Utility vehicle two speed drive motor control

A power machine having an engine, a drive pump driven by the engine to provide a hydraulic power output, a drive motor configured to receive the hydraulic power output from the drive pump and in response to rotate a rotational output member, wherein the drive motor is configured to selectively operate in a low range mode having high-displacement and in a high range mode having low-displacement, wherein the power machine further comprises:

• a travel speed sensor for providing a signal indicative of the travel speed of the power machine;
• a shift actuator operably coupled to the drive motor and configured to control the displacement of the drive motor;
• a gearbox that selectively operably couples the rotational output member of the drive motor to a selected one of a plurality of gear reduction sets;
• a gear sensor configured to provide an indication of which of the plurality of gear reduction sets is selected;
• and
• a controller in communication with the shift actuator, the travel speed sensor, and the gear sensor, and configured to control the shift actuator to cause the drive motor to provide infinitely variable displacement between the high-displacement of the low range mode and the low-displacement of the high range mode, wherein the controller is configured to select a control curve for controlling the shift actuator based upon which of the plurality of gear reduction sets is selected, and wherein the controller controls the shift actuator to vary the displacement of the drive motor being as a function of the travel speed of the machine.

A method of selecting a displacement of a drive motor between a minimum motor displacement and a maximum motor displacement in a power machine, the drive motor having a rotational output provided to a gearbox having a plurality of gear reduction sets configured to be engaged with the rotational output, the method comprising:

• measuring a travel speed of the power machine;
• determining, using a gear sensor, which of the plurality of gear reduction sets is engaged with the rotational output;
• selecting a control curve from a plurality of control curves based upon the determination of which of the plurality of gear reduction sets is engaged with the rotational output;
• and
• providing a control signal from a controller as a function of the selected control curve and of the measured travel speed to select a drive motor displacement between the maximum displacement and the minimum displacement, and varying the control signal to provide infinitely variable drive motor displacement as the power machine speed increases from a first set point speed to a second set point speed.