One of the component parts of the engine is the crank mechanism (abbreviated as KShM). This is what we will discuss in our article.
The main purpose of the crankshaft is to change the linear movements of the piston to the rotational actions of the crankshaft in the engine, and vice versa.
Scheme of the crank mechanism (CSM): 1 – Connecting rod bearing shell; 2 – Bushing of the upper head of the connecting rod; 3 – Piston rings; 4 – piston; 5 – Piston pin; 6 - Retaining ring; 7 – Connecting rod; 8 – Crankshaft; 9 – Connecting rod bearing cover
This KShM part is presented in the form of a cylinder made of aluminum and some impurities. The components of the piston are: skirt, head, bottom, connected into a single part, but having different functions. At the bottom of the piston, which can have different shapes, there is a combustion chamber. The oblong recesses of the head are intended for rings. Compression rings protect the mechanism from gas breakthroughs. In turn, oil scraper rings ensure the removal of excess oil from the cylinder. The skirt contains two bosses that help position the piston pin, which serves as the connecting link between the piston and connecting rod.
At its core, a piston is a part that transforms fluctuations in gas pressure into a mechanical process and promotes the reverse action - it pumps up pressure through reciprocating activity.
The main purpose of the connecting rod is to transfer the force received from the piston to the crankshaft. In the structure of the connecting rod, there are upper and lower heads; the parts are connected using hinges. An integral part of the part is an I-beam rod. The dismountable lower head creates a strong and precise connection to the crankshaft journal. As for the upper head, it contains a rotating piston pin.
The main role of the crankshaft is to process the force coming from the connecting rod to transform it into torque. The crankshaft is made up of several main connecting rod journals located in bearings. There are special holes in the necks and cheeks that are used as oil lines.
The flywheel is located at the end of the crankshaft. The mechanism is presented in the form of 2 combined disk plates. The toothed side of the part is directly involved in starting the motor.
The purpose of the KShM cylinder is to direct the operation of the pistons. The cylinder block contains mounting points for units, cooling jackets, and bearing cushions. The head of the cylinder block contains the combustion chamber, bushings, seats for spark plugs, valve seats, and channels for intake and exhaust. The top of the cylinder block is protected by a special sealed gasket. At the same time, the cylinder head is covered with a rubber gasket, as well as a stamped cover.
The crank mechanism is designed to convert the reciprocating motion of the piston into the rotational motion of the crankshaft.
The parts of the crank mechanism can be divided into:
In addition, the crank mechanism includes various fasteners, as well as main and connecting rod bearings.
Block crankcase- the main element of the engine frame. It is subject to significant force and thermal influences and must have high strength and rigidity. The crankcase contains cylinders, crankshaft supports, some gas distribution mechanism devices, various components of the lubrication system with its complex network of channels and other auxiliary equipment. The crankcase is made of cast iron or aluminum alloy by casting.
Cylinders are guide elements ⭐ of the crank mechanism. Pistons move inside them. The length of the cylinder generatrix is determined by the stroke of the piston and its dimensions. Cylinders operate under conditions of sharply changing pressure in the above-piston cavity. Their walls come into contact with flames and hot gases with temperatures up to 1500... 2500 °C.
Cylinders must be strong, rigid, heat and wear resistant with limited lubrication. In addition, the cylinder material must have good casting properties and be easy to machine. Typically, cylinders are made from special alloy cast iron, but aluminum alloys and steel can also be used. The inner working surface of the cylinder, called its mirror, is carefully processed and plated with chrome to reduce friction, increase wear resistance and durability.
In liquid-cooled engines, the cylinders may be cast together with the cylinder block or as separate liners installed in the block bores. Between the outer walls of the cylinders and the block there are cavities called a cooling jacket. The latter is filled with liquid that cools the engine. If the cylinder liner is in direct contact with the coolant with its outer surface, then it is called wet. Otherwise it is called dry. The use of replaceable wet liners makes engine repair easier. When installed in a block, wet liners are reliably sealed.
Air-cooled engine cylinders are cast individually. To improve heat dissipation, their outer surfaces are equipped with annular fins. On most air-cooled engines, the cylinders and their heads are secured with common bolts or studs to the top of the crankcase.
In a V-shaped engine, the cylinders of one row may be slightly offset relative to the cylinders of the other row. This is due to the fact that two connecting rods are attached to each crankshaft crank, one of which is intended for the piston of the right half of the block, and the other for the piston of the left half of the block.
A cylinder head is installed on the carefully processed upper plane of the cylinder block, which closes the cylinders from above. In the head above the cylinders there are recesses that form combustion chambers. For liquid-cooled engines, a cooling jacket is provided in the body of the cylinder head, which communicates with the cooling jacket of the cylinder block. With the valves located at the top, the head has seats for them, inlet and outlet channels, threaded holes for installing spark plugs (for gasoline engines) or injectors (for diesel engines), lubrication system lines, mounting and other auxiliary holes. The material for the block head is usually aluminum alloy or cast iron.
A tight connection between the cylinder block and the cylinder head is ensured using bolts or studs with nuts. To seal the joint in order to prevent leakage of gases from the cylinders and coolant from the cooling jacket, a gasket is installed between the cylinder block and the cylinder head. It is usually made of asbestos cardboard and lined with thin steel or copper sheet. Sometimes the gasket is rubbed with graphite on both sides to protect it from sticking.
The lower part of the crankcase, which protects the parts of the crank and other engine mechanisms from contamination, is usually called the sump. In relatively low-power engines, the pan also serves as a reservoir for engine oil. The pallet is most often cast or made from steel sheet by stamping. To eliminate oil leakage, a gasket is installed between the crankcase and the sump (on low-power engines, a sealant - “liquid gasket”) is often used to seal this joint.
The fixed parts of the crank mechanism connected to each other are the core of the engine, which absorbs all the main power and thermal loads, both internal (related to the operation of the engine) and external (due to the transmission and chassis). The force loads transmitted to the engine frame from the vehicle's supporting system (frame, body, housing) and back significantly depend on the method of engine mounting. Usually it is attached at three or four points so that loads caused by distortions of the supporting system that occur when the machine moves over uneven surfaces are not taken into account. The engine mounting must exclude the possibility of its displacement in the horizontal plane under the influence of longitudinal and transverse forces (during acceleration, braking, turning, etc.). To reduce vibration transmitted to the supporting system of the vehicle from a running engine, rubber cushions of various designs are installed between the engine and the sub-engine frame at the mounting points.
