Title

“SUCTION VALVE FOR A HIGH PRESSURE PUMP FOR FEEDING FUEL TO AN INTERNAL COMBUSTION ENGINE AND PUMP COMPRISING SUCH A VALVE”

Technical field

The technical field of the present invention relates to pumps for supplying fuel, preferably diesel oil, to an internal combustion engine. In particular, the technical field of the present invention relates to a specific form of high pressure pump, namely a pump comprising at least one pump piston cyclically suppled with fuel through an intake valve made in the form of a movable shutter configured to be coupled cyclically in sealing manner to a corresponding valve body.

In this technical context, the present invention will tackle the problem of how to optimize the geometry of the sealing surface of the shutter.

Prior art

There are known pump units configured to supply pressurized fuel from a tank to an internal combustion engine. These pump units comprise a low pressure pump and a high pressure pump. The reference high pressure pump for the present invention is a pump with at least one pump piston. As is known, a piston pump comprises a pump body configured to receive a head in which at least one cylinder is formed for housing a corresponding pump piston. Each piston comprises a first end that is mostly inside the pump body, and is known as the “foot” of the piston, and a second, opposite end known as the “head” of the piston. The foot of the piston is coupled to a camshaft (or to another drive device). The rotation of the camshaft about its own axis (orthogonal to the piston axis) drives the reciprocating motion of the piston in the cylinder. As is known, each piston is kept pressed against the shaft by a suitable pre-loaded spring. As it moves along the cylinder in reciprocating motion, each piston performs a suction stroke, in which it draws fuel into the cylinder at the piston head, and a compression stroke, in which it compresses the fuel that was made to enter the cylinder in the preceding suction stroke. The cylinder is usually supplied through a first conduit located near the outer surface of the head, while the compressed fuel is discharged along a second conduit. The part of the cylinder where the piston head acts and where compression takes place is called the compression chamber. Evidently, suitable valves are present, and are placed along the fuel supply and discharge conduits. Before entering the cylinder, the fuel is fed into a suction chamber that is outside the head and is in communication with the compression chamber via a valve called the suction valve. On the other hand, the delivery valve is associated with the conduit for delivery to the engine, and controls the flow directed towards a common manifold having a plurality of injectors which, in turn, are connected to the engine.

The suction chamber is delimited by a cap fixed in a sealing manner against the outer surface of the head near the suction valve. The suction valve comprises a shutter member which is movable with respect to a valve body, which may be made in one piece with the head (or may simply be the upper portion of the cylinder), or may be made as a separate cylindrical body that is held in a sealing manner against the outer surface of the head. In both cases, the valve body provides a guide axis for a stem portion of the shutter member, which, on opposite sides of the valve body, comprises a first end that projects into the suction chamber and a second end, which is shutter-shaped or mushroomshaped, and which projects into the compression chamber. As is known, during the compression phase the upper surface of the shutter (or sealing surface) bears in a sealing manner against a corresponding surface of the valve body to prevent backflows of fuel into the suction chamber. A suitable spring interposed between the head of the stem (that is to say, the end in the suction chamber) and the outer surface of the valve body has the purpose of pushing the valve to the closed position and setting a minimum opening pressure for the valve. As will be apparent from the rest of this description, and particularly with reference to Figures 2 - 7, there is currently a need to optimize the coupling between the sealing surface of the shutter and the corresponding surface of the valve body. Such optimization has the purpose of preventing the appearance of localized pressure peaks that may locally deform the shutter, thus shortening its service life.

Description of the invention

The main object of the present invention is therefore to provide an innovative suction valve for a high pressure pump configured for feeding fuel to an internal combustion engine. The high pressure pump of the present invention comprises a pump piston housed in a cylinder formed in a head. In this context, as is known, the suction valve is configured for selectively opening and closing a channel that connects the suction chamber (outside the cylinder) and the compression chamber (inside the cylinder). A suction valve designed for this purpose therefore comprises: a) a shutter member (substantially of the mushroom-shaped type) comprising a cylindrical stem having a first (cylindrical) end and a second end provided with a shutter (a portion that is enlarged with respect to the stem); b) a valve body of cylindrical shape, extending between the suction chamber and the compression chamber, a through hole being formed in this valve body for slidably housing the stem of the shutter member.

