Steering Control Device Reaction Force Feedback for Output Limiting
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Solution Overview
Problem
In steer-by-wire steering devices, the existing methods for increasing the steering reaction force during output limiting processes may not sufficiently inform the driver when the steering speed is slow, leading to a lack of recognition of the output limitation.
Innovation Solution
A steering control device that calculates a reaction force torque command value by subtracting an axial force torque from an assist torque command value, and limits the assist torque command value or first state variable when an output limiting event occurs, thereby increasing the steering reaction force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the damping component of the steering reaction force is increased to enhance the reaction force during output limiting, then the driver can recognize the output limitation through steering feedback, but the steering reaction force is not sufficiently increased when the steering speed is slow
Solution Approach 1:
The invention changes the control parameter from solely damping component adjustment to direct reaction force component adjustment. By controlling the reaction force component Fr based on steering angle and steering angle derivative, the system ensures sufficient reaction force generation across all steering speeds, not just high speeds where damping would be effective.
Solution Approach 2:
The invention introduces dynamic control of the reaction force by making Fr proportional to both the steering angle θ and its derivative dθ/dt. This dynamic relationship ensures that the reaction force automatically adapts to the current steering state, providing adequate feedback regardless of whether the steering is performed slowly or quickly.
2Reliability
If the current limit value is decreased to limit the turning motor output, then the motor protection is achieved, but the steering reaction force may not be sufficiently increased to inform the driver of the limitation
Solution Approach 1:
The invention implements a feedback mechanism where the reaction force motor generates a reaction force that feeds back to the steering wheel based on the steering operator's input. This closed-loop feedback ensures that when the turning motor output is limited, the driver immediately perceives this limitation through increased reaction force, creating a direct causal link between motor limitation and driver perception.
Solution Approach 2:
The reaction force motor acts as a counterweight system that compensates for the loss of turning force. When the turning motor is limited, the reaction force motor generates an opposing force through the steering shaft, effectively balancing the system and providing the driver with tactile feedback about the limitation while protecting the turning motor from damage.
3Reliability
If the steering reaction force is increased through damping component adjustment, then the turning followability recognition is improved, but the steering feel may become unnatural at low steering speeds
Solution Approach 1:
The invention changes the fundamental parameter being controlled from damping coefficient to reaction force magnitude. By directly controlling Fr as a function of steering angle and its derivative, the system maintains natural steering feel at low speeds while ensuring adequate reaction force for followability recognition, avoiding the artificial heaviness that would result from pure damping adjustment.
Solution Approach 2:
The dynamic control strategy makes the reaction force adaptive to steering conditions. At low steering speeds, the reaction force naturally scales with the steering angle and its derivative, maintaining smooth and natural steering characteristics. At higher speeds, the same dynamic relationship ensures sufficient reaction force for followability recognition, all while preserving natural steering feel across the entire operating range.
Data Source
AI summary
An assist torque command value calculation unit of a steering control device is configured to calculate an assist torque command value based on a first state variable reflecting a steering state of a steering wheel. An axial force torque calculation unit is configured to calculate an axial force torque based on a second state variable reflecting a turning state of turning wheels. A calculator is configured to calculate a reaction force torque command value by subtracting the axial force torque from the assist torque command value. A limiting processing unit is configured to limit the first state variable or the assist torque command value in a case where an event in which an output of the turning motor is limited occurs.