JPH11315760A - Diagnosis device of evaporative fuel processing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid misdiagnosis by continuous leak diagnosis even during sloshing. SOLUTION: When leak diagnosis begins, decompression maintaining means 41 maintains channels 33, 36 from a fuel tank 31 to a purge control valve 37 at low pressure using a drain cutting valve 38 and a purge control valve 37. Diagnosis means 42 diagnoses leaks by a change in pressure P of the channels 33, 36 after these channels 33, 36 are maintained at low pressure. In this case, maximum values and minimum values of the fluid surface level in a predetermined period in the fuel tank 31 are sampled by sampling means 43 and the difference of these maximum values and minimum values are calculated by calculating means 44. When determining means 45 determines that the difference exceeds the determination value by comparing this difference with a determined value, inhibiting means 44 inhibits leak diagnosis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device for a fuel vapor treatment device, and more particularly to a device for diagnosing a leak.

[0002]

2. Description of the Related Art Evaporated fuel generated in a fuel tank while an engine is stopped is adsorbed on activated carbon in a canister, a purge passage is opened under predetermined operating conditions after the engine is started, and suction negative pressure is utilized. There is an evaporative fuel processing device that desorbs fuel particles from activated carbon with fresh air entering a canister and guides the fuel particles to an intake pipe downstream of a throttle valve for combustion.

In this case, if a leak hole is formed in the middle of the flow path from the fuel tank to the intake pipe, or if the seal at the joint of the pipes is defective, the evaporated fuel is released into the atmosphere. Some have been proposed (Japanese Unexamined Patent Publication
-139439). The flow path is a closed space, and the pressure change after the closed space has a pressure difference relative to the atmospheric pressure can be seen to determine the presence or absence of a leak. A drain cut valve that opens and closes this release port is provided at the atmosphere release port of the canister in order to make a closed space, and a pressure sensor is provided at the flow path for monitoring the pressure change of the gas confined in the closed space. The leak diagnosis is performed by creating a negative pressure in the flow path by using the negative pressure generated in the flow path.

[0004]

By the way, the fuel jumps and the liquid level fluctuates in the fuel tank due to running, sudden acceleration, rapid deceleration, lane change, or the like on a road having an uneven road surface (hereinafter simply referred to as a bad road). Movement (these phenomena are hereinafter referred to as sloshing), when the fuel vapor is rapidly generated by the sloshing and the pressure in the flow path increases, the negative pressure is used until the sloshing occurs. Erroneous determination that there is a leak may occur when the leak diagnosis is performed.

To explain this, FIG. 4 shows a model of a pressure waveform when there is no leak, and FIG. 5 shows a model of a pressure waveform when there is a leak. Here, a method of performing a leak diagnosis by comparing a leak hole area with a determination value is disclosed in Japanese Patent Laid-Open No. 7-1898.
No. 25), DT3 shown in FIGS. 4 and 5 (elapsed time from the start of depressurization), DP3 (initial after elapse of time t5 when gas flow stops after pressure reduction is completed and pressure loss disappears). Pressure difference between pressure P ₀ and flow path pressure P), DP4 (DP
Four values of the differential pressure between the initial pressure P ₀ and the flow path pressure P when 3 becomes equal to or more than the predetermined value p3) and DT4 (time from completion of depressurization to timing when DP4 is sampled) are measured.
Using these four values, the leak hole area AL2 is calculated by Equations 1 and 2 described below.

In this case, when sloshing does not occur, even if the leak hole area AL2 is equal to or larger than the determination value and it is determined that there is a leak, as shown in FIG. 6 after the delay time t5 shown in FIG. When sloshing occurs,
The timing at which the above-mentioned DP3 becomes equal to or more than the predetermined value p3 is advanced, and DT4 is measured to be shorter by that amount. At this time, if the leak hole area AL2 calculated by Equations (1) and (2) described below becomes apparently smaller and falls below the determination value, it is erroneously determined that there is no leak.

As described above, if sloshing occurs during a leak diagnosis, an erroneous determination may occur.

Accordingly, the present invention prevents the leak diagnosis when sloshing is determined based on a change in the liquid level in the fuel tank or the acceleration generated in the fuel tank, thereby avoiding erroneous diagnosis accompanying sloshing. Aim.

