2003-01-0443

Kalathur S.Narasimhan

Hoeganaes Corporation, Cinnaminson, New Jersey 08077

Thomas J. MillerChicago Powder Metals Products Co.,Schilier Park,1160176

Copyright@ 2003 SAE International

ABSTRACT Volt system would increase the power (Watts)availability, since W = EI, where E is the voltage and I is

The 42-Volt electrical system is being introduced inautomobiles to provide the extra power needed forvarious electromagnetic devices. These paper discusesthe opportunity offered by the 42Volt for powder metalparts and the challenges. Major opportunities are inmotors. A brief discussion of motors and theperformance requirements for the magnetic core materialused is included. Brushless motor design can benefit themost from insulated iron powder compacts because ofthe design simplicity of powder metal parts and threedimensional flux capability which is most beneficial inrotating devices. -

INTRODUCTION 1995 2000 2005 2010 2015V.a,

the current. Several advancements are in progress to

Figure ~: Projected automotive power needs.The demand for fuel efficiency, pollution reduction andcreature comforts is forcing the automotive companies,to evaluate alternate electrical systems. The mostpopular choice to date is the introduction of a 42-voltsystem, which uses 3 batteries in tandem with 14 volts ofpeak power. The current 14-volt battery system power isabout 3000 watts, which will be exceeded by theelectroflic gadgets planned for future introduction in mostvehicles (See Figure 1). Further refinements in powerelectronics may extend the wattage available using thecurrent 14-volt system. In a few years, the 42-voltsystem may be the only option available. Theintroduction of a 42-volt system opens up an opportunityfor powder metal parts in small motors. This articlediscusses the performance of powder metal parts invarious motors.

Implement 42 Volt system by the automobile companiesthroughout the world. The packaging of the wires andharness become smaller as the voltage increasesamperes of current decreases. The availability of higherpower allows several electromagnetic options whichincrease fuel efficiency Major improvements are listedbelow:

1 Alternator efficiency improvement can improve fuelefficiency by 16%. An integrated starter alternator(ISA) which connects directly to crankshaft betweenengine and transmission achieves this. ISA canaccelerate engine rpm to idle speed before fuelcombustion starts, thus eliminating incompletecombustion at idle speed. The ISA is an opportunityfor powder metal insulated iron product. This isdiscussed further later on in this paper.

BACKGROUND

Figure 1 shows the limit of the existing 14-volt systemand possible extensions that could be made withadvancements in power electronics. Large cars wouldexhaust the available power by the year 2005. The 42

2 Electric power steering will improve the fuelefficiency by 6%. Permanent magnet motors

powered by the battery achieve this,brush less D.C. motors.

These are Electromagnetic valvetrain (EMV) forgreater control over emissions and engineperformance.(P/M)

3. Electric water pumps. Will improve fuel efficiency by2%. These are also electric motors that could befabricated using P/M. The power for the pumpcomes from the battery and not from the engine.

4 Electror:nagnetic valve operation will improve fuelefficiency by 12%. These are valves that can beprogrammed to open and close and eliminate camlobes and camshaft. It is believed that theelectromagnetic option can provide infinite camprofile possibility. This will have a profound impacton P/M parts.

IMPACT ON P/M

The following is a discussion on the individual areas ofan automobile that can benefit from the 42-Volt system.P/M is shown in parenthesis to indicate an opportunity ora threat.

Power Generation and Storage

- DC/DC Converters, Inverters for 14 Volt

Lighting(P/M)- 36 V Battery Power Storage

- Integrated Starter Alternator (ISA) (P/M)

- Regenerative Braking with Reduced Break Wear

- ISA Assisted Acceleration

- Electric water pumps with no power take off from

engine.(P/M)- EGR and turbocharger control and

actuation.(P/M)- Catalyst heaters for emission reduction at start

up.- Ignition systems and fuel systems.(P/M)

Chassis Systems

- Electric power steering (EPS) "By Wire."(P/M)

- Electromechanical braking (EMB) "By

Wire."(P/M)- Active and adaptive suspension systems.(P/M)

Thermal Systems

- Electric air conditioning compressors with nopower take off from engine.(P/M)

- HVAC blower motors, electrical heaters, andelectrical engine cooling fans.(P/M)

- ijPreheat catalytic converters to work at operatingtemperature for' emission control.

