Chassis is the main part of a vehicle. Generally, chassis system is the supporting frame of the structure. The chassis system consists of the elements which connected to suspension system, steering system and provide space for provides space for transmission system, fuel tank, engine and other system.
A vehicle will depend on the chassis to keep the original state. Even after force is applied, the vehicle should be in original state because of the chassis. The chassis system must be able to withstand the load acting on it. These force usually in the vertical directional and longitudinal direction. For example, in the vertical directional, a chassis will apply load from passengers and loads from vehicle parts. And for longitudinal direction, if a car accident, the car will depend on the chassis to prevent injuries to passengers and loads.
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There are several types of chassis system namely ladder chassis, tubular space frame chassis, monoque chassis and backbone chassis. The ladder chassis is indicated by its name, looks like a ladder which is consist of two longitudinal rail interconnected by several lateral and cross braces. The tubular space frame chassis employs dozens of metal tubes and position in different directions. While the monoque chassis is a one-piece structure which defines the overall shape of the car and it is already incorporated with the body in a single piece. Meanwhile the backbone chassis is a strong tubular backbone, usually in rectangular section, connects the front and rear axle. Inside there is space for the drive shaft in case of front-engine and rear-wheel drive.
Usually, the ladder chassis is used by sport utilities vehicle (SUV), while the tubular space frame is used by high performance sport cars, meanwhile the monoque chassis is used by nearly all mass production cars and backbone chassis mostly used by heavy vehicles like buses and trucks.
Generally, chassis system for Formula Varsity Racing Car can be divide by three main concept, platform chassis, space frame chassis and monoque chassis.
The platform chassis style is the oldest automotive chassis style in the world. The chassis is simple and easy to manufacture yet it tends to be heavy if rigid. The platform chassis style is constructed with beams especially longitudinal beams, which is need depth and mass for rigidity. Furthermore, it can be develop by using inexpensive components. Meanwhile it can be made by considerable longitudinal rigidity. Yet the chassis is heavy if it develop by rigid material and it contributes a little to the overall rigidity of the vehicle because of its body along for ride.
The space frame chassis is very suitable for racing car because it simplicity has light weight with a high strength and rigidity. However, the space frame chassis need intensive technician with specialized welding and heat treatment (if necessary). After all, the design is just suitable for short production run.
On the other hands, the mostly use chassis in present is the monocoque chassis style. The chassis also like space frame chassis which has light weight with a very high strength and rigidity. Yet, the design needs suitable mass production and also need specialist skill and equipment. After all, the design is expensive in general include tooling.
Every engineering project is subjected to constraint and the Formula Varsity Racing Car chassis designing process is no different on this respect and the project is subjected to the following criteria:
Low cost in production and maintenance
Easy to maintain and safe to repair
In every project, the main subject to consider is about cost. The low cost in production will give the monocoque chassis style is unsuitable because it needs high cost in general. And yet, the platform chassis is very suitable according to the criteria.
Maintenance for a chassis system usually is all about corrosion. In the case, it is all about coating. If the coating fails and causes corrosion for the chassis, then the cost needed will increase and to get rid the rust is not an easy job. To avoid the corrosion, the chassis must be constructed by using cannot rust coating material such as carbon steel or stainless steel yet still must consider about its cost.
Realiable is a huge topic but it always the most important rule when designing virtually anything. In this case, the frame will not be check for crack or fatigue. So, the frame must has the ability, hard to fatigue and toughness, hard to crack. The chassis also should have ability bear to defect. Any defect at the chassis only can be noiticed when the frame member completely fail. And the last point, the chassis should have a long lifetime. The chassis is expected to have a lifetime longer or same to the vehicle.
Safety issues is most important from everything. Compared to all style of chassis, only the monocoque chassis and the space frame chassis are selected. It is because only these two type can add in hoop such as crash hoop for crashing zone.
For the design, concept of tubular space frame is selected to be used due to several reasons. The reasons are:
Safety regulation needs crashing zone and hoop to protect driver
Low weight to reduce drag
High strength and rigidity
Simplicity of manufacturing and design
Can be develop in a small workshop
Can be easily modified if required
Need low cost both construction and modified
Having decided on the type of chassis to be used, the next step was to decide on the details. The details will be discussed on next chapter.
The objective of the project is to design and to analysis a chassis system for Formula Varsity Racing Car. The design must be reviewed about force applied. However, the objective can be divided into three objectives to perform the main objective. The objectives are
To design a chassis for Formula Varsity Racing Car using Solidworks.
To calculate the load distribution for the torsion case.
To analyze the chassis due to bending and torsion using Nastran and Patran.
1.3 Scope of Work and Limitations
The scope of the project will be the guideline to make sure the project will be completed within its intended objective. The scopes of the project are:
Design of a chassis system for Formula Varsity Racing Car.
Structural analysis for torsion case (calculation)
Analysis of bending and torsion using Solidworks
Analyze the result of analysis
1.4 Expected outcome
Obtain the optimum design with based on parameters and load applied
Obtain the critical point of the chassis system
The effect of the chassis system due to torsion and bending cases
The design will be used for Formula Varsity Racing Car
2.1 History of chassis systems
The space frames have been used in the construction of chassis for racing car, since the introduction of car racing in the 1940’s. The space frames are still commonly used today although they are losing their competitiveness to the monocoque chassis design. Nowadays the monocoque chassis is commonly used by vehicle. The performance of a vehicle on the road or race track is related to the chassis design. There has been much research how the chassis set up effect the vehicles performance. Fenton in his study said the chassis system requires rigidity for precise handling, minimize weight and inertia, and toughness or crashworthiness to survive the quite severe fatigue loads produce by the road surface, occupants and power plant.
2.2 Function of chassis system
The chassis system is one of the factors that affect successful of the vehicle. Metz a considered that having a correct chassis set up and will allow for the system to approach the maximum potential.
The chassis also affect of the stability and handling for the vehicle because the chassis is connected to suspension system. Reimpell deemed that the most common vehicle with poor handling usually effected by poor chassis designs. Excess body roll is the most common chassis deficiency caused by excessive deflection. During cornering, when the lateral loads are high, it will produce deflection that allows the vehicle to lean outwards of the turn and will lean and roll the tyres onto one side of the tyres track. This situation will reduce the contact surface between the tyres and the road. With high lateral loads, contact surface will break and the vehicle will start to drift laterally. When the vehicle start to drift it will lose positive velocity and the set driving line, this situation will hard for the driver to control the vehicle and recover from the drift. Body roll can be reduced by increasing the rigidity of the chassis and decreasing the deflection. The body roll can be reduced by lowering the center of gravity of the chassis. Thompson, Rajic and Law  said by increasing torsional stiffness of a chassis will improve the vehicle handling. Smith  stated that it is because it allow suspension components most of the vehicle’s kinematics. Then the suspension can allowed do its job properly. The research made torsional rigidity increase by 232%.
2.3 Design of the chassis
By using space frame concept also will reduce weight of the chassis and will reduce budgets compared to the monocoque chassis. The space frame chassis and the monocoque chassis also give the same performance in strength. Oosthuizen said in his research, how the monocoque chassis resist deflection and stresses similar to the space frame yet instead of having one diagonal, it has an entire panel to provide enough strength as shown in Figure 2.1.
F:man anafyp!draftachieving the same result oosthuizen 2004.JPG
Figure 2.1: Achieving the same result Oosthuizen
Reimpell considered that the common theory of the space frames is to create a chassis frame in a triangulated form to provide minimum deflection and maximum strength. If the frame is made from just a rectangular form which is not triangulated, it will be easily distorted under loads as shown in Figure 2.2. Triangulating the box by inserting a diagonal member and be a braces for the frame will effectively reducing the amount of deflection. Strength will increase even when the section is applying force as shown in Figure 2.3. The diagonal member, the braces would stress in tension and the end members are stressed in compression. If the force was applied in the opposite direction, the diagonal member would be placed under compression and the rest will be placed in tension. If the diagonal member is longer or the members apply higher loads, there is more capable of buckling if compression loads are applied. In this situation, it is important for engineers to know the load paths are and design strength so that design will be in expected result.
