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`SAE TECHNICALPAPER SERIES 910247Electric Hybrid Drive Systems for PassengerCars and TaxisA. KalberlahVolkswagen AG
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`Wolfsburg, Germany
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`Reprinted from SP-862—Electric Vehicle Design and DevelopmentThe Engineering SocietyFor Advancing MobilityLand Sea Air and Space®INTERNATIONALlnternational Congress and ExpositionDetroit, MichiganFebruary 25-March 1, 1991400 COMMONWEALTH DRIVE, WARRENDALE, PA 15096-0001 U.S.A.
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`VWGoA - Ex. 1011
`Volkswagen Group of America, Inc. - Petitioner
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`Global
`Mobility
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`910247Electric Hybrid Drive Systems for PassengerCars and TaxisA. Kalberlah
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`Volkswagen AG
`Wolfsburg, Germany
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`Abstract
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`Various h y b r i d d r i v e configurations aredescribed and their advantages and disadvan-t a g e s f o r a p p l i c a t i o n i n p a s s e n g e r c a r s a r ed i s c u s s e d ; s p e c i f i c a l l y , t h e s e a r e t h e s e r i e shybrid, t h e p a r a l l e l h y b r i d , h y b r i d d r i v e sw i t h a d d e d t o r q u e a n d s p e e d , s i n g l e a n dtwo-shaft hybrids.The Volkswagen and AUDI group has deve-l o p e d d i f f e r e n t v e h i c l e s w i t h h y b r i d d r i v ef o r v a r i o u s a p p l i c a t i o n s . T h e s e v e h i c l e s a r ed e s c r i b e d a n d t e s t r e s u l t s a r e p r e s e n t e d o nt h e i r energy consumption, emissions anddriving performance. I n c o n c l u s i o n , somec o n s i d e r a t i o n s a r e p u r s u e d c o n c e r n i n g t h e i rchances on the market in different scenarios.1. INTRODUCTIONA hybrid drive, comprising b o t h e l e c t r i cdrive and internal combustion engine, can, ifsuitably designed, combine the advantages ofthe conventional vehicle drive system (largec r u i s i n g range, good performance) with thoseof a purely electric drive (low noise and ex-h a u s t e m i s s i o n s , conservation of petroleumresources). Vehicles equipped with such drive systemsa r e t h u s f a r m o r e f l e x i b l e t h a n e l e c t r i cvehicles; they are often just as versatile asv e h i c l e s with an internal combustion engineand consequently are not confined from theoutset to the "second car" market.Hybrid drives thus have far more extensivep o t e n t i a l a p p l i c a t i o n s t h a n e l e c t r i c d r i v e s ;h i g h e r p r o d u c t i o n r a t e s c o u l d i n p r i n c i p a ltherefore be achieved, leading to low manu-facturing costs. Surprisingly, t h e r e i s a w e a l t h o f p o s s i -b i l i t i e s f o r r e a l i z i n g s u c h h y b r i d d r i v e s .Some of t h e s e p o s s i b i l i t i e s a r e o u t l i n e dbelow and the advantages and disadvantages oft h e s e d i f f e r e n t d e s i g n s a r e investigated byconsidering vehicles already manufactured.2. SYSTEM ANALYSIS OF HYBRID DRIVES2.1 SERIES HYBRID DRIVE - Taking the purelye l e c t r i c d r i v e a s a s t a r t i n g p o i n t , i t i ss i m p l e t o c o n c e i v e o f a h y b r i d d r i v e : theb a t t e r i e s o f t h e e l e c t r i c v e h i c l e a r e r e -charged when driving as required via genera-tor driven by an internal combustion engine.This is not only simple in concept, but alsoi n p r a c t i c e ; s e v e r a l V W E l e c t r i c T r a n s p o r -t e r s , fitted with a suitable motor/generatora s s e m p l y i n t h e l o a d i n g a r e a , h a v e b e e nt r a n s f e r r e d f r o m W o l f s b u r g t o E s s e n . I na c t u a l f a c t , n o t o n l y i m p r o v i s e d v e h i c l ed r i v e s h a v e b e e n b u i l t a c c o r d i n g t o t h i sp r i n c i p l e , b u t a l s o r e a l d r i v e s , e . g . b yDaimler Benz (l)* for a city bus.The main advantage of the series hybrid:I t i s p o s s i b l e t o o p e r a t e t h e i n t e r n a lcombustion engine at a fixed operating pointwithin i t s e n g i n e - s p e e d / t o r q u e m a p . Thispoint c a n b e s e l e c t e d s o t h a t t h e e n g i n ef u n c t i o n s w i t h t h e g r e a t e s t e f f i c i e n c y o rproduces particularly low emissions.Nevertheless, t h e e f f i c i e n c y o f t h e e n t i r ed r i v e i s n o t s a t i s f a c t o r y . A s t h e s t r u c t u r eo f t h i s s o - c a l l e d s e r i e s d r i v e i n F i g . 1c l e a r l y s h o w s , the 3 components V (internalcombustion e n g i n e ) , G ( g e n e r a t o r ) a n d E( e l e c t r i c m o t o r ) a r e a r r a n g e d i n s e r i e s : t h emechanical energy generated b y t h e p e t r o l
