JPH0137585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a fuel injection device for an engine.

(Prior art) Two fuel injection valves are arranged for each cylinder of an engine, and the amount of fuel injected from each fuel injection valve is controlled according to operating conditions such as engine load. Fuel is injected in the entire operating range, including the low intake air volume range, and fuel is injected from the second injection valve in the high intake air volume range, providing highly accurate fuel supply control from low load ranges to high load ranges. A fuel injection device that achieves this is known, for example, as seen in Japanese Utility Model Publication No. 57-50536.

In the above-mentioned fuel injection device, the injection valve is generally provided with an electromagnetic solenoid type, and there is a limit to the minimum pulse width that can respond, and below this pulse width, it is not possible to ensure the accuracy of controlling the fuel injection amount with respect to the pulse width. . Therefore, when attempting to inject a large amount of fuel under high load by supplying fuel from a single fuel injection valve, the maximum injection time is regulated by the engine speed, and the required amount cannot be injected within this time. In order to do so, the amount of injection per unit time must be increased by using an injector with a large injection capacity or by increasing the fuel pressure. When performing injection, the required injection time becomes shorter, and as described above, the control accuracy of the fuel supply amount decreases.

On the other hand, the fuel supply is divided between two injection valves, and in the high flow area, fuel is injected from both injection valves to reduce the maximum supply amount of each injection valve, and in the low flow area, the first injection The technique of the above-mentioned prior art is to supply fuel only from the valve in a certain amount of time to obtain injection control accuracy.

However, when injection is shared between multiple injection valves, it is difficult to obtain even better injection characteristics in the entire range if the fuel pressure in each injection valve is set constant. A switching shock may occur when the second injection valve starts injection, which may adversely affect drivability.

In other words, in the low injection amount range, when the fuel pressure is high, the time (pulse width) for injecting a predetermined amount (small amount) of fuel becomes shorter, reducing its controllability, so the injection time becomes longer when the fuel pressure is low. Excellent controllability. On the other hand, when shifting to the high injection region and starting injection from the second injector, if the fuel pressure is low, the scattering distance of the fuel injected into the intake passage is short, and there is a delay in the time until the fuel flows into the combustion chamber. When this occurs, engine output temporarily decreases due to the supply of a mixture with a lean air-fuel ratio, causing a shock to drivability.In this state, if the fuel pressure is high, the shock at the time of switching is reduced and the engine output is reduced. This promotes atomization of fuel and improves combustibility.

(Object of the Invention) In view of the above-mentioned circumstances, the present invention aims to simultaneously satisfy the demands for improving fuel supply accuracy and reducing shock during switching in fuel injection by the first and second injectors, thereby achieving good combustibility. The object of the present invention is to provide a fuel injection device for an engine that achieves the following.

(Structure of the Invention) The fuel injection device for an engine of the present invention includes a first injection valve that injects fuel in the entire operating range including a low intake air amount area, and a second injection valve that injects fuel in a high intake air amount area. A first fuel pressure adjusting means that adjusts the pressure of the fuel discharged from the fuel pump to a first fuel pressure and supplies the fuel to the first injection valve, and a second fuel pressure that adjusts the fuel pressure to a predetermined amount higher than the first fuel pressure. The present invention is characterized in that it is provided with a second fuel pressure adjusting means for supplying the fuel to the second injection valve.

(Effects of the Invention) According to the present invention, by lowering the fuel pressure of the first injector that injects fuel in the entire operating range including the low intake air amount range, even in the low intake air amount range where the fuel supply amount is small, the fuel pressure is lowered to a certain extent. You can get the fuel injection time,
This improves the accuracy of fuel supply control. In addition, in the high intake air amount region, fuel is injected from the second injection valve with high fuel pressure to promote fuel atomization, while when switching to inject fuel from the second injection valve in addition to the first injection valve. The scattering distance of the injected fuel is large, and the time it takes for the injected fuel to reach the combustion chamber is shortened, which improves fuel delay during switching and improves responsiveness, reducing switching shocks. It is something.

(Example) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram of an engine equipped with two intake ports. Two first and second intake ports 3 and 4 open to the combustion chamber 2 of each cylinder of the engine 1, and two 1st and 2nd
Exhaust ports 5 and 6 are open, respectively.

