760121
`
`Hybrid Vehicl.e for
`Fuel Economy
`
`L. E. Unnewehr, J. E. AuHer 1 L R. Foote,
`D. F. Moyer, and H. L. Stadler
`Research Staff, For.d'Motor C.o.
`
`A HEAT 'EtmINE/ELECTRIC drive train has
`been evaluated as a means of improving the
`fuel economy of varielos t,ype.s of
`automotive vehicles . Computer simulation
`studies and dynamometer tests on a
`prototype system indicate that
`improvement.s in CVS-Hot fuel economy
`(miles/gall.on) of from 30% to 100% can be
`realized with this .system in a vehicle of
`ii:len'tical weight ,and performance
`characteristics, Pre.liminacy test data
`also indicates that thes.e .fuel economies
`may be realizable while meeting the
`1975/76 Federal Emission Standards (l , 5HC,
`15CO, 3 . l NO ) :with the use of external
`emissions c~nt1cols such as catq1ytic
`converters , Although similar .in
`configuration to a s·.tandard ·parallel
`hyhrid drive train.,. the control st1:ategies
`and energy flow of .this .system are
`considerably different from any known
`hybrid drives. This· system does not
`appear to be of equal merit for all
`classes of vehicles , but gives the
`greatest ruel economy improvements when
`applied to delivery vans> 'b uses, .and large
`passenger c.ars. There are certain
`drawbacks to this particular hybrid
`
`system, principally i n increased init:i:al
`cost ·as com.pared to conventional systems,
`but this cost different'ial may be reduced
`as improved electrical components are
`developed and as automotive production and
`marketing techniques are applied to the
`elec~rical compon~ci,ts. Other ,potential
`limitations of this hybrid s ystem are
`reduce.d driving range a,t very low speed.s
`and reduced. capability to supply vehicle
`auxiliaries at stands.till.
`In gene.ral,
`the replacement of a conventional drive
`train ~y this particular hybrid train will
`not increase the vehicle curb weight .
`From almost the beginning of the
`Automotive Age , various combtnations of
`:drive systems have been tried in order to
`achieve vehicle performance
`characteristics superior to tho.se that can
`be obtained using a s-ingle t yp.e of dri.ve .
`These efforts have been made in the name
`·of ·many ·worthwhile goals, such as
`,increased v·ehicle a-c;celeration capability,
`audible noi.se reduction, operation of an
`engine. or turbine .at optimum efficiency ,
`'redu c.t :io.n of no·xiou$ emissions , and
`improved fu.el economy. These efforts have
`so far .not led to .any· colll11Jercial
`
`A heat engine/electric hyhTid d.rive
`train is proposed as a means for impt'oving
`CVS-Hot fuel economy by an estimated 30%
`to 100% in various types ·of automotive
`vehicles . This drive train, classified as
`a parallel hybrid , has been analyzed by
`means o.f computer s:tmulat:i.on stud;l;es to
`evalua.te 'its fuel economy, pe rformance,
`
`and .emissions characteristics , anti has
`been compar,ed w:lth exis t'iing internal
`combustion engi.ne drive trains and other
`types of hy'bri<l drives , A pr o.totype
`system has been assembled and evaluated on
`a dynamomet,er test stand and ·has
`cori;o.bor ated the comput.er analysis ~d
`predict.ion s , P'toblems and limitation s of
`this system ai::e dis£ussed .
`
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`applications, although several
`e xperimental nybdd _buses and ·rapid
`transi t vehicles are being evaluated at
`the present time (1, 2 ,3). Fo"l? p~ivate
`vehicle applications, hybrid drive systems
`have generally been fo1,1nd to offer
`improvement in meeting one or
`insu fficien t
`tn0re of the. goals stated above to justify
`the added cost .and complexity compared to
`a singular drive. system, ,particularly
`compared to tlie conventio.nal Otto cycle
`internal combustion engine d .rive system.
`Two extensive ,EPA-sponsored studi.es of
`heat engine/electr.ical hybrid systems have
`been published (.4, 5) and generally c.oncur
`in this conclusion ~ as does the more.
`recent JPL Report . (6)
`It is therefore with sol!le trepidat:i.on
`that the subject of this paper, a heat
`engin~/electric hybrid drive system, is
`proposed as a viable drive tr,ain for
`tnodern automotive vehicles of -many
`varieties. However,
`.this proposition has
`been developed - and to large ext!!nt,
`confirmed - on premises somewhat different
`from those upon which the EPA. studies were
`based:
`
`1. The critical fuel situation in the
`lJ. s. and most Weste·rn count,ries has
`placed incx·eased e!llphasis on improved
`fuel economy for all types of vehicles
`since the initiation of tn.e EPA
`studies of 'Reference 3 and 4 .. Recent
`large mcreases in gasoline p-rices
`have l ed to the conclusion that a
`sizable increase in initial vehicle
`c.os.t (resulting from t he use of a
`hybrid drivetrain) c an be justified if
`a sufficient iiµprovement in vehicle
`fuel economy is realized.
