Automobile chassis body & aerodynamics of vehicle

Automobile chassis body & aerodynamics of vehicle

1.1             Introduction to chassis frame.

      Chassis is the French term which denotes the whole vehicle. A vehicle Frame also known as its chassis, is the main supporting structure of a motor vehicle, to which all other components are attached, comparable to the skeleton of an organism.

1.2             Layout of chassis frame & its components.

      Frame is a under carriage or structure that supports the engine & cab (body) of the automobile. It is made up of long two members riveted together with the help of number of cross members.

In automobile there are 3 major types of construction based on frame.

Ø  Conventional frame construction.

Ø  Integral frame construction.

Ø  Semi-integral frame construction.

                                                                      

Chassis layout Fig- 1.2

1.2. A. Conventional frame construction.

                  In this type of chassis the body is made separate unit & then joined with ladder frame. It supports all the system in a vehicle such as the engine, transmission system, steering system, suspension system.

Advantages

·         Higher load carrying capacity & strength.

Disadvantages

·         The vehicle body tends to vibrate easily & the overall vehicle handling & refinement is lower.

·         It is used in truck, bus and in SUV cars bigger vehicles.

 

Conventional chassis Frame Fig-1.2.A

1.2. B. Integral frame construction.

                    In some vehicle half frame is fixed in the front end on which engine gear box & front suspension is mounted.

Advantages

·         It has the advantage when the vehicle is met with an accident the front frame can be taken easily to replace the damage chassis frame.

·         This type of frame is used in some of the European & American cars.

Integral Frame chassis construction Fig-1.2.B

1.2. C. Semi-integral frame construction.

                 This frame is used now days in most of the cars. There is no frame and all the assembly units are attached to the body. All the functions of the frame are carried out by the body itself.

Advantages

·         Due to elimination of long frame it is cheaper & due to less weight most economical also.

Disadvantages

·         The disadvantage is repairing.

Semi-integral chassis frame construction Fig- 1.2.C.

1.2. D. Different types of chassis construction

A.      Composite construction.

B.      Unibody construction.

C.      Tubular space frame

D.     Glass-fiber  body

E.      Carbon-fiber  Monocoque  chassis

F.       Aluminium monocoque

G.     Ladder chassis frame

A.   Composite construction

·         Composite construction was the most common type of structure and on the earliest cars of 1900’s.

·         The chassis & the body are built as the two separate units.

·         The body is assembled on the chassis with mounting bracket.

·         These flexible mountings allow the body to move slightly when the car is in motion.

Latest trends of composite construction

·         The chassis structure contains the powertrain & mechanical components, while the body is a separate structure.

·         There are no mechanical links between the body & chassis, which makes it easy to produce the rolling chassis in large quantities separate from the bodies, and place different body styles on top of a common structure.

Composite chassis Frame

A.   Tubular space frame

·         Consists of dozens of circular section tubes (uses square section tubes; for easier connection to the body panels or circular section provides more strength.   

·         High performance cars require high strength.

·         Tubular space frame chassis usually incorporate a strong structure under both doors.

·         Eg of space frame construction is Audi A8, Audi R8, Ferrari 360, Lamborghini Gallardo, Mercedes –Benz SLS AMG, Pontiac  Fiero (GM motors) & Saturn s- series. 

Tubular space Frame

Advantages

·         Very strong in any direction. (Compare with ladder chassis & monocoque chassis of the same weight).

Disadvantage

·         Very complex, costly & time consuming to build.

·         Impossible or mass production.

·         Raised door sills result in difficult access to the cabin.

B .a. Ultra-light steel auto body

Advantages

·         Stronger & lighter than conventional

Disadvantages

·         Not strong & light enough for the best sport cars.

·         Same structure as that of conventional monocoque.

·         Use of hydro form parts, sandwiched steel & laser beam welding.

Ultra-light steel auto body

B. b. Aluminium space frame

·         ASF consists of extruded aluminium sections; vacuum die cast components & aluminium sheets of different thickness.

·         At the highly stressed corners & joints, extruded sections are connected by complex aluminium die casting. 

Advantages

·         Lighter then steel Monocoque. As space efficient as it.

Disadvantages

·         Still expensive for mass production.

B .c   Lotus aluminium space frame

·         Chassis is made of extruded aluminium sections joint by glue & rivets.

·         Aluminium extruded sections can be made much thinner then tradition welding techniques.

·         Welded joints are weak, so the thickness of material should be increase throughout a member just to make a joint strong enough.

Aluminium space frame

Advantages

·         Cheap or low production. Offers the highest rigidity to weight ratio besides carbon fibre monoloque.

Disadvantages

·         Not very space efficient.

A.    Glass-Fiber body

·         In 1957 lotus pioneered glass –fiber monocoque chassis is elite.

·         Whole car weighted as light as 660kg.

Advantages

·         Lightweight.

·         Cheap to be produced in small quantity.

·         Rust proof.

Disadvantages

·         Lower visual quality.

·         Unable to act as stressed member.

                                                             Glass-Fiber body

A.   Monocoque  (Unibody)

·         Monocoque construction was first widely used in aircraft , starting in the 1920’s

·         Introduction of monocoque in automobiles in 1922 (Lancia lambda)

·         Monocoque is one -piece structure which defines the overall  shape of the car.

·         Made by welding several piece together.

·         They are spot welded together by robot arms (some even use laser welding) in a stream production line.

·         After that some accessories like doors, bonnets, boot lid, side panels & roofs are added.

 

                          Monocoque chassis Frame

Advantages

·         Cheap or mass production.

·         Inherently good crash protection.

·         Space efficient.

Disadvantages

·         It’s very heavy.

·         Impossible for small volume production.

A.   Carbon fiber monocoque frame

·         A unique and distinct appearance that’s nearly impossible to replicate.

·         Excellent strength to weight ratio, compared to other materials.

·         Suitable for complex contours and designs.

·         Superior fatigue properties.

·         High Stiffness.

·         High heat tolerances and resistance.

·         Flexible thermal and electrical properties.

·         Corrosion-resistance (with proper resins).

·         Varying classifications (tensile modulus) of strength.

·         The strongest carbon fiber is 10x stronger and 5x lighter than steel.

·         The strongest carbon fiber is 8x stronger and 1.5x lighter than aluminium.

                                                          Carbon fiber monocoque frame

Disadvantages ·         One downside to carbon fiber body is a lack of flexibility. ·         For instance a metallic chassis can be heated and straightened or welded if it is slightly bent or cracked. ·         Carbon fiber will not bend, once the force of impact is large enough it will crack or break and repairing it in most cases is not an option.

·         Carbon fiber can be recycled but it loses its strength. Steel and aluminium can be recycled and become just as strong and useful as it was before.

B.   Ladder chassis frame

          It referred to as a body-on-frame. It gets the ladder in its name from the way it looks. The frame consists of two long, heavy beams of steel, held together by two shorter pieces.

                                                   Ladder chassis frame

Advantages

·         The reason it proved so popular, is its simplicity.

·          A ladder frame is easy to design, Build and can be used in multiple applications with minimal modification.

·         Vehicles with a ladder frame are easier to assemble, which means a manufacturer can charge less for them

·         heavier good for towing and durability

Disadvantages

·         The construction is heavier, bad for fuel economy because of the extra weight. .

·         Poor resistance to torsion.

1.4. Various load & Forces acting on chassis Frame.

Loads on the chassis frame

CHASSIS LOADING  

i.                    Longitudinal Torsion

ii.                  Vertical Bending

iii.                Lateral Bending

iv.                Horizontal Lozenging.

i. Longitudinal Torsion

·         Application of equal and opposite forces act at a certain distance from an axis tends to rotate the body about the same axis.

·          The frame can be thought as a torsion spring connecting the two ends where suspension loads act.

·         The resistance to torsional deformation is called as stiffness and it is expressed in Nm/degree in SI units.

·          Torsional rigidity is a foremost and primary determinant of frame performance of cars.

    

 

longitudinal Torsion

II. Vertical Bending

·         Weight of driver, engine, drive-train, radiator and shell etc. under an effect of Gravity produces sag in the frame as shown in Figure 2.

·         Frame is assumed to act as simply supported beam and four wheels as supports tend to produce reactions vertically upward at the axles.

·         Vertical dynamic forces due to acceleration/deceleration further increase the vertical deflections, hence stresses in chassis.

Vertical Bending

III. Lateral Bending

·         Lateral bending deformation occurs mainly due to the centrifugal forces caused during Cornering and wind forces to some extent.

·         Lateral forces act along the length of chassis and is resisted by axles, tires and frame members viz. hoops, side impact members and diagonal hoops etc. 

Lateral Bending

IV. Horizontal Lozenging.

·         This deformation is caused by forward and backward forces applied at opposite wheels

·         These forces may be caused by vertical variations in the pavement or the reaction from the road driving the car forward.

·         These forces tend to distort the frame into a parallelogram shape as shown in the Figure.

·          The magnitude of these loads changes with the operating mode of the car.