Figure 2.2: Rectangular box, Reimpell
Figure 2.3: Triangulated box, Reimpell
Metz b in his research said the primary set up for a chassis is to be aware of the center of gravity (CG) of the vehicle. The best position of CG is as low as possible to the ground. The CG of the vehicle is where center of mass that effect of wheel traction, braking and cornering focus on. The CG can be determined by using set up of location and weight of all part of the vehicle include engine, transmission system, driver seat, driver, fuel tank and chassis itself. For racing car, usually the designers will position the CG as low as possible by using an underweight racing car built in ballast. The purpose of the ballast is to reduce height CG of the vehicle. Then the ballast can be positioned in the car to assist in tuning for varying track conditions.
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On the other hands, the chassis is only the part that has ability to absorb force when the vehicle applying an impact loading like accident and only the chassis will protect passenger from having badly injured. Crashworthiness is an ability of a vehicle to protect the cargo and passenger from affected by an accident. Metz c stated that from an engineering perspective, crashworthiness is an ability of the vehicle to prevent occupant injuries if the vehicle facing an accident. In the research also stated that crashworthiness is not the same as vehicle safety and the two topics must be distinguished. The structure must be analyzed under rapidly applied loads to provide a better understanding of the impact experienced during a collision. That is why every chassis has a cockpit for the driver and it is very important to the structural behavior of the chassis under impact loads is known. Usually, an impact can held at any angle on all vertical surfaces of the vehicle. Metz c stated way to improve crashworthiness is to prevent ‘second collision’ where the occupant collides with the vehicle internals. Meanwhile Reimpell has conducted impact tests with racing car chassis and in the research said, the majority of serious injury is caused by sudden deceleration of the vehicle. The situation is likely a vehicle collides with a solid object that can produce a large amount of energy to absorb by the vehicle. A chassis for racing car is designed for performance they are very rigid and therefore not very accepting energy absorbtion. To absorb the impact energy, energy crumble zones or absorbtion zone have to attach to the bulk head of the chassis to assist absorbing high energy collisions. That is why organizer set requirement for Formula Varsity Racing Car must have crush zone at the front of the vehicle.
In a project of designing a chassis, calculation is must to assume the expected load that would be applied by the chassis. These loads must include the known static loads and variable as expected dynamic loads. The loads need to be calculated in order to avoid the vehicle failure.
Static load is a load due to the total weight from various components like engine, driver, transmission system, fuel tank, auxiliary components and frame itself. The static load must be calculated to define CG of the vehicle. And it is very important for its stability.
Dynamic load is variable load that imposed to the chassis during the vehicle operation like cornering, braking (decelerating) and accelerating. It also can be effected by external factor such as bumps and dips. While engine is operating, the engine torque reaction will produce dynamic load and when in a motion, it is produced by drive train.
The dynamic loads are proved by the Newton’s First Law. The law said when a vehicle is in braking condition, large forces are produce by the brake calipers pressing between them on the disk brake. Giancoli stated the analysis is proved by the Newton’s Second Law. To analyze the accelerating and decelerating (braking) forces, usually the analysis will be used the law.
F = ma (2.1)
F = Applied Force
m = Mass of Component
a = Acceleration
From the research, the new formula was created by Giancoli:
a = (2.2)
a = Acceleration
vf = Final velocity
vi = Initial velocity
dt = Time
188.8.131.52 Cornering loads
Due to the centrifugal acceleration, there are forces direct to the outside of the corner. The force is proportional to the velocity at the corner. Centrifugal acceleration usually use in terms of G, gravity.
An acceleration of 1 G’s will be used to estimate the forces applied on the chassis
Horizontal Force Produced = Mass of Engine x (Gravity x 1)
This force will be applied at 90 degrees to the direction of vehicle travel. The
The engine mounts will also have to transmit this load to the chassis.
