Patent GB-1460288-A (GB)
Title: Ignition
IPC: F02P3/04
Filed: 1973-12-14
Abstract: 1460288 Ignition systems; timing ignition HITACHI Ltd 14 Dec 1973 [18 Dec 1972] 58032/73 Heading F1B An ignition system for an internal-combustion engine comprises means 1, 2 for producing first and second signals of differing phase during each ignition cycle of the engine, means 7 for counting and storing the clockpulses of a first clock signal which are generated between the first and second signals, means for counting, after the second signal, the clockpulses of a second clock signal whose frequency is in a predetermined proportion to that of the first clock signal and means 9 for causing a pulse of energy derived from a D.C. source to pass through the primary winding 11a of an ignition coil 11 when the difference between the result of counting the clockpulses of the second clock signal and the stored count of the clockpulses of the first clock signal reaches a predetermined value. As shown a clock generator 3 delivers a clockpulse signal # 1  whose pulse repetition rate f 1  is selected from 200 KHz to 10Mhz. A divide-by-N counter 4 consists of, for example, m stages of binary counters and serves to reduce the repetition rate of the clock signal # 1  by a factor ¢m the counter 4 delivering an output signal # 2  having a repetition rate f 2 . When the output of the pick-up 2 is at high level the AND gate 6 is closed and the AND gate 5 is opened. Then the clock signal # 1  is prevented from reaching the counter 7 and the clock signal # 2  is delivered to an up terminal of the up-down counter 7 through the AND gate 5 so that the counter 7 counts up the clock signal pulses # 2  delivered from the AND gate 5. When the large diameter portion on the motor 1 has passed the pick-up 2 the small diameter portion on the rotor faces the pick-up. Since the output from the pick-up 2 is then at low level the AND gate 6 is opened and the AND gate 5 is closed. The clock signal # 1  is delivered to the down count terminal of the updown counter 7. The count value of the clock signal # 2  stored in the counter 7 is counted down by the clock signal # 1 . The select gate 8 is now able to deliver an output to the univibrator 9 because there is no longer an inhibiting signal from the pick-up 2. Thus when the count value of the counter 7 reaches a certain value N 2  the select gate 8 outputs a pulse to the univibrator 9. The univibrator 9 is triggered by the output of the select gate to deliver an output pulse having a constant duration. A transistor 10 is rendered conductive while the univibrator 9 is delivering its output pulse. When the transistor 10 is cut off the electromagnetic energy stored in the primary winding 11a of the ignition coil 11 is released to induce a high voltage across the secondary winding 11b. The ignition timing can be altered by changing the value of N of the divide by N counter in accordance with the rotational speed of the engine or the load condition or by resetting the value of N 2  or changing the frequency of the clock signal. The ignition system may be of the capacitor discharge type. Electrical charges stored in a capacitor may be released to the ignition coil 11 when the univibrator output drops to zero.