Browse Topic: Gear lubricants
Bench-level boundary-lubricated fretting experiments were conducted to compare the relative wear of all-steel and hybrid material pairs. Roller-on-raceway contacts were simulated using both AISI M50 steel and Si3N4 cylindrical rollers on flat AISI M50 steel disks. The rollers were 9 mm long with a 9 mm diameter. Tests were conducted with constant amplitude, oscillation frequency, and load. All tests were boundary-lubricated with 0.1 ml of DOD-PRF-85734, MIL-PRF-32538, MILPRF-23699, or unclassified ISO VG 68 aviation gear oil. Wear volume was calculated from 3D measurements on the roller and disk samples after each test. Wear tracks were inspected with light and scanning electron microscopy. It was concluded that hybrid pairs exhibited less wear than all-steel pairs when boundary-lubricated with three of the four aviation gear oils. Both hybrid and all-steel pairs exhibited similar wear when boundary-lubricated with MIL-PRF-23699 oil.
Oil churning and windage power losses in dip-lubricated gearboxes can significantly affect overall transmission efficiency, particularly at high rotational speeds. As modern gearbox systems are pushed toward higher efficiency and reliability, understanding and predicting these losses becomes increasingly important. In addition to energy dissipation, the associated multiphase flow phenomena—such as oil splashing, thin film formation along gear surfaces, and aeration of the sump—strongly influence lubrication effectiveness, heat transfer, and component durability. Capturing these effects requires a robust numerical strategy that can resolve both power loss mechanisms and multiphase flow dynamics with sufficient accuracy. In this study, a single spur gear is numerically analyzed under varying oil depths and rotational speeds to quantify total power loss and investigate oil flow patterns. The computational approach employs a volume-of-fluid multiphase framework, and the predictions are systematically validated against experimental data from the OSU Lab. Validation is carried out in two stages: first, by comparing the simulated oil free-surface shapes with experimental flow visualizations for various operating conditions; and second, by comparing total power loss across a range of rotational speeds and immersion depths. The findings confirm that qualitative comparisons of oil behavior show good agreement with experimental observations including splash generation, oil streak formation, and gear surface wetting. Furthermore, predicted power loss trends align with experiments, exhibiting exponential growth with RPM and a transition toward quadratic scaling as oil depth increases. Overall, this work highlights the capability of the numerical framework to predict both churning losses and multiphase flow behavior in gear lubrication systems, providing a foundation for future gearbox design and optimization.
Electric vehicle (EV) transmission efficiency is crucial for optimizing energy use and enhancing performance. It minimizes power losses during energy transfer from the motor to the wheels, directly impacting the vehicle's range and battery life. High efficiency ensures smoother acceleration and better driving dynamics, improving the overall user experience. Unlike internal combustion engine (ICE) transmissions, EV transmissions often employ simpler, single-speed systems, reducing complexity and energy loss. Efficient transmissions help reduce energy usage, lower costs, and minimize environmental impact. As a result, transmission efficiency plays a vital role in ensuring the sustainability and reliability of EV designs. This paper proposes a simulation model based methodology to estimate EV transmission efficiency based on modelica models developed on simulation X. A single speed EV model is developed which contains whole transmission layout discretized into simple components which include shafts, gears, bearing inertias and power loss components. The developed model considers load dependent losses which occur due to frictional losses because of surface contact between gear teeth, bearings, shafts and inertial losses based on operating conditions of the transmission required to accelerate or decelerate rotating components. Other losses due to oil churning, bearing drag and drag due to gears spinning in gear oil can be modelled using elements present in default library provided in simulation X. In the initial simulation runs, efficiency under operating region of torque speed curve of the electric motor are estimated by considering equidistant points and in subsequent runs overall power loss and efficiency over a duty cycle is estimated. Simulation results show good co-relation with measurements carried out at bench level on physical prototypes. The developed model is capable of modification to suit other single-speed EV transmissions with room left out for developing the same for multi-speed EV transmissions.
