Slit Nut Structure for Steering Feed Screw Backlash Control
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Solution Overview
Problem
Conventional feed screw mechanisms for steering wheel position adjustment suffer from excessive resistance to relative rotation and backlash due to uneven contact between the nut and rod, particularly when using multi-thread screws with large lead angles, which increases reaction force and makes it difficult to suppress backlash.
Innovation Solution
A nut with a slit orthogonal to the thread grooves' lead angle and a bolt for expanding or contracting the slit, along with a pair of tightening holes, is used to maintain consistent surface contact and reduce backlash, allowing for smoother operation by adjusting the inner diameter and minimizing reaction force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-thread screw with large lead angle is used in the feed screw mechanism, then the adjustment speed and productivity are improved, but the resistance to relative rotation between nut and rod increases excessively and backlash cannot be suppressed
Solution Approach 1:
The patent applies local quality by making the slit width variable along the axial direction of the nut. The slit width is set to be larger at positions corresponding to larger lead angles and smaller at positions corresponding to smaller lead angles. This local variation in geometry allows the nut to accommodate the uneven contact caused by multi-thread screws with large lead angles, reducing resistance to rotation while maintaining adjustment speed.
Solution Approach 2:
The patent changes the geometric parameter of the nut by introducing a slit whose width varies along the axial direction. This parameter change allows the nut to adapt to the varying contact conditions created by the multi-thread screw's lead angle, reducing friction and resistance to rotation while preserving the high adjustment speed provided by the multi-thread configuration.
2Ease of operation
If the slit width in the nut is increased to reduce reaction force, then the ease of operation is improved, but the manufacturing precision and backlash control deteriorate
Solution Approach 1:
The patent applies local quality by varying the slit width along the axial direction of the nut. The slit is wider at positions corresponding to larger lead angles where more clearance is needed, and narrower at positions corresponding to smaller lead angles where precision is more critical. This localized variation allows the nut to reduce reaction force where needed while maintaining manufacturing precision and controlling backlash where required.
Data Source
AI summary
The nut according to the present invention includes: a cylindrical portion having a female screw portion provided with spiral shaped thread grooves on an inner circumferential surface thereof; and a slit provided at one location in a circumferential direction of the cylindrical portion and opening to an outer circumferential surface and an inner circumferential surface of the cylindrical portion. The slit extends in an extending direction orthogonal to a direction of a lead angle in a portion of the thread grooves crossed by the slit.