DESCRIPTION This invention refers to a composite or modular piston for use on endothermic motors, compressors and pumps.

As known, pistons are mainly formed by a cylindrical bell-shaped body with seal rings on its head.

In said pistons, substantially monolithic type, it is not possible to obtain optimal performance of several functions as these are executed by components commonly made of one same material (generally an aluminum alloy). As an example, the low weight necessary to reduce the inertia forces generated by the alternate straight motion requires the use of aluminum alloys; however, since these alloys are excellent heat conductors, they cause a reduction of the thermodynamic output and generate very different polytropic cycle lines from the ideal adiabatic lines.

As a further example, the side surface forming the piston skirt is subject to heavy creeping inside the cylinder. As a result, many situations require to have this surface covered by special alloys to reduce wear and friction.

Another example is given by the head of monolithic pistons fitted with slots to house the seal rings, which have to be manufactured as an open ^ς C ^" configuration to allow their assembly, with an ensuing problem of consistent pressurized gas blow- by.

It is the object of this invention:

- to provide a piston for use on endothermic motors, compressors and pumps, consisting of several parts suitable to perform their own functions in an optimal way;

- to provide a piston as above, where said parts are efficiently joined together;

- to define a piston as above, suitable for the assembly of continuous seal rings,

also of the spiral type;

- to provide a piston as above, whose structure comprises plastic parts.

These and other objects will become apparent from the following detailed description, illustrating a piston for use on endothermic motors, compressors and pumps, which is featured by a configuration consisting of several parts to allow the assembly of entire or continuous seal rings also of the spiral type, as well as the eventual use of optimal materials for each one of its specific working areas, to reduce its weight and improve its output.

This invention is illustrated by way of non limiting example in the annexed drawings, where:

- Fig. 1 is a diametral section view of a piston associated with a connecting rod small end and a piston pin, consisting of two parts with some piston seal rings enclosed.

- Fig. 2 is a diametral section view of a piston consisting of two external parts joined by a third internal part for the anchoring of a constraint piston pin of a connecting rod small end.

- Fig. 3 is a diametral section view of a piston consisting of various parts, joined by a common supporting piston pin of a connecting rod small end;

- Fig. 4 represents a partially sectioned side view of a seal ring in a preferred embodiment of the invention, with closed turns;

- Fig. 5 represents a schematic view being similar to Fig. 4, wherein the seal ring with closed turns is mounted on a piston, this latter being represented in section;

- Fig. 6 represents a schematic section of a piston having an elastic ring in accordance with a first possible change of the present invention; - Fig. 7 represents 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 Fig. 1, a piston 1 consists of a cover 2 and a skirt 3. The cover 2 has two opposite projections extending lengthwise 4 over an arch of

about 90°; which is enough for a hole 5 to house a piston pin 6 for the constraint of a connecting rod small end 7. Said two projections 4 have an external cylindrical surface 9 coupled with the internal surface of the skirt 3 to provide for exact or slightly forced coupling. Also the skirt 3 has a substantially radial hole 8, similar to the hole 5, suitable to house one of the two ends of the piston pin 6.

In this instance, the cover is constrained both lengthwise and twistwise to the skirt 3. Since both parts are also coupled by the precision of their common cylindrical surface 9, the piston thus obtained will substantially be monolithic type; however, this has the advantage that before assembly both parts 2 and 3 will be able to enclose one or more seal rings 10 between two end flat plates 1 1 and 12 .

The continuity of the rings allows in fact stricter pressure tightness levels, since they can ensure a stricter roundness while the ring gap typical of the prior art can be removed. Although said gaps have the purpose of generating centrifugal thrusts caused by the flexion pre-charge exerted by the cylinder walls on the retracted ends of the seal rings, this does not exclude that such a requirement is connected with the other need of retracting the single rings during their assembly stage for insertion in the slots.

As a result, if the latter requirement is not needed, the centrifugal thrusts causing the creeping contact between the seal rings and the cylindrical sliding chamber (cylinder liner) can be derived from other technological solutions.

One of these, for instance, is the use of cylindrical spiral seal elements or dual flat ring seal elements, which are overlapping and joined by a common inclined end, similar to the known double lamellar labyrinth seals for rotary shafts. According to the solution described in Fig. 1 it can be easily understood how the cover 2 is obtained using a completely different material from the material used to manufacture the skirt 3. As a matter of fact, the cover is directly in contact with combustion and operates in a high temperature environment, so it should form an isolating shield to avoid deflagration or combustion heat being dispersed over the

motor structure instead of being converted to thrust pressures. Therefore, it can be manufactured in materials other than aluminum, but light and resistant. Ceramics would be an example of such materials.

The small surface of the projections 4 generating a thermal contact with the skirt causes a further difficulty for the thermal flow to dispersing surfaces, which means a general advantage for the thermodynamic output.

Moreover, since the skirt 3 operates at a low temperature, it can be manufactured with a very low friction alloy; according to the present state of the art, this material would not have been used as the same material would have been required for the piston head too.

