The HNBR elastomer Therban® can cope with high engine block temperatures
Made with Therban®
Leading engine technology, despite being so advanced nowadays, still offers astonishing potential both in terms of driver enjoyment and environmental compatibility. One example lies in the new diesel engines available from Volkswagen AG for its Golf, Audi A2, A4 and Lupo models.
The highly promising injection pump and nozzle technology offers improved performance and is more environment-friendly in terms of exhaust emissions - and as far as the Lupo 3L TDI is concerned, fulfils the dream of a three-liter car. Despite performance levels that are more than up to comparison with "standard" small cars, this vehicle can run for 100 kilometers on three liters of fuel. Close to the "beating heart" of the new diesel driving gear is an elastomer made by LANXESS. The camshaft absorber made from the high-performance polymer Therban® plays a direct role in controlling the injection pump and nozzle unit, operating at long-term temperatures of up to 150 °C, and plays no small part in ensuring the long service life of this new showcase engine.
The principle behind the injection pump and nozzle technology is quite simple: instead of relying on a central pump to compress the diesel and inject it into the cylinders, the engineers at Volkswagen have given each cylinder its own compression pump. Because the pressure is now produced within a more confined space, with the compressed fuel no longer having to be transported along a pipe to the cylinder, the injection pump and nozzle unit injects the fuel into the combustion chamber at a higher pressure: at 2,050 bar in fact, which is 700 bar higher than the level otherwise achievable with conventional technology. This means that more fuel is forced through the tiny holes in the injection nozzle within a shorter space of time - resulting in more accurate combustion and greater power coupled with lower revolutions (engine torque in a 1.9 liter 4-cylinder engine with 85 kW: 285 Nm instead of 235 Nm), quieter running and a significantly cleaner combustion process with favorable consumption figures.
The quantity of fuel to be injected and the overall injection choreography of the solenoid valves is mechanically controlled reliably in the new Volkswagen engines via the camshaft, which is driven by a toothed belt. The absorber on this toothed belt - an important damping element - is crucial to the operating safety and thus the service life of the engine. It must be precisely tuned to guarantee smooth performance. Should it fail to perform and cease to function properly, the finely balanced engine control system would be thrown off course.
The vulcanized part - the camshaft absorber used in Volkswagen's new diesel model - consists of two metal rings. The hub - which provides the link to the camshaft and to which the toothed belt is fixed - is attached on the inside, whilst the flywheel rim of the dynamic damper is pressed on to the outside. The two rings are joined via a cushioning and damping layer of Therban® "rubber". Responsible for the design of this inconspicuous yet sensitive component was the company Paguag GmbH, in Düsseldorf. The engineers at Paguag opted for Therban® because vulcanizates from this oil-resistant elastomer, in addition to the damping properties typical of rubber and excellent dynamic strength, offer absolutely constant compression set behavior and a constant torsion modulus. And - almost more importantly - the material is up to the demanding property profile even when located in direct proximity to the hot engine components. When the car is running the long-term temperature can rise to 150 °C, even hitting 160 ° at times. In this environment, Therban clearly outperformed other high-performance elastomers such as NBR.
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