Abstract:
A grommet providing triple sealing feature when mounted in an opening of a panel is disclosed. When the panel into which the grommet is mounted is between a compartment exposed to ambient conditions and a passenger compartment, a seal minimizes water, fumes, dust, and noise from entering into the passenger compartment. The triple seal, according to an embodiment, provides higher sealing forces than shown previously. The disclosed grommet can be engaged with a flat, non-flanged panel as well as a panel having a flange near the opening. The disclosed grommet has multiple longitudinal slits sawed through a tubular portion of the grommet through which the wiring harness is threaded. The cuts allow a subset of wires to be splayed out from the grommet at a different routing than the remainder of the wires in the wiring harness bundle.

Description:
BACKGROUND 
     1. Technical Field 
     The present development relates to grommets and more particularly to sealing an opening in a panel. 
     2. Background Art 
     In automotive vehicle applications, there are various vehicle body panels through which a wiring harness is passed, such as the firewall or door panels. Typically, an opening is punched, or otherwise formed, in the body panel. A grommet is fitted into the opening, with the grommet having a passage through which the wiring harness can be threaded. A cross-section of a grommet installed into a body panel, according to the prior art, is shown in  FIG. 1 . A body panel  2  has an opening into which a grommet  4  is installed. Grommet  4  has multiple wires forming a wiring harness  6  passing through a tubular portion  8  of grommet  4 . Typically, tape  10  is wrapped around the wiring harness  6 . Grommet  4  has a channel  12  (or groove) into which a portion of panel  2  near the opening is held. The opening in panel  2  and channel  12  are sized to cooperate when installed. On either side of channel  12 , grommet  4  is larger in circumference than the opening in panel  2 . An insertion force is applied to grommet  4  so that one of the sides adjacent to channel  12 , which is larger than the opening in panel  2 , deforms. As inserted, an edge of the opening of panel  2  is engaged with channel  12  with contact on three sides of channel  12 . 
     The grommet is provided for a number of reasons. If the panel through which the wires travel is between an inside compartment and a harsher environment, the grommet provides a seal so that water, fumes, dust, etc. that might be part of the harsher environment are largely prevented from entering the inside compartment. If the grommet is placed in a body panel with a noisy environment on one side, another function of the grommet is to limit the transmission of noise from one side to the other through the opening in the panel. 
     Some body panels through which wires may be passed are sufficiently stiff preventing excessive deformation when a grommet is inserted and providing a surface to which the grommet can be secured and sealed. Such an example is shown in  FIG. 1 , where panel  2  is flat, or nonflanged, at the opening. 
     In some applications, a flange is formed on the panel opening, an example of which is shown in  FIGS. 2 and 3 , according to the prior art. Panel  20  has an opening  22  with a flange  24  formed near opening  22 . Flange  24  resists deformation in panel  20  in the region around opening  22 . In  FIG. 2 , grommet  26  is shown uninstalled. Grommet  26  has a wiring harness  28  inserted through a cylindrical portion  30  of grommet  26 . Tape  32  is applied near a tip of grommet  26 . In the example shown in  FIG. 2 , grommet  26  has a conical section  34 . Grommet  26  has a channel  36  for accepting plate  20 . Channel  36  has a first surface  38 , second surface  40 , and third surface  42 . Extending from third surface  42  is a lip  44 . 
     In  FIG. 3 , grommet  26  is shown installed into opening  22  of panel  20 . Surface  40  has a raised portion on which flange  24  rests. First surface  38  contacts a first side  46  of panel  20 . A second side  48  of panel  20  is in contact with a tip of lip  44 . Because the tip is thin in cross section, it deforms readily and provides little force on panel  20  when installed. Consequently, the sealing force is minimal. Also, grommet surface  38  deforms easily because it is a thin wall. When deformed upon engagement with panel  20 , it contacts side  46  of panel  20  along the length of first surface  38 . 
     It is known to design channels in grommets to accommodate non-flanged panel openings, such as shown in  FIG. 1 , and to accommodate flanged panel openings, such as shown in  FIG. 3 . It would be desirable, however, to have a single grommet design that can be used for both flanged and non-flanged panel openings and one that exerts a strong sealing force to prevent water, dust, fumes, noise, etc. to pass through the grommet. 
