Control systems for hydraulic transmission systems

Claim 2

An hydraulic control system for a transmission system of the kind specified comprising a positive displacement type auxiliary pump arranged to be driven by a prime mover whereby the transmission system is driven, passage means affording communication between the downstream side of said auxiliary pump and the interior of said ported member, valve means affording communication between said passage means and whichever of two ports in the member is at a lower pressure, a relief valve whereby fluid from said lower pressure port can escape, further passage means in the ported member whereby fluid from the higher pressure port can reach the relief valve to tend to oppose the opening thereof under the influence of the pressure of fluid from the lower pressure port, the area of the relief valve on which the higher pressure acts being substantially smaller than that on which the lower pressure acts, the relief valve being arranged to regulate the pressure in the lower pressure port in accordance with the pressure existing in the higher pressure port, a piston and cylinder type servo device arranged to move the ported member to vary the piston strokes of the pump and motor respectively, and further valve means whereby, when the pressure at the delivery side of said auxiliary pump reaches a predetermined value, fluid at the pressure existing in said lower pressure port is permitted to enter one end of the cylinder of the servo device whilst fluid from the other end is permitted to escape.

Claim 3

An hydraulic control system as claimed in claim 1 in which a shuttle valve is disposed in the ported member, said shuttle valve being arranged to determine which of the two ports is at a higher pressure and permits flow to the relief valve from the lower pressure one of the ports, said flow through the relief valve being determined by the position of the relief valve in the ported member, in relation to a seating provided therein, said seating serving as a closure for the valve.

Claim 4

An hydraulic control system as claimed in claim 1 in which the ported member contains the valve means which comprises a shuttle valve, whereby the pressure in the lower pressure port is admitted to the passage means.

Claim 5

An hydraulic control system as claimed in claim 1 in which the piston of the servo device carries a rack engaging with teeth on the ported member, movement of the piston causing angular movement of the ported member.

Claim 6

An hydraulic control system as claimed in claim 1 in which the servo device has an angularly movable rod extending through the piston, the piston and rod having cooperating openings whereby the angular position of the rod in relation to the piston determines the permitted movement of the piston in its cylinder under the influence of hydraulic pressure.

Claim 7

An hydraulic control system as claimed in claim 5 in which the opening in the rod is a wide helical groove which can communicate with drillings in the bore of the piston in which the rod engages, angular movement of the rod determining the axial position of the piston at which such communication takes place.

Claim 8

An hydraulic control system as claimed in claim 1 in which there is a manually controllable valve arranged, in one position to permit fluid from the auxiliary pump to flow to one end of the cylinder of the servo device and also permits escape of fluid from the other end, and in another position allows flow to ocCur into said other end and out of said one end.

Claim 9

An hydraulic control system as claimed in claim 1 in which the passage means has a further valve for controlling flow of fluid therethrough, said further valve being positioned in accordance with the position of a throttle lever for controlling the speed of the prime mover whereby the transmission system is driven.

Claim 10

An hydraulic control system as claimed in claim 8 in which said further valve is connected to a mechanism which varies the rate of opening of said further valve in response to opening of said prime mover throttle lever in accordance with the position of the piston of the servo device in its cylinder.

Claim 11

An hydraulic control system as claimed in claim 8 in which the throttle lever is movable about a fulcrum member which is connected to a device which is responsive to the pressure of fluid in said passage means, to vary the position of said fulcrum member.

Claim 12

An hydraulic transmission system of the kind specified having a control system comprising a positive displacement type auxiliary pump arranged to be driven by a prime mover whereby the transmission system is driven, passage means affording communication between the downstream side of said auxiliary pump and the interior of said ported member, valve means affording communication between said passage means and whichever of two ports in the member is at a lower pressure, a relief valve whereby fluid from said lower pressure port can escape, further passage means in the ported member whereby fluid from the higher pressure port can reach the relief valve to tend to oppose the opening thereof under the influence of the pressure of fluid from the lower pressure port, the area of the relief valve on which the higher pressure acts being substantially smaller than that on which the lower pressure acts, the relief valve being arranged to regulate the pressure in the lower pressure port in accordance with the pressure existing in the higher pressure port, a piston and cylinder type servo device arranged to move the ported member to vary the piston strokes of the pump and motor respectively, and further valve means whereby, when the pressure at the delivery side of said auxiliary pump reaches a predetermined value, fluid at the pressure existing in said lower pressure port is permitted to enter one end of the cylinder of the servo device whilst fluid from the other end is permitted to escape.

Claim 13

An hydraulic transmission system of the kind specified having a control system comprising a positive displacement type auxiliary pump arranged to be driven by a prime mover whereby the transmission system is driven, passage means affording communication between the downstream side of said auxiliary pump and the interior of said ported member, valve means affording communication between said passage means and whichever of two ports in the member is at a lower pressure, a relief valve whereby fluid from said lower pressure port can escape, further passage means in the ported member whereby fluid from the higher pressure port can reach the relief valve to tend to oppose the opening thereof under the influence of the pressure of fluid from the lower pressure port, the area of the relief valve on which the higher pressure acts being substantially smaller than that on which the lower pressure acts, the relief valve being arranged to regulate the pressure in the lower pressure port in accordance with the pressure existing in the higher pressure port, a piston and cylinder type servo device arranged to move the ported member to vary the piston strokes of the pump and motor respectively, and further valve means whereby, when the pressure at the delivery side of said auxiliary pump reaches a predetermined value, fluid at the pressure existing in said lower pressure port is permitted to enter one end of the cylinder of the servo device whilst fluid from the other end is permitted to escape.