2/25/2019

1

INTRODUCTION TO AUTOMOTIVE ENGINEERING

Prof. Dr. Engin TANIKCopyright 2019

1 VEHICLE CLASSIFICATIONS1.1 Wheeled motor vehicle categorization1.2 Passenger car categorization

2 CHASSIS and BODY2.1 Overview2.2 Most common chassis-body types

2.2.1 Unibody2.2.2 Ladder chassis2.2.3 Space-frame chassis2.2.4 Tub chassis2.2.5 Stressed member engine

2.3 Body and chassis materials2.4 Body surface2.5 Aerodynamics2.6 Safety

2.6.1 Active safety2.6.2 Passive safety (Crashworthiness)

2/25/2019

2

1. VEHICLE CLASSIFICATIONS

1.1 Wheeled motor vehicle categorization

A vehicle is machine used for transporting passengers or goods. An automotive vehicle or wheeled motor vehicle moves on wheels that apply steering and traction forces against the ground. The most common examples are; car, truck, bus and motorcycle. This course focuses on the fundamentals of wheeled vehicles and particularly on passenger cars.

In order to separate the vehicles according taxes, driving licenses and traffic rules etc. should be categorized. EU general classification [2] of some wheeled motor vehicle is as follows:

Category M: Motor vehicles with at least four wheels designed and constructed for the carriage of passengers:

M1: Vehicles designed and constructed for the carriage of passengers and comprising no more than eight seats in addition to the driver's seat.

M2: Vehicles designed and constructed for the carriage of passengers, comprising more than eight seats in addition to the driver's seat, and having a maximum mass not exceeding 5 tons.

M3: Vehicles designed and constructed for the carriage of passengers, comprising more than eight seats in addition to the driver's seat, and having a maximum mass exceeding 5 tons.

2/25/2019

3

Category N: Motor vehicles with at least four wheels designed and constructed for the carriage of goods.

N1: Light commercial vehicles - designed and constructed for the carriage of goods and having a maximum mass not exceeding 3,5 tons.

N2: Large goods vehicles - designed and constructed for the carriage of goods and having a maximum mass exceeding 3,5 tons but not exceeding 12 tons.

N3: Large goods vehicles constructed for the carriage of goods and having a maximum mass exceeding 12 tons.

Category L: L1e: (Moped) Two-wheel vehicles with a maximum design speed of not more than 45 km/h and characterized by an engine whose: cylinder capacity does not exceed 50 cm3 in the case of the internal combustion type, or maximum continuous rated power is no more than 4 kW in the case of an electric motor.

L3e: (Motorcycles) Two-wheel vehicles without a sidecar fitted with an engine having a cylinder capacity of more than 50 cm3 if of the internal combustion type and/or having a maximum design speed of more than 45 km/h.

L6e: Quadricycles whose unloaded weight is not more than 350 kg, not including the mass of the batteries in case of electric vehicles, whose maximum design speed is not more than 45 km/h, and whose engine cylinder capacity does not exceed 50 cm3 for spark (positive) ignition engines, or whose maximum net power output does not exceed 4 kW in the case of other internal combustion engines, or whose maximum continuous rated power does not exceed 4 kW in the case of an electric motor.

2/25/2019

4

L7e: Quadricycles other than those referred to in category L6e, whose unloaded mass is not more than 400 kg (550 kg for vehicles intended for carrying goods), not including the mass of batteries in the case of electric vehicles, and whose maximum net engine power does not exceed 15 kW.

The Twizy Z.E. model range starts with the 'Urban 45' which is priced at €6,990 in Europe with a monthly battery lease charge of €45. It has an engine power of 4 kW (5 hp), a maximum speed of 45 km/h and can thus be driven in most European countries by drivers from 16 years old.The 'Urban' model features a 13 kW (18 hp) engine and can drive up to 80 km/h (50 mph). It is priced at €7,690 plus a monthly battery lease of €49.

Example: Renault Twizy, L6e/L7e vehicle

2/25/2019

5

1.2 Passenger car categorization

Passenger cars do not have formal categorization further than Category M1. However, models segments tend to be based on comparison to well-known brand models. For example, a car such as Volkswagen Golf might be described as being in Ford Focus size class. VW Polo is smaller, so it belongs one segment below the Golf, while the bigger Passat is one segment above. Some common and accepted segments known are presented in Table

Segment Examples

A: mini cars Renault Twingo, Peugeot 107, Ford Ka

B: small cars Ford Fiesta, Volkswagen Polo, Opel Corsa

C: medium cars Ford Focus, Opel Astra, Toyota Auris

D: large cars Ford Mondeo, Volkswagen Passat

E: executive cars Lexus GS, Mercedes E-Class, BMW 5 Series

F: luxury cars AudiA8, Mercedes S-Class

S: sport coupés Chevrolet Corvette, Porsche 911

M: multi-purpose cars Renault Scenic, Opel Zafira, Ford C-Max

J: sport utility cars BMW X3, Honda CR-V

2 CHASSIS and BODY

2.1 Overview

Chassis is the base frame of a vehicle. Components of a vehicle like engine, transmission, suspensions, controlling systems (braking, steering etc.) and also electrical parts are mounted on the chassis. It is the main mounting for all the components including the body. So it can also be called as carrying unit. During a crash a chassis should provide maximum protection for passengers. Torsional and bending rigidity of a chassis should be as high as possible to ensure a good handling and road holding. Also a high rigidity is essential to minimize deformation of the housing of the movable body components as; doors, hood and luggage-compartment lid.

2/25/2019

6

Body refers to the outside shell of a vehicle. Hood, lid, fenders, doors, roof, windshield and rear-side windows form typical body of a vehicle. Body shape is formed by a number of factors. The main purpose of the bodywork is to provide comfortable accommodation for driver and passengers, with suitable protection against wind and weather. The body must attract customers and should have a good aerodynamic shape to increase dynamic performance of the vehicle. Ergonomics of a body is also an important concern; entering and exiting the vehicle should be practical, reaching the controls should be with a minimum effort etc.

2/25/2019

7

2.2 Most common chassis-body types

Unibody (unitized body) is a design in which chassis and body are built as a single integrated structure This structure offers superior crash protection with the crumple zones and is most spacious among all types. Manufacturing cost of a unibody for high volume mass production is generally lowest. However, high initial investment for large molds of a unibody makes it unfeasible for small-scale production. Unibody construction examples are; passenger cars, SUVs and light commercial vehicles etc.

Conventional unibody is built up of hollow sheet-steel tubes onto which sheet metal panels are welded. Generally, around 5000 spot welds are made along a total flange length of 100-200 m. The parts like front fenders, doors, hood and lid are bolted to the supporting structure of the body.

2/25/2019

8

Ladder chassis is the simplest and oldest of all designs. It consists of two beams and cross members connecting them. The result looks like a ladder. Connecting pieces hold various components such as the engine and transmission. This design is simple and robust but offers poor torsional rigidity to weight ratio. Also poor crash behavior of ladder chassis is due to the lack of crumple zones. Ladder chassis are generally made from steel.

Today, ladder chassis remains the preferred construction method for heavy-duty commercial vehicles especially those intended to carry or pull heavy loads, such as trucks, busses and rugged off-road vehicles

2/25/2019

9

A space frame is a truss-like, lightweight rigid structure constructed from struts in a geometric pattern. Tubes of such a chassis may be curved shaped and subjected to considerable bending moment unlike the conventional space-frame. Components like suspension, engine and body panels are attached to a skeletal frame of tubes.

The body of space-frame chassis has a minor contribution to rigidity and crash characteristics of a vehicle. Common space-frame chassis material are steel and aluminium. Body of space frame chassis is usually made of fiber composites to keep weight low.

