Making Cars More Fuel Efficient with Tribological Measurements

Car parts that rub against each other and create friction cause great energy losses. Therefore, novel materials for car components and lubricants with improved frictional (or tribological) properties are developed all the time. Benchtop mechanical testing technology has advanced to the point where a variety of customized tribological measurements can be performed by a single instrument, which is ideal for the fast-moving automotive industry.

Image credit: Shutterstock / Vixit

To make cars more environmentally friendly, safe and durable, governments frequently release new rules and standards for car manufacturers. As a result, the entire automotive industry must quickly adapt and create new innovations. A challenge that many car manufacturers face at the moment is to improve the fuel efficiency of cars [1].

The greatest improvement in fuel efficiency can be made by minimizing energy losses in the car engine. In particular, energy can be lost when bearings, pistons, transmissions, clutches and gears rub against each other, and create friction. The study of friction between surfaces is called tribology. Of Greek origin, the word literally translates to “the study of things that rub” [2]. After certain periods of friction, the surface layers of the parts can wear off.

How to reduce friction

Three different strategies are usually employed to avoid friction between two engine parts: they can be lubricated, the surfaces of the components can be coated, or parts can be designed with better tribological characteristics from the start. But how can car manufacturers measure the characteristics of the components or lubricants?

Traditionally, manufacturers have had to design and build individual, highly specific test systems that measured the materials’ properties for each type of engine. This, however, is time-consuming, expensive, and makes it hard to compare the results from different test systems [3].

More recently, a lot of work has been done to use benchtop systems for standardised tribological tests of new parts. A benchtop system is comparably small, and fits on top of a laboratory work surface, which provides a more economic and versatile solution than the previously used large, very individualised systems. Most current benchtop systems, however, do come with a disadvantage of not being able to perform customised and more complex tests [4].

New customisable and versatile benchtop testing

The design of benchtop testers have advanced tremendously in the last decade. For example, the versatile UMT TriboLab from Bruker precisely controls many different parameters, such as the force, torque, speed, temperature and humidity. The system’s modules can be quickly interchanged, which enables users to perform an extremely wide variety of tests on a single system. With such a system, one can measure friction and wear of many automotive components, and also test the performance of lubricants.

The UMT TriboLab already features a history of diverse applications in the research and development of new engine materials, lubricants and other automotive additives [5-10]. One example is the development of nanoparticle-based lubricants for engine parts by researchers in the Southern University of Science and Technology in China (SUSTC) [5].

UMT TriboLab from Bruker

Nanoparticles make lubricants more temperature-resistant

Through a protective fluid film between the surfaces, lubricants prevent moving parts from touching each other and causing wear-off. With the ongoing innovations of engine parts, manufacturers are required to develop matching lubricants. The high demands on lubricants make that difficult. For example, they are required to withstand high temperatures and to be stable under engine conditions.

A promising trend in the world of automotive lubricants are nanolubricants, which are liquid lubricants with added solid carbon-based, metal, metal oxide or other inorganic nanoparticles. Researchers have observed that they can reduce friction better than traditional lubricants and that they can also increase the maximum load on a machine [6].

Optimising nanolubricants

One problem with nanolubricants, however, is that they often are unstable. Instead of being homogenously distributed, the solid particles can separate from the liquid of the lubricant. To counteract this, Associate Professor Dazhi Sun and his co-workers from SUSTC have stabilised one kind of metal oxide nanoparticles composed of zirconium dioxide (ZrO2) with another kind of metal oxide particles called yttrium oxide (Y2O3), and mixed the resulting functionalised nanoparticles into commercial lubricants.

To find the optimal amount of functionalised nanoparticles in the lubricants, the researchers tested the tribological properties of the novel lubricant mixtures using the UMT TriboLab. With a customised setup, they concluded that friction was most reduced and anti-wear properties were best improved when the particles were used in concentrations between 0.1 and 0.5% by weight.

Conclusions

In this example, benchtop testing made it possible for the Chinese research team to quickly and cost-effectively examine and optimise their novel nanolubricants. This and other studies help manufacturers decrease the friction and wear of car parts, which in turn leads to a higher fuel efficiency of cars. This allows for compliance with ever more stringent standards, and makes cars more environmentally friendly.

Request more information about the UMT TriboLab from Bruker

References

  1. EPA locks fuel economy standards through 2025 – Washington Times
  2. Rapid Testing of Automotive Components at Very High Temperatures – Bruker Tribology Webinar, Feb 2017
  3. Understanding Engine Tribology: Performing Reciprocating Tests of a Piston Ring’s Interaction with the Cylinder Liner
  4. “Automotive Tribology” in “Modern Tribology Handbook”, Kapoor A, Tung SC, Schwartz SE, Priest M, Dwyer-Joyce RS, CRC Press LLC, 2000
  5. “Surfactant-assisted preparation of Y2O3-stabilized ZrO2 nanoparticles and their tribological performance in mineral and commercial lubricating oils”, Li D, Xie Y, Yong H, Sun D, RSC Advances, 2017, DOI:10.1039/C6RA26346A
  6. “Improved tribological and thermal properties of lubricants by graphene based nano-additives”, Zin V, Barison S, Agresti F, Colla L, Pagura C, Fabrizo M, RSC Advances, 2016, DOI:10.1039/C6RA12029F
  7. “Development of a new high entropy alloy for wear resistance: FeCoCrNiW0.3 and FeCoCrNiW0.3 + 5 at.% of C”, Poletti MG, Fiore G, Gili F, Mangherini D, Battezzati L, Materials & Design, 2017, DOI:10.1002/adem.200700240
  8. “Rose of Boron in the Tribochemistry of Thermal Films Formed in the Presence of ZnDTP and Dispersant Additives”,Spadaro F, Rossi A, Lainé E, Woodward P, Spencer ND, Tribology Letters, 2017, DOI:10.1007/s11249-016-0795-3
  9. “Nanodiamond-based nanolubricants for motor oils”, Ivanov M, Shenderova O, Current Opinion in Solid State and Materials Science, 2017, DOI:j.cossms.2016.07.003
  10. “Friction, wear and tribofilm formation with a [NTf2] anion-based ionic liquid as neat lubricant”, Hernández Battez A, Blanco D, Fernández-González A, Mallada MT, González R, Viesca JL, Tribology International, 2016, DOI:j.triboint.2016.06.038

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