Steer-by-Wire Non-Linear Feedback Torque Scaling During Degradation
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in maintaining fault tolerance and desirable steering feel during degradation, with existing methods often leading to undesirable steering behavior due to linearly limited feedback actuator output torque.
Innovation Solution
Implement a non-linear scaling function to limit feedback actuator output torque during system degradation, increasing the limitation with increasing torque values, and optionally reducing vehicle speed to maintain steering functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linear limitation of feedback actuator output torque is applied during degradation, then the torque output is restricted, but the steering feel is hardly influenced and undesirable steering behavior may occur
Solution Approach 1:
The patent applies parameter changes by transitioning from linear to non-linear scaling of the feedback actuator output torque during degradation. The non-linear scaling function modifies the torque characteristics to maintain adequate steering feel while respecting the limited torque range, thereby resolving the contradiction between reliability (fault tolerance) and ease of operation (steering feel).
Solution Approach 2:
The patent implements dynamics by making the feedback actuator output torque adaptive through non-linear scaling that responds to system degradation states. The scaling function dynamically adjusts torque characteristics based on the actual torque values and degradation level, allowing the system to maintain desirable steering behavior throughout the degradation process.
2Power
If the gain of feedback actuator output torque is limited, then the torque range is reduced, but this can lead to undesirable steering behavior
Solution Approach 1:
The patent changes the parameter of torque scaling from linear to non-linear, where the scaling factor varies with the torque value. This allows the system to reduce the overall torque gain during degradation while maintaining desirable steering behavior through the non-linear relationship, preventing the undesirable steering behavior that would result from simple gain limitation.
Solution Approach 2:
The patent applies preliminary action by pre-defining non-linear scaling functions that anticipate degradation scenarios. These scaling functions are prepared in advance to ensure that when degradation occurs, the torque is scaled appropriately to maintain steering quality, preventing undesirable behavior before it occurs.
3Reliability
If scaling down the overall steering feel is applied to fit the remaining torque range, then the torque matches the degraded capacity, but this results in reduced steering feedback quality
Solution Approach 1:
The patent changes the scaling approach from uniform (linear) to variable (non-linear), where different portions of the torque range are scaled by different factors. This allows the system to adapt to degraded torque capacity while preserving steering feedback quality in critical operating regions, avoiding the uniform quality reduction that would result from simple scaling down.
Solution Approach 2:
The patent applies local quality by making the torque scaling location-dependent through the non-linear scaling function. Different torque values receive different scaling treatments, with critical regions maintaining higher quality feedback while less critical regions accepting greater reduction. This ensures that steering feedback quality is preserved where most needed while still adapting to the degraded torque range.
Data Source
AI summary
A method to control a steer-by-wire steering system of a road vehicle, the steer-by-wire steering system including a feedback actuator to apply a feedback torque to a steering wheel and a road wheel actuator to turn steerable road wheels, the method including calculating a feedback actuator output torque, and when degradation of the steer-by-wire-steering system occurs or an end of life of the steer-by-wire-steering system is detected, the feedback actuator output torque is limited by a limiter with a non-linear scaling function.