Vehicle Body Engineering & safety

welcome to this course on vehicle dynamics we are going to spend the next 35 hours on

understanding the dynamics of vehicle as the name indicates vehicle dynamics simply means

that we are going to study vehicles in motion so we are going to look at how vehicles are

going to behave before we go into a formal introduction of this course let us first look

at what are the books that i am going to follow we will follow that with the syllabus and then brief introduction this will be the first

class this class will be towards motivating you to look at vehicle dynamics

so these are the text books that i am going to follow the text books are you know gillespie

fundamentals of vehicle dynamics a very well-known textbook in this field reza jazar vehicle

dynamics theory and applications springer book hans pacejka tire and vehicle dynamics

slightly advanced when compared to the first 2 books and then bernd heibing chassis handbook

where we will take some data in order to illustrate the practicality of what we are going to see

in this course so i suggest that you periodically look at these books in order to understand what is

being done in this course okay let us now start with the formal introduction this is

going to be chalk and talk i may use or i will use the power point presentations especially

when the figures and the drawings are bit difficult i may use that if it is difficult

to draw in the board or else it will only be with the chalk that i am going to talk

the reason is that i want to give you time to assimilate things especially there will be lot of derivations in this course and it is important that you have the time to assimilate

as i write down these equations hence the course will completely be based on this method

okay we will have the class on mondays tuesdays tomorrow at 8 o’ clock and wednesday at

12 o’ clock okay it has been 3 hours

okay as i told you vehicle dynamics is a dynamics or the vehicle in motion and we are going

to study what happens in motion of course when you talk about vehicle a number of things come to your mind the first thing that come to your mind is the part of the vehicle so

if you study this as a course what constitutes a vehicle just briefly let us review quickly

what are the components of vehicle that will be involved in what we are going to study

now so if you look at the vehicle per se you can broadly classify them into the power module

okay which involves engine and so on the chassis module

and if you want to add you can further divide this and say that you can involve this what

i call as a body module say anything and everything of the vehicle can be brought into these 3

categories for example if you look at the power train or the power which gives the power

to the vehicle you can include the engine which is of course the most important thing for power as well

as other subsidiary equipments or the components which actually take the power to the wheel

so if you look at the power that is given to the vehicle it is given by the engine and

the power that is developed by the engine goes to the wheel so you can include all those

transmission systems that go to the wheel which you can say gearbox etc okay

now if you want you can also in this category include also the axles it does not matter

we are only categorizing them okay if you are looking at the chassis then you are looking

at a number of subsystems which is say for example the suspension systems you are looking

at the steering system

and you are looking at tires and wheels which you can include here or you can include in

the axle system okay of course you are the body okay which makes you comfortable to sit in the vehicle or carry

goods and so on so broadly in other words this is not complete but i know that you know

all these things you know the mechanisms of many of these things so i am not going to cover that broadly vehicle consists of a number of subsystems all these subsystems are going

to act in order that you carry from one place to the other

and so what is the fundamental requirement of a vehicle or what does these subsystems

do when you go in a vehicle? or in other words what are the requirements of the vehicle?

of course it has to carry people do not tell me that it has to carry people yes of course it has to carry people but they have 3 important requirements when it carries people obviously

safety it has to carry people safely it has to carry people comfortably

and of course economically okay so these are the 3 fundamental requirements

if you look at vehicle as it moves

the second category i am not saying it is not important as important as the first one

is the driver interaction with the vehicle so in other words the vehicle has to listen

to the driver

it has to do what he wants him to do and it has to do that again in a prompt and effective

way so in this course this is what essentially we are going to study what are the factors

which affects safety? now when i say safety we are not looking at things like crash that is not our interest

okay that is not our interest so for example when we say safety what is that we mean? for

example when a vehicle takes a turn okay how does it behave? okay when you brake how does

it behave and so on? so when we say safety we are not looking at situations like crash

okay so we are looking at safety for our dynamics point of view comfort we are going to look

at how your comfort as you travel in the vehicle is affected? how do you characterize comfort?

