WO2019015859A1

WO2019015859A1 - Piston pump

Info

Publication number: WO2019015859A1
Application number: PCT/EP2018/065014
Authority: WO
Inventors: Siamend Flo; Kerstin Koch; Frank Nitsche; Andreas PLISCH; Dietmar Uhlenbrock; Jurij Giesler; Ekrem CAKIR
Original assignee: Robert Bosch Gmbh
Priority date: 2017-07-20
Filing date: 2018-06-07
Publication date: 2019-01-24
Also published as: CN110945240A; DE102017212490A1; CN110945240B

Abstract

The invention relates to a piston pump (16), in particular high-pressure fuel pumps for an internal combustion engine, comprising a pump housing (26), a pump piston (28) and a conveying chamber (39) defined at least by the pump housing (26) and the pump piston (28). According to the invention, a seal (50) for sealing the conveying chamber (39) and a separate guide element (56) for guiding the pump piston (28) are arranged preferably between the pump piston (28) and the pump housing (26). The seal (50) is designed as a plastic ring and rests on the pump piston (28).

Description

PISTON PUMP

State of the art

The invention relates to a piston pump, in particular a high-pressure fuel pump for an internal combustion engine, according to the preamble of claim 1.

Piston pumps are known from the prior art, the example. At

Internal combustion engines with gasoline direct injection are used.

Such piston pumps have a gap seal between

Pump cylinder and pump piston. Pump cylinders and pump pistons are typically made of stainless steel. Such a gap seal requires high accuracy in the manufacture and assembly of pump cylinder and pump piston, resulting in high costs. The ever-present gap, the size of which, for example, can not be arbitrarily reduced due to the thermal expansion coefficients used, leads to a suboptimal degree of delivery, especially at low speeds.

Disclosure of the invention

The invention has the object to provide a piston pump which has a sufficient degree of delivery even at low speeds, has a small size and is inexpensive to produce.

This object is achieved by a piston pump with the features of claim 1. Advantageous developments of the invention are in the dependent claims specified. For the invention essential features are also found in the following description and in the drawings.

The piston pump according to the invention has a pump housing, a

Pump piston and a limited at least by the pump housing and the pump piston delivery chamber. According to the invention it is proposed that between the pump piston and pump housing, a seal for

Sealing of the pumping chamber and a separate guide member for guiding the pump piston are arranged, wherein the seal is formed as a plastic ring and sits on the pump piston, that moves relative to the pump housing during operation with the pump piston.

Such a piston pump can be produced comparatively easily, which reduces the component costs. This is due to the fact that the complex to be manufactured pump cylinder is replaced by a seal assembly with a seal and at least one guide. By the

Design of the seal as a plastic ring, an advantageous sealing of the delivery chamber is achieved, so that the degree of delivery is improved, especially at low speeds. Due to the new seal assembly, a comparatively small overall size of the piston pump can be achieved. The guiding and sealing function are now realized by separate components, namely by the guide element and the seal (plastic ring).

When used as a sealing ring (plastic ring) seal is in particular a piston seal. In particular, the pump piston has a seat, for example a shoulder on which the seal is seated. Through the seat, the seal is secured against displacement along an axial direction of the pump piston, in particular against displacement from the pumping chamber away.

The seal has a radially inner ring edge, a radially outer ring edge, a first end face and a second end face opposite the first end face. The first end face may face the delivery chamber. The second end face may be remote from the delivery chamber, in particular facing the seat of the pump piston. The pump piston may be received in a recess in the housing and reciprocate therein. The inner wall of the recess (inner surface) may form at least a portion of a tread for the pump piston. The recess may be formed as a bore, possibly as a stepped bore.

Between pump piston and pump housing, a pump cylinder may be arranged. This can be manufactured with a lower manufacturing accuracy and thus more cost-effective than a conventional stainless steel pump cylinder, since the sealing and guiding function are taken over by the seal and the guide element. The pump cylinder may be formed as a sleeve and arranged at a stage of the recess for the pump piston. The inner surface of the pump cylinder forms at least a portion of the tread for the pump piston. Alternatively, the pump cylinder can be omitted, whereby the number of components is reduced. A possible omission is i.a. Depending on which medium is promoted, how high the efficiency requirements and / or how long life of the piston pump should fail.

The gasket may be made of a PEEK (polyetheretherketone), PEAK, polyamideimide (PAI, e.g., a PAI available under the name Torion) or comparable materials. The materials may additionally be reinforced and / or optimized by fillers. The seal is in particular a high-pressure seal which has a high-pressure region (delivery chamber) in relation to a low-pressure region (region at the end of the delivery)

Pump chamber facing away from the seal) seals.

In a preferred embodiment, another

Guide element may be provided, which is arranged in a seal carrier of the piston pump. This is a comparatively large bearing distance to the (first) guide element realized. The leadership of the pump piston is thus significantly improved. The further guide element may be annular (guide ring).

Advantageously, a cap (fixing cap) can be provided, which is applied to the pump piston and the seal secures axially.

As a result, a secure attachment of the seal is achieved on the pump piston. Through the cap, the seal is secured against displacement along an axial direction of the pump piston, in particular against displacement to

Pumping room. The cap can be pressed onto the pump piston. The cap has, in particular to the pumping chamber, a pressure relief hole. As a result, no pressure field can build up between the pump piston and the cap, which could widen the cap.

In the context of a preferred embodiment, the seal may have a sealing lip. The sealing lip can with a corresponding surface, for example. With the running surface for the pump piston (inner surface of the recess for the

Pump piston), cooperate. This is a pressure-activated seal realized. This means that due to the pressure in the delivery chamber and on the side facing the pump piston sealing lip side (inside), the sealing lip more strongly against the running surface for the pump piston (inner surface of the recess) applies. As a result, the sealing lip seals to the pump piston with increasing

Always press better (self-reinforcing effect). Thus, in the

Delivery chamber a relatively high pressure to be built. The largest deformation can take place at the tip of the sealing lip. Thus, will

ensures that the dynamic sealing effect takes place at a defined point. The sealing lip extends from a base portion of the gasket in

Direction of the delivery room.

The geometry of the seal can be designed such that upon reaching the system pressure of the piston pump, a defined force on the running surface for the pump piston (inner surface of the recess for the pump piston) sets. This application force depends on the desired requirements (degree of delivery, wear over the service life, etc.). By the pressure activation comparatively high system pressures can be driven, since with increasing system pressure, the seal deforms more and more and thus the contact pressure of the sealing lip on the tread for the pump piston increases more and more.

By the pressure activation of the seal, it is possible to compensate for wear on the sealing lip of the seal. Due to the pressure activation (pressure and thus acting force on the inside of the sealing lip) deforms the Strengthened by wear, the sealing lip stronger and continues to form the running surface for the pump piston a dynamic sealing point.

Concretely, the seal may be based on a U-ring seal, but optimized in design and having a sealing lip. This sealing lip can be used for the tread for the pump piston and / or the inner surface of the

Pump cylinder have an oversize (pressure), an undersize (play) or a transition fit. For a particularly secure seal, the seal can be designed with pressure to the running surface for the pump piston, for example, with an excess of 0.001 -0.3 mm (millimeters).

Conveniently, a retaining ring may be arranged on the outer circumference of the seal, which limits or prevents a radial widening of the seal by the pressure acting on the seal. This counteracts the force in the radial direction which attempts to widen the seal in diameter. This ensures that the seal is applied in a targeted manner, but not over a large area, to the running surface (inner surface of the recess for the pump piston). Friction and wear can thus be kept low. The retaining ring may be formed of metal, in particular stainless steel, or the like. The retaining ring may be fixed to the seal by pressure, adhesion, snap-in or the like. The seal can be one

Have ring receiving portion, in particular a radial taper.

Advantageously, the seal may have at its radially inner edge of the ring to the outer surface of the pump piston a game. Or, in other words: the seal can be movable relative to the pump piston in the radial direction. Thus, the seal in the radial direction can be aligned concentrically with the pump cylinder. The game can be 0.1 - 1 mm (millimeters). It is advantageous if this radial clearance is greater than the clearance between the guide elements and the pump piston (further guide element) or the pump piston and the tread for the

Pump piston (first guide element). This ensures that the seal no or only negligible transverse forces must absorb.

In the axial direction, the seal can be clamped, in particular between the seat (paragraph) and the cap. However, a positioning in radial Direction and an angular compensation between piston and seal should be present on the seal an axial clearance, for example. Of 0.01 -1 mm, in particular between the cap and the seal. In each suction phase of the pump piston (pump piston moves from

Pumping away) there is the possibility of a reorientation of the seal towards the pump piston, since the seal to the pump piston (radially inward) game, as described above. In the delivery phase (pump piston moves towards the delivery chamber, compresses and promotes fuel), a delivery pressure builds up on the side of the seal facing the delivery chamber which acts on the seal (first end side of the seal). This experiences the

Seal in the axial direction of a force (contact pressure), which presses the seal away from the pumping chamber on the seat on the pump piston. During this phase, the seal can not or only slightly move in the radial direction due to the axial force.

In a preferred embodiment, the pump piston may have a shoulder on which the seal is seated and which rises radially outward toward the seal. The seal may have an end portion corresponding to the heel and rising radially inward toward the heel. In this way, a sufficient seal in the form of a static sealing point is created. This prevents fuel from escaping from the delivery chamber and thus reduces the degree of delivery. The shoulder surface (sealing surface) may be conical or conical, i. the shoulder surface describes a portion of a lateral surface of a cone. The (second) end face of the seal (axial sealing surface) may be spherical, i. the face describes a section of a

Spherical surface (spherical zone). This "ball-cone-shape" results in a closed Dichtlinienzug, so that is statically sealed. Since the

Aligning the seal with the running surface of the pump piston, it may be due to the play of the guide that the pump piston is not sufficiently orthogonal to the seal. Due to the "ball-cone-shape" an angle compensation between seal and piston is possible. In the region of the transition from the seal (base portion of the seal) to the sealing lip, the sealing lip, in particular on its outer contour, should have a continuous, preferably linear, geometry. In particular, this area should be notch. As a result, notch effect can be avoided, so that the service life of the seal increases.

Advantageously, the guide element may be formed as a radially projecting or raised portion of the cap, said portion with the running surface for the pump piston (inner surface of the recess for the

Pump piston) cooperates. The section may be formed on the cap in particular circumferential. The guide element is arranged on the conveying chamber facing side of the seal. This is advantageous in terms of cavitation. The cap serves in this case both for fastening the seal and for guiding the pump piston. The main part of

Cavitation bubbles are created in the intake phase on the front side of the pump piston.

In the delivery phase is prevented by the narrow gap between the guide element and the tread for the pump piston that this

Move cavitation bubbles up to the seal. Damage to the seal can thus be avoided.

Alternatively, the guide member may be formed as a radially protruding or raised portion of the pump piston, wherein the portion cooperates with the running surface for the pump piston (inner surface of the recess for the pump piston). The section may be formed on the pump piston in particular circumferentially. In this way, the cap only fulfills the function of attaching the seal. The guide is now taken over by the pump piston itself, in particular on the side facing away from the pumping chamber side of the seal. In this way, an application of the cap on the pump piston, in particular a pressing of the cap, simplified because even with a strong and / or different widening of the cap in the radial direction during application still allows accurate and reliable guidance by the pump piston.

As part of a preferred embodiment, spiral grooves can be formed in the lateral surface of the cap. Thus, possibly present on the seal cavitation bubbles from the sensitive area for the sealing function the sealing lip are promoted away. The spiral grooves can be arranged in particular in the raised portion of the cap. Due to the spiral grooves flows in the delivery phase, the fluid and thus generates a

Rotational flow, which promotes any existing cavitation bubbles from the region of the sealing lip away.

For a high degree of delivery and / or a long life, the surfaces for guidance and sealing, i. the seal and the or the

Guide elements, have a sufficient distance between each other, so that when running back and forth of the pump piston, the sections passed through the seal and the guide element do not overlap.

As a result, the risk occurring during an overlap that the surfaces, especially the sealing surfaces are too rough due to wear and / or shrinkage and thus no longer provide sufficient sealing effect, can be reduced. Alternatively, such an overlap of the sections passed through the seal and the guide element can be accepted. Due to smaller distances between the seal and the guide element in the axial direction, a compact design of the piston pump is favored.

The invention will be explained in more detail below with reference to the figures, wherein identical or functional same elements possibly only once with

Reference numerals are provided. Show it:

Figure 1 is a schematic representation of a fuel system with a

High-pressure fuel pump in the form of a piston pump;

Figure 2 is a partial longitudinal section through the piston pump of Figure 1;

Figure 3 is an enlarged view of a pump piston, a seal, a retaining ring and a cap of the piston pump of Figure 1;

Figure 4 shows the seal and the retaining ring of Figure 3 in an enlarged and sectional view;

Figure 5 of the pump piston, the seal, the retaining ring, and the cap

Figure 3 in an enlarged view; FIG. 6 shows the cap from FIG. 3 in a side view; and

7 shows a longitudinal section through an alternative embodiment of

Piston pump of Figure 1.

In FIG. 1, a fuel system of an internal combustion engine bears the reference numeral 10 as a whole. It comprises a fuel tank 12 from which an electric prefeed pump 14 conveys the fuel to a high-pressure fuel pump designed as a piston pump 16. This promotes the fuel further to a high-pressure fuel rail 18, to which several

Fuel! are connected injectors 20 which inject the fuel into combustion chambers, not shown, of the internal combustion engine.

The piston pump 16 includes an inlet valve 22, an outlet valve 24, and a pump housing 26. In this, a pump piston 28 is reciprocally accommodated. The pump piston 28 is set in motion by a drive 30, wherein the drive 30 is shown only schematically in FIG. For example, the drive 30 may be a camshaft or an eccentric shaft. The inlet valve 22 is designed as a quantity control valve, through which the pumped by the piston pump 16

Fuel quantity can be adjusted.

The structure of the piston pump 16 is shown in more detail from Figure 2, wherein only the essential components are mentioned below. It can be seen first that the pump piston 28 is designed as a stepped piston with a lower plunger section 32 in FIG. 2, a middle section 34 adjoining this and an upper end section 36 in FIG

Center section 34 has a larger diameter than the plunger section 32 and the end section 36.

The end portion 36 of the pump piston 28 bounded by means of a cap 38 applied to the end portion 36 together with the pump housing 26 a delivery chamber 39. The pump piston 28 is reciprocally received in the pump housing 26 in a recess 40 formed there, which formed as a stepped bore 42 is. At a stage 43 of the bore 42, which is radially expanded, a pump cylinder 44 is arranged. The

Pump cylinder 44 is sleeve-shaped. The inner surface 46 of the

Pump cylinder 44 forms a portion of a tread 48 for the

Pump piston 28.

In embodiments not shown, the pump cylinder 44 can be omitted. In this case, the pump piston 28 can run directly in the pump housing 26. The recess 40 in the pump housing 26 may then form the running surface for the seal 50 and also the guide surface for the pump piston 28. The recess 40 can then as a continuous (non-stepped)

Bore 42 may be formed.

Between pump piston 28 and pump housing 26, a seal 50 for sealing the delivery chamber 39 is arranged. The seal 50 is as

Formed by the cap 38, which is pressed onto the end portion 36 of the pump piston 28, the seal 50 against displacement in the axial direction of the pump piston 28 (FIG. to the

Pumping chamber 39; secured in Figure 2 to "above"). The cap 38 has a pressure relief bore 54.

In addition, a separate guide element 56 for guiding the pump piston 28 is arranged between pump piston 28 and pump housing 26. The guide member 56 is formed as a radially protruding or raised portion 58 of the cap 38 and cooperates with the tread 48. The

Section 58 is formed on the cap 38 circumferentially.

In addition, a further guide element 60 is provided for guiding the pump piston 28, which is arranged in a seal carrier 62 of the piston pump 16. The further guide element 60 is annular

(Guide ring) and cooperates with a guide surface 64 (inner ring edge) with the plunger portion 32 of the pump piston 28.

The seal 50 has a sealing lip 66, which cooperates with the running surface 48 for the pump piston 28 (see FIG. 3). In the exemplary embodiment, the sealing lip 66 interacts with the inner surface 46 of the pump cylinder 44 together. The sealing lip 66 extends from a base section 68 of the seal 50 in the direction of the delivery chamber 39 (in FIG. 3 "upwards"). The sealing lip 66 rests with its free end 67 on the tread 48. By concerns of the sealing lip 66 on the tread 48 under pressure coming from the delivery chamber 39 creates a dynamic sealing effect. The sealing lip 66 is not scored in the transition 69 from the sealing lip 66 to the base portion 68 of the seal 50, in particular on the outer surface 71st

On the outer circumference of the seal 50 may optionally be arranged a retaining ring 70 which limits a radial expansion of the seal 50. The retaining ring 70 may be disposed on a ring receiving portion 72 of the seal 50, which is radially tapered and having a shoulder 74 at one end. The retaining ring 70 is attached to the seal 50. The seal 50 has at its radially inner annular edge 76 to the outer surface of the pump piston 28, namely to the lateral surface of the end portion 36 of the pump piston 28, a radial clearance 77. In this way, the seal 50 can align concentrically with the pump cylinder 44.

As already described, the pump piston 28 has a shoulder 52 on which the seal 50 is seated. The shoulder 52 rises radially outward to the seal

50 out. The shoulder 52 has a shoulder surface 78, which forms a sealing surface. The shoulder surface 78 is conical or conical, i. the shoulder surface 78 describes a portion of a lateral surface of a cone. The seal 50 has an end-side section 80 which corresponds to the shoulder and rises radially inward toward the shoulder 52. The end-side section 80 has an end face 82, which forms a sealing surface. The end face 82 is spherical, i. the end face 82 describes a portion of a spherical surface (spherical zone). This "ball-cone shape" results in a closed Dichtlinienzug, so that a static

Dichstelle 83 is formed.

The portions of the tread 48, which are used for the guiding and sealing function, can overlap each other axially, so that it can come here to an overlap 85 (see Figure 5). This means that depending on the axial position of the pump piston 28, a portion of the tread 48 from Guide element 56 and (before or after) can be traversed by the sealing lip 66.

In non-illustrated embodiments, the portions of the tread 48 which are used for the guiding and sealing function may have a sufficient distance between each other so that the

Guide member 56 and the sealing lip 66 when reciprocating the

Pump piston 28 do not pass through identical sections of the tread 48. The cap 38 has a lateral surface 84 on which spiral grooves 86 are formed (see FIG. 6). In this case, the spiral grooves 86 are located in particular in the raised portion 58. Through the spiral grooves 86, a rotational flow can be generated in the delivery phase, which promotes any existing cavitation bubbles from the region of the sealing lip 66 away. The seal is based on the following effect: In the delivery phase (pump piston

28 moves toward the delivery chamber 39; in the figures "up"), a delivery pressure builds up on the side of the seal 50 facing the delivery chamber 39, which pressure acts on the seal 50 from the first end face 86. As a result, the seal 50 experiences in the axial direction a force F (contact pressure) which presses the seal 50 onto the shoulder 52 on the pump piston 28 (see FIG. 3). Thus, a static seal 83 is formed between shoulder surface 78 and end face 82. As a result of the force F (arrow 81) acting on the sealing lip 66 on the basis of the radial play 77 and the pressure prevailing there, the sealing lip 66 deforms and rests against the running surface 48 (see FIG. 4). Also on the base portion 68 acts a force F (arrow 87), which tries to widen the seal 50 axially, wherein the retaining ring 70 limits the radial extension. At lower pressures and a lower force F, the gasket 50 can counteract the force F itself sufficiently. The retaining ring 70 can then be omitted.

An alternative embodiment of the piston pump 16 is shown in Figure 7, which largely corresponds to the embodiment described above and are provided in the same or functionally identical elements with identical reference numerals. Notwithstanding this, in the alternative embodiment, the guide member 56 is designed to guide the pump piston 28 as a radially projecting or raised portion 88 of the pump piston 28 and cooperates with the tread 48. The section 88 is formed on the pump piston 28 circumferentially. In this embodiment, the cap 38 serves only for axial securing of

Seal 50. The guide function takes over the pump piston 28 itself, through the section 88th

Claims

claims

1 . Piston pump (16), in particular high-pressure fuel pump for a

Internal combustion engine, with a pump housing (26), a pump piston (28) and at least one of the pump housing (26) and the

Pump piston (28) limited delivery chamber (39), characterized in that preferably between the pump piston (28) and the pump housing (26) has a seal (50) for sealing the delivery chamber (39) and a separate guide element (56) for guiding the pump piston (28 Are arranged), wherein the seal (50) is formed as a plastic ring and on the pump piston (28) sits.

2. Piston pump (16) according to claim 1, characterized in that the seal (50) has a sealing lip (66).

Piston pump (16) according to claim 1 or 2, characterized in that the pump piston (28) has a shoulder (52) on which the seal (50) sits and which rises radially outwardly, in particular is conical, and in that the seal ( 50) has an end portion (80) corresponding to the shoulder (52) and rising radially inwardly,

in particular spherical.

Piston pump (16) according to one of the preceding claims,

characterized by a further guide element (60), which is arranged in a seal carrier (62) of the piston pump (16).

Piston pump (16) according to one of the preceding claims, characterized in that a cap (38) is provided, which on the

Pump piston (28) is applied and the seal (50) secures axially

Piston pump (16) according to one of the preceding claims, characterized in that on the outer circumference of the seal (50) has a retaining ring (70) is arranged, which limits a radial expansion of the seal (50).

7. Piston pump (16) according to one of the preceding claims, characterized in that the seal (50) at its radially inner annular edge (76) to the outer surface of the pump piston (28) has a clearance (77).

8. Piston pump (16) according to any one of the preceding claims, characterized in that the guide element (56) as a radially projecting portion (58) of the cap (38) is formed, which cooperates with the running surface (48) for the pump piston (28) ,

9. piston pump (16) according to one of claims 1 to 7, characterized

characterized in that the guide element (56) is formed as a radially protruding portion (88) of the pump piston (28), which is connected to the

Running surface (48) for the pump piston (28) cooperates.

10. Piston pump (16) according to one of the preceding claims, characterized in that in the lateral surface (84) of the cap (38) spiral grooves (86) are formed.