JPH05171990A - Fuel injection control method for engine with variable valve timing control mechanism - Google Patents

Abstract

PURPOSE:To prevent discharge of unburnt gas into an exhaust pipe due to intake air blow-by in all operating conditions. CONSTITUTION:A fuel injection valve 4 is provided in an intake pipe 2 of an engine 1, and a step motor for changing the opening time of an intake valve is provided to the engine 1. A control device 6 is synchronized with engine crank angle of rotation to perform fuel injection of the required amount, and performs variable valve timing control for changing the overlapping time of an intake valve and an exhaust valve of an engine cylinder, depending on the operating condition of the engine. When the overlapping time is long enough to produce blow-by from the intake. valve to the exhaust valve when asynchronous fuel injection is requested as a vehicle is accelerated, the control device does not perform the asynchronous fuel injection, adds the amount of fuel to be increased based on the asynchronous fuel injection request to the amount of synchronous fuel injection, and injects the total amount of fuel simultaneously. Thus, discharge of unburnt gas is prevented, and since the increased amount of fuel for the asynchronous fuel injection request is compensated, the accelerating performance is not reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control method for an engine with a variable valve timing (VVT) control mechanism.

[0002]

2. Description of the Related Art In recent years, variable valve timing control has been performed in order to improve engine output and reduce fuel consumption by changing the opening / closing timing of intake valves and exhaust valves of each cylinder of an engine in accordance with the load state of the engine.

In such timing control, if the overlap time in which the intake valve and the exhaust valve are simultaneously open becomes long, the intake air sucked into the combustion chamber through the intake valve reaches the exhaust pipe as it is through the exhaust valve. A so-called stairwell occurs. Therefore, when the fuel is injected into the intake pipe during such a period, the fuel also passes through the combustion chamber and reaches the exhaust pipe in an unburned state, resulting in damage to the exhaust gas purification catalyst and deterioration of emission.

Therefore, for example, JP-A-61-185628
In Japanese Patent Laid-Open No. 61-187543,
It has been proposed that fuel is injected after the exhaust valve is closed to prevent problems due to blow through.

[0005]

By the way, in order to improve the acceleration in electronic fuel injection, when the throttle valve is greatly depressed, in addition to the injection synchronized with the engine crank rotation angle in the steady state, , The required amount of fuel is asynchronously and immediately injected, and if this is performed immediately before or during the overlap operation, the above-mentioned problem due to blow-through may occur.

Therefore, the present invention solves such a problem, and provides a fuel injection control method of an encidin with a variable valve timing control mechanism, which does not cause a problem of blow-through of injected fuel even in any operating state of an internal combustion engine. The purpose is to

[0007]

The structure of the present invention will be described. A variable valve timing for changing the valve opening period or the valve opening timing of at least one of an intake valve and an exhaust valve of an engine according to an operating state of the engine. In an engine equipped with a control mechanism, a required amount of fuel is injected in synchronization with a crank rotation angle of the engine, and when an asynchronous fuel injection request is made in accordance with an operating state, the intake valve and the exhaust valve are simultaneously operated. When the open overlap period is long enough to cause blow-through to the intake valve, the asynchronous fuel injection is not performed.

[0008]

In this structure, the asynchronous fuel injection is stopped when the overlap time of the intake valve and the exhaust valve becomes long and there is a risk of blow-by. Therefore, a defect due to blow-by does not occur.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of an engine control system to which the method of the present invention is applied. A throttle valve 3 is provided at an upstream position in an intake pipe 2 of the engine 1, and an electromagnetic fuel injection valve 4 is provided in a manifold 22 that branches into each cylinder of the engine 1 downstream of a surge tank 21.

The engine 1 is provided with a step motor 5 for driving a cam shaft (not shown) for changing the valve opening timing of each cylinder intake valve, and the rotation of the step motor 5 and the fuel injection valve 4 are provided. Is controlled by the output of the I / O port 61 of the controller 6.

The oxygen sensor 7 is connected to the I / O port 61.
1, the throttle opening sensor 72, the intake air amount sensor 73, the engine rotation sensor 74, the cooling water temperature sensor 75, the intake air temperature sensor 76, and other signals are input to the control device 6
The microcomputer 62 controls the operation of the step motor 5 and the fuel injection valve 4 based on the signals of the above-mentioned sensors, as described later. Hereinafter, the microcomputer 62
The control procedure of is shown in FIGS.

FIG. 2 shows a variable valve timing control routine that is activated by interruption every 32 ms. In step 101, the throttle opening TA and the engine speed Ne are fetched, and the intake valve is selected from a map value determined in advance. The target advance position θT is determined (step 102).

In step 103, the target advance position θT and the actual advance position θR are compared. If they do not match, the step motor 5 is rotated one step to the advance side or the retard side according to the comparison result (step 104, 105, 10
7) Then, the actual advance position θR is counted up or down (steps 106 and 108).

FIG. 3 shows an asynchronous fuel injection control routine during vehicle acceleration, which is interrupted every 64 ms. Step 20
At 1, the throttle opening TA is taken in, and then it is confirmed whether the difference from the previous throttle opening TAo is larger than a predetermined value ΔTA. If it is larger, it is determined that there is an acceleration request, and the process proceeds to step 203 and thereafter. In step 203, the engine speed Ne, the intake air amount Q, and the actual advance position θR are fetched, and the pulse width T'of the asynchronous pulse is obtained from these values and the magnitude of (TA-TAo) (step 204).

