Oils for lubricating manual transmissions and differentials of motor vehicles

The task of gears, transmissions and differentials is to transfer engine power to the axles and wheels of the vehicle. In doing so, the gear teeth are exposed to extremely high pressures. The highest pressures occur when starting and stopping a vehicle. The development of motor vehicles is in the direction of increasing power and better starting, which results in the appearance of higher slip forces, ie higher operating temperatures on the gearboxes and differentials.

For lubrication of gearboxes in such harsh operating conditions, only lubricating oils produced on the basis of high quality base oils and the selected additive package can satisfy. Base oils may be mineral refiners, hydrocracked oils or synthetic hydrocarbons. The additives used in the production of these oils are: corrosion and rust additives, high pressure and wear protection additives, point-of-cure additives, oxidation protection additives, metal deactivators, anti-foam additives and friction modifiers.

In order to satisfy all the factors that increase the severity of working conditions, special EP (Extreme Pressure) additives are added to the oil, which also give different quality levels of these oils. EP additives are based on sulfur, phosphorus or chlorine. At elevated temperatures, which are the result of high pressures and impact loads, these additives chemically react with the metal surface, forming appropriate compounds and films that protect the metal surface from wear and damage to the gear teeth. It should be borne in mind that EP additives can cause corrosion on non-ferrous metal parts, so their amount in the oil must be balanced so that they can create a protective film without causing corrosion on metal surfaces. The task of gear oils: reduction of friction and wear, cooling, removal of metal particles and impurities from contact zones and corrosion protection.

Viscosity data and data on the quality of the oil and its performance are required for the selection of the oil. As with engine oils, SAE viscous oil grades for gearboxes and differentials refer solely to viscosity and do not determine the quality level of the oil.

The classification of oils for gearboxes and differentials of motor vehicles by viscosity (SAE J 306 of 1998) is shown in Table 36. According to the viscosity range multigrade gearbox and differential oils can be divided into two categories:

• SAE 80W-90 i narrow range multigrade oils
• multigrade oils with wide viscosity SAE 75W-90, SAE 85W-140

Widespread viscosity oils must contain a higher percentage of viscosity enhancer additives to meet the prescribed viscosity requirements. For this reason, ASTM introduced a 20-hour shear stability test CEC L-45-T-93, which assesses the ability of an oil to retain the strength of an oil film and to protect parts in contact with each other, ie to keep the oils in gradation.

There is no relationship between SAE viscous grades of engine oils and gearbox and differential oils but they can be compared in terms of application:

• SAE 75W corresponds to the viscosity of SAE 10W engine oils
• SAE 80W corresponds to the viscosity of SAE 15W, SAE 20W, SAE 20W-20 engine oils
• SAE 85W corresponds to the viscosity of SAE 30W engine oils
• SAE 90 corresponds to the viscosity of SAE 40W and SAE 50 engine oils
• SAE 140 corresponds to the viscosity of SAE 60W engine oils

Viscosity has a significant effect on the load carrying capacity, on the ease of gear shifting and on possible fuel savings. Recently used multigrade oils have made a compromise between the required viscosity at high temperatures, the easy shifting of speeds and the small internal friction when starting the vehicle at low temperatures.

Table 1: Classification of gear oils by viscosity SAE J 306, 1998

Table 2: Classification of transmission oils by performance - SAE J 308, 1989

Table 3: Overview of MIL-L specifications

Table 4: Motor vehicle manufacturer's requirements for gearbox oil

Table 5: Requirements of motor vehicle manufacturers in relation to differential oil

FSS - serviceable systems include the processing of parameters that are registered with the built-in encoders: operating modes, load, number of starts, data on fresh oil and changes. These parameters are collected in a database for processing diagnostics of the condition of oils and parts of motor vehicles and decisions are made on the necessary intervention.

Table 6: MAN manufacturer specifications for gearbox and differential oils

Figure 2: Transaxle and differential layout

Table 7: MB specifications for gear oils for differentials (hypoid oils)

Table 8: MB specifications for gearbox gear oils

Transmission and Differential Oil Quality Requirements:

• Passenger cars are characterized by high speed and trucks and buses with high torque. These oils must satisfy both operating conditions.

