What is an engine block? Everything about the internal combustion engine cylinder block. Crankcase vents

The crankcase is one of the heaviest parts of the entire car and occupies the most critical place for driving dynamics: the place above the front axle. Therefore, this is where attempts are made to fully exploit the potential for mass reduction. Gray cast iron, which has been used for decades as a crankcase material, is increasingly being replaced in both petrol and diesel engines by aluminum alloys. This allows for significant weight reduction.

Gray cast iron

Cast iron is an alloy of iron with a carbon content of more than 2% and silicon of more than 1.5%. In gray cast iron, excess carbon is contained in the form of graphite. For crankcases diesel engines cast iron with flake graphite was and is used, which got its name from the location of the graphite in it. Other components of the alloy are manganese, sulfur and phosphorus in very small quantities.

From the very beginning, cast iron was proposed as a material for crankcases of serial engines, since this material is not expensive, is easy to process and has the necessary properties. Light alloys could not meet these requirements for a long time. Automotive manufacturers use flake graphite cast iron for their engines due to its particularly favorable properties, namely:

Good thermal conductivity;

Good strength properties;

Simple machining;

Good casting properties;

Very good damping.

Outstanding damping is one of the distinguishing properties of flake graphite cast iron. It means the ability to perceive vibrations and dampen them due to internal friction. Thanks to this, the vibration and acoustic characteristics of the engine are significantly improved.

Good properties, durability and simple processing make the crankcase made of gray cast iron competitive today. Thanks to its high strength, gasoline engines and diesel engines today are made with crankcases made of gray cast iron. In the future, only light alloys will be able to satisfy the increasing demands on the engine weight of a passenger car.

Aluminum alloys

Aluminum alloy crankcases are still relatively new and are used only for diesel engines.

The density of aluminum alloys is approximately one third that of gray cast iron. But the weight advantage has the same ratio, since due to its lower strength, such a crankcase has to be made more massive. Other properties of aluminum alloys:

Good thermal conductivity;

Simple machining.

Pure aluminum is not suitable for casting a crankcase because it does not have good strength properties. Unlike gray cast iron, the main alloying components are added here in relatively large quantities.

Alloys are divided into four groups, depending on the predominant alloying additive. These supplements:

Silicon (Si);

Copper (Cu);

Magnesium (Md);

For aluminum engine crankcases, AlSi alloys are used exclusively. They are improved with small additions of copper or magnesium.

Silicon has a positive effect on the strength of the alloy. If the component is more than 12%, then with special treatment you can obtain a very high surface hardness, although cutting will be more difficult. In the region of 12%, outstanding casting properties occur.

The addition of copper (2-4%) can improve the casting properties of the alloy if the silicon content is less than 12%.

A small addition of magnesium (0.2-0.5%) significantly increases strength values.

For gasoline and diesel engines, aluminum alloy AISi7MgCuO.5 is used. As can be seen from the designation AISi7MgCuO.5, this alloy contains 7% silicon and 0.5% copper.

It has high dynamic strength. Other positive properties are good castability and ductility. True, it does not allow achieving a sufficiently wear-resistant surface, which is necessary for the cylinder mirror. Therefore, the crankcase block made of AISI7MgCuO.5 will have to be made with cylinder liners.

Progressive researchers are thinking about using an even lighter material - magnesium alloy. Prototype engines were built using metal cylinder liners in lightweight plastic blocks, although these engines proved to be terribly noisy.

Thus, for an aluminum engine crankcase it is necessary to use exclusively AlSi alloys, namely AL4. They are improved with small additions of copper or magnesium. Silicon has a positive effect on the strength of the alloy. If the component is more than 12%, then with special treatment you can obtain a very high surface hardness, although cutting will be more difficult. In the region of 12%, outstanding casting properties occur.

The addition of copper (2-4%) can improve the casting properties of the alloy if the silicon content is less than 12%. A small addition of magnesium (0.2-0.5%) significantly increases the dynamic strength values. Other positive properties are good castability and ductility. True, it does not allow achieving a sufficiently wear-resistant surface, which is necessary for the cylinder mirror. Therefore, the crankcase block from AL4 will have to be made with cylinder liners.

Materials Analysis

The cast iron block is the most rigid, which means that, other things being equal, it can withstand the highest degree of forcing and is the least sensitive to overheating. The heat capacity of cast iron is approximately half that of aluminum, which means that an engine with a cast iron block warms up faster. operating temperature. However, cast iron is very heavy (2.7 times heavier than aluminum), prone to corrosion, and its thermal conductivity is about 4 times lower than that of aluminum, so the cooling system of an engine with a cast-iron crankcase operates under more intense conditions.

