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Field of the invention

The present invention refers to the field of connections of high-pressure pipes for distributing high-pressure fuel to the injectors when the high-pressure rail is external to the head of the internal combustion engine.

Discussion of the prior art

Common rail injection systems comprise a high-pressure fuel pump that supplies a so-called common rail. Smaller pipes branch off from the common rail (or simply rail) pipe to supply each single injector.

The rail comprises a number of connectors, generally referred to as sleeve nipples, the number of which is the same as the number of injectors to be supplied. The same number of high- pressure pipes are connected to these connectors, by means of complementary connectors, preferably screwed, to supply the injectors. Said pipes are normally called injector pipes. The rail may be obtained by welding the connectors or by casting or forging the rail in a single piece.

There are basically two methods of arrangement of the common rail of the high-pressure fuel circuit:

-rail inside the head of the engine, i.e., arranged in the compartment housing the valve actuating tappets, hereinafter the "tappet compartment",

- rail external to the head of the engine, with the single high-pressure pipes branching off from the rail and each one being connected to a respective injector, passing through a wall of the tappet compartment.

The pressure inside the tappet compartment is different from the ambient pressure. In particular, in diesel engines an overpressure is created with respect to the external pressure, and it is therefore necessary to seal the points in the wall of the tappet compartment through which the high- pressure fuel pipes pass.

So-called "passing-wall" are used for that purpose, that is to say, tubular elements that are fixed transversely to a part to be crossed, using connecting means provided with specific sealing gaskets.

An example of such sealing systems is provided in JP2000257528.

The fittings of the high-pressure pipes used for fuel injection systems are manufactured to withstand extremely high pressures and made of deformable metal material to guarantee the required sealing properties.

Unlike low-pressure fittings, a high-pressure fitting can only be used once. Therefore, when an injector has to be disconnected, the fittings of the pipes that are disconnected, including any so-called "passing-wall", must be replaced.

It is clear that using fewer pipes and fittings enables considerable savings to be made in terms of costs and simplifies assembly of the parts.

Summary of the invention

The purpose of the present invention is to reduce the components used for the hydraulic connections of a common rail fuel circuit, in which the rail is external to the head and specifically external to the tappet compartment of the internal combustion engine.

The idea at the basis of the present invention is to use the output connectors of the rail to pass through respective through holes in a wall of the cylinder head to enter the tappet compartment and to use the same output connectors as caps for said through holes.

Thus the output connectors, produced in one piece with the common rail, consist, according to the present invention, in a set of caps joined and integral with one another through the common rail suitable to close corresponding through holes in a wall of the head of the internal combustion engine.

The tightness or seal of the tappet compartment towards the outside environment is achieved in two alternative ways. According to a first embodiment of the invention, appropriate seats are obtained in the openings in the wall of the head of the internal combustion engine into which radial gaskets are inserted, preferably with good backlash recovery.

According to a second preferred embodiment of the invention, the fittings are made in one piece with the rail and each fitting comprises an annular base with a flat contact surface complementary to the wall of the head of the engine. Between said complementary surfaces there is a flat annular gasket through which the respective fitting passes. Means for fastening the rail to the head of the internal combustion engine keep the rail pressed against said head, to guarantee the necessary uniform compression of the annular gaskets. The first solution, based on radial gaskets, is particularly advantageous for implementations in which the rail is produced by means of welding, in that it enables the backlash and machining tolerances to be recovered. Advantageously, with a sufficiently long rail, the high-pressure pipes that branch off from the rail can all be the same and interchangeable .

The second solution, based on flat annular gaskets, is particularly advantageous in implementations in which the rail is produced by means of casting or forging, and in particular when the machining tolerances of the rail are such to enable a high degree of precision in the assembly of the head of the engine.

An object of the present invention is a sealing system of a head of an internal combustion engine with common rail external to the head, as claimed in claim 1.

Another object of the present invention is a method for sealing a head of an internal combustion engine with common rail external to the head.

Another object of the present invention is an internal combustion engine provided with said sealing system.

A further object of the present invention is a vehicle or fixed installation provided with said internal combustion engine .

