JPS62237051A - Fuel cut control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To continually perform an optimum synchronous increase so as to prevent an engine stall, by changing a decision value of engine speed change in which fuel is increased in accordance with the time of a fuel cut when supply of the fuel is restarted. CONSTITUTION:In a control circuit 10, fuel is cut thereafter a throttle valve 21, detected by a throttle switch 22, is placed in the fully-closed position, further when an engine speed, detected by a crank angle sensor 6, decreases to a predetermined speed lower than the fuel injection-cut engine speed, supply of the fuel is restarted. Here the control circuit, which small decrease a decision value of engine speed change in a predetermined time after restarting of the fuel supply when the fuel is cut for a long time, performs a synchronous increase in the earlier timing. While the control circuit, which large increases the decision value of the engine speed change in the predetermined time after the restarting of the fuel supply when the fuel is cut for a short time, performs the synchronous increase delaying its start timing. In this way, air-fuel ratio can be prevented from being placed in overlean and overrich conditions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel cut control device for an internal combustion engine, and in particular,
A fuel cut system for internal combustion engines that cuts fuel when the engine is running at deceleration, and then increases the amount of fuel supplied to prevent the engine from stalling when the fuel supply is restarted? 111 device.

[Conventional technology]

Conventionally, the basic fuel injection amount is determined based on the engine load (intake pipe pressure or intake air amount per engine revolution) and engine speed, and the basic fuel injection amount is determined using various correction coefficients such as intake air temperature and engine cooling water temperature. A synchronous fuel injection device is known that corrects the amount of fuel to be injected, opens the fuel injection valve at every predetermined crank angle, and injects an amount of fuel corresponding to the amount of fuel in the engine intake stroke at every predetermined crank angle. In this fuel injection system, from the viewpoint of improving fuel efficiency, a so-called fuel cut is performed in which synchronous injection is stopped 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 carried out. Additionally, if the throttle valve is no longer in the idle position during fuel cut, or if it is in the idle position and the engine speed falls below the fuel injection restart speed (for example, 1600 rpm), the fuel injection cut will be stopped to prevent engine stalling. The system then restarts synchronous fuel injection.

However, when the fuel is cut, the fuel adhering to the inner wall of the intake manifold evaporates, so when fuel injection is restarted, the injected fuel adheres to the inner wall of the intake manifold, reducing the amount of fuel supplied to the combustion chamber, and reducing the air-fuel ratio. The engine becomes lean, resulting in a drop in output, and if the engine speed drops quickly, there is a problem that undershoot of the engine speed or engine stall occurs.

In order to solve this problem, a fuel injection method (Japanese Unexamined Patent Application Publication No. 1983-1995) is designed to synchronously increase the amount of engine rotation if the amount of change in the engine speed within a predetermined time after the fuel cut is stopped is greater than or equal to the determination value. 75741) is known.

[Problem that the invention aims to solve]

However, in the above-mentioned method, since the amount is increased synchronously only based on the magnitude of the change in engine speed within a predetermined time after the fuel cut is stopped, the fuel cut time before resuming fuel supply is very long. Since all the fuel on the inner wall of the intake manifold will evaporate, the air-fuel ratio will become over lean even if the fuel is increased synchronously, making it easy for the engine to stall.On the other hand, if the fuel cut time is very short, Since fuel still remains in the intake manifold, there is a problem in that when synchronous increase is performed, the air-fuel ratio becomes over-rich, making it easy for the engine to stall. and,
These problems are particularly noticeable in so-called single-point injection internal combustion engines, in which one fuel injection valve is provided upstream 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 a fuel cut, and to always perform an optimal synchronous increase after resuming fuel supply, 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 that can prevent the engine from stalling when fuel supply is restarted.