Where the valve body is concerned, according to the present invention this component has not undergone any modification from those currently in use. Therefore, also according to the present invention, the dimensions of the hole in the valve body and those of the actuating member are such that, when the valve is assembled, the first end of the shutter member (the cylindrical end without a shutter) projects from one side of the valve body into the suction chamber. As is known, this cylindrical end is coupled to a plate (which is interference fitted, for example) and acts as a support for a spring acting between said plate and a first outer surface of the valve body. This spring has the purpose of forcing the valve into a closed condition and setting an opening pressure threshold. At the opposite end to the plate, the stem of the shutter member comprises an enlarged end, known as the shutter, which projects beyond the valve body and is intended to be located in the compression chamber when in use. This shutter is usually circular in plan view (that is to say, when viewed along the axis of the stem) and comprises a lower surface that is substantially flat and orthogonal to the axis of the stem. At the opposite end to the flat lower surface, the shutter comprises a sealing surface configured for selectively bearing in a sealing manner against a second outer surface of the valve body (in other words, the surface of the valve body facing the compression chamber). For the purposes of the present invention, “sealing surface” is taken to mean at least the surface part of the shutter that is configured for making contact with the valve body in the closing phases. As is known, the hole in the valve body that houses the stem comprises an enlarged portion upstream of the aforesaid second outer surface, so as to provide a distribution chamber inside the valve body, supplied with fuel leaving the suction chamber. This distribution chamber is, in particular, supplied by at least one channel (radial, for example) formed in the valve body. As is known, the stem is movable along the hole in the valve body between a first position, in which the shutter bears against the aforesaid second outer surface of the valve body (and in which the fuel is therefore unable to pass from the distribution chamber to the compression chamber), and a second position, in which the shutter does not bear against the aforesaid second outer surface of the valve body (and in which, therefore, a channel is present for the free passage of fuel from the distribution chamber to the compression chamber). The dynamics of the opening and closing of the suction valve will not be described further, as they are known to those skilled in the art, and therefore do not constitute a specific and innovative object of the present invention.

As mentioned above, the object of the present invention is to improve the sealing coupling between the sealing surface of the shutter and the second outer surface of the valve body, in which this second outer surface of the valve body is a truncated conical surface. This truncated conical form is known, and has a first inner edge at the outlet from the distribution chamber into the compression chamber and a second outer edge (that is to say, an edge farther from the valve axis), said second edge being at a greater depth in the compression chamber.

As will be apparent from the rest of this description, and particularly with reference to Figures 2 - 7 which describe the prior art, at the present time the shutter has a sealing surface with a truncated conical or spherical profile that is coupled to the aforesaid truncated conical surface. However, both of these known solutions exhibit drawbacks which are described below.

According to the most general aspect of the present invention, the sealing surface is no longer conical or spherical, but is a surface that can prevent local peaks of contact pressure, not only when the component is new but also when it is in a worn condition. According to the general aspect of the present invention, the sealing surface 21 exhibits what may be defined as a “double radius” form, comprising:

- a spherical central portion (where the middle contact point is located), defined by a first radius of curvature R;

- two spherical lateral portions (the portions facing the edges of the valve body) defined by a second radius of curvature R’ which is smaller than the first radius R.

Because of this geometry, the lateral portions of the sealing surface, namely the spherical portions defined by a second radius of curvature R’, progressively exhibit a distance (calculated along the shutter axis) that gradually increases with respect to the development that the surface with a single radius of curvature R would have. This greater distance from the edges creates two different advantages. The first is the fact that, even in a worn condition, the edges do not come into contact with the shutter, or do so only after a longer life of the component. In the absence of such contact, other local contact pressures are not created; the component is therefore preserved. The second advantage is the smaller negative effect that the cavitation phenomenon may have on the component. This is because the presence of a greater volume between the valve body and the shutter reduces this undesirable phenomenon. Furthermore, since the second radii R’ are smaller than the radius R, the length of the sealing surface in the present invention is reduced with respect to the known solution with a spherical surface. This reduced sealing length helps to reduce the concentration of vapour in this area, and thus helps to mitigate the aforesaid cavitation phenomenon. The terms “central portion” and “lateral portion” are used above to facilitate the understanding of the invention in relation to the contact points of the coupling and with reference to the attached drawings. Evidently, those skilled in the art will be aware that the sealing surface is actually a surface with circular symmetry centred on the shutter axis, in other words a toroidal surface centred on the shutter axis. In this sense, the sealing surface of the present invention may be defined as:

- a central portion defined by a portion of a first circular generatrix having a first radius (R) and in contact with at least a point substantially in the middle of the truncated conical surface between the edges (25, 26);

- two lateral portions defined by respectively by two portions of two circular generatrices having a second radius (R’) less than the first (R) so that the distance between the edges (25, 26) is increased with respect to the theoretical extension of the first circular generatrix.

Preferably, the centre of the circular generatrix defining the central portion is on the axis A’ below the shutter, while the centres of the circular generatrices defining the lateral portions are located within the shutter.