what are the subsystems of the vehicle which you are going to have an effect on comfort? okay how does the road profiles interact with the vehicle and affect your comfort? and more

importantly what defines comfort? so these are the things that we are going to look at in terms of comfort we are not

going to spend lot of time on economical part of your travel but we are going to concentrate

here and there the economics of vehicle operations in this course we are not going to cover for

example engines that is the separate course okay but we will talk about certain other

subsystems like tires how that affects the economics of vehicle motion?

so essentially we will be concentrating on these 3 aspects safety is linked with the

second part of this categorization safety is the result of the vehicle properly listening

to the driver hence that is why i have put that as a second category and that the vehicle

has to listen listen in such a fashion that it is safe for the people inside so we are

going to look that as well okay so for example we are going to pick up the difference between a formula 1 car and for

example the cars you drive what is the difference between that 2? we are going to look at that

kind of very exciting things in this course right so these are the things that we are

going to look at it the same thing can be looked at in different perspective in other

words there are various perspectives to look at these 3 aspects and that is what we are going to cover in the next 30 minutes

in other words a broad picture emerges when we talk about this in terms of a driver this

is simple maybe you very easily understand this and already know it but this gives us

a picture of what we are going to do a driver a vehicle a response and then effect so the

most important thing is that triangle the driver interacts with the vehicle because

of his interaction say for example what is meant by interaction? he may give a steering input he may accelerate the vehicle he may brake the vehicle and so

on so he interacts with the vehicle okay by means of things which are around him okay

because of that there is a response of the vehicle the vehicle responds the vehicle decelerates

the vehicle takes a turn and so on so this is the response to the input okay and the

response may make him modify or not you know depending upon what is the response

so there is a lot of feel depending upon what is the response the driver may modify his

input okay so in other words there is a very close interaction between the driver vehicle

and the response okay the response has another effect the response has an effect on the occupants

of the vehicle so in other words the effect on occupants okay is also important right

now this is what we are going to look at we will not be going into details of what is the effect of the occupants and so on but

we will definitely point out under normal circumstances what is the effect on the occupants?

okay so we are going to look at these 3 things very carefully so the driver of course as

i said accelerates and brakes now how are we going to study this? we are going to study

this using mathematical models

now what do i mean by mathematical model? so i have a vehicle is represented by means

of a set of differential equations so vehicle which was introduced 5 minutes back to have

subsystems consisting of a number of them okay can be also looked at from a very different

perspective okay as a set of differential equations okay so this forms a very important

part of this course or the core of this course a mathematical model of the vehicle

so what are the things that participate in this mathematical model will come to that in a minute so this mathematical model will have an input okay which will be from the

driver so we are going to deal with this input and you will get a set of output so in other

words the vehicle will be reduced to a system with an input and an output of course you

can add a feedback you can modify this like in what you did in control systems and so

on we will do that we will use a lot of control system concepts in this course okay we will

of course revise some of them as we go along but the perspective now of a vehicle is that

of a mathematical model okay so what is this mathematical model and what is it based on?

very simple all of us know it okay when you talk about dynamics we have to talk about

newton we have to talk about euler of course we have to talk about newton-euler equations

and so on so these equations okay will form the basis of our development of mathematical model so

that being the basis the language of defining the vehicle is going to be different it is

not in terms of the subsystems which we had defined it will be in terms of mass of the

vehicle we will talk in terms of moment of inertias of the vehicle moment of inertia

and say i xx i yy and i zz and so on okay

we will see that we will use 3 moment of inertias and not i xy and so on we will talk about

stiffness or in other words we will include in this stiffnesses we will talk about the

stiffness of the springs which form a part of the suspension system we will talk about

damping so damping stiffness these are the things that enters into the mathematical model

the other things which enter into the model are compliances just opposite of stiffnesses

and there are going to be very special terms which may also be used here and we will introduce

that as we go along so in other words the mathematical model looks at the vehicle from

a very different perspective or in terms of very different quantities whose definition

most of it at least you already know clear okay so i hope you remember all the dynamics

that you did in your previous classes which will be used and which will be applied in this course clear

from another perspective the vehicle dynamics study can be broadly classified into what

is called as longitudinal dynamics

lateral dynamics and vertical dynamics in other words a mathematical

model covers the vehicle behavior in the longitudinal direction the lateral direction which is perpendicular

