Powertrain

Tribology has been an essential part of the development of improved powertrains for decades and, even with a growing shift to electrical vehicles, this continues to be the case today.

The powertrain of a vehicle encompasses every component that is involved in the conversion of power to movement. This is true for any sort of vehicle, from boats to planes and cars to bikes, although each of these will have very different requirements placed on powertrain components. One thing all will have in common though, is that they will consist of many moving parts that are in contact with other components. It is in these contacts, found throughout any powertrain, that tribological research has been focussed to continually improve and optimise designs.

PCS’ range of instruments are used extensively by industry and academia to achieve this continual improvement. The MTM and ETM are key tools used for this work. Both have independently driven specimens which enable a wide range of contact conditions to be replicated and together cover an impressive range of contact pressures from close to 0 to 3.5 GPa with standard specimens, and even more with non-standard specimens. This versatility means that researchers can use these instruments to investigate all the different contacts you would find in a whole host of powertrain applications, investigating wear, friction and film build up. The EHD is also extensively used in this area for investigating film thicknesses and traction coefficients of lubricants found in the systems; and the MPR is used to investigate how parts and lubricants will stand up to prolonged use over the years.

As an area of significant power wastage in vehicles, powertrains have always been of interest to tribologists. This interest is only going to continue to increase because the frictional losses in the powertrains of electric vehicles are a larger portion of total losses than in internal combustion engines. As such, powertrain research and the developments tribology can bring are only going to become more important in the future.

Powertrain research areas include:

  • CV Joints
  • Gearboxes
  • Marine specific lubricants
  • Engine systems
  • Wind turbines
  • Bearings and gears

Powertrain Industry includes the following:

Agriculture

Agriculture

The powertrains in agricultural vehicles must regularly deal with high-stress forces, and be very reliable to prevent down-time. One way this reliability is improved is through the optimisation of tribological contacts.

Automotive

Automotive

Automotive powertrains are an area ripe for continual improvement through tribological study, and this study is important now more than ever as the industry adapts to more complicated systems incorporating electric power.

Aviation

Aviation

With reliability forming the cornerstone of the aviation industry, knowing how components in your powertrain will wear and fail is fundamentally important for knowing when they need to be inspected and replaced.

Machinery

Machinery

The requirements on powertrains in machinery are as varied as the jobs performed by the machines. Every one of them will need lubricating, and choosing the right lubricant comes down to knowing the tribology of the contacts involved.

Marine

Marine

Marine powertrains can be large or small, and some have to deal with as much as 80MW of power and 7.6MNm of torque. These conditions mean lubrication and part protection are critical to the longevity of an engine.

Mining

Mining

Facing constant high loads, harsh and dirty environments, and huge costs associated with downtime, the powertrains in mining vehicles have to be reliable even in the most adverse conditions. Tribological studies helps ensure this is the case.

Trains

Trains

Trains often now work by using a diesel engine to generate power, which is then converted to electrical power, which run the motors to drive the train. These myriad components and processes are designed with tribology and lubrication in mind.

Wind Turbines

Wind Turbines

Wind power remains one of the most rapidly growing renewable power sources, so the tribological problems found in the powertrain - from the blades to the generator - are the focus of significant research.

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Powertrain Industry Articles & Papers

Paper

In-situ Observations of the Effect of the ZDDP Tribofilm Growth on Micropitting

The ongoing trend for using ever lower viscosities of lubricating oils, with the aim of improving the efficiency of mechanical …

The ongoing trend for using ever lower viscosities of lubricating oils, with the aim of improving the efficiency of mechanical systems, means that machine components are required to operate for longer periods under thin film, mixed lubrication conditions where the risk of surface damage is increased. For this reason, the role of zinc dialkyldithiophosphate (ZDDP) antiwear lubricant additive has become increasingly important in order to provide adequate surface protection. It is known that due to its exceptional effectiveness in reducing surface wear, ZDDP may promote micropitting by preventing adequate running-in of the contacting surfaces. However, the relationship between ZDDP tribofilm growth rate and the evolution of micropitting has not been directly demonstrated. To address this, we report the development of a novel technique using MTM-SLIM to obtain micropitting and observe ZDDP tribofilm growth in parallel throughout a test. This is then applied to investigate the effect of ZDDP concentration and type on micropitting. It is found that oils with higher ZDDP concentrations produce more micropitting but less surface wear and that, at a given concentration, a mixed primary-secondary ZDDP results in more severe micropitting than a primary ZDDP. Too rapid formation of a thick antiwear tribofilm early in the test serves to prevent adequate running-in of sliding parts, which subsequently leads to higher asperity stresses and more asperity stress cycles and consequently more micropitting. Therefore, any adverse effects of ZDDP on micropitting and surface fatigue in general are mechanical in nature and can be accounted for through ZDDP's influence on running-in and resulting asperity stress history. The observed correlation between antiwear film formation rate and micropitting should help in the design of oil formulations that extend component lifetime by controlling both wear and micropitting damage.

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Paper

The Influence of Slide–Roll Ratio on the Extent of Micropitting Damage in Rolling–Sliding Contacts Pertinent to Gear Applications

Micropitting is a type of surface damage that occurs in rolling–sliding contacts operating under thin oil film, mixed lubrication conditions, …

Micropitting is a type of surface damage that occurs in rolling–sliding contacts operating under thin oil film, mixed lubrication conditions, such as those formed between meshing gear teeth. Like the more widely studied pitting damage, micropitting is caused by the general mechanism of rolling contact fatigue but, in contrast to pitting, it manifests itself through the formation of micropits on the local, roughness asperity level. Despite the fact that micropitting is increasingly becoming a major mode of gear failure, the relevant mechanisms are poorly understood and there are currently no established design criteria to assess the risk of micropitting occurrence in gears or other applications. This paper provides new understanding of the tribological mechanisms that drive the occurrence of micropitting damage and serves to inform the ongoing discussions on suitable design criteria in relation to the influence of contact slide–roll ratio (SRR) on micropitting. A triple-disc rolling contact fatigue rig is used to experimentally study the influence of the magnitude and direction of SRR on the progression of micropitting damage in samples made of case-carburised gear steel. The test conditions are closely controlled to isolate the influence of the variable of interest. In particular, any variation in bulk heating at different SRRs is eliminated so that tests are conducted at the same film thickness for all SRRs. The results show that increasing the magnitude of SRR increases the level of micropitting damage and that negative SRRs (i.e. the component where damage is being accumulated is slower) produce more micropitting than the equivalent positive SRRs. Measurements of elastohydrodynamic film thickness show that in the absence of bulk heating, increasing SRR does not cause a reduction in EHL film thickness and therefore this cannot be the reason for the increased micropitting at higher SRRs. Instead, we show that the main mechanism by which increase in SRR promotes micropitting is by increasing the number of micro-contact stress cycles experienced by roughness asperities during their passage through the rolling–sliding contact. Therefore, the asperity stress history should form the basis of any potential design criterion against micropitting.

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