Improving Car Chassis Stiffness

Improving Car Chassis Stiffness inst aloneationThe purpose of the project is to enlarge the ung acceleratefulness and reduce the pack of the lively railway car figure, without disturbing the shape provided for locomotive mountings and number sensation woods station and divergent constraints provided by the animated physique sham.Why is it so important to increase the awkwardness and reduce the free burden down of the general anatomy?In general to define shape in this way, first a clear meaning of structure should be known. In general perspective a structure discharge be defined as a specific arrangement of stuff to live luxuriant lashings. This structure should too enable to the location of the components such as engine mountings, transmission, displace tank, suspension system etc.So it essential repulse bear downs without breaking, and without more buckle. If the systema skeletale can non endure preventative up it leads to a severe handling task s, and exit non support the engine and transmission system, as well as the chassis should be light enough to maintain weight to causation ratio and better handling in trees.1.1 Background to projectThe ruler gobs that implys on the chassis argon, by the engine, the aerodynamics, brakes, road irregularities, the inertia fill up due to masses under quickenings and vibrations. Also the chassis must(prenominal)(prenominal) with stand regard bay windows, having absorbed part of crash energy by optical aberration which includes the flexure, deformation, combined crook and crookedness, also lateral and longitudinal lots. So the chassis structure should be strong in severity in protrude occurrence rather than strength.The chassis and body developments should also reduce weight be showcase it improves the fomite ride, handling, improves the surgical operation of car by reducing the drag be answer of soaring weight to manlike monarch ratio, and also allow reduce t he need for situation there by increases the fuel efficiency. Because of this now even mass produced passengers cars lightened up by the most detailed weight-watcher engineering techniques due to corporate add up Fuel Economy (CAFE) regulations of the federal government. Lighter fomite requires less power, consequently less fuel, for equal performance.HistoryThe take away for the chassis with high torsion stiffness and low weight had increased from the World War 2. This demand had led to the innovation of umpteen kinds such as dummy commit, punctuate skin etc. These types had become universal among the European road race cars following its appearance in the lotus MK and the Mercedes-Benz 300SL in 1952. These atomic number 18 the cars which utilise strictly situation condition chassis and the attention they received had popularized the conceit.major(ip) automobile industries in present era be purchasing the militant fomites and disassembled them cargonfully to study t he weight and stiffness of car for comparison with the akin part of their own vehicle. So this lead to a competitive reasons than for increase fuel economy.Today have been include to expand the following trey reasonsA means for recognising opportunities for over each(prenominal) weight reduction for better fuel economy.The means for determining centre of soberness (CG) location and polar min of inertia.Detail weight estimates provides target figure of cost estimates of all parts.To resist inertial loads under quickenings, accidents etc. structural efficiencyA initiationer can achieve enough stiffness for a chassis from all form of construction, if enough material is used. This is non the criteria of a former, to evaluate the efficiency of structure its stiffness must be con alignred in sexual relation to the weight. The below shows the absolute increase in stiffness achieved in modern social classs is the increase in stiffness to weight ratio.VehicleyearTorsional stiffn ess(lb-ft/degree)Structure weight(lb)Stiffness/weight ratioLotus 21 F1196170082.08.5Lotus 24 F119621,0007213.9Mc L ben F1196611,000NaNaLotus 79F119793,0009531.6Lotus 79 F1Late 19795,0008558.8Lotus F1198010,00075133.33Lola F1199330,00080375Table1 Demand for increase in structural efficiency.Literature refreshenIntroductionThe loads that are experienced on a chassis are light commercial loads due to normal rivulet particularizes are con fontred. That is caused as the vehicle transverses uneven ground as the driver performs various manoeuvres. Basically there are five load cases to consider. diversion case.Torsion case.Combined bending and torsion case.Lateral essence. former and aftermost load.2.1.1. Bending caseThis type of loading is caused due to the weight of components distri moreovered along the frame of the vehicle in the vertical plane which causes the bending astir(predicate) y-axis.The bending case depends mainly on the weight of the major components in the car a nd the payload. First the static condition is considered by determining the load distribution along the vehicle. The axle response loads are obtained by firmness the military postures and by taking the moments form the weights and positions of the components.2.1.2. Torsion caseThe vehicle body is subjected to the moments applied at the axels centre funds by applying both upward and downward loads are at the each axle in this case. Because of this it results in a bend action or torsion moment about x-axis of the vehicle.The condition of virginal torsion does not exist on its own because of the vertical loads always exist due to gravity. However for the calculation purpose the delicate torsion is assumed. The maximum torsion moments are base on loads at the lighter riled axle, its value can be mensurable by the motorbike load on the lighter loaded axle figure by the wheel track. The loads at the wheels are shown in the preceding(prenominal) figure. So the torsion moment is given asRFtf =RRtr2 2Where tfand trare front and rear track respectively and Rfand Rrare front and rear loads. These loads are based on the static reaction loads but dynamic factors in this case are typically 1.3 for road vehicles (Pawlowski, 1964).2.1.3. Combined bending and torsionIn practice the torsion will not exist without bending as gravitational forces are always present. So the two cases must be considered when matching a real situation.Fig3 combined bending and torsion.2.1.4. Lateral loadingThis type of loading is experienced by the vehicle at the corner or when it slides once against a Kerb, i.e. loads along the y-axis. The lateral loads are generated while cornering at the tyre to ground contact patches which are equilibrize by the centrifugal force MV2/ R, M stands for vehicle mass, V vehicle velocity , R is the radius of the corner.The disaster occurs when the wheel reactions on the privileged of the turn drop to zero, that means that the vehicle ready to turn ov er. In this case vehicle will be subjected to bending in x-y plane. The condition that applies to the roll over is shown in the below figure and it also depends up on the height of the vehicle centre of gravity and the track. At this particular condition the resultant of the centrifugal force and the weight that passes along the removed wheels contact patch.And hence lateral acceleration is V2/R=gt/2hLateral force at the centre of gravity MV2/R = Mgt/2h. scarer tyre side forces YF= Mgt b/2h(a+b).At the rear tyres YR= Mgt a/ 2h(a+b).From the lateral acceleration it is clear that it is t/2h prison terms that of the gravitational acceleration. Kerb bumping will cause high loads and will roll over in stupendous circumstances. And also this high loads will cause in the bending in the x-y plane are not captious as the width of the vehicle will provide the sufficient bending strength and stiffness.2.1.5. Fore and aft loadingAt the time of acceleration and breaking longitudinal forces will come into shew along the x-axis. Traction and braking forces at the tyre to ground contact points are reacted by mass times acceleration inertia forces as shown in below figure. The important cases such as bending, torsion, bending and torsion will come into play as these turn back the satisfactory structure (Pawlowski, 1964).2.1.5.1 Longitudinal loadingAt the time of vehicle accelerates or decelerates, the inertia forces are generated. The loads generated can be transferred from one axle to anformer(a) by the inertia forces as the centre of gravity of the vehicle is above the road surface. While accelerating the weight is transferred from front axle to the rear axle and wickedness versa at the time breaking and decelerating condition.To have a clear picture of forces acting on the body a height of the centres of gravity of all structures are required. And its not so easy to determine. A simplified model considering one inertia force generated at the vehicle centre of gravit y can provide useful schooling about the local loading at the axle positions due to breaking and traction forces. depend wheel drive, the reaction on the driving wheel isRF = Mg(L-a) Mh(dV/dt)LRear wheel drive, the reaction on the driving wheel isRR = Mga + Mh(dV/dt)LIn braking case the reactions on the axles areRF = Mg(L-a) + Mh(dV/dt)L2.1.6. Allowable stressesFrom the above discussed loads it is clear that it will induce stresses in all over the structure. So it is important that under the get through load conditions that the stresses induced into the structure are kept to acceptable limits. In consideration of the static loads of a curb amount should give a stress level sure below the get stress. If analysed the bending case for a road buzzer car is considered the maximum allowable stress should be limited as followsStress due to static load Dynamic factor 2/3 yield stress.The above equation says that under any worst load condition the stress should not exceed 67% of the yield stress. Alternatively the safety factor against yield is 1.5 for the worst possible load condition.2.1.7 Bending stiffnessIt is equally important to consider the bending stiffness weather to say the structure is sufficiently strong or not. So an equal and important assessment is given to the structural stiffness. Therefore many designers consider the stiffness is most important than strength. It is possible to design a structure which is sufficiently strong but yet unsatisfactory because of meagre stiffness. Designing for acceptable stiffness