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`*Numbers in parentheses designate referencesat end of paper
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`Fig 1 Structure of the series hybrid drive
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`engine is converted into electrical energy byt h e g e n e r a t o r and t h i s i s again convertedback into mechanical energy in the electricmotor. Each process of conversion is afflic-t e d w i t h l o s s e s r e s u l t i n g i n relatively bade f f i c i e n c y . T h i s i s a l s o c o n f i r m e d b y t e s tr e s u l t s f r o m a f l e e t o f h y b r i d b u s e s w h i c hwere operated in Esslingen.
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`A f u r t h e r d i s a d v a n t a g e o f t h i s s e r i e shybrid drive is its heavy weight.I f p o w e r P max i s r e q u i r e d a t t h e d r i v eaxle e.g. for the maximum speed, the electricmotor must be designed to produce this powerP max . I f t h e d r i v e r w i s h e s t o d r i v e l o n gdistances at this maximum speed, the power,which the battery c o u l d c o n t r i b u t e , c a n b ed i s r e g a r d e d s o t h a t b o t h , t h e g e n e r a t o r a n dthe internal combustion engine must be de-signed for the power P max (because of thec o n v e r s i o n l o s s e s i n t h e e l e c t r i c m o t o r a n dt h e g e n e r a t o r , t h e p o w e r to be employed bythe internal combustion engine would be eveng r e a t e r ) . A total power of over 3 P max isrequired t o d r i v e a t P max . T h a t m a k e s t h isdrive difficult to use in a universal vehicle( e . g . passenger cars) and expensive - parti-cularly due to the two electric components.F o r a v e h i c l e , w h i c h o n l y t r a v e l s i n t h ec i t y , e . g . a delivery van or city bus, it mays u f f i c e , i f t h e i n t e r n a l c o m b u s t i o n e n g i n ea n d g e n e r a t o r o f t h e s e r i e s h y b r i d a r e d e -s i g n e d f o r a v e r a g e p e r f o r m a n c e , s i n c e t h eb a t t e r y c o u l d t h e n p r o v i d e f o r t h e p o w e rpeaks. If this average performance is set at1 / 2 P max , i t c a n b e s e e n t h a t , e v e n i n t h e s eurban v e h i c l e s , engines would have to beinstalled with power of more than 2 P max .O n l y i f the combustion engine and theg e n e r a t o r a r e v e r y s m a l l c o m p a r e d t o t h ee l e c t r i c m o t o r - e . g . l i k e i n a r a n g e e x t e n -d e r f o r e l e c t r i c v e h i c l e s ( 2 ) , t h e s e r i e sh y b r i d s t r u c t u r e m a y b e a c c e p t a b l e b e c a u s eadditional weight, volumes a n d c o s t s a r esmall. T h e p r o b l e m o f e n e r g y e f f i c i e n c y i s n e -g l e c t a b l e i n t h i s c a s e b e c a u s e m o s t o f t h edriving energy comes as electricity from thep u b l i c n e t w o r k o v e r t h e b a t t e r y a n d t h eelectric motor to the wheels and only a smallamount c o m e s o u t o f t h e f u e l t a n k o v e r t h eIC-engine, t h e g e n e r a t o r a n d t h e e l e c t r i cmotor. Another situation would be given, i f t h ee f f i c i e n c y of the generator and the electricmotor together are as good as the efficiencyo f the conventional gearbox. I n t h i s c a s e ,n o t o n l y a s e r i e s h y b r i d c o u l d m a k e s e n s e ,but even a generator-motor-set instead of themechanical gearbox. Some companies hope to bea b l e t o d o t h i s b y u s i n g h i g h s p e e d s y n -chronous g e n e r a t o r s a n d m o t o r s w i t h n e wpermanent magnets having a very high magneticenergy density (3).B u t r e g a r d i n g F i g 2 s h o w i n g t h a t t h ee f f i c i e n c y of a mechanical gearbox is in awide range over 90 %, it seems to be a longway to the "electrical gearbox".Fig. 2 E f f i c i e n c y o f a t y p i c a l m e c h a n i c a lg e a r b o x o v e r t h e t o r q u e o f t h e i n p u tshaft for different rotation numbers.
