Electric Power Steering Four-Wheel Angle Estimation
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Solution Overview
Problem
Conventional electric power steering systems require a steering angle sensor, increasing costs and potentially misestimating the steering angle during vehicle slip conditions, leading to incorrect handle-returning control.
Innovation Solution
An electric power steering apparatus calculates the front-wheel and rear-wheel estimated steering angles from wheel speeds and vehicle speed, adjusting weights based on running states like acceleration, deceleration, and road conditions to determine the four-wheel estimated steering angle, eliminating the need for a steering angle sensor and correcting control outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a steering angle sensor is provided to obtain accurate steering angle, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts the steering angle measurement function from a dedicated steering angle sensor and relocates it to the existing wheel speed sensors. By using the wheel speed sensors already present in the four-wheel drive system, the patent eliminates the need for an additional steering angle sensor while still obtaining steering angle information through calculation based on wheel speed differences.
Solution Approach 2:
The invention creates a calculated copy of the steering angle information by processing wheel speed data. Instead of directly measuring steering angle, the system calculates it from the differential wheel speeds, effectively copying the steering angle information from an indirect measurement source. This approach maintains measurement capability while avoiding additional hardware.
2Device complexity
If steering angle is estimated from wheel speeds during vehicle slip, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The invention dynamically adjusts the steering angle calculation method based on vehicle operating conditions. When vehicle slip is detected (through comparison of calculated steering angle with actual sensor data or through slip detection algorithms), the system switches between different calculation approaches or applies correction factors, ensuring accurate steering angle estimation across varying road conditions including acceleration, deceleration, and slippery surfaces.
Solution Approach 2:
The system implements feedback mechanisms to monitor the accuracy of steering angle estimation. By comparing calculated steering angle with expected values or using feedback from the steering system, the patent can detect when wheel speed-based estimation becomes unreliable due to vehicle slip and adjust the calculation accordingly, maintaining precision even when using simplified hardware.
3Device complexity
If handle-returning control is implemented without steering angle sensor, then device complexity is reduced, but control reliability deteriorates
Solution Approach 1:
The invention makes the wheel speed sensors serve multiple functions: they simultaneously provide wheel speed information for drive control and steering angle information for handle-returning control. This multi-functional use of existing sensors enables the patent to implement handle-returning control without additional steering angle sensors while maintaining reliability through the use of accurate, multi-purpose measurement data.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that calculates a front-wheel estimated steering angle from a front-wheel left and right wheel speeds, calculates a rear-wheel estimated steering angle from a rear-wheel left and right wheel speeds, calculates a four-wheel estimated steering angle by using the front-wheel estimated angle and the rear-wheel estimated angle, and prevents from an incorrect output by correcting a certainty of the four-wheel estimated steering angle with the front-wheel estimated angle, the rear-wheel estimated angle and a vehicle speed or a running condition in addition to them, or by correcting the output of the control with the four-wheel estimated steering angle. [Means for solving the problem] The present invention is the electric power steering apparatus that comprises a torque sensor to detect a steering torque, a current command value calculating section to calculate a current command value, a motor to generate a steering assist torque applied to a steering mechanism, and a motor control section to driving-control the motor based on the current command value, comprising: a steering angle estimating calculating section to vary a front-wheel weight X of a front-wheel estimated steering angle and a rear-wheel weight Y of a rear-wheel estimated steering angle corresponding to a running state of the vehicle and calculate a four-wheel estimated steering angle based on the front-wheel weight X and the rear-wheel weight Y.