Friction-Based State of Health Indicator for Electric Power Steering
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Solution Overview
Problem
Electric power steering systems in vehicles lack effective methods for determining their state of health, particularly in hybrid vehicles where conventional hydraulic systems are not viable, leading to difficulties in steering due to potential failures.
Innovation Solution
A method and system using a controller to estimate self-aligning torque values through tire dynamics models and extended state observers, calculating variance, and monitoring trends to determine the state of health of the EPS system, enabling automatic control actions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional hydraulic power steering systems are used in hybrid vehicles, then mechanical torque from the engine can be utilized for steering assistance, but the system becomes inoperable when the engine is off in EV mode
Solution Approach 1:
The patent replaces the engine-driven hydraulic pump with an electric motor to provide steering assistance. This substitution allows the steering system to operate independently of the engine, enabling it to function in both hybrid and pure EV modes. The electric motor can be powered by the battery system, ensuring steering assistance is available regardless of engine operation status.
Solution Approach 2:
The EPS system is designed to serve multiple functions and operate in multiple modes. It can provide steering assistance during hybrid operation when the engine is running, and independently during EV mode when the engine is off. The system adapts to different powertrain configurations and operating conditions, making it universally applicable across various driving scenarios.
2Use of energy by moving object
If EPS systems are implemented without effective health monitoring, then energy consumption is reduced compared to hydraulic systems, but steering failures can occur without early detection
Solution Approach 1:
The patent implements a feedback-based health monitoring system that continuously tracks EPS system performance using the extended state observer. The SOH indicator provides real-time feedback on system condition, allowing the control unit to detect degradation trends and predict potential failures before they occur. This enables proactive maintenance while maintaining the energy efficiency of the EPS system.
Solution Approach 2:
The system performs preliminary health assessment and failure prediction before actual steering failures occur. By continuously monitoring system parameters and calculating the SOH indicator, the system can detect early signs of degradation and take preventive actions, such as alerting the driver or adjusting control parameters, to avoid complete system failure and ensure safe operation.
3Device complexity
If friction effects in the EPS system are not monitored, then the system operation is simple, but undetected friction increases can lead to steering difficulties and system failure
Solution Approach 1:
The extended state observer acts as an intermediary that indirectly monitors friction effects without requiring direct friction sensors. By observing the relationship between motor torque, steering angle, and vehicle dynamics, the observer calculates the SOH indicator that reflects friction changes. This approach provides reliable friction monitoring while keeping the physical system architecture simple and avoiding additional complex sensing hardware.
Data Source
AI summary
A method for determining a state of health (SOH) value for an electric power steering (EPS) system in a vehicle includes estimating a first Self-Aligning Torque (SAT) value using a tire dynamics model, which includes modeled dynamics in the linear region of a lateral force acting on the vehicle tires. The method also includes estimating a second SAT value using an extended state observer and nominal parameters for the EPS system, and calculating a variance between the first and second SAT values. The controller monitors a progression of the calculated variance over a calibrated interval using the controller to thereby determine the SOH value, and automatically executes a control action using the SOH value. An EPS system for a vehicle includes a steering wheel, torque and angle sensors, a rack and pinion assembly, a steering motor, and the controller. A vehicle is also disclosed having the same controller.