`2. S,tudies performed during the
`development of th.is system have shown
`that. the relati'-re si.ze and power
`rating of the hybrid drive tr.lin
`components with respect to the vehicle
`wei.ght and perf.o:tmance rating have an
`important influence on vehicle fuel
`ec.onomy. Hybrid drive trains may not
`improve fue.l economy for vehicles of
`every si.ze , weight , and application
`category. Stated in another way,
`hybrid ·drive ·t-rains ar~ n.ot 11 scalable11
`as a funct.ion of vehicle size or
`weight as are singular drive trains;
`3. The modus operandi or control
`philosophy o-f a hybrid can have a
`p:rofound i nfluence on both fu.el
`economy and emissions. Past hybrid
`developmen.ts have tended to use the
`heat engine primarily as a battery
`charger; the subject hybdd reverses
`this philosophy and ~~es minimum use
`of the electric system.
`
`It :f,s hoped that the val:l.dity of
`these princ.iples will be amplifie<l by
`sub-sequent sections of this. paper.
`
`SYSTEM DESCRIPTION
`
`A block diagram of the system
`illustrating functional pe.rf.o~ance and
`energy flow paths :ls shown in Figure 1.
`This drive system is intended to re,place
`the eng:i.ne-transmission system in
`convent.tonal vehicl.es with the result of
`inc1:·easing the vehicle CVS-Hot fuel
`economy (miles/gallon,) from 30% to 100% a.t
`1975/76 .F.ederal em:i.ssion levels uaing the
`CVS-Hot cycle while maintaining
`a·ppro:id.mately equivalent accelei::a.ting,
`braking, and pa1:rsing chatacteristics. The
`hybrid-electric system consists of the
`following Ttlaj o:r components~
`l .. A different internal combusion engine,
`cor.isiderably smaller in displacement,
`and, hence, horsepower ·capabili'tY,
`than the eng.ine. in the original drive
`train.
`:2 . An electric motor/generator (one unit)
`which may be on a CJ)llll!lon shaft with
`the engine output shaft' or connected
`to the engine output shaft by means of
`a gear, belt, ot chain syst~. The
`motor/geneJ:ator may be of the DC
`commutator, DC homopolar, synchronous,
`or inductiott types .
`3 , A means of controlling power flow
`between the motor}genera·tor a11d
`bat.tery. This m.iy be :an el~ctronic
`controller using power thyristors or
`transisto't"S, a.on tac tor cbnt'toller
`using ba·ttery sw:f.tching techniques, or
`similar devices. The contx-oller must
`be cap.able of two-way power flow and
`should have higb energy .efficiency.
`4, An energy storage device. Th.is may be
`any device c-apable of har1dling the
`high bursts of pow.er required by the
`, drive train during acceleration and
`braking and of supplying the energy
`needs for low-spe.ed d:riving and the
`operation of vehicle. auxiliaries at
`low speeds and standstill. At the
`>resent time, batteries are the niost
`practical energy storage device, w.i th
`the nt cke1-cadmiUlll batt.ery having
`almost ideal ch.ara.c.teristi:cs for this
`applic.ation but. suffering a cost
`penalty. Flywheels. fuel cells in
`combination with batteries, closed
`loop cryogenic expander systems; are
`other po.ssibili ties.
`5 . A differential and a drive shaft.
`general, it is desired ta use the
`original drive shaft an.d differe.ntial
`of 'the vehicle .
`The system can be classified as a
`
`lo
`
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`parallel hybrid with e.ng-.1.ne on-off
`control, and bears some similarity in
`configuration with two other recent hybrid
`development.s , (9), (10)
`ln addition. to these major power
`components, other components required by
`the. bybr.id drive train include: control
`ci.l;'cuitry for the pr.oper operation of the
`pow-er con.troller; modified engine throttle
`and carburetor; sensors for converting
`vehicle speed, battery voltage. and charge
`level, .component tempe.ratures, etc , • to
`electrical. signals suitable for use in
`control and protection systems ; protection
`systems for both engine and elect1:ical
`sys-tem emission controls; and an overall
`vehicle control system.
