US3567294A - Articulated chain assembly - Google Patents

Abstract

IMPROVED ARTICULATED CHAIN ASSEMBLY FOR A TRACK-TYPE VEHICLE WHEREIN MID-PITCH DRIVING LUGS ARE LOCATED ON THE ASSEMBLY SUBSTANTIALLY EQUIDISTANT THE CENTERS OF THE ARTICULATED JOINTS, AND WHEREIN SAID LUGS HAVE A GEOMETRIC

RELATIONSHIP RELATIVE TO A DRIVING SPROCKET TO PERMIT LIMITED ROCKING OF THE ASSEMBLY ON SAID SPROCKET.

Description

F. E. SIMPSON L ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet 1 Filed Sept. 1967 INVENTORS FRED E; SIMPSON EUGENE J. HNILICKA Roy E MAYO 'JOHN S. RICCA JR. GAIL G. AVERY CHARLES E. WAGAMAN F. E. SIMPSON ETAL 3,567,294

ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet 1 Filed Sept. 20. 1967 -INVENTORS FRED E SIMPSON EUGENE J. HNILICKA Rov E MAvo JOHN S. RlccA JR. CHARLES E. WAGAMAN M1 ATTORNE s GAIL G. AVERY Mflch Z, 9 F. SIMPSON A 3,567,294

ARTICULATED CHAIN ASSEMBLY Filed Sept. 20. 1967 e Sheets-Sheet s ISVENTORS A OF FRED ESIMPSON EUGENE .HNILICKA BUSH'NG ROY E. MAYO JOHN S. RlccA JR. GAIL G. AVERY CHARLES EWAGAMAN March 2, 1971 E, SI S ETAL 3,567,294 7 ARTICULATED CHAIN ASSEMBLY 6 Sheets-Sheet 4 Filed Sept. 20. 1967 INVENTORS EUGENE/1U. HNILICKA JOHN S RlccA JR. CHARLES E. WAGAMAN a 0 1 'fimg E?S FRED E. SIMPSON Rov E. MAYO GAIL G. AVERY Mad! 1 1 F. E. SIMPSON L 3,567,294

ARTICULATED CHAIN ASSEMBLY 6 Sheets-Sheet 5 Filed Sept. 20. 1967 ENTORS HNILICKA JOHN S. RICCA JR. GAIL G. AVERY INV FRED E. Suw som EUGENE J. Rev E. MAvo CHARLES E WAGA MA N BY 7") ?i"" {,A. T'FBRNJS F. E. SIMPSON ETAL 3,567,294

ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet 6 Filed Sept. 20. 1967 E A LE .18

INVENTORS EUGENE J. HNILICKA JOHN S. RICCA JR. CHARLES E. WAGAMAN FRED E. SIMPSON Rev E. MAYO GAIL G- AVERY ATRRNE S United States Patent O M 3,567,294 ARTICULATED CHAIN ASSEMBLY Fred E. Simpson, Washington, and Eugene J. Hnilicka, Peoria, Ill., Roy E. Mayo, Santa Barbara, Calif., and John S. Ricca, Jr., Bartonville, and Gail G. Avery and Charles E. Wagaman, Peoria, 111., assignors to Caterpillar Tractor Co., Peoria, Ill.

Filed Sept. 20, 1967, Ser. No. 669,218 Int. Cl. B62d 55/20 US. Cl. 305-57 13 Claims ABSTRACT OF THE DISCLOSURE Improved articulated chain assembly for a track-type vehicle wherein mid-pitch driving lugs are located on the assembly substantially equidistant the centers of the articulated joints, and wherein said lugs have a geometric relationship relative to a driving sprocket to permit limited rocking of the assembly on said sprocket.

BACKGROUND OF THE INVENTION This invention relates to an improved articulated drive chain assembly for a track-type vehicle, such as a crawler tractor. More particularly, the invention relates to an articulated drive chain assembly having a driving lug located substantially equidistant the centers of the articulated joints, referred to as mid-pitch, wherein the lug is formed to cooperate with a chain driving sprocket or sprockets to permit limited rocking of the assembly on the sprocket to thereby reduce horsepower losses in the chain drive and to simultaneously limit external wear at the articulated joints.

