GB1429749A - Multi-ratio transmission - Google Patents

Abstract

1429749 Change-speed control VOITH GETRIEBE KG 24 April 1974 [26 April 1973 16 March 1974] 17946/74 Heading F2D In a multi-ratio transmission in which pressure-fluid operable devices such as brakes or clutches are actuated to effect ratio changes and means is provided whereby two such devices are temporarily simultaneously engaged to give positive engagement overlap during upward changes, the fluid operable devices are controlled by electromagnetically actuated valves governed by electronic circuitry with timing means for each upward change to determine the duration of the engagement overlap. The apparatus described provides also for negative overlap during downward changes. The figure shows part of a control circuit for effecting changes between second and third ratios. An amplifier stage 26 consisting of a voltage comparator receives a reference voltage U L derived from voltage divider resistors 23, 24 connected across a supply voltage U B , and a control voltage U v obtained from means responsive to transmission output speed and engine load sensed by throttle position. The voltage U v may alternatively be dependent on speed alone and the voltage U L on load. When U v exceeds U L the amplifier stage 25 causes a transistor T 1 to become conconductive and energize a solenoid valve 16 which controls engagement of the brake or clutch for third ratio, and at the same time a capacitor 20 is discharged through a resistor 33 and diode 31 so that a voltage U c applied through a resistor 34 to an amplifier stage 35 drops exponentially to cause the amplifier stage 35 to switch a transistor T 2 to the non-conductive state after an interval determined by the time constant of the components 20, 33. When the transistor T 2 is non-conductive a solenoid valve 15 de-energizes the clutch or brake which establishes second ratio. When the voltage U v drops, requiring a change back from third to second ratio, the transistor T 1 is rendered non-conductive to de-energize the the valve 16 and, after an interval determined by the time constant of a resistor 32 and the capacitor 20, the capacitor is charged to a degree such that the voltage U c causes the amplifier stage 35 to switch the transistor T 2 to be conductive and thereby energize the second ratio valve 15. Additional circuit elements may be provided to adjust the duration of overlap in accordance with engine load or transmission output speed.