JPH0625550B2 - Fuel cut control device for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fuel cut control device for an internal combustion engine, and in particular,
The present invention relates to a fuel cut control device for an internal combustion engine that cuts fuel in a decelerating operation state of the engine and then increases the supplied fuel amount so that the engine does not stall when fuel supply is restarted.

[Conventional technology]

Conventionally, the basic fuel injection amount is determined by the engine load (intake pipe pressure or intake air amount per engine revolution) and the engine speed, and the basic fuel injection amount is determined using various correction factors such as intake air temperature and engine cooling water temperature. There is known a synchronous fuel injection device in which the fuel injection amount is obtained by correcting the fuel injection amount, the fuel injection valve is opened at every predetermined crank angle, and an amount of fuel corresponding to this fuel injection amount is injected in the engine intake stroke. In such a fuel injection device, from the viewpoint of improving fuel efficiency, a so-called fuel cut that stops synchronous injection during deceleration, that is, when the throttle valve is in the idle position (fully closed) and the engine speed is equal to or higher than the fuel injection cut speed (for example, 2500 rpm) Is being done. When the throttle valve is not in the idle position during fuel cut, or when the engine speed is below the fuel injection restart speed (for example, 1600 rpm) in the idle position, the fuel injection cut is stopped from the viewpoint of engine stall prevention. Then, the synchronous fuel injection is restarted.

However, at the time of fuel cut, the fuel adhering to the inner wall of the intake manifold evaporates, so the fuel injected at the time of restarting fuel injection adheres to the inner wall of the intake manifold, and the fuel supplied to the combustion chamber becomes less, resulting in less air-fuel ratio. However, if the engine speed drops rapidly, undershooting of the engine speed or engine stall occurs.

In order to solve this problem, when the amount of change in the engine speed within a predetermined time after the fuel cut is stopped is larger than a judgment value, a synchronous injection is performed (Japanese Patent Application Laid-Open No. Sho-2004-29138).
No. 60-75741) is known.

[Problems to be solved by the invention]

However, in the above method, since the synchronous increase is performed only by the magnitude of the judgment value of the change in the engine speed within the predetermined time after the fuel cut is stopped, the fuel cut time before restarting the fuel supply is very long. Since all the fuel on the inner wall of the intake manifold evaporates, the air-fuel ratio becomes over lean even if the synchronous increase is performed and the engine easily stalls. Conversely, if the fuel cut time is extremely short, Since the fuel still remains in the intake manifold, there is a problem that when the synchronous increase is performed, the air-fuel ratio becomes overrich and the engine easily stalls. And
These problems are particularly remarkable in a so-called single-point injection type internal combustion engine in which one fuel injection valve is provided on the upstream side of the throttle valve and the air-fuel mixture is introduced into the combustion chamber through a relatively long intake passage.

[Means for solving problems]

An object of the present invention is to solve the problems of the conventional fuel injection method for an internal combustion engine that performs fuel cut, and to ensure that the optimum synchronous fuel increase is always performed after the fuel supply is restarted regardless of the length of the fuel cut time. An object of the present invention is to provide an excellent fuel cut control device for an internal combustion engine, which can prevent the engine from stalling when the fuel supply is restarted.

The fuel cut control device for an internal combustion engine of the present invention that achieves the above object cuts fuel when the throttle valve is at the fully closed position and the engine speed is equal to or higher than the fuel injection cut speed, and the throttle valve is fully closed. A fuel cut control device for an internal combustion engine, which restarts fuel supply when the throttle valve is not closed, or when the throttle valve is at the fully closed position and the engine speed reaches a predetermined speed lower than the fuel injection cut speed, If the fuel cut time is long, consider that the fuel in the intake manifold has evaporated and decrease the judgment value of the change in the engine speed within the predetermined time after restarting the fuel supply to reduce the synchronous increase. To prevent over lean even if the engine speed change rate is small, and when the fuel cut time is short, consider that fuel still remains in the intake manifold. , Not be performed and the determination value is increased to the engine speed change rate synchronous increase of the engine speed changes in a predetermined time period after the fuel supply restart is not large to some extent so that to prevent over-rich,
The determination value is changed according to the fuel cut time.

