Patent GB-866609-A (GB)
Title: Improvements in or relating to the control of a hydrostatic transmission
Inventor: COOPER FREDERICK DOUGLAS
IPC: F16H39/14
Filed: 1958-09-18
Abstract: 866,609. Hydraulic transmission of power. FORD MOTOR CO. Ltd. Aug. 18, 1959 [Sept. 18, 1958], No. 29948/58. Class 69 (2). A control for a hydrostatic transmission comprising a variable-delivery pump 13, Figs. 1 and 3, supplying a variabledelivery motor 14 operates so that the initial acceleration takes place by increasing the pump output and, when the maximum pump flow is reached, higher speeds are achieved by decreasing the motor displacement, the pump and motor being controlled by a pair of hydraulic servo-rams 7, 9 and 8, 10 simultaneously controlled by a cam 4. The pump and motor may be of an axial-piston type, the swash-plates 11, 12 being controlled by the hydraulic servo-rams 7, 9 and 8, 10, respectively. The cylinders of the servo-rams are supplied with fluid pressure under the control of valves 15, 16, actuated by the cam 4 which is rotatable by a control lever. The cam is shaped to actuate the valves so that, for forward drive, the pump output is increased to maximum and thereafter the stroke of the motor is reduced to a minimum, and, for reverse drive, both the pnmp and motor are adjusted simultaneously. The Provisional Specification describes also a transmission having a pump P and motor M of the swash-plate type, the swash-plate of the pump being adjustable by a lever L1 movable between stops ST1 and ST2 representing maximum reverse and forward positions, respectively, and the swash-plate of the motor being adjustable by a lever L2 movable between stops ST4 and ST3, stop ST4 determining the maximum stroke position of the motor and stop ST3 a position of minimum stroke, the latter stop being operable during use of a towing-bar T. Lever L1 is connected to a cylinder C having a piston P1 connected by a ball to the lever L2; a rod R also interconnects the levers L1, L2. Fluidpressure is suppliedto one or other ends of the cylinder from a valve V controlled by solenoids S1, S2 energized by movement of a control lever CL. The electric circuit also includes a " neutral-find " switch NF operable from a cam CA connected to the swash-plate of the pump and a switch CC having a pair of contacts actuated by a member frictionally-slidable on the rod of the piston P1. In operation, the engine driving the shaft SH1 of the pump is started by moving the control lever to the " start " position. If forward drive is then selected, the solenoid S1 is energized and the valve V moves to the left to connect the righthand side of piston P1 to the fluid-pressure to move the cylinder to the right and increase the output from the pump until the lever L1 abuts the stop ST2, the motor during this operation remaining in the position of maximum stroke. Further increase in speed is effected by the fluid pressure then moving the piston to the left until the lever L2 abuts the stop ST3, the motor now being positioned for minimum stroke. Reduction in speed is obtained by the reverse process. When reverse drive is engaged, solenoid S2 is energized to move the valve V so that fluid-pressure moves the cylinder C to the left to increase the pump flow until the ball on the rod R engages the lever L2 whereupon both levers are moved simultaneously until lever L1 abuts stop ST1, the pump then being at maximum stroke and the motor on part stroke to restrict the maximum speed of the vehicle in reverse. The ball connections between the lever L2 and piston P1 and rod R permit the lever L2 to move independently when the vehicle is towing. Any selected speed may be retained by moving the control lever CL to neutral wherein both solenoids are de-energized, any movement occurring between the piston P1 and cylinder, however, closing the contacts CC to energize the respective solenoid to return the piston and cylinder to the selected position. The vehicle is stopped by moving the controllever to the " emergency stop " position wherein the " neutral find " switch becomes operative to energize the solenoids so that the piston-andcylinder returns the pump to the inoperative position.