High-Pressure Pump for a Fuel Injection System of an Internal Combustion Engine

Abstract

A high-pressure pump having at least one pump element, with a pump piston which is driven in a reciprocating motion and is guided displaceably in a cylinder bore of a pump housing part and which in the cylinder bore defines a pump work chamber that can be filled with fuel via a suction valve in the intake stroke of the pump piston. The suction valve has a valve member, which opens into the pump work chamber and cooperates with a valve seat. In its end region toward the suction valve, the pump piston has a blind bore, into which the valve member of the suction valve plunges, and in which a closing spring is disposed, which acts on the valve member and is braced on one end on the pump piston and on the other on the valve member. The valve member is guided displaceably in the blind bore of the pump piston.

Description

PRIOR ART

The invention is based on a high-pressure pump for a fuel injection system of an internal combustion engine as generically defined by the preamble to claim 1.

One such high-pressure pump is known from German Patent Disclosure DE 198 48 035 A1. This high-pressure pump has at least one pump element, with a pump piston which is driven in a reciprocating motion and is guided displaceably in a cylinder bore and in that bore defines a pump work chamber. The pump work chamber can be filled with fuel via a suction valve. The suction valve has a valve member, opening into the pump work chamber, that cooperates with a valve seat. The pump piston, in its end region toward the suction valve, has a blind bore into which the valve member of the suction valve plunges, and in which a closing spring acting on the valve member is disposed that is braced on one end on the pump piston and on the other on the valve member. The valve member has a shaft, which is surrounded by the closing spring and with which the valve member is guided displaceably in the closing spring. The outside diameter of the closing spring is only slightly smaller than the diameter of the blind bore in the pump piston, so that the closing spring is guided in the blind bore of the pump piston. In this embodiment, there is accordingly only an imprecise guidance of the valve member, which is disadvantageous for the function of the suction valve. This can in turn impair the filling of the pump work chamber and can thus impair the overall function of the high-pressure pump.

ADVANTAGES OF THE INVENTION

The high-pressure pump of the invention having the characteristics of claim 1 has the advantage over the prior art that the valve member of the suction valve is guided precisely in the pump piston, and as a result the function of the suction valve and hence of the high-pressure pump is improved.

In the dependent claims, advantageous features and refinements of the high-pressure pump of the invention are recited. The version shown in claim 3 makes a long guidance length of the valve member in the blind bore possible, while at the same time enabling a space-saving disposition of the closing spring. The version according to claim 4 makes it possible to fill and evacuate the spring chamber during the motion of the valve member, and by suitable dimensioning of the at least one opening in the valve member, its opening and/or closing motion can be varied in a purposeful way. The embodiment according to claim 5 makes very precise guidance of the valve member relative to the valve seat possible, since the cylinder bore for the pump piston and the valve seat can both be produced in the same piece of manufacturing equipment and can therefore be aligned very precisely to one another.

DRAWING

One exemplary embodiment of the invention is shown in the drawing and described in further detail in the ensuing description.

FIG. 1 shows a high-pressure pump for a fuel injection system of an internal combustion engine in a longitudinal section;

FIG. 2 shows a detail, marked II in FIG. 1, of the high-pressure pump with a suction valve in the open state; and

FIG. 3 shows the detail II with the suction valve in the closed state.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIGS. 1 through 3, a high-pressure pump for a fuel injection system of an internal combustion engine is shown. The high-pressure pump has a pump housing 10, in which a drive shaft 12, which can be driven to rotate by the engine, is rotatably supported, for instance via two bearing points spaced apart from one another axially. In a region located between the two bearing points, the drive shaft 12 has at least one portion that is eccentric to its pivot axis 13, or cam 16; the cam 16 may also be embodied as a multiple cam. The high-pressure pump has at least one, or more, pump elements 18 disposed in the pump housing 10, each with a pump piston 20 that is driven in a reciprocating motion by the eccentric portion or the cam 16 of the drive shaft 12, in a direction that is at least approximately radial to the pivot axis 13 of the drive shaft 12.

