TECHNICAL FIELD

The invention relates to a mechanical seal and, especially, to a mechanical seal adapted to be interposed between a rotating shaft and an opening through which the shaft is mounted. The invention finds advantageous - though not exclusive - application in the seals of rotary pumps and, in particular, in engine coolant recirculation pumps installed in motor vehicles, hereinafter simply referred to as "water pumps".

BACKGROUND ART

As it is known, the water pump of a motor vehicle comprises a pump body, an operating shaft and an impeller, which is housed inside the pump body and is splined to the shaft. The latter is operated by a pulley an is mounted so as to pass through an opening of the pump body, where it is supported by means of a bearing.

The seal between the shaft and the pump body is usually obtained by means of a mechanical seal, which is fitted on the shaft in the area that is axially comprised between the impeller and the bearing of the shaft.

The mechanical seal comprises a sealing ring, which is integral to the shaft and rotates with it, and a sealing ring, which is rotation-fixed and is constrained to the pump body. The two sealing rings axially cooperate with one another and, therefore, create a front sliding seal.

According to a first known solution, a first sealing ring is constrained to a metal container, which is adapted to be fitted into the opening of the pump body through the interposition of an elastomeric material bellows having its ends fixed to the container and to the first sealing ring, respectively; a second sealing ring is mounted on a metal sleeve, which is adapted to be fitted on the shaft, with the interposition of an elastomeric material ring or bellows in contact both with the sleeve and with the second sealing ring, so as to obtain a static seal.

The mechanical seal finally comprises a spring, which is housed in the container and is directly or indirectly compressed between a bottom wall of the container and the first sealing ring, so as to push the first sealing ring against the second sealing ring with a predetermined working load.

The aforesaid solution is suitable for conventional applications, where the diameter of the opening of the pump body that is going to house a mechanical seal ranges from 28 to 30 mm, whereas the diameter of the shaft is 12 mm; therefore, a radial space of 8-9 mm is available for the seal .

In applications in which the available dimensions are smaller, manufacturers usually use lip seals, which do not ensure the same performances as mechanical seals in terms of reliability and duration.

In order to solve this problem and make it possible for manufacturers to use a mechanical seal even with reduced radial spaces available, equal to less than half the radial space of a conventional mechanical seal, the Applicant suggested a miniaturized mechanical seal disclosed in Italian patent application no. 102015000006018 owned by the Applicant.

In this solution, in order to reduce radial spaces, the spring that provides the elastic load of the sealing rings was transferred to the fixed part of the movable part and acts between a flange of the sleeve and a metal cup housing the rotating sealing ring. The fixed sealing ring is mounted through interference inside the metal container with the interposition of an elastomeric material bellows.

DISCLOSURE OF INVENTION

The object of the invention is to provide an improved mechanical seal, which allows manufacturers to obtain optimal performances with reduced dimensions and is simple and economic to be manufactured.

In order to do so, the invention provides a mechanical seal according to claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be best understood upon perusal of the following detailed description of a preferred embodiment, which is provided by way of non-limiting example, with reference to the accompanying drawings, wherein :

figure 1 is a diametrical section of a mechanical seal according to the invention;

figure 2 shows a detail of figure 1 on a larger scale; and

figure 3 schematically shows the coupling between two components of the seal.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figure 1, number 1 indicates, as a whole, a mechanical seal, which is adapted to be interposed between a rotating shaft 3 and a fixed casing 3, which is provided with an opening 4, through which the shaft 2 is mounted. By way of example, the shaft 2 and the casing 3 can consist of the shaft and the body of a water pump of a motor vehicle (not shown) .

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 mounted so as to be integral to the shaft 2 and rotate with it. The two sealing rings 6, 8 axially cooperate with one another and create a front sliding seal.

The sealing rings 6, 8 are conveniently made of a ceramic material, for example silicon carbide, or of a carbon-based material.

