EP1682771B1 - Valve for a fuel injection pump - Google Patents

Description

The invention relates to a valve for a fuel injection system of an internal combustion engine having the features specified in the preamble of claim 1, in particular for an injector of a common rail injection system.

State of the art

Common rail injection systems have a plurality of injectors, which are supplied with fuel under the control of an electronic engine control by a high-pressure pump from a designated as common rail central high-pressure accumulator and inject the fuel via a valve in the combustion chambers of the cylinders of the internal combustion engine. Such a valve is among others from the DE 199 40 296 A1 Known by the applicant and is used depending on the valve position to connect a high-pressure region of an injector of the injection system with a low pressure region or to separate from this, when fuel is injected through the valve into the combustion chamber of a cylinder or the supply of fuel to be interrupted.

When the fuel flows with the valve open at high speed through the annular channel formed between the valve seat and the sealing surface, whose cross section widens considerably behind the valve seat, it can lead to cavitations in the fuel. In this case, vapor bubbles form in the fuel when the pressure drops locally below the vapor pressure of the fuel. When the pressure rises again, the fuel condenses in the vapor bubbles, beating at high speed against adjacent boundary surfaces of the annular channel. As a result, cavitation damage can occur directly behind the valve seat, as a result of which, as erosion progresses, the valve seat itself is also attacked.

To solve this problem was in the DE 199 40 296 A1 proposed to extend the cross-section of the annular channel, starting from a minimum cross-section in the region of the valve gap with a constant gradient. However, it has been shown that this measure is not always sufficient to safely prevent cavitation damage.

From the DE 101 34 526 A1 Furthermore, a valve of the aforementioned type is known in which a circumferential groove arranged in the flow direction directly behind a sealing surface of the valve member is delimited together with a circumferential cross-sectional thickening of the valve member and with the valve housing an annular space. Between the groove and the cross-sectional thickening, the valve member has a circumferential edge against which contiguous outer peripheral surface portions of the groove and cross-sectional thickening meet at an angle of 270 °, with a peripheral surface portion adjacent the edge on the side of the groove at an angle of 90 degrees is aligned with the central axis of the valve member.

When using the valve according to the invention with the features mentioned in claim 1 cavitation damage could be prevented with good success, because the fuel flow behind the valve seat is not simply deflected in the axial direction. Instead, as it flows through the groove, it receives a velocity component in a direction pointing away from the central axis of the valve member so that, after exiting the groove, it impinges on an opposite region of an inner wall of an outlet bore of the valve housing. On impact, part of the fuel flow is directed along the inner wall back toward the valve gap, leaving immediately behind the opposite wall portion of the inner wall forms a vortex. By this vortex, on the one hand, additional fuel is introduced into the annular space behind the valve gap, so that there is more fuel there, which counteracts cavitation phenomena in the vicinity of the valve gap and thereby caused long-term cavitation damage to the valve seat. On the other hand, the fuel conducted back in the direction of the valve gap flows along the inner wall of the valve housing, whereby additional fuel can be introduced into this particularly cavitation-prone area and local steam bubble formation due to fuel pressure drop can be avoided.

In the context of the present invention, a hollow groove is understood to mean a concave annular groove in the circumference of the valve member, while cross-sectional thickening means an adjacent part of the valve member in the direction of flow whose diameter is greater than the diameter in the region of the annular groove.

A particularly good vortex formation in the enlarged annular space behind the valve gap is achieved in a preferred embodiment of the invention in that between the groove and the cross-sectional thickening an undercut circumferential trailing edge is arranged on the both sides of this edge adjacent outer peripheral surface portions of the groove and the cross-sectional enlargement under a blunt Angle meet.

While the outer peripheral surface portion adjacent to the edge on the side of the cross-sectional thickening is preferably aligned substantially parallel to a central axis of the valve member is opposite to the flow direction at an angle between 20 and 80 degrees, preferably between 30 and 60 degrees, inclined to the central axis of the valve member, so that the two peripheral surface portions at an angle between 200 and 260 degrees, preferably between 190 and 240 degrees.

A particularly simple and cost-effective production of the spoiler lip is in accordance with a further preferred embodiment of the invention possible in that one abrades the outer peripheral surface at least in the region of the valve seat opposite sealing surface and the groove to the final diameter during the finishing of the valve member, but not in the Area of cross-sectional thickening, so that the material remaining there automatically leads to the formation of the spoiler edge. In this case, the cross-section of the valve member tapers in the flow direction behind the cross-sectional thickening, but this need not necessarily be the case.

In order to provide a cost-effective for serial production geometry of the valve member, the concave groove expediently has a radius of curvature which is preferably at least 0.2 mm and is expedient over the entire width of the groove uniformly large.

