Every gram counts

March 2011Designers have to comply with the EU Commission’s strict CO2 specifications while still focusing on driving comfort. With drive belts in the timing chain and accessory drive, both are possible.

Many things can be tweaked to reduce the harmful emissions from combustion engines. These include two new drive belts from the ContiTech Power Transmission Group. The CONTI® GREEN RUNNER timing belt replaces the timing chain in the engine and is used to synchronize the camshaft and the crank shaft. The frictional losses with the timing belt are 30 % lower than those with the chain drive. This reduces the fuel consumption by up to 0.2 liters per 100 kilometers and thus the CO2 emissions by two grams per kilometer. These advantages of the belt drive over the chain drive have also been confirmed in a study conducted by the engine development service provider FEV GmbH.

Another advantage of the belt is that there is less noise buildup than with chain drives due to contact occurring between rubber and metal instead of steel and metal. Furthermore, by using oval crankshaft pulleys, the timing belt allows for reduced design widths that are 30 % narrower than those of conventional timing belt drives. The original advantage of chains – their narrower design width – is thus eliminated. What’s more, for less complicated drives, the tensioning rail previously required for chain drives is rendered superfluous.

It is not just in the timing chain that drive belts can help improve the carbon footprint. The drive for the auxiliary units such as the alternator, water pump or A/C compressor currently still accounts for about 13 % of an engine’s mechanical losses – for example, through frictional losses. The V-ribbed belt is a starting point for reducing the losses in the accessory drive. Its power losses are particularly high due to the regular flexing in the belt drive. To reduce the power loss, ContiTech has developed a belt with greater flexural flexibility. This is because the more flexible the belt, the fewer its losses during its regular flexing in the accessory drive. A fiber-free EPDM compound has been used for the CONTI® UNIPOWER ECO2-FLEX. The developers combine this material compound with a lower belt profile height, known as a flex profile. The result: 10 % less power loss than with the previously used standard belts from ContiTech. This result was obtained through tests on the ContiTech test bench.