Abstract:
An isolator fan fastener for securing a cooling fan housing to the interior chassis of a computer is described. The fastener is comprised of a pin made of a hard impact resistant plastic and an isolator grommet made of a soft resiliently flexible plastic. The pin is frictionally engageable with the isolator grommet. In operation the isolator grommet is preinstalled in the fan housing. Insertion of the pin through the chassis and into the isolator grommet completes the mounting. An isolator fan fastener in accordance with the invention yields enhanced acoustical properties when compared to prior art fasteners.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a fastener for joining two parts, and more particularly, to a plastic fastener comprising a pin and an isolator grommet for joining the housing of a computer cooling fan to the chassis of the computer. The isolator grommet is preinstalled in the fan housing. Insertion of the pin through the chassis and into the isolator grommet completes the mounting. 
     2. Description of the Prior Art 
     Fasteners for joining apertured work pieces are well known in the prior art, and are usually manufactured of metal or plastic. The nut and bolt and the screw are examples of common metallic fasteners, while examples of plastic fasteners are shown in U.S. Pat. Nos. 2,882,780 and 2,941,439. 
     When joining the cooling fan housing of a computer to the chassis of the computer, however, many prior art fasteners have proven unsatisfactory. With regard to metallic fasteners, they generally have a high elastic modulus, making them poor isolators of the vibrations caused by the operation of the fan, often resulting in bothersome and unacceptable noise. Second, metallic fasteners are relatively more difficult to install than plastic fasteners, often requiring use of a tool, such as a wrench or a screwdriver. Third, metallic fasteners are conductive and thus could prove hazardous if lost inside the computer. 
     With respect to plastic fasteners, many plastic fasteners have proven unsatisfactory in that they, as with metallic fasteners, insufficiently isolate the vibrations caused by the operation of the fan. Other plastic fasteners are difficult to install and/or remove, and yet other fasteners provide a weak coupling between the fan housing and the chassis. 
     It is therefore an object of the present invention to provide a plastic fastener for securing a fan housing to the chassis of a computer which results in a quieter mounting than that achieved by currently used fasteners. Another object of the present invention is to provide a plastic fastener which provides a secure connection between the housing and the chassis. Yet another object of the present invention is to provide a fastener which can be easily installed and removed. Other objects will become apparent from the discussion below. 
     SUMMARY OF THE INVENTION 
     An isolator fan fastener in accordance with the present invention achieves the above and other beneficial objects by providing a plastic fastener having a pin and a separate isolator grommet with an axial bore extending therethrough. The pin has a head and a shank. The shank has a first engaging portion, a second engaging portion, a third engaging portion and a fourth engaging portion. The four engaging portions have varying diameters and, as discussed below, are frictionally engageable with corresponding portions of the interior walls of the isolator grommet. 
     The isolator grommet has a head, a shank, a circumferential lip, and an axial bore of varying dimension extending therethrough for receiving the pin. The bore forms a first interior wall portion for receiving the first engaging portion of the pin shank in releasable frictional engagement, a second interior wall portion for receiving the second engaging portion of the pin shank in releasable frictional engagement, a third interior wall portion for receiving the third engaging portion of the pin shank in releasable frictional engagement, and a fourth interior wall portion for receiving the fourth engaging portion of the pin shank in releasable frictional engagement. 
     In operation the shank of the isolator grommet is inserted into a hole in the fan housing such that the wall of the fan housing is situated between the head and lip of the isolator grommet and the head and lip bear against the outer and inner surfaces of the housing, respectively. The isolator grommet is dimensioned in the manufacturing process to mate with a fan housing of predefined thickness, i.e. the thickness of the fan housing corresponds to the distance between the head and lip on the grommet. 
     The bore in the grommet is then aligned with the hole on the computer chassis with the isolator grommet head bearing against the inside of the chassis. The pin is inserted into the grommet until the pin head bears against the outside surface of the chassis. The pin is dimensioned in the manufacturing process for use with a computer chassis of predefined thickness. When the pin is fully inserted into the chassis the first engaging portion on the pin shank is in releasable frictional engagement with the first interior wall portion of the grommet, the second engaging portion on the pin shank is in releasable frictional engagement with the second interior wall portion of the grommet, the third engaging portion on the pin shank is in releasable frictional engagement with the third interior wall portion of the grommet, and the fourth engaging portion of the pin shank is in releasable frictional engagement with the fourth interior wall portion of the grommet. 
     At that point the fan housing is firmly and releasably fastened to the chassis. The isolator grommet is manufactured of a soft plastic such that it isolates a large portion of the vibration of the fan, thereby reducing the noise level. The pin, on the other hand, is manufactured of a hard plastic to ensure secure coupling with the isolator grommet, thereby securely fastening the fan housing to the chassis. 
     An isolator fan fastener in accordance with the present invention offers numerous advantages over the prior art. First, the noise caused by the operation of the fan is reduced as compared to many prior art fasteners. Second, the frictional engagement of the pin and the isolator grommet ensures a secure fastening. Third, the fan housing may be attached or detached to the computer chassis by simple insertion or extraction of the pin into or out of the isolator grommet without use of excessive force or a special tool. Other advantages will become apparent from the discussion below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a front view of the pin; 
     FIG. 2 is a front view of the isolator grommet; 
     FIG. 3 is a front cross-sectional view of the assembled fastener joining a fan housing to the chassis of a computer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The aforementioned Figures illustrate an isolator fan fastener in which the same numbers represent identical elements. 
     With reference to FIG. 1, numeral  10  represents the fastener pin in accordance with the preferred embodiment of the invention. The pin has a head  12 , a spacer  14 , a tapered shoulder  16  and a shank  18 . The shank is further comprised of a cylindrical first engaging portion  20 , a tapered second engaging portion  22 , a spherical third engaging portion  24  and a cylindrical fourth engaging portion  26 . Pin  10  is circular in cross section and is molded from a hard, impact resistant plastic, such as nylon 6/6 or hard santoprene. 
     First engaging portion  20  and fourth engaging portion  26  have the same diameter. Second engaging portion  22 , adjacent first engaging portion  20 , tapers on a circular arc to a minimum diameter to form a neck  28 . Third engaging portion  24 , adjacent second engaging portion  22 , expands spherically from said minimum diameter to a maximum diameter and then tapers to a diameter equal to that of first engaging portion  20  and fourth engaging portion  26 . 
     With reference to FIG. 2, numeral  30  represents the isolator grommet in accordance with the preferred embodiment of the invention. Isolator grommet  30  is circular in cross section and has a head  32 , a shank  33 , a headwardly flexible circumferential outer lip  34  and a circular bore  36  for receiving pin  10 . Bore  34  is of varying diameter and forms a mouth portion  38  for receiving pin shoulder  16 , a coextensive cylindrical first interior wall portion  40  for receiving shank first engaging portion  20  in releasable frictional engagement, a coextensive tapered second interior wall portion  42  for receiving shank second engaging portion  22  in releasable frictional engagement, a coextensive expanding third interior wall portion  44  for receiving shank third engaging portion  24  in releasable frictional engagement, and a cylindrical fourth interior wall portion  46  for receiving shank fourth engaging portion  26  in releasable frictional engagement. Fourth interior wall portion  46  should generally be at least coextensive with shank fourth engaging portion  26 . However, in practice it is generally longer as this allows isolator grommet to be positioned in the fan housing by a pulling action. Second interior wall portion  42  and third interior wall portion  44  form a neck  48  which receives shank neck  28 . 
     First interior wall portion  40  and fourth interior wall portion  46  are of equal diameter, and said diameter is slightly smaller that the diameter of shank first and fourth engaging portions  20 ,  26 , thereby allowing for a friction fit therebetween. Typically, the diameter of first and fourth interior wall portions  40 ,  46  will be on the order of 14% smaller than the diameter of shank first and fourth engaging portions  20 ,  26 . Similarly, tapered second interior wall portion  42  has a shape complementary to that of shank second engaging portion  22  and has a minimum diameter smaller than the minimum diameter of shank second engaging portion  22 . Typically, the minimum diameter of second interior wall portion  42  will be on the order of 21% smaller than the minimum diameter of shank second engaging portion  22 . Expanding third interior wall portion  44  has a maximum diameter approximately 26% smaller than the maximum diameter of shank third engaging portion  24 . From comparison of FIGS. 1 and 2 it is clear that third interior wall portion  44  is not complementary in shape to shank third engaging portion  24 , i.e. third interior wall portion  44  is not spherical. This configuration ensures that in addition to a tight friction fit, the engagement of shank neck  28  and grommet neck  48  will provide an additional retention force to resist the extraction of pin  10  since spherical shank third engaging portion  24  would have to pass through the narrow passage formed by neck  48 . 
