GB2164092A

GB2164092A - Ignition timing and EGR control system for an automotive engine

Info

Publication number: GB2164092A
Application number: GB08521361A
Authority: GB
Inventors: Kiyoshi Ohtaki; Kazuo Hara
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1984-08-30
Filing date: 1985-08-28
Publication date: 1986-03-12
Also published as: DE3530882C2; DE3530882A1; GB8521361D0; GB2164092B; JPS6158973A

Abstract

The control system has a primary vacuum-advance mechanism 2 operated by vacuum in an intake passage 8 of the engine to advance the ignition timing of the engine, and a secondary vacuum-advance mechanism 3 operated by vacuum in the intake passage to further advance the ignition timing in addition to the operation of the primary vacuum-advance mechanism. A first solenoid operated valve 4 is provided to render the secondary vacuum-advance mechanism inoperative, and a second solenoid operated valve 6 is provided for preventing operation of an EGR valve 5. An electronic control unit 7 responds to engine operating conditions in a low engine speed range (other than idling) to close the first and second solenoid operated valves to cut off the EGR system and to cut off the secondary vacuum- advance mechanism, thereby preventing over advance of the ignition timing. <IMAGE>

Description

SPECIFICATION Ignition timing control system for an automotive engine The present invention relates to an ignition timing control system for an automotive engine having an exhaust gas recirculation (EGR) system.

In an engine for a motor vehicle, an EGR system is employed to lower the combustion temperature for reducing nitrogen oxides (NOx). The engine is so controlled that the ignition timing is advanced to a maximum extent during EGR operation, in order to prevent the reduction or driveability of the vehicle and the increase of fuel consumption due to the EGR. However when the requirement of emission control regulation becomes severe, the amount of EGR must be increased to meet the requirement. When the amount of EGR increases, the deterioration of driveability and fuel consumption cannot be avoided by advancing the ignition timing.Accordingly, it has been proposed to cut off the EGR system or to leak the vacuum to operate an exhaust gas recirculation valve to control the recirculated gas so as to render the EGR system inoperative under particular conditions in order to prevent the deterioration of operating characteristics, although the engine operation is in an EGR operative range. However, if the ignition timing remains advanced in the inoperative condition of the EGR system, the engine is operated with greatly advanced ignition timing, which will cause the engine to knock, reduce driveability and increase fuel consumption.

The present invention seeks to provide an ignition control system which operates to prevent advancing of the ignition timing of an engine when the EGR system is rendered inoperative in the normal EGR operating range of the engine.

According to the invention, there is provided an ignition timing control system for an automotive engine of the type having an exhaust gas recirculation system including an exhaust gas recirculation passage and an exhaust gas recirculation valve operated by a vacuum operated actuator provided in the recirculation passage, the control system comprising:: a primary vacuum-advance means responsive to the vacuum at a first vacuum port located in the intake passage of the engine at a position just upstream of the throttle closed position so as to advance the ignition timing of the engine; a secondary vacuum-advance means responsive to the vacuum at a manifold vacuum port so as to apply an additional advance to the ignition timing in cooperation with the primary vacuum-advance mechanism; a first solenoid valve connected between the secondary vacuum-advance mechanism and the manifold vacuum port; a second solenoid valve connected between a second vacuum port of the intake passage and the vacuum chamber of the vacuum operated actuator for the exhaust gas recirculation valve;; an electronic control unit responsive to engine operating conditions in a low engine speed range, other than idling speed, for closing the first and second solenoid valves so as to cut off the exhaust gas recirculation system and for closing the passage to the first solenoid valve, thereby preventing operation of the secondary advance means.

In one embodiment of the present invention, the first vacuum port is situated in the intake passage just above a closed throttle position and the second vacuum port is located at a position slightly above the first vacuum port in the intake passage.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration showing a system according to the present invention; Figure 2 is a block diagram showing a control circuit according to the present invention; Figure 3 is a graph showing the relationship between intake manifold pressure and ignition advance angle; and Figure 4 is a graph showing operating ranges of the system.

Referring to Fig. 1, an automotive engine E has a distributor 1. The distributor 1 is provided with a primary vacuum-advance mechanism 2 and a secondary vacuum-advance mechanism 3. The primary vacuum-advance mechanism is a conventional type. Namely, the vacuum operated actuator (not shown) of the primary vacuum-advance mechanism 2 communicates with a first vacuum port 10a provided in a carburettor 8 at a portion just above a throttle valve 9 when it is closed.

The vacuum operated actuator of the secondary vacuum-advance mechanism 3 communicates through a first three-way solenoid valve 4 with a manifold vacuum port 12 formed in an intake manifold 11. The first three-way solenoid valve 4 comprises a solenoid 4a, valve body 4b, valve port 4c, and vent port 4d. An EGR valve 5 comprises a vacuum chamber 5a, defined by a diaphragm Sc and a valve body 5b provided in an exhaust recirculation passage 13 communicating an exhaust pipe 14 of the engine with an intake pasage 15. The valve body 5b is operatively connected to the diaphragm Sc so as to be operated by the deflection of the diaphragm. The vacuum chamber 5a is communicated with a second vacuum port 10b through a second three-way solenoid valve 6.The second three-way solenoid valve 6 comprises a solenoid 6a, valve body 6b, valve port 6c, and vent port 6d.

The second port 10b is positioned at a location slightly above the first vacuum port 10a.

