US Patent 8978795 Auxiliary roller

An additional roller has a rigid frame, with a drivable wheel which is mounted in the frame and has an axle. The wheel together with the frame can be raised or lowered by pivoting relative to a chassis, on which the additional roller is to be mounted. A compression spring is coupled rotatably at one end to the chassis, in order, in the lowered position, to load the wheel in respect of ground contact. A transverse connection connects two frame parts in the direction of an axle of the wheel. The compression spring is coupled at the other end to the transverse connection. The compression spring together with the frame pivots about the chassis-mounted pivot point during raising and lowering of the wheel.