HIGH-PRESSURE PUMP FOR A FUEL SYSTEM OF AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to a high-pressure pump for a fuel system of an internal combustion engine, having at least one inlet valve device with a valve element, a valve seat for the valve element, and an actuating tappet which can positively push the valve element in an opening direction. In order to create a high-pressure pump for a fuel system of an internal combustion engine which can be produced even more cost-effectively and which has a lower level of wear and therefore a longer service life, it is proposed that the valve element have a positioning mechanism which centers the valve element on the valve seat when the valve element comes into contact or is in contact with the valve seat.

Description

PRIOR ART

The invention relates to a high-pressure pump for a fuel system of an internal combustion engine, having at least one inlet valve device with a valve element, a valve seat for the valve element, and an actuation tappet, which can press the valve element by force in an opening direction.

It is known to embody high-pressure pumps with such inlet valve devices, also known as quantity control valves. Such known quantity control valves have means for precise radial guidance of an actuation tappet and typically include a valve element with a flat seat. Moreover, for varying a pumping rate of the high-pressure pump, they can either be kept in an open position, or put into such an open position by force, by means of current supplied to an electromagnetic actuation device. Such quantity control valves are therefore also called quantity control valves that are closed when without current.

DISCLOSURE OF THE INVENTION

It is the object of the invention to create a high-pressure pump for a fuel system of an internal combustion engine that can be produced even more economically and that has low wear and thus a longer service life.

This object is attained by a high-pressure pump having the characteristics of claim 1. Advantageous refinements are recited in dependent claims. Characteristics important to the invention are also found in the ensuing description and the drawings, and the characteristics may be important alone or in various combinations, without explicit reference to this being made again.

In the realization of the high-pressure pump of the invention, by means of the more-precise positioning of the valve element relative to the valve seat, a more-uniform fluid flow over the entire circumference of the valve element is attained. This leads to reduced turbulence of a fuel flowing past the valve element, resulting in a higher flow rate when the inlet valve device is open.

It is especially preferred that the positioning means include a spherical, preferably spherical-segmental first contact region that is present on the valve element. A spherical shape of the valve element makes it possible to lessen the flow deflection when the inlet valve device is open, so that the flow rate can be increased further. Moreover, with the aid of a spherical or spherical-segmental contact region, the positioning means can be realized especially simply. In particular, no additional components have to be provided.

On the other hand, it can also be provided that the positioning means include a conical first contact region that is present on the valve element. In this way, a high-pressure pump that can be produced simply, quickly and economically can be furnished.

It is furthermore preferred that the positioning means include a second contact region, present on the valve seat, that is embodied as complementary to the first contact region and/or conically. As a result, a reliable, replicable closure of the inlet valve device with little wear and thus great durability is attained. If the first contact region of the valve element is embodied as spherical and the second contact region of the valve seat is embodied conically, then complicated manufacturing steps, such as grinding operations, are not necessarily required.

The actuation tappet can be supported in “overhung” fashion with radial play in a housing of the inlet valve device or of the high-pressure pump. Thus a precise radial guidance of the actuation tappet is dispensed with, which makes production simpler. As a result, because of the reduced friction, better axial mobility of the actuation tappet and hence a fast-switching inlet valve device are obtained. Moreover, the components required for the radial guidance can be dispensed with, so that the number of parts and thus the production costs of the high-pressure pump are reduced.

It may be provided that the actuation tappet and the valve clement are two separate parts, which at least when the valve element is pressed by force in the opening direction are fixed radially to one another by means of radially acting fixation means. The embodiment by means of two separate parts facilitates the manufacture of these parts and their assembly. Nevertheless, with the inlet valve device open by force, decentering of the valve element and the actuation tappet relative to one another is avoided. A uniform flow around the valve element is accordingly ensured not only when the inlet valve device is opened automatically but also when it is opened by force.

