Valve Arrangement and a High Pressure Pump for a Fuel Injection System of an Internal Combustion Engine

Abstract

Embodiments relate to a valve arrangement for a fuel injection system, including a valve disc that has a valve opening. A deformable valve sheet that is movable in a movement direction is provided to open and close the valve opening, and a valve shaft of a movement-activation arrangement, provided to activate the movement of the valve sheet, is secured to the valve sheet. The embodiments also relate to a high-pressure pump which includes the valve arrangement.

Claims

1. A valve arrangement for a fuel injection system of an internal combustion engine, comprising: a valve disk including at least one valve opening arranged in the valve disk, wherein the valve opening fluidly connects to one another a first valve disk side and a second valve disk side situated opposite the first valve disk side, which first and second valve disk sides are separated from one another by the valve disk, a deformable valve lamella which is movable along a movement direction and which serves for opening and closing the valve opening, which valve lamella, in order to close the valve opening, is selectively brought into contact with a valve disk surface on the first valve disk side, and a movement activation arrangement for activating a movement of the valve lamella along the movement direction, the movement activation arrangement having a valve shank which is fixed to the valve lamella.

2. The valve arrangement as claimed in claim 1, further comprising a screw element, wherein the valve shank is fixed to the valve lamella by the screw element, wherein the screw element which bears against the valve lamella on a first valve lamella side facing away from the second valve disk side, and extends through the valve lamella.

3. The valve arrangement as claimed in claim 1, wherein the valve shank is fixed to the valve lamella by a welded connection, wherein a weld seam of the welded connection is arranged on a second valve lamella side facing toward the second valve disk side, and the weld seam exerts a pressure on the valve lamella such that the valve opening remains open.

4. The valve arrangement as claimed in claim 1, further comprising a sleeve-shaped receiving element, the sleeve-shaped receiving element is arranged on the valve lamella and is in engagement with the valve shank, wherein the sleeve-shaped receiving element is crimped to the valve shank, formed as a circlip, formed as a clip element which engages behind a first valve lamella side facing away from the second valve disk side, or formed as opening walls of a valve lamella opening in the valve lamella.

5. The valve arrangement as claimed in claim 1, wherein the valve lamella is formed integrally with an end facing toward the first valve disk side of the valve shank, or wherein the valve lamella has an engagement shank which engages through the valve opening into a recess of the valve shank, such that the engagement shank engages through the valve lamella and is fastened to the valve lamella by welded connections to a first valve lamella surface on the first valve lamella side and to a second valve lamella surface on the second valve lamella side.

6. The valve arrangement as claimed in claim 1, wherein the valve lamella forms a spring element whose spring force is directed counter to a force which acts on the valve lamella from a first valve lamella side.

7. The valve arrangement as claimed in claim 6, wherein the spring force is greater than a predetermined force which corresponds to a maximum hydraulic force on the first valve lamella side during operation of the valve arrangement.

8. The valve arrangement as claimed in claim 1, wherein the valve lamella is fixed at least in sections to the valve disk.

9. The valve arrangement as claimed in claim 1, wherein the movement activation arrangement further comprises a magnetic actuator with a static pole piece and an armature which is connected to the valve shank and serves as a positioning element, wherein the armature and the pole piece are, in all operating positions of the valve arrangement, arranged so as to be spaced apart from one another, and wherein a spring element is formed by the valve lamella, the spring element preloads the armature into a rest position with a maximum spacing to the pole piece.

10. A high-pressure pump for a fuel injection system of an internal combustion engine, comprising: a pressure chamber for applying high pressure to fuel disposed in or associated with the high-pressure pump, and an inlet valve for admission of the fuel into the pressure chamber, wherein the inlet valve comprises a valve arrangement, the valve arrangement comprising: a valve disk including at least one valve opening arranged in the valve disk, wherein the valve opening fluidly connects to one another a first valve disk side and a second valve disk side situated opposite the first valve disk side, which first and second valve disk sides are separated from one another by the valve disk, a deformable valve lamella which is movable along a movement direction for opening and closing the valve opening, the valve lamella, in order to close the valve opening, is selectively brought into contact with a valve disk surface on the first valve disk side, and a movement activation arrangement for activating a movement of the valve lamella along the movement direction, the movement activation arrangement having a valve shank which is fixed to the valve lamella, wherein the pressure chamber is formed on the first valve disk side.

