FIELD OF THE INVENTION

The present invention generally relates to a fixing arrangement for retaining a fixing element and a method of forming such fixing arrangement.

BACKGROUND OF THE INVENTION

A bushing, respectively a bush, is conventionally used in fixing arrangements of various components. The bushing is over-molded with plastic and defines a passageway for a fixing element, e.g. a rotatable screw, which allows fixing the component to a structure or other component.

A conventional bushing for a fixing arrangement is shown in Fig.lA. Reference sign 50 designates a metal bushing that has been formed by pressing and rolling a rectangular blank into a more or less cylindric form having a central axis A. A plurality of recesses/indents 52 are formed on the outer surface 54 of the cylindric wall 56 of the bushing 50 to improve anchoring in plastic. The bushing 50 also presents three notches 58, distributed around the bushing 14. The notches 58 are formed by stamping/punching, in such a way as to deform the bushing wall 56 and form protruding features 60 on the inside of the bushing 50 (see Fig.1 B). The protruding features 60 extend from the inner surface 62 of the bushing 50.

In Fig.1 B bushing 50 is seen from above, integrated in a fixing region of a component, e.g. a plastic housing of a component (e.g. an ignition coil). The bushing 50 is thus over-molded with plastic from the component’s casing and forms a fixing arrangement 1 . The central passage 64 in the bushing 50 forms a passageway for a fixing element such as a screw. The protrusions 60 permit retaining/holding a screw or like fixing element (not shown) introduced in the passageway 64 before assembly of the component. In this respect, Fig. 1 C illustrates a cross-sectional view of the bushing 50 in the plastic of the component of Fig.1 B. In Fig. 1 D a fixing element is inserted in the fixing arrangement of Fig.1 C. Despite the wide use of such fixing arrangements, it comprises a number of disadvantages. First of all, the manufacturing process of the bushing (rolling) leads to tolerance variations, since the bushing is not perfectly round/symmetrical. Furthermore, the fixing screw must be carefully introduced in the passageway in order to properly engage the screw threads on the protruding features 60, in such a way as to avoid damaging these threads (metal to metal interface). In this context, the positioning of the protruding features 60 must be adapted to the screw threads (helical positioning matching the thread pitch, which increases part diversity. This further requires rather small tolerances on the protruding features for the screw threads to pass, when rotating the screw.

OBJECT OF THE INVENTION

The object of the present invention is to provide an improved fixing arrangement that overcomes the above-mentioned disadvantages.

This object is achieved by a fixing arrangement according to the first independent claim and a method of forming a fixing arrangement according to the second independent claim.

SUMMARY OF THE INVENTION

The invention proposes a fixing arrangement for a component, wherein the fixing arrangement comprises: a bushing having a cylindrical wall longitudinally extending along a central axis and defining an axial through-bore. The fixing arrangement comprises a plastic body over-molding the bushing such that a passageway extending along the central axis is formed, which can accommodate a fixing element that may be engaged in the passageway. The fixing arrangement further comprises at least one retaining element in the passageway to, in use, engage the fixing element and hold it in the passageway. The at least one retaining element is made from plastic and integrally formed with the plastic body to protrude into the passageway.

The present invention is based on the finding that a specific arrangement of a bushing comprising one or more retaining elements made from plastic material eliminates the difficulties encountered with metallic protruding features. Indeed, with plastic retaining elements, a fixing element can be quickly pushed through the bushing passageway without risking being damaged, such that process time and/or tooling expenses may be significantly reduced in an industrial setting. In addition, there is no need to slowly and carefully rotate the fixing element.

The fixing element is thus retained temporarily in the passageway, in an intermediate position referred to as pre-assembled state.

The invention hence takes advantage of the injection molding process that is used for creating / forming the plastic body, to also form one or more retaining elements inside the bushing. The plastic retaining elements are thus normally formed in the same injection molding stage as the body of the fixing arrangement, which over-molds/surrounds the bushing itself. The thus formed retaining elements can be formed with precise dimensions, to compensate the possible larger tolerances of the bushing. In addition, they have the resilience/flexibility of plastic, so that they will engage and deform in contact with a fixing element introduced in the passageway (providing force-fit or form fit), with the ability of holding the fixing element without risk of damage.

