Patent GB-1464641-A (GB)
Title: Electronic circuit for controlling the ignition timing of an internal combustion engine
IPC: F02P5/155
Filed: 1974-01-18
Abstract: 1464641 Timing ignition SGS-ATES COMPONENTI ELETTRONICI SpA 18 Jan 1974 [18 Jan 1973] 02525/74 Heading F1B The ignition timing of an I.C. engine is controlled by an electronic circuit which receives, during each compression stroke at a fixed angular position preceding top dead centre and equal to that of maximum advance, a pulse, the circuit being arranged to measure the time between successive pulses and to determine the desired ignition time on the basis of the pulses. A bi-stable Q 1 , Q 2  is triggered by the opening of the contact breaker P into the state in which Q 1  conducts and Q 2  is cut off, whereupon Q 6  and Q 13  are cut off and Q 19  is rendered conductive. A capacitor C 1  is now rapidly discharged via Q 19  and R 38  until the charging of a capacitor C 6  cuts off Q 19 , whereupon C 1  begins to be charged by a constant-current generator Q 18 . A capacitor C 3  is charged by a constant-current generator Q 12  which is controlled by the voltage across R34, which is proportional to the collector current of the Darlington pair Q 16 , Q 17  and therefore dependent on the voltage across C 1 . Another Darlington pair Q 14 , Q 15  having an emitter resistor R 33  in common with the Darlington pair Q 16 , Q 17  so as to form therewith a differential amplifier is controlled by the voltage across C 3 . The effect of this arrangement is that after the voltage across C 1  has become equal to that across C 3 , the voltage across C 3  then rises in unison with the voltage across C 1 . The voltage continues to rise until the contact breaker P again opens, whereupon, as before, C 1  is first rapidly discharged and then begins to be charged again. The voltage to which C 1  and C 3  are charged is thus a measure of the time elapsing between successive openings of P and therefore is a measure of the engine speed, decreasing as the speed increases. The voltage on C3 is retained when C 1  is discharged. After each opening of P, a capacitor C 2  is charged via a constant-current generator Q 5 . A further differential amplifier comprising Darlington pairs Q 7 , Q 8  and Q 10 , Q 11  with a common emitter resistor R25 compares the voltage across C 2  with the voltage across C 3 . When the voltage across C 2  has become equal to that across C 3  a transistor Q 9  switches on Q 2 , whereupon Q 1  is cut off. A Darlington pair Q 3 , Q 4 , or a monostable, connected to the ignition coil I is switched off by Q 2 , thereby producing ignition. Q 6  and Q 13  are now rendered conductive, and rapidly discharge C 2  and C 3  via R 18  and R 29  respectively. C 2  remains discharged until the contact breaker P opens again, while C 3  resumes charging after Q 13  has been cut off by the charging of C 4 . The opening of the contact breaker P occurs at a fixed angular position before TDC. The time at which ignition occurs, measured from this angular position, depends on the charge held on C 3 , which in turn depends on the engine speed as sensed by C 1 . As the voltage across C 2  increases, the charging current supplied to it by the constantcurrent generator Q 5  is altered in three discrete steps by means of voltage-sensing circuits E 1 , E 2 , E 3  which act at three respective levels of the voltage across C 2 , or C 1  to alter the base voltage of Q 5 , whereby the slope of the characteristic curve of ignition advance versus engine speed is altered in three steps.