JP3707520B2 - Evaporative fuel processor diagnostic device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diagnostic apparatus for a fuel vapor processing apparatus, and more particularly to a diagnostic apparatus for diagnosing leakage.
[0002]
[Prior art]
The evaporated fuel generated in the fuel tank while the engine is stopped is adsorbed to the activated carbon in the canister, the purge passage is opened under the predetermined operating conditions after the engine starts, and the suction negative pressure is used to enter the canister. There is an evaporative fuel treatment device in which fuel particles are desorbed from activated carbon and led to an intake pipe downstream of a throttle valve for combustion.
[0003]
In this case, if there is a leak hole in the middle of the flow path from the fuel tank to the intake pipe, or if the seal at the joint of the pipe becomes poor, evaporated fuel will be released into the atmosphere. (See Japanese Patent Application Laid-Open No. 5-240117). Since the presence or absence of a leak can be understood by looking at the pressure change after the flow path is a closed space and the closed space has a pressure difference relative to the atmospheric pressure, A drain cut valve that opens and closes the release port at the atmosphere release port of the canister to make the closed space open, and a pressure sensor is installed in the flow path to observe the pressure change of the gas confined in the closed space, and the throttle valve downstream A leak diagnosis is performed by reducing the pressure of the flow path using the negative pressure generated in the gas flow.
[0004]
[Problems to be solved by the invention]
By the way, traveling on a road with uneven road surface (that is, bad road), sudden acceleration, sudden deceleration, lane change, etc., fuel jumps in the fuel tank and liquid level fluctuation (these phenomena are called sloshing). When this occurs, the fuel vapor is suddenly generated by the sloshing, and the pressure in the flow path rises. Therefore, if the leak diagnosis is performed using the negative pressure until the sloshing occurs, there is a leak. In the above apparatus, the pressure reduction of the flow path is started after the vehicle speed becomes 0 km / h.
[0005]
However, when the engine is idling while the vehicle speed is 0 km / h (that is, when the vehicle is stopped), if the negative pressure generated downstream of the throttle valve is guided to the flow path, the evaporated fuel present in the flow path The mixed air (vapor) flows into the intake pipe, and the air-fuel ratio is greatly disturbed, which tends to make the engine unstable.
[0006]
In addition, a predetermined time is required to complete the decompression of the flow path, and a predetermined time is also required to see a change in pressure while maintaining the reduced pressure state. In other words, the leak diagnosis cannot be performed unless the vehicle continues in a stopped state for the combined time, and therefore the diagnosis does not end if the stopped state of the vehicle is short.
[0007]
Therefore, the present invention greatly reduces the influence of the air-fuel ratio disturbance caused by the pressure reduction by completing the pressure reduction of the flow path from the fuel tank to the purge control valve while the vehicle is running or the engine is not idling. When the vehicle is in a stopped or near-stop state after that, the flow path is kept in a decompressed state and the return of the pressure is measured. The purpose is to increase the chance of ending the diagnosis while avoiding the diagnosis.
[0008]
[Means for Solving the Problems]
As shown in FIG. 6, the first invention is a second passage that communicates the first passage 33 that guides the vapor in the upper part of the fuel tank 31 to the canister 32, and the intake pipe 35 downstream of the canister 32 and the throttle valve 34. A passage 36, a purge control valve 37 that opens and closes the second passage 36, a drain cut valve 38 that opens and closes the atmosphere opening 32 a of the canister 32, and a flow path from the fuel tank 31 to the purge control valve 37. Means 39 for detecting the pressure P, and adjusting the opening of the purge control valve 37 with the drain cut valve 38 closed when the vehicle is running or the engine is running and not in an idle state. under reduced pressure the pressure of the road to the target value, the vehicle is stopped or the vehicle speed is below a stopped state determining value thereafter A means 40 for holding the purge control the flow path valve 37 fully closed can in a vacuum state, and a determining means 41 the leak in response to pressure changes in the flow path in the vacuum holding state.
