Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/269,157 filed Dec. 18, 2015. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a dig system for a four-wheel drive vehicle, which allows the vehicle to maneuver a turn or change direction by performing a front dig maneuver or a reverse dig maneuver. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are many different types of vehicles which are taken off-roading for recreational use. Many of these vehicles have various features to prevent the vehicle from being limited in off-road travel, and increase capability to maneuver through difficult terrain. 
         [0004]    Some vehicles are manufactured specifically for the purpose of off-road driving, while some vehicle owners make modifications to their vehicle to improve the vehicle&#39;s off-road capability. On some off-road trails, it may difficult to maneuver exceedingly tight turns. The width and accessibility of various off-road trails is often very different when compared to a two-lane road. Some turns and other maneuvers require the use of the reverse gear and one or more forward gears such that the vehicle is moved forward and reverse several times to change the position of the vehicle, and thereby allowing the vehicle to continue onward through the trail. Many off-road enthusiasts do not prefer to maneuver through trails in this manner, but prefer to have a vehicle with increased maneuverability. To avoid changing between the forward gears and the reverse gear several times when performing a turning maneuver, some owners of off-road vehicles modify their vehicles such that the vehicle may turn and change position without the use of the reverse gear, essentially performing a maneuver referred to as a “front dig.” If the proper modifications are made, the vehicle is able to perform a front dig, and is not required to use the reverse gear to complete the turn. A front dig maneuver involves the driver disconnecting the rear axle output at the transfer case, either through the use of pneumatics, or mechanically. The driver of the vehicle then applies the brakes such that braking pressure is applied to the rear axle only, the vehicle is steered in the desired direction, and the driver then applies the accelerator pedal. With the rear axle disconnected, all of the output of the engine is sent to the front axle, which causes the front wheels to rotate and pull the vehicle in the desired direction. With brake pressure applied to the rear wheels only, the rear wheels do not roll, and the vehicle pivots about the rear axle. This allows the driver to perform extremely tight turns without the use of the reverse gear in the transmission. 
         [0005]    With current production vehicles, modifications to the transfer case and brakes are needed to enable the vehicle to complete a front dig maneuver. The transfer case splits the output of the engine between the front axle and rear axle. Some transfer cases have the ability to disconnect output to either the front axle or rear axle using a selection lever located in the interior of the vehicle. If the transfer case of the vehicle does not have this capability, it is common for an additional tail housing to be installed between the transfer case and the rear differential. The additional tail housing may be equipped with a selection lever, or utilize air pressure to disconnect the rear output, allowing for control of the distribution of power to the front wheels or rear wheels. 
         [0006]    The needed modification to the braking system involves replacing the stock brake master cylinder with twin master cylinders, and replacing the pedal assembly with two brake pedals. When the twin master cylinders are used, one master cylinder is plumbed to the rear axle brakes and the other master cylinder is plumbed to the front brakes. The EBS also includes a pump, valves, and an electronic controller. The EBS is connected to each brake via brake lines. At any time, the EBS controls the valves to maintain, dump, or build pressure at any wheel. 
         [0007]    However, incorporating these types of modifications into a vehicle may also alter or change the drivability of the vehicle in a negative manner. 
         [0008]    Accordingly, there exists a need for a system that is incorporated into a vehicle during the manufacturing process, which allows the vehicle to perform a dig maneuver, without sacrificing vehicle drivability. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is a dig system which allows for a vehicle to perform a front dig maneuver, or rear dig maneuver, without sacrificing the drivability of the vehicle. 
         [0010]    In one embodiment, the present invention is a dig system for a vehicle, including a first front wheel and a second front wheel connected to a front axle, a first rear wheel and a second rear wheel connected to a rear axle, and a transfer case for distributing power between the front axle and the rear axle. 
         [0011]    The dig system also includes a first front brake unit operable for preventing rotation of the first front wheel, a second front brake unit operable for preventing rotation of the second front wheel, a first rear brake unit operable for preventing rotation of the first rear wheel, and a second rear brake unit operable for preventing rotation of the second rear wheel. A hydraulic control unit is operable for controlling the first front brake unit, the second front brake unit, the first rear brake unit, and the second rear brake unit. A first axis extends through the first rear wheel, a second axis extending through the second rear wheel, a third axis extends through the first front wheel, and a fourth axis extends through the second front wheel. 
         [0012]    An actuator is operable for placing the dig system in a first mode of operation, a second mode of operation, a third mode of operation, and a fourth mode of operation. 
