CN110945241B - Piston pump, in particular high-pressure fuel pump for an internal combustion engine - Google Patents

Abstract

The invention relates to a piston pump (16), in particular a high-pressure fuel pump for an internal combustion engine, comprising a pump housing (26), a pump piston (28) and a delivery chamber (38) which is delimited at least by the pump piston (28) and the pump housing (26). According to the invention, a seal (44) for sealing the delivery chamber (38) and a separate guide element (46) for guiding the pump piston (28) are preferably arranged between the pump piston (28) and the pump housing (26), wherein the seal (44) is designed as a sealing ring and is located on the pump housing (26).

Description

Piston pump, in particular high-pressure fuel pump for an internal combustion engine

Technical Field

The invention relates to a piston pump, in particular a high-pressure fuel pump for an internal combustion engine.

Background

Piston pumps are known from the prior art, which are used, for example, in internal combustion engines having gasoline direct injection. Such piston pumps have a gap seal between the pump cylinder and the pump piston. The pump cylinder and pump piston are typically made of stainless steel. Such gap seals require high precision in the manufacture and assembly of the pump cylinder and the pump piston, which results in high costs. The always present gap, the size of which cannot be reduced arbitrarily, for example due to the thermal expansion coefficient of the materials used, leads to a suboptimal volumetric efficiency, in particular at low rotational speeds.

Disclosure of Invention

The invention has the following task: a piston pump is provided which has sufficient volumetric efficiency even at low rotational speeds, has a small overall size and can be produced inexpensively.

This object is achieved by the piston pump according to the invention. The invention relates to a piston pump, in particular a high-pressure fuel pump for an internal combustion engine, having a pump housing, a pump piston and a delivery chamber which is delimited at least by the pump piston and the pump housing, wherein preferably a seal for sealing the delivery chamber and a separate guide element for guiding the pump piston are arranged between the pump piston and the pump housing, wherein the seal is designed as a sealing ring and is located on the pump housing, wherein a securing ring for the seal is arranged between the pump piston and the pump housing, wherein the securing ring has a projection on which the seal is located, and wherein the seal has a slot which corresponds to the projection. The piston pump according to the invention has a pump housing, a pump piston and a delivery chamber which is delimited at least by the pump housing and the pump piston. According to the invention, a seal for sealing the delivery chamber and a separate guide element for guiding the pump piston are arranged between the pump piston and the pump housing, wherein the seal is designed as a sealing ring and is located on the pump housing and is therefore at least substantially stationary relative to the pump housing.

Such a piston pump can be produced in a simpler manner, thereby reducing the component costs. This is related to the following way: the pump cylinder body to be produced in a complex manner is eliminated and replaced by a new assembly having a sealing element and at least one guide element. By configuring the seal as a sealing ring, a favorable sealing of the conveying chamber is achieved, so that the volumetric efficiency is improved, in particular at low rotational speeds. The new sealing arrangement makes it possible to achieve a smaller overall size of the piston pump. The guidance and sealing are now realized by separate components, i.e. by the guide element and the seal (sealing ring). In particular, the sealing ring can be designed as a plastic ring or as a ring made of another material, for example as a ring made of a nonferrous metal (nonferrous metal ring).

The seal configured as a sealing ring is in particular a rod seal. The seal is located on or in the pump housing, in particular in a slot which receives the pump piston. In particular, the pump housing or an element fixed in the pump housing has a seat on which the seal is located. The seal is secured against displacement in the axial direction of the pump piston, in particular against displacement away from the delivery chamber, by means of the seat.

The seal has a radial inner annular edge, a radial outer annular edge, a first end side and a second end side opposite the first end side. The first end side may face the transport chamber. The second end side can face away from the delivery chamber, in particular facing the seat of the pump piston.

The pump piston may be received in a slot in the housing and moved back and forth in the slot. The inner wall (inner surface) of the slot can at least in sections form the running surface of the pump piston. The notches can be designed as bores, if appropriate stepped bores.

The seal may be made of PEEK, PEAK, polyamideimide (PAI; e.g., PAI available under the name Torlon), or similar materials. The material may additionally be reinforced and/or optimized by fillers. The seal is in particular a high-pressure seal which seals the high-pressure region (delivery chamber) against the low-pressure region (region on the side of the seal facing away from the delivery chamber).

The guide element can be arranged on the side of the seal facing the delivery chamber, in particular fixed in a slot for the pump piston. This is advantageous in terms of cavitation. The main part of the cavitation bubbles is formed in the suction phase on the pump piston end side. During the delivery phase, these cavitation bubbles continue to move to the seal, prevented by the narrow gap between the inner surface of the guide element and the circumferential surface of the pump piston. Possible damage on the seal can be avoided. The guide element can be designed in the form of a ring (guide ring).

Within the scope of a preferred embodiment, a further guide element can be provided, which is arranged in the seal carrier of the piston pump and is preferably fixed to the seal carrier. This results in a larger bearing distance, so that the guidance of the pump piston is optimized. The further guide element can be designed in the form of a ring (guide ring).

Advantageously, the seal can have a sealing lip which interacts with the circumferential surface of the pump piston. The sealing lip extends from the base section of the seal on a radially inner annular edge of the seal. A pressure activated seal is achieved. This means that the sealing lip bears more strongly against the pump piston as a result of the pressure in the delivery chamber and on the side of the sealing lip facing away from the pump piston (back side). Due to the back pressure acting on the sealing lip, the latter deforms and seals better and better against the pump piston when the pressure increases. This is a self-enhancing effect that continues until the system pressure is reached. This makes it possible to build up a higher pressure in the conveying chamber. The largest deformation may occur at the tip of the sealing lip. Thus ensuring a dynamic sealing action at a defined location.

In particular, the seal may be based on a grooved ring seal, but optimized in design and having a sealing lip. The sealing lip may have an interference dimension (press fit), a clearance dimension (clearance) or a transition fit with respect to the pump piston. For a particularly reliable seal, the seal can be embodied with a press fit relative to the pump piston, for example with an interference dimension of 0.001-0.1mm (millimeters).

Furthermore, the seal geometry can be designed in such a way that a defined force acting on the pump piston occurs when the system pressure is reached. The applied force depends on the current requirements (volumetric efficiency, wear during service life, etc.). The pressure-activated sealing makes it possible to achieve high system pressures, since the sealing lip is increasingly deformed at higher system pressures, and the contact pressure of the sealing lip on the pump piston increases and the tightness becomes greater. The wear on the sealing lip can be compensated for by pressure activation of the seal. Thus, by pressure activation, the sealing lip, which is shorter due to wear, is deformed more strongly and further forms a dynamic sealing point with respect to the pump piston.

In the region of the transition from the seal (base section of the seal) to the sealing lip, the sealing lip should have a continuous, for example linear, geometry profile, in particular on its outer contour. In particular, the area should be free of cuts (no cuts). This prevents a notching effect, so that the service life of the seal is increased.

In a suitable manner, a securing ring for the seal can be arranged between the pump housing and the pump piston. The fixing ring constitutes a seat for the seal. The seal is thereby secured against axial displacement, in particular away from the conveying chamber. The securing ring can be fixed, for example pressed into a groove which receives the pump piston. In particular, the fixing ring and the sealing element can be designed such that a static sealing point is formed when the sealing element rests against the fixing ring.

In the context of a preferred embodiment, the securing ring can have an axial projection on which the seal is located. The seal may have a notch corresponding to, i.e. complementary to, the protrusion. A long sealing gap can thereby be obtained, so that a reliable sealing is achieved. Preventing fuel from escaping from the delivery chamber and thus reducing volumetric efficiency.

In a expedient manner, the projection can increase radially inward toward the seal. Complementary thereto, the notches may increase radially outward toward the securing ring. In addition to a sufficiently long sealing gap, a secure arrangement of the sealing element on the securing ring is thus also achieved. It is also conceivable that the projection is not enlarged, but is configured such that the sealing surface between the seal and the piston is planar. This will not give angular compensation to the piston.

In particular, the projection of the securing ring can have a sealing surface on the end face, which is conical or pyramidal, i.e. the sealing surface on the projection is a segment of the cone circumference. The groove of the seal can have a sealing surface on the end face, which is spherically formed, i.e. the sealing surface on the groove is a segment (spherical region) of a spherical surface. The "ball-cone shape" results in a closed sealing line, so that it is statically sealed. Since the seal is aligned with the pump piston, this can be the case due to the gap-oriented gap, the pump piston not being oriented orthogonally to its true working trajectory in the slot. The angle compensation between the seal and the housing can be achieved by means of a ball-and-cone shape.

The seal can be clamped in the axial direction. However, in order to be able to achieve positioning in the radial direction and to achieve angular compensation between the piston and the seal, an axial clearance of, for example, 0.01-1mm should be present.

In particular, the seal may have a radial clearance, for example 0.1-1mm, on its radially outer annular edge relative to the inner surface of the slot receiving the pump piston. The seal can thus be oriented concentrically in the radial direction relative to the pump piston. In this case, the radial play is advantageously greater than the play between the guide element and the pump piston. The seal therefore does not have to withstand or only negligibly small transverse forces.

The possibility of reorienting the seal is present during each pumping phase of the pump piston (movement of the pump piston away from the delivery chamber). Since the seal has a clearance radially outwardly with respect to the pump housing as explained above. In the delivery phase (the pump piston moves toward the delivery chamber, compresses and delivers the fuel), a delivery pressure is built up on the side of the seal facing the delivery chamber, which delivery pressure acts on the end face of the seal. The sealing element is thereby subjected to a force (pressing force) in the axial direction, which presses the sealing element out of the conveying chamber and in particular against the securing ring. During this phase, the seal cannot or only insignificantly move in the radial direction due to the axial forces.

The seal can, as explained, have a gap (gap) radially outward relative to the pump housing in order to enable radial and angular compensation relative to the piston. By loading the seal with pressure in the delivery chamber, the seal is subjected radially inward to a force due to the gap, which attempts to reduce the diameter of the seal. In order not to impair the sealing function, the seal should have a sufficient distance between the radially inner ring edge of the seal and the pump piston outside the sealing lip. This reduces the risk of the seal partially or completely bearing against the pump piston beyond the sealing lip.

In an advantageous manner, a spring element can be provided, which presses the seal against the securing ring. The seal is thus not moved out of its position by the stroke movement of the piston. Preventing the seal from lifting. Therefore, reliable pressure formation can be achieved. The spring element is preferably configured as a compression spring. It is contemplated to implement a coil spring or a wave spring.

Advantageously, the pump piston can have a DLC layer (diamond-like carbon) on its circumferential surface. The surface coating is extremely hard, so that no or only negligibly small surface damage occurs on the pump piston during the service life. In this way, the sections of the pump piston passing through the seal and the guide element can overlap when the pump piston moves back and forth. Thus, a gap between the circumferential surface of the pump piston and the corresponding surface of the seal and/or the guide element can be dispensed with. This contributes to the structural height.

In an advantageous manner, the guide element and the securing ring can be jointly constructed as one component (one-piece construction). In this way, the number of structural elements to be produced and assembled is reduced. Furthermore, the slot receiving the pump piston can be configured more simply and with fewer steps. This contributes to a cost-effective configuration of the piston pump.

In a suitable manner, a helical groove can be formed in the circumferential surface of the pump piston, in particular in the region of the circumferential surface of the pump piston that interacts with the guide element (guide section). As a result, any cavitation bubbles that may be present can be transported away from the region of the sealing lip that is sensitive to the sealing function. In the conveying phase, the conveying medium flows through the helical groove and generates a rotating flow which conveys any cavitation bubbles away from the region of the sealing lip.

Drawings

The invention is explained in detail below with reference to the drawings, wherein identical or functionally identical elements may be provided with reference numerals only once. The figures show:

FIG. 1 is a schematic illustration of a fuel system having a high pressure fuel pump in the form of a piston pump;

FIG. 2 is a longitudinal section of the piston pump of FIG. 1;

FIG. 3 is an enlarged view of a pump piston, a pump housing, seals, guide elements and a retaining ring of the piston pump of FIG. 1;

FIG. 4 is an enlarged view of the seal and retaining ring;

FIG. 5 is an enlarged partial view of a pump piston of the piston pump of FIG. 1;

fig. 6 shows a simplified longitudinal section of a piston pump.

Detailed Description

The fuel system of an internal combustion engine is generally indicated by reference numeral 10 in fig. 1. The fuel system comprises a fuel tank 12, from which an electric prefeed pump 14 delivers fuel to a high-pressure fuel pump in the form of a piston pump 16. The fuel high-pressure pump delivers the fuel further to a high-pressure fuel rail 18, to which a plurality of fuel injectors 20 are connected, which inject the fuel into combustion chambers of an internal combustion engine, not shown.

The piston pump 16 includes an inlet valve 22, an outlet valve 24, and a pump housing 26. A pump piston 28 is received in the pump housing so as to be movable back and forth. The pump piston 28 is set in motion by a drive 30, the drive 30 being illustrated only schematically in fig. 1. The drive means 30 may be, for example, a camshaft or an eccentric shaft. The inlet valve 22 is designed as a flow control valve, by means of which the quantity of fuel delivered by the piston pump 16 can be adjusted.

The pump piston 28 is designed as a stepped piston having a lower tappet section 32, a guide section 34 (see fig. 2) adjoining it, and an upper end-side end section 36 (see fig. 5). The guide section 34 has a larger diameter than the tappet section 32 and the end section 36.

The end section 36 of the pump piston 28 and the guide section 34 together with the pump housing 26 delimit a delivery chamber 38, which is not shown in detail. The pump housing 26 may be constructed as a generally rotationally symmetrical part. The pump piston 28 is received in a slot 42 present there in the pump housing 26, which is designed as a stepped bore 43. The bore 43 has a plurality of steps (three steps 43',43", 43"; see fig. 2).

A seal 44 is arranged between the guide section 34 of the pump piston 28 and the inner circumferential wall (step 43") of the bore 43. This seal seals directly between the pump piston 28 and the pump housing 26 and, therefore, seals the delivery chamber 38 from the region (low-pressure region) in fig. 2 which is arranged below the seal 44, in particular in which the tappet section 32 of the pump piston 28 is located. The seal 44 is configured as a sealing ring, in particular a plastic ring.

Between the guide section 34 of the pump piston 28 and the inner circumferential wall (step 43') of the bore 43, a guide element 46 is arranged, separate from the seal 44, for guiding the pump piston 28. The guide element 46 can be axially adjacent to the seal 44 and in fig. 2 be arranged above the seal 44 (facing the conveying chamber). The guide element 46 is designed in the form of a ring (guide ring) and can be fixed to the step 43'.

The piston pump 16 has a further guide element 48, which is arranged in a seal carrier 50 of the piston pump 16. The guide element 46 and the further guide element 48 serve to guide the pump piston 28. The further guide element 48 is designed in the form of a ring (guide ring) and can be fixed to the seal carrier 50.

Furthermore, the piston pump 16 has a spring element 52 and a securing ring 54 for the seal 44 between the guide section 34 of the pump piston 28 and the inner circumferential wall of the bore 42 (see fig. 3). The spring element 52 bears against an end face 56 of the seal 44 and presses the seal 44 against a retaining ring 54 (compression spring). The spring element 52 is designed as a helical spring 58. The seal 44, the guide element 46, the spring element 52 and the securing ring 54 constitute a sealing assembly.

The seal 44 has a sealing lip 60 which interacts with the circumferential surface of the pump piston 28, in particular with the guide section 34 (see fig. 3 and 4). The sealing lip 60 extends from a base section 63 of the seal 44 on a radially inner annular edge 62. When the delivery chamber 38 is pressurized, the sealing lip 60 is pressed by a force 61 onto the guide section 34 of the pump piston 28 (see fig. 5).

The fixing ring 54 and the seal 44 are designed in such a way that a static sealing point 64 is formed when the seal 44 is placed against the fixing ring 54. The securing ring 54 has a projection 66 which interacts with a corresponding notch 68 of the seal 44. The projection 66 has a sealing surface 70 which is conical or conical in shape, i.e. the sealing surface 70 is a segment of the cone circumference. The recess 68 has a sealing surface 72 in the form of a sphere, which is a segment (spherical zone) of a spherical surface. In this way, the seal 44 can be oriented relative to the retaining ring 54 and/or the pump housing 26 (angular compensation).

The seal 44 has a radial clearance 76 on its radially outer annular edge 74 with respect to the inner surface of the slot 42 (step 43") receiving the pump piston 28. Thereby facilitating orientation of the seal 44. The radial gap 76 should be greater than the gap 77 between the guide section 34 and the guide element 46.

The seal 44 has a distance 78 from the circumference of the pump piston 28, in particular from the guide section 34, in the region of its radially inner ring edge 62 in the region of the base section 63. The distance 78 is selected such that, when the seal 44 is subjected to a pressure (delivery stroke) and the forces resulting therefrom act on the seal 44 (arrow 81; see fig. 4), only the sealing lip 60, but not the base section 63 of the seal 44, rests on the guide section 34. At the transition 79 from the base section 63 of the seal 44 to the sealing lip 60, the sealing lip 60 has a continuous geometry trend and is designed without cutouts.