Solenoids 4a and 6a of three-way valves 4 and 6 are supplied with an EGR cut off signal from an electronic control unit 7. The valve bodies operate by excitation of the solenoid 4a (or 6a) to close the valve port 4c (or 6c) and to open the vent port 4d (or 6d).

Fig. 2 shows an example of the electronic control unit 7. There is provided a vehicle speed sensor 16, coolant temperature sensor 17, engine speed signal generator 18 for producing an output signal dependent on the primary coil signal of an ignition coil, and intake manifold vacuum sensor 19. The output signals of the sensors 16 and 17 are applied to an EGR decision circuit 20. The EGR decision circuit 20 is provided to produce an EGR signal having a high level when vehicle speed exceeds a predetermined value (for example 45km/H) and coolant temperature is lower than a predetermined value (70 C). Output signals of generator 18 and sensor 19 are applied to an engine load detecting circuit 21 for detecting the partial load of the engine and to an idling speed detecting circuit 22.The partial load range detecting circuit 21 produces an output signal having a high level when engine speed is lower than a predetermined value (1200 rpm) and intake manifold vacuum is lower than a predetermined value (--350mm Hg). The idling speed detecting circuit 22 is adapted to produce an output signal having a low level when engine speed is lower than 1400 rpm and intake manifold vacuum is higher than -350mm Hg. Output signals of circuits 20 and 21 are applied to an AND gate 23 through an OR gate 24, and the output signal of the circuit 22 is directly applied to the AND gate 23. The output signal of the AND gate is applied to a driver 25 so as to excite solenoids 4a and 6a.

In idling operation, since the output of the idle speed detecting circuit 22 is at a low level, AND gate 23 is closed. Accordingly, solenoids 4a and 6a are not actuated, so that the secondary vacuum-advance mechanism 3 communicates with the intake manifold 11 and vacuum chamber 5a of EGR valve communicates with the second vacuum port 10b.

Since the throttle valve 9 is at the idling position, the pressure at the port 10b is atmospheric. Accordingly, the valve body 5b closes the passage 13. On the other hand, the secondary vacuum-advance mechanism 3 is operated by the intake manifold vacuum to advance the ignition timing. Thus ignition advance control can be performed during idling, thereby improving fuel consumption. A range C in Fig. 4 shows the advance control range at idling.

When the EGR decision circuit 20 produces an output signal at a high vehicle speed, and the output of the circuit 22 is at a high level, the driver 25 operates to energise solenoids 4a and 6a, so that ports 4c and 6c are closed. Thus, the EGR system does not operate and the ignition timing is advanced by the primary vacuum-advance mechanism 2. When engine speed is lower than 1200 rpm and intake manifold vacuum is lower than -350mm Hg, the output of the partial load range detecting circuit 21 is at a high level.

Accordingly, solenqids 4a and 6a are energised to close ports 4c and 6c. Thus, EGR is cut off and the ignition timing is set by the primary advance mechanism 2. Ranges A and B in Fig. 4 show such a control range.

In Fig. 4, in the range above a line I, the vacuum at the port 10a is at a level sufficient to operate the advance mechanism 2 to advance the ignition timing, and in the range above a line II, the vacuum at the port 10b opens the EGR valve 5.

In the range B, in a conventional system, the EGR system is cut off, but the ignition timing remains greatly advanced, which causes the occurrence of engine knock. However, in the system of the present invention, the EGR system is cut off and the ignition timing is retarded by cutting off the circuit of the secondary vacuum-advance mechanism 3. Thus the driveability of the vehicle can be improved.

Further, in the range A, the EGR system does not operate. In the conventional system, ignition timing is advanced in such a range, which may cause the occurrence of knock. In this embodiment of the present invention, the ignition timing is retarded by cutting off the system of the advance mechanism 3, thereby preventing engine knock.

In Fig. 3, a line a shows an advance characterised by the secondary advance mechanism 3, line b shows an advance characterised by the primary advance mechanism 2, and line c is a combined advance characteristic of lines a and b. The difference between lines c and b is the retard angle in the ranges A and B of Fig. 4 in accordance with the present invention.

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

Claims

claims. CLAIMS

1. An ignition timing control system for an automotive engine of the type having an exhaust gas recirculation system including an exhaust gas recirculation passage and an exhaust gas recirculation valve operated by a vacuum operated actuator provided in the recirculation passage, the control system comprising:: a primary vacuum-advance means responsive to the vacuum at a first vacuum port located in the intake passage of the engine at a position just upstream of the throttle closed position so as to advance the ignition timing of the engine; a secondary vacuum-advance means responsive to the vacuum at a manifold vacuum port so as to apply an additional advance to the ignition timing in cooperation with the primary vacuum-advance mechanism; a first solenoid valve connected between the secondary vacuum-advance mechanism and the manifold vacuum port; a second solenoid valve connected between a second vacuum port of the intake passage and the vacuum chamber of the vacuum operated actuator for the exhaust gas recirculation valve; ; an electronic control unit responsive to engine operating conditions in a low engine speed range, other than idling speed, for closing the first and second solenoid valves so as to cut off the exhaust gas recirculation system and for closing the passage to the first solenoid valve, thereby preventing operation of the secondary advance means.

2. A control system according to claim 1 wherein the second vacuum port is located slightly upstream of the first vacuum port, and the manifold vacuum port is located at a position downstream of the throttle valve of the engine.

3. An ignition timing control system substantially as herein described with reference to the accompanying drawings.