The piston group of the crank mechanism is formed by piston assembly with a set of compression and oil scraper rings, piston pin and its fastening parts. Its purpose is to perceive gas pressure during the power stroke and transmit force to the crankshaft through the connecting rod, carry out other auxiliary strokes, and also seal the above-piston cavity of the cylinder to prevent gases from breaking through into the crankcase and the penetration of engine oil into it.
Piston is a metal glass of complex shape, installed in a cylinder with the bottom up. It consists of two main parts. The upper thickened part is called the head, and the lower guide part is called the skirt. The piston head contains a bottom 4 (Fig. a) and walls 2. Grooves 5 for compression rings are machined in the walls. The lower grooves have drainage holes 6 to drain oil. To increase the strength and rigidity of the head, its walls are equipped with massive ribs 3 that connect the walls and bottom with bosses in which the piston pin is installed. Sometimes the inner surface of the bottom is also ribbed.
The skirt has thinner walls than the head. In its middle part there are bosses with holes.
Rice. Designs of pistons with different bottom shapes (a-z) and their elements:
1 - boss; 2 - piston wall; 3 - rib; 4 - piston bottom; 5 - grooves for compression rings; 6 - drainage hole for oil drainage
The piston heads can be flat (see a), convex, concave and shaped (Fig. b-h). Their shape depends on the type of engine and combustion chamber, the adopted method of mixture formation and the manufacturing technology of the pistons. The simplest and most technologically advanced is the flat form. Diesel engines use pistons with concave and shaped bottoms (see Fig. e-h).
When the engine is running, the pistons heat up more than cylinders cooled by liquid or air, so the expansion of the pistons (especially aluminum ones) is greater. Despite the presence of a gap between the cylinder and the piston, jamming of the latter may occur. To prevent jamming, the skirt is given an oval shape (the major axis of the oval is perpendicular to the piston pin axis), the diameter of the skirt is increased compared to the diameter of the head, the skirt is cut (most often a T- or U-shaped cut is made), and compensation inserts are poured into the piston to limit thermal expansion skirts in the plane of swing of the connecting rod, or forcefully cool the internal surfaces of the piston with jets of engine oil under pressure.
A piston subjected to significant force and thermal loads must have high strength, thermal conductivity and wear resistance. In order to reduce inertial forces and moments, it must have a low mass. This is taken into account when choosing the design and material for the piston. Most often the material is aluminum alloy or cast iron. Sometimes steel and magnesium alloys are used. Promising materials for pistons or their individual parts are ceramics and sintered materials that have sufficient strength, high wear resistance, low thermal conductivity, low density and a small coefficient of thermal expansion.
Piston rings provide a tight movable connection between the piston and the cylinder. They prevent the breakthrough of gases from the above-piston cavity into the crankcase and the entry of oil into the combustion chamber. There are compression and oil scraper rings.
Compression rings(two or three) are installed in the upper grooves of the piston. They have a cut called a lock and can therefore spring back. In the free state, the diameter of the ring should be slightly larger than the diameter of the cylinder. When such a ring is inserted into the cylinder in a compressed state, it creates a tight connection. In order to ensure that the ring installed in the cylinder can expand when heated, there must be a gap of 0.2...0.4 mm in the lock. In order to ensure good running-in of compression rings, rings with a tapered outer surface, as well as twisting rings with a chamfer on the edge on the inside or outside, are often used on cylinders. Due to the presence of a chamfer, such rings, when installed in a cylinder, are skewed in cross-section, fitting tightly to the walls of the grooves on the piston.
Oil scraper rings(one or two) remove oil from the cylinder walls, preventing it from entering the combustion chamber. They are located on the piston under the compression rings. Typically, oil scraper rings have an annular groove on the outer cylindrical surface and radial through slots to drain oil, which passes through them to the drainage holes in the piston (see Fig. a). In addition to oil scraper rings with slots for oil drainage, composite rings with axial and radial expanders are used.
To prevent gas leakage from the combustion chamber into the crankcase through the locks of the piston rings, it is necessary to ensure that the locks of adjacent rings are not located on the same straight line.
Piston rings operate under difficult conditions. They are exposed to high temperatures, and lubrication of their outer surfaces, moving at high speed along the cylinder mirror, is not enough. Therefore, high demands are placed on the material for piston rings. Most often, high-grade alloy cast iron is used for their manufacture. Upper compression rings, which operate under the most severe conditions, are usually coated on the outside with porous chrome. Composite oil scraper rings are made of alloy steel.
Piston pin serves for a hinged connection of the piston with the connecting rod. It is a tube passing through the upper head of the connecting rod and installed at its ends into the piston bosses. The piston pin is secured to the bosses by two retaining spring rings located in special grooves of the bosses. This fastening allows the finger (in this case it is called a floating finger) to rotate. Its entire surface becomes working, and it wears out less. The pin axis in the piston bosses can be shifted relative to the cylinder axis by 1.5...2.0 mm in the direction of the greater lateral force. This reduces piston knock in a cold engine.
Piston pins are made of high quality steel. To ensure high wear resistance, their outer cylindrical surface is hardened or carburized, and then ground and polished.
Piston group consists of a fairly large number of parts (piston, rings, pin), the mass of which may fluctuate for technological reasons; within certain limits. If the difference in the mass of the piston groups in different cylinders is significant, then additional inertial loads will arise during engine operation. Therefore, piston groups for one engine are selected so that they differ insignificantly in weight (for heavy engines by no more than 10 g).
The connecting rod group of the crank mechanism consists of:
connecting rod connects the piston to the crankshaft crank and, transforming the reciprocating motion of the piston group into the rotational motion of the crankshaft, performs a complex movement, while being subjected to alternating shock loads. The connecting rod consists of three structural elements: rod 2, upper (piston) head 1 and lower (crank) head 3. The connecting rod rod usually has an I-section. To reduce friction, a bronze bushing 6 with a hole for supplying oil to the rubbing surfaces is pressed into the upper head to reduce friction. The lower head of the connecting rod is split to allow assembly with the crankshaft. For gasoline engines, the head connector is usually located at an angle of 90° to the axis of the connecting rod. In diesel engines, the lower head of the connecting rod 7, as a rule, has an oblique connector. The lower head cover 4 is attached to the connecting rod with two connecting rod bolts, precisely matched to the holes in the connecting rod and the cover to ensure high precision assembly. To prevent the fastening from loosening, the bolt nuts are secured with cotter pins, lock washers or lock nuts. The hole in the lower head is bored together with the cover, so the connecting rod covers cannot be interchangeable.
