TECHNICAL FIELD

The present invention relates to a mechanical seal, and particularly to a mechanical seal configured to be interposed between a rotating shaft and an aperture through which the shaft extends. The present invention finds a preferred application, although not exclusive, in the seals of rotary pumps and in particular in the recirculation pumps of cooling fluid in engines of motor vehicles, hereinafter for brevity indicated as "water pump" .

BACKGROUND ART

As is known, the water pump of a motor vehicle comprises a pump body, a drive shaft and a rotor housed in the pump body and fitted to the shaft. The latter is driven by a pulley and is extends through an aperture of the pump body, in which it is supported by means of a bearing.

The seal between the shaft and the pump body is normally made by means of a mechanical seal fitted on the shaft in the area axially comprised between the rotor of the pump and the bearing of the shaft.

The mechanical seal comprises a first sealing ring rotationally fixed constrained to the pump body, and a second sealing ring mounted integral with the shaft and rotatable therewith. The two sealing rings cooperate with each other axially under the elastic load exerted by a spring and thereby form a creeping front seal.

In order to ensure a correct operation of the seal, in the contact zone between the two sealing rings the presence of a fluid flow-path suitable to prevent premature wear, unwanted noise and overheating must be ensured. A small amount of loss, called "micro leaks" or "cosmetic losses", may therefore be present in the seals of this type.

The amount of loss is a function of the contact pressure between the two sealing rings, which is in turn conditioned by the materials used.

Such losses, even though completely harmless, may be visible to the user, for example in the form of stains visible below the vehicle after a stop, or in the case of inspection of the engine during maintenance. This may lead to a false indication of failure of the pump and its replacement even in cases in which it is in perfect efficiency. Analysis performed, revealed that more than 50% of replacements are due to this cause.

To solve the above problem, it is known of to provide a collection sump provided with an overflow hole for the leaks in the pump. A first problem associated with this solution is represented by the cost of the additional components for making the sump and related production equipment. In addition, the liquid in the collection sump has a small free surface exposed to air, and thus the evaporation is very weak. As a result, consecutive accumulations can result in an overflow of the liquid from the overflow hole and thus be visible anyway.

DISCLOSURE OF INVENTION

The object of the invention is therefore to provide an improved seal that is free of the drawbacks related to the known seals.

Said purpose is achieved by a seal according to claim

1.

According to the present invention, an absorbing material element with such characteristics as to easily absorb and evaporate the liquid is applied to the fixed part of the seal, via a mechanical coupling of any type, gluing or other fastening system.

The absorbing material may be either integrated in the mechanical seal, or be an accessory applicable to existing seals .

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, some preferred embodiments will be described below by way of non-limiting examples and with reference to the appended drawings, wherein:

figure 1 is an axial cross-section of a seal according to a first embodiment of the present invention;

figure 2 is an axial cross-section of a second embodiment of the present invention; and

figure 3 is a schematic axial cross-section of a third embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figure 1, reference numeral 1 globally denotes a mechanical seal configured to be interposed between a rotating shaft 2 and a fixed body 3 provided with an aperture 4 through which the shaft 2 extends. By way of example, the shaft 2 and the body 3 may consist of the shaft and the body of a water pump of a motor vehicle (not illustrated) .

The seal 1 comprises, in a known manner, a fixed part 5 comprising a first sealing ring 6 constrained to the pump body 3, and a rotating part 7 comprising a second sealing ring 8 integrally mounted to the shaft 2 and rotating with it. The two sealing rings 6, 8 cooperate with each other axially and form a creeping front seal.

The sealing rings 6, 8 are suitably made of ceramic material, for example silicon carbide, and may for example be made using the method described in WO2007/057934.

The seal 1 comprises a cup-shaped element 9, made of sheet metal by deep drawing and having a C-shaped radial cross-section open towards the sealing rings 6, 8. The cup- shaped element 9 comprises a cylindrical outer wall 12, a substantially cylindrical inner wall 13 and a flat bottom wall 14. The outer wall 12, provided with an annular flange 15 on the outer radial end, is set inside the aperture 6 of the pump body 3; the flange 15, in axial abutment with the pump body 3, determines the axial positioning of the seal 1 with respect to it.

The inner wall 13 surrounds the shaft 2 with a certain radial clearance.

The first sealing ring 6 is constrained to an end portion 16 of the inner wall 13 of the cup-shaped element 10 by means of a splined coupling 17 with clearance which allows the relative axial free sliding and a limited freedom of relative rotation.

The first sealing ring 6 is also sealingly constrained to the cup-shaped element 9 by means of a bellows 24 of elastomeric material, which has one end 25 of a smaller diameter constrained to the inner wall 13 of the cup-shaped element 10 by means of a locking ring 26 and an opposite end 27, of greater diameter, which is sealingly interposed between the first sealing ring 6 and a metallic ring 28 which surrounds and encloses it partially. More in particular, the ring 28 has a substantially L-shaped cross- section, with a radial flat wall 29 and an outer cylindrical wall 30. The second sealing ring 8 is mounted with the interposition of a ring 31 of elastomeric material on a sleeve 32 set on the shaft 2 and extending partially inside the inner wall 13 of the cup-shaped element 10.

The sleeve 32 integrally forms an annular flange 33 with a profiled end, housing the second sealing ring 8, prismatically coupled to it and having an axial stop function .

The mechanical seal 1 also comprises a spring 34 housed in the cup-shaped element 9 and compressed between the bottom wall 14 of the latter and the wall 29 of the metal ring 28, so as to push the first sealing ring 6 against the second sealing ring 8 with a predetermined work load .

In the example illustrated, the spring 34 is a helical wave spring made of a flat band, such as the springs marketed under the name Crest-to-Crest® by Smalley. Alternatively, the spring 34 could be replaced by an annular wave spring or by a conventional helical spring or a plurality of annular springs (Belleville or wave type) stacked on each other.

According to the present invention, the cup-shaped element 9 is applied to an absorbing material element 35 having the purpose of collecting the micro-leaks which may seep between the two sealing rings 6 and 8 and reach the aperture 4, where the support bearing of the shaft 2 is housed (not shown) .

The element 35 has advantageously the form of a ring (hereinafter, for brevity, the "ring 35"), it is housed in the aperture 4, and can be fixed in any way to the cup- shaped element 9. For example, it can be partially housed in a housing 36 arranged to leave exposed at least a part of its surface to allow the elimination of the leaks by evaporation .

In the example in Figure 1, the housing 36 is composed of an annular casing which encloses an outer annular portion of the ring 35 and is welded, for example by means of a plurality of welding points equally spaced along its circumference, to the bottom wall 14 of the cup-shaped element 9.

The absorbing material may be of any type: it can for example be a non-woven fabric, a porous solid material such as a low density ceramic, or made from powders of any type (carbonaceous, limestone, silica, etc. ) , gels of any type, salts (sodium or other) .

One important property of the material is to absorb and diffuse the liquid through its structure, so as to avoid the permanence of liquid in the first contact area and facilitate the subsequent evaporation.

A preferred embodiment of the absorbent material is a tufted mixed wool/viscose felt with a weight of 0.160 km/m for each mm of thickness and a temperature resistance up to at least 100°C.

The functioning of the seal 1 is as follows. In use, the first sealing ring 6 is fixed, while the second sealing ring 8 rotates integrally with the shaft 2. Between the two rings 6, 8 a rotational movement therefore occurs with relative sliding under the load of the spring 32.

Should micro-leaks occur between the two sealing rings 6, 8 they tend to flow towards the aperture 4 and are intercepted by the absorbing ring 35, in which they are diffused and subsequently eliminated by evaporation.

Such micro leaks are thus prevented from being visible to the user.

Figure 2 shows a second embodiment of a seal according to the present invention, globally denoted by reference numeral 40, which is described below insofar as it differs from the seal 1 described, using the same reference numbers to indicate parts identical or corresponding to parts already described.

The seal 40 differs from the seal 1 essentially in that the spring 34 is carried by the rotating part of the seal 7, rather than by the fixed part 5.

Therefore, the fixed part 5 is simplified, with the result that the dimensions of the seal in the radial direction can be reduced, making it possible to install in areas with a reduced diameter.

More precisely, the cup-shaped element 9 of the seal 40 is free of the inner wall 13 and therefore comprises a cylindrical wall 12 from the opposite ends of which an annular wall 14 and a flange 15 extend radially, respectively towards the inside and towards the outside and which resting against the pump body 3 determine the axial positioning of the seal 1 with respect to it.

The cylindrical wall 12 is set inside the aperture 4 of the pump body 3, which has a reduced diameter, for example of 20 mm.

The first sealing ring 6 is sealingly mounted ( static) in the cup-shaped element 9, and blocked therein by a hood 41 of elastomeric material, which is substantially cup- shaped and has an annular flat wall 42 axially interposed between the flat wall 14 of the cup-shaped element 9 and the first sealing ring 6, and a cylindrical outer wall 43 extending axially projecting from the annular wall 42 and radially compressed between the first sealing ring 6 and the cylindrical wall 12 of the cup-shaped element 9.

