Mixture lubrication
The mixture lubrication , colloquially called mixed lubrication referred to is a form of engine lubrication . It describes the lubrication of the moving parts in the internal combustion engine by a mixture of fuel and oil , which is known as a two-stroke mixture . The mixture can be purchased in various ratios of oil and fuel (usually 1:25, 1:33, 1:50 or 1: 100) or you can mix it yourself from carburetor fuel and engine oil. The engine manufacturers stipulate the ratio required for the operation of the respective types.
The fuel-air mixture generated in the carburetor is sucked into the crankcase for pre-compression , fuel parts evaporate and the oil is deposited on the metal parts there, lubricating the crankshaft bearings , connecting rod bearings and pistons , i.e. all moving parts. It reaches the combustion chamber via the overflow ducts and is ultimately partly burned, partly as an aerosol via the exhaust pipe and is a cause of the unsatisfactory exhaust gas behavior of such engines (especially with regard to unburned hydrocarbons ).
Mixture lubrication is used almost exclusively in two-stroke gasoline engines with external mixture formation , which suck in the fuel mixture together with the oil via the crankcase and therefore otherwise (for example in large two-stroke diesel engines) could only be lubricated with forced lubrication with channels through the crankshaft and connecting rod .
The problem with vehicle drives with mixed lubrication is dragging or pushing operation (longer downhill journeys using the engine braking effect ), since the throttle valve or throttle valve are closed and only very little fuel and therefore also oil reaches the lubrication points, even though the engine is running at increased speed. However, the braking effect of the two-stroke engines is low anyway, which is why many vehicles were equipped with a freewheel .
Mixture lubrication is generally prohibited on conventional four-stroke engines , as the fresh gas - even if it would contain lubricating oil - has no contact with components requiring lubrication due to the design and reaches the combustion chamber directly from the carburetor and the inlet valve. The plain bearings on the camshaft and crank drive usually used in four-stroke engines also require pressure lubrication with an oil pump. However, there are also single-cylinder engines with displacements between 30 and 70 cm 3 on the market that use the crankcase space as a pump for distributing the air / fuel / oil mixture - at least a branched off partial flow of the amount sucked in - for lubricating the roller-bearing crank drive and valve drive with use (for example Stihl 4-Mix as a drive for hand tools such as leaf blowers and brushcutters) and thus combine the advantages of both processes within certain limits. This advantage is due to the combination of the low gas exchange losses of the four-stroke engine with the simplicity and position independence of the mixture lubrication.
There are also very small four-stroke engines (from approx. 4 cm 3 displacement) with glow ignition , which are built into model construction (e.g. remote-controlled cars, model airplanes, etc.) and which manage with mixture lubrication even though the fresh gas is not sucked through the crankcase. The fuel intended for such drives, however, usually has a higher oil content; the crank drive is lubricated by the oil deposited on the cylinder wall, which passes the piston into the crankcase as a blowby .
literature
- Jan Drummans: The car and its technology. 1st edition, Motorbuchverlag, Stuttgart, 1992, ISBN 3-613-01288-X
Web links
Individual evidence
- ↑ Description of the 4-Mix engine on the company website , accessed on June 4, 2016