The claims describe preferred embodiments of the invention and form an integral part of the present description .

Brief description of the drawings

Further purposes and advantages of the present invention will become clear from the following detailed description of a preferred embodiment (and alternative embodiments) thereof and from the accompanying drawings which are merely illustrative and not limiting, in which: figure 1 illustrates a portion of a section perpendicular to a drive shaft of an internal combustion engine, showing a wall of a head of the internal combustion engine, a common rail pipe and a first embodiment of the sealing system according to the present invention,

figure 2 illustrates a second embodiment of the system in a view similar to that of figure 1,

figure 2a illustrates a broader overall view than that shown in figure 2,

figures 3 and 4 illustrate perspective views of two preferred implementations of the present invention, conforming respectively to the embodiments of figure 1 and 2,

figures 5 and 6 illustrate two side views perpendicular to one another, respectively, of a common rail pipe produced to implement the embodiment of figures 1 and 3 and of a common rail pipe produced to implement the embodiment of figures 2 and 4,

figure 7 shows an axial cross section of a gasket implemented in the embodiments of figures 1, 3 and 5.

In the figures the same reference numerals and letters indicate the same parts or components.

Within the scope of the present description, the term "second" component does not imply the presence of a "first" component. Such terms are simply used for the sake of clarity and should not be considered as limiting the scope of the invention .

Detailed description of embodiments of the invention

Figures 1 and 2 illustrate a head H of an internal combustion engine E with common rail CR external to the head. The common rail has a longitudinal tubular shape, perpendicular to the sheet of the drawings. The common rail has two or more output connectors SN in one piece with the common rail and distributed along said common rail and aligned with one another so as to lie on a common plane PL.

Generally, the output pipes, in turn, extend axially in a tubular shape that intersects the common rail. Thus, the axes of extension of the output connectors lie on the same common plane PL.

If the common rail has a circular cross section, the fact that the output connectors SN are aligned with one another so as to lie on a same common plane PL, corresponds to the fact that they intersect the common rail in a same angular position, even though they are distributed along the longitudinal extension of said common rail.

The head H of the internal combustion engine E comprises a wall HW provided with through holes TH in the same number as said two or more output connectors SN.

According to the present invention the sealing system is defined by - the output connectors SN,

- said through holes TH which are distributed so as to be simultaneously engaged by the output connectors SN and

- sealing means G interposed between the wall HW and the output connectors .

More in detail, according to figure 1, the sealing means G consist of a radial gasket, concentrically inserted into the through holes TH so as to at least partially engage a related thickness TK.

Preferably, each through hole TH comprises an annular stop tooth TD1 which determines the axial stop of the radial gasket G during insertion of the related output connector SN into the corresponding through hole TH.

The stop tooth TD1 is therefore implemented so as to prevent the radial seal from falling into the tappet compartment TH. The output connectors SN preferably have a tapered shape and define a base area B, in one piece with the common rail, which defines a sort of transition zone between the common rail and the output connector, which defines another stop tooth TD2 suitable to maintain the radial gasket G in the respective through hole TH, when the common rail is operatively associated with the head H of the internal combustion engine E.

As can be seen in figure 1, the axial section of the radial seals G defines a sort of W capable of recovering any relevant backlash and tolerances in the distribution of the output connectors along the common rail, which could occur in case of common rails produced by welding.

With reference to figure 7, the radial gasket G has a substantially cylindrical shape with a knurled outer cylindrical wall GWE to ensure better adherence to the respective seat obtained in the through holes TH - i.e. in the thickness TK of the wall in which the through holes are obtained .

When the gasket G is operatively inserted into the wall HW of the head of the engine E, the face Fl of the gasket G is visible from the outside of the head H of the engine. Said face Fl preferably defines an annular stop tooth GTD that cooperates with the stop tooth TD1 to prevent the gasket from falling into the tappet compartment. Converging from said surface Fl, on the inside of the outer cylindrical wall GWE, is a further wall GWl having a substantially truncated cone shape, tapering towards the face F2 opposite the face Fl .

