Patent GB-950076-A (GB)
Title: Means for automatically controlling speed changes in variable speed power transmission mechanisms
Inventor: LAMBURN ALAN SALISBURY
IPC: F16H61/02
Filed: 1960-06-29
Abstract: 950,076. Change-speed control. AUTO TRANSMISSIONS Ltd. June 12, 1961 [June 29, 1960], No. 22722/60. Heading F2D. A shift valve controlling a change-speed gear in a motor car comprises two coaxial pistons 14, 15 in a ported cylinder 11, the piston 14 having an extension 20 engaging a bore 29 in the end of the piston 15 and coacting with a stud 30 therein to provide a positive lost-motion connection between the two pistons. The piston 15 has a groove 32 which either connects a port 35, leading to a ratio establishing clutch &c., to a venting port 36, or, upon leftwards sliding of the piston, connects the port 35 instead to an inlet port 34 connected through an accelerator pedal controlled valve 49 to a source of fluid pressure 39. The left-hand end of the piston 15 is either, as shown, acted upon by fluid pressure supplied through a valve 17 opened by depression of the accelerator pedal of the motor car turning a cam 48 acting upon a spring 48, or alternatively is directly engaged by an accelerator controlled spring. Fluid pressure is supplied to the right-hand end of the piston 14 through a valve 16 opened to the fluid pressure source 39 by a car speed proportional fluid pressure applied through a port 45. When the car is proceeding at a low speed, the accelerator-variable pressure acting on the piston 15 biases the valve to the position shown, so that the port 35 and the ratio establishing clutch &c., are vented to the port 36. With increasing car speed, the valve 16 is opened, so that pressure acts leftwards on the piston 14, which is given a small initial movement. A port 28 formed in an extension 19 of the piston 14 is then opened to the fluid pressure, which acts upon the end of the piston to give both pistons 14, 15 a rapid leftwards movement, so that the groove 32 in the piston 15 connects the inlet port 34 to the port 35 and the ratio establishing clutch. At the same time, pressure fluid supplied through the inlet port 34 passes through the groove 32 and a hole 37 therein to the space between the two pistons 14, 15, separating the two pistons and partly returning the piston 14 towards its initial position. Movement apart of the pistons 14, 15 is limited by the extension 20 on the piston 14 coacting with the stud 30 in the bore 29 of the piston 15. Pressure fluid supplied through the valve 16 still acts upon the piston 14 to bias the latter leftwards, but a lower pressure can sustain the valve pistons 14, 15 in their present positions than is necessary to initiate leftward movement of the two pistons together. When the car speed has decreased somewhat below the speed at which the port 35 was connected to the inlet port 34, the pressure acting rightwards on the piston 15 overcomes the pressure acting leftwards on the piston 14, the two pistons are slidden rightwards back to the position shown, and the port 35 and the ratio establishing clutch &c., are vented to the port 36. Alternatively, the two pistons 14, 15 can be slidden rightwards back to the position shown at a constant car speed by opening the car throttle and correspondingly increasing the opening of the valve 17. As shown, the shift valve is suitable for controlling a planetariy overdrive or underdrive gear. A multiple rat o planetary gear may be likewise controlled by using several similar shift valves.