JP3255472B2 - Failure diagnosis system for evaporative fuel supply system of engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis device for determining whether a failure has occurred in an evaporative fuel supply system of an engine.

[0002]

2. Description of the Related Art A conventional failure diagnosis apparatus for an evaporative fuel supply system of an engine opens a purge valve at a predetermined opening when the engine is idle, as shown in, for example, JP-A-4-5462. calculating a feedback correction amount CFB from the detected value of 0 ₂ sensor at a predetermined time,
Normal when the value of CFB is leaner than a predetermined value,
It determines that failure otherwise, failure and wide open turn again purge valve when it is determined, similarly to the first time, then calculates the feedback correction amount CFB from the detected value of 0 ₂ sensor at a predetermined time has elapsed, CFB Is normal when the value is lean or more than a predetermined value, and is determined to be faulty when it is not.

[0003]

In the above-described failure diagnosis apparatus, since the amount of fuel evaporative gas trapped in the canister cannot be detected, the air-fuel ratio of the fuel evaporative gas in the canister is equal to the control air-fuel ratio. In this case, even if the purge valve is opened, the value of the feedback correction amount CFB does not change, and it is determined that the fuel vapor supply system is abnormal even though it is normal.

When the purge valve is opened with a large duty ratio when the amount of fuel evaporative gas in the canister is large,
The air-fuel ratio of the engine intake became excessively rich, and the engine became rough idle and could stall.

Conversely, when the purge valve is opened with a small duty ratio when the amount of fuel evaporative gas in the canister is small, the change in the value of the feedback correction amount CFB is small,
Although the evaporative fuel supply system is normal, it may be determined that the system is abnormal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an evaporative fuel supply for an engine capable of accurately determining the presence or absence of a failure regardless of the amount of fuel evaporative gas in a canister. An object of the present invention is to provide a system fault diagnosis device. It is another object of the present invention to provide a failure diagnosis device for an evaporative fuel supply system of an engine which does not cause engine stall at the time of failure determination regardless of the amount of fuel evaporative gas in a canister.

[0007]

SUMMARY OF THE INVENTION In order to attain the above object, the present invention provides a method for detecting a failure of an evaporative fuel supply system based on a shift amount of a signal related to an air-fuel ratio to a rich side or a lean side after a purge valve is opened at a predetermined opening. A failure diagnosis device for an evaporative fuel supply system of an engine for determining presence / absence includes first failure determination means, second failure determination means, and control means, wherein the first failure determination means opens a purge valve in response to a command from the control means. Degree
The first failure determination of the evaporative fuel supply system is performed stepwise, and the control unit confirms that the engine warm-up operation has been completed when the first failure determination unit determines that there is a failure. Thereafter, the fuel evaporative gas amount is confined in the evaporative fuel supply system by a predetermined amount or more, and the second failure determination means performs the second failure determination similar to the first failure determination.

Further, in the above-mentioned present invention, the predetermined amount changes according to the fuel temperature.

[0009]

[0010]

The control means 40 controls the first failure determination means 41 and the second failure determination means 42 as shown in FIG.
For example, when the engine 1 is feedback condition is established in the idle state, the first failure judgment means 41 of the purge valve
The first degree of failure determination of the evaporative fuel supply system is performed by gradually increasing the opening . This is the amount of deviation of a signal (for example, a signal indicating the feedback correction amount CFB output from the CFB calculation unit 44) related to the air-fuel ratio after the purge valve 24 is opened by a predetermined degree by the valve driving unit 43 to the rich side or the lean side. Is detected, the presence or absence of a failure in the evaporative fuel supply system is determined. The degree of opening of the purge valve 24 is gradually increased.
By making the failure judgment larger,
Engine 1 becomes rough idle at the time of judgment and stalls
It will not be. When the first failure determination unit 41 determines that a failure has occurred , the control unit 40 confirms that the warm-up operation of the engine 1 has been completed, and then fully closes the purge valve 24 to evaporate the amount of fuel vaporized gas. A predetermined amount or more is confined in the fuel supply system, and the second failure determination means 42 performs the second failure determination in the same manner as the first failure determination. Thus, the failure determination is performed by recognizing the amount of the fuel evaporative gas trapped in the fuel vapor supply system, so that the failure determination becomes extremely accurate. In addition, the above-mentioned predetermined amount is
By making a change in accordance with the fuel temperature detected in 9a, the failure determination becomes even more accurate.

[0011]

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a failure diagnosis apparatus for an evaporative fuel supply system of an engine according to the present invention will be described with reference to FIGS.

FIG. 2 shows the overall configuration of an embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes an engine. The engine 1 includes a cylinder block 3 having a cylinder 2, a cylinder head 4 joined to an upper surface of the cylinder block 3, and a piston 5 reciprocating in the cylinder 2. , Cylinder 2
Inside, a combustion chamber 6 defined by a lower surface of the cylinder head 4 and a top surface of the piston 5 is formed. Reference numeral 7 denotes an intake passage for supplying intake air into the combustion chamber 6, and reference numeral 9 denotes an intake valve for opening and closing a downstream end opening of the intake passage 7. Reference numeral 10 denotes an exhaust passage for discharging exhaust gas from the combustion chamber 6, reference numeral 11 denotes an exhaust valve for opening and closing an upstream end opening of the exhaust passage 10, and reference numeral 12 denotes an exhaust gas purification device provided in the exhaust passage 10.

In the intake passage 7, an air flow meter 13 for detecting an intake air amount Q, a throttle valve 14 for controlling the intake air amount, a surge tank 15 for absorbing intake pulsation and the like, and fuel are injected in order from the upstream side. An injector 16 for supplying is provided, and an upstream side of the intake passage 7 is connected to an air cleaner 17. Reference numeral 8 denotes a bypass passage for bypassing the throttle valve 14 and supplying air to the combustion chamber 6.
On the way, when the engine 1 is idling, the bypass passage 8
An idle speed control valve 18 composed of a proportional solenoid valve for controlling the amount of air flowing through the engine and adjusting the engine speed (idling speed) is provided.

A fuel tank 19 is connected to the injector 16 via a fuel supply passage (not shown). A fuel thermometer 19a is disposed in the fuel tank 19;
The fuel thermometer 19a detects the temperature of the fuel, converts the temperature into an electric signal, and outputs the electric signal.

In the upper part of the fuel tank 19, an upstream end of a purge passage 20 for supplying the evaporated fuel (fuel evaporated gas) in the tank 19 to the engine 1 is opened. Intake passage 7 in surge tank 15
It is open to. In the middle of the purge passage 20, in order from the upstream side (the fuel tank 19 side), a separator 21 for separating the liquid fuel from the evaporated fuel, a two-way valve 22a,
A way valve 22b, a canister 23 for adsorbing the evaporated fuel, and a purge valve 24 as a purge adjusting valve composed of a solenoid valve for opening and closing the purge passage 20 to adjust the supply (purge) of the evaporated fuel to the intake passage 7 are arranged. The separator 21 is connected to the fuel tank 19 via a fuel return passage 25 for returning the separated liquid fuel. The purge passage 20, the separator 21, the 2-way valve 22a, and the 3-way valve 22
b, a canister 23 and a purge valve 24 constitute an evaporative fuel supply system.

