Hydraulic drive control

A power machine comprising:

• a drive system having at least one drive pump and at least one drive motor which selectively receives hydraulic oil from the at least one drive pump to move the power machine in forward and reverse directions of travel, the drive pump having a variable hydraulic displacement up to a maximum displacement corresponding to a full pump stroke;
• a temperature sensor configured to measure a temperature of hydraulic oil and to provide a temperature signal indicative of the measured temperature;
• a user input device configured to provide a user input signal, to command movement of the power machine using the drive system, responsive to actuation of the user input device by a user;
• and
• a controller coupled to the user input device to receive the user input signal, to the temperature sensor to receive the temperature signal, and to the at least one drive pump of the drive system, the controller configured to generate drive control signals to control the at least one drive pump responsive to the user input signal such that the controller prevents the drive system from moving the power machine if the temperature of the hydraulic oil is below a first set point temperature, allows the drive system to move the power machine using a drive pump displacement varying between a first percentage of the full pump stroke when the temperature of the hydraulic oil is at the first set point temperature and a second percentage of the full pump stroke when the temperature of the hydraulic oil is at a second set point temperature higher than the first set point temperature, and allows the drive system to move the power machine using the maximum displacement corresponding to the full pump stroke if the temperature of the hydraulic oil is above the second set point temperature.

A method of controlling a drive system of a power machine, the drive system having at least one drive pump and at least one drive motor, the at least one drive pump having a variable hydraulic oil displacement up to a maximum displacement corresponding to a full pump stroke, the method comprising:

• measuring a temperature of hydraulic oil in a hydraulic system including the drive system;
• receiving a user input signal from a user input device;
• determining whether the temperature of the hydraulic oil is below a first set point temperature;
• controlling the at least one drive pump of the drive system to prevent movement of the power machine by the drive system if the temperature of the hydraulic oil is below the first set point temperature;
• determining, if the temperature of the hydraulic oil is above the first set point temperature, whether the temperature of the hydraulic oil is above or below a second set point temperature;
• controlling the at least one drive pump of the drive system to move the power machine, responsive to the user input signal, using a drive pump displacement varying between a first percentage of the full pump stroke when the temperature of the hydraulic oil is at the first set point temperature and a second percentage of the full pump stroke when the temperature of the hydraulic oil is at the second set point temperature;
• controlling the at least one drive pump of the drive system to move the power machine, responsive to the user input signal, using the maximum displacement corresponding to the full pump stroke, if the temperature of the hydraulic oil is above the second set point temperature.