Steering Control Device Viscous Load Application
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Solution Overview
Problem
Conventional steering control devices face challenges in applying a stable viscous load to drivers, especially when the assist torque magnification ratio is high, as they struggle to reduce impact shock at the steering wheel's rotation limit position without increasing the steering torque unnecessarily.
Innovation Solution
The proposed steering control device generates a corrected steering torque by decreasing the assist torque based on the steering torque detection value, using a steering torque correction unit that calculates a product gain from steering angular velocity, steering angle, and vehicle speed gains to apply a stable viscous load, even at high assist magnification ratios, by adjusting the assist torque to follow a target steering torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the assist torque magnification ratio is increased to enhance steering assist, then the steering effort is reduced, but the ability to apply viscous load to the driver deteriorates and impact shock increases at rotation limit
Solution Approach 1:
The steering control device segments the assist torque into two distinct components: a basic assist torque component that provides continuous steering assistance, and a viscous load component that applies speed-dependent resistance. This segmentation allows the system to maintain high assist magnification for ease of operation while simultaneously applying viscous load through the separate control mechanism, resolving the contradiction between steering effort and viscous load application.
Solution Approach 2:
The system dynamically changes the parameter of assist torque magnification ratio based on operating conditions. By calculating different magnification ratios for the basic assist torque and viscous load component based on steering angular velocity, steering angle, and vehicle speed, the system achieves both high steering assist and stable viscous load application without the limitations of a fixed magnification ratio.
2Object-affected harmful factors
If the assist torque is decreased to reduce impact shock at rotation limit, then the impact shock is reduced, but the viscous load application to the driver is compromised
Solution Approach 1:
The system dynamically adjusts the viscous load component based on real-time steering angular velocity feedback. When the steering wheel approaches rotation limits and angular velocity increases, the viscous load component is automatically increased to apply damping force, reducing impact shock. This dynamic control maintains viscous load application reliability while protecting against mechanical impact, resolving the contradiction between impact shock reduction and viscous load maintenance.
Solution Approach 2:
The steering control device incorporates feedback mechanisms that continuously monitor steering angular velocity, steering angle, and vehicle speed. This feedback information is used to dynamically calculate and adjust the viscous load component, ensuring that viscous load is applied appropriately during normal operation and increased during high-speed steering near rotation limits to reduce impact shock, thereby maintaining viscous load application reliability while mitigating harmful impact forces.
3Reliability
If high gains are used to apply viscous load, then the viscous load magnitude is increased, but the system becomes less stable and more complex
Solution Approach 1:
Instead of using high fixed gains, the system changes the approach by calculating variable gains based on operating parameters such as steering angular velocity, steering angle, and vehicle speed. The viscous load component is calculated as a function of these parameters, allowing the system to achieve high viscous load magnitude when needed (during rapid steering) while maintaining stability during normal operation, thereby avoiding the need for high overall gains and reducing control complexity.
Data Source
AI summary
A steering control device (ECU) comprises a base assist unit for generating a basic assist torque and a steering torque correction unit. The steering torque correction unit outputs a corrected steering torque, which is decreasingly corrected so that an absolute value becomes smaller than an absolute value of a steering torque when a viscous load is requested to be applied to a driver by decreasing the assist torque. The base assist unit includes a target steering torque calculation unit and a servo controller. The target steering torque calculation unit calculates the target steering torque based on a steering torque. The servo controller calculates the basic assist torque to cause the corrected steering torque to follow the target steering torque.