Engine control system
First Claim
1. An internal combustion engine in which the ignition timing and the fuel-to-air ratio are determined by an open loop control system including tables (12,22,14) stored in a microcomputer, the tables providing signals indicating predetermined settings of the ignition timing and the fuel to air ratio in dependence upon sensed parameters and in which a closed loop control circuit (16,18,20,24) incorporating an ionisation sensor disposed within a combustion chamber is provided for sensing a burn period duration and applying a correction to one of the signals derived from the tables stored in the microcomputer in dependence upon the sensed burn period duration, characterised in that the closed loop applies a correction to the signal for regulating the fuel-to-air ratio and has a response time substantially greater than the response time of the open loop, and in that changes in the correction effected by the closed loop are permitted only when the engine is operating within a predetermined range for which the operation of the ionisation sensor is accurately representative of the burn period duration.
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Accused Products
Abstract
The invention describes a control system in which open loops control the mixture strength and spark timing by means of look-up tables (14, 12) stored in a computer and a closed loop (16, 18, 20, 24) with much greater response time corrects the air fuel ratio to compensate for long term drift in the open loops under the control of an ionization sensor sensitive to the duration of the burn period. The ionization sensor output is used only in operating ranges where its output accurately reflects the burn period duration.
Consequently, the high speed response of an open loop is achieved at the same time as the long term stability of a feedback loop sensitive to the burn period duration.
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Citations
3 Claims
- 1. An internal combustion engine in which the ignition timing and the fuel-to-air ratio are determined by an open loop control system including tables (12,22,14) stored in a microcomputer, the tables providing signals indicating predetermined settings of the ignition timing and the fuel to air ratio in dependence upon sensed parameters and in which a closed loop control circuit (16,18,20,24) incorporating an ionisation sensor disposed within a combustion chamber is provided for sensing a burn period duration and applying a correction to one of the signals derived from the tables stored in the microcomputer in dependence upon the sensed burn period duration, characterised in that the closed loop applies a correction to the signal for regulating the fuel-to-air ratio and has a response time substantially greater than the response time of the open loop, and in that changes in the correction effected by the closed loop are permitted only when the engine is operating within a predetermined range for which the operation of the ionisation sensor is accurately representative of the burn period duration.
Specification