Design and analysis of a motorcycle rear suspension

Background

Figure 1 shows basic design of the so-called rising-rate rear suspension, which is widely used in motorcycle design and manufacturing. In this type of suspension, the wheel is suspended by a swing arm. The mono-tube shock absorber is linked to the swing arm through a 4-bar mechanism. Assume that the unsprung mass of the rear of the motorcycle is 20 kg. The tyre is known to have a vertical stiffness of 100 N/mm, and a damping value of 1200 Ns/m.

Tasks

This is an individual assignment which comprises of four sections:

1) The first element is to conduct research into the geometry of a typical motorcycle suspension and specify a typical wheel diameter and sprung mass. These parameters will be used for your following tasks.

2) The second element of the task is to design a rising rate linkage mechanism that will permit at least 120 mm of rear wheel travel. The above figure can be used as a basis for your design. Your design should clearly show the joints you have chosen, and you should justify your choices. The linkage should be demonstrated in ADAMS model with wheel travel and raising spring rate. It is suggested that you investigate current motorcycle suspension linkages.

3) The third element of the task is to specify the springs and dampers. Your rates should be chosen to provide appropriate ride behaviour under an absolute bump limit (a vertical load equivalent to 3 m/s2). You may analyse it by varying your specified values. You may

optimise your design to ensure that the suspension does not reach the end of its travel when it passes the "absolute bump limit".

4) The fourth element of your task is to analyse the behaviour of the motorcycle under motorway conditions with a road profile of a +/- 3 mm input at a wavelength of 30 m. The frequency of the road profile depends on the vehicle speed. You may vary the driving speed and compare your result with the theory you've learned. You should try to ensure that the rear suspension you have designed will provide the maximum comfort for the rider (the student will need to define this criteria), and the minimum force transmissibility on the motorcycle.
There are also marks available for the production of a well presented, professional report, etc. (see marking scheme).

Scope

Some tasks may be suitable for hand calculations, whilst others may be suitable for multi-body software analysis. An integral part of this assignment is being able to choose the most appropriate analysis methods. You should justify your choices, and state any consequent compromises that result. You should accompany your simulations with hand calculations where possible using either MATLAB or EXCEL to plot appropriate graphs.

The brief is deliberately quite open, and you will receive higher marks if you support and justify your design with appropriate research. Higher marks will also be given for novel solutions, as long as those solutions are valid and justified. Higher marks will be awarded for models with an appropriate level of complexity. Over complex models that add little to the accuracy of the solution will not attract higher marks, nor will over simplified models that sacrifice accuracy.

Module outcomes addressed

This assignment allows you demonstrate the outcomes (1), (2), (4) and (5) of the module:
1) Have a systematic understanding of how to model and analyse vibrating systems.
2) Be able to deploy accurately established techniques in order to analyse and synthesise planar and spatial mechanisms.
4) Apply vibration reduction methods to solve problems involving mechanical vibrating systems.
5) Use computer software packages to critically evaluate mechanisms and vibrating systems.