JPH06147032A - Trouble diagnosing device of evapo-purge system - Google Patents

Abstract

PURPOSE:To diagnose something wrong with an evapo-purge system which purges the vaporized fuel of an internal combustion engine and carry out combus tion and prevent any wrong diagnosis from occurring. CONSTITUTION:When a purge flow rate calculated in a step 203 is more than Y, netative pressure is inducted into an evaporative passage (steps 204 and 205), and thereby a leak judging timer is stepped (step 211). When the purge flow rate becomes less than Y in the midway of the vacuum conduction (step 204), this vacuum conduction into the evaporative route is suspended (step 213), and tank internal pressure PE at that time is stored in memory (step 215). When the purge flow rate becomes more than Y agains, the vacuum conduction is resumed (steps 204 and 205, and thereby the stepping of the leak judging timer is reopened since the tank internal pressure has come to higher the aforesaid (steps 209 and 211).

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 introduced a negative pressure in the intake passage of an internal combustion engine to a fuel tank for a predetermined time through a throttle in Japanese Patent Application No. 4-296051 as a failure diagnosis device for an evaporation purge system. In the device that detects the negative pressure by the pressure sensor provided in the vapor passage from the vapor introduction hole of the canister to the fuel tank, and compares the detected negative pressure with the judgment value to determine whether there is a failure or not. We have proposed a failure diagnosis device that makes the judgment value and the negative pressure introduction time variable according to the purge flow rate at that time, and makes a judgment only when the state above a certain purge flow rate continues for a certain time or longer.

According to the failure diagnosis apparatus for the evaporative purge system proposed by the present applicant, the operating conditions (intake pipe negative pressure, intake air amount, etc.) of the internal combustion engine and the opening degree (duty ratio) of the purge control valve. Even if the maximum level of the negative pressure applied to the fuel tank changes due to the change in the purge flow rate due to the purge flow rate, the judgment value and the negative pressure introduction time can be changed according to the purge flow rate, Since the determination is made only when the above continues, the possibility of erroneous detection can be greatly reduced.

[0005]

However, according to the failure diagnosis apparatus for the evaporative purge system proposed by the present applicant, the purge flow rate which is the basis for setting the judgment value and the negative pressure introduction time is set at the start of diagnosis. If the purge flow rate changes above the certain value after the start of diagnosis, if the purge flow rate is above the certain value, the failure diagnosis is performed. There is a possibility that the negative pressure value varies and a false diagnosis is made.

The present invention has been made in view of the above points, and solves the above problems by introducing a negative pressure by selecting only when the purge flow rate is substantially the same as the purge flow rate at the start of introducing the negative pressure. It is an object of the present invention to provide a failure diagnostic device for the evaporative purge system.

[0007]

FIG. 1 is a block diagram showing the principle of the present invention for achieving the above object. As shown in the figure, according to the present invention, the evaporated fuel from the fuel tank 11 is adsorbed by the adsorbent in the canister 13 through the vapor passage 12, and the adsorbed fuel in the canister 13 is passed through the purge passage 14 during the predetermined operation. The apparatus for diagnosing the failure of the evaporative purge system for purging the intake passage 10a includes a purge flow rate detecting means 16, a pressure introducing means 17, a negative pressure introducing interrupting means 18, a pressure detecting means 19 and a determining means 20. It is configured.

The purge flow rate detecting means 16 substantially detects the purge flow rate in the purge passage 14. When the purge flow rate detected by the purge flow rate detection means 16 is equal to or higher than a predetermined value, the pressure introducing means 17 introduces the negative pressure in the intake passage 10a into the evaporation path 15 which is the diagnosis target for a predetermined time.

