Captive Pin Mechanism for Trailer Hitch Drawbar Retention

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Solution Overview

Problem

Existing trailer hitch systems require users to manually align and insert a pin through the drawbar and receiver tube, which can be cumbersome, especially when accessories like bike carriers are attached, leading to awkward positions and potential misalignment.

Innovation Solution

A captive pin mechanism is integrated into the drawbar, attached to an arm that extends beside the pin receiving hole and is urged by a spring to automatically align and insert into both the drawbar and receiver tube holes at a specific depth, ensuring secure retention without manual alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a manual pin insertion method is used, then the user can control the pin placement, but the operation becomes cumbersome and time-consuming, especially with accessories attached

Engineering Contradiction:

Improveease of pin insertionVSAvoidtime for pin alignment and insertion

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The pin is pre-positioned in a retained position on the drawbar before insertion into the receiver tube. The spring mechanism pre-loads the pin so that when the drawbar is inserted to the correct depth, the pin automatically engages with the receiver tube hole without requiring manual alignment or insertion operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The captive pin mechanism performs the pin insertion operation automatically through spring force when the drawbar reaches the proper insertion depth. The system serves itself by using the insertion motion to trigger the pin engagement, eliminating the need for separate manual pin placement actions.

Inventive Principle:

Principle #25Self-service

2Adaptability or versatility

If accessories like bike carriers are attached to the drawbar, then the drawbar functionality is enhanced, but the user's ability to manually insert the pin is obstructed causing awkward positions

Engineering Contradiction:

Improveability to attach accessoriesVSAvoidaccessibility to pin insertion point

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The pin is pre-positioned and retained on the drawbar in advance, so when accessories are attached, the pin is already in place and does not require manual manipulation behind or around the accessory structure. The preliminary positioning eliminates the need for users to reach awkward positions during pin insertion.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The spring-loaded captive pin mechanism automatically performs the pin engagement function without requiring user intervention. This self-service capability allows accessories to be attached without interfering with the pin operation, as the system handles pin insertion autonomously.

Inventive Principle:

Principle #25Self-service

3Ease of operation

If the pin is held separately for manual insertion, then the user has control over pin placement, but the risk of pin loss increases and the operation becomes more complex

Engineering Contradiction:

Improvesimplicity of pin insertion processVSAvoidretention of pin during operation

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The pin mechanism is merged with the drawbar structure through the arm and spring assembly, creating a captive pin system. The pin is permanently associated with the drawbar via the retaining arm, eliminating the possibility of pin loss while maintaining the functionality of secure retention when engaged with the receiver tube.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The spring mechanism continuously retains the pin in a ready position on the drawbar, automatically preparing it for engagement. This self-retaining system ensures the pin is always secured to the drawbar structure, preventing loss while maintaining operational readiness for immediate engagement with the receiver tube.

Inventive Principle:

Principle #25Self-service

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 fast, convenient, and secure coupling of the drawbar to the trailer hitch receiver, preventing pin loss and ensuring proper alignment, even with attached accessories, by allowing the pin to automatically fall into place during insertion, reducing user effort and improving usability.

Implementation Method 1

The captive pin is urged by a spring into the pin receiving hole in the drawbar

Methodology Applied

Scientific EffectSpring force: Spring

Data Source

PatentUS9902222B1Captive pin apparatus for retention of a drawbar in a trailer hitch receiver

Publication Date: 2018.02.27 PHILLIPS CAL M

AI summary

An arm (26, 56) attached to a trailer hitch drawbar (22) at an attachment point behind a given depth (D) of insertion of the drawbar into a trailer hitch receiver tube (24). At this depth a pin receiving hole (22A) in the drawbar aligns with a pin receiving hole (24A) in the receiver tube. The arm extends forward beside the drawbar to a position beside the pin receiving hole in the drawbar. A captive pin (21, 71) on the forward end of the arm is urged by a spring to slide into the aligned receiving holes (22A, 24A). The pin has a range of motion (T) sufficient for insertion into the pin receiving holes and retraction of the pin to clear the outer surface of the receiver tube when the drawbar is inserted into the receiver tube. A knob (42) on the pin provides for manual retraction.