crank mechanism(KShM) serves to convert the rectilinear reciprocating motion of the piston into the rotational motion of the crankshaft.
The crankshaft consists of fixed and moving parts. The group of stationary parts consists of the cylinder block, cylinder heads, liners, liners, and main bearing caps.
The group of moving parts includes pistons, piston rings, piston pins, connecting rods, and a crankshaft with a flywheel.
Cylinder block is the basic part (frame) of the engine (Fig. 3). All main mechanisms and engine systems are installed on it.
Figure 3. Fixed parts of the crank mechanism: 1 – timing gear block cover; 2 – steel asbestos gasket; 2 – cylinder head; 4, 10 – inlet holes of the water jacket; 5, 9 – outlet holes of the water jacket; 6, 8 – channels for supplying a combustible mixture; 11 – valve seat; 12 – sleeve; 13 – fastening studs; 14 – upper part; 15 – cylinder block; 16 – sleeve sockets
In automobile and tractor multi-cylinder liquid-cooled engines, all cylinders are made in the form of a common casting, which is called a cylinder block. This design has the highest rigidity and good manufacturability. Currently, only air-cooled engines are manufactured with separate cylinders.
The cylinder block operates under conditions of significant up to 2000 °C and uneven heating and pressure (9.0...10.0 MPa). To withstand significant force and temperature loads, the cylinder block must have high rigidity, ensuring minimal deformation of all its elements, guarantee the tightness of all cavities (cylinders, cooling jacket, channels, etc.), have a long service life, simple and technological design .
Gray cast iron or aluminum alloys are used to make the cylinder block. The most preferred material for the manufacture of a cylinder block is currently cast iron, because... it is cheap, has great strength and is not susceptible to temperature deformation.
At the end of the sixties, the domestic industry mastered the casting of cast iron blocks with a wall thickness of 2.5...3.5 mm. Such blocks are characterized by high strength, rigidity and dimensional stability, and are almost equal in weight to aluminum ones.
A significant disadvantage of blocks made of aluminum alloys is their increased thermal expansion and relatively low mechanical qualities.
The arrangement of the cylinders can be single-row (vertical or inclined), double-row or V-shaped, with a camber angle between the cylinders of 60°, 75°, 90°. Engines with a camber angle of 180° are called boxer engines. The V-shaped layout became widespread in the 80s of the 20th century, as it ensures greater compactness and a lower specific weight of the engine. In this case, the rigidity of the crankshaft and its supports increases, which helps to increase the service life of the engine. The shorter length of the engine makes it easier to arrange it on a vehicle and, with the same wheelbase, allows for a larger usable area of the cargo platform.
On engines with a single-row cylinder arrangement, they are numbered starting from the front one. On V-shaped engines, numbers are first assigned to the right bank of cylinders, starting with the front one, and then the left bank is marked.
The cylinder in most automobile and tractor engines is made in the form of liners installed in the block. Based on the installation method, sleeves are divided into dry and wet.
Wet liners, washed from the outside with coolant, provide better heat removal and are more convenient for repairs, because can be easily replaced without the use of special tools and accessories.
The tightness of the wet sleeve is ensured by sealing the lower part with a rubber ring and installing a copper gasket under the upper shoulder. The use of wet liners improves the removal of excess heat from the cylinders, but reduces the rigidity of the cylinder block.
Dry liners are used primarily in two-stroke engines, where the use of wet liners is difficult.
The sleeve perceives high pressure of working gases having a significant temperature. Therefore, liners are made, as a rule, from alloy cast iron, which is well resistant to erosive and abrasive wear and has satisfactory corrosion resistance. The inner surface of the liner - the cylinder mirror - is carefully processed.
Since the operating conditions of the upper part of the liner are the most severe, and it wears out most intensively, in modern engines, uniform wear of the cylinders along the height is ensured by short inserts made of anti-corrosion high-alloy austenitic cast iron (niresist). The use of such an insert increases the service life of the sleeves by 2.5 times.
Cylinder head serves to accommodate combustion chambers, intake and exhaust valves, spark plugs or injectors.
During engine operation, the cylinder head is exposed to high temperatures and pressures. The heating of individual parts of the head is uneven, because some of them come into contact with combustion products having a temperature of up to 2500 ° C, while others are washed by coolant.
Basic requirements for the design of the cylinder head: - high rigidity, eliminating deformation from mechanical loads and warping at operating temperatures; simplicity; manufacturability of design and low weight.
