GB1437433A - Hydrostatic transmission systems - Google Patents

Abstract

1437433 Controlling winches RICHIER 23 July 1973 [28 July 1972] 35093/73 Heading B8B [Also in Division F2] In a hydrostatic transmission for raising and lowering a load, comprising a variable displacement pump 2 and a motor 3, a further, auxiliary, pump 9 is provided which delivers through a line 13 and check valve 14 to the high pressure line 8 between pump 2 and motor 3 and through a line 12 and a variable throttle 15 to a reservoir 10, the variable throttle 15 being variable electrically by a controller 18 which receives an input from a sensor 20 (or alternatively 46) such as a strain gauge to measure the load 22 and an input from a sensor 27, indicative of the pressure in line 8 and compares these to produce a pressure in line 8 by variation of throttle 15 so that, with the pump 2 displacement at zero, a brake 29 can be automatically released and the load 22 held up by hydraulic pressure alone. For this to happen a lever 37 is moved from a position A to a position B, to close a switch 39 and actuate a relay 40 to close the switch 17 in the circuit 16 to valve 15. For slow movement up or down of the load 22 the lever 37 is moved a little way towards positions C or D, this actuating a potentiometer 42 which gives a further input to controller 18 and varies valve 15 to increase or reduce pressure in line 18. Further movement of lever 37 toward positions C or D causes variation in the displacement of pump 2 and the pump 2 drives the motor 3, this variation being via a controller 43 which also receives an input from a tachometer 45 to maintain a constant lifting or lowering speed. The arrangement is such that any variation of the load 22 during slow movement, or with the load stationary, is sensed by sensor 20 (or alternatively 46) and compensated for. The sensor 20 is between a pivotable frame supporting the motor 3 and a fixed bracket 34, and the alternative position 46 shown is at the end of a cable 24 supporting the load. A feed pump 5 and pressure limiting valves 4 are provided for the transmission. Fig. 3 shows an embodiment of a connection between motor 3 and a winding drum 25 in which the motor rotates when the drum is stationary, the motor providing one input 32 to differential gearing 50 whose casing 52 is the input to a reduction gear-box 35 driving the drum 25, the other input 54 to the gearing 50 being connected to an hydraulic coupling 56 and a brake 55, the motor 3 driving the gearing 35 directly when brake 55 is engaged, and the coupling 56 ensuring that the motor 3 must rotate to hold the drum and the load connected to it stationary when the brake 55 is disengaged. The hydraulic coupling 56 may be replaced by an eddy current coupling (Fig. 5, not shown) and in either case one part of the coupling may be driven instead of attached to a fixed casing as shown (Figs. 4 and 6, not shown). A yet further embodiment (Fig. 7, not shown) has the coupling replaced by an hydraulic pump, pumping around a closed circuit through an electrically controlled pressure limiting valve.