Prior art articulated chain drive assemblies are in general constructed such that the articulated joints provide fo two important functions. Firstly, the articulated joints provide hinged connections between adjacent chain sections so that the chain, under driving conditions, may conform to either a linear path or a curvilinear path (i.e. when traveling on the sprocket or over rough terrain). Secondly, the aticulated joints of prior art structures provide a drive means for co-action wtih the sprocket teeth whereby the chain is forcefully driven by rotational move ment of the sprocket.

Since the articulated joints of prior art structures are the driven members of the chain assembly they are subjected to severe loads applied at the sprocket, which loads result in a high rate of external joint wear and/ or fatigue cracking that materially reduces the useful life of the chain.

These prior art articulated joints usually comprise a pin connection wherein the pin is fitted with an external bushing. It is these bushings which are subjected to great external wear and fatigue cracking when engaged by the sprocket.

An additional disadvantage of conventional prior art articulated joint chain structures relates to power losses due to impact forces of the chain drive as it enters upon the driving sprocket. Although very little information has been published on power losses due to impact, it will be recognized from later description in this specification that such losses present a serious problem which is greatly reduced by the special construction of the mid-pitch drive of the present invention.

Another advantage of the invention, somewhat related to the impact aspect, resides in the power savings realized from the present mid-pitch construction which permits the chain link to rock as it enters upon the drive sprocket. As will be descibed in particular detail later in the specification, the construction of the present invention reduces the distance through which the incoming chain link must 3,567,294 Patented Mar. 2, 1971 travel. Such a reduction results in a decrease in acceleration and deceleration of the incoming chain which in turn results in a power savings.

A further advantage of the mid-pitch drive construction of the present invention over prior art structures relates to a power savings effected after impact of the chain With the driving sprocket. In conventional prior art chain drive constructions the articulated joints are prevented from rocking upon the drive spocket because the pins and bushings forming the articulated joints are the driven members and are engaged in the notched portions of the sprocket such that they are in effect held against movement. As will be further pointed out in greater detail, such conventional structures are subjected to frictional power losses due to the scrubbing action of the articulating bushings against the sprocket. In the case of track-type vehicles this scrubbing action normally occurs as the track engages the sprocket when the tractor i in reverse or as it leaves the sprocket when the tractor is in a forward gear, but the situation may be vice versa depending upon the design. The scrubbing action also, of course, leads to an extremely high rate of external bushing wear which materially shortens the useful operational life of the chain, since the bushings must be replaced much sooner than would be the case if this external bushing wear problem could be substantially reduced.

The present invention provides a mid-pitch drive construction which allows for a limited amount of rocking of the chain link upon the sprocket to keep the articulated joint out of engagement with the sprocket during the initial portion of the driving cycle, which substantially eliminates external bushing wear caused by scrubbing of the bushing upon the sprocket and also reduces power losses caused by the scrubbing action. Thus, in the construction of the present invention the articulating bushing may eventually bottom out on the sprocket, but only after articulation is substantially completed and when it is not subjected to the driving load.

Other objects and advantages of the invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view illustrating one preferred embodiment of the invention;

FIG. 2 is a side elevation of the embodiment illustrated in FIG. 1;

FIG. 3 is a schematic illustration of a typical prior art construction;

FIG. 4 is a schematic illustration of an embodiment of the present invention for comparison with FIG. 3 relative to power loss caused by impact with a driving sprocket;

FIG. 5 is a schematic illustration of a typical prior art construction;

FIGS. 69 schematically illustrate an embodiment of the present invention for comparison with FIG. 5 relative to power loss caused by chordal action of articulated chain members as they enter upon a driving sprocket;

FIG. 10 schematically illustrates a prior art construction with regard to wear and power loss caused by scrubbing action;

FIG. 11 schematically illustrates an embodiment of the present invention for comparison with FIG. 10;

