JP2001207920A - Fuel vapor purge control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel vapor purge control device of an internal combustion engine capable of restraining unstabilization of an air-fuel ratio caused by temporary lowering of engine speed and lowering of operability. SOLUTION: This device controls an air-fuel ratio and is furnished with an evaporated fuel treatment mechanism to adsorb evaporated fuel produced in a fuel tank on a canister and to purge the adsorbed evaporated fuel to an air intake system with air. Purging is allowed when a difference between injection time TAU0 of a fuel injection valve before adjustment by purge control and injection time (TAU0×FPG) required to inject fuel quantity of purge gas is higher than a permission judgement value TAUH which is injection time in the neighborhood of minimal time when fuel is actually started to inject after a valve element in a fuel injection valve opens and when engine speed NE is higher than allowable rotating speed (N-A) which is rotating speed that a constant A is deducted from idle target rotating speed N.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor purge control device for an internal combustion engine, which is mounted on a vehicle or the like and controls the purge of fuel vapor generated from a fuel tank to an intake system of the internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as this kind of fuel vapor purge control device, for example, devices described in Japanese Patent Application Laid-Open Nos. 5-172011 and 8-218915 are known.

In general, in an internal combustion engine equipped with such a device, in addition to a normal fuel supply path, a canister connected to a fuel tank via a vapor passage, and a purge connecting the canister to an intake passage of the engine. A passage, a purge control valve for opening and closing the purge passage, and the like are provided. In addition to the air-fuel ratio control of the air-fuel mixture supplied to the combustion chamber of the engine, a purge control based on the opening and closing of the purge control valve is performed by an electronic control unit that performs overall control of each part of the engine. In order to execute such controls, the electronic control unit includes various sensors for detecting the operation state of the internal combustion engine, such as an intake pressure sensor for detecting the magnitude of the pressure (intake pressure) in the surge tank, an engine speed, and the like. A rotation speed sensor or the like for detecting the number is connected. The detection signals from these sensors are appropriately taken into the electronic control unit.

[0004] With this configuration, the evaporated fuel generated in the fuel tank can be adsorbed by the canister, and the adsorbed fuel can be discharged (purged) into the intake passage as purge gas. The purge gas discharged into the intake passage is introduced into the combustion chamber of the engine together with the intake air.

On the other hand, in the air-fuel ratio control, the weight ratio of the intake air amount to the fuel injection amount, that is, the air-fuel ratio (A /
F) is kept close to the stoichiometric air-fuel ratio.
Further, while the purge is being performed by the purge control, the air-fuel ratio control is performed in such a manner that the fuel amount of the purge gas estimated and calculated by the electronic control unit is subtracted from the fuel injection amount injected from the fuel injection valve. Have been done.

Here, with reference to FIGS. 4 and 5, a description will be given of the purge control performed in the conventional apparatus, particularly control during idling operation of the engine. FIG. 4 is a flowchart showing a start procedure (start condition) of the purge control. FIG. 5 is a time chart showing an execution mode of the control corresponding to changes in the engine speed and the fuel injection time of the fuel injection valve.

In this control, first, as shown in FIG. 4, when the purge is turned off, a sufficient fuel injection including the invalid injection time of the fuel injection valve after the correction by the purge control is ensured. It is determined whether or not the predetermined time is equal to or longer than TAUH (step S110). Specifically, the injection time is obtained by subtracting the injection time corresponding to the fuel amount of the purge gas calculated by the electronic control unit from the injection time TAU0 of the fuel injection valve at the time of purging “off”, and TAU0 × (1- FPG). Here, FPG is a coefficient for subtracting the fuel amount from the injection amount from the fuel injection valve at the start of the purge.

If it is determined that the conditional expression of step S110 is not satisfied (step 110: NO), purging is not permitted and if it is determined that the conditional expression of step S110 is satisfied (step 110: YES). Is permitted (step S120).

According to the execution conditions of the purge control, as shown in FIGS. 5B and 5C, at time t1.
When the injection time TAU0 × (1−FPG) after the correction by the purge control becomes equal to or longer than the predetermined time TAUH at the time of the purge “off” after 1 (time t in FIG. 5).
At 12), the purge permission condition is satisfied and the purge is turned on, and the purge control valve is opened. Thereafter, when the injection time TAU0 × (1-FPG) becomes equal to or less than a predetermined time TAUL shorter than the predetermined time TAUH (time t13 in FIG. 5), the purge prohibition condition is satisfied and the purge is turned off. The purge control valve is closed.

The injection time TAU0 × (1-FP)
G) changes substantially corresponding to the fluctuation of the engine rotational speed NE as shown in FIG. More specifically, the change is opposite to the increase / decrease of the engine speed NE with respect to the idle target speed N. That is, when the engine rotational speed NE increases (decreases) with respect to the idle target rotational speed N, the injection time TAU0 × (1-FPG) decreases (increases). This is for the following reason.

As described above, the fuel injection amount is adjusted in accordance with the intake air amount introduced into the combustion chamber by the air-fuel ratio control even during the idle rotation. In general, the pressure loss of the intake air due to the throttle valve in the intake passage (fully closed in an engine having a bypass passage for idle speed control (ISC)) and the pumping action of the piston in the combustion chamber,
As the engine speed decreases, the amount of intake air per cycle increases. Therefore, when the air-fuel ratio control is also used, the fuel injection amount also increases, and the fuel injection time increases. On the other hand, when the engine speed increases, the amount of intake air per cycle decreases. For this reason, the fuel injection amount also decreases, and the fuel injection time decreases.

[0012]

As described above, by executing the purge control under the above conditions and modes, it is possible to use the purge control together with the air-fuel ratio control even during the idle operation of the engine.

By the way, when a load is temporarily applied to the engine, for example, when a light of a vehicle on which the engine is mounted is turned on or when a power steering is operated, “λ” in FIG. A temporary rotation undershoot as shown will occur. Therefore, when the above-described air-fuel ratio control is performed, the injection time of the fuel injection valve is temporarily increased corresponding to the rotation undershoot λ, and shortly thereafter, the injection time is shortened. And in this case,
Even in the purge control in which the execution condition is controlled in the mode shown in FIG. 4, the purge start condition is temporarily satisfied and the purge is turned “ON” as the injection time becomes longer. Soon after the purge prohibition condition is satisfied, the purge is turned off. However, since the fuel amount of the purge gas is the estimated value as described above, the switching of the purge from “on” to “off” and the switching from “off” to “on” are performed within a short period of time. In addition, problems such as instability of the air-fuel ratio and deterioration of drivability arise.

[0014] Such a problem occurs not only when the engine is idling, but also when the vehicle is decelerated (particularly when returning from a fuel cut). The present invention has been made in view of such circumstances, and its purpose is to
An object of the present invention is to provide a fuel vapor purge control device for an internal combustion engine that can suppress instability of the air-fuel ratio and reduction in drivability due to a temporary decrease in engine speed.

[0015]

The means for achieving the above object and the effects thereof will be described below. The invention according to claim 1 includes an evaporative fuel processing mechanism that adsorbs the evaporative fuel generated in the fuel tank to the canister and purges the adsorbed evaporative fuel together with air into an intake system of the internal combustion engine. In a fuel vapor purge control device for an internal combustion engine that controls whether or not to perform fuel purging in accordance with the operation state of the internal combustion engine, the rotation speed of the internal combustion engine is monitored, and the rotation speed is higher than a target constant speed rotation speed. The gist of the present invention is to prohibit the execution of the purge when the temperature is lower than a predetermined value.

According to the above configuration, even if a temporary rotation undershoot of the engine speed occurs, it is possible to prevent the switching of the purge from "on" and "off" from being repeated within a short period of time. As a result, it is possible to prevent the air-fuel ratio from becoming unstable or the drivability from being reduced.

According to a second aspect of the present invention, in the fuel vapor purge control device for an internal combustion engine according to the first aspect, the target constant speed is a target idle speed of the internal combustion engine. Make a summary.

Normally, the purge amount is controlled at a fixed ratio to the intake air amount. However, in the case of a light load such as during idling operation, the remaining fuel amount after subtracting the fuel amount to be purged is injected. When an attempt is made to inject from the valve, the influence of the rotational undershoot becomes more remarkable because the absolute value is small.

