Crank mechanism. Crank mechanism (CSM). Purpose, device, principle of operation Purpose of the crank mechanism and its structure

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:

• stationary - crankcase, cylinder block, cylinders, cylinder head, head gasket and pan. Typically the cylinder block is cast together with the upper half of the crankcase, which is why it is sometimes called a block crankcase.
• moving parts of the crankshaft - pistons, piston rings and pins, connecting rods, crankshaft and flywheel.

In addition, the crank mechanism includes various fasteners, as well as main and connecting rod bearings.

Block crankcase

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.

Cylinder

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.

Cylinder 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.

Engine frame

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

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 are machined in the walls for compression rings. 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

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

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
• upper and lower connecting rod heads
• bearings
• connecting rod bolts with nuts and elements for their fixation

connecting rod

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. It generates torque, 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

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

crank mechanism

The crank mechanism perceives gas pressure during the combustion-expansion stroke and converts the rectilinear, reciprocating movement of the piston into rotational movement of the crankshaft. Crank-rod. The mechanism consists of a cylinder block with crankcase, cylinder head, pistons with rings, piston pins, connecting rods, crankshaft, flywheel and oil pan.

Rice. 2.12. Crank mechanism of the SMD-14BN engine:

Flywheel crown; 2 - leading fingers; 3 - flywheel; 4 - piston; 5 - finger; 6 - retaining ring; 7 - connecting rod; 8, 12 - upper and lower connecting rod bearings, respectively; 9 - crankshaft; 10 - gear block; 11 - connecting rod cover; 13 - screw.

crank mechanism crank repair

crank mechanism consists of the following parts: pistons with rings and pins, connecting rods, crankshaft and flywheel. The pistons are placed in cylinders, which are installed in a crankcase, closed on top by the cylinder head.

The crankcase is the main body part of the engine, which is made in the form of a general casting from cast iron. The upper part, where all the cylinders are located, is called the cylinder block, and the lower widened part, where the crankshaft is located, is called the crankcase. Inside the crankcase there are partitions that give it rigidity and also serve as supports for the crankshaft. The lower parts of the partitions, the front and rear crankcase foams have special bosses, which together with the covers form beds for the crankshaft main bearing liners. The main bearing caps are securely fastened to the crankcase.

The timing gear housing with a cover is attached to the front machined wall of the crankcase, and the flywheel housing is attached to the rear wall. A stamped steel pan is bolted to the bottom of the crankcase and serves as a container for oil.

Cylinder liners made of high-strength cast iron are installed in the vertical cylindrical bores of the crankcase. The space between the walls of the cylinder block and the outer walls of the cylinders is filled with coolant. To prevent its penetration into the crankcase, the liners in the lower part are sealed with rubber rings, which are placed in special grooves.

Sleeves washed by coolant are called wet. In addition to the rubber rings, the tight fit of wet sleeves in the upper part is ensured by the tight fit of a specially treated collar and sleeve belt. Sometimes a soft metal O-ring is installed under the liner collar.

The upper end of the liner protrudes slightly above the plane of the cylinder block, which, when tightening the cylinder head, ensures reliable fixation of the liner in the socket and thorough sealing of the joint.

In the top plate of the block, in addition to borings for cylinder liners, the following is made:

special channels for the passage of coolant from the cylinder block to the cylinder head;

channel for supplying oil to the valve mechanism;

holes for push rods;

threaded holes for the studs securing the cylinder head to the cylinder block.

The YaMZ-2E8NB engine cylinders are arranged in two rows at an angle of 90°, the right row is shifted relative to the left by 35 mm. Each row of cylinders has a separate head.

The TDT-55A tractor engine has one cylinder head, and the TT-4 tractor engine has two. The cylinder heads are covered on top with aluminum alloy caps. The cylinder heads and crankcases of both engines have a similar design.

The joint between the cylinder head and the cylinder block is sealed with a special gasket, which ensures a reliable tightness of the connection between the head and the block, preventing the breakthrough of gases from the cylinders and the leakage of coolant from the coolant jacket. The internal cavity of the head is a jacket for coolant, which communicates with the coolant jacket of the cylinder block through holes located in the lower cavity of the head and on the gasket.

The cylinder head has holes for installing injectors to supply fuel to the combustion chamber. Each injector of the TDT-55A tractor diesel engine is secured with two studs, and each injector of the TT-4 and K-703 tractor engines is secured with a special bolt with a nut and bracket. The valve and decompression valve control mechanisms are located on top of the cylinder head.

