The principle of operation of the cshm engine. crank mechanism

The crank mechanism is designed for converting reciprocating piston motion into rotary motion crankshaft.

The details of the crank mechanism can be divided into:

• fixed - crankcase, cylinder block, cylinders, cylinder head, head gasket and sump. Usually, the cylinder block is cast with the upper half of the crankcase, which is why it is sometimes referred to as a block crankcase.
• moving parts of KShM - 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 skeleton. It is exposed to significant force and heat and must have high strength and rigidity. In the crankcase, cylinders, crankshaft supports, some devices of the gas distribution mechanism, various nodes of the lubrication system with its complex network of channels and more are installed auxiliary equipment... The crankcase is made of cast iron or aluminum alloy by casting.

Cylinder

Cylinders are the guiding elements ⭐ of the crank mechanism. Pistons move inside them. The length of the cylinder generatrix is ​​determined by the piston stroke and its dimensions. The cylinders operate under conditions of abruptly changing pressure in the above-piston cavity. Their walls are in contact with flames and hot gases with temperatures up to 1500 ... 2500 ° C.

The cylinders must be strong, rigid, heat and wear resistant with a limited amount of lubrication. In addition, the material of the cylinders must have good casting properties and be easy to machine. Usually cylinders are made from special alloyed cast iron, but aluminum alloys and steel can also be used. The inner working surface of the cylinder, called its mirror, is carefully machined and chrome-plated to reduce friction, increase wear resistance and increase durability.

In liquid-cooled engines, the cylinders can be cast together with the cylinder block or as separate liners installed in the bores of the block. There are cavities between the outer walls of the cylinders and the block, called a cooling jacket. The latter is filled with liquid that cools the engine. If the outer surface of the cylinder liner is in direct contact with the coolant, then it is called wet. Otherwise, it is called dry. The use of replaceable wet liners facilitates engine repair. When installed in the block, the wet sleeves are securely sealed.

Air cooled engine cylinders are individually cast. To improve heat dissipation, their outer surfaces are provided with annular ribs. In most air-cooled engines, the cylinders, along with their heads, are attached with common bolts or studs to the top of the crankcase.

In a V-shaped engine, the cylinders of one row can 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 crank of the crankshaft, one of which is for the right piston, and the other for the piston of the left half of the block.

Cylinder block

On the carefully processed upper plane of the cylinder block, a block head is installed, which closes the cylinders from above. Recesses are made in the head above the cylinders to form combustion chambers. For liquid-cooled engines, a cooling jacket is provided in the body of the block head, which communicates with the cooling jacket of the cylinder block. With the upper arrangement of the valves, the head has sockets for them, inlet and outlet channels, threaded holes for installing spark plugs (for gasoline engines) or injectors (for diesel engines), lubrication lines, fastening and other auxiliary holes. The material for the head of the block is usually aluminum alloy or cast iron.

A tight connection between the cylinder block and the block head is ensured by bolts or studs with nuts. To seal the joint in order to prevent gas leakage from the cylinders and coolant from the cooling jacket, a gasket is installed between the cylinder block and the block head. It is usually made of asbestos board and lined with thin steel or copper sheet. Sometimes the gasket is rubbed on both sides with graphite to protect it from burning.

The lower part of the crankcase, which protects the parts of the crank and other engine mechanisms from contamination, is usually called a sump. In engines of relatively low power, the sump also serves as a reservoir for engine oil. The pallet is most often cast or made of 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 skeleton

The fixed parts of the crank mechanism connected to each other are the skeleton of the engine, which perceives all the main power and thermal loads, both internal (associated with the operation of the engine) and external (due to the transmission and chassis). The power loads transmitted to the engine frame from the vehicle carrying system (frame, body, body) and vice versa depend significantly on the engine mounting method. Usually it is attached at three or four points so that the loads caused by the distortion of the supporting system that occur when the machine moves over unevenness are not taken. Mounting the engine must exclude the possibility of its displacement in the horizontal plane under the action of longitudinal and transverse forces (during acceleration, braking, turning, etc.). To reduce vibration transmitted to the vehicle carrying system from a running engine, rubber cushions of various designs are installed between the engine and the sub-frame, at the attachment points.

The piston group of the crank mechanism is formed by piston assembled with a set of compression and oil scraper rings, a piston pin and its fastening parts. Its purpose is to perceive the gas pressure during the working stroke and transfer the force to the crankshaft through the connecting rod, to carry out other auxiliary strokes, and also to seal the piston cavity of the cylinder to prevent gas breakthrough into the crankcase and the penetration of engine oil into it.

