Material or article handling – Elevator or hoist and loading or unloading means therefor – Elevator wherein means comprises guide mounted for relative...
Reexamination Certificate
2000-10-27
2002-06-04
Bratlie, Steven A. (Department: 3652)
Material or article handling
Elevator or hoist and loading or unloading means therefor
Elevator wherein means comprises guide mounted for relative...
C414S635000, C414S641000, C414S673000, C187S222000, C180S209000
Reexamination Certificate
active
06398480
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates to a fork-lift truck.
Fork-lift trucks prove to be universal-use equipment to pick up pallets from the floor and to handle and stack them. They may be provided with a combustion motor or an electric motor. The fork-lift truck picks up the load and carries it to the desired place of destination. The front wheels are supported on a wheel bearing means wherein this one, e.g. in fork-lift reach trucks, may also have wheel arms extending in the vehicle longitudinal direction between which the load can be lowered. Since the load is picked up outside the basis of standing a load moment will arise which might cause the fork-lift truck to tilt about the front axle. The load moment has to be compensated for by a corresponding righting moment. The purpose is served by the dead weight of the vehicle that can be increased by separate counterweights at the other end of the vehicle (counterweight-type fork-lift truck). Thus, a defined working load of the fork-lift truck is opposed by a relatively large dead weight which requires to be accelerated and decelerated again during each driving and braking action. Also, the dead weight will increase the resistance to vehicular motion as well as the loads imposed on the wheels and presupposes a sufficient load-carrying capacity of the floor. Therefore, if lifting heights are larger the ultimate load admissible requires to be reduced as otherwise the stability of the vehicle will be jeopardized, especially when the load is lifted.
Different attempts were made in the past to increase the stability in standing of a fork-lift truck. A mobile fork-lift truck having a rearwardly inclinable lift mast is known from the patent specification DE 1 047 719 open to public inspection. The document discusses several designs of fork-lift trucks. For improved stability, it describes that if a lift mast inclines backwards an automatic approach of the inclinable hinge of the lift mast and the front wheel to each other is effected simultaneously. The mentioned document also describes a lift mast hinged to the vehicle which may be swiveled by a hydraulic cylinder, this one being hinged to the lift mast and the vehicle. If the lift mast is inclined backwards the front wheels undergo forward swiveling at the same time. The known devices have numerous drawbacks when in practical use. When stacking goods the lift frame should stand as vertical as possible and, hence, the frame requires to be pivoted first from the inclined position to an upright one before a pallet can be picked up or delivered at larger heights. For the rest, it will be left to the driver, in the known case, to move to appropriate inclinations of the lift frame.
It is the object of the invention to provide a mobile fork-lift truck which, while having a dead weight as low as possible and being of a simple structure, may selectively be given a larger stability in standing, especially if lifting heights are large.
BRIEF SUMMARY OF THE INVENTION
According to the invention, the object is attained by a fork-lift truck of the type described at the beginning the wheel bearing means of which has a shifting device interacting with the vehicle body, which selectively shifts the wheel bearing means with respect to the vehicle body in the vehicle longitudinal direction while varying the distance between the front and rear wheels and the distance between the centre of gravity of a load disposed on the load-carrying means and the front wheel. The fork-lift truck has a vehicle body on which the rear wheels are supported. The front wheels of the fork-lift truck are supported on the wheel bearing means which is connected to the vehicle body via the shifting device. At this point, each front wheel may have a wheel bearing means of its own or a common wheel bearing means for two front wheels may be provided. The shifting device causes the wheel bearing means and the vehicle body to be shifted relative to each other. The shifting action changes the distance between the front wheels and rear wheels of the fork-lift truck. Likewise, the distance between the load centre of a load disposed on the wheel bearing means and the front axle is changed in the opposite sense. Thus, the fork-lift truck has an axle base adjustable by the shifting device. The advantage in using a wheel bearing means with a shifting device is that the distance between the front and rear wheels can be adjusted by it. Since a tilting motion of a fork-lift truck handling a load is performed via the front axle shifting the front wheels away from the rear wheels of the vehicle body will displace the tilting edge to the front and reduce the tipping moment. At the same time, the righting moment of the vehicle body will be increased with the weight being the same.
In a particularly preferred aspect of the inventive fork-lift truck, the rear wheel has a braking device which, while responding to an actuation of the shifting device, blocks the rear wheel for the duration of the shifting operation. If the rear wheel is not blocked the front and rear wills will roll on the surface on which the fork-lift truck stands if the wheel position is varied. Depending on the nature of the surface on which the truck stands and the rolling drag on the wheels, the wheels will roll through a varying portion of the push length. For example, if the fork-lift truck has loaded a heavy load the rear wheel usually runs more easily so that if the wheel bearing means is shifted the vehicle body will be shifted rearwards by a certain portion of the shifting length. Such a rearward travel of the vehicle body is undesirable because the rearward travel makes it more difficult to manoeuvre and to precisely lift the load which was picked up. To avoid shifting backwards the vehicle body while the wheel bearing means is shifted forwards the rear wheel is blocked for the duration of the shifting operation whereas the front wheel is free to rotate.
As an alternative or in addition to the above described braking device, the fork-lift truck may have a front wheel provided with a drive and a control connected to a sensor where the sensor determines the push length traveled by the wheel bearing means with respect to the vehicle body and the control translates the push length determined into a control signal for the drive which causes the front wheel to roll in a sense of rotation and at an angle of rotation which correspond to the push length which has already been traveled. The purposive actuation of the front wheel prevents a counterforce to be applied to the vehicle body which will shift it rearwards. Rather, the front wheel is driven in order to move the wheel bearing means forwards, especially if the fork-lift truck carries a load. The driven front wheel rolling motion is such that the wheels are driven according to the push length. As a result of a controlled drive of the wheels, the position of the vehicle body is not changed by the shifting operation whereas the wheel bearing means moves away from the vehicle body or approaches it.
For a simple structure of the shifting device, it is opportune for the shifting device to have a linear guide element along which the wheel bearing means is designed to be shifted by a displacing element mounted on the vehicle body. Using a guide element permits to simply shift the wheel bearing means. Also, the two-part structure of the shifting device comprising a guide element and a displacing element proves to be easy in manufacture and particularly sturdy.
In a preferred embodiment of the inventive fork-lift truck, the guide element has at least one straight guide rail. Using a guide rail for the shifting device permits to simply incorporate the shifting device in the wheel bearing means and the vehicle body. The fact that two guide rails can be disposed in parallel and above each other in the lower area of the vehicle body makes it unnecessary to modify the rest of the vehicle body structure.
In a
Baginski Ralf
Hunte Ing. Torsten
Magens Ernst Peter
Niebuhr Michael
Rickers Paul
Bratlie Steven A.
Jungheinrick Aktiengesellschaft
Vidas Arrett & Steinkraus P.A.
LandOfFree
Fork lift truck does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fork lift truck, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fork lift truck will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2929330