Patent GB-1377851-A (GB)
Title: Regulating and control system for a variable-stroke hydraulic machine
IPC: F04B49/08
Filed: 1972-01-12
Abstract: 1377851 Hydrostatic transmissions ROBERT BOSCH GmbH 12 Jan 1972 [15 Jan 1971] 1514/72 Heading F2D In an hydraulic transmission, wherein a reversible variable stroke pump 53 drives a motor 102, a pressure biased servo piston 57 acts on the control element 54 for the pump 53, which servo piston 57 is controlled by a followup servo comprising a valve 69, and can also be controlled by a pressure limiting valve 14 and/ or a flow regulating valve 15 and/or a torque control valve 106 (Fig. 2), each of which acts independently on a pilot valve 40 which in turn adjusts servo control valve 69 and hence piston 57. The pressure, torque and flow rate control valves are characterized in that they are constructed as independent units, inserted in bores of a regulator housing 11. The normal operation of the apparatus of Fig. 1, in which pressure and flow limiting valves 14, 15 respectively are shown, comprises movement of control lever 97, clockwise, say, which, through links 98 and 99, interconnected non-positively by a spring connection 96, 95 and 94 adjusts the servo valve 69, piston 71 being moved to the left to interconnect passages 73 and 75, and so pressure supply from pump 53 which can have a small output in neutral (or an auxiliary pump may be used) may pass via a changeover valve 64 from whichever line, 61 or 52, is the output from the pump, and then by lines 67 and 76 to the servo piston 57 to adjust the pump output, the followup action returning valve 69 to its neutral position. In the event of too great a pressure being delivered by the pump, the pressure limiter 14, which receives this pressure via lines 67, 91 and passages 37, rises against spring 20, tilts a plate 38 against which its piston 20 abuts, and so adjusts pilot valve 40 which is lifted to bring passages 48 and 50 into communication which, if line 50 is high pressure, causes pressure in chamber 83 (from line 48) to move the valve spool 71 to the right to lower pump displacement, and if line 50 is low pressure moves the spool the opposite way to again lower pump displacement by adjustment of piston 57. The spring connection 96 permits these adjustments to occur without movement of lever 97. The flow limiter has the connection 37 connected, via various lines, to the point at which line 61 joins main line 49 between pump and motor, and has a connection (to the opposite side of a piston 28 of the limiter) to line 49 (from line 89) to the opposite side of a throttle 90, the flow limiter moving upwards for too great a difference in pressure across the throttle and, via the pilot valve 40, as before, reducing the displacement. This only works for one direction of the pump. The torque regulator 106 comprises a piston 108 acted on by the pressure from the pump, from passage 37, and acts on a plate 114, pivoted about a fulcrum M, movable with respect to the point of contact of the pin 108 by a lever 121 attached to the piston 57, the plate 114 on pivoting moving a pivoted plate 124 which in turn moves the plate 38 via pin 51 (see Fig. 1 also). The plate 124 is held down by a spring 130 acting through a piston 131 and roller 129 on a cam track 128, the position of roller on cam track determining the component of force from the spring acting on the plate 124 via the roller 129. The position of the roller may be movable by the accelerator pedal of the engine A (Fig. 1) or may be variably fixed, the plate 124 also being tiltable about pivot 126. In the construction shown in Fig. 3 the accelerator pedal 135, when released, corresponds to zero pump torque, the roller 129 being positioned such that the force from the spring 130 acts entirely through the pivots of the plate 124, movement of the brake pedal 148 causing, via the torque regulator, adjustment of the pump to cause braking. - The brake pedal, 148, on further movement, operates the normal brakes 151. The system of Fig. 1 also regulates hydrostatic braking, the pump displacement being increased automatically if the pressure of oil delivered to it by the motor becomes too great.