JPH09303214A - Diagnostic method for evaporation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of evaporative emission by prohibiting or interrupting diagnosis when a pressure in an engine intake pipe exceeds a prede termined value. SOLUTION: Pull-down is started at a predetermined purge valve opening and a deviation in pressure of an evaporation system, and after predetermined periods of time, a target pressure is found. When the deviation is more than predetermined value, it is determined that a pull-down speed needs to be increased to change a control duty of a purge valve 21 from 20% to 35% for example based on the deviation, and the pull down speed is increased. Thereby, the pressure in the evaporation system 23 reaches the target pressure quickly. At this time, in order to prevent a diagnosis in the condition of not being appropriate for pall-down including the case where a great deal of evaporation gas is generated, pull down is suspended when the time required for pull down reaches a predetermined time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis method for an evaporation system. Diagnosis of the so-called evaporative purge system in which the evaporative gas (evaporated fuel) generated in the fuel tank is adsorbed by the adsorbent in the canister, and the adsorbed fuel is released (purged) and burned into the intake system of the internal combustion engine under predetermined operating conditions. A method, especially including a pull down step of introducing a negative pressure from an engine intake pipe.

[0002]

2. Description of the Related Art In this evaporative system, the inside of the evaporative system is sealed in order to prevent the evaporative gas from being released into the atmosphere. However, if the evaporative gas passage is damaged or the pipe is disconnected for some reason, the evaporative gas in the canister is released into the atmosphere. It also causes trouble if the purge passage is blocked. Therefore, it is necessary to diagnose the occurrence of such a failure of the evaporation system.

In Japanese Patent Laid-Open No. 6-193518, negative pressure of intake air is applied to an evaporative system through a purge valve, a pressure sensor detects a pressure change of the evaporative system, and the pressure change detects a failure of the evaporative system. Is described.

Further, Japanese Patent Laid-Open No. 7-166974 discloses a purge control valve according to the pressure state in the intake pipe by the pressure sensor in the intake pipe and the fuel amount in the fuel tank by a fuel gauge when an abnormality is detected in the fuel evaporation prevention mechanism. Is controlled to be opened and closed by an electronic control circuit, and the negative pressure introduction speed from the intake pipe is appropriately changed. Therefore, the pressure in the closed section is adjusted without being affected by the pressure state in the intake pipe or the fuel amount in the fuel tank. Japanese Patent Laid-Open No. 6-193520 describes that when the flow rate of the evaporated fuel exceeds a predetermined value, the opening of the purge valve is increased to prevent the evaporated fuel from overflowing from the canister to the atmosphere. ing.

Further, Japanese Patent Laid-Open No. 6-249095 discloses a diagnosis by a tank pressure sensor. The fuel tank liquid amount inspection is performed, and the duty ratio of the tank ventilation valve control is determined based on the obtained liquid charge. A method is disclosed in which the ventilation valve is opened and the shutoff valve is closed at the determined duty ratio, and the leak diagnosis is performed from the negative pressure decreasing gradient of the negative pressure decreasing in the tank. It is also possible to open the ventilation valve at a predetermined duty ratio, determine the duty ratio from the negative pressure increase gradient of the negative pressure increasing in the tank, and open the ventilation valve at the determined duty ratio during diagnosis. Says.
In any case, the duty ratio is determined in advance, and the ventilation valve is controlled with the determined duty ratio.

[0006]

As described above, in evaporative diagnosis, it is already known that negative pressure is introduced into the evaporative system and the evaporative system is diagnosed by the change in the pressure. However, when the pressure in the intake pipe is above a predetermined value, the time until the pressure inside the evaporative system reaches the predetermined value becomes too long, and the purge is not performed during this time, the purge balance of the evaporative gas collapses, and the evaporative emission value deteriorates. To do.

An object of the present invention is to provide control of an evaporation system that does not deteriorate the evaporation emission even in such a case.

[0008]

[Means for Solving the Problems] When the pressure in the engine intake pipe is equal to or higher than a predetermined value, the diagnosis of the evaporative system is prohibited, or the diagnosis is interrupted if the diagnosis has already been started. When the means for introducing the pressure into the evaporative system has an opening of a predetermined value or more, it is determined that the evaporative system has a failure, and the diagnosis can be stopped to achieve the purpose.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a system for realizing the present application will be described with reference to FIG.

The engine body 1 is provided with an air cleaner 2, an air flow sensor 3, a throttle opening sensor 4, a cooling water temperature sensor 5, an air-fuel ratio sensor 6, etc.
It is taken into the ECU 7 and the fuel injection amount, ignition control value, idle speed control (ISC) value, etc. are calculated. Then, the fuel injection amount is determined by the injector 8 by the fuel injection pulse width signal.
Is supplied and the ignition control output value is finally ignited by the spark plug 9 at an optimum timing. Further, the ISC control amount is output to the ISC control valve 10 to supply the optimum amount of auxiliary air. In addition, a fuel pump 12 for pressurizing the fuel supplied from the fuel tank 11 to the injector 8.
Or a fuel pressure adjusting valve 13 for adjusting the pressure of the pressurized fuel
Is provided.

The fuel injected from the injector 8 flows into the cylinder while forming an air-fuel mixture with intake air, explodes and burns by ignition during compression in the piston motion, and exhaust gas is discharged to the exhaust pipe. The catalyst 14 installed in the middle of the exhaust pipe accelerates the redox action of this exhaust gas, and purifies HC, CO, and NOx which are harmful components in the exhaust gas. In order to make maximum use of the purification efficiency by the catalyst 14, in this system, an air-fuel ratio feedback system (E) which feedback-controls the air-fuel mixture ratio in a density alternate near the stoichiometric air-fuel ratio in accordance with the output of the air-fuel ratio sensor 6 (E
(Controlled by CU7).

Further, the fuel tank 1 containing the fuel 15 therein.
Evaporated fuel (evaporative gas) generated from No. 1 is adsorbed to the adsorbent 18 in the canister 17 through the evaporative communication pipe 16, and the adsorbed fuel is purged to the downstream side of the throttle valve 20 of the engine through the discharge pipe 19. Burns in a cylinder. The discharge pipe 19 is provided with a purge valve 21 to control the purge timing and the purge amount. The purge valve 21 is, for example, a duty valve that is electrically controlled, and controls the equivalent opening area.

The pressure sensor 22 detects the pressure of the evaporation system 23. In addition, the drain valve 24
Is installed at the fresh air introduction port (drain) of the canister 17 and controls the fresh air introduction amount from the drain. ECU7
Controls the purge valve 21 and the drain valve 24,
By measuring and processing the pressure of the evaporation system 23, a failure (leakage) in which fuel leaks from the evaporation system 23 to the atmosphere is diagnosed.

The influence of the position of the pressure sensor 22 on the diagnosis will be described with reference to FIGS.

FIG. 2 shows a canister 17 and a fuel tank 11.
It is an example of a system in which the pressure sensor 22 is arranged between the and.
In this system example, the fuel tank 11 and the pressure sensor 22
Due to the pressure loss of the pipe between and and the influence of the flow in the pipe, the pressure in the fuel tank 11 and the pressure at the installation position of the pressure sensor 22 are slightly deviated. Therefore, it is necessary to construct a diagnostic method that takes this pressure deviation into consideration.

FIG. 3 shows a canister 17 and a purge valve 2.
1 is an example of a system in which a pressure sensor 22 is arranged between the pressure sensor 22 and the pressure sensor 1. In this case, there is a problem that the influence of the pressure loss of the pipe becomes larger than that in FIG.

However, in the case of the installation position of the pressure sensor 22 shown in FIG. 3, even if the pipe between the canister 17 and the fuel tank 11 is clogged when the negative pressure is introduced into the evaporation system, the canister 17 is installed. The purge valve 21 can be appropriately controlled according to the detection result of the pressure sensor 22 so that an excessive negative pressure is not applied. Therefore, when the canister 17 has no pressure resistance, the mounting position of the pressure sensor 22 shown in FIG. 3 is a preferable mounting position.

Although not shown in the drawing, the fuel tank 11
When the pressure sensor 22 is arranged directly in the pipe, the influence of the pressure loss of the pipe and the flow in the pipe is small, and the pressure of the evaporation system 23 is measured most accurately as compared with the case where the pressure sensor 22 is arranged in the above-mentioned position. can do.

As described above, each pressure sensor arrangement position has its own characteristic. Therefore, when the arrangement position of the pressure sensor 22 is selected according to the purpose of use, or when the arrangement position is limited due to mounting restrictions. In the above, it is preferable to adapt the control constant and the like while sufficiently considering the characteristics of the arrangement position.

