Patent Description:
A screwboss is a common solution to ensure correct positioning of a metal self-tapping screw into a plastic hole. A typical example of a screwboss, alternatively termed a screw post or stalk, comprises a cylindrical body made from a deformable plastics material with a hole (e.g. a blind bore) formed at its central axis to receive a self-tapping screw. The body is formed to be upstanding from and integral with a support surface/base and may include two or more ribs radiating from the central axis that provide additional stability for mitigating lateral movement and absorbing twisting forces applied to the body relative to its support surface while a screw is turning into the hole.

In use, one or more separate component elements may be secured by virtue of their own through holes aligning with that of the screwboss and a self-tapping screw compatible with the hole dimensions being introduced through both the component(s) and into the boss. By virtue of a harder material (e.g. metal) the screw thread bites into the plastic inner wall of the hole and is drawn thereinto. The hole may have surface features (e.g. bevels/internal ribs) for guiding the screw or be relatively smooth, but it is always deeper than the length of the screw, so as it accommodate the screw shaft fully up to its head when components are in place. The deformable wall of the hole/body may marginally expand to accommodate the screw, further reinforced by the radial ribs.

A screwboss serves to separate component surfaces by virtue of its body height and mounts said components securely in place, often for the lifetime of the assembled product. However, a self-tapping screw is removable by turning in a reverse direction of the screw thread and thereby withdrawing it from the hole. As such, component elements of a product can be disassembled if required.

A screwboss is subject to torsion forces as the self-tapping screw is engaged. Design of the screwboss must therefore account for being able to withstand these forces, traded off against material (e.g. plastics, alloy, aluminium) use in manufacturing the component. Particularly, the relative resilience of the screwboss to torsion forces will affect the speed at which a screw can be screwed into its hole, thereby having an impact on the overall cycle time for assembling a component/product, which may have multiple screwbosses integrated therewith. Ribs are provided as a support structure and also contribute reinforced strength to the boss and its ability to expand to accommodate a screw. It is known to skilled persons that if an excessive torque force is applied, e.g. due to high speed screwing, then a screwboss can fail. Examples of screwbosses known in the field include: <CIT> and <CIT>.

In light of the above, the present invention seeks to address shortcomings associated with known screwboss structures and proposes an improvement, particularly a solution that may enable a reduction in cycle time/increase in turning speed of a screw for an equivalent or reduced materials usage during manufacture.

A first aspect of the invention is outlined according to claim <NUM> of the appended claims. For example, a screwboss may be comprised of: a base; a main body, upstanding from the base, having an external sidewall and an opening for fixing a screw threaded element thereinto; and a plurality of ribs, each spanning between / adjoining the base and main body; wherein at least one rib of the plurality of ribs extends from a location on the external sidewall parallel with but angularly offset from a normal radial line taken from a centre of the opening. The offset may be at least a half thickness of a rib from the radial line. The rib, at the point it is connected to the boss sidewall, is positioned to extend parallel tc the radial line offset toward (which includes coinciding with or beyond) a parallel tangent line from the opening for fixing a screw, so as to be offset from the normal radial line it is parallel with.

In this way, the screwboss of the invention has the effect of providing an alternative rib location to better accommodate the torque forces created by self-tapping screws and, hence, enable a potentially increased speed of screwing. Thereby, the problem of slow cycle time during screwing into plastic is solved, e.g. by offsetting where a rib is attached to the body to be located to one side of an imaginary radial line taken from the hole/boss centre, exactly where the forces distributed during self-tapping are found.

By virtue of the novel structure disclosed herein, ribs are located at a place where forces are best distributed in order to correctly enforce the screwing process. The boss body maintains a freedom to expand while reinforced by the ribs, thereby resulting in decreased cycle time and/or reduced chance of breakage/failure of the boss.

In conventional designs, supporting ribs are arranged radially in a uniform cross configuration from a centre of the screw-hole, whereas ribs of the invention are offset from that normal radial position taken from a centre of the fixing opening. The offset may be either counter-clockwise or clockwise. In one form the rib offset from a normal radial line is counter/anti-clockwise, to account for a clockwise screw direction as is most common. However, the configuration would be reversed to a clockwise offset for an intended lefthand screw direction.

