Abstract:
A skateboard wheel truck assembly has a suspension including a non-circular base bushing with wings or arms extending laterally outwardly, providing for increased stability and control and reduction of wobble in use of the skateboard.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns skateboards, and especially wheel trucks supported beneath the skateboards on elastomeric bushings. 
     Skateboards have developed and evolved over the years. A relatively crude form of skateboard was available in the 1960s but did not achieve very wide use. The development of better wheel trucks and wheels, especially polyurethane wheels, brought skateboards much greater popularity, and in fact the development of these skateboard wheels led to better wheels on roller skates. The design of the skateboards, wheel trucks and suspension systems was continually improved, producing better steerability, agility and control in use of skateboards. 
     Elastomeric shock absorbing bushings have improved suspension, and also provided steerability. This type of mounting, shown in U.S. Pat. Nos. 6,105,978 and 6,739,603, has a base plate fixed to the bottom of the skateboard, with a threaded post extending down at an angle from the base plate. A wheel truck is secured to the threaded post in a sandwiched connection between two elastomeric bushings, one above and one below an opening in the wheel truck, tightened down by a nut on the threaded bolt or stud. A pivot point for steering is established by a pivot post that extends usually integrally from the wheel truck body into an elastomerically-lined bore or socket in the base plate, positioned about 1½″ or so from the threaded stud. Tipping of the skateboard platform, by shifting the weight of the user, rocks the wheel truck relative to the skateboard and causes a small turn angle of the wheel truck to occur relative to the skateboard platform, by swinging the wheel truck about the steering pivot point. Adjustments in stiffness can be made by tightening or loosening the nut on the threaded bolt or stud, or using elastomeric materials of different hardnesses. 
     U.S. Pat. No. 7,044,485 shows a modified form of the above-described wheel truck suspension, utilizing three discrete elastomeric bushing support points, one with a threaded post secured to a base plate as just described, and additional bushing seats at left and right, in a non-linear positional relation with the threaded bolt, upon which the metal wheel truck body rests. The outboard elastomeric supports are characterized as shock absorbers that can be interchanged for different response. 
     SUMMARY OF THE INVENTION 
     The current invention improves over prior skateboard wheel truck suspension designs by providing a better elastomeric suspension system that can use an essentially standard style base plate while achieving improved stability, control and reduction of wobble through the design of the wheel truck and the base elastomeric bushing that resides on a threaded post between the wheel truck and the fixed base plate. In one sense the invention can be said to achieve the benefits of the outboard bushing suspension shown in U.S. Pat. No. 7,044,485 discussed above, without the larger and more complex bracket and wheel truck assembly shown in that patent. This is a simpler and more efficient design for accomplishing improved stability and control. 
     In a preferred embodiment the base bushing, of elastomeric material such as polyurethane, is shaped not as a cylinder or slightly conical as in previous designs, but with a pair or wings or arms which extend outwardly and forwardly relative to the skateboard (referring to the front wheel truck). These arms act somewhat as flexible buttresses. The truck-engaging surface of this base bushing with its wings approximates a triangle but with the rear side of this surface preferably rounded, although it could be otherwise shaped. This surface engages in a similarly shaped recess in the upper side of the wheel truck body, toward the rear, with the threaded stud or bolt from the base plate extending up through the recess. The upper surface of this base bushing could be flat, or it could be convex or concave to match with a complementarily-shaped washer surface for a stable seat with the washer. The footprint shape of this top side of the base bushing can be round, or other shapes such as similar to the lower, truck-engaging side, but preferably with a narrower width at the middle of the bushing, or a generally hourglass shape to the bushing to allow greater deflection of the buttress arms. Even an hourglass shape round at both ends can be effective; it is important that the bushing not be a solid cylinder (or partially tapered cylinder) of enlarged diameter, because this will cause an undesired degree of increasing resistance to bending as one goes deeper into a turn. 
     Another bushing, which can be round or otherwise shaped (optionally shaped similarly to the base bushing) is secured at the outer end of the threaded stud or post. This assembly of a portion of the truck body sandwiched between two elastomeric bushings is compressed together by tightening a nut. 
     As the wheel truck rocks left or right relative to the fixed base plate or bracket, the arms or wings of the base elastomeric bushing compress, deflect and bend on the compression side, i.e. the direction of turning, but the opposite arm migrates out of the truck body recess. The surfaces of the arms, and the configuration of the truck body recess, are shaped to establish smooth return of the bushing back into the recess when the turn is complete. 
