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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE DISCLOSURE 
       [0001]    This disclosure relates to a hinge for a door and, more specifically, to a self locking and unlocking hinge for a door. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    The operating mechanisms for doors having multiple locked open positions tend to be either complex or space consuming. Space may be costly and complexity may be a drawback when such doors are located on work vehicles. 
       SUMMARY OF THE DISCLOSURE 
       [0003]    The challenges described above are overcome via the use of a self locking hinge having one or more brackets and a spring loaded pin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  illustrates a vehicle which may use the invention; 
           [0005]      FIG. 2  illustrates an exemplary embodiment of the invention when the door is closed; 
           [0006]      FIG. 3A  illustrates an exemplary embodiment of the pin assembly with the pin in the lock position; 
           [0007]      FIG. 3B  illustrates an exemplary embodiment of the pin assembly illustrated in  FIG. 3A  with the pin in the unlocked position; 
           [0008]      FIG. 4  is a view of an exemplary embodiment of the door weldment; 
           [0009]      FIG. 5  is an exemplary embodiment of the door frame; 
           [0010]      FIG. 6A  is a perspective view of an exemplary embodiment of the first bracket; 
           [0011]      FIG. 6B  illustrates another view of the exemplary embodiment of the first bracket of  FIG. 6A ; 
           [0012]      FIG. 6C  illustrates another view of the exemplary embodiment of  FIG. 6A ; 
           [0013]      FIG. 7  illustrates three positions of the unlocking portion as the door becomes completely open; 
           [0014]      FIG. 8A  is a detailed perspective view of an exemplary embodiment of the second bracket; 
           [0015]      FIG. 8B  is a second detailed perspective view of the embodiment of  FIG. 8A ; 
           [0016]      FIG. 8C  is a third detailed perspective view of the embodiment of  FIG. 8A ; when the door has been moved beyond the second locked position and the hinge is unlocked and set to return to the closed door position; 
           [0017]      FIG. 9A  is a perspective view of an exemplary embodiment of the door frame with the first and second brackets attached; 
           [0018]      FIG. 9B  is a second detailed perspective view of the embodiment of  FIG. 9A ; 
           [0019]      FIG. 10  is a detailed perspective vie of an exemplary embodiment of the third bracket; and 
           [0020]      FIG. 11  is a perspective view of an alternative embodiment of the unlocking hinge. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]      FIG. 1  illustrates a vehicle in which an exemplary embodiment of the invention may be used. This particular vehicle, i.e., a dozer  10 , includes a cab  20 , tracks  30  through which the dozer  10  may be propelled, a frame  40 , a door frame  101  and a door  102  which, in this particular example, opens in a side direction. In other words the door  102  is hinged on one of its sides  102 ′,  102 ″ and may open from side  102 ′ to the side  102 ″ or vice versa. In this exemplary embodiment, the door opens from side  102 ′ to side  102 ″, i.e., the door  102  is hinged on side  102 ″. 
         [0022]      FIG. 2  illustrates an exemplary embodiment of the invention, i.e., the self locking hinge  100  when the door  102  is closed. As illustrated, the hinge  100  includes a door frame  101  which may be rigidly connected to the frame  40 ; a first bracket  110  which may be rigidly connected to a second bracket  120  via nut and bolt (the second bracket  120  may be rigidly connected to the door frame  101  via conventional nuts and bolts); a third bracket  130  which may be rigidly connected to the door  102  and a pin assembly  140  which may be operably connected to the door  102  via a rigid connection with the third bracket  130 . The terms “rigid” and “rigidly” as used in this description are employed to denote a connection which allows zero Degrees (0°) of relative movement between the connected parts. Accordingly, as the door  102  rotates toward open and closed positions indicated by arrows R 1  and R 2 , respectively, the third bracket  130  and pin assembly  140  may rotate about an axis of rotation A 1  for the door as a portion of the hinge  100 . 