Preferably an entire thickness of a rib is outside the radial line from the centre, but at least begins parallel thereto. A rib thickness may be approximately equal to a diameter of the opening, but any suitable dimensions are contemplated.

Each rib is typically of a uniform shape with other ribs, but different rib configurations/shapes are possible.

Furthermore, a rib may be configured to taper outwardly from a connecting position at the body's sidewall distant from the base, toward the base. In other words, the ribs are wider where connected at the base than where connected further up the main body. Outward tapering of a rib may be either in the longitudinal direction of the upstanding body or radially from the body, or both. In the case of a radial taper or draft angle design, reinforcement at upper portions of the boss is minimised for less resistance to screw forces, compared to at the base where the upstanding main body must be supported from breaking off laterally during finalisation of the screw cycle and for a lifetime of the assembled product. Torque is greatest at the end of the cycle where a screw head abuts the main body and is prevented from further entry into the hole.

A height of the main body may be determined by assembly parameters, particularly the length of screw that is to be inserted/fixed into the hole. The depth of receiving hole is preferably beyond total invasive length of a screw shaft, taking into account the thickness of component elements secured to the boss.

In practice the screwboss is formed in one piece such that the base, body and ribs are integrally formed and made from a continuous piece of material, e.g. by injection moulding, however, co-moulding or other manufacturing methods may be possible. The screw boss may be formed from plastics, metal (e.g. aluminium) or other flowable/mouldable material.

The screwboss may be aligned for mounting and securing various components or sandwiches of multiple components, e.g. a PCB alone or with a cover plate, that is screwed to a base component which featuring an upstanding screwboss according to the invention.

Preferably, an upstanding leading edge of an outside face of the rib, where it is connected to the side wall, extends approximately <NUM> degrees from an imaginary line normal to the sidewall, to optimally provide support resisting the torque force applied by a turning screw during assembly and for a final torque applied to hold components in place. As mentioned, such a configuration is able to accommodate faster screwing speeds at the beginning and during the screwing cycle for the same material use as conventional radial ribs.

In an alternative expression of the invention, a plane (e.g. a central plane) of the rib is approximately tangential to an edge of the screw-receiving opening or between a tangent of the opening and a tangent of the main body. In other words, at least part of the thickness of the rib, where it connects with the boss side wall, is tangential or overlaps with a tangential line from the opening. In this way, forces developed at the wall of the opening, where a screw thread contacts the wall and applies force, are transferred evenly to the rib.

Broadly, the invention is embodied by a screwboss comprised of: a base; a main body; an opening into an end of the main body, distal from the base, for fixing a threaded fastener thereinto; and at least one rib, adjoining the base and main body, to support the main body in an upstanding position; wherein the at least one rib extends from the main body at a position in line with a tangent line from the opening. The rib position should be interpreted as anywhere between a tangent line from the opening to a tangent line of the main body.

The tangent line coincides within a thickness of the at least one rib. In one form, the at least one rib is parallel and offset to the side of a radial line extending from a centre of the opening.

Preferably, the at least one rib is tapered inwardly in a longitudinal direction from the base toward the main body. Alternatively, or in addition, the at least one rib may extend outwardly from the main body, with a draft angle.

Preferably, the at least one rib may comprise a plurality of ribs, each at a position in line with a tangent line from the opening. Each rib of the plurality of ribs may radiate at an even spacings about the main body.

Preferably, the screwboss is configured for a right hand screw threaded fastener, wherein the at least one rib is offset in a counter-clockwise direction from the radial line.

Preferably, the at least one rib is offset far enough so as not to overlap with the radial line.

The invention extends to a component incorporating a screwboss according to any desirable feature herein, e.g. configured for use in assembly of a vehicle.

The invention further extends to a method for mounting a first component part to a base component part, according to claim <NUM>, e.g. in a vehicle.

Preferably there are four ribs, however, the solution may suffice with one rib, especially if the boss body is set into the corner of a component. Two, three or five or more ribs may also be appropriate depending on space constraints and scale of the boss.

