SCREW GROMMET

Abstract: A one-piece plastics screw grommet has a hollow shank 3 with a flange 4 at one end and a pre-threaded plug 2 detachable therefrom on rotating a screw to pull the parts together. The outside of the shank 3 is shaped at 9 to retain it in a hole in a support until the screw is tightened, and has diverging end walls 23 which are spread apart by a wedge-shaped configuration of the end wall 22 of the advancing plug 2. The shank 3 and plug 2 may have interlocking configurations 20, 21 to hold them together after tightening the screw. The grommet is convenient to use in fixing parts together where the remote one is thin metal with a hole in it to receive the grommet before placing the other part over it and introducing the screw. In particular, there is little or no tendency for the nut to rotate on turning the screw.

Description: Screw Grommet The present invention relates to a screw grommet for use in connecting a member such as a panel to a vehicle body or the like. A commonly-known screw grommet comprises a shank and a flange and is used to connect a panel to a vehicle body by inserting the shank into a mounting hole of the vehicle body for engagement and by screwing the screw, which has been passed through a mounting hole of the panel, into a hole of the shank. This screw grommet is convenient as it can connect a panel by screwing without fixing a nut in the case of a vehicle body made of a thin plate. A self-tapping screw is often used with such a screw grommet as just referred to, and the screwing operation is done with the aid of an impact wrench (or screw driver). Therefore, when the mounting hole of the vehicle body is round, the screw grommet tends to rotate together with the screw, failing to achieve a sufficiently secure connection. To prevent this, a square hole may be formed in the vehicle body. Alternatively in the case of a round hole, it is also a practice for another hole to be formed adjacent to the mounting hole for engagement by a transversely-extending finger provided on the screw grommet which prevents the grommet from rotating. However, these second holes cannot readily be formed without appropriate presswork on the vehicle body. Otherwise, forming an additional hole increases the number of steps. Accordingly, it is desirable to provide a screw grommet which can produce a sufficiently strong attaching force with only one round hole formed by simple drilling. It is therefore an object of the present invention to provide a screw grommet which does not rotate together with the screw when the latter is screwed in even if the mounting hole is round. According to the invention, there is provided a screw grommet for connecting together two plate members by inserting the grommet into a hole in one of the members and introducing a screw through a hole in the other member and into the grommet complete. Preferably the shank of the body portion of a grommet in accordance with the invention has longitudinal slits extending along it from where the diverging end walls meet. A grommet in accordance with the invention may also comprise engagement means to lock the nut portion and the shank of the body portion together as tightening of the screw is completed, and such engagement means may take the form of annular groove in the nut portion and complimentary shoulders on the inside of the shank. There now follows a detailed description of a grommet in accordance with the invention, and selected to illustrate the invention by way of example, which description is to be read reference to the accompanying drawings, in which Figures l(a) - (i) shows the illustrative grommet, (a) in front view, (b) in plan view, (c) in underneath view, (d) in side view, (e) in sectional view taken along the line (e) (e) of Figure 1 (a), (f) in sectional view taken along the line (f) (f) of Figures 1(a); (g) in sectional view taken along the line (g) (g) of Figure 1 (a). (h) in sectional view taken along the line (h) (h) of Figure I (b), and (i) is a sectional view taken along the line (i) (i) of Figure 1 (b); Figure 2 is an explanatory illustration showing how the illustrative grommet may be used; Figure 3 is a sectional view showing a completed fixing; Figure 4 (a) - (i) are similar to Figures 1 (a) (i) but depict a modified form of the illustrative grommet using the same reference numerals for corresponding parts. Figure 5 is a sectional view showing the grommet of Figure 4 in partially secured condition. Figure 6 is a sectional view similar to Figure 5 but showing the grommet in fully secured condition; and Figure 7 is a front view of the fully secured grommet of Figure 6. In Figures 1 (a) - (i), the screw grommet according to the present invention comprises a body 1 and a hollow plug or nut 2. The body 1 has a hollow shank 3 and a flange 4 at the upper end thereof, and the plug 2 is disposed at the lower end of the shank 3. The body 1 and plug 2 are made of a plastic material and are formed as one-piece initially connected through semi-annular thin portions 6. The shank 3 of the body is hollow, preferably with the inside diameter of its upper portion made slightly larger than that of the lower portion so as to facilitate the insertion of the screw. It is preferable that both inside diameters are made slightly larger than the outside diameter of the screw. As shown in Figure 1 (a), the plug 2 is formed preferably in a wedge-like shape with converging end walls 22 to be driven into the shank 3 of the body. Further, it is preferred that the shank 3 of the body is formed in a complementary configuration to the plug 2, with diverging end walls 23. Preferably, slits 7 extending upwardly from the lower end when the wall 23 are formed in the side surface of the shank 3. With these features, the plug 2 can easily enter the shank 3 from the lower end of the latter and can easily expand lower end portions 8, 8 of the shank radially outwardly. Engagement protrusions 9, 9 are formed on the outer side of the shank 3 to lightly engage with a mounting hole of a vehicle body or the like to serve for temporary connection against accidental ejection. An internally threaded portion 10 is formed on the inner side of the plug 2 so as to prevent the grommet from rotating together with the screw even at the early stage of the screw rotation. Figure 2 shows the procedure to connect a panel 13 to a vehicle body 12 by the use of the screw grommet. To begin with, as indicated by Arrow I, the plug 2 and the shank 3 of the body are inserted into a round mounting hole 14 of the vehicle body 12, and the grommet is lightly engaged with the vehicle body by means of the lower surface of the flange 4 and the engagement protrusions 9, 9 of the shank 3 so that it will not fall out. Next, as indicated by Arrow II, a mounting hole 15 of the panel 13 is brought in line with the hollow portion-of the shank 3, and a screw 16 is screwed in by an impact wrench (or screw driver) as indicated by Arrows III and IV. Alternatively, the screw 16 may be inserted into the mounting hole 15 of the panel 13 before the panel is brought into engagement with the body 1. With the rotation of the screw 16, firstly the tip of the screw is screwed into the internally threaded portion 2. The screw 16 advances inside the internally threaded portion, and a head 17 of the screw 16 comes into surface-contact with the panel 13 to push it. By further rotating the screw 16, the plug 2 is drawn upward gradually to break the thin portions 6. After the thin portions 6 have been broken, the wedge-like tip of the plug comes in contact with inclined surfaces of the lower ends 8, 8 of the body shank which are in the complementary configuration. Then the plug, on further advance towards the body 1, expands them radially in opposite directions from the slits 7 as shown in Figure 3. With the expansion, the attaching force of the shank of the body to the vehicle body 12 increases. The attaching force is strengthened by drawing the plug upward, and the grommet is prevented from being rotated by frictional resistance between the body 1 and panel 13, which is greater than the frictional force between the screw 16 and the internally threaded portion 10. Thus, even if the mounting hole 15 of the vehicle body is formed as a round hole (not as a square one), the grommet does not rotate with the screw 16. Of course, the mounting hole 15 can be a square one. In this case, a tapping screw or the like can be used without threading the inner surface of the plug if the outer surface of the shank is formed to be square. Figures 4 (a) - (i) show a second embodiment of the present invention. This screw grommet is identical to the first embodiment in which the body 1 comprises the shank 3 and the flange 4 and the plug 2 is integrally connected through the thin portions 6 of the body. In this embodiment, engagement pawls 20 are formed at the lower end of the shank 3 at either side of the slits 7, and an annular engagement groove 21 is formed on the outer surface of the plug 2. Thus, the engagement pawls 20 and the engagement groove 21 compose engagement means to connect the plug to the body. In operation, the lower end of the shank of the body is expanded slightly radially outwardly by drawing the plug 2 into the shank 3 of the body as shown in Figure 5, and the plug 2 is further drawn in by the rotation of the screw 16 as shown in Figure 6. Then, the engagement pawls 20 of the shank of the body enter the engagement groove of the plug 2 and the plug 2 is connected to the body 1. This condition is shown in Figure 7. Since the plug 2 and the body 1 are connected to each other as described above, when the screw 16 is removed to change the panel 13 or for other purposes, the plug 2 is prevented from falling off the body 12 to eliminate the trouble to pick up and hold the plug against the body for reuse. The second embodiment is also provided with the engagement means comprising engagement pawls of the shank of the body and an annular groove of the plug. So far as it enables the plug to engage with the body when the former is drawn into the shank of the body, however, any suitable engagement means can be adopted. For example, it can be a combination either of a protrusion and a recess or of two shoulders to be engaged with each other.

Claims: Claims: 1. A screw grommet for use in connecting together two plate members by inserting the grommet into a hole in one of the members and introducing a screw through a hole in the other member and into the grommet, the grommet comprising a body portion (3) and a nut portion (2) moulded as one piece of thermoplastic material, the body portion comprising a hollow shank with a head flange (4) at one end to engage the exposed surface of said one of the members when the grommet is inserted into the hole in it, and the shank having an external surface which provides shoulders (9) to lightly engage the other surface of said one of the members to resist accidental e-jection of the grommet from said hole after insertion, and the nut portion being hollow with an internal screw thread (10) to be engaged by that of the screw, the body portion and nut portion being interconnected by thin wall portions (6) which break on said portions being drawn together by advance of the nut portion when a screw introduced thereinto is rotated, confronting complementary ends of the body portion and nut portion being V-shaped with wedge-shaped end walls (22) of the nut portion accommodated in diverging end walls (23) of the body portion whereby, when the nut portion advances, the body portion spreads out in opposite directions to overlie the blind side of the said one of the members and thereby firmly secure the grommet against withdrawal. 2. A grommet according to claim 1 further characterised in that longitudinal slits (7) extend along the shank of the body portion (3) from where the diverging end walls (23) meet. 3. A grommet according to claim 2 further characterised in that it comprises engagement means (20,21) to lock the nut portion (2) in the shank of the body portion (3) as tightening of the screw is completed. 4. A grommet according to claim 3 further characterised in that said engagement means takes the form of an annular groove (21) in the nut portion and complementary shoulders (20) on the inside of the shank. 5. A screw grommet for use in connecting together two plate members by inserting the grommet into a hole in one of the members and introducing a screw through a hole in the other member and into the grommet, the grommet comprising a body portion (3) and a nut portion (2) moulded as one piece of thermoplastic material, the body portion comprising a hollow shank with a head flange (4) at one end to engage the exposed surface of said one of the members when the grommet is inserted into the hole in it, and the shank having an external surface which provides shoulders (9) to lightly engage the other surface of said one of the members to resist accidental ejection of the grommet from said hole after insertion, and the nut portion being hollow to be engaged by the screw, the body portion and nut portion being interconnected by thin wall portions (6) which break on said portions being drawn together by advance of the nut portion when a screw introduced thereinto is rotated, confronting complementary ends of the body portion and nut portion being V-shaped with wedge-shaped end walls (22) of the nut portion accommodated in diverging end walls (23) of the body portion whereby, when the nut portion advances, the body portion spreads out in opposite directions to overlie the blind side of the said one of the members and thereby firmly secure the grommet against withdrawal, the grommet also comprising engagement means (20, 21) to lock the plug portion (2) in the shank of the body portion (3) as tightening of the screw is completed.

Inventors: YUTA, KIYOTERU
Applicants: EMHART INDUSTRIES, INC., TUCKER FASTENERS LIMITED
Application year: 1986
Main classification: F16B13
IPC codes: F16B13