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`Fig. 3 Structure of a parallel hybrid drive
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`2.2 PARALLEL HYBRID DRIVES - Fig. 3 illus-t r a t e s a p a r a l l e l h y b r i d d r i v e . H e r e , t h einternal combustion engine V and the electricmotor E a r e not arranged i n s e r i e s(considering their power flow) but in paral-l e l . The power provided by the two motorscould be added to the vehicle drive. In thisway, the power P max required to drive a cityvehicle, could be provided by designing e.g.both the internal combustion engine and thee l e c t r i ceach. m o t o r t o g i v e t h e p o w e r l / 2 P m a x( F o r a s e r i e s h y b r i d u n d e r t h e s a m econditions, a t l e a s t 2 P max would have to bei n s t a l l e d . )
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`Whilst t h e s e r i e s h y b r i d r e q u i r e s 2 e l e c -t r i c machines, only o n e i s p r e s e n t i n t h ep a r a l l e l h y b r i d . N e v e r t h e l e s s , e v e n w i t h t h ep a r a l l e l h y b r i d , n e i t h e r r e g e n e r a t i v e b r a k i n gnor r e c h a r g i n g t h e b a t t e r y w h e n d r i v i n gs h o u l d b e d i s r e g a r d e d , s i n c e t h e e l e c t r i cmotor E c a n a l s o f u n c t i o n a s a g e n e r a t o r ,e . g . i f t h e t o t a l p o w e r o f t h e i n t e r n a lcombustion engine is not required to drivet h e a x l e s . Turning to a parallel hybrid for a univer-sal vehicle requires the drive power P max forl o n g e r p e r i o d s , e . g . for long distances onthe motorway. In this case, the power of theinternal combustion engine must be P max . Thepower of the electric motor could be selectedfrom this completely independently. If P maxi s s e l e c t e d f o r t h i shybrid t o o , s i n c e t h e s e r i e s- i f t h e b a t t e r y p o w e r p e r m i t s - c a nd r i v e p u r e l y e l e c t r i c a l l y a t P max , a t o t a ld r i v e p o w e r o f o n l y 2 P max n e e d s t o b e i n -s t a l l e d . For a series hybrid under the sameconditions, t h i s w o u l d r e q u i r e more than 3P max .I n r e a l i t y i t i s m o r e s e n s i b l e t o s e l e c t amuch lower value for the power of the elec-t r i c d r i v e i n s u c h a p a r a l l e l h y b r i d ; i . e . al e v e l w h i c h p e r m i t s p u r e l y e l e c t r i c i n n e r - c i -ty driving with acceptable performance. Thisi s a n o t h e r p o i n t i n f a v o u r o f t h e p a r a l l e lhybrid. The advantages of the parallel hybridover the series hybrid can be summarized as follows:- Improved efficiency and thereby lower fuelconsumption i n t h e i n t e r n a l c o m b u s t i o nengine, s i n c e i t s m e c h a n i c a l e n e r g y i sdirectly passed on to the drive axle. (Onlyif the battery is charged during driving -which s h o u l d b e a v o i d e d f o r r e a s o n s o fconserving energy - is the same unfavour-able e f f i c i e n c y c h a i n p r e s e n t a s i n t h es e r i e s h y b r i d . )- The generator is no longer required- The weight is lower- Costs are lower2.3 STRUCTURES OF PARALLEL HYBRID DRIVES -P a r a l l e l h y b r i d d r i v e s c a n b e r e a l i z e d i n t h emost diverse forms, since the two mechanicalpower plants can be combined in various ways.T h e v e r s i o n a l r e a d y d i s c u s s e d i s i l l u s t r a -ted at the far left of Fig. 4. Because of itstwo parallel-running drive shafts, we like tocall this the two-shaft configuration.I n t h e n e x t s t r u c t u r e b o t h d r i v e u n i t s a r ea r r a n g e d a r o u n d a s i n g l e s h a f t . A s i n t h etwo-shaft configuration, the torques a r ea d d e d ( o r , i n g e n e r a t o r o p e r a t i o n , s u b t r a c -ted), and this provides