• Anti-wear and tear-resistant property for extreme pressures and shock loads.
• Good viscous-temperature characteristics, which means easy transfer at cold start and sufficient oil film strength at high operating temperatures.
• Good oxidation and thermal stability, which ensures long oil use. In modern vehicles, the oil fill temperature can be up to 140 ⁰C.
• Corrosion protection especially in the presence of water.
• Compatible with gaskets.
• Anti-foam property.

In the vehicle's propulsion system, gearboxes should allow optimum matching between engine speed and wheel speed. This is achieved through gearboxes and differentials. In addition, in the case of longitudinally mounted motors, the energy flow must be diverted by 90^o. The compensation gear compensates for the difference in speed when cornering. When choosing oil, the vehicle manufacturer's recommendations regarding viscous SAE grades and the corresponding API GL categories should be followed in the first place. For all models "SOUTH“SAE 80W-90 API GL-3 is recommended. In these models, the integrated gearbox-differential includes non-ferrous metal parts, so API GL-4 or API GL-5 hypoid oils are not recommended.

Synchronized gearboxes:  Due to the synchronous rings, the use of highly additive API GL-5 oils is not allowed, but API GL-4 is exclusively recommended. Some manufacturers of synchronized transmissions require API GL-3 and even GL-1, and some even prescribe oils for automatic transmissions and even engine oils, which of course should be respected.

Non-synchronous gearboxes are relatively insensitive to EP additives, so oils of both specifications -API GL-4 or API GL-5 can be used.

Differentials: As a pair of hypodermic gears can withstand very high loads over a very small touch surface, almost a point, it is imperative that lubricants are recommended for hypoid oils that meet API GL-5 specification.

For lamellar (plywood) differentials special requirements are set in relation to friction. For these types of differentials, special oils are produced that are marked LS (Limited slip).

It has been used since 1990 modified CVT gearbox - Continnously Variable Transmission due to increased economy especially in city driving. Experience shows that vehicles with CVT gearboxes have up to 17% less fuel consumption than vehicles with hydrodynamic gearboxes, but also set the most stringent shear oil resistance requirements.

Lubricating oils for automatic transmissions of motor vehicles - ATF

Automatic Transmission Fluid (ATF) oils are relatively low-viscosity oils (approximately comparable to SAE 75W) with a high viscosity index and a flow point below –40⁰C. They have high oxidation stability, good viscous temperature and low temperature characteristics, provide good corrosion protection and excellent foaming and air release properties. They must also satisfy the requirement of constant friction coefficients.

They consist of base oils and additives. Base oils can be conventional raffinate, hydrocracked oil or synthetic hydrocarbon. Additives are used: to protect against corrosion and rust, to improve viscosity, friction coefficient modifiers, to protect against high pressures and wear, to improve the flow point, oxidation protection additives, to prevent foam and metal deactivators.

The gearbox oil needs to handle more gear in the gearbox. In addition to the lubrication function of the planetary gears, which form the main assembly of automatic transmissions, ATF oil performs the function of hydraulic oil, which allows for easy gear shifting in the complex hydraulic system, as well as smooth operation of the hydraulic torque converter, which plays the role of a coupling connecting the input shaft to the planetary system. gears. With all of these tasks, the automatic gearbox oil must maintain an adequate coefficient of friction.

Automatic transmission oils are used to lubricate automatic transmissions, power steering and torque converters. They are required: good lubrication and cooling to allow the transmission of power to the gear flanges or torque converters, adequate friction coefficient for optimum gear change, wear and corrosion protection, seal compatibility, high oxidation stability and foaming resistance.

Oxidation and thermal stability - The new constructions of automatic transmissions are smaller and lighter constructions, and such are required to transmit higher torques, which results in increased thermal load per unit volume of oil. In addition, there is a constant demand for extended oil filling life. These reasons require oxidationally very stable oils for automatic transmissions.

ATF oils must have good oxidation stability at temperatures up to 150⁰C. At these elevated temperatures and with the presence of air, there is an accelerated process of oil oxidation and many unintended consequences such as:

• the acids formed, as products of intense oxidation, have a corrosive effect on the bushes and other structural materials as well as on the sealing materials and the composition of the coupling plates
• changing friction characteristics causes excessive slip of the couplings
• sludge as a product of oxidation can block hydraulically controlled valves and other narrow channels for fluid passage
• resins and varnishes, as oxidation products, can cause the control valves to become stuck and transmission failures
• the viscosity of the oil increases which leads to a decrease in automatic transmission functionality

The oxidation stability of automatic transmission oils is determined by changing the acid number according to the DEXRON and MERCON specifications, or by changing the kinematic viscosity according to the ZF specification. The requirement for increased oxidation stability indicates the use of quality base oils, that is, the transition from API Group I to API Group II, III, or IV base oils.

