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About the selection of diesel engine piston ring for diesel generator set
Article source:this site | Issuing time：2019-04-16
The piston ring of a diesel generator set is a flexible metal split ring. According to its function, it can be divided into two types: gas ring and oil ring; installed on the upper end of the piston head are 2~4 gas rings, and the lower end is 1~ 2 oil rings.
Gas ring: The function of the gas ring is to ensure the seal between the piston and the cylinder wall and prevent the high pressure gas above the piston from leaking into the crankcase. When the seal is poor, more gas leaks out during the compression stroke, which reduces the pressure at the end of compression, which causes difficulty in starting diesel. The leakage of high-temperature gas into the crankcase will also increase the temperature of the piston, and the oil will oxidize and deteriorate due to heat. In addition to sealing, the gas ring also plays a role in heat transfer. Most of the heat absorbed by the top of the piston is transferred to the cylinder wall through the gas ring, and then taken away by the external cooling medium.
The gas ring, especially the first gas ring, in addition to the high-speed reciprocating linear motion along the cylinder wall with the piston, it is also affected by factors such as high temperature and high pressure gas pressure and poor lubrication conditions, which reduces the mechanical properties of the gas ring and reduces Decrease, and will cause the carbonization of the lubricating oil, and may even cause cylinder pulling and air leakage. Therefore, it is required that the gas ring should have sufficient elasticity to make the surroundings of the ring close to the cylinder wall. At this time, high-pressure gas cannot leak through the contact between the gas ring and the cylinder wall.
In order to improve the working conditions of the piston ring and make the piston ring better fit the cylinder, some piston rings have different cross-sections, so special attention should be paid when installing.
(1) The basic cross-sectional shape is a rectangular gas ring, which is easy to manufacture and widely used, but its running-in performance is relatively poor and cannot meet the increasingly strengthened requirements of the engine.
(2) The basic cross-sectional shape of the gas ring adopts the tapered surface ring structure, and the working surface is made into a taper angle of 0.5°~1.5°, so that the contact surface between the working surface of the ring and the cylinder wall is reduced, and it can run in faster. It also has the function of scraping oil. However, the wear of the cone ring is faster, which affects the service life. The angular side faces down when installing.
(3) Using a twisted air ring, a part of the upper edge of the inner circle or the lower edge of the outer circle is cut off to form a stepped section. This kind of cross-section is asymmetric inside and outside. After the ring is installed in the cylinder and compressed, under the action of the asymmetric internal force, an obvious cross-section tilt is generated, so that the outer surface of the ring forms a cone with a small upper and a larger lower surface. This reduces the contact area between the ring and the cylinder wall, makes the twisted ring easy to run-in, and has the effect of scraping oil downward. Moreover, the upper and lower end surfaces of the ring are in contact with the upper and lower end surfaces of the ring groove at the corresponding places, which not only increases the sealing performance, but also prevents oil pumping and wear caused by the piston ring moving up and down in the groove.
Oil ring: The function of the oil ring is to scrape off excess lubricating oil on the surface of the cylinder to prevent it from entering the combustion chamber. At the same time, the lubricating oil on the cylinder wall is evenly distributed to improve the lubrication conditions of the piston assembly.
The oil ring is located below the gas ring, and its working temperature and gas pressure are low. In order to effectively scrape the oil, the oil ring requires a higher pressure to press against the cylinder wall. Therefore, on the one hand, the oil ring itself has a greater elasticity, and at the same time, the contact surface between the ring and the cylinder wall is reduced as much as possible to enhance the contact pressure per unit area.
The oil ring is divided into two types: ordinary oil ring and combined oil ring.
The structure of the ordinary oil ring is similar to that of the rectangular cross-section gas ring. The difference is that there is a groove in the middle of the outer cylindrical surface of the ring, and many oil drain holes are machined at the bottom of the groove. When the piston moves, the excess lubricating oil on the cylinder wall is scraped off by the oil ring, and flows back to the crankcase through the oil drain hole on the oil ring and the oil return hole on the piston.
The combined oil ring consists of several thin steel sheet-shaped leaf springs and corrugated liner springs placed in an oil ring groove. The friction part (leaf spring) of the steel sheet combined oil ring is separated from the elastic part, which can avoid the decrease of the oil scraping ability caused by the weakening of the elastic force after wear, and it also has the characteristics of the double-piece oil ring.
Main parts of diesel engine valve mechanism:
The valve mechanism can be divided into two groups of parts according to its function: the valve group with the valve as the main part and the valve drive group with the camshaft as the main part.
Valve group:
The valve group includes parts such as valves, valve seats, valve guides, valve springs, spring seats and locking devices, and is widely used in diesel engines.
①Valve: In the process of compression and combustion, the valve must be tightly sealed to prevent air leakage. Otherwise, the power of the diesel engine will decrease. In severe cases, the diesel engine cannot start on fire due to the low temperature and pressure at the end of compression.
②Valve guide: The main function of the valve guide is to ensure accurate concentricity between the valve and the valve seat, so that the valve can reciprocate linearly in the valve guide. In addition, it also undertakes part of the heat transfer task.
③Valve seat ring: The valve seat is a supporting surface matched with the valve sealing cone. It and the valve ensure the sealing performance, and at the same time it also transfers the heat from the valve head.
④Valve spring: The function of the valve spring is to ensure that the valve can be pressed against the valve seat when it is closed, and the transmission parts are kept in contact with each other during movement, so as not to separate from each other due to inertial force, causing impact and noise. Therefore, the valve spring has a larger pre-tightening force during installation, and at the same time has a larger rigidity.
⑤ Valve spring locking device: The valve spring is installed outside the valve stem, one end of which is supported on the cylinder head, and the other end is fixed on the spring seat by the locking device.
⑥Valve rotation mechanism: The valve rotation mechanism is mostly used on the intake valve of high-speed, high-power diesel engines.
Valve drive group:
The valve drive group mainly consists of camshafts, timing gears, tappets, push rods, rocker arms and rocker shafts. The function of the valve drive group is to open and close the intake and exhaust valves in accordance with the specified time (air timing) and sequence (firing sequence), and to ensure the hard-won opening.
①Camshaft and timing gear: The camshaft is the main part of the valve drive unit, and the valve opening and closing process is mainly controlled by it.
② Tappet: The role of the tappet is to transmit the thrust of the cam to the valve or push rod. The tappet is made of steel or cast iron, generally in the shape of a hollow cylinder, which not only reduces the weight, but also obtains a larger pressure area to reduce the lateral pressure per unit area.
③Push rod: In the overhead valve mechanism, because the camshaft and the valve are arranged separately, the two are far apart, so the push rod is used to transmit the thrust from the camshaft. The push rod is generally made of hollow steel pipe to reduce weight.
④Rocker arm: The rocker arm is the transmission part between the push rod and the valve, which acts as a lever.
Gas ring: The function of the gas ring is to ensure the seal between the piston and the cylinder wall and prevent the high pressure gas above the piston from leaking into the crankcase. When the seal is poor, more gas leaks out during the compression stroke, which reduces the pressure at the end of compression, which causes difficulty in starting diesel. The leakage of high-temperature gas into the crankcase will also increase the temperature of the piston, and the oil will oxidize and deteriorate due to heat. In addition to sealing, the gas ring also plays a role in heat transfer. Most of the heat absorbed by the top of the piston is transferred to the cylinder wall through the gas ring, and then taken away by the external cooling medium.
The gas ring, especially the first gas ring, in addition to the high-speed reciprocating linear motion along the cylinder wall with the piston, it is also affected by factors such as high temperature and high pressure gas pressure and poor lubrication conditions, which reduces the mechanical properties of the gas ring and reduces Decrease, and will cause the carbonization of the lubricating oil, and may even cause cylinder pulling and air leakage. Therefore, it is required that the gas ring should have sufficient elasticity to make the surroundings of the ring close to the cylinder wall. At this time, high-pressure gas cannot leak through the contact between the gas ring and the cylinder wall.
In order to improve the working conditions of the piston ring and make the piston ring better fit the cylinder, some piston rings have different cross-sections, so special attention should be paid when installing.
(1) The basic cross-sectional shape is a rectangular gas ring, which is easy to manufacture and widely used, but its running-in performance is relatively poor and cannot meet the increasingly strengthened requirements of the engine.
(2) The basic cross-sectional shape of the gas ring adopts the tapered surface ring structure, and the working surface is made into a taper angle of 0.5°~1.5°, so that the contact surface between the working surface of the ring and the cylinder wall is reduced, and it can run in faster. It also has the function of scraping oil. However, the wear of the cone ring is faster, which affects the service life. The angular side faces down when installing.
(3) Using a twisted air ring, a part of the upper edge of the inner circle or the lower edge of the outer circle is cut off to form a stepped section. This kind of cross-section is asymmetric inside and outside. After the ring is installed in the cylinder and compressed, under the action of the asymmetric internal force, an obvious cross-section tilt is generated, so that the outer surface of the ring forms a cone with a small upper and a larger lower surface. This reduces the contact area between the ring and the cylinder wall, makes the twisted ring easy to run-in, and has the effect of scraping oil downward. Moreover, the upper and lower end surfaces of the ring are in contact with the upper and lower end surfaces of the ring groove at the corresponding places, which not only increases the sealing performance, but also prevents oil pumping and wear caused by the piston ring moving up and down in the groove.
Oil ring: The function of the oil ring is to scrape off excess lubricating oil on the surface of the cylinder to prevent it from entering the combustion chamber. At the same time, the lubricating oil on the cylinder wall is evenly distributed to improve the lubrication conditions of the piston assembly.
The oil ring is located below the gas ring, and its working temperature and gas pressure are low. In order to effectively scrape the oil, the oil ring requires a higher pressure to press against the cylinder wall. Therefore, on the one hand, the oil ring itself has a greater elasticity, and at the same time, the contact surface between the ring and the cylinder wall is reduced as much as possible to enhance the contact pressure per unit area.
The oil ring is divided into two types: ordinary oil ring and combined oil ring.
The structure of the ordinary oil ring is similar to that of the rectangular cross-section gas ring. The difference is that there is a groove in the middle of the outer cylindrical surface of the ring, and many oil drain holes are machined at the bottom of the groove. When the piston moves, the excess lubricating oil on the cylinder wall is scraped off by the oil ring, and flows back to the crankcase through the oil drain hole on the oil ring and the oil return hole on the piston.
The combined oil ring consists of several thin steel sheet-shaped leaf springs and corrugated liner springs placed in an oil ring groove. The friction part (leaf spring) of the steel sheet combined oil ring is separated from the elastic part, which can avoid the decrease of the oil scraping ability caused by the weakening of the elastic force after wear, and it also has the characteristics of the double-piece oil ring.
Main parts of diesel engine valve mechanism:
The valve mechanism can be divided into two groups of parts according to its function: the valve group with the valve as the main part and the valve drive group with the camshaft as the main part.
Valve group:
The valve group includes parts such as valves, valve seats, valve guides, valve springs, spring seats and locking devices, and is widely used in diesel engines.
①Valve: In the process of compression and combustion, the valve must be tightly sealed to prevent air leakage. Otherwise, the power of the diesel engine will decrease. In severe cases, the diesel engine cannot start on fire due to the low temperature and pressure at the end of compression.
②Valve guide: The main function of the valve guide is to ensure accurate concentricity between the valve and the valve seat, so that the valve can reciprocate linearly in the valve guide. In addition, it also undertakes part of the heat transfer task.
③Valve seat ring: The valve seat is a supporting surface matched with the valve sealing cone. It and the valve ensure the sealing performance, and at the same time it also transfers the heat from the valve head.
④Valve spring: The function of the valve spring is to ensure that the valve can be pressed against the valve seat when it is closed, and the transmission parts are kept in contact with each other during movement, so as not to separate from each other due to inertial force, causing impact and noise. Therefore, the valve spring has a larger pre-tightening force during installation, and at the same time has a larger rigidity.
⑤ Valve spring locking device: The valve spring is installed outside the valve stem, one end of which is supported on the cylinder head, and the other end is fixed on the spring seat by the locking device.
⑥Valve rotation mechanism: The valve rotation mechanism is mostly used on the intake valve of high-speed, high-power diesel engines.
Valve drive group:
The valve drive group mainly consists of camshafts, timing gears, tappets, push rods, rocker arms and rocker shafts. The function of the valve drive group is to open and close the intake and exhaust valves in accordance with the specified time (air timing) and sequence (firing sequence), and to ensure the hard-won opening.
①Camshaft and timing gear: The camshaft is the main part of the valve drive unit, and the valve opening and closing process is mainly controlled by it.
② Tappet: The role of the tappet is to transmit the thrust of the cam to the valve or push rod. The tappet is made of steel or cast iron, generally in the shape of a hollow cylinder, which not only reduces the weight, but also obtains a larger pressure area to reduce the lateral pressure per unit area.
③Push rod: In the overhead valve mechanism, because the camshaft and the valve are arranged separately, the two are far apart, so the push rod is used to transmit the thrust from the camshaft. The push rod is generally made of hollow steel pipe to reduce weight.
④Rocker arm: The rocker arm is the transmission part between the push rod and the valve, which acts as a lever.
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