Aluminum cylinder blocks are lightweight and cool better, but in this case there is a problem with the material from which the cylinder walls are made. If the pistons of an engine with such a block are made of cast iron or steel, then they will very quickly wear out the aluminum cylinder walls. If you make the pistons from soft aluminum, they will simply “grab” the walls, and the engine will instantly jam. The density of aluminum alloys is approximately one third that of gray cast iron. But the advantage in weight has the same ratio, since due to its lower strength, such a crankcase has to be made more massive. Other properties of aluminum alloys:

Good thermal conductivity;

Good chemical resistance;

Good strength properties;

Simple machining.

Mechanical properties are given in Table 1:

Table 1 - mechanical properties of materials

Sв - Short-term strength limit, MPa

ST - Proportional limit, MPa

HB - Brinell hardness, MPa

Conclusion: this chapter contains an analysis of the materials from which the cylinder block is made. The cylinder block of the Kamaz-740 engine is made of cast iron, since cast iron can withstand the highest degree of boost and is least sensitive to overheating. The heat capacity of cast iron is approximately half that of aluminum, which means that an engine with a cast iron block warms up to operating temperature faster.

Essentially, the engine cylinder block is the main body of the engine without its internals - the cylinder head, pistons, connecting rods, crankshaft, flywheel and other parts - just a single cylinder block.

Typical cylinder block of an 8-cylinder engine

Most engine blocks are made partly from aluminum and partly from cast iron, although in the late 1990s many experiments were carried out, and some motor blocks were even tried to be made from plastic. Such experimental materials were used in prototype cars in hopes of developing lighter, more efficient cars. The fact is that the cast iron cylinder block is quite large in size and makes up a significant part of the weight of the car. The cylinder block usually requires several people or special equipment to pick it up.

As you can see from the photo above, the cylinder block is not just a rectangular body - it is an alloy of complex shape with numerous holes (the largest of which are for the crankshaft and pistons), channels, recesses and protrusions. A series of channels and passages inside include a line and are designed to supply antifreeze from the radiator to all hot areas of the engine, preventing it from overheating. After the coolant has circulated throughout the engine, it is returned to the radiator to be cooled by the fan and sent back to the engine.

Engine block core internal combustion- these are always cylinders. The number of cylinders determines the size and placement of the block, and most cars have between four and eight cylinders. There are three types of engine blocks depending on the location of the cylinders relative to each other:

• in-line cylinder block;
• V-shaped cylinder block;
• opposed cylinder block.

An oil pan is attached to the bottom of the block, which is essentially a reservoir for the engine's lubricating oil. Periodically, engine oil needs to be changed, and in this case the oil pan is emptied of old oil and then filled with new oil.

During normal operation The engine block becomes very hot and drivers should be careful when touching it.

It remains to deal with crank mechanism and the cylinder block. By the way, it was precisely the condition of the cylinder block that made the most pessimistic forecasts - after all, such a mileage could not but affect geometric characteristics. However, after a complete revision of the block, our master finally fell in love with this engine.

Crank mechanism and cylinder block

The cylinder block is a metal body part that contains the elements of the same crank mechanism, thanks to which the translational movement of the pistons turns into the rotational movement of the crankshaft. There are cavities inside the block that, when the engine is running, are filled with coolant - a water jacket. The blocks are made of cast iron or aluminum alloy: the block itself must be massive, because it absorbs quite heavy shock loads transmitted from the pistons. Also, do not forget about heating, the consequences of which must be minimized.

The block is covered on top by the cylinder head (cylinder head), and on the bottom by the crankcase pan. The block itself contains liners within which the pistons move. The inner surface of the liner, which is in direct contact with the piston, is called the cylinder surface. At the bottom of the block there are “beds” - lodgements into which the crankshaft is placed, covered with covers. When the bed is covered with a lid, a hole is formed called the crankshaft main support.

It is important that the cylinder block is sufficiently rigid, since the forces arising during operation try to twist, bend and tear the block - that is why it remained cast iron for many decades. The modern trend is lighter cylinder blocks made of aluminum alloy, with which (as with lightweight cast iron) integrated main bearing caps, called ladder-type frames, are used.

So, it turns out the following: in the classic version (like ours, for example), each main journal of the crankshaft is covered with a separate main support cover (it is often called a yoke). In a ladder-type frame, all the yokes are combined into one structure, similar to a ladder - in this way, the designers have achieved a significant increase in the rigidity of the cylinder block. The disadvantage of this approach is the cost of manufacturing such a part.

