SAE TECHNICAL
`PAPER SERIES
`
`910247
`
`Electric Hybrid Drive Systems for Passenger
`Cars and Taxis
`
`A. Kalberlah
`Volkswagen AG
`Wolfsburg, Germany
`
`The Engineering Society
`For Advancing Mobility
`Land Sea Air and Space ®
`I N T E R N A T I O N A L
`
`Reprinted from SP-862—
`Electric Vehicle Design and Development
`
`lnternational Congress and Exposition
`Detroit, Michigan
`February 25-March 1, 1991
`
`4 0 0 C O M M O N W E A L T H D R I V E , W A R R E N D A L E , P A 1 5 0 9 6 - 0 0 0 1 U . S . A .
`
`

`

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`Mobility
`Database®
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`are abstracted and indexed in the
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`
`ISSN 0148-7191
`Copyright 1991 Society of Automotive Engineers, Inc.
`
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`Printed in U.S.A.
`
`

`

`910247
`Electric Hybrid Drive Systems for Passenger
`Cars and Taxis
`
`A. Kalberlah
`Volkswagen AG
`Wolfsburg, Germany
`
`Abstract
`
`c onf i gu ra t i o n s a re
`Various
`h y b r i d d r i v e
`described 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 e
`d 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 s
`hybrid,
`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 s
`w 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 d
`two-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 e
`f or va r i o us a p pl i c a t i o ns . T he s e v eh i c l e s a r e
`d 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 n
`t h e i r
`energy
`consumption,
`emissions
`and
`dr i vi n g
`I n c o n c l u s i o n ,
`some
`performance.
`c on s i de r a t i on s a re pu r s u ed c o nc e r n i ng
`t h e i r
`chances on the market in different scenarios.
`
`1.
`
`INTRODUCTION
`
`b o t h e l e c t r i c
`A h yb r i d dr i ve , co m pr i s i n g
`drive and internal combustion engine, can, if
`s ui t a bl y d es i g ned , c om bi ne t he a dv a nt ag es o f
`t he c onv ent i ona l ve hi c l e dri ve s y s t e m ( l ar ge
`range, good performance) with those
`c r u i s i ng
`of a pu r e l y el ec t r i c dr i v e (l ow no i s e a nd e x-
`conservation
`of petroleum
`h a u s t e m i s s i o n s ,
`resources).
`
`equipped with such drive systems
`Vehicles
`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 c
`a r e
`t he y a re of t en j u s t as ve r s at i l e a s
`ve h i c l e s ;
`ve h i c l e s w i t h a n i nt e r n a l c om b us t i o n en gi ne
`not
`confined from the
`and
`consequently are
`outset to the "second car" market.
`
`Hybrid drives thus have far more extensive
`p 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 l
`t he r e for e be a c hi e ve d, l e ad i ng t o l o w m a nu-
`f ac t u r i ng co s t s .
`
`t h e re i s a we a l t h o f p os s i -
`S ur p r i s i ng l y,
`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 .
`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 d
`Some of
`below and the advantages and disadvantages of
`i nve s t i gat e d b y
`t h e s e d i f f e r e n t d e s i g n s a r e
`considering vehicles already manufactured.
`
`2. SYSTEM ANALYSIS OF HYBRID DRIVES
`
`2.1 SERIES HYBRID DRIVE - Taking the purely
`a s t a r t i n g p o i n t , i t i s
`e l e c t r i c d r i v e a s
`t he
`s 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 :
`t h e e l e c t r i c v e h i c l e
`a r e r e -
`b a t t e r i e s o f
`charged when driving as required via genera-
`t or d ri v en by a n i n t e rna l co m b us t i on en gi ne .
