ELECTRIC AND HYBRID VEHICLES - PowerPoint Presentation

Slide1

ELECTRIC AND HYBRID VEHICLES

Slide2

Hybridization

Ratio

Some new concepts have also emerged in the past few years, including

full

hybrid,

mild

hybrid, and micro hybrid.

These

concepts are usually related to

the power

rating

of the main electric motor

in a HEV. For example, if the HEV contains a fairly

large

electric

motor and associated batteries, it can be considered as a full hybrid. On the

other

hand

, if the size of the electric motor is relatively small, then it may be considered as

a

micro

hybrid

.

Slide3

Typically, a full hybrid should be able to operate the vehicle using the electric

motor

and

battery up to a certain speed limit and drive the vehicle for a certain amount of

time.

The

speed threshold is typically the speed limit in a residential area. The typical

power

rating

of an electric motor in a full hybrid passenger car is approximately

50–75 kW.

Slide4

The micro hybrid, on the other hand, does not offer the capability to drive the

vehicle

with

the electric motor only. The electric motor is merely for starting and stopping

the

engine

. The typical rating of electric motors used in micro hybrids is

less than 10 kW.

A

mild

hybrid is in between a full hybrid and a micro hybrid.

Slide5

An effective approach for evaluating HEVs is to use a hybridization ratio to

reflect

the

degree of hybridization of a HEV.

In

a parallel hybrid, the

hybridization ratio

is

defined

as the ratio of electric power to the total powertrain power.

Slide6

For example, a HEV

with a motor rated at 50

kW and an engine rated at 75

kW will have a hybridization

ratio of 50/(50+75)kW=40%.

A conventional gasoline-powered vehicle will have a

0% hybridization ratio and a battery EV will have a hybridization ratio of 100%. A series

HEV will also have a hybridization ratio of 100% due to the fact that the vehicle is

capable of being driven in EV mode.

Slide7

Interdisciplinary

Nature of HEVs

HEVs involve the use of

electric machines, power electronics converters, and batteries,

in

addition

to conventional ICEs and mechanical and hydraulic

systems.

The

HEV

field

involves

engineering

subjects beyond traditional automotive engineering, which was

mechanical

engineering

oriented.

Power

electronics, electric machines, energy storage systems,

and

control

systems

are now integral parts of the engineering of HEVs and PHEVs.

Slide8

The general nature and required engineering field by HEVs

Slide9

In addition,

thermal management

is also important in HEVs and PHEVs, where

the

power

electronics, electric machines, and batteries all

require a much lower

temperature

to

operate properly,

compared to a non-hybrid vehicle’s powertrain components

.

Modeling

and

simulation, vehicle dynamics, and vehicle design and optimization

also

pose

challenges

to the traditional automotive engineering field due to the increased

difficulties

in

packaging the components and associated thermal management systems, as well as

the

changes

in vehicle weight, shape, and weight distribution.

Slide10

State of the Art of HEVs

In the past 10 years, many HEVs have been deployed by the major automotive manufacturers

.

It is clear that HEV sales have

grow

significantly

over

the last 10 years.

Slide11

Breakdown of HEV sales by model** in the United States in 2009 (in thousands)

Slide12

The

Toyota

Prius

(2010 model)

Slide13

Partial list of HEVs available in the United States

Slide14

The powertrain layout of the Toyota Prius (EM, Electric Machine; PM,

Permanent

Magnet

)

Slide15

The powertrain layout of the Honda Civic hybrid

Slide16

The Ford Escape hybrid SUV

Slide17

The Chrysler Aspen two-mode hybrid

Slide18

Challenges and Key Technology of HEVs

HEVs

can overcome some of the disadvantages

of battery-powered pure EVs and

gasoline

-

powered

conventional

vehicles.

These

advantages

include

:

optimized

fuel

economy

,

reduced

emissions when compared to conventional

vehicles

,

increased range

reduced

charging

time,

reduced

battery size (hence reduced cost) when compared to pure EVs.

Slide19

However, HEVs and PHEVs still face many

challenges

:

including

higher cost

when

compared

to conventional

vehicles

,

electromagnetic

interference caused by

high-power

components

,

safety

and reliability concerns due to increased components and

complexity,

packaging

of the system,

vehicle

control,

power management

.

