DESIGN OF CHASSIS OF STUDENT FORMULA RACE CAR

DESIGN OF CHASSIS OF STUDENT FORMULA RACE CAR Shubhanandan Dubey 1, Rahul Jaiswal 2, Raunak Mishra 3 1, 2, 3 Department of Automobile, Theem College of Engineering, University of Mumbai, Maharashtra, India Abstract SUPRA SAEINDIA is a national level competition organized by Society of Automobile Engineers India. Student of under-graduation and post-graduation can take part in this event from all over India. Student teams design the car and fabricate to compete with other participants. The main aim to design a car which is light weighted and of low cost without compromising with the safety of the driver. This paper is an introduction to the design process of SUPRA SAEINDIA race car chassis. Tubular space frame chassis for use in SUPRA SAEINDIA based on the instruction mentioned in SUPRA Rulebook 2015 and the driver s comfort allowing fast entrance and exit from the car. The simple methods for designing the chassis are also presented for new teams to get the idea about chassis design. CAD software SOLIDWORKS 2015 is used as design software because it is powerful and effective for making the changes in basic design and due to the effectiveness and availability it is used for designing and simulating the other parts of the car. It has been an ideal tool for the team for work. All the process is done according to the steps and requirement mentioned in the supra Rulebook and the basic knowledge of chassis design. Keywords SAE INDIA, Tubular Space Frame chassis, Chassis modelling, CAD. I. INTRODUCTION Society of Automobile Engineers India organize the competition SUPRA SAEINDIA every year. Students from all over India take the challenge of designing, manufacturing and race an open wheel racing car. It is really helpful for the student to improve the knowledge about designing and manufacturing of a vehicle.it also improve the ability to work in team. More than 200 colleges participate every year in this competition from all over India. The technical inspection are the sub events which include the static events like tilt test, brake test, cost report presentation, engineering design report and business presentation, dynamic events like acceleration test, skid pad, autocross and endurance test. The car is expected to survive in front, rear and the side impact. It also expected to be comfortable for diver in Handling, braking and acceleration. The main purpose is to design a chassis which is easy to manufacture within the cost limit provided for the chassis and the chassis should be strong enough to carry all the loads acting on it. II. CHASSIS DEVELOPMENT Chassis is the main part of the car; it is use to mount all the important component. It also connects the front and rear suspension. The difference in motion between the front and rear suspension attachment points can make handling more difficult. The frame must also provide attachment points which will not yield within the car s performance envelope. There are many different styles of frames; space frame, monocoque, and ladder are examples of race car frames. The most popular style for SUPRA SAEINDIA is the tubular space frame. Space frames are a series of tubes which are joined together to form a structure that connects all of the necessary components together. However, most of the concepts and theories can be applied to other chassis designs. A Space frame chassis was chosen over a monocoque in spite of being heavy, as its manufacturing is cost-effective, requires simple tools and damages to the chassis can be easily rectified. The chassis design started with fixing of suspension mounting coordinates and engine hard points. DOI : 10.23883/IJRTER.2017.3064.WRMMN 179

2.1 Design Considerations Many steps have to be followed while designing a chassis. Starting from assuming the initial design and then start collecting the dimensions according to the rulebook. To match the performance, fulfill the design requirement needs to identify the restrictions from the initial stage. Design any chassis, it need to study the laws and researches done on the race car chassis. According to the data we start design on the software. Main thing is to keep the target in mind while designing to get the better result. Assignment to the task of chassis design to the start of construction. These steps are; to identify the restriction, determine the required performance criteria, research design techniques and methodology, use of CAD software to design chassis and lastly start construction. Throughout these steps, choices must be made based on the targets that are to be achieved to meet the performance requirement. The designer of the chassis must have an idea as to how all components of the car are going to function in relation to each other. As a result, the designer must know how all parts must interact and take this interaction into account when designing the frame. The design of a racing car chassis, or any racing chassis for that matter, is going to be based on suspension points, powertrain layout, driver position controls, safety, etc. These important points must come together to form an effective package for the car to perform as intended. Stiffness - The stiffness of the chassis is an important factor which need to be tested on the model. Design of the suspension is all depends on the stiffness of the vehicle. If the chassis is not rigid enough to take the load throughout the event, then I can result in failure. Vehicle is designed with the goal of keeping all tires in touch with the ground throughout the performance range of the vehicle. If the frame is not stiff enough it can result as unbalance chamber and toe. An image of a frame subjected to a torsional load is superimposed on an undeflected frame. Generally, a chassis that is stiff enough for competition will not yield. However, some care should be taken to ensure that the attachment points of the frame do not yield when subjected to design loads. Torsional Stiffness - Resistance to the torsional loads is called as torsional stiffness. Ansys software was used to analyze the torsional stiffness of the chassis. The car design must be design for the maximum torsional stiffness and it test on basis of the equation given below.. (1) The above equation is a simple formula that relates the angle of twist to the applied torque, with J representing the shafts polar moment of inertia, with θ denoting the resultant twist of the shaft, G representing the shear modulus of the material and l being the length of the shaft. Now a chassis can be made extremely stiff by adding significant amounts of material to the frame. However, this additional material might degrade the performance of the car because of the added mass. Therefore, while designing a race car chassis it is important to get a balance between the weight and stiffness of the chassis. Triangulation - Triangulation involves adding a diagonal member to an arrangement of four members to break the section into two three member sections. The resulting triangles are able to carry all forces in pure tension or compression without introducing bending stresses into the joints. Triangulation can be used to increase the torsional stiffness of a frame. Obviously, a frame which is a structure will be torsionally stiffer than a mechanism. Therefore, an effort should be made to triangulate the chassis as much as possible. Visualizing the frame as a collection of rods which are connected by pin joints can help frame designers locate the mechanisms in a design. @IJRTER-2017, All Rights Reserved 180

