Lightweight Electric Hybrid Vehicle Design Episode 9 pptx

Powertrain: 3 phase, AC induction motor Transmission: Single-speed integrated Front-wheel drive Power: 56 kW Maximum torque Nm: 193 Maximum speed rpm: 13 500 Battery type: Sodium–sulphur

Battery/fuel-cell EV design packages 133

rpm and maximum torque 193 Nm at zero rpm Regenerative braking comes from the motor acting as a generator, so recharging the battery

The supply from the sodium–sulphur battery is fed along special heavy-duty cables to the power electronics centre (PEC), which is housed in the engine compartment The candy-striped, red-on-black cables are strikingly marked to avoid confusion with any other wiring in the van Encased in aluminium, the PEC incorporates the battery charging electronics and inverters that convert the

330 volt DC supply to AC power It also includes a transformer which enables a 12 volt auxiliary battery to be recharged from the high voltage traction batteries The electrical supply to the PEC

is connected and isolated by power relays inside a contactor box, controlled by the ignition key and the electronic modules

On-board microprocessors are linked by a multiplex database that allows synchronous, highspeed communication between all the vehicle’s systems The vehicle system controller (VSC) acts as the user/vehicle interface and is operated by electrical signals from the accelerator pedal This ‘drive-by-wire’ system has no mechanical connection to the speed controller It is supplemented by a battery controller that monitors the sodium–sulphur operating temperature, the state of charge and recharging The control system also incorporates a diagnostic data recorder which stores information from all the on-board electronic systems This locates any operational malfunctions quickly and precisely

A fault detection system (known as the power protection centre (PPC)), has also been built into the battery controller to monitor continuously the main electrical functions Every 4 seconds it checks for internal and external leakage between the high-voltage system, the vehicle chassis and the battery case Should a leak be detected in any wire, a warning light tells the driver that service action should be taken The vehicle can then be driven safely for a short distance so that repairs can be made If leakage is detected from both battery leads, the vehicle system cuts off the power

to the motor and illuminates a red warning light The auxiliary power supply is maintained to operate the battery cooling system An inertia switch is also fitted, which is activated in the event

of a vehicle collision and isolates power from the main battery pack Auxiliary power to the battery coolant pump is also cut off to reduce the risk of hot fluids escaping The vehicle incorporates

a small amount of ‘creep’ whereby slight brake pressure is required to prevent it from moving forwards (or backwards when in reverse gear) This results in easier manoeuvring and smoother transmission of power Auxiliary vehicle systems are powered by a standard automotive 12 volt lead–acid battery, the exception being the electrically driven cabin air conditioning system, which

is powered directly from the main sodium–sulphur traction batteries, via a special AC inverter in the PEC module

The climate control unit handles both the air conditioning and a highly efficient 4.5 kW ceramic element PTC heater The heater elements are made from barium titanate with a multi-layer metallic coating on each side, impregnated with special chemical additives The material has low resistance

at low temperature for a very fast warm-up, while at higher temperatures the power supply is automatically regulated to save electrical energy A strip of solar panels across the top of the windscreen supply power to a supplementary extractor fan that ventilates the cabin when the vehicle is parked in direct sunlight This relieves the load on the air conditioning system when the journey is resumed Some lightweight materials have been used in the Ecostar to offset the 350 kg weight of the battery pack

Elimination of the clutch, torque converter and additional gearing is supplemented by a magnesium transmission casing, aluminium alloy wheels, air conditioning compressor and power electronics housing Plastic composite materials have been used for the rear suspension springs, load floor and rear bulkhead Use of these materials has helped keep the Ecostar’s kerb weight to between 1338 and 1452 kg, which is 25% heavier than a standard diesel-powered van The vehicle

also has a useful load carrying capacity of up to 463 kg and retains similar load space dimensions

to the standard Escort van The Ecostar has been developed for optimum performance in urban conditions, where it is expected to be driven most frequently Its top speed is restricted to 70 mph, whilst 0 to 50 mph takes approximately 12 seconds Because of the high torque at low speed, acceleration from standing to 30 mph is quicker than diesel and petrol driven vehicles of the same size The average vehicle range between charges to date has been 94 miles, with a maximum recorded range of 155 miles

Powertrain: 3 phase, AC induction motor

Transmission: Single-speed integrated

Front-wheel drive

Power: 56 kW

Maximum torque (Nm): 193

Maximum speed (rpm): 13 500

Battery type: Sodium–sulphur

Energy rating at 80% DOD: 30 kWh

Power ratings:

peak intermittent (kW/bhp): 50/70

max continuous (kW/bhp): 30/40

On-board charger (120/240 V)

with 2 metre charging cord on reel.

