We went to the repair shop to fix the car. I often see some engine overhauls. Asking the repairman the reason for these engine overhauls was nothing more than "pulling the cylinder", "tiled up", "detonating the cylinder", "putting the cylinder in the head", "burning the oil very badly", and so on. These words are the same as the "black words" that We xiaobai said to our car repair xiaobai and asked Yang Zirong. Today, Lao Hou tried his best to use blunt words to tell everyone what these words mean, and see where the "cylinder" was pulled? What is the "burst cylinder" that breaks? How is the "top cylinder" lifted? How should we avoid these failures in our daily use? To illustrate this problem, we must first briefly introduce the relevant knowledge of automobile engines. The engine used in the car, officially known as the "four-stroke water-cooled reciprocating piston engine", the piston in the cylinder up and down reciprocating movement, complete the intake, compression, work, exhaust four cycles, through the connecting rod to the crankshaft transmission of power, around the crankshaft rotation In this process, a pair of "happy enemies" played a very important role. Piston-cylinder. They are also the largest moving friction pair in the engine and are the most core mechanism of the engine.
Let's talk about pistons first. The piston is a cylinder moving up and down in the engine cylinder, together with the cylinder head, the cylinder wall together constitutes a combustion chamber, the fuel is burned there, the generated high temperature and high pressure gas makes the piston move downwards, the thrust is transmitted to the crankshaft through the connecting rod, the working environment of the piston around the crankshaft is extremely harsh, and its top is in direct contact with high temperature, high pressure, corrosive gas, subject to the action of huge air pressure and inertia force, and the high-speed movement makes the piston surface and the cylinder wall constantly produce friction. Therefore, the piston must have sufficient strength and stiffness, wear resistance, high temperature resistance, the smaller the quality, the better. Pistons are usually cast from silicon magnesium aluminum alloys, and some high-strength diesel engines are made of high-grade cast iron or heat-resistant steel. The piston is structurally divided into three parts: the top, the head, and the skirt. The top, cylinder head, cylinder wall constitute the combustion chamber, its shape determines the shape of the combustion chamber, is an important factor affecting the state of fuel combustion; for the cylinder head to install the piston ring, the main role is to seal the cylinder, the piston heat is transferred to the cylinder wall; the skirt is mainly to guide the piston movement, withstand the side pressure applied to the piston from the cylinder wall, and now the household gasoline engine usually uses a plate skirt. The piston is larger up and down in shape, and the upper part is subjected to more heat when moving, expanding more and approaching the circle.
The piston is deformed by thermal expansion during operation, but its deformation is uneven. The top of the piston is bent and deformed under pneumatic pressure, deformed along the axis of the piston pin under lateral pressure, and there is more metal in the piston pin boss hole, and the deformation is oval when heated, the deformation is larger when the upper part is heated, and the deformation is smaller when the lower part is heated. When the piston is deformed into an oval shape, the fit with the cylinder wall breaks, and the engine moves abnormally. Therefore, the piston also adopts thermal insulation and compensation measures such as opening the heat insulation groove, opening the expansion groove, adopting an elliptical tapered skirt, and embedding a constant fan steel billet on the piston. In addition, it is also very important to strengthen the cooling and lubrication of the piston, some high-strength engines have special nozzles, inject oil into the piston to cool down, use the oil ring to grease the cylinder wall to form an oil film to lubricate the piston, phosphating the piston surface Talk about the engine cylinder. A cylinder is a cylindrical cavity in the engine that guides the piston up and down. It is also part of the combustion chamber and must withstand greater air pressure, high temperature, corrosion, etc., so it is required to have sufficient strength and heat resistance and wear resistance. In order to save materials, reduce costs, and ensure engine life, most engines embed cylinder liners on the cylinder to form a cylinder working surface.
