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Design of a Suspension for a Formula Student Race Car

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Design of a Suspension for a Formula Student Race Car Design of a Suspension for a Formula Student Race Car Adam Theander VEHICLE DYNAMICS AERONAUTICAL AND VEHICLE ENGINEERING ROYAL INSTITUTE OF TECHNOLOGY TRITA-AVE-2004-26 ISSN 1651-7660 Postal Address Visiting Address Internet Telephone Telefax KTH Teknikringen 8 www.ave.kth.se +46 8 7906000 +46 8 7909290 Vehicle Dynamics Stockholm SE-100 44 Stockholm Sweden Abstract In July of 2004 KTH Racing will attend at the Formula Student event in England. The Formula Student event is a competition between schools that has built their own formula style race cars according to the Formula SAE rules. In January of 2004 the Formula Student project started at KTH involving over seventy students. The aim of this thesis work is to design the suspension and steering geometry for the race car being built. The design shall meet the demands caused by the different events in the competition. The design presented here will then be implemented into the chassis being built by students participating in the project. Results from this thesis work shows that the most suitible design of the suspension is a classical unequal length double A-arm design. This suspension type is easy to design and meets all demands. This thesis work is written in such a way that it can be used as a guidebook when designing the suspension and steering geometries of future Formula Student projects at KTH. Acknowledgements This master thesis has been conducted at the Division of Vehicle Dynamics, Department of Aeronautical and Vehicle Engineering at the Royal Institute of Technology, KTH, in Stockholm, Sweden. The work has been carried out from December 2003 to May 2004. There are a few persons to whom I would like to especially express my gratitude. Professor Annika Stensson, my examiner, who gave me the opportunity to carry out this thesis work; research engineer Mats Beckman, my supervisor, for his engagement and time spent helping me; Fredrik Westin, Ph.D student at Division of Internal Combustion Engines, who has had a major role in KTH Racing as project leader and spent almost all of his spare time working with the project; all students participating in the KTH Formula Student project, without all of you there wouldn’t have been any KTH Racing. Finally I would like to take the opportunity to give a special thank to the students known as “Järngänget”, you know who you are. Without their effort the last couple of weeks there would never have been a car to show on the 14th of May. Stockholm, May 2004 Adam Theander Table of Contents 1 Introduction ..................................................................................... 12 1.1 Background..................................................................................................12 1.2 Aim of the work...........................................................................................12 1.3 Competition Objective .................................................................................12 1.3.1 Vehicle Design Objectives .......................................................................13 1.4 Competition Events and Judging of the Cars ................................................13 1.4.1 Acceleration Event...................................................................................14 1.4.2 Skid-Pad Event ........................................................................................14 1.4.3 Autocross Event.......................................................................................15 1.4.4 Endurance and Fuel Economy Event ........................................................15 1.4.5 Judging of the cars ...................................................................................16 1.5 Rules Relevant to the Chassis Design...........................................................17 1.5.1 Wheelbase and Vehicle Configuration......................................................17 1.5.2 Vehicle Track Width................................................................................17 1.5.3 Ground Clearance ....................................................................................17 1.5.4 Wheels and Tires......................................................................................17 1.5.5 Suspension...............................................................................................17 2 Suspension Design Aspects.............................................................. 18 2.1 Wheelbase ...................................................................................................18 2.2 Track Width.................................................................................................19 2.3 Kingpin and Scrub Radius............................................................................20 2.4 Caster and Trail............................................................................................21 2.5 Instant Centre and Roll Centre .....................................................................21 2.6 Tie Rod Location .........................................................................................22 2.7 Anti Features ...............................................................................................23 2.8 Ackerman steering .......................................................................................25 2.9 Camber ........................................................................................................26 2.10 Toe ..............................................................................................................27 3 Benchmark....................................................................................... 28 4 Methods............................................................................................ 30 4.1 Track width and wheelbase ..........................................................................30 4.2 Front Suspension Design..............................................................................33 4.2.1 The Rims .................................................................................................33 4.2.2 The Brakes...............................................................................................34 4.2.3 Front View Geometry...............................................................................34 4.2.4 Side View Geometry................................................................................35 4.2.5 Control Arm Pivot Axis ...........................................................................36 4.2.6 Tie Rod Location and Ackermann Geometry............................................38 4.3 Rear Suspension Design...............................................................................38 5 Model Building ................................................................................ 40 5.1 Front Suspension Modelling.........................................................................41 5.2 Rear Suspension Modelling..........................................................................42 5.3 Steering Modelling.......................................................................................43 5.4 Wheels Modelling........................................................................................44 5.5 Body............................................................................................................44 5.6 Simulation ...................................................................................................44 6 Parameter Study.............................................................................. 46 6.1 The Taguchi Methods ..................................................................................46 6.2 Parameters of Interest...................................................................................47 6.2.1 Parameter Levels......................................................................................47 6.3 Results.........................................................................................................48 6.3.1 Parameter Study of Front Suspension.......................................................48 6.3.2 Parameter Study of Steering Geometry.....................................................53 6.3.3 Parameter Study of Rear Suspension ........................................................57 7 Discussion and Design Results ........................................................ 62 7.1 Track Width and Wheelbase ........................................................................62 7.2 Front Suspension Geometry .........................................................................64 7.2.1 Camber Characteristics ............................................................................65 7.2.2 Anti Features............................................................................................65 7.2.3 Roll Centre Characteristics.......................................................................66 7.3 Steering........................................................................................................66 7.3.1 Bump Steer ..............................................................................................66 7.3.2 Ackerman ................................................................................................67 7.4 Rear Suspension Geometry ..........................................................................68 7.4.1 Camber Characteristics ............................................................................69 7.4.2 Anti Features............................................................................................69
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