Piston ring
The piston ring is a sealing element on the piston of an internal combustion engine or a piston compressor, for example .
general description
Piston rings have several tasks:
- Sealing of the work area
- Dissipation of the heat of combustion from the piston to the cooled cylinder wall
- Dosing of the lubricating oil between the running surface of the ring and the cylinder wall
Piston rings are not closed rings, but have an opening on the circumference even when installed, the so-called ring joint . In the free, ie not installed, condition, piston rings are not circular, but have a defined non-circular shape and an opening - the mouth width . The rings are only pressed into a circular shape when they are installed. Piston rings are made of cast or steel materials, depending on the requirements placed on the modulus of elasticity , mechanical strength and wear resistance . To improve the wear behavior, coatings on the rings are sometimes necessary. In this case come electrochemical methods such. B. chrome plating, or thermal spray coatings and ceramic coatings are used. On steel rings, the outer layer on the cylinder surface is often hardened by nitriding .
In today's internal combustion engines , three piston rings per cylinder are generally used. Their design differs according to the installation position on the piston, since the function of a ring depends on its position on the piston. The top ring - closest to the combustion chamber - is the so-called compression ring and must primarily seal and dissipate heat. The lowest ring, the oil control ring, strips lubricating oil from the cylinder wall and in doing so meters the oil film on which the upper piston rings slide during the stroke. The middle ring seals against combustion gases and can significantly influence the blowby of the engine by interacting with the movement of the first ring . This second piston ring also has an important role to play in controlling the oil balance of the engine. The oil film must both ensure sufficiently good tribological conditions and be thin in order to keep the oil losses through evaporation low. In the area of the upper piston rings, the oil film thickness is sometimes less than a thousandth of a millimeter and is therefore less than the surface roughness of the piston and cylinder.
Compression rings / compression rings
The main task of the KV rings is to seal the combustion chamber from the crankcase and to ensure the flow of heat from the piston to the cylinder. In addition, they are also of great importance for regulating the lubricating oil balance.
Compression rings are one-piece rings that get their contact pressure on the cylinder wall mainly from the gas pressure. In order to secure the seal at the start and to avoid ring flutter at high speeds, the rings are mechanically preloaded by bending stress between the free and built-in form. The amount of contact pressure is usually given in the form of the tangential force of the ring.
Oil control ring
The main task of the ring in the lowest piston groove is to wipe the oil off the cylinder wall, ie the oil control ring has a significant influence on the oil balance of an internal combustion engine. In order to effectively influence the consumption of lubricating oil, various one-, two- or three-part designs are available.
Butt play
The joint clearance of the piston rings is the distance - i.e. the joint - between the piston ring ends when installed. To measure the joint clearance - the distance between the piston ring ends - the piston ring in the cylinder must be perpendicular to the cylinder wall or raceway. It is best to slide the piston rings into the correct position with the piston in the cylinder. This will align them sufficiently. The cylinder wall should be most abraded in the area just below the upper ring edges. The joint clearance should also be measured here. The measurement can be carried out very well with a feeler gauge. A piston manufacturer (Grand-Sport) specifies the following formula as a guide value for the joint clearance: at least 0.036 mm joint clearance per 10 mm bore => 57 mm bore = at least 0.21 mm joint clearance.
Footnotes
- ^ Franz Pischinger: Internal combustion engines , lecture reprint, Volume 1, self-published, Aachen, October 1995, p. 254
- ↑ Check pistons and piston rings - page 4 of 5. (No longer available online.) In: Waspenblech - Archiv. August 20, 2014, archived from the original on October 17, 2016 ; accessed on October 17, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
Web links
- The tasks of the piston rings. In: Oldtimer in Focus
- Chapter on piston rings. In: Expertise in sealing technology (PDF)