JPH0868351A - Fuel cut control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To increase an effect to improve fuel consumption by enlarging a fuel cut engine speed region during deceleration. CONSTITUTION: A control circuit 20 stops injection of fuel from a fuel injection valve 7 and conducts fuel cut when it is decided from an output signal from an idle switch 6 and an output signal from a crank rotation angle sensor 10 that a throttle valve 6 is fully closed and the number of revolutions of an engine exceeds a given value, and when the number of revolutions of an engine is reduced to a value lower than the given number of return revolutions, injection of fuel is restarted. Decision of whether the number of revolutions of an engine exceeds a given value is usually executed as a part of the main routine of a control circuit, and executed by an interruption routine at intervals of a crank rotation angle 30 deg. only during the stop of injection of fuel. This constitution reduces an answer delay in decision of fuel cut stop, whereby the number of return revolutions is set to a low value as an engine stall is prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cut control device for cutting fuel supply to an internal combustion engine during deceleration operation.

[0002]

2. Description of the Related Art During deceleration operation of an internal combustion engine, that is, when the throttle valve in the engine intake passage is fully closed and the engine speed is higher than a predetermined value, fuel supply to the engine is stopped by stopping fuel supply to the engine. Fuel cut control techniques for improvement are generally known. In such fuel cut control, if the engine speed drops below a predetermined value (return speed) during the fuel cut, fuel supply to the engine is restarted,
This prevents engine stall due to excessive reduction in engine speed.

In order to improve the fuel efficiency of the engine, it is desirable to set the return rotational speed for restarting the fuel supply as low as possible to expand the fuel cut rotational speed region. However, if the return rotational speed is set too low, the engine rotational speed will drop beyond the permissible range due to a response delay when the fuel supply is restarted, and engine stall will occur.

For this reason, conventionally, the return rotational speed for restarting the fuel supply must be set higher than the allowable minimum rotational speed of the engine in consideration of the response delay, and the return rotational speed is sufficiently high. Since it cannot be set low, there is a problem that the effect of improving the fuel efficiency of the engine due to the fuel cut cannot be sufficiently obtained. In order to solve the above-mentioned problems, Japanese Patent Application Laid-Open No. 58-25527 discloses that the engine speed falls below a predetermined return speed during fuel cut and that the engine speed falls below a predetermined reduction rate. When at least one of the above occurs, a fuel cut control method is proposed in which fuel supply to the engine is restarted.

When the speed of decrease in engine speed is large,
Since the engine speed drops significantly during the response delay from when the engine speed becomes equal to or lower than the return engine speed until the effect of restarting the fuel supply appears, the engine speed is increased before the effect of restarting the fuel supply appears. The engine speed may drop below the permissible engine speed and engine stall may occur. For example, when the air conditioner compressor operates during fuel cut, the decrease in engine speed becomes extremely large due to an increase in load. Conventionally, it is necessary to set the return rotation speed to a high value with a sufficient margin to prevent engine stall even when the engine rotation speed is greatly reduced, and the fuel cut rotation speed region cannot be set sufficiently wide. It was one of the causes.

According to the method disclosed in the above publication, when the compressor for an air conditioner operates during fuel cut and the engine speed rapidly decreases due to an increase in load, the engine speed is higher than the return speed. Even if there is, by restarting the fuel supply, it is not necessary to consider the margin in the case where the above-mentioned speed reduction rate is large, so it is possible to set the return speed somewhat low. This is possible and has the effect of expanding the fuel cut rotation speed range.

[0007]

In an electronically controlled internal combustion engine that performs fuel injection, ignition timing control, etc. using a microcomputer, the above fuel cut control is also executed by the microcomputer. In this case, the microcomputer executes a routine at every predetermined timing and determines whether the engine speed is equal to or higher than a predetermined set speed. Then, when deceleration of the engine is started in a state where the engine speed is higher than the set speed, the fuel supply to the engine is stopped, and
When it is determined that the engine speed has fallen below the set speed, fuel supply to the engine is restarted to perform the above fuel cut control.