     So that it may act as a vibration isolator and deform so as to frictionally engage with pin  10 , isolator grommet  30  is manufactured of a soft, resiliently deformable plastic such as a thermoplastic elastomer (TPE) or soft santoprene. 
     In operation the fastener is used as follows. FIG. 3 shows the assembled fastener joining a fan housing  50  to the chassis of a computer  52 . Isolator grommet  30  is inserted into the hole in fan housing  50 . This is done by insertion of distal end  54  of shank  33  into the hole and the pulling of said distal end until circumferential lip  34  flexes and fan housing  50  becomes positioned between head  32  and circumferential lip  34  such that surface S 1  bears against the underside of head  32  and surface S 2  bears against circumferential lip  34 , as shown in FIG.  3 . Because the distance between head  32  and lip  34  corresponds to the thickness of the fan housing, isolator grommet  30  is manufactured for use with a fan housing of a predetermined thickness. Next, grommet bore  36  is aligned with the hole in the computer chassis  52  such that the upper side of grommet head  32  bears against the interior surface S 3  of the chassis  52 . Pin  10  is then inserted into isolator grommet  30  until spacer  14  bears against the exterior surface S 4  of chassis  52 . Because pin  10  and isolator grommet  30  are made of plastic, a relatively small axial force is needed to effect interengagement, which may even be accomplished by hand. 
     In order for pin  10  to mate with isolator grommet  30 , the length of shoulder portion  16  is adjusted in the manufacturing process for the thickness of chassis  52 , i.e. the axial length of shoulder portion  16  is equal to the sum of the thickness of chassis  52  plus the axial length of grommet mouth  38 . Thus, pin  10  and isolator grommet  30  are manufactured for use with a fan housing and chassis of predetermined thicknesses. 
     When pin  10  is fully inserted into isolator grommet  30  the fastener is locked and fan housing  50  is securely fastened to chassis  52 . Because the diameter of pin shank  18  is everywhere larger than the diameter of grommet bore  36 , insertion of pin  10  into isolator grommet  30  causes expansion of the interior walls of isolator grommet  30 , thereby frictionally engaging pin  10  and isolator grommet  30 . Thus, first interior wall portion  40  expands to receive shank first engaging portion  20 , second interior wall portion  42  expands to receive shank second engaging portion  22 , third interior wall portion  44  expands to receive shank third engaging portion  24 , and fourth interior wall portion  46  expands to receive shank fourth engaging portion  26 . Thus, pin shank  18  is everywhere frictionally engaged with isolator grommet  30 . In addition, the engagement of shank neck  28  with neck  48  provides an additional retention force since spherical shank third engaging portion  24  must pass through the narrow passage formed by neck  48  in order to extract pin  10 . 
     The fastener is thus releasably locked and the fan housing is securely and releasably fastened to the chassis. If one desires to remove the fan housing, pin  10  may simply be extracted from isolator grommet  30  by the application of relatively little axial force. Pin spacer  14  provides a space between pin head  12  and outer surface S 4  of chassis  52 , thereby facilitating the use of an extracting tool, such as a pair of pliers, a screwdriver or even a human hand. 
     The improved acoustical properties of the fastener are achieved by the use of the soft plastic isolator grommet in connection with the hard plastic pin. The isolator grommet is in direct contact with the fan housing and is able to isolate a significant portion of the fan&#39;s vibration. The use of a hard pin, on the other hand, ensures that a tight coupling will be achieved with the isolator grommet and that fan housing will be securely fastened to chassis. 
     While the present isolator fan fastener is suitable for use with a cooling fan housing and a computer chassis, it should be understood that the fastener is not limited to such use and can be used to join any apertured parts.