Patent GB-1449909-A (GB)
Title: Motor vehicle having a system for the control of the main pressure in an automatic gearbox
IPC: F15B21/00
Filed: 1973-10-12
Abstract: 1449909 Change-speed control ROBERT BOSCH GmbH 12 Oct 1973 [14 Oct 1972] 47768/73 Heading F2D [Also in Division H3] The level of hydraulic pressure, operating ratio-establishing clutches and brakes in a planetary transmission driven by an i.e. engine on a motor vehicle, is controlled by the setting of the engine throttle valve 62, monitored by a mechanical-electrical transducer 12, such as a sliding or tapped resistor, operating, through electronic evaluating and regulating circuits 16, 17, an electrical-mechanical transducer such as a solenoid-loaded regulator valve 21, one of the monitor 12, the evaluating and regulating circuits 16, 17, and the regulator 21, having an output-input characteristic which is non-linear as a function of the throttle setting. Thus non- linearity may be produced mechanically in the throttle-resistor linkage; electrically in the throttle resistor 12; in the switching elements of the circuits 16, 17; or in the relation between the movement of the regulator valve armature and the amplitude of the current feeding its solenoid. In addition to being controlled by the engine throttle setting, the pressure regulator 21 may also be controlled by an exhaust gas monitor, exhaust gas recirculation, and ignition timing. Also provided are temperature compensation; prevention of friction hysteresis in the solenoid regulator valve 21 by use of a superimposed alternating current; and protection against reverse polarity voltage surge, and current failure, which latter automatically causes selection of maximum hydraulic pressure. A stabilized voltage is provided from positive and negative supply lines 22, 23 at a point 29 by a resistor 24, capacitor 27 and Zener diode 25. In the evaluation circuit 16 the emitter of a transistor 33 receives variable current from the throttle-operated resistor 12, modified by switches 14, 13 responsive respectively to a gatevalve 67 controlling exhaust gas recirculation and an ignition timing switch 64, the last two being connected through resistors 58, 53 to the function of resistors 55, 56 forming a potential divider. The collector of the transistor 33 controls a Darlington pair 36, variably energizing the regulator valve solenoid 21, and its base receives feed back 18 from the voltage drop across a resistor 38, through a Zener diode 39, resistor 41 and a resistor 42 by-passing a diode 44. Also applied to the base of the Darling- ton pair 36, through a capacitor 48 and resistor 49 is an alternating current picked up from the ignition contact breaker 51, to prevent friction hysteresis in the valve solenoid 21. Temperature compensation is achieved as follows. The Zener diode 25 and a diode 26 have opposed temperature dependent changes which cancel. Temperature dependent baseemitter voltage changes in the transistor 33 are limited by a diode 44 in the feed back line 18. In the output transistors 36 temperature changes due to solenoid current are avoided by regulating that current by using the voltage drop across the resistor 38 as feed back to the transistor 33. A Zener diode 39 protects the output transistors 36 against excessive voltage, and thus diode 39, together with a diode 28 protect against component damage if the supply polarity is reversed.