EP3655650B1 - Piston pump - Google Patents

Description

State of the art

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

Piston pumps are known from the prior art, which are used, for example, in internal combustion engines with gasoline direct injection. Such piston pumps have a gap seal between the pump cylinder and the 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 the pump cylinder and pump piston, resulting in high costs. The gap that is always present, the size of which cannot be reduced arbitrarily, for example due to the thermal expansion coefficients of the materials used, leads to a suboptimal degree of delivery, especially at low speeds.

Piston pumps are also known from DE 10 2014 202 809 A1 and from the DE 10 2013 226 062 A1 .

Disclosure of Invention

The object of the invention is to create a piston pump which has a sufficient degree of delivery even at low speeds, is small in size and can be produced inexpensively.

This object is achieved by a piston pump having the features of claim 1. Advantageous developments of the invention are specified in the dependent claims. Features essential to the invention can also be 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 pumping chamber which is also delimited at least by the pump housing and the pump piston. According to the invention, it is proposed that a seal for sealing off the pumping chamber and a separate guide element for guiding the pump piston are arranged between the pump piston and the pump housing, the seal being designed as a plastic ring with an essentially sleeve-shaped base section which, for example, has a cylindrical outer surface.

Such a piston pump can be manufactured comparatively easily, as a result of which the component costs are reduced. This has to do with the fact that the gap seal and its pump cylinder, which is expensive to manufacture, are replaced by a seal assembly with a seal and at least one guide. By configuring the seal as a plastic ring, an advantageous sealing of the conveying space is achieved, so that the degree of delivery is improved, particularly at low speeds. A comparatively small overall size of the piston pump can be achieved by the new sealing assembly. The guiding and sealing functions are now realized by separate components, namely by the guiding element and the seal (plastic ring).

The pump piston may be received in a recess in the housing and reciprocate therein. The inner wall of the recess (peripheral wall) can form at least a section of a running surface for the pump piston. The recess can be designed as a bore, in particular as a stepped bore.

Specifically, the (first) guide element can be ring-shaped (guide ring). The guide element can be arranged on the side of the seal facing the pumping chamber. Optionally it can Guide element to the pump piston have a radial gap (guide gap), which is so small that the guide element serves as cavitation protection for the seal. The guide gap is small enough so that no vapor bubbles can reach the seal. The risk of damage to the seal is thus reduced.

The seal may be made of a PEEK (polyetheretherketone), PEAK, polyamideimide (PAI; e.g. a PAI sold under the name Torlon) or comparable materials. The materials can additionally be reinforced and/or optimized by fillers. The seal is, in particular, a high-pressure seal that seals a high-pressure area (conveying chamber) from a low-pressure area (area on the side of the seal facing away from the conveying chamber).

The seal has a radially outer annular edge (outer lateral surface), a radially inner annular edge, a first face and a second face. The seal can have a greater length in the axial direction of the pump piston than the guide element and/or the fastening ring. In this way, space can be gained for different configurations of the seal, with the axial length being able to be kept short.

The seal can be based on a U-ring seal, but optimized in design and have different cross-sections. The wall thickness of the seal (wall thickness in the radial direction) is designed depending on the system pressure. The wall thickness can be 0.1mm - 3.0mm (millimeters). The seal can be oversized (compression), undersized (play) or a transition fit to the pump piston. For low friction and low wear, a design of the seal with radial play towards the pump piston is advantageous, in particular with a play of 0.001 mm - 0.1 mm.

In the simplest case, the seal, as already mentioned above, can be designed in the form of a sleeve. The seal then has an I-shaped cross section, in particular with a profile that is rectangular in cross section. The I-shaped cross-section may form a base portion of the gasket. Alternative to an I-shaped Cross section, the seal may have an L-shaped or a U-shaped cross section.

According to the invention, a further guide element is provided, which is arranged in a seal carrier of the piston pump. This achieves a comparatively large bearing distance from the (first) guide element. The guidance of the pump piston is thus optimized. The further guide element can be ring-shaped (guide ring).