The operation of the injector 16, idle speed control valve 18 and purge valve 24 is controlled by a control unit 30 having a built-in CPU. The control unit 30 includes a detection signal of the above-described fuel thermometer 19a, a detection signal of the air flow meter 13, a detection signal of an intake air temperature sensor 31 for detecting an intake air temperature in the intake passage 7 immediately downstream of the air cleaner 17, and A detection signal of a throttle sensor 32 for detecting an opening degree of the throttle valve 14, a detection signal of a crank angle sensor 33 for detecting a crank angle of the engine 1 based on a rotation angle of the camshaft 26 in the cylinder head 4, and a rotation signal of a distributor 34 The detection signal of the O ₂ sensor 35 disposed in the exhaust passage 10 on the upstream side of the exhaust purification device 12, and the water jacket 3 in the cylinder block 3.
a and a detection signal of a water temperature sensor 36 for detecting the temperature of the cooling water inside the apparatus. The throttle sensor 32 is provided with an idle switch (not shown) for outputting an ON signal when the throttle valve 14 is fully closed and the throttle opening becomes zero.

Next, a procedure for judging a failure in the fuel vapor supply system by controlling the operation of the purge valve 24 in the control unit 30 will be described with reference to the flow charts of FIGS.

Referring to FIGS. 3 and 4, after the ignition switch is turned on and the operation is started, various signals are initialized (step S1). Next, an idle state and a state where the feedback condition is satisfied (hereinafter referred to as a determination possible state). )
It is determined whether or not it is (step S2). If the determination is possible, the timers T1, T2 and T3 are set (step S2).
3).

After setting the timer, the duty ratio for opening the purge valve 24 is set to 10% (step S4), and the value of the feedback correction amount CFB is read (step S5). CF
When T1 has elapsed from the reading of B, the value of CFB is read (steps S6 and S7), and the difference ΔCFB between the value of CFB in step S5 and the value of CFB in step S7 is calculated, and whether or not the value of ΔCFB is equal to or greater than Δ1 Is determined (step S8). The reason for providing the time T1 is that the fluctuation of the air-fuel ratio based on the evaporated fuel supplied by opening the purge valve 24 is caused by the interposition of the pipe 7, the pipe 10, and the engine 1,
4 is not immediately appear at the site of the O ₂ sensor 35 is open, is because those detected O ₂ sensor 35 after a certain time.

If .DELTA.CFB.gtoreq..DELTA.1 in step S8, the evaporated fuel is normally supplied to the intake pipe 7 via the purge valve 24. Therefore, the failure determination is terminated assuming that the evaporated fuel supply system is normal. I do. Step S
If ΔCFB <Δ1 in 8, it is determined that the presence or absence of a failure is unknown. That is, ΔCFB <Δ1 is satisfied not only when the fuel vapor supply system is out of order but also when the amount of fuel vapor gas in the canister 23 is small even when the fuel vapor supply system is normal. Therefore, ΔCF
Even if B <Δ1, the failure is not immediately determined, and the same failure determination is performed by setting the duty ratio of opening the purge valve 24 to 50% (steps S9 to S12).
ΔCFB in this case is the difference between the CFB value of step S7 and the CFB value of step S11.

If ΔCFB <Δ2 still holds even at the above-mentioned duty ratio of 50%, the same determination is finally made with the duty ratio of 100% (steps S13 to S13).
Step S16). If ΔCFB <Δ3 even at this duty ratio of 100%, a failure determination is made by changing the state of the evaporative fuel supply system. This is shown after step S17. Steps S4 to S16 described above correspond to the operation of the first failure determination unit 41.

If ΔCFB <Δ3 in step S16, the process shifts to step S17 to determine whether or not warm-up is completed. In step S17, if the engine intake air temperature ≧ TA and the engine cooling water temperature ≧ TB, it is determined that the warm-up is completed.
TA and TB are constant temperature values. If it is determined that the warm-up is completed, the duty ratio of opening the purge valve 24 is set to 0%, that is, the purge valve 24 is completely closed (step S18), and the integrated value of the amount of generated fuel vapor gas (evaporative gas) is calculated. This calculation is performed based on the fuel temperature detected by the fuel thermometer 19a and the elapsed time since the purge valve 24 was completely closed.