     SUMMARY 
     A grommet is disclosed which is adapted to engage with an opening in a panel of predetermined thickness. The thickness of the panel in, for example, a vehicle door application, is as thin as 0.7 millimeters (mm). In an automotive firewall, the thickness is 1 mm or greater. In other applications the panel is as thick at 3 mm. The grommet is a unitary molded piece made of an elastomeric material having first and second tubular portions through which a wire harness is passed. The grommet has a body portion with the first tubular portion extending from a first side of the body portion and the second tubular portion extending from a second side of the body portion. The body has a channel with a bottom surface of a channel having a predetermined width, a first side wall, the first side wall having a first lip extending generally toward a center of the channel, the first lip being distally located with respect to the bottom surface, and a second side wall, the second side wall having a second lip extending generally toward the first lip, the second lip being distally located with respect to the bottom surface. The second lip overlaps the first lip by more than the predetermined thickness when the grommet is not engaged with a panel, i.e., uninstalled. A cross-section of the tip generally has the shape of a half circle. In one embodiment, the diameter of the half circle is about 2 mm and the predetermined width (distance between the first side wall and the second side wall) is about 4 mm. 
     The channel can engage a non-flanged panel or a flanged panel having a flange not greater than the predetermined width. The grommet has a body portion with a wall around its periphery in which the channel is formed and a first surface extending across a first end of the wall and a second surface extending across a second end of the wall. The first surface slopes out toward the first tubular portion and has a plurality of generally trapezoidal ribs, in cross section, extending outward. A first portion of ribs have a first width and a second portion of ribs have a second width, the second width being at least twice as wide as the first width. 
     The second tubular portion has a plurality of slits cut through the second tubular portion and the slits are generally parallel with an axis of the second tubular portion. The second tubular portion has at least one ridge on an internal surface of the second tubular portion. 
     Also disclosed is a method to manufacture a grommet having a body, a first tube protruding from a first surface of the body, a second tube protruding from a second surface of the body, a wall around a periphery of the body, the wall being adjacent to the first surface on one end of the wall, the wall being adjacent to the second surface on another end of the wall, and the wall having a channel formed therein. The method includes molding the grommet and sawing at least two vertical slits in the first tube, the slits extending from a distal end to the proximate end with the slits roughly parallel to the axis of the first tube. The method may also include sawing at least two horizontal slits into the first surface starting at the proximate end of the vertical slits and arranged contiguously with the vertical slits. The width of the vertical slits is less than about 1 mm. 
     An advantage of the present development is that lips adjacent to the channel overlap by at least the thickness of the panel to which it is to be engaged, thereby providing a strong sealing force between the lop and the panel. This overlap exerts a strong force to seal the panel by virtue of the tips of the lips pressing on either side of the panel. A third seal is provided between the bottom of the channel and the opening surface of the panel when the size and shape of the panel opening is equally sized and shaped to match the channel in the grommet. In this way, a friction seal is formed between the inside surface of the panel opening and the bottom surface of the channel. This provides a triple seal to prevent ambient fumes, dust, air, noise, etc. from passing through the panel in the vicinity of the opening. 
     Yet another advantage of the present development is that by providing a wide bottom surface of the channel and an overlap of the sealing lips, a single grommet is capable of engaging with a flanged or non-flanged panel with sufficient sealing force. By doing so, the number of different parts that a manufacturer purchases is reduced. Parts complexity and the number of parts that are inventoried are also reduced. 
     The present development yields another advantage in that by sawing the slits in the tubular portions of the grommet, the resulting slit is smaller in width than that which can be molded in place. As described below in more detail, the purpose of the slits is to yield a greater flexibility in the grommet application. In some applications, the slits are not used because the wiring harness passing through the tubular portion simply traverses straight through the tube of the grommet. In such cases, the tubular portion is taped up and the sawed slits fit together with little or no gap yielding a tight seal. In other applications, subsets of the wires of the wiring harness are splayed out due to packaging constraints. In one example, a subset of the wires is routed along the panel and thus cannot accommodate traversing through the tube of the grommet prior to attaining such orientation. Furthermore, various subsets of the wires of the wiring harness may be routed in different directions immediately on the other side of the panel. 
     To accommodate this, the prior art has slits molded in the grommet. However, the tubular portions on either side of a molded slit do not mate well and provide a less than optimal seal when taped. Also, molded slits are wider and don&#39;t seal well. 
