Automobile Engineering Notes

Automobile Engineering

MEPC22
Dr. Bishweshwar Babu
Department of Mechanical Engineering
NIT Tiruchirappalli
email: bishweshwar@nitt.edu

Introduction

• An automobile is a wheeled vehicle carrying its own motive power unit.
• Automotive engineering is a branch of vehicle engineering, incorporating elements of mechanical, electrical, electronic, material, software, and safety engineering as applied to the design, manufacturing and operation of automobiles, and their respective engineering subsystems.
• It also includes modification, repair and maintenance of vehicles.

Requirements of an Automobile

The motor vehicles should fulfill certain requirements:

• Be lightweight.
• Have a minimum number of components.
• Have long, fatigue life; durable and reliable.
• Have uniformly distributed load.
• Have good ride and handling dynamics.
• Have sufficient space for passengers and luggage.
• Have good access to the engine, suspension system and other auxiliaries.
• Have minimum noise, vibrations and harshness levels when vehicle is running.
• Have minimum resistance to air.
• Be cheap and easy in manufacturing, running and maintenance.
• Have clear all-round vision through glass areas.
• Have an attractive shape and color.
• Be fast, comfortable, safe and non-polluting type.

History of Automobiles

• Nicolas Cugnot, a French artillery officer, designed and built the world’s first self-propelled road vehicle, a crude three-wheeled steam tractor for handling canon (1769).
• Jean Etienne Lenoir, a Belgian inventor, built the first practicable coal gas IC engine (1860).
• Nicklaus A. Otto, a German engineer, invented compressed charge four stroke engine with in-cylinder compression (1876).
• Dugald Clerk, a Scottish engineer, designed the first two-stroke engine with in-cylinder compression (1878).
• Gottlieb Daimler and Wilhelm Maybach, German inventors, built and patented the first motorcycle (1885).
• Karl Friedrich Benz, a German engine designer and automotive engineer, installed an Otto cycle petrol engine at the back of a tricycle (1886).
• Rudolf Diesel, a German engineer, invented four stroke diesel engine (1895).
• Karl Friedrich Benz invented the accelerator for speed regulation, battery ignition system, spark plug, clutch, gear shift and the radiator for cooling of the engine and started production of automobiles, the first in the world (1888).
• In France, production of automobiles was started by Émile Levassor and Armand Peugeot, using the Daimler engine (1890).
• In U.K., production of automobiles was started by Harry J. Lawson (1897).
• The first American car with a petrol engine was designed by George Baldwin Seldon in 1877, although he built an automobile only in 1905.
• Large-scale production-line manufacturing of automobiles was started by Ransom Eli Old (1902) and the concept was vastly expanded by Henry Ford, with an initial run of 20,000 vehicles (1908).
• Benz produced 25 vehicles and Daimler-Maybach made almost 30 vehicles in the first five years of their production, almost 94 million automobiles were produced worldwide in the year 2023.

History of Indian Automobiles

• In the pre-Independence days, cars used to be imported into India and it was later, when car manufacture was started in the country with foreign collaborations.
• Hindustan Motors was the first to set up shop in the eastern region (1946).
• Premier Automobiles was the next to enter the industry (1947).
• Mahindra and Mahindra arrived to produce jeeps in the western region (1949).
• Standard Motors started producing passenger cars in the southern region (1950).
• Tata introduced a plant for the manufacture of commercial vehicles at Jamshedpur (1954).
• In 1980, Hindustan Motors produced only 21,572 cars, Premier Automobiles 8,729, while Standard motors produced only 6 cars, which was far below the nation’s demand.
• In the period of the oil crisis (1973) that the small car concept came into being and Maruti took shape. In 1982, Maruti was established in collaboration with Suzuki Motor Corporation of Japan.

