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Introduction of 48 V Belt Drive System New tensioner and decoupler solutions for belt driven mild hybrid systems N O D H I O E A S M I O u e n l O A N G A D F J G I O J E R U I N K O P J E W L S P N Z A D F T O I E O H O I O O A N G A D F J G I O J E R U I N K O P O A N G A D F J G I O J E R O I E U G I A F E D O N G I U A m u H I O G D N O I E R N G M D S A U K Z Q I N K J S L O G D W O I A D U I G I r z H I O G D N O I E R N G M D S A U K n m H I O G D N O I E R N G N G R E E O M N Y A Z T E F N a X J R C N I F Z K M N D A N K R E W S P L O C Y Q D M F E F B S A T B G P D r D D L R a E F B A F V N K F N K R E W S P D L R n E F B A F V N K F N U D M G R D C K G R D C K D i B D L d B E u B A F V N K F N K R E W S P L O C Y Q D M F E F B S A T B G P D B D D L R B E z B A F V r K F N K R E W S P z L R B E o B A F V N K F N x A t R U A N D D N G I U o h N H I f G D N l I E R N G M j B N D S A U K Z Q I N K J S L W O I E P AndreasN N b AStufferU A H I O G D N p I E R N G M D S A U K Z Q H I O G D N w I E R N G M D A m O G N A t R H W o e U A N G R E E O M N Y A Z T E F N a X J R C N I F Z K M N D A O Q T V I E P DanielN z R HeinrichA U A H I r G D N O I q R N G M D S A U K Z Q H I O G D N O I y R N G M D E K J S O C E S H P L D C K I O P M N E S W L N C a W Z Y K F E Q L O P N G S A Y B G D S W L Z U K ChristianO G I K HauckC K P M N E S W L N C u W Z Y K F E Q L O P P M N E S W L N C t W Z Y K M O T J G Y A t P N L S Q O M G D N V U S G R V L G R a K G E C L Z E M S A C I T P M O S G R U C Z TimoG Z SchmidtM O Q O D N V U S G R V L G R m K G E C L Z E M D N V U S G R V L G R x K G T N U L R P M e D B S X I N G R E E O M N Y A Z T E F N a X J R C N I F Z K M N D A B O N Y A M E C HermannR J G N StiefI N E E O M N Y A Z T E W N l X J R C N I F E E O M N Y A Z T E W N y X D C O E E B o n E B M N V C S E Y L i N E W C L V V V H N V u a J K U V X E S Y M N R E E W C L O M E P S C V C Y L i N E W C L V V F H N V o a J K U V Y L i N E W C L V V F H N V J Y I A d D A s Y I C W Q Y J A O B R n L N F X T J G L D Q F H B v t G U P W Q V Z E S L N F A M U A N J Y Q Y O B R n L N F X T J O L D Q F H B w n G O B R n L N F X T J O L D Q K P E A e D K i O e U N O P L M Q A Y C B E F V B N C T E N A O D F E C K t a C T S V Q D E F B N I M B L P O P Q A Y C B E F V B N R T E N A O D F E C Q A Y C B E F V B N R T E N Z B P K c I O o Q D D E G B E Q P M N E S W L N C a P Z Y K F E Q L O P N G F G r g H N W E D W C Y Q B E B G B A Y X S W A D C B P L M I J N T B G H U A Y X S W A D C B P L M I J T N E O o N N n P S C V B N H Z U I O P L K U H G F T S A C V B O F E T Z H N A X C F t j K J Z M H Z D H N B N U I O P L K U H G F D S A C V B O F E T U I O P L K U H G F D S A C C R O P u l l e y r U Z T R E W Q H G F D L G E N D R R T C A S N I N R O A X E V E D K D L a g Q S W I E R T R Q H G F D L G E N D E R T C A S N I N R Q H G F D L G E N D E R T C B E F C p S o r M N O K H E S C B U P S K U P P L U Y G S G E B E R Z Y L I N D E R Z N U B F I M b C H S E H E B U P S K U P P L U N G S G E B E R Z Y B U P S K U P P L U N G S G S O B Y l H A N C W N J I O P S D C V F E W C V T E E N M Z G O H A S E D C K L P S X W E W C E C B S t P O I O D C V F E W C V T E B N M Z G O 33H A S E D C V F E W C V T E B N M Z F E I P e S K B U N Z T R E W Q L K J H G F D S A M O B V C X Y M L M O K N I J B H U Z G F D G V T Q U j x R E L K J H G F D S A M M B V C X Y M L M O L K J H G F D S A M M B V C C W D B r O O B D E E S Y W A T P H C E Q A Y W S X Z E C R F V E G B Z H N U J M I K O Q A Y L M R T X A g Y W P H C E Q A Y W S X E E C R F V E G B Z P H C E Q A Y W S X E E C R P J M N Z W N D C V K N I J U H B Z G V T F C R D X V S N W A S R E C V F H K N U T E Q T F C X V N H O U b I J B Z G V T F C R D X E S N W A S R E C V B Z G V T F C R D X E S N W C G T R W P Q I U Z O A D G J L Y C B M W R Z I P V O N M I Q W u R T O I J E U H B Z G W R Z V T F L U J a D G Y C B M W R Z I P S F H K T V N Z L M O Y C B M W R Z I P S F H K T J T Z E C E I H O K W Q E T U O M B C Y N V X A D G B L K H E S Y S C B F G M H T I L Q N V X D B P O R U T E T M B C Y N V X A D G J L K H E S Y S C B M B C Y N V X A D G J L K H V W M R C K O I J G I Z R W O U Z T W H N E D K U N W P O N C A N S t R E C L t Q A J P N E D C S K U P O W R W Z T W H N E D K U N W P O N C A L V I K Z T W H N E D K U N W P O N A K D Y Q O G N T Z G H J K L P O I U Z T R E W Q Y X C V B N M D i O P N G S e Y B D G T R E H K L P F L K J K O I U Z T R E W Q Y X C V B N M I Q W u O I U Z T R E W Q Y X C V B L S J E I N R L U J G F D S A Y V N P I Z R W Q S C G Z N J I M E Z E M S A C n T P C E Z R W D X A Y H A S g S V N P I Z R W Q S C G Z N J I M N S t R V N P I Z R W Q S C G Z N J E K J O V C E S O P R D C K I O P M N E S W L N C X W Z Y K F E R N I F Z K M s