"Fixing arrangement" as used herein generally relates to an arrangement of a bushing encapsulated in a plastic body. The fixing arrangement may be generally part of a component, where the fixing arrangement forms a fixing region of that component, for fixation to another component such as e.g. a structure, a chassis, and engine block. The plastic body of the fixing arrangement can be molded together with the plastic portion (body / portion / housing /casing) of the component to which the fixing arrangement is integrated.

"a plastic body over-molding said bushing" generally refers to the fact that the bushing is encapsulated/embedded in plastic. The term ‘over-molding’, respectively over molding or overmolding, should be taken in its broadest sense, meaning that upon plastic injection the bushing is surrounded by (coated with) plastic, in intimate contact therewith. The over-molding is however carried out to keep a passageway along the central axis of the bushing, to receive the fixing element. The bushing may generally be made from metal, e.g. steel, aluminum (alloy) or brass. This provides mechanical strength for the fixing arrangement.

The bushing can be cut from a metal tube. Alternatively, the bushing can be rolled from a sheet metal (blank). The bushing has a cylindrical wall extending along the central axis. The cross-section of the cylinder may generally be circular, although other cross-sections can be envisaged. It should be noted that depending on the forming process, the bushing may not be entirely cylindrical, and/or circular at each point.

"Retaining element" generally refers to a flexible/resilient constructional element formed of plastic. The retaining element is configured to retain, respectively to engage with a fixing element and to hold said fixing element in the passageway. The retaining elements are normally made from the same plastic as the body (also referred to as case plastic). Furthermore, the retaining elements are advantageously integral with the plastic body. "Integrally formed" generally refers to a connection or to a case wherein two elements, such as e.g. the retaining element and the plastic body, are formed in one piece, e.g. by injection molding. In such arrangements, the plastic body may provide a secure anchoring/connection for the retaining element and keeps said retaining element in place when a fixing element is inserted into the bushing. There may be a plurality of retaining elements arranged within the passageway. The shapes may also vary. Although the use of annular and/or rotationally symmetrical shapes are easier to implement, the invention is not limited thereto. The retaining elements can extend over part of the internal periphery of the passageway, or over the entire circumference. They can be arranged at the same or different levels. Their shapes can be similar or different. In general, the number, dimensions and shapes of the plastic retaining elements will be designed for a particular use, i.e. for a particular type or range of fixing elements.

"Passageway", respectively central passage, generally refers to a space within the bushing, wherein the passageway is configured to hold and/or accommodate a fixing element. The passageway may be smaller than the through-bore of the bushing. The retaining element is arranged in the passageway in order to engage with the fixing element and to hold it in the passageway.

In embodiments, the bushing comprises at least one through-hole extending through the cylindrical wall, wherein the through-hole is configured to allow plastic to flow therethrough during molding, whereby the at least one retaining element is integral with an outer plastic layer of the plastic body surrounding the bushing through the at least one through-hole. The through-hole thus allows plastic to flow inside the bushing and provides a secure fixing for the retaining element. Generally, a plurality of such through holes may be peripherally distributed to provide support around the bushing. It should be noted that the term "through- hole" may generally refer to a hole, an opening or a slot or a similar structure. Through-hole may also refer to the axial slot where the bushing is formed as a rolled metal sheet.

In embodiments, an over-molded inner plastic layer covers an inner surface of the bushing. The at least one retaining element extends from this inner plastic layer and is integral therewith.

Such inner plastic layer with the retaining elements can be formed with a simple/plain bushing, without trough-holes in the cylindrical wall. In such case, the molten plastic is flown from the interior of the bushing and the inner plastic layer may not integral with the outer plastic body (case plastic) through the wall of the bushing.

From a manufacturing point of view, it is however advantageous to use a bushing with through holes at the level of the retaining elements, to facilitate flow of plastic to the interior of the bushing. Through holes in the bushing wall at other levels will also help in that respect. As a result, the inner plastic layer is integral with the outer plastic layer forming the body, and so is/are the retaining element(s).