The pump piston 20 is guided tightly displaceably in a cylinder bore 22 that is embodied in the pump housing 10, and with its face end remote from the drive shaft 12, the pump piston defines a pump work chamber 24 in the cylinder bore 22. Via a fuel delivery conduit 26 extending in the pump housing 10, the pump work chamber 24 has a communication with a fuel delivery means, such as a feed pump 14. At the mouth of the fuel delivery conduit 26 into the pump work chamber 24, there is a suction valve 28 which opens into the pump work chamber 24. Via a fuel outflow conduit 30 extending in the pump housing 10, the pump work chamber 24 also has a communication with an outlet, which for instance communicates with a high-pressure reservoir 110. One or preferably more injectors 120 disposed at the cylinders of the engine communicate with the high-pressure reservoir 110, and through them fuel is injected into the cylinders of the engine. At the mouth of the fuel outflow conduit 30 into the pump work chamber 24, there is an outlet valve 32 that opens out of the pump work chamber 24.

Between the pump piston 20 and the eccentric portion or cam 16 of the drive shaft 12, a support element may be disposed, in the form of a tappet 34, by way of which the pump piston 20 is braced at least indirectly on the cam 16. The pump piston 20 is coupled to the tappet 34 in a manner not shown in detail in the direction of its longitudinal axis 21. The tappet 34 may be braced directly on the eccentric portion or cam 16. The tappet 34 is displaceably supported in the pump housing 10 in a bore 36 and absorbs transverse forces that occur upon the conversion of the rotary motion of the drive shaft 12 into the reciprocating motion of the pump piston 20, so that these forces do not act on the pump piston 20. The tappet 34 is engaged by a prestressed restoring spring 38, by which the tappet 34 and the pump piston 20 connected to it are pressed toward the cam 16.

The suction valve 28 will now be described in further detail, referring to FIGS. 2 and 3. The cylinder bore 22 of the pump housing 10 is adjoined, toward the outside of the pump housing 10 facing away from the drive shaft 12, by a bore 40 in the pump housing 10, which is at least approximately coaxial with the cylinder bore 22 and has a smaller diameter than the cylinder bore 22. At the transition from the cylinder bore 22 to the bore 40, an annular shoulder is formed, on which a valve seat 42 is embodied, which is for instance at least approximately frustoconical. The bore 40 discharges into the fuel delivery conduit 26. The suction valve 28 has a valve member 44, which is disposed in the pump work chamber 24 and which cooperates with the valve seat 42 for controlling the communication of the pump work chamber 24 with the fuel delivery conduit 26. The valve member 44 is embodied as piston-like and cup-shaped, and the closed end of the valve member 44 is oriented toward the valve seat 42. The valve member 44 has a sealing face 45, which is for instance at least approximately frustoconical, and with which it cooperates with the valve seat 42.

The pump piston 20, in its end region oriented toward the valve seat 42, has a blind bore 46, which extends at least approximately coaxially with the longitudinal axis 21 of the pump piston and into which the valve member 44 of the suction valve 28 plunges with its open end. The valve member 44, over a large portion of its length, is guided displaceably, with slight radial play, in the blind bore 46 in the pump piston 20. By means of the pump piston 20 and the valve member 44, a spring chamber 48 is defined in the blind bore 46; a closing spring 50 of the suction valve 28 is disposed in this spring chamber, braced on one end on the bottom of the blind bore 46 on the pump piston 20 and on the other on the valve member 44. The closing spring 50 is embodied as a helical compression spring and protrudes into the valve member 44 and is braced in it on an annular shoulder formed by a reduction of the inside cross section of the valve member 44. By means of the closing spring 50, the valve member 44 is pressed toward the valve seat 42.

In the valve member 44, at least one opening 52 is provided, through which the spring chamber 48 communicates with the pump work chamber 24. The at least one opening 52 makes it possible to fill and evacuate the spring chamber 48 upon a motion of the valve member 44 relative to the pump piston 20, and by the dimensioning of the at least one opening 52, the flow rate in the filling and evacuation of the spring chamber 48 can be varied.

