JP2697506B2 - 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 device for diagnosing a failure of an evaporative purge system that discharges (purges) an intake system of an engine and burns the engine.

[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 canister air inlet to the atmosphere. Therefore,
It is necessary to diagnose whether a failure has occurred in such an evaporation purge system.

Therefore, the present applicant has previously filed Japanese Patent Application No. 3-138.
No. 002, a first control valve for opening and closing a purge passage for purging evaporative fuel stored in a canister to an intake system of an internal combustion engine, and a second control valve for opening and closing an atmospheric hole of the canister, At the time of failure diagnosis, after closing the second control valve,
A failure diagnosis of an evaporative purge system in which the first control valve is closed after a predetermined negative pressure is reached, and the hermetic seal is maintained for a predetermined time, and whether or not a failure has occurred is diagnosed based on a change in pressure at that time. The device was proposed.

[0004]

However, in the failure diagnosis apparatus proposed by the present applicant, after the air hole of the canister is shut off by the second control valve for failure diagnosis,
Since the first control valve is opened to introduce the negative pressure of the intake passage into the system, the negative pressure is applied to the entire evaporation system from the first control valve to the fuel tank at one time. As a result, both the vapor generated in the fuel tank and the vapor desorbed from the activated carbon in the canister are drawn into the intake passage at one time, resulting in a poor air-fuel ratio, degraded drivability and exhaust emissions. Would.

[0005] 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 introducing a negative pressure in a stepwise manner.

[0006]

FIG. 1 is a block diagram showing the principle of the present invention for achieving the above object. As shown in the figure, the present invention uses the fuel vapor from the fuel tank
In a device for diagnosing a failure of an evaporative purge system for adsorbing the adsorbent in the canister 13 through a purge passage 14 to an intake passage 15 of the internal combustion engine 10 during a predetermined operation, the pressure introducing means 17 Pressure detecting means 18 for detecting the pressure in the evaporation system 16 from the purge passage 14 to the fuel tank 11.
And a determination means 19.

Here, the pressure introducing means 17 first introduces the negative pressure of the intake passage 15 into a part of the evaporation system 16 not including the fuel tank 11 among the evaporation systems 16 from the purge passage 14 to the fuel tank 11. Thereafter, a negative pressure is introduced stepwise so as to introduce a negative pressure to the entire evaporation system 16.

The pressure detecting means 18 detects the pressure inside the evaporation system 16. Further, when the judgment means 19 introduces a negative pressure into the entire evaporation system by the pressure introduction means 17,
Based on the negative pressure value detected by the pressure detecting means 18, the degree of change in the pressure in the evaporative system 16 is measured, and the presence or absence of a failure in the evaporative purge system is determined from the comparison result between the measured value and the determination value. .

[0009]

At the time of failure diagnosis, the intake negative pressure is introduced into a part of the evaporative system 16 by the pressure introducing means 17, and then introduced into the entire evaporative system 16 including the fuel tank 11. Therefore, in the present invention, the amount of vapor sucked into the intake passage 15 from the purge passage 14 with one introduction of the negative pressure can be reduced as compared with the related art.

[0010]

FIG. 2 shows a system configuration diagram of an embodiment of the present invention. In the drawing, the air from which dust, dust and the like in the atmosphere have been removed by an air cleaner 22 is measured by an air flow meter 23, and the flow rate thereof is controlled by a throttle valve 25 in an intake pipe 24. Further, the gas flows into a combustion chamber (both not shown) through a surge tank 26 and an intake manifold 27 (which constitutes the intake passage 15 together with the intake pipe 24) during the opening of an intake valve of the internal combustion engine.

The opening of the throttle valve 25 is controlled in conjunction with an accelerator pedal (not shown), and the opening is detected by a throttle position sensor 28. Further, a fuel injection valve 29 is provided for each cylinder so that a part thereof projects into the intake manifold 27. The fuel injection valve 29 injects the fuel 31 in the fuel tank 30 into the air flow passing through the intake manifold 27 for a time specified by the microcomputer 21.

The fuel tank 30 is the same as the fuel tank 11 described above.
And the fuel 45 is stored. Reference numeral 31 denotes a fuel tank internal pressure control valve, which is a mechanical control valve for conducting (opening) or shutting off between the vapor passages 32a and 32c and 32d. When the tank internal pressure is a positive pressure value from the set pressure of the spring 31a, When the diaphragm 31b is located as shown in the drawing and communicates between the vapor passages 32a and 32c and 32d, and when the tank internal pressure is a negative pressure value below the set pressure of the spring 31a, the diaphragm 31b moves downward and the vapor passage 32a And between 32c and 32d.
Thereby, the tank internal pressure of the fuel tank 30 is maintained at a positive pressure, and the amount of generated vapor is suppressed as low as possible. In addition, 31c is an air opening port.

One end of the vapor passage 32a is
The canister 33 communicates with the vapor introduction port 33a together with the vapor passage 32b. This canister (corresponding to the canister 13) is of a type in which a vapor introduction port 33a and a purge port 33b are communicated in the same space, and is filled with activated carbon 33c as an adsorbent and partially in the atmosphere. An introduction hole 33d is provided.

Further, in this embodiment, at the time of failure diagnosis, control of the tank internal pressure by the fuel tank internal pressure control valve 31 is prohibited, and a negative pressure is introduced into the fuel tank 30. Vapor passage 32 between outlets
A tank internal pressure switching valve (VSV) 34 is provided for bypassing via b and 32c and for conducting (opening) or shutting off between the vapor passages 32b and 32c. The tank internal pressure switching valve 34 is an electromagnetic valve that is turned on or off by an output control signal of the microcomputer 21.

The air introduction hole 33 d of the canister 33 is connected to a canister air hole vacuum switching valve (VSV) 36 through an air passage 35. The canister air vent VSV 36 is a microcomputer 21
Based on the control signal, the air introduction hole 36a and the air passage 35
Is a control valve that conducts or shuts off between

The purge port 33 of the canister 33
“b” is connected to a purge side VSV 38 via a purge passage 37. The purge side VSV 38 connects the other end of the purge passage 39 having one end communicating with, for example, the surge tank 26 and the other end of the purge passage 37 to the microcomputer 2.
A control valve that conducts or shuts off based on a control signal from

The pressure sensor 40 is provided in the middle of the vapor passage 32d, and is provided for substantially detecting the internal pressure of the fuel tank 30 by detecting the pressure of the vapor passage 32d. Is composed.
The warning lamp 41 is provided to notify the driver of the abnormality when the microcomputer 21 detects the abnormality.

The microcomputer 21 is a control device for realizing the pressure introducing means 17 and the judging means 19 together with the VSVs 34 and 36 by software processing.
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, the microcomputer 21
Denotes a central processing unit (CPU) 50, a read only memory (ROM) 51 storing a processing program, and a random access memory (RA) used as a work area.
M) 52, a backup RAM 53 that retains data even after the engine is stopped, an input interface circuit 54 with a multiplexer, an A / D converter 56, an input / output interface circuit 55, and the like. It is connected.

The input interface circuit 54 sequentially switches over the intake air amount detection signal from the air flow meter 23, the detection signal from the throttle position sensor 28, the pressure detection signal from the pressure sensor 40, and the like, and combines them in time series. The signal is supplied to a single A / D converter 56 for analog-to-digital conversion, and then transmitted to a bus 57 sequentially.

The input / output interface circuit 55 receives a detection signal and the like from the throttle position sensor 28 and inputs the detection signal and the like to the CPU 50 via a bus 57. The valve 29, the tank internal pressure switching valve 34, the canister atmosphere vent VSV 36, the purge side VSV 38, and the warning lamp 41 are selectively sent to control them.

Next, an evaporative purge operation of such a system configuration will be described. The evaporative purge is performed by the microcomputer 21 according to a purge control routine shown in FIG. The purge control routine is executed, for example, as a part of a main routine. Based on an output of a water temperature sensor (not shown), the engine cooling water temperature THW of the internal combustion engine is warmed up to a predetermined value A or more (step 101), or the air-fuel ratio feedback (F /
B) It is determined whether the operation is in progress (step 102) or the engine is idling based on the output of the throttle position sensor 28 (step 103). If at least one of these cases is not satisfied, the purge side VSV 38 is shut off. Then, when all of these conditions are satisfied, the purge side VSV 38 is opened (step 105).

After the processing of step 104 or 105, the canister vent VSV 36 is subsequently opened (step 106). Note that the tank internal pressure switching valve 34 is always shut off. As a result, step 101
Unless the operation state satisfies all the three conditions determined in (1) to (3), the purge is not performed, and if the operation state satisfies all the three conditions, the purge is enabled.

That is, the tank internal pressure in the fuel tank 30 increases in accordance with the amount of generated vapor, but when the pressure is equal to or lower than the positive pressure set by the fuel tank internal pressure control valve 31, the fuel tank internal pressure control valve 31 is shut off. Therefore, the vapor is not supplied to the canister 33. When the amount of vapor generated in the fuel tank 30 becomes large and the tank internal pressure becomes higher than the pressure set by the fuel tank internal pressure control valve 31, the fuel tank internal pressure control valve 31 is opened, and the vapor in the fuel tank is removed from the vapor passage 32d. , Is sent to the canister 33 through the fuel tank internal pressure control valve 31 and the vapor passage 32a,
It is adsorbed by the activated carbon 33c and is prevented from being released to the atmosphere.

By sending the vapor to the canister 33,
When the tank internal pressure in the fuel tank 30 falls below the set pressure of the fuel tank internal pressure control valve 31, the fuel tank internal pressure control valve 31
Is turned off again. By repeating the above operation, the pressure in the fuel tank 30 is maintained at the set pressure of the fuel tank internal pressure control valve 31.

On the other hand, in the vapor adsorbed by the activated carbon 33c in the canister 33, the negative pressure of the intake system in the predetermined operation state is introduced into the canister 33 through the purge passage 39, the purge VSV 38 and the purge passage 37, and thereby the atmosphere is released. From the inlet 36a to the canister air hole VSV3
6. The atmosphere is sent into the canister 33 through the atmosphere passage 35 and the atmosphere introduction hole 33d.

Then, the fuel adsorbed on the activated carbon 33c is desorbed, and the fuel is drawn into the surge tank 26 from the purge port 33b through the purge passage 37, the purge VSV 38 and the purge passage 39. The activated carbon 33c is regenerated by the above-mentioned desorption and prepares for the next vapor adsorption.

Next, failure diagnosis of the evaporative purge system performing the above operation will be described. In this case, the CPU 50 of the microcomputer 21 starts the failure diagnosis routine shown in FIGS. 5 and 6 every 65 ms, for example, according to a program stored in the ROM 51. In the figure, first, it is checked whether the execution flag is set (the value is "1") (step 201). Since the execution flag has been cleared (the value is "0") by the initial routine at the time of starting the engine, it is not set at first, so the next step 202
Proceed to.

In step 202, it is checked whether or not the tank side pressure release is being performed, based on whether or not the tank side pressure release flag is set. Since the tank-side depressurizing flag has been cleared by the initial routine, it is determined that the tank-side depressurizing is not being performed at first, that is, it is determined that the purge system for introducing a negative pressure into the fuel tank 30 has not been depressurized. Proceed to.

In step 203, it is checked whether a leak determination flag described later is set. Since the leak determination flag is also cleared by the initial routine, it is not initially set, and initially the tank internal pressure switching valve 34
Is released (step 204), the first timer is added (step 205), and it is determined whether or not the value is a value after elapse of γ minutes (step 206). If γ minutes have not elapsed, this routine is temporarily terminated.

If the opening of the tank internal pressure switching valve 34 in step 204 is performed at time t ₁ as schematically shown in FIG. 7B, at time t _{1 the} canister air hole VSV 36 as shown in FIG. Is in an open state, and the purge side VSV 38 is in a closed (closed) state, so that the fuel tank 30 has vapor passages 32d and 32c, a tank internal pressure switching valve 34, a vapor passage 32b, a canister 33, and a canister atmospheric hole VSV3.
6 and communicate with the air inlet 36a,
The tank pressure of the fuel tank 30, which has been controlled to the set pressure by the fuel tank pressure control valve 31 until then, is shown in FIG.
From the positive pressure from the time t ₁ as shown in (A) towards the atmospheric pressure will change.

After that, the failure diagnosis routine shown in FIGS. 5 and 6 is started several times, and when a predetermined time γ has elapsed after the opening of the tank internal pressure switching valve 34, it is determined from the value of the first timer. Then (step 206), step 20 in FIG.
7. Based on the detection signal of the pressure sensor 40 in step 7, the tank internal pressure is determined as the negative pressure introduction start pressure.
It is determined whether the following has occurred.

When the tank internal pressure is more positive than Y (Pa), it is estimated that the amount of fuel vapor generated is large and there is no leakage, and that accurate failure diagnosis cannot be performed. So that the canister air hole VSV
36 (step 228), shut off the tank internal pressure switching valve 34 (step 229), and clear various timers (step 228).
230), and set the execution flag (step
231), the leak determination in progress flag is cleared (step 232).
), End this routine.

At step 207, when the tank internal pressure is equal to or lower than Y (Pa), that is, when the tank internal pressure is a value on the atmospheric pressure and negative pressure side of Y (Pa), the amount of generated vapor is small, and it is determined that accurate failure diagnosis is possible. Start setting.

First, the tank pressure switching valve 34 and the canister air vent VSV 36 are shut off (steps 208 and 209), and the purge side VSV 38 is opened (step 210). As a result, the negative pressure of the surge tank 26 passes through the purge passage 39, the purge side VSV 38,
3 and further into the vapor passages 32a and 32b. Here, the negative pressure introduced into the vapor passage 32a causes the fuel tank internal pressure control valve 31 to close, and the negative pressure introduced into the vapor passage 32b causes the tank internal pressure switching valve 34 to be shut off in step 208. Negative pressure is fuel tank 3
It is not introduced to zero.

Accordingly, in this embodiment, the purge side VSV 38
Of the purge system from the fuel tank 30 to the fuel tank 30
Negative pressure is first introduced only to a part of the evaporation system from the SV 38 to the vapor passages 32a and 32b. Thereby, the vapor adsorbed on the activated carbon 33c in the canister 33 is removed at this time, and the purge passage 37 and the purge side VSV 38
And the gas is sucked into the intake manifold 27 from the surge tank 26 through the purge passage 39.
The vapor in 0 is not sucked.

In the above step 208, the tank internal pressure switching valve 3
4, shut off, step 209, canister air vent VSV36
Blocking and opening of the purge side VSV38 step 210, FIG. 7 (B), the when to that performed at time t ₂ as shown schematically in (C) and (D), in step 211 the subsequent Figure 5 The second timer is added, and in step 212, it is determined whether the value of the second timer after the addition is equal to or less than η minutes.

Time t_TwoUntil η minutes elapse
Steps 208 to 212 are repeated to form part of the above evaporative system.
By continuing the introduction of the negative pressure to the canister 33,
The inside vapor is substantially empty. When η minutes have passed,
Time t determined in step 212 _ThreeFIG. 7B schematically shows
As shown, the tank internal pressure switching valve 34 is opened (step 213).
 ), Thereby releasing the tank pressure from the purge side VSV 38.
Exchange valve 34, vapor passages 32c and 32d, and fuel tank 3
Negative pressure is introduced into the entire evaporation system including zero.

Therefore, after time t ₃ , the vapor in the fuel tank 30 is sucked from the surge tank 26 into the intake manifold 27 while a part of the vapor is adsorbed by the activated carbon 33 c in the canister 33. As shown in FIG. 7A, when there is no leak in the evaporative system, the pressure changes in the negative pressure direction. The above steps 208 to 213 are performed together with the VSVs 34, 36 and 38 together with the pressure introducing means 17.
Is composed.

