Dynamic Output Limit Threshold for Electric Motor Thermal Protection
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Solution Overview
Problem
Existing control devices for electric motor-driven vehicles often experience output limits due to temperature rises in the source power supply circuit, leading to frequent overloading when the required driving force increases, especially on uphill roads.
Innovation Solution
A control device that dynamically adjusts the output limit threshold of the electric motor based on the required driving force, setting a lower threshold for low driving forces to prevent overheating and allowing operation without output limits when the driving force increases, while preventing one-phase concentration in polyphase electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the output torque of the electric motor is decreased to prevent overheating when temperature reaches the threshold, then the temperature rise is suppressed, but the vehicle cannot provide sufficient driving force when the required driving force increases
Solution Approach 1:
The patent applies dynamics by making the threshold value dynamic rather than fixed. The threshold value for output limit control is adjusted based on the variation rate of required driving force, allowing the system to adapt between preventing overheating during stable operation and providing sufficient power during acceleration or uphill driving.
Solution Approach 2:
The patent changes the parameter of threshold value based on driving conditions. When the variation rate of required driving force exceeds the threshold, the threshold value is set to a higher value (allowing more power output); when the variation rate is low, the threshold value is set to a lower value (preventing overheating).
2Device complexity
If a fixed threshold value is used for output limit control, then the control logic is simple, but the electric motor frequently hits the output limit immediately after the required driving force increases from a stalled state
Solution Approach 1:
The system transitions from a static threshold value to a dynamic threshold value that responds to driving conditions. The threshold value is adjusted based on the variation rate of required driving force, preventing frequent output limit activation while the vehicle accelerates or climbs hills, thereby improving operational reliability.
Solution Approach 2:
The patent implements feedback by continuously monitoring the variation rate of required driving force and adjusting the threshold value accordingly. This feedback mechanism allows the system to distinguish between temporary stalls and genuine overheating conditions, reducing unnecessary output limits while maintaining thermal protection.
Data Source
AI summary
A control device for a transport vehicle configured to travel with a driving force output from an electric motor is provided. When the transport vehicle is driven by a driving force of the electric motor and a variation rate is equal to or less than a predetermined value while a parameter relating to a traveling speed of the transport vehicle is less than a first predetermined value, the control device sets a threshold value, at which an output limit of the electric motor is started based on a parameter relating to a temperature of the electric motor or a temperature of an electric device for driving the electric motor, to a variable value corresponding to a required driving force to the transport.