This study introduces a method to examine the flow path of the lubricant inside a transmission housing of a tractor. A typical gearbox has several loads bearing elements which are in relative sliding motion to each other which causes heat to be released. The major sources of friction as well as heat are the meshing teeth between gears (sun/planet, planet/ring & power/range drive gear), thrust washers, thrust bearings and needle roller bearings. The churning of oil performs the vital function of both lubricating these sliding interfaces and cooling these sources of heat, thereby preventing failure of the gearbox. In this paper, we have applied VOF multiphase flow model and sliding meshing to simulate the fluid flow during splashed lubrication within a mating gear box. Lubrication oil dynamics and oil surface interaction with the air is modeled using VOF multiphase approach. The gear motion is imparted through sliding mesh technique, it automatically reconfigures the mesh for the space in accordance with the rotation of physical objects, which divides the space around the gears, centering on the axis of rotation to simulate the motion of the gears. The method captures the effect of rotation of the gears and shaft in a transmission. The entire transmission unit is considered for the analysis to study the cumulative effect of the motion of all the gears on the oil flow against the general practice of studying the local effect. After solving for 3 seconds in high speed forward boundary condition, volume fraction of oil at the at the oil holes that carry the oil to the bush & the gear interface, reveled two locations one on the fourth gear of drive shaft and another at the first gear of the driven shaft. By volume the quantity was very less when compared to the other gear. The supply of lubricant to the bush & gear interface depends on the location of oil supply hole on the gears and shafts. After running the transmission for 150 hours on test bed scoring marks were observed between the gears inner diameter & bush outer diameter due the relative motion between the inner surfaces. This failure was attributed to scarcity & delay of oil to bush. Estimating the lubrication in advance during the design step helps reduce the development period & expenses for prototypes. This paper explains how the CFD simulation can we used to understand the lubrication flow inside the tractor transmission.
Dual-clutch transmission (DCT) output shaft 1 (OS1) mount position is higher than the transmission lubricant level. Needle bearings and idler gears on OS1-insufficient lubrication issues and the transmission lubrication system were investigated. In the design model, the transmission housing lubrication channel and oil guide component design were studied. For numerical analysis, the STAR-CCM+ software was used to simulate transmission internal complex oil-gas multiphase transient flow morphology that monitored the four bore oil churning volumes of OS1. Finally, lubrication test results affirm simulation predictions that idler gears, needle bearings, and synchronizer rings on OS1 obtain sufficient lubrication provided that a reliable method to inspect lubrication design functions is available.
The paper investigates the oil flow through a multi plate clutch for a hydro-mechanical variable transmission under actual operating conditions. The analysis focuses on the numerical approach for the accurate prediction of the transient behavior of the lubrication in the gear region: the trade-off between prediction capabilities of the numerical model and computational effort is addressed. The numerical simulation includes the full 3D geometry of the clutch and the VOF multi-phase approach is used to calculate the oil distribution in the clutch region under different relative rotating velocities. Furthermore, the lubrication of the friction disks is calculated for different clutch actuation conditions, i.e. not-engaged and engaged positions. The influence of different geometrical features of the clutch lubricating circuit on the oil distribution is also determined. The results show the areas where poor lubrication occurs and extend the experiments where measurements are difficult to carry out. The simulation highlight the regions where high thermal stresses are observed during tests.
Differential in Gear Box play vital role in Tractors for assisting it in turning and also to take straight path. Light weight machine always have advantage in terms of fuel economy and performance. Weight optimized rotating part have additional benefits of saving power loss, against stationary dead weight. Differential Housing is such a part, which rotates during the vehicle motion and torque transmission. [1] This paper describes a method by which weight of the Differential Housing is optimized. In this particular body of work, additional constraints of avoiding any change in existing cold forged parts like Bevel Gear & Pinion. This also have additional benefit of enhanced flow of Oil inside Differential Housing for better lubrication of Bevel Gears and Pinion. This resulted in weight saving of Differential Housing and finally fuel economy of Tractor.
