Patent GB-1035679-A (GB)
Title: Improvements in and relating to hydrostatic drive control systems
Inventor: MIDGELEY PETER JOHN
IPC: B60K17/10
Filed: 1963-10-17
Abstract: 1,035,679. Change speed control. BRITISH AIRCRAFT CORPORATION (OPERATING) Ltd. Nov.27. 1964 [Oct. 17, 1963], No. 41142/63. Headings F2C and F2D. A control system for a motor vehicle hydrostatic gear having a variable displacement swash-plate pump 1 supplying motors 4 which drive and brake the vehicle wheels comprises a servomotor 2 controlling the displacement of the pump 1 in response to movement of a pedal 12, and valves 3, which normally connect the pump and motor circuits, are controlled by valves 20 responsive to depression of a brake pedal 14 to provide a restriction in the motor outlets for vehicle braking. The front or rear motors 4 may be isolated from the pump 1 by the valves 3 in response to movement of handles 59, 59a. Each motor 4 has two banks of cylinders and single or double bank operation may be selected manually at 15 or automatically (Figs. 5 and 6, not shown). Cooling and make-up circuits are provided. Pump displacement control.-the servomotor 2 has two chambers 40, 41 respectively connected through restrictions 10b, 10a with the pump inlet and outlet lines 21b, 21a and with normally open relief valves 11b, 11a As shown with the valves 11a, 11b open the pump swash plate is in its zero displacement position. Anticlockwise rotation (toe down) or clockwise rotation (heel down) of the pedal 12 closes the respective valve 11a or 1 1b and causes a pressure build-up in the chamber 41, or 40 which moves the pump swash plate to the forward or reverse drive position. The pump displacement increases and the movement of the swash plate continues until the pressure in the chamber 41 or 40 and line 31a or 31b reopens the relief valve 11a or 11b whereupon the latter maintains the pressure in the chamber 41 or 40 at a value depending on the position of the pedal 12. 'Vehicle braking and by-pass control.-The brake/by-pass valves 3 between the pump 1 and front and rear motors 4 each comprise four control pistons 46 ... 49 biased inwardly by springs 52. Control ports 42... 45 are connected in pairs 42, 44; 43, 45 by lines 33a, 33b supplied with pressure liquid from the high pressure motor line 23a or 23b through a shuttle valve 53 and the lines 33a, 33b are connected through the valve 20 to a line 32 normally vented through the brake relief valve 13 and a line connected to a pre-set relief valve 19. For forward or reverse drive the valve 20 is positioned as shown and the line 33a is vented through the valve 13 whilst the line 33b is connected to the preset relief valve 19. The ports 42, 44 are thus vented and circuit pressure moves the pistons 46, 48 to the position shown whilst the pressure determined by the valve 19 acts on the pistons 47, 49 and together with the springs 52 holds the pistons in their innermost position. The valve 3 thus connects the pump and motor supply and return lines 22a, 23a; 22b, 23b. Depression of the brake pedal 14 closes the valve 13 and causes a pressure rise in the line 32 a branch of which acts on the spool 16 of the valve 20 to move it up and connect the line 33a to the preset relief valve 19 and the line 33b to the line 32. The pistons 46, 48 are thus moved inward to close the pump supply and return lines 22a, 22b whilst the pressure in the lines 32, 33a acts on the pistons 47, 49 to throttle the motor outlet and provide vehicle braking. On rotation of the by-pass selector handle 59 a cam thereon raises the valve spool 16 whereupon the piston 46, 48 move inward to close the motor lines 22a, 22b and the line 33b is vented at 13 and the pistons 47 and 47 open ports 50, 51 to short-circuit the motor. Motor control.-Each motor contains a valve 157, Fig. 5, which selects single or double bank operation of the motors. The valve is biased left by a spring 58 to the position shown in which the motor supply and return lines 24a, 24b are connected to the inlet and outlet ports 4a, 4b of one bank of cylinders only. When fluid pressure is supplied from a make-up pump 5 through a manually controlled valve 15 and shuttle valve 17 to the left of the valve 157 its spool moves right to supply the inlet pressure 24a to the inlet ports 4a, 4b of both banks of cylinders. The shuttle valve 17 is also connected to the line 32 so that when the brake pedal 14 is depressed pressure is supplied to the valve 157 to ensure double bank operation of the motors during vehicle braking. In Figs. 6 and 7 (not shown) pressure is automatically applied to the valve 157 when the maximum swash plate angle is reached. Cooling and make-up circuit. A make-up pump 5 draws liquid from the motor outlet line 23a or 23b through a shuttle valve 6 and cooler 7 and supplies liquid at a predetermined pressure to various points of the circuit through non-return valves 9.