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.