Electric Power Steering Smooth Mode Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric power steering systems experience uncomfortable switching between automatic and manual steering controls, leading to unnatural steering wheel behavior and feelings of being 'caught' during mode transitions, due to rapid variations in motor current command values and accumulated integral values.
Innovation Solution
An electric power steering apparatus with a target steering angle correction mechanism, a switching section, and a limiter that adjusts the motor current command values based on steering torque and vehicle velocity, ensuring smooth transitions by aligning the output directions of automatic and manual steering controls, and limiting the motor velocity command value with a gradually varying gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the motor current command value is rapidly varied during switching between automatic and manual steering controls, then the steering response speed is improved, but the driver experiences uncomfortable feelings and unnatural steering wheel behavior
Solution Approach 1:
The patent applies dynamics by making the switching characteristic variable rather than fixed. The control unit varies the switching characteristic based on the absolute value of the motor current command value, using a first switching characteristic when the absolute value is below a threshold and a second switching characteristic when above the threshold. This dynamic adjustment smooths transitions during low-current phases while maintaining responsiveness during high-current phases, eliminating uncomfortable driver feelings while preserving steering performance.
Solution Approach 2:
The patent changes the parameter of switching characteristic between two distinct modes. By switching between a first switching characteristic (softer transition) and a second switching characteristic (faster transition) based on the motor current command value threshold, the system optimizes both driver comfort and response speed without compromise.
2Ease of operation
If the motor current command value is limited to prevent rapid variations, then driver comfort is improved, but the steering response becomes sluggish and unnatural
Solution Approach 1:
The system dynamically adjusts the switching characteristic based on operating conditions. During low motor current phases, a softer first switching characteristic is applied to ensure comfort. During high motor current phases, a faster second switching characteristic is applied to maintain natural steering response, preventing sluggishness while ensuring comfort during critical transition periods.
Solution Approach 2:
The patent changes the switching characteristic parameter based on the absolute value of the motor current command value. This parameter change allows the system to apply different levels of limitation depending on the operational context, maintaining both comfort and responsiveness.
3Stability of the object's composition
If the integral value accumulates excessively during mode transitions, then the steering assist torque is maintained, but the steering wheel exhibits excessive angle responses and unnatural behavior
Solution Approach 1:
The patent applies preliminary action by setting the switching characteristic before the actual mode transition occurs. The control unit determines which switching characteristic to use based on the current motor current command value and threshold comparison, preparing the transition parameters in advance. This prevents excessive integral accumulation and unnatural steering wheel behavior during the transition itself.
Solution Approach 2:
The system dynamically selects the switching characteristic based on real-time motor current conditions. By adapting the transition behavior to the current operational state, the system maintains steering assist torque stability while preventing excessive steering wheel angle responses during mode 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 is capable of smoothly switching the steering when a driver steers a steering wheel during the automatic steering control and in the case that a steering direction of the automatic control is different from a direction of the steering wheel steering by the driver. [Means for solving the problem] An electric power steering apparatus comprising: a target steering angle correcting section that outputs a target steering angle correction value for a steering torque; a correction output section that corrects a target steering angle with the target steering angle correction value to output a corrected target steering angle; a steering angle control section that calculates a second motor current command value based on corrected target steering angle from the correction output section, an actual steering angle and a motor angular velocity; and a switching section that inputs a first motor current command value and the second motor current command value to switch, wherein the switching section is switched depending on a switching command of an automatic steering control and a manual steering control, and a motor is drive-controlled based on the second motor current command value in the automatic steering control.