CA1299528C - Adjustable anti-friction slide bearing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A self-lubricating slide bearing in an anti-friction bearing system of a lift mast assembly on a forklift vehicle includes a hearing block holder welded to at least one member of separate pairs of nested slidably displaceable support members in the assembly. Two laterally spaced upstanding end walls of the holder are integrally joined to a base wall thereof by means of a thick web to define a fixed shelf for securably retaining one high-molecular weight plastic low-friction bearing block on one side of the web.
On the other side of the web, a laterally displaceable spacer bar disposed between the end walls defines an adjustable shelf on which a positionable like plastic bearing block is engageably retained. A pair of machine screws between the bar and web threadedly engage corresponding threaded bores in the web and function to controllably position the latter block to compensate for block wear and mechanical tolerance variations in the mast.

Description

F ~

This invention relates to a slide bearing generally and more particularly to a lift truck slid~ bearing that is adjustable to eompe~sate for mechanica:L tolerances and bearing w~ar.

BACKGROUND OF THE INVENTION

Material handling machines in the form of lift vehicles are typified by forklift trucks which are widely used in industry. Notwithstanding the great variety of applications in which forklift trucks are used, a generally similar anti-friction bearing system utili2ing heavily lubricated rollers and sliding members is used throughout.
~hile adequate in relatively clean environments, bearing failures are common under harsh conditions where lift mast loads are high, usually induced by heavy loads carried over rough terrain, and where bearings and lubricants are subject to abrasive contamination. The logging industry is typical where machinery is subject to rough outdoor working conditions.
A recognition of some problems experienced by lift trucks in the logging industry is briefly discussed in United States Patent 4,403,904 Chelin which issued on September 13, 1983. ~ specific problem addressed by the Chelin patent relates to high loads encountered by log-moving lift trucks when operating over rough ground and the damage that such loads inflict on hydraulic apparatus and related structural members. Chelin alleviates these problems to a degree by providing additlonal mechanlcal support through fixed sliding blocks and bearings fabriaated from a hiyh molecular weight ~ 5 2~

low-friction plastic. There is, however, no suggestion in Chelin to utilize an adjus~able slide bearing to compensate for either bearing wear or mechanical tolerance variations.
Maintenance problems associa-ted with accelerated wear under harsh operating conditions continue, therefore, as a chronic problem.

SUMMARY OF THE INVENTION

A principal objective o~ the present invention is to provide an adjustable slide bearing that utilizes low-friction high molecular weight plastic bearing blocks in amast assembly of a llft truck.
Another provision o~ the invention is an adjustable slide bearing assembly that may be rPadily adjusted by a semi-skilled machine operator to facilitate maintenance in the field.
Yet another provision of the inventi~n is an adjustable slide bearing assembly that is simple in design and rugged in structure to withstand harsh environments.
Yet another provision o~ the invention is a bearing system in the mast assembly of a li~t truck wherein all bearings are adjustable slide bearings that are self-lubricating, requiring no external lubrication.
~ he problems associated with the prior art may be substantially overcome and the aforenoted provisions achieved by recourse to my invention which comprises an adjustable slide bearing adapted to receive and retain at least one low-~riction bearing block between a pair oE longitudinally displaceable surfaces positioned in slidable spaced parallel relatlon therewith. The sllde bearing comprises bearing block holder means having a base wall adapted to be Eixedly mounted on one of the surfaces, a pair o~ upstanding end walls spaced apart and disposed orthogonally to the base wall, and a thick web lntegrally joining the base and end walls to define a fixed shelf for a first bearing block on one side of the web, guide means disposed between the end walls on the other side of the web, spacer means operably engaging the guide means intermediate the end walls and displaceable therealong outwardly of the web, and means disposed between the web and the spacer means for controllably positioning the latter to de~ine an adjustable shelf for a second low-friction bearing block.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be more particularly described with reference to embodiments thereof shown, by way of example~ in the accompanying drawings wherein:
Fig. 1 is a perspective view of a lift mast assembly indicating the locations of adjustable slide bearings used therein in accordance with the invention;
Fig. 2 is a top plan view of an adjustable slide bearing in accordance with the present invention wherein bearing blocXs are illustrated in chain line form;
Fig. 3 is a rear elevation view of Fig. 2;
Fig. 4 is a front elevation view of Fig. 2;
Fig. 5 is a side elevation view o~ Fig. 2;
Fig. 6 is a top plan view of a spacer shown in Fig.
;

Fig. 7 is a side elevation view of the spacer of Flg~ 6 î
Fig. 8 is a co~bination of cross-sectional views taken along the lines A-A and B-B in Fig. 1; and ~2g~S~;~

Fig. 9 is a cross-sectional view taken along the lines C-C in Fig~ 1.