Therefore, if the execution interval of the routine for determining whether or not the engine speed is higher than the set value is set to be short, it is more quickly determined that the engine speed is lower than the return speed during the fuel cut. Therefore, the above-mentioned response delay at the time of restarting the fuel supply can be shortened, and the return speed can be set to a low value near the allowable minimum speed.

Normally, the fuel cut control is executed as a part of the main routine of the control microcomputer. However, the main routine has a large number of steps and the execution is interrupted by various interrupt routines, so that the execution is once executed. It takes a relatively long time to execute the routine. Therefore, the interval at which the determination of whether the engine speed is higher than the set value is executed becomes long, and the response delay at the time of restarting the fuel supply cannot be sufficiently shortened. There is a problem that the return speed must be set high.

In order to solve this problem, for example, the determination of the engine speed is performed by an interrupt routine which is executed at regular time intervals or constant rotational angle of the engine crankshaft separately from the main routine. It is also possible to shorten the execution interval of the numerical judgment. For example, the main routine is generally executed every 20 to 40 ms, but if the rotation speed determination routine is executed at intervals of about several ms, the response delay can be greatly shortened.

However, in practice, if the interrupt routine is executed at regular intervals at extremely short intervals as described above, the load on the CPU (central processing unit) of the microcomputer is greatly increased and the main routine is executed. However, there is a problem that the execution interval of is longer than the allowable limit, which adversely affects other control of the engine. Further, when the above-described rotation speed determination is executed by the crank angle interruption routine executed at each relatively small crank rotation angle (for example, every 30 °), although the engine speed is low, the engine speed is high. Since the number of interrupts increases during operation, there arises a problem that the CPU load increases as described above.

According to the control method described in Japanese Patent Laid-Open No. 58-25527, although the margin for a rapid decrease in rotation speed due to the operation of the air conditioner compressor can be reduced when setting the return rotation speed, the engine rotation speed is reduced. The execution interval for determining whether the number of revolutions is greater than or equal to the return speed has not been shortened,
The response delay cannot be shortened. Therefore, in the method of the above publication, it is still necessary to set the return rotational speed with a margin in consideration of the response delay with respect to the allowable minimum rotational speed, and there is a problem that the return rotational speed cannot be set sufficiently low. is there.

In view of the above problems, the present invention reduces the response delay when restarting the fuel supply when the engine speed is lower than the return speed, and sets the return speed sufficiently low while preventing engine stall. It is an object of the present invention to provide a fuel cut control device capable of achieving the above.

[0014]

According to the present invention, there is provided a fuel cut control device for stopping fuel supply to the engine during deceleration operation of the internal combustion engine, wherein the engine speed is predetermined at predetermined timings. The determination means for determining whether the engine speed is equal to or higher than the set speed, and the fuel supply to the engine is stopped when the engine is decelerating and the engine speed is determined to be the set speed or higher by the determination means Internal combustion engine comprising fuel cut-off means for stopping the fuel supply, and fuel cut-off means for restarting the fuel supply to the engine when the determination means determines that the engine speed has dropped below the set speed. In a fuel cut control device for an engine, during the fuel supply stop, a timing setting means for setting the execution interval of the rotation speed judgment by the judging means to be shorter than when the fuel supply stop is not executed. When the fuel cut control apparatus for an internal combustion engine having a are provided.

[0015]

The determining means determines whether or not the engine speed is equal to or higher than the set speed at every predetermined timing during the normal operation except when the fuel supply of the engine is stopped. The determination execution timing is set to an interval that does not affect other control of the engine. On the other hand, when the fuel supply to the engine is stopped, the timing setting means sets the determination execution interval by the determining means shorter than that during normal operation. As a result, the execution interval of the rotational speed determination by the determination means is shortened only during the fuel supply cut operation of the engine.