The radial fixation means can include a peg on the one part and a complementary recess in the other part. This realization of the fixation means functions reliably and is low in wear. Production is especially simple if the peg is provided on the actuation tappet and the complementary recess is provided on the valve element.

It is especially preferred that the peg and the recess are conical. Such fixation means can in fact be produced especially simply and yet still function reliably, since any decentering that has occurred can be reliably eliminated.

If it is provided that on an end of the actuation tappet remote from the valve element, the pump has a damping spring, then a hard impact of the actuation tappet upon closure of the valve device is avoided. This leads to a further reduction in wear and operating noise.

It is especially preferred that on a side of the valve element remote from the actuation tappet, a valve spring is disposed, which urges the valve element in the closing direction; and that the damping spring and the valve spring cooperate in such a way that a motion of the actuation tappet in the closing direction is damped, at least beyond a defined remaining stroke. By this kind of adaptation of the damping spring and the valve spring, reliable closure of the valve device, that is, the seating of the valve element on the valve seat, is assured, and at the same time the return motion of the actuation tappet upon closure of the inlet valve device that was initially opened by force is damped.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, exemplary embodiments of the present invention are described in further detail with reference to the accompanying drawings. Identical elements have the same reference numerals and as a rule are described in detail only once. In the drawings, in schematic illustration:

FIG. 1 shows a fuel system of an internal combustion engine with a high-pressure pump in accordance with a preferred embodiment of the present invention;

FIG. 2 shows an inlet valve device of the high-pressure pump of FIG. 1 in a closed state;

FIG. 3 shows a detail of FIG. 2 for an automatically opened inlet valve device;

FIG. 4 is a view similar to FIG. 3, but with the inlet valve device opened by force; and

FIG. 5 shows a further detail of FIG. 2 for an inlet valve device opened by force.

EMBODIMENTS OF THE INVENTION

FIG. 1 shows a fuel system 1 of an internal combustion engine in a highly schematic illustration. A high-pressure pump 3 communicates with a fuel tank 9 upstream via an intake line 4, a prefeed pump 5, and a low-pressure line 7. Downstream, a high-pressure reservoir 13 (“rail” 13) is connected to the high-pressure pump 3 via a high-pressure line 11. The high-pressure pump 3 has an inlet valve device 14 with an electromagnetic actuation device 15. The inlet valve device 14 is disposed hydraulically between the low-pressure line 7 and a pump cylinder 17. Inlet openings 16 of the inlet valve device 14 are connected to the low-pressure line 7, and the pump cylinder 17 communicates with outlet openings 18 of the inlet valve device 14. The pump cylinder 17 and the high-pressure line 11 communicate with one another via an outlet valve 19 embodied as a check valve. The pump cylinder 17 and a piston 21 supported displaceably in it define a work chamber 23. The piston 19 is acted upon by an eccentric portion 25 of a drive shaft (not identified by reference numeral).

In operation of the fuel system 1, the prefeed pump 5 pumps fuel from the fuel tank 9 into the low-pressure line 7. The piston 21 moves back and forth, driven by the rotating eccentric portion 25 (arrow 27), which leads to a periodically repeating enlargement and reduction in size of the work chamber 23. If the work chamber 23 is becoming larger, the piston 21 is in an intake stroke, and fuel is then aspirated into the work chamber via the inlet valve device 15. The inlet valve device 14 opens automatically because of a pressure difference, caused by the intake stroke, between the inlet openings 16 and the outlet openings 18, and thus connects the low-pressure line to the pump cylinder 17. When the work chamber 23 is decreasing in size (piston 21 is in a pumping stroke), the fuel located in the work chamber 23 is subjected to a pressure. This pressure also acts on the inlet valve device 14 and the outlet valve 19. If the actuation device 15 of the inlet valve device 14 is not receiving current, then the inlet valve device can close automatically at the end of the intake phase, because of the force of a valve spring 45 (see FIG. 2). If the opening pressure of the outlet valve 17 is exceeded, that valve opens, so that the fuel is pumped into the high-pressure line 11.

To limit a pumping rate of the high-pressure pump 3, current can be supplied to the electromagnetic actuation device 15 during the intake stroke, so that at the beginning of the pumping stroke that follows the intake stroke as well, the inlet valve device 14 remains open by force. The fuel is then pumped back into the low-pressure line 7. If the current supply to the electromagnetic actuation device 15 is already stopped during the pumping stroke, the inlet valve device 14 closes, and the fuel that still remains in the work chamber 23 is pumped into the high-pressure line 11 via the outlet valve 19. By a choice of the instant at which the current supply to the electromagnetic actuation device 15 is ended, the effective pumping volume of a pumping stroke is thus defined.

FIG. 2 shows the construction of the inlet valve device 14. The inlet valve device has a valve element 31, a valve seat 33, and an actuation tappet 35. The actuation tappet 35 is guided radially inside a housing 37 with considerable play, of up to several tenths of a millimeter. When the inlet valve device 14 is open, the valve element 31 likewise has a radial play. In that sense, the valve element 31 and the actuation tappet 35, except in their closed terminal positions, are supported in “overhung” fashion inside the inlet valve device 14.

The inlet openings 16, which extend radially and into which fuel can flow out of the low-pressure line 7, are located in the housing 37, above the valve element 31 in terms of the illustration in FIG. 2. The inlet openings 16 extend at a right angle to a longitudinal axis 39. While in the operating state shown in FIG. 2, the actuation tappet 35 rests on a top side 41 at the valve element 31, a valve spring 45 is disposed on an underside 43 of the valve element 31; this spring is retained by a spring holder 47 structurally connected to the housing. The spring holder 47 has the outlet openings 18.

On its top side 41, the valve element 31 has a first spherical-segmental, convex contact region 49. A second contact region 51 of the valve seat 33 has a complementary spherical-segment-like and concave shape that is complementary to the shape of the first contact region 49. The two contact regions 49, 51 together form positioning means 52, which center the valve element 31 on the valve seat 33. In an embodiment not shown, the second contact region 51 is conical and the first contact region 49 is again spherical-segmental, and in a further embodiment not shown, both contact regions 49, 51 are conical. In principle, instead of a spherical-segment-like shape, some other spherical form of the first contact region 49 or of the second contact region 51 may be provided; the latter shape must be adapted to the first in order to ensure reliable closure of the inlet valve device 14.

The actuation tappet 35 has a conical peg 53 on its end oriented toward the valve element 31. There is also a recess 55 in the top side 41 of the valve element 31, the shape of which recess is complementary to the conical shape of the peg 53. The peg 53 and the recess 55 form radial fixation means 57.

On its side remote from the valve element 31, the actuation tappet 35 has an armature 59 solidly connected to it. The armature is movable back and forth inside a capsule 61 along the longitudinal axis 39. A coil 63 is disposed around the capsule 61, offset somewhat downward toward the valve element 31 relative to the armature 59, and is covered toward the outside by a housing jacket 65 and a covering disk 67. Between the armature 59 and the housing 37, there is a remanent air gap disk 69, throughout the actuation tappet 35 protrudes. The armature 59, on its side remote from the housing 37, has a recess 71, in which, depending on the operating state of the inlet valve device 14, a damping spring 73 is located either in part or entirely. The inlet valve device 14 furthermore has a plug element 75, connected electrically to the coil 63, for the electrical connection of the coil 63, for instance to an engine control unit. The inlet valve device 14 thus has a magnet group 77, which includes the plug element 75, the coil 63, the housing jacket 65, and the covering disk 67.

The mode of operation of the inlet valve device 14 will be described in further detail below in conjunction with FIGS. 2 through 5 for various operating states (closed, automatically, and open by force).

