Electric Power Steering Compensator Layout for High Assist Gain
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering systems face challenges in applying assist torque to larger vehicles due to limitations in the compensator structure, leading to an upper limit on the gradient of the assist map, which affects the ability to provide sufficient steering assist force.
Innovation Solution
The system employs a control device with multiple stages of low-order filters connected in series for both the first and second compensators, and additional compensators for motor speed signals, to enhance the control of output torque based on steering torque and motor speed signals, allowing for increased torque proportional gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the torque proportional gain is increased to provide sufficient steering assist force for larger vehicles, then the steering assist performance is improved, but vibration and oscillation of the control system occur
Solution Approach 1:
The compensator is divided into multiple stages (first stage, second stage, third stage) with each stage having specific filter characteristics. This segmentation allows the system to achieve high torque proportional gain while maintaining stability by distributing the compensation function across multiple controlled stages.
Solution Approach 2:
The patent specifies particular parameter ranges for each compensator stage (e.g., time constants T1, T2, T3; gains K1, K2, K3) to optimize the balance between steering assist force and control stability. By carefully tuning these parameters, the system achieves both high assist force and suppressed vibration.
2Device complexity
If a simple compensator structure is used, then the device complexity is reduced, but the degree of freedom of the controller is limited and performance cannot be maximized
Solution Approach 1:
The compensator is segmented into three distinct stages, each with specific filter characteristics and parameter ranges. This segmentation provides the controller with sufficient degree of freedom to achieve high torque proportional gain while maintaining stability, without requiring an overly complex overall structure.
3Adaptability or versatility
If the torque proportional gain is increased to apply electric power steering to larger vehicle types, then the adaptability to different vehicle types is improved, but the gradient of the assist map reaches an upper limit
Solution Approach 1:
The multi-stage compensator structure enables the system to achieve higher torque proportional gains than previously possible, thereby increasing the assist map gradient and enabling application to larger vehicle types that require greater steering assist force.
Solution Approach 2:
By optimizing the parameters of each compensator stage (time constants and gains within specific ranges), the system achieves higher torque proportional gain values that were previously unattainable, thus increasing the assist map gradient for larger vehicles.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An electric power steering control device that controls output torque of a motor, which outputs assist torque based on a steering torque signal from a torque sensor that determines steering torque applied to a steering wheel by a user, controls the output torque by using, as a current command corresponding to a command value of the output torque, a signal obtained by adding a correction signal obtained by causing the steering torque signal to pass through a second compensator to an assist torque signal approximately proportional to a compensated steering torque signal obtained by causing the steering torque signal to pass through a first compensator, and in each of the first compensator and the second compensator, at least two or more stages of low-order filters of which an order is 1 or 2 are connected in series.