19 Belt drive 19 Belt drive Belt drive 19

Belt drive systems

Potenti al for CO2 reducti ons and how to achieve them

Hermann Sti ef Rainer Pfl ug Timo Schmidt Christi an Fechler 19

264 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 265 19 Belt drive Belt drive 19

If required, double-row Introducti on Tension pulleys and angular contact ball Single and double eccentric tensioners bearings (Figure 3) are Schaeffl er has volume produced components for idler pulleys used that also have an belt drive systems since 1977. For the past 15 years, opti mized grease sup- Schaeffl er has worked on the development of com- One use of INA idler pulleys is to reduce noise in ply volume. These plete belt drive systems in ti ming drives (Figure 1) criti cal belt spans, to prevent collision problems bearings are equipped as well as in accessory drives (Figure 2). with the surrounding structure, to guide the belt with high-temperature or to increase the angle of belt wrap on neighbor- rolling bearing greases ing pulleys. These pulleys have the same rati ng and appropriate seals. life and noise development requirements as belt Standard catalog bear- tensioning systems. For this applicati on, high-pre- ings are not as suitable Pulleys Variable camsha ming cision single-row ball bearings with an enlarged for this applicati on. grease supply volume have proven suffi cient. The tension pulleys in- stalled consist of single or double-row ball bearings specially de- veloped, opti mized and manufactured by INA for use in belt drive ap- Idler pulleys plicati ons. Depending on the applicati on, pulleys made from glass fi ber reinforced poly- amide or corrosion pro- tected steel can be added. Thanks to Schaeffl er’s highly developed tool- Belts (preferably by CT) ing and manufacturing Figure 1 Timing drive technology, the pulleys made from highly tem- Considering the fact that over 100 million belt Figure 3 Steel pulley 19 perature resistant, glass drive components are produced annually, this fi ber reinforced polyam- means that, on average, almost two belt drive ide (Figure 4) are just as components manufactured by Schaeffl er are in- good as the steel pulleys stalled in every vehicle. when it comes to round- ness and running char- acteristi cs and may off er signifi cant cost and weight benefi ts. Adjust- ed dust covers made from steel or plasti c may Figure 5 Products in the ti ming drive also be used.

internal combusti on engines for 40 years. In older designs, the ti ming belt was preloaded via either Timing drive an accessory with eccentric bearings in the ti ming belt drive (e.g. water pumps) or through manually Timing belt drives (Figure 5) that drive camshaft s adjustable, fi xed tension pulleys (e.g. eccentric Figure 2 Accessory drive Figure 4 Plasti c pulley or balancer shaft s have been volume produced for tensioners).

266 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 267 19 Belt drive Belt drive 19

This type of system does not allow for opti mal ad- Reduced fricon - Comparison chain vs. belt drive and a chain drive has shown that the tim- justment of the belt force since neither belt force ing belt drive has considerable benefits. The test Accessory drive fl uctuati ons resulti ng from temperature or wear 5 was performed on a 1.6 liter, 4-cylinder gasoline nor dynamic eff ects (belt vibrati ons, impacts from 4 engine. The test was initially conducted on the In modern internal combusti on engines, accesso- the valve train) are compensated. Compensati on original version with a timing chain and then ries are almost exclusively driven by poly-V belts. 3 of such fl uctuati ons and eff ects by means of auto- with the timing belt version. The test setup is The primary requirements for accessory drive sys- mated belt tensioning systems is essenti al in mod- 2 shown in Figure 7. tems (Figure 8) and their automated tensioning ern ti ming belt drives since this is the only way that 1 The timing belt in oil has already operated for systems are listed below: a system life of up to 240 000 km and more (de- more than 240 000 vehicle kilometers in the ve- pending on the engine life) required in today’s au-  Automated belt force adjustment during initi al Mot. fricon torqueMot. fricon - CR in Nm 1000 2000 3000 4000 5000 6000 hicle fleet owned by Continental and thus dem- tomoti ve industry can be achieved. installati on and maintenance (tolerance compen- Cranksha speed in 1/min onstrated its endurance capability. This also sati on of all drive components) Belt drive systems not opti mally preloaded are sus- Chain drive means that the oil-resistant timing belt lasts the cepti ble to noise and suscepti ble to wear. Using an Belt in oil drive entire life of the engine.  Nearly consistent belt force during the enti re automated belt tensioning system considerably re- life of the belt drive (compensati on of belt Figure 6 Fricti on curves of chain vs. belt It will initi ally be used for oil pump drives and ti m- duces preload force dispersion during initi al instal- elongati on and wear) ing drives. This innovati on will later also be devel- lati on and also keeps the preload force across the ti on by 1 to 2 %, also decreasing the emission of oped for additi onal applicati ons, such as higher  Nearly consistent belt force across the enti re engine’s operati ng temperature range at nearly carbon dioxide (CO ). Figure 6 shows a comparison 2 demanding balance shaft drives, to further reduce engine temperature range (compensati on of heat consistent levels. Automated belt tensioning sys- of the fricti on curves for ti ming drives and chain CO emissions. expansion of all components aff ecti ng the drive) tems have been used in ti ming belt drives in inter- drives. 2 nal combusti on engines since the early 90s and A test completed at IFT, Clausthal-Zellerfeld that have largely replaced fi xed systems for the reasons compared the measurements for a timing belt described above. Tension pulleys / pulleys Mechanical auto tensioners The above conditi ons result in the following pri- Test Program: 4 Cyl. Gasoline Engine mary requirements for automated tensioning sys- tems:  Provide simple adjustment of the specifi ed belt force during initi al installati on and maintenance (compensati on of belt, diameter and positi on E-Motor tolerances)  Maintain a defi ned belt force that is as consistent as possible under all operati ng 19 conditi ons for the durati on of the required Pulley decoupler Hydraulic auto tensioner System tuning together ConTech system life (compensati on of heat expansion, with belt elongati on and wear, considerati on of crankshaft and camshaft dynamics) Belt drive  Ensure an opti mal noise level while also reducing Chain drive belt vibrati ons  Prevent gear teeth jump

Potenti al for CO2 reducti ons in ti ming drives Overunning alternator pulley Waterpump bearings Compared to chain drives, both dry and oil lubri- cated ti ming belts, that can be used to drive oil pumps, balance shaft s and camshaft s, signifi cantly reduce fricti on (measurements have determined up to 30 %), thus helping reduce fuel consumpti on. The fricti on benefi t of ti ming drives compared to chain drives can reduce a vehicle’s fuel consump- Figure 7 Test setup Figure 8 Products in accessory drives

268 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 269 19 Belt drive Belt drive 19

 Reducti on of dynamic belt force peaks belt preload force is usually generated by the Advantages torque of a torsion spring as well as the lever  Minimizati on of slip, noise and belt wear arm and the tension pulley. The damping pack- The positi ve eff ects on the accessory drive include:  Rati ng life increase for the enti re belt drive age consists of a friction element (disk, ring and  Minimizati on of belt vibrati ons system cone) that is preloaded by the torsion spring. As the lever arm moves, a relative motion in the  Reducti on of force peaks in belt drives  Opti mal reliability of the overall belt drive damping package is generated, causing friction system  Reducti on of tensioner movement and, consequently, damping. The belt preload Tensioner with  Minimizati on of fricti on loss in the overall system force (via the spring’s torque) and damping are Rubber bellows  Increase in belt life adjusted to match the application. The materials (RSEHB) Modern, opti mally adjusted accessory drive sys-  Improved noise behavior in the belt drive used allow consistent damping values to be tems (Figure 8) are maintenance free and can run achieved via the temperature and frequency and  Reducti on of belt slip on the alternator pulley for up to 240 000 km, given by opti mal system de- with minimal run-in effects. Different designs during upshift (parti cularly in fast shift ing dual- velopment. permit optimum usage of the available design clutch and automati c transmissions) package. Mechanical belt tensioning  Less strain on the overall system during engine Hydraulic belt tensioning start and stop-and-start functi on units  Preload force reducti on in the overall system, systems leading to reduced CO and fricti onal loss Mechanical belt tensioning units (Figure 9) rep- 2 resent a cost-optimized solution for automati- Hydraulic belt tensioning systems provide a solu- cally tensioned poly-V belt drives. The required tion for poly-V belt drives with high require- Decoupling functi on ments. They consist of The large mass of the generator cannot follow a hydraulic compo- Component overview Tensioner with the high irregularities of the crankshaft at en- nent with an integrat- Piston rod seal Protecve cap gine start and drive resonances. Thus it comes to ed pressure spring (RSEHK) differences of rotation angle speeds of crank- and hydraulic leakage shaft to alternator. Contrary to a rigid wheel the gap damping as well Figure 10 Hydraulic belt tensioner Thrust washer overrunning alternator pulley opens in overhaul- as a lever arm with an dency in combination with excellent resistance ing direction. The alternator mass and their in- attached tension pul- Pulley bolt to aging – all with hardly any wear. An example fluences are decoupled from the accessory Single self-lubricang ley. The hydraulic design is shown in Fig- thermoplasc plain bearing leakage gap damping – opmized NVH behaviour ure 10. acts in a controlled Sealing ring – balanced load distribuon way and in proportion 19 to the speed, causing Overrunning Hub damping to be gener- Plasc pulley Clutch unit ated only when need- alternator alternave: Pulley steel pulley ed. The optimal ad- pulley justment of the required belt preload Alternators have the Sealing frontside Lever arm force to the relevant largest inertial torque application is carried in an accessory drive, Radial loaded fricon element out via the integrated greatly affecting belt self-lubricang thermoplasc pressure spring and drive behavior. An Outer sleeve the converted lever overrunning alterna- Support bearing Torsion spring ratio. The required tor pulley decouples Cap without legs damping is set by se- its inertial torque Clutch cage lecting the leakage from the cyclic irregu- Needle rollers gap. The properties of larities of the crank- Support bearing 2 Backplate / sleeve unit the hydraulic oil used shaft in an internal Inner sleeve with ensure the lowest combustion engine. Ramp profile possible damping Figure 9 Mechanical belt tensioner temperature depen- Figure 11 Overrunning alternator pulley

270 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 271 19 Belt drive Belt drive 19

drive. In addition, the overrunning alternator opmal range Figure 14) or a spring- Reference: mech. tensioner, no decoupling, 350 N pulley decouples the alternator’s inertial torque elastic alternator de- Decoupling: OAP GEN Decoupler OAP GEN Decoupler during a significant engine speed deceleration coupler is introduced, Pretension: 350 N 350 N 280 N 280 N 0 % (shifting gears, upshifting). the preload can po- tentially be reduced -1.3 % -1.5 % -1.0 % -1.6 % to 280 N, resulting in - 5 % Structural design friction and loss sav- ings of 14 to 20 % in -10 % -20.3 % -14.2 % -20.0 % -15.5 %

The overrunning alternator pulley (Figure 11) Loss in % the drive system (Fig- consists of a pulley with an outside diameter ure 14). suitable for using a poly-V belt, a one-way -15 % clutch unit with bearing supports, an inner ring Even greater savings Possible decrease

and two seals. Following installation, an end Pretension in N can be achieved when -20 % of stac pretension cover is snapped onto the front of the alterna- Figure 12 Fricti on curve a pulley decoupler tor shaft to protect it from ambient media (e.g. is used right on the Accessories base load penetration of contamination, salt water de-  Load at 1st crankshaft bearing (is not considered crankshaft itself. Accessories full load posits). in analysis below) Compared to the ba- sic system, a frictional Figure 14 Potenti al savings for fricti on losses A modular system has been developed for over- When the functional limits and system toler- loss reduction of up running alternator pulleys to provide an eco- ances are considered, an engine-specific opti- to 36 % can be achieved in the drive system double-clutch transmissions. LuK also solves nomical and flexible solution for customer inqui- mal preload range can be determined (Fig- (Figure 15). In this example, a preload of 230 N torsional vibration problems in internal com- ries. The one-way clutch unit and the seal ure 12). ensures optimal friction reduction while main- bustion engines and has developed the product components are standard parts. Figure 13 compares potential savings using a taining the system’s functional operation and group of engine dampers. The internal crank- Unlike spring decouplers, an overrunning alter- sample drive layout. Assuming a basic system rating life. shaft damper (ICD) was presented during the nator pulley does not have its own resonant fre- with a mechanical belt tensioner and a preload 2002 LuK Symposium [1]. The ICD has been vol- quency and does not have to be adjusted to of 350 N required for this system, the potential ume produced successfully for several years in varying alternator sizes. savings when using an alternator decoupler can Reference: mech. tensioner, no decoupling, 350 N addition to other engine dampers. Develop- be determined. Some savings can be achieved ment activities currently focus on the reduction Decoupling: Pulley Decoupler Pulley Decoupler compared to the basic system without changing Pretension: 350 N 230 N of torsional vibrations for belt drives. One re- Potenti al for CO2 reducti on the belt preload. If an alternator decoupler 0 % lated development is the Pulley decoupler. with an overrunning alternator pulley (“OAP” in in accessory drives -4.6 % -3.4 % -10 % The details of accessory drive components de- cranksha pulley scribed above show that a wide range of pa- -20 % -35.7 % -24.2 % damper decoupling 19 rameters must be considered to achieve the functional operation and rating life of the over- -30 % all system. Targeted investigations through dy- namic simulation with Simdrive 3D™ and test- -40 % ing have yielded belt preload as the main Possible decrease of stac pretension influencing parameter with regard to friction Accessories base load losses in the accessory drive. Belt preload has a Accessories full load significant effect on: Figure 15 Potenti al savings for fricti on losses  Bearing fricti on in tension pulleys and idler pulleys  Belt expansion Pulley decoupler  Belt bending LuK is a well-known specialist for transmission and clutch components and has an extensive  Contact losses between the belt and the pulley, portfolio of products for the reduction of tor- parti cularly the radial compression of the belt sional vibrations in vehicle power trains. These  Bearing fricti on within all accessories (is not products include dampers in clutch disks, dual- Figure 16 Pulley decoupler with integrated crankshaft considered in analysis below) Figure 13 Simulated drive mass flywheels, torque converter clutches and damper

272 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 273 19 Belt drive Belt drive 19

The decoupled pulley on the crankshaft of the in- Belt drive decoupler ternal combusti on engine has two main func- ti ons: The periodic igniti on in the internal combusti on engine generates a cyclic irregularity that is applied 1. Driving the belt drive for accessory drives while to the accessories via the belt in the form of tor- simultaneously decoupling this belt drive sys- sional vibrati ons. When the engine operates at the tem from the cyclic irregulariti es of the crank- eigenfrequencies of the belt drive system, the sys- shaft . tem can be excited to generate resonance vibra- 2. Providing damping for the torsional vibrati ons ti ons. resulti ng from the eigenfrequencies in the A pulley decoupler mounted on the crankshaft is crankshaft – fl ywheel vibrati on system. Figure 19 Exploded diagram of pulley decoupler used to minimize belt vibrations induced by The functi on and structure of the two parti al sys- these cyclical irregularities of the crankshaft. from elastomers. Although these elastomers ity between the plasti c cups and the contacti ng tems (Figure 16) are described below. The measurements in Figure 17 show a compari- represent a relatively inexpensive material for sheet metal parts. son of a belt drive system with overrunning al- spring elements, their functional operation and This results in a characteristi c curve for the decou- ternator pulley (OAP) and fixed pulley on the lifetime greatly depend on the temperature and pler (Figure 20) composed of several diff erent crankshaft with a belt drive decoupling system number of load cycles. As requirements increase Belt drive with OAP on alternator curves including the characteristi c curve of the arc- 150 (4. gear with load on accessory) (the second order of the engine speed for each). (increasing cyclic irregularities of the engine, shaped spring package C2 as well as two relief an- The isolation of the entire belt drive can be im- larger number of engine starts, higher drag gle curves. Transiti onal springs have been integrat- 125 proved significantly by the decoupler on the torques, rising ambient temperatures), the ap- ed in the component for the transiti on between crankshaft. plication range for “elastomer decouplers” be- 100 the curves that, via their serial connecti on with the comes more and more limited. In many applicati ons, the fi rst eigenfrequency of a arc-shaped springs, result in a soft transiti on C1 for 75 belt drive without decoupling is in a speed range of In the LuK Pulley decoupler, the spring element de- the enti re spring curve. Isolati on is further im- 50 1000 and 1500 1/min. With the pulley decoupler sign uti lizes coil springs in the component shown proved by reducing the total spring rate in the low- a further spring system is added to the vibrati on (Figure 18 and 19). The three arc springs and the er moment range. 25 system. This lowers the natural frequency clearly force transmission are guided in two plasti c cups With the design and curve structure described below the idle speed of the internal combusti on located under the belt track. The pulley is guided 0 above, there is an additional option of a bidirec-

Speed irregularity (2. order) in 1/min (2. order) Speed irregularity engine, and the belt drive is operated in the above- with a plain bearing on the hub. 0 500 1000 1500 2000 2500 3000 tional transmission of the moment in the decou- Engine speed in 1/min criti cal range, resulti ng in a reduced load for all In the decoupler and for the enti re belt drive, an pler. Besides driving the accessories in the belt Cranksha components in the belt drive. eigenfrequency via the arc-shaped springs is drive, the decoupler can be used in applications Pulley OAP Decoupled pulleys for crankshafts available on shown. This frequency is below idle speed and al- that call for a start function of the internal com- Alternator today’s market contain spring elements made lows the required above-criti cal operati on of the bustion engine or a boost function via the alter- belt drive. When starti ng the engine, this eigen- nator in the belt drive. In these cases, the mo- 19 frequency must be passed through. In an unfavor- ment flow runs in the opposite direction in the Belt drive with decoupling on cranksha Pulley able case, a resonance may be generated that belt drive. 150 (4. gear with load on accessory) 1. Spring coincides with the ei- 125 2. Spring genfrequency in the dual-mass fl ywheel – C 2 100 power train combina- ti on. Since a relief an- 75 gle functi on is C 1 Torque 50 integrated in the pul- Cranksha ley decoupler, reso- 25 nances are prevented Angle from passing through 0 Speed irregularity (2. order) in 1/min (2. order) Speed irregularity 0 500 1000 1500 2000 2500 3000 the eigenfrequencies Engine speed in 1/min of the belt drive in Cranksha their earliest stages. Pulley 3. Spring The required clearance Alternator angle is realized in the component by an ad- Figure 17 Belt drive measurements Figure 18 Cross secti on of pulley decoupler justed torsion capabil- Figure 20 Characteristi c curve of a pulley decoupler

274 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 275 19 Belt drive Belt drive 19

to the crankshaft by means of a vulcanized or Timing drives must be Combinaon of belt drive components and fuel consumpon pressed-in rubber track [3]. In larger engines, this reanalyzed to take low applicati on may also include viscous dampers. The fricti on characteristi cs Hydraulic belt tensioner + Pulley decoupler opti mal adjustment of the mass, spring and damp- into account. The bene- ing reduces resonance vibrati ons in the crankshaft fi ts of a chain drive are and achieves an improvement in the NVH behavior counteracted by the dis- Mechanical belt tensioner + Pulley decoupler as well as lifeti me of the crankshaft . advantage of increased fricti on among others. Hydraulic belt tensioner + OAP System evaluati on with engine and Here, results clearly power train point to the benefi ts of Efficiency ti ming belt drives. Mech. belt tensioner + OAP or hydr. belt tensioner

Pulley decouplers and the adjacent accessories Technical effort In accessory drives, de- and components in a belt drive are designed using coupling in the crank Mechanical belt tensioner state-of-the-art simulati on tools. Besides Sim- shaft pulley provides sig- drive 3D™ the Schaeffl er Group also uses DyFaSIM. nifi cant advantages for This program was developed by LuK and is the re- Fixed tensioner the enti re belt drive. Re- sult from many years of development and design ducing the applied cyclic of torsion dampers and dual-mass fl ywheels. The Potenal for fuel consumpon / CO2 reducon irregulariti es allows the program permits the simulati on of the enti re vehi- load for all components Figure 22 Potenti al for opti mizati on cle power train from the engine through the vehi- in the drive to be re- cle to the wheel as well as belt drives and their duced. In combinati on Figure 21 Dual pulley decoupler for alternator start behavior. and 2-belt systems with the pulley decou- Using the simulati on technology employed for the pler including arc- For applicati ons that require a higher torque for development of the dual-mass fl ywheel [4] allows shaped steel springs, the alternator start or boost functi ons compared to a complete evaluati on by expanding the power potenti al for opti miza- the actual drag functi on, an asymmetrical charac- train models to include models for belt drive sys- ti on can be seen. The teristi c curve can be achieved in a dual damper tems. Interacti ons of the belt drive with the en- potenti al savings shown Mech. tensioner (Figure 21). gine, the coupled single or dual mass fl ywheel and in Figure 23 are possible. Hydr. tensioner the power train can be integrated into the investi - Mech. tensioner + OAP/Decoupler

The skillful applicati on Loss in % gati on. Hydr. tensioner + OAP/Decoupler Torsional vibrati on damping and combinati on of oupler tensioner + Pulley decoupler When parameters such as slip, belt vibrati ons, belt products in Schaeffl er’s Mech. sioner + Pulley dec A torsional vibrati on damper has been integrated tensioner forces and bearing forces in the acces- portf olio allows the Hydr. ten in the assembly for another main functi on (Fig- 19 sories are considered, simulati ons allow an opti mal greatest possible CO ure 16). This is used to reduce resonance vibrati ons 2 belt decoupler design decoupling the belt drive savings to be achieved in the crankshaft that are generated by the igniti on from the excitati ons of the internal combusti on en- in belt drive systems. frequency of the engine [2]. Here the crankshaft - Pretension in N gine. This results in a reducti on of accessory losses fl ywheel vibrati on system is excited in several ei- which in turn leads to a reducti on in fuel consump- Figure 23 Opti mizati on curve genfrequencies. ti on and CO2 emissions for the internal combusti on The torsional vibrati on damper will be tuned on engine. Literature the fi rst eigenfrequency within a range from 300 to 400 Hz. Depending on the number of cylinders, [1] Gerhardt, F.; Fechler, C.; Lehmann, S.; Lan- [3] Hafner, Maass: Torsionsschwingungen in crankshaft design and the masses of the crankshaft geneckert, H.: Internal Crankshaft Damper; der Verbrennungskraft maschine, Band 4, and the fl ywheel, the eigenfrequencies are excited Summary 7th LuK Syposium, 2002 1. Aufl age ,Springer-Verlag, 1985, p. 361 ff . by the dominant exciter orders in the engine's en- [2] van Basshuysen; Schäfer: Handbuch Ver- [4] Fidlin, A.; Seebacher, R.: DMF simulati on ti re speed range. In this process, the fl ywheel vi- In the past, high-quality belt drive components brennungsmotor, 2. Aufl age, Vieweg-Ver- techniques; 8th LuK Symposium, 2006 brates against the crankshaft with the att ached were oft en regarded as the necessary “problem lag, 2002, pp. 78-79 masses such as connecti ng rods and pistons. solvers” in diffi cult applicati ons. In future, highly This eigenfrequencies can be dampened by a free effi cient complete systems (Figure 22) in ti ming mass via a spring and damping element at the free drives and accessory drives will be indispensable to

end of the crankshaft . In small or medium series increase comfort and reduce CO2 emissions as engines, this is usually a mass ring that is coupled much as possible.

276 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 277