A fuel cut control device for an internal combustion engine according to the present invention that achieves the above object cuts fuel when the throttle valve is in the fully closed position and the engine speed is equal to or higher than the fuel injection cutoff speed, and A fuel cut control device for an internal combustion engine that resumes fuel supply when the valve is no longer fully closed, or when the throttle valve is in the fully closed position and the engine speed reaches a predetermined speed lower than the fuel injection cutoff speed. However, if the fuel cut time is long, take into account that the fuel in the intake manifold has evaporated, and reduce the judgment value for the change in engine speed within a predetermined time after restarting fuel supply. to prevent over-lean from occurring even if the rate of change in engine speed is small, and if the fuel cut time is short, the fuel supply is increased taking into account that there is still fuel left in the intake manifold. Depending on the fuel cut time, the judgment value for the change in engine speed within a predetermined period of time after restart is increased, and a synchronous increase is not performed until the rate of change in engine speed increases to a certain extent to prevent overlean. The invention is characterized in that the judgment value is changed.

[For production]

In the fuel cut control device for an internal combustion engine of the present invention, 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 cutoff speed, and when the throttle valve is in the fully closed position and the engine speed is When the number reaches a predetermined rotation speed lower than the fuel injection cut rotation speed, fuel supply is resumed,
At this time, depending on the fuel cut time, that is, if the fuel cut time is long, the judgment value of the change in engine speed within a predetermined time after restarting the fuel supply is made smaller, and the synchronous increase is performed at an earlier time. If the cut-off time is short, the determination value of the change in engine speed within a predetermined period of time after restarting fuel supply is increased, and the synchronous fuel increase start timing is delayed.

Embodiments of the present invention will be described in detail below using the drawings.

〔Example〕

Next, an embodiment of an internal combustion engine (engine) (2) 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 shows a single point injector type engine.

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

The throttle body 20 is connected to an intake manifold 9 having branch pipes connected to each cylinder of the engine, and the intake manifold 9 is provided with an intake temperature sensor 13.

A riser portion 23 is provided at the upstream bottom portion 9a of the intake manifold 9, through which engine cooling water is circulated to heat intake air.

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 in through the intake valve 27 is ignited by a spark plug 28. A water jacket 29 is formed around the cylinder 25 in which engine cooling water circulates, and the temperature of the cooling water inside the water jacket 29 is detected by a cooling water temperature sensor 15 attached to the cylinder block 30. .

An exhaust manifold 8 is connected to an exhaust boat (not shown) of the cylinder head 31, and on the downstream side of the exhaust manifold 82 is an 02 sensor 12 that detects the residual oxygen concentration in the exhaust gas.
is provided. Further, the exhaust manifold 8 is connected to the exhaust passage 11 via a catalytic converter 18 filled with a three-way catalyst.
It is connected to the.

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

Crank angle sensors 5 and 6 are connected to the distributor 4, and the crank angle sensor 6 outputs, for example, one pulse for every 30' crank angle (30° CA). In this case, one pulse is output at the reference position (e.g. top dead center of a specific cylinder) every time the distributor shaft rotates once, that is, every time the engine rotates twice (every 720° CA) to determine the cylinder of the engine. . Note that 19 is a brake switch that 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, and a RAM 105.
, bank-up RAM 106, input/output interface (
110) 108, A/D converter 101, and buses 10 such as data buses and control buses that connect these
It is composed of 7. A cylinder discrimination signal from the crank angle sensor 5, an engine speed signal from the crank angle sensor 6, a brake signal from the brake switch 19, a vehicle speed signal from the vehicle speed sensor 6, and an idle signal from the throttle switch 22 are input to l10102. At the same time, an injection signal for controlling the fuel injection valve 7 and an ignition signal for controlling the igniter 17 are output.

The down counter 108, flip-flop 109, and drive circuit 110 drive and control the fuel injection valve 7, and when the fuel injection ITAU is calculated in the routine described later, the fuel injection amount TAU is preset in the down counter 108 and It is also set in 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 coefficients a clock signal (not shown) and the carrier voltage terminal finally becomes 1" level, the flip-flop 109 is reset and the drive circuit 110 controls the injection of the fuel injection valve 7. The output of the signal is stopped.In other words, the fuel injection valve 7 opens and injects fuel by the above-mentioned fuel injection amount TAU,
An amount of fuel corresponding to 1 TAU of fuel injection is sent into the combustion chamber of the engine 1.

