MXPA97002840A - Pis aro cover - Google Patents

Abstract

The present invention relates to a system for preventing the micro-welding of a piston ring to a piston, characterized in that it comprises: a piston ring having a surface coated with a thermosetting resin composition polytetrafluoroethylene and molybdenum disulfide

Description

PISTON RING COVER FIELD OF THE INVENTION The present invention relates to lubricating compositions and more particularly to lubricating compositions for use in the coating of piston rings installed in internal combustion engines.

BACKGROUND OF THE INVENTION Great strides have been made in extending the useful life of the internal combustion engine. Many of these improvements have been made possible by the use of materials which reduce friction between moving components used within the internal combustion engine. For example, coating the cylinder wall that couples the surface of a piston ring with polytetrafluoroethylene (PTFE) to reduce sliding friction between the piston ring and the cylinder wall is a well-known technique for reducing engine friction. . It is also known to deposit PTFE between the respective rod bearings and the crankshaft surface of an internal combustion engine to minimize friction. Despite these advances, several areas of intense friction of conventional motor designs still remain, which have not been adequately resolved using even the most advanced friction reduction coatings. One area of such problem is related to the interface between the pistons and the piston rings of internal combustion engines. In the vast majority of internal combustion engines, which use alternating pistons, the pistons are surrounded by piston rings to create a relatively efficient gas seal between the piston and the cylinder wall. In this way, when a load inside the cylinder of the engine is ignited, creating pressures in the combustion chamber, elevated, the expanding gases which are formed during the burning process are confined to the combustion chamber. The confined gases exert a downward force on the piston and are not allowed to escape between the piston and the cylinder wall. Although the piston ring is typically captured within a groove, which is cut along an outer circumferential surface of the piston, the ring is sized relative to the groove, such that it is free to rotate within the groove. . It is important that the piston ring is movable with respect to the groove, because its relative movement results in a more uniform heat transfer between the piston and the cylinder walls. There is a critical time period for new engines known as the interposition period during which the moving surfaces of the bonded components are adjusted to fit one another. During this interposition period, the interface of the piston ring / piston is particularly susceptible to a condition known as micro welding, in which there is a propensity for the piston ring to stick to the side walls of the piston groove. Micro-welding is a phenomenon which causes the contact areas between the piston and the piston ring to be literally welded together as a result of the pressure and temperature experienced by the contact points. If during interposition, the piston ring can be kept free to move relative to the walls of the piston groove, the piston ring / piston ring groove will evenly engage and micro-welding will not occur.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to a system for preventing micro-welding of a ring to a piston and includes a ring which is coated with a thermosetting resin composition, polytetrafluoroethylene and molybdenum disulfide. The present invention is also directed to a system for preventing micro-welding of a ring to a piston and includes a piston, which is adapted to alternate within a combustion chamber of a motor. The piston has an outer surface with a circumferential groove placed therein. A ring is placed inside the circumferential groove, the ring includes a cylinder wall that engages the surface and a piston slot that engages the surface. The piston groove that engages the surface is coated with a thermosetting resin composition, polytetrafluoroethylene and molybdenum disulfide. Preferably, the ring includes a radially extending upper surface and a radially extending lower surface, wherein the piston slot engaging the surface includes the bottom surface of the ring. The present invention is also directed to a method for preventing micro-welding of a piston ring to a piston. A composition comprising thermosetting resin, polytetrafluoroethylene and molybdenum disulfide is placed on a surface of a piston ring. The composition is preferably cured by exposing the piston ring to an elevated temperature for a predetermined period of time.

BRIEF DESCRIPTION OF THE DRAWINGS The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims and drawings of which the following is a brief description: Figure 1 is the piston ring of the present invention, installed in a circumferential groove of a piston. Figure 2 is a first embodiment of the piston ring of the present invention. Figure 3 is a partial cross-sectional view taken along lines 3-3 of Figure 1. Figure 4 is a second embodiment of the preferred piston ring of the present invention. Figure 5 is a graphic representation of the comparative test results.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In a preferred system 10 of the present invention, as shown in Figure 1, a piston 12 fits with at least one circumferential groove 13 (see Figure 3). The slot 13 is defined by radially upper and lower walls 18, 20 respectively and a vertical wall 22. A piston ring 14 is typically installed within the slot 13. It is common for a piston 12 to have two or more rings 14. , 14 ', 14' 'to ensure efficient sealing of combustion chamber gases and to also ensure the minimum flow of lubricating oil inside the combustion chamber of the engine crankcase. As shown in Figure 3, a first embodiment of the piston ring 14 includes radially, upper and lower radially extending surfaces 24, 26, a radially inner vertical surface 28, and a cylinder wall engaging the surface 30, radially outer . The lower surface 26 is coated with a composition 32 of thermosetting resin, polytetrafluoroethylene and molybdenum disulfide. In a second embodiment, shown in Figure 4, the entire outer surface of the ring 14 is coated with a composition 32 'of the thermosetting resin, polytetrafluoroethylene and molybdenum disulfide. The composition is currently sold under the tradename Xylan 1620MR, Whitford Corporation, Box 507, Westchester, PA 19381-0507 (telephone number 215-436-0600).

The Xylan 1620MR is normally applied to the parts to reduce wear. In the case of the present invention, however, it is used to allow the ring 14 to move relative to the walls 18, 20 and 22 of the piston groove 13 and thus prevent micro-welding. In some extremely demanding applications, it may be necessary to coat the surfaces of the piston ring 24, 26, 28 and 30 with Xylan 1620MR. However, the current test indicates that in most applications it is only necessary to coat the lower coupling surface 26 of the piston ring 14 to prevent micro-welding. After the filing period has ended, the Xylan 1620MR usually spent is separated and no longer plays any role. The Xylan 1620MR prevents micro-welding from occurring by allowing the surfaces of the piston groove and piston ring to move in relation to one another. In this way, uniform coupling is promoted throughout the critical period of engine interposition. The Xylan 1620MR reduces or eliminates the direct contact between the ring 14 and the walls of the piston groove 18, 20 and 22. The piston ring 14 is typically formed of iron or ductile cast steel. The piston 12 is typically formed of aluminum. By separating the piston 12 and the ring 14 composed differently during the period of critical interposition, the heat transfer between them becomes uniform at the interface between the ring 14 and the walls 18, 20 and 22 of the piston groove. In this way, the two surfaces conform to each other, without high localized pressures and temperatures, which should not be experienced in any other way except by the presence of Xylan 1620MR. It is preferred that the Xylan 1620MR be applied to the surface of the ring or surfaces instead of the walls 18, 20 and 22 of the piston groove 13. It is much easier to control the thickness and the placement of the Xylan 1620MR coating when the Xylan 1620MR is deposited on the ring on the contrary to the walls of the piston groove. Additionally, when applied to the piston 12, the Xylan 1620 ^ can act as a thermal barrier, resulting in much more resistance to piston heat and possible piston failure. Furthermore, if the softer aluminum of the piston groove 13 is coated, Xylan 1620MR can undesirably separate from the walls 18, 20 and 22 during the period of critical interposition. Preferably, the Xylan 1620MR is applied to the piston ring by means of drip, spray or roller. Afterwards, the ring is cured in an oven according to the recommendations of the Xylan manufacturer. In the tests discussed in the following, Xylan 1620MR was applied by dripping and then the rings were cured for approximately ten minutes at a temperature of approximately 232 ° C.

