GB1031258A - Hydraulic system - Google Patents

Abstract

1,031,258. Fluid-pressure servomotor systems. NEW YORK AIR BRAKE CO. March 1, 1965 [June 29, 1964], No. 8623/65. Heading G3P. A variable delivery hydraulic pump 1 supplies fluid to a distributing valve 2 through a conduit 5, the displacement of the pump being controlled by a motor 24 loaded by a spring 23 to zero displacemeat. The valve 2 controls the connection of the conduit 5 to conduits 8 or 9 leading to opposite ends of a working motor 3, the loads 16,17 of the valve having notches 16a, 17a whereby both conduits 8 and 9 are connected to the reservoir 13 when the valve 2 is centred. The conduit 5 is connected by conduits 5a, 5b to value 25h. The valve 25b comprises a valve member 62 loaded by a spring 66 to the position shown in which an auxiliary supply 63 is connected to a conduit 65 leading to a valve 25a but when the pressure in conduit 5 exceeds a predetermined valve, the valve member 62 is bored to connect the conduit 65 to the reservoir 13. The valve 25a comprises a valve member 48 loaded to the left by a spring 54 and controls the connection of a conduit 46 to the conduit 65 and the reservoir 13. The valve member 48 is connected to a piston 55 forming chambers 55a,55b, the chamber 55a being connected to the conduit 5 by conduit 5a and the chamber 55b being connected by a conduit 56 to a valve 57 whereby the high pressure in conduit 8 or 9 is connected to chamber 55b. Thus the valve member 48 is positioned in response to the pressure difference across the distributing valve 2. The conduit 46 may lead direct to the left hand side of rotor 24 or may be connected to a valve 25 which comprises a normally movable valve member 38 controlling the connection of conduits 27,28 to the conduit 46 or the reservoir 13. The valve 25 has a movable valve seat 32 connected by a lever 44 to motor 24. The load 53 of valve 48 and the loads 41, 42 of valve 38 are of such a width that conduit 46 and conduits 27,28 can be connected to both conduit 65 and reservoir 13 and conduit 46 and reservoir 13 at the same time. Operation. Assume that the valves are all in the position shown and the pump is at zero displacement. If the lever 45 is now moved to maximum displacement, the valve 38 is moved to the left and fluid from line 63 flows through valve 25b, valve 25a, conduit 46 and conduit 27 to be left load side of motor 24 and the displacement of pump 1 increases. Movement of the motor 24 also acts through lever 44 to move valve sleeve 32 to follow the valve 38. As the pump delivery pressure increases, this acts in chamber 55a and at a certain pressure the valve 48 moves to the right until the load 53 is positioned relative to the groove 47 such that some of the fluid from conduit 65 flows to conduit 46 and some to the reservoir 13. The valve 48 then reaches a position in which the flow to conduit 46 is only sufficient to make up leakage and the pump displacement is held at a position to provide a constant low pressure (say 200 p.s.i with reservoir pressure at 50 p.s.i) in the conduit 5. If now the valve 2 is moved to actuate the motor 3, the pressure in line 8 or 9 rises and consequently the pressure in chamber 55 b. The valve 48 is thus moved to the left to increase pump displacement until a pressure differential (say 150 p.s.i) exists across the valve 2 when the valve 48 is then again positioned as above to hold the displacement constant. The valve 48 then operates to vary the pump displacement to maintain the pressure drop constant. The valve 25b acts in the event of the pressure in conduit 5 exceeding a predetermined value (say 3, 000 p.s.i) when the valve 62 moves to the right to close conduit 65 from the supply 63 to stop or reduce pump displacement. The sleeve 32 of valve 25 would not normally recentre with respect to valve 38 when moved to its maximum displacement position but if this was set to an intermediate position, the valve 25 would limit the pump displacement which could be achieved by valve 25a.