Electric Power Steering Angle Estimation via Motor Torque
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Solution Overview
Problem
Existing electric power steering systems face challenges in fully reflecting driver interventions during autonomous driving, leading to feelings of strangeness and discomfort, and rely on expensive angle sensors for accurate steering angle control, which increases production costs and is prone to measurement limitations and communication lag.
Innovation Solution
A control device for electric power steering that estimates the steering angle using motor angle and steering torque, eliminating the need for expensive angle sensors and implementing gradual change gains to smooth the transition between steering angle control and assist control, thereby enhancing the reflection of driver inputs and reducing unnatural steering behaviors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an angle sensor is used to detect the steering angle, then the steering angle control accuracy is improved, but the production cost increases
Solution Approach 1:
The patent extracts the steering angle detection function from the expensive angle sensor and implements it through software calculation using readily available data from the motor angle sensor and steering torque sensor. The steering angle is calculated by integrating the steering angular velocity derived from motor angle changes, eliminating the need for a dedicated angle sensor while maintaining detection accuracy.
Solution Approach 2:
The patent creates a virtual copy of the angle sensor functionality through computational methods. By using the motor angle sensor to detect motor shaft rotation and calculating the corresponding steering wheel angle through integration and gear ratio conversion, the system replicates the measurement capability of a physical angle sensor without its cost and complexity.
2Speed
If abrupt switching is done between steering angle control and assist control, then the responsiveness to driver input is improved, but the driver experiences unnatural steering behavior and discomfort
Solution Approach 1:
The patent implements dynamic switching between control modes by continuously adjusting the blending ratio between steering angle control and assist control based on driver input detection. When driver steering torque exceeds a threshold, the system dynamically transitions from autonomous steering control to manual assist control, ensuring smooth adaptation to driver intentions without abrupt changes that would cause discomfort.
Solution Approach 2:
The system preliminarily detects driver steering intentions by monitoring steering torque before fully switching control modes. This preliminary detection allows the system to prepare for the transition and smoothly blend between control strategies, preventing sudden abrupt changes that would create unnatural steering behavior while maintaining quick responsiveness to genuine driver inputs.
3Stability of the object's composition
If gradual change gains are used to switch between control commands, then the steering smoothness is improved, but the actual motor speed lags behind the commanded speed
Solution Approach 1:
The patent employs feedback control by continuously monitoring the actual motor speed and position, then adjusting the electric current command values to compensate for lag caused by gradual change gains. The steering angle control section uses feedback from the motor angle sensor to calculate corrective actions, ensuring that the motor follows the commanded trajectory accurately despite the smoothing applied to command transitions.
Solution Approach 2:
The system dynamically adjusts control parameters including gradual change gains and electric current command values based on real-time operating conditions. By changing these parameters adaptively rather than using fixed values, the system maintains smooth steering transitions while compensating for motor response lag, optimizing both smoothness and speed performance across different operating scenarios.
Data Source
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AI summary
There is provided a control device for an electric power steering device, which determines an estimate of a steering angle without using an expensive angle sensor to realize highly accurate steering angle control using the determined estimate of the steering angle. A steering angle calculating section 201 acquires a motor rotation angle θs (i.e., motor angle θ) output from a rotation sensor and acquires a steering torque Tt output from a torque sensor in a steering angle control mode. The steering angle calculating section 201 determines an estimate θr of an actual steering angle using the acquired motor angle θ and steering torque Tt to realize highly accurate steering angle control using the determined estimate θr of the actual steering angle.