`Tl.to modifications of the above sys.tern
`(_Figure 1) have ca,pabili'ties for improved
`system performance but usually add some
`cost penal.ties:
`I . The use of an automat.ieally-cont·;olled
`decoupler to perm.it the engine to be
`detached from the electrical lllOtor
`drive shaft when the vehiale is
`operating in an all-electric drive
`mode or in a braking mode.
`It has
`bee.i shown that the use of such a
`clutch will result in a further
`imp't'oveinent in fuel economy (see
`F.igure 5) .
`2 . The use of an e1ectr.ical.ly .... controlled
`gear changing system. This will often
`result in a reduce electrical system
`weight and an improved el.ect1=ical
`system efficiency .
`
`WffHL
`
`ENGi NE l=:::====::3==::0R:::::::IV:::::E:::::SH:::Af:::::T==:::(). DIFFERENTIAL
`GEAR
`
`M-OTO.R
`
`POWER
`CONTROL
`I BAT~-ERYI
`
`Fig, l -Ford parallel hybrid
`
`SYSTEM OPEMT10N
`
`The system has six modes of
`operation . The first five modes are shown
`in Figure 2. Mode I is all electric at
`spe.etls below 10 to 15 MPH.
`In Mode II the
`engine is the primary source of propulsion
`and there is no energy· in or out of the
`
`WHEEL
`t
`fNCINE F====Q9===~===d .
`-
`· -
`
`All
`I ELECTRIC
`
`rr ENGi NE
`ALOHE
`
`ID CHARGE
`
`JI ACOEL
`
`]: BRAKING
`
`Fig.2 -Five hyb.rid modes of operation
`
`elec\;:rioal system. Mode III is the.
`battery charging mo-de . The eng·ine stilt
`drives the rear wheels; however, excess
`energy is used to charge the battery.
`When acceleration demands exceed the power
`input of the engine, the motor p,ovides
`the needed additional po,wer. This is
`shown as Mode IV . Mode V i :s reg.eneracive
`breaking . The dece,leration energy of the
`vehicle is us·ed to chatge the batte:ry •
`. Fuel is shut c,>ff to the engine du:t·ing the
`all ele,ctx:ical mode and during bt'aking.
`The batt.ery stat-e of ch.a'l."ge is maintained
`between fairly nanow limit,s b.y the
`control system around a state of charge of
`about 75% of foll ·charge .
`'l'his strateg,y
`prevent:s cleep dis.cha.rge cycles on .the
`battery. The sixth mode is a.t vehicle
`standstill , during which condition botQ
`the engine and electrical motor are
`inoperative or ''dead;; ~ Required vehicle
`auxiliaries ai;e suppli.ed electrically ~t
`.standstill .•
`The ,objective of this system is to
`p.rovide an increase in .fuel e'conomy over a
`conventional automotive dr;i.ve system while
`maintaining equivalent acceleration
`perfor.mance .
`.Comparisons between the
`hybrid system and conventional systems
`have been stressed in all studies. The
`manne-r in which this com{?ar:Lson is viewed
`f't'om an overaLl systems standpoint i.s
`important in understanding the
`significance of this par,ticuiar hybrid
`configuration and its opera-tion .
`Figures 3 and 4 show that the fuel
`economy · for both a conventional ana hybrid
`sy·stem can be expi:essed ·as follo\.'1'S:
`
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`

`EN.GIIIE E
`F--IC5c;::=l
`
`L7JE·'·
`7lp'f _ _ -,,::::::;:~
`li----- ---71sys·--- - ---i
`
`ENGINE EFFICIEltOY
`
`POIERJRAlft EfflCl.fMCY
`
`SYSTEM f fflCIEN CY
`
`77E 77Pr ( QIN / GAL)
`.
`MPG= ·
`·
`- ·
`. (Ew / MI LE)
`
`Fig, 3 -Average fuel ec<mci>my for a conven(cid:173)
`tional vehicle in terms of system ~f:f:icien(cid:173)
`cies
`
`ENGINE EHICIENCY
`
`ELECTRICAL SYSTEM Eff lCIENC~
`
`Etc
`.
`TJE ~ Qlt.l
`T/ • .!.!L..
`EL E<:H
`Ew
`71 · -
`. tp1· E1.c
`Ew
`'TJSYS• QIN
`. MPG. "IE 1lpr ( o,N I GAL)
`(fw / MILE)
`.
`Fig,4 -Aver.age fuel economy for a hybrid
`vehicle in terms of system efficiencies
`and energies
`
`POWERTRAIN. EFFICIENCY
`
`SYSTf tt EFFfCIE,NCY
`
`t4PG OllLES / GALLON)
`
`MPG
`
`riE 11PT (Q/Gal)
`(~/Mile)
`
`where nE is the a'Vex·age engine brake
`termal efficiency , TIP! is the average
`eran:;imission efficiency , (Q/Gal) is the
`energy content per gallon gasoline.