     Because the grommet, according to the present development, provides two surfaces covering the opening in the panel, there are two barriers to noise transmission over the opening in the panel. It was found that the noise transmitted is reduced by 20% by having a second surface barrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional representation of a grommet according to the prior art; 
         FIGS. 2 and 3  are cross-sectional representations of a grommet according to the prior art, in uninstalled and installed states, respectively; 
         FIG. 4  is a cross-sectional representation of a grommet according to an embodiment of the present development; 
         FIGS. 5-7  are cross-sectional representations of a portion of a grommet according to an embodiment of the present development showing details of the channel: uninstalled ( FIG. 5 ), installed with a non-flanged panel ( FIG. 6 ), and installed with a flanged panel ( FIG. 7 ); 
         FIGS. 8 and 9  are isometric views of a grommet according to an embodiment of the present development: from an engine compartment view ( FIG. 8 ) and from a passenger compartment view ( FIG. 9 ); 
         FIG. 10  is portion of a grommet as viewed from a passenger compartment view showing trapezoidal raised flats projecting from the grommet&#39;s surface; and 
         FIG. 11  is an isometric view of a tubular portion of a grommet, according to the prior art. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. The representative embodiments used in the illustrations relate generally to a grommet adapted to be installed into an opening of a body panel on an automotive vehicle. However, the grommet may be incorporated into various other types of vehicles, such as boats, private airplanes, etc. as well as other applications such as a control room of a plant, a refrigeration unit, as two examples. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     A cross-section of a grommet  50 , according to an embodiment of the present development, is shown in  FIG. 4 . Grommet  50  has a first tubular portion  52  extending from a body portion  54 . Grommet  50  also has a second tubular portion  56  extending from body portion  54 . The embodiment shown in  FIG. 4  shows axes of first and second tubular ports  52  and  56  being arranged orthogonally. However, this is a non-limiting example as axes of first and second tubular ports  52  and  56  may be collinear, parallel, intersect non-perpendicularly, or at any angle which is consistent for the particular installation. First and second tubular ports  52  and  56  can accommodate a wiring harness (not shown). Tubular port  56  has one or more annular ridges  57  formed on the inside surface of tubular port  56  to assist in retaining a wire harness. As described above, it is desirable for a single grommet design to be used in a variety of applications. Depending on the application, the number of wires in the wiring harness differs. Ridges  57  allow for a greater range in the diameter of wiring bundles to be secured than a smooth internal surface for tubular port  56 . Such ridges in grommet  50  allows it to be used in a greater number of applications. 
     Continuing to refer to  FIG. 4 , grommet  50  has a service port  58 , allowing access through grommet  50  for wires that need to be added after vehicle assembly, for example, if a wire in the wire harness breaks and needs to be replaced without disturbing the wire harness or a service fix requires running an additional wire. Service port  58  is closed on one end with a knob; the knob is cut off when service port  58  is needed. 
     Channel  60 , in  FIG. 4 , is formed in the periphery of grommet  50  to engage with a panel (not shown). In  FIG. 5 , a section of grommet  50  with more detail of channel  60  is shown. Channel  60  is defined by a bottom surface  62 , a first side wall  64 , and a second side wall  68 . First side wall  64  has a lip  66 . Second side wall  68  has a lip  70  extending generally toward lip  66 . The tips of lips  66  and  70  overlap each other by a distance, indicated as  72  in  FIG. 5 . Distance  72  is at least as thick as a panel with which it is designed to be engaged. 
     In  FIG. 6 , a section of the grommet is shown in which a non-flanged panel  74  of thickness  76  is installed into channel  60 . Tips  66  and  70  are pushed back from their undeformed position to accommodate panel  74 . The deformation of lips  66  and  70  and the resilient material behind lips  66  and  70  cause forces F 1  and F 2  to be applied to panel  74 . The applied forces cause tips of lips  66  and  70  to seal against the faces of panel  74 . In addition, when the opening in panel  78  is sized to cooperate with channel  60 , a surface  78  of panel  74  seals against bottom surface  62 . In this way, the grommet provides three sealing regions between panel  74  and surfaces  62 ,  64 , and  68  defining channel  60 . 
       FIG. 7  is very similar to  FIG. 6 , except that the panel installed, panel  82 , has a flange  84 . The bottom surface  62  of groove  60  contacts flange  84  over a flange width  86 . Like in  FIG. 6 , triple sealing of panel  82  is provided by: lip  66 , lip  70 , and surface  62 . 