11. The high-pressure pump of claim 10, wherein the valve arrangement further comprises a screw element, and the valve shank is fixed to the valve lamella by the screw element, wherein the screw element bears against the valve lamella on a first valve lamella side facing away from the second valve disk side, and extends through the valve lamella.

12. The high-pressure pump of claim 10, wherein the valve shank is fixed to the valve lamella by a welded connection, wherein a weld seam of the welded connection is arranged on a second valve lamella side facing toward the second valve disk side, and the weld seam exerts a pressure on the valve lamella such that the valve opening remains open.

13. The high-pressure pump of claim 10, wherein the valve arrangement further comprises a sleeve-shaped receiving element, the sleeve-shaped receiving element is arranged on the valve lamella and is in engagement with the valve shank, and wherein the sleeve-shaped receiving element is crimped to the valve shank formed as a circlip, formed as a clip element which engages behind a first valve lamella side facing away from the second valve disk side, or formed as opening walls of a valve lamella opening in the valve lamella.

14. The high-pressure pump of claim 10, wherein the valve lamella is formed integrally with an end facing toward the first valve disk side of the valve shank, or wherein the valve lamella has an engagement shank which engages through the valve opening into a recess of the valve shank such that the engagement shank engages through the valve lamella and is fastened to the valve lamella by welded connections to a first valve lamella surface on the first valve lamella side and to a second valve lamella surface on the second valve lamella side.

15. The high-pressure pump of claim 10, wherein the valve lamella is in the form of a spring element whose spring force is directed counter to a force which acts on the valve lamella from a first valve lamella side.

16. The high-pressure pump of claim 10, wherein the valve lamella is fixed at least in sections to the valve disk.

17. The high-pressure pump of claim 10, wherein the movement activation arrangement further comprises a magnetic actuator including a static pole piece and an armature which is connected to the valve shank and serves as a positioning element, wherein the armature and the pole piece are, in all operating positions of the valve arrangement, arranged so as to be spaced apart from one another, and wherein a spring element is formed by the valve lamella, the spring element preloads the armature into a rest position with a maximum spacing to the pole piece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Refinements of the invention will be discussed in more detail below on the basis of the appended drawings, in which:

[0033] FIG. 1 is a schematic illustration of a fuel injection system of an internal combustion engine having a high-pressure pump and having valve arrangements arranged thereon;

[0034] FIG. 2 shows a longitudinal section of the high-pressure pump and the valve arrangements arranged thereon from FIG. 1;

[0035] FIG. 3 is a first schematic illustration, in longitudinal sectional view, of the high-pressure pump from FIG. 2 with a valve arrangement fully open;

[0036] FIG. 4 is a second schematic illustration, in longitudinal sectional view, of the high-pressure pump from FIG. 2 with a valve arrangement fully open;

[0037] FIG. 5 is a third schematic illustration, in longitudinal sectional view, of the high-pressure pump from FIG. 2 with a valve arrangement fully closed;

[0038] FIG. 6 is a first detailed longitudinal sectional illustration of the valve arrangement from FIGS. 3-5;

[0039] FIG. 7 is a second detailed longitudinal sectional illustration of the valve arrangement from FIGS. 3-5;

[0040] FIG. 8 is a schematic illustration of the connection of a valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to a valve shank of the valve arrangement, according to a first example embodiment;

[0041] FIG. 9 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement, according to a second example embodiment;

[0042] FIG. 10 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a third example embodiment;

[0043] FIG. 11 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a fourth example embodiment;

[0044] FIG. 12 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a fifth example embodiment;

[0045] FIG. 13 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a sixth example embodiment;

[0046] FIG. 14 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a seventh example embodiment;

[0047] FIG. 15 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to an eighth example embodiment;

[0048] FIG. 16 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a ninth example embodiment;

[0049] FIG. 17 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a tenth example embodiment;

[0050] FIG. 18 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to an eleventh example embodiment; and

[0051] FIG. 19 is a schematic illustration of the connection of the valve lamella of the valve arrangement from FIG. 6 and FIG. 7 to the valve shank of the valve arrangement according to a twelfth example embodiment.

