GB816143A - Improvements in fluid pressure motors - Google Patents

Abstract

816,143. Compressed-air engines. SPRAGUE DEVICES Inc. Sept. 1, 1955, No. 25158/55. Classes 122 (1), 122 (2) and 122 (3). A fluid-pressure motor for driving a windscreen wiper comprises a double-ended piston 66 reciprocating in a cylinder 10 by the action of fluid supplied alternately to opposite ends of the cylinder under the control of a two-position spool valve 98 which has inlet and outlet openings 110, 114 and is mounted at one end of the cylinder 10 from which it is separated by a multiple-port wall 80, 94 having passages communicating with passages in the cylinder; the two positions of the valve provide for the opposite flow of fluid to and from the cylinder to reciprocate the piston, and the necessary movement of the valve from one position to the other to reverse the flow is effected by the action of the piston in each of its strokes in uncovering one of two openings 152, 154 communicating with two (27, 29) of the passages in the cylinder. The valve 98 consists of four spools on a shaft 142 movable endwise in a cylinder 100 having a base plate 94 by which it is screwed to one end of the cylinder 10, with the interposition of an end plate 80; the plate 94 may be formed integrally with or separate from the cylinder. Ports 138, 136, 132, 130, 124, 120 in the plate 94 connect the interior of the cylinder 100 either directly or through grooves 126, 134, Fig. 7, in the plate with corresponding ports in the plate 80 and a passage 114 for conveying exhaust to a tubular member formed integral with the cylinder 100. The plate 80 has four ports 88, 86, 84, 82 which on the inner side connect respectively with the right-hand end of the cylinder, a longitudinal bore 31 in the cylinder wall communicating through a port 32 with the left-hand end of the cylinder, and two longitudinal bores 27, 29 in the cylinder wall communicating by the ports 152, 154 with the interior of the cylinder. With the valve 98 positioned as shown in Fig. 2, air from the inlet 110 is discharged into the left-hand end of the cylinder via the port 132, groove 134, port 86, longitudinal bore 31 and port 32, and air is exhausted from the opposite end of the cylinder via the ports 88, 120, cylinder 100, port 130, groove 126 and outlet 114. When the piston in its stroke uncovers the port 152, air from the left-hand end of the cylinder passes via this port, longitudinal bore 27 and ports 82, 136 into the upper end of the cylinder 100 and so moves the valve to its lowered position. Air then passes to the right-hand end of the cylinder 10 via the ports 120, 88 and is exhausted from the other end via the port 32, longitudinal bore 31, port 86, groove 134, port 132, cylinder 100, port 124, groove 126 and outlet 114. Uncovering of the port 154 by the left-hand movement of the piston results in flow of air through the port 130 to the lower end of the cylinder 100 and return of the valve to its upper position. The piston unit 66 consists of a piston 62 formed integrally at each end of a longitudinal central member of H cross-section, this member being formed with gear teeth 74 meshing with a gear sector 58 on a transverse shaft 44 carrying the mounting arm of the windscreen wiper. The cylinder 10, cylinder 100 with the plate 94, plate 80, piston unit 66 and gear 58 may each be cast or moulded from natural or synthetic rubber, synthetic resin such as polyethylene or one of the polyamide resins, or metal, and a removable closure is formed in the cylinder 100 in the region of the sector 58 for the purpose of access.