FIGS. 4 to 6 show pulldown (purge valve 21 and drain in FIG. 1) of the remaining amount in the fuel tank at the time of evaporative system diagnosis, the presence / absence of a leak in the evaporative system 23, the size of the leak, and the amount of evaporative gas generated. Valve 24
When the evaporative system 23 including the fuel tank 11 is made into one closed space in the closed state and the purge valve 21 is then opened, the pressure in the intake pipe is a negative pressure.
FIG. 6 is a diagram for explaining the effect on the pressure reduction rate when the pressure in the system is rapidly reduced). FIG. 4 shows that the smaller the remaining amount in the fuel tank at the time of the evaporation system diagnosis, that is, the larger the empty volume in the fuel tank, the more time it takes to pull down the internal pressure of the evaporation system to the target pressure P0. Shows. Further, FIG. 5 shows that the larger the leak in the evaporation system 23, the more time it takes to pull down the internal pressure of the evaporation system to the target pressure P0. Further, FIG. 6 shows that the larger the amount of evaporative gas generation, the more time it takes to pull down the internal pressure of the evaporative system to the target pressure P0. Therefore, there is a large pull-down time difference between the condition in which the elements that most require the pull-down time to the target pressure P0 overlap and the condition in which the elements that most require the pull-down time to the target pressure P0 overlap are large. If the opening (pull-down speed) is applied to all conditions, the diagnosis time will also differ greatly. For this reason, it is necessary to appropriately adjust the pull-down speed according to those states. For example, a method of directly detecting the pressure in the evaporative system during pulldown and adjusting the pulldown speed according to the pressure state is effective.

For example, when there is a small amount of fuel in the fuel tank, a leak exists in the evaporative system 23, and a long pulldown time is required when the operating state under high temperature where a large amount of evaporative gas is generated is continued. . This is because if the above operating conditions are continued, the evaporative system diagnostic process cannot be completed over time, and even if a serious failure (leak) has occurred in the evaporative system, the failure state will remain for a long time. It indicates that it may be left alone. If the failure is neglected, a large amount of evaporative gas (unburned fuel) is released into the atmosphere, which causes air pollution.

FIG. 7 shows the operation timing of each valve for diagnosing the evaporative system and the pressure change in the evaporative system. Normally, the drain valve 24 is open. The evaporative gas generated in the fuel tank 11 is adsorbed by the adsorbent 18 in the canister 17. When the purge valve 21 is opened according to the operating state of the engine, since the inside of the intake pipe has a negative pressure, the evaporative gas once adsorbed is desorbed from the adsorbent 18 together with the air flowing in through the drain valve 24 opened to the atmosphere. It is transported to the intake pipe and used for combustion in the engine. In this way, the fuel vapor generated in the fuel tank 11 is prevented from being released into the atmosphere.

When diagnosing the evaporation system 23, first, the purge valve 21 is once closed and the drain valve 24 is closed. In this state, the evaporation system 23 including the fuel tank 11 becomes one closed space. Next, when the purge valve 21 is opened, the pressure in the intake pipe is a negative pressure, so the pressure inside the evaporative system 23 is rapidly reduced (pulled down). Then, the pressure in the evaporation system is measured by the pressure sensor 22 as a pressure difference Pt from the atmospheric pressure Pa. The differential pressure Pt is the target pressure P0 (set to about -20 to -30 mmHg)
When it becomes the following or when the difference between Pt and P0 falls within the predetermined range, the purge valve 21 is closed and the differential pressure Pt1 is measured. This will seal the evaporative system again, so the pressure inside the evaporative system will be kept constant if there is no leak, but if there is a leak somewhere in the evaporative system, the pressure inside the evaporative system will depend on the size of the leak. Gradually approaching atmospheric pressure. Predetermined time (from time t1 to t2 in FIG. 7)
Up to a predetermined value (Pt.
The change amount from 1 is a predetermined value, or Pt itself is Pt1.
If it becomes a predetermined value different from the above), the differential pressure Pt2 is measured. After that, the drain valve 24 is opened and the purge valve 21 is opened (return to the normal control state). The above process is controlled by the ECU 7, and the leak of the evaporation system 23 is determined based on the measured values of the differential pressures Pt1, Pt2 and the like.

When the purge valve 21 is closed at the beginning of the above process and a predetermined time interval elapses, the atmospheric pressure is applied to the pressure sensor 22 via the drain valve 24. The error of the pressure sensor 22 can be corrected by measuring the deviation of the output from the atmospheric pressure (deviation from 0 in the case of the differential pressure sensor 22) and correcting the subsequent measured value of the pressure in the evaporation system.

