Design, Manufacture and Testing of Suspension for a Formula SAE Car - Adam Mapson, 2011
Monash Motorsport Final Year Thesis Collection
The Final Year Thesis, is a technical engineering assignment undertaken by students of Monash University. Monash Motorsport team members often choose to conduct this assignment in conjunction with the team.
These theses have been the cornerstone for much of the team’s success. The purpose of the team releasing the Monash Motorsport Final Year Thesis Collection is to share knowledge and foster progress in the Formula Student and Formula-SAE community.
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SUMMARY:
This report details the design, manufacturing and testing of a suspension system for Monash's 2011 Formula SAE car. The car was a 'clean sheet' design, built around parameters determined through a newly devised simulation. The resulting package was smaller and lighter than previous designs, with a significant increase in aerodynamic downforce. A suspension system had to be designed to suit, with a strong focus on manufacturability to meet a strict and early deadline. An appropriate degree of analysis
was carried out to generate a reliable, nearly trouble free system. Testing to date has shown a marked performance improvement through suspension testing, and the completed car promises to be Monash's most competitive to date.
Introduction:
Formula SAE is the world's foremost student engineering design competition. Monash University has fielded an entry in the Australasian competition every year since the inaugural competition in 2000, recently achieving wins in the 2009 and 2010 competitions.
The role of suspension on a Formula SAE car, or any race car for that matter, is to control the angle, position and velocity of each wheel to maintain a high value of mechanical grip, while transmitting the forces generated by the tyres to the chassis. The handling of the car can be modified by subtly changing the kinematics of the suspension linkages and relative stiffnesses of springs, bars and dampers (Smith 1995, p64.) Formula SAE is held on tight, winding tracks, making the handling of the car, and by extension the suspension, critical in gaining competition points.
The major parts of the suspension system on almost every Formula SAE car are the tyres, wheels, wishbones, uprights, hubs, push and pull rods, bell cranks, springs, dampers and anti roll bars. All these parts vary in the degree of difficulty to design and manufacture, but failure in almost any of them could have serious consequences. The design of these parts must therefore be undertaken in the knowledge that the safety of drivers depends on the job being done well.
In recent years, the focus of the competition has changed in accordance with societal demands for greater fuel efficiency and sustainable technology. To this end, the Society of Automotive Engineers (SAE) have increased the points value of fuel economy in the 'endurance' part of the competition, a move that favours lightweight cars with small capacity engines, in contrast to the relatively heavy and high powered cars that have proved successful for Monash in recent competitions. The competition organisers have also changed the rules to reduce the limitations on cars using aerodynamic enhancements, with substantial implications for Monash as one of the leading 'wing car' teams.
2010 saw the team develop a basic Excel based competition points simulator (Webb, finished) to allow a reasonable comparison between different concepts. Based on the results of this simulator the team chose to use a single cylinder KTM 450 SX-F engine to power the car for the 2011 season and several seasons beyond, replacing the Honda CBR 600RR four cylinder engine used in every Monash car to date. The narrower footprint of this engine has allowed the team to reduce the overall width of the car, which can show a measurable time advantage through the tight slaloms and lane changes of typical Formula SAE tracks. Despite the drag penalty, it can be shown downforce can be increased to a very high
level before drag and the consequently increased fuel consumption start to detract from its traction advantages in overall points terms. The team will therefore be taking full advantage of the more liberal 2011 aero rules and increasing downforce by a factor of approximately two.
These and other fundamental changes from the previous car required a completely new suspension design to suit. This report reviews the large body of vehicle dynamics theory that has built up since the invention of the automobile, then focuses on the mechanical layout of modern suspension systems. The report then goes through the aims and constraints of the project, detailing the design process for each major part in turn. The report concludes by analysing the successes and failures of the completed system in practice, and suggests improvements for future designs.
Conclusion:
The 2011 suspension system represents an excellent achievement by Monash Motorsport - a complete system designed from scratch and manufactured in record time. This is a result of goal setting which acknowledged the tight timeline faced by designers.
The clear imperative to get the most out of the car through robust, reliable designs filtered down to the component design level. The few failures experienced in testing to date resulted from neglecting small issues, rather than fundamentally flawed approaches to design.
All component weights met their targets according to CAD modelling, and physically weighing the parts should confirm this. Shortly after this report is written, the car will be broken down, giving an opportunity to weigh parts and check for compliance with the targets set out in section 4.6.
The large range of adjustments built into the system has already been very well utilised, even though the team is in a relatively early stage of testing. The car as a whole shows great promise at the testing stage, and is expected to continue the success of the Monash team into the future.