`cons~m-ed and (Ew/Mile ) is the total enetgy
`requir-emeut at. the driv.e wheels per mile
`nec:essary to accelerate ·the vehicle ;an.d to
`overcome veh:icJ.e friction and aerodynami.c
`drag. The quant.ities in thi.s expression
`represe.nt aver·age values ·ove'I a prescr ibed
`driving cycle .. It should be noted that
`the. ave.rage powertrain efficiency i .s
`defined as t'he ratio of. total p.ositive
`engine shaft work to total positive energy
`requirement at the drive ,iheels . Stat,ed
`in another way, this represent·s th·e
`fraction .6£ total engine work used to
`propel the vehicle . For
`the hybrid drive
`tra in s-tate of chal;'ge is assumed to be the
`same at the begin·ning and end of the d·rive
`cyc:1e, thus 'the net energy input to th!:!
`transmiss:Lon from the hatt;ery iB zero.
`The task facing .the .hybrid system can
`now be clearly seen .
`In order to p.rovide
`an it1c;t'ettse. in fuel e¢onom,y over a
`conventional sys.te.m the -quant ity nE riPl'
`/(~wfMHe) must be increased , The present.
`hybrid system will be described in terms
`of how it strives to main-ta.in high average
`engine efficiency, high average
`transmission efficiency and low work
`requirements at ·the drive wheels while
`maintaining the eqt1ivalent acceleration
`l)erform.ance of the conventional system it
`,replaces.
`A. High Average Engine Efficiency
`1. Small engine - T.he engine used in
`tl\e convention al system is
`replace.cl by a much smaller engine
`in the hybrid system. The smaller
`eng.ine operates at higher load
`factors , res.ulting in increased
`efficiencies . The hybrid engine
`is sized to mee t vehicle c.ruise
`requirements up to a spec_i.Eied
`roa.d speed . This enables the
`veJ1icle to be propelled by the
`engine alone for extended cruise
`periods. This corresponds, to Mode
`II in Figure 2.
`2 , Fuel off duri ng idle and
`deceleration - Approximately 20~
`of the CVS-H fu.el consumption is
`used durin!} idle and braked
`deceJ.eration for the conventional
`vehicles with a utqmatic
`transmission consi.dered 1n this
`study . Elimin ation of idle and
`braked deceleration fuel flow in
`the hybr id configuration re.su.1.ts
`in significant improvements in
`aver.age engine efficiency •.
`3, Fuel off during .lovt speed
`.operation - Since. the engine is
`
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`

`gear-ed directly to the dr,ive
`whe:els the fuel is shut off .it
`low
`veh:i.cle speeds and the vehic.le is
`ptopelled by the electrical
`system. This correeponds: to Mode
`I in Figure 2.
`the fuel savings
`must be weighed against the
`electrical energy dissipated that
`Jnust be repla<.ed. by charging the
`baC:C;ery bter in the driving
`cycle . Since this charging i s
`done at a higher engine
`efficiency, this mode has a
`positive effect: on the average
`engine efficiency . However, this
`charging has an advers,e effect on
`the average transmission
`efficiency since a l ower !;);action
`of the engine work shows up as
`use.fol work at the drive wheels.
`The t otal gasoline us~d to :replace
`tll.e battery energy expended during
`this mode can actually e>tceed the
`amount of gasoline used :i,.n a
`·conventi,onal vehicle in
`accelerating up to the
`c.orr.espondi.ng vehicle speed, The
`energy requirements of this mode
`can be substat:ttially itt)proved by
`lowet'ing the work required to
`motor the engine by opening the
`throttle, collapsing the va.lves or
`by de-clut.ching the engine . Othe.r
`approaches in·clude gear changes or
`use of motors with better
`low-.speed effic.ie.ncies .
`4. Charg:!.ng the battecy at
`high-engine efficiency - When the
`battery requires charging from the
`,engine as represented by Hode III
`in Figure 2 , the basic strategy :Ls
`to provide the charging energy at
`.the most efficient engine
`operat.ing point.. This contribµt.es
`to a high overall engine energy
`efficiency, however , this ef.fect
`must be weighed again~t the e.ffect
`on transmission efficiency since
`the optimum engine efficienc:y will
`not in .general corre.spond to the
`most efficient charging torque
`level for the electrical system.
`Additional trade-offs appear whe11
`the effect of engine torque on
`emissions i-s discussed in a la tet ..
`sectio.n.
