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Three Parts of Engine Piston and Unique Structure

Piston is widely used in the diesel engine, gasoline engine and air compressor. Engine piston structure consists of three parts, piston top, piston head and piston skirt. Different parts have their own functions and advantages, we will introduce you these structures. Several pistons have unique design to suit different requirements of piston for better working performance and longer service life.

Piston top

Piston top has three different types. Flat piston top, concave top and convex top.

  • Flat piston top. Flat piston top with an flat surface is simple and easy to produce. It is widely used in the gasoline piston and rarely used in the diesel engine piston.
  • Concave piston top. Concave top engine piston has an concave top surface, which is conducive to the burning of combustible mixture. The shapes of concave are double vortex shapes, ball shapes and U shapes. Concave top engine piston is commonly used in the diesel engine.
  • Convex piston top. Convex top engine piston is in raised ball shape, which has high strength. It can improve gas exchange process and act as the guide role. Convex top engine piston is widely used in the two-stroke gasoline engines of motorcycle.
A concave top aluminum alloy engine piston on the gray background.

Concave top engine piston.

A flat top aluminum alloy engine piston on the gray background.

Flat top engine piston.

A convex top aluminum alloy engine piston on the gray background.

Convex top engine piston.

Piston head

Piston head refers to the location from bottom line of piston top to the bottom line of first oil ring groove.

Piston head is mainly used for piston ring installation. piston ring groove has two to five lines. Quantity of piston ring on the gasoline piston is less than the diesel piston. Piston ring has compression ring and oil-control ring two types.

Compression ring groove uses with compression ring to seal cylinder and prevent combustible mixture from entering the crankcase. Oil-controlling ring groove uses with oil-control ring to scrape extra engine oil off cylinder.

Another function of piston head is transfer the heat to cylinder wall through piston ring.

A aluminum alloy piston with top anodic oxidation surface and three piston ring grooves.

Three piston ring groove engine piston.

A aluminum alloy piston with concave piston top and four piston ring grooves.

Four piston ring groove engine piston.

Piston skirt

A aluminum alloy piston with graphite coating on the piston skirt.

Graphite coating on the piston skirt can improve the wear resistance of piston.

Piston skirt locate the bottom of piston from bottom line of first oil ring groove to the bottom line of piston including piston pin hole.

The function of piston skirt is mainly for guidance and heat dissipation. Piston skirt has sufficient bearing area to form thick lubricating oil film. It can not only bear the lateral thrust from connecting rod, but also ensure the good guiding performance.

Contact area between piston skirt and cylinder wall can affect the wear loss of engine. Lots of piston adopt the graphite painting surface treatment on the piston skirt to improve the wear resistance and lubrication performance.

Unique structure

Alfin.
The abrasion of piston groove will affect the whole motion of piston, lower working efficiency and reduce service life of piston. To solve these problems, a type of abrasion resistant ring is added onto the first ring groove. Sometimes, the second ring groove is also installed this wear resistant ring. Anti-wear ring is made of austenite high nickel cast iron, which can improve the wear resistance performance of piston.

A aluminum alloy piston with one alfin on the first ring groove.

One alfin on the piston ring groove,

A aluminum alloy piston with double alfin.

Double alfin engine piston.

Copper bush.

With the increase of volume power and improvement of technology, the pressure of piston top becomes larger than before. At the same time, the abrasion between piston pin hole and piston pin is more serious. So, we add two copper bush into the piston hole to add the abrasion resistance of piston pin hole. Copper has better abrasion resistance than aluminum, it can protect piston pin and piston pin hole from abrasion. Copper has good ductility, which can be used for transition and buffering in the alternating motion of piston pin. additional, the copper bush have outstanding lubrication performance.

A profile map of aluminum alloy piston with two copper bushes in the piston pin hole.

Copper bush can protect piston pin from abrasion.

Steel piece insert.

Steel piece insert is a special design to reduce thermal expansion of piston skirt. This structure is more and more widely used in the car piston. Steel piece is inserted into piston skirt or piston pin hole. The material of steel piece is invar alloy steel, which contains 33% - 36% nickel. Its expansion coefficient is only 1/10 of aluminum alloy. The piston pin hole connects with piston skirt through steel piece to contain thermal expansion deformation of the piston skirt.

A aluminum alloy piston with steel piece insert in the piston skirt.

Steel piece insert structure can contain thermal expansion deformation of the piston skirt

Cooling channel.

Temperature of piston head is an important factor of durability. It can help to improve the fuel oil economy. High temperature of piston head will lower working efficiency and reduce service life. Insert the cooling channel into piston head can help to lower the temperature of piston head and whole piston.

A profile map of phosphating coating aluminum alloy piston with cooling channel.

Cooling channel can lower temperature of piston head and whole piston.

Meanwhile, it can lower the temperature of first ring groove to reduce the carbon deposit and clamping stagnation of piston ring. In this way, we can save fuel oil and improve sealing performance.

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Hengshui Juneng Machine Fittings Co., Ltd.
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