Electric Vehicle Slip Control via Torque Directive and Speed Reference
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Solution Overview
Problem
Electric vehicles with individual motors for each wheel face challenges in controlling slip, particularly on slippery roads, as existing methods struggle to maintain stable traction and prevent wheel locking, especially when turning.
Innovation Solution
A slip control device that calculates torque directives for each motor based on acceleration pedal input and steering angles, using reference speed calculations to determine permissible speed ranges and restrict torque to prevent speed differences between wheels, thereby stabilizing wheel rotation and maintaining road holding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If individual electric motors are attached to each driving wheel to achieve lightweight and high performance, then vehicle performance and weight are improved, but wheel slip control becomes difficult when load or friction coefficient decreases on one side
Solution Approach 1:
The control device continuously monitors wheel rotation speeds, calculates speed differences between left and right wheels, and dynamically adjusts motor torque based on feedback signals. When slip is detected through speed difference calculation, the system automatically reduces torque to the slipping wheel to restore traction and maintain stable vehicle operation.
Solution Approach 2:
The system changes operational parameters by calculating reference speeds based on vehicle speed and steering angle, then comparing actual wheel speeds against these references. When deviations exceed thresholds indicating slip, the control device modifies motor torque parameters to eliminate the speed difference and restore balanced wheel rotation.
2Reliability
If torque control is performed based on rotation speed difference between master and slave drive wheels, then slip control is achieved, but it cannot be applied to controlling slips of left and right wheels considering speed differences during turning
Solution Approach 1:
The control device applies different control strategies to left and right wheels based on their individual conditions. During turning, the system calculates appropriate speed differences as normal operation and only intervenes when speed differences exceed the threshold for slip, allowing each wheel to operate with locally optimized torque control that adapts to turning requirements while preventing pathological slip.
Solution Approach 2:
The system dynamically adjusts the reference speed calculation by incorporating steering angle information. When the steering angle indicates a turn, the reference speed difference between left and right wheels is adjusted to accommodate the kinematic requirements of turning, allowing the control system to distinguish between normal turning speed differences and abnormal slip conditions.
3Reliability
If first delay processing is applied to rotation speed to suppress initial slip, then initial slip is restricted, but rotation speed control becomes difficult once slip occurs
Solution Approach 1:
The control device performs preliminary slip detection by continuously calculating wheel speed differences and comparing them against predetermined thresholds before significant slip occurs. This early detection mechanism triggers torque reduction before the slip fully develops, preventing the wheel from entering a locked or severely slipped state and maintaining control throughout the event.
4Reliability
If slip control restricts wheel speed differences to prevent slip, then road holding is improved, but driving feel may deteriorate or shock may occur
Solution Approach 1:
The control device applies partial torque reduction rather than complete torque cutoff when slip is detected. By reducing torque to the slipping wheel by a controlled amount rather than eliminating it entirely, the system maintains sufficient traction to prevent slip while preserving natural vehicle handling characteristics and avoiding abrupt torque changes that would create shock or degrade driving feel.
Data Source
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AI summary
A slip control device, a slip control method, and a vehicle provided with such a slip control device are provided, with which the vehicle can travel stably even on a slippery road surface maintaining good road holding. The device is provided with a torque directive control means (23) for calculating torque directives for the left and right electric motors (7,9) respectively based on acceleration pedal depressions (24) and steering angles (26) and outputting them to each of motor control sections (21,22) of the motors. A first reference speed calculation means (48) calculates a first reference speed of one of the pair of left and right motors (7;9) to be controlled based on rotation speed of the other motor (9;7) of the pair of motors. A restriction puffing means (20) puts restriction to each of the torque directives sent from the torque directive control means (23) based on a permissible speed range determined for each of the motors (7,9) by putting prescribed permissible speed deviation to each of the calculated reference speeds. Further claims are included in which a second reference speed is calculated based on steering angle, in particular during hard turns. In this case, the first reference speed is disregarded.