GB455813A - A new or improved valve system for controlling intermittent movement of a piston in a cylinder under fluid pressure - Google Patents

Abstract

455,813. Fluid-pressure servomotors. BENDIX, Ltd., and WYNNE, C. H. L., King's Road, Tyseley, Birmingham. Aug. 6, 1935, No. 22094. [Class 135] A valve device for controlling the intermittent movement of a piston 2 in a cylinder 1, for instance in the gear-shifting mechanism of change-speed gears or of reversing gear for marine power units, comprises a main ported control piston 12 which can be moved a certain distance before entraining two auxiliary ported control-pistons 20, 24, the three pistons being slidable in a bore 4 having ports 5, 7, 8 leading to the cylinder 1 and a port 11 connected to a source of vacuum or fluid-pressure. The piston 2 may occupy either end position or the central position in the cylinder 1 according to the position of the piston 12. The latter has a groove 14 continuously in communication with the port 11, which groove communicates through passages 15, 16 with three ports 17, 18, 19 so spaced with respect to the ports 5, 7, 8 that only one of them communicates with the cylinder at once. The piston 20 is loose on a reduced part of the operating spindle 13 which is terminated by a collar 23 whilst the piston 24 is similarly loose on a headed rod 25 screwed into the piston 12. The ends of the cylinder 1 are connected to the ports 7, 8 by passages 9, 10 respectively and are vented through the open ends of the bore 4 by longitudinal passages 21, 26 in the respective auxiliary pistons when the piston 12 has moved out of contact therewith and clear of the respective port 7 or 8. Further ports 22, 27 lead into the passages 21, 26 respectively and vent the ends of the cylinder in the respective end positions of the valve device. Unlike the piston 12, the pistons 20, 24 need only be a loose fit in the bore 4 and their movement therein due to vibration may be prevented by spring-pressed balls 28. When the piston 12 is moved from the position shown back to the central position in which the ports 5, 17 register, the port 8 is first cut off from the atmosphere. The vacuum in the left hand end of the cylinder 1 then draws the piston 2 back to the central position where it cuts off the port 5. To prevent the piston 2 overshooting the central position due to a sudden cessation of the resistance to its movement, a passage 31 thersthrough is opened by a plunger valve 32 opened by the vacuum through ports 5, 33 against the action of a spring in the centre position. Alternatively the two sides of the piston may communicate through a small permanently-open passage in the piston rod 3. The ports 17, 18, 19 may communicate directly with a segmental groove which dispenses with passages 15, 16.