Engine lubrication system
Parts of the crank and gas distribution mechanisms move relative to each other. This movement is impeded by the friction force, the magnitude of which depends on the relative speed of movement, the specific pressure of the parts on one another, and on the accuracy of processing the rubbing surfaces. The engine power is wasted to overcome the frictional forces. In addition, friction between parts causes them to heat up. With excessive heating, the gaps between the parts will decrease so much that the part stops moving, i.e. jammed.
One of the most effective ways to reduce friction is to introduce a layer of lubricant between the rubbing surfaces. The grease, adhering to the surface, creates a strong film on it, which, separating the parts, replaces the dry friction between them by the friction of the lubricant particles among themselves. Since the oil circulates continuously in a running engine, it simultaneously cools the rubbing parts and carries away the solid particles formed as a result of their wear. In addition, oil lubricated parts are less susceptible to corrosion, and the gaps between them are significantly tightened.
For modern lubrication systems, in addition to the above,
management functions are also assigned. Engine oil works in hydraulic compensators for valve thermal clearances, hydraulic tensioners of the timing drive, and in variable valve timing systems.
The oil supply to the rubbing surfaces must be uninterrupted. In case of insufficient oil supply, engine power is lost, wear of parts increases, and as a result of their heating, bearings may melt, piston seizure and engine stop. Oversupply of oil will seep into the combustion chamber, which increases carbon build-up and impairs spark plug performance.
🚗 How it works
Since individual engine parts operate in different conditions, their lubrication must also be different. Oil is supplied to the most loaded parts under pressure, and to less loaded parts - by gravity or spray. Systems in which parts are lubricated in different ways are called combined systems.
When the engine is running, the oil pump ensures continuous circulation of oil through the system. Under pressure, it enters the oil filter, and then to the main and connecting rod bearings of the crankshaft, piston pins, supports and cams of the camshaft, the axles of the rocker arms of the valve drive. Depending on the design of the engine, oil is supplied under pressure to the turbocharger shaft, to the inner surface of the pistons for cooling them, to the valve pushers and actuators of the phase rotation systems.
Oil enters the cylinder surface by splashing through holes in the lower connecting rod head or a nozzle in the lower part of the cylinder block. When it hits the cylinder walls, it reduces friction during piston movement and provides freedom of movement of the compression and oil scraper rings.
Oil drops fall from the pressure-lubricated parts into the sump. Getting on the rotating parts of the crank mechanism, they spray out, creating a so-called oil mist in the crankcase. By settling on engine parts, it provides lubrication. The precipitated oil then flows into the oil pan and the cycle is repeated again.
🚗 Lubrication system design
The engine lubrication system includes a sump with an oil drain plug, an oil pump with a pressure reducing valve, an oil receiver with a strainer, an oil filter with safety and bypass valves, a system of oil channels in the cylinder block, cylinder head, crankshaft and camshafts, oil pressure sensor with control lamp and oil filler neck. Some engines include an oil cooler in the lubrication system.
The sump is a storage tank for oil. The oil level in the sump is monitored using a dipstick, on which the marks of the maximum and minimum possible level are applied. From the sump, the oil flows through an oil receiver with a strainer to the oil pump. The oil receiver can be fixed or floating type. The capacity of the lubrication system of a passenger car, depending on the volume and type of engine, can be from 3.5 to 7.5 liters. Moreover, the capacity indicated in the instructions has two meanings - one refers directly to the engine lubrication system, and the second indicates the required amount of oil, taking into account the capacity of the oil filter.
The engine oil pressure must be between 2 and 15 bar, depending on the design. The oil pump serves to create the required pressure in the lubrication system and supply oil to the rubbing surfaces. The oil pump can be driven by a crankshaft, camshaft or an additional drive shaft.
Gear pumps are mainly used in automobile engines due to their simplicity and low cost. They are of two types: with external and internal gearing. In the first, the pump gears are located side by side, and in the second - one gear inside the other. Therefore, the internal gear pump is more compact. The drive gear is mounted on the drive shaft, and the driven gear rotates freely. The gears are installed in the pump housing with small clearances. During operation, gears rotating in different directions capture oil from the sump and transfer it in the cavities between the teeth into the oil line. With an increase in the crankshaft speed, the pump performance increases proportionally, while the oil consumption by the engine itself does not change significantly. In addition, gear pumps do not create high pressure, take up to 8% of engine power and are not always capable of ensuring the operation of modern car systems (for example, variable valve timing systems). Therefore, variable displacement oil pumps have been developed that are capable of generating higher oil pressures, take less power from the engine and maintain constant system pressure regardless of crankshaft speed. Such designs include, for example, a vane (vane) pump, a gerotor pump, and a swing valve pump.