Other Systems

- Electric motors, wiper motors, solenoids, lighting,and video systems. (P/M)

THREATS TO P/M

The following is a list of possible negative impact that the42-volt system would have on current P/M applications:

. Loss of P/M mechanical take off components suchas pulleys and sprockets.

- Loss of starter motors and alternators which containvarious P/M components.

. Loss of the reverse gear in transmissions.

. Since air conditioning unit can be operated by HV ACmotors and this will be outside the enginecompartment plastic gears which are traditionallytemperature sensitive can now become a threat toP/~.

MAJOR ISSUES WITH 42VOLT SYSTEM:

A

Power Distribution

- Wires / Wiring Harness of Smaller Size andWeight Because Amps Decrease with VoltageIncrease

- Connectors, Switches and Relays of SmallerSize and Weight

- Fuses and Circuit Protection Devices,Semiconductors

- Provisions for Dual and Third Voltage

Powertrain Systems

Three types of ISA motors are possible withpower take off from either in line or are beltdriven.

Induction - High efficiency with smoothertorque and is an established technology. At the present time arcing is a major issue with 42-Volt

system. Arcs can be self-sustaining and damaging.Several efforts are underway to contain this. The supplybase for the components of the 42-Volt system is slowlyevolving. Electromagnetic valve closure is not reliable atthe present time. Corrosion of the connectors getsaccelerated with higher voltage. Several infrastructureissues need to be resolved. These are issues currently

2 Permanent Magnet - Most efficient becauseit does not require an external fieldexcitation.(P/M)

3 Switched Reluctance: Scalable poweroutput with no generated heat issues andNVHproblems(P/M)

being addressed and will be resolved sometime in thefuture. While all the projected devices might not happeneither due to NVH issues or performance issues, theseneed to be continuously monitored.

lamination steel and this field is opposite to the appliedfield. Due to a variety of technical reasons, separation ofhysteresis and eddy current losses in a clear distinct wayis not preferred. In stead, total core loss is generallymonitored. Another important distinction that needs tobe made is that motors and transformers behavedifferently. In motors, the core magnetic material issubjected to rotating magnetic fields, which alternate inthe magnetic direction and also changes direction inSDace whereas in a transformer the field is stationarY.

OPPORTUNITIES FOR THE POWDERED METALINDUSTRY:

The major opportunities lie in the motors using eitherinsulated iron powders or sintered pole pieces. Since thisis an area of great interest for P/M we discuss below thevarious types of motors and how P/M can benefit. Hysteresis losses are inherent in the processing of

lamination steel and by processing control are kept to aminimum. The eddy current losses are reduced to aminimum by making the electrical steel as thin aspossibl~ and isolating the individual laminations with acoating to prevent electrical contact between thelaminations.

Electric motors transform electrical energy intomechanical energy in the form of rotating shaft power.Motors consist of four different components - stator, rotor(armature), enclosure and shaft. The armature ismounted on the shaft. Operationally, the essential partof an electric motor is the stator and armature. The statoris made from a stack of lamination steel stamped to aspecific tooth profile, which has windings that carrycurrent, which induce a magnetic field on the steel.These windings can be replaced by a permanent magnetin certain cases. The rotor or armature also is made ofstamped lamination steel attached on a shaft withwindings. Again, permanent magnets can be mountedon a rotor shaft directly to provide the magnetic flux andthe windings can be eliminated(1).

SOFT MAGNETIC P/M MATERIALS

The development of the powder metal process (2) forreplacing lamination steel was inspired by the fact thatcore loss can be confined to an individual particle in acompact as long as these particles are electricallyisolated by a coating. (3.4.5)

There are four general types of motors:

2

3.

4.

Synchronous motors - Alternating current (A.C.) isapplied to one winding and direct current (D.C.) tothe other field, generally the rotor.

D.C. motors - A D.C. field is applied to both rotorand stator windings.