The operating conditions of a typical motorcycle are considerably different than those of a typical passenger car and thus require an oil capable of handling the unique demands. One primary difference, wet clutch lubrication, is already addressed by the current JASO four-stroke motorcycle engine oil specification (JASO T 903:2011). Another challenge for the oil is gear box lubrication, which may be addressed in part with the addition of a gear protection test in a future revision to the JASO specification. A third major difference between a motorcycle oil and passenger car oil is the more severe conditions an oil is subjected to within a motorcycle engine, due to higher temperatures, engine speeds and power densities. Scooters, utilizing a transmission not lubricated by the crankcase oil, also place higher demands on an engine oil, once again due to higher temperatures, engine speeds and power densities. However, because scooter oils do not need to lubricate a wet clutch or protect gears, scooter oils can provide more fuel economy benefits than motorcycle oils, when properly formulated. First, this study compares the piston deposit performance of motorcycle oils and passenger car oils in the API Sequence III Test and in a fired-engine motorcycle piston deposit evaluation. While the API Sequence III Test is certainly an effective tool for ensuring passenger car motor oil piston deposit performance, the results show that some oils formulated to meet the performance requirements of the Sequence III test do not match the performance of motorcycle-specific oils in a motorcycle piston deposit evaluation. Second, this study compares the performance of different oils in the JASO clutch friction test (SAE#2) and in a fired-engine Scooter Fuel Economy Test. The results indicate that JASO MB performance, as determined by the SAE#2 clutch friction test, is not necessarily a predictor of real fuel economy benefit.
Scuffing is an instantaneous failure which occurs when the meshed gear flanks undergo adhesive wear under extreme operating temperatures at medium- or high-speed conditions. It is one of the common failures in transmission gears, which tend to operate under long-duty cycle hours. The tip and the root regions often experience higher contact pressures because of the loading and surface curvature. These higher pressures, coupled with higher sliding velocities and heat generation, make the tip and root regions in the gear susceptible to scuffing. Gear geometry, material composition and lubricant properties influence scuffing. A balanced gear tooth design with lower sliding velocities is often chosen as an approach to avoid scuffing. However, in the current scenarios of transmissions with high power density requirements, achieving a balanced gear tooth design is rare. Lubricants with higher viscosity avoid scuffing, but have adverse effects on the transmission efficiency. As per ISO 6336, there are no sufficient methods or techniques available to measure and prevent scuffing failures on gears. AGMA 925-A03 provides a method for determining the scuffing risk based on lubricant and gear macro-geometry properties through quantifying critical scuffing temperature. Higher quality gear materials, better manufacturing process and scuffing additives in lubricants avoid scuffing but involve significant costs. In this study, we have used a statistical-based model to highlight the influence of gear mesh micro-geometries on the contact pressure and temperature distribution for an indication of scuffing risk in an automotive transmission. There is a discussion of the sensitivity of modifications on scuffing temperature and an optimal solution for a particular gear-mesh loading.
The need for advanced lubricants is increasing rapidly due to the current wide range of operational usage, i.e., high loads and speeds of motion between friction pairs, broader temperature range, and the overall requirements for increased reliability and service life of machinery. It is essentially important to develop specialized anti-friction and anti-wear materials that will help in preventing wear and decreasing friction, thereby saving fuel and electricity. Simultaneously, such materials are also expected to reduce vibration, noise and maintenance of machine parts. Thus, the research into extending the service life of such materials continues to be imperative. Nanoparticles (NPs) present a novel approach in this regard, as they can be used in lubricants in between two mating contact surfaces as a third body. When compared with the widely used conventional micro-particles for tribological applications, NPs have unique features owing primarily to their much higher specific surface area. This is true for studies of both nanostructured coatings of friction surfaces as well as for new lubricant compositions containing Nanoparticles. When compared to a pure fluid, this category of fluids containing nanoparticles (1-100 nm) has displayed fascinating behavior during experiments including augmented heat transfer coefficient and higher thermal conductivity. The products so developed can find applications in metal working fluids, industrial gear oils, and automotive gear lubricants, either alone or in formulations. Present research investigates the influence of NPs as lubricant additive on the relative motion of a plane surface over the other having circular surface in contact. A pin-on-disk setup as per ASTM G99 has been used to conduct the experiments in starved and fully flooded conditions at various loads and relative speeds at the pin and disc contact. The lubricant SAE 20W-40 with nano-additives has been used to study the influence on friction and specific wear rate at the interface. Based on the experiments, tribological behavior of lubricant with NPs has been compared with the lubricant without NPs. The coefficient of friction and specific wear rate were found to be decreased in lubricant containing NPs. The addition of NPs to the lubricant SAE 20W40 has proved to be profoundly promising in reducing the friction and specific wear rate.
