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[0001]    This application is related to four other concurrently filed copending patent applications, namely U.S. patent application No. ______, entitled “Snow Plow Quick Connect/Disconnect Hitch Mechanism and Method,” U.S. patent application No. ______, entitled “Snow Plow Having an In-Line Frame Design and Method of Making the Same,” U.S. patent application No. ______, entitled “Cushion Stop and Method for Absorbing Bidirectional Impact of Snow Plow Blade Tripping,” U.S. patent application No. ______, entitled “Back Blade Wearstrip for Efficient Backward Operation of Snow Plows and Method for Facilitating the Same,” all assigned to the assignee of the present patent application, which four patent applications are hereby incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Field of the Invention—The present invention relates generally to snow plows for use with light and medium duty trucks, and more particularly to an improved snow plow with blade trip springs which are mounted using brackets located to direct the forces of the springs in directions which are orthogonal to the axis upon which the plow blade pivots, thereby increasing the predictability of the tripping forces exerted by the trip springs as well as eliminating lateral trip spring forces which could warp the plow blade.  
           [0003]    Once the exclusive domain of municipality-operated heavy trucks, snow plows have been used with light and medium duty trucks for decades. As would be expected in any area of technology which has been developed for that period of time, snow plows for light and medium duty trucks have undergone tremendous improvement in a wide variety of ways over time, evolving to increase both the usefulness of the snow plows as well as to enhance the ease of using them. The business of manufacturing snow plows for light and medium duty trucks has been highly competitive, with manufacturers of competing snow plows differentiating themselves based on the features and enhanced technology that they design into their products.  
           [0004]    When plowing snow, a not infrequent occurrence is striking an object which is concealed beneath the snow. This occurs particularly often when plowing roads which are not paved, such as, for example, gravel roads or dirt roads. Since roads being plowed are typically frozen, it is common for an object of significant size to become frozen into the road. For example, medium size rocks or sticks which would not present a significant obstacle were they loose on the surface of the road can present a problem when they are frozen into the surface of the road and concealed beneath a layer of snow. In addition, when significant snow depth covers the area being plowed, the operator may miscalculate and drive the snow plow into a fixed obstacle such as a curb.  
           [0005]    For this reason, snow plow blades have been manufactured for some time with a blade trip mechanism which allows the bottom of the blade to yield upon substantial impact. This is typically accomplished through the mounting of the snow plow blade on its support structure using a pivoting mechanism. The snow plow blade is mounted onto the support structure at a position between eight and sixteen inches above the ground in a manner which permits the bottom of the snow plow blade to pivot back when an object is struck. Simultaneously as the bottom of the snow plow blade pivots back, the top of the snow plow blade will pivot forward.  
           [0006]    This movement between the normal plowing position of the snow plow blade to the position in which the bottom of the snow plow blade pivots fully backward is referred to as blade tripping. The movement of the snow plow blade from the normal plowing position to the tripped position is resisted by two or more strong trip springs which are mounted behind the snow plow blade, typically running from positions near the top of the snow plow blade to the snow plow blade support structure. Even when the snow plow blade is in its normal plowing position, the trip springs are under tension. Accordingly, it will be appreciated that when the bottom of the snow plow blade is forced backward, the trip springs will provide a strong resistance to the movement, tending to absorb some of the force of the impact of the snow plow blade with the object which has been struck.  
           [0007]    In a typical embodiment, the snow plow blade is supported at two pivot points on the right and left sides of the snow plow blade by a swing frame. The snow plow blade has a plurality of vertically extending curved ribs which are connected between top and bottom plow frame members, and two of these ribs have apertures located between approximately eight and sixteen inches from the bottom of the snow plow blade. The snow plow blade is pivotally mounted to the swing frame using these apertures. The trip springs are mounted between the snow plow blade and the swing frame to provide the tripping resistance force.  
           [0008]    The trip springs are mounted to the snow plow blade using apertures located either in the ribs or in the top frame member, or using brackets mounted onto one or more of these members. The trip springs may be mounted at one end to the top frame member and the ribs from which the snow plow blade is pivotally supported. The other ends of each of the trip springs are mounted to the snow plow blade support structure, typically using brackets which may be mounted, for example, on the swing frame. The points of connection of the trip springs on the swing frame or other snow plow blade support structure are typically located closer to the center of the snow plow than is the point of connection of the trip springs to the snow plow blade.  
           [0009]    Although the predominant force exerted by the trip springs on the snow plow blade is orthogonal to the axis on which the snow plow blade pivots, a significant portion of the force is exerted in a lateral direction which is parallel to that axis. This component of the spring force is detrimental to the structural integrity of the snow plow blade frame, which is not constructed to resist forces in a lateral direction. Although the trip springs are located on both sides of the snow plow blade, and the lateral forces exerted by them thus tend to offset, over time their presence can cause blade distortion or other damage. In addition, it will be appreciated by those skilled in the art that since not all of the force exerted by the trip springs is in the direction orthogonal to the axis on which the snow plow blade pivots, the trip springs must be larger in order to provide the desired force in this orthogonal direction than they would otherwise be if all of the force which they exerted were in this orthogonal direction.  
           [0010]    It is accordingly the primary objective of the present invention that it mount the trip springs on a snow plow in a manner whereby all of the force exerted by the trip springs is exerted in a direction which is orthogonal to the axis about which the snow plow blade pivots. It is a closely related objective of the present invention that it provide mounting brackets which facilitate the mounting of the trip springs in a manner which eliminates the exertion of any lateral force by the trip springs. It is a further related objective of the present invention that it minimize the size of the trip springs by ensuring that all of the force which they exert is directed properly to provide the required force in the requisite direction.  
           [0011]    It is another primary objective of the present invention that the force exerted by the trip springs is exerted proximate a plane which is orthogonal to the pivot points at which the snow plow blade is mounted to the snow plow blade support structure. It is a related objective that the force of the trip springs is exerted on appropriate areas of the snow plow blade so that any potential distortion of the snow plow blade is inhibited. It is a further objective of the present invention that it facilitate the use of either a single trip spring on either side of the snow plow blade or two trip springs on each side of the snow plow blade.  
           [0012]    The snow plow trip spring mount of the present invention must also be of a construction which is both durable and long lasting, and it should also require little or no maintenance to be provided by the user throughout its operating lifetime. In order to enhance the market appeal of the snow plow trip spring mount of the present invention, it should also be of inexpensive construction to thereby afford it the broadest possible market. Finally, it is also an objective that all of the aforesaid advantages and objectives of the snow plow trip spring mount of the present invention be achieved without incurring any substantial relative disadvantage.  
         SUMMARY OF THE INVENTION  
         [0013]    The disadvantages and limitations of the background art discussed above are overcome by the present invention. With this invention, the trip springs which control the tripping action of the snow plow blade are each mounted such that they exert force only in a plane which is perpendicular to the axis of rotation of the snow plow blade&#39;s tripping movement. The snow plow blade itself is supported at two pivot points on the right and left sides of the snow plow blade by a swing frame, and the trip springs are each mounted between the swing frame and the snow plow blade.  
           [0014]    The snow plow blade has a plurality of vertically oriented curved ribs which are connected between top and bottom plow frame members, and two of these ribs have apertures located between approximately eight and sixteen inches from the bottom of the snow plow blade. The swing frame itself is based upon a rectangular steel swing frame tube, which has a pivot made of steel tubing extending between two opposite sides of the swing frame in a location intermediate the ends of the swing frame. The swing frame will be pivotally supported by a snow plow frame, which in turn will be mounted onto the front of a truck. The swing frame has a pair of parallel blade pivot mounts located at each end thereof, which blade pivot mounts extend forwardly from a swing frame tube upon which they are mounted.  
           [0015]    Located near the front of each of the blade pivot mounts are apertures which are aligned in each pair of blade pivot mounts. Each pair of blade pivot mounts will receive a portion of one of the ribs on the snow plow frame which have the apertures therein, with one of the blade pivot mounts in each pair being located on either side of the rib to which that side of the swing frame is being mounted. A pin extends through the aligned apertures on each side of the snow plow blade to pivotally mount it on the swing frame.  
           [0016]    Located on the swing frame near each of the ends thereof is a bracket for mounting one end of one or two trip springs, the other ends of which trip springs will be mounted to corresponding brackets which are mounted onto the frame of the snow plow blade. In the preferred embodiment, the brackets on the swing frame are mounted on the blade pivot mounts, and the brackets on the snow plow blade are mounted on the ribs of the snow plow blade which are pivotally mounted to the blade pivot mounts on the swing frame. Since these brackets are aligned with each other, the trip springs mounted between the corresponding pairs of brackets will be oriented front to rear, and as such will not exert any lateral pull on the snow plow blade.  
           [0017]    In the preferred embodiment, two trip springs are mounted at each side of the snow plow blade. Alternately, a single trip spring may instead be used on each side of the snow plow blade. As the snow plow blade pivots between its trip return position and its tripped position, the trip springs always exert force only within a plane which is parallel to the axis of the pivoting movement of the snow plow blade.  
           [0018]    It may therefore be seen that the present invention teaches an apparatus and method for mounting the trip springs on a snow plow in a manner whereby all of the force exerted by the trip springs is exerted in a direction which is orthogonal to the axis about which the snow plow blade pivots. The mounting brackets of the present invention facilitate the mounting of the trip springs in a manner which eliminates the exertion of any lateral force by the trip springs. The size of the trip springs required by the present invention is minimized by ensuring that all of the force which they exert is directed properly to provide the required force in the requisite direction.  
           [0019]    The force exerted by the trip springs of the snow plow trip spring mount of the present invention is exerted proximate a plane which is orthogonal to the pivot points at which the snow plow blade is mounted to the snow plow blade support structure. In addition, the force of the trip springs is exerted on appropriate areas of the snow plow blade so that any potential distortion of the snow plow blade is inhibited. The snow plow trip spring mount of the present invention facilitates the use of either a single trip spring on either side of the snow plow blade or two trip springs on each side of the snow plow blade.  
           [0020]    The snow plow trip spring mount of the present invention is of a construction which is both durable and long lasting, and which will require little or no maintenance to be provided by the user throughout its operating lifetime. The snow plow trip spring mount of the present invention is also of inexpensive construction to enhance its market appeal and to thereby afford it the broadest possible market. Finally, all of the aforesaid advantages and objectives of the snow plow trip spring mount of the present invention are achieved without incurring any substantial relative disadvantage.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0021]    These and other advantages of the present invention are best understood with reference to the drawings, in which:  
         [0022]    [0022]FIG. 1 is a perspective view of a plow A-frame;  
         [0023]    [0023]FIG. 2 is a partial cross-sectional view of the plow A-frame illustrated in FIG. 1;  
         [0024]    [0024]FIG. 3 is a perspective view of a plow swing frame which will be pivotally mounted on the front end of the plow A-frame illustrated in FIGS. 1 and 2 and which will support a plow blade therefrom;  
         [0025]    [0025]FIG. 4 is a cross-sectional view of the plow swing frame illustrated in FIG. 3;  
         [0026]    [0026]FIG. 5 is a bottom plan view of the plow swing frame illustrated in FIGS. 3 and 4;  
         [0027]    [0027]FIG. 6 is a perspective view of a pivoting lift bar which will be pivotally mounted at the rear end of the plow A-frame illustrated in FIGS. 1 and 2;  
         [0028]    [0028]FIG. 7 is a perspective view of a hitch frame nose piece which will be mounted on a truck under the front bumper thereof;  
         [0029]    [0029]FIG. 8 is a perspective view of a bellcrank which is used to operate the pivoting lift bar illustrated in FIG. 6;  
         [0030]    [0030]FIG. 9 is a perspective view of a lift link which connects the bellcrank illustrated in FIG. 8 to the pivoting lift bar illustrated in FIG. 6;  
         [0031]    [0031]FIG. 10 is a cutaway view of the various components of the snow plow frame assembled together, showing the hydraulic cylinder used to pivot the lift bar;  
         [0032]    [0032]FIG. 11 is a perspective view of a plow blade from the rear side which will be mounted onto the plow swing frame illustrated in FIGS. 3 through 5;  
         [0033]    [0033]FIG. 12 is an exploded view of the plow blade illustrated in FIG. 11, showing the assembly of a moldboard made of man-made material onto the plow blade frame;  
         [0034]    [0034]FIG. 13 is a partial cross-sectional view of the top of the plow blade illustrated in FIG. 11, showing how the top of the moldboard is retained by the plow blade frame;  
         [0035]    [0035]FIG. 14 is a partial cross-sectional view of the bottom of the plow blade illustrated in FIG. 11, showing how the bottom of the moldboard is retained by the plow blade frame and the plow cutting edge;  
         [0036]    [0036]FIG. 15 is a partial cross-sectional view of a side edge of the plow blade illustrated in FIG. 11, showing how the side of the moldboard is retained by the plow blade frame;  
         [0037]    [0037]FIG. 16 is a partial perspective view of the rear of the plow blade illustrated in FIG. 11, showing the installation of a wear strip onto the rear of the plow blade;  
         [0038]    [0038]FIG. 17 is an exploded, partial cross-sectional view showing the assembly of the plow swing frame illustrated in FIGS. 3 through 5 onto the plow A-frame illustrated in FIGS. 1 and 2;  
         [0039]    [0039]FIG. 18 is a partial cross-sectional view showing the plow swing frame and the plow A-frame illustrated in FIG. 17 assembled together;  
         [0040]    [0040]FIG. 19 is a perspective view of a blade stop cushion;  
         [0041]    [0041]FIG. 20 is a cross-sectional view from the side showing the installation of the blade stop cushion illustrated in FIG. 19 onto the plow swing frame, with the plow blade in its normal position as stopped by the blade stop cushion;  
         [0042]    [0042]FIG. 21 is a cross-sectional view of the components illustrated in FIG. 20, from the top side thereof;  
         [0043]    [0043]FIG. 22 is a cross-sectional view from the side similar to the view of FIG. 20, but with the plow blade in a rotated position as stopped by the blade stop cushion;  
         [0044]    [0044]FIG. 23 is a perspective view of portions of the plow blade and the plow swing frame, showing the spring mounts on one side of the plow blade and the plow swing frame, and also showing two springs in phantom lines;  
         [0045]    [0045]FIG. 24 is a partial rear plan view of the plow blade, the plow swing frame, and the spring mounts illustrated in FIG. 23;  
         [0046]    [0046]FIG. 25 is a perspective view of an alternate embodiment similar to the view shown in FIG. 23, but with a single spring mount on one side of the plow blade and the plow swing frame, and also showing a spring in phantom lines;  
         [0047]    [0047]FIG. 26 is a partial rear plan view of plow blade, the plow swing frame, and the spring mount illustrated in FIG. 25;  
         [0048]    [0048]FIG. 27 is a cross-sectional view from the side of the assembled plow blade and the plow swing frame, showing the plow blade in its normal position;  
         [0049]    [0049]FIG. 28 is a cross-sectional view from the side of the assembled plow blade and the plow swing frame, showing the plow blade in its rotated position;  
         [0050]    [0050]FIG. 29 is a perspective view of the assembled snow plow of the present invention;  
         [0051]    [0051]FIG. 30 is a top view of the assembled snow plow illustrated in FIG. 29;  
         [0052]    [0052]FIG. 31 is a partial view from the top showing the hitch mounting mechanism on one side of the snow plow illustrated in FIGS. 29 and 30 prior to installation;  
         [0053]    [0053]FIG. 32 is a partial view from the top showing the components illustrated in FIG. 31 in a mounted position;  
         [0054]    [0054]FIG. 33 is a partial cross-sectional view from the front showing the components illustrated in  
         [0055]    [0055]FIGS. 28 and 29 in a mounted position with the retaining pin inserted;  
         [0056]    [0056]FIG. 34 is a side view of the snow plow illustrated in FIGS. 29 and 30 as the hitch frame nose piece is brought into engagement with a mounting pin on the pivoting lift bar;  
         [0057]    [0057]FIG. 35 is a schematic depiction of the engagement of the mounting pin with a slot in the hitch frame nose piece;  
         [0058]    [0058]FIG. 36 is a side view similar to that of FIG. 34, with the pivoting lift bar beginning to pivot to bring the mounting pin into engagement with the slot in the hitch frame nose piece;  
         [0059]    [0059]FIG. 37 is a side view similar to that of FIGS. 34 and 36, with the pivoting lift bar pivoted to bring the mounting holes in the pivoting lift bar into alignment with the mounting holes in the hitch frame nose piece; and  
         [0060]    [0060]FIG. 38 is a perspective view of an alternate embodiment snow plow having blade shoes mounted thereupon.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0061]    The preferred embodiment of the present invention is illustrated in a series of figures, of which the FIGS. 1 through 9 and  11  are components of the snow plow which embodies the present invention. FIGS. 10, 12 through  24 , and  27  through  29  illustrate the assembly of the snow plow embodying the present invention, and FIGS. 30 through 37 illustrate the manner in which the snow plow is attached to the hitch. Finally, FIGS. 25, 26, and  38  illustrate two alternate embodiments. The snow plow of the present invention includes five novel aspects: a novel frame design which has a lower profile and an enhanced linear strength which is attained by that design; a novel hitch quick connect, quick release design; a novel plow blade trip spring placement; a novel plow blade stop design which uses replaceable cushion stop blocks to absorb the impact of plow blade movement between extreme positions; and a novel back blade wearstrip which allows the plow blade to be used to plow backward as well as forward.  
         [0062]    The first of these five novel aspects of the snow plow of the present invention resides in the innovative design of its two-piece frame. Referring first to FIGS. 1 and 2, the first of these two pieces, a plow A-frame  50 , is illustrated. The plow A-frame  50  as illustrated in FIG. 2 has its front end shown at the left of FIG. 2 and its rear end shown at the right of FIG. 2, and is symmetric around an axis running from the front to the rear thereof. The plow A-frame  50  tapers from a narrower width at the front thereof to a wider width at the rear thereof.  
         [0063]    The basic shape of the plow A-frame  50  is formed by a top plate  52  and a bottom plate  54 , which are essentially parallel and are spaced apart from each other. The configurations of the top plate  52  and the bottom plate  54  as viewed from the top (or from the bottom) resemble a portion of the capital letter “A,” with the portions of the sides of the “A” above the crossbar of the “A” being absent. There is a large aperture extending through each of the top plate  52  and the bottom plate  54  above the crossbar of the “A,” which apertures resemble an isosceles trapezoid. The top plate  52  and the bottom plate  54  are preferably made of steel plate.  
         [0064]    Mounted between the sides of the top plate  52  and the bottom plate  54  at the location of the crossbar of the “A” and extending rearwardly so as to resemble abbreviated legs of the “A” below the crossbar are two lugs  56  and  58  made of flat bar stock. The lugs  56  and  58  are also preferably made of steel, and are welded onto the sides of the top plate  52  and the bottom plate  54 . The portion of the lug  56  which extends rearwardly from the top plate  52  and the bottom plate  54  has an aperture  60  extending therethrough, and the portion of the lug  58  which extends rearwardly from the top plate  52  and the bottom plate  54  has an aperture  62  extending therethrough.  
         [0065]    Portions of three sides of the top plate  52  are bent downwardly at a ninety degree angle to extend to the top of the bottom plate  54 . Only one of these sides, a left side  64 , is visible in FIGS. 1 and 2. The left side  64  of the top plate  52  extends from just in front of the lug  58 , and extends approximately two-thirds of the way toward the front end of the plow A-frame  50 . A right side of the top plate  52  (which is the mirror image of the left side  64  of the top plate  52 ) and a rear side of the top plate  52  extending between the lugs  56  and  58  are also bent downwardly at ninety degree angles to extend to the top of the bottom plate  54 . These three sides are all welded to the bottom plate  54  to create a box-like structure. A rectangular plate  66  is located just in front of the isosceles trapezoid-shaped apertures in the top plate  52  and the bottom plate  54 , and extends between the sides of the top plate  52  and the bottom plate  54 . The rectangular plate  66  is also preferably made of steel, and all four sides of the rectangular plate  66  are welded onto the top plate  52  (including the left side  64  and right side thereof) and the bottom plate  54  to provide the fourth side of the box-like structure.  
         [0066]    Extending from the sides of the lugs  56  and  58  are U-shaped swing cylinder mounts  76  and  78 , respectively. The swing cylinder mounts  76  and  78  are also preferably made of steel, and are welded onto the lugs  56  and  58 , respectively, with the legs of the U&#39;s of the swing cylinder mounts  76  and  78  being located on the top and the bottom of the plow A-frame  50 . An aperture  80  is located in each leg of the U in the swing cylinder mount  76 , and an aperture  82  is similarly located in each leg of the U in the swing cylinder mount  78 .  
         [0067]    Located between the rear of the top plate  52  at the location of the crossbar of the “A” and the rear of the bottom plate  54  at the location of the crossbar of the “A” are two lift cylinder mounts  84  and  86 . The cylinder mounts  84  and  86  are parallel both to each other and to the plane which divides the plow A-frame  50  into left and right sides thereof. The cylinder mounts  84  and  86  each extend from slots  88  and  90 , respectively, located in the crossbar of the “A” of the top plate  52  and slots  92  and  94 , respectively, located in the crossbar of the “A” of the bottom plate  54 . The cylinder mounts  84  and  86  are also preferably made of steel, and their ends are welded into the slots  88  and  90 , respectively, in the top plate  52  and the slots  92  and  94 , respectively, in the bottom plate  54 . The cylinder mounts  84  and  86  each have an aperture  96  or  98 , respectively, located therein which apertures  96  and  98  are coaxial.  
         [0068]    Located at the top of the aperture in the “A” in the plow A-frame  50  are two parallel, spaced-apart, pivot mount plates  100  and  102 . The pivot mount plates  100  and  102  are also preferably made of steel, and are welded onto the rectangular plate  66 , the portion of the top plate  52  adjacent thereto, and the portion of the bottom plate  54  adjacent thereto. The pivot mount plates  100  and  102  are mounted on opposite sides of the centerline of the plow A-frame  50 , and extend rearwardly and upwardly from the rectangular plate  66 , and are beneath a portion of the bottom plate  54 . Located near the rearmost and uppermost ends of the pivot mount plates  100  and  102  are apertures  104  and  106 , respectively, which are coaxial.  