a free choice, withinc e r t a i n limits, in determining the extent towhich the two units contribute t o t h e t o t a ldrive torque. This provides e.g. the opportu-n i t y to compensate for rapid changes in thedesired torque with the electric motor torqueand to permit only very slow changes in thet h r o t t l e - v a l v e s e t t i n g i n t h e i n t e r n a l c o m -b u s t i o n e n g i n e . T h i s s l u g g i s h n e s s i n t h et h r o t t l e - v a l v e h a s t h e e f f e c t o f r e d u c i n gexhaust emissions. However, the engine speedsa r e d e t e r m i n e d b y t h e g e a r b o x t r a n s m i s s i o n .There is no opportunity for selection here.T h e s i t u a t i o n i s r e v e r s e d i n t h e t h i r ds t r u c t u r e i l l u s t r a t e d i n F i g . 4 . H e r e , t h epower combination i s p e r f o r m e d b y a d d i n gtogether t h e s p e e d s o f r o t a t i o n o f b o t hd r i v e s i n a d i f f e r e n t i a l g e a r b o x p o s i t i o n e db e t w e e n t h e t w o u n i t s . T h e r e i s , t h e r e f o r e , acertain freedom in dividing the speed betweent h e t w o u n i t s , b u t t h e t o r q u e s a r e f i x e d b ythe desired drive torques. In consequence, iti s i m p o s s i b l e t o r e t a r d t h e t h r o t t l e v a l v e . Af u r t h e r d i s a d v a n t a g e a r i s e s f r o m t h e f a c tt h a t t h e e l e c t r i c m o t o r torque, on the onehand, a n d t h e p e t r o l e n g i n e t o r q u e , o n theother hand, must always be equal, althought h e t o r q u e - s p e e d maps o f b o t h u n i t s a r evastly different. Therefore, it is impossiblet o u t i l i z e e . g . the high torque of the elec-tric motor at low speeds of revolution, whichwould basically be advantageous for traction.
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`Fig.
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`4 Structures of parallel hybrid drives
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`F o r t h e s e r e a s o n s a n d b e c a u s e o f t h eproblems connected with the construction of ad i f f e r e n t i a l gearbox for combining highspeeds with simultaneous high torques, we didnot t h i n k i t o p p o r t u n e t o c o n s t r u c t s u c hhybrid drives with speed combination. Subse-quently, the following chapter only presentsh y b r i d d r i v e s w i t h t o r q u e c o m b i n a t i o n a n dwith combination of traction forces. t h e i n n e r c i t i e s w i t h o u t p r e s e n t i n g a n o b s t a c -l e t o t r a f f i c . T h e p e t r o l e n g i n e i s s t a r t e doutside the city centre. The power plants ofboth the petrol engine and the electric motora r e n o w a v a i l a b l e f o r a c c e l e r a t i o n . I f t h etotal power from t h e p e t r o l e n g i n e i s n o tr e q u i r e d f o r d r i v i n g , i t i s u s e d t o d r i v e t h ee l e c t r i c motor w h i c h n o w f u n c t i o n s a s ag e n e r a t o r . T h i s s e r v e s t o r e c h a r g e t h e b a t t e -r y .This p r i n c i p l e i s i l l u s t r a t e d b y t h es t r u c t u r e o n t h e f a r r i g h t i n F i g . 4 . I t c a nb e s e e n t h a t t h e r e i s n o m e c h a n i c a l c o n n e c -tion between the driving shaft of the combus-tion engine V operating on one axle and thee l e c t r i c m o t o r E d r i v i n g t h e o t h e r a x l e . T h i sis a parallel hybrid too, because both motorsc o u l d c o n t r i b u t e i n p a r a l l e l t o t h e t r a c t i o nforce needed by the car.3. CONSTRUCTED VW HYBRID DRIVES IN THE VW/AUDI-GROUPE v e n i f w e l i m i t o u r s e l v e s t o h y b r i dd r i v e s with torque combination, we can stillget vastly differing drives depending on thetype of vehicle and the application for whichthe drive is designed.3.1 VW CITY