The role of the lubrication system

The lubrication system of diesel engines, like other engine lubrication systems, serves to deliver a certain amount of clean, temperature-appropriate lubricating oil to various friction surfaces for lubrication, reducing wear on moving parts; to clean and cool friction surfaces; to enhance the sealing performance of sealed moving parts such as piston rings and cylinder walls; and to act as a rust inhibitor for all moving parts.

2. Lubrication Method

There are three types of lubrication methods for engine oil delivery to the friction surface of moving parts: splash, pressure, and composite.

(1) Splash lubrication is also known as spray lubrication. It is suitable for lightly loaded friction parts, such as cylinder walls, camshafts, tappets, and other components in the valve mechanism. The lubricating oil is splashed onto the friction surface from the gap between the main crankshaft bearing and the connecting rod bearing. Alternatively, the lubricating oil in the oil pan is splashed up by the lower end of the connecting rod, forming oil droplets or mist that fall onto the friction parts for lubrication. After lubrication, the oil returns to the oil pan. This lubrication method has a simple structure, but it is not very reliable, consumes a large amount of oil, and is prone to oxidation and contamination.

(2) Pressure-lubrication is used for friction surfaces that bear heavy loads and have relatively high speeds of relative motion, such as main bearings, connecting rod bearings, camshaft bearings, and other components. It employs the pressure from an oil pump to deliver engine oil from the oil pan through channels and pipes to the friction surfaces of all moving parts for lubrication. This method ensures reliable and effective lubrication, along with excellent cleaning and cooling properties.

(3) Composite Lubrication Composite lubrication employs both pressure and splash lubrication methods to supply oil to the various friction surfaces of the engine. This method is widely used in modern multi-cylinder engines. Not only is it reliable in operation, but it also simplifies the structure of the entire lubrication system.

Due to the basic similarity in the lubrication systems of various engines, only the containment methods of lubricating oil for some medium and large diesel engines differ, which are categorized into two types: dry and wet circulating systems.

The Dry Circulation System: The dry circulation system refers to the separate storage of engine oil in an external oil tank. The oil pan on the engine only collects the returned engine oil from various lubrication points, which is then sent to the oil tank for storage via an oil pump. The engine oil in the oil tank is delivered to the friction surfaces by a pressure pump. This system is suitable for mobile large and medium-sized low-speed diesel engines.

② Wet Sump System: The engine oil is directly stored in the oil pan, known as the wet sump system. Its feature is that it does not require an oil pump; only two pressure pumps are needed to circulate the oil. This circulation system is used in both medium and small-sized engines.

3. Composition of the lubrication system

The composition of the lubrication system is determined based on the specific needs of the engine. A modern engine's lubrication system consists of the following basic components:

(1) The oil storage and transportation device includes an oil pump, oil pipeline, and oil pan, allowing the engine to circulate oil.

(2) The oil filter assembly includes a coarse filter and a fine filter, both designed to remove various impurities from the engine oil.

(3) The oil cooling system includes an oil cooler or oil radiator, which is designed to cool the engine oil and prevent excessive temperatures that could affect the normal operation of the engine.

(4) Safety protection devices include safety valves, pressure relief valves, various alarm systems for high-power engines, and automatic shutdown devices for low oil pressure.

(5) The indicator device includes an oil temperature gauge, an oil pressure gauge, etc., for monitoring the operation of the lubrication system.