`Th i s i s n ot o nl y s i m pl e i n c o nc ep t , but a l s o
`i 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 ns p o r -
`f i t t e d wi t h a s ui t a bl e m ot o r/ g en e ra t or
`t e r s ,
`a 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 n
`f r o m W o l f s b u r g t o E s s e n . I n
`t r a n s f e r re d
`a 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 e
`d 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 s
`b u t a l s o r e a l d r i v e s , e . g . b y
`p r i n c i p l e ,
`Daimler 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 l
`e ngi n e a t a f i xe d ope r at i ng po i n t
`combustion
`wi t hi n
`i t s e n g i n e - s p e e d / t o r q u e m a p .
`This
`point
`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 e
`f 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 r
`produces particularly low emissions.
`
`t h e e f f i c i e n c y o f t h e e n t i r e
`Nevertheless,
`d 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 e
`o 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 . 1
`c l e a r l y s h o w s ,
`the 3 components V (internal
`e ng i ne ) , G ( g e n e r a t o r ) a n d E
`combustion
`( e l e c t r i c m o t o r ) a r e a r ra n g e d i n s e r i e s : t h e
`m e ch ani c a l en er gy ge ne ra t e d
`b y t h e p e t r o l
`
`Numbers
`in parentheses designate references
`at end of paper
`
`6 9
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`

`engine is converted into electrical energy by
`and
`t h i s i s
`again converted
`t h e g e n e r a t o r
`ba c k i nt o m ec ha ni c a l en er gy i n t h e el e c t ri c
`motor.
`Each process of conversion is afflic-
`r el a t i ve l y ba d
`t e d w i t h l o s s e s r e s u l t i n g i n
`e 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 t
`r 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 h
`were operated in Esslingen.
`
`Fig 1 Structure of the series hybrid drive
`
`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 s
`hybrid drive is its heavy weight.
`
`a t t h e d r i v e
`I f p o w e r P max i s r e qu i r e d
`a xl e e . g.
`for the maximum speed, the electric
`motor must be designed to produce this power
`Pmax .
`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 g
`distances at this maximum speed,
`the power,
`which
`c ou l d c on t r i b ut e , ca n b e
`t he ba t t er y
`di s r e ga r d e d s o t h at b ot h , t he g e n e ra t o r a n d
`the
`internal combustion
`engine must be de-
`signed
`for
`the power P max
`
`(because of
`the
`c on ve r s i on l os s es i n t he el e ct ri c m ot or a n d
`t h e g e ne r a t o r , t he p ow e r
`to be employed by
`the internal combustion engine would be even
`total power of over 3 Pmax is
`g r e a t e r ) . A
`required t o d r i v e a t P max . T h a t m a k e s t h i s
`dr i ve di f fi c u l t t o u s e i n a uni ve r s al ve h i cl e
`passenger cars) and expensive - parti-
`( e . g .
`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 e
`c i t y , e . g . a del ive ry van or ci t y bus , it m ay
`s 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 e
`a 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 e
`t h e n p r o v i d e f o r t h e p o w e r
`b a t t e r y c o u l d
`peaks.
`I f t h i s a ve r ag e pe rf or m a nc e i s s e t a t
`i t c an be s e e n t h a t , e ve n i n t he s e
`1 / 2 P max,
`urban
`engines would have
`to be
`ve h i c l e s ,
`installed with power of more than 2 Pmax.
`O n l y i f
`the combustion
`and the
`engine
`g 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 e
`e l e c t r i c m o t or - e .g . l i ke i n a r a ng e e xt 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 s
`hy br i d s t r uc t u re m a y be a c c e pt a b l e b e ca u s e
`volumes
`a ddi t i ona l weight,
`a n d c o s t s
`a r e
`small.
`
`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 e
`dr ivi ng ene rgy c om es a s el e ct ri c i t y fro m t he
`p 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 e
`electric motor to the wheels and only a small
`amount
`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 e
`IC-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 c
`motor.
`
`situation would be given,
`Another
`i f t h e
`of t h e ge ne ra t o r a nd t he e l e c t ri c
`e f f i c i e n c y
`motor
`together are as good as the efficiency
`o 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 the
`mechanical gearbox. Some companies hope to be
`a 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 w
`permanent magnets having a very high magnetic
`energy 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 e
`e f f i c i e n c y
`of a m e ch an i ca l ge a rb o x i s i n a
`wide
`range over 90 %, it seems
`to be a long
`way to the "electrical gearbox".
