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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
The wear between piston rings and cylinder liners of automotive engines has the following characteristics:
1. The piston ring oscillates between the top and bottom dead center, and the speed changes from a standstill to a maximum of 30m/s. This is repeated and changes greatly.
2. During reciprocating motion, 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 high temperature and high pressure and combustion products, the oil film is difficult to establish. It is more difficult to achieve complete lubrication, 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 surface is mainly composed of fusion wear and abrasive wear; the upper and lower end surfaces are mainly caused by impact abrasion 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-fuse 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 amount of wear of the first ring is the largest, the second ring is about half of the first track, and the wear of the oil ring is the smallest.
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, the 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 anti-friction 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, 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.