ਇੰਜਣ ਦਾ ਗਿਆਨ – ਪਿਸਟਨ

ਇੰਜਣ ਦਾ ਗਿਆਨ – ਪਿਸਟਨ

For the Pistons, who know the engine knows that it is the most important parts of the engine.
    Piston rod set is composed of the piston, piston rings, piston pins, connecting rod, connecting rod bearings and other components.
    Function: The function of the piston is under gas pressure, and passed through the connecting rod piston pin driven by the crankshaft rotation, the piston or the top part of the combustion chamber.
    Working conditions: the piston in the high temperature, high pressure, high-speed, poor lubrication conditions. Direct contacts with the hot gas piston, the instantaneous temperature up to 2500K or more, therefore, serious heat, and thermal conditions and poor, so the piston working temperature is high, the top up 600 ~ 700K, and the temperature distribution is very uneven; piston top Department under gas pressure, especially pressure for maximum power stroke, gasoline engine up to 3 ~ 5MPa, diesel engines up to 6 ~ 9MPa, which makes an impact piston, and the role of lateral pressure to bear; piston in the cylinder at high speed (8 ~ 12m / s) reciprocating motion, and the speed is constantly changing, which creates a great deal of inertia, so that the piston be a great additional load. Piston in such a bad working conditions, will produce distortion, and accelerated wear and tear, but also generate additional load and thermal stress, and chemical corrosion by the gas. Therefore asked: (1) should have sufficient stiffness and strength, power transmission reliability; (2) thermal conductivity and good resistance to high pressure, high temperature, wear-resistant; (3) the quality of small, light weight, to minimize the reciprocating inertia force. Aluminum alloy is basically meet the above requirements, therefore, the Pistons are generally made of high strength aluminum alloy, but in some low-speed diesel engine using advanced heat-resistant cast iron or steel.
    Construction: Piston can be divided into three parts, piston, piston head and piston skirt.
    1 piston: piston under gas pressure, which is part of the combustion chamber, its shape, position, size, and all specific forms of the combustion chamber, are to meet the combustible mixture formation and combustion requirements, top shape can be divided into four categories, flat-topped piston, the piston top convex, concave top of the piston and the piston top shape. Flat top piston is a flat, simple, easy to manufacture, heat a small area, at the top of the stress distribution is more uniform, generally used in gasoline, the diesel engine is rarely used. Top of the piston was raised convex dome-shaped top, the top of the high strength, from the guide will help to improve the ventilation process, two-stroke gasoline engine is often used convex top of the piston. Concave-shaped top piston was hollow, pit shape and location must be conducive to the burning of combustible mixture, a double vortex pits, ball pits, U-shaped pit, and so on.
    (2) Piston head: piston head refers to the first piston ring groove over part of the piston pin hole. Several said it ring groove, for the installation of piston rings, the seal, also known as leak-proof department. Diesel enginecompression ratio, generally there are four ring groove, the upper three installation ring, install the lower oil ring. Gasoline generally have three ring groove, which prescribe the gas tank and an oil ring ring groove, oil ring in the bottom surface of the radial drilling many holes, so that the oil ring was scraped from the engine cylinder walls of oil through the holes flow back into the sump. The first ring groove worst working conditions, these should generally be far away from the top. The heat absorbed by the main piston is passed through the leak-proof piston cylinder wall by the Ministry, and then spread out from the cooling water. In short, the role of the engine piston head in addition to installation of piston rings, there are seal and heat transfer effects, together with the piston cylinder seal to prevent leakage of combustible gas mixture to the crankcase, and will also (70 ~ 80)% heat to pass through the piston cylinder walls.
3 piston skirt: skirt piston oil ring groove means from the end until the next part of the bottom of the piston, which includes the sales of seat mounted piston pin hole. Piston skirt on the piston in the engine cylinder reciprocating motion from the guide, and to withstand lateral pressure. Skirt depends on the size of lateral pressure and the piston diameter. The so-called lateral pressure in the compression stroke and is as successful tour, the role of gas pressure in the engine piston at the top of the horizontal component of the pressure piston to the cylinder wall. Compression stroke and power stroke for the direction of the gas pressure on the opposite side, due to combustion pressure much higher than the compression pressure, so, successful trip for the lateral pressure is also much higher than the compression stroke of the lateral pressure. Piston skirt to withstand lateral pressure of the two sides called the thrust surface, they are in phase with the piston pin axis perpendicular to the direction. Structural features:
    (1) pre-made oval, in order to withstand the side skirt and the engine cylinder gas pressure and maintain a small and safe space, requiring the piston in the engine cylinder with the correct work. However, due to the thickness of the piston skirt is very uneven, the piston pin bore part of the metal thickness, large thermal expansion along the axis of engine piston pin seat deformation is greater than the other direction. In addition, the side skirt to withstand the pressure of the gas, leading to deformation along the piston pin over the vertical to the direction of large piston pin. Thus, if the cold when the piston skirt is circular, then the work becomes an oval piston, the piston and the cylinder gap between the circumference are not equal, causing the piston in the cylinder stuck, the engine will not work. Thus, in the pre-processing of the engine piston skirt made of oval shape. Long axis of the ellipse and the vertical seat sales, marketing seat along the short axis direction. This work closer to perfect circle piston.
    (2) the direction of the temperature along the height of the piston is very uneven, the upper piston temperature is high, lower low, inflation is a corresponding amount of the upper large, lower small. In order to work the piston up and down tends to equal the diameter, is cylindrical, the piston must be made in advance to the next big step on the shape of small, conical.
    (3) In order to reduce the engine piston skirt by heat, usually in the horizontal insulation skirt open slot, in order to compensate for heat skirt after deformation, skirt opened a vertical expansion slot. Slot shape “T” shaped or “Π”-shaped slot. Horizontal slot in the most general, under an open slot below the ring, skirt the edge of pin seat on both sides (and there are open among the oil ring groove), head to reduce heat transfer to the skirt, it is called heat slot. Vertical slot will skirt has a certain flexibility, so that between the engine piston and cylinder assembly with a gap as small as possible, and in the hot Shiyou with compensation, not to cause the piston in the cylinder stuck, it will be said vertical slot for the expansion slot. Skirt open vertical slot, the slot side of the stiffness will make it smaller so that it is made in the assembly should withstand the lateral pressure power stroke the smaller side. Diesel engine piston by the force, is generally not slotted skirt.
    (4) Some of the piston in order to reduce weight, hole in the skirt or the skirt is not cut out part of the lateral pressure on both sides to reduce the inertia force, reducing the engine pin near the hot seat deformation, the formation of the piston plate or short delay piston skirt drag elastic plate structure, the quality is small, with the gap between the engine piston and cylinder smaller for high-speed engines.
    (5) In order to reduce the aluminum piston skirt of thermal expansion, and some gasoline in the piston skirt or piston pin seat embedded steel. Heng Fan structural characteristics of steel piston, due to constant range of 33% nickel steel is 36% of low-carbon iron-nickel alloy, and its expansion coefficient of aluminum is only 1 / 10, while the steel pin seat by Heng Fan connected with the skirt, a skirt to contain the thermal expansion deformation.
    (6) Some gasoline engine, the piston pin hole centerline is deviated from the centerline plane of the piston, power to make the trip by the main party to offset the lateral pressure of 1 ~ 2mm. This structure allows the piston from the compression stroke to power stroke for softer to the cylinder from the pressure side of the transition to the other side of the cylinder pressure to reduce the knock sound. At installation time, this piston pin offset direction can not hold against, or for power will increase to hit, damage to the skirt.