ELE293: INTRODUCTION TO ELECTRIC AND HYBRID VEHICLES

Contents

• Introduction to Hybrid Electric Vehicles

• Micro, Mild and Full Hybrid Vehicles

• Components and control of HEV

• Battery Charging in HEVs

• Plug-in Hybrid Vehicles

• Series/Parallel/series-parallel HEVs

Introduction to HEVsThe power train of a HEV is quite complex because it

contains all the components of an ICE vehicle plus mostof the components of a pure electric vehicle (EV). Also,depending on the level of hybridization, it needs twoenergy sources, the fuel tank for the engine and abattery for the electric machine.

If we have an ICE vehicle, in order to transform it into aHEV, we need to add:

a high voltage battery (between 200 and 400 V)a power electronics controller (inverter)an electric machinea DC-DC converter

The main disadvantages of a HEV are: it’s adding more weight tothe vehicle due to additional electric components, it’s moredifficult to build and the total price of purchasing andownership increases (compared to a ICE vehicle).

A hybrid electric vehicle can perform at least one or more of the following functions:

engine idle stop/start

electric torque assistance (fill and boost)

energy recuperation (regenerative braking)

electric driving

battery charging (during driving)

battery charging (from the grid)

Why Hybrid Vehicles

• There are three main reasons for which the automotive manufacturers are developing and selling HEVs:

• reduction of the CO2 emissions (by reduction of the fuel consumption)

• reduction of the exhaust gas toxic emissions

• improvement of the power train dynamics (by increasing total power and torque)

Degree of hybridization is the ratio of power developed by anelectric motor in a hybrid vehicle to the total power consumed bythe vehicle hybridization. According to the degree ofhybridization the vehicles can be classified has Micro, Mild, Fullor Plug-in Hybrid.

Types of HEVsMicro HEVs have a degree of hybridization of less than 5%. Theelectric motor, in the form of a small integrated starter/generator,is used to shut down the engine when the vehicle comes to acomplete stop and start it up when the driver releases the brakepedal. Once in motion, the vehicle is propelled by ICE and the EMdoes not provide additional torque to the vehicle, the fuelefficiency increase around 5 to 10% with the use of a micro HEVssystem

Image: Renault 1.6 dCiengine (Micro Hybrid)Credit: Renault

An example for idle stop/startand energy management functions isthe Renault engine 1.6 dCi. It comeswith an Energy Smart Management(ESM) function which allows energycreated under braking and decelerationto be stored in the low voltage battery,helping to further reduce fuelconsumption.Vehicles that have idle stop/start andenergy management functions arecalled Micro Hybrids.

• Mild HEVs are very similar to a micro HEV, but with anincreased size of the EM of up to 10% of the ICE power and abattery which permits power assist during vehicle propulsion.Typical fuel efficiency increases for mild HEVs are in the rangeof 20%–30% for real-world driving situation when comparedwith a non-hybrid .

• This hybrid only supports assist mode and regenerativebraking mode. Battery size is lower than full hybrid and it isoperated only in charge sustaining zone. Volvo 7900 Hybrid isan example of this type of hybrid.

Types of HEVs

Mild Hybrid electric vehicles (MHEV) there are two distinct types:

(i) with a belt-integrated starter generator(ii) with a crankshaft-integrated motor generator

The belt-integrated starter generator (BiSG) is using an electric machinemounted on the front end accessory drive (FEAD), being connected with theinternal combustion engine through a belt. This is the most commons solutionused by the automotive manufacturers for mild hybrid electric vehicles. Valeohas developed a BiSG system for MHEV, which is used by several vehiclemanufacturers.

The crankshaft-integrated motor generator (CiMG) is using an electric machinefitted on the crankshaft, between the engine and transmission. An example ofCiMG system is the Integrated Motor Assist (IMA) technology from Honda. Themain difference between the BiSG and CiMG is that the crankshaft-integratedmotor generator solution is using a more powerful electric machine and anbattery with higher voltage and power.

• Full HEVs, the EM and batteries are significantly bigger thanthose of the micro HEVs and mild HEVs. As such, dependingon the vehicles power demand, the electric motor can beused as the sole power source. Compared to micro HEVs andmild HEVs, full HEVs have much smaller engines and requiremore sophisticated energy management systems. Typical fuelefficiency increases for full HEVs are around 30%–50% forreal-world driving compared to a non-hybrid.

• Volvo 7900 Electric Hybrid is available in market with fullhybrid architecture. Other modes like assisting the vehicle athigh power demand time and assisting at the event of brakingvia regenerative braking are also available.

Types of HEVs

Comparison of HEVs

Drive train• Electric Motors/Controllers

• Electric Energy Storage systems

• Hybrid power units

• Transmission

• Basic Components

– An Armature or Rotor

– A Commutator

– Brushes

– An Axle

– Field Magnet

– DC Power Supply

Electric Motors/Controllers

Electric Motor/Controllers Advanced electronics allows the motor to act as a generator

Draws energy to accelerate and regenerates the battery when slowing down

Motor uses magnets and magnetism to create motion

Electric Energy Storage Systems• Batteries: Lithium Ion and Nickel-metal hydride batteries

• Ultracapacitors

• Flywheels

Electric Energy Storage Systems

Desirable attributes:

High-peak and pulse specific power

High specific energy at pulse power

High charge to maximize regenerative braking

Long life

Challenges:

Accurate techniques to determine battery state of charge

Develop abuse-tolerant batteries

Recycleability

Batteries Nickel-Metal Hydride Lithium Ion

Current Uses Computer and Medical equipment Laptops and Cell phones

Life Cycle Much larger than lead acid batteries Low

Current

contribution

Used successfully in low production

of HEVs

Challenges High Cost

High self-discharge

Heat generation

Control losses of hydrogen

Low cell efficiency

Life cycle

Cell and battery safety

Abuse tolerant

Acceptable cost

Miscellaneous Reasonable specific energy and

power

Components are recyclable

Abuse-tolerant

High specific energy and power

High energy efficiency

Good high-temperature

performance

Low elf-discharge

Recyclable parts

NA

Energy Storage: Ultracapacitors

Store energy as an electric charge in a polarized liquid layer between an

ionically electrolyte and conducting electrode

Primarily used for acceleration, climbing hills and regenerative braking

Energy Storage: Flywheel

Store kinetic energy within a rapidly spinning

wheel

Complex, heavy, and large

Contains no acid or hazardous material

Not affected by temperature

Delivers a smooth flow of power

Regenerative Braking

When the driver brakes, the motor becomes a generator and the kinetic energy generates electricity stored into the battery

The Toyota Prius uses about 30% of the heat lost kinetic energy from braking

Compression Ignition Direct Injection Engines (CIDI)

Spark Ignition Engines

Gas Turbines

Fuel Cells

Hybrid Power Units

4 Types:

Hybrid Power Units: CIDIMost promising power unitAchieves combustion through compressions without the use of a spark plugHigh pressure injection of the fuel into the combustion chamberThrottle and heat losses travels into the combustion chamber increasing thermal efficiency

Hybrid Power Units: Spark Ignition

Runs on an Otto cycle

Uses a homogeneous air-fuel mixture before entering the combustion chamber

When the combustion chamber is compressed, the spark plug is ignited

Controlled by limiting the amount of air allowed into the engine

An Otto cycle is an idealizedthermodynamic cycle that describesthe functioning of a typical sparkignition piston engine. It is thethermodynamic cycle most commonlyfound in automobile engines.

Hybrid Power Units: Gas Turbines

Runs on a Brayton cycle

A compressor raises the pressure and temperature of the inlet air

Air is moved to the burner and fuel is injected and combusted to raise the air temperature

Power is produced when the heated pressure mixture is expanded and cooled through the turbine

The Brayton cycle is athermodynamic cycle thatdescribes the operation ofcertain heat engines thathave air or some other gas astheir working fluid. Theoriginal Brayton engines useda piston compressor andpiston expander, but moderngas turbine engines and airbreathing jet engines alsofollow the Brayton cycle.

Hybrid Power Units: Fuel CellsGenerate electricity through anelectrochemical reaction combininghydrogen with ambient air

Pure hydrogen or any fossil fuelproduced is used as hydrogen-richgas

Water vapor is emitted

https://www.youtube.com/watch?v=Rwy6WozMbt8

– Continuous Variable Transmission (CVT)

– Automated shifted transmission

– Manual transmission

– Traditional automatic transmission with torque converter

Transmission

4 Types:

Transmission: CVT

Infinite number of variable transmissions

Currently not able to compete with 4-speed and 5-speed transmissions in size, cost, and reliability

Provides seamless, step-less acceleration and deceleration

The Toyota Prius uses this

QUIZ

Energy saving is approximately 20-30% is in

A. Micro hybrid

B. Mild hybrid

C. Full hybrid

QUIZ

In electric car propulsion system Gas turbines run on

A. Otto cycle

B. Brayton cycle

QUIZ

Fuel cells produce electricity using

A. combustion

B. electrochemical reaction

C. magnetism

QUIZ

• CO2 emission is minimum in

A. Micro hybrid

B. Mild hybrid

C. Full hybrid

Battery charging during driving in HEVs

Battery charging (during driving)Every battery has a minimum state of charge (SOC) which

needs to be maintained in order to avoid permanentdamage. The state of charge represents the theoreticalamount of electrical energy available in the battery. Ifthe SOC of a battery is 100% means that there is amaximum theoretical amount of electrical energywhich can be used. If the minimum SOC for the batteryis 20% we can only use 80% of the theoreticalmaximum.

Depending on the size, power and chemistry of thebattery, the minimum SOC is different.

In any hybrid electric vehicle, function of the SOC level, thebattery can be is several states:

charge deplete

charge sustain

Charging

When the battery is fully charged, the electrical energy isavailable for use. In this case the battery is in charge depletemode.

When the SOC of the battery reaches the minimum level, theinternal combustion engine is responsible to charge thebattery so that the SOC doesn’t go under the minimum level.In this case the battery is in charge sustain mode.

When the vehicle is braking, the kinetic energy of the vehicle isconverted in electrical energy and stored in the battery. In thiscase, the battery is in charging mode.

Battery charging (from the grid)

In terms of battery charging, the main difference between a fullhybrid electric vehicle and a plug-in electric vehicle is that thePHEV can also be charged by connecting it to a power socket.The power electronics control module of a plug-in hybridelectric vehicle contains a rectifier, which converts thealternating current (AC) of the power socket into directcurrent (DC) and stored into the high voltage battery.

Depending on the functions that can be handled by the electric system, we distinguish the following types of hybrid electric vehicles:

How Do Plug-In Hybrid Electric Cars Work?

• Plug-in hybrid electric vehicles (PHEVs) use batteries to poweran electric motor and another fuel, such as gasoline, to poweran internal combustion engine (ICE). PHEV batteries can becharged using a wall outlet or charging equipment, by the ICE,or through regenerative braking. The vehicle typically runs onelectric power until the battery is nearly depleted, and thenthe car automatically switches over to use the ICE.

Key Components of a Plug-In Hybrid Electric Car

Battery (auxiliary): In an electric drive vehicle, the auxiliary battery provides electricityto start the car before the traction battery is engaged and also powers vehicleaccessories.

Charge port: The charge port allows the vehicle to connect to an external power supplyin order to charge the traction battery pack.

DC/DC converter: This device converts higher-voltage DC power from the tractionbattery pack to the lower-voltage DC power needed to run vehicle accessories andrecharge the auxiliary battery.

Electric generator: Generates electricity from the rotating wheels while braking,transferring that energy back to the traction battery pack. Some vehicles use motorgenerators that perform both the drive and regeneration functions.

Electric traction motor: Using power from the traction battery pack, this motor drivesthe vehicle's wheels. Some vehicles use motor generators that perform both thedrive and regeneration functions.

Exhaust system: The exhaust system channels the exhaust gases from the engine outthrough the tailpipe. A three-way catalyst is designed to reduce engine-outemissions within the exhaust system.

Fuel filler: A nozzle from a fuel dispenser attaches to the receptacle on the vehicle to fillthe tank.

• Fuel tank (gasoline): This tank stores gasoline on board the vehicle until it'sneeded by the engine.

• Internal combustion engine (spark-ignited): In this configuration, fuel isinjected into either the intake manifold or the combustion chamber, where it iscombined with air, and the air/fuel mixture is ignited by the spark from a sparkplug.

• Onboard charger: Takes the incoming AC electricity supplied via the charge portand converts it to DC power for charging the traction battery. It alsocommunicates with the charging equipment and monitors batterycharacteristics such as voltage, current, temperature, and state of charge whilecharging the pack.

• Power electronics controller: This unit manages the flow of electrical energydelivered by the traction battery, controlling the speed of the electric tractionmotor and the torque it produces.

• Thermal system (cooling): This system maintains a proper operatingtemperature range of the engine, electric motor, power electronics, and othercomponents.

• Traction battery pack: Stores electricity for use by the electric traction motor.

• Transmission: The transmission transfers mechanical power from the engineand/or electric traction motor to drive the wheels.

