Topic: “Purpose and design of the crank mechanism of internal combustion engines. The crank mechanism is the heart of a car engine. Research on the design of the crank mechanism.

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 for compression rings are machined in the walls. The lower grooves have drainage holes 6 to drain oil. To increase the strength and rigidity of the head, its walls are equipped with massive ribs 3 that connect the walls and bottom with bosses in which the piston pin is installed. Sometimes the inner surface of the bottom is also ribbed.

The skirt has thinner walls than the head. In its middle part there are bosses with holes.

Rice. Designs of pistons with different bottom shapes (a-z) and their elements:
1 - boss; 2 - piston wall; 3 - rib; 4 - piston bottom; 5 - grooves for compression rings; 6 - drainage hole for oil drainage

The piston heads can be flat (see a), convex, concave and shaped (Fig. b-h). Their shape depends on the type of engine and combustion chamber, the adopted method of mixture formation and the manufacturing technology of the pistons. The simplest and most technologically advanced is the flat form. Diesel engines use pistons with concave and shaped bottoms (see Fig. e-h).

When the engine is running, the pistons heat up more than cylinders cooled by liquid or air, so the expansion of the pistons (especially aluminum ones) is greater. Despite the presence of a gap between the cylinder and the piston, jamming of the latter may occur. To prevent jamming, the skirt is given an oval shape (the major axis of the oval is perpendicular to the piston pin axis), the diameter of the skirt is increased compared to the diameter of the head, the skirt is cut (most often a T- or U-shaped cut is made), and compensation inserts are poured into the piston to limit thermal expansion skirts in the plane of swing of the connecting rod, or forcefully cool the internal surfaces of the piston with jets of engine oil under pressure.

A piston subjected to significant force and thermal loads must have high strength, thermal conductivity and wear resistance. In order to reduce inertial forces and moments, it must have a low mass. This is taken into account when choosing the design and material for the piston. Most often the material is aluminum alloy or cast iron. Sometimes steel and magnesium alloys are used. Promising materials for pistons or their individual parts are ceramics and sintered materials that have sufficient strength, high wear resistance, low thermal conductivity, low density and a small coefficient of thermal expansion.

Piston rings

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 are often used on cylinders, as well as twisting rings with a chamfer on the edge on the inside or outside. 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

The crank mechanism device is designed to convert the reciprocating motion of the piston into rotational motion, which can act as the movement of the crankshaft in an internal combustion engine of a car, and vice versa.

The parts of the crank mechanism are divided into two groups, which include: moving parts and stationary parts. The moving parts are: piston together with, crankshaft device with bearings, connecting rod, piston pin, flywheel and crank. Fixed parts include: cylinder block, which are the basic parts of an internal combustion engine (is a single casting with the crankcase); clutch and flywheel housing, cylinder head, lower crankcase, block covers, cylinder liners, block cover gaskets, fasteners, crankshaft half-rings, brackets.

1. Purpose and characteristics of the connecting rod mechanism.

The crank mechanism is the main device of a piston internal combustion engine. This system is designed to perceive gas pressure at a certain stroke. In addition, this mechanism allows you to convert the movements of the reciprocating pistons into rotational movements of the car’s crankshaft.

This standard device consists of pistons that have piston rings, liners and cylinder heads, crankcase, connecting rods, crankshaft, flywheel, connecting rod and main bearings. During the moments of direct operation of the internal combustion engine, the inertial forces of reciprocating moving masses, gas pressure, inertia of various kinds of unbalanced rotating masses, friction and gravity directly affect the parts of the crank mechanism.

All of the above forces, except, of course, gravity, affect the change in the value and direction of all the quantities under consideration. All this directly depends on the angle of rotation of the crankshaft device and the processes that occur directly in the cylinders of the internal combustion engine.

2. Design of the connecting rod mechanism.

Since all the components of the crank mechanism are already known, it is worth starting to consider the crankshaft structure. The crankshaft is one of the main elements of an internal combustion engine, which, along with other parts of the cylinder-piston group, determines the life of the engine itself.

Thus, the service life of the device will be characterized by several indicators: wear resistance and fatigue strength. The crankshaft takes on all the forces that act on the pistons with the help of connecting rods. After this, the crankshaft transmits all these forces to the transmission mechanism. It will power various types of internal combustion engine mechanisms. The crankshaft structure consists of: main journals, connecting rod journals, connecting cheeks, a shank and a toe.