The cylinder head is made of cast iron or aluminum alloy. The choice of material depends on the type of engine. In carburetor engines, where the combustible mixture is compressed, preference is given to more thermally conductive aluminum alloys, since this ensures knock-free operation. In diesel engines where air is compressed, a cast iron cylinder head helps raise the temperature of the walls of the combustion chambers, which improves the flow of the operating process, especially when starting in cold weather.
Cylinder heads can be made individual or common. Individual heads are typically used in air-cooled engines. Most liquid-cooled engines use common heads for each cylinder bank. In some cases, with a large cylinder block length, heads are used for a group of two or three cylinders (for example, for the YaMZ-240 and A=01 L engine).
The YaMZ-740 engine has separate cylinder heads for each cylinder. The use of separate heads increases engine reliability, avoids head skewing due to uneven tightening and gas breakthrough through the gasket.
In carburetor engines and some types of diesel engines, the combustion chambers are usually located in the cylinder heads. The shape and location of the combustion chambers, intake and exhaust channels are an important design parameter that determines the power and economic performance of engines.
The shape of the combustion chamber should provide the best conditions for filling the cylinder with fresh charge, complete and knock-free combustion of the mixture, as well as good cleaning of the cylinder from combustion products.
Currently, diesel engines prefer combustion chambers located in the pistons. Such chambers have a smaller surface and, therefore, small heat losses. Engines with combustion chambers in the piston have higher anti-knock properties and an increased filling factor.
The technology for manufacturing cylinder heads in engines with a combustion chamber in a piston is not complicated. The chamber in the piston is easy to obtain by casting and subsequent machining to bring the volume of the chamber to the specified volume with high accuracy.
Long-term operation of the cylinder head without deformation and warping is ensured by rational cooling, i.e. more intensive heat removal from its most heated parts.
connecting rod technical repair
Purpose of KShM. The crank mechanism converts the rectilinear reciprocating movement of the pistons, which perceive gas pressure, into the rotational movement of the crankshaft.
Types and types of CVM
Composition of the KShM. The parts of the crank mechanism can be divided into two groups: moving and stationary. The first includes the piston with rings and piston pin, connecting rod, crankshaft and flywheel, the second includes the cylinder block, cylinder head, timing gear block cover and sump (crankcase). Both groups also include fasteners.
Design of parts. The cylinder head is designed to close the cylinder and houses the intake and exhaust ports and valves, as well as the injector or spark plug. By type, cylinder heads are divided into individual (a), group (b) and general (c).
The cylinder head is usually made of aluminum alloys using precision casting methods followed by machining and has a very complex shape. The head is attached to the cylinder block with bolts or studs, which are tightened in a certain sequence and with a certain tightening torque recommended by the manufacturer.
A cylinder is one of the main parts of machines and mechanisms: a hollow part with a cylindrical inner surface in which a piston moves. Cylinders, just like the cylinder head, are: individual, group and general.
There are two types of sleeves:
“Dry” are liners that do not have direct contact with the coolant.
“Wet” are liners whose outer surface is washed by coolant.
Wet sleeves provide good heat dissipation and can be easily replaced during repairs. They are most often used in diesel engines with a cylinder diameter greater than 120 mm, but are sometimes used in engines with a smaller cylinder diameter. Dry cartridges are easier to manufacture. Engines equipped with dry liners have good maintainability. In case of wear, the liner can be easily replaced without boring the cylinders. Dry liners can also be used when rebuilding an engine that has not previously used liners.
In most modern passenger car engines, the cylinders are made directly by boring into the cylinder block. In the case where the block is aluminum, special coatings are applied to the cylinder walls, and special requirements are imposed on the mating parts (pistons and rings).
The inner surface of the liner is subjected to special treatment - honing, chrome plating, nitriding. The sleeves are cast from high strength cast iron or special steels. The cylinder block jackets and housing are usually made of the same material as the engine frame.
A piston is a part designed to cyclically perceive the pressure of expanding gases and convert it into translational mechanical movement, which is then perceived by the crank mechanism. It also serves to perform auxiliary strokes for cleaning and filling the cylinder. As a rule, it is equipped with piston rings to improve the tightness of the cylinder-piston system. Pistons can be composite or non-composite.
The piston is divided into two parts: the head and the guide part (skirt). The head includes the bottom, combustion chamber and ring grooves. The skirt has two tabs for a finger hole. There are two types of rings: compression rings, which serve to prevent gas leakage from the space above the piston, and oil scraper rings, designed to remove oil from the cylinder walls.
