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Friction Tailored to Your Requirements You wish, we deliver 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 E 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 U N O D H I O E A S M I 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 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 O I E U G I A F E D O t F I U 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 A U D M P B D B H M G R r 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 WTimZ Y HosenfeldtK A U 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 U D M P B S B H M G R i J D P H I O G D N O I p R N G M D S A U K Z Q I N K J S L W O Q T V I E P EdgarN z R SchulzA 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 A A t R U u N D O N G o u A R 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 JuergenO G I KGierlC 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 A m O e F R i c t i o n F P a r t n e r s 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 StefanG Z M SteinmetzO 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 E K J I C f O I J G R d A K I 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 R J G N I 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 M O T M Q A G N T Z D u F O M 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 T N U G I c R L U J G r V N G 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 D C O S V e E S O P M N V C S 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 J Y I J Q D A H I N C W Q Y J 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 K P E L O S M S E B U N O P L 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 E T R W P O I 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 S H E C E F H 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 P I O S G B Z 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 23H A S E D C V F E W C V T E B N M Z F E I W R E Q R I U 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 A Y W T R D X 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 F I J H L M O 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 V D G L E T U 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 G E F O I Z R 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 C R r 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 L V I K n D V S G W 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 P J i 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 I Q W u R T Z B C S 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 T D c 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 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 R C t 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 Y Q i 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 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 E L o 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 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 I n 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 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 Z A Y A H I N C W Q Y J A O B R E L N F X T J O L k Q F H B Q F G U P W Q V Z E 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 V I L R A K D O B N J O R O I D F N G K L D F M G O I Z P M F D R N Q B O Y R 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 V i 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 U K Z Q I N K J 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 t O G D N O I E R N G M k U D M S e n s o t e c t B D P B D L R B E F B A F V N K F N k R E W S P L O C Y Q g 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 K i 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 g K Z Q I N K o S L 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 O n 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 L Z E M S A C I T P 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 g 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 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 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 M L M O K N I J B H 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 E G B Z H N U J M I 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 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 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 Z L M O I J E U H B 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 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 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 L V I K n D V S G W 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 I Q W u R T Z B C S 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 332 Customized 23 333

Fn v Introduction Basic principles r Counter body 2

Ff Ft

In any discussion about reducing fuel Main body 1 consumption, attention quickly turns to Tribological system powertrain hybridization. However, the Boundary layer fact that a saving of 15 % can be achieved System details outside simply by minimizing friction is often According to conventional definitions, a tri- HV1 < HV2 F F F F overlooked. This has been demonstrated bological system consists of four elements n n n n 2 v 2 v 2 v 2 v by Schaeffler in various studies over the [1]: The part and the counterpart – these r r r r past few years. The costs required to re- two move relative to each other – and the 1 1 1 1 duce CO2 emissions by 1 g/km can be interfacial medium as well as the ambient cracks scratch fracture particles kept well below those of electrifying the medium. Now, new types of coating sys- zone drive. tems in the micrometer and nanometer Surface spalling Abrasion Adhesion Tribochemical reaction However, friction is not a parameter range are adding another element that has (fatigue (cutting, cracking, (burning off of the that must be minimized in every case. a significant influence on the properties of delamination) furrowing) tribochemically Without friction, movement is not possi- tribological systems and that can be used to modified barrier layer) – fretting corrosion ble in our daily lives – and this includes adjust these systems for a specific purpose – friction oxidation driving cars. Both involve requirements (Figure 1). – tribooxidation that can only be met if different friction Figure 2 Overview of mechanisms conditions interact in the desired fashion FN – similar to a classic cross-country skier: Counterpart –– The hardness and Young’s modulus used to plot the relative of the active The skier hopes that in his tribological v(t) of the materials used. A hard surface surfaces for a lubricated contact in relation system – consisting of the shape of the Intermediate alone does not protect a component if to the friction that occurs (Figure 3). skis, their sliding layer, and the snow – Coating the basic material underneath can eas- friction will remain as low as possible ily undergo plastic deformation. Part Stribeck curve when going downhill. By contrast, when –– The surface structure not only affects Counter body going uphill, the skier ideally requires ad- Ambient medium lubricant film formation but also the Lubricant hesive friction to move up the hill quickly applied to the surface and thus Particles R and without having to use too much en- Figure 1 Structure of the tribological surface fatigue. Mixed Fluid film friction ergy. system [1] –– Interaction of the surface and the lubri- regime EHD lubrication que M Even when seen from a tribological cant. No material contact standpoint, the optimization of a system Generally, a distinction is made between or of an entire powertrain must always be Friction in tribological systems four wear mechanisms (Figure 2). Abrasive subjected to a cost-benefit analysis and The amount of friction that occurs in a tribo- wear occurs as a result of the mechanical Friction tor ensure that the functional requirements logical system is influenced by a range of impact of a harder active surface on another for the overall system and its compo- factors. In addition to the load applied and surface or hard particles. Adhesive wear re- Relative velocity v nents are fulfilled. The service life, for in- the lubricant characteristics, the surface of sults from the molecular interaction when Interfacial regime stance, must not be less than that stipu- the active areas is particularly significant. surface contact occurs in the contact inter- lated in the requirements specification. The most important surface characteristics face. Tribochemical reactions change the Figure 3 Curve of the friction torque in relation That is why the experts working at that determine friction and wear include the contact interfaces by oxidation, for instance. to the relative speed (Stribeck curve). Schaefflers’ Surface Technology Com- following [2]: Surface fatigue occurs if the material micro- The black curve shows the classic petence Center depend on the systems –– The chemical composition of the sur- structure changes under mechanical stress. profile, the red curve shows the torque expertise available in the company when faces that can be changed by pretreat- There are various types of friction. The profile when using nano-structured, developing highly specific coating solu- ment or during operation by reactive Stribeck curve is a good way to distinguish diamond-like coating systems in the tions. layers on the component surface. between the various types, as it can be valve train. 334 Customized Friction 23 335

