Steering Control Device Axial Force Compensation
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Solution Overview
Problem
Existing steering systems, such as steer-by-wire and electric power steering systems, face challenges in accurately transmitting road-surface reaction forces to the steering wheel, leading to unsatisfactory steering feeling and controllability due to friction and efficiency differences in the steering mechanism.
Innovation Solution
A steering control device that includes a rotation angle control circuit, estimated axial force computation circuit, determination circuit, and compensation circuit to accurately reflect road-surface reaction forces by compensating for changes in the estimated axial force, ensuring the target rotation angle is achieved, thereby improving torque application to the steering wheel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the estimated axial force is computed based on the current flowing in the steering motor using a predetermined map, then the friction component can be removed from the estimated axial force, but a hysteresis is generated between the estimated axial forces computed in normal efficiency and reverse efficiency directions
Solution Approach 1:
The patent changes the parameter of transmission efficiency from a fixed value to a variable that switches between normal efficiency and reverse efficiency based on the direction of axial force. By determining which efficiency value to use based on the direction of the axial force from road surface reaction, the system eliminates hysteresis and achieves consistent steering feeling while maintaining accurate road-surface reaction force reflection.
2Reliability
If the road-surface reaction force is reflected in the estimated axial force, then the steering angle of the steering wheel should be independently controlled, but the steering angle is not independently controlled due to hysteresis in the estimated axial force computation
Solution Approach 1:
The patent dynamically changes the transmission efficiency parameter based on the direction of axial force to eliminate hysteresis. This allows the road-surface reaction force to be accurately reflected in the estimated axial force while maintaining independent steering angle control, thereby improving both reliability of force reflection and ease of steering operation.
3Ease of manufacture
If a ball screw mechanism and rack-and-pinion mechanism are used in the steering system, then the steering system can function, but transmission efficiency differs between forces applied on the steering wheel side and forces applied on the steered wheels side
Solution Approach 1:
The patent addresses the inherent efficiency difference in ball screw and rack-and-pinion mechanisms by dynamically changing the transmission efficiency parameter based on force direction. This allows the system to maintain standard mechanical components for ease of manufacture while achieving consistent transmission efficiency measurement for accurate road-surface reaction force reflection.
Data Source
AI summary
A steering control device that can more appropriately transmit a road-surface reaction force to a steering wheel is provided. The steering control device feedback controls a steering angle to a target steering angle that is a target value of the steering angle. The steering control device includes an estimated axial force computation circuit that computes an estimated axial force so as to reflect a road-surface reaction force in a reaction force generated by a reaction force actuator. The estimated axial force computation circuit computes the estimated axial force by causing a friction compensation amount computation circuit and an efficiency compensation gain computation circuit to compensate an initial estimated axial force computed by an initial estimated axial force computation circuit.