·         It is generally thought that if torsional and vertical bending stiffness is satisfactory, then the chassis structure is expected to perform well. But torsional stiffness is given more weight-age as the total cornering traction is the function of lateral weight transfer.

Load acting on the frame

·         Material properties of the Truck Chassis (high strength structure steel)

Material Properties

·         Young Modulus  200GPa 

·         Poisson Ratio 0.33

·         Density 7827.08kg/m³

Symmetry   Linear isotropic 76

In the finite element analysis of the truck chassis, the linear

Isotropic material model of high strength structural steel was used. 

 OVER ALL DIMENSIONS OF THE CHASSIS

All over length   :  7956 mm 

All over width   :  4400 mm

All over height   : 4500 mm

Wheel base: 4100 mm

Wheel tread: 3450 mm

·         Weight of the Vehicle

·         Total Weight of the Vehicle and Payload.

Pay load	534645N
NVW	426735 N
Maximum GVW	961380 N

Convert =kg X 9.81=N

3.3.1 Calculation of Bending and Torsion Case Load 

Consider a simply supported beam.

FFT   =   F1V + F2V   

                          FRT   =   F3V + F4V   

Where,         WB =   Wheel Base

                    FFT   =   Force at Front Tire

                    FRT =   Force at Rear Tire

According to the equation of equilibrium condition

∑H = 0, ∑V = 0, ∑M = 0   

                                                            

Force at front tire (FFT).                                                                 

2/3 WB =0.66x4100= 2706 mm

1/3 WB = 0.33 x 4100=1366 mm

Taking moment at front (F) i.e. MF = 0

FRT × 4100 = 961380 x2706

FRT = 961380x2706/4100= 634510N

Force at front tire (FRT).       

Taking moment at front (F) i.e. MR = 0

FFT × 4100 = 961380 x1366

FFT = 961380 x 1366/4100= 320303N

·         Bending load acting on the frame.

 Assume around 24 bolts used on Front side & 4 used on rear side

·         Front suspension load at each bolt: FFT = 320303/24=13345N.

·         Rear suspension load at each bolt: FRT = 634510/4=158627N

Torsion Load acting on the frame

Load distribution of the tire for torsion load conditions

Torsion Load acting on the frame

Right ramp loading.

F1v = 0 N

FFT = F1v + F2v

FFT = F2v = 320303N

F4v × RT = (GVW x RT/2) + {RT+ (FT-RT)/2 F2v}

Taking moment at a rear right tire point i.e. (M F4v = 0)

Left Ramp Loading

F2v = 0 N

F3v × RT = (GVW x RT/2) - (F2v) x (FT-RT)/2 +RT

F RT = F3V + F4V

GVW = 961380 N

RT =2920 mm

FT = 3480 mm

F2v = 320303 N

F4v × RT = (GVW x RT/2) + {RT+ (FT-RT)/2 F2v}

F4v × 2920 = (961380 x 2920/2) + {2920+ (3480-2920)/2 x 320303}

F4V ×2920 =1403614800+89687760

F4V = 511404.9N.

160250 = F3V + 511404

F3V = 160250 – 511404

F3V= -351154N.

1.5 Explain different types of drive train.

1.5. A. Front-wheel-drive layouts

            Front-wheel-drive layouts are those in which the front wheels of the vehicle are driven. The most popular layout used in cars today is the front-engine, front-wheel drive – with the engine transversely in front of the front axle, driving the front wheels.

·         Advantages of FWD

                                                   Front-wheel-drive layouts

·         Interior space:-  Since the powertrain is a single unit contained in the engine compartment of the vehicle, there is no need to devote interior space for a driveshaft tunnel or rear differential, increasing the volume available for passengers and cargo.

·         Weight: - Fewer components usually mean lower weight. Improved fuel efficiency due to less weight.

·         Cost: -   Fewer material components and less installation complexity overall.

·         Improved drivetrain efficiency:-  the direct connection between engine and transaxle reduce the mass and mechanical inertia of the drivetrain compared to a rear-wheel-drive vehicle

·         Assembly efficiency: - the powertrain can often be assembled and installed as a unit, which allows more efficient production.

·         Traction: - Placing the mass of the drivetrain over the driven wheels moves the centre of gravity farther forward than a comparable rear-wheel-drive layout, improving traction and directional stability on wet, snowy, or icy surfaces.

Disadvantages of FWD

·         Front-engine front-wheel-drive layouts are "nose heavy" with more weight distribution forward, which makes them prone to under steer, especially in high horsepower applications. 

