Steering Control Device Axial Force Distribution
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Solution Overview
Problem
Steering control devices in steer-by-wire systems fail to accurately reflect road conditions and vehicle behavior to the driver, especially when a host control device intervenes in steering, leading to inconsistent steering reaction forces and reduced driver feedback.
Innovation Solution
A steering control device that calculates and adjusts axial forces based on state quantities and distribution commands from a host control device, allowing for distinct control strategies when the host is intervening versus when it is not, ensuring appropriate response to steering interventions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feedback axial force is always calculated based on vehicle state quantities regardless of host control intervention, then road conditions are reflected in the steering reaction force, but the steering reaction force does not align with host control demands during automated driving
Solution Approach 1:
The distribution rate between feedforward axial force and feedback axial force is dynamically adjusted based on whether the host control device is intervening in steering. When host control intervenes, the distribution rate for feedback axial force is reduced, allowing the system to adapt its behavior according to the operational context while maintaining the ability to reflect road conditions when appropriate.
2Reliability
If the feedback axial force is always calculated based on vehicle state quantities, then steering reaction force reflects road conditions, but unnecessary steering wheel motion occurs during automated driving
Solution Approach 1:
The system dynamically adjusts the distribution rate of feedback axial force based on host control intervention status. During automated driving when host control intervenes, the feedback axial force contribution is reduced, preventing unnecessary steering wheel motion while still maintaining the capability to reflect road conditions when the driver is manually operating the vehicle.
3Device complexity
If the distribution rates of axial forces are fixed, then the control calculation is simple, but the steering reaction force cannot adapt to different driving modes
Solution Approach 1:
The distribution rates are made dynamic rather than fixed, adjusting automatically based on whether the host control device is intervening in steering. This dynamic adjustment mechanism allows the system to adapt to different driving modes (manual driving vs. automated driving) while adding only minimal complexity to the control calculation through a conditional adjustment of distribution rates.
Data Source
AI summary
A control device controls a reaction force motor that generates a steering reaction force to be applied to a steering mechanism of a vehicle, based on a steering reaction force command value calculated according to a steering state. An axial force distribution calculation circuit of the control device calculates a mixed axial force by summing values obtained by multiplying an ideal axial force and estimated axial forces by individually set distribution rates. The axial force distribution calculation circuit calculates a final axial force to be reflected in the steering reaction force command value, by summing values obtained by multiplying the ideal axial force and the mixed axial force by individually set distribution rates. The axial force distribution calculation circuit sets the distribution rates of the ideal axial force and the mixed axial force, based on a distribution command generated by the host control device when intervening in steering control.