DETAILED DESCRIPTION

[0052] FIG. 1 is a schematic illustration of a fuel injection system 10 of an internal combustion engine, which fuel injection system delivers a fuel 12 from a tank 14 via a predelivery pump 16, a high-pressure pump 18 and a fuel high-pressure accumulator 20 to injectors 22 which then inject the fuel 12 into combustion chambers of the internal combustion engine.

[0053] The fuel 12 is introduced into the high-pressure pump 18 via a valve arrangement 24, and is discharged from the high-pressure pump 18 under pressure via a further valve 26.

[0054] FIG. 2 shows a longitudinal section through the high-pressure pump 18 with the valve arrangement 24 as inlet valve 28 and with the valve 26 as outlet valve 30, which valve arrangement and valve are arranged at a pressure chamber 32 of the high-pressure pump 18. During the operation of the high-pressure pump 18, a piston 34, which performs a translational movement, periodically varies the volume of the pressure chamber 32. Here, the piston 34 is driven by a camshaft 36 which, in the present example embodiment, is in operative contact with the piston 34 via a tappet 38.

[0055] FIG. 3 to FIG. 5 schematically show different operating states of the piston 34 and of the inlet valve 28 in longitudinal sectional view through the high-pressure pump 18 during the operation of the high-pressure pump 18.

[0056] Here, in the present embodiment, the outlet valve 30 is a simple check valve 40 which opens passively owing to a pressure prevailing in the pressure chamber 32 and which automatically closes again in the absence of the pressure.

[0057] In the present embodiment, the inlet valve 28 is an active magnetic valve 42 which has a magnetic actuator 44 with a static pole piece 46 and with a movable armature 48 as a positioning element 50. To the armature 48 there is fastened a valve shank 52 which engages through a valve opening 54 in a valve disk 55 and to which there is fastened a valve lamella 56 which, when moved in the direction of the pole piece 46, may be placed in contact with a valve disk surface 58 on a first valve disk side 60 of the valve disk 55, in order to thereby close the valve opening 54. In the present embodiment, the inlet valve 28 is an inlet valve 28 which is open when de-energized, that is to say, when the magnetic valve 42 is not energized, the pole piece 46 and the armature 48 are, owing to a spring 62, arranged with a maximum spacing 64 to one another, such that the valve lamella 56 is situated in an open position. At the same time, the piston 34 is on the path toward the bottom dead center of the piston, as indicated by the arrow P.sub.1. Owing to the movement of the piston 34 and the open position of the valve lamella 56, fuel 12 flows, as indicated by the arrows P.sub.2, into the pressure chamber 32 of the high-pressure pump 18. The outlet valve 30 is in its closed position.

[0058] FIG. 4 schematically illustrates, in longitudinal sectional view, how the piston 34 moves toward the top dead center thereof. The valve lamella 56 remains in the open position owing to the spring force of the compression spring 62, because the pressure built up in the pressure chamber 32 by the piston 34 is not yet sufficient to overcome the spring force of the compression spring 62 and close the valve lamella 56. The outlet valve 30, too, is still situated in the closed position thereof. Owing to the valve lamella 56 being in the open position, fuel 12 flows out of the pressure chamber 32 again through the inlet valve 28.

[0059] In FIG. 5, the piston 34 is situated a short distance before the top dead center thereof, and the pressure that has been built up in the pressure chamber 32 by the movement of the piston 34 is sufficient to close the valve lamella 56. At the same time, the pressure is also sufficient to open the outlet valve 30.

[0060] The spring force of the compression spring 62 prevents the high-pressure pump 18 from operating with full delivery action, that is to say all of the fuel 12 that has flowed into the pressure chamber 32 is, as a result of immediate closure of the valve lamella 56, charged with pressure, and thus all of the elements situated downstream of the pressure chamber 32 are subjected to load.

