Abstract:
A snow vehicle propelled by gravitation has a frame supported by four posts attached to four skis. The two rear skis are attached to the supporting posts using hinges with one degree of liberty. The two front skis are rigidly attached to the support posts and the posts are attached to the frame at a 45 degree angle using hinges with two degrees of liberty. Two linear actuators are attached to the frame and to the rear of the front skis using hinges with two degrees of liberty. The actuators are remotely controlled by a human using an on board computerized steering/braking controller that works in such a manner as to replicate the human wedge style of skiing (a.k.a. plow skiing).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Provisional Pat. Appl. No. 61/819,009, filed 2012 May 3, from which priority is claimed under 35 USC 119(e). All said patent documents are incorporated herein in full by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     The present invention relates to Class D12, Transportation, Subclass 6, Sled. The present invention relates to various systems used for steering and speed control of snow vehicles. 
     The control of the direction of movement of a snow vehicle is usually obtained by either changing the position of the front ski of a vehicle using a total of two or three skis (one front ski used for steering/support and one or two rear skis used only for support on the snow) or by changing the direction of the two front skis of a vehicle using three or four skis (two front skis used for steering/support and one or two rear skis used only for support on the snow). In the case of a powered snow vehicle like a snowmobile, the rear support is replaced by a powered endless track. 
     Vehicles using a single front ski for steering must use different means for braking or must rely on the ability of the operator to stop by turning the vehicle perpendicular to the initial direction of motion. The U.S. Pat. No. 8,523,195 describes a snow vehicle that employs braking members that are lowered to contact the snow, so as to create friction or resistance with respect to the snow on the ground. The disadvantage of the method is that the steering ability is substantially reduced during braking due to the increased friction from the braking members. By contrast, the U.S. Pat. No. 5,863,051 describes a snow vehicle that has no braking provisions. 
     Vehicles using two front skis for steering usually turn both skis in the same direction for steering and they are facing the same problem as the single front ski vehicles when they need to brake. The U.S. Pat. No. 8,590,654 B2 describes a snowmobile that uses the endless track for braking by decupling it from the motor and locking it. To avoid skidding, an antilock braking system (ABS) can be used. 
     Vehicles using two front skis for steering could use the wedge technique (plow skiing) for speed control and steering, as described in U.S. Pat. No. 3,682,495. In this embodiment, the operator&#39;s ability to control the front skis will determine the precision of the steering and the efficiency of the braking. 
     SUMMARY OF THE INVENTION 
     This invention presents a new method for controlling the angle between the snow and the front skis, used for steering and braking. Also, this invention describes a new approach to control the steering and braking of a snow vehicle using a computer assisted servo mechanism that can be easily controlled via a joystick, making it usable by persons with disabilities. The joystick could use a wireless connection to the computer, allowing the vehicle to be remotely controlled, for example by a ski patroller using the vehicle to transport an injured skier. This snow vehicle could steer while braking using the wedge technique (plow skiing) even on steep slopes, permitting its usage as transport vehicle for materials or personnel. 
     In one embodiment, a vehicle is provided comprising a frame, a plurality of ground engaging members including two front ground engaging members supporting the front portion of the frame and one or more rear ground engaging members supporting the rear portion of the frame. A steering/braking assembly consisting of two linear actuators operatively coupled to the two front ground engaging members is used to orient one or both front ground engaging members. The front ground engaging members are rotatable relative to the frame about a first set of axes that are parallel to each other and angled back at 45 degrees relative to the frame and also are rotatable about a second set of axes that are perpendicular to the first set of axes. An electronics unit controls the steering/braking assembly according to the commands issued by a human operator or by an autonomous navigation system. The vehicle is gravity propelled. 
     In another embodiment, a vehicle is provided comprising a frame, a plurality of ground engaging members including two front ground engaging members supporting a front portion of the frame and one or more rear ground engaging members supporting the rear portion of the frame. A power train system is supported by the frame and operatively coupled to at least one of the plurality of the rear ground engaging members. A steering/braking assembly consisting of two linear actuators is operatively coupled to the two front ground engaging members to orient one or both front ground engaging members. The front ground engaging members are rotatable relative to the frame about axes that are parallel to each other and angled back at 45 degrees relative to the frame. An electronics unit controls the steering/braking assembly according to the commands issued by a human operator or by an autonomous navigation system. The vehicle could be gravity propelled when going down the slopes or power train propelled on flat terrain or uphill. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a front, left, perspective view of an exemplary snow vehicle 