The closed state shown in FIG. 2 of the inlet valve device 14 occurs when the inlet valve device 14 is not supplied with current, or in other words no current is flowing through the coil 63, and a pressure difference between a pressure at the inlet openings 16 and a pressure at the outlet openings 18 is slight or zero. In that case, a force exerted by the valve spring 45 on the valve element 31 counter to an opening direction 79 is greater than the sum of the force exerted on the valve element 31 by the damping spring 73 via the actuation tappet 35 and the force exerted on the valve element 31 in the opening direction 79 by the pressure difference. This yields a resultant force, acting counter to the opening direction 79, which presses the valve element 31 against the valve seat 33.

If the piston 21 is in the intake stroke, then the pressure prevailing at the outlet openings 18 of the inlet valve device 14 decreases, and the pressure difference between the inlet openings 16 and the outlet openings 18 increases. If the sum of the force of the damping spring 73 and the compressive force exerted on the valve element 31 attains a value which exceeds the force of the valve spring 45, then the valve element 31 moves away from the valve seat 33, and the inlet valve device 14 opens. In the ideal case, the opening motion of the valve element 31 extends parallel to the longitudinal axis 39. However, because of transverse forces that may be caused by the valve spring 45 or by an asymmetrical flow around the valve element 31, the valve element 31 may also open in slightly tilted fashion; that is, a deviation in the opening motion, from the course that is parallel to the longitudinal axis 39, is possible. After the opening of the inlet valve device 14, the actuation tappet 35, which because of its relatively high mass in comparison to the valve element 31 is sluggish, moves somewhat toward the valve element 31, driven by the valve spring 73, but without touching the valve element. The state shown in FIG. 3 is now established.

If in operation of the high-pressure pump a pumping rate of the high-pressure pump is to be reduced, then typically current is supplied to the coil 63 already during the intake stroke. As a result of this current supply, a magnetic flux is created in the armature 59 and leads to the buildup of a magnetic force there that acts essentially parallel to the longitudinal axis 39 toward the valve element 31—that is, in the opening direction 79. Because of the magnetic force, the armature 59 together with the actuation tappet 35 moves toward the valve element 31. The farther the actuation tappet 35 moves toward the valve element 31, the more deeply does the peg 53 of the actuation tappet 35 protrude into the recess 55 in the valve element 31. As a result, a radial freedom of motion of the valve element 31 relative to the actuation tappet 35 is successively reduced, until finally, when the actuation tappet 35 is seated on the valve element 31, as shown in FIG. 4, it becomes nearly zero. The fixation means 57, formed by the peg 53 and the recess 55, thus cause the actuation tappet 35 and the valve element 31 to be radially fixed relative to one another, in the operating state in which the inlet valve device 14 is open by force.

As shown in FIG. 5, the damping spring 73, in the operating state of the inlet valve device 14 in which it is open by force, is prestressed with a slight force. In an embodiment not shown, in the operating state of the inlet valve device 14 in which it is open by force, the damping spring 73 is completely relaxed, and a gap is created on one or both ends of the damping spring 73.

If the current flowing through the coil 63 is switched off again, then the magnetic force acting on the armature 59 dissipates, and the valve spring 45 presses the valve element 31 toward the valve seat 33, parallel to the longitudinal axis 39. During the motion of the valve element 31, a radial play of the valve element 31 relative to the valve seat 33 decreases gradually, because of the spherical shape of the two contact regions 49, 51. Thus the valve element 31 is centered relative to the valve seat 35 during the closing motion.

At the end of the closing motion, the armature 59 presses the damping spring 73 against the capsule 61, so that the damping spring 73 is compressed, and the motion of the actuation tappet 35 is damped; the state of the inlet valve device 14 shown in FIG. 2 is then restored. The valve spring 45 and the damping spring 73 are adapted to one another in such a way that on the one hand, the motion of the actuation tappet 35 and of the armature 59, which together have a comparatively high mass, is damped such that the armature 59 does not strike the capsule 61 hard, and on the other, the valve device 14 reliably closes.

Claims

1-10. (canceled)

11. A high-pressure pump for a fuel system of an internal combustion engine, comprising:

at least one inlet valve device with a valve element;

a valve seat for the valve element;

an actuation tappet, which can press the valve element by force in an opening direction; and characterized in that the inlet valve device has

positioning means for the inlet valve device, which center the valve element on the valve seat when the valve element comes into contact with or when the valve element is in contact with the valve seat.

12. The high-pressure pump as defined by claim 11, wherein the positioning means include a spherical, preferably spherical-segmental first contact region that is present on the valve element.

13. The high-pressure pump as defined by claim 11, wherein the positioning means include a conical first contact region that is present on the valve element.

14. The high-pressure pump as defined by claim 11, wherein the positioning means include a second contact region, which is present on the valve seat and is embodied as complementary to the first contact region and/or conically.

15. The high-pressure pump as defined by claim 12, wherein the positioning means include a second contact region, which is present on the valve seat and is embodied as complementary to the first contact region and/or conically.

16. The high-pressure pump as defined by claim 13, wherein the positioning means include a second contact region, which is present on the valve seat and is embodied as complementary to the first contact region and/or conically.

17. The high-pressure pump as defined by claim 11, wherein the actuation tappet is supported in “overhung” fashion with radial play in a housing of the inlet valve device or of the high-pressure pump.

18. The high-pressure pump as defined by claim 14, wherein the actuation tappet is supported in “overhung” fashion with radial play in a housing of the inlet valve device or of the high-pressure pump.

19. The high-pressure pump as defined by claim 11, wherein the actuation tappet and the valve element are two separate parts, which at least when the valve element is pressed by force in the opening direction are fixed radially to one another by means of radially acting fixation means.

20. The high-pressure pump as defined by claim 14, wherein the actuation tappet and the valve element are two separate parts, which at least when the valve element is pressed by force in the opening direction are fixed radially to one another by means of radially acting fixation means.

21. The high-pressure pump as defined by claim 19, wherein the radial fixation means include a peg on the one part and a complementary recess in the other part.

22. The high-pressure pump as defined by claim 21, wherein the peg and the recess are conical.

23. The high-pressure pump as defined by claim 17, wherein on an end of the actuation tappet remote from the valve element, the pump has a damping spring.

24. The high-pressure pump as defined by claim 19, wherein on an end of the actuation tappet remote from the valve element, the pump has a damping spring.

25. The high-pressure pump as defined by claim 21, wherein on an end of the actuation tappet remote from the valve element, the pump has a damping spring.

26. The high-pressure pump as defined by claim 22, wherein on an end of the actuation tappet remote from the valve element, the pump has a damping spring.

27. The high-pressure pump as defined by claim 23, wherein on a side of the valve element remote from the actuation tappet, a valve spring is disposed, which urges the valve element in the closing direction; and that the damping spring and the valve spring cooperate in such a way that a motion of the actuation tappet in the closing direction is damped, at least beyond a defined remaining stroke.

28. The high-pressure pump as defined by claim 24, wherein on a side of the valve element remote from the actuation tappet, a valve spring is disposed, which urges the valve element in the closing direction; and that the damping spring and the valve spring cooperate in such a way that a motion of the actuation tappet in the closing direction is damped, at least beyond a defined remaining stroke.

29. The high-pressure pump as defined by claim 25, wherein on a side of the valve element remote from the actuation tappet, a valve spring is disposed, which urges the valve element in the closing direction; and that the damping spring and the valve spring cooperate in such a way that a motion of the actuation tappet in the closing direction is damped, at least beyond a defined remaining stroke.

30. The high-pressure pump as defined by claim 26, wherein on a side of the valve element remote from the actuation tappet, a valve spring is disposed, which urges the valve element in the closing direction; and that the damping spring and the valve spring cooperate in such a way that a motion of the actuation tappet in the closing direction is damped, at least beyond a defined remaining stroke.