DESCRIPTION OF TE~E ILLUSTRATED EMBODIMENTS

Having regard to the illustrated embodiments of the lnvention and the descriptions thereof which ~ollow, it will be observed that certain structural features are common therein. Therefore, in order that continuity of structure may be readily recognized in the various embodiments, like numerals are used to designate like structural features.
A forklift assembly 10 of a known type described in Uni~ed States Patent 4,177,001 Blackwood, which issued December 4, 1979, is illustrated in Fiy. 1. ~lthough outwardly similar to the prior art, the assembly 10 differs therefrom through its adoption of an adjustable slide bearing system, hidden from external view, which will be described in ~reater detail hereinbeIow. In this regard, the speci~ic disposition within the system of individual ones of ad~ustable slide bearings 11 (Fig. 2) would be known to those skilled in the art. For example, reference to the Blackwood 2Q Patent shows where the bearings 11 would be substituted for wheels on a mast carriage of a forklift attachm~nt for a highway vehicle~ Additionally, it will be understood in Fig. 1 that cross-section lines A-A, B-B and C-C show the approximate locations in the assembly 10 of different embodiments of the bearing 11~
The assembly 10 is shown hingedly attached to a forkll~t ~ruak 12 vi.a a known arrangement of a pair of hingas 13 and a aorresponding pair o~ hydraulic rams 14 that ard ~L29~

each fixedly attached at one end of a cylinder thereof to the truck 12 and hingedly attached at a free end of a piston rod thereof to a pair of hinges 15. The application of hydraulic fluid pressure to the rams 14 in a known manner provides tilt control of the assembly 10. Similarly, the application of hydraulic fluid pressure to a hydraulic ram 16 effects lift of an inner mast 20 through linear displacement of a piston rod 17 having its free end attached to a cross member 18 of the mast 20. Reference to Fig. 8 shows that the mast 20 comprises a pair of inner channels 21 which are vertically disposed in spaced parallel relation. As shown in Fig. 1, a cylinder 23 of the ram 16 is fixedly attached to a cross member 22 which in turn is affixed to a pair of outer channels 25 that constitute an outer mast 26.
Having regard to Fig. 1 and to the cross-sectional views thereof shown in Figs. 8 and 9, it will be observed that the channels 21 and 25 are longitudinally displaceable and include a pair of ~acing surfaces 30 and 31, respectively. A nested relationship between the channels 21 and 25 is apparent together with the bearing 11 therebetween that provides a low-friction support for the channels as well as predetermined spacing to prevent physical inter-channel contact as described hereinbelow in greater detail.
As previously noted, the ram 16 longitudinally displaces the nested channels 21 and 25. In the course of such displacement, a carriage 32 is correspondingly dis~laced-in a known manner via a pair of roller chain~ 33, each having one end anchored to a cross member 3~ with the other end entrained about a respective one of a pair of rotatably mounted sprockets 35 and connected to the carriage 32. As the ~ast 20 rises, the length o~ chain 33 between the sprockets 35 and the carriage 32 shortens, causing the 5~`~