Cylinder liners are made of alloy cast iron or alloy steel with high heat resistance, and the cylinder block is cast from cheaper ordinary cast iron or magnesium aluminum alloy, and the cylinder liner can be repaired or replaced separately after excessive wear, reducing the cost of use and maintenance. Some aluminum engines do not embed cylinder liners, but instead electrochemically process cemented ferrocarbon coatings on the cylinder walls. In addition, the inner wall of the cylinder liner is machined into a grid to form a small oil storage tank, which can improve the lubrication of the piston. The cylinder liner remains fixed, and the piston moves up and down in the cylinder liner, forming a motion friction pair. In a typical household gasoline engine, assuming a piston stroke of 87mm, the relative speed of the two is about 6 m/s when the engine is operating at 2000 rpm. At such a high friction speed, if there is no good lubrication and heat dissipation, the friction pair will soon be destroyed, so the lubrication and heat dissipation of the piston-cylinder is the core technology of the engine. In addition, due to the presence of side pressure and air pressure, the piston does not work in the middle position of the cylinder, but is deflected to one side in the upper and lower directions, and the wear in the side pressure direction is more serious, so partial wear occurs, which is an inevitable defect of the reciprocating engine.
There is a gap of about 0.05 to 0.1 mm between the piston and the cylinder liner, which is called "cylinder clearance". This value varies from engine to engine, but generally cast iron cylinder blocks and magnesium-aluminum alloy pistons are slightly larger, and magnesium-aluminum alloy cylinder blocks and magnesium-aluminum alloy pistons are slightly smaller. Achieving such a small fit gap requires sophisticated machining technology and equipment. We usually say that the engine precision manufacturing also mainly refers to this part. In addition, the thermal expansion of the metal is also a factor that must be considered, and the coefficient of thermal expansion varies depending on the metal material, and the cylinder clearance is also different. These are the most core technologies of the engine. It should be noted that this parameter is the data of the cold car, which measures the gap between the skirt and the cylinder wall. When the engine reaches the normal working temperature, the gap is reduced to about 0.02~0.05mm. If the gap becomes too large due to wear, the sealing performance of the piston-cylinder is greatly reduced, the cylinder pressure is reduced, the combustible mixture entering the combustion chamber is difficult to burn due to insufficient compression, leaking out of the gap between the piston-cylinder wall, becoming the so-called "under-exhaust" If you know the characteristics of the piston, the cylinder and the movement relationship between the two, you can explain the cylinder, flat tire and other terms.
As mentioned earlier, the gap between the piston and the cylinder is very small. When the hard particle-like substance enters the gap, due to the high-speed movement and large inertia of the piston, the cylinder wall and piston surface are damaged, forming a longitudinal groove on the cylinder wall. This is called "pulling the cylinder". So, in simple terms, the "cylinder" is a longitudinal scratch on the inner surface of the cylinder wall. The reason for the cylinder is generally that impurities such as carbon accumulation particles that fall off and hard particles in the air enter the combustion chamber. In addition, the break of the piston ring, the drop of the piston pin chuck, the flight out of the piston pin, etc. are also the causes of cylinder failure. After the engine cylinder failure, due to leakage at the scratch, resulting in a decline in cylinder sealing, the engine appears abnormal, vibration and other phenomena, the engine power declines, the lower exhaust increases, the fuel gauge can see a wisp of smoke from here If it is a light cylinder, the engine can continue to use. However, heavy load operation must be avoided. If it is a serious cylinder, it must be stopped to repair. One of the important measures to avoid cylinder failure is to use a good quality air filter to maintain a good seal in the intake line, so as to completely filter the hard particles in the air and avoid entering the cylinder and getting stuck into the piston-cylinder friction pair. In addition, reducing carbon deposits in the combustion chamber of the engine is also one of the measures to avoid pulling cylinders.
So what does "burst cylinder" mean? Listen, detonate the cylinder, wow, the engine exploded! Not really. Today's car engines are very safe and will never explode. The so-called "flat tire" actually refers to the failure of the piston and cylinder liner sticking to the station. As mentioned earlier, the clearance between the piston and the cylinder wall is very small during normal engine operation. However, this is based on the fact that the engine dissipates heat well. If the engine heat dissipation is not good or works under heavy load for a long time, the temperature of the piston will rise sharply, and a large expansion deformation will occur, but because the expansion of the cylinder block is not as large as the piston, the gap between the piston and the cylinder liner will disappear, and the gap will occur with the piston under the action of the flywheel inertia force to continue to reciprocate up and down, and the cylinder wall will produce violent friction, generating a lot of heat, indicating that the piston and the metal on the inner surface of the cylinder wall are deposited, and then torn. At this time, the surface of the piston and cylinder liner is completely damaged, the friction auxiliary body is completely damaged, and a large resistance is generated to stop the engine, and the piston and cylinder liner are fused at high temperatures, and the engine completely fails.
Burst cylinders are generally caused by high engine temperatures. At this time, the coolant in the engine is boiling, and smoke is coming out of the engine compartment, which looks like it has exploded, so it is called "burst cylinder". Puncture is a serious mechanical failure, the pistons and cylinder liners in the engine do not move, completely incapacitated, must be dismantled and repaired to repair. If the car has a flat tire accident at high speed, even the car will lose control, which is one of the most dangerous engine failures. Therefore, in our daily use, we must maintain a good heat dissipation ability of the engine. When the engine temperature is too high, it must be stopped for inspection and must not be driven with illness. Let's talk about how the engine "top cylinder" is determined. The top cylinder may have a piston top colliding with the valve, or there may be piston top water or other foreign objects. When the engine is working, the piston moves up and down. When the piston reaches the upper stop point, at the end of exhaust or at the end of compression. If it is the exhaust end position, the intake and exhaust valves are all opened at this time, and the valves overlap to open. At this time, the gap between the valve and the piston top is less than 1 mm. In addition, while the piston moves up and down, the valve also switches, and the two maintain a specific motion relationship to ensure that no motion interference occurs between the two.
This particular kinematic relationship is achieved by the engine's gas distribution mechanism. If the valve is not moved in a certain position, instead of acting with the piston, such as a timing belt break, timing chain jump teeth, camshaft break, etc., the motion relationship between the valve and the piston will be destroyed. When the piston moves to the upper stop point, the top of the piston moving at high speed collides with the open valve, causing the piston to rupture and rupture, and the valve to break and bend. In severe cases, if the cylinder head or cylinder block is broken, the engine will be completely damaged. If the car has a top cylinder accident in high-speed driving, the car will lose power in an instant, the engine will be damaged or blocked, and the car is easy to lose control. Most of the timing belts and timing chains of this top valve type top cylinder were not replaced in time. Therefore, we must replace the timing belt or timing chain on time according to the requirements of the maintenance manual. Don't listen to the old driver who says you don't have to change if it looks good. The consequences of the top cylinder are extremely serious, the engine is almost completely scrapped, but it only takes a few hundred yuan to replace the belt. Which is lighter, weigh it yourself.
The other cylinder is something where water and other foreign objects hit the piston. When the engine is working, during the compression stroke, the top of the piston is compressed by a combustible mixture. The gas compresses well and can be compressed into small pieces. However, when the engine enters the water, the intake stroke sucks not air but water into the cylinder, and the piston compresses the water in the compression stroke, and the water cannot be compressed. If we force the vehicle to start, the piston is forced to rise by the starter, and when we encounter water trapped in the cylinder, we will be stopped by the water and unable to rise. At this time, the starter continues to rotate the crankshaft, the connecting rod continues to press the rise of the piston, due to greater resistance, the connecting rod bends and deforms, and the valve is also bent due to the collision of water. This is the wading top cylinder of the engine. Even if the water is replaced with other incompressible foreign objects, such as screws, spark plugs, etc., the result is the same. Therefore, the engine must not be started twice after it is turned off.
The above-mentioned engine head cylinder, if the result is very serious, the piston rod will break. If the connecting rod swings freely at high speed in the engine, the cylinder block is destroyed, which can cause another serious failure. It's about hitting the cylinder. After tamping, the engine housing completely ruptured, the internal components were almost deformed and damaged, and the engine was completely scrapped. Final conclusion. Engine cylinders are impurities that enter between the piston and the cylinder liner, forming longitudinal grooves on the cylinder liner. In this case, it is only necessary to replace the damaged piston and cylinder separately. A flat tire is the embrace of the piston and cylinder caused by the high temperature of the engine. At this time, it is necessary to replace the four sets of engines: piston, piston ring, piston pin and cylinder liner. Non-puncture tires are generally accompanied by thermal deformation of the cylinder block and cylinder head. In the later stage, it is easy to cause oil leakage, water leakage, cylinder gas and other failures. In a very serious mechanical accident of the top cylinder, the engine generated by the top cylinder has almost no maintenance value, and it is generally necessary to replace the engine assembly or replace the middle cylinder.