In this respect, according to the above configuration, the execution of the purge at that time is prohibited with respect to the temporary rotation undershoot from the target idle rotation speed. As for stabilization, this can be effectively suppressed.

According to a third aspect of the present invention, in the fuel vapor purge control apparatus for an internal combustion engine according to the first or second aspect, after the prohibition condition of the execution of the purge is canceled, the purging by the fuel injection valve of the internal combustion engine is performed. Means for permitting execution of the purging based on a difference between the assumed fuel injection amount and the estimated fuel amount to be purged being equal to or more than a predetermined value capable of securing sufficient fuel injection by the fuel injection valve. That is the gist.

According to the above configuration, the injection amount of the fuel injection valve after the correction by the purge control, that is, the difference between the fuel injection amount assuming no purge by the injection valve and the estimated fuel amount to be purged is determined by the invalid injection time. The purge is permitted when the pressure becomes equal to or higher than a predetermined value that ensures a sufficient fuel injection. For this reason, it becomes possible to preferably suppress the air-fuel ratio from becoming unstable.

According to a fourth aspect of the present invention, in the fuel vapor purge control device for an internal combustion engine according to the third aspect, after the execution of the purge is permitted, the fuel injection is performed on the assumption that there is no purge by the fuel injection valve of the internal combustion engine. The system further comprises means for stopping the execution of the purge based on a difference between the amount of fuel and the estimated amount of fuel to be purged being close to a minimum value of the amount of fuel injected by the fuel injection valve. And

According to the above construction, the fuel injection amount after the correction by the purge control, that is, the difference between the fuel injection amount assuming no purging by the same injection valve and the estimated fuel amount to be purged is determined by the fuel injection valve. Purging is performed until the fuel injection amount becomes close to the minimum value of the injection fuel amount that can be injected. Therefore, a long purge permission period can be ensured.

According to a fifth aspect of the present invention, there is provided an evaporative fuel processing mechanism for adsorbing the evaporative fuel generated in the fuel tank to the canister and purging the adsorbed evaporative fuel together with air into the intake system of the internal combustion engine. In the fuel vapor purge control device for an internal combustion engine, which controls whether or not the purge of the evaporated fuel is performed according to the operation state of the internal combustion engine, a predetermined value is subtracted from a target constant speed rotation speed of the internal combustion engine. A predetermined value that is higher than the determination value and that the difference between the fuel injection amount assuming no purging by the fuel injection valve of the internal combustion engine and the estimated fuel amount to be purged can ensure sufficient fuel injection by the fuel injection valve The gist of the present invention is to permit execution of the purge based on the above.

According to the above configuration, it is only necessary to add a process for determining whether the rotation speed of the internal combustion engine is higher than a determination value obtained by subtracting a predetermined value from a target constant speed rotation speed to a program. The desired purge control can be performed without particularly changing the basic processing procedure. Moreover, the functions and effects of the first and third aspects of the present invention are similarly exhibited.

[0026]

1 to 3 show an embodiment of a fuel vapor purge control device for an internal combustion engine according to the present invention.

First, an outline of the fuel vapor purge control device according to the embodiment will be described with reference to FIG. As shown in FIG. 1, the internal combustion engine 10 has a fuel injection valve 12 for injecting fuel from a fuel tank 21 to a combustion chamber 11 thereof through a fuel supply path (not shown). A spark plug 13 for igniting an air-fuel mixture is provided. The combustion chamber 11 is connected to an intake passage 14 forming part of an intake system and an exhaust passage 15 forming part of an exhaust system. In the middle of the intake passage 14, the surge tank 1
A throttle valve (for example, an electronically controlled type) 17 for adjusting the amount of intake air is provided further upstream thereof.
Is provided.

On the other hand, the fuel vapor purge control device is provided with an evaporated fuel processing mechanism 30. The evaporative fuel processing mechanism 30 includes a canister 31 connected to the fuel tank 21 via a vapor passage 32,
A purge passage 33 connecting the surge tank 16 to the intake system, an air introduction passage 34 for introducing air into the canister 31, and a purge control valve 35 for opening and closing the purge passage 33 are provided.

Here, the fuel vapor generated in the fuel tank 21 is introduced into the canister 31 from the fuel tank 21 through the vapor passage 32, and is once adsorbed by the adsorbent provided therein. Then, when the purge control valve 35 is opened and the atmosphere is introduced into the canister 31 through the atmosphere introduction passage 34, the fuel adsorbed in the canister 31 is discharged as purge gas into the surge tank 16 through the purge passage 33. (Purge). The fuel contained in the purge gas is burned in the combustion chamber 11 together with the fuel injected from the fuel injection valve 12.
Further, the fuel amount of the purge gas purged into the intake system (surge tank 16) in this manner is adjusted based on the opening degree of the purge control valve 35. The purge control valve 35 is an electromagnetic valve whose opening is adjusted based on an electric signal. The opening of the purge control valve 35 is duty-controlled in response to a duty signal.

The purge control for the internal combustion engine 10 and the air-fuel ratio control for controlling the fuel injection amount by the fuel injection valve 12 are collectively performed by the electronic control unit 40. In order to execute such controls, the electronic control unit 40 is connected with various sensors that detect the operating state of the internal combustion engine 10 and the like, and appropriately receives detection signals from these sensors.

For example, the electronic control unit 40 is provided with an intake pressure sensor 51 for detecting the magnitude of the pressure (intake pressure) in the surge tank 16 and the oxygen concentration of the combustion gas (air mixture air) provided in the exhaust passage 15. Oxygen sensor 5 for detecting fuel ratio)
2. Rotation speed sensor 5 for detecting engine rotation speed
3. Detection signals from an accelerator sensor 54 and the like for detecting the amount of depression (accelerator opening) of an accelerator pedal (not shown) are input.

Each control such as purge control and air-fuel ratio control is executed by the electronic control unit 40 based on the operating state of the internal combustion engine 10 and the running state of the vehicle detected by the sensors 51 to 54 and the like. Also, the electronic control unit 40
Is provided with a memory 41 for storing a program and an operation map for executing such controls, various data calculated when the control is executed, and the like.

Here, the air-fuel ratio control will be briefly described. This air-fuel ratio control is based on the output of the oxygen sensor 52 so that the weight ratio of the intake air amount to the fuel injection amount, that is, the air-fuel ratio (A / F) is basically kept close to the stoichiometric air-fuel ratio. This is performed by feedback-controlling the fuel injection amount of the injection valve 12. While the purge is being performed by the purge control, the fuel injection amount is adjusted by subtracting the fuel amount of the purge gas from the fuel injection amount injected from the fuel injection valve 12. Generally, the adjustment of the fuel injection amount is performed by adjusting the valve opening time of the fuel injection valve 12. The fuel amount of the purge gas is estimated and calculated at predetermined time intervals by the electronic control unit 40 based on the learned concentration and the opening degree of the purge control valve 35. Then, based on the calculated fuel amount, the injection time required to inject the fuel amount from the fuel injection valve 12 is calculated as follows.

TAU0 × FPG (1) Here, TAU0 is the fuel injection time of the fuel injection valve 12 before adjustment by the purge control, and FPG is the injection time corresponding to the fuel amount of the purge gas at the start of the purge. This is a coefficient to be subtracted from the fuel injection time, and is a value calculated and calculated from the fuel amount of the purge gas and the intake air amount.

Next, the purge control executed by the fuel vapor purge control device of the present embodiment will be described with reference to FIGS. First, the purge control will be described in detail with reference to FIG.

In this purge control device, the fuel injection valve 12
Purge control is performed based on the fuel injection time.
More specifically, the determination is based on a permission determination value TAUH as a predetermined value that is one of the determination values of the purge permission condition and a prohibition determination value TAUL that is a determination value of the purge prohibition condition. The permission judgment value TAUH and the prohibition judgment value TAUL are set near the minimum time at which fuel actually starts to be injected after the valve element (not shown) in the fuel injection valve 12 is opened. It is set to a value slightly larger than the prohibition determination value TAUL. And basically purge "off"
At the time, the fuel injection valve 12 adjusted by the purge control
When the fuel injection time is equal to or greater than the permission determination value TAUH, the purge is permitted.
When the value becomes L or less, purging is prohibited. Here, the fuel injection time of the fuel injection valve 12 after the adjustment by the purge control is the injection time obtained by subtracting the amount of the purge gas fuel shown in the above formula (1) from the injection time TAU0, and the following formula (2)
It is represented as

TAU0 (1-FPG) (2) By setting the above judgment values TAUH and TAUL in this way, the purge "on" period is as long as possible and the purged gas is adsorbed in the canister 31. Allows more fuel to be purged.

In this embodiment, the purge permission condition is based on the engine rotation speed of the internal combustion engine 10, and a permission rotation speed at which execution of the purge is permitted is newly set. As shown in FIG. 3A, the permissible rotational speed is the idle target rotational speed N of the internal combustion engine 10.
It is a rotation speed in the vicinity, and a value (NA) obtained by subtracting a constant A, for example, 50 rpm from the idle target rotation speed N.
Is set as Then, when the engine speed NE becomes equal to or higher than the permission rotation speed (NA), one of the purge permission conditions is satisfied.

Next, a procedure for starting the purge control will be described with reference to FIG. A series of processes shown in the flowchart of FIG. 2 is executed by the electronic control unit 40 as an interrupt process at predetermined time intervals.

In this process, first, it is determined whether or not engine speed NE ≧ (idling target speed N−constant A) (3) is satisfied when the purge is “off” (step 3). S10).

Here, if it is determined that the expression (3) is not satisfied (step S10: NO), the purging is not started and the present processing routine is temporarily ended. on the other hand,
When it is determined that the expression (3) is satisfied (step S
10: YES), it is determined whether the following expression (4) is satisfied (step S20).

(Injection time TAU0 × (1−coefficient FPG)) ≧ permission determination value TAUH (4) Here, if it is determined that Expression (4) is not satisfied (step S20: NO), purge is performed. Is not started, the present processing routine is temporarily terminated, and purging is started only when it is determined that the expression (4) is satisfied (step S20: YES) (step S30).

As described above, in the purge control device according to the present embodiment, purging is not permitted unless both the expressions (3) and (4) are satisfied. That is, as shown in FIG. 3, in the purge “off” state (after time t1), the execution of the purge is not permitted unless at least the condition of the expression (3) is satisfied (period L1). Conventionally, the calculated fuel injection time (TAU0 (1-FPG)) is equal to the permission determination value TAUH.
In the period L2 after the time t2 described above, the purge “OFF” state is maintained.

According to the fuel vapor purge control apparatus of this embodiment in which the purge control is performed in the manner described in detail above, the following excellent effects can be obtained. (1) Even if a temporary rotational undershoot of the engine rotational speed NE occurs as indicated by “λ” in FIG. 3A or FIG. It can be prevented from being repeated in a while,
As a result, it is possible to suppress the air-fuel ratio from becoming unstable or the drivability from decreasing.

(2) The purge amount is controlled at a fixed ratio to the intake air amount. However, in the case of a light load such as during idling operation, the remaining fuel amount minus the purged fuel amount is calculated. Is attempted from the fuel injection valve, the influence of the rotational undershoot λ becomes more remarkable because the absolute value is small. In fact, by providing the purge permission condition of the above equation (4), it is possible to suitably suppress the air-fuel ratio from becoming unstable while securing a long purge permission period.

(3) Further, the desired purge control can be performed only by adding the processing relating to step S10 in FIG. 2, that is, without particularly changing the conventional basic processing procedure.

The configuration of the above embodiment can be changed as appropriate, for example, as follows. In the above embodiment, as shown in FIG. 2, purging is permitted when step S10 which is one of the purge start conditions is satisfied, and then step S20 which is the other of the same conditions is satisfied. Alternatively, the same control may be performed by changing the order of step S10 and step S20. Also according to this, it is possible to obtain the effect according to the above-described embodiment.

