Moving parts of diesel generator set machine consists of a piston, connecting rod group, crankshaft flywheel sets and other components. Its role is to withstand the gas pressure of the piston rod to pass through the crankshaft, and the reciprocating linear motion of the piston into rotary motion of the crankshaft output mechanical energy.

(A) a piston rod group

Set by the piston rod piston, piston rings, piston pins, connecting rods and other parts, as shown in the right shows.

1. piston

The piston and the cylinder, the cylinder head combustion chamber composed of, and the mechanical energy transmitted through the piston rod and the crank pin. Piston top is part of the combustion chamber when the engine work, which bear directly on top (5880 ~ 8820) kPa[pressurized diesel engine (7840 - 11760) kPa] pressure and instantaneous temperature outbreaks role, top, the highest temperature reached 300 ~ 4003 C, and the piston is very uneven temperature distribution, is not constant speed and the linear reciprocating motion of the piston which requires a high strength, low coefficient of thermal expansion, good wear resistance and corrosion resistance, good thermal conductivity and lighter weight.

Top of the piston engine usually has a variety of pits. Pits to change the shape of the combustion chamber is provided, so that the formation of combustible mixture is more favorable, more complete combustion process.

A higher degree of intensity set piston cooling oil channel head should be to reduce the temperature. Cummins NT Series diesel cut above the piston head has three installation sealing ring (gas rings) slot, a slot for the installation of the following scraper ring (oil ring) tip. The bottom surface of the oil ring groove with many small holes drilled so that the cylinder wall from the oil scraper ring of excess lubricant scraped back into the crankcase through the orifice.

Piston skirt for linear motion guide piston in the cylinder and the rod lateral force to the cylinder wall, so. There should be sufficient pressure area. There piston skirt piston pin seat, the air force Hugh rod passed through the piston pin.

As the engine cylinder pressure, so the piston skirt is not open grooving. Only the tapered piston and make large the skirt portion of the oval, so that the fitting clearance between the piston and the cylinder wall is greater than the gasoline engine. In order to ensure end-compression engine with sufficient pressure and temperature, better sealing is required, therefore, the diesel engine should have more sealing rings and oil scraper rings.

In use, the clearance due to wear between the piston and the cylinder increases. If the repair requires honing the cylinder gap is greater than 0.5mm, and then press the appropriate size matching the size of the cylinder piston, restore the standard gap, according to the original size of the cylinder to increase the size of 0.25mm as a repair, there should be a corresponding matching piston sizes to ensure its tightness.

After the piston into the cylinder, the piston assembly gap between the skirt and the cylinder wall.

In assembly of the piston, the piston should be noted that the various marks engraved on top to ensure a balance of the engine during operation.

2 piston ring

Piston rings are divided into gas and oil ring, as shown in Figure 2.7. Piston ring shape as the cutout 2.7 (b), the straight incision to facilitate processing; oblique incision leakage passage area decreases; stepped cutout smallest leak path, but the processing difficult.

The effect of the sealing ring gas cylinder, and the heat absorbed by the piston into the cylinder walls to pass the cooling system, which is the main path of the piston cooling. Especially the first ring, passing 40% -50% of the total calories. The role of the oil ring is to splash too much oil on the cylinder wall scraped against oil channeling human combustion chamber. Reciprocating piston rings work moving at high speed due to friction, lubrication conditions are poor, it is easy to wear, so the piston ring material should have good abrasion resistance, heat resistance, thermal conductivity, corrosion resistance, toughness, flexibility and cylinder According to co-resistance and other properties of the material. currently used are of high quality cast iron or iron alloys, in order to improve the wear resistance, often in the first ring of the work surface be porous chrome, to accelerate the run-in of the new ring, a layer about the rest of the ring 0.01 mm thick tin layer or vulcanized or phosphate treatment. In recent years, domestic materials and processing certain aircraft piston rings, conducted a lot of research and improvements, such as the use of rare earth magnesium ductile iron, cast iron, calcium or rare earth Tong added tungsten, titanium, boron and other alloying elements, and the use of powder metallurgy , sprayed molybdenum and other technology, greatly improved its performance

Piston rings and cylinder walls should be tight fitting, light leakage inspection when, at the ring of light leakage should not more than two, each of the leaked length should be less than 30 arc, turning the light between Chen should be less than 0.02-0.04mm, more than should be updated.

Piston rings opening gap should be appropriate, no expansion room for the opening is too small, easy to get stuck, otherwise it will cause leakage.

When Cummins NT Series diesel engine piston ring attached to the piston, should have marked (TOP) side facing the piston classes, and make a few rings with staggered opening 120 degrees, and may not be facing the piston pin opening direction to ensure that the cylinder seal.

3 piston pin

Piston pin is used to connect the piston and connecting rod mechanism, through which the piston afford to live complex battle between the gas pressure and force the group to pass live link.

When working at high piston pin disheartened by large cyclical impact bending loads, and poor lubrication conditions, which requires that it should have sufficient strength and rigidity, wear well with good toughness and scrambling.

Piston usually low carbon or alloy steel grinding process into a hollow cylindrical, conical or circular shape to the composition, the surface hardened by carburizing heat treatment to improve its hardness. Structure and piston pin fixation.

When installing central piston pin bushing rod small end through the hole, which is supported on both ends of the pin bore in the piston skirt and axial positioning with lock spring to prevent axial movement while scratching the cylinder walls. When working piston pin in the connecting rod small end bush and shoot freely rotatable seat central hole, therefore, required to meet the gap between them appropriately. The gap is too large, will produce percussion, and increased wear; gap is too small will get stuck or the piston deformation.

Piston pin installed in the often disheartened when there should be some interference between the pin and the bore in order to ensure that there is a gap in the high normal ju work. In the use and maintenance, matching piston pin size should be appropriate, the surface should be free of scars, spots, cracks or bumps, roughness is higher.

4 link rod

The piston rod member is connected to the crankshaft, which is the role of the gas acting on the piston pressure to the crankshaft, and by the reciprocating motion of the piston rod into rotary motion of the crankshaft. Small head with the piston rod for reciprocating movement of the connecting rod with crank rod journal rotates around the entire rod piston pin swing.

Linkage group consists of connecting rod, connecting rod bolt, nut, connecting rod bearings, bushings and rod benefit small head and other parts.

Diesel engine connecting rod to withstand the gas pressure and inertia force of the piston when the group is rapidly changing, with its load impact. Swing link itself and to withstand tensile and compressive bending stress complex work, therefore, requires the link must have sufficient strength and stiffness, and each connecting rod and the center of gravity of the weight I f the allowable deviation should be within the range of the field .

Cummins Diesel NT series rod made of high quality alloy steel made chess proud. The structure of the domestic diesel engine connecting rod, like a small head, body and connecting rod linkage of three parts, as shown in Figure 2.10. Hole in the connecting rod head is equipped with good wear resistance bronze pressure piston pin bearing (bush), tank and bore hole has to profits slip. Connecting rod to separate ceremony. Using flat incision, separate part of the connecting rod pots, rod bolts and connecting rod body with high strength fastening and has two locating pins to ensure correct assembly. Big hole in the aluminum rod bearing equipped with good wear resistance, with the best fit clearance between the inner diameter of the connecting rod and crankshaft journal, and in the circumferential direction and the axial opened a tank, which will help lubricate. Connecting rod bearing thin-walled aluminum alloy material, easy to replace and assembly. When installed, the back of the pad should be embedded in the link chain stud projections corresponding recesses, so that both fit tightly to prevent movement or rotation of the pad new interchangeable rod bearing, the pad after use When reloading after overhaul, should be allowed to exchange pairing mark refitted. When people cylinder piston rod assembly should note the more convex rod bearing camshaft chain toward the direction.