Electric Power Steering Wheel Return Control via Angular Acceleration
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Solution Overview
Problem
Conventional electric power steering systems face challenges in smoothly returning the steering wheel to a neutral position, especially at low vehicle speeds due to high friction and inertia, leading to driver discomfort and unstable vehicle characteristics.
Innovation Solution
An electric power steering apparatus that calculates a steering wheel return control current based on steering angle, vehicle speed, and steering torque, using a compensation current command value to adjust the motor drive, incorporating angular acceleration calculation, target steering angle velocity setting, and control gain calculations to achieve smooth return control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional feedback control is used to generate assist torque, then the steering system can provide basic steering assist, but the steering wheel cannot return smoothly to the neutral position at low vehicle speeds due to high friction and inertia
Solution Approach 1:
The system performs preliminary action by calculating and applying a steering wheel return control current before the steering wheel naturally returns to neutral. This current is calculated based on steering angle, vehicle speed, and steering torque, and is added to the basic assist current to proactively overcome friction and inertia effects that would otherwise prevent smooth return at low speeds.
Solution Approach 2:
The system changes parameters dynamically by adjusting the steering wheel return control current based on vehicle speed and steering angle. At low vehicle speeds where friction dominates, a larger return current is applied. As vehicle speed increases, the return current is reduced or eliminated, preventing overshoot and maintaining stable vehicle characteristics across different operating conditions.
2Ease of operation
If steering wheel return control current is applied to overcome friction and inertia, then the steering wheel can return to neutral position, but excessive current may cause overshooting and unstable vehicle characteristics
Solution Approach 1:
The system employs feedback by continuously monitoring the steering angle and steering torque, and using this information to dynamically adjust the steering wheel return control current. The control current is calculated as a function of the current steering state, ensuring that sufficient current is applied to overcome friction and inertia, while the feedback loop prevents excessive current that would cause overshooting, thereby maintaining stable vehicle characteristics.
3Ease of operation
If high assist torque is provided to overcome friction at low speeds, then the steering wheel can be returned to neutral, but the system complexity increases due to additional control calculations
Solution Approach 1:
The system achieves universality by integrating the steering wheel return control function into the existing electric power steering control architecture. The same motor and control unit that provide basic steering assist are also used to generate the steering wheel return control current. The control algorithm calculates a single compensation current that simultaneously addresses friction compensation, steering wheel return, and overshoot prevention across all operating conditions, avoiding the need for separate control systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively returns the steering wheel to a neutral position smoothly, reducing driver discomfort and stabilizing vehicle characteristics by accounting for friction and inertia through feedback control.
Implementation Method 1
An electric power steering apparatus which provides a steering mechanism of a vehicle with an assist torque by means of a rotational torque of a motor
Implementation Method 2
the adjustment of the voltage supplied to the motor is generally performed by an adjustment of duty command values of pulse width modulation (PWM) control
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that is capable of realizing smooth steering wheel return without the uncomfortable feeling even if a driver intervenes in steering in a going straight state. [Means for solving the problem] An electric power steering apparatus comprising: a steering wheel return control section that calculates a steering wheel return control current by a steering angle, the steering torque, the vehicle speed and a steering angle velocity, and drives the motor by a compensation current command value made by adding the steering wheel return control current to the current command value, wherein the steering wheel return control section comprises an angular acceleration calculating section that calculates an angular acceleration corresponding to the steering angle, the vehicle speed and the steering torque, a correcting section that corrects a double integral value of the angular acceleration by a square of an angle velocity corresponding to the steering torque, a target steering angle velocity setting section that sets a target steering angle velocity based on a square root of a correction value from the correcting section, a steering wheel return control gain calculating section that calculates a steering wheel return control gain by multiplying a deviation between the target steering angle velocity and an actual steering angle velocity by a vehicle speed gain and a steering torque gain, and a steering wheel return control current calculating section that performs at least one control calculation among a P-control calculation, an I-control calculation and a D-control calculation to the steering wheel return control gain, and calculates the steering wheel return control gain that is limited by means of the vehicle speed gain and the steering torque gain.