storage locations from i = 10 to 0 in order to store the pressure sensor sample values. In the actual process, a preset number of storage locations are used. FIG. 4 shows a state in which sample values PTSL (6) to PTSL (0) are stored in storage locations 6 to 0. In this case, i is sequentially set from 6 to 0 in step S107 for each sampling cycle, and in step S109, the detected value PTANK of the tank internal pressure is stored in the storage location PTSL (0).
[0036]
The process up to step S109 is repeated until the sample values are stored for a predetermined number S of sample points. Until the sample point of S is reached, the process is terminated after S109 without proceeding to step S111. When sample values are stored for the sample points of S, the process proceeds to step S111, and a difference DSLOSH0 between the first sample value PTSL (6) and the sample value PTSL (3) at the intermediate sample point is calculated (S111). Further, the difference DSLOSH1 between the sample value PTSL (3) at the intermediate sample point and the sample value PTSL (0) at the last sample point is calculated (S113). FIG. 5 shows this process.
[0037]
In step S115, a difference DDSLOSH between DSLOSH1 and DSLOSH0 is calculated. Next, if the start flag is set to 1, the process proceeds to S121. However, since it is not initially set, the process proceeds to S133. If DDSLOSH is equal to or greater than the predetermined judgment value, DDSLMAX (set in S121 described later) is set to 0, the start flag is set to 1 (S137), and the sampling period value is set to the SLOSH timer. (S139) and the process ends.
[0038]
Next, when this process is started, since the start flag is set to 1 (S117), the process proceeds to step S121, and the difference between the sample values in the predetermined number S of sampling cycles, whichever is larger of the differences DDSLOSH Set the value to DDSLMAX.
[0039]
Here, one fuel fluctuation SLOSH period will be described with reference to FIG. The start of SLOSH is determined when DDSLOSH is equal to or greater than the start determination value (S133). The end of fuel shaking is similarly determined when DDSLOSH is equal to or less than the end determination value (S123). One leak check mode takes, for example, about 2 minutes, and fuel shaking may occur several times during this time. FIG. 7 referred later shows a state in which two fuel fluctuations occur during one leak check mode.
[0040]
If DDSLOSH has not reached the determination value for determining the end of fuel shake SLOSH (S123), the value of DDSLMAX is set to REVSLOSH (S131). When DDSLOSH is equal to or less than the end determination value, the process proceeds to S125, and the value of REVSLOSH is added to the previous value of REVSLTTL to obtain the current REVSLTTL (S125). Referring to FIG. 7, REVSLTTL is an integrated value of DDSLOSH maximum value REVSLOSH calculated for each occurrence of fuel fluctuation, and is expressed by the following equation.
[0041]
[Expression 1]
REVSTTL = REVSLOSH0 + REVSLOSH1 + ・ ・ ・ + REVSLOSHn
[0042]
Next, REVSLOSH is reset to 0 (S127), the start flag is reset to 0 (S129), the time of the sample period is set in the SLOSH timer (S139), and the process proceeds to step S141. Here, it is determined whether or not the end flag of the leak check mode, that is, the flag indicating the end of the fluctuation amount calculation is set to 1 (S141), and if not set to 1, the processing is ended. If it is set to 1, the flow proceeds to S143, and the REVVARIB is obtained by adding the maximum value REVSLOSH of the current DDSLOSH to the integrated value REVSLTTL over the plurality of shakes of the maximum value of the DDSLOSH for each shake. If the end of shaking is determined in S123, REVSLTTL integration processing is performed in step S125, and REVSLOSH is reset to 0 in S127. Therefore, the value calculated in S143 is equal to the value calculated in S125.
[0043]
When the end determination is NO in step S123, the maximum value of DDSLOSH of the current shaking is set in REVSLOSH in step S131. Subsequently, the process proceeds to S141 via S139, and if the flag indicating the end of the leak check mode is set, the process proceeds to S143, and REVVARIB is calculated using REVSLOSH set in S131.
[0044]
Through these processes, the routine proceeds to step S145, where the slope PTVARIB of the variation amount of the tank internal pressure during the leak check mode is calculated according to the following equation.
[0045]
[Expression 2]
PTVARIB = {(PTLK1-PTLK0)-(REVVARIB × coefficient)} / leak check time [0046]
Here, PTLK1 is the fuel tank internal pressure PTANK value at the end of the leak check mode, and PTANK0 is the fuel tank internal pressure PTANK value at the start of the leak check mode. The coefficient in the above equation is 1 in this example.
[0047]
In one embodiment, a value PTJDG obtained by subtracting the variation amount (slope) of the tank internal pressure in the correction check mode (FIG. 2, S6) from the slope PTVARIB of the variation amount of the tank internal pressure obtained in this way is used as the value used for the determination. If PTJDG is less than the reference value, it is determined that the monitor has passed (no hole), and if PTJDG exceeds the reference value, it is determined that the monitor has failed (has a hole).
[0048]
Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to such embodiments.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.
FIG. 2 is a flowchart showing an overall processing flow in one embodiment of the present invention.
FIG. 3 is a flowchart showing a process for calculating the gradient of the fuel tank internal pressure fluctuation amount in one embodiment of the present invention;
FIG. 4 is a diagram for explaining a slosh determination process in one embodiment of the present invention.
FIG. 5 is a diagram for explaining how to take a differential DSLOSH of sample values in one embodiment of the present invention;
FIG. 6 is a view for explaining how to determine the end point of fuel shake slosh in one embodiment of the present invention;
FIG. 7 is a diagram for explaining a state in which fuel slosh has occurred a plurality of times in one processing cycle and integration of REVSLOSH in one embodiment of the present invention.
[Explanation of symbols]
3 Engine 20 Evaporative fuel system 21 Fuel tank 26 Pressure sensor

Claims (4)

A leak determination device in an evaporative fuel processing system that temporarily adsorbs evaporative fuel generated in a fuel tank to a canister and supplies it to an intake system of an internal combustion engine,
Detecting means for detecting pressure in the processing system;
Sway determination means for determining whether or not fuel sway has occurred in the fuel tank according to the pressure change state in the processing system detected during the leak determination period;
Means for obtaining a maximum value of a pressure change generated in the processing system by the shaking when the shaking judging means determines that the fuel shaking has occurred;
Leak determination means for determining the presence or absence of a leak in the processing system according to a value obtained by correcting the fluctuation amount of the detected pressure in the processing system detected during a predetermined leak determination period based on the maximum value of the pressure change When,
An evaporative fuel processing system leak determination device comprising: The leak determination device includes sampling means for sampling the detection pressure by the detection means at a predetermined cycle during a leak determination period,
The leak determination apparatus according to claim 1, wherein the shake determination unit determines the occurrence of the shake based on a difference between sample values generated by the sampling unit. The leak determination according to claim 1, wherein the means for obtaining the maximum value obtains a maximum value of a difference between a difference in a predetermined interval of the sample value generated by the sampling means and a difference in a predetermined interval following the predetermined interval. apparatus. The means for obtaining the maximum value includes an integration means for integrating the maximum value of the difference difference obtained each time the fuel shakes over the leak determination period, and the leak determination means is The leak determination apparatus according to claim 3, wherein the fluctuation amount of the detected pressure is corrected based on the integrated value.

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