GB2197091A

GB2197091A - IC engine fuel control

Info

Publication number: GB2197091A
Application number: GB08723567A
Authority: GB
Inventors: Shigeto Niitsuma; Mineo Kashiwaya
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1986-10-08
Filing date: 1987-10-07
Publication date: 1988-05-11
Also published as: DE3734065A1; GB8723567D0; KR880005349A; JPS6394039A; FR2605048A1

Description

1 GB2 197091A 1

SPECIFICATION

Method and system for fuel control of internal combustion engine BACKGROUND OF THE INVENTION The present invention relates to a fuel control system, or more in particular to a fuel control system for an internal combustion engine in which the amount of supplied fuel is controlled in accordance with the engine speed and the opening of the throttle valve and the engine speed in idle state is regulated by controlling the amount of air bypassing the throt- tle valve through an idle engine speed control unit.

In a conventional method of fuel control for the internal combustion engine, as disclosed in JP-A-60-204933, the amount of supplied fuel is computed by microcomputer on the basis of an engine speed signal and a throttle valve opening signal, and the fuel injection valve is thus controlled thereby to control the amount of supplied fuel.. There is also a conventional method of controlling the engine speed in idle state by controlling the amount of air bypass ing the throttle valve.

In a combination of the above-mentioned conventional systems, the throttle valve is not operated and therefore a throttle valve open- 95 ing sensor does not produce an output during the engine idling. As a result, these methods have a disadvantage that fuel control commen surate with the change in the amount of in take air is impossible during engine idle state. 100 SUMMARY OF THE INVENTION

The object of the; present invention is to provide a fuel control system in which fuel is controlled in accordance with the change in the amount of intake air even when the output of a throttle valve opening sensor does not undergo a change.

According to the present invention, there is provided a fuel control system and method in which the amount of supplied fuel is corrected in accordance with the amount of bypass air in engine idle state by detecting the idling op eration of the engine.

The present invention thus configured, in which the amount of supplied fuel is deter mined in accordance with a bypass air amount signal and an engine speed signal in engine idle state, makes possible accurate fuel control without a throttle valve opening signal. 120 BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram showing an engine control system using a fuel control system ac- cording to an embodiment of the present invention.

Fig. 2 is a flowchart showing details of the control processes.

Fig. 3 and Fig. 4 are diagrams showing functional blocks of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be explained with reference to Fig. 1. The amount of air supplied to the engine is controlled by a throttle valve 10. The opening degree of the throttle valve 10 is detected by a throttle valve opening degree sensor 2 and, after being converted into a voltage, is applied to a control unit 7. The detection of the engine speed is effected by a crank angle sensor (not shown) mounted in the distributor, and applied to the control unit 7 as an. engine speed signal. In response to the opening.degree signal of the throttle valve opening degree sensor 2, the engine speed signal from the distributor 6 and an output signal of an air-fuel ratio sensor 5, the control unit 7 com- putes the amount of supplied fuel of a proper air-fuel ratio, and applies a drive signal to an electromagnetic fuel injection valve. 1 thereby to control the amount of fuel.

Now, explanation will be made of the case in which the engine speed is increased under load (such as when a car air conditioner is actuated) in idle state. In this case, the driver operates to turn on a load switch 11, while the opening signal of the throttle valve sensor 2 produces an idle opening signal. The control unit 7 produces a drive signal to a solenoid valve 4 to control the position of a valve 4a of the solenoid valve 4, so that a bypass inlet 4b is opened by an amount corresponding to the drive signal, thus supplying the bypass air by way of a bypass outlet 4c. In synchronism with this operation, the control unit 7 obtains fuel injection signal under idle load increase from a map in accordance with the drive cur- rent of the -solenoid valve 4, that is, the amount of bypass air, and thus controls the fuel injection valve in accordance with the same signal, thereby injecting a corrected amount of fuel commensurate with the increase of the bypass air amount.

According to the embodiment under consideration, the amount of supplied fuel in accordance with the change in bypass air amount corrected by the load condition in idle state is obtained from a map set in advance, and on the basis of the resulting signal, a drive signal is applied to the electromagnetic fuel injection valve, with the result that the proper fuel control is effected in accordance with the load condition without production of an output from the throttle valve opening sensor.

Fig. 2 is a flowchart showing details of control according to the embodiment under con- sideration.

Step 101 decides whether the load switch (such as a switch for an air conditioner or headlight) 11 is on or not. If the load switch 11 is off, the flow is terminated to shift to another control flow without regard to the 2 GB2197091A 2 other conditions.

If the load switch 11 is on, on the other hand, step 102 decides whether the idle switch is on or not. (Whether the throttle valve opening is idle or not may be decided alternatively by comparing an output signal of the throttle valve sensor 1 mined opening signal).

If the idle switch is off, the bypass air is not supplied even if the load switch is on, and therefore the flow shifts to another control flow.

In the case where step 102 decides that the idle switch is on and that the engine is idling, step 103 obtains from the map an opening degree signal of the solenoid valve 4 corresponding to the amount of bypass air required for attaining a predetermined idle speed, and applies a corresponding drive current to the coil of the solenoid valve 4.

Then, step 104 determines a time pulse signal representing the opening time of the electromagnetic fuel injection valve necessary for giving a corrected amount of fuel corresponding to the particular signal, and compensates for the amount of fuel in accordance with the bypass air amount.

The throttle valve is closed up during deceleration as under idle state. Under this condi- tion, the corrected fuel control in accordance with the amount of bypass air is not necessary. Therefore, this condition may be detected by a gear switch 8 showing whether the transmission gear is at neutral position or not, and if the throttle valve is positioned to idle state at other than neutral position, the fuel amount is not compensated substantially.

The present invention described above will be explained further with reference to the functional block diagram of Fig. 3.

A fuel control system according to the present invention comprises supplied fuel amount computation circuit for computing the amount of fuel supplied to each cylinder of the engine from a signal representing the number N of r.p.m. of the engine and a signal representing the opening of the throttle valve. An injector for fuel supply supplies a predetermined amount of fuel to the intake manifold in re- sponse to an output signal (generally a valve opening pulse signal) of this computation circuit. This injector is not confined to a single point injection type for upstream injection shown in the embodiment, but may be in the form of another single point injection type for 120 downstream injection provided by a signal injection valve downstream of the throttle valve, a multi-point injection type in which an injector is mounted on each branch pipe connected to each cylinder, or a division-type single-point injection type in which the intake system is divided into a plurality of groups downstream of the throttle valve with a single injection valve allocated to each group.

The supplied fuel computation circuit is so 0 with a predeter- constructed as to be affected by the corrected fuel computation circuit, so that the amount of supplied fuel may be obtained as a solution of three variables including a fuel compensation signal X in addition to the throttle valve opening signal a and the engine speed signal N, or as another alternative, the basic fuel amount determined from a and N may be added to or subtracted from a corrected fuel amount sepa- rately obtained.

This corrected fuel amount or the fuel compensation signal may be obtained in accordance with the amount of bypass air.

Whether the amount of supplied fuel is compensated in accordance with the amount of bypass air is determined depending on whether the engine is idle or running. This decision is rendered basically by detection through a switch adapted to close when the throttle valve is closed up. Nevertheless, the decision as to whether the engine speed signal N is included in the idle speed range set in advance and whether the transmission gear is represented by a neutral signal may also form conditions for distinction from the deceleration region. Also, the magnitude of the throttle valve opening signal a in place of the idle switch may be observed to decide that the throttle valve is closed up when the particular signal is zero.

The compensation amount may also be controlled by deciding whether or not the engine is under a load in place of the amount of bypass air. In such a case, a load switch is used to determine whether such a power load as car air conditioner is connected to the battery, and when a load is applied, a predetermined amount of compensation fuel is added in addition to the fuel compensation amount based on the bypass air amount.

The intention involved is to increase the fuel when a load is applied, and when the devices are so designed to increase the bypass air amount under a load applied, an increase in the amount of bypass air automatically increase the fuel amount accordingly. In this case, it is not necessary to compute the compensation amount directly on the basis of the condition of the load switch.

Further, it is totally unnecessary to make computation of the compensation fuel amount independently of the computer of the amount of supplied fuel. As a computation factor of the supplied fuel, a signal representing the bypass air amount, may be added to the computation formula to carry out the compensation of the amount of fuel.

Also, in view of the fact that the engine is not sufficiently heated in the initial stage of starting warm-up under idle state, it is necessary to increase the amount of fuel in order to obtain a sufficient torque. This concept may also be applied to the present invention, in which case the fuel compensation signal for the system, may be further corrected by an 3 GB2 197091A 3 engine temperature represented by such the engine cooling water temperature.

In this case, if the amount of bypass air is designed to increase in accordance with the engine temperature, as in the case of turning on a load switch mentioned above, the amount of fuel is not required to be directly increased by a signal indicating the engine temperature.

Fig. 4 is a diagram showing functional blocks viewing the present invention from another standpoint.

A signal representing the amount of supplied fuel is normally obtained by computation with the throttle valve opening signal a and the engine speed signal N as functions or obtained by reading from a map stored in the control unit 7. In idle state, such an amount is computed from the compensation fuel amount signal with the bypass air amount control signal as a function or by reading from the map.

One of these fuel signals is selected for control of the fuel injection valve by operating a switch circuit supplied with an idle decision circuit.

It will thus be understood from the foregoing description that according to the present invention, fuel compensation is ef fected by use of a fuel compensation signal value re- lated to a bypass air amount control signal to drive an electromagnetic fuel injection valve without regard to the output of the throttle valve opening sensor, and therefore a proper fuel supply control is practica - ble even while the engine is idling with the throttle valve opening signal kept unchanged.

Claims

1. A method of fuel control for an internal combustion engine, in which the amount of fuel supplied to the engine is controlled by an opening signal of a throttle valve adapted to control the intake air amount and an engine speed signal, and the idle engine speed is controlled by controlling the amount of air bypassing the throttle valve, the amount of supplied fuel being controlled in accordance with the amount of bypass air under idle engine state.

2. A fuel control system for an internal combustion engine, comprising computation means for determining the amount of fuel supplied to the engine from an engine speed signal and an opening signal for a throttle valve adapted to control the amount of intake air, idle decision means for detecting. an idle condition of the engine, and an idle speed control unit for controlling the idle speed by controlling amount of air bypassing the throttle valve under idle engine condition, said computation means including compensation means for compensating the fuel amount in accordance with a control signal of the idle speed control means when said idle decision means decides an idle engine condition.

3. A method of fuel control substantially as herein described with reference to and as shown in the accompanying figures.

4. A fuel control system substantially as herein described with reference to and as shown in the accompanying figures.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.