Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
anti-wear and extreme pressure additives and friction modifiers in greases as lubricants. Development of CVJ greases indicates that MoS2, MoDTP and MoDTC are widely used to reduce friction in order to improve efficiency for the fuel economy. ZDTP is used as a typical anti wear additive. Sulphurised esters/olefins and organic phosphate are used as extreme pressure additives, (Ref.6). Pursuit of a synergy between additives plays one of the most important rules in development of new generations of lubricants in powertrain systems because good performance could be achieved by active tribochemical reaction, (Ref.7). The synergy becomes important, not only between additives, but also between additives and metal contact surfaces inside CVJs. Additives could react with metal surfaces tribo-chemically to form a complex surface layer, (Fig.5). That might, be with MoS2 in nano scale and/or a complex organic compound with iron, sulphur, phosphate, oxygen, Zn, Mo..., (Ref.8).
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In Fig.6, it is seen that much smaller surface areas are covered for a combination of primary ZDTP with 12% Cr steel comparing to others, (Ref.9). At the same time, the chemically active additives could attack sealing materials badly. If the sealing system fails, CVJ system would also be out of order. Consequently, an understanding of tribology systems in powertrain products is one of the keys to develop lubricants for improving fuel economy.
Challenge for new generation of lubricants in powertrain systems
Challenge from durability in new design related to fuel consumption
GKN Driveline is a technology orientated company. In the 2000s, GKN developed new countertrack technology. Independent engineering analysis has proved that GKN’s countertrack technology improves fuel economy by an average of 0.2 mpg on a typical front wheel drive mid-size vehicle. This results in a CO2
emission reduction of 1 g/km. With new countertrack reductions up to 3 g/km.
technology, GKN is able to increase the efficiency over 1%. For special vehicle segments such as SUV’s, case studies have shown that countertrack technology can lead to CO2
emission Fig.7 shows a basic concept of GKN countertrack technology.
Figure 5. Tribo-chemistry in tribology performance.
Research shows that, if the additives are chemically active, they could generate the surface layer fast and stronger in different systems. For instance, as an anti-wear additive, a tribochemical reaction takes place on metal surfaces with ZDTP. It generates a complex surface layer to prevent the surfaces from wear. However, the quality and quantity of surface layers are dependent on the additive molecular structures and metal composition.
Figure 6. Influence of metal surface characteristics on surface layers from tribo-chemical reaction.
28 LUBE MAGAZINE NO.134 AUGUST 2016
Figure 7. GKN Driveline countertrack technology (SX) and efficiency improvement.
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