[0061] The valve lamella 56 is designed to be so thin that the lamella is deformable. Furthermore, for the closure of the valve opening 54, the valve lamella moves along a movement direction 57 which is oriented along a longitudinal axis of the valve shank 52.

[0062] FIG. 6 and FIG. 7 show a longitudinal section through the valve arrangement 24, in the form of an inlet valve 28, in two different embodiments.

[0063] Here, FIG. 6 shows an arrangement which has the compression spring 62, whereas, in FIG. 7, the compression spring 62 has been omitted, because the valve lamella 56 itself forms a spring element 70.

[0064] The elements of the magnetic valve 42, specifically the pole piece 46 and the armature 48, and the valve shank 52 together form a movement activation arrangement 72 which may actively move the valve lamella 56. If the valve arrangement 24 is an open valve, the movement activation arrangement 72 moves the valve lamella 56 into the closed position when energized. However, if the valve arrangement 24 is designed to be closed when de-energized, the movement activation arrangement 72, when energized, moves the valve lamella 56 into the open position. For the separation of the pressure chamber 32 from a suction line 74, the valve disk 55 is provided, which valve disk separates the first valve disk side 60 on the side of the pressure chamber 32 from a second valve disk side 76 on the side of the suction line 74. The two valve disk sides 60, 76 are fluidly connected to or in fluid communication with one another by the valve opening 54. To shut off the fluidic connection, the valve lamella 56 is provided, which is deformable such that the lamella may bear closely against the valve disk surface on the first valve disk side 60 in order to thereby sealingly close off the valve opening 54.

[0065] By virtue of the fact that the valve shank 52 and the valve lamella 56 are firmly fastened to one another, it may be achieved that the pole piece 56 and the armature 48, which is connected to the valve shank 52, are spaced apart from one another in all operating positions of the valve arrangement 24. Specifically, if the valve shank 52 is so short that the armature 48 fastened thereto does not strike the pole piece 46 when the valve opening 54 is fully closed by the valve lamella 56, a permanent spacing 64 between the pole piece 46 and the armature 48 is realized. In this way, a loud impacting noise during the operation of the valve arrangement 24 may be prevented.

[0066] FIG. 6 and FIG. 7 show embodiments in which the valve arrangement is designed as a valve which is open when de-energized. Here, in FIG. 6, when the valve arrangement 24 is in the rest position, the compression spring 62 holds the armature 48 with a maximum spacing 64 to the pole piece 46, and thus holds the valve lamella 56 in the open position.

[0067] By contrast, no compression spring 62 is provided in FIG. 7, it rather being the case that the valve lamella 56 itself is in the form of a spring element 70, the spring force of which acts counter to a force acting on the valve lamella 56 from the pressure chamber 32, and the valve lamella thus holds itself open. In this way, the compression spring 62 between armature 48 and pole piece 46 is omitted.

[0068] If the valve lamella 56 was not connected to the valve shank 52, and the valve lamella 56 was not in the form of a spring element 70, this relieving of the downstream elements of load would function only until the valve shank 52 experiences a malfunction, for example a breakage. As a result of a breakage, the valve shank 52, because the valve shank is not connected to the valve lamella 56, would no longer be able to hold the valve lamella in the open position, and the valve lamella 56 would immediately close as soon as only a low pressure is built up in the pressure chamber 32. As a result, the high-pressure pump 18 would impart a full delivery action. This normally makes it necessary to provide a safety valve which relieves the downstream elements of load in the event of the high-pressure pump 18 imparting a full delivery action.

[0069] Provision is, however, now made for the valve shank 52 to be connected to the valve lamella 56, and for the valve lamella 56 to be formed as a spring element 70. Now, if the valve shank 52 breaks, the valve arrangement 24 remains permanently in the open state, such that it is not possible for an excessive pressure to act on the following elements downstream of the pressure chamber 32. This is because the high-pressure pump 18 no longer imparts a full delivery action, it rather being the case that the valve lamella 56 remains permanently in the open position, such that pressurized fuel 12 may flow back again to the suction line 74 and does not exert load on those elements of the fuel injection system 10 which are situated downstream of the high-pressure pump 18.

