Steering Control Device Grip State Axial Force Feedback
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in providing a superior steering feeling due to inaccuracies in grip state determination, which affects the appropriateness of steering reaction forces, especially on low-μ roads, as existing methods rely on assist torque parameters not applicable to these systems.
Innovation Solution
A steering control device that calculates a target steering angle considering a grip state quantity, using multiple axial force calculations and feedback control to adjust steering reaction forces, incorporating inertia, viscosity, and angular velocity feedback to enhance steering feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the steering control device uses the configuration from JP 2017-165219 A with road-surface axial force and ideal axial force calculations, then the steering reaction force can be applied considering road surface information, but the grip state determination becomes inaccurate on low-μ roads due to increased difference between road-surface axial force and ideal axial force when vehicle behavior changes
Solution Approach 1:
The patent replaces the mechanical grip detection method (based on assist torque in EPS) with an electrical field-based detection method. It uses a sensor to detect the axial force acting on the turning shaft and calculates the grip state quantity based on this detected force, substituting mechanical parameter analysis with direct force sensing and calculation.
Solution Approach 2:
The patent changes the parameter used for grip state detection from assist torque (in EPS) to axial force on the turning shaft (in SBW). It introduces a grip state quantity calculated from the detected axial force, vehicle speed, and steering angle, replacing the previous parameter set with a new one suited for steer-by-wire systems.
2Adaptability or versatility
If the steering control device applies steering reaction force based on distributed axial force calculation, then road surface information can be transmitted to the driver, but the steering feeling remains insufficient due to inaccurate grip state detection methods
Solution Approach 1:
The patent implements a feedback mechanism where the grip state quantity (calculated from detected axial force, vehicle speed, and steering angle) is used to adjust the steering reaction force. The sensor detects axial force, the controller calculates grip state, and this information feeds back to modify the steering reaction force applied to the driver, creating a closed-loop system that adapts to actual grip conditions.
Data Source
AI summary
A steering control device includes a control unit, and the control unit includes a target steering angle calculating unit configured to calculate a target steering angle based on a steering torque and is configured to calculate a target reaction torque based on execution of feedback control for causing the steering angle to match the target steering angle. The control unit includes a plurality of axial force calculating units configured to calculate a plurality of kinds of axial forces acting on a turning shaft based on different state quantities and a grip state quantity calculating unit configured to calculate a grip state quantity based on the plurality of kinds of axial forces. The target steering angle calculating unit is configured to calculate the target steering angle in consideration of the grip state quantity.