design and engineering of electric and hybrid automobiles

Design and Engineering of Electric and Design and Engineering of Electric and Hybrid AutomobilesHybrid Automobiles

P. T. KreinP. T. Krein

Grainger Center for Electric Machinery and ElectromechanicsGrainger Center for Electric Machinery and ElectromechanicsDepartment of Electrical and Computer EngineeringDepartment of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign, USAUniversity of Illinois at Urbana-Champaign, USA

© 2005, 2006 P. T. Krein. All rights reserved.

Grainger Center for Electric Machines and Electromechanics University of Illinois at Urbana-ChampaignGrainger Center for Electric Machines and Electromechanics University of Illinois at Urbana-Champaign

22

OverviewOverview

• Early electric cars and advantages; hybridsEarly electric cars and advantages; hybrids• Energy and power issues.Energy and power issues.• ArchitecturesArchitectures• MotivationMotivation• Battery needsBattery needs• Engine needsEngine needs• Electric motor needsElectric motor needs• Inverter needsInverter needs• System integrationSystem integration• Commercial hybridsCommercial hybrids


33

Early Electric CarsEarly Electric Cars

• Electric vehicles are clean and easy to use.Electric vehicles are clean and easy to use.• Low maintenance, available infrastructure.Low maintenance, available infrastructure.• Dc motors were easy to control.Dc motors were easy to control.• Motors haveMotors have

high power-to-high power-to-weight ratio.weight ratio.

• 19141914DetroitDetroitElectricElectriccar.car.

Source: I. Pitel.


44

Early Hybrid CarsEarly Hybrid Cars

• The advantages of electric drives are The advantages of electric drives are substantial.substantial.

• Hybrids can deliver energy for long intervals.Hybrids can deliver energy for long intervals.• Retain the reliabilityRetain the reliability

and ease-of-useand ease-of-useadvantages ofadvantages ofelectric cars.electric cars.

• No gear box.No gear box.• The 1900 PorscheThe 1900 Porsche

hybrid.hybrid.www.hybridvehicle.org


55

HybridsHybrids

• The advantages of hybrids (no mechanical The advantages of hybrids (no mechanical drive train) have long dominated for the drive train) have long dominated for the heaviest vehicles.heaviest vehicles.

• At the largest sizesAt the largest sizes – ships and – ships andlocomotives – thelocomotives – thediesel-electricdiesel-electrichybrid is the usualhybrid is the usualarchitecture.architecture.


66

Energy and Power NeedsEnergy and Power Needs

• Energy and power in a vehicle must meet the Energy and power in a vehicle must meet the following requirements:following requirements:– Move the car against air resistance. Force is Move the car against air resistance. Force is

proportional to speed squared, to “frontal area,” and proportional to speed squared, to “frontal area,” and to “drag coefficient.”to “drag coefficient.”

– Overcome energy losses in tires. Force is Overcome energy losses in tires. Force is proportional to vehicle weight and to “rolling proportional to vehicle weight and to “rolling resistance.”resistance.”

– Overcome gravity on slopes.Overcome gravity on slopes.– Overcome friction and other losses.Overcome friction and other losses.– Deliver any extra power for accessories, air Deliver any extra power for accessories, air

conditioning, lights, etc.conditioning, lights, etc.


77


• Examples, typical car (1800 kg loaded):Examples, typical car (1800 kg loaded):– 4600 N of thrust to move up a 25% grade.4600 N of thrust to move up a 25% grade.– 15 kW of axle power to drive on level road at 65 mph15 kW of axle power to drive on level road at 65 mph

(18 kW at 70 mph).(18 kW at 70 mph).– 1400 N of thrust to maintain 65 mph up a 5% grade.1400 N of thrust to maintain 65 mph up a 5% grade.– 40 kW to maintain 65 mph up a 5% grade.40 kW to maintain 65 mph up a 5% grade.– 40 kW to maintain 95 mph on level road.40 kW to maintain 95 mph on level road.– Peak power of about 110 kW (150 hp) to provide 0-Peak power of about 110 kW (150 hp) to provide 0-

60 mph acceleration in 10 s or less.60 mph acceleration in 10 s or less.– 110 kW to maintain 137 mph.110 kW to maintain 137 mph.