3. Malfunctions of the connecting rod mechanism.

During direct operation of an internal combustion engine, as a result of the action of unstable and excessively high dynamic loads, from the inertial forces of moving and rotating parts, from gas pressure, the shaft is subjected to bending and torsion, and individual surfaces of the device simply wear out.

All fatigue damage accumulates directly in the metal structure, resulting in microcracks and various types of defects. The wear of elements is determined by using universal and special measuring tools. In order to detect cracks, you need to use a magnetic flaw detector. With constant use of the crankshaft, it is subject to defects.

The most common is a wear defect. But many parts of the entire device are subject to wear. When the main journals and connecting rods are worn out, out of ovality and taper, it is necessary to grind to the size required for repair. Applying surfacing coatings, electrical contact welding of tape, metallization, filling the surface with powder materials is the solution to this problem.

In addition, it is recommended to install new half-rings and perform a plastination procedure. In addition, wear can affect the seats that are needed for the timing gear, pulley and flywheel. Wear also affects oil threads, flywheel flange surfaces, flywheel pins, and keyways. In order to solve all the above problems it will not take a lot of resources and time.

For the first problem, you need to perform conventional metallization, surfacing or electronic welding of the tape. The problem with the thread is solved by simply deepening the thread with a cutter to a normalized profile. The pins simply need to be replaced, but for the grooves you need to mill for the increased size of the keys and for new keyways. After this you need to do welding and the problem will disappear.

In addition, wear can also affect the seat for the outer rings at the end of the shaft, holes for the pins, flywheel mounting and threads. Everywhere you need to bore the seats and press in the bushings. In addition, the pins need to be reamed for repair size and welded. Threading also requires countersinking or boring with enlargement of the thread in a subsequent process. All threaded holes are also deepened.

In addition to wear, problems also arise with shaft twisting, which results in disruption of the crank alignment. In this case, you need to grind the journals to a special repair size and fuse the journals with subsequent processing. The most problematic can be cracks in the shaft journals, since in addition to grinding them to the repair size, it will be necessary to cut the cracks using an abrasive tool. In principle, this is quite enough for the motorist, since other problems and malfunctions may require professional intervention from outside.

4. Servicing the connecting rod mechanism.

Proper maintenance of the internal combustion engine and its normal operation will ensure minimal wear of all its parts and its uninterrupted operation. In addition, the crank mechanism will not need repair for quite a long time.

In order to ensure normal operating conditions for all structural components of the crank mechanism during its operation strictly NOT allowed following:

- prolonged operation when the engine is overloaded;

Operating the engine under conditions of low oil pressure;

Operating the engine at very low crankcase oil temperatures;

Prolonged idling of the engine, which will cause coking of the piston rings;

Operation of a motor in which there is no fan casing or there is one, but its fit is loose to the mating surface;

Engine operation where there is no air cleaner or it is in a faulty condition;

Intermittent engine operation, accompanied by smoky exhaust and knocking.

When directly disassembling the internal combustion engine device for its repair, the cavities of the connecting rod journals of the crankshaft mechanism should be cleaned. In order to completely clean all the cavities, you need to pull out the cotter pins and unscrew the screw plugs. The effective composition of the centrifugal cleaning of oil from the cavities of the connecting rod journals will depend on all the rules for maintaining the lubrication system and on how correctly the oil is stored and refilled into the engine.

If the recommended rules are not followed, then the cavities of the connecting rod journals will quickly fill with various deposits, and oil purification will generally disappear into oblivion. If the power has decreased greatly, the smoke and gases are quite strong, starting the engine is difficult, and abnormal knocking noises occur that are associated with a malfunction of the crank mechanism, you should immediately “get into” the device and inspect it. Disassembly of the internal combustion engine should be done indoors.

Greetings to the readers of our cozy blog! Now let's talk about the heart of our iron horses, internal combustion engines. More precisely, this time we will consider the purpose of the crank mechanism - one of the key mechanisms of the motor.

It is difficult to overestimate the purpose of the crank mechanism. In fact, it is he who we must thank for the fact that our iron horses do not stand still, but can transport our mortal bodies and give us the joy of driving.

Speaking in dry technical language, the purpose of the crank mechanism (CPM) is to convert the energy of the burnt fuel-air mixture into mechanical rotation.

Naturally, the KShM is not a monolithic structure and consists of a number of simpler parts, which will be discussed below.

Conventionally, the elements of the crank mechanism can be divided into two large subgroups: moving and stationary parts.

The first includes pistons with rings and pins, connecting rods, a crankshaft (in common parlance, a crankshaft), and a flywheel.

