GB2090704A

GB2090704A - System for grounding electric circuits on a vehicle

Info

Publication number: GB2090704A
Application number: GB8133557A
Authority: GB
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1980-11-07
Filing date: 1981-11-06
Publication date: 1982-07-14
Also published as: DE3143758A1; FR2494052B1; JPS6329662B2; FR2494052A1; GB2090704B; JPS5780945A

Abstract

An electric circuit on a vehicle comprises a detector, e.g. an exhaust oxygen sensor 19, a control circuit 21 responsive to the output of the detector, and a driving circuit 22 responsive to the control circuit for operating an actuator to control the engine operation, e.g. air valves 14,15. The earth-line of the control circuit is connected to the vehicle engine by one lead 25, and the earth-line of the driving circuit is connected to the vehicle body by another lead 26, so that the earth level of the control circuit is unaffected by variation of the earth level of the driving circuit. <IMAGE>

Description

SPECIFICATION System for earthing electric circuits on a vehicle The present invention relates to a system for "earthing" circuits on a vehicle, such as air-fuel ratio control system for an internal combustion engine emission control system.

An emission control system employing a threeway catalytic convertor comprises a feedback control system. In such a system, an 2 sensor is provided to sense the oxygen content of exhaust gases to generate an electrical signal as an indication of the air-fuel ratio of air-fuel mixture supplied by a carburetor. The electrical signal is applied to an electric circuit for judging the electric signal and for producing driving output for an actuator. The electric circuit comprises a comparator for comparing the output signal of the 02 sensor with a predetermined value, a proportional and integrating circuit connected to the comparator, and a driving circuit for producing pulses in accordance with the output signal of the proportional and integrating circuit.The pulses pass through an on-off type electromagnetic valve as an actuator for correcting the air-fuel ratio of the mixture. The comparator operates to judge whether the feedback signal from 2 sensor is higher or lower than a predetermined reference value corresponding to the stoichiometric air-fuel ratio for producing an error signal and the signal is integrated by the proportional and integrating circuit to produce an integrated output. The integrated output is converted to pulses for actuating the on-off electromagnetic valve to thereby control the air-fuel ratio of the mixture.

Circuit earths in a conventional electric circuit for such a control system are connected to the vehicle body by a common line.

Figure 1 shows a conventional control system. A control circuit unit A comprises a control circuit B and a driving circuit C. The earth circuits of the control circuit B and driving circuit Care connected to the body of a vehicle by a common line D. The control circuit B receives an input signal F from a detector (not shown) and a battery is connected to a load G and to the control unit A.

When the driving circuit C operates in dependency on control signal from the control circuit B, a comparatively higher current passes through the load G and driving circuit C. Since a resistance E exists between the circuit ground of the control circuit unit A and the negative pole of the battery, a potential difference occurs on the earth circuit of the control circuit unit.

Further, the voltage level of the earth circuit varies according to the variation of the current passing through the load, which varies greatly in dependency on the input signal F and the voltage variation of the battery caused by the speed variation of the engine. The variation of the level of the earth circuit causes fluctuation of the level of the input signal in the control circuit B, which causes malfunction of the actuator (load G).

Figure 2 (H) shows the variation of the input signal F and Figure 2 (1) shows the variation of the level of the earth line in the control circuit B. Accordingly, the input signal F is changed to a signal based on the varying earth level of the control circuit B. The actual input signal for the control circuit B is the difference between the signal of Figure 2(H) and the earth circuit level of Figure 2 (1). Figure 2 (J) shows the actual input signal.

The present invention seeks to provide a system for earthing electric circuits in a control system which may prevent the malfunction of the control system caused by the variation of the earth circuit voltage level.

According to the present invention, there is provided a system for earthing an electric circuit mounted on a vehicle, the electric circuit comprising a detector for detecting engine operation, a control circuit responsive to the output of the detector to produce an output signal, and a driving circuit responsive to the output of the control circuit for operating an actuator for controlling the engine operation, characterized in that the earth-line of the control circuit is earthed to the body of the vehicle by one lead, and that the earth-line of the driving circuit is earthed to the body by another lead.

Our embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a block diagram showing a convention air-fuel ratio control system; Figures 2(11), (1) and rJ) are graphs showing variations of earth levels in the control system of Figure 1; Figure 3 is a schematic view of a system of the present invention; Figure 4 is a perspective view showing a feedback control circuit unit employed in the system of Figure 3; Figure 5 is a perspective view showing an earthing system of the prsent invention; and Figure 6 is an example of an electrical circuit employed in the system of the present invention.

Referring to Figure 3 showing schematically an air-fuel ratio control system, the reference numeral 1 designates a carburetor provided upstream of an engine 2 mounted on a vehicle, a correction air passage 8 communicating with an air-bleed 7 which is provided in a main fuel passage 6 between a float chamber 3 and a nozzle 5 in a venturi 4. Another correction air passage 13 communicates with another air-bleed 12 which is provided in a slow fuel passage 11 which diverges from the main fuel passage 6 and extends to a slow port 10 open in the vicinity of a throttle valve 9. These correction air passages 8 and 13 are communicated with respective electro-magnetic on-off type valves 14, 15 induction sides of which are communicated with atmosphere through an air cleaner 16.Further, a three-way catalytic converter 18 is provided in an exhaust pipe 17 downstream of the engine, and 2 sensor 19 is provided between the engine 2 and the converter 18 to detect oxygen concentration of exhaust gases as the air-fuel ratio of the mixture burned in the cylinder of the engine. The output of the 2 sensor 19 is connected to a feedback control circuit unit 20. The feedback control circuit unit 20 comprises a control circuit 21, a driving circuit 22, and a constant voltage circuit 24. The earth line of the control circuit 21 is connected to the engine 2 by a lead 25 and the earth line of the driving circuit 22 is connected to the body of the vehicle by a lead 26.

The voltage of a battery 23 is supplied to the circuit 21 through the constant voltage circuit 24 by a lead 27 and also supplied to the driving circuit 22.

Referring to Figure 6 which is a block diagram showing the control circuit unit 20, output of the 2 sensor 19 is applied to a PI (proportion and integration) control circuit 30 through a comparator 34, output of the Pl control circuit 30 is applied to a comparator 32 and triangular wave signal from a triangular wave pulse generator 33 is applied to the comparator 32 for producing square wave pulses.

Duty ratio of the square wave pulses varies according to the level of the output of the Pl control circuit 30. The driving circuit 22 comprising a transistor is applied with the square wave pulses from the comparator 32 to drive electromagnetic valves 14,15 at duty ratios of the square wave pulses. Thus, the air-fuel ratio is made lean by supplying correction air to the carburetor at a great feed rate and the air-fuel ratio is made rich by reducing the correction air supply, in order to control air-fuel ratio to the stoichiometry. In Figure 6, the constant voltage circuit 24 is omitted in the control circuit unit 20.

Referring to Figure 5, the control circuit 20 is mounted on the body of the vehicle. The earth line of the control circuit 21 (Figure 6) is connected to the engine 2 at a position near a generator 31 by the lead 25 and the earth line of the driving circuit 22 is connected to the vehicle body by the lead 26.

Positive pole of the battery 23 is connected to the control circuit unit by the lead 27.

In the system of this embodiment of the present invention, the earth line of the control circuit is grounded by a lead different from that of the driving circuit, so the level of the earth circuit of the control circuit does not vary with the variation of the voltage level of the earth line of the driving circuit. Therefore, the level of the input signal of the control circuit does not fluctuate, and hence exact control operation of the system may be achieved. Further, since the control circuit is earthed near the generator forming the power supply source, fluctuation of the earth level caused by impedance between the circuit and the power supply source may be reduced (to a minimum level).

Claims

1. An electrical control circuit for a vehicle, said circuit comprising a detector for detecting engine operation, a control circuit responsive to the output of said detector to produce output signal, and a driving circuit responsive to said output of said control circuit for operating an actuator for controlling the engine operation, characterized in that the earth line of said control circuit is connected to the body of said vehicle by a first lead, and that the earth line of said driving circuit is connected to said body by a second lead.

2. An electric control circuit for a vehicle in accordance with claim 1 wherein the earth circuit of said control circuit is connected to said engine.

3. An electrical circuit for a vehicle in accordance with claim 1, wherein the earth circuit of said control circuit is connected to said engine near a generator of the engine.

4. An electric control circuit for a vehicle, substantially as herein described with referent to Figures 3 to 6 of the accompanying drawings.