Separate lubrication

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The separate lubrication or fresh oil lubrication is a form of engine lubrication in two-stroke engines . From a technical point of view, it is a loss of lubrication , since the lubricant is lost after the engine has passed through.

In contrast to the so-called mixed lubrication , in which the two-stroke oil is added directly to the fuel, the separate lubrication usually takes place via a metering pump that is mechanically driven by the crankshaft and that only transfers the two-stroke oil, which is in a separate, small tank, to the engine in the intake system (e.g. in front of the diaphragm block). The delivery rate of the pump can be speed-dependent, but also speed and load-dependent (= position of the throttle grip).

This design has advantages over mixed lubrication, especially in everyday operation: Thanks to the separate lubrication, it is not necessary to add a precisely defined amount of oil to the fuel quantity each time you fill up; it is sufficient to check and, if necessary, refill the oil tank. In addition, the oil consumption is lower than that of the mixture lubrication, since the engine is supplied with more needs and does not always run with maximum lubrication. An essential advantage is the maintenance of the engine lubrication in overrun mode, for example on long downhill drives with closed gas, since sufficient oil is still injected due to the speed-dependent control characteristics of the oil pump, while with the mixture lubrication in this operating state only extremely little oil is in the engine due to the closed gas slide got. Alternatively, this problem could also be avoided by an overrun cut-off (automatic shutdown of the ignition in overrun mode) or by using a freewheel (automatic disengagement in overrun operation).

The disadvantages of separate lubrication include the additional weight and space requirements as well as the additional, complex units that run counter to the basic idea of ​​the simply designed two-stroke engine.

The Auto Union resulted in Type Auto Union 1000 model year 1961/62 together with Bosch "fresh oil automatic" developed a. The system was used in the DKW F11 / F12 , F102 and occasionally in the Munga off-road vehicle until 1966 . Many two-wheelers with two-stroke engines were also equipped with separate lubrication. In principle, no separate lubrication was used in the numerous two-stroke vehicles of the GDR . Instead, attempts were made to counter the increasing emissions problem by reducing the oil content in the mixture and using lean economy carburettors . Mixture lubrication was and is mainly used in motor sports and small engines, especially for types that have to be operated in any position (e.g. chain saws , model drives).

Ultimately, even with the use of separate lubrication, it was not possible to get the exhaust gas problems of the two-stroke engine under control, which is why it has meanwhile also been pushed out of the market in the field of motorcycles and small motorcycles.

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Wikibooks: Engines from a technical point of view / engine maintenance  - learning and teaching materials