US2854294A - Crawler tumbler and track shoe - Google Patents

Description

Sept 3@, $58 H. v. BANNISTER CRAWLER TUMBLER AND TRACK SHOE 3 Sheets-See; 1'

Filed Feb. 2, 1955 Sept. 3@, 198 H. v. BANNISTER 2,854,294

CRAWLER TUMBLER AND TRACK SHOE Filed Feb. 2, 1955 3 Sheets-Sheet 2 jive/7 for; Harold V. Bcnnisier 37 53, M L/v 777m A TY Sept. 3%, 1958 Filed Feb. 2, 1955 H. V. BANNISTER CRAWLER TUMBLER AND TRACK SHOE 5 Sheets-Sheet 3 Harold V. @unnisier United States Patent CRAWLER TUMBLER AND TRACK SHOE Harold V. Bannister, Waverly, Iowa, assignor to Schield 3antam Company, Waverly, Iowa, a corporation of owa Application February 2, 1955, Serial No. 485,797

21 Claims. (Cl. 305-) This invention relates to improvements in final drive assemblies for endless track mechanisms and more particularly to improvements in the construction of the driving sprocket or tumbler for endless tracks and in the construction of an endless track associated therewith.

In present constructions, endless tracks are formed from a plurality of pivotally connected or linked track shoes or pads, each of which has an upstanding lug thereon for engagement by a driving sprocket or tumbler. The lugs are usually of rectangular configuration and the driving sprocket or tumbler associated therewith simultaneously engages several of these lugs for movement of the vehicle along the endless track. Although this conventional method of drive is entirely satisfactory under most conditions, the action between the tumbler and the lugs on the track pads is largely one of sliding engagement. Necessarily, therefore, a high quality of materials must be used. However, under some conditions such as in sandy soil or where the soil is highly abrasive, very rapid wear is encountered. So much so, in fact, that in some cases an endless track as well as the drive tumblers may be entirely worn out and may require complete replacement within a period of two or three weeks. This, of course, is an expensive proposition and presents a very real problem in the art.

It is, therefore, one of the aims of this invention to provide an improved drive for endless track vehicles which will reduce wear between the drive sprockets and tumblers and the track pad lugs.

Another object of this invention is to provide an improved drive for endless track vehicles wherein rolling contact is efiected between the tumblers and the track pad lugs, to minimize friction and wear.

Another object of this invention lies in an improved drive in accordance with the preceding object wherein the drive is equally capable of satisfactory operation in both forward and reverse directions.

Another object of this invention is to provide an improved drive sprocket or tumbler construction which utilizes roller means as the drive elements and which is so constructed that the rollers may be easily interchanged or replaced to compensate for wear while at the same time the construction does not detract from the rigidity and strength of the sprocket.

Another object of this invention is to provide an involute form of track pad lug and a drive sprocket associated therewith having roller drive means thereon whereby frictionand wear-reducing characteristics are imparted to the assembly.

Still another object of this invention resides in the provision of an improved endless track and drive sprocket association wherein the pitch of the sprocket drive elements is greater than the pitch of the track pads engaged volute construction of a track pad lug and drive introductory ramp portions associated therewith.

Still another object of this invention lies in the pro vision of an improved form of endless track and drive sprocket therefor wherein the pitch between the drive rollers of the sprocket is greater than the pitch between adjacent track pad lugs engaged therewith and in the construction of the track pad lugs wherein they are of involute configuration and have drive introductory ramp portions associated therewith to effect a rolling contact with the rollers and guide the same therealong for smooth and shockless drive introduction with the involute lugs.

Another object of this invention is to provide an improved form of final drive for endless tracks in which a tumbler or sprocket incorporates circumferentially spaced pin members whereas the track shoes embody upstanding involute form lugs and drive introductory ramps merging smoothly therewith so that the centers of pivotal connection between lugs revolve at a constant radius from the center of the sprocket while portions of the shoes are permitted of radial shifting with respect to the sprocket or tumbler.