to the vehicle and in the vertical direction okay as it goes over a bump or as it goes

in a rough road and so on so basically the mathematical models are the ones which are written in such a fashion that

we understand what happens in these 3 directions clear okay now you may ask a question what

is this input? say steering behavior what do you mean by steering behavior? what is

deceleration acceleration and so on? because the question that may come to your mind is when i drive my vehicle in a crowded road okay in the traffic then i give all sorts

of inputs okay it can be a sudden braking or i can do a maneuver which is very fast maneuver i can do lane

change and so on in other words there are so many things that i do when i drive the

vehicle and what do you mean by this input and what are the types of input that you are

going to give or in other words are you going to create every scenario that happens outside

on the road here in order to understand the vehicle behavior

very important to understand that first that we are not going to build scenarios in this

course and that is not what when you develop a vehicle v2 there are a set of standard tests

okay which are available in order to understand the vehicle in other words there is an iso

standard which tells you what are the inputs that are required in order to understand the

vehicle behavior so we have iso standard for understanding the vehicle behavior these are called by different

names and there are number of them okay so i am going to list a few of them not going

to complete list here but we will see that later in the course so when we come to the

input part we are going to talk about say for example you want to overtake a vehicle

in the actual scenario okay suppose you are driving in a highway and you want to overtake a vehicle of course i want

to understand how my vehicle is going to behave if i want to overtake a vehicle okay and so

what do you do? suppose the vehicle is going like this and there is a vehicle before you

so in order to overtake the vehicle you go okay and then you go back right so you do

what is called as double lane change

so there is a test called double lane change okay or you can just do a single lane change

right in other words which to a great extent mimics what happens in reality but there are

other tests which may not exactly mimic but is used in order to understand the dynamics

of the vehicle they are much more technical for example there will be a test which we

will talk about a lot in this course which is called as the pulse test or pulse steer

in this test i am going to give a steering input okay 40 degree change in less than a

second okay so i just change it and then bring it back right this is called a pulse test

you may ask me are you using this anywhere? may not or will not be using it in your day

to day driving but it brings out the dynamics of the vehicle okay so this is one of the

tests that we will be doing or which will be given as an input to this

in other words input has been very carefully defined by this iso standard in order to understand

the dynamics of the vehicle okay or to bring out certain scenarios there is other tests

like constant radius cornering or constant radius tests and there are tests okay which

say for example there is a test called j-hook test and so on which bring out extremity conditions

so in other words what is that we are going to do or what is usually done? there are tests the tests involve either an input through steering or through brake and

acceleration we will mostly be using braking conditions okay so these conditions there

are number of tests these tests are given as an input to this mathematical model which

is based on a good old newton-euler techniques and so on now what are the outputs that we

are going to look at? okay ultimately as i said i want to look at comfort level i want to look at safety this

is what i said the whole ideal of studying vehicle dynamics is to study the safety economics

and so on let us take the condition of braking let us say that i want to brake a vehicle

okay suddenly i see some obstacle and i want to brake the vehicle okay so i said that i

want safety during braking actually what does it mean or how does this output look like?

if i want to be safe then i have to look at braking distance for example i cannot have

a vehicle whose braking distances are large we will see what typically they are later is large right if the braking distances are large then obviously i am not going to satisfy

this condition of safety and i may go and crash with that obstacle so in other words

we are going to look at as outputs okay quantities which are related to what i said before

this at least is simple braking distance okay so we are going to look at that kind of output

distance and there are other outputs that typically what i said is that we are going

to go back to newton “professor - student conversation starts” so what are the things when you look at newton’s equation? what are the things that comes to your mind? lateral

and longitudinal dynamics “professor - student conversation ends” yeah so what comes to your mind is accelerations what comes to your mind is velocity and so

on right so the outputs will now be in terms of these quantities distances accelerations

velocities and so on there will be other things we will see that later but all of them are

to do with the dynamics clear now how is this related to say for example comfort? i may

ask you a question okay you get acceleration how do i deduce my comfort levels or in other words what is the effect?