Horizontal Force Produced = Mass of Driver x (Gravity x 1)
2.4.2 Analysis Using Software
2.4.3 Failure Analysis
Further analysis of critical component of suspension system using CAE tool (MSC.PATRAN / NASTRAN) is to predict the maximum stress and deformation of structure. Muhammad Zakaria state that the finite element method(FEM) was developed by engineers using physical insight. FEM allows detailed visualization of where structures bend or twist, and indicates the distribution of stresses and displacements.
Figure 2.4 Example of designed chassis using SolidWorks and analyzed using Nastran and Patran
MSC Nastran is the world’s most widely used Finite Element Analysis (FEA) solver. It built by NASA scientists and researchers, and is trusted to analysis components critical systems in every industry. Nearly every spacecraft, aircraft, and vehicle designed in the last 40 years has been analyzed using MSC Nastran.
The methodology is a method used to achieve the objectives of a study. Methods for this study can be divided into three levels of review literature, the design and analysis of the design. For analysis, the two-way conducted to study the analysis using ordinary calculations and analysis using computer software. The methodology is one way of beginning Setting to conduct a study. With the existence of certain rules, these studies will be easier to run and to avoid any problems that will arise from the study without planning.
For FYP 1, the study is more focuses on the method in designing the conceptual design of the tubular space frame chassis system. Most engineering designs involve safety, ecological and societal considerations. It is a challenge to the engineers to recognize all of these in proper proportions. Fundamental actions proposed for the design process are establishing the quest for design problem, problem identification, and evaluation of possible solutions and concluding the best solution. The work includes finding as much methods, information and samples that relate to this study. Throughout this work, various methods and information has been identified that can be used to solve the problem but for FYP 1 the method used in this project emphasized on the use of computers especially computer aided design (CAD) which come to the implementation of Solidworks software. It has been used in designing the conceptual design of the anti-torque pedal. Figure 3.0 shows the overall flow chart for FYP 1 and 2.
Figure 3.1: Flow chart for FYP 1 and 2
3.2 Parametric Study
In Part 1 and Part 2, the tubular space frame was selected. The tubular space frame chassis will provide maximum strength against forces from any direction. The steel tube will be welded together and form a very complex structure that connects all of the necessary components together as shown in Figure 3.2, Figure 3.3 and Figure 3.4.The space frame fabrication techniques are mainly use by racing vehicle categories. The tubular steel is found to be much more resistant to torsion loads because it has constant axis for the moment of inertia, which is desirable in chassis performance. By using space frame concept also will reduce weight of the vehicle. F:man anafyp!draftsection joining.JPGF:man anafyp!draft31.JPG
Figure 3.2: Section joining Figure 3.3: Welded steel tube
Figure 3.4: A tubular space frame chassis system
3.3 Design Process
Process in designing has been done by referring and studying several design samples in Chapter 2. To study the design, specific parameter is needed on the suspension system which is its dimension but the dimension of the suspension system is depend on dimension of chassis, trackwidth and chamber angle. By taking consideration on that factor,a new design has been produced. Figure 3.6 show the dimension of the formula varsity car. More detail drawing shown in appendix.
3.3 Conceptual Design
Figure 3.2: Chassis system when apply torsion force
Figure 3.3: Chassis system when apply bending force
The analysis was conducted for ensure they can withstand the load as specified or not. For purposes of analysis, the software has been chosen is the MSC Nastran and MSC Patran. From this software, the analysis can be performed using the finite element method, FEM. The design has been made with specified material selection and to be known after the design resistance force is applied to the design.
3.4 Preliminary Design
The focus of preliminary design is to determine approximate dimensions, material and other physical characteristics for an optimum suspension system. The main areas of concern were lower and upper arm and chamber angle. The entire design is based on the conceptual design, with carefully considering the specific requirement formula varsity racing car. Figure 3.7 show the preliminary design of the Double Wishbone suspension system for the formula varsity racing car.
Generally all the required process in designing has been done but still the process in finding information will still continue until end of the study. Several problems have been encountered in order to get a preliminary design. Thank you to all personnel that have been guiding in the design process especially to the supervisor. The conclusion for the study is still early to be made but for the time being, the preliminary design is to be thought suitable with the helicopter because it cover almost all the identified problems. For sure is the design might have some changes from time to time as the best and suitable design for the car is needed.
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