[Action]

In the fuel cut control device for an internal combustion engine of the present invention, the fuel is cut when the throttle valve is in the fully closed position and the engine speed is equal to or higher than the fuel injection cut speed, and the throttle valve is in the fully closed position and the engine speed is When the number reaches a predetermined number of revolutions lower than the fuel injection cut number of revolutions, fuel supply is restarted,
At this time, according to the fuel cut time, that is, when the fuel cut time is long, the determination value of the engine speed change within a predetermined time after the fuel supply is restarted is reduced, and the synchronous increase is performed at an early timing, When the fuel cut time is short, the determination value of the change in the engine speed within the predetermined time after the restart of the fuel supply is increased, and the synchronous increase start timing is delayed.

Embodiments of the present invention will be described in detail below with reference to the drawings.

〔Example〕

Next, an embodiment of an internal combustion engine (engine) 1 to which the fuel cut control device for an internal combustion engine of the present invention is applied will be described with reference to FIG. This engine represents a single point injector engine.

The air cleaner 3 is connected to the throttle body via the intake passage 2.
Connected to 20. One fuel injection valve 7 is attached on the upstream side of the throttle body 20.
A throttle valve 21 is arranged on the downstream side of the valve to adjust the amount of the air-fuel mixture sucked into the combustion chamber of the engine in conjunction with an accelerator pedal (not shown). Attached to the throttle valve 21 is a throttle switch 22 which is turned on when the throttle valve 21 is in the idle position and turned off when the throttle valve 21 is opened apart from the idle position. A pressure sensor 14 that detects the intake pressure in the intake pipe is provided downstream of the throttle valve 21.

The throttle body 20 is connected to an intake manifold 9 having a branch pipe connected to each cylinder of the engine, and the intake manifold 9 is provided with an intake temperature sensor 13. A riser portion 23, which circulates engine cooling water and heats intake air, is provided on the upstream bottom 9a of the intake manifold 9.

A combustion chamber 26 is formed by the bottom surface of the piston 24 of the engine 1 and the inner wall of the cylinder 25, and the air-fuel mixture sucked through the intake valve 27 is ignited by the ignition plug 28. A water jacket 29 through which engine cooling water circulates is formed around the cylinder 25, and the cooling water temperature in the water jacket 29 is detected by a cooling water temperature sensor 15 attached to the cylinder block 30. .

The exhaust port (not shown) of the cylinder head 31 is connected to an exhaust manifold 8, 0 ₂ sensor 12 for detecting the residual oxygen concentration in the exhaust gas on the downstream side of the exhaust manifold 8 are provided. Further, the exhaust manifold 8 is connected to the exhaust passage 11 via a catalytic converter 18 filled with a three-way catalyst.

The spark plug 28 is the distributor 4 and the igniter 17.
It is connected to the control circuit 10 via.

Crank angle sensors 5 and 6 are connected to the distributor 4, and the crank angle sensor 6 is, for example, a crank angle sensor.
One pulse is output every 30 ° (30 ° CA), and the crank angle sensor 5 is, for example, in the case of a 6-cylinder engine, every one revolution of the distributor shaft, that is, every two revolutions of the engine (every 720 ° CA). One pulse is output at a reference position (eg, top dead center of a specific cylinder) to determine the cylinder of the engine.
Incidentally, 19 is a brake switch which is turned on during braking, and 16 is a vehicle speed sensor.

The control circuit 10 is configured as a microcomputer, for example, and includes a CPU 103, a ROM 104, a RAM 105, a backup RAM 106, an input / output interface (I / O) 108, an A /
It is configured to include a D converter 101 and a bus 107 such as a data bus or a control bus connecting these. I
/ O102 is a cylinder discrimination signal from the crank angle sensor 5,
Injection for controlling the fuel injection valve 7 while the engine speed signal from the crank angle sensor 6, the brake signal from the brake switch 19, the vehicle speed signal from the vehicle speed sensor 16 and the idle signal from the throttle switch 22 are input. A signal and an ignition signal for controlling the igniter 17 are output.

Down counter 108, flip-flop 109 and drive circuit
Reference numeral 110 is for driving and controlling the fuel injection valve 7. When the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and also set in the flip-flop 109. As a result,
The drive circuit 110 outputs an injection signal to the fuel injection valve 7. On the other hand, when the down counter 110 factors a clock signal (not shown) and finally its carry-out terminal becomes the "1" level, the flip-flop 109 is reset and the drive circuit 110 causes the fuel injection valve 7 to operate. The output of the injection signal is stopped. That is, the fuel injection valve 7 is opened to inject the fuel by the above-mentioned fuel injection amount TAU, and the fuel of the amount corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine 1.