         FIG. 2  illustrates a front elevation view of the exemplary vehicle of  FIG. 1   
         FIG. 3  illustrates a right side elevation view of the exemplary vehicle of  FIG. 1   
         FIG. 4  illustrates a bottom view of the exemplary vehicle of  FIG. 1   
         FIG. 5  illustrates a front elevation view of the right front ski of the exemplary vehicle of  FIG. 1  in the turning/braking position 
         FIG. 6  illustrates a front view elevation of the front skis of the exemplary vehicle of  FIG. 1  in the left turning position (rear skis not shown) 
         FIG. 7  illustrates a bottom view of the exemplary vehicle of  FIG. 1  in the left turning position 
         FIG. 8  illustrates a front elevation view of the front skis of the exemplary vehicle of  FIG. 1  in the braking position (rear skis not shown) 
         FIG. 9  illustrates a bottom view of the exemplary vehicle of  FIG. 1  in the braking position 
         FIG. 10  illustrates a front elevation/section view of an exemplary two degrees of freedom (DOF) hinge 
         FIG. 11  illustrates a left side elevation view of the exemplary hinge of  FIG. 10   
         FIG. 12  illustrates a top plan view of the exemplary hinge of  FIG. 10   
         FIG. 13  illustrates an exemplary flow chart of the steering/braking control system of the exemplary vehicle of  FIG. 1   
         FIG. 14  illustrates a top plan view of the front skis of the exemplary vehicle of  FIG. 1  executing a left turn when the skis are initially turned less than half way 
         FIG. 15  illustrates a top plan view of the front skis of the exemplary vehicle of  FIG. 1  executing a left turn when the skis are initially turned more than half way 
         FIG. 16  illustrates a top plan view of the front skis of the exemplary vehicle of  FIG. 1  executing a speed increase command 
         FIG. 17  illustrates a top plan view of the front skis of the exemplary vehicle of  FIG. 1  executing a speed decrease (brake) command 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. While the present disclosure is primarily directed to a snow vehicle, it should be understood that the features disclosed herein may have application to other types of vehicles. 
     Referring to  FIG. 1 , an illustrated embodiment of vehicle  100  is shown. Vehicle  100  as illustrated includes a plurality of ground engaging members: a pair of front skis  107 L and  107 R supporting the front portion of the vehicle, and a pair of rear skis  108 L (and  108 R, not visible) supporting the rear portion of the vehicle. Further, front skis  107 L and  107 R are rigidly coupled to posts  110 L and  111 L and respectively  110 R (and  111 R, not visible). Upper end of the posts  111 L and  111 R are coupled to blocks  114 L (and  114 R, not visible) by means of hinges  101 L and  101 R. Blocks  114 L (and  114 R, not visible) are rigidly attached to the frame  112 . Upper end of posts  110 L (and  110 R, not visible) are attached to the end of the rods  106 L (and  106 R, not visible) of the actuators  105 L (and  105 R, not visible) by means of the hinges  103 L (and  103 R, not visible). Actuators  105 L (and  105 R, not visible) are attached to the frame  112  (by means of hinges  102 L and  102 R, not visible). Rear skis  108 L (and  108 R, not visible) are coupled to posts  109 L (and  109 R, not visible) by means of the hinges  113 L (and  113 R, not visible). Upper ends of the posts  109 L (and  109 R, not visible) are rigidly attached to the frame  112 . 
     Referring to  FIG. 2  and  FIG. 3 , vehicle  100  includes a frame  112  which is generally attached to the ground engaging members  107 L,  107 R,  108 L and  198 R by the posts  111 L,  111 R,  109 L and  109 R. Posts  111 L and  111 R are coupled to the prismatic blocks  114 L and  114 R using hinges  101 L and  101 R. Blocks  114 L and  114 R are rigidly attached to the frame  112  and the face of the blocks  114 L and  114 R on which the hinges  101 L and  101 R are mounted has a 45 degree angle relative to the plane of the frame  112 . The hinges  101 L and  101 R permit rotation and tilting of the posts  111 L and  111 R relative to the frame  112 . Since the left side is the mirror image of the hinge  101 R, only the hinge  101 R will be discussed. The hinge  101 R permits the rotation of the post  110 R about a first axis that is perpendicular to the face of the prismatic block  114 R on which the hinge  101 R is mounted and simultaneously and independently permits rotation of the post  110 R about another axis that is perpendicular to the first axis. An embodiment of such a hinge is illustrated in  FIG. 12 ,  FIG. 13  and  FIG. 14 . The posts  110 R and  111 R are rigidly attached to the ski  7 R. The post  110 R is attached at the other end to the moving rod  106 R of the actuator  105 R using a hinge  103 R that is similar to the one illustrated in  FIG. 10-12 . The body of the actuator  105 R is attached to the frame  112  using a hinge  102 R that is similar to the one illustrated in  FIG. 10-12 . This arrangement permits the front skis to follow the uneven snow surface while maintaining as much contact with the snow as possible. In this embodiment of the vehicle  100 , the actuators  105 L and  105 R are linear electric motors controlled by the electronics control unit  115 , which is mounted under the frame  112  and is connected to the actuators  105 L and  105 R using cables  116 L and  116 R respectively. 
