This invention relates to a lift assembly for a lift truck and, more particularly, to a hydraulic cylinder arrangement for lifting uprights of a mast and a load-carrying carriage supported by the uprights.
Conventional lift trucks have on their front end a mast or lift assembly including telescoping uprights and a fork lift carriage supported by the uprights. The uprights, when extended, permit high lifting of a load while allowing the truck to have relatively low overall height when the extended uprights are lowered.
In addition, in one type of lift truck, the load carriage is movable vertically without extension of the uprights. A carriage which has this kind of movement is said to have "free lift", which is desirable since it allows a load to be lifted without extension of the uprights. The carriage engages the load in a lower position and thereafter can be raised to a desired elevation without extension of the uprights. In this raised position the load may be transported to another location, and the carriage then lowered and unloaded. Thus, with a "free lift" type of carriage, the load can be lifted without increasing the overall height of the assembly, thereby permitting operation in areas of low overhead.
The uprights and carriage usually are lowered and raised by hydraulic cylinder assemblies which are strategically positioned on the truck. In considering this positioning, one goal is to utilize hydraulic cylinder assemblies and their connections to the uprights and carriage which are simple in design. Another object is to use components for the cylinder assemblies which are as small as possible so that the weight of the lift assembly is kept to a minimum.
Furthermore, it is also important to design a load-lifting assembly which will give the driver of the truck maximum visibility in the forward direction. Consequently, it is desirable to position the hydraulic cylinder assemblies and their connections to the uprights and carriage in such a manner as to minimize their interference with the driver's line of sight.
While there are many types of lift assemblies for lift trucks, one problem is that they sacrifice one or more advantageous features to obtain another. Thus, for example, in one assembly where free lift is provided, a cylinder rod has to be raised into the line of sight of the driver to raise the carriage, thereby impairing visibility. Or, in other assemblies, hydraulic cylinders for extending the uprights are positioned directly behind the uprights to improve visibility; however, these cylinders typically are relatively long, extending almost the entire length of the mast. Consequently the mast must be located further from the truck to allow room for positioning of the long cylinders, but this positioning must be done at the sacrifice of producing additional, undesirable load moments.