An intake passage 7 for supplying intake air is connected to the intake ports 3 and 4. This intake passage 7 has an air cleaner 8 at the upstream end, and an intake air amount detection means 9 (air flow meter) for detecting the intake air amount is installed downstream of this air cleaner 8, and downstream from this intake air amount detection means 9. The side intake passage 7 is
It is branched into a first intake passage 7a and a second intake passage 7b. The first intake passage 7a is connected to the first intake port 3 of each combustion chamber 2 via an expansion chamber 7c, while the second intake passage 7b is connected to the first intake port 3 of each combustion chamber 2 via an expansion chamber 7d. The two intake ports 4 are connected to each other.

A first throttle valve 10 for controlling the amount of intake air flowing through the first intake passage 7a is interposed at the inlet portion of the first intake passage 7a, and a first throttle valve 10 is provided at the entrance of the first intake passage 7a.
A second throttle valve 11 for controlling the amount of intake air flowing through the second intake passage 7b is interposed at the entrance of the intake passage 7b, and both throttle valves 10 and 11 are opened and closed in conjunction with throttle operation. be done. The first throttle valve 10 opens when the load is low and becomes fully open as the load increases, and the second throttle valve 11 begins to open when the opening of the first throttle valve 10 reaches or exceeds the set opening. As it rises, it becomes fully open.

In the first intake passage 7a, a first injection valve 12 that injects fuel in all operating ranges including the low intake air amount range is provided for each cylinder, and in the second intake passage 7b, a first injection valve 12 is provided for each cylinder. A second injection valve 13 that injects fuel in a high intake air amount region is provided for each cylinder. These first and second injection valves 12,
A fuel injection pulse is output to 13 as a fuel control signal from a control unit 14 (microcomputer), and a predetermined amount of fuel is injected according to the width of the injection pulse.

The control unit 14 receives the intake air amount signal from the intake air amount detecting means 9, and also receives the engine speed signal from the rotation speed sensor 15, and corresponds to both signals to determine the fuel injection amount and time (injection The number of times) is calculated to inject a fuel injection pulse having a predetermined pulse width at a predetermined time into each injector 1.
Output to 2 and 13.

The fuel pressure of the second injection valve 13 for the high flow range is set higher than the fuel pressure of the first injection valve 12 for the low flow range. That is, FIG. 2 shows a fuel system for the first injection valve 12 and the second injection valve 13, and the fuel in the fuel tank 16 is connected in parallel from a fuel pump 17 via a filter 18 to a fuel supply passage 19. The first injection valve 12 and the second
A throttle 20 is interposed between the first injection valve 12 and the second injection valve 13, so that the pressure on the second injection valve 13 side is supplied to the first injection valve 12. This allows the pressure to rise from the side. The pressure regulators 21 and 22 that adjust the injection pressure in accordance with the intake pressure adjust the pressure regulator for the second injection valve 13 from the set pressure of the pressure regulator 21 for the first injection valve 12. The set pressure of the regulator 22 is increased, and thereby the fuel pressure of the second injection valve 13 becomes higher than that of the first injection valve 12 by a predetermined value.

FIG. 3 is a flowchart for explaining the operation of the control unit 14. After the start, in step S1, the fuel injection amount corresponding to the operating condition is calculated, and the intake air amount detection means 9 calculates the fuel injection amount corresponding to the operating condition. Air amount Qa, rotation speed sensor 15
The fuel injection pulse width τ (injection time) is determined from the engine rotation speed N, constant K, correction coefficient α, etc.
Note that the correction coefficient α is used to correct for cold times, etc., and the additional correction value τo is used to determine whether fuel is actually injected even if the fuel injection pulse is output to the first or second injection valve 12, 13. This is to correct the rise time since it takes a certain amount of time for the start of the rise. Further, τa is the basic injection time taking cold correction etc. into consideration, and τb is the acceleration increase time.

