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A method and system for configuring a hydromechanical transmission having a hydraulic pump and a hydraulic motor driven by the hydraulic pump and a pressure-driven actuator employs a particular torque-pressure curve configuration to maximize torque resolution with respect to actuator pressure change

A method and system for configuring a hydromechanical transmission having a hydraulic pump and a hydraulic motor driven by the hydraulic pump and a pressure-driven actuator employs a particular torque-pressure curve configuration to maximize torque resolution with respect to actuator pressure changes while ensuring that the curve is substantially monotonic in each dimension and at any available motor speed within a predetermined motor speed limit and any available actuator pressure within predetermined actuator pressure limits. The resultant four-dimensional association between actuator pressure, motor speed, primary power source speed and motor torque allows selection of an actuator pressure to provide a desired torque.

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1. A method of configuring a transmission having an engine input for receiving power from a primary power source and a motor input linked to a hydraulic variator comprising a hydraulic pump and a hydraulic motor driven by the hydraulic pump, the variator further including a pressure-driven actuator

1. A method of configuring a transmission having an engine input for receiving power from a primary power source and a motor input linked to a hydraulic variator comprising a hydraulic pump and a hydraulic motor driven by the hydraulic pump, the variator further including a pressure-driven actuator for controlling a displacement of the hydraulic pump, the method comprising: establishing a torque-pressure curve of the transmission, wherein the torque-pressure curve relates motor output torque to motor speed, actuator pressure, and pump speed to maximize output torque resolution of the variator with respect to actuator pressure changes while maintaining the curve substantially monotonic in each dimension at any available motor speed, without exceeding a predetermined motor speed limit and without exceeding available actuator pressure limits; andconfiguring the transmission to output a torque by determining an actuator pressure to be applied based on the established torque-pressure curve, the desired torque, a current motor speed, and a current pump speed. 2. The method of configuring a transmission according to claim 1, wherein the motor speed is a normalized motor speed. 3. The method of configuring a transmission according to claim 1, wherein the transmission is a hystat transmission. 4. The method of configuring a transmission according to claim 1, wherein the transmission is a hydromechanical transmission. 5. The method of configuring a transmission according to claim 1, wherein the transmission further includes one or more pressure control valves to apply pressure to control the actuator, the method further comprising: generating and transmitting to the one or more pressure control valves one or more signals to activate the one or more pressure control valves to cause the determined actuator pressure to be applied to the actuator. 6. The method of configuring a transmission according to claim 5, wherein the determined actuator pressure is a pressure differential. 7. The method of configuring a transmission according to claim 5, further comprising monitoring the pump speed and motor speed after the step of generating to determine whether to alter the determined actuator pressure. 8. An improved hydraulic transmission comprising: a primary input for receiving power from a primary power source;a motor input linked to a hydraulic variator comprising a hydraulic pump and a hydraulic motor driven by the hydraulic pump, the variator further including a pressure-driven actuator for controlling a displacement of the hydraulic pump; anda controller for receiving an indication of desired torque and for controlling the transmission to supply the desired torque by applying a predetermined mapping to identify an actuator pressure to apply to create the desired output torque, wherein the predetermined mapping relates motor output torque to motor speed, actuator pressure, and pump speed, and wherein the resolution of output torque as a function of actuator pressure is substantially maximized while maintaining the map substantially monotonic in each dimension without exceeding a predetermined motor speed limit and without exceeding available actuator pressure limits. 9. The improved hydraulic transmission according to claim 8, wherein the motor speed is a normalized motor speed. 10. The improved hydraulic transmission according to claim 8, wherein the transmission is a hystat transmission. 11. The improved hydraulic transmission according to claim 8, wherein the transmission is a hydromechanical transmission. 12. The improved hydraulic transmission according to claim 8, wherein the transmission further includes one or more pressure control valves to apply pressure to control the actuator, and wherein the controller is further adapted to generate and transmit to the one or more pressure control valves one or more signals to activate the one or more pressure control valves to cause the determined actuator pressure to be applied to the actuator. 13. The improved hydraulic transmission according to claim 12, wherein the determined actuator pressure is a pressure differential. 14. The improved hydraulic transmission according to claim 12, wherein the controller is further adapted to monitor the pump speed and motor speed, after transmitting the one or more signals to activate the one or more pressure control valves, to determine whether to alter the determined actuator pressure. 15. A method of generating a torque-pressure curve for a hydraulic transmission including a hydraulic pump and a hydraulic motor driven by the hydraulic pump via a pump port plate having a port plate angle, the variator further including a pressure-driven actuator for controlling a displacement of the hydraulic pump, the actuator having one or more springs biased to center the actuator, the method comprising: selecting a port plate angle for the pump port plate and selecting one or more respective spring rates for the one or more actuator springs so as to maximize output torque resolution of the hydraulic motor with respect to actuator pressure changes while allowing the motor to reach maximum available torque without the transmission exceeding a predetermined motor speed limit and actuator pressure limits; andapplying a plurality of actuator pressures at a plurality of motor speeds and pump speeds to generate a respective plurality of motor torques, and recording the respective plurality of motor torques in association with the applied actuator pressures, motor speeds and pump speeds to create a torque-pressure curve for the transmission. 16. The method of generating a torque-pressure curve according to claim 15, wherein the motor speed is a normalized motor speed. 17. The method of generating a torque-pressure curve according to claim 15, wherein the transmission is a hystat transmission. 18. The method of generating a torque-pressure curve according to claim 15, wherein the transmission is a hydromechanical transmission. 19. The method of generating a torque-pressure curve according to claim 15, wherein the actuator pressures are pressure differentials. 20. The method of generating a torque-pressure curve according to claim 15, further comprising reducing the port plate angle after selecting a port plate angle and after selecting the one or more spring rates, but prior to applying a plurality of actuator pressures at a plurality of motor speeds and pump speeds, wherein the reduction in port plate angle is selected so as to reduce pump noise by a predetermined amount.