`5. Accelerate at high- engine
`efficiency - When the vehicle
`acceleration demands exceed the
`power capacity of the eri.gine , the
`electrical .system i s used to
`provi.de the extra ne·eded power.
`This is descr~bed as Mode IV in
`Figure 2..
`In general the eng;ine
`
`t.orqu.e level at which the
`electrical system is called upon
`corresponds to a h igh-engine
`efficiency po:Lnt, The effect on
`transmission efficiency must also
`be considered since a lower engine
`torque requires more electricaL
`energy .
`.B. Transmissi.on Efficiency - The
`transmi'ssion in a hybrid drive tr.i.in
`is the portion of the system th,',it
`'transmits use.fol wot'.k from- the engine.
`to the drive wheels . Since all the
`energy needed to propel th.e vehicle
`ultimately ,comes from the engi ne
`(assuming the. battery ends the drive
`cycle at the same state of charge) the
`basic objective of the cransmission i.s
`to minimize the amount of engine
`.ene.rgy used for other purposes . This
`is achieved as folLow.s:
`1. Engine geared directly to r.ear
`''l'lheels for primary source of
`propulsion~ When the electdcal
`system is not in use , the energy
`from the engine is transmitted
`directly t:o the r ear wheels
`through the diffe.rential. This is
`Mode II in Figure. 2 . The
`instantaneous transm1ssion
`eCficiency during this mode is
`essentially equal to the
`differential efficiency. The
`engine is sized to provide
`sufficient to.rque. in this mode fo r
`extended high-speed cruise .
`2. Use of electrlcal system only when
`needed - To keep the use of the
`el ectri.cal system to a min.imum,
`the motor is used only when
`needed.. The two modes requiring
`the motor are the all electric
`made at low speed (Mode I) and
`during heavy accelerations (Mode
`IV) .
`3. Use of regener.ative braking -
`Dur.ing braking the kinetic. energy
`of the vehicle is used to charge
`the battery. This is desctibed as
`Mode Vin Figure 2 . This has. a
`substant.ial effect on transmission
`efficiency by reducing the charge
`.energy required from ·the engine .
`c. Drive Wheel Energy - In converting a
`conventional vehi.c.le to a hybrid
`configuration the total energy
`requir.ement s at the drive wheel, must
`also be considered in. assessing the
`potential fuel economy gaips .
`· The
`·primary factot's that could reduce fuel
`economy are an increase in the vehicle
`weight and an increase in the
`rotational i nertia due to higher
`rotational speeds of the eng:i.ne and
`
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`

`motor. System weights wil.1 vacy
`c.,onsiderabl y with the vehicle
`acceleration requir.ements. For ·the
`nyhrid configurations con.sidered in
`this study small weight savings were
`realized. These .differences were
`generally not enough to change the
`inertial weight class of the v.e.hicle
`and were not co.nsidered in the fuel
`economy projections. The effects of
`increased rotati.onal inertias were
`also seen to be minimal ( or the
`configurations investigated.
`
`METHOD OF ANA,LYSIS
`
`A computeT program was deve.loped to
`simul.ate all elements of the drive t.rain
`for the six basic modes of ope·rat;ion over
`an arbitrary drive cycle. The required
`power at the driv·e whee.I is computed from
`the drive cyde data, the vehicle
`friction, aerodynami c drag, inertial
`acceleration and rotational ine't'ti.as. The
`corresponding power levels. are computed
`t:hrou.ghou.t the drivetrain based on
`rotational speeds and torques and
`component perfonoance characteristics.
`Motor/g~ner~r;.or qnQ. (:Otltl:Qll.er
`efficienci es are computed from efficiency
`tabies in terms of torq.ue and RPH. The
`efficiency tables used for the D. C. system
`are based on experimental data from
`reference (7). Similar tables for a
`brushless synchronous motor system ~re
`based on experimental data from reference
`(8). Batte.ry efficiency is computer from
`equivalent ci'rcuit mqdels fo1: specific
`battery types as described in Reference
`(16).
`The engine is sized tp provide
`sufficient :powe r for extended cruise
`witho1,1t the electrica1. system. Fuel flows
`are computed in. terms of engine speed and
`torque.
`In general , automatic calibration
`fuel island data is used with simulated
`exhau.st system, fan on, alternator
`operated at one-half charge and power
`steering pump load.ed. Engine motori ng
`torque is computed as a function of engine
`RPH f rom experimental da·ta .•
`Axle ratio 'between the engine and
`drive wheels and gear ratio between the
`mot.or and engine are. varied i n the
`analys:L.s untU a suitable compromise is
`reached betwe~n fuel economy, top speed,
`acceleration., maint'aining ba.tte ry charge
`and., in some cases• emissions .