`
`F ig.
`
`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 l
`ge a r bo x ov er t he t o rq ue o f t he i np ut
`s ha ft f or di f fe re nt rot a t i on num b e rs .
`
`70
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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 e
`internal combustion engine V and the electric
`motor
`E
`not
`a r e
`arranged
`i n s e r i e s
`(considering
`their power flow) but in paral-
`The power provided by the two motors
`l e l .
`c oul d b e ad de d t o t he ve h i cl e d r i ve . I n t hi s
`the power Pmax r eq ui r e d t o d ri ve a c i t y
`way,
`ve hi c l e ,
`could be provided by designing e.g.
`bo t h t h e i n t e rna l c om b us t i on e ng i ne a nd t h e
`e l e c t r i c
`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
`each.
`( 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 e
`c ondi t i o ns ,
`a t l e a s t 2 P max would have to be
`i n s t a l l e d . )
`
`Fig. 3 Structure of a p arallel hybrid drive
`
`Whilst
`t h e s e r i e s h y br i d r e qu 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 e
`pa r a l l e l h yb ri d. Ne v er t h e l e s s , e ve n wi t h t h e
`pa r a l l e l h ybr i d , n ei t h e r re g e n e r a t i ve b r a ki ng
`nor
`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 g
`s h o u l d b e d i s r e g a r d e d ,
`s i n c e t he
`e l e c t r i c
`motor 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 l
`combustion
`e ngi n e i s
`not
`required to drive
`t h e a x l e s .
`
`Tu r ni ng t o a pa r al l e l h ybr i d f or a uni ve r -
`sal vehicle requires the drive power Pmax for
`l o n g e r p e r i o d s , e . g .
`f or l ong di s t a nc es on
`t he m ot or wa y. In t h i s c as e , t he powe r of t h e
`internal combustion engine must be Pmax . The
`power of the electric motor could be selected
`from
`this completely
`independently.
`If Pmax
`i s s e l e c t e d f o r t h i s
`t oo , s i n c e
`t h e s e r i e s
`hybrid
`-
`i f t h e ba t t e ry po we r pe r m i t s - c a n
`d r i v e p u r e l y e l e c t r i c a l l y a t
`Pmax, a t o t a l
`d 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 same
`c ondi t i o ns ,
`t h i s wo u l d r e qu i r e more than 3
`Pmax.
`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 a
`m uc h l o w er va l ue f or t he p owe r o f t he el e c -
`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 . a
`l e v el w hi c h pe r m i t s p ur e l y e l e c t r i c i n n e r - ci -
`ty driving with acceptable performance. This
`i 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 l
`hybrid. The advantages of the parallel hybrid
`over
`the series hybrid can be summarized as
`
`follows:
`
`-
`
`Improved efficiency and thereby lower fuel
`i n t h e i n t e r n a l c o m b u s t i o n
`consumption
`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 s
`engine,
`di r e ct l y p a s s e d on t o t he d ri ve ax l e. (O nl y
`i f t he ba t t e ry i s c ha rg ed dur i ng dr i vi ng -
`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 f
`which
`i s t he s am e unf a vour -
`c ons e r vi ng e ne r gy -
`c h a i n p r e s e n t a s i n t h e
`able
`e f f i c i e n c y
`s e r i e s hy br i d . )
`
`- The generator is no longer required
`
`- The weight is lower
`
`- Costs are lower
`
`2.3 STRUCTURES OF PARALLEL HYBRID DRIVES -
`P a r a l l e l hy b r i d dr i ve s c a n b e r e a l i z e d i n t he
`most diverse forms, since the two mechanical
`power plants can be combined in various ways.
`
`T he v e rs i on a l r e a dy d i s c u s s e d i s i l l us t r a-
`t ed at t he fa r l eft of F i g. 4. Be ca us e of it s
`t w o pa r al l el -r un ni n g d r i ve s ha f t s , we l i ke t o
`c al l t hi s t h e t wo -s ha ft c on f i gur at i on .
