Journaled Armrest Structure for High Torque Bearing Points
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Solution Overview
Problem
Pivoting armrests in vehicle and marine seating applications often shear at their bearing points due to high torque and shear stresses, which conventional plastics cannot handle effectively, while steel armrests are expensive and require complex manufacturing processes.
Innovation Solution
A hollow armrest with a rigid steel journal member featuring a torque-bearing end with multiple planar surfaces parallel to the interior wall of the bearing portion, reducing shear stress and allowing the armrest to rotate relative to the seatback without angular displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional plastics are used to manufacture armrests, then manufacturing cost is reduced and ease of manufacture is improved, but the armrest cannot adequately handle shear stresses and torques applied at the bearing points
Solution Approach 1:
The armrest combines plastic and steel materials to create a composite structure. The plastic housing provides cost-effective manufacturing and foam adhesion capabilities, while the steel journal member embedded within the bearing portion provides the necessary strength to withstand shear stresses and torques. This composite approach resolves the contradiction by integrating the advantages of both materials.
2Strength
If steel armrests are used, then strength and torque-bearing capacity are improved, but manufacturing cost increases and device complexity increases due to additional assembly and machining steps
Solution Approach 1:
Instead of manufacturing the entire armrest from steel, the invention applies steel only locally at the bearing portion where strength is critically needed to withstand shear stresses and torques. The remainder of the armrest is made from plastic, which is easier and more cost-effective to manufacture. This localized material application resolves the contradiction by providing strength only where necessary.
Solution Approach 2:
The steel journal member is nested within the hollow bearing portion of the plastic armrest housing. This nesting arrangement allows the steel component to provide structural strength while being contained within the plastic housing, simplifying the overall structure and reducing the number of separate assembly steps compared to traditional steel armrest constructions.
3Ease of manufacture
If the journal member has a cylindrical surface contact with the bearing portion, then manufacturing is simplified, but shear stress between the surfaces increases
Solution Approach 1:
The invention modifies the cylindrical surface of the journal member by adding circumferential grooves that create flattened contact regions. These grooves transform the continuous cylindrical surface into a series of localized contact zones, increasing the effective contact area and distributing shear stresses more evenly across the interface between the journal member and bearing portion.
Data Source
AI summary
A journaled armrest for a furniture piece includes an arm with, a hollow bearing portion with a rigid inner journal member. The journal member has a torque-bearing end and a connecting end. The connecting end is adapted to be connected to a seatback of a furniture piece. The torque-bearing end has three equally spaced planar surfaces formed in each of first and second annular portions. Each planar surface has an indention formed in it. The armrest is cast by way of injection molding around the journal member so that each of the equally spaced planar surfaces is parallel to an interior wall of the bearing portion. The new armrest is lightweight and capable of withstanding extreme amounts of torque without shearing at the connecting end.