EP0868390A1

EP0868390A1 - Lift mast roller assembly for a lift structure of a fork lift truck

Info

Publication number: EP0868390A1
Application number: EP96943454A
Authority: EP
Inventors: Torbjörn HOLMQVIST; Per-Olof Johansson
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 1995-12-19
Filing date: 1996-12-18
Publication date: 1998-10-07
Also published as: AU1218497A; SE9504525D0; WO1997022546A1; JPH11500992A; SE9504525L

Abstract

A lift mast roller assembly (10) for a lift structure of a fork lift truck, comprising in combination an axle bar (9) fixedly attached to a component of a lift mast structure of the fork lift truck and a substantially annular lift mast roller (13), journalled on said axle bar (9) in a rolling bearing (12) having an inner race ring (24), an outer race ring (20) and a number of rollers (21) disposed therebetween, wherein the inner race ring (24) is fitted with a tight fit on the axle bar (9), the outer race ring (20) is axially affixed relative to the lift mast roller (13), and the rolling bearing is a self-aligning roller bearing wherein the rollers (21) and race tracks provided in the race rings (20, 21) have correspondingly curved longitudinal section profiles with radius of curvature substantially greater than the greatest distance between the central bearing axis and the surfaces of the race tracks, wherein the rollers are axially moveable without restrictions from axial limitations.

Description

LIFT MAST ROLLER ASSEMBLY FOR A LIFT STRUCTURE OF A FORK LIFT TRUCK

The present invention refers to a lift mast roller assembly for a lift structure of a fork lift truck.

One of the main parts of a fork lift truck is the lift structure, which incorporates a fixed outer mast comprising two spaced apart and interconnected uprights with U-shaped grooves facing inwards and an inner mast having two intercon¬ nected uprights arranged to be guided by and moved vertically in the grooves of the outer mast. At its lowermost portion the inner mast supports a fork spread carriage, which in turn via fork brackets carries the two lift forks. The mast structure is provided with a number of lift mast rollers arranged to make possible vertical adjustability of the inner mast and the lift forks. Those lift mast rollers are of different types and some of them are intended for radial loads only, whereas other such rollers shall support combined loads. The lift mast rollers which support combined axial and radial loads can be supported in double row angular contact ball bearings or in two taper roller bearings.

Those lift mast rollers, which shall support only radial loads, can be journalled in deep groove ball bearings if the loads are low, but if the loads are increased it is necessary to use either two taper roller bearings or a cylindrical full complement roller bearing. An important and evident drawback of using such bearings is however their very limited capacity of coping with misalignment. Misalignment however is some¬ thing which often must be expected as the uprights or beams against which the rollers run are not quite parallel over their entire longitudinal extension, and use of such bearings therefore would lead to detrimental edge loads in the bearing or on the envelope surface of the roller, which will result in a comparatively short life span for the bearing. In order to manage this, a spherical roller bearing is sometimes used. The envelope surface of the lift mast roller is guided by the groove of the upright, and therefor there is no risk that the bearing rings will get a too big angular misalignment during operation, which however can occur if the bearing is used as a wheel bearing without an external guidance . Another draw¬ back with the spherical roller bearing is the comparatively big sectional height of the bearing, which means either that the lift mast roller, in which the bearing outer race ring shall be pressed in, must be given a smaller sectional height, or that a smaller bearing, having lower load capac¬ ity, must be used as the outer diameter of the lift mast roller is given. In the case with using a lift mast roller of lower sectional height results in a lower carrying capacity of the roller, which means increased stresses in the bearing and a negative influence from the load upon the internal geometry of the bearing.

The purpose of the present invention therefore is to provide a lifting mast roller assembly in accordance with the preamble of the accompanying claim 1, designed in such a manner that the above drawbacks are highly eliminated, and this has been achieved in that the assembly has been given the features defined in the characterizing part of the appended claim 1.

Hereinafter the invention will be further described with reference to an embodiment shown in the accompanying drawing.

Fig. 1 shows in a diagrammatic view in perspective an embodiment of a fork lift with a lift mast.

Fig. 2 is a more detailed perspective view of the lift mast structure,

Fig. 3 is a perspective view of the inner, movable frame part of the lift mast structure of Fig. 2,

Fig. 4 is a similar view of the outer frame part of the lift mast structure of Fig. 2, which is intended to be fixedly connected to the truck structure.

Fig. 5 shows in an exploded view components forming part of a lift mast roller according to the invention and positioned e.g. where indicated in Fig. 3, and Fig. 6 shows in a cross section the lift mast roller assembly according to the invention.

The contours of an embodiment of a fork lift truck 1 is shown in perspective in Fig. 1. The wheeled truck body is provided with a lift structure or lift mast 2, which incorporates a first, substantially vertical frame 3 fixedly connected to the truck body 1 and consisting of two uprights 3a, 3b inter¬ connected by transverse beams 4, and a second frame 5, also having two uprights 5a, 5b and transverse interconnecting beams 6. This second frame 5 is movable longitudinally in vertical direction between the uprights 3a, 3b of the first, fixed frame 3 and carries at its lower end a fork spread carriage 7 on which two forks 8 are mounted. Lift mast roller assemblies according to the invention are provided in different positions between the two frames 3 and 5 and also in connection to the fork spread carriage for allowing mutual displacement and guiding and retaining the structures in their respective positions.

Fig. 2 shows more in detail and in perspective an embodiment of the lift mast structure 2 with its outer mast 3 and inner mast 5, and in Fig.s 3 and 4 the inner mast 5 and the outer mast 3 are shown separately.

From these figures can be seen that the uprights 3a and 3b of the outer mast frame 3 are U-beams, each having their channel-formed open side facing the other upright, thus that the outer frame 3 has two opposed, parallel channels in which the uprights 5a and 5b of the inner frame 5 are received and guided during mutual longitudinal displacement of the inner frame in the outer one. The inner frame 5 is formed in a manner similar to that of the outer frame 3, and is - in the embodiment shown - provided with axle bars 9 projecting from the outside of its uprights 5a, 5b, i.e. into the channels provided in the outer frame 3. These axle bars 9 support each one a lift mast roller assembly 10, which supports and guides the inner frame 5 during its motion relative to the outer frame 3 and also when they are kept in position relative to each other. The lower cross bar 4 of the outer mast 3 is also equipped with guide roller assemblies 11 for the fork spread carriage (Fig. 4) . It should be noted that the lift mast structure of course incorporates a number of other compo¬ nents, such as chain wheels, hose wheels, etcetera, but those components have been excluded from the drawings for the sake of clarity and as they have no direct influence on the mast roller assembly according to the invention.

Fig. 5 shows in an exploded view the main components of a lift mast roller assembly 10 according to the invention, i.e. the axle bar 9, a rolling bearing 12 and a mast roller 13.

In Fig. 6 finally is shown the complete mast roller assembly 10 according to the invention. The axle bar 9 is fixed with welding joints 14 to a supporting structure 15, e.g. the wall of the inner frame 5, and in such a manner that the rear end of the axle bar 9 via a hole in the structure 15 is access¬ ible from the opposite side of the supporting structure. The rear end of the axle bar is provided with a lubricant nipple 16, which communicates with a central duct 17 extending through and opening at the opposite end of the axle bar 9. The mast roller 13 itself has a through hole 18 with a shoulder 19 provided at one end thereof. Fitted with a tight fit in the through hole 18 and against said shoulder 19 is the outer race ring 20 of a roller bearing 12 of a type being able to take up misalignments and thermal expansions, thereby allowing the rollers 21 to move axially and adjust themselves to proper positions, thereby permitting relative inclination and axial displaceability of the race tracks. Such a bearing is described e.g. in European Patent 0 175 858, which publication hereby is entered as a reference in this applica¬ tion. In the bore 18 outside the outer race ring 20 is positioned a spacer ring 22 spacing apart the outer race ring 20 from a disc-shaped cover member 23 fitted as a hub cap outside the bearing. This hub cap 23 prevents contaminants from entering the bearing and leakage of lubricant from the free end of the lift mast roller 10 during operation. The inner race ring 24 of the bearing 12 is pressed up on the free end of the axle bar 9 to be fitted thereupon with a tight fit, and the position thereof is further secured by means of a locking ring 25.

