The piston ring is one of the key parts of the engine, and its work directly affects the performance of the engine. At the same time, the piston ring is also a wearing part. When the piston ring is inspected, the piston is usually lifted. Therefore, the time to repair or replace the piston ring is often used as the first maintenance period of the engine.

In recent years, due to the development of the engine in the direction of high speed and strengthening, the working conditions of the piston rings have become increasingly demanding, and higher demands have been placed on their wear resistance.

Piston Ring Wear and Influencing Factors Wear between the piston rings and cylinder liners of automotive engines has the following characteristics:

1. The piston ring moves back and forth between the top and bottom dead center, and the speed changes from a static state to a maximum of 30m/s, and this is repeated and changes greatly.

2. When reciprocating, the cylinder pressure varies greatly during the intake, compression, work, and exhaust strokes of the work cycle.

3. Because of the influence of the combustion stroke, the movement of the piston ring is often performed at a high temperature, especially the first air ring. Under the chemical effects of the high temperature and high pressure and the combustion products, the oil film is difficult to establish to complete Lubrication is difficult, and it is often in a critical lubrication state.

According to the wear mechanism, piston ring wear can be classified into normal wear, fusion wear (scratches, scratches), abrasive wear, and corrosion wear. However, these wear phenomena do not appear alone, but they exist at the same time and influence each other. According to the wear part, piston ring wear can be divided into sliding surface wear and upper and lower end wear. In general, the wear of the sliding surface is greater than that of the upper and lower surfaces. The sliding surfaces are mainly the wear and abrasive wear; the upper and lower surfaces are mainly caused by the reciprocating motion of the piston.

The maximum wear of the sliding surface of the piston ring often occurs at the top dead center position of the cylinder, because the high temperature gas acts on the piston ring, destroying the oil film, resulting in easy to melt conditions, thereby accelerating the wear of the piston ring. Normally so-called normal wear actually contains slight fretting wear and abrasive wear. The amount of wear on the sliding surface of each ring is not the same. The first ring has the largest amount of wear, the second ring is about half of the first, and the oil ring has the smallest amount of wear. For example, after a 500-hour reliability test of a piston ring mounted on a Steyr WD615 engine, the first air ring opening clearance wear is 0.4-0.6 mm, the second opening clearance wear is 0.25-0.4 mm, and the oil ring opening clearance Wear is 0.3 to 0.55 mm. However, sometimes the ring wear is larger than the middle rings, which is due to the distribution of lubricant on the cylinder surface and the influence of adsorbed impurities.

The wear on the upper and lower end faces of the piston ring is mainly due to the mechanical residue formed on the upper and lower end surfaces due to the hard residue in the oil and the dust particles mixed in from the atmosphere, and is essentially abrasive wear. However, when the abnormal thermal deformation of the piston occurs and the ring groove backlash becomes small, melt wear may also occur.

There are many factors that affect the piston ring wear. The material and shape of the piston ring, the material and structure of the cylinder sleeve piston, the lubrication status, the structure of the engine, the operating conditions, and the quality of the fuel and lubricant are the main factors. Of course, in the same cylinder, the effect of the lubrication state on the wear of the piston ring is the greatest. It can be said that the wear of the piston ring largely depends on the lubrication state. The ideal inter-ring lubrication is a uniform film of oil between the two sliding surfaces. However, this condition does not exist in fact, especially the first air ring, due to the influence of high temperature, it is difficult to establish a better lubrication state. .

Piston ring wear reduction measures There are many factors that affect the piston ring wear, and these factors are often intertwined. In addition, the type of the engine and the use of different conditions, the piston ring wear is also very different, and therefore can not rely solely on improving the structure and material of the piston ring to solve the problem, mainly from the following aspects: Piston ring and cylinder liner Materials and good match; surface treatment; structural condition; selection of lubricating oils and additives; deformation of cylinder liners and pistons due to heating during assembly and operation.

The following discussion focuses on materials, structures, and surface treatments.

1. Choosing materials that match good performance to reduce wear, as the material of the piston rings, must first have good wear resistance and oil storage. In general, it is inevitable that the first air ring wears more than the other rings, so it is particularly necessary to use materials that are good at keeping the oil film intact. One of the reasons that cast iron with graphite structure is valued is that it has good oil storage and wear resistance.

In order to further improve the wear resistance of the piston ring, various types and amounts of alloying elements can be added to the cast iron. For example, chromium-molybdenum-copper alloy cast iron rings commonly used in engines now exhibit obvious advantages in terms of wear resistance and oil storage. .

In short, the material used for the piston ring is preferably a wearable structure that can form a reasonable soft matrix plus a hard phase, so that the piston ring is easy to wear during initial wear and is difficult to wear after being worn out.

In addition, the material of the cylinder matched with the piston ring has a great influence on the abrasion of the piston ring. In general, when the hardness difference of the grinding material is zero, the wear is minimal, and as the hardness difference increases, the wear increases. However, at the same time of material selection, it is better to make the piston ring reach the wear limit earlier than the cylinder under the condition that the two parts have the longest lifespan. This is because replacing the piston ring is more economical and easier than replacing the cylinder liner.

For the abrasive wear, in addition to considering the hardness, the elastic effect of the piston ring material must also be taken into account. The toughness of the material is difficult to wear and the wear resistance is also high.

2. Structural improvements Over the past few decades, many improvements have been made at home and abroad regarding the structure of the piston rings, and the effectiveness of changing the first gas ring to a barrel ring has been the most significant. Because the barrel surface ring has a series of advantages, as far as wear is concerned, the barrel surface ring moves upwards or downwards irrespective of whether or not the lubricating oil can lift the ring by the action of the oil wedge to ensure good lubrication. In addition, the barrel ring also avoids edge loading. At present, the barrel ring is generally used as the first ring in the enhanced diesel engine, and the barrel ring is more commonly used in other types of diesel engines.

As for the oil ring, the internally-supported spiral spring cast iron oil ring commonly used at home and abroad has great advantages. The oil ring itself is very flexible and has excellent adaptability to the deformed cylinder liner so that it can be maintained well. Lubrication reduces wear.

In order to reduce the wear of the piston rings, the cross-sectional structure of the piston ring group must be properly matched to maintain a good seal and lubricating film.

In addition, in order to reduce the wear of the piston rings, the structure of the cylinder liner and the piston should be designed rationally. For example, the cylinder liner of the Steyr WD615 engine adopts a platform textured structure. During the running-in process, the contact area between the cylinder liner and the piston ring is reduced. Can maintain the liquid lubrication, the amount of wear is minimal; moreover, the mesh acts as an oil sump to improve the ability of the cylinder liner to maintain the lubricating oil, so it is very beneficial to reduce the wear of piston rings and cylinder liners. The cylinder liner structure shape is now commonly used in engines. In order to reduce the wear on the upper and lower surfaces of the piston ring, the piston ring and the end face of the ring groove must maintain a proper clearance so as to avoid excessive impact load. In addition, in the piston ring groove inlaid with wear-resistant austenitic cast iron liner, you can also reduce the upper and lower end of the wear, but this method does not need to be fully promoted except for special circumstances. Because its technology is more difficult to master, the cost is higher.

3. Surface treatment can significantly reduce the wear of piston rings by surface treatment. There are many methods for surface treatment that are used today. As far as their functions are concerned, they can be classified into the following three categories:

1) Increase surface hardness to reduce abrasive wear. That is, a very hard metal layer is formed on the working surface of the ring, so that the loose cast iron abrasive is not easily embedded on the surface, and the wear resistance of the ring is improved. The most widely used is the porous hole chrome plating, not only the hardness of the chrome plating layer (HV800 ~ 1000), the friction coefficient is very small, and the porous hole chrome plating layer has a good oil storage structure, which can significantly improve the wear resistance of the piston ring. In addition, chrome plating has low cost, good stability, and good performance in most cases. Therefore, the first ring of modern car engines uses chrome-plated rings, and the oil ring uses almost 100% chrome-plated rings. Practice has proved that after the piston ring is chrome plated, not only its own wear is small, but also other piston rings and cylinder sleeves that are not chrome-plated wear less.

For high-speed or enhanced engines, the piston rings not only have to be chrome plated on the outer surface, but also have to be chrome plated on the upper and lower end faces to reduce wear on the end face. All outer surfaces of the ring set are preferably chrome plated to reduce wear of the entire piston ring set.

2) Improve the oil storage capacity and anti-melting ability of the working surface of the piston ring to prevent fusion wear. Lubricating oil film on the working surface of the piston ring is destroyed at high temperature, and sometimes forms dry friction. If a layer of surface oil coating and anti-friction coating is applied on the surface of the piston ring, the wear of the ring can be reduced, and the ring can be improved. Pull cylinder capacity. Molybdenum sprayed on the piston ring has extremely high resistance to wear. On the one hand, the molybdenum sprayed layer is the porous structure of oil storage coating; on the other hand, the melting point of molybdenum is relatively high (2630 °C), and it can still work effectively when dry friction. In this case, the sprayed molybdenum ring has a higher resistance to melting than the chromed ring. For example, for the R4100 diesel engine, a chrome-plated ring was used at the beginning and it was found that the piston ring pulls the cylinder. After the molybdenum ring is sprayed, this problem is basically solved. However, the wear ability of the molybdenum sprayed ring wear-resistant material is worse than that of the chrome plating ring. In addition, the sprayed molybdenum ring has a high cost and the structure strength is difficult to be stabilized. Therefore, it is best to use chrome plating unless it is necessary to spray molybdenum.

3) Improve the initial surface treatment. This surface treatment is to cover the surface of the piston ring with a layer of soft and elastic vulnerable material, so that the ring contacts the protruding part of the cylinder liner to accelerate the wear, thereby shortening the running-in period and enabling the ring to enter a stable working state. . Phosphate treatment is currently widely used. A phosphate film with soft texture and easy to wear is formed on the surface of the piston ring. Because the equipment required for the phosphating treatment is simple, the operation is convenient, the cost is low, and the efficiency is high, it is commonly used in the piston ring process of a small engine. In addition, tin plating and oxidation treatment can also improve initial run-in.

In the piston ring surface treatment, chrome plating and molybdenum spray are the most commonly used methods. In addition, depending on the type, structure, application, and operating conditions of the engine, there are other surface treatment methods such as soft nitriding, sulfidation, and filling with ferroferric oxide.

The wear of piston rings is a complex phenomenon. There are many factors and they are often complex intertwined. Therefore, when solving the problem of wear of piston rings, various factors must be comprehensively analyzed in order to design, materials, manufacturing processes, and surfaces. Treatment and lubricants and other aspects of reasonable arrangements, and ultimately achieve satisfactory results.