         [0069]    Mounted near the front of the plow A-frame  50  are two hollow cylindrical swing frame pivots  108  and  110 . The swing frame pivots  108  and  110  are centrally mounted near the front end of the plow A-frame  50  in apertures  112  and  114 , respectively, which are located in the top plate  52  and the bottom plate  54 , respectively. The swing frame pivots  108  and  110  are also preferably made of steel, and are welded into the apertures  112  and  114 , respectively. The swing frame pivots  108  and  110  are coaxial and are orthogonal to the top plate  52  and the bottom plate  54 .  
         [0070]    Located on the inside of each of the legs of the “A” of the plow A-frame  50  near to the top of the “A” are two support sides  116  and  118 . The support sides  116  and  118  extend perhaps one-fourth of the way from the top of the opening of the “A” toward the crossbar of the “A.” The ends of the support sides  116  and  118  oriented closest to the crossbar of the “A” extend between the top side of the top plate  52  and the bottom side of the bottom plate  54 , and the support sides  116  and  118  increase in height above the top plate  52  and below the bottom plate  54  as the support sides  116  and  118  extend towards the front of the plow A-frame  50 . The support sides  116  and  118  are preferably made of steel, and are welded to the top plate  52 , the bottom plate  54 , and the rectangular plate  66 .  
         [0071]    Four U-shaped ribs  120 ,  122 ,  124 , and  126  extend between the support sides  116  and  118  and the swing frame pivots  108  and  110 . The bases of the “U” of each of the U-shaped ribs  120 ,  122 ,  124 , and  126  are much wider than the legs of the “U” are tall. The U-shaped ribs  120  and  122  are mounted on top of the top plate  52 , and the bases of the “U&#39;s” of the U-shaped ribs  120  and  122  are located close adjacent the right and left sides, respectively, of the top plate  52 . The U-shaped rib  124  and  126  are mounted on the bottom of the bottom plate  54 , and the bases of the “U&#39;s” of the U-shaped ribs  124  and  126  are located close adjacent the right and left sides, respectively, of the bottom plate  54 . In the preferred embodiment, the U-shaped rib  120 , the support side  116 , and the U-shaped rib  124  are manufactured as a single component, and likewise the U-shaped rib  122 , the support side  118 , and the U-shaped rib  126  are also manufactured as a single component.  
         [0072]    One leg of the U-shaped rib  120  extends between the base of the “U” and the support side  116 , and the other leg of the U-shaped rib  120  extends between the base of the “U” and the swing frame pivot  108 . One leg of the U-shaped rib  122  extends between the base of the “U” and the support side  118 , and the other leg of the U-shaped rib  122  extends between the base of the “U” and the swing frame pivot  108 . One leg of the U-shaped rib  124  extends between the base of the “U” and-the support side  116 , and the other leg of the U-shaped rib  124  extends between the base of the “U” and the swing frame pivot  110 . One leg of the U-shaped rib  126  extends between the base of the “U” and the support side  118 , and the other leg of the U-shaped rib  126  extends between the base of the “U” and the swing frame pivot  110 .  
         [0073]    The U-shaped ribs  120 ,  122 ,  124 , and  126  are preferably made of steel, and the U-shaped ribs  120  and  122  are welded onto the top plate  52 , while the U-shaped ribs  124  and  126  are welded onto the bottom of the bottom plate  54 . As mentioned above, the U-shaped ribs  120  and  124  may be made integrally with the support side  116 , while the U-shaped rib  122  and  126  may be made integrally with the support side  118 . The swing frame pivots  108  and  110  define an axis upon which a swing frame which will be described below in conjunction with FIGS. 3 through 5 will be mounted, and the area between the top plate  52  and the bottom plate  54  and in front of the rectangular plate  66  is the area in which the swing frame will be mounted.  
         [0074]    Referring next to FIGS. 3 through 5, a swing frame  140  is illustrated which will be mounted as described above on the plow A-frame  50  (illustrated in FIGS. 1 and 2). The swing frame  140  is based upon a rectangular swing frame tube  142  having a hollow cylindrical pivot  144  extending through the thinner cross section thereof at the midpoint of the length of the rectangular swing frame tube  142 . The rectangular swing frame tube  142  has an aperture  146  located in the top side thereof and another aperture  148  located in the bottom side thereof. The apertures are closer to the rear side of the rectangular swing frame tube  142  than they are to the front side thereof. Both the rectangular swing frame tube  142  sand the pivot  144  are preferably made of steel, and the pivot  144  is welded to the rectangular swing frame tube  142 . The pivot  144  extends slightly above and below the top and bottom, respectively, of the rectangular swing frame tube  142 .  
         [0075]    A guide plate  150  extends from the rear of the rectangular swing frame tube  142 . The guide plate  150  is shaped like an isosceles trapezoid with a low triangle mounted on the top thereof, with the base of the isosceles trapezoid mounted onto the rectangular swing frame tube  142 . The width of the guide plate  150  is perhaps half of the length of the rectangular swing frame tube  142 , and the guide plate  150  is centrally mounted both as to the length of the rectangular swing frame tube  142  and as to its height as well. The guide plate  150  is preferably also steel, and is welded onto the rectangular swing frame tube  142 .  
         [0076]    Mounted on the rear edge of the guide plate  150  is a guide/stop bar  152  which is made of a segment of flat stock which is wider than the height of the rectangular swing frame tube  142 . The guide/stop bar  152  is bent to conform to the guide plate  150 , and its ends contact the rear side of the rectangular swing frame tube  142 . The guide plate  150  and the guide/stop bar  152  together form a T-shaped configuration in cross-section, as best shown in FIG. 4. The guide/stop bar  152  thus extends both slightly above and slightly below the rectangular swing frame tube  142 , as is also best shown in FIG. 4. The guide/stop bar  152  is preferably made of steel, and is welded onto the guide plate  150 , with the ends of the guide/stop bar  152  being welded onto the rear of the rectangular swing frame tube  142 . When the swing frame  140  is mounted onto the plow A-frame  50  (illustrated in FIGS. 1 and 2), the guide/stop bar  152  will contact the rectangular plate  66  when the swing frame  140  is rotated between its extreme positions, with the guide/stop bar  152  thus acting to prevent rotation of the swing frame  140  in either direction beyond these positions.  
         [0077]    Four triangular swing cylinder mounting plates  154 ,  156 ,  158 , and  160  are mounted onto the rectangular swing frame tube  142  at positions approximately halfway between the center and the ends of the rectangular swing frame tube  142 , and project rearwardly. The swing cylinder mounting plates  154  and  156  are mounted on the top of the rectangular swing frame tube  142  near the rear edge thereof and the right and left sides thereof, respectively. The swing cylinder mounting plates  158  and  160  are mounted on the bottom of the rectangular swing frame tube  142  near the rear edge thereof and the right and left sides thereof, respectively. The swing cylinder mounting plates  154 ,  156 ,  158 , and  160  are preferably made of steel, and are welded onto the rectangular swing frame tube  142 .  
         [0078]    The swing cylinder mounting plates  154 ,  156 ,  158 , and  160  each have a slot  162 ,  164 ,  166 , or  168 , respectively, cut therein to receive an end of the guide/stop bar  152 . The ends of the guide/stop bar  152  fit into these slots  162 ,  164 ,  166 , or  168  and are welded therein. Located in each of the swing cylinder mounting plates  154 ,  156 ,  158 , and  160  near the rearmost corner thereof is an aperture  170 ,  172 ,  174 , or  176 , respectively. The apertures  170  and  174  are coaxial, and the apertures  172  and  176  are coaxial.  
         [0079]    Four blade pivot mounts  178 ,  180 ,  182 , and  184  are mounted on the rectangular swing frame tube  142  in spaced-apart pairs located at each end thereof. The blade pivot mounts  178 ,  180 ,  182 , and  184  have rectangular apertures  186 ,  188 ,  190 , and  192 , respectively, extending therethrough to receive therein the rectangular swing frame tube  142 . The blade pivot mount  178  is mounted at the end of the rectangular swing frame tube  142  which will be on the right when the swing frame  140  is mounted on the plow A-frame  50  (illustrated in FIGS. 1 and 2), and the blade pivot mount  180  is spaced away from the blade pivot mount  178  on the rectangular swing frame tube  142 .  
         [0080]    Similarly, the blade pivot mount  184  is mounted at the end of the rectangular swing frame tube  142  which will be on the left when the swing frame  140  is mounted on the plow A-frame  50 , and the blade pivot mount  182  is spaced away from the blade pivot mount  184  on the rectangular swing frame tube  142 . The spacing between the blade pivot mount  178  and the blade pivot mount  180 , and between the blade pivot mount  182  and the blade pivot mount  184  is sufficient to admit cushion stops which will be discussed below in conjunction with FIG. 19. The blade pivot mounts  178 ,  180 ,  182 , and  184  are preferably also made of steel, and are welded onto the rectangular swing frame tube  142 .  
         [0081]    It should be noted that the blade pivot mounts  178 ,  180 ,  182 , and  184  are identical in construction, with each extending forwardly in front of the rectangular swing frame tube  142  (as best shown in FIG. 4) and rearwardly and upwardly behind the rectangular swing frame tube  142 . Located near the front of the blade pivot mounts  178 ,  180 ,  182 , and  184  are apertures  194 ,  196 ,  198 , and  200 , respectively, which will be used to pivotally mount the snow plow blade (illustrated below in FIG. 11). The apertures  194 ,  196 ,  198 , and  200  are coaxial. Located in the blade pivot mounts  178 ,  180 ,  182 , and  184  intermediate the apertures  194 ,  196 ,  198 , and  200 , respectively, and the front of the rectangular swing frame tube  142  are apertures  202 ,  204 ,  206 , and  208 , respectively, which will be used to retain cushion stops which will be discussed below in conjunction with FIG. 19. The pairs of apertures  202  and  204 , and  206  and  208  are coaxial.  
         [0082]    As mentioned above, each of the blade pivot mounts  178 ,  180 ,  182 , and  184  also extends rearwardly of the rectangular swing frame tube  142 , resembling the profile of a vertical tail fin of a plane as best shown in FIG. 4. Mounted to each pair of each pair of the blade pivot mounts  178  and  180 , and  182  and  184 , are two trip spring brackets  210  and  212 . The trip spring brackets  210  and  212  are preferably also made of steel, are generally oval in configuration, and are mounted with the wider sides being oriented between the left and right sides of the swing frame  140 . The trip spring bracket  210  is welded onto the blade pivot mounts  178  and  180 , and the trip spring bracket  212  is welded onto the blade pivot mounts  182  and  184 . The trip spring bracket  210  has apertures  214  and  216  disposed near opposite ends thereof, and similarly the trip spring bracket  212  has apertures  218  and  220  disposed near opposite ends thereof.  