Some engines are fitted with two-section oil pumps. The first section is designed to supply oil to the engine lubrication system, the second - to supply oil to the oil cooler.
The performance of the oil pump is calculated with a margin so that even under the most unfavorable operating conditions (high temperatures, wear of parts, etc.), the pressure in the system remains sufficient to supply oil to the rubbing surfaces. However, in this case, the oil pressure in a cold engine may exceed the permissible values. To prevent the destruction of oil lines in lubrication systems with an unregulated pump, a pressure reducing valve is used. The most common design is a plunger and spring mounted in a body with holes. With excess pressure in the system, the plunger, compressing the spring, moves, and part of the oil goes back to the oil pan. The amount of pressure at which the valve is triggered depends on the stiffness of the spring. A pressure reducing valve is installed at the outlet of the oil pump. In some systems, a pressure reducing valve is also installed at the end of the oil line - to prevent pressure fluctuations due to changes in the hydraulic resistance of the system and oil consumption.
The quality of the oil in the engine decreases over time, as it becomes clogged with fine metal dust, which appears as a result of wear of parts, and carbon particles that form as a result of its combustion on the cylinder walls. At high temperatures of parts, the oil is coked, resins and lacquer-like products are formed. All these impurities are harmful and have a significant effect on accelerating the wear of car parts. To clean the oil from harmful impurities, a filter is installed in the lubrication system, which is replaced with each oil change.
During hot seasons and when the vehicle is used in difficult road conditions, the oil temperature rises so much that it becomes very liquid and the pressure in the lubrication system drops. Oil coolers may be included in the lubrication system to prevent oil dilution. They come in two types: air-cooled and liquid-cooled. The first are installed before
🚗 Major malfunctions of the lubrication system
Outward signs of a lubrication system malfunction are low or high oil pressure in the system and deterioration of oil quality due to contamination.
A decrease in pressure is possible as a result of an insufficient oil level, its dilution, leakage through leaks in the connections, contamination of the oil receiver strainer, wear of the oil pump parts, jamming of the pressure reducing valve in the open position and due to wear of the crankshaft and camshaft bearings.
The oil level should be checked on a warm engine, but not immediately after stopping it, but after 3-5 minutes so that the oil has time to drain. If the level is below normal, it is necessary to add oil to the oil pan, having previously identified and eliminated the cause. An external inspection reveals oil leaks from under the camshaft drive cover, valve cover, cylinder block, oil filter, as well as from the filler plug, through the oil pressure sensor fitting, from under the oil separator cover of the crankcase ventilation system and through the dipstick seal. The oil level can drop due to worn valve stem seals, wear and coking of piston rings or breakage, wear of pistons and their grooves, wear of engine cylinders, wear of valve stems and their guide bushings, as well as coking of oil scraper ring slots or filling them with oil deposits. These faults lead to increased oil consumption and, consequently, a drop in system pressure.
An increase in pressure in the lubrication system is possible due to the use of oil with a high viscosity, a seized pressure reducing valve in the closed position and clogged oil lines.
Since the crankshaft makes a rotational movement, under the action of centrifugal forces, engine wear products are deposited on the walls of its oil channels. Over time, the flow area of these channels decreases so much that the connecting rod bearing begins to experience oil starvation. Increased contamination of the channels is facilitated by the use of low-quality oil or not appropriate for the engine, regular operation of the engine in intensive modes and untimely oil change.
The channels for supplying oil to the hydraulic compensators can also coke over time, and then the hydraulic compensator stops working. If it gets stuck when the valve is open, it will knock the valve out by the piston. In this case, the hydraulic compensator itself is destroyed and damage to the camshaft, pistons, connecting rods and the appearance of cracks in the cylinder head are possible. Oil problems are also likely with the hydraulic tensioners, which provide tension on the belts and camshaft drive chains. Their channels are also clogged, which can cause timing breakdown and destruction of the cylinder head. If there is a timing mechanism for changing the valve timing, dirt can provoke a failure or disruption of its operation.
When operating the vehicle, there may be cases when the oil pressure gauge may be faulty. To check the correct operation of the pressure indicator, instead of the sensor, screw the connection of the control pressure gauge and, comparing the readings with the tested device, judge its operation.