Fastener assembly useful as drain plug

Abstract: A fastener assembly (10) comprises a metal screw (20) and a sealing ring (22) made from an elastomeric material and is useful, in an exemplary application, as a drain plug for an oil pan for an internal combustion engine. The screw head (30) has an undercut (18), annular recess (40), within which the sealing ring (22) is seated. The sealing ring (22) has a sealing portion (60), which when unstressed has an axial thickness smaller than the recess depth, and an adjoining portion or web (62) extending radially inwardly. When unstressed, the adjoining portion (62) has an inner diameter smaller than the major diameter of the threaded portion (36) of the screw shank (34). The sealing ring (22) when unstressed has an outer diameter larger than the outer diameter of the recess (40). Moreover, the recess volume is sufficient for the recess (40) to contain the sealing ring (22) over a wide range of cumulative, dimensional tolerances.

Description: Technical Field of the Invention This invention pertains to a fastener assembly comprising a metal screw and a sealing ring, according to the preamble of claim 1. In an exemplary application, the fastener assembly contemplated is useful as a drain plug for an oil pan of an internal combustion engine, as for a motor vehicle. The sealing ring is seated within an undercut, annular recess in the screw head. To avert problems encountered with such fastener assemblies heretofore and attributable to cumulative, dimensional tolerances, the ring and the recess are shaped to enable the ring to form a seal and to enable the recess to contain all of the ring over a wide range of such tolerances. Background of the Invention Fastener assemblies comprising metal screws and sealing rings, such as O-rings made from synthetic rubber, are used widely in various sealing applications. In one widespread application, such fastener assemblies are used as drain plugs for oil pans of internal combustion engines, as for motor vehicles. In one known arrangement of the kind mentioned above, the screw head has an undercut, annular recess to accommodate an O-ring, which is intended to form a seal between the screw head and a workpiece when a threaded portion of the screw shank is driven into a threaded aperture in the workpiece. Such a fastener assembly is disclosed by the generic US-A-2 752 814. A similar fastener is disclosed by the US-A-4 701 088. Problems are encountered with the known arrangement noted in the preceding paragraph and are attributable to cumulative, dimensional tolerances associated with the O-ring dimensions, the recess dimensions, and any countersink dimensions. One such problem is that, if the O-ring material has excessive volume relative to the recess and any countersink, the screw head cannot achieve metal-to-metal contact with the workpiece and can bear only against the O-ring material. Eventually, the O-ring material exhibits cold flow, which results in a loosened seal. Another such problem is that, if the O-ring material has insufficient volume relative to the recess and any countersink, an effective seal is not achievable. These two problems present particular difficulties when the fastener assembly is used as a drain plug for an oil pan of an internal combustion engine, as for an automobile or a truck, in which oil leaks can lead to severe engine damage. There has been a need, to which this invention is addressed, for improvements averting both of these problems in such a fastener assembly. Summary of the Invention This invention provides a fastener assembly useful with a metal workpiece having a sealing surface and a threaded aperture opening from the sealing surface. Because it does not exhibit either of the problems noted above, the fastener assembly provided by this invention can be advantageously used as a drain plug for an oil pan of an internal combustion engine, as for an automobile or a truck. The fastener assembly provided by this invention comprises a metal screw having a head portion and a shank portion integral with the head portion and defining an axis. The head has an undercut, annular recess with an axial depth. The recess may be generally rectangular when viewed in a radial plane through the axis defined by the shank. The shank portion has a threaded portion with a major diameter. Also, the fastener assembly provided by this invention comprises a sealing ring made from an elastomeric material, such as synthetic rubber. The sealing ring is seated within the recess. To avert both of the problems noted above, the ring and the recess are shaped to enable the ring to form a seal and to enable the recess to contain all of the ring over a wide range of cumulative, dimensional tolerances in the metal screw, in the sealing ring, and in the metal workpiece. The sealing ring is made so as to have a special shape relative to the recess and has a sealing portion and an adjoining annular web portion extending from the sealing portion. The sealing ring is made so that its volume is substantially less than the volume of the recess. The sealing ring is made so that the sealing portion, which may resemble an O-ring, has an axial depth greater than the axial depth of the recess. The sealing ring is made so that the adjoining web portion, which extends radially inwardly from the sealing portion, has an axial length smaller than the axial depth of the recess. When the sealing ring is seated within the recess so that the sealing portion extends radially from the recess before the fastener assembly is mounted to such a workpiece, the adjoining web portion serves an important function, by positioning the sealing ring concentrically within the recess. The fastener assembly is arranged so that, when the threaded portion of the shank is threaded into the threaded aperture until the head bears against the sealing