The cylinder heads of tractor engines are cast from cast iron. The head of carburetor engines has holes for installing spark plugs. In the head of the P-10UD starting engine there is a hole that is covered with a lid for purging the cylinder during startup or pouring fuel into it. The cylinder heads are secured to the cylinder block with studs and nuts, which are tightened in a certain sequence and to a certain torque.

For all tractor diesel engines under consideration, the combustion chamber is formed by corresponding recesses in the piston and the upper planes of the cylinder heads. The cylinders, together with the combustion chambers, piston and cylinder head, form the volumes in which all the working processes of the engine operating cycle take place. The inner walls of cylinder liners, called the cylinder bore, provide direction for the movement of the pistons.

Piston group and connecting rod

The piston with sealing rings, pin and fastening parts makes up the piston group. A piston with sealing rings ensures the tightness of the variable volume in which the engine’s working process takes place, and also perceives gas pressure and transmits the resulting force through the pin and connecting rod to the crankshaft. The piston is also used to fill the cylinder with a combustible mixture or air, compress it and remove exhaust gases from the cylinder. In addition, in two-stroke engines, the piston opens the intake, exhaust and bypass ports. The piston operates under conditions of high pressures, high temperatures and rapidly changing speeds.

Piston consists of an upper sealing part (head) and a lower guide part (skirt). The piston head has a bottom that absorbs gas pressure, and a side surface with grooves machined on it for piston rings: on the bottom of diesel engine pistons, grooves are machined to accommodate oil scraper rings; The pistons of carburetor engines do not have grooves for rings in the lower part.

To better remove heat and increase the strength of the piston, the bottom has stiffening ribs on the inside. From the outside, the bottom can be flat, concave, convex, or shaped.

In diesel engines, shaped bottoms are widely used, the shape of which depends on the method of mixture formation in the diesel engine, the location of valves and injectors, and the surface forms the combustion chamber. Skidder engine pistons have concave shaped combustion chambers.

The sealing part of the piston heads of diesel tractors TDT-55A, TT-4 and K-703 has four annular grooves: three upper ones for compression rings and one for oil scraper rings. There is a fifth groove on the piston skirt for the lower oil scraper ring. In the grooves for the oil scraper rings, holes are drilled to drain the oil removed by the rings from the cylinder walls into the oil pan.

The side surface of the piston has a complex cone-elliptical shape, and its diameter is smaller than the diameter of the cylinder, and the piston head has a smaller diameter than the skirt, and the major axis of the ellipse is perpendicular to the axis of the piston ring. All this allows, when heating and expanding the piston, to provide a gap between the cylinder walls and the piston, which allows the piston, when heated, to freely expand and move in the cylinder.

The skirt provides the direction of movement of the piston in the cylinder and transmits lateral forces to its walls. In the upper part, the skirt is equipped with boss bosses, in which there are holes for the piston pin connecting the piston to the connecting rod. The pin axis intersects with the piston axis, but sometimes it moves away from the piston axis. This allows you to reduce the load on the piston at the moment it passes TDC. To improve the running-in of pistons to the cylinders, reduce wear and protect them from scuffing, the piston skirt is coated with a thin layer of tin. The piston itself is cast from a special aluminum alloy.

Piston rings are divided into compression and oil scraper rings. They are designed to prevent the gap between the walls of the cylinder and the piston from breaking through, and oil from entering the crankcase into the combustion chamber, where, when burned, the oil forms carbon deposits. The rings are involved in removing heat from the piston to the cylinder. In the free state, the outer diameter of the ring is larger than the diameter of the cylinder, so after its installation the ring fits tightly to the walls of the cylinder.

For installation in the piston grooves, the rings are split with a gap of 0.2 - 0.5 mm. I call the cuts of the piston rings locks, which are mostly straight in shape, sometimes oblique or stepped. Diesel engines of skidders use piston rings with straight locks. When installing rings, the locks of adjacent rings are shifted relative to each other along the circumference by approximately an angle of 120°.

During operation and wear, the elasticity of the piston rings decreases, and as a result, the tightness of the cylinder deteriorates. To eliminate this, in the diesel engines of the TDT-55A and TT-4 tractors, a steel spring ring - an expander - is installed between the piston oil scraper ring and the wall of the piston groove.

Piston rings are made of alloy cast iron by casting followed by machining, as well as steel. The height of the rings is 0.03 - 0.08 mm less than the height of the groove in the piston.

The material for the manufacture of piston rings must have good elasticity and sufficient strength at high temperatures, have high wear resistance, but not more than the wear resistance of the cylinder mirror. To reduce wear on the ring and cylinder, the supporting surface of one or two upper compression piston rings is coated with a layer of chromium up to 0.16 - 0.20 mm thick with a porous surface that holds lubricant well. To improve running-in, the working surfaces of the lower rings are often coated with a layer of tin or other easily abraded material.

Piston pin serves to articulate the piston with the connecting rod and is made hollow from high-quality wear-resistant steel. Its inner surface is cylindrical or conical-cylindrical.

The ends of the pin are placed in the holes of the piston bosses, and the middle passes through the hole in the connecting rod head. If the fingers rotate freely both in the bosses and in the connecting rod head, then they are called floating. This connection is most widespread, since when the piston and connecting rod move, the entire surface of the floating pin is working, which reduces wear and the possibility of jamming.

In some engines, the pin can be fixedly fixed to the connecting rod head and its length is less than the piston diameter. To limit the axial movements of the pin and avoid damage to the cylinder walls, the pin is secured with locking rings installed in the grooves of the bosses, end plugs inserted into the bosses and a locking ring placed in the grooves of the pin and the upper head of the connecting rod.

The piston pin is lubricated through drillings in the rod or slots in the upper head of the connecting rod and oil channels in the piston bosses.

The connecting rod consists of an upper and lower head and a rod connecting them:

The upper head is one-piece and serves to install the piston pin, which pivotally connects the piston to the connecting rod. To reduce friction and wear, one or two bronze bushings are pressed into it;

The lower head of many engines is made composite with a straight (90°) or oblique (30 - 60°) connector relative to the axis of the connecting rod rod. The connector plane can be smooth or have a slotted lock. The oblique connector facilitates the passage of the piston with the connecting rod through the cylinder, as well as the connection of the connecting rod to the crankshaft crank.

The removable part of the lower connecting rod head is the cover. It is attached to the rod with two bolts, which have nuts or are screwed into the body of the connecting rod and are securely locked after tightening.

Thin-walled steel liners (upper and lower) with a thin layer of 0.1 - 0.9 mm antifriction alloy are installed in the lower head of the connecting rod. The connecting rod bearing shells in the diesel engines of the TDT-55A and TT-4 tractors are made of low-carbon steel coated with special aluminum alloys, and in the engines of the K-703 tractor - with lead bronze. The liners perform the function of a sliding bearing and are held in the connecting rod and in the cap by a tight fit and the presence of antennae that fit into the corresponding recesses in the connecting rod and cap.

The connecting rod rod usually has an I-section, expanding towards the lower head, a streamlined shape and smooth transitions to the heads. Some connecting rods have a channel in the rod for supplying oil under pressure to the piston pin.

When the engine is running, gas pressure forces and inertial forces act on the connecting rod, which compress, stretch and bend the connecting rod in the longitudinal and transverse directions. Therefore, its shape, design and material must ensure strength, rigidity and lightness. Connecting rods are made from high-quality carbon and alloy steels by stamping heated blanks followed by mechanical and heat treatment.

To ensure good engine balance, the difference in mass of individual connecting rods and connecting rod-piston sets should be minimal. To properly assemble the piston and connecting rod and install them in the engine, the serial number of the cylinder for which the connecting rod is intended, as well as other marks, are stamped on the lower head of the connecting rod and its cover.

Crankshaft and flywheel

The crankshaft receives the forces transmitted from the pistons by the connecting rods and converts them into torque, transmitting it to the drive systems and mechanisms of the tractor engine and transmission. During operation, the crankshaft is in a very complex state of stress: it is subject to compressive and tensile forces, inertial and centrifugal forces, torsional and bending moments. The crankshaft must be: strong, rigid, wear-resistant, statically and dynamically balanced, streamlined, not subject to resonant and torsional vibrations, and have a small mass.

Crankshaft consists of main and connecting rod journals connected by cheeks, a flange for attaching the flywheel and a toe.

The connecting rod journals of the diesel shafts of the TDT-55A, TT-4 and K-703 tractors have cavities closed with threaded plugs, in which additional centrifugal cleaning of the oil is carried out before entering the connecting rod bearings.

