Tie-Rod Force Estimation in Power Steering via Friction Compensation
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Solution Overview
Problem
Accurately determining the tie-rod force in power steering systems is challenging due to the coarse approximation methods, which lead to significant differences between the actuating force and the real tie-rod force, especially during steering reversals and under varying temperature and wear conditions, making the assessment uncertain and unreliable.
Innovation Solution
A method that determines the tie-rod force by calculating the algebraic sum of the actuating force and dry friction force, with a low-pass filter applied to smooth the result during steering reversals, effectively accounting for dry friction and its sensitivity to temperature and wear conditions, thereby improving accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensors are placed at the junctions between the rack and the tie-rods to measure tie-rod force, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary calculation method that uses readily available sensor data (torque sensor, assistance motor set point) combined with a friction model to estimate tie-rod force, rather than directly measuring it with dedicated force sensors. This intermediary approach achieves acceptable measurement precision without adding complex hardware.
Solution Approach 2:
The patent creates a virtual model of the tie-rod force by copying and processing existing sensor signals through mathematical relationships and friction compensation, rather than creating a physical measurement system. This allows accurate estimation without additional physical sensors at the critical measurement points.
2Device complexity
If the tie-rod force is estimated by summing the driver force and assistance force, then device complexity is reduced, but measurement precision deteriorates, especially during steering reversals
Solution Approach 1:
The patent changes the parameters used in the estimation by introducing friction force as an additional parameter. Instead of simply summing driver force and assistance force, the method calculates friction force based on operating conditions (temperature, wear status) and adds it to the estimation, significantly improving accuracy without increasing hardware complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the estimated tie-rod force is continuously refined by incorporating friction compensation based on real-time operating conditions. The system monitors temperature and wear status, adjusts the friction model accordingly, and feeds this corrected information back into the tie-rod force calculation, maintaining high precision throughout various operating phases.
3Ease of operation
If the approximation method is used to estimate tie-rod force, then ease of operation is improved, but reliability deteriorates under varying temperature and wear conditions
Solution Approach 1:
The patent transforms the static approximation method into a dynamic estimation system that adapts to changing operating conditions. By incorporating friction models that respond to temperature variations and wear status, the system maintains reliability across different operating phases while keeping the calculation process relatively simple through automated model selection and parameter adjustment.
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
This method provides a more accurate and reliable estimation of the tie-rod force in all vehicle situations, including during steering reversals, by considering dry friction and using a low-pass filter to stabilize the calculation, maintaining the calculated tie-rod force close to the real value.
Implementation Method 1
a filtering sub-step (c2) during which a low-pass filter is applied, in order to be able to smooth the result of said expression when said expression is calculated at the moment of a steering reversal of the steering mechanism
Implementation Method 2
a step (b) of assessing a dry friction, during which the dry friction force exerted on the steering mechanism at the considered instant is assessed
Data Source
AI summary
A method determines a link force within a power-steering mechanism of a vehicle, the method including a step (a) of determining an actuation force, which involves determining the actuation force that results from the assistance force exerted by the assistance motor and the driver force exerted by the driver of the vehicle on the steering mechanism; a step (b) of assessing dry friction; and a step (c) of calculating the link force, which has a summation sub-step which involves calculating an expression representing the link force, which uses the algebraic sum of the actuation force and the dry friction force, and a filtering sub-step which involves applying a low-pass filter in order to smooth the result of the expression when the expression is calculated upon a steering reversal of the steering mechanism.