JP2667072B2 - Evaporative fuel control system for internal combustion 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 fuel vapor control system for an internal combustion engine.

[0002]

2. Description of the Related Art In general, in an automotive internal combustion engine, a passage provided with a check valve for evaporative fuel generated from an evaporation source such as a fuel tank is provided for the purpose of preventing air pollution by fuel evaporative gas (mainly harmful HC components). Is introduced into the canister to adsorb and collect, and is supplied to the intake system through an evaporative fuel supply passage provided between the canister and the intake system of the internal combustion engine. If the supply is performed unconditionally, the air-fuel ratio of the air-fuel mixture will fluctuate greatly and the operating performance of the internal combustion engine will deteriorate, so a purge control valve is provided in the evaporative fuel supply passage, and the purge control is performed by a purge control command from the control device. An evaporative fuel control device that supplies evaporative fuel to the intake system only under operating conditions where there is no problem even if the valve is opened to supply the evaporative fuel to the intake system is used.

Further, from the viewpoint of strengthening the prevention of air pollution in recent years, when a failure occurs in the evaporated fuel control device such as damage to the evaporated fuel supply passage, deterioration / damage to the canister, failure of the purge control valve, this failure is detected early. It is conceived that a warning will be issued and repair will be urged.

[0004] As a device for detecting the above-mentioned failure,
Since the supply of the fuel adsorbed and collected by the canister to the intake system temporarily causes a rich-side shift of the air-fuel ratio, the correction value of the air-fuel ratio feedback correction value in the air-fuel ratio feedback control using the exhaust sensor provided in the exhaust system is determined. Utilizing the fact that a sudden change occurs, a device that determines that the air-fuel ratio feedback correction value is normal if a sudden change of a predetermined value or more occurs after an open command of a purge control valve, and that the air-fuel ratio feedback correction value is a failure if the sudden change is a predetermined value or less. Proposed.

[0005]

In the above-described apparatus, when the amount of fuel adsorbed and collected in the canister is very small, even when the evaporative fuel control device is normal, the purge control valve is operated after the opening operation. Since the sudden change in the air-fuel ratio feedback correction value is so small that it is erroneously determined as a failure, it is necessary to detect the amount of fuel adsorbed on the canister and perform the failure determination on condition that the fuel amount equal to or more than a predetermined value is adsorbed. is there.

FIG. 7 shows a state in which the purge control valve is closed (purge OF
FIG. 7A shows an example of the movement of the air-fuel ratio feedback correction value after opening of the purge control valve (after the purge ON), and FIG. 7A shows a case where the amount of adsorbed fuel in the canister is large when the purge control valve is closed (for example, about 80% vol. ), FIG. 7b shows a case where the amount of adsorbed fuel is small (for example, at about 15% vol), and the range of correction values during normal air-fuel ratio feedback control (C in FIG. 7).
_pp ) is about 10%, so that when the fuel concentration in the canister is low when the purge control valve is closed, the correction value width C _pp during normal operation and the fluctuation width Δ of the correction value due to the purge control valve open circuit
Indicates that it is difficult to distinguish from C.

The present invention provides an apparatus for detecting the amount of fuel adsorbed in a canister without using a special fuel concentration sensor whose characteristics such as resistance value change according to the fuel concentration, for example. It is another object of the present invention to provide an evaporative fuel control device for an internal combustion engine that accurately detects a failure of the evaporative fuel control device.

[0008]

According to the present invention, there is provided an evaporative fuel control apparatus for an internal combustion engine, comprising: a canister for adsorbing and collecting evaporative fuel generated by an evaporator such as a fuel tank; and an evaporator for communicating between the evaporator and the canister. A check valve is provided in the fuel introduction passage, and a purge control valve is provided for controlling the supply of the fuel adsorbed and collected by the canister to the internal combustion engine. By controlling the purge control valve, the fuel vapor to the internal combustion engine is reduced. In the evaporative fuel control device for controlling the supply, a pressure detection sensor for detecting the internal pressure of the evaporation source is provided, and the opening and closing operation of the check valve is detected in accordance with the output of the pressure detection sensor, and the accumulation of the open time of the check valve is performed. On time
Based on the detected amount of fuel adsorbed on the canister,
Changes in the output of the pressure detection sensor while the check valve is open
The amount of adsorbed fuel is corrected according to the moving width . or,
An evaporative fuel control device for an internal combustion engine according to the present invention is an
When the charge is equal to or higher than the predetermined value, the purge control valve is closed.
Of the internal combustion engine and the air / fuel ratio when the purge control valve is open
Whether the evaporative fuel control operation is correct or not based on the
It is to judge.

[0009]

In the fuel vapor control apparatus for an internal combustion engine according to the present invention, the amount of fuel adsorbed in the canister is detected by detecting the internal pressure of the vapor source in a vapor fuel introduction passage communicating between the vapor source and the canister. In order to detect the open operation of the check valve and to detect the amount of adsorbed fuel in the canister based on the length of the open period of the check valve, for example, a special fuel whose characteristics such as resistance value changes according to the fuel concentration. There is no need to use a density sensor.
Also, without using a special fuel concentration sensor,
Can be determined with high accuracy.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a fuel vapor control system showing an embodiment of the present invention. A control unit 3 including a driver unit for driving various loads to control a fuel system, an ignition system (not shown), and the like of the engine 1 is an intake pipe of the engine 1. Reference numeral 4 denotes an air flow meter for measuring an intake air amount of the engine 1, and for example, a heat-sensitive flow meter is used.

5 is a slot opening sensor for detecting the opening of the throttle valve 51; 6 is an intake pipe pressure sensor for detecting the pressure of the intake pipe 3; 7 is an exhaust sensor for detecting oxygen concentration in exhaust gas; A rotation sensor for detecting the rotation speed of 1,
Reference numeral 9 denotes a fuel injection valve for injecting fuel into the intake pipe 3. The control unit 2 is required for the engine 1 based on signals from the air flow meter 4, the throttle opening sensor 5, the intake pipe pressure sensor 6, the rotation sensor 8, and the like. The basic fuel amount is calculated, the operating state is detected, and the fuel injection amount from the fuel injection valve 9 is calculated according to the operating state to obtain a predetermined air-fuel ratio. And
Feedback control of the air-fuel ratio is performed based on this correction value.
The control unit 2 also performs optimal control on an ignition system (not shown) according to the operation state based on the signals from the above-described sensors and the like.

Reference numeral 10 denotes a fuel tank, 11 denotes a canister filled with an adsorbent 12 such as activated carbon, and 13 and 14 communicate between the fuel tank 10 and the canister 11 to evaporate fuel generated inside the fuel tank 10. Is a one-way check valve that allows the evaporative fuel to pass only from the fuel tank 10 to the canister 11, and is provided inside the fuel tank 10, for example, after the engine operation is stopped. When the pressure increases due to the generation of fuel vapor, the fuel tank 10 is opened in a direction from the fuel tank 10 to the canister 11 at a predetermined pressure. The fuel vapor is sent to the canister 11 and temporarily adsorbed and captured by the adsorbent 12. To be gathered. Reference numeral 16 denotes a pressure detection sensor that detects the internal pressure of the fuel tank 10, for example, a pressure sensor that generates an output signal proportional to the pressure is used.

The intake pipe 3 downstream of the throttle valve 51
And the canister 11 are communicated with each other through the evaporative fuel supply passages 17 and 18, and a purge control valve 19 is provided in the middle thereof.
The purge control valve 19 opens and closes the evaporative fuel supply passages 17 and 18 in response to an open / close command from the control unit 2 to supply evaporated fuel to the intake pipe 3 under conditions (hereinafter referred to as purge ON conditions). , The purge control valve 19 is opened, and the intake pipe 3 is opened.
The vaporized fuel adsorbed and collected in the canister 11 is supplied by the negative pressure of. In the embodiment shown in FIG. 1, the control unit 2 is configured to simultaneously perform the evaporated fuel control and the failure detection operation of the control device.

First, the relationship between the opening and closing operation of the check valve 15 and the internal pressure _PT of the fuel tank 10 will be described with reference to FIG. Figure 2 is a diagram showing the relationship between the opening and closing operation of the internal output P _T and the check valve 15 of the fuel tank 10, when the internal pressure P _T in Figure 2a is the fuel tank 10 is in a predetermined open pressure P _C of the check valve 15 when the check valve 15 is opened, FIG. 2b for example shows a case where abnormal check valve 15 malfunctions such as a check valve 15 is not opened at a predetermined open pressure P _C.

Next, a method of detecting the opening / closing operation of the check valve 15 in the control unit 2 will be described. The control unit 2 detects the internal pressure P _T of the fuel tank 10 based on the output signal of the pressure detection sensor 16 and the pressure P _L slightly lower than the predetermined open circuit pressure P _C of the check valve 15.
And comparing the P _T, the check valve 1 in the case of P _T> P _L
5 is determined to be open.

In the above determination, the fuel tank 1
Although internal output P _T 0 check valve 15 when the predetermined pressure or more P _L is judged to be open, for example, the in the case the check valve 15 is such abnormality occurs so as not to open the like, P If the check valve in the condition in which the _T> P _L is not open circuit occurs.

In the case where the above-mentioned troubles are assumed to occur, the check valve 15 does not open even though a large amount of fuel vapor is generated inside the fuel tank 10, so that the fuel tank 10 as shown in FIG. Since the internal pressure _PT of the valve continues to rise, for example, the check valve 1
5 of a predetermined open pressure P _C slightly higher than the pressure P _H as the upper limit comparison pressure, determines that the check valve 15 when the condition of P _H> P _T> P _L is opened, for example, P _T> P _H
By deciding such a state as a failure of the check valve, it is possible to prevent the erroneous decision at the time of occurrence of the above-mentioned trouble.

Further, by adding a time condition for judging that the circuit is opened after P _H > P _T > P _L continues for a predetermined time, for example, when the check valve is abnormal, P _T
By further prohibiting the open circuit determination in the case where P _H > P _T > P _L is temporarily established in the ascending process, the operation of the check valve 15 can be more reliably determined.

As described above, according to the determination of the opening operation of the check valve 15 according to the present invention, the open / close operation of the check valve 15 requires a check valve having a complicated structure such as adding a contact or the like for opening / closing detection to the check valve. Instead, for example, the opening / closing operation of the check valve can be detected by using a pressure detection sensor having a simple structure that applies resistance strain as is generally used.

Next, the operation of the embodiment of the evaporated fuel control device using the opening / closing operation of the check valve 15 detected as described above will be described with reference to the flowchart of FIG.
(Note that the opening and closing operation of the check valve in the following description is based on the result of detection using the pressure detection sensor described above.) FIG. 4 shows that the purge control valve 19 is opened (ON) → closed (OFF). 4) shows an example of a flowchart of an operation for measuring the accumulated time during which the check valve 15 is open (ON) since the previous switching and detecting the amount of evaporated fuel adsorbed on the canister 11.

First, in step S1, the cumulative time (T _m-1 ) of the opening of the check valve 15 measured according to the above-described operation flow chart is read from a storage means (not shown), and in step S2, a purge control valve 19 described later is read. Is determined to be in the "set" state, the purge control valve 19 is opened and the canister 1 is opened.
In step S3, the accumulated time is reset (T _m-1 = 0) to indicate that the adsorbed fuel in 1 has been supplied to the engine 1 and is purged, and the purge flag is "reset" in step S4. When the purge flag is not in the "set" state in step S2, it indicates that the purge control valve 19 is not opened, and indicates that the canister 11 continues to adsorb the evaporated fuel in steps S3 and S4. The process proceeds to step S5 without performing the "reset" of.

Next, at step S5, the pressure sensor 16
Whether the check valve is open or not is determined by the above-mentioned method based on the output signal of the above. If it is open, the time T _C until the check valve is opened is determined in step S6, and the open circuit accumulation up to the previous time is determined in step S7. The time T _m-1 is added to the current open time T _C , and the addition result (T _m-1 + T _C ) is stored as the current accumulated time T _m . If it is determined in step S5 that the circuit is being closed, the flow proceeds to step S8. , stores the cumulative time T _m-1 up to the last as the current cumulative time T _m.

Next, in step S9, step S
Check valve 15 updated and stored in 7 or S8
Cumulative open circuit time compares the T _m with a predetermined value of the canister 1
By utilizing the fact that the amount of evaporated fuel adsorbed and collected in step 1 is proportional to the cumulative open circuit time, if _Tm is equal to or more than a predetermined value, in step S10, the amount of adsorbed fuel is equal to or more than a predetermined amount and _Tm is equal to a predetermined value. If not, it is determined in step S11 that the amount of adsorbed fuel is equal to or less than a predetermined amount.

In the above description, the generation of evaporative fuel inside the fuel tank 10 occurs constantly and continuously, and even when the check valve 15 is opened, the internal pressure _PT is substantially reduced as shown in FIG. The operation in a constant case has been described. For example, when the check valve 15 is opened, and the check valve 15 is opened and the evaporative fuel is discharged from the fuel tank 10 to the canister 11, and the generated amount of evaporative fuel is small, for example, FIG. As shown in FIG. 3, the internal pressure of the fuel tank fluctuates with the opening of the check valve 15, and the check valve 15 may repeatedly open and close.

The above-described order becomes different amount adsorbed fuel be, for example, the same time the T _m in the case, the average value or the fluctuation range of the variation in the internal pressure of the fuel tank 10 in such a case (FIG. 3 By correcting the detection result according to the magnitude of P _HL ), detection can be performed more accurately.

Next, FIG. 5 shows an example of an operation flowchart for detecting a failure of the vapor deposition fuel control device using the method for detecting the amount of adsorption in the canister 11 which is constructed as shown in FIG. 1 and which is performed according to the operation flowchart shown in FIG. It will be described using FIG.

FIG. 5 is an operation flowchart for causing the control unit 2 to detect a failure of the evaporative fuel control device. In step S20, the control unit 2 firstly operates the air flow meter 4, the throttle opening sensor 5, the intake pipe pressure. The operation state of the engine 1 is detected by signals from the sensors such as the sensor 6 and the rotation sensor 8, and it is determined whether or not the state of the engine is in a purge ON condition.
If the condition is FF, the purge control valve is closed in step S21 and the operation flowchart ends.

[0028] When it is determined that the condition of the purge ON at step S20, read the step S7, S8 in the cumulative open circuit time of the operation the stored check valve the T _m of operating the flow chart shown in FIG. 4 in step S22, in step S23 The determination of the amount of adsorption is performed in the same manner as in steps S9 to S11 in the operation flowchart of FIG. 4, and if it is determined that the amount of adsorption is equal to or more than the predetermined amount, the process proceeds to step S26 and before the purge valve is opened, the air-fuel ratio feedback control by the exhaust gas sensor is performed. After reading the feedback correction value C _OFF in step S27, an instruction to open the purge control valve is issued in step S27, and a purge flag indicating that the purge control valve is opened in step S28 is set to a "set" state.

Next, at step S29, the feedback correction value C _ON after the command to open the purge control valve is read again, and
In step S30, the difference (C _OFF -C _ON ) between the correction values before and after the opening command of the purge control valve is calculated, and in step S31, it is determined whether the difference between the correction values is equal to or larger than a predetermined value.

In the above operation, when the operation of the evaporated fuel control device is normal, the evaporated fuel temporarily adsorbed and collected in the canister 11 is supplied to the intake pipe 3. Since the air-fuel ratio temporarily shifts to the rich side due to the temporarily supplied excess fuel, the air-fuel ratio feedback control operation based on the signal of the exhaust sensor 7 shifts the correction value to the lean side to obtain a predetermined air-fuel ratio. Control is performed to converge on the fuel ratio. Therefore, the result of (C _OFF -C _ON ) calculated in step S30 is equal to or greater than a predetermined value, and the evaporative fuel control apparatus performs step S30
At 33, it is determined to be normal.

Further, a malfunction of the fuel vapor control device, for example, the fuel vapor introducing passages 13 and 14, the fuel vapor supply passages 17 and 1
8, damage to the canister, deterioration of the adsorbent 12, malfunction of the purge control valve 19, and other failures.
Although the output command from the control unit 2 instructs the purge control valve 19 to open, the excess fuel is not supplied to the intake pipe 3 as in the normal case described above.
There is no change or little change in the feedback correction value after the command to open the purge control valve (C _OFF -C _ON )
Is less than or equal to the predetermined value, it is determined to be abnormal in step S32.

When it is determined in step S23 that the cumulative open time T _m of the check valve is less than or equal to the predetermined value and the adsorbed fuel amount in the canister 11 is less than or equal to the predetermined amount, the operation of the evaporated fuel control device is normal. In this case as well, the change of the feedback correction value (C _OFF −C _ON ) is small and it is difficult to make a determination. In this case, only the command to open the purge control valve in step S24 and “set” of the purge flag in step S25 are performed. Finish the flowchart.

[0033] FIG 6 is a flowchart showing the operation of the embodiment cumulative open circuit time plus the T _m of a check valve in the determination conditions for open purge control valve in the fault detection operation of the evaporative fuel control system, FIG. 5 Steps that perform the same operations as those described above are given the same step numbers as in FIG. 5, and descriptions thereof are omitted. Detecting the adsorbed amount of fuel in the canister 11 on the basis of the cumulative open circuit time T _m of a check valve in step S23 in FIG. 6, in the case of less than a predetermined value the operation of FIG. 5 except that the command to close the purge control valve 19 6 and FIG.
In the case of the operation shown in FIG. 5, since the purge control valve 19 is controlled so as not to open until the vaporized fuel equal to or more than the predetermined amount is adsorbed on the canister 11, the same operation as in the embodiment shown in FIG. In addition to being able to determine the presence or absence of a failure of the device, if the amount of evaporated fuel adsorbed and collected in the canister 11 is small, the operation of the purge control valve 19 is not performed. Therefore, the durability of the device can be improved.

As described above, the failure detection of the evaporative fuel control device is performed by detecting the amount of adsorbed fuel in the canister before the purge control valve is instructed to open the purge control valve by using the above-described method. Only in the case where the failure of the evaporative fuel control device is determined by detecting the air-fuel ratio feedback correction value before and after the purge control valve opening command, the change of the feedback correction value due to the presence or absence of the failure can be determined with great reliability. This makes it possible to detect failures with a high degree of failure.

[0035]

As described above, according to the present invention, it is not necessary to use a special fuel concentration sensor whose resistance value changes in accordance with the concentration of fuel, for example. detection of detecting the opening and closing operation of the check valve without the need for check valves of complex structures such as opening and closing amount of fuel adsorbed by the canister high precision
The evaporative fuel control device can be performed at any time . In addition,
Evaporative fuel control without the need for complicated check valves
Evaporative fuel system that can judge the correctness of operation with high accuracy
Control device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an evaporative fuel control device showing one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an internal pressure of an evaporation source such as a fuel tank and an operation of a check valve.

FIG. 3 is a characteristic diagram showing a relationship between an internal pressure of an evaporation source such as a fuel tank and an operation of a check valve.

FIG. 4 is a flowchart showing an operation of the apparatus according to the embodiment of the present invention.

FIG. 5 is a flowchart showing a failure detection operation of the device according to the embodiment of the present invention.

FIG. 6 is a flowchart showing a failure detection operation of the device according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing an example of the movement of the air-fuel ratio feedback correction value when the purge control valve is closed and after the purge control valve is opened.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Control unit 3 Intake pipe 7 Exhaust sensor 10 Fuel tank 11 Canister 13, 14 Evaporated fuel introduction passage 15 Check valve 16 Pressure detection sensor 17, 18 Evaporated fuel supply passage 19 Purge control valve

Claims (2)

(57) [Claims] 1. A canister for adsorbing and collecting evaporative fuel generated from an evaporating source such as a fuel tank, and a check valve provided in an evaporative fuel introduction passage communicating between the evaporating source and the canister. A purge control valve for controlling supply of the fuel to the internal combustion engine, and controlling supply of the vaporized fuel to the internal combustion engine by controlling the purge control valve. provided the pressure detecting sensor for detecting the pressure, and detects the opening and closing operation of the check valve in accordance with the output of the pressure detection sensor, based on the accumulated time of an open circuit time of the check valve,
The amount of fuel adsorbed to the canister is detected, and the pressure detection cell is opened while the check valve is open.
The adsorbed fuel amount is corrected according to the fluctuation range of the sensor output.
Evaporative fuel control apparatus for an internal combustion engine, characterized in that that. 2. The case where the amount of adsorbed fuel indicates a predetermined value or more.
The air-fuel ratio of the internal combustion engine when the purge control valve is closed
And the air-fuel ratio deviation from the air-fuel ratio when the purge control valve is open.
To determine whether the evaporative fuel control operation is correct based on
The fuel vapor control system for an internal combustion engine according to claim 1, wherein
Place.