         [0083]    Completing the swing frame  140  are two additional components which are used both to act as a stop for rotational movement of the plow blade (which will be discussed below in conjunction with FIG. 11) as well as to help define an enclosure for the cushion stops (which will be discussed below in conjunction with FIG. 18). A stop  222  is mounted at the top of, intermediate, and at the bottom of the blade pivot mounts  178  and  180 . The stop  222  extends rearwardly from a point above the apertures  202  and  204 , drops down in front of the rectangular swing frame tube  142 , and extends rearwardly below the rectangular swing frame tube  142  to a point halfway between the front edge of the rectangular swing frame tube  142  and the pivot  144 .  
         [0084]    Similarly, a stop  224  is mounted at the top of, intermediate, and at the bottom of the blade pivot mounts  182  and  184 . The stop  224  extends rearwardly from a point above the apertures  206  and  208 , drops down in front of the rectangular swing frame tube  142 , and extends rearwardly below the rectangular swing frame tube  142  to a point halfway between the front edge of the rectangular swing frame tube  142  and the pivot  144 . The stops  222  and  224  are both preferably also made of steel, and are welded to the blade pivot mount pairs  178  and  180 , and  182  and  184 , respectively.  
         [0085]    Referring next to FIG. 6, a lift bar  230  is illustrated which forms part of the hitch mechanism of the snow plow. The lift bar  230  has two lift bar support members  232  and  234 , which are located on the right and left sides, respectively, of the lift bar  230 . Each of the lift bar support members  232  and  234  has a configuration consisting of three segments: rear mounting supports  236  and  238 , respectively, which extend upward vertically; central support arms  240  and  242 , respectively, which extend forwardly and upwardly from the top of the rear mounting supports  236  and  238 , respectively; and front light bar supports  244  and  246 , respectively, which extend upwardly from the forwardmost and upwardmost ends of the central support arms  240  and  242 , respectively. The lift bar support members  232  and  234  are preferably made of steel plate.  
         [0086]    Extending inwardly from the rear sides of rear mounting supports  236  and  238  are segments of angled stock  248  and  250 , respectively. It should be noted that the angle defined by each of the segments of angled stock  248  and  250  is less than ninety degrees, as, for example, approximately seventy degrees. The reason for this angle will become apparent below in conjunction with the discussion of FIGS. 31 and 32. The angled stock segments  248  and  250  are also preferably made of steel, and are welded onto rear mounting supports  236  and  238 , respectively, so that the rear mounting supports  236  and  238  and the angled stock segments  248  and  250  together form vertically-oriented channels which are essentially U-shaped. Referring for the moment to FIG. 1 in addition to FIG. 6, the space between the rear mounting support  236  and the angled stock segment  248  of the lift bar  230  is designed to admit the lug  56  of the plow A-frame  50  with space between the lug  56  and the inside of the angled stock segment  248 , and similarly the space between the angled stock segment  250 , and the rear mounting support  238  of the lift bar  230  is designed to admit the lug  58  of the plow A-frame  50  with space between the lug  58  and the inside of the angled stock segment  250 .  
         [0087]    Referring again solely to FIG. 6, a rectangular reinforcing segment  252  (preferably also made of steel) is located at the bottom of the U-shaped channel formed by the rear mounting support  236  and the angled stock segment  248 , and is welded to the bottoms of the rear mounting support  236  and the angled stock segment  248 . Similarly, a rectangular reinforcing segment  254  (preferably also made of steel) is located at the bottom of the U-shaped channel formed by the rear mounting support  238  and the angled stock segment  250 , and is welded to the bottoms of the rear mounting support  238  and the angled stock segment  250 .  
         [0088]    Not illustrated in the figures but used to reinforce the construction of the lift bar  230  are two additional rectangular reinforcing segments which are respectively located above the reinforcing segments  252  and  254 . On the right side of the lift bar  230 , the first of these additional reinforcing segments (preferably also made of steel) is located near the top of the U-shaped channel formed by the rear mounting support  236  and the angled stock segment  248 , and is welded to the tops of the rear mounting support  236  and the angled stock segment  248 . Similarly, the other of these reinforcing segments (preferably also made of steel) is located at near the top of the U-shaped channel formed by the rear mounting support  238  and the angled stock segment  250 , and is welded to the tops of the rear mounting support  238  and the angled stock segment  250 .  
         [0089]    Extending between the lift bar support members  232  and  234  are a larger diameter hollow round upper pin support tube  256  and a smaller diameter round light bar brace  258 . The upper pin support tube  256  and the light bar brace  258  are both also preferably made of steel. One end of the upper pin support tube  256  extends through an aperture  260  located in an intermediate position in the central support arm  240  of the lift bar support member  232 , and the other end of the upper pin support tube  256  extends through an aperture  262  located in an intermediate position in the central support arm  242  of the lift bar support member  234 . The ends of the upper pin support tube  256  are welded onto the central support arms  240  and  242 . One end of the light bar brace  258  is welded onto the lift bar support member  232  at the intersection of the central support arm  240  and the light bar support  244 , and the other end of the light bar brace  258  is welded onto the lift bar support member  234  at the intersection of the central support arm  242  and the light bar support  246 .  
         [0090]    Two upper pin hanger plates  264  and  266  are mounted on the upper pin support tube  256  in spaced-apart fashion near the middle of the upper pin support tube  256 . The upper pin hanger plates  264  and  266  have apertures  268  and  270 , respectively, extending therethrough near one end thereof, and the upper pin support tube  256  extends through these apertures  268  and  270 . The upper pin hanger plates  264  and  266  are both also preferably made of steel, and are welded onto the upper pin support tube  256  in a manner whereby they are projecting forwardly. A tubular upper pin  272  extends through apertures  274  and  276  in the upper pin hanger plates  264  and  266 , respectively, near the other end thereof. The upper pin  272  is also preferably made of steel, and is welded onto the upper pin hanger plates  264  and  266 .  
         [0091]    Located in the rear mounting support  236 , the angled stock segment  248 , the angled stock segment  250 , and the rear mounting support  238  near the bottoms thereof are apertures  278 ,  280 ,  282 , and  284 , respectively, which are aligned with each other and which together define a pivot axis about which the lift bar  230  will pivot when it is mounted onto the plow A-frame  50  (Illustrated in FIG. 1). Located in the rear mounting support  236 , the angled stock segment  248 , the angled stock segment  250 , and the rear mounting support  238  nearer the tops thereof than the bottoms thereof are apertures  286 ,  288 ,  290  (not shown in FIG. 6), and  292 , which are aligned with each other.  
         [0092]    The apertures  286  and  288  define a first location into which a retaining pin (not shown in FIG. 6) will be placed to mount the snow plow of the present invention onto a truck, and the apertures  290  and  292  define a second location into which another retaining pin (not shown in FIG. 6) will be placed to mount the snow plow of the present invention onto the truck. Located in the light bar support  244  are three apertures  294 , and located in the light bar support  246  are three apertures  296 . The apertures  294  and  296  will be used to mount a light bar (not illustrated in FIG. 6) onto the lift bar  230 .  
         [0093]    Referring now to FIG. 7, a hitch frame nose piece  300  which will be mounted onto a truck under the front bumper (not illustrated in FIG. 7) thereof is illustrated. The hitch frame nose piece  300  has a square hitch frame tube  302  which is horizontally oriented. Four hitch brackets  304 ,  306 ,  308 , and  310  are mounted on the square hitch frame tube  302  in spaced-apart pairs located nearer the ends of the square hitch frame tube  302  than the center thereof. The hitch brackets  304 ,  306 ,  308 , and  310  have square apertures  312 ,  314 ,  316 , and  318 , respectively, extending therethrough to receive therein the square hitch frame tube  302 . Both the square hitch frame tube  302  and the hitch brackets  304 ,  306 ,  308 , and  310  are preferably made of steel, and the hitch brackets  304 ,  306 ,  308 , and  310  are welded onto the square hitch frame tube  302 .  
         [0094]    Referring for the moment to FIG. 6 in addition to FIG. 7, the space between the hitch bracket  304  and the hitch bracket  306  of the hitch frame nose piece  300  is designed to admit the rear mounting support  236  and the angled stock segment  248  of the lift bar  230 , and similarly the space between the hitch bracket  308  and the hitch bracket  310  of the hitch frame nose piece  300  is designed to admit the angled stock segment  250  and the rear mounting support  238  of the lift bar  230 . The hitch brackets  304 ,  306 ,  308 , and  310  have rectangular notches  320 ,  322 ,  324 , and  326 , respectively, cut into the front sides thereof.  
         [0095]    Located in the hitch brackets  304 ,  306 ,  308 , and  310  in the bottoms of the rectangular notches  320 ,  322 ,  324 , and  326 , respectively, are slots  328 ,  330 ,  332 , and  334 , respectively. The slots  328 ,  330 ,  332 , and  334  have rounded bottoms, and are axially aligned. Also located in the hitch brackets  304 ,  306 ,  308 , and  310  above the tops of the rectangular notches  320 ,  322 ,  324 , and  326 , respectively, are apertures  336 ,  338 ,  340 , and  342 , respectively. The apertures  336 ,  338 ,  340 , and  342  are also axially aligned.  
         [0096]    Unlike the hitch brackets  306  and  308  which are flat, the hitch brackets  304  and  310  have their forward-most portions flanged outwardly to act as guides to direct the lift bar  230  (illustrated in FIG. 6) into engagement with the hitch frame nose piece  300 . Thus, the portions of the hitch brackets  304  and  310  at the front of the rectangular notches  320  and  326 , respectively, extend outwardly, both on the top of the rectangular notches  320  and  326  and on the bottom of the rectangular notches  320  and  326 . It should be noted that, if desired, the hitch brackets  304  and  310  may also be flat. The ramifications of having them flat instead of flanged will eliminate the utility of the right and left sides of the lift bar  230 .  
         [0097]    The respective ends of the square hitch frame tube  302  are mounted onto mounting plates  344  and  346 . The mounting plates  344  and  346  are also preferably made of steel, and the ends of the square hitch frame tube  302  are welded onto the mounting plates  344  and  346 . Located in the mounting plates  344  and  346  are a plurality of apertures  348  and  350 , respectively, which will be used to mount the hitch frame nose piece  300  onto the frame of a truck (not shown in FIG. 7) using mounting brackets (not shown in FIG. 7) in a manner which is conventional.  
         [0098]    Referring next to FIG. 8, a bellcrank  360  is illustrated. The bellcrank  360  has parallel, spaced apart triangular pivot plates  362  and  364 . One of the sides of the triangle is shorter than the other two in each of the pivot plates  362  and  364 . A gusset plate  366  is mounted between the pivot plates  362  and  364  with one side thereof near the shortest side of the triangle to support the pivot plates  362  and  364  in their spaced-apart configuration. In the preferred embodiment, both the pivot plates  362  and  364  and the gusset plate  366  are made of steel, and are welded together.  
         [0099]    The pivot plates  362  and  364  have apertures  370  and  372 , respectively, located therein near a first corner of the triangle which will be used to mount the bellcrank  360  for pivotal movement from the apertures  104  and  106  of the pivot mount plates  100  and  102 , respectively (illustrated in FIG. 1). The pivot plates  362  and  364  have apertures  374  and  376 , respectively, located therein near a second corner of the triangle which will be connected via the element to be discussed in FIG. 9 below to drive the upper pin  272  of the lift bar  230  (illustrated in FIG. 6). The pivot plates  362  and  364  have apertures  378  and  380 , respectively, located therein near the third corner of the triangle will be connected to a hydraulic cylinder (not shown in FIG. 9). The short side of the triangle is between the first and third corners of the triangle. The side of the gusset plate  366  adjacent this short side will act as a lift stop to limit pivotal movement of the gusset plate  366  when this side of the gusset plate  366  contacts the pivot mount plates  100  and  102  (illustrated in FIG. 1).  