TAXI WITH HYBRID DRIVE - The Cityt a x i i s a v e h i c l e b a s e d o n a V W b u s ( 5 , 6 ) .I t s two-shaft hybrid drive is schematicallyrepresented in Fig. 5.Fig. 6 shows an exploded view of the compo-n ent s. The power from the 37 kW IC-engine 0is transmitted to the rear axle via a hydro-dynamic c o n v e r t e r W a n d a p n e u m a t i c a l l yoperated clutch K. The electric motor torquei s s u p e r i m p o s e d o n t h e p e t r o l e n g i n e t o r q u evia the fixed transmission.T h e e l e c t r i c d r i v e i s r e l a t i v e l y p o w e r f u lwith 16 kW continous output. With it, thetaxi c a n b e o p e r a t e d p u r e l y e l e c t r i c a l l y i n
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`Fig. 6 s h o w s t h a t t h i s d r i v e i s a b l e t ofunction without the conventional transmis-sion, which, of course, makes it very easyfor the driver to use. He only has to selectwhether he wishes to drive in purely electricm o d e o r h y b r i d , i . e . using both units, andexpress his wishes by operating the accelera-t o r a n d b r a k e p e d a l s . A c e n t r a l c o n t r o l u n i tt h e n c o n t r o l s t h e e l e c t r i c m o t o r ( v i a t h ee l e c t r o n i c c o n t r o l ) and t h e p e t r o l e n g i n e( v i a a s e r v o o n t h e t h r o t t l e v a l v e ) , t a k i n ginto account the battery charge.I n a d d i t i o n , t h e f o l l o w i n g f u n c t i o n s a r eensured :- Protection of battery against completedischarge and overcharging- Regenerative braking
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`Fig. 5 Hybrid drive with torque combination
`in the VW City Taxi
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`Fig. 6 Exploded view of the components of the VW City Taxi hybrid drive
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`- Sluggishness of the petrol engine in dyna-mic procedures by means of slow changes int h e t h r o t t l e v a l v e s e t t i n g . ( T h e d e s i r e dchanges are temporarily taken over by thee l e c t r i c m o t o r ) . However, the limitations of this City Taxidrive should also be recognized; a mountainroad with a gradient over 10 % of such lengthT h e v e h i c l e h a s b e e n t e s t e d o v e r 1 0 0 . 0 0 0km with the objective of obtaining informa-t i o n o n p e t r o l consumption and emissions.When the battery was mainly charged in dri-v i n g ( a n d n o t i n t h e g a r a g e w i t h a b a t t e r ycharger), p e t r o l c o n s u m p t i o n r o s e b y u p t o25 % against a conventional VW Bus. Ther e a s o n f o r t h i s i s t h e g r e a t e r w e i g h t o f t h evehicle and the unfavourable efficiency chainf o r c h a r g i n g t h e b a t t e r y i n t h e v e h i c l e .However, pollutant emissions dropped conside-rably i n c o m p a r i s o n t o t h e c o n v e n t i o n a lvehicle; specifically, CO by 27 % and HC by85 %. If the operation of the electric motoras a l t e r n a t o r i s r e d u c e d ( b y l i m i t i n g t h ec h a r g e c u r r e n t ) , f u e l c o n s u m p t i o n a n d e m i s -s i o n s f a l l ( 6 ) .T h e t r a c t i v e r e s i s t a n c e d i a g r a m i n F i g . 7shows t h a t t h e v e h i c l e d i s p l a y s r e s p e c t a b l eperformance although all driving conditionsare met in a single gear.This is due firstly to the ideal, hyberbo-l i c t r a c t i v e f o r c e c u r v e o f t h e e l e c t r i cmotor, secondly to the torque converter andt h i r d l y to the p rin cip le of torque addition.T h i s m e a n s t h a t e v e n a f u l l y l a d e n v e h i c l ec a n i n c r e a s e i t s a b i l i t y to climb by up to23 %. In many areas, t h e t r a c t i v e f o r c e s a r eeven higher than if a conventional VW Bus isdriven by a 37 kW petrol engine with 4-speedmanual gearbox.