Piston

Piston is a metal glass of complex shape, installed in the cylinder with the bottom up. It has 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 drain holes 6 for oil drainage. To increase the strength and rigidity of the head, its walls are equipped with massive ribs 3 connecting the walls and the bottom with the 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. Piston designs with different bottom shapes (a-h) and their elements:
1 - boss; 2 - the wall of the piston; 3 - rib; 4 - the bottom of the piston; 5 - grooves for compression rings; 6 - drainage hole for oil drainage

The heads of the pistons can be flat (see a), convex, concave and curly (Fig. B-h). Their shape depends on the type of engine and combustion chamber, the adopted mixture formation method and the piston manufacturing technology. The simplest and most technologically advanced is the flat form. In diesel engines, pistons with concave and shaped heads are used (see Fig. E-h).

When the engine is running, the pistons heat up more than the cylinders cooled by liquid or air, therefore the expansion of the pistons (especially aluminum ones) is greater. Despite the presence of a gap between the cylinder and the piston, seizure 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 axis of the piston pin), the diameter of the skirt is increased in comparison with the diameter of the head, the skirt is cut (most often, a T- or U-shaped cut is made), compensation inserts are poured into the piston to limit thermal expansion skirts in the rocking plane of the connecting rod, or forcibly cool the inner surfaces of the piston with jets of engine oil under pressure.

A piston exposed to significant power and thermal loads must have high strength, thermal conductivity and wear resistance. In order to reduce inertial forces and moments, it must have a small 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 separate parts are ceramics and sintered materials with sufficient strength, high wear resistance, low thermal conductivity, low density and low coefficient of thermal expansion.

Piston rings

Piston rings provide a tight movable connection between the piston and the cylinder. They prevent the blow-out of gases from the piston cavity into the crankcase and the ingress of oil into the combustion chamber. Distinguish between compression and oil scraper rings.

Compression rings(two or three) fit into the upper piston grooves. They have a slit called a lock and can therefore be springy. In the free state, the diameter of the ring should be slightly larger than the diameter of the cylinder. When such a ring is introduced into a cylinder in a compressed state, it creates a tight connection. In order to ensure the possibility of expansion of the ring installed in the cylinder during heating, there must be a gap of 0.2 ... 0.4 mm in the lock. In order to ensure good running-in of compression rings to cylinders, rings with a tapered outer surface are often used, as well as twisting rings with a beveled edge on the inner or outer side. Due to the presence of a chamfer, such rings, when installed in a cylinder, are skewed in cross section, tightly adhering 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 for draining oil, which passes through them to the drain holes in the piston (see Fig. A). In addition to oil scraper rings with slots for oil drainage, split rings with axial and radial expanders are used.

To prevent gas leakage from the combustion chamber into the crankcase through the piston ring locks, it is necessary to ensure that the locks of adjacent rings are not aligned.

Piston rings work in difficult conditions. They are exposed to high temperatures, and lubrication of their outer surfaces moving at high speed along the cylinder bore is not enough. Therefore, high demands are placed on the material for the piston rings. Most often, high-grade alloyed cast iron is used for their manufacture. The upper compression rings, which work in 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 to pivot the piston to the connecting rod. It is a tube that passes through the upper connecting rod head and is installed at the ends in the piston bosses. The fastening of the piston pin in the bosses is carried out by two retaining spring rings located in the special grooves of the bosses. This attachment allows the pin (in this case it is called floating) to rotate. Its entire surface becomes working, and it wears out less. The pin axis in the piston bosses can be displaced relative to the cylinder axis by 1.5 ... 2.0 mm towards the action of a greater lateral force. This reduces the piston knocking in a cold engine.

The piston pins are made of high quality steel. To ensure high wear resistance, their outer cylindrical surface hardened or carburized, and then grinded 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 some 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, 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 fixing elements

Connecting rod

Connecting rod connects the piston with the crank of the crankshaft and, converting the reciprocating movement of the piston group into the rotational movement of the crankshaft, makes a complex movement, while being subjected to the action of alternating shock loads. The connecting rod consists of three structural elements: the rod 2, the upper (piston) head 1 and the lower (crank) head 3. The connecting 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 in order to be able to be assembled with the crankshaft. On gasoline engines, the head connector is usually located at a 90 ° angle to the connecting rod axis. 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, which are precisely matched to the holes in the connecting rod and the cover to ensure high assembly accuracy. To prevent the fastening from loosening, the bolt nuts are secured with cotter pins, lock washers or lock nuts. The hole in the bottom head is bored together with the cap, so the connecting rod caps cannot be interchangeable.

Rice. Details of the connecting rod group:
1 - the upper head of the connecting rod; 2 - rod; 3 - the lower head of the connecting rod; 4 - lower head cover; 5 - inserts; 6 - bushing; 7 - diesel connecting rod; S - main connecting rod of the articulated connecting rod assembly

To reduce friction in the connection of the connecting rod to the crankshaft and to 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 antifriction alloy. The inner surface of the liners is precisely matched to the crankshaft journals. To fix the inserts relative to the head, they have bent antennae that fit into the corresponding grooves of the head. The oil supply to the friction surfaces is provided by annular grooves and holes in the liners.