The piston pin, which serves to articulate the piston with the connecting rod, is made of hollow steel with surface hardening by high-frequency currents. From longitudinal movement, which could cause scuffing on the cylinder walls, the pin is held in the piston bosses by means of two retaining rings inserted into the annular recesses. Fingers can be fixed or loose.
The connecting rod is designed to connect the piston to the crankshaft through a pin. Performs a complex rocking motion. Consists of three parts: the upper head of the connecting rod, the rod, the lower head with a cover for mounting on the crankshaft.
The crankshaft is designed to transmit torque to the consumer and at the same time provide reciprocating movement of the piston due to rotation of the crank. The crankshaft has a nose and a shank on which the flywheel is mounted.
The flywheel is a massive metal disk that is mounted on the engine crankshaft. During the power stroke, the piston, through the connecting rod and crank, spins the engine crankshaft, which transfers the reserve of inertia to the flywheel. The flywheel transmits torque through the clutch to the gearbox.
The inertia stored in the mass of the flywheel allows it, in reverse order, through the crankshaft, connecting rod and piston to carry out the preparatory strokes of the engine operating cycle. That is, the piston moves up (during the exhaust and compression stroke) and down (during the intake stroke), precisely due to the energy given off by the flywheel. If the engine has several cylinders operating in a certain order, then the preparatory strokes in some cylinders are performed due to the energy developed in others, and of course the flywheel also helps.
The main moving parts of the internal combustion engine are part of the crank mechanism, the purpose of which is to convert the reciprocating motion of the piston into the rotational motion of the crankshaft. Depending on the design of the crank mechanism, engines, like their pistons, are trunk and crosshead, single and double acting. Unlike trunk engines, crosshead engines have, along with a piston, connecting rod and crankshaft, a piston rod and a slider (crosshead) that moves along the cross member.
The trunk piston is at the same time a kind of slider, so it has a long guide part called a skirt or trunk. An example of such a piston is the piston of a four-stroke diesel engine, shown in Fig. 43. The piston consists of a head 1 and a throne 7, which has a chamber inside. The piston head includes a bottom and a side surface on which grooves for piston sealing rings 2 and oil scraper rings 3 are located. The same. The groove for the oil scraper rings is located on the bottom of the trunk.
The guide part of the piston has a device for connecting it to the connecting rod, consisting of a piston pin 5, bushings 6 and plugs 4. In practice, two methods of installing a piston pin in the bosses of the guide part of the piston are common: the pin is fixed in the bosses rigidly, the connecting rod is mounted on it motionlessly; the pin is not fixed in the bosses; the connecting rod also has the ability to rotate around it (the so-called floating pin). In the latter case, the pin design (Fig. 43, item 5) has undoubted advantages, since pin wear is reduced and occurs more evenly, and the working conditions of the pin are improved.
Rice. 43. Trunke piston of a four-stroke engine.
With a cylinder diameter of more than 400 mm, the pistons of trunk engines are made detachable.
The pistons of crosshead engines differ from trunk engines in that they have a rigid connection between the piston and the rod. The piston rod usually ends in a flange, which is connected to the piston via studs.
To avoid overheating of the piston bottom in engines with sliders, as well as in trunk engines with large diameter cylinders, artificial cooling of the bottoms is used. For this purpose, fresh or sea water and oil are used.
In Fig. 44 shows a shortened piston of a modern two-stroke supercharged diesel engine. In such diesel engines, the lower cavity of the cylinder is used as a scavenge pump, so the guide part of the piston is significantly shortened (short or shortened piston). The forged steel piston head 4 has grooves on the outside for sealing rings 3, and inside the piston head there is a displacer 5, designed to accelerate the movement of the cooling oil. The guide part of the piston 1, made of cast iron, has grooves for guide rings 2. Inside the guide part there are studs 7 for fastening the piston rod 8 with the piston head through the holes in the guide part. The bottom of the piston is cooled by oil, which is supplied through channel 9 in the piston rod, and discharged from the upper cavity through pipe 6. The most loaded part of all types of pistons is the piston head. During engine operation, hot gases are pressed onto the bottom of the head, which heat it and, in addition, tend to break into the engine. As a result, the bottom of the piston head has a special configuration, determined by the required shape of the combustion chamber, and a cooled inner surface.
Rice. 44. Shortened piston of a two-stroke supercharged diesel engine.