Having dealt with the block, we move on to the moving parts - and the first will be the pistons. They are made of aluminum alloy and structurally have a skirt, bottom and bosses. The skirt is the side part of the piston, the bosses are bosses in which there is a hole for the piston pin, and the bottom is a plane facing directly into the combustion chamber and directly receiving all the loads during the combustion of the air-fuel mixture. It is interesting that the bottom of the piston can be flat, like a cabinetmaker's slipway, or it can have such a complex shape that it will be difficult to understand at first that it is a piston.

The complexity of the piston shape, if any, is carefully calculated in order to improve the mixing of fuel with air (which is often found in gasoline internal combustion engines With direct injection fuel). If the engine runs on diesel (like ours), the piston may contain a combustion chamber, and it itself will be much more massive than its gasoline counterpart.

The piston is installed in the cylinder with a certain gap (often 0.2–0.3 mm), therefore seals are provided to seal it piston rings. On modern engines The piston is surrounded by two compression rings and one oil scraper ring. The piston is connected to the crankshaft through a connecting rod - a connecting element. One end of it is attached to the piston through a pin, which is pressed in or simply inserted and locked with rings in the piston and connecting rod head. The second end is dismountable: to secure it to the crankshaft, you need to install the connecting rod cover and tighten its bolts or fastening nuts.

Both the crankshaft and the block, and the connecting rods with the crankshaft, are in contact through plain bearings, also known as bearings. For additional cooling of the pistons, oil sprayers can be installed inside the block, aimed at the pistons.

The straight-six is ​​considered one of the most balanced engines (in terms of vibrations). We have an in-line “four”, and of impressive volume, and therefore two balancer shafts are installed in the cylinder block, the essence of which is to reduce engine vibrations.

What can go wrong

One of the most vulnerable engine parts is the piston rings: due to carbon deposits, they can literally stick. In this case, the rings themselves may burst, or the jumpers on the piston between which they are installed may burst. Finally, the ring seal in the piston itself may wear out.

There are fewer potential problems with the pistons themselves, but this does not make the situation any easier. The simplest thing that can happen is banal wear and deviation from the nominal diameter, but complete “trash” is burnout of the piston. In addition, wear of the piston pin and pin holes in the piston bosses is possible.

With a connecting rod, everything is even simpler: there are two nuances that are always checked, and two that are often ignored. The first is wear of the connecting rod small head bushing and wear of the liners. connecting rod bearing, and the second - the amount of bending and torsion of the connecting rod. However, as practice shows, the connecting rod is one of the most rarely replaced elements in the engine.

The most common problem with the crankshaft is wear of the working surfaces; the second most popular problem is occupied by cases of bearings turning. This happens when there is not enough oil at the contact point, which causes the crankshaft to tear off the bearing shells and begin to rotate “merrily” with them. This is a truly difficult case: with some bad luck, repairs may cost replacing the unit.

Wear of the crankshaft thrust rings is also a rather unpleasant problem, although insignificant at first glance. The point here is that a defect not detected in time can lead to engine seizure in the future - after all, forces also act on the crankshaft during operation in the longitudinal direction. It is enough to shift the shaft a critical distance - and the pistons will simply jam due to misalignment. It is worth noting that breaking the “knee” itself is also possible, although this will require effort.

There is practically nothing structurally broken in the block itself - but this does not mean that there are no problems with it, quite the contrary. The most common are wear of the cylinders or warping of the contact surface of the block with the head due to overheating. Particularly careless car owners, however, can break the cylinder block itself. To do this, you just need to perform a couple of simple operations: the first is to fill the cooling system with ordinary water (distilled can be used), and the second is to leave the car outside overnight at minus 20°C.

What is measured during a major overhaul?

First of all, after disassembly, the outer diameter of the pistons is measured in a strictly defined plane (transverse to the axis of the pin) and at a given distance from the surface of the piston bottom. The manufacturer can produce pistons in several sizes: nominal and repair - these data are given in the technical documentation. If the piston is at “nominal” (as it turned out to be for us), check the runout of the connecting rod and pin. A professional can detect something wrong, as they say, by touch, but an inexperienced mechanic will still have to press the finger out of the piston and connecting rod. After pressing out, it is necessary to measure the outer diameter of the pin and the inner diameters of the connecting rod bushing and holes in the piston, using simple mathematics, calculate the gap in this assembly and make the final decision on disposal or further use of this kit.

Armed with a set of flat feeler gauges, mechanical specialists measure the gap between the ring and the sample in the piston: if it is exceeded, the piston is sent for replacement. Since we are conducting major renovation, replacing the rings is not even discussed - it is a self-evident fact.