A helical groove 80 is formed in the circumferential surface of the pump piston 28, in particular in the guide section 34 (see fig. 5). This spiral groove serves to transport cavitation bubbles that may be present on the seal away from the region of the sealing lip 60.

The pump piston 28 has a DLC layer (diamond-like carbon) on its circumferential surface, in particular in the guide section 34. As a result, no or only negligibly small surface damage occurs on the pump piston. Therefore, the sections on the pump piston 28 passing through the seal 44 and the guide element 46 overlap when the pump piston 28 moves back and forth (overlap 75).

The sealing is based on the following effects: in the delivery phase (movement of the pump piston 28 toward the delivery chamber 38; upward in the figure), a delivery pressure is built up on the side of the seal 44 facing the delivery chamber 38, which delivery pressure acts on the seal 44 from the first end side 56. As a result, the seal 44 is subjected to a force F (pressing force) indicated by an arrow 88 in the axial direction, which presses the seal 44 onto the fixing ring 54 (see fig. 3). Thus, a static seal 64 is formed between the sealing surface 70 of the stationary ring 54 and the sealing surface 72 of the seal 44. Due to the force F (arrow 61) acting on the sealing lip 60, the sealing lip 60 is deformed (deformed sealing lip 60') and rests against the circumferential surface of the pump piston 28, in particular against the guide surface 34 (see fig. 4). The deformation occurs primarily at the tip 90 of the sealing lip 60. Where a dynamic seal is formed.

Fig. 6 shows an alternative embodiment of the piston pump 16, which largely corresponds to the embodiment described above and in which identical or functionally identical elements are provided with the same reference symbols.

In contrast, in this alternative configuration, the seal assembly is configured to be simpler and less costly. The guide element 46 and the securing ring 54 are combined into one component 82. The member 82 assumes both a securing and guiding function. The section of the component 82 above, facing the seal 44 corresponds in its configuration to the securing ring 54. The seal 44 is placed over this section of the member 82. The seal 44 and its mode of action are unchanged.

The spring element 52 is arranged on the side of the seal 44 facing away from the component 82 and presses the seal 44 onto the component 82. The static seal between the member 82 and the seal 44 is thereby always kept closed. The spring element 52 is configured as a wave spring 84.

The notch 42, which is designed as a stepped bore 43, has two steps 43',43 ″. In fig. 6, a gap 86 is provided above the seal 44 between the pump piston 28, in particular the guide section 34, and the pump housing 26, which gap serves as a cavitation protection for the seal 44. This is achieved by keeping the gap 86 sufficiently narrow.

Claims (9)

1. A piston pump (16) having a pump housing (26), a pump piston (28) and a delivery chamber (38) which is bounded at least by the pump piston (28) and the pump housing (26), wherein a seal (44) for sealing the delivery chamber (38) and a separate guide element (46) for guiding the pump piston (28) are arranged between the pump piston (28) and the pump housing (26), wherein the seal (44) is designed as a sealing ring and is located on the pump housing (26), wherein a fixing ring (54) for the seal (44) is arranged between the pump piston (28) and the pump housing (26),

characterized in that the fixing ring (54) has a projection (66) on which the seal (44) is located and in that the seal (44) has a notch (68) corresponding to the projection (66).

2. Piston pump (16) according to claim 1, characterized by a further guide element (48) which is arranged in a seal carrier (50) of the piston pump (16) which receives a further seal.

3. Piston pump (16) according to claim 1 or 2, characterized in that the seal (44) has a sealing lip (60) which interacts with the circumferential surface of the pump piston (28).

4. Piston pump (16) according to claim 1 or 2, characterized in that the projection (66) increases radially inwardly towards the seal (44) and the slot (68) increases radially outwardly towards the fixing ring (54).

5. A piston pump (16) according to claim 1 or 2, characterized in that the seal (44) has a gap (76) on its radial outer ring edge (74) relative to the inner surface of the pump housing (26) of the slot (42) receiving the pump piston (28).

6. Piston pump (16) according to claim 1 or 2, characterized in that a spring element (52) is provided which presses the seal (44) against the fixing ring (54).

7. Piston pump (16) according to claim 1 or 2, characterized in that the guide element (46) and the fixing ring (54) are integrated in one component (82).

8. Piston pump (16) according to claim 1 or 2, characterized in that a helical groove (80) is formed in the circumferential surface of the pump piston (28).

9. Piston pump (16) according to claim 1, characterized in that the piston pump (16) is configured as a high-pressure fuel pump for an internal combustion engine.

Images