DESCRIPTION

This invention refers to cylindrical spiral seal rings, specifically for pistons of the composite or modular type for endothermic motors, compressors and pumps. As known, pistons for endothermic motors are fitted on their head with seal rings. Such rings, also known as "spring rings" or "spring bands" are generally made of nodular cast iron, whereas under special conditions, their typical operation mode may eventually request Cr or Mo facings on their working surfaces. Said rings are open, i.e. they have a cut to interrupt them, called 'gap' or 'light gap', which is essential for the required flexibility to widen them and place them inside appropriate slots in the cylinder head. Said gap should be as tiny as possible though enough to compensate thermal expansions and avoid any shrinkage that may cause piston seizure. However, such a 'C open structure implies a roundness that may only be a theoretic one and which, in fact, prevents a perfect adjustment of the ring surface to the cylinder wall. Moreover, since said usual piston seal rings are located in their seats with both radial and axial clearances, they are subject to rotation. Thus, they will not stick, but there is a chance that said above cuts of several overlaying rings may come to be aligned and form a pernicious transit channel: on one hand this allows oil flow to the explosion chamber with a consequent production of ashes that may possibly cause the rings to stick, while on the other hand it will also allow a through-flow of the gases in the combustion chamber with a consequent power loss for the motor.

Said specific seal rings are generally associated with other rings called 'oil scrapers', whose function is to remove the lubricating oil from the cylinder during the downward stroke of the piston. Said rings have steps and/or slots, either with or

without centrifugal thrust springs, which make them particularly expensive.

Steel lamellar sealing segments are also known, as fitted on rotating shafts, which form labyrinths with the use of spirals alternatively mounted on the fixed seat and on the rotating shaft. However, said segments are not suitable to carry out the function currently ensured by conventional spring elements. Since they are conceived for insertion in their seat by flexible deformation, they cannot offer the limit warranties required for a motor-driven application nor a suitable profile to comply with the various functions such as seal elements, oil film spreading elements, oil scraper elements from inside the cylinder. It is the object of this invention to provide piston seal rings, specifically for pistons of the composite or modular type for endothermic motors, having a higher sealing capacity with respect to conventional rings.

It is another object of this invention to provide seal rings that will not stick.

A further object is to provide seal rings suitable to execute all the functions required for conventional seal rings.

One more object is to provide seal rings that will not form typical blow-by channels due to their notch gap alignment.

These and other objects will be apparent from the following detailed description, illustrating some seal rings, specifically for pistons of the composite or modular type for endothermic motors, compressors and pumps, having the characterizing features of the annexed claims.

The present invention is described by way of non limiting example in the annexed drawings, wherein:

- Fig. 1 shows a piston in a diametrical halfsection; - Fig. 2 shows a plurality of sections of a foil wound to a cylindrical spiral, whose purpose is to realize the typical conventional functions of specific piston seal rings;

- Fig. 3 shows a partially sectioned side view of a seal ring in a preferred

embodiment of the invention, with closed turns;

- Fig. 4 shows a schematic view being similar to Fig. 3, wherein the seal ring with closed turns is mounted on a piston, this latter being represented in section;

- Fig. 5 shows a schematic section of a piston having an elastic ring in accordance with a first possible change of the present invention;

- Fig. 6 shows a schematic section of a piston having an elastic ring in accordance with a second possible change of the present invention.

With reference to the above figures, a piston 1 has its sealing elements 2 'packed' together, as they are formed by foils having substantially a rectangular section 3 wound to a cylindrical spiral whose outside diameter is in line with the one of a sliding chamber 4.

Such a spiral may consist of one-piece having a constant section or one-piece of variable form, or still of a plurality of adjacent and/or overlapping segments, each one with a specific section to comply with a specific function: compression tightness, oil spreading, oil scraper.

At any rate, said spiral, either continuous or interrupted, has the advantage of extending freely to prevent generation of radial forces to such a high level capable of a likely seizure. However, the relative sliding of the turns due to the length variations of the spiral wound foil determined by temperature changes will prevent accumulation of carbon deposits. Therefore, the seal elements pack can freely adjust itself to the configurations of the sliding cylinder liner through which it slides creepingly with an exactly predeterminable and substantially constant pre-charge. Fig. 1 shows an example of a composite or modular piston, fitted with a movable retaining plate 5 to let the seal elements 2 be placed in their appropriate slots without deformation.

This allows the use of less flexible materials, since deformation required for the spiral seal ring 2 is just the one needed for pre-charge against the sliding cylinder

liner after piston assembly.

Thus, said spring interference is possible with an extremely high precision to warrant consistent optimal pre-charges for a minimum sliding friction and perfect compression tightness. In Fig. 1 the plate 5 is shown pertaining to a cover 5A screwed on a skirt 6. However, it may be obtained according to any of the solutions already known. Said solution of assembling the seal elements 2 without deformation is preferable but it does not exclude other solutions where such elements are placed in their seats by way of their typical deformability according to the twisting direction of their section.

