Forklift truck mounted on a carrier vehicle

A forklift truck mounted on a carrier vehicle, said truck comprising;

• a frame,
• forks for handling of the load and coupling of the truck to a carrier vehicle,
• a connection between the forks to the frame, said connection including at least one lifting jack to drive the forks and the frame in relative displacement in the direction of approach towards one another and moving away from one another in order to permit raising of the forks in a so-called handling operating mode, wherein the forks are mounted such as to be free in upward and downward displacement relative to ground,
• and to permit raising of the frame in a so-called transport operating mode, wherein the forks are in a high position and their displacement upwards and downwards relative to ground is then immobilized,
• the at least one lifting jack comprising at least one body and a piston rod which divides the body into two chambers, said lifting jack being a double-effect lifting jack, each chamber of which is equipped with a fluid duct for connection of the chamber to a hydraulic source comprising a pump and a reservoir via a distributor to permit supply of fluid to one or the other of the chambers,
• wherein, in the so-called handling operating mode, under the effect of their weight, the forks form a driving element for actuation of the or each lifting jack for the passage of the forks from the high position to the low position, and in that, for the or each lifting jack, the fluid ducts for connection of the chambers of the lifting jack to the hydraulic source are connected to one another by a fluid connection, in order to permit a transfer of fluid from one of the chambers in the direction of the other chamber of the jack, this fluid connection being equipped with a closing unit which is mounted such as to be mobile between a closed position and an open position of the fluid connection,
• this closing unit being in the open position when the forks form a driving element for actuation of the or each lifting jack for the passage of the forks from the high position to the low position when a predetermined pressure is reached;
• and
• this closing unit being in the closed position at least in the transport operating mode, in a state in which the frame is raised.