Rice. Connecting rod group details:
1 - upper connecting rod head; 2 - rod; 3 - lower head of the connecting rod; 4 - lower head cover; 5 - liners; 6 - bushing; 7 - diesel connecting rod; S - main connecting rod of the articulated connecting rod unit
To reduce friction in the connection of the connecting rod with the crankshaft and facilitate engine repair, a connecting rod bearing is installed in the lower head of the connecting rod, which is made in the form of two thin-walled steel liners 5 filled with an antifriction alloy. The inner surface of the liners is precisely adjusted to the crankshaft journals. To fix the liners relative to the head, they have bent antennae that fit into the corresponding grooves in the head. The supply of oil to the rubbing surfaces is provided by annular grooves and holes in the liners.
To ensure good balance of the parts of the crank mechanism, the connecting rod groups of one engine (as well as the piston ones) must have the same mass with its corresponding distribution between the upper and lower heads of the connecting rod.
V-twin engines sometimes use articulated connecting rod assemblies, consisting of paired connecting rods. The main connecting rod 8, which has a conventional design, is connected to the piston of one row. An auxiliary trailing connecting rod, connected by the upper head to a piston of another row, is pivotally attached with a pin to the lower head of the main connecting rod by the lower head.
Connected to the piston by means of a connecting rod, it absorbs the forces acting on the piston. A torque is generated on it, which is then transmitted to the transmission, and is also used to drive other mechanisms and units. Under the influence of inertial forces and gas pressure that sharply change in magnitude and direction, the crankshaft rotates unevenly, experiencing torsional vibrations, being subjected to twisting, bending, compression and tension, and also receiving thermal loads. Therefore, it must have sufficient strength, rigidity and wear resistance with a relatively low weight.
Crankshaft designs are complex. Their shape is determined by the number and arrangement of cylinders, the order of operation of the engine and the number of main bearings. The main parts of the crankshaft are main journals 3, connecting rod journals 2, cheeks 4, counterweights 5, front end (toe 1) and rear end (shank 6) with a flange.
The lower heads of the connecting rods are attached to the connecting rod journals of the crankshaft. The main journals of the shaft are installed in the bearings of the engine crankcase. The main and connecting rod journals are connected using cheeks. A smooth transition from the journals to the cheeks, called a fillet, avoids stress concentrations and possible breakdowns of the crankshaft. Counterweights are designed to unload the main bearings from the centrifugal forces that arise on the crankshaft during its rotation. They are usually made as one piece with the cheeks.
To ensure normal engine operation, engine oil must be supplied under pressure to the working surfaces of the main and connecting rod journals. Oil flows from holes in the crankcase to the main bearings. Then it reaches the connecting rod bearings through special channels in the main journals, cheeks and crankpins. For additional centrifugal oil purification, the connecting rod journals have dirt-collecting cavities closed with plugs.
Crankshafts are made by forging or casting from medium-carbon and alloy steels (high-quality cast iron can also be used). After mechanical and thermal treatment, the main and connecting rod journals are subjected to surface hardening (to increase wear resistance), and then ground and polished. After processing, the shaft is balanced, i.e., such a distribution of its mass relative to the axis of rotation is achieved in which the shaft is in a state of indifferent equilibrium.
Main bearings use thin-walled wear-resistant liners similar to the liners of connecting rod bearings. To absorb axial loads and prevent axial displacement of the crankshaft, one of its main bearings (usually the front one) is made thrust.
Flywheel is attached to the crankshaft shank flange. It is a carefully balanced cast iron disk of a certain mass. In addition to ensuring uniform rotation of the crankshaft, the flywheel helps overcome compression resistance in the cylinders when starting the engine and short-term overloads, for example, when starting a vehicle. A ring gear is attached to the flywheel rim to start the engine from the starter. The surface of the flywheel that comes into contact with the clutch driven disc is ground and polished.
Rice. Crankshaft:
1 - sock; 2 - connecting rod journal; 3 - molar neck; 4 - cheek; 5 - counterweight; 6 - shank with flange
DEVICE AND MAINTENANCE
VEHICLE"
Topic No. 2. General structure and operation of the engine
Lesson No. 2.2. Crank mechanism (CSM)
for training specialists in VUS-837 “drivers of category “C” vehicles”
Moscow 2011
Topic No. 2. General design and operation of the engine(SLIDE No. 1)
Lesson No. 2.2 Crank mechanism (CCM)
Study questions (SLIDE No. 2)
Time: 2 hours.
Location: audience.
Type of lesson: lecture.
Methodical instructions.
Justify to students the importance of the educational issue under consideration. The main provisions should be written down in the notes.
Give specific examples from car operating experience.
Pay attention to the correct note-taking.
Present educational material using frames in Microsoft PowerPoint, diagrams and posters.
Maintain connection with the audience.
Quality control of learning material is carried out by a short survey on the material presented.
Summarize the issue discussed and proceed to present the next educational issue.
Draw conclusions based on the lesson material, summarize the lesson, answer students’ questions. Give a task for independent work.
Introduction
With the rapid increase in the vehicle fleet in Russia, the consumption of fuels and lubricants has increased significantly. Proper operation of the crankshaft, as well as maintaining it in good condition, can significantly reduce fuel consumption. These requirements will only be met if the vehicle is serviced in a timely manner to the prescribed extent.
Proper maintenance is the responsibility of drivers, who must know the rules for caring for the crankshaft and its design.
This lecture discusses the general structure of the CVM, the principle of its operation, the features of the CVM of the KamAZ-740, YaMZ-238 engines, as well as the main causes and symptoms of CVM malfunctions.
Study Question #1.
Purpose, general structure, principles of operation of the crankshaft
The crank mechanism is designed to convert the rectilinear reciprocating movement of the pistons, perceiving the force of gas pressure, into the rotational movement of the crankshaft (Fig. 1), (SLIDE No. 4).