         [0013]    During the first mode of operation, the first front wheel and the second front wheel are placed in a first configuration, the hydraulic control unit releases the first front brake unit, the second front brake unit, and the first rear brake unit, and maintains the actuation of the second rear brake unit such that the second rear wheel is prevented from rotating. The transfer case is configured to transfer power to the first front wheel and the second front wheel, is disconnected from the first rear wheel and the second rear wheel, such that when the first front wheel and second front wheel are rotated by the transfer case, the vehicle pivots about the second axis. 
         [0014]    During the second mode of operation, the first front wheel and second front wheel are placed in a second configuration, the hydraulic control unit releases the first front brake unit, the second front brake unit, and the second rear brake unit, and maintains the actuation of the first rear brake unit such that the first rear wheel is prevented from rotating. The transfer case is configured to transfer power to the first front wheel and the second front wheel, and is disconnected from the first rear wheel and the second rear wheel, such that when the first front wheel and second front wheel are rotated by the transfer case, the vehicle pivots about the first axis. 
         [0015]    During the third mode of operation, the first front wheel and the second front wheel are placed in the first configuration, the transfer case is configured to transfer power to the first rear wheel and the second rear wheel, and disconnect from the first front wheel and the second front wheel. The braking system is configured to prevent rotation of the second front wheel, such that when the first rear wheel and the second rear wheel are rotated by the transfer case, the vehicle pivots about the fourth axis. 
         [0016]    During the fourth mode of operation, the first front wheel and the second front wheel are placed in the second configuration, the transfer case is configured to transfer power to the first rear wheel and the second rear wheel, and disconnect from the first front wheel and the second front wheel. The braking system is configured to prevent rotation of first front wheel, such that when the first rear wheel and the second rear wheel are rotated by the transfer case, the vehicle pivots about the third axis extending through the first front wheel. 
         [0017]    The dig system of the present invention also includes an actuator for controlling the operation of the dig system. The actuator is used to configure the dig system in either of the first mode of operation, the second mode of operation, the third mode of operation, or the fourth mode of operation 
         [0018]    The first rear bake unit and the second rear brake unit may be the brake units used to stop the vehicle when driving, or in other embodiments, the first rear brake unit and the second rear brake unit may be parking brake units, used to perform the front dig maneuver, where the parking brake units are controlled directly by the ECU of the vehicle. 
         [0019]    When the first front wheel and the second front wheel are placed in either the first configuration or the second configuration, both the first front wheel and the second front wheel are positioned at a desired steering angle to direct the vehicle in a desired direction as the dig maneuver is performed. 
         [0020]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0022]      FIG. 1  is a diagram of a top view of the powertrain system of a vehicle having a dig system, according to embodiments of the present invention; 
           [0023]      FIG. 2  is a diagram of a top view of the powertrain system of a vehicle having a dig system, with the front wheels placed in a first configuration, according to embodiments of the present invention; 
           [0024]      FIG. 3  is a diagram of a top view of the powertrain system of a vehicle having a dig system, with the front wheels placed in a second configuration, according to embodiments of the present invention; and 
           [0025]      FIG. 4  is diagram of a perspective view of the powertrain system of a vehicle having a dig system, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0027]    A diagram of part of a vehicle incorporating a dig system according to the present invention is shown in  FIG. 1 , generally at  10 . The vehicle  10  includes an engine  12  connected to a transmission  14 , and a transfer case  16  connected to the transmission  14 . The transfer case  16  controls the power transfer from the engine  12  between a front drive shaft  18 , and rear drive shaft  20 . The front drive shaft  18  is connected to a front differential  22 , and the rear drive shaft  20  is connected to a rear differential  24 . The front differential  22  is connected to a front axle  26 , which transfers power to a first front wheel  28   a  and a second front wheel  28   b . The rear differential  24  is connected to a rear axle  30 , and the rear axle  30  is connected to and transfers powers to a first rear wheel  32   a  and a second rear wheel  32   b.    
         [0028]    The vehicle  10  also includes a brake system, where the brake system includes a hydraulic control unit  34  in electrical communication with an electronic control unit (ECU)  36 . There are several brake units in communication with the hydraulic control unit  34 . There is a first front brake unit  38   a  which applies braking force to the first front wheel  28   a , a second front brake unit  38   b  which applies braking force to the second front wheel  28   b , a first rear brake unit  38   c  which applies for to the first rear wheel  32   a , and a second rear brake unit  38   d  which applies force to the second rear wheel  32   b . There is also a first parking brake unit  38   e  which applies braking force to the first rear wheel  32   a , and a second parking brake unit  38   f  which applies braking force to the second rear wheel  32   b . Each of the parking brake units  38   e , 38   f  is controlled directly by the ECU  36 . 
