Patent Application
20100014792
This invention relates generally to automotive suspension struts and, more particularly, to arrangements for seating a suspension spring against a ring bearing at the upper end of the strut.
A typical automotive suspension strut assembly includes a suspension spring and shock absorber supported at their bottom end by an associated wheel and engaged with the vehicle chassis at their upper end so as to suspend the vehicle chassis over the wheel. The chassis can be supported on the suspension spring by way of an annular bearing with a spring seat disposed underneath the bearing to receive the suspension spring. To reduce the transmission of vibration and noise through the spring to the chassis, a rubber isolator is typically added at the surface of the spring seat so that the suspension spring directly engages the isolator rather than the spring seat itself.
The rubber isolators commonly used are a separate component assembled in place by hand as a part of the overall strut assembly process. Typically, the isolator is held in place due to a portion of the weight of the vehicle being applied through the bearing and spring seat which presses the isolator against the spring. Being a separate component, vibrations arising from use of the vehicle can travel up the strut assembly causing the isolator to roll out or otherwise work itself out of position. Thus, there is a need for a spring seat and isolator arrangement for suspension strut assemblies that can provide better retention of the isolator in place while simplifying assembly of the strut assembly itself.
In accordance with one aspect of the invention, there is provided a ring bearing assembly for use with a suspension spring in an automotive suspension strut. The bearing assembly includes a bearing, spring seat, and isolator that is positioned within the spring seat such that it fits between the spring seat and a suspension spring of the vehicle. The spring seat has an exterior surface having a mechanical retention feature. The isolator has an interior surface in contact with the exterior surface of said spring seat, and the isolator includes a complementary retention feature at its interior surface that mates with the mechanical retention feature to thereby help maintain the isolator in position in the spring seat.
In accordance with another aspect of the invention, there is provided a ring bearing assembly that includes a bearing, spring seat, and an isolator molded in place against the spring seat such that the isolator is permanently bonded to the spring seat. This bond can be achieved in various ways, such as by a suitable selection of materials and molding process. In one embodiment, glass-filled nylon is used for the spring seat and a TPE or MPE thermoplastic is used for the isolator with the isolator either being overmolded to the spring seat or co-molded with the spring seat by injection molding. Retention features can optionally be used in combination with the molded bond to provide a dual means of retaining the isolator to the spring seat.
Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
The lower bearing member 16 provides a dual function—it serves as a lower housing for the bearing and includes a unitary spring seat 18 that provides the bearing member 16 with a contour that is shaped and sized to receive a suspension coil spring (not shown). For this purpose, the lower bearing member 16 has both a radially-extending flange 30 and an axially-extending hub 32 located radially-inwardly of the flange. The junction of the flange 30 and hub 32 defines the integral spring seat 18 that accommodates the upper end of the suspension spring. To dampen vibrations transmitted by the coil spring, the spring seat 18 includes the integral isolator 20 that can be formed from any suitable resilient material. Conventional isolator materials such as rubber can be used; however, there are numerous other commercially available materials that provide suitable dampening and resilience for a typical vehicle application. For example, a thermoplastic elastomer (TPE), melt processible elastomer (MPE), or thermoplastic polyurethane (TPU) can be used, as will be discussed below in greater detail.
Isolator 20 can be made integral with the spring seat 18 using one or more means of attaching the two components together. In the embodiment shown in
Before describing the molding and bonding of the spring seat 18 and isolator 20, the alternative embodiments 50 and 70 of respective
The annular bearing members 14, 16 (and, thus, spring seat 18) can be made from a nylon or other glass or fiber filled thermoplastic; for example, PA66.GF33, PA66.GF43, PA66.GF35, or PA66.GF25. Alternatively, other suitable materials can be used for these components; for example, POM; and the material used can include PTFE, Silicon or PFPE (Perfluoropolyether Modifier) added in. Preferably, the material selected provides a very rigid spring seat. Glass fiber and rare earth additives can be included in varying amounts, preferably in an amount that does not exceed 50%. As noted above, for the isolator 20, any suitable vibration dampening material can be used; for example, a TPE, MPE, or TPU. As a more specific example, Alcryn™ Melt-Processible rubber is available from the Advanced Polymer Alloys division of Ferro™. This MPE rubber can operate in a range of −70° C. to +130° C. and has a hardness of 40 to 90 Shore A. For a spring seat made from glass filled nylon, the retention of an isolator made from this material against the spring seat will be primarily through the retention features described above, as it does not bond well to the nylon. As another specific example, Ferro's APA DuraGrip™ TPE line provides a high quality rubber-like material with a temperature range of −40° C. to +70° C. and a hardness can range between 20 and 90 Shore A. An advantage of the DuraGrip materials (such as DuraGrip 6100) is that it can form a strong bond with the glass filled nylon. Furthermore, the material can be recycled and reused again as a TPE.