FIG. 8 is a diagram for explaining a flow chart when the ECU 7 executes the diagnosis process. In step 101, the purge valve 22 is closed, then the drain valve 24 is closed to leave the evaporation system 23 as a closed space, and in step 102 the barge valve 21 is opened. The gas in the evaporative system is sucked into the negative pressure intake pipe, and the inside of the evaporative system is rapidly depressurized. When the predetermined pressure Pt0 is reached, the purge valve 21 is closed in step 104, and step 1
Pt1 is measured at 05. After a lapse of a predetermined time or when the pressure change exceeds a predetermined value, Pt2 is measured in step 107. Since the measurement necessary for the leak determination is completed by the above process, the drain valve 24 is opened in step 108 and the purge valve 21 is opened in step 109 to return the evaporative system 23 to the normal state (return to the normal control state). ). Using the above measurement results Pt1 and Pt2, in step 110, the pressure change D for the leak determination
P = (Pt2-Pt1) / time required is calculated.

Next, if the pressure change DP is greater than or equal to a predetermined value (leakage judgment threshold value), it is judged to be abnormal in step 111. Further, processing such as an alarm to the driver, a failure code, a memory of the operating state when the failure is detected, and a fail-safe operation according to a predetermined process are executed. If the pressure change DP is less than the predetermined value, step 1
In step 13, it is determined to be normal, and the processing associated therewith is executed.

FIG. 9 shows a method of detecting a deviation between the actual internal pressure of the evaporation system during pulldown and the pulldown target pressure P0 and changing the pulldown speed according to the deviation. Since the pull-down time greatly changes due to the factors described in FIGS. 4 to 6, a long diagnosis time may be required depending on the operating conditions and the evaporation system state. If such a state persists for a long period of time, the problems in the case where the failure state is left because the diagnosis cannot be executed despite the serious failure of the evaporative system are as described above. is there. As an example of this countermeasure, a method of directly detecting the change in the pressure in the evaporation system during pull-down and appropriately adjusting the pull-down speed to deal with the above problem will be described below.

The pull-down speed is adjusted by changing the opening area of the purge valve 21.

At time t1 in FIG. 9, pulling down is started with a predetermined purge valve opening degree, and time t after a predetermined period has elapsed.
In 2 the deviation Dp between the internal pressure of the evaporation system and the target pressure P0
Ask for. When the deviation Dp is equal to or more than the predetermined value, it is determined that the pulldown speed needs to be increased, and for example, the control duty of the purge valve 21 is changed from 20% to 35% according to the deviation Dp, and the pulldown speed is increased. Speed up. As a result, the pressure in the evaporation system can quickly reach the target pressure P0. At this time, in order to prevent performing a diagnosis in a state not suitable for pulldown, including when the amount of evaporative gas is very large, pulldown is stopped when the time required for pulldown reaches a predetermined time.

FIG. 10 shows how the diagnosis of the evaporation system is interrupted when the pressure in the intake pipe is equal to or higher than a predetermined value. This is because when the throttle 20 is wide open and the pressure in the intake pipe is high, the time required for pulling down becomes long, or the pressure change in the evaporative system necessary for the diagnosis of the evaporative system cannot be realized. During the period (a), the pressure in the intake pipe is introduced into the evaporation system 23 to change the pressure in the evaporation system 23. In this process, since the intake pipe internal pressure reaches the limit value in (b), the introduction of the intake pipe internal pressure is stopped.
As a result, the internal pressure of the evaporation system 23 changes due to the evaporation gas from the fuel tank 11 and the leak flow rate existing in the evaporation system 23.

FIG. 11 shows a case where the pressure in the intake pipe becomes equal to or higher than the limit value in (b) and then becomes equal to or lower than the limit value in (d) within the predetermined period (c). In this case, the intake pipe internal pressure is continuously introduced into the evaporation system 23 when the intake pipe internal pressure becomes equal to or lower than the limit value.

Further, as shown in FIG. 12, after the intake pipe internal pressure exceeds the limit value and the introduction into the evaporation system 23 is interrupted, the intake pipe internal pressure is kept above the limit value for a predetermined period (c) or more. In this case, even if the intake pipe internal pressure falls below the limit value in (e), the intake pipe internal pressure is not introduced as part of a series of diagnoses.

FIG. 13 shows the evaporation system 2 for measuring the pressure in the intake pipe.
3 shows that the introduction of the pressure in the intake pipe is stopped when the speed to be introduced into No. 3 exceeds a predetermined value. In (a), the purge valve 21 is opened by a predetermined opening, and the intake pipe internal pressure is introduced into the evaporation system 23. At this time, when the opening of the purge valve 21 reaches a predetermined limit value in (c), it is determined that there is a leak failure in the evaporation system, the drain valve 24 is opened, and the purge valve control duty is gradually changed to the normal purge control state. Restore.

