EV Torque Control During Steering Return on Low-Friction Roads
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Solution Overview
Problem
Electric vehicles with independent left and right driving motors face drivability issues when transitioning from turning to straight driving on low-friction surfaces, as the inner driving wheel can slip, leading to deteriorated performance.
Innovation Solution
A control apparatus that includes a requested torque calculator, a command torque calculator with a change rate adjuster, and a driving controller, which adjusts the upper limit change rates of the driving motors based on steering angle operations to prevent sudden torque changes, particularly lowering the inner wheel's upper limit change rate compared to the outer wheel's during steering angle turning back, thereby controlling the motors to output calculated torques and prevent slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the upper limit change rate of the inner driving wheel is kept high during steering angle turning back, then the response speed of torque output is improved, but the inner driving wheel slips on low-friction surfaces
Solution Approach 1:
The patent applies dynamics by making the upper limit change rate adjustable based on steering operation conditions. The system dynamically switches between a first upper limit change rate (higher) for normal conditions and a second upper limit change rate (lower) when steering angle turning back is detected, allowing optimal performance across different operating states.
Solution Approach 2:
The patent changes the parameter of upper limit change rate based on steering operation detection. When the steering operation unit is detected to perform steering angle turning back, the system switches to using the second upper limit change rate for the inner driving wheel, which has a lower value than the first upper limit change rate, thereby preventing slip while maintaining acceptable response.
2Reliability
If the upper limit change rate of the inner driving wheel is lowered to prevent slip, then drivability is maintained, but the response speed of torque output decreases
Solution Approach 1:
The system dynamically adjusts the upper limit change rate based on real-time steering operation detection. During steering angle turning back, the lower second upper limit change rate is applied to prevent slip. When steering angle turning back is not detected, the system switches to the higher first upper limit change rate, restoring fast response capability.
Solution Approach 2:
The patent implements parameter changes by switching between two distinct upper limit change rate values based on steering conditions. The first upper limit change rate provides fast response for normal driving, while the second upper limit change rate (lower value) prevents slip during steering angle turning back, optimizing both performance and reliability.
3Productivity
If sudden torque changes are allowed during steering angle turning back, then acceleration performance is improved, but the inner driving wheel slips on low-friction surfaces
Solution Approach 1:
The patent applies preliminary anti-action by detecting steering angle turning back in advance and preemptively applying the lower second upper limit change rate to the inner driving wheel. This prevents slip from occurring in the first place, rather than correcting it after the fact, by anticipating the harmful condition before it manifests.
Solution Approach 2:
The system changes the torque change rate parameter based on steering operation detection. When steering angle turning back is detected, the second upper limit change rate (lower value) is applied to the inner driving wheel to prevent slip. When such operation is not detected, the first upper limit change rate (higher value) is used to maintain good acceleration performance.
Data Source
AI summary
A control apparatus for an electric vehicle includes a requested torque calculator, a command torque calculator, and a driving controller. The requested torque calculator is configured to calculate requested torque. The command torque calculator includes a change rate adjuster configured to adjust respective upper limit change rates of left command torque and right command torque that follow the requested torque. The change rate adjuster is configured to, on the basis of a predetermined operation of turning back a steering angle performed on a steering unit of the electric vehicle, lower the upper limit change rate of a driving wheel, serving as an inner wheel among left and right driving wheels of the electric vehicle before turning back the steering angle, than the upper limit change rate of the driving wheel, serving as an outer wheel among the left and the right driving wheels before turning back the steering angle.