What does the piston assembly consist of?
The piston assembly is an important part of the automobile engine, which is mainly composed of the following six components:
1. Piston: It is a part of the combustion chamber and is equipped with several ring grooves to install the piston ring.
2. Piston ring: It is installed on the piston to seal, usually composed of gas ring and oil ring.
3. Piston pin: Connecting the piston and the small head of the piston connecting rod, there are two modes of full floating and semi-floating.
4. Piston connecting rod: connecting rod of piston and crankshaft, divided into big head and small head on both sides, small head connected to the piston, big head connected to the crankshaft.
5. Connecting rod bearing: a lubricating component installed in the big head of the connecting rod.
6. Connecting rod bolt: bolt that fixes the big end of the connecting rod on the crankshaft.
Piston ring is the core component inside the fuel engine, it and cylinder, piston, cylinder wall together to complete the seal of fuel gas. Commonly used automotive engines have two kinds of diesel and gasoline engines, due to their different fuel performance, the use of piston rings are not the same, the early piston rings are formed by casting, but with the progress of technology, steel high-power piston rings were born, and with the function of the engine, environmental requirements continue to improve, a variety of advanced surface treatment applications, such as thermal spraying, electroplating, chrome plating, etc. Gas nitriding, physical deposition, surface coating, zinc manganese phosphating treatment, etc., greatly improve the function of the piston ring.
The piston pin is used to connect the piston to the connecting rod and pass the force on the piston to the connecting rod or vice versa.
The piston pin is subjected to a large periodic impact load under high temperature conditions, and because the swing Angle of the piston pin in the pin hole is not large, it is difficult to form a lubricating film, so the lubrication condition is poor. For this reason, the piston pin must have sufficient stiffness, strength and wear resistance. The mass is as small as possible, and the pin and the pin hole should have appropriate matching gaps and good surface quality. In general, the stiffness of the piston pin is particularly important, if the piston pin bending deformation, may cause damage to the piston pin seat.
In short, the working condition of the piston pin is that the pressure ratio is large, the oil film cannot be formed, and the deformation is not coordinated. Therefore, its design requires a high enough mechanical strength and wear resistance, but also a high fatigue strength.
The connecting rod body is composed of three parts, and the part connected with the piston pin is called the connecting rod small head; The part connected with the crankshaft is called the big head of the connecting rod, and the part connecting the small head and the big head is called the connecting rod body.
In order to reduce the wear between the small head and the piston pin, the thin-walled bronze bushing is pressed into the small head hole. Drill or mill grooves into the small heads and bushings to allow the splash of oil to enter the mating surface of the lubricating bushing-piston pin.
The connecting rod body is a long rod, and the force in the work is also large, in order to prevent its bending deformation, the rod body must have enough stiffness. For this reason, the connecting rod body of the vehicle engine mostly adopts the shape I section, which can minimize the mass under the condition that the stiffness and strength are sufficient, and the high-strength engine has the H-shaped section. Some engines use connecting rod small head injection oil cooling piston, which must be drilled through the longitudinal hole in the rod body. In order to avoid stress concentration, the connecting rod body, small head and big head are connected by a large circular smooth transition.
In order to reduce the vibration of the engine, the quality difference of the cylinder connecting rod must be limited to the minimum range, in the factory assembly of the engine, generally in grams as a unit of measurement according to the large and small mass of the connecting rod, the same engine to choose the same group of connecting rod.
On the V-type engine, the corresponding cylinders in the left and right columns share a crank pin, and the connecting rod has three types: parallel connecting rod, fork connecting rod and main and auxiliary connecting rod.
The tiles that are mounted on the fixed brackets of the crankshaft and cylinder block and play the role of bearing and lubrication are usually called crankshaft bearing pads.
Crankshaft bearing is generally divided into two types: bearing (Figure 1) and flanged bearing (Figure 2). Flanged bearing bushing can not only support and lubricate the crankshaft, but also play the role of axial positioning of the crankshaft (there can only be one place on the crankshaft to set the axial positioning device).
When we use connecting rod bolts, we will find that there are many problems with connecting rod bolts, there will be appearance problems, tolerance length problems, fracture problems, tooth thread problems, problems found during installation, and so on.
The simple way is to test the connecting rod bolt, find out where the problem lies and change it. The connecting rod bolt test needs a method. Connecting rod bolt is an important bolt that connects the bearing seat of the big end of the connecting rod and the bearing cover. The connecting rod bolt is subjected to the action of preloading force during assembly, and the connecting rod bolt is also subjected to the action of reciprocating inertia force when the four-stroke diesel engine is running. The diameter of the connecting rod bolt is small because it is limited by the diameter of the crank pin and the outer porch size of the big end of the connecting rod.
A bolt that connects the split connecting rod cover to the big end of the connecting rod. On each pair of bearings, two or four connecting rod bolts are generally used to secure them. The type of bolt varies. The head is often machined with a positioning plane or convex block for installation and embedding with the bearing support surface to prevent the connecting rod bolt from rotating when tightening the nut. The diameter of the bolt rod body at each section surface of the bearing is large, so that it can be positioned with the bolt hole during assembly; The diameter of the rest of the bolt rod body part is smaller than the diameter of the bolt hole, and the length is longer, so that the load of the thread part can be reduced when the bending and impact load is borne. The thread part usually adopts fine thread with higher precision.
In order to prevent the threaded connection from loosening itself, the connecting rod bolt has a permanent anti-loosening device, which is generally cotter pin, anti-loosening washer and copper plating on the thread surface. Connecting rod bolts often bear alternating loads, which are easy to cause fatigue damage and break, which will cause extremely serious consequences. Therefore, it is often made of high-quality alloy steel or high-quality carbon steel, and after tempering heat treatment. In management, attention should be paid to checking its firmness to prevent loosening; Regular disassembly check it for cracks and excessive elongation, etc., should be replaced in time if necessary. When installing, it is necessary to cross and gradually tighten according to the prescribed pre-tightening force, which can not be too large or too small, so as to avoid accidents such as rod bolt breakage in the work.
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