·         Torque steer is the tendency for some front-wheel-drive cars to pull to the left or right under hard acceleration

·         In a vehicle, the weight shifts back during acceleration, giving more traction to the rear wheels. This is one of the main reasons nearly all racing cars are rear-wheel drive. 

·         Turning circle – FWD layouts almost always use a transverse engine ("east-west") installation, which limits the amount by which the front wheels can turn, thus increasing the turning circle of a front-wheel-drive car compared to a rear-wheel-drive one with the same wheelbase.

·         The FWD transverse engine layout (also known as "east-west") restricts the size of the engine that can be placed in modern engine compartments, so it is rarely adopted by powerful luxury and sports cars.

·         It makes heavier use of the front tyres (i.e., accelerating, braking, and turning), causing more wear in the front than in a rear-wheel-drive layout.

1.5. B.  Rear -wheel-drive layouts

                Rear-wheel drive (RWD) typically places the engine in the front of the vehicle and the driven wheels are located at the rear, a configuration known as front-engine, rear-wheel-drive layout (FR layout).

Rear -wheel-drive layout

Advantages of RWD

·         Weight transfer during acceleration – During heavy acceleration, weight is placed on the rear, or driving wheels, which improves traction.

·         Better braking – the more even weight distribution helps prevent lockup from the rear wheels becoming unloaded under heavy braking.

·         Can accommodate more powerful engines as a result of the longitudinal orientation of the drivetrain, such as the inline-6, 90° big-bore V8, V10 and V12 making the FR a common configuration for luxury and sports cars.

·         Road grip feedback – front wheels are not affected by engine and gearbox, thus allowing for better feeling of tyre grip on road surface.

Disadvantages of RWD

·         Under heavy acceleration (as in racing), over steer and fishtailing may occur as the rear wheels break free and spin.

·         On snow, ice and sand, rear-wheel drive loses its traction advantage to front- or all-wheel-drive vehicles, which have greater weight on the driven wheels.

·         Decreased interior space – Though individual designs vary greatly, rear-wheel-drive vehicles may have: Less front leg room as the transmission tunnel takes up a space between the driver and front passenger, less leg room for centre rear passengers.

·         Increased weight – The components of a rear-wheel

-drive vehicle's power train are less complex, but they are larger. The driveshaft adds weight.

·         Higher initial purchase price – Modern rear-wheel-drive vehicles are typically more expensive to purchase than comparable front-wheel-drive vehicles.

·         The long driveshaft (on front engine cars) adds to drivetrain elasticity.

1.5. C. Four wheel drive layout

             Four-wheel drive, also called 4×4 ("four by four") or 4WD refers to a two-axle vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case providing an additional output drive-shaft and, in many instances, additional gear ranges.

Four wheel drive layout

Advantages of 4WD

·         Traction is nearly doubled compared to a two-wheel-drive layout. Given sufficient power, these results in unparalleled acceleration and driveability on surfaces with less than ideal grip, and superior engine braking on loose surfaces.

·         A well-balanced 4WD configuration will not degenerate into either under steer or over steer, but instead break traction of all 4 wheels at the same time into a four-wheel drift.

Disadvantages of FWD

• 4WD systems require more machinery and complex transmission components, and so increase the manufacturing cost of the vehicle and complexity of maintenance procedures and repairs compared to 2WD designs
• 4WD systems increase powertrain mass, rotational inertia and power transmission losses, resulting in a reduction in performance in ideal dry conditions and increased fuel consumption compared to 2WD designs
• The handbrake may not be used to induce over steer for manoeuvring purposes, as the drivetrain couples the front and rear axles together. To overcome this limitation, some custom prepared stage rally cars have a special mechanism added to the transmission to disconnect the rear drive if the handbrake is applied when the vehicle is moving.

1.5. D.  Individual Wheel Drive (IWD)

                  IWD is the drivetrain used in most electric cars, which are gaining more popularity as we are heading towards an electric car-driven world the figure below shows individual wheel drive system. As each wheel is powered by a separate motor, greater traction. 

Individual Wheel Drive (IWD

Advantages of individual wheel drive (IWD)

·         Control is achieved, compared to Front wheel drive or Rear wheel drive, in which, the non-powered wheels also.

·         Contribute to the resistance but doesn’t contribute much to traction. The gears are only used to increase the torque.

·         An Electric vehicle with individual wheel drive has greater control. These vehicles don’t need long and heavy duty

·         It provides sportier handling and traction for a wide range of car

Disadvantages of individual wheel drive (IWD)

·         It increases fuel consumption.

·         It increases the complexity and weight of cars.

·         It is not suitable for extreme off-road condition.