Required 240 V at 30 amp AC single phase

for maximum charging rate

Maximum vehicle weight (kg): 1851

Kerb weight (kg): 1406

Payload (kg): 400–463

Rated top speed (governed): 70 mph

Rated 0–50 mph acceleration: 12 seconds

Range (Federal Urban Driving Schedule)

100 miles

Lightweight 14 inch aluminium alloy

wheels with specially developed P195/

70R14 low resistance tyres

Fig 5.21 Ecostar package, motor and specification.

Climate control module

Power electronics centre Auxiliary battery

AC compressor Charger cord/reel

Cooling system Motor transaxle

Battery I/O module

Contactor box Contactor box

Battery tray assembly

Planetary differential

Speed sensor Right CV joint

Drive motor cooling tube Drive motor rotor Drive motor stator Park mechanism

Reduction gears Lube and cooling pump

Left CV joint

Battery/fuel-cell EV design packages 135

Axel/differential Hydraulic drum brakes Tubular steel frame construction

Battery boxes

Solid state speed controller location

Hydraulic disc brakes

Automatic charger location

Fig 5.22 Bradshaw Envirovan.

5.6.6 BRADSHAW ENVIROVAN

DC drive is used on the higher payload capacity purpose-built Bradshaw Envirovan Figure 5.22 shows the Envirovan built in conjunction with US collaborator Taylor-Dunn This can carry 1500 lb on a 3.55 square metre platform at speeds up to 32.5 mph and is aimed specifically

at city deliveries The vehicle relies on 12 6 volt deep-cycle, rechargeable lead–acid batteries for a total of 72 V All accessories, such as internal lights, windscreen wipers, and gauges, run off the 72 V system through a DC/DC converter, which steps the power down to 12 V, so that all batteries discharge equally This distributes power requirements evenly across all 12 batteries and prevents one or two of the batteries from draining prematurely A battery warning indicator shows the current percentage of battery power available, with a visual warning when battery charge is below 20% An on-board battery charger, featured on the Envirovan, can be used to recharge the battery packs simply by plugging it into any standard 240 V AC power socket The entire 72 V system requires approximately 9.5 hours to fully charge the batteries from an 80% state of discharge (20% remaining charge) The battery pack provides approximately 1000 recharging cycles before replacement is required Battery packs are available for less than £1000 which equates to less than 2p per mile Recharging costs add an additional 1p per mile giving a total cost per mile of 3p A 20 bhp General Electric motor has been designed for the Envirovan

A range of 8 hours/50 miles is available for the vehicle which measures 4.21 metres long× 1.65 wide It can accelerate to 25 mph in 6 seconds and its controller can generate up to 28 bhp for quick response

5.7 Fuel-cell powered vehicles

5.7.1 GENERAL MOTORS ZAFIRA PROJECTS

GM and its Opel subsidiary are aiming at a compact fuel-cell driven vehicle by 2004, Fig 5.23

By 2010, up to 10% of total sales are expected to be taken by this category The efficiency of cells tested by the company is over 60% and CO2 emissions, produced during the reformation of methanol to obtain hydrogen, are about half that of an equivalent powered IC engine Fuel cells have already been successfully exploited in power generation, at Westervoort in the Netherlands, and experimental versions have been shown to successfully power lap-top computers According

to GM, in principle four basic fuels are suitable: sulphur-free modified gasoline, a synthetic fuel, methanol or pure hydrogen Modified gasoline is preferred because of the existing distribution infrastructure but CO2 emission in reforming is higher than with methanol Synthetic

2

4

5

6

7

8 9 3

Fig 5.23 GM fuel-cell developments: (a) Zafira conversion package; (b) under-bonnet power-pack; (c) reformer and

cells; (d) flow diagram; (e) latest package with on-board hydrogen storage.

(a)

(b)

(c)

(d)

1 battery; 2 drive motor; 3

con-verter; 4 air intake; 5 fuel-cell stack;

6 humidifier; 7 compressor; 8

cool-ing water circuit; 9 reformer.

