Electric Power Steering Control Device Torque Feedback
Solution Overview
Problem
Existing electric power steering systems face challenges in improving steering feeling due to trade-offs between stability, disturbance suppression, and responsiveness, making it difficult to adjust elements effectively.
Innovation Solution
A control device that includes a reaction force controller, an assist controller, and a state feedback circuit to generate and adjust input torque, correction torque, and state compensation values, constraining the transfer function of the steering mechanism to a nominal model in specific frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional control elements are adjusted to improve steering feeling, then one characteristic (e.g., responsiveness) is improved, but other characteristics (stability, disturbance suppression) deteriorate due to trade-off relationships
Solution Approach 1:
The patent changes the fundamental parameter of the control approach by introducing a disturbance observer that estimates disturbance torque, allowing independent adjustment of control gains without traditional trade-offs. This enables improvement in steering feeling while maintaining stability through active disturbance compensation rather than passive gain tuning
Solution Approach 2:
The disturbance observer acts as an intermediary element that estimates and compensates for disturbance torque before it affects the steering system. This mediator allows the system to maintain stability while improving responsiveness by preemptively counteracting disturbances rather than relying on reactive gain adjustments
2Speed
If control gains are adjusted to improve responsiveness, then disturbance suppression capability deteriorates
Solution Approach 1:
The disturbance observer performs preliminary action by estimating disturbance torque in advance and generating compensation torque before the disturbance fully manifests. This allows the system to maintain high responsiveness with aggressive control gains while preemptively suppressing disturbances through the observer-based compensation mechanism
3Object-generated harmful factors
If control gains are adjusted to improve disturbance suppression, then stability deteriorates
Solution Approach 1:
The control system is segmented into distinct functional blocks: the disturbance observer for disturbance estimation, the compensation torque generator for disturbance counteraction, and the main control gains for steering response. This segmentation allows aggressive disturbance suppression in the observer block without destabilizing the main control loop, as each segment operates semi-independently with its own tuning parameters
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 solution enhances the steering feeling by effectively managing reaction forces, correcting torque imbalances, and compensating for inertial, viscous, and frictional forces, thereby improving the overall control and responsiveness of the steering system.
Implementation Method 1
an output shaft connected to the input shaft via a torsion bar, and the motor connected to the output shaft
Data Source
AI summary
A control device includes a reaction force controller to generate an input torque input to the control target and control a reaction force transmitted from a steering wheel to a steering person, an assist controller to generate a correction torque to correct the input torque based on an output of the control target and a nominal model, and a state feedback circuit to feed back a state compensation value to the input torque based on the output of the control target. The assist controller is configured or programmed such that the transfer function of the control target is constrained by the transfer function of the nominal model in the frequency band where the gain in the gain characteristic of the complementary sensitivity function with respect to the modeling error between the control target and the nominal model is approximately 1.