EP3655649B1 - Piston pump, in particular high-pressure fule injection pump for a combustion engine - 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, according to the preamble of claim 1.

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 at will, for example due to the thermal expansion coefficients of the materials used, leads to a suboptimal degree of delivery, especially at low speeds.

More piston pumps are in the DE 195 19 833 A1 , the DE 10 2015 202 632 A1 and the DE 10 2014 225 925 A1 disclosed

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 in the dependent claims specified. 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 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 metal sleeve with a radially outwardly projecting web.

Such a piston pump can be manufactured comparatively easily, as a result of which the component costs are reduced. This is due to 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 metal sleeve with a web, 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 realized by separate components, namely by the guiding element and the seal (metal sleeve with web).

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. The guide element can have a radial gap (guide gap) towards the pump piston, which gap can be so small that the guide element serves as cavitation protection for the seal. The guide gap can be sufficient be small so that no steam bubbles can reach the seal. The risk of damage to the seal is thus reduced.

The seal is designed as a metal sleeve with a web that protrudes radially outwards, so that the seal has a profile that is particularly L-shaped in cross section. The seal thus has a sleeve section and a web section. The seal is based on a U-ring seal, but has been optimized in terms of design and has a radial web. The seal is in particular a high-pressure seal which seals off 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 can be centered in the radial direction in the piston pump (recess) by the web. In this way, the seal can be installed in a fixed position in the pump housing. The wall thickness of the metal sleeve depends on the system pressure and is designed accordingly. The wall thickness can be, for example, 0.05mm - 1.0mm (millimeters).

As part of a preferred embodiment, a further guide element can be 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).

A fastening ring for the seal can advantageously be 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. To position in To allow radial direction between piston and seal, it is advantageous if the seal has an axial play, for example from 0.01mm - 1mm (millimeter). It can therefore be a "floating seal" that is not fixed either axially or radially. The seal can thus be optimally positioned axially to the pump piston.

Within the scope of a preferred embodiment, the guide element and the fastening ring can be combined to form one component, that is to say in particular can be formed in one piece. The combined component can then assume the function of guiding and fastening. The number of elements to be manufactured and assembled can be reduced as a result. This favors a cost-effective design of the piston pump. The combined component and seal may axially overlap each other. A section of the combined component can thus be arranged radially between the pump piston and the pump housing.

According to the invention, the web of the seal has a radial play of, for example, 0.01 mm-1 mm at its radially outer edge relative to the peripheral wall of the recess accommodating the pump piston. In other words, the ridge has an outside diameter that is slightly smaller than the inside diameter of the recess (bore) that accommodates the pump piston at the location where the ridge is located. Or, to put it more generally: the seal can move radially relative to the pump housing. This play or the radial mobility 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 ("floating seal").

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 towards the delivery chamber, compresses and delivers fuel), delivery pressure builds up above the seal (facing the delivery chamber) and radially outside the seal. The delivery pressure acts on the face of the seal and on the web of the seal and causes the seal to experience a force in the axial direction (axial direction of the pump piston), which pushes the seal onto the fastening ring presses. During this phase, the seal cannot move in the radial direction, or only to an insignificant extent, due to the axial force. This axial force creates a contact pressure that presses the seal onto the fastening ring. A static sealing point is created between these two surfaces (seal and fastening ring). This prevents fuel from escaping from the pumping chamber and thus reduces the degree of delivery.

A spring element, which presses the seal against the fastening ring, can preferably be arranged between the pump piston and the pump housing. This ensures that the seal is always in contact with the static sealing point between the seal and the fastening ring. The spring can be a compression spring. The compression spring can be designed as a helical spring or as a corrugated spring.

As an alternative to this, the seal can have at least one spring element which is connected to the seal and which presses the seal against the fastening ring. This can also be used to ensure that the seal is in contact with the static sealing point. In concrete terms, the spring element or elements can be formed in one piece with the seal. This reduces the number of components to be manufactured and assembled. The spring element or elements can extend from the sleeve section or from the web section of the seal. The spring element or elements can be designed as spring arms.