• These are at the axle, and don’t account for These are at the axle, and don’t account for other losses.other losses.


88


• A car needs to store energy for range.A car needs to store energy for range.• Alternatives:Alternatives:

– Capacitors or inductorsCapacitors or inductors– Flywheels or springsFlywheels or springs– Compressed air tanksCompressed air tanks– BatteriesBatteries– Liquid fuelLiquid fuel

• Figures of merit:Figures of merit:– Useable storage per unit massUseable storage per unit mass– Useable energy rate per unit massUseable energy rate per unit mass


99


Storage technologyStorage technology Mass energy densityMass energy density Volume densityVolume density

Lead-acid batteriesLead-acid batteries 100 kJ/kg (30 W-h/kg)100 kJ/kg (30 W-h/kg)

Compressed air, 10 MPaCompressed air, 10 MPa 80 kJ/kg80 kJ/kg Need tankNeed tank

Conventional capacitorsConventional capacitors 0.2 kJ/kg0.2 kJ/kg

UltracapacitorsUltracapacitors 20 kJ/kg20 kJ/kg

Lithium-ion batteriesLithium-ion batteries 600 kJ/kg600 kJ/kg

GasolineGasoline 43000 kJ/kg43000 kJ/kg 29000 kJ/L29000 kJ/L

Hydrogen (liquid)Hydrogen (liquid) 120000 kJ/kg120000 kJ/kg 8000 kJ/L8000 kJ/L


1010


• Lead-acid battery energy density is only Lead-acid battery energy density is only about 1% of the usable energy in gasoline.about 1% of the usable energy in gasoline.

• Sample test car: 275 kg batterySample test car: 275 kg batterypack pack equivalent to 4 L of gas! equivalent to 4 L of gas!


1111


• Rate is also a problem.Rate is also a problem.• Example: refill a gas tank with 60 L in 5 min.Example: refill a gas tank with 60 L in 5 min.• This is an energy rate of about 6 MW – probably This is an energy rate of about 6 MW – probably

far more than this building is using now!far more than this building is using now!• It is costly and problematic to fillIt is costly and problematic to fill

batteries quickly.batteries quickly.• Also a driving problem: 110 kWAlso a driving problem: 110 kW

is a high rate.is a high rate.• Good batteries deliver up to 500 W/kg.Good batteries deliver up to 500 W/kg.• The best are limited to 1000 W/kg.The best are limited to 1000 W/kg.


1212


• Gasoline – or nearly any liquid fuelGasoline – or nearly any liquid fuel– stores a lot of energy and– stores a lot of energy anddelivers energy quickly.delivers energy quickly.

• Batteries store more than mostBatteries store more than mostother methods.other methods.

• The most intractable limitation ofThe most intractable limitation ofall-electric vehicles is energy storage.all-electric vehicles is energy storage.

• Hybrids get around this problem by Hybrids get around this problem by converting fuel from liquid form.converting fuel from liquid form.

www.nbsa-hleague.com


1313


• To produce 400 miles (640 km) of range, a To produce 400 miles (640 km) of range, a typical car must carry 15 gal (57 L) of typical car must carry 15 gal (57 L) of gasoline.gasoline.

• This is 42 kg, and stores 1.81 GJ, or about This is 42 kg, and stores 1.81 GJ, or about 500 kW-h. (My family uses about 30 kW-h 500 kW-h. (My family uses about 30 kW-h per day of electrical energy.)per day of electrical energy.)

• Only about 25% of this energy can do useful Only about 25% of this energy can do useful work, so with batteries about 125 kW-hr work, so with batteries about 125 kW-hr would be needed.would be needed.

