CN118414484A - Piston pump - Google Patents

Abstract

A piston pump (10), in particular a high-pressure fuel pump, comprises a pump housing (16), a pump piston (20), a housing-side guide section (18), in which the pump piston (20) is guided, and at least one first sealing device (38), which seals the pump piston (20) relative to the guide section (18), wherein the sealing device (38) comprises at least one sealing ring (40), which is arranged in a circumferential groove (30) in the pump piston (20). It is proposed that the sealing device (38) comprises a preload device (50), which loads the sealing ring (40) against a side wall (36) of the groove (30).

Description

Piston pump

Technical Field

The invention relates to a piston pump according to the preamble of claim 1 .

Background technique

Piston pumps are known on the market, which belong to the fuel injection system of an internal combustion engine. These piston pumps include a pump housing with a guide section provided by a piston bushing, in which the pump piston is guided movably. The seal between the pump piston and the guide section is achieved on the one hand by a gap seal and additionally by a sealing device. The sealing device includes a sealing ring, which is arranged in a circumferential groove of the pump piston and moves with the pump piston relative to the guide section.

Summary of the invention

The problem on which the invention is based is achieved by a fuel pump having the features of claim 1. Advantageous developments are given in the dependent claims.

The piston pump according to the invention has the advantage that the axial play of the sealing ring in the groove is reduced in the piston pump. Without the preload device provided according to the invention, this axial play would result in the sealing ring not being in contact with the side wall of the groove and therefore not being in contact with the sealing surface of the pump piston at the reversal point of the movement of the pump piston between the suction stroke and the delivery stroke. This would result in leakage at the beginning of the delivery stroke, which would reduce the volumetric efficiency of the piston pump.

In the piston pump according to the invention, however, the sealing ring rests reliably against a side wall of the groove in the pump piston during every movement phase or operating situation of the pump piston, so that the desired seal is present at all times. The sealing ring thus contacts the side wall immediately at the start of the desired delivery and does not reach the sealing position only after the piston has passed through the idle stroke. The contact forces with the side wall and with the guide section can be low, since the pressure build-up and thus the hydraulic contact forces also ensure the necessary seal. For this purpose, it is advantageous if the corresponding contact gap is relatively small, for example less than approximately 5 μm.

The preload force of the preload device should be selected in such a way that the friction between the sealing ring on the one hand and the mating surface on the guide section on the other hand is overcome at all times. Wear of the sealing ring that occurs during normal operation also does not lead to a loss in the volumetric efficiency of the piston pump. Therefore, the entire piston stroke is always utilized for delivery, which leads to a high volumetric efficiency of the piston pump. Since the axial wear of the sealing ring is compensated according to the invention, materials can also be used for the sealing ring that were previously not conceivable due to wear.

This is achieved in particular by means of a piston pump, in particular a high-pressure fuel pump for a fuel injection system of an internal combustion engine. Such piston pumps are used both in diesel and gasoline internal combustion engines. Usually, the piston pump compresses the fuel to a very high pressure and delivers it to a fuel collecting line ("rail"), from which the fuel is injected directly into the corresponding combustion chamber of the internal combustion engine by means of an injector.

The piston pump according to the invention comprises a pump piston which is accommodated in a guide section on the housing side, for example a piston bushing which is pressed into the housing body of the pump housing, for example. The pump housing, together with the pump piston and possibly also with other components, delimits a delivery chamber in which the fuel can be compressed.

The pump piston comprises a sealing device in the form of at least one sealing ring, which is arranged in a circumferential groove in the pump piston. The sealing device also comprises a preload device, which loads the sealing ring against the side walls of the groove. In the present case, the side walls of the groove are understood to be walls that extend substantially orthogonally to the longitudinal axis of the pump piston. The sealing ring is thus pressed against the side walls of the groove by the preload device in the direction of the longitudinal axis of the pump piston, whereby, viewed in the direction of the longitudinal axis of the pump piston, the sealing ring always maintains its axial orientation independently of the direction of movement of the pump piston and rests sealingly against the side walls.