`
`I n t h e n e xt s t r uc t u re b ot h dr i v e u ni t s a re
`a 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 e
`a r e
`the
`torques
`c onfi g ur at i on,
`two-shaft
`a 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 -
`t e d) , a n d t hi s pr ov i de s a f r e e c hoi ce , wi t h i n
`l i m i t s , i n de t er m i ni ng t he e xt en t t o
`c e r t a i n
`t o t h e t o t a l
`w hi c h t he t w o un i t s c ont r i bu t e
`drive torque. This provides e.g. the opportu-
`changes in the
`to compensate for rapid
`n i t y
`desired torque with the electric motor torque
`to permit only very slow changes in the
`and
`t 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 e
`t 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 g
`exhaust emissions. However, the engine speeds
`a re de t e r m i ne d by t h e ge a rb ox t r a ns 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 d
`s 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 e
`power
`combination
`i s p e r f o r m e d b y a d d i n g
`o f b o t h
`t h e s p e e d s
`o f r o t a t i o n
`together
`d 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 d
`be t w e e n t he t wo u ni t s . The r e i s , t h e r ef or e , a
`certain freedom in dividing the speed between
`t 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 y
`the desired drive torques. In consequence, it
`i s i m po s s i bl e t o r e t a r d t h e t hr ot t l e va l v e . A
`a r i s e s f r o m t h e f a c t
`f u r t h e r d i s a d v a n t a g e
`one
`t h e e l e c t r i c m ot or
`torque, on the
`t h a t
`the
`a nd t he p e t r ol e ng i n e t o rq ue , on
`hand,
`ot h er h a nd, m us t a l w ay s be eq ual , a l t ho ugh
`t he t o r qu e - s p e e d maps
`o f b o t h u n i t s a r e
`va s t l y d i ff er e nt . The r ef or e, i t i s i m po s s i bl e
`t o u t i l i z e e . g .
`t he hi gh t o rq ue o f t he el e c -
`tric motor at low speeds of revolution, which
`would basically be advantageous for traction.
`
`71
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`

`

`Fig.
`
`4 Structures of parallel hybrid drives
`
`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 e
`problems connected with the construction of a
`d i f f e r e n t i a l
`ge a rb ox f or c o m bi ni ng
`hi gh
`speeds with simultaneous high torques, we did
`not
`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 h
`hybrid drives with speed combination. Subse-
`quent l y,
`the following chapter only presents
`h 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 d
`with combination of traction forces.
`
`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 e
`o n t h e f a r r i g h t i n F i g . 4 . I t c a n
`s t r u c t u r e
`be s e en t h at t h er e i s no m e c ha ni ca l c o nn e c -
`tion between the driving shaft of the combus-
`t i o n e ng i ne V ope r at i ng on one a xl e a nd t h e
`e l e c t r i c m o t or E dr i vi ng t h e ot h e r a xl e . Th i s
`is a parallel hybrid too, because both motors
`c 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 n
`force needed by the car.
`
`3.
`
`CONSTRUCTED VW HYBRID DRIVES IN THE
`VW/AUDI-GROUP
`
`E 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 d
`d ri ve s with torque combination, we can still
`va s tl y di f fe ri ng dri ve s d epe ndi ng on t he
`ge t
`type of vehicle and the application for which
`the drive is designed.
`
`3.1 VW CITY TAXI WITH HYBRID DRIVE - The City
`t a xi i s a v e hi c l e b a s e d o n a V W bu s ( 5, 6 ) .
`I t s
`t wo- s haf t hy bri d dri ve i s s che m at i c al l y
`represented in Fig. 5.
`
`Fig.
`6 shows an exploded view of the compo-
`ne n t s .
`The power from the 37 kW IC-engine 0
`i s t ra n s m i t t e d t o t he r ea r a xl e v i a a hy dr o-
`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 y
`operated
`clutch K. The electric motor torque
`i s s up e r i m p o s e d o n t h e p e t r o l e ng i n e t or q u e
`vi a t he fi x ed t r a ns m i s s i o n .
