Patent GB-880828-A (GB)
Title: Fluid supply system for constant speed hydraulic drives
IPC: F16H39/00
Filed: 1960-07-25
Abstract: 880,828. Hydraulic apparatus. GENERAL ELECTRIC CO. July 25, 1960 [Aug. 13, 1959], No. 25787/60. Class 69 (2). A fluid supply system for an hydraulic drive 64 having a rotatable cylinder and race assembly 66, 68 comprises a pump 12 supplying fluid under pressure from a source 14 at a greater rate than required to supply normal leakage flow of the drive, a scavenger pump 13 for returning the leakage flow from the drive through a return line to the source, a reservoir 11 in the return line, and means 48 sensitive to a reduction in fluid supply pressure from the main supply source to close the return line, the reservoir upon such reduction in pressure providing fluid through a check-valved emergency line 61 to the hydraulic drive for recirculation by the scavenger pump. The system may be used for the drive of a generator at a constant speed from the engine of an aircraft which may be subjected to negative gravity conditions. The drive consists of an input shaft 65 connected to a race 66 formed integrally with a block 68 having cylinders 75 containing ball pistons 76. The race 66 co-operates with ball pistons in a cylinder block 69 splined to a shaft 72 connected by a one-way clutch 74 to an output shaft 70 driving the generator, a speed governor and the pumps in the system. Pump 12, and a booster pump 15, supply fluid through a line 18, filter 19, line 22 and passage 78 to the pintle 23 of the drive to replenish leakage of fluid from the drive. A valve 25 by-passes excess fluid to a compartment 28 in the casing 10, and a further relief valve 32 is provided to by-pass fluid at an excess pressure level. Leakage of fluid from the drive falls to the bottom of a second compartment 31 from which it is passed by the scavenger pump 13 to the reservoir 11. A valve 38, which opens at a predetermined pressure differential between the pressure in the compartment 28, vented to atmosphere by a line 17, and the reservoir 11, passes fluid to the sensitive valve means 48 which has a spool 53 positioned so that the fluid passed by the valve 38 can be returned through a port 51 to the tank 14 when the pump 12 is supplying fluid through the line 18, the pressure therein moving the spool against a spring 55. A pressure-relief valve 42 is provided to prevent the pressure differential between the reservoir 11 and compartment 31 exceeding a predetermined value. During normal operation, the pump 12 supplies fluid to the pintle 23 of the drive, excess fluid being by-passed by the valves 25, 32 back to the compartment 28, and overspill from the compartment 28 into compartment 31 together with leakage fluid from the drive into the latter compartment being returned by the pump 13 to the tank 14. On a condition of negative gravity occurring, the fluid in the tank 14 moves upwardly, some being retained in the vicinity of the inlet pipe 16a of the pumps 12, 15 by a baffle 63. The fluid in the compartments 28, 31 also moves upwardly so that the inlet 30 of the pump 13 is no longer in communication with the fluid which is therefore no longer returned to the tank 14. The fluid trapped by the baffle 63 and supplied by the pump 12 to the drive increases the volume of fluid in the compartments sufficiently for the rotating race 66 and cylinder block 68 to cause the fluid to swirl around the casing and pass through the inlet 30 to the pump 13. When the fluid trapped by the baffle 63 is exhausted, the pressure in line 18 drops permitting the spring 55 to move the spool 53 of the valve 48 to a position disconnecting the port 51 and the line 47 from the valve 38. The pressure in the reservoir, which is now controlled by the valve 42, causes fluid to flow through the emergency line 61 past a oneway valve 62 into the line 22 to replenish leakage from the drive 64, excess fluid being bypassed, as before, by the valves 25, 32. A checkvalve 21 prevents fluid flowing back to the line 18, and a further check valve 20 is provided to permit maintenance of the filter 19 to be effected. When the spool 53 is in its upper position, a passage 60 in the spool connects the line 18 to the port 51 to vent air from the system.