[0016]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration when the present invention is applied to a vehicle internal combustion engine. In FIG. 1, 1 is an internal combustion engine body, 2 is an intake passage, and 3 is an exhaust passage. The intake passage 2 is provided with a fuel injection valve 7 for injecting pressurized fuel into each cylinder intake port of the engine.

Further, the intake passage 2 is provided with a throttle valve 6 having an opening degree according to an operation of an accelerator pedal (not shown) by a driver. Reference numeral 8 in FIG. 1 denotes an idle switch that detects the opening of the throttle valve 6 and outputs a fully closed signal (LL signal) when the throttle valve 6 is in the fully closed state. In this embodiment, a crank rotation angle sensor 10 is provided on the crankshaft. The crank rotation angle sensor 10 is composed of a proximity sensor such as a magnetic pickup, and generates a pulse signal every time the teeth of the gear 11 attached to the crankshaft pass near the sensor 10. In the present embodiment, the gear 11 is provided with twelve teeth at equal intervals, and the crank rotation angle sensor 10 generates a pulse signal for each crank rotation angle of 30 °.

Reference numeral 20 in FIG. 1 denotes a control circuit of the engine 1. The control circuit 20 is a ROM (Read Only Memory)
22, RAM (random access memory) 23, CPU
(Central processing unit) 24, an input port 25, and an output port 26 are connected to each other by a bidirectional bus 21. The control circuit 20 performs basic control such as fuel injection control and ignition timing control of the engine 1, and also performs fuel cut control during engine deceleration as described later in this embodiment.

For these controls, the input port 25 of the control circuit 20 receives a voltage signal (not shown) indicating the engine intake air amount from the air flow meter 4 provided in the intake passage 2
In addition to being input via the / D converter, the LL signal from the idle switch 8 and the 30 ° pulse signal from the crank rotation angle sensor 10 are input. The output port 26 of the control circuit 20 is connected to the fuel injection valve 7 of each intake port via a drive circuit (not shown).
The fuel injection amount from is controlled.

The engine rotation speed is calculated by an interrupt routine executed by the control circuit 20 at each predetermined crank rotation angle. For example, in the present embodiment, the control circuit 20 inputs the 30 ° pulse signal from the rotation angle sensor 10 each time
That is, the pulse intervals of the past two output pulses of the crank rotation angle sensor 10 are calculated for each crank rotation angle of 30 °, and stored as T ₆₀ in a predetermined area of the RAM 23. That is, T ₆₀ is the time required for the crankshaft to rotate 60 ° and is updated every 30 ° rotation of the crankshaft (see FIG. 2). Similarly, the control circuit 20 calculates the pulse intervals of the past six output pulses of the rotation angle sensor 10 for each crank rotation angle of 180 ° and stores them as T ₁₈₀ in a predetermined area of the RAM 23. T ₁₈₀ is the time required for the crankshaft to rotate 180 °, and is updated every 180 ° rotation of the crankshaft.

The times T ₆₀ and T ₁₈₀ are used for various controls of the engine 1 such as fuel injection control and ignition timing control. For example, the control circuit 20 calculates the engine speed N from T ₆₀ in the fuel injection amount calculation routine executed by the interruption every 360 ° rotation of the crankshaft, and calculates the engine intake air amount Q detected by the air flow meter 4 as , This engine speed and intake air amount Q / N per engine revolution
Is calculated and the fuel injection amount TAU is set based on Q / N.

Next, the fuel cut control of the present invention will be described with reference to FIGS. FIG. 3 is a flowchart of the fuel cut control operation executed as part of the main routine of the control circuit 20. The main routine is T ₆₀ described above.
Since the execution is interrupted by various crank rotation angle interrupt routines such as the T ₁₈₀ calculation routine and the T ₁₈₀ calculation routine, the execution interval varies depending on the engine speed, but is approximately 20 ms.
From about 40 ms.

