Dual-Motor Ball Screw Steering Actuator Without Rotation Stop
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Solution Overview
Problem
The existing turning devices for steer-by-wire steering systems face issues where the divided turning shafts may not move axially due to excessive torque from the sliding screw mechanism, leading to failure in turning the wheels, necessitating a rotation stopping mechanism that increases size and cost.
Innovation Solution
The turning device employs a first and second power transmission part with opposing torques acting on the turning shaft, eliminating the need for a rotation stopping mechanism by canceling each other's torque, allowing axial movement without rotation, thus reducing size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rotation stopping mechanism such as a rack and pinion is added to prevent rotation of the divided turning shafts, then the reliability of axial movement is improved, but the device size and manufacturing cost increase
Solution Approach 1:
The invention converts the harmful rotational torque generated by the sliding screw mechanism into a beneficial self-locking effect. By designing the sliding screw mechanism with specific friction characteristics, the torque that would otherwise cause unwanted rotation is transformed into a force that automatically prevents rotation, eliminating the need for additional rotation stopping mechanisms while maintaining reliability of axial movement
Solution Approach 2:
The sliding screw mechanism is designed to automatically prevent rotation of the divided turning shafts through its own structural characteristics and friction properties, without requiring external rotation stopping mechanisms. The system serves itself by using the inherent friction in the screw threads to lock against rotation, thereby simplifying the overall device structure and reducing size
2Power
If the output of the motors is increased to turn the wheels to the maximum, then the turning capability is improved, but the load on the rotation stopping mechanism increases requiring larger size or stronger materials
Solution Approach 1:
The invention converts the potentially harmful rotational torque into a beneficial self-locking effect through the sliding screw mechanism's friction characteristics. This transformation allows the system to handle high motor outputs without proportionally increasing the size or strength requirements of rotation stopping mechanisms, as the friction-based locking automatically adapts to the applied load
3Ease of operation
If a sliding screw mechanism is used to move the divided turning shafts in the axial direction, then the turning function is achieved, but the sliding screw mechanism and divided turning shafts may rotate together causing failure to move axially
Solution Approach 1:
The invention addresses the reliability issue by converting the harmful rotational coupling effect into a beneficial self-locking mechanism. By carefully designing the friction characteristics of the sliding screw mechanism, the torque that would cause simultaneous rotation is transformed into a force that automatically locks the divided turning shafts against rotation, ensuring reliable axial movement while maintaining ease of operation
Solution Approach 2:
The invention changes the friction parameter of the sliding screw mechanism to optimize the balance between enabling axial movement and preventing rotation. By adjusting the friction coefficient through material selection or surface treatment, the system achieves the desired reliability of axial movement while maintaining ease of operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables the turning device to effectively turn wheels without a rotation stopping mechanism, reducing size and cost while ensuring reliable operation even if one motor fails, improving reliability and reducing manufacturing costs.
Implementation Method 1
a sliding screw mechanism formed by screw shaft portions having a relation of left and right screws with respect to respective divided turning shafts and a sliding screw nut
Implementation Method 2
The turning shafts (divided turning shafts) are connected to the wheels to be turned through ball joints in the turning device for allowing the wheels to be turned supported by a suspension to move in a vertical direction
Implementation Method 3
there is a possibility that the sliding screw mechanism and the divided turning shafts rotate together around an axis by the driving force in a case where the driving force (torque) added from the sliding screw nut to the divided turning shafts exceeds a frictional force of the ball joints
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A turning device (10) includes a turning shaft (11) having a first ball screw groove (11a2) as one of a left screw and a right screw and a second ball screw groove (11b2) as the other of the left screw and the right screw and turning wheels to be turned by moving in an axial direction, a first electric motor (15) generating a first driving force, a second electric motor (16) operating independently of the first electric motor (15) and generating a second driving force, a first ball screw nut (17) transmitting the first driving force generated by the first electric motor (15) to the first ball screw groove (11a2), a second ball screw nut (18) transmitting the second driving force generated by the second electric motor (16) to the second ball screw groove (11b2), and a rotation regulating part (19) regulating relative rotation of the turning shaft (11) around an axis with respect to a housing (14) .