The main journals are used to install the crankshaft in bearings located in the engine crankcase. Using connecting rod journals, the shaft is connected to the lower heads of the connecting rods. The connecting rod and main journals are connected using cheeks. To unload the main bearings from the inertial forces of the moving parts of the connecting rod and piston group, counterweights are installed on the shaft cheeks, with which the shaft is balanced. Counterweights can be manufactured integrally with the cheeks or in the form of separate, securely fastened parts. The connecting rod journal, together with the cheeks adjacent to it, forms the shaft crank or crank.

To avoid destruction of the crankshafts, roundings - fillets - are made in the places where the cheeks pass to the main and connecting rod journals. Channels for supplying oil under pressure to the connecting rod bearings are drilled in the main and connecting rod journals and in the cheeks.

On the front part of the crankshaft are mounted: a camshaft drive gear, a drive belt pulley, an oil deflector, an oil seal and a ratchet for turning the shaft with a handle. The flywheel is bolted to the crankshaft shank. The shaft shank has an oil scraper thread and an oil deflector collar, and at the end there is a socket for installing the front bearing of the clutch shaft.

The nose and shaft shank are sealed with rubber self-clamping cuffs. The crankshaft rotates in main bearings with liners made of steel-aluminum tape.

Crankshafts are made from carbon and alloy steels by stamping or casting, followed by mechanical and heat treatment. To increase the wear resistance of the main and connecting rod journals, they are subjected to surface hardening, and then ground and polished.

The shape of the crankshaft depends on the number and arrangement of cylinders, the clock cycle and the order of operation of the engine. It must ensure uniform alternation of working strokes in the cylinders according to the angle of rotation of the crankshaft, the accepted sequence of cylinder operation and engine balance.

The number of connecting rod journals on the crankshaft of an engine with a single-row arrangement of cylinders is equal to the number of cylinders. For engines with a V-shaped cylinder arrangement, the number of connecting rod journals is equal to half the number of cylinders: these engines have two connecting rod heads installed side by side on each journal. The number of crankshaft journals in v-shaped engines is usually one more than in connecting rod engines. For example, the eight-cylinder diesel engine YaMZ-2E8NB has five journals, and the crankshaft of the six-cylinder diesel engine A-01ML has seven journals. The more supports in the form of main journals the crankshaft has, the more rigid and reliable the engine design is, the load on the support bearings is lightened, but the structure of the shaft and crankcase becomes more complicated, the length of the engine increases, and the cost of manufacturing and repairs increases.

Main bearing shells are installed in the bed of the crankcase and main bearing caps, and fixation is carried out in the same way as for connecting rods.

During the working stroke in a single-cylinder engine, the crankshaft with the flywheel receives the force from the piston through the connecting rod and spins, accumulating energy, which is then, first of all, used to perform the remaining preparatory strokes of the working process. As the number of cylinders and the frequency of power strokes in the engine increases (in two-stroke engines), the need for flywheel energy to perform preparatory strokes decreases. Therefore, the size of the flywheel and its mass are smaller in such engines.

When starting the engine, the flywheel, having received energy after a power stroke in one of the cylinders, ensures rotation of the crankshaft due to inertia, while conditions are created in the remaining cylinders for power strokes to occur, as a result of which the engine begins to work.

The flywheel is cast from cast iron in the form of a disk. To increase the moment of inertia of the flywheel, the bulk of its metal is placed along the rim, i.e. at the maximum distance from the axis of rotation of the flywheel. A steel ring gear is pressed onto the flywheel rim, with which the starter gear meshes when the engine is started, and marks are applied to determine the position of the piston in the first cylinder and set the ignition timing or fuel supply timing.

Assembled with the crankshaft, the flywheel is balanced. This is done so that when they rotate, vibration and beating from centrifugal forces do not occur and increased wear of the engine main bearings does not occur. Clutches are mounted at the rear end of the flywheel.

When the engine is running, the crankshaft is subject to axial forces from the operation of helical gears of the gas distribution drive, engagement of the clutch and heating of the shaft. To limit the axial movements of the crankshaft, one of the main bearings (rear, front or middle) is a thrust bearing. For this purpose, the shells of such bearings are equipped with flanges, thrust rings or half rings. The crankshaft of the diesel engines of the TDT-55A, TT-4 and K-703 tractors is secured against axial movements by four half rings, which are installed in the grooves of the middle (SMD-14BN) or rear main bearing.

