Track system

Track system for a vehicle having a chassis and a drive shaft extending laterally outwardly from the chassis includes: An attachment assembly having a leading pivot and a trailing pivot. A multi-member frame assembly including: a leading frame member pivotably connected to the attachment assembly via the leading pivot for pivoting about a leading pivot axis; a trailing frame member pivotably connected to the attachment assembly via the trailing pivot for pivoting about a trailing pivot axis; a leading wheel-bearing frame member at least indirectly pivotably connected to the leading frame member; a trailing wheel-bearing frame member at least indirectly pivotably connected to the trailing frame member. A damper interconnecting the leading frame member and the trailing frame member. A leading idler wheel assembly; a trailing idler wheel assembly; support wheel assemblies; a gearbox; a sprocket wheel; and an endless track.

TECHNICAL FIELD

The present technology relates to track systems for vehicles.

BACKGROUND

Conventionally, such vehicles had have large wheels with tires on them to move the vehicle along the ground surface. Under certain conditions, such tires may have poor traction on some ground surfaces and, as these vehicles are generally heavy, the tires may compact the ground surface in an undesirable way owing to the weight of the vehicle. As an example, when the vehicle is an agricultural vehicle, the tires may compact the soil in such a way as to undesirably inhibit the growth of crops. In order to reduce the aforementioned drawbacks, to increase traction and to distribute the weight of the vehicle over a larger area on the ground surface, track systems were developed to be used in place of at least some of the wheels and tires on the vehicles.

The use of track systems in place of wheels and tires, however, does itself present some inconveniences. One of the drawbacks of conventional track systems is that they tend to decrease the ride comfort experienced by the operator of the vehicle because the air cushion provided by a tire (between each wheel and tire) is not present in such track systems. Thus, vehicles equipped with such track systems in place of wheels and tires are typically subjected to an increased amount of vibration and vertical displacement when driven on uneven surfaces (as compared with the same vehicle having a wheel and tire), because the lack of an air cushion means there is no damping that would otherwise be provided if there were. In addition to potential increased operator discomfort, these vibrations and vertical displacements can potentially lead to premature wear of the vehicle, its component parts, and/or its attached accessories and equipment. Under certain conditions and at certain speeds, vertical displacements and vibrations transferred to the chassis can be so significant that it may be required to slow down the vehicle.

United States Patent Application Publication No. 2015/0266524 A1, published Sep. 24, 2015, and entitled “Crawler Vehicle”, provides what is purported to be an improved track system in view of the vibrations which may occur with track systems described hereinabove. According to its abstract, the '524 US Publication describes a technology wherein: “A crawler vehicle has a body and at least one left and one right track roller unit. The track roller units are connected to the body via a machine axis. The track roller units comprise a first and a second guide roller as well as a first and a second supporting arm on which the guide rollers are mounted. The first and the second supporting arms of each roller unit are mounted to be pivotable independently of one another about the machine axis.”

While the technology described in the '524 US Publication may indeed ameliorate some of the drawbacks of conventional track systems, continued improvement in this area is desirable.

SUMMARY

It is therefore an object of the present technology to ameliorate the situation with respect to at least one of the inconveniences present in the prior art.

It is also an object of the present invention to provide an improved track system at least in some instances as compared with some of the prior art.

According to an aspect of the present technology, there is provided a track system for use with a vehicle having a chassis and a drive shaft extending laterally outwardly from the chassis for driving the track system. In the context of the present technology, the “drive shaft” of the vehicle should be understood to be the vehicle drivetrain component that ultimately transmits rotational forces generated by the engine to the ground engaging assembly of the vehicle (e.g. the vehicle vehicle's wheel assembly when such is mounted on the vehicle, or the vehicle's track system when such is mounted on the vehicle, etc.).

The track system includes an attachment assembly that is connectable to the chassis of the vehicle. The attachment assembly has a leading pivot and a trailing pivot extending laterally outwardly therefrom. In the context of the present technology, the “leading” components of the track system are those that are disposed toward the front end of the vehicle (when the track system is properly installed on the vehicle), and the “trailing” components are those that are disposed toward the rear end of the track vehicle (when the track system is properly installed on the vehicle).

The track system further includes a multi-member frame assembly disposed laterally outwardly from the attachment assembly. The multi-member frame assembly includes a leading frame member pivotably connected to the attachment assembly via the leading pivot for pivoting about a leading pivot axis and a trailing frame member pivotably connected to the attachment assembly via the trailing pivot for pivoting about a trailing pivot axis. The leading and trailing frame members are structural components of the track system capable of supporting a material portion of the weight of the vehicle. They may be termed “primary” frame members in embodiments where they generally define the overall structure of the track system, or in embodiments where they are the frame members of the track system that first receive the load of the vehicle.

The track system further includes a leading wheel-bearing frame member at least indirectly pivotably connected to the leading frame member and a trailing wheel-bearing frame member at least indirectly pivotably connected to the trailing frame member. In the context of the present technology, the qualification of a wheel-bearing member as “at least indirectly pivotably connected” includes a wheel-bearing member that is directly pivotably connected to a frame member as well as a wheel-bearing member that is pivotably connected a frame member through an intermediate structure or structures, be they intermediate frame members or otherwise.

The track system further includes a damper interconnecting the leading frame member and the trailing frame member; a leading idler wheel assembly rotatably connected to the leading wheel-bearing frame member; a trailing idler wheel assembly rotatably connected to the trailing wheel-bearing frame member; and a plurality of support wheel assemblies disposed intermediate the leading idler wheel assembly and the trailing idler wheel assembly.

The track system further includes a gearbox having an input shaft operatively connectable to the drive shaft of the vehicle and an output shaft; a sprocket wheel operatively connected to the output shaft of the gearbox; and an endless track extending around the sprocket wheel, the leading idler wheel assembly, the trailing idler wheel assembly, and the plurality of support wheel assemblies, and drivable by the sprocket wheel.

The track system of the present technology is directed towards improving the ride comfort experienced by the operator of the vehicle under certain conditions. For example, improvement to the ride comfort might be perceived by the operator when vertical displacements of the chassis of the vehicle due to the unevenness of the ground surface are reduced and/or when vibrations generated as the vehicle travels over the ground surface are damped before being transferred from the track assembly to the vehicle chassis.

The leading and trailing frame members of the track system of the present technology define a somewhat scissor-like structure, with each frame member pivots about its respective pivot, and the damper interconnected therebetween. Each one of the leading and trailing wheel-bearing members is in turn pivotably connected to the leading or trailing frame member, respectively. The pivoting of each of these structures, along with the damper, may assist in reducing the vertical displacements and vibrations transferred to the chassis under certain conditions.

In addition, having a track system with a scissor-like structure may have other advantages in different situations. For example, as the weight of the vehicle increases, e.g. during harvesting operations, the scissor-like structure can open and the ground-contacting portion of the endless track occurs over an increased surface area (i.e. the ground contacting area can increase in size as the load borne by the track system increases—at least for some increases in load—depending on the design of a specific track system). As a result, in some circumstances, the pressure applied to the ground by the endless track (owing to the weight of the vehicle) increases at a lower rate than the weight of the vehicle. In certain embodiments, this will allow a track system of the present technology to bear additional loads as compared with conventional track systems.

