JP2699774B2 - Failure diagnosis device for evaporation purge system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis apparatus for an evaporative purge system, and more particularly to a method for adsorbing fuel vapor (vapor) of an internal combustion engine into an adsorbent in a canister and subjecting the adsorbed fuel to internal combustion under predetermined operating conditions. The present invention relates to a failure diagnosis device for an evaporative purge system that discharges (purges) into an intake system of an engine and burns it.

[0002]

2. Description of the Related Art Fuel evaporated in a fuel tank (vapor)
In order to prevent the air from being released to the atmosphere, each part is sealed, and the vapor is temporarily adsorbed by the adsorbent in the canister, and the fuel adsorbed while the vehicle is running is drawn into the intake system and burned to evaporate. In an internal combustion engine equipped with a system, when a vapor passage is damaged or a pipe is disconnected for any reason, vapor is released to the atmosphere. Therefore, it is necessary to diagnose whether a failure has occurred in such an evaporation purge system.

Accordingly, as the above-mentioned failure diagnosis apparatus, the applicant of the present invention provided a tank internal pressure control valve for maintaining the internal pressure of the fuel tank at a predetermined positive pressure value or less in an evaporation path from the fuel tank to the canister. A pressure change detecting means for detecting a pressure change of the system, and a failure of the evaporative purge system which determines that an abnormality occurs when a value detected by the pressure change detecting means or a value obtained by calculating the pressure change is within a predetermined range. A diagnostic device was proposed (Japanese Patent Application No. 4-182549).
issue).

[0004]

However, the pressure in the fuel tank is affected by the fuel consumption (tank space volume), fuel temperature and other various variables (parameters), and it is difficult to predict the pressure. The failure diagnosis device proposed by the present applicant may not be able to perform accurate failure diagnosis. For example, during a cold start of the engine, in a normal state where there is no leakage in the evaporative system, as shown by a solid line I in FIG. Due to the decrease in fuel volume, the pressure temporarily decreases to a negative pressure.
Thereafter, the fuel temperature gradually rises due to the exhaust heat, and the amount of generated vapor increases, so that the tank internal pressure becomes positive.

On the other hand, if there is a leak in the evaporative system during a cold start, the tank internal pressure remains at a value near the atmospheric pressure as shown by a broken line II in FIG. Therefore, in the proposed device of the present applicant, when a predetermined time or more has elapsed, the tank internal pressure becomes more negative than the predetermined negative pressure, or a predetermined positive pressure (this is higher than the set pressure of the tank internal pressure control valve). It is determined whether the pressure has become more positive than the value (slightly smaller value). When any of the states is reached, the state is normal, and when none of these states is reached, the state is indicated by broken line II in FIG. judge.

However, during a warm start such as restarting in a short time after stopping the engine, if the evaporative system is normal, a large amount of vapor is generated in the fuel tank. As shown by the dashed line III in FIG.
It changes with positive pressure. In this case, after the start, the predetermined positive pressure may be equal to or more than the predetermined positive pressure determination value until a predetermined time elapses. However, the tank internal pressure changes due to a combination of various parameters as described above, and Since the determination value may not be reached, in such a case, an abnormal (failure) is erroneously detected even though the evaporative system is normal.

[0007] The present invention has been made in view of the above points,
An object of the present invention is to provide a failure diagnosis device for an evaporative purge system that solves the above-mentioned problem by performing a failure diagnosis at a cold start.

[0008]

According to the present invention, as shown in FIG. 1, the fuel vapor from a fuel tank 11 is adsorbed on an adsorbent in a canister 13 through a vapor passage 12 so that the fuel in the canister 13 is maintained during a predetermined operation. In the apparatus for diagnosing the failure of the evaporative purge system for purging the adsorbed fuel into the intake passage 15 of the internal combustion engine 10 through the purge passage 14, a cold start detection unit 16, a setting unit 17, a valve unit 18, a pressure detection unit 19, By providing the determination means 20, the above object is achieved.