FIG. 12 schematically illustrates another embodiment of the present invention;

FIG. 13 illustrates the manner in which the rocking angle or degrees of rocking may be calculated for the various embodiments of the invention; and

FIGS. l4l9 illustrate various embodiments of midpitch drive lug construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2 there is shown one preferred embodiment of an improved articulated chain assembly employing a mid-pitch drive pin or lug constructed in accordance with the present invention. The track link section generally shown at 11 is somewhat conventional and comprises a pair of links 12 which are retained in spaced relationship by a pair of track bushings 14 fitted about the outer diameter of a pair of track pins 16, which are received in bores 17 of the links 12. As best shown in FIG. 2, a track shoe 18, provided with the usual grouser 19, extends across the bottom of the links 12 and is secured to each of the links by a plurality of bolts 20.

The mid-pitch drive pin or lug is shown at 22 and is disposed at a central point midway between the track pin bushings 14. In the embodiment of FIGS. 1 and 2, the mid-pitch drive lug 22 is rigidly secured to the track shoe 18 by a plurality of bolts shown at 23. FIG. 2 also illustrates a portion of a driving sprocket 26 and the manner in which the mid-pitch lug co-acts with the sprocket 26 which will be more fully explained hereinafter.

In order to properly appreciate the novel mid-pitch drive construction of the present invention, it will be necessary to compare the structure thereof with prior art conventional articulated chain link constructions. It will be assumed for purposes of illustration with respect to the following material that the tractor is stationary and that the track is being driven by the sprocket.

As previously mentioned, one of the factors which contributes to horsepower loss in conventional articulated track link structures is the impact energy loss caused when the driven articulated link member strikes the driving sprocket. FIG. 3 illustrates a typical prior art construction which may be compared with the mid-pitch drive construction of FIG. 4 to illustrate how the construction of FIG. 4 results in a reduction of impact energy loss caused when the driven member strikes the sprocket.

In FIG. 3 a section of track (track link) denoted by the articulating bushing connections A and B is shown entering upon a driving sprocket. As the articulated section of track enters the sprocket, the trailing bushing portion B moves inwardly toward the sprocket center at a given velocity. It will be understood that impact of the trailing bushing B (schematically shown in phantom lines) with the driving sprocket takes place through a radius R emanating from the center of the leading bushing A of the articulated joint. Since the radius R is relatively large, the impact velocity of the bushing B with the driving sprocket is also relatively large depending upon the rotative speed of the sprocket.

The illustration in FIG. 4 depicts a mid-pitch drive construction according to the present invention schematically showing the point of impact (in phantom lines) of an articulated track section as it enters upon a driving sprocket. It will be observed that in FIG. 4 as contrasted with FIG. 3, the driven element of the articulated track section comprising bushings A and B is the mid-pitch lug member C located midway between the bushings A and B. Thus, as the articulated track section of FIG. 4 enters upon the driving sprocket the over-all motion of the track section is the same as that shown with regard to the conventional track link shown in FIG. 3. However, it should be noted that contact with the driving sprocket is established through a radius R/2, which is 4- approximately one-half the distance R denoted in FIG. 3 and therefore the impact velocity of the track section shown in FIG. 4 is correspondingly reduced as compared with the prior art structure shown in FIG. 3. This, of course, results in a corresponding reduction in power loss caused by the impact of the driven articulated member with the driving sprocket. In addition there is less chatter of the chain as it enters the sprocket, and a substantial reduction in the noise created by the chain entering upon the drive sprocket.

Another advantage of the invention, somewhat related to the impact aspect, resides in the power savings realized from the present mid-pitch construction which permits a special type of rocking action by the chain link as it enters upon the drive sprocket. The particular type of rocking action produced by the present mid-pitch construction produces a horsepower savings over conventional structures by reducing the chordal action or the total distance through which the incoming chain link must travel as it enters upon the driving sprocket.