In the following step 205, it is determined whether or not it is the blow-through area. The determination of this blow-through area is made, for example, in Japanese Patent Laid-Open No. 63-63.
In consideration of the fact that the overlap time of the intake valve and the exhaust valve is determined by the engine speed Ne and the intake air amount Q as shown in Japanese Patent Publication No. 297746, the areas Ne and Q indicating the blow-through area are prepared in advance in a map. And then refer to this.

If it is not determined in step 205 that the blow-through region is present, an asynchronous pulse is immediately output, the fuel injection valve 4 is opened for a time corresponding to the pulse width T ', and asynchronous fuel injection is performed ( Step 206). On the other hand, when it is determined that the blow-through area is not set, the asynchronous injection is not performed, the injection correction flag fA is set (step 207), and the current throttle opening TA is set to TAo (step 208).

FIG. 4 shows an injection amount calculation routine that is interrupted every 16 ms. In step 301, the intake air amount Q, the engine speed Ne, the cooling water temperature THW, and the intake air temperature THA are taken in, and the basic injection time TD corresponding to Q / Ne is calculated in step 302. Then, the signals of the THW, THA and the oxygen sensor 71 The effective injection time Ti is calculated by obtaining the correction coefficients K1, K2 and K3 based on
3).

In step 304, the injection correction flag fA is confirmed, and if it is set, the asynchronous injection pulse width T'calculated in step 204 of FIG. 3 is added to the effective injection time Ti calculated in step 303. In addition, the final effective injection time Ti is set (step 305).

FIG. 5 is an injection output routine that is started in synchronization with the crankshaft rotation angle, and is started at each predetermined angle (for example, the angular position where the exhaust valve is closed) after the top dead center TDC in each cylinder. In step 401, the effective injection time Ti is added with the invalid injection pulse width TV corresponding to the battery voltage to determine the pulse width Tout of the output pulse.

In step 402, an output pulse is applied to the fuel injection valve 4 of the cylinder in the intake stroke to open the fuel injection valve 4, and a predetermined amount of fuel is injected. In step 403, the state of the injection correction flag fA is determined, and if it is set, the counter K is incremented in step 404. When the counter K is counted up to a value equal to the number of cylinders (4 in this embodiment), the injection correction flag fA is reset (steps 405 and 406) and the counter K is reset (step 407).

In this way, in the blow-through area, the asynchronous injection is stopped and the unburned fuel is prevented from being discharged to the exhaust pipe. Since the fuel increase amount based on the asynchronous injection request is injected in addition to the synchronous injection amount, the vehicle acceleration performance is not diminished.

In the variable valve timing control of FIG. 2, the actual rotation angle of the step motor 5 may be fed back by a potentiometer or the like.

In step 305 of FIG. 4, the asynchronous pulse width T
Instead of adding ', the final effective injection time Ti may be obtained by multiplying the effective injection time Ti by a correction coefficient K4 according to (TA-TAo), for example.

Further, in order to compensate for insufficient atomization caused by delaying the asynchronous injection until the synchronous injection time, (T '+ α), which is obtained by adding an appropriate compensation time α to the pulse width T', is Ti.
It may be added to.

Further, when the deterioration of the vehicle acceleration performance is not so serious, the synchronous injection is not increased and
Alternatively, only the asynchronous injection may be stopped.

[0026]

As described above, according to the engine fuel injection control method of the present invention, it is possible to reliably prevent a problem that the increased fuel due to vehicle acceleration reaches the exhaust pipe while being unburned due to blow-by.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a control device to which a method of the present invention is applied.

FIG. 2 is a flowchart illustrating a control method.

FIG. 3 is a flowchart illustrating a control method.

FIG. 4 is a flowchart illustrating a control method.

FIG. 5 is a flowchart illustrating a control method.

[Explanation of symbols]

 1 engine 2 intake pipe 22 manifold 3 throttle valve 4 fuel injection valve 5 step motor 6 controller

Claims (2)

[Claims] 1. An engine provided with a variable valve timing control mechanism for changing a valve opening period or a valve opening timing of at least one of an intake valve and an exhaust valve of the engine according to an operating state of the engine, wherein the crank of the engine is provided. A required amount of fuel is injected in synchronism with the rotation angle, and when an asynchronous fuel injection request is made in accordance with the operating state, the overlap period in which the intake valve and the exhaust valve open simultaneously is from the intake valve to the exhaust valve. A fuel injection control method for an engine with a variable valve timing control mechanism, wherein the asynchronous fuel injection is not performed when it is long enough to cause blow-through. 2. An engine provided with a variable valve timing control mechanism for changing a valve opening period or a valve opening timing of at least one of an intake valve and an exhaust valve of the engine according to an operating state of the engine, wherein a crank of the engine is provided. A required amount of fuel is injected in synchronism with the rotation angle, and when an asynchronous fuel injection request is made in accordance with the operating state, the overlap period in which the intake valve and the exhaust valve open simultaneously is from the intake valve to the exhaust valve. If it is long enough to cause blow-through, the engine with variable valve timing control mechanism is characterized in that the asynchronous fuel injection is not performed, and the synchronous fuel injection amount is increased and corrected based on the asynchronous fuel injection request. Fuel injection control method.