In order to promote the vortex formation, according to a further advantageous embodiment of the invention can also be provided, not parallel to the central axis of the valve member or to align with the center axis of the discharge hole, sondem one of the groove substantially opposite inner wall portion of the outflow to install in this section a step or slope which helps to redirect part of the fuel flow in the direction of the valve gap.

drawings

Figur 1

eine Seitenansicht eines Ventilglieds oder Ventilbolzens eines erfindungsgemäßen Ventils; 0

Figur 2

eine vergrößerte Querschnittsansicht des Ventils im Bereich des Ventilspalts gemäß Ausschnitt Z aus Figur 1;

Figur 3

eine Ausschnittsvergrößerung entsprechend Figur 2, jedoch mit einer anderen Geometrie des Ventilglieds in Strömungsrichtung hinter dem Ventilspalt;

Figur 4

eine Ausschnittsvergrößerung entsprechend Figur 2, jedoch mit einer noch anderen Geometrie des Ventilglieds und des Ventilgehäuses in Strömungsrichtung hinter dem Ventilspalt.

The invention will be explained in more detail in an embodiment with reference to the accompanying drawings. Show it:

FIG. 1

a side view of a valve member or valve pin of a valve according to the invention; 0

FIG. 2

an enlarged cross-sectional view of the valve in the region of the valve gap according to section Z out FIG. 1 ;

FIG. 3

an enlarged detail accordingly FIG. 2 but with a different geometry of the valve member in the flow direction behind the valve gap;

FIG. 4

an enlarged detail accordingly FIG. 2 but with still another geometry of the valve member and the valve housing in the flow direction behind the valve gap.

Description of the embodiment

The valve 2 shown only partially in the drawing is part of an injector of a common rail injection system of an internal combustion engine, which serves to fuel from a common rail inject central high-pressure accumulator into the combustion chambers of the cylinders of the internal combustion engine.

The complete structure of such an injector is for example in the DE 196 19 523 A1 The applicant described in detail while more details on the structure of its valve from the already mentioned DE 199 40 296 A1 let the applicant, so that at this point waives a more detailed explanation and reference is made to the cited documents for this purpose.

The valve 2 consists essentially of a valve housing 4, in which a rotationally symmetrical valve pin 6 (see. FIG. 1 ) is used axially movable. The valve pin 6 has a conical, tapered in the flow direction sealing surface 8, which bears sealingly against a complementary conical valve seat 10 of the housing 4 when the valve 2 is closed. How best in the FIGS. 2 to 4 shown limited at the valve 2 open the sealing surface 8 together with the valve seat 10 surrounding the valve pin 6 valve gap 12 in the form of an annular flow channel through which the fuel to be injected flows from the high pressure side 14 of the valve 2 to the low pressure side 16.

The valve pin 6 further comprises a circumferentially disposed in the direction of flow immediately behind the sealing surface 8 in its outer circumference circumferential groove 18, that is a concave recess in longitudinal section or groove over the axial width of the diameter of the valve pin 6 is smaller than before or behind, where the valve pin 6 is provided with an adjacent to the groove 18 cross-sectional thickening 20.

The groove 18 serves to deflect at least a portion of the fuel flow discharged substantially behind the valve seat 10 in the axial direction such that it has a velocity component directed away from a central axis 22 of the valve pin 6 and, after its exit from the groove 18, against an opposite region the inner wall 24 of an outflow bore 26 of the valve housing 4 rebounds. How best in FIG. 2 . 3 and 4 represented by arrows, while dividing the fuel flow into two partial streams, of which the larger is directed after the impact along the inner wall 24 of the discharge hole 26 in the downstream part of the bore 26, while the smaller against the flow direction to the valve gap 12 directed back out becomes. In the subsequent in the flow direction of the valve gap 12 widened annular space 30 between the groove 18 and the opposite wall portion of the inner wall 24 of this partial flow forms together with the effluent from the valve gap 12 fuel flow a vortex 32, the valve housing 4 in the area immediately behind the valve seat 10th protects against erosion caused by cavitation, so that the valve seat 10 remains undamaged even over a long period of operation.

To form this protective vortex 32, the angle of inclination of the fuel flow emerging from the groove 18 with respect to the central axis 22 of the valve pin 6 must not be too small, since otherwise the entire fuel is directed directly into the outflow bore 26. Therefore, on the one hand, the groove 18 should not be formed too flat, but with respect to the subsequent cross-sectional thickening a certain minimum depth T (FIG. FIG. 1 ), which at a diameter of the valve pin 6 in the middle of Sealing surface of 1.35 mm should preferably be greater than 0.04 mm. On the other hand, the groove 18 should not be rounded at the transition to the cross-sectional thickening, because thereby the inclination angle of the emerging from the groove 18 fuel flow with respect to the central axis 22 is also smaller. Instead, a circumferential edge 34 is provided between the groove 18 and the cross-sectional thickening 20, at the adjoining outer peripheral surface portions 36, 38 of the groove 18 and the cross-sectional thickening 20 has a superficial angle β (FIG. FIG. 1 ), which should be at least 200 degrees and preferably between 220 degrees and 240 degrees. Unlike a rounded transition at such an edge 34, the flow of fuel from the peripheral surface of the valve pin 6 breaks off, but this has no cavitation due to the hardened surface of the valve pin 6 result. The stall at the edge 34 causes the fuel to exit the fillet 18 at an angle of inclination to the central axis 22 that substantially corresponds to the angle of inclination α of the peripheral surface portion 36 adjacent the edge 34 within the fillet 18. Depending on how large this angle of inclination is selected, more or less fuel is directed back in the direction of the valve gap 12 upon impact of the fuel flow on the opposite region of the inner wall 24 of the discharge bore 26. By a suitable choice of this angle of inclination, which is preferably between 20 and 60 degrees, therefore, the proportion of the returning fuel can be adjusted to such a value that on the one hand vortex formation avoids cavitation damage immediately behind the valve seat 10, on the other hand, the vortex formation the flow of fuel after its exit from the valve gap 12 is not affected.

