Patent GB-1342675-A (GB)
Title: Hydraulic control devices
IPC: B64C13/24
Filed: 1971-06-04
Abstract: 1342675 Hydraulic control systems for aircraft E-SYSTEMS Inc 4 June 1971 [4 June 1970] 19016/71 Heading B7G A control device including; an inlet 72 connectible to a source of hydraulic fluid under pressure and an outlet or return line 54a; a control valve CVA for selectively transmitting fluid under pressure from said inlet to either one of two passages C1 and C2, said passages being connectible to respective passages 151, 155 of a hydraulic motor controlling an aircraft elevator 12 or the like, or preventing flow through both passages C1, C2; and a deactivating valve DVA for providing a by-pass flow passage between said passages C1, C2 in response to malfunction of the control valve CVA. Pressure fluid is supplied, in operation, to a pressure passage P via annular grooves 104, 105, an annular recess 101 in the piston of a by-pass valve BVA (see below), annular grooves 114, 115, a passage 112, annular grooves 110, 111 and ports 108. The pressure passage is formed between lands 160, 165 of the control valve spool 39, which close respectively the passages Cl, C2 and so prevent flow through the passages. To supply pressure fluid to the passage C1 which consists of annular grooves 132, 141, a passage 145 and annular grooves 147, 148, the valve spool is moved to the left thereby opening the passage C1 to the pressure passage P and opening the passage C2 to a chamber R2 which communicates with the return line 54a via annular grooves 56, 57 and ports 60. To supply pressure fluid to the passage C2 which is similar to C1 the valve spool 39 is moved to the right, thereby opening the passage C2 to the pressure passage P and opening the passage C1 to a chamber R1 which communicates with the return line 54a via ports 67, annular grooves 64, 65 and a passage 112. The valve spool is slidable on a control rod 33 including a central portion 177 and an end portion 211, A piston 171 or 172 is slidable on the rod 33 at each side of the central portion 177, the pistons 171, 172 causing the valve spool 39 to move with the control rod 33 because of hydraulic pressure in piston chambers 190, 220 respectively, the pressure being caused by pressure fluid supplied from the pressure passage P via inter alia passages 193, 194, and 234. The control rod 33 is controlled by an arm 30 fixed to a control shaft 28 and having legs 31 engaging a recess 32 in the rod 33. On malfunction of the control valve CVA, for example when the valve spool 33 becomes stuck in the control valve body 40, the control rod 33 moves relative to the valve spool 39. The end 211 of the control rod 33 is formed with various grooves and passages which, on such relative movement, communicate the pressure fluid to the left end of the bore 240 of the deactivating valve assembly DVA via a passage 244. The pressure of the fluid pushes the piston 241 of the valve DVA against the force of a spring 271 towards the spring so that an annular recess 291 in the piston 241 forms a by-pass passage between the passages C1 and C2; at the same time the piston engages a switch 303 which illuminates a warning lamp 309 on a display panel of the aircraft cockpit. When pressure in the inlet 72 falls below a predetermined amount, the pressure to the left of the piston 75 of the by-pass valve BVA is no longer sufficient to overcome the force of a spring 76 and the piston moves away from the spring to close the pressure passage P from the inlet 72 by the surface 335 and to connect the passages C1, C2 which then are open to a recess 125 in the piston 75 via respective passages 133 and 136. A further by-pass passage is thereby provided.