Rail Fastening Cam Axial Locking Mechanism
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Solution Overview
Problem
Existing rail fastening devices are prone to movement due to lateral forces and subsidence, especially when friction is reduced by environmental factors like oil or grease, leading to potential derailment risks.
Innovation Solution
A rail fastening device featuring a cam with a ramp or circumferentially extending shoulder that moves axially within a base aperture as it rotates, providing enhanced engagement and stability through helical surfaces, allowing for secure locking against the rail flange and resisting rotational forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a cam with radial offset aperture is used to allow lateral adjustment, then the clip can be positioned correctly against the rail, but the cam can rotate under lateral forces especially when friction is reduced by oil or grease
Solution Approach 1:
The patent replaces the traditional radial offset aperture cam with a cam that has a circumferential ramp surface. This curved ramp surface engages with a corresponding ramp surface on the base aperture, creating a helical engagement path. The curvature of these ramp surfaces transforms the rotational movement into controlled axial movement, preventing unwanted rotation while maintaining positioning capability.
Solution Approach 2:
The invention adds a new dimension of control by introducing axial movement through the ramp surfaces. Instead of relying solely on rotational positioning, the cam now moves axially within the base aperture along a helical path defined by the ramp surfaces. This dimensional change provides an additional degree of freedom for control, allowing the cam to be firmly seated against the base while preventing rotation under lateral forces.
2Force
If the cam is rotated to tighten the clip against the rail, then lateral forces are resisted, but the cam can rotate back under applied forces when friction is reduced
Solution Approach 1:
The helical ramp surfaces create a self-locking mechanism through their curved geometry. When the cam is rotated to tighten the clip, the ramp surfaces engage in a way that creates mechanical interlocking. The curvature of the ramps ensures that any reverse rotation force is converted into axial compression rather than allowing the cam to rotate back, providing automatic self-locking without relying on friction alone.
Solution Approach 2:
The ramp surface geometry is designed to preemptively counteract reverse rotational forces. The helical engagement path is configured so that any lateral force attempting to rotate the cam back is met with an opposing axial force from the engaged ramps. This preliminary anti-action prevents the cam from rotating back under lateral forces, even when friction is reduced by environmental factors.
3Device complexity
If a traditional cam with radial offset aperture is used, then the structure is simple, but it cannot withstand substantial lateral forces in environments with reduced friction
Solution Approach 1:
The patent maintains relative structural simplicity while dramatically improving lateral force resistance through the use of curved ramp surfaces. The cam and base aperture each have a ramp surface, creating a helical engagement mechanism. This curved surface approach achieves high reliability under lateral forces without requiring complex multi-component systems, as the geometry itself provides the locking mechanism.
Solution Approach 2:
The invention adds axial movement capability through the ramp surfaces without significantly increasing overall device complexity. The helical engagement path allows the cam to move axially within the base aperture while maintaining a relatively compact structure. This dimensional change enables substantial lateral force resistance while keeping the device design efficient and manufacturable.
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 device effectively resists substantial lateral forces and prevents movement of the rail, ensuring secure fastening even in environments with reduced friction, thereby reducing the risk of derailment and subsidence-related issues.
Implementation Method 1
the cam comprises a ramp or circumferentially extending shoulder which seats on a ramp or shoulder extending around the base aperture, the ramp or shoulders having complimentary engaging surfaces which extend helically such that rotation of the cam causes the cam to move axially of the base aperture
Implementation Method 2
the forces applied by the rail to the clip can cause rotation of the cam, especially where the frictional resistance between the cam and the body of the clip is reduced by oil or grease in the environment
Data Source
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AI summary
A rail fastening device comprises a clip (10) having a base (11) and a nose (12) for engaging a rail flange (F). The base (11) comprises circular aperture (14) in which a circular cam (13) is rotatably mounted, the cam (13) being provided with an eccentric aperture (24) for receiving a ground anchor (25), the cam aperture (24) being radially offset from the rotational centre of the cam (13) to define a cam lobe (15). The cam (13) may comprise a ramped circumferential shoulder (18) to engage a complementary shoulder (21) inside the base aperture (14) such that any rotation of the cam (13) under the applied load of the rail causes the cam (13) to move axially of the base aperture (14) thereby tightening the engagement of the anchor (25) on the cam (13) and preventing movement of the clip (10). The degree of rotation of the cam (13) may be limited so that it can only turn in the tightening direction under load.