surface of the workpiece in metal-to-metal contact, the sealing ring is compressed into the recess. The sealing portion is compressed axially to form a seal with the sealing surface of the workpiece. It is important for the recess volume to be sufficiently greater than the volume of the sealing ring when compressed into the recess to contain all of the sealing ring over a wide range of cumulative, dimensional tolerances in the metal screw, in the sealing ring, and in the metal workpiece. The sealing ring is made so that the adjoining web portion when unstressed has an inner diameter smaller than the major diameter of the threaded portion of the shank so as to retain the sealing ring on the screw. The outer peripheral portion of the sealing ring is disposed in contact with the outer peripheral surface of the annular recess. Preferably, the sealing ring when unstressed has an outer diameter larger than the outer diameter of the recess, so that the sealing ring fits snugly into the recess before the sealing ring is compressed. In the following a preferred embodiment of this invention is described with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is an exploded, elevational view partially sectioned along a radial plane to show a fastener assembly according to this invention and comprising a metal screw and a sealing ring. Figure 2 is a plan view of the sealing ring apart from the metal screw. Figure 3 is a partly sectioned, elevational view showing the sealing ring seated within an undercut, annular recess in the screw head, as the fastener assembly is assembled before being mounted to a metal workpiece. Figure 4 is a partly sectioned, elevational view showing the fastener assembly mounted to a metal workpiece having a threaded aperture, into which the threaded portion of the screw shank is threaded. Detailed Description of Preferred Embodiment As shown in the drawings, a fastener assembly 10 constitutes a preferred embodiment of this invention. As shown in Figure 4, the fastener assembly 10 is mountable to a metal workpiece 12 having a sealing surface 14 and a threaded aperture 16 opening from the sealing surface 14. As shown, the workpiece has a frusto-conical countersink 18, where the aperture 16 opens from the sealing surface 14. The fastener assembly 10 comprises a metal screw 20 and a sealing ring 22 made from an elastomeric material, such as synthetic rubber or polypropylene. The sealing ring 22, which is shown separately in Figure 2, is molded from the elastomeric material. Because of this invention, the fastener assembly 10 is effective over a wide range of cumulative, dimensional variations in the metal screw 20, in the sealing ring 22, and in the metal workpiece 12. In one application contemplated by this invention, the metal workpiece 12 is an oil pan of an internal combustion engine, as for an automobile or a truck, and the fastener assembly 10 is a drain plug for the oil pan. For such an application, the sealing ring 22 is made from an elastomeric material that does not degrade when exposed to motor oil, polypropylene being a suitable material. In such an application, the fastener assembly 10 and the metal workpiece 12 would be inverted from their positions in Figures 1, 3, and 4. The fastener assembly 10 is expected to be also useful in other similar and dissimilar applications. The screw 20 has a driving head 30, which includes an integral washer 32, and an integral shank 34 adjoining the integral washer 32 and defining an axis. The shank has a threaded portion 36 with a major (crest) diameter. Where the shank 34 adjoins the integral washer 32, the shank 34 has a short portion 38 with a diameter less than the major diameter of the threaded portion 36. In the integral washer 32, the head 30 has an undercut, annular recess 40, which is generally rectangular when viewed in a radial plane. See, e.g., Figure 1. The recess 40 has an annular sealing surface 42, an outer cylindrical surface 44 with a diameter defining the outer diameter of the recess 40, and an inner cylindrical surface 46 defining the inner diameter of the recess 40. The head 30 has an outer, annular bearing surface 48, as shown. The recess 40 has a volume measured between the sealing surface 42 and a plane comprising the bearing surface 48. The recess 40 has an axial depth measured therebetween. Preferably, as shown, the diameter of the inner cylindrical surface 46 is equal approximately to the major diameter of the threaded portion 36 of the shank 34. Preferably, as shown, the difference between the radius of the outer cylindrical surface 44 and the radius of the inner cylindrical surface 46 is approximately three times the axial depth of the recess 40. The sealing ring 22 is made so as to have a special shape relative to the recess 40. As shown, the sealing ring 22 is made so as to have a sealing portion 60 and an adjoining portion or web 62, which extends radially inwardly from the sealing portion 60. The sealing portion 60 resembles an O-ring, which has a diameter defining the axial thickness of the sealing portion 60. The sealing ring 22 is made so that, when it is unstressed, the axial thickness of the sealing portion 60 is substantially greater than the axial depth of the recess 40. Preferably, as shown in Figure 1, the axial thickness of the sealing portion 60 is approximately four-thirds the axial depth of the recess 40. Thus, as shown in Figure 3, the sealing portion 60 extends axially from the recess 40 when the sealing ring 22 is seated within the recess 40 so that the sealing portion 60 engages the sealing surface 42 before the fastener assembly 10 is mounted to the workpiece 12. Also, as shown in Figure 3, the adjoining portion 62 positions the sealing ring 22 concentrically within the recess 40 before the fastener assembly 10 is mounted to the workpiece 12. The sealing ring 22 is made so that, when it is unstressed, the adjoining portion 62 has an axial thickness substantially smaller than the axial depth of the recess 40. Preferably, as shown in Figure 1, the axial thickness of the adjoining portion 62 (except at its outer and inner extremities) when the sealing ring 22 is unstressed is approximately one-half the axial thickness of the sealing portion 60 and approximately two-thirds the axial depth of the recess 40. The sealing ring 22 is made so that, when it is unstressed, the adjoining portion 62 has an inner diameter slightly smaller than the major diameter of the threaded portion 36 of the screw shank 34 and slightly smaller than the diameter of the inner cylindrical surface 46 of the recess 40 and the sealing portion 60 has an outer diameter slightly greater than the outer diameter of the recess 40. As the fastener assembly 10 is being assembled, the sealing ring 22 is stretched slightly as it is forced along the threaded portion 36 of the shank 34, toward the head 30. When the fastener assembly 10 is assembled properly, as shown in Figure 3, the adjoining portion 62 embraces the inner cylindrical surface 46 snugly and the sealing portion 60 is confined snugly by the outer cylindrical surface so as to retain the sealing ring 22 in its seated position within the recess 40. However, even if the sealing ring 22 becomes dislodged accidentally so that the adjoining portion 62 surrounds the short portion 38 of the shank 34 between the integral washer 32 and the threaded portion 36 of the shank 34, the adjoining portion 62 retains the sealing ring 22 on the screw 20 until the sealing ring 22 is forced along the threaded portion 36 of the shank 34, away from the head 30. The sealing ring 22 is made so as to have a volume substantially less than the volume of the recess 40 when the sealing ring 22 is unstressed. Thus, when the fastener assembly 10 is mounted to the workpiece 12, the volume of the recess 40 is sufficiently greater than the volume of the sealing ring 22 when compressed into the recess 40 to contain all of the sealing ring 22 over a wide range of cumulative, dimensional tolerances in the metal screw 20, in the sealing ring 22, and in the metal workpiece 12. As shown in Figure 4, the fastener assembly 10 is mountable to the workpiece 12 so that the threaded portion 36 of the shank 34 is threaded into the threaded aperture 16 until the bearing surface 48 on the integral washer 32 of the head 30 bears against the sealing surface 14 of the workpiece 12 in metal-to-metal contact. Thus, the sealing ring 22 is compressed into the recess 40. Also, the sealing portion 60 forms a seal with the head 30, at the sealing surface 42 of the recess 40, and a seal with the workpiece 12, at the sealing surface 14. Moreover, the volume of the recess 40 is sufficiently greater than the volume of the sealing ring 22 when compressed into the recess 40 to contain all of the sealing ring 22 over a wide range of cumulative, dimensional tolerances in the metal screw 20, in the sealing ring 22, and in the metal workpiece 12. Although the countersink 18 may accommodate a small part of the adjoining portion 62, a countersink is not needed to accommodate any part of the sealing ring 22.

Claims: A fastener assembly, to be mounted upon a workpiece having a sealing surface and a threaded aperture extending from the sealing surface, comprising a metal screw (10) having a head portion (30) and a shank portion (34) integral with the head portion (30) and being threaded (36), the head portion (30) having an annular recess (40) surrounding the shank portion (34) and having a predetermined volume, a predetermined axial depth, an outer peripheral surface (44) and an inner peripheral surface (46), and a sealing ring (22), having an annular sealing portion (60), and a volume which is less than that of the recess (40), an inner peripheral portion of the sealing ring (22) being disposed in contact with the inner surface (46) of the annular recess (40) so that the annular sealing ring (22) is able to be seated and retained within the annular recess (40), the annular sealing portion (60) having an axial depth which is greater than the depth of the annular recess (40) so as to project axially outwardly from the annular recess (40) prior to a compression by the workpiece, characterized in that the outer peripheral portion of the sealing ring (22) is disposed in contact with the outer peripheral surface (44) of the annular recess (40), the annular sealing ring (22) has an annular web portion (62) projecting radially from the annular sealing portion (60), having an axial length which is less than the depth of the annular recess (40) and defining the inner peripheral portion which contacts the inner peripheral surface (46) of the annular recess (40). The fastener assembly of claim 1, wherein the web portion (62) when unstressed has an inner diameter smaller than the major diameter of the threaded portion of the shank (34). The fastener assembly of claim 1, wherein the sealing ring (22) is fabricated from an elastomeric material. The fastener assembly of one of the claims 1 to 3, wherein the annular web portion (62) is disposed within a plane which is located at an axial position with respect to the sealing portion (60) of the sealing ring (22) which is disposed centrally of the axial depth of the sealing portion (60) of the sealing ring. The fastener assembly of one of the claims 3 or 4, wherein the elastomeric material comprises polypropylene. The fastener assembly of one of the claims 1 to 5, wherein the axial depth of the web portion (62) is approximately one half of the axial depth of the sealing portion (60) of the sealing ring (22).

Inventors: JONES JAMES D JR, JONES, JAMES D., JR.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1993
Main classification: F16B43
IPC codes: F01M11, F16B43