Patent GB-1028964-A (GB)
Title: Improvements in or relating to devices for controlling electromagnetic clutches of motor vehicles
IPC: B60K23/02
Filed: 1963-01-29
Abstract: 1,028,964. Clutch control. REGIE NATIONALE DES USINES RENAULT. Jan. 29, 1963 [Feb. 2, 1962], No. 3710/63. Heading F2L. The current to a coil 7 of a vehicle clutch 8, 9 is varied, up to a maximum, in accordance with the engine speed, the current being modified by a number of factors such as release of the accelerator pedal 38, the gear ratio engaged, the vehicle speed and overrun of the vehicle. The clutch coil 7 is connected through a switch 54 which is opened during gear shift to the collector 6 of a power transistor 5 which is under the control of a transistor 14 having its base 19 connected to a capacitor 21 and also connected through a diode 23 to a secondary coil 24 of a transformer 25 having a primary coil 26 in circuit with an ignition coil 27 and a contact breaker 28. When contact 28 breaks the circuit of the primary coil 26, the capacitor 21 is charged and blocks the transistor 14 so that the power transistor 5 becomes conductive and "current flows in the clutch coil 7. When contact 28 closes, the capacitor 21 is discharged, transistor 14 becomes conductive and blocks transistor 5 and the clutch coil current dies. The current through the coil 7 thus depends on the frequency of operation of the contact 28 and hence on the engine speed. Auxiliary coils 32, 33 of the transformer 25 are provided in circuits with an accelerator controlled switch 34 which occupies the position shown when the accelerator is released; output speed responsive switches 35, 36 occupying the positions shown below a predetermined speed, and a switch 37 which is open unless the output part 9 of the clutch overruns the input part 8. On starting, and with the switches 34-36 in the positions shown and with a gear engaged so that the switch 54 controlled by the gear lever is closed, the auxiliary coils 32, 33 are shorted out through the switches 34, 35 and thus greatly reduce the amplitude of the current, pulses charging the capacitor 21 to prevent engagement of the clutch. On depressing the accelerator pedal, the circuit of the auxiliary coils 32, 33 is broken and the current pulses attain their maximum amplitude to give the maximum clutch engaging current for the engine speed attained. The engine speed at which the maximum current is obtained may be adjusted by varying a resistor 49; the shape of the current/engine speed curve can be independently set by a resistor 11. At a vehicle speed of about 10 m.p.h. (selected so as to be below that speed at which the first gear change is desired) the switches 35, 36 are shifted to their other positions, switch 35 ensuring that the coils 32, 33 cannot be short circuited irrespective of the accelerator position, and switch 36 completing a circuit from the coils 32, 33 through a resistor 48 so that the amplitude of the current pulses charging the capacitor 21 is reduced in order to soften clutch engagement after changing gear. The resistor 48 may have its value varied according to the ratio selected. On changing down to a lower ratio the contact 37 will close since the driven plate 9 will rotate faster than the driving plate 8, and, if the accelerator pedal is depressed, the auxiliary coils 32, 33 will be short circuited so that the clutch is only very lightly engaged and the engine may pick up speed rapidly. When the speed of the driving part 8 exceeds that of the driven part 9, the short circuit of the coils 32, 33 is broken and resistor 48 is inserted in the circuit so that the clutch engaging current is dependent on the engine speed and the ratio engaged. If, on downshift, the accelerator pedal is released, the coils 32, 33 will be in circuit with a capacitor 46 shunted by a resistor 47, resulting in a low clutch energizing current at high engine speeds which increases to a relatively strong current at engine idling speed.