Friction Estimation in Power Steering via Motor and Wheel Force Averaging
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Solution Overview
Problem
Existing methods for estimating friction in power steering systems of vehicles, such as the empirical friction model described in patent EP 3120124, result in unacceptable errors greater than +/-30N due to dependency on a predefined correlation law, failing to meet the criteria of car manufacturers for uniform driving experience across similar vehicles.
Innovation Solution
A method that estimates friction by averaging the sum of steering wheel and assist motor efforts on the rack during specific conditions of uniform speed and steering wheel angle, incorporating a step to calculate a nominal friction value using a recurrence function and weighting by a reliability coefficient, and processing data with a low-pass filter to filter variations and ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an empirical friction model with a predefined correlation law is used to estimate friction values, then the estimation can be performed over a wide range of Rack Force values, but the estimation accuracy deteriorates with errors greater than +/-30N
Solution Approach 1:
The patent changes the fundamental parameter of the estimation approach by abandoning the predefined correlation law in favor of a dynamic, data-driven method. It uses real-time measurement of actual friction values and adjusts the estimation model parameters (gain and offset) dynamically based on operating conditions, thereby achieving high accuracy across wide ranges without relying on fixed correlation laws
Solution Approach 2:
The system performs self-calibration by automatically measuring actual friction values during vehicle operation and using these measurements to update its own estimation parameters. The control unit continuously learns from actual friction data and adjusts the model without external intervention, enabling the system to adapt to different vehicles and conditions while maintaining accuracy
2Reliability
If mechanical elements are adjusted to meet friction criteria during production, then driving feeling consistency between vehicles improves, but the complexity of production adjustment increases
Solution Approach 1:
The patent replaces mechanical adjustment methods with an electronic control solution. Instead of physically adjusting mechanical elements during production, the system uses a control unit that calculates and compensates for friction variations through software algorithms, thereby maintaining driving consistency without increasing mechanical complexity
Solution Approach 2:
The system creates a virtual model of the actual friction characteristics by measuring and storing friction data during production and operation. This digital copy of the friction behavior is then used by the control unit to compensate for variations, eliminating the need for precise mechanical adjustments while ensuring consistent driving feel
Data Source
AI summary
A method for estimating a value for friction exerted on a power steering system of a vehicle, during turning resulting in the crossing of a straight line angle, the turning being achieved at a substantially uniform speed included within a predefined range, and an angle of a steering wheel included within a predefined range, including: a step (1) of acquiring a plurality of vehicle-related data items, including at least one value of a force of a power steering motor on a rack and pinion, and a value of a force of the steering wheel on the rack and pinion; a step (4) of estimating the value for friction by averaging the sum of the forces of the steering wheel and the forces of the power steering motor on the rack and pinion.