Subsequently, at step 214 in FIG. 6, the tank internal pressure is changed to the diagnosis start pressure X based on the detection signal of the pressure sensor 40.
(Pa) or less, and if the tank internal pressure is a value on the atmospheric pressure side from the negative pressure X (Pa), a negative pressure release flag is set to continue the negative pressure setting (step 215). ), This routine is temporarily terminated. 65ms until tank pressure becomes more negative than X (Pa)
Steps 201, 202, 214, and 215 are repeatedly executed each time. Then, when it is determined in step 214 that the tank internal pressure has become larger than X (Pa) on the negative pressure side, the tank side pressure release flag is cleared (step 216), and the purge side VSV 38 is shut off (step 217).

The purge-side VSV 38 at the step 217
Is shut off at time t ₄ as schematically shown in FIG. 7D, since both VSVs 36 and 38 are closed, the pressure in the evaporation system from the purge side VSV 38 to the fuel tank 30 is reduced. If there is no failure in the system, it is kept tightly closed and drops very slowly to atmospheric pressure. When the purge side VSV 38 is shut off in step 217, the processing of the determination means 19 is realized in the following steps 218 to 225.

That is, first, it is determined whether or not the leak determination timer is "0" (step 218). Since the leak determination timer has been cleared to "0" by the above-mentioned initial routine, when the determination in step 218 is first performed, it is determined to be "0" and the routine proceeds to step 219, where the pressure sensor 40 The present detection value is used as the diagnosis start pressure value P
_It is stored in the RAM 52 as _S.

Subsequently, the value of the leak determination timer is incremented by a predetermined value (step 220), the leak determination flag is set to "1" (step 221), and this routine is terminated. Next, when this routine is started again, it is determined in step 203 of FIG.
The program jumps from step 4 to step 216, and further proceeds to step 218 via step 217.

Since it is determined in step 218 that the leak determination timer is not "0", it is determined whether the value of the leak determination timer is a value corresponding to the diagnosis time (leak determination time) α (step 218). 222) If the time has not reached α, this routine is terminated via steps 220 and 221.

Thus, steps 201 to 203, 21
Processing of 7, 218, 222, 220, 221 is repeated every 65 ms
And the value of the leak determination timer corresponds to the leak determination time α.
Value, the value detected by the pressure sensor 40 at that time is diagnosed.
End pressure value P_EIn the RAM 52 (step
223). Then, the pressure value read from the RAM 52
P _S, P_EBased on (P_E−P_S) / Α (seconds)
The rate of change in pressure is calculated from the equation (step 224).

Subsequently, it is determined whether or not the calculated rate of change is equal to or greater than a predetermined threshold value β (step 225). To turn on the warning lamp 41 (step 22).
6) After notifying the driver of the occurrence of a failure in the evaporative purge system, the leak failure code is stored, for example, in the backup RAM 53 (step 227), and the flow proceeds to step 228. The leak failure code is read out from the backup RAM 53 at the time of subsequent repair to notify the cause of the failure of the evaporative purge system. On the other hand, the calculated change rate is β
If it is determined that the leakage is less than the specified value, it is determined that the leakage is normal, and steps 226 and 227 are jumped to proceed to step 228.

When it is determined whether there is a failure in the evaporative purge system as described above, the canister air vent VSV 36 is then opened to release the negative pressure of the evaporative system (step 228). In order to make the operation of the internal pressure control valve 31 effective, the tank internal pressure switching valve 34
Is turned off (step 229).

As a result, the atmosphere is introduced into the system through the canister atmosphere hole VSV 36 and the canister 33 from the atmosphere introduction port 36a in FIG. Changes to

Thereafter, the various timers and the leak determination timer are cleared (step 230), the execution flag is set to "1" (step 231), and the leak determination flag is cleared to "0" (step 232). Then, the failure diagnosis processing ends. Thereafter, even if this routine is started, step 201
, The execution flag is determined to be "1", so that this routine will not be executed until restarting thereafter.

As described above, according to the present embodiment, when introducing the negative pressure of the intake system into the evaporative system at the time of failure diagnosis,
First, the vapor passages 32a and 32
The negative pressure is introduced only into a part of the evaporative system not including the fuel tank 30 up to b, so that the suction vapor in the canister 33 is sucked into the surge tank 26, and then the evaporative system including the fuel tank 30 is formed. Since the negative pressure is introduced to the entirety so that the vapor in the fuel tank 30 is sucked into the surge tank 26, the pressure per one time at the time of introducing the negative pressure at the time of failure diagnosis is smaller than that of the device proposed by the present applicant. Since the amount of vapor suction can be reduced, the roughening of the air-fuel ratio is suppressed small,
Therefore, deterioration of exhaust emission can be significantly reduced.