The seal can be a pressure activated seal. This means that the small gap between the guide element and the pump piston is sufficient to generate 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 (sleeve section). 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 is deformed more due to the higher pressure and the gap to the pump piston is further reduced. This is a self-reinforcing effect, which continues until the system pressure is reached.

The seal geometry can be designed in such a way that when the system pressure is reached, either a very small gap is created, e.g. from 0.001 mm to 0.1 mm, or the seal rests directly on 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 half the running time of the piston pump. In the suction phase (during which no pressure activation takes place), the seal is flushed, in particular, by 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.

In the context of a preferred embodiment, an O-ring can be arranged between the outer lateral surface of the seal and the pump housing. The O-ring has a radial sealing effect. The O-ring supplements the static sealing point and improves the sealing effect. The O-ring sits in particular on the ridge of the seal, specifically on the side of the ridge facing the pumping chamber.

The seal can advantageously be arranged in such a way that the web rests on the fastening ring. A static sealing point can thus form between the web of the seal and the contact surface of the fastening ring, on which the web rests. As a result, a pressure-activated seal, in particular as described above, can be implemented with a simple design.

Alternatively, the mounting ring may have an axially projecting collar on which the web rests, and the sleeve portion of the seal and the collar may overlap axially. The static sealing point is thus formed between the web of the seal and the collar of the fastening ring. The seal is then not pressure-activated because there is no high system pressure behind the seal (at the radially outer ring edge of the seal). Since there is no pressure activation, the seal material and/or the geometry can be designed in such a way that there is little or no deformation (expansion) of the seal when the system pressure is applied.

This can be achieved by a sufficiently large wall thickness (sleeve section) of the seal, with the wall thickness being 0.25 mm - 2 mm, for example. The seal can be oversized (compression), undersized (play) or a transition fit to the 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 0.001-0.1 mm. The guidance of the piston and the fastening of the seal can be largely identical to the previously described pressure-activated variant. The advantage of the non-pressure-activated sealing concept is that if the seal is designed with undersize (play) to the piston, there is no solid body contact between the seal and the piston at any operating point, since the system pressure, which is present in the dynamic sealing point, always closes the seal forces an expansion. As a result, there is no wear and tear on the seal or on the piston over the service life.

At least one spring element that is separate or arranged on the seal can also be provided in the non-pressure-activated seal in order to ensure that the seal rests against the static sealing point. This structure also has the advantage that excess pressure cannot occur in the high-pressure system, since the seal expands even more in the event of excess pressure, thus allowing a pressure drop. With an advantageous design of this effect, it may be possible that a pressure limiting valve installed internally in the piston pump or externally in the fuel system can be omitted.

In a preferred embodiment, the seal can be made of stainless steel. This achieves good corrosion resistance. The seal is preferably made of stainless steel with an identical or comparable coefficient of linear expansion as the pump piston and the housing. As a result, the seal is independent of the thermal expansion of the pump piston and the pump housing.

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, eines Befestigungsrings und eines Federelements 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 weitere alternative Ausgestaltung der Kolbenpumpe aus Figur 1;

Figur 7

in mehreren, teilweise geschnittenen Ansichten die Dichtung der Kolbenpumpe aus Figur 1 mit verbundenen Federelementen;

Figur 8

in mehreren, teilweise geschnittenen Ansichten die Dichtung der Kolbenpumpe aus Figur 1 mit verbundenen Federelementen in alternativer Ausgestaltung;

Figur 9

in mehreren, teilweise geschnittenen Ansichten die Dichtung der Kolbenpumpe aus Figur 1 mit verbundenen Federelementen in alternativer Ausgestaltung; und

Figur 10

in mehreren, teilweise geschnittenen Ansichten die Dichtung der Kolbenpumpe aus Figur 1 mit verbundenen Federelementen in alternativer Ausgestaltung.

