Variable Helix Angle Cam for Bicycle Saddle Clamping
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Solution Overview
Problem
Existing clamping devices for bicycle saddles with helical cam surfaces of constant pitch suffer from instability in both open and closed positions, leading to uneven pressure distribution and potential damage or wear, and require excessive force for adjustment due to the cam's complex dynamic and static behavior.
Innovation Solution
The clamping device features a cam surface with a varying helix angle, allowing stable cooperation between the cam and cam follower surfaces in the closed position and reversible operation in the open position, using a thermoplastic material for the cam surfaces to reduce friction and wear, and a screw-nut connection system for secure locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a helical cam surface with constant pitch is used, then the cam mechanism can be manufactured with simple geometry, but the pressure distribution becomes uneven and the mechanism exhibits instability in both open and closed positions
Solution Approach 1:
The cam surface is designed with locally varying properties: the helix angle changes along the axial direction, with steeper angles in the open position region and shallower angles in the closed position region. This local variation in geometric properties enables different functional behaviors at different locations of the same cam surface, achieving stability in both positions while maintaining manufacturability.
2Device complexity
If a helical cam surface with constant pitch is used, then the cam structure remains simple, but wear and damage occur due to uneven pressure distribution
Solution Approach 1:
The cam surface incorporates local quality variations through axial-dependent helix angles. The shallower helix angles in the closed position region reduce contact pressure and wear, while the steeper angles in the open position region facilitate smooth transitions. This localized optimization of geometric parameters enhances wear resistance without complicating the overall cam structure.
3Device complexity
If a helical cam surface with constant pitch is used, then the cam mechanism maintains simple geometry, but excessive force is required for adjustment due to complex dynamic behavior
Solution Approach 1:
The variable helix angle design creates favorable local mechanical characteristics: steeper angles near the open position provide higher mechanical advantage for lever actuation, reducing the force required for adjustment. The shallower angles near the closed position ensure stable locking with minimal holding force. This local optimization of the helix angle profile simplifies the overall cam geometry while dramatically improving ease of operation.
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 design ensures stable and efficient clamping with reduced wear, lower operational torque, and improved user experience by maintaining the cam surface's high contact pressure only during transient phases, preventing creep and distributing axial force effectively.
Implementation Method 1
a cam system (30) which connects the lever (20) to the ends (11, 12) of the clamping collar (10) and which acts in translation, along the tilting axis (Y20), on the ends (11, 12) of the clamping collar (10) so as to bring these ends (11, 12) closer together, when the lever (20) is tilted around the tilting axis (Y20) between the open and closed positions
Implementation Method 2
using a thermoplastic material for the cam surfaces to reduce friction and wear
Implementation Method 3
a screw-nut connection system for secure locking
Implementation Method 4
a clamping collar (10) coaxially surrounding the tube (5) and open so as to present two ends (11, 12) which, by deformation of the clamping collar (10), move closer together to clamp the tube (5)
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
This clamping device (1) includes a clamping collar (10) designed to surround a clamping element (2) and open so as to present two ends (11, 12) capable of coming together to clamp the element to be clamped. This device also includes a lever (20), mounted to pivot on the ends (11, 23) of the collar about a pivot axis (Y20) perpendicular to a central axis (X10) of the collar, and connected to the collar by a cam system (30) actuated by pivoting the lever (20). The cam system (30) includes at least one pair associating a cam surface (33, 34) and a counter-cam surface (25, 26), which are each generally helical and which are respectively rotationally linked to the collar and the lever (20). The cam surface (33, 34) of each pair includes a first portion of a surface (33.1), against which the counter-cam surface is pressed when the lever (20) is in the open position and is tilted from the open position to the closed position, and a second surface portion (33.2), which is connected to the first portion and against which the counter-cam surface is pressed when the lever (20) is in the closed position and is tilted from the closed position to the open position. The counter-cam surface includes a main portion (25.1), which is helical, being centered on the tilting axis (Y20) and having a constant pitch, and which is pressed along the tilting axis against the second surface portion (33.2) of the associated cam surface (33, 34) when the lever (20) is in the closed position.In addition, the cam surface (33, 34) defines a support helix at the level of which the support constraints between the cam surfaces (33, 34) and counter-cam are applied, this support helix winding around the tilting axis extending at least partially over the first (33.1) and second portions (33.2). In order to improve this clamping device (1), particularly for its use on self-service cycles, the support helix of the cam surface (33, 34) has a helix angle which is greater on the first portion (33.1) than on the second portion (33.2) of the cam surface (33, 34) while this second portion (33.2) of the cam surface (33, 34) has a pitch which is substantially equal to the constant pitch of the main part (25.1, 26.1) of the associated counter-cam surface (25, 26).