Low Loss, Wear and Friction - Fundamental Additives for Wear Friction

In the last issue we focused on the oil film,
As we all know, engine oil is not made of oil alone.
This time we will focus on additives that reduce wear and friction.

Last time, to prevent valve train and piston wear and reduce drag,
We talked about the need to compromise camshaft resistance.

Now, if we can protect the cam and piston in some way, and if we can reduce the resistance,
I can thin the oil film on the camshafts and reduce the resistance even more.

The "anti-wear agents," "friction modifiers (or friction reducers)," and "oiliness enhancers" play an active role in this process.

A typical anti-wear agent is ZnDTP.
ZnDTP decomposes under heat and pressure, attaches to metal surfaces, and forms a film to prevent wear.

Since it is an anti-wear agent, ZnDTP by itself is not effective in reducing friction.
Therefore, ZnDTP can be used for wet clutches (except for those with automated clutch operation) and mechanical LSDs, which must not slip.

On the other hand, ZnDTP also has its disadvantages.
Too much can cause sludge, though the same can be said for other additives,
It is not a matter of adding too much.
Also, the zinc and phosphorus contained in ZnDTP will reduce the capacity of the exhaust catalyst, so careful use is required for vehicles with high oil consumption and blowing white smoke.
ZnDTP also acts as an antioxidant, but its disadvantage is that it is subject to oxidative degradation.
Therefore, in order to achieve long-lasting effects, it is important to balance ZnDTP with other antioxidants and clean dispersants.

(Antioxidants (those that themselves interfere with oxidation and stop the oxidation chain reaction, those that indirectly interfere with oxidation, and those that prevent oxidation by taking over the responsibility for oxidation)
There are various types of antioxidants, but ZnDTP itself interferes with oxidation and stops the oxidation chain reaction, and the oxide of ZnDTP itself also has an antioxidant effect).

MoDTC is a typical friction modifier.
It is also called organic molybdenum or oil-soluble molybdenum.
It too decomposes under heat and pressure to produce molybdenum disulfide on the friction surface.
Molybdenum disulfide is a layered material that tends to shift, and when subjected to friction, it slips like stepping on a banana peel.

Notably, the interaction with ZnDTP can be expected to reduce friction even more than when used alone.
When ZnDTP forms a film on a metal surface, it also incorporates molybdenum, which creates a stronger film,
This is a great synergy effect, which further lowers friction and has a long-lasting effect.

The combination of ZnDTP and MoDTC has a wide range of effects from mixed lubrication to boundary lubrication,
It is an additive that should be used by all means.

As oiliness enhancers, typical examples are esters.
They are not as strong as those mentioned above, but they adhere to metal surfaces and increase the oil film retention capacity.
As a result, they expand the lowest resistance area at the bottom of the Stribeck curve, which was explained in the previous section, to the left.
In other words, it has the effect of expanding the range of fluid lubrication.
It also makes it more difficult for the oil film to fall off, thereby alleviating cold start wear and noise.

Another advantage is that unlike solid lubricants, oil improvers do not produce sludge.
Furthermore, since they do not require heat or pressure to work, they are effective at low temperatures and from cold starting.

Another advantage is that it does not adsorb as strongly to metal as MoDTC.
Wet clutches are at risk of slipping due to molybdenum, because the ester cannot withstand strong pressure,
If a small amount is added, it will not interfere with the wet clutch connection, but will maintain lubrication in other parts of the clutch.

On the other hand, the polarity (ability to stick to parts) and durability of esters tend to be difficult to reconcile.
The more polar the ester is, the more vulnerable it is to hydrolysis, and exposure to air or combustion gases will cause viscosity loss.

There are other disadvantages to high polarity as well.
This is a long story and will be continued at another time.
*** Translated with www.DeepL.com/Translator (free version) ***

Share this post

← Older Post Newer Post →