Patent GB-1497539-A (GB)
Title: Electrical control signal generating apparatus for use in internal combustion engine ignition systems
IPC: F02P5/15
Filed: 1975-02-05
Abstract: 1497539 Timing ignition COMPTEURS SCHLUMBERGER 5 Feb 1975 [6 Feb 1974] 05465/74 Heading F1B Apparatus for generating an electrical control signal for controlling the ignition system of an internal combustion engine comprises detector means 308 for detecting first and second given positions of a member, piston 302, in a housing which defines a variable volume working chamber of the engine, counter means 312 responsive to the detector means to count pulses in such a manner as to generate a digital signal representative of the time taken by the member to move from the first to the second given position and means responsive to the digital signal for generating the control signal after a period of time which commences when the member passes a predetermined reference position and whose duration is a function of the time represented by the digital signal. The sensor 308 delivers successive squarewave signals. The leading edge of each squarewave signal corresponds to a first given low position of the piston 302 and the trailing edge corresponds substantially to the position of the top dead centre of the piston 302. The leading edge of a squarewave signal makes it possible through the reset circuit 311 to reset the content of the counter 312 which immediately after resetting begins to count the pulses delivered by the pulse generator 316. The pulses delivered at the output of the generator 316 are obtained from pulses delivered by the generator 327 delivering fixed frequency pulses which are then multiplied in the multiplier 328 by a number X which is obtained at the output of an add-subtract unit 325. The counting in the counter 312 is stopped on the trailing edge of the squarewave signal through the stop circuit 313. The content M' of the counter 312 is compared with a predetermined number M in a binary comparator 330. The add-subtract unit readjusts the value # so that the number of pulses N obtained at the output of the generator 327 multiplied by the number X in the multiplier 328 determines a new number M' which is as close as possible to M. The signal corresponding to the number # obtained at the output 326 of the add-subtract unit 325 is sent to the input of a permanent memory 318 which delivers at its output the binary signal representing a number N'. This signal corresponding to N' is applied to the input of a binary comparator 320. When the output of the counter 312 delivers a signal corresponding to the signal determining the number of pulses equal to N' while the sensor delivers the squarewave signal following the one which enables the determination of the value of #, the comparator 320 then delivers at the output 322 a pulse which allows control of the ignition system of the engine. As shown the engine comprises the piston 302 which reciprocates in a cylinder 303 but the invention could be applied to a rotary engine. The sensor may employ a photo-cell or comprise a high frequency induction type proximity sensor. The invention is described as applied to two stroke cycle engines but it can be applied to four stroke cycle engines. Other embodiments and modifications are described in the Specification.