The sleeve 32 comprises a tubular portion 44 passing through the cup-shaped element 9 and the sealing rings 6, 8 and suitable to be set on the shaft 2, and a flat radial end flange 33 arranged on the side of the second sealing ring 8.

The second sealing ring 8 is also housed inside a metal ring 45 which has a substantially L-shaped cross- section and comprises a cylindrical wall 46 inside which the second sealing ring 8 is mounted with radial interference and a radial flat wall 47 extending inwardly from one end of the cylindrical wall 46 facing towards the flange 33.

The wall 47 ends on the inside with an edge 48 folded axially towards the flange 19 from which a plurality of axial tabs 48 extend which engage with clearance respective apertures 49 in the flange 33, in order to prismatically constrain the ring 45 to the sleeve 32.

The seal 40 further comprises an elastomeric element 50 which is sealingly mounted so as to slide on the tubular portion 43 of the sleeve 32. The elastomeric element 50 comprises a radial intermediate wall 51, which is axially compressed between the second sealing ring 8 and the wall 46 of the ring 44 and forms the static seal between the second sealing ring 8 and the ring 44. The axial forcing is maintained thanks to the radial interference between the second sealing ring 8 and the cylindrical wall 46 of the ring 45. The elastomeric element 50 further comprises a first annular portion 52 extending axially from the intermediate wall 51 inside the second sealing ring 8, and a second annular portion 53 extending towards the flange 33 and in radial contact with the tubular portion 44 of the sleeve 32, with a coupling such as to create a static seal but rotationally and axially free.

Such coupling is preferably realized by means of a cylindrical wire helical spring 54 fitted around the second annular portion 53 and exerting on the same a radial load sufficient to achieve the static seal but insufficient to achieve a locking in the rotational and axial direction.

Conveniently, the spring 54 consists of a helical spring with a small number of coils, preferably less than three, and a reduced pitch between the coils, preferably less than double the diameter of the wire. In the example illustrated, the spring 30 has two coils packed together, and is housed between the second annular portion 53 and the edge 47 the ring 44.

The mechanical seal 1 lastly comprises a spring 34 compressed between the flange 33 of the sleeve 32 and the wall 47 of the ring 45, so as to axially push the second sealing ring 8 against the first sealing ring 6 with a predetermined work load.

In the example illustrated the spring 34 is an annular wave spring made by shearing a flat tape.

Conveniently, the annular wall 42 of the hood 41 cooperates in sliding with the tubular portion 44 of the sleeve 32, so as to define a sort of dust lip suitable to protect the seal 1 from external contamination.

According to the present invention, the cup-shaped element 9 is applied to an absorbing material ring 35 having the purpose of collecting the micro-leaks which may seep between the two sealing rings 6 and 8 and reach the aperture 4, where the support bearing of the shaft 2 is housed (not shown) . In this embodiment, the housing 36 is composed of a plurality of clips made entirely by the cup- shaped element 9 and folded to hook around an inner edge of the ring 35 so as to keep it in contact with the flat wall 14 of the cup-shaped element itself.

Figure 3 shows a third embodiment of the invention, particularly for industrial applications. In this embodiment, globally denoted by reference numeral 59, the fixed part 5 comprises a hood 55 of elastomeric material housed in a seat 56 of the pump body 3 defined by the aperture 4. The hood 55 comprises a cylindrical wall 57 mounted with radial interference inside the seat 56, and a annular wall 58 placed in axial abutment against a shoulder 59 defined by said seat 56.

Inside the hood 55 are housed the fixed sealing ring 6 and a ring 35 of absorbing material, conveniently housed inside a housing 36. The sealing ring 6 is mounted inside the cylindrical wall 57 with radial interference, so as to ensure the static seal between the sealing ring 6 and the pump body 3. The ring 35 of absorbing material is axially housed between the sealing ring 6 and the flat annular wall

58 of the hood 55.

Only the dimensions of the rotating part 7 of the seal

59 are shown schematically.

In this case too, any micro-leaks leaking between the fixed sealing ring 6 and the corresponding rotating sealing ring (not shown) of the rotating part 7 are retained by the ring 35 of absorbing material.

Lastly, it is clear that further variations may be made to the seals 1, 40, 59 while remaining within the scope of the claims. In particular, the element 35 of absorbing material can be fixed in any way to the fixed part 5 of the seal.