Space-frame designs offer best torsional and bending rigidity to the weight ratio among all the chassis types. Therefore, many race cars, sports cars and special purpose vehicles are built with a space-frame chassis. However, this chassis encloses much of the working volume of a vehicle that causes ergonomic problems. Also building a space-frame chassis requires a complex 3D fixture and hard labor. Thus, this design is never used in high volume mass production

2/25/2019

10

Stressed member engine term is used for vehicles where engine and transmission used as an active structural part of chassis to transmit forces and moments. In vehicles where weight reduction is required for performance reasons or simplicity, it is common to observe a stressed member. Tractors and motorcycles are the common applications of this type. Unlike the other vehicles where engine is integrated to chassis with rubber mounts, in stressed member engine type vibration of the engine is directly transferred to the driver. Thus comfort level of the driver decreases seriously.

2.3 Body and chassis materials

Sheet steel of various alloys is used in vehicle chassis and body structure. Sheet thicknesses range from 0.6-3.0 mm, with most pieces being between 0.75 and 1.0 mm thick. Due to the mechanical properties of steel with regard to stiffness, strength, ductility and economy, steel is the most popular material.

In order to reduce weight, aluminium is also commonly used for body and chassis components. There are many chassis that are constructed from aluminium extruded sections and sheet components. Mass produced aluminium bodies are being used increasingly. Nowadays, in order to reduce weight, aluminium can also be partially used for separate body components such as the hood, lid, etc. for vehicles where the rest of the body and chassis is made of steel.

2/25/2019

11

Another body material is the fiber-glass (glass reinforced plastics). Fiber-glass body and body panels are light can be built with relatively cheap molds. Thus fiber-glass bodies are popular among the companies that produce limited numbers of sport cars. For chassis fiber-glass is not preferred due to low strength and ductility of the fiber-glass structure.

Bodies and chassis that are made of carbon-fiber provide best strength to weight ratio among all others. However, carbon-fiber is an exotic material; cost of building a structure made of carbon-fiber is extremely high and labor time is long. Thus carbon fiber is preferred where cost is not very important (F1 cars and expensive sports cars).

For separate body components thermoplastics are commonly used such as bumper, spoiler, radiator grill, mirror casing. In some vehicles whole body is made of thermoplastic to save cost and weight. Also corrosion is not an issue for thermoplastic.

A car with thermoplastic body

2/25/2019

12

2.4 Body surface

One of the most important body-chassis problems is the corrosion particularly in metals. Corrosion is the gradual destruction of materials (usually metals) by chemical reaction with their environment. In the case of metals with iron in them, part of the anode metal becomes rust and weakens. Thus sheet steel is pre-coated (inorganic zinc, electrolytically galvanized, hot-dip galvanized) for the components that are endangered.

Galvanization is the process of applying a protective zinc coating to steel, inorder to prevent rusting. Although galvanization can be made withelectrochemical processes, the most common method in current use is the hot-dip galvanization in which steel parts are submerged in a bath of molten zinc. Itshould be also noted that painting after galvanization also acts as a barrierbetween the metal and oxygen in the atmosphere.

A car body going through galvanization bath

2/25/2019

13

Beside galvanization process to avoid corrosion some geometrical shapes are to be designed accordingly. For example; flanged joints, sharp corners must be minimized. Ventilation of hollow spaces must be added. The surfaces that can hold water must be avoided and if essential, water draining must be opened.

2.5 Aerodynamics

Automotive aerodynamics aims to reduce drag force, wind noise, and preventing lift force. For racing cars and sports car, it is also important to produce downforce to improve road holding.

In the case of ground vehicles since the vehicle moves in air, the major drag source is due to pressure variations. The skin friction is relatively small since viscosity of air is very small. The drag equation is the force of drag experienced by an object during moving through a fluid and given by:

𝐹 =1

2𝜌𝐶𝑑𝐴𝑣

2

Where Cd: drag coefficient, A: vehicle largest cross-section, v: air flow speed, : density of air. This formula is accurate only under certain conditions (blunt form factor and turbulence behind the object requirement) and valid for motion’s most automotive vehicles.