In an alternative expression of the invention, a screwboss is provided where each of a plurality of ribs is parallel with but offset from a directly radial line taken from a centre of the screw boss.

The invention is applicable not just to self-tapping screws but also threaded members such as bolts. In these cases, a corresponding thread may be tapped/moulded into the receiving hole. Torque forces are still developed in such an arrangement, especially at the end of the cycle when a fastener may be set at a desired torque to hold a component in place.

Illustrative embodiments will now be described with reference to the accompanying drawings in which:.

The following description presents exemplary embodiments and, together with the drawings, serves to explain principles of the invention. However, the scope of the invention is not intended to be limited to the precise details of the embodiments or exact adherence with all features and/or method steps, since variations will be apparent to a skilled person and are deemed also to be covered by the description. Terms for components used herein should be given a broad interpretation that also encompasses equivalent functions and features. In some cases, several alternative terms (synonyms) for structural features have been provided but such terms are not intended to be exhaustive. Descriptive terms should also be given the broadest possible interpretation; e.g. the term "comprising" as used in this specification means "consisting at least in part of" such that interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. Directional terms such as "vertical", "horizontal", "up", "down", "sideways", "upper" and "lower" are used for convenience of explanation usually with reference to the orientation shown in illustrations and are not intended to be ultimately limiting if an equivalent function can be achieved with an alternative dimension and/or direction. Indeed, in the present case a term such as "horizontal" axis or "vertical" axis can be affected by the orientation imposed on the screwboss structure. Therefore, all directional terms are relative to each other.

The description herein refers to embodiments with particular combinations of steps or features, however, it is envisaged that further combinations and cross-combinations of compatible steps or features between embodiments will be possible.

It will be understood that the illustrated embodiments show applications only for the purposes of explanation.

<FIG> outlines a series of views from various perspectives of a screwboss <NUM> according to the invention. Screwboss <NUM> is generally comprised of a base <NUM> (which will in practice be part of a larger component element than that illustrated), an upstanding main body <NUM> and a plurality of ribs <NUM>.

In the illustrated form, main body <NUM> is generally cylindrical in shape, although it may have other elongate forms, and features a central opening <NUM> for receiving a screw fastener. In the illustrated example, the opening has a bevelled edge or annular inset, but otherwise has smooth walls down to a specified depth (e.g. seen in <FIG> example). In principle the opening may be all the way through body <NUM> and base <NUM>, but is more likely a blind bore that at least leaves an open space beyond the distal end of a screw.

As best seen in the plan views of <FIG>, each rib <NUM> extends away from a side wall of body <NUM> in a position that is parallel but offset to a radial line (R) taken from a central axis (X) of the opening/body. In this way, ribs extending from opposite sides of the body <NUM> are not aligned and appear offset from one another. Yet, in the illustrated form with four ribs, the offset between adjacent ribs is still ninety degress as it would be for a regular cross configuration, as shown by <FIG>. Ribs are shown with even spacing therebetween.

With reference to <FIG>, a desirable position of a rib according to the invention can be described in several ways. Firstly, a central plane P of a rib <NUM> is shown as parallel to and offset from a radial line R, e.g. by more than half a thickness of rib <NUM>. Secondly, central plane P of rib <NUM> is substantially tangential to a wall of opening <NUM> where, in use, a screw fastener would contact the boss body <NUM> and apply force thereto, e.g. in a clockwise direction assuming a common right hand screw thread. A directional force line F is shown in <FIG>, resulting from a torsion force T caused by rotation of a screw fastener. Thirdly, an upstanding leading edge of an outside face of the rib, where it is connected to the side wall <NUM>, begins approximately <NUM>-<NUM> degrees from the centre axis X of the hole. In all explanations, the position of the rib <NUM> optimally provides support for resisting the torque force F applied by a turning screw during assembly and for a final torque applied to hold a component in place.

In general, it is apparent that rib <NUM> is offset to one side of radial line R and not overlapping therewith. At the point where rib <NUM> is connected with body <NUM>, it extends from and overlaps with a tangent of opening <NUM>. Any part across the thickness of a rib <NUM> may coincide with a tangential line from the hole/opening <NUM>. According to <FIG>, the centre plane P coincides with tangential line G.

