Patent GB-1007612-A (GB)
Title: Improvements relating to clutches
IPC: F16D37/02
Filed: 1962-07-27
Abstract: 1,007,612. Clutch control. ROBERT BOSCH G.m.b.H. July 27, 1962 [July 28, 1961], No. 28896/62. Heading F2L. In a control system for an electromagnetic clutch for a vehicle operating current impulses are supplied to the magnetizing coil of the clutch at a frequency related to the engine speed, the impulse length being independent of speed, and the clutch automatically engages when the engine speed is increased to about twice the idling speed. During drive the clutch can be engaged in order to re-establish the transmission of power by accelerating the engine, but this may be undesirable when the vehicle is moving down hill if it is desired to utilize the braking power of the engine, and a circuit is provided including a gear change lever-operated switch which on completion of a gear change automatically engages the clutch for a brief period. As described, a magnetic powder clutch having a magnetizing coil 30 is supplied with operating pulses by a monostable relaxation oscillator 53 to which control pulses are applied from the vehicle ignition system. The ignition system includes a cam 45 rotated at half the engine speed and opening a switch 43 in the line to a primary winding 42 of the ignition coil. The resulting voltage in the winding 42 is applied through a resistor 46, a condenser 49 and a rectifier 80 to the base of an input transistor 60 of the monostable relaxation oscillator and blocks this transistor which is normally current-conducting. A current amplifying transistor 62 and an output transistor 61, which are normally blocked, thereupon become current-conducting and supply an operating current pulse through switches 74, 77 to the clutch coil 30. The input transistor 60 remains blocked for a period determined by a timer circuit comprising a condenser 63 which was charged during the current conducting state of the transistor 60 and which is discharged through resistors 68, 69, 66 and through resistors 64 and 65 to again block the input transistor 60. The resistor 65 has a negative temperature coefficient and is subject to the engine temperature and serves to shorten the length of the operating impulses when the engine is cold so that the engine idling speed can be raised without increasing clutch torque. To start the vehicle from rest it is only necessary to accelerate the engine by depressing the accelerator pedal. The increased frequency of the operating impulses in the monostable relaxation oscillator increases the clutch torque, which is further increased by a switch 84 which closes when the accelerator is depressed, and which shorts out a resistor 83 in the circuit of the clutch coil 30. When the gear-change lever is operated for changing gear, a switch 78 is closed and energizing current flows through a relay coil 79 to open the switch 77 and break the connection between the transistors and the magnetizing coil 30. After changing gear the clutch can be re-engaged by accelerating the engine. In order to avoid the necessity for accelerating the engine for reengaging the clutch, a circuit is provided which supplies a control impulse independent of the speed of the engine when the gear-change lever is released. This control impulse is of short duration and renders the two transistors 61, 62 conducting for this period, thereby reengaging clutch. The circuit comprises a rectifier 86, a resistor 87, and a condenser 88. During gear change, when the switch 78 is closed, the condenser 88 is charged through a switch 91 which is opened only in first gear and in reverse. When the gear-change lever is released, the switch 78 is opened and the condenser 88 is then connected by the plate which was previously connected to a negative lead 40, to a positive lead 41 through the relay coil 79, and this raises the potential of the base of the input transistor 60 to a positive value above the potential of the positive lead 41. The transistor 60 is therefore blocked and the transistors 61, 62 become conducting until the condenser is discharged through a rectifier 67 and the resistor 69. The clutch is therefore engaged for this period and can accelerate the engine to a sufficiently high speed, if the vehicle speed is sufficiently high, that the control pulses are sufficiently frequent to maintain the clutch torque. During operation of the vehicle if the engine speed is such that insufficient time is available for charging the condenser 63 in the intervals between operating impulses, or if the speed is further increased so that the following control pulse occurs during a previously initiated operating current impulse, the control pulse is stored in a pulse-storing apparatus 54 until the operating impulse has expired. The pulse-storing apparatus is similar to that described in Specification 1,007,611.