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

an enlarged view of a pump piston, a seal, a guide element, a fastening ring and a spring element 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 a further alternative embodiment of the piston pump figure 1 ;

figure 7

the seal of the piston pump in several, partially sectioned views figure 1 with connected spring elements;

figure 8

the seal of the piston pump in several, partially sectioned views figure 1 with connected spring elements in an alternative configuration;

figure 9

the seal of the piston pump in several, partially sectioned views figure 1 with connected spring elements in an alternative configuration; and

figure 10

the seal of the piston pump in several, partially sectioned views figure 1 with connected spring elements in an alternative configuration.

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 construction 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 delimit, together with the pump housing 26, a pumping chamber 38, which is not shown in detail be formed 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 metal sleeve with a web 45 projecting radially outwards. The gasket 44 has an L-shaped cross section including a sleeve portion 43 and the portion formed by the ridge 45 (ridge portion).

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 is axially in particular directly adjacent to the seal 44 and 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 fastening ring 52 in such a way that the web 45 rests on the fastening 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 sealing assembly. The seal 44 can be formed from stainless steel.

The web 45 projecting radially from the seal 44 has radial play 54 on its radially outer edge relative to the inner 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 . A spring element 56 is arranged between the pump piston 28 and the pump housing 26 and presses the seal 44 against the fastening ring 52 . The spring element 56 is a helical spring 58 designed as a compression spring. This can rest, for example, on the guide element 46 at one end and on the web 45 of the seal 44 at the other end.

The pressure 61 prevailing in the pumping chamber 38 reaches the seal 44 via the radial gap 60 (guide gap), which as described above can serve as cavitation protection for the seal 44. There this pressure acts with a force F (arrow 62) on the first end face 64 of the seal 44 (see figure 4 ). This forces the seal 44 against the mounting ring 52 . In addition, the pressure 61 also acts on the outer lateral surface 66 of the seal 44, so that the seal 44 experiences a deformation 70 due to the force F (arrow 68) acting there. A dynamic sealing point is thus formed between the pump piston 28, in particular between the guide section 34, and the seal 44 (radially inner annular edge 72). An O-ring 74 can optionally be arranged between the outer lateral surface 66 of the seal 44 and the pump housing 26 (stage 42"). The O-ring 74 can rest on the web 45. The O-ring 74 has a radial sealing effect and supports the static sealing point 53. The second face of the seal 44 bears the reference number 65.

figure 5 shows an alternative embodiment of the piston pump 16 figure 2 . This configuration largely corresponds to the piston pump 16 described above, with identical or functionally identical elements being provided with identical reference symbols.

The fastening ring 52 has according to figure 5 an axially projecting collar 76 (in the axial direction of the pump piston 28) which extends into the recess 40 protrudes. The seal 44 is arranged in such a way that the web 45 rests on the collar 76 . The sleeve portion 43 of the seal 44 and the collar 76 overlap each other axially. The collar 76 is arranged radially between the sleeve section 43 and the inner peripheral wall of the recess 40 (step 42"). The seal 44 is formed on the sleeve section 43 and on the web section 45 with a greater wall thickness. The static sealing point 53 is formed between the web 45 and the collar 76. The spring element 56 is designed as a compression spring in the form of a corrugated spring 78.

The radially inner annular edge 72 of the seal 44 has a clearance 80 relative to the pump piston 28 , in particular to the guide section 34 of the pump piston 28 . Thus, there is no contact between the seal 44 and the pump piston 28 in any operating state of the piston pump 16, since the pressure reaching the dynamic sealing point 82 from the pumping chamber 38 acts on the seal 44 in such a way that it undergoes a deformation 84 and is expanded. As a result, there is no wear on the seal 44 or the pump piston 28 over the service life.

figure 6 shows a further alternative embodiment of the piston pump 16 figure 2 . This configuration corresponds largely to the above Figures 1 to 4 described piston pump 16, wherein identical or functionally identical elements are provided with identical reference numerals.

In the present configuration, the first guide element 46 and the fastening ring 52 are combined to form a component 95 (one-piece configuration). The component 95 takes over the management and fastening function. The united member 95 and the packing 44 axially overlap each other (axial direction of the pump piston 28). Thus, an overlapping portion 93 of the unified component 95 is disposed radially between the pump piston 28 (guide portion 34) and the pump housing 26 (peripheral wall 42' of bore 42).