Induction Motors - A.C. is applied to the statorwinding and by induction to the rotor windings.

A.C. series motors - A.C. is applied to both windings,which are connected in series. Figure 2: Fluidized bed powder coating process

There are number of different variations of the abovewhich lead -sub-classifications of innumerable number ofmotor types.

..The efficiency of electric motors is defined in terms ofconversion of input power to output power. There are anumber of losses that occur within the motors that resultin wastage of input power. Factors such as friction andwinding and magnetic core losses, which are, termed asno-load losses. 12R losses from the stator and rotor andstray losses due to leakage fluxes are termed as loadlosses. Every motor design optimizes the efficiency,taking into consideration ease of production, costs etc.

~

Figure 3: Comparison of lamination steel and insulatedpowder processing routes.

The losses experienced by the lamination steel (oftencalled electrical steel) during the magnetization by thealternating field consists of eddy current losses andhysterisis losses. Eddy current losses arise from theinduced field generated by the circulating current within

A powder coating process was developed to individuallycoat the iron particles to maintain electrical isolation

.between the particles after they are compacted into ashape. The insulated iron powder compact will behavelike stacked lamination steel.

The coating process is shown in Figure 2. The coatingthickness can be varied precisely by the control of theconcentration of the plastic solution. These coated ironpowders are used successfully in ignition coils.

Powder metal has the potential to replace laminationsteel used in the stator or rotor. The advantage ofpowder metal to lamination steel is shown in Figure 3.The figure shows that manufacturing simplicity is thebest advantage that PIM offers. For instance, the powdermetal process eliminates stamping, stacking, weldingand lends itself to three-dimensional structures and caneliminate several assembly steps.

Figure 4:iron.

1,000 10,000 100,000 1,OOO,<XXJ

Frequency (~)

Permeability of warm compacted insulated

1 00000The characteristics of the several-coated powdersmanufactured by Hoeganaes Corporation are shown inTable I. the processing of these powders into compactsrequire warm compaction. The powders are heated andfed into a die at elevated temperature. This processallows extremely high green strength to be reached.Green strength of nearly 276 MPa (40,000 psi) can beachieved using this process route.

10000

1000

100~~.,.9

8

10

0.1

i0.01

TableGrades

Warm Compacted Insulated Iron Powder

Figure 5: Core loss of warm compacted insulated iron.

MOTOR APPLICATIONS FOR P/M MATERIALS

Various motor designs for the applicability of insulatediron powders were evaluated. The basic premise is toreplace the stacked laminations with compactedinsulated iron, called soft magnetic composite. Thefollowing sections outline potential P/M motor

applications.

Further advances have been made to eliminate the needfor warm compaction and achieve comparable propertiesshown in Table I. However, the maximum greenstrength of only 104 MPa (15,000 psi) is achievable bythis technique. The new grades are shown in Table II.The frequency response of permeability and core loss isshown in figures 4 and 5. Insulated iron compactsexceed core loss performance of lamination steels athigher frequencies. The constant permeability over afrequency range has certain design benefits as well.

SWITCH RELUCTANCE MOTOR

The basic design of switched reluctance motor is shownin figure 6. (6) This has a salient pole structure on bothits rotor and stator, but is only singly excited with phasewindings on the stator. A shaft encoder is installed inorder to synchronize the phase currents with rotor'sangular position. It is inherent in the design of this typeof motor that there be different numbers of poles on thestator ~nd rotor. The greatest torque per ampere ofcurrent is achieved if ttle following criteria for the corematerial are met:

Table II: Newly Developed Insulated Iron PowderGrades

A large unsaturated aligned inductance achievedusing the smallest air gap, the widest poles and the

highest possible permeability.

A small unaligned inductance achieved byimplementing design parameters such as a largeintprnnl::lr rntnr ::Ir,.,

100 1,000 . 10,000 100,000 1,000,000

Frequency (Hz)

The highest possible saturation flux density pole structure. Claw poles are stamped lamination steeland welded together.