so this is the output response is the output yes i can understand that if the braking is

not happening as the driver wishes it to be maybe he can jam or press the brakes hard

fine that i understand okay from braking distance if you want to reduce the velocity or increase

the velocity he either presses the brake pedal all that i can understand okay

but you are talking about effect of the occupants what is that? you know say for example i want

to be comfortable sitting in the back seat and you know enjoying my ride so how does

this give me or how does this outputs give me that feeling of goodness? so whole lot

of research has been done as to how say for example the acceleration levels affect your

comfort levels inside the vehicle or in other words we will map certain of the outputs like for example vertical acceleration

okay lateral acceleration and so on we will map them into your comfort level by lot of

research has been done on this topic map them into your comfort level okay and tell you

what is the effect of the occupation so it is a large topic we are going to give a glimpse of this towards the end of the course as to the effect

the cause and the effect on the occupants clear so in a nutshell this is what we are

going to look at in this course we are going to look at first the mathematical model input

output and so on clear okay in order to understand the mathematical model itself okay we will

introduce to you or i will introduce to you a certain technical information to write down

these equations if you remember newton’s equations on one side we have quantities or newton-euler equations

if you want to call it you have these quantities on the left hand side or right hand side however

you write on the other side of the equation you have forces moments and so on so we have

to understand those as well so i should add to these lists the right hand side of the

equation which i would call as generalized force moment and so on okay

so we also have to understand the source of these forces how does this force originate?

how does it act on the vehicle? how is it transferred to the vehicle? so this is one

of things also when we come to the mathematical model becomes important just to give you an

example if i have to brake the vehicle or accelerate the vehicle then i need a braking

force and a traction force alright yeah you can tell me that the braking force emanates when i press the brake pedal yes

of course that is the braking system but we are not going to look at you know the braking

system per se in this course but ultimately as a vehicle when it brakes the forces emanate

from that interface between the tire and the ground so we are going to look at actually

how the vehicle talks to the road how actually the traction is developed? how actually the force is developed? so when you

take a turn also you should look at what generally called as the grips

in all these conditions i have to talk about the grip of the vehicle or grip of the tire

okay with the road so in that process of understanding the mathematical model we will go into the

details of tire mechanics and tire behavior because that forms the basis for one of the

quantities on the right hand side there are other quantities as well

the other quantity or other force which is important in that mathematical model is aerodynamic

forces

so we have to look at the aerodynamic forces how do they act on the vehicle? and what are

the design parameters of the vehicle which affects aerodynamics? we will follow let say

a book at that time i will give you a reference so we will follow that also in this course

okay and there will be a short introduction on aerodynamics the effect of the body okay on

the aerodynamic forces okay so in other words yes there is i would say an environmental

interaction with the vehicle and this is due to various components body of the vehicle

and so on so we are going to look at that because that forms a basis for the vehicle

model right okay this is we are talking about the equation part of it okay so the point of view i do

not want you to get confused is at force is force and input or an output so you may look

at it like that yes okay braking force can be an input but in the equation that is formed

okay the force naturally comes and that is why i wrote this along with that equation

clear any questions? so the view that we are going to take is that we have a mathematical

model we have an input and we have an output okay because of this mathematical model

and how does the vehicle behave or how is that i convert a vehicle into a mathematical

model? so that is the perspective that we are going to look at in this course clear

okay we are going to introduce of course a number of terminologies no course is complete

if you do not understand the words call it jargons or call a technical terms okay the

course is not complete unless you understand these terms so you cannot converse okay or express your ideas if you do not understand the corresponding

language of a course so from that perspective there will be a lot of new jargons or definitions

or terms that we will introduce in this course okay how does this jargons look like? okay

let us look at it from a different perspective so we now know what we are expecting from

this course? what is that we are going to do? the other way of looking at it also the another perspective is look at the course or look

at what we are going to study from 3 different angles the first angle is what i call as driving

dynamics same thing but termed in a different way another what i would call ride comfort

and the third one is safety okay so when i say jargon what are the type of things that

we are going to introduce? so of course when i say driving dynamics i am going to look at the vehicle in driving

dynamics the first thing that comes is straight-line tracking where we are studying we want to