         [0023]    As illustrated in  FIGS. 3   a ,  3   b  and  3   c , the pin assembly  140  may include a pin  141 ; a pin holder  142 ; and a spring  143 . The pin  141  includes a locking portion  141   a  having a diameter of D 1 ; an unlocking portion  141   b  having a diameter of D 3 ; and a connecting portion  141   c  having a diameter of D 2  smaller than, and concentric with diameter D 1 . As illustrated, the size difference in diameters D 1  and D 2  may be sufficient to form a first wall  141   d  against which the spring  143  may abut. The pin holder  142  includes a first pin holder portion  142   a  and a second pin holder portion  142   b  each having first and second cylindrical holes  142   c,    142   d  which may be concentric. The diameters of cylindrical holes  142   c,    142   d  are D 3  and a larger D 4 , respectively. As illustrated, the size difference in diameters D 3  and D 4  is sufficient to form a second wall  142   e  against which the spring  143  may abut. As illustrated, the diameter D 5  of the spring  143  is sufficient to fit over the connecting portion  141   c  and abut first and second walls  142   e  and  141   d,  yet small enough to fit within the second cylindrical hole  142   d.  The second pin holder portion  142   b  may have an outer diameter D 4 ′ that is smaller than an outer diameter D 3 ′ of the first pin holder portion  142   a.    
         [0024]    The pin assembly  140  illustrated in  FIG. 3   a  has the pin  141  in the lock position, i.e., the locking portion  141   a  is protruding from the pin holder  142  and the connecting portion  141   c  is retracted into the pin holder  142 . As illustrated, in this position, the spring  143  is extended.  FIG. 3   b  illustrates the pin assembly  140  with the pin in the unlock position, i.e., the locking portion  141   a  is retracted into the pin holder  142  and the connecting portion  141   c  is now protruding from the pin holder  142 . As illustrated in  FIGS. 3   a  and  3   b , the spring  143  may be compressive, biasing the pin  141  to the lock position. In this exemplary embodiment the spring  143  may be compressed, exerting a greater compressive force to return the pin  141  to the lock position than the compressive force it exerts when the pin  141  is in the lock position. 
         [0025]      FIG. 4  illustrates an exemplary embodiment of the door  102  which may be a weldment including: a wall  102   a;  the third bracket  130 ; and conventional hinge pins  102   b.    
         [0026]      FIG. 5  illustrates an exemplary embodiment of the door frame  101  including first bracket attachment holes  101   a,  frame attachment holes  101   b  and conventional cylinders  101   c  for conventional connections with the hinge pins  102   b  of the door. 
         [0027]      FIGS. 6A-6C  are detailed perspective views of the first bracket  110 . As illustrated, the first bracket  110  may have a cylindrical locking portion  111 , having inner and outer locking diameters D 5 , D 6 , and a cylindrical mounting portion  112 , having inner and outer mounting diameters D 7 , D 8 . The cylindrical locking portion  111  may have first and second end surfaces  111 ′ and  111 ″ at first and second ends  110   a,    110   b,  respectively. Two locking grooves, i.e., a first locking groove  113  and a second locking groove  114  may be located on the second end surface  111 ″. Additionally, a free rotation area  115 , which may be considered an enlarged groove, is also located on the second end surface  111 ″. 
         [0028]    As illustrated, the first locking groove  113  may include a first blocking surface  113   a,  a first resting surface  113   b  which may be adjacent and generally orthogonal to the first blocking surface  113   a,  and a first ramp surface  113   c  which may be adjacent to the first resting surface  113   b.  The first locking groove  113  may have a length L 1  sufficient to contain the locking portion  141   a  (of diameter D 1 ) of the pin  141  between the first blocking surface  113   a  and the first ramp surface  113   c  and allow the surface of the locking portion  141   a  to touch the resting surface  113   b.  The first locking groove  113  may also include a first transitional plateau surface  113   d.    
         [0029]    Similarly, the second locking groove  114  may include a second blocking surface  114   a,  a second resting surface  114   b  adjacent and generally orthogonal to the second blocking surface  114   a,  and a second ramp surface  114   c  which may be adjacent to the second resting surface  114   b.  The second locking groove  114  may have a length L 2  sufficient to contain the locking portion  141   a  (of diameter D 1 ) of the pin  141  between the second locking surface  114   a  and the second ramp surface  114   c  and allow a surface of the locking portion  141   a  to touch the second resting surface  114   b.  L 2  may be equal to L 1 . The second locking groove  114  may also include a second transitional plateau surface  114   d.    
         [0030]    The free rotation area  115  may include a third blocking surface  115   a,  a third resting surface  115   b  adjacent to the third blocking surface  115   a,  and a step surface  115   c.  The third bracket  130  and attached pin assembly  140  may rotate freely when the locking portion  141   a  is between the blocking surface  115   a  and the step surface  115   c,  i.e., when the locking portion  141   a  is in the free rotation area  115 . A third ramp surface  115   c ′ may be included adjacent the step surface  115   c.  A third transitional plateau surface  115   d  may also be included adjacent the third ramp surface  115   c′.    
         [0031]    As illustrated, the first, second and third ramp surfaces  113   c,    114   c,    115   c ′ may be shaped, i.e., angled, so as to ease a movement of the locking portion  141   a  to the second locking groove  114 , the free rotation area  115  and the first locking groove  113 , respectively. However, the purpose of these surfaces may be dual and include: (1) transitioning the pin assembly  140  from one locked state to another; and (2) resisting a movement of the locking portion  141   a  from the locking grooves  113 ,  114  and the free rotation area  115  in the first direction. As such, these surfaces may have alternative shapes. The first, second and third ramp surfaces  113   c,    114   c ,  115   c ′ may be angled or shaped such that a desired turning torque is necessary to transition the door  41  from one locking state to another. As illustrated in  FIGS. 6A and 6C , first bracket mounting holes  112 ′ of diameter D 9  may be located on opposite sides of the cylindrical mounting portion  112  and aligned with each other. 
         [0032]      FIGS. 8A-8C  illustrate detailed perspective views of the second bracket  120 . As illustrated, the second bracket  120  may be formed such that it includes an outer portion  120 ′ and an inner portion  120 ″. As illustrated, the outer portion  120 ′ may be arcuate in a first section  121  and flat in a second section  122 . The first section  121  includes a first end  121   a;  a second end  121   b;  an axis A b2  aligned with A b1;  and an inner radius R b2  equal to or greater than an outer radius R b1  of the first bracket  110 , where R b1  is calculated as D 6 /2. As illustrated, the first section  121  may include an arcuate tab  121 ′ on the second end  121   b  formed by a slot  122   a  on a first side  121   a  of the arcuate tab  121 ′ and a transitional relief  123  on a second side  121   b  of the arcuate tab  121 ′. The transitional relief  123  may include a transition surface  123 ′ in the general shape of an “S” as illustrated. The slot  122   a  may have a width of X 1  and a depth of Y 1  and the transitional relief  123  may have a depth of Y 2  which is smaller than Y 1 . The slot  122   a  may be formed in the flat section  122  which may be in a tangential relationship with the arcuate first section  121  as illustrated. The flat section  122  may include holes  127  to be aligned with holes  101   a  for attachment to the door frame  101  via conventional methods such as nuts and bolts as illustrated in  FIGS. 9 and 10 . 
         [0033]    As illustrated, integral to the transitional relief  123  may be an unlocking ramp  124  in the form of a straight tab having a ramp outer surface  124 ′ in a positional relationship with the transitional relief  123  such that points on the tab that are farther away from an edge of the transitional relief  123 ″ may be closer to the inner portion  120 ″ than points closer to the edge of the transitional relief  123 ″. The unlocking ramp  124  may be situated such that, while the locking pin assembly is in the locking position, the unlocking portion  141   b  of the locking pin assembly  140  is capable of contacting or engaging the ramp outer surface  124 ′ as the locking portion  141   a  falls to contact the third resting surface  115   b  of the first bracket  110  and the locking pin assembly  140  falls to its lowest height. As previously mentioned, and illustrated in  FIGS. 8A-8C , the second bracket  120  may also include a cylindrical inner portion  120 ″ having a cylindrical outer radius R b3  less than R b2  and an inner diameter D 7  equal to or greater than an outer diameter of the first bracket D 6  as well as aligned second bracket through holes  126  on opposite sides of the inner cylindrical portion  120 ″. Ideally, D 7  and D 6  are designed for the respective parts to fit together snugly. As illustrated in  FIG. 2 , the first bracket  110  is assembled to the second bracket  120  by fitting the first bracket  110  and the second bracket  120  together as shown, aligning the aligned first bracket through holes  112 ′ with the aligned second bracket through holes  126  and using a conventional nut and bolt arrangement to secure the first bracket  110  to the second bracket  120  via the aligned first and second bracket through holes  112 ′ and  126 . 