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`Fig. 7 Tractive resistance diagram of the VW
`City Taxi
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`t h a t e v e n a n i n i t i a l l y f u l l y c h a r g e d b a t t e r yw o u l d n o t s u f f i c e , cannot be overcome witht h e p e t r o l e n g i n e a l o n e , s i n c e , i n t h i s t y p eo f o p e r a t i o n , t h e m a x . g r a d i e n t c a p a b i l i t yamounts to barely 10 %.As much as this hybrid drive proved itselfi n t h e C i t y t a x i , i t i s , h o w e v e r , n o t s u i t a -ble for use as a u n i v e r s a l d r i v e e . g . f o rpassenger cars.3.2 TWO SHAFT HYBRID DRIVE EVW2 - The objec-tives in developing this hybrid drive were:a ) U n i v e r s a l v e r s a t i l i t y(Even with a flat battery the vehicleshould be fully usable and still displayapproximately the same performance as aconventional vehicle.)b) Economy with energy (No battery charging in driving!)c) Low additional costs in comparison to aconventional drive.Since the requirements a and b point to ani n t e r n a l combustion engine of approximatelynormal power, t h e r e q u i r e m e n t c i n d i c a t e st h a t t h e a d d i t i o n a l e l e c t r i c d r i v e shouldh a v e t h e s m a l l e s t p o w e r o u t p u t p o s s i b l e ; t h equestion is however, what can you do with it.I f e . g . a 5 kW motor is selected for a VWGolf, its power is s u f f i c i e n t t o d r i v e thevehicle on level ground at constant speeds upto 50 kph. This leads one to suppose that thep e t r o l engine is often operated at very lowp o w e r i n i n n e r c i t y t r a f f i c . T h i s i s c o n f i r -med in Fig. 8: T h i s r e p r e s e n t s t h e w o r k i n gp r e s s u r e , a measurement of the petrol engine torque, as af u n c t i o n o f e n g i n e s p e e d . T h i s m a p a l s ocontains t h e l i n e s o f c o n s t a n t s p e c i f i cconsumption. T h e s h a d e d a r e a i l l u s t r a t e s t h er a n g e i n w h i c h t h e p e t r o l e n g i n e o p e r a t e swhen the vehicle drives the European Cyle. Itcan be seen that very high specific consump-tions, i . e . b a d e f f i c i e n c y l e v e l s , a r e p r e -s e n t h e r e . I t s h o u l d b e c l e a r t h a t t h e 5 k We l e c t r i c m o t o r w h i c h c a n c o v e r t h e h a t c h e darea of the map, can take over a considerablep r o p o r t i o n o f t h e s e u n f a v o u r a b l e o p e r a t i n gconditions. The p e t r o l e n g i n e a n d e l e c t r i c m o t o rcomplement one another very w e l l i n s u c h ad i s t r i b u t i o n o f t a s k s , s i n c e e a c h d r i v e i sallocated t h e t a s k s w h i c h i t c a n p e r f o r mp a r t i c u l a r l y e f f e c t i v e l y : t h e p e t r o l e n g i n edrive rapid acceleration and high speeds, thee l e c t r i c d r i v e s m a l l e r l o a d s , s u c h a s o c c u ri n i n n e r c i t y d r i v i n g . I n a d d i t i o n , l o w e renergy consumption - the sum of petrol f o rthe IC-engine and e l e c t r i c a l e n e r g y f o rcharging the battery - i s t o b e e x p e c t e d . I n1 9 8 3 , t h e 1 s t p r o t o t y p e o f t h i s s p e c i a lhybrid design was manufactured in cooperationwith t h e E l e c t r i c i t é N e u c h a t e l o i s e S.A. andinstalled in a 1982 Golf (7).T h e s t r u c t u r e o f t h e r e a l i z e d d r i v e i ss c h e m a t i c a l l y r e p r e s e n t e d i n F i g . 9 ; a g a i n ,this is a two-shaft hybrid. The IC-engine islinked to the gearbox via an automatic elec-tromechanical clutch K 0 . T h e e l e c t r i c m o t o ris connected to the other end of the gearboxi n l e t s h a f t v i a f i x e d t r a n s m i s s i o n a n d a nautomatic, electromagnetic clutch K E . Inc o n t r a s t t o t h e C i t y t a x i , a conventionalm a n u a l g e a r b o x i s p r e s e n t , t h i s b e i n g a4 - s p e e d s e m i - a u t o m a t i c . A c e n t r a l c o n t r o lu n i t r e g u l a t e s the use of t h e t w o d r i v em o t o r s , i . e . i t d e c i d e s w h i c h o f t h e t w omotors should take over the current require-ment for driving performance.
