Lift trucks and extensible mast structures therefor

An extensible mast structure for a lift truck comprising a fixed mast section, at least one movable mast section mounted on said fixed mast section for vertical movement relative to said fixed mast section and a load carrying carriage mounted on said at least one movable mast section for vertical movement relative to said at least one movable mast section, a primary jack including a movable part, means operatively connecting said movable part to said load carrying carriage for moving said load carrying carriage relative to said movable mast section, a secondary jack connected to said fixed mast section and to said at least one movable mast section for moving said at least one movable mast section relative to said fixed mast section to extend said extensible mast structure, said primary jack and said secondary jack having relative operational cross-sectional areas selected to sequence the stroke of said primary jack to raise said load carrying carriage before the beginning of the stroke of said secondary jack to move said at least one movable mast section to extend said extensible mast structure, stop means on said fixed mast section and means carried by said movable part of said primary jack for engaging said stop means on said fixed mast section at an intermediate point in the stroke of said primary jack to thereby enable said primary jack to assist said secondary jack to move said at least one movable mast section to extend said extensible mast structure during the remainder of the stroke of said primary jack while continuing to raise said load carrying carriage relative to said at least one movable mast section, and said secondary jack continues its stroke to extend said extensible mast structure;

• whereby said movement of said at least one movable mast section to extend said extensible mast structure is substantially uninterrupted.