A further object of the invention lies in the provision of a final drive assembly for endless track vehicles in accordance with the preceding object, wherein the tumbler or sprocket incorporates a pair of spaced but rigidly interconnected wheel plates and mounting pins associated therewith upon which replaceable roller means are mounted.

A further object of the invention lies in the provision of a final drive assembly for endless track vehicles in.

accordance with the preceding object, wherein the tumbler or sprocket incorporates a pair of spaced but rigidly interconnected wheel plates and mounting pins associated therewith upon which replaceable roller means are mounted, the roller means being of selectively larger diameters whereby to compensate for wear of the track lugs and drive introductory ramps as well as to compensate for wear occurring in the hinge joints between track lugs.

Another object of this invention resides in the provision of an improved final drive in accordance with the preceding object wherein portions of said wheel plates on opposite sides of said pins serve to absorb and compensate for side thrust and prevent lateral shifting of associated endless track elements.

These, together with other objects inherent in the construction and functioning of the apparatus will appear as this description proceeds.

Illustrative embodiments of the invention are shown in the accompanying drawings but it is to be understood that this showing is illustrative only, and is not intended to be limiting to the exact construction shown, since obviously changes can be made both in detailed construction and arrangement of parts without forming a departure from the spirit and scope of this invention as set forth and defined in the appended claims.

In the drawings:

Fig. 1 is an elevational view partly broken away, showing a portion of an endless track constructed in accordance with this invention and showing the drive sprocket associated therewith;

Fig. 2 is a vertical transverse section taken generally along the plane of section line 2-2 in Fig. 1;

Fig. .3 is a perspective view of one of the track pads constructed in accordance with this invention;

Fig. 4 is an elevational view showing one endless track assembly and its associated supporting and driving mechanisms in their entirety;

Fig. 5 is an enlarged elevation showing a portion of the drive sprocket and endless track and illustrating the relationship therebetween;

Fig. 6 is a side elevational view of a modified form of drive sprocket; and

by .any suitable means suchas welding .or the like, and

which projects on opposite .sides "thereofin the-manner shown mostclearlyinFig. 2. The hub is provided with .a;longitudinal.bore and .a:keyway 16 intersecting the bore..whereby to receive a driveaxle of .the associated ehicle as indicated by the reference character 17 in .ig. 4. I

The contour or marginal edge of the wheel plates em bodiesa series of valleys 18 interconnected by :radially projecting guide or thrust portions 19. Each guideportion 19 presents a flat chordal edge20 and arcuatecorner ,porti0ns21 and 22. Theguide portions 19 are additionally each provided with a pair of apertures 23 and 24 adjacent the respective corners 21 and 22.

It will benoted that the two wheel plates are secured together in staggered relationship such that the valleys .18 of .onewheel plate are disposedbetween twozadjacent valleys 18 of the other wheel plate and suchtthat-the guideportions 19:of one plate .are .in bridging relation .to the valleysof the other plate. .The apertures :23 "and 24 are spaced atequal circumferential distances around the periphery of the drive plates and eachregistering pair of these apertures is adapted to receive a pin member .25 therethrough. As seen most clearly in Fi-g...2, for the purpose of retaining the pins 25 properly t in place alock collar or .sleeve 28 .is engaged :over the end .27 ,of each pin and a lock pin 29 is projected through .the lock collar andtheend 27 of thepin to hold .thecollar or sleeve in place in the manner shown. In this respect, it will be noted that the end 27 of the .PlHfPI'QjCCtS .outwardlyof the innerwheel plate12 so that the lock collar .28 is .engaged .againsttheinner .side of the inner wheel .p1ate.12.

Rotatably carried by each of the pins :is a cylindrical roller member 30 which rollers .form the drive-elements ,of thetumbler assembly as will be more readily apparent as this description proceeds.