Slide20

CONCEPT OF HYBRIDIZATION

OF THE AUTOMOBILE

Vehicle

Basics

Constituents

of a

Conventional

Vehicle

Present-day engine-propelled automobiles have evolved over many years.

Today’s

automobiles

initially started with steam propulsion and later transitioned into ones

based

on

the internal combustion engine (ICE).

Slide21

Cutaway view of an ICE

Slide22

The engine has a chamber where gasoline or diesel is ignited, which creates a

very

high

pressure to drive the pistons. A piston is connected through a reciprocating arm

to

a crankshaft.

The crankshaft is connected to a flywheel

which

is

then connected to a transmission system. The purpose of the transmission system

is

to

match the torque speed profile of the engine to the torque speed profile of the

load.

The

shaft from the transmission system is ultimately connected to the wheels

through

some

additional mechanical interfaces such as differential gears.

Slide23

Transmission system and engine connected together

Slide24

Vehicle

and Propulsion

Load

The power generated from the engine is ultimately used to drive a load. In an

automobile

this

load includes

the road resistance due to friction, uphill

or

downhill drive

related

to the road profile, and the environmental effect of, for example, the wind, rain, snow,

and

so

on.

In

addition, some of the energy developed in the vehicle is wasted in

overcoming

the

internal resistance within the vehicle’s components and subsystems, none of

which

are

100% efficient.

Examples

of such subsystems or components include the radiator

fan,

various

pumps, whether electrical or mechanical, motors for the wipers, window lift,

and

so

on. These items are just a few examples from a whole list of vehicular loads. The

energy

lost

in these devices is released eventually as heat and expelled into the atmosphere.

Slide25

Normally “load” can be related to the

amount of opposing force or torque.

But a

more

scientific

definition of load comes from the fact that it is not defined by a single number

or

numerical

value.

Load

is a collection of a set of numbers defined by the speed–torque

or

speed–force

characteristics in the form of a table or graph, that is, through a

mathematical

equation

relating speed and torque.

Similarly

the engine is also defined by

speed–torque

characteristics

in the form of a table or graph, that is, through a mathematical

equation.

The

operating point of the combination of the engine and the load system together

will

then

be at the intersection of these characteristics.

Slide26

Load and engine characteristics of a vehicle

Slide27

A complete vehicle or automotive system has various loads. Some of these are

electrical

devices

, and others are mechanical devices. The electrical loads are normally run at a

low

voltage

(nominally 12 V). The reason for this, i.e. running the non-propulsion loads

at

low voltage, is primarily related to safety issues. There is an existing

manufacturing

base

for many of these non-propulsion loads (as indicated below), where it is easier

to

take

advantage of the situation and use the existing low-voltage components, rather

than

transform

the

voltage

system

.

Slide28

Examples of these loads are:

brakes – mechanical (hydraulic or low-voltage electrically assisted);

air-conditioner

–

generally

mechanical

;

radiator

fan – can be belt driven mechanically (or low-voltage electrical);

various

pumps – can be mechanical (or low-voltage electrical);

window

lift –

electrical

;

door

locks

–

electrical

;

wipers

–

electrical

;

various

lights – non-motor load, low-voltage electrical;

radio

, TV, GPS – non-motor, low-voltage electrical;

various

controllers

–

for

example

, engine

controller

,

transmission

controller

,

vehicle

body

controller

;

and

various computational microprocessors – non-motor, low-voltage electrical.

Slide29

Drive Cycles and Drive Terrain

Since a vehicle will be driven through all kinds of road profiles and environmental

conditions,

to

exactly know beforehand about which loads the vehicle will encounter under

all

circumstances

is

difficult

.

It is of course possible for one to perform experiments and

place

sensors

etc. to monitor the speed and torque of a vehicle, but to do so under all

circumstances

for

all vehicle platforms is simply impossible.

Slide30

Hence, for the

engineering

studies

, a few limited situations have been developed which more or less cover

typical

road

profiles and the terrains one can expect to encounter

.

Using a

few of these profiles,

one can create or synthesize various arbitrary road profiles.

