GB1238861A - - Google Patents

Abstract

1,238,861. Hydrostatic transmissions. ROBERT BOSCH G.m.b.H. 8 July, 1968 [8 July, 1967], No. 32410/68. Heading F2D. An hydraulic transmission comprises a motor 5, Fig. 1, and a pump 1 whose adjusting member 27 is adjustable by a follower control mechanism 16 actuated by a travel lever 31, a pressure limiter 44 which at a predetermined transmission pressure regulates the transmission pump to a smaller cubic capacity, the pressure at which the pressure limiter responds being variable by a braking device whose actuation influences the follower control mechanism to appropriately adjust the hydraulic transmission and brake the vehicle. The I.C. engine driven reversible pump 1 drives the motor 5, the supply and return lines 3 and 4 being connected to the inlets 11 and 8 of a double non-return valve 9 from which an outlet 14 leads to the follower return mechanism 16. The latter has a differential piston 19, shown in the zero delivery position, which acts on the member 27 to adjust the delivery of pump 1. Forward travel. Travel lever 31 is pivoted anti-clockwise to displace a control slide 29 into the piston 19 thereby establishing connection between chambers 23 and 22 via bore 39, groove 34, bore 36, throttle 38 and bore 37. Pressure fluid from pump 1 flows via valve inlet 8 and line 14 to chamber 23 and thence to chamber 22 at a reduced pressure causing piston 19 to be displaced to the right to follow the movement of the control slide 29 whilst moving member 27. During forward travel line 4 is the high pressure line, line 3 is the low-pressure line and the high pressure acts on a control piston 46 which is moved against spring 53 to establish a connection between bores 68 and 43 at a predetermined pressure. This allows flow from chamber 22 to the low pressure line 3 causing the piston 19 to move towards its neutral position whilst reducing the delivery of the pump 1 which causes the pressure in line 4 to drop to the desired value. During the movement of the piston 19 the engagement of a pin 40 with the control slide causes pivoting of the travel rod 31. Braking in forward travel: (1) By travel lever 31. When lever 31 is pivoted clockwise the differential piston is moved towards its neutral position pump 1 becomes the motor, motor 5 becomes the pump, line 3 becomes the high pressure line and line 4 becomes the low pressure line. Pump 1, acting as a motor is braked by the engine 2. The operation of the double-non-return valve 9 again admits the high pressure now from line 3 to act on the piston 46 of the pressure limiter 44 as described previously. (2) By brake pedal 60.-When pedal 60 is pivoted anti-clockwise a cam plate 57 is rotated until a follower engages a cam radius r 1 thereby relieving spring 53 to reduce the transmission pressure to a very low valve. Further movement of the brake pedal 60 causes a spring- loaded pin 63 to engage the travel lever 31 which is pivoted clockwise thereby causing movement of the piston 19 to its neutral position resulting in reduced delivery from the pump 1. The pump and motor exchange functions as described above and vehicle is braked. Reverse travel.-The adjusting rod is displaced upwardly by lever 33<SP>1</SP> and the travel lever 31 is pivoted anti-clockwise to pull the control slide 29 to the left. Communication is established between chamber 22 and a pressurefree space via bore 37, throttle 38 and bores 36 and 28. The piston 19 is displaced to the left causing adjustment of the pump delivery. The pressure at which the pressure limiter responds is adjusted by screw 64, Fig. 1. In a modification the pressure limiter spring 53 is replaced by an hydraulic pressure in chamber 78, Fig. 2. Bores 43, 68 correspond to the bores 43, 68 to Fig. 1 and cam plate 90 is identical with that in Fig. 1. Pressure from the high pressure line is admitted via line 48 to chamber 73, bore 77, restriction 77<SP>1</SP> and bore 78. Bore 79 is vented via bore 83 to a pressure-free space. A valve 87 opens to relieve the pressure in chamber 78 in dependence on the pressure applied by cam 90 through follower 78 in dependence on the pressure applied by cam 90 through follower 88 and spring 85. In a further modification the brake pedal also activates a friction brake master cylinder (96), Fig. 3 (not shown).