Using a 6:4 combination, the motor parameters (note inthe figure above the combination is 12:8) will be:

Number of poles on stator (Ns) = 6

Number of poles on rotor (Nr) 4

For a three-phase (q) current total number of steps perrevolution would be Figure 7: Claw pole motor with permanent magnet rotor

qNr 12

For a motor of 4000 rpm (n = 67 rev/sec) the requiredswitching frequency of current in the phases is

nNr 268 Hz

The field frequency in the rotor is

nN" 402Hz

The insulated iron with better frequency response thanlamination steel will be a good candidate for thisapplication. However, the output power of the motor isclosely related to the maximum permeability, which is1500 for M19 lamination steel, and 500 for insulated ironcompacts. However, the manufacturing simplicity ofinsulated iron compacts makes P/M attractive for thisapplication even with the lower permeability.

Using the conventional two-phase excitation sequence,the fields in the stator and rotor pole sections cyclebetween lower limits when the teeth are unaligned andupper limits when they are aligned. A typical steppermotor rtlay have 50 rotor teeth yielding 200 steps perrevolution with a stroke of 1.8 degree per step. At 480rpm, n=8 rev/sec, 1600 steps/sec, the required switchingfrequency is 800 Hz. The field in the rotor and statorteeth cycles up and down between its minimum andmaximum at a frequency of 400 Hz. Insulated ironcompacts are likely to compete for these applications inthese types of motors due to their simplicity ofmanufacture and their better frequency response.

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,.. ..Figure 8: Claw pole motor with permanent magnet rotci

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A.C. INOUCTION MOTORS

The A.C. induction motor has a very simple and ruggedconstruction and is favored for a wide range of industrialand consumer applications. The major limitation is thatits synchronous speed is determined by the A.C. supplyfrequency. Induction motors use conventional windingson the rotor or a squirrel cage rotor, which areconducting bars shorted together at the ends byconducting rings. These bars are embedded in the slotsin the rotor, which is a stack of lamination steel. Theselamination steels can be replaced by compactedinsulated iron powder. However, the magnetic materialproperties most significantly influence the currentrequired to establish the flux in the magnetic circuit andthe induced m.m.f. These are represented by thepermeability and saturation induction of the corematerial. Insulted iron compacts are not ideally suited forthese motors unless additional supply current is madeavailable to compensate for the excessive magnetizingcurrent.

STEPPER MOTOR

Stepper motors usually contain permanent magnets toprovide the bias field, which simplifies the excitationwindings. The rotor contains permanent magnets and isin a known angular position, and subsequently pulsed toanother known position. The simplest version of this is"can stack" motor. Bonded neodymium-iron-boronmagnets on the rotor are magnetized into a multiple polearray. These poles interact with two separate phases,each of which is a single coil contained within a claw-

PERMANENT MAGNET D.C. MOTOR (PMDC)

PMDC motors provide the best opportunity for insulatediron compacts. Permanent magnet motors offer betteroverall performance than induction motors if the outputpower is below 10kW. The basic structure of PMDCmotor is shown in figure 9. (6)

High saturation flux density and capacity to carry flux

circumferentially

Saturation flux density and the capacity to carrymagnetic field radially across the teeth.

LoJ core loss to provide higher efficiency machine.

High thermal conductivity to dissipate heat and allowgreater electrical loading.

~

Figure 9: PMDC motor layout,

For comparison with the saturation flux density ofcompacted insulated powders, the measuredcharacteristic provided for M 19 lamination steel does notextend to the field levels that are typically used inelectrical machines. The published curve indicates thata flux density of 13 kG may be sustained withoutrequiring any significant driving m.m.f. For the adoptionof insulated iron powders in a brush less D.C. motor, thesaturation flux density must not be an issue, for thefollowing two reasons:

J

In this D.C. motor, the commutator windings on the rotorare excited through brushes. There are severaldisadvantages of these brushed D.C. motors also calledD.C. commutator motors:

1 The cross-sectional area of the stator core wouldhave to be increased and the overall diameter ofthe motor will grow to carry the same flux.

2 The cross sectional area of the stator teeth wouldhave to be increased to carry the same fluxresulting in less available slot area, therefore theoverall diameter must increase or the electriclo~ding must be reduced to compensate for thischange. .

None of these are attractive scenarios for the insulatediron powders, so the powder compact componentsshould operate at essentially the same flux density asM19 laminations - it will just take more m.m.f. To driveflux through these components.

Radio frequency interference and spark associatedwith the brushes.

The accumulation of brush dust.

Brush friction.

The armature has poor conduction path to dissipateheat from the armature winding.

The space required for commutator and brush gear.

Most new D.C. motors use the brushless version whereinthe commutation is achieved by sensors located in thestator. The essential feature of brushless motor is: The use of compacted iron powder is therefore a good fit

with the brushless D.C. motor, since its inferiorpermeability (compared to lamination steel) can beovercome simply by providing additional m.m.f. from thepermanent magnets and the trend in modern grades ofneodymium-iron-boron magnets is towards increasinglyhigher coercivities. The m.m.f. can be increased eitherby adopting a higher coercivity permanent magnetmaterial, or by increasing the magnet's length.

Permanent magnets on the rotor.

Field winding coils on the stator.

Electronic commutation.

Sensor coils for switching (Hall or optical sensors).

Transistors replace brushes and-commutator bars,

Linear control of speed and torque.

Higher efficiency over wide speed range.

BRUSH LESS D.C. MOTOR DESIGN EXAMPLE

A typical brush less D.C. motor will have two, four or sixpermanent magnet poles. In a 2-pole machine, the fluxin the stator core will fluctuate at one cycle per revolutionof the rotor. Because of the simple, well-balanced rotorconstruction, output speeds may be very high, frequentlywell over 10,000 rpm. However, the most commonapplications have more modest speeds. 3600 rpm will beconsidered, so that the insulated iron test data can beutilized. Hence n = 60 rpm, and the field in the stator

core and teeth will cycle at a frequency of 60 Hz.

Insulted iron compacts can fit very well for this type ofmotor application. The rotor does not experience anymeasurable eddy current or hysteresis loses as the highcoercivity magnetic materials provide enough fieldstrength and are not influenced by armature reaction.The stator could be solid steel. The stator experiencesalternating magnetic fields due both to the rotatingmagnet assembly and switched phase currents in thearmature winding. The magnetic material for the statorcore should possess:

The test performed on M 19 laminations, compactedSC120 and LCM (LCM are advanced insulated ironpowders designed to provide low core loss) powdersshow that the core losses in all of these materials aresubstantial due to hysteresis, with just a smallcontribution from eddy-currents. Each was tested at 60Hz, and it is apparent that the core loss per unitfrequency (in units of watts/lb/cycle) is approximatelyproportional to the excitation field (in Oersted). Theconstants of proportionality are shown in Table III.

Table V: Core loss and flux density for insulated ironmaterials

These losses may represent a loss in motor efficiency of-1 % using compacted LCM powder, and of -2% usingSC-120 powder.

Table III: Proportionality constants for insulated ironmaterials -

The efficiency loss may not be significant considering thesimplicity of powder metal process and the threedimensional flux capability of insulated iron compacts.Lamination steels are processed to maximize flux in theplane of the sheet. No such limitation exist with insulatediron. compacts.

0.00100.00220.0006

To achieve a flux density of 13 kG in a stator made fromeach of these materials, requires different excitationfields; which are approximately as shown in table IV; theresulting core loss at 60 Hz is also given.

Unique Mobility developed a brushless motor replacingstator made of Ni-Fe laminations with insulated ironpowder compact. (7) The total cost was reducedsignificantly with a very small compromise inperformance. The stator segments are shown in figure10.

