Not so long ago, engine oil was pretty much a standard product, to which most of us seldom gave much thought. But nowadays, with alternative powertrains, it is being brought increasingly to the consumer’s attention. Matthew Beecham caught up with Nevil Hall of Millers Oils to understand more about the important issues.
Could you tell us more about the ways you are developing lubricants for different drivetrains?
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Electric and hybrid powertrains bring new challenges through increased torque loads, tighter package constraints and intermittent operation. Oils with higher film strength are required, to provide greater protection for loaded metal surfaces which would otherwise be forced into contact. At these very high loads, it’s more about surface chemistry than conventional lubrication. When a fully laden EV, such as a delivery van, pulls away from a standstill, the maximum motor torque is available from zero rpm and is carried by a single pair of meshing teeth at the final drive. The contact stresses won’t break the teeth, but without a suitably formulated oil they will lead to micro-pitting and eventually, cracking. Developments like nanotechnology are allowing oils to be created that create a hard surface layer on both metal surfaces, protecting them under more extreme loads.
Are special lubricants used for cars with stop-start engines?
There’s a potential issue with temperature fluctuation in stop-start operation. Most people are aware of the effect of oil viscosity, in that efficiency is reduced at lower temperatures because the oil is thicker, but few realise that film strength is also affected by temperature. We have seen some alarming shortfalls in film strength at certain temperatures when benchmarking competitor oils. Many oil additives only react chemically from around 70 degrees C upwards, so they don’t offer the same protection when cold. To formulate oils suitable for engines with stop-start, we have developed additive packages that ensure consistent film strength across a wide temperature range.
Could you tell us more about how you evolved your Nanodrive oil to include a range of engine applications?
Our first Nanodrive oils were for transmission applications with high levels of rolling contact. Engine applications involve much more sliding contact so our priority was to provide maximum protection with minimum friction under these conditions. By careful formulation, incorporating nanoparticles alongside conventional additives, we achieved consistently robust oil films over a wide range of surface temperatures and pressures. This is always a challenge because each additive is only chemically active over a given temperature range. Nanoparticles also contribute to lower friction by helping metal surfaces to pass over each other more easily, enabling the use of thinner oil without risking metal-to-metal contact.
What are the driving factors in lubricant development?
The demand for improved fuel economy is driving the development of thinner oils. The industry wants to reduce losses by cutting friction, but without any reduction in durability. We have become accustomed to 5w30 grade oils and now there is a 0w16 specification for some 2013 Honda engines. Even though oils become gradually thicker in use, the benefits of a thinner oil will remain throughout the service life. Nanoparticles are a key enabler for such thin oil grades, preventing engine wear by keeping metal surfaces apart.
I guess a significantly down-sized engine requires a special lubrication?
Downsizing strategies present a range of challenges for lubricating oil, as a result of the increased thermal and mechanical loads. Engines with fewer cylinders typically also have smaller oil pans that hold less oil, yet longer drain intervals are required by the market. Even the shift from port injection to direct injection on a petrol engine can cause a 30 percent increase in bearing load. When you add the effect of turbo- or supercharging, cylinder pressures can double, with higher torque across a wider rev range.
Deactivation of several cylinders at times of light load operation is a form of ‘virtual’ downsizing for large multi-cylinder engines, but it has consequences for the engine oil. Normally the oil film on the bore in a firing cylinder is 0.5 to 1.0 microns thick, but in a motored cylinder it increases to as much as 30 microns and is expelled in a single firing event once the cylinder is re-activated. In order to avoid poisoning the catalyst, oil with a low sulphur, ash and phosphorous content – low SAP – must be specified.
As we understand it, you have been working with a couple of F1 teams and managed to reduce heat generation. Could you tell us how you achieved that and the benefits?
The remainder of this interview is available on just-auto’s QUBE research service
