Patent GB-933641-A (GB)
Title: Improvements in variable speed power transmissions
Inventor: KEMPSON BERTRAM CARL
IPC: F16H61/42
Filed: 1958-12-02
Abstract: 933,641. Fluid-pressure servomotor control systems. DOWTY HYDRAULIC UNITS Ltd. Nov. 26, 1959 [Dec. 2, 1958; July 13, 1959], Nos. 38890/58 and 24026/59. Classes 69 (2) and 135. [Also in Group XXXI] An hydraulic power transmission comprises a positive displacement hydraulic pump in hydraulic connection with a positive displacement hydraulic motor arranged for a transmission of power from a power source to a load having a speed ratio varying means adapted to control the ratio between the pump and motor displacements and overload means operable in response to overloading of the power source to reduce the speed ratio selected by the speed ratio varying means in an overriding sense. In a first example, Fig. 1, a diesel engine drives a reversible variable positive displacement pump 2 connected by lines 3, 4 to a positive displacement hydraulic motor 5 connected by a shaft 6 to vehicle wheels. A make-up pump 7 supplies a line 8 connected to lines 3 and 4 via non-return valves 11 and 12, respectively. The displacement of the pump 2 is controlled by a vertically displaceable control element 13 connected by a link 16, a bell-crank 15 and a link 14 to the end 19 of the piston-rod 21 of a jack 22 carried by the manually operable lever 17 movable about a fulcrum 18. The position of the piston 24 determines the movement imparted to the element 13 to maintain the engine 1 at the speed called for by the lever 17. The control bar 33 of the fuel injection pump 32 is controlled by a diaphragm 28 subject to the pressure at a Venturi 25 in the inlet manifold 26. The pipe 8 is connected by a pipe 69 to the jack 22 so that the piston 24 is normally urged to its lowermost position. The pressure drop at the Venturi is proportional to the engine speed. The rod 33 has a limited range of movement between minimum and maximum fuel positions. If there is an excessive load increase caused by an excessive movement of the lever 17 or by vehicle climbing an incline the rod 33 moves far enough to actuate a spring-loaded three-way spool valve 34 to supply fluid pressure from the pump 7 via a valve unit 48 to the lower end of the jack 22 and the piston 24 moves upwardly to reduce the displacement of the pump 2. The bar 33 returns to its maximum fuel position and the spool valve 36 assumes a position in which it keeps the piston 24 in a balanced position. The maximum torque exerted on the vehicle wheels is determined by the setting of a hand wheel 63 which determines the spring-loading on a spool valve 61 actuated by pressure fluid from the line 3 or 4 in accordance with the position of the valve 51 connected by a link 53 to the lever 17. In the second example, Fig. 2, the overriding control unit is electro-hydraulic. The lever 17 is connected to the pump displacement element 13 via a piston-rod 71, piston 72, springs 75, 76, cylinder 74, bell-crank 15 and link 16. The fluid pressures on the sides of the piston 72 are controlled by solenoid-actuated valves 85, 86. The lever 17 carries a cam 89 which co-operates with a two-way switch S3 which prepares one or other of the solenoids for energization which takes place if, due to overloading of the engine, the rod 33 moves far enough to actuate the switch S4. One or other side of the piston 72 is connected to exhaust and the piston moves to reduce the selected pump displacement until the bar 33 allows the switch S4 to re-open. If an excessively high psessure occurs in either of lines 3 or 4 one or other of the Bourdon tubes 90, 91 actuates an associated switch S2 or S1 to energize the corresponding solenoid to reduce pump displacement. Specification 933,644 is referred to.