FIG. 14 is a flow chart showing a series of controls shown in FIGS. 10 to 13. Step 20
At 1, it is determined whether a condition suitable for the diagnosis of the evaporation system 23 is satisfied. As the items of determination, the engine rotation, engine load, engine intake air amount, cooling water temperature, vehicle operating condition, and the like, and their changes are used. If it is determined that the conditions suitable for the diagnosis of the evaporation system 23 are satisfied, step 202
Then, the amount of evaporation gas generated from the fuel tank 11 is determined. If it is determined that the amount of evaporative gas generation is equal to or less than the predetermined value, or if it is determined in step 201 that the diagnostic condition is not satisfied, normal purge control is performed in step 218. When it is determined in step 202 that the amount of evaporative gas generation is larger than the predetermined value, it is determined in step 203 whether the intake pipe internal pressure is equal to or lower than the predetermined value. If it is less than the specified value, step 2
At 04, it is determined whether the evaporative system 23 is being diagnosed. If it is not under diagnosis, the drain valve 24 and the purge valve 21 are operated in step 205 to start pulling down. In step 206, it is judged whether or not the pressure inside the evaporative system detected by the pressure sensor 22 has reached the pull-down target pressure P0.
Continue to diagnose. If the internal pressure of the evaporation system has not reached the target pressure P0 in step 206, it is determined in step 207 whether the difference Dp between the measured value of the internal pressure of the evaporation system and the target pressure P0 is less than or equal to a predetermined value. The predetermined value used in this case is a function of the elapsed time from the start of pull-down. If Dp is less than or equal to the predetermined value, it is determined that the pull-down is normally performed. If Dp is larger than the predetermined value, step 20
8 and step 211, the purge valve control duty is operated to accelerate the change in the pressure in the evaporation system. If the purge valve control duty has reached the limit value in step 208, it is determined that the pull-down is alienated due to leak, and it is determined in step 209 that the evaporation system 23 has a leak failure. When it is determined in step 203 that the intake pipe internal pressure is higher than the predetermined value, the diagnosis of the evaporation system 23 is interrupted. That is, when the diagnosis of the evaporation system 23 is suspended in step 212,
In step 213, it is determined whether or not the interruption period has reached a predetermined period, and if it reaches, the diagnosis is stopped and the normal purge control is restored in step 214. Step 212
If the diagnosis of the evaporative system 23 is not being interrupted in step 215, it is determined in step 215 whether the evaporative system 23 is being diagnosed. If the diagnosis is in progress, the diagnosis of the evaporative system 23 is temporarily interrupted in step 216. In step 215, the evaporative system 2
If 3 is not under diagnosis, normal purge control is performed in step 217.

[0035]

When the negative pressure is used from the engine intake pipe in the evaporative diagnosis, the deterioration of the evaporative emission can be prevented by determining the cause of the long pull-down time and prohibiting or interrupting the diagnostic. .

[Brief description of drawings]

FIG. 1 shows an embodiment for realizing the present application.

FIG. 2 is a system configuration example.

FIG. 3 is another example of the system configuration.

FIG. 4 Effect of remaining fuel amount on pull-down time.

FIG. 5: Effect of leak charge on pulldown time.

FIG. 6 shows the effect of evaporative gas generation on pulldown time.

FIG. 7 is an operation timing of each valve.

FIG. 8 is a flowchart of processing.

FIG. 9 shows an example of pulldown.

FIG. 10: Discontinuation of diagnosis due to pressure in the intake pipe.

FIG. 11: Discontinuation and restart of diagnosis due to the pressure in the intake pipe.

FIG. 12: Discontinuation of diagnosis due to intake pipe pressure.

FIG. 13: Diagnosis stop by purge valve control duty.

FIG. 14 is a control flowchart.

[Explanation of symbols]

7 ... ECU, 11 ... Fuel tank, 16 ... Evaporation pipe, 17
... canister, 18 ... intake agent, 19 ... discharge pipe, 21 ... purge valve, 22 ... pressure sensor, 23 ... evaporation system.

Claims (3)

[Claims] 1. A method for diagnosing an evaporative system in which evaporative gas generated in a fuel tank is introduced to temporarily adsorb it and discharge the adsorbed evaporative gas to an engine intake pipe by a pressure in the evaporative system. The method for diagnosing the evaporative system includes a pull-down step of making the evaporative system a negative pressure, and when the pressure in the engine intake pipe is a predetermined value or more, the diagnosis is prohibited or interrupted. Diagnostic method. 2. The method for diagnosing an evaporation system according to claim 1, wherein, when the diagnosis is suspended, the diagnosis is suspended instead of the suspension when the diagnosis suspended state continues for a predetermined time. 3. The method for diagnosing an evaporation system according to claim 1, wherein when the negative pressure control value in the pull-down step is equal to or more than a predetermined limit value, the evaporation system is determined to be out of order. .