Patent CA-1093184-A (CA)
Inventor: GUNDA RAJAMOULI
IPC: F02D41/34
Filed: 1977-07-08
Granted: 1981-01-06
Abstract: FREQUENCY MODULATED SINGLE POINT FUEL INJECTION CIRCUIT WITH DUTY CYCLE MODULATION            ABSTRACT OF THE DISCLOSURE UNDER RULE 72-(b) A frequency modulated control circuit for an electronic fuel injection system to control the pulse-type injection of fuel at a single point of the fuel intake of an internal combustion engine in accordance with the derived mass air flow rate into the engine comprising a pressure sensor for sensing the manifold pressure of the internal combustion engine, and an engine speed sensor, both of which generate an analog signal which varies in accordance with the manifold pressure and rotary speed of the engine, respectively.  The analog signals representative of the manifold pressure and the engine speed are multiplied by a multiplier circuit to provide a signal representative of the mass air flow to the engine.  The multiplier circuit includes a separate control input for varying the output signal level of the multiplier circuit by a preselected factor determined by the final output of the control circuit.  The output of the multiplier circuit is fed to a voltage controlled oscillator to produce an output signal taking the form of a pulse train, the frequency of which varies with the amplitude of the mass air flow signal.  The output of the voltage controlled oscillator is fed to a pulse generator which generates a fixed on-time pulse for each pulse in the pulse train being fed from the voltage controlled oscillator.  Thus, the off-time of the output wave train from the pulse generator will vary as an inverse function of the frequency being fed to the pulse train.  The output of the pulse generator is fed to an OR gate, the output of which is connected to the fuel injector for producing a series of fuel injections into the fuel intake of the internal combustion engine for each engine revolution, the pulses being asynchronous with the engine rotation.  The output of the OR gate is sensed by a duty cycle switch which senses when the output frequency of the voltage controlled oscillator results in a high duty cycle for the output pulses.  In this high duty cycle situation, the output analog signal of the multiplier is reduced by a preselected fraction.  The duty cycle switch also generates an output signal which varies the duration of the pulse output from the pulse generator as a reciprocal of the variation being applied to the multiplier from the duty cycle switch or enable a secondary injector.          The system also includes a temperature sensor and coolant temperature circuit which generates an analog voltage signal which varies as a function of the engine coolant temperature.  The analog temperature signal, VH2O , is fed to the voltage controlled oscillator to increase its output frequency, and thus-increase fuel flow to the engine, with decreasing coolant temperature.  The temperature analog signal, designated VH2O, is fed to a cold start circuit to control the output pulse width from the cold start circuit which, in turn, is fed to the output OR gate. Thus, during the cold start operation of the engine, the cold-start circuit will be the controlling factor as to the amount of fuel being injected into the engine.