Track Rod Force Estimation for Park-to-Drive Tire Torsion Release
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Solution Overview
Problem
Existing power steering systems struggle to accurately estimate the 'link force' at low speeds and during transitions between parking and driving situations, as current models are not valid below 50 km/h and fail to account for the elastic torsional deformation of tires during these conditions.
Innovation Solution
A method that corrects the estimated link force as a function of longitudinal vehicle speed, accounting for the yaw twisting force due to tire friction and elastic relaxation, using a model that includes components for elastic yaw twist and friction, to simulate the force on the steering mechanism during these transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing models are used to estimate link force, then the estimation is accurate at high speeds (above 50 km/h), but the estimation becomes inaccurate at low speeds and during transitions between parking and driving
Solution Approach 1:
The patent applies parameter changes by modifying the link force estimation model to include speed-dependent parameters. Specifically, the model transitions from using only lateral acceleration and yaw rate to incorporating longitudinal speed as an additional parameter that modifies the estimation calculation. This allows the model to adapt its behavior across different speed ranges, accurately capturing the elastic torsional release effect at low speeds while maintaining accuracy at high speeds.
2Reliability
If the vehicle transitions from parking to driving, then the tire undergoes elastic torsional release, but existing models fail to capture this transient phenomenon
Solution Approach 1:
The patent applies dynamics by making the estimation model dynamic rather than static. The model continuously adapts its calculation based on the current longitudinal speed, allowing it to capture the transient elastic torsional release phenomenon during transitions. The dynamic nature of the model enables it to respond to changing vehicle states in real-time, improving reliability during transitions without requiring overly complex additional sensors or systems.
3Ease of operation
If a steering system provides reliable road feeling at low speeds, then the driver gains better vehicle behavior feedback, but the existing models cannot provide accurate force data for this purpose
Solution Approach 1:
The patent applies feedback by using the accurate link force estimation (which incorporates longitudinal speed effects) to provide feedback to the steering system. This enhanced estimation enables the steering system to provide more accurate force feedback to the driver through the steering wheel, improving road feeling and vehicle behavior feedback at low speeds where the speed-dependent elastic torsional release effects are most significant.
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 precise and reliable estimation of link force across a wide range of speeds, from 0 to 30 km/h, effectively capturing the changes in elastic torsional stress and providing a reliable feeling of road behavior to the driver.
Implementation Method 1
due to the existence of static friction between the ground and the tread of the tire, which tends to retain said tread against the yaw movement of the rim
Implementation Method 2
Due to the elastic deformation of the tire sidewalls, which connect the rim to the tread, there is an angular yaw offset
Implementation Method 3
as soon as the vehicle begins to roll, the rotation of the wheel has the effect of causing a progressive elastic return of the tire, that is to say an elastic release of the yaw torsion
Data Source
Figure 1~2
Figure 3
Figure 4~6
AI summary
The present invention relates to a method for estimating a track rod force (Fb) which is exerted, in a power steering system (1) with which a vehicle (2) is equipped, on a track rod (3) belonging to a steering mechanism (4) which connects an actuator, such as a steering wheel (5) or a power steering motor (6), to a steered wheel (7) which is orientable in the yaw direction and which bears a tyre (8) of which the tread (8BR) is in contact with the ground (9), the value of the estimated track rod force (Fb) being corrected as a function of the longitudinal speed of the vehicle (V_vehic) by means of a force component (F2) that models the release of the elastic torsion of the tyre (8) so as to reduce, in terms of absolute value, the estimated track rod force (Fb) according to the longitudinal speed of the vehicle (V_vehic), when the vehicle transitions from a park situation in which the longitudinal speed of the vehicle (V_vehic) is zero to a drive situation in which the longitudinal speed of the vehicle (V_vehic) is non-zero.