JP2697525B2 - 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 sucked into the intake system and burned. In an internal combustion engine equipped with a system, when the vapor passage is damaged or the pipe is disconnected for any reason, the vapor is released to the atmosphere, and when the purge passage to the intake system is blocked,
The vapor in the canister overflows, and the vapor leaks from the air holes of the canister into the atmosphere. Therefore, it is necessary to diagnose whether a failure has occurred in such an evaporation purge system.

[0003] Conventionally, as a failure diagnosis apparatus for an evaporative purge system, there is one disclosed in Japanese Patent Application No. 3-323364. This device introduces a negative pressure of an intake pipe into an evaporative system up to a fuel tank, and diagnoses whether a failure such as leakage has occurred in the evaporative system based on a negative pressure value introduced within a predetermined time. .

[0004]

In the conventional apparatus, the negative pressure introduced into the fuel tank within a predetermined time due to the flow rate tolerance of the purge control valve for introducing the negative pressure of the intake pipe, the fluctuation of the pressure loss of the canister, and the secular change. The magnitude of the pressure fluctuates. For this reason, for example, when the flow rate of the purge control valve is large, the introduced negative pressure becomes large, and even if there is a leak, the detected negative pressure becomes large to some extent, and it is erroneously determined to be normal. Therefore, even if there is no leakage, the negative pressure is small, and it is erroneously determined to be a failure, and there is a problem that an accurate failure determination cannot be performed.

[0005] The present invention has been made in view of the above points,
By making a failure determination based on the amplitude of the pulsation generated by the duty control when negative pressure is introduced, accurate failure determination is always performed without being affected by the flow control tolerance of the purge control valve, the pressure loss difference of the canister, or the change over time. It is an object of the present invention to provide a possible failure diagnosis device for an evaporation purge system.

[0006]

As shown in FIG. 1, the failure diagnosis apparatus for an evaporative purge system according to the present invention adsorbs fuel vapor from a fuel tank M1 to an adsorbent in a canister M3 through a vapor passage M2. In the evaporative purge system for purging the adsorbed fuel in the canister into the intake passage M6 of the internal combustion engine M5 through the purge passage M4, the negative pressure introducing means M8 introduces the intake negative pressure into the evaporation systems M2 to M4, and the pressure detecting means M7. In the failure diagnosis device of the evaporative purge system in which the failure is determined by the determination means M9 based on the detected pressure of the evaporation system, a duty control valve is used as the negative pressure introduction means M8, and an evaporative pressure generated by the duty control of the negative pressure introduction means M8. Failure determination is performed based on the amplitude of the pressure pulsation in the system.

[0007]

In the present invention, a duty control valve is used as the negative pressure introducing means M8. The determining means M9 is provided with an evaporative system M2 generated by the duty control of the negative pressure introducing means M8.
A failure determination is made based on the amplitude of the pressure pulsation within M4.

[0008]

FIG. 2 shows a system configuration diagram of the apparatus of the present invention.
In FIG. 1, the fuel tank 21 includes 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. Also,
A rollover valve 23 is provided above the fuel tank 21. The rollover valve 23 is provided to prevent 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 part of the fuel tank 21 passes through a vapor passage and an internal pressure control valve 29, respectively, and is connected to a canister 30.
Is communicated to. Check ball 2 for internal pressure control valve 29
9a and a spring 29b.
Is exerting an urging force on the check ball 29a in the right direction in the figure, and the pressure in the fuel tank 21 is maintained at a predetermined value (for example, 250 mmAq) or less by the spring 29b.

The canister 30 has activated carbon 30a therein as an adsorbent, and has 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 the vapor passage 28 between the pressure control valve 29 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 by 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.
And a purge control valve 33 which is an electromagnetic valve (VSV), and is connected to a position downstream of the throttle valve 35 in the intake passage 36. An air cleaner (A) for filtering air and removing dust is provided upstream of the throttle valve 35.
C) 34 is provided.

The throttle valve 35 is a valve whose opening is controlled by the depression amount of an accelerator pedal operated by the driver.
7 is detected. The fuel temperature sensor 40 detects the temperature of the fuel in the fuel tank 21, the intake temperature sensor 41 detects the temperature of the intake air in the intake passage 36, and the fuel level sensor 42
Detects the remaining amount of fuel in the fuel tank 21 and supplies each detection signal to the microcomputer 38.

