SEALED PIVOT JOINT

Abstract: A sealed pivot joint suitable for joining together the adjacent links of an endless belt, for example, a tank track. The joint has a bearing (10) rotatable on a pin (8), and an elastic sleeve (20) whose extremities are in sealed relationship to the pin and bearing thereby preventing the ingress of abrasive material into, and the egress of lubrificant from, the bearing surface (12). The sleeve is maintained in circumferential tension by tensioning members (14, 16, 18) between the sleeve and the pin which act to prevent wrinkling of the sleeve when the pin and bearing are rotated relative to one another thereby reducing abrasive wear on the outer surface of the sleeve.

Description: SEALED PIVOT JOINT Technical Field This invention relates to sealed pivot joints of the type in which a pin pivots within a bearing. It is particularly, but not exclusively, applicable to hinge joints suitable for joining the adjacent links of endless belts such as used for the tracks of tracked vehicles and conveyor belts. Background Art Sealed pivot joints are known in which the interface between the pin and the bearing is protected against the ingress of abrasive material, or the loss of lubricant, by one or more sleeves the axial extremities of each being sealed to the pin and bearing respec¬ tively, either directly or by way of intermediate sealing members. In applications where the angular displacement of the pin relative to the bearing is limited the interface between the sleeve and the member to which it is sealed may be made as a stationary seal to reduce wear. In known sealed pivot joints utilising such stationary seals the angular displacement of the ends of the sleeve that results when the pin and bearing oscillate relative to one another is accomodated by providing the sleeve with folds or corrugations that are free to flex and distort. However, when such sleeves are used to seal pivot joints that are used in abrasive environments it has been found that the outer surfaces of the sleeves wear preferentially in the vicinity of the corrugations. This limits the useful life of the sleeve resulting in the need more frequent maintenance of the pivot joints. It is an object of the invention to provide a sealed pivot joint which is less susceptible to such preferential wear. Disclosure of the Invention According to the invention there is provided a sealed pivot joint having a pin rotatable in a bearing characterised in that there is included an elstic sleeve disposed about the pin. ; the sleeve having a first and second axial extremity in sealed relation- ship with the bearing and the pin, respectively, and an intermediate portion maintained in circumferential tension by one or more ten- sioning members disposed within the sleeve. The circumferential tensioning of the sleeve acts to prevent the sleeve wrinkling when the pin and bearing oscillate relative to one another*. The tensioning members may comprise a suitably configured portion of the pin, of the bearing end portion, a cylinder rotatably disposed on the pin between the pin and the elastic sleeve, or a combination of these. The elastic sleeve is preferably of chloroprene polymer. The seals may be maintained by wire or garter springs at each extremity, but the preferred arrangement is to use two pairs of circlips one pair being located at each of the extremities of the sleeve by a pair of spaced circumferential ribs formed on the outer surface of the sleeve during its -manufacture. Sealing by adhesives has been found to be unsatisfactory with a chloroprene polymer sleeve because the sleeve develops cuts on its inner surface along the edge of the adhesive area next to the intermediate portion of the sleeve, although it may be satisfactory with a sleeve of a different material. Description of the drawings Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which - Figure 1 is an axial section of a sealed pivot joint showing one of the elastic sleeves sealing the joint; Figure 2 is an axial section of a pivot cartridge having three bearing surfaces, each being sealed by sleeves in the manner shown in Figure 1 ; and Figure 3 is a part cut-away view of the pivot cartridge of Figure 2 applied between the adjoining track links of an endless track of a tracked vehicle. Referring to Figure 1 there is shown a pivot joint 2 which provides articulation between a pin collar . and a bearing collar 6 so as to permit relative angular rotation about an axis A. The joint 2 includes a pin 8 which is a running fit in an annular bearing 10 at a bearing surface 12, the bearing 10 being fixed within the bearing collar 6. The bearing 10 extends axially beyond the bearing collar 6 in a direction towards the pin collar _ to provide an annular support collar 14. The pin collar 4 is an interference fit on the pin 8, the axial extremity of the pin collar 4 nearer the bearing collar 6 forming an annular support collar 16 of the same external diameter as the annular collar 14. A rigid, cylinder 18, constituting with the support collars 14 and 16 the tensioning members, is freely mounted oo-iaxially on the pin 10 and has the same external diameter as the annular collars 14 and 16, and occupies the gap between them. A chloroprene polymer sleeve 20 having axial extremities 22 and 24, and an intermediate portion 25 is located circumjacent the support sleeve 18. The axial extremities 22 and 24 are sealed to the support collars 14 and 16, respectively, by pairs of spring steel circlips 26 and 27. Each pair of circlips is retained in .position by a pair of parallel, circumferential ribs 28 moulded integrally with sleeve 20. The sleeve 20 has an untensioned inner diameter which is smaller than the external diameter of the support collars 14 and 16 and the support sleeve 18. In use the circum¬ ferential tension induced in the elastic sleeve 20 by the support collars 14 and 16 and the cylinder 18 acts to prevent wrinkling or corrugation of the sleeve 20 when the members 4 and 6 are angu¬ larly displaced with respect to one another about the axis A, although wrinkling may occur if the displacement is sufficiently large. In the embodiment of Figure 1 the sleeve 20 has an untensioned inner diameter of 24mm, is 1mm thick and has a length of 20mm. The annular collars 14 and 16 and the cylinder 18 have external dia¬ meters of 28mm. Each pair of circlips 26 and 27 is arranged so that the gap betwen the ends of each circlip do not overlap to ensure that the sleeve is compressed to form a seal round all its periphery. This arrangement allows a relative angular displacement of more than 15" to be imparted to the sleeve extremities 22 and 24 without wrinkling the sleeve 20. Slippage may take place between the inner surfaces of the sleeve extremities and the outer diameters of the collars 14 and 16 at large angular displacement but this can be used advantageously when initially setting the sleeve in position. A further advantage of the non-corrugating property of the sleeve according to the present invention is that the exterior of the sleeve may be covered with a protective layer of mastic material such as a preformed sealant strip as it will not be subject to disturbance by moving folds as occurs if used with previously known sleeve arrangements. Such a mastic layer further extends c the wear life of the sleeve seals of the pivot joint in abrasive environmen s. A particular application of the invention as hereinbefore describee, with reference to Figure 1 is illustrated in Figure 2, namely a pivot cartirdge 40 suitable for use in joining the adjacent ■JQ links of an endless belt. The cartridge 40 comprises a pin 42 which is a running fit in three annular bearings 44, 46 and 48 at bearing surfaces 50, 52 and 54 respectively. Bearing collars 56, 58 and 60 are fixed co—xially on the bearings 44 to 48 respectively. Pin collars 64, 66, 68 and -I5 70 are each an interference fit on the pin 42 and are fixed relative to it by weld at the base of radial holes 72, 74, 76 and 78 in the collars 64 to 70 respectively. Each of the bearing surfaces 50 to 54 is sealed by means of a pair of sleeves 80, 82 and 84 between the respective bearings 44 to o 48 and its two neighbouring pin collars 64 and 66, 66 and 68, 68 and 70, in the manner illustrated in Figure 1. In Figure 3 there is illustrated the use of the pivot cartridge 40 as hereinbefore described with reference to Figure 2 to join adjoining track links 92 and 94 of an endless track. The track 5 links 92 and 94 are respectively provided with inter-digitating lugs .96 to 102 and 104 to 108. The track links 92 and 94 are able to articulate relative to each other by means of the pivot cartridge 40 disposed within the inter-digitating lugs 96 to 108 such that the pin collars 64 to 70 connect the pin (8) to lugs 96 to 102 of the 0 link 92 and bearing collars 56 to 60 connect the bearings (44-68) to the lugs 104 to 108 of the link 94. The cartridge 40 is located in the track links 92 and 94 by means of two S-hooks 110 and 112 welded to respective ends of the cartridge 40 and to the track link 92. The weld is light enough to 5 be readily broken to allow easy replacement of the cartridge 40. In the particular application illustrated with reference to Figure 3 the degree of articulation to be accommodated by the pivot joint is determined by the number of teeth on the vehicle sprocket wheel (not shown) with which the track is to be engaged, a 12 tooth sprocket wheel requiring an articulation of 1/12th of 360", ie-30 * , between successive track links. The cartridge 40 is installed with the links 92 and 94 relatively inclined at an angle midway between the limits of intended .articulation in order that the sleeves will, in this example, be operative between +_ 15". A particular advantage of this assemblage is that once a pivot cartridge has been assembled in clean condition the bearing surfaces are sealed from contamination before the cartridge is inserted through the articulating lugs of the track links. This permits the pivot joint to be replaced in an adverse environment without risk of contamination of the .bearing surfaces.

