US3435908A - Articulated crawler tractor construction - Google Patents

Description

Sheet INVENTORS DONALD ESU/VDE/PL/N JACOB E. STA/4B DORRANCE 0L DENBU/PG 7 PW ATTORNEYS A i ams Q N w gi D'. E. SUNDERLIN ETAL ARTICULATED CRAWLER TRACTOR CONSTRUCTION April 1,1969 I Filed March 1, 1967 April 1, 1969 Filed March 1., 1967 DJE. SUNDERLIN ETAL 3,435,908 ARTICULATED CRAWLER TRACTOR CONSTRUCTION Sheet 2 ore V 7 1Y6 7 l/ g' C I M2 :58 29 62. If; 5 x b 4 1 l 43 5 47 JM 48? INVENTORS Qf/VALD ESU/VDERL/IV A605 5. 5774/45 ATTORNEYS April 1, 1969 D. E. SUNDERLIN ETAL 3,

ARTICULATED CRAWLER TRACTOR CONSTRUCTION Sheet of 6 Filed Earth 1, 1967 m M 50 WNW mNTM N 5 ES L V .0 1 www A A N R 0mm 0 0 2 i -012mm April 1, 1969 D. E. SUNDERLIN' ETAL 4- I of 6 Sheet M M L R3 0 mm w N? NU D V W Q WE E mew M3 AR 0J ?,,?.,v +71% I I I RNEYS A ril 1, 1969 D. E. SUNDERLIN ETAL 3,435,908 ARTICULATED CRAWLER TRACTOR CONSTRUCTION Filed March 1, 1967 Sheet 5 of 6 PRIOR ART 1N ENTORS DONALD E. UNDERL/N JACOB 5. 577MB DORIPA/VCE 0L DENBURG A NEYS E L5 EA V April 1, 5 I D. E. SUNDERLIN ETAL 3,435,908.

ARTICULATED CRAWLER TRACTOR CONSTRUCTION Filed alarm 1, 1967 Sheet 6 of 6 F 1;-75- PRIOR ART ELE Y E I NVENTORS DONALD E. Sumo/2mm JACOB E. 5774 46 DO/PRANCE 0L DE/VBZ/RG ATTORNEYS United States Patent 3,435,908 ARTICULATED CRAWLER TRACTOR CONSTRUCTION Donald Edward Sunderlin, Washington, and Jacob Emor Staab and Dorrance Oldenburg, Peoria, 111., assignors to Caterpillar Tractor Co., Peoria, 111., a corporation of California Filed Mar. 1, 1967, Ser. No. 619,676 Int. Cl. B62d 55/00; 1302f 3/ 76 US. Cl. ISO-9.44 13 Claims ABSTRACT OF THE DISCLOSURE Background of the invention This invention relates to powered vehicles, and more particularly to articulated tractor vehicles of the class which ride on endless track chains.

Crawler tractors were first designed primarily to replace draft animals in the pulling of agricultural machinery or other similarly drawn loads. Such operations generally took place on reasonably even ground and in most instances frequent turning of the vehicle was unnecessary. In the later stages of development, tractor vehicles have been adapted to a variety of other purposes which may involve the carrying of a working implement, such as a loader bucket or bulldozer for example, on the tractor itself and operations may involve frequent maneuvering over very rough and steep terrain. The basic tractor construction has not heretofore been changed in a fundamental way to accommodate to these very different functions but retains operating characteristics which are primarily suited for drawing loads along a substantially straight path and over fairly even ground.

The conventional crawler tractor rides on a pair of track assemblies disposed one at each side of the rigid tractor body. While yieldable suspensions have been provided in some instances, each track assembly has structural connections to the front and back of the track assembly which are necessary to support the body. Thus the track assembly as a unit is either rigidly fixed to the body or at best is capable of only a very limited rocking motion relative thereto.

One result of this construction is that turning of the tractor necessarily involves a substantial amount of sideward sliding of track shoes over the ground surface with the rate of lateral slippage being larger for short radius turns. The sideward track motion is a serious inefficiency in that it consumes a sizable proportion of the tractor engine power output. Further, the ground surface under the track is disrupted and wearing of components of the track assembly is accelerated' As a practical matter, the forces involved in this kind of turning make it necessary to provide more massive track assembly elements than would otherwise be needed.

A further very serious disadvantage of the conventional crawler tractor in many usages is that irregularities of the ground surface translate into sharp pitching movements of the vehicle including any working implement which is carried thereon. For example, in travelling over an obstacle, the tractor will suddenly rock forward as Patented Apr. 1, 1969 the center of gravity of the vehicle passes over the elevation. The jarring may then be compounded as the forward end of the tracks strike the ground surface. Several other conditions, to be hereinafter discussed, also contribute to riding instabilities of this kind.

Sharp, violent movements of the tractor body have the effect of seriously limiting production rates and job quality where working implements are an element of the vehicle. For example, materials may be ejected from a loader bucket by sharp pitching motion of the vehicle. In the case of bulldozing, both speed and precision are adversely affected by uncontrollable movements of the tractor. In order to minimize such effects, tractors are very frequently operated more slowly than would otherwise be possible. Moreover, jarring movements of the tractor body are extremely discomforting and may cause the operator to limit vehicle speed for this reason alone.

Still another difficulty in the operation of conventional crawler tractors results from the fact that large areas of track may lift from the ground. This is a very pronounced problem where a working implement is mounted on the vehicle. The loading forces on a loader bucket, bulldozer, or the like, are often sufficiently large to lift portions of the tractor while concentrating the weight on some other portion. Because of this effect, the available traction varies substantially and the weight of the vehicle together with any load carried thereon, may be concentrated on a very small region of the track assemblies. This again requires the construction of track assemblies with more massive components than might otherwise be necessary. Further, the effect contributes to the unwanted motions of the tractor inasmuch as a pronounced imbalance of traction between the two tracks tends to turn the vehicle.

Some of the difiiculties discussed above are avoided by utilizing wheel tractors, particularly those of the articulated class in which the tractor body is divided between the front and rear wheels into two sections which can be pivoted with respect to each other to steer the vehicle. However, others of the problems are more pronounced and there are further limitations unique to wheel tractors. Such tractors have much less traction to begin with and in operation one, and sometimes two, of the wheels may lift from the ground at times. On sharp rock surfaces tire wear is a very severe problem. Wheel tractors are particularly unstable on irregular terrain because of the tire deflections and bounce which result from shocks and shifting loading. Sizable transient deformations of the tires cause spillage from such implements as loader buckets, interfere with precise control of other attachments, and the resultant motions tend to produce operator uneasiness. For these and other reasons, wheel tractors including the articulated type are not fully capable of resolving the operational problems discussed above.

In order to avoid certain of the limitations of conventional tractor design, the articulation of crawler tractors has 'heretobore been proposed. US. Patent No. 2,673,616 issued Mar. 30, 1954 and entitled Pivotally Connected Steerable and Driven Tractor Units, discloses one example of such a design. These designs have been directed primarily to providing for more efiicient steering with increased traction and have not attempted to overcome the riding instabilities and related problems discussed above. Insofar as such factors as pitching movements, uneven traction, concentrated stresses and the like are concerned, such vehicles perform in a manner somewhat similar to that of the more conventional two-track crawler tractor, except that some improvement may be gained from the longer wheel base which is present. In particular, the track assemblies have been coupled to these articulated tractor bodies in an essentially conventional manner so that many of the riding characteristices of the vehicle are necessarily those of an elongated two-track machine. One

result has been that the full potential advantages of an articulated crawler tractor for many purposes have not heretofore been realized.

Summary of the invention The present invention is an articulated crawler tractor Vehicle providing a high degree of riding stability, maneuverability, and more constant increased traction, particularly on rough terrain. These characteristics, together with other advantages, provide for more rapid operation, more efficient power utilization and markedly facilitate the operation of working implements which may be combined with the vehicle as a component thereof.

Four powered track assemblies are coupled to a tractor body which is hinged at a point between the forward and rearward pairs of tracks so that the forward body section may be pivoted relative to the rear section about a vertical axis for steering purposes, by means such as hydraulic jacks. Each of the track assemblies is joined to the tractor body through a single pivot connection preferably situated at the central region of the track assembly. Thus each track assembly is free to oscillate relative to the tractor body about an axis transverse thereto. Within wide limits, each track is free to assume any angular position relative to the tractor body which may be appropriate to the localized irregularity of the ground surface underlying the track. Such oscillation of each track assembly is independent of oscillatory movements of the other tracks and at any given time each of the four tracks may be inclined at a different angle with respect to the tractor body. To provide for still greater automatic adjustment of the tracks to the ground surface, the two rear track assemblies may be carried on a transverse axle structure which is itself coupled to the tractor body for oscillation about a central longitudinal axis.

