Abstract:
A system and method of increasing the traction and mobility of a tandem axled vehicle by disposing an endless track  16  around the vehicle tires  18,20  and using a tensioning device  22  to impart a force on the endless track  16  to maintain an optimal track tension. The tensioning device  22  may impart a constant force, a force within a set range, or a variable force controlled by a processor  64  on the endless track  16 . The processor  64  monitors vehicle parameters to determine if endless track slipping is occurring. The slip-control processor  64  sends signals to the tension device  22  to increase endless track tension when a track slip condition is sensed, and sends signals to decrease endless track tension when slipping is not occurring, thereby allowing for greater suspension movement and improving overall vehicle mobility.

Description:
The invention was made in part with Government support. The Government may have certain rights to the invention. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to track over tire systems and methods on vehicles with multiple axle sets connected to the vehicle through a vehicle suspension system. 
     BACKGROUND 
     Endless tracks have been used on vehicles to increase the surface area on the ground upon which the vehicle traverses. This increased vehicle footprint results in a lower force per unit area on the ground being traversed than a conventional wheeled vehicle of the same weight. 
     Most tracked vehicles utilize an endless track driven by a sprocket in which teeth of the sprocket engage links of the track to drive the track and the vehicle forward. Road wheels are attached to the vehicle through independent suspensions and roll over the track as the vehicle traverses the ground. In this design, the road wheels do not drive the vehicle forward, only the sprocket is used for movement. The direct engagement of the sprocket does not allow for track slippage relative to the sprocket. 
     Track over tire systems have been used on vehicles used in agriculture, construction equipment, and off-highway systems in the past. These systems utilize an endless track disposed around the existing tires of the vehicle. The tires drive the vehicle forward by driving over the track. However, these systems experienced tires slipping relative to the tracks and greatly restrict, or completely lock, the suspension movement. 
     The following references were considered before filing this application: U.S. Pat. No. 6,296,328 to Wilkinson, U.S. Pat. No. 4,810,043 to McIntosh, U.S. Pat. No. 2,059,213 to Dorst, U.S. Pat. No. 1,660,100 to Smyth, U.S. Pat. No. 7,083,241 to Gunter, and U.S. Pat. No. 5,851,058 to Humbek et al. 
     SUMMARY 
     One embodiment of the present invention is to provide a method of increasing vehicle traction and mobility on a multiple axled vehicle. A multiple axled vehicle has two or more axles which are in series and close proximity to one another. The axles have wheels and tires, and are connected to the vehicle through a suspension. An endless track is disposed around the tires of the multiple axle set and increases the vehicle&#39;s footprint. In this embodiment, a tensioning device is attached to the vehicle so as to impart a force on the endless track to maintain an optimal track tension, decreasing endless track slippage relative to the tires, allowing for optimum suspension travel, and in combination with the increased vehicle footprint, increasing the overall vehicle traction and mobility of the vehicle. 
     In another embodiment of the present invention, the tensioning device exerts a variable force on the endless track in order to increase, decrease, or maintain endless track tension as needed. When the variable force is increased, the endless track will achieve a greater tension around the tires and decrease track slippage relative to the tires. When the variable force is decreased, the endless track will achieve a lower tension around the tires and allow for greater suspension travel. Decreasing track tension, especially when increased track tension is not needed, also increases fuel economy and reduces wear of the mating components. 
     In one version of the variable tensioning device embodiment, the tensioning device is designed to maintain an endless track tension within an optimum range. As the suspension moves creating greater distance between the wheels of the axle, the tensioning device lowers the force applied to maintain a substantially constant tension around the tires. As the suspension moves bringing the tires closer together, the tensioning device applies a greater force to take up the resulting slack and thus still maintaining a substantially constant track tension. This version of the variable tensioning device uses mechanical devices such as a constant pressure source from the vehicle pneumatic system and pressure relief valves. 
     In another version of the variable tensioning device embodiment, the system utilizes a slip-control processor to control the tensioning device. In this version, the tension of the endless track may be varied depending on the vehicle parameters. The processor monitors the vehicle parameters utilizing a control loop algorithm to determine if endless track slipping is occurring or whether the vehicle may allow for greater suspension travel. In this version, the slip-control processor sends signals to the tension device to increase or decrease endless track tension as needed during operation to improve overall vehicle mobility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a multiple axle set vehicle with an endless track around the front and rear tires of the multiple axle set; 
         FIG. 2  is a bottom view of a multiple axle set vehicle with an endless track around the left side front and rear tires of the multiple axle set; 
         FIG. 3  is a cross-sectional view taken along line  3 - 3  in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 2  showing an embodiment of a tensioning device; 
         FIG. 5  is a cross-sectional view taken along line  4 - 4  in  FIG. 2  showing an embodiment of a tensioning device with a track speed sensor; 
         FIG. 6  is a perspective view of an embodiment of a tensioning device; 
         FIG. 7  is a perspective view of an embodiment of a tensioning device with a track speed sensor; 
         FIG. 8  is a block diagram flowchart illustrating a slip control algorithm using comparative velocities; and 
         FIG. 9  is a block diagram flowchart illustrating a slip control algorithm using comparative pressure or force. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and/or as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     In regards to  FIG. 1 , an embodiment of a vehicle  10  (illustrated as a generic representative vehicle model) is shown with a multiple axle set  12  connected to the vehicle  10  through a suspension  14  (axles and suspension illustrated as a generic representative axle/suspension model, best seen in  FIGS. 2 and 3 ). In this embodiment an endless track  16  is shown partially disposed around a front tire  18  and a rear tire  20  of the axle set  12 . The endless track  16  is tensioned around the front tire  18  and rear tire  20  by a tensioning device  22 . 
     Vehicle  10  may be any vehicle that has multiple axles grouped in axle sets, also known as tandem axles, which are connected to a vehicle through a suspension. A tandem axle set is two or more axles in series and grouped close together. Vehicle  10  is designed such that it typically does not require an endless track for operation. Examples of vehicles that fit this description are trucks with tandem axles from the Family of Medium Tactical Vehicles (FMTV), Medium Tactical Vehicle Replacement (MTVR) trucks, United States Army M35 family of trucks, United States Army M939 family of trucks, 6×4 and 6×6 versions of the Navistar 7000 series of trucks, and Heavy Expanded Mobility Tactical Trucks (HEMTT). This list is given to better understand the usage of the invention and should not be viewed as limiting, as the invention may be used with any vehicle with a multiple axle set. 
     As shown in the embodiment in  FIG. 1 , Vehicle  10  typically has an axle set  12  with two driven axles  24  having wheels  26  and tires  18 , 20  on the ends of each of the axles  24 . The term axle  24  may refer to the shaft itself, its housing, half-shaft, or a transverse pair of wheels. The axle shaft, or half-shaft, typically rotates with the wheel  26  being either bolted or splined in fixed relation (not shown) to the axle shaft. The housing around the axle shaft is also commonly referred to simply as an axle as well, usually encompassing the housing and shaft combination. An even broader sense of the word refers to every transverse pair of wheels on a vehicle, whether they are connected to each other or not, thus even transverse pairs of wheels in a vehicle with an independent suspension are also included in the term axle or axle set as used herein. 
     The suspension  14  is traditionally a system of springs, shock absorbers and linkages that connect the vehicle  10  to its wheels  26  through the axle  24 . Common forms of suspensions include leaf spring suspensions, torsion beam suspensions, coil spring suspensions, and air suspensions, although any form of suspension may be used with this invention. 
       FIG. 1  shows the endless track  16  partially disposed around the front tire  18  and the rear tire  20  associated with the multiple axle set  12 . In this embodiment, the endless track  16  is shown with a main track body  30  having an inner surface  32  (best seen in  FIG. 3 ) and an outer surface  34  opposite the inner surface. Portions of the inner surface  32  of the endless track  16  contact portions of the front tire  18  and portions of the rear tire  20 . Portions of the outer surface  34  of the endless track  16  are designed to contact the ground. 
     In this embodiment, the endless track  16  also has a plurality of edge guide projections  36  connected to the main track body  30  and extending away from the inner surface  32 . As seen in  FIG. 1 , some of the edge guide projections  36  are designed to contact portions of the front and rear tires  18 , 20 . The edge guide projections  36  are designed to allow the endless track  16  to track around the tires  18 , 20  during use. It should be noted that other guide designs may be used, such as center guide projections used with dual wheel and tire sets that project between the opposing tire faces of the dual wheel/tire set. 
       FIG. 1  also shows an embodiment in which the tensioning device  22  is disposed between the front and rear tires  18 , 20  of the axle set  12 . The tensioning device  22  uses an idler wheel  40  in contact with the inner surface  32  of the endless track  16  to maintain track tension on the endless track  16  around the tires  18 ,  20 . 
       FIG. 2  is a bottom view of the embodiment as shown in  FIG. 1 .  FIG. 2  shows an endless track  16  disposed around the vehicle&#39;s left side front and rear tires of the multiple axle set  12 . As well, this figure only shows a tensioning device  22  installed on the left side of the vehicle. The vehicle&#39;s right side front and rear tires  18 , do not have an endless track disposed around them, nor is there a tensioning device installed on the right side of the vehicle in this figure. In practice, a vehicle would likely be symmetrically fitted with a track over tire system on both the left and the right side of the vehicle, although the vehicle could continue to operate even if only one side had a track installed. 
       FIG. 3  is a cross-sectional view taken along line  3 - 3  of the embodiment in  FIG. 1 .  FIG. 3 , like  FIG. 2 , only has an endless track  16  partially disposed around the vehicle&#39;s left side front and rear tires  20  of the axle set  12 . The cross-sectional view shown here looks to the rear of the vehicle and shows the endless track  16  partially disposed around the rear tire  20 .  FIG. 3  also shows an embodiment in which the tensioning device  22  has an actuator  42  disposed between a base  44  and the idler wheel  40 . The base  44  is shown attached to the vehicle  10 . In some embodiments, the tensioning device  22  may also be attached to the vehicle  10  by an upper articulating arm  46 . 
     The actuator  42  may actuate away from the base  44  applying a force to the inner surface  32  of the endless track  16  through the idler wheel  40 . The tensioning device  22  places a load on the endless track  16  thereby producing a track tension around the front and rear tires  18 , 20 . As the track tension is increased, so is the friction between the tires  18 , 20  and the inner surface  32  of the endless track  16 . The increased friction reduces slippage between the endless track  16  and the front and rear tires  18 , 20 , and the endless track  16  and the tensioning device  22  cooperate to increase vehicle traction and allow for axle suspension movement. 
     In one embodiment, the actuator  42  actuates providing a varying force through the idler wheel  40  to the endless track to maintaining a substantially constant endless track tension around the front and rear tires  18 , 20 . The tensioning device  22  uses mechanical means to vary the force applied to the endless track  16  to maintain a substantially constant endless track tension while allowing variable distances between the front tire and the rear tire caused by axle suspension  14  movement. When the vehicle  10  is traveling over level ground, the distance between the center point of the front tire  18  and the center point of the rear tire  20  is relatively constant. As the vehicle  10  begins traveling over uneven ground, the suspension  14  allows for the front and rear tires  18 , 20  to rise and fall with the terrain. As the front and rear tires  18 , 20  rise and fall with the terrain, the distance between the center points of the tires  18 , 20  change. As the distance between the front and rear tires  18 , 20  change, so too does the tension on the endless track  16  disposed around the tires  18 , 20 . To accommodate for the change in distances, and to maintain a substantially constant track tension, the tensioning device  22  will take up the slack achieved when the tires come closer. 
     In one embodiment, the tensioning device  22  maintains a nearly constant 4000 pound force on the endless track  16 , regardless of suspension travel. In another embodiment, the tensioning device  22  applies a force the endless track  16  between 3600 pounds and 4400 pounds. As the suspension  14  allows the tires to move further apart, thus tightening the endless track  16 , the tensioning device  22  does not allow the tension to exceed the 4400 pound threshold. This may be accomplished by dumping pressure in the actuator  42 . As the suspension  14  allows the tires to move closer together, giving more slack to the endless track  16 , the tensioning device  22  does not allow the tension to fall beneath 3600 pounds. This may be done by increasing pressure in the actuator  46 . By maintaining a nearly constant force on the track, the endless track  16  maintains a nearly constant tension, thus translating into a nearly constant friction between the tires  18 , 20  and the inner surface  32  of the endless track  16 . This system maintains superior vehicle traction while allowing varying distance changes between the front tire  18  and the rear tire  20  caused by axle suspension  14  movement. 
     It should be noted that the endless track  16  may be made of any number of materials, such as, but not limited to, rubber, steel or composite materials. The endless track  16  may also be a single piece with one joint connecting the two ends together around the tires, or may be an endless track  16  made up of a plurality of smaller track shoe assemblies in which there is a joint in the endless track between each shoe. Due to the variation in materials, number of joints, and overall length of the endless track, along with the size and type of the tire the endless track is used in combination with, the endless tracks used with this system will experience a different level of stretchability and thus react differently to the amount of force imparted on it by the tensioning device. Testing is conducted to optimize the kind of endless track to be used with the kind of vehicle and the amount of force to be imparted on to the endless track to increase overall vehicle mobility. Thus the 3600 to 4400 pound range from the previous paragraph was optimized on a FMTV with a single piece rubber Camoplast endless track, and this force range should not be considered limiting, as the force range would change for differing vehicles and endless tracks. 
       FIG. 4  is a magnified cross-sectional view taken along line  4 - 4  in  FIG. 2  showing an embodiment of a tensioning device  22  mounted to the vehicle  10 . In this embodiment, the cross-sectioning is taken through the tires  18 , 20  and the endless track  16  to show the idler wheel  40  in contact with the inner surface  32  of the endless track  16 . 
     In the embodiment as seen in  FIG. 4 , the tensioning device  22  also has a pneumatic port  48  in the bottom of the actuator  42 . The pneumatic port  48  is designed to be fluidly connected with a vehicle pneumatic system through a hose (not shown). In one embodiment, the vehicle pneumatic system provides a constant pressure to the actuator  42  through the pneumatic port  48 . As slack occurs in the endless track  16 , the vehicle pneumatic system pumps in more air to maintain the pressure. As tension builds in the endless track  16 , pressure relief valves (not shown) may open to dump off the pressure in the actuator  42 . It should be noted that the actuator  42  is a mechanical device that moves the idler wheel  40  back and forth. 
     The actuator  42  in this invention is not limited to a pneumatic actuator, rather any form of actuator could be used. Actuators  42  may be, but are not limited to, an electric actuator, a hydraulic actuator, a pneumatic actuator, a piezoelectric actuator, or any now known or future design actuating unit. As well, the internal mechanism of the actuator could be a jackscrew, a ball screw, a roller screw, a linear actuator, a rack and pinion, a worm gear, a planetary gear set, a chain drive, a belt drive, a rigid chain, a rigid belt, a cam actuator, hydraulic cylinders, hydraulic pumps, hydraulic pistons, pneumatic cylinders, pneumatic pumps, pneumatic pistons, components employing a piezoelectric effect, an air spring, or any combination of the above. 
     In other embodiments, the track over tire system employs active systems to modify the force applied through the tensioning device  22  to the endless track  16  to maintain an endless track tension within a desired range.  FIG. 5  is an embodiment of the track over tire system in which a track speed sensor  60  is used to measure the speed, of the endless track  16 , track velocity V 1  (see  FIG. 8 ). In this embodiment there is also a means for determining tire velocity V 2  (see  FIG. 8 ), such as a wheel speed sensor  62  (represented in block flow diagram). If the track velocity V 1  is lower than the tire velocity V 2 , this indicates that the tires  18 , 20  are slipping within the endless track  16 . When this condition is sensed by comparing the velocities of the endless track  16  and tires  18 , 20 , then the actuator may be employed to apply a greater force on the endless track  16 , thus increasing the endless track tension and increasing the friction between the inner surface  32  of the endless track  16  and the tires  18 , 20 . This increased friction, in combination with the greater footprint on the ground created by the endless track  16 , will increase the overall traction of the vehicle  10 . The algorithm used to control the active system is discussed in further detail below. 
       FIGS. 6 and 7  show perspective views of embodiments of tensioning devices  22  with a base  44 , an upper articulating arm  46 , an actuator  42 , and an idler wheel  40 .  FIG. 7  shows an additional embodiment of the track speed sensor  60 . 
     In regards to  FIG. 8 , a block diagram flowchart is shown illustrating a slip control algorithm embodiment using comparative velocities. The flowchart represents when a track speed sensor  60  measures the rotational speed of the endless track  16 , track velocity V 1 , a wheel speed sensor  62  measures the rotational speed of at least one of the tires  18 , 20 , tire velocity V 2 , and a slip control processor  64  sends a signal to the actuator  42  to increase track tension when the velocities do not match. The slip control processor  64  is electrically connected to the track speed sensor  60 , the wheel speed sensor  62 , and the actuator  42 , such that the slip control processor  64  executes a control loop algorithm to increase force applied to the endless track  16  through the idler wheel  40  when needed. 
     The slip control algorithm embodiment using a track wheel sensor has the steps of:
         1. Receiving a track speed signal V 1  from the track speed sensor  60 ;   2. receiving a wheel speed signal V 2  from the wheel speed sensor  62 ;   3. determining a track slip condition if the track speed signal differs from the wheel speed signal; and   4. sending an actuation signal to the actuator  42  to increase the force applied by the actuator  42  to the endless track  16  if a slip condition is determined.       

     It should be noted that a track slip condition may also be determined using other sources such as, but not limited to, change in location of the vehicle using a Global Positioning System, GPS (not shown). If the wheel speed sensor  62  tracking vehicle speed does not correlate with the GPS system indicating vehicle speed, then the likely reasoning is that the tires  18 , 20  are slipping inside the endless track  16 . In this condition, the tensioning device  22  may exert a greater force on the endless track  16  creating greater friction between the endless track  16  and the tires  18 , 20  allowing the vehicle to achieve greater traction forces bringing the tire velocity in alignment with the vehicle velocity. 
     In yet another embodiment, the slip control processor  64  may be used to monitor when less tension is needed on the endless track  16 , such as when the endless track  16  is in a no-slip condition. Reducing tension on the endless track when unneeded will allow for greater suspension  14  movement, allow for lower wear on the endless track  16  and tires  18 , 20 , and reduce fuel consumption when using the track over tire system on the vehicle  10 . 
     The no-slip condition algorithm embodiment using a track wheel sensor has the steps of:
         1. Receiving a track speed signal V 1  from the track speed sensor  60 ;   2. receiving a wheel speed signal V 2  from the wheel speed sensor  62 ;   3. determining a track no-slip condition if the track speed signal is substantially equivalent to the wheel speed signal; and   4. sending a reduction signal to the actuator  42  to decrease the force applied by the actuator  42  to the endless track  16  if a no-slip condition is determined.       

     In regards to  FIG. 9 , additional embodiments are illustrated via a block diagram flowchart showing a control algorithm using either comparative pressures found within the actuator  42  or comparative forces applied to the endless track  16  by the tensioning device  22 . 
     In the embodiment using comparative forces, a force sensor  66  (represented in block of flow diagram as F) is used in cooperation with the tensioning device  22  to measure the force applied by the tensioning device  22  on the endless track  16 . A slip control processor  64  is electrically connected to the force sensor and the tensioning device  22  such that the slip control processor executes a control loop algorithm to increase vehicle traction, the algorithm having the steps of:
         1. receiving a tensioning device force signal from the force sensor;   2. comparing the force signal to a predetermined operating force range;   3. determining if the force signal is above or below the predetermined operating force range; and   4. sending an increasing actuation signal to the actuator to increase force applied to the endless track by the actuator if the force signal is below the predetermined operating force range, or sending a reduction signal to the actuator to decrease force applied to the endless track by the actuator if the force signal is above the predetermined operating force range.       

     In the embodiment using comparative pressures, a pressure sensor  68  (represented in block flow diagram as P) is used in cooperation with the tensioning device  22  to measure pressure in tensioning devices that use an actuator  42 . In this embodiment, a pneumatic regulator (not shown) may be fluidly connected between the pneumatic port  48  and the vehicle pneumatic system, such that the pneumatic regulator:
         1. receives an actuator pressure reading from the pressure sensor;   2. compares the actuator pressure reading to a predetermined operating pressure range;   3. determines if the actuator pressure reading is above or below the predetermined operating pressure range; and   4. increases pressure inside the actuator through the pneumatic port if the actuator pressure is below the predetermined operating pressure range or decreases pressure inside the actuator if the actuator pressure is above the predetermined operating pressure range.       

     The figures show a track over tire system disposed around a vehicle  10  with a tandem axle set  12  in which there are only two axles  24 , but the track overt tire system is not limited to only two axle designs and may function with vehicles that have multiple axles. In vehicles having multiple axles, the track over tire system cooperates with a front axle having at least one front wheel with a front tire  18 , and a rear axle having at least one rear wheel with a rear tire  20 . The endless track  16  wraps around the front tire  18  and the rear tire  20 . The additional tires associated with the multiple axle set drive over the endless track  16  instead of having direct contact with the ground. The tensioning device  22  in contact with the endless track  16  is attached to the vehicle  10  and disposed between the front tire  18  and the rear tire  20 . 
     The tensioning device  22  may be symmetrically or asymmetrically disposed between the front tire  18  and rear tire  20 . In a symmetrically disposed tensioning device  22  there is an equal distance from the front wheel  18  to the tensioning device  22  as from the rear wheel  20  to the tensioning device  22  when the vehicle is on level ground. In an asymmetrically disposed tensioning device  22 , the tensioning device  22  is placed closer to one tire than the other. Asymmetric designs work well with three axle vehicles for packaging concerns. As well, multiple tensioning devices  22  may be used with the track over tire system for packaging concerns as well as load sharing. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and various changes may be made without departing from the spirit and scope of the invention.