Electric Power Steering Fade Processing for Smooth Mode Switching
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Solution Overview
Problem
Conventional electric power steering systems face challenges in smoothly switching between torque control and position/speed control, leading to unintentional self-steering due to torque variations during system switching.
Innovation Solution
The system implements a fade processing mechanism that gradually changes the control torque and steering-angle command values between torque control and position/speed control, with adjustable fade times and the use of an external disturbance observer to compensate for inertia and friction, ensuring smooth transitions without self-steering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the control system switches between torque control and position/speed control, then the steering system can adapt to different driving conditions, but torque variations occur during switching causing unintentional self-steering
Solution Approach 1:
The patent introduces a fade processing mechanism as an intermediary transition phase between torque control and position/speed control modes. During this fade period, the control system gradually blends the two control modes rather than switching abruptly, using a transition parameter that smoothly changes from one control mode to another. This intermediary transition prevents sudden torque variations and eliminates unintentional self-steering while maintaining adaptability to different driving conditions.
Solution Approach 2:
The patent implements dynamic control mode switching with adjustable fade times based on driving conditions. The fade processing duration and characteristics are dynamically adjusted according to vehicle speed, steering angle, and other operational parameters. This dynamic approach allows the system to adapt the transition smoothness to different driving scenarios, ensuring steering stability during mode changes while maintaining overall system versatility.
2Reliability
If the fade processing time is extended to reduce torque variations, then steering stability improves, but the response time to switch between control modes increases
Solution Approach 1:
The patent employs parameter-based fade processing where the transition characteristics are controlled by adjustable parameters including fade time, blend ratio, and transition curvature. By optimizing these parameters, the system achieves smooth torque transitions that eliminate self-steering while keeping the fade duration sufficiently short for practical response requirements. The parameters can be tuned based on specific application needs to balance stability and response time.
Solution Approach 2:
The patent applies partial fade processing in certain conditions, where the full fade duration is not always necessary. When switching between control modes under stable conditions, a shorter fade period suffices. The system adjusts the extent of fade processing based on the urgency of the mode switch and the current operational state, applying just enough transition smoothness to prevent self-steering without unnecessarily delaying the control response.
3Device complexity
If the fade processing time from position/speed control to torque control is the same as from torque control to position/speed control, then the control logic is simplified, but the driving experience may be suboptimal in different scenarios
Solution Approach 1:
The patent implements asymmetric fade processing times for different control mode transitions. The fade time from torque control to position/speed control differs from the fade time from position/speed control to torque control, based on the specific requirements of each transition scenario. This asymmetric approach optimizes driving comfort for each direction of mode switching while maintaining manageable control logic through structured parameter management.
Data Source
AI summary
An electric power steering apparatus including a torque sensor to detect a steering torque and a motor control unit to control a motor that applies an assist torque to a steering system of a vehicle, including: a function to switch a control system of the motor between a torque control system to control a motor output torque and a position/speed control system to control a steering angle of a steering in accordance with a predetermined switching trigger. The fade processing time from the torque control system to the position/speed control system and the fade processing time from the position/speed control system to the torque control system are individually set.