Since the seal rings 10 can be assembled without deformation, they can be manufactured also with unusual materials, eg. graphite, as usual springs can be used to obtain the low centrifugal forces for contact seal. With reference to the above Fig. 2, a piston 13 has an internal structure 14 with diametral holes 15 to house a usual constraint pin 16 for a connecting rod small end 17. Said internal structure 14 has a cover 18 anchored on its top and a skirt 19 on its lower part. These two parts define a circumferential slot wherein continuous seal rings 33 are housed, for instance according to the type mentioned above. As previously mentioned, it is obvious that the cover 18 and the skirt 19 have different materials to optimize their functions.

Should the cover 18 and the skirt 19 be made of steel-sheet or equivalent material, their fastening to the internal structure 14 would be obtained by upsetting, i.e. by rolling appropriate areas 20 and 21, respectively. If the material of the internal structure 14 is elastomeric material, eg. polyurethane for spring manufacture, said anchorage may even be snap type by forcing the ring upsettings 20, 21 already available on the cover and the skirt inside the ring slots on the internal structure. Such a spring snap fitting would obviously provide a flexible constraint suitable to withstand pull-off caused by inertial forces.

Preferably, assembly of the piston pin on an elastomeric structure 14 or other material with suitable characteristics will reduce both the inertia forces on the piston pin and power forces progress related to fast combustion of the explosion stage. It should be noticed that the coupling between the cover and the skirt of the piston according to the invention could be obtained directly by means or a resilient material, being apt at reducing the vibrations between the said two components and the forces generated by the resultant of the connecting rod within the cylinder. Said reciprocal fixing could be realized by means of an internal structure in an elastomeric material, for instance of the type which allows for a snap-fitting with the cover and the skirt.

The use of said coupling structure in elastomeric material can allow, during the piston operation, a slight misalignment between the cover and the skirt of the same; in this way it is possible to obtain a reduction in the stress of some zones of the piston, which are usually defined ' ^; skids'\ on the cylinder. In accordance with this embodiment, the connecting rod small end could also be coupled only to the skirt of the piston, and/or only to the cover of the same by an usual piston pin. With reference to the above Fig. 3 a composite or modular piston 22 has an internal structure 23 on which a cover 24 is riveted on 25. Said internal structure 23 comprises the holes 26 for the assembly of a constraint pin 27 for a connecting rod small end 28.

Two risers 29 pertaining to a base constraint are engaged on the pin 27 for a friction free skirt 30. Such a constraint on the pin 27 causes a slight flexible interference with the contact on the base 31 of the internal structure 23 to avoid clearances or beats during operation. The continuous piston seal rings 33 are interposed between the cover and the skirt constrained by the pin, according to the appropriate clearances suggested by the present state of the art, and they are arranged to rub inside a cylinder liner 32. As previously mentioned, the piston according to the present invention is

particularly useful for the use ⁷ of closed or spiral seal piston rings.

In Fig. 4 a spiral seal element with closed turns is represented, through a partially sectioned side view, for the use on the piston according to the present invention.

Said spiral seal element, which is indicated as a whole with reference number 102, consists of a series of seal turns or rings; as it can be noticed, the end portions of the spiral have a shape which is different with respect to the central portion of the spiral.

In particular, it can be noticed how the turns 103' being at the two ends of the spiral have an external diameter which is smaller than the diameter of the turns 103 of the intermediate or central portion of the spiral. However, as it can be noticed in Fig. 4, said thickness reduction is not limited to the end rings 103 ', but it can start already from the rings 103" being immediately adjacent to the end rings 103'. As shown, therefore, the reduced diameter portions of rings 103" defines, along with rings

103 ', steps being indicated with 1 15.

Said steps 115, in the preferred embodiment of the invention, are inserted within appropriate circumferential seats being obtained in the cover 105 A and/or the skirt

106 of the piston.

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

1 16 and 117, can be seen in Fig. 5, wherein the ring 102 is in view, while the relevant piston is represented in section. As it can be noticed in such a Fig. 5, the plate 105 of the cover 105A has a circumferential seat 1 16 and, similarly, a circumferential seat 117 is present in the skirt 106.

Turns 103' and the part of reduced diameter of turns 103" therefore realize their seal action on the walls of the circumferential seats 1 16 and 117, i.e. onto surfaces which are part of the piston 101, 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 116 and/or 117, turns 103' 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 1 15 within seat 1 16 or 117 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 103' and 103": 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 115, and therefore of the extreme surfaces of the spiral, within the circumferential seats 1 16 and/or 1 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. 6, a first possible change of the spiral ring described with reference to Figs. 4 and 5 is represented. In the case of Fig. 6, the seal turns of the piston ring 102, being generally indicated with 103, are distinctly inclined with respect to the axis of the piston 101 , 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 102 on the wall of the sliding chamber, either during the compression and the combustion phase, in the case of combustion engine. In Fig. 7 a further possible change of the invention is described, where two seal elements 102 are present, in accordance with the embodiment of Figs. 4 and 5; a spacer 118, having preferably the shape of a closed ring, is interposed between said two seal elements 102.

As it can be noticed, the spacer 1 18 is provided with opposite circumferential seats 119, substantially similar to the above mentioned seats 116 and/or 117, wherein the lower step 1 15 of the upper seal element 102, and the upper step 1 15 of the lower

seal element 102 are inserted.

As it can be imagined, in this way it is possible to obtain a modular composition of the seal elements 102, 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 118 of suitable dimensions allows to position the seal elements 102 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.