General Classification of Automobiles

• Use
  • Mopeds/Motorcycles/Scooters
  • Auto-rikshaw/tempo
  • Cars
  • Vans/Buses/Trucks
• Capacity
  • Heavy transport vehicles (HTV) – trucks, lorries and buses etc.
  • Light transport vehicles (LTV) – delivery vans, auto-rikshaws etc.
• Make and model (e.g., Royal Enfield ‘Bullet’, TATA ‘Nexon’ etc.)
• Fuel used
  • Petrol vehicles – scooters, motorcycles, cars (petrol models).
  • Diesel vehicles – buses, trucks, cars (diesel models).
  • Hybrid vehicles and EVs
• Body style
  • Closed cars such as saloon, coupe, etc.
  • Open cars such as sports car, convertible car, etc.
  • Special styles such as estate car, station wagon, MUV, etc.
• Wheels
  • 2-wheelers, e.g., scooters, motorcycles, mopeds.
  • 3-wheelers, e.g., auto-rikshaw, tempo.
  • 4-wheelers, e.g., cars, vans.
  • 6-wheelers and more, e.g., trucks, buses.
• Drive
  • Whether the vehicle can be driven sitting towards left or right side:
    • Left-hand traffic or right-hand drive – India and most of the commonwealth countries (75 countries and territories)
    • Right-hand traffic or left-hand drive – rest of the world (165 countries and territories)
  • Whether the front axle, rear axle or both axles are driving axles:
    • Front-wheel drive, e.g., passenger cars.
    • Rear-wheel drive, e.g., low-end SUVs.
    • 4-wheel drive (FWD / 4×4) or All wheel drive (AWD) , e.g., high-end SUVs.
• Transmission
  • Manual transmission (MT) – ordinary crash type gear box.
  • Fully-automatic transmission (AT) – combination of epicyclic gear trains and torque converters.
  • Semi-automatic / Intelligent Manual Transmission (iMT) / Clutch-less Manual Transmission (CMT)
  • Automated Manual Transmission (AMT) – hydraulically and electrically operated MT.
  • Dual Clutch Automatic Transmission (DCT) – Two separate clutches for odd and even gear sets.
  • Continuously Variable Transmission (CVT) / Infinitely Variable Transmission (IVT) – change seamlessly through a continuous range of gear ratios.

Classification of Automobiles in India

• Heavy Commercial Vehicles (HCVs) – Gross Vehicle Weight (GVW) > 16.2 metric tons (MT).

• Medium Commercial Vehicles (MCVs) – 7.5 < GVW ≤ 16.2 MT

• Light Commercial Vehicles (LCVs) – $GVW ≤ 7.5$ MT

• Passenger cars or Light Motor Vehicles (LMVs) – seating capacity of up to 6 persons, excluding the driver.

• Utility Vehicles (UVs) – Seating capacity of 7 to 12 persons, excluding the driver.

• Multi Purpose Vehicles (MPVs) – Van-type vehicles, seating capacity of 7 to 12 persons, excluding the driver.

• Passenger car segments in India:

  • A1: Up to 3500 mm (Ultracompact cars)
    • Car models: Suzuki Alto, Tata Nano, MG Comet EV
  • A2: 3501 to 4000 mm (Sub-four metre)
    • Car models: Suzuki Wagon R, Suzuki Swift, Suzuki Baleno, Suzuki Brezza, Hyundai i10, Hyundai i20, Hyundai Aura, Tata Nexon, Tata Altroz, Honda Amaze, Kia Sonet, Skoda Kylaq
  • A3: 4001 to 4500 mm
    • Entry-level mid-size sedans
    • Car models: Hyundai Verna, Honda City, Maruti Suzuki Ciaz, Škoda Slavia, VW Virtus
  • A4: 4501 to 4700 mm
    • Small family cars
    • Car models: Toyota Corolla, Škoda Octavia, Honda Civic
  • A5: 4701 to 5000 mm
    • Mid-size (D) Executive cars (E)
    • D-segment: Toyota Camry, Škoda Superb, Honda Accord
    • E-segment: Mercedes-Benz E-Class, BMW 5 series
  • A6: > 5000mm (Grand saloons)
    • Car models: Mercedes-Benz S-Class, Audi A8, BMW 7 series, Jaguar XJ
  • B1:
    • < 4000 mm (Small vans)
    • Car models: Maruti Suzuki Eeco, Tata Venture, Renault Triber
  • B2:
    • > 4000 mm (Mid-size MPVs/minivans)
    • Car models: Toyota Innova, Maruti Suzuki Ertiga, Mahindra Marazzo, Kia Carnival
  • SUV: Any (SUVs)
    • Car models: Tata Safari, Mahindra XUV700, MG Hector, Hyundai Creta, Audi Q7, Toyota Land Cruiser

Components of an Automobile

The main units of an automobile are:

• Basic structure/chassis
  • Frame
  • Suspension system
  • Axles
  • Wheels
    • Frame
      • Conventional pressed steel frame
      • Integral or frameless construction
• Power plant
  • SI or CI type IC engines
  • Battery powered electric motors
  • Hybrid of both
  • Gas turbines
  • Fuel cell powered power unit
• Transmission system
  • Clutch
  • Gear box
  • Bevel pinion and crown wheel
  • Universal joints
  • Differential
• Controls
  • Steering system
  • Brakes
• Auxiliaries
  • Supply system – battery and generator; starter; ignition system – battery and magneto ignition; Ancillary devices
    • Ancillary devices
      • Driving lights (head-lights; fog-lights; side-lights; tail-lights; number plate illumination; etc.)
      • Signaling (horn; direction indicators; brake light; etc.)
      • Other lights (roof light; panel light; reverse light; ambient light; boot light etc.)
      • Miscellaneous (instrument panel; infotainment system – radio, GPS, speakers, android auto/apple car play; HVAC system – heater, AC, blowers, air purifier, glove box cooling; lighter; electric fuel pump; electric windshield wipers; power windows; power adjustable ERVMs; engine start/stop button; central locking and key-less entry; sun-roof controls; etc.)
• Superstructure/body (shape of the body depends upon the ultimate use for which the vehicle is meant)

Automobile Body Styles

• Closed cars
  • Saloon or Sedan – 2 or 4 doors; a single compartment with 2 rows of seats and a fixed roof which is at full height up to the rear windows; separate luggage space usually at the rear.
  • Hatchback – A sedan with a door at the back.
  • Coupe – A sedan with only one row of seats and only 2 doors; roof-line at decreased height (sometimes).
  • Limousine – Six-seater or bigger passenger compartment; driving compartment is separated from the rear compartment usually by a sliding glass division.
  • Fast back – Roof slopes down at a smooth angle to the tail of the car; no separate door at the end.
• Open cars
  • Sports – Relatively small, low-slung car; high performance engine; excellent handling.
  • Convertible – Soft folding type roof; windows of special wind-up design.
  • Cabrio Coach or Semi-convertible – Retractable textile cover often acts as a large sun- roof; rarely found in modern cars.
  • Coupe Convertible – Rigid roof that can be retracted inside the lower part of the vehicle body.
• Special style cars
  • Estate Car / Station Wagon – A sedan with the passenger roof extended right up to the rear end; rear door for loading; rear seats usually collapsible.
  • Sports Utility Vehicle (SUV) – Large tires; higher seating and more ground clearance; engine area is separate, but passenger and luggage area are enclosed together; usually these have FWD system or an option for the same.
• Transport vehicles
  • Van – Light transport vehicles; seats at the front and luggage space at the rear; side doors are usually of sliding type; rear is door used for loading or unloading.
  • Truck – Heavy goods commercial vehicles with all axles attached to a single frame; twin wheels are generally fitted on the non-steered axles; depending up on the load capacity, there are two or more axles.
  • Articulated Vehicle – Heavy goods vehicle consisting of a tractor and a detachable semi- trailer; smaller turning circle than a rigid truck; steering is more difficult.
  • Bus – Used for carrying large number of people over short distances often in a dense traffic; not much space for luggage; usually two doors for passengers and one for the driver; double decker buses have two floors.
  • Coach – Used for transporting large number of people over long distances; luxurious interior with comfortable, adjustable seats and amenities like infotainment, HVAC and Wi-Fi.
• 2-wheelers
  • Standard Bike – Basic form of motorcycle; also known as ‘street bike’.
  • Cruiser – Riding position with the hands up and the feet forward with the spine erect; quite comfortable for long-distance riding.
  • Sports Bike – During driving, the rider has the hands low, the feet backwards, and the spine inclined forward; high performance bikes.
  • Tourers – Very upright and comfortable riding position with extremely large fairings and bodywork.
  • Sports Tourers – A hybrid between sports bike and tourers; convenient long distance travelling at higher speeds.
  • Scooters – Smaller wheels; small engines; configuration which allows the rider to drive with both feet on a running board and knees together.
  • Moped – Low-capacity engine, usually 50c.c.; hybrid between bicycle and motorcycle.

