Automotive

The mechanical properties of oils are determined using test methods. There are standardized test methods for determining viscosity and density. The characterization of transmission oil based on its dynamic viscosity alone is not sufficient for the physical explanation of different levels of noise emissions in vehicle transmissions. For this reason, the test procedure for determining the coefficient of friction is used in the following to enable a further differentiation between the oils according to mechanical properties.
In gear transmissions with involute gear teeth, rolling friction occurs in the gear pair meshing along the line of action due to the variation in the equivalent curvature radii throughout the meshing cycle. This is rolling friction on which a sliding friction component, so-called slip, is superimposed. Pure rolling friction only occurs in the pitch point. From the pitch point to the start and end of the meshing, there is a superimposed sliding friction component that increases with increasing distance from the pitch point. Slip values occur in the range of 5–50% depending on tooth geometry.
These friction conditions during tooth flank lubrication can be assessed using the Stribeck curve. The Stribeck curve represents the coefficient of friction as a function of the speed. A mini traction machine from PCS Instruments with a ball/plate measurement setup was used to determine the coefficient of friction behavior of gear oils. This allows the coefficient of friction of an oil to be assessed at low speeds in the range from boundary and mixed friction to elastohydrodynamic fluid friction at high speeds.
The investigations show that the coefficient of friction behavior of a gear oil depends on the oil viscosity and above all on the chemical composition. The lower the coefficient of friction, the less energy is required to shear the lubricating film and the lower the power transmission through the fluid. The coefficient of friction is a property that is dominated by the type of base oil and the type of VI improver in the area of mixed and fluid friction, especially with additional sliding in contact.
It will be shown in the paper that the use of a gear oil that has been optimized with regard to the coefficient of friction curve can reduce the entry impacts of meshing gear pairs under vibration excitation and the gear transmission thus generates lower noise emissions.

Climate change demands urgent actions towards CO2 emission reduction. Through their effect on friction losses, new engine lubricants play a key role in reducing fuel consumption and, consequently, CO2 emissions. Besides oil viscosity optimization, friction contributions are primarily dependent on friction reducer (FR) chemistry, although secondary impacts exist for detergent, dispersant, and antiwear additives. Eni has been working for several years in the development of innovative friction reducer additives as well as in the definition of testing methods for evaluating the performances of a large number of molecules and selecting the most promising ones for engine or vehicle tests. According to this approach, a tribological method has been firstly set up by using the Mini Traction Machine (MTM); this equipment allows to measure friction coefficient under various operating conditions and can also reproduce the Stribeck curve, which embraces all the lubrication regimes, thus qualitatively predicting friction behaviour of a lubricant. The performances of a large quantity of candidate additives were evaluated, both as fresh and after appropriate aging. Among these, a very promising metal –free additive, derived from renewable sources, was selected and then put in low viscosity engine oils for the engine and vehicle tests evaluation; standard engine tests, like Sequence VIE and JASO M366 Fuel Economy, as well as chassis-dyno tests were carried out, obtaining results that meet API SP/ILSAC GF-6 and JASO GLV-1 limits. The same additive was also evaluated as fuel-borne FR in chassis-dyno tests based on an in-house procedure composed by a 48h running at low oil and coolant temperature, aiming at transferring the friction reducer additive into the oil, followed by different WLTCs for CO2 measurement and fuel consumption calculation. The additive in 95 RON gasoline was compared with the same fuel without additives. The promising behavior of friction reducer additives at the different scales is the subject of this paper aimed to give a valid support in the roadmap towards CO2 reduction.