EV Drive Torque Distribution to Avoid Backlash and NVH
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Solution Overview
Problem
Existing torque control methods in electric vehicles fail to prevent backlash in the drive system, leading to issues such as driveshaft torsion, gear backlash hits, and impulsive drivability deterioration, while also failing to address NVH problems and responsiveness delays.
Innovation Solution
A torque control method that determines front and rear wheel torque commands to evade the backlash band by maintaining continuous torque direction, using a controller to ensure the front wheel torque command is less than or equal to a negative maximum threshold and the rear wheel torque command is greater than or equal to a positive minimum threshold, thereby preventing gear alignment changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If torque change rate is set to be high, then acceleration/deceleration responsiveness is improved, but driveshaft torsion, gear backlash hits, and NVH problems occur
Solution Approach 1:
The controller determines front and rear wheel torque commands in advance to evade the backlash band, maintaining continuous torque direction. This preliminary action prevents gear alignment changes before they occur, avoiding backlash hits and driveshaft torsion while enabling rapid torque changes for improved responsiveness.
Solution Approach 2:
The patent changes the torque command parameters by setting the front wheel torque command to be less than or equal to a negative maximum threshold and the rear wheel torque command to be greater than or equal to a positive minimum threshold. This parameter change ensures torque direction continuity and prevents entry into the backlash band, resolving the contradiction between rapid torque change and NVH reduction.
2Object-affected harmful factors
If torque change rate is set to be low, then NVH is reduced, but vehicle responsiveness deteriorates
Solution Approach 1:
The controller proactively determines torque commands that evade the backlash band before torque changes occur. This preliminary action allows rapid torque changes to be implemented without causing backlash-related NVH, as the gear alignment is maintained continuously throughout the torque transition.
Solution Approach 2:
The patent introduces an intermediary control strategy that distributes torque between front and rear wheels with opposite sign constraints. This intermediary approach enables rapid overall torque changes while maintaining local torque direction continuity in each axle, preventing backlash and reducing NVH simultaneously.
3Object-affected harmful factors
If backlash post-correction control is applied, then vibration suppression is improved, but vehicle responsiveness deteriorates chronically
Solution Approach 1:
Instead of correcting backlash effects after they occur, the patent applies preliminary anti-action by determining torque commands that evade the backlash band entirely. The front and rear wheel torque commands are constrained to maintain continuous torque direction, preventing gear alignment changes and backlash-related vibration before they can occur, thus preserving vehicle responsiveness.
Solution Approach 2:
The controller proactively determines torque commands that prevent backlash occurrence rather than reacting to it. By maintaining torque direction continuity through opposite sign constraints on front and rear wheel torque commands, the system prevents vibration generation at its source while enabling rapid responsiveness.
Data Source
AI summary
A method of controlling torque of a drive system of an electric vehicle includes determining, by a controller, required torque according to a vehicle driving state while the vehicle is driven, and determining a total torque command based on the determined required torque, and performing, by the controller, a front wheel and rear wheel torque distribution process on the total torque command, so that a front wheel torque command and a rear wheel torque command following the total torque command are determined.