The felloe portion of the wheel plates Hand 12 -are provided with apertures 31 and it will be noted that these apertures are equal in number to the guide portions 19 and project partially into such guide portions. .T he openings 31 serve not only for the purpose of lightening the wheel plates. but also serve to 2 permit dirt clods, rocks and other foreign material to be expelled from the drive tumbler assembly.

i the iarcuate ;p.ortion 45,'is also arcuate.

The specific contour of the wheel plates 11 and 12,"

that is, the formation of the alternate valleys .and guide portions, serves also to lighten the construction .whereas the-staggered relationship between the valleys of the inner and outer wheel plates; assures that the'maximumamount of material may be removed from the valleys; Thatyis, more material can be removed. from each valley-1.8 by staggering the relationship of thevalleys between the @two wheel plates than would be possible suchvalleys were in transverse registry.

.It will benoted that the staggered relationship ,of .the .guide or thrust portions .19 does .notdetract fromythe lateral thrust stability which theyaccomplish; The -here- :inaftendescribed track shoe lugs so cooperate with :the drive or thrust portions that every other track :shoe :is prevented from shifting laterally by the .guiderportions 'onzone; side of the sprocket while;the,; intermediate alternate shoes bear against the other guidennthrust'portions 19 to prevent lateral shifting of the shoes in the opposite direction.

The construction of each of the track pad members 32 will be most readily apparent from Figs. 1 and 3. The track pads are'conventional insofar as each includes a main body portion 33 having aground-engaging surface 34 on one side thereof, and having at opposite ends lug portions v 3.5, .36 and 37 whichareapertured .fortthe reception of interconnecting pin members 38 by meansof which'the plurality 'of track pads :are linked *or pivotdlly interconnected for--cooperation in the 'well known manner. The surface 39 of the main body portion 33 which is oppositeito.thegroundiengaging surface .34;is provided with an upstanding lug. indicated generally by the reference character 40 which'is'also conventionally provided although the specific configuration of the lug departs from that which is normally utilized. In this respect, it will be rooted that each .lug -40 :includes a. relatively ;wide

.base portion 41 joined with and extending; longitudinally of the main .body portion -33,the base tapering or:.b,eing involutely formed in. such-.a-manner that it: presents :;a relatively ,narrow upper .orfree ends-portion 142. The roller engaging face- .43 .of each'lug is of involute :configuration.

:Adjacent the drive face of each, lug :.and,formed1integrally therewith-and with ,the ;main body portion 33 .-a :drive introductory ramp 44. This drive introductory ramp,extends-;from a;point adjacent one end 10f theztrack gpaddn. a direction toward the jdrive face 43 .1.and ;merges smoothly-therewithvin :an :arcuate face portion 45. .fI'he freeendof lthe ramp-46 is -,the.1highest point .thereofzand the surface 471 ofethe ramp in thisivicinitynnergingioward Therelationship of the :surface 47 ofthe;ramp with the arcuatersurface .45 and therelationship of the involute drive ;face:43 cof the log with the ramp-surface .45.--is.tangentialxsuchzthat smooth and 1 shockless: rolling. contact 'can behadbetween the tumbler -.ro1lers :30 as these members .roll along :the

drive introductory-surface into: contact with ctheinvohte. drive surface of the lugs. -As=will ,bezseemmostcclearly :from Fig. -5,;the radius -rof the ramp surface .45 is :equal to the radii of the drive roller members whereas the. radius ,R of-the ramp :surface .47, is .equal to the radiussofanzarc tangent torall of :the drive .rollers. Thus, as :thefrlrivc :rollers; progressively roll along .the ramp surfaceA'l, the centers of the hinge pins 38. remain at; afixe'd .eandconsttint .distance,fromdtheacenter ofv rotation of thed'rivenprocket. Atfthe same-time, when any onevdrive roller'reachcsrathe point at which it engages the ramps-surface 45, thatrroller will impart the drive tothetrack and-will do ,so inia very efficient manner inasmuchas a maximum-portion .of the roller zsurface equal in lengt-hto thelengtht-ofathe ramp surface 45 'wilLbe engaged.

Of prime consideration with respectto the properpop- .eration of this invention. is the. fact that the; circumferential pitch between the rotational centers of the;roller members 30 is greater than .the circumferential pitchi between adjacent track pad lugsas the pads are'engaged upon the tumbler assembly. This relationship of pitches assures that the-interen gagement ,bet-weenthe successive drive rollers 30 and the correspondingutrack pad,lugs.is had .in the manner illustrated in z-Eig. l. ';That;is,.'the roller 48 in Big, 1 awhichv has, justengaged-withzthegramp portion of the-track pad 49in that fignreengages-upon the end ramp ,surface 47 .outsoficontact with the involute drive surface of the associated lug=;40 whereas; the. drive roller which isin'dicated bylthe reference ,charactcr SO in 'Fig. Land .whichris removed asubstantial circumferential distance, from .the previously mentioned roller 48.11215 justengaged with :the lowermost ,portion-of-the involute face ofits associated lug 40. "From the position. -of .the roller 48 with relation to its correspondinglugtdrivegsur face 43, the intermediate -rollers.which; are ,designatediby the reference characters 51, .52 and.- 53,ware,"progressively closer to their associated involute lug ,drive; surfacesuifi,

this being effected by the differential in pitch previously discussed. Thus, as the tumbler assembly is rotated in a counter clockwise direction in Fig. l, the roller 48 will progress from its position shown on the drive introductory ramp surface 47 along this surface into contact with the arcuate surface 45 at approximately the point that the roller53 is disposed and will, when the roller 48 has attained the position of the roller 50, engage the lowermost portion of the involute drive face 43 of its associated lug. The relationship between the roller 54 and its vassociated lug in Fig. l is such that these members are completely out of contact, this being due to the fact that the associated track pad and lug member is not as closely engaged with the sprocket assembly due to the upward inclination of this pad by virtue of the positioning of the idler pulley member 55 as seen in Fig. 4. Of course, even if the idler pulley 55 is so positioned that the lug assembly associated with the roller 54 rests upon such roller, there will be no drive transmitted between the roller 54 and this lug since the upper flight of the endless track assembly will not be under sufiicient tension to assure this drive.

It will be understood that one important effect of the single drive engagement between the tumbler and the track assembly is that there can be no localized overstressing of parts, such as is inherent in conventional drive ,drive elements and the lugs, the presence of foreign material between any one driving element and its associatedlug will tend to place an undue strain upon an adjacent drive element and the interposed lug and associated track pads since the foreign material will act as a wedge which cannot be compensated for since several track pad lugs are drivingly engaged at the same time. In the present device, such presence of foreign material will only shift the relative positioning of all the rollers and their associated lugs, that is, compensation can be had for the presence of such foreign material without placing any further strain on the tumbler or endless track. It is also important to note that not only do the drive rollers reduce friction and wear by virtue of their rolling engagement with the track lugs, but also they present a far greater area of wearing surface than is ordinarily used in drive tumblers. Their rolling action assures even wearing throughout their circumferential surfaces. In this respect, it is desirable that the dimensions of the drive rollers and track lug surfaces be such that an infinite number of driving engagements between the rollers and lugs will be required before the same surface portion of any roller will be twice in precisely the same drive engagement with the lug surfaces 45.

A further important consideration in respect to this invention will be seen to exist as a result that the effective pitch differential between the drive rollers and the track pad lugs can be maintained substantially constant even though wear does occur on both the rollers and the lugs by merely replacing, as the lugs and rollers become worn, the worn rollers With rollers of larger diameter than were initially used. Further, should any rollers become damaged unduly during use, they are rapidly and easily replaced.

Another important consideration with regard to this invention is that the track shoes rotate around the tumbler about a fixed radius, thus assuring uniform tension in the chain of linked track shoes. This is, of course, due to the fact that the ramp surfaces 47 always lie along an are which is tangent to all of the drive rollers, as shown most clearly in Fig. 5.

' ing pins.