[0009]
In the second invention, when the engine is operating and not in the idle state in the first invention, (1) when the engine speed exceeds the determination value, (2) when the engine load exceeds the determination value, (3) When the intake air amount exceeds at least one of the determination values.
[0010]
【The invention's effect】
In each of the first and second inventions, decompression of the flow path from the fuel tank to the purge control valve is completed during traveling (or when the engine is not idling), and then the vehicle is stopped ( Alternatively, the flow path is held in a depressurized state when it is close to a stop), and leakage is determined according to a change in the pressure of the flow path in the depressurized hold state. For this reason, it is only necessary to measure the change in the flow path pressure when the vehicle is stopped, and it is not necessary to complete the decompression of the flow path when the vehicle is stopped. More chances to end).
[0011]
In addition, the point which measures the pressure change of a flow path in a vehicle stop state is the same as that of a conventional apparatus, and this can avoid a misdiagnosis accompanying sloshing.
[0012]
Further, during traveling, the amount of intake air to the engine is usually large, so even if the vapor is introduced into the intake pipe to reduce the flow path, the disturbance of the air-fuel ratio can be kept small.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, 1 is a fuel tank, 4 is a canister, and vapor (air containing evaporated fuel) at the top of the fuel tank 1 is guided to a canister 4 via a passage (first passage) 2 so that only fuel particles are present. The remaining air is adsorbed by the activated carbon 4 a in the canister 4, and the remaining air is discharged to the outside through an air release port 5 provided in a vertically lower portion of the canister 4 (shown in the upper portion of the canister 4 in the figure).
[0014]
Reference numeral 3 denotes a mechanical vacuum cut valve that is opened when the fuel tank side becomes lower than the atmospheric pressure. As shown by the flow characteristics in FIG. 2, the fuel tank is also opened when the fuel tank side reaches a predetermined pressure (for example, +10 mmHg) due to the generation of fuel vapor in the fuel tank 1. In FIG. 2, the atmospheric pressure is a reference (that is, 0 mmHg), and “+” is added to the numerical value when the atmospheric pressure is higher than “−”, and “−” is added to the numerical value when the atmospheric pressure is lower than the atmospheric pressure.
[0015]
The canister 4 is also communicated with an intake pipe 8 downstream of the throttle valve 7 through a purge passage (second passage) 6, and a normally closed purge control valve 11 driven by a step motor is provided in the purge passage 6. When the purge control valve 11 is opened in response to a signal from the control unit 21 under a certain condition (for example, a low load region after warm-up), the air release port of the canister 4 is caused by the suction negative pressure that develops greatly downstream of the throttle valve. From 5, fresh air is introduced into the canister 4. With this fresh air, fuel particles are introduced from the activated carbon 4a together with fresh air into the intake pipe 8 through the purge passage 6, and burned in the combustion chamber. In the leak diagnosis using negative pressure (described later), the purge control valve 11 is configured as a variable orifice.
[0016]
On the other hand, a normally open drain cut valve 12 is provided at the atmosphere opening 5 of the canister 4. The valve 12 is closed together with the purge control valve 11 at the time of leak diagnosis, which will be described later, and is necessary for reducing the pressure of the flow path from the purge cut valve 9 to the fuel tank 1.
[0017]
In addition, a pressure sensor 13 is provided in the purge passage between the canister 4 and the purge control valve 11, and this pressure sensor 13 is used to adjust the pressure of the flow path (closed relative pressure based on the atmospheric pressure) that is closed during leak diagnosis. A proportional voltage is output as shown in FIG. The position where the pressure sensor 13 is provided may be the fuel tank 1.
[0018]
The vacuum cut valve 3 is provided with a normally closed bypass valve 14 in parallel therewith. This is to allow the fuel tank 1 and the canister 4 to communicate with each other via the first passage 2 when the negative pressure on the canister 4 side is introduced to the fuel tank 1 side.