Rice. 1. Crank mechanism (SLIDE No. 4)
Composition of the engine crankshaft.
The engine crank mechanism includes two groups of parts: fixed and movable.
To the motionless details include: the cylinder block, which serves as the core of the engine, the flywheel housing, the cylinders, the cylinder head or cylinder head, and the oil pan. (SLIDE No. 5)
Movable details are pistons with rings and piston pins, connecting rod, crankshaft, flywheel. (SLIDE No. 6)
Cylinder block designed for fastening and assembly on it and inside its main mechanisms and parts of engine systems.
Block head- this is the cover that covers the cylinders
Pallet- protects the crankshaft parts from contamination
Pistons- to perceive gas pressure during the power stroke and transmit force through the pin and connecting rod to the crankshaft.
Composition: bottom, head, skirt. The bottom is flat and absorbs gas pressure. Has reinforcing ribs (to increase strength and heat removal).
The head has annular grooves for compression and oil scraper rings, which serve to seal the combustion chamber and ensure tightness. When the working mixture or diesel fuel burns, a significant amount of heat is absorbed by the piston and removed from it by the piston rings to the cylinder surface.
Compression rings- fit tightly to the surface of the cylinder, which prevents gases from breaking through into the engine crankcase and oil from entering the combustion chamber from the cylinder walls.
Oil scraper ring- removes excess oil from the cylinder walls and takes it to the pin. Two through grooves - to drain oil into the piston.
The oil scraper ring is dismountable.
Piston pin designed to attach the connecting rod to the piston and transfer force from the piston to the connecting rod. Type - floating.
connecting rod- to perceive the force from the piston pin and transmit it to the crankshaft, as well as to convert the reciprocating movement of the piston into rotational movement of the crankshaft.
There are liners installed in the lower head of the connecting rod. The inserts have holes for oil passage. A hole is drilled in the lower head of the connecting rod to supply oil to the cylinder walls and to the camshaft.
Crankshaft designed to absorb forces from individual connecting rods, convert translational motion into rotational motion together with them, and transmit torque to the vehicle transmission, as well as to drive various mechanisms and engine parts (timing mechanism, water pump, oil pump, fan, power steering pump, generator, compressor). KV - steel, with channels for lubrication of main and connecting rod journals and centrifugal traps for oil purification.
The connecting rod journals and cheeks form the CRANK. Counterweights - to unload the main bearings from the action of inertial forces, as well as to balance the CV from the action of the moments of centrifugal forces.
Flywheel- to accumulate energy during the power stroke, rotate the CV during auxiliary strokes, reduce the unevenness of shaft rotation, smooth out the moment of transition of the crankshaft parts through dead spots, facilitate engine starting and moving off the vehicle. A ring gear is installed on the rim to start the engine from the starter. The flywheel is attached to the crankshaft flange with high quality steel bolts. The crankshaft assembly with flywheel and clutch is subjected to static and dynamic balancing so that unbalanced inertial forces do not cause engine vibration and severe wear of the main bearings.
The operating principle of the crank mechanism.(SLIDE No. 7).
The piston is farthest from the crankshaft. The connecting rod and crank (cheeks) of the crankshaft seem to stretch out in one line. The fuel begins to burn in the cylinder. Expanding gases (combustion products) begin to move the piston towards the crankshaft, the connecting rod also moves along with the piston. At this time, the lower head of the connecting rod, connected to the crankshaft, rotates the crankshaft relative to its axis. By rotating the crankshaft 180°, the lower end of the connecting rod, together with the connecting rod journal, will begin to move back to its original position towards the piston. Therefore, the piston will also begin to move in reverse. Thus, the piston either moves away or approaches the crankshaft. At these extreme points, the piston seems to stop instantly and its speed is zero. Therefore, such points were called “dead.” The position occupied by the piston when it is farthest from the crankshaft - top dead center - is abbreviated as TDC, and the position when the piston is closest to the crankshaft is bottom dead center , - n.m.t.
Rice. 2. The principle of operation of the crank mechanism (SLIDE No. 7)
Conclusions on the issue.
Study Question #2
Features of the design of the main parts of the crankshaft of the studied engines
Block - crankcase. For KamAZ-740 and YaMZ-238 engines, the crankcase is a single casting that combines the cylinder block and the upper half of the crankcase. The cylinder block is designed for mounting and assembly on it and inside its main mechanisms and parts of engine systems (SLIDE No. 9).
The V-shaped engines KamAZ-740 (Fig. 3) and YaMZ-238 have two machined surfaces (planes) in the upper part of the cylinder block on which the heads are installed. The lower part of the block ends with a machined flange for connecting a lubricant tank.
In the middle part of the cylinder block there are holes for installing plain bearings under the camshaft bearing journals. The plane of the block connector can run along the axis of the crankshaft or be shifted downwards relative to it. A stamped steel lubricant container is attached to the bottom of the crankcase to serve as an oil reservoir. Through channels in the block, oil from the lubricant tank is supplied to the rubbing parts of the engine.
The cylinder blocks of the KamAZ-740 and YaMZ-238 engines are cast from alloyed gray cast iron integral with the upper part of the crankcase. They have machined mounting holes for cylinder liners, and on the surfaces mating with the heads there are holes for supplying coolant from the water jacket to the cylinder heads.
For KamAZ-740, the left row of cylinders is shifted forward relative to the right by 29.5 mm. For YaMZ-238, on the contrary, the right is 35 mm relative to the left, which is caused by the installation of two connecting rods on one crankpin of the crankshaft.
The crankcase part of the block is connected to the main bearing caps with main and tie bolts. Centering of the main bearing caps is done by horizontal pins, which are pressed into the joint between the block and the caps, but mostly included in the block to prevent them from falling out when removing the caps.
In addition, the cover of the fifth main support is centered in the longitudinal direction by two vertical pins, ensuring accurate alignment of the bores for the crankshaft thrust half-rings on the block and covers.
