GB2156431A

GB2156431A - Exhaust-gas recirculation control system for an internal combustion engine

Info

Publication number: GB2156431A
Application number: GB08506467A
Authority: GB
Inventors: Ryuji Kataoka
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1984-03-14
Filing date: 1985-03-13
Publication date: 1985-10-09
Also published as: JPS60192869A; GB2156431B; GB8506467D0; DE3508800A1

Abstract

An exhaust-gas recirculation system for an internal combustion engine has a recirculation passage 12 connected between the exhaust passage 8 and the intake passage 7 of the engine, and a valve 13 disposed in the recirculation passage 12 adapted to be opened by intake manifold vacuum to recirculate some of the exhaust gas. A solenoid operated valve 16 is provided for holding the valve 13 closed, when the ratio of intake air to engine speed is less than a reference value. <IMAGE>

Description

SPECIFICATION Exhaust-gas recirculation control system for an internal combustion engine The present invention relates to an exhaust-gas recirculation control system for an automotive engine, and more particularly to a system for controlling the exhaust-gas recirculation at high engine speed under light engine load.

Japanese laid open specification no. 53-32233 discloses an exhaust-gas recirculation control system provided with means for detecting a high engine speed at heavy engine load and for producing an output which operates to close an exhaust-gas recirculation (EGR) valve, thereby increasing the output power of the engine. The EGR valve is opened by a vacuum at a carburettor signal port positioned just above the upward swinging end of a throttle valve in the closed position. Accordingly, the EGR valve is opened to recirculate a part of the exhaust gas, when the throttle valve is partly opened under a light load, even at a high engine speed. Therefore, the combustion process at high engine speed under light load is affected, causing the vehicle to become difficult to drive smoothly.

The present invention therefore seeks to provide a system for controlling the exhaust-gas recirculation of an engine, which operates to cut off the recirculation of the gas at high engine speeds when the engine load is light, thereby improving the performance of the engine.

According to the present invention, there is provided an exhaust-gas recirculation system for an internal combustion engine of the type having an intake passage, an exhaust passage, a throttle valve in the intake passage, a recirculation passage connected between the exhaust passage and the intake passage, an EGR valve including a vacuum chamber, vacuum operated disphragm, and valve connected to the diaphragm and disposed in the recirculation passage, a signal port arranged in the intake passage at a position just above the upward swinging end of the throttle valve in its closed position, and a vacuum passage communicating the signal port with the vacuum chamber; the system comprising a solenoid operated valve provided in the vaccum passage, an air flow meter for sensing the flow rate of the intake air and for producing a first signal dependent on the said flow rate, an engine speed sensor for producing a second signal dependent on speed of the engine, first means for producing an output signal representing the amount of intake air in relation to engine speed, second means for comparing the output signal with a reference value and for producing a third signal when the output is less than the reference value, and third means responsive to the third signal for closing the solenoid operated valve to cut off the vacuum applied to the vacuum chamber.

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 of an exhaustgas recirculation control system according to the present invention; and Figure 2 is a flow chart showing the operation of the system of Figure 1.

Referring to Figure 1, an internal combustion engine 1 mounted on a motor vehicle (not shown) is provided with an intake pipe 4 having an air cleaner 2 and an air flow meter 3. A throttle body 6 having a throttle valve 5 is disposed between the intake pipe 4 and an intake manifold 7. A catalytic converter 9 is provided in an exhaust manifold 8 of the engine 1. The output of the air flow meter 3 is applied to a microcomputer control unit 10 which controls the amount of fuel injected from fuel injection valves 11 dependent on the signal from the air flow meter 3.

An exhaust-gas recirculation system comprises a recirculation passage 12 connected between the exhaust manifold 8 and intake manifold 7, and an EGR valve 13. The EGR valve 13 having a vacuum chamber 13a defined by a diaphragm 13b and a valve 13c provided in the recirculation passage 12.

