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An apparatus and method for controlling a discharge pressure of a variable displacement hydraulic pump. The apparatus and method includes a swashplate pivotally attached to the pump, a valve plate located on the pump to allow hydraulic fluid to enter the pump through an intake port on the valve plat

An apparatus and method for controlling a discharge pressure of a variable displacement hydraulic pump. The apparatus and method includes a swashplate pivotally attached to the pump, a valve plate located on the pump to allow hydraulic fluid to enter the pump through an intake port on the valve plate, and to exit the pump through a discharge port on the valve plate, the hydraulic fluid entering and exiting the pump responsively creating a pressure carry over angle .gamma., a control servo operable to control an angle of the swashplate relative to the pump, a servo valve having an output port hydraulically connected to the control servo and an input port hydraulically connected to the pump output port, and means for controlling the servo valve as a function of the discharge pressure of the pump and responsively balancing a torque induced by the pressure carry over angle .gamma. with a torque generated by a control pressure Pc at the control servo.

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1. An apparatus for controlling a discharge pressure of a variable displacement hydraulic pump, the discharge pressure being located at a pump output port, comprising:a swashplate pivotally attached to the pump; a valve plate located on the pump to allow hydraulic fluid to enter the pump through an

1. An apparatus for controlling a discharge pressure of a variable displacement hydraulic pump, the discharge pressure being located at a pump output port, comprising:a swashplate pivotally attached to the pump; a valve plate located on the pump to allow hydraulic fluid to enter the pump through an intake port on the valve plate, and to exit the pump through a discharge port on the valve plate, the hydraulic fluid entering and exiting the pump responsively creating a pressure carry over angle .gamma.; a control servo operable to control an angle of the swashplate relative to the pump; a servo valve having an output port hydraulically connected to the control servo and an input port hydraulically connected to the pump output port; and means for controlling the servo valve as a function of the discharge pressure of the pump and responsively balancing a torque induced by the pressure carry over angle .gamma. with a torque generated by a control pressure Pc at the control servo.