Wheel Slip Balancing for Efficient Heavy-Duty Electric Propulsion
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Solution Overview
Problem
Existing drive arrangements for electrically powered heavy-duty vehicles face challenges in optimizing energy efficiency and endurance braking, particularly in vehicles with limited computational resources, and require improved control mechanisms to balance wheel slip across multiple electric machine arrangements.
Innovation Solution
A vehicle control unit that balances wheel slip requests to electric machine arrangements based on their efficiency characteristics, using gradient descent and power consumption methods to optimize propulsion and braking efficiency, while considering tire wear and energy storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If advanced optimization methods are used to optimize energy efficiency, then energy efficiency is improved, but computational complexity increases and robustness verification becomes difficult
Solution Approach 1:
The patent transforms the control parameter from torque distribution to wheel slip distribution. This parameter change enables the use of efficiency maps that directly relate wheel slip to energy consumption, allowing optimization without complex computational algorithms. The wheel slip parameter can be directly controlled by the EM control units, making the optimization process simpler and more robust while maintaining high energy efficiency.
Solution Approach 2:
The patent replaces complex computational optimization algorithms with a control mechanism based on physical efficiency maps. Instead of using advanced mathematical optimization that requires high computational power, the system uses pre-characterized efficiency maps that guide wheel slip control, substituting computational complexity with physics-based control that can be implemented on resource-constrained devices.
2Reliability
If friction brakes are used for prolonged periods, then braking capability is maintained, but brake fading occurs
Solution Approach 1:
The patent converts the typically harmful effect of wheel slip (energy loss, tire wear) into a beneficial mechanism for endurance braking. By intentionally allowing controlled wheel slip during braking, the system activates regenerative braking through the EM arrangements, converting kinetic energy into electrical energy that can be stored. This reduces reliance on friction brakes and prevents brake fading during prolonged downhill driving.
Solution Approach 2:
The patent introduces wheel slip control as an intermediary mechanism between the vehicle's kinetic energy and the energy storage system. During braking, controlled wheel slip enables the EM arrangements to act as generators, mediating the conversion of mechanical energy to electrical energy. This intermediary process reduces the burden on friction brakes and provides sustained braking capability through regenerative energy recovery.
3Use of energy by moving object
If wheel slip is increased to activate regenerative braking, then energy recovery is improved, but tire wear increases
Solution Approach 1:
The patent applies partial wheel slip rather than complete lock-up braking. By controlling the wheel slip to be partial (not exceeding what is necessary for regenerative braking activation), the system achieves energy recovery while limiting tire wear. The wheel slip is maintained at levels that are sufficient to engage the EM arrangements as generators but not so high as to cause excessive tire degradation.
4Use of energy by moving object
If multiple EM arrangements with different efficiency characteristics are used, then overall efficiency is improved, but control complexity increases
Solution Approach 1:
The patent assigns different wheel slip control strategies to different EM arrangements based on their local efficiency characteristics. Each EM arrangement is controlled according to its specific efficiency map, allowing the system to exploit the unique strengths of each arrangement. The vehicle control unit coordinates these local control strategies, balancing wheel slip distribution to maximize overall system efficiency without requiring complex centralized optimization.
Data Source
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AI summary
A vehicle control unit (130, 140) arranged to control motion of a heavy-duty vehicle (100) comprising first and second electric machine, EM, arrangements (EM1, EM2), where the first EM arrangement has different efficiency characteristics compared to the second EM arrangement, wherein the vehicle control unit (130, 140) is arranged to control the first and the second EM arrangement (EM1, EM2) by transmitting wheel slip requests to respective EM control units, wherein the control unit (130, 140) is arranged to obtain a desired total longitudinal force (Fx) to be jointly generated by the first and second EM arrangements, wherein the control unit (130, 140) is arranged to determine a desired first wheel slip (λ1) corresponding to a first longitudinal force (F1) generated by the first EM arrangement, and a desired second wheel slip (λ2) corresponding to a second longitudinal force (F2) generated by the second EM arrangement, where the sum of the first longitudinal force (F1) and the second longitudinal force (F2) is matched to the desired total longitudinal force (Fx), wherein the control unit (130, 140) is arranged to balance a magnitude of the first wheel slip (λ1) relative to a magnitude of the second wheel slip (λ2) in dependence of the respective efficiency characteristics of the first and the second EM arrangements (EM1, EM2).