Patent GB-1481673-A (GB)
Title: Multi-ratio transmission
IPC: F16H59/40
Filed: 1975-10-14
Abstract: 1481673 Change-speed control VOITH GETRIEBE KG 14 Oct 1975 [16 Oct 1974] 42076/75 Addition to 1429749 Heading F2D In a multi-ratio transmission having hydraulically operable ratio-establishing friction devices (clutches or brakes) controlled by solenoid valves under electronic control and in which a shift between two adjacent ratios is effected by a first signal which triggers activation of one solenoid valve and a second signal which triggers de-activation of another solenoid valve, each solenoid valve has its own timing means, e.g. an R-C combination, to determine the overlap, positive or negative, of clutch or brake engagement during the shift, and at least one of the timing means is variable by an operational parameter, e.g. engine load or hydraulic medium temperature. The Figure shows that part of a control circuit for effecting automatic ratio shifts between second and third ratios in accordance with the difference between a voltage U L  related to engine load and a voltage U V  related to transmission output speed, these voltages being applied to the input terminals of a voltage comparator 25. When U L  is greater than U V  the output from 25 is positive, and compacitors 8, 9 are charged to voltages U 8 , U 9 . The voltage U 9  fed to a voltage comparator 45 is greater than a voltage U Y  derived from a potentiometer 46, 47 so that the output from 45 results in a transistor T 2  being conductive, causing energization of a solenoid valve 12, and the voltage U 8  fed to a comparator 35 is greater than a voltage U X  derived from a potentiometer 36, 37 so that the output from 35 results in a transistor T 3  being non-conductive causing a solenoid valve 13 to be de-energized. When U V  exceeds U L , signalling the requirement for the 2-3 upshift, the output from 25 becomes negative so that the capacitor 8 discharges through a diode 31 at a rate determined by a resistor 33, and the capacitor 9 discharges through a diode 41 at a rate determined by a resistor 43. As U 9  falls below U Y  the output from 45 causes T 2  to become non-conductive to de-energize the solenoid 12, and as U 8  falls below U X  the output from 35 causes T 3  to conduct and thereby energize the solenoid 13. U 9  discharges at a lower rate than U 8  so that 13 is energized before 12 is de-energized to give a positive clutch or brake overlap during the shift. When U L  again exceeds U V  to initiate the 3-2 downshift the output from 25 becomes positive and 8 is charged through a resistor 32, and 9 through a resistor 42. The resulting changeover of the conductivity states of the transistors T 2 , T 3  provides positive or negative overlap of clutch or brake engagement depending on the rate of charge of 8 through the resistor 32 which consists of low and high value components 32a, 32b either of which is effective through a switch 29 actuated by the accelerator pedal 28. Instead of the switched resistors 32a, 32b a sliding resistor actuated by the pedal 28 may be provided. Also, other resistors may be variable to adapt the overlap periods for different engines, transmissions or vehicles. A protective circuit is described using AND- gates &c. and limit switches associated with the solenoid valves, or pressure switches, to cut off the hydraulic medium or reverse a ratio shift in the event of a malfunction causing persistent overlap of clutch or brake engagement.