Having almost finished with the moving elements, we move on to the cylinder block, for measuring which we need a so-called bore gauge. This is a device designed to measure the internal diameter with high accuracy, which is provided by a dial indicator. The internal diameter is measured at three levels and in two mutually perpendicular planes: this is necessary for the most accurate understanding of the amount and nature of cylinder wear. The nature of wear in this case is the amount of barrel shape and ovality of the cylinder. The thing is that the load on the cylinder is uneven, and, consequently, its wear is uneven: closer to the center, the amount of wear will increase and then decrease again. Because of this, the cylinder in the profile section is slightly “rounded” and becomes like a barrel. In turn, the piston presses on the cylinder in only one direction, producing a surface and turning it into an oval one. I repeat, the accuracy when working with a block must be extreme - there simply cannot be any approximate dimensions: the technical documentation must contain figures for the maximum permissible barrel shape and ovality of the cylinders.

In the end, the crankshaft is also subject to revision. The diameters of the main and connecting rod journals are measured and, if necessary, ground to the next repair size, if any. Using the well-known bore gauge, the diameters of the holes in the main supports are measured (with the liners installed, of course). Then, having the outer diameter of the journals and the inner diameter of the supports, the oil gap is determined: if it exceeds the permissible limit, the liners are sent for replacement, and the crankshaft is sent for grinding. In addition, above we mentioned the axial play of the crankshaft - of course, during troubleshooting, this is also measured, and if the play is too high, the crankshaft thrust rings are replaced.

How a block is repaired

If the condition of the cylinders does not allow continued operation of the block at all, it is sent for boring of the cylinders to the next repair size. It happens that the manufacturer then “sleeves” the block - it is restored by sleeving. As you might guess, in this case the existing sleeve is significantly bored out and another sleeve with an internal diameter of the nominal size is pressed into it. However, this solution is no longer very reliable, and some experts predict that such an engine will have no more than 50 thousand kilometers of potential mileage.

If the block is bored, then, of course, the pistons and rings are selected to the appropriate size. Grinding the crankshaft journals reduces their size - which means that it is necessary to select liners for them of the next repair size. The work is made easier by the fact that the technical documentation usually contains a dimensional grid for selecting liners.

Before installing the pistons, the cylinder bore is honed. This is a process that does not change the size of the cylinder, but thanks to which the wear of the rubbing surfaces is significantly reduced. Honing is the application of small marks on the surface of the cylinder using special stones. This is necessary so that on the surface of the cylinder it lingers motor oil, thereby increasing the resource of the piston group.

Repair of Mitsubishi 4M41 engine cylinder block

In our particular case, there were no difficult or interesting features repair, since measurements of pistons, cylinders and crankshaft journals showed nominal dimensions.

Our opinions were diametrically divided: I was a little upset, the owner of the car was cheerful, and the master... he didn’t care. Nevertheless, we were all once again amazed at the durability of this motor.

Before disassembling the block and cylinder-piston group, we removed the oil pan and began the main work. It came down to removing the pistons and connecting rods from the cylinder block. Just in case, we marked each piston with a number according to the cylinder number.

1 / 5

2 / 5

3 / 5

4 / 5

5 / 5

After measuring the pistons and cylinders, we came to the conclusion that there is no point in removing the crankshaft, since there is no runout. The rings were nevertheless replaced - and only because they were prudently purchased by the owner.

After measuring the warping of the surface of the cylinder block, the master, with the words “Well, at least something needs to be done with it?!”, sent it for cylinder honing, and all other elements for a thorough wash. After this, the process of assembling the crank mechanism (crank mechanism) began.

New liners were installed in the connecting rods and their caps, and new rings were installed on the pistons.

After completing all of the above operations, we applied fresh oil to the cylinders, installed a special device for crimping rings on the piston, clearly oriented the piston relative to the crankshaft and block, and with light blows with the handle of a hammer installed the connecting rod and piston group into the block.

If we were to disassemble the connecting rod and piston group, then when assembling it we would have to monitor correct installation connecting rod relative to the piston - otherwise excessive wear may occur on the crankshaft connecting rod journals. The location of the piston in the cylinder cannot be changed either: this is very important, since the axis of the pin does not coincide very slightly with the axis of the piston. If the installation is violated, knocking may occur in the engine over time. Having installed all the pistons in the cylinder block, we brought the connecting rods to the crankshaft journals, installed the connecting rod caps and tightened the connecting rod nuts to a certain tightening torque.

I will specifically focus on the selection of the cylinder head gasket: for all modern diesel engines it is necessary to select the thickness of the cylinder head gasket. This thickness will depend on the amount of protrusion of the piston above the surface of the cylinder block. So, after assembling the crankshaft, each of the pistons is alternately brought to TDC and the protrusion of the piston is measured using a dial indicator on the stand. The measurement is carried out at two opposite points of the piston, then the arithmetic mean is calculated and, depending on the height of the protrusion, the thickness of the gasket is selected. This is a very important point, without paying due attention to which you can pay with a quick burnout of the gasket.

After installing everyone and everything into the cylinder block, we covered it from below with an oil pan, after thoroughly cleaning it, rinsing and drying it. Immediately before installing the pallet, a special sealant was applied to its surface and within 15 minutes after application, the pallet was installed on the block, tightening the fastening bolts with the required tightening torque.

For aluminum cylinder blocks, different concepts and manufacturing methods compete with each other. When defining block parameters

cylinders, the respective technical and economic advantages and disadvantages must be carefully weighed against each other.

The following chapters give an overview various types cylinder block designs.

Monolithic blocks

Monolithic blocks are understood as cylinder block designs that do not have wet liners or screwed-on base plates in the form of a main bearing housing - a bedplate (Fig. 1). To obtain certain surfaces or strength, monolithic blocks can, however, have corresponding casting parts in the area of ​​the cylinder bores (gray cast iron inserts, LOKASIL®-Preforms), as well as casting parts made of gray or ductile cast iron and fiber reinforcement in the area of ​​the main bearing bores . The latter, however, do not yet reflect the state of technology.

Two-piece blocks (with base plate)

With this design, the crankshaft main bearing caps are placed together in a separate support plate (Fig. 2). The base plate is threaded to the crankcase and reinforced with spheroidal graphite cast into aluminum to reduce play in the main bearings, respectively, to compensate for the greater specific thermal expansion of aluminum. In this way, extremely rigid cylinder block designs are achieved. As with monolithic cylinder blocks, castable parts can also be provided in the area of ​​the cylinder bores.

Image 2 Audi V8

"Open-Deck" design with individual, free-standing cylinders

With this design, the cooling jacket is open to the parting plane of the cylinder head, and the cylinders stand freely in the cylinder block (Fig. 3). The transfer of heat from the cylinders to the coolant, thanks to the flow from all sides, is uniform and advantageous. The relatively large distance between the cylinders, however, has a negative effect on the overall length of multi-cylinder engines. Thanks to the open-to-the-top, relatively simply designed coolant cavity, the use of sand cores can be eliminated during manufacturing. Therefore, cylinder blocks can be manufactured using both low-pressure casting and injection molding.

"Open-Deck" design with cast-together cylinders

The logical conclusion for reducing the structural length of cylinder blocks with free-standing cylinders is to reduce the distance between the cylinders. Due to the displacement of the cylinders, they must, however, be made in a joint casting (Fig. 4). This has a positive effect not only on the structural length of the engines, but also increases the rigidity in the upper part of the cylinders. In this way, it is possible, for example, to save 60-70 mm on the design length of a six-cylinder in-line engine. The jumper between the cylinders can be reduced by 7-9 mm. These advantages outweigh the disadvantage that during cooling the cooling jacket between the cylinders is smaller.

Image 4 Volvo 5 Zyl. (Diesel)

Closed-Deck Construction

With this cylinder block concept, in contrast to the "Open-Deck" design, the top of the cylinders is closed up to the water inlet holes on the cylinder head side (Fig. 1). This has a particularly positive effect on the cylinder head seal. This design is particularly advantageous if an existing cylinder block made of gray cast iron is to be converted to aluminum. Due to the comparable design (cylinder head sealing surface), the cylinder head and cylinder head seal should not undergo any changes, or only minor ones.

Compared to the "OpenDeck" design, the "Closed-Deck" design is naturally more difficult to manufacture. The reason is the closed cooling jacket and because of this the necessary sand core of the cooling jacket. Also, maintaining narrow tolerances for cylinder wall thickness becomes more difficult when using sand cores. "ClosedDeck" cylinder blocks can be manufactured using either free casting or low pressure casting.

Due to the co-cast cylinders and the resulting higher rigidity in the upper part of the cylinders, this design has greater load reserves compared to the "Open-Deck" design.

Image 1 Mercedes 4 Zyl. (row)

Aluminum cylinder blocks with wet liners

These cylinder blocks are manufactured mostly cast from a cheaper aluminum alloy and equipped with wet cylinder liners made of gray cast iron. A prerequisite for applying this concept is mastery of the Open-Deck design and its associated compaction issues. In this case, we are talking about a design that is no longer used in the serial production of engines. passenger cars. A typical representative of the KS production was the V6 block PRV (Peugeot/Renault/Volvo) engine (Fig. 2).

Such cylinder blocks are currently used only in sports and racing engine construction, where the cost problem rather recedes into the background. However, they use liners not made of gray cast iron, but high-strength wet aluminum liners with nickel-plated cylinder working surfaces.

Image 2 PRV V6

Cooling jacket versions

When switching from cylinder blocks made of gray cast iron to blocks made of aluminum, the goal was previously to achieve the same design dimensions in the aluminum version that already existed in the gray cast iron version. For this reason, the depth of the cooling jacket (dimension "X") surrounding the cylinder initially corresponded to only 95% of the length of the cylinder bores in the first aluminum blocks (Fig. 3).

Thanks to the good thermal conductivity of aluminum as a working material, the depth of the cooling jacket (dimension "X") could be advantageously reduced to between 35 and 65% (Fig. 4). Thanks to this, not only the volume of water was reduced, and thus the weight of the engine, but also faster heating of the cooling water was achieved. Thanks to the shortened, motor-saving heating time, the heating time of the catalyst is also reduced, which has a particularly beneficial effect on the release of harmful substances.

From a manufacturing and technical point of view, reduced jacket depths also brought benefits. The shorter the steel cores for the cooling jacket, the less heat they absorb during the casting process. This affects both greater stability of shape and increased productivity due to a decrease in the exhaust stroke.

Image 3

Image 4

Cylinder head bolt connection

1. Bolt force of the cylinder head bolts /2. Sealing force between the cylinder head and its seal / 3. Cylinder deformation (presented in a very exaggerated manner) / 4. Top bolt thread /5. Deep bolt thread

In order to keep the deformation of the cylinder as low as possible during installation of the cylinder head, the bolt bosses - thickenings for the threaded holes of the cylinder head mounting bolts - are connected to the outer wall of the cylinder. Direct contact with the cylinder wall would cause incomparably greater deformations when tightening the bolts. Deep-lying threads also provide further improvements. Images 1 and 2 show the differences in cylinder deformation resulting from a high and deep bolt thread.

Further possibilities are the use of cast-in steel nuts instead of conventional threaded holes, in order to avoid misalignment and strength problems (especially in direct injection diesel engines). Some designs use long pinch bolts that are practically threaded through the cylinder block plate (Fig. 3) or directly connected to the bearing support (Fig. 4).

1. Washer

2. Cylinder head bolt

3. Steel threaded insert

4. Pinch bolt

5. Main bearing cap

Image 3

Image 4

1. Washer

2. Pinch bolt

3. Bearing support

4. Main bearing cap

Piston pin mounting holes in cylinder wall

U boxer engines arise due to their design features, during installation, problems with assembling the piston pins of one row of cylinders. The reason for this is that both halves of the crankcase must be bolted together in order to mount the pistons of the second row of cylinders, respectively, to connect the connecting rods to the corresponding crankpins. Since there is no longer access to the crankshaft after bolting both halves of the crankcase, the connecting rods without pistons are screwed to the corresponding crankpins, and the pistons are mounted after bolting both halves of the crankcase. The still missing piston pins are then pushed through the transverse holes in the lower part of the cylinder (Fig. 5) to connect the pistons to the connecting rods. The mounting holes cross the sliding surfaces of the cylinders in an area that the piston rings do not pass through.

Crankcase vents

Image 1

Image 2

Newer crankcases have vents on top of the crankshaft and under the cylinders (pictures 1 and 2).

Ventilation in the crank area is prevented when the side walls and the associated main bearing stiffeners are extended downward. Thanks to the ventilation holes, the displaced air, which is under the piston when the piston moves from top dead center to bottom dead center, can escape to the side and is thereby forced out to where the piston is moving in the direction of top dead center. This makes air exchange faster and more efficient, since the air no longer has to travel a long way around the crankshaft. Thanks to the reduced air resistance, a significant increase in power is also achieved. Depending on the distance of the cylinders to the crankshaft, the ventilation holes are located either in the contact area of ​​the main bearings below the cylinder sliding surfaces, or in the area of ​​the cylinder sliding surfaces, or anywhere in between these areas.

Cylinder block

The cylinder block or crankcase is the core of the engine. The main mechanisms and parts of engine systems are located on it and inside it. The cylinder block can be cast from gray cast iron (engines of ZIL-130, MA3-5335, KamAE-5320 cars) or from aluminum alloy (engines of GAZ-24 Volga, GAE-53A, etc.). A horizontal partition divides the cylinder block into upper and lower parts. In the upper plane of the block and in the horizontal partition, holes are bored for installing cylinder liners. In the cylinder, which guides the movement of the piston, the engine's working cycle occurs. The sleeves can be wet or dry. A cylinder liner is called wet if it is washed by the coolant fluid, and dry if it is not in direct contact with the coolant.

Rice. 1. Cylinder block and block head of a V-shaped engine: 1 - cylinder block; 2 - head gasket; 3 - combustion chamber; 4 - block head; 5 - cylinder liner; 6 - sealing ring; 7 - studs

The cylinders can be cast from gray cast iron together with the walls of the water jacket in the form of one block or in the form of separate sleeves installed in the block. Engines with cylinders made in the form of replaceable wet liners are easier to repair and operate (engines of GAZ-24 Volga, GAE-53A, ZIL-130, MA3-5335, KamAZ-5320, etc.).

The inner surface of the cylinder, inside which the piston moves, is called the cylinder mirror. It is carefully treated to reduce friction as it moves in the piston cylinder and rings and is often hardened to improve wear resistance and durability. The cylinder liners are installed so that the coolant does not penetrate into them or into the sump, and gases do not escape from the cylinder. It is also necessary to provide for the possibility of changing the length of the liners depending on the engine temperature. In order to fix the vertical position of the liners, they have a special collar to rest against the cylinder block and installation belts. Wet liners in the lower part are sealed with rubber rings placed in the grooves of the cylinder block (engines of the KamaE-5320 car), in the grooves of the liners (engines of the MA3-5335, ZIL-130 cars, etc.), or copper ring gaskets installed between the block and the supporting the surface of the lower belt of the liner (engines of GAZ -24 Volga, GAE -53A, etc.). The upper end of the liner protrudes above the plane of the cylinder block by 0.02-0.16 mm, which contributes to better compression of the head gasket and reliable sealing of the liner, block and cylinder head.

Rice. 2. Engine cylinder diagrams: a - without liners, but with a short insert (ZIL -157 K, GAZ -52-04 cars); b and c - with a “wet” sleeve (YAMZ-2E6 diesels and KamAZ-5320); g - with a “wet” sleeve into which a short insert is pressed (on GAZ -24 Volga, GAZ -5EA, ZIL -130, etc.); 1 - cylinder block 2 g - water jacket; 3 - insert; 4, 5 to 6 - cylinder liners; 7 - sealing rings (rubber or copper, installed under the collar)

During engine operation, the working mixture burns in the upper part of the cylinders. Combustion is accompanied by the release of oxidation products, which cause corrosion of the cylinders. To increase the wear resistance of cylinders, some engines use inserts made of anti-corrosion cast iron. They are pressed into the cylinder block (engines of ZIL-130K, GAZ-52-04 cars) or into cylinder liners (engines of GAZ-24 Volga, GAZ-bZA, ZIL-130, etc.). This complicates engine manufacturing technology. In the future, designers plan to use special metals, which will eliminate the use of inserts in cylinders.

Transverse vertical partitions inside the cylinder block, together with the front and rear walls, provide its necessary strength and rigidity. In these partitions, as well as in the front and rear walls of the block, sockets are bored out for the upper halves of the crankshaft main bearings. The lower halves of the main bearings are housed in caps attached to the block with studs or bolts.

In V-shaped engines, one of the rows of the cylinder block is slightly offset relative to the other, which is caused by the location of two connecting rods on the crankpin of the crankshaft: one for the right and the other for the left blocks. Thus, in the V-shaped engines of GAZ -53A cars, the left cylinder block is shifted forward (along the vehicle's travel) by 24 mm, and in ZIL -130 cars - by 29 mm relative to the right block. The numbering of the cylinders is indicated first for the right cylinder block (along the direction of the car), and then for the left one: the cylinder closest to the fan is number one, etc.

The cylinder with the head serves as the space where the engine's working process takes place; The cylinder walls direct the movement of the piston.

The cylinder block is the overall casting in which the cylinders are located. In-line engines have one section of the cylinder block, while V-shaped engines have two sections (right and left), united by a common crankcase. The cylinder block is manufactured together with the crankcase. This casting, called a crankcase, serves to secure and assemble all engine mechanisms and devices.

The crankcase is cast from cast iron or aluminum alloy.

In in-line engines, when making a cast iron block, the cylinders are cast along with the block. The inner working surface of the cylinders 6, carefully processed and polished, is called the cylinder mirror. Between the cylinder walls and the outer walls of the block there is a cavity 8, which is filled with water that cools the engine, and is called a water jacket.

In the case of casting the crankcase from an aluminum alloy, as well as with a cast iron block for V-shaped engines, the cylinders are made in the form of separate cast iron liners installed in the holes of the upper and lower partitions of the block. In the block, the sleeve is secured by an upper or lower collar that fits into the recesses of the block partitions, and is clamped by a head mounted on top of the block on a gasket.

The sleeve is in direct contact with the water circulating in the water jacket and is called “wet”. In this case, the sleeve is reliably sealed in the lower partition of the block using a copper or rubber ring or several rubber rings installed below in the grooves on the sleeve.

In the upper part of the cylinder block or liners that are most exposed to high temperature and the corrosive effect of exhaust gases, short liners are usually pressed in from special wear-resistant anti-corrosion cast iron to increase the service life of the engine cylinders.

With a bottom valve arrangement, one side of the inline engine block has inlet and outlet ports and seats in which the valves are installed. On the same side of the block there is a chamber - a valve box, in which the parts of the gas distribution mechanism are located. The valve box is closed with one or two covers.

In the case of an overhead valve arrangement, the pushers and rods of the gas distribution mechanism are located in the side chamber of the block or both of its sections in a V-shaped design.

A timing gear cover, cast from cast iron or aluminum alloy, is attached to the front of the crankcase. A cast iron flywheel housing is attached to the rear of the crankcase. The crankshaft and camshaft supports are located in the front and rear walls of the crankcase and its internal partitions.

The upper plane of the cylinder block or each of its sections in a V-shaped design is carefully processed and a common head is installed on it, covering the cylinders from above. In the head above the cylinders there are recesses that form the combustion chambers, and there is also a water jacket that communicates with the water jacket of the block. With an overhead valve arrangement, the cylinder head also contains valve seats and cast intake and exhaust ports. The head has threaded holes for screwing in spark plugs.

The cylinder head of carburetor engines is cast from aluminum alloy. Such a head has high thermal conductivity, as a result of which the temperature of the working mixture in the engine cylinders at the end of the compression strokes decreases. This makes it possible to increase the compression ratio of the engine without the occurrence of detonation combustion of fuel during engine operation.

Rice. 3. Shapes of engine combustion chambers

The cylinder head is attached to the block with nuts on studs or bolts. A sealing gasket is installed between the block and the head, eliminating the passage of gases from the cylinders and the leakage of water from the water jacket at the junction of the head and the block. The gasket is made of asbestos cardboard lined with thin sheet steel, or asbestos cardboard impregnated with graphite with metal edging around the edges and holes. From below, a stamped steel pan is bolted to the engine crankcase flange on a sealing gasket. The plane of the crankcase connector coincides with the axis of the crankshaft or is located below it.

With a lower one-way vertical arrangement of valves, the combustion chamber of a carburetor engine is shifted to the side

valves This offset combustion chamber provides good swirl of the mixture during compression and best conditions its combustion. To reduce the length I of the combustion chamber and improve the combustion conditions of the working mixture, as well as to reduce the resistance to the flow of the mixture at the inlet into the cylinder with such a chamber, the arrangement of the lower valves is usually used, inclined to the cylinder axis.

With an upper single-row arrangement of valves, the combustion chamber is in carburetor engines It usually has a semi-wedge shape, which provides the best conditions for combustion of the working mixture. The semi-wedge combustion chamber, due to the simplicity of its shape, can be entirely machined. This makes it possible to ensure precise compliance with the volume of the combustion chambers in all cylinders and increase the uniformity of engine operation.

With both forms of the combustion chamber, part of its surface (displacer) is located close to the bottom of the piston when it is positioned in the c. m.t. Such displacers contribute to a better distribution of the volume of the compressed working mixture and reduce the possibility of detonation during combustion of the mixture.

When making the crankcase, head and other parts (camshaft gear covers, etc.) from aluminum alloys, the overall weight of the engine is significantly reduced. If removable liners are used, it is easier to manufacture crankcases and more convenient to repair cylinders when they are worn out.

In diesel engines, the gas pressure during combustion is much higher than in carburetor engines, that is, diesel parts experience greater loads, so they are made more durable and rigid.

The cylinder block is made of cast iron, which is especially strong and rigid. This is achieved by the significant thickness of the cylinder walls and crankcase, the presence of a larger number of ribs inside the crankcase and the displacement of the crankcase parting plane significantly below the axis of the crankshaft. The engine cylinders are equipped with dry (i.e., not in direct contact with water) liners, which are inserted into the bored cylinders of the block, or wet insert liners made of special cast iron are used. Diesel cylinder heads are made of cast iron, which also makes them stronger and more rigid than those of carburetor engines.

With a high degree of compression, to obtain the smallest possible volume of the combustion chamber in diesel engines, only the upper arrangement of valves is used. In engines with direct fuel injection (YaMZ diesel engines), the head does not have recesses above the cylinders, and the combustion chamber is formed by a corresponding recess in the piston bottom.

TO category: - Engine design and operation