Abstract:
A compression spring assembly which includes a compression spring and a pair of identical but oppositely disposed guide members. The guide members have cooperating transversely extending keyways which are aligned to receive a key to maintain the assembly in a retracted, inoperative, condition. When placed in its operative environment, the spring assembly is suitably oriented and the key is removed from the keyway, thereby permitting the spring to expand to the greatest length possible under the circumstances. The spring assembly is capable of a broad range of movement along the axis of the spring. Subsequently, the spring assembly can be removed and returned to its retracted, inoperative condition by reversing the procedure just described.

Description:
BACKGROUND OF THE INVENTION 
     a. Related Application 
     Reference is hereby made to my copending application filed on the same date as the present application, Ser. No. 403,571, entitled &#34;Self-Positioning Belt Tensioner&#34; 
     b. Field of the Invention 
     The present invention relates generally to spring assemblies and, more particularly, to a captured spring assembly and its components which can be readily inserted and attached with accuracy to adjoining components and subsequently removed with minimal effort. It also assures support of the spring in operation over a wide range of lengths. 
     c. Description of the Prior Art 
     Any mechanical assembly utilizing a spring, such as a compression spring, which requires that it be somewhat compressed to enable its insertion and attachment to adjoining components calls for substantial expertise on the part of the installer. Springs subjected to compression have a well known tendency to buckle, that is, their central regions intermediate their ends tend to move laterally away from a position coaxial with their longitudinal axes. When this happens, the spring fails and the insertion step must be attempted again. However, while the spring may fail during installation, it may also fail during use if it has an aspect ratio, free length to mean coil diameter, greater than about 2.7 and is not laterally restrained, assuming hinged ends. See Kent&#39;s Mechanical Engineers, Handbook, Colin Carmichael, Editor, John Wiley &amp; Sons, Inc., New York, 1965. 
     SUMMARY OF THE INVENTION 
     The invention herein relates to a spring assembly and its components which particularly aid in the installation and support of the spring. In one embodiment of the invention, that of a compression spring, the foregoing problems of installation and operation are solved. By so doing, it enables use of a spring having an aspect ratio which is far in excess of 2.7 thereby permitting narrow constructions which are often sought. To this end, a compression spring assembly is disclosed which can be readily assembled, then held for an indeterminate time in an inoperative condition. At installation time, the inoperative spring assembly is properly positioned and a key member withdrawn allowing it to expand into engagement with the components intended to be biased apart. For removal of the spring assembly from those components, it is compressed to a length at which the key member can be re-inserted, thereby returning the spring assembly to the inoperative condition. 
     Each of a pair of identical but oppositely disposed guide members has a head and a pair of elongated legs extending from a shoulder defining one surface of the head. The legs of one of the guide members are interdigitably, slidably, matingly engaged with the legs of the other of the guide members. When fully engaged, the tip ends of one of the guide members are proximate to the head of the other of the guide members. A compression spring is slidably engageably received on the elongated legs of both guide members such that its opposite ends bear against the mutually facing shoulders of the opposed heads. When the heads are moved toward one another so that the tip ends of one of the guide members engages the shoulder of the other of the guide members, and vice versa, transverse keyways formed, respectively, in the head of one of the guide members and proximate to the tip ends of the other of the guide members are aligned to receive therethrough a key member which serves to retain the entire assembly in a retracted, inoperative, condition. Extreme opposed portions of the heads are bearing surfaces. When it is desired to install the spring assembly into an operating environment, the bearing surface of one of the heads is engaged with its intended mating component and the spring assembly is moved to its general intended orientation. Thereupon, the key member is withdrawn from the keyway. Under the bias of the compression spring, the spring assembly is caused to expand until the other of the heads also becomes engaged with its intended mating component. For this operation, the installer may guide the free head into engagement with its intended mating component. 
     The compression spring assembly of the invention is able to accommodate a wide range of lengths and still remain effective to apply a bias on one or both of its mating components. The actual range of lengths which it can accommodate depends upon the dimensions of its component parts. 
     Thus, the invention is of extremely simple design, utilizes known materials, can be inexpensively manufactured, easily installed, and just as easily removed from an installation. 
     When, for any reason, the compression spring assembly is to be removed from its installed state, it is merely compressed to its retracted or collapsed condition at which the transverse keyways are again aligned enabling the associated key member once again to be inserted to maintain the assembly in that condition for so long as is desirable. In its retracted condition, the spring assembly of the invention remains ready for immediate use at any future time. 
     Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and, together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a detail front elevation view of an installation incorporating a compression spring assembly embodying the invention; 
     FIGS. 2 and 3 are side elevation views illustrating, respectively, the retracted condition and the expanded condition of the compression spring assembly of the invention; 
     FIG. 4 is an exploded view, in perspective, of the compression spring assembly of the invention; 
     FIG. 5 is a cross section view taken generally along line 5--5 in FIG. 2; 
     FIG. 6 is a cross section view taken generally along line 6--6 in FIG. 3; 
     FIGS. 7 and 8 are detail side elevation views illustrating two successive relative positions of component parts of the spring assembly of the invention; 
     FIG. 9 is a detail front elevation view of one component of the spring assembly; 
     FIG. 10 is a front elevation view of the spring assembly in its retracted condition; 
     FIG. 11 is a detail front elevation view of the spring assembly illustrating a possible undesirable situation; 
     FIGS. 12 and 13 are detail front elevation views, similar to FIG. 11, illustrating another embodiment of the invention for correcting the FIG. 11 situation; 
     FIG. 14 is a cross section view of another embodiment of the invention; 
     FIG. 15 is a detail perspective view, partially cut away and in section, of the embodiment illustrated in FIG. 14; and 
     FIGS. 16 and 17 are detail perspective views illustrating two different bearing arrangements utilized by the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although this invention is described herein by way of a compression spring embodiment used for supporting a drive belt, the invention is not to be so limited. The inventive concept and features can be used with any type of spring to which it can be adapted and in any environment in which the spring may be useful. 
     Turn now to the drawings and, initially, to FIG. 1 which illustrates a compression spring assembly 20 embodying the invention incorporated into a typical installation 22. In the depicted installation, a drive belt 24 is advanced in the direction of an arrow 26 and passes around and in engagement with a pulley 28 as it continues on its way. 
     For purposes of the installation 22, it is desired to maintain tension on the drive belt 24 at all times and, therefore, it is necessary to take up any slack which occurs. Thus, as the pulley 28 moves between one extreme position illustrated by solid lines in FIG. 1 to another extreme position illustrated by dotted lines, the spring assembly 20 is effective to accommodate those changes and maintain substantially constant tension on the drive belt 24. 
     For a more specific description of the spring assembly, turn now to FIGS. 2, 3, and 4. The assembly is comprised of a pair of identical, oppositely disposed guide members 30, 32 each of which includes a head 34 and an elongated leg member 36 integral with the head. The guide members 30, 32 are composed of a self lubricating plastic material, preferably of a low cost, low density injection molded plastic such as polyethylene. The head 34 generally extends between a bearing surface 38 at a terminal end and a shoulder 40 spaced from the bearing surface. Each leg member 36 extends from the shoulder 40 in a direction away from the bearing surface 38 and includes a trunk 42 which is immediately adjacent the shoulder 40 and a pair of parallel, spaced apart legs 44 which extend away from the trunk and define a crotch 46 at the interface of the legs and the trunk. 
     The guide members 30, 32 are mutually, matingly, slidably, engageable (see especially FIGS. 5 and 6) such that, when fully engaged, tip ends 48 at the extremities of the legs 44 are received in an undercut region 50 of the head and able to bear against a recess surface 52 (FIGS. 4, 7, and 8) within that undercut region. The outer surface 54 of the leg member 36 (see FIGS. 5 and 6) in cylindrical and has a substantially constant radius of curvature for its entire length. A compression spring 56 is slidably, engageably, received on the joined guide members, viewing especially FIGS. 2 and 3, so as to overlie the leg members 36 and extend between the shoulders 40. Indeed, the opposed ends of the compression spring 56 engage the facing shoulders 40 of the mating guide members 30, 32. When so assembled, the spring assembly is capable of movement along its longitudinal axis between a retracted condition as seen in FIG. 2 and an expanded condition as seen in FIG. 3. A size relationship between the spring 56 and the leg members 36 is chosen such that when the spring 56 is fully expanded, portions of the legs 44 of one guide member remain in proximity to those of the other guide member. Also, when the guide members are in the retracted condition, the spring itself is under compression. 
     The inner diameter of the compression spring 56 and the outer diameter of the leg members 36 are preferably about the same size, but the members are sufficiently smaller than the diameter of the spring to enable easy movement of one relative to the other. By reason of this fact and the interdigitated relationship among the legs 44 of the opposed guide members 30, 32, the spring 56 is adequately supported throughout its movement between its retracted and expanded conditions and is prevented from buckling throughout its entire range of axial movement. 
     Turn now to FIGS. 7-10 which illustrate a key arrangement by reason of which the first and second guide members 30, 32 with the compression spring received thereon between the heads 34 is selectively maintained in the retracted condition. For this purpose, each head member is suitably formed with a transversely extending keyway 58 and each leg 44 is formed with a similar transversely extending, cooperating keyway 60. When the guide members 30, 32 are matingly engaged such that the tip ends 48 bear against the recess surface 52, the keyways 58, 60 are aligned so as to be coaxial with the guide members 30, 32. So positioned, a key member 62 may be inserted into and through the cooperating keyways 60, 62 to thereby prevent any further relative longitudinal movement between the guide members 30 and 32. By reason of the fact that the inner diameter of the spring 56 is substantially similar to the outer diameter of the leg members 36, the keyways 58, 60 are held closely together. Once inserted, the key member 62 is firmly retained within the keyways until its removal is desired. Although the cross sectional shape of the key member 62 and of the keyways 58, 60 is illustrated as being circular, any appropriate configuration such as square or rectangular would also serve the purposes of the invention. 
     On occasion, the inner diameter of the spring 56 may be larger than the outer diameter of the leg member 36 or does not have substantial hoop strength such that, as illustrated in FIG. 11, the keyway 58 at the tip end 48 of the leg 44 is able to become dislodged from the key 62. When this occurs, the continued bias of the spring 56 may be effective to cause the entire assembly to fly apart. To guard against such an occurrence, a modified construction of the invention is illustrated in FIGS. 12 and 13. In this embodiment, modified keyways 58A, 60A are formed, respectively, in a modified head 34A and in a modified leg 44A. A modified key member 62A is elongated as is the key member 62. However, the key member 62A is of a non round cross section defining opposed major sides and minor sides, it being the minor sides which are respectively engaged with the hooked key ways 58A, 60A. With this construction, FIG. 12 illustrates the situation in which the leg 44A is contiguously positioned with the trunk 42 while in FIG. 13 it has started to move longitudinally in the direction of an arrow 64. With such movement, however, the modified key member 62A merely pivots to a new orientation while still remaining in engagement with the modified keyway 60A. Thus, in this instance, even though the spring 56A is unable to maintain a contiguous relationship between the leg 44A and the trunk 42, the spring assembly continues to be effectively retained in a retracted condition. 
     There may be instances in which it may be desirable for the diameter of the compression spring to be relatively large. At the same time, it would not be desirable for the leg members 36 to be of a solid construction such that its outer surface has a diameter substantially similar to the inner diameter of the spring. This would result in a spring assembly having a substantially increased mass which may be undesirable. Another embodiment of the invention is illustrated in FIGS. 14 and 15 which serves to accommodate a larger spring without substantially increasing the mass of the spring assembly. In this embodiment, each leg member, which is to say each trunk 42B and each leg 44B, has an associated integral longitudinally extending and generally radially directed fin 66. The fins 66 have terminal edges 68 which lie in a common cylindrical plane and are adapted to slidably, engageably, receive the compression spring (FIG. 14) thereon. In all respects, however, a spring assembly constructed in accordance with FIGS. 14 and 15 operates in the same manner as previously described. 
     Turn now to FIGS. 16 and 17 for a description of the bearing construction utilized in the installation 22 which enables the spring assembly 20 to operate with optimal efficiency. As previously noted, the spring assembly 20 is positioned between opposed components which are intended to be biased apart. In this instance, the head 34 of the guide member 32 is engaged with a journal bearing 70 suitably formed in an outer wall of a casing 72 which houses the installation 22. In this instance, the bearing 70 has substantially the same width as the bearing surface 38 of the head 34 so that proper engagement is assured. Also, the opposed walls of the journal bearing 70 are flared to enable a wide range of angular movement of the head 34 relative to the casing 72. 
     At the opposite end of the spring assembly 20, the head 34 of the guide member 30 is journaled on a support plate 74 on which the pulley 28 is rotatably mounted. This construction is more clearly seen in FIG. 17. For this purpose, the bearing surface 38 of each head 34 is formed with a notch 76 which is of a width slightly larger than the thickness of the support plate 74. Opposed lateral surfaces 77 partially define the notch 76. For itself, the support plate 74 is provided with a similar notch 78 which is suitably formed to engageably receive the notch 76. The opposed lateral surfaces prevent lateral movement of the head 34 relative to the support plate 74. Also in the instance of the journal bearing 70, the notch 78 is flared in order to accommodate a range of pivotal motions of the head 34 relative to the support plate 74. Thus, the bearing constructions depicted in FIGS. 16 and 17 enable the range of movements of the spring assembly 20 as depicted in FIG. 1. However, the head 34 is adaptable to a variety of modes of connection between spaced apart mechanical elements, other than by means of the endmost bearing surfaces 38, for example, by means of mating pins and holes. 
     It is noteworthy that, when faced with the need for &#34;working&#34; springs, product and machine designers generally prefer compression springs over tension springs for reliability, long life, and compactness. It will be appreciated that a compression spring, expanding from a tightly coiled condition, provides a more constant force in a smaller envelope with less opportunity for failure than does a tension spring intended for the same purpose. However, the use of long, thin, compression springs requires special attention and often calls for the use of ancillary components in the form of metal guide rods, retainers, end fittings, bearings, and the like. Additionally, in operation, lubrication is a constant problem, often times resulting in eventual wear, friction losses, noise, and corrosion of the components. The design of the invention presents designers with the best of all worlds, offering a spring assembly which is cost effective and yet operates flawlessly in a continuous manner. 
     While preferred embodiments of the invention have been disclosed in detail, it should be understood by those skilled in the art that various other modifications may be made to the illustrated embodiments without departing from the scope of the invention as described in the specification and defined in the appended claims.