It will be evident from the description of Figures 8 - 10, which show a preferred embodiment of the invention, that the present innovative solution both ensures an optimal seal and enables the useful duration of the life of the valve to be increased safely. Because of this innovative geometry, the contact surface is centred on the conical surface of the valve body, and has a distance from the edges at its ends such that, even in a worn condition, there is no local contact at these edges. As is known, it is the contact with such edges, particularly the inner edge, that generates a very high local pressure, resulting in greater local deformation and wear of the sealing surface in the prior art.

The present invention also relates to a high-pressure pump for supplying fuel to an internal combustion engine, wherein this pump comprises a valve with a sealing surface as claimed in the attached claims. This high pressure pump comprises a head in which at least one cylinder is formed, in which a corresponding pump piston slides. In this configuration, the valve body of the suction valve may be an independent component coupled in a sealing manner to the head, or may be a portion (a single piece) of the head itself.

Description of an embodiment of the invention

Further characteristics and advantages of the present invention will be made clear by the following description of a non-limiting example of embodiment of the invention, with reference to the attached drawings, in which:

- Figure 1 is a schematic sectional view of a portion of an example of a high pressure piston pump that may be provided with a suction valve according to the present invention; - Figure 2 is a schematic view of a suction valve according to a first example of the prior art;

- Figures 3a and 3b show the variation of the contact pressure of the embodiment of Figure 2 in conditions of re-use;

- Figures 4a and 4b show the variation of the contact pressure of the embodiment of Figure 2 in conditions of wear;

- Figures 5a-5c show schematic views of a suction valve according to a second example of the prior art;

- Figures 6a and 6b show the variation of the contact pressure of the embodiment of Figures 5a-5c in conditions of re-use;

- Figures 7a and 7b show the variation of the contact pressure of the embodiment of Figures 5a-5c in conditions of wear;

- Figure 8 shows an example of a suction valve according to the present invention;

- Figures 9a and 9b show the variation of the contact pressure of the embodiment of Figure 8 in conditions of re-use;

- Figures 10a and 10b show the variation of the contact pressure of the embodiment of Figure 8 in conditions of re-use;

- Figures 11a and lib show the differences in the lengths of the sealing area between the prior art (spherical surface and larger working area) and the present invention.

With reference to the aforesaid figures, Figure 1 shows a schematic sectional view of a part of a high pressure pump that may be provided with a suction valve according to the present invention. In particular, such a high pressure pump may form part of a pump assembly (not shown) configured to supply fuel from a tank to an internal combustion engine.

The high pressure pump 1 of Figure 1 is a pump with pump pistons (Figure 1 shows a single piston), and is configured to supply fuel from a tank to an internal combustion engine (neither of these are shown). Between the tank and the high pressure pump, the pump assembly may also comprise a low pressure pump, for example a gear pump (not shown) configured for supplying the fuel from the tank to the high pressure pump. In a known way, the high pressure pump 1 and the low pressure pump may be driven by a common drive (such as a camshaft (not shown)). The high pressure pump 1 comprises a pump body (not shown) coupled to a head 2. At least one cylinder 3 has been formed in the head 2, this cylinder extending along an axis Al and housing a pump piston (not shown). As is known, the piston is coupled slidably to the cylinder 3. A suction conduit 4, configured for supplying the fuel to a suction chamber 5 located outside the head 2, is also formed in the head 2. The suction chamber 5 is in communication with the cylinder 3 via a suction valve 6. The upper portion of the cylinder 3 between the head of the piston and the suction valve 6 is called the compression chamber and, in its turn, is in communication with a delivery conduit 7 formed inside the head 2. This delivery conduit 7 is provided with a delivery valve 8 for controlling the flow of fuel towards the internal combustion engine. The suction valve 6 comprises a shutter member 9 housed in a through hole in the head 2 formed along the axis Al of the cylinder. This portion of the head 2 housing the shutter member 9 is known as the valve body 10, and may not necessarily be made in one piece with the head 2. As is known, the motion of the pump piston is driven by a drive device (usually a camshaft, not shown in the attached figures). As a result of the rotation of the cam, the piston slides along the cylinder 3 with a reciprocating rectilinear motion including a stroke for the suction of fuel into the cylinder 3 and a stroke for the compression of the fuel contained in the cylinder 3, for compressing the fuel that has been sucked in. In the example of Figure 1, the suction chamber 5 is defined by a cap 11, coupled to the head and positioned at the opposite end of the valve 6 from the pump piston. In this example, the cap 11 comprises a cover and a ring nut that fixes the cover to the head 2. Everything described is known to those skilled in the art, and therefore no further details of construction are given.

