Why Electricity is Needed in Automobiles

8/13/2019 Why Electricity is Needed in Automobiles

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Application of Electricity in

Automobile


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Outline

Why Electricity is needed in automobiles?Safety and other reasons.

Target power levels.

Architectures.

Points about engineering research needs.

Major applications: power steering,starter-alternators, etc.

Mild hybrid designs based on 42 V. Research opportunities.

Conclusion.


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Why Electricity is needed in automobiles?

The electrification of the automobile is amajor step in its evolution.

Electrical applications are beneficial for thesame reasons as for systems in aircraft:

Better efficiency More flexible control

Ease of energy conversion

Low-cost control and conversion of energy is

a key point. Electric power is rising because of electric

auxiliaries as well as more features.


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When electricity is used to power variouscomponents (steering, brakes, suspension,

air conditioning), the results are better

efficiency and more flexible performance.

Performance is decoupled from the engine.

Many estimates have been made, such as

10% fuel economy improvements by simple

electrification of existing functions.


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Possible new features: Combined starter-alternator to reduce costs and

enhance performance.

Regenerative braking.

Start on demand arrangements to avoid idleengines.

Improved, more efficient power steering and other

subsystems.

Active suspensions.

Electrical valves and engine elements --

ultimately the self-starting engine.


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Why Electricity needed in automobiles?

The conventional car is rapidly becoming more

electric.

The total electric load is about 1500 W today,

and is increasing toward 5000 W.

Conventional alternators cannot deliver morethan about 2000 W, and are not efficient.

A higher voltage system supports lower

current and loss.


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Three alternatives: Stick with 12 V. This limits effective power levels.

Get the voltage as high as possible (>100 V). This

requires a major overhaul of safety systems and

basic designs. Push the voltage as high as possible before

significant safety issues come into play.

42 V tries to do the last: get the voltage as

high as possible while avoiding severe safetyissues.


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Safety Issues

A cars electrical system is typically open. Complicated wiring harnesses with close

contact and hundreds of connections.

Regulatory agencies have set a level of about

60 V dc as the maximum reasonable level in

an open system.

Headroom is required to stay below this level

under all allowed conditions.


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Safety Issues

Industry premise: stay with an open electricalsystem for the foreseeable future.

This philosophy supports the option for

evolutionary change of automotive electric

power.


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Safety Issues

There are also fully regulated and batteryregulated systems.

Battery-regulated system ultimately defer to

the battery to set the voltage level.

A battery-regulated system must allow for

Polarity reversal

Disconnection: momentary or continuous

Wide voltage swings Inductive spikes from corrosion or deliberate

disconnect are significant.


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Safety Issues

12 V battery systems require undamagedoperation at12 V or from short-term spikes

up to 75 V.

At higher battery voltages, surge suppressors

and other add-ons will be needed to limit

these extremes to present levels.

In a battery regulated system, 36 V is about

the highest possible level (but these arecharged at 42 V) without excessive possibility

of damage and spikes much beyond 60 V.


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Safety Issues

In a fully regulated system, there is somebuffering between the battery and the rest of

the system.

With full regulation, the wide swings of a

battery system are not necessarilyencountered by the user.

48 V batteries are possible within the 60 V

limit, with such regulation. The higher voltages also support extra

efforts, such as anti-reversing diodes.


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Safety Issues

We can also consider a closed system, inwhich electrical contact is more protected.

Closed systems are used in todays hybrid

and electric cars.

The voltage levels there can exceed 300 V

dc.


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Power Levels

At 42 V, a cars electrical system rivals that ofa house.

But, 10 kW is not enough for traction power.

Voltage Typicalpower level

Maximumpower level

12 V 1200 W 2000 W

42 V 5000 W 10 kW

300 V 30 kW 100 kW


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Architectures

Each automotive voltage level hasadvantages for some loads.

12 V or less for lamps, sensors,

electronics, controls.

42 V for motors, pumps, and fans.

High voltage for electric traction

power.

Incandescent lamps, for example, are morerugged and more reliable at low voltages (but

they are disappearing).


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Architectures

Many possible architectures are possible. Most retain some 12 V capacity.

They are typically divided into single-battery

and dual-battery systems.

There is no consensus on which to select,

and we are likely to see several.


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ENGINE42V

ALTERNATOR

42V

BATTERY

42V

LOADS

12V LOADS

DCDC

Architectures

Single battery at 42 V:

Problem: jump starts?

Problem: charge balance.

www.hoppecke.com


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ENGINE42V

ALTERNATOR

BIDIRECTIONAL

DCDC

42V

BATTERY

42V

LOADS

12V LOADS

12V

BATTERY

Architectures

Dual battery:

The dc-dc converter mustbe bidirectional to support

starting and reliability.


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ENGINE

42V

STARTER/

ALTERNATOR

REGULATOR

42V

LOADS

12V LOADS

12V

BATTERY

BIDIRECTIONAL

DCDC

Architectures

12 V battery

Here a starter-alternatoris shown as well.


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ENGINE

42V

STARTER/

ALTERNATOR

42V

LOADS

LOADS

LOCAL

DC/DC

42V

BATTERY

Architectures

Distributed converters with 42 V battery.

Here there are many dc-dc

converters at the various

loads.


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Architectures

The ultimate is a true multiplexed system: Deliver a single 42 V power bus throughout the

vehicle, with a network protocol overlaid on it.

Local dc-dc converters provide complete local

operation and protection. A ring bus or redundant bus structure could be

used to enhance reliability.

What about fuses? No central point is available.


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Architectures

Costs would seem to dictate a single-batteryarrangement.