The height of the side surface of the piston head depends on the size and number of piston sealing rings. Piston rings provide not only cylinder seals against gas breakthrough, but also heat transfer from the piston head to the walls of the cylinder working liner. These functions are usually performed by two or three upper rings, and the rest are, as it were, auxiliary, increasing the reliability of their operation. In low-speed engines, five to seven piston rings are usually installed, and in high-speed engines, due to the reduction in the time of gas flow through the leaks between the piston and the cylinder walls, three to five are sufficient.
Piston rings are made of a rectangular or, less commonly, trapezoidal cross-section from a softer metal than the cylinder liner. To make it possible to install the rings in the grooves of the piston, they are made split, and the joint, called the lock, is made with an oblique, stepped (overlapping) or straight cut. Thanks to the split design and spring properties of the material, the piston rings are pressed tightly against the walls of the cylinder liner, preventing the piston from friction against them. This improves the operating conditions of the piston and reduces bushing wear.
Unlike sealing rings, oil scraper rings serve to prevent oil from entering the combustion chamber and removing excess oil from the walls of the cylinder liner.
The engine connecting rod is designed to transmit force from the piston to the crankshaft. It consists of three main parts (Fig. 45): lower head I, rod II and upper head III. Connecting rods, like pistons, are either trunk or crosshead. Their difference is determined mainly by the design of the upper head and the location of the connecting rod in relation to the piston.
Rice. 45. Connecting rod for trunk engine.
The upper connecting rod head of trunk engines (low and medium power engines) is made one-piece. A bronze bushing 2 is pressed into the hole in head 1 (Fig. 45), which acts as a head bearing and serves to connect the connecting rod to the piston using a piston pin. Bushing 2 has an annular groove 3 on the inner surface and holes 4 for supplying lubricant from the central channel 5 drilled in the rod.
Connecting rods of crosshead engines, which mainly include high-power engines (usually two-stroke diesel engines with a cylinder power of more than 300 hp), are made with a split upper head. This head is bolted to the top of the connecting rod, which has the shape of a fork or a rectangular flange. The rod 6 of the connecting rod is made of a circular cross-section with a central channel 5, which is typical for low-speed engines.
The connecting rod rods of high-speed engines usually have an annular or I-beam sectional shape and are often manufactured integrally with the upper half of the lower head, which helps reduce the weight of the connecting rod. The lower head of the connecting rod serves to house a crank bearing, through which the connecting rod is connected to the crank journal of the crankshaft. The head consists of two halves equipped with bronze or steel interchangeable liners, the inner surface of which is filled with a layer of babbitt.
In low-speed engines, the connecting rod is made with a detachable lower head 9, consisting of two steel halves - castings without liners. In this case, a layer of babbitt is poured onto the working surface of each half of the head. This design of the lower head allows it to be quickly replaced in case of failure and makes it possible to adjust the height of the compression chamber of the engine cylinder by changing the thickness of the compression gasket 7 between the connecting rod heel and the upper part of the head. To center the lower head with the connecting rod rod, a protrusion 11 is provided on its upper part.
Both halves of the crank bearing are pulled together by two connecting rod bolts 8, which have two seating belts each, secured with castle nuts and cotter pins. A set of shims 10 in the bearing connector is necessary to regulate the oil gap between the crankshaft journal and the antifriction filler. The gaskets are fixed in the connector with studs and screws.
The crankshaft is one of the most critical, difficult to manufacture and expensive engine parts. The crankshaft experiences significant loads during operation, so high-quality carbon and alloy steels, as well as modified and alloyed cast iron, are used for its manufacture. Due to the complexity of the design, the manufacture of the crankshaft involves labor-intensive and complex processes, and its cost, including material, forging and machining, sometimes amounts to more than 10% of the cost of the entire engine.
The crankshafts of high-speed engines of low and medium power are made solid forged or solid stamped, the shafts of engines of medium and high power are made of two or more parts connected by flanges. For large diameter journals, shafts are made with composite cranks.
Depending on the design and number of engine cylinders, the crankshaft may have a different number of elbows (cranks): in single-row engines it is equal to the number of cylinders, and in double-row (V-shaped) engines it is equal to half the number of cylinders. The shaft elbows are rotated relative to each other at a certain angle, the magnitude of which depends on the number of cylinders and the order of their operation (the order of flash for engines with four, six or more cylinders).
The main elements of the crankshaft (Fig. 46, a) are: crank (or connecting rod) journals 2, frame (or main) journals I and cheeks 3, connecting the journals to each other.