In FIG. 5 a conventional prior art section of track denoted by the articulating bushing connection A, B and D, is shown entering upon a driving sprocket. Bushing B has just seated on the sprocket, and as the sprocket rotates the center line of bushing B follows the are described by the pitch radius. After the bushing B seats on the sprocket and the sprocket continues to rotate the bushing B assumes the phantom line position 0 and the effective pitch radius for purposes of calculating the velocity of the bushing increases from P to P. Thus, the incoming chain must accelerate and decelerate with each engagement of a new section of chain and the amount of acceleration and deceleration is related to the change in effective pitch radius as each bushing travels the path from B to O to A. It will, therefore, be appreciated that the incoming track in such prior art constructions is accelerated and decelerated with each bushing engagement with concomitant power loss due to the energy expended during such acceleration and deceleration.

Turning now to FIG. 6, a mid-pitch drive construction according to the present invention is schematically shown an instant after the mid-pitch drive lug C thereof has contacted the driving sprocket. Summation of moments about the center of mid-pitch lug C shows a sizable applied clockwise moment caused by the chain load as shown. A resistive counterclockwise moment must occur for equilibrium and the bushing A moves until it bottoms out against the sprocket.

The actual position of an entering mid-pitch drive section of the preferred construction is shown in FIG. 7. That portion of the track already on the driving sprocket will adjust itself accordingly. As the sprocket rotates through the articulation angle which is approximately 28 to 30, bushing B takes the position formerly occupied by bushing A. In order for this change of position to take place, some rocking action must occur. This rocking is compatible with the applied moment throughout the articulation angle. For approximately the first 7 of articulation a clockwise moment caused by the chain load keeps the bushing B away from the sprocket.

At approximately 7 of rotation there is no applied moment about the center of the mid-pitch lug C since the chain load force is applied directly through the center of said lug as shown in FIG. 8 wherein the bushing center lines are also shown to be on the pitch radius. From this time on the chain load force applies a counterclockwise moment about the center of mid-pitch drive lug C with bushing B finally bottoming out in the position formerly occupied by bushing A as shown in FIG. 7. The center line of bushing B therefore does not follow an are described by the pitch radius, but rather follows a path as shown in FIG. 9.

As shown in FIG. 9, the net effect of the rocking action resulting from the mid-pitch drive construction of the present invention causes the bushing B to follow the path shown which, as can be seen, results in a substantial reduction in the chordal action or distance through which the incoming track section must move. FIG. 9 shows by way of comparison the distance E which represents the chordal movement of conventional prior art articulated track link sections as compared with the distance F which represents the chordal action of mid-pitch drive constructions according to the present invention. The net savings or reduction in chordal action of the mid-pitch drive construction over conventional track link constructions is shown by reference letter G.

It will be understood that the reduction in chordal action or distance through which the incoming track section must move results in a decrease in the energy expended for acceleration and deceleration of the track section, which ultimately results in a horsepower savings. This power savings is due to the special construction of the mid-pitch drive of the present invention which allows limited rocking action. It should also be noted that the mid-pitch chain construction of the invention definitely results in smoother chain action upon entering the driving sprocket than can be obtained with conventional articulated joint chain constructions.

Thus far in the comparison of the mid-pitch drive construction of the present invention with conventional prior art articulated chain constructions we have emphasized horsepower savings due to a reduction in impact force and also power savings due to a reduction in chordal action. Another significant advantage, however, of the present mid-pitch construction over prior art constructions relates to the reduction of external bushing wear at the articulated joint of the chain.

FIG. 10 illustrates a prior art construction entering upon a driving sprocket when the tractor is in reverse. The articulated joints of conventional prior art chain constructions are subjected to a high degree of bushing wear, especially when the tractor moves in reverse, due to a phenomenon generally referred to as scrubbing.

This scrubbing action consists of relative rotation between the bushing and the notched portion of the driving sprocket as will now be described with respect to FIG. 10. Bushing A has just seated on the sprocket and its motion now starts to leave a linear path and enter into a curvilinear path. Note that the reference marks between bushing A and the sprocket are in line.

