Patent GB-922044-A (GB)
Title: Improvements in or relating to clutches
IPC: H02P29/00
Filed: 1961-05-04
Abstract: 922,044. Transistor switching - circuits. ROBERT BOSCH G.m.b.H. May 4, 1961 [May 5, 1960], No. 16150/61. Class 40 (6). [Also in Group XXIV] An electromagnetic clutch system (see Group XXIV) for use with internal combustion engines, includes a transistorized circuit which varies the duration of the impulses as a function of the speed of the engine and thus with frequency of occurrence of the impulses. In one form, electrical impulses derived from the usual make-and-break switch 56, Fig. 3, feeding the primary coil 52 of the car ignition, are fed through a resistor 60, a capacitor 61, and a rectifier 74 to the base of a normally-conducting transistor 70 forming part of a flip-flop circuit 70, 71. The collector of the transistor 70 feeds a transistor 71, normally holding it non- conducting so that an amplifying transistor 87 is held non-conducting together with a further amplifying transistor 90 feeding the clutch coil 35. When the ignition impulse fed to the transistor 70 renders the latter non- conducting, the transistor 71 is rendered conducting, together with the transistors 87, 90, so that current begins to flow through the clutch coil 35. Flow of current through the transistor 71 energizes the primary coil 83 of a transformer 82 and thus induces a current in the secondary coil 81 thereof, the potential of this current acting across a resistor 75 to raise gradually the potential of a junction B to which the ignition was fed. Due to the inherent reluctance of the transformer 82, the potential at the junction B changes gradually, until it reaches a point at which the transistor 70 is again rendered conducting. When this happens, the transistors 71, 87, 90 in turn become non-conducting, and current is no longer fed through the clutch coil 35. To change the duration of the impulses produced in the clutch coil 35, a resistor 78 is adjusted by an engine-driven centrifugal governor 66. The arrangement is that, with increasing engine speed, the impulses fed through the clutch coil 35 become of increasing duration and frequency, until a continuous current is fed through the coil. In a modified form, Fig. 4, the engine-speed governor 66 is replaced by an electronic circuit 100 sensitive also to changes in engine temperature, to raise the engine speed permissible when the engine is cold before clutch-engagement is commenced. Transistors 70, 71, 87, 90, controlled by impulses from 74, are provided as before to feed the clutch coil 35. A transistor 102 is rendered increasingly conductive with rising engine speed, the current passing therethrough to a resistor 103 raising the potential of the base B of transistor 70, which thus becomes non-conducting. At low temperatures, the resistance of a negative temperature co-efficient resistor 113 falls, raising the potential at a junction D to tend to render a transistor 101 non-conducting, thus tending to make the transistor 102 conducting and raising the potential at the junction B, to make the transistor 70 non-conducting. Impulses from the primary ignition coil 52 are fed in through a time-control circuit comprising a resistor 114 in parallel with a capacitor 116. A second negative temperature co-efficient resistor 110 causes higher gain at low temperatures. The two negative temperature coefficient resistors 110, 113 are in contact with the engine coolant. In a further modified form, the clutch-control circuit includes means for disengaging the clutch gearing ratio shifts, and obtaining cushioned re-engagement following establishment of a new ratio (see Group XXIV). In this circuit, a switch 140, Fig. 6, is opened at load speeds above 15 k.p.h. so that a transistor 130 feeding the input transistor 71 is rendered non-conductive. Accordingly the transistor 71 conducts, so that it is not effected by high speeds of the car engine causing missing of individual pulses, due to the inherent delay of the circuitto become effective and cause clutch dis, engagement. In a further modification, the mechanical speed-actuated switch 140 preventing accidental disengagement of the clutch above road speeds of 15 k.p.h. is in series with an electronic circuit producing the same effect. Ignition impulses at the junction D, Fig. 8, are superimposed on the voltage at the junction C and with increasing speed render a transistor 170 non-conducting, so that a transistor 171 becomes conducting. This in turn renders the transistor 130 non-conducting. Accordingly, if the speed control switch 140 is closed below 15 k.p.h. the transistor 130 is still rendered non-conducting and the clutch coil is continuously energized. In another modification, a preceding impulse is used to prolong the duration of a following impulse if the subsequent impulse follows quickly, as at high engine speeds, or to reduce it, when the engine speed is low. In this form, the moment the transistor 87, Fig. 9, is rendered non-conducting, a capacitor 206 is charged, and thus renders the transistor 102 conducting. The capacitor 206 discharges through a resistor 205, the potential at a junction Q drops sharply, and then gradually rises. Thus the current through the transistor 102 drops slowly, and the potential across the resistor 76 gradually rises. If the transistor 70 is now rendered non-conducting by the next impulse, so that the transistor 71 conducts, the transistor 87 induces a current which flows through the resistor 75, holding the transistor 70 non- conducting until the rising potential applied from the transistor 102 is greater. The transistor 70 then again conducts. If the frequency of the impulses is low, the duration of produced impulse is short.