According to the invention, a fastening ring for the seal is arranged between the pump housing and the pump piston. The fastening ring is arranged in particular on the side of the seal facing away from the pumping chamber. The mounting ring forms a seat for the seal. This secures the seal against axial displacement, in particular away from the pumping chamber. The fastening ring can be fastened to the recess accommodating the pump piston, for example screwed in, glued in or pressed in. In particular, the fastening ring and the seal can be designed in such a way that a static sealing point is formed when the seal rests on the fastening ring. In order to enable positioning in the radial direction between the piston and the seal, the seal can have an axial play, for example of 0.01 mm - 1 mm. ("Floating seal"). The seal, the guide element, the further guide element and the fastening ring form a seal assembly.

A spring element can preferably be arranged between the pump piston and the pump housing, which spring element presses the seal against the fastening ring. The spring element can be arranged (in the axial direction of the pump piston) between the guide element and the seal. The spring element can bear axially at one end, for example on the guide element, and at the other end can press the seal against the fastening ring. The spring element can be designed as a compression spring, in particular as a spring washer or helical spring. The spring element can at least partially surround the pump piston. An axial force acts on the seal through the spring element, this force pressing on the axial end face of the seal facing the pumping chamber. The axial force causes the seal to open up rests on the fastening ring so that an initial tightness at the static sealing point is guaranteed. In connection with the throttling at the dynamic sealing point between the seal and the piston, this allows an initial pressure to be built up in the pumping chamber in the pumping phase, which promotes the pressure activation of the seal.

Within the scope of a preferred embodiment, the seal can have a radially outwardly protruding, in particular circumferential web at a (first) axial end. In other words, the web protrudes radially on the outer lateral surface of the seal (base section). The seal thus has an L-shaped cross section. The rigidity of the seal is increased by the web. In addition, the seal can be centered in the radial direction in the pump housing. This allows the seal to be installed in a fixed position in the pump housing. The axial end with the web can face the conveying chamber or can face away from the conveying chamber. The web can be designed as an annular shoulder. The length of the bar must be adapted to the application and the prevailing system pressure. The web can, for example, have a length of 0.2 mm - 2 mm.

Advantageously, the seal can have a further radially outwardly protruding web at a second axial end (another web protrudes from the base section). The seal thus has a C or U-shaped cross section. The rigidity of the seal is further increased by the further web. The centering of the seal in the radial direction in the pump housing is improved again. The arrangement of the seal in a fixed position in the pump housing is favoured. The further web can be designed as an annular shoulder. The additional web can have a length of 0.2 mm-2 mm, for example.

According to a preferred embodiment, the web and/or the further web can have a radial play of, for example, 0.001-1 mm at their radially outer edge relative to the peripheral wall of the recess accommodating the pump piston. In other words, the webs have an outer diameter that is slightly smaller than the inner diameter of the recess (bore) that accommodates the pump piston at the point where the seal is seated.

This play means that the radial position of the seal can be adjusted precisely to the position of the pump piston. This can result in a uniform and symmetrical gap to the pump piston.

In each suction phase of the pump piston (pump piston moves away from the pumping chamber) there is the possibility of a realignment of the seal. In the delivery phase (pump piston moves to the delivery chamber, compresses and delivers fuel), delivery pressure builds up on the side of the seal facing the delivery chamber. This pressure acts on the (first) face of the seal and causes the seal to experience a force in the axial direction, which presses the seal onto the fastening ring.

During the pumping phase, the seal cannot move in the radial direction, or only to an insignificant extent, due to the axial force acting on it. A static sealing point can develop between the contact surfaces of the seal (second face) and the fastening ring. This prevents fuel from escaping from the pumping chamber and reducing the degree of delivery. The contact surfaces of the seal and the fastening ring can be oriented transversely, in particular orthogonally (angle of 90±2°), to the axial direction of the pump piston.