         [0100]    Referring now to FIG. 9, a lift link  390  is illustrated. The lift link  390  has parallel, spaced apart arms  392  and  394 . A gusset plate  396  is mounted between the arms  392  and  394  in their spaced-apart configuration. The side of the gusset plate  396  which is oriented toward one end of the arms  392  and  394  has a notch  398  cut therein. In the preferred embodiment, both the arms  392  and  394  and the gusset plate  396  are made of steel, and are welded together. The one end of the arms  392  and  394  have apertures  400  and  402 , respectively, located therein, and the other ends of arms  392  and  394  have apertures  404  and  406 , respectively, located therein.  
         [0101]    Referring next to FIG. 10, the linkage used to attach the snow plow of the present invention to the hitch frame nose piece  300  is illustrated. The components which are linked together are the plow A-frame  50 , the lift bar  230 , the bellcrank  360 , and the lift link  390 . Accordingly, reference may also be had to FIGS. 1, 6,  8 , and  9  as well as to FIGS. 31 and 32 in the following description of the interconnection of these components. The lift bar  230  is pivotally mounted on the plow A-frame  50  using two pins  408  and  410  (the pin  410  is not shown in FIG. 10) which are each of a length longer than distance between the opposite-facing sides of the pairs of the hitch brackets  304  and  306 , or  308  and  310  (illustrated in FIG. 7). The pins  408  and  410  are preferably made of steel.  
         [0102]    In the preferred embodiment, a hollow cylindrical collar  4099  (shown in FIGS. 31 and 32) having a setscrew  411  (also shown in FIGS. 31 and 32) is used with the pin  410  as a spacer. A similar collar which a setscrew (not shown in the drawings) is used with the pin  408  as a spacer. The collar  409  will be located intermediate the lug  58  on the plow A-frame  50  and the angled stock segment  250  on the lift bar  230 . The setscrew  411  on the collar  409  may be used to lock the collar  409  in place on the pin  410 . The other collar will be located intermediate the lug  56  on the plow A-frame  50  and the angled stock segment  248  on the lift bar  230 , with a setscrew in that collar being used to lock that collar in place on the pin  408 .  
         [0103]    The pin  408  will thus extend sequentially through the aperture  278  in the rear mounting support  236  of the lift bar  230 , the aperture  60  in the lug  56  of the plow A-frame  50 , the collar, and the aperture  280  in the rear mounting support  238  of the lift bar  230 . The pin  408  will be retained in place by the setscrew on the collar, which will contact the pin  408  when it is screwed into the collar. Approximately equal lengths of the pin  408  extend outwardly beyond the rear mounting support  236  and the angled stock segment  248  at each end of the pin  408 . Alternately, the pin  408  may be welded in place on the rear mounting support  236  and the angled stock segment  248  of the lift bar  230 , or C-clips (not shown herein) could be installed in annular groves (not shown herein) in the pin  408  at locations which correspond to the ends of the collar.  
         [0104]    The pin  410  will thus extend sequentially through the aperture  282  in the angled stock segment  250  of the lift bar  230 , the collar  409 , the aperture  62  in the lug  58  of the plow A-frame  50 , and the aperture  284  in the rear mounting support  238  of the lift bar  230 . The pin  410  will be retained in place by the setscrew  411  on the collar  409 , which will contact the pin  410  when it is screwed into the collar  409 . Equal lengths of the pin  410  extend outwardly beyond the angled stock segment  250  and the rear mounting support  238  at each end of the pin  410 . Alternately, the pin  410  may be welded in place on the angled stock segment  250  and the rear mounting support  238  of the lift bar  230 , or C-clips (not shown herein) could be installed in annular groves (not shown herein) in the pin  410  at locations which correspond to the ends of the collar  409 .  
         [0105]    It will thus be appreciated by those skilled in the art that the lift bar  230  is pivotally mounted onto the plow A-frame  50  using the pins  408  and  410 . When the snow plow of the present invention is mounted onto a vehicle using the hitch frame nose piece  300 , the ends of the pins  408  and  410  will be received in the pairs of slots  328  and  330 , and  332  and  334  in the hitch frame nose piece  300  (illustrated in FIG. 7). Thus, the pins  408  and  410  function both to pivotally mount the lift bar  230  onto the plow A-frame  50 , and to help to mount the snow plow onto the hitch frame nose piece  300 .  
         [0106]    The bellcrank  360  is pivotally mounted on the plow A-frame  50  using two bolts  412  and two nuts  414 . The pivot plates  362  and  364  of the bellcrank  360  will fit outside of the pivot mount plates  100  and  102 , respectively. One of the bolts  412  will extend through the aperture  104  in the pivot mount plate  100  of the plow A-frame  50  and the aperture  370  in the pivot plate  362  of the bellcrank  360 , and one of the nuts  414  will be mounted on that bolt  412  to retain it in place. The other one of the bolts  412  will extend through the aperture  106  in the pivot mount plate  102  of the plow A-frame  50  and the aperture  372  in the pivot plate  364  of the bellcrank  360 , and the other one of the nuts  414  will be mounted on that bolt  412  to retain it in place.  
         [0107]    The bolts  412  allow the bellcrank  360  to pivot on the plow A-frame  50 . In the preferred embodiment, a spacer and two washers (not shown) may be used with each of the bolts  412 , the spacer going through the apertures in the parts being pivotally joined and being longer than the combined thickness of the apertures in the parts, and a washer being located on either end of the spacer to facilitate free rotation of parts, here movement of the bellcrank  360  with reference to the plow A-frame  50 . It will be understood by those skilled in the art that a spacer and two washers will preferably be used at other points of relative movement between two elements of linkage of the snow plow described herein, although the spacer and two washers will not be specifically mentioned in conjunction with each of these pivoting connections made between two elements using a bolt. In addition, it will be understood by those skilled in the art that a pin retained by a cotter pin (not shown herein) could be used instead of a bolt and nut in many of the applications for a fastener used in the linkage discussed herein.  
         [0108]    A hydraulic cylinder  416  is mounted at one end to the cylinder mounts  84  and  86  of the plow A-frame  50  using a bolt  418  which extends through the aperture  96  in the cylinder mount  84  and the aperture  98  in the cylinder mount  86 , with a nut  420  being used to retain the bolt  418  in place. The other end of the hydraulic cylinder  416  drives the third corner of the triangular pivot plates  362  and  364  of the bellcrank  360 , with a bolt  422  extending between the aperture  378  in the pivot plate  362  of the bellcrank  360  and the aperture  380  in the pivot plate  364  of the bellcrank  360 . A nut  424  is used to retain the bolt  422  in place. The bolts  418  and  422  allow the hydraulic cylinder  416  to move as it drives the bellcrank  360 . Spacers (not shown herein) may be used on each side of the other end of the hydraulic cylinder  416  on the insides of the pivot plates  362  and  364  to center the hydraulic cylinder  416 .  
         [0109]    The lift link  390  is used to connect the bellcrank  360  to pivot the lift bar  230 . A bolt  426  is used to connect the lift link  390  to the lift bar  230 , with the bolt  426  extending sequentially through the aperture  404  in the arm  392  of the lift link  390 , the upper pin  272  from the end extending through the upper pin hanger plate  264  to the end extending through the upper pin hanger plate  266  of the lift bar  230 , and the aperture  406  in the arm  394  of the lift link  390 . A nut  428  is used to retain the bolt  426  in place. The bolt  426  allows the lift link  390  to pivot on the lift bar  230 , and a spacer and two washers may also be used as mentioned hereinabove.  
         [0110]    The second corner of the triangle formed by the pivot plates  362  and  364  of the bellcrank  360  drives the ends of the arms  392  and  394  of the lift link  390  which are not connected to the lift bar  230 . Two bolts  430  are used to connect the bellcrank  360  to the lift link  390 , with one of the bolts  430  also being used to mount a stand  432 . The stand  432  is described in U.S. Pat. No. 5,894,688, to Struck et al., which patent is assigned to the assignee of the inventions described herein. U.S. Pat. No. 5,894,688 is hereby incorporated herein by reference.  
         [0111]    One bolt  430  (not shown) extends through the aperture  400  in the arm  392  of the lift link  390  and the aperture  374  of the pivot plate  362  of the bellcrank  360 , with a nut  434  being used to retain the first bolt  430  in place, and a spacer and two washers may also be used as mentioned hereinabove. The other bolt  430  extends sequentially through an aperture (not shown) in the upper portion of the stand  432 , the aperture  376  of the pivot plate  364  of the bellcrank  360 , and the aperture  402  in the arm  394  of the lift link  390 , with a nut  434  being used to retain the second bolt  430  in place. The second bolt  430  allows the lift link  390  to pivot on the bellcrank  360 , and a spacer and two washers may again be used as mentioned hereinabove. A removable pin (not shown) extending through an aperture near the top of the stand  432  and apertures located in the lift link  390  is used to link the stand  432  with the lift link  390 .  
         [0112]    The hydraulic cylinder  416  is shown in FIG. 10 nearly in its fully retracted position. When the hydraulic cylinder  416  is fully extended, it will be appreciated by those skilled in the art that the lift bar  230  will rotate counterclockwise from the position in which it is shown in FIG. 10, and the stand  432  will be lowered to engage the ground (not shown) and thereby tend to lift the rear end of the plow A-frame  50  upwardly. It will also be appreciated that once the pins  408  and  410  are in engagement with the slots  328 ,  330 ,  332 , and  334  in the hitch brackets  304 ,  306 ,  308 , and  310 , respectively, of the hitch frame nose piece  300 , the hydraulic cylinder  416  may be used to align the apertures  286 ,  288 ,  290 , and  292  on the lift bar  230  with the apertures  336 ,  338 ,  340 , and  342 , respectively, in the hitch brackets  304 ,  306 ,  308 , and  310 , respectively, of the hitch frame nose piece  300 .  
         [0113]    Turning next to FIGS. 11 through 16, a plow blade  440  and various aspects thereof are illustrated. The plow blade  440  has a frame which may be fundamentally thought of as a horizontal top plow frame member  442 , a bottom plow frame member  444 , and a plurality of vertical ribs  446 ,  448 ,  450   452 ,  454 ,  456 , and  458  extending between the top plow frame member  442  and the bottom plow frame member  444 . The top plow frame member  442  is made of a triangular tube as best shown in FIG. 13. The bottom plow frame member  444  is made of a three sided channel resembling a wide, inverted “U” with the tops of the legs of the “U” angling outwardly as best shown in FIG. 14.  
