Patent GB-780306-A (GB)
Title: Improvements in or relating to automatic variable torque hydraulic transmission
IPC: F16H61/448
Filed: 1954-12-22
Abstract: 780,306. Rotary pumps and motors. BERRY, F. Dec. 22, 1954, No. 37027/54. Class 110 (2). [Also in Group XXIX] An automatic variable-torque hydraulic transmission for vehicles comprises a rotary-abutment type pump driving a motor of the same type, a by-pass being provided between the pump inlet and outlet and having an automatic hydraulically operated valve opening the bypass under idling conditions and closing the by-pass under driving conditions. The motor comprises a number of sections, and valve means are provided so that as the difference between the speeds of the input and output shafts decreases, the sections are successively removed from the pump circuit, a stage finally being reached in which all of the motor sections are out of the circuit and the pump rotates solid to give a direct drive. The transmission comprises a pump 15 having a pair of rotors 36 and a rotary abutment 18 fast on an output shaft 17. The rotors 36 are carried round bodily by the pump casing, which is driven by a shaft 22. The rotors 36 are also fast with pinions 33 meshing with teeth on the shaft 17. The shaft 17 is formed with recesses 79 constituting rotary abutments for a motor 16. The motor comprises three pairs of cylinders 58, 59, 60 each containing a pair of rotors fixed to shafts 73, 74 carrying pinions 75, 76 meshing with a pinion on the output shaft 17. The motor rotors are mounted in a stationary casing. A by-pass channel 41 connects the pump inlet 42 to the outlet 43 and is controlled by a differential piston valve 46. Operation.-When the pump is idling the by-pass valve 46 is held open by a spring 49. On increasing the speed of the pump 15 the pressure at the outlet 42 increases and acts through a bore 50 to move the valve 46 to the right, thus closing the by-pass 41. Liquid then passes through passages 52, 19, 82, 83 to a control valve assembly 85. For forward drive a piston 97 of the control valve assembly is locked in the position shown and the liquid acts on a differential piston 98 to move it to the left to uncover ports 104 leading to the motor cylinders 58, 59, 60. As the output shaft 17 begins to rotate, abutment 18 rotates with it, and the pump output begins to decrease and the pressure drops. As the pressure falls, the piston 98 is moved to the right by a spring 106, successively closing the ports 104, and finally closing all the ports, in which condition a direct drive is obtained through the locked pump 15. If the output shaft rotates faster than the input, the abutment 18 rotates faster than the speed of bodily rotation of the pump, creating pressure in what is normally the inlet 43. This pressure acts via a bore 51 on the centre of the by-pass valve 46 to close the by-pass 41. The pump therefore drives the engine and free wheeling is prevented. Reverse drive is obtained by unlocking the piston 97 and locking the piston 98 in the extreme right-hand position. To start the vehicle engine both pistons 97, 98 are unlocked and an electric starting mechanism is engaged with teeth 86 formed on the pump casing to rotate the shaft 22. Specifications 780,305 and 780,307, [Group XXIX], are referred to. Reference has been directed by the Comptroller to Specification 610,068.