Sometimes, to balance the centrifugal forces of the knee, a counterweight 2 is attached to the cheeks 1 (Fig. 46.6). The crank journals are covered by the bearing of the lower head of the connecting rod, and the frame journals lie in frame bearings located in the foundation frame or crankcase of the engine and are the supports of the crankshaft. Lubrication of the journals is carried out as follows. Oil is supplied to the frame journals under pressure through drillings in the cover and in the upper shell of the frame bearing, then through drillings in the cheek (Fig. 46, c) it is supplied to the crank journal. In hollow crankshafts of high-speed engines, oil enters the shaft cavity and enters the working surfaces of the journals through cavities and radial holes made in them.
Rice. 46. Engine crankshaft.
Frame bearings absorb all loads transmitted to the crankshaft. Each frame bearing consists of two halves: a housing, cast integrally with the frame, and a cover, bolted to the housing. A steel liner is fixed inside the bearing, consisting of two interchangeable halves (upper and lower), filled with an antifriction alloy - babbitt - on the working surface. The length of the liner is usually chosen less than the length of the shaft journal journal. One of the frame bearings (the first from the transmission of rotation to the camshaft) is designed as an installation bearing (Fig. 47).
Rice. 47. Installation frame bearing of the crankshaft.
The length of the insert 7 of the mounting bearing is equal to the length of the shaft journal; it has anti-friction filling 1 not only inside, but also on the end surface. In turn, the frame journal of the shaft at the landing site of this bearing has protruding annular collars. Thus, the mounting bearing ensures a very specific position of the crankshaft relative to the foundation frame. The bearing shell 7 is prevented from rotation and axial movement by an insert 5 located between the bearing cover 3 and the upper half of the shell. The plane of the liner connector coincides with the plane passing through the shaft axis, which is located below the plane of connection of the frame with the engine frame. In the plane of the connector, gaskets 6 are installed on two control pins, designed to regulate the oil gap between the liner and the shaft journal.
Bearing cover 3 is made of cast steel. It has a through vertical hole in the center for supplying lubricant to the shaft journal. In the upper half of the liner there is the same coaxial hole, from which the oil enters the annular oil groove 4 on the surface of the anti-friction filling, and then into the oil cooler 2.
A flywheel is usually attached to the rear end of the crankshaft, designed to reduce and equalize the angular speed of rotation of the shaft. In addition, the inertia of the flywheel facilitates the transition of the connecting rod with the piston through dead spots. The size and weight of the flywheel are inversely related to the number of engine cylinders: the greater the number of cylinders, the less the weight of the flywheel should be. Often, a flywheel, in particular its disk, is used to connect to the propeller shaft, gearbox shaft or electric generator shaft using an elastic coupling.
Main dimensions of KShM VAZ 2110, 2111, 2112
themselves VAZ 2110 engine, they have a lot
interchangeable parts for crankshafts with engines
VAZ 2108, VAZ 2109
Crank mechanism (CSM) converts the rectilinear reciprocating movement of the pistons, which perceive gas pressure, into rotational movement of the crankshaft.
The KShM device can be divided into two groups: movable and .
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connecting rod pivotally connects the piston to the crankshaft crank. It receives from the piston and transmits to the crankshaft the gas pressure force during the power stroke, ensures the movement of the pistons during auxiliary strokes. The connecting rod operates under conditions of significant loads acting along its longitudinal axis. The connecting rod consists of the upper head, in which there is a smooth hole for the piston pin bearing; an I-section rod and a lower head with a split hole for mounting with the crankpin of the crankshaft. The lower head cover is secured with connecting rod bolts. The connecting rod is made by hot stamping from high-quality steel. For a more detailed study, a section "" has been created. |
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To lubricate the piston pin bearing (bronze bushing), there is a hole or slots in the upper head of the connecting rod. In YaMZ engines, the bearing is lubricated under pressure, for which there is an oil channel in the connecting rod rod. The parting plane of the lower head of the connecting rod can be located at different angles to the longitudinal axis of the connecting rod. The most common are connecting rods with a connector perpendicular to the axis of the rod. In YaMZ engines with a larger diameter than the cylinder diameter, the size of the lower head of the connecting rod, an oblique connector of the lower head is made, since with a direct connector, mounting the connecting rod through the cylinder during engine assembly becomes impossible . To supply oil to the cylinder walls, there is a hole on the lower head of the connecting rod. In order to reduce friction and wear, they are installed in the lower heads of the connecting rods.plain bearings, consisting of two interchangeable liners (upper and lower).
