Patent GB-1165755-A (GB)
Title: Improvements in Control Devices for Electromagnetic Clutches in Motor Vehicles
IPC: B60K23/02
Filed: 1966-10-03
Abstract: 1,165,755. Clutch control; friction clutches. ROBERT BOSCH G.m.b.H. 3 Oct., 1966 [2 Oct., 1965], No. 44011/66. Addition to 1,075,150. Headings F2C and F2L. [Also in Divisions G3 and H3] In a control for a motor vehicle electromagnetic clutch (Fig. 2), a mono-stable multivibrator 85 controls voltage pulses to produce in a clutch coil 35 a pulsating clutch current whose mean value with respect to time determines clutch torque, said mean value being variable in dependence upon engine speed and engine throttle position. The circuit comprises a contact breaker arm 52 which is raised twice per engine shaft revolution by a four-lobed cam 54 in the usual distributer to interrupt ignition current J through an ignition primary winding 51 and thereby feed voltage pulses to the multivibrator 85 via a resistor 56, a differentiating circuit 57, 58 and a diode 59. The multivibrator 85 comprises transistors 63, 71 and is followed by a control transistor 75. When the multivibrator is stable, and a switch 66 is open, the transistor 63 is conductive and the transistors 71, 75 are blocked. When a voltage pulse is fed to the multivibrator the latter is rendered unstable for approximately 2 ms., as determined by a resistor 60 and a capacitor 61, and the control resistor 75 becomes conductive. Before the transistor 75 becomes conductive, the potential on its collector is determined by a circuit 114. The latter comprises a potentiometer 88 which is mechanically coupled to the throttle and supplied by a voltage stabilizing circuit 117 (see Division G3) with a voltage stabilized at 4 volts when the vehicle battery 50 is at 5 to 8À5 volts. The circuit 114 further particularly comprises an impedance matching N-P-N transistor 80 and a diode 83 so arranged that the potential on the collector of the control transistor 75 is non-linearly dependent upon the throttle position. When the control transistor 75 becomes conductive there appears on its collector a positive voltage step varying between 2À1 volts at full throttle to 1À1 volts at idling. The collector of the control transistor 75 is connected to a capacitor 89 in a circuit 111, the output of which is connected to an amplifier circuit comprising an input transistor 101, amplifying transistors 103, 106 and a power transistor 110. The collector of the power transistor 110 is connected to the clutch coil 35 having a diode 108 in parallel therewith. When the control transistor 75 becomes conductive, the potential at the right-hand side of the capacitor 89 becomes more positive, a capacitor 93 is simultaneously charged via a diode 92, and thus the transistor 101 is blocked, the transistors 103, 106, 110 become conductive and current in the clutch coil 35 commences to increase. Immediately after said voltage step, the capacitors 89, 93 commence to discharge independently. The period during which the power transistor 110 is conductive, i.e. the pulse duration ti, depends upon (a) the time constant determined by the capacitor 93 and a resistor 97 and (b) the height of said voltage step which in turn is dependent upon throttle position. When the multivibrator 85 relaxes after the 2 ms., the control transistor 75 is again blocked and its collector potential moves exponentially in the negative direction with a time constant determined by the capacitor 89 and a resistor 74. The exponential negative movement is limited by a diode 76. Up to 1800 r.p.m. engine speed the pulse duration ti is not dependent upon engine speed; however, above 1800 r.p.m. the multivibrator 85 is triggered each time at an instant at which the capacitor 89 has not yet reached its maximum voltage. The level of said voltage step, together with the pulse duration ti, is therefore reduced with increasing engine speed above 1800 r.p.m. Above 15 to 20 k.p.h. the switch 66 is closed, mechanically or electronically, and, providing the engine speed is lower than about 1250 r.p.m., the multivibrator 85, including a capacitor 65 and a resistor 68 forming one of the two timing components, behaves in an astable manner with a freely oscillating period of about 24 ms. (i.e. corresponding to 1250 r.p.m. engine speed), so that the clutch current does not reduce with engine speed but remains constant for a given throttle position. This arrangement enables towed or hill-rolling starts. The stabilization provided by the circuit 117 allows the voltage step charging the capacitor 93 to be independent of the vehicle battery voltage. On the other hand the discharge of the capacitor 93 is dependent on the battery voltage. The pulse duration ti is therefore reduced with increasing battery voltage, and hence the clutch current Ik is substantially independent of battery voltage. When the knob of the usual gear shift lever is gripped during shift, a switch 94 is closed, thereby rendering the amplifier input transistor 101 conductive, the transistor 110 blocked, and the clutch torque zero. Clutch.-The electromagnetic clutch comprises a driven plate 27 gripped between a plate 28 fast with the driving flywheel 21 carrying the coil 35 and a plate 29 fast with an axially movable armature 25 disposed between the flywheel 21 and the plate 28. Current is supplied to the coil 35 via brushes 33, 34 co-operating with slip rings 31, 32 respectively connected to the plate 29 and one end of the coil 35, the other end of the coil being connected to the flywheel.