         [0029]    The ECU  36  is in electrical communication with an instrument cluster, shown generally at  40 , which is part of a dashboard  42  of the vehicle  10 . The instrument cluster  40  may include several different gauges, such as a speedometer, tachometer, fuel gauge, temp gauge, and the like. The ECU  36  communicates to the instrument cluster  40  various information about the vehicle  10 , such as engine rpm, vehicle speed, engine temperature, and the like, such that the driver is aware of how the vehicle  10  is operating. There is also an accelerator pedal  44  and a brake pedal  46  which are positioned relative to the instrument cluster  40 . 
         [0030]    The instrument cluster  40  also includes an actuator, such as a button  48  located on the instrument cluster  40 , buttons  68  on a steering wheel  54 , or other type of actuator which is used with an interface to activate and control the operation of the dig system of the present invention. The dig system is used to rotate the vehicle  10  about a first axis  50 , a second axis  52 , a third axis  64 , or a fourth axis  66 , depending on the mode of operation of the dig system. The interface may be a screen  58 , such as a driver information center, which is used to provide warnings and notifications about the various operating conditions of the vehicle  10 . The screen  58  is part of the instrument cluster  40 , where the screen  58  may function as an indicator as part of the dig system, to indicate to the driver of the vehicle  10  that the dig system is active, as well as in which mode of operation the dig system is presently operating. 
         [0031]    The movement of the front wheels  28   a , 28   b  during normal driving operation is controlled by the steering wheel  54 . The steering wheel  54  is rotated in a first direction, as indicated by arrow  56 , which causes the front wheels  28   a , 28   b  to turn right, as shown in  FIG. 2 , or a second direction, as indicated by arrow  60 , which causes the front wheels  28   a , 28   b  to turn left, as shown in  FIG. 3 . The degree which the front wheels  28   a , 28   b  are pivoted to steer the vehicle is the steering angle  62 . The steering angle  62  may be negative, as shown in  FIG. 2 , or positive, as shown in  FIG. 3 . The steering angle  62  may also be controlled by the dig system, were the driver of the vehicle  10  may activate the dig system, and command the front wheels  28   a , 28   b  to be placed at a specific steering angle  62  to perform a dig maneuver, where, along with the current active mode of operation, the steering angle  62 , and which of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  are active and inactive, may be shown on part of the screen  58 . 
         [0032]    The dig system may be placed in two different modes of operation to perform a front dig. In the first mode of operation, the accelerator pedal  44  is released, the brake pedal  46  is applied such that the vehicle  10  is not moving, and the driver of the vehicle  10  activates the dig system by pressing one of the buttons  48 , 68 , or other type of actuator. Once the dig system is activated, the front brake units  38   a , 38   b  and either the rear brake units  38   c , 38   d  or the parking brake units  38   e , 38   f  remain activated such that each of the wheels  28   a , 28   b , 32   a , 32   b  is prevented from rotating. The brake units  38   a , 38   b , 38   c , 38   d , may remain activated when the driver of the vehicle  10  continues to press the brake pedal  46 , such that the hydraulic control unit  34  actuates each of the brake units  38   a , 38   b , 38   c , 38   d , or any combination of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  may remain activated automatically, where the ECU  36  actuates the parking brake units  38   e , 38   f , or the ECU  36  commands the hydraulic control unit  34  to continue to actuate one or more of the brake units  38   a , 38   b , 38   c , 38   d  once the dig system is activated (eliminating the need for the driver to continue to press the brake pedal  46 ). 
         [0033]    The front wheels  28   a , 28   b  are then placed in a first configuration, as shown in  FIG. 2 , where the front wheels  28   a , 28   b  are turned to the right, and are positioned at a specified steering angle  62  commanded by the driver of the vehicle  10 , either by rotating the steering wheel  54  in the first direction  56 , or when the driver of the vehicle  10  activates the dig system and a specific command is received from the driver of the vehicle  10  to place the front wheels  28   a , 28   b  in the first configuration (eliminating the need to rotate the steering wheel  54 ). 