In embodiments, the at least one retaining element is formed as an annular tongue protruding inside the passageway. This tongue thus forms a ring-shaped projection or protrusion in the passageway, in particular projecting towards the central axis. The annular tongue may have a ring-like form. The tongue may be configured to generate a form-fix and/or force-fix connection with a fixing element. In embodiments, the annular tongue has a radially inwardly tapering profile. In other words, the tongue may be arranged concentrically around the central axis whilst protruding towards said central axis.

In embodiments, the bushing comprises a plurality of recesses / indentations on its outer surface, which will fill with plastic during injection molding and thus improve anchoring of the bushing in the plastic body. Such recess(es) may also be provided on the inner surface of the bushing to improve anchoring with an inner plastic layer.

The plastic body and retaining elements may be made from any appropriate synthetic material, herein referred to as plastic. In particular, any appropriate polymer can be used, which is suitable for injection molding and has desirable properties for the application. For example, PET or PBT may be employed.

According to another aspect, the invention also concerns a method of forming/producing a fixing arrangement.

The method comprises the steps of: providing a bushing having a cylindrical wall longitudinally extending along a central axis and defining an axial through-bore; positioning the bushing in a mold; injecting plastic into said mold to form a plastic body over-molding the bushing while leaving a passageway extending along the central axis, which can accommodate a fixing element;

It shall be appreciated that two opposite core pins are inserted in the mold into the bushing’s through-bore, the ends of the core pins being configured to define, together with the inner surface of the bushing, one or more cavities to form, upon plastic injection, one or more plastic retaining elements protruding in the passageway.

“Positioning the bushing in a mold” refers to the act of inserting / arranging the bushing as an insert element into a plastic injection mold. The positioning can be done manually or automatically (with a robot). The core pins are inserted in the bushing to prevent its filling up with plastic and, according to the invention, form the plastic retaining elements. In embodiments, the core pins have a diameter substantially equal to that of the bushing, whereby no plastic layer is formed on the inner surface of the bushing. Alternatively, the core pins may be dimensioned smaller than the through-bore (in terms of diameter / cross-section).

The core pins remain within the through-bore during the plastic injection and are extracted after the molten plastic has cooled down and formed the retaining element and the plastic body. The shape and configuration of the cooperating ends of the core pins define the shapes and dimensions of the one or more retaining elements. In the context of the invention, the retaining element(s) is/are designed to present a form that resiliently engages with a fixing element. In other words, the retaining element may thus provide a form that is configured to retain to a portion of the fixing element.

The bushing and/or mold are advantageously configured such that the plastic retaining element(s) is/are integral, respectively integrally made, with the plastic body. This can be done by providing apertures / through-holes in the bushing wall, or by providing flow features in the mold to allow plastic flowing inside the bushing.

In embodiments, the bushing includes one or more though-holes extending through its cylindrical wall, the core pins being positioned so that their respective ends are in the vicinity of the trough holes, whereby during plastic injection, molten plastic flows through the through-hole(s) into the one or more cavities. As a result, the at least one retaining element is integral with an outer plastic layer of the plastic body surrounding the bushing through the at least one through-hole.

In embodiments, during plastic injection, an over-molded inner plastic layer is formed on the inner surface of the bushing, whereby the at least one retaining element is integral with the inner plastic layer.

In embodiments, the ends of the core pins are configured to define an annular cavity, whereby the retaining element takes the form of an annular tongue protruding inside said passageway. For example, the ends of the core pins may be configured to define a wedge-shaped annular cavity, whereby the annular tongue has a radially inwardly tapering profile.

According to a further aspect, the invention concerns a fixing arrangement for a component, wherein the fixing arrangement comprises: a bushing having a cylindrical wall longitudinally extending along a central axis (A) and defining an axial through-bore; a plastic body over-molding the bushing such that the bushing is sandwiched between an outer plastic layer and an inner plastic layer, the inner plastic layer defining a passageway extending along said central axis (A); a fixing element, preferably a screw, engaged in said passageway; characterized in that the inner plastic layer has a wall thickness adapted to engage with the fixing element such that it is temporarily held in the passageway in a pre-assembly state.

