WO2001060683A1

WO2001060683A1 - Half-track assembly with suspended idler

Info

Publication number: WO2001060683A1
Application number: PCT/US2001/004561
Authority: WO
Inventors: Ignacy Puszkiewicz
Original assignee: Jlg Industries, Inc.
Priority date: 2000-02-18
Filing date: 2001-02-14
Publication date: 2001-08-23
Also published as: AU2001236957A1

Abstract

A half-track assembly includes a movable idler wheel assembly secured to the vehicle chassis. A track is disposed engaging the idler wheel assembly and the drive wheel. Configuration characteristics of the idler wheel assembly serve to limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction. With this construction, driving over level terrain is easier to control and more comfortable while the vehicle maintains greater traction over uneven terrain or terrain that is difficult to traverse. Moreover, because the moving idler can accept only a limited amount of rear wheel load, inherent stability characteristics are preserved.

Description

HALF-TRACK ASSEMBLY WITH SUSPENDED IDLER

BACKGROUND OF THE INVENTION

The present invention relates to half-track assemblies for construction vehicles and the like and, more particularly, to a half-track assembly including a suspended idler incorporating configuration characteristics for controlling an amount of drive wheel load support.

Tracked vehicles can outperform wheeled vehicles when traction and floatation are important due to soft or slippery ground conditions such as mud, snow or sand. Full tracks, known as crawlers, offer the lowest ground bearing pressure and the highest traction but have limitations due to high cost, damage to terrain when steering and the tendency to "teeter-totter" over obstacles. Many of the advantages of full tracks can be achieved without the disadvantages, by the use of a half-track system.

A half-track vehicle incorporates track assemblies that are attached to the non-steering wheels and have steered wheels with conventional steering mechanisms. Traction and floatation are improved, without the need to alter the method of driving or steering. Military transport trucks are sometimes equipped with half-track systems, as are some types of construction equipment.

Road vehicles, such as military trucks, utilize a fully suspended half-track system. That is, each drive wheel along with one or more idler wheels are spring- suspended and move vertically in response to ground conditions. This construction is necessary to provide some level of driver and passenger comfort while traveling at highway speeds. Construction equipment, on the other hand, includes wheels that are generally rigidly mounted to the chassis without the use of any type of suspension. The construction equipment is manufactured in this manner because it is necessary to provide the most stable possible base for supporting overhanging loads such as the boom mechanism, workers and material. Ride quality is not as important because of the relatively lower travel speeds.

By utilizing tracks developed for skid steer loaders, so called over-the-tire tracks, and adding an idler wheel at about the same distance from the drive wheel as the wheel base of a skid steer loader, a conventional four-wheel machine can be converted to a half-track vehicle. An important difference between conventional crawler tracks and those made for skid steer loaders is that the crawler tracks are sprocket-driven and have a track tensioning mechanism, while the skid steer tracks rely on friction between the drive tire and the track and usually use free-running (not tensioned) track. With this construction, there is high importance on maintaining sufficient load on the drive tires under all driving conditions in order to maintain traction. It is of no use to improve traction between the track and the ground if traction is lost between the drive wheel and the track. By rigidly mounting an idler wheel to the chassis, the machine will pivot about the idler wheels while traversing rough terrain and may even be supported by the steer wheels and idler wheel alone. When this happens, the load on the drive wheels is reduced or eliminated. Since traction is a function of wheel load, the tire simply spins inside the track, and the machine is less functional than if it were not equipped with tracks. As such conditions commonly occur when crossing curbs, ditches and other obstacles commonly found on job sites, conventional half-track systems are of limited value. SUMMARY OF THE INVENTION

An object of this invention is to provide a half-track system for construction vehicles and the like that permits the rigid mounting of the drive wheel to the chassis and prevents the teeter-tottering and loss of drive traction associated with conventional configurations. An idler wheel mechanism moves in response to terrain and load conditions, thus allowing the drive wheels and steering wheels to maintain contact with the ground in a conventional manner, and maintains the drive wheel load necessary to provide traction. With this system, the operator receives the benefit of a tracked vehicle without having to operate the machine in any way differently than a conventional rubber tired model. Because the moving idler can accept only a limited amount of rear wheel load, inherent stability characteristics are preserved. In addition, the tracks and idlers may easily be removed to convert the machine to a rubber-tired configuration, thus providing one machine for use in all applications.

In an exemplary embodiment of the invention, a half-track assembly is provided for a vehicle including at least one drive wheel supported by a drive axle attached to a chassis. The half-track assembly includes an idler wheel assembly secured to the chassis adjacent the drive wheel. The idler wheel assembly has a pivoting arm movably secured to the chassis, an idler tire attached to the pivoting arm, a biasing member engaging the pivoting arm and biasing the pivoting arm in a first direction, and a stop disposed adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction. A track is disposed engaging the idler wheel assembly and the drive wheel of the vehicle. The idler wheel assembly is provided with configuration characteristics that limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

The configuration characteristics may include a spring constant of the biasing member and/or a position of the stop. The vehicle typically includes two drive wheels supported by the drive axle, and in this context, the half-track assembly includes a first idler wheel assembly for one of the drive wheels, a second idler wheel assembly for the other of the drive wheels, and two tracks disposed engaging the first and second idler wheel assemblies and the drive wheels, respectively.

The stop in the idler wheel assembly may be constructed of a lower stop and an upper stop, with the lower stop limiting the pivoting arm range of motion in the first direction such that on even terrain, the idler wheel is maintained above ground. The upper stop limits the pivoting arm range of motion in the second direction such that the drive wheel load is distributed between the idler wheel assembly and the drive wheel. In this context, the configuration characteristics may additionally include a position of the upper stop.

A pivot for the pivoting arm is preferably disposed in a vicinity of a center of the drive wheel. Additionally, a diameter of the idler tire is preferably smaller than a diameter of the drive wheel. The configuration characteristics may be set to limit the amount of idler wheel assembly load support to between 10% and 50% of the drive wheel load.

In one embodiment, the pivoting arm is pivotally secured to the chassis. In an alternative, the pivoting arm includes a vertically disposed cylinder and piston, and the biasing member incluc es structure for driving the piston in the first direction. Generally, the biasing member is preferably a spring.

In another exemplary embodiment of the invention, a construction vehicle includes a chassis supporting a vehicle frame and a driving power system, at least two drive wheels secured to the chassis and operatively coupled with the driving power system, and the half-track assembly according to the invention. In this context, the half-track assembly includes a pair of idler wheel assemblies and a pair of tracks disposed engaging a pair of idler wheel assemblies and the two drive wheels, respectively.

In accordance with still another aspect of the invention, an idler wheel assembly kit includes the idler wheel assembly of the invention attachable to a vehicle chassis and the track engageable with the idler wheel assembly and the drive wheel of the vehicle.

In accordance with yet another aspect of the invention, a method of converting a vehicle including at least one drive wheel supported by a drive axle attached to a chassis to a half-track vehicle includes securing an idler wheel assembly to the chassis adjacent the drive wheel by movably securing a pivoting arm to the chassis, attaching an idler tire to the pivoting arm, engaging a biasing member with the pivoting arm for biasing the pivoting arm in the first direction, and disposing a stop adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction. The method also includes attaching a track engaging the idler wheel assembly and the drive wheel, and providing the idler wheel assembly with configuration characteristics that limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the present invention will be described in detail with reference to the accompanying drawings, in which:

FIGURE 1 is a perspective view of a half-track vehicle including the idler assembly according to the present invention;

FIGURE 2 is a side view of the idler assembly in a raised position on uneven terrain;

FIGURE 3 is a perspective view of the idler wheel;

FIGURE 4 is an assembly drawing of the idler wheel assembly;

FIGURE 5 is a perspective view of a first alternative embodiment according to the invention; and

FIGURE 6 is a perspective view of another alternative embodiment according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGURE 1 is a perspective view of a construction vehicle 10 incorporating the half-track assembly 12 of the present invention. Referring to FIGURE 2, the half-track assembly 12 includes an idler wheel assembly 14 secured to the vehicle chassis adjacent a drive wheel DW of the vehicle and a track 16 disposed engaging the idler wheel assembly 14 and the drive wheel DW.

As shown in FIGURE 3, the idler wheel assembly 14 includes a pivoting arm 18, an idler tire 20 attached to the pivoting arm 18, a biasing member 22, and a stop 24. An idler wheel assembly supporting bracket 26 is secured to the vehicle chassis by bolts 28 or the like.

In order to effect the desired traction and function of the half-track assembly according to the invention, the idler tire is movable in first and second opposite directions (substantially up and down in the FIGURES, perpendicular to a vehicle driving direction). In this context, the pivoting arm 18 is pivotally secured to the chassis about a pivot pin 30 via the wheel assembly bracket 26. As a consequence, when the vehicle 10 is traversing uneven terrain, for example as shown in FIGURE 2, the idler tire 20 of the half-track assembly may be deflected by the terrain while the drive wheels DW maintain ground traction. The pivot point for the pivoting arm 18 via the pivot pin 30 is preferably positioned as close as possible to the axial center of the drive wheel DW.

The biasing member 22 such as a compression spring or like elastic member is secured between the pivoting arm 18 and the support bracket 26 by an attaching screw 32 or the like. As shown in FIGURE 4, the attaching screw 32 includes a bolt extending through the bracket 26 and the pivoting arm 18 that is secured with an upper securing nut 32A and a lower bolt head or additional securing nut 32B. The biasing member 22 is preferably compressed between the bracket 26 and the pivoting arm, thereby biasing the pivoting arm 18 in a downward direction. The securing nut 32A and bolt head 32B define upper and lower stops 24, limiting the pivoting arm 18 range of motion in counterclockwise and clockwise (upward and downward) directions. The positions of the stops 32A, 32B and the amount of initial compression of the biasing member 22 can be readily controlled by an amount that the securing nut 32A is threaded onto the bolt 32. In the event that two securing nuts are used, of course, both nuts can be adjusted.

With this construction, the lower stop can be positioned so that the idler tire 20 is maintained slightly above ground level when the vehicle is traversing improved surfaces or otherwise level terrain. As a consequence, the vehicle can be steered in a conventional manner without scuffing the tracks along the ground.

Moreover, the idler wheel assembly 14 can be constructed according to controllable configuration characteristics to customize the half-track assembly 12 for a particular use. In particular, the configuration characteristics enable the idler wheel assembly to support no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction. The drive wheel to track traction (friction x load) is a result of friction and to some extent mechanical engagement between thread bars (blocks) and track pads. The effectiveness of the friction and engagement forces is proportional to the load on the drive wheels. The configuration characteristics include, for example, positions of the upper and lower stops 24, size and elasticity of the biasing member 22, size of the idler tire 20, pivoting arm 18 geometry, and the like. For example, the size and elasticity of the biasing member 22 along with the position of at least the upper stop 32A determine at what load ratio the idler wheel assembly and track begin to share rear wheel load with the drive wheels to reduce the ground bearing pressure, e.g.. when the drive tire starts to sink in soft ground. Preferably, the idler wheel assemblies will support between 10-50% c f the rear wheel load, depending on ground conditions.

The pivot location for the pivoting arm 18 is selected to prevent unintended arm movement when driving in reverse, wherein track tension would tend to pull the idler 20 away from the ground. The location of the pivot also affects the amount the track 16 becomes tighter or looser during arm movement.

As shown in FIGURES 1 and 2, the idler tire 20 preferably has a smaller diameter than a diameter of the drive wheel DW, which allows the idler wheel assembly 14 to move through its entire range of motion without interfering with any machine components above the height of the drive wheel DW. The use of a smaller tire also allows the track 16 to be relatively shorter than otherwise, which permits the use of this assembly on machines having a shorter wheel base.

FIGURES 5 and 6 illustrate alternatives to the pivoting movement of the arm 18. In FIGURE 5, the idler wheel assembly is shown secured to the chassis via a bracket assembly 34 that enables the idler tire 20 to move up and down by pivoting about an axis perpendicular to the drive wheel axis. As shown, the bracket includes two pivoting arms 36 secured to the idler tire, although fewer or additional arms may also be used. FIGURE 6 shows the idler wheel assembly sliding up and down in a vertical direction on one or more shafts 28 that are secured to the vehicle chassis by brackets 40.

With the structure according to the present invention, a half-track system for construction vehicles or the like permits the rigid mounting of the drive wheel to the chassis while preventing teeter-tottering and loss of drive traction. The idler wheel mechanism moves in response to terrain and load conditions, allowing the drive wheels and steering wheels to maintain contact with the ground and maintain the drive wheel load necessary to provide traction.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A half-track assembly for a vehicle including at least one drive wheel supported by a drive axle attached to a chassis, the half-track assembly comprising: an idler wheel assembly secured to the chassis adjacent the drive wheel, the idler wheel assembly including a pivoting arm movably secured to the chassis, an idler tire attached to the pivoting arm, a biasing member engaging the pivoting arm and biasing the pivoting arm in a first direction, and a stop disposed adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction; and a track disposed engaging the idler wheel assembly and the drive wheel, wherein the idler wheel assembly comprises configuration characteristics that limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

2. A half-track assembly according to claim 1 , wherein the configuration characteristics comprise a spring constant of the biasing member.

3. A half-track assembly according to claim 2, wherein the configuration characteristics further comprise a position of the stop.

4. A half-track assembly according to claim 1 , wherein the vehicle includes two drive wheels supported by the drive axle, and wherein the half-track assembly comprises a first idler wheel assembly for one of the drive wheels, a second idler wheel assembly for the other of the drive wheels, and two tracks disposed engaging the first and second idler wheel assemblies and the drive wheels, respectively.

5. A half-track assembly according to claim 1 , wherein the stop comprises a lower stop and an upper stop, the lower stop limiting the pivoting arm range of motion in the first direction such that on even terrain, the idler wheel is maintained above ground, and the upper stop limiting the pivoting arm range of motion in the second direction such that drive wheel load is distributed between the idler wheel assembly and the drive wheel.

6. A half-track assembly according to claim 5, wherein the configuration characteristics comprise a position of the upper stop.

7. A half-track assembly according to claim 1 , wherein a pivot for the pivoting arm is disposed in a vicinity of a center of the drive wheel.

8. A half-track assembly according to claim 1 , wherein a diameter of the idler tire is smaller than a diameter of the drive wheel.

9. A half-track assembly according to claim 1. wherein the configuration characteristics are set to limit the amount of idler wheel assembly load support to between 10% and 50% of the drive wheel load.

10. A half-track assembly according to claim 1 , wherein the pivoting arm is pivotally secured to the chassis.

1 1. A half-track assembly according to claim 10, wherein the pivoting arm pivots about an axis substantially perpendicular to an idler tire axis.

12. A half-track assembly according to claim 1 , wherein the pivoting arm is linearly displaceable on at least one shaft secured to the vehicle chassis.

13. A half-track assembly according to claim 1 , wherein the biasing member is a spring.

14. A construction vt hide comprising: a chassis supporting a vehicle frame and a driving power system; at least two drive wheels secured to the chassis and operatively coupled with the driving power system; a pair of idler wheel assemblies secured to the chassis adjacent the two drive wheels, respectively, each of the idler wheel assemblies comprising a pivoting arm movably secured to the chassis, an idler tire attached to the pivoting arm, a biasing member engaging the pivoting arm and biasing the pivoting arm in a first direction, and a stop disposed adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction; and a pair of tracks disposed engaging the pair of idler wheel assemblies and the two drive wheels, respectively, wherein each of the idler wheel assemblies comprises configuration characteristics that limit an amount of idler wheel assembly load support so that each of the idler wheel assemblies supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

15. A construction vehicle according to claim 14, wherein the configuration characteristics comprise a spring constant of the biasing member.

16. A construction vehicle according to claim 15, wherein the configuration characteristics further comprise a position of the stop.

17. A construction vehicle according to claim 14, wherein the stop comprises a lower stop and an upper stop, the lower stop limiting the pivoting arm range of motion in the first direction such that on even terrain, the idler wheel is maintained above ground, and the upper stop limiting the pivoting arm range of motion in the second direction such that drive wheel load is distributed between the idler wheel assembly and the drive wheel.

18. A construction vehicle according to claim 17, wherein the configuration characteristics comprise a position of the upper stop.

19. A construction vehicle according to claim 14, wherein a pivot for each pivoting arm is disposed in a vicinity of a center of the drive wheel.

20. A construction vehicle according to claim 14, wherein a diameter of the idler tires is smaller than a diameter of the drive wheels.

21. A construction vehicle according to claim 14, wherein the configuration characteristics are set to limit the amount of idler wheel assembly load support to between 10% and 50% of the drive wheel load.

22. A construction vehicle according to claim 14, wherein the pivoting arm is pivotally secured to the chassis.

23. A construction vehicle according to claim 22, wherein the pivoting arm pivots about an axis substantially perpendicular to an idler tire axis.

24. A construction vehicle according to claim 14, wherein the pivoting arm is linearly displaceable on at least one shaft secured to the vehicle chassis.

25. A construction vehicle according to claim 14, wherein the biasing member is a spring.

26. An idler wheel assembly kit comprising: an idler wheel assembly attachable to a vehicle chassis adjacent a drive wheel, the idler wheel assembly including a pivoting arm movably securable to the chassis, an idler tire attached to the pivoting arm, a biasing member engaging the pivoting arm and biasing the pivoting arm in a first direction, and a stop disposed adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction; and a track engageable with the idler wheel assembly and the drive wheel, wherein the idler wheel assembly comprises configuration characteristics that limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

27. A method of converting a vehicle including at least one drive wheel supported by a drive axle attached to a chassis to a half-track vehicle, the method comprising:

(a) securing an idler wheel assembly to the chassis adjacent the drive wheel by movably securing a pivoting arm to the chassis, attaching an idler tire to the pivoting arm, engaging a biasing member with the pivoting arm for biasing the pivoting arm in a first direction, and disposing a stop adjacent the pivoting arm that limits the pivoting arm range of motion in at least a second direction, opposite from the first direction;

(b) attaching a track engaging the idler wheel assembly and the drive wheel; and

(c) providing the idler wheel assembly with configuration characteristics that limit an amount of idler wheel assembly load support so that the idler wheel assembly supports no more than a percentage of drive wheel load that is not required to maintain drive wheel to track traction.

28. A method according claim 27, wherein step (c) is practiced by controlling a spring constant of the biasing member.

29. A method according to claim 28, wherein step (c) is further practiced by controlling a position of the stop.

30. A method according to claim 27, wherein the stop comprises a lower stop and an upper stop, the method further comprising limiting, with the lower stop, the pivoting arm range of motion in the first direction such that on even terrain, the idler wheel is maintained above ground, and limiting, with the upper stop, the pivoting arm range of motion in the second direction such that drive wheel load is distributed between the idler wheel assembly and the drive wheel.

31. A method according to claim 30, wherein step (c) is practiced by controlling a position of the upper stop.

32. A method according to claim 27, wherein step (c) is practiced by setting the configuration characteristics to limit the amount of idler wheel assembly load support to between 10% and 50% of the drive wheel load.