GB2090018A

GB2090018A - Automatic Control of Fuel Supply in an Internal Combustion Engine

Info

Publication number: GB2090018A
Application number: GB8135612A
Authority: GB
Original assignee: Mitsubishi Motors Corp
Current assignee: Mitsubishi Motors Corp
Priority date: 1980-11-26
Filing date: 1981-11-25
Publication date: 1982-06-30
Also published as: DE3146509A1; JPS5791339A; FR2494771A1

Abstract

A fuel feed system for an internal combustion engine is provided with a differentiation circuit 10 between a throttle valve sensor 9 and control means 5 so that the amount of fuel fed from electromagnetic valve 7 can be increased or decreased according to the opening or closing speed of the throttle valve 8, and thus a delicate control of the amount of fuel supplied is attainable. Preferably the injector valve 7 is situated upstream and in a wider part of the inlet duct 2 than the throttle valve 8. The overall control of fuel is by sensing air flow rate using a Karman vortex sensor. The sensor 9 may consist of a non-linear potentiometer. <IMAGE>

Description

SPECIFICATION Fuel Feed System for an Internal Combustion Engine This invention relates to a fuel feed system for an internal combustion engine using an electromagnetic valve capable of feeding fuel towards an intake passage and more particularly to a fuel feed system for an engine capable of electronically controlling the amount of fuel to be fed.

Heretofore, there has been proposed a fuel feed system for an engine wherein a measurement of the rate of intake of air is converted to an electric signal and the opening or closing of an electromagnetic valve is controlled by a pulse signal based on this electric signal to achieve electronic control of the amount of fuel to be fed. However, such a conventional system is still insufficient to provide high-accuracy control or to provide adequate reliability of the control mechanism, and a further improvement is required.

It is an object of the present invention to provide a fuel feed system for an engine wherein the amount of fuel to be fed is controlled electronically according to the state of operation of the engine in such a way as to provide improved delicacy of control and improved accuracy and reliability as compared with certain known systems.

According to the invention, there is provided a fuel feed system for an internal combustion engine, comprising an electromagnetic valve operable to feed fuel into an intake passage of the engine, control means capable of controlling the amount of fuel to be fed from said electromagnetic valve, a throttle valve opening sensor for detecting the degree of opening of a throttle valve mounted in said intake passage, and a differentiation circuit disposed between said throttle valve opening sensor and said control means for differentiating a signal provided from said throttle valve opening sensor and transmitting a differentiated signal to said control means to thereby increase of decrease the amount of fuel to be fed from said electromagnetic valve according to the opening or closing speed of said throttle valve.

An embodiment of the invention is described below with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a fuel feed system, for an internal combustion engine, embodying the present invention, Figure 2 is a diagrammatic sectional view illustrating the operation of the fuel feed system in the vicinity of an electromagnetic valve disposed in an intake passage, and Figures 3(a), 3(b) and 3(c) are waveform diagrams illustrating the operation of the system.

Referring to Figure 1, an air flow rate detecting device 3 is mounted in an intake passage 2 of an internal combustion engine 12 downstream of an air cleaner 1.

The airflow rate detecting device 3 is adapted to detect the frequency of Karman's vortex street produced in the air flowing through the intake passage 2, and on the basis of the detected frequency it provides an electrical analog signal having a frequency proportional to the rate at which air is drawn through the intake passage 2.

This electrical analog signal is subjected to analog-to-digital conversion in an analog/digital converter (hereinafter referred to as the "A/D converter") 4 and the digitized signal is input to a central processing unit (hereinafter referred to as the "CPU") 5 which constitutes a portion of a digital computer as control means.

From the CPU 5 there is output a pulse train signal which is synchronized with the cyclically varying electrical signal provided by the air flow rate detecting device 3, or with a signal obtained by dividing down, in frequency, said signal from device 3, so that one pulse of the pulse train is provided for every nth cycle of the signal from device 3, where n is an integer.

Alternatively, the pulse train signal may simply be produced at the same frequency as the signal from device 3, or at 1/n of said frequency. From a driver 6 connected to the CPU 5 there is output a driving pulse train signal in synchronism with the above pulse train signal.

In a portion of the intake passage 2 downstream of the air flow rate detecting device 3 and upstream of a branch portion of the same passage there is disposed an electromagnetic fuel injection valve 7 (hereinafter referred to as the "electromagnetic valve") for injecting fuel into the intake passage 2, the electromagnetic valve 7 being connected to the driver 6.

The electromagnetic valve 7 is adapted to open or close in synchronism with a driving pulse train signal provided from the driver 6; as a result, fuel is fed from the electromagnetic valve 7 at a rate proportional to the rate of flow of air through the intake passage 2.

Furthermore, downstream of the electromagnetic valve 7 in the intake passage 2 there is disposed a throttle valve 8, and associated therewith is a throttle valve opening sensor 9 for detecting the degree of opening of the throttle valve 8. The throttle valve opening sensor 9 comprises a variable resistor whose resistance value varies according to the degree of opening of the throttle valve 8, with one end of the variable resistor being connected to the ungrounded terminal of a power supply and the other end thereof connected to the grounded terminal of the power supply, whereby the throttle valve opening sensor 9 can provide a voltage signal S1 (see Figure 3(a)) corresponding to the degree of opening of the throttle valve 8.The output thus obtained from the throttle valve opening sensor 9 is input to a differentiation circuit 10 wherein it is differentiated with respect to time and circuit 10 provides at its output a differential signal S2 such as shown in Figure 3(b).

The differential signal S2 is subjected to analog-to-digital conversion in the A/D converter 4 and then is input to the CPU 5, wherein on the basis of the digitized differentiated signal there is performed a pulse width modulation for a pulse train signal to be output from the CPU 5.

During acceleration during which the throttle valve 8 is gradually opened, differentiated signal S2 becomes positive as is shown in the period 'a' in Figure 3(b), and therefore the CPU 5 lengthens the pulse width according to this positive differentiated signal as is shown in Figure 3(c), thus resulting in an increase in the amount of fuel injected by the electromagnetic valve 7 according to the opening speed of the throttle valve 8, and consequently the acceleration performance is improved.

On the other hand, during deceleration during which the throttle valve 8 gradually closes, the differentiated signal S2 becomes negative as is shown in the period 'b' in Figure 3(b), and when the differentiated signal S2 reaches a value below a predetermined negative value, namely, a value indicative of a closing speed faster than a predetermined valve closing speed, the CPU 5 shortens the pulse width by a predetermined width as is shown in Figure 3(c) whereby the reduction rate of the amount of fuel to be fed from the electromagnetic valve 7 can be held at a predetermined value, thus resulting in a saving in fuel consumption and smo--,th operation while simplifying the control for the reduction rate of the amount of fuel to be fed.

As indicated, by reducing the amount of fuel to be injected during deceleration during which the throttle valve 8 gradually closes, it is possible to attain not only the saving in fuel consumption but also a smooth operation, and the reason for this will be stated hereinunder.

In a bent portion 2a of the intake passage 2 formed downstream of the electromagnetic valve 7 a quantity of fuel is retained while the throttle opening is relatively large, and in the intake passage 2 wherein the electromagnetic valve 7 is disposed in such a way as shown in Figures 1 and 2, the portion of the intake passage 2 downstream of the electromagnetic valve 7 is formed narrower to dispose the throttle valve 8 so that if the throttle valve 8 is open to a certain degree, a quantity of fuel often adheres to a shoulder portion 2b of the intake passage 2 due to a reverse flow 11 (Figure 2).

In the former case, if the throttle valve 8 is closed suddenly without making the reduction rate control for the amount of fuel to be fed from the electromagnetic valve 7, the negative pressure within the intake passage 2 increases to that the fuel remaining downstream of throttle 8 will undergo reduced-pressure boiling, so that an enriched fuel/air mixture is fed temporarily to the internal combustion engine 12 and the engine output therefore falls more than necessary, thus causing excessive engine braking to be produced, while in the latter case, if the throttle valve 8 is closed suddenly without making the reduction rate control for the amount of fuel to be fed from the electromagnetic valve 7, the component of the reverse flow 11 decreases and at the same time the flow velocity near the throttle valve 8 increases along with a reduction in area of the flow cross-section, so that the fuel which has adhered to the shoulder portion 2b of the intake passage 2 is drawn into the internal combustion engine 12, and also in this case an enriched mixture is temporarily fed to the internal combustion engine 12 and the engine output falls more than necessary, thus again causing excessive engine braking.

Therefore, if the mount of fuel to be fed from the electromagnetic valve 7 is controlled so as to be reduced during a deceleration during which the throttle valve 8 gradually closes, the supply of an enriched fuel/air mixture to the internal combustion engine 12 based on the aforesaid residual fuel or adhering fuel ought to be prevented, and for this reason the amount of fuel to be fed during deceleration is reduced in the embodiment described, whereby not only a saving in fuel consumption is attainable but also smooth operation of the engine is obtained while ensuring an appropriate air/fuel ratio.

The fuel feed system described is constructed so that during acceleration during which the throttle valve 8 gradually opens, the pulse width of the driving pulse train signal to be delivered to the electromagnetic valve 7 is made longer according to the throttle valve opening speed, whereby the opening time per cycle of the electromagnetic valve 7 becomes longer and the amount of fuel fed is so much increased, and thus the acceleration performance is improved.

On the other hand, during deceleration during which the throttle valve 8 gradually closes, if the valve closing speed exceeds a predetermined value, the pulse width of the aforesaid driving pulse train signal is shortened by a predetermined value whereby the opening time of the electromagnetic valve 7 becomes shorter and the amount of fuel fed is so much decreased, so that the foregoing inconvenience caused by the entering of the foregoing residual or trapped fuel or adhering fuel into the internal combustion engine 12 is eliminated, thus permitting both a saving in fuel consumption and a smooth operation based on an appropriate air/fuel ratio.

While the degree of opening of the throttle valve 8 remains unchanged, the pulse width of the driving pulse train signal is chosen to have a suitable value shorter than the pulse width during acceleration and longer than the pulse width during deceleration.

In the hereinbefore described embodiment, a two-stage control is utilised, wherein when the closing speed of the throttle valve 8 during deceleration exceeds a predetermined value, the pulse width of the driving train signal is shortened by a predetermined value: but instead of making such a two-stage control the above pulse width may be shortened with a characteristic similar to that shown in Figure 3 (b) according to changes in negative differentiated signals provided from the differentiation circuit to thereby continuously control the reduction rate of the amount of fuel to be fed.

Moreover, the air flow rate detecting device 3 may be of a type which delivers an electrical pulse train signal having a frequency proportional to the amount of air drawn through the intake passage 2, and in this cas.e the electrical pulse train signal is input to the CPU 5 without passing through the A/D converter 4.

Additionally, the differentiation circuit may be of a type which differentiates a digital signal instead of differentiating an analog signal. In this case, the A/D converter can be omitted, and the function of this differentiation circuit can be performed in the CPU 5.

The differentiation circuit may be provided in two stages in tandem to detect opening and closing accelerations of the throttle valve 8 thereby increasing or decreasing the amount of fuel to be fed, and in this case the predictability of accelerative or decelerative driving is improved.

Furthermore, in the hereinbefore described embodiment the opening or closing of the electromagnetic valve is controlled with a driving pulse train which synchronises with or follows the frequency of an electric signal output of the air flow rate detecting device or a frequency obtained by dividing such frequency; but in place of such a way of control the opening or closing of the electromagnetic valve may be controlled with a driving pulse train which synchronizes with or follows an electric signal corresponding to the rotational speed of the engine or a frequency obtained by dividing such frequency.

By means of the fuel feed system described with reference to the drawings, it is possible to realise electronic fuel injection control of high accuracy and reliability capable of attaining a saving in fuel consumption.

Claims

1. A fuel feed system for an internal combustion engine, comprising an electromagnetic valve operable to feed fuel into an intake passage of the engine, control means capable of controlling the amount of fuel to be fed from said electromagnetic valve, a throttle valve opening sensor for detecting the degree of opening of a throttle valve mounted in said intake passage, and a differentiation circuit disposed between said throttle valve opening sensor and said control means for differentiating a signal provided from said throttle valve opening sensor and transmitting a differentiated signal to said control means to thereby increase or decrease the amount of fuel to be fed from said electromagnetic valve according to the opening or closing speed of said throttle valve.

2. A fuel feed system according to claim 1, wherein said electromagnetic valve is disposed in said intake passage upstream side of said throttle valve.

3. A fuel feed system according to Claim 1, wherein an air flow rate detecting means for measuring the rate of intake of air along said intake passage is disposed in said intake passage, and said electromagnetic valve is disposed in said intake passage downstream side of said air flow rate detecting means and upstream of said throttle valve.

4. A fuel feed system according to claim 1, wherein the portion of said intake passage downstream of the electromagnetic valve is narrower than the portion in which the electromagnetic valve is disposed.

5. A fuel feed system according to claim 1, wherein said control means performs pulse width modulation of a pulse train signal supplied therefrom to the electromagnetic valve, according to a signal provided from said differentiation circuit.

6. A fuel feed system according to claim 1, wherein said control means provides a pulse train signal which is synchronised with a cyclically variable electrical signal provided from said air flow rate detecting means, and at the same time it performs a pulse width modulation of said pulse train signal according to a signal provided from said differentiation circuit.

7. A fuel feed system according to claim 1, wherein said control means provides a pulse train signal which is synchronised with a signal obtained by dividing down, in frequency, a cyclically varying electric signal provided by said air flow rate detecting means, and at the same time it performs pulse width modulation of said pulse train signal according to a signal provided from said differdntiation circuit.

8. A fuel feed system according to claim 1, wherein said control means provides a pulse train signal at the same frequency as a cyclically varying electric signal provided by said air flow rate detecting means, and at the same time it performs a pulse width modulation of said pulse train signal according to a signal provided from said differentiation circuit.

9. A fuel feed system according to claim 1, wherein said control means provides a pulse train signal at a frequency which is a simple fraction of the frequency of an electric signal provided by said air flow rate detecting means, and at the same time it performs a pulse width modulation of said pulse train signal according to a signal provided from said differentiation circuit.

10. A fuel feed system according to claim 1, wherein when the output of said differentiation circuit reaches a value above a predetermined valve closing speed, said control means controls the rate of feeding of fuel from said electromagnetic valve by maintaining the rate of reduction of flow of fuel from said electromagnetic valve at a predetermined value.

11. A fuel feed system according to claim 1, wherein said throttle valve opening sensor comprises a variable resistor whose resistance value varies according to the degree of opening of said throttle valve.

12. A fuel feed system according to claim 1, wherein said differentiation circuit comprises an active circuit using an operational amplifier.

13. A fuel system for an internal combustion engine, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

14. Any novel feature or combination of features described herein.