This second aspect solves the same problem as the first embodiment, taking advantage of plastic material inside the bushing to interact with the fixing element received in the passageway. The inner plastic layer is dimensioned so that a portion of the outer periphery of the fixing element (e.g. threads of a screw) is in contact with the inner surface of the inner plastic layer. The fitting is such that there is a slight friction or slight engagement between the fixing element and plastic inner layer, sufficient to retain the fixing element in place, but such that the fixing element can normally be moved by exerting a force by hand or by tooling. The fixing element is thus held in place inside the over-molded bushing, for the purpose of assembly.

With such inner plastic layer (without retainer element), a very precise and precisely located passageway can be obtained, even with bushings having relatively large tolerances.

The inner plastic layer may have a generally flat surface defining the passageway, typically of substantially constant diameter. In embodiments, the inner plastic layer entirely covers an inner surface of the bushing. Alternatively, the inner plastic layer extends over only part of the length of the bushing.

In embodiments, the inner plastic layer has a tight tolerance so that there is a tight contact and/or slight engagement with the fixing element.

The bushing may comprise at least one though-hole or other aperture extending through the cylindrical wall, wherein the through-hole / aperture is configured to allow plastic to flow therethrough during molding. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are now described by way of example and with reference to the attached drawings, wherein

Fig.1 illustrates (A) a perspective view of a prior art bushing and (B) a top view of the bushing overmolded with plastic in a fixing arrangement of a component; (C) illustrates a cross-sectional view of the prior art bushing as illustrated by (A) without a fixing element; (D) illustrates a cross-sectional view of the prior art bushing as illustrated by (A) with a fixing element;

Fig. 2 illustrates a section of an over-molded bushing according to an embodiment, wherein the bushing presents through-holes and a retaining element;

Fig. 3 (A) is a detailed view of detail C of Fig. 2; (B) is a further detailed view of detail C of Fig. 2; (C) illustrates a schematic principle view of (B) when a fixing element is inserted in the bushing; Fig. 4 is a cross-sectional view of a fixing arrangement according to a further embodiment of the invention;

Fig. 5 is a cross-sectional view of a fixing arrangement according to a further embodiment of the invention;

Fig.6 is principle sketch showing the core pins in the bushing, in position in within the mold before and during plastic injection; and Fig.7 is a perspective view of a non-circular bushing.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 2 illustrates a cross-sectional view of a fixing arrangement 10 according to an embodiment of the present invention, wherein the fixing arrangement 10 is part of a component 12. The shown fixing arrangement 10 constitutes a fixing region of the component. Initially, the fixing arrangement is used to hold a threaded screw (not shown) within the bushing 14, wherein the screw may be longer than the bushing. A tip portion of the thread may be engaged into another component or structure, such as, for example, a chassis or a motor block of a vehicle (not shown).

As can be derived from Fig. 2, the fixing arrangement 10 comprises a bushing 14 with a substantially cylindrical wall 24 which extends longitudinally along a central axis B. The bushing 14 has a cylindrical wall 24 which defines, respectively delimits, an axial through-bore 15. The bushing 14 is embedded into a plastic body 16 as a result of injection molding. The bushing is thus over-molded with plastic material. This plastic body 16 forms part of the component 10 (e.g. integral with the plastic casing/housing of the component). It should be noted that the plastic body 16 may be likewise arranged on, or fixedly mounted to, the component 10. The molding step is carried out such that the interior of the bushing is not filled with plastic, whereby a passageway 18 extending along the central axis B is formed.

The passageway 18 is configured to hold, respectively to accommodate the fixing element (not shown). One retaining element 20 made from plastic is provided in the passageway 18. During an insertion of a fixing element, such as a screw, the fixing element is pushed through the passageway 18 and the retaining element 20. Since the retaining element 20 is made of plastic, the retaining element 20 can engage the fixing element and hold it in place in the passageway 18, without damaging the fixing element. In consequence, the fixing element may be pushed quickly through the passageway. It is thus not necessary to slowly rotate the fixing element into the fixing arrangement as would be the case with the bushing 50 of Fig.1 .