         [0034]      FIG. 10  presents an exemplary perspective view of the third bracket  130 . As illustrated the third bracket  130  may include a first cylindrical portion  131  having a first portion diameter D 9  and a pin mounting hole  131   a  therethrough for mounting the pin assembly  140 , a second cylindrical portion  132  having a second portion diameter D 10  which is smaller than the first portion diameter D 9  and a cone portion  133  for ease of assembly and operation. As illustrated, the first cylindrical portion  131  may may also include a threaded set screw hole  131   b  and a set screw  131   c  (or some other conventional arrangement) for rigidly mounting the pin assembly  140 , i.e., attaching the pin assembly  140  to the first cylindrical portion  131  with zero (0) degrees of freedom for relative movement between the pin assembly  140  and the third bracket  130 . The third bracket  130  may be appropriately oriented and welded to the door  102  along the surface of the first cylindrical portion  131  or rigidly attached to the door  102  via some other conventional means (see  FIG. 7 ). 
         [0035]    As described earlier, the first bracket  110  and the second bracket  120  may be arranged to have zero degrees (0°) of freedom for relative movement between these brackets, the door frame and, thus, the frame  40  as the first bracket  110  may be rigidly attached to the door frame  101  via conventional methods such as screws and the second bracket  120  may be rigidly attached to the first bracket  110  via conventional methods. The third bracket  130  and the locking pin assembly  140  may be arranged to have zero degrees (0°) of freedom for movement between these parts and the door  102  where the third bracket  130  may be rigidly attached to the door  102  and the locking pin assembly  140  may be rigidly attached to the third bracket  130  via the pin mounting hole  131   a  and the set screw  131   c.    
         [0036]    In operation, the first bracket  110 , the second bracket  120 , the third bracket  130  and the pin assembly  140  may be arranged such that, as the door  102  rotates in a first direction (e.g., an opening direction), the locking portion  141   a  may contact ramp surfaces  115   c  and  113   c  and, respectively, engage first and second locking grooves  113 ,  114  in that order. Ramp surfaces  115   c  and  113   c  aid in engagement of the first and second locking grooves  113 ,  114  by providing a more gradual transition to resting surfaces  113   b,    114   b,  respectively, and transitional plateau surfaces  115   d  and  113   d  smoothen the engagements by, respectively, providing buffer zones, while blocking surfaces  113   a,    114   a  tend to prevent rotation of the door  102  in a second direction (e.g., in a closing direction). As illustrated, the second end surface  111 ″ of the first bracket  110  may support the weight of the door  102  (see W d ). Thus the weight of the door  102  may tend to cause the locking hinge  100  to resist movement along any of the ramp surfaces  113   c,    115   c,    114   c  in the first direction and to prevent movement past the blocking surfaces  113   a,    114   a,    115   a  in the second direction, urging the door  102  to remain in the first or second groove  113 ,  114  via action W D  against the corresponding first or second resting surfaces  113   b,    114   b  and, thus, holding or locking the door  102  in place when the locking portion  141   a  enters either of the locking grooves  113 ,  114 . 
