| 摘要 |
<p>1,183,362. Vehicle braking systems; valves. GIRLING Ltd. 19 Jan., 1968 [21 Feb., 1967], No. 8216/67. Headings F2F and F2V. A brake pressure control valve comprises a piston slidable in a sleeve which in turn is slidable in a bore, an increase in inlet pressure first causing the piston to move in one direction relative to the sleeve and thereby shut off the outlet from the inlet, further increase in inlet pressure then being transmitted to the outlet at a reduced rate by the piston moving in the opposite direction relative to the sleeve. In Fig. 3 a piston 7 is biased in an upward direction by a spring 21 enclosed in two relatively movable cups 28, 29 and acting on a stem 8. In this position a collar 27 on the piston holds a ball 9 off its seat and allows communication between the inlet 2 and outlet 3. The valve seat is formed in a sleeve 6 which is also biased upwardly by a spring 11 assisted by a stronger spring 26 acting against a washer 24 held against a collar 7A on the piston. On increase of inlet pressure, e.g. from a master cylinder, the piston is forced downwardly against the spring 21 and the ball valve 9 closes. Further increase of inlet pressure acts on a step in the piston to force it upwards again, the valve 9 opening to bleed fluid to the outlet with a pressure drop. On release of the inlet pressure the piston and sleeve both move downwards and thus reduce the outlet pressure. When the inlet pressure drops below the outlet, the ball valve opens and allows free return of fluid, after which the piston and sleeve assume their original positions. In a modification (Fig. 4, not shown) the spring 21 is in a sealed cavity around the stem 8 and the spring 26 is omitted. Alternatively, the cup enclosing the end of the spring 21 can be screwed to adjust the pressure relationship (Fig. 2, not shown). In another form (Fig. 1, not shown) the stem 8 receives a spring load depending on the loading of the vehicle. The ball valve 9 may be spring-biased towards a closed position in case gravity should hold it open.</p> |