         [0034]    The ECU  36  then detects the wheels  28   a , 28   b  are in the first configuration, and configures the transfer case  16  such that power is no longer transferred to the rear wheels  32   a , 32   b , and power from the engine  12  transferred only to the front wheels  28   a , 28   b . The driver of the vehicle  10  is then notified by the indicator  58  that the dig system is active, and (if the brake pedal  46  has been applied) the brake pedal  46  is then to be released. After the front wheels  28   a , 28   b  have been placed in the first configuration, the ECU  36  commands the hydraulic control unit  34  to release three of the brake units  38   a , 38   b , and  38   c  (or  38   e , depending on which of the brake units  38   c  or  38   e  were activated), and maintains the activation of the second rear brake unit  38   d  (or parking brake unit  38   f ) such that the second rear wheel  32   b  is still prevented from rotating. 
         [0035]    Once the second rear brake unit  38   d  (or the parking brake unit  38   f ) is the only brake unit activated, the driver of the vehicle  10  then presses the accelerator pedal  44  such that power is transferred to the front wheels  28   a , 28   b , causing the front wheels  28   a , 28   b  to rotate. The rotation of the front wheels  28   a , 28   b  rotates the vehicle  10  about the second axis  52 , allowing the vehicle  10  to change direction without having to perform a back up or reverse maneuver. The amount the vehicle  10  pivots about the second axis  52  depends upon how long the driver of the vehicle  10  presses the accelerator pedal  44 , and the steering angle  62  of the front wheels  28   a , 28   b . If the driver of the vehicle  10  is aggressive, and the front wheels  28   a , 28   b  are rotated at a high rate of speed, the vehicle  10  may not only pivot about the axis  52 , but also move across the ground such that the second rear wheel  32   b  slides across the ground, as the remaining wheels  28   a , 28   b , 32   a  rotate because of the front wheels  28   a , 28   b  being driven by the transfer case  16  and the first rear wheel  32   a  being allowed to rotate free. Once the desired amount of rotation about the second axis  52  is achieved, the accelerator pedal  44  is released, such that the vehicle  10  stops rotating about the axis  52 . The driver of the vehicle  10  then deactivates the dig system by again pressing the button  48  (or buttons  68 ), or touches the brake pedal  46 , where the ECU  36  then commands the hydraulic control unit  34  to release the second rear brake unit  38   d  (or the ECU  36  directly releases the parking brake unit  38   f ), such that all of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  return to functioning as expected when the dig system is inactive, and the transfer case  16  is configured such that the transfer case  16  is transfers power to all four wheels  28   a , 28   b , 32   a , 32   b.    
         [0036]    In the second mode of operation, the accelerator pedal  44  is again released, the brake pedal  46  is applied such that the vehicle  10  is not moving, and the driver of the vehicle  10  activates the dig system by pressing the button  48  (or buttons  68 ). Once the dig system is activated, the front brake units  38   a , 38   b  and either the rear brake units  38   c , 38   d  or the parking brake units  38   e , 38   f  remain activated such that each of the wheels  28   a , 28   b , 32   a , 32   b  is prevented from rotating. As with the first mode of operation, the brake units  38   a , 38   b , 38   c , 38   d  in the second mode of operation may remain activated when the driver of the vehicle  10  continues to press the brake pedal  46 , such that the hydraulic control unit  34  actuates each of the brake units  38   a , 38   b , 38   c , 38   d , or any combination of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  may remain activated automatically, where the ECU  36  actuates the parking brake units  38   e , 38   f , or the ECU  36  commands the hydraulic control unit  34  to actuate one or more of the brake units  38   a , 38   b , 38   c , 38   d  once the dig system is activated. 
         [0037]    The front wheels  28   a , 28   b  are then placed in a second configuration, as shown in  FIG. 3 , where the front wheels  28   a , 28   b  are turned to the left, and are positioned at a specified steering angle  62  as commanded by the driver of the vehicle  10 , either by rotating the steering wheel  54  in the second direction  60 , or when the driver of the vehicle  10  activates the dig system and a specific command is received from the driver of the vehicle  10  to place the front wheels  28   a , 28   b  in the second configuration (eliminating the need to rotate the steering wheel  54 ). 
         [0038]    The ECU  36  then detects the wheels  28   a , 28   b  are in the second configuration, and configures the transfer case  16  such that power is no longer transferred to the rear wheels  32   a , 32   b , and power from the engine  12  transferred only to the front wheels  28   a , 28   b . The driver of the vehicle  10  is then notified by the indicator  58 , that the dig system is active, and (if the brake pedal  46  has been applied) the brake pedal  46  is to be released. After the front wheels  28   a , 28   b  have been placed in the second configuration, the ECU  36  commands the hydraulic control unit  34  to release three of the brake units  38   a , 38   b , and  38   d  (or  38   f , depending on which of the brake units  38   d  or  38   f  were activated), and maintains the activation of the first rear brake unit  38   c  (or parking brake unit  38   e ) such that the first rear wheel  32   a  is still prevented from rotating. 
