Regenerative Braking Torque Control for Wheel Slip Stability
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Solution Overview
Problem
Existing regenerative braking control strategies in hybrid/electric vehicles can degrade anti-lock braking performance and cause wheel slip during anti-lock braking events, affecting vehicle dynamics and stability, especially when equipped with a single axle electric motor and open differential.
Innovation Solution
A unified control architecture, referred to as the RBS-ABS event control system, integrates regenerative braking and friction braking by converting regenerative braking torque into an effective control variable, using a pre-compensator and closed-loop feedback control to maintain desired wheel slip, and includes a feed-forward compensator to compensate for driveline dynamics, ensuring stable wheel slip during anti-lock braking events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative braking is applied during anti-lock braking events, then energy recovery is improved, but wheel slip control deteriorates
Solution Approach 1:
The braking torque is segmented into two independent controllable components: regenerative braking torque from the electric machine and friction braking torque from the friction brakes. This segmentation allows independent control of each braking source, enabling the system to optimize energy recovery through regenerative braking while simultaneously maintaining wheel slip control through friction brakes, thus resolving the contradiction between energy recovery and wheel slip control reliability
Solution Approach 2:
The controller dynamically changes the weighting coefficient allocated to regenerative braking torque based on wheel slip conditions. When wheel slip is detected during anti-lock braking events, the weighting coefficient for regenerative braking is reduced and friction braking is increased to maintain control. This parameter adjustment allows the system to maximize energy recovery during normal braking while ensuring wheel slip control reliability when needed
2Use of energy by moving object
If regenerative braking torque is increased to maximize energy recovery, then fuel economy is improved, but vehicle stability deteriorates
Solution Approach 1:
The controller continuously monitors wheel slip ratio and dynamically adjusts the regenerative braking torque weighting coefficient based on feedback from actual wheel slip conditions. When wheel slip exceeds desired thresholds, the system reduces regenerative braking torque and increases friction braking torque to restore stability. This feedback mechanism enables the system to maximize fuel economy through regenerative braking while maintaining vehicle stability by automatically correcting instability conditions
Solution Approach 2:
The braking control system transitions from static torque allocation to dynamic torque distribution. The weighting coefficient for regenerative braking is not fixed but dynamically adjusted based on real-time wheel slip conditions, vehicle speed, and braking demand. This dynamic adjustment allows the system to optimize fuel economy during stable braking conditions while automatically adapting to maintain vehicle stability when slip conditions change
3Device complexity
If a single axle electric motor with open differential is used, then device complexity is reduced, but braking performance deteriorates
Solution Approach 1:
The single axle electric motor with open differential is made multi-functional by enabling it to provide both regenerative braking torque and friction braking torque through coordinated control. The electric machine operates in regeneration mode while friction brakes provide supplemental braking, allowing this simpler mechanical configuration to achieve braking performance comparable to more complex systems with separate regenerative and friction braking circuits
Solution Approach 2:
The controller acts as an intermediary that coordinates between the regenerative braking system and friction braking system. It manages the interaction between these two braking sources, optimizing their combined effect to maintain braking performance and wheel slip control. This intermediary control enables the simpler single-axle electric motor configuration to achieve reliable braking performance by intelligently coordinating multiple braking mechanisms
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RBS-ABS event control system effectively integrates regenerative and friction braking, stabilizing wheel slip and maintaining vehicle stability during anti-lock braking, enhancing braking performance and reducing the impact of regenerative braking on anti-lock braking systems.
Implementation Method 1
an electric machine may operate as a generator to convert the kinetic energy of the vehicle into electrical energy which is in turn used to charge a battery
Implementation Method 2
The friction brakes are configured to apply torque to wheels of the vehicle to slow the vehicle
Data Source
AI summary
A vehicle includes an electric machine, friction brakes, a drivetrain, and a controller. The electric machine is configured to recharge a battery during regenerative braking. The friction brakes are configured to apply torque to wheels of the vehicle to slow the vehicle. The controller is programmed to, in response to and during an anti-locking braking event, generate a signal indicative of a total torque demand to brake the vehicle based on a difference between a desired wheel slip ratio and an actual wheel slip ratio, adjust a regenerative braking torque based on a product of the signal and a regenerative braking weighting coefficient, adjust a friction braking torque based on a product of the signal and a friction braking weighting coefficient, and further adjust the regenerative braking torque based on a closed-loop control of an estimated regenerative braking torque feedback.