Tower crane

Claim 1

A mobile tower crane comprising mobile platform means, a tower pivotally mounted at its base on said platform means for tilting movement between a vertical operating position and a substantially horizontal travelling position, raising means interconnecting said tower and said platform means for moving the tower between said positions, jib support means mounted at the top of the tower and including at least a part rotatable about a vertical axis when the tower is vertical, pivot means connecting said jib to said tower, said pivot means including a jib pivot connecting said jib to said jib support means to allow luffing movement of said jib, and jib luffing hydraulic cylinder means connected at one end to said jib and operative to cause said luffing movement of said jib, and wherein there is provided jib alignment means operatively connected between the jib support means and the jib movable to alter the relative disposition of said tower, the jib pivot and an end of the jib luffing hydraulic cylinder means in such manner as to alter the angle between the jib and the tower axis without operation of said jib luffing hydraulic cylinder means, the jib alignment means being arranged to move between an operating position and a folded position, in which operating position the jib luffing hydraulic cylinder means is capable of luffing the jib between a raised position above the top of the tower and a lowered position in which the jib forms a substantial angle of the order of 90° with the tower axis, and in which movement of the jib alignment means to the folded position causes angular movement of the jib through a folding angle roughly equivalent to said substantial angle, whereby the jib can be moved to a folded position in alignment with the tower by combined operation of said jib alignment means and said jib luffing cylinder means, and wherein said pivot means are so arranged that the jib lies close to the tower when in said aligned position.