(c)

(e)

Propulsion

Electric motor

Fuel Cell unit

Reformer

Fuel tank

Methanol

Catalytic burner

Residues

Gas from anode

Gas from cathode

Heat

Water

CH3OH

H

2 O CO

2

H2 CO2, CO Air

Battery/fuel-cell EV design packages 137

fuel and methanol can be obtained from some primary energy sources including natural gas Transportation and storage of hydrogen is still at the development stage for commercial viability, Liquefying by low temperature and/or pressure being seen as the only means of on-vehicle storage

Currently GM engineers are working on a fuel-cell drive version of the Zafira van (a) in which electric motor, battery and controller are accommodated in the former engine compartment (b) The ‘cold combustion’ of the fuel-cell reaction, hydrogen combining with oxygen to form water, takes place at 80–90oC and a single cell develops 0.6–0.8 V Sufficient cells are combined to power a 50 kW asynchronous motor driving the front wheels through a fixed gear reduction The cell comprises fuel anode, electrolyte and oxygen cathode Protons migrate through the electrolyte towards the cathode, to form water, and in doing so produce electric current Prospects for operating efficiencies above 60% are in view, pending successful waste heat utilization and optimization of gas paths within the system The reforming process involved in producing hydrogen from the fuel involves no special safety measures for handling methanol and the long-term goal is to produce no more than 90 g/km of CO2 In the final version it is hoped to miniaturize the reformer, which now takes up most of the load space, (c), and part of the passenger area, so that it also fits within the former engine compartment Rate of production of hydrogen in the reformer, and rate of current production in the fuel cell, both have to be accelerated to obtain acceptable throttle response times – the flow diagram is seen at (d) The 20 second start-up time also has to be reduced to 2 seconds, while tolerating outside temperatures of −30°C

Currently GM Opel are reportedly working in the jointly operated Global Alternative Propulsion Centre (GAPC) on a version of their fuel-celled MPV which is now seen as close to a production design A 55 kW (75 hp) 3 phase synchronous traction motor drives the front wheels through fixed gearing, with the complete electromechanical package weighing only 68 kg (150 lb) With

a maximum torque of 251 Nm (181 lb ft) at all times it accelerates the Zafira to 100 km/h (62 mph) in 16 seconds, and gives a top speed of 140 km/h (85 mph) Range is about 400 km (240 miles)

In contrast to the earlier vehicle fuelled by a chemical hydride system for on-board hydrogen storage, this car uses liquid hydrogen Up to 75 litres (20 gallons) is stored at a temperature of

−253°C, just short of absolute zero, in a stainless steel cylinder 1 metre (39 in) long and 400 mm (15.7 in) in diameter This cryostat is lined with special fibre glass matting said to provide insulating properties equal to several metres of polystyrene It is stowed under the elevated rear passenger seat, and has been shown to withstand an impact force of up to 30 g Crash behaviour in several computer simulations also been tested

Fuel cells as well as the drive motor are in the normal engine compartment In the 6 months since mid-2000 the ‘stack’ generating electricity by the reaction of hydrogen and oxygen now consists of a block of 195 single fuel cells, a reduction to just half the bulk Running at a process temperature of about 80°C, it has a maximum output of 80 kW Cold-start tests at ambient temperatures down to −40°C have been successfully conducted

GAPC has created strong alliances with several major petroleum companies to investigate the creation of the national infrastructures needed to support a reasonable number of hydrogen-fuelled vehicles once they reach the market, possibly in 5 years’ time Fuel cost is another critical factor Although hydrogen is readily available on a commercial basis from various industrial processes, its cost in terms of energy density presents a real problem for the many auto-makers who research both fuel cells and direct combustion

According to one calculation based on current market prices, the energy content of hydrogen generated by electrolysis using solar radiation with photovoltaic cells equals gasoline at roughly

$10 a gallon

5.7.2 FORD P2000

Mounting most of the fuel-cell installation beneath the vehicle floor has been achieved on Ford’s FC5, seen as a static display in 1999, with the result of space for five passengers in a medium-sized package Their aim is to achieve an efficiency twice that of an IC engine The company point out that very little alteration is required to a petrol-distributing infrastructure to distribute methanol which can also be obtained from a variety of biomass sources Oxygen is supplied in the form of compressed air and fed to the Ballard fuel-cell stack alongside reformed hydrogen Ford use an

