Design Optimization of Racing Motorcycle Swingarm for Additive Manufacturing

Introduction

World Superbike is a motorcycle series sanctioned by the FIM and constitutes the highest level of international production motorcycle racing. The motorcycles used in these competitions are highly modified production motorcycles used solely for closed-circuit racing. The machines used in these competitions can weigh as little as 168kg, produce over 250 horsepower, are capable of cornering at over 65˚ of lean angle, and generate 1.3G of lateral grip.

The swingarm is the primary component of a motorcycle's rear suspension. The function of a swingarm is to connect the rear wheel to the chassis, pivoting with one degree of freedom while acting on a spring damper to absorb bumps in the road. While moving a straight line, the direction of the force is in-line swingarm and damper travel and road forces can be completely absorbed by the damper. While learned over a turn, only a component of the force will act in-line with suspension travel and the rest will act laterally with respect to the motorcycle. These forces must be absorbed or will induce variation tire—road contact, causing loss of grip and reduction in the ability to accelerate, brake, or turn4.

A typical high-performance swingarm is constructed from welded aluminum components or a carbon fiber structure. The swingarm must effectively perform two tasks, be flexible in one plane to absorb lateral forces while rigid in another to efficiently transmit vertical forces to the damper. Construction of a swingarm using these techniques require extensive machining and manually fabrication with several variations of a design being produced with a small lot size. Each of these factors contributes to increased cost and time.

The purpose of this research is to discretize the two functions of a swingarm into two separate components facilitated by additive manufacturing. The swingarm of an Erik Buell Racing 1190RS campaigned in World Superbike for the 2014 and 2015 series was selected as the basis of this design optimization research. The first component is a generatively designed rigid swingarm structure and the second components are compliant blocks utilizing negative-stiffness honeycombs to provide lateral damping.