The guide can take place on a lower section 97 of the component 95 . The component 95 can be fastened in the bore 42 in the lower section 97 or in the overlapping section 93 of the component 95, for example by means of interference fit, caulking or a projection 99 projecting radially outwards from component 95.

the Figures 7 to 10 show possible configurations of the seal 44, in which the seal 44 itself has at least one spring element 56 (one-piece configuration). A separate spring element can be dispensed with. This simplifies the manufacture and assembly of the piston pump 16 . Such a seal 44 with spring element 56 formed thereon can be used in both a piston pump 16 according to FIG figure 2 as well as in a piston pump 16 according to figure 5 or figure 6 be used.

figure 7 shows a seal 44 which has three spring elements 56 which are designed as small spring arms 86 . The spring arms 86 extend starting from the web section 45 of the seal 44. The spring arms 86 each extend from an edge section 88 protruding radially beyond the outer edge of the web section 45. The spring arms 86 have an arcuate shape in plan view and protrude from the web section 45 axially from the web portion 45 (towards the end face 64 of the seal 44).

The seal 44 according to figure 8 also has three small spring arms 86 which extend axially from the web section 45 of the seal 44 away from the web section 45 . The spring arms 86 extend from the radially outer edge of the web section 45. The spring arms 86 each have an arm section 90 parallel to the sleeve section 43 of the seal 44 and an angled arm section 92.

The seal 44 according to figure 9 also has three spring arms 86 which extend from the sleeve portion 43 of the seal 44 away. The small spring arms 86 protrude from the first end face 64 of the seal 44 and are angled toward the sleeve section 43 .

The design of the seal 44 according to figure 10 largely corresponds to the in figure 7 shown seal 44. Deviating from this extend in the seal 44 according to figure 9 the small spring arms 86 from the web section 45 to the side of the web section 45 facing away from the sleeve section 43 Spring arms 86 beyond the second end face 65 of the seal 44 .

Claims (9)

1. Piston pump (16), in particular high-pressure fuel pump for an internal combustion engine, having a pump housing (26), a pump piston (28) and a delivery chamber (38) delimited at least also by the pump piston (28) and the pump housing (26), 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), characterized in that the seal (44) is in the form of a metal sleeve with a radially outwardly projecting flange (45), wherein the flange (45) has a clearance (54) at its radially outer edge with respect to the peripheral wall of the recess (40) accommodating the pump piston (28).
2. Piston pump (16) according to Claim 1, characterized in that a fastening ring (52) for the seal (44) is arranged preferably between the pump piston (28) and the pump housing (26).
3. Piston pump (16) according to Claim 2, characterized in that the guide element (46) and the fastening ring (52) have been combined to form one component ().
4. Piston pump (16) according to one of the preceding claims, characterized by a further guide element (48) which is arranged in a seal carrier (50) of the piston pump (16).
5. Piston pump (16) according to one of the preceding claims, characterized in that a spring element (56) is arranged preferably between the pump piston (28) and the pump housing (26), said spring element (56) pressing the seal (44) against the fastening ring (52) .
6. Piston pump (16) according to one of Claims 1 to 4, characterized in that the seal (44) has at least one spring element (56) which is connected to the seal (44) and which presses the seal (44) against the fastening ring (52).
7. Piston pump (16) according to one of the preceding claims, characterized in that an O-ring (74) is arranged between the outer lateral surface (66) of the seal (44) and the pump housing (26), and/or in that the steel (44) is made from stainless steel.
8. Piston pump (16) according to one of the preceding claims, characterized in that the seal (44) is arranged in such a way that the flange (45) rests on the fastening ring (52).
9. Piston pump (16) according to one of Claims 1 to 7, characterized in that the fastening ring (52) has an axially projecting collar (76) on which the flange (45) rests, and in that the sleeve portion (43) of the seal (44) and the collar (76) axially overlap one another.

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