Electric Drive Wheel Slip Control With Axle Brake Coordination
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Solution Overview
Problem
Existing vehicle control systems, particularly those with central electric drives, struggle to dynamically and precisely manage wheel slip, leading to limited vehicle stability and propulsion efficiency under varying road conditions.
Innovation Solution
A method and drive control unit that integrates wheel-individual and axle-individual drive control with a braking system, using actual wheel dynamics variables and threshold values to adjust driving torque and rotational speed, and generate braking demands to maintain stable wheel behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If brake interventions are used to control wheel slip in central drive systems, then wheel slip control is achieved, but control dynamics are limited due to the brake control unit's response time
Solution Approach 1:
The patent segments the wheel slip control function into two independent control units: a drive control unit that rapidly limits setpoint driving torque, and a brake control unit that applies brake interventions. This segmentation allows each unit to operate at its optimal speed, with the drive control unit providing high-dynamics response and the brake control unit providing supplemental control, thereby resolving the contradiction between control dynamics and control effectiveness.
Solution Approach 2:
The drive control unit performs preliminary action by rapidly limiting the setpoint driving torque before the brake control unit needs to intervene. This preliminary limitation of driving torque prevents excessive wheel slip from developing, reducing the need for slower brake interventions and thereby improving overall control dynamics while maintaining reliability.
2Reliability
If setpoint driving torque is limited to control wheel slip, then wheel slip is reduced, but propulsion performance deteriorates
Solution Approach 1:
The patent applies local quality by enabling independent control of driving torque and braking for each wheel or axle. The drive control unit can limit setpoint driving torque only on wheels experiencing slip, while the brake control unit can apply brake interventions selectively. This localized control maintains propulsion performance on wheels with adequate traction while controlling wheel slip only where necessary, resolving the contradiction between wheel slip control and overall propulsion performance.
Solution Approach 2:
The system dynamically changes the setpoint driving torque parameter based on actual wheel slip conditions. When wheel slip is detected, the drive control unit limits the setpoint driving torque to control slip. When slip is controlled or conditions improve, the limitation is relaxed or removed, allowing full propulsion performance. This dynamic parameter adjustment resolves the contradiction by making torque limitation conditional rather than constant.
3Speed
If wheel-individual electric drives are used, then wheel slip control dynamics are improved, but device complexity increases compared to central drives
Solution Approach 1:
The patent makes the central drive system universal by enabling it to perform wheel-individual slip control functions through the combination of drive control unit and brake control unit. The drive control unit can limit torque on individual wheels, and the brake control unit can apply individual brake interventions, giving the central drive system the multi-functionality of wheel-individual control without requiring physical wheel-individual electric drives, thus improving control dynamics while avoiding the complexity of fully distributed drives.
Data Source
AI summary
A method is for controlling a vehicle having an electric drive for driving wheels. A drive control unit generates a target torque and/or a target rotation speed and outputs them to the relevant drive. The method includes: determining a speed; determining an actual wheel dynamics variable which characterizes the rotational behavior of an individual wheel; determining thresholds associated with the wheels; determining a deviation between the actual wheel dynamics variable and the threshold and, if an impermissible deviation is present: limiting the target torque and/or the target rotation speed for the wheel with the impermissible deviation. If control deviations for the wheels of an axle which are different on different sides are determined, a brake request signal is output by the drive control unit. The limit torque and/or the limit rotation speed is specified/adjusted depending on the braking torque applied by the service brakes.