Further, the negative pressure introduction interrupting means 18 prohibits the introduction of the negative pressure by the pressure introducing means 17 at the same time as holding the negative pressure in the evaporation path 15 when the purge flow rate is less than the predetermined value, and The predetermined time counting is interrupted. Further, when the negative pressure is introduced into the evaporation path 15 by the pressure introducing means 17, the determining means 20 detects the pressure detecting means 19
Based on the pressure value detected by, the degree of change of the pressure in the evaporation path 15 is measured, and the presence or absence of a failure of the evaporation purge system is determined from the comparison result of the measured value and the determination value.

[0010]

The present invention uses the pressure introducing means 17 to evaporate the path 1
The negative pressure is introduced into the evaporation path 15 by selecting only the purge flow rate near the purge flow rate when the negative pressure is started to be introduced into 5.
When the purge flow rate is less than the predetermined value, the negative pressure introduction interruption means 18
Therefore, the introduction of the negative pressure by the pressure introducing means 17 is prohibited, the negative pressure is maintained in the evaporation path 15, the time counting is interrupted, and the negative pressure introduction and the time counting are restarted after the purge flow rate becomes a predetermined value or more. To do.

Therefore, in the present invention, since the negative pressure is introduced for a predetermined time while the pressure in the fuel tank 11 is equal to or higher than the predetermined value, it is set based on the situation at the start of the negative pressure introduction even if the negative pressure changes. It is possible to determine the leakage of the evaporation route 15 under the conditions.

[0012]

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, When the diaphragm 31b is positioned as shown in the drawing and communicates between the vapor passages 32a and 32c and 32d, and the tank internal pressure is a value in the negative pressure direction due to the set pressure of the spring 31a, the diaphragm 31b resists the spring force of the spring 31. And then move down to the vapor passages 32a and 32
Block between c 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 connected to the vapor introducing port 33a of the canister 33 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, 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 the present embodiment, at the time of failure diagnosis, the tank internal pressure control by the fuel tank internal pressure control valve 31 is prohibited, and in order to introduce a negative pressure into the fuel tank 30, 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.

A throttle (orifice) 35 is provided in the vapor passage 32c. Further, the purge port 33 b of the canister 33 is connected to the purge side VSV 38 via the purge passage 37. The purge-side VSV 38 is a control valve that connects or disconnects the other end of the purge passage 39, which has one end communicating with the surge tank 26, and the other end of the purge passage 37, based on a control signal from the microcomputer 21. The pressure sensor 40 has a vapor passage 32.
It is provided in the middle of d and is provided to substantially detect the internal pressure of the fuel tank 30 by detecting the pressure in the vapor passage 32d, and constitutes the pressure detecting means 19. 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, bypassing the throttle valve 25, the intake pipe 24 and the surge tank 26 on the downstream side of the air cleaner 22.
A bypass passage 45 that communicates with and 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, the negative pressure introducing interrupting means 18, the pressure detecting means 19 and the determining means 20 as the V.
The control device is realized by software processing together with the SVs 34 and 38, and has a known hardware configuration as shown in FIG. 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 FIG. 3, a microcomputer 21 includes a central processing unit (CPU) 50 and a read only memory (RO) storing a processing program.
M) 51, random access memory (RAM) 52 used as a work area, backup RAM 53 that retains data even after the engine is stopped, input interface circuit 54 with multiplexer, A / D converter 56, 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 and 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. Valve 47, tank internal pressure switching valve 34, purge side VSV3
8, selectively outputs to the warning lamp 41 and the ISCV 46 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. 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 two 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 according to the amount of vapor generated, but when the internal pressure of the fuel tank 30 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, 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 the 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. The atmosphere is sent into the canister 33 through the 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.

In this embodiment, at the time of failure diagnosis, the tank internal pressure switching valve 34 is opened (opened), and the purge side VSV 38 is provided.
Is opened (opened), and the intake pipe negative pressure generated by the passage resistance of the canister 33 is applied to the fuel tank 30 by bypassing the fuel tank internal pressure control valve 31.

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.
By 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 a throttle (orifice) 63 is provided in the middle of the vapor passage 32c. Have.

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, and the same evaporation path as in the first embodiment is configured, and the tank internal pressure of the fuel tank 30 is controlled to the set pressure of the fuel tank internal pressure control valve 31. At the same time, the vapor generated in the fuel tank 30 is adsorbed by the activated carbon 33c in the canister 33.

Since the tank internal pressure switching valve 34 is opened at the time of failure diagnosis, the vapor passage 32c is connected to 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

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 repeating the opening and closing of the valve at a ratio of the period corresponding to the duty ratio of the drive pulse, the purge flow rate is as shown in FIG. 5, it is determined by the engine intake pipe negative pressure and the duty ratio of the drive pulse. As can be seen from FIG. 5, 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.

In the case of the on / off control type in which the purge side VSV 38 has only one of fully open and fully closed, 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 and the like by using the characteristics shown in FIG. 5 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. 7A, 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.

A negative response occurs in the intake pipe negative pressure as in the above case. Therefore, in the purge flow rate calculation routine of FIG. 8 described below, the duty ratio is smoothed to obtain the duty ratio corresponding to the change in the purge flow rate as indicated by II in FIG. In the same manner as above, the purge flow rate is accurately calculated by performing the smoothing process to obtain the intake pipe negative pressure that is close to the actual change of the intake pipe negative pressure. The purge flow rate calculation routine itself shown in FIG. 8 is the same as that of the proposed device of the applicant of the present invention.

The purge flow rate calculation routine shown in FIG.
The black computer 21 will be described later at predetermined intervals, for example.
Start as a subroutine used in the failure diagnosis processing routine
Then, the CPU 50 firstly determines that the current purge side VSV 38
Drive pulse duty ratio (hereinafter simply referred to as “purge VSV
"Duty ratio") D_RRead (step 10
1), and then the purge that has been annealed in this routine last time
VSV duty ratio D _RNRead from RAM52 (
Step 102), and their difference (D_R-D_RN) Is calculated
And change the duty ratio ΔD_R(Step 10
3).

Next, 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.

[0040]

[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 intake pipe negative pressure MV _N (NEW) that has been smoothed is calculated by the following equation.

[0044]

[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. 5 stored in M51, the purge VSV duty ratio smoothing processing value D _RN (NEW) calculated in step 105 and the intake pipe negative pressure smoothing processing calculated in step 111 The purge flow rate α is calculated from the value MV _N (NEW).

Next, a method of diagnosing a failure based on the purge flow rate α calculated as described above will be described. In the present embodiment, the intake pipe negative pressure is introduced into the fuel tank 30 for failure diagnosis. At this time, the change over time in the fuel tank internal pressure is as shown in FIG. 9C, for example.

FIG. 9 shows the atmosphere introducing hole 33d of the canister 33.
Of the purge side VSV 38 when 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 path while the canister 33 is being purged. The open / closed state ((A) in the figure), the purge flow rate ((B) in the figure), and the tank internal pressure of the fuel tank 30 ((C) in the figure) are respectively shown.

VSV3 on the purge side from time t ₁ to t ₂
When the negative pressure is introduced at a constant flow rate of the purge flow rate or more as shown by the solid line in FIG.
The tank internal pressure is the negative pressure generated by the passage resistance of the canister 33, as shown by the solid line in FIG.
Since it is being applied to the negative pressure, the pressure increases to the negative pressure side with the lapse of time from the time t ₁ when the negative pressure starts to be applied.
Negative pressure of passage resistance (This is the negative pressure side of the judgment value β)
Stabilizes at.

However, even if the passage resistance of the canister 33 is the same, if the original purge flow rate changes as shown by the one-dot chain line I in FIG. 9 (B), the negative pressure level applied to the fuel tank 30 (one point in FIG. 9 (C)). It changes as shown by a chain line II. This change decreases the maximum value of the negative pressure level applied to the fuel tank 30 as the purge flow rate decreases.

On the other hand, when the purge flow rate is constant and there is a leak in the evaporation path, the maximum internal pressure of the fuel tank is the judgment value β, as indicated by the broken line III in FIG. 9C. It is a value on the side of atmospheric pressure. At this time, the maximum value of the negative pressure level applied to the fuel tank 30 becomes smaller as the diameter of the leak hole in the passage of the evaporation path becomes larger, and the internal pressure of the fuel tank remains the atmospheric pressure above a certain diameter and does not change.

Therefore, even if there is no leak in the evaporation diameter, if the original purge flow rate changes to a value smaller than that at the start of the introduction of the negative pressure, as shown by the one-dot chain line I in FIG. 9 (C) does not exceed the judgment value β as shown by the alternate long and short dash line II, the tank internal pressure value at time t ₂ varies, and the tank internal pressure when there is a leak in the evaporation route (broken line III in FIG. 9 (C)) ) And cannot be distinguished from each other, resulting in false detection.

Therefore, in one embodiment of the failure diagnosis processing routine of the main part of the present invention shown in FIG. 10, the negative pressure introduction time is made variable, and the purge flow rate is once lowered so that the negative pressure level falls below a predetermined value. In this case, the time count is interrupted, the tank internal pressure at that time is stored, the purge flow rate increases next, and the reference purge flow rate is exceeded, and the time count is returned to the previously stored fuel tank internal pressure. By restarting, the above erroneous detection is prevented.

Next, one embodiment of the failure diagnosis processing routine of FIG. 10 will be described. When the failure diagnosis processing routine is interrupted by the microcomputer 21 at a rate of once every 65 ms, for example, the execution flag is first set. "1"
It is checked whether or not it is set to (step 201). This execution flag is a flag that is set to "1" only in step 224, 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 process 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 established. If not established, this routine is once terminated, and if it is established, 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.

Subsequently, it is determined whether or not the calculated purge flow rate α is equal to or greater than a predetermined value Y that provides a fuel tank internal pressure that can be determined with a predetermined fixed determination value β (step 20).
4) When α ≧ Y, the purge-side VSV 38 is opened (this is also referred to as “negative pressure introduction VSV opening” hereinafter), and the intake pipe negative pressure is supplied to the fuel tank 30 via the canister 33. The introduction is started (step 205). Note that the tank internal pressure switching valve 34 is always open during failure diagnosis.

After that, after the leak determination flag is set to "1" (step 206), it is checked whether or not the flag A is "1" (step 207). This flag A
Is a flag that is set only in step 216 described below and indicates whether or not the negative pressure introduction is being interrupted, and the initial value is set to "0" by the initial routine. Therefore, when this step 207 is executed for the first time, the flag A is not set, so steps 208, 209 and 210 are branched and the routine proceeds to step 211, where a predetermined value is added to the leak determination timer.

Then, it is judged whether or not the value of the leak judgment timer after the addition indicates a time of a predetermined negative pressure introduction time X seconds or more (step 212). Exit the routine. Therefore, time t
_{If the} execution condition is satisfied in ₁ and the purge flow rate is equal to or greater than the reference purge flow rate Y and the state continues until time t ₂ that is less than X seconds, the processes of steps 201 to 212 are repeatedly executed every 65 ms. The leak determination timer is shown in Fig. 11.
As shown in (A), counting up by a predetermined value,
The purge side VSV 38 is opened as shown in FIG.
The tank internal pressure of the fuel tank 30 increases in the negative pressure direction as shown in FIG. The leak determination flag is shown in Fig. 1.
1 (E), the flag A is "0" as shown in FIG.

Then, at time t ₂ which is less than X seconds after the introduction of the negative pressure, the purge flow rate becomes the reference purge flow rate Y as shown in FIG. 11 (C).
If it falls below less, the failure diagnosis processing routine of FIG. 10 proceeds from step 204 to step 213, the negative pressure introduction VSV (purge side VSV 38) is shut off, and as a result, the negative pressure introduction to the fuel tank 30 is interrupted. , The negative pressure at that time is kept closed in the evaporation path.

Subsequently, the leak determination flag is "1".
It is determined whether or not (step 214).
The routine of FIG.
The leak determination flag is set to "1"
Proceed to step 215 to set the tank internal pressure when the negative pressure introduction is interrupted.
It is read from the output value of the pressure sensor 40, and it is read as P _E
Is stored in the RAM 52 and then stored in the RAM 52.
6 sets flag A to "1", and determines whether leakage is in progress.
Clear the lag to "0" and exit this routine.

Thereafter, the processing of steps 201 to 204, 213 and 214 is repeated until the purge flow rate becomes equal to or higher than the reference purge flow rate Y at time t ₃ as shown in FIG. Is interrupted. Then, at time t ₃ , when the purge flow rate becomes Y or more, the failure diagnosis processing routine of FIG. 10 opens the purge-side VSV 38 in step 205 via steps 201 to 204 to restart the introduction of negative pressure, and then to step The process proceeds to step 207 via 206, and it is determined that the flag A is set to "1". As a result, the routine proceeds to step 208, where the tank internal pressure at time t ₃ is read, and then step 2
At 09, it is judged whether or not the read tank internal pressure is equal to or higher than the tank internal pressure P _E at the time when the negative pressure introduction is interrupted.

The tank internal pressure rises in the negative pressure direction from the time t ₃ at which the introduction of the negative pressure is resumed. Normally, however, when the introduction of the negative pressure is resumed, the tank internal pressure at that time is changed except when the negative pressure introduction interruption time is extremely short. It is determined to be less than P _E , and in this case, this routine is once terminated. When the tank pressure in the subsequent step 209 it is determined at time t ₄ or more P _E, after clearing the flag A (step 210), leakage determination timer by adding a predetermined value (step 211), leakage determination after the addition It is determined whether or not the value of the timer indicates a value of X seconds or more (step 212). Thus, operation of the leakage determination timer as shown at time t ₄ after diagram 11 (A) is resumed, also increases in the negative pressure direction by the negative pressure introduction resumed as the time t ₃ after the tank internal pressure is shown in FIG. 11 (D) I will do it.

Thereafter, the same operation as described above is repeated, and when it is determined in step 212 that the value of the leak determination timer indicates the value C ₁ corresponding to X seconds (time at this time is t
₅ ), the tank internal pressure is read based on the output detection value of the pressure sensor 40 (step 217), and it is further determined whether the read tank internal pressure is the fixed determination value β or more (step 218). The tank internal pressure shown in FIG. 11D is equal to or greater than the fixed determination value β at the time t ₅ , and in this case, it is determined that there is no leakage in the evaporation route and the warning lamp 41 is turned off (step 219). The leak determination failure fail code is cleared (step 220).

On the other hand, when it is determined in step 218 that the tank internal pressure is on the atmospheric pressure side of the fixed determination value β,
It is determined that there is a leak in the evaporation path, the warning lamp 41 is turned on (step 221), the driver is notified of the failure occurrence of the evaporation purge system, and the failure failure code is stored in the backup RAM 53, for example. (Step 222). This 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 220 or 222 is executed, the leak determination timer is subsequently cleared (step 223), and the execution flag "1" is set. Is set (step 224) and the failure diagnosis process is terminated. After that, even if this routine is started, step 20 in FIG.
Since the execution flag is determined to be "1" at 1, this routine is not executed until it is restarted thereafter.

As described above, according to the present embodiment, when the purge flow rate is equal to or higher than the reference purge flow rate Y and the intake pipe negative pressure is introduced into the evaporation path, and the purge flow rate becomes less than the reference purge flow rate during the introduction. The tank internal pressure at that time is stored, the negative pressure in the evaporation path is maintained, and the time counting (addition of the leak determination timer) is interrupted. After that, when the purge flow rate becomes equal to or higher than the reference purge flow rate, the introduction of the intake pipe negative pressure is restarted. , The storage tank internal pressure P _E is repeatedly counted after the tank internal pressure is returned (addition of the leak determination timer), and finally the tank internal pressure and the determination value β are reached after a predetermined time X seconds elapses.
Therefore, even if the purge flow rate decreases to less than Y during the introduction of the negative pressure, the same conditions as when the negative pressure introduction is continuously continued for X seconds in the state of the purge flow rate of the reference purge flow rate Y or more. It becomes possible to make a judgment and prevent a false diagnosis.

Further, according to the present invention, the tank internal pressure switching valve 34 is not opened, and the canister 33 is installed more than the tank internal pressure control valve 34.
The failure diagnosis may be finished by introducing the negative pressure only to the side path (the negative pressure is not introduced to the fuel tank 30). In this case, a three-way valve is provided instead of the tank internal pressure switching valve 34, and the pressure sensor 40 is connected to the three-way valve.

This three-way valve is a 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 40
And the vapor inlet 33a of the canister 33 communicate with each other via the three-way valve, the pressure sensor 40 detects that the pressure value is on the negative pressure side of the predetermined threshold value, and determines that it is normal. When it is determined to be abnormal. An open / close valve for closing the atmosphere introducing hole 33d of the canister 33 at the time of this failure diagnosis is also provided. This is to keep the pressure in the evaporation path.

[0069]

As described above, according to the present invention, even if the purge flow rate changes while the intake pipe negative pressure is being introduced into the evaporation path, the condition set based on the situation at the time of starting the negative pressure introduction. Since it is possible to determine the leakage of the evaporation route, it is possible to prevent erroneous diagnosis.

[Brief description of drawings]

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

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

FIG. 3 is a 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 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 under duty control.

FIG. 6 is a diagram showing a relationship between an intake pipe negative pressure and a purge flow rate when the purge side VSV is on / off controlled.

FIG. 7 is a diagram showing a relationship between a purge-side VSV duty ratio and a purge flow rate.

FIG. 8 is a flowchart showing an example of a purge flow rate calculation routine by a smoothing process.

FIG. 9 is a diagram showing changes in purge flow rate and fuel tank internal pressure.

FIG. 10 is a flow chart showing an embodiment of a failure diagnosis processing routine of essential parts of the present invention.

11 is a time chart explaining the operation of the failure diagnosis processing routine of FIG.

[Explanation of symbols]

10 Internal Combustion Engine 11,30 Fuel Tank 12,32a to 32d Vapor Passage 13,33 Canister 14,37,39 Purge Passage 15 Evaporative Passage 16 Purge Flow Rate Detection Means 17 Pressure Introducing Means 18 Negative Pressure Introducing Means 19 Pressure Detecting Means 20 Judgment Means 21 Microcomputer 31 Fuel tank internal pressure control valve 34 Tank internal pressure switching valve 35,63 Throttle (orifice) 38 Purge side VSV (vacuum switching valve) 41 Warning lamp 45,65 Bypass passage 46 Idle speed control valve ( I
SCV) 47 Fuel injection valve

Claims (1)

[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 in the purge passage, and the negative pressure in the intake passage when the purge flow rate detected by the purge flow rate detecting means is a predetermined value or more. When the purge flow rate detected by the purge flow rate detection means is less than the predetermined value, the introduction of the negative pressure by the pressure introduction means is prohibited, and at the same time, the introduction of the negative pressure by the pressure introduction means is prohibited. Negative pressure introduction interruption means for holding the negative pressure in the evaporation path and interrupting the counting of the predetermined time; Pressure detection means for detecting the pressure in the path, based on the pressure value detected by the pressure detection means, to measure the degree of change in the pressure in the evaporation path, from the comparison result of the measured value and the judgment value. A failure diagnosing device for an evaporative purge system, comprising: a determining unit that determines whether or not the evaporative purge system has a failure.