Patent GB-644766-A (GB)
Title: Improvements in or relating to pneumatic suspension struts
IPC: F16F9/32
Filed: 1948-10-04
Abstract: 644,766. Pneumatic suspension devices. LEVITATION, Ltd., and THORNHILL, P. W. Oct. 4, 1948, No. 25853. [Class 108(iii)] The invention relates to pneumatic suspension struts of the kind comprising a cylinder 10 in which the air is compressed on shortening of the strut by a plunger 15 having a piston head 12 dividing the cylinder into two chambers, the passage of air past the head 12 being controlled to damp movements of the strut in such a way that on extension, a pressure can be built up in an annular working chamber 25 below the head 12, which is greater than the pressure simultaneously existing in the working chamber 24 above the head 12. According to the invention, a passage 44 extends from the upper surface of the piston head 12 to a point in the plunger below the head 12, the annular working chamber 25 containing oil in which the lower end of the passage 44 is immersed during at least part of the extension stroke. When the air pressure in the space 25 is greater than that in the space 24 during such immersion, oil is forced to the upper surface of the piston head to lubricate valves and other mechanism therein. The plunger 15 is clamped between the head 12, and a plug 16 (not shown) formed with a socket for cooperating with a ball-headed mounting member. A mounting bracket (not shown) for the cylinder 10 is clamped between rubber discs 21. The head 12 has a piston valve 27 similar to that described in Specification 570,813. The valve 27 is slidable against the action of a spring 34 in a recess 26 connected by a passage 36 of small bore and has an annular recess 33 in its surface. Two axially-spaced sets 28. 30 of radial ports connect the recess 26 respectively with a circumferential groove 29 and relieved portions 31 on the surface of the head 12. A packing ring 35 in frictional engagement with the cylinder wall is of smaller axial width than the groove 29. The upper end of the head 12 is formed with radial slots 32. In each of the ports 30 is mounted a rotary pad member (47, Fig. 3, not shown) of the kind described in Specification 595,388, for the purpose of deriving relative rotation of the plunger 15 and cylinder 10. A rubber packing ring 41 supported by a split washer 40 is engaged by a spring (Fig. 1, not shown) in the space 25, when the strut is sufficiently extended, so as to close the air passage afforded by the relieved portions 31, as described in Specification 573,275. Operation. On extension, or rebound movement after compression, differential pressure acting on the valve 27 causes it to move outwards from the normal position (shown) to connect the slots 32 with the ports 28 by the recess 33. Friction maintains the ring 35 against the upper wall of the groove 29 and air can pass from the chamber 25 through the relieved portions 31, ports 28, recess 33 and slots 32 into the space 24. On excessive extension or rebound when the ring 41 closes the passage afforded by the portions 31, pressure in the space 25 rises above that in the space 24 and oil in the lower part of the space 25 is forced into the passage 44 and out over the top of the piston to lubricate the valve 27 and the pad members in the recesses 30. A recess 46 in the wall of the recess 26 is connected with the passage 44.