Surface technology State-of-the-art carbon thin film coating Results: Parameter optimization Actual systems usually do not consist of a single system In addition to the lubricant, the material layer but of up to 100 layers in the nano- using data mining and surface quality of a bearing also have meter range that perform certain func- significant influence on friction and wear tions. The exact layer structure is matched behavior. The properties of the material to the relevant application and require- close to the surface are changed to im- ments [3]. prove the tribological characteristics of engine and transmission bearings. The initial approach here is to achieve smooth- ing by reducing the roughness peaks, Analysis, calculation, and such as by honing the raceways. Addi- simulation tional improvement can be achieved by n F Load changing the surface through heat treat- R System analysis Relative motion ment and coating. Conventional methods FN 1 Primary body here are black oxide finishing and carbo- It is not unusual for tribological aggregate 2 Counter body 2 3 Interfacial medium 2 nitriding. Chrome-plated surfaces are of- loading conditions not to be fully known as 4 Ambient medium 3 ten used for engine and transmission part of component development. That is 5 Coating system 4 5 components that are subjected to high why the services of Schaeffler’s Surface Modeling + stress collective 1 stress levels. Technology Competence Center include a and tribological model tests

Figure 5 Data mining as part of the development process for coatings [4]

Prediction System comprehensive analysis of the initial situa- lubricated and coated with customized Data mining (e.g. artificial neural networks – ANN) tion. A standardized procedure ensures, for diamond-like carbon coating systems. instance, that all relevant parameters are Due to the high complexity and interac- Empirical data set entered. tions imminent to the system, the possi- A good development strategy always bilities for analytically calculating tribologi- Mechanical, structural, chemical and tribological parameters takes the overall system into consider- cal behavior is limited. The development SYSTEM ation. This is the only way to develop a and optimization of coatings for the sur- Tribological stress collective: rolling bearing that is optimally designed faces of cams and bucket tappets that – Kinematics – Pressure, for a specific application. Against this come into contact with each other has – Temperaturures background, Schaeffler has expanded its thus so far been based on experimental tried and tested Bearinx® calculation pro- investigations and the experience of spe- SYSTEM gram to include an analytical model for cialists. This method can be time-con- Local and temporal Analytical calculating rolling bearing friction. This suming and expensive. overlapping of friction prediction model takes a wide range of parameters For this reason, Schaeffler has devel- and wear mechanisms: not possible! into consideration, such as real pressure oped a method that can predict the tribo- – Chemical reactions distribution and internal bearing geome- logical behavior of camshaft and bucket – Surface fatigue – Adsorption try. In addition to load distribution and tappet systems, for example. It is based Lubricant chemistry: – Adhesion Coating, part, service life, it permits the calculation of on a combination of data mining and an – Base oil – Abrasion countero part: rolling bearing frictional torque and thus artificial neural network and can be prac- – Additives – ... – Composition – Materials the power loss of entire shaft systems or ticed with available experimental data [4] transmissions. (Figure 4). Schaeffler has been breaking new In this process, the artificial neural net- ground in the development of the tribo- work learns the phenomenological corre- Figure 4 Method for predicting friction based on empirical data [4] logical system of components that are oil lations on which these data are based. 336 Customized Friction 23 337

Their capability to “learn” non-linear cor- The use of such methods capable of “learn- Rear differential unit New: relations allows artificial neural networks ing” can therefore reduce the time and Bearing supports to predict an input variable – such as the costs spent on experimenting, secure avail- with tandem friction value – even in complex tribologi- able knowledge and use it efficiently for angular contact cal systems. Influencing factors include product development. ball bearings Differential the type of coating and its hardness, the Standard: surface quality, lubricant oil additives and Bearing supports Ring gear their concentration, the base oil and its with tapered roller , and the material of the counter- efficiency through bearings body and its structure. minimized friction The suitability of an artificial neural net- Pinion shaft work for this kind of application depends on its predictive accuracy. This is deter- Figure 6 Use of tandem angular contact ball bearings in the rear axle differential (blue) instead of mined by entering data from an experiment tapered roller bearings (red) that was not used to practice the model. Influence of bearing designs Finally, the prediction is compared to the stance, this is true for balance shafts in the Coatings for specific value measured in the experiment. The The friction occurring on the active sur- engine. Changing to rolling bearings while requirements data mining process is thus integrated into faces of bearings is primarily determined also designing the components with an op- the development process of coatings for by the selection of the bearing system timized weight can reduce CO2 emissions The Schaeffler Coatings Center uses all of tribological systems (Figure 5). and the bearing type and then by its de- by up to 2 % at a cost of less than ten euros the coating technology methods and has a Although data mining programs al- sign details. One example here are the per shaft. The cost-benefit ratio is just as modular system for validated coatings that ready contain automated optimization al- bearing supports of the main shafts in favorable when switching from plain bear- can meet any requirement: Corrotect® gorithms, expertise is required to design the transmission. Locating non-locating ings to rolling bearings in the camshaft coatings made from a zinc-iron or zinc- the optimum network topology of the arti- bearings are increasingly used as an al- bearing supports. nickel alloy provide corrosion protection, ficial neural network. The challenge lies in ternative for conventionally adjusted ta- Durotect® desig- finding the optimum number and arrange- pered roller bearings. Schaeffler has an- nates tribological ment of neurons, the optimum number of alyzed various applications to determine coatings that are input variables, the optimum parameters the effect a change in the bearing system produced chemi- of the learning algorithm, and much more can have on fuel reduction. For a com- cally. The coating for specific data with a given number of pact car with a double clutch transmis- configuration with examples. sion, consumption was reduced by 3.8 % iron oxide com- Since artificial neural networks only in the NEDC simply by changing the pounds is charac- approximate functional correlations in bearing system to locating non-locating terized by the fact most cases, the evaluation of a learned bearings. Tandem angular contact ball that it has good dry model is one of the most important steps bearings offer significant benefits in the running character- in data mining. This can be achieved rear axle differential. They replace the ta- istics in the event of through various methods. Schaeffler has pered roller bearings used in the past insufficient lubrica- found that a 10x10 cross validation or and develop a smaller contact surface tion. Insutect® – boot strap cross validation supplies the and thus a lower friction torque while which can be used best results to predict the tribological be- maintaining the same load carrying ca- as an aluminum ox- havior of a camshaft and bucket tappet pacity (Figure 6). With regard to the ve- ide coating, for in- system. Upon comparison with an exter- hicle, this results in a potential CO2 re- stance – has been nally driven cylinder head, a deviation of duction of 1.5 % that can be achieved at used primarily in only 8 % was found – a very good result, low cost. energy production especially when considering that the Over the past few years, significant for current insula- measurement error with reference to fric- progress has been made by using rolling Figure 7 Schaeffler modular coating system as a basis for coatings for tion; at Schaeffler, tion is at 5 % [4]. bearings instead of plain bearings. For in- specific requirements it is mainly used 338 Customized Friction 23 339

for railway bearings, generators, and ship cle, this means a reduction in CO2 emis- Friction loss Functional friction engines. With the hybridization of the pow- sions of 1 to 2 % (Figure 8). Triondur® ertrain, this coating has become more and coating here offers excellent wear protec- more important for the automotive industry tion and hardly requires any design space as well (Figure 7). at all with its layer thickness of only 2 to Characteristic Mainly undesired effect Specific friction value and friction not required for function behavior required for function Over the past few years, nano-struc- 3 microns. in friction systems tured coating systems based on carbon Schaeffler has standardized both its have been used increasingly as an alter- coating processes and its coating facili- Goal Reducing friction Achieving a specific friction level native for conventional surface technolo- ties. The same machines used in volume gy processes, such as those developed production are used for new develop- by Schaeffler under the Triondur® brand ments or adjustments from the start. The name. In the power train, this type of coat- manufacturing process is developed ing system was initially used in bucket along with the product. This ensures that tappet valve trains because the cost-ben- the transfer from development in the Low friction High friction efit ratio appeared to be especially inter- coating process to worldwide volume 0 0.1 0.2 esting: By using a customized Triondur® production is stable and free of errors. diamond-like carbon (DLC) layer on the The result is a consistently high level of tappet base, the sliding contact surface quality irrespective of the manufacturing for the cam, the tribological properties location. have improved so much that friction in the Figure 9 Functional targets on the friction axis with product examples valve train has been reduced by half. The mechanical bucket tappet thus almost Functional friction sliding speed, temperature, and pres- reaches the friction values of a roller finger sure, the system environment must be follower [5]. In relation to the entire vehi- optimized continuously to supply cus- tomized friction. Similar to the cross-country skier men- One of the requirements is under- Roller finger follower tioned earlier, friction in an automobile is standing friction phenomena. Analyses with hydraulic not always a bad thing. In a bearing, the were previously limited to specific dimen- valve lash aim is to minimize friction, in an engaged sions or scale levels; friction phenomena adjustment element Mechanical bucket tappet clutch, a brake, or in a press fit, the aim are often analyzed at the machine dy- polished and coated is to maximize it. Here, friction is used for namics level. This means that the friction “customized Triondur® coating systems” a very specific purpose. The latter can system is tested for a specific applica- thus also be called “functional friction” tion, and conclusions are drawn from (Figure 9). this. However, since friction occurs in the Mechanical bucket tappet with adjusted Classic application examples of func- friction contact, the scale levels of con- combination of coating, lubricant and oduction costs tional friction are clutches with a dry and tact mechanics must also be taken into

Pr counter body oil-lubricated design, damping systems consideration, such as the micro, meso, such as torsion dampers for clutch disks, and nano levels. The atomic scale level and the synchronizing units in the trans- can be left out here as it is used more for Mechanical bucket tappet carbonitrided, tempered, polished mission. fundamental scientific research. Like all systems in an automobile, the The consistency of methods and tools 50 100 tribological system is in line with the across the various scale levels – from mate- Mechanical bucket tappet Friction reduction in % downsizing trend, resulting in improved rials to production – is an essential compo- carbonitrided and tempered performance: Specified requirements for nent for the detailed analysis and optimiza- the friction value must be met with small- tion of friction systems. The tools used at Figure 8 Triondur® DLC coatings improve friction behavior by up to 50 % and offer a high level of er components. In addition to the param- Schaeffler range from methods for analyz- wear protection [5] eters relevant for , such as the ing systems and data to scale-specific test friction level [-]

340 Customized Friction 23 341

stands and materials analyses. The experts are assessed by determining the damping Judder test, 30,000 cycles, 0.16 of the Schaeffler Group work together in an behavior or excitation behavior of the running-in at 120 °C, 16 KJ (light load judder test) interdisciplinary fashion to use these meth- friction material on a judder test stand 100 0.14 ods efficiently. (Figure 12). These inspections often show that damping decreases as the mean friction 75 value increases; this means that friction 0.12 50 Dry running friction linings for increase. This behavior can be not disruptive disruptive in vehicle in vehicle clutches observed for all friction systems and ap- 25 Friction level

Distribution in % 0.10 pears to be a universally valid principle. A dry running double clutch system rep- The consistent application of standardized 0 -0.4 -0.3 -0.2 -0.1 0 0.05 0.2 0.3 resents a much greater challenge for the methods and tools has lately achieved Required damping in Nm/s 0.08 friction materials of the clutch than con- considerable success. Figure 11 shows an 50 900 1,800 Speed difference in rpm ventional manual transmissions. Inspec- example: The damping and excitation val- damping excitation tions here range from the system level to ues were taken from a large number of Initial state Wet lining with average porosity Optimization 1 Wet lining with ideal porosity sub-components and partial lining (Fig- tests with components that have different Wet lining with insufficient porosity ure 10). load profiles and plotted on a frequency Optimization 2 An essential parameter are the comfort scale. The significant improvement in the Figure 12 Improvements in friction value properties of the friction material. These friction materials is clearly visible and re- Figure 11 Optimization of lining damping behavior through lining porosity through use of a judder test stand permits the oil to be distributed uniformly flected primarily in a much lower disper- to the various friction surfaces and to en- Component test stand sion. Due to the internal damping of the sure that the aquaplaning effect can be power train, excitation values of more than prevented reliably. This is achieved – material inspection 0.05 Nm/s are a disturbance and notice- through the use of specific groove geom- (screening method) able for the driver as judder vibrations. etries. Adequate porosity of the lining supports this effect. If these and other findings are imple- Wet linings for twin clutches mented consistently, the friction value be- havior of wet clutches can be improved Clutch test stand For wet linings, oil is the third tribological significantly. Figure 12 shows an example. – material testing component in addition to the lining and The correlations described here should – standard tests steel or cast iron that function as the fric- suffice to show that the development of tion contact surfaces. The oil serves to an efficient tribological system is only dissipate the frictional heat, but it can possible if all conceivable boundary con- also have negative effects. Too much oil ditions have been taken into consider- between the friction contact surfaces ation. Vehicle leads to hydroplaning, similar to the aquaplaning of tires on a road wet with Challenges for friction linings in – validation rain, and thus results in a low and uncon- synchronization trollable friction value. In addition, drag The friction value structure and consis- losses occur in open clutches that sig- tency are important variables in the devel- nificantly reduce efficiency. If there is not opment of synchronizing materials. The enough oil, there is a risk of partial mixed transmission oil must be pushed away Benefits: – systematic product development friction or even dry friction; this has a quickly from the friction contact to achieve – profound material knowledge considerable impact on comfort behav- these variables. If the microstructure of ior. For this reason, the macrostructure of the friction materials cannot ensure this, Figure 10 Comprehensive lining development from partial lining investigation to complete clutch the lining must be designed in a way that other solutions must be found. One solu- 342 Customized Friction 23 343

0.15 system with the aid of an electronic con- Its new thin-layer sensor Sensotect® pro- an external control unit. Based on tribo- trol system. Mechatronics differs from tri- vides Schaeffler with a basis for imple- logical algorithms, these signals are used botronics in that it only uses information menting tribotronics in automotive engi- to perform calculations that indicate 0.10 Limit for µ dyn from the inputs and functional outputs of neering and industrial applications. Going whether the operating temperature of the the mechanical system to control its op- forward, this will permit output parame- component has to be corrected or 0.05 Dynamic eration. Such functional outputs supply ters such as the force, torque, and tem- whether a dimensional change is re- Friction value friction level information about speeds, , tem- perature of a component to be measured quired, to name just two examples. too low 0 peratures and loads. in places where conventional sensors, Actuator coating systems carry out the 0.1 0.15 0.2 0.25 0.3 Tribotronics, on the other hand, not such as glued strain gauges, cannot be necessary corrections. Completely au- Shifting time in s only considers additional output param- used because they are susceptible to ma- tonomous and self-regulating systems without grooves eters such as friction, wear, or vibrations, terial aging or signal drifting due to poly- are feasible if additional functions are in- spiral groove but influences them by means of an elec- mer glues or transfer foil. tegrated into the component surface, axial grooves tronic control system. The goal is to in- With Sensotect®, a thin, strain-sensi- such as telemetric components or trans- crease the performance, efficiency, and tive PVD coating performs the actual fer structures for energy supply and en- Figure 13 Effect of macro-geometry on the reliability of the tribological system and measurement function. The coating is ergy production. torque curve thus of the entire application. In tribo- structured by micromachining. These tronics, the component becomes a sen- structures are deformed at the same tion is the targeted macro-structuring of sor or actuator – or, put another way: The rate as the carrier component. Deforma- the friction material by using grooves or sensor or actuator becomes a compo- tion results in a change in electrical re- Summary and outlook groove patterns. The diagram in Figure 13 nent (Figure 14). This opens up an entire- sistance in the sensor layer. This change shows the torque curve of a gear shift ly new range of applications for coating is a measurement, for instance, of the mechanism with a friction material with a technology. contacting torque or the forces impact- groove and without a groove. Without the ing on thrust bearings, drive shaft, or The optimization of tribological systems groove, only a very small dynamic initial steering column shafts. Measurements in drives still offers considerable potential friction value can be observed. It results in are taken during continuous operation for reducing fuel consumption. Opportu- longer shifting times and, in extreme cas- and with extreme levels of sensitivity nities can be found in the selection of an es, prevents the transmission from shift- and precision, or, to be more precise, optimum bearing system as well as a ing altogether. with minimal hysteresis errors and mini- coating customized for a specific appli- Modifying the macroscopic surfaces – mal linearity deviations. Schaeffler has cation. Customized, nano-structured di- in this case by means of spiral or axial already been able to show the function amond-like Triondur® DLC coating sys- grooves – can help improve the torque of this type of sensor system in demon- tems can help optimize sliding contacts curve. As the oil is pushed away rapidly, stration vehicles – both in passenger in such a way that their friction losses oc- the dynamic friction value is already at a cars and bicycles. cur in the same range as rolling friction. much higher level even at the start of the One of the greatest challenges of such The new Triondur® coating systems help shifting operation, guaranteeing a high lev- sensory coating systems is manufacturing. mechanical bucket tappets achieve fric- el of shifting comfort and short shifting The use of highly efficient coating sources tion values that are almost identical to times. and compliance with very stringent re- those of a roller finger follower. At the quirements for cleanliness in the manufac- same time, coating offers excellent wear turing process has helped Schaeffler to protection – without requiring additional achieve a quality level even for typical design space. Since these systems can- Tribotronics three-dimensional rolling bearing compo- not be calculated analytically, Schaeffler nents that was previously known only for has broken new ground in their develop- planar substrates in the semiconductor in- ment: Data mining is combined with an dustry. artificial neural network to generate a The term “tribotronics” is used to describe Figure 14 Sensotect® coating measures the In the continued development of tri- procedure that can predict the tribologi- a fairly new field within tribology that inte- force on the rolling bearing. The botronics, Schaeffler focuses on pro- cal behavior of such complex tribological grates mechatronics into a tribological component becomes a sensor. cessing signals from surface sensors in systems. 344 Customized Friction 23 345

At the other end of the imaginary “friction Literature axis”, one of the development goals is to produce the required friction values with components that continuously decrease in size and weight. The analysis of friction phe- [1] Musayev, Y.: Verbesserung des tribologischen nomena must be expanded to include all Verhaltens von Stahl/Stahl Gleitpaarungen für dimensions and scale levels in order to Präzisionsbauteile durch Diffusionschromier- achieve the best results from a system eval- ung im Vakuum. Friedrich-Alexander-Univer- uation. sität Erlangen-Nürnberg, Dissertation, 2001 Tribotronics opens up an entirely new [2] Czichos, H.; Habig, K.: Tribologie-Handbuch. range of applications for coating technolo- Reibung und Verschleiß. 2. Auflage. Wies- gy. In future, the combination of force con- baden: Vieweg, 2003 verters, data transfer, and transfer struc- [3] Hosenfeldt, T.; Musayev, Y.; Christgen, W.: tures for energy supply and energy Energieeffizienz durch Reibungsreduzierung production will make autonomous mea- mittels Oberflächentechnik als Konstruktion- surement systems a possibility even for ro- selement. 2. ATZ-Fachtagung Reibungsminim- tating parts. ierung im Antriebsstrang, 2011 Schaeffler has combined all of the im- [4] Schulz, E.; Musayev, Y.; Tremmel, S.; Hosen- portant expertise, from fundamental tri- feldt, T.; Wartzack, S.; Meerkamm, H.: Reibung bological research, coating develop- und Verschleiß vorhersagen - Durch neue ment, and coating facility engineering to Methoden der virtuellen Produktentwicklung volume production and quality control Schmierstoff und Schichtsystem optimal measures. The most important goal here aufeinander abstimmen. mo – Magazin für Ober- is to derive the best integrated surface flächentechnik 65, 2011, no. 1-2, pp. 18-21 technology-based solution from custom- [5] Hosenfeldt, T.; Musayev, Y.; Schulz, E.: Cus- er requirements so that the customer is tomized Surface Technology – A Modern De- provided with a product that has a sig- sign Element to Increase Energy Efficiency by nificant added value – and with the best Friction Reduction, VDI Fachtagung Ventiltrieb quality. und Zylinderkopf, 2012