Coating Can Be Key to
Lighter Vehicles


The Keronite process is an advanced plasma electrolytic oxidation (PEO) technology

Tomorrow’s energy efficient vehicles could still be based around internal combustion engines, thanks to coatings that allow smaller, lighter units, says Steve Montisci of UK-based Keronite.

The demise of the internal combustion engine has been greatly exaggerated. While battery electric vehicles, hybrids, plug in hybrids and fuel cell technology all offer exciting possibilities for the automotive sector, the reality is that internal combustion engines look set to be around for many years to come.

However, one of the strongest trends of recent years has been towards developing smaller, more powerful, turbocharged engines in relatively lightweight materials, such as aluminium. But this shift to smaller, lighter engines comes with greater pressure on the structural and mechanical components involved.

As far as the powertrain is concerned, engines and their components need to be strong enough to withstand the power and heat they produce. At the same time, manufacturers face tougher emissions regulations and consumer demand for more environmentally friendly vehicles – without compromising performance.

According to Montisci, his company’s globally commercialized Plasma Electrolytic Oxidation (PEO) treatment for light alloys is an enabling technology, producing a hard-wearing and corrosion-resistant ceramic coating to alloys based-on aluminium, magnesium and titanium.

“We’ve been working in conjunction with vehicle OEMs to develop technologies to improve performance and reliability of these smaller engines: improving wear resistance, thermal performance and the lubricity of the engine; enabling the development of smaller, more powerful, ‘cleaner’ power plants.”

Pistons are subjected to very high mechanical and thermal loads. Now surface coatings are seen as a way of modifying the thermal characteristics of the piston – particularly on the crown. Toyota has already patented its SiRPA coating (silica reinforced porous anodized aluminium) which is to be used on its range of GD engines. Increasingly, car manufacturers are looking at SiRPA-like coatings, with Keronite PEO being a possible alternative.

Other areas of the piston, such as the skirt and first piston ring groove, are also being considered for PEO as a wear-enhancer. It is also being investigated as a treatment for the cylinder bore, which would not only be wear-resistant, but could also act as a friction modifier due to its ability to hold an oil film.

Engine valve spring retainers are typically made from steel. Aluminium is 65% lighter but lacks the required mechanical properties for an engine environment in its basic form. Using a Keronite treatment provides wear resistance against the high-hardness steel springs, enabling the use of the lighter-weight retainers.

Changes to automotive emissions laws are leading to radical redesigns of exhaust recirculation and turbocharger systems. With compressor wheels being directly in the path of the recirculated exhaust gas, this causes increased blade corrosion, wear and fatigue. Keronite has developed a duplex coating that solves this problem, allowing manufacturers to extend the performance limits of lightweight aluminium compressor rotors.

With EU funding, Keronite has embarked on a research and innovation programme to develop a lightweight ceramic-coated aluminium brake disc utilising PEO technology. The aim is to produce a cost effective, lightweight, wear-resistant, highly temperature-resistant, recyclable alternative to traditional cast iron brake discs. Another benefit of PEO is that it generates negligible dust due to its very low wear rate – which is of interest as it has been shown that cast iron discs generate potentially harmful iron oxide particulates.
Using the Keronite process to improve a variety of parameters means that more powertrain and drivetrain components can now be produced from alloys that weren’t previously suitable, enabling real weight (and therefore fuel efficiency) savings. Until battery technology advances significantly and their weight, size, cost, and endurance issues have been resolved, the automotive combustion engine is going to be around for a good while yet.

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