Chassis

• Chassis is a French term which denotes the whole vehicle except body in case of heavy vehicles.

• It consists of the following components suitably mounted:

  • Frame
  • Engine, radiator, silencer and other fitments
  • Transmission system
  • Suspension system
  • Steering system
  • Brakes
  • Road wheels, axles
  • Fuel tank
  • Electrical systems

• Remaining: Superstructure, Auxiliaries.

• Various loads acting on the frame

  • Short duration Load - While crossing a broken patch.
  • Momentary duration Load - While taking a curve.
  • Impact Load - Due to the collision of the vehicle.
  • Inertia Load - While applying brakes and during sudden acceleration.
  • Static Loads - Loads due to chassis parts.
  • Overloads - Beyond design capacity.

• Characteristics of good chassis

  • Fast pickup
  • Speed
  • Safety
  • Dependability
  • Quietness
  • Power accessibility
  • Low center of gravity
  • Load clearance
  • Good springing
  • Shape/ Styling
  • Strength
  • Durability
  • Ease of control
  • Economy of operation
  • Structural integrity and stability
  • Braking ability
  • Simplicity of lubrication
  • Cost (Material + Production)
  • Mass production
  • Recyclability

• Types of chassis frames:

  • Conventional frame
    • Channel Section - Good resistance to bending
    • Tubular Section - Good resistance to torsion
    • Box Section - Good resistance to both bending and torsion
  • Integral frame
    • Used now a days in most of the cars.
    • No frame; all the assembly units are attached to the body.
    • Due to elimination of long frame, it is lighter and cheaper.
    • Lesser load carrying capacity; repairing is difficult.
  • Semi-integral frame
    • Half frame is fixed in the front end on which engine gear box and front suspension is mounted.
    • It has the advantage when the vehicle is met with accident the front frame can be taken easily to replace the damaged chassis frame.
    • This type of frame is used in FIAT cars and some of the European and American cars.

• Classification of chassis:

  • Based on layout
  • Based on engine fitment location
  • Based on wheel drives
  • Based on fabrication

• Classification based on layout:

  • Conventional control chassis: Outside the driver cabin or seat, avoids full utilization of space (Cars, Mahindra jeeps)
  • Semi-forward control chassis: One half is in the driver's cabin and the other half in the front, outside the driver’s cabin (Tata SE series of vehicles)
  • Full-forward control chassis: Totally in the driver cabin which provides increase in floor area (Tata E series of vehicles)

• Classification based on engine fitment location:

  • Engine fitted at front (drive is given to front wheel)
    1. Low floor is available since long propeller shafts are eliminated.
    2. Vehicle has more road holding capacity.
    3. Clutch, gear box & differential are usually made as one unit, thereby cost is reduced.
       • Most passenger cars
  • Engine fitted at front (drive is given to rear wheel)
    1. Enough space is available for luggage behind the rear seat.
    2. The weight of vehicles is well balance.
    3. Increased efficiency of cooling system.
       • Mahindra SUVs
  • Engine fitted at front but crosswise
    1. Most compact cars use this layout as it requires very small space to fit the engine.
    2. Design is more complicated as compared to longitudinally placed engine as it does not leave enough space for accessories.
       • BMC, Maruti Suzuki
  • Engine fitted at Back
    1. Flat floor is available since long propeller shafts are eliminated.
    2. With elimination of propeller shaft the center of gravity lowered, giving stable driving.
    3. Better adhesion on road specially when climbing hill.
    4. While climbing hill, the weight on the front wheel is reduced.
    5. As a result of grouping of the engine with clutch, gear box and differential, the repair and adjustment become difficult due to congestion at the rear.
       • Volkswagen Beetle, Leyland bus of England
  • Engine fitted at center
    1. Drive is given to the rear/front.
    2. This arrangement provide full space of floor for use
       • Sports cars, Royal tiger world master buses of Delhi transport

• Classification based on number of wheels fitted in the vehicles and the number of driving wheels:

  • 4X2 drive chassis
    • 4 Wheels, 2 Driving Wheels
  • 4X4 drive chassis
    • 4 Wheels, 4 Driving Wheels
  • 6X2 drive chassis
    • 6 Wheels, 2 Driving Wheels
  • 6X4 drive chassis
    • 6 Wheels, 4 Driving Wheels

• Classification based on fabrication:

  • Ladder / body-on-frame
  • Monocoque / unibody
  • Tubular Space
  • Backbone

• Aluminum monocoque

  • Audi A8 is the first mass production car featuring Aluminum Space Frame (ASF) chassis (1994).
  • To replace conventional steel monocoque mainly for the benefit of lightness. Aluminum is about 3 times lighter than steel per unit volume but can be made just as strong using certain alloys/shapes/bonding methods. Because of this, AL parts can be thicker, and thus stronger, than their steel counterparts, all while weighing less.
  • There are some manufacturing methods that can only be done with aluminum, such as extrusions. These extrusions allows the ASF to have about half the number of parts as a traditional steel monocoque.
  • Audi claimed A8’s ASF is 40% lighter yet 40% stiffer than steel monocoque.
  • Some other cars which use Aluminum frame: Jaguar XJ, Corvette Z06 (GM), Honda NSX, Audi A2, Audi R8
  • Advantage: lighter than steel monocoque, space efficient
  • Disadvantage: expensive (even for mass production)

• Carbon fiber monocoque

  • Carbon fiber is the most sophisticated material using in aircrafts, spaceships and racing cars because of its superior rigidity-to-weight ratio.
  • Examples of road cars featuring Carbon-Fiber body panels: Ferrari 288 GTO, Porsche Carrera GT, Porsche 959.
  • There are several Carbon fibers commonly used in motor industry. Kevlar, which was developed by Du Pont, offers the highest rigidity-to-weight ratio among them. Because of this, army's helmets and bullet-proof vests are made of Kevlar. Kevlar can also be found in the body panels of many exotic cars, although most of them simultaneously use other kinds of carbon-fiber in even larger amount.
  • Production process: Carbon fiber panels are made by growing carbon fiber sheets (something look like textile) in either side of an aluminum foil. The foil, which defines the shape of the panel, is sticked with several layers of carbon fiber sheets impregnated with resin, then cooked in a big oven for 3 hours at 120°C and 90 psi pressure. After that, the carbon fiber layers will be melted and form a uniform, rigid body panel.

Automotive Materials

• Materials selection in the automotive industry is governed by the demands emerging from customers’ expectations and legal requirements. Light weight, fuel/energy efficient, environment-friendly, and cheaply available materials are in great demand by automotive industries.

• The main factors for selecting the material, especially for the automobile body, are numerous and include thermal, chemical or mechanical resistance, easy manufacturing, durability, and many other mechanical properties including cost and availability of course.