Such

profiles

can

involve

things like driving within a city, on a highway, across some

special uphill or

downhill

terrain

, to name

but

a few.

Slide31

Drive cycles only provide time,

an

corresponding

speed

fluctuations,

and

labels attached to these tell us what kind of drive cycle it is, for

example,

city

, highway, and so on

.

So, if a vehicle goes through different driving situations, partly city, partly

highway,

and

so on, then one can obtain speed vs. time data by synthesizing multiple

typical

drive

cycles

.

Slide32

A typical automotive drive cycle

Slide33

The question then arises about the ways to utilize the drive cycle information.

Assume

that

we want to know about the fuel economy of a particular vehicle X. It is not

sufficient

to

say that vehicle X does 25 MPG. We also need to say under what conditions this

was

obtained

. That is, whether it was under a city drive cycle, or highway drive cycle,

and

so

on. Then one can compare another vehicle Y against X, under similar drive

cycle

conditions

, and make a fair comparison.

Slide34

As there are different kinds of drive cycles, that of a passenger car cannot be

compared

against

the drive cycle of a refuse truck or a postal mail vehicle, since they have

very

different kinds of stop and go driving.

Similarly

the drive cycle of a heavy mining

vehicle

cannot

be compared with the above either

.

Slide35

Finally, it should be noted that a drive cycle concerns the road profile through

which

a

vehicle goes and hence is a situation external to the vehicle.

However

, the

response

of

a vehicle to a given drive cycle, in terms of fuel economy, will be different

depending

on

whether the vehicle is a regular ICE vehicle, fully electric vehicle (EV), hybrid

electric

vehicle

(HEV), and so on.

Slide36

Basics of

the

EV

Why

EV

?

Although these days people talk more about HEVs which have become very

popular,

their

underlying system is complex because it has two propulsion sources. A pure

EV

is

relatively

simpler

since it has only one source of energy, that is,

a battery or perhaps

a

fuel

cell.

Similarly

its propulsion is performed by an electric motor and the need for

an

ICE

is not there. If the ICE is gone, the vehicle will not need any fuel injectors,

various

complicated

engine controllers, and all the other peripherals associated with the

engine

and

transmission. With a reduced parts count and a simpler system, it will be more

reliable

as

well

.

Slide37

In addition, an EV is “virtually” a zero-emission vehicle (since nothing has

technically

zero

emissions in a true global sense).

Of course, if one considers the ultimate

source

of

energy, by tracing the path backward from the battery to the utility industry, it

will

be

found that the location of pollution has been essentially shifted from the vehicle

to

elsewhere

.

Furthermore

, an EV is virtually quiet. In fact it can be so quiet that

people

have

even talked about introducing

artificial noise

in the vehicle so that they can

hear

it

, which is something important to know from a

safety point of

view.

Slide38

From a technical viewpoint, the EV has another benefit. In the ICE, which is a

reciprocating

engine

, the

torque produced is pulsating

in nature. The flywheel helps

smooth

the

torque which would otherwise cause vibration. In the EV the motor can create a

very

smooth

torque

and, in fact, it is possible to do away with the flywheel, thus saving

material

and

manufacturing cost, in addition to reducing weight.

And

finally, the efficiency of

an

ICE

(gasoline to shaft torque) is very low. The engine itself has about 30–37%

efficiency

for

a gasoline and about 40% for a diesel engine, but by the time the power arrives

at

the

wheel, the efficiency is just 5–10%. On the other hand, the efficiency of the

electric

motor

is very high, on the order of 90%. The battery and power electronics to drive

the

motor

also have high efficiency. If each of these components has an efficiency on

the

order

of 90%, by the time the battery energy leaves the motor shaft, the overall

efficiency

will

be something like 70%. This is still substantially higher than that in the ICE.

Slide39

Constituents

of an EV

The complete EV consists of not only the electric drive and power electronics

for

propulsion

, but also other subsystems to make the whole system

work.

O

ne

needs

a battery (or a fuel cell) to provide the electrical energy.

Slide40

System-level diagram of an EV.

