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1The machine piston connecting rod set- detailed exposition of pistonThe piston connecting rod set is composed of the piston, piston wreath, piston pin, connecting rod, connecting rod axle bush, etc.Ⅰ. effect: The effect of the piston is to bear the air pressure, and pass to connecting rod to drive the bent axle to revolve through connecting rod axle bush, the piston coping is still a part of the burning room. The work condition: Piston works under the condition of heat, high pressure, high speed, and bad lubrication .Piston directly contacts with the heat air. The temperature can amount to above 2500 Ks in a moment .The piston is heated severely, but the condition of spreading the hot is bad .So while the piston works, the temperature is very high and the coping is up to the 600-700 Ks: And the temperature distributes asymmetrically; The piston coping bears great air pressure, especially the pressure is greatest in the route of doing efficacy. The gasoline machine is up to the 3-5MPas, the diesel engine is up to the 6-9MPas.This makes the piston produce pound, and bear the function of the side pressure. Therefore, the piston should have enough heat-proof, try to decrease the heating area,, strengthen the cooling of the piston, to make the highest temperature of the coping descend .The piston moves at very high speed(8-12 ms/ s) back and forth in the air cylinder, and speed changes constantly, This produces very great inertial dint, making the piston bear great additional load working under such bad condition, the piston will become deformed heating power. At the same time ,it slitters the chemical corrosive power of the burning gas .In order to descend the inertial dint of back and forth, we must ease the weight of the piston as possible .Piston works under the condition of the heat, high pressure, high speed(the average speed can amount to the 101115 m/ s), and its lubricant condition is bad and the frication between 2the piston and the air cylinder wall is very great. In order to descend the friction, the surface of the piston surface must be wear-resistant..Request: (1) To have enough rigidity and strength, and the reliable dint; (2) Transmit heat well, bear the high pressure, bear the heat and bear to wear away; (3) the quantity is small, the weight is light, descend the inertial dint of back and forth as possible　　The aluminum metal alloy material satisfies the top requests basically, therefore, the piston generally adopts the high strength aluminum metal alloy, but some low speed diesel engines adopt high class iron casting or heat-proof steel Ⅱ, structure: The piston can be divided into three parts, piston coping, the piston head and piston skirt departments. 1. The piston copingThe piston coping bears the air pressure, it is a part of the burnable room .Its shape, position, size are relevant to the concrete from of the burnable room. They are made to satisfy the combustible hybrid spirit formation and burnable requests. Its coping shape can be divided into four major types, a flat coping piston, a convex coping piston, a concave coping piston and model piston. A convex coping piston is usually used on the two blunt distance I.C. engines, It is good to improve the process exchanging the gas .Modern four blunt the distance gasoline machine also adopts the convex coping piston in order to strengthen the effect of pushing the gas or extend the ratio of compressing .Convex of a piston coping presents a form of ball, its coping strength is high, having an effect of leading, being advantageous to improve the process of exchanging the gas, two route of travel gasoline machines often adopt the convex coping piston　　3A piston coping presents the hollow form, the shape and positions of the cave pit must be advantageous to the combustion of the combustible and hybrid gas, having a pair of eddies concave pit ball, concave pit, U concave pit, and so on. 2.Piston headThe piston refers to the first piston wreath to the part above the piston pin.It has several wreath slots, which are used to install the piston wreath and have an effect of sealing completely. It is also called the leak proof department .The diesel engine’s compress ratio is high, and generally have four wreath slots, The three upper wreaths are used to install, the lower part installs the oil wreath. The gasoline machine has three wreath slots generally, which are two jet of gas wreath slots and an oil wreath slots. At the bottom of oil wreath slot many paths toward eyelet are drilled to make the quilt oil wreath flow from the air cylinder wall to the oil bottom hull through these eyelets. The working condition of the wreath slot is the worst and should leave the coping generally a little farther. Above the gas wreath, a narrow insulating slot is usually set to cut off the heat flow which is spread from the piston coping to the first gas wreath and make parts of calories from a piston wreath spread, thus easing the hot burden of the first gas wreath. On some engines small wreathe slots are often made between the coping head and the first gas wreathe, sometimes till a few more wreath. This kind of small wreath can adsorb the lubricant because it accumulates the carbon. It can keep piston and the air cylinder walls from biting to match when it work in the condition of losing oil, so it is called accumulating the carbon slot.The calories that the piston coping absorbs also mainly passes the air cylinder wall through the piston wreath to leak proof department, again spread by the cool water.In a word, the function of the piston head is in addition to install the piston wreath, still seal 4completely function and transmit heat function, sealing completely the air cylinder together with the piston wreath, keeping combustible admixture spirit from leak crankcase, at the same time pass the(70-80)%calories to the air cylinder wall through the piston wreath.3. Piston skirt departmentThe piston skirt department refers to the parts from the bottom of the oil wreathe slot. It includes the pin which is used to pack the piston. The piston skirt department exercises to rise to lead to the function to the piston in the back and forth in the air cylinder, and bear the side pressure. The length of the skirt department is decided by the size and the piston diameter of the side pressure. The so-called side pressure mean in the compression route of travel and make route of travel of efficacy .The level component of the gas pressure which take effect on the piston coping presses the piston to the air cylinder wall. Compress the route of travel and make the side pressure direction of the efficacy route of travel air exactly the opposite, because of the combustion pressure consumedly high in compress the pressure, so, make the side in the route of travel of efficacy pressure also consumedly high in compress the side in the route of travel pressure. Two on the sides that bear the side pressure of the piston skirt department be called to push the dint to face, they be placed in to sell the mutually perpendicular direction of the stalk line with piston up. Structure characteristics: (1) make into oval in advance:The wall thick of the piston skirt department is bigger along the direction of the pin and the hot inflation have great capacity. While working under the common function of hot burden and the side pressure the skirt ministry becomes the oval pillar form. Following the piston to pin direction it has the elongation slightly, but the perpendicularity pin 5direction it has slightly short. In order to make piston in working condition still keep the cylinder form and prevent from resulting in piston choked to death or the part wore away big because of oval transform, the piston skirt department processes generally and in advance oval, its major axis and pistons sell the stalk direction perpendicular. In order to reduce the heat transform around the piston, we can also make the surface of skirt cast into bottom to sink the 0.5-1 mms In order to make both sides of skirt bear the air pressure and keeping with air cylinder small but safety of cleft, while working the piston must have right of cylinder form. But, because the thickness of the piston skirt department is very asymmetry, the piston pin the metals of a bore part thick, be subjected to the hot inflation to have great capacity, follow the piston to sell a stalk line direction of transform to have great capacity in other directions. Moreover, the function that bears the air side pressure, causes the piston to transform the more perpendicular piston of quantity pin the direction big.Thus, if the piston in cold state hour skirt department is a circular, while working the piston will become on oval, making a circumference cleft of the piston and air cylinder not equal, resulting in piston block in the air cylinder and the machine can't work normally. Therefore, while processing we make the piston skirt department into the oval shape in advance. The direction of oval major axis is perpendicular with the pin. The direction of the minoraxis follows the direction of the pin. Thus while working the piston work tend the near positive circle. (2)The temperate of the piston along the direction of the length is very asymmetry. The temperature of the upper part of the piston is high, the lower part is low, it is upper part that the inflation quantity also correspond big, the lower part is small. In order to make the piston top and bottom diameter tend equal, that is to say the cylinder form, must make the piston into the top smaller the bottom the big stairs form in advance, taper. 6(3) In order to reduce the calories of the piston skirt department ,we usually open the hot slot horizontally in the skirt department. In order to compensa the skirt department after be subjected to the heat of transform the quantity, the skirt department opens lengthways of inflation slot. The shape of the slot contain" T" form or" Π " form slots. The horizontal slot opens generally under most the underneath of a wreath slot, both the edge pin sides ( also opened in the oil wreath slot) of on the skirt department so as to reduce the head calories delivered toward the skirt department, so it is called separating the hot slot. The vertical slot will make the skirt department have the certain flexibility so as to the possibly small cleft with the air cylinder while thus making piston assemble, but at hot state have the in expiation of function again, result in piston choked to death in the air cylinder unlikely, past be called vertical slot inflation slot. The skirt department will make it open a side of the slot after open the vertical slot just the degree diminish, bearing the side a side that pressure is smaller in assemble should make it locate make route of travel of efficacy .The diesel engine piston is subjected to the dint big, the skirt department does not open the slot generally. (4) In order to ease the weight some pistons slice one part in both sides that opens the bore or is free from the side pressure to the skirt department, to eliminate the inertial dint, to reduce neighborhood of heat transform the quantity, and form drag along the plank type piston or short piston.The flexibility between of the plank structure skirt is good, the quantity is small, the matching cleft between the piston and air cylinder is smaller, so it is applicable to the high speed engine.(5)In order to reduce the hot inflation degree of the aluminum metal alloy piston skirt department, some gasoline machine piston imbeds the steel slice in the piston skirt department or pin. The structure characteristics of the permanent model steel is as the permanent model steel is the low carbon iron nickel metal alloy with33% ～ 36% 7nickel, its coefficient of expansion is only 1/10 of that of aluminum metal alloy. But pin through the permanent model steel slice and the skirt departments connect with each other and curb the degree of the coefficient of expansion.(6) the gasoline that have is on board, the center line of the piston pin is to deviate the piston center line flat surface, subjected to the main side in the route of travel of efficacy a square of the pressure partial to move the 1-2 mms. This kind of structure can make piston compare in from compress route of travel go to make route of travel of efficacy mildly from press toward air cylinder of a the noodles transfer to press toward air cylinder of another one side, reducing the sound of knocking the urn. While installing, the direction that this kind of piston pin is partial to place can't pack anti-, otherwise change to pound the dint and will enlarge, making the skirt department damaged