         [0039]    Once the first rear brake unit  38   c  (or the parking brake unit  38   e ) is the only brake unit activated, the driver of the vehicle  10  then presses the accelerator pedal  44  such that power is transferred to the front wheels  28   a , 28   b , causing the front wheels  28   a , 28   b  to rotate. The rotation of the front wheels  28   a , 28   b  rotates the vehicle  10  about the first axis  50 , allowing the vehicle  10  to change direction without having to perform a back up or reverse maneuver. The amount the vehicle  10  pivots about the first axis  50  depends upon how long the driver of the vehicle  10  presses the accelerator pedal  44 , and the steering angle  62  of the front wheels  28   a , 28   b . If the driver of the vehicle  10  is aggressive during the second mode of operation, and the front wheels  28   a , 28   b  are rotated at a high rate of speed, the vehicle  10  may not only pivot about the axis  50 , but also move across the ground such that the first rear wheel  32   a  slides across the ground, as the remaining wheels  28   a , 28   b , 32   b  rotate because of the front wheels  28   a , 28   b  being driving by the transfer case  16  and the second rear wheel  32   b  being allowed to rotate free. Once the desired amount of rotation about the first axis  50  is achieved, the accelerator pedal  44  is released, such that the vehicle  10  stops rotating about the axis  50 . The driver of the vehicle  10  then deactivates the dig system by again pressing the button  48  (or buttons  68 ), or touches the brake pedal  46 , where the ECU  36  then commands the hydraulic control unit  34  to release the first rear brake unit  38   c  (or the ECU  36  directly releases the parking brake unit  38   e ), such that all of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  return to functioning as expected when the dig system is inactive, and the transfer case  16  is configured such that the transfer case  16  transfers power to all four wheels  28   a , 28   b , 32   a , 32   b.    
         [0040]    The dig system also includes a third mode of operation and a fourth mode of operation used to perform a rear dig. In the third mode of operation, the accelerator pedal  44  is again released, and the brake pedal  46  is applied such that the vehicle  10  is not moving, and the driver of the vehicle  10  activates the dig system by pressing the button  48  (or buttons  68 ). Once the dig system is activated, the brake pedal  46  is released, and the front brake units  38   a , 38   b  and either the rear brake units  38   c , 38   d  or the parking brake units  38   e , 38   f  remain again activated such that each of the wheels  28   a , 28   b , 32   a , 32   b  is prevented from rotating. The front wheels  28   a , 28   b  are again placed in the first configuration, as shown in  FIG. 2 , where the front wheels  28   a , 28   b  are turned to the right, and are positioned at a specific steering angle  62  commanded by the driver of the vehicle  10 . 
         [0041]    The ECU  36  then detects the wheels  28   a , 28   b  are in the first configuration, and configures the transfer case  16  such that power is no longer transferred to the front wheels  28   a , 28   b , and power from the engine  12  transferred only to the rear wheels  32   a , 32   b . After the front wheels  28   a , 28   b  have been placed in the first configuration, the ECU  36  releases the parking brake units  38   e , 38   f  (if the parking brake units  38   e , 38   f  are activated), and commands the hydraulic control unit  34  to release all of the other brake units  38   a , 38   c , 38   d , except the second front brake unit  38   b , where the activation of the second front brake unit  38   b  is maintained such that the second front wheel  28   b  is still prevented from rotating. 
         [0042]    Once the second front brake unit  38   b  is the only brake unit activated, the driver of the vehicle  10  then presses the accelerator pedal  44  such that power is transferred to the rear wheels  32   a , 32   b , causing the rear wheels  32   a , 32   b  to rotate. The rotation of the rear wheels  32   a , 32   b  rotates the vehicle  10  about a fourth axis  66 , again allowing the vehicle  10  to change direction without having to perform a back up or reverse maneuver. The amount the vehicle  10  pivots about the fourth axis  66  depends upon how long the driver of the vehicle  10  presses the accelerator pedal  44 , and the steering angle  62  of the front wheels  28   a , 28   b . If the driver of the vehicle  10  is aggressive, and the rear wheels  32   a , 32   b  are rotated at a high rate of speed, the vehicle  10  may not only pivot about the axis  66 , but also move across the ground such that the second front wheel  28   b  slides across the ground, as the remaining wheels  28   a , 32   a , 32   b  rotate because of the rear wheels  32   a , 32   b  being driven by the transfer case  16  and the first front wheel  28   a  being allowed to rotate free. Once the desired amount of rotation about the fourth axis  66  is achieved, the accelerator pedal  44  is released, such that the vehicle  10  stops rotating about the axis  66 . The driver of the vehicle  10  then deactivates the dig system by again pressing the button  48 , or touches the brake pedal  46 , where the ECU  36  then commands the hydraulic control unit  34  to release the second front brake unit  38   b , such that all of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  return to functioning as expected when the dig system is inactive, and the transfer case  16  is configured such that the transfer case  16  transfers power to all four wheels  28   a , 28   b , 32   a , 32   b.    