Slide41

Vehicle

and Propulsion

Loads

There is a significant amount of commonality between the loads in an EV and a

regular

automobile

. Hence, just like a regular vehicle, some of these loads are electrical

devices

and

others are mechanical devices. As noted earlier, those loads which are

electrical

normally

run at a low voltage (nominally 12 V), with the exception of the propulsion

load,

that

is, the propulsion motor, which runs at a high voltage (several hundred volts).

The

reason

for this has to do with safety primarily. And, of course, the existing

manufacturing

base

for many of these non-propulsion loads can be used to advantage by using

the

existing

low-voltage components, rather than transforming the voltage system.

Slide42

Examples

of these loads are same as those noted

previously

:

propulsion or traction motor – high-voltage electrical load;

brake

motor (if a fully or partially electrical brake system is used) – low voltage;

air-conditioner

motor (if electrical) – low voltage;

radiator fan

(if electrical) – low voltage;

various

pumps (if electrical) – low voltage;

window

lift –

low

voltage

;

door

locks

–

electrical

;

wipers

–

electrical

;

various

lights – non-motor load, low-voltage electrical;

radio

, TV, GPS – non-motor, low-voltage electrical;

various

controllers, for example, engine controller, transmission controller, vehicle body

controller

;

various

computational

microprocessors

,

digital

signal

processors

(

DSPs

) –

non

-motor,

low-voltage

electrical

.

Slide43

The above list more or less covers the various loads in the vehicle, including

propulsion

loads

. The propulsion load can be several kilowatts for a mild hybrid vehicle

regenerative

braking

system, up to say 50kW or a few hundred kilowatts for propulsion in a

hybrid

vehicle

. The various pumps and fans can be only a few hundred or less watts,

whereas

some

small motors like door lock motors could be just a few tens of watts. Similarly

the

lights

can range from a few tens to about a hundred watts.

Slide44

Basics of

the

HEV

Why

HEV

?

P

revious

ly

we discussed the architecture of a purely EV. As we saw, the

EV

propulsion

uses an electric motor for propulsion. The energy comes from the battery (

or

perhaps

a fuel cell). The battery bank in a pure EV can be quite large if the vehicle

is

to

go a few hundred miles on one full charge to begin with. The reason for this is

that

battery

technology, as it stands today, does not have a very high energy density for

a

given

weight and size, compared to a liquid fuel like gasoline. Although new

batteries

like

lithium-ion batteries have a much higher energy density than the existing lead

acid

or

nickel metal hydride batteries, it is still much lower compared to liquid fuel.

Slide45

As noted earlier, the HEV is a complex system since it has

two propulsion

sources.

Comparatively

a pure EV is simpler since it has only one source of energy, namely,

a

battery

or perhaps a fuel cell. In the EV the propulsion is produced by only the

electric

motor

and there is no ICE. This removes the need for fuel injectors, complicated

engine

controllers

, and all other peripherals. Hence, with a reduced parts count, the system

is

simpler

and

more

reliable

.

Slide46

Of course, there is an efficiency improvement in the HEV compared to the ICE, but

it

will

still be lower than in the EV. The overall efficiency will depend on the relative

size

of

the ICE and the electric propulsion motor power.

Slide47

A variant of the HEV is found in locomotives and in very high powered

off-road

vehicles

. In a number of variants of such systems there is no battery. The ICE is

used

to

drive a generator which creates

AC power.

This power is translated to DC and

then

to

another AC power required to drive an electric motor.

The

problem with this

system

is

that the engine has to be run continuously to produce the electricity. The

advantage

is

that it does not need a battery. Furthermore, the ICE can be run at an optimal

speed

to

achieve the best possible efficiency. One problem with this system is that it does

not

lend

itself to regenerative energy recovery during braking. The battery helps

regenerative

energy

recovery by allowing storage and it can also be coordinated more optimally

in

terms

of when the ICE or the electric motor should be run.

Slide48

Constituents

of a HEV

As noted

earlier

, an EV is simpler than a HEV

.

As we can see, the only difference between this diagram and the one for the EV is

that

this

one has an additional subsystem called

IC engine,

along with the necessary

interface

and

the controller. Otherwise the two diagrams are identical.

Slide49

System-level diagram of a HEV.

Slide50

Basics of Plug-In Hybrid Electric Vehicle (PHEV)

Why

PHEV?