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Improving fuel efficiency is a major goal of the automotive industry. One approach is to lower an engine oils viscosity grade raising durability concerns and requiring engine re-design. Study [6] demonstrates that higher fuel efficiency is also achieved in the same SAE grade by increasing the Noack evaporation loss and using advanced viscosity index improvers like comb polymers. Increased Noack volatility might raise concerns of oil consumption. Evonik investigated this in a state-of-the- art engine using a test matrix including multiple Noack volatilities, SAE grades and base stocks. Additionally base oil viscosities and VII treat rate were investigated. All parameters showed no correlation with engine oil consumption. This allows to maximize fuel efficiency within the same SAE grade through optimized viscometric performance.

Durability remains a primary concern when formulating heavy-duty (HD) diesel engine oils, but in future there will be increased attention to fuel efficiency, particularly in Europe where the European Commission is proposing the first ever CO2 emission targets for heavy-duty vehicles. Although there are no internationally recognised fuel efficiency tests for HD diesel engines, there have been some regional and OEM developments pushing in the direction of improved fuel efficiency. In Japan the relatively new JASO DH-2F standard adds a fuel efficiency requirement, measuring fuel efficiency using the Hino N04C engine which is also used within the standard for other performance testing. In North America API have introduced the FA-4 performance standard to allow users to specify an xW-30 oil of lower HTHS150 to help achieve fuel efficiency, but with no accompanying test to quantify. In Europe ACEA are planning a HD fuel economy “F” classification which may be something like API FA-4.

In the recent years, the achievement of fuel economy through lower viscosity engine oil has been a topic of wide discussions among experts in the industry. Along this journey of engine oil evolution, new classes of Viscosity Index Improver (VIIs) have been developed in order to meet the challenges arising from either hardware re-engineering, environmental protection or both. In relation to this, the continuous tightening of the CO2 emission level from the authorities has made the situation even tougher for many OEMs and formulators worldwide. While the fuel economy performance in an engine has been intensively investigated, little has been published on the durability aspects of these VIIs nor other aspects such as cleanliness and piston deposits. In this paper, we will present no-harm test results for deposit formation comparing novel comb polymers and conventional hydrocarbon VIIs such as OCPs.

Fuel economy has become the dominant criterion in the design of new automobiles. The globally enacted targets for fleet average emissions pose true challenges to automobile manufacturers. Increasing fuel economy requires enhancements both in hardware as well as in lubricant performance. As a key component of the lubricant, poly(alkyl methacrylate) PAMA viscosity index improvers have been identified as crucial design element due to their multiple modes of action. In their original application, they serve the well-known mechanism of polymer coil expansion at high temperatures and collapse at low temperatures. They help to flatten the viscosity/temperature relationship of the lubricant and allow for reduced low temperature viscosities and reduced internal friction, which directly translates into fuel economy. In addition to this bulk application, interfacial tribological phenomena contribute significantly to efficiency and fuel economy.

Viscosity index improvers based on poly(alkyl methacrylates) as well as polyolefins have been well known to the industry as key additives to formulate lube oils for decades. Recent efforts to combine these two chemistries to prepare well-defined comb polymer architectures have led to a performance breakthrough. Specifically, the concept of temperature dependent comb polymer coil expansion and collapse allows to achieve extraordinary viscosity temperature properties. Viscosity indices and thickening efficiencies are well beyond the levels achievable by conventional chemistries at the same shear stability level. After a general introduction of viscometric key properties, the paper describes synthetic pathways towards these novel comb polymers. Standard radical polymerization of polyolefin macromonomers with alkyl methacrylate backbone comonomers is the most straightforward process for their preparation, and allows for an easy transfer to manufacturing.