Patent GB-1008074-A (GB)
Title: Improvements relating to clutches for mechanically propelled vehicles
IPC: H02P29/00
Filed: 1962-08-02
Abstract: 1,008,074. Controlling clutches. ROBERT BOSCH G.m.b.H. Aug. 2, 1962 [Aug. 3, 1961], No. 29657/62. Heading F2L. [Also in Division H3] An electric circuit controlling a clutch in a motor car, and operative with increasing engine speed to cause automatic clutch engagement, comprises a monostable relaxation oscillator supplying current impulses to the control coil of the clutch, and means providing trigger pulses at a frequency corresponding to engine speed to a pulse former within the oscillator, the pulse former producing from each trigger pulse a two-part pulse, the first pulse-part being followed by a second pulse-part of opposite polarity, the second pulse-part initiating operation of the relaxation oscillator from its stable inactive condition into its unstable active condition to supply an operating current impulse to the clutch coil, the first pulse-part acting only at high engine speed to terminate the previously triggered operating current impulse. The arrangement is such as to ensure that once a sufficiently high engine speed has been achieved to cause complete clutch engagement, a further increase in engine speed does not cause partial clutch disengagement .by overlapping of a second trigger impulse with an operating clutch engaging impulse. The control circuit is shown applied to a conventional magnetic powder clutch, Fig. 2 (not shown), arranged as usual between the car engine and a hand-operated change-speed gear (not further described). Fig. 1 (not shown). , The monostable relaxation oscillator 20 is supplied with trigger impulses by an engine driven A.C. generator 11 feeding through rectifiers 15 to the car battery 18 and through a condenser 55 and a rectifier 60 to the base of a pulse-forming transistor 44. In the stable condition of the relaxation oscillator 20, the pulse-forming oscillator 44 is rendered conducting by the potential applied to its base from a potentiometer 58,59 connected between positive and negative lines 16, 17. The collector of the pulse-forming transistor 44 feeds through a resistor 49 and a condenser 53 to the base of an input transistor 41, which is likewise maintained conducting in the stable condition of the relaxation oscillator by the potential applied to its base through potentiometer resistors 63, 64, 69 connected between the positive and negative lines 16, 17. The collector of the input transistor 41 is connected through resistors 70, 46 to the negative line 17 and also to the base of a current amplifier transistor 42, accordingly under these conditions maintained non-conducting. A power transistor 43, connected in parallel with the amplifier transistor 42, has its base connected through a resistor 71 to the positive line 16, so that it, too, is in the stable condition rendered non-conducting. The two transistors 42, 43 are connected through a clutch-engaging coil 32 to the negative line 17. Since understable conditions both these transistors 42, 43 are non-conducting, the clutch coil 32 is not energized. At the same time, the condenser 62 of a timer circuit, having one side connected to the negative line 17, is charged through the resistors 63, 64, a rectifier 65 and a rectifier 67. When a trigger pulse is fed from the A.C. generator 11 to the condenser 55 and the rectifier 60, and thence to the base of the pulseforming transistor 44, the latter, which was previously in its conducting state, is rendered non-conducting. Accordingly, the condenser 53 is discharged and causes a change in the potential applied to the base of the input transistor 41. An initial negative pulse 83 is applied to the base of this transistor, followed immediately by a positive pulse 84. Since, under the stable condition described, the input transistor 41 was previously conducting, the negative pulse 83 has no effect. However, the positive pulse 84 immediately causes the input transistor 41 to the rendered non-conducting. Accordingly, the potential applied to the base of the current amplifier transistor 42, connected to the negative line 17 through the resistors 70, 46, falls, so that the current amplifier transistor 42 becomes conducting and supplies current to the clutch engaging coil 32. Simultaneously, the power transistor 43 is rendered conducting and also supplies current to the clutch coil 32. Transmission of current through the clutch coil 32 raises the potential of the negative side of the condenser 62 above that of the negative line 17, so that the timer condenser 62 now discharges through the resistors 66, 69, 46 to earth. The base of the input transistor 41 is thereby maintained at such a potential as to hold this transistor non-conducting, although the initiating trigger impulse 84 has died away. Thus an operating impulse of some duration is supplied through the transistors 42, 43 to the clutch-operating coil 32. Ultimately, the timer condenser 62 is sufficiently discharged to allow the input transistor 41 to be rendered once more conducting. The amplifier and power transistors 42, 43 now again become non-conducting, and the clutch-engaging coil 32 is no longer energized. When this condition is achieved the timer condenser 62 is once more charged through the resistors 63, 64 and the rectifiers 65, 67. A further current operating impulse is supplied to the clutch coil 32 when another trigger impulse is supplied by the A.C. generator 11. With increasing engine speed, the frequency with which the trigger impulses are received by the pulse forming transistor 44 increases, so that ultimately a trigger impulse is received before the timer condenser 62 has sufficiently discharged to restore the input transistor 41 to its conducting condition. When this occurs, the initial negative pulse 83 produced on discharge of the condenser 53, when the pulse-forming transistor 44 is rendered non- conducting, is applied to the base of the input transistor 41, and renders the latter conducting, over-riding the still-acting discharge of the timer condenser 62. The immediately following positive impulse 84 formed by the discharge of the condenser 53 then restores the input transistor 41 to its non-conducting condition, for the production of a further operating current impulse in the clutch coil 32. Thus a condition in which a succeeding trigger impulse 84 follows too soon behind the preceding trigger impulse to be effective upon the input transistor 41, with consequential non-production of a current-operating impulse in the clutch coil 32 and partial clutch disengagement is avoided.