Electrically-Assisted Steering Stiction Characterization
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Solution Overview
Problem
Electrically-assisted steering systems face challenges in diagnosing and correcting stiction conditions due to their transient and unpredictable nature, which affects steering precision and feel.
Innovation Solution
A method and system that induce a controlled stiction condition in the steering system using a calibrated steering conditioning phase, measuring torque spikes, and generating a stiction metric to identify unsatisfactory performance, facilitating system validation and design improvement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transient impingement occurs in gears or torque transfer mechanisms, then stiction condition is induced, but steering precision and feel are degraded
Solution Approach 1:
The patent applies preliminary action by executing a steering conditioning phase before the actual steering test. This conditioning phase involves applying controlled steering inputs at specific frequencies and amplitudes to pre-condition the steering system, thereby inducing stiction conditions in a controlled manner before the main test. This allows the system to be prepared in advance for the detection of stiction conditions during normal steering operations.
Solution Approach 2:
The patent implements feedback by continuously monitoring torque spikes during steering operations and comparing them against threshold values. The controller receives torque signals from the steering system, processes them to identify stiction conditions, and provides feedback about the system's steering characteristics. This feedback mechanism enables real-time detection and characterization of stiction conditions, allowing for targeted corrections to improve steering precision.
2Measurement precision
If stiction condition is transient and unpredictable, then problem isolation and diagnosis are complicated, but steering precision is affected
Solution Approach 1:
The patent uses preliminary action by implementing a controlled steering conditioning phase that deliberately induces stiction conditions before the main diagnostic test. This pre-conditioning step transforms the transient and unpredictable stiction occurrences into more consistent and reproducible conditions, making them easier to detect and diagnose. The conditioning phase prepares the system in a known state, thereby simplifying the subsequent measurement and diagnostic processes.
Solution Approach 2:
The patent applies periodic action by using a steering conditioning signal with a specific frequency (e.g., 10 Hz) and amplitude pattern. This periodic steering input repeated over multiple cycles systematically works up stiction conditions in the steering system. The periodic nature of the conditioning signal makes the induced stiction conditions more predictable and easier to characterize through consistent torque spike patterns, thereby reducing diagnostic complexity.
3Reliability
If controlled steering conditioning phase is executed to induce stiction, then stiction metric can be generated, but test duration is increased
Solution Approach 1:
The patent applies preliminary action by executing the steering conditioning phase as a preparatory step before the main steering test. This conditioning phase, while adding time, establishes the necessary conditions for accurate stiction detection in subsequent operations. By preparing the system in advance with controlled inputs, the patent ensures that stiction conditions are properly induced and characterized, making the additional time investment worthwhile for improved measurement reliability.
Solution Approach 2:
The patent uses periodic action through the steering conditioning signal applied at a calibrated frequency (e.g., 10 Hz) for a predetermined duration. This periodic conditioning efficiently works up stiction conditions through repeated cyclic inputs, minimizing the total time required compared to random or prolonged testing approaches. The structured periodic pattern ensures consistent and reproducible stiction induction, optimizing the balance between test duration and characterization accuracy.
Data Source
AI summary
A method for characterizing a stick-slip or stiction condition in an electrically-assisted steering system includes transmitting a first steering control signal from a controller to a rotary actuator as a periodic steering conditioning signal, receiving a second steering control signal via a steering assist motor throughout the test to electrically assist steering, transmitting a third steering control signal to the rotary actuator to cause alternate rotation of the steering shaft to a target angle rate at constant acceleration/deceleration, and measuring a steering torque output from the rotary actuator. A control action is executed when a difference in local maximum and minimum peak amplitudes of the steering torque output exceeds a calibrated threshold difference indicative of stiction. A system includes a rotary actuator, the steering system, a torque transducer operable for measuring a steering torque imparted to the steering shaft by the rotary actuator, and the controller noted above.