In the intake stroke of the pump piston 20, in which the pump piston together with the tappet 34 is moved radially inward by the restoring spring 38, a low pressure prevails in the pump work chamber 24, and thus the suction valve 28 opens in that its valve member 44, with its sealing face 45, lifts from the valve seat 42, since because of the pressure prevailing in the fuel delivery conduit 26, a greater force is generated in the opening direction than the total of the force of the closing spring 50 and of the force generated by the pressure prevailing in the pump work chamber 24. In FIG. 2, the suction valve 28 is shown in the open state, during the intake stroke of the pump piston 20. From the fuel delivery conduit 26, with the suction valve 28 open, fuel flows into the pump work chamber 24. Upon the intake stroke of the pump piston 20, this piston, together with the closing spring 50 braced on it, moves away from the valve seat 42 of the suction valve 28, so that the prestressing of the closing spring 50 is lessened. The suction valve 28 therefore already opens at a lesser pressure difference between the fuel delivery conduit 26 and the pump work chamber 24. By suitable dimensioning of the at least one opening 52 in the valve member 44, it can be attained that the spring chamber 48 can fill only slowly with fuel, as a result of which, in the intake stroke of the pump piston 20, the valve member 44 is moved with the pump piston 20, and as a result, fast and wide opening of the suction valve 28 is assured. The valve member 44 is guided displaceably in the blind bore 46 with high precision coaxially with the valve seat 42, since the cylinder bore 22, in which the pump piston 20 is guided, and the valve seat 42 are embodied in the same pump housing 10. As a result, upon closing, the valve member 44, with its sealing face 45, securely comes to rest on the valve seat 42 and thus reliably closes.

At low pressure in the pump work chamber 30 during its filling, the outlet valve 38 is closed. In the pumping stroke of the pump piston 20, in which the pump piston together with the tappet 34 moves radially outward, fuel in the pump work chamber 24 is compressed by the pump piston 20, so that because of the increased pressure in the pump work chamber 24, the suction valve 28 closes, while fuel at high pressure is pumped through the fuel outflow conduit 30, with the outlet valve 32 open, to the high-pressure reservoir 110. In FIG. 3, the suction valve 28 is shown in the closed state, during a pumping stroke of the pump piston 20.

As an alternative to the version described above, it may also be provided that the valve seat 42 is embodied on some other part of the pump housing 10 than the cylinder bore 22 in which the pump piston 20 is guided. In that case, however, it must be assured that the part of the pump housing 10 on which the valve seat 42 is embodied is aligned very precisely relative to the part of the pump housing 10 in which the cylinder bore 22 is embodied, so as to achieve the requisite coaxial alignment of the valve seat 42 with the cylinder bore 22.

Claims

1-5. (canceled)

6. In a high-pressure pump for a fuel injection system of an internal combustion engine, the high-pressure pump having at least one pump element, which has a pump piston driven in a reciprocating motion and guided displaceably in a cylinder bore of a pump housing part, the piston in the cylinder bore defining a pump work chamber that can be filled with fuel via a suction valve in the intake stroke of the pump piston, the suction valve having a valve member opening into the pump work chamber and cooperating with a valve seat, and the pump piston, in its end region oriented toward the suction valve having a blind bore into which the valve member of the suction valve plunges and in which a closing spring, acting on the valve member is disposed, the closing spring being braced on one end on the pump piston and on the other on the valve member, the improvement wherein the valve member is guided displaceably in the blind bore of the pump piston.

7. The high-pressure pump as defined by claim 6, wherein the closing spring in the blind bore is disposed in a spring chamber defined by the pump piston and the valve member.

8. The high-pressure pump as defined by claim 7, wherein the valve member is embodied as cup-shaped and protrudes with its open end into the blind bore in the pump piston; wherein the closing spring protrudes into the valve member; and wherein the valve member, with its closed end protruding out of the blind bore, cooperates with the valve seat.

9. The high-pressure pump as defined by claim 8, wherein the valve member has at least one opening through which the spring chamber communicates with the pump work chamber.

10. The high-pressure pump as defined by claim 6, wherein the valve seat is embodied in the same pump housing part as the cylinder bore in which the pump piston is guided.

11. The high-pressure pump as defined by claim 7, wherein the valve seat is embodied in the same pump housing part as the cylinder bore in which the pump piston is guided.

12. The high-pressure pump as defined by claim 8, wherein the valve seat is embodied in the same pump housing part as the cylinder bore in which the pump piston is guided.

13. The high-pressure pump as defined by claim 9, wherein the valve seat is embodied in the same pump housing part as the cylinder bore in which the pump piston is guided.