Further, the intake pipe pressure signal from the pressure sensor 14, the water temperature signal from the intake temperature sensor 13, and the air-fuel ratio signal from the O ₂ sensor 12 are input to the A / D converter 101, and these signals are received in accordance with instructions from the CPU 108. The signals are sequentially converted into digital signals.
The RAM 105 stores in advance a control program, a fuel injection cut rotation speed, a fuel injection restart rotation speed, etc., which are shown in the following processing routine. This fuel injection restart speed is
When the engine cooling water temperature is low, the possibility of engine stall is high, so when the cooling water temperature is low (eg -25 ° c),
It is set to a high rotation speed (eg 2600 rpm) so that the rotation speed decreases as the cooling water temperature rises (eg 80 °).
It is set to 1200 rpm in C). Further, the fuel injection cut rotational speed is set to a rotational speed higher by a predetermined value (for example, 600 rpm) than the fuel injection restart rotational speed determined as described above. Further, since the negative acceleration applied to the vehicle is large during the operation of the braking device, the occupant feels little impact after restarting fuel injection. Therefore, in order to lengthen the fuel injection cut period without giving an unpleasant impact feeling to the occupant, the fuel injection restart speed during braking is set to, for example, 1000 rpm, the normal fuel injection restart speed is set to, for example, 1600 rpm, and these fuel injections are performed. The restart speed may be switched. That is, the fuel injection restart speed during braking may be lower than the normal fuel injection restart speed.

When the vehicle enters the acceleration state after the fuel injection is cut and the off signal is input from the throttle switch 22, the fuel injection is restarted regardless of the engine speed.

Next, the operation of the control circuit 10 in the engine 1 configured as described above will be described with reference to the flowcharts of FIGS.

FIG. 2 is a fuel injection amount routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 201, the basic injection amount TP is calculated. That is, the data of the intake air amount Q and the engine speed Ne are read from the RAM 105 and calculated by the following equation, TP ← KQ / Ne (where K is a constant). In step 202, it is determined whether or not the fuel increase flag ZF determined by the increase determination routine described later is "1". When ZF = "1" (YES), the process proceeds to step 203 to increase the injected fuel amount. Increase amount Z is a predetermined value, for example 3
ms, and when ZF = “0” (NO), the routine proceeds to step 204 to set the increase value Z to 0 so that the injected fuel amount is not increased.

Then, in step 205, the fuel injection amount TAU is calculated by TAU ← TP · FAF · α + β + Z. Where FAF is the air-fuel ratio correction coefficient,
α and β are other correction coefficients or correction amounts, and correspond to, for example, warm-up increase correction, intake air temperature correction, transient correction, power supply voltage correction, and the like. Next, at step 206, it is judged if the fuel cut flag FCF is "1", and FCF ≠
In the case of "1" (NO), it means that fuel cut is not required, so the routine proceeds to step 207, where the injection amount TAU is decreased by the counter 1
Set to 08, set flip-flop 109 to start fuel injection, and return. As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 1 is turned on by the carry-out of the down counter 108.
09 is reset and fuel injection ends.

Next, the fuel cut determination routine of FIG. 3 will be described. In the present invention, the fuel cut flag FCF is set to "1" in order to execute the fuel cut when the throttle valve is fully closed (YES in step 301) and the engine speed Ne is set.
When the fuel injection cut speed NFC is exceeded (step
Yes in 302). Also, when not performing fuel cut,
Or to stop the fuel cut and restart the fuel supply,
When the throttle valve is no longer fully closed (Step 301
NO), or the throttle valve is fully closed (step 301
YES) and when the engine speed Ne becomes equal to or higher than the fuel injection restart speed NFR (YES in step 303). When the throttle valve is fully closed and NFR <engine speed Ne <NFC (YES in step 301 and step
If NO in 302 and NO in step 303), the value of the fuel cut flag FCF which has become "1" in step 304 is held.

FIG. 4 shows a synchronous increase determination routine, which is performed, for example, every 32 ms. In step 401, the engine rotation speed Ne1 captured last time is subtracted from the engine rotation speed Ne1 captured this time to obtain a change amount ΔNe of the engine rotation speed within a predetermined time, and in step 402, the current engine rotation speed Ne1 is set to Neo. Prepare for calculation. Then, in step 403, the engine speed change amount ΔNe is smoothed and averaged by a known method.

