Motorcycle rear suspension swingarm assembly

Abstract

An off-road motorcycle incorporates a swingarm assembly for pivotally supporting a rear wheel relative to a frame of the motorcycle. Preferably, the swingarm includes right and left arms extending rearwardly from a forward connecting portion. Right and left rear wheel mount members are secured to the right and left arms, respectively, to rotatably support the rear wheel of the motorcycle. Preferably, the arms of the swingarm assembly are formed at least partially by a hydroforming process and the center of each of the arms has a width that is greater than the width of either a forward or rearward end of the arm. In addition, the forward end of each of the right end left arms preferably is bent inward such that the forward portion of the swingarm assembly is narrower than the rear portion of the swingarm assembly. The hydroforming process permits the inner wall of the arms to be vertical and substantially planar along the region where the arms are bent about a generally vertically extending axis. In addition, a vibration absorbing coating can be applied to the wheel support members in a manner to be interposed between an inner surface of the wheel support members and the outermost portion of a hub of the rear wheel.

What is claimed is:  
     
         1 . An off-road motorcycle comprising a frame, a front suspension assembly rotatably supported by the frame and rotatably supporting a front wheel, a rear swingarm assembly pivotably supported by the frame and rotatably supporting a rear wheel, an internal combustion engine supported by the frame and being drivingly coupled to the rear wheel, the swingarm assembly comprising at least one hydroformed arm extending along a side of the rear wheel in a direction substantially aligned with a vertical, central plane of the motorcycle, the arm comprising an intermediate portion that is curved about a generally vertical axis and the intermediate portion having a generally planar vertical wall.  
     
     
         2 . The off-road motorcycle of  claim 1 , wherein the arm also has a first height and a second height, the first height being forward of the second height and the first height being greater than the second height.  
     
     
         3 . The off-road motorcycle of  claim 2 , wherein the swingarm further comprises a second hydroformed arm that generally extends in parallel with the first arm, the second arm also comprising an intermediate portion that is curved about a generally vertical axis and the intermediate portion having a generally planar vertical wall.  
     
     
         4 . The off-road motorcycle of  claim 3 , wherein a forward portion of the first arm and a forward portion of the second arm are joined by a connecting member.  
     
     
         5 . The off-road motorcycle of  claim 3 , wherein a portion of the arm having the first height is proximate the connecting portion.  
     
     
         6 . An off-road motorcycle comprising a frame, a front suspension assembly rotatably supported by the frame and rotatably supporting a front wheel, a rear swingarm assembly pivotably supported by the frame and rotatably supporting a rear wheel, an internal combustion engine supported by the frame and being drivingly coupled to the rear wheel, the swingarm assembly comprising at least one hydroformed arm extending along a side of the rear wheel in a direction substantially aligned with a vertical, central plane of the motorcycle, the arm comprising an inner surface facing the rear wheel, the arm being curved at an intermediate region such that a forward portion of the arm is canted toward the rear wheel, and a portion of the inner surface within the curved intermediate region being substantially planar.  
     
     
         7 . The off-road motorcycle of  claim 6 , wherein the arm has an upper surface and a lower surface defining a height of the arm therebetween, the height of an intermediate portion of the arm being greater than the height of a rearward end of the arm.  
     
     
         8 . The off-road motorcycle of  claim 6 , wherein the at least one arm comprises a first arm and a second arm, the first and second arms being positioned on opposing sides of the rear wheel.  
     
     
         9 . The off-road motorcycle of  claim 8 , wherein the swingarm assembly additionally comprises a support bridge extending between the first and second arms on a forward side of the rear wheel, the intermediate region being located to a rearward side of the support bridge.  
     
     
         10 . A motorcycle comprising a frame, an engine mounted to the frame, a rear swingarm pivotally connected to the frame, a rear wheel supported by the swingarm and driven by the engine, the swingarm having an arm portion that is unitarily formed and that has an curved intermediate region, the curved intermediate region comprising a first wall and a second wall that are curved about a radius in the form of a part of a cylinder, neither the first wall nor the second wall not being bowed toward the other, the arm portion being formed by providing an elongated tubular workpiece, providing a die having a first portion and a second portion, the first portion and second portion of the die cooperating to define a die cavity sized and shaped substantially identical to a desired final shape of an outer surface of the arm, placing the workpiece within the die cavity and closing the die, introducing a fluid into an internal space of the workpiece, and pressurizing the fluid to a sufficient level such that the workpiece conforms substantially to the size and shape of the die cavity.  
     
     
         11 . The method of  claim 10 , wherein mating surfaces of the first and second portions of the die meet to define a parting line around a perimeter of the die cavity, the first and second portions of the die being arranged such that the parting line is substantially aligned with a portion of the die cavity forming an upper, inner corner of the arm and a portion of the die forming a lower, outer corner of the arm.  
     
     
         12 . A rear suspension swingarm assembly for an off-road motorcycle, the swingarm assembly configured to be pivotably supported by a frame of the motorcycle and rotatably supporting a rear wheel of the motorcycle, the swingarm assembly comprising a connecting portion defining a pivot axis of the swingarm assembly relative to the frame of the motorcycle, the swingarm assembly additionally comprising a first elongated, tubular arm and a second elongated, tubular arm, the first and second arms being fixed to the connecting portion and extending in a rearward direction therefrom, each of the first and second arms having an inner surface facing the rear wheel, each of the first and second arms being curved at an intermediate region such that a forward portion of the arm is canted toward the rear wheel, wherein a portion of the inner surface within the intermediate region is substantially planar.  
     
     
         13 . The swingarm assembly of  claim 12 , wherein each of the first and second arms has an upper surface and a lower surface defining a height of the arm therebetween, the height of an intermediate portion of the arm being greater than the height of a rearward end of the arm.  
     
     
         14 . The swingarm assembly of  claim 12 , wherein the first and second arms are positioned on opposing sides of the rear wheel.  
     
     
         15 . The swingarm assembly of  claim 14 , additionally comprising a support bridge extending between the first and second arms on a forward side of the rear wheel, the intermediate region being located to a rearward side of the support bridge.