In one embodiment, the preload device loads the sealing ring against a side wall facing away from the delivery chamber. That is, the preload device acts facing away from the delivery chamber, as viewed in the direction of the longitudinal axis of the pump piston. This has the advantage that the sealing ring mainly rests during the delivery stroke, during which particularly high pressure drops must be sealed by the sealing ring, against the side wall of the groove against which it is pressed anyway due to the movement of the pump piston and the friction between the sealing ring and the guide section. The preload device can be correspondingly simpler and have a lower preload force.

In one embodiment, it is provided that the prestressing device comprises a steel spring. This is inexpensive and ensures the function according to the invention independently of the fuel and even at high temperatures.

In one embodiment, the preload device comprises a corrugated spring and/or a disc spring. Viewed in the circumferential direction of the sealing ring, the two springs distribute the preload force relatively evenly, which is beneficial to the service life of the sealing ring. If a disc spring is used, it should be ensured that there is no complete seal between the sealing ring and the disc spring.

In one embodiment, the preload device is integrated into the sealing ring. This can significantly simplify assembly. Thus, by such integration, two functions can be implemented in one component, namely sealing and preload. For example, a steel spring can be integrated into a plastic sealing ring as an insert.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are explained below with reference to the accompanying drawings. In the drawings:

FIG. 1 shows a longitudinal section through a piston pump with a pump piston and a sealing arrangement; and

FIG. 2 shows a schematic cross-sectional view of the pump piston and the sealing arrangement of FIG. 1 .

Detailed ways

A piston pump in the form of a high-pressure fuel pump is generally designated in Figure 1 by reference numeral 10. The piston pump 10 belongs to a fuel system (not shown in greater detail) of an internal combustion engine. The piston pump usually delivers fuel to a fuel rail to which a plurality of injectors are attached, which inject the fuel into the combustion chambers of the internal combustion engine.

The piston pump 10 comprises a controllable inlet valve 12 and an outlet valve 14 configured as a non-return valve, as well as a pump housing 16. In the pump housing there is a piston bushing 18, in which a pump piston 20 is guided in a sliding manner. The piston bushing 18 is pressed, for example, into a housing body (without reference numerals) of the pump housing 16. In this respect, the piston bushing 18 forms a housing-side guide section for the pump piston 20. The pump piston 20 can move in the piston bushing 18 parallel to the longitudinal axis 22 of the piston bushing 18. A drive not shown in the drawings is used for this purpose. The drive can be, for example, a camshaft or an eccentric shaft of an internal combustion engine. The longitudinal axis 22 of the piston bushing 18 is at least approximately also the longitudinal axis of the pump piston 20.

In the present case, the pump piston 20 is designed as a stepped piston, which comprises a section 24 with a smaller diameter and a section 26 with a larger diameter. The section 26 with a larger diameter of the pump piston 20 delimits a delivery chamber 28 together with the pump housing 16. The delivery chamber is fluidically connected to the inlet valve 12 and the outlet valve 14 via a channel (not shown in detail). The pump housing 16 can be designed as a generally rotationally symmetrical component.

The section 26 of the pump piston 20 with the larger diameter is also the section with which the pump piston 20 is guided in a sliding manner in the piston bushing 18. In this section 26, in the present example over approximately half of its axial length, there is a groove 30 which is continuous and circumferential in the circumferential direction of the pump piston 20. In the present example, the groove 30 has an approximately rectangular cross section with a first side wall 32, a groove bottom 34 and a second side wall 36.

The first side wall 32 is a side wall that is closer to the delivery chamber 28 than the second side wall 36, and the second side wall 36 is a side wall that is farther from the delivery chamber 28 (i.e., further away from the delivery chamber) than the first side wall 32. The two side walls 32 and 36 extend at least approximately orthogonally to the longitudinal axis 22 of the pump piston 20. The groove bottom 34, on the other hand, extends at least approximately parallel to the longitudinal axis 22 of the pump piston 20.

A sealing device 38 is arranged in the groove 30. In the present case, the sealing device 38 comprises, by way of example, a sealing ring 40 which is continuous in the circumferential direction of the pump piston 20. The sealing ring 40 can be made of a plastic material, for example. In the present case, by way of example, the sealing ring has an at least approximately rectangular cross section, which has a first side wall 42, an inner peripheral wall 44, a second side wall 46 and an outer peripheral wall 48. The two side walls 42 and 46 extend at least approximately orthogonally to the longitudinal axis 22 of the pump piston 20. The two peripheral walls 44 and 48 extend at least approximately parallel to the longitudinal axis 22 of the pump piston 20. The first side wall 42 is the wall of the sealing ring 40 which is closer to the conveying chamber 28, and the second side wall 46 is the side wall which is further from the conveying chamber 28 (i.e., away from the conveying chamber) than the first side wall 42.

Compared to the diameter of the groove bottom 34, the inner diameter of the sealing ring 40 is selected such that there is a certain small gap relative to the groove bottom 34 of the groove 30. This ensures that the sealing ring 40 rests with its outer circumferential wall 48 in a sealing manner on the inner circumferential wall (without reference numeral) of the piston bushing 18 uniformly and with the same force when viewed in the circumferential direction, and more precisely, independently of the radial position of the pump piston 20.

The sealing device 38 also includes a preload device 50, which is arranged in the present example in such a way that it loads the sealing ring 40 with its second side wall 46 against the second side wall 36 of the groove 30, so that the sealing ring always rests there in a sealing manner. The preload device 50 is only shown symbolically in the figures. It can, for example, include a plurality of helical springs arranged evenly distributed in the circumferential direction, which engage the sealing ring 40 either directly or via a relatively rigid annular element connected in between.

Alternatively, the preload device 50 comprises a corrugated spring, more precisely a corrugated spring either in the form of a single corrugated spring ring or as a cylindrical corrugated spring with nested turns. In principle, the use of a disk spring is also conceivable, provided that no seal is provided between the sealing ring 40 and the spring. In this case, a relatively rigid annular element can also be interposed between the sealing ring 40 and the corrugated spring or the disk spring in order to apply the force of the spring uniformly to the sealing ring 40.

Preferably, a steel material is used for the preload device 50, which is resistant to many different fluids, is temperature-resistant and can permanently apply the necessary spring preload force over the service life of the piston pump 10. Preferably, the preload force of the preload device 50 in the direction of the longitudinal axis 22 of the pump piston 20 is selected such that the friction forces between the sealing ring 40 and the piston bushing 18 are overcome during the movement of the pump piston 20 and the sealing ring 40 thus rests with its second side wall 46 against the second side wall 36 of the groove 30 at all times, that is, regardless of the movement direction or movement state of the pump piston 20.

In the presently depicted embodiment of the piston pump 10 , the groove 30 and the sealing ring 40 both have an overall approximately rectangular cross section. Of course, other suitable cross sections are also conceivable in principle. In particular, the sealing ring 40 can have an oval or circular cross section.

Claims (5)

1. A piston pump (10), in particular a high-pressure fuel pump, comprising a pump housing (16), a pump piston (20), a housing-side guide section (18), and at least one first sealing device (38), in which the pump piston (20) is guided, the first sealing device sealing the pump piston (20) relative to the guide section (18), wherein the sealing device (38) comprises at least one sealing ring (40), which is arranged in a circumferential groove (30) in the pump piston (20), characterized in that the sealing device (38) comprises a preload device (50), which loads the sealing ring (40) against a side wall (36) of the groove (30). 2. The piston pump (10) according to claim 1, characterized in that the preload device (50) loads the sealing ring (40) against a side wall (36) facing away from the delivery chamber (28). 3. The piston pump (10) according to at least one of the preceding claims, characterized in that the prestressing device (50) comprises at least one steel spring. 4. The piston pump (10) according to at least one of the preceding claims, characterized in that the prestressing device (50) comprises a corrugated spring and/or a disc spring. 5 . The piston pump ( 10 ) according to claim 1 , characterized in that the preload device ( 38 ) is integrated into the sealing ring ( 40 ).