[0009]

According to a first aspect of the present invention, as shown in FIG.
2, a second passage 36 that communicates the canister 32 with an intake pipe 35 downstream of the throttle valve 34, a purge control valve 37 that opens and closes the second passage 36, and the canister 32. A drain cut valve 38 for opening and closing the atmosphere release port 32a, a means 39 for detecting a flow path pressure P from the fuel tank 31 to the purge control valve 37, and determining whether a leak diagnostic condition is satisfied. Means 40 and means 41 for holding the flow path from the fuel tank 31 to the purge control valve 37 in a reduced pressure state using the drain cut valve 38 and the purge control valve 37 when the leak diagnosis condition is satisfied based on the determination result. Means for performing a leak diagnosis based on a change in the flow path pressure P after maintaining the reduced pressure state In the diagnostic apparatus of the evaporative fuel processing system and a 2, means 4 for sampling the maximum and minimum values of the liquid level within a predetermined time period in the fuel tank 31
3, means 44 for calculating the difference between the maximum value and the minimum value,
Means 45 for determining that sloshing has occurred when the difference exceeds the determination value by comparing the difference with the determination value, and means 46 for inhibiting the leak diagnosis when sloshing has occurred based on the determination result.

According to a second aspect of the present invention, in the first aspect, the predetermined period is a value corresponding to a period of fluctuation of the liquid level due to running on a rough road.

According to a third aspect, in the first aspect, the predetermined period is a value corresponding to a time required for rapid acceleration, rapid deceleration, or lane change.

In a fourth aspect, in any one of the first to third aspects, when the sloshing is stopped after the leak diagnosis is prohibited due to the occurrence of the sloshing, the leak diagnosis is restarted.

[0013]

According to the first to third aspects of the present invention, it is determined whether or not sloshing has occurred based on the maximum fluctuation width of the liquid level within a predetermined period, and when the sloshing has occurred, the leak diagnosis is prohibited. , Driving on rough roads, sudden acceleration, sudden deceleration,
It is possible to avoid erroneous diagnosis due to continuation of leak diagnosis even when sloshing occurs due to a lane change or the like, and it also occurs when it is determined whether or not sloshing has occurred from the amount of change in liquid level per predetermined time. Misjudgment can be avoided.

According to the fourth aspect of the invention, when the sloshing is stopped after the sloshing is stopped due to the occurrence of the sloshing, the leak diagnosis is restarted. Therefore, when the sloshing is determined, the leak diagnosis is stopped until the engine is stopped. In comparison, the chance of leak diagnosis is not unnecessarily reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a fuel tank,
Reference numeral 4 denotes a canister. Vapor (air containing evaporated fuel) in the upper part of the fuel tank 1 is guided to the canister 4 through a passage (first passage) 2, and only the fuel particles are adsorbed by the activated carbon 4 a in the canister 4. The remaining air is discharged to the outside through an atmosphere release port 5 provided in a vertically lower portion of the canister 4 (shown above the canister 4 in the figure).

Reference numeral 3 denotes a mechanical vacuum cut valve which is opened when the fuel tank side becomes lower than the atmospheric pressure.
As shown by the flow rate characteristics in FIG. 2, the fuel tank side generates the fuel vapor in the fuel tank 1 and the fuel tank side has a predetermined pressure (for example, +1).
0mmHg). In FIG. 2, the atmospheric pressure is set as a reference (that is, 0 mmHg), and a numerical value higher than the atmospheric pressure is indicated by “+” and a numerical value lower than the atmospheric pressure is indicated by “−”. This indication of pressure is the same in FIG.

The canister 4 is also connected to 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. Certain conditions
(For example, in a low load region after warm-up), the purge control valve 11
Is opened, fresh air is introduced into the canister 4 from the air release port 5 of the canister 4 by the suction negative pressure largely developed downstream of the throttle valve. With the fresh air, fuel particles from the activated carbon 4a together with the fresh air are passed through the purge passage 6 through the intake pipe 8.
And is burned in the combustion chamber. In the leak diagnosis using the negative pressure (described later), the purge control valve 11 is configured as a variable orifice.

On the other hand, a normally open drain cut valve 12 is provided at the atmosphere release port 5 of the canister 4. This valve 1
2 is closed together with the purge cut valve 9 at the time of leak diagnosis described later, and the fuel tank 1 is
This is necessary to make the flow path up to the closed space.

A pressure sensor 13 is provided in a purge passage between the canister 4 and the purge cut valve 9.
The pressure sensor 13 outputs a voltage proportional to the pressure (relative pressure based on the atmospheric pressure) of the flow path that is closed when the leak diagnosis is performed, as shown in FIG. The position where the pressure sensor 13 is provided may be the fuel tank 1.

The above-described vacuum cut valve 3 is provided with a normally closed bypass valve 14 in parallel with the vacuum cut valve 3. This is for making the fuel tank 1 and the canister 4 communicate with each other via the first passage 2 when introducing the negative pressure on the canister 4 side to the fuel tank 1 side.