Here, the cold start detecting means 16 detects whether or not a cold start is being performed. The setting means 17 is provided only when the cold start detecting means 16 detects the cold start.
Set the judgment permission flag.

The valve device 18 closes the vapor passage 12 communicating with the fuel tank 11 at least when the determination permission flag is set. The pressure detecting means 19 detects the pressure in the path from the fuel tank 11 to the valve device 18.

[0011] Then, when the determination means 20 detects that the determination permission flag is set,
If the pressure detected by the pressure detecting means 19 is equal to or higher than a predetermined value even after a predetermined time has elapsed, it is determined that the pressure is abnormal.

[0012]

After the cold start of the internal combustion engine 10, the fuel tank 1
There is almost no amount of evaporated fuel in 1 and the only variable affecting the tank internal pressure is the fuel consumption (tank air-fuel specific volume). Since the fuel is consumed after the cold start, if there is no leak in the vapor passage 12, the pressure detected by the pressure detecting means 19 changes to the negative pressure once, and then increases as the fuel temperature increases. . On the other hand, when there is a leak in the vapor passage 12, the pressure hardly changes near the atmospheric pressure. Therefore, only at the time of the cold start, the path from the fuel tank 12 to the valve device 18 depends on whether or not the pressure becomes a negative pressure less than a predetermined value (the differential pressure from the atmospheric pressure is more than a predetermined value). It is possible to reliably detect whether or not there is a leak.

[0013]

FIG. 2 shows a system configuration diagram of a first embodiment of the present invention. In the figure, a fuel tank 21 is a main tank 21a.
And a sub tank 21b. The sub-tank 21b is located in the main tank 21a, communicates with the main tank 21a, and has a fuel pump 22 disposed therein. Further, a rollover valve 23 is provided above the fuel tank 21. This rollover valve 23
Is provided to prevent the fuel from flowing out when the vehicle rolls over.

The fuel pump 22 is connected to a fuel injection valve 26 via a pipe 24 and a pressure regulator 25, respectively. The pressure regulator 25 is provided to make the fuel pressure constant, and the fuel injection valve 26
The excess fuel not injected in the step (b) is returned into the sub tank 21b via the return pipe 27.

The upper portion of the fuel tank 21 passes through a vapor passage 28 (corresponding to the vapor passage 12) and an internal pressure control valve 29 (corresponding to the valve device 18) to a canister 30 (corresponding to the canister 13). Are in communication. The internal pressure control valve 29 includes a check ball 29a and a spring 29b. The spring 29b applies a biasing force to the check ball 29a in the right direction in the drawing, and the spring 29b increases the pressure in the fuel tank 21 to a predetermined positive pressure value (for example, 250 mmAq) or less.

The canister 30 has an activated carbon 30a as an adsorbent inside, and an air introduction hole 30 opened to the outside.
This is a known configuration in which b is formed. Fuel tank 21
A pressure sensor 31 is provided in a path (a vapor passage 28) between the pressure sensor 31 and the internal pressure control valve 29. The pressure sensor 31 is a kind of strain gauge for detecting strain of the silicon wafer by a bridge circuit, and measures a difference between a pressure in a space formed between the fuel tank 21 and the internal pressure control valve 29 and an atmospheric pressure.

The canister 30 is connected to a purge passage 32.
(Corresponding to the purge passage 14) and a vacuum switching valve (VSV) 33 which is an electromagnetic valve, and communicates with a position of the intake passage 36 (corresponding to the intake passage 15) downstream of the throttle valve 35. ing. An air cleaner (AC) 37 that filters air to remove dust is provided upstream of the throttle valve 35. An intake air temperature sensor 38 for detecting an intake air temperature is provided near the air cleaner 37.

The throttle valve 35 is a valve whose opening is controlled by the amount of depression of an accelerator pedal operated by the driver.
4 is detected. The microcomputer 40 is an electronic control unit that controls the evaporative purge system. The microcomputer 40 realizes the pressure detecting means 19, the cold start detecting means 16, the setting means 17, and the determining means 20 by software operations. The warning light 41 is turned on to notify the driver of the occurrence of the abnormality. The microcomputer 40 receives a start signal from the starter 39.

The microcomputer 40 has a known hardware configuration as shown in FIG. 2, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 3, a microcomputer 40 includes a central processing unit (CPU) 50, a read-only memory (ROM) 51 storing a processing program, and a random access memory (RAM) 5 used as a work area.
2. Backup R to retain data even after engine stop
It comprises an AM 53, an input interface circuit with a multiplexer 54, an input / output interface circuit 55, an A / D converter 56, and the like, which are connected via a bidirectional bus 57.

The input interface circuit 54 sequentially switches the pressure detection signal from the pressure sensor 31, the detection signal from the throttle position sensor 34, the intake temperature detection signal from the intake temperature sensor 38, the start signal from the starter 39, and the like, in a time series. And then supplies it to the A / D converter 56. The A / D converter 56 converts the input signal into an analog signal.
The digital data is converted and sequentially transmitted to the bus 57. The input / output interface circuit 55 is a throttle position sensor 3
4 is sent to the bus 57 while the fuel injection valve 2
6. Control signals are selectively sent to the VSV 33 and the warning light 41 to control them.

Next, the normal operation of the evaporative purge of the system shown in FIG. 2 will be described. When the starter 39 is turned on, the fuel pump 22 shown in FIG. 2 is operated by the microcomputer 40 via a controller (not shown), whereby the fuel in the sub tank 21b is discharged to the pressure regulator 25 through the pipe 24,
Here, the pressure is made constant and sent to the fuel injection valve 26, and the fuel is injected from the fuel injection valve 26 into the intake passage 36 during the fuel injection time from the microcomputer 38. The surplus fuel is returned to the sub tank 21b via the return pipe 27.

On the other hand, the evaporated fuel (vapor) generated in the fuel tank 21 passes through the vapor passage 28 to the internal pressure control valve 2.
It reaches 9. Here, when the tank internal pressure is smaller than the pressure set by the internal pressure control valve 29 (for example, 250 mmAq),
Check ball 29a due to spring force of spring 29b
Is located at the position shown in the figure and blocks the vapor passage 28, so that the delivery of the evaporated fuel to the canister 30 is prevented.

When evaporative fuel is generated and the tank internal pressure exceeds the set pressure, the check ball 29 of the internal pressure control valve 29
2 is pushed to the left in FIG. 2 against the spring force of the spring 29b. As a result, the evaporated fuel is sent into the canister 30 through the vapor passage 28 and the internal pressure control valve 29, and is adsorbed on the activated carbon 30a inside. Is done. When the evaporated fuel is sent to the canister 30, the tank internal pressure decreases, and when the tank internal pressure falls below the set pressure, the internal pressure control valve 29 is closed again as shown.

As the operation continues, the amount of evaporated fuel increases,
When the tank internal pressure becomes equal to or higher than the set pressure again, the internal pressure control valve 29 opens again to feed the evaporated fuel to the canister 30. Hereinafter, in the same manner as above, the internal pressure control valve 2 is normally operated.
9 keeps the tank internal pressure at the set pressure by repeating the on-off valve.

When there is no leak in the vapor passage 28 or the fuel tank 21, the evaporated fuel is adsorbed on the activated carbon 30 a in the canister 30 through the internal pressure control valve 29 as described above. Immediately after the engine is started, the VSV 33 is closed because the purge control condition is not satisfied.

The above-mentioned purge control conditions are operating conditions which can minimize adverse effects on operability and exhaust emission even if the air-fuel ratio is roughened by the purge. During the feedback control of the fuel injection, the microcomputer 40 determines that the purge control condition is satisfied when the intake air amount is equal to or more than a predetermined value and the fuel cut is not performed.

If it is determined that the purge control condition is satisfied, the microcomputer 40 determines that the VSV3
3 is opened. Then, due to the negative pressure of the intake passage 36, the atmosphere is introduced into the canister 30 from the atmosphere inlet 30b, the fuel adsorbed on the activated carbon 30a is desorbed, and passes through the purge passage 32 and the VSV 33, respectively.
Evaporated fuel is sucked into the inside. The activated carbon 30a is regenerated by the above-mentioned desorption, and prepares for the next vapor adsorption.
As a result, the purge flow rate gradually increases. Next, the processing operation of the failure diagnosis of the evaporative purge system that executes the above-described evaporative purge system will be described. This failure diagnosis is executed by the microcomputer 40.
FIG. 4 shows a flowchart of the first embodiment of the failure diagnosis routine of the main part of the present invention. When the failure diagnosis routine is started, first, it is determined whether or not the engine is at the start according to whether the starter signal is input from the starter 39 (step 10).
1).

Immediately after the starter signal is input, that is, at the time of startup, the process proceeds to step 102, in which the CPU 50 detects the engine cooling water temperature from a water temperature sensor (not shown in FIG. 2) attached to the water outlet and the intake air temperature. Based on the output value of each of the A / D converters 56 from the intake air temperature detection signal from the sensor 38, it is determined whether or not the detected values are substantially equal.

If the detected water temperature is substantially equal to the detected intake air temperature, the routine proceeds to step 103, where it is determined whether the detected intake air temperature is less than 30 ° C. When it is determined in step 103 that the detected intake air temperature is less than 30 ° C., it is determined that the engine is in a cold start, the process proceeds to step 104, the determination permission flag is set to “1”, and the routine is temporarily terminated. . On the other hand, when it is determined in step 102 that the detected water temperature and the detected intake air temperature are not substantially equal, or when it is determined in step 103 that the detected intake air temperature is 30 ° C. or more, it is not during the cold start. Then, the routine proceeds to step 105, where the determination permission flag is cleared to "0", and this routine is once ended.

If it is determined in step 101 that the engine is not in the starting state, the process proceeds to step 106, in which it is determined whether the determination permission flag is set to "1".
Only when it is set, that is, immediately after the cold start, the failure diagnosis after step 107 is executed.

In step 107, it is determined whether or not a predetermined time has elapsed since the start of the engine. If the predetermined time has not elapsed, the CPU 50 proceeds to step 108 to determine the tank internal pressure P based on the pressure detected by the pressure sensor 31. Read.
Then, it is determined whether or not the read tank internal pressure P is a negative pressure greater than a predetermined threshold value of -50 mmAq (step 109). If the tank internal pressure P is not a negative pressure greater than -50 mmAq, this routine is temporarily terminated. I do.

Until a predetermined time has elapsed after the cold start, the processing of steps 101, 106, 107, 108 and 109 is repeated at a predetermined cycle, and the read tank pressure P
Is determined to be a value on the negative pressure side of -50 mmAq, the routine proceeds from step 109 to step 110, in which the normal flag is set to "1". It is determined that there is a leak in the passage 28 or the fuel tank 21 and the normal flag is not set.

Thereafter, if it is determined in step 107 that a predetermined time has elapsed after the cold start, the process proceeds to step 111,
It is determined whether the normal flag is set to "1". When the normal flag is set to "1", that is, when the tank internal pressure P becomes -50 m within a predetermined time immediately after the cold start.
When the value on the negative pressure side exceeds mAq, the vapor passage 28
Then, it is determined that there is no leakage in the fuel tank 21 and the fuel tank 21 is normal, and the warning lamp 41 is turned off (step 112).

On the other hand, if it is determined in step 111 that the normal flag is not set, it is determined that there is a leak in the vapor passage 28 or the fuel tank 21, and the warning lamp 41 is turned on (step 113). The driver can use this warning light 41
Can be determined that there is a leak in the evaporation system from the internal pressure control valve 29 to the fuel tank 21.

As described above, according to the present embodiment, the tank internal pressure P is reduced to the predetermined threshold value −50 m only immediately after the cold start in which the variable affecting the tank internal pressure is only the fuel consumption.
Since failure diagnosis is performed by determining whether or not the pressure becomes lower than mAq, erroneous detection is eliminated and reliability can be improved.

Further, according to the present embodiment, even if the negative pressure is not introduced into the fuel tank 21, the internal pressure control valve 29, the pressure sensor 3
1 and the microcomputer 40, it is possible to diagnose the failure of the evaporative purge system, so that it is possible to prevent the deterioration of the exhaust emission and the rapid fluctuation of the air-fuel ratio, and to have a simple and inexpensive structure without using many control valves. Trouble diagnosis can be performed.

Next, a second embodiment of the failure diagnosis will be described. FIG. 5 shows a flowchart of a second embodiment of the failure diagnosis routine of the main part of the present invention. In the figure, the same reference numerals are given to the same processing steps as in FIG. 4, and the description thereof will be omitted. In this embodiment, in consideration of the fact that the tank internal pressure changes in the negative pressure direction according to the fuel consumption until a predetermined time elapses immediately after the cold start, the determination value to be compared with the tank internal pressure according to the fuel consumption is determined. It is designed to be variable.

In FIG. 5, after the CPU 50 reads the tank internal pressure P before a predetermined time has elapsed since the cold start in step 108, the process proceeds to step 121, where the CPU 50
The map of FIG. 6 calculates the decision value P _L with reference fuel consumption QF previously stored in. As shown in FIG. 6, the determination value P _L is a negative pressure, and is a value that increases in the negative pressure direction as the fuel consumption QF (unit second) increases. The value is set to the positive pressure side with a margin more than the actual tank internal pressure immediately after the cold start.

Here, as a method of calculating the fuel consumption QF, for example, as shown in FIG. 7, it is calculated in a fuel injection routine started at every predetermined crank angle. That is, FIG.
, The fuel injection time (amount) TAU is calculated by, for example, the following expression: TAU = TP × F, and is read by the CPU 50 (step 201). Here, in the above equation, TP is a basic fuel injection amount, which is an intake air amount (or intake pipe pressure) per engine speed, and F is various corrections such as a warm-up increase, an air-fuel ratio feedback correction coefficient, and a post-start increase. It is a coefficient.

Subsequently, the previous fuel consumption QF is added to the fuel injection time TAU to update the current fuel consumption QF (step 202). And the fuel injection time T
Based on the AU, the CPU 50 causes the fuel injection valve 26 to execute fuel injection (step 203). Thus, the fuel consumption QF is calculated as an integrated value of the fuel injection time TAU.

Referring back to FIG. 5, step 1 will be described.
When the determination value P _L is calculated based on the fuel consumption amount QF at 21, a magnitude comparison between the tank internal pressure P and the determination value P _L is performed at subsequent step 122. As described above, since the determination value P _L is set to a value on the positive pressure side from the tank internal pressure P within a predetermined time after the cold start during normal operation of the evaporative system without tank leakage or the like, P <P _{L in} step 122. Is determined as normal, the normality flag is set to "1" (step 123), and this routine ends.

On the other hand, when it is determined that P ≧ P _L in step 122, because the tank internal pressure P even when the fuel consumption is the value of the positive pressure side than the determination value P _L, the possibility of abnormalities such as leakage tank Is determined, and this routine ends without setting the normal flag.

According to this embodiment, it has the same features as the failure diagnosis routine of FIG.
More detailed failure diagnosis can be performed.

FIG. 8 shows a system configuration diagram of the second embodiment of the present invention. 2, the same components as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. The second embodiment of FIG. 8 is characterized in that a vacuum switching valve (VSV) 43 which is an electromagnetic control valve is provided in the vapor passage 28 instead of the internal pressure control valve 29.

The VSV 43 is a microcomputer 4
0, the valve is opened and closed when the tank internal pressure becomes larger than a _first judgment value P1 of positive pressure.
1 is supplied to the canister 30, and after the valve is opened, the valve is closed when the tank internal pressure becomes smaller than a _second predetermined value P ₂ (P ₂ <P ₁ ) of positive pressure. Maintain the tank internal pressure at positive pressure.

Although the VSV 43 and the internal pressure control valve 29 are provided in the middle of the vapor passage 28 in FIGS. 8 and 2, the invention is not limited to this, and the connecting portion (the connecting portion between the canister 30 and the vapor passage 28) may be used. It may be provided on the inside of the canister 30) or on a connection portion (tank wall surface) between the fuel tank 21 and the vapor passage 28.

Further, the valve device 18 of the present invention is not limited to the internal pressure control valve 29 or the VSV 43, and may be a valve device that closes the vapor passage 28 at least while the determination permission flag is set. All right, so Figure 9
As shown in FIG.
As VSV 8, a VSV 45 that opens or shuts off the air introduction hole of the canister 30 may be provided.

The present invention is not limited to the above embodiment. For example, a cold start may be determined as a start when the fuel temperature in the fuel tank 21 is lower than a predetermined temperature. Further, the fuel consumption may be substantially calculated from parameters such as the engine speed and the load.

[0049]

As described above, according to the present invention, the differential pressure between the tank internal pressure and the atmospheric pressure is determined from the pressure in the vapor passage only immediately after a cold start in which the only variable affecting the tank internal pressure is the fuel consumption. Since the failure diagnosis is performed based on whether the value exceeds the value, it is possible to reliably detect whether or not there is a leak in the path from the fuel tank to the valve device. In addition, there is a feature that the reliability of failure diagnosis can be improved.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration diagram of a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a hardware configuration of a microcomputer in FIG. 2;

FIG. 4 is a flowchart of a first embodiment of a failure diagnosis routine of a main part of the present invention.

FIG. 5 is a flowchart of a failure diagnosis routine according to a second embodiment of the present invention.

6 is an explanatory diagram of a map for calculating a determination value during the failure diagnosis routine of FIG. 5;

FIG. 7 is a flowchart showing a fuel injection routine having a fuel consumption calculation step.

FIG. 8 is a system configuration diagram of a second embodiment of the present invention.

FIG. 9 is a system configuration diagram of a third embodiment of the present invention.

FIG. 10 is a diagram showing each example of a state of a change in the tank internal pressure after the engine is started.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11, 21 Fuel tank 12, 28 Vapor passage 13, 30 Canister 14, 32 Purge passage 15 Intake passage 16 Cold start detection means 17 Set means 18 Valve device 19 Pressure detection means 20 Judgment means 29 Internal pressure control valve 31 Pressure sensor 40 Microcomputer 41 Warning light 43, 45 Vacuum switching valve (VS
V)

Continuation of front page (56) References JP-A-4-153553 (JP, A) JP-A-3-24967 (JP, A) JP-A-2-130255 (JP, A)

Claims (1)

(57) [Claims] 1. A failure of an evaporative purge system for adsorbing fuel vapor from a fuel tank to an adsorbent in a canister through a vapor passage and purging the adsorbed fuel in the canister to a suction passage of an internal combustion engine through a purge passage during a predetermined operation. A cold start detecting means for detecting whether or not a cold start is performed, and a determination permission flag is set only when the cold start is detected by the cold start detecting means. Setting means, a valve device for closing the vapor passage communicating with the fuel tank when at least the determination permission flag is set, and pressure detecting means for detecting a pressure in a path from the fuel tank to the valve device. The pressure detecting means detects that the determination permission flag is set even after a predetermined time has passed. It is when the pressure is higher than a predetermined value, the trouble diagnosis device for the evaporative emission control system comprising: a determination means that an abnormality.