AC drive motor, requiring conversion of the fuel cell’s DC output Even the boot is accessible on the 5-door hatchback so much miniaturization has already been done to the propulsion system The vehicle also uses an advanced lighting system involving HID headlamps, with fibre-optic transmission of light in low beam, and tail-lights using high efficiency LED blade manifold optics The company’s running P2000 demonstrator, Fig 5.24, uses fuel in the form of pure gaseous hydrogen in a system developed with Proton Energy Systems

5.7.3 LIQUID HYDROGEN OR FUEL REFORMATION, FIG 5.25

Renault and five European partners have produced a Laguna conversion with a 250 mile range using fuel-cell propulsion The 135 cell stack produces 30 kW at a voltage of 90 V, which is transformed up to 250 V for powering the synchronous electric motor, at a 92% transformer efficiency and 90–92% motor efficiency Nickel–metal hydride batteries are used to start up the fuel cell auxiliary systems and for braking energy regeneration Some 8 kg of liquid hydrogen is stored in an on-board cryogenic container, (a), at −253°C to achieve the excellent range Renault insist that an on-board reformer would emit only 15% less CO2 than an IC engine against the 50% reduction they obtain by on-board liquid hydrogen storage

According to Arthur D Little consultants, who have developed a petrol reforming system, a fuel-cell vehicle thus fitted can realize 80 mpg fuel economy with near zero exhaust emissions The Cambridge subsidiary Epyx is developing the system which can also reform methanol and ethanol It uses hybrid partial oxidation and carbon monoxide clean-up technologies to give it a claimed advantage over existing reformers The view at (b) shows how the fuel is first vaporized (1) using waste energy from the fuel cell and vaporized fuel is burnt with a small amount of air in

a partial oxidation reactor (2) which produces CO and O2 Sulphur compounds are removed from

Fig 5.24 Ford P2000 fuel cell platform with two 35 kW Ballard stacks.

Battery/fuel-cell EV design packages 139

the fuel (3) and a catalytic reactor (4) is used with steam to turn the CO into H2 and CO2 The remaining CO is burnt over the catalyst (5) to reduce CO2 concentration down to 10 ppm before passing to the fuel cell (6)

5.7.4 PROTOTYPE FUEL-CELL CAR

Daimler-Chrysler’s Necar IV, Fig 5.26, is based on the Mercedes-Benz A-class car and exploits that vehicle’s duplex floor construction to mount key propulsion systems The fuel cell is a Ballard proton exchange membrane type, 400 in the stack, developing 55 kW at the wheels to give a top speed of 145 km/h and a range of 450 km Fuel consumption is equivalent to 88 mpg and torque response to throttle movement is virtually instantaneous While the first prototype weighs 1580

kg, the target weight is 1320 kg, just 150 kg above the standard A-class Tank to wheel efficiency

is quoted as 40% now, with 88% in prospect for a vehicle with a reformer instead of compressed hydrogen The American Methanol Institute is predicting 2 million thus-fitted cars on the road by

2010 and 35 million by 2020

Fig 5.25 Liquid hydrogen or reformed fuel: (a) Renault cryogenic storage; (b) Arthur D Little reformer.

Fig 5.26 D-C Necar and Ballard PEM fuel cell.

1 Fuel-cell stack; 2 air pumps; 3 cell membrane; 4 heat exchanger; 5 catalyst; 6 filters; 7 fuel tank; 8 refuelling hardware; 9 pipes and fittings; 10 motor drives;

11 fuel reformer ; 12 sensors; 13 coolants;

14 powertrain controller; 15 battery; 16 package module;

17 seals

1

3 5

17

6

13

2

10 14

15 11 7,8

Electricity

Plates

Membrane Electrode Assembly

Air

In a summer 1999 interview Ballard chief Firoz Rasul put the cost of electricity produced by fuel cells as $500/kW so that car power plants between 50 and 200 kW amount to $25–100 000 PEM cells operate at 80°C and employ just a thin plastic sheet as their electrolyte The sheet can tolerate modest pressure differentials across it, which can increase power density Ballard’s breakthrough in power density came in 1995 with the design of a stack which produced 1000 watts/litre, ten times the 1990 state of the art Cell energy conversion efficiency, from chemical energy to electricity, is about 50% and the cell does not ‘discharge’ in the manner of a conventional storage battery Electrodes are made from porous carbon separated by the porous ion-conduction electrolyte membrane It is both an electron insulator and proton conductor and is impermeable to gas A catalyst is integrated between each electrode and the membrane while flow field plates are placed on each side of the membrane/electrode assembly These have channels formed in their surface through which the reactants flow The plates are bi-polar in a stack, forming the anode of one cell and the cathode of the adjacent one The catalyst causes the hydrogen atoms to dissociate into protons and electrons The protons are carried through to the cathode and the free electrons conducted as a usable current

References

1 Origuchi et al., Development of a lithium–ion battery system for EVs, SAE paper 970238

2 Saito et al., Super capacitor for energy recycling hybrid vehicle, Convergence 96 proceedings

3 Van der Graaf, R., EAEC paper 87031

4 Prigmore et al., Battery car conversions, Battery Vehicle Society, 1978

5 Harding, G., Electric vehicles in the next millennium, Journal of Power Sources, 3335, 1999

6 Huettl et al., Transport Technology USA, 1996

7 SAE paper 900578, 1990

Further reading

Smith & Alley, Electrical circuits, an introduction, Cambridge, 1992

Copus, A., DC traction motors for electric vehicles, Electric Vehicles for Europe, EVA conference

report, 1991

EVA manual, Electric Vehicle Association of GB Ltd

Unnewehr and Nasar, Electric vehicle technology, Wiley, 1982

Huettl et al., Transport Technology USA, 1996

Argonne National Laboratory authors, SAE publication: Alternative Transportation Problems,

1996

Strategies in electric and hybrid vehicle design, SAE publication SP-1156, 1996

(ed.) Dorgham, M., Electric and hybrid vehicles, Interscience Enterprises, 1982

Electric vehicle technology, MIRA seminar report, 1992

Battery electric and hybrid vehicles, IMechE seminar report, 1992

(ed.) Lovering, D., Fuel cells, Elsevier, 1989

The urban transport industries report, Campden, 1993

The MIRA electric vehicle forecast, 1992

Niewenhuis et al., The green car guide, Merlin, 1992

Combustion engines and hybrid vehicles, IMechE, 1998

Hybrid vehicle design 141

6

Hybrid vehicle design

6.1 Introduction

The hybrid-drive concept appears in many forms depending on the mix of energy sources and propulsion systems used on the vehicle The term can be used for drives taking energy from two separate energy sources, for series or parallel drive configurations or any combination of these Here the layout and development of systems for cars and buses is described in terms of drive configuration and package-design case studies of recent-year introductions

6.1.1 THE HYBRID VEHICLE

This solution is considered by coauthor Ron Hodkinson to be a short-term remedy to the pollution problem It has two forms, parallel and series hybrid which he illustrates in Fig 6.1 Conventionally, parallel hybrids are used in lower power electric vehicles where both drives can be operated in parallel to enhance high power performance Series hybrids are used in high power systems Typically, a gas turbine drives a turbo-alternator to feed electricity into the electric drive It is this

Fig 6.1 Types of hybrid drive.

Clutch

Clutch Clutch

Wheel

Wheel Engine

Battery

X

X

Differential

Diff

Wheel

Wheel

Motor converterPower

Power converter

Battery

Prime

X (a) Parallel hybrid vehicle

(b) Series hybrid vehicle

(c)

(d)

Fig 6.2 HYZEM research programme: (a) characterizing a hybrid powertrain; (b) use of vehicle per day; (c) daily

distances and trip lengths; (d) synthetic urban drive cycle.

(b)

type of drive that would be used on trucks between 150 kW and 1000 kW In pollution and fuel economy terms, hybrid technology should be able to deliver two-thirds fuel consumption and one-third noxious emission levels of IC engined vehicles This technology would just about maintain the overall emissions status quo in 10 years overall If hybrid vehicles were used on battery only

in cities, this would have a major impact on local pollution levels

9 8 7 6 5 4 3 2 1 0

Electric energy consumption (kWh/100 km)

‘Independent hybrid’ ‘Substitution hybrid’

SOC balanced with

an assumed battery

SOC balanced with

an ideal lossless battery

5 - 8

30% 32%

1 to 4

30 20 10

0

0 20 40 60 80 200 250 200 Last Days Number in %

Daily Distance travelled (km)

Daily distances

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Trip Number in %

Trip length distribution

Trip length distribution

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0 10 20 30 40 50 60

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