Electric Power Steering Anti-Loss Control via Torque Limiting
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Solution Overview
Problem
Modern electric power steering systems face sudden loss of steering assist torque due to insufficient electrical power from reduced battery voltage or increased resistance in the EPS power circuit, leading to unexpected torque assist failure.
Innovation Solution
The method involves a controller that adjusts the electric motor's operation to provide a reduced level of power steering assist torque by limiting the maximum assist torque or pulse-width modulation duty cycle based on calculated electrical resistance, ensuring continuous operation and providing diagnostic notifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is controlled to provide nominal assist torque, then the steering assist performance is optimized, but the system becomes vulnerable to sudden loss of assist when electrical power is insufficient
Solution Approach 1:
The controller performs preliminary detection of electrical power availability by monitoring battery voltage and circuit resistance before attempting to provide full assist torque. When insufficient power is detected, the controller preemptively reduces the assist torque demand to match available power, preventing sudden loss of assist and maintaining continuous operation at a reduced but stable assist level.
2Reliability
If the maximum assist torque is limited based on electrical resistance, then sudden loss of assist is prevented, but the maximum steering assist performance is reduced
Solution Approach 1:
The controller dynamically adjusts the maximum assist torque based on real-time detection of electrical resistance and battery voltage conditions. Rather than using a fixed limit, the system continuously adapts the assist torque demand to match the currently available electrical power, ensuring optimal and reliable operation under varying electrical conditions while maximizing assist within available power constraints.
Solution Approach 2:
The system changes the operational parameters of the electric motor by adjusting the pulse-width modulation duty cycle and current limits based on detected electrical conditions. When resistance increases or voltage drops, the controller modifies these parameters to reduce power consumption and prevent sudden assist loss, thereby maintaining system reliability at the expense of maximum available power.
3Use of energy by moving object
If the pulse-width modulation duty cycle is limited, then electrical power consumption is reduced, but the motor output torque is reduced
Solution Approach 1:
The controller implements feedback control by continuously monitoring the electrical resistance and battery voltage, then adjusting the PWM duty cycle and motor current demand accordingly. This closed-loop approach ensures that power consumption is optimized to match available electrical power while maintaining the highest possible assist torque within those constraints, preventing both waste and sudden failures.
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 solution prevents abrupt loss of steering assist, allowing the vehicle to maintain some level of power steering assistance even under power constraints, and provides diagnostic information for proactive maintenance.
Implementation Method 1
an electric motor coupled to the steering gear to generate a steering assist torque
Implementation Method 2
supplies a pulse-width modulation duty cycle to the electric motor
Implementation Method 3
increased resistance in the EPS power circuit, e.g. increased power connector resistance
Data Source
AI summary
A method of operating an electric power steering system installed on a vehicle. The electric power steering system includes a controller that receives a desired assist torque value and supplies a pulse-width modulation duty cycle to an electric motor. The method includes the step of controlling the electric motor to achieve a nominal value of power steering assist torque when the electrical power available to the motor is sufficient to achieve the nominal value of power steering assist torque. The method further includes the step of controlling the electric motor to achieve a reduced value of power steering assist torque less than the nominal value when the electrical power available to the motor is not sufficient to achieve the nominal value of power steering assist torque.