Control unit 2 composed of a microcomputer
1, the three valves (purge control valve 11, drain cut valve 12, bypass valve 1)
By controlling the opening and closing of 4), it is diagnosed during the operation of the engine whether or not there is a leak hole in the flow path from the fuel tank 1 to the purge control valve 11. As a guideline, the frequency of the leak diagnosis is about once in one operation.

The leak diagnosis here is a leak diagnosis using suction negative pressure. This will be outlined with reference to FIGS. 4 and 5 (FIG. 4 is a model of a pressure waveform when there is no leak, and FIG. 5 is a model of a pressure waveform when there is leak). The leak diagnosis is the same as that described in JP-A-7-189825 and Japanese Patent Application No. 9-77853.

When there is a sufficient suction negative pressure (for example, -300
When the value becomes smaller than mmHg), it is determined that the diagnostic condition is satisfied, and even during the purge, the purge control valve 11 is closed to temporarily stop the purge, and the bypass valve 1
4 to open the fuel tank 1 side and the canister 4 side,
By closing the drain cut valve 12, the flow path from the fuel tank 1 to the purge control valve 11 becomes a closed space. Stores the flow path pressure P at this time as the initial pressure P _0.

The purge control valve 11 is opened to introduce a suction negative pressure, and the flow path from the fuel tank 1 to the purge control valve 11 is made negative. At this time, the purge control valve 11 is set to a predetermined opening (the flow rate is, for example, several liters / min), which is smaller than the maximum opening during the purge control.

The differential pressure P ₀ -P between the initial pressure P ₀ and the flow path pressure P
If this value exceeds a predetermined value p2 (for example, p2 is a value sufficiently smaller than the magnitude of the suction negative pressure and + several tens of mmHg), the elapsed time from the start of the pressure reduction is set to the third time Sampling is performed as DT3 [sec], and the purge control valve 11 is closed. Further, when a predetermined time t4 (for example, several minutes) has elapsed from the start of the pressure reduction without P ₀ -P not exceeding p2, the time at that time is sampled as DT3. During the depressurization, there must be a continuous suction negative pressure equal to or higher than a predetermined value.

After a time (delay time) t5 (for example, several seconds) in which the gas flow stops after the purge control valve 11 is fully closed and the pressure loss disappears (for example, several seconds), the _value of P ₀ -P is set to a third value.
Is sampled as the pressure DP3 [mmHg]. DP3
Represents the actual pressure withdrawn.

DP3 is a predetermined value p3 (for example, + several mmHg)
Waiting for the above, the P ₀ -P at that time as the fourth pressure DP4 [mmHg], also the time from closing the purge control valve 11 to the timing of sampling a fourth pressure DP4 fourth DT4 [sec]. Further, when a predetermined time t4 has elapsed since closing the purge control valve 11 without the predetermined value or more p3, the P ₀ -P at that time DP
4 and t4 as DT4.

Two pressures (DP3 and DP4) and two times (DT3 and DT4) sampled as described above.
From the leak hole area AL2 [mm ² ],

[0029]

## EQU1 ## AL2 = K × A '

[0030]

A ′ = C × (DT3 / DT4) × Ac × ((DP
3) ¹ /2-(DP4) ^1/2 ) / DP3 where Ac: orifice area [mm ² ] of the purge control valve at the time of pressure reduction C: correction coefficient for unit adjustment (for example, 26.6957) K: correction coefficient ( = F (A ')). The leak hole area AL2 in Expression 1 is a value obtained by simply solving the gas transfer expression.

By comparing the leak hole area AL2 with the determination value c2, it is determined whether to turn on the warning lamp. The value of AL2 when an orifice with a desired opening area (1 mmφ) is opened is determined in advance, and the determination value c2 is provided between this value and the value of AL2 when there is no leak. When AL2 becomes equal to or greater than the determination value c2, the diagnostic code is stored as the value on the side with the leak, and the code is stored even after the engine is stopped.

This concludes the outline of the leak diagnosis.

When sloshing occurs in the fuel tank due to rough road running, rapid acceleration, rapid deceleration, lane change, or the like, fuel vapor is rapidly generated by the sloshing, and the pressure in the flow path increases. From that
If a leak diagnosis is performed using a negative pressure until sloshing occurs, an erroneous determination that there is a leak may occur.

To explain this, when there is no sloshing, sloshing occurs as shown in FIG. 6 after the delay time t5 shown in FIG. 5, even if it is determined that there is a leak as shown in FIG. In the above, D
The timing at which P3 becomes equal to or more than the predetermined value p3 is advanced, and DT4 is measured to be shorter. At this time, if the leak hole area AL2 calculated by the above equation (2) is apparently small and falls below the determination value c2, it is erroneously determined that there is no leak although there is actually a leak.

To cope with this, in the embodiment of the present invention, it is determined whether or not sloshing has occurred based on the liquid level in the fuel tank 1, and when it is determined that sloshing has occurred, leak diagnosis is prohibited.

The contents of the control executed by the control unit 21 will be described with reference to the flowchart of FIG. FIG. 7 is executed at regular intervals.

In step 1, a timer (initialized to 0 at startup) is incremented, and the value of this timer is compared with a reference value in step 2.

Here, the reference value is a value that determines a period for determining sloshing from a change in the liquid level in the fuel tank. For example, when sloshing caused by sudden acceleration, sudden deceleration, or lane change is targeted, the reference value is determined based on the time at which the sloshing is performed. Also, when traveling on a rough road, the liquid level fluctuates at a constant cycle, so the reference value may be determined according to the cycle.

When the value of the timer is within the reference value, the process proceeds to step 3 to sample the maximum value and the minimum value of the liquid level during the sloshing determination period.

In step 3, the output F from the fuel remaining amount sensor 22 (see FIG. 1) provided in the fuel tank is read. The sensor 22 detects the remaining fuel level from the liquid level in the fuel tank. When the liquid level fluctuates, the sensor output increases or decreases in response to the fluctuation (see the lower part of FIG. 6). ). That is, the liquid level can be known using the remaining fuel sensor 22.

In step 4, the output F of the remaining fuel sensor is compared with Fmax, and only when F exceeds Fmax, the routine proceeds to step 5, where the value of F is shifted to Fmax. Fmax is F, which will be described later.
This is a memory prepared in advance with min. Similarly, in step 6, the output F of the remaining fuel sensor is compared with Fmin, and only when F is less than Fmin, the process proceeds to step 7 to shift the value of F to Fmin. Steps 3 to 7 are repeated at regular intervals until the value of the timer exceeds the reference value.
In x, the maximum value of the fuel remaining amount sensor output during the sloshing determination period is sampled, and in Fmin, the minimum value of the fuel remaining amount sensor output during the sloshing determination period is sampled.

When the value of the timer exceeds the reference value by repeating the increment of the timer in step 1, the process proceeds to step 8, and after the timer is cleared, in step 9, the fluctuation width ΔF of the liquid level during the sloshing determination period is calculated. ΔF
= Fmax−Fmin, and the fluctuation width ΔF is compared with the determination value in step 10. When the swing width ΔF exceeds the determination value (sloshing has occurred), the routine proceeds to step 11, where the leak diagnosis is prohibited. As a result, it is possible to avoid erroneous diagnosis caused by continuing the leak diagnosis even when sloshing occurs.

It is conceivable to determine whether sloshing has occurred based on the amount of change in the liquid level per predetermined time. For example, in FIG. 8 (an enlarged view of the liquid level movement in FIG. 6), at the timings of A and B,
If the liquid level is sampled, the difference ΔF2 becomes the amount of change in the liquid level per predetermined time, and this difference ΔF2
Is greater than the determination value, it is determined that sloshing has occurred. However, if the sampling period is long, or the sampling period is short, but the level of the liquid level fluctuates more greatly, and the next sampling timing of A comes to C or D, the liquid level at A And therefore the level difference Δ
F2 becomes equal to or less than the determination value, and there is a possibility that erroneous determination that sloshing has not occurred.

On the other hand, since it is determined whether sloshing has occurred based on the maximum fluctuation width of the liquid level during the sloshing determination period, such erroneous determination can be avoided.

In step 13, Fmax is cleared, F at that time is moved to Fmin, and preparation is made for the next calculation of the fluctuation level of the liquid level.

Thus, according to the flow of FIG.
It is periodically determined whether or not sloshing has occurred, and when sloshing has occurred, leak diagnosis is prohibited.

When the vehicle travels on a rough road or completes rapid acceleration, rapid deceleration, and lane change, the liquid level becomes stable, so that the swing width ΔF becomes equal to or smaller than the determination value. In this case, the process proceeds from step 10 to step 12, and the leak diagnosis is permitted. Even when the leak diagnosis is prohibited during the leak diagnosis, the leak diagnosis is restarted at the timing when the leak diagnosis is permitted thereafter.

As described above, in the embodiment of the present invention, it is determined whether or not sloshing has occurred based on the change in the liquid level, and when the sloshing has occurred, the leak diagnosis is prohibited. Even when sloshing occurs due to sudden acceleration, sudden deceleration, lane change, or the like, erroneous diagnosis due to continuing leak diagnosis can be avoided.