     In one embodiment, the rear ground engaging members are the skis  108 L and  108 R which are attached to the posts  109 L and  109 R using hinges  113 L and  113 R. The posts  109 L and  109 R are rigidly attached to the frame  112 . The hinges  113  L and  113 R permit the rotation of the skis  108 L and  108 R about an axis parallel to the frame  112  and perpendicular to the longitudinal axis of the frame  112 . This arrangement permits the rear skis to follow the uneven snow surface while maintaining as much contact with the snow as possible. The vehicle is gravity propelled. 
     In another embodiment, the rear ground engaging member is an endless track operatively coupled to a power train system supported by the frame  112 . 
     Referring to  FIG. 5 , the front right ski  107 R is illustrated in the turning/braking position. The actuator  105 R extends the rod  106 R that pushes the post  110 R toward the exterior of the vehicle, thus moving the rear end of the front ski  107 R toward the exterior of the vehicle. The result is that the front ski  107 R is not only rotated with an angle α from the straight position, but is also tilted about the snow surface with an angle α/2 due to the fact that the hinge  101 R is mounted on the face of the prismatic block  114 R that is built to have a 45 degrees angle about the plane of the frame  112 . This tilting of the ski  107 R ensures that the ski is making contact with the snow mainly on the edge, in the manner used by a skier turning or braking with the plow technique. 
     Referring to  FIG. 6 , a front view of the snow vehicle  100  making a left turn is illustrated. For clarity, only the front skis are shown. Beside the fact that posts are elevating the frame from the snow, another advantage of mounting the front skis  107 R and  107 L on posts  110 R,  111 R and  110 L,  111 L is that when turning or braking, the skis that are rotated are also pushed toward the exterior of the body of vehicle  100 , increasing the efficiency of the turning or braking manoeuver. 
     A bottom view of the snow vehicle  100  making a left turn is illustrated in  FIG. 7 . 
     A front view of the snow vehicle  100  braking is illustrated in  FIG. 8 . For clarity, only the front skis are shown. 
     A bottom view of the snow vehicle  100  braking is illustrated in  FIG. 9 . 
     Referring to  FIG. 10 , a semi-section front view of an embodiment of a two degrees of freedom (DOF) hinge like the one used for hinges  101 L,  101 R,  102 L,  102 R,  103 L and  103 R is presented. The ball bearings  123  permit the bracket  121  to pivot about the axis of the bolt  124 . The second object  119  is connected to the hinge with the pin  122  that passes through holes in the bracket  121  and second object  119 . The second object  119  can pivot about the axis of the pin  122 . The sleeve  120  is made of bronze and will insure a smooth rotation of the second object  119  about pin  122 . This type of hinge will offer second object  119  two DOF of movement about the first object  128 : rotation about first axis OY that is perpendicular to the mounting surface of the first object  128  and rotation about second axis OX that is perpendicular to the first axis. Specifically, for the hinge  101 , the first object  128  is the face of the block  114  that is angled at 45 degrees with respect to the frame  112  and the second object  119  is the post  111 ; for the hinge  102 , the first object  128  is the frame  112  and the second object  119  is the body of the actuator  105 ; for the hinge  103 , the first object  128  is the end of the post  110  and the second object  119  is the rod  106  of the actuator  105 . 
     Referring to  FIG. 11 , a lateral view of the two DOF hinge from  FIG. 10  is presented. 
     Referring to  FIG. 12 , a top view of the two DOF hinge from  FIG. 10  is presented. The base  127  is attached to the mounting surface of first object  128  with screws  126 A,  126 B,  126 C and  126 D. 
     Referring to  FIG. 13 , an exemplary flow chart of a steering/braking control system is presented. The steering/braking controller receives directional instructions from a human interface device such as a joystick. The exemplary steering/braking controller uses a proportional approach in translating the simple and proportional movements of the joystick (forward, backward, left, right) to proportional and coordinated movements of the skis so that the snow vehicle will move forward (no brake), brake, turn left, turn right. The exemplary steering/braking controller utilizes a finite state machine, with a default state in which both front skis remain motionless and at the same relative extension position for the actuators. This state is stored in a collective position variable. Upon reception of a turn command, the state machine enters a turn state using proportional control. If the collective leg position variable was closer to the full retraction of the actuators, the robot entered the extension turn state. The robot turned by extending the actuator for the outside leg in accordance with the following equation:
 
