Friction Coefficient Determination in Elastically Connected Subsystems
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Solution Overview
Problem
Existing methods for determining friction coefficients in elastically connected subsystems, such as steering systems, face challenges in accurately distinguishing between static and sliding friction states due to high system friction and the need for reliable detection of friction changes caused by factors like aging and temperature, which complicates driver assistance functions.
Innovation Solution
A method involving exciting the subsystems with vibrations of varying amplitudes and frequencies to record phase differences between the vibration and reaction torque, allowing for the determination of static and sliding friction coefficients by identifying transitions between these states without causing nonlinearities, and an apparatus to implement this method using a vibration generator and sensor to measure reaction torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If indirect measurement using characteristic parameters of the steering system is used to detect driver contact, then additional costs from direct sensor systems are avoided, but detection accuracy is reduced due to high system friction superimposed on the measurement
Solution Approach 1:
The patent applies mechanical vibration by oscillating the steering system at a defined frequency and analyzing the phase difference between excitation and reaction torque. This vibration-based measurement method enables accurate friction coefficient determination without requiring additional direct sensors, thus maintaining cost efficiency while improving detection accuracy through precise phase analysis
Solution Approach 2:
The patent changes the measurement parameter from direct force/torque measurement to phase difference measurement. By measuring the phase shift between excitation and response at different amplitudes, the system can accurately detect friction state transitions (static to sliding) without being overwhelmed by the high friction levels that plague direct measurement approaches
2Reliability
If the excitation amplitude is increased to overcome static friction and induce sliding, then the friction state transition can be detected, but nonlinearities are introduced in the system response
Solution Approach 1:
The patent applies preliminary action by first determining the static friction coefficient through a controlled amplitude sweep, then using this information to set an appropriate operating amplitude that is sufficient to overcome static friction but small enough to maintain system linearity during normal operation. This preliminary characterization enables reliable friction state detection without introducing nonlinearities
Solution Approach 2:
The patent employs dynamic amplitude adjustment, varying the excitation amplitude during the measurement process to map out the friction characteristic curve. By dynamically sweeping through different amplitude levels and observing phase transitions, the system accurately identifies friction coefficients while maintaining control over the excitation levels to avoid excessive nonlinearities
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate characterization of friction states in elastically connected subsystems, allowing for reliable detection of transitions between static and sliding friction, even at small amplitudes, thereby improving driver assistance systems by reducing awareness thresholds and accounting for external state variables like temperature and wear.
Implementation Method 1
The overall system is excited with a vibration having a variable excitation amplitude at a defined excitation frequency
Implementation Method 2
A phase difference between the vibration and a measured reaction torque is recorded together with the excitation amplitude as a function of time, wherein no phase difference occurs in the static friction state and a phase difference of 180° occurs in the sliding friction state
Implementation Method 3
The elastic connection has at least one static friction state and a sliding friction state for prescribed external state variables
Implementation Method 4
at least two subsystems are connected to one another by an elastic connection
Data Source
AI summary
A method for friction coefficient determination on elastically connected subsystems, in which an overall system includes multiple subsystems and at least two subsystems are connected to one another by an elastic connection. The elastic connection has at least one static friction state and a sliding friction state for prescribed external state variables, in which the overall system is excited with a vibration having a variable excitation amplitude at a defined excitation frequency. The excitation amplitude is varied, in which a phase difference between the vibration and a measured reaction torque together with the excitation amplitude are recorded as a function of time, in which no phase difference occurs in the static friction state and a phase difference of 180° occurs in the sliding friction state. In a first step, the excitation amplitude is increased until a transition in the phase difference from 0° to 180° indicates the transition from the static friction state to the sliding friction state.