`
`t h e i n ne r c i t i e s w i t h o u t p r e s en t i n g an o bs 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 d
`ou t s i de t he ci t y ce nt r e . T he pow er pl a nt s o f
`both the petrol engine and the electric motor
`a 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 e
`t ot a l p o we r f ro m t h e p e t r o l e n g i n e i s n o t
`r e q ui re d f or d r i vi ng, i t i s u s e d t o d r i ve t he
`e 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 a
`g e ne r a t or . T hi s s e rv e s t o r e c h a r ge t h e ba t t e -
`r y .
`
`Fig. 5 Hybrid drive with torque combination
`in the VW City Taxi
`
`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 o
`fu nct i o n w i t hout t he c onve n t i ona l t r an s m i s -
`s i o n, which, of course, makes it very
`easy
`f or t he dri v er t o u s e. H e onl y h as t o s e l ec t
`whether he wishes to drive in purely electric
`m o d e o r h y b r i d , i . e .
`using both units,
`and
`express his wishes by operating the accelera-
`t o r a n d b r ak e pe d a l s . A c en t r a l c o nt r o l un i t
`t 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
`( vi a t he
`e l e c t r o n i c
`c on 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 g
`i nt o ac c oun t t he ba t t e ry c ha r ge .
`
`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 e
`ensured :
`
`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 l
`w i t h 1 6 kW c ont i n ou s ou t pu t . Wi t h i t ,
`t he
`t a xi
`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
`
`- P ro t ec t i o n o f b at t er y a ga i n s t c om p l et e
`discharge and overcharging
`- Regenerative braking
`
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`

`Fig. 6 Exploded view of the components of the VW City Taxi hybrid drive
`
`- Sluggishness of the petrol engine in dyna-
`mic procedures by means of slow changes in
`t h e t h ro t t l e va l v e s et t i ng . ( T he d e s i r e d
`changes are temporarily taken over by the
`e l e c t r i c m ot or ) .
`
`T 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 0
`km w i t h t he obj e c t iv e of o bt ai ni n g i nf orm a -
`t i o n o n
`consumption and emissions.
`p e t r o l
`W hen t he ba t t er y wa s m a i nl y cha rg ed i n dr i -
`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 y
`charger),
`pe t r o l c on s um pt i o n r o s e by up t o
`The
`conventional VW Bus.
`25 % against a
`r 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 e
`vehicle and the unfavourable efficiency chain
`f 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-
`ra bl y
`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 l
`ve hi c l e ;
`specifically, CO by 27 % and HC by
`85 %. I f t he ope r at i on o f t h e el e c t r i c m ot or
`as
`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 e
`c ha r ge c ur re n t ), f ue l c on s um p t i o n a nd e m i s -
`s i o n s f a l l ( 6 ) .
`
`T he 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 . 7
`shows
`t h a t t h e v e hi c l e di s pl a y s re s p e c t a bl e
`performance
`conditions
`a l t ho ugh al l dr i vi ng
`are met in a single gear.
`
`Th i s i s due fi r s t l y t o t h e i de al , h ybe rbo -
`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 c
`motor,
`s e c ond l y t o t he t or qu e co n ve r t er a nd
`t h i r d l y
`t o t h e p ri nc i pl e o f t or qu e ad di t i on.
`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 e
`c a n i n c r e a s e i t s a b i l i t y
`t o cl i m b by up t o
`23 %.
`In many areas,
`t h e t r a c t i v e f or c es a r e
`even higher than if a conventional VW Bus is
`driven by a 37 kW petrol engine with 4-speed
`manual gearbox.
`
`t he l i m i ta t ions of t hi s Ci t y Ta xi
`However,
`dr i ve s h ou l d a l s o b e re c ogn i z ed ; a m oun t a i n
`road with a gradient over 10 % of such length
`
`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 y
`w o u l d n o t s u f f i c e ,
`cannot be overcome with
`t 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 e
`o 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 y
`amounts to barely 10 %.