Further details of the suction valve are as follows: the shutter member 9 shown in Figure 1 is substantially of the mushroom-shaped type and comprises a cylindrical stem 12 having a first (cylindrical) end 13 and a second end 14 provided with a shutter 15 (a portion enlarged with respect to the stem). The valve body 10 is of cylindrical shape and extends between the suction chamber and the compression chamber. A through hole being formed in this valve body for slidably housing the stem 12 of the shutter member 9. Where the valve body 10 is concerned, this component has not undergone any modification from those currently in use. As is known, the valve body 10 comprises a hole 16 housing the stem 12. The dimensions of the hole 16 in the valve body 10 and those of the actuating member 9 are such that, when the valve 6 is assembled, the first end 13 of the shutter member 9 (the cylindrical end without a shutter) projects from one side of the valve body 10 into the suction chamber 5 (obviously, when the valve is assembled in the corresponding pump). As is known, this cylindrical end 13 is coupled to a plate 17 (which is interference fitted, for example) for supporting a spring 18 between said plate 17 and a first outer surface of the valve body 10. This spring 18 has the purpose of generating an elastic force configured for forcing the closure of the valve and for setting a minimum opening pressure. As mentioned, at the opposite end from the plate 17 the stem 12 of the shutter member 9 comprises an enlarged end, known as the shutter 15, which projects beyond the valve body 10 and is intended to be located in the compression chamber 19 of the pump when in use. This shutter 15 preferably circular in plan view (that is to say, when viewed along the axis of the stem Al) and comprises a lower surface 20 that is substantially flat and orthogonal to the axis of the stem. At the opposite end to the flat lower surface 20, the shutter 15 comprises a sealing surface 21 configured for selectively bearing in a sealing manner against a second outer surface 22 of the valve body 10 (in other words, the surface of the valve body 10 facing the compression chamber 19). For the purposes of the present invention, “sealing surface” 21 is taken to mean at least the surface part of the shutter 15 that is configured for making contact with the valve body 10 when the suction valve 6 shuts off the supply of fuel into the compression chamber 19. As is known, the hole 16 in the valve body 10 that houses the stem 12 comprises an enlarged portion upstream of the aforesaid second outer surface 22 of the valve body 10, so as to provide a distribution chamber 23 inside the valve body 10, supplied with fuel leaving the suction chamber 5. This distribution chamber 23 is, in particular, supplied by at least one channel 24 (radial, for example) formed in the valve body 10. As is known, the stem 12 is movable along the hole 16 in the valve body 10 between a first position, in which the shutter 15 bears against the aforesaid second outer surface 22 of the valve body 10 (and in which the fuel is therefore unable to pass from the distribution chamber 23 to the compression chamber 9), and a second position, in which the shutter 15 does not bear against the aforesaid second outer surface 22 of the valve body 10 (and in which, therefore, a channel is present for the free passage of fuel from the distribution chamber 23 to the compression chamber 19). The dynamics of the opening and closing of the suction valve 6 will not be described further, as they are known and do not constitute an object of the present invention. As mentioned above, the object of the present invention is to improve the sealing coupling between the sealing surface 21 of the shutter 15 and the second outer surface 22 of the valve body 10, particularly when this surface is a truncated conical surface. This truncated conical form is known, and has a first inner edge 25 at the outlet from the distribution chamber 23 into the compression chamber 19 and a second outer edge 26 (that is to say, an edge farther from the valve axis), said second edge being 26 at a greater depth in the compression chamber 19. In the example shown, the valve body 10 is made in one piece with the head 2, and therefore there is no interruption with the rest of the cylinder 3 beyond the edge 26. As will be apparent from the rest of this description, and particularly with reference to Figures 2 - 7 which describe the prior art, a sealing surface 21’ with a truncated conical profile (Figures 2-4b) or a spherical profile 21” (Figures 5a-7b) that is coupled to the aforesaid truncated conical surface 22. However, neither of these solutions is free of drawbacks.

With reference to Figure 2, this figure shows a schematic view of a suction valve according to a first example of the prior art. As described above, the truncated conical surface 22 is delimited by the first inner edge 25 and the second outer edge 26. In the example of Figure 2, the coupling between the sealing surface 21’ and the truncated conical surface 22 is substantially reduced to the single inner edge 25, since the sealing surface 21’ also exhibits a truncated conical form. According to the prior art, this coupling is referred to as a “sealing cone”.

Figure 3a shows an enlargement of the configuration of Figure 2 in a non-worn coupling condition, and the corresponding Figure 3b shows the variation of the contact pressure in such a coupling. Because there is substantially a single theoretical point of contact, the pressure reaches a peak at the edge 25 and then falls rapidly along the sealing surface 21’ until it disappears (exponentially) halfway along its length.

