GB1570359A - Piston rings - Google Patents

Description

(54) IMPROVEMENTS IN PISTON RINGS (71) We, MAHLE GMBH, a German Body Corporate, of 26-46 Pragstrasse, Stuttgart, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention concerns a surface-treated piston ring, made of materials containing iron, for aluminium piston of internal combustion engines, especially of two-stroke engines, operating in housings with working surfaces treated or coated to prevent wear in which the piston ring is prevented from twisting.

In the case of piston rings made of the stated materials and secured against twisting, such as are used, for example, in two-stroke engines, there is the problem that, when they are seated in aluminium grooves, depositing takes place, that is to say, particles of the aluminium material from the surfaces of the grooves are deposited on the upper. and even more so on the lower edges of the ring. Due to the reciprocal movement of the piston, the edges of the ring are subjected mainly to impact stresses, leading to deposits on the edges of the rings.

To prevent this, it has already been suggested that the edges of such cast iron rings be phosphatised. Although this process has already led to improvements, the results obtained have so far remained unsatisfactory, because deposits still form relatively quickly.

The aim of the invention is to achieve a further improvement.

According to the invention we provide an aluminium piston of an internal combusion engine having a piston ring made of a material containing iron, said ring having flat surfaces on its opposite sides and provided on both of its said opposite flat surfaces with a coating consisting of said iron converted into iron sulphide (FeS).

It is true that, in principle, the coating of cast iron materials with surface layers of iron sulphide (FeS), in order to achieve good sliding and wearing properties in such materials, is known from, for example, DT-AS 22 58 280. As compared with this known state of the technology, the main difference, as far as the invention is concerned, is precisely that no sliding surface has to be sulphidised. On the contrary, it has, surprisingly, been found that the surface treatment of cast iron materials by sulphidising which, up to now, has proved itself satisfactory in connection with problems involving sliding friction, is also a first-class means of preventing the depositing of aluminium on the upper and lower edges of piston rings.In accordance with the invention, this primarily concerns piston rings in piston-cylinder assemblies in which the bearing surface of the rings does not have to be provided with a special bearing surface coating because of a cylinder surface which has been specially treated in order to obtain good running and wearing properties.

An example of one version is shown in the drawing and is described below.

In the case of a piston made of an aluminium-silicon alloy composed of 11 - 13 Si, 0.8 - 1.5 Cu, 0.8 - 1.3 Mg, 1.3 Ni, 0.7 Fe, 0,2 Ti, 0.3 Mn, 0.3 Zn, remainder aluminium, with a diameter of 52 mm, intended for a two-stoke engine, a rectangular piston ring 1 of untempered grey case iron with lamellar graphite, 1.5 mm high and with a radial depth of 2.1 mm, is used at least for the top ring. The piston and the ring 1 slide in a chromium-plated aluminium cylinder, the surface of which is ceramically honed.

The ring 1 is secured against twisting in the groove in the piston in which it is located.

The piston rings have a layer 2 of FeS, 5 um thick, on their flat sides. This layer 2 can be obtained in the following manner: The ready-machined piston ring is placed in a fused salt bath made up of 75% KSCN and 25% NaSCN, with electrolytic precipitation. The temperature of the bath is about 1900C, the period of immersion about 10 minutes and the current density at the anodically poled piston ring is about 3.2 A/dm2. No further machining of the ring takes place after treatment in the salt bath.

WHAT WE CLAIM IS: 1. An aluminium piston of an internal combustion engine having a piston ring made of a material containing iron, said ring having flat surfaces on its opposite sides and provided on both of its said opposite flat surfaces with a coating consisting of said iron converted into iron sulphide (FeS).

2. A piston as claimed in claim 1 wherein said coating has a depth of 5 to 10 Clam.

3. A piston substantially as described.

4. A method of making an aluminium piston for an internal combustion engine said ring having a piston made of a material containing iron which includes treating the ring with a fluid containing sulphur thereby converting said iron into iron sulphide (FeS) on both of its opposite flat surfaces, and fitting said rinp to the Diston.

tation. aid iron into iron sulphide (FeS) bn both of its opposite flat surfaces, and fitting said ring to the piston.

5. A method as claimed in claim 4 wherein the fluid is a fused salt bath and the treatment consists of electrolytic deposition on said bath.

6. A method as claimed in claim 5 wherein the salt bath is a mixture of KSCN and NaSCN; the temperature of the mixture is about 1900C the period of immersion is about 10 minutes and the current density at the piston ring is about 3.2 A/dm2.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. The ready-machined piston ring is placed in a fused salt bath made up of 75% KSCN and 25% NaSCN, with electrolytic precipitation. The temperature of the bath is about 1900C, the period of immersion about 10 minutes and the current density at the anodically poled piston ring is about 3.2 A/dm2. No further machining of the ring takes place after treatment in the salt bath. WHAT WE CLAIM IS:

1. An aluminium piston of an internal combustion engine having a piston ring made of a material containing iron, said ring having flat surfaces on its opposite sides and provided on both of its said opposite flat surfaces with a coating consisting of said iron converted into iron sulphide (FeS).

2. A piston as claimed in claim 1 wherein said coating has a depth of 5 to 10 Clam.

3. A piston substantially as described.

4. A method of making an aluminium piston for an internal combustion engine said ring having a piston made of a material containing iron which includes treating the ring with a fluid containing sulphur thereby converting said iron into iron sulphide (FeS) on both of its opposite flat surfaces, and fitting said rinp to the Diston.

tation. aid iron into iron sulphide (FeS) bn both of its opposite flat surfaces, and fitting said ring to the piston.

5. A method as claimed in claim 4 wherein the fluid is a fused salt bath and the treatment consists of electrolytic deposition on said bath.

6. A method as claimed in claim 5 wherein the salt bath is a mixture of KSCN and NaSCN; the temperature of the mixture is about 1900C the period of immersion is about 10 minutes and the current density at the piston ring is about 3.2 A/dm2.