Fastening assembly for fastening a first member to a second member

Abstract: A fastening assembly for fastening a first member (10) to a second member (40) comprising at least one threaded fastener (20,22) having a head (24,26) at one end thereof, said head having engagement surfaces for a tool, a threaded shank (28,30), the other end of said shank having engagement surfaces (32,44) for a tool, at least one receiving bore (12,14) in the first member (10) into which said threaded shank (28,30) is threaded in a pre-mounted state from one end thereof, with the head (24,26) being spaced from the associated surface of the first member (10), the second member (40) being preferably of thin sheet material and having at least one elongated opening (42,44), said opening having a first portion (46,48) adapted to allow the entrance of said head (24,26) and a smaller portion (50,52) adapted to accommodate said shank while said head grips behind the edge of said opening (42,44).

Description: The invention refers to a fastening assembly fastening a first member to a second member according to patent claim 1. When fastening a sensor, e. g. for an airbag, it is required that the fastener means, e. g. one or a plurality of threaded fasteners must not project beyond the sensor, otherwise the danger is to be seen that the safety belt which is attached to a column of the car body contacts the end of a solid fastener and thus may be damaged. A fastening of such a housing from the opposite side normally is not possible as the hollow column does not admit access to the interior thereof. Fastener means used in automobiles are known from EP-A-0 654 372. The invention provides a fastening assembly consisting of a member to be fastened, in particular a housing for a sensor, and a support member which allows a safe and extremely simple and quick fastening without leaving unnecessarily protruding parts. The fastening assembly according to the invention provides a threaded fastener which is accommodated by a through-going bore of the member, e. g. sensor housing. The threaded fastener has a head at one end thereof which may be additionally formed with a flange portion serving as a washer. The threaded shank of the fastener is accommodated by an inner thread of the bore and has engagement surfaces for a tool at the free end thereof, e. g. a so-called Torx-portion. The second member which is preferably of thin sheet material, e. g. a column of the body of an automobile, has an opening or a hole which comprises two portions, namely a larger portion allowing the passage of the fastener head and a smaller sized portion which allows the head to grip behind the edge of the hole while contemporarily accommodating the fastener shank. The fastener is pre-assembled in the member such that the head is spaced from the associated surface of the member. According to an embodiment of the invention, the fastener shank can be threaded into an insert which for example forms an interference fit with the bore. If, however, the member is of metallic material in the area of the bore, the bore can be provided with an inner thread. In any case it is appropriate if the thread of the shank has an adhering portion by which the threaded fastener is held in the pre-position. With the pre-mounted threaded fastener the member is then brought into engagement with the support member, with the head being introduced through the larger portion of the hole. Thereafter, the member is displaced along the outer surface of the support member so that the head grips behind the edge of the hole, and the shank enters the smaller portion thereof. Now, the threaded fastener can be tightened in that the tool engages the end of the shank. When tightened the head of the fastener engages the inner side of the sheet material of the support member. It is understood that the threading movement at the end of the shank is opposite to that at the end of the head. As the most screw drivers normally are turning right-hand, it is recommended according to an embodiment of the invention to provide the threaded shank with a left hand thread. For the pre-assembling in this case a driver is necessary which turns left hand. If as explained above a protruding of the fastener is not desired it must be taken care that sufficient space is prevailing for the engagement of the driver. If an insert is used the space between shank and wall of the bore is automatically larger. If, however, the fastener is directly threaded into the bore, the bore preferably has an enlarged portion at the end opposite to the fastener head to allow engagement of the screw driver. The hole in the support member preferably has the shape of a keyhole with the smaller portion being below the larger one. The fastener assembly according to the invention allows a pre-assembling of the member with the threaded fastener so that the final assembling can be carried out within shortest time. The portion of the shank which is free of a thread adjacent to the head thus cannot be damaged which would not allow an assembling or a threading. For example, the fastener shank can have a clearance with respect to the wall of the hole in order to allow the precise positioning of the member. The fastener assembly according to the invention for example allows the attachment of the housing of an airbag sensor to the column such that unnecessarily protruding parts are avoided. The fastener assembly according to the invention is extremely simple structured. A simple threaded fastener is used only having the particularity that the end of the shank is provided with engagement surfaces for a tool. A nut which normally is used for the screw attachment is not necessary. An embodiment example is subsequently explained along accompanying drawings. Fig. 1 shows a cross section through an attachment of an airbag sensor to a column of the body of an automotive vehicle. Fig. 2 shows a view on the assembly of Fig. 1 in the direction of arrow A. Fig. 3 shows a detail B of Fig. 1 without the column and in a pre-assembled condition of the sensor housing with a threaded fastener. By cross hatching in Fig. 1 the housing 10 of an airbag sensor is indicated. The housing 10 has two through-bores 12, 14 into which inserts 16 and 18 are inserted by an interference fit. The inserts 16, 18 have an inner thread. Threaded fasteners 10 and 12 are provided with a head 24, 26, threaded shanks 28, 30 and ends 32, 34. The threaded shank is threaded into the inner thread of the inserts 16,18. The ends 32, 34 of the shank have a Torx-portion. The heads 24, 26 have integrally formed radial flanges 36, 38. A non-threaded portion 29 joins the heads 24, 26. A column 40 of a body of an automotive vehicle not shown in detail is hollow and formed of sheet material. At the inner side the column 10 has two holes 42, 44 in vertical alignment. The holes 42, 44 are shaped like a keyhole with an upper circular larger portion 46, 48 and a smaller portion 50, 52 below the larger position. The larger portion is so dimensioned that the head 24, 24 with flange 36, 38 can be inserted. The smaller portion 50, 52 is dimensioned such that the flange may grip behind the edge of the hole 42, 44 as can be seen in Figs. 1 and 2. In Fig. 3 two different embodiments are to be seen. In the lower portion of Fig. 3 the illustration corresponds to that of Fig. 1. In the upper portion of Fig. 3 the insert 16 is omitted. Rather, bore 12a has an inner thread into which the threaded shank 28 is threaded immediately In order to allow the engagement of a screw driver with the Torx-portion 32 in Fig. 3 the bore 12a is provided with an enlarged portion 12b. In Fig. 3 it can be finally seen that the fastener 20 has a pre-assembled position wherein flange 36 has still a distance from the associated surface of the housing, the distance being somewhat larger than the thickness of the sheet material into which the holes 42, 44 are formed. The shank is partially provided with a plastic coating 60 which allows the fastener 20 to remain in the pre-assembled position. The coating 60 not only secures the pre-assembled state, rather locks the screw when finally tightened as shown in Fig. 1. The shank 28 for example has a left hand thread so that during pre-assembling the fastener is threaded into bore 12 by a left hand screw driver. In the pre-assembled state the sensor housing 10 is brought against column 40 with the heads 24, 26 inserted through the portion 46, 48 of holes 42, 44. Then the housing can be released so that the shank 28, 30 enters the smaller portion 50, 52 of hole 42, 44, and flange 36, 38 grips behind the edge of the hole. Now the fastener 20, 22 can be tightened by a right hand screw driver in order to attach the housing 10 tightly to column 40. The end of the shaft does not project beyond the housing so that a damage of the safety belt does not occur.

Claims: A fastening assembly fastening a first member to a second member comprising at least one threaded fastener (20, 22) having a head (24, 26) at one end thereof, said head having engagement surfaces for a tool, a threaded shank (28, 30), the other end of said shank having engagement surfaces (32, 44) for a tool, at least one receiving bore (12, 14) in the first member (10) into which said threaded shank (28, 30) is threaded from one end thereof, to allow the head (24, 26) to be spaced from the associated surface of the first member (10) in a pre-mounted state, the second member (40), being preferably of thin sheet material, having at least one elongated opening (42, 44), characterised in said opening having a first portion (46, 48) adapted to allow the entrance of said head (24, 26) and a smaller portion (50, 52) adapted to accommodate said shank while said head grips behind the edge of said smaller portion (42, 44). The assembly of claim 1, wherein said threaded shank (28, 30) has a left hand thread. The assembly of claim 1 or 2, wherein a cylindrical insert (16, 18) is pressed into said bore, said insert having an inner thread adapted to receive said threaded shank (28, 30). The assembly of one of the claims 1 to 3, wherein said threaded shank has a local plastic coating (60). The assembly of one of the claims 1 to 4, wherein said engagement surfaces (32, 34) of the end of said shank having a Torx-portion, an inner or outer hexagon.

Inventors: BREHMER LOTHAR, JAKOB ANDREAS, JAKOB, ANDREAS
Applicants: ITW AUTOMOTIVE PROD GMBH & CO, ITW AUTOMOTIVE PRODUCTS GMBH & CO. KG
Application year: 1998
Main classification: F16B5
IPC codes: B60R11, B60R21, F16B5, F16B35