As noted above, in at least some embodiments, the isolator can be molded to the spring seat to form a composite single component that operates as (1) the lower bearing housing, (2) the spring seat, and (3) the isolator. This can be accomplished in various ways. For example, two shot or the over molding of TPE or other isolator material onto a rigid spring seat substrate can result in a visually appealing assembly. It can also provide a savings in terms of labor and floor space. The two shot molding of the isolator and spring seat can be carried out in the same machinery with the spring seat being at least partially molded first followed by the isolator material being added and molded to the spring seat that is still in the mold. This can be done using an injection press having two runner systems which can allow the use of two different resins. One can be the more rigid material such as glass filled nylon noted above and the other the dampening material used for the isolator. The injection machine can have two injection units that fill the two runners and allow the different materials to flow into the different cavities. Once the cavities fill the mold rotates 180°, the mold closes and the cycle begins again. The hot substrate is usually in a semi-solid state. This permits melt and chemical bonding, resulting in a permanent connection of the isolator to the spring seat. Co-injection molding is an alternative process that can be used. When co-molding, the two materials can be injected simultaneously with the substrate material for the spring seat moving to the outer mold surface. This approach can provide a good resulting bond of the materials.
When over molding the isolator dampening material to the more rigid spring seat (and lower bearing member), the interconnection of two components can be achieved in several fashions. One is the mechanical interlocking noted above wherein the spring seat is formed with a mechanical retention feature such that the isolator material flows into or around that retention feature and forms a complementary retention feature. This gives a mechanical connection. The grooves, undercuts, etc. that are used should be strategically placed so the integrity of the rigid spring seat is not compromised. This can be confirmed by the use of FEA (finite element analysis). As long as the overmolded polymer does not require a high processing temperature as compared to the base material of the spring seat, any TPE can be used. This mechanical attachment locks the isolator against movement and escape from the spring contact in the strut assembly. In this regard, the more locking features that can be added the better the solution assuming the rigidity is not significantly decreased. A second way in which the molding process can provide a suitable interconnection of the two components is by melt or chemical adhesion between the base material and the isolator material. This provides a permanent bond between the components. For this, the two materials used should have a similar melting point and chemical structure that permits the two parts to solvate at the mating surfaces and form a bond to some degree. This bond will vary based on the materials that are chosen, but should not be greater than the shear strength of the weaker material. In some embodiments, this bond will be sufficient to permanently connect the two components together without the need for grooves or other mechanical retention features discussed above.
The foregoing description is of several embodiments of a ring bearing assembly having an integrated spring seat and isolator as it might be utilized in an automotive strut assembly for an automobile. However, it will be appreciated by those skilled in the art that the disclosed bearing arrangement is useful in other types of struts and in other bearing applications which involve a suspension spring or other annular supporting structure. Thus, it is to be understood that the invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. For example, although the lower annular member 16 and spring seat 18 are depicted together as being a unitary one-piece component, it will be appreciated that a separate plastic or metal spring seat can be used that is integrally attached to the isolator using any of the approaches described above. The separate spring seat/isolator functions as a load distributor and for this purpose can be constructed to have a high stiffness relative to the lower bearing member and thus can be used to more equally distribute the load of the coil spring to the plastic base. In this regard, some coil springs do not completely surround the spring seat surface. For example, a coil spring may only engage a portion of the entire circumference of the spring seat surface, which may lead to uneven loading of the plastic base. To improve the load distribution the isolator can have a helical form that follows the spring coil profile. This and all such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “for example,” “for instance,” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
