GB978661A - Hydraulic apparatus - Google Patents

Abstract

978,661. Hydraulic transmission of power; valves; change-speed gear and control. DOWTY HYDRAULIC UNITS Ltd. Nov. 6, 1961 [Nov. 10, 1960], No. 38696/60. Headings F2C, F2D and F2V. An hydrostatic power transmission comprises a pump 2 and motor 5 connected in series with and in front of a mechanical changespeed gear 7 for the transmission of power from a source 1 to a load, such as the road wheels of a vehicle, and an hydraulic slipping means 33 for permitting slip between the pump and motor to limit the shock loading which might occur on change of mechanical speed ratio. The pump, which may be of the reversible variable positive displacement type, is connected by pipes 3, 4 to the positive displacement motor which may also be variable and has a coupling 6 to a shaft 8 having gears 9, 11 selectively engageable with gears 15, 16 on an output shaft 12. The gears 15, 16 are carried by a sleeve 17 movable by a lever 19 having a lost motion connection 23, 24 with a hand lever 22 formed with a cam 25 which, when the lever is moved from an end position to take up the lost motion, displaces a piston 61 and a rod 66 to unseat a ball valve 55. The unseating of the ball valve connects the space to the left of a piston 44 to a passage 58 leading to a reservoir 27 so that the compression of a spring 47 retaining a valve 48 on a seating connected by a pipe 34 and oneway valves 35, 36 to the pipes 3, 4 is reduced; the valve 48 can then lift as the pressure in pipe 3 or 4 increases to a relatively low pressure, say, 1500 1bs./square inch, as a result of shock to the transmission when the lever 22 is moved further to change the gear ratio. The liquid discharged past the valve 48 flows through passages 41, 42 to a line 28 connected by oneway valves 31, 32 to the pipes 3, 4 to make up for the liquid discharged. When the lever 22 is moved to its furthest position, the cam 25 is disengaged from the rod 62 of the piston 61 to permit the piston to return at a slow speed determined by a throttle 67 and provide a time delay before the ball valve 55 engages its seating and liquid from the line 41, which is connected to a make-up pump 26 also connected to the line 28, passes through a restriction 52 to move the piston 44 to the right whereby the compression of the spring 47 is increased to retain the valve 48 on its seating except if a relatively high pressure, say 5,000 1bs./square inch occurs in pipes 3 or 4. In an alternative embodiment, the ball valve 55 is opened by movement of the piston 61 as before to permit the valve 48 to open at the lower pressure but the valve 48 is hydraulically locked in the closed position when the ball valve is closed and a separate high pressure relief valve is provided. The changespeed gear may comprise a plurality of gear trains constantly in mesh and engaged one at a time by friction clutches.