Further, a vapor passage between the fuel tank 21 and the internal pressure control valve 29 and the internal pressure control valve 29 and the canister 30
Is connected to a bypass control valve 45 which is an electromagnetic valve (VSV). When the bypass control valve 45 is opened, the internal pressure control valve 29 is bypassed and the vapor passage 28 is connected to the fuel tank 21 and the canister 30. Connect directly between. The microcomputer 38 is an electronic control unit that controls the evaporative purge system. When an abnormality is determined, the microcomputer 38 turns on a warning lamp 39 to notify the driver of the occurrence of the abnormality.

The microcomputer 38 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. 3, a microcomputer 38 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 A / D converter 56 sequentially switches and takes in the pressure detection signal from the pressure sensor 31, the detection signal from the throttle position sensor 37, and the detection signals of the fuel temperature sensor and the intake temperature sensor through the input interface circuit 54. It is converted from analog to digital and transmitted to the bus 57 sequentially. I / O interface circuit 5
5 transmits a signal from the throttle position sensor 37 to the bus 57, while the fuel injection valve 26 and the purge control valve 3
3. Control signals are selectively sent to the warning light 39 and the bypass control valve 45 to control them.

Next, the operation of the normal evaporative purge in the system shown in FIG. 2 will be described. When an ignition switch (not shown) is turned on, the fuel pump 22 shown in FIG.
The fuel in the sub tank 21b is removed by the operation of the pipe 24.
Is discharged to the pressure regulator 25, where the pressure is made constant and sent to the fuel injection valve 26, and the fuel injection time from the microcomputer 38 and the fuel injection valve 26
Is injected into the intake passage 36. 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 reaches the internal pressure control valve 29 through the vapor passage 28 because the bypass control valve 45 is open. Here, when the tank internal pressure is smaller than the pressure set by the internal pressure control valve 29 (for example, 250 mmAq), the spring 29
The check ball 29a is at the position shown in the figure due to the spring force of b and blocks the vapor passage 28, so that the delivery of the evaporated fuel to the canister 30 is prevented.

For example, during a cold start of the engine, the tank internal pressure is near the atmospheric pressure. Immediately after that, the fuel volume decreases due to the fuel consumption by the fuel injection valve 26, so that the tank internal pressure temporarily decreases to the negative pressure. However, thereafter, the fuel temperature gradually rises due to the exhaust heat, the amount of fuel vapor generated increases, and the tank internal pressure increases in the positive pressure direction and reaches the pressure set by the internal pressure control valve 29.

When the fuel vapor is further generated and the tank internal pressure exceeds the set pressure, the check ball 29a of the internal pressure control valve 29 is pushed leftward 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 by the activated carbon 30a inside. 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 described above, 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 start of the engine, the purge control valve 33 is closed because the purge control conditions are not satisfied.

The above-mentioned purge control conditions are operating conditions that 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 38 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 conditions are satisfied, the microcomputer 38 opens the purge control valve 33. Then, due to the negative pressure of the intake passage 36, the air is introduced into the canister 30 from the air inlet 30 b, the fuel adsorbed on the activated carbon 30 a is desorbed, and the air flows through the purge passage 32 and the purge control valve 33, respectively. Evaporated fuel is sucked into the passage 36. 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, a failure diagnosis process executed by the microcomputer 38 in the above system will be described. FIG.
4 shows a flowchart of an embodiment of a failure diagnosis routine. This routine is, for example, an interrupt routine every 4 msec.

In FIG. 5, in step S10, air-fuel ratio feedback control is executed, and it is determined whether or not failure diagnosis execution conditions such as a cooling water temperature of 80 ° C. or more are satisfied. The process proceeds to step S12, and if not satisfied, the process ends.

In step S12, it is determined whether or not a predetermined time of, for example, about 1 to 2 minutes has elapsed after the execution conditions are satisfied. If not, the process proceeds to step S14.
In step S14, the bypass control valve 45 is opened and the purge control valve 33 is opened and closed at a duty ratio of 50%.
In the next step S16, the tank internal pressure (differential pressure from atmospheric pressure) P is read based on the detection signal of the pressure sensor 31. Further, in step S18, a difference pressure ΔP is calculated by subtracting the previously read tank internal pressure P _OLD from the tank internal pressure P, and the tank internal pressure P is set to the previous tank internal pressure P _OLD .