PHEV

PHEV BenefitsThe increased all-electric capability reduces fossil fuel use andresults in lower emissions and improved fuel efficiency versus aconventional hybrid, which helps satisfy regulators.PHEVs earn automakers credits toward meeting zero-emissionsvehicle requirements in states that have so-called ZEV (ZeroEmissions Vehicle) programs.Lower emissions are good, but it’s the PHEV’s’ all-electric rangeand ability to keep running after their batteries are depletedthat have made them attractive.Ideally, they combine practical EV range but eliminate the rangeanxiety that was common with the EVs of the 2010s.A Toyota RAV4 hybrid, with 1.6kWh of battery capacity, cantravel only short distances in all-electric mode and typicallyuses its electric motor only to boost the gas engine’s power. Buta RAV4 Prime, with an 18.1 kWh battery, can deliver up to 42miles or all-electric travel, much of it at highway speeds.

The RAV4 Hybrid is EPA rated at 40 mpg in combined cityand highway driving, while the RAV4 Prime gets a lowerrating of 38 mpg in hybrid mode. However, with its initial 42miles of all-electric mode, the PHEV’s real fuel efficiency isgreater than in the standard hybrid: The RAV4 Prime woulduse only one gallon of gas to travel 80 miles, two gallons totravel 118 miles, and five gallons for 212 miles if it startedthe trip with a full battery.

A PHEV’s battery is so much larger than that of aconventional hybrid, it can take greater advantage of thevehicle’s self-generated electricity, using the electricpropulsion system more often to augment the gas engine oreven, for short bursts, to replace it altogether. That’s whathelps gives PHEVs greater fuel efficiency than regularhybrids.

• Series “Power Assist”

• Parallel “Range Extender/Extended-range”

• Dual-Mode: Combination of a series and parallel “Power Split”

Propulsion

Comparison

Series Configuration Parallel Configuration

Benefits Engine never idles reducing

emissions

Engine drives a generator to run

at optimal performance

Allows a variety of options in

mounting the engine

Some don’t need a transmission

Has more power from

simultaneous power from motor

and engine

Don’t need a separate

generator because the motor

generates the battery

Power is directly coupled to the

road so can be more efficient

Series Hybrid• A series hybrid is like a battery electric vehicle

(BEV) in design.

• Here, the combustion engine drives an electricgenerator instead of directly driving thewheels. The generator both charges a batteryand powers an electric motor that moves thevehicle.

• When large amounts of power are required,the motor draws electricity from both thebattery and the generator. Series hybrids mayalso be referred to as power assist since the gasengine only generates electricity to be used bythe electric motor and never directly drives thewheels. Modern examples include the CadillacELR, Chevrolet Volt, and Fisker Karma.

•

The Chevrolet Volt operates primarily as a series hybrid.

HEV – Series Architecture

Parallel Hybrid

• A parallel hybrid is propelled by both an internalcombustion engine (ICE) and an electric motorconnected to a mechanical transmission.

• Power distribution between the engine andthe motor is varied so both run in their optimumoperating region as much as possible.

• There is no separate generator in a parallel hybrid.Whenever the generator's operation is needed, themotor functions as generator.

• In a parallel mild hybrid, the vehicle can never drivein pure electric mode. The electric motor turns ononly when a boost is needed.

HEV –Parallel Hybrid Vehicle

Series-Parallel• Also known as Power-split hybrid incorporates power-

split devices, allowing for power paths from the ICE tothe wheels that can be either mechanical or electrical.These vehicle can be powered by the gasoline engineworking alone, the electric motor by itself, or by bothenergy converters working together.

• Power distribution between the engine and motor isdesigned so that the engine can run in its optimumoperating range as much as possible.

• The main principle is to decouple the power suppliedby the primary source from the power demanded bythe driver.

Power-splitter series-hybrid Toyota Prius

HEV- Series Parallel

Planetary gear set

PHEV – Advantages/ Disadvantages

• Range not limited by the battery

• Most energy can come from electricity with relatively

small (<100 km range) battery

• Drive train cost and maintenance is high compared to

BEV

• Less energy and emission savings in compared to BEV

Battery Electric Vehicle –BEV/ Full Electric Vehicle-FEV

Battery Electric Vehicle –BEV/ Full Electric Vehicle-FEV

• Battery is the only power source

• Runs entirely on cheap, small and efficient

electric motor

• Low maintenance

• One pedal driving with regeneration

• Big battery for long range

• Fast charging capability

FCEV

FCEV – Hydrogen Fuel Cell Electric Vehicle

• Electric vehicle with hydrogen range extender

• Small battery but long range

• Refuelling is very fast

• Efficiency is lower than FEV/BEV

• Future depends on price developments in fuel

cells, storage and electrolysis

Summary

Conclusion

• Hybrids are more complex than both ICE and

FEV

• The internal combustion engine is on the way

out

• Possible that we shift from PHEVs and go directly

for FEV