carriage 32 to rise.
Interposed between the surfaces 30 and 31 (Fig. 8) the bearing 11 functions in cooperation with a second bearing 11' (Fig. 9) to maintain the position of the channels 21 and 25 in slidably spaced parallel relation. Reference to these figures shows clearly that such relationship is maintained through mutually contacting surfaces on the channel 21 and a pair of low-friction hearing blocks 40 and 41.
Fig~ 1 reveals that the spaced parallel relation ship between the vertically disposed channels 21 of the mast 20 is maintained by cross members 1 a and 36. Correspon-dingly, the spaced parallel relationship between the vertically disposed channels 25 of the mast 26 is maintained by cross members 22, 34 and 37. This fixed relationship between corresponding pairs of channels 21 and 25 permits the blocks 40 and 41 to maintain the nesting relationship to which reference has heretofore been made. In this regard, the ad~ustable feature of each bearing 11 facilitates uniform alignment between the channels 21 and 25 to prevent physical contact and consequent wear or galling of their facing surfaces as may be best seen in Figs. 8 and 9.
A top plan view of one embodiment of the bearing 11 is illustrated in Fig. 2 and shows the relative placement within the bearing of the blocks 40 and 41 which are shown in chain line form so as not to obstruct the various structural features of the bearing.
Figs. 2-5 show that the bearing 11 comprises a bearing block holder 42 having a base wall 43 (Figs. 3-4) that is adapted to be fixedly mounted on one of the sur~aces 30 and 31 (Figs. 8-9) as by welding for exampleO The holder 42 further includes upstanding end walls in the orm oE a palr of inner end walls 44 disposed inwardly of a pair of ~z~

outer end walls 45. The end walls ar~ each disposed orthogonally to the wall 43 as shown in Figs. 3 and 4.
Integrally joining the walls 43 and 45, a thick web 46 completes a fixed shelf 47 ~or the block 41 on one side of the web. Although various means are suitable for retaining the block 41 upon the shelf 47, a suitable arrangement is to lengthen the block 41 so as to provide an interference fit between the ~aclng surfaces of the walls 45.
It will be observed in Figs~ 2 and 4 that guide means are provided on the facing surfaces of the walls 44 where such guide means take the form of a pair of semi-cylindrical guide rails 48. The rails 48 may be formed integrally with the. walls 44 or may be attached thereto separately as by weldin~. In the latter instance, short cylindrical rods welded to the ~acing surfaces form suitable rail~ 48.
Referring next to Flg. 2, it will be observed that an ad~ustable spacer in the form of a rectangular bar 49 is posltioned between the facing surfaces of the walls 44 on the side of the web 4~ opposite the shelf 47. Reference to Figs.
6 and 7 shows that the bar 49 has notched ends 50 which correspond in shape to the guide rails 48. In thi~ manner, the bar 49 is laterally displaceable along the rails 48 over the wall 43 outwardly of the web 46.
Lateral displacement of the bar 49 is effected by means o~ a pair of socket head machine screws 51 which threadedly engage a pair of corresponding tapped bores 52 ~oxmed in the web 46 intermediate the rails 48. It will be understood that positioning the screws 51 correspondingly po~itions the bar ~9 and in so doing defines an adjustable shelf 53 as be~t seen in Fig. 2.
More detalled views of the bar ~9 appear in Flgs. 6 5~

and 7 which reveal a pair of outstanding studs 54 that are receivably engaged by the recessed heads of the screws 51 to provide a more firm support for the bar 49.
Adjustment of the bearing 11 is readily achieved to compensate for wear in the blocks 40 and 41 or to allow for manufacturing tolerance var.iations discovered at initial assembly and interfitting of the channels 21 and 25. As previously described, the block 41 is held on the shelf 47 by means of an interference fit between the walls 45. On the 10 other hand, the block 40 is retained in a laterally displaceable position between the rails 48 as a result of corresponding groo~es 55 that engage the rails which also hold the block 40 slidably captive between the bar 49 and a contactlng surface of the channel 21 (Fig. 8~ or a corresponding surface of the channel 25 ~Fig. 9).
It will be observed in Fig. 9 that the wall 43' is fixedly secured to the surface 30 rather than to the surface 31 as in the embodlmen-t lllustrated in ~ig. 8. Therein, since the channel 25 ls fixed in the mast 26 it will be understood that th~ bearing 11 is likewise fixed, the relative motion between the channels being provided by the displaceable channel 21. In Fig~ 9, however, as the bearing 11' i~ attached to the channel 21, the bearing is displaced with the channel. In this arrangement slidable contact between the block 40' and the facing i~terior surface of the channel 25 ts achieved h~ forming a slot 56 in a flange 57 of the channel 21 to permit the block 42' to extend therethrough a~ shown in Fig. 9.
The cross-section taken along the lines B-B and superlmposed on the cross-section taken along the lines A-A
~Fig. 8)~ shows one of two suppork angles 58 in the carriage 32. A~ ln the case o~ longitudinal displacement between the 5~