Maintenance of the crank mechanism

The parts of the crank mechanism become very hot during operation and perceive large variable loads, therefore, to ensure long-term operation of the engine in good condition, it is necessary to follow the following recommendations:

a new or repaired engine must be run-in;

starting the engine at an ambient temperature below -5°C should be done using a pre-heater or only after pre-heating with water;

do not give the engine full load until it warms up;

do not overload the engine for a long time and do not allow abnormal knocking and smoking during operation;

maintain the coolant temperature within 82 - 85°C;

Do not allow prolonged idling.

The main external signs of a faulty crank mechanism are: increased oil consumption, smoky exhaust gases and abnormal knocking noises. All this occurs as a result of wear of parts and an increase in gaps in the joints, which causes a drop in oil pressure in the line. Before checking the clearance in the bearings, you should make sure that the pressure gauge readings are correct, check the contamination of the filters and the condition of other elements of the lubrication system. A preliminary assessment of the condition of the crankshaft bearings based on the oil pressure in the oil line is carried out using the KI-4940 device: the nominal pressure of a warmed-up engine to normal thermal state at a rated speed should be 250 - 350 kPa (2.5 - 3.5 kgf/cm2), and maximum permissible 100 kPa (1.0 kgf/cm2). A drop in oil pressure in the line below the maximum permissible is one of the reasons for wear of the crankshaft journals and bearings. The permissible clearance in the connecting rod and main bearings of the crankshaft should be 0.3 mm.

Bearing clearances can be checked in the following way. After draining the oil and removing the pan, it is necessary to loosen the nuts securing the caps of the main and connecting rod bearings, and remove the cap of the bearing being tested along with the lower liner. Then place a brass gasket measuring 25x13x0.3 mm on it along the axis of the crankshaft, i.e. thickness equal to the maximum allowable gap, put the cover in place and tighten the nuts. Tightening is done using a torque wrench. The connecting rod bolt nuts should be secured with new cotter pins. The tightening torque of the main bearing nuts is 200 - 220 N m (20 - 22 kgf-m), and the connecting rod nuts are 150 - 180 N m (15 - 18 kgf-m).

Then check the possibility of rotation of the crankshaft, having previously turned on the decompression mechanism. If the shaft rotates freely, the clearance in the bearing exceeds the permissible value.

An increase in the gap between the parts of the cylinder-piston group leads to a drop in engine power, increased oil loss and the release of gases from the breather. To assess the condition of the cylinder-piston group, you can use various methods, but the simplest are those that allow you to determine the technical condition of the parts without disassembling the engine. These methods include: determining compression in engine cylinders using a KI-861 compression meter or the technical condition of the cylinder-piston group by gas leakage into the engine crankcase using a gas flow indicator KI-4887-1.

The final decision on the technical condition of the cylinder-piston group can only be made after partial disassembly of the engine and measuring the gaps between individual mating parts. For example, the maximum gaps between the main parts of the cylinder-piston group, by which the technical condition of the A-OZML engine is assessed, are equal to:

the gap between the piston skirt and the cylinder liner in the upper working belt is 0.60 mm;

the gap between the remaining rings is 0.40 mm; gap at the joint of the compression ring - 6.00 mm; the gap at the joint of the oil scraper ring is 3.00 mm; the gap between the piston bosses and the pin is 0.10 mm; the gap between the upper head of the connecting rod and the pin is 0.30 mm; the protrusion of the cylinder liner relative to the plane of the block is 0.165 mm.

To install the piston pins, the pistons are heated in oil to a temperature of 80 - 100°C before assembly. Piston rings are selected according to the liner, and then according to the grooves in the piston. To check the gap in the ring lock, it is installed in the sleeve using a piston to a depth of 25 mm from the top end. The adjustment of the gap in the lock is carried out using a personal file, and the alignment of the ring along the grooves in the piston in height is carried out by grinding on a cast iron plate.

Cylinder liners are replaced with new ones if their wear in the upper zone of the first compression ring exceeds 0.60 mm. The pistons are replaced if the gap between the groove and the new compression ring exceeds 0.50 mm in height. Tightening the nuts on the studs when fastening the engine cylinder head is carried out in a certain sequence, the torque is 200 - 220 N m (20 - 22 kgf-m)

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.

Fixed parts of kshm

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.

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

KShM structure

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 pads. 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.

