Apr 25, 2019
Posted by Keith Howard, Strategic Technology Manager, Ping Zhu, Director of Technology, Asia
In previous articles, we touched on how high performance lubricants are essential enablers of low emission, fuel efficient vehicles in China. In this, the final article of the series, we will take a look under the skin to see how they do this in a little more detail.
High performance lubricants help reduce emissions in three key ways:
- They keep the hardware in good operating condition.
- They are compatible with exhaust aftertreatment systems, enabling emissions reduction to continue effectively throughout the life of the vehicle.
- They reduce friction and so reduce fuel consumption, which in turn reduces emissions and supports compliance with China’s strict fuel consumption regulations.
Hardware ProtectionProtection of hardware has always been at the heart of the lubricant’s role. The engine must be kept clean under challenging conditions, requiring highly effective detergents, dispersants and anti-oxidants. These work across a range of temperatures in key areas such as piston ring grooves, the valve deck area and the oil pump. Wear of the valve train, cylinders and bearings will produce a deterioration in performance, fuel consumption and emissions. Effective anti-wear chemistry and performance polymers are therefore essential.
The driveline has a different balance of requirements. While contamination from combustion gases is not an issue, driveline lubricants must provide wear protection for gears and bearings, prevent corrosion and oxidation, manage proper friction for smooth gear shifts and enable the best system performance and efficiency possible throughout the life of the vehicle. When it comes to axles where a hypoid gear is used, lubricants must also provide extreme pressure protection. Friction control is an essential performance requirement for transmissions. Each transmission type—e.g. stepped AT, dual clutch, CVT or manual transmission—requires a specific fluid designed to provide acceptable operation. Matching lubricants with hardware is critical in the safe and efficient operation of the vehicles.
China 6 brings a step change in exhaust aftertreatment requirements, and therefore a step change in the engine oil compatibility challenge. The use of particulate filters will be almost universal amongst China’s passenger cars and commercial vehicles; these need lower ash oils to prevent long-term filter blockage and resulting performance deterioration. Catalyst coatings are widely used to reduce pollutants directly, and to promote filter regeneration (burn-off of accumulated soot); these catalysts can be affected by lubricant chemistry, so a different approach to formulating is required. The foundations for solutions have been established previously, notably in Europe where particulate filters have been widely used for over a decade, though aftertreatment compatible engine oils for China may have added requirements.
Viscosity Trends and Friction Modifiers
Great strides in efficiencies of both engine and driveline have been made over recent years. This is reflected in lubricant efficiency improvements. Lubricant viscosities are steadily trending lower to reduce churning loss because it takes less energy to move a thinner fluid. However, reducing viscosity typically means a thinner fluid film. The performance additive of a lubricant plays an even larger role in hardware protection to compensate for the thinner fluid film. Below we use automotive gear oil as an example.
Group I mineral oil-based SAE 80W90 and SAE 85W140 fluids have been the choice to lubricate axles for decades. They offer a low initial cost, but are susceptible to oxidation and oil thickening which means more frequent oil changes, leading to increased maintenance time and waste oil disposal. They also thicken substantially at lower temperatures, which hurts efficiency.
Group III or PAO-based SAE 75W140, SAE 75W90 and SAE 75W85 axle fluids offer improved oxidation stability, cleanliness and hardware protection, longer life and oil drain interval. These wide-span multi-grade gear oils, when formulated with shear stable viscosity modifiers, maintain a more consistent viscosity across a wide temperature range, and are recognized as a contributor to overall fuel economy.
In North America, when run under real-world line-haul conditions, the use of SAE 75W90 can improve the efficiency of a Class 8 vehicle (with gross vehicle weight greater than 33000 lb. or 14969 kg) axle by an average of 0.5% over an axle using SAE 80W90. This is significant considering that axles themselves are 95% efficient. Similar benefits have been observed in China. In a Chinese light duty commercial vehicle axle test using local OEM defined drive cycles, a 0.49% efficiency gain was achieved with SAE 75W90 axle fluid over a SAE 85W90 fluid. The improvement can be more pronounced in transmissions. For example, in Chinese light-duty commercial vehicle manual transmission tests, a SAE 75W85 manual transmission fluid delivered 0.7% and 1.8% efficiency gains over SAE 75W90 and SAE 85W90 fluids respectively.
Friction modifiers provide further efficiency improvements. There are many friction modifier chemistries available. Their general effect is to produce microscopic layers on the surface of moving parts, helping to keep them apart and moving smoothly over one another, especially under boundary conditions. This provides a positive contribution to fuel efficiency.
Hardware Diversity and Electrification
A wide variety of hardware has been introduced to improve emissions and efficiency. Engines have many types of fuel injection equipment, turbocharging and new materials. Drivelines may include manual transmissions (increasingly with dual clutch systems), conventional stepped automatic (with up to 10 speeds) or continuously variable transmissions. Diversification of hardware leads to more individual OEM specifications, adding another dimension to the lubrication challenge: in a complex and fragmented fluid market, a “one size fits all” approach is becoming less and less suitable.
Electrified drivetrains are a key contributor to efficiency improvements, but they create new challenges for lubricating fluids, especially when the electric motor is incorporated within the housing and comes into contact with the lubricant. For example, a high-speed e-motor confined in the transmission housing provides an extra source of heat and causes frequent excursions to high temperatures and localized hot spots. The lubricant must effectively transfer heat away to keep the transmission cool, and have good thermal durability to maintain its integrity during the temperature excursions. In addition, an increasing diversity of electrical components, plastic wire insulation and polymeric materials are used. Fluid properties such as electrical conductivity, compatibility with existing and new polymeric materials and optimization of corrosion protection against yellow metals need to be carefully evaluated. In many cases existing conventional lubricants are simply not optimized for the electrified driveline hardware, which may hold back the full potential of the electrified vehicles.
China 6 and the associated fuel consumption standards pose a real challenge for the whole power train from the engine through the driveline to the wheels. In turn, this drives the need for new lubricant solutions. We believe that technology that covers the full spectrum of China 6 hardware is an essential enabler of long-term, low emission, high efficiency vehicle performance. We are proud to be playing our part in making China 6 successful, helping achieve clean air in China and ultimately to improving the lives of China’s citizens.
If you would like additional information on China 6, please visit the China 6 section, or contact your Lubrizol representative: