Multi-Axle EV Drivetrain Torque Shaping for Clunk and Shuffle
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Solution Overview
Problem
Multi-motor, multi-axle electrified drivetrains in electric vehicles experience clunk and shuffle phenomena due to varying backlash and compliance between drivetrain components, which are exacerbated by manufacturing variations and CAN communication delays, leading to uncomfortable noise and vehicle jerking.
Innovation Solution
A coordinated torque shaping control system is implemented, using a primary and secondary drive control module to command sequential lash crossings for front and rear axles, with one axle providing compensatory torque during the other's lash crossing, minimizing clunk and shuffle through coordinated torque shaping and feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If torque is increased rapidly in response to accelerator pedal input, then acceleration responsiveness is improved, but clunk and shuffle phenomena occur due to backlash traversal
Solution Approach 1:
The control system performs preliminary action by detecting when an axle is approaching its lash zone and preemptively adjusting torque before the backlash is traversed. This allows the system to prepare for the upcoming lash crossing and execute a controlled transition, preventing sudden torque changes that cause clunk and shuffle while maintaining overall acceleration responsiveness.
Solution Approach 2:
The system dynamically adjusts torque delivery based on real-time detection of lash zone conditions. When an axle approaches its lash zone, the control system modifies the torque profile to slow down the traversal through the backlash region, then resumes normal torque delivery after crossing. This dynamic adaptation allows the system to balance responsiveness with noise reduction.
2Adaptability or versatility
If wheel-end disconnect hubs are installed to improve wheel torque control, then drivetrain flexibility is improved, but backlash increases leading to more clunk
Solution Approach 1:
The control system uses feedback from wheel speed sensors and torque measurements to detect when a wheel-end disconnect hub is present and when the axle is approaching its lash zone. This feedback allows the system to identify axles with larger backlash and apply targeted torque shaping to compensate for the increased play, maintaining consistent drivetrain behavior despite the presence of disconnect hubs.
3Ease of manufacture
If manufacturing tolerances are relaxed to reduce costs, then manufacturing precision is improved, but backlash and compliance variations increase causing more clunk
Solution Approach 1:
The control system compensates for manufacturing variations by dynamically adjusting torque parameters based on detected lash zone conditions. Instead of requiring tight manufacturing tolerances, the system adapts its torque delivery characteristics to account for varying backlash and compliance across different vehicles and axles, achieving consistent performance despite manufacturing variations.
4Object-affected harmful factors
If sequential lash crossing control is implemented to reduce clunk, then noise reduction is improved, but control system complexity increases
Solution Approach 1:
The control system segments the torque control task by axle, independently detecting and managing lash zone crossings for each front and rear axle. This segmentation allows the system to handle each axle's backlash separately using coordinated torque shaping, reducing overall clunk while maintaining manageable control complexity through modular processing of individual axle conditions.
Data Source
AI summary
Methods and systems are provided for a drivetrain system comprising: a first prime mover for supplying a torque to a front axle; a second prime mover for supplying a torque to a rear axle; and a controller configured to, in response to a torque reversal, command the front axle and the rear axle to cross lash zones sequentially.