• This requires 4.2 metric tons of batteries.This requires 4.2 metric tons of batteries.


1414

ArchitecturesArchitectures

• Efficiency and emissions improvements Efficiency and emissions improvements motivate modern hybrid designs.motivate modern hybrid designs.

• Power electronics is nearly routine.Power electronics is nearly routine.• General types: series and parallel.General types: series and parallel.

Series hybrid: energy “assembled” electrically.


1515


• Parallel hybrid: energy is assembled Parallel hybrid: energy is assembled mechanically.mechanically.

Credit: Honda

Source: Mechanical Engineering Magazineonline, April 2002.


1616


• The Toyota and Ford “dual” The Toyota and Ford “dual” hybrids are parallel designs withhybrids are parallel designs withsome series modes.some series modes.

• The Honda “mild” parallel hybrid The Honda “mild” parallel hybrid uses a small electric machine touses a small electric machine torecover braking energy and allowrecover braking energy and allow easy engine start easy engine start and stop.and stop.

Source: Toyota


1717

ArchitectureArchitecture

• Any hybrid design includes a mechanical Any hybrid design includes a mechanical drive and electrical drive system.drive and electrical drive system.

• Two hard problems:Two hard problems:– Packaging (jam two systems together into Packaging (jam two systems together into

a safe car)a safe car)– Choose tradeoffs and carry out design.Choose tradeoffs and carry out design.


1818

MotivationMotivation

• Energy flexibility and efficiency.Energy flexibility and efficiency.• Good designs double the fuel economy.Good designs double the fuel economy.• In principle, it might be possible to triple the In principle, it might be possible to triple the

fuel economy while maintaining conventional fuel economy while maintaining conventional performance.performance.

• The overall efficiency is similar to thermal The overall efficiency is similar to thermal electric plants.electric plants.

• Emissions can be made much lower.Emissions can be made much lower.


1919


An HEV has at least five characteristics that An HEV has at least five characteristics that reduce emissions:reduce emissions:

1.1. The engine is smaller since the electric motor does The engine is smaller since the electric motor does some of the work, especially during peaks.some of the work, especially during peaks.

2.2. The engine can shut off when the car stops.The engine can shut off when the car stops.

3.3. We can choose to operate the engine only at its We can choose to operate the engine only at its highest efficiency.highest efficiency.

4.4. The electrical system can be used to prepare The electrical system can be used to prepare emission controls for cold starts.emission controls for cold starts.

5.5. Braking energy can be recovered and stored in the Braking energy can be recovered and stored in the batteries.batteries.


2020


• In addition, efficient engines that might not be In addition, efficient engines that might not be good for direct use can be installed.good for direct use can be installed.– Atkinson cycleAtkinson cycle– Brayton cycle (includes turbines)Brayton cycle (includes turbines)

• The Prius achieves about 90% reduction in The Prius achieves about 90% reduction in exhaust emissions, with no sacrifice in exhaust emissions, with no sacrifice in performance.performance.

• Large improvements in hydrocarbons and Large improvements in hydrocarbons and carbon monoxide. HC: 10 mg/mile or less.carbon monoxide. HC: 10 mg/mile or less.

• Possibility of zero-emission electric operation.Possibility of zero-emission electric operation.


2121

Battery NeedsBattery Needs

• Battery size is closely tied to architecture.Battery size is closely tied to architecture.• Commercial designs seek relatively small Commercial designs seek relatively small

batteries.batteries.• Some design choices:Some design choices:

– Integrated starter-alternator: batteries big enough Integrated starter-alternator: batteries big enough for repeated starts and stops.for repeated starts and stops.

– Mild hybrid: batteries big enough to store most Mild hybrid: batteries big enough to store most braking energy in city driving.braking energy in city driving.