         [0043]    In the fourth mode of operation, the accelerator pedal  44  is again released, and the brake pedal  46  is applied such that the vehicle  10  is not moving, and the driver of the vehicle  10  again activates the dig system by pressing the button  48  (or buttons  68 ). Once the dig system is activated, the brake pedal  46  is released, and the front brake units  38   a , 38   b  and either the rear brake units  38   c , 38   d  or the parking brake units  38   e , 38   f  remain activated such that each of the wheels  28   a , 28   b , 32   a , 32   b  is prevented from rotating. The front wheels  28   a , 28   b  are then placed in the second configuration, as shown in  FIG. 3 , where the front wheels  28   a , 28   b  are turned to the left, and are positioned at a specified steering angle  62  as commanded by the driver of the vehicle  10 . 
         [0044]    The ECU  36  then detects the wheels  28   a , 28   b  are in the second configuration, and configures the transfer case  16  such that power is no longer transferred to the front wheels  28   a , 28   b , and power from the engine  12  transferred only to the rear wheels  32   a , 32   b . After the front wheels  28   a , 28   b  have been placed in the second configuration, the ECU  36  releases the parking brake units  38   e , 38   f  (if the parking brake units  38   e , 38   f  are activated), and commands the hydraulic control unit  34  to release all of the other brake units  38   b , 38   c , 38   d  except the first front brake unit  38   a , where the activation of the first front brake unit  38   a  is maintained such that the first front wheel  28   a  is still prevented from rotating. 
         [0045]    Once the second front brake unit  38   b  is the only brake unit activated, the driver of the vehicle  10  then presses the accelerator pedal  44  such that power is transferred to the rear wheels  32   a , 32   b , causing the rear wheels  32   a , 32   b  to rotate. The rotation of the rear wheels  32   a , 32   b  rotates the vehicle  10  about the third axis  64 , again allowing the vehicle  10  to change direction without having to perform a back up or reverse maneuver. The amount the vehicle  10  pivots about the third axis  64  depends upon how long the driver of the vehicle  10  presses the accelerator pedal  44 , and the steering angle  62  of the front wheels  28   a , 28   b . If the driver of the vehicle  10  is aggressive, and the rear wheels  32   a , 32   b  are rotated at a high rate of speed, the vehicle  10  may not only pivot about the axis  64 , but also move across the ground such that the first front wheel  28   a  slides across the ground, as the remaining wheels  28   b , 32   a , 32   b  rotate because of the rear wheels  32   a , 32   b  being driven by the transfer case  16  and the second front wheel  28   b  being allowed to rotate free. Once the desired amount of rotation about the third axis  64  is achieved, the accelerator pedal  44  is released, such that the vehicle  10  stops rotating about the axis  64 . The driver of the vehicle  10  then deactivates the dig system by again pressing the button  48  (or buttons  68 ), or presses the brake pedal  46 , where the ECU  36  then commands the hydraulic control unit  34  to release the first front brake unit  38   a , such that all of the brake units  38   a , 38   b , 38   c , 38   d , 38   e , 38   f  return to functioning as expected when the dig system is inactive, and the transfer case  16  is configured such that the transfer case  16  transfers power to all four wheels  28   a , 28   b , 32   a , 32   b.    
         [0046]    The dig system of the present invention also includes certain operational features to prevent damage to the components of the vehicle  10 . One of these features includes the ECU  36  automatically deactivating the dig system after the vehicle  10  reaches a certain speed, or if the steering wheel  54  to rotated such that the front wheels  28   a , 28   b  are no longer in the first configuration or the second configuration. The dig system is also automatically deactivated if any one of the vehicle&#39;s velocity, steering wheel angle, or transfer case mode is unavailable, faulted, or unknown. 
         [0047]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Technology Category: b