1.6. Different types of cars.

a. Convertible

·         A convertible is a car which features a retractable roof – in other words, a roof that can be folded down or removed either partially or in its entirety.

·         Convertible cars have a roof which may either be folded via an electronic or manual mechanism, or alternatively the top roof panel may be removable and stored in a compartment somewhere when the driver wants to experience open-top driving.

·          E.g. Mazda MX-5, Porsche 718 Boxster, Audi A3, Mercedes E-Class, Porsche 911 , Audi A5 Cabriolet, Jaguar F-Type, BMW 4 Series Convertible.

Convertible 

bb. SUV cars

•         An SUV is a passenger vehicle, which combines the towing capacity of a pickup truck with the passenger-carrying space of a sedan.

•         They have a powerful engine, have sufficient passenger space along with luggage compartment behind the rear row seats and are designed for all terrains.

•         They are non-commercial vehicles with the BIW built on the chassis similar to a light truck or a crew cab

•         An off roader needs a long hood and an upright position. That lends the Vehicle self-assuredness and power.

•         E.g.- Maruti Suzuki Vitara, Mahindra KUV100 Facelift, Mitsubishi Pajero Sport Facelift, BMW X2, Nissan Qashqai, Isuzu MU-X Facelift 2018.

C. Coupe cars

·         A coupe, or French coupé, has two doors and a low, fixed roof, giving it a sporty feel.

·         Coupes are stylish cars best for singles or couple

·         The doors tend to be wider and the roof lower. It is shorter than a sedan and may or may not have a back seat. If there is back seating, it might be a little tighter than you may find comfortable.

·         E.g. - Mercedes-Benz, Mercedes-AMG C-Class: Recall Alert, Mercedes-AMG S63, Maserati GranTurismo, Lexus, Subaru.

coupe car

d. Hatchback cars

·         A hatchback is smaller than an SUV or minivan, but larger than a sedan. The main difference between a hatchback and a sedan is the extended trunk. Instead of the back sloping downwards, the back area is lifted, providing extra space for cargo.

·         Typically, the hatchback has a top-hinged trunk with rear seats that fold down for even more cargo space. As a result, hatchbacks are usually marketed as small family cars or executive cars.

·         Since the interior space can be made to prioritize passengers or cargo, they are a popular and practical choice for those who need both. From small city hatchbacks to large luxury models, there is a wide variety of hatchbacks available to you.

·         E.g. Maruti Swift, Maruti Baleno, Maruti Alto, Hyundai Elite i20, Renault KWID. Maruti Wagon R.

Hatchback cars

e. Sedan cars

·         A sedan, also known as a saloon in other countries, is the most popular body style. It typically features two rows of seats, 4 doors, and a 3-box configuration.

·         Sedans tend to provide better fuel economy, affordability, handling, and performance.

·         Since they are closer to the ground and have a lower centre of gravity, they tend to perform better around corners and sharp turns than larger vehicles such as SUVs. As a result, they are much less prone to tipping and rolling over than trucks and SUVs.

·         E.g. Fiat Viaggio, Tata Tiago EV, Renault Talisman, Volvo C70, Hyundai Sonata Facelift, Honda Civic. 

Sedan cars

f. Crossover cars

·         A cross between a sedan and an SUV, crossovers (also known as Crossover Utility Vehicles) give you the best of both worlds.

·         They are available in four-wheel, rear-wheel, and all-wheel drives.

·         They are cheaper and have better fuel economy than full-sized SUVs while still giving you extra ground clearance and a more commanding view of the road.

·         E.g. Mahindra U321 MPV, Mahindra TUV300 Plus, Nissan Kicks, Renault Duster facelift, Tata Q501 (codename), MG GS Concept, Datsun Go-Cross.

            

 Crossover cars

g. Electric cars

The heart of an electric car is the combination of:

·         The electric motor

·         The motor's controller

·         The batteries

The controller takes power from the batteries and delivers it to the motor. The accelerator pedal hooks to a pair of potentiometers (variable resistors), and these potentiometers provide the signal that tells the controller how much power it is supposed to deliver. The controller can deliver zero power (when the car is stopped), full power (when the driver floors the accelerator pedal), or any power level in between.  

       

E.g. - Tata Tiago, Tata Tigor, Renault Zoe, Mercedes-Benz EQ Concept, Hyundai Ioniq

Advantage of Electric Vehicle

·         Zero emission

·         Power Regeneration

·          Low noise pollution

·          Instant start and direct drive.

Disadvantage of Electric Vehicle

·         Limited Range

·         Long Refuelling Time

·         Higher Cost

·         Lack of Consumer Choice

h. Fuel Cell Electric Vehicle (FCEV)

·         FCEVs also go by the name Fuel Cell Vehicle (FCV).