Almost any piston engine installed in a car, tractor, walk-behind tractor uses a crank mechanism. They are also used in compressors for producing compressed air. The energy of expanding gases, combustion products of the next portion of the working mixture, is converted by the crank mechanism into rotation of the working shaft, transmitted to the wheels, tracks or drive of the brush cutter. In a compressor, the opposite phenomenon occurs: the rotational energy of the drive shaft is converted into potential energy of air or other gas compressed in the working chamber.

Mechanism design

The first crank devices were invented in the ancient world. In ancient Roman sawmills, the rotational motion of a water wheel, driven by the river current, was transformed into a reciprocating motion of the saw blade. In antiquity, such devices were not widely used for the following reasons:

• wooden parts wore out quickly and required frequent repairs or replacement;
• slave labor was cheaper than high technology for that time.

In a simplified form, the crank mechanism has been used since the 16th century in village spinning wheels. The movement of the pedal was converted into rotation of the spinning wheel and other parts of the device.

Steam engines developed in the 18th century also used a crank mechanism. It was located on the driving wheel of the locomotive. The steam pressure on the piston bottom was converted into the reciprocating movement of a rod connected to a connecting rod pivotally mounted on the drive wheel. The connecting rod gave the wheel rotation. This arrangement of the crank mechanism was the basis of mechanical transport until the first third of the 20th century.

The locomotive design was improved in crosshead engines. The piston in them is rigidly attached to the crosshead rod, which slides back and forth in the guides. A hinge is attached to the end of the rod, and a connecting rod is attached to it. This scheme increases the range of working movements and even makes it possible to make a second chamber on the other side of the piston. Thus, each movement of the rod is accompanied by a working stroke. Such kinematics and dynamics of the crank mechanism make it possible to double the power with the same dimensions. Crossheads are used in large stationary and ship diesel installations.

The elements that make up the crank mechanism are divided into the following types:

• Movable.
• Fixed.

The first include:

• piston;
• rings;
• fingers;
• connecting rod;
• flywheel;
• crankshaft;
• crankshaft plain bearings.

The fixed parts of the crank mechanism include:

• cylinder block;
• sleeve;
• block head;
• brackets;
• crankcase;
• other minor elements.

Pistons, pins and rings are combined into a piston group.

Each element, as well as the detailed kinematic diagram and operating principle, deserves a more detailed consideration

This is one of the most complex engine parts in terms of configuration. The schematic three-dimensional drawing shows that inside it is pierced by two non-intersecting systems of channels for supplying oil to the points of lubrication and coolant circulation. It is cast from cast iron or light metal alloys and contains places for pressing cylinder liners, brackets for crankshaft bearings, space for the flywheel, lubrication and cooling systems. The unit is connected to the pipes for the fuel mixture supply and exhaust gas removal system.

An oil sump-lubricant reservoir is attached to the bottom of the block through a sealed gasket. It is in this crankcase that the main work of the crank mechanism, abbreviated KShM, takes place.

The liner must withstand the high pressure in the cylinder. It is created by gases formed after the combustion of the fuel mixture. Therefore, the place of the block where the liners are pressed must withstand high mechanical and thermal loads.

The sleeves are usually made of durable steel, less often - of cast iron. During engine operation they wear out and can be replaced during a major engine overhaul. There are two main layouts for their placement:

• dry, the outer side of the liner transfers heat to the material of the cylinder block;
• wet, the liner is washed from the outside with coolant.

The second option allows you to develop more power and tolerate peak loads.

Pistons

The part is a steel or aluminum casting in the form of an inverted glass. Sliding along the walls of the cylinder, it takes on the pressure of the burnt fuel mixture and turns it into linear movement. Then, through the crank assembly, it turns into rotation of the crankshaft, and then is transmitted to the clutch and gearbox and through the cardan to the wheels. The forces acting in the crank mechanism set the vehicle or stationary mechanism in motion.

The part performs the following functions:

• on the intake stroke, moving downwards (or in the direction from the crankshaft if the cylinder is not located vertically) on, it increases the volume of the working chamber and creates a vacuum in it, drawing in and evenly distributing the next portion of the working mixture throughout the volume;
• on the compression stroke, the piston group moves upward, compressing the working mixture to the required degree;
• Next comes the power stroke, the part under pressure goes down, transmitting a rotational impulse to the crankshaft;
• on the exhaust stroke it goes up again, displacing exhaust gases into the exhaust system.

At all strokes, except for the working stroke, the piston group moves due to the crankshaft, taking away part of the energy of its rotation. On single-cylinder engines, a massive flywheel is used to accumulate such energy; on multi-cylinder engines, the cylinder strokes are shifted in time.

Structurally, the product is divided into the following parts:

• bottom, which absorbs gas pressure;
• seal with grooves for piston rings;
• a skirt in which a finger is secured.

The pin serves as an axis on which the upper arm of the connecting rod is fixed.

Piston rings

The purpose and design of piston rings is determined by their role in the operation of crank devices. The rings are made flat, they have a cut a few tenths of a millimeter wide. They are inserted into the annular grooves machined for them on the seal.

The rings perform the following functions:

• Seal the gap between the liner and the piston walls.
• Provide direction of piston movement.
• Cool. Touching the liner, the compression rings remove excess heat from the piston, protecting it from overheating.
• Isolate the working chamber from lubricants in the crankcase. On the one hand, the rings retain droplets of oil sprayed into the crankcase by the impacts of the counterweights of the crankshaft cheeks; on the other hand, they allow a small amount of oil to pass through to lubricate the cylinder walls. The lower oil scraper ring is responsible for this.

The connection between the piston and connecting rod also needs to be lubricated.

Lack of lubrication within a few minutes renders the cylinder parts unusable. The rubbing parts overheat and begin to collapse or become jammed. Repair in this case will be difficult and expensive.

Piston pins

The kinematic connection between the piston and connecting rod is carried out. The product is fixed in the piston skirt and serves as the axis of the sliding bearing. The parts withstand high dynamic loads during the working stroke, as well as changes in stroke and reversal of the direction of movement. They are machined from high-alloy heat-resistant alloys.

The following types of finger designs are distinguished:

• Fixed. They are fixedly mounted in the skirt, only the cage of the upper part of the connecting rod rotates.
• Floating. They can rotate in their fastenings.

The floating design is used in modern engines; it reduces the specific loads on the components of the crank group and increases their service life.

This critical element of the engine crank mechanism is made dismountable so that the bearing shells in its cages can be changed. Sliding bearings are used on low-speed engines; on high-speed engines, more expensive rolling bearings are installed.

In appearance, the connecting rod resembles a spanner. To increase strength and reduce weight, the cross section is made in the form of an I-beam.

During operation, the part experiences alternate loads of longitudinal compression and tension. For manufacturing, castings from alloy or high-carbon steel are used.

The transformation is carried out with help.

Of the parts of the crank group, the crankshaft has the most complex spatial shape. Several articulated joints move the rotation axes of its segments away from the main longitudinal axis. The lower races of the connecting rods are attached to these remote axles. The physical meaning of the design is exactly the same as when securing the connecting rod axis to the edge of the flywheel. In the crankshaft, the “extra”, unused part of the flywheel is removed and replaced with a counterweight. This allows you to significantly reduce the weight and dimensions of the product and increase the maximum available speed.

The main parts that make up the crankshaft are as follows:

• Shakey. Serve for fastening the shaft in the crankcase brackets and connecting rods on the shaft. The first are called main, the second - connecting rod.
• Cheeks. They form the knees that give the knot its name. Rotating around the longitudinal axis and pushed by connecting rods, they convert the energy of the longitudinal movement of the piston group into rotational energy of the crankshaft.
• Front exit part. A pulley is placed on it, from which the shafts of the auxiliary systems of the engine - cooling, lubrication, distribution mechanism, and generator - rotate using a chain or belt drive.
• Main output part. Transfers energy to the transmission and further to the wheels.

The back part of the cheeks, protruding beyond the axis of rotation of the crankshaft, serves as a counterweight for their main part and the connecting rod journals. This allows you to dynamically balance a structure rotating at high speed, avoiding destructive vibrations during operation.

For the manufacture of crankshafts, castings from light high-strength cast iron or hot stampings (forgings) from hardened steel are used.

Crankcase

It serves as the structural basis of the entire engine; all other parts are attached to it. External brackets extend from it, on which the entire unit is attached to the body. A transmission is attached to the crankcase, transmitting torque from the engine to the wheels. In modern designs, the crankcase is made as a single part with the cylinder block. Within its spatial framework, the main work of the components, mechanisms and parts of the motor takes place. A pan is attached to the bottom of the crankcase to store oil to lubricate the moving parts.

Operating principle of the crank mechanism

The operating principle of the crank mechanism has not changed over the past three centuries.

During the power stroke, the working mixture ignited at the end of the compression stroke quickly burns, the combustion products expand and push the piston down. He pushes the connecting rod, which rests on the lower axis, spaced apart from the main longitudinal axis. As a result, under the influence of tangentially applied forces, the crankshaft rotates a quarter of a turn in four-stroke engines and half a turn in two-stroke engines. Thus, the longitudinal movement of the piston is converted into rotation of the shaft.

Calculation of the crank mechanism requires excellent knowledge of applied mechanics, kinematics, and strength of materials. It is entrusted to the most experienced engineers.

Malfunctions that occur during the operation of the crankshaft and their causes

Malfunctions can occur in different elements of the crank group. The complexity of the design and combination of parameters of engine connecting rod mechanisms makes it necessary to pay special attention to their calculation, manufacture and operation.

Most often, failures result from non-compliance with the operating modes and maintenance of the motor. Poor quality lubrication, clogging of oil supply channels, untimely replacement or replenishment of oil in the crankcase to the specified level - all these reasons lead to increased friction, overheating of parts, and the appearance of scuffs, abrasions and scratches on their working surfaces. The oil filter should be changed every time you change the oil. In accordance with the maintenance schedule, fuel and air filters also need to be changed.

Malfunction of the cooling system also causes thermal deformation of parts, up to their jamming or destruction. Diesel engines are especially sensitive to the quality of lubrication.

Problems in the ignition system can also lead to carbon deposits on the piston and its rings. Coking of the rings causes a decrease in compression and damage to the cylinder walls.

It also happens that the cause of a breakdown is low-quality or counterfeit parts or materials used during maintenance. It is better to purchase them from official dealers or trusted stores that care about their reputation.

List of KShM malfunctions

The most common mechanism failures are:

• wear and destruction of the crankshaft connecting rod and main journals;
• grinding, chipping or melting of plain bearing shells;
• contamination of piston rings by combustion carbon deposits;
• overheating and breakage of rings;
• accumulation of carbon deposits on the piston head leads to its overheating and possible destruction;
• Long-term operation of the engine with detonation effects causes the piston crown to burn out.

The combination of these faults with a malfunction in the lubrication system can cause misalignment of the pistons in the cylinders and engine seizure. Elimination of all these breakdowns involves dismantling the engine and its partial or complete disassembly.

Repairs take a long time and are expensive, so it is better to identify malfunctions in the early stages and correct problems in a timely manner.

Signs of malfunctions in the operation of the crankshaft

For timely detection of failures and negative processes beginning to develop in the crank group, it is useful to know from external signs:

• Knocks in the engine, unusual sounds during acceleration. Ringing sounds are often caused by detonation phenomena. Incomplete combustion of fuel during the power stroke and its explosive combustion during the exhaust stroke lead to the accumulation of carbon deposits on the rings and the piston crown, deterioration of their cooling conditions and destruction. It is necessary to fill in high-quality fuel and check the operating parameters of the ignition system on the stand.
• Dull knocks indicate wear on the crankshaft journals. In this case, you should stop operating, grind the journals and replace the liners with thicker ones from the repair kit.
• A sound that “sings” at a high, loud note indicates the possible beginning of melting of the liners or a lack of oil when the speed increases. You also need to urgently go to the service center.
• Blue clouds of smoke from the exhaust pipe indicate excess oil in the working chamber. The condition of the rings should be checked and replaced if necessary.
• A drop in power can also be caused by ring coking and decreased compression.

If you notice these alarming symptoms, do not postpone your visit to the service center. A seized engine will cost much more, both in money and time.

KShM maintenance

In order not to damage the crankshaft parts, you must comply with all the manufacturer’s requirements for periodic maintenance and regular inspection of the vehicle.

The oil level, especially on a vehicle that is not new, should be checked daily before leaving. It takes less than a minute, and can save months of waiting in the event of a serious breakdown.

Fuel should be filled only from proven gas stations of well-known brands, without being seduced by the two-ruble difference in price.

If you notice the alarming symptoms listed above, you should immediately go to a service station.

You should not try to bore cylinders, remove carbon deposits from rings, or perform other complex repair work on your own, based on videos from the Internet. If you do not have many years of experience in such work, it is better to turn to professionals. Self-installation of the connecting rod mechanism after repair is a very difficult operation.

It is reasonable to use various patented means “to transform carbon deposits on cylinder walls” or “to decarbonize” only when you are absolutely sure of both the diagnosis and the medicine.

You may also be interested in the following articles:

Crank-slider mechanism: device, principle of operation, application