In all the illustrated embodiments, the fuel flowing back along the inner wall 24 protects the latter from cavitation-related damage, which might otherwise be caused by a pressure drop in the fuel as it exits the valve gap 12 into the annulus 30, just past the valve gap 12.

While FIG. 2 a valve pin 6, wherein the within the groove 18 adjacent to the edge 34 peripheral surface portion 36 is aligned at an inclination angle α of about 60 degrees to the central axis 22 of the valve pin 6, the fuel therefore bounces quite steeply on the inner wall 24 of the discharge bore 26 and thus relatively much fuel is directed back in the direction of the valve gap 28, show the Figures 3 and 4 two valve bolts 6, in which this inclination angle α is about 35 degrees or about 20 degrees, and therefore correspondingly less fuel is directed back toward the valve gap 28 to form a vortex 34.

Since the inclination angle α in FIG. 4 is already in the border area, in which still forms a vortex 34, where the opposite inner wall 24 of the discharge bore 26 is provided there with a small step 40. This step 40, due to its surface inclined to the central axis 22 of the valve pin 6 and the discharge bore 26, promotes the return of a portion of the fuel flow in the direction of the valve gap 12.

The concave boundary of the groove 18 is circular in all embodiments, wherein the radius of curvature should not fall below 0.2 mm in order to allow cost-effective mass production of the valve pin 6. At its side facing the valve gap 12, the groove 18 preferably transitions seamlessly into the sealing surface 8, as shown in all exemplary embodiments.

The sharp tear-off edge 34 on the other side of the groove 18 can be inexpensively produced in a series production of the valve pin 6, that the valve pin 6 is ground at its final diameter on both sides of the cross-sectional thickening 20, but not in the region of the cross-sectional thickening 20, so that there existing in front of the abrasive finishing of the valve pin 6 existing diameter is maintained, which automatically leads to the formation of the tear-off edge 34 at the transition to the groove 18.

Claims (8)

1. Valve (2) for a fuel injection system, having a valve seat (10) which is formed in a valve housing (4), and having a valve member (6) which is movable in the valve housing (4) and which has a sealing surface (8) which bears against the valve seat (10) when the valve (2) is closed, which sealing surface, when the valve (2) is open, serves together with the valve seat (10) to delimit a valve gap (12) through which fuel flows, wherein the valve member (6) has an encircling hollow groove (18) which is arranged directly downstream of the sealing surface (8) in the flow direction and which is adjoined by an encircling cross-sectional thickening (20) of the valve member (6), and wherein between the hollow groove (18) and the cross-sectional thickening (20) there is arranged an encircling edge (34) at which outer circumferential surface portions (36, 38), which adjoin one another, of the hollow groove (18) and of the cross-sectional thickening (20) converge at a reflex angle (β), characterized in that the circumferential surface portion (36) which adjoins the edge (34) at the side of the hollow groove (18) is inclined with respect to a central axis (22) of the valve member (6) by an angle (α) of between 20 and 80 degrees.
2. Valve according to Claim 1, characterized in that the circumferential surface portion (36) which adjoins the edge (34) at the side of the hollow groove (18) is inclined with respect to a central axis (22) of the valve member (6) by an angle (α) of between 20 and 60 degrees.
3. Valve according to Claim 1 or 2, characterized in that the outer circumferential surface portion (38) which adjoins the edge (34) at the side of the cross-sectional thickening (20) is aligned substantially parallel to a central axis (22) of the valve member (6).
4. Valve according to one of the preceding claims, characterized in that a radius of curvature of the hollow groove (18) is greater than 0.2 mm.
5. Valve according to one of the preceding claims, characterized in that the hollow groove (18) and the sealing surface (8) merge seamlessly into one another.
6. Valve according to one of the preceding claims, characterized in that the cross section of the valve member (6) narrows in the flow direction downstream of the cross-sectional thickening (20).
7. Valve according to one of the preceding claims, characterized in that an outer circumferential surface of the valve member (6) is ground at least in the region of the sealing surface (8) and of the hollow groove (18) but not in the region of the cross-sectional thickening (20).
8. Fuel injection pump characterized by a valve according to one of the preceding claims.

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