Electric Power Steering Torque Damping via Column Velocity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power assisted steering systems face challenges in providing adequate damping during high-speed maneuvers, leading to oscillatory and unstable yaw responses, particularly during rapid handwheel changes or when the driver releases the steering wheel, resulting in 'fish-tailing' of the vehicle.
Innovation Solution
The system incorporates a signal processing unit that generates a torque damping component as the sum of a linear and quadratic function of column velocity, along with a torque-dependent multiplier, to provide enhanced damping. This includes a first processing sub-unit for a linear column velocity term, a second for a quadratic term, and an optional third for additional damping, combined with filters and scaling functions to optimize damping at various vehicle speeds and conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple torque sensor and motor arrangement is used, then the system structure is simple and cost-effective, but the system exhibits oscillatory yaw response and fish-tailing during high-speed maneuvers
Solution Approach 1:
The patent implements feedback control by measuring column velocity using a resolver or encoder and feeding this information back to the controller. The controller then adjusts the motor torque based on the measured velocity to provide velocity-dependent damping, which stabilizes the yaw response during high-speed maneuvers without requiring complex mechanical modifications to the basic EPS structure.
Solution Approach 2:
The patent changes the control parameter from static torque assistance to dynamic torque assistance that varies with column velocity. The controller modifies the assistance torque parameter based on measured velocity, applying higher damping at high velocities and reducing it at low velocities, thereby achieving stable yaw response across different operating conditions while maintaining system simplicity.
2Stability of the object's composition
If velocity-dependent damping is implemented to reduce oscillations, then yaw stability improves, but the system requires additional sensors and control complexity
Solution Approach 1:
The patent makes the existing resolver or encoder serve multiple functions: it provides both position feedback for basic steering control and velocity feedback for damping control. By utilizing the same sensor for both position and velocity measurements through signal processing, the system achieves velocity-dependent damping without adding dedicated velocity sensors, thereby reducing overall system complexity.
Solution Approach 2:
The patent replaces mechanical damping elements (such as viscous friction devices or mechanical dampers) with an electronic control system. The controller electronically generates velocity-dependent damping torque through the motor, eliminating the need for complex mechanical damping mechanisms while achieving the same stabilizing effect.
3Stability of the object's composition
If high damping is applied during rapid handwheel changes, then overshoot and oscillation are reduced, but the steering feel becomes artificial and less natural
Solution Approach 1:
The patent implements dynamic damping that automatically adjusts with column velocity. At low velocities during normal steering, minimal damping is applied preserving natural steering feel. At high velocities during rapid handwheel changes, damping automatically increases to reduce overshoot and oscillation. This dynamic adaptation allows the system to provide different damping characteristics for different operating conditions, maintaining natural feel during normal operation while ensuring stability during extreme maneuvers.
Data Source
AI summary
An electric power assisted steering system comprises a steering mechanism which operatively connects a steering wheel to the road wheels of the vehicle, an electric motor operatively connected to the steering mechanism; a torque signal generator adapted to produce a torque signal indicative of the torque carried by a portion of the steering mechanism, a column velocity signal generator for producing a column velocity signal indicative of the angular velocity of the steering wheel or steering column and a signal processing unit adapted to receive the output signals from the sensing means and to produce therefrom a torque demand signal representative of a torque to be applied to the steering mechanism by the motor.The signal processing means includes a processing means which generates a torque damping component which is representative of the sum of a first column velocity term which is a linear function of column velocity and a second column velocity term which is a function of the square of column velocity, or a higher order factor and in which the torque demand signal is dependent upon the value of the torque damping component.