FIGS. 8 and 9 are flowcharts showing a second embodiment of the failure diagnosis routine of the main part of the present invention.
The same processing steps as those in FIGS. 5 and 6 are denoted by the same reference numerals,
The description is omitted. In FIG. 8, at step 212, η
If it is determined that the elapsed time has elapsed, the purge side VSV 38 is shut off (step 301), the negative pressure is held in the canister 33, and then the tank internal pressure switching valve 34 is opened to open the canister 33.
Is introduced into the fuel tank 30 (step 302).

Subsequently, the third timer is added (step
303), it is determined whether the value of the third timer after the addition is equal to or less than θ minutes (step 304). Purge side VSV38
Is stopped and the tank internal pressure switching valve 34 is opened, and when θ minutes have elapsed, the process proceeds to step 214 in FIG. 9, and the same processing as in FIG. 6 is executed.

In this embodiment, after the negative pressure of the surge tank 26 is once stored in the canister 33, a negative pressure is introduced into the fuel tank 30 using the canister 33 as a negative pressure source, and the tank internal pressure becomes X
(Pa) until the pressure becomes larger than the negative pressure side.
Steps 208 to 212 and 301 to 304 are repeated. This embodiment also has the same effects as the first embodiment.

The present invention is not limited to the above embodiment. For example, the canister may be of a type in which the vapor introduction port and the purge port do not communicate with each other in the same space. Further, the pressure sensor 43 may be directly attached to the fuel tank 30, or the purge portion of the vapor may be provided in the intake passage near the throttle valve 25.

[0054]

As described above, according to the present invention, when the negative pressure is introduced, the negative pressure is introduced stepwise into the evaporative system, so that the amount of vapor introduced into the intake passage every time the negative pressure is introduced is reduced. The present invention has the features of being able to reduce as compared with the prior proposed device of the applicant, thereby preventing the roughening of the air-fuel ratio at the time of introducing the negative pressure, and the deterioration of the drivability and the exhaust emission.

[Brief description of the drawings]

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

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

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

FIG. 4 is a flowchart showing a purge control routine.

FIG. 5 is a flowchart (part 1) illustrating a first embodiment of a failure diagnosis routine that is a main part of the present invention.

FIG. 6 is a flowchart (part 2) showing a first embodiment of a failure diagnosis routine which is a main part of the present invention.

FIG. 7 is a time chart for explaining the operation of FIGS. 5 and 6;

FIG. 8 is a flowchart (part 1) illustrating a second embodiment of a failure diagnosis routine that is a main part of the present invention.

FIG. 9 is a flowchart (part 2) illustrating a second embodiment of a failure diagnosis routine that is a main part of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11, 30 Fuel tank 12, 32a-32d Vapor passage 13, 33 Canister 14, 37, 39 Purge passage 15 Intake passage 17 Pressure introduction means 18 Pressure detection means 19 Judgment means 21 Microcomputer 31 Fuel tank internal pressure control valve 34 Tank internal pressure switching valve (VSV) 35 Atmospheric passage 36 Canister atmospheric hole vacuum switching valve (VSV) 38 Purge side vacuum switching valve (V
SV) 40 Pressure sensor

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Akinori Nagauchi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References 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. In the apparatus for diagnosing, the negative pressure of the intake passage is first introduced into at least a part of the evaporative system not including the fuel tank in the evaporative system from the purge passage to the fuel tank. Pressure introducing means for introducing the negative pressure in a stepwise manner so as to introduce the negative pressure; pressure detecting means for detecting the pressure in the evaporative system; and introducing the negative pressure to the entire evaporative system by the pressure introducing means. Then, based on the negative pressure value detected by the pressure detecting means, the degree of change in the pressure in the evaporative system is measured, and the measured value and the determination value are compared. A failure diagnosing device for determining whether or not a failure has occurred in the evaporative purge system from the comparison result.