study the vehicles interaction with the external atmosphere we are going to see simple things

first we are looking at maneuverability then we are going to introduce some other jargons we are going to introduce things like

self-steer behavior watch out that from the terms which you understand from pure english

we are going to terms which you are not going to make out that easily unless you know the

definitions so self-steer behavior if i am going to define now you would not understand

anything but we are going to do that later is the difference in the slip angle between the front and the

rear tires does not make sense right now to you okay but we are going to talk about this

okay what is called a slip angle? how is slip angle developed and so on? we are also going

to study driving dynamics okay since it is dynamics okay and this is a dynamical system

or system which is controlled by equations from dynamics immediately you would say that that can be what are called as oscillatory behaviors

and does the vehicle also have this oscillatory behavior? if so how does that affect the vehicle?

there are lot of very interesting things happen when you give or when you maneuver a vehicle

things like what is called as load shift you would have realized that when you take a turn

in a vehicle you would have realized that okay you are pushed to one side and then you can easily

realize that there is going to be load shift okay in other words certain of this driving

dynamics gives rise to certain effects like for example load shifts so maneuverability

changing gives rise to load shifts okay

now one of the things that i want why i am writing one of the things i want you to realize

is that your mathematical model should be able to capture all that driving dynamics

okay which i am going to put forth here so when i say there is a load shift okay the

first thing you have to ask is is this going to captured by my mathematical model? you

will see that mathematical model is a general term there are simple models the simplest model you can think of is just vehicle consisting

of mass m okay one mass the vehicle as an acceleration a okay and has a force opposing

its motion so a becomes deceleration will call that s a we will not call acceleration

deceleration every time we just call that depending about positive or negative you can come to your own conclusion

so you can look at simple mathematical model f=ma right this does not talk about various

driving dynamics so that is the reason why i have put this on the other hand this also

does not talk about what happens when the vehicle goes over a bump goes over a rough road and all these things right so mathematical model is a very general term okay

and that you have to understand many of these things in order to understand the limitations

or what can be achieved using the mathematical model so if i just give you a braking force

and if i say mass is this one tell me the deceleration okay simple calculation back

of the envelop you can tell me what is this from this equation okay now when i say that

the vehicle is taking a turn i want to know what is the role of the vehicle and so on

this would not work so in other words what is also required is a proper understanding of the physics okay

which would be the result of your input and whether your mathematical model will capture

that physics okay so from that sense mathematical model can be very simple like what we had seen or it

can be complex and the complexity is increased as we increase what is called as the degrees

of freedom as we increase the degrees of freedom so that is the reason why we look at driving

dynamics suppose i want to look at oscillatory motion of the vehicle as it goes over a bump

okay you would immediately reject this and you would go back to your vibration class and

say oh this we had studied okay that is the vehicle let me replace all your suspension

by a spring okay let me replace the damping bla bla bla of the suspension system by a

damper okay so let me say that the tire is just another spring and that the tire goes

over a rough road and so on so what did i do?

the same vehicle okay a different mathematical model or a different view of the vehicle’s

behavior i have given and the type of degrees of freedom here what i have chosen is different

from what i have given here and so on so the mathematical model in simple terms should

capture what you want to analyze in driving dynamics okay in other words whether it is

a longitudinal dynamics or vertical dynamics or you can say lateral dynamics because it

should be able to capture the vehicle it is usual practice to start with to d-link the behavior of the vehicle in the longitudinal

direction okay in the vertical direction and in the lateral direction i can d-link them

okay and study them with simple models as if nothing happens in the other directions

so this model quite good maybe you would have done problems in vibration class with this

kind of models for the vehicle but if i ask you what happens during a cornering behavior you know i am going to say that so

in other words i will have another model so the models can also bring out the behavior

in a particular direction or a particular dynamics clear okay we will go into some details

on the technicalities that have involved before we jump into what is going to be the longitudinal

dynamics? in other words we are going to have models which are like this but much more complex

than this okay to study longitudinal dynamics so the intellectual property right of this

whole thing belongs to newton-euler and we have to salute him for whatever he has done

to us with that we will stop this class and we will continue in the next class