[0070] It is thus possible to dispense with an additional safety valve which relieves the system of load when the high-pressure pump 18 imparts a full delivery action.

[0071] An additional advantage is that, when the energization of the valve arrangement 24 has ended, the spring force of the spring element 70 has the effect that the valve shank 52 no longer strikes the valve disk 55 at such a high speed, because the impacting speed and thus the energy is lower. This also contributes to a reduction of the generation of noise by the valve arrangement 24.

[0072] To ensure the above-described functionality of the valve arrangement 24 even in the event of malfunctions of the valve shank 52, it is advantageous if, here, the spring force of the valve lamella 56 is configured so as to be greater than the maximum hydraulic force exerted on the valve lamella 56 by the pressurized fuel 12. As a result, when not moved by the movement activation arrangement 72, the valve lamella 56 remains permanently in the open position, such that it is not possible for the high-pressure pump 18 to impart a full delivery action. In this way, it is, for example, also possible to dispense with a further safety valve, because even in the event of a breakage of the valve shank 52, the valve lamella 56 remains in the open position.

[0073] The valve lamella 56 may, for stabilization, also be advantageously connected at least in sections at a circumferential edge 78 to the valve disk 55.

[0074] FIG. 8 to FIG. 18 schematically show different embodiments for fixing the valve shank 52 to the valve lamella 56. In all embodiments, the valve shank 52 is advantageously connected to the valve lamella 56 such that an end 79, facing toward the first valve disk side 60 of the valve shank 52, is arranged in a central region 81 of the valve lamella 56.

[0075] Here, FIG. 8 shows a screw connection 80, in which a screw element 82 engages through the valve lamella 56 proceeding from a first valve lamella side 84, facing away from the second valve disk side 76, and bears against the valve lamella 56. The screw element 82 is then screwed into the valve shank 52.

[0076] FIG. 9 shows an embodiment in which the valve shank 52 is connected to the valve lamella 56 by a welded connection 86. Here, a weld seam 88 of the welded connection 86 is arranged so as to be situated on a second valve lamella side 90 situated opposite the first valve lamella side 84, so as to exert a pressure on the valve lamella 56 such that the valve openings 54, which would be closed off by the valve lamella 56, remain open. By virtue of the fact that the end 79 of the valve shank 52 is arranged in the central region 81 of the valve lamella 56, and by virtue of the fact that the weld seam 88 exerts a pressure on the valve lamella 56, the valve lamella 56 is preloaded and acts as a spring element 70 counter to a force acting on the valve lamella 56 from the first valve lamella side 84.

[0077] FIG. 10 to FIG. 16 schematically show embodiments with sleeve-shaped receiving elements 92 which are used to connect the valve shank 52 to the valve lamella 56.

[0078] Here, in FIG. 10, the sleeve-shaped receiving element 92 is formed by a sleeve 94 which is fastened to the first valve lamella side 84. Here, FIG. 11 shows a bead 96 which is arranged as a sleeve-shaped receiving element 92 on the valve lamella 56 and at which the valve shank 52 is crimped, and thus connected by a form fit, to the receiving element 92. As shown in FIG. 12, a valve lamella opening 98 is provided in the valve lamella 56 in the central region 81, wherein the valve shank 52 is then in engagement with the opening walls 100 of the valve lamella opening 98. FIG. 13 shows an embodiment in which a punched-out or otherwise outwardly bent portion 102 is formed as the sleeve-shaped receiving element 92 on the valve lamella 56. In FIG. 14, as the sleeve-shaped receiving element 92, a circlip 104 is in engagement with the valve shank 52. FIG. 15 shows an arrangement in which an additional clip element 106 is the sleeve-shaped receiving element 92, which clip element is clipped into a valve lamella opening 98 of the valve lamella 56 in the central region 81, and into which clip element the valve shank 52 is inserted. FIG. 16 also shows a sleeve-shaped receiving element 92 which is welded to the valve lamella 56, wherein here, however, the valve disk 55 is of angled form, such that a spring force of the deformable valve lamella 56 is automatically realized without the valve lamella 56 having to be preloaded. FIG. 17 and FIG. 18 show valve lamellae 56 which are formed integrally with the valve shank 52. In FIG. 19, the valve lamella 56 has an engagement shank 108 which is welded to the valve lamella 56 and which engages through the valve opening 54 into a recess 110 of the valve shank 52. It is advantageous for the engagement shank 108 to also engage through the valve lamella 56 and to be fastened to the valve lamella 56 both at a first valve lamella surface 112 and at a second valve lamella surface 114.

