Patent GB-560662-A (GB)
Title: Improvements in or relating to hydraulic transmissions
IPC: F16H39/10
Filed: 1942-04-25
Abstract: 560,662. Hydraulic transmission of power; pumps. WAHLMARK, G. A. April 25, 1942, No. 5577. Convention date, June 5, 1941. [Class 69 (ii)] [Also in Group XXVIII] In a device for the hydraulic transmission of power of the kind embodying pump and motor devices of the swash-plate type the pump displacement is adjusted automatically in response to torque or speed changes in the transmission, and the motor is driven with a step-less acceleration, and the pump is constructed so that constant pressure is maintained on the swash plate although the working pressure on the pistons varies. As applied to the driving of an automobile the input shaft 45, Fig. 1, drives a swash-plate 55 which can pivot about a pin 61 under control of a movable cylinder 68 which is slidably adjustable relatively to a fixed piston 66 by means of liquid admitted by,passages 190, 193, Fig. 15, from an auxiliary make-up pump MP which is driven by the shaft 45 and serves to supply make-up liquid to the casing 25 in which the pump P and motor M, Fig. 1, are arranged. The casing 25 is arranged in an outer housing 20 which is fixed, and the casing 25 may rotate under reaction or may be held from rotation by a brake 40 operated hydraulically by liquid delivered by the pump MP which controls pistons 153<1> operating geared bell-cranks 141<1>, 1421 connected to the brake bands. The bellcranks may be operated by a cam on a single piston and cylinder device. The pump MP may be of the kind described in U.S.A. Specification 2,132,813. The supply of liquid to the cylinder 68 is controlled by a valve VM, Fig. 15, which can be set to cause the motor to be in neutral, or in direct or reverse drive. The inlet 237 of the valve VM is supplied by a pressure-controlling valve VP which maintains a supply of liquid at constant pressure to the valve VM and the other valves shown in Fig. 15, include a pressure-reducing valve VR, a valve VA associated with the accelerator pedal AP, and brake applying and release valves UBA, VBR for controlling the brakes, and a valve VS<11> which opens under centrifugal force against the action of a spring and which causes the inclination of the swash-plate to increase as the speed of the pump shaft 45 increases, and so causes an automatic increase in the speed of the motor M. As shown in Fig. 15 the valve VM is in neutral position and the swash-plate is not inclined so that the hollow pistons 53 of the pump are not reciprocated so that no driving of the motor M takes place; To start tHe drive the valve VM is moved to forward position and the accelerator lever AP depressed into contact with the accelerator A, and the result of these two operations is to cause a differential pressure in the cylinder 68 tending to move the cylinder to the right, and also an operation of the valves VBA, VBR causing application of pressure to the brake bands. The motor M is thus driven by the liquid expelled by the pump piston 53 passing under control of valves 82, 121, and pump ports 90 in a valve block 28 to the cylinder bores 104 in which work pistons 105 which act upon a fixed swash plate 109 mounted on the shaft 100. The valve mechanism is of the kind described in Specification 516,721 and there are seventeen cylinders 104 as compared with fourteen in the pump P. The bores 104 are formed with diametrically opposed recesses 133, Fig. 1, and 134, Fig. 12 (not shown), connected by ducts to the valve chamber in such a manner as to counteract side-thrust, and adapted also to reduce generation of heat. On further depression of the accelerator, and consequent increase in the speed of the pump shaft, the valve VS<11> opens under centrifugal action so as to diminish the pressure in the right side of the cylinder 68 and thus cause it to move gradually towards the left and thereby increase the throw of the pumps 53 and increase the speed of the motor M. The differential pressure on the cylinder 68 is finally completely under the control of the centrifugal force. The exact position of the swash-plate depends upon the speed of shaft 45 and also upon the load on the transmission since the reaction of the pistons is such as to tend to return the swash-plate to its no-stroke position. This is due to the formation of curved surfaces 59 on the swash-plate and the engagement therewith of the curved ends 60 of the pistons 53 which are of small diameter. The swash-plates are mounted on ball-andthrust bearings, and motion is transferred from the cylinder 68 to the plate 55 by means of an arm 69 with a spherical end 71 engaging a radial bore 72 in the plate 55.