Steer by Wire Diagnostic Using Reference Tracking Error
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Solution Overview
Problem
Steer by wire (SbW) systems face challenges in distinguishing between normal operational errors and fault conditions, leading to potential continuous unintended vehicle movement due to unsynchronized handwheel and roadwheel actuator responses, which can cause lag and incorrect steering ratios.
Innovation Solution
A diagnostic apparatus within the SbW system computes a reference position and tracking error, using a rack velocity capability module and limit block to differentiate between normal operational errors and fault conditions by accounting for the roadwheel actuator's force and velocity limitations, allowing for appropriate system responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SbW system monitors position errors between handwheel and roadwheel actuators, then fault detection capability is improved, but false fault indications increase due to normal operational errors
Solution Approach 1:
The patent changes the parameter used for fault detection from absolute position error to reference tracking error. The reference position is computed based on the commanded position and the roadwheel actuator's force-velocity capabilities, transforming the monitoring parameter to account for normal operational limitations. This allows the system to distinguish between acceptable position deviations due to actuator limitations and actual fault conditions.
Solution Approach 2:
The patent introduces dynamic computation of reference position that adapts to the roadwheel actuator's instantaneous force and velocity capabilities. The reference position is not a fixed value but dynamically adjusted based on the actuator's operational state, allowing the system to accommodate varying operational conditions while maintaining accurate fault detection.
2Measurement precision
If the system accounts for actuator force and velocity limitations, then operational accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent performs preliminary computation of the reference position based on the commanded position and pre-established force-velocity capability models of the roadwheel actuator. By pre-computing the reference position that accounts for actuator limitations, the system avoids the need for complex real-time optimization calculations, reducing computational burden while maintaining accuracy.
Solution Approach 2:
The patent replaces complex mechanical monitoring systems with computational models. Instead of using additional sensors and mechanical feedback mechanisms to account for actuator capabilities, the system uses software-based computation of reference position based on commanded position and pre-characterized actuator force-velocity relationships, simplifying the physical system while maintaining precision.
Data Source
AI summary
According to one or more embodiments a steer by wire steering system includes a handwheel actuator that provides a commanded position for a rack of a vehicle. The steer by wire steering system further includes a roadwheel actuator that moves the rack to a rack position based on the commanded position from the handwheel actuator. The steer by wire steering system further includes a diagnostic apparatus to compute a reference position based on the commanded position, and to compute a reference tracking error based on a difference between the reference position and the rack position. The diagnostic apparatus further determines a fault condition with the steer by wire system using the reference tracking error.