The A/D converter 101 also receives an intake pipe pressure signal from the pressure sensor 14, a water temperature signal from the intake air temperature sensor 13, and
□The air-fuel ratio signal from the sensor 12 is input, and the CPU 10
These signals are sequentially converted into digital signals in accordance with the instructions at 8. The RAM 105 stores in advance a control program shown in the following processing routine, a fuel injection cut rotation speed, a fuel injection restart rotation speed, and the like. This fuel injection restart rotation speed is determined when the engine cooling water temperature is low (for example, -25
°C), high rotational speed (e.g. 2600rpm+)
The rotation speed is set to decrease as the cooling water temperature increases (for example, 120 rpm at 80° C.).

Further, the fuel injection cut rotation speed is a predetermined value (for example, 600 rpm) from the fuel injection restart rotation speed determined as above.
It is set to high rotation speed. Since the negative acceleration applied to the vehicle is large while the brake system is in operation, the impact felt by the occupant after fuel injection is restarted is small. Therefore, in order to lengthen the fuel injection cut period without giving an unpleasant shock feeling to the occupants, the fuel injection restart rotation speed during braking is set to, for example, looOr
mra, and the normal fuel injection restart rotation speed is, for example, 160.
0 rpm, and these fuel injection restart rotation speeds may be switched. That is, the fuel injection restart rotation speed during braking may be lower than the normal fuel injection restart rotation speed.

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

Next, the operation of the control circuit 10 in the engine 1 configured as described above will be explained using the flowcharts shown in FIGS. 2 to 5.

FIG. 2 shows a fuel injection amount routine, which is executed at every predetermined crank angle, for example, 360° CA. Step 201
Now, the basic injection amount TP is calculated. That is, intake air 4]Q
, and the engine speed Ne are read from the RAM 105 and calculated using the following equation, TP=KQ/Ne (where K is a constant). In step 202, the fuel increase flag ZF determined in the fuel increase determination routine to be described later is set to "
1", and when ZF="1" (YES), proceed to step 203 and set the increase value Z to a predetermined value, for example, 3IllS, to increase the amount of injected fuel, and when ZF="0" If (No), the process proceeds to step 204 and the increase value Z is set to O so that the amount of injected fuel is not increased.

Then, in step 205, fuel is injected! ITAU, T
Calculate by AU←TP −FAF・α+β+Z. Here, 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 temperature correction, transient correction, power supply voltage correction, etc. Next, in step 206, it is determined whether the fuel cut flag FCF is "1" or not, and FCF≠"
If the answer is 1 (NO), there is no need to cut the fuel, so proceed to step 207 and set the injection 1TAU in the down counter 108 and flip-flop 109.
Set to start fuel injection and return. Note that, as described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier gate of the down counter 108, and the fuel injection ends.

Next, the fuel cut determination routine shown in FIG. 3 will be explained. In the present invention, the fuel cut flag FCF becomes "1" to execute the fuel cut when the throttle valve is fully closed (YES at step 301) and the engine speed Ne is equal to or higher than the fuel injection cut speed NFC. When it became (
(YES in step 302). In addition, when not performing a fuel cut, or when stopping a fuel cut and restarting fuel supply, the throttle valve is no longer fully closed (NO in step 301), or when the throttle valve is fully closed (step 301). 301 (YES) and herring rotation speed N
This is when e becomes equal to or higher than the fuel injection restart rotation speed NPR (YES in step 303). Then, when the throttle valve is fully closed and NFR<engine speed N e <NF
In the case of C (YES in step 301 and step 302
and NO in step 303), step 304
The value of the fuel cut flag FCF which became 1'' is held.

Figure 4 shows the synchronous increase determination routine, for example, 32m5
It is done every. In step 401, the engine rotation speed N obtained last time is calculated from the engine rotation speed Nel obtained this time.
The amount of change Δ in the engine speed within a predetermined time by subtracting eo
Ne is calculated, and in step 402, the current engine rotation speed N
Prepare for the next calculation by setting al to Neo. Then, in step 403, the amount of change ΔNe in the engine speed is smoothed and averaged using a well-known method.

