Patent GB-1056968-A (GB)
Title: Hydrostatic variable-ratio transmission
IPC: F16H61/42
Filed: 1965-03-30
Abstract: 1,056,968. Hydraulic variable ratio transmission and control; linkwork. SUNDSTRAND CORPORATION. March 30, 1965 [April 1, 1964], No. 13530/65. Headings F2C, F2D and F2K. In a variable ratio hydrostatic transmission, for tractors, comprising an engine driven pump 14 in closed circuit with a motor 16, a first centrifugal governor 101 (Fig. 1, not shown), responsive to engine speed controls the engine throttle to maintain engine speed at a predetermined value, and a second centrifugal governor 102 (Fig. 1, not shown) also responsive to engine speed is operable, should the engine be incapable of maintaining speed under heavy load conditions and approach stalling, to increase motor displacement to reduce transmission output speed upon a drop in engine speed to a value lower than said predetermined value. The pump, which is reversible, and the motor are of the variable-displacement swash-plate type and are connected by lines 21, 22. The swash-plate angles are respectively controlled by fluid pressure servomotors 28, 30 and 36, 38 energized through control valves 52, 54. Follow-up control is provided by floating levers 48, 50 which are pivoted on the spools of the valves 52, 54 and have their opposite ends respectively pivotally connected to a common manual Forward-Neutral-Reverse control cam 42 and to the swash-plates. Pivoted torsion springs 45, 47 connected between the cam and the floating levers provide normally rigid connections which yield to prevent damage to the valves on excess cam movement, the spring 47 having the additional function of permitting an overriding actuation of the valve 54 (described below). Slots 42a, 42b in the cam are so formed that first the pump displacement is increased while the motor displacement is held at a maximum, and then the motor displacement is reduced while the pump displacement is held at a maximum. An engine driven gear type make-up and cooling pump 56 draws from a reservoir 58 and, through a filter 62, feeds lines 21, 22 through spring-biased check valves admitting pressure only to the low pressure side of the transmission. The pump 56 also feeds the valves 52, 54 and a valve 68 which is actuated by said second centrifugal governor 102. Excess fluid from the pump 56 is drained through a spring-biased relief valve 73. A pair of high pressure relief valves 74, 76 across the lines 21, 22 relieve surge pressure during rapid acceleration or braking. A shuttle valve 80 connects that of the lines 21, 22 at low pressure with a low pressure relief valve 78 so as to drain heated oil. A heat exchanger 88, together with a by-pass means 90, is provided between the fluid drain and the reservoir 58. A spring- returned by-pass valve 91 between the lines 21, 22 is actuable by the vehicle brake pedal to maintain pressure across the lines 21, 22 at a safe level during braking. The first centrifugal governor 101 comprises engine-driven fly weights 132 (Fig. J, not shown), acting, against a spring 127, in a closing direction on a rod 126 connected to the engine throttle 130. The second centrifugal governor 102 comprises engine-driven fly weights 138 acting, against a spring 134, in a closing direction on the spool 133 of the valve 68, the outlet of which is connected through a line 137 to one end of the motor control valve 54. The governors 101, 102 are simultaneously set by a handle 100 respectively through a lever 117 acting on the spring 127 and a cam 125 acting on the spring 134, the arrangement being such that at any setting, the governor 102 senses an engine speed reduction at a lower speed than that sensed by the governor 101. In operation, when the governor 101 is incapable of maintaining engine speed, the governor 102 responds to open the valve 68, thereby leftwardly moving the spool of the valve 54, the spring 47 allowing this override, and increasing motor displacement to reduce output speed and increase output torque.