Work vehicle

A work vehicle, comprising:

• an engine;
• a hydraulic pump driven by the engine;
• a hydraulic cylinder driven by hydraulic fluid delivered from the hydraulic pump;
• a work device moved with elongation and contraction of the hydraulic cylinder;
• a motor generator rotated by the engine to generate electric power;
• a first inverter that controls the motor generator;
• a traveling electric motor driven by the electric power generated by the motor generator;
• a second inverter connected to the first inverter through a DC bus to control output torque of the traveling electric motor;
• and
• a controller that controls a voltage of the DC bus, wherein,
• the controller is configured to decrease the output torque of the traveling electric motor when the voltage of the DC bus drops below a first threshold value as a load on the traveling electric motor increases;
• and wherein,
• the controller is configured to decrease the output torque of the traveling electric motor according to an amount of decrease in the voltage of the DC bus when the rate of change in the voltage of the DC bus is not exceeding a preset value in a case where the voltage of the DC bus drops below the first threshold value, and to decrease the output torque of the traveling electric motor to zero or a value within a range of magnitude with which the work vehicle stays stationary on a level ground when the rate of change in the voltage of the DC bus is exceeding the preset value in the case where the voltage of the DC bus drops below the first threshold value.

A work vehicle, comprising:

• an engine;
• a hydraulic pump driven by the engine;
• a hydraulic cylinder driven by hydraulic fluid delivered from the hydraulic pump;
• a work device moved with elongation and contraction of the hydraulic cylinder;
• a motor generator rotated by the engine to generate electric power;
• a first inverter that controls the motor generator;
• a traveling electric motor driven by the electric power generated by the motor generator;
• a second inverter connected to the first inverter through a DC bus to control output torque of the traveling electric motor;
• and
• a controller that controls a voltage of the DC bus, wherein,
• the controller is configured to decrease the output torque of the traveling electric motor when the voltage of the DC bus drops below a first threshold value as a load on the traveling electric motor increases;
• and wherein,
• the controller is configured to provide a hysteresis characteristic such that a timing at which the output torque of the traveling electric motor begins to increase is delayed when the voltage of the DC bus restores after the voltage of the DC bus is dropped below the first threshold value and the output torque of the electric motor decreases to a minimum value.