The embodiment of <FIG> features four ribs <NUM> in the form of right angle triangular wedges, where the right angle corner is located at the join between base <NUM> and upstanding main body <NUM>. The thickness is uniform, although alternative configurations are possible.

<FIG> illustrates an alternative embodiment of screw boss <NUM> where a rib <NUM> is configured to taper with a draft angle outwardly from the main body <NUM>, toward base <NUM> where the rib is thickest. Indeed, in some embodiments body <NUM> may be independently tapered outwardly from the opening end <NUM> toward the base <NUM>. A draft of the type illustrated may assist with removal from an injection moulding tool, without significantly affecting its strength for accommodating torsion forces. As shown in the plan view of <FIG>, the positional arrangement of ribs <NUM> is otherwise analogous to that of <FIG>, <FIG>.

<FIG> illustrates a variation of the embodiment of <FIG>, where the effective upstanding height of body <NUM> is reduced. However, the function and position of ribs <NUM> remains the same. Any embodiment of the screwboss may have a height tailored to the length of screw needed for securing a component or to provide clearance or surface features on a component.

<FIG> illustrates a variation where substantive external surfaces of the rib <NUM> are at positions approximately in line with a tangent line G from the opening and a radial line R from the centre axis X respectively. As before, rib <NUM> is generally offset from and parallel with the radial line R, but now with a thickness that is approximately equal to the radius of the opening <NUM> (i.e. half the diameter). This may exemplify an optimum position for a rib which uses less material but is best positioned for absorbing torque forces from a screw. It is noteworthy that, for all embodiments, a rib begins to extend from a position in line with (i.e. with any part of its thickness overlapping or at least an external surface in line with) a tangent to the opening, but an end of the rib distal from its connection to the main body may deviate from a straight line. A rib could be curved so long as it begins at a tangential position.

<FIG> illustrates a cross section view of an assembled product/component where a (e.g. self-tapping) screw fastener, having a threaded shaft <NUM> and head <NUM>, has been driven into the blind hole <NUM> of a boss body <NUM>. Head <NUM> is generally rotated into engagement by a tool at a predetermined torque force, where shaft <NUM> passes through aligned openings of one or more component flanges <NUM> and <NUM>. It will be apparent that flange layer <NUM> (e.g. a PCB) is mounted in contact with screw boss <NUM> so as to distance electrical components on its surface from undesirable contact with a base (not shown) of the boss or a cover component <NUM>.

While not easily visible in <FIG>, outwardly extending ribs of the invention are arranged to accommodate the torque force as shaft <NUM> engages and drives into hole <NUM> and at conclusion of the screw cycle where head <NUM> contacts the components (<NUM>, <NUM>) being secured.

<FIG> illustrates a plan view of base component <NUM> incorporating a boss <NUM> and rib structure <NUM> as described above. Ribs <NUM> may be incorporated with other strengthening ribs of the base <NUM>. In a case where boss <NUM> is located in the corner of a component, upstanding side walls extending from base <NUM> may provide a supporting function with a variation in size and/or number of supporting ribs according to the invention.

In consideration of the above, the improved rib structure is configured for mitigating forces applied during driving of a screw into a boss. Cycle time during the screwing process may be reduced. Assuming a similar amount of materials used in constructing the boss <NUM>, heat generation during screwing is expected to remain the same, or a bit higher due to faster screwing.

Claim 1:
A screwboss (<NUM>) comprised of:
a base (<NUM>);
a main body (<NUM>);
an opening (<NUM>) into an end of the main body (<NUM>), distal from the base (<NUM>), for fixing a threaded fastener (<NUM>) thereinto; and
at least one rib (<NUM>), adjoining the base (<NUM>) and main body (<NUM>), to support the main body (<NUM>) in an upstanding position;
characterized in that the at least one rib (<NUM>) extends from the main body (<NUM>) at an offset position coinciding with a tangent (G) from the opening (<NUM>) and toward a radial line (R), parallel with the tangent (G), from a centre axis (X) of the opening (<NUM>).