Patent GB-570069-A (GB)
Title: Improvements in fluid controlled mechanisms, particularly for steering endless trackvehicles
IPC: B62D5/24
Filed: 1940-11-13
Abstract: 570,069. Valves. PRATT, J. H., MANLEY, G. E., and GIRLING, A. H. G. Nov. 13, 1940, No. 16427. [Class 135] [Also in Group XXXI] In mechanism for steering endless-track vehicles of the kind in which a fluid-pressure control provides for straight-ahead travel, a gradual turn and a sharp turn, the fluidpressure control comprises a multi-ported rotary valve co-operating with a balancing valve which ensures that a gradual turn may be made with a degree of responsiveness or " feel " in the controlling agency or operating lever which is proportional to the gradualness of the turn it is desired to make. In the construction shown, which is applied to a vehicle steered by means of two epicyclic change-speed gears of known type, each controlled by an operating lever 7, each lever 7 rotates a valve 8 in a chamber 27 connected by an inlet 28 to a source of compressed air. The valve has two ports 8a, 8b and rotates over a face having three ports 4<1>, 4<2>, 4<3>. The lever 7 is spring- biassed to the straight-ahead position shown in which the pressure port 8a of the valve admits air to port 4<3> and a passage 26 leading to the straight-ahead piston of the corresponding gear-box. For a gradual turn the valve 8 is rotated until ports 8a, 4<2> register so that air is supplied through a passage 23 to a chamber 2,0 ; this chamber being then connected to a " gradual-turn " passage 4c by a balancing valve 18 opened simultaneously with the movement of the valve 8 to its second position. At the same time the exhaust port 8b of valve 8 registers with port 4<3> and air exhausts from passage 26 through a bore 5a in the valve shaft 5. For a sharp turn the valve 8 is rotated until port 8a registers with port 4<1> and port 8b with port 4<2>, so that air is admitted by the valve to the port 4<1> and passage 25 leading to the piston controlling the corresponding gear of the gear-box, and the gradual-turn passage 4c is connected to exhaust through chamber 20, passage 23, ports 4<2>, 8b and bore 5a. The valve shaft 5 operates the balancing valve 18 through a cam 10 acting on a roller. 11 carried by a slide 13 bearing through a spring 14 on a control valve 15 co-operating with flexible diaphragms 16a, 16b and adapted to open the balancing valve. In the normal position shown, the valve 15 is clear of the valve 18, and the passage 4c is connected to an exhaust port 4d through ,the hollow valve 15 and radial bores 15b therein. When the cam 10 moves the slide 13 to the left, the valve 15 first bears against the valve 18 and closes the exhaust outlet ; further movement of valve 15 opens valve 18 and admits pressure air from chamber 20 to . the gradual-turn passage 4c. The pressure now established in chamber 17 between valve 18 and diaphragm 16b opposes the spring 14 forming the connection between the slide 13 and valve 15 and allows the valve 18 to close when the pressure in the chamber 17 corresponds to the position of the slide 13 and, therefore, of the operating lever 7. Thus, to increase the pressure in the chamber 17, and therefore the steering effect, the driver rotates valve 8 to load the spring 14 more strongly, and to reduce the pressure in 17 the driver partly returns valve 8 to reduce the load on the spring. The cam 10 has a gradual rise 10<2> in the port corresponding to the control of the pressure in the chamber 17, and a steep rise 10<3> which leads up to the final port 10<4> which comes into use for a sharp-turn, this steep-rise offering increased resistance which warns the driver of the position of the valve 8 and the cam.