EV Drive Torque Control to Avoid Backlash During Mode Switching
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Solution Overview
Problem
Existing methods for controlling torque in electric vehicles fail to prevent the occurrence of backlash in the driving system, leading to issues such as vibration, noise, and harshness, as well as reduced responsiveness and stability.
Innovation Solution
A method of controlling torque by evading the backlash band in the driving system through separate operating torque regions for front and rear-wheel motors, using a controller to limit the slope of torque commands based on vehicle driving states, switching between responsiveness and power priority modes to minimize backlash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the torque change rate is set too high, then the acceleration/deceleration responsiveness is improved, but vibration, noise, and harshness occur due to backlash and torsion
Solution Approach 1:
The controller predicts future torque requirements based on driving patterns and proactively adjusts torque commands to avoid sudden changes that would cause backlash. By anticipating torque demands before they occur, the system prevents backlash events rather than reacting to them, thereby maintaining both responsiveness and NVH performance.
Solution Approach 2:
The system dynamically adjusts the torque change rate based on real-time driving conditions, vehicle state, and predicted backlash risk. Rather than using a fixed torque profile, the controller continuously adapts the torque command slope to optimize the balance between responsiveness and backlash prevention, allowing high torque change rates when backlash risk is low and reducing them when backlash is predicted.
2Object-affected harmful factors
If the torque change rate is limited too small, then vibration and noise are reduced, but the acceleration/deceleration responsiveness deteriorates
Solution Approach 1:
The controller continuously monitors actual torque delivery, vehicle acceleration, and driving system state to detect early signs of backlash. When backlash is detected or predicted, the system provides feedback-adjusted torque commands that compensate for the backlash effect, thereby maintaining responsiveness despite the need to limit torque change rates for NVH control.
Solution Approach 2:
The system changes multiple parameters simultaneously including torque command slope, torque distribution between axles, and motor operating points to achieve the desired torque effect while avoiding backlash. By adjusting multiple parameters, the system can maintain torque responsiveness without relying solely on high torque change rates that cause backlash.
3Object-affected harmful factors
If advanced backlash post-correction control is applied, then vibration suppression is improved, but vehicle responsiveness deteriorates due to hardware characteristics
Solution Approach 1:
Instead of correcting backlash after it occurs, the system applies preliminary anti-action by predicting potential backlash events and applying counteracting torque commands before the backlash can develop. This preventive approach eliminates the need for post-correction control that would compromise responsiveness, as the backlash is prevented in the first place while maintaining torque delivery effectiveness.
Solution Approach 2:
The controller performs preliminary torque adjustment based on predicted driving maneuvers and known backlash-prone conditions. By preparing the torque command in advance to account for potential backlash, the system avoids the need for reactive correction that would delay the torque response and reduce vehicle responsiveness.
4Object-affected harmful factors
If slope limiting and filters are used to generate optimal torque command, then NVH performance is improved, but torque delivery speed and responsiveness are reduced
Solution Approach 1:
The torque control is segmented into different phases: a prediction phase where future torque needs are anticipated, a planning phase where optimal torque profiles are generated considering NVH constraints, and an execution phase where torque is delivered. This segmentation allows the system to perform computationally intensive NVH optimization in advance without impacting real-time torque delivery speed.
Solution Approach 2:
The system uses dynamic torque profiling that adapts the torque command shape and rate of change based on real-time conditions. Rather than applying fixed slope limiting and filters that always reduce torque delivery speed, the controller dynamically adjusts the torque profile to be aggressive when conditions permit and conservative when NVH control is prioritized, thereby maintaining productivity while improving NVH performance.
Data Source
AI summary
A method of controlling a driving system torque of an electric vehicle includes limiting, by a controller, a slope of a front wheel torque command for front wheel torque control and a slope of a rear wheel torque command for rear wheel torque control by a slope limit value determined according to a vehicle driving state in a mode transition process in which a torque control mode upon travel of a vehicle is switched from one mode selected among a responsiveness priority mode and a power priority mode to another mode among the responsiveness priority mode and the power priority mode.