[0019]
In the control unit 21 composed of a microcomputer, a leak hole is formed in the flow path from the fuel tank 1 to the purge control valve 11 by opening and closing the above three valves (purge control valve 11, drain cut valve 12, bypass valve 14). Diagnosis is made while the engine is running. The frequency of leak diagnosis is about once in one operation.
[0020]
In this case, when sloshing occurs in the fuel tank due to bad road running, sudden acceleration, sudden deceleration or lane change, fuel vapor is suddenly generated by this sloshing and the pressure in the flow path increases. If the leak diagnosis using negative pressure is performed until the occurrence of sloshing, there may be a false determination that there is a leak. Therefore, after the vehicle speed reaches 0 km / h, Some start to depressurize.
[0021]
However, when the engine is idling while the vehicle speed is 0 km / h (that is, when the vehicle is stopped), if the negative pressure generated downstream of the throttle valve is guided to the flow path, the vapor existing in the flow path is reduced. The air flows into the intake pipe 8 and the air-fuel ratio is greatly disturbed, which tends to make the engine unstable.
[0022]
In addition, a predetermined time is required to complete the decompression of the flow path, and a predetermined time is also required to see a change in pressure while maintaining the reduced pressure state. In other words, the leak diagnosis cannot be performed unless the vehicle continues in a stopped state for the combined time, and therefore the diagnosis does not end if the stopped state of the vehicle is short.
[0023]
In order to cope with this, in the embodiment of the present invention, the decompression of the flow path from the fuel tank to the purge control valve is completed while the vehicle is running or the engine is not idling, and then the vehicle is stopped. Immediately when it becomes (or a state close to a stop), the leak diagnosis is performed by holding the flow path in a reduced pressure state and performing pressure return measurement.
[0024]
This diagnosis procedure executed by the control unit 21 will be described with reference to FIG.
[0025]
<1> At a timing t1 delayed by a predetermined time from t0 when the vehicle starts running (the vehicle speed exceeds the judgment value), the drain cut valve 12 is closed, the bypass valve 14 is opened, and the purge control valve 11 is opened for fuel. The flow path from the tank 1 to the purge control valve 11 is depressurized. At that time, a target value for pressure reduction (first target value to be described later) is determined, and the purge control valve opening is feedback controlled so that the flow path pressure matches this target value.
[0026]
<2> After that, at time t4 when the vehicle is stopped (the vehicle speed is equal to or lower than the determination value), the purge control valve 11 is fully closed and the flow path from the fuel tank 1 to the purge control valve 11 is in a reduced pressure state. And the channel pressure P at that time is sampled as P0.
[0027]
<3> The passage pressure P is set at the timing t5 where the elapsed time from the timing t4 sampled with the passage pressure P set as P0 coincides with the time (determination time shown) necessary for measuring the pressure return. Sampling is performed as P1 (P1> P0), and a pressure change ΔP (= P1-P0) from P0 is calculated.
[0028]
Here, if the case where there is no leak in the flow path from the fuel tank 1 to the purge control valve 11 is compared with the case where there is a leak, the value of the pressure change ΔP becomes larger when there is a leak.
[0029]
Therefore, the pressure change ΔP is compared with the determination value, and if ΔP is less than the determination value, it can be determined that there is no leak, and if ΔP is equal to or greater than the determination value, it can be determined that there is leak.
[0030]
<4> Open the drain cut valve 12 and close the bypass valve 14 to complete the leak diagnosis.
[0031]
The flowchart of FIG. 5 is for specifically executing the above-described leak diagnosis procedure. FIG. 5 is executed at regular time intervals.
[0032]
Whether or not the leak diagnosis is finished in step 1 is confirmed by a diagnosis experience flag (initially set to “0” at the start). If the leak diagnosis has not been completed (when the diagnosis experience flag = 0), the diagnosis is started, so that the process proceeds to step 2 where the drain cut valve 12 is closed and the bypass valve 14 is opened.
