Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent

Definitions

• the present invention relates to a method for producing piston rings for internal combustion engines and a piston with piston rings produced according to the invention.
• the piston rings inserted into the piston ring grooves in the head of pistons for internal combustion engines have the task of sealing the gap between the piston head and the cylinder wall with respect to the combustion chamber.
• the piston ring slides on the one hand with its outer circumferential surface in constant resilient contact against the cylinder wall, on the other hand the piston ring slides oscillating in its piston ring groove due to the tilting movements of the piston, its flanks, i.e. the top and bottom of the piston ring alternately rest on the upper or lower groove flank of the piston ring groove.
• sliding layers on a piston ring and a cylinder wall
• these sliding layers e.g. Nickel
• the particulate inclusions can consist of silicon carbide or diamond.
• a cast-in piston ring carrier which generally consists of austenitic gray cast iron (cf. on this, Nüral Piston Manual, edition 1983, pages 128 to 131, in particular Fig. 166).
• ring carriers solve the problem of groove wear satisfactorily and are therefore also used on a large scale.
• a ring carrier is also associated with a considerable disadvantage, since it increases the piston weight and requires complex manufacturing technology both when the piston is cast and when it is mechanically machined, which overall causes considerable additional costs.
• piston ring carriers occupy a space in the piston head that restricts the arrangement of cooling channels and does not permit them where they would be most desired, namely as close as possible to the uppermost ring groove.
• Alternatives to ring carrier castings which are also known from the prior art, are, for example, reinforcements of the uppermost ring groove by cladding or welding alloys of the groove flanks and surface layers applied by flame spraying.
• these processes also prepare large manufacturing technology Problems and very high costs so that they do not offer a satisfactory solution.
• a piston ring blank is first produced from a material customary for piston rings, for example gray cast iron or steel, machined in a known manner, provided on the outer peripheral surface with a suitable coating as a running layer opposite the cylinder liner and, if necessary, by final fine machining in brought a ready-to-install condition.
• a material customary for piston rings for example gray cast iron or steel
• the piston ring thus obtained is then coated in the plasma CVD process with a doped hard carbon layer, preferably with the formula a-C: H, where a denotes an amorphous material and C and H denote carbon and hydrogen as material constituents.
• Such a doped, super hard carbon layer is also offered under the trade name Dynamant (registered trademark) and is based on the contribution by Dr. Knut Enke "Known with modified super hard carbon against wear, corrosion and friction", which appeared in the year booktrentechnik Volume 45, 1989, of the metal publishing house. It is based on this state of the art expressly referenced with respect to the superhard, doped carbon layer and its content is considered to be part of the disclosure of this application. Ion bombardment creates a carbon modification that is neither pure graphite nor pure diamond, but rather lies between these two materials.
• the general formula aC: H means that it is an amorphous (“a”), ie non-crystalline material, which consists essentially of carbon, which contains an unspecified proportion of hydrogen.
• the hard carbon layer provided according to the invention serves primarily as a running layer opposite the groove flanks of the piston ring grooves and not necessarily as a running layer opposite the cylinder liner which is usually made of gray cast iron.
• the hard carbon layer can also be applied to the outer circumferential surface of the piston ring, since it does not interfere there, it does not bring any significant additional advantages to gray cast iron liners.
• the reinforcement of the piston ring according to the invention on its top and bottom sides, that is to say on the surfaces which come into contact with the groove flanks of the piston ring groove brings very considerable advantages.
• the hard carbon layer in the pairing of the piston ring and the piston ring groove protects both the piston ring flanks and the groove flanks in the piston material against inadmissibly high wear, even when used in highly loaded diesel engines.
• the piston rings produced according to the invention to dispense with reinforcement of the piston ring grooves, which significantly reduces the manufacturing costs of the pistons.
• a ring carrier insert for the uppermost piston ring groove can therefore be dispensed with, which makes it possible for the first time to bring the cooling channel in the piston head into the proximity to the uppermost ring groove desired from a thermal point of view. This lowers the operating temperature in the area of the uppermost ring groove and thus also contributed effectively to the operational safety of the uppermost ring groove.
