Steering Controller Variable Ratio Road Input Compensation
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Solution Overview
Problem
In steer-by-wire systems, the control of the steering wheel can be taken over by road surface inputs when the steer angle ratio is high, leading to instability and reduced driver control.
Innovation Solution
A steering controller that allows for a variable steer angle ratio, with a high angle ratio mode that adjusts the reaction force and viscosity compensation to prevent the steering wheel from being taken over by road surface inputs, using a reaction force motor and a tire turning motor controlled by a microcomputer-based control section, which includes a high angle ratio switch for mode selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the steer angle ratio is increased to improve steering precision, then the steering wheel control can be taken over by road surface inputs, but driver control is reduced and instability occurs
Solution Approach 1:
The control device applies preliminary counteracting actions by detecting road surface input torque and generating compensating torque through the reaction force motor before the road surface input can significantly affect steering wheel position. This prevents the steering wheel from being taken over by road surface inputs while maintaining high steer angle ratio for precise steering control.
Solution Approach 2:
The control device continuously detects the actual steering wheel position and road surface input torque, compares these with target values, and adjusts the reaction force motor output accordingly. This feedback mechanism ensures that driver control is maintained even when operating at high steer angle ratios that would otherwise amplify road surface inputs.
2Measurement precision
If the steer angle ratio is increased to improve steering precision, then steering wheel vibration increases, but driver control is reduced
Solution Approach 1:
The control device converts the harmful effect of road surface inputs and steering wheel vibration into beneficial information by detecting them through torque sensors and using this data to generate compensating torque commands. The vibration and road surface inputs are transformed from disturbances into control signals that enable the reaction force motor to counteract them, thereby reducing their harmful effects while maintaining precise steering control.
Solution Approach 2:
The control device dynamically adjusts control parameters including reaction force magnitude, damping characteristics, and stiffness compensation based on detected steering conditions, vehicle speed, and road surface inputs. These parameter changes enable the system to maintain optimal vibration suppression and driver control across varying operating conditions while preserving high steer angle ratio precision.
Data Source
AI summary
A steering controller sets a steer angle ratio to a high value in a high angle ratio mode that is high relative to a reference value in a normal mode. A control section controls operation of a reaction force motor and a tire turning motor based on a steer angle ratio mode input to a switch. The control section controls an output of the reaction force motor provided for a driver based on (i) a “reaction force amount” based on road surface information calculated from output of the tire turning motor and (ii) a “viscosity compensation amount” negatively correlated with a steering speed of a steering device.