Patent GB-1021723-A (GB)
Title: Hydrostatic transmission control system
IPC: F16H61/42
Filed: 1963-06-28
Abstract: 1,021,723. Hydraulic transmission control; variable speed gears. BENDIX CORPORATION. June 28, 1963 [July 9, 1962], No. 25827/63. Headings F2C and F2D. In a hydrostatic transmission for an agricultural vehicle having positive-displacement motor 12 fed by a variable positive-displacement pump 10 and manual means to control the pump displacement, a pressure-sensitive valve 58 overrides the manual control when the pump output exceeds a predetermined value which value decreases with increased pump displacement (i.e. increased output speed). General system.-As shown, a swash-plate pump 10 feeds a swash-plate motor 12 through ports 24, 28 and the pump displacement is varied by a servomotor 161 in response to movement of a lever 22. The port (e.g. 24) at the higher pressure is connected by a valve 32 to a line 33 which supplies the high pressure fluid to a plunger 191 of the valve 58. The valve spool 57 is loaded by a spring 66 the compression of which is varied by a cam 54 fast with a cylinder 52 of the servomotor control. When the pump output pressure exceeds the spring force, determined by the cam 54 for a given pump displacement, the valve spool 57 is moved up to connect a servomotor outlet line 60 to vent at 62 and thus cause a decrease in the pump displacement. A rapid increase of pump output pressure moves the valve spool 57 up further than normal to connect a line 193 to vent at 194. A chamber 74 of a valve 36 is thus vented and its spool 38 is moved left to connect the high-pressure line 33 through lines 37, 34 and valve 32 to the low pressure side 28 of the pump which is thus short-circuited. A makeup pump 76 supplies make-up fluid through a heat-exchanger 96, filter 80, non-return valve 84 and valve 32 to the low-pressure port 28. A low-pressure relief valve 122 is provided. A servomotor supply line 50 is fed from the highpressure line 33 through a pressure regulator valve 44. A by-pass valve 88 between the high- and low-pressure lines 33, 34 prevents the low pressure falling below a predetermined value. If the filter 80 becomes blocked it is by-passed through a non-return valve 82. Starting control.-Opening a valve 102 by depressing a pedal 108 supplies low-pressure fluid through a restrictor 112 to the lower end of the valve spool 57 which is moved upward to initially reduce pump displacement and finally short-circuit the pump and thus stop the transmission of power. The transmission may be retained in the neutral state by opening a lockout valve 70 which vents the chamber 74 at 71. Manual servomotor control.-The lever 22 acts through cards 17, 25 on a valve spool 132, a land 141 of which controls the admission to and exhaust from interconnected chambers 144, 151 of pressure fluid which acts on a piston 146. The piston 146 acts on the swash-plate 14 andopposes a constant force applied thereto by a smaller piston 53. The servomotor supply pressure 50 is supplied to a chamber 142 of the valve 132 through lines 49, 186, 189. Movement of the lever 22 to the forward position permits a spring 134 to move the valve spool 132 left and supply pressure fluid to the chambers 144, 151 to move the piston 146 right. A spring-pressed rod 130 follows the movement of the piston 146 until the valve spool 132 is returned to the position shown, Fig. 2. Movement of the lever 22 to the reverse position moves the valve spool 132 right against the action of spring 134 and vents the chambers 144, 151 at 139 whereupon the piston 53 acts through the swash-plate 14 to move the piston 146 left. During movement of the lever 22 the tensioning of the cord 25 moves the rod 130 left against the action of a spring 145; The piston 146 moves left until it abuts the rod 130 and slackens the cord which permits the spring 134 to return the valve spool 132 to the position shown, Fig. 2. Override servomotor control.-With the servomotor in the forward position, upward movement of the valve spool 57 directly vents the servomotor chambers 144, 151 through the line 60 to effect a reduction in the pump displacement. With the servomotor in the reverse position. Fig. 4B (not shown), upward movement of the valve spool 57 vents chamber 176 and inner valve spool 178 moves left under servomotor supply pressure supplied through lines 186, 188, 190, 191 to chamber 177. Servo pressure is then supplied through lines 192, 180, 171, 167 to chambers 144, 151 to move the swash-plate 14 towards its zero setting. Hydromechanical gearing.-The hydrostatic transmission may be used in a hydromechanioal gear, Fig. 6 (not shown), having an output planet carrier 223 the planets of which mesh a sun gear 218 fast with the motor 12 and a ring gear 224 driven from an input shaft 228 which also drives the pump 14. A power-take off shaft 220 is provided.