Japanese Patent Laying-open No. 2003-304604 discloses a device driving a motor mounted as a source driving electric vehicles, hybrid vehicles, fuel cell vehicles and other various types of vehicles.
In this device, if a temperature detection means detects that the motor has a temperature equal to or higher than a temperature limit, a motor output control means limits the output of the motor. Herein a means for detecting a rate of change in temperature detects the rate of change in temperature of the motor and modifies a setting of the temperature limit in accordance with the rate of change detected.
More specifically, if the motor's rate of change in temperature is equal to or larger than a predetermined rate of change, the means for detecting a rate of change in temperature determines that the motor has a large increase in temperature, and accordingly the means sets the current temperature limit to be a first temperature limit, and when the motor attains the first temperature limit or higher the motor output control means limits the output of the motor.
In contrast, if the motor's rate of change in temperature is smaller than the predetermined rate of change, the means for detecting a rate of change in temperature determines that the motor has a small increase in temperature, and accordingly the means sets the current temperature limit to be a second temperature limit higher than the first temperature limit, and when the motor attains the second temperature limit or higher the motor output control means limits the output of the motor.
This device allows a vehicle to run an increased distance without limiting the output of the motor, can protect the motor from high temperature, and also allows the motor to fully exhibit its performance.
However, the motor drive device disclosed in Japanese Patent Laying-open No. 2003-304604 only limits the output of the motor in accordance with the rate of change in the temperature of the motor in view of protecting the motor from high temperature. It does not give consideration to the state of the vehicle.
For example, when a vehicle is in a state in which while it is running up hill it may fall downhill, such state should first and most of all be avoided. The above described motor drive device, despite the vehicle's such state, may prioritize protecting the motor from high temperature and stringently limit the motor's output. Thus with the above described motor drive device there is a possibility that while the vehicle is running uphill it may fall downhill.