Low-temperature properties - Automatic gearboxes are sophisticated electronic control systems that require adequate rheological properties even at the lowest temperatures. The low temperature properties of the oils are expressed as the maximum permissible value of dynamic viscosity at -40⁰C as measured by a Brookfield viscometer. Increasingly stringent requirements for better low-temperature properties require the use of higher quality base oils than API Group I. The use of viscosity index enhancers must be limited.

Shear stability - Due to the mechanical loads to which the oils for automatic transmissions are exposed, the chains of molecules, especially the higher molecular weight, break, and there is a permanent drop in the viscosity of the oil. These problems are solved by using shear-stable viscosity modifiers while using quality base oils.

Anti-wear properties - Oils for automatic transmissions must have good anti-wear properties that are necessary for the durability of assemblies and parts of automatic transmissions, and thus the extension of the oil change interval is ensured. A Vickers vane pump is used to evaluate the anti-wear properties of the oil. The results are expressed by the loss of mass of the vanes and rings of the pump after the end of the test.

Friction properties - Friction properties of oil are very important for reliable and smooth operation of automatic transmissions. The values ​​of the oil friction coefficients must be within precisely defined permissible limits because the engagement of the gear is carried out by means of lamellar couplings and belt brakes lined with friction linings. It is this feature that makes the basic difference between individual oils for automatic transmissions, ie the specifications of individual manufacturers. Further development of ATF oil goes in the direction of the development of additives, especially friction modifiers that provide the optimal coefficient of friction while keeping it within the prescribed limits.

Viscous gradations for ATF fluids are not prescribed (SAE, ISO VG), but are an integral part of the given specification. Performance is defined by the specifications of General Motors and Ford and is shown in Tables 9 and 10. Most other manufacturers (MAN, Mercedes Benz, Renk, Voith, ZF) have accepted one or another specification, although some prescribe additional tests. , to ensure compatibility with their automatic transmissions.

The General Motors specification includes the requirements of automatic gearbox oils in terms of: high oxidation stability, high ignition points, foaming resistance, compatibility with seals, proper friction coefficient, ie balanced friction and lubrication.

Ford introduced the M 1959C 2-G specification in 33. The new Ford specification is labeled Ford Mercon. This new specification, and also the two previous ones (M 2C 166-H and M 2C 138-CJ), require oil containing friction modifiers, which satisfies with respect to the coefficient of friction, GM-Dexron requirements.

In automatic transmissions for passenger cars and commercial vehicles today, with few exceptions, Dexron II D / E or Dexron III is used. When using an ATF according to the Ford specification SQM-2C 9007 A (M 2C-33G), caution should be exercised as this product has completely different friction characteristics than all other ATFs and should therefore not be mixed with other automatic transmission oils. However, ATF fluids of specification M 2C - 33 G (G-oils) are very rarely used today.

Dexron IID specification oil is often recommended for heavy duty power steering, turbo couplings and torque converters, and sometimes for manual gearboxes as required by the manufacturer. Ford MERCON and General Motors DEXRON IIE / III are very similar so automatic transmissions known manufacturers meet the requirements of both specifications.

Motor vehicle manufacturers recommend replacing automatic transmission oil at 40.000 km. For some new gearbox models: ZF 5HP18 or ZF 5HP30 and ATF Dexron III oil filling is permanent.

Automatic transmission oil can be used for a variety of hydraulic systems in industry, shipping and transportation, for hydraulic vehicle control systems, for screw compressors, and for heavy-duty hydraulic gears.

Table 9: GENERAL MOTORS specification for ATF oils

Table 10: FORD specifications for ATF oils

Table 11: Equipment manufacturer specifications

Table 12: Mercedes Benz specifications for ATF oils

Table 13: MAN specifications for ATF oils

Table 14: ZF (Zahnradfabrik Friedrichshafen) specifications

Source: www.nisotec.eu