GB684233A - Improvements in or relating to variable-speed hydraulic power-transmission mechanism - Google Patents

Abstract

684,233. Revolving cylinder pumps. ROLLSROYCE, Ltd. March 16, 1950 [March 16, 1949], No. 7240/49. Class 102 (i) [Also in Group XXIX] A variable speed power transmission of the type employing an hydro-static (or positive displacement) torque converter through which power is transmitted from an input shaft to an output shaft comprises a mechanical coupling between the power input shaft to the pump of the torque converter and the output shaft from the liquid motor of the torque converter which mechanical coupling comprises a free wheel clutch arranged to become locked when a predetermined ratio of speeds tends to be exceeded and a dog clutch or the like arranged to become effective after the free wheel clutch is locked. An hydro-static transmission suitable for vehicles is described. Fig. 1 shows a swash plate type hydraulic pump 12 driven by an input or driving shaft 1 and a swash plate type hydraulic motor 16 driving an output or driven shaft 17. The pump supplies liquid to drive the motor through a piping system (not shown). A pinion 13 on the driving shaft drives a sleeve 19 around the driven shaft, and a oneway clutch is provided so that the driving shaft is connected to the driven shaft whenever the driven shaft tends to run faster than the driving shaft. A positive engagement of the driving and driven shafts may be effected by engagement of a dog clutch 19a, 21 which is operable by an operating piston controlled by fluid pressure supplied to a cylinder 25. The control of the transmission is effected by the arrangement shown in Fig. 4. A gear pump 50 driven by the vehicle propeller shaft and a gear pump 51 preferably of larger capacity driven by the engine, supply liquid under pressure to a pipe 52 leading to a governor 54 comprising a centrifugally-controlled valve 58 which is contained in a housing 54a driven by the propeller shaft of the vehicle. The valve controls the pressure in a pipe 56 fed by the governor. This pipe leads to valves 64, 85 through which the operation of the transmission is controlled. The displacement of the pump 12 is controlled by a piston 62 and the displacement of the motor 16 by a piston 80. With a lever 65 in the position F for forward running, pressure from the pipe 56 is applied to the left hand side of the piston 62, and this pump assumes a position determined by the torque reaction and the pressure in the pipe 56 which pressure is proportional to the speed of the vehicle. The valve 85 comprises a valve member 85a, Fig. 8, which is loaded by a spring 87 interconnected with an engine throttle control pedal 90, Fig. 4, and at its opposite end by the pressure in the pipe 56. When the pressure on the left hand end of the valve reaches a predetermined relation to the load of the spring 87, i.e. when the vehicle speed reaches a predetermined relation to the engine torque, the piston valve reaches a position in which liquid is supplied to pipe lines 27, 82 and 86. This produces engagement of the dog clutch by means of the piston 24, the motor unit is moved to its neutral position and the piston valve element 64a of the valve 64 is shifted (Fig. 5) to the left to admit pressure fluid to the right hand side of the piston 62 which moves the pump to its neutral position, this movement being permitted by a slotted connection 28a. If the lever 65 is shifted to its position R the valve element 64a is correspondingly shifted and pressure fluid is supplied to the right hand side of the piston 62 to shift the pump into a position in which it supplies liquid for operation in the reverse direction. Since the positions of the piston 62 and the valve element 85a are both dependent on vehicle speed and engine torque, it can be arranged that the piston valve reaches the position in which pressure is supplied to the pipes 27, 82 and 86 when the piston 62 reaches its F position, i.e. when a slight overdrive and locking of the free wheel clutch occurs. The spring 87 moves the valve when conditions allow to re-establish the hydraulic drive. It may be arranged that at about quarter throttle unity ratio is reached at a vehicle speed of 20 m.p.h. and, for instance, at full throttle, unity ratio is reached at a vehicle speed of 65 m.p.h. The spring 87 may be acted on by an adjustable abutment 88. A locking device 104 provides for locking the valve 85 in two positions. In a modification a clutch valve similar to the valve 85 is fluid pressure operated under control of a second valve interconnected with the throttle pedal and acted on by the pressure in the pipe 56 and also arranged to be positively operated by an extension of the piston rod 28 when the piston 62 is moved to its F position. When the vehicle speed and the fluid pressure acting on the second valve fall, the valve is moved to the left by a spring into a position in which the clutch valve re-establishes the hydraulic drive. The travel of the valve element of the second valve to a position in which the clutch valve is operated to cancel the hydraulic drive is less than the travel of the piston 62 between a unity position and its F position. If desired the fluid drive can be restored by rapidly depressing the throttle pedal to actuate the second valve. The positive drive may be engaged at an overdrive or underdrive speed ratio. A suitable step-up or reduction gearing will be included in the free-wheel clutch connection. Fig. 3 shows the construction of the pump or motor. It comprises a casing 32 which can swing about pivots 33 through which liquid is supplied and exhausted. A rotating cylinder block 42 is centred by a shaft element 43.