Elevator – industrial lift truck – or stationary lift for vehicle – Stationary lift for roadway vehicle or required component... – Having specific drive means for support
Patent
1981-03-16
1984-04-17
Noland, Kenneth W.
Elevator, industrial lift truck, or stationary lift for vehicle
Stationary lift for roadway vehicle or required component...
Having specific drive means for support
187 95, 308 3B, 182 625, 212269, 52117, B66B 920
Patent
active
044429223
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates generally to slider bearings and more particularly to adjustable slider bearings for a mast of a lift truck.
2. Background Art
Many of the most significant problems faced by designers of lift trucks have centered around the development of an improved lift mast. There is significant competition in the industry to provide a less expensive mast of decreased mast weight to load ratio which is sufficiently rigid to resist deformation yet which does not unduly restrict visibility.
Typically, lift truck masts include a support frame borne by the lift truck, at least one pair of uprights vertically extensible within this support frame, and a load supporting carriage movable along these uprights. Such a lift mast is disclosed by Hastings et al in U.S. Pat. No. 3,213,967 issued Oct. 26, 1965. This and other known mast designs for lift trucks include at least one set of connecting members joining the carriage to the uprights and another set for joining the uprights to the support frame. Typically these connecting members are fashioned and positioned such that they impose an unbalanced sideways torque about the longitudinal axis of each of the uprights (that is, torque about the vertical axis of each upright tending to twist each upright in a sideways manner toward or away from the other of the uprights). The unbalanced stresses caused by these torques can result in deformation of the uprights which often causes uneven wear and undue friction of the components in the mast assembly.
The connecting members include bearings to provide substantially unimpeded moving contact between the elements joined by the connecting members. In most lift mast designs these bearings are roller bearings. As compared to slider bearings, the use of roller bearings introduces several problems: they are high in cost; they require relatively smooth finishing of the surfaces on which they act; they make more difficult the assembly and disassembly of the mast; they may require lubrication; and, they create significant amounts of noise in their operation.
For all of their advantages, slider bearings have not come into significant commercial use for lift truck masts. This has been due in part to the lack of an adequate device for positioning the slider bearing between the members it joins. During use the slider bearings wear. This causes gaps to develop between the bearings and the members between which the bearings are interposed. This excessive tolerance, known in the art as "slop," between adjoining members causes a loss of mast ridigity, a decrease in controllability, increased impact loadings, uneven and accelerated slider bearing wear, and is otherwise disadvantageous as is known to those skilled in the art.
The more advanced slider bearing assemblies for lift mast assemblies incorporate shims for accommodating slider bearing wear. When the bearing wear reaches the point where an unacceptable gap exists, a shim may be inserted thereby improving the tolerances between the relevant members. Eventually the wear becomes sufficiently great that the bearing must be replaced. Such a system is disclosed in U.S. Pat. No. 3,999,675 issued to Forry et al on Dec. 28, 1976. Inserting this shim is an awkward and time-consuming maintenance measure which it would be highly advantageous to avoid.
A related disadvantage of existing lift truck mast slider bearing assemblies is that they are supported by one planar surface and are slidingly contacted by an opposing planar surface. If these two surfaces are not perfectly parallel the slider bearing, which is also planar, will be unevenly loaded. As a result the sliding friction is increased and the slider bearing is unevenly worn.
A further disadvantage of known lift masts incorporating slider bearings is that no known connecting member design serves to substantially eliminate side to side tilting of the carriage attendant side thrust loading. It would be beneficial if an arrangement of simple slider bearing type connecting member assemblies avoided this pr
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Hickman Alan J.
Noland Kenneth W.
Towmotor Corporation
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