In the above embodiment, the value of the constant A for determining the permitted rotation speed is set to 50 rpm, but this value is arbitrary. Further, this may be a variable that changes according to the driving state of the vehicle. For example, this may be a variable that changes according to the shift position of the transmission of the vehicle. Further, it is not always necessary to set the permissible rotation speed near the idle target rotation speed N. In addition, the permission rotation speed can be arbitrarily set, for example, using the rotation speed after returning from the fuel cut at the time of vehicle deceleration as a guide. . What is essential is that the permissible rotation speed be a speed lower than the target constant speed by a predetermined value.

Also, in the above embodiment, the permission judgment value T
Although the AUH and the prohibition determination value TAUL are set in the vicinity of the minimum time at which the fuel actually starts to be injected after the valve element in the fuel injection valve 12 is opened, these values can also be set arbitrarily.

In the above embodiment, the throttle valve 1
Assuming that an electronic control type (electronic throttle) is used as 7, the idle speed control is performed through the opening control during idling operation.
The throttle valve 17 may be of a link type, and a bypass passage bypassing the link valve and an idle speed control valve (ISCV) may be separately provided.

[0051] Even in such a case, it is possible to obtain the functions and effects similar to those of the above embodiment.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of the configuration of an embodiment of a fuel vapor purge control device according to the present invention.

FIG. 2 is a flowchart showing a processing procedure when starting purge control in the embodiment.

FIG. 3 is a time chart showing a purge control mode of the embodiment.

FIG. 4 is a flowchart showing a processing procedure when starting purge control in a conventional fuel vapor purge control device.

FIG. 5 is a time chart showing a purge control mode of the conventional apparatus.

[Explanation of symbols]

21: fuel tank, 30: evaporated fuel processing mechanism, 31: canister, 32: vapor passage, 33: purge passage, 35
... Purge control valve, 40 ... Electronic control device, 51 ... Intake pressure sensor, 52 ... Oxygen sensor, 53 ... Rotation speed sensor, 54
... accelerator sensor.

Claims (5)

[Claims] An evaporative fuel processing mechanism is provided for adsorbing evaporative fuel generated in a fuel tank to a canister, purging the adsorbed evaporative fuel together with air into an intake system of an internal combustion engine, and purging the evaporative fuel. In the fuel vapor purge control device for the internal combustion engine, which controls the presence or absence of the internal combustion engine according to the operation state of the internal combustion engine, the rotational speed of the internal combustion engine is monitored, and when the rotational speed is lower than a target constant speed rotational speed by a predetermined value or more. A fuel vapor purge control device for an internal combustion engine, wherein execution of the purge is prohibited. 2. The fuel vapor purge control device for an internal combustion engine according to claim 1, wherein the target constant speed is a target idle speed of the internal combustion engine. 3. The fuel vapor purge control device for an internal combustion engine according to claim 1, wherein after the prohibition condition of the execution of the purge is released, the fuel injection amount assuming that no purge by the fuel injection valve of the internal combustion engine is performed, and An internal combustion engine further comprising: means for permitting execution of the purge based on a difference between the estimated amount of fuel to be purged and a predetermined value capable of ensuring sufficient fuel injection by the fuel injection valve. Fuel vapor purge control device. 4. The fuel vapor purge control device for an internal combustion engine according to claim 3, wherein after the purge execution is permitted, a fuel injection amount assuming no purging by a fuel injection valve of the internal combustion engine and the purge estimation are performed. Means for stopping the execution of the purge based on a difference between the fuel amount and a minimum value of the injected fuel amount that can be injected by the fuel injection valve. Purge control device. 5. An evaporative fuel processing mechanism for adsorbing evaporative fuel generated in a fuel tank to a canister, purging the adsorbed evaporative fuel together with air to an intake system of an internal combustion engine, and purging the evaporative fuel. In the fuel vapor purge control device for the internal combustion engine that controls the presence or absence of the internal combustion engine according to the operating state of the internal combustion engine, the rotation speed of the internal combustion engine is higher than a determination value obtained by subtracting a predetermined value from a target constant speed rotation speed, and Based on the fact that the difference between the fuel injection amount assuming no purging by the fuel injection valve of the internal combustion engine and the estimated fuel amount to be purged is equal to or greater than a predetermined value that can ensure sufficient fuel injection by the fuel injection valve. A fuel vapor purge control device for an internal combustion engine, wherein execution of the purge is permitted.