The track system of the present technology, under certain conditions, can provide improved capability when the vehicle to which it is installed is travelling over soft ground. In this respect, in conventional track systems, there is a tendency of the leading edge of the endless track to pitch negatively (also known sometimes as to “dive” in the art) into soft ground when high tractive forces are requested of the track system. Such negative pitching of the leading edge of the track system can lead to track system and/or vehicle damage under some conditions. In some embodiments, the geometrical configuration of the track system of the present technology is constructed with the aim of reducing this tendency under certain conditions.

Another potential drawback found in many conventional track systems is that the track system is attached in place of the wheel on the vehicle's wheel axle. As the weight of the vehicle is borne via the axle, the weight of the vehicle is transmitted to the sprocket wheel assembly of the track assembly as it is the sprocket wheel assembly that is attached to the axle. This necessitates particular track system design parameters that in some cases are suboptimal. It may also lead to undesirable bending forces in the output shaft as the output shaft is already transmitting rotational forces to the sprocket wheel assembly of the track system. This, in turn, may lead to accelerated wear of the gearbox and of the components thereof, and to higher maintenance cost.

The track system of the present technology may reduce such issues under certain conditions as a large part of the weight of the vehicle is transferred from the chassis to track system's attachment assembly, then to the leading and trailing frame members, then to the leading and trailing wheel-bearing members and finally to the idler and support wheels and to the endless track. Thus, the sprocket wheel assembly need not (and in most embodiments, does not) bear a material amount of the vehicle weight, and does not need to be designed to do so (in most embodiments).

Having each of the leading and trailing frame members pivoting about their own pivot (as opposed to about the same pivot), may, depending on the embodiment, provide certain advantages. For example, in some embodiments, the leading and trailing pivots each bear a portion of the load borne by the track system, as opposed to a single pivot having to bear the entirety of the load borne by the system. This splitting of the load may allow for pivots that are less robust (and therefore less expensive and simpler to manufacture) than would be the case if both frame members had to be borne by a single pivot. Additionally, as in many embodiments efficient mechanical packaging is important, the dual pivot design may allow for more efficient packaging than the single pivot design, as a certain minimum contact area between the pivot and the knuckle of the frame member is required, and in many cases a dual pivot design can have more available contact area for a given width of the track system than can a single pivot design. Further, given that this is the case, the pressure between the pivot and the knuckle, in many cases, can be lower in a dual pivot design than in a single pivot design, thus again allowing for the uses of less robust components.

In some embodiments of the track system of the present technology, at least one of the leading frame member and the trailing frame member has an aperture therein. At least one of the gearbox input shaft and the drive shaft of the vehicle (e.g. the vehicle wheel axle) extends through the aperture. The aperture is shaped and dimensioned so as to allow pivotal motion of the at least one of the leading frame member and the trailing frame member notwithstanding a presence of the at least one of the gearbox input shaft and the drive shaft of the vehicle extending through the aperture. This feature assists in allowing embodiments of track systems of the present technology to be efficiently mechanically packaged, reducing the volume and/or mass of the track system, in embodiments where such is judged to be important.

In some embodiments, the leading frame member has a first aperture therein, the trailing frame member has a second aperture therein, at least one of the gearbox input shaft and the drive shaft of the vehicle extends through one of the first aperture and the second aperture, the one of the first aperture and the second aperture being shaped and dimensioned so as to allow pivotal motion of the one of the leading frame member and trailing frame member notwithstanding a presence of the at least one of the gearbox input shaft and the drive shaft of the vehicle extending therethrough. A stop extends within the other of the first aperture and the second aperture, the stop being structured and dimensioned to limit pivotal movement of the other of the leading frame member and trailing frame member. This feature may also assist in allowing embodiments of track systems of the present technology to be efficiently mechanically packaged, in embodiments where such is judged to be important.

In some embodiments, the leading pivot axis is disposed above the trailing pivot axis. In some embodiments, this feature reduces the variations in the effective perimeter of the track (which occur owing to changes in position of the idler wheel(s) and/support wheels), thus reducing the required operating range of the track tensioner.

In some embodiments, the leading wheel-bearing frame member is directly pivotably connected to the leading frame member about a first axis. The trailing wheel-bearing frame member is directly pivotably connected to the trailing frame member about a second axis. The first and second axes, the leading pivot axis and the trailing pivot axis extend perpendicularly to a plane extending parallel to a longitudinal direction of the track system, and in a rest position of the track system, the second axis is above the first axis. The rest position is defined as when the track system is attached to the vehicle, the vehicle is in its operating condition, is at rest, is unloaded, and is disposed on flat level ground.

In some embodiments, the endless track has leading, trailing and ground engaging edges. A first angle is formed between the trailing and ground engaging edges, and a second angle is formed between the leading and ground engaging edges. The first angle has a bisector, and the bisector of the first angle passes below the trailing pivot axis. In some embodiments of track systems of the present technology, this feature may assist in causing in some embodiments of track systems of the present technology a torque to be generated that reduces the tendency of the track system to have a negative pitch.

In some embodiments, the leading wheel-bearing frame member is directly pivotably connected to the leading frame member about a first axis. The trailing wheel-bearing frame member is directly pivotably connected to the trailing frame member about a second axis. Idler wheels of the leading idler wheel assembly rotate about a third axis. Idler wheels of the trailing idler wheel assembly rotate about a fourth axis. The first, second, third and fourth axes, the leading pivot axis and the trailing pivot axis extend perpendicularly to a plane extending parallel to a longitudinal direction of the track system, and the second and fourth axes intersect the bisector of the first angle.

In some embodiments, the second angle has a bisector, and the bisector of the second angle passes below the leading pivot axis. In some embodiments of track systems of the present technology, this feature may also assist in causing in some embodiments of track systems of the present technology a torque to be generated that reduces the tendency of the track system to have a negative pitch.

In some embodiments, the first and third axes intersect the bisector of the second angle.

In some embodiments, a shortest distance defined in the plane between the bisector of the first angle and the trailing pivot axis is greater than a shortest distance defined in the plane between the bisector of the second angle and the leading pivot axis.

In some embodiments, the leading wheel-bearing frame member is directly pivotably connected to the leading frame member about a first axis, the trailing wheel-bearing frame member is directly pivotably connected to the trailing frame member about a second axis, and in a rest position of the track system, the second axis is above the first axis.

In some embodiments, idler wheels of the leading idler wheel assembly rotate about a third axis and idler wheels of the trailing idler wheel assembly rotate about a fourth axis. The first, second, third and fourth axes, the leading pivot axis and the trailing pivot axis extend perpendicularly to a plane extending parallel to a longitudinal direction of the track system. A first line defined in the plane and extending between the first and third axes passes below the leading pivot axis. A second line defined in the plane and extending between the second and fourth axes passes below the trailing pivot axis.

In some embodiments, a first longitudinal distance defined in the plane between the leading pivot axis and the first axis is greater than a second longitudinal distance defined in the plane between the trailing pivot axis and the second axis.

In some embodiments, a shortest distance defined in the plane between the second line and the trailing pivot axis is greater than a shortest distance defined in the plane between the first line and the leading pivot axis.

In some embodiments, a load supported by the trailing wheel-bearing frame member is greater than a load supported by the leading wheel-bearing frame member.

In some embodiments, a trailing support wheel assembly is pivotably connected to the trailing wheel-bearing frame member about a fifth axis, and a third longitudinal distance defined in the plane between the second axis and the fourth axis is greater than a fourth longitudinal distance defined in the plane between the second axis and the fifth axis.

In some embodiments, leading support wheels are rotatably connected to the leading wheel-bearing frame member about a sixth axis, and the fourth longitudinal distance is greater than a fifth longitudinal distance defined in the plane between the first axis and the sixth axis.

In some embodiments, a trailing support wheel assembly is pivotably connected to the trailing wheel-bearing frame member, the trailing support wheel assembly including a support wheel frame member, a pair of forward support wheels rotatably connected to the support wheel frame member, and a pair of rearward support wheels rotatably connected to the support wheel frame member.

In some embodiments, the leading idler wheel assembly and the trailing idler heel assembly each include idler wheels of a same diameter.

In some embodiments, the attachment assembly includes a plate having leading pivot receiving hole shaped and dimensioned to receive the leading pivot and a trailing pivot receiving hole shaped and dimensioned to receive the trailing pivot, and the leading pivot extends through the leading pivot receiving hole and the trailing pivot extends through the trailing pivot receiving hole. This feature assists in allowing some embodiments of track systems of the present technology to be easier to manufacture, more solid, and precisely machined (as opposed to when the pivots and the plate are a single unitary article; e.g. a single cast article).

In some embodiments, the plate has a shoulder recess defined around each of the leading pivot receiving hole and the trailing pivot receiving hole. The leading pivot has a shoulder portion shaped and dimensioned to abut the shoulder recess of the leading pivot receiving hole of the plate, and the trailing pivot has a shoulder portion shaped and dimensioned to abut the shoulder recess of the trailing pivot receiving hole of the plate. This feature assists in allowing some embodiments of track systems of the present technology to be able to better distribute the load on the plate.

In some embodiments, the track system further includes fasteners extending axially through the leading pivot and the trailing pivot to fasten the gearbox. This feature may also assist in allowing embodiments of track systems of the present technology to be efficiently mechanically packaged, in embodiments where such is judged to be important.

In some embodiments, the drive shaft is connected to the input shaft of the gearbox via a constant velocity joint. This feature assists in allowing some embodiments of track systems of the present technology to interconnect the vehicle's drive shaft and the gearbox's input shaft when the two are at an angle to one another.

In some embodiments, the damper is disposed laterally inwardly from the gearbox. This feature may also assist in allowing embodiments of track systems of the present technology to be efficiently mechanically packaged, in embodiments where such is judged to be important.

In some embodiments, the track system further comprises a bracket connecting the gearbox to the attachment assembly, the bracket extending above and around the damper. The bracket may assist in protecting the damper from environmental debris entering the track system.

In some embodiments, the stop is connected to the gearbox. This feature may also assist in allowing embodiments of track systems of the present technology to be efficiently mechanically packaged, in embodiments where such is judged to be important.

In some embodiments, the track has a ground-contacting area that increases in size as a load borne by the track system increases.

DETAILED DESCRIPTION

Introduction

The track system40is for use with a vehicle60having a chassis62and a drive shaft64extending laterally outwardly from the chassis62for driving the track system40. The chassis62supports the components of the vehicle60, such as the cabin70, the engine, the gearbox72and other drivetrain components (not shown). In this embodiment, the drive shaft64is the drivetrain component that transmits the driving force from the engine and gearbox72of the vehicle60to the track system40, i.e. the drive shaft64is the output shaft of the gearbox72.

In the context of the following description, “outwardly” or “outward” means away from a longitudinal centerline66of the chassis62of the vehicle60, and “inwardly” or “inward” means toward the longitudinal centerline66. In addition, in the context of the following description, “longitudinally” means in a direction parallel to the longitudinal centerline66of the chassis62of the vehicle60, and “transversally” means in a direction perpendicular to the longitudinal centerline66. Note that in all the Figures, a “+” symbol is used to indicate an axis of rotation. In the context of the present technology, the term “axis” may be used to indicate an axis of rotation, or the term may refer to a “pivot joint” that includes all the necessary structure (bearing structures, pins, axles and other components) to permit a structure to pivot about such axis, as the case may be. Moreover, the direction of forward travel of the track system40is indicated by an arrow80(FIG. 3A). In the present description, the “leading” components are identified with an “a” added to their reference numeral and the “trailing” components are identified with a “b” or a “c” added to their reference numeral. In addition, some components that are disposed proximate to the longitudinal centerline66of the vehicle60have a reference numeral with a “1” in index, and some components that are disposed away from the longitudinal centerline66of the vehicle60have a reference numeral with a “2” in index. In the following description and accompanyingFIGS. 1 and 3A to 18C, the track system40is configured to be attached to a right side of the chassis62of the vehicle60. A track system being another embodiment of the present technology, configured to be connected to a left side of the chassis62of the vehicle60, is a mirror image of the track system40with the necessary adaptations, as seen in2B to2D; that embodiment will not be further described herein.

General Description of the Track System

Referring toFIGS. 1 to 5, the track system40will be generally described. The track system40includes an attachment assembly100connectable to the chassis62of the vehicle60. The attachment assembly100includes a plate102, leading and trailing pivots130a,130b(FIGS. 3B and 4) extending laterally outwardly from the attachment assembly100through the plate102.

The track system40further includes a multi-member frame assembly160disposed laterally outwardly from the attachment assembly100(FIG. 5). The multi-member frame assembly160includes a leading frame member170apivotably connected to the attachment assembly100via the leading pivot130afor pivoting about a leading pivot axis180a(FIG. 3B). The multi-member frame assembly160also includes a trailing frame member170bpivotably connected to the attachment assembly100via the trailing pivot130bfor pivoting about a trailing pivot axis180b(FIG. 3B). The multi-member frame assembly160also includes a leading wheel-bearing frame member200apivotably connected to the leading frame member170a, and a trailing wheel-bearing frame member200bpivotably connected to the trailing frame member170b. A trailing support wheel assembly210is pivotably connected to the trailing wheel-bearing frame member200b. The track system40further includes a damper230(in this embodiment a shock absorber) interconnecting the leading frame member170aand the trailing frame member170b. A leading idler wheel assembly260ais rotatably connected to the leading wheel-bearing frame member200aand a trailing idler wheel assembly260bis rotatably connected to the trailing wheel-bearing frame member200b. A plurality of support wheel assemblies290a,290b,290care disposed intermediate the leading idler wheel assembly260aand the trailing idler wheel assembly260b. The support wheel assembly290ais rotatably connected to the leading wheel-bearing frame member200a. The support wheel assemblies290b,290care rotatably connected to the trailing support wheel assembly210.

Still referring toFIGS. 1 to 5, the track system40further includes a gearbox320having an input shaft322operatively connectable to the drive shaft64of the vehicle60. InFIGS. 2B to 2D, the connection of the input shaft322to the drive shaft64is shown. The gearbox320also includes an output shaft324. The track system40further includes a sprocket wheel350operatively connected to the output shaft324, and an endless track380extending around the sprocket wheel350, the leading idler wheel assembly260a, the trailing idler wheel assembly260b, and the plurality of support wheel assemblies290a,290b,290c. The endless track380is drivable by the sprocket wheel350.

Endless Track

Referring toFIGS. 3A to 4, the endless track380is an endless polymeric track380. The endless track380has an inner surface382engaging the leading idler wheel assembly260a, the trailing idler wheel assembly260b, the plurality of support wheel assemblies290a,290b,290cand the sprocket wheel350. The inner surface382has lugs384disposed on a central portion of the inner surface382. The endless track380also has an outer surface386with a tread388configured for ground engagement. The tread388can be varied according to the type of vehicle on which the track system40is to be used with and/or the type of ground surface on which the vehicle will be driven. It is contemplated that within the scope of the present technology, the endless track380may be constructed of a wide variety of materials and structures including metallic components known in track systems. The specific properties and materials of the endless track380are not central to the present technology and will not be described in detail.

Referring toFIGS. 16 and 18A, the endless track380has a leading edge390, a ground engaging edge392and a trailing edge394. The “edges” of the endless track380are the segments of the endless track380.

Attachment Assembly

Referring toFIGS. 4 to 10, the attachment assembly100will be described. The plate102has an inward face104and outward face106(FIGS. 9A and 9B). A bolt pattern108is defined on the inward face104of the plate102. The holes110of the bolt pattern108are threaded bore holes, but could be through holes in other embodiments. The bolt pattern108that is illustrated is exemplary only and can be varied according to the type of vehicle60with which the track system40is to be used. A compatible bolt pattern74is defined on the chassis62of the vehicle60(FIGS. 2C and 2D). The attachment assembly100is connected to the chassis62of the vehicle60through fasteners112extending from the chassis62and engaging the thread of the holes110. As a result, when the track system40is attached to the chassis62, the weight of the vehicle60is supported by the clamping load provided by the fasteners112extending between the chassis62and the attachment assembly100of the track system40. Under certain conditions, the configuration of the attachment assembly100and of the rest of the track system40is such that the chassis62of the vehicle60has the same ground clearance as when the vehicle60is equipped with wheels and tires in place of the track system40. Accordingly, under certain conditions, the overall height of the vehicle60from ground surface is the same when the track system40is used in place of wheels and tires.

Plate of the Attachment Assembly

Referring toFIGS. 9A and 9B, the plate102has leading and trailing pivot receiving holes120a,120btherein. The leading and trailing pivot receiving holes120a,120bare shaped and dimensioned to receive the leading and trailing pivots130a,130b. The pivot receiving holes120a,120bextend between the inward and outward faces104,106of the plate102. The plate102has a reinforced portion122in a region adjacent to the pivot receiving holes120a,120bto reduce bending of the pivots130a,130b. In the present embodiment, the reinforced portion122has a thickness that is greater than that of the remainder of the plate102. In other embodiments, the reinforced portion122could be otherwise configured or omitted.

The leading and trailing pivots130a,130bextend through the corresponding leading and trailing pivot receiving holes120a,120b. The pivots130a,130bextend horizontally and perpendicular to the attachment plate102. The plate102has shoulder recesses124a,124bdefined on the inward face104around each one of the leading and trailing pivot receiving holes120a,120b. The plate102also has countersinks126a,126bdefined on the inward face104around each one of the leading and trailing pivot receiving holes120a,120b. The leading and trailing pivots130a,130beach have a shoulder portion132(FIGS. 12A and 12B) at their respective inward end134, opposite to their outward end136. Each shoulder portion132is shaped and dimensioned to abut in the corresponding shoulder recess124a,124bwhen the leading and trailing pivots130a,130bare inserted in the leading and trailing pivot receiving holes120a,120b(FIG. 12B). A fillet133is provided between the shoulder portion132and the inward end134of each pivot130a,130b. The radius of the fillet133can be selected to reduce stress concentrations in regions adjacent to the inward end134.

Loads on the chassis62of the vehicle (including the vehicle's weight) are transferred to the plate102when the plate102is connected to the chassis62with the fasteners112. They are then transferred to the leading and trailing pivots130a,130band then to the leading and trailing frame members170a,170b, and so on. Other configurations of the plate102and pivots members130a,130bare contemplated, in other embodiments. In some embodiments, the pivots130a,130bcould further include a countersunk portion at their inward end134. The countersunk portion could be shaped and dimensioned to abut a corresponding one of the countersinks126a,126b. In some embodiments, the pivots130a,130bcould be integrally formed with the plate102.

Referring toFIGS. 4, 7 and 12B, fasteners138a,138bextend axially through the leading and trailing pivots130a,130bto be fastened to a housing326of the gearbox320. The fasteners138a,138bengaged with threaded connection holes328a,328bdefined in the housing326of the gearbox320(FIGS. 12B and 15A—the figures are schematic and as such do not show the threads of the fasteners138a,138bnor those of the threaded connection holes328a,328b). As a result, the housing326is fastened to the attachment assembly100via the fasteners138a,138b. The fasteners138a,138balso hold in place the leading and trailing pivots130a,130bwith respect to the plate102when the shoulder portions132of the pivots130a,130babut the recessed shoulder portions124a,124b(FIG. 9B) of the plate102. The fasteners138a,138bextend coaxially with the leading and trailing pivot axes180a,180b. The housing326is also connected to the attachment assembly100via a bracket150connected to the plate102, as best seen inFIGS. 5, 6 and 10. The bracket150extends above and around the damper230. The damper230is disposed laterally inwardly from the housing326of the gearbox320. In some embodiments, the bracket150offers some protection to the damper230from debris or projections that could impact the damper230during operation of the vehicle60equipped with the track system40. Other configurations of the bracket150are contemplated. For instance, in other embodiments, the bracket150could be integrally formed with the plate102or omitted.

Pivot Axes and Stop

Referring back toFIGS. 4 to 10, the leading pivot axis180ais disposed above the trailing pivot axis180b, as best seen inFIGS. 8 to 10. Such configuration has been found to assist in reducing vibrations in the track system40and to assist in reducing the variations in the perimeter of the endless track380. Other configurations, however, are contemplated. In other embodiments, the leading and trailing pivot axes180a,180bcould be at a same height with respect to the ground surface. In yet other embodiments, the leading and trailing pivot axes180a,180bcould be disposed one above the other. In some embodiments, the positioning of the leading and trailing pivot axes180a,180bis determined by the bolt pattern108since the positioning of the leading and trailing pivot130a,130band of the reinforced portion122adjacent thereto should not interfere with the bolt pattern108.

A stop152is integrally formed in the plate102of the attachment assembly100(FIG. 9A). The stop152extends laterally outwardly from the outward face106of the plate102. The stop152extends through an aperture172bdefined in the trailing frame member170b. The stop152is structured and dimensioned to limit the pivotal movement of the trailing frame member170babout the trailing pivot axis180b. The aperture172bis arcuate, but it could be otherwise. In some embodiments, the center of the arc of the aperture172bcoincides with the trailing pivot axis180b. When the trailing frame member170bpivots about the trailing pivot axis180b, upper and lower walls173b,175b(FIGS. 7 and 16) of the aperture172bcan abut the stop152and thus limit the pivotal movement of the trailing frame member170b. The stop152and/or the aperture172bcould be otherwise configured in other embodiments and limit the pivotal movement of the trailing frame member170bto a lesser or greater extent than the one illustrated. The stop152is further connected to the housing326using fasteners340(FIGS. 4 and 6). In some embodiments, the stop152is only connected to the attachment assembly100. In some embodiments, the stop152is a separate component from the plate102and is connected thereto using fasteners and/or bonding techniques. In some embodiments, the stop152has a coating made of a compliant material such as rubber or an elastomer, or has rubber parts attached thereto. In some embodiments, the stop152deflects along its length when contacted by the trailing frame member170b. In some embodiments, the trailing frame member170bdoes not have an aperture172bdefined therein and one or more stops extending from the outward face106of the plate102could engage the trailing frame member170bon a top or bottom sidewall thereof. In some embodiments, the stop152could be omitted.

Leading and Trailing Frame Members

Referring toFIGS. 11, 12A, 12B, 16 and 17, the leading and trailing frame members170a,170bwill be described. The leading and trailing frame members170a,170bare pivotably connected to the attachment assembly100as they are supported by the leading and trailing pivots130a,130b. The leading and trailing frame members170a,170bare disposed laterally outwardly from the attachment assembly100(FIG. 5). In order to facilitate the pivoting of the leading and trailing frame members170a,170bon the leading and trailing pivots130a,130b, in this embodiment, spherical bearings are disposed between each pivot member130a,130band each frame member170a,170b. For illustrative purposes, the configuration of the pivot, frame member and spherical bearings will be described with reference to the trailing frame member170b, as, in this embodiment, the leading frame member170ahas a similar configuration.

Referring toFIGS. 12A and 12B, spherical bearings174b1,174b2are disposed between the trailing frame member170band the trailing pivot130b. The spherical bearings174b1,174b2are spaced apart along the length of the pivot130b, one proximate the inward end134and the other proximate the outward end136thereof. In some embodiments, the spherical bearings174b1,174b2could be replaced by bushings, plain bearings or tapper rollers disposed between the pivot130band the trailing frame member170b.

Referring toFIGS. 9A and 12B, a seal176bis disposed between the trailing frame member170band the attachment assembly100, proximate the inward end134of the pivot130b. Grooves177b1,177b2are defined in the plate102and in the inward face of the trailing frame member170bto receive a portion of the seal176b. A similar configuration is found on the leading frame member170aproximate the leading pivot130a. A seal178bis disposed between the leading and trailing frame members170a,170band the housing326proximate to the outward end136of the pivots130a,130b. Grooves179b1,179b2(FIGS. 12B and 15A) are defined in the outward face of the trailing frame member170band the inward face of the housing326to receive a portion of the seal178b. A similar configuration is found on the leading frame member170aproximate the leading pivot130a. The leading and trailing frame members170a,170bdo not contact the plate102nor the housing326as there is a gap181b1between the bearing174b1and the plate102. Another gap181b2exists between the bearing174b2and the housing326. In some embodiments, the gap181b1is smaller than the gap181b2. In some embodiments, the leading and trailing frame members170a,170bare movable axially on the pivots130a,130brespectively.

Referring toFIGS. 10 to 17, the leading frame member170ahas an aperture172adefined therein. The input shaft322of the gearbox320extends laterally inwardly through the aperture172a(FIG. 2D) for operative connection to the drive shaft64of the vehicle60. In some embodiments, the input shaft322extends completely through the aperture172afor operative connection to the drive shaft64. The input shaft322and the drive shaft64are operatively connected through a constant velocity joint342(FIGS. 2B to 2D). The input shaft322and the drive shaft64could be operatively connected otherwise. For example, in some embodiments, the input shaft322and the drive shaft64could be coaxial and operatively connected together using a splined sleeve or a coupling. The aperture172ais shaped and dimensioned so as to allow pivotal motion of the leading frame member170anotwithstanding the presence of the input shaft322and/or the drive shaft64extending through the aperture172a. In other words, the aperture172ais shaped and dimensioned such that the input shaft322and/or the drive shaft64extending through the aperture172aare prevented from contacting the upper and lower walls173a,175aof the aperture172a(FIGS. 10 and 16) when the leading frame member170apivots. The aperture172ais arcuate in this embodiment, but the aperture172acould be otherwise in other embodiments. In some embodiments, the center of the arc of the aperture172acoincides with the leading pivot axis180a. In some embodiments, the aperture172aextends until one of the upper and lower sidewalls of the frame member170aand forms a slot in the frame member170a.

In some embodiments, the gearbox320could be configured such that the input shaft322extends through the aperture172bdefined in the trailing frame member170band the attachment assembly100could be configured such that the stop152extends through the aperture172adefined in the leading frame member170a.

It is noted that in embodiments of the present technology, the drive shaft64of the vehicle60does not bear a material portion of the weight of the vehicle60but only transmits rotational forces to the gearbox320via the operative connection with the input shaft322. The output shaft324of the gearbox320does not bear a material portion of the weight of the vehicle60either. The output shaft324is subjected to bending forces due to the tension present in the endless track320and to rotational forces transmitted by the input shaft322.

Damper

Referring toFIGS. 16 and 17, the leading and trailing frame members170a,170beach have upper and lower portions182a,182b,184a,184b. The upper portions182a,184aextend above the corresponding pivot axes180a,180band the lower portions extend below the pivot axes180a,180b. The damper230is rotatably connected to the upper portions182a,182bof the leading and trailing frame members170a,170b. The damper230includes a hydro-pneumatic cylinder232and a coil spring234. The damper230biases the upper portions182a,182bof the leading and trailing frame members170a,170baway from each other. When the track system40supports the weight of the vehicle60, the coil spring234is deformed (i.e. compressed) and the cylinder232provides for a damped pivotal motion of the leading and trailing frame members170a,170bwith respect to each other.

The positioning of the damper230between the upper portions182a,182bof the leading and trailing frame members170a,170ballows for a long stroke of the cylinder232of the damper230. As a result, the damping action of the damper230is generally more refined than in conventional track systems where the stroke of a damping cylinder is shorter. A spring rate of the coil spring234is also decreased compared to conventional track systems where the stroke of the damper is shorter. Such configuration provides for a smoother damping action of the damper230and may reduce the risks of fully compressing the damper230. Under certain conditions, vibrations that are due to the surface of the ground on which the track system40travels and transferred to the leading and trailing frame members170a,170bare dampened by the damper230.

As described above, the stop152limits the pivotal motion of the trailing frame member170b, and the pivotal motion of the leading frame member170ais limited by the stroke of the cylinder232.

In some embodiments, the damper230has variable damping characteristics as described in commonly owned International Patent Application No. PCT/CA2016/050418, filed Apr. 11, 2016, entitled “Progressive Damping System for a Track System” and published as WO 2016/161527. (This application is incorporated herein by reference in its entirety.)

Gearbox and Sprocket Wheel

Referring toFIGS. 2, 4, 11, 12 and 15A to 15C, the gearbox320and the sprocket wheel350will be described. The gearbox320is disposed outwardly from the leading and trailing frame members170a,170b. The gearbox320is disposed inwardly from the sprocket wheel350. Teeth352of the sprocket wheel350pass around the gearbox320when the sprocket wheel350is rotated. The input shaft322is connected to an input gear330located inside the housing326of the gearbox320. The input shaft322and the input gear330rotate about an axis334. The input gear330drives an output gear332connected to the output shaft324. The output gear332is also located inside the housing326of the gearbox320. The output shaft324and the output gear332rotate about an axis336. The axes334,336are parallel and offset, but could be coaxial in other embodiments. The engagement of the input gear330and the output gear332is direct, but a chain or belt could be used in other embodiments to transmit rotational movement from the input gear330to the output gear332.

The output shaft324is connected to the output gear332and extends laterally outwardly from the housing326. The output shaft324has a flanged portion325. (FIG. 15C). The sprocket wheel350is connected to the flanged portion325of the output shaft324using fasteners354(FIG. 4). The teeth352of the sprocket wheel350engage the lugs384defined on the inner surface382of the endless track380and drive the endless track380. As such, the track system40is a “positive drive” track system.

Leading and Trailing Wheel-Bearing Frame Members and Idler Wheels

Referring toFIGS. 1 to 4 and 16 and 17, in this embodiment the leading wheel-bearing frame member200ais directly pivotably connected to the lower portion184aof the leading frame members170aabout an axis202a. In this embodiment, the trailing wheel-bearing frame member200bis directly pivotably connected to the lower portion184bof the trailing frame members170babout an axis202b(FIG. 17).

InFIGS. 16 to 18A, the track system40is shown in a rest position. In this embodiment, the nominal load of the track system corresponds to the track system being attached to the vehicle with the track system bearing its ordinary portion of the weight of the vehicle60when the vehicle60is at its tare weight, with no attachments at the front or rear and no payload in its container or tank. As shown inFIGS. 2 and 17, the axis202bis above the axis202a. Having the axis202babove the axis202ahas been found to reduce the variations of the perimeter of the endless track380under certain conditions.

Referring toFIGS. 1 to 4, 10, 16 and 17, idler wheels262a1,262a2of the leading idler wheel assembly260arotate about an axis264adefined by an axle assembly266arotatably connecting the leading idler wheel assembly260ato the leading wheel-bearing frame member200a. Idler wheels262b1,262b2of the trailing idler wheel assembly260brotate about an axis264bdefined by an axle assembly266brotatably connecting the trailing idler wheel assembly260bto the trailing wheel-bearing frame member200b. The idler wheels262a1,262b1are disposed inwardly of the lugs384of the endless track380, and the idler wheels262a2,262b2are disposed outwardly of the lugs384of the endless track380. The endless track380is guided between the inwardly disposed idler wheels262a1,262b1and the outwardly disposed idler wheels262a2,262b2along the ground engaging edge392of the endless track380(FIG. 16). The idler wheels262a1,262a2,262b1,262b2have a same diameter, but in other embodiments the diameter of the leading and idler wheels262a1,262a2,262b1,262b2could differ.

Referring toFIGS. 8, 10 and 14, the leading wheel-bearing frame member200aincludes a tensioner410having first and second ends412,414. The first end412is rotatably connected to the leading wheel-bearing frame member200aat a proximal tensioning pivot416. The proximal tensioning pivot416includes a spherical joint (not shown). A wheel linkage418is rotatably connected to the leading wheel-bearing frame member200aat an axis420that is offset from the axis264a. The second end414of the tensioner410is rotatably connected to the wheel linkage418at a distal tensioning pivot422which is offset from the axis264a. In some embodiments, the distal tensioning pivot422includes a spherical joint and the proximal tensioning pivot416does not. In some embodiments, both the proximal and distal tensioning pivots416,422include a spherical joint. The leading axle assembly266ais operatively connected to the wheel linkage418. The distal tensioning pivot422and the axis420are angularly displaced around the axis264asuch that the wheel linkage418forms a lever with the axis420being the fulcrum thereof. In some embodiments, the tensioner410could be included on the trailing wheel-bearing frame member200b.

The action of the tensioner410and the wheel linkage418bias the leading axle assembly266aand the leading idler wheel assembly260atoward the forward end of the track system40with a biasing force501(FIGS. 16 and 18A). The endless track380opposes the biasing force501provided by the action of the tensioner410and the wheel linkage418and tension502,504(FIGS. 16 and 18A) appears in the leading edge390and the ground-engaging edge392of the endless track380.

In some embodiments, the tensioner410is used to reduce the variations in the perimeter of the endless track380due to the pivoting of the leading and trailing frame members170a,170band wheel-bearing frame members200a,200b.

In addition, under certain conditions, if debris becomes stuck between one of the wheels and the endless track380, the tensioner410is configured to apply less biasing force501and/or contract so as to reduce variation in the perimeter of the endless track380. When debris are ejected from the track system40, the tensioner410is configured to apply more biasing force501and/or extend to provide for adequate tension forces502,504in the endless track380.

In some embodiments, the tensioner410is a dynamic tensioning device as described in International Patent Application No. PCT/CA2016/050419, filed Apr. 11, 2016, entitled “Dynamic Tensioner Locking Device for a Track System and Method Thereof”, and published as WO 2016/161528. The content of this application is incorporated herein by reference in its entirety.

Tracking Adjustment

Referring toFIGS. 8, 14 and 17, the leading wheel-bearing frame member200aalso includes a tracking adjustment system430. The tracking adjustment system430includes a support432that is pivotable with respect to the leading wheel-bearing frame member200aabout an axis434. The axle assembly266ais rotatably connected to the support432. Adjustment screws4361,4362(FIGS. 8 and 17) are connected to the leading wheel-bearing frame member200a, rearwardly offset of the axis434. A portion (not shown) of the support432extends rearward of the axis434. Each one of the adjustment screws4361,4362abuts the portion of the support432and each one of the adjustment screws4361,4362can be adjusted to pivot the support432inwardly or outwardly. As a result, the leading idler wheel assembly260acan provide for tracking adjustment of the endless track380as it is driven around the sprocket wheel350, the leading idler wheel assembly260a, the trailing idler wheel assembly260b, and the plurality of support wheel assemblies290a,290b,290c.

Support Wheels

Referring toFIGS. 8, 14, 16 and 17, the support wheel assembly290aincludes support wheels292a1,292a2that are rotatably connected to the leading wheel-bearing frame member200avia an axle assembly294a. The support wheels292a1,292a2rotate about an axis296a. The support wheel assemblies290b,290cinclude support wheels292b1,292b2,292c1,292c2that are rotatably connected to the trailing support wheel assembly210via axle assemblies294b,294c. The support wheels292b1,292b2rotate about an axis296band the support wheels292c1,292c2rotate about an axis296c.

The trailing support wheel assembly210includes a support wheel frame member212(FIG. 17). The support wheel member212has a body that is longitudinally elongated. The support wheel member212extends above the lugs384of the ground-engaging edge392of the endless track380. The support wheel frame member212pivots about an axis216with respect to the trailing wheel-bearing frame member200b. As such, the support wheel assemblies290b,290care indirectly pivotably connected to the trailing wheel-bearing frame member200b. The support wheel assembly290bis disposed forward of the axis216, and the support wheel assembly290cis disposed rearward of the axis216.

The endless track380is guided between the inwardly disposed support wheels290a1,290b1,290c1and the outwardly disposed support wheels290a2,290b2,290c2as the lugs384of the ground-engaging edge392of the endless track380extend therebetween. The support wheels292a1,292a2,292b1,292b2,292c1,292c2have a smaller diameter than that of the idler wheels262a1,262a2,262b1,262b2. In some embodiments, the leading wheel bearing member200acould include a support wheel frame member pivotably connected thereto and including leading support wheels.

Material and Manufacturing

The various components of the track system40are made of conventional materials (e.g. metals and metal alloys in most cases, such as steel) via conventional manufacturing processes (e.g. casting, molding, etc.). The present technology does not require any specific materials nor methods of manufacture. The present technology merely requires that each component be suitable for the purpose for which it is intended and the use to which it is to be put. Any material(s) or method(s) of manufacture which produce such components may be used in the present technology.

Lines and Resultant Forces

Referring toFIG. 5, a plane500extends parallel to a longitudinal direction of the track system40and extends parallel to a height direction of the track system40.FIGS. 16 to 18Cillustrate the track system40in a plane view that is parallel to the plane500. The pivot axes180a,180band the axes202a,202b,216,264a,264b,296a,296b,296care perpendicular to the plane500.

Referring toFIGS. 16 to 18A, the leading pivot axis180aand the axis202aare spaced apart by a longitudinal distance600adefined in the plane500. The trailing pivot axis180band the axis202bare spaced apart by a longitudinal distance600bdefined in the plane500. In this embodiment, the longitudinal distance600ais greater than the longitudinal distance600b. As a result, the leading frame member170adefines a lever arm between the leading pivot axis180aand the axis202athat is greater than the lever arm defined by the trailing frame member170bbetween the trailing pivot axis180band the axis202b. As a portion of the weight of the vehicle60is transferred from the chassis62to track system40via the attachment assembly100and to the pivots130a,130b, and in turn to the leading and trailing frame members170a,170b, the trailing frame member170bsupports a greater load than the leading frame member170asince the lever arm defined by the trailing frame member170bbetween the trailing pivot axis180band the axis202bis shorter. To support the additional load on the trailing frame member170band in order to more evenly distribute the weight of the vehicle60over the endless track380, the trailing wheel-bearing frame member200bhas more support wheel assemblies indirectly rotatably connected thereto than the leading wheel-bearing frame member200a(namely the support wheel assemblies290b,290crotatably connected to the trailing support wheel assembly210).

The axes296a,202aare spaced apart in a longitudinal direction by a longitudinal distance620adefined in the plane500. The axes264a,202aare spaced apart in a longitudinal direction by a longitudinal distance630adefined in the plane500. In this embodiment, the distance620ais shorter than the distance630a. A portion of the weight of the vehicle60is transferred at the axis202afrom the leading frame member170ato the leading wheel-bearing member200a. Since the lever arm defined by the portion of the leading wheel-bearing member200asupporting the leading support wheel assembly290ais shorter than the portion of leading wheel-bearing member200asupporting the leading idler wheel assembly260a, the leading support wheel assembly290asupports more load than the leading idler wheel assembly260a.

The axes216,202bare spaced apart in a longitudinal direction by a longitudinal distance620bdefined in the plane500. The axes264b,202aare spaced apart in a longitudinal direction by a longitudinal distance630bdefined in the plane500. In this embodiment, the distance620bis shorter than the distance630b. A portion of the weight of the vehicle60is transferred at the axis202bfrom the trailing frame member170bto the trailing wheel-bearing member200b. Since the lever arm defined by the portion of the leading wheel-bearing member200bsupporting the support wheel frame member212is shorter than the portion of trailing wheel-bearing member200bsupporting the trailing idler wheel assembly260b, the support wheel frame member212and the support wheel assemblies290b,290csupport more load than the trailing idler wheel assembly260b.

The axes296b,216are spaced apart in a longitudinal direction by a longitudinal distance640bdefined in the plane500. Similarly, the axes296c,216are spaced apart in a longitudinal direction by a longitudinal distance640cdefined in the plane500. In this embodiment, the distances640b,640care equal. As such, the trailing support wheel assemblies290b,290csupport equal loads.

By using the teachings in the present description and by selecting the dimensions of the various components described herein, a designer of track systems is able to set a distribution of pressure applied to the endless track380by the leading and trailing idler wheel assemblies260a,260band the support wheel assemblies290a,290b,290cto meet the requirements of a particular application.

In the present embodiment, the distances600a,600b,620a,620b,630a,630b,640b,640c, the diameter and width of the idler and support wheel assemblies260b,290a,290b,290care selected to equalize the pressure applied to the endless track380by the leading support wheel assembly290a, the trailing support wheel assemblies290b,290cand the trailing idler wheel assembly260b. In this embodiment, the pressure applied to the endless track380by the leading idler wheel assembly260ais less than the pressure applied by each one of the leading support wheel assembly290a, the trailing support wheel assemblies290b,290cand the trailing idler wheel assembly260b.

Other configurations in other embodiments are contemplated. For instance, the distances600a,600b,620a,620b,630a,630b,640b,640c, the diameter and width of the idler and support wheel assemblies260a,260b,290a,290b,290ccould be selected to equalize the pressure applied to the endless track380by the support wheel assemblies290a,290b,290c. In yet other embodiments, the distances600a,600b,620a,620b,630a,630b,640b,640c, the diameter and width of the idler and support wheel assemblies260a,260b,290a,290b,290ccould be selected to equalize the pressure applied to the endless track380by the leading and trailing idler wheel assemblies260a,260b.

Note that in the accompanying Figures, the arrows indicating the tension forces, torques and biasing force are not to scale (they are schematic). Referring toFIG. 18Aand as described above, the action of the tensioner410and the wheel linkage418on the leading idler wheel assembly260agenerate a biasing force501at the axis264a. As a result, opposed tension forces502,504exist in the leading and ground engaging edges390,392of the endless track380. A resultant force510(e.g. the combination of tension forces502,504) is applied to the leading idler wheel assembly260aat the axis264aand opposes biasing force501. The leading and ground engaging edges390,392of the endless track380form an angle700a. The resultant force510is colinear with a bisector702aof the angle700a.

The leading wheel-bearing frame member200acarries the resultant force510to the axis202aalong a line550aextending between the axis264aand the axis202a, the line550abeing shown as a dashed line inFIGS. 16 and 18A to 18E. In the present embodiment, the line550ais colinear with the bisector702a, but it could be otherwise in other embodiments as other configurations of the leading wheel bearing frame member200aare contemplated. Having the resultant force510passing at the axis202ahas the effect of preventing the generation of a torque that is applied to the leading wheel-bearing member200aabout the axis202a. The line550aand the bisector702apass below the leading pivot axis180a. The bisector702aand the pivot axis180aare spaced apart by a shortest distance552adefined in the plane500. The distance552adefines a lever arm between the bisector702aand the pivot axis180a. As the resultant force510is applied along the bisector702a, the resultant force510passes below the leading pivot axis180a. A torque540ais applied to the leading frame member170aabout the leading pivot axis180a. From the perspective ofFIG. 18A, the torque540ahas the effect of inducing a clockwise rotation of the leading frame member170aabout the pivot axis180a. The torque540aalso has the effect of increasing the load supported by the leading support wheel assembly290aand the load supported by the leading idler wheel assembly260a.

To oppose the tension forces504, equally opposed tension forces520are applied on the ground-engaging edge392of the endless track380proximate to the trailing idler wheel assembly260b. Tension forces522also appear in the trailing edge394of the endless track380and oppose tension forces524,526appearing in the endless track380adjacent to the sprocket wheel350. InFIG. 18A, tension forces502,504,520,522,524,526are equal. A resultant force530(e.g. the combination of tension forces520,522) is applied to the trailing idler wheel assembly260band the resultant force530is applied at the axis264b.

The trailing and ground engaging edges394,392of the endless track380form an angle700b. The resultant force530is colinear with a bisector702bof the angle700b. The trailing wheel-bearing frame member200bcarries the resultant force530to the axis202balong a line550bextending between the axis264band the axis202b, shown as a dashed line inFIGS. 16 and 18A to 18E. In the present embodiment, the line550bis colinear with the bisector702b, but it could be otherwise in other embodiments as other configurations of the trailing wheel bearing frame member200bare contemplated. Having the resultant force530passing at the axis202bhas the effect of preventing the generation of a torque that is applied to the trailing wheel-bearing member200babout the axis202b. The line550band the bisector702bpass below the trailing pivot axis180b. The bisector702band the pivot axis180bare spaced apart by a shortest distance552bdefined in the plane500. The distance552bdefines a lever arm between the bisector702band the pivot axis180b. As the resultant force530is applied along the bisector702b, the resultant force530passes below the trailing pivot axis180b. A torque540bis applied to the trailing frame member170babout the trailing pivot axis180b. From the perspective ofFIG. 18A, the torque540bhas the effect of inducing a counter-clockwise rotation of the trailing frame member170babout the pivot axis180b. The torque540balso has the effect of increasing the load supported by the support wheel assemblies290b,290cand the load supported by the trailing idler wheel assembly260b.

In the present embodiment, the distance552bis greater than the distance552a. In addition, the magnitude of the resultant force530is greater than the resultant force510. Thus, the torque540bhas a greater magnitude than the torque540a. Thus, a net torque (e.g. the combination of torques540a,540b) having the same direction than torque540bis applied to the track system40.

It is noted that, in some embodiments, the bisector702acould pass above the leading pivot axis180a. In such cases, the distance552acould be greater than the distance552bas the net torque applied to the track system40would still have the same direction as torque540b.

When the track system40is driven, additional tension forces appear in the endless track380because of the tractive forces applied by the sprocket wheel350to the endless track380. As such, the magnitude of tension forces524,522and520increases. Simultaneously, the tensioner410is configured to increase its biasing force501and maintain adequate tension forces502,504in the endless track380. These additional tension forces make the magnitude of the resultant force530greater when the track system40is driven, and higher than the magnitude of the resultant force510.

When the track system40is driven, the pressures applied to the endless track380under the leading idler wheel assembly260aand leading support wheel assembly290aare decreased, and the pressures applied to the endless track380under the support wheel assemblies290b,290cand trailing idler wheel assembly260bare increased. As a result, under certain conditions, the track system40has a reduced tendency to pitch negatively, especially when driven on soft grounds.

Moreover, under certain conditions, heat generation and wear of the outer surface386(FIG. 4) of the endless track380are reduced when comparing the track system40to conventional track systems attached to the same vehicle60for the following reasons. First, as there is a reduced pressure applied under the leading idler wheel assembly260a, there is a reduced pressure applied to endless track380as it engages the ground and the tread388has improved engagement with the ground before being parallel thereto and being subjected to tractive forces. Second, as the weight of the vehicle60increases, the surface area of the endless track380over the ground increases due to the scissor-like structure of the track system40. Thus, the pressure on the ground increases at a rate that is less than the rate of increase in weight of the vehicle60.

FIGS. 18B, 18C, 18D and 18Eillustrate different positions of the track system40when stationary. InFIGS. 18B and 18D, the track system40is shown with the damper230fully compressed. Such configuration would be found when the track system40supports a load that is greater than the nominal load. InFIGS. 18C & 18D, the track system40is shown with the damper fully extended. Such configuration would be found when the track system40supports a load that is smaller than the nominal load.

Referring toFIG. 18B, when the damper230is fully compressed, the leading frame member170ais pivoted counter-clockwise and the trailing frame member170bis pivoted clockwise, in the perspective ofFIG. 18B. The lines550a,550band the bisectors702a,702bstill pass below the leading and trailing pivot axes180a,180brespectively. Furthermore, the distance552bremains greater than the distance552a.

Referring toFIG. 18C, when the damper230is fully extended, the leading frame member170ais pivoted clockwise and the trailing frame member170bis pivoted counter-clockwise, in the perspective ofFIG. 18C. The lines550a,550band the bisectors702a,702bstill pass below the leading and trailing pivot axes180a,180brespectively. Again, the distance552bremains greater than the distance552a.

As such, the track system40maintains its reduced tendency to pitch negatively when it is driven, regardless of the load of the vehicle60.

Referring toFIG. 18D, when the damper230is fully compressed, the leading idler wheel assembly260ais spaced apart from the trailing idler wheel assembly260b, by a distance800(measured between the axes of rotation of each of the idler wheel assemblies260a,260b). Referring toFIG. 18E, when the damper230is fully extended, the leading idler wheel assembly260ais spaced apart from the trailing idler wheel assembly260b, by a distance800(measured between the axes of rotation of each of the idler wheel assemblies260a,260b). The distance800inFIG. 18Dis greater than the distance800inFIG. 18E. Thus, the track380has a ground-contacting area that increases in size as a load borne by the track system40increases (and the damper compresses).

In addition to the reduced tendency of the track system40to pitch negatively, when the track system40encounters an obstacle such as a bump or a depression along its path of travel, the pivoting of the leading and trailing wheel-bearing members200a,200b, and of the leading and trailing frame members170a,170bhas the effect of reducing vertical displacements of the leading and trailing pivots130a,130b. Accordingly, vertical displacements of the chassis62of the vehicle60are reduced. Notably, at certain speed regimes, the pivoting of the leading and trailing wheel-bearing members200a,200balone is sufficient to reduce the vertical displacements of the leading and trailing pivots130a,130b. At other speed regimes, it is the combined action of the pivoting of the leading and trailing wheel-bearing members200a,200band of the leading and trailing frame members170a,170b, and the damping action of the damper230that reduce the vertical displacements of the leading and trailing pivots130a,130b.