is therefore often more critical than designing for sufficient strength.For vehicles the bending stress is determined by the limits of deflection of the side frame door apertures. In case of excessive deflection the doors will not shut properly. Local stiffness of floor is also important because it minimises the safety of the passenger.2.1.8 Torsion stiffnessIf the stiffness is low the driver may feel that the vehicle in front will be sh aking with the front wing structures moving up and down. The practical problems of doors impuissance to close properly will also be seen. A equal thing will be seen in the jacking points that are positioned at the corners of the vehicle. For fast moving cars the torsion stiffness is truly important because it may cause serious handling problems. Therefore care should be taken in maintaining sufficient torsion stiffness.So from the all above dimensions of forces and handling of a vehicle chassis should be stiff enough and also should be less in weight.2.1.9 Chassis typesChassis are classified into some(prenominal)(prenominal) types they areLadder frames.Cruciform frames.Torque tube back off-white frame.Space frame.Monocoque.In the present era of automotive industry designers are using the lacuna frame and monocoque for the justification of design problems and to sufficient structural stiffness.2.1.9.1 Space frameA space frame chassis is a development of four tube chassis, both of them look quite similar. moreover the space frame differs in several call areas and offers very beneficial advantages when compared to the predecessor. A space frame is an arrangement of many straight tubes in which the loads acting are either in tenseness or compression. The figure below shows the clear idea of a space frame. unless from the above figure it is clear that the diagonal member is pulled in tension when a load is acted on it. This above illustration is the simple idea of the space frame chassis.This experiencing of loads in either tension or compression is a major advantage. So none of the tubes will be subjected to the load will tend to bend in the middle. Since the space frames are very good in torsion stiffness.The three dimensional space frame chassis are used for specialist cars such as sports racing cars. This type of vehicle design is used for low meretriciousness and mass production as well. In this type of structure it is despotic to ensure that all planes fully triangulated by doing so the beam elements are essentially loaded in tension and compression.In the space frame welded joints are through with(p) it retains bending and torsion at the joints, but to verify on this restrains will render the structure less stiff. The stiffness is provided by the diagonal member subject to direct tension or compression.2.1.9.2 Space frame principlesA space frame is three dimensional arrangements of tubes loaded in pure tension and compression. The joints between them can be replaced by the ball joints without affecting the stiffness. Other important feature is all loads enter and leave the structure at the points of intersection of three or more tubes. The structural elements do not have to be tubes and the joints do not have to be welded. In terms of torsional stiffness the space frame attempts to connect the four spring anchorages so that is impossible to call on the pair without stretching and compressing the tube.AIMSThe first thing to undertake this look for is to commit some basic poses that need to be achieved.As the aim of the project is stated to reduce the weight and increase the stiffness of existing vehicle chassis. So the main aims are in terms of weight, stiffness, and size.3.1. freightWeight was a main consideration in the search it is very crucial to reduce it to that of maestro weight. It helps in improving the weight to power ratio, better fuel efficiency and performance.3.2. StiffnessIt is also an different key factor to be considered in the research. The stiffness must be improve to that of existing one in case of torsion, bending.3.3. SizeLast but not the least, the above reduction in weight and increase in stiffness must be achieved without riging the size and shape of the chassis. This is important because it should not affect the driver to get in the car, and appearance of the car. And also the constraints set for the positioning of the engine etc should not be changed.3.4. Requirem entsCertain requirements beyond my research boundary and aims are needed to be specified, to call for up and achieving succeeder in my research they areThe elements in the space frame which should not disturb must be specified.The dimensions of the chassis, and the materials used must be specified.The condition of the loads on the chassis.The original weight of the chassis which is going to be modified.The stiffness that chassis must be in terms of torsion, bending. spue ObjectivesThe objectives of the project areTo analyse the original chassis, its structure, weight, stiffness, torsion, and materials used.Research the characteristics of space frame chassis and discover the effects with respect to vehicle handling and performance in case of bending and torsion loads.The benefits and performance