     A grommet  90  according to an alternate embodiment is shown in  FIG. 8 . A tubular portion  92  has a generally rectangular cross-section with rounded corners. Herein, tubular refers to a tube of any cross section, not limited to a round tube. Grommet  90  has a wall  94  around its periphery. A surface  96  is extended across one end of wall  94 . From the other side of grommet  90 , as seen in  FIG. 9 , a second tubular portion  100  can be viewed; tubular portion  100  has a generally rectangular cross-section with rounded corners. A surface  99  extends across walls  94 . By providing two surfaces  96  and  99  across the two ends of wall  94 , a greater barrier to noise transmission is provided. (Note that in  FIG. 4 , the two surfaces are not so clear, because as shown, the cross-section is through the tubes through which the wiring harness travels.) It has been found that by providing a second surface, as opposed to one such as in grommets of  FIGS. 2 and 3 , the noise level is reduced by about 20%. Surface  99  is not a flat surface but has three-dimensional engagement features. It is known in the prior art that a smooth surface that is cone shaped in the direction of tubular portion  100  requires too high an insertion force due to high friction between the panel opening and the conical surface. To reduce that insertion force, it is known to have an undulating surface. In the embodiment shown in  FIG. 9 , trapezoidal shaped features  106  and  108  extending out from surface  99  are shown. In the embodiment shown, wider trapezoidal shaped features  106  provide additional stiffness in areas that might be prone to collapse. The remainder of the trapezoidal shaped features  108  is narrower, thereby allowing easier deformation in such regions not prone to collapsing, thereby lessening overall installation force. The trapezoidal shaped features  106  and  108  are shown in more detail in  FIG. 10 . 
     In the embodiment shown in  FIG. 9 , tubular port  100  is cut parallel to its axis in four places around its periphery. The cuts, or slits, are shown continuing into surface  99 . In some applications, a subset of wires routed through tubular port  100  is routed in a different direction than other wires. Furthermore, in some applications, there is insufficient packaging space to allow all the wires of the wiring harness to traverse through tubular port  100  before being routed in their various directions. By providing slits  102  through tubular port  100  and slits  104  through surface  99 , as many as four groups of wires can be routed into four directions by bending a cut section of tubular port  100  into the desired direction. To seal these various wire groupings, tape is applied. In applications in which all wires in the wiring harness are routed together, at least as far as through tubular port  100 , tape can be applied around all sections of tubular port  100  to cause the slits to press together.  FIG. 9  showing four slits  102  in tubular port  100  is exemplary, but not limiting. 
     Referring now to  FIG. 11 , it is known in the prior art to provide slits  112  in a tubular port  110  of a grommet with the slits molded in. In an application in which the slits are not needed to accommodate wiring that splays out in different directions, the gaps of slits  112 , which are several mm in width, aren&#39;t readily sealed by winding with tape. Furthermore, in situations in which slits  112  are not cut down the length of tubular port  110  a sufficient distance, tearing of tubular port  110 , and possibly the grommet, may occur when attempting to route a subset of the wires of a wiring harness in a particularly tight angle. According to an embodiment of the present disclosure, as shown in  FIG. 9 , slits  102  are cut into tubular port  100  after molding grommet  90 . Slits  102  are cut with as thin a blade as possible, while still maintaining blade integrity: 1 mm thickness in one embodiment. This yields a much narrower slit than with molding. Furthermore, the edges of slits  102  are squarer causing them to mate for a better seal than a molded edge of the prior art. Also, slits  102 , as shown in  FIG. 9 , continue into surface  99  as slits  104 , forming one contiguous slit. Thus, depending on the application, a portion of tubular port  100  can be folded back at an extreme angle without having to resort to tearing grommet  90 . 
     The triple sealing feature of the embodiment shown in  FIGS. 5-7  presents an improvement over the prior art. Lip  44  and wall  38  ( FIG. 2 ) do not overlap as much as the thickness of the panel in which it is to be installed. Thus, they are easily deformed and act with little force against the panel, and therefore form a weaker seal. The tips of lips  66  and  70 , according to an embodiment of the present disclosure ( FIG. 5 ) are hemispherical compared with pointed tip of prior art lip (element  44  of  FIG. 2 ). The sealing force equilibrates between the two sides of the panel with the weaker side controlling the total amount of force applied to the panel. Because lips ( 66  and  70  of  FIG. 5 ) according to an embodiment of the present disclosure have more material at the tips and in the vicinity of the tips, they are more difficult to deform than prior art lips which are more pointed and thinner, and consequently provide a greater force to form a seal than shown in the prior art. Also, according a prior art example ( FIG. 2 ), behind side wall  38 , a hollow  43  is provided. Thus, side wall  38  is easily deformed. According to an embodiment of the present disclosure, no such hollow is formed in the material behind either side wall  64  and  68 . Such a configuration as shown in  FIG. 5  requires a greater installation force and thereby exerts a greater sealing force when installed. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.