Lucas Industries Public Limited Company

Ian J Harvey

John Howard Moore

Alan P Ogburn

Peter L Anthony

A transducer means for sensing the movement of a component between first and second extreme positions includes a transducer 18 the output of which is applied to one input terminal of a differential amplifier. The output of the amplifier is applied to one input of a comparator at the output of which appears the output signal. The other input of the comparator is a voltage obtained from a resistor chain connected to the outputs of first and second sample and hold circuits the first of which is connected to the output of the differential amplifier and the second of which is connected to a peak hold circuit. The other input of the differential amplifier is connected to an integrator which integrates the signal provided by the first sample and hold circuit.

Output correction circuit for transducer means

An electronic control system for a solenoid based actuator for a fuel system of an engine includes a switchable transistor connected in a series circuit with a current sensing resistor and the solenoid of the actuator. A power circuit supplies switching pulses to the transistor through an AND gate. A control circuit supplies a control signal to the power circuit and also a trigger signal to a monostable circuit. The monostable circuit supplies an enable signal to the AND gate. The control circuit receives a feedback signal from the sensing resistor and as long as this lies within prescribed limits the control circuit will supply the control signal and the trigger signal. If the feedback signal lies outside the prescribed limits at least the trigger signal will be halted so that after the time period of the monostable circuit has lapsed the transistor will receive no further switching pulses. A fuse is connected in series with the solenoid which will blow in the event that the solenoid remains energized for longer than a prescribed time.

Control system

A drive circuit for an electromagnetic device including a solenoid includes a transistor in series with the solenoid and a current sensing resistor. A comparator receives a voltage signal depending on the current flow in the solenoid and by way of an 'AND' gate renders the transistor conductive when a control signal appears and non conductive when the current flow exceeds a set value. A first monostable circuit modifies a reference voltage applied to the comparator and reduces the set value of the current after a predetermined time so that the solenoid is initially energised at a high current value which is then reduced to a holding value. The circuit includes a second monostable circuit which causes the transistor to be switched on and off when the current has attained the high value and when the current is at its holding value.

Drive circuits

An electronic control system for a fuel pump of an internal combustion engine includes a power circuit which controls the flow of electric current in an electromagnetic device coupled to a spill valve of the fuel pump. Power is supplied to the power circuit through a resistor through which power is also supplied to an engine speed sensing circuit. The system also includes a control unit which supplies control signals to the power circuit to effect closure of the valve and hence delivery of fuel, in timed relationship with the engine. The control unit receives the speed signal from the speed sensing circuit and also senses the voltage applied thereto. In addition it receives a demand signal from a transducer and controls current flow in a relay winding having contacts in parallel with the resistor. In normal operation the contacts are closed but in a fault situation with the demand low and the speed high the winding is de-energized and the voltage applied to the power circuit and speed sensing circuit falls below a standby level which is sensed by the control unit to maintain the winding energized.

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Cricklade, United Kingdom

Ian J Harvey