Thereafter, the determination value of the amount of change ΔNe in the engine speed for synchronous fuel increase is changed depending on the magnitude of the previous fuel cut time. That is, when the previous fuel cut time is long, the judgment value of the change amount ΔNe in the engine rotation speed for which the synchronous fuel increase is performed is made small, and the synchronous fuel fuel increase is performed even if ΔNe is small, and when the previous fuel cut time is short, The determination value of the amount of change ΔNe in the engine rotational speed for performing a synchronous increase is increased so that the synchronous increase will not be performed unless ΔNe is large to a certain extent. In this embodiment, as shown in step 404, the fuel cut time CFCON is determined by a predetermined period of time, for example, in one step of less than 23 or above ZsE, and CFCO<
In the case of 2 (YES), it is determined that the fuel cut time is short, and the process proceeds to step 406, where the determination value of the amount of change ΔNe in the engine speed for synchronous fuel increase is increased to 5° rpm. If CFCO≧2 (NO), the fuel cut time is long, so the process proceeds to step 405, where the determination value of the engine speed change amount ΔNe is reduced to 12 rpm. If the amount of change ΔNe in the engine speed is larger than the determination value (
YES in step 405 or YES in step 406
), the process proceeds to step 40B, where the value of the fuel increase flag ZF is set to 1'' so that the synchronous fuel increase is executed in the routine of FIG. NO or step 406
(NO), proceed to step 407 and set the fuel increase flag ZF.
The value of is set to "O" to prevent synchronous increase in the amount in the routine shown in FIG.

Note that in this example, the judgment value for synchronous increase is changed by 1.
Although the determination value is changed in stages, the change in the determination value may be performed in multiple stages depending on the fuel cut time.

FIG. 5 shows a routine for setting the fuel capturing time CFCON used for the determination in step 404 of FIG.

In this routine, when the throttle valve is fully closed ('IEs'' in step 501) and the fuel cut flag FA is
Only when F="l" (YES at step 502), the process advances to step 503 and the value of the fuel cut time CFCON is set to 1.
Increment by 1 to measure the fuel cut time. When the throttle valve is not fully closed (NO at step 501), the process proceeds to step 504 and clears the fuel cut time CFCON, and when the fuel cut state is not set (No at step 502), the fuel cut time CFCON is neither measured nor cleared. Not done.

As described above, in the fuel cut control device for an internal combustion engine of the present invention, when fuel supply is restarted after a fuel cut is executed, the determination value of the amount of change ΔNe in the engine rotation speed is determined to increase the amount of fuel by the same amount according to the fuel cut time. is changed.

〔Effect of the invention〕

As explained above, according to the present invention, when the fuel supply is restarted after the fuel cut is executed, the determination value of the amount of change ΔNe in the engine speed for increasing the fuel quantity is changed according to the fuel cut time. This has the effect that the optimal synchronous fuel increase is always performed, and it is possible to prevent the engine from stalling when fuel supply is restarted.

[Brief explanation 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 according to the present invention, and FIGS. 2 to 5 are flowcharts showing the operating procedure of the control circuit shown in FIG. 1. 1... Engine, 2... Intake passage, 4... Distributor, 5, 6... Crank angle sensor, 7...
- Fuel injection valve, 10... Control circuit, 12... 0□ sensor, 14... Pressure sensor, 20... Throttle switch. Figure 2 Figure 3

Claims (1)

[Claims] 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 cutoff speed, and when the throttle valve is no longer fully closed, or when the throttle valve is fully closed, the fuel is cut. A fuel cut control device for a combustion engine that restarts fuel supply when the engine is in a closed position and the engine speed reaches a predetermined speed lower than the fuel injection cut speed, the device comprising: a time measuring means for measuring a fuel cut time; a rotation change rate detection means for detecting a rate of change in the engine rotation speed after the fuel cut is stopped; a fuel increase means for increasing the amount of injected fuel when the rotation change rate exceeds a determination value; A fuel cut control device for an internal combustion engine, comprising: a determination value changing means for changing the determination value according to the invention.