In FIG. 3, in step 301, the RAM
The latest value of T ₁₈₀ is read from a predetermined area of 23. Next, at steps 303 and 305, it is determined whether the fuel cut execution condition is satisfied. That is, in step 303, the LL from the idle switch 8
Whether or not the signal is on (whether or not the throttle valve 6 is fully closed) is determined, and in step 305, the value of T ₁₈₀ read in step 301 is the predetermined value N.
It is determined whether or not RT is ₁₈₀ or less. Here, NRT _{18 0}
Is the time required for the crankshaft to rotate 180 ° when the engine is rotating at the above-described return rotational speed (NRT). That is, in step 305, it is determined whether the engine speed is equal to or higher than the return speed.

When both steps 303 and 305 are satisfied, that is, when the throttle valve 6 is fully closed and the engine speed is equal to or higher than the return speed, the process proceeds to step 307 and the value of the fuel cut flag XFC is 1 Is set to.
When the value of the fuel cut flag XFC is set to 1, in the fuel injection control routine which is separately executed by the control circuit 20, the fuel injection is performed regardless of the value of the fuel injection amount TAU calculated in the above-mentioned fuel injection amount calculation routine. Fuel injection from the valve 7 is stopped.

If either of steps 303 and 305 is not satisfied, step 309 is executed and the value of the fuel cut flag XFC is reset to zero. As a result, even when the fuel cut is being performed, when the engine speed becomes lower than the return speed (step 305), the value of the fuel cut flag XFC is reset to zero, and the fuel injection amount calculation routine from the fuel injection valve 7 is performed. Fuel injection of the amount of fuel injection amount TAU calculated in step 3 is executed.

As described above, if the engine speed becomes lower than the preset return speed during the fuel cut by executing the main routine, the fuel cut is stopped,
Fuel supply to the engine is restarted. However, as described above, since the execution interval of the main routine is relatively long, about 20 ms to 40 ms, if the restart timing of fuel supply is determined only by the main routine, the response delay becomes large. Further, the engine speed determination in the main routine is based on T ₁₈₀ , and the engine speed data is updated only every 180 ° rotation of the crankshaft. Therefore, if the update timing of the rotation speed data deviates from the main routine execution timing, the determination itself becomes inaccurate. Therefore, in this embodiment, the crank rotation angle interrupt routine shown in FIG. 4 is separately executed to determine whether or not the fuel supply should be restarted.

FIG. 4 shows a fuel cut stop determination routine executed by the control circuit 20 by interruption at every crank rotation angle of 30 °. When the routine starts in FIG. 4, it is determined in step 401 whether the value of the flag XFC is set to 1. XFC is a fuel cut flag set in the routine of FIG. 3, and XFC =
1 means that fuel cut is currently being performed during deceleration.

If XFC ≠ 1 in step 401, that is, if fuel cut at the time of deceleration is not currently executed, steps 403 and thereafter are not executed and this routine is immediately terminated. If XFC = 1 in step 401, that is, if fuel cut is currently being performed during deceleration, step 4
In 03, the latest value of the time T ₆₀ is read from the RAM 23. In step 405, this T ₆₀ is the predetermined value NRT.
_It is determined whether it is greater than ₆₀ .

Here, NRT ₆₀ is T ₆₀ time when the engine crankshaft is rotating at the return rotational speed NRT.
That is, in step 405, it is determined whether or not the engine speed has decreased below the predetermined return / return speed NRT using the time T ₆₀ . If it is determined in step 405 that T ₆₀ > NRT ₆₀ , that is, if the engine speed is lower than the return speed NRT, step 407 is executed and the flag XFC is executed.
The value of is reset to zero. As a result, fuel injection from the fuel injection valve 7 is restarted. In addition, step 405
T ₆₀ ≦ NRT ₆₀ , that is, the engine speed is the return speed N
When it is determined that the value is equal to or more than RT, the value of the fuel cut flag XFC is not changed and the routine is ended as it is. As a result, the fuel cut being executed is continued.

