Simulated Axle Lock for Electric AWD Torque Control
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Solution Overview
Problem
All-wheel-drive electric vehicles face challenges in controlling wheel speed and motor torques due to traction differentials between front and rear axles, leading to issues like wheel flare and torque shuffle, as they lack the mechanical connection provided in conventional four-wheel drive systems.
Innovation Solution
A controller is programmed to manage torques and speeds in a user-selected four-wheel drive mode by commanding torques to each electric machine based on driver-demanded torque, axle speeds, and traction conditions, simulating a mechanical connection between the axles through blended torque and speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate electric axles are used in all-wheel-drive electric vehicles, then independence of axle control is improved, but mechanical connection between axles is lost leading to wheel flare and torque shuffle
Solution Approach 1:
The controller continuously monitors wheel speeds and torque applications, using feedback signals to dynamically adjust torque distribution between axles. This closed-loop control compensates for the lack of mechanical connection by actively responding to speed differentials and traction conditions, preventing wheel flare and torque shuffle while maintaining independent axle control capability
Solution Approach 2:
The patent replaces the mechanical connection between axles (found in traditional four-wheel-drive systems) with an electronic control system that uses sensors, processors, and actuators to simulate the coupling effect. The controller electronically coordinates torque delivery and wheel speed management to achieve the functional equivalent of a mechanical linkage without physical connection
2Reliability
If conventional four-wheel drive mechanical connection is used, then traction stability is improved, but device complexity and weight increase
Solution Approach 1:
The patent eliminates complex mechanical connections between axles by substituting them with an electronic control architecture. The controller uses electronic signals to coordinate the independent electric machines, achieving traction stability through software-based torque management rather than physical mechanical linkages, thereby reducing system complexity and weight
Solution Approach 2:
The invention extracts and removes the mechanical connection components from the four-wheel-drive system, retaining only the essential function of coordinated axle operation. By taking out the mechanical linkage and replacing it with electronic control, the system achieves the desired traction stability without the complexity and weight of mechanical coupling components
3Speed
If independent electric machines power each axle, then responsiveness to torque changes is improved, but coordination between axles deteriorates
Solution Approach 1:
The controller employs real-time feedback from wheel speed sensors and torque monitors to continuously adjust the operation of independent electric machines. This feedback mechanism ensures that while each machine responds quickly to torque demands, their operations remain coordinated through dynamic adjustment based on actual axle speed differentials and traction conditions
Solution Approach 2:
The system dynamically adjusts the control parameters of each independent electric machine based on real-time operating conditions. The controller modulates torque delivery and speed control parameters adaptively, allowing each axle to respond independently to local traction conditions while maintaining overall coordination through dynamic parameter adjustment rather than fixed mechanical coupling
Data Source
AI summary
A vehicle includes a first axle having a first electric machine, a second axle having a second electric machine and a controller. The controller is programmed to, in a user-selected four-wheel drive mode, command a first torque to the first electric machine based on a driver-demanded torque and a speed of the second axle, and command a second torque to the second electric machine based on a comparison of the driver-demanded torque and the first torque and further based on a speed of the first axle.