Figure 1: Frame Triangulation Making the square frame triangulated can be done by adding one diagonal member. A diagonal member separates the square into two triangles. Triangulated portions are capable of transferring the stress to most of the part of the frame. If each point of joint consists of more than three rods, then it can be said that it is triangulated. Main components should be attached to triangulated points Suspension Points - The suspension geometry is what determines how well the car controls the tires that connect the vehicle to the ground. Should the suspension not control the tires correctly, the car will not corner as quickly and therefore be slower overall. Through testing, data analysis, and simulation we have developed effective suspension geometry for our SUPRA SAEINDIA race car. Packaging of the suspension to the frame is generally not an interference problem since most of the components are exterior to the frame. However, it is especially important to attach the suspension components to stiff portions of the chassis to correctly distribute the loads that will be passed through these components. 2.2 Design Process Designing process is completed in many stages. starting from taking the dimensions and writing it on the paper and then making the sketch according to the requirement of the rulebook. Chassis design was mostly based on the previous design made by the different university. Following the previous methods, we draw the sketch with dimension on the paper and then started to design in software. We used Solidworks 2015 software and weldment feature to model tube according to rulebook. Initial Setup We started by taking the dimension like height, total length, wheel base, front hoop and main hoop of the vehicle. Suspension points were selected by the type of suspension system is to be used. Once the dimension of cockpit, engine mounting points, hoops and differential position are decided we start modeling on Solidworks 2015 according to the dimension. As it was not considered as the final design, some dimensions may change while manufacturing process according to comfort of the drivers. Safety In designing process the first criteria was to keep the driver safe in the event of any accident.in SAE SUPRA rulebook the proper dimension for the classis pipe is given. It is different according to the effect of load during accident. Main hoop and front hope should have more strength compare to other portion because in the case of any accident hoops can keep the driver safe. Front bulkhead and side impact tubing are having certain thickness to observe the shock and impact in case of accident. @IJRTER-2017, All Rights Reserved 181

Modeling of Fixed Elements - Fixed elements are front bulkhead, suspension points, roll hoop and engine mounts. Fix points cannot be changed while designing so that the other portion built around these fixed points. Because of this fabrication can be faster. The roll hoop and bulkhead shapes are decided upon to minimize the length of tubing for the elements. Since the roll hoops and bulkhead are required to be at least 25.4mm x 2.4mm wall and 25.4mm x 1.65mm wall, respectively, the lengths of this heavy tubing need to be minimized to reduce weight. Once shapes of the features are decided upon, they are drawn on their respective planes. A structural member feature is added to the sketch and the first tubes of the model are drawn. The suspension mounting points are the next to be designed. These are drawn as fixed points in space in the Solidworks model. During suspension design, an optimal a-arm span was determined and this dimension must now be integrated into the chassis. Suspension mounts needs to be welded to the chassis so the position of this mounts are needed to be acquired from the suspension calculation. Engine mounting locations are also decided upon and fixed so that the engine design team can accurately place their individual part models in the car assembly without having to change their parts. This keeps the team from making drastic changes when farther along in the design process. Modeling of Variable Elements Now we design the connection to the main elements with each other. These tubes provide the strength to the main element and most of the weight of the chassis is carried by these tubes. Arrangements of these tubes are variable and careful consideration of manufacturability and chassis stiffness must be taken, so that the chassis does not become heavy and too flexible. The competition rules must also be taken into account when drawing these connecting tubes. We have chosen all the tube of the size mentioned in the rule book. Only the main hoop and front hoop rods are different from the other parts. Thickness of these parts are more as compare to other parts. First we design a chassis which was strong enough for all the impact test. It has the great torsional stiffness. First model consists of many members which increase the overall weight of the vehicle. The first chassis design below had a lot of structural members which in-fact increased the weight of the chassis. The main intention of increasing the number of structural members was to increase the torsional stiffness. By FEA members which weren t of any use were removed and hence it reduced the weight without affecting much the torsional stiffness. @IJRTER-2017, All Rights Reserved 182

