Patent GB-1225654-A (GB)
IPC: B60K17/10
Filed: 1968-06-12
Abstract: 1,225,654. Hydrostatic transmissions. ROBERT BOSCH G.m.b.H. 12 June, 1968 [13 June, 1967], No. 27874/68. Heading F2D. A hydrostatic transmission has a motor 13 and a reversible pump 1 whose displacement is varied by an arrangement having an adjusting piston 19 which separates two fluid spaces 21, 22 and acts on an adjusting member, a control slide valve 30 operable by a lever 51 to control the position of the piston and a brake pedal associated with a brake valve 60 which, when the pedal is depressed, is influenced by a brake pressure produced in the low pressure side of the transmission when the motor then acts as a pump, the brake valve controlling a connection between at least one of the pressure spaces and the side of the transmission carrying the brake pressure so that the adjusting piston moves towards its zero delivery position, the piston stopping when the brake pressure has attained a specific valve not exceeding that produced by the brake pedal. Pump 1 driven by motor 2 supplies fluid through the closed circuit 11, 12 to the pump 13. The delivery of pump 1 is varied by an inclinable disc 8 connected by a bar 8 to the differential piston 9 of the follower adjusting arrangement. Forward drive.-On. moving off a motordriven auxiliary pump 84 supplies pressure fluid via non-return valves 86, 87 to the circuit 11, 12 and thence via non-return valves 26, 27 and line 24 to a pressure space 22 on one side of piston 19. The space 21 communicates with a pressureless space via a passage 36 containing non-return valve 36<SP>1</SP>, grooves 34, 32, 32<SP>1</SP> and bore 37, the grooves 32, 34 having been brought into register by displacing lever 51 into slot 52, thus pulling the slide valve to the left. The pressure differential acting on piston 19 moves it to the left, thereby pivoting disc 6 so that pump 1 then delivers pressure fluid into line 11. When the pressure closes valve 86 the pump 1 feeds the pressure space via non-return valves 26, 25 and line 24. Pressure fluid from line 11 flows via non-return valve 26, line 48, grooves 41, 43 and line 80 to brake valve 60 and passes via groove 68 to groove 70. Piston 62 blocks line 77 when pedal 82 is not depressed. Simultaneously, pressure fluid flows to a changeover valve located in position I in which a connection a is blocked and the vehicle moves forward. Reverse drive.-Lever 51 is moved into slot 53 to register groove 31 with groove 33. Pump 84 fills spaces 22, 21 and the piston is displaced to the right to pivot disc 6 so that line 12 becomes the high pressure line and line 11 becomes the low pressure line. Collar 42 is moved to the right of groove 43 so that pressure fluid cannot escape from space 41. Changeover valve 56 is in position II with connection b blocked. Braking in forward drive.-When the vehicle is travelling forward and pedal 82 is depressed to move piston 62 against spring 72, pressure fluid then flows into space 21 via line 77 to displace the follower adjusting arrangement towards the right into its neutral position. Fluid in space 22 flows to line 80 via lines 24, 48, grooves 45 and 43. Pressure builds up in line 12 and is communicated via line 57, connections b and c and line 59 to act on piston 65 which is displaced to stop 69 to cut off communication between lines 80 and 75 so that pressure in line 12 cannot increase beyond that produced by pedal 82. The brake pressure increases in proportion to the travel of the brake pedal. Braking in reverse.-When the control lever is in slot 53, the changeover valve is in position II and if the pedal is depressed when the differential piston is on the right of its neutral position, line 11 carries the brake pressure. The pressure in space 22 moves the piston 19 to the left since pressure in space 21 flows to the pressureless space via lines 77, 75, 80, grooves 43, 44 and line 46. Connection is established between grooves 33 and 31 as the movement continues until collar 42 interrupts the connection between lines 80 and 46 to stop the movement of the psiton at the position for zero pump delivery. Pedal 82 is retained in its fully depressed condition by stop 83. In a modification the brake valve has a onepiece piston (86), Fig. 2 (not shown), depressed by a pedal through a spring.