     It is among the objects of the invention to improve stability and control of a skateboard, with smooth transition through turns and less wobble, in a compact and efficient wheel truck assembly. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a typical prior art skateboard wheel truck assembly. 
         FIG. 2  is a sectional elevation view showing the prior art wheel truck assembly. 
         FIG. 3  is a perspective view showing a skateboard wheel truck assembly of the invention. 
         FIG. 4  is a view showing a base bushing in a configuration pursuant to the invention. 
         FIG. 5  is another view showing the base bushing and a washer. 
         FIG. 6  is a bottom view of a wheel truck body of the invention. 
         FIG. 7  is a perspective view of the base plate and wheel truck body and showing the base bushing of the invention. 
         FIG. 8  is a sectional view generally as seen along the plane  8 - 8  in  FIG. 7 , and showing a part of the wheel truck body and the manner in which the base bushing seats against a recess on the wheel truck body. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the drawings,  FIGS. 1 and 2  show a typical prior art arrangement for the front wheel truck of a skateboard. The wheel truck assembly  10  includes a base plate or base bracket  12 , to be attached by fasteners up against the bottom surface of the skateboard, which is not shown.  FIG. 1  can be considered to show a front wheel truck assembly viewed from the rear. The base plate  12  for the front wheel truck has a rear platform or pedestal  14  which supports a threaded stud or bolt  16 , extending downward and angled slightly forwardly as shown particularly in  FIG. 2  (the near end of the skateboard is to the left in  FIG. 2 ). At the front end  18  of the base plate is a raised portion or boss  20  having a recess  22  with a rubbery insert member  24 , i.e. an elastomeric grommet that lines the recess. Within this grommet  24  is received a pivot post  26  that is part of the wheel truck base plate  12  and a portion of which can be seen at  26  in  FIG. 1 . The threaded stud or bolt  16  supports and secures a wheel truck body  27  in a flexible, cushioned manner. Assembled onto the threaded bolt  16  is a first cup shaped washer  28 , a base bushing  30 , an outer bushing  32 , and a second cup shaped washer  34 , with the assembly retained by a nut  36 . The two bushings sandwich a rearward flange  38  of the wheel truck body between them, as shown in both  FIGS. 1 and 2 . As is well known in the operation of this type of skateboard wheel truck suspension, when the user leans the skateboard to one side, the wheel truck pivots in a rocking sort of motion relative to the base plate  12  and the skateboard. This pivoting is generally about the tip of the pivot post  26 . The rearward flange  38  of the wheel truck sways to left or right, which it is permitted to do by a hole  40  in this rearward flange  38 , the hole being larger than the threaded bolt  16 . Thus, shifting the weight and tipping the skateboard to the left, for example, will cause the skateboard to rock to the left, tipping relative to the wheel truck, swinging the angle of the bolt  16  in the flange hole  40 , and changing the angle of the wheel truck with the skateboard by a degree or two or more. Thus, the skateboard turns to the left. 
     The invention, as explained above, improves the steerability and control of a skateboard and eliminates or reduces wobble, adding to stability and safety of the skateboard, through an improved suspension connecting the wheel truck to the skateboard.  FIG. 3  shows a wheel truck  45  of the invention, without wheels, secured to a base plate  46  that is to be secured by fasteners to the bottom side of a skateboard, not shown. The wheel truck  45  and base plate  46  are shown inverted in this view. 
     The base plate  46  can be the same as the base plate  12  shown in the prior art views just described. The base plate has a recess with a grommet for receiving a pivot post  48  ( FIG. 6 ) of the wheel truck body, although the pivot recess is not seen in these drawing views. The suspension for the wheel truck  45  utilizes a modified base bushing  50 , and the wheel truck&#39;s upward surface, seen in  FIG. 6 , is modified to receive this base bushing.  FIG. 6  shows a generally triangular recess  52  in the upper surface of the wheel truck body. This is shaped as a seat to receive the generally flat surface  54  of the base bushing (although that surface  54  could be somewhat rounded). The lower surface of the base bushing is shown in  FIG. 4 , and the bushing  54  is shown positioned in the upper cup-shaped washer  30  in the perspective view of  FIG. 5 .  FIG. 3  shows the preferably rounded (e.g. generally cylindrical) rear surface  56  of the base bushing, while  FIG. 5  shows the forward side  58 , assuming the truck assembly is at the front of a skateboard (typically the rear truck is the same, oppositely directed). The wheel axle is shown at  53 . 