Cylinder block

The fixed elements of the crankshaft are represented by the cylinder block and the cylinder head, the crankcase, as well as the gasket located between the block and the head.

And now a little more about the role of each of the actors in the theater of the crank mechanism. It is one of the first to take the blow of the burning fuel-air mixture.

This heroic element is a cylindrical metal piece, roughly speaking, shaped like a glass.

In fact, its shape is quite complex - with grooves, bulges, holes and cutouts.

All these complex shapes are needed not only for the efficient operation of the engine, but also so that there is where to place the piston rings, as well as where to insert the piston pin, to which the next important part of the mechanism is attached -.

The reason for the existence of a connecting rod is as simple as five kopecks - transmitting the translational motion of the piston to the crankshaft.

Quite a boring but important role. The connecting rod itself looks like a metal I-section rod.

At one end there is a hole for attaching to the piston using a piston pin, and at the other there is a half-ring, which is put on the crankpin of the shaft and secured with bolted joints with a special cover.

It is worth noting that the connection between the connecting rod and the crankshaft is movable - it must rotate.

Crankshaft

The importance of the next element of the CVM is difficult to overestimate - this.

Of course, it is quite difficult to call this part a shaft in the usual sense - its shape is complex and all due to the fact that all the connecting rod-piston ligaments of the engine are attached to it.

The crankshaft is the key rotating element of the engine and it has to withstand incredible loads, therefore the requirements for the quality of its workmanship and the strength of the materials are the highest.

The main parts of the crankshaft are the crankpins (the places where the connecting rods are attached), the journals, the main journals, and the counterweights. By the way, the crank-connecting rod mechanism got its name precisely because of the part of the crankshaft, or, to be precise, the crank - this is what is sometimes called the combination of the connecting rod journal and the cheeks on either side of it.

The crankshaft is crowned on one side.

It should be noted that, despite its relative external simplicity, the flywheel plays several roles at once.

Firstly, its main task is to maintain uniform rotation of the crankshaft while the engine is running.

Secondly, it is this modest metal wheel that acts as the connecting link between the starter and the same crankshaft when you turn the ignition key to start the engine.

Almost all the moving parts of the crank mechanism are located in the cylinder block, and the cylinder head closes all this spinning and rotating disgrace from our eyes.

As a rule, valves, spark plugs and channels for supplying coolant, oil, and air-fuel mixture are built into it.

It should be noted that it is together with the head that determine such an important parameter of the engine as its mass.

In the classic version, these elements are made of cast iron, but thanks to modern technologies, automakers are increasingly using aluminum in their construction, which has a beneficial effect on the weight of the engine and, as a result, the entire car.

The use of light alloys has become possible even in such a critical element of the block as cylinder liners (the pistons move up and down in them), which must be resistant to wear and withstand high temperatures.

How many cylinders does your horse have?

In conclusion, our dear readers, I would like to say a few words about the types of layout of internal combustion engines and cylinder layouts.

Automobile concerns complete their creations with several types of motors, namely:

• in-line;
• V-shaped;
• opposite;
• W-shaped.

From a balance point of view, in-line and boxer engines are the most optimal.

The former are quite common in the auto world - in-line four-cylinder units are found all the time, but the fate of the boxer units is not so public - they have become synonymous with a certain exclusivity and “clubiness”.

So, for example, they can be found in the depths of sports Porsches or Subaru.

V-shaped and their related W-shaped engines have the optimal combination of characteristics. They are used to build cars that are accessible to the average car enthusiast, as well as crazy supercars, the cost of which is as incredible as their character.

W-motor operation:

//www.youtube.com/watch?v=xKBpiNorQYQ

Dear blog visitors, in this short article we tried to clarify the purpose of the crank mechanism and consider its components in general terms. I would appreciate your subscription.

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

What is a KShM and why is it needed?

During operation, the engine must provide some kind of constant movement, and it is most convenient for this to be uniform rotation. However, the power part (cylinder-piston group, CPG) produces translational motion. This means that we need to make sure that one type of movement is transformed into another, and with the least losses. This is why the crank mechanism was created.
In essence, a KShM is a device for receiving and converting energy and transmitting it further to other nodes that are already using this energy.

Strictly speaking, the crankshaft of a car consists of the crank itself, connecting rods and pistons. However, talking about a part without talking about the entire structure would be completely wrong. Therefore, the design and purpose of the KShP and related elements will be considered in a comprehensive manner.