The following example will serve by way of illustration and not by way of limitation, the system of the present invention and the results obtained by them in comparison with other materials. As summarized in Figure 5, a series of experiments was carried out. For each experiment, six experimental piston rings installed in the six-piston upper groove were used in a six-cylinder internal combustion chamber. A conventional piston ring is installed in the lower groove of each piston. The pistons, the experimental piston rings and the lower conventional piston rings were replaced after each experiment. Each experimental piston ring had a diameter of 94 mm (3.7 inches), a flange width of 2 mm (5/64 inches) and a radial wall dimension of 3.5 mm (0.136 inches). The experimental rings were all formed of ductile cast iron. In a control experiment no coating was used. All six experimental piston rings featured micro-welding within the thirty-minute baseline time. In a second series of experiments, several hard coatings were used. A first experiment involved an electrodeposition coating of chromium applied using an electrolytic bath. A second experiment involved a coating surface of titanium nitride using an ion electrodeposition method known in the art. A third experiment involved a surface coating of chromium nitride using the ion electrodeposition method known in the art. A fourth experiment involved a gaseous nitration surface coating in which the gaseous nitride was applied using a gas furnace. In each of the four experiments, all six experimental piston rings exhibited micro-welding within the thirty-minute baseline time. In a third series of experiments several solid lubricants were used. First and second experiments involved coatings based on molybdenum disulfide sold by Dow Corning under the tradenames Molykote D10MR and 106MR, respectively. For each experiment the coatings were sprayed on six experimental piston rings and cured for about one hour at about 150 ° C. A third experiment involved the spraying of tungsten disulfide onto the experimental piston rings. In each of the three experiments an average of four rings showed micro-welding within the thirty-minute baseline time. In a fourth series of experiments several liquid lubricants were used. A first experiment involved immersing the experimental piston rings in engine oil. A second and a third experiment involved immersing the experimental piston rings in two different products sold under the brand name Biotron ™. The first was a formulation for the engine and the second was a penetration lubrication. In each of the three experiments, all six rings exhibited micro-welding within the thirty-minute baseline time. In a fifth series of experiments, the experimental piston rings were coated with a thermosetting resin composition, polytetrafluoroethylene and molybdenum disulfide. The composition is completely sold under the commercial name of Xylan 1620MR. The Xylan 1620MR is applied by immersing the experimental piston rings in Xylan 1620MR and then curing the rings for approximately ten minutes at a temperature of approximately 232 ° C. As shown in Figure 5 none of the rings exhibited micro-welding after the thirty-minute baseline time. Only one ring presented micro-welding after 13 hours. None of the additional experimental piston rings had micro-welding after 21 hours. In a sixth series of experiments the experimental piston rings were sprayed with polytetrafluoroethylene and then the rings were cured for approximately ten minutes at a temperature of approximately 232 ° C. Three of the six rings exhibited micro-welding within the thirty-minute baseline time. Preferred embodiments of the present invention have been described. A person with ordinary skill in the art would understand that certain modifications could come with the teachings of this invention. Thus, the following claims must be studied to determine the true scope and content of the invention.

Claims (11)

1. A system for preventing micro-welding of a piston ring to a piston, characterized in that it comprises: a piston ring having a surface coated with a thermosetting resin composition, polytetrafluoroethylene and molybdenum disulfide.

2. The system according to claim 1, characterized in that the piston ring includes a cylinder wall that engages the surface and at least one piston slot that engages the surface, wherein only the mating surface of the groove of the piston is coated with the composition.

3. The system according to claim 2, characterized in that the piston ring includes a radially extending upper surface and a radially lower extending surface, wherein the coupling surface of the piston ring piston groove comprises the lower surface.

4. The system according to claim 1, characterized in that the ring is formed of cast iron.

5. The system according to claim 1, characterized in that the ring is formed of steel.

6. A system for preventing micro-welding of a piston ring to a piston, characterized in that it comprises: a piston adapted to alternate within a combustion chamber of a motor, in which the piston includes walls that extend radially inward from a surface external radial piston, the walls define a circumferential groove; and a piston ring positioned within the circumferential groove, the ring includes a mating surface of the cylinder wall and at least one mating surface of the piston groove, wherein at least one of the mating surfaces of the ring piston groove and circumferential piston groove is coated with a thermosetting resin composition, polytetrafluoroethylene and molybdenum disulfide.

7. The system according to claim 6, characterized in that the piston is formed of aluminum.

8. The system according to claim 7, characterized in that the ring is formed of cast iron and steel.

9. The system in accordance with the claim 6, characterized in that the ring includes a radially upper extending surface and a radially lower extending surface, wherein the mating surface of the piston groove consists of the lower radial surface.

10. A system for preventing micro welding of a ring to a piston, characterized in that it comprises the steps of: (A) depositing on a surface of a piston ring a composition comprising thermosetting resin, polytetrafluoroethylene and molybdenum disulfide, (B) curing the composition by exposing the piston ring to an elevated temperature for a predetermined period of time.

11. The system in accordance with the claim 7, characterized in that step A further includes only depositing the composition on a lower portion of the piston ring.