Control device for four-wheel-drive vehicle and control method for four-wheel-drive vehicle

A control method for a four-wheel-drive vehicle,

• the vehicle including an input shaft, a first output shaft, a second output shaft, a high-low gear shift mechanism, a clutch, a mode switching device, a mode selection operating device, and an electronic control unit,
• the first output shaft being configured to output a driving force to one of front wheels and rear wheels,
• the second output shaft being configured to output the driving force to the other of the front wheels and the rear wheels,
• the high-low gear shift mechanism being configured to shift a rotation speed of the input shaft to one of a high gear stage and a low gear stage and being configured to transmit the driving force to the first output shaft,
• the clutch being configured to disengage and engage to cut off and establish transmission of power between the first output shaft and the second output shaft,
• the mode switching device being configured to mechanically switch between a high-gear four-wheel driving mode and a low-gear driving mode via a high-gear two-wheel driving mode,
• the high-gear four-wheel driving mode being a first driving mode of the vehicle in which the high-low gear shift mechanism is set to the high gear stage and the clutch is in an engagement state,
• the high-gear two-wheel driving mode being a second driving mode of the vehicle in which the high-low gear shift mechanism is set to the high gear stage and the clutch is in a disengagement state,
• the low-gear driving mode being a third driving mode of the vehicle in which the high-low gear shift mechanism is set to the low gear stage,
• the mode selection operating device being a device that is operated by a driver to select the low-gear driving mode,
• the control method comprising:
• controlling, by the electronic control unit, the mode switching device such that the driving mode is switched to the low-gear driving mode when the electronic control unit determines that all of a first condition, a second condition, and a third condition are satisfied;
• controlling, by the electronic control unit, the mode switching device such that the driving mode is switched from the high-gear four-wheel driving mode to the high-gear two-wheel driving mode when the electronic control unit determines that the first condition and the second condition are satisfied at a time of driving in the high-gear four-wheel driving mode;
• and
• controlling, by the electronic control unit, the mode switching device such that the driving mode is switched from the high-gear two-wheel driving mode to the low-gear driving mode when the electronic control unit determines that the third condition is satisfied in a state in which the first condition and the second condition have been satisfied,
• the first condition being a condition of the vehicle being in a stop state, the second condition being a condition of transmission of power being in a neutral state in which transmission of power between a driving force source and the input shaft is cut off, and the third condition being a condition of the low-gear driving mode being selected by operation of the mode selection operating device.