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1.3.5 Application: Internal Combustion Engine and Powertrain

1.3.5.1    Short application description

The powertrain refers to the group of components that generate power and deliver it to the road surface.
The main elements of the powertrain are drive wheels, transfer case, driveshaft, differential, transmission, clutch, crankshaft (also called crank), flywheel, torsion damper and engine. In the internal combustion engine (ICE) (four-stroke engine), the key parts include the crankshaft, connecting rod, one or more camshafts and valves. All of these parts are assembled in the engine block.
Hybrid and electric powertrains are gaining more and more importance for the automotive industry, due to the environmental and competitiveness issues mentioned in the previous chapter. However, it is foreseen that IC Engines will be still leading in the next decades. According to PWC Automotive Institute, in 2014 a total of 770 million automobile engines will be produced, of which around 74% engines will be combustion gasoline, 24% combustion diesel and only 2% hybrid gasoline.
"Despite new hybrid and full electric powertrains being developed, many carmakers expect the combustion engine to remain the dominant powertrain concept over the next decades" Dr. Klaus Draeger BMW.

Materials used in the engines and powertrains
According to PWC, for an average upper medium car, the powertrain (including the engine) accounts for about one third of the vehicle weight. The greatest part is the engine, whose weight can vary from 70 to 180 kg.
Of all engine's components, the engine block is the heaviest one weighting more than 20 kg.
Therefore, an important trend in the engines and powertrains is weight reduction, and accordingly heavy metals, like the cast iron used in the engine blocks (density: 7.9g/cm3) have been widely replaced by lighter materials. For instance, switching from a cast iron engine block to a magnesium alloy version can save 13kilograms, a 40% weight reduction.

 
Figure 9 shows how aluminium has replaced cast iron in the production of cylinder heads.
 Figure 9: Production of cylinder heads in Europe
Source: Hydro Aluminium

On the other hand, every replacement normally implies some problems and changes and the appropriate balance always has to be found. For instance, replacing cast iron blocks in the engine by aluminium faces some problems due to the fact that engine lubricants' formulations have been tailored to cast iron properties. The current aluminium surface or coatings are not compatible with engine oil formulation. To overcome this, the aluminium bores require cast iron sleeves inside.
A material that has not been widely used much in powertrains and engines even though its proved thermal qualities are ceramics. Till now, the inherent brittleness of ceramics kept them out of the market for large parts, (e.g. engine blocks) and were used for smaller components (e.g. valve parts and bearings). The main reason is the tendency to form micro-cracks during manufacture, which results in high rates of product rejection and consequently higher production costs.
Related to the materials used in the powertrains, it has to be taken into account that the trend in modern engine design is downsizing, i.e. making the components smaller. The effect of the materials is that as smaller sizes of the components often lead to higher load and stresses on the component itself. The risk of component failure increases.

 
Friction in the engine and powertrains
Reducing friction and wear in engine and drive train components is a vital issue for automotive manufactures, and it is estimated that could save the US economy as much as US $120 billion per year.
As shown inFigure 10, only about 13% of the energy available in the fuel is available to drive the wheels. The losses are mainly due to engine inefficiencies and mechanical losses in the driveline.
 
Figure 10: Energy losses along a powertrain

There are technologies, mainly coatings, which can reduce the friction and therefore the energy losses. One example would be carbide-based wear-resistance coatings for cylinder walls, pistons, bearings and other engine components (crankshaft, valve train, etc.).
The applicability of these specific coating in these complicated parts bears sometimes manufacturability problems. For example, in the pistons, it has to be taken into account that their different rings need different types of coating: while the top compression ring usually has a wear resistance coating such as flame-sprayed molybdenum, the second compression ring is not normally coated and the bottom ring used to have a chromium plating, to improve the oil retention. Another example in the powertrain is cylinder bores: most of them have inner radius of 70-110 mm and such dimensions call for special tooling for applying the coating.
 
1.3.5.2    Nanotechnology impact in the IC engine and powertrain

Nanotechnology improvements in metals and composites could contribute to reduce the powertrain weight and therefore to reduce the energy consumption of the vehicle. Nanocomposites, mainly metal matrix composites or polymer nanocomposites, could replace steel parts, offering an important weight reduction potential. Nanostructured metals, controlling the material in a nano-scale can provide customised characteristics in the different parts of the components. As an example of research, nanostructured Al casting alloys are being researched by Ford and the Northwestern University in collaboration to develop stronger and better performing parts.
Tribological nanocoatings can be applied in automotive powertrains to improve their mechanical efficiency, like advanced PVD and CVD coating. Novel hard and / or low friction coatings made of nanocomposites with SiC, SiO2, TiO2, BN3, C, diamond, even Teflon with matrix material such as Ni, Al, Fe and alloys offer an improved mechanical stability, which mean less wear, better gliding, thinner coating and less lubricant, longer service interval and reduced fuel consumption. The wider application of tribological nano-coatings could reduce significantly the energy losses in the engine and the driveline.
To complement all the above-mentioned, nano-enabled lubrication can improve the efficiency and reduce the maintenance in powertrains. As well, nanoceramic materials offer an opportunity to rethink the internal structure of the internal combustion engine and its component coatings.

1.3.5.3    Functional requirements
Corrosion resistance is a vital issue for engines and powertrains.

A critical part is the cylinder: In addition to wear (due to mechanical interactions), corrosive wear may occur in the upper part of the cylinder region during short-trip service in a winter climate.
As well, pars that are inside or close to the engine have to be heat resistant. The materials have to be thermally stable and also able to dissipate the heat.
Failure in the engine or in the powertrain can imply high risks for the passengers. Therefore, their parts have to comply with stringent reliability and durability standards.
Besides, the engine and powertrain parts have to be accurate enough in their functioning to produce the minimum vibrations (and noise) possible and some parts also have to absorb them.
Last but not least, as parts of the vehicle, the powertrain parts also have to be assessed regarding their life cycle and have to comply with all the relevant recycling standards.
 
1.3.5.4    Product examples

• NanoLub^TM (ApNano Materials Inc): Solid lubricants with nano-spheres of inorganic compounds have been developed by the company ApNano Materials Inc (Israel) together with Volkswagen Group. These solid lubricants would avoid the oil changes.
• Carbon NanoSphere Chain^TM (CleanTechnology International Corp): Nanocarbon material that can be used for composite applications in automotive industry and as additive to the fuel for improving lubricity.
• Catalytic converter (Nissan Motors): Nissan Motors has introduced a catalytic converter for gasoline engines that uses only half the catalyst as conventional catalysts. It has been developed as part of a joint collaboration between Renault and Nissan. Using nanotechnology, Nissan has succeeded in keeping the particles separated under high temperature. With the clustering reduced, the amount of catalyst required is also reduced. This is achieved with no degradation of performance in cleaning up the exhaust. In turn this will reduce the cost to the auto manufacturer and the consumer.
• Toyota timing belt cover (Toyota): Nylon timing belt of nylon-nanoclay composite. Its main characteristics are its toughness and heat resistance.

1.3.5.5    Some key companies
Engine & powertrain suppliers

• Robert-Bosch GmbH
• Magna International
• Electrovac
• Aveka Group
• GE Plastics
• Synkera
• Emil Bröll GmbH
• ZF Friedrichshafen AG

Adhesives, rubber and lubricants

• Fuchs Petrolub
• ARC Seibersdorf research GmbH
• ApNano Materials Inc.
• Hatco Corp.
• IAVF Antriebstechnik AG
• Trelleborg