`Comparisons with conventional
`d:i;ivetrains are mad:e by applying the same
`basic techni que of starting at the rear
`wheel:s and describing each element
`individual.ly.
`·Transmission efficiencies
`are computed for each gear f:ro111 o.utput
`
`speed. Automatic transmission shift
`sehedules are determined from driveshaft
`RPM and manifol.d vacuum. Manifold vacuum
`must be implied from engine ··torque which
`cannot be computed until tbe proper gear
`i.s deternine.d. The engine to1:que ancl
`transmission shi ft schedule must.
`lr:here,Eo:re, be matched it,eratively.
`The approach is similar to techniques
`described in Reference (11) £or
`•e.onventi.onal vehi cles and in Refet"ence
`(16) for electric vehicles.
`
`PYNAMOMETER TESTS
`
`£arly in the course of the ·computer
`simulation and other analytical studies of
`the hybrid concept., the nee4 for so.me
`experimental evidence to support the
`computer p·redic:t:ions of fuel eco~1-0my and
`perfoi;mance was r .ecognized. Also,
`emission measurements and engine sn:ategy
`£·or emissi.on control were required. Th,e
`first. step in such ~peri.mental
`evaluations has been the testing. of an
`engine- elect.de d.rivetT:ain with a
`dyna111ometer and inertia wheel as loading
`devices.. Ultimate evaluation of any
`·
`alternate engine or .o.ther drivetrain
`component must of necessity by ma.de
`through a long series .of vehicular tests
`under typical or pre.sc·dbed driving
`cbndit:t.ons. Howeve1:, for syst;.ems so far
`removed from conventional automotive
`p.ractice ·l:IS a hybrid driyetrain;
`dynam.ometer testing appears essential
`before vehicula1: testing is initiated.
`The principal goals of the hybrid
`dynamome·ter tests were:.
`1. To test th.e computer predictions of
`fuel economy·., performance, and
`emission.s using a production engine .
`2. To establish that .the fuel economy
`improvement is atta:inab1e at
`acceptable emission levels . This
`required that near optimQm. engine
`st.rategy regarding spark, air-fuel
`ratio , and exhaust gas recirculation
`be developed . This was done by
`dividing the speed torque plane in a:
`grid pattern, studying each a:rea in
`the gi--id and summing the total for
`hybrid operation. This process is
`called engin.e map·ping in subseq1.1ent
`discussions .
`3. To determine ,that ·t:he on-off fuel
`co·ntrol required by the hybrid wits
`p1:actical at acceptable ~r.fomance.
`emissions and cost. This was
`deterll!ined using a -carburetor and
`minor modification:s .
`4. To determine that the selected battery
`was .idequ.a t;e .
`5 . To determine that the engine is
`
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`basically suite.d to th~ 4nique o.r
`unusual operations in this concept,
`such a,s:
`a. Ho.taring the engine between O and
`800 RPM as requir.ed by the direct
`coupling to <the wheels. Normally
`an engine is cranked and
`immediately accelerated to an idle
`speed of 700 RPM or more.
`b. Qpera,tion at high torque most o.£
`the time.
`c. Higher than norm~l total use attd
`long duration of high torque at
`high speed .
`The experimental hybrid drivetrain
`was configured as in the block dia.gram of
`Figur ,e I with 'two e)tce:ptions: The
`·electric motor was on a common shaft with
`the engine, and the driveshaft was
`directly coupled to a dynamomet·er and
`inertia wheel to simulat~ the vehicle
`1;oad , aerodynamic , and inertial loads .
`The p.rinci.pal components used were :
`1. Engine: Ford 2. 3:L, 4-cylindeI ,
`'7 4
`production engine , modified for fuel
`'off operation.
`2 . Motor: Westinghouse • 40HP, 240 V. ,
`1750 RPM industrial shunt moi:or;
`blower cooied .
`3 . Controller : SCR chopper for motor
`armatur~ control during motoring ,and
`:i;egenerati:v.e braking (designed and
`assembled at Ford) ; separate power
`supply for field control,
`4. Battery: 140 cells connected in
`series of Marathon , type 20Dl20, NiCd;
`auxiliary forc..ed-air cool.fog to
`maintain cells at approidtnately 20 C;
`plus required monitoring e.quipment .
`5. Loading Device! Absorpt2on
`dynamometer of 150 lb~f2 inertia a:nd
`a flyvheel of 360 lb- ft
`inertia,
`The comb.ined inertias of the rotating
`members of the experimental system are
`equivalent to a vehicle of 7500 lb.
`ine·rtia. weight based upon ,an engine
`RPM/vehicle MPH (N/V) r;:1tio of 5J.5.