After that, the determination value of the engine rotation speed change amount ΔNe for performing the synchronous increase is changed depending on the magnitude of the previous fuel cut time. That is, when the previous fuel cut time is long, the determination value of the change amount ΔNe of the engine speed for performing the synchronous increase is decreased to perform the synchronous increase even if ΔNe is small. When the previous fuel cut time is short, The determination value of the engine speed change amount ΔNe for performing the synchronous increase is increased so that the synchronous increase is not performed unless ΔNe is large to some extent. In this embodiment, as shown in step 404, the fuel cut time CFCON is judged for a predetermined time, for example, less than 2 seconds or 2
It is done in one step of s or more, and if CFCO <2 (YES)
Determines that the fuel cut time is short and proceeds to step 406 to increase the determination value of the engine rotation speed change amount ΔNe for performing the synchronous increase to 50 rpm. If CFCO ≧ 2 (NO)
Since the fuel cut time is long, the routine proceeds to step 405, where the determination value of the engine speed change amount ΔNe is reduced to 12 rpm. When the engine speed change amount ΔNe is larger than the determination value (YES in step 405 or Y in step 406).
ES) proceeds to step 408, where the value of the fuel increase flag ZF is set to "1" so that the synchronous increase is executed in the routine of FIG. 2, and when the engine speed change amount ΔNe is smaller than the determination value (step) NO at 405 or NO at step 406)
Advances to step 407 to set the value of the fuel increase flag ZF to "0" so that the synchronous increase is not performed in the routine of FIG.

It should be noted that in this embodiment, the change of the judgment value for performing the synchronous increase is set to 1
Although the determination value is changed in stages, the determination value may be changed in multiple stages according to the fuel cut time.

FIG. 5 is a routine for setting the fuel cut time CFCON used for the determination in step 404 of FIG. In this routine, when the throttle valve is fully closed (YES in step 501)
And fuel cut flag FAF = "1" (step 502)
If YES), proceed to step 503 only and fuel cut time CF
Increment the CON value by 1 and measure the fuel cut time. When the throttle valve is not fully closed (step 501
NO) in step 504, the fuel cut time CFCON is cleared. If the fuel cut state is NO in step 502, the fuel cut time CFCON is neither measured nor cleared.

As described above, in the fuel cut control apparatus for an internal combustion engine of the present invention, when the fuel supply is restarted after the fuel cut is executed, the determination value of the engine speed change amount ΔNe for performing the synchronous increase according to the fuel cut time is changed. To be done.

〔The invention's effect〕

As described above, according to the present invention, when the fuel supply is restarted after the fuel cut is executed, the determination value of the engine rotation speed change amount ΔNe for increasing the fuel amount is changed according to the fuel cut time. There is an effect that the optimum synchronous increase is always performed and the stall of the engine can be prevented when the fuel supply is restarted.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of a fuel cut control device for an internal combustion engine of the present invention, and FIGS. 2 to 5 are flow charts showing the operating procedure of the control circuit of FIG. 1 ... Engine, 2 ... Intake passage, 4 ... Distributor, 5,6 ... Crank angle sensor, 7 ... Fuel injection valve, 10 ... Control circuit, 12 ... O ₂ sensor, 14 ... Pressure sensor , 20 …… Throttle switch.

Claims (1)

[Claims] 1. The fuel is cut when the throttle valve (21) is in the fully closed position and the engine speed is equal to or higher than the fuel injection cut speed, and when the throttle valve is not fully closed or the throttle valve is closed. Is a fuel cut control device for an internal combustion engine that restarts fuel supply when the engine speed is a fully closed position and the engine speed reaches a predetermined engine speed lower than the fuel injection cut speed, and a time measuring means for measuring a fuel cut time. (Step 50
3), rotation change rate detection means for detecting the change rate of the engine speed after the fuel cut is stopped (step 401), and fuel increase means for increasing the injected fuel amount when the rotation change rate exceeds a judgment value. (Step 203), and a judgment value changing means for changing the judgment value in such a direction as to decrease the judgment value when the cutting time is long and increase the judgment value when the cutting time is short according to the fuel cut time ( Steps 405 and 406), and a fuel cut control device for an internal combustion engine comprising: