Brake-Assisted Traction Motor Torque Limiting on Uphill Launch
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Solution Overview
Problem
In hybrid or electric vehicles, the traction motor can overheat if stalled excessively during hill-hold functions, as it continues to produce torque without launching, leading to potential damage and inefficiency.
Innovation Solution
A controller is implemented to limit torque generation by the traction motor when the vehicle is on a positive gradient and held by the brake, preventing overheating by setting a pre-launch threshold that restricts torque output and rate of increase, which can be adjusted based on gradient, driving mode, and temperature, ensuring the motor and power electronics are protected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the traction motor produces torque continuously during hill-hold to prevent roll-back, then the vehicle remains stationary on the gradient, but the traction motor overheats due to excessive stalling time
Solution Approach 1:
The controller applies a torque limit before thermal damage occurs. When hill-hold is activated, the controller proactively limits the traction motor torque output to a predetermined threshold, preventing excessive heat buildup before it causes overheating. This preliminary protective action avoids the need for reactive thermal derating.
Solution Approach 2:
The controller changes the torque parameter from full capability to a limited threshold value when hill-hold conditions are detected. By dynamically adjusting the torque output parameter based on the hill-hold state, the system prevents overheating while maintaining sufficient torque to prevent roll-back.
2Temperature
If the traction motor is limited to prevent overheating during hill-hold, then the motor temperature remains controlled, but the vehicle may experience roll-back if torque is insufficient
Solution Approach 1:
The brake system acts as an intermediary that compensates for the limited motor torque. When hill-hold is active and the motor torque is restricted to prevent overheating, the brake system provides the additional holding force needed to prevent roll-back, bridging the gap between limited motor capability and required holding force.
Solution Approach 2:
The hill-hold function combines multiple functions: the traction motor provides limited torque to prevent overheating while the brake system simultaneously provides holding force. This multi-functional approach allows the system to maintain both temperature control and adequate holding capability.
3Speed
If the torque limit is removed immediately when hill-hold ends, then the vehicle launches quickly, but the traction motor experiences thermal stress from sudden high torque demand
Solution Approach 1:
The controller gradually increases torque demand before full launch to prepare the thermal management system. By ramping up torque demand progressively rather than abruptly, the system allows thermal management to adjust and prevents sudden thermal stress on the traction motor during launch.
Solution Approach 2:
The torque limit threshold is dynamically adjusted based on real-time temperature feedback. As the traction motor temperature changes during operation, the controller adapts the torque threshold accordingly, allowing higher torque when cool and limiting torque when warm, creating a dynamic balance between performance and thermal protection.
4Power
If the torque threshold is set high to meet launch demand, then the vehicle launches effectively, but the traction motor overheats during hill-hold
Solution Approach 1:
The controller changes the torque parameter from full capability to a limited threshold value when hill-hold conditions are detected. By dynamically adjusting the torque output parameter based on the hill-hold state, the system prevents overheating while maintaining sufficient torque to prevent roll-back.
Solution Approach 2:
The controller applies a torque limit before thermal damage occurs. When hill-hold is activated, the controller proactively limits the traction motor torque output to a predetermined threshold, preventing excessive heat buildup before it causes overheating. This preliminary protective action avoids the need for reactive thermal derating.
5Temperature
If the torque threshold is set low to prevent overheating, then the traction motor remains cool, but the vehicle launch performance is reduced
Solution Approach 1:
The torque limit threshold is dynamically adjusted based on real-time temperature feedback. As the traction motor temperature changes during operation, the controller adapts the torque threshold accordingly, allowing higher torque when cool and limiting torque when warm, creating a dynamic balance between performance and thermal protection.
Data Source
AI summary
A controller (104) and method for controlling torque generated by at least one traction motor (116a, 116b) of a vehicle (100) before a vehicle launch, comprising: means to determine that the vehicle is on a positive gradient; means to determine that the vehicle is prevented from roll-back by at least one vehicle brake (111); means to, in dependence on the determining that the vehicle is on a positive gradient and is prevented from roll-back, limit torque generation 10 by the traction motor in response to torque demand; and means to remove the limit when a vehicle launch condition is satisfied.