Electric Vehicle Motor Torque Control via Slip Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Highly responsive motors in electric vehicles can cause sudden tire rotation when tires lose contact with the road, leading to unstable vehicle travel, and uniform torque limitations across varying road conditions often result in unnecessary restrictions, affecting vehicle performance.
Innovation Solution
An electric vehicle system that includes a motor unit, slip ratio estimator, disturbance observer, applied torque estimator, coefficient of friction estimator, and motor torque command value limiter, which dynamically adjusts the motor torque based on estimated slip ratio, external forces, and road friction to prevent tire slip without hindering vehicle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If highly responsive motors are used in electric vehicles, then response characteristics are improved, but sudden tire rotation occurs when tires lose contact with the road surface, jeopardizing stable vehicle travel
Solution Approach 1:
The system performs preliminary detection of tire slip conditions using sensors that monitor wheel speed, vehicle speed, and lateral acceleration. When slip is detected, the control system preemptively adjusts motor torque to prevent sudden tire rotation and maintain stable vehicle travel, rather than reacting after the problem occurs.
Solution Approach 2:
The control system continuously monitors tire slip conditions through sensors and feeds this information back to the motor control unit. Based on the feedback signal indicating slip magnitude, the system dynamically adjusts motor torque output to suppress sudden tire rotation while maintaining responsive acceleration characteristics.
2Reliability
If motor torque command value is limited uniformly under all conditions, then tire slip is prevented, but unnecessary limitation of torque occurs, jeopardizing vehicle travel performance
Solution Approach 1:
The control system applies different torque limitation strategies to different wheels based on their individual slip conditions. When only one wheel slips, torque is limited specifically to that wheel while maintaining full torque to other wheels, thereby preventing slip without unnecessarily limiting overall vehicle performance.
Solution Approach 2:
The torque command value limitation is dynamically adjusted based on real-time detection of slip magnitude and road conditions. The control system varies the degree of torque limitation adaptively - applying stronger limitation when slip is severe and reducing or eliminating limitation when slip is minimal or absent, thus optimizing both slip prevention and travel performance.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electric vehicle includes a slip ratio estimator (42) that estimates a slip ratio (λ) based on rotational frequencies (N1, N2) of respective driven and drive wheels. The vehicle also includes a disturbance observer (43) that determines an estimate (^Te) of a torque attributable to external force. The vehicle also includes an estimator (44) that may estimate an entire torque (T) to the drive wheel (2), based on a motor torque command value (Tm) and the estimate (^Te) of torque. The vehicle also includes an estimator (45) that estimates a coefficient (µ) of friction between a road surface and a tire, based on the entire torque and the slip ratio. The vehicle also includes a determiner (46) that determines a maximum acceptable torque Tmax, based on the coefficient (µ) of friction and a vertical load component (^Fz). Torque limitation is performed such that the motor torque command value (Tm) does not exceed the maximum acceptable torque Tmax.