However, this involves either a high-power

42V to 12V converter (bidirectional) or a

troublesome 42 V battery.

Some researchers talk about a small dc-dc

converter just for jump starts.

Most systems are partially multiplexed (powerand network distribution rather than individual

loads).


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Issues

Key off loads: sensors, alarms, clocks,remote systems. All draw down power.

Flat loads draw roughly fixed power,

although the alternator output can vary.

Connectors.

Fusing.

Arcs: much above 12 V, it becomes possible

to sustain an arc in close quarters.


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Connectors

150 A connector for 42 V (AMP, Inc.prototype).


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Points About Research Needs

Many of the new challenges of 42 V havebeen addressed in other contexts:

48 V systems throughout the telephone network

(with battery regulation)

Higher dc voltages in several aerospaceapplications (with bigger arcing problems in low-

pressure ambients)

Methods need to be adapted to the low-cost

high-vibration automotive case.


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Motors are of keen interest. Dc motors are cheap to build because of the

convenient wound-rotor structure.

The small machine design methods for cars do not

translate well to 42 V. At 42 V, ac motors make sense.

Butsmall ac motors have been expensive

in most contexts.

How to build cheap, small ac motors (with

electronic controls)?


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Fusing is critical. Power semiconductor circuits capable of

acting as self fuses active devices used as

circuit breakers based on local sensing.

Actual fuses and circuit breakers with cost-

effective arc management suitable for

automotive environments.

Fusing issues (among others) have sloweddown the development of 42 V systems.


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Major Applications

Electric power steering. Two forms: assist pump and direct electric.

The assist pump uses an electric motor to

drive a conventional hydraulic unit.

The direct system

uses electric motors with

the steering rack.

In both cases, action canbe controlled independent

of the engine.Source: Delphi Corp., Saginaw Steering Systems Div.


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Major Applications

Electric air conditioning. Remove the air conditioning

system from engine belt drive.

Provides much better control

and flexibility.

Easier cycling,possible

heat pump application.


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Major Applications

Integrated starter-alternator (ISA). Build an electric machine into

or around the flywheel.

Both permanent magnet and

induction types are being

studied.

Source: Mechanical Engineering

Magazine online, April 2002.


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Major Applications

Provides on-demand starts. Supports regenerative braking.

The very fast dynamics of an ac machine

allows even active torque ripple cancellation.

If ripple can be cancelled, there is promise for

much quieter engines and much lower

vibration levels.


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Major Applications

Electromechanical engine controls. Valves.

Fuel.Source: FEV Engine Technology, Inc.


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Major Applications

Active suspensions. Use electromechanical actuators in

conjunction with mechanical suspension

members.

With enough actuator power, road bumps

(large and small) can be cancelled with an

active suspension.


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Major Applications

Catalyst management systems and exhausttreatment.

Today, most automotive emissions occur in

the first few minutes of operation, when the

catalyst is too cold to be effective.

Catalyst heaters or short-term exhaust

management systems can drastically reduce

tailpipe emissions in modern cars and trucks. Electrostatic precipitator methods can be of

value with diesel particulate exhaust.


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Additional Applications
http://auto.mit.edu/consortia_dis.nsf/DocId/DA54330A7588430F852569CF00763577/$file/autot1.gif


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Mild Hybrids

The key limitation of 42 V is that it really doesnot support electric traction power levels.

As the promise of electric and hybrid vehicles

becomes clearer, engineers push for higher

power levelsbeyond the reach of 42 V.

A compromise is possible: the mild hybrid

vehicle.


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Mild Hybrids

A light hybrid or mild hybrid uses a smallmotor to manage

performance.

The engine can be

shut down at stops.

Braking energy

can be recovered.

The car does not operate in anall-electric regime.

The Honda Insight is a good example.

Source: www.familycar.com


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Mild Hybrids

For a mild hybrid approach, about 5 kW or socan provide a useful level of traction power.

The technique is accessible in a 42 V system,

although higher voltage (144 V in the Insight)

is beneficial.

A 42 V ISA has substantial promise for fuel

economy improvements, and straddles the

boundary between a conventional car with anISA and a mild hybrid.


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Other Hybrids

Higher-power hybrids require high voltage(240 V and up) for traction power.

Electrical accessories are essential.

Such cars can benefit from 42 V systems.


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Other Hybrids

All key

accessories areelectric.

The Toyota hybridsystem operates at

288 V, and reaches

30 kW.

Source: www.familycar.com
http://www.familycar.com/RoadTests/ToyotaPrius/Images/HybridSystem.jpg


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Electric and Hybrid Gallery

General Motors EV1. 1300 lb battery pack at

312 V, 102 kW motor.

0-60 mph in less than 9 s.

Volvo turbine-based

hybrid prototype.


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Electric and Hybrid Car Gallery

This Ford Escort was the first true practicalprototype hybrida complete station wagon.

Second-gen

diesel hybrid.


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Electric and Hybrid Car Gallery


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Research Opportunities

Low-cost small ac motor systems: 42 V dc bus

Cheap inverters

Small ac motors that can be manufactured easily

Engine electromechanical devices andcontrols.

Protection and semiconductor fusing.

System-level analysis.


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Conclusion

The continuing increase in electric powerlevels in automobiles will require highervoltages.

42 V systems (batteries at 36 V or 48 V) are

the highest possible in an open electricalsystem.

There are fuel economy improvements just atthis level, but the extension to mild hybrids

offers much more. While the industry is now is a go slow mode

for 42 V, no one doubts its eventual use.


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The End!

Documents

Why Electricity is Needed in Automobiles