To ensure a good balance of the parts of the crank mechanism, the connecting rod groups of one engine (as well as piston ones) must have the same mass with a corresponding distribution between the upper and lower connecting rod heads.

V-engines sometimes use articulated connecting rod assemblies consisting of twin connecting rods. The main connecting rod 8, which has a conventional structure, is connected to a piston of one row. The auxiliary trailed connecting rod, connected by the upper head with the piston of another row, is hinged by the lower head with the help of a pin to the lower head of the main connecting rod.

Connected to the piston by means of a connecting rod, it absorbs the forces acting on the piston. A torque arises on it, which is then transmitted to the transmission, and is also used to drive other mechanisms and assemblies. Under the influence of the forces of inertia and gas pressure, which are sharply changing in magnitude and direction, the crankshaft rotates unevenly, experiencing torsional vibrations, being subjected to twisting, bending, compression and tension, as well as perceiving 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 (nose 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. With the main journals, the shaft is installed in the bearings of the engine crankcase. The main and connecting rod journals are connected with the help of cheeks. A smooth transition from necks to cheeks, called a fillet, avoids stress concentration and possible crankshaft damage. Counterweights are designed to unload the main bearings from centrifugal forces arising on the cranks of the shaft during its rotation. They are usually made in one piece with the cheeks.

To ensure normal engine operation, it is necessary to supply engine oil under pressure to the working surfaces of the main and connecting rod journals. Oil flows from the holes in the crankcase to the main bearings. Then, through special channels in the main journals, cheeks and connecting rod journals, it enters the connecting rod bearings. For additional centrifugal oil cleaning, there are dirt trapping cavities in the connecting rod journals, which are 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 heat treatment, the main and connecting rod journals are surface hardened (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.

In the main bearings, thin-walled wear-resistant liners are used, similar to those 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 attaches to the crankshaft shank flange. It is a carefully balanced cast iron disc of a certain weight. In addition to ensuring uniform rotation of the crankshaft, the flywheel helps to overcome the compression resistance in the cylinders when starting the engine and short-term overloads, for example, when starting the vehicle. On the rim of the flywheel, a gear ring is fixed for starting the engine from the starter. The surface of the flywheel, which is in contact with the clutch driven plate, is ground and polished.

Rice. Crankshaft:
1 - sock; 2 - connecting rod neck; 3 - root neck; 4 - cheek; 5 - counterweight; 6 - shank with flange

The crank mechanism (CRM) is perhaps the most important engine system.
The purpose of the crank mechanism is to convert the reciprocating motion into rotary motion and vice versa.

All parts of the crank mechanism are divided into two groups: movable and fixed. Moving ones include:

• piston,
• crankshaft,
• flywheel.

To motionless:

• cylinder head and block,
• crankcase cover.

Crank mechanism device

The piston is like an upside-down cup in which the rings fit. On any of them there are two types of rings: oil scraper and compression. There are usually two oil scraper valves, and one compression valve. But there are also exceptions in the form: two such and two such - it all depends on the type of engine.

The connecting rod is made of an I-section steel section. It consists of an upper head, which is connected to the piston with a pin, and a lower head, which is connected to the crankshaft.

The crankshaft is mainly made of high strength cast iron. It is a misaligned bar. All necks are carefully ground in compliance with the required parameters. There are main journals - for the installation of main bearings, and connecting rod - for installation through the bearings of the connecting rods.

The role of sliding bearings is performed by split half rings made in the form of two bushings, 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. To make the liners work well, they are grooved for oil access. If the bushings are cranked, it means that there is insufficient oil supply to them. This usually occurs when the oil system is clogged. The inserts cannot be repaired.

Longitudinal movement of the shaft is limited by special thrust washers. At both ends, it is imperative to use different oil seals to prevent oil from escaping from the engine lubrication system.

Attached to the front of the crankshaft is a pulley for the cooling system drive and a sprocket that drives the camshaft using a chain drive. On the main models of cars produced today, it has been replaced by a belt. A flywheel is attached to the rear of the crankshaft. It is designed to eliminate shaft imbalance.

It also has a ring gear for starting the engine. So that there are no problems during disassembly and further assembly, the flywheel is fastened according to an asymmetric system. The timing of ignition also depends on the location of the marks of its installation - therefore, the optimal operation of the engine. When manufactured, it is balanced with the crankshaft.

The crankcase is manufactured together with the cylinder block. It serves as the basis for attaching the timing and KShM. There is a pallet that serves as a container for oil, as well as to protect the engine from deformation. A special engine oil drain plug is provided at the bottom.

The principle of operation of KShM

The piston is pressured by gases that are generated during the combustion of the fuel mixture. At the same time, it performs reciprocating movements, forcing the engine crankshaft to turn. 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 in:

The main signs of a malfunction of the KShM:

• knocking on the engine;
• loss of power;
• lowering the oil level in the crankcase;
• increased smoke of exhaust gases.

The crank mechanism of the engine is very vulnerable. Timely oil change is essential for efficient operation. It is best done at a service station. Even if you have recently changed the oil, and it is time for seasonal maintenance, be sure to switch to the oil that is indicated in the operating instructions for the machine. If any problems arise in the operation of the engine: noises, knocks - contact the specialists - only in an authorized center you will be given an objective assessment of the condition of the car.

Kripoship (Fig. 32) - a link of the crank mechanism, which can make a full revolution around a fixed axis. The crank (I) has a cylindrical protrusion - spike 1, the axis of which is offset relative to the axis of rotation of the crank by a distance r, which can be constant or adjustable. The more complex rotating link in the crank mechanism is the crankshaft. Eccentric (III) - a disc mounted on a shaft with eccentricity, that is, with a displacement of the disc axis relative to the shaft axis. The eccentric can be considered as a constructive version of the crank with a small radius.

Rice. 32

Crank mechanism- a mechanism that transforms one type of movement into another. For example, uniformly rotational - into translational, rocking, uneven rotational, etc. The rotating link of the crank mechanism, made in the form of a crank or crankshaft, is connected to the rack and other link by rotary kinematic pairs (hinges). It is customary to distinguish between such mechanisms for crank-connecting-rod, crank-rocker, crank-rocker, etc., depending on the nature of the movement and the name of the link, in tandem with which the crank works.

Are used crank mechanisms v piston engines, pumps, compressors, presses, in the motion drive of metal-cutting machines and other machines.

crank mechanism is one of the most common motion transformation mechanisms. It is used both for converting rotary motion into reciprocating (for example, piston pumps), and for converting reciprocating into rotational (for example, internal combustion engines).

Connecting rod- a part of the crank (slider) mechanism that transmits the movement of the piston or slider to the crankshaft crank. The part of the connecting rod that serves to connect to the crankshaft is called the crank head, and the opposite part is the piston (or slider) head.

The mechanism consists of a rack 1 (Fig. 33), a crank 2, a connecting rod 3 and a slider 4. The crank performs continuous rotation, the slider - reciprocating movement, and the connecting rod - a complex, plane-parallel movement. , The full stroke of the slider is obtained equal to twice the length of the crank. Considering the movement of the slider from one position to another, it is easy to see that when the crank is turned by equal angles the slider travels a different distance: when moving from the extreme position to the middle position, the sections of the slider's path increase, and when moving from the middle position to the extreme position, they decrease. This indicates that at uniform movement crank slider moves unevenly. So the speed of the slider changes from zero at the beginning of its movement and reaches its maximum value when the crank and the connecting rod form a right angle with each other, then again decreases to zero at the other extreme position.

Rice. 33

The uneven stroke of the slide causes the appearance of inertial forces, which have a negative effect on the entire mechanism. This is the main disadvantage of the crank-slider mechanism.

In some crank mechanisms, it becomes necessary to ensure the straightness of the movement of the piston rod 4 (Fig. 34). For this, between the crank 1, the connecting rod 2 and the slider 5, the so-called crosshead 3 is used, which takes over the swinging movements of the connecting rod (4 is an intermediate rod).

Rice. 34

The main moving parts of the internal combustion engine are part of the crank mechanism, the purpose of which is to convert the reciprocating movement of the piston into the rotational movement of the crankshaft. Depending on the design of the crank mechanism, engines, like their pistons, are trunk and crosshead, simple and double acting. Unlike trunk-type engines, crosshead engines have, along with the piston, connecting rod and crankshaft, a piston rod and a crosshead (crosshead) moving along the crosshead.

The trunk piston is at the same time a slider, so it has a long guiding part, called a skirt or trunk. An example of such a piston is the piston of a four-stroke diesel engine shown in Fig. 43. The piston consists of a head 1 and a trunk 7 with a chamber inside. The piston head includes a bottom and a side surface on which grooves for piston sealing 2 and oil scraper 3 rings are located. The same. a groove for oil scraper rings is located on the bottom of the trunk.

The guiding part of the piston has a device for connecting it to the connecting rod, consisting of the piston pin 5, bushings 6 and plugs 4. In practice, two methods of installing the piston pin in the bosses of the piston guide part are common: the finger is rigidly fixed in the bosses, the connecting rod is fixed on it; the pin is not fixed in the bosses, the connecting rod also has the ability to rotate around it (the so-called floating pin). In the latter case, the design of the pin (Fig. 43, item 5) has undoubted advantages, since the wear of the pin is reduced and occurs more evenly, the working conditions of the pin are improved.

Rice. 43. Trunk piston of a four-stroke engine.

With a cylinder diameter of more than 400 mm, the pistons of trunk engines are made split.

Pistons of crosshead engines differ from trunk engines in that they have a rigid connection between the piston and the rod. The piston rod usually ends with a flange that is connected to the piston by means of studs.

To avoid overheating of the piston bottom, engines with sliders, as well as trunk engines with large-diameter cylinders, use artificial cooling of the bottoms. For this purpose, fresh or sea water and oil are used.

In fig. 44 shows the shortened piston of a modern two-stroke supercharged diesel engine. In such diesel engines, the lower cylinder cavity is used as a purge pump, therefore the guiding part of the piston is significantly reduced (short or shortened piston). The forged steel piston head 4 has grooves on the outside for the O-rings 3, and a displacer 5 is located inside the piston head, designed to accelerate the movement of the cooling oil. In the guide part of the piston 1, made of cast iron, there are grooves for the guide rings 2. Inside the guide part there are pins 7 for fastening the piston rod 8 with the piston head through the holes in the guide part. The bottom of the piston is cooled with oil, which is supplied through channel 9 in the piston rod, and withdrawn from the upper cavity through pipe 6. The most loaded part of all types of pistons is the piston head. During engine operation, hot gases are pressed onto the bottom of the head during engine operation, which heat it up and, in addition, tend to break through into the engine. As a result, the bottom of the piston head has a special configuration due to the required shape of the combustion chamber and the inner surface to be cooled.

Rice. 44. Shortened piston of a two-stroke supercharged diesel engine.

The height of the side surface of the piston head depends on the size and number of piston seal rings. Piston rings provide not only cylinder seals against gas breakthrough, but also heat transfer from the piston head to the walls of the cylinder liner. These functions are usually performed by two or three upper rings, and the rest are, as it were, auxiliary, increasing the reliability of their operation. In low-speed engines, five to seven piston rings are usually installed, and in high-speed engines, due to a decrease in the time of gas flow through leaks between the piston and the cylinder walls, three to five are enough.

Piston rings are made of rectangular or less often trapezoidal cross-section from a softer metal than the cylinder bushing. To be able to install the rings in the grooves of the piston, they are made split, and the joint, called the lock, is performed with an oblique, stepped (overlapping) or straight cut. Due to the split design and the springy properties of the material, the piston rings are tightly pressed against the walls of the cylinder liner, preventing the piston from rubbing against them. This improves the working conditions of the piston and reduces the wear of the bushing.

Unlike sealing oil scraper rings, they serve to prevent oil from entering the combustion chamber and to remove excess oil from the walls of the cylinder sleeve.

The engine connecting rod is designed to transmit power from the piston to the crankshaft. It consists of three main parts (Fig. 45): the lower head I, the shaft II, and the upper head III. Connecting rods, like pistons, are trunk and crosshead. Their difference is mainly determined by the design of the upper head and the position of the connecting rod in relation to the piston.

Rice. 45. The connecting rod of the trunk engine.

The upper connecting rod head of trunk motors (low and medium power engines) is one-piece. A bronze bushing 2 is pressed into the hole in the head 1 (Fig. 45), which acts as a head bearing and serves to connect the connecting rod to the piston using a piston pin. The sleeve 2 has an annular groove 3 and holes 4 for supplying lubricant from the central channel 5 drilled in the rod along the inner surface.

The connecting rods of crosshead engines, which mainly include high-power engines (as a rule, two-stroke diesel engines with a cylinder power of more than 300 e.h.p.), are manufactured with a split upper head. Such a head is bolted to the top of the connecting rod, which is in the form of a fork or rectangular flange. The rod 6 of the connecting rod is made of a circular cross-section with a central channel 5, which is typical for low-speed engines.

The rods of the connecting rods of high-speed engines are usually circular or I-shaped in cross-sections, often manufactured in one piece with the upper half of the lower head, which helps to reduce the weight of the connecting rod. The lower head of the connecting rod serves to locate the crank bearing in it, by means of which the connecting rod is connected to the crank journal of the crankshaft. The head consists of two halves equipped with bronze or steel interchangeable liners, the inner surface of which is filled with a layer of babbitt.

In low-speed engines, the connecting rod is made with a detachable bottom head 9, consisting of two steel halves - castings without liners. In this case, the working surface of each half of the head is poured with a layer of babbitt. This design of the lower head allows it to be quickly replaced in case of failure and makes it possible to adjust the height of the compression chamber of the engine cylinder by changing the thickness of the compression gasket 7 between the connecting rod heel and the upper part of the head. To center the lower head with the connecting rod, a protrusion 11 is provided on its upper part.

Both halves of the crank bearing are pulled together by two connecting rod bolts 8, which have two seating belts, fastened with castle nuts and cotter pins. A set of gaskets 10 in the bearing connector is required to adjust the oil gap between the crankshaft crank journal and antifriction filling. The spacers are fixed in the connector with studs and screws.

The crankshaft is one of the most critical, difficult to manufacture and expensive engine parts. The crankshaft undergoes significant loads during operation, therefore, high-quality carbon and alloy steels, as well as modified and alloyed cast irons, are used for its manufacture. Due to the complexity of the design, the manufacture of a crankshaft is associated with labor-intensive and complex processes, and its cost, including material, forging and machining, sometimes amounts to more than 10% of the cost of the entire engine.

The crankshafts of high-speed engines of low and medium power are made one-piece forged or one-piece stamped, the shafts of engines of medium and high power are made up of two or more parts connected by flanges. With a large diameter of the necks, the shafts are made with composite cranks.

Depending on the design and the number of cylinders of the engine, the crankshaft may have a different number of knees (cranks): in single-row engines - equal to the number of cylinders, and in two-row (V-shaped) - equal to half the number of cylinders. The shaft elbows are deployed in relation to each other at a certain angle, the value of which depends on the number of cylinders and the order of their operation (flash order for engines with four, six or more cylinders).

The main elements of the crankshaft (Fig. 46, a) are: crank (or connecting rod) journals 2, frame (or main) journals I and cheeks 3, connecting the journals to each other.

Sometimes, to balance the centrifugal forces of the knee, a counterweight 2 is attached to the cheeks 1 (Fig. 46.6). The crank journals are covered by the bearing of the lower connecting rod head, and the frame journals lie in the frame bearings located in the base frame or the engine crankcase and which are the crankshaft bearings. The necks are lubricated as follows. Oil is supplied to the frame journals under pressure through the holes in the cover and in the upper shell of the frame bearing, then through the holes in the cheek (Fig. 46, c) it is supplied to the crank journal. In hollow crankshafts of high-speed engines, oil enters the shaft cavity and enters the working surfaces of the journals through the cavities and radial holes made in them.

Rice. 46. ​​Engine crankshaft.

The frame bearings take all the loads transmitted to the crankshaft. Each frame bearing consists of two halves: a housing, molded in one piece with the frame, and a cover bolted to the housing. A steel insert is fixed inside the bearing, consisting of two interchangeable halves (upper and lower), cast in work surface antifriction alloy - babbitt. The length of the liner is usually chosen less than the length of the frame journal of the shaft. One of the frame bearings (the first from the transmission of rotation to the camshaft) is performed as an installation one (Fig. 47).

Rice. 47. Crankshaft mounting frame bearing.

The length of the insert 7 of the locating bearing is equal to the length of the journal of the shaft; it has an antifriction filling 1 not only inside, but also from the end surface. In turn, the frame journal of the shaft at the seat of this bearing has protruding annular collars. Thus, the positioning bearing provides a well-defined position of the crankshaft relative to the base frame. The bearing insert 7 is prevented from turning and axial movement by the insert 5 located between the bearing cover 3 and the upper half of the insert. The plane of the bushing part coincides with the plane passing through the shaft axis, which is below the plane of the frame-to-engine connection. In the plane of the connector, gaskets 6 are installed on two control pins, designed to adjust the oil gap between the liner and the shaft journal.

Bearing cover 3 is made of cast steel. It has a vertical through hole in the center for supplying lubricant to the shaft journal. The same coaxial hole is located in the upper half of the liner, from which oil enters the annular oil groove 4 on the surface of the anti-friction filling, and then into the oil cooler 2.

A flywheel is usually attached to the aft end of the crankshaft, designed to reduce and equalize the angular speed of rotation of the shaft. In addition, the inertia of the flywheel makes it easier for the connecting rod to cross the dead center. The size and weight of a flywheel is inversely related to the number of cylinders in the engine: the greater the number of cylinders, the less the weight of the flywheel should be. Often a flywheel, in particular its disk, is used to connect to a propeller shaft, gearbox shaft or generator shaft using an elastic coupling.

If there is one thing strongly associated with any car, it is the engine mechanism. Oddly enough, its principle of operation has changed little since Karl Benz patented his first car 120 years ago. The system became more complicated, overgrown with complex electronics, improved, but the crank mechanism (KShM) remained the most recognizable "portrait" of any motor.

What is CSM and what is it for?

The engine in the process of operation should give some kind of constant movement, and it is most convenient for this to be uniform rotation. However, the power unit (cylinder-piston group, CPG) generates translational motion. This means that it is necessary to make sure that one type of motion is transformed into another, and with the least loss. This is why the crank mechanism was created.
In fact, KShM is a device for receiving and converting energy and transmitting it further to other nodes that already use this energy.

Strictly speaking, the car's KShM consists of the crank itself, connecting rods and pistons. However, it would be fundamentally wrong to talk about a part without talking about a holistic structure. Therefore, the scheme and purpose of the KSHP and adjacent elements will be considered in a complex.

KShM device: (1 - main bearing on the main journal; 2 - connecting rod bearing on the connecting rod journal; 3 - connecting rod; 4 - piston pin; 5 - piston rings; 6 - piston; 7 - cylinder; 8 - flywheel; 9 - counterweight; 10 - crankshaft.)

1. Cylinder block- this is the beginning of all movement in the motor. Its components are pistons, cylinders and cylinder liners in which these pistons move;
2. Connecting rods Are the connecting elements between the pistons and the crankshaft. In fact, the connecting rod is a solid metal bridge, which is attached to the piston with one side using a connecting rod pin, and the other is fixed to the crankshaft neck. Thanks to the finger connection, the piston can move relative to the cylinder in one plane. In the same way, the connecting rod covers the crankshaft seat - the connecting rod journal, and this mount allows it to move in the same plane as the connection with the piston;
3. Crankshaft- a crankshaft of rotation, the axis of which passes through the nose of the shaft, the main (support) journals and the flywheel flange. But the connecting rod journals go beyond the axis of the shaft, and due to this, when it rotates, they describe a circle;
4. Flywheel- an indispensable element of the mechanism that accumulates the inertia of rotation, due to which the engine runs smoothly and does not stop at the “dead center”.

These and other elements of the KShM can be conditionally divided into movable ones, those that perform direct work, and fixed auxiliary elements.

Mobile (working) group of KShM

As the name implies, the moving group includes elements that are actively involved in the operation of the engine.

1. Piston... When the engine is running, the piston moves in the cylinder liner under the action of the buoyant force during combustion of the fuel - on the one hand, and by turning the crankshaft - on the other. To seal the gap between it and the cylinder, piston rings (compression and oil scraper) are located on the side surface of the piston, which seal the gap and prevent loss of power during fuel combustion.

   
   Piston group device: (1 - oil-cooling channel; 2 - combustion chamber in the piston crown; 3 - piston crown; 4 - groove of the first compression ring; 5 - first (upper) compression ring; 6 - second (lower) compression ring; 7 - oil scraper ring; 8 - oil nozzle; 9 - hole in the head of the connecting rod for supplying oil to the piston pin; 10 - connecting rod; 11 - piston pin; 12 - piston pin retaining ring; 13 and 14 - partitions of piston rings; 15 - fire belt.)

2. Connecting rod... It is the connecting piece between the piston and the crankshaft. The upper connecting rod head is attached to the piston with a pin. The lower head has a removable part so that the connecting rod can be put on the crankshaft journal. To reduce friction between the crankshaft neck and the connecting rod head, connecting rod bushings are installed - plain bearings in the form of two plates bent in a semicircle.

   
   Connecting rod device

3. Crankshaft... This is the central part of the engine, without which it is difficult to imagine how it works. Its main part is the axis of rotation, which at the same time serves as a support for the crankshaft in the cylinder block. The elements protruding beyond the axis of rotation are intended for connection to the connecting rods: when the connecting rod moves down, the crankshaft allows it to describe the lower part of the circle simultaneously with the movement of the piston. As in the case of the connecting rods, the bearing journals of the crankshaft rest on plain bearings - liners.

   
   Crankshaft device

4. Flywheel... It is attached to a flange on the end of the crankshaft. The flywheel rotates with the engine shaft and partially dampens the jerky loads inevitable in any internal combustion engine. But the main task of the flywheel is to spin the crankshaft (and with it the cylinder-piston group) so that the pistons do not freeze at the “dead center”. Thus, some of the engine power is expended in supporting the rotation of the flywheel.

Flywheel device

Fixed group KShM

The fixed group can be called the external part of the engine, in which the KSHP is located.

1. Cylinder block... In fact, this is a body in which the cylinders, the channels of the cooling system, the seats of the camshaft, crankshaft, etc. are located. It can be made of cast iron or aluminum alloy, and today manufacturers are increasingly using aluminum to facilitate construction. For the same purpose, instead of solid casting, stiffeners are used, which facilitate the structure without loss of strength. On the sides of the cylinder block there are seats for engine auxiliary mechanisms.

   
   Cylinder block

2. Cylinder head(Cylinder head). Installed on the cylinder block and closes it from above. The cylinder head provides holes for valves, intake and exhaust manifolds, camshaft mounts (one or more), mounts for other engine elements. To the cylinder head, from below, is attached pad(1) - plate that seals the joint between the cylinder block and the cylinder head. It has holes for cylinders and mounting bolts. And from above - valve lid(5), - it closes the cylinder head from above when the engine is assembled and ready to start. Valve cover gasket. This is a thin plate that fits around the perimeter of the cylinder head and seals the joint.

Cylinder head device: (1 - cylinder head gasket; 2 - cylinder head; 3 - oil seal; 4 - cylinder head cover gasket; 5 - valve cover; 6- pressure plate; 7 - oil filler plug; 8 - plug gasket; 9 - valve guide sleeve; 10 - an installation sleeve; 11 - a bolt for attaching the head of the block.)

The principle of operation of KShM

The operation of the engine mechanism is based on the expansion energy during the combustion of the fuel-air mixture. It is these “micro-explosions” that are the driving force that the crank mechanism transforms into a comfortable shape. In the video below, a detailed description of the principle of operation of KShM in 3D animaya.

The principle of operation of the KShM:

1. Fuel atomized and mixed with air is burned in the engine cylinders. Such dispersion does not imply slow combustion, but instantaneous, due to which the air in the cylinder expands sharply.
2. The piston, which is at the top point at the beginning of fuel combustion, drops sharply downward. it straight motion piston in the cylinder.
3. The connecting rod is connected to the piston and the crankshaft so that it can move (deflect) in one plane. The piston pushes the connecting rod, which is put on the crankshaft journal. Due to the movable connection, the impulse from the piston through the connecting rod is transmitted to the crankshaft tangentially, that is, the shaft makes a turn.
4. Since all the pistons take turns pushing the crankshaft in the same way, their reciprocating motion translates into crankshaft rotation.
5. The flywheel adds momentum to rotation when the piston is at dead center.

Interestingly, to start the engine, you first need to spin the flywheel. For this purpose, a starter is needed, which engages with the flywheel ring gear and spins it until the engine starts. The law of conservation of energy in action.

The rest of the engine elements: valves, camshafts, pushers, cooling system, lubrication system, timing and others are the necessary parts and assemblies to ensure the operation of the KShM.

Major malfunctions

Considering the loads, both mechanical and chemical, and temperature, the crank mechanism is susceptible to various problems. Competent maintenance helps to avoid troubles with the KSHP (and, therefore, with the engine), but still no one is insured against breakdowns.

Engine knocking.

One of the scariest sounds when a strange knocking and other extraneous noises suddenly appear in the engine. This is always a sign of problems: if something starts knocking, then there is a problem with it. Because the elements in the engine are micron-sized, knocking is a sign of wear. We'll have to disassemble the engine, see what was knocking, and change the worn out part.

The main cause of wear is often poor-quality engine maintenance. Engine oil has its own resource, and its regular replacement is of paramount importance. The same applies to filters. Hard particles, even the smallest ones, gradually wear out finely fitted parts, form seizures and wear.

Knocking can also indicate wear on the bearings (liners). They also suffer from a lack of lubrication, since it is on the bushings that a huge load is placed.

Decrease in power.
Loss of engine power may indicate piston ring stuck. In this case, the rings do not fulfill their function, engine oil remains in the combustion chamber, and the combustion products break through into the engine. A breakthrough of gases also speaks of a waste of energy, and this is felt by the car owner as a decrease in dynamic characteristics. Long-term work in such a situation can only worsen the condition of the engine and bring the standard, in general, problem to the engine overhaul.

You can check the condition of the motor yourself by measuring the compression in the cylinders. If it is lower than the standard for this engine modification, then the engine needs to be repaired.

Increased oil consumption.
If the engine starts to "eat" oil, this is a clear sign of sticking piston rings or other problems with the cylinder-piston group. The oil burns along with the fuel, black smoke comes out of the exhaust pipe, the temperature in the combustion chamber exceeds the calculated one, and this does not add health to the engine. In some cases, cleaning without dismantling the engine can help, but in most cases, disassembly and troubleshooting of the engine will have to be done.

Nagar.
Deposits on pistons, valves, and spark plugs indicate a problem with the engine. If the fuel does not burn out completely, you need to look for the cause of the malfunction and eliminate it. Otherwise, the motor is threatened with overheating due to the deterioration of the thermal conductivity of surfaces with a layer of carbon.

White smoke from the exhaust pipe.
Appears when antifreeze enters the combustion chamber. The reason is most often the wear of the cylinder head gasket or microcracks in the engine cooling jacket, and to fix the problem, it needs to be replaced.

It is undesirable to hesitate in this situation: a small leak can turn into a water hammer. The combustion chamber is filled with liquid, the piston moves up, but the liquid, unlike air, is not compressed, and the effect of hitting a hard surface is obtained. The consequences of such a disaster can be any, up to the “fist of friendship” and the sale of a car for parts.

Conclusion

Despite the high loads, critical working conditions and even the negligence of the owners, the crank mechanism is distinguished by enviable survivability. It can be disabled by improper maintenance, abnormal loads, breakdown of adjacent elements. Yes, the engine can almost always be repaired, but this service will cost many times more than just competent regular maintenance. It is not for nothing that there are million-plus engines that can serve for decades without causing problems to the owner of the car.