JPH06147031A - Trouble diagnosing device of evapo-purge system - Google Patents

Abstract

PURPOSE:Carry out an accurate trouble diagnosis by comparing a measured value pertaining to a variation degree of pressure in an evaporative route with an judged value, and making this judged value variable according to a purge flow rate at the time of diagnosing whether there is something wrong with an evapo-purge system or not. CONSTITUTION:An amount of vaporized fuel in a fuel tank 11 is adborbed in a canister 13 through a vapor passage 12 and then this vaporized fuel is purged to an intake passage 10a of an internal combustion engine 10 through a purge passage 14. In a suchlike system, a purge flow rate in this purge passage 14 is detected by a means 16. Negative pressure in the intake passage 10a is conducted into an evaporative passage 15 or diagnostic object by a means 17. In addition, pressure in this evaporative passage 15 is detected by a means 18. On the basis of the pressure value detected, a variation degree of pressure in the evaporative route 15 is measured, while this measured value is compared with the judged value, whereby whether there is something wrong with the system or not is judged by a means 19. Thus, on the basis of the detected purge flow rate, the judged value is made variable with a means 20.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Fuel (vapor) evaporated in a fuel tank
In order to prevent air from being released into the atmosphere, each part is hermetically sealed, and the vapor is once adsorbed by the adsorbent in the canister, and the fuel adsorbed while the vehicle is running is sucked into the intake passage and burned by evaporative purging. In an internal combustion engine equipped with a system, if the vapor passage is damaged for some reason or if the pipe is disconnected, the vapor is released to the atmosphere, and if the purge passage to the intake system is blocked, The vapor in the canister overflows and leaks into the atmosphere through the canister air inlet. Therefore, it is necessary to diagnose whether or not such a failure of the evaporative purge system has occurred.

Therefore, the applicant of the present invention has previously provided a bypass passage between the vapor introducing hole of the canister and the purge passage according to Japanese Patent Application No. 3-323364 as a failure diagnostic device for the evaporative purge system. By opening the control valve at the time of failure diagnosis, the negative pressure in the intake passage of the internal combustion engine is introduced to the fuel tank through the throttle, and the pressure sensor provided in the path from the vapor introduction hole of the canister to the fuel tank. Has proposed a device which detects a negative pressure and judges a failure when the negative pressure is less than a predetermined negative pressure.

[0004]

However, in the failure diagnosis apparatus for the evaporative purge system proposed by the applicant of the present invention, the level of the negative pressure introduced into the fuel tank at the time of failure diagnosis is the occurrence of vapor in the fuel tank. Volume, the ventilation and passage resistance on the open end side of the canister, and the purge flow rate, so if the resistance on the open end side of the canister is set to be approximately constant when the amount of vapor generated in the fuel tank is small, the purge flow rate causes The negative pressure level of changes.

The purge flow rate changes depending on the operating conditions (intake pipe negative pressure, intake air amount) of the internal combustion engine and the opening degree (duty ratio) of the purge control valve. Therefore, according to the apparatus proposed by the applicant of the present application, when the failure is judged from the change in the negative pressure of the fuel tank during the predetermined time when the purge control valve is opened, the purge flow rate is set to the above engine operating condition. Or the opening degree of the purge control valve changes, the negative pressure level applied to the fuel tank changes, and the negative pressure value after the predetermined time varies, resulting in erroneous detection.

The present invention has been made in view of the above points, and provides a failure diagnostic device for an evaporation purge system that solves the above problems by setting a determination value or a negative pressure introduction time using a purge flow rate as a parameter. The purpose is to do.

[0007]

FIG. 1 is a block diagram showing the principle of the invention according to claim 1 for achieving the above object. As shown in the figure, according to the present invention, the evaporated fuel from the fuel tank 11 is made to adsorb the adsorbent in the canister 13 through the vapor passage 12, and the adsorbed fuel in the canister 13 is made to pass through the purge passage 14 during the predetermined operation. In the device for diagnosing the failure of the evaporative purge system for purging the intake passage 10a, the purge flow rate detecting means 16 and the pressure introducing means 17 are provided.
The pressure detecting means 18 for detecting the pressure in the evaporation path 15 to which the pressure is introduced, the judging means 19, and the judging value varying means 20 are provided.

The purge flow rate detecting means 16 substantially detects the purge flow rate in the purge passage 14. The pressure introducing means 17 introduces the negative pressure in the intake passage 10a into the evaporation path 15 to be diagnosed. Further, the pressure detection means 18 detects the pressure in the evaporation path 15.

Further, the judging means 19 determines the degree of change in the pressure in the evaporation path 15 based on the pressure value detected by the pressure detecting means 18 when the negative pressure is introduced into the evaporation path 15 by the pressure introducing means 17. The measurement is performed, 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. Further, the judgment value changing means 20 changes the judgment value of the judging means 19 according to the purge flow rate detected by the purge flow rate detecting means 16.