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`Fig. 8 Map of a petrol engine with: lines of
`constant consumption, working range of
`the petrol engine in the European
`Cycle, working range of a 5 kW elec-
`tric motor
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`Fig. 9 Arrangement of the components in the
`EVW2 hybrid drive for a VW Golf
`
`I n o p e r a t i o n o f t h e r e a l i z e d d r i v e i s r e l a t i -v e l y s i m p l e . T h e f a m i l i a r a c c e l e r a t o r p e d a lalone i s u s e d t o c o n t r o l a n d o p e r a t e bothmotors and their clutches. There is no clutchpedal p r e s e n t . A s i n e v e r y c o n v e n t i o n a lvehicle, the Hybrid Golf is started via theignition lock. When the IC-engine has reached
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`a s u f f i c i e n t o p e r a t i n g t e m p e r a t u r e a n d t h evehicle is standing s t i l l , both motors areswitched off. When 1st gear is selected, theI C - e n g i n e i s a u t o m a t i c a l l y s t a r t e d a n d t h eclutch between the IC-engine and gearbox isa u t o m a t i c a l l y c l o s e d w h e n t h e a c c e l e r a t o rpedal is depressed; the vehicle moves off anda c c e l e r a t e s . Releasing the accelerator pedal(to zero) causes the IC-engine clutch to openand the next gear can be selected.I f t h e t r a f f i c s i t u a t i o n r e q u i r e s l e s sperformance when driving with the IC-engine,t h e a c c e l e r a t o r p e d a l s h o u l d b e l i f t e d . I ft h e a c c e l e r a t o r p e d a l i s f u l l y r e l e a s e d a n dn o f u r t h e r a c t i o n o c c u r s f o r l o n g e r t h a n0 . 5 s . i.e. no renewed acceleration and noo p e r a t i o n o f t h e t r a n s m i s s i o n s e l e c t o r l e v e r ,t h e I C - e n g i n e s w i t c h e s o f f a n d t h e v e h i c l enow runs on without power. When the accelera-t o r p e d a l i s d e p r e s s e d a g a i n , t h e e l e c t r i cmotor takes over the driving. If the electricmotor’s 5 kW drive power is not sufficient,because t h e d r i v e r w i s h e s t o g o f a s t e r o ra c c e l e r a t e , he should "give more gas", i.e.increase the accelerator-pedal travel beyonda c e r t a i n p o i n t . T h e I C - e n g i n e i s r e - s t a r t e ds o t h a t t h e v e h i c l e c a n d r i v e o n u n d e r t h epower of the IC-engine.I t i s a l s o p o s s i b l e t o d r i v e w i t h e i t h e rthe electric motor alone or with the IC-en-gine alone: I f r e q u i r e d , it would be possible to driveu n d e r p u r e l y e l e c t r i c p o w e r - albeit withreduced c a p a c i t y f o r a c c e l e r a t i o n . A t aconstant speed of 50 kph, a distance of 36 kmc a n b e c o v e r e d u n d e r p u r e l y e l e c t r i c p o w e rwith the 200 kg lead-acid battery.F o r l o n g e r j o u r n e y s , e . g . h o l i d a y s , thet r a c t i o n b a t t e r y c a n be removed from thevehicle to obtain additional luggage spaceand i n c r e a s e d l o a d s . D r i v i n g i s t h e n d o n ewith the IC-engine.During braking and downhill driving thevehicle’s kinetic energy, which would other-wise be absorbed at the brakes or even resultin additional petrol consumption on accounto f e n g i n e overrun, can be stored in thetraction battery as electrical energy.After completion of the vehicle, consump-tion and exhaust emission measurements forthe European Cycle were first carried out ona r o l l e r d y n a m o m e t e r ( 8 ) . F o r t h i s , t h ep e r c e n t a g e d i s t r i b u t i o n o f d i s t a n c e c o v e r e dand time spent i n e a c h o f t h e 4 o p e r a t i n gconditions " E l e c t r i c d r i v e " , "IC-enginedrive", "Coasting" and "Stopping" were mea-sured. These were intered in Fig. 10. It canb e s e e n t h a t t h e I C - e n g i n e i s o n l y u s e d t oc o v e r 2 1 . 7 % o f t h e d i s t a n c e , w h i l s t t h eelectric motor is used for 53.3 %.
