Method and apparatus for controlling fuel management for an internal combustion engine
AssigneeRobert Bosch GmbH
InventorsHarro Herth, Hans Schnurle, Ulrich Drews, Erich Singer, Bernd Kraus, Peter Werner
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Abstract
A control circuit of a fuel management control system for internal combustion engines monitors the operation of an exhaust line sensor. When the oxygen sensor is perceived to be inoperative, for example, due to low ambient temperature, the previously closed loop control process governing the fuel management control signals is interrupted and a direct forward control process is substituted therefor. The reference voltage is changed during this time for eventual adaptation to the changeover to closed loop feedback control after the oxygen sensor again becomes operational.
Claims42
A method of controlling the operation of a fuel management system of an internal combustion engine, said system including fuel allocation means, control means for generating fuel control signals related to engine rpm and air flow rate, and also including an oxygen sensor for generating a sensor signal related to a fuel-air ratio of a fuel-air mixture supplied to the engine which is fed back in a closed loop to said control means, comprising the steps of:
- generating a single variable reference signal:
- comparing said reference signal with said sensor signal;
- continuously detecting the occurrence of sensor signal changes in a time interval;
- automatically disabling the closed-loop control of said system based on feedback of said sensor signal when no sensor signal changes are detected in said time interval indicating a malfunction of said oxygen sensor and substituting therefor an open-loop control based on engine rpm and air flow rate;
- automatically altering the magnitude of said reference signal by a predetermined value;
- re-engaging the closed-loop control of said system based on feedback of said sensor signal when sensor signal changes are again detected indicating an operative state of said oxygen sensor;
- and
- thereafter returning the magnitude of said reference signal gradually to a normal level appropriate for an operative oxygen sensor whereby said reference signal is maintained at a value which is bracketed by said sensor signal, to effect said closed-loop control based on feedback of said sensor signals.
An apparatus for controlling the operation of a fuel management system of an internal combustion engine, said system including fuel allocation means and means for generating signals related to engine rpm and air flow rate and further including an oxygen sensor for generating a sensor signal related to exhaust gas composition which is fed back in a closed loop to said signal generating means, said sensor signal normally switching between a relatively high value indicating a rich fuel-air mixture and a relatively low value indicating a lean fuel-air mixture, said apparatus comprising:
- a comparator means for providing and comparing a reference signal with said sensor signal from said oxygen sensor, said comparator means generating an output signal having a first value when the sensor signal is lower than the reference signal and having a second value when the sensor signal is higher than the reference signal;
- an integrating means, connected to receive the output signal from said comparator means, for supplying a fuel control signal to said fuel management system;
- a first timer means, having an input connected to receive said comparator means output signal and an output, for switching said signal generating means between closed loop and open loop control, said first timer means generating a timer output signal at its output to be applied to said integrating means to terminate integration and to supply a constant fuel control signal to said fuel management system after a period of time during which the output signal of said comparator means remains approximately constant, indicating an oxygen sensor malfunction;
- and
- a second timer means, controlled by said first timer means, having an input connected to said first timer means input and having an output, for raising said reference signal subsequent to the occurrence of an oxygen sensor malfunction and gradually lowering it when the oxygen sensor operates properly.
Dependencies are inferred from the claim text.