2/25/2019

14

Drag area, Cd.A, is the fundamental parameter that determines aerodynamic resistance which is determined from geometrical shape of a vehicle’s body. Although only Cd (drag coefficient) is given in many sources, solely Cd does not determine the drag force.

Cd CdA (m2) Vehicle

0.7 6 Typical Bus

0.57 2.46 Hummer H2/2003

0.36-0.41 0.74 Bugatti Veyron/2005

0.32 0.576 Toyota Prius/2014

0.26 0.565 Nissan GT-R/2008

1.0 0.5 City Bicycle+Rider

0.25 0.25 Loremo Concept/2006

0.024 Boeing 787

Drag coefficients of various vehicles

Lift is the force that is applied to a body in the direction perpendicular to the air flow. If the direction of this force is towards the ground it is called as down force. A typical ground vehicle (without wings) generates lift by nature of its shape. Too much lift unloads tires of a vehicle, thus road holding and stability is negatively affected at high speeds. Reducing the amount of lift is essential during body design.

2/25/2019

15

In Figure, pressure distribution of a typical sedan car is given. The plus sign (red region) indicates pressure higher than ambient and the minus sign (green region) indicates pressure lower than ambient (not absolute negative pressure or vacuum). According to the region, these pressure variations create drag, lift or down forces.

2/25/2019

16

The Cd value can be influenced by individual aerodynamic or design measures. Airflow

through the vehicle as well as roof-mounted fixtures will always increase the Cd value.

Examples (– = better, + = worse). Examples are given in Table.

2.6 Safety

Vehicle collisions are the leading cause of injury-related deaths, an estimated total

of 1.2 million in a year, or 25% of the total from all causes.

Safety is the study and practice of vehicle design, construction, and equipment to

minimize the occurrence and consequences of automobile accidents.

"Active safety" is used to refer to technology assisting in the prevention of a crash

and "passive safety" to components of the vehicle (primarily airbags, seatbelts and

the physical structure of the vehicle) that help to protect occupants during a crash.

2/25/2019

17

2.6.1 Active Safety

Some common active safety systems are:

Traditional active safety systems:

1-Good visibility from driver's seat:

Obscuration caused by the A-pillars for both of the driver's eyes should be reduced. Rear

cam should be installed for the cases where rear visibility is limited.

2-Low noise level in interior:

Conditional safety results from keeping the physiological stress that the vehicle occupants

are subjected to by vibration, noise, and climatic conditions down to as low a level as

possible. Noises in and around the vehicle can come from internal sources (engine,

transmission, axles) or external sources (tire/road noises, wind noises), and are

transmitted through the air or the vehicle body.

3- Good handling & road holding:

Optimum dynamic vehicle behavior should be obtained by a harmonious chassis and

suspension and consistent wheel, suspension, steering and braking design.

Modern active safety systems:

4- Anti-lock braking system (ABS)

The ABS prevents the wheels from locking when the vehicle is over braked. The

vehicle therefore retains its directional stability and steerability even under

emergency braking on a slippery road surface. The stopping distance is often shorter

than compared to locked wheels. However, on loose surfaces like gravel or snow-

covered pavement, an ABS can significantly increase braking distance, although still

improving vehicle control

2/25/2019

18

A typical ABS includes a central electronic control unit (ECU), four wheel speed

sensors, and at hydraulic valves within the brake hydraulics. The ECU constantly

monitors the rotational speed of each wheel; if it detects a wheel lock, it actuates

the valves to reduce hydraulic pressure to the brake at the affected wheel, thus

reducing the braking force on that wheel; till the wheel is unlocked. This process

is repeated continuously and can be detected by the driver via brake pedal

pulsation. Some anti-lock systems can apply or release braking pressure 15 times

per second.

