Patent GB-860075-A (GB)
Title: Improvements in or relating to control apparatus in hydrostatic power transmission sy
IPC: F15B11/08
Filed: 1957-07-23
Abstract: 860,075. Hydraulic apparatus. GESELLSCHAFT DER L. VON ROLL SCHEN EISENWERKE A.G. July 23, 1957 [July 23, 1956], No. 23302/57. Class 69 (2). In an hydrostatic power transmission system, such as for a press or vehicle, in which a primary member 2, Fig. 1, consisting of a pump is connected to a secondary member 5, 6 by means of two pressure fluid pipes 3, 4, the primary and/or the secondary member being regulatable and reversible, an automatically regulatable control device 20 comprises a slide valve or piston 26, Fig. 2, which regulates the primary member 2 and is controlled by a further piston 33 urged by a spring 32 against the pressure of the medium in the pipes, a change-over valve 36 interposed between the further piston and pipes for causing the pressure fluid in one or other of the pipes to act upon the further piston, and a further change-over valve 40 or linkage for reversing the primary member or the secondary member. The primary member 2, which may be an axial piston pump of the swash-plate type, is driven by an electric motor 1, Fig. 1, and connected by the pipes 3, 4 to the upper and lower ends of a cylinder 5 containing the piston 6 of a press. The primary unit is pivotable between positions P and H to regulate and reverse the output from the unit which is supplied to chambers 8 and 9 in the cylinder. On the downward stroke of the piston, the difference between the displaced fluid from the chamber 9 and the fluid entering chamber 8 is compensated for by additional fluid from an accumulator 12 entering the system through a ball valve 10. On the upward stroke, an increase in pressure in line 4 opens a valve 15 to permit excess fluid to return to the accumulator. Pipes 3, 4 are connected by pipes 18, 19 to the valve 36, Fig. 2, of the control device 20, in turn connected by a pipe 35 to the piston 33. The pressure in whichever of pipes 18, 19 is connected to the high pressure side of the piston 6, urges the piston 33 downward against the spring 32, the other end of which has a follower engaging a substantially hyperbolically-shaped cam 31 connected by a link 29 to the primary member 2. If, during downward movement of the piston 6, an increase in pressure occurs in pipe 18, this will move the piston 33 downward and connect a pipe 37 connected by the valve 40 to an accumulator or, as shown, an axial piston pump 21, which may be of the constant displacement type combined with an excess oil valve and is driven by a motor 22 and provided with a pressure regulator 23, to a pipe 39 connected by a valve 42 to the upper surface of the piston 26, the lower end of which is connected to the member 2. Downward movement of the piston 26 caused by pressure from the pump 21, pivots the member 2 to reduce its output and, at the same time, move the cam 31 to increase the pressure exerted on the piston 33 by the spring 32 until the spring pressure equals the increased fluid pressure in the pipe 18 and return the piston to its initial position to disconnect the pipes 32, 39 directing fluid to the upper surface of the piston 26. A decrease in pressure in pipes 3 and 18 permits the spring 32 to move the piston 33 upwardly and connect the upper surface of the piston 26 to a drain 40b and the member 2 to move towards the position P of maximum output. The power output of the member 2 thus remains constant and equals the product of the pressure and the angular position of the member 2. When the piston 6 of press is to be raised, and the output from the member 2 reversed, the piston 36, which may be automatically responsive to the higher pressure in one or other of the pipes 18, 19, and valve 40, which is electrically connected to valve 36 for simultaneous movement therewith are moved to their alternative positions so that the higher pressure in pipe 4 is connected to piston 33 and the pump 21 connected by pipes 38 and 41 also to piston 33. Any increase in pressure in line 19 displaces piston 33 downwardly against spring 32 and interconnects pipes 37 and 39 so that the upper surface of piston 26 is connected to a drain pipe 40b and the piston rise by pressure from the unit 21 through pipe 24 displacing the cam 31 as before. The press is placed inoperative by actuation of valves 42, 45, which are electrically connected together, valve 45 connecting the pump 21 to the upper surface of an auxiliary piston 27 to move the latter to a position abutting a shoulder 25a and valve 42 connecting the upper surface of piston 26 to a drain 42b. The control device may be applied to a vehicle transmission system consisting of a primary member 51, Fig. 5, and secondary member 52 connected to a drive axle, and each member may be controlled by a device 58, 59, as described above. The members are connected together by pipes 53, 54, associated with a feed pump of constant or variable displacement or an accumulator 57 and valves 56, 57a. A control device adapted for constant pressure regulation of a primary or secondary unit 52, Fig. 6, comprises a valve 60 connected by a pipe 63 to a piston 64 backed by a spring 65. Movement of the piston caused by change of pressure in either pipe 53 or 54, is conveyed by a link 66 pivoted at 67, to an adjustable nut 68 connected by a link 72 to the unit 52 to vary the output therefrom. In a modification, the valve 60, Fig. 7, is connected to a piston 76 and slide valve 77, one side of which abuts a spring 78. Movement of the valve 77 connects the upper or lower side of the piston 76 to the change of pressure and thus rocks a lever 80 about a pivot 81 to regulate the unit 52. A piston 82 on the lever may be displaced between two end positions by pressure from one or other pipes 83a, 84a.