Expediently, the seal can have a peripheral collar on the face side at the (first) axial end on which the web is arranged. The collar ensures that the axial force acting on the seal from the pumping chamber runs through the seal with an optimal distribution of force and is introduced precisely into the static sealing point (contact surface between the seal and the fastening ring). This results in increased surface pressure and an even better static sealing effect. The collar protrudes from the seal in the axial direction. The collar is arranged on the face side, in particular on the radially inner annular edge of the seal.

Advantageously, the (first) guide element and the fastening ring can be combined to form one component—that is to say, in particular, in one piece. The combined component then assumes the function of guiding and fastening. The number of to be manufactured and to mounting elements can be reduced. This favors a cost-effective design of the piston pump. The component and the seal can overlap each other axially. A section of the component can thus be arranged radially between the pump piston and the pump housing.

In the context of a preferred embodiment, an O-ring can be arranged between the radially outer lateral surface of the seal and the pump housing (peripheral wall of the recess for the pump piston). The O-ring has a radial sealing effect. The O-ring supplements the static sealing point and improves the sealing effect.

In addition, a support ring for the O-ring can be arranged between the radially outer lateral surface of the seal and the pump housing (peripheral wall of the recess for the pump piston). This protects the O-ring since damage, such as extrusion of the O-ring, can be prevented. The support ring is arranged in particular on the side of the O-ring facing away from the pumping chamber and can have a triangular profile in cross section. The hypotenuse of the triangular profile may face the O-ring.

The seal is in particular a pressure-activated seal. This means that a small gap between the seal and the pump piston is sufficient to build up an initial pressure in the pumping chamber and thus also on the radially outer edge of the ring (back of the seal). The back pressure on the seal deforms it and thus reduces the gap to the pump piston on the inner edge of the ring. Due to the smaller sealing gap, greater pressure can be built up in the pumping chamber and thus also on the back of the seal, so that the seal deforms more due to the higher pressure and the gap to the pump piston is further reduced. This is a self-reinforcing effect that continues until system pressure is reached.

The deformation can take place, for example, when there are two webs between the two webs. As a result, the sealing effect takes place at a defined point. The seal geometry can be designed so that at When the system pressure is reached, there is either a very small gap, e.g. 0.001 mm - 0.01 mm, or the seal comes into contact with the pump piston and the sealing surfaces (of the seal and the pump piston) touch. Whether there is still a gap at system pressure or whether the seal is in direct contact with the piston depends on the specific requirements (degree of delivery, wear over service life, etc.). Due to the pressure activation, very high system pressures can be run, since the higher the system pressure, the more the seal deforms and the sealing gap becomes smaller and smaller.

Due to the principle, the seal is low-wear, since a tribological contact only occurs in the pumping phase (during the pressure activation of the seal). This corresponds to exactly half the running time of the piston pump. In the suction phase (during which there is no pressure activation), the seal is flushed with fuel. In this way, new fuel is constantly introduced into the sealing gap, which acts as a lubricant. Pressure activation of the seal makes it possible to compensate for wear. When the sealing surface of the seal wears, the pressure activation causes the seal to deform regularly to the gap designed in the basic design or to contact the pump piston.

Figur 1

eine schematische Darstellung eines Kraftstoffsystems mit einer Kraftstoff-Hochdruckpumpe in Form einer Kolbenpumpe;

Figur 2

einen teilweisen Längsschnitt durch die Kolbenpumpe von Figur 1;

Figur 3

eine vergrößerte Ansicht eines Pumpenkolbens, einer Dichtung, eines Führungselements und eines Befestigungsrings der Kolbenpumpe aus Figur 1;

Figur 4

die Dichtung aus Figur 3 in einer vergrößerten Schnittansicht;

Figur 5

einen teilweisen Längsschnitt durch eine alternative Ausgestaltung der Kolbenpumpe aus Figur 1;

Figur 6

einen teilweisen Längsschnitt durch eine alternative Ausgestaltung der Kolbenpumpe aus Figur 1 mit Dichtung in einer 1. Orientierung;

Figur 7

die Kolbenpumpe aus Figur 6 mit Dichtung in einer 2. Orientierung;

Figur 8

die Kolbenpumpe aus Figur 6 mit einem Federelement;

Figur 9

die Dichtung aus Figur 3 in einer vergrößerten Schnittansicht mit O-Ring und Stützring;

Figur 10

die Dichtung aus Figur 6 in einer vergrößerten Schnittansicht mit O-Ring und Stützring; und

Figur 11

eine alternative Ausgestaltung einer Dichtung für die Kolbenpumpe aus Figur 2.