of materials when replaced by the original one in terms of weight and stiffness.The research should be make with resources available.From testing and changing the elements, dimensions oth er than the constraints in lab, modifying the improvements in chassis.Analysing the results to that of the original chassis and comparing.Research QuestionsWhat are the materials used for the chassis construction?What are positions in the chassis which should not be disturbed?What is maximum allowable weight, stiffness and loads that being subjected by the chassis?What will be effect on stiffness and weight if certain elements of the chassis were replaced by the other materials?If the diameter and size of the elements were changed what will be the effect on weight and stiffness?If the positions of the elements other than the elements which should not be disturbed, i.e. by mix and matching, transposition the positions. What will be the effect on stiffness and weight?If the pecker tube cross-sectional elements of the chassis in some areas are replaced by square tube cross-sectional elements, what will be the effect on stiffness and weight?Research speak to and Design6.1. Introducti onThe problem being researched is quantitative rather than qualitative. It deals in numerical values and variable stars, mold categories, focuses on specific knowledge and control of variables. The approach of this research is different to that of qualitative research which would involve human subjects, questionnaires and interviews. The approach will be analytical which will include experimental analysis, analysing the data, interpreting the results, comparisons etc.6.2. Approach and designThe research is about how to increase the stiffness and reduce the weight of existing vehicle chassis. The research is based on a lot of literature, experimental design and analysis. It should be well designed, planned and managed to ensure that the results can be analysed, interpreted and presented. Throughout the period of the research a work was followed to produce a successful report on the analysis done with that of the original chassis they areSetting some benchmarks in regarding to the d esign of chassis.Analyse the previous chassis, and getting an idea in terms of stiffness, weight, shape. create the modelling, and analysing techniques that allows the process to be simple and can be modified easily.Gaining the information regarding the dimensions of the chassis from the designers and the areas in the chassis which should not be disturbed in terms of design.Looking for the possibility of the new considerations that were not previously included in the design.Considering the feedback of the supervisor as the process of the research goes on.6.3. Experiment designIt includes a statement of problem to be solved. Before going to do the research on the experimental design it is important to consider all points of view of what the experiment is intended to do.6.3.1 Response variableThe problem must include reference to at least on characteristic of a unit on which information is to be obtained. Those characteristics are called response or dependent variables. In this resear ch the response variables are weight and stiffness, which are dependent on material, design, etc. In addition to reference of the response variable, some questions should be asked. They are measurements methods, what tools are required to measure the variable? Can variable can be measured accurately or not?6.3.2 Independent variablesThe variables which control the response variables are called Independent variables. In this piece of work the independent variables areLoad on the space frame chassis.Material used for the chassis.Design of the chassis.Size and shape.The independent variables will be chosen randomly one at a time or by considering more than one independent variable. The response on the dependent are analysed and compared to that of original chassis.6.3.3. DesignBefore the data is placid and results are drawn, it is important to know how to solve the problem with a limited amount of time and available resources. It is important to note how many observations should be ta ken, what is the maximum amount of deviation in terms of stiffness and weight in comparable to original one. Also attention is required in handling the independent variables.6.3.4. Analysis comparisonThe final step in the experiment is to compare the results of the optimised chassis to that of the results on the original one, and approach the problem by checking and comparing the results. This will be done by the grooming of the graphical displays of the values in terms of weight and stiffness. Its important to make sure that the results are inwardly the prescribed limits. If its not, follow the investigation again by controlling the independent variables.6.4. FSAE chassis Rules and Requirements.There are some rules that must be followed throughout the design and construction of chassis. If these rules are not followed strictly the FSAE car will be eliminated from the competition. The rules that have to be followed are. morphological requirements. minimum material requirements.Al ternative underground and material.Steel subway system requirements. aluminium tubing requirements.Composite material requirements. cast off hoops requirements.Tube frames.6.4.1 Structural requirements.The structure of the vehicle must include two roll hoops, front volume corpus with support system and pertain Attenuator, and side impact structures.6.4.2 Minimum material requirements.6.4.2.1 Baseline Steel Material.The structure of the car must be constructed withRound, mild or alloy, poise tubing (minimum 0.1% carbon) of the minimum dimensions check to the following table.Item or ApplicationOutside diameter contend thickness important and Front hoops,Shoulder harness mounting bar. move on (25.4 mm) x 0.095 march on (2.4 mm)25.0 mm x 2.50 mm metric emplacement Impact Structure, Front BulkheadRoll basket Bracing, Drivers Restraint Harness addition.inch (25.4mm) 0.0065 inch (1.65mm)or 25.0mm 1.75mm metricor 25.4mm 1.60mm metric.Front bulk head support.1.0 inch (25.4mm) 0 .049 inch (1.25 mm)Or 25.0 mm 1.5 mm metric or 26.0mm 1.2 mm metric.Table 6.4.2 Minimum material requirements. (Source FAE rules 2008)6.4.2.2 Alternative thermionic valve and MaterialThe chassis can be constructed with alternative tubing and material but not for the Main Roll pack and Main Roll Hoop Bracing. These must be constructed only with the Steel, to say in other words the use of Composites and other materials such as Aluminium or alloys are strictly veto. If the chassis was to constructed with alternate tubing rather than material, the tubing must not be thinner than as shown below.6.4.2.2.1 Minimum bulwark thickness for firebrand tubing requirementsMaterial and ApplicationMinimum groin thicknessSteel tubing for front and Main Roll hoop2.0 mm (0.079 inch)Steel tubing for Roll hoop Bracing, Front bulk head drivers harness attachment.1.6 mm (0.063 inch)Steel tubing for side impact structure front bulk head support.1.2 mm (0.047 inch)Table 6.4.2.2.1 Minimum rampart th ickness for steel tubing requirementsSource FSAE 2008 rules.6.4.2.3 Aluminium tubing requirementsMinimum wall thicknessMaterial Application Minimum wall thicknessAluminium tubing3.0 mm (0.118 inch)Table 6.4.2.3 Aluminium tubing requirements. (Source FSAE 2008 rules).6.4.3. Roll HoopsThe Roll hoop design criteria must prune the following6.4.3.1. Main HoopThe drivers head and hands must not contact the ground in any rollover attitude.The frame must include both Main Hoop and Front HoopsThe Main Hoop must be constructed of single uncut tubing made of steel as per the minimum tubing requirements.The use alternate material is prohibited for construction of main hoop.The main hoop must extend from the lowest member on one side of the frame, to the down towards the lowest clay member on the other side of the frame.In the side of the car the portion of the attachment of the Main Roll Hoop which lies above the attachment point of the main structure of the frame must be within 10 degrees to the vertical.The vertical members of the Main Hoop must be at least 380mm apart at the location where the Main Hoop is committed to the Major Structure of the Frame. In the Front view of the vehicle.6.4.3.2. Front HoopThe Front Hoop must be constructed of closed structure of steel as minimum tubing requirements.The use composite materials are prohibited.The Front Hoop Frame member must extend from one side of the Frame, to the down over and towards the lowest Frame member on the other side of the Frame.The covering fire most surface of the Front Hoop should not be below the top of the steering wheel in any angular position.The front Hoop should be no more than 250 mm forward of the steering wheel when measured horizontally through the vehicle centre line.No part of the Front Hoop should be habituated at not more than 20 degrees in the side view.6.4.3.3. Main Hoop General RequirementsA straight line drawn from the top of the main hoop to the top of the front hoop must be clear b y 50.8 mm of the helmet of the teams drivers and the helmet of a 95thpercentile male. When sit down normally and restrained by the Drivers Restraint system.95th Percentile phallic Template DimensionsA two dimensional template used to move the 95th percentile male is made to the following dimensionsA dance orchestra of diameter 200 mm (7.87 inch) will represent the hips and buttocks.A dance orchestra of diameter 200 mm (7.87 inch) will represent the shoulder/cervical region.A circle of diameter 300 mm (11.81 inch) will represent the head (with helmet).A straight line measuring 490 mm (19.29 inch) will connect the centres of the two200 mm circles.A straight line measuring 280 mm (11.02 inch) will connect the centres of the upper200 mm circle and the 300 mm head circle.The 95th percentile male template will be positioned as follows the seat will beSource FSAE rules 2008.6.4.4. Front Impact StructureThe drivers feet are always with in the Major structure of the Frame.No part of the drivers feet should be above or outside the Frame in the side and front views, while signature the pedals.Forward of the Front bulk head must be energy- absorb Attenuator.6.4.4.1. Bulk HeadThe requirements of the Bulk head in a Front impact structure areIt should be constructed of closed section tubing.