Lightweight garage #13 composite tunnel reinforcement @ Jeep Grand Cherokee (WL)

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Lightweight garage, News

The vehicle

This time, a Jeep Grand Cherokee WL75 has been imported from America into our lightweight garage. With a length of 5.20 m and a wheelbase of over 3 m, this SUV offers enough space for a third row of seats. The 5.7 liter naturally aspirated V8 engine delivers up to 357 hp and 357 Nm.

©Automotive Rhythms, Jeep Grand Cherokee L 2021, CC BY-NC-ND 2.0

In addition, different all-wheel drives are available depending on the equipment and the Jeep can conquer ramp angles of up to around 23°.

The technology

A new feature of this vehicle is the reinforcement of the tunnel with a pultrusion-manufactured structure based on Elastocoat polyurethane and continuous glass fibers. In pultrusion, a semi-finished fiber product (e.g. roving) is impregnated with the resin system in an impregnation tank and formed into the desired cross-sectional shape in the tool. The fiber-reinforced plastic composite is then cured. In the next step, the profile is pulled out of the mold and cut to the specified length.

This manufacturing process, also known as the extrusion process, makes it possible to produce large quantities of fiber-reinforced profiles economically. By improving the production process in particular, it was possible to double the output quantity for the Jeep compared to the industry average.

The lightweight aspect

Characteristic material properties combined with the advantages of the manufacturing process result in a higher specific strength than ultra-high-strength steel. In order to exploit the anisotropic material properties, the material behavior has been simulated and designed for the critical load case.


The load-optimized design of the tunnel reinforcement results in a primary weight saving of 40 % and 20 % for the subsystem. The solution also received the Altair Enlighten Award for "Module Lightweighting" for the weight saving of around 2.1 kg. The required installation space was also reduced thanks to the optimization.

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