Quantifying Viscous Damping in Electric Power Steering
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Solution Overview
Problem
Calibrating electric power steering systems to achieve desired hysteresis and viscous damping characteristics is challenging due to the difficulty in mathematically modeling these systems accurately, leading to subjective evaluation methods that are time-consuming, costly, and limited in scope and repeatability.
Innovation Solution
A hardware-in-the-loop simulator system that includes a rotary actuator, kingpin actuators, position and load transducers, and a simulator controller with a vehicle dynamics mathematical model, which applies controlled steering inputs and analyzes outputs to quantify viscous damping steering feel by deconvoluting hysteresis curves and calculating average torques at zero steering wheel velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If subjective assessment methods are used to evaluate viscous damping steering feel, then the evaluation can capture natural steering characteristics, but the process becomes time-consuming and costly
Solution Approach 1:
The patent creates a virtual copy of the vehicle dynamics system through mathematical modeling. The virtual vehicle model replicates the physical vehicle's steering characteristics, allowing objective measurement of viscous damping without requiring actual physical testing. This copying approach maintains evaluation accuracy while eliminating time-consuming physical testing requirements.
Solution Approach 2:
The patent replaces the mechanical physical testing system with a computational mathematical model. Instead of physically testing vehicles on test tracks with human operators, the system uses equations and algorithms to simulate steering behavior. This substitution transforms a mechanical, time-intensive process into a computational, efficient process while preserving measurement fidelity.
2Adaptability or versatility
If physical testing vehicles are used for subjective evaluation, then comprehensive steering conditions can be assessed, but the cost and scope limitations increase
Solution Approach 1:
The mathematical modeling system serves multiple testing functions simultaneously. A single virtual vehicle model can evaluate various steering conditions, vehicle configurations, and operating parameters without requiring separate physical test vehicles for each scenario. This multi-functionality expands testing scope while reducing the need for multiple expensive physical platforms.
Solution Approach 2:
The virtual vehicle model acts as a universal copy that can be configured to represent different vehicle types and conditions. Rather than building multiple physical test vehicles, the system creates computational replicas that can be adjusted to simulate various steering scenarios, reducing costs while maintaining comprehensive testing capability.
3Productivity
If mathematical modeling is used to quantify viscous damping, then objective measurement is achieved, but the modeling accuracy is insufficient
Solution Approach 1:
The patent incorporates feedback mechanisms where the mathematical model's predictions are compared against actual steering data, and the model parameters are adjusted accordingly. This iterative refinement process improves modeling accuracy over time while maintaining the efficiency benefits of objective computational measurement versus subjective physical testing.
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 approach allows for objective and efficient quantification of viscous damping steering feel, reducing the need for subjective assessments and enabling more comprehensive testing across various conditions, thereby improving the calibration process.
Implementation Method 1
a rotary actuator connected to the EPS gear via the steering shaft... The simulator controller is programmed to transmit a steering control input to the rotary actuator to rotate the steering shaft
Implementation Method 2
position and load transducers that are operable to support an electric power steering system, and apply input forces to the electric power steering system
Implementation Method 3
The simulator controller receives, from the test bench including the rotary actuator, a steering torque output, a steering angle output
Implementation Method 4
Hysteresis feel can be described as the differences in driver applied steering torque required when steering the steering wheel away from center and returning the steering wheel to center... determine a phase shift time between the lateral acceleration and the steering angle; deconvolute each steering cycle to remove the phase shift time
Implementation Method 5
Hysteresis feel is the combined result of steering friction, steering inertia effects, and steering wheel velocity damping, also referred to herein as viscous damping
Data Source
AI summary
A method of quantifying a viscous damping steering feel characteristic of a vehicle equipped with an electric power steering system includes connecting the electric power steering (EPS) system to a rotary actuator and kingpin actuators of a simulator system, communicating a triangle wave control input from a simulator controller to the rotary actuator, and receiving outputs from sensors in the simulator system by the simulator controller in response to the triangle wave control input. The simulator controller is programmed to execute logic embodying a method using the triangle wave control input provided via the rotary actuator and deconvolution of the outputs remove phase lag between the input and output signals, to generate a deconvoluted hysteresis loop for each of a plurality of steering cycles conducted during a vehicle simulation event, and to characterize a viscous damping steering feel characteristic of the EPS system.