JPS5846669B2 - Internal combustion engine fuel supply system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel supply system for an internal combustion engine, and more particularly to a fuel supply system for an internal combustion engine that can appropriately control the amount of fuel supplied in a low intake air volume region.

In recent years, a fuel injection valve (fuel injector) has been developed as a fuel supply means in place of a carburetor, which controls the fuel supply amount electrically, that is, by setting the valve opening time corresponding to the width of one drive pulse. The nozzle area of the fuel injector is set so that the maximum required fuel supply amount is satisfied when the driving pulse width corresponding to the injector opening time is maximum, that is, the injector is continuously kept fully open. In the low intake air amount region, especially during idling, the aforementioned drive pulse width becomes extremely small.

This is because, in the example, the nozzle area of the fuel injection valve is constant, so in order to reduce the amount of fuel supplied, the width of the drive pulse corresponding to the valve opening time must be reduced.

However, since the accuracy of the opening time of an electromagnetic fuel injector is determined by the delay in the activation of the fuel injector relative to the drive voltage, the variation in the activation time becomes extremely large in the region where the drive pulse width is small, and therefore in the region of low intake air amount. It has been extremely difficult to maintain good accuracy of the reduced fuel supply in .

In particular, the number of fuel injectors is small compared to the number of cylinders, such as the so-called single point injection (SPI) system in which one or more fuel injectors are arranged at the gathering point of a plurality of branches in the intake manifold. Indeed, it is difficult to ensure the accuracy of the fuel supply amount in the low intake air amount region and also to ensure the maximum required fuel supply amount for the engine.

Further, in the SPI type, the number of opening and closing times per fuel injection valve is extremely large, so there is a problem in the durability of the fuel injection valve itself.

The present invention was devised to solve these problems, and in particular, a fuel supply device is constructed by a fixed venturi type carburetor without a slow system and a fuel injection valve installed downstream of the throttle valve. The configuration is such that fuel is supplied independently from the fuel injection valve in the low intake air amount region and from the carburetor in the high intake air amount region, and the fuel is injected at the connection between the low intake air amount region and the high intake air amount region. Fuel is supplied from both the valve and the carburetor, and the fuel supply amount of the fuel injection valve at this time is the intake air amount corresponding to the stoichiometric air-fuel ratio and the intake air amount detected during operation. control in proportion to the difference between

Furthermore, during a cold start, fuel is also supplied from the fuel injection valve in order to eliminate fuel shortage in the carburetor, which is matched to the high intake air amount region.

The present invention will be explained in detail below using examples according to the drawings.

In the internal combustion engine 1 shown in FIG. 1, the intake passage is composed of an intake pipe 4 that takes in air via an air cleaner 2 and an air flow meter 3, a carburetor 5, and an intake manifold 6.
The exhaust passage is composed of an exhaust manifold 7 and an exhaust pipe 9 having a three-way catalyst 8 in the middle.

Here, the bottom constituting wall of the gathering portion of the plurality of branches of the intake manifold 6 is a riser portion 10 adjacent to the exhaust manifold 7 for heat exchange.

The carburetor 5 is a fixed venturi type carburetor without a slow system, as shown in detail in FIG. is a choke valve, and 16 is a throttle valve.

A fuel injection valve 17 is arranged downstream of the throttle valve 16 of the carburetor 5 and upstream of the riser part 10.

The fuel injection valve 17 is supplied with fuel from a Tsuyuel tank 18 via a Tsuyuel pump 19, a Tsuyuel damper 20, and a Tsuyuel filter 21, and a Tsuyuel pipe 22. The pressure of the fuel in the Tsuyuel pipe 22 is regulated by a pressure regulator 23, and excess fuel is removed from a Tsuyuel return pipe 24. It is designed to be returned to Tsuyuel Tank 18.

This fuel injection valve 17 is connected to a control unit 26 by a conductor 25 in order to control its opening time by the width of an electrical drive pulse.

The control unit 26 includes the aforementioned air flow meter 3 that detects the amount of intake air, and a rotation speed sensor 41 that detects the engine speed. and an 02 sensor 27 that detects the 02 concentration in the exhaust gas are connected, and the amount of fuel supplied by the fuel injection valve 17 is controlled based on input signals from these sensors.

The control unit 26 also includes a water temperature sensor that detects the engine cooling water temperature for control during cold starting, etc., which will be described later, and a throttle switch (none of which are shown) that detects a specific opening of the throttle valve 16. A signal is also input.

In other words, the fuel supply means consists of two systems: the carburetor 5 and the fuel injection valve 17. Referring to FIG. 3, the predetermined intake air amount Q1 (
For example, in a low intake air amount region below (the vehicle speed is approximately 80 Ian/h, and the fuel supply from the carburetor 5 is set to start at this point), only the fuel injection valve 17 is used to control the stoichiometric air-fuel ratio (excess air ratio λ =1).

From the predetermined intake air amount Q1 at which fuel supply to the carburetor 5 begins,
Until the intake air amount Q3 when the amount of fuel supplied only by the carburetor 5 is λ-1 with respect to the intake air amount at that time, that is, the connection between the low intake air amount region and the high intake air amount region is as follows.
When using both the carburetor 5 and the fuel injection valve 17, the sum of the amount of fuel supplied by the carburetor 5 and the amount of fuel supplied by the fuel injection valve 17 for any amount of intake air between them is λ in relation to the amount of intake air. The amount of fuel supplied by the fuel injection valve 17 is decreased by feedback control from the 02 sensor 27 so that the amount becomes -1.

In a high intake air amount region where the intake air amount is 03 or more, fuel supply by the fuel injection valve 17 is stopped and fuel is supplied only by the carburetor 5, so that the output mixture ratio can be obtained.

Alternatively, it goes without saying that depending on the fuel flow characteristics of the carburetor 5, the correction may be made to achieve the output mixture ratio without stopping the fuel injection valve.

Such control of the fuel supply amount can be performed by controlling the fuel injection valve 1 by the control unit 26, if the fuel supply amount characteristic with respect to the intake air amount of the carburetor 5 is set as a unique characteristic.
This can be done by controlling the width of the drive pulses in No.7.

FIG. 4 shows a control unit 26 that performs such control.
The circuit is shown below.

The control unit 26 includes a comparator circuit 31 which receives the output signal of the 02 sensor 27 manually and compares it with a reference signal corresponding to λ=1, and a comparator circuit 31 which receives the output signal of the 02 sensor 27 manually and compares it with a reference signal corresponding to λ=1. a λ control circuit 32 which outputs a signal with a driving pulse width of 1000 Ω, and a subtraction circuit 33 to which the output signal of the air flow make 3 is input and which subtracts it from a reference signal corresponding to the intake air amount Q3; A multiplication circuit 34 which receives the output signal of the subtraction circuit 33 and multiplies it by a certain constant, and a rotation speed calculation circuit 40 which calculates the engine rotation speed based on the output signal of the multiplication circuit 34 and the signal from the rotation speed sensor 41. A pulse width calculation circuit 35 is provided, which receives an output signal from and outputs a signal with one drive pulse width corresponding to the output signal.

The control unit 26 also includes a discrimination circuit 36 to which the output signal of the airflow make 3 is input, and an output signal of the discrimination circuit 36 to which the output signal of the λ control circuit 32 and the pulse width calculation circuit 35 are input. A switching circuit 37 that selectively outputs at most one of the input signals from the λ control circuit 32 and the pulse width calculation circuit 35 according to the output signal of the discrimination circuit 36 that is input separately; and the output of the switching circuit 37. The fuel injection valve 17 includes a drive circuit 38 for the fuel injection valve 17 to which a signal is input.

To further explain in detail with reference to FIGS. 3 and 4, the intake air amount Q is determined by the discrimination circuit 36 to be
<Q < Q3, Qa≦Q (here, Q2 is set higher than Ql) is discriminated, and if Q≦Q2, the switching circuit 37 drives the λ control circuit 32 based on the output signal. Connect to circuit 38.

Therefore, in the low intake air amount region of Q≦Q1, the fuel injector 17
The fuel supply amount is feedback-controlled (λ-controlled) by the 02 sensor 27 with the 0-A line (λ-1) in FIG. 3 as the target value and the shaded area as the control range.

Fuel supply by the carburetor 5 is started in the region of Ql<Q<Q2, but λ control is continued even in this region, and the amount of fuel supplied by the carburetor 5 and the amount of fuel supplied by the fuel injection valve 17 are The width of the drive pulse to the fuel injection valve 17 is controlled so that the sum becomes λ-1.

If Q2<Q<Q3, the switching circuit 37 connects the pulse width calculation circuit 35 to the drive circuit 38.

Therefore, in this case, the subtraction circuit 33 calculates Q3Q, the multiplication circuit 34 multiplies it by a certain constant, and the pulse width calculation circuit 35 gives a drive pulse width proportional to Q3-Q. The driving pulse width is decreased as the value increases.

Here, the constant of the multiplication circuit 34 is such that the sum of the amount of fuel supplied by the carburetor 5 and the amount of fuel supplied by the fuel injection valve 17 is approximately λ=
1.

In the case of Q3≦Q, that is, in the high intake air amount region, the switching circuit 37 does not output either signal, and therefore the operation of the fuel injection valve 17 is stopped, so fuel is supplied only by the carburetor 5 according to its characteristics. be done.

Since the maximum required fuel supply amount for the engine can be secured by the carburetor 5 in this way, the fuel injection valve 17 can be set to a small capacity,
A desired fuel supply amount can be ensured with sufficient precision even when the fuel supply amount is reduced in a low intake air amount region.

In addition, in the above-mentioned λ control, since the fuel injection valve 17 is located downstream of the throttle valve 16, fuel adhesion to the throttle valve 16 and the wall upstream of the throttle valve 16 is avoided, resulting in good responsiveness and improved control accuracy. .

Next, the response to a cold start in this system will be explained with reference to FIG.

The air-fuel ratio during cranking during cold starting (lV = 1~
2) can be obtained by appropriately setting the opening degree of the choke valve 15 of the carburetor 5, as in the past. Specifically, the choke valve 15 is kept in a nearly fully closed state until complete explosion occurs. Set it to supply fuel to the carburetor 5.

However, due to the above-mentioned matching of the carburetor 5 in the high intake air amount region, it is difficult to obtain the desired air-fuel ratio using only the choke mechanism at the time of starting. The fuel injection valve 17 is operated to compensate for the shortage of fuel supply by the choke mechanism until the rotational speed increases to a certain extent due to complete explosion. The duty (ratio of pulse width to pulse period) is fixed to a certain value.

In the warm-up process after the complete explosion, the fuel injection valve 17 only supplies fuel and the duty of the drive pulse width is fixed so that the air-fuel ratio is at or slightly thinner than the stoichiometric air-fuel ratio.

Of course, the λ control by the 02 sensor 27 is cut off in these areas.

Thus, during the warm-up process, the air-fuel ratio is set by the choke mechanism as shown in FIG.

Then, when the cooling water temperature rises and is detected by the water temperature sensor, in this state the exhaust temperature has already risen and the 02 sensor 27 is activated, so λ control is started and the drive is started as described above. The amount of fuel supplied is controlled by changing the pulse width.

Also, in order to provide the output mixture ratio in the low rotation range,
The signal from the throttle switch detects that the throttle valve opening has exceeded a certain level and cuts the λ control.
D u at or near the upper limit of the λ control range in Figure 3
It is sufficient to fix ty.

In addition, in the example, the case of a fixed venturi type carburetor without a slow system was explained, but the present invention is applicable to a variable venturi type carburetor (so-called SU carburetor) or a variable stage type carburetor (in conjunction with an accelerator or negative pressure). Even if the vane member is operated by moving the vane member, it can be applied to cases where the slow system does not have a slow system or the slow system does not operate with substantially high precision.

As explained above, according to the present invention, the maximum fuel supply amount of the fuel injection valve can be reduced by ensuring the maximum required fuel supply amount of the engine with the carburetor. The drive pulse width during idling can be kept large, and the accuracy of fuel supply can be improved.

In addition, at the connection between the low intake air amount region and the high intake air amount region and during cold start, fuel is supplied from both the fuel injection valve and the carburetor, and the fuel supply amount can be appropriately controlled. The amount of fuel supplied can be maintained at an appropriate level over the entire operating range of the engine.

Moreover, since the fuel injection valve does not operate in the high intake air amount region, the number of times it opens and closes is reduced, and therefore its durability can be increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the device of the present invention, FIG. 2 is an enlarged sectional view of the carburetor of the same embodiment, and FIG. 3 is a fuel supply controlled in relation to the intake air amount according to the present invention. FIG. 4 is a block circuit diagram of the control unit of the same embodiment, and FIG. 5 is a diagram illustrating the response to a cold start. 1... Internal combustion engine, 3... Air flow make, 5... Carburetor, 16... Throttle valve, 17... Fuel injection valve , 26...control unit, 27...02 sensor, 33
・・・・・・Subtraction circuit, 34 ・・・Multiplication circuit, 3
5...Pulse width calculation circuit, 40...Rotation speed calculation circuit, 41...Rotation speed sensor.

Claims (1)

[Claims] 1. At least one fuel injection valve is provided downstream of the throttle valve of the carburetor, and a device for detecting the intake air amount of the engine is provided, and fuel injection is performed in a low intake air amount region according to the output signal of the device. The valve is operated and fuel is supplied only by this, and in the high intake air amount region, the fuel injection valve is stopped and fuel is supplied only by the carburetor, and the fuel is supplied only by the carburetor in the low intake air amount region and the high intake air amount region. At the connection part, fuel is supplied by both the fuel injection valve and the carburetor, and the fuel supply amount of the fuel injection valve at the connection part is such that the fuel supply amount of only the carburetor corresponds to the stoichiometric air-fuel ratio. 1. A fuel supply device for an internal combustion engine, characterized in that the fuel supply device for an internal combustion engine is controlled in proportion to the difference between an intake air amount and a detected intake air amount. 2. Claim 1, characterized in that the fuel supply amount of the fuel injection valve in a low intake air amount region is configured to be feedback-controlled to the stoichiometric air-fuel ratio by detecting the air-fuel ratio.
A fuel supply device for an internal combustion engine as described in 2. 3. The fuel supply system for an internal combustion engine according to claim 1 or 2, wherein the carburetor is a fixed venturi type carburetor without a slow system. 4 At least one fuel injection valve is provided downstream of the throttle valve of the carburetor, and a device is provided to detect the intake air amount of the engine, and the fuel injection valve is operated in the low intake air amount region according to the output signal of the device. In the high intake air amount region, the fuel injection valve is deactivated and fuel is supplied only by the carburetor, and in the connection between the low intake air amount region and the high intake air amount region, the fuel is supplied only by the carburetor. Fuel is supplied by both the injection valve and the carburetor, and the fuel supply amount of the fuel injection valve at the connection portion is detected as the intake air amount such that the fuel supply amount of only the carburetor corresponds to the stoichiometric air-fuel ratio. A fuel for an internal combustion engine, characterized in that the fuel is controlled in proportion to the difference between the intake air amount and the intake air amount, and the fuel is supplied from both a carburetor choke mechanism and a fuel injection valve from startup to warm-up. Feeding device. 5. Claim 4, characterized in that the fuel supply amount of the fuel injection valve in a low intake air amount region is configured to be feedback-controlled to the stoichiometric air-fuel ratio by detecting the air-fuel ratio.
A fuel supply device for an internal combustion engine as described in 2. 6. The fuel supply system for an internal combustion engine according to claim 4 or 5, wherein the carburetor is a fixed venturi type carburetor without a slow system.