By this arrangement both race rings 20 and 24 of the bearing 12 are fitted with tight fit and due to the properties of the bearing used, the bearing in the assembly will not take up any axial load. This possibility to apply both rings with a tight fit means that there will be no wear between the race rings and their respective seats, which in turn means that there is no risk that the axle bar will be worn down or that fretting corrosion will form, which could lead to that the roller was stuck giving axial loads which could crack the bearing, which would be the case if a bearing of conventional type, as mentioned in the introduction, was used.

The bearing 12 has a very low structural height compared to e.g. a spherical roller bearing, and thiε means that the structural height of the mast roller 13 itself can be kept at a rather high value, whereby the outer race ring will be supported rigidly, thereby giving the bearing a long service life.

The bearing 12 can either be used in a version with cage for the rollers or without such cage, but with a full complement of rollers, whereby the strength of the outer mast roller ring 13 will be further increased.

It even is possible to design the outer race ring of the bearing as the mast roller itself, thereby further increasing the strength of the outer race ring although such a modifica¬ tion of the bearing would be adapted just for this specific task.

By using the hub cap 23 on the side of the bearing where the lubricant (grease) is fed into the mast roller assembly it is obtained that the grease is urged back through the bearing. The spacer ring 22 between the hub cap and the outer race ring 20 guarantees that there is enough free space even when the bearing is displaced axially during operation. On the opposite side i.e. in the region of the shoulder 19 of the through bore 18, the axle bar 9 has a portion of bigger diameter, which portion together with the mast roller forms a slot seal 26, which also acts for limiting the possible inclining of the bering.

The invention is not limited to the embodiment shown and described but modifications are possible within the scope of the appended claims.

Claims

1. A lift mast roller assembly (10) for a lift structure of a fork lift truck, comprising in combination anaxle bar (9) fixedly attached to a component of a lift mast structure of the fork lift truck and a substantially annular lift mast roller (13) , journalled on said axle bar (9) in a rolling bearing (12) having an inner race ring (24) , an outer race ring (20) and a number of rollers (21) disposed therebetween, c h a r a c t e r i z e d t h e r e i n, that the inner race ring (24) is fitted with a tight fit on the axle bar (9) , that the outer race ring (20) is axially affixed relative to the lift mast roller (13) , and that the rolling bearing is a self aligning roller bearing wherein the rollers (21) and race tracks provided in the race rings (20, 21) have correspondingly curved longi¬ tudinal section profiles with radius of curvature substan¬ tially greater than the greatest distance between the central bearing axis and the surfaces of the race tracks, wherein the rollers are axially moveable without restrictions from axial limitations.

2. A lift mast roller assembly (10) as claimed in claim 1, c h a r a c t e r i z e d t h e r e i n, that also the outer race ring (20) of the bearing is fitted with tight fit in a seat in the lift mast roller (13) .

3. A lift mast roller assembly (10) as claimed in claim 1, c h a r a c t e r i z e d t h e r e i n, that the outer race ring of the bearing is formed integral with the lift mast roller.

4. A lift mast roller as claimed in anyone of the preceding claims, c h a r a c t e r i z e d t h e r e i n, that the axle bar (9) is provided with a lubricant duct (17) extending through the axle bar and opening on the opposite side of the bearing (12) , the space outside the opening of said lubricant duct being covered by a cover member (23) urging lubricant introduced through the lubricant duct (17) to be returned through the bearing (12) .

5. A lift mast roller assembly as claimed in claim 4, c h a r a c t e r i z e d t h e r e i , that the said cover member (23) is spaced apart from the outer race ring (20) of the bearing, for permitting that the bearing is displaced axially.