Caterpillar Tractor Co.

Tom E Robinson

Cyril W Habiger

The invention is concerned with an improvement in a load lifting apparatus which comprises a primary load member pivotally mounted about a generally horizontal axis on a frame, a tilt cylinder and a tilt piston movable relative to one another pivotally connected to the frame and the primary load member to provide impetus for pivotal movement therebetween, a secondary load member movable relative to the primary load member, a lift cylinder and a lift piston movable relative to one another connected to the primary load member and the secondary load member to provide impetus for linear relative movement therebetween, tilt cylinder valve means for controlling flow of pressurized fluid from pump means to the tilt cylinder and lift cylinder valve means for controlling flow of pressurized fluid from the pump means to the lift cylinder. The improvement of the invention provides protection which prevents the apparatus from overbalancing. The improvement operates by sensing a moment created by a load on the apparatus. Most particularly, the improvement comprises a valve sensing simultaneously a lift pressure force proportional to a lift pressure in a head end of the lift cylinder and a tilt pressure force proportional to a tilt pressure in a rod end of the tilt cylinder. The valve blocks flow of pressurized fluid from the tilt cylinder to the tilt cylinder valve means and from the lift cylinder valve means to the lift cylinder responsive to the greater of the lift pressure force and the tilt pressure force exceeding a predetermined value. The improvement of the present invention is particularly useful in the lift trucks wherein the primary load member is a lift truck mast and the secondary load member is the forks of a lift truck.

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Peoria, IL, United States of America

Tom E Robinson