As the sprocket rotates through the angle 6 in reverse, the bushing A moves to the position of bushing B. Note that the reference mark on bushing B has rotated through the angle 4) with respect to the sprocket. This relative rotation o-r scrubbing motion is one of the main factors in external bushing wear on track bushings. The scrubbing action also occurs while going forward, however, chain loads are greatly diminished by the time the top of the sprocket is reached.

It can be readily observed from FIG. 11 that this scrubbing action is substantially reduced, if not almost entirely eliminated, in the mid-pitch drive construction of the present invention. In FIG. 11 lug C has just seated on the sprocket. Note that the reference marks between lug C and the sprocket are in line. As the sprocket rotates in reverse through the angle 0, lug C moves to the position of lug K. Even though the lug C undergoes a limited amount of rocking, the reference marks at the lug K location are still substantially in line indicating the substantial elimination of scrubbing action.

It should be noted that the articulating bushings A and B experience little or no external wear because these articulating bushings contact the sprocket for only a brief period during the critical portion of the driving cycle when detrimental scrubbing action occurs.

In summary, the mid-pitch drive construction of the instant invention drastically reduces external wear on the articulating bushings and results in a minimal amount of wear on the easily replaced mid-pitch drive lug member. This is accomplished notwithstanding a slight amount of rocking action which rocking action results in track horsepower saving due to a reduction of power losses through impact, reduced chordal action, and power saved through the elimination of scrubbing action.

Various configurations of mid-pitch drive can be designed, however, as will be noted from the subsequent description, some configurations have definite advantages over others. The most important factors in mid-pitch drive constructions relate to (l) the relationship of the mid-pitch drive lug center point to the centers of the articulated joints, and (2) the degree of clearance or degrees of rocking provided between the driving sprocket and the articulating bushings. Either or both of these factors can alter the performance of mid-pitch drive construction.

Initially it can be stated that the preferred constructrons are those depicted in FIGS. 2 and 6 wherein the center point of the mid-pitch drive lug is located either on or radially outwardly of a straight line drawn between the centers of the articulating bushings (bushings 14 in FIG. 2 and bushings A and B in FIG. 6). In other words, the center of curvature of the cylindrical top portion of the mid-pitch lugs should be located on or below a straight line drawn between the centers of the pins at the articulated joints on each side of the lugs. These constructions are preferred because as previously pointed out, and as shown in FIGS. 6, 7 and 8, the incoming bushing B is prevented from having a significant counterclockwise moment about the center point of midpitch drive lug C, caused by the force of the chain load, from engaging with the sprocket during the portion of the driving cycle when detrimental scrubbing action would occur.

FIG. 12 illustrates a mid-pitch drive lug construction wherein the center point of the drive lug C is located radially inwardly of a straight line drawn between the centers of the articulating bushings A and B". As illustrated therein, summation of forces at the center point of mid-pitch drive lug C results in an applied counterclockwise moment thereabout due to the force of the chain load. This applied counterclockwise moment exists throughout the articulation angle and causes scrubbing action or external wear on the articulating bushing B". This scrubbing action occurs especially in reverse because the trailing bushing bottoms out against the sprocket near the beginning of the articulation angle and stays in this position until it reaches the position formerly occupied by the leading bushing. Thus, while the midpitch drive construction of FIG. 12 possesses advantages over conventional prior art constructions due to a reduction in power losses caused by impact and reduced chordal action, it is nonetheless not as advantageous as those mid-pitch drive constructions wherein the center point of the mid-pitch drive lug is located at or radially outwardly of a straight line drawn between the centers of the articulating bushings as previously described.

Another extremely important factor in the construction of mid-pitch drive assemblies in accordance with the present invention relates to the relative size of the articulating bushings with respect to the notched-out portions of the driving sprocket. It will be understood that this relative size factor is one of the determinative factors with respect to the amount of rocking action about the center point of the mid-pitch drive lug. Thus, if the bushings are too large with respect to the sprocket notches, insufiicient rocking will occur with resultant horsepower losses due to impact, chordal action and scrubbing action. correspondingly, however, the bushings may be reduced in size to such a degree that excessive wear occurs on the mid-pitch drive lug per se which would of course substantially lessen the advantages obtained through the use of said drive lug.

