BACKGROUND OF THE INVENTION

[0002] The present invention relates to a lift truck, in particular a lift truck for use in warehouses. The present invention additionally relates to a method of operating a lift truck.

[0003] Lift trucks are known and fall into two broad categories, building trucks and warehouse type trucks.

[0004] Building trucks are used outside to transport material around building sites. Typically building trucks will have a mast with vertically movable forks upon which the material can be lifted and carried.

[0005] Building sites have contrasting types of terrain, such as soft ground, rough ground and surfaces having loose material, in addition to the possibility of the terrain being wet and sloping. Therefore building trucks have particular features which enable them to negotiate such terrain.

[0006] To operate over rough terrain, the building truck must have a suitably high ground clearance in addition to the suspension properties of pneumatic tires. The tire footprint loading of the building truck must be sufficiently low to prevent it from sinking into soft ground. Consequently, high flotation tires are employed, and the weight of the building truck is minimised, the weight being determined by the structural strength requirements of the truck.

[0007] To maintain traction over the various terrain, particularly when conditions are wet, and the surface is inclined, building trucks often employ drive to all four wheels. This is particularly necessary when taking into consideration the low weight of the building truck. Furthermore the center of gravity is located at the approximately the central position of the building truck to load all four wheels evenly, thus ensuring each wheel is capable of providing tractive force.

[0008] Building trucks must also be sufficiently manoeuvrable, and generally have the ability to turn the forks and steering up to a maximum of about 45 degrees either side of the forward direction (i.e. in a yaw direction). However, angles significantly above 45 degrees are not used since they tend to make the building truck unstable.

[0009] Building trucks are powered by petrol or diesel driven internal combustion engines where the harmful emissions are diluted in the atmosphere.

[0010] Building trucks are not required to lift loads to very great heights because:—

[0011] other forms of lifting devices are available e.g. cranes.

[0012] lifting a load to a significant height, when the building truck is on uneven ground is dangerous since the truck may tip over as the load is raised. This is particularly significant on building trucks, which have pneumatic tires (and hence allow roll or pitch of the truck body as the load is raised) and, as mentioned previously, building trucks are designed to be light (in line with strength requirements) and have a relatively high ground clearance (thus raising the center of gravity of the truck).

[0013] Conversely warehouse type trucks are required to lift loads to significant heights and thus use a telescopic mast and fork arrangement to load and unload goods in loading bays, typically in the aisles of warehouses. To maximise space efficiency in the warehouse, the aisles are narrow, and goods are stacked vertically in the loading bay.

[0014] The conditions and the requirements of a lift truck in a warehouse, and the associated problems these conditions bring, contrast strongly with those conditions found on a building site and the requirements of a building truck.

[0015] Warehouses are inside and hence dry, the warehouse floor is generally hard and smooth, usually of concrete, as well as being flat. Therefore there are no associated traction problems associated with the warehouse type truck when moving along an aisle, and for this reason warehouse type trucks employ drive to the two rear wheels.

[0016] Operating inside a warehouse requires warehouse type trucks to be powered by power sources where there are minimal harmful emissions, such as gas fuelled internal combustion engines or electric motors. Therefore it would be inappropriate to use a lift truck powered by a petrol or diesel fuelled internal combustion engine in a warehouse.

[0017] To maintain the stability of the warehouse type truck, particularly when it is loading and unloading goods into the loading bays, extra weight is added to the rear of the warehouse type truck. The combined extra weight and the weight of the heavy goods exhibits high loading on the tires of the warehouse type truck, and hence solid tires are used, i.e. non-pneumatic tires, which do not significantly deform during loading and unloading. Such tires exert high loadings on the ground which must be sufficiently strong to resist such loads, hence the use of concrete.

[0018] The added extra weight results in the center of gravity being located towards the rear of the truck. Thus, the stability of the truck is improved when steering at high steer angles.

[0019] Storage space is generally at a premium in warehouses and hence goods are stacked to a very significant height and aisles between rows of goods can be narrow. Consequently, it is difficult for a conventional warehouse lift truck to retrieve and deposit goods that are located at right angles to the truck's direction of travel. If the goods are located at some height above the position of the lift truck driver this manoeuvre is further complicated by the difficulty of the driver in seeing whether the forks are at the correct height and lateral position to enter a pallet or the like upon which the goods are stored.

[0020] Prior art trucks have attempted to overcome this problem by employing pallet forks mounted on a traversing arrangement at 90° to the truck's direction of travel. The arrangement permits the forks to move into a pallet and retrieve the pallet with no movement of the remainder of the truck occurring. Such truck designs limited to working at this 90° angle, may suffer from stability problems at height, and can be relatively complex to manufacture.

SUMMARY OF THE INVENTION

[0021] The present invention seeks to overcome, or at least mitigate, the problems of the prior art.

[0022] One aspect of the present invention provides a lift truck comprising a first portion having a carriage mounted on a carriage mast and one or more first wheels, and a second portion distinct from the first and comprising a cab mounted on a cab mast to enable the raising of the cab, and one or more second wheels, the first portion being pivotally mounted to the second portion, to permit the truck to be steered by adjusting the angle of the first portion relative to the second, wherein substantially all controls for controlling the functioning of the truck during depositing and pickup of goods are arranged so as to permit the raising thereof together with the cab.

[0023] A second aspect of the present invention provides a method of operating a lift truck comprising a first portion having a carriage mounted on a carriage mast and one or more first wheels, and a second portion distinct from the first and comprising a cab mounted on a cab mast to enable the raising of the cab, and one or more second wheels, the first portion being pivotally mounted to the second portion, to permit the truck to be steered by adjusting the angle of the first portion relative to the second, wherein substantially all controls for controlling the functioning of the truck during depositing and pickup of goods are arranged so as to permit the raising thereof together with the cab comprising the steps of:

[0024] positioning the carriage at the required height to engage goods to be picked up;

[0025] maneuvering the entire truck into the required position to engage the goods by driving at least one of the first or second truck wheels;

[0026] raising the carriage to pick up the goods.