Rotary-Linear Shift Actuator Screw Joint With Elastic Anti-Wear Contact
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Solution Overview
Problem
In actuator systems, particularly in outboard motors, the difficulty in achieving contact between the stepped surface of the nut and the end surface of the output shaft leads to insufficient axial force on the screwed portion, causing wear due to vibration, especially when the female screw portion is made of softer alloys like light metals.
Innovation Solution
A connecting structure featuring a male screw on one member and a female screw on another, with a rotation restraining member and an elastic member applying axial direction elasticity to prevent relative rotation and ensure proper contact between the screw threads, reducing wear through elastic contact during vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the nut and output shaft are connected by screwing male and female screw portions without additional restraining mechanisms, then the structure is simple, but relative rotation occurs causing wear on the screwed portion
Solution Approach 1:
A rotation restraining member is introduced as an intermediary component between the nut and output shaft. This member prevents relative rotation between the screwed portions by mechanically restraining their rotational movement, thereby eliminating wear caused by vibration-induced relative rotation while maintaining the simplicity of the screw connection structure
2Reliability
If a rotation restraining member is placed between the nut and output shaft, then relative rotation is prevented, but the stepped surface of the nut cannot contact the end surface of the output shaft, causing insufficient axial force
Solution Approach 1:
The solution introduces a second degree of freedom restriction by adding axial contact between the stepped surface of the nut and the end surface of the output shaft. This axial contact in the axial dimension complements the rotational restriction, ensuring both rotation prevention and sufficient axial force transmission to the screwed portion
3Weight of moving object
If the female screw portion is made of light alloys to reduce weight, then the overall weight decreases, but wear occurs more easily due to softer material
Solution Approach 1:
The rotation restraining member acts as a protective intermediary that prevents relative rotation between the soft light alloy female screw portion and the male screw portion. By eliminating the relative motion that causes wear, the softer material can be used for weight reduction without sacrificing durability
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
The solution effectively prevents wear at the screwed portion by ensuring consistent elastic contact between the male and female screw threads, even under vibration, thereby enhancing the durability of the actuator system.
Implementation Method 1
an elastic member that applies elasticity in an axial direction between the first member and the second member
Data Source
AI summary
A connecting structure includes a first member having a male screw portion on its outer-circumferential surface, a second member having a female screw portion on its inner-circumferential surface that is screwed with the male screw portion, a rotation restraining member placed between the first member and the second member and preventing relative rotation between the first member and the second member, and an elastic member applying elasticity in the axial direction between the first member and the second member.