Electric Power-Assisted Steering End-of-Travel Shock Reduction
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Solution Overview
Problem
Electric power-assisted steering systems in motor vehicles experience shocks and noise when the steering rack reaches its mechanical end of travel due to sudden deceleration, which existing control methods fail to adequately address, particularly as they do not consider dynamic parameters like wheel rotation speed.
Innovation Solution
A method that controls the maximum intensity of the electric current flowing through the power assistance motor based on the acceleration value of the steering wheel rotation to target a deceleration profile, activating an independent loop to reduce shocks and noise by adapting the power assistance torque, allowing for earlier and smoother action.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum intensity of electric current is controlled based on steering wheel rotation angle only, then the power assistance motor is protected from excessive heating, but shocks and noise at end of travel are not adequately reduced
Solution Approach 1:
The control method changes from using only rotation angle as a parameter to using multiple parameters including rotation angle, angular speed, and angular acceleration. This multi-parameter approach allows the system to adapt the power assistance torque more precisely to the actual dynamic state, reducing shocks and noise while maintaining motor protection.
Solution Approach 2:
The system implements feedback control by continuously monitoring the actual angular speed and acceleration of the steering wheel, comparing these with target values, and adjusting the power assistance torque accordingly. This closed-loop control enables dynamic adaptation to reduce end-of-travel shocks while protecting the motor.
2Temperature
If the power assistance torque is reduced only based on rotation angle, then motor heating is prevented, but the steering feel becomes unnatural and shocks remain
Solution Approach 1:
The control system transitions from a static angle-based torque reduction to a dynamic multi-parameter control that adapts in real-time based on angular speed and acceleration. This dynamic approach maintains natural steering feel by adjusting torque according to the actual motion state while preventing motor overheating.
Solution Approach 2:
The system changes the control parameters from static rotation angle to dynamic parameters including angular speed and acceleration. This allows the power assistance torque to be adjusted dynamically, preserving natural steering feel during normal operation while reducing shocks near end of travel and preventing motor heating.
3Temperature
If the electric current intensity is continuously decreased beyond predetermined rotation angle, then motor heating is avoided, but end of travel shocks are not sufficiently reduced
Solution Approach 1:
The system takes preliminary action by monitoring angular acceleration and predicting the tendency toward end-of-travel shocks before they occur. By detecting high angular acceleration early, the system can adjust power assistance torque in advance to prevent shocks, while maintaining appropriate current levels to avoid motor heating.
Solution Approach 2:
The control system uses feedback from angular acceleration sensors to continuously adjust power assistance torque. This real-time feedback allows the system to reduce shocks by adapting torque based on actual dynamic conditions while maintaining motor temperature within safe limits through coordinated current control.
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 effectively reduces end-of-travel shocks and noise, providing a natural feel to the driver without altering the steering experience, even in varying adhesion conditions, and can completely cancel or counter-assist power assistance as needed, enhancing the system's effectiveness.
Implementation Method 1
An electric power-assisted steering of a motor vehicle has an electric power assistance motor, by which a torque or a force, amplifying the effort manually exerted by the driver of the vehicle on the steering wheel, is applied on the steering column or on the steering pinion, or even directly on the rack
Data Source
AI summary
A method for controlling a steering system having an electric assistance motor in view of reducing shocks against end-of-travel stop, the method including getting a distance information of the rack with respect to the end of travel stop, getting an actual rotation speed information of the steering wheel, identifying a maximum allowed acceleration for the steering wheel, the maximum allowed acceleration being such that, in view of the distance information and the actual rotation speed information, the rotation speed of the steering wheel can decrease pursuant to a target deceleration value of a target deceleration profile so as to be lower than a required maximal speed when arriving at the end-of-travel stop, determining a maximum power assistance torque from the maximum allowed acceleration for controlling the power assistance torque applied to the assistance motor so as to target the deceleration value or profile of the rotation of the steering wheel.