Motorola Corporation

Chi Sun Lai

Zbynek A Capurka

Philip D Gunderson

An electronically adjustable spark timing signal is provided for an internal combustion engine to be used in conjunction with a breakerless constant percent dwell output electronic ignition system. A monostable multivibrator circuit uses two constant current sources, one of which is adjustable, to produce an electrical signal the pulse width of which, under static conditions, is representative of the predetermined amount of desired advance or retardation required for efficient engine operation at all speeds, the pulse width of the output signal also varies as a function of engine speed and provides automatic dynamic advance with increasing speeds. This electronic timing adjustment signal is then combined, in a delay circuit, with the digital output of a constant percent dwell circuit to provide an adjusted spark timing signal which controls the operation of the ignition coil.

Electronic spark timing adjustment circuit

A first sensor couples to an internal combustion engine and generates a first set of pulses suitable for ignition firing. A second sensor operates in synchronism to the first sensor producing a second set of multiple pulses, during the interval between a first set of pulses, whose occurrence corresponds to specified angles of engine revolution and whose time duration is inversely related to engine RPM. The second pulse set is processed through a digital-to-analog converter having a staircase output voltage which is representative of instantaneous engine position. The second pulse set is further processed through an integrator, modified to produce an output approximating an inverse, or hyperbolic, functional relationship to the input, whereby output pulses are generated whose peak amplitude is representative of instantaneous engine speed, i.e. RPM. Comparator circuitry produces a trigger signal corresponding to a predetermined relationship between the positive voltage signal and speed pulses. The trigger signal activates a switch which initiates ignition coil dwell time such that the time interval from initiation of dwell time for recharging the coil to the next ignition firing is constant over substantially the entire range of operating RPM's thereby always recharging the coil to the same energy level between firings.

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Lake Zurich, IL, United States of America

Chi Sun Lai