According to the second aspect of the present invention, negative pressure introducing time varying means is provided in place of the judgment value varying means 20, and the negative pressure introducing time varying means responds to the purge flow rate detected by the purge flow rate detecting means 16. Then, the introduction time of the negative pressure introduced into the evaporation path 15 by the pressure introducing means 17 is varied.

Further, in the invention according to claim 3, a control means is provided in place of the judgment value varying means 20, and when the control means detects a state where the purge flow rate is below a predetermined value, the judgment means 19 makes a judgment. Prohibit

[0012]

According to the first and second aspects of the invention, the judgment value of the judgment means 19 or the pressure introduction time of the pressure introduction means 17 is made variable in accordance with the purge flow rate detected by the purge flow rate detection means 16. The determination can be made under substantially the same conditions without being affected by the purge flow rate.

Further, in the third aspect of the invention, the judgment by the judgment means 19 can be executed only in the situation where the judgment can be made by the judgment value set by the judgment means 19 by the control means.

[0014]

First, each embodiment of the system configuration of the present invention will be described. FIG. 2 shows a system configuration diagram of the first embodiment of the present invention. The present embodiment is an example applied to an automobile engine as the internal combustion engine 10, and the operation of each part is controlled by a microcomputer 21. The flow of the air from which dust and dust in the atmosphere has been removed by the air cleaner 22 is controlled by the throttle valve 25 in the intake pipe 24, and the surge tank 26, the intake manifold 27 (the intake pipe 24 together with the intake passage 10a And a combustion chamber 29 of the engine (corresponding to the internal combustion engine 10) while the intake valve 28 is open. A pressure sensor 23 for detecting the intake pipe pressure is attached to the surge tank 26.

The fuel tank 30 is the fuel tank 11 described above.
Corresponding to, and contains the fuel 42. Reference numeral 31 denotes a fuel tank internal pressure control valve, which is a mechanical control valve for connecting (opening) or shutting off between the vapor passages 32a and 32c and 32d, and when the tank internal pressure is a value in the positive pressure direction from the set pressure of the spring 31a, The diaphragm 31b is positioned as shown in the drawing to communicate between the vapor passages 32a, 32c and 32d, and when the tank internal pressure is a value in the negative pressure direction from the set pressure of the spring 31a, the diaphragm 31b moves downward to move the vapor passage 32a. And between 32c and 32d.
As a result, the tank internal pressure of the fuel tank 30 is maintained at a positive pressure, and the amount of vapor generation is suppressed as low as possible. In addition, 31c is an atmospheric opening.

Further, one end of the vapor passage 32a is
Together with the vapor passage 32b, it communicates with the vapor introduction port 33a of the canister 33. 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, the inside thereof is filled with activated carbon 33c as an adsorbent, and part of the atmosphere An introduction hole 33d is provided.

Further, in this embodiment, in order to inhibit the tank internal pressure control by the fuel tank internal pressure control valve 31 and introduce a negative pressure into the fuel tank 30 at the time of failure diagnosis, the inlet and the guide of the fuel tank internal pressure control valve 31 are introduced. Vapor passage 32 between the exits
A tank internal pressure switching valve (VSV) 34 is provided to bypass (b) and 32c and to conduct (open) or shut 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 from the microcomputer 21.

The atmosphere introducing hole 33d of the canister 33 is communicated with a canister atmosphere hole vacuum switching valve (VSV) 36 through an atmosphere passage 35. The canister atmosphere hole VSV36 is a microcomputer 21.
Based on the control signal of the
It is a control valve that connects or disconnects between and.

The purge port 33 of the canister 33
b is communicated with the purge-side VSV 38 via the purge passage 37. One end of the purge side VSV 38 is connected to the surge tank 26, for example, and the other end of the purge passage 39 and the other end of the purge passage 37 are connected to the microcomputer 2
It is a control valve that conducts or shuts off based on a control signal from 1.

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

An intake air temperature sensor 43 for detecting the intake air temperature is attached near the air cleaner 22. The throttle position sensor 44 is attached to the throttle body and has a structure for detecting the movement of the throttle valve 25 by various contacts. When the throttle valve 25 is in the fully closed state (idle position), its IDL contact is turned on. Further, a bypass passage 45 that bypasses the throttle valve 25 and connects the downstream side of the air flow meter 23 and the surge tank 26 is provided.

Further, the bypass passage 4 has the bypass passage 4
An idle speed control valve (ISCV) 46 for increasing or decreasing the amount of air flowing through 5 is provided. Further, a fuel injection valve 47 is provided for each cylinder so that a part thereof projects into the intake manifold 27. The fuel injection valve 47 injects the fuel 42 in the fuel tank 30 into the air flow passing through the intake manifold 27 for a time instructed by the microcomputer 21.

The microcomputer 21 includes the purge flow rate detecting means 16, the pressure introducing means 17, and the determining means 19 described above.
Also, the control device which realizes the judgment value varying means 20 together with the VSVs 34 and 36 by software processing has a known hardware configuration as shown in FIG. In the figure,
The same components as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 3, a microcomputer 21 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 that retains data even after the engine is stopped
It is composed of an AM 53, an input interface circuit 54 with a multiplexer, an A / D converter 56, an input / output interface circuit 55, etc., which are connected via a bus 57.