The invention is explained in more detail below with reference to the figures, with identical or functionally identical elements being provided with reference symbols only once, if necessary. Show it:

figure 1

a schematic representation of a fuel system with a high-pressure fuel pump in the form of a piston pump;

figure 2

a partial longitudinal section through the piston pump from figure 1 ;

figure 3

Figure 12 shows an enlarged view of a pump piston, a seal, a guide element and a fastening ring of the piston pump figure 1 ;

figure 4

the seal off figure 3 in an enlarged sectional view;

figure 5

a partial longitudinal section through an alternative embodiment of the piston pump figure 1 ;

figure 6

a partial longitudinal section through an alternative embodiment of the piston pump figure 1 with seal in a 1st orientation;

figure 7

the piston pump off figure 6 with seal in a 2nd orientation;

figure 8

the piston pump off figure 6 with a spring element;

figure 9

the seal off figure 3 in an enlarged sectional view with O-ring and support ring;

figure 10

the seal off figure 6 in an enlarged sectional view with O-ring and support ring; and

figure 11

an alternative embodiment of a seal for the piston pump figure 2 .

A fuel system of an internal combustion engine carries in figure 1 overall reference numeral 10. It includes a fuel tank 12, from which an electric pre-supply pump 14 delivers the fuel to a piston pump 16 designed as a high-pressure fuel pump. This conveys 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 the internal combustion engine (not shown).

The piston pump 16 comprises an inlet valve 22, an outlet valve 24, and a pump housing 26. A pump piston 28 is accommodated in this housing such that it can be moved back and forth. The pump piston 28 is set in motion by a drive 30, the drive 30 in the figure 1 is shown only schematically. The drive 30 can be a camshaft or an eccentric shaft, for example. The inlet valve 22 is designed as a quantity control valve, through which the quantity of fuel delivered by the piston pump 16 can be adjusted.

The structure of the piston pump 16 is shown in more detail figure 2 , whereby only the essential components are mentioned below. The pump piston 28 is designed as a stepped piston with an in figure 2 lower plunger section 32, a guide section 34 adjoining this and an upper end section, not shown in detail. The guide section 34 has a larger diameter than the plunger section 32 and the end section.

The end section and the guide section 34 of the pump piston 28, together with the pump housing 26, delimit a pumping chamber 38, which is not shown in detail. The pump housing 26 can be designed as an overall rotationally symmetrical part. The pump piston 28 is accommodated in the pump housing 26 in a recess 40 present there, which is designed as a stepped bore 42 . The bore 42 has several stages (three stages 42', 42", 42‴; see figure 2 and 3 ).

A seal 44 is arranged between the guide section 34 of the pump piston 28 and an inner peripheral wall of the bore 42 (step 42"). It seals directly between the pump piston 28 and the pump housing 26, and thus seals the pumping chamber located above the seal 44 (high-pressure area ) compared to the in figure 2 below the seal 44 arranged area (low pressure area), in which, inter alia, the plunger portion 32 of the pump piston 28 is located. The seal 44 is designed as a plastic ring. Gasket 44 includes a generally sleeve-shaped base portion 45 having a cylindrical outer surface.

A guide element 46 separate from the seal 44 is arranged between the guide section 34 of the pump piston 28 and the inner peripheral wall of the bore 42 (step 42 ′). The guide element 46 may be axially adjacent to the seal 44 and is in figure 2 arranged above the seal 44 (facing the pumping chamber). The guide element 46 is ring-shaped (guide ring) and can be attached to the step 42'.