The seal element shown in detail in Fig. 2 provides better understanding of the different sections that can be performed in it, also intended as a continuous element, since the various profiles provided for the sliding contact with the cylinder can be obtained by special grinding machines on the rotating turn. To this purpose some turns 7 may have a slight crowning to favour an oil film; other turns 8 may have sharp edges to reduce gas infiltration; other turns 9 may have an inclined face profile 9A to favour oil scraping from the cylinder liner. Some turns may even have some channels 10 for oil flow inside the piston, as performed by conventional oil scrapers but in a more functional manner. In Fig. 3 a spiral seal element with closed turns is represented, through a side view, being realized in accordance with a preferred embodiment of the present invention. Said spiral seal element, which is indicated as a whole with reference number 2, consists of a series of seal turns or rings, of the type already mentioned with reference to Fig. 1. As it can be noticed, however, the end portions of the spiral have a shape which is different with respect to the central portion ofthe spiral.

In particular, it can be noticed how the turns 3 ' being at the two ends of the spiral have an external diameter which is smaller than the diameter of the turns 3 of the intermediate or central portion of the spiral. However, as it can be noticed, said

thickness reduction is not limited to the end rings 3 ', but it can start already from the rings 3" being adjacent to the end rings 3 '.

As shown, therefore, the reduced diameter portions of rings 3" defines, along with rings 3', steps being indicated with 15. Said steps 15, in the preferred embodiment of the invention, are inserted within appropriate circumferential seats being obtained in the cover 5A and/or the skirt 6 of the piston.

An example of said seats, which are indicated respectively with reference numbers

16 and 17, can be seen in Fig. 4, wherein the ring 2 is in view and partial section, while the relevant piston 1 is represented in section.

As it can be noticed in such a Fig. 5, the plate 5 of the cover 5 A has a circumferential seat 16 and, similarly, a circumferential seat 17 is present in the skirt

6.

Turns 3 ' and the part of reduced diameter of turns 3" therefore realize their seal action on the walls of the circumferential seats 16 and 17, i.e. onto surfaces which are part of the piston 1, instead of the wall of the chamber within which the piston is inserted.

It should be considered that, by virtue of the presence of the suitable seats 16 and/or

17, turns 3 ' can be interrupted at the end of the spiral even without the necessity of flattening their surfaces, inasmuch as this would not determine substantial seal losses or passages for oil or gas blow-by.

On the contrary, the insertion of the steps 15 within seat 16 or 17 realizes a sort of labyrinth, which makes it difficult for the gases to blow-by towards the inside of the piston and push against the internal diameter of the seal turns 3' and 3": this results in an advantage, due to the fact that said turns bear the main consequences of the gas pressure and the explosion phase.

In addition, the insertion of steps 15, and therefore of the extreme surfaces of the spiral, within the circumferential seats 16 and/or 17 eliminates the risks of piston

seizures, which in the prior art are mainly due to the entrance of the ends of the traditional open piston rings in the ports being provided in the sliding wall of the chamber where the piston is inserted.

In Fig. 5, a first possible change of the spiral ring described with reference to Figs. 3 and 4 is represented.

In the case of Fig. 5, the seal turns of the piston ring 2, being generally indicated with 3, are distinctly inclined with respect to the axis of the piston 1, so that their surface can be advantageously bigger, while the distance between the piston and the relevant sliding chamber remains the same. In this way, it is therefore possible to have seal surfaces being wider and is also possible to increase the adhesion of the piston ring 2 on the wall of the sliding chamber, either during the compression and the combustion phase, in the case of combustion engine.

In Fig. 6 a further possible change of the invention is described, where two seal elements 2 are present, in accordance with the embodiment of Figs. 3 and 4; a spacer 18, having preferably the shape of a closed ring, is inteφosed between said two seal elements 2.

As it can be noticed, the spacer 18 is provided with opposite circumferential seats 19, substantially similar to the above mentioned seats 16 and/or 17, wherein the lower step 15 of the upper seal element 2, and the upper step 15 of the lower seal element 2 are inserted.

As it can be imagined, in this way it is possible to obtain a modular composition of the seal elements 2, so choosing with a full flexibility the sections of the same and their material, in accordance with the needs. By this solution, it is not necessary to modify the working section of a same spiral for obtaining different functions (sealing, oil scraping, oil spreading); in addition, the use of spacers 18 of suitable dimensions allows to position the seal elements 2 only in the zone where the same are necessary. Among the other possible changes, the possibility is cited of realizing an elastic

spiral ring whose end turns are completely closed, i.e. which do not present interruptions or gaps.

In accordance with said embodiments, each end portion of the seal ring can be realized by a sort of tubular element, wherein a reduction of the external diameter is obtained; in this way, at least two parts having a different diameter could be defined, and therefore the cited step to be inserted within the suitable seat provided in the cover and/or the skirt and/or the spacers of the piston. Said embodiment can obviously be realized only in the case of composite or modular pistons, where the recess for housing the piston ring is defined in the junction point between the cover and the skirt.

A further possible change is that of realizing the end turns of the piston ring, and eventually the adjacent turns, so as to define a plurality of steps, in order to increase the gas tightness; it is clear that, in this case, the seat being provided in the cover and/or the skirt and/or the spacers of the piston will have a shape suitable for receiving said plurality of steps.

It is finally clear that the described elastic piston ring could be used on composite or modular piston being different with respect to the piston described in Fig. 1, without departing form the idea of mounting the elastic piston ring between two components (cover and skirts) which are then reciprocally joined. For instance the piston cover, instead of being screwed on the skirt as is the case of Fig. 1 , could be provided with at least one projection having an hole, within which an usual piston pin is constrained; in this way, therefore, the fixing between the cover and the skirt, with at least one piston ring according to the invention being interposed, could be realized just by means of said piston pin.