The input interface circuit 54 is a detection signal from the throttle position sensor 44, the pressure sensor 2
The pressure detection signals from 3 and 40, the output detection signal of the intake air temperature sensor 43, etc. are sequentially switched and combined in time series, and the combined signal is supplied to a single A / D converter 56 to perform analog / digital conversion. After that, the data is sequentially sent to the bus 57.

The input / output interface circuit 55 receives a detection signal from the throttle position sensor 44, inputs it to the CPU 50 via the bus 57, and at the same time processes each signal input from the bus 57 appropriately to inject fuel. The valve 47, the tank internal pressure switching valve 34, the canister atmosphere hole VSV 36, the purge side VSV 38, the warning lamp 41 and the ISCV 46 are selectively sent to control them.

Next, the evaporative purge operation of the system configuration will be described. The evaporative purge is performed by the microcomputer 21 according to a purge control routine. The purge control routine is executed, for example, as part of the main routine, and it is determined whether the engine has been warmed up, the air-fuel ratio feedback (F / B) is being executed, or whether the engine is idling based on the output of the throttle position sensor 44. ,
If even one of these cases is not satisfied, purge side V
When the SV 38 is shut off and all of these conditions are satisfied, the purge side VSV 38 is opened.

Subsequently, the canister atmosphere hole VSV36 is opened. The tank internal pressure switching valve 34 is always closed. As a result, purging is not executed unless the operating conditions satisfy all of the above three conditions,
When the operating condition satisfies all of the three conditions, the purge can be executed. Note that purging is not executed during failure diagnosis.

That is, the tank internal pressure in the fuel tank 30 increases in accordance with the amount of vapor generated. However, when the internal pressure of the fuel tank 30 is less 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, so that the vapor in the fuel tank can be transferred to the vapor passage 32d. , 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 prevented from being released into the atmosphere.

By sending vapor to the canister 33,
When the tank internal pressure in the fuel tank 30 becomes equal to or lower than the set pressure of the fuel tank internal pressure control valve 31, the fuel tank internal pressure control valve 31
Is cut 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 on the activated carbon 33c in the canister 33, the negative pressure of the intake system in the above-mentioned predetermined operating state is introduced into the canister 33 through the purge passage 39, the purge side VSV 38 and the purge passage 37, whereby the atmosphere is released. Canister atmosphere hole VSV3 from the inlet 36a
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 sucked into the surge tank 26 from the purge port 33b through the purge passage 37, the purge side VSV 38 and the purge passage 39. In addition, the activated carbon 33c is regenerated by the above desorption and prepared for the next adsorption of vapor.

FIG. 4 shows a system configuration diagram of the second embodiment of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. The second embodiment shown in FIG.
It is characterized in that the canister atmosphere hole VSV36 of the first embodiment is eliminated, and a throttle (orifice) 61 is provided in the vapor passage 32c.

In the second embodiment shown in FIG. 4, the tank internal pressure switching valve 34 is opened (opened) and the purge side VSV 38 is opened (opened) at the time of failure diagnosis, and the ventilation resistance of the canister 33 is used. The generated intake pipe negative pressure is applied to the fuel tank 30 by bypassing the fuel tank internal pressure control valve 31.

FIG. 5 shows a system configuration diagram of the third embodiment of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. The third embodiment shown in FIG.
By removing the canister atmosphere hole VSV36 of the first embodiment and connecting the vapor passage 32c to the purge passage 37 via the tank internal pressure switching valve 34 and the bypass passage 65, the canister 33 is bypassed and the vapor passage is formed. It is characterized in that a diaphragm (orifice) 63 is provided in the middle of 32c.

In this embodiment, since the tank internal pressure switching valve 34 is shut off (closed) during normal purging, the vapor passage 3
2c and the purge passage 37 do not communicate with each other and are independent of each other, the same evaporation path as in the first and second embodiments is configured, and the tank internal pressure of the fuel tank 30 is set by the fuel tank internal pressure control valve 31. The vapor generated in the fuel tank 30 is controlled by the pressure, and the activated carbon 3 in the canister 33
Adsorbed to 3c.

Since the tank internal pressure switching valve 34 is opened at the time of failure diagnosis, the vapor passage 32c communicates with the purge passage 37 through the bypass passage 65. As a result, the negative pressure in the surge tank 26 is maintained by the purge passage 39, the purge VSV 38, the purge passage 37, when the purge VSV 38 is opened.
Bypass passage 65, tank internal pressure switching valve 34, throttle 63,
It is introduced into the fuel tank 30 through the vapor passages 32c and 32d.