·         They got the name because the heart of such vehicles is fuel cells that use chemical reactions to produce electricity.

·          Hydrogen is the fuel of choice for FCVs to carry out this reaction, so they are often called ‘hydrogen fuel cell vehicles’.

·          FCVs carry the hydrogen in special high pressure tanks, another ingredient for the power generating process is oxygen, which it acquires from the air sucked in from the environment.

·          Electricity generated from the fuel cells goes to an electric motor which drives the wheels. Excess energy is stored in storage systems like batteries or super capacitor 

·         E.g. Hyundai Tucson Fuel Cell, Toyota Mira, Honda Clarity Fuel Cell.

Working

·         The Fuel gas (hydrogen rich) is passed towards the anode where the following oxidation reaction occurs:

                        H2 (g) = 2H+ + 2e-

·         The liberated electrons from hydrogen in anode side do not migrate through electrolyte.

·         Therefore, they pass through the external circuit where work is performed, then finally goes into the cathode.

·         On the other hand, the positive hydrogen ions (H+) migrate across the electrolyte towards the cathode

·         At the cathode side the hydrogen atom reacts with oxygen gas (from air) and electrons to form water as byproduct according to:

Fuel + oxidant               product + heat

H₂ + ½ O₂ +2e-              H₂O + Heat

·         The liberated electrons from the hydrogen are responsible for the production of electricity.

·         The water is produced by the combination of hydrogen, oxygen and liberated electrons  and is sent out from the cell.

·         The DC current produced by fuel cell is later converted into AC current using an inverter for practical application.

·         The voltage developed in a single fuel cell various from 0.7 to 1.4 volt.

·         More power can be obtained by arranging the individual fuel cell as a stack. In this case, each single cell is sandwiched with one another by a interconnect.

Advantages

·         Zero Emissions: a fuel cell vehicle only emits water vapors. Therefore, no air pollution occurs.

·         High efficiency: Fuel cells convert chemical energy directly into electricity without the combustion process. As a result, Fuel cells can achieve high efficiencies in energy conversion.

·         High power density: A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints.

·         Quiet operation: Fuel cells can be used in residential or built-up areas where the noise pollution can be avoided.

·         No recharge: Fuel cell systems do not require recharging.

Disadvantages

·         It is difficult to manufacture and stores a high pure hydrogen

·         It is very expense as compared to battery

I . Hybrid cars

A hybrid vehicle uses two or more distinct types of power, such as internal combustion engine to drive an electric generator that powers an electric, e.g. in diesel-electric trains using diesel engines to drive an electric generator that powers an electric motor, and submarines that use diesels when surfaced and batteries when submerged. Other means to store energy include pressurized fluid in hydraulic hybrids.

E.g. - Toyota Camry Hybrid, Toyota Avalon Hybrid, Chevrolet Bolt, Ford Fusion Hybrid, Toyota Prius, Kia Optima Hybrid, Hyundai Ioniq, Honda Accord Hybrid. Find Best Price.

I. Series hybrid cars

               The series hybrid has the generator driven by the engine. This generator is used to charge the batteries and also drive the electric motor, which drives the transmission. Thus power to the vehicle is never directly given by the engine. 

II. Parallel hybrid cars

             In a parallel hybrid vehicle an electric motor and an internal combustion engine are coupled such that they can power the vehicle either individually or together. Most commonly the internal combustion engine, the electric motor and gear box are coupled by automatically controlled clutches. For electric driving the clutch between the internal combustion engine is open while the clutch to the gear box is engaged. While in combustion mode the engine and motor run at the same speed.

Advantages of Hybrid Cars

·         Very less pollution.

·         Better mileage.

·         More reliable and comfortable.

·         Very clean cars due to less emission.

·         Batteries need not be charged by an external source.

·         Warranties ava

ilable for batteries as well as motors.

·         Less dependence on fuels.

Disadvantages of Hybrid Cars

·         The initial cost will be very high – higher than other cars.

·         Since a lot of batteries will be needed, the car will be very heavy.

·         As there are electrical components, there is risk of shock during an accident.

·         The vehicle can be repaired only by professionals.

·         Spare parts will be very costly and rare.

Power transmission

1.7 Aerodynamics of a car body

                A branch of dynamics that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in motion relative to such fluids.

1.7. a. Advantages of aerodynamics

          It is essential that aerodynamics be taken into account during the design of cars as an improved aerodynamics in car would attain.