`Conventional gas analysis equipment was
`used to measure emissions unde·r conditions
`of steady state e ngine ope.ration.
`Measurements of exhaust CO,, CO2 , HC; o2
`a~d . ijOx and intake co2 ~ere made.
`.Fuel
`flow ·was measured by weight .
`Since the hybrid application requires
`operating .an engine under conditions
`considerably dif.fetent froin those
`associated with con.ventional vehicles,
`preliminary evaluation and modification of
`the 2. 3L engine was nece.ssary:
`l. The engine was modified to pe.rroit: fuel
`to be turned o,ff during deceleration
`and, at speeds below 1'5 MPH. This was
`ac.complishe'd by means of a small
`so;Lenoid valve to block fuel flow in
`
`the idle jet, removal of t:he throttle
`stop to permit full closure of the
`throttle pla:te,. a means of admitting
`air below the thl:ottle, and PCV
`modification .
`2, A sequence con t rol was required for
`minimum emiss'ions and quality
`performance during engine fu.el turn-on
`and turn- off . For ex:ample , during
`turn-off, the following sequence· was
`(a) close throttle , idle
`1,JSed :
`solenoid, and PCV valve, (b) open
`by-pass air valve around throttle to
`permit air without fuel into intake
`manifold, (c) turn-off ignition, with
`elapsed time between these events .
`3. Removal of some engine au:dl iaries ;
`for example, ,the engine. alternator is
`not required in a hybrid drive.; air
`conditioner w:as not used. The power
`steering pump ~as connected and
`driven.
`In a
`4. Low-speed engine .friction:
`conventional vehicle , the engine is
`operated below the idle sp~ed (about
`800 RPM) for only a few seconds duri.ng
`start-up.
`In the hybrid. much longer
`operation may be required .
`rhe
`low-speed .friction torques. of the 2. 3L
`engine were measured .
`5. Low-speed lubr.ication was evaluated ,
`6. The EGR valve and plumbing were
`enlarged to permit large EGR flow at
`wide- open th.i:ottlP. operation.
`Another. in.t:eresting problem for which
`the,re was almost no precedent wa.s the
`measurement of HC emissions during the
`frequent engine off/on transitions that
`the engine p~sses through during a typical
`driving cycle . Sine~ CVS equipment fot
`this measurement. was not available a
`technique using #luted samples from the
`engine-off pe.riod was d.eveloped. and
`cons idered to give reasonable accuracy.
`This method was used to predict the.
`emissions discusse.d in la.te:r sections of
`thi:;i paper.
`The resulting expe:r:imental system
`proved to be very " driveable" with smoo·th
`transitions between t he various operating
`modes . The system was 11ar:1ven'·' through
`several of the standard test driv ing
`cycles with ease ·and accuracy after a few
`learning cycles by the operator.
`In order to experimentally verify the
`calculat:ed values of fuel economy that had
`been obtained from the various computer
`simulations described ,ab.ove, several
`dynamic runs ove.r both CVS-H and SAE ( 17)
`driving cycles were performed on the
`experimental hybrid system mounte,cl on a
`dynamometer test stand . The SAE driving
`cycle is a simplified version. of .the CVS-H
`cycle developed mainly for the electric
`
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`

`veh'.i.cle tests . Many comparison.s of the
`two driving cycles have shown. that both
`re.sttlt in .apprPxin1ately the same fuel
`consumption for both 'ICE :and electric
`vehicles . Since the ",driving" of an
`experimental drivetrain on a dynamome:tet
`test stand ave.: the SAE cycle is much
`simpler than over the CVS-li cycle, .\lnd
`since the control of the system was not
`fully :automated but requirel;l consideraole
`manual control , the SAE cycle w-as chosen
`as the means for coml?aring calculated with
`measur·ed fuel economy of the hybrid
`It Y.as found. that after only
`driv etrain .
`a few tries , manual control was able to
`follow t'he requixed speed and accelerat.ion
`variations specified by the SAE. cycle
`almost perfectly. The actual e£ficienc1.es
`of the components in the electric branch
`o.f the hyb.rid and the actual road load
`simulated by the dynamometer wete fed int:o
`the computer mod-el to obtain the
`calculated fuel economy . The engine
`throttle positions were likewise rnade t;o
`correspo.nd between the measure and
`calculated test ·r uns. The results are
`summarized below:
`
`TABLE l
`COMPARISON OF MEASURED AND CALCULAXED
`DY.NAfiIC FUEL ECONOMY OF HYBRID
`
`Simulated vehicle
`inertia. weight
`Length of test run
`
`Calculated fuel economy
`Measured fuel economy
`
`7500 lbs
`3 SAE cycles
`(3 miles)
`15 . 2 mpg
`15.8 mpg
`
`FUEL ECONOMY STUDIES WITH AUTOMATIC .ENGINE
`C'ALIDRATlONS
`
`A variety of studies was conducted by
`applying t he computer program to hybrid
`and conventional vers ions of the same
`vehicle using fuel island data .for stock
`engines with automatic e:alibrations . The
`hybrid ele·ctrical systems were sized to
`p·rovide approximately: equivalent
`acceleration periformance. The r.esults of
`these stud.ies are summarized in Figure 5 .