Figure 4a shows an enlargement of the configuration of Figure 2 in a worn coupling condition. Because of the high localized pressure at the edge 25, local deformation occurs on the conical sealing surface 21’, exactly at the position of the inner edge 25. Evidently, this deformation shortens the service life of the valve. With reference to Figure 5a, this figure shows a schematic view of a suction valve according to a second example of the prior art. In the example of Figure 5a, while it is still the case that the truncated conical surface 22 is delimited by the first inner edge 25 and the second inner edge 26, the coupling between the sealing surface 21” and the truncated conical surface 22 is not restricted to a single point as in the preceding example, owing to the fact that the sealing surface 21” has a spherical form with its centre on the axis of the stem 12. Figures 5b and 5c show progressive enlargements of the area of coupling between the truncated conical surface 22 and the spherical sealing surface 21” in this configuration. In particular, Figure 5B shows that the radius of the sphere defining the spherical geometry of the sealing surface 21” is greater than both the radius of the shutter 15 and the radius of the cylinder 3. In particular, Figure 5c shows that the area of coupling is substantially centred on the truncated conical surface 22 and greatly extended, so that it practically reaches the edges 25 and 26.

Figure 6a shows an enlargement of the configuration of Figure 5c in a non-worn coupling condition, and the corresponding Figure 6b shows the variation of the contact pressure in such a coupling. Since there is a wide contact area, there are no points of peak pressure, and in fact the pressure exhibits a parabolic variation and disappears at the points of detachment near the edges 25 and 26.

Figure 7a shows an enlargement of the configuration of Figure 5c in a worn coupling condition. In particular, owing to the wear, the coupling area extends until it also includes the edges 25 and 26 which were outside the original contact area. As may be seen in Figure 7b, two peaks develop at these edges and, as in the preceding case, cause a deformation of the shutter and a consequent shortening of the service life of this component.

With reference to Figure 8, this figure shows a schematic view of a suction valve according to an example of embodiment of the present invention. In the example of Figure 8, while it is still the case that the truncated conical surface 22 is delimited by the first inner edge 25 and the second inner edge 26, the coupling between the sealing surface 21 and the truncated conical surface 22 is not restricted to a point as in the preceding example, nor does it involve the edges (even in a worn condition) as in the second example of the prior art described. In particular, according to the present invention, the sealing surface 21 exhibits what may be defined as a “double radius” form, comprising:

- a spherical central portion defined by a first radius of curvature R, which could be the spherical radius R of the prior art example of Figures 5-7;

- two spherical lateral portions defined by a second radius of curvature R’ which is smaller than the first radius R.

Because of this geometry, the lateral portions of the sealing surface 21, namely the spherical portions defined by a second radius of curvature R’, progressively exhibit a distance (calculated along the shutter axis) that gradually increases with respect to the development that the surface with a single radius of curvature R would have. The form that the surface 21 would have if it were spherical with a single radius R is shown in broken lines in Figure 8.

Figure 9a shows the configuration of Figure 8 in a non-worn coupling condition, and the corresponding Figure 9b shows the variation of the contact pressure in such a coupling. As may be seen, there is a wide contact area and there are no points of peak pressure; in fact, the pressure exhibits a parabolic variation which disappears at the points of detachment, which are distant from the edges 25 and 26.

Figure 10a shows an enlargement of the configuration of Figure 8 in a worn coupling condition. Because of the geometry with a double radius of curvature, even in conditions of wear the coupling area does not extend to include the edges 25 and 26. In the absence of contact at the edges, as may be seen in Figure 10, there are no pressure peaks. In the absence of pressure peaks, the deformation of the shutter is limited and not restricted to a point, thus lengthening the service life of this component.

In addition to this advantage in terms of prolonging the life of the component, the present invention provides a second advantage. The greater distance (along the shutter axis) between the edges of the valve body and the sealing surface 21 mitigates what is known as the cavitation phenomenon, well known to those skilled in the art, which also contributes to a shortening of the life of the component. Figures 11A and 11B provide a comparison between the spherical solution according to the prior art (11A) and the solution of the present invention. It should also be noted that, owing to the effect of the radii R’, the length of the sealing surface in the present invention is reduced by comparison with the length D of Figure 11. This smaller sealing length helps to reduce the concentration of vapour in this area, and thus helps to mitigate the aforesaid cavitation phenomenon.

Finally, it is evident that the suction valve described herein with reference to the figures may be modified and varied without departure from the scope of the attached claims.