• The development of materials application in the near future will be determined by ecological needs like consumption reduction, used vehicle disposal, and by the necessity to reduce overall costs.

• The main materials currently being used for automobiles parts and components, along with the futuristic trends are described below.

  • Steel
  • Iron
  • Aluminum
  • Metal Matrix Composites
  • Magnesium
  • Titanium
  • Copper
  • Lead*
  • Zinc
  • Ceramics
  • Plastics
  • Silicones
  • Elastomers
  • Adhesives
  • Textile
  • Natural Materials
  • Bio-materials
  • Smart Materials
  • Graphene Paper
  • Asbestos*

• Steel: Different grades of steel have been traditionally, a major part of automobile. It is strong, cheap, easy to work and fabricate, and readily available. The prime reason for using steel in the body structure is its inherent capability to absorb impact energy in a crash situation.

• Iron:

  • Cast Iron (CI): It is the conventional material for engine cylinder heads and blocks. It has a much lower melting point than steel and is more fluid and less reactive with molding materials, making it excellent casting material. However, it is not ductile enough to be rolled or forged like steel. Gray cast iron, which is mostly used for automotive application, has about 92% iron, 3.4% carbon, 2.5% silicon and 1.8% manganese. During solidification, carbon becomes graphite and enhances the machinability, damping, and self-lubricating properties.
  • Compacted Graphite Iron (CGI): It is stronger than cast iron and can be made thinner and lighter. A CGI block is very good for performance engines, which are supercharged or turbocharged. CGI roughly doubles the strength of the casting without additional mass. However, it is slightly costlier.

• Aluminum:

  • Aluminum usage in automotive industry has grown within past years for making body structures, chassis applications, closures and exterior attachments such as crossbeams, doors or bonnets, pistons, cylinder heads, blocks, and even connecting rods.
  • Advantages:
    • It has one-third the density of steel which means a component can be 1.5 times thicker compared to a steel version, while still being 50% lighter.
    • It can absorb twice as much energy as steel per unit mass.
    • It has a naturally high resistance to corrosion.
    • It can be recycled again and again without loss of quality (95% recyclable).
  • Disadvantages:
    • It is more difficult to weld, form, and stamp than steel.
    • The cost per kg it currently four to five times more than steel.
    • It behaves differently when stressed.

• Magnesium: It is a light metal that is becoming increasingly common in interior applications: steering wheels, steering lock housings, air bag housings, sun-roof track assemblies, instrument panels, transfer cases, clutch and brake pedals etc.

  • Advantages:
    • 33% lighter than aluminum and 75% lighter than steel/cast iron components.
    • Better machinability than aluminum and induces less wear and tear on tools.
    • Best strength-to-weight ratio of any of the commonly used structural metals.
    • Its low heat content per unit volume permits die casting rates that are frequently 1.5 times faster than aluminum.
    • Its low reactivity with iron usually results in twice the die life as compared to a similar aluminum part.
    • It is dimensionally stable because of its consistent shrink rate.
  • Disadvantages:
    • Costlier.

• Zinc: It is used to manufacture die cast components for vehicles. Zinc die casting is used wherever safety and maximum stability are required in a vehicle. These parts are often concealed and invisible to the eyes of drivers and passengers.

• Titanium: Primarily used in premium cars - suspension springs, valve springs, valves, connecting rods, and exhaust systems.

• Copper: Copper/brass has traditionally been used for car and truck radiators, which has now been almost entirely replaced by aluminum due to lighter mass and cheaper prices.

• Metal Matrix Composite (MMC): It is an aluminum-graphite particle composite which can be used for brake drums, pistons and cylinder liners. It reduces friction and give aluminum lubricity in low-temperature, low-oil conditions.

• Plastics: The term ‘plastics’ means organic materials of large molecular weight bonded together chemically that can be shaped by flow. However, it usually refer to the final product with fillers, plasticizers, pigments and stabilizers included; whereas the polymeric, starting material is termed the resin.