As a result of this construction, all four tracks tend to maintain ground contact and provide driving traction in the presence of severe irregularities in the ground surface. Moreover, this extensive ground contact is maintained when very large loading forces are exerted against the vehicle through a working implement carried thereon. Vertical or oblique pitching motions of the tractor body, the operator, and any working implement, are much reduced relative to conventional crawler tractors. For example, as a track assembly passes over a sharp elevation, it must rock forward at some point in the movement as do the tracks of a conventional tractor. While some minor direct lifting of the body may occur, the rocking motion is not transmitted to the tractor body inasmuch as each of the tracks is itself free to rock independently of the body. Still other characteristics of the structure, to be hereinafter discussed, further contribute to riding stability so that much more rapid and precise maneuvering becomes safe, comfortable, and feasible.

Accordingly, it is an object of this invention to provide a powered crawler vehicle having greater operational stability, more constant high traction, and increased efficiency, particularly on uneven terrain.

The invention, together with further objects and advantages thereof, will be better understood by reference to the following description of a preferred embodiment and by reference to the accompanying drawings.

Brief description of the drawings In the accompanying drawings FIGURE 1 is a side elevation view of a crawler tractor loader embodying the invention;

FIGURE 2 is an elevation section view taken along line 22 of FIGURE 1 showing details of the supporting and driving connections between the tractor body and a track assembly thereof;

FIGURE 3 is an elevation view taken along line 3-3 of FIGURE 1 showing structure which connects the rear track assemblies to the tractor body thereof;

FIGURE 4 is a perspective view illustrating operation characteristics on uneven terrain of a tractor vehicle embodying features of the invention;

FIGURE 5A is a side elevation view of the four track loader tractor of FIGURE 1 illustrating operational effects which occur when the apparatus of FIGURES l to 3 is loading a very heavy mass of material;

FIGURE 5B is a side elevation view of a conventional crawler tractor loader showing the effect which results from a loading situation similar to that of FIGURE 5A;

FIGURE 5C is a side elevation view of a conventional articulated wheel loader showing the effect which occurs therewith in a loading situation similar to that of FIGURE 5A;

FIGURE 6A is a side elevation view of the four track loader tractor of FIGURE 1 carrying a load on a steep slope and illustrating schematically an improved ground pressure distribution under the vehicle;

FIGURE 6B is a side elevation view of a conventional crawler tractor loader under conditions similar to those of FIGURE 6A;

FIGURE is a side elevation view of a conventional articulated wheel tractor loader under conditions similar to those of FIGURE 6A;

FIGURE 7A is a side elevation view of the four track loader tractor of FIGURE 1 showing vertical movement effects which occur as the vehicle passes over an obstacle;

FIGURE 7B is a side elevation view of a conventional crawler tractor loader illustrating effects which occur in a situation similar to that shown in FIGURE 7A; and

FIGURE is a side elevation view illustrating the action of a conventional articulated wheel tractor loader in a situation similar to that of FIGURE 7A.

Description of the preferred embodiments Referring now to the drawing, and more particularly to FIGURE 1, a tractor vehicle 10 in accordance with invention has a body with a front section 11 and rear section 12 coupled together by a kingpin hitch 13. The driving engine 14 is carried on the rear body section '12 in this example of the invention and a shelf 16 of the rear section extends forwardly above the back portion of the front section 11 to support an operators station 17 directly above the hitch 13. This placement enables the operator to be aware of the position of the rear section 12 of the vehicle without looking backward and provides an excellent view of the forward section 11 including any working implement carried thereon. In this embodiment of the invention, the implement is a loader bucket 15 carried at the forward end of the vehicle on pivoting arms 18, with tilt linkage 20 to control the inclination of the bucket relative to the arms.

Hitch 13 provides for pivoting the front body section 11 relative to the rear section 12 about a vertical axis which intersects the center line of the vehicle, the connection between the two body sections being such as to prevent flexing in any other direction. To provide this form of coupling, the hitch 13 may have a pair of upper hinge members 19 which extend forward from the rear section 12 and are spaced apart vertically to receive an intermediate hinge member 21 which extends rearwardly from the front body section 11. An upper pivot pin 22 couples the three members. To provide greater strength and rigidity against unwanted forms of flexing at hitch 13, a pair of lower hinge members 23 project rearwardly from the front body section 11 at a level substantially below that of the upper hinge members 19 and 21, and are spaced apart to receive a lower intermediate hinge member 24 which extends forward from the rear body section 12. A lower pivot pin 26 couples the hinge members 23 and 24 and is aligned along the vertical pivot axis of the upper pin 22.

Steering of the tractor 10 is effected by a pair of double-acting hydraulic jacks 27 which are connected between the front and rear body sections 11 and 12 with one at each side of the articulation at hitch 1.3 so that contraction of one jack accompanied by extension of the other acts to pivot one body section relative to the other about the axis of the hitch.

Considering now the novel structure which supports and drives the tractor body with improved traction, greater stability, and other advantages, four endless track assemblies 28 are utilized including a forward pair 28' and a rearward pair 28". To minimize side slipping of the tracks during turning, the forward and rearward sets of track 28 and 28" are located equidistantly from the hitch 13. Referring now to FIGURES 2 and 3 in conjunction with FIGURE 1, the mode of coupling each track assembly 28 to the tractor body is of particular significance with respect to the objectives of the invention. Each of the four track assemblies 28 is joined to the tractor body through a single axle structure, such as front axle members 29 which extend sidewardly at each side of the front body section 11 and rear axle members 29 at the sides of the rear section 12.

As will hereinafter be discussed in greater detail, this form of coupling provides for independent oscillatory motion of each of the four track assemblies 28 about an axis which is transverse to the tractor body and coaxial with the associated axle 29. Each track assembly 28 is thus free to oscillate in a vertical plane in response to irregularities in the ground surface 32 underlying the track and in such a manner that each track tends to maintain driving contact with the ground under virtually all circumstances. In extremely rough terrain, as illustrated in FIGURE 4, each of the four track assemblies 28 may be inclined at a different angle at any given time, and each may be continually changing its individual inclination as it passes over localized surface irregularities.

Referring again to FIGURE 1, the highly advantageous operational characteristic will generally be facilitated by situating the pivot connection to the tractor body at the central region of the track assembly 28. More specifically, it is usually preferable to situate the axles 29 at the mid-point of the zone of contact of the associated track with the ground. This balanced arrangement provides for optimum performance in both forward and reverse, provides for a better distribution of stresses, and aids in avoiding troublesome torque reactions on the track assembly from the driving connections thereto.

In order to impart to the tractor a still greater ability to conform the available track surface to ground irregularities, and to further reduce jolting and pitching of the tractor body, the two rear track assemblies 28" are capable of still another form of oscillation. In particular, the rear track assemblies 28" may oscillate about an axis longitudinal to the rear body section 12. Referring now to FIGURE 3 in conjunction with FIGURE 1, the two rear track assemblies 28 are carried at opposite ends of a transverse axle housing 33 which is itself coupled to the rear section 12 of the tractor body at a pivot connection 34 situated midway between the sides of the body.

The pivot axis of coupling 34 is horizontal and longitudinal with respect to the tractor body 12 so that the axle housing 33 together with rear track assemblies 28" may oscillate as a unit in a vertical direction as indicated by arrow 36. To receive the axle housing 33 and pivot coupling 34, a transverse slot 37 is provided at the underside of the rear body section 12 and stops 38 are disposed at the top of the slot at each side of the tractor body to limit the vertical oscillation of the axle housing 33.

Referring again to FIGURE 4 which shows an articulated crawler tractor 10' of this general type on very irregular terrain, it may be seen that this additional form of oscillation of the rear track assemblies 28" further increases the ability of the tracks to maintain ground contact at four separate areas. The construction also provides for a very desirable three point support of the tractor body as a whole.

Referring again to FIGURE 1 each of the four track assemblies 28, may, if desired, be of essentially similar construction. Each assembly 28 may have a track frame member 42 which is journalled on the axle 29 and connects with longitudinal track frame rails 43. 'Frame rails 43 carry a track drive sprocket 44 at the rearward end, a front idler 46 with recoil mechanisms 45 mounted at the forward end, and a series of track rollers 47 disposed along the underside of the rails. Each of the track assemblies 28 has an endless track chain 48 carried on sprocket 44, idler 46 and rollers 47. While it has heretofore been customary to provide flanges 41 on all track rollers 47 to assure good engagement with the track chains 48, this also has the effect of increasing the spacing between rollers and thereby increasing the stress concentration which may be experienced by an individual roller. To strengthen the track structure by providing for closer roller spacing, one or more unflanged rollers 47' may be used between flanged rollers without loss of good engagernent with the track chains 48.

Each of the track chains 48 is driven by the drive sprocket 44 which is itself operated through a secondary drive sprocket 49 turned by still another sprocket 51 which is coaxial with the axle 29 that joins the track assembly to the tractor body, the sprockets 49 and 51 being coupled through a drive chain 52. In order to minimize torque reactions which would tend to pivot the entire track assembly 28 about the single axle connection 29 to the tractor body the sprockets 49 and 51 may be of equal diameter.

To avoid interference with the freedom of each track assembly 28 to oscillate vertically about its axle 29, drive may be transmitted to each track assembly from the engine 14 through a system which is coaxial with file axle 29. Referring now to FIGURE 2 in particular, there is shown a suitable structure for the connection between each track assembly 28 and the vehicle body which includes a coaxial drive system of the type discussed above. The axle member 29 in this construction is stationary and has a flange 53 at an intermediate point which is bolted to a gear housing 54. Housing 54 is situated at the inside of the track assembly 28 and is secured to the axle housing 33' that projects sidewardly from a differential housing 57 at the central region of the vehicle body 11. The differential housing 57 at the front section 11 of the tractor is rigidly attached thereto while the differential housing at the rear section may oscillate as hereinbefore described.

Axle 29 is situated at a level slightly below that of axle housing 33' and has an inner end section 58 which extends from gear housing 54 and is engaged in a socket 59 secured to the underside of the axle housing 33' to impart additional strength and rigidity to the connection between the axle shaft and the tractor body. A curved structural member 55 has a forward end journalled to axle end section 58 and extends rearwardly and outward as shown in FIGURE 3 to connect with the inner track rail 43 thereby strengthening the oscillatable connection between the track assembly 28' and the tractor body 11.

Referring again to FIGURE 2, to attach the track assembly 28 to the axle shaft 29, the previously described frame member 42 has a sleeve 61 which fits coaxially on the outer end of the axle and roller bearings 62 are disposed therebetween. An end cap 63 on the axle shaft 29 locks the outer bearing 62 and sleeve 61 thereon.

An annular drive gear 64 is disposed within gear housing 54 in coaxial relationship to axle 29 and has a sleeve 65 extending toward the track assembly 28 and carrying the hereinbefore described sprocket 51 at a spline connection 66. As previously described the track assembly drive chain 52 is engaged on the sprocket 51. Drive is trans mitted to the gear 64 from a drive shaft 67 extending within axle housing 33' by means of a pinion gear 68 within gear housing 54. Suitable structure for transmitting the drive from the tractor engine to a drive shaft 67, including suitable differential constructions, are well understood within the art.

While the chain drive system described above has pronounced advantages, it should be understood that other mechanisms for transmitting drive from the region of axle 29 to the rear sprocket 44 may also be employed.

An articulated crawler tractor having four track assemblies coupled thereto in the unique manner described above .has pronounced operational advantages which are best understood by comparing the action of such a tractor with conventional forms. Referring now to FIGURE A, an articulated crawler tractor loader 10 of the type hereinbefore described is shown in the loading position at which bucket is lowered, tilted forward and driven into a volume of material 74 which is to be lifted, transported and deposited in a truck, for example. At this point in the operation of a loader, the forward portion of the vehicle is subjected to an extremely heavy load which seriously interferes with the functioning of a more conventional form of loader.

In a conventional two-track crawler tractor-loader 76 as shown in FIGURE SB for example, the heavy loading at the forward end of the vehicle may cause the tracks 75 to pivot up away from the ground about the forward end 77 thereof. This drastically reduces traction, creates jarring vibrations, and generates extremely high stresses in the structural components at the forward end of the tracks 75. Further, the relatively short machine length limits the degree of leverage available to produce break-out force. Referring now to FIGURE 5C similar undesirable effects occur in this situation utilizing a conventional articulated wheel loader 78. In this case it is common for the rear wheels 79 to lift completely from the ground throwing the entire load on the front wheels 81. Traction is even less in this case resulting in excessive wheel slip and costly tire wear. While the pneumatic tires 82 cushion some forms of shock, other forms of undesired motion are aggravated thereby. In particular, tires 82 cause the vehicle to bounce at some resonant frequency. Further, there are limitations to the amount of loading which can be sustained by the wheeled vehicle and difliculties can be encountered in extremely broken terrain.

Referring now again to FIGURE 5A, these problems are not encountered or are much reduced in the articulated crawler track loader 10 of the present invention. In the loading position the rear section 12 of the vehicle body may rise as in the other cases, however, the rear track assemblies 28" maintain contact with the ground. At the same time the front track assemblies 28' need not lift at all but remain flat against the ground or, in the case of irregularities maintain an optimum adjustment thereto. Thus traction reduction is relatively very small and there is very little concentrated loading on any localized region of the track.

Referring now to FIGURE 6A, the articulated crawler tractor loader 10 exhibits highly advantageous characteristics in still other operational situations. In descending a steep slope 83 with the bucket 15 loaded and in the carry position, a much more favorable distribution of ground engagement pressure, indicated by arrows 84, is present. As indicated graphically in FIGURE 6A the track loading between the front and rear portions of both sets of track assemblies 28 varies only slightly along the zone of ground contact.

In a similar situation involving the conventional two track crawler loader 76 as shown in FIGURE 6B, the load is concentrated on the forward portion of the tracks 77 as indicated by arrows 84 and diminishes very rapidly towards the rear of the tracks. In an articulated wheel tractor loader 78 as shown in FIGURE 6C, a relatively extreme concentration of loading occurs under each wheel as indicated by arrows 84" with the maximized loading being directly beneath the forward wheels 81. These unfavorable pressure distributions reduce traction and concentrate stress in both cases. As the principal load is carried forwardly from the vehicle, there is a pronounced risk that the loader will suddenly tip forward in this situation. In the case of the wheel loader, deflections and bounce in the front wheels 81 can cause detrimental shift- 8 ing of the center of gravity which may also create instability with respect to forward tipping and with respect to side swaying as well.

Referring now to FIGURE 7A the superior riding characteristics of the present invention are particularly evident when the loader 10 embodying the invention must override a sharp irregularity in the ground surface such as a boulder 86 which is smaller than the length of the track assembly 28. As shown in FIGURE 7B a conventional crawler tractor loader 76 in a similar situation must suddenly rock forward with a violent motion at somepoint in passing over the obstacle 86 inasmuch as the tracks must first tilt upward as indicated at and subsequently tilt downward as indicated at 75'. Inasmuch as the tracks are rigidly coupled to the tractor body 76 the entire vehicle including the operator and the loader bucket 15 must undergo a similar pitching motion. In addition to the resulting jarring, operator discomfort, and concentrated stress at localized points in the vehicle, this sharp pitching tends to eject material from the bucket 15'. One practical consequence of these problems is that the operator will tend to reduce the vehicle speed under such conditions. Referring now to FIGURE 70, similar effects occur when an articulated Wheel loader 78 must override the sharp obstacle 86. The bucket 15" of such a loader must undergo an even sharper pitching motion as the front wheels 81 override the obstacle 86 and a somewhat similar motion occurs again as the rear wheels 87 pass over the obstacle. Under these conditions, rebound of the tire wheels 81 and 87 causes high amplitude loping which further contributes to spillage.

Referring now again to FIGURE 7A the articulated crawler loader 10 of the present invention overrides the obstacle 86 with a much smoother motion. The vertical movement of the bucket 15 which does occur is of smaller amplitude and is less sudden. Pitching movement of the operators station 17 is reduced even more. Although some lifting of the tractor body is necessary, the rocking motions of the track assemblies 28' and 28" which occur in the course of overriding the obstacle 86 are not transferred fully to the body of the vehicle inasmuch as each track assembly may rock independently of both the vehicle and all other track assemblies.

While the invention has unique advantages when embodied in a loader as described above, many of these desirable characteristics are retained where an essentially similar tractor construction is utilized for other purposes, particularly in the other instances where a working implement must be carried on the body of the tractor itself. In FIGURE 4, for example, an essentially similar tractor 10' is shown with a bulldozer blade 88 mounted at the forward end thereof. The improved riding characteristics, reduction of vertical and sideward motion, the more constant traction, and certain other of the advantages heretofore discussed are also present in this application of the invention and jointly contribute to realizing greater precision in the control of the blade 88 with high operating speeds.

Thus, it will be apparent that many modifications and variations are possible within the scope of the invention.

What is claimed is:

1. A powered articulated crawler vehicle comprising:

a forward body section having a front axle member at each side thereof,

a rearward body section disposed behind said forward section and having a rear axle member at each side,

a pivot joint disposed between said forward and rearward body sections and forming a coupling therebetween having a single vertically directed pivot axis,

four endless track assemblies, each being mounted at a separate on of said front and rear axle members, each of said track assemblies being oscillatable about the axis of the associated axle member independently of oscillation of any of the other track assemblies, each of said four track assemblies being substantially equidistantly spaced from said pivot joint between said forward and rearward body sections, and

means driving each of said four track assemblies.

2. The combination defined in claim 1 wherein:

each of said axle members is situated at the central region of the associated one of said track assemblies.

3. The combination defined in claim 1 wherein:

each of said axl members is situated substantially midway between the ends of the zone of contact of the associated track assembly and the ground.

4. The combination defined in claim 1 wherein said rear axle members and said rear track assemblies are movable in a vertical direction relative to said rearward body section.

5. The combination defined in claim 1 wherein:

said rear axle members are at opposite ends of a rigid rear axle structure which is disposed transversely with respect to said rearward body section and pivoted thereto for oscillation about an axis longitudinal to said rearward body section.

6. The combination defined in claim 1 further comprising:

an engine carried on one of said body sections, and

four rotary drive elements each being disposed coaxially with respect to a separate one of said axle members for transmitting rotary drive from said engine to the associated one of said track assemblies without interfering with said oscillation of said track assemblies.

7. The combination defined in claim 6 wherein each of said track assemblies is of the class having a drive sprocket engaging an endless track chain, further com prising:

a drive transmitting element at each of said track assemblies coupling said rotary element thereof to said drive sprocket thereof, said drive transmitting elements being of the class having substantially a one to one drive ratio.

8. The combination defined in claim 1 further comprising a material manipulating implement attached to said forward body section of said tractor vehicle.

9. The combination defined in claim 8 wherein said implement is of the class having a load carrying component normally situated at the front of said forward body section and further comprising:

support means rigidly secured to said forward body section and holding each of said front axle members in a fixed perpendicular relationship to a vertical longitudinally aligned plane through said forward body section.

10. The combination defined in claim 8 wherein said implement is a bulldozer blade.

11. The combination defined in claim 8 wherein said implement is an elevatable loader bucket.

12. A powered loader comprising:

forward and rearward body sections each having an axle at opposite sides thereof,

a pivot hitch coupling said forward and rearward body sections, said hitch providing for pivoting therebetween about a vertical axis and being inflexible with respect to pivoting about a horizontal axis,

steering means for selectively pivoting said forward and rearward body sections relative to each other,

at least one selectively elevatable arm having a rearward end pivoted to said forward body section,

a loader bucket carried at the forward end of said arm,

four endless track assemblies with a forward pair thereof being disposed at opposite sides of said forward body section and a rearward pair thereof being disposed at opposite sides of said rearward body section, each of said four track assemblies being coupled to one of said axles and being oscillatable relative to the associated body section about an axis transverse thereto, each of said track assemblies being oscillatable independently of oscillation of any of the other track assemblies, each of said four track assemblies being substantially equidistantly spaced from said pivot joint between said forward and rearward body sections, and

means for driving each of said four track assemblies.

13. A powered loader as defined in claim 12 further comprising:

a transverse axle beam carrying the rearward pair of said axles and coupling said rearward pair of track assemblies to said rearward body section, said axle beam being coupled to said rearward body section for oscillation about an axis longitudinal thereto, and

support means holding the forward pair of said axles in a fixed orientation relative to a longitudinal axis through said forward body section.

References Cited UNITED STATES PATENTS 2,393,324 1/1946 Joy 18022 X 2,598,863 6/1952 Tucker 180-50 3,253,671 5/1966 Fielding 180-51 1,321,774 11/1919 Schneider 180-954 X 2,219,533 10/1940 ROSS l-l4 2,519,974 8/1950 Mork -95 X 2,673,616 3/1954 Moores Isa-9.46 X 3,299,978 l/l967 Sponsler ISO-22 X 3,349,863 10/1967 Wagner 180-51 X RICHARD J. JOHNSON, Primary Examiner.

US. Cl. X.R.

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