Phase Plane Transitional Damping for Electric Power Steering
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Solution Overview
Problem
In electric power steering systems, a faulty hand wheel torque sensor can lead to sudden changes in assist torque, causing discomfort to the driver due to the instantaneous removal of stored energy, which existing systems fail to effectively manage.
Innovation Solution
A method and system that generate a damping torque command based on hand wheel velocity and angle to combine with the assist torque command, smoothing the transition and reducing undesired torque changes by determining when to apply the damping torque command, particularly using a phase plane to define when to dampen the reaction torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the assist torque is instantly switched off when the torque sensor degrades, then the EPS system can operate in a limited fashion (Limp Home mode), but the driver may feel a sudden perceptible change on the hand wheel torque due to stored energy back-driving the motor
Solution Approach 1:
The control module determines whether to send the damping torque command based on hand wheel velocity and angle conditions before the assist torque is completely removed. This preliminary action of applying damping torque based on predicted system state prevents the sudden perceptible change that would otherwise occur when stored energy back-drives the motor during mode transition.
Solution Approach 2:
The damping torque command acts as an intermediary between the normal assist torque and the Limp Home mode operation. By combining the assist torque command and damping torque command, the system smoothly transitions between operating modes, eliminating the abrupt torque change that would directly affect the driver without completely removing the assist torque functionality.
2Object-affected harmful factors
If the damping torque command is applied continuously, then the stored energy can be effectively managed, but the device complexity increases due to the need for phase plane analysis and conditional determination
Solution Approach 1:
The control module dynamically determines whether to send the damping torque command based on real-time hand wheel velocity and angle conditions. Rather than applying damping continuously or using a fixed threshold, the system adaptively adjusts damping application based on the current operating state, allowing effective stored energy management while avoiding unnecessary complexity in non-critical operating conditions.
Solution Approach 2:
The system uses changes in hand wheel velocity and angle parameters to trigger the damping torque command. By monitoring these dynamic parameters and determining damping application based on their relationship (phase plane analysis), the system effectively manages stored energy through parameter-based control logic rather than requiring complex mechanical or electronic damping mechanisms.
Data Source
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AI summary
A method for controlling a motor in an electrical power steering system is provided. The method generates a damping torque command for reducing an undesired torque to be generated by the motor. The method generates an assist torque command that specifies a desired torque to be generated by the motor. The method determines whether to send the damping torque command to the motor as a function of a hand wheel velocity and a hand wheel angle. The method combines the assist torque command and the damping torque command to send to the motor when it is determined that the damping torque command is to be sent to the motor.