When it is determined that the engine speed has fallen below the return speed by executing this routine as described above, the fuel supply is restarted without waiting for the determination in the main routine. Further, this routine is executed every 30 ° of crank rotation angle, and it is determined whether the engine rotation speed is lower than the return rotation speed by using the latest engine rotation speed data which is also updated every 30 ° of crank rotation angle. Therefore, an extremely short interval (for example, 5 ms when the engine speed is 1000 rpm)
It is possible to determine the current engine speed at a certain interval. Therefore, it is possible to significantly reduce the response delay when resuming fuel supply.

Also, in this routine, the operations after step 403 are executed only when the flag XFC is set to 1 in step 401, that is, during the fuel cut during deceleration. Crank rotation angle 3 as in this routine
If the interrupt routine for every 0 ° is constantly executed, the number of interrupts increases during high-speed operation of the engine and the interruption time of the main routine increases, which may deteriorate the response of other controls executed in the main routine. However, if the fuel cut during deceleration is not executed in this routine (XFC = 0 in step 401), the routine ends immediately from step 401, so the main routine is interrupted even during engine high speed operation. The time is kept to a minimum and is prevented from adversely affecting other controls.

FIG. 5 is a diagram comparing the response delays when the necessity of restarting the fuel supply is determined only by the main routine (that is, the case of the conventional fuel cut control) and the case of the fuel cut control of the present invention. is there. In FIG. 5, the dotted line shows the engine speed change in the conventional fuel cut control, and the solid line shows the engine speed change in the fuel cut control of the present invention.

Lines A, B, and C in the figure respectively show the case where the engine speed lowering speed is high, the case where it is medium, and the case where it is small. As can be seen from FIG. 5 and the solid line, in the present invention, the delay time (the time indicated by d in FIG. 5) from when the engine speed falls below the return speed to when fuel supply is restarted is the conventional case (FIG. 5). , D ′), the return speed NRT is set to the idle speed (NI in FIG. 5).
Even when set to the vicinity (indicated by DL), engine stall does not occur in all cases of A, B, and C.

On the other hand, as shown by the dotted line in FIG. 5, in the conventional control, if the return speed is set to the same value as in the case of the present invention, the engine speed drop when the fuel supply is restarted becomes large,
If the speed reduction speed is high (line A in FIG. 5), engine stall will occur. Therefore, conventionally, it is necessary to set the return rotation speed to a high value (for example, the rotation speed indicated by NRT 'in FIG. 5), and it is understood that the return rotation speed cannot be set sufficiently low.

[0035]

As described above, according to the present invention, during the fuel cut during deceleration, the fuel cut is performed at the execution interval for determining whether or not the engine speed has become lower than the return speed. By shortening it compared to when it is not used, it is possible to reduce the time delay when restarting the fuel supply and set the return speed sufficiently low. There is an effect that can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration when the present invention is applied to a vehicle internal combustion engine.

FIG. 2 is a diagram illustrating a detection interval of an engine speed.

FIG. 3 is a flowchart illustrating a part of a main routine executed by the control circuit of FIG.

FIG. 4 is a flowchart illustrating an interrupt routine executed every 30 ° of crankshaft rotation angle.

FIG. 5 is a diagram showing a difference between the response of the fuel cut control of the present invention and the response of the conventional fuel cut control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine body 7 ... Fuel injection valve 6 ... Throttle valve 8 ... Idle switch 10 ... Crank rotation angle sensor 20 ... Control circuit

Claims (1)

[Claims] 1. A fuel cut control device for stopping fuel supply to an engine during deceleration operation of an internal combustion engine, wherein whether or not the engine speed is equal to or higher than a predetermined set speed at every predetermined timing. A fuel cut means for stopping the fuel supply to the engine when the engine is decelerating and the engine speed is determined to be equal to or higher than the set speed by the judgment means, and the fuel supply stop In the fuel cut control device for an internal combustion engine, comprising: a fuel cut stop unit that restarts fuel supply to the engine when the engine speed is determined to be lower than a set speed by the determination unit. A fuel for an internal combustion engine comprising: a timing setting means for setting the execution interval of the rotation speed determination by the determination means shorter than the time when the fuel supply stop is not performed during the supply stop. Tsu door control device.