Torque Clipping for BEV Drivability
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Solution Overview
Problem
Electric vehicles experience drivability issues due to rapid decreases in wheel torque as vehicle speed increases, caused by battery discharge power limitations, leading to inconsistent acceleration and operator dissatisfaction.
Innovation Solution
A method that selectively limits torque delivery to vehicle wheels based on battery discharge power limits, clipping torque below the deliverable output to maintain consistent acceleration and reduce discrete impulses, ensuring sustained torque and improved drivability by adjusting torque delivery according to battery conditions and operator demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If torque is reduced to a threshold torque to reduce battery power output, then battery discharge power is limited, but wheel torque rapidly decreases as vehicle speed increases causing inconsistent acceleration
Solution Approach 1:
The system dynamically adjusts the torque clipping threshold based on vehicle speed. At lower speeds, a higher torque threshold is applied to maintain acceleration, while at higher speeds, the threshold is reduced to manage battery power output. This dynamic adjustment resolves the contradiction by adapting the torque limitation strategy to different operating conditions, ensuring both battery protection and consistent acceleration perception.
Solution Approach 2:
The system changes the torque delivery parameter (clipping threshold) as a function of vehicle speed. By implementing a speed-dependent torque clipping strategy, the system optimizes acceleration consistency at low speeds while managing battery power output at high speeds, thereby resolving the contradiction between energy loss and acceleration stability.
2Speed
If a brief impulse of acceleration (higher wheel torque delivery) is provided immediately after accelerator pedal tip-in, then initial acceleration is improved, but subsequent drop in acceleration causes drivability issues
Solution Approach 1:
The system implements dynamic torque clipping where the threshold is highest at vehicle startup and accelerator pedal tip-in, providing strong initial acceleration. As vehicle speed increases, the clipping threshold is progressively reduced to maintain smooth, consistent acceleration. This dynamic behavior resolves the contradiction by adapting torque delivery to match driver expectations across different speed ranges.
Solution Approach 2:
The torque clipping strategy operates in distinct phases: an initial high-torque phase during accelerator pedal tip-in for strong launch, followed by a transition to lower torque clipping as speed increases. This periodic action pattern matches typical driving cycles and resolves the contradiction between initial acceleration performance and sustained drivability.
3Duration of action of stationary object
If deliverable torque is clipped lower than the maximum deliverable torque output, then torque delivery is sustained over a range of vehicle speeds, but peak acceleration capability is reduced
Solution Approach 1:
The system dynamically adjusts the torque clipping threshold based on vehicle speed, allowing maximum torque delivery at low speeds for sustained acceleration over a wide speed range. As vehicle speed increases and battery power limits become constraining, the system progressively reduces the clipping threshold, thereby extending torque delivery duration while managing peak power requirements to maintain acceleration capability.
Data Source
AI summary
Methods and systems are provided for adjusting a torque delivered to wheels of an electrically propelled vehicle based on a battery discharge power. In one example, a method may include, during conditions of a lower than threshold battery output power, reducing the torque delivered to the vehicle wheels from a deliverable torque output.