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- these are the connecting elements between the pistons and the crankshaft. Essentially, the connecting rod is a strong metal bridge, which is attached to the piston on one side using a connecting rod pin, and the other is fixed to the crankshaft journal. Thanks to the pin 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 fastening 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 shaft toe, the main (support) journals and the flywheel flange. But the connecting rod journals extend beyond the axis of the shaft, and due to this, when it rotates, they describe a circle;
4. Flywheel- an essential element of the mechanism that accumulates rotational inertia, thanks to which the engine runs smoother and does not stop at a “dead point”.

These and other elements of the flywheel can be divided into moving elements, 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 fuel combustion on the one hand, and by rotation of the crankshaft on the other. To seal the gap between it and the cylinder, there are piston rings (compression and oil scraper) on the side surface of the piston, which seal the gap and prevent loss of power during fuel combustion.

   
   Piston group structure: (1 - oil-cooling channel; 2 - combustion chamber in the piston bottom; 3 - piston bottom; 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 connecting rod head for supplying oil to the piston pin; 10 - connecting rod; 11 - piston pin; 12 - piston pin retaining ring; 13 and 14 - piston ring partitions; 15 - flame belt.)

2. connecting rod. This is the connecting element between the piston and crankshaft. The upper head of the connecting rod is attached to the piston using a pin. The lower head has a removable part so that the connecting rod can be placed on the crankshaft journal. To reduce friction, connecting rod bearings are installed between the crankshaft journal and the connecting rod head - plain bearings in the form of two plates curved in a semicircle.

   
   Connecting rod device

3. Crankshaft. This is the central part of the engine, without which it is difficult to imagine its operating principle. Its main part is the axis of rotation, which simultaneously serves as a support for the crankshaft in the cylinder block. The elements protruding beyond the axis of rotation are intended to be attached to the connecting rods: when the connecting rod moves down, the crankshaft allows it to describe a circle with its lower part simultaneously with the movement of the piston. Just as in the case of connecting rods, the crankshaft journals 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 that are 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 a “dead point.” Thus, part of the engine power is used to support the rotation of the flywheel.

Fixed group KShM

The fixed group can be called the outer part of the engine in which the manual transmission gearbox is located.

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

   
   Cylinder block

2. Cylinder head(cylinder head). It is installed on the cylinder block and closes it from above. The cylinder head has holes for valves, intake and exhaust manifolds, camshaft mounts (one or more), and mounts for other engine elements. To the cylinder head, from below, attached pad(1) - a 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.

Operating principle of KShM

The operation of the engine mechanism is based on the expansion energy during combustion of the fuel-air mixture. It is these “micro-explosions” that are the driving force that the crank mechanism transforms into a convenient form. The video below describes in detail the principle of operation of the KShM in 3D animation.

Operating principle of the KShM:

1. Fuel atomized and mixed with air burns in the engine cylinders. This dispersion does not involve slow combustion, but instantaneous combustion, due to which the air in the cylinder expands sharply.
2. The piston, which is at the top point at the moment the fuel begins to burn, drops sharply down. This is the linear movement of the piston in the cylinder.
3. The connecting rod is connected to the piston and crankshaft so that it can move (deviate) in the same plane. The piston pushes the connecting rod, which is placed on the crankshaft journal. Thanks to the movable connection, the impulse from the piston through the connecting rod is transmitted tangentially to the crankshaft, that is, the shaft rotates.
4. Since all the pistons take turns pushing the crankshaft using the same principle, their reciprocating motion translates into rotation of the crankshaft.
5. The flywheel adds rotational momentum when the piston is at its “dead” points.

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

The remaining engine elements: valves, camshafts, pushers, cooling system, lubrication system, timing belt and others are necessary parts and components to ensure the operation of the crankshaft.

Basic faults

Given the loads, both mechanical and chemical, and temperature, the crank mechanism is susceptible to various problems. Competent maintenance helps to avoid troubles with the automatic transmission (and therefore with the engine), but still no one is immune from breakdowns.

Engine knock.

One of the most terrible sounds is when a strange knocking and other extraneous noise suddenly appears in the engine. This is always a sign of problems: if something starts knocking, then there is a problem with it. Since the elements in the engine are adjusted with micron precision, knocking indicates wear. You will have to disassemble the engine, see what was knocking, and replace the worn part.

The main cause of wear is most often poor engine maintenance. Motor oil has its lifespan, and its regular replacement is extremely important. The same applies to filters. Solid particles, even the smallest ones, gradually wear out fine-fitting parts, forming scuffs and wear.

A knock may also indicate wear of the bearings (liners). They also suffer from a lack of lubrication, since the bearings bear a huge load.

Reduced power.
A loss of engine power may indicate stuck piston rings. In this case, the rings do not perform their function, engine oil remains in the combustion chamber, and combustion products break into the engine. The breakthrough of gases also indicates a waste of energy, and the car owner feels this as a decrease in dynamic characteristics. Prolonged operation in such a situation can only worsen the condition of the engine and lead to a standard, in general, problem leading to engine overhaul.

You can check the condition of the engine yourself by measuring the compression in the cylinders. If it is below the standard for a given engine modification, it means that the engine needs to be repaired.

Increased oil consumption.
If the engine begins to “eat” oil, this is a clear sign of stuck 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 design value, and this does not add health to the engine. In some cases, cleaning without dismantling the engine may help, but in most cases the engine will have to be disassembled and troubleshooted.

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

White smoke from the exhaust pipe.
Appears when antifreeze enters the combustion chamber. The cause most often is wear of the cylinder head gasket or microcracks in the engine cooling jacket, and to eliminate the problem it is necessary to replace it.

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

Conclusion

Despite high loads, critical operating conditions and even the negligence of the owners, the crank mechanism is distinguished by enviable survivability. It can be damaged by improper maintenance, abnormal loads, or 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’s not for nothing that there are million-dollar engines that can serve for decades without causing problems to the owner of the car.

Internal combustion engines used in cars operate by converting the energy released during combustion of a combustible mixture into a mechanical action - rotation. This transformation is ensured by the crank mechanism (CCM), which is one of the key ones in the design of a car engine.

KShM DEVICE

The engine crank mechanism consists of three main parts:

1. Cylinder-piston group (CPG).
2. Connecting rod.
3. Crankshaft.

All these components are located in the cylinder block.

CPG

The purpose of the CPG is to convert the energy released during combustion into mechanical action - forward motion. The CPG consists of a liner - a stationary part placed in a block in the cylinder block, and a piston that moves inside this liner.

After the air-fuel mixture is supplied inside the liner, it ignites (from an external source in gasoline engines and due to high pressure in diesel engines). Ignition is accompanied by a strong increase in pressure inside the liner. And since the piston is a moving element, the resulting pressure leads to its movement (in fact, gases push it out of the liner). It turns out that the energy released during combustion is converted into the translational movement of the piston.

For normal combustion of the mixture, certain conditions must be created - the maximum possible tightness of the space in front of the piston, called the combustion chamber (where combustion occurs), an ignition source (in gasoline engines), the supply of a combustible mixture and the removal of combustion products.

The tightness of the space is ensured by the block head, which covers one end of the liner, and by piston rings mounted on the piston. These rings also belong to the CPG parts.

CONNECTING ROD

The next component of the crankshaft is the connecting rod. It is designed to connect the CPG piston and the crankshaft and transmit mechanical action between them.

The connecting rod is an I-shaped cross-section rod, which provides the part with high bending resistance. At the ends of the rod there are heads, thanks to which the connecting rod is connected to the piston and crankshaft.

In fact, the connecting rod heads are eyes through which shafts pass, providing a hinged (movable) connection of all parts. At the junction of the connecting rod with the piston, a piston pin (referred to as a CPG) acts as a shaft, which passes through the piston bosses and the connecting rod head. Since the piston pin is removed, the upper head of the connecting rod is one-piece.

At the junction of the connecting rod with the crankshaft, the connecting rod journals of the latter act as a shaft. The lower head has a split design, which allows the connecting rod to be secured to the crankshaft (the removable part is called the cap).

CRANKSHAFT

The purpose of the crankshaft is to provide the second stage of energy conversion. The crankshaft converts the forward motion of the piston into its own rotation. This element of the crank mechanism has a complex geometry.

The crankshaft consists of journals - short cylindrical shafts connected into a single structure. The crankshaft uses two types of journals - main and connecting rod. The first ones are located on the same axis, they are supporting and are designed to movably secure the crankshaft in the cylinder block.

The crankshaft is fixed in the cylinder block with special covers. To reduce friction at the junction of the main journals with the cylinder block and connecting rods with the connecting rod, friction bearings are used.

The connecting rod journals are located at a certain lateral distance from the main ones and the connecting rod is attached to them with the lower head.

The main and connecting rod journals are connected to each other by cheeks. In diesel crankshafts, counterweights are additionally attached to the cheeks, designed to reduce the oscillatory movements of the shaft.

The connecting rod journals together with the cheeks form a so-called U-shaped crank, which converts translational motion into rotation of the crankshaft. Due to the remote location of the connecting rod journals, when the shaft rotates, they move in a circle, and the main journals rotate about their axis.

The number of connecting rod journals corresponds to the number of engine cylinders, while the main ones are always one more, which provides each crank with two support points.

At one end of the crankshaft there is a flange for attaching the flywheel - a massive disk-shaped element. Its main purpose: the accumulation of kinetic energy due to which the reverse operation of the mechanism is carried out - the transformation of rotation into the movement of the piston. At the second end of the shaft there are seats for drive gears of other systems and mechanisms, as well as a hole for fixing the drive pulley of motor attachments.

OPERATING PRINCIPLE OF THE MECHANISM

We will consider the operating principle of the crank mechanism in a simplified manner using the example of a single-cylinder engine. This engine includes:

• crankshaft with two main journals and one crank;
• connecting rod;
• and a set of CPG parts, including a liner, piston, piston rings and pin.

Ignition of the combustible mixture occurs when the volume of the combustion chamber is minimal, and this is ensured by the maximum lifting of the piston inside the liner (top dead center - TDC). In this position, the crank also “looks” up. During combustion, the energy released pushes the piston down, this movement is transmitted through the connecting rod to the crank, and it begins to move downward in a circle, while the main journals rotate around their axis.

When the crank is rotated 180 degrees, the piston reaches bottom dead center (BDC). After reaching it, the mechanism operates in reverse. Due to the accumulated kinetic energy, the flywheel continues to rotate the crankshaft, so the crank rotates and pushes the piston up through the connecting rod. Then the cycle repeats completely.

If we consider it more simply, then one half-turn of the crankshaft is carried out due to the energy released during combustion, and the second - due to the kinetic energy accumulated by the flywheel. Then the process is repeated again.

FEATURES OF ENGINE OPERATION. SO YOU

A simplified diagram of the operation of the crankshaft is described above. In fact, in order to create the necessary conditions for normal combustion of the fuel mixture, preparatory steps are required - filling the combustion chamber with mixture components, compressing them and removing combustion products. These stages are called “engine strokes” and there are four of them - intake, compression, power stroke, exhaust. Of these, only the power stroke performs a useful function (it is during this stroke that energy is converted into movement), and the remaining strokes are preparatory. In this case, the execution of each stage is accompanied by a rotation of the crankshaft around the axis by 180 degrees.

The designers have developed two types of engines - 2-stroke and 4-stroke. In the first version, the strokes are combined (the power stroke is with exhaust, and the intake is with compression), so in such engines the full working cycle is performed in one full revolution of the crankshaft.

In a 4-stroke engine, each stroke is performed separately, therefore, in such engines, a full working cycle is performed in two revolutions of the crankshaft, and only one half-turn (at the “power stroke”) is performed due to the energy released during combustion, and the remaining 1.5 revolutions - thanks to the energy of the flywheel.

MAIN FAULTS

Despite the fact that the crank mechanism operates under harsh conditions, this component of the engine is quite reliable. With proper maintenance, the mechanism works for a long time.

If the engine is operated correctly, repair of the crankshaft will only be required due to wear of a number of component parts - piston rings, crankshaft journals, and plain bearings.

Failures of the components of the CVM occur mainly due to violation of the rules of operation of the power plant (constant operation at high speeds, excessive loads), failure to perform maintenance, and the use of unsuitable fuels and lubricants.

The consequences of such use of the motor can be:

• occurrence and destruction of rings;
• piston burnout;
• cracks in the cylinder liner walls;
• connecting rod bend;
• crankshaft rupture;
• “winding” of plain bearings onto journals.

Such breakdowns of the crankshaft are very serious; often the damaged elements cannot be repaired; they only need to be replaced. In some cases, crankshaft failures are accompanied by destruction of other engine elements, which renders the motor completely unusable without the possibility of restoration.

KShM MAINTENANCE

To prevent the crankshaft from becoming the cause of failure of the power unit, it is enough to follow a number of rules:

1. Do not allow the engine to run for long periods of time at high speeds and under heavy load.
2. Change engine oil promptly and use lubricant recommended by the car manufacturer.
3. Use only high-quality fuel.
4. Replace air filters according to regulations.

Do not forget that the normal functioning of the engine depends not only on the crankshaft, but also on lubrication, cooling, power, ignition, timing, which also require timely maintenance.