·         More fuel efficiency

·         Higher speeds

·         Good aesthetics & stylish appearance of car

·         More stability of car at higher speed

·         Reduces noise level

1.7. b. Methods of Aerodynamic Testing

     The two main alternative test methods, which are the most commonly used in aerodynamic development and testing of cars, are Computational Fluid Dynamics (CFD) and wind tunnel testing.

·         Wind tunnel Testing

          Wind tunnel testing has the big advantage that once the vehicle model is produced and rigged in the wind tunnel test section, it can quickly provide highly accurate data. Data for different boundary conditions, such as different wind speeds and yaw angles, can be acquired quickly. If similar changes in conditions are done on a computer model, the whole simulation has to be run over again for each case. On  the other  hand, wind  tunnel testing  can  be  both highly  costly  and  time  consuming.

       Open & close  circuit wind tunnel testing

·         Computational Fluid Dynamics

                    Computational fluid dynamics (CFD) is one of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyse problems that involve fluid flows. Computers are used to simulate the interaction of liquids and gases with surfaces defined by boundary conditions.  Even with high-speed supercomputers only approximate solutions can be achieved in many cases.

1.7. c. Aerodynamics forces acting on body

                 In order to improve the aerodynamics of cars, we must know how the flow of air past a car. The major forces which affecting the motion of car in fluid flow are.

·         Drag force

·         Lift or down force

·         Side force

·         Drag force

            Some energy is lost to move the car through the air & this energy is used to overcome a drag force. In vehicle aerodynamics drag is due to frontal pressure & Rear vacuum.

 For calculating drag force following formula is use

           F= ½ CDAV²  

Where F= Aerodynamics   drag force        A= frontal area 

             C=coefficient of drag                      V=velocity of object

             D= density off air

·         The drag coefficient is a function of the shape of the object and the Reynolds Number (Re)

·         Re = (velocity * length-scale) / (kinematic viscosity)

·         There are several good ways to calculate the frontal area of your vehicle. One is to simply measure the height multiplied by the width and take 85% of it to acuminate the smaller green house.
F.A. = (height x width) x 0.85

Calculating drag force for Toyota Prius C

Dimensions

Wheel base - 2550mm

Length – 4000mm

Width – 1690mm

Height – 1450mm

F _drag =1/2 x δxV² x D x A

T _air = 67⁰F      

 T⁰C = (T⁰F – 32) x (5/9)   = (67-32) x (5/9) = 19.4⁰C

 Ꝭ = density of air =1.204 kg/m³ at 19.4⁰C temp

D= drag coefficient for Toyota Prius C = 0.28

A= Frontal area of Car = W x H x 0.85 = 1690 x 1450 x 0.85= 2.0336m²

V= 6km/hr. x 1hr/3600sec x 1000/1km = 1.6Km/hr. 

F _drag =1/2 x 1.204 x (1.6)² x 0.28 x 2.0336 = 0.87461W

Y=0.2275 X² +0.3187X   (as per equation y=ax²+bx)

As the car is moving 30km/hr from 0 to 9.25sec

F _drag =0.2275 t² +0.3187t

9.25                      9.25                                                                                9.25

ʃ F _drag  dt =            ʃ (0.2275t²  + 0.3187 t ) dt =  [ 0.2275t3/3 + 0.3187t2/2]     

0                          0                                                                                        0

=73.653N.S

                 9.25                                                                                                                

F _drag =      ʃ F _{drag dt} /Δt       = 73.653/9.25 = 8N

                0

·         Lift force

              It is the force produced by the pressure difference between above & below of the vehicle.

(F_L) = C_L q A = (C_L (1/2) r V²) A

Where

C_L = Coefficient of Lift

q = Dynamic Pressure in the Test Section
r = Mass Density of Air
A = Frontal Area of Vehicle
V = Velocity

·         Side force

            It is produced by the action of side winds.

(F_S) = C_S q A = (C_S (1/2) r V²) A

Where

C_S = Coefficient of Side Force

q = Dynamic Pressure in the Test Section
r = Mass Density of Air
A = Frontal Area of Vehicle
V = Velocity

1.7. f. METHODS TO REDUCE DRAG

·         Vortex Generators

·         Diffuser

·         Rear Fairing

·         Streamlining

·         Spoilers

·         Vortex Generators

            A vortex generator (VG) is an aerodynamic device, consisting of a small vane usually attached to  a lifting surface  (or airfoil, such as  an aircraft  wing) or  a rotor  blade  of a  wind turbine. VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a vortex, which,  by removing some part of the  slow-moving boundary  layer  in contact with the airfoil surface, delays  local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators, ailerons, and rudders. If the air that makes up the vortex can be tripped before it leaves back of the car, it will make smaller vortices, which will have a smaller effect on the overall aerodynamics of the vehicle.