2/25/2019

19

5- Electronic Stability Control

Electronic stability control (ESC) improves the safety of a vehicle's stability by detecting

and minimizing skids. When ESC detects loss of steering control, it automatically applies

the brakes to help "steer" the vehicle where the driver intends to go. Braking is

automatically applied to wheels individually, such as the outer front wheel to counter

oversteer (rear tires skid) or the inner rear wheel to counter understeer (front tires skid).

Some ESC systems also reduce engine power until control is regained. ESC does not

improve a vehicle's cornering performance; instead, it helps to minimize the loss of

control.

According to Insurance Institute for Highway Safety and the U.S. National Highway Traffic

Safety Administration, one-third of fatal accidents could have been prevented by the

technology.

2/25/2019

20

6-Traction control

Traction control system (TCS), is typically (but not necessarily) a secondary function of

the anti-lock braking system (ABS), designed to prevent loss of traction of driven road

wheels in the cases of wheel slip occurs. The system is actuated by one or more of the

following actions:

•Reduce fuel supply to one or more cylinders

•Brake force applied at one or more wheels

•Close the throttle, if the vehicle is fitted with drive by wire throttle

7- Collision warning/avoidance

A collision avoidance system is a system of sensors that is placed within a car to warn its

driver of any dangers that may lie ahead on the road.

The system uses sensors that send and receive signals from things like other cars,

obstacles in the road, and tell it of any weather or traffic precautions

Passive safety (Crashworthiness)

Crashworthiness is the science of minimizing risk of serious injuries and fatalities in

motor vehicle collisions

1-Vehicle-chassis deformation behavior

There are five basic requirements to be fulfilled by a vehicle chassis during an

accident:

• Maintain Survival Space

• Restrain the Occupants

• Prevent Ejection

• Transfer Energy (survival space acceleration minimization)

• Prevent Fire

2/25/2019

21

The vehicle body is to minimize the accelerations and thus forces acting on the vehicle

occupants in the event of an accident, to provide sufficient survival space, and to

ensure the operability of those vehicle components critical to the removal of

passengers from the vehicle after the accident has occurred.

Crumple zones absorb and dissipate the energy of a collision, displacing and diverting

it away from the passenger compartment and reducing the deceleration impact force

on the vehicle occupants. Vehicles will include a front, rear and maybe side crumple

zones too.

Safety Cell the passenger compartment is reinforced with high strength materials, at

places subject high loads in a crash, in order to maintain a survival space for the

vehicle occupants. (e.g side impact bars)

2/25/2019

22

The yellow area marks; the crumple zone and the orange areas indicate the stiff safety cell.

Two different vehicle body behaviors in a crash

2/25/2019

23

The other main passive safety equipment is

2- Seatbelts limit the forward motion of an occupant, stretch to absorb energy, to lengthen the time

of the occupant's deceleration in a crash, reducing the loading on the occupants body. They prevent

occupants being ejected from the vehicle and ensure that they are in the correct position for the

operation of the airbags.

3-Airbags inflate to cushion the impact of a vehicle occupant with various parts of the vehicle's

interior. The most important being the prevention of direct impact of the driver's head with the

steering wheel and door pillar.

4-Head restraints are attached or integrated into the top of the seats in each seating position to limit

the rearward movement of an adult occupant's head relative to his torso in a crash, so as to reduce

the danger of whiplash.

Padding of the instrument panel and other interior parts, laminated windows, collapsible steering

columns etc.

Crash test:

A crash test is a form of destructive testing usually performed in order to ensure safe

design standards in crashworthiness for various modes of transportation or related

systems and components. Crash tests are performed under attentive scientific and safety

standards. Each crash test is very expensive so the maximum amount of data must be

extracted from each test.

2/25/2019

24

Acceleration, speed and distance traveled, of a passenger compartment when impacting a

barrier impacting a barrier at 50 km/h