Multi-Axle EV Drivetrain Lash Transition Control for Clunk Reduction
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Solution Overview
Problem
Multi-motor electric vehicles with separate drivetrains experience clunk and shuffle due to differing backlash and compliance in front and rear axles, exacerbated by CAN communication delays, leading to uncomfortable noise and vehicle jerking.
Innovation Solution
A coordinated torque shaping control strategy is implemented across independent electronic controllers for each axle, transitioning the prime movers through lash zones sequentially to minimize clunk and shuffle, accounting for CAN delays and axle-specific parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If torque is applied rapidly in response to accelerator pedal input, then vehicle acceleration response is improved, but clunk and shuffle phenomena occur due to rapid backlash traversal
Solution Approach 1:
The control system performs preliminary action by detecting when the drivetrain is approaching the lash zone and proactively adjusting the torque rate of change before the backlash is traversed. This prevents rapid lash crossing by pre-modifying the torque profile, thereby eliminating clunk and shuffle while maintaining acceptable acceleration response.
Solution Approach 2:
The system dynamically changes the torque parameter by adjusting the rate of change of torque (dT/dt) based on drivetrain state. When approaching lash zone, the torque slope is reduced; when clear of lash zone, normal torque application resumes. This parameter modulation eliminates harmful noise while preserving acceleration performance.
2Object-affected harmful factors
If torque shaping is applied to minimize clunk by slowing traversal through lash zone, then noise is reduced, but acceleration response becomes sluggish
Solution Approach 1:
The control system dynamically adjusts torque shaping based on real-time drivetrain state. Rather than applying constant torque limiting, the system actively monitors lash zone proximity and modulates torque rate of change accordingly. This dynamic approach minimizes clunk only when necessary, preserving acceleration response during normal operation.
Solution Approach 2:
The system uses feedback from drivetrain state estimation (including lash zone detection) to continuously adjust torque application. This closed-loop control ensures torque shaping is applied selectively based on actual drivetrain conditions, preventing clunk when needed while maintaining responsive acceleration when the drivetrain is in a favorable state.
3Device complexity
If distributed control is used for front and rear motors, then system complexity is reduced and modularity is improved, but CAN communication delays cause clunk and shuffle
Solution Approach 1:
The control system is segmented into independent motor controllers that each operate with local decision-making capability. Each controller independently monitors its own drivetrain state and applies torque shaping locally, eliminating the need for synchronized communication across the CAN network. This segmentation preserves modularity while eliminating communication-delay-induced clunk.
Solution Approach 2:
Each motor controller serves itself by independently detecting lash zone conditions and adjusting its own torque output without requiring commands from a central controller. This self-service approach eliminates dependency on CAN communication timing, allowing each axle to optimize its own torque application and avoid clunk caused by communication delays.
4Adaptability or versatility
If wheel-end disconnect hubs are installed on one axle, then drivetrain flexibility and efficiency are improved, but backlash increases leading to more clunk
Solution Approach 1:
The control system applies localized torque shaping to the specific axle with the wheel-end disconnect hub. Rather than uniformly controlling both axles, the system identifies which axle has the disconnect hub and applies lash-zone-aware torque modulation only to that axle. This local quality approach compensates for the increased backlash at the disconnect hub while preserving the efficiency benefits of the flexible drivetrain configuration.
Data Source
AI summary
Methods and systems are provided for an electric vehicle are provided. In one example, a method for an electric vehicle having a first prime mover for supplying a torque to a first axle and a second prime mover for supplying a torque to a second axle comprises transitioning the first prime mover and the second prime mover to cross a lash zone one before the other, where the lash zone of the second prime mover does not overlap with the lash zone of the first prime mover. In one example, the first prime mover is controlled with a first electronic controller and the second prime mover is controlled with a second electronic controller positioned separately in the vehicle from the first electronic controller. In one example, the method further comprises communicating information from the first electronic controller to the second electronic controller via a communication area network.