Work vehicle, controller for work vehicle, and speed control method for work vehicle

A work vehicle comprising:

• a vehicle body;
• a first traveling device and a second traveling device provided on a left side and a right side of the vehicle body, respectively;
• a first hydraulic motor configured to drive the first traveling device;
• a second hydraulic motor configured to drive the second traveling device;
• a first hydraulic pump configured to supply hydraulic fluid to the first hydraulic motor;
• a second hydraulic pump configured to supply the hydraulic fluid to the second hydraulic motor;
• a control mechanism configured to control a displacement volume of the first hydraulic pump and a displacement volume of the second hydraulic pump;
• a prime mover configured to rotate the first hydraulic pump and the second hydraulic pump;
• a storage configured to store a plurality of speed stages corresponding to a plurality of sets of target rotation speeds at which the first hydraulic motor and the second hydraulic motor respectively rotate to move the work vehicle straight;
• a first operation member configured to receive an input corresponding to a setting stage of the plurality of speed stages;
• a second operation member configured to receive an input corresponding to a target moving direction of the work vehicle determined by a speed difference between a target rotation speed of the first hydraulic motor and a target rotation speed of the second hydraulic motor;
• a sensor configured to detect an operation of the second operation member;
• and
• a hardware processor configured to control the motor and the control mechanism;
• the hardware processor being configured to:
• receive the setting stage from the first operation member;
• receive information corresponding to the target moving direction from the sensor to obtain the target moving direction;
• determine an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when the second operation member is operated such that a deviation amount between the target moving direction and a straight direction is within a first range predetermined, a displacement volume of the first hydraulic pump being determined by the first control parameter, a displacement volume of the second hydraulic pump being determined by the second control parameter;
• determine a boost stage among the plurality of speed stages based on the deviation amount to determine at least one operating range based on the boost stage, when the second operation member is operated such that the deviation amount is out of the first range, each of the at least one operating range being an operating range of each of at least one control parameter of the first control parameter and the second control parameter, the boost stage corresponding to a set of target rotation speeds higher than the target rotation speeds of the setting stage;
• control the control mechanism such that the first control parameter is within the operating range of the first control parameter and the second control parameter is within the operating range of the second control parameter, the operating ranges of the first control parameter and the second control parameter being determined based on a boost stage or the setting stage, and
• set a displacement volume of the first hydraulic motor and a displacement volume of the second hydraulic motor to respective constant volumes regardless of the plurality of speed stages to drive the first traveling device and the second traveling device by rotating the first hydraulic motor and the second hydraulic motor, respectively.

A controller for a work vehicle, comprising:

• a hardware processor configured to:
• receive a setting stage set by the first operation member among a plurality of speed stages, the plurality of speed stages corresponding to a plurality of sets of target rotation speeds at which a first hydraulic motor and a second hydraulic motor respectively rotate to move the work vehicle straight, the first hydraulic motor being configured to drive a first traveling device provided on a left side of a vehicle body of the work vehicle, the second hydraulic motor being configured to drive a second traveling device provided on a right side of the vehicle body;
• obtain a target moving direction of the work vehicle by receiving information corresponding to the target moving direction from a sensor to detect operation of a second operation member via which the target moving direction is set, the target moving direction being determined by a speed difference between a target rotation speed of the first hydraulic motor and a target rotation speed of the second hydraulic motor;
• determine an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when the second operation member is operated such that a deviation amount between the target moving direction and a straight direction is within a first range predetermined, a displacement volume of the first hydraulic pump configured to supply the hydraulic fluid to the first hydraulic motor being determined by the first control parameter, a displacement volume of the second hydraulic pump configured to supply the hydraulic fluid to the second hydraulic motor being determined by the second control parameter;
• determine a boost stage, which is among the plurality of speed stages based on the deviation amount to determine at least one operating range based on the boost stage, when the second operation member is operated such that the deviation amount is out of the first range, each of the at least one operating range being an operating range of each of at least one control parameter of the first control parameter and the second control parameter, the boost stage corresponding to a set of target rotation speeds higher than the target rotation speeds of the setting stage;
• based on the magnitude of the deviation amount, and determines an operation range of at least one control parameter of the first control parameter and the second control parameter based on the boost stage when the second operation member is operated such that the deviation amount is out of the first range,
• control the control mechanism such that the first control parameter is within the operating range of the first control parameter determined based on the boost stage or the setting stage;
• control the control mechanism such that the second control parameter is within the operating range of the second control parameter determined based on the boost stage or the setting stage;
• control a prime mover configured to rotate the first hydraulic pump and the second hydraulic pump to drive the first hydraulic pump and the second hydraulic pump such that the first hydraulic motor and the second hydraulic motor of which the displacement volumes are set to respective constant volumes regardless of the plurality of speed stages.