As can be further derived from Fig. 2, the retaining element 20 is made materially integral with the plastic body 16. In other words, the plastic body 16 and the retaining element 20 are formed as one piece. Indeed, the retaining element 20 is formed together with the plastic body 16 by injection molding.

It may be noted that the bushing 14 comprises at least one opening, respectively a through-hole 22 extending through the cylindrical wall 24. In practice the bushing 14 may include a set of through holes 22 (e.g. 2, 3 or 4) that are arranged at the same level along the bushing 14 and distributed peripherally. The through- holes 22 are used to allow molten plastic to flow therethrough during the injection molding step. Due to the through-holes 22 the retaining element 20 is integral with the outer plastic layer 26 of the plastic body 16 surrounding the bushing 14. In other words, the retaining element 20 and the plastic layer 26/body 16 are formed as one single piece.

It should be noted that a bushing 14 may present a plurality of through-holes 22 on different locations. Also, a plurality of retaining elements 20 may thus be formed at different locations within the axial through-bore 15.

As can be further seen in Fig. 2, as well as in more detail in Fig.3A, the retaining element 20 is formed as an annular tongue (or ring). The annular tongue 20 projects from the inner surface 30 of the bushing 14, hence protruding inside the passageway 18. The annular tongue 20 extends over the whole inner circumference and has a profile that tapers radially inwardly towards the central axis B. This is also illustrated as a cross-sectional view in Fig. 3B. The tapering profile is convenient as it can easily engage and be deformed by a fixing member introduced into the passageway 18, as a result of, e.g., form-fit, force-fit, interlocking or interference. Fig. 3C shows a screw 50 engaged in the passageway and retained therein by friction forces due to resilient deformation of the retaining element 20.

It should be noted that in alternative embodiments, the annular tongue may present a different form, such that e.g. the annular tongue may extend over a part of the merely partially along the inner circumference, have a different cross- section or be formed as a plurality of segments.

From the manufacturing point of view, the retaining tongue 20 is formed by means of a pair of opposite core pins 40, 42 introduced inside the bushing 14 in the injection mold. Fig.6 shows the two core pins 40, 42, respectively introduced from below and above, in position for injection. As can be seen, the respective ends of the pins 40, 42 meet approximately at the level of the through holes 22. The interface between the pin ends forms a wedge-shaped annular cavity 44 in front of the though holes 22. In this embodiment, the bottom pin 40 end face is flat, whereas the end face of the opposite pin 42 has an annular chamfer, hence providing this wedge shape. During injection, the molten plastic will flow from outside the bushing 14 through though-holes 22 into the annular cavity 44, hence forming the annular tongue 20.

Fig. 4 illustrates a cross-sectional view of a fixing arrangement 10 according to a further embodiment of the invention. Contrary to the embodiment illustrated in Fig.2, the bushing 14’ here includes two sets of through holes 22 at two different levels: three through-holes 22 (of which two are visible in fig. 2) in an upper region and three through-holes 22 (of which two are visible) in a lower region. As can be derived from fig. 4, the retaining member 20 has only been formed in the upper region of the bushing 14. It should be noted that the term "upper" generally refers to an end portion of the bushing 14. In fig. 4, the upper region corresponds also to an upper section of the figure. In alternative embodiments (not shown), the retaining member may be formed in a lower region of the bushing.

It may be noted that the two sets of through holes 22 are arranged at the same distance from the bushing extremities. Accordingly, the bushing 14’ can be introduced into the injection mold without paying attention to the orientation of the bushing (top/down). The position and shape of the retaining feature is determined by the mould.

