Fluid control apparatus

Claim 2

Apparatus of the kind specified comprising a member, passage means whereby fluid from a positive displacement pump can reach one side of the member, a restricted passage affording communication between one side of the member and the other, the pressure at said other side being controlled by the rate of escape of fluid therefrom which is, in turn, controlled by the position of said member, and a further passage also affording communication between said one side and said other side of the member, said further passage including a restrictor, the pressure drop created thereby being variable by means responsive to changes in a predetermined parameter, the arrangement being such that the pressure at said other side of the member is applied, in use, to the pressure responsive means.

Claim 3

Apparatus as claimed in claim 1 In which the member is a piston in a cylinder and the member serves as a closure for controlling escape of fluid from the cylinder in accordance with the position of the piston in the cylinder.

Claim 4

Apparatus as claimed in claim 2 in which the piston has fixed to it a further coaxial smaller piston disposed in a coaxial smaller cylinder, the fluid pressure at said one side of the larger piston also being applied to the smaller piston to oppose the action of such pressure on the larger piston.

Claim 5

Apparatus as claimed in claim 1 in which the restrictor is of fixed size and the passage means in which it is located contains a valve which is arranged to modify the fluid pressure drop created by the restrictor, the valve being controlled in response to changes in said parameter.

Claim 6

A transmission system of the kind specified having a hydraulic pump arranged to supply fluid under pressure to a hydraulic motor, comprising a positive displacement type auxiliary pump arranged to be driven by a prime mover which drives the transmission system, a piston and cylinder-type servo device arranged to move a ported member to vary piston strokes of the pump and the motor respectively, a control valve for controlling the supply of fluid to the servo device from the auxiliary pump and for controlling the escape of fluid from the servo device and apparatus for varying the pressure of the fluid delivered by the auxiliary pump through the control valve to the servo device, said apparatus comprising a member, passage means whereby fluid from the auxiliary pump can reach one side of the member, a restricted passage affording communication between one side of the member and the other, the pressure existing at said other side being controlled by the rate of escape of fluid therefrom, which is, in turn, controlled by the position of said member, and a further passage also affording communication between said one side and said other side of the member, said further passage including a restrictor, the pressure drop created thereby being controlled by means responsive to changes in the position of a throttle control for the prime mover, the pressure in said other side being applied to the servo device through the control valve, and the arrangement being such that increasing pressure from the auxiliary pump causes the pressure at the servo device to be increased to tend to cause the ported member of the transmission system to be moved in a direction to increase the speed ratio of the transmission system.

Claim 7

A transmission system of the kind specified having a hydraulic pump arranged to supply fluid under pressure to a hydraulic motor, comprising a positive displacement type auxiliary pump arranged to be driven by a prime mover which drives the transmission system, a piston and cylinder-type servo device arranged to move a ported member to vary piston strokes of the pump and the motor respectively, a control valve for controlling the supply of fluid to the servo device from the auxiliary pump and for controlling the escape of fluid from the servo device and apparatus for varying the pressure of the fluid delivered by the auxiliary pump through the control valve to the servo device, said apparatus comprising a member, passage means whereby fluid from the auxiliary pump can reach one side of the member, a restricted passage affording communication between one side of the member and the other, the pressure existing at said other side being controlled by the rate of escape of fluid therefrom, which is, in turn, controlled by the position of said member, and a further passage also affording communication between said one side and said other side of the member, said further passage including a restrictor, the pressure drop created thereby being controlled by means responsive to changes in the position of a throttle control for the prime mover, the pressure in said other side being applied to the servo device through the control valve, and the arrangement being such that increasing pressure from the auxiliary pump causes the pressure at the servo device to be increased to tend to cause the ported member of the transmission system to be moved in a direction to increase the speed ratio of the transmission system.