 

Bump shape vertex generator                    

·         Concept of a Vortex      

               The laminar boundary layer flow is a very smooth flow, with no disruption between the layers. It has low skin friction drag but it is unstable, which means that flow separation is easier when it has laminar behavior at high angles of attack.  Laminar flow airfoils tend to provide low drag at cruise but nasty stall characteristics. Turbulent boundary layer is characterized by chaotic property changes. The flow has more energy and has rapid variations of pressure and flow velocity in space and time  - turbulence is complex and therefore turbulent flow is more complex to simulate. In turbulent flow, drag caused by boundary layer skin friction increases. shows a good intuitive approach of the transition process.

Vertex flow of Air

·         Diffusers

            It works by providing a space for the under body airflow to decelerate and expand (in area, as density is assumed to be constant at the speeds that cars travel) so that it does not cause excessive flow separation and drag, by providing a degree of "wake infill" or more accurately, pressure recovery. The diffuser itself accelerates the flow in front of it, which helps generate down force.

 

                                                           Diffusers

·         Operation

The pressure under the car is affected by the diffuser so that it can expand back to ambient in the diffuser, as the car moves through the air. It uses Bernoulli's principle, such that the pressure decreases while the velocity increases. Since the pressure below the car is lower than on the side and above the car, down force is produced if implemented correctly. The diffuser "drives" the under body, which produces the down force.    

·         Rear Fairing

               A structure on various parts of a vehicle, for example an aircraft, automobile, or motorcycle, that produces a smooth exterior and reduces drag.

Rear fairing in jet

·         Streamlining

               A streamlined body is a shape that lowers the friction drag between a fluid, like air and water, and an object moving through that fluid. Drag is a force that slows down motion; friction drag is a special kind of drag. It occurs when the fluid closest to the object sticks to its surface, exerting a force that opposes the object’s motion.

                 Particles of a continuous fluid can be considered to travel along smooth continuous paths which are given the name streamlines.  These streamlines can be curved or straight, depending on the flow of the fluid. This type of motion is also called laminar flow. Streamline motion is not the only possible kind of fluid motion.  When the motion becomes too violent, eddies and vortices occur.  The motion becomes turbulent.

Streamlining

·         Effect of wake on streamlining

                      The rear-end shape of a car is one of the most important parts from the view point of aerodynamics. It governs the aerodynamic characteristics of the car, especially drag and rear lift. However, a rear-end shape like a spoiler often increases drag on recent low-drag cars. The relation of rear-end shape to drag and lift is studied by consideration of the wake structure, which is obtained by wind tunnel testing and CFD. Finally, a new rear shape which reduces rear lift without increasing drag and front lift is discussed

Effect of wake

·         Spoilers

           A spoiler is an automotive aerodynamic device whose intended design function is to “spoil” unfavorable air movement across a body of a vehicle in motion, usually described as drag. Spoilers on the front of a vehicle are often called air dams, because in addition to directing airflow they also reduce the amount of air flowing underneath the vehicle, which generally reduces aerodynamic lift and drag. Spoilers are often fitted to race and high-performance sports cars, although they have become common on passenger vehicles as well. Some spoilers are added to cars primarily for styling purposes and have either little aerodynamic benefit or even make the aerodynamics worse.The goal of many spoilers used in passenger vehicles is to reduce drag and increase fuel efficiency. Passenger vehicles can be equipped with front and rear spoilers. Front spoilers, found beneath the bumper, are mainly used to decrease the amount of air going underneath the vehicle to reduce the drag coefficient and lift.  Sports cars are most commonly seen with front and rear spoilers.

 

Spoilers

·         CFD(Computational fluid dynamics)

            “CFD (Computational fluid dynamics) is a set of numerical methods applied to obtain approximate solution of problems of fluid dynamics and heat transfer.”

             The physical characteristics of the fluid motion can usually be described through fundamental mathematical equations, usually in partial differential form, which govern a process of interest and are often called governing equations in CFD.  The computational part simply means the study of the fluid flow through numerical simulations, which involves employing computer programs or software packages performed on highspeed digital computers to attain the numerical solutions. 

            CFD codes are structured around the numerical algorithms that can handle fluid flow problems. All the CFD commercial packages available in the market have three basic elements, which divide the complete analysis of the numerical experiment to be performed on the specific domain or geometry. The three basic elements are

I .                    Pre-processor

ii.                   Solver

iii.                  Post-Process