[0033]
In step 3, the vehicle speed detected by the sensor 22 (see FIG. 1) is compared with the determination value. Here, the determination value is a value that divides whether the vehicle is in a stop state (or a state close to a stop) or traveling. From this, when the vehicle speed exceeds the determination value (that is, during traveling), the process proceeds to the negative pressure processing of the flow path in steps 4 to 7.
[0034]
In step 4, the timer value TM is reset to zero. This timer is necessary for measuring a determination time described later.
[0035]
Steps 5, 6, and 7 are parts for feedback control of the purge control valve opening so that the pressure in the flow path from the fuel tank 1 to the purge control valve 11 becomes the target negative pressure. The first target value in step 5 is the target negative pressure. Therefore, when the flow path pressure P detected by the sensor 13 exceeds the first target value (for example, about −23 mmHg) (that is, the pressure reduction of the flow path is not sufficient), the process proceeds from step 5 to step 6 to perform purge control. When the valve opening is increased by a predetermined amount and the flow path pressure P is less than or equal to the first target value (that is, the negative pressure of the flow path has progressed too much), the process proceeds from step 5 to step 7 to set the purge control valve opening. Reduce only quantitative.
[0036]
When this is seen in FIG. 4, the purge control valve opening gradually increases from the timing t1, reaches the fully open position at t2, and the flow path pressure P gradually decreases accordingly. The flow path pressure P is maintained at the first target value by increasing or decreasing the purge control valve opening from the timing t3 when the flow path pressure P matches the first target value.
[0037]
On the other hand, when the vehicle speed thereafter decreases and becomes equal to or less than the determination value (that is, the vehicle is in a stopped state), the process proceeds from step 3 to pressure return measurement after step 8.
[0038]
In step 8, the purge control valve 11 is fully closed, so that the flow path from the fuel tank 1 to the purge control valve 11 is maintained in a reduced pressure state.
[0039]
In step 9, the timer value TM is compared with 0. When the process proceeds to step 9 for the first time, since TM = 0, the process proceeds to step 10 where the flow path pressure P at that time is moved to P0, and then in step 11, the flow path pressure P and the second target value (for example, Compare about -20mmHg). Here, the second target value is a limit value on the most atmospheric pressure side among the reduced pressure values necessary for performing pressure return measurement. That is, the flow path pressure is basically maintained at the first target value by depressurization. However, if the pressure can be reduced to the second target value even if the pressure cannot be reduced to the first target value, the pressure return measurement is performed. Is possible.
[0040]
When the flow path pressure P is larger than the second target value (that is, the pressure reduction is insufficient), the current process is terminated without proceeding to Step 12. This is to cope with a case where the time when the vehicle speed exceeds the determination value is short and the flow path pressure cannot be reduced to the first target value. According to the flow of FIG. 5, the process proceeds to step 8 and subsequent steps even when the vehicle speed becomes equal to or lower than the determination value immediately after exceeding the determination value. That is, when the vehicle speed has exceeded the determination value and the flow passage pressure cannot be reduced to the first target value for a short time, the flow passage pressure is larger than the second target value (steps on the atmospheric pressure side). Diagnosis is impossible. Therefore, in this case, in order to stop the diagnosis, the process of measuring the pressure return is removed.
[0041]
When the flow path pressure is smaller than the second target value, sufficient pressure reduction has been performed (diagnosis is possible), so the process proceeds to step 12 where the timer value TM is incremented, and this timer value TM is compared with the determination time in step 13. To do. Here, the determination time is the time required to measure the pressure return. When the timer value TM is less than or equal to the determination time, the increment of TM is repeated. When TM exceeds the determination time, the process proceeds to step 14 and thereafter.
[0042]
In steps 14 and 15, the flow path pressure P is shifted to P 1, a pressure change ΔP (= P 0 −P 1) is calculated, and the pressure change ΔP is compared with a determination value in step 12.
