GB848165A - Position-responsive servo-control unit - Google Patents

Abstract

848,165. Steering motor vehicles. NEW YORK AIR BRAKE CO. Sept. 9, 1958 [Sept. 18, 1957], No. 28849/58. Class 79(5). [Also in Group XXIX] A servo-control unit comprises a double-acting motor 11, Fig. 8, which is supplied with fluid from a pump 29 under the control of a primary distributing valve 27 manually actuated e.g. by the linkage shown to which linkage the motor is also connected to provide follow-up. The primary valve 27 also acts as a pilot valve for a secondary distributing valve 41 which controls the supply of fluid to the motor 11 from a second pump 31 having a higher rate of flow than the pump 29. Only when the valve 27 is moved beyond a minimum range is the second valve 41 moved to connect the motor 11 to the pump 31. The primary and secondary valves 27, 41, Fig. 3, are each of the plunger open-centre type disclosed in Specification 576,309. The supply ports 42, 43 of each valves 27, 41 are normally connected to the discharge port 35 which leads back to the sump. The exhaust ports 45, 46 of valve 27 and 47, 48 of valve 41 are interconnected as shown by passages 49, 51. The pressure in the supply ports 42, 43 may be relieved into extensions 49a, 49b of the passage 49 via similar poppet relief valves 54 which each have an adjustable loading spring 62. The working ports 63a, 63b and 64a, 64b of the valves 27, 41 are interconnected by passages 63, 64 connected respectively to the lines 36, 37, Fig. 3, leading to the doubleacting motor 11. The plunger 27 has two bores separated by a central partition 65, each bore having a spring loaded poppet valve 68, 69 which controls ports 76 leading to ports 63a, 64a. The plunger 41 also has two bores separated by a central partition 81 and each bore has a poppet valve 82 or 83, loaded by a spring 86, 87 retained by a plug 88 or 89. The plug 89 co-operates with a centering unit 91-95. The working chambers 99, 101 at each end of the plunger 41 are connected to ports 102, 103 controlled by ports 104, 105 in the plunger 27. In operation, slight movement of the plunger 27 connects one or other of the passages 63, 64 to the pump 29 and theother one to exhaust so causing appropriate movement of the double-acting motor 11. The follow-up mechanism acts to restore the plunger 27 to its initial position. If the plunger 27 is moved beyond a narrow range i.e. if the rate of movement of wheel 16 is greater than that of the motor 11, the supply from port 42 passes via the appropriate check valve 68 or 69 and port 102 or 103 to chamber 99 or 101 so moving the plunger 41 and connecting the pump 31 to the motor 11 through one or other of the passages 63, 64 and lines 36, 37. Each passage 63, 64 is provided with a back pressure valve 106, Fig. 7 (not shown) which ensures that if the motor 11 is only lightly loaded when the plunger 27 is moved beyond its initial range, there is still sufficient back pressure to shift the plunger 41. To relieve shocks, two reversely set spring loaded relief valves Fig. 6 (not shown) permit throttled cross flow between passages 63, 64.