Joints and connections – Interfitted members – Radially interposed shim or bushing
Reexamination Certificate
1998-09-22
2001-10-02
Kim, Harry C. (Department: 3629)
Joints and connections
Interfitted members
Radially interposed shim or bushing
C403S332000, C403SDIG007
Reexamination Certificate
active
06296417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to circlips and apparatus incorporating circlips for connecting two components.
2. Description of the Prior Art
Circlips are used in many engineering applications to inhibit relative axial displacement of two components one of which is at least partially received within the other.
FIG. 1
of the accompanying drawings shows a schematic cross-section through part of an assembly incorporating a conventional circlip. Here, the circlip is shown mounted in the mouth of a cylinder
2
for attaching the cylinder to a cylinder base
3
having a radial flange
4
which is received in the cylinder mouth. As illustrated, the circlip is rectangular in transverse cross-section, and its outer diameter edge is received in an annular groove
5
, of rectangular cross-section, in the interior surface of the cylinder mouth. For this internal circlip configuration, the circlip is fitted by slipping the circlip over the end of the male, base portion
3
, and compressing the circlip radially to allow the circlip to move past the internal lip of the cylinder mouth to register with the annular groove
5
, whereupon the circlip springs outwardly into the groove
5
. The ends of the circlip adjacent to the discontinuity may be provided with inwardly projecting “ears” having holes to enable installation and removal using circlip pliers for example. Such “eared” circlips (whether internal or external type) cannot be keystoned and are not therefore self-locking. Earless types of circlip may be keystoned, by providing an abutment shoulder (as indicated by the broken line in the figure) on the male portion
3
of the assembly. In both cases, however, since the major transverse dimension of the circlip is disposed radially, significant radial clearance is required for installation and removal.
In the arrangement shown, the central longitudinal axis of the assembly is indicated by the dash-dotted line. In the assembled state, the circlip
1
inhibits relative axial displacement of the components
2
,
3
against the action of an axial force F in the direction of the arrow in the figure, for example due to pressure of gas in the cylinder. It can be seen that the circlip operates in shear, with the plane of its reaction surfaces generally at 90° to the force which the circlip is resisting. Under continuous, high axial load, the circlip can deform to shallow conical form. Differential coefficients of expansion of the male and female portions (or uneven heating of materials with the same expansion coefficient) can cause relative radial displacement of the male and female components resulting in increased conic deformation of the circlip due to the increased moment. This situation is illustrated in
FIG. 2
of the drawings. In this situation, pressure on the circlip is increased significantly since the load is applied to the circlip along the contact edges shown as points P in cross-section. The change of loading on the circlip during operation of the assembly is therefore substantial. Moreover, for the assembly to restore itself as the cylinder
2
contracts radially with reducing temperature, the work done against applied axial force for the edge P of the cylinder to ride up the inclined upper surface of the circlip in the figure is also significant. Even when the assembly reverts to its original temperature, the continuation of axial load, and the circlips conical inclination to the plane of restoration, can mean that, instead of restoration, racking loads lead to increased tensile load in the female component and increased compressive load in the male component.
The problems described above are common to both internal and external circlips and are exacerbated at large component diameters and for components with large expansion differentials These constraints mean that, for large diameter components and high axial loads, such as occur in a Stirling engine for example. conventional circlips are entirely unsuitable. The conventional alternative of fixing components with a ring of bolts also has numerous drawbacks such as high costs. potential access problems, and less than 360° pressure bearing.
SUMMARY OF THE INVENTION
According to the present invention there is provided a circlip comprising a band of material forming an incomplete ring, and having bearing surfaces, which are curved in transverse cross-section, at opposite ends of the major transverse dimension of the band, wherein the said major dimension is generally orientated at less than 90° to the central axis of the ring in the unstressed state of the circlip.
In accordance with the invention, therefore, the major transverse dimension of the circlip is at an angle of less than 90° to its central axis, in contrast to a conventional circlip as shown in
FIG. 1
where the major transverse dimension is parallel to the radial plane of the circlip and hence at 90° to its central axis. In embodiments of the present invention, therefore, the major transverse dimension of the circlip is orientated at an angle of less than 90°, and preferably a small acute angle, to the axial force which the circlip is intended to resist in the assembled state. The aforementioned angle may vary depending on the particular construction and application, and may be 0° in some cases (ie. major transverse dimension parallel to central axis). However, it is preferred that the angle is an acute angle greater than 0° and preferably less than about 45° and most preferably less than about 15°.
The curved bearing surfaces allow for reduced contact pressures and good articulation in use as discussed further below. Advantageously the bearing surfaces are part-circular in transverse cross-section. While concave bearing surfaces might be envisaged for some applications, it is preferred that the part-circular surfaces are convex. That is, the band is preferably provided with rounded sides at each end of its major transverse dimension. Further, while other arrangements may be envisaged, it is preferable for the bearing, surfaces to be continuous around the circumferential extent of the circlip.
Circlips embodying the invention may have various shapes in transverse cross-section. In a particularly simple construction, the transverse band cross-section has substantially straight, parallel major sides and is symmetrical about its major axis. It is to be appreciated however that curved, irregular or other non-symmetrical sections may be envisaged. In some embodiments, particularly if the circlip is nonmetallic, the band cross-section may be tapered on each side of its minor axis toward the bearing regions. In this case, the increased thickness of the mid-section of the band mav increase the compressive strength, ie. resistance to buckling, of the circlip. although such a construction is unlikely to be necessary in most practical situations.
The invention also provides apparatus for connecting of first and second members, which apparatus comprises: a male portion of the first member; a female portion of the second member for reception of the male portion of the first member: and a circlip as hereinbefore described, wherein the male and female portions have respective annular regions for abutting the bearing surfaces at opposite ends of the major transverse dimension of the circlip, whereby, in use, the circlip inhibits relative axial displacement of said portions tending to compress the circlip. Thus, applied force tending to cause relative axial displacement in a direction so as to compress the circlip is resisted. Since the circlips major transverse dimension is at less than 90°, and preferably a small acute angle, to its central axis, axial force applied to the assembly has at least a component, and preferably a major component, along the direction of the circlips major transverse dimension. The smaller the angle, the greater, proportionally speaking, the component of the force directed along the major dimension of the circlip, and hence the more effective the circlip in resisting that force.
The said annular regio
Kim Harry C.
Nixon & Vanderhye P.C.
Sustainable Engine Systems Limited
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