`
`Fig. 10 Distance and time percentage
`distribution in the European Cycle
`with the EVW2 hybrid drive
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`T h i s n a t u r a l l y h a s s t r o n g i n f l u e n c e o nreducing consumption and emissions. TheHybrid-Golf only consumes 33 % of the petrolwhich the conventional Golf required for theEuropean Cycle. The quantities of CO and HCi n t h e e x h a u s t g a s e s w e r e g r e a t l y r e d u c e d ,but the quantity of NO x changed little.Extensive road tests were then carried outin public traffic in Brunswick (7). The fuelsaving in this case was not as high as in theEuropean Cycle, but it still amounted to 40 %over the Standard Golf. The additional elec-t r i c a l energy r e q u i r e d f r o m t h e t r a c t i o nbattery is 8.3 kWh/100 km or 13.8 kWh/100 kmf r o m t h e p u b l i c s u p p l y n e t w o r k . A t 0 . 2 0DM/kWh that is around 2.80 DM/100 km.I n t h e B r u n s w i c k - C y c l e , 6 0 k m c a n b ecovered i n h y b r i d d r i v i n g w i t h a s i n g l ebattery charge.3.3 ONE SHAFT HYBRID DRIVE EVW1 - The aim oft h i s p r o j e c t i s t o t u r n t h e b a s i c c o n c e p t o fthe EVW2 drive - optimal division of t a s k sbetween a relatively weak electric motor anda relatively powerful IC-engine - into reali-ty in a considerably more compact construc-t i o n s u i t a b l e f o r m o t o r c a r s .T h e p r e l i m i n a r y s t a g e c a n b e s a i d t o b et h e s i n g l e - s h a f t h y b r i d d r i v e j o i n t l y b u i l tby Volkswagen and General Electric and com-m i s s i o n e d b y t h e A m e r i c a n Energy Ministy(DOE) (9). The EVW1 hybrid drive for a VU Golf deve-loped in the last few years by VW also incor-p o r a t e s a s i n g l e - s h a f t c o n f i g u r a t i o n ( 1 0 ) .As Fig. 11 shows, both the IC-engine andt h e e l e c t r i c m o t o r o p e r a t e o n t h e g e a r b o xinput shaft. The rotor of the electric motorreplaces the gearbox flywheel and is flankedon each side by a clutch.
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`Fig. 11 Single-shaft hybrid drive EVW1 with
`disk electric motor between two
`clutches Kl and K2
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`T o f i t s u c h a d r i v e i n t o v e h i c l e s a t t h el o w e r e n d o f t h e m i d d l e r a n g e , t h e e l e c t r i cmotor must be constructed in disk form with-out commutators, as already indicated in Fig.11. In cooperation with Bosch and LUK, VW hasdeveloped an asynchronous motor/generator inwhich the two clutches are integrated.This compact construction means t h a t t h ee n g i n e / g e a r b o x d r i v e u n i t o n l y i n c r e a s e s i nlength by 58 mm. The weight of themotor/gene