Patent GB-1200838-A (GB)
Title: Improvements in hydraulic correctors for controlling a member, notably of an automatic change-speed transmission
IPC: F16H61/02
Filed: 1968-12-13
Abstract: 1,200,838. Variable-speed control. SOC. ANON. AUTOMOBILES CITROEN. 13 Dec., 1968 [20 Dec., 1967], No. 59527/68. Heading F2D. The control circuit fluid pressure of a motorvehicle automatic change-speed gear is regulated by a floating slide valve 36 responsive to the accelerator position A acting through an hydraulic device C to apply a first force f 1  to the slide valve 36, and a centrifugal detector D responsive to engine and/or vehicle speed to apply a second force f 2  thereto, the slide valve 36 being responsive to a third force f 3  formed by the automatic control circuit fluid pressure at E, which is applied, via a duct 46, and acts in opposition to the first two forces, whereby any resulting unbalance moves the slide valve temporarily to adjust and balance the control circuit pressure in accordance with accelerator position A and engine and/or vehicle speed, or, the third force f 3  may be effected by a spring (50) (Figs. 4 and 5, not shown) directly acting on the slide valve, the hydraulic device C modifying the slide-valve force f 1  according to the speed of depression of the accelerator A, whereby the faster the accelerator pedal depression the greater the reduction ratio automatically selected for increased vehicle acceleration, release of the accelerator A temporarily disconnecting it from the hydraulic device C which then retards further ratio change, whereby untimely and too frequent gear changes caused by irregular or jerky actuation of the accelerator are prevented. As shown, the hydraulic device C has a first piston 2, positively connected via a flange 7 and lever 30 to the accelerator pedal A only during depression thereof, a second piston 5, connected via a flange 6 and lever 33 to apply the force f 1  to the slide valve 36, and a third floating piston 10 connected via a spring 14 to the second piston 5 which is spaced from the first piston 2 and the cylinder base 18 by springs 13 and 17 respectively. The spaced pistons 5, 10, 2 form fluid-filled chambers 19, 20, 22 which are interconnected by orifices 24, 25 in the pistons 2, 10 and by limited flow leakage around the pistons, a by-pass line 23 incorporating a non-return valve 29 interconnecting the chambers 19, 22. Depression of the accelerator raises piston 2 and, via the fluid-filled chambers 20, piston 10 which forces fluid from chamber 19 to 20, via the by-pass 23, maintaining pressure balance in these latter chambers 19, 22, the pressure in chamber 20 increasing as the piston 10 is retarded during its movement by the spring 14, transmitting to piston 5 an effort adding itself to that of spring 13 biasing the flange 6 to reduce the force f 1 . Thus at any vehicle speed a rapid depression of the accelerator pedal down to a given position will tend to increase the reduction ratio more than when the pedal is slowly depressed to the same position, and still more than when the pedal is stabilized in this depressed position. On release of the pedal A, the piston 2 is urged by spring 13 &c. to compress the fluid in chamber 22, the by-pass 23 now being closed by the non-return valve 29, oil leaking from the chamber 22 via the orifice 24 and clearance 26 to slowly return the piston 2 to re-engage the pedal via arm 30. Thus, quick release of the accelerator is not accompanied by an immediate change (i.e. decrease), in the reduction ratio, whereby the smooth transition period damps out irregular pedal movements. Fig. 3 (not shown) illustrates a similar hydraulic device modified to connect the accelerator A at the opposite end of the cylinder. Further modifications (Figs. 4 and 5, not shown) illustrate hydraulic devices similarly operated by the accelerator A to act on a spring-loaded slide valve (49) the position of which directly effects ratio-change.