Tests have illustrated that the ideal size for the bushings in order to provide all the aforementioned advantages of the invention is such that the bushings are permitted to rock through an angle which is no greater than approximately FIG. 13 illustrates how this rocking angle or degrees rocking may be calculated. FIG. 13 shows a mid-pitch drive construction in accordance with the present invention wherein the particular articulated connection in question is shown in a neutral position with respect to the driving sprocket. The rocking angle is measured between a line drawn between the center point of the lug C and the center of the trailing bushing B when the bushing is at its maximum outward position and a line drawn between the center points of lug C and bushing B after the bushing has rocked to a bottomed out position with respect to the sprocket. This rocking angle is denoted oz in FIG. 13. Studies have indicated that the rocking angle should not exceed approximately 20 and preferably should be about 12 for best results.

FIG. 14 illustrates a modified embodiment of the invention which is similar to that shown in FIGS. 1 and 2. In FIG. 14 the mid-pitch driving lug is bolted as at 31 across the track links 32 rather than directly to the track shoe 34.

FIG. 15 illustrates another embodiment wherein a removable mid-pitch driving lug 36 is provided with a projection 38 which fits in a slot 40 formed in the track shoe 42. The tongue or projection could be formed on the track shoe rather than the lug and could be of any suitable shape to lend rigidity to the structure.

FIG. 16 illustrates a driving lug embodiment wherein a mid-pitch driving lug 44 is provided with a removable wear tip portion 46. The tip portion 46 may be formed of harder material than the base portion 44.

FIG. 17 illustrates an embodiment wherein the midpitch driving lug comprises two driving elements 48 one of which is shown for attachment to link 50 as by bolts 52. This embodiment allows for the provision of a gap between the driving elements 48 whereby dirt may escape from between the two driving elements. The track shoe is provided with an aperture to allow the dirt to pass outwardly through the assembly.

FIG. 18 illustrates an embodiment wherein the midpitch driving lug 54 is hollow and is attached to a raised portion 56 of the track shoe by bolts 58.

FIG. 19 illustrates an embodiment wherein the midpitch driving lug takes the form of a pin 60 press fitted into bores formed in the track links 62. This embodiment has excellent rigidity due to the nature of the press fits. It is also possible to retain the pin 60 by suitable hinged joints to permit the pin to be rotated as wear occurs and then tightened again without disassembling the chain.

What is claimed is:

1. In an articulated chain assembly for track-type vehicles wherein an endless track is driven about a driving sprocket and an idler wheel each sprocket having a plurality of notches of uniform configuration, and wherein each articulated element of said track comprises a pair of laterally spaced apart links having a track shoe connected thereto and extending across the bottom thereof, and wherein said articulated elements are hingeably connected to adjacent elements by a cylindrical pin fitted through aligned bores in said links, said pin having an external cylindrical bushing fitted thereabout, the improvement comprising, a mid-pitch driving lug for each articulated element located centrally of said track shoe and generally equidistant the centers of said track pins, said mid-pitch lug having a cylindrical top portion shaped to cooperate with the correspondingly configured notches in the driving sprocket so that relative rocking movement may occur when the mid-pitch lug enters and leaves the notches of the driving sprocket; and wherein the cylindrical bushings at the articulated joints have an outside diameter which is smaller than the outside diameter of the cylindrical top portion of the mid-pitch lug; said outside diameter of the cylindrical bushings having a size relative to the cylindrical top portion of the mid-pitch lug which permits the mid-pitch lug to contact the notches in the sprocket prior to contact by either cylindrical bushing as each articulated element enters the sprocket and further permits each articulated element of the chain assembly to rock as said articulated element enters and leaves the driving sprocket, thereby reducing power losses and reducing external bushing wear.

2. An improved articulated chain assembly as set forth in claim 1 wherein said mid-pitch driving lug is provided with a replaceable upper wear surface for contacting the notched portions of said driving sprocket.

