GB2157853A

GB2157853A - Fuel injection system for a multi-cylinder engine

Info

Publication number: GB2157853A
Application number: GB08509823A
Authority: GB
Inventors: Kenji Mochizuki
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1984-04-17
Filing date: 1985-04-17
Publication date: 1985-10-30
Also published as: JPS60222537A; DE3513656A1; GB2157853B; GB8509823D0

Abstract

The cylinders of the engine are divided into two notional groups, and the control system is provided with an engine speed sensor, a throttle closed sensor, and a fuel cut off circuit responsive to a signal of the throttle sensor provided engine speed N is greater than n1 for producing a fuel cut off signal. A cylinder group selecting circuit responds to the fuel cut off signal by disabling fuel injectors in one of the groups of cylinders, and then disabling fuel injectors in the other group after a delay. When engine speed N is less than n2 fuel supply is resumed in the same two stage way. <IMAGE>

Description

SPECIFICATION Fuel injection system for a multi-cylinder engine The present invention relates to a fuel injection system for a multi-cylinder internal combustion engine in a motor vehicle, and more particularly to a system for interrupting the fuel supply during deceleration.

In order to improve fuel consumption and emission control, a system for cutting off fuel supplied to all cylinders at deceleration to idle the cylinders is known. In such a system, the fuel injectors are closed to stop the fuel supply when the vehicle is decelerated, and the fuel is resupplied when engine speed (RPM) decreases below a predetermined low speed in order to prevent stalling of the engine.

However, when the fuel is cut off, the torque of the engine quickly decreases, causing jerking of the vehicle, which in turn causes discomfort to the occupants.

In order to reduce such shocks, a system for gradually decreasing the quantity of injected fuel is proposed, for example in Japanese Patent Laid Open 54-76725. However, when air-fuel mixture is diluted by reducing the fuel supply during very light loads on the engine, such as when the vehicle decelerates, the combustion in the cylinders becomes insufficient, which causes a decrease in driveability of the vhicle and deterioration of the emission control.

In order to mitigate such disadvantages, a system for reducing the number of working cylinders by cutting off the fuel supply for respective fuel injectors in accordance with engine speed is proposed, for example in Japanese Patent Laid Open 54-148928 and 54-148929. However, the decrease of engine torque in such an engine is related to the magnitude of deceleration. Thus at large decelerations, the shock effect is hardly decreased, and on the other hand, during small decelerations, a plurality of shocks occur sequentially each time the cylinders are shut off.

Accordingly the present invention seeks to provide a fuel injection system which can reduce shocks caused by reduction of engine torque irrespective of the magnitude of deceleration of an engine.

In accordance with the present invention, the cylinders of the engine are divided into groups and the groups are operated in a stepwise fashion so as to gradually decrease the number of working cylinders.

According to the present invention, there is provided a full injection system for a multicylinder engine having a throttle valve for controlling the amount of fuel supplied to cylinders of the engine, and a fuel injector for each cylinder or group of cylinders, the system comprising: first means for generating an engine speed signal, second means responsive to closing of the throttle valve for producing a throttle signal, comparing circuit means for comparing the engine speed signal with a first preset level corresponding to a speed at which the fuel supply is to be cut off and for comparing the engine speed signal with a second preset level corresponding to a speed lower than the first speed for resupplying the fuel, and fuel cut-off circuit means responsive to the throttle signal and to outputs of the comparing circuit means for producing a fuel cut off signal when the engine speed is lower than the first level and for producing a fuel resupply signal when the engine speed signal is lower than the second level.

In accordance with the present invention, the fuel injectors are divided into at least two groups, and selecting circuit means are arranged to be responsive to the fuel cut off signal so as to disable the fuel injector in one selected group and to then disable the fuel injector in the other group with a delay, and to be responsive to the fuel resupply signal to re-enable the fuel injectors.

In one embodiment of the present invention, the selecting circuit means is arranged so as to respond to the fuel resupply signal so as to enable the fuel inector in one selected group and to then enable the fuel injector in the other group with a delay.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram showing an engine to which the present invention is applied; Figure 2 is a block diagram showing an embodiment of the present invention; and Figure 3 is a flowchart showing the operation of the system of Fig. 2.

Referring to Fig. 1 showing an opposed cylinder engine of a type which is provided with fuel injectors for every cylinder (called multi-point type fuel injection), the engine comprises an engine body 7 provided with four cylinders, an intake manifold 6 communicating with the cylinders and connected to an intake pipe 3 through a throttle body 1 having a throttle valve 2. The intake pipe 3 communicates with the atmosphere via an air cleaner 4. An air flow meter 5 is provided in the intake pipe downstream of the air cleaner.

Four fuel injectors 8a to 8d are provided for the four cylinders, respectively. Fuel in a fuel tank 9 is supplied to the fuel injectors 8a-8d by a fuel pump 10, and return fuel is regulated by a pressure regulator 11 which is operated by vacuum in the intake manifold 6.

The fuel returns to the fuel tank 9 through passages 1 2. Thus, the pressure of fuel at the injectors is kept to a higher value than the pressure in the intake manifold by the regulator 11. A fuel control system has a control unit 1 4 which is applied with ignition pulses from an ignition coil 13 and with a signal representative of quantity of intake air from the air flow meter 5. The control unit 14 computes fuel injection time from the signals to control the amount of fuel injected from each injector.

Referring to Fig. 2 showing a control system according to the present invention, a base pulse computing circuit 1 5 is supplied with a signal representing the amount Q of the intake air from the air-flow meter 5 and a signal representing the engine speed N from the ignition coil 13, so that the pulse width of the base pulse can be computed. A throttle switch 1 7 is arranged to be closed to produce a signal, when the accelerator pedal of the vehicle is released to close throttle valve 2, and a coolant temperature sensor 1 8 is provided to produce a signal when coolant temperature is lower than a predetermined value.

Output signals of base pulse computing circuit 15, throttle switch 17, coolant temperature sensor 18, and other sensors 1 9 are applied to an injection pulse computing circuit 1 6 which produces an injection pulse width signal corrected by the signals from the switch 17 and sensors 18, 19.

The firing order of the opposed four-cylinder engine is 4t1#3#2#4. In the systems of the present invention, the cylinders are divided into two groups, in each of which cylinders fire at an interval of 360 . That is to say, the cylinders are divided into a first group comprising &num;1 and &num;2 cylinders and a second group comprising #3 and #4 cylinders.

The injectors 8a, 8b of the first group are driven by output of a first driving circuit 20a and the injectors 8c, 8d of the second group are driven by output of a second driving circuit 20b. A cylinder group selecting circuit 22 is provided with a timer 21 and receives the outputs of injection pulse computing circuit 1 6 and a fuel cut off circuit 25 for operating the driving circuits 20a and 20b.

The output N of the ignition coil 1 3 is compared with a fuel cut off speed n, at a comparing circuit 23, and compared with a fuel resupply speed n2 at a comparing circuit 24. Outputs of throttle switch 17, coolant temperature sensor 18, comparing circuits 23 and 24 are applied to the fuel cut off circuit 25, where the fuel cut off condition is decided. The cylinder group selecting circuit 22 responds to the output of the fuel cut off circuit 25 to produce output signals to operate one of driving circuits 20a and 20b and then to operate the other driving circuit with a delay by the timer 21.

Explaining the operation of the system with reference to Fig. 2 and 3, when the coolant temperature is lower than a predetermined value, the cylinder group selecting circuit 22 produces a signal for operating both driving circuits 20a and 20b. Thus, all fuel injectors 8a-8d inject fuel regardless of the position of the accelerator pedal, so as to warm up the engine.

When the throttle switch 1 7 is closed under normal warm engine operating conditions, and when engine speed N is higher than the fuel cut off speed n1, which implies the condition that the fuel should be cut off, the cylinder group selecting circuit 22 produces a signal for interrupting the operation one of the groups of cylinders. For example, the second driving circuit 20b is disabled to stop the fuel injection of the injectors 8c and 8d. The fuel injectors 8a and 8b of &num;1 and &num;2 cylinders operate at an interval of 360 to fire the cylinders. Thus, engine torque decreases by half. After a delay time set by the timer 21, the fuel injectors 8a and 8b also stop injecting fuel. Thus, the fuel supply for all cylinders is cut off.

When the engine speed decreases below the fuel resupply speed n2, the cylinder group selecting circuit 22 produces a fuel resupply signal, so that the first driving circuit 20a is operated to actuate the fuel injectors 8a and 8b. Accordingly, #1 and #2 cylinders are fired so as to produce half the normal engine torque. After a delay time decided by the timer 21, the fuel injectors 8c and 8d operate. Thus, all cylinders are fired to prevent stalling of the engine.

From the foregoing, it will be understood that the present invention provides a fuel injection system which gradually decreases the number of working cylinders at deceleration of a motor vehicle, so as to reduce shock caused by decrease of engine torque.

While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and the various changes and modifications may be made within the scope of the appended

Claims

claims. CLAIMS

1. A fuel injection control system for a multi-cylinder engine having a throttle valve for controlling the amount of fuel supplied to cylinders of the engine, and a fuel injector for each cylinder, the system comprising: first means for generating an engine speed signal; second means responsive to closing of the throttle valve for producing a closed throttle signal; the fuel injectors being divided into at least two notional groups; comparing circuit means for comparing the engine speed signal with a first preset level corresponding to a speed at which the fuel supply is to be cut off and for comparing the engine speed signal with a second preset level corresponding to a speed lower than the first speed for resupplying the fuel;; fuel cut off circuit means responsive to the throttle signal and to outputs of the comparing circuit means for producing a fuel cutt off signal when the engine speed signal is lower than the first level, and for producing a fuel resupply signal when the engine speed is lower than the second level; and selecting circuit means responsive to the fuel cut off signal for disabling each fuel injector in the selected group, on receipt of the fuel cut-off signal and for disabling each fuel injector in the other group with a delay, and responsive to the fuel resupply signal so as to re-enable the fuel injectors.

2. A system according to claim 1 wherein the selecting circuit means is so arranged as to respond to the fuel resupply signal to select the groups of cylinders and for enabling the fuel injector in the selected group and for enabling the fuel injector in the other group with a delay.

3. A system according to claim 1 further comprising a coolant temperature sensor for producing a temperature signal when the temperature of the engine is lower than a predetermined value, and the selecting circuit means responds to the temperature signal so as to enable all fuel injectors regardless of the throttle signal.

4. A system according to claim 1 wherein the fuel injectors are divided into groups so that the intervals between fuel injection timings in each group are equal in angle.

5. A fuel injection control system substantially as herein described with reference to the accompanying drawings.