         [0114]    The right side rib  446  is located on the right side of the plow blade  440 , and the left side rib  458  is located on the left side of the plow blade  440 . The ribs  448 ,  450 ,  452 ,  454 , and  456  are located at evenly spaced intervals intermediate the right side rib  446  and the left side rib  458 . Note that all of the ribs  446 ,  448 ,  450   452 ,  454 ,  456 , and  458  have an arcuate shape when viewed from the side. The ribs  448 ,  450 ,  452 ,  454 , and  456  all extend between the back side of the top plow frame member  442  and the top side of the bottom plow frame member  444 , while the right side rib  446  and the left side rib  458  are mounted on the ends of the top plow frame member  442  and the bottom plow frame member  444 , thereby overlying them as best shown in FIGS. 11 through 14. The top plow frame member  442 , the bottom plow frame member  444 , and the ribs  446 ,  448 ,  450   452 ,  454 ,  456 , and  458  are all preferably made of steel, and are welded together.  
         [0115]    Located in front of the ribs  450  and  454  are curved reinforcing plates  460  and  462  which serve to strengthen the ribs  450  and  454 , which will be used to mount the plow blade  440  to the swing frame  140  (shown in FIGS. 3 through 5). The rib  450  has a mounting aperture  464  which extends therethrough and which is located near to the bottom end of the rib  450 . Similarly, the rib  454  has a mounting aperture  466  which extends therethrough and which is located near to the bottom end of the rib  454 . The curved reinforcing plates  460  and  462  are welded to the ribs  450  and  454 , respectively, and to the top plow frame member  442  and the bottom plow frame member  444 .  
         [0116]    Four arcuate torsional stiffeners  468 ,  470 ,  472 , and  474  are used to provide stiffness to the configuration of the plow blade  440 . The torsional stiffener  468  extends from the bottom of the rib  448  to a position near the top of the right side rib  446 . The torsional stiffener  470  extends from the bottom of the rib  450  to a position near the top of the rib  448 . The torsional stiffener  472  extends from the bottom of the rib  454  to a position near the top of the rib  456 . The torsional stiffener  474  extends from the bottom of the rib  456  to a position near the top of the left side rib  458 . The torsional stiffeners  468 ,  470 ,  472 , and  474  are also preferably made of steel, and are welded to other components in the plow blade  440 .  
         [0117]    Located on the left side of the right side rib  446  and on the right side of the left side rib  458  are curved support plates  476  and  478 , respectively. The curved support plates  476  and  478  are recessed back from the front edges of the right side rib  446  and the left side rib  458 , respectively, as best shown in FIG. 15 for the curved support plate  478 . The curved support plates  476  and  478  are preferably also made of steel, and are welded to other components in the plow blade  440 . The frontmost portions of the top plow frame member  442 , the curved support plate  476 , the rib  448 , the curved reinforcing plate  460 , the rib  452 , the curved reinforcing plate  462 , the rib  456 , and the curved support plate  478  together define a curved support surface which will support a moldboard  480  thereupon. The right side rib  446  and the left side rib  458  extend slightly forward of the top plow frame member  442 , the bottom plow frame member  444 , and the ribs  448 ,  450 ,  452 ,  454 , and  456 , to thereby prevent the moldboard  480  from moving laterally. The moldboard  480  may be made of a man-made material such as polycarbonate, which may be clear, or other man-made materials such as ultra-high molecular weight (UHMW) polyethylene, or steel.  
         [0118]    Extending across the front side of the top plow frame member  442  is a moldboard retainer strip  482  (best shown in FIG. 13), into which the top edge of the moldboard  480  fits and is retained. The moldboard retainer strip  482  is bent slightly toward the top plow frame member  442 , which ensures that the top edge of the moldboard  480  fits snugly therein. Thus, it will be appreciated that the top, right, and left sides of the moldboard  480  are retained in position on the plow blade  440 . The front of the bottom plow frame member  444  extends forwardly with respect to the curved moldboard support surface defined by the frontmost portions of the top plow frame member  442 , the curved support plate  476 , the rib  448 , the curved reinforcing plate  460 , the rib  452 , the curved reinforcing plate  462 , the rib  456 , and the curved support plate  478 . The bottom edge of the moldboard  480  comes just to the top of the bottom plow frame member  444 , as best shown in FIG. 14.  
         [0119]    The front of the bottom plow frame member  444  has a plurality of tapped apertures  484  located therein across the entire width thereof. A wearstrip  486  which is approximately the same width as the bottom plow frame member  444  has a matching plurality of apertures  488  located therein. The wearstrip  486  is preferably made of a high carbon steel such as AISI  1080  high carbon steel. The wearstrip  486  is bolted onto the bottom plow frame member  444  with a plurality of bolts  490 . Alternately, if the apertures  484  are not tapped, bolts and nuts could be used to mount the wearstrip  486  onto the bottom plow frame member  444 . Optionally, the apertures  488  in the wearstrip  486  may be countersunk to recess the heads of the bolts  490  to the level of surface of the wearstrip  486 . The front of the bottom plow frame member  444  is arranged and configured such that the wearstrip  486  will be mounted with its bottom edge angled forwardly with respect to the ground at angle of between approximately zero and forty-five degrees, with between approximately fifteen and thirty degrees being preferred, and an angle of approximately twenty-five degrees being most preferred.  
         [0120]    The wearstrip  486  retains the bottom of the moldboard  480  in place, and it will at once be appreciated that the moldboard  480  may be replaced by merely removing the wearstrip  486 , making the replacement substantially easier than in earlier snow plow blade designs. When the wearstrip  486  is bolted to the bottom plow frame member  444 , it will be appreciated by those skilled in the art that it extends well below the bottom of the bottom plow frame member  444 , so that as it is worn down, the bottom plow frame member  444  will not be damaged by contact with the ground.  
         [0121]    Mounted on the back of the ribs  450  and  454 , respectively, are two trip spring brackets  492  and  494 . The trip spring brackets  492  and  494  are mounted approximately three-quarters of the way up the ribs and  454 , and are bent at a ninety degree angle, the bends being on an axis parallel to the lateral axis of the plow blade  440 . The portions of the trip spring brackets  492  and  494  facing forward have notches  496  and  498 , respectively, cut into them from the forwardmost edges thereof to the bends therein. The rear edges of the ribs  450  and  454  fit into the notches  496  and  498 , respectively, and the portions of the spring brackets  492  and  494  facing rearwardly fit against the ribs  450  and  454 , respectively. The spring brackets  492  and  494  are also preferably made of steel, and are welded onto the ribs  450  and  454 , respectively. The rear-facing portion of the trip spring bracket  492  has two apertures  500  and  502  located therein on which lie on opposite sides of the rib  450 , and the rear-facing portion of the trip spring bracket  494  has two apertures  504  and  506  located therein on which lie on opposite sides of the rib  454 .  
         [0122]    Located on the right side of the plow blade  440  in the right side rib  446  near the top thereof are two apertures  512 . Similarly, located on the left side of the plow blade  440  in the left side rib  458  near the top thereof are two apertures  514 . The apertures  512  and  514  serve to allow a marker bar or the like (not shown in FIGS. 11 through 13) to be attached to the plow blade  440 .  
         [0123]    Located at the rear of the plow blade  440  at the bottom thereof is a back blade wearstrip  516 , which is mounted onto the bottom plow frame member  444  and extends substantially across the width of the plow blade  440 . The back blade wearstrip  516  has a plurality of apertures  518  therein, and the bottom plow frame member  444  has matching tapped apertures  520  located in the rear-facing side thereof. Bolts  522  are used in the back blade wearstrip  516  to mount it onto the bottom plow frame member  444 . Alternately, if the apertures  520  are not tapped, bolts and nuts could be used to mount the back blade wearstrip  516  onto the bottom plow frame member  444 . Optionally, the apertures  518  in the back blade wearstrip  516  may be countersunk to recess the heads of the bolts  522  to the level of surface of the back blade wearstrip  516 .  
         [0124]    The back blade wearstrip  516  is permanently mounted at an optimum angle with respect to the ground which is defined by the angle of the rear side of the bottom plow frame member  444 . The rear of the bottom plow frame member  444  is arranged and configured such that the back blade wearstrip  516  will be mounted with its bottom edge angled rearwardly with respect to the ground at angle of between approximately zero and forty-five degrees, with between approximately fifteen and thirty degrees being preferred, and an angle of approximately twenty-five degrees being most preferred. In the preferred embodiment, the wearstrip  486  and the back blade wearstrip  516  will be mounted at the same angles, but with the wearstrip  486  being angled forwardly and the back blade wearstrip  516  being angled rearwardly.  
         [0125]    In the preferred embodiment, the back blade wearstrip  516  is made of an UHMW polyethylene material which is used instead of steel to decrease the weight of the plow blade  440 . Alternately, the back blade wearstrip  516  could be made of rubber, urethane, steel, aluminum, or any other suitable material. Also, if desired, the back blade wearstrip  516  can be manufactured as multiple identical narrower segments if desired.  
         [0126]    Turning next to FIGS. 17 and 18, and making reference also to FIGS. 1 and 3 through  5 , the installation of the swing frame  140  onto the plow A-frame  50  is illustrated. The rectangular swing frame tube  142  of the swing frame  140  is inserted between the top plate  52  and the bottom plate  54  of the plow A-frame  50 , with the pivot  144  of the swing frame  140  being brought into alignment intermediate the swing frame pivot  108  and the swing frame pivot  110  of the plow A-frame  50 . A pivot pin  524  having a threaded distal end  526  is inserted sequentially through the swing frame pivot  108  in the plow A-frame  50 , the pivot  144  in the swing frame  140 , and the swing frame pivot  110  in the plow A-frame  50 , and is retained in place by a locking nut  528 . Washers (not shown herein) may also be used if desired.  
         [0127]    Thus, the swing frame  140  is pivotally mounted on the plow A-frame  50 , and it will be appreciated by those skilled in the art that the movement of the swing frame  140  is limited by the guide/stop bar  152  on the swing frame  140  which interacts with the rectangular plate  66  on the plow A-frame  50  to limit movement to approximately thirty degrees either to the right or to the left. The swing frame  140  will be pivoted by two hydraulic cylinders, the installation of which will be described later in conjunction with FIG. 30.  
         [0128]    It will be appreciated by those skilled in the art that the design of the plow A-frame  50  and the swing frame  140  represents a substantial improvement over past snow plow frame designs since their centerlines are in the same horizontal plane. Thus, rather than having the swing frame  140  being located on top of the plow A-frame  50 , the swing frame  140  is located in the same plane as is the plow A-frame  50 . In the preferred embodiment, the apertures  60  and  62  in the lugs  56  and  58 , respectively, as well as the pins  408  and  410 , are also in the same horizontal plane.  
         [0129]    Moving now to FIG. 19, a cushion block  530  is illustrated which will be used to absorb the impact of the plow blade  440  (shown in FIG. 11) as it moves between its limits. Such movement of the plow blade  440  is caused by the plow blade  440  striking an object, and is designed to prevent damage to the snow plow by allowing the plow blade  440  to “trip,” that is, for the bottom of the plow blade  440  to move rearwardly and the top of the plow blade  440  to simultaneously move forward, resulting in a rotation of the plow blade  440  around a horizontal axis. Such a rotation is inhibited by springs, which act as a shock absorbing mechanism, and which return the plow blade  440  to a normal or “trip return” position. The springs are quite strong, since they must prevent the plow blade  440  from rotating when it is plowing snow, and the metal-to-metal impacts of both a blade trip and a blade trip return can be substantial. The cushion block  530  is designed to cushion the impacts on both the blade trip and the blade trip return.  