`
`As much as this hybrid drive proved itself
`i 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 -
`a u n i v e r s a l d r i v e e . g . f o r
`ble
`for
`use
`as
`passenger cars.
`
`3.2 TWO SHAFT HYBRID DRIVE EVW2 - The objec-
`tives in developing this hybrid drive were:
`
`a ) Un i v e r s a l ve r s a t i l i t y
`( Eve n w i t h a fl at ba t t er y t he ve hi c l e
`s houl d b e f u l l y us abl e an d s t i l l d is pl ay
`approximately the same performance as a
`c onv en t i ona l v eh i cl e . )
`
`b) Economy with energy
`(No battery charging in driving!)
`
`c) Low additional costs in comparison to a
`conventional drive.
`
`Since the requirements a and b point to an
`combustion engine of
`i n t e r n a l
`approximately
`normal power,
`t h e r e q u i r e m e n t c i n d i c a t e s
`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
`t h a t
`should
`ha v e t h e s m a l l e s t p ow e r ou t pu t p os s i b l e ; t he
`question is however, what can you do with it.
`I f e . g . a 5 kW motor is
`selected for a VW
`its power is
`s u f f i c i e n t t o d r i v e
`the
`Golf,
`vehicle on level ground at constant speeds up
`to 50 kph. This leads one to suppose that the
`p e t r o l
`engine is often operated
`at very low
`p 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 -
`m e d i n F i g. 8 :
`T hi s r e p r e s e n t s t h e w or k i n g
`p r e s s u r e , a
`
`measurement of the petrol engine torque, as a
`f 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 o
`contains
`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 c
`consumption.
`T he s h a de d a re a i l l u s t r a t e s t he
`r 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 s
`when the vehicle drives the European Cyle. It
`can be seen that very high specific consump-
`t i o ns ,
`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 W
`e 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 d
`area of the map, can take over a considerable
`p r o p o r t i o n o f
`t h es e unf a vo ur a bl e op e ra t i ng
`c ondi t i o ns .
`
`The
`a n d e l e c t r i c m o t o r
`p e t r o l e n g i n e
`complement
`one another very w e l l i n s u c h a
`d 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 s
`a l l oc a t e d
`t h e t a s k s w h i c h i t c a n p e r f o r m
`p 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 e
`drive rapid acceleration and high speeds, the
`e 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 r
`i 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 r
`e ner g y c ons um p t i on - t he s um of p et r ol
`f o r
`the
`I C -e ngi ne a nd
`e l e c t r i c a l e n e r g y f o r
`charging
`t he ba t t e r y -
`i s t o b e e x pe c t e d . I n
`1 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 l
`hybrid design was manufactured in cooperation
`with
`t h e El e c t r i c i t é Ne u c ha t e l o i s e
`S.A. and
`installed 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 s
`s 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 ,
`t hi s i s a t wo- s h af t hybr i d. The IC - e ngi n e i s
`l i n ke d t o t he ge a rb ox vi a a n a ut om at i c e l e c-
`t ro m ec han i ca l cl ut c h K 0 . Th e e l e ct ri c m ot o r
`is connected
`to
`the other end of
`the gearbox
`i 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 n
`In
`e l e ct r om a gn et i c c l ut c h KE .
`automatic,
`c o n t r a s t t o
`t h e C i t y t a x i ,
`a conventional
`m 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 a
`4 - 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 l
`u 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 e
`m 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 o
`motors
`should take over the current require-
`ment for driving performance.
`
`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
`
`Fig. 9 Arrangement of the components in the
`EVW2 hybrid drive for a VW Golf
`
`I n o pe r a t i o n o f t he r e a l i z e d dr 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 l
`alone
`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
`both
`motors and their clutches. There is no clutch
`pedal
`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 l
`ve hi c l e ,
`t he H ybr i d Go lf i s s t a rt e d vi a t h e
`ignition 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 e
`ve hi c l e
`i s s t an di n g
`s t i l l ,
`both motors are
`s w i t c hed o ff . W he n 1s t ge ar i s s e l e c t ed , t he
`I 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 e
`clutch between the IC-engine and
`gearbox is
`a 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 r
`pedal is depressed;
`the vehicle moves off and
`a c c e l e r a t e s .
`Releasing the accelerator pedal
`(to zero) causes the IC-engine clutch to open
`and 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 s
`performance 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 f
`t 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 d
`n 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 n
`0 . 5 s .
`i .e . n o re ne w ed a c c el er a t i o n an d no
`op e ra t i on of t he t ra n s m i s s i o n s e l e c t or l ev 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 e
`now 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 c
`m ot o r t ak es ove r t he dr i vi n g . If t h e e l e c t ri c
`m ot or ’s 5 kW dr i ve p ow e r i s not s uf fi c i e nt ,
`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 r
`because
`a c c e l e r a t e ,
`he s houl d " gi ve m o re g as " , i . e .
`increase
`the accelerator-pedal travel beyond
`c e r t a i n p oi nt . Th e I C - e n g i ne i s r e - s t a r t e d
`a
`s 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 e
`power 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 r
`electric motor alone or with the IC-en-
`the
`gine alone:
`
`I f r e qu i r ed ,
`it would be possible to drive
`u n d e r p u r e l y e l e c t r i c p o w e r -
`a l be i t w i t h
`reduced
`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 a
`constant speed of 50 kph, a distance of 36 km
`c a n b e c ov e re d un de r pu r e l y e l e ct r i c po we r
`with 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 ,
`the
`t r a c t i o n
`b a t t e r y c a n
`be re m ove d fr o m t he
`ve hi c l e
`t o obt a i n a dd i t i ona l l u gga ge
`space
`and
`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 e
`with the IC-engine.
`
`D ur i ng br ak i ng a n d d ow nh i l l d ri vi ng t h e
`vehicle’s kinetic energy, which would other-
`wise be absorbed at the brakes or even result
`i n
`additional petrol consumption
`on account
`o f e n g i n e
`overrun,
`can
`be
`stored
`in
`the
`t r ac t i o n ba t t e r y a s e l ec t r i c al en er g y .
`
`After completion of the vehicle, consump-
`t i on and exh au s t
`emission measurements for
`the European Cycle were first carried out on
`a 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 e
`pe r c e nt a g e di s t r i bu t i o n of d i s t a n ce c o ve r e d
`and
`time spent
`i n e a c h o f t h e 4 o p e r a t i n g
`conditions
`" E l e c t ri c
`dr i ve " ,
`"IC-engine
`drive",
`"Coasting" and "Stopping" were mea-
`sured.
`These were intered in Fig. 10. It can
`b 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 o
`c 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 e
`electric motor is used for 53.3 %.
`
`Fig. 10 Distance and time percentage
`distribution in the European Cycle
`with the EVW2 hybrid drive
`
`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 n
`The
`consumption and emissions.
`reducing
`Hybrid-Golf only consumes 33 % of the petrol
`which the conventional Golf required for the
`European Cycle. The quantities of CO and HC
`i 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 NOx changed little.
`
`Extensive road tests were then carried out
`i n pub l i c t r a ff i c i n B r un s w i c k ( 7) . The fu el
`saving in this case was not as high as in the
`European Cycle, but it still amounted to 40 %
`ov er t h e S t a nd a r d G ol f . Th e ad di t i o na l e l e c -
`r e q u i r e d f r o m t h e t r a c t i o n
`t r i c a l
`energy
`battery is 8.3 kWh/100 km or 13.8 kWh/100 km
`f 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 0
`DM/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 e
`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 e
`covered
`battery charge.
`
`3.3 ONE SHAFT HYBRID DRIVE EVW1 - The aim of
`t h i s p ro j e c t i s t o t ur n t he ba s i c c on c e pt o f
`t a s ks
`the EVW2 drive - optimal division of
`between a