When evaluating the efficiency of a vehicle, drivers are paying closer attention to fuel consumption now. For a number of reasons, CO2 emissions are becoming more and more important as a factor, since they also form the basis for emission limits and subsidy programmes. As a result, the automotive industry is focusing on weight reduction measures and downsizing. Today, the efficiency of a motor vehicle can be increased in various ways.
The quality of the cylinder surfaces, for example, has a major influence on the consumption of combustion engines. After all, surface hardness, roughness and texture are not only the determining factors for fuel consumption but also the performance characteristics of the engine. Up to 25 percent of fuel energy in the part-load operational range is required to overcome the engine's internal friction.
To reduce frictional losses on cylinder surfaces, Daimler AG developed an innovative thermal spraying technology that received several national and international awards, enabling the coating of cylinder bores of aluminium lightweight crank-cases for car engines using twin-arc spraying. To generate the NANOSLIDE® surface, the molten material is sprayed onto the cylinder wall by means of a gas flow and deposited as a layered, ultrafine to nano-crystalline coating. Subsequently, the NANOSLIDE® coating is smoothed to an extremely high degree in a specially developed mirror honing process, which gives a thickness of only 0.1 to 0.15 millimetres and a surface that is almost like a mirror. The honing process also exposes pores in the material, which are able to retain oil and help optimise lubrication of the piston assembly. All in all, the process enables to reduce mechanical friction loss by up to 50 percent whilst providing extremely high wear resistance.
Although the coating process is considered extremely cost-effective and technologically superior, quality-determining parameters such as current, voltage, wire feed and process gas flow need to be carefully adjusted and matched to the coating procedure.
Working together on the industrialisation of the process
In 2012, Gebr. Heller Maschinenfabrik GmbH in Nürtingen and Daimler AG established a successful cooperation for the further industrialisation of the process. The goal for HELLER was to industrialise all steps of the process and to develop it into a dependable application for the global markets under the name of HELLER CBC (CylinderBoreCoating) based on a global network of systems and services for the complete process chain of crankcase manufacturing.
In the same year, HELLER gave the go-ahead with the official opening of the HELLER CBC TechnologyCenter at the company's headquarters in Nürtingen during the Automotive Dialog 2012 and started with the coating of customer-specific prototypes. Initially, the process was used for exclusive small-batch series. With the entry into mid-sized batch production, a viable alternative to existing liner technology was born. The production rules and criteria for the automotive industry had been fulfilled and thus the preconditions for high-volume production.
To implement this next step, market-oriented solutions in terms of system supply and services were required. In 2013, Mercedes-Benz introduced NANOSLIDE® to the US market for the turbocharged V6 spark-ignition engines in the context of the BlueEFFICIENCY technologies. NANOSLIDE® helps to reduce engine weight by several kilogrammes and reduces fuel consumption by up to three percent by eliminating the need for thick grey cast iron liners used in the predecessor engine.
Meanwhile the technology is also used for the latest generation of 4-cylinder and 8-cylinder engines of Mercedes-AMG. In 2013, HELLER commissioned enhanced manufacturing systems and integrated the process, including the process steps for pre- and finish-machining, into the process chain of engine production, whilst ensuring the necessary high degree of process quality and dependability.
Awards in the most important categories
In 2013, HELLER and Daimler received the German Innovation Award for Climate and Environment in the category “Process Innovations for Climate Protection”. In 2014, NANOSLIDE® received an award from US trade journal R&D Magazine, the so-called Oscar of Invention, naming it one of the most important high-tech products. Today, the two partners see this as another award for a technology that has also had a share in winning the first F1 Constructor's Championship and the Drivers' Championship in 2014. NANOSLIDE® also realises its full potential in the V6 turbo engine of the current world champion's car, the Mercedes-Benz PU 106A Hybrid.
The NANOSLIDE® process
By means of twin-wire arc spraying technology the cylinder surfaces in the aluminium crankcases are coated with an extremely thin layer based on an iron-carbon alloy. The result is a very wear-resistant nano to ultrafine material structure with micropores, ensuring lubrication during operation. As a result, heavy grey cast iron liners in the aluminium crankcases that can be several millimetres thick are eliminated. The result is a surface as smooth as glass, providing up to 50 percent less friction between piston, piston rings and cylinder surface and a weight reduction of several kilogrammes. Meanwhile, the process incorporates numerous inventions and ideas and is protected by more than 90 patent families and more than 40 patents.
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