Electric Power Steering Control Mode Transition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric power steering systems experience uncomfortable driver feedback and unintended handle variations due to sharp changes in motor current command values during mode switching, leading to excessive accumulation of integral values in speed control.
Innovation Solution
The system gradual-changes steering angle control and assist control command values using specific gains, limits the steering angle speed command values, and adjusts gains to prevent excessive accumulation of integral values, ensuring smooth transitions between control modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the control mode is switched sharply between assist control and steering angle control, then the response speed is improved, but the driver feels uncomfortable due to unintended handle variations
Solution Approach 1:
The patent applies preliminary action by gradually changing the command values before the actual mode switching occurs. The steering angle speed command value and steering angle control command value are gradually changed using predetermined gradual-changing gains, and the assist control command value is gradually changed using an assist control gradual-changing gain. This preliminary gradual adjustment prevents sudden handle variations that would cause driver discomfort, while still achieving timely mode transition.
2Measurement precision
If the motor current command value is sharply changed during mode switching, then the control accuracy is improved, but the integral value accumulates excessively causing instability
Solution Approach 1:
The patent performs preliminary gradual changing of command values before mode switching to prevent excessive integral accumulation. By gradually adjusting the steering angle speed command value and assist control command value using predetermined gains, the system avoids sudden large deviations that would cause the integral term to accumulate excessively, thereby maintaining control stability while achieving accurate mode transition.
Solution Approach 2:
The patent applies dynamics by making the gradual-changing gain variable rather than fixed. The gradual-changing gain is adjusted based on the current operating state, allowing the system to adapt the rate of command value change dynamically. This dynamic adjustment ensures smooth transitions while preventing excessive integral accumulation, resolving the contradiction between control accuracy and stability.
3Object-affected harmful factors
If the steering angle control command value is gradually changed with a fixed gain, then the handle variation is suppressed, but the transition time becomes too long
Solution Approach 1:
The patent makes the gradual-changing gain variable rather than fixed, allowing it to be adjusted based on the current operating state and deviation magnitude. When the deviation is large, a larger gain is used to accelerate the transition; when the deviation is small, a smaller gain is used to prevent overshoot. This dynamic gain adjustment suppresses handle variation while reducing the overall transition time compared to a fixed conservative gain.
Solution Approach 2:
The patent implements periodic adjustment of the command values through continuous feedback control. The system repeatedly adjusts the steering angle speed command value and assist control command value in small increments until the mode transition is complete. This periodic incremental adjustment suppresses handle variation while achieving timely transition through cumulative changes.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that gradual-changes a steering angle control command value, an assist control command value and also a steering angle speed command value, suppresses an excessive accumulation of an integral value in a speed control by being provided a steering speed command value with a limiter, and does not give the driver an uncomfortable feeling. [Means for solving the problem] The present invention is the electric power steering apparatus that has a function to switch between an assist control mode and a steering angle control mode, wherein the steering angle control section comprises a position control section that inputs a target steering angle and an actual steering angle and outputs a first steering angle speed command value; a gradual-changing limiting section that limits an upper limiting value and a lower limiting value by gradual-changing a first steering angle speed command value corresponding to a steering angle control gradual-changing gain; a speed control section that processes a second steering angle speed command value, which is outputted from the gradual-changing limiting section, based on an actual steering angle speed and a steering angle control gradual-changing gain; and a first gradual-changing section that gradual-changes the first steering angle control command value, which is outputted from the speed control section, corresponding to a steering angle control gradual-changing gain and outputs a second steering angle control command value, further comprises a second gradual-changing section that gradual-changes a first assist control command value, which is outputted from an assist control section, with an assist control gradual-changing gain and outputs a second assist control command value, wherein a steering angle control section, and a motor current command value is generated based on the second steering angle control command value and the second assist control command value . [Designated Figure] FIG.5