3. An improved articulated chain assembly as set forth in claim 1 wherein said mid-pitch driving lug is removably secured to said track shoe.

4. An improved articulated chain assembly as set forth in claim 1 wherein tongue and groove means are provided between said mid-pitch driving lug and said track shoe for providing a more rigid connection therebetween.

5. An improved articulated chain assembly as set forth in claim 1 wherein said mid-pitch driving lug is formed in two portions and provided with a spaced gap between the two portions.

6. An improved articulated chain assembly as set forth in claim 1 wherein said mid-pitch driving lug is removably secured to said links.

7. An improved articulated chain assembly as set forth in claim 6 wherein said mid-pitch driving lug comprises a pin member press fitted into bores formed in each pair of laterally spaced apart links.

8. An improved articulated chain assembly as set forth in claim 1 werein the mid-pitch driving lugs are removable.

9. An improved articulated chain assembly as set forth in claim 8 wherein said mid-pitch driving lug is removably secured to said links.

10. In an articulated chain assembly for track-type vehicles wherein an endless track is driven about a driving sprocket and an idler wheel, each sprocket having a plurality of notches of uniform configuration, and wherein each articulated element of said track comprises a pair of laterally spaced apart links having a track shoe connected thereto and extending across the bottom thereof, and wherein said articulated elements are hingeably connected to adjacent elements by a cylindrical pin fitted through aligned bores in said links, said pin having an external cylindrical bushing fitted thereabout, the improvement comprising, a mid-pitch driving lug for each articulated element located centrally of said track shoe and generally equidistant the centers of said track pins, said mid-pitch lug having a cylindrical top portion shaped to cooperate with the correspondingly configured notches in the driving sprocket, said top portion of the mid-pitch lug extending upwardly from the track shoe to a height greater than the height of the cylindrical bushings, said cylindrical bushings having a smaller outside diameter than the diameter of the cylindrical top portion of the mid-pitch lug; and wherein the center of curvature of the cylindrical top portion of the mid-pitch lug is located on or below a straight line drawn between the centers of the pins at the articulated joints on each side of said lug, whereby each articulated element is permitted to rock as it enters and leaves the driving sprocket.

11. In an articulated endless track link assembly of the type used on a crawler tractor having a notched drive sprocket, each said link comprising: a pair of laterally spaced and vertically disposed side bars each presenting an upper rail portion, parallel pin and cylindrical bushing elements secured to and interconnecting corresponding opposite ends, respectively, of said side bars, a track shoe, connecting means releasably securing said shoe to the bottoms of said side bars, and a drive lug releasably secured to said shoe independently of said side bars and elements and disposed laterally between said side bars and intermediate the axes of said pin and bushing elements, said drive lug having front and rear convexly curved sprocket engaging surfaces facing in diverging d1- rections and extending laterally substantially the full distance between said side bars, the top of said drive lug being of less height than said rail portions and lying substantially above the plane formed by said parallel axes, said sprocket engaging surfaces of said drive lugs being more gradually curved than said bushing elements and having a size and disposition relative to said bushing elements to permit the drive lugs to be engaged by the sprocket notches prior to contact of said notches by either cylindrical bushing as each link enters the sprocket.

12. An improved articulated chain assembly as set forth in claim 11 wherein said mid-pitch driving lug is provided with a replaceable upper Wear surface for contacting the notched portions of said driving sprocket.

in claim 11 wherein tongue and groove means are provided between said mid-pitch driving lug and said track shoe for providing a more rigid connection therebetween.

References Cited UNITED STATES PATENTS 1,186,785 6/1916 Holt 305-58X 1,339,786 5/1920 Porter 305-59X 1,377,450 5/1921 Whipple 30552X 1,513,459 10/1924 Jett 305-52X 1,678,149 7/1928 Lamb 305-58X 2,598,828 6/1952 Phelps 30557 3,359,044 12/1967 BOggs 305-57 13. An improved articulated chain assembly as set forth 15 RICHARD J. JOHNSON, Primary Examiner

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