It will be noted from Fig. 5 that the leading side 56 of each track lug is of involute configuration and that at the base of each lug is an arcuate surface 57 Whose radius r is equal to the radii of the drive rollers. Thus, the surfaces 45 and 57 are similar but are disposed oppositely to each other. The purpose of forming the track lugs with forward involute surfaces is to permit the track to be driven in the reverse direction. It will be noted that in Fig. 5, the full line position of the rollers illustrates the positioning of the drive rollers when the same are reversely driving while the dotted lines illustrate the forward drive position of the rollers.

Preferably, the leading sides of the track lugs are not provided with surfaces corresponding to the drive introductory surfaces 47 on the opposite sides since the introductory surface 47 of each adjacent track shoe will serve this purpose. This reduces to a minimum the amount of lost motion permitted of the drive tumbler between forward and reverse drive.

Referring now more particularly to Figs. 6 and 7, wherein a modified form of tumbler is shown, the tumbler or sprocket will be seen to be formed as an integral unit, preferably a casting, and includes a central hub 58 and a plurality of generally radial spoke plates 59, each provided with a triangular opening 60. All of the spoke plates are joined to the hub substantially midway between the ends of the latter and from this point the plates are angulated longitudinally of the hub alternately in opposite directions so that every other plate terminates adjacent one end of the hub while the other plates terminate adjacent the opposite end of the hub. The spoke plates are generally triangular in configuration and are apically joined to the hub so that their base portions 61 are remote from the hub. A series of longitudinally extending and circumferentially spaced radial webs 62 are positioned on the hub so as to integrally connect adjacent plates along their side edges. This particular construction serves to present a very rigid drive member which at the same time offers practically no depressions or pockets within which dirt and the like may lodge temporarily to be later deposited on the track lugs and drive rollers.

The base portions 61 terminate at opposite ends in apertured bosses adapted to receive the drive roller mount- The bosses 63 in the plates adjacent one end of the hub 58 are merely thickened whereas the bosses 64 on the other plates are both thickened and provided with transverse slots 65. When the drive roller mounting pins are mounted in the plate bosses, the apertured ends of the pins are aligned with the slots 65 whereby a lock pin may be inserted therein.

It is preferred that the hub 58 be provided with a longitudinally extending rib 66 to maintain a substantially uniform thickness of metal in the vicinity of the keyway 67.

I claim:

1. A track shoe or pad comprising, a main body portion having a ground-engaging face on one side thereof, an upstanding lug formed on the opposite face of said main body portion, said lug being of involute configuration, a drive introductory ramp formed on said opposite face of the main body portion extending longitudinally therealong and merging with the base of said involute lug.

2. A track shoe or pad comprising, a main body portion having a ground-engaging face on one side thereof, an upstanding lug formed on the opposite face of said main body portion, said lug having a drive face on one 'side thereof adjacent one end of the main body portion, said drive face being of involute configuration, a drive introductory ramp formed on said opposite face of the main body portion extending from adjacent said one end of the main body portion to the drive face of the lug and merging smoothly with the latter.

lug. 1

4. A track shoe or ,pad comprising, a main body portionhaving a ground-engaging face onone side thereof, an upstanding lug formed on-the opposite "face of said main body portion, said'lug having a drive face on one .side thereofadjacentgoneendof the main body portion, said drive face being of jinvolute configuration, a drive introductory. ramp formed on said opposite face of the main body portion extending from adjacent said one end of the main body portion to the drive face of the .lug and merging smoothly with the latter, saidrampbeing arcuated fromadjacent the one end of :the main *body portion to merge smoothly and tangentially with the arcuate base portion of said involute drive face.

'5. In a drive assembly for endless track vehicles, a drive sprocket, said drive sprocket having a plurality of circumfe'rentially spaced drive elements, an endless, flexible tread trained about a portion of the circumference of said drive sprocket, said endless tread including a plurality of pivotally linked track pads, each tra'ckpad 'having'an upstanding lug thereon engageable by the .drive elements of ,the sprocket, the pitch between the drive elements on the sprocket being greater than 'the pitch between the track pad lugs engaged upon the drive sprocket, whereby driving engagement between the sprocket andthe tread is had substantially only'between one drive element and one lug at any one given point ofrotation of the drive sprocket.

6.'The drive assembly according'to claim "5 wherein said lugs are of involute configuration.

'7. The drive assembly according to claim '5 wherein said lugs are of involute configuration, said drive-elements being of cylindrical configuration;

8. A track shoe or pad comprising a main bodypor- ,tion'having aground-.engaging'lower surface, a d'riveLlug formed on the upper "surface of said main body portion, .said lug'having onesurfacethereof formed of involute configuration.

9.In a drive assembly for endless track vehicles, a "drive sprocket, a plurality of circumferentially spaced rollers journaled onsaid sprocket, a plurality of pivotally interconnected track pads trained about a portion of said sprocket, each of said track pads having an upstanding lug formed on one surface thereof engageable by's aid rollers, each of said lugs being of involute configuration on at least one surface thereof.

10. A track shoe or pad comprising a maintbody portion having a ground-engaging lower surface, adrive lug projecting from the upper surface of said ,mainihody portion, said lug having opposite drive surfaces facing the opposite *endsof said main-body portion,-each drive:surfacebeing of involute configuration, and a driveintro- "ductory ramp :extendingirom adjacent one .end of .the main body; portion to;mergersmoothiy:with the baseqof .one involute drive surface.

glil. In adrive assembly for endless track vehicles, a drive rsprocket, a plurality of circumferentially spaced rollersjjournaled onsaid-sprocket, a plurality of pivotally interconnected track pads trained about a portion of-said sprocket, each of said track pads having an upstanding luggformed on one surfacethereof engageable by said rollers, each oftsaidllugs being of involute configuration ,on atleast one surface thereof, and an arcuate drive introductory ramp extending f-romadjacent one end of each track'pad to mergesmoothly with the base of the involute surface of the associated lug.

I ,12..'In'a drive assembly 7 drive sprocket, ,a' plurality of ,circurnferentially. "spaced,

' or endless track vehicles, ;a

rollers journaled on said sprocket, -a pluralityof pivotally interconnected.trackpads trained about apor'tion of -said sprocket, eachgofsaid track pads havingan upstanding lug formed on one surface thereof engagableby said rollers, each of said flugs being of'involute configuration on at least one surface thereof, the pitch between said sprocketrollers being greater than the pitch between the track pad lugs, whereby driving engagement between the sprocket and the endless track is hadsubstantially only between one roller and onelug at any one .givenpoint of rotation of the drive sprocket.

uration on at least one surface thereof, and pan; arcuate drive introductory ramp extending fromadjacentnneend of each'trac'k pad'to merge srnoothlywith the 'base of-the involute surface ofthe associated'lug, 'the pitch-between said sprocket rollersbe'ing, greater than the pitch betweenv the 'track pad lugs, whereby driving engagement ihetween the sprocket. and the endless track is bad substantially only between one roller and one lug at ,anylone given pointof rotation'ofthe drive-sprocket.

'14. In "a drive assembly for endless track-vehiclesya gdrive sprocket, said drive sprocket havingap1urality'of circumferentially spaced cylindrical drive "elementsgan endless flexible tread trained about a portion 'ofpsaid sprocket, said endlesstread including aplurality of pivot- ,ally linkedtrackpads, each track pad having an'upstanding lugthereonengageable 'by the drive elements ofthe sprocket, :eachlug having aninvolute drive-surface'jthe pitch between drive elements of the sprocket being greater 'than'the pitch between-the track padlugs,-wherebydriving engagement between the sprocket and-treadis had substantially only'betweengone drive element and one-lug at any given time.

1'5.'In a drive assemblyffor endless track vehicles, a drive sprocket, said drive sprocket having apluraIityof circumferentially spaced cylindrical ;drive elements, an endlessfiexible tread gtrained about 'a portion "of said sprockehsaid endless 'treadincludinga plurality of 'pivotally linked' tr-ack pads, 'each track pad having an upstanding -lug thereon :engageable by the drive elements 'ofthe sprocket, each lug having an involute drive surface, the pitch between drive elements of the 'sprocket being 'greater than the pitch between the track pad lugs, wherebydriving engagement between the sprocket and ,tread is had substantially only between one drive-elementandone lug at any given time, the base of said involute-drive surface having an arcuate surface'fonned thereon whose radius is equal to the radii ofsaid drive elements. I

,16. In a drive assemblyfor endless "track vehicles, 'a drive sprocket, said drive sprocket having a plurality of circumferentially spaced cylindrical jdrive elements, an endless flexible tread ;.trained about a portion of ,said sprocket, said endless tread including ,a plurality of pivotally linked track pads, each track pad, havingan upstandinglug thereon engageable by the drive elementsof the sprocket, each lug having an involute drive sur'face,'the

pitch between drive elements of the sprocket being greater than the pitch between the track pad'lugs, .whereby fdriving engagement between the sprocket an'd tread jishad substantially only between one drive element and ,onelug at anygiven time, the base of said involute drive surface having an arcuate surface formed thereonwhose radius is equalto the radii of said 'drive elements, and an arcuate drive introductory ramp .on each pad merging smoothly with said arcuate surface.

17. In a drive assembly for endlesstrack vehicles a drive sprocket, a plurality of circumferentially spaced rollers journaled on said sprocket, a plurality of pivotally interconnected track pads trained about a portion of said sprocket, each of said track pads having an upstanding lug engageable by said rollers, each lug presenting a pair of involute drive surfaces facing opposite ends of said pads.

18. In a drive assembly for endless track vehicles, a drive sprocket, a plurality of circumferentially spaced rollers journaled on said sprocket, a plurality of pivotally interconnected track pads trained about a portion of said sprocket, each of said track pads having an upstanding lug engageable by said rollers, each lug presenting a pair of involute drive surfaces facing opposite ends of said pads, the base of said involute drive surface having an arcuate surface formed thereon whose radius is equal to the radii of said drive elements.

19. In a drive assembly for endless track vehicles, a drive sprocket, a plurality of circumferentially spaced rollers journaled on said sprocket, a plurality of pivotally interconnected track pads trained about a portion of said sprocket, each of said track pads having an upstanding lug engageable by said rollers, each lug presenting a pair of involute drive surfaces facing opposite ends of said pads, the base of said involute drive surface having an arcuate surface formed thereon Whose radius is equal to the radii of said drive elements, and an arcuate drive introductory ramp on each pad merging smoothly with said arcuate surface.

20. In a drive assembly for endless track vehicles, a drive sprocket, said drive sprocket having a centrally disposed hub, a plurality of drive rollers arranged in circumferentially spaced relation around said hub with the axes of said rollers parallel z 7 the axis of said hub, a plurality of plate portions arranged in laterally and circumferentially spaced relation and centrally connected to said hub, said plate portions being alternately staggered adjacent opposite ends of said hub, each plate portion having a pair of apertures therein in registry with similar apertures in laterally spaced adjacent plate portions, a mounting pin received in each pair of registering apertures, said drive rollers being rotatably mounted on said pins.

21. The drive of claim 20 wherein said plate portions are of triangular configuration and each is apically connected to said hub adjacent the center thereof, alternate plate portions being divergently, radially angulated from said hub.

References Cited in the file of this patent UNITED STATES PATENTS 618,642. Clouser Jan. 31, 1899 1,304,357 Norelius May 20, 1919 1,795,618 Ronk Mar. 10, 1931 1,934,627 Norelius Nov. 7, 1933 2,704,942 Koile Mar. 29, 1955 FOREIGN PATENTS 276,712 Great Britain Sept. 5, 1927 588,981 Great Britain June 9, 1947 577,304 Germany May 29, 1933

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