Tribological Performance Within the Automotive Industry

The automotive industry is a fast moving and global market, valued at $1,653.7 billion in 2015.¹ Innovation in the automotive industry is mainly fueled by increasing concerns about energy efficiency, safety, and environmental impact.

Image credit: Shutterstock / AMatveev

Therefore, car manufacturers, research organizations, and part suppliers are routinely involved in extensive research and development, in the hope that new innovations will help them to stand out in an increasingly competitive market.

As a result of increasing environmental and safety concerns surrounding the automotive industry, there are increasingly rigorous standards for fuel efficiency, emissions, safety, and durability. In the US, the Environmental Protection Agency has set a standard for new cars to reach 36 miles per gallon by 2025.²

In order to increase fuel efficiency and decrease the amount of fuel required to power a vehicle, it is important to minimize energy losses from cars.  Approximately 62% of the energy lost in a vehicle is lost from the engine, so optimizing the performance of engines seems to be the ideal place to start when attempting to improve fuel efficiencies. One way to improve the energy efficiency of an engine is to improve its tribological performance.³

How tribology affects vehicle performance

Tribology is the study of interacting surfaces and describes the effects of friction, wear, and lubrication, factors that can all affect energy losses from an engine. The word tribology comes from Greek, meaning ‘the study of things that rub’.³

There are many tribological engine components including bearings, pistons, transmissions, clutches, and gears. Improvements to the tribological performance of engine components and additives can provide reduced fuel consumption, increased engine power outputs, reduced oil consumption, a reduction in exhaust emissions, improved durability, and reduced vehicle maintenance.

Improved tribological performance can be achieved in three ways: enhancing the tribological properties of the materials used for the mechanical parts; coating surfaces to improve tribological behavior; or developing lubricants that improve tribological behavior.⁴

Download the PDF brochure for more information about the UMT Tribolab benchtop analyzer from Bruker

Previously, testing the tribological properties of new materials or lubricants has involved building entire systems to run individual specialized tests, which is reliable but can be costly and time-consuming.

More recently, benchtop testing has provided a versatile and economical way to test the tribological properties of newly developed materials for automotive innovation. Standardized tribological tests are used to compare the performances of new parts, materials, and additives.

However, it is also important to be able to perform custom tests that may be requested by part manufacturers and may give further insight into the performance of the new materials.⁴

Figure 1. The UMT TriboLab (left) and four-ball set up (right) in which three balls are held in a ball cup mounted on a specimen table on a lower rotary module. The ball cup was filled with lubricant, and a fourth ball is held stationary on the upper carriage. Load is applied vertically downward through the upper ball.

Developing improved automotive lubricants

Lubricants are substances that form a protective fluid film between moving parts, preventing direct contact. To optimize the tribological performance of an engine, it is essential to achieve effective lubrication of all the moving and interacting parts of the engine.⁴ Traditional fluid lubricants are not able to meet the demands of new engine parts, and so there is significant on-going research in the area of automotive lubricant development. Automotive lubricants must pass rigorous standard tests. They must be able to withstand high temperatures, and be stable under engine conditions

Recently, the addition of nanoparticles to lubricating oils to create ‘nanolubricants’ has been a hot topic in the development of new automotive lubricants. Inorganic, metal, metal oxide, and carbon-based nanoparticles are added to lubricating oils to improve their anti-wear and friction reducing properties.

Metal oxide nanoparticles are particularly promising as they are relatively cheap, and their particle size and morphologies can be easily controlled. Adding solid nanoparticles to liquid lubricants can be particularly beneficial in reducing friction in mixed lubrication regimes, and appears to lead to improvements in load-carrying capacity.⁵

However, nanolubricants are often unstable due to the tendency of nanoparticles to ‘settle out’ of the lubricant liquid. Therefore, nanoparticles for nanolubricants are often functionalized to improve the stability of the resulting nanolubricant. Ongoing research is centered on the development of functionalized nanoparticles for the production of stable and effective nanolubricants.

A group of researchers from the Southern University of Science and Technology in China added varying amounts of Y₂O₃-stabilized ZrO₂ nanoparticles to KR7 and Mobil 1 automotive lubricating oils and used a UMT TriboLab (Figure 1) equipped with a four-ball setup to observe the effects of the nanoparticles on the tribological properties of the oils.⁶

The Y₂O₃-stabilized ZrO₂ nanoparticles were synthesized using surfactants to control their quality and size. The nanoparticles were effective in reducing the friction coefficients (Figure 2) and improved the anti-wear properties (Figure 3) of the commercial oils. Based on the tribological properties of the resulting lubricants, the optimal nanoparticle concentration was found to be 0.1-0.5 wt%.