– Parallel hybrid: batteries provide difference Parallel hybrid: batteries provide difference between maximum engine power and peak powerbetween maximum engine power and peak power

– Series hybrid: batteries can provide power Series hybrid: batteries can provide power independent of engineindependent of engine


2222


• Lead-acid batteries:Lead-acid batteries:– Cheap, readily available, matureCheap, readily available, mature

technology.technology.– Efficiency is about 80% or so for charge-discharge Efficiency is about 80% or so for charge-discharge

cycles.cycles.– Work best when full. Tend to wear out quickly.Work best when full. Tend to wear out quickly.

• Nickel batteries (nickel metal hydride)Nickel batteries (nickel metal hydride)– Common use in hybrids today.Common use in hybrids today.– Work best when about half full.Work best when about half full.– Last many cycles, but less efficient (about 70%).Last many cycles, but less efficient (about 70%).– In use because they offer long life.In use because they offer long life.


2323


• Lithium-ion batteriesLithium-ion batteries– Newer and not mature.Newer and not mature.– Expensive.Expensive.– Efficient (over 90%), but wear-out is not well Efficient (over 90%), but wear-out is not well

understood.understood.– Many types have extreme failure modes.Many types have extreme failure modes.

• Typical hybrid today uses roughly 50 kg of Typical hybrid today uses roughly 50 kg of NiMH batteriesNiMH batteries

• Future hybrids will need 100-200 kg to Future hybrids will need 100-200 kg to provide longer engine-off range.provide longer engine-off range.


2424

Engine NeedsEngine Needs

• The engine should be sized to provide full The engine should be sized to provide full averageaverage power requirements for long-term power requirements for long-term cruising.cruising.

• In parallel designs, this might require some In parallel designs, this might require some oversizing to account for a portion of short-oversizing to account for a portion of short-term needs.term needs.

• In series designs, average power is the key In series designs, average power is the key issue.issue.

• Worst case is high-speed cruising with heavy Worst case is high-speed cruising with heavy load.load.


2525


• The system aims to operate the engine over a The system aims to operate the engine over a relatively narrow range.relatively narrow range.

• Engines have a small region of highest efficiency.Engines have a small region of highest efficiency.

www.queensu.ca


2626


• In a series design, the engine drives an In a series design, the engine drives an electrical generator, and it is possible to electrical generator, and it is possible to control the operating point precisely.control the operating point precisely.

• In parallel designs, a key innovation has been In parallel designs, a key innovation has been a sun-planet gearset that keeps engine a sun-planet gearset that keeps engine operation inside a limited window.operation inside a limited window.

• Either choice delivers similar results: engine Either choice delivers similar results: engine operation near highest efficiency under a operation near highest efficiency under a range of conditions.range of conditions.


2727

Motor NeedsMotor Needs

• In a hybrid car, there is no “rated power” for In a hybrid car, there is no “rated power” for the electrical system.the electrical system.

• The electric motor handles many of the The electric motor handles many of the transients. It is most active when derivatives transients. It is most active when derivatives of power are high.of power are high.

• This means a motor with excellent efficiency This means a motor with excellent efficiency and performance over a wide range of and performance over a wide range of speeds and loads is needed.speeds and loads is needed.

• Researchers have examined many motor Researchers have examined many motor types. All work today is on ac machines.types. All work today is on ac machines.


2828


• Modern commercial hybrids use “interior Modern commercial hybrids use “interior permanent magnet” machines, but operate permanent magnet” machines, but operate them over a relatively limited speed and load them over a relatively limited speed and load range.range.

• Induction machines show the best promise Induction machines show the best promise for hybrids with extended electric-only range.for hybrids with extended electric-only range.


2929


• Motors are not used in “direct drive” applications – Motors are not used in “direct drive” applications – too heavy.too heavy.

• Motor power-to-weight ratio can be raised by Motor power-to-weight ratio can be raised by spinning a machine faster.spinning a machine faster.

• Gears between motor and axleGears between motor and axlefor speed and torque matching.for speed and torque matching.