D A G D S W L Z U K O G I K C K P M N E S W L N C X W Z Y K F E D i O P P M N E S W L N C X W Z Y K M O T Z Q Y A H I N D S Q O M G D N V U S G R V L G R V K G E C J K U V X E S i M N M O S G R U C Z G Z M q g O D N V U S G R V L G R V K G E C E Z E M D N V U S G R V L G R V K G T N U V N J R A K D G D I N G R E X O M N Y A Z T E W N F X J L V i b R a t i o n s B O i z q a t s l o k z I N E X O M N Y A Z T E W N F X J L R N I F E X O M N Y A Z T E W N F X D C O O U A N D O N M N V C S E Y L J N E W C L V V F H N V R D M F D R N Q B n Y R R E z W C L O M E P S C V C Y L J N E W C L V V F H N V R D J K U V Y L J N E W C L V V F H N V J Y I B B D B H M G C W Q Y J A O B R E L N F X T J O L k Q F H U K Z Q I N K O S L n g L N F A M U A N J Y Q Y O B R E L N F X T J O L s Q F H B Q F G O B R E L N F X T J O L a Q N J K E U A N D O N O B N J O R O I D F N G K L D F M G O I Z P E W S P L O C p Q g X w N G K M N S R D O J N J O I D F N G K L D F M G O I Z P M F D R O I D F N G K L D F M G O I A A O O U A N D O N G I U A R N H I O G D N O I E R N G M g S A g K Z Q I N K u S L t O m p l I E P N N R A U A H I O G D N O I E R N G M t S A U K Z Q H I O G D N O I E R N G M k U D M B B D B H M G R e B D P B D L R B E F B A F V N K F N k R L Z E M S A C l T P M F E F B S A T B G P D B D D L R B E F B A F V N K F N q R E W S P D L R B E F B A F V N K F N A A O E U A N D O N G I U A R N H I O G D N O I E R N G M D S A E W S P L O C l Q D W i k a p I E P N N R A U A H I O G D N O I E R N G M D S A l K Z Q H I O G D N O I E R N G M D M O T M Q O G N T Z D S Q O M G D N V U S G R V L G R V K G E C M L M O K N I e B H M O S G R U C Z G Z M O Q O D N V U S G R V L G R V K G E C L Z E M D N V U S G R V L G R V K G U D M T B D B H M G R I B D P B D L R B E F B A F V N K F N K R E G B Z H N U y M I M F E F B S A T B G P D B D D L R B E F B A F V N K F N K R E W S P D L R B E F B A F V N K F N F E I D R E Q R I U Z T R E W Q L K J H G F D S A M M B V C X Y R E C V F H K N U T U Z G F D G V T Q U o t R E L K J H G F D S A M M B V C X Y M L M O L K J H G F D S A M M B V C C I M N S t R E C L P Q A C E Z R W D X A Y H B M W R Z I R F V Z L M O I J E U H B K O Q A Y L M R T X A z Y W P H C E Q A Y W S X E E C R F V E G B Z P H C E Q A Y W S X E E C R P J M N I J H L M O K N I J U H B Z G V T F C R D X E S N W A S Y S C B F G M H T I E Q T F C X V N H O U b I J B Z G V T F C R D X E S N W A S R E C V B Z G V T F C R D X E S N W C G T J D G L E T U O A D G J L Y C B M W R Z I P S F H K T V N L V I K n D V S G W Z G W R Z V T F L U J r D G Y C B M W R Z I P S F H K T V N Z L M O Y C B M W R Z I P S F H K T J T Z U E T O I Z R W Q E T U O M B C Y N V X A D G J L K H E S I Q W u R T Z B C S L Q N V X D B P O R U T E T M B C Y N V X A D G J L K H E S Y S C B M B C Y N V X A D G J L K H V W M O R W U U M P I Z R W O U Z T W H N E D K U N W P O N C A N S t R E C L P Q A J P N E D C S K U P O W R W Z T W H N E D K U N W P O N C A L V I K Z T W H N E D K U N W P O N A K D L J K P S D F G H J K L P O I U Z T R E W Q Y X C V B N M D i O P N G S A Y B D G T R E H K L P F L K J K O I U Z T R E W Q Y X C V B N M I Q W u O I U Z T R E W Q Y X C V B L S J A D S Y K J H G F D S A Y V N P I Z R W Q S C G Z N J I M N S t R E C L P Q A C E Z R W D X A Y H A S e S V N P I Z R W Q S C G Z N J I M N S t R V N P I Z R W Q S C G Z N J E K J I C K O I J G R D C K I O P M N E S W L N C X W Z Y K F E D i O P N G S A Y B G D S W L Z U K O G I K C K P M N E S W L N C X W Z Y K F E D i O P P M N E S W L N C X W Z Y K L S J A D S Y K J H G F D S A Y V N P I Z R W Q S C G Z N J I M N S t R E C L P Q A C E Z R W D X A Y H A S u S V N P I Z R W Q S C G Z N J I M N S t R V N P I Z R W Q S C G Z N J E K J I C K O I J G R D C K I O P M N E S W L N C X W Z Y K F E D i O P N G S A Y B G D S W L Z U K O G I K C K P M N E S W L N C X W Z Y K F E D i O P P M N E S W L N C X W Z Y K M O T M Q O G N T Z D S Q O M G D N V U S G R V L G R V K G E C E Z E M S A C I T P M O S G R U C Z G Z M o x O D N V U S G R V L G R V K G E C E Z E M D N V U S G R V L G R V K G T N U G I N R L U J G D I N G R E X O M N Y A Z T E W N F X J L R N I F Z K M N D A B O B N x z p e w n q m I N E X O M N Y A Z T E W N F X J L R N I F E X O M N Y A Z T E W N F X D C O S V C E S O P M N V C S E Y L J N E W C L V V F H N V R D J K U V X E S Y M N R E i W C L O M E P S C V C Y L J N E W C L V V F H N V R D J K U V Y L J N E W C L V V F H N V M O T M Q O G N T Z D S Q O M G D N V U S G R V L G R V K G E C E Z E M S A C I T P M O S G R U C Z G Z M a x O D N V U S G R V L G R V K G E C E Z E M D N V U S G R V L G R V K G A A O R U A N D O N G I U A R N H I O G D N O I E R N G M D S A U K Z Q I N K J S L W O z w u I E P N N R A U A H I O G D N O I E R N G M D S A U K Z Q H I O G D N O I E R N G M D 482 Belt Drive Systems 33 483

Introduction Conventional belt drives Water bearings Mechanical and belt-driven belt tensioners

The market for belt drives is in motion. applications At the 2010 Schaeffler Symposium, the focus was exclusively on conventional belt drives with pure load operation of In modern internal combustion engines, the the accessories [1]. Since then, systems accessories are driven almost exclusively by Overunning alternator Hydraulic (OAP) with belt starter alternators have in- V-ribbed belts. These belt drives and their belt tensioners creased in importance for belt drive de- automatic tensioning systems must meet velopment. They serve to support addi- the following requirements: tional functions like recuperation, boost –– Automated belt force adjustment dur- operation, and engine starts, and thus ing initial installation and maintenance offer advantages for the fuel economy (tolerance compensation of all drive and function of the engine. components) The introduction of 48-volt electrical –– Practically constant belt force over the Pulley decoupler Tensioner and idler pulleys systems can mean a new boost for belt entire life of the belt drive (compensa- Belts starter alternators. These enable an in- tion of belt elongation and wear) from ContiTech creased electric power output and mild –– Practically constant belt force over the hybridization of drives at justifiable entire engine temperature range (com- costs. Through expanded functions – pensation of heat expansion of all com- such as recuperation and electric boost- ponents that affect the drive) ing – considerable fuel consumption –– Reduction of dynamic belt force peaks savings of up to 14 percent in the NEDC in the drive Figure 1 Schaeffler product portfolio for the belt drive can be achieved. –– Minimization of slip, noise, and belt The of ever-increasing wear by using decoupling elements. At Schaef- alternators, the power is transferred from the levels of power and means belts –– Operating life increase for the entire fler, the OAP (overrunning alternator pulley) alternator to the engine at some operating are subjected to higher dynamic loads. belt drive system has therefore been in volume production points (alternator start and boost operation). At the same time, vibrations are increas- –– Optimum reliability of the entire belt since 1996 as a belt pulley on the For conventional belt drives, tension- ingly introduced into the belt drive, as drive system alternator; the belt pulley coupler has been ers with mechanical and hydraulic damp- more and more frequently engines with –– Minimization of losses in the en- in volume production as a mechanical ing units are common. In addition, an a reduced number of cylinders, but high tire system decoupler on the since 2013. overrunning is often used on the al- mean pressures and thus high rotational Schaeffler has been using the OAP (over- ternator, which compensates fast torque irregularities are used. Innovative auto Modern accessory drives, which are opti- running alternator pulley) as a mechanical changes when vibrations occur and thus tensioners and crankshaft decouplers mally adjusted to the entire system, are decoupler on the alternator since 1996 and reduces dynamics. This approach is not from Schaeffler are able to transmit the maintenance-free and can run for more the pulley decoupler as a mechanical de- used in systems with belt starter alterna- higher safely and also to reduce than 240,000 km (nearly 150,000 miles). coupler on the crankshaft since 2013 in vol- tors because the torque must be trans- the vibration with the right design. Schaeffler offers a variety of products ume production. In addition to individual ferred in both directions, which makes the for the design of the front-end accessory components, Schaeffler also offers system dynamics in the belt drive much more crit- drive. Mechanical and hydraulic belt ten- development for the entire belt drive togeth- ical overall. sioners provide a nearly constant belt force er with ContiTech (Figure 1). For starting via the belt, an expanded across tolerances, throughout the operating The function of conventional belt drives is belt tensioning function is needed in order life and the entire temperature range characterized by the accessories being in to allow a transfer of torque in both direc- of the engine, and also damp vibrations in load operation; the power is thus always tions in the belt drive. This function is shown the belt drive. Additional damping and de- transferred from the engine to the belt drive. in Figure 2 based on two mechanical belt of vibrations can be achieved In contrast, in applications with belt starter tensioners. 484 Belt Drive Systems 33 485

Start of combustion engine Recuperation and Conventional Micro Hybrid 12 VMild Hybrid 48 V Hybrid > 48 V and boost operation load operation accessory drive The alternator drives the engine The engine drives the alternator Provide belt Compensate Provide belt Compensates Provide belt Compensates Provide belt Compensates tension tolerances tension tolerances tension tolerances tension tolerances

Change Comfort Change Comfort Change Comfort of mind start-stop of mind start-stop of mind start-stop Tight Slack Electrical power Electrical power Electrical power span span Recuperation Recuperation Recuperation < 5 kW < 12 kW > 12 kW Alternator Slack Tight Increase of Increase of load point Boost load point Boost span span Belt drive Pull-away Pull-away Electric drive assistance assistance Belt drive systems

Complexity / functionality Crankshaft Belt A/C compressor Figure 3 Functions of different hybrid stages Figure 2 Belt drive load in boost and load direction For the accessory drive system, a belt replaced with a 48-volt belt starter alter- When the engine is driven by the alternator board electrical system, which provides up drive with air conditioning and a 180 A al- nator. It thus becomes necessary to make – in belt start or boost operation – the pow- to 12 kW of power. The existing 12-volt on- ternator is assumed. This an adjustment to the belt drive. The pos- er is transferred via the upper run (indicat- board electrical system is connected to a combination is widely used among differ- sible operating range for both alternator ed on the left as the driving run). For the voltage converter on the expanded 48-volt ent manufacturers for mid-class . systems is shown in Figure 4. load operation of the alternator (for exam- network, which includes a 48-volt battery In expanding the belt drive to a 48-volt In order to obtain a representative ple during recuperation), torque is trans- with additional capacity and a 48-volt alter- system, the air conditioning remains, depiction of drive performance, refer- ferred from the crankshaft to the alternator nator in the belt drive. The increased ca- however, the conventional alternator that ence is made here to the WLTP cycle [3] (right belt run, shown in the figure on the pacity of the 48-volt network enables ad- previously allowed load-only operation is (Figure 5). right as the driving run). The purpose of the ditional functions for the belt starter, which The figure shows the power of the inter- tensioner system is to maintain the preten- are shown in Figure 3. The expansion of Operating range nal combustion engine and the 48-volt belt sion in the entire system and to prevent the the on-board electrical system to 48-volt in 40 of the alternator starter alternator for the example applica- belt load from falling in the slack run. combination with a belt starter alternator is tion. The ranges with recuperation (negative 20 Boost Belt starter applications were already designated in general as a “mild hybrid,” operation power range) and boost operation (positive being researched extensively in the early which is positioned, in terms of functions 0 power range) are easily recognizable from 2000s [2]. However, development proved and cost, between the existing 12-volt on- the alternator power signal. -20 Load to be difficult due to the limited power of board electrical system and the full hybrid operation 12-volt on-board electrical systems and with a high-voltage power supply. -40 The mild hybrid system offers the following the unusually problematic vibration iso- New challenges arise for the belt advantages: lation. In 2005, Citroën was the first drive configuration due to the higher Torque on alternator in Nm 0 2,000 4,000 6,000 8,000 10,000 –– Boost operation manufacturer to put an application with power transfer via the belt. This is shown Alternator speed in rpm –– Recuperation a belt starter alternator into volume in the following application example, a 48-volt belt-driven starter alternator –– Faster and more comfortable engine production. mild hybrid in a 1.6-liter four- Conventional 12-volt alternator starts via the alternator, as well as A new generation of belt starter alter- gasoline engine with 130 kW power and –– Electric driving at low speeds (e.g., as a nators with significantly expanded func- a torque of 260 Nm in a mid-class Figure 4 Operating range for a conventional comfort function in stop-and-go opera- tions has been in development since 2011. (1,400 kg curb weight) with a 6-speed 12-volt alternator and a 48-volt belt tion or to prevent exhaust emissions in This is possible by using a 48-volt on- double clutch transmission. starter alternator underground parking garages). 486 Belt Drive Systems 33 487

100

Two Mechanical + Hydraulic Hydraulic Generator Decoupling mechanical hydraulic tensioner tensioner 50 tensioner tensioner tensioners tensioners in tight strand in slack strand

Velocity in km/h Start function + + + + ++ - 0 (generator start) Operation under ++ load + + 0 0 0 40

30 Packaging - - + 0 + 0 20 Costs + -- 0 0 0 0 10

Power in kW 0 Transient operation + + 0 0 ++ - -10 0 1,000 1,800 s Tensioner variants considered on the following pages Combustion engine 48-volt alternator Figure 6 Design of different tension system solutions for the belt drive Figure 5 WLTP driving profile according to [3] systems in volume production. An alterna- operation; dips into the negative indicate In contrast to the full hybrid, the electric mo- Belt tensioner configuration tive design requires only one tensioner, vehicle braking with recuperation. To eval- tor is coupled with the internal combustion for the mild hybrid with belt starter which can swivel about the alternator’s uate the dynamics in the belt drive, the engine as a belt starter alternator in the mild alternator axis of rotation. These, known as decou- hubload on the belt pulley of the belt start- hybrid. Recuperation and electric driving pling tensioners, offer the greatest advan- er alternator is shown. are only possible when the internal com- tages. Figure 7 shows the function of the Significantly higher dynamic loads bustion engine is turning – the engine fric- In the entire system, the mild hybrid offers belt drive system for different operating can be seen for the system with two me- tion must thus be overcome, reducing the a noteworthy advantage with regard to points. A part of the WLTP cycle is shown chanical belt tensioners. The area of effective available power. driving dynamics and fuel consumption, in which boost and recuperation opera- maximum transferable torque is limited, The internal combustion engine can thus which is achieved with assistancefrom the tion is used. An alternator start also takes however, because the two tensioners in be run at operating points with greater effi- internal combustion engine via the 48-volt place at the beginning of the depicted the belt drive cannot completely maintain ciency, which results in optimized consump- belt starter alternator. This requires a suit- range. the pretension. If the tensioner is adjust- tion in combination with the braking energy able torque transmission in the belt drive, Engine speed and vehicle speed are ed so that the torque for the alternator recovery and sailing phases. Current discus- which differs from the tensioner and shown in the top diagram. The shifting of start can be fully transferred, the result is sions involve fuel consumption advantages damper solutions for the conventional belt the double clutch transmission and en- a limit on the maximum possible recu- in the range of 4 % to 14 % [4, 5], depending drive. In addition to the solution already gine irregularities due to the engine’s igni- peration torque. In this example, the belt on the base driving cycle, engine, and sys- presented with two individual tensioners, tion can clearly be seen from the engine slips above at an alternator torque of ap- tem tuning. At the same time, there is in- other tensioner systems are also conceiv- signal. It is easy to tell the vehicle’s oper- prox. 30 Nm during recuperation. Over- creased driving comfort for the driver due to able, and are shown in Figure 6 with their ating mode from the torque of the engine all, these results show that the conven- a very comfortable start function, assistance different requirements. and belt starter alternator (both shown tional design approach using two for the engine from the boost operation, and From the classic solution with two me- as torque appearing on the crankshaft), mechanical tensioners is not a match for the possibility of moving off under electric chanical belt tensioners, there are already shown in the middle. A positive torque on the increased requirements. The belt power only in stop-and-go operation. a few systems in combination with 12-volt the belt starter alternator indicates boost drive is simply overloaded. 488 Belt Drive Systems 33 489

km/h FEAD with engine stopped FEAD during alternator-driven (BSA) reciprocating move- 100 start ment of the entire 2,000 80 tensioner about 60 the electric mo- 1,000 40 E E tor’s axis causes

Speed in rpm 20 the driving half of 0 0 the tensioner to be 200 pressed away from the drive and the 100 KW KW AC AC other tensioner pul- 0 ley to automatically

Torque in Nm retension the slack -100 side by means of N 3,000 Figure 9 Function of the decoupling tensioner, alternator start with the the geometric decoupling tensioner connection, so that 2,000 it is pushed into the 1,000 Depending on whether load torque is being drive. In a solution with two independent applied to the electric motor (alternator op- tensioners, this geometric connection does 0 eration or recuperation) or it is generating not exist, which leads to the slack side ten- 1,020 1,040 1,060 1,080 1,100 s

Alternator hubload in in hubload Alternator torque (belt start, boosts), the driving run sioner receiving no additional support from Engine speed Internal combustion engine Two mechanical tensioners occurs in either the right or the left belt run the driving half tensioner for tensioning the Vehicle speed Belt-driven starter alternator System with decoupling tensioner and the slack run is on the other side. The slack side (Figure 10).

Figure 7 Function of the belt drive system in the WLTP cycle Decoupling Separate tensioners tensioner By contrast, one decoupling tensioner on are the significantly lower dynamic loads Belt force F Belt force F 1 the alternator has distinct advantages. in the belt drive due to engine excitation. 1 E Improved retention of the pretensioned By introducing this type of decoupling load in the slack run is one of these, as tensioner, the dynamics in the belt drive Start scenario can be managed and the functional ad- Belt force F Belt-driven starter alternator 2 Housing vantages are fully achieved with the mild Belt force F2 (BSA) hybrid system. These requirements cor- KW respond to a decoupling tensioner re- AC cently developed by Schaeffler, which is illustrated in Figure 8. The tensioner consists of a housing Belt force which is connected to the electric motor by Belt force F1 a plain bearing and can be rotated by 360° 1,522 N about the electric motor’s axis. A tensioner 1,254 N pulley is permanently fixed to this housing. Belt forces F1/F2 with engine stopped Lever arms The second tensioner pulley is located on a 324 N

moving lever and is spring-mounted against Belt force F2 164 N the housing by means of an arc spring as- Tensioner pulleys sembly. This allows the tensioner pulley to Tensioner path (angle) create the necessary belt pretensioning Decoupling tensioner Separate tensioners Figure 8 Overview: Decoupling tensioner load and to compensate tolerances in the design belt drive (Figure 9). Figure 10 Comparison of the belt tension during engine start 490 Belt Drive Systems 33 491

4,500 900 5 The relevant criteria for a decoupling on the crankshaft are: 4,000 850 Effect of 4 –– The decoupling of the belt drive in the- 3,500 pulley decoupler 800 operating range and 3,000 3 Effect of 750 –– The transmission of the alternator 2,500 decoupling tensioner torque for alternator start, boost, and 700 2 2,000 recuperation operation. 650 1 1,500 These requirements can be covered with Angular amplitude in ° the LuK pulley decoupler (PYD). This de- 1,000 600 0 Speed of crankshaft in rpm Speed of crankshaft in rpm 1,000 2,000 3,000 4,000 couples the belt drive from the rotational 500 550 irregularities of the internal combustion en- 20 30 40 50 60 70 80 1,479.0 1,480.0 1,481.0 1,482.0 Engine speed in rpm gine, with a specifically designed arc spring Time in s Time in s Crankshaft 2.0-liter isolating the belt pulley from the crank- Speed of electric drive Crankshaft 1.6-liter diesel engine shaft. The PYD is mounted directly on the Speed of crankshaft Crankshaft pulley crankshaft. It usually also contains a tor- Belt pulley starter alternator sional vibration damper, which is needed Figure 11 Decoupling effect of the tensioning system to limit the natural vibrations of the crank- Figure 13 Engine dynamics of the example shaft in the upper speed range to a level Figure 11 clearly shows the additional de- measures is still necessary because of in- application permissible for durability and acoustic coupling effect of the tensioning system: creased rotational irregularities as a result comfort (Figure 14). Only a small portion (green) of the rotation- of smaller engines with higher specific the assumption that the geometry is lim- al irregularity introduced into the drive power and a lower number of cylinders. ited by the available installation space. Torsional vibration damper from the internal combustion engine (grey) This means an additional guide pulley is Arc spring reaches the electric motor shaft via the required in the belt drive and the working reciprocating movement of the decoupling range of the decoupling tensioner is lim- tensioner. Belt starter systems with ited as a result. This decoupling effect is sufficient for crankshaft decoupling Figure 13 shows the vibration angle many belt drives with belt starter alterna- of the engine on the front crankshaft end tors. The use of advanced decoupling as a function of the engine speed. This engine has a significantly greater belt When power is transferred between belt drive excitation via the crankshaft than starter alternator and engine, the decou- the 1.6-liter gasoline engine application pling tensioner automatically damps vi- from the first part of this paper. The in- brations in the belt drive due to its de- creased irregularities of the internal sign. This function is dependent on the combustion engine excite the belt drive E belt drive layout and the position of the to higher vibrations, which can no longer accessories as well as on the internal be managed by a decoupling tensioner combustion engine excitation. The ex- alone. Therefore, to reduce vibrations, a ample of a mild hybrid drive with a highly direct decoupling on the crankshaft turbocharged 2-liter four-cylinder diesel must be used via a decoupled belt drive engine (470 Nm engine torque, 140 kW (dashed line). engine performance, in a mid-size, up- The dynamics in the belt drive are re- KW per-class vehicle with a six-speed double duced to an acceptable value by crankshaft AC Connection clutch transmission) shows the necessity decoupling. Whether crankshaft decoupling to crankshaft Belt pulley of an additional decoupling of the belt is necessary for a belt drive depends on drive by means of a crankshaft decou- such parameters as the crankshaft excita- Figure 14 Overview: Design of the pulley Figure 12 Layout of the belt drive pler. Figure 12 shows a layout based on tion, belt drive layout, and accessory loads. decoupler 492 Belt Drive Systems 33 493

km/h Air conditioning in the ber of limitations regarding the maximum 100 amount of storable energy. They must be 2,000 80 charged regularly by running the engine. 60 vehicle interior with the 1,000 40 In contrast, electric AC compressors or internal combustion AC compressors driven by the starter al-

Speed in rpm 20 0 0 engine switched off ternator allow for longer phases without 200 the engine running. The electric AC compressor, however, 100 requires an additional electric motor and

0 reduces the efficiency of the AC compres- With the increasing hybridization of the sor when the engine is running, since Torque in Nm -100 automobile, the amount of time during losses also occur in this state due to the

N 3,000 which the engine is actually running is transfer of the power through the electric growing shorter and shorter. This effect is ower supply. 2,000 already apparent from an examination of As an alternative to an additional elec- 1,000 the WLTP cycle when considering sailing tric motor, it is possible to use the existing and stop-start operation, and, depending belt starter alternator to power the AC 0 1,020 1,040 1,060 1,080 1,100 s on the driving profile, is very much in- compressor when the engine is not run-

Alternator hubload in in hubload Alternator creased for city driving (Figure 16). ning if the belt drive can be decoupled Engine speed Combustion engine Without belt pulley decoupler Measures that allow air conditioning from the engine. Vehicle speed Belt-driven starter generator With belt pulley decoupler of the interior without the engine run- This requires a clutch in the crank- Figure 15 Function of the belt drive with belt pulley decoupler ning include a latent heat storage unit in shaft pulley. Regardless of this comfort the air conditioning system, an electric function, decoupling is necessary, as in The crankshaft pulley is decoupled from In comparison with decouplers with elastomer AC compressor or a mechanical AC the conventional belt drive. The decou- the vibrations of the crankshaft. Arc springs, which use a rubber layer for resiliency, compressor that is positioned in the pling is also used in the switchable pulley springs, such as those in a dual mass fly- the mechanical arc springs have a significantly standard belt drive and is driven by the decoupler (PYDS) from Schaeffler to wheel, are used for this, placed in a steel larger spring capacity and thus allow for the starter alternator. greatly reduce the dynamic torques that channel. From the crankshaft, the torque transmission of higher torques and power out- Latent heat storage units provide the act on the separation coupling. This en- is transferred via a flange to the arc puts. Thus, the increased power requirements air conditioning function by means of a sures acoustically and dynamically flaw- springs, which are supported on stops on for mild hybrid applications with belt start-stop built-in heat storage unit and have a num- less operation. the belt pulley. The torsion characteristics can be covered. The characteristic curve can of the belt pulley decoupler can be flexibly be flexibly adjusted by using multiple spring influenced by the selection and combina- stages. This helps avoid resonances during 120 tion of the springs used. The system func- engine start and driving operation. 100 tion with the belt pulley decoupler is The system is designed in a way that shown in Figure 15. durability requirements are optimally fulfilled 80 The function representation is analo- throughout the operating life. The design 60 gous to Figure 7 with the engine speed, ve- takes into account: hicle speed, and engine torque acting on –– More than one million engine starts 40

the crankshaft and belt starter alternator through sailing and stop-start opera- Velocity in km/h 20 and the hubload on the belt starter alterna- tion, depending on the application, 0 tor pulley for the system variants with and –– A constant decoupling function over 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 s without a belt pulley decoupler. In compari- the engine’s temperature range and ve- son to the system without a belt pulley de- hicle operating life, as well as Coasting possible coupler, there is an additional reduction of –– A decoupling of the belt drive through- Vehicle stopped the dynamics in the belt drive throughout out the functional range of the engine the entire operating range. and alternator. Figure 16 Example application in the WLTP cycle 494 Belt Drive Systems 33 495

The switchable pulley decoupler is Actuation unit sults in a more compact design with low Summary and outlook mounted directly on the crankshaft (Fig- weight. ure 17). Like the standard decoupler, it Figure 18 shows the function of the has a vibration damper to reduce the tor- switchable pulley decoupler based on indi- sional vibrations of the crankshaft and vidual points in the WLTP cycle for the ex- Compared to just four years ago, [1], sys- arc springs to isolate the belt drive from ample application. The decoupling of the belt tems with belt starter alternators now play the rotational irregularities caused by the drive makes the operation of the AC unit pos- a more important role in belt drive devel- combustion process. This means that all sible even when the engine is at a standstill. opment. This is primarily due to the devel- of the advantages of conventional pulley When the engine is running, the belt drive is opment of 48-volt mild hybrid systems. decouplers are retained. A clutch unit is isolated from irregularities by the crankshaft Mild hybrid systems can contribute to also fitted between the arc springs and decoupling as in the non-switchable design. improvements in driving dynamics and belt pulleys. In addition to the advantages in the belt fuel economy. However, they also lead to The belt drive can now be turned free- drive arising from crankshaft decoupling, new requirementsfor belt drive design. ly while the engine is stopped by disen- such as the reduction of dynamic loads and Decoupling tensioners and pulley decou- gaging the clutch unit. The mechanical AC lower frictional losses by decreasing the plers, whether switchable or not, are not compressor can thus be operated auton- pretension in the belt, the switching function just expanding the current Schaeffler omously despite the engine being allows further advantages. AC comfort is product range for belt drives (Figure 19). stopped. For the restart, the belt drive is maintained both while the engine is stopped Innovations are also expanding the de- slowed down to a near standstill and the and in sailing operation – this also results in sign options for mild hybrid systems with

clutch is engaged. During normal driving a further CO2 benefit because the periods of a belt starter alternator. operation, both boost and recuperation Switchable belt time during which the engine is switched off Now that the first systems with belt torques can be transmitted. pulley decoupler may be extended. starters with 12-volt systems are on the mar- The switch unit can be integrated into the existing space of the decoupler – it re- Figure 17 Design of the switchable belt pulley Water pump bearings Mechanical belt tensioners Belt pulley decoupler decoupler

2,000

1,500 Overunning alternator pulley 1,000 (OAP) Hydraulic belt tensioners

Speed in rpm 500

0 Switchable 20 Travel Stop Tension / idler pulleys belt pulley decoupler

10 Decoupling tensioner

Velocity in km/h Belts from ContiTech 0 1,450 1,460 1,470 1,480 Time in s Engine Air conditioning system

Figure 18 Function of the decoupler during AC operation while driving and with the engine stationary Figure 19 Overview of the Schaeffler product portfolio for belt drives 496 Belt Drive Systems 33 497

ket, new developments are driven by the can be incorporated into development us- expectation that belt starter alternators will ing Schaeffler’s unique expertise. For vehi- become significantly more important in the cle manufacturers, Schaeffler offers the ad- coming years because of the change to vantage that during belt drive development, 48-volt mild hybrid systems and – in addi- the design of the individual components tion to the conventional belt drive – will play can be optimally tailored to each other. an expanded role in the future. The require- ments for belt drive design will increase to a greater or lesser extent, depending on the engine class. These can be met individually Literature with products from Schaeffler – from the re- duction of vibrations with the decoupling tensioner and the completely decoupled belt drive with standard air conditioning [1] Stief, H.; Pflug, R.; Schmidt, T.; Fechler, C.: function through to switchable belt pulley Belt Drive Systems. 9th Schaeffler Symposium, decouplers. 2010, pp. 265-277 Schaeffler is focusing on a system ap- [2] Bonkowski, M.; Bogner, M.: Der riemenget- proach in belt drive development in which riebene Startergenerator (RSG) als aktuelle the interactions of the individual compo- Herausforderung für eine funktionsoptimierte nents within the entire system are taken into Riementrieb-Systementwicklung. VDI- Umsch- account. This approach is gaining signifi- lingungsgetriebe, 2003 cance due to increasing requirements. [3] Tutuianu, M.; Marotta, A.; Steven, H.; Ericsson, E.; Therefore, the development of belt drives in Haniu, T.; Ichikawa, N.; Ishii, H.: Development the future will take the interactions with the of a World-wide Worldwide harmonized Light entire vehicle system more closely into ac- duty driving Test Procedure (WLTP) – Draft count. This focus on the whole system in- Technical Report cludes the interactions of the individual [4] Hackmann, W.; Klein, B.; Götte, C.; Schmid, R.; components and their use over the vehicle’s Pujol, F.: 48V – The Way to a High Volume operating life. While up to now systems Electrification. 22nd Aachen Colloquium Auto- have been designed based on individual mobile and Engine Technology, 2013 operating points, these increased interac- [5] Uhl, M.; Wüst, M.; Christ, A.; Pörtner, N.; tions are now shifting the focus to account- Trofimov, A.: Electrified Powertrain at 48 V – nd ing for entire trips and the use of the vehicle More than CO2 and Comfort. 22 Aachen Col- by different drivers over the life of the vehi- loquium Automobile and Engine Technology, cle. The interactions in the entire system 2013