ABSTRACT This paper presents a new nanolubricant for the intermediate gearbox of the Apache aircraft. Historically, the intermediate gearbox has been prone for grease leaking and this natural-occurring fault has negatively impacted the airworthiness of the aircraft. In this study, the incorporation of graphite nanoparticles in mobile aviation gear oil is presented as a nanofluid with excellent thermo-physical properties. Condition-based maintenance practices are demonstrated where four nanoparticle additive oil samples with different concentrations are tested in a full-scale tail rotor drive-train test stand, in addition to, a baseline sample for comparison purposes. Different condition monitoring results suggest the capacity of the nanofluids to have significant gearbox performance benefits when compared to the base oil.
This paper presents an experimental study of external gear pump efficiency based upon an analysis of the Stribeck values. The volumetric, mechanical, and overall efficiencies of a variety of external gear pumps were measured under steady state conditions. Straight grade antiwear hydraulic fluids were evaluated at 50°C and 80°C. Stribeck values for mechanical, volumetric, and overall efficiency were compared to classic pump efficiency curves. The experimental curves for pump volumetric and overall efficiency were consistent with the classic pump efficiency model. Mechanical efficiency diverged from model behavior at low Stribeck numbers; declining at low speeds and high pressures as contact conditions transitioned from the hydrodynamic to the mixed-film lubrication regime. Lubrication of external gear pumps can be enhanced by using hydraulic fluids that optimize the Stribeck value. A simple expression for relating the Stribeck number to volumetric and mechanical efficiency is presented.
The ASTM D6121 (L-37) is a key hypoid gear lubricant durability test for ASTM D7450-08 (API Category GL-5) and the higher performance level SAE J2360. It is defined as the ‘Standard Test Method for Evaluation of Load-Carrying Capacity of Lubricants Under Conditions of Low Speed and High Torque Used for Final Hypoid Drive Axles’. Pass/fail is determined upon completion of the test by rating the pinion and ring gears for several types of surface distress, including wear, rippling, ridging, pitting, spalling and scoring. Passing the L-37 in addition to the other tests required for API Category GL-5 credentials, as well as the more strenuous SAE J2360 certification, requires in-depth formulating knowledge to appropriately balance the additive chemistry. This paper describes the results of ASTM D6121 experiments run for the purposes of better understanding gear oil durability. Two gear lubricants, differing only in the antiwear chemistry, were used: gear lubricant A was designed to pass the test, while gear lubricant B was intentionally formulated to fail for gear ridging. In this series of experiments: the cooling demand required to maintain a constant oil temperature was monitored continuously; the oil was sampled every two hours for evaluation of changes in oil chemistry and particulate levels; and surface analysis was performed on end-of-test gears not only from tests run to completion, but also from tests stopped early. It will be shown that gear ridging is an abrupt process, characterized by a sharp increase in cooling demand, iron content and particulate levels. Protective phosphate films are formed on the gear surfaces in the earliest stages of both passing and failing tests, but in ridging failures the phosphate is replaced by sulfide films not capable of providing adequate gear tooth protection, which then allows ridging.
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