Electric Power Steering Wheel Return Control via Estimated Angles
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Solution Overview
Problem
Conventional electric power steering apparatuses face issues with steering wheel returnability due to high friction and the need for a steering angle sensor, which increases costs, and erroneous steering angle estimation during vehicle slip conditions.
Innovation Solution
An electric power steering apparatus calculates front-wheel and rear-wheel estimated steering angles based on wheel speeds, using these estimates to calculate a 4-wheel estimated steering angle, which is then used to correct control outputs without requiring a steering angle sensor, employing a correction gain calculation and steering wheel return control mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a steering angle sensor is used to improve steering wheel returnability, then steering wheel returnability is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts the steering angle sensing function from a dedicated steering angle sensor and implements it through estimation algorithms using existing wheel speed sensors. This removes the need for the additional sensor while maintaining the steering wheel returnability function through calculated steering angle values derived from wheel speed differences.
Solution Approach 2:
The system uses its existing wheel speed sensing capability to self-determine the steering angle without requiring external sensing equipment. By processing wheel speed data through estimation algorithms, the system serves its own steering angle measurement needs, eliminating the requirement for separate steering angle sensors.
2Device complexity
If wheel speed-based steering angle estimation is used to reduce device complexity, then device complexity is reduced, but measurement precision deteriorates during vehicle slip conditions
Solution Approach 1:
The invention dynamically adjusts the steering angle estimation strategy based on detected vehicle slip conditions. When slip is detected through wheel speed analysis, the system switches from relying on wheel speed-based estimation to using alternative calculation methods or reducing reliance on the estimated steering angle, thereby maintaining measurement precision under varying operational conditions.
Solution Approach 2:
The system changes operational parameters by switching between different steering angle determination methods based on vehicle state. Under normal conditions, it uses wheel speed-based estimation; under slip conditions, it transitions to alternative parameters or methods, ensuring accurate steering angle information is maintained across all driving scenarios.
3Manufacturing precision
If conventional feedback control is used to maintain manufacturing precision, then manufacturing precision is maintained, but adaptability to slip conditions deteriorates
Solution Approach 1:
The control system dynamically changes operational parameters by detecting wheel speed discrepancies that indicate slip conditions. When slip is detected, the system modifies control parameters including switching from estimated steering angle-based control to alternative control strategies, thereby maintaining control precision while adapting to varying road conditions.
Solution Approach 2:
The invention makes the control system dynamic by enabling it to adapt its control strategy based on real-time wheel speed analysis. The system transitions between different control modes - using estimated steering angles under normal conditions and switching to alternative approaches during slip - ensuring both precision and adaptability across diverse operating conditions.
Data Source
AI summary
An electric power steering apparatus which has a steering torque sensor to detect a steering torque, a current command value calculating section to calculate a current command value based on the steering torque, a motor to apply an assist torque, and a motor driving control section to drive and control the motor, comprises: a control function with an input steering angle; and a steering angle estimating/calculating section to calculate a front-wheel estimated steering angle and a rear-wheel estimated steering angle based on a 4 wheel speeds and calculate a 4-wheel estimated steering angle. The 4-wheel estimated steering angle is used for a steering angle control.