Further, since it is determined whether or not sloshing has occurred based on the maximum fluctuation width of the liquid level within a predetermined period, it is determined whether or not sloshing has occurred based on the amount of change in the liquid level per predetermined time. It is possible to avoid erroneous determination that occurs in such a case.

In the embodiment, the case has been described where it is determined whether or not sloshing has occurred based on the fuel remaining amount sensor. However, the method of determining sloshing is not limited to this. For example, when the vehicle travels on a rough road, suddenly accelerates, suddenly decelerates, changes lanes, etc., this appears as a change in acceleration in the vertical direction of the vehicle, the longitudinal direction of the vehicle, or the lateral direction of the vehicle. Therefore, if sensors for detecting the acceleration in the vertical direction of the vehicle, the traveling direction of the vehicle, and the lateral direction of the vehicle are installed in the fuel tank, it is not good if the detection value from the vehicle vertical acceleration sensor exceeds the determination value. When the vehicle is traveling on the road, when the detection value from the vehicle longitudinal acceleration sensor exceeds the determination value When rapid acceleration or sudden deceleration is performed, or when the detection value from the vehicle lateral acceleration sensor exceeds the determination value It can be determined that a lane change has been made (sloshing occurs in any case).

In the embodiment, the case where it is determined whether or not there is a leak by comparing the calculated leak hole area with the determination value has been described. However, the present invention is not limited to such a diagnosis method. For example, in FIG. 6, the negative pressure of the closed flow path is ended at the timing of t1, and the flow path pressure P1 at the timing of the end of the negative pressure and the pressure at the timing of t2 after a certain period has elapsed from this timing. Change ΔP from P2
(= P2−P1) is measured, and the change ΔP is compared with the determination value to determine that there is a leak when the change ΔP is less than the determination value, and that there is no leak when ΔP is equal to or greater than the determination value. Can be similarly applied. In this case, even when the change ΔP is less than the determination value and the leak is stabilized in a state where there is no sloshing (see the broken line in FIG. 6), due to the occurrence of the sloshing (see the lower part of FIG. 6), If ΔP becomes larger than the determination value and becomes greater than or equal to the determination value, it is erroneously determined that there is no leak. Therefore, by prohibiting the leak diagnosis when the occurrence of sloshing is determined, the erroneous diagnosis can also be avoided in this case. It is.

[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 the pressure sensor 13.

FIG. 4 is a model waveform diagram showing a pressure change when it is diagnosed that there is no leak at the time of leak diagnosis using a negative pressure.

FIG. 5 is a model waveform diagram showing a pressure change when a leak is diagnosed during a leak diagnosis using a negative pressure.

FIG. 6 is a waveform diagram showing a pressure change when sloshing occurs.

FIG. 7 is a flowchart for explaining sloshing determination and prohibition and permission of leak diagnosis performed in accordance with the determination result.

FIG. 8 is a waveform chart showing a change in liquid level.

FIG. 9 is a diagram corresponding to claims of the first invention.

[Explanation of symbols]

 Reference Signs List 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 fuel remaining amount sensor

Claims (4)

[Claims] A first passage for guiding a vapor at an upper portion of a fuel tank to a canister; a second passage for communicating the canister with an intake pipe downstream of a throttle valve; and a purge control valve for opening and closing the second passage. A drain cut valve that opens and closes an air release port of the canister; a unit that detects a flow path pressure from the fuel tank to the purge control valve; and a unit that determines whether a leak diagnosis condition is satisfied. Based on the determination result, when the leak diagnosis condition is satisfied, means for maintaining the flow path from the fuel tank to the purge control valve in a reduced pressure state using the drain cut valve and the purge control valve, and after maintaining the reduced pressure state, Means for performing a leak diagnosis based on a change in the flow path pressure. Means for sampling a maximum value and a minimum value of the liquid level within a predetermined period in the fuel tank; means for calculating a difference between the maximum value and the minimum value; and comparing the difference with a determination value. A means for determining that sloshing has occurred when the difference exceeds a determination value, and a means for inhibiting the leak diagnosis when sloshing has occurred based on the determination result. . 2. The diagnostic apparatus according to claim 1, wherein the predetermined period is a value corresponding to a period of fluctuation of a liquid level due to running on a rough road. 3. The diagnostic apparatus according to claim 1, wherein the predetermined period is a value corresponding to a time required for rapid acceleration, rapid deceleration, or lane change. 4. The evaporative fuel processing apparatus according to claim 1, wherein when the sloshing is stopped after the prohibition of the leak diagnosis due to the occurrence of the sloshing, the leak diagnosis is restarted. Diagnostic device.