PURPOSE: To simplify the structure of a joint by providing a power-operated pillar which is pivotally connected at its opposite ends to a vehicle section by a joint for enabling the pillar around three axes which are orthogonal to one another.

CONSTITUTION: A means for controlling vertical motions of two vehicle sections 4, 5, incorporates a power-operated pillar 24 located underneath a tongue-like protrusion 13 extending between both sections 4, 5 and connected to an upper fork 17, and including a cylinder 25 and a piston 26. The power-operated pillar 17 is spaced from the upper fork 17 underneath the latter, and is connected to the rear wheel section 5 by means of a piston rod 26 received by a lower fork 18. Two arms 19, 20 of the lower fork 18 are located above and below the piston rod 26 so that a pin 21 extends between the two legs 19, 20 through a hole in the rear end part of the piston rod 26.