Wheel Slip Control Using Brake-Motor Torque Distribution
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Solution Overview
Problem
Existing slip regulation methods in electric vehicles struggle to effectively utilize the dynamic torque potential of electric machines while avoiding the wear and energy inefficiencies associated with friction brakes, particularly during sudden changes in friction coefficient.
Innovation Solution
A method that controls multiple actuators, including electric machines and friction brakes, to achieve precise slip regulation by specifying torque and slip target values, ensuring each actuator operates at its maximum potential without prioritization, and includes a central control apparatus to manage actuator interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction brake is used for slip regulation, then slip control is achieved, but brake wear and energy inefficiency occur
Solution Approach 1:
The patent replaces the purely mechanical friction brake system with a hybrid system that incorporates electric machines (motors/generators) to provide torque for slip regulation. The electric actuators substitute for friction-based braking in many operating conditions, eliminating wear while maintaining slip control functionality through electromagnetic torque application to the wheel.
Solution Approach 2:
The patent changes the operating parameters by introducing electric torque as a controllable variable alongside friction brake torque. By dynamically adjusting the torque contribution from electric machines based on slip conditions, the system optimizes the balance between wear-free operation and effective slip regulation, reducing friction brake usage and associated wear.
2Speed
If electric machine is used for slip regulation, then dynamic torque and precision are improved, but operating limits restrict torque availability
Solution Approach 1:
The patent merges the friction brake system and electric machine system into a unified slip regulation system. The friction brake provides high-torque, slow-response contribution while the electric machine provides low-torque, fast-response contribution. By combining these two actuation systems with different characteristics, the overall system achieves both high torque availability and rapid dynamic response that neither system could achieve alone.
Solution Approach 2:
The patent implements dynamic allocation of torque between the friction brake and electric machine based on real-time operating conditions. The control system continuously adjusts the torque distribution ratio, assigning more torque to the electric machine during rapid transients and more to the friction brake during steady-state high-torque requirements, optimizing performance across the entire operating range.
3Device complexity
If actuator prioritization is implemented, then control strategy is simplified, but slip operating point is lost during actuator switching
Solution Approach 1:
The patent ensures continuous slip regulation by having both the friction brake and electric machine actuators actively contributing to torque control simultaneously, rather than switching between them. This continuous dual-actuator operation eliminates gaps in control authority that occur during actuator switchover, maintaining uninterrupted slip operating point stability while the control system manages the complexity of coordinating both actuators.
Data Source
AI summary
A method for operating a motor vehicle. The motor vehicle has at least one axle with at least one wheel. A wheel brake device with a controllable first actuator is assigned to the wheel. A drive device with a controllable second actuator is assigned to the wheel. Depending on an acceleration request or braking request, at least one target torque value and at least one further target value, selected from a slip target value and a rotational speed target value, are specified. For the target torque value, a distribution factor for distributing the target torque value to the actuators is specified. At least one, in particular exactly one, of the actuators is controlled to fulfill the acceleration request or braking request depending on the specified target values and the distribution factor.