Patent GB-905677-A (GB)
Title: Improvements in or relating to fluid operated reciprocating motors
IPC: B60S1/12
Filed: 1959-05-26
Abstract: 905,677. Windscreen wipers. CURTISSWRIGHT CORPORATION. May 26, 1959 [May 28, 1958], No. 17960/59. Class 138 (1). [Also in Group XXIX] A liquid-pressure engine for operating a windscreen wiper comprises a member P, Fig. 1, reciprocated by a supply of fluid alternately supplied to chambers C, C<SP>1</SP> under the control of a reversing valve 6 operated by the rise in pressure in the then-acting chamber at the ends of the strokes of the member P, the stroke L normally being limited by a variable-length device 28, 33, the effective length of which is decreased as a function of a decrease in the pressure of the fluid supply under the control of a metering valve 1 whereby the member P moves a distance L<SP>1</SP> outside the normal stroke length to park the wiper blade outside the normal wiped area. The member P consists of a piston having a head 2 4 at each end between which is a rack 25 connected to the wiper blade. The piston is reciprocated in the cylinder by liquid pressure alternately supplied to the chambers through pipes 14, 16 under the control of the valve 6 and the metering valve 1. At the end of a stroke to the left, during normal operation, the piston abuts the device 28, 33 and the pressure rises in the chamber C<SP>1</SP> to a valve which moves a reversing piston 17 connected by a drive device 12a to a spring-loaded toggle mechanism 12 which, in turn, moves plugs 18, 19 to reverse the fluid and exhaust connections to the chambers C, C<SP>1</SP>. The device 28, 33 is formed as a piston-andcylinder defining a space D sealed at its outer end by a wall 28<SP>1</SP>, its inner end being sealed except for a small orifice 45<SP>1</SP>. During normal operation liquid cannot escape through the orifice at a rate sufficient to prevent the pressure in the chamber C<SP>1</SP> operating the reversing valve 6. However, when the supply of liquid to the system is reduced to a value below that required to actuate the valve 6 by adjustment of the metering valve 1, liquid escapes from the space D through the orifice 45<SP>1</SP> and the piston 33 can move to the left in the cylinder 28 to permit the piston P also to move to the left a distance L<SP>1</SP> and the wiper to be parked in a position outside the normal wiped area. To recommence normal operation, the metering valve 1 is operated to increase the supply of liquid, the increase in pressure then actuating the reversing valve to direct the liquid to the chamber C and move the piston P to the right. A plate 45, in which is the orifice 45<SP>1</SP>, is at the same time moved to the left by the liquid pressure to permit rapid filling of the space D and the piston 33 to be positioned for normal operation of the piston P. In an alternative embodiment, the piston P<SP>1</SP>, Fig. 2, is provided at its ends with portions 50, 51 which engage cylinders 52, 53 and have slots 50<SP>1</SP>, 51<SP>1</SP> serving as orifices to reduce the flow of liquid from the cylinders at the ends of the strokes of the piston P<SP>1</SP> and provide a dashpot effect. The piston P<SP>1</SP> is also formed at one end with a cylindrical bore 55 in which slides a piston 60 having one end 61 extending from the piston P, the piston 60 forming a space D4 sealed by a plate 62 spring-urged against a seal 62<SP>1</SP>. During normal operation; when the piston P<SP>1</SP> is moving to the left, the extension 61 acts as a stop to permit the pressure in chamber C<SP>1</SP> to rise and actuate the reversing valve. When the wiper blade is to be parked, the metering valve is operated to reduce the flow so that the pressure will not rise sufficiently to actuate the valve and the leakage from the space D permits the piston 60 to move into the portion 50 and the piston P<SP>1</SP> to move further to the left to park the wiper blade outside the normal wiped area.