Fig. 5 illustrates a cross-section through a perspective view of a further embodiment of a fixing arrangement 10 having an over-molded inner plastic layer 28 that covers an inner surface 30 of the bushing 14”. The inner plastic layer 28 is useful in that, compared to a rolled bushing, the geometry and/or the position in the fixing arrangement can be precisely defined. In this embodiment, the inner plastic layer 28 has a smooth inner surface- defining passageway 18, and of constant diameter (except for retaining element). The inner plastic layer 28 may generate friction with a fixing element inserted therein. In other words, due to the inner plastic layer 28, the engagement between a fixing element and the fixing arrangement may further be enhanced. In order to form the inner plastic layer 28, a plurality of through-holes 22 extend through the cylindrical wall 24. The through holes 22 are placed at an upper section, a middle section and a lower section of the bushing 14

The retaining element 20 (again an annular tongue) is formed at the through- holes of the middle section of the bushing 14”. However, it should be noted that in alternative embodiments, the annular tongue may also be formed at different locations, e.g. locations in vicinity to the through-holes or further away from said through-holes.

This is obtained by positioning the core pins such that the interface is at the height of the center through holes 22. It may also be noted that the core pins should have a smaller diameter than those shown in Fig.6, to allow room for the plastic forming the inner layer 28. The plastic will flow through the various through holes and/or from above/below the bushing.

As it will be understood, the provision of 1 or more through holes at several axial positions also allows providing the retaining element(s) 20 at different axial positions with the same bushing, by simply adapting the position of core pins in the mold (aligning the end faces with the desired through holes).

It may be noted that while in this embodiment and previous embodiments, the through-holes 20 are shown to be perpendicular to the central axis, they may have an orientation angled in respect to the central axis. The through-holes 22 are generally configured to conduct a flow of molten plastic therethrough onto the inner surface 30 of the bushing 14 during molding. Due to this arrangement, the retaining element 20 as well as the uniform plastic layer 28 can be formed. As can be derived from Fig. 5, the retaining element 20 is integral with the inner plastic layer 28. However, via the through-holes 22, the inner plastic layer 28 is likewise integral with the outer plastic layer 26 of the plastic body 16, which embeds, respectively surrounds, the bushing 14. In embodiments, the inner plastic layer 28 may have a thickness in a range of 0.2 mm to 1.00 mm, for example 0.3 mm to 0.7 mm, or between 0.4 mm to 0.6 mm. These are only exemplary values and should not be construed as limiting; depending on the application, the dimensions may vary considerably.

As can be derived from Fig. 7, a bushing 14’” may be provided with a cylindrical- like shape, wherein said cylindrical like shape yet has several "unround" portions, respectively non-circular sections, at its inner or outer perimeter. As shown in Fig. 5, the inner plastic layer 28 may form an inner wall generating a very precise and precisely located passage 18, even if the bushing is non-circular such as the bushing 14’” shown by Fig. 6. In other words, since the bushing 14”’ is over molded, and since this over-mold creates also the inner plastic layer 28, said inner plastic layer 28 may compensate the irregularities of the non-circular bushing, such that a precise passageway 18 may be formed.

According to another aspect of the invention, a fixing arrangement, not represented in the figures, comprises a bushing 14 as described above, with or without holes/openings, which is over-molded such that the bushing is sandwiched between an outer plastic layer 26 and an inner plastic layer 28, the inner plastic layer 28 defining a passageway 18 extending along the central axis A. This further embodiment is similar to that of Fig. 5, but there is no retaining element 20. Here however, the inner plastic layer 28 has a wall thickness adapted to engage with the fixing element such that it is temporarily held in the passageway in a pre-assembly states

The idea is that a fixing element, such as a screw, is held in place by engaging the outer periphery of the fixing element, e.g. the screw threads. By providing a tight fitting, the screw may slightly engage the plastic inner surface of the inner layer 28. The screw may be simply inserted into the passageway, by exerting a slight axial force or by screwing. The screw threads will press against or slightly cut into the inner surface of the inner plastic layer 28.

It may be noted that in this last embodiment, or in the embodiment of Fig.5, the plastic molded inner layer is advantageous in that it allows forming a precise and precisely located passageway 18, even with an irregular bushing. Indeed, the inner diameter of inner plastic layer 28 (here constant diameter in both embodiments) and position of the passageway 18 are defined by the injection mold.