Mercedes-Benz wins MATERIALICA awards for diesel passenger car steel pistons and CFRP struts

25 October 2014

Mercedes-Benz received two MATERIALICA Design and Technology Awards at the MATERIALICA 2014 trade fair for materials applications, surface technology and product engineering in Munich. The first was for the new steel pistons for diesel engines (earlier post), the second for high-strength carbon-fiber reinforced plastic (CFRP) struts.

The MATERIALICA Award 2014 comprised five categories: Material; Surface Technology; Product; CO₂ Efficiency; and Student. The MATERIALICA Design + Technology Award focuses on product and technological developments in all sectors which implement a successful bundling of competencies.

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Aluminium piston (left) the new steel piston (right). Click to enlarge.

Steel pistons for passenger-car diesel engines. Mercedes-Benz passenger-car diesel engines are the first engines worldwide being equipped with innovative steel pistons in conjunction with a lightweight aluminum cylinder case. The result is a 2 to 4 percent reduction in fuel consumption and CO₂ emissions.

The reduction in fuel consumption is even more pronounced at lower and mid-range engine speeds—i.e., the ranges which play an important part in everyday driving. Mercedes-Benz received a MATERIALICA “Best of Award” for the innovative steel pistons in the category CO₂ Efficiency.

At first glance, the combination of aluminum cylinders and steel pistons seems problematic: steel expands less than aluminum when heated; it conducts heat worse and is heavier than aluminum. These are the reasons why aluminum pistons have been used to date. The Mercedes-Benz engine designers turned these apparent disadvantages into advantages.

For example, the lower expansion of steel as operating temperatures rise ensures increasing clearance between the piston and the aluminum housing. This reduces friction by 40 to 50 percent.

At the same time, the fact that steel is stronger than aluminum allows very compact, lightweight pistons that even offer additional strength reserves. Finally, the lower thermal conductivity of steel leads to increased component temperatures, thus improving the thermodynamic efficiency with higher ignition performance and reduced burn time.

CFRP struts. Click to enlarge.

High-strength CFRP struts. All vehicle designers aim to produce a vehicle body that is as stiff as possible, since having a stiff body shell as a basis allows dynamic handling and also helps to minimize vibrations and noise. Fiber composites, particularly those that include carbon fibers, are ideal for ensuring maximum stiffness with minimum weight. Until now high costs have prevented their widespread use in vehicles.

Mercedes-Benz’ innovation allows automatic, low-waste and therefore, cost-effective production of ultra-stiff and extremely light CFRP struts, making mass production possible. Mercedes-Benz received a MATERIALICA “Gold Awards” for this innovation in the category Material.

The core of this innovation is the combination of several components: carbon-fiber layers provide maximum stiffness and additional outer layers, applied at different angles ensure high pressure resistance. A third component, which was developed by Mercedes-Benz, are the innovative force elements which transfer all loads safely to the CFRP-struts.

The results are extremely lightweight struts that are up to 70 percent lighter than standard steel struts. The lighter weight also helps to reduce fuel consumption. The CO₂ break-even point (i.e. the distance the more fuel-efficient vehicle has to travel before the increased amount of CO₂ used to produce the carbon-fiber components is saved) is only approximately 50,000 kilometers (31,000 miles). Furthermore, this Mercedes-Benz innovation allows a production process for more than 300,000 vehicles per year.