[0079] By way of the valve arrangement 24 described above, the component costs in some embodiments may be lowered because the compression spring 62 is omitted and, for example, it is also possible for a holder for the valve lamella 56 to be omitted. It is thus the case, in general, that the risk of failure of the high-pressure pump 18 is lowered. Furthermore, it is also possible for the machining costs to be lowered because, for example, owing to the permanent spacing 64 of the pole piece 46 and armature 48, the two elements no longer require a chromium coating and ground portions. The generation of noise by the valve arrangement 24 during operation may also be considerably reduced overall. Since it is possible to realize lower power consumption during operation, it is also possible for the switching time to be optimized, and also to realize an optimization of the calibration on the vehicle. Altogether, the robustness of the valve arrangement 24 and thus also of the high-pressure pump 18 are increased. It is also possible for hydraulic pulsations in the low-pressure region to be reduced, and a safety valve that is normally provided may be omitted. It is also achieved that the power consumption is reduced, because the valve arrangement 24 no longer has to be switched to the full extent because, through the use of the valve lamella 56 in the embodiment as a spring element 70, the stroke is greatly reduced. In this way, it may be achieved that the vehicle calibration no longer has to be calibrated to that point in the current profile at which the armature 48 strikes the pole piece 46, but rather merely has to be calibrated to the point at which the valve lamella 56 is situated fully in the closed position thereof. Since the chromium layer on the pole piece 46 and armature 48 may be omitted, it is also the case that wear no longer occurs here. Furthermore, failures at the compression spring 62, or at a holding element that has acted as a stopper for the previously loose valve lamella 56, may no longer occur. The safety valve may be omitted entirely, or no longer has to be designed for robustness, because the safety valve only has to be designed for special cases such as, for example, the “hot soak” of the high-pressure pump 18. The pulsations in the low-pressure region are significantly reduced because the pole piece 46 and the armature 48 now no longer strike one another during switching, and thus the medium situated in between no longer has to be displaced to zero.

[0080] During the manufacturing process, it is possible for the valve shank 52 to be installed into a complete valve arrangement element in advance, wherein then, the valve lamella 56 together with the installed valve shank 52 is pushed through the valve disk 55. The arrangement may then be inserted as an entire element into the pump housing of the high-pressure pump 18.

[0081] It is furthermore also possible for the valve disk 55 to be fixedly incorporated as a constituent part of the housing, which is more robust with respect to high combustion chamber pressures. Here, it is then the case that the valve lamella 56 with the valve shank 52 installed thereon is inserted from the high-pressure side, that is to say from the direction of the pressure chamber 32, and the other elements of the valve arrangement 24 are inserted from the other side, specifically from the direction of the suction line 74.

[0082] As a third possibility, it is also possible for the valve disk 55 to be inserted, with a preassembled assembly composed of valve shank 52 and valve lamella 56, into the structural space, for a supporting ring to then be pushed in, and for such supporting ring to be fixed by a weld seam.

[0083] It is particularly advantageous if, in the de-energized state, the valve lamella 56 is no longer planar but has a concave internal stress, that is to say a spring force. The internal stress is advantageously of such a magnitude that the backflowing medium in the pressure phase cannot push the valve lamella 56 back. The preload makes it possible, in a partial delivery situation, for a flow cross section for backflowing medium to be kept free.

[0084] Embodiments have been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The description above is merely exemplary in nature and, thus, variations may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.