Retractable Strap Load Hold-Down with Ratchet Tensioning
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Solution Overview
Problem
Existing load securing devices for vehicles face challenges in achieving tension due to the need for large diameter spools, which reduce leverage and make it difficult to create sufficient strap tension, often requiring materials that are hard to construct and maintain.
Innovation Solution
A retractable hold-down system using a cylindrical metal tensioning shaft with ratchet gears and a flat helical spring, where the strap is wound around the shaft, allowing for efficient tensioning and retraction by rotating the shaft and disengaging pawls, enabling secure load handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a large diameter spool is used to secure the strap, then the strap can be stored and tensioned, but the leverage is reduced and it becomes harder to create tension
Solution Approach 1:
The device separates the spool (for strap storage) from the tensioning shaft (for tension creation). The strap is spooled on a large diameter spool for storage, but tension is applied to a smaller diameter tensioning shaft that provides better leverage. This segmentation allows each component to be optimized for its specific function without the compromise of a single large spool.
Solution Approach 2:
The strap itself acts as an intermediary element that connects the spool and the tensioning shaft. The strap is spooled on the large spool for storage, then routed through the tensioning shaft where tension is applied. This intermediary strap allows the system to benefit from both the storage capacity of a large spool and the leverage advantage of a smaller tensioning shaft.
2Quantity of substance
If a large diameter spool is used, then the strap can be stored, but the device requires materials that are hard to construct and maintain
Solution Approach 1:
The device divides the spool and tensioning shaft into separate components with different size requirements. The spool can be constructed from simpler, easier-to-manufacture materials since it only needs to store the strap, while the tensioning shaft is smaller and requires less robust materials. This segmentation reduces overall construction difficulty and maintenance requirements compared to a single large spool system.
3Ease of operation
If a smaller diameter shaft is used for tensioning, then leverage is improved, but the strap must be routed through the shaft
Solution Approach 1:
The tensioning shaft serves multiple functions: it acts as a leverage point for tensioning, a guide for the strap, and a mounting point for the ratchet mechanism. By making the shaft multi-functional, the design avoids adding separate components for each function, thereby reducing overall device complexity despite the added strap routing requirement.
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 system allows for effective tensioning and retraction of the strap, providing secure load handling with reduced material stress and improved leverage, enabling efficient use of a smaller diameter shaft for securing loads on vehicles.
Implementation Method 1
disposed in the interior of the spool is a flat helical spring having one end anchored to the stationary shaft and the other end connected to an inner end of an elongated web strap that winds about an exterior of the tubular spool
Implementation Method 2
As the strap is drawn out through the opening in the housing and used to secure a load, it stores energy in the helical spring for effecting retraction of the strap when the strap is no longer held fixed
Implementation Method 3
The pawls are pivotally joined to the ears of the frame and are adapted to cooperate with the ratchet gears to limit the direction of rotation of the tensioning shaft during manual reciprocal action of the hand grip member
Data Source
AI summary
A retractable strap load tie-down device includes a housing containing a tubular spool with a flat helical spring in its interior and a flexible tie-down strap wrapped on its exterior. The housing also includes a frame journaling a tensioning shaft for rotation where the tensioning shaft includes a slot through which the strap passes. Keyed to the end portions of the shaft are ratchet wheels and associate with the ratchet wheels are pawls that engage and disengage from the teeth of the ratchet wheels by action of a handle mounted, squeezable release bar that selectively displaces slide rods leading to the pawls. The handle will selectively rotate the tensioning shaft depending on the engagement of the pawls with the ratchet wheels. Swinging of the handle through an arc will tension the strap when the free end of the strap is anchored.