A speed control system for an agricultural system having an agricultural vehicle includes a control system. The control system instructs an engine to maintain a constant speed, determines a first estimated speed of the agricultural vehicle associated with increasing a gear index of a step ratio transmission, determines a second estimated speed of the agricultural vehicle associated with decreasing the gear index of the step ratio transmission, instructs the step ratio transmission to increase the gear index if the first estimated speed is closer to a target speed than the second estimated speed and a current speed of the agricultural vehicle, and instructs the step ratio transmission to decrease the gear index if the second estimated speed is closer to the target speed than the first estimated speed and the current speed.

A mode transition control device a hybrid vehicle has a transmission control unit that prevents a second power generation system from overheating while traveling in a series HEV mode. When a battery is at a power generation request threshold value or lower, the vehicle travels in a series HEV mode, in which the first electric motor is utilized as a drive source and receives electrical power from the second motor/generator and the battery. The transmission control unit controls the traveling mode to transition from the series HEV mode to a parallel HEV mode when the vehicle speed has reached a switchover vehicle speed. When a temperature rise of the second power generation system is predicted while traveling in the series HEV mode, the transmission control unit changes the switchover vehicle speed to a slower switchover vehicle speed that was used prior to a determination of the temperature rise.

A mode transition control device a hybrid vehicle has a transmission control unit that prevents a second power generation system from overheating while traveling in a series HEV mode. When a battery is at a power generation request threshold value or lower, the vehicle travels in a series HEV mode, in which the first electric motor is utilized as a drive source and receives electrical power from the second motor/generator and the battery. The transmission control unit controls the traveling mode to transition from the series HEV mode to a parallel HEV mode when the vehicle speed has reached a switchover vehicle speed. When a temperature rise of the second power generation system is predicted while traveling in the series HEV mode, the transmission control unit changes the switchover vehicle speed to a slower switchover vehicle speed that was used prior to a determination of the temperature rise.

A speed control system for an agricultural system having an agricultural vehicle includes a control system, wherein at least during steady-state operation of the agricultural vehicle. The control system instructs an engine to maintain a constant speed, determine a first estimated speed of the agricultural vehicle associated with increasing a gear index of a step ratio transmission, determine a second estimated speed of the agricultural vehicle associated with decreasing the gear index of the step ratio transmission, instruct the step ratio transmission to increase the gear index if the first estimated speed is closer to a target speed than the second estimated speed and a current speed of the agricultural vehicle, and instruct the step ratio transmission to decrease the gear index if the second estimated speed is closer to the target speed than the first estimated speed and the current speed.