The seal 1 comprises an annular container 9, which is made of sheet metal, is manufactured through deep drawing and comprises an annular flat end wall 10, an outer cylindrical wall 11 extending from an outer edge of the flat wall 10 towards the sealing rings 6, 8, an outer flange 12 radially extending from an axial end of the outer wall 11 opposite the flat wall 10, and an inner tubular wall 13 extending from an inner edge of the flat wall 10 towards the sealing rings 6, 8 coaxially to the outer wall 11. The outer wall 11 is fitted and sealed inside the opening 4 of the pump body 3, which has a reduced diameter, for example 20 mm. The flange 12, which axially strikes against the pump body 3, determines the axial position of the seal 1 relative to the latter.

The first sealing ring 6 is inserted in the container 9. The inner surface 14 of the first sealing ring 6 is coupled to the inner wall 13 of the container 9 through a pseudo-prismatic coupling, which is adapted to permit a limited possibility of relative rotation, though preventing the first sealing ring 6 from being dragged in rotation - through friction - by the second sealing ring 8.

The term "pseudo-prismatic" is used herein to indicate a coupling that can axially slide and cannot rotate except for the aforesaid limited possibility of relative rotation.

Said pseudo-prismatic coupling is obtained due to the fact that the inner surface 14 of the first sealing ring 6 and the tubular inner wall 13 of the container have an elliptical cross section, as you can schematically see in figure 3.

More in particular, the section of the inner surface

14 of the first sealing ring 6 has a minor axis (A) that is greater than the minor axis (a) of a section of the outer surface 15 of the inner wall 13 of the container 9, but smaller than the major axis (b) of the section of the aforesaid surface 15. The major axis (B) of the section of the inner surface 14 of the first sealing ring 6 is greater than the major axis (b) of the section of the outer surface

15 of the tubular inner wall 13 of the container 9.

For example, the measures of the aforesaid axes can be the following: A = 14,4 mm, B = 13,8 mm, a = 14 mm and b = 13,4 mm

The first sealing ring 6 is mounted inside a cup 16, which is housed in the container 9 in an axially sliding manner. An elastomeric material bellows 33 is interposed between the first ring 6 and the cup 16.

More in particular (figure 2), the cup 16 comprises an annular flat wall 17, which faces the flat wall 10 of the container 5, and an outer cylindrical wall 18, which axially extends from an outer edge of the flat wall, so as to at least partially enclose the first sealing ring 6. The flat wall 17 has an inner edge 19, which is axially bent towards the flat wall 10 of the container 9 and has, in its cross section, a rounded inner profile. The bellows 33 comprises, in a corresponding manner, an annular flat wall 20, which is axially interposed between the flat wall 17 of the cup 16 and the first sealing ring 6, and an (optional) outer cylindrical wall 21, which axially projects from the annular wall 20 and is radially interposed between the cylindrical wall 18 of the cup and the first sealing ring 6. The latter is axially locked inside the cup 16 through radial interference, namely by radially compressing the cylindrical wall 21 of the bellows 33, and - in the absence of the wall 21 - the wall 16 is in direct contact with the ring 6, so as to define a fixed relative axial position, in which the annular wall 20 is axially compressed between the flat wall 17 of the cup 16 and the first sealing ring 6.

The bellows 33 finally comprises a lip seal portion

22, which cooperates with inner cylindrical wall 13 of the container .

The lip seal portion 22 comprises a first lip 23 with an annular blade, which is radially arranged on the inside of the annular wall 20, a second intermediate lip 24 with a convex rounded profile, which is arranged on the inside of the inner edge 19 of the cup 16, and a third radially flexible lip 25, which axially extends towards the flat wall 10 of the cup 9. The second lip 24 elastically cooperates with the inner wall 13 of the container 9 and ensures the static seal between the cup 16 and the inner wall 13 of the container 9; the first and the third lip (23; 25) cooperate with the second lip 24 for the seal, but are mainly aimed at protecting the area of the seal from dirt particles. Furthermore, the first and the third lip (23; 25) delimit, with the second lip 24, respective annular chambers, which can be optionally filled with a lubricant .

The seal 1 comprises, furthermore, a spring 26, which is housed in the container 9 and is axially compressed between the flat wall 10 of the container and the flat wall 17 of the cup 16, so as to axially push the first sealing ring 6 against the second sealing element 8.

In the example shown herein, the spring 26 is a helical- wave spring made with a flat band, like for example the springs sold under the name of Crest-to-Crest® by Smalley. However, the spring 26 could be replaced by an annular-wave spring or by a conventional cylindrical helical spring or even by a plurality of annular springs (such as Belleville or wave springs) stacked together .

The rotating part 7 of the seal 1 (figure 1) comprises a sleeve 27 formed by a tubular portion 29, which is arranged through the container 9 and is adapted to be fitted on the shaft 2, and by an annular housing portion 29, which is integral to the tubular portion 28 and houses the second sealing ring 8. The housing portion comprises, more in particular, an inner wall 30, which is defined by a wide end portion of the tubular portion 28, a radial flat end flange 31, which defines an axial stop for the second sealing ring 8, and an annular outer edge 32, which is axially bent so as to enclose and lock the second sealing ring 8 in a radial direction. The edge 32 can also be non- continuous or absent.

Conveniently, the second sealing ring 8 is coupled in a rotary manner to the inner wall 30 of the housing portion 29 by means of a pseudo-prismatic elliptical coupling, which is similar to the one described with reference to the first sealing ring 6 and shown in figure 3 and, therefore, will not be further described for the sake of brevity.

The static seal between the second sealing ring 8 and the housing is conveniently obtained by means of a FIP (formed in place) sealant, which is interposed between the ring 8 and the walls 30 and 31 or one of them. The FIP sealant can also be replaced by an elastomeric cap.

The seal 1 works as follows:

In use, not considering the angular clearance allowed by the elliptical couplings, the first sealing ring 6 is fixed, whereas the second sealing ring 8 rotates with the shaft 2 in an integral manner. Therefore, between the two sealing rings 6, 8 there is a relative rotation with sliding under the load of the spring 26.

The rotary coupling between the sealing rings 6, 8 and, respectively, the container 9 and the sleeve 27 is obtained by means of elliptical couplings with very small radial dimensions .

The reduction of the radial dimensions is also supported by the use of a sealant - instead of an elastomeric element - for the creation of the static seal between the second sealing ring 8 and the sleeve 27. Besides the reduced dimensions, this solution offers the advantage of allowing manufacturers to install the second sealing ring 8 without errors of perpendicularity between the front sealing surface and the axis of the sleeve.

The static seal between the bellows 33 and the container 9 is exclusively obtained through the geometry of the lip seal portion 22, without any rigid or elastic element that helps compress said portion against the inner wall 13 of the container, except for the pressure of the fluid. The element 19 has the function of containing the swelling of the lip 13 in case of pressure on the inside, for example when a vacuum is generated before filling the cooling circuit.

The lip seal portion 22 is free to axially slide and rotate relative to the container 9; by so doing, you can avoid self-induced vibrations caused by stick-slip phenomena between the sealing rings 6, 8 and the consequent noise. Furthermore, the number of components is reduced, thus improving the simplicity, the cost-effectiveness and the reliability of the seal.

The lip seal portion 22 has a geometry that is such as to prevent dirt from getting into the area of the static seal with the container 9 and, at the same time, it can act as "tank" for a possible lubricant.

The bellows 33, as it can freely slide in an axial direction, does not generate an elastic load acting upon the sealing rings 6, 8 to obtain the dynamic seal. The consequent absence of elastic deformations helps reduce radial dimensions and assign the load to the sole spring 26, thus obtaining a greater stability of the load during the entire life of the seal .

Finally, it is clear the the seal 1 can be subjected to further changes, without for this reason going beyond the scope of protection set forth in the appended claims.

In particular, the fixed part of the seal could be directly installed in the outer ring of the bearing of the shaft, which needs to be elongated accordingly.

Furthermore, the first sealing ring 11 could be directly fitted into the cup 14, without the interposition of the wall 21 of the bellows 33.