Patent GB-1073484-A (GB)
Title: Damping device for hydraulic actuators
Inventor: PETTY JOHN WILLIAM LEDWARD
IPC: F16H15/38
Filed: 1964-08-07
Abstract: 1,073,484. Variable-ratio friction gears. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 30, 1965 [Aug. 7, 1964], No. 32183/64. Heading F2D. The invention relates to damping units for use with a plurality of hydraulic actuators which are supplied in parallel from a common source, the pressure being variable to operate the actuators. As described each actuator controls the ratio angle of a roller of a toroidal race friction gear, the damping unit permitting rapid movement of all the actuators simultaneously in response to a change in control pressure or in response to a change in the torque reaction at the rollers so as to permit a rapid change in ratio of the gear, while damping the movements if one roller changes ratio so that, for example, a fall in the torque reaction at one roller causes the torque reaction of the rollers to rise, so that they would tend to oscillate out of phase in the absence of such damping means. As shown a control pressure is supplied to a chamber 9 of a stepped piston 5 providing chambers 2-1 in a stepped cylinder which are connected to actuators controlling the gear rollers. The piston is biased to a mid-position by springs 25, 26 and the chambers are interconnected by a passage 19 and restrictions 15-18. A change in the position of the piston 5 causes the chamber 9 to change in volume by an amount equal and opposite to the sum of the changes of the other chambers. Sudden movement of the rollers will shift the piston 5 up or down which will equalize the pressures between chamber 9 and chambers 2-4. If the displacement of the rollers persists one of the springs will restore the piston to its central position by displacing fluid through the restrictions. If one roller tends to move independently of the others, movement of the piston 5 will tend to make the other rollers move in the same sense. The transmission as a whole changes ratio. If the raised torque reaction at one roller is sustained it may be assumed to be due to a structural inaccuracy in the transmission unit and should be corrected by a ratio change on the part of that roller individually. This correction will take place subject to a delay, by flow of liquid from the associated chamber into the chambers associated with the other actuators via the restrictions. The delay caused by the restrictions damps out any oscillations. Any oscillation of the rollers in unison will cause the piston 5 to reciprocate and the resulting oscillation of the ratio of the gear will act through the servo control system to produce corrective fluctuations in the pressure applied to the chamber 9. As shown, two damping units 27, 28 are provided and each is individually supplied with fluid from a third damping unit 29 having output chambers 33, 34 connected to the chambers 9 of the damping units 27, 28. The arrangement is intended for use with a gear having two outer discs rotating together and a central disc each side of which is provided with a toroidal surface, two sets of rollers being provided and being respectively associated with the damping units 27, 28. If the rollers of the set associated with unit 27 were to start oscillating in unison without any similar oscillation in the part of the set of rollers associated with unit 28, piston 5 would be subjected to a fluctuating pressure and would reciprocate and cause pressure fluctuations in the chamber 33 of damper unit 29. Unless the fluctuations are very slow piston 35 will reciprocate and the resulting pressure variations in chamber 34 will be communicated through unit 28 to the associated roller set so that both sets of rollers tend to oscillate in unison. This produces oscillatory changes of ratio of the gear as a whole which react on the servo control system which can readily be designed to counteract such oscillations. As a modification the restricted passage between the chambers can be external to the piston. (In another modification, Fig 3, not shown, a damping unit for two sets of three rollers is provided by a single piston having six steps providing six output chambers and a common control chamber all interconnected by a restricted passage. In another modification, Figs. 4-8, not shown, twelve axial cylinders 68, 69 are arranged around the periphery of a circle, diametrically opposite cylinders being interconnected and connected to an actuator. A piston assembly 60 has a central body 61 fast with plungers extending into the chambers, with leakage past the plungers providing a restricted interconnection between the chambers. The plungers at their opposite ends cooperate with chambers 66, 67 which are interconnected to form the common chamber. The piston assembly 60 is biased to a central position by springs 79, 80.) (In another modification, Fig. 9, not shown, twelve cylinders 98-109 are provided in three rows of four, pairs of cylinders being interconnected and connected to an actuator, and a common piston assembly 60 having plungers entering the cylinders and being biased to a central position by springs 80, 79. The space 78 above the piston assembly forms a common chamber which is in restricted communication with the cylinders by leakage past the plungers.)