Boring of the cylinder block for the main bearing shells is carried out assembled with the caps, so the main bearing caps are not interchangeable and are installed in a strictly defined position. They are made of high-strength cast iron. The covers are secured using vertical and horizontal coupling bolts, which are tightened with a regulated torque. For the KamAZ-740 engine, the fastening bolts have a tightening torque of 275-295 N∙m (28-30 kgf∙m), and the coupling bolts have a tightening torque of 147-167 N∙m (15-16 kgf∙m). On each cover there is a serial number of the support, the numbering of which begins from the front end of the block. For the YaMZ-238 engine, vertical bolts are tightened with a torque of 425-455 N∙m (43-47 kgf∙m), and horizontal bolts - 97-117 N∙m (10-12 kgf∙m). The covers are also not interchangeable; each of them has its own number.
On the KamAZ-740 engine, a cover is attached to the front of the block to cover the fluid coupling of the fan drive. At the rear is the flywheel housing, which serves as a cover for the accessory drive mechanism located at the rear end of the block. On the right side of the flywheel housing there is a clamp used to set the fuel injection advance angle and regulate thermal clearances in the valve mechanism. The locking handle is installed in the upper position during operation. It is set to the lower position during adjustment work, while the latch is in engagement with the flywheel, and the piston of the first cylinder is at TDC on the compression stroke.
On the YaMZ-238 engine, a cover is attached to the front of the cylinder block to cover the distribution gears, and the clutch housing is attached to the rear plane of the block. On the right side wall of the cylinder block there are two machined brackets for attaching the starter.
Rice. 3. Cylinder block of a V-engine (SLIDE No. 9):
1 – cylinder block; 2 – crankshaft main bearing cover;
3 – cover fastening bolt; 4 – cover fastening bolt
Cylinder liners. The engines are equipped with “wet” type liners, easily removable, made of special cast iron, volumetrically hardened to increase wear resistance. The shell mirror is honed.
The top of the liner is sealed by clamping the top flange of the liner between the block and the head through a gasket. In the “liner – cylinder block” connection, the water cavity is sealed with rubber rings. In the upper part, the ring is installed under the collar in the groove of the liner, and in the lower part - in the bores of the block.
The primary use of wet liners in engines is due to the fact that they provide better heat dissipation. This increases the performance and service life of parts of the cylinder-piston group.
The KamAZ-740 cylinder heads (Fig. 4) are separate for each cylinder, made of aluminum alloy, and for cooling they have a cavity communicating with the cooling cavity of the block.
Each cylinder head is mounted on two guide pins pressed into the cylinder block and secured with four 3 alloy steel bolts. The head has a hole for draining engine oil from under the valve cover into the rod cavity. The intake and exhaust ports are located on opposite sides of the cylinder head.
Rice. 4. Cylinder head with valves assembly of the KamAZ-740 engine: (SLIDE No. 10):
1 – cylinder head; 2 – cylinder head cover gasket; 3 – head mounting bolt;
4 – cylinder head cover; 5 – cover fastening bolt; 6 – filler gasket;
7 – cylinder head gasket
The “cylinder head – liner” joint (gas joint) is gasketless. The tightness of the seal is ensured by high precision machining of the mating surfaces of the sealing ring and the cylinder liner. To reduce harmful volumes, a fluoroplastic filler gasket is installed in the gas joint. The use of a filler gasket reduces specific fuel consumption and exhaust smoke.
To seal the coolant bypass channels, silicone rubber O-rings are installed in the holes in the bottom of the head.
The space between the head and the block, the engine oil drain holes and the rod holes are sealed with a cylinder head gasket made of heat-resistant rubber. The gasket additionally has a sealing collar for the oil supply bushing and a groove for draining oil into the rod holes.
Each cylinder head is closed with a cylinder head cover 4 (Fig. 5) and secured with a bolt 5.
Unlike the KamAZ-740.11 engine, on the YaMZ-238 the heads common to each row of cylinders are cast from gray cast iron. They are installed on studs and secured with nuts through a steel-asbestos gasket. Each head is closed from above with a lid through an oil-resistant rubber gasket (Fig. 5).
Rice. 5. Cylinder head of the YaMZ-238 engine (SLIDE No. 11):
1 – cylinder head; 2 – cylinder head cover gasket; 3 – head fastening nut; 4 – cylinder head cover; 5 – wing fastenings of the cover; 6 – head mounting pin; 7 – cylinder head gasket; 8 – valve seat; 9 – washer; 10 – intake manifold stud; 11 – filler plug
Each head is common to four cylinders. Valve guides are pressed into the upper part of the head. Each cylinder head is secured with six evenly spaced studs 6. In the lower part of the head there are holes for pressing in valve seats. On the upper plane of the head there are valves with springs, valve rocker arms with stands, as well as brass cups for injectors. The top of the cylinder head is closed with a steel stamped cover 4, which is attached to the head with wings 5. The seal between the cover and the head is ensured by a gasket 2. The cover has a neck closed with a plug 11 for filling the crankcase with oil.
Particular attention must be paid to the sequence of tightening the nuts and bolts securing the cylinder heads. On KamAZ-740.11, YaMZ-238 engines, bolts and nuts are tightened in the sequence shown in Fig. 6.
Rice. 6. Sequence of tightening the nuts (bolts) securing the block heads
cylinders: (SLIDE No. 12):
a – YaMZ-238 engines; b – KamAZ-740
Let's look at the piston group and connecting rods.
Piston. During the power stroke, the piston receives gas pressure and transmits it through the connecting rods to the crankshaft. The piston consists of three main parts (: (SLIDE No. 13): the bottom 5, the sealing part 6 with grooves machined in it for the piston rings 3, 4 and the skirt 7, the surface of which is in contact with the cylinder mirror. The piston bottom with the inner surface of the cylinder head, forming the combustion chamber, directly perceives the gas pressure: it can be flat, convex, and on KamAZ-740.11 and YaMZ-238 - shaped.KAMAZ and Ural (YAMZ) pistons (Fig. 7).
Rice. 7. Pistons: (SLIDE No. 14):
a – carburetor engines; b – KamAZ diesel engines; c – YaMZ diesel engines
The shape of the combustion chambers has a significant influence on the mixture formation process, both in carburetor and diesel engines. The design of the piston depends on how the combustion chamber on the engine is designed (Fig. 7).
Diesel pistons (Fig. 6, b, c) are cast from aluminum alloy. The piston heads contain a combustion chamber, which in the KamAZ-740.11 is shifted relative to the piston axis away from the valve recesses by 5 mm, and in the YaMZ-238 it is located in the center. There are three (on YaMZ-238 - four) grooves on the cylindrical head of the piston: the upper ones are used for installing compression rings in them, and the lower one is for installing a collapsible oil scraper ring. In the middle part of the piston there are two bosses with holes with a diameter for the piston pin. The piston skirt has the shape of an oval cone, which gives it the necessary strength. In addition, in the lower part of the piston skirt of the KamAZ-740.11 engine there are side recesses for passages of the crankshaft counterweight.
To reduce the inertial forces of reciprocating moving masses, pistons are usually made from lightweight silicon aluminum alloys to reduce their mass. For the engine, pistons are selected whose mass does not differ by more than 2-8 g.
Piston rings. As previously mentioned, the main function of piston rings is to seal the combustion chamber and ensure the tightness of the connection between the piston - cylinder - groove parts. In addition, during combustion of the working mixture, a significant amount of heat is absorbed by the piston and removed from it by the piston rings.
Structurally, the piston ring (Fig. 8) is a flat split spring with a gap called a lock. The lock allows the rings to be installed on the piston and ensures their free expansion when heated during engine operation. Piston rings are divided into compression and oil scraper rings.
Rice. 8. Piston rings: (SLIDE No. 14):
a – types of piston rings; b – arrangement of rings on the piston
Compression rings 2 (Fig. 8, a) are selected in such a way that they roll freely along the piston groove. When installing the piston into the cylinder, the rings are compressed to the diameter of the cylinder and fit tightly to its surface, which prevents gases from breaking through into the engine crankcase and oil from entering the combustion chamber from the cylinder walls.
Oil scraper ring 3 removes excess oil from the cylinder walls and drains it into the lubricant reservoir.
Piston rings are made of alloy cast iron. The surface of the upper compression ring is subjected to porous chrome plating to increase wear resistance, and the remaining rings are coated with a thin layer of tin or molybdenum to speed up running-in.
The cast iron oil scraper ring 3 differs from the compression ring by slots 1 for the passage of oil. One or two rows of holes are drilled in the piston groove for the oil scraper ring to drain oil into the piston. Many engines use steel composite oil scraper rings.
KamAZ-740 engines have two compression rings and one oil scraper, and YaMZ-238 engines have three compression rings and one oil scraper. Compression rings have a trapezoidal cross-section. The upper ring is covered with chromium, the lower one - with molybdenum (on YaMZ-238 - with tin). Box-section oil scraper ring with twisted spring expander and chrome-plated working surface.
The oil scraper ring is collapsible, made of steel, has two annular disks, radial and axial expanders. Two annular disks remove excess oil from the cylinder mirror, which is discharged into the engine crankcase through holes in the piston. The working cylindrical surface of steel disks is coated with hard chrome. The ring lock is straight. After installing the rings into the cylinder, the mounting gap in the lock should be 0.3-0.5 mm. When installing them on the piston, the locks of all rings are positioned around the circumference at an angle of 120°. When installing a steel composite oil scraper ring at equal angular intervals, only the compression ring locks are displaced.
Piston pin - designed for a hinged connection of the piston with the upper head of the connecting rod. Significant forces are transmitted through the fingers, so they are made of alloy or carbon steels, followed by carburizing or hardening with high-frequency currents. Piston pin 10 (Fig. 9) is a thick-walled tube with a carefully ground outer surface, passing through the upper head of the connecting rod and resting on the ends of the piston bosses 2 (Fig. 8). According to the method of connection to the connecting rod, the most widely used are floating piston pins, which rotate freely in the bosses and in the bushing installed in the upper head of the connecting rod. The axial movement of the piston pin is limited by retaining rings 9 (Fig. 9), located in the recesses of the piston bosses.
Rice. 9. Connecting rod and piston group of the KamAZ-740 engine (SLIDE No. 15):
1 – piston; 2 – bushing of the upper head of the connecting rod; 3 – connecting rod; 4 – connecting rod bolt; 5 – connecting rod cover; 6 – nuts; 7 – pairing marks; 8 – liner of the lower head of the connecting rod; 9 – retaining ring; 10 – finger; 11 – oil scraper ring; 12 – compression rings
Connecting rod - with It serves to connect the piston to the crankshaft crank and ensures that during the power stroke the force is transferred from the gas pressure on the piston to the crankshaft, and during auxiliary strokes, on the contrary, from the crankshaft to the piston.
Connecting rods 3 of YaMZ-238 and KamAZ-740 engines have an I-section and consist of an upper head, a lower head and a cover 5. The lower head of the connecting rod is equipped with replaceable liners 8, the upper head is equipped with a pressed-in bronze bushing 2.
To lubricate the piston pin, there is a cutout in the upper head of the connecting rod, and in the bushing there is a hole that coincides with the cutout in the connecting rod. During forced lubrication of the floating piston pin (YaMZ-238), a through hole is drilled in the connecting rod rod - an oil channel.
The lower head of the connecting rod, as a rule, is made detachable in a plane perpendicular to the axis of the connecting rod. In cases where the lower head has significant dimensions and exceeds the diameter of the cylinder (YaMZ-238), the head parting plane is made at an angle (oblique cut), which allows the connecting rod to be mounted through the cylinder during repairs by reducing the radius of the circle described by the lower part of the connecting rod.
The connecting rod cover is made of the same steel as the connecting rod and is machined together with the lower head, so moving the covers from one connecting rod to another is not allowed. For this purpose, marks 7 are made on the connecting rods and covers. To ensure high accuracy when assembling the lower head of the connecting rod, its cover 5 is fixed with polished belts of bolts 4, which are tightened with nuts 6 and secured with cotter pins or washers. A connecting rod bearing in the form of thin-walled steel liners 8, which are coated on the inside with a layer of anti-friction alloy, is installed in the lower head.
The liners are held against axial displacement and rotation by protrusions (antennae) that fit into the grooves of the lower head of the connecting rod and its cover.
For better balance of the crank mechanism, the difference in the mass of the connecting rods should not exceed 6-8 g. In V-shaped engines, there are two connecting rods on each crankpin of the crankshaft. In these engines, for proper assembly of the connecting rod and piston group, the pistons and connecting rods are installed strictly according to the marks.
On the cover and connecting rod of the KamAZ-740 diesel engine, marks are stamped in the form of three-digit numbers. In addition, the cylinder serial number is stamped on the cap and connecting rod.
The YaMZ-238 connecting rod (Fig. 10) has the cylinder serial number stamped on the cover and connecting rod on the side of the short bolt. At the joint, on the side of the long bolt, pairing marks are stamped in the form of a two-digit number, the same for the connecting rod and the cover, and marks covering the connecting rod and the cover.
Rice. 9. Piston with connecting rod (SLIDE No. 15):
1 – piston; 2 – retaining ring; 3 – connecting rod; 4 – liners; 5 – connecting rod cover; 6 – lock washer; 7 – long bolt of the connecting rod cover; 8 – short bolt; 9 – bushing; 10 – piston pin; 11 – oil scraper rings; 12 – compression rings; 13 – toroidal combustion chamber
The crankshaft perceives the force of gas pressure on the piston and the inertial forces of the reciprocating and rotating masses of the crank mechanism.
The forces transmitted by the pistons to the crankshaft create torque, which is transmitted to the wheels of the car using the transmission.
The crankshaft of the KamAZ-740 (Fig. 11), YaMZ-238 (Fig. 12) engine is made of steel, made by hot stamping, subjected to nitriding or hardening by high-frequency currents of the connecting rod and main journals. It has five main bearings and four crankpins. The connecting rod journals of the shaft have internal cavities that communicate with oil channels in the main journals.
Rice. 11. KAMAZ-740 engine crankshaft assembly (SLIDE No. 16):
1 – front counterweight; 2 – oil pump drive gear; 3 – bushing; 4 – connecting rod journal plug; 5 – rear counterweight; 6 – drive gear; 7 – oil deflector; 8 – crankshaft
Rice. 12. Crankshaft of the YaMZ-238 engine with flywheel (SLIDE No. 16):
1 – crankshaft; 2 – lower bearing shell; 3 – flywheel; 4 – thrust bearing half ring; 5 – right locking plate; 6 – flywheel mounting bolt; 7 – rear oil deflector; 8 – upper bearing shell; 9 – front oil deflector; 10 – lock washer; 11 – nut for fastening the front counterweight; 12 – pulley; 13 – pulley washer; 14 – pulley bolt; 15 – front counterweight; 16 – crankshaft gear; 17 – key
Motor oil contaminants settle in these cavities under the influence of centrifugal force. Contaminant particles accumulate in bushings 3 (Fig. 11). The external cavities are closed with plugs 4. The crankshaft is sealed by rubber self-clamping oil seals installed in the flywheel housing and the camshaft cover.
Mounted on the toe and shank of the crankshaft are: oil pump drive gear 2 and drive gear 6 assembled with oil deflector 7. Remote counterweights 1 and 5 are removable, fixed to the shaft with a press fit
On the KamAZ-740 engine, the axial movements of the crankshaft are limited by four steel-aluminum half-rings installed in the grooves of the rear main bearing so that the side with the grooves is adjacent to the thrust ends of the shaft, and the shoulder fits into the groove on the rear main bearing cover.
On the YaMZ-238 engine (Fig. 12), to balance the engine and unload the main bearings from the inertial forces of the reciprocating masses of pistons and connecting rods and unbalanced centrifugal forces, counterweights are installed on the cheeks of the crankshaft, with which the shaft is balanced. In addition, the balancing system includes external masses located in the flywheel and mounted as a counterweight on the toe of the crankshaft. The shaft is secured against axial displacement by four bronze half-rings installed in the recesses of the rear main support.
The main and connecting rod journals are cast hollow. The cavities of the connecting rod journals are hermetically sealed with screw plugs.
The rear end of the crankshaft is sealed with an oil seal consisting of two half-rings made of asbestos cord impregnated with graphite. The half rings are placed in cages and work in direct contact with the polished surface of the crankshaft journal.
The flywheel (Fig. 13) serves to ensure the removal of the pistons from dead spots, more uniform rotation of the crankshaft of a multi-cylinder engine during idle mode, facilitating engine starting, reducing short-term overloads when starting the car and transmitting torque to transmission units in all engine operating modes.
Rice. 13. Flywheel of the KamAZ-740 engine (SLIDE No. 17):
1 – ring gear; 2 – flywheel clamp; 3 – flywheel; 4 – installation sleeve; 5 – clutch release lever; 6 – flywheel mounting bolt; 7 – persistent spring ring; 8 – installation sleeve; 9 – gearbox input shaft cuff
Flywheel 3 is made of cast iron and is dynamically balanced as an assembly with the crankshaft. On the flange, the flywheel is centered in a strictly defined position using pins or bolts 6, with which it is attached to the flange. A gear ring 1 is pressed onto the flywheel rim (and on the YaMZ-238 it is secured with bolts, which are secured with lock washers) and is designed to rotate the crankshaft with the starter when starting the engine. In the KamAZ-740 diesel engine, the flywheel is centered using two pins and bolted directly to the crankshaft . On the end or rim of the flywheel of many engines, marks are applied by which the piston of the first cylinder can be set to TDC on the compression stroke to set the ignition for carburetor engines or the injection timing for diesel engines.
The YaMZ-238 flywheel is attached to the crankshaft with eight bolts, which are secured against self-loosening with locking washers (one washer for two bolts).
The crank mechanism (CCM) is perhaps the most important engine system.
The purpose of the crank mechanism is to convert reciprocating motion into rotational motion and vice versa.
All parts of the crank mechanism are divided into two groups: moving and stationary. Movable ones include:
To the stationary:
The piston looks like an inverted glass into which the rings are placed. On any of them there are two types of rings: oil scraper and compression. There are usually two oil scrapers, and one compression valve. But there are exceptions in the form: two of these and two of those - it all depends on the type of engine.
The connecting rod is made of an I-beam steel profile. It consists of an upper head, which is connected to the piston using a pin, and a lower head, which is connected to the crankshaft.
The crankshaft is made mainly of high strength cast iron. It is a misaligned rod. All necks are carefully polished in compliance with the required parameters. There are main journals - for installing main bearings, and connecting rod journals - for installation through connecting rod bearings.
The role of sliding bearings is performed by split half rings, made in the form of two liners, which are treated with high frequency currents for strength. All of them are covered with an anti-friction layer. The main ones are attached to the engine block, and the connecting rods are attached to the lower head of the connecting rod. In order for the liners to work well, they have grooves for oil access. If the bearings are turned, it means that there is insufficient oil supply to them. This usually occurs when the oil system is clogged. The inserts cannot be repaired.
The longitudinal movement of the shaft is limited by special thrust washers. It is necessary to use different seals at both ends to prevent oil from escaping from the engine lubrication system.
A cooling system drive pulley and a sprocket are attached to the front of the crankshaft, which drives the camshaft using a chain drive. On the main models of cars produced today, it was replaced by a belt. The flywheel is attached to the rear of the crankshaft. It is designed to eliminate shaft imbalance.
It also has a ring gear designed to start the engine. To avoid problems during disassembly and further assembly, the flywheel is fastened using an asymmetrical system. The ignition timing also depends on the location of its installation marks - hence, optimal engine operation. During manufacture, it is balanced together with the crankshaft.
The engine crankcase is manufactured together with the cylinder block. It serves as the basis for fastening the timing belt and crankshaft. There is a pan that serves as a container for oil, as well as to protect the engine from deformation. There is a special plug at the bottom for draining engine oil.
The piston is under pressure from the gases produced during combustion of the fuel mixture. At the same time, it performs reciprocating movements, causing the engine crankshaft to rotate. From it, the rotational motion is transmitted to the transmission, and from there to the wheels of the car.
But the video shows how the KShM works:
The main signs of a crankshaft malfunction:
The crank mechanism of the engine is very vulnerable. For efficient operation, timely oil changes are necessary. It is best done at service stations. Even if you recently changed the oil, and it’s time for seasonal maintenance, be sure to switch to the oil specified in the machine’s operating instructions. If any problems arise in the engine operation: noises, knocking, contact a specialist - only an authorized center will give you an objective assessment of the condition of the car.
Greetings to the readers of our cozy blog! Now let's talk about the heart of our iron horses, internal combustion engines. More precisely, this time we will consider the purpose of the crank mechanism - one of the key mechanisms of the motor.
It is difficult to overestimate the purpose of the crank mechanism. In fact, it is he who we must thank for the fact that our iron horses do not stand still, but can transport our mortal bodies and give us the joy of driving.
Speaking in dry technical language, the purpose of the crank mechanism (CPM) is to convert the energy of the burnt fuel-air mixture into mechanical rotation.
Naturally, the KShM is not a monolithic structure and consists of a number of simpler parts, which will be discussed below.
Conventionally, the elements of the crank mechanism can be divided into two large subgroups: moving and stationary parts.
The first includes pistons with rings and pins, connecting rods, a crankshaft (in common parlance, a crankshaft), and a flywheel.
The fixed elements of the crankshaft are represented by the cylinder block and the cylinder head, the crankcase, as well as the gasket located between the block and the head.
And now a little more about the role of each of the actors in the theater of the crank mechanism. It is one of the first to take the blow of the burning fuel-air mixture.
This heroic element is a cylindrical metal piece, roughly speaking, shaped like a glass.
In fact, its shape is quite complex - with grooves, bulges, holes and cutouts.
All these complex shapes are needed not only for the efficient operation of the engine, but also so that there is where to place the piston rings, as well as where to insert the piston pin, to which the next important part of the mechanism is attached -.
The reason for the existence of a connecting rod is as simple as five kopecks - transmitting the translational motion of the piston to the crankshaft.
Quite a boring but important role. The connecting rod itself looks like a metal I-section rod.
At one end there is a hole for attaching to the piston using a piston pin, and at the other there is a half-ring, which is put on the crankpin of the shaft and secured with bolted joints with a special cover.
It is worth noting that the connection between the connecting rod and the crankshaft is movable - it must rotate.
The importance of the next element of the CVM is difficult to overestimate - this.
Of course, it is quite difficult to call this part a shaft in the usual sense - its shape is complex and all due to the fact that all the connecting rod-piston ligaments of the engine are attached to it.
The crankshaft is the key rotating element of the engine and it has to withstand incredible loads, therefore the requirements for the quality of its workmanship and the strength of the materials are the highest.
The main parts of the crankshaft are the crankpins (the places where the connecting rods are attached), the journals, the main journals, and the counterweights. By the way, the crank-connecting rod mechanism got its name precisely because of the part of the crankshaft, or, to be precise, the crank - this is what is sometimes called the combination of the connecting rod journal and the cheeks on either side of it.
The crankshaft is crowned on one side.
It should be noted that, despite its relative external simplicity, the flywheel plays several roles at once.
Firstly, its main task is to maintain uniform rotation of the crankshaft while the engine is running.
Secondly, it is this modest metal wheel that acts as the connecting link between the starter and the same crankshaft when you turn the ignition key to start the engine.
Almost all the moving parts of the crank mechanism are located in the cylinder block, and the cylinder head closes all this spinning and rotating disgrace from our eyes.
As a rule, valves, spark plugs and channels for supplying coolant, oil, and air-fuel mixture are built into it.
It should be noted that it is together with the head that determine such an important parameter of the engine as its mass.
In the classic version, these elements are made of cast iron, but thanks to modern technologies, automakers are increasingly using aluminum in their construction, which has a beneficial effect on the weight of the engine and, as a result, the entire car.
The use of light alloys has become possible even in such a critical element of the block as cylinder liners (the pistons move up and down in them), which must be resistant to wear and withstand high temperatures.
In conclusion, our dear readers, I would like to say a few words about the types of layout of internal combustion engines and cylinder layouts.
Automobile concerns complete their creations with several types of motors, namely:
From a balance point of view, in-line and boxer engines are the most optimal.
The former are quite common in the auto world - in-line four-cylinder units are found all the time, but the fate of the boxer units is not so public - they have become synonymous with a certain exclusivity and “clubiness”.
So, for example, they can be found in the depths of sports Porsches or Subaru.
V-shaped and their related W-shaped engines have the optimal combination of characteristics. They are used to build cars that are accessible to the average car enthusiast, as well as crazy supercars, the cost of which is as incredible as their character.
W-motor operation:
//www.youtube.com/watch?v=xKBpiNorQYQ
Dear blog visitors, in this short article we tried to clarify the purpose of the crank mechanism and consider its components in general terms. I would appreciate your subscription.
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