Steering Control Device Motor Assist Response
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Solution Overview
Problem
Electric power steering devices with friction elements often experience a time lag between the start of steering wheel rotation and the application of assist force from the electric motor due to the motor's driving force being unable to overcome frictional forces.
Innovation Solution
A steering control device that includes an electric motor, a torque detection unit to set a base driving force based on steering torque, and a determination unit to decide whether a larger driving force is needed based on the motor's rotation speed, allowing for the timely application of assist force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electric motor uses a friction element for deceleration, then the motor can be compact and cost-effective, but the frictional force prevents the driving force from overcoming friction and moving the rack, causing time lag in assist force application
Solution Approach 1:
The control unit applies a preliminary driving force to the electric motor before the friction element engages, ensuring the motor overcomes static friction and begins moving the rack. This preliminary action eliminates the time lag between steering wheel rotation and assist force application, while maintaining the compact friction element design.
2Productivity
If the target current is generated based on steering torque alone, then the control system is simple, but the driving force cannot overcome frictional force at low speeds, causing time lag
Solution Approach 1:
The control unit incorporates rotation speed feedback from the electric motor into the target current calculation. When the rotation speed is low (indicating the motor is struggling against friction), the control unit increases the target current to provide additional driving force. This feedback mechanism eliminates time lag without significantly complicating the control system.
3Productivity
If the electric motor applies assist force immediately upon steering wheel rotation, then responsiveness is improved, but the driving force may be insufficient to overcome static friction
Solution Approach 1:
The control unit dynamically adjusts the target current based on the real-time rotation speed of the electric motor. At startup when rotation speed is zero or very low, the control unit applies a higher current to overcome static friction. As the motor accelerates and rotation speed increases, the control unit reduces the current to match the reduced frictional requirements, maintaining optimal responsiveness throughout the steering operation.
Data Source
AI summary
A steering control device includes: an electric motor configured to apply an assist force to steering of a steering wheel; a torque sensor configured to detect steering torque of the steering wheel; a base target current setting unit configured to set a base driving force of the electric motor on the basis of the steering torque detected by the torque sensor; and an addition determination unit configured to determine whether a driving force larger than the base driving force is to be set, on the basis of a rotation speed of the electric motor.