At this time, since the diameter of the throttle 63 is set to be quite small, the large air flow resistance of the throttle 63 causes the upstream side (fuel tank 30 side) of the throttle 63 to become a substantially static system, and the throttle 63. Upstream vapor passages 32c, 32
When there is no leak in d, the negative pressure is introduced to the upstream side of the throttle 63, whereas when there is a leak, the negative pressure can be prevented from being applied at all, thereby improving the detection accuracy of the pressure sensor 40. You can

FIG. 6 shows a system configuration diagram of the fourth embodiment of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. In this embodiment, the canister atmosphere hole VSV36 and the tank internal pressure switching valve 3 of the first embodiment shown in FIG.
4 are respectively deleted, and a bypass passage 67 that connects the upstream side and the downstream side of the fuel tank internal pressure control valve 31 is provided, and a throttle (orifice) is provided in the middle of the bypass passage 67.
69 is provided.

This embodiment is basically the same as the second embodiment in FIG. 4, but the negative pressure of the surge tank 26 is changed to the purge passage 39 and the purge VSV 38 each time the purge VSV 38 is opened. Is introduced into the fuel tank 30 through the purge passage 37, the canister 33, the bypass passage 67, the throttle 69, and the vapor passage 32d.

Next, the purge flow rate detecting means 16 will be described. Purge passages 37 and 39 passing through the purge side VSV 38
Flow rate, that is, the purge flow rate, is determined by the passage area of the VSV 38 and the differential pressure before and after. The passage area of the VSV 38 is obtained as a flow rate characteristic when a certain differential pressure is applied. Since the differential pressure between the front and rear is the intake pipe negative pressure and the atmospheric pressure, it is substantially determined only by the intake pipe negative pressure.

In the case of the duty control type in which the purge-side VSV 38 determines the entire opening by alternately opening and closing the valve at a rate of a period corresponding to the duty ratio of the drive pulse, the purge flow rate is as shown in FIG. As shown in FIG. 7, it is determined by the engine intake pipe negative pressure and the duty ratio of the drive pulse. As can be seen from FIG. 7, the purge flow rate increases as the duty ratio increases when the intake pipe negative pressure is constant, and increases as the intake pipe negative pressure increases at a constant duty ratio.

Further, in the case of the on / off control type in which the purge side VSV 38 has only one of the fully open and fully closed positions, the purge flow rate increases in proportion to the engine intake pipe negative pressure as shown in FIG. Shows a monotonically increasing characteristic.

Therefore, the purge flow rate can be estimated from the engine intake pipe negative pressure or the like by using the characteristics shown in FIG. 7 or FIG. In the present embodiment, the purge-side VSV 38 will be described as a duty control type. here,
When the drive pulse of the purge-side VSV 38 of duty control increases stepwise as shown by I in FIG. 9 (A), the purge flow rate does not immediately follow this duty ratio,
A response delay occurs as shown in FIG. Purge side VS
The same applies when V38 is on / off controlled and is switched from off to on. This is piping and canister 33
It is caused by the volume and ventilation resistance.

The intake pipe negative pressure also has a response delay as in the above case. Therefore, in the purge flow rate calculation routine of FIG. 10, which will be described next, the duty ratio is smoothed and the result is shown in FIG.
As shown in, the duty ratio corresponding to the change in the purge flow rate is obtained, and the intake pipe negative pressure is also smoothed to obtain the intake pipe negative pressure that is similar to the actual change in the intake pipe negative pressure. The purge flow rate is calculated.

The purge flow rate calculation routine shown in FIG.
It will be described later, for example, every predetermined period by the micro computer 21.
It is started as a subroutine used in the failure diagnosis processing routine of
When moved, the CPU 50 firstly determines that the current purge side VSV3.
8 drive pulse duty ratio (hereinafter simply referred to as “purge VS
"V duty ratio") D_RRead (step 1
01), followed by the par that was previously annealed in this routine
The VSV duty ratio D_RNRead from RAM52
(Step 102), and then the difference (D_R-D _RN)
Calculate and change the duty ratio ΔD_R(Step
103).

Then, it is judged whether or not the current purge VSV duty ratio D _R and the previous purge VSV duty ratio D _RN are equal (step 104). If they are not equal, the purge VSV duty ratio D is determined in steps 105 and 106. The smoothing calculation of _R is performed, and when they are equal, there is no change from the previous smoothing processing value D _RN, and since the smoothing processing is unnecessary, the smoothing processing is not performed and the routine proceeds to step 107.

In step 105, the smoothing process is performed by the following equation.
Purged VSV duty ratio D _RNCalculate (NEW)
To do.

[0048]

[Equation 1]

However, in the above equation, n is "4", "16",
It is a positive constant such as "32". In the following step 106, the calculated _smoothing processing value D _RN (NEW) is stored in the RAM 52, and then the process proceeds to step 107.

At step 107, the current intake pipe negative pressure MV is read based on the signal detected by the pressure sensor 23. Then, the intake pipe negative pressure MV _N obtained by the smoothing processing in this routine last time is read from the RAM 52 (step 108), and the subtraction of (MV-MV _N ) is performed to calculate the change amount ΔMV of the intake pipe negative pressure. Yes (Step 10
9).

Next, the current and previous intake pipe negative pressures MV and MV _N are compared (step 110). If they are not equal, the process proceeds to step 113, which will be described later, and if they are equal, steps 111 and 112 are executed. The moderation calculation of the intake pipe negative pressure MV is performed. In step 111, the smoothed intake pipe negative pressure Mv (NEW) is calculated by the following equation.

