Hydraulic control systems

Abstract

A hydraulic control system for a continuously-variable-ratio-vehicle transmission of the toroidal-race rolling-traction type, in which the mechanism for positioning each roller includes a double-acting ram (11). The two opposed faces of the ram are exposed in normal use to the pressures of two separate lines of fluid (21, 23), each being pressure-controlled by separate valves (32, 34) located downstream of the respective ram face. The outputs of those separate valves combine in a common region (31), and further valve means (40, 41) open to connect that region to each line in response to the occurrence of a predetermined difference in pressure between the region and that line. In such circumstances such connection and the resulting transfer of fluid from the region to the line helps to counteract any tendency to fluid starvation in the line. This might otherwise occur for instance in response to the rapid movement of all the double-acting rams in the same direction, for example when the vehicle is approaching wheel-lock during emergency braking.

Dependencies are inferred from the claim text.