Views: 0 Author: Site Editor Publish Time: 2021-10-24 Origin: Site
The engine contains a large number of parts rubbing against each other, they are all metal, and they all need lubrication, because they heat up and, as a result, can jam. Therefore, the engine has a lubrication system: with channels (lines), with a sump and with an oil pump. A simplified diagram of the lubrication system is shown in Figure 4.38.
In addition to lubrication, oil also acts as a cooler for hot rubbing engine parts. That is why, often in diesel, and sometimes in gasoline engines, special sprayers are installed, aimed at the lower parts of the pistons, but more on that later.
Figure 4.38 Simplified diagram of the lubrication system.
The purpose of this device is indicated by its name. An oil pump is required to pump engine oil from the oil pan, which is located at the very bottom of the engine, to all rubbing parts through special oil channels.
For this purpose, gear-type pumps with external and internal gearing are used. Pumps of the first type are now very rare due to their dimensions, therefore we will consider the type of pump that is most relevant today - gear with internal gearing, an example of which can be seen in Figure 4.39.
Figure 4.39 Internal gear oil pump.
The oil pump is usually driven from the crankshaft by a chain, belt or gear, depending on the type of timing mechanism drive, or directly mounted on the crankshaft. The operation of the pump consists in the fact that when rotating, the small gear rolls over the large gear, carrying the engine oil along with it, and supplies it through the channels under pressure to the rubbing parts.
The pressure reducing valve serves to limit the oil pressure in the oil lines of the lubrication system. Oil pressure can rise at very high engine speeds or excessively thick oil, for example in a cold engine. The pressure reducing valve is usually installed in the pump housing. It is a ball pressed by a spring. While the oil pressure is normal, the ball is pressed tightly against the spring, when the pressure begins to rise excessively, the ball moves, compressing the spring, thus opening the bypass channel through which the oil from the sump through the pump again flows into the sump.
The engine is running, the oil lubricates, however, one way or another, wear products of rubbing parts appear. Wear products are rather small particles of metal shavings formed during friction and, as a result, wear of parts. Also, the oil is contaminated with carbon and dust particles entering the crankcase. These mechanical impurities, getting along with the oil to the rubbing parts, increase their wear and therefore must be removed from the oil.
Note
Oil filters are used to clean the oil from mechanical impurities, which increases the duration of its operation.
Figure 4.40 Oil filter.
Often, the engine has two oil filters: one - mesh - is installed on the oil receiver (which is shown in Figure 4.38), and the second - in its own housing in the most accessible place on the engine block.
Such a filter consists of a housing and a filter element inserted into the housing.
Having learned that during operation all engine parts get very hot, you could assume that the oil that lubricates these very parts also heats up, reaching decent temperatures. And with severe overheating, engine oil begins to lose its properties very rapidly - all this can result in rather disastrous consequences for the engine.
Note
When the engine is running, the temperature of the engine oil should not rise too much to avoid a drop in its viscosity.
To keep the temperature of the engine oil in the most effective range, an oil cooler is installed, which is sometimes similar to a radiator for a cooling system (see figure 4.33). With air cooling, a tubular-type oil cooler included in the oil line is placed in front of the radiator of the engine water cooling system.
Note
If the design assumes liquid cooling of the oil, then it is called a cooler, not a radiator (schematically, such a cooler can be seen in Figure 4.32).
Note
The water-cooled radiator provides not only cooling of the oil during heavy-duty operation, but also a quick warm-up of the oil when the engine is started.
An oil pan is most often a stamped part that looks like a bowl or kitchen tray. This is a container in which the engine oil is located, from there it is supplied through the oil receiver (Figure 4.38) to all rubbing parts and flows down there after lubricating these parts. The chapter "Maintenance" describes the dipstick with which the engine oil level is measured. So, this probe, or rather its thin plate with applied marks, is inserted into the pallet.
Attention
Oil must be poured into the sump to a certain level, which must be maintained during engine operation. If the crankcase is overfilled, oil will spray excessively onto the cylinder walls and can enter the combustion chambers, thereby increasing carbon formation in the combustion chambers. Foaming of the oil is also possible, which leads to a significant drop in pressure in the system and, if not stopped in time, to engine failure.
It is also obvious that a lack of oil in the system can lead to the so-called oil starvation, which is why there are frequent cases of cranking of the liners in the main bearings of the crankshaft.
The crankcase is the largest body part of the engine. It can be cast with the cylinder block, or it can be a separate piece bolted to the cylinder block.
In most modern cars, crankcase forced ventilation systems are installed. Such a system usually includes valves and pipes that connect the crankcase cavity to the intake manifold.
The crankcase ventilation itself is extremely important for the normal operation of the engine. The fact is that, one way or another, the exhaust gases through the gaps of the piston group enter the engine crankcase. Gases are also formed when engine oil comes into contact with hot engine parts. The escaping exhaust gases, acting on the engine oil, dilute it, which leads to a decrease in service life and a loss of efficiency. Also, depending on the operating mode of the engine, gases trapped in the crankcase can sharply increase the excess pressure, which will lead to the extrusion of the sealing cuffs (oil seals) and gaskets. It is for this that the valves are installed, controlled by electronics, which are responsible for the ventilation of the crankcase.
For the lubrication of engines, oils of mineral (now rare), semi-synthetic and synthetic origin are used.
To improve the quality of the oil, special additives (special chemical compounds) are added to it, which increase the lubricity of the oil, make its viscosity more stable, lower the pour point, and reduce the oxidizing effect of the oil. Additives in the oil also help to wash out resinous deposits from the gaps of rubbing parts, etc.
Depending on the season and climatic conditions, oils of different viscosities should be used to lubricate the engine. In winter, the viscosity of the oil should be less, since oil with a high viscosity at low temperatures thickens and in a cold engine it will not penetrate well into the gaps of rubbing parts, and it will also be difficult to fill in oil and start a cold engine.
In summer, the viscosity of the oil should be higher, since oil with a low viscosity at elevated temperatures becomes even more liquid and does not provide normal engine lubrication. However, at the moment, multigrade engine oils are common.
Below we consider the designation of the viscosity of oils according to the SAE classification (Society of Automotive Engineers).
This designation has two numbers separated by the letter W - this indicates that the oil is multigrade. In this case, the first figure indicates the minimum negative temperature at which the engine crankshaft can be cranked. So, 0W40 oil should be pumped from -35 ° С, 15W40 - from -20 ° С. The second figure determines the viscosity of the oil at a temperature of 100 ° C, or more precisely, not the viscosity itself, but the permissible range of its change. So, for "30" the viscosity at 100 ° C can vary in the range from 9.3 to 12.5 cSt (centistokes are the units of viscosity measurement), for "40" - from 12.5 to 16.5 cSt, and for "50" - from 16.3 to 21.9 cSt ... That is, the kinematic viscosity within the permissible range can vary by 10 ... 15%.
In parallel with the SAE classification, which characterizes the viscosity of engine oil, there is an API (American Petroleum Institute) classification, which determines its applicability to a particular engine.
The oil brand includes an index consisting of two letters, the first of which determines the type of engine: S (Service Station) - gasoline engines and C (Commercial) - diesel engines; the second (A, B, C, D, E, F, G, H, J, L, M) determines the level of performance. The brand of oil can be fractional, then the oil is universal from the point of view of application - for gasoline and diesel engines.
