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INJECTOR FAULT TESTING METHODS

IP.com Disclosure Number: IPCOM000005496D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2001-Oct-09
Document File: 6 page(s) / 161K

Publishing Venue

Motorola

Related People

Robert W. Deutsch: AUTHOR

Abstract

The following are several methods for detection of a fault on the controlling side of a fuel injector. Due to the growing use of electric fuel pumps and electrically-activated fuel injectors and the in- creased concern for operator safety, the supervision of such critical circuitry as the injector driver has been considered and evaluated by several automotive companies.

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Volume 3 March 1983

INJECTOR FAULT TESTING METHODS

By Robert W. Deutsch

   The following are several methods for detection of a fault on the controlling side of a fuel injector. Due to the growing use of electric fuel pumps and electrically-activated fuel injectors and the in- creased concern for operator safety, the supervision of such critical circuitry as the injector driver has been considered and evaluated by several automotive companies.

   Each of the following methods has advantages and disadvantages. As shown in Fig. I, each method assumes that the injector is being controlled by a circuit which has as an input at least a logic signal which represents the desired injector state, a signal which resets the test circuitry, and a signal which indicates that the engine is running. In general, the output of the test circuitry is used to remove power from the injector upon detection of a fault and until the circuitry is reset.

INJECTOR FAULT TEST (VOLTAGE METHOD)

   The voltage methods, as seen in Fig. 2a, assumes that when the injector is off the voltage on the controlling side of the injector is high so that the output of ICl is high impedance and the voltage Vl is determined by R2, R3 and Cl. When the injector DESIRED signal goes from high to low (turning the in- jector off), C2 discharges from approximately VREF to a lower voltage determined by R5, R6 and C2. If the injector becomes shorted, even momentarily, while it is supposed to be off, V2 will go lower than Vl and the fault output will go low, thus latching the circuit until reset goes low. Typical waveforms and voltage levels are shown in Fig. 2b.

INJECTOR FAULT TEST (AC SENSING)

    This method (Fig. 3) assumes that for any AC signal on the DESIRED signal input there will be an AC signal on the ACTUAL input. A difference indicates a fault condition. The DESIRED and ACTUAL signal inputs are capacitively coupled and provide a source and sink of current, respectively. The capacitor C2 is charged through R2 on every falling edge of the DESIRED signal and is discharged through Rl on every rising edge of the ACTUAL signal. If C2 does not get discharged over the period of several fuel pulses, it will charge to the threshold of the comparator and force the fault output low.

INJECTOR FAULT TEST (FLYBACK SENSING)

   This method (Fig. 4) assumes that, since the injector is an inductor, every time the current is re- duced through the injector a high voltage pulse will occur due to the collapse of the magnetic field of the injector. The capacitor Cl is charged through R2...