Table IV: Core loss and flux density for insulated ironmaterials

Novel B~shl.essDC Stator Design"

While compacted LCM powder offers a significantimprovement in core loss over SC-120 powder, LCM'smuch poorer permeability requires a considerably higherexcitation to establish the operating flux, and thissubstantially negates the core loss advantage. While thefinal choice between SC-120 and LCM would bedetermined by a detailed design study on an actualmotor, the view is that this data favors the use ofcompacted SC-120. It is felt that while m.m.f. in abrush less D.C. motor can be increased either byadopting a- higher coercivity magnet material or byincreasing the magnet's length, this should be done tothe least extent possible in order to minimize theadditional cost in the permanent magnet materials. Thismeans that there will actually be a core loss penalty inexciting compacted insulated powders to the requisiteflux levels, but it is felt this can be managed in thedetailed design of an actual motor using these materials.For example, a typical fractional horsepower brush lessD.C. motor may have a stator core mass of 225 g (0.5Ib), in which case the core losses at 13 kG and 60 Hz willbe as shown in Table V:

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-- 1 jn~./11:2.~n:IHl!lghr

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- J2r30"'.AicSegm9r1tA

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-3.2indh:21.on:rOD

'1~"i;jilH.~j*'ilv-"""1.~","~ "f,~rl(jj.lJI~

Figure10: Novel DC Stator Design using segments ofcompacted insulated iron.

Nil'e Laminajitjn

40

35

30

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~25~ .:.~20: !

~!&15

10

5 .,

0:", ."'-' 'A0 1000 2000 3000 4000 5000 6000 7000

Snned !fr'm )..v"'"

.UniqueMobility-SAE Technical Pap&r93..1008

Figure 11: Power vs. Speed for the novel Uniquemobility motor

The segments shown in figure10 .are assembled andtested in motor and the performance of the core materialis shown in fig11 and 12.

2. For brief review of Powder Metallurgy see "RecentAdvances in Ferrous Powder Metallurgy," K.S.Narasimhan, Advanced Performance Materials, 3,7-27 (1996), Kluwer Academic Publishers, Netherland!

3. H.G. Rutz, F .G. Hanejko, US Patent #5,063,011

(NoJ5, 1991)

600-'

NtFeLammation

500

4. H.G.Rutz, C. Oliver, F.G. Hanejko ,B. Quin, USPatent #5,268,140 (Dec7,1993)

4'00~".,$

-..0300~ J.e-ot.-o 200 5. C.G. Oliver and H.G. Rutz "Powder Metallurgy in

Electronic Applications," Advances in PowderMetallurgy and Particulate Materials Vol. 3, part 11pp. 87-102,1995.

100

00 1000 2000 3000 4000

Speed (rpm)"UniqueMobility - SAE TechnicaiPaper 93.1000

5000 6000 70006. For a good review on motor operation see "Basic

Motor Theory Operation and Applications" William HYeadon, SMMA 20th Exposition, October 8,1991.

Figure 12:Mobility Motor.

Torque vs. Speed for the novel Unique7. Huang H., Debruzzi M., Riso T.,"A Novel Stator

Construction for Higher Power Density and HighEfficiency Permanent Magnet Brushless DC motors"SAE technical paper No.931008.

These are few of the examples among a variety of motordesigns that are being developed with insulated ironpowder compacts. These materials offer designerunrestricted options.

CONCLUSION

A brief review of impact of 42Volt system on powdermetal parts is presented. The major opportunity is inmotors and hence a detailed discussion is provided. Thecore magnetic material performance requirements arediscussed. _Insulated iron powder developed to reduceassembly costs and increase design flexibility providecost effective alternate to conventional lamination stacksin brushless D.C. motor. Opportunity also exists forvariety of other motors including switch reluctancemotors for 42V electrical system. The threats to P/M arealso presented. There are several major hurdles thatneed to be overcome in the implementation of 42 Voltand these advancements need a constant scrutiny.

ACKNOWLEDGEMENTS

Thanks are due to Mike Marucci, Fran Hanejko and themarketing department of Hoegana~s for valuable inputfor this presentation. Special thanks to Dr. PeterCampbell of Princeton Electro technology Inc. for anumber of discussions and evaluations on the insulatediron compacts.

REFERENCES

The information on 42 volt was gathered from number ofdiscussions with automobile manufacturers and SAEjournal articJes.

Permanent magnet motor technology, Design andApplications, Jacek F. Gieras and Mitchell Wing,Marcel Dekker Inc.NewYork, 1997.