Wheel Speed Sensing With Eccentricity Compensation Filters
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Solution Overview
Problem
Existing methods for determining the rotational frequency of a motor vehicle wheel in safety braking systems, such as ABS or ESP systems, are affected by manufacturing-related eccentricity and static imbalance, leading to sinusoidal indexing errors and modulation of the dynamic rolling radius, which are not velocity-dependent and complicate accurate frequency determination.
Innovation Solution
A method using an optimal filter with modulation parameters adapted by a sequential least-squares method to compensate for the angle-periodic modulation caused by eccentricity, incorporating a short-term mean value calculation and frequency-selective filters to improve signal conditioning and reduce residual ripple, with parameters reset below a predefinable rotational frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If manufacturing-related eccentricity and static imbalance are present in the pulse generator wheel, then the wheel can be manufactured with standard tolerances, but sinusoidal indexing errors and modulation of the dynamic rolling radius occur which complicate accurate frequency determination
Solution Approach 1:
The patent applies the 'Blessing in disguise' principle by using the sequential least-squares method to identify and compensate for the sinusoidal modulation caused by manufacturing eccentricity. Instead of treating the manufacturing tolerances as purely harmful, the system characterizes the modulation parameters (amplitude and phase) and uses this information to correct the frequency measurement, converting the manufacturing imperfection into a correctable signal characteristic.
Solution Approach 2:
The patent applies the 'Parameter changes' principle by dynamically adjusting the frequency measurement through parameter identification. The sequential least-squares method continuously estimates modulation parameters (amplitude A and phase φ) and uses these parameters to compensate the measured frequency, thereby changing the measurement parameters to account for manufacturing variations.
2Measurement precision
If an optimal filter with modulation parameters adapted by sequential least-squares method is used to compensate for eccentricity-induced modulation, then the accuracy of rotational frequency determination is enhanced, but the device complexity and computational resources increase
Solution Approach 1:
The patent applies the 'Self-service' principle by implementing a self-adapting filter system. The sequential least-squares method automatically identifies the modulation parameters from the sensor signal itself, and the optimal filter uses these identified parameters to compensate the frequency measurement. The system serves itself by using its own output signal to generate the correction parameters, eliminating the need for external calibration or manual parameter setting.
Solution Approach 2:
The patent applies the 'Feedback' principle through the sequential least-squares identification algorithm that continuously monitors the sensor signal, extracts modulation parameters, and feeds this information back to adjust the frequency compensation. This closed-loop approach allows the system to adapt to changing operating conditions and maintain measurement accuracy across different rotational velocities.
Data Source
AI summary
A method for determining a rotational frequency of a wheel, in particular of a motor vehicle, uses a rate of rotation sensor that has a rotary sensor assigned to the wheel and a sensor element assigned to the rotary sensor. The rotary sensor has pulse generators that are arranged in a manner distributed over its circumference and spaced evenly from one another and whose edges are recorded by the sensor element so as to determine the rotational frequency of the rotary sensor. There is provision to use an optimal filter in order to compensate a modulation caused by an eccentricity, and to adapt modulation parameters of the optimal filter through a sequential least-squares method. A time-equidistant frequency signal is subjected to short-term averaging, for example using a PT1 filter, and the modulation is modelled as sinusoidal interference and compensated.