The piston pump 16 has a further guide element 48 which is arranged in a seal carrier 50 of the piston pump 16 (see FIG figure 2 ).

The guide element 46 and the further guide element 48 are used to guide the pump piston 28 . The further guide element 48 is ring-shaped (guide ring) and can be fastened to the seal carrier 50 .

The piston pump 16 has a fastening ring 52 for the seal 44 between the guide section 34 of the pump piston 28 and the inner peripheral wall of the bore 42 (step 42 ‴). The seal 44 rests on the mounting ring 52 . A static sealing point 53 is formed by the contact surfaces of seal 44 and fastening ring 52 (see Fig figure 3 ). The seal 44, the guide element 46, the further guide element 48 and the fastening ring 52 form a seal assembly.

At its first axial end 54, the seal 44 has a radially outwardly protruding web 56 (see FIG figure 4 ) protruding from the base portion 45. The web 56 is designed as an annular shoulder which protrudes radially beyond the outer lateral surface 58 of the seal 44 . The web 56 surrounds the seal 44 (shell surface 58) completely.

At its second axial end 60 , the seal 44 has a further radially outwardly protruding web 62 which protrudes from the base section 45 . The further web 62 is also designed as an annular shoulder, which protrudes radially beyond the outer lateral surface 58 of the seal 44 . The further web 62 completely surrounds the seal 44 (lateral surface 58). The seal 44 has a U-shaped cross section.

The web 56 and the further web 62 have radial play 64 on their radially outer edge relative to the peripheral wall of the recess 40 (step 42") receiving the pump piston 28 (see FIG figure 3 ). As a result, the seal 44 can be aligned in the radial direction with respect to the pump piston 28 . In addition, the pressure 65 prevailing in the conveying chamber also reaches the outer lateral surface 58 via this gap (play 64), so that the sealing wall 66 undergoes a radial inward deformation 69 due to the force acting there (arrow 68) (see Fig figure 4 ). Thus forms between the pump piston 28, in particular between the guide section 34 and the seal 44 (radially inner annular edge 70) from a dynamic sealing point.

The pressure prevailing in the conveying chamber also ensures that a force F (arrow 72) acts on the first end face 74 of the seal 44 (see figure 4 to the right). Optionally, the seal 44 has a circumferential collar 76 on the face side at the first axial end 54 on which the web 56 is arranged. This ensures that the force F (axial force; arrow 72) runs optimally through the seal 44 and is introduced exactly into the static sealing point 53. The peripheral collar 76 is formed on the radially inner annular edge 70 of the seal 44 on the second end face 78 .

According to an alternative embodiment, the first guide element 46 and the fastening ring 52 can be combined into one component 80 (see FIG figure 5 ). The component 80 takes over the guiding and fastening function. The component 80 and the seal 44 overlap each other axially (axial direction of the pump piston 28). Thus, an overlapping portion 82 of the unified component 80 is disposed radially between the pump piston 28 (guide portion 34) and the pump housing 26 (peripheral wall of the bore 42). The tour can take place on an in figure 5 lower section 84 take place. The component 80 can be fastened in the bore 42 in the lower section 84 or in the overlapping section 82, e.g. by means of a projection 86 protruding radially outwards.

figure 6 shows an alternative embodiment of the piston pump 16 figure 3 , wherein the seal 44 has only the first web 56 emanating from the base section 45 and the circumferential collar 76 . The other web 62 is omitted. The seal 44 thus has an L-shaped cross section. The web 56 faces the fastening ring 52 . When pressure is applied to the seal 44 (delivery phase) by the force F (arrow 68), this causes a deformation 88 of the seal 44 in in figure 6 upper range 90.

figure 7 shows a further alternative embodiment of the piston pump 16 figure 3 , which the design of the piston pump 16 from figure 6 corresponds with the seal 44 being oriented such that the land 56 corresponds to the (first) Guide member 46 faces. When pressure is applied to the seal 44 (delivery phase) by the force F (arrow 68), this causes a deformation 88 of the seal 44 in in figure 7 lower portion 92 (facing the mounting ring 52).

figure 8 shows a further alternative embodiment of the piston pump 16 figure 3 , Which largely the design of the piston pump 16 from figure 6 corresponds and additionally has a spring element 47 . A spring element 47 can be arranged between the pump piston 28 and the pump housing 26 and presses the seal 44 against the fastening ring 52 . The spring element 47 can be arranged in the axial direction of the pump piston 28 between the guide element 46 and the seal 44 . The spring element 47 can be designed as a compression spring in the form of a spring washer or helical spring. The spring element 47 bears axially at one end, in particular on the guide element 46, and at the other end presses the seal 44 against the fastening ring 52.

An O-ring 94 can be arranged between the radially outer lateral surface 58 of the seal 44 and the pump housing 26 (see FIG figure 9 and 10). This serves to reinforce the static sealing point 53 and improves the sealing effect. In addition, a support ring 96 for the O-ring 94 can be arranged between the radially outer lateral surface 58 of the seal 44 and the pump housing 26 . The support ring 96 serves to protect the O-ring 94, for example to prevent the O-ring 94 from being extruded. figure 9 12 illustrates the O-ring 94 and backup ring 96 configuration on the U-shaped profile seal 44 according to FIGS Figures 3 and 4 . figure 10 12 illustrates this configuration for a seal 44 with only one land 56 (L-shaped profile) according to FIGS figures 6 , 7 and 8th .

figure 11 shows an alternative, simplified design of a seal 44, which has only the base section 45 and is sleeve-shaped overall. The seal 44 has a constant sealing wall 66 in which the inner lateral surface 70 and the outer lateral surface 58 are parallel to one another. The seal 44 thus has an I-shaped cross section. Thus, when a force F (arrow 68) acts on the seal 44, it occurs to a parallel displacement 102. This can be advantageous if a larger sealing surface is required. Such a configuration of the seal with a profile that is rectangular in cross section is comparatively simple in the manufacturing process.

Claims (8)

1. 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) delimited at least by the pump housing (26) and the pump piston (28), wherein a seal (44) for sealing off 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 formed as a plastic ring with a substantially sleeve-shaped base portion (45),
   characterized in that
   a fastening ring (52) for the seal (44) is arranged between the pump housing (26) and the pump piston (28), wherein a further guide element (48) is arranged in a seal carrier (50) of the piston pump (16).
2. Piston pump (16) according to Claim 1, characterized in that a spring element (47), which presses the seal (44) against the fastening ring (52), is preferably arranged between the pump piston (28) and the pump housing (26).
3. Piston pump (16) according to one of the preceding claims, characterized in that the seal (44) has, at one axial end (54), a radially outwardly projecting web (56) which is formed on the sleeve-like base portion (45), so that the seal (44) has an overall L-shaped cross section.
4. Piston pump (16) according to one of the preceding claims, characterized in that the seal (44) has, at a second axial end (60), a further radially outwardly projecting web (62) which is formed on the sleeve-like base portion (45), so that the seal (44) has an overall U-shaped or C-shaped cross section.
5. Piston pump (16) according to Claim 3 or 4, characterized in that the web (56) and/or the further web (62) have play (64) at their radially outer edge relative to the circumferential wall of the recess (40) which receives the pump piston (28).
6. Piston pump (16) according to one of the preceding claims, characterized in that the seal (44) has a circumferential collar (76) on the end face at the axial end (54).
7. Piston pump (16) according to one of Claims 1 to 6, characterized in that the guide element (46) and the fastening ring (52) are combined to form one component (80) .
8. Piston pump (16) according to one of the preceding claims, characterized in that an O-ring (94) is arranged between the radially outer lateral surface (58) of the seal (44) and the pump housing (26), preferably wherein a supporting ring (96) for the O-ring (94) is arranged between the radially outer lateral surface (58) of the seal (44) and the pump housing (26).

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