Earbuds are made from steel profiled tape with a thickness of 1.3-1.6 mm for carburetor engines and 2-3.6 mm for diesel engines. An antifriction alloy with a thickness of 0.25-0.4 mm is applied to the tape - a high-tin aluminum alloy (for carburetor engines). KamAZ diesel engines use three-layer liners filled with lead bronze. The connecting rod bearings are installed in the lower head of the connecting rod with an interference fit of 0.03-0.04 mm. From axial mixing and rotation, the liners are held in their sockets by antennae that fit into grooves, which, when assembling the connecting rod and cap, should be located on one side of the connecting rod.
2. Engine crankshaft malfunctions
A crank mechanism is a mechanism that carries out the working process of the power unit. Main purpose crank mechanism- conversion of the reciprocating movement of all pistons into rotational movement of the crankshaft.
The crank mechanism determines the type of power unit by the arrangement of the cylinders. In automobile engines (see the design of a car engine), various options for crank mechanisms are used:
The components of the crank mechanism are divided into
In addition, the crank mechanism includes a variety of fasteners, as well as connecting rod and mounting bearings.
When considering the design of a crankshaft, it is necessary to highlight the main elements of its design: crankshaft, main journal, connecting rod journal, connecting rods, liners, piston rings (oil scraper and compression rings), pins and pistons (see piston operation).
The complex design of the shaft ensures the receipt and transmission of energy from the piston and connecting rod to subsequent components and assemblies. The shaft itself is assembled from elements called elbows. The knees are connected by cylinders located offset relative to the main central axis in a certain order. In technical language, the name of these cylinders is necks. Those journals that are offset are attached to the connecting rods, hence the name - connecting rods. The necks located along the main axis are molars. Due to the arrangement of the connecting rod journals with an offset relative to the central axis, a lever is formed. The piston, moving downwards, causes the crankshaft to rotate through the connecting rod.
Shaft design options are shown in the following figure.
Depending on the number of cylinders, as well as the design solutions of the internal combustion engine according to the arrangement of the cylinders, it can be single-row or double-row.
In the first case (1), the cylinders are located in the same plane relative to the crankshaft. More specifically, they are all located vertically on the engine, along the central axis, and the shaft itself is located at the bottom. In a two-row engine (items 2 and 3), the cylinders are placed in two rows at an angle to each other of 60, 90 or 180°, that is, opposite to each other. The question arises: “Why?” Let's turn to physics. The energy from the combustion of the working mixture is very large and a significant share of its repayment falls on the main journals of the crankshaft, which, although iron, have a certain margin of strength and service life. In a four-cylinder car engine, this issue is solved simply: 4 cylinders - 4 strokes of the working cycle in turn. As a result, the load on the crankshaft is evenly distributed in all areas. In those internal combustion engines where there are more cylinders or more power is required, they are placed in a “V” shape, further softening the load on the crankshaft. Thus, the energy is not absorbed vertically, but at an angle, which significantly softens the load on the crankshaft.
After a brief examination of the crankshaft design, it is also necessary to pay attention to the crankshaft. Speaking about the load on the crankshaft, it is worth focusing on the bearings of the crankshaft journals. Consider the connection of the connecting rod to the engine crankshaft.
The overloads that the shaft experiences are beyond the strength of ball bearings. Here there is enormous pressure, high temperature, inaccessibility of lubrication of rubbing elements and high rotation speed. Therefore, it is for the journals that sliding bearings are used, which ensure the operation of the entire engine. The crankshaft rotates on the bearings. Liners are divided into main and connecting rod. The main bearings form a ring around the main journals of the shaft. From the connecting rod bearings, by analogy - around the connecting rod journals. To reduce friction, the sliding surfaces of the bearings and journals are lubricated with oil supplied through the holes in the crankshaft under high pressure.
Significant work to ensure uniformity and smooth operation of the car engine is performed by the flywheel, which was mentioned earlier. This gear at the end of the shaft smoothes out interruptions in the rotation of the crankshaft and ensures that all “idle” strokes of the working cycle of each cylinder of the internal combustion engine are completed.
Now let's look at the design of the engine piston.
The piston itself is a can turned upside down. This very bottom has a smoothly concave shape, which improves the uniformity of the load on the piston during the working stroke and the formation of the working mixture. The piston is attached to the connecting rod through a pin with a bearing, which ensures the oscillatory movements of the connecting rod. The walls of the piston are called the “skirt”. At first glance, it has a rounded shape, but there are subtle differences.
The first is the thickening of the walls of the skirt in the directions of movement of the connecting rod. The piston and connecting rod alternately press on each other through the mounting pin in the same plane. In the one that actually moves the connecting rod relative to the piston. Consequently, the piston walls experience greater load and pressure there, which is why they are made thicker.
The second is a narrowing of the diameter of the skirt towards the bottom. This was done to prevent the piston from jamming in the cylinder when heated and to ensure lubrication of the rubbing surfaces of the piston skirt and cylinder wall. The walls of the cylinder themselves are so smooth and exquisitely made that they are comparable to the surface of a mirror. But then a gap remains, which significantly affects the tightness of the cylinder during the compression stroke and power stroke.
To solve these opposite problems, there are rings on the piston skirt. It is through them that the piston itself comes into contact with the walls of the cylinder. Each piston has two types of rings - compression and oil control. Comp-res-si-on rings ensure tightness due to the pressure of combusted gases.
The oil scraper rings speak for themselves. Residues of oil supplied to soften friction in the piston-cylinder connection should not remain during the combustion of the fuel-air mixture. Otherwise, detonation or clogging of spark plugs or injectors with residues of heavy fractions of petroleum products present in the oil is possible. And all this disrupts the entire work cycle. Therefore, the oil injected onto the cylinder walls during the “idle” strokes is removed by oil scraper rings during the working stroke of the piston.
All of the engine's cylinders are housed in a single housing called the engine block. Its design is quite complex. It contains a large number of passages for all engine systems, and also serves as a supporting base for many parts and components for the power plant as a whole.
Let's consider the operation diagram of the crankshaft.
The piston is located at the maximum distance from the crankshaft. The connecting rod and crank are aligned in one line. The moment fuel enters the cylinder, the combustion process occurs. Combustion products, in particular expanding gases, help move the piston towards the crankshaft. At the same time, the connecting rod also moves, the lower head of which rotates the crankshaft 180°. Then the connecting rod and its lower head move and rotate back to their original position. The piston also returns to its original position. This process occurs in a circular sequence.
From the description of the operation of the crankshaft, it is clear that the crank mechanism is the main mechanism of the motor, on the operation of which the serviceability of the transport vehicle completely depends. Thus, this unit must be constantly monitored, and if there is any suspicion of a malfunction, you should intervene and fix it immediately, since various breakdowns of the crank mechanism can result in a complete breakdown of the power unit, the repair of which is very expensive.
The main symptoms of a crankshaft malfunction include the following:
Noises and knocks in the motor arise due to wear of its main components and the appearance of an increased gap between the mating components. When the cylinder and piston wear out, as well as when a larger gap occurs between them, a metallic knock appears, which can be clearly heard when the engine is running cold. A sharp and loud metallic knock under any engine operating modes indicates an increased gap between the bushing, the upper head of the connecting rod and the piston pin. Increased knocking and noise with a rapid increase in crankshaft speed indicates wear of the connecting rod or main bearing shells, and a dull knock indicates wear of the main bearing shells. If the wear of the liners is sufficiently large, then, most likely, the oil pressure will drop sharply. In this case, extrusion of the motor is not recommended.
Power drop engine damage occurs when cylinders and pistons wear out, piston rings wear out or get stuck in the grooves, or the cylinder head is not properly tightened. Such malfunctions contribute to a drop in compression in the cylinder. To check compression, there is a special device - a compression meter; measurements must be performed on a warm engine. To do this, you need to unscrew all the spark plugs, and then install the tip of the compression gauge in place of one of them. With the throttle completely open, crank the engine with the starter for three seconds. Using a similar method, all other cylinders are checked sequentially. The compression value must be within the limits specified in the technical specifications of the motor. The compression difference between the cylinders should not be higher than 1 kg/cm2.
Increased oil consumption, excessive fuel consumption, and the formation of smoke in exhaust gases usually occurs when cylinders and rings wear out or when piston rings become stuck. The issue with the position of the ring can be resolved without disassembling the engine by pouring the appropriate liquid into the cylinder through special holes for the spark plug.
Carbon deposits on the combustion chambers and piston heads, it reduces heat and water conductivity, which contributes to engine overheating, increased fuel consumption and a drop in power.
Cracks on the walls of the cooling jacket of the block, as well as the cylinder head, can form due to freezing of the coolant, as a result of overheating of the engine, as a result of filling the cooling system (see engine cooling system) of a hot engine with cold coolant. Cracks in the cylinder block can allow coolant to leak into the cylinders. As a result, the exhaust gases become white.
The main malfunctions of the crankshaft are discussed above.
Fastening works
To prevent the passage of coolant and gases through the cylinder head gasket, you should periodically check the head fastening with a wrench with a special torque handle with a certain sequence and force. The tightening position and sequence of tightening the nuts indicate automobile factories.
A cast iron cylinder head is attached when the engine is in a hot position; an aluminum head, on the contrary, is attached to a cold engine. The need to tighten the fastening of aluminum heads in a cold state is explained by the different coefficient of linear expansion of the material of the studs and bolts and the material of the head. In this regard, tightening the nuts on a very hot engine does not ensure proper tightness of fit to the cylinder head block after the engine has cooled.
The tightening of the crankcase pan attachment bolts to prevent crankcase deformation and leaks is also checked in compliance with the sequence, that is, alternately tightening diametrically opposite bolts.
Checking the condition of the crank mechanism
The technical condition of crank mechanisms is determined:
Oil consumption in a slightly worn engine it is insignificant and can be equal to 0.1-0.25 liters per 100 km. With general significant wear of the engine, oil consumption can be 1 liter per 100 km or more, which, as a rule, is accompanied by copious smoke.
Oil system pressure the motor must comply with the limits established for the given type of motor and the type of oil used. A decrease in oil pressure at low crankshaft speeds of a warmed-up power unit indicates a malfunction in the lubrication system or the presence of unacceptable wear on the engine bearings. A drop in oil pressure on the pressure gauge to 0 indicates a malfunction of the pressure relief valve or pressure gauge.
Compression is an indicator of the tightness of the engine cylinders and characterizes the condition of the valves, cylinders and pistons. The tightness of the cylinders can be determined using a compression gauge. The change in pressure (compression) is checked after pre-heating the engine to 80°C with the spark plugs removed. Having installed the tip of the compression gauge in the holes for the spark plugs, turn the engine crankshaft 10 - 14 revolutions with the starter and record the readings of the compression gauge. The check is performed 3 times for each cylinder. If the compression readings are 30 - 40% below the established norm, this indicates a malfunction (burning of piston rings or their breakage, damage to the cylinder head gasket or leaking valves).
Vacuum in the intake pipe the motor is measured with a vacuum gauge. The vacuum value for engines operating in steady state can vary from the wear of the cylinder-piston group, as well as from the condition of the gas distribution elements (see gas distribution mechanism), carburetor adjustment (see carburetor structure) and ignition installations. Thus, this verification method is general and does not make it possible to identify a specific malfunction based on one indicator.
The volume of gases penetrating the engine crankcase, changes due to looseness of the cylinder + piston + piston ring interfaces, which increases with the degree of wear of these parts. The amount of penetrating gases is measured at full engine load.
Maintenance of the crankshaft consists of constantly monitoring the fasteners and tightening loose nuts and bolts of the crankcase, as well as the cylinder head. The cylinder head mounting bolts and stud nuts should be tightened on a warm engine in a certain sequence.
The engine should be kept clean, wiped or washed every day with a brush dipped in kerosene, then wiped with a dry cloth. It must be remembered that dirt saturated with oil and gasoline poses a serious fire hazard if there are any malfunctions in the engine ignition system and engine power supply system, and also contributes to the formation of corrosion.
Periodically, you need to remove the cylinder head and remove all carbon deposits that have formed in the combustion chambers.
Carbon deposits do not conduct heat well. At a certain level of carbon deposits on the valves and pistons, heat transfer to the coolant sharply deteriorates, the engine overheats and its power indicators decrease. In this regard, there is a need for more frequent inclusion of low gears and the need for fuel increases. The intensity of soot formation depends entirely on the type and quality of oil and fuel used for the engine. The most intense carbon formation occurs when using low-octane gasoline with a sufficiently high boiling point. The knocks that occur in this case during engine operation are of a detonation nature and ultimately lead to a decrease in the service life of the engine.
Carbon deposits must be removed from the combustion chambers, from the valve stems and heads, from the inlet channels of the cylinder block, and from the piston heads. It is recommended to remove carbon deposits using wire brushes or metal scrapers. Pre-soften the carbon deposits with kerosene.
When subsequently assembling the engine, the head gasket must be installed in such a way that the side of the gasket, on which there is a continuous edging of the jumpers between the edges of the holes for the combustion chambers, is directed towards the head of the block.
It is worth considering that while driving a car outside the city for 60 minutes at a speed of 65-80 km/h, the cylinders are burned off (cleaned) of carbon deposits.
With proper regular maintenance of the crankshaft, its service life will extend for many years.