         [0130]    The cushion block  530  is brick-shaped with a corner cut off to create a beveled face  532 , and will be mounted with the beveled face  532  of the cushion block  530  facing both forwardly and downwardly. Above the beveled face  532  of the cushion block  530  and facing forwardly when the cushion block  530  is mounted is a front face  534 . Extending laterally through the cushion block  530  at a central location is an aperture  536 , which will be used to mount the cushion block  530  on the swing frame  140  (shown in FIGS. 3 through 5). A cushion block  530  will be mounted between each pair of the blade pivot mounts  178  and  180 , and  182  and  184 . The apertures  202  and  204  in the blade pivot mounts  178  and  180 , respectively, will align with the aperture  536  in one cushion block  530 , and the apertures  206  and  208  in the blade pivot mounts  182  and  184 , respectively, will align with the aperture  536  in the other cushion block  530 .  
         [0131]    Turning next to FIGS. 20 through 22, and referring also to FIGS. 3, 11, and  19 , the installation of both the cushion blocks  530  and the plow blade  440  onto the swing frame  140  is illustrated. One of the cushion blocks  530  is shown installed between the blade pivot mounts  182  and  184 , with a bolt  538  extending sequentially through the aperture  208  in the blade pivot mount  184 , the aperture  536  in the cushion block  530 , and the aperture  206  in the blade pivot mount  182 , and with a nut  540  being used to retain the bolt  538  in place. The top and the rearwardly facing side of the cushion block  530  are retained in position by the stop  222  in the swing frame  140 . The other cushion block  530  would be similarly mounted between the blade pivot mounts  178  and  180 . Alternately, silicone adhesive (or any other suitable type of adhesive) may be used instead of bolts to retain the cushion blocks  530  in place. Another alternate retaining mechanism would be to have the cushion blocks  530  fit in place with an interference fit.  
         [0132]    The plow blade  440  will pivot around an axis defined by the mounting apertures  464  and  466  located in the ribs  450  and  454 , respectively, and is mounted onto the swing frame  140  using two pins  542 . One of the pins  542  extends sequentially through the aperture  200  in the blade pivot mount  184 , the mounting aperture  466  in the rib  454 , and the aperture  198  in the blade pivot mount  182 . The other one of the pins  542  extends sequentially through the aperture  196  in the blade pivot mount  180 , the mounting aperture  464  in the rib  450 , and the aperture  194  in the blade pivot mount  180 . Retaining pins  544  are installed into diametrically extending apertures located in the distal ends of each of the pins  542 , and retain the pins  542  in place, thereby pivotally mounting the plow blade  440  on the swing frame  140 .  
         [0133]    The plow blade  440  thus may pivot between the trip return position shown in FIG. 20 and the tripped position shown in FIG. 22. It will be appreciated by those skilled in the art that when the plow blade  440  hits an object on the ground sufficiently hard, it will be driven to the tripped position shown in FIG. 22, at which time the portion of the rib  454  and also the portion of the rib  450  (which is not shown in FIG. 22) below the pins  542  will contact the beveled faces  532  of the cushion blocks  530 , which will absorb the impact. Similarly, when the plow blade  440  is driven back into the trip return position shown in FIG. 20, the portion of the rib  454  and also the portion of the rib  450  (which is not shown in FIG. 22) above the pins  542  will contact the front face  534  of the cushion blocks  530 , which will absorb the impact. In the preferred embodiment, the cushion blocks  530  are made of polyurethane, such as, for example, Quazi formulated methylenebisdiphenyl diisocyanate (MDI) polyester-based 93 durometer (Shore A scale) polyurethane, available commercially from Kryptonics, Inc. under the trademark Kaptane 93 black.  
         [0134]    Referring now to FIGS. 23 and 24, portions of the left side of the swing frame  140  and the plow blade  440  are illustrated in the blade trip return position. In the principal design described herein and shown in the drawings, four trip springs  550 ,  552 ,  554 , and  556  (the first two of which are not shown in FIGS.  23  or  24 ) will be used to bias the plow blade  440  into the trip return position, and to resist movement of the plow blade  440  into the tripped position. Two trip springs  550  and  552 , or  554  and  556  will be located on each side of the swing frame  140  and the plow blade  440 . The trip springs  554  and  556  are shown in phantom lines in FIG. 23, with the trip spring  554  being connected between the aperture  218  of the trip spring bracket  212  and the aperture  504  of the trip spring bracket  494 , and the trip spring  556  being connected between the aperture  220  of the trip spring bracket  212  and the aperture  506  of the trip spring bracket  494 .  
         [0135]    It will at once be appreciated by those skilled in the art that the trip springs  554  and  556  are located immediately on either side of the pivoting connection between the plow blade  440  and the swing frame  140 . The trip springs  554  and  556  exert a force in a plane which is parallel to the plane of rotation defined by the pivoting connection between the plow blade  440  and the swing frame  140 . Thus, the trip springs  554  and  556  do not pull in a direction which is even in part at an angle to the plane of rotation. This represents a major advantage over previously known snow plow trip spring mounting designs, which without exception are located at an angle to the plane of rotation defined by the pivoting connection between the plow blade and the swing frame of such previously known snow plows. The design of the snow plow described herein utilizes all of the trip spring force for the blade trip operation, and thus provides more consistent blade trip operation as well as eliminating lateral trip spring force being exerted on the frame of the plow blade  440 .  
         [0136]    Turning next to FIGS. 25 and 26, an alternate embodiment is illustrated in which two trip springs are used to bias the plow blade  440  into the trip return position, and to resist movement of the plow blade  440  into the tripped position. One trip spring will be located on each side of the swing frame  140  and the plow blade  440  (the trip spring  560  on the left side of the swing frame  140  and the plow blade  440  is illustrated in the blade trip return position in FIG. 25). In the alternate embodiment illustrated in FIGS. 25 and 26, the design of the trip spring brackets which are mounted on the back of the ribs  450  and  454  differs from the design of the trip spring brackets  210  and  212  (shown in FIGS. 3 through 5). A trip spring bracket  562  having a single aperture  564  located therein is mounted on the blade pivot mounts  182  and  184 . The trip spring bracket  562  is also preferably made of steel, and is welded onto the blade pivot mounts  182  and  184  with the aperture  564  being located between the blade pivot mounts  182  and  184 . An identical spring trip bracket (not shown) would also be used on the right side of the swing frame  140 .  
         [0137]    In the alternate embodiment illustrated in FIGS. 25 and 26, the design of the trip spring brackets which are mounted on the back of the ribs  450  and  454  also differs from the design of the trip spring brackets  492  and  494  (shown in FIGS. 11 and 12). A trip spring bracket  566  is mounted approximately three-quarters of the way up the rib  454 , and is bent at a ninety degree angle, the bend being on an axis parallel to the lateral axis of the plow blade  440 . The portion of the trip spring bracket  566  facing forward has a notch  568  cut into it from the forwardmost edge thereof to the bend therein. The rear edge of the rib  454  fits into the notch  568 , and the portion of the spring bracket  566  facing rearwardly fits against the rib  454 . The rear-facing portion of the trip spring bracket  566  has an aperture  570  located therein which lies in the same plane as the rib  454 . The spring bracket  566  is also preferably made of steel, and is welded onto the rib  454 . An identical spring trip bracket (not shown) would also be used on the right side of the plow blade  440 .  
         [0138]    It will be appreciated by those skilled in the art that the trip spring  560  is located, and exerts a force, in the plane of rotation defined by the pivoting connection between the plow blade  440  and the swing frame  140 . Thus, the trip spring  560  does not pull in a direction which is even in part at an angle to the plane of rotation (unlike previously known snow plow trip spring mounting designs). The alternate embodiment design of the snow plow of FIGS. 25 and 26 utilizes all of the trip spring force for the blade trip operation and provides more consistent blade trip operation as well as eliminating lateral trip spring force being exerted on the frame of the plow blade  440 .  
         [0139]    Referring next to FIGS. 27 and 28, the movement of the plow blade  440  between the trip return position shown in FIG. 27 and the fully tripped position shown in FIG. 28 is illustrated. From these figures (and also by looking at the orientation of the trip springs  550 ,  552 ,  554 , and  556  in the top plan view of FIG. 30), it will be appreciated that the trip springs  550 ,  552 ,  554 , and  556  (which are already under tension even in the trip return position) are all further stretched as the plow blade  440  moves from the trip return position to the tripped position, and thus serve to return the plow blade  440  to the trip return position when the force which caused the plow blade  440  to be tripped is removed.  
         [0140]    Turning next to FIGS. 29 and 30, the assembly of several additional components is illustrated. First, all four of the trip springs  550 ,  552 ,  554 , and  556  are illustrated as mounted onto the swing frame  140  and the plow blade  440 . In addition, right and left light support towers  572  and  574 , respectively, are mounted on the light bar supports  244  and  246 , respectively, of the lift bar  230 , and a light support bar  576  is mounted on the top ends of the right and left light support towers  572  and  574 . Lights (not shown herein) would be mounted on the light support bar  576 , in a manner well known to one skilled in the art.  
         [0141]    In addition, right and left swing cylinders  578  and  580 , respectively, are mounted between the plow A-frame  50  and the swing frame  140 . The right swing cylinder  578  extends between the swing cylinder mount  76  on the plow A-frame  50  (where it is secured with a pin  582 ) and the swing cylinder mounting plates  154  and  158  on the swing frame  140  (where it is secured with a pin  584 ), and the left swing cylinder  580  extends between the swing cylinder mount  78  on the plow A-frame  50  (where it is secured with a pin  586 ) and the swing cylinder mounting plates  156  and  160  on the swing frame  140  (where it is secured with a pin  588 ). It will be understood that the pins  582 ,  584 ,  586 , and  588  are all retained in place with cotter pins (not shown) as is well known to those skilled in the art.  
         [0142]    Also not shown or discussed herein is the hydraulic system to operate the snow plow, the construction and operation of which is also well known to those skilled in the art. The right and left swing cylinders  578  and  580  are used to pivot the swing frame  140  and the plow blade  440  on the plow A-frame  50 . The hydraulic cylinder  416  (shown in FIG. 10) is used to operate the stand  432  (also shown in FIG. 10) prior to the snow plow being mounted onto a truck, to facilitate the mounting of the snow plow onto the truck (as will become apparent below in conjunction with the discussion of FIGS. 31 through 37), and to raise and lower the plow A-frame  50 , the swing frame  140 , and the plow blade  440  after the snow plow has been mounted onto the truck. The hydraulic system for the snow plow may be mounted on the plow A-frame  50  at the front thereof, and if so mounted would have a hydraulic system cover  590  mounted thereupon to protect it, as shown in phantom lines.  
         [0143]    Referring now to FIGS. 31 through 37, the operation of the mounting system used to mount the snow plow on the hitch frame nose piece  300  is shown. Referring first to FIGS. 31 through 33, in conjunction with FIGS. 1, 6,  7 , and  10 , the mechanism used to connect the snow plow to the hitch frame nose piece  300  is shown. In the discussion herein, all references are to the left side of the snow plow and the hitch frame nose piece  300 , but those skilled in the art will understand that the principles thereof are equally applicable to the right side of the snow plow and the hitch frame nose piece  300 .  
         [0144]    The snow plow is mounted onto the hitch frame nose piece  300  with the plow standing on the stand  432  (shown in FIG. 10). In this position, the pin  410  which extends laterally at the rear of the snow plow on the left side will be at a height such than when the truck having the hitch frame nose piece  300  mounted thereon moves forward, the pin  410  will fit into the rectangular notches  324  and  326  at the front of the hitch brackets  308  and  310 , respectively. The pin  410  is brought fully into the rectangular notches  324  and  326  by moving the truck forward. It will be noted that the flange at the front of the hitch bracket  310  as well as the approximately seventy degree bend in the angled stock segment  250  will assist in guiding the rear mounting support  238  and the angled stock segment  250  of the lift bar  230  into position intermediate the hitch bracket  308  and  310 .  
         [0145]    A this point, the hydraulic cylinder  416  (shown in FIG. 10) is actuated to begin to retract it to raise the stand  432  (also shown in FIG. 10), causing the pin  410  to drop into the slots  332  and  334  in the hitch brackets  308  and  310 , respectively. By continuing to actuate the hydraulic cylinder  416  to retract it, the lift bar  230  is pivoted to bring the apertures  290  and  292  in the angled stock segment  250  and the rear mounting support  238 , respectively, of the lift bar  230  into alignment with the apertures  340  and  342  in the hitch brackets  308  and  310 , respectively, of the hitch frame nose piece  300 . At this point, a retaining pin  592  having a handle  594  may be inserted sequentially through the aperture  342  in the hitch bracket  310 , the aperture  292  in the rear mounting support  238 , the aperture  290  in the angled stock segment  250 , and the aperture  340  in the hitch bracket  308 . The retaining pin  592  has an aperture  596  extending through near the distal end thereof, and a retaining spring pin  598  is used to retain the retaining pin  592  in place.  
         [0146]    Referring next to FIGS. 34 through 37, the installation of the snow plow onto the hitch frame nose piece  300  mounted on a truck  600  (shown in phantom lines in FIG. 37) is illustrated. In FIG. 34, the snow plow is shown in its stored position, supported on the stand  432 . In this position, the hydraulic cylinder  416  is in its fully extended position, and the rear end of the snow plow is raised. In this position, the pin  408  (not shown in FIGS. 34 through 37) at the right rear of the snow plow will be received by the rectangular notches  320  and  322  (not shown in FIGS. 34 through 37) at the front of the hitch brackets  304  and  306  (not shown in FIGS. 34 through 37), respectively, at the right side of the hitch frame nose piece  300 . Similarly, the pin  410  at the left rear of the snow plow will be received by the rectangular notches  324  (not shown in FIGS. 34 through 37) and  326  at the front of the hitch brackets  308  (not shown in FIGS. 34 through 37) and  310 , respectively, at the left side of the hitch frame nose piece  300 . The truck  600  may be driven forward to fully engage the pins  408  and  410  with the hitch frame nose piece  300  as shown in FIG. 34.  
         [0147]    Next, as shown in FIG. 36, as the hydraulic cylinder  416  begins to retract, the plow A-frame  50  will lower at the rear end thereof as the stand  432  begins to move upwardly relative to the plow A-frame  50 . This causes the pin  408  (not shown in FIGS. 34 through 37) to drop into the slots  328  and  330  (not shown in FIG. 36) in the hitch brackets  304  and  306  (not shown in FIG. 36), respectively, at the right side of the hitch frame nose piece  300 . Similarly, the pin  410  drops into the slots  332  (not shown in FIG. 36) and  334  in the hitch brackets  308  (not shown in FIG. 36) and  310 , respectively, at the left side of the hitch frame nose piece  300 . This initial retraction of the hydraulic cylinder  416  also causes the lift bar  230  to begin to rotate clockwise as viewed from the left side of the snow plow, as is evident from the movement of the right light support towers  572  and  576  and the light support bar  576 .  
         [0148]    As shown in FIG. 37, as the hydraulic cylinder  416  continues to retract, the lift bar  230  rotates clockwise until the light support towers  572  and  576  are oriented nearly vertically. As this further rotation occurs, the pin  408  (not shown in FIG. 37) remains in the slots  328  and  330  in the hitch brackets  304  and  306 , respectively (none of which are shown in FIG. 37). Similarly, the pin  410  remains in the slots  332  (not shown in FIG. 37) and  334  in the hitch brackets  308  (not shown in FIG. 37) and  310 , respectively. On the right side of the lift bar  230  and the hitch frame nose piece  300  (best shown in FIGS. 6 and 7), the apertures  286  and  288  in the rear mounting support  236  and the angled stock segment  248 , respectively, of the lift bar  230  move into engagement with the apertures  336  and  338  in the hitch brackets  304  and  306 , respectively, of the hitch frame nose piece  300 . Likewise, on the left side of the lift bar  230  and the hitch frame nose piece  300  (portions of which are also best shown in FIGS. 6 and 7, respectively), the apertures  290  and  292  in the angled stock segment  250  and the rear mounting support  238 , respectively, of the lift bar  230  move into alignment with the apertures  340  and  342  in the hitch brackets  308  and  310 , respectively, of the hitch frame nose piece  300 .  
         [0149]    At this point, one of the retaining pins  592  is inserted sequentially through the aperture  336  in the hitch bracket  304 , the aperture  286  in the rear mounting support  236 , the aperture  288  in the angled stock segment  248 , and the aperture  338  in the hitch bracket  306  (all of which are best shown in FIGS. 6 and 7). The other one of the retaining pins  592  is inserted sequentially through the aperture  342  in the hitch bracket  310 , the aperture  292  in the rear mounting support  238 , the aperture  290  in the angled stock segment  250 , and the aperture  340  in the hitch bracket  308  (many of which are also best shown in FIGS. 6 and 7). The retaining spring pins  598  are then inserted into the apertures  596  near the distal ends of the retaining pins  592  to retain the retaining pins  592  in place. At this point, the stand  432  may also be moved to a stowed position by disconnecting it from the lift link  390  (by removal of the pin (not shown)) and rotating it to the stowed position as is taught in U.S. Pat. No. 5,894,688, which was incorporated by reference above.  
         [0150]    Also shown in FIG. 37 is a marker bar  602 , one of which may be mounted on each side of the plow blade  440  at the top thereof using the apertures  512  and  514  (not shown in FIG. 37) on the right and left sides of the plow blade  440 , respectively, using bolts  604  and nuts (not shown herein). The marker bars  602  are used to allow the driver of the truck  600  to see where the front of the plow blade  440  is at any given time (since the driver may not be able to see the plow blade  440  over the hood of the truck  600  from the cab of the truck  600 ).  
         [0151]    Referring finally to FIG. 38, a snow plow having an alternate embodiment is illustrated in which shoes  610  and  612  are installed on the plow blade  440 . The shoes  610  and  612  are designed to ride in sliding contact with the surface to be plowed, and are particular useful on gravel or during the spring when the ground may not be fully frozen. The shoes  610  and  612  are mounted to the plow blade  440  using shoe mounts  614  and  616 , respectively. The shoe mount  614  is mounted on the bottom plow frame member  444  near the right side thereof, and the shoe mount  616  is mounted on the bottom plow frame member  444  near the left side thereof. The shoe mounts  614  and  616  are preferably made of steel and are welded onto the bottom plow frame member  444 .  
         [0152]    The shoes  610  and  612  are mounted on posts  618  and  620 , respectively, which posts  618  and  620  are received by the shoe mounts  614  and  616 , respectively. The shoes  610  and  612  are adjusted using a combination of washers and tubular spacers, which are placed on the posts  618  and  620  either below or above the shoe mounts  614  and  616  to adjust the height of the shoes  610  and  612 . The position of the shoes  610  and  612  relative to the plow blade  440  may be adjusted to adjust the height of the plow blade  440  relative to the surface to be plowed. This allows the degree to which the wearstrip  486  scrapes the surface to be plowed to be controlled. Retaining pins  622  and  624  are used on the posts  618  and  620 , respectively, to retain them in the shoe mounts  614  and  616 .  
         [0153]    The shoes  610  and  612  are typically made out of cast iron. It should be noted that although the back blade wearstrip  516  is not shown in the embodiment illustrated in FIG. 38, it can in fact be used with the shoes  610  and  612 , so long as the shoe mounts  614  and  616  extend sufficiently back to clear the back blade wearstrip  516 . The shoes  610  and  612  have feet which are adapted to ride in sliding contact with the surface to be plowed. The position of the feet relative to the plow blade may be adjusted to adjust the height of the plow blade relative to the surface to be plowed. In this way, the degree to which the blade edge scrapes the surface to be plowed may be controlled.  
         [0154]    It may therefore be appreciated from the above detailed description of the preferred embodiment of the present invention that it teaches an apparatus and method for mounting the trip springs on a snow plow in a manner whereby all of the force exerted by the trip springs is exerted in a direction which is orthogonal to the axis about which the snow plow blade pivots. The mounting brackets of the present invention facilitate the mounting of the trip springs in a manner which eliminates the exertion of any lateral force by the trip springs. The size of the trip springs required by the present invention is minimized by ensuring that all of the force which they exert is directed properly to provide the required force in the requisite direction.  
         [0155]    The force exerted by the trip springs of the snow plow trip spring mount of the present invention is exerted proximate a plane which is orthogonal to the pivot points at which the snow plow blade is mounted to the snow plow blade support structure. In addition, the force of the trip springs is exerted on appropriate areas of the snow plow blade so that any potential distortion of the snow plow blade is inhibited. The snow plow trip spring mount of the present invention facilitates the use of either a single trip spring on either side of the snow plow blade or two trip springs on each side of the snow plow blade.  
         [0156]    The snow plow trip spring mount of the present invention is of a construction which is both durable and long lasting, and which will require little or no maintenance to be provided by the user throughout its operating lifetime. The snow plow trip spring mount of the present invention is also of inexpensive construction to enhance its market appeal and to thereby afford it the broadest possible market. Finally, all of the aforesaid advantages and objectives of the snow plow trip spring mount of the present invention are achieved without incurring any substantial relative disadvantage.  
         [0157]    Although an exemplary embodiment of the snow plow trip spring mount of the present invention has been shown and described with reference to particular embodiments and applications thereof, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. All such changes, modifications, and alterations should therefore be seen as being within the scope of the present invention.

Summary:
An improved snow plow for use with light and medium duty trucks is disclosed which has blade trip springs which are mounted using brackets located to direct the force of the springs in directions which are orthogonal to the axis upon which the plow blade pivots, thereby increasing the predictability of the tripping forces exerted by the trip springs as well as eliminating lateral trip spring forces which could warp the plow blade. The forces exerted by the trip springs are exerted proximate planes which are orthogonal to the pivot points at which the snow plow blade is mounted to the snow plow blade support structure. Either a single trip spring on either side of the snow plow blade or two trip springs on each side of the snow plow blade may be used, and the size of the trip springs is minimized by ensuring that all of the forces which they exert are directed properly in the requisite directions.