[0052]

[Equation 2]

Then, in step 112, the smoothing processing value MV _N (NEW) is stored in the RAM 52, and the process proceeds to the next step 113.

In step 113, the CPU 50 preliminarily performs RO
Referring to the map shown in FIG. 7 stored in M51, the purge VSV duty ratio smoothing process value D _RN (NEW) calculated in step 105 and the intake pipe negative pressure smoothing process calculated in step 111 The purge flow rate α is calculated from the value MV _N (NEW).

Next, a method of performing a failure diagnosis based on the purge flow rate α calculated as described above will be described. In this embodiment, the intake pipe negative pressure is introduced into the fuel tank 30 for the purpose of failure diagnosis. At this time, the change over time in the fuel tank internal pressure is as shown in FIG. 11, for example.

FIG. 11 shows the atmosphere introducing hole 33 of the canister 33.
d is in an open state, and while the purge of the canister 33 is being performed, the negative pressure of the purge passages 37 and 39 generated by the passage resistance of the canister 33 is applied to the fuel tank 30, and there is no leakage in the evaporation passage in the fuel tank. The change in pressure is shown. In this case, since the negative pressure generated by the passage resistance of the canister 33 is applied to the fuel tank 30, the negative pressure increases toward the negative pressure side with the lapse of time from the start of applying the negative pressure, and the negative pressure corresponding to the passage resistance of the canister 33 is generated. Stabilize.

However, even if the passage resistance of the canister 33 is the same, the negative pressure level applied to the fuel tank 30 also changes when the original purge flow rate changes, and as shown in FIG. 11, the negative pressure level applied to the fuel tank 30 decreases as the purge flow rate decreases. The maximum pressure level becomes smaller.

On the other hand, the pressure in the fuel tank changes with time as shown in FIG. 12 when the purge flow rate is kept constant and the diameter (leak diameter) of the small hole that causes leakage in the evaporation path is changed. As can be seen from the figure, when there is no leakage in the evaporation route, a large maximum value (negative pressure) of the negative pressure level applied to the fuel tank 30 is obtained as indicated by III.

[0059] In contrast, when the leak size exists than when there is no leakage diameter, the maximum value of the negative pressure level according to the fuel tank 30 is small, and the addition IV ₁ 12 as the leak size becomes large, IV ₂ and IV ₃ , the internal pressure of the fuel tank becomes small, and when it exceeds a certain leak diameter, the internal pressure of the fuel tank remains at atmospheric pressure and does not change as shown by IV ₄ .

Therefore, if a constant purge flow rate can be obtained, a leak diameter of a certain value or more exists by using a value slightly on the atmospheric pressure side as a judgment value from the negative pressure level when there is no leakage in the evaporation path. I know whether to do it or not. However, FIG.
As shown in, even if there is no leakage in the evaporation path, the maximum negative pressure level applied to the fuel tank 30 changes depending on the purge flow rate. Therefore, a simple comparison between a constant judgment value and the fuel tank pressure is made. If it is determined whether or not there is a failure, whether the purge flow rate is small and the negative pressure level is smaller than the judgment value (value on the atmospheric pressure side) or whether the negative pressure level is smaller than the judgment value depending on the leak diameter. Can not be distinguished and will be erroneously detected.

Therefore, in the first embodiment of the failure diagnosis processing routine shown in FIG. 13, the judgment value is determined according to the purge flow rate.
1 (a), (b), and (c), and in the second embodiment of the failure diagnosis processing routine shown in FIG. 15 described later, the negative pressure introduction time is shown in FIG. 11 according to the purge flow rate. Accurate failure diagnosis is performed by varying the values as shown in (d), (e) and (f).

Next, the pressure introducing means 17, the pressure detecting means 18, the judging means 19 and the judging value varying means 20 (or the negative pressure introducing time varying means according to claim 2 or the controlling means according to claim 3) are realized. The failure diagnosis process to be performed will be described in detail. The failure diagnosis process differs depending on the system configurations shown in FIGS. 2, 4, 5, and 6. First shown in FIG.
In the system of the embodiment, after a negative pressure is introduced into the evaporation path at the time of failure diagnosis, the negative pressure in the evaporation path is sealed for a predetermined time, and then the degree of pressure change in the sealed evaporation path is measured.
On the other hand, in the system of each embodiment shown in FIG. 4 and FIG. 5, the tank internal pressure switching valve 34 and the purge side VSV3 are set at the time of failure diagnosis.
8 is opened for a predetermined period of time, the degree of change in the negative pressure introduced into the evaporation path for the fixed period is measured by the pressure sensor 40, and when the measurement result changes by a predetermined value or more, it is determined to be normal. The system of the fourth embodiment shown in FIG. 6 has a purge side VSV38.
Is opened for a predetermined period of time, and it is determined whether or not there is a leak in the evaporation route in the same manner as above.

The details of the above-mentioned failure diagnosis processing will be described as a representative of the case where it is applied to the system shown in FIGS. FIG. 13 shows a flowchart of the first embodiment of the failure diagnosis processing routine. When this failure diagnosis processing routine is started by the microcomputer 21 at a rate of once every 65 ms, for example, it is first checked whether or not the execution flag is set to "1" (step 201). This execution flag is a flag that is set to "1" only in step 216, which will be described later, and indicates whether or not the failure diagnosis has been executed. Since the initial value is set to "0" by the initial routine, this failure diagnosis process is performed first. When the routine is started and step 201 is executed, it is determined that the execution flag is not "1" and the routine proceeds to step 202.

In step 202, it is judged whether or not the execution condition (for example, the purging of the canister 33 is completed) is satisfied. If not satisfied, this routine is once terminated, and if it is satisfied, Proceeding to step 203, the purge flow rate α is calculated by the smoothing process by the purge flow rate calculation routine shown in FIG.

Then, the tank internal pressure switching valve 34 and the purge side VSV 38 are opened to introduce the intake pipe negative pressure into the fuel tank 30 (step 204). Then, a predetermined value is added to the leak determination timer (step 205), and it is determined whether the value of the leak determination timer is a value corresponding to X seconds (step 2).
06), when the value corresponding to X seconds has not been reached, this routine is once terminated, and when the value corresponding to X seconds has been reached, the routine proceeds to step 207.

In step 207, the average purge flow rate of each purge flow rate calculated in step 203 is calculated every 65 ms until X seconds elapse after the intake pipe negative pressure is introduced into the fuel tank 30, and then in step 208. ROM 51 in advance
The determination value β is calculated by referring to the map shown in FIG. In the map shown in FIG. 14, the determination value β increases as the average purge flow rate increases.
It is a dimensional map. This is because, as shown in FIG. 11, the maximum level of the negative pressure applied to the fuel tank 30 changes depending on the purge flow rate, so the optimum determination value also changes.

Returning to FIG. 13 again, subsequently, after the substantial fuel tank internal pressure is read from the output detection signal of the pressure sensor 40 (step 209), the fuel tank internal pressure is the judgment value calculated in step 208. It is determined whether or not β or more (step 210). When the measured fuel tank internal pressure is equal to or higher than the determination value β (value on the negative pressure side), it is determined that there is no leakage in the evaporation path and it is normal, the warning lamp 41 is turned off (step 211), and the leakage failure fail code is cleared. (Step 212). On the other hand, when it is determined in step 210 that the measured fuel tank internal pressure is less than the determination value β (atmospheric pressure side value), it is determined that there is a leak in the evaporation path and it is abnormal, and the warning lamp 41
Is turned on (step 213), the driver is notified of the failure occurrence of the evaporative purge system, and the leak failure fail code is stored in, for example, the backup RAM 53 (step 214). The leak failure fail code is read from the backup RAM 53 at the time of subsequent repair, and informs the cause of failure of the evaporative purge system.

When the presence or absence of a failure in the evaporative purge system is determined as described above and the processing of step 212 or 214 is executed, the leak determination timer is subsequently cleared (step 215) and the execution flag is set to "1". Is set to "" (step 216), and the failure diagnosis process is terminated. After that, even if this routine is started, step 2 in FIG.
Since the execution flag is determined to be "1" in 01, this routine is not executed until it is restarted thereafter.

Next, a second embodiment of the failure diagnosis processing routine will be described with reference to FIGS. When the failure diagnosis routine shown in FIG. 15 is started by the microcomputer 21 once every 65 ms, for example, step 3
After performing the same processing (determination of execution flag setting, determination of execution condition satisfaction and calculation of purge flow rate) of steps 201 to 203 of FIG. 13 in steps 01 to 303, it is determined in step 304 whether the timer flag is “1”. If it is "0", the process proceeds to step 305, and if it is "1", the process proceeds to step 309.

Since this timer flag is cleared by the initial routine, when step 304 is executed for the first time, the routine always proceeds to step 305 to start failure detection. In step 305, the determination time T is calculated by referring to the map shown in FIG. 16 stored in advance in the ROM 51 with the purge flow rate calculated in step 303. The map shown in FIG. 16 is a two-dimensional map in which the determination time T decreases as the purge flow rate increases. This is because, as shown in FIG. 11, the negative pressure introduction time until reaching the preset fuel tank internal pressure becomes longer as the purge flow rate becomes smaller.

Returning to FIG. 15 again, if the determination time T is calculated in step 305, then step 30 is continued.
6, the tank internal pressure switching valve 34 and the purge side VSV3
8 are opened to start introducing the intake pipe negative pressure into the evaporation path to the fuel tank 30. In step 307, the leak determination timer is set to the above determination time T, and in step 308, the timer flag is set to "1". After setting, this routine is once ended.

When this failure diagnosis processing routine is started again after 65 ms, the routine proceeds to step 304 via steps 301 to 303, and this time the timer flag is judged to be "1". Then, the process proceeds to step 309 and the fuel tank 3
The intake pipe negative pressure is continuously introduced to 0, a predetermined value is subtracted from the leak determination timer in step 310, and it is determined in step 311 whether the leak determination timer is "0".

In this way, when the introduction of the intake pipe negative pressure into the evaporation path continues for the judgment time T, the value of the leak judgment timer is judged to be "0" in step 311, and therefore step 3
After proceeding to step 12 and reading the fuel tank internal pressure at that time based on the output detection signal of the pressure sensor 40, step 3
At 12, it is determined whether the read fuel tank pressure is equal to or higher than a predetermined fixed determination value γ (value on the negative pressure side).

When the pressure in the fuel tank is equal to or greater than the fixed judgment value γ, it is judged to be normal, and the warning lamp 41 is turned off and the leakage failure fail code is cleared (step 314).
315), when it is less than the fixed judgment value γ, it is judged to be abnormal, lighting of the warning lamp 41 and storage of the leakage failure fail code in the backup RAM 53 (steps 316 and 317), and then the timer flag is cleared (step 318). ), The execution flag is set to "1" (step 319), and this routine ends. In the present embodiment and the first embodiment, since the negative pressure introduction time or the judgment value is made variable according to the purge flow rate, the maximum value of the negative pressure level applied to the fuel tank as shown in FIG. Even if is changed, it is possible to make a judgment based on the relationship between the optimum pressure in the fuel tank and the judgment value, so that it is possible to prevent erroneous diagnosis.

Next, a third embodiment of the failure diagnosis processing routine will be described with reference to FIG. In FIG. 17, the same processing steps as those in FIG. 13 are designated by the same reference numerals, and the description thereof will be omitted. In the failure diagnosis processing routine of FIG. 17, when the calculation of the purge flow rate by the smoothing process is completed in step 203, it is determined whether the purge flow rate is a value equal to or greater than a predetermined value Y that can be determined by a predetermined fixed determination value γ. (Step 401).

When the calculated purge flow rate is less than the predetermined value Y, it is determined that reliable failure diagnosis cannot be performed, the leak determination timer is cleared (step 402), and the tank internal pressure switching valve (VSV) 34 is closed. (Step 403), this routine is once ended. On the other hand, when it is determined that the purge flow rate calculated in step 401 is equal to or greater than the predetermined value Y, it is first determined whether or not the leak determination timer is "0" to start the leak failure diagnosis (step 404).

Since the leak determination timer is cleared by the initial routine, the routine always proceeds to step 405 when the step 404 is first executed so that the pressure in the fuel tank is the predetermined value P ₀ (this is the atmospheric pressure or the predetermined value). If the internal pressure of the fuel tank is less than the predetermined value P ₀ , the leakage failure diagnosis is not performed, and this routine is ended once, while the internal pressure of the fuel tank is set to the predetermined value P 0. _If it is determined to be ₀ or more, the routine proceeds to step 204, where the tank internal pressure switching valve 34 and the purge side VSV 38 are opened to introduce the intake pipe negative pressure to the fuel tank 30.

As shown in FIGS. 11 and 12, in the initial state before the intake pipe negative pressure is introduced into the fuel tank 30, the pressure of the fuel tank 30 is a value near the atmospheric pressure and a negative pressure is applied. In this embodiment, the optimum judgment value γ is compared with the fuel tank internal pressure when a predetermined time X seconds has elapsed after the introduction of the negative pressure (steps 408 and 313 described later). ), The leak determination timer is cleared if the purge flow rate becomes less than Y even once before the predetermined time X seconds has elapsed after the introduction of the negative pressure (step 40).
1, 402), and in this case, when the purge flow rate subsequently returns to Y or more, the negative pressure is introduced for X seconds from the state where the negative pressure remains in the fuel tank 30 to some extent.
This is because the judgment value γ is no longer the optimum value.

Therefore, in step 405, it is first confirmed that there is no negative pressure in the fuel tank 30, and then the failure diagnosis processing in step 204 and thereafter is executed. Therefore, when the purge flow rate falls below Y before the lapse of X seconds after the introduction of the negative pressure, it is necessary to wait until the pressure in the fuel tank returns to its original value, and then start over from the beginning.

When the intake pipe negative pressure is started to be introduced into the fuel tank 30 in step 204, a predetermined value is added to the leak determination timer (step 205), and a predetermined time X seconds has elapsed from the value of the leak determination timer after the negative pressure is introduced. It is determined whether or not (step 406), after a lapse of X seconds, the substantial fuel tank pressure is read based on the output detection signal of the pressure sensor 40 (step 407), and the magnitude is compared with the fixed determination value γ. Then, it is determined whether or not the evaporation route is leaked (step 40).
8).

Then, after the leak determination timer is cleared (step 215), the tank internal pressure switching valve 34 is closed (step 409). Note that the tank internal pressure switching valve 34 may be closed together with the execution flag being set in each of the routines shown in FIGS. 13 and 15. According to the present embodiment, since the leak determination is performed only with the purge flow rate and the negative pressure introduction time, which enables the accurate leak determination with the fixed determination value γ,
Misdiagnosis can be prevented.

Alternatively, the tank internal pressure switching valve 34 may not be opened, and a negative pressure may be introduced to a path closer to the canister 33 than the tank internal pressure control valve 34 to complete the failure diagnosis (in this case, the fuel tank). Negative pressure is not introduced until 30). In this case, as shown in the system configuration diagram of FIG. 18, a three-way valve 71 is provided instead of the tank internal pressure switching valve 34, and the pressure sensor 40 is connected to the three-way valve 71.

The three-way valve 71 is the microcomputer 21.
Thus, switching control is performed so that the pressure sensor 40 and the vapor introducing port 33a of the canister 33 are communicated with each other or the pressure sensor 40 and the vapor passage 32c are communicated with each other. Then, the VSV 38 is opened and the pressure sensor 4
0 and the vapor introduction port 33a of the canister 33 are in communication with each other via the three-way valve 71, when the pressure value detected by the pressure sensor 40 is on the negative pressure side of the predetermined threshold value, it is determined to be normal, If not, it is determined to be abnormal.

[0084]

As described above, according to the first aspect of the present invention, since the determination value is set to the optimum value in accordance with the purge flow rate, erroneous diagnosis can be prevented, and the second aspect is described. According to the invention, since the maximum level of the negative pressure applied to the fuel tank is predicted according to the purge flow rate and the optimum negative pressure introduction time is set, it is possible to prevent erroneous diagnosis. Further, according to the third aspect of the present invention, since the leak determination is executed only under the conditions of the purge flow rate and the negative pressure introduction time that enable the optimum leak determination with the set determination value, the erroneous diagnosis is prevented. It has features such as being able to.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the invention according to claim 1.

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

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

FIG. 4 is a system configuration diagram of a second embodiment of the present invention.

FIG. 5 is a system configuration diagram of a third embodiment of the present invention.

FIG. 6 is a system configuration diagram of a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between an intake pipe negative pressure and a duty ratio and a purge flow rate when the purge side VSV is duty controlled.

FIG. 8 is a diagram showing the relationship between the intake pipe negative pressure and the purge flow rate when the purge side VSV is on / off controlled.

FIG. 9 is a diagram showing a relationship between a purge-side VSV duty ratio and a purge flow rate.

FIG. 10 is a flowchart showing an example of a purge flow rate calculation routine by a smoothing process.

FIG. 11 is a diagram showing a change in the fuel tank internal pressure when the purge flow rate is changed.

FIG. 12 is a diagram showing a change in pressure inside the fuel tank when the leak diameter is changed.

FIG. 13 is a first part of a failure diagnosis processing routine according to the present invention.
It is a flow chart which shows an example.

14 is a diagram showing an example of a map used in the routine of FIG.

FIG. 15 is a second routine of the failure diagnosis processing routine of the essential part of the present invention.
It is a flow chart which shows an example.

16 is a diagram showing an example of a map used in the routine of FIG.

FIG. 17 is a third routine of the failure diagnosis processing routine of the essential part of the present invention.
It is a flow chart which shows an example.

FIG. 18 is a system configuration diagram of another embodiment 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 Evaporation path 16 Purge flow rate detecting means 17 Pressure introducing means 18 Pressure detecting means 19 Judging means 20 Judgment value varying means 21 microcomputer 31 fuel tank internal pressure control valve 34 tank internal pressure switching valve 36 canister atmosphere hole VSV (vacuum switching valve) 38 purge side VSV (vacuum switching valve) 41 warning lamp 45, 65, 67 bypass passage 46 idle Speed control valve (I
SCV) 47 Fuel injection valve 61, 63, 69 Throttle (orifice) 71 Three-way valve

Claims (3)

[Claims] 1. A failure of an evaporation purge system for adsorbing evaporated fuel from a fuel tank to an adsorbent in a canister through a vapor passage and purging the adsorbed fuel in the canister through a purge passage into an intake passage of an internal combustion engine during a predetermined operation. In the device for diagnosing, the purge flow rate detecting means for substantially detecting the purge flow rate of the purge passage, the pressure introducing means for introducing the negative pressure of the intake passage into the evaporation path to be diagnosed, and the inside of the evaporation path Based on the pressure detection means for detecting the pressure and the pressure value detected by the pressure detection means, the degree of change of the pressure in the evaporation route is measured, and the evaporation purge system is obtained from the comparison result between the measured value and the judgment value. Determination means for determining the presence or absence of a failure of the determination means of the determination means according to the purge flow rate detected by the purge flow rate detection means. Trouble diagnosis device for the evaporative emission control system characterized by having a determination value varying means for varying the value. 2. The negative pressure introduction time varying means for varying the introduction time of the negative pressure introduced into the evaporation path by the pressure introducing means according to the purge flow rate detected by the purge flow rate detecting means, The failure diagnosis device for the evaporative purge system according to claim 1, wherein the device is provided in place of the judgment value varying means. 3. The control means for prohibiting the determination by the determining means when the purge flow rate detected by the purge flow rate detecting means is below a predetermined value is provided in place of the determination value varying means. The failure diagnosis device for an evaporative purge system according to claim 1, wherein: