Abstract:
A loader type construction vehicle includes a chassis having a longitudinal axis, a plurality of wheeled ground-engaging structures pivotally coupled to the chassis, and a steering control system. Each of the plurality of ground-engaging structures includes a wheel pivotable about a steering axis and drivable about a drive axis, wherein each of the wheeled ground-engaging structures is shaped and configured so that the wheel of each of the ground-engaging structures can be pivoted from a first angular position in which the drive axis is perpendicular to the longitudinal axis, to a second angular position that is at least 90° degrees from the first angular position. The steering control system is operatively connected to each of the ground engaging structures for pivoting the wheel of each of the ground-engaging structures about the steering axis. The steering system may be operable to selectively configure the ground engaging structures into a plurality of different steering configurations, such as crab steering and side steering. The loader vehicle may include a telescopic loader arm.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional application Ser. No. 60/791,452. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to compact construction vehicles and more particularly to the mobility and working reach of compact loader type construction vehicles. 
       BACKGROUND OF THE INVENTION 
       [0003]    Compact loader type construction vehicles are common and popular vehicles used in the construction industry. One of the most common variations is the compact skid steer loader. 
         [0004]    Skid steer loaders were first developed approximately 30 to 40 years ago to fill the requirement for a highly maneuverable construction vehicle capable of digging, lifting, transporting and loading earth, gravel and other construction materials. Compact skid steer loaders are typically small with a length of approximately 10-12 feet, and a narrower width. 
         [0005]    The most common form of compact skid steer loaders have two fixed length loader arms mounted on the vehicle structure and pivotable in the vertical direction to allow for the lifting and lowering of a variety of work implements connected to the distal end of the loader arms. The most widely recognized work implement is the loader bucket, which allows the vehicle operator to dig, lift, transport and otherwise load any number of different materials, including materials common to construction sites, such as particulate type construction materials (e.g. sand, earth and gravel, etc.). 
         [0006]    While the dual loader arm configuration provides the skid steer loader the ability to dig and load, the extent to which the work implement can be utilized forwardly of the front of the vehicle is limited to the reach afforded by the fixed length loader arms. To accurately position a work implement such as a loader bucket or post-hole auger in the desired work position, the vehicle must be carefully maneuvered into a fairly precise location in order for the work implement to be usable in the desired work position. While in some situations there is adequate room in the work area to easily maneuver the vehicle as needed, in many cases the work area is sufficiently confined that it becomes difficult to maneuver even compact skid steer loaders as needed. 
         [0007]    This problem can be aggravated by the wheel configuration on most skid steer loaders. In their most common form, compact skid steer loaders have two wheels on the left side of the vehicle and two wheels on the right side of the vehicle. For convenience and to provide a common frame of reference, left and right are described from the perspective of an operator who is sitting in the loader and looking forward. The wheels on each of the left and right sides of the vehicle can be driven and controlled independently from the wheels on the other side of the vehicle. 
         [0008]    This independent control of the wheels on each side of the vehicle allows the wheels on each side to turn at different speeds and also in different directions. When all wheels are rotating in the same direction (e.g. in a forward or reverse direction), varying the speed of the wheels on each side of the vehicle allows the vehicle to turn left or right while moving in either a general forward or reverse direction. This allows the vehicle to make relatively smooth and gentle turns without the need for a steering mechanism (such as a rack and pinion or linkage) to actually pivot the front or rear wheels of the vehicle. 
         [0009]    However, turning in this manner is not always desirable for working in a confined work space, as the resulting turning radius can be quite large relative to the size of the vehicle. As a result, it becomes difficult using this type of steering to maneuver the vehicle as desired to properly position the work implement. 
         [0010]    Alternatively, because the wheels on each side of the vehicle are independently driven, the wheels on each side can be rotated in opposite directions relative to each other. For example, the wheels on the right side can be driven in a forward direction while the wheels on the left side can be driven in a rearward or reverse direction. This will result in the vehicle turning in a generally counter-clockwise direction (from the perspective of a person positioned about the vehicle and looking down at the vehicle) about a vertical axis located proximate the center point of the vehicle, effectively turning in place. This as also known as making a “zero radius turn” or “skidding”. This type of steering allows skid steer vehicles to more easily maneuver within some confined spaces on a worksite, and is one of the reasons that skid steer vehicles have become a desired vehicle for construction work. 
         [0011]    However, skid steer vehicles driven in either steering mode still have a number of undesirable characteristics. Most notably, the action of the wheels rotating in opposite directions can impart significant skidding stresses at the interface between the wheels of the vehicle and the ground surface on which the vehicle is moving. These skidding stresses tend to tear the terrain over which the vehicle travels or result in increased wear on the wheels. For instance, when a skid steer vehicle is used on soft surfaces that are common on construction sites (such as grass or muddy fields), the surfaces can quickly become torn up. Any grass or other organic matter contacted by the wheels of a skid steer vehicle tends to be rapidly destroyed. If the vehicle moves repeatedly in one particular area, this can also result in the formation of large ruts caused by the action of the tires. The overall result is a generally undesirable amount of damage to property. 
         [0012]    Furthermore, when used on harder surfaces, such as asphalt or concrete, rotating the wheels in opposite directions or “skidding” of the wheels can cause increased rates of wear to the tires on the vehicle, which can result in poor performance and increased operating costs. 
         [0013]    One further problem presented by conventional skid steer vehicles relates to their performance on uneven terrain. Skid steer vehicles commonly employ four ground-contacting wheels that are rigidly fixed to the vehicle structure. While this provides generally acceptable performance characteristics when the vehicle is used on even ground, when the skid steer vehicle is used on uneven terrain, one wheel of the vehicle tends to lift off the ground and lose traction. This can lead to instability during use of the skid steer, which is dangerous when the operator is using the work implement, and also makes the skid steer loader more difficult to carefully maneuver. Furthermore, this problem tends to aggravate the damage to the terrain since only three of the four drive wheels may be in contact with the ground. 
         [0014]    The ground disturbance problems associated with the use of skid steer vehicles on soft ground, the wear problems associated with their use on hard surfaces and the loss of vehicle traction on uneven terrain tends to limit the use of skid steer vehicles to construction sites and other locations where damage to the ground is permissible and where the terrain is relatively even. Furthermore, the limited reach afforded by the fixed length loader arms has precluded their use where it is difficult or impossible to maneuver the vehicle close enough to the desired work position. 
         [0015]    Therefore, there is a need in the art for a compact and highly maneuverable construction vehicle that is operable on uneven terrain, that reduces damage to the ground and wear to the vehicle tires, and that is capable of providing reach for a work implement to achieve the desired work position. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is directed to a compact loader type construction vehicle comprising a chassis having a longitudinal axis, a plurality of wheeled ground-engaging structures pivotally coupled to the chassis, and a steering control system. Each of the plurality of ground-engaging structures comprises a wheel pivotable about a steering axis and drivable about a drive axis, wherein each of the wheeled ground-engaging structures is shaped and configured so that the wheel of each of the ground-engaging structures can be pivoted from a first angular position in which the drive axis is perpendicular to the longitudinal axis, to a second angular position that is at least 90° degrees from the first angular position. The steering control system is operatively connected to each of the ground-engaging structures for pivoting the wheel of each of the wheeled ground-engaging structures about the steering axis. 
         [0017]    The steering control system is preferably operable to selectively configure the ground-engaging structures into a plurality of different steering configurations and to steer the chassis in each of the plurality of different steering configurations. 
         [0018]    According to one embodiment of the invention, each of the wheeled ground-engaging structures comprises a pivot member pivotally coupled to the chassis for movement about the steering axis, a drive motor having a motor housing rigidly coupled to the pivot member and a drive shaft extending along the drive axis, the drive axis being orthogonal to and pivotable about the steering axis, a hub fixedly coupled to the drive shaft for releasably securing the wheel thereto, and an actuator coupled to the pivot member and to the chassis for pivoting the pivot member about the steering axis. 
         [0019]    The invention is also directed to a loader vehicle including a chassis, a plurality of wheeled ground-engaging structures, a loader arm, a telescopic actuator, and an arm actuator. The plurality of wheeled ground-engaging structures are pivotally coupled to the chassis for supporting and steering the loader vehicle. The telescopic loader arm has a first section secured to and pivotable with respect to the chassis and a second section shaped to receive a work implement, the second section being telescopically movable with respect to the first section. The telescopic actuator is configured for moving the second section with respect to the first section, to retract and extend the second section with respect to the first section along a longitudinal arm axis. The arm actuator is configured for pivoting the loader arm with respect to the vehicle. 
         [0020]    According to one embodiment of the invention there is provided a compact loader type construction vehicle having a chassis with a front end, a rear end, a right side and a left side. On the right side of the vehicle there is a first pair of wheels, each wheel being driven by one of a first pair of hydraulic wheel drive motors. On the left side of the vehicle there is a second pair of wheels, each wheel being driven by one of a second pair of hydraulic wheel drive motors. 
         [0021]    In some embodiments, the vehicle includes a vehicle engine, which can be any suitable engine such as an internal combustion or electric engine. Also attached to the vehicle structure are two hydraulic hydrostatic drive pumps each connected to and driven by the vehicle engine. The first hydraulic hydrostatic pump provides power to propel the first pair hydraulic wheel drive motors to drive the wheels on the right side of the vehicle. The two drive motors on the right side of the vehicle are connected to the hydrostatic pump such that each drive motor will turn each wheel in the same rotational direction when pressure is provided by the corresponding hydrostatic drive pump. Similarly, the second hydraulic hydrostatic pump provides power to propel the second pair of hydraulic wheel drive motors on the left side of the vehicle to drive the wheels on the left side of the vehicle. Similar to the drive motors on the right side, the drive motors on the left side of the vehicle are connected to the second hydraulic hydrostatic pump such that each drive motor will turn each of the second wheels in the same rotational direction when a hydraulic pressure is applied during use. 
         [0022]    In some embodiments, the chassis of the vehicle is coupled to and supported by the four wheels via steerable ground-engaging structures coupled to the four hydraulic wheel drive motors. As discussed in further detail below, the front left and rear left hydraulic wheel drive motors are attached to steerable ground-engaging structures located on the left side of the vehicle. Similarly, the front right and rear right hydraulic wheel drive motors are attached to steerable ground-engaging structures located on the right side of the vehicle. 
         [0023]    In one embodiment, each steerable ground-engaging structure is coupled to at least one hydraulic actuator that can be used to rotate the steerable ground-engaging structure about a pivot axis to provide a predetermined amount of rotation. In one exemplary embodiment, each steerable ground-engaging portion can be rotated about its pivot axis at least 135 degrees of rotation in total. In another embodiments, each steerable ground-engaging portion can be rotated about its pivot axis at least 90 degrees of rotation. In this manner, the wheels of the vehicle can be configured in a number of different steering configurations to provide the vehicle with the desired level of mobility and steering characteristics when in use at a worksite. 
         [0024]    In some embodiments, each steerable ground-engaging structure also generally has at least one electronic feedback sensor, which can be coupled to the hydraulic actuators, and which provides information such as position information about the angular position of the ground-engaging structure. 
         [0025]    According to some embodiments, during use, the hydraulic actuators are coupled to each ground engaging-structure and can be controlled by an operator using control devices, such as a joystick, an operator steering mode switch or other input devices. The control devices function in cooperation with an electronic microcontroller containing steering algorithms, which receives feedback from the electronic feedback sensors and controls at least one hydraulic steering control valve to adjust the steering configuration of the vehicle. The electronic microcontroller is used to rotationally position each of the four ground-engaging structures by adjusting each of the four hydraulic actuators according to desired operator input. The four electronic feedback sensors can transmit information about the angular position of each of the four ground-engaging structures back to the electronic microcontroller, providing a feedback control loop. 
         [0026]    In some embodiments, the control system can also continually monitor the operator&#39;s control inputs, including desired steering position and steering mode, and compare these inputs against the angular rotational position of each ground-engaging structure to ensure each wheel is in the desired steering position. In some embodiments, the control system can also collect information from the sensors to monitor velocity and acceleration of the hydraulic actuators and ground engaging structures to ensure that desired vehicle operating characteristics are being met. 
         [0027]    In some embodiments, the ground-engaging structures located on the front right and front left of the vehicle are coupled to the vehicle chassis in a rigid manner without any shocks or suspension system. This rigid configuration tends to provide improved stability of the vehicle when the vehicle is subjected to uneven loads. In other embodiments, the ground engaging structures can be coupled to the vehicle chassis by a suspension system, which may include a passive or active spring-damper suspension apparatus, which may provide the operator with a smoother ride and finer control over the vehicle operation, particularly when in use on uneven terrain. 
         [0028]    In some embodiments, the distance between the steering pivot points (e.g. the axis about which each of the ground-engaging structures pivots) on the front right and front left ground-engaging structures has been maximized within the limits of the vehicle size in order to further enhance vehicle stability. 
         [0029]    In some embodiments, the ground-engaging structures located on the rear of the vehicle are mounted to and pivotable about a single rear assembly comprising a rear transverse frame member that defines a transverse axis. The rear assembly is then pivotally mounted on the vehicle chassis about a single pivot point such that the entire rear assembly can pivot with respect to the vehicle chassis. The single pivot point is preferably located rearwardly of the vehicle and proximate the middle of the vehicle chassis. The corresponding pivot point on the rear assembly is generally located in the middle of the rear assembly. 
         [0030]    According to some embodiments, during use, the rear assembly can pivot with respect to the vehicle pivot point when the vehicle is traveling over uneven terrain, which helps to keep the wheels on the rear of the vehicle in constant contact with the ground. This tends to provide improved traction and stability when compared to prior art skid steer loaders because all four wheels on the vehicle tend to stay in contact with the terrain, even when the vehicle travels over uneven terrain. During operation of the skid steer vehicle, the speed and direction of the hydraulic wheel drive motors on the left side of the vehicle and on the right side of the vehicle are independent, but can preferably be easily controlled by the operator using the control devices, including the joystick and an operator steering mode switch. The inputs from the operator are provided to the electronic microcontroller, which contains a propulsion algorithm and controls the hydraulic hydrostatic pumps accordingly. 
         [0031]    In some embodiments, the electronic microcontroller will provide the operator with the ability to select a variety of different steering modes or configurations. Within each distinct steering mode, the operator will have the ability to manipulate the pivotal position of each of the wheels within a predetermined pivotal range through the use of the control devices, including the joystick. 
         [0032]    In some embodiments, the range of movement of the ground-engaging structures will be determined by the direction and angle of movement of the electronic joystick and the steering mode selected by the operator. The electronic joystick will also allow the vehicle operator to proportionally change the rotation drive speed and direction of rotation of each hydraulic wheel drive motor, within a predetermined range set by the electronic microcontroller, in order to obtained the desired maneuvering characteristics. 
         [0033]    In some embodiments, the vehicle also includes a loading arm that includes two relative telescoping sections. The first section of the loading arm is mounted pivotally on the chassis using a pivot mount, and configured for pivotal rotation in a vertical direction with respect to the ground surface. The pivot mount is generally located towards the rear of the vehicle chassis, preferably above the rear wheels. 
         [0034]    In some embodiments, the first section of loading arm includes a curved portion permitting the telescopic loading arm to reach below the ground contact surface of wheels for use in digging or other operations. 
         [0035]    In some embodiments, the second section of loading arm is coupled to the first section and is generally movable with respect to the first section. In some embodiments, the second section fits over the first section such that the first and second section can telescope relative to each other. The telescopic movement is effected by a hydraulic cylinder or other telescopic actuator which can be located internally of the telescopic boom arm assembly. In such embodiments, the second portion can be extended or retracted according to inputs from the operator. 
         [0036]    In other embodiments, the second section can be coupled to the first section in any number of other suitable manners. For example, the second portion could be pivotally coupled to the first section such that it is pivotable with respect to the first section in one or more of a horizontal or vertical direction. At the distal end of loading arm (furthermost from the chassis) is a support structure that is mounted on the second section of the loading arm. In some embodiments, the support structure is pivotally coupled to the second section of the loading arm, while in other embodiments the support structure is rigidly coupled to the second section. The support structure preferably includes a tool supporting structure allowing for the connection of work implements, such as loader buckets, pallet forks, excavator buckets and other implements, to the loading arm. 
         [0037]    Further aspects and advantages of the embodiments described herein will appear from the following description taken together with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment, and in which: 
           [0039]      FIG. 1  is a perspective view from the front and right side of a vehicle made in accordance with an embodiment of the invention; 
           [0040]      FIG. 2  is a perspective view of the vehicle of  FIG. 1  showing the chassis with the wheels and body removed; 
           [0041]      FIG. 2A  is a close-up perspective view of a front ground engaging structure on the vehicle of  FIG. 1 ; 
           [0042]      FIG. 3  is a perspective view of the vehicle of  FIG. 1  showing the chassis with wheels mounted thereon for movement in a forward and reverse direction; 
           [0043]      FIG. 4  is a perspective view of a rear transverse frame member and rear ground-engaging structure of the invention; 
           [0044]      FIG. 4A  is a close-up perspective view of a portion of the right-rear ground-engaging structure of  FIG. 4 ; 
           [0045]      FIG. 5  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a rear wheel steering condition; 
           [0046]      FIG. 6  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a front wheel steering condition; 
           [0047]      FIG. 7  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in an all-wheel steering condition; 
           [0048]      FIG. 8  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a crab steering condition; 
           [0049]      FIG. 9  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a counter rotating steering condition; 
           [0050]      FIG. 10  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a side steering condition; 
           [0051]      FIG. 11  is a perspective view of the vehicle of  FIG. 1  showing the vehicle in a second all-wheel steering condition; 
           [0052]      FIG. 12  is schematic illustrating steering and propulsion control systems for use with the vehicle of  FIG. 1  in accordance with one embodiment; and 
           [0053]      FIG. 13  is a side elevation view of the vehicle of  FIG. 1  showing the loader arm in an extended and a retracted position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0054]    It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements or steps. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Furthermore, this description is not to be considered as limiting the scope of the embodiments described herein in any way, but rather as merely describing the implementation of the various embodiments described herein. 
         [0055]    Referring now to  FIGS. 1 to 4A  generally, illustrated therein is compact loading vehicle  10  made in accordance with one embodiment of the present invention. For ease of reference, there are also shown axes M which are not part of the vehicle  10  but which simply serve as a tool for more clearly describing the structure and operation of the vehicle  10 . The axes M include an x-axis, a y-axis and a z-axis, indicated in the positive direction by the direction of the arrows as shown. For consistency, the term “forward” as used herein generally refers to the direction of the positive x-axis of axes M, while the terms “rear”, “reverse” and “rearward” generally refers to the direction of the negative x-axis of axes M. Similarly, the term “right side” generally refers to the direction of the positive y-axis of axes M, while the term “left side” generally refers to the direction the negative y-axis of the axes M. 
         [0056]    Vehicle  10  generally includes a chassis  12  on which there is provided an operator&#39;s compartment  14  in which an operator Q is shown seated. The compartment  14  is positioned forwardly and to left side of the chassis  12  from the perspective of the operator Q as seated in the compartment  14 . The chassis  12  is supported by a front right wheeled ground-engaging structure  16 , a front left wheeled ground-engaging structure  18  and rear wheeled ground-engaging structures  20  (including pivoting members  54 ,  56 ), as will be described in greater detail below. To the rear of the operator&#39;s compartment  14  and extending across the vehicle chassis  12  is a bonnet structure  22  which houses a vehicle engine  24  for powering the vehicle  10 . The bonnet structure  22  is connected to a cowling  22   a,  which can be a metallic mesh structure or other suitable cover, and is configured to prevent unauthorized access to the vehicle engine  24  and to protect the operator Q and others from the moving parts of the engine  24  when the vehicle  10  is in use. 
         [0057]    The vehicle  10  also generally includes a body  23  designed to protect the operator Q from exposure to flying debris during use by acting as a shield between the operator Q and the chassis  12 . The body  23  can be one continuous piece or alternatively can include a number of different panel members, and the body  23  can be made of any suitable material such as a metal or strong plastic. 
         [0058]    Referring now specifically to  FIG. 2 , there is provided first and second hydrostatic hydraulic pumps  26  and  28  connected to, and driven by, the vehicle engine  24 . Also shown in  FIG. 2  are right-side hydraulic wheel drive motors  30 ,  32  which are in fluid communication with the first hydrostatic hydraulic pump  26  and left-side hydraulic wheel drives  34 ,  36  which are in fluid communication with the second hydrostatic hydraulic pump  28 . 
         [0059]    During use, the first hydrostatic pump  26  provides hydraulic power for the right-side drive motors  30  and  32  that are located on the right side of the vehicle  10 . Hydrostatic pump  26  has the ability to provide oil flow in two directions such that hydraulic wheel drive motors  30  and  32  can be rotated in either a clockwise direction or a counterclockwise direction based on the desired direction of vehicle travel. In some embodiments, both hydraulic wheel drive motors  30  and  32  will rotate in the same clockwise or counterclockwise direction during use. 
         [0060]    Similarly, the second hydrostatic pump  28  provides hydraulic power for the left-side hydraulic wheel drive motors  34  and  36  located on the left side of the vehicle. Hydrostatic pump  28  has the ability to provide oil flow such that the left-side drive motors  34  and  36  rotate in either a clockwise direction or counterclockwise direction, according to the desired direction of vehicle travel. In one embodiment, both hydraulic wheel drive motors  34  and  36  will rotate in the same clockwise or counterclockwise direction during use. 
         [0061]    Referring now to  FIG. 2A , the front right wheeled ground-engaging structure  16  is shown in greater detail and generally includes pivot member  15  having an inverted L-shape as defined by an upper arm portion  15   a  being generally horizontal and a lower arm portion  17  being generally vertical and extending downwards from the upper arm portion  15   a.  The lower arm portion  17  is coupled to and supports the drive motor  32 . The drive motor  32  includes motor housing  32   a  rigidly coupled to lower arm portion  17 , and a drive shaft  32   b  extending along a drive axis U, which is orthogonal to steering axis B. Hub portion  33  is fixedly coupled to the drive shaft  32   b.  Wheel  16   a  is releasably secured to the hub portion  33  during use, as shown for example in  FIG. 3 . 
         [0062]    The upper arm portion  15   a  is coupled to and rotatable with respect to a fixed tubular member  19 , which is generally cylindrical in shape and has an opening  19   a  for receiving a shaft affixed to the upper arm portion  15   a.  Tubular member  19  is rigidly coupled to a front transverse frame member  21 , preferably by welding. As best shown in  FIG. 2 , the front transverse frame member  21  connects the front right ground-engaging structure  16  to the front left ground-engaging structure  18  and to longitudinal frame members  25  and  27  that run along the longitudinal axis L of the chassis  12 . 
         [0063]    During use, the front right ground-engaging portion  16  is steered by the operation of a hydraulic actuator  38 , the first end  38   a  of the actuator  38  being coupled to the front transverse frame member  21  at point P 1 . The other end  38   b  of the hydraulic actuator  38  is coupled to a first end  40   a  of a first link member  40  (or first steering structure member). The first link member  40  is pivotally connected at a second end  40   b  to the front transverse frame member  21  at point P 2 . The first link member  40  and hydraulic actuator  38  are also pivotally coupled to a first end  42   a  of a second link member  42  (or second steering structure member). In turn, the second link member  42  is pivotally coupled at a second end  42   b  to a first end  43   a  third link member  43 , the other end of which is rigidly secured to the upper arm portion  15   a  of the front right ground-engaging portion  16 . The third link member  43  can be rigidly coupled to the upper arm portion  15   a  in any suitable fashion, such as by welding or bolting. As described in more detail below, as the hydraulic actuator  38  retracts and extends, it causes the front right ground-engaging structure  16  to rotate about a steering axis B, which is an axis that is generally vertical with respect to the ground surface. The pivoting of ground-engaging structure  16  results in drive axis V pivoting about steering axis B. 
         [0064]    Similar to the right side wheeled ground-engaging structure  16 , and as shown in  FIG. 2 , the left-side wheeled ground-engaging structure  18  includes pivot member  37  mounted to the front left side of the front transverse member  21  of the vehicle chassis. Pivot member  37  has an inverted L-shape, and includes an upper arm portion  37   a  that is generally horizontal and a lower arm portion  39  which extends vertically downwards from the upper arm portion  37   a  and carries the drive motor  36  having a drive shaft extending along drive axis R, which is orthogonal to and pivotable about steering axis A. The upper arm portion  37   a  is pivotably coupled to fixed tubular member  19   a,  which is rigidly coupled to the front transverse frame member  21 . 
         [0065]    The left-side ground-engaging structure  18  is pivotable about steering axis A, which is an axis generally vertical with respect to the ground surface. Pivoting of the ground-engaging structure  18  is effected by hydraulic actuator  46 , which is coupled at a first end  46   a  to the front transverse frame member  21  at point P 2 , and at a second end  46   b  to a first link  48  (as shown in  FIG. 2 ). The first link  48  is also pivotally coupled to the front transverse frame member  21 , and is connected to the hydraulic actuator  46  and a second link  50 . Second link  50  is pivotally connected to a third link member  51 , which is rigidly coupled to the upper arm portion  37   a  of the ground-engaging structure  18 . 
         [0066]    The lateral distance along the front transverse member  21  between the steering axis B for ground-engaging structure  16  and the steering axis A for ground-engaging structure  18  is preferably maximized within the limits of the vehicle structure to enhance lateral vehicle stability when lifting uneven loads or when the vehicle  10  is traveling over uneven terrain. 
         [0067]    Referring now specifically to  FIG. 3 , the chassis  12  of the vehicle  10  is shown with the body  23  removed but with the wheels  16   a,    18   a,    20   a,    20   b  attached in a forward steering configuration with the wheels  16   a,    18   a,    20   a,    20   b  being pivot to rotate in a forward and rearward direction (generally parallel to the x-axis and running along the longitudinal axis of the chassis  12 ).  FIG. 3  clearly shows that the steering axes A and B lie substantially within the wheels  16   a,    18   a,  which is provided by the upper arm portions  15   a,    37   a  overhanging the wheels  16   a,    18   a  respectively. By placing the pivot axis in line with the front wheels  16   a,    18   a,  with the upper arm portions  15   a,    37   a  overhanging, the front wheels  16   a,    18   a  can be pivoted to significant degrees of angular rotation without interfering with the front transverse member  21 . 
         [0068]    Turning now to  FIGS. 4 and 4A , the rear wheeled ground-engaging structures  20  of the vehicle  10  shown in greater detail. The ground-engaging structures  20  comprise pivot members  54  and  56 , which are pivotally coupled to a rear transverse frame member  29 , the pivot members  54 ,  56  supporting two rear wheels  20   a  and  20   b.    
         [0069]    The rear transverse frame member  29  is pivotally coupled to frame member  35  by member pivot mount  33  and pivot mount  41  positioned beneath a frame member  35  on the chassis  12  (as shown in  FIG. 3 ). The rear transverse frame member  29  generally includes a first straight portion  31   a  that defines a rear transverse axis T (as shown in  FIG. 4 ), a right curved end  31   b,  and a left curved end  31   c.  The curved ends  31   b,    31   c  allow the steering or pivoting axes C, D of the rear wheels  20   a,    20   b  to be longitudinally offset from the transverse axis T and straight portion  31  a such that the wheels  20   a,    20   b  will not interfere with the rear transverse frame member  29  during pivoting. 
         [0070]    As shown in  FIG. 4A , the rear transverse frame member  29  has a generally I-shaped cross section, with an upper plate  31   d  and a lower plate  31   e  separated by a web member  31   f.    
         [0071]    The interoperability between the pivot mounts  33  and  41  allows the rear transverse frame member  29  to be pivotally mounted to the vehicle chassis  12  such that the rear frame member  29  can pivot about rotational axis H (as shown in  FIG. 4 ) with respect to the vehicle chassis  12  in response to changes in ground elevation during operation of the vehicle  10 . The pivoting tends to keep the rear wheels  20   a,    20   b  in better contact with the ground surface, particularly on uneven terrain. 
         [0072]    The corresponding pivot point  41  on the frame member  35  of the chassis  12  is generally located to the center and the rear of the vehicle chassis  12 . 
         [0073]    As best shown in  FIG. 4A , the pivot member  54  generally has a C-shaped profile as defined by an upper plate member  55  and a lower plate member  57  that is generally parallel and spaced apart from the upper plate member  55 . The lower plate member  57  and the upper plate member  55  are joined by a connecting plate member  59  that is perpendicular and is secured at ends  55   a,    57   a  of the upper plate  55  and lower plate  57  proximate the wheel  20   a.  Although not shown in the figures, a corresponding connecting plate member is also provided towards a rear end  55   b  of the upper plate  55  and a rear end (not visible) of the lower plate  57 . 
         [0074]    As best shown in  FIG. 2 , the drive motor  30  on the rear pivot member  54  includes a motor housing  36   a  rigidly coupled to the pivot assembly  54 , and a drive shaft (not shown) extending along drive axis W, which is orthogonal to steering axis C. Hub portion  45  is fixedly coupled to the drive shaft for releasably securing the wheel  20   a  to the drive motor  30 . Steering axis C is generally vertical with respect to the ground surface, and passes through a lower plate member  57  of the pivot member  54 . 
         [0075]    During use, wheel  20   a  and pivot member  54  can be pivoted about steering axis C by movement of hydraulic actuator  58 , which is coupled at a first end  58   a  to the rear transverse frame member  29  at point P 3  (as shown in  FIG. 4 ). The other end  58   b  of the hydraulic actuator  58  is coupled to a link member  61  that is rigidly coupled to the connecting plate member  59 . As the hydraulic actuator  58  retracts and expands, it causes a corresponding movement in the pivot member  54  about the steering axis C, which results in drive axis W pivoting about steering axis C. The angular position of the pivot member  54  and wheel  20   a  can be measured by an electronic feedback sensor  60 , which can be located at any suitable location such as internally of hydraulic actuator  58 . 
         [0076]    Similar to the right side, pivot member  56  generally has a C-shaped profile. The wheel  20   b  and pivot member  56  of the left side can be pivoted with respect to the rear transverse frame member  31  by hydraulic actuator  62 , which results in drive axis V pivoting about steering axis D. Hydraulic actuator  62  is pivotally coupled at a first end  62   a  to the transverse frame member at point P 4  and at a second end  62   b  to a second link arm  63 , which is rigidly coupled to the left side pivot member  56 . The angular position of pivot member  56  and wheel  20   b  can be measured by an electronic feedback sensor  64 , which can be located at any suitable location such as internally of hydraulic actuator  62 . 
         [0077]    As best shown in  FIG. 4 , hydraulic actuators  58  and  62  are mounted within the rear transverse frame member  29  in a generally crossed configuration to make the rear transverse frame member  29  fairly compact. 
         [0078]    Referring now to  FIGS. 1 and 13 , vehicle  10  may comprise a loading arm  66  that includes two sections, a first section  68  and a second section  70 . In some embodiments, the first section  68  and the second section  70  are telescopic with respect to each other, such as by having the second section  70  be slightly larger that the first section  68  and configured to fit over the first section  68 . The loading arm  66  extends longitudinal along the longitudinal axis L of the vehicle  10 , generally parallel to the longitudinal frame member  25  and  27  towards the front of the vehicle, running alongside the operator&#39;s compartment  14 . 
         [0079]    In some embodiments, the first section  68  and second section  70  each have hollow interiors. The hollow interior of the second section  70  is shaped to receive the straight portion of the first section  68 . 
         [0080]    In some embodiments, the second section  70  of the loading arm  66  fits over the first section  68  and can be moved telescopically along the longitudinal axis of the arm  66  (extending and retracting) by one or more telescopic actuators  74  located within the hollow interior of the arm  66 . Actuators  74  can be any suitable type actuator, such as a hydraulic or electric actuator. 
         [0081]    The first section  68  of loading arm  66  is mounted pivotally on the vehicle chassis  12  at a pivot mount  67  for vertical pivoting movement with respect to the ground surface about a generally horizontal axis E, as effected by one or more actuators  72 . Pivot mount  67  is generally located towards the rear of the vehicle  10  and is preferably mounted above and slightly to the rear of the rear wheels  20   a  and  20   b.  Actuator  72  is pivotally connected at a first end  72  to the first section  68  a point P 5  and at a second end  72   b  to the chassis  12  at point P 6 , as best shown in  FIG. 13 . 
         [0082]    In some embodiments, the first section  68  of loading arm  66  includes a curved portion  68   a  as best shown in  FIG. 13  that permits the telescopic loading arm  66  to be angled generally downwards to reach below the ground contact surface S of wheels  16   a  and  18   a.    
         [0083]    At a distal end  66   a  of loading arm  66  (furthermost from the vehicle chassis  12 ) there is provided a support structure  76  that is pivotally mounted to loading arm  66  about a generally horizontal axis F for vertical movement of the structure  76  effected by one or more actuators  78 . 
         [0084]    At a distal end  76   a  of support structure  76  (furthermost from axis of rotation F) there is provided a work implement  80  such as an excavating bucket or loading bucket, which can be releasably connected to the support structure and which is pivotal about axis of rotation G for vertical movement of the work implement  80  by actuator  82 . 
         [0085]    In some embodiments, elements of the loading arm  66  such as the first section  68 , the second section  70 , the support structure  76  and the work implement  80  can be pivotable about an axis of rotation for horizontal movement with respect to the ground surface S to provide improved mobility of the excavating tool  80 . 
         [0086]    Referring now to  FIGS. 2 and 5  to  11  generally, the chassis  12  of the vehicle  10  is shown in various different steering configurations. As discussed above, to achieve the different steering configurations, the wheels  16   a,    18   a,    20   a,    20   b  are generally pivotable about the steering axes B, A, C, D respectively. This allows the wheels  16   a,    18   a,    20   a,    20   b  to be oriented in various different directions to achieve the desired steering configurations and provide a desired level of mobility to the vehicle  10  during use. 
         [0087]    For example, as shown in  FIG. 6  the front right ground-engaging structure  16  can be rotated pivotally about the vertical axis B. The rotation can be measured by angle  01 , defined as the angle swept by the ground-engaging structure  16  as it rotates from an origin located at axis B running in the negative x-direction, looking down at the vehicle  10  from above. For consistency, θ 1  is defined as being positive in the counter-clockwise direction and negative in the clockwise direction. 
         [0088]    According to some embodiments, the front right ground-engaging structure  16  can be pivoted by the hydraulic actuator  38  clockwise such that θ 1  can reach −30 degrees, and counterclockwise such that θ 1  can reach +105 degrees. The ability to pivot to this extent is provided by the specific shape and configuration of the ground-engaging structure  16 , which allows the wheel  16   a  to pivot without interference from any structural members. 
         [0089]    The angle θ 1  of rotation of the ground-engaging structure  16  can be measured by an electronic feedback sensor  44 , which can be located internally of hydraulic actuator  38  or at any other suitable location. 
         [0090]    Similarly, and again as shown in  FIG. 6 , the left front ground-engaging structure  18  can be rotated pivotally about axis A, and measured by angle θ 2  with reference to a second origin located at the axis A and being parallel to the first origin. For consistency, θ 2  is defined as being positive in the counter-clockwise direction and negative in the clockwise direction. 
         [0091]    The left side ground-engaging structure  18  can be pivoted counterclockwise such that θ 2  can reach +30 degrees and clockwise such that θ 2  can reach −105 degrees. The angle θ 2  of rotation of the ground engaging structure  18  can be measure by electronic feedback sensor  52  which can be located internally of hydraulic actuator  46  or at any other suitable location. 
         [0092]    In this manner both the front wheels  16   a,    18   a  can be independently pivoted by a significant amount (up to 135 degrees total) to provide the various steering configurations as described in detail below. As shown in  FIG. 6 , the wheels  16   a,    18   a  have been pivoted in the same direction such that θ 1  and θ 2  are about 30 degrees in the counter-clockwise direction. 
         [0093]    In some embodiments, as described above, the ground-engaging structure  16 ,  18  are pivotable in an asymmetric manner such that they can pivot in one angular direction more than they can pivot in the other direction. It will be appreciated that the amount of angular rotation that is possible and the asymmetry achieved is generally dictated by the geometry of the linkages  40 ,  42 ,  43 ,  48 ,  50 ,  51  cooperating with the actuators  38 ,  46 . As described below, as the steering control system is able to independently control the pivoting and rotation of each wheel  16   a,    18   a,  it is generally not required that the wheels  16   a,    18   a  be pivotable in a symmetric fashion. What is generally desirable is that the wheels  16   a,    18   a  be pivotable in at least one direction up to at least 90 degrees. This will allow the wheels  16   a,    18   a  to be configured in a side steering configuration, as well as other steering configurations, and provide the desired vehicle  10  mobility. 
         [0094]    In some embodiments, the rear wheels  20   a,    20   b  of the vehicle  10  are similarly pivotable. For example, and as shown in  FIGS. 2 and 5 , the right side rear pivot member  54  can generally be rotated by angle θ 3  as measured from a third origin located at steering axis C and running in the negative x-direction. For consistency, θ 3  is defined as being positive in the counter-clockwise direction and negative in the clockwise direction. The rear pivot member  54  can be pivoted clockwise such θ 3  can reach −50 degrees, and counterclockwise such that θ 3  can reach +105 degrees about steering axis C. 
         [0095]    Similarly, as shown in  FIG. 5 , left side rear pivot member  56  can generally be rotated by angle θ 4  as measured from a fourth origin located at steering axis D and running in the negative x-direction. For consistency, θ 4  is defined as being positive in the counter-clockwise direction and negative in the clockwise direction. Rear pivot member  56  can be pivoted counter-clockwise such that θ 4  can reach +50 degrees, and clockwise such that θ 4  can reach −105 degrees about axis D. 
         [0096]    In this manner, the wheels  16   a,    18   a,    20   a,    20   b  can be pivoted about their respective steering axes B, A, C, D to provide the vehicle  10  with many different possible steering configurations. For example, the wheels  16   a,    18   a,    20   a,    20   b  can be pivoted to provide the vehicle with the following exemplary steering configurations: 
         [0097]    (1) Rear Wheel Steering, as shown in  FIG. 5 . Rear wheel steering can be provided by pivoting both rear pivot members  54 ,  56  such that θ 3  and θ 4  can be up to ±30 degrees in the same direction (either the clockwise direction, as shown in  FIG. 5 , or the counterclockwise direction. This configuration of the rear wheels  20   a,    20   b  provides rear wheel steering for the vehicle  10 , while the front wheels  16   a,    18   a  are kept parallel to the longitudinal axis L of the vehicle  10  (such that the drive axes of the wheels  16   a,    18   a  are perpendicular to the longitudinal axis L), allowing the vehicle  10  to turn in either a clockwise or counter-clockwise direction while moving the vehicle  10  in either a forward or reverse direction. 
         [0098]    (2) Front Wheel Steering, as shown in  FIG. 6 . Front wheel steering can be provided by pivoting both front ground engaging structures  16 ,  18  such that θ 1  and θ 2  can be up to ±30 degrees in the same direction (either the counter-clockwise direction, as shown in  FIG. 6 , or the clockwise direction). This allows wheels  16   a,    18   a  to provide front wheel steering, while the rear wheels  20   a,    20   b  are kept parallel to the longitudinal axis L of the vehicle  10  (such that the drive axes of the wheels  20   a,    20   b  are perpendicular to the longitudinal axis L), allowing the vehicle  10  to turn in either the clockwise or counter-clockwise directions generally when the vehicle  10  is moving in either the forward or reverse directions. 
         [0099]    (3) All Wheel Steering, as shown in  FIG. 7 . All wheel steering can be provided by pivoting both rear pivot members  54 ,  56  such that θ 3  and θ 4  are up to ±30 degrees in the same direction (either the clockwise direction, as shown in  FIG. 7 , or the counterclockwise direction), while simultaneously pivoting both front ground engaging assemblies  16 ,  18  such that θ 1  and θ 2  are up to ±30 degrees in a direction which is opposite the angular direction of the rear pivot members  54 ,  56  (either in the counter-clockwise direction, as shown in  FIG. 7 , or the clockwise direction. 
         [0100]    (4) Crab Steering, as shown in  FIG. 8 . Crab steering can be provided by pivoting both rear pivot members  54 ,  56  such that θ 3  and θ 4  are up to ±30 degrees in same direction (either the clockwise direction, as shown in  FIG. 8 , or the counterclockwise direction), while simultaneously rotating both front ground engaging structures  16 ,  18  such that θ 1  and θ 2  are up to ±30 degrees in the same angular direction as the rear pivot members  54 ,  56  (either in the clockwise direction, as shown in  FIG. 8 , or the counter-clockwise direction). As shown in  FIG. 8 , this configuration provides “crab” steering somewhat to the right when the vehicle  10  is moving in the forward direction, and to the left when the vehicle  10  is moving in the reverse direction. 
         [0101]    (5) Zero Turning Radius Steering, as shown in  FIG. 9 . Zero turning radius steering can be achieved by rotating the front right ground-engaging structure  16  and rear left pivot member  56  counter clockwise such that θ 1  and θ 4  are approximately +45 degrees, and rotating the front left ground engaging structure  18  and rear right pivot assembly  54  clockwise such that θ 2  and θ 3  are approximately −45 degrees. This steering configuration allows the vehicle  10  to counter-rotate about the approximate center point of the chassis  12  in either the clockwise or counter-clockwise directions, as shown in  FIG. 9 . 
         [0102]    (6) Side Steering, as shown in  FIG. 10 . The vehicle can be caused to side steer by rotating the front right ground engaging structure  16  and rear right pivot member  54  counter-clockwise such that θ 1  and θ 3  are substantially +90 degrees (such that the drive axes of the wheels  16   a,    20   a  is parallel to the longitudinal axis L), and rotating the front left ground engaging structure  18  and rear left pivot member  56  clockwise such that θ 2  and θ 4  are substantially −90 degrees (such that the drive axes of the wheels  18   a,    20   b  is also parallel to the longitudinal axis L). This steering configuration will align the wheels  16   a,    18   a,    20   a,    20   b  in generally the same direction perpendicular to the normal alignment shown for example in  FIG. 3 . This steering configuration allows the vehicle  10  to drive in a straight-line direction towards the left or right side of the vehicle  10 , as shown in  FIG. 10 . 
         [0103]    (7) All Wheel Side Steering, as shown in  FIG. 11 . Similar to the all wheel steering shown in  FIG. 7 , all wheel side steering can be provided by rotating the front right ground-engaging structure  16  and rear right pivot member  54  such that θ 1  and θ 3  are between +75 degrees and +90 degrees, and rotating the front left ground engaging structure  18  and the rear left pivot member  56  such that θ 2  and θ 4  are between −75 degrees and −90 degrees. This will allow the vehicle  10  to move towards either the left or the right side of the vehicle  10 , steering in a rearward arc, as shown in  FIG. 11 . 
         [0104]    Alternatively, rotating the front right ground-engaging structure  16  and rear right pivot member  54  such that θ 1  and θ 3  are between +90 degrees and +105 degrees, and rotating the front left ground-engaging assembly  18  and the rear left pivot member  56  such that θ 2  and θ 4  are between −90 degrees and −105 degrees will allow the vehicle  10  to move towards the right side or the left side of the vehicle  10  and steer in a forward arc (not shown). 
         [0105]    Referring now to  FIG. 12 , the vehicle  10  is generally controlled by a control system  100 , which controls the drive pumps and steering system. According to an embodiment, the control system includes an electronic microcontroller  102  that contains steering and drive algorithms  104 , which can be stored in a memory (not shown) or other suitable device. During use of the vehicle  10 , the operator Q can select from a variety of steering configurations, such as the various steering configurations described above, using an input device such as the mode selection position switch  108 , which is coupled to the microcontroller  102 . Based on the selection of the operator Q, the mode selection position switch  108  sends a signal to the microcontroller. 
         [0106]    Within each distinct steering configuration, for example the exemplary steering modes described above, the operator Q will have the ability to adjust the pivotable position of the steerable wheels  16   a,    18   a,    20   a,    20   b  and the rotational speed and direction of the wheel drive motors  30 ,  32 ,  34 ,  36  through the movement of a steer/drive joystick  106  in order to obtain the desired movement of the vehicle  10 . 
         [0107]    The signal from the joystick  106  will be sent as a steering and propulsion input to the electronic microcontroller  102 . Based on the position of the operator joystick  106 , the electronic microcontroller  102  will then output an electronic signal to each of the hydrostatic pumps  26 ,  28  for driving the wheels  16   a,    18   a,    20   a,    20   b  in forward or reverse drive directions. The microcontroller  102  will also send a control signal to the steering control valve  110 . The steering control valve  110  in turn controls the hydraulic actuators  38 ,  46 ,  58 ,  62  for effecting clockwise and/or counterclockwise pivoting of the pivot members  15 ,  37 ,  54 ,  56  of the ground-engaging structures  16 ,  18 ,  20  to achieve the desired steering configuration. 
         [0108]    The steerable pivot members  15 ,  37 ,  54 ,  56  will pivot in the required direction according to commands provided to the steering control valve  110  by the electronic controller  102 . The rotational position of each pivot member  15 ,  37 ,  54 ,  56  will be provided back to the microcontroller  102  by the steer angle sensors  44 ,  52 ,  60 ,  64 . The signal from each steer angle sensor  44 ,  52 ,  60 ,  64  will used to continually monitor the rotational position of each pivot members  15 ,  37 ,  54 ,  56  with relation to the steer angle on the joystick input device  106 . The electronic microcontroller  1 θ 2  will then pivot each pivot member  15 ,  37 ,  54 ,  56  to ensure that each wheel  16   a,    18   a,    20   a,    20   b  is in the correct rotational position based on the joystick input device  106  and the mode selected by the steering mode switch  104 . 
         [0109]    While the above description includes a number of exemplary embodiments, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes.