Patent GB-982015-A (GB)
Title: Improvements in or relating to overspeed controls for internal combustion engines
IPC: F02P9/00
Filed: 1962-06-19
Abstract: 982, 015. Controlling internal combustion engines. D. E. ATKINSON. June 19, 1962 [July 3, 1961], No. 23624/62. Heading G1N. An overspeed control for use with I.C. engines of the type which includes a primary circuit having a contact beaker for generating ignition pulses comprises means for generating a control signal when the time lapse between two successive breaks of the contact breaker points is less than a pre-set valve, and means responsive to the control signal for interrupting the ignition. Fig. 1 shows an ignition circuit comprising a contact breaker 14 in series with the primary 13 of the ignition coil, and a distributer 22 between the secondary 21 and the spark plugs 24. The pulses occurring at the point 26 each time the contact breaker points are opened are fed to a control 31 which generates an output when the time lapse between successive pulses is less than a pre-set value corresponding to the maximum operating speed of the engine. The output triggers a monostable multivibrator 32 which in turn, generates a square pulse (which may be amplified), this pulse energizing a relay 76 to open the relay contacts 17, thereby interrupting the ignition circuit and causing the engine to lose speed. At the end of the pulse generated by the multivibrator 32, the contacts 17 close. These events are repeated at each successive opening of the contact breaker points until the engine speed no longer exceeds the maximum operating value and the control 31 consequently ceases to generate an output. The control 31 may comprise a monostable multivibrator 36, Fig. 2, which responds to the negative spike only of the oscillatory pulse set up at the point 26. The square pulse generated by the multivibrator 36 is differentiated in a circuit 38, the resultant negative spike at the end of this pulse being used to trigger a monostable multivibrator 41 which consequently generates a square pulse, the width of which can be adjusted to pre-set the maximum operating speed of the engine. Both square pulses are applied to a coincidence circuit 46, which generates an output if a pulse from the multivibrator 36 arrives before the termination of a pulse from the multivibrator 41. A transistorized circuit embodying the elements 32, 36, 38, 41 and 46 is described, component values being given. The circuit includes a monostable multivibrator for converting the output of the coincidence circuit 46 into a square pulse of constant duration for energizing the relay. The ignition circuit is interrupted by a transistor acting as a switch and controlled by the relay contacts. The multivibrator 36 and differentiating circuit 38 may be omitted. During over speeding instead of opening and closing at each break of the contact breaker points, the relay contacts may be arranged to remain open continuously. For this purpose, a resistor 136, Fig. 6, is connected across the relay contacts 17, or where the relay is followed by a switching transistor, between the emitter and collector of the transistor. When the ignition circuit is otherwise interrupted, the resistor 136 allows a reduced current to flow, sufficient to maintain the generation of pulses at the point 26 but insufficient to give rise to sparks. The output pulses 137 from the coincidence circuit are fed to a transistor 141, causing a capacitor 142 in parallel with the emitter load resistor 143 to be charged to a voltage indicated by the waveform 147. This voltage is applied to the base of a transistor 144 to maintain the relay 146 energized continuously during over speeding. With this arrangement, the output of the multivibrator can be integrated to give an indication of revolutions.