`The .purpose of this section is to discuss
`the reasons for the fuel ec.onomy
`illiprovement re.sulting from a hybrid syiit!!m
`and to discuss the ef'fects of fundamental
`system c.hanges on fuel economy.
`A.. Reaso,ns fo r Fuel Ec<mOmy Improvemen t
`ResulUng from a Hybrid System - The
`Econoline Van and the Mark IV
`config.urations received t:he most
`emphasis in these. studies. Figures 6
`and 7 ptesent SUl!llllaries of comparisons
`made between typical hybrid and
`conventional versions of the Econoline
`Van and Mark IV, re.spectively. The
`computations were done for the CVS-H
`drive cycle and both comparisons a~e
`based on equivalent acceleration
`I?erformance between the r~sp~cti.ve
`hybrid and coQv.entional
`configurations . Both hybrid sys te.111a
`represent t:ypi.cal configtt,rations witb
`automatic engin.e calibrations• DC
`motor and cont.roller an·d nonnal idl,e
`throttle engine moto~ing .friction
`during fuel off modes.
`In Figure 6 a 4500 lb .
`conventional van with 300 ClD engine
`
`C.alcuJ.-atccl. fucI ·E~o.:tcu,x(c),
`(Ml'd·)
`
`~
`
`v"n <a)
`Von.
`
`\llu'.
`
`Van
`
`Va_~
`
`V4tr
`
`VM,
`
`\Im,
`
`n_y_Ori~ Pnwo.r ! ·rat,,,
`
`i!rul~.t
`1.1 vi.th .closod ~hrottl<>
`
`l. l
`
`'!1th 11id4•ovcn throttl~
`
`1.1 ., vn.l v.cu clo1cd
`
`I.I . cl\Jtt:h
`
`2,) dloo•l
`
`l!:te;5cl, clutch
`
`2.3
`
`I. I . clutch
`
`2, 3 di(!_QC, l , clutch
`
`Mark.. IV(b)
`
`2. 3
`
`(1Ct:) , <:lu.t:Ch
`
`K4rl< r:,/
`
`2, l
`
`( [CE)• c lvtc:l,
`
`~
`oc
`
`DC
`
`DC
`
`l)Q
`
`DC
`
`DC
`
`IJUc(o)
`
`Dloc
`
`DC
`
`i.1oc(eJ
`
`llybrld
`
`18. l
`1a,e
`
`19. ~
`
`20. 0
`
`22.0
`
`2). 7
`
`23. a
`
`28. ~
`
`18 .. 1
`
`21, 9
`
`ill
`14.I, (4)
`
`14 ,4
`
`tli ,,.
`
`I ~. 4
`
`14. 4.
`
`14 , 4
`
`U.4
`
`) 1;,4
`
`10 ... ~<H
`
`10 . )
`
`;
`
`{cp ruv.eaen t
`l!X~Hd/{CE
`
`28
`
`ll
`
`,.,
`
`3?
`
`53
`
`6S
`
`6'5
`
`97
`.n
`
`109
`
`.(a.) 4SOO lb. Incn1o lit,
`{b) 5500 lb. lr.o·rUa \l.t.
`tc) All futl economy ••lculatloM '°oscd upqn v~hl.ol.e . dtlv1ng the FcJcru1. CJ~-tt cycle; no nc: cl14ngc l.n bAttt.r,y
`Qt.4te-of"-cha~ae.,
`.(d) Cqlculnt<>d for unomheionlo:.,d, 240 CID ongln.c, Col.eulnt.to,u !>o•cd upon tlic 1915, .,,,.,~nlo<1lt<d JOO cro engb'lc ••cd
`on l975' vchlc1ee t-eau.1.ti:d 1n a fuel ec.o.nomy ~( {3. • .4 Hl'-C..,
`(c,J Axl4l olr•&•P reluo~on.co ,,,,.or d.cve.topcd by Fo(d..
`{Sec ·Kcfatt>ncoo ( 6) on.d {16)).
`(f'1 Cnlculaccd tor 1974 4