Next, the set pulse width τv for starting fuel injection to the second injection valve 13 is read out (S2), and the step S1 is repeated.
It is determined whether the injection pulse width τa + τb calculated in is greater than or equal to this set pulse width τv (S3), and if this determination is
When NO (low intake air amount region), it is determined whether the asynchronous acceleration switch is on (S4), and when the asynchronous acceleration switch is on (YES) and the engine is in a large acceleration state, asynchronous injection is performed at step S5. When the asynchronous acceleration switch is off (NO), the injection pulse τp for the first injection valve 12 and the injection pulse τs for the second injection valve 13 are calculated without performing asynchronous injection (S6). In the low intake air amount region, the injection pulse τs for the second injector 13 is set to zero, and the step is performed only by the first injector 12 without injecting fuel from the second injector 13. The first injection valve 12 is driven to perform fuel injection using the control signal having the injection pulse width τp determined in S1 (S10).

On the other hand, if the judgment in step S3 is YES and the intake air volume is in the high intake air volume region, it is similarly determined whether the asynchronous acceleration switch is on (S7), and if the asynchronous acceleration switch is on (YES) and the intake air is in a high acceleration state, then While performing asynchronous injection in step S8,
When the asynchronous acceleration switch is off (NO), the injection pulse τp for the first injection valve 12 and the injection pulse τs for the second injection valve 13 are calculated (S9) and the control signal is Therefore, the first and second injection valves 12 and 13 are driven to perform fuel injection (S10). Note that in this example, the first injection valve 12
and the second injection valve 13 are set to inject the same amount (half each) of fuel.

In the above fuel injection, the output of injection pulses τp and τs when performing asynchronous injection in the high injection amount region is
The result will be as shown in the figure.

FIG. 5 shows a modified example, in which one intake port 3 and one exhaust port 5 are formed in each cylinder 2 of the engine 1, and one intake passage 7 is connected to the intake port 3. A first valve is connected to the intake passage 7 connected to each cylinder 2 from the expansion chamber 7c downstream of the throttle valve 10 on the downstream side close to the combustion chamber 2.
The injection valve 12 has a second injection valve 13 on the upstream side.
A fuel injection pulse is output to the first injection valve 12 and the second injection valve 13 by the same control unit 14 as in the previous example, and the injection amount and switching timing are controlled. is provided in the same manner as in the previous example, and the fuel pressure of the second injection valve 13 is set higher than the fuel pressure of the first injection valve 12.

In addition, in the above embodiment, FIGS. 1 and 5
As shown in the figure, the first injector 12 is relatively connected to the combustion chamber 2.
The first injector 12 is arranged in the downstream part of the intake passage 7 close to the first injector 12, so that the fuel injected from the first injector 12 is quickly supplied to the combustion chamber 2, thereby improving the responsiveness of the fuel to increases and decreases in the amount of intake air. This is what we do,
On the other hand, the second injection valve 13 is disposed in the intake passage 7 on the upstream side of the first injection valve 12 to improve mixing and atomization of the injected fuel and intake air, thereby promoting atomization. It is.

Further, the first throttle valve 10 that controls the amount of intake air flowing through the first intake passage 7a is connected to the first throttle valve 10 as shown in FIG.
In addition to intervening at the inlet of the intake passage 7a, the same control effect can be obtained by interposing the throttle valve at the intake passage 7 upstream of the second throttle valve 11.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an engine fuel injection system according to an embodiment of the present invention, Fig. 2 is a system diagram showing a fuel supply system to an injection valve, Fig. 3 is a flowchart of a control unit, and Fig. 4 FIG. 3 is an explanatory diagram showing an example of a fuel injection pulse output to an injection valve, and FIG. 5 is a schematic configuration diagram of a fuel injection device for an engine in a modified example. 1... Engine, 2... Combustion chamber, 3, 4... Intake port, 7, 7a, 7b... Intake passage, 10,
11... Throttle valve, 12... First injection valve, 13...
Second injection valve, 14...Control unit, 1
7... Fuel pump, 21, 22... Pressure regulator.

Claims (1)

[Claims] 1. In a fuel injection device for an engine equipped with a first injection valve that injects fuel in all operating ranges including a low intake air amount area, and a second injection valve that injects fuel in a high intake air amount area, the fuel is discharged from a fuel pump. a first fuel pressure adjusting means that adjusts the pressure of the fuel discharged from the fuel pump to a first fuel pressure and supplies it to the first injection valve; and a second fuel pressure that adjusts the fuel discharged from the fuel pump to a second fuel pressure that is higher than the first fuel pressure by a predetermined amount. 1. A fuel injection device for an engine, further comprising a second fuel pressure adjusting means for supplying the fuel to the second injection valve.