Patent GB-955602-A (GB)
Title: Improvements in or relating to clutches
IPC: F16D37/02
Filed: 1960-09-16
Abstract: 955,602. Clutch control. ROBERT BOSCH G.m.b.H. Sept. 16, 1960 [Sept. 30, 1959], No. 31893/60. Heading F2L. [Also in Divisions G1 and H2] In a control for an electromagnetic powder clutch, for motor vehicle I.C. engines, to enable the clutch to transmit, above idling speed, a torque rising with engine speed, a winding 35 thereof is fed in current pulses by a monostable multivibrator which is equipped with transistors and brought into its unstable condition by an electrical impulse generating means coupled, at least indirectly, to the engine crankshaft for actuation at least once per crankshaft revolution, the current pulses fed to the clutch winding being of approximately rectangular form, of a length determined by the multivibrator, and of a frequency determined by the impulse generating means and thus by the engine speed. The circuit comprises a battery 50, an ignition switch 54 and positive and negative leads 73, 75. An arm 56 is raised twice per crankshaft revolution by a four-lobed cam 58 in the usual distributer to interrupt ignition current through an ignition coil primary winding 52 and induce thereon a voltage U which is fed to the monostable multivibrator by way of a resistor 60, a capacitor 61 and a diode 62, there being a capacitor 63 leading to the positive lead 73. The capacitor 61 forms, together with diodes 64, 65 and two resistors 66, 67, a differentiating circuit through which a very small control impulse is delivered to the base of an input transistor 70 of the multivibrator at each ignition interruption. With the engine stationary, no current flows through the diode 62, and the transistor 70, held conductive by its base current flowing through a resistor 74, blocks a transistor 71 thereby permitting full charging of a capacitor 81. A transistor 83 is also blocked preventing transistors 90, 92 from supplying current. As soon as ignition is interrupted and the induced voltage U raises the potential at the end of the primary winding 52 connected to the resistor 60 for a short period, the transistor 70 is blocked and transistors 71, 83, 90 and 92 become conductive. The transistor 70 is held blocked after the voltage U has vanished by the capacitor 81 until the latter has discharged, whereupon the transistor 70 reverts to its conductive condition and again blocks the transistors 83, 90 and 92. Current pulses J 2  are delivered by the transistor 92 to the winding 35. To provide for enging braking, a relay 100 controlled by a centrifugally actuated switch 101 actuates a changeover switch 96 to disconnect the winding 35 from the transistor 92 collector and connect it directly to the positive lead 73 at vehicle speeds above 15 k.p.h. For automatic disengagement during gear changing a relay 113 energized by touching a gear change lever knob actuates a changeover switch 111, 112 to disconnect the winding from the transistor 92 collector and reversely connect it to the positive lead 73 through a resistor 120 which latter ensures a demagnetizing current J 0  which cancels residual magnetism but does not reach a value sufficient for torque transmission in the clutch. To weaken voltage peaks occurring at the end of the current pulses J 2  a diode D is connected in parallel with the winding 35. The switch-off time constant of the clutch, which is arranged smaller than the switch-on time constant, is reduced relatively to said switch-on time constant to modify the speed dependent value of the mean current flowing through the winding by a resistor W connected in series with the diode D. The resistance of the resistor W is at least equal to, or preferably higher than, the direct current resistance of the winding 35. In the electromagnetic powder clutch (Fig. 2) the driving member, secured to the crankshaft and forming the fly-wheel therefor, comprises half shells 21, 22 enclosing the winding 35, and the driven member comprises a circumferentially grooved rotor 25 secured to the usual gear-box input shaft. Magnetizable powder 30 is centrifuged, during running, into an annular gap, 1 to 2 millimetres wide, between the shells and the rotor periphery. The winding 35 is fed through insulated brushes and slip rings 38, 39 and 36, 37 respectively secured to an engineflanged casing 12 and the shell 22.