  • Polymers containing mainly carbon and hydrogen are classified as organic polymers, whereas those having silicon primarily are called synthetic polymers or silicones.
  • A thermoplastic is a polymer in which the molecules are held together by weak secondary bonding forces that can be softened and melted by heat, then shaped or formed before being allowed to cool and ‘freeze’. The heating and cooling processes can be repeated many times without significant chemical changes.
  • A thermoset is a polymer that solidifies irreversibly when heated due to a chemical reaction involving cross-linking between chains. They have excellent temperature resistance, with no melting or softening.
  • A composite consists of a reinforcing fiber in a polymer matrix. Polyester, vinyl ester, and epoxy resins are the commonly used matrices. Composites combine the strength and rigidity of metals and the light weight, flexibility and corrosion resistance of plastics. e.g., carbon fiber reinforced plastics (CFRP) or glass fiber reinforced plastics (GFRP).
  • Advantages:
    • Resistant to harsh chemicals, corrosion.
    • Provide both thermal and electrical insulation.
    • Good noise, vibration and harshness (NVH) characteristics.
    • Excellent strength-to-weight ratio.
    • Great design flexibility.
    • Many production options.
    • More resistant to impact damage.
    • Mostly cheap*.
  • Disadvantages:
    • Degradation by UV light.
    • Expensive and difficult to recycle.
    • Dimensional instability at higher temperatures.
    • Special painting processes are required.
    • Special mechanical attachment systems are required.
    • Structural plastic components are difficult to integrate with the remaining structure due to which they are generally restricted to components that can be added after the steel structure has been completed.

Vehicle Dynamics

• Forces Acting on the Vehicle

$F - (R<em>a + R</em>{rlf} + R<em>{rlr} + R</em>g) = ma$
$F = ma + R<em>a + R</em>{rl} + R<em>g$$R</em>{rl} = R<em>{rlf} + R</em>{rlr}$
$R<em>g = W sin(\theta)$$F = F</em>g$

Rolling Resistance

• It is composed primarily of resistance from tire deformation (90%), tire penetration and surface compression (4%), tire slippage and air circulation around wheel (6%) and many other factors.
• Viscoelastic nature of the tire material is responsible for rolling resistance. Energy is dissipated due to hysteresis (deformation/recovery cycle) which is converted to heat and sound energy.
• How to reduce rolling resistance in tires?
  • Material change: rubber to silicone
  • Dimensional change: Wider
  • Higher pressure: sidewalls not to touch flat surface
  • Tread thickness to be reduced
  • Larger wheel with lower aspect ratio

$R<em>{rl} = f</em>{rl} W \cos(\theta<em>g) \approx f</em>{rl} W$

Grade Resistance

• It is the resistance due to the gravitational force acting on the vehicle while moving up or down an inclination.
• It can be positive or negative depending on whether the vehicle is moving downhill or uphill.

$R<em>g = W \sin(\theta</em>g)$

Tractive Effort

• Tractive Force (Effort): Pulling force exerted by the vehicle.
  • Maximum tractive effort: Maximum force beyond which the wheel spins & is a function of vehicle’s weight distribution and road-tire interaction.

$F<em>{max} = \mu W</em>{normal}$
* Engine generated tractive effort:

$P<em>e = M</em>e n_e / 1000$

$F<em>e = M</em>e \epsilon<em>0 \eta</em>d / r$

Where:

$F_e$ = Engine generated tractive effort reaching wheels (N)

$M_e$ = Engine torque (N-m)

$\epsilon<em>0$ = Gear reduction ratio $\eta</em>d$ = Driveline efficiency
r = Wheel radius (m)
* Available tractive effort:

$min (F<em>e, F</em>{max})$

Aerodynamics

• When objects move through air, forces are generated by the relative motion between air and the surfaces of the body. Study of