Timing Belt in Oil Reduces Friction and Noise
Number of engines with belt drives growing faster than those with chain technology / Timing belts in oil can be narrower than the dry-running version / System competence for the entire drive
This is one of the reasons why the timing belt in the timing assembly has gained significantly in importance once again in recent years. Volkswagen is again fitting belts instead of chains in the Golf VII and Audi A1. And other manufacturers too are increasingly designing their new engines for high-tech drive belts made from rubber and plastic, because they know that belts have distinct advantages over chains in reducing fuel consumption and CO2 emissions from combustion engines.
Studies also confirm this: According to FEV GmbH, an independent engine designer, the belt drive lowers fuel consumption compared to the chain, and therefore reduces CO2 emissions. In a 1.6 liter gasoline engine, for example, the belt drive reduces fuel consumption by more than 1% and saves up to 1.5 grams of CO2 per kilometer. "Belt drives are lighter and run a lot more quietly too. Belts don't tend to lengthen either," says Hermann Schulte, head of Timing Belt Development at the ContiTech Power Transmission Group. "A significant advantage, because a lengthening chain alters the engine timing. As a result, consumption increases and performance drops. Emissions levels are quickly exceeded." In endurance tests, a belt lengthened by just 0.1% after 240,000 kilometers of service life - the figure was five times greater with a chain.
Many large automotive manufacturers in Europe are now making use of the benefits of timing belts in their engines and this number is growing. ContiTech supplies dry-running timing belts to manufacturers including Audi, Volkswagen, Volvo, Ford, Opel, and PSA. It's not only camshafts that are controlled by timing belts, but injection systems and oil pumps too. ContiTech developers are already considering whether to use a timing belt to drive balance shafts as well and therefore make spur gears superfluous. And their focus is on unconventional yet safe solutions, such as the timing-belt-in-oil system. "Since the start of 2013, the ContiTech Power Transmission Group has been part of the group of series production suppliers for these applications. Timing belts are already in use for oil pump and timing drives in the newer Ford, PSA, and Volkswagen engines," says Ralf Berger, head of Key Account Management and Application Engineering at the ContiTech Power Transmission Group.
What was previously unthinkable is today running along without a hitch in series production. To achieve this, ContiTech has adapted the elastomer, the fabric, and the cord to the new environment. In addition to polyamide and aramid fabric with a Duralon coating containing Teflon, an ultra-durable rubber compound made from ACN-HNBR (hydrogenated acrylonitrile butadiene rubber), as well as E-glass and K-glass, is also being used for high length stability. Because of these special components, even impurities in the oil cannot harm the belt, whereas simple soot particles in the oil can destroy chains.
The advantage of the timing belt in oil is that it has a narrower construction than the dry-running version and it is even quieter. In the case of a crankshaft pulley with 19 teeth, no noise can be detected, even with the engine operating under full load, because the oil not only reduces friction, it absorbs sound as well. This is important for the simple reason that the increasingly popular downsized engines generally run less smoothly. Here is where a belt can help minimize vibration and make driving a pleasant experience despite the use of environmentally friendly technology.
Benchmark trials also demonstrate that belts today have at least the same and often even better properties than chain drives with their hydraulic tensioners and plastic guides. This is why developers are no longer concentrating on durability - this has long been a given. In on-road tests, the belts still ran without a hitch even after 300,000 kilometers.
The question today is one of making the belts even narrower - every millimeter counts, because installation space in vehicles is becoming ever tighter. "This is where the belt has another advantage. The engine designer has more flexibility in designing the belt drive than with a chain," says developer Hermann Schulte. The aim is to reduce belts for the camshaft drive in the next generation of engines from today's 16 - 20 mm width to 14, 12 or even 10 mm. Belts for oil pump drives currently measure just 9 mm - and so are as narrow as a chain.
Yet when it comes to the issue of reducing weight, it is not enough to consider the belt alone. Tensioners, idlers, and toothed pulleys are critical too. This is why developers at the joint venture company ContiTech-INA are already working on drives that can make do with simpler, and therefore lighter, tensioning systems. Or even none at all. In this way more grams can be saved and the CO2 emissions ultimately reduced even further. Vehicle manufacturers are backing this trend with their development commissions and in so doing reveal their confidence in ContiTech's many years of experience in the field of drives.
The many advantages offered by modern timing belts, including their long service life, reduced friction and reduced noise, will again expand the market share of timing belts. Experts estimate that it will include at least two thirds of European vehicles in 2015 and over 70% in 2017. The share of belts running in oil will more than double from today's 8% to over 20%. A development that will benefit the environment and motorist alike.
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