Displacement control for a hydraulic pump or motor with failure override

A displacement control for a variable displacement pump having a swash plate for controlling displacement, a circuit including a control device operatively connected to said swash plate and a control valve having connections to a source of pressure and a drain for hydraulically operating said control device, said control valve having a neutral position wherein said swash plate is in a neutral position for zero displacement and a range of other positions wherein said swash plate is in a displacement-setting position, position-controlling means for setting the position of the control valve, said control valve having a control position other than said neutral position which enables the swash plate to move to said neutral position, and means operative in response to an operative failure of said position-controlling means for moving the control valve to said control position.

A displacement control for a variable displacement pump having a swash plate for controlling displacement, a fluid circuit including a pair of control pistons and cylinders operatively connected to said swash plate with spring means urging the swash plate to a neutral position and a control valve having connections to a source of pressure and a drain for hydraulically operating said control cylinders, said control valve having a neutral position wherein said control cylinders are connected to drain and the swash plate is in a neutral position and at least one other position wherein said swash plate is in a displacement-setting position, position-controlling means for controlling the position of the control valve including feedback means between the swash plate and the control valve, said control valve being movable to a control position other than said neutral position which connects the cylinders to drain whereby the swash plate moves to said neutral position, and means operative in response to an operative failure of said position-controlling means for moving the control valve to said control position.

A displacement control for a variable displacement motor having a swash plate for controlling displacement, a circuit including a control device operatively connected to said swash plate and a control valve having connections to a source of pressure and a drain for hydraulically operating said control device, means hydraulically connecting the control valve and control device, said control valve having a neutral position and at least one other position wherein said swash plate is in a displacement-setting position, position-controlling means for setting the position of the control valve, said control valve being movable to a control position not normally used in control of the swash plate which causes the swash plate to move to a maximum displacement position, and means operative in response to an operative failure of said position-controlling means for moving the control valve to said control position.

A displacement control for a variable displacement motor having a swash plate for controlling displacement, a circuit including a pair of control pistons and cylinders operatively connected to said swash plate and a control valve having connections to a source of pressure and a drain for hydraulically operating said control cylinders, means hydraulically connecting the control valve and control device, said control valve having a neutral position wherein said cylinders are blocked from pressure and at least one other position wherein said swash plate is in a displacement-setting position, position-controlling means for controlling the position of the control valve including feedback means between the swash plate and the control valve, said control valve being movable to a control position not used in normal positioning of the swash plate which connects one of the cylinders to pressure and moves the swash plate to a maximum displacement position, and means operative in response to an operative failure of said position-controlling means for moving the control valve to said control position.