|
|
 |
 |
 |
Gear Lubricants
Lubricants used for lubrication of gear drive systems. The gear oils must combine the following complex features:
- Anti-wear features (layer strength, good lubrication characteristics and EP (extreme pressure) effect.
- Optimum fluidity (lower possible viscosity at low temperature, viscosity ensuring an adequate load bearing capacity film layer at high temperature, sufficiently low yield temperature).
- Anti-corrosion properties (minimum value of temporary anti-corrosion effect and corrosion wear).
- Compatibility with sealants.
- Long-term retention of properties: ageing resistance, oxidation stability and mechanical stability etc.
The function of the oil is to form a film between the tooth surfaces that is sufficiently resistant to being expelled by the tooth pressures to which it is exposed, which has an appropriate degree of viscosity at operating temperature and which provides for a sufficient level of cooling. The temperature of the oil bath is around 45-55 oC in gearboxes and around 70-90 oC in worm drives. It is important that the oil should adhere adequately to the teeth at the given operating temperature.
Vehicle transmission oils
The vehicle transmission oils category contains the lubricants used in transmissions (gearboxes, differentials, and transfer boxes ? usually torque transfer power trains).
Classification of vehicle transmission oils by viscosity
Classification by viscosity is based on the prevailing international system, the standard SAE J 306. The standard MIL-2105 D also contains multigrade transmission oil specification. The following table shows the two specifications combined.
| SAE viscosity class | Viscosity at 100 oC, mm2/s |
|
Temperature belonging to 150.000 mPas viscosity, oC, max. |
|---|---|---|---|
|
|
min. |
max. |
|
|
70W |
4.1 |
- |
-55 |
|
75W |
4.1 |
- |
-40 |
|
80W |
7.0 |
- |
-26 |
|
85W |
11.0 |
- |
-12 |
|
80 |
7.0 |
<11.0 |
- |
|
85 |
11.0 |
<13.5 |
- |
|
90 |
13.5 |
24.0 |
- |
|
140 |
24.0 |
41.0 |
- |
|
250 |
41.0 |
- |
- |
|
80W-90 |
13.5 |
24.0 |
-26 |
|
85W-140 |
24.0 |
41.0 |
-12 |
Classification by performance level
The API performance level classification system is shown in the table below, with an indication of the individual features and fields of use. The abbreviation GL stands for Gear Lubricant.
| API designation | Operating conditions | Engine manufacturer approval |
|---|---|---|
|
GL-1 |
Rust and oxidation preventive, non-EP-effect lubricant without additives. Very few fields of use, mainly for light load helical serration transmissions and drive shafts. |
Volvo |
|
GL-2 |
Transmission oil with a higher additive level than the previous, without EP effect. For medium load vehicle worm drives. For use in a very limited range of European equipment. |
|
|
GL-3 |
Lubricant with light EP effect for transmissions and non-hypoid gear drives. Used by several vehicle manufacturers for first fill of transmissions. |
Fiat |
|
GL-4 |
Medium EP effect lubricant for synchromesh transmissions and moderate load hypoid gear drives. The most widely used specification. Most vehicle manufacturers specify this performance level. |
Mercedes-Benz 235.1 |
|
GL-5 |
High EP effect lubricant for hypoid gear drives, rear axles, differentials exposed to heavy loads and transmissions exposed to shock loads. Not always suitable for lubrication points requiring a lower performance level. |
Mercedes-Benz 235 |
With a growth in popularity of the various disk-type, oil lubricated, limited slip differential locks, the demand arose for a new lubricant feature, mainly in the API GL-5 performance class: the requirement for limited friction coefficient, so-called LS (limited slip) transmission oils. Here the limited lower-value-friction coefficient of the lubricant assures the torque transfer between multiplate disks and thus the partial locking effect of the differential. This specialised capability can be ensured through the use of special additives designated by the abbreviation LS. The use of other transmission oils where this type of oil is required could result in serious malfunctions.
Industrial gear oils
Industrial gear oils perform the lubrication function of the various types of industrial drive gears operating under different load conditions.
The DIN 51517 standard, widely known and used in Europe, contains the following selection:
Performance level & Viscosity selection
| C |
|
7 |
10 |
22 |
32 |
46 |
68 |
100 |
150 |
220 |
320 |
460 |
680 |
| CL |
5 |
7 |
10 |
22 |
32 |
46 |
68 |
100 |
150 |
220 |
320 |
460 |
680 |
| CLP |
- |
- |
- |
- |
- |
46 |
68 |
100 |
150 |
220 |
320 |
460 |
680 |
C: Recommended mainly for constant-circulation and immersion lubrication of places requiring only modest lubrication (additive-free lube oil raffinate)
CL: Gear oil with age-resistant and anti-corrosion properties enhanced by an R + 0 additive, mainly for constant-circulation lubrication
CLP: Recommended for constant-circulation and immersion lubrication. Besides its anti-corrosion and counter-oxidant properties, it also has excellent anti-wear characteristics.