channels 21 and 25, a similar displacement occurs between the angle 58 and the channel 21. Attachment o the bearing 11'' to an inner surace 59 of the angle 58, as shown in Fig. 8, permits the bearing 11'' to function in the same manner as described for the bearing 11. Thus, corresponding blocks 40'' and 41'' are adjustably set into low-friction contact with mating surfaces of the channel 21.
In all of the embodiments illustrated and described, the blocks 40 and 41 are praferably fabricated from a high molecular weight plastic having physical properties that are similar to those provided by virgin or reprocessed U.H.M.W. polyethylene. A suitable plastic would have beneficial characteristics that include, a low coefflcient of friction, high specific gravity with a typical value of 2.532, good wear and abrasion resistance, self-lubrication and good corrosion and chemical resistance. An acceptable plastic meeting these requirements is known as SYNS~EEL, a trade marked product available from Redwood Plastics Ltd. of Surrey~ British Columbia.
It will be apparent to those skilled in the art that ~he aforenoted embodiments may be varied to meet particular specialized requirements without departing from the true spirit and scope of the invention disclosed. For example, whereas separate end walls 44 and 45 are disclosed ln the bearing 11, such-end walls may be readily replaced by a single pair of end walls. In this case the blocks 40 and 41 would be of substantially uniform length instead of the block 40 being shorter as illustrated in Fig. 2.
Furthermore, the channel 21 need not be configured in the manner illustrated with an addltional ~lange necessitating a slot 56 and may be readily substituted with a convent:lonal channel struature. Moreover, although screw~ 51 are g _ 5~

illustrated and described as controllably positioning the bar 49, coil springs could be readily substituted to apply a con~tant force to the bar 49 whereby a zero tolerance conditlon may be achieved between the blocks 40 and 41 and their respective contactiny surfaces on the channels 21 and 25. These embodiments are thereore not to be taken as indicative of the limits of the invention which is defined by the claims appended hereto, but xather as exemplary structures thereof.

Claims (11)

1. An adjustable slide bearing adapted to receive and engageably retain at least one low-friction bearing block between a pair of longitudinally displaceable surfaces positioned in slidable spaced parallel relation therewith, comprising:
bearing block holder means having a base wall adapted to be fixedly mounted on one of the surfaces, a pair of upstanding end walls spaced apart and disposed ortho-gonally to the base wall, and a thick web integrally joining the base and end walls to define a fixed shelf for a first bearing block on one side of the web;
guide means disposed between the end walls on the other side of the web;
spacer means operably engaging the guide means intermediate the end walls and displaceable therealong outwardly of the web; and means disposed between the web and the spacer means for controllably positioning the latter to define an adjustable shelf for a second low-friction bearing block.

2. A slide bearing as claimed in Claim 1 wherein the guide means comprises a protruding rail on each inwardly facing surface of the end walls extending between the web and the free end of each end wall.

3. A slide bearing as claimed in Claim 2 wherein the means for controllably positioning the spacer means comprises at least one machine screw and wherein the web is bored and tapped for threadedly engaging the screw.

4. A slide bearing as claimed in Claim 3 wherein the spacer means comprises a flat bar having notched ends corresponding to the guide rails.

5. A slide bearing as claimed in Claim 4 wherein the flat bar further comprises a pair of protruding studs facing the machine screws in coaxial alignment therewith.

6. A slide bearing as claimed in Claim 5 wherein the machine screws include recessed heads adapted to receivably engage the studs.

7. A slide bearing as claimed in Claim 6 wherein the end walls comprise a pair of inner walls disposed on the adjustable shelf inwardly of a pair of outer walls disposed on the fixed shelf.

8. A slide bearing as claimed in Claim 7 wherein the first bearing block engages the facing surfaces of the fixed shelf in an interference fit.

9. A slide bearing as claimed in Claim 8 wherein the second bearing block includes grooved ends corresponding to the guide rails.

10. A slide bearing as claimed in Claim 9 wherein the bearing blocks are fabricated from a high molecular weight plastic.

11. A slide bearing as claimed in Claim 10 wherein the high molecular weight plastic has a specific gravity of at least 2.532.