The subframe is the foundation of your rolling house.
It has the task of connecting the body to the chassis, just as the foundation of a house has the task of anchoring the house on the property.
If a house is on a slope, on a sandy beach, on rocky ground or even in an earthquake area – each time the foundation looks different – each time it is adapted to the special conditions of the subsoil.
In the same way, in vehicle construction, the connection between the body and the chassis must be adapted to the selected chassis, the body size, the body weight and the intended use.
There are two fundamentally different categories of use – on-road and OFF-ROAD.
For pure road use – and thus is for 99.9% of all trucks – the simple connection of body and chassis recommended by the truck chassis manufacturers is sufficient. It rigidly bolts the body to the chassis transferring torsion into the body. This is acceptable for a normal transport structure without cutouts in the side walls and without interior fittings.
However, if the body is a container for the transport of gases or liquids, then a more complex subframe is already prescribed for this type of body (which would crack due to the twisting) by the truck chassis manufacturers even for pure road use.
The principle of partly flexible mounting is used in order to isolate the limited chassis twisting that occurs in road use.
Rigidly bolting is by no means sufficient for OFF-ROAD use, even a partly flexible mounting system would be a bad compromise.
The Mercedes-Benz bodybuilder regulations therefore mandate the use of a torsion free subframe for the Unimog.
The fact that the engineers at Mercedes-Benz Unimog have developed a special torsion free subframe especially for their all-terrain chassis shows the need for a high-quality technical solution and is in the best tradition of the company.
The question of whether such a floor pan is only necessary for the Unimog or also for all-wheel drive trucks in off-road use is reduced to the easy-to-answer question of whether or not different physical laws apply to the Unimog.
UNICAT has therefore designed and used torsion-free subframes from the very beginning – and for all vehicles we have ever built.
How does the torsion free UNICAT subframe work?
The chassis, on the one hand, should be as off-road capable as possible and offer good driving stability when driving fast.
For this purpose, the flexibility designed by the manufacturer must not be restricted. The twisting of the frame ensures that the vehicle keeps all wheels in contact with the ground, even on extremely uneven terrain. This is the only way to drive safely off-road.
The body, on the other hand, is designed as a stable box and should deform as little as possible. Of course, this also applies to the built-in furniture and technical equipment.
Anyone who has ever released ice cubes from an ice cube tray knows what causes the deformation of the container – namely the loosening of the ice cubes from the container.
What is wanted here – the falling out of the ice cubes – should be avoided between the body and the furniture!
The chassis and body must therefore be connected in such a way that no torsional forces whatsoever are transferred from the chassis to the body.
The torsion free UNICAT subframe therefore – like the Unimog subframe – always consists of a fixed bearing and 1, 2 or even 3 self-aligning bearings.
The fixed bearing fixes the body in the middle and transfers forces in all directions.
The self-aligning bearings in the front and rear areas only transmit forces in certain directions, so that the vehicle frame underneath can rotate completely unhindered.
Since the weight forces of the structure can no longer be introduced evenly when the frame is twisted, the UNICAT subframe introduces the forces into defined areas on the frame. The main forces are introduced exactly where the rear axle is attached to the frame, so that the load on the frame is even reduced.
The intended movement between the frame and the body must of course also be taken into account when installing tubes, cables, tanks and other frame attachments.
An overall complex task that can only be optimally solved if the body and torsion free subframe are created under one roof – as with UNICAT.
Here you can see a video about the subframe