The researchers utilized benchtop tribology assessments provided by the UMT TriboLab to quickly and cost-effectively test and optimize their new nanolubricant. Research into the relationship between the lubricating formulations and the nanoparticles is currently on-going.

Figure 2. Comparison of the friction coefficients for different Y₂O₃-stabilized ZrO₂ (3YSZ) nanoparticle concentrations in base mineral oil, KR7, and Mobil 1. The tests were performed using a Bruker UMT-2 equipped with a four-ball setup under a load of 80 N and a rotational speed of 400 rpm for 1 h.⁶

Figure 3. Average wear scar diameters (WSD) as a function of 3YSZ nanoparticle concentration in base mineral oil, KR7, and Mobil 1. The tests were performed sing a Bruker UMT-2 equipped with a four-ball setup under a load of 80 N and a rotational speed of 400 rpm for 1 h, followed by characterization with a microscope.⁶

The UMT TriboLab in the development of new automotive lubricants, coatings, and materials

Download the PDF brochure for more information about the UMT Tribolab benchtop analyzer from Bruker

The UMT TriboLab (Bruker, San Jose, CA) provides the ideal benchtop testing system for newly developed automotive materials, lubricants, coatings, and additives.

As the most versatile tribology test system ever designed, the UMT TriboLab has a broad range of capabilities due to its precision control of force (1mN to 2kN), torque (up to 5 N·m) speed (0.1 to 500 rpm), temperature (–30 to 1000°C), humidity (5 to 85%RH), and position.

The UMT Tribolab has interchangeable modules and can therefore perform multiple standardized and customized tests on a single platform. The UMT TriboLab provides a variety of tribological measurements and can measure the friction and wear of components such as clutch materials, brake materials, bearings, tires, piston rings, and cylinder liners.

Furthermore, the UMT TriboLab can also effectively evaluate and rank automotive lubricants. The UMT TriboLab has already to the test in automotive research and development activities including the development of new materials, lubricants, and other automotive additives.^5-11

In conclusion, innovation in the automotive industry on increasing the energy efficiency, safety, and durability of vehicles. As friction, wear, and lubrication major factors in engine energy losses and durability, the study of these properties in the field of tribology is a vital component of research and development in the automotive industry.

The UMT TriboLab from Bruker represents the ideal benchtop solution for testing the tribological properties of new materials, lubricants, and additives in automotive research.

Request more information about the UMT Tribolab

References

1. Automotive Manufacturing Industry to Reach 1.7 Trillion by 2015 - MarketResearch.com
2. EPA locks fuel economy standards through 2025 - Washington Times
3. Rapid Testing of Automotive Components at Very High Temperatures - Bruker Tribology Webinar, Feb 2017
4. Kapoor A, Tung SC, Schwartz SE, Priest M, Dwyer-Joyce RS,  “Automotive Tribology” in “Modern Tribology Handbook” CRC Press LLC, 2000.
5. Zin V, Barison S, Agresti F, Colla L, Pagura C, Fabrizo M, “Improved tribological and thermal properties of lubricants by graphene based nano-additives” RSC Advances, 6:59477, 2016.
6. Li D, Xie Y, Yong H, Sun D, “Surfactant-assisted preparation of Y₂O₃-stabilized ZrO₂ nanoparticles and their tribological performance in mineral and commercial lubricating oils” RSC Advances, 7:3727-3735 2017.
7. Understanding Engine Tribology: Performing Reciprocating Tests of a Piston Ring's Interaction with the Cylinder Liner - AZoMaterials
8. Poletti MG, Fiore G, Gili F, Mangherini D, Battezzati L, “Development of a new high entropy alloy for wear resistance: FeCoCrNiW_0.3 and FeCoCrNiW_0.3 + 5 at.% of C” Materials & Design 115:247-254, 2017.
9. Spadaro F, Rossi A, Lainé E, Woodward P, Spencer ND, “Rose of Boron in the Tribochemistry of Thermal Films Formed in the Presence of ZnDTP and Dispersant Additives” Tribology Letters 65:11, 2017.
10. Ivanov M, Shenderova O, “Nanodiamond-based nanolubricants for motor oils” Current Opinion in Solid State and Materials Science 21(1):17-24, 2017.
11. Hernández Battez A, Blanco D, Fernández-González A, Mallada MT, González R, Viesca JL, “Friction, wear and tribofilm formation with a [NTf2] anion-based ionic liquid as neat lubricant” Tribology International 103:73-86, 2016.

This information has been sourced, reviewed and adapted from materials provided by Bruker Nano Surfaces.

For more information on this source, please visit Bruker Nano Surfaces.