Vehicle roof structure

Abstract

A vehicle assembly includes a roof structure having a roof panel formed of aluminum or an aluminum-based alloy and a vehicle body formed of steel or a steel alloy supporting the roof structure. The vehicle body includes a pair of laterally spaced side panels, a front roof rail and a rear roof rail. A bracket formed of steel or a steel alloy secures the roof structure to the vehicle body. The bracket has a first portion fastened to the roof panel and a second portion extending away from the roof structure and welded to the vehicle body. An adhesive located inward of the connection of the vehicle body and second portion of the bracket bonds the second portion to the vehicle body. The adhesive seals the connection of the roof panel and bracket first portion and reduces thermal distortion of the attached roof panel relative to the vehicle body.

Description

BACKGROUND[0001]The substitution of aluminum or aluminum-based alloy roof panels for the low-carbon steel or steel alloy roof panels most commonly used in motor vehicles is an attractive option for vehicle mass reduction. Often, however, the remainder of the vehicle body structure continues to be fabricated of steel. Joining an aluminum roof panel to a steel body panel is difficult due to the thermal expansion considerations of the dissimilar materials. The combination of the aluminum roof panel attached to the steel body may create compressive stresses in the aluminum roof panel when the body is subjected to elevated temperatures such as those required to cure or bake the paint applied to the body. These stresses may lead to unacceptable appearance features in the visible segment of the roof panel.[0002]Manufacturers currently secure the aluminum roof panel to the steel body panel after the weld process in assembly. This process typically includes an adhesive bonding operation. Sel...

AI Technical Summary

Benefits of technology

[0004]In accordance with one aspect, a vehicle assembly comprises a roof structure including a roof panel formed of aluminum or an aluminum-based alloy and a vehicle body supporting the roof structure and formed of steel or a steel alloy. The vehicle body includes a pair of laterally spaced side panels, a front roof rail and a rear roof rail. Each roof rail spans between the side panels. At least one bracket secures the roof structure to the vehicle body. The bracket has a first portion fastened to the roof panel and a second portion extending away from the roof structure and welded to the vehicle body. The bracket is formed of steel or a steel alloy. An adhesive located inward of the weld connection of the vehicle body and second portion of the bracket bonds the second portion to the vehicle body. The adhesive seals the fastened connection of the roof panel and first portion of the bracket from moisture to prevent galvanic corrosion between the dissimilar materials of the roof panel and bracket. The adhesive further reduces thermal distortion of the attached roof panel relative to the vehicle body when the vehicle assembly is heated in a paint bake oven during the manufacture of the vehicle assembly.

[0005]In accordance with another aspect, a vehicle assembly comprises a vehicle roof structure including a roof panel and a vehicle body. The vehicle roof structure is formed of aluminum or an aluminum-based alloy. The vehicle body includes a pair of laterally spaced side panels and a front roof rail and a rear roof rail spanning between the side panels. The side panels together with the front and rear roof rails support the vehicle roof structure. The vehicle body is formed of steel or a steel alloy. A pair of side brackets connects the side panels to roof panel, a front bracket connects the front roof rail to the roof panel, and a rear bracket connects the rear roof rail to the roof panel. Each bracket has a first portion fastened to the roof panel and a second portion extending outwardly of the roof panel and welded to the vehicle body. Each bracket is formed of steel of a steel alloy. The vehicle roof structure is bonded to the vehicle body via an adhesive. Each of the brackets provides a continuous vertical spacing between the roof panel and the vehicle body of approximately 4 mm to approximately 6 mm, and the adhesive is provided in the spacing. The adhesive seals the fastened connection of the roof panel and first portion of the bracket from moisture to prevent galvanic corrosion between the dissimilar materials of the roof panel and bracket. The adhesive further reduces thermal distortion of the attached roof panel relative to the vehicle body when the vehicle assembly is heated in a paint bake oven during the manufacture of the vehicle assembly.

Problems solved by technology

Joining an aluminum roof panel to a steel body panel is difficult due to the thermal expansion considerations of the dissimilar materials.

The combination of the aluminum roof panel attached to the steel body may create compressive stresses in the aluminum roof panel when the body is subjected to elevated temperatures such as those required to cure or bake the paint applied to the body.

These stresses may lead to unacceptable appearance features in the visible segment of the roof panel.

This approach, though appealing from a vehicle mass-reduction viewpoint, raises issues due to the significantly different coefficients of thermal expansion of aluminum and steel (about 22.5×10−6 m / m K for aluminum and about 13×10−6 m / m K for steel).

Further, because the steel and aluminum are permanently joined together by the rivets, this difference in thermal expansion of steel and aluminum will develop stresses in the aluminum and steel whenever the vehicle body temperature differs from the temperature at which the joint was made.

Since plastic deformation is not reversed on cooling, any such deformation may result in an appearance feature such as a crease or buckle in the roof panel which could be unacceptable to the customer.

Further, having the roof and vehicle body panels in contact or electrically connected can create galvanic corrosion.

The risk for this corrosion is increased when water is present, such as in the roof gutter areas.

However, the heat from the paint bake ovens can cause distortion of the aluminum roof panel relative to the steel body, creating a bowing effect.

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