Preferably, the smaller base of the inner truncated cone shaped wall has a diameter comprised between 10 and 16 mm, with a preferred value of 13.5.

Said smaller base, as can be seen in figure 1, cooperates with the output connector SN which has, at least in the portion that comes into contact with said gasket G, a cylindrical shape.

Preferably, said cylindrical portion has a diameter comprised between 16 and 10 mm, with a preferred value of 13 mm. According to figure 2, instead, said sealing means consist of a flat annular gasket Gl interposed between the outer face HWE of the wall HW of the head of the engine E and the base B of the output connector SN.

Both the outer wall HWE and the base B define respective flat surfaces TDl and TD2 complementary to each other between which the flat annular gasket Gl is interposed.

Note that the flat surfaces TDl and TD2 in figure 2 and the teeth TDl and TD2 in figure 1 are indicated by the same reference signs because in both cases they act axially on the gaskets G and Gl according to the insertion of the output connector SN in the respective through hole TH obtained in the wall HW of the head H of the internal combustion engine. It is worth pointing out that instead of using separate flat gaskets Gl, a single gasket can be used for the entire extension of the common rail, substantially a single sheet provided with respective holes to enable the output connectors to pass through said gasket.

The surfaces TDl in figure 2 are preferably obtained by milling the outer face HWE of the wall HW.

With reference to figure 3, note that the longitudinal extension of the common rail CR is very similar to or the same as the extension of the head H of the engine E.

A similar extension, in large displacement internal combustion engines, can currently only be obtained with common rails where the output connectors SN are welded to the tubular longitudinal body.

Therefore, the radial gaskets G produce a synergistic effect with this method of production of the common rail.

A further advantage of this solution is that the output connectors can have the same centre distance as the cylinders of the head so that the high-pressure pipes EJP are all the same with clear savings in terms of costs and storage space. In particular, each one has a first end provided with a connector EJPC1 complementary to an output connector SN of the common rail and a second end opposite the first end provided with a connector EJPC2 complementary to the connector of the injector EJ.

Vice versa, figure 4 shows a common rail having a shorter extension than that of the head H of the engine.

It is immediately clear that to have at least the high- pressure pipes EJP in groups of three having the same shape, the centre distance between the output connectors SN must be different, with the fourth output connector SN placed before the third output connector SN counting both from one end and from the other end of the common rail.

In figures 3 and 4 a tappet cover closing the top of the compartment TPF in which the valve actuating tappets are housed is not shown, but is implicit. The springs VS of the valves are clearly visible.

A further comparison between the common rails is illustrated in figures 5 and 6. In particular, in figure 5 the linear sequence 1 - 6 of the common rail is ordered, whereas in figure 6 the numbers 3 and 4 are inverted.

Moreover, the solution in figure 5 envisages a far smaller number of fastening points FM than the solution in figure 6. Indeed, in order to operate efficiently, the flat annular gaskets Gl of figures 2, 4 and 6 require low tolerances between the couplings TD1 and TD2 and a good connection pressure .

On the contrary, the radial seals G of figures 1, 3 and 5 do not require such conditions and the fastening points must therefore only guarantee that the common rail is held in place with respect to the head H of the engine when the latter is running.

Fastening screws SC, clearly visible in figures 1 and 2, are inserted through the flanges defined by the fastening points, in one piece with the rail.

Other embodiments of the non-limiting example of the invention described herein may be implemented without departing from the scope of protection of the present invention, including all the equivalent embodiments implemented by the person skilled in the art.

From the above description it will be possible for the person skilled in the art to implement the object of the invention without the need for any additional construction details. The elements and the characteristics illustrated in the different preferred embodiments, including the drawings, may be combined without departing from the scope of protection of the present application. That described in the description of the state of the art serves merely to ensure a better understanding of the invention and does not constitute a declaration concerning the existence of that described. Moreover, unless specifically excluded in the detailed description, what is described in the description of the state of the art is to be considered in combination with the features of the present invention, thus forming an integral part of the present invention. None of the features of the alternative embodiments are essential. Therefore, the individual features of each preferred embodiment or drawing may be combined with the other embodiments that are described .