Claims: CLAIMS 1. A sealed pivot joint having a pin (8) rotatable in a bearing (10) characterised in that there is included an elastic sleeve (20) disposed about the pin, the sleeve having a first and a second axial extremity (22, 24) in sealed relationship with the bearing (10) and the pin (8), respectively, and an intermediate portion (25) εain- tained in circumferential tension by one or more tensioning members (14, 16, 18) located within the sleeve (20). 2. A sealed pivot joint as claimed in claim 1 further charac¬ terised in that the second extemxty (24) of the sleeve (20) is in sealed relationship with an intermediate sealing member (4) fixed coaxially about, and in sealed relationship with, the pin (8). 3. A sealed pivot joint as claimed in claim 1 further charac¬ terised in that one of the tensioning members is a cylinder (18) rotatable on the pin (8) between the pin (8) and the sleeve (20). 4. A sealed pivot joint as claimed in claim 1 further charac¬ terised in that each of the first and second " axial extremities (22, 24) of the sleeve (20) are maintained in sealed relationship with the bearing (10) and the pin (8).respectively, by a pair of adjacent circlips (26, 27)- 5. A pivot cartridge for joining together a first and a second adjacent link (92, 94) of an endless belt having a first and a second set of one or more linking lugs (96-102, 104-108), respec¬ tively, characterised in that there is at least one pivot joint as claimed in claim 1 and that there is a first connecting means (64-70) whereby the pin (42) is connectable to each lug of the first set of lugs and a second connecting means (56-60) whereby each bearing (44-48) is connectable to a lug of the second set of lugs. 6. An endless belt comprising a plurality of joined links charac¬ terised in. that each pair of adjacent links is joined by a pivot cartridge as claimed in claim 5.

Inventors: MACDONALD WILLIAM JAMES JOHNST, MACDONALD, WILLIAM, JAMES, JOHNSTONE
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNI
Application year: 1985
Main classification: B62D55
IPC codes: B62D55