• the hard carbon layer provided according to the invention also has extremely good dry running properties.
• the outer circumferential surface of the piston ring can be coated in a known manner with chromium, molybdenum, nickel, diamond or similar materials in order to reduce the wear on the circumferential running surface of the piston ring.
• the method according to the invention can be modified such that the coating of the outer peripheral surface with a special running layer is omitted, but the piston ring is coated on all sides with the hard carbon layer.
• a light metal cylinder liner i.e. for cylinder running surfaces made of aluminum alloys, for example.
• the piston rings should be coated with an end face running layer, the pairing of a piston ring coated with hard carbon on all sides, which has no further coating from the running layer on the outer circumferential surface, with a light metal cylinder liner also leads to satisfactory sliding behavior on the end face of the ring .
• nitrided steel rings can be provided without any previous end face allocation.
• an electroplated chrome coating of the end face can also be provided.
• this relates to a piston which produces at least one piston according to the invention Has piston ring.
• the piston can be made according to the invention from a heat-resistant aluminum alloy, which in particular has a composition according to claim 11.
• Such an alloy is known from DE 43 26 978 A1.
• a piston made of such an aluminum alloy which is combined with a piston ring produced according to the invention, has decisive advantages.
• the heat-resistant aluminum alloy for the piston material proposed according to the invention is advantageous not only in terms of frictional wear, but also in particular in terms of the striking stress on the ring groove flanks under the action of the oscillating in the groove with the motorized piston movement in the ring groove Piston ring.
• Other preferred heat-resistant aluminum alloys are Al-Si-Mg alloys with relatively high levels of heavy metals such as Ni, Cu, Mn and Fe. With piston alloys of this type, even the uppermost ring groove can be worked directly into the piston material when using the piston rings produced according to the invention.
• the combination according to the invention of the piston ring produced according to the invention, which is coated with hard carbon, with a piston made of a heat-resistant aluminum alloy, which has an unreinforced annular groove offers a simple, inexpensive and, in every respect, advantageous solution to the problem mentioned at the beginning.
• a piston ring blank is first produced from steel using known methods and the surface is nitrided.
• the outer circumferential surface of the piston ring is provided with a running layer opposite the cylinder liner, which consists, for example, of electroplated chrome.
• the piston ring thus obtained is machined to a roughness of Rz ⁇ 1 ⁇ m ready for installation.
• the piston ring In order to provide the piston ring thus obtained with the coating according to the invention, it is coated on all sides in the plasma CVD process with a doped hard carbon layer which has a thickness of 3 ⁇ 0.5 ⁇ m.
• This hard carbon layer which is known under the trade name Dynamant and is defined by the general formula a-C: H, makes the surfaces of the piston ring particularly slidable against the groove flanks of the respective piston ring groove with which the ring is engaged. This protects both the piston ring flanks and the groove flanks from excessive wear.
• the piston provided according to the invention is cast from a heat-resistant aluminum alloy as claimed in claim 11 and described in DE 43 26 978 A1. With regard to the alloy composition, this document is also made the subject of the disclosure of this application.
• the piston ring grooves are pierced directly into the material of the piston in the course of the usual mechanical processing, without special flank reinforcement being provided.
• the piston rings according to the invention are inserted into the piston ring grooves of the piston in a conventional manner.
• piston rings produced according to the present invention have been described above for pairing with unreinforced grooves in an aluminum piston alloy, they can also be used advantageously for pairings in grooves in ferrous materials, for example in built pistons with a light metal lower part and an upper part made of steel or cast iron.
• the piston rings produced according to the invention can also be used in pairs with grooves in the known ring carriers. Here, too, they can extend the service life of the equal surfaces under extreme loads.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)

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• 1995
  • 1995-08-18 DE DE19530511A patent/DE19530511C1/de not_active Revoked
• 1996
  • 1996-08-02 EP EP96112522A patent/EP0759519B1/fr not_active Expired - Lifetime
  • 1996-08-02 DE DE59609811T patent/DE59609811D1/de not_active Expired - Fee Related

Patent Citations (4)

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