     As shown in the drawings, the generally triangular shaped lower surface  54  of the base bushing of the invention provides a pair of buttress-like wings or arms  60  at each of left and right sides. The truck body recess  52  is shaped to receive this surface, and in fact the recess  52  has sloped or ramp-like edges  62  on the left and right sides of the triangle, for a smoother transition of the arms  60  into and out of the recess as the wheel truck sways or rocks during turns. This provides for a smooth transitioning into and out of a turn, avoiding a snagging of an arm as it is displaced or as it re-enters the recess after being displaced in a turn. In fact, at left and right corner regions  63  there is preferably no ledge at all but can be a slight incline, as shown particularly in  FIG. 8 . In that sectional view a ledge  64  is seen beyond the viewing plane, but at and near the corners  63  this ledge tapers down to a flat or a slight incline. The neutral position of the base bushing  50  is generally and schematically illustrated in dashed lines. 
     As an example of a preferred embodiment, the base bushing  50  may have a base diameter of about 24 mm to 25 mm, i.e. a radius as shown at r in  FIG. 4  of about 12 mm. The upper side of this bushing preferably (but not necessarily) is generally circular as shown in dashed lines in  FIG. 4 , and as shown in  FIG. 5  where that end is engaging in the cup shaped washer  28  (other shapes can be used for the upper side of this bushing, as described above). A bolt hole  65  is preferably at the circular center. The arms, however, extend considerably beyond this base radius r, and may have an arm length a from the radius center, for example, of about 24 mm, 12 mm beyond the normal radius. The total span s across the two arms  60 , i.e. the length of the rear side  58  where it meets the generally flat surface  54 , may be about 40 mm to 42 mm, or greater if desired. It is this width, the approximately 40 to 42 mm width represented by the span of the arms, that provides for the increased stability and control in the skateboard suspension, and this width preferably is at least about 40 mm. This compares to a width on a round base bushing of about 24 to 25 mm as typical in prior art suspensions, typically on a truck body about 12.8 cm (5 inches) wide excluding the axle protrusions, and it compares to a front to back depth (at a maximum point) of the bushing  50  of about 26 mm. Note that the dimensions of the bushing  50  of the invention can vary. The span of the arms could be longer or slightly shorter, or the overall size of the base bushing could be different, but with the bottom side width or arm span still wide in relationship to the base diameter of the bushing as referred to above, or in comparison to the depth of the bushing (front to back), or as a minimum ratio of width as compared to truck body width (wheel span). For example, in a preferred embodiment the arm length a may be at least about twice the radius r, or at least about 1.6 times the radius. The arm span across the two arms  60  (the width of the bottom side), is substantially larger than the base end width or the depth of the bushing. For example, it may be at least about 1.75 times the diameter at the upper end of the base bushing or 1.75 times the maximum depth of the bushing, or at least about 1.5 times the diameter or 1.5 times the maximum depth. As compared to the truck body width (axle excluded), the width s is preferably at least about one-third the truck body width, or at least about 5/16 the truck body width, as compared to a typical bushing face about 3/16 the truck body width. Note that although the general shape of the base bushing shown in  FIGS. 3 through 7  is preferred, other shapes for the lower end, i.e. the surface  54 , can be used. Instead of a generally triangular shape as shown, the surface  54  could be something like an ellipse, with the two arm ends in line with the center bolt hole  65 . The arm ends can be more pointed than those of an ellipse. The reason a generally triangular shape is preferred, with the arms  60  offset from the bolt hole  65 , is that the wheel truck body  45  can be more compact, as can be seen from  FIGS. 6 and 7 , with a generally triangular shape in which the buttress-like arms and the corresponding arm positions in the recess  52  on the truck body are generally in line with the main structure of the wheel truck body. The arms could be moved outwardly (up the page in  FIG. 6 ), but this would require additional truck body structure. 
     As shown in  FIG. 3 , the suspension assembly includes a second or lower bushing  66 , another washer  34 , and a nut  36  to tighten the assembly as desired, with the truck body flange  38   a  sandwiched between the two bushings.  FIG. 6  shows the hole  40   a  through the truck body flange  38   a , within the recess area or bushing seat  52 . The hole is substantially larger than the bolt, e.g. about 4-5 mm larger in diameter, to allow for the swaying motion of the wheel truck in turning. 
       FIG. 7  shows the base bushing  50  of the invention as seated in the generally triangular recess or bushing seat  52  of the wheel truck body  45 . 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.