The vacuum chamber 13a communicates with a signal port 14 positioned just above the upward swinging end of the throttle valve 5 in its closed position by a vacuum passage 15, interposing a solenoid operated valve 16. Further, the facuum chamber 13a communicates with the intake pipe 4 via a passage 17 having an orifice plate 18. An engine speed sensor 19 is provided to produce an output dependent on the speed of the engine (e.g.

speed of the crankshaft of the engine), which is applied to the control unit to control the solenoid operated valve 16 together with the output of the airflow meter 3.

The operation of the system will now be explained with reference to Figure 2: the engine 1 inducts air dependent on the opening degree of the throttle valve 5, and the amount of the intake air is measured by the air flow meter 3. The control unit 10 controls the fuel injection valves 11 dependent on the amount (A) of intake air from the air flow meter 3.

The control unit 10 also computes the speed (N) of engine from the output of the engine speed sensor. The quantity of intake air (A) is then divided by the engine speed (N) (N/nN = L, n is any whole number). In this way, the ratio (L) of the amount of intake air in relation to one revolution of the crankshaft of the engine is obtained. The ratio L is compared with a reference value Lo which is the level at which the recirculation of exhaust gas is started or stopped.

When the ratio L (amount of intake air per unit engine speed) is smaller than the reference value Lo, which means that although the engine speed is at a high value, the amount of intake air is small because of a small opening degree of the throttle valve at light load, the control unit 10 produces an output signal for the solenoid operated valve 13.

The solenoid operated valve 13 is closed by the output signal of the control unit 10, so that the vacuum to the vacuum chamber 13a is cut off and the vacuum in the chamber 13a is reduced by the air induced from the intake pipe 4 passing through the orifice plate 18 and passage 17. Thus, the valve 13c closes the EGR passage 12 to cut off the recirculation of exhaust gas.

On the other hand, when the ratio L is larger than the reference value Lo meaning that the amount of intake air is large and the engine speed is also high, the control unit does not produce the output signal. Thus, the solenoid operated valve is opened, applying the intake manifold vacuum to the vacuum chambers 13a to open the valve 13c.

Thus, a part of exhaust gas is recirculated in accordance with the opening degree of the throttle valve 5.

From the foregoing, it will be understood that the present invention provides a control system which operates to cut off the recirculation of exhaust gas at high engine speed when engine load is light, thereby improving engine performance.

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 that various changes and modifications may be made within the scope of the appended claim.

Claims

1. A control system for exhaust-gas recirculation in an internal combustion engine of the type having an intake passage, an exhaust passage, a throttle valve in the intake passage, a recirculation passage connected between the exhaust passage and the intake passage, an EGR valve having a vacuum chamber, vacuum operated diaphragm, and valve connected to the diaphragm and disposed in the recirculation passage, a signal port positioned in the intake passage so as to be open to induction pressure in the intake manifold by movement of the throttle valve away from its closed position, and a vacuum passage communicating the signal port with the vacuum chamber, the control system comprising:: a solenoid operated valve provide in the vacuum passage; an air flow meter for sensing the flow rate of intake air and for producing a first signal dependent on the flow rate; an engine speed sensor for producing a second signal dependent on speed of the engine; first means for computing the ratio of intake air to engine speed from the first and second signals and for producing an output; second means for comparing the output with a reference value and for producing a third signal when the output is less than the reference value, and third means responsive to the third signal for closing the solenoid operated valve so as to cut off the vacuum applied to the vacuum chamber.

2. A control system according to claim 1 wherein the first means produces the said output by dividing the first signal by the second signal.

3. A control system according to claim 1 wherein the first means, second means and third means are constituted by a microcomputer control unit.

4. An internal combustion engine having exhaust gas recirculation with a control system in accordance with any preceding claim.

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

6. A method of controlling recirculation of exhaust gases in an internal combustion engine, comprising the steps of: (a)measuring the flow of intake air; (b)measuring the engine speed; and (c)cutting off the said recirculation if the ratio of intake air to engine speed is less than a predetermined value.

7. A method of controlling recirculation of exhaust gases in an internal combustion engine in accordance with claim 6 and substantially as herein described.