Figure 2:Initial design Figure 3: Final design As the designing completed, we start for manufacturing. It s a very important factor to be consider from the very first stage of designing. It is true that the manufacturing effects on the overall cost of the vehicle and manufacturing depends on the modeling. Manufacturing should be as easy as I can be so that it can reduce the time for completing the care III. MATERIAL SELECTION Material selection is as important as modeling. Material must provide enough strength to the chassis to withstand the loads acting on it. Material with high density can increase the weight of the chassis and material with low density may result in breakdown in the middle of racing environment. While selecting the material, its availability in the market and the cost of the material is must be considered. Light weight and stiffness are the most important properties of the chassis and the stiffness of a complex chassis will be effect by the stiffness of the material from which it built. It was decided that the frame would be constructed from steel due to its availability and relatively low cost There are many different grades of steel available such as AISI 4130,AISI 1020,AISI 4027,e.t.c.. But however @IJRTER-2017, All Rights Reserved 183

many of the SAE teams around the world use 4130 SAE grade steel (which contains Chromium and Molybdenum alloying elements) due to its higher yield strength. In the first part of the design phase when the chassis material was chosen, the team had a limited budget which resulted in the decision to use AISI4130. Lightweight and stiffness are the most important properties of a chassis and the stiffness of the completed chassis will be affected by the stiffness of the material from which it is built. Material stiffness is known as Young s Modulus and the controlling mechanism for stiffness in a material is the inter-molecular forces. So stiffness or Young s Modulus is a material constant which cannot be significantly changed by any mechanical or chemical processes. AISI 4130 alloy steel contains chromium and molybdenum as strengthening agents. It has low carbon content, and hence it can be welded easily. The datasheet given below provides more details about AISI 4130 alloy steel. A. Mechanical Properties The mechanical properties of AISI 4130 alloy steel are outlined in the following table. Property Matric Imperial Tensile strength, ultimate 560 MPa 81200 psi Tensile strength, yield 460 MPa 66700 psi Modulus of elasticity 190-210 GPa 27557-30458 ksi Bulk modulus (Typical for steel) 140 GPa 20300 ksi Shear modulus (Typical for steel) 80 GPa 11600 ksi Poisson s ratio 0.27-0.30 0.27-0.30 Elongation at break (in 50 mm) 21.50% 21.50% Reduction of area 59.6 59.60% Hardness, Brinell 217 217 Hardness, Knoop (Converted from Brinell hardness) 240 240 Hardness, Rockwell B (Converted from Brinell hardness) 95 95 IV. CONCLUSION The main aim of this paper is to design a student formula race care chassis which has to sustain all the various parameter which is required for racing condition under SUPRA SAEINDIA. But for designing a chassis we have to consider it under various parameter to determine whether this chassis can withstand all the forces and load acting on it or not. A car which is to be design should be light weighted and of low cost without compromising with the safety of the driver. The material selection also plays a very important role while designing a chassis. Material must provide enough strength to the chassis to withstand the loads acting on it. Material with high density can increase the weight of @IJRTER-2017, All Rights Reserved 184

the chassis and material with low density may result in breakdown in the middle of racing environment. While selecting the material, its availability in the market and the cost of the material is must be considered. By looking up these criteria we have selected the material as AISI 4130. As this paper has sole focus on design, it is very important to test the car so that any design oversights will be highlighted before competition. REFERENCES [1] A.hari kumar, V.deepanjali, Design & Analysis of Automobile Chassis, International Journal of Engineering Science and Innovative Technology, ISSN: 2319-5967, Volume 5, Issue 1, January 2016. [2] Chartree Sithananun,,Nuksit Noomwongs, SAE Student Formula Space Frame Design and Fabrication, The Second TSME International Conference on Mechanical Engineering 19-21 October, 2011, Krabi. [3] N. G. Jogi, Akshay P. Take, Yogesh Asolkar, Sheikh M Aftab, Review work on analysis of F1 car frame using Ansys, IJRET, Apr-2014. [4] G.Guru Mahesh,"Design and analysis of a single seater race car chassis"issn 2014. [5] Micheal broad, design development and analysis of SCSHFH.09 chassis,2009 SAE International. [6] Ravinder Pal Singh, Structural performance analysis of formula sae car, Jurnal Mekanikal December 2010, No. 31, 46-61. [7] Abhijit Das, Design of student formula race car chassis,ijret-2015 [8] William B. Riley and Albert R. George, Design, Analysis and Testing of a Formula SAE Car Chassis, SAE TECHNICAL PAPER SERIES 2002-01-3300. [9] (2017) INDIAMART website. [Online]. Available: http://www.indiamart.com/ [10] (2017) ALIBABA website. [Online]. Available: http://www.alibaba.com/ @IJRTER-2017, All Rights Reserved 185