Next, in step S22, it is determined whether or not the differential pressure ΔP is positive. If ΔP ≦ 0, it is determined in step S24 whether or not the previous differential pressure ΔP _OLD is positive. If ΔP _OLD > 0, the tank internal pressure P is increased to the maximum tank internal pressure P in step S26.
Set to _max . On the other hand, if ΔP> 0 in step S22, it is determined in step S28 whether or not the previous differential pressure ΔP _OLD is equal to or less than 0. If ΔP _OLD ≦ 0, step S30 is performed.
Then, the tank internal pressure P is set to the minimum tank internal pressure P _min, and a smoothed value Pa of the pulsation amplitude of the tank internal pressure is calculated by the following equation in step S32.

Pa = k (P _max −P _min ) + (1−k) Pa where k is a smoothing coefficient, for example, ８.

If ΔP _OLD ≦ 0 in step S24, or if ΔP _OLD > 0 in step S28, or after execution of steps S26 and S32, the process proceeds to step S34, where the differential pressure ΔP is reduced to the previous differential pressure ΔP _OLD . Then, in step S36, it is determined whether or not the smoothed value Pa of the pulsation amplitude exceeds a predetermined value α (for example, several mmHg). Only when Pa> α, the normal flag is set in step S38 and the processing is performed. finish.

The normal flag is reset immediately after the start.

On the other hand, if it is determined in step S12 that a predetermined time has elapsed after the execution condition is satisfied, step S4
Go to 0 to make a diagnosis. In step S40, it is determined whether or not the normal flag is set. If the normal flag is set, the warning light 39 is turned off in step S42, and if the normal flag is not set, step S4 is performed.
At 4, the warning light 39 is turned on and the process is terminated.

Here, when the duty of the purge control valve 33 is controlled, the duty ratio is set to 0 as shown in FIG.
% And 100%, the purge control valve 33 is
As shown in FIG. 5B, if the valve is kept closed and open, but the duty ratio is 50%, the intake pipe negative pressure is intermittently introduced with the opening and closing of the purge control valve 33 shown in FIG. The tank internal pressure causes pressure pulsation as shown in FIG. When there is no leakage in the evaporative system, the pulsation amplitude Pa ₁ is large as shown by the solid line in FIG. 5C, but when there is leakage in the evaporative system, the pulsation amplitude Pa _{2 as} shown by the broken line in FIG. 5C. Becomes smaller. The present invention utilizes this principle to determine that the evaporation system is normal when the amplitude of the pulsation exceeds a predetermined value α.

The amplitude of the pressure pulsation hardly changes due to the flow rate tolerance of the purge control valve 33, the pressure loss difference of the canister, the change with time, and the like. The failure is accurately determined by performing the failure determination based on the amplitude of the pulsation. Judgment becomes possible.

In this embodiment, the pressure pulsation appearing in the vapor passage when the negative pressure is introduced to the fuel tank is detected. However, it is easier to introduce the negative pressure only to the internal pressure control valve or the canister. Thus, a failure diagnosis may be made by detecting a pressure pulsation appearing in the purge passage.
In that case, the diagnosis on the fuel tank side may be performed by another method. Further, since the fuel tank side has a large space capacity and weak pressure pulsation, the diagnosis range is narrowed by performing the diagnosis based on the relatively clear pressure pulsation on the canister side, but the accuracy is improved.

[0035]

As described above, according to the failure diagnosing apparatus for an evaporative purge system of the present invention, accurate failure determination is always performed without being affected by the flow rate tolerance of the purge control valve, the pressure loss difference of the canister, or the change with time. It is possible and very useful in practice.

[Brief description of the drawings]

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

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

FIG. 3 is a configuration diagram of hardware of a microcomputer.

FIG. 4 is a flowchart of one embodiment of a failure diagnosis routine according to the present invention.

FIG. 5 is a diagram for explaining the operation of the present invention.

[Explanation of symbols]

 M1, 21 Fuel tank M2, 28 Vapor passage M3, 30 Canister M4, 32 Purge passage M6, 36 Intake passage M7 Pressure detection means M8 Negative pressure introduction means M9 Judgment means 26 Fuel injection valve 29 Internal pressure control valve 31 Pressure sensor 33 Purge control Valve 38 Microcomputer 39 Warning light 45 Bypass control valve

Claims (1)

(57) [Claims] 1. 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. In the failure diagnosis device of the evaporative purge system for introducing the intake negative pressure by the negative pressure introducing means and performing a failure determination based on the pressure of the evaporative system detected by the pressure detecting means, using a duty control valve as the negative pressure introducing means, A failure diagnosis device for an evaporative purge system, wherein a failure is determined based on the amplitude of pressure pulsation in an evaporative system generated by duty control of the negative pressure introducing means.