[0043]
If ΔP is greater than or equal to the determination value, the process proceeds to step 18 where there is a leak, and if ΔP is less than the determination value, the process proceeds to step 17 where it is determined that there is no leak.
[0044]
In steps 19 and 20, the drain cut valve 12 is opened, the bypass valve 14 is closed, and the diagnosis experience flag = 1 is set. Due to this diagnosis experience flag = 1, the process does not proceed to step 2 and subsequent times.
[0045]
Here, the operation of the embodiment of the present invention will be described.
[0046]
As in the conventional apparatus, when the pressure reduction of the flow path from the fuel tank 1 to the purge control valve 11 is completed while the vehicle is in a stopped state, and then the return of the pressure is measured to perform the leak diagnosis, the vehicle If the vehicle is stopped for a short time during the driving, the leak diagnosis is not completed.
[0047]
On the other hand, in the embodiment of the present invention, the decompression of the flow path from the fuel tank 1 to the purge control valve 11 is completed during traveling, and the flow path is immediately opened when the vehicle stops thereafter. Leak diagnosis was performed by maintaining the pressure under reduced pressure and measuring the pressure return. For this reason, it is only necessary to perform pressure return measurement when the vehicle is stopped, and it is not necessary to complete the decompression of the flow path when the vehicle is stopped, so the vehicle is stopped for a time sufficient to perform pressure return measurement. If it can be made, the leak diagnosis ends.
[0048]
In addition, the point which performs pressure return measurement in a vehicle stop state is the same as that of a conventional apparatus, and this can avoid a misdiagnosis accompanying sloshing.
[0049]
Further, during traveling, the amount of intake air to the engine is usually large, so even if the vapor is introduced into the intake pipe 8 to reduce the pressure in the flow path, the disturbance of the air-fuel ratio is small.
[0050]
In the embodiment, the case where the decompression of the flow path is completed during traveling has been described. However, the present invention is not limited to this. (1) When the engine speed exceeds the determination value, (2) The engine load is When the determination value is exceeded, (3) When the intake air amount exceeds one of the determination values, the pressure reduction of the flow path may be completed.
[Brief description of the drawings]
FIG. 1 is a system diagram of an embodiment.
FIG. 2 is a flow characteristic diagram of a vacuum cut valve 3;
FIG. 3 is an output characteristic diagram of a pressure sensor 13;
FIG. 4 is a waveform diagram showing a pressure change at the time of leak diagnosis.
FIG. 5 is a flowchart for explaining leak diagnosis;
FIG. 6 is a diagram corresponding to a claim of the first invention.
[Explanation of symbols]
1 Fuel tank 2 passage (first passage)
4 Canister 6 Purge passage (second passage)
7 Intake throttle valve 8 Intake pipe 9 Purge cut valve 11 Purge control valve 12 Drain cut valve 13 Pressure sensor 21 Control unit 22 Vehicle speed sensor

Claims (2)

A first passage leading the vapor above the fuel tank to the canister;
A second passage communicating the canister and an intake pipe downstream of the throttle valve;
A purge control valve for opening and closing the second passage;
A drain cut valve for opening and closing the air release port of the canister;
Means for detecting the pressure in the flow path from the fuel tank to the purge control valve;
By adjusting the opening of the purge control valve while the drain cut valve is closed when the vehicle is running or the engine is not in an idle state, the pressure in the flow path is reduced to a target value, and then Means for completely closing the purge control valve and holding the flow path in a depressurized state when the vehicle is stopped or when the vehicle speed is equal to or lower than a stop state determination value ;
A diagnostic apparatus for an evaporated fuel processing apparatus, comprising: means for determining a leak according to a change in pressure of the flow path in the reduced pressure holding state. When the engine is running and not idle ,
(1) When the engine speed exceeds the judgment value,
(2) When the engine load exceeds the judgment value,
(3) The diagnostic apparatus for an evaporative fuel processing apparatus according to claim 1, wherein at least one of when the intake air amount exceeds a determination value is satisfied.

Images