When it is determined that the integrated value of the evaporative gas generation amount is equal to or larger than the predetermined amount GA (step S19), it is determined that the fuel vapor is sufficiently accumulated in the canister 23, and T1, T2,
The timer of T3 is set again, and the failure is determined again (steps S20 to S33). In this failure determination again, since the fuel evaporative gas is sufficiently accumulated in the canister 23, it is possible to prevent an erroneous determination when the fuel evaporative gas accumulated in the canister 23 is small. The predetermined amount GA varies depending on the fuel temperature as shown in FIG. This is because the higher the fuel temperature, the more the fuel evaporative gas.

In steps S20 to S33, ΔCF
If none of B ≧ Δ1, ΔCFB ≧ Δ2, and ΔCFB ≧ Δ3 holds, it is determined that a failure has occurred, a failure is warned, and displayed (step S34). Steps S21 to S3
Reference numeral 3 corresponds to the operation of the second failure determination means 42. Steps S1 to S3, steps S17 to S20, and step S34 correspond to the operation of the control means.

As described above, since the purge valve 24 is fully closed to confine the fuel evaporative gas in the canister 23 and a predetermined amount is confined to determine the failure, the failure determination becomes extremely accurate.

Further, since the predetermined amount is changed in accordance with the fuel temperature detected by the fuel thermometer 19a, a failure determination is made in accordance with the generation speed of the fuel evaporative gas, and the failure determination is more accurate. It will be.

Further, the first and second failure judgment means 41, 4
In 2, the failure determination is performed by gradually increasing the opening degree of the purge valve 24, that is, the duty ratio, so that the intake air supplied to the engine 1 is prevented from being excessively rich, and therefore the engine 1 is rough. You will not be stuck as an idol.

[0029]

As described above in detail, the failure diagnosis apparatus for an evaporative fuel supply system of an engine according to the present invention recognizes the amount of fuel evaporative gas trapped in the evaporative fuel supply system and makes a failure determination. The judgment becomes extremely accurate.

Further, since the amount of the fuel evaporative gas to be confined is changed according to the fuel temperature, a failure determination is made in accordance with the generation speed of the fuel evaporative gas, and the failure determination becomes more accurate.

Further, since the failure determination is performed by gradually increasing the opening degree of the purge valve, that is, the duty ratio, it is possible to prevent the engine from becoming idle and stalling.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a failure diagnosis device for an evaporative fuel supply system of an engine according to the present invention.

FIG. 2 is a configuration diagram showing one embodiment of a failure diagnosis device for an evaporative fuel supply system of an engine according to the present invention.

FIG. 3 is a flowchart for explaining the operation of the apparatus shown in FIG. 2;

FIG. 4 is a flowchart for explaining the operation of the apparatus shown in FIG. 2, which is linked to FIG. 3;

FIG. 5 is a graph showing a relationship between a predetermined amount and a fuel temperature.

[Explanation of symbols]

 Reference Signs List 1 engine 7 intake passage 19 fuel tank 19a fuel thermometer 20 purge passage 23 canister 24 purge valve 40 control means 41 first failure determination means 42 second failure determination means 43 valve drive means 44 CFB calculation means

Claims (2)

(57) [Claims] 1. A failure diagnosis device for an evaporative fuel supply system of an engine for determining whether or not a failure has occurred in an evaporative fuel supply system based on a shift amount of a signal related to an air-fuel ratio to a rich side or a lean side after opening a purge valve by a predetermined opening degree. And a first failure determination means, a second failure determination means, and a control means, wherein the first failure determination means opens a purge valve in response to a command from the control means.
When the first failure determination unit determines that a failure has occurred, the control unit determines that the engine warm-up operation has been completed. After the confirmation, the amount of fuel evaporative gas is confined in the evaporative fuel supply system by a predetermined amount or more, and the second failure determination means makes a second failure determination similar to the first failure determination. System failure diagnosis device. 2. The failure diagnosis device according to claim 1, wherein the predetermined amount changes according to a fuel temperature.