Why simple storage is not enough for us
The vehicle body, living cabin and frame, as well as their attachment to the torsionally flexible ladder frame, are subject to the translatory and rotary movements shown during normal operation. Acceleration and braking processes cause forces acting on the vehicle in the direction of travel, transverse swinging when cornering horizontally, transversely to the direction of travel, and lifting and lowering when the level of the ground changes vertically to the direction of travel. Rolling, pitching and yawing in the longitudinal, transverse and vertical directions occur in conjunction with the translatory directions of movement.
Due to the force exerted when driving on flat and uneven terrain, the elaborately constructed living cabins must be connected to the torsionally flexible ladder frame via an interface. Cabin frames are made from torsionally rigid rectangular or tubular profiles, which can hardly adapt to the geometric changes of the ladder frame. The tendency of the ladder frame to twist on hilly terrain is suppressed by a rigid screw or welded connection.
If the cabin frame does not adjust to the twisting ladder frame, this can lead to costly and dangerous frame breakages, which can no longer guarantee the safe driving of the vehicle. Frame breakages are often caused by stress peaks on the welded or screwed connections.
If the cabin frame is not stiff enough and does not follow the geometric length and angle changes of the longitudinal beams, it will twist and transfer forces to the rigid living cabin attached to it. This can lead to stress cracks in the walls and breaks in the cabin frame that may be required. Damage to the cabins is not immediately dangerous for driving, but it does affect the heat and cold insulation and the installed interior fittings. Repairs to the cabin and living area often require higher repair costs.
The consequences of the destruction of some vehicle and cabin components, as well as the massive reduction in off-road capability due to the desired but suppressed frame torsion, are countered with suitable body mounting.
To counteract this problem, there are some other concepts, a few of which are briefly highlighted here:
1. The concept of the spring bearing:
The connection of the body to the ladder frame using a spring mounting concept is often used in the construction machinery sector. The torsionally rigid frame (yellow) supporting the body is attached to the end of the ladder frame (grey) by means of several bolted connections (1). The bolted connections absorb the majority of the dynamic forces occurring in and transverse to the direction of travel.
One or more spring elements (3) (red) are designed to prevent the cab frame (yellow) from constantly lifting off the ladder frame longitudinal member by means of pre-tensioning.
The problem:
If the frame twists unexpectedly, the pre-tensioned springs reach their minimum working length. If the coils of the springs collide in this situation, loads are transferred from the car frame to the side member. At the same time, forces are also transferred to the cabin frame which, if it is not stiff enough, transfers the torsion of the frame further into the cabin walls. Both situations are known to cause damage to the cabin and ladder frame.
2. Diamond bearing concept:
Connecting the structure to the ladder frame using a diamond bearing concept is a more suitable bearing concept. The diamond bearing concept owes its name to the diamond-shaped arrangement of the rocker-like bearing geometry, on which the cabin frame can rotate freely in relation to the longitudinal axis of the rocker. The rockers are mounted transversely (yellow arrow) and longitudinally (red arrow) in the direction of travel via rocker supports on the upper chord or on the web of the U-shaped ladder frame.
The problem:
In their guidelines, manufacturers specify where the translational dynamic forces of the body, i.e. the living cabin, should be introduced. These points are often at the height of the rear axle. If a long living cabin is to be placed on the rough-road chassis, it is no longer possible to maintain the uniform geometric distances between the opposing diamonds, which allow rotational movements around the longitudinal axis in the direction of travel, for weight distribution reasons. With this arrangement, the longitudinal axis of the living cabin moves faster than that of the symmetrical diamond. Forces are exerted on the cylinder bearings transverse to the direction of travel. However, these can only absorb forces in the direction of travel. The cylindrical bearings can be damaged in this case. The resulting vertical forces, introduced onto the web surface, lead to high stresses and thus to cracking of the support.
Our solution
The connection of the structure to the ladder frame by means of a dynamic pendulum support bearing represents a highly developed bearing concept and has been protected by us since March 17, 2021 by the registration of a utility model.
The storage concept consists of several components.
The auxiliary frame (1) is used to attach the so-called rockers (2) to the ladder frame of the rough-road chassis. The pendulum supports (3) arranged to the left and right of the vehicle's longitudinal axis connect the living cabin frame to the outside of the web of the U-shaped longitudinal members of the ladder frame. The push rod (4) and the hat profile (5) support the entire living cabin structure in the direction of travel.
The task of the auxiliary frame (1) is to establish the connection between the rocker and the longitudinal beam. It must meet two criteria. The torsional movement when the longitudinal beam underneath it twists must not be hindered, and at the same time it ensures an even load distribution on the upper chords of the longitudinal beams.
The rockers (2) enable torsion of the vehicle frame without transferring force to the cabin frame.
The pendulum supports (3) stabilize the cabin and absorb shifts from the vehicle frame to the cabin frame.
The push rod and the hat profile (4) absorb the translational acceleration forces of the living cabin via the third shaft.