• Example: commercial acExample: commercial acmachine, 12.5 HP, 1800 RPM atmachine, 12.5 HP, 1800 RPM at60 Hz (about 45 kg).60 Hz (about 45 kg).

• Can deliver 56 HP continuousCan deliver 56 HP continuous(41 kW) and 104 kW peak at 8000 RPM.(41 kW) and 104 kW peak at 8000 RPM.Full vehicle operation.Full vehicle operation.

A 75 kW electric motor based on automotive duty.


3030


• More typical designs size the motor for only More typical designs size the motor for only part of the needs.part of the needs.

• Example: peak power capability of 50 kW.Example: peak power capability of 50 kW.• This can be done with roughly 22 kg motor This can be done with roughly 22 kg motor

size – smaller if cooled with liquid.size – smaller if cooled with liquid.

www.kingoftheroad.net

General Motors EV1 drive motor


3131

Inverter NeedsInverter Needs

• An inverter converts dc power (from the An inverter converts dc power (from the battery) to adjustable ac power for the motor.battery) to adjustable ac power for the motor.

• The inverter will need to deliver peak motor The inverter will need to deliver peak motor power.power.

• In a full-power design, this means 100 kW In a full-power design, this means 100 kW and up.and up.

• In a modern commercial hybrid, the levels are In a modern commercial hybrid, the levels are in the range of 20-50 kW.in the range of 20-50 kW.

• Inverters are designed with IGBTs (insulated-Inverters are designed with IGBTs (insulated-gate bipolar transistors) that switch to give gate bipolar transistors) that switch to give the conversion function.the conversion function.


3232

Inverter NeedsInverter Needs

• Inverter cooling and inverter reliability are important Inverter cooling and inverter reliability are important engineering aspects of any hybrid car.engineering aspects of any hybrid car.

• Prius inverter is in the box at right. Liquid cooling Prius inverter is in the box at right. Liquid cooling loop.loop.

www.kingoftheroad.net


3333

System IntegrationSystem Integration

• The hardest part of the engineering challenge The hardest part of the engineering challenge is to put everything together.is to put everything together.

• Basic example: brakes. How to have the Basic example: brakes. How to have the electric machine and mechanical brakes electric machine and mechanical brakes interact for best results?interact for best results?

• Other examples:Other examples:– Cooling (engine, motor, inverter, batteries)Cooling (engine, motor, inverter, batteries)– Energy tradeoffs (when and how to use motor and Energy tradeoffs (when and how to use motor and

engine)engine)– Driver controls (keep it simple)Driver controls (keep it simple)


3434

Hybrid Electric Cars -- ProductionHybrid Electric Cars -- Production

• Honda InsightHonda Insight

• Toyota PriusToyota Prius

Source: www.familycar.com


3535


• Honda CivicHonda Civic

• Toyota PriusToyota Prius(2(2ndnd generation) generation)

Source: www.auto-sfondi-desktop.com

Source: www.theautochannel.com


3636


• Ford EscapeFord Escape

• Lexus Hybrid SUVLexus Hybrid SUV

Source: www.edmunds.com

Source: msnbcmedia.msn.com


3737

ConclusionConclusion

• Hybrid cars represent comprehensive Hybrid cars represent comprehensive multidisciplinary engineering challenges.multidisciplinary engineering challenges.

• A design team must understand basic energy A design team must understand basic energy issues, vehicle requirements, capabilities of issues, vehicle requirements, capabilities of all subsystems, and how to integrate them.all subsystems, and how to integrate them.

• Even with this, detailed operating strategies Even with this, detailed operating strategies and implementation aspects lead to a wide and implementation aspects lead to a wide range of possible outcomes.range of possible outcomes.

design and engineering of electric and hybrid automobiles

Documents

electric machines

electric machinery

engineering of electric

power needsgrainger

dieselelectric hybrid

detroit electric car

advantages of electric

high power