Hybridization and the Ghost of Aunt Minnie

Hybridization and the Ghost of Aunt Minnie

May 29, 2019
Posted by Craig Paterson, Vice President, Product Management

There’s a decent chance you’ve heard of the phenomenon of the “little old lady” car. Maybe it belonged to a grandma or a great aunt. Maybe it’s 10 years old, but since she doesn’t drive very often or far, it only has 8,000 miles (12,800 kilometers) on it.

Theoretically, it should still be in great shape. Right?

Not necessarily. A few decades ago, with older engine and lubricant technology, this was a bigger issue, and it prompted what became colloquially known as the “Aunt Minnie” test to evaluate the effects of infrequent driving on engine oil. The concern was this: If an engine is only driven for short, infrequent trips, it might never get up to full temperature. Water is generated during combustion, but operating conditions never get up to full temperature for that water to evaporate. Thus, rust in the engine becomes a significant cause for concern, and higher-performing engine oil could help prevent it.

As engine and drivetrain technology became more robust, though, rusting became less of an issue. And today, engine and drivetrain technology is evolving faster than ever before, with a broad diversity of new technologies being explored by different automakers around the globe. And increasingly, we’re seeing electrification strategies being more aggressively pursued by most of the well-known car manufacturers in the world.

What does any of this have to do with Aunt Minnie? The most common electrification architecture adopted by the industry is powertrain hybridization, where some combination of battery power and traditional engine technology work together to provide significantly improved efficiency and fuel economy. In plug-in hybrids (PHEVs), specifically, an electric motor (or e-Motor) will be the power source of the vehicle up to a certain range—let’s say 40 miles (65 kilometers). If the driver is traveling for a longer distance than 40 miles (65 kilometers)—let’s say 50 miles (80 kilometers)—the internal combustion engine (ICE) will kick in to complete the remainder of the journey. For that final 10 miles (16 kilometers), the ICE may not reach its normal operating temperature, which can potentially lead to unevaporated water droplets and oil dilution from fuel. Sound familiar?

While historical forms of rust may no longer be the primary concern in PHEV, unevaporated water can end up in the oil sump, leading to performance issues including acid induced corrosion. Fuel dilution of the oil leads to a reduction in the viscosity of the oil, which in turn can lead to other issues in the engine. Meanwhile, range-extender hybrid technology (REEV) operates differently, with the ICE’s sole purpose being to recharge the battery. Here, the ICE (often small displacement, comparable to a motorcycle engine) works very hard, very rapidly, and at a high temperature to complete that recharge, which leads to higher stress on the engine oil.

All the more reason that the lubricant industry needs to continue thinking critically about electrification, hybridization and increasingly stringent demands on lubricants throughout the e-powertrain. There is a lot of interesting work currently being undertaken to study and further understand how increased electrification will impact engine lubricants and driveline fluids. Through internal research and collaboration with OEMs and its Tier 1 partners, Lubrizol is continually investigating how increased electrification will impact tomorrow’s engine oils and driveline fluids.

And like the development of the “Aunt Minnie” test, the methods we use to test and certify lubricants for use in future vehicles will continue to evolve.

Our view

The path forward for the lubricants industry is twofold: Firstly, we must continue to be proactive in the development of new technologies and lubricant formulations that can help ensure a wide variety of new engine technology can operate reliably over the long term; secondly, we must also ensure we’re able to get those lubricants to market quickly.

Vehicle electrification in its various guises is here to stay, it will certainly develop further. The additives and lubricants must become part of the design criteria for new OEM technologies in order to optimize their efficiency and minimize the risk of issues in the field. We need to be ready to meet the changing needs of tomorrow.

For more information on electrification, contact your Lubrizol representative.

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