Work machine and method for controlling work machine

Abstract

A work machine includes a vehicle body, a lift frame rotatably supported around a lift axis with respect to the vehicle body, a blade rotatably supported around a pitch axis with respect to the lift frame, a lift actuator connected to the lift frame and the vehicle body, a pitch actuator connected to the blade and the lift frame, a sensor that detects a height of the blade from a reference height determined based on the vehicle body, and a controller that controls the pitch actuator to change a pitch angle of the blade according to the height of the blade. The lift actuator causes the lift frame to perform a lift motion up and down around the lift axis. The pitch actuator causes the blade to perform a pitching motion around the pitch axis.

1 . A work machine comprising:
 a vehicle body;   a lift frame rotatably supported around a lift axis with respect to the vehicle body;   a blade rotatably supported around a pitch axis with respect to the lift frame;   a lift actuator connected to the lift frame and the vehicle body, the lift actuator being configured to cause the lift frame to perform a lift motion up and down around the lift axis;   a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to cause the blade to perform a pitching motion around the pitch axis;   a sensor configured to detect a height of the blade from a reference height determined based on the vehicle body; and   a controller configured to control the pitch actuator to change a pitch angle of the blade according to the height of the blade.   
     
     
         2 . The work machine according to  claim 1 , wherein
 the controller is configured to control the pitch actuator to tilt the blade more forward when the blade is positioned above the reference height than when the pitching motion of the blade is fixed.   
     
     
         3 . The work machine according to  claim 2 , wherein
 when the blade is positioned above the reference height, the controller is configured to control the pitch actuator to change the pitch angle of the blade in a direction to tilt the blade forward according to increasing in the height of the blade.   
     
     
         4 . The work machine according to  claim 1 , wherein
 the controller is configured to control the pitch actuator to tilt the blade more rearward when the blade is positioned below the reference height than when the pitching motion of the blade is fixed.   
     
     
         5 . The work machine according to  claim 4 , wherein
 when the blade is positioned below the reference height, the controller is configured to control the actuator to change the pitch angle of the blade in a direction of tilting the blade backward in accordance with decreasing in the height of the blade.   
     
     
         6 . The work machine according to  claim 1 , wherein
 the vehicle body includes a crawler belt, and   the reference height is a height of a ground contact surface of the crawler belt.   
     
     
         7 . The work machine according to  claim 1 , wherein
 the controller is configured to
 store pitch angle data that defines a relationship between the height of the blade and a target pitch angle of the blade, 
 determine the target pitch angle from the height of the blade with reference to the pitch angle data, and 
 control the pitch actuator so that the pitch angle of the blade becomes the target pitch angle. 
   
     
     
         8 . The work machine according to  claim 1 , further comprising:
 an operating device for manually operating the pitch angle of the blade, the controller being configured to
 acquire an operation signal indicating an operation of the operating device, 
 control the pitch actuator to change the pitch angle of the blade according to the operation of the operating device, and 
 control the pitch actuator to maintain the pitch angle of the blade when the operating device is not operated. 
   
     
     
         9 . A method for controlling a work machine, the work machine including a vehicle body, a lift frame rotatably supported with respect to the vehicle body around a lift axis, a blade rotatably supported with respect to the lift frame around a pitch axis, a lift actuator connected to the lift frame and the vehicle body, the lift actuator being configured to cause the lift frame to perform a lift motion up and down around the lift axis, and a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to case the blade to perform a pitching motion around the pitch axis, the method comprising:
 detecting a height of the blade from a reference height determined based on the vehicle body; and   controlling the pitch actuator to change a pitch angle of the blade according to the height of the blade.   
     
     
         10 . The method according to  claim 9 , further comprising:
 controlling the pitch actuator to tilt the blade more forward when the blade is positioned above the reference height than when the pitching motion of the blade is fixed.   
     
     
         11 . The method according to  claim 10 , further comprising:
 controlling the pitch actuator to change the pitch angle of the blade in a direction of tilting the blade forward according to increasing in the height of the blade when the blade is positioned above the reference height.   
     
     
         12 . The method according to  claim 9 , further comprising:
 controlling the pitch actuator to tilt the blade more rearward when the blade is positioned below the reference height than when the pitching motion of the blade is fixed.   
     
     
         13 . The method according to  claim 12 , further comprising:
 controlling the pitch actuator to change the pitch angle of the blade in a direction of tilting the blade backward in accordance with decreasing in the height of the blade when the blade is positioned below the reference height.   
     
     
         14 . The method according to  claim 9 , wherein
 the vehicle body includes a crawler belt, and   the reference height is a height of a ground contact surface of the crawler belt.   
     
     
         15 . The method according to  claim 9 , further comprising:
 determining a target pitch angle from the height of the blade with reference to pitch angle data that defines a relationship between the height of the blade and the target pitch angle of the blade; and   controlling the pitch actuator so that the pitch angle of the blade becomes the target pitch angle.   
     
     
         16 . The method according to  claim 9 , further comprising:
 obtaining an operation signal indicating operation of an operating device for manually operating the pitch angle of the blade;   controlling the pitch actuator to change the pitch angle of the blade according to the operation of the operating device; and   controlling the pitch actuator to maintain the pitch angle of the blade when the operating device is not operated.