β ot =β os +δ
 
where:
         β ot  is the outside leg&#39;s turning angle,   β os  is the collective leg position angle and   δ is the steering increment.
 
The steering increment angle δ is proportional with the magnitude of the joystick&#39;s movement. A top view of the front skis of the exemplary vehicle of  FIG. 1  executing a left turn when the skis are initially turned less than half way is illustrated in  FIG. 14 .
       

     If the collective leg position variable was closer to the full extension of the actuators, the robot entered the ski retraction turn state. The robot turned by retracting the actuator for the inside leg in accordance with the following equation:
 
β it =β is −δ
 
where:
         β it  is the inside leg&#39;s turning angle,   β is  is the collective leg position angle and   δ is the steering increment.
 
The steering increment angle δ is proportional with the magnitude of the joystick&#39;s movement. A top view of the front skis of the exemplary vehicle of  FIG. 1  executing a left turn when the skis are initially turned more than half way is illustrated in  FIG. 15 . Using two different turn states ensured that during a turn, the skis could execute turning motions fully, guaranteeing that the robot would turn as desired. Once the turning command was discontinued, the state machine would return to the neutral state, and the skis would return to the previously established collective leg position.
       

     If a speed increase command was received, the robot switched to differential control, and the collective leg position variable was decreased, bringing in tandem both skis closer to parallel position by retracting both actuators. The change was determined by the following equation:
 
β f =β i −δ
 
where:
         β f  is the new collective leg position,   β i  is the old collective leg position and   δ is the position change increment.       

     The speed increment angle δ is proportional with the magnitude of the joystick&#39;s movement. A top view of the front skis of the exemplary vehicle of  FIG. 1  executing a speed increase command is illustrated in  FIG. 16 . 
     If a speed decrease command was received, the collective leg position variable was increased, bringing in tandem both skis to form an angle by extending both actuators. The change was determined by the following equation:
 
β f =β i +δ
 
where:
         β f  is the new collective leg position,   β i  is the old collective leg position and   δ is the position change increment.
 
The speed decrease angle δ is proportional with the magnitude of the joystick&#39;s movement. A top view of the front skis of the exemplary vehicle of  FIG. 1  executing a speed increase command is illustrated in  FIG. 17 . If the skis were at a maximum extension or retraction of the actuators, commands to continue extension or retraction of the actuators will not further change the current position of the actuators.
       

     An exemplary implementation of the steering/braking control system used a Phidgets brand high current two channel motor controller to control the two electric linear motors (actuators) made by Servo City (Winfield Kans.). The motors were powered by a high power 12V DC battery. The rods of the two linear actuators were mechanically attached to potentiometers. The positional information from the potentiometers was read by a Phidgets brand analog interface kit and transformed into an electric signal. The Phidgets brand motor controller, interface kit and a wireless joystick were connected via USB ports to a Dell laptop computer running Windows XP. The software program to control the steering/braking of the snow vehicle is written in Pyton. The computer listing of the program is provided as a text only file: Vehicle_Control_Software.txt.