Patent GB-794606-A (GB)
Title: Improvements in fluid pressure operated motors
IPC: B60S1/06
Filed: 1955-11-17
Abstract: 794,606. Windscreen cleaners. GENERAL MOTORS CORPORATION. Nov. 17, 1955 [Nov. 29, 1954], No. 32925/55. Class 138(1). [Also in Groups XXVI and XXIX] A hydraulic motor for actuating a windscreen wiper comprises a double-acting piston reciprocated in a cylinder under the control of a distributing valve provided in the piston, the distributing valve being hydraulically actuated to reverse the stroke of the piston. As shown in Fig. 2 a piston 28 divides a cylinder 21 into chambers 29, 30, and liquid is admitted from a supply passage 55 past a manually controlled throttle valve 27 through passages (not shown) to a supply port 35, and thence, in the position of distributing valve 32 shown, through a passage 47 into the chamber 30. Chamber 29 is open to drain through a passage 46 in the piston and a drain port 33. The piston is thus moved to the right. In the right hand limit position for normal reciprocation, shown ports 49, 53 in the piston co-operate with port, in the cylinder and liquid is supplied from the passage 55, past valve 27 and through passages 82, 51, 83, 84 to act on a valve land 41 to move the distributing valve to its other end position, the opposite end of the valve bore being drained through a passage 81. The connections of chambers 29, 30 are thus reversed, the supply port 35 communicating with chamber 29 through the passage 46, and the chamber 30 communicating through the passage 47 with a drain port 37. When the piston reaches its left hand end position liquid is supplied through the passage 82, port 53 and passages 51, 48, 78 and a port 80 to act on a valve land 38 and thus move the distributing valve to its original position. To stop the motor the valve 27 is move to its left hand end position. Liquid is still supplied slowly past the valve 27, but the passage 84 is blocked off, so that when the piston reaches the position of Fig. 2 the distributing valve does not reverse, and the piston continues further to the left so that the windscreen wipers are held in a " parked " position beyond the normal limit of reciprocation. In the embodiment shown in Fig. 18 a piston 113 is provided with a distributing valve 123 actuated by a pilot valve 124, the pilot valve being actuated by contact with the cylinder housing at one end of the stroke of the piston and by contact with a throttle valve 125 at the other end of the stroke. Valve 125 is manually operated and throttles the supply of oil to the motor, and in the " parking " position shown a groove 142 in the valve is aligned with the pilot valve which is consequently not actuated so that the piston continues beyond its normal limit position into engagement with the left hand end of the cylinder. In both embodiments a trunnion 64 is journaled in the piston and provided with a diametral passage in which a lever, fixed on a drive shaft, is slidable. The drive shaft is mechanically connected to the wipers. The drive shaft is thus oscillated with increasing torque and decreasing speed from its centre of oscillation. This eliminates " wiper slap" and prevents stalling of the blades due to a possible accumulation of snow or ice at the boundaries of oscillation.