         [0037]    As illustrated in  FIG. 7 , as the door  102  rotates from the first locking groove  113  to the second locking grove  114  the door  102  may be lifted against W d  as points along second ramp  113   c  may be higher than points on the first resting surface  113   b  and the second resting surface  114   b  may be at a higher level than the first resting surface  113   b.  As illustrated, as the locking portion  141   a  leaves the second locking groove  114  and rises along the ramp surface  114   c,  the door  102  and the pin assembly  140  may reach their highest point along the first bracket  110  and the unlocking portion  141   b  may rise to a height greater than that of the unlocking ramp  124 . As the locking portion  141   a  reaches the end of the second ramp surface  114   c , the unlocking portion may be located at a radius greater than that of a contact surface  124   b  on the unlocking ramp  124  as well as at a higher location than the unlocking ramp  124 . Once the locking portion  141   a  clears the ramp surface  114   c  and the plateau surface  114   d,  and as the door  102  continues to turn in the first direction, the locking portion  141   a  falls to the level of the third resting surface  115   b  and the height of the unlocking portion  141   b  falls such that the unlocking portion  141   b  may contact or engage the contact surface  124   b.  As the door  102  then rotates in a second direction, the unlocking portion  141   b  slides along the contact surface  124   b  resulting in an increasing distance of the unlocking portion from the axis A 1  and, thereby, withdrawing the locking portion  141   a  from contact with the second end surface  111 ″. Once the unlocking portion  141   b  is in contact with the contact surface  121   c  of the arcuate portion  121 , the locking portion  141   a  may be completely withdrawn from the surface of the second end  110   b,  i.e., the unlocking portion  141   b  may have completely retracted the locking portion  141   a  from contact with the second end surface  111 ′. When the unlocking portion  141   b  reaches the transition side  123 ′, the pin assembly moves along the “S” shape to a greater height along the clearance surface  121   d  of the arcuate portion  121  and the unlocking portion  141   a  and the locking portion  141   b  rise to a level above that of the first and second locking grooves  113 ,  114  taking the locking pin assembly  140  and the third bracket  130  along with them. 
         [0038]    As illustrated, as the door  102  nears or reaches the closed position, the unlocking portion  141   b  may fall to the level of the second clearing surface  125  of the slot  122 , under the weight W D  of the door  102 . Once the unlocking portion  141   b  enters the slot  122 , the biased spring  143  may then return the pin assembly  140  to the locking mode, i.e., withdraw the unlocking portion  141   b  and extend the locking portion  141   a  for contact with the third resting surface  115   b  or the step surface  115   c  and, ultimately, contact with the third ramp surface  115   c ′ on the second end surface  111 ″ of the first bracket  110  when the door  102 , once again, begins to open. The slot  122  is sufficiently large to allow the unlocking portion  141   b  to pass through it. Finally, as the door  102  is rotated in the first direction, the locking portion  141   a,  once again, contacts the third and first ramp surfaces  115   c,    113   c  and the corresponding first and second locking grooves  113 ,  114 . Note: In this exemplary embodiment, the door  102  may be closed from any lock position by physically lifting the door  102  high enough for the locking portion  141   a  to clear locking grooves  113 ,  114  and simultaneously rotating the door  102  in the second direction. 
         [0039]      FIG. 11  illustrates an alternative exemplary embodiment of the invention for use on a door  102  opening in a vertical direction. As illustrated, this embodiment of the invention includes a two part cylindrical portion  132 ′ including first cylindrical portion  132 ′ a  which may be rigidly attached to the door  102  and second cylindrical portion  132 ′ b  which may be constrained to rotate with the first cylindrical portion via the shape of a connecting rod  132 ′ c , e.g. a connecting rod  132 ′ c  with a non-circular cross section such as a square or rectangular cross section, yet have limited translational freedom of movement, for an adjustable translational distance from the first cylindrical portion  132 ′ a  and a mechanism such as, for example, locking spring  132 ′ d  biasing the second cylindrical portion  132 ′ b  away from the first cylindrical portion  132 ′ a . In this exemplary embodiment, the locking spring  132 ′ d  may act as a substitute for the weight of the door  102  in holding the locking portion  141   a  in each of the locking grooves  113 ,  114  with sufficient force to keep the door  102  from rotating unless something external acts with sufficient force to rotate the door  102 . The strength of the locking spring  132 ′ d  may be adjusted to the level desired for resistance of rotational door movement. With the exception of the locking spring  132 ′ d , the alternative self locking hinge  100 ′ would operate in a manner identical to the self locking hinge  100 . Note: In this exemplary embodiment, the door  102  may be closed from any lock position by physically pushing the door  102  against the locking spring  132 ′d far enough for the locking portion  141   a  to clear locking grooves  113 ,  114  and simultaneously rotating the door  102  in the second direction.

Summary:
A self locking hinge is disclosed which can index a door to multiple open positions and hold it in place. The door may be closed by opening it completely and then returning it to the closed position or by lifting the door to clear a portion of a locking mechanism and simultaneously closing it.