Patent GB-837641-A (GB)
Title: Hydraulic drive with coupling
IPC: F16H61/04
Filed: 1957-09-16
Abstract: 837,641. Change-speed gearing; clutches. THOMA, H. Sept. 16, 1957, No. 29162/57. Class 80 (2). A hydrostatic drive mechanism having functtionally interchangeable pump/motor units is superimposed on a transmission having at least one releasable dog-clutch to relieve torque on, or to synchronize, the clutch parts for clutching. The hydrostatic drive unit may comprise an axial piston unit (Fig. 1) in which a driving- shaft 101 is universally coupled to a driving flange 115 in which are mounted the spherical heads 112 of piston-rods 102 associated with pistons 103 reciprocable in a cylinder block 104. The block 104 is free to rotate in a housing 108 and is ported at 111, 109 to the housing and thence through hollow trunnions 113, 114 about which the housing 108 can swivel. Angular movement of the housing 108 about the axis 117 of the trunnions varies the stroke of the pistons and can cause the unit to act as pump or motor. A prime-mover 1 drives a gear 11 through a dog-clutch 7, the gear 11 meshing with a gear 12 rigid with the ring gear 9 of an epicyclic train, the sun 22 being connected to a hydrostatic unit 23 and the planet carrier 21 is rigid with a shaft 3. A dog clutch 8 on the shaft 3 can be slid axially to provide a twospeed drive to an output-shaft 4 through gears 15, 16 or 13, 14. A reversing gearing 17, 18, 19, 20 may also be provided. A second hydrostatic drive unit 23<SP>1</SP> is coupled to the shaft 2 and connected to the unit 23. A further unit 23<SP>11</SP> may be coupled to the shaft 3. The two units 23, 23<SP>1</SP> in conjunction with epicyclic gear enable the torque load on the clutch 8 to be relieved for disengagement and then the shaft 3 increased or decreased in speed to provide synchronization for engagement of the other speed gear. The movement of the unit 23<SP>1</SP> may be produced by a piston 31 and cylinder 30 responsive to the pressures in the pipes connecting the units under the control of a four-way cock 32. To provide low speed, high-torque characteristics, such as for starting a vehicle, the dogclutch 7 may be disengaged and a detent 36 used to hold the gear 11. Under these conditions the hydrostatic units transmit the whole of the drive to the shaft 3 and units 23, 23<SP>11</SP> assist the operation of the clutch 8 if required. Alternatively a brake 37, which may be electromagnetic, a fluid torque converter or a mechanical brake, as shown, may be used to hold the sun-gear 22 locked, in which case the drive units 23<SP>1</SP>, 23<SP>11</SP> will provide slow speed forward or reverse drives. To prevent the brake 37 being engaged when the unit 23 is running in a forward sense at the upper end of the regulating range a cam 119 on the control-rod 118<SP>1</SP> closes a valve 28 in the supply to the brake-operating cylinder 26. In one modification, the control-rod 118<SP>1</SP> is actuated by a rack-and-pinion mechanism operated through a differential and corresponding ratio two-speed gearing from the shafts 3 and 4, to provide correct synchronizing speeds for the clutch 8. In another modification two further interconnected hydrostatic units are driven from the shafts 3 and 4 and their outputs are connected across the valve 32 to control the piston and cylinder 30, 31. In another embodiment the clutch 7 is provided with a second pair of gears to provide a two-speed drive to the ring gear 9. In other embodiments the epicyclic gear is replaced by the units 23, 23<SP>1</SP> bridging the dog clutch and being controlled by further hydrostatic units driven from the gears providing the two ratios, or the gearing may comprise a bevel, or a spur gear hydraulic, differential with two or one hydrostatic units respectively bridging the differential and a direct drive dog clutch. Specification 402,502 and U.S.A. Specification 2,430,764 are referred to.