Assembly unit including a component and at least one screw

Details Assembly unit including a component and at least one screw Assembly unit including a component and at least one screw

2002-02-01

2003-09-23

Wilson, Neill (Department: 3679)

Expanded, threaded, driven, headed, tool-deformed, or locked-thr

Headed fastener element with nut, washer, securing means or cap

Metallic resilient securing means

C411S107000, C411S542000, C411S970000, C411S999000

Reexamination Certificate

active

06623226

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of co-pending German Patent Application No. 101 04 672.3-12 entitled “Montageeinheit aus einem Bauteil und mindestens einer Schraube”, filed on Feb. 2, 2001.
FIELD OF THE INVENTION
The present invention generally relates to an assembly unit including a component and at least one screw. More particularly, the present invention relates to an assembly unit including a bush being made of plastic material.
Generally, assembly technology increasingly requires assembly units in which a plurality of components forms a pre-assembled unit. The assembly unit including a component and usually a plurality of screws is then connected to a work piece. As a typical example for this technology, an upper element and a lower element have to be connected by one or more screws. The upper element as the component and the plurality of screws are combined to form a pre-assembled assembly unit to which the screws are captively connected. The assembly unit is then connected to the lower element by tightening the screws one after the other or simultaneously, especially with the use of a multi-spindle automatic screwing apparatus. Such assembly units are typically used in the production of automobiles. For example, the cast cover of a cast housing—which for example is made of plastic, aluminum or magnesium—or a cover of a transmission forms the component which is to be connected with the work piece by screws. In this case, the work piece means the housing and the housing of the transmission, respectively. Realizing such assembly units allows for a great level of pre-manufacture. The screws are already located at the component in a captive, aligned and pre-assembled way. During transportation, they are safe from being damaged, and they allow for fast connection with the work piece.
BACKGROUND OF THE INVENTION
An assembly unit is known from International Application WO 95/21335. The known assembly unit includes a component, for example a cover of a housing, and at least one fixing element in the form of a screw. A third element is associated with each screw. This third element is a bush which is used to capture the screw. The bush is made of metal, especially of sheet metal. The bush increases the cost of manufacture of the known assembly unit. The bush is pressed into a respective through hole being located at the component which requires a separate pre-assembly step. The bush is fixed in the through hole of the component due to frictional engagement. The bush has a structural height which is a multiple of the structural height of the component in the region of the through hole. The screw itself also has a respective complicated shape and a great axial length. A ring flange is located in the region of the shank of the screw, the ring flange including ring channels at both sides. The ring flange has to be produced at the shank of the screw in addition to the thread. The size of the ring flange is coordinated with the size of a collar being located at the bush in a way that an axial lock is formed, the axial lock still allowing for a respectively great axial movement in a certain region of movement in a way that the screws in the pre-assembled position are located to be captive, but not fixed at the component. There also is the possibility of not arranging a ring flange at the screw. In this case, special elements have to be arranged at the bush, the elements in combination with the screw forming an axial lock. Consequently, the bush gets a more complicated design. In this case, the thread of the screw may fulfill part of the axial lock. There only is a relation between the diameter of the through hole being located in the component and the diameter of the shank of the screw in a way that the screw together with the bush pass through the through hole and have to be inserted into the through hole, respectively. However, exact axial alignment of the screw at the component does not take place since the screw is arranged to be only movable to a limited extent. This fact may be advantageous for screwing the screw into the work piece if it is ensured that the screw finds the entrance into the thread being located into the work piece in a centered way. Due to the possibility of tilting the axes of the screws with respect to one another, entrance of the free end of the shank into the thread in the work piece may only be realized to some limited extent. These disadvantages may be counteracted by the bush as third component within the assembly unit having a relatively great axial length. Especially, it may be designed to be substantially longer than the thickness of the wall of the component. Due to the length of the bush, the length of the screw also has to be increased. As a result, not only costs are increased, but in some cases there is a negative effect on function. Using such bushes in assembly units including at least three single elements is disadvantageous since the bush is subjected to tension while the screw is being screwed into the work piece. In case the bushes are made of comparatively thin deformable sheet metal, there even is the danger of different deformations of the bushes occurring during tightening of the screws in a way that it is only possible to apply reproducible pre-tensioning forces to a limited extent.
German Patent Application No. 196 51 838 A1 shows a component being made of plastic material, the component being designed to be connected to a work piece by screws with an intermediate arrangement of a seal. A bush being made of a metallic material, protruding through the component and being connected to the seal is used. The screw has to include a separately produced ring flange which cooperates with the bush in the sense of an axial lock. In this way, the screw is arranged in a lose, but captive way at the bush. The bush is a third element of the assembly unit in addition to the component and to the screw. The bush does not necessarily have to extend through the entire through hole in the component.
German Patent No. 195 46 072 C2 shows a bush having a shorter axial length and including a conical collar only partly engaging a partially conical through hole in the component under frictional engagement. The captive arrangement is realized by frictional forces in a way that the construction is respectively unsafe. The bush being designed in the form of a disc finally is located between the supporting surface at the head of the screw and the respective counter surface at the component. In this way, the bush is clamped, and there generally are similar disadvantages, as this has been described above.
SUMMARY OF THE INVENTION
The present invention generally relates to an assembly unit. More particularly, the present invention relates to an assembly unit including at least one component and at least one screw including a shank having an outer diameter and at least partially including a thread. The head of the screw is designed and arranged to rotate the screw. A supporting surface of the screw faces the component. The component for each screw includes a through hole having a diameter. At least one bush is associated with the at least one screw, and it is designed and arranged to be insertable into the respective through hole. The bush is made of plastic material, and it is designed and arranged to be fixedly connected in the through hole resulting in elastic deformation of the bush. The inner diameter of the bush is slightly more than the outer diameter of the shank. The supporting surface is designed and arranged to operatively contact the component after assembly without contacting the bush to transmit an axial force. The bush, the screw and the component are designed and arranged to be captively connected.
The novel assembly unit is also suitable for screws which do not produce a thread, for example screws having a metric thread, and in which the respective bush of the pre-assembled assembly unit is not located in the force flux while the screw is screwed into the work piece. Furthermore, the screw and the screws, re

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