EP1633971B1 - Radial piston pump for generating high pressure for fuel in fuel injection systems of combustion engines - Google Patents

Description

The invention relates to a radial piston pump for fuel high pressure generation in fuel injection systems of internal combustion engines, in particular in a common rail injection system, with a mounted in a pump housing drive shaft with an eccentric shaft portion on which a roller is mounted, and preferably with a plurality of radial relative to the drive shaft arranged in a respective cylinder piston, at whose ends facing the roller respectively a Kolbenfußplatte is arranged, which contacts the peripheral surface of the roller, according to the preamble of claim 1.

Such a radial piston pump is known for example from DE 198 09 315 A1. The Kolbenfußplatte and the roller of the known radial piston pump are usually made of case-hardened steel or made of tempered steel. Over time, however, these components may experience sliding wear due to adhesion, abrasion, or surface disruption. This undesirable wear can lead to a failure of the radial piston pump and thus also to a failure of the internal combustion engine.

In EP 1 310 577 A1 a radial piston pump is described in which the piston foot plate consists of an alloyed tool steel which has a nitriding layer on the surface.

DE 199 05 462 A1 discloses a radial piston pump with a piston made of zirconia, alumina-zirconia or alumina ceramic.

The present invention has for its object to further develop a radial piston pump of the type mentioned in such a way that its reliability is increased.

According to the invention this object is achieved by the characterizing features of claim 1.

For the first time, the area of the piston footplate contacting the peripheral surface of the roller has an insert made of a wear-resistant material, namely hard metal, a ceramic material, a cast carbide material or cermet, and / or at least part of the roller, in particular at least one part The circumferential surface of the roller of a wear-resistant material, namely made of hard metal, a sintered tool steel or an alloyed nitriding steel, the wear tendency of the Kolbenfußplatten-roller friction pairing is significantly reduced. The materials mentioned have a significantly higher modulus of elasticity compared with the steel materials used hitherto, which results in lower deformations under load and consequently also in a more uniform surface pressure without appreciable stress peaks. When using ceramic materials, especially their lower weight plays a role, resulting in a low inertia of the roller and the Kolbenfußplatte.

Preferably, the piston is made of a ceramic material, preferably of a Si ₃ N ₄ - or a ZrO ₂ ceramic and is produced by extrusion and has a porosity of less than 5%, wherein the surface is infiltrated with MoS ₂ . In particular, the piston is isostatically extruded and sintered. This results in a very smooth surface with a low coefficient of friction, which also has a favorable effect on the wear behavior.

In this case, the roller can be made entirely of the wear-resistant material or it consists as before of case-hardened steel or tempered steel and carries at least one insert of the wear-resistant material. The use of inserts brings the advantage of a modular construction, ie that of a standardized roller and a standardized

Kolbenfußplatte can each be provided with inserts of different material and thus a variety of mating variants can be generated.

Due to the material properties of the wear-resistant materials used, the following sliding pairings are to be particularly preferred:

The roller is made of tempered steel and has tungsten carbide inserts such as G20, GC37 or GC20, and the piston footplate has a ceramic insert such as Si ₃ N ₄ ceramic, shell casting such as SoGSH or cermet.

The castor consists of a precision casting such as GX-210WCr13 H and the piston foot disc has a ceramic insert such as Si ₃ N ₄ ceramic, carbide such as G20 or cermet.

The castor is made of a cast carbide material such as SoGGH shell casting and the piston footplate has a ceramic insert such as Si ₃ N ₄ ceramic, hard metal such as G20 or cermet.

The roller is made of sintered tool steel such as ASP23 or an alloyed nitriding steel and the piston footplate has a ceramic insert such as Si ₃ N ₄ ceramic, hard metal such as G20, cermet or a cast carbide material such as SoGGH. The alloyed nitriding steel can contain C and / or Cr and / or V and / or Mo, is gas-nitrided and, in the area of contact with the piston footplate, free of bonding layers.

Another measure provides that the surface of the Kolbenfußplatte and / or the roller has a roughness R _z between 0.15 microns and 2 microns. Specifically, the ceramic material has a roughness R _z between 0.15 microns and 0.5 microns, the carbide a roughness R _z between 0.3 microns and 1.0 microns and the cast carbide a roughness R _z between 0.5 microns and 2.0 μm.

Particularly preferably, the roller has on its peripheral surface at least one transverse groove extending transversely to the direction of movement. In addition, the piston foot plate may also have at least two intersecting grooves on its surface facing the roller. Fuel can accumulate in these grooves acting as a stagnation gap, which promotes the formation of a hydrodynamic sliding film due to the sliding movement between the circumferential surface of the roller and the piston foot plate, whereby the wear on the sliding surfaces is further reduced.

Fig.1

eine Querschnittsdarstellung einer Radialkolbenpumpe mit einer Kolbenfußplatte und einer Antriebswelle gemäß einer ersten Ausführungsform der Erfindung;

Fig.2

eine vergrößerte Querschnittsdarstellung eines Kolbens und einer Kolbenfußplatte gemäß einer weiteren Ausführungsform;

Fig.2a

einen vergrößerten Ausschnitt von Fig.2;

Fig.2b

einen weiteren vergrößerten Ausschnitt von Fig.2;

Fig.3

eine Ansicht von unten auf die Kolbenfußplatte von Fig.2;

Fig.4

eine Querschnittsdarstellung eines Kolbens mit Kolbenfußplatte und einer Antriebswelle gemäß einer weiteren Ausführungsform;

Fig.5

eine Querschnittsdarstellung einer Antriebswelle gemäß einer weiteren Ausführungsform;

Fig.6

eine Ansicht entlang der Linie VI-VI von Fig.5;

Fig.7

eine Ansicht entlang der Linie VII-VII von Fig.6.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. In the drawings shows:

Fig.1

a cross-sectional view of a radial piston pump with a Kolbenfußplatte and a drive shaft according to a first embodiment of the invention;

Fig.2

an enlarged cross-sectional view of a piston and a Kolbenfußplatte according to another embodiment;

2a

an enlarged section of Figure 2;

2b

a further enlarged section of Figure 2;

Figure 3

a bottom view of the Kolbenfußplatte of Fig.2;

Figure 4

a cross-sectional view of a piston with Kolbenfußplatte and a drive shaft according to another embodiment;

Figure 5

a cross-sectional view of a drive shaft according to another embodiment;

Figure 6

a view along the line VI-VI of Figure 5;

Figure 7

a view taken along the line VII-VII of Figure 6.

The radial piston pump 1 shown in FIG. 1 is preferably used for generating the system pressure for the high-pressure accumulator (rail) of a common-rail injection system of a self-igniting internal combustion engine. It comprises a drive shaft 4 mounted in a pump housing 2 and having an eccentric shaft section 6 on which a polygonal roller 8 rotatable relative to the shaft section 6 is received. The polygonal roller 8 has along its peripheral surface 10 with circumferential distance from one another arranged, planar flat portions 12.

On the flat portions 12 of the roller 8 is supported in each case one in a cylinder 14 to the drive shaft 4 radially guided piston 16 with its Kolbenfußplatte 18 from. The piston foot plate 18 is preferably connected by means of a spherical bearing 20 with the drive shaft 4 facing the end of the piston 16 pivotally. The spherical bearing 20 is realized, for example, in that the piston end is formed as a partial ball 22, which engages in a complementarily formed spherical recess 24 in the Kolbenfußplatte 18. In addition, the Kolbenfußplatte 18 is biased together with the piston 16 by a spring 26 against the associated flat portion 12 of the roller 8. The operation of such a radial piston pump 1 is for example in DE 198 02 475 A1 described, therefore, should not be discussed further here.

At least the peripheral surface 10 of the roller 8 contacting surface 28 of the Kolbenfußplatte 18 consists of a wear-resistant material, namely of hard metal, a ceramic material, a cast carbide material or cermet. This is preferably realized in that the Kolbenfußplatte 18 has on its facing the roller 8 surface 28 at least one example disc-shaped insert 30 of the wear-resistant material. The insert 30 may be positively and / or materially connected to the remaining Kolbenfußplatte 18, for example by gluing or by soldering. The insert 30 may, as shown in Figure 1, extend over the entire contact surface 28 of the Kolbenfußplatte 18 with the roller 8 or only over part of it. Alternatively, the entire Kolbenfußplatte 18 may be made of the wear-resistant material, so that no additional insert 30 is necessary.

When using a ceramic material for the Kolbenfußplatte 18 this preferably contains silicon nitrite Si ₃ N ₄ . Hard metals may for example consist of G20, GC37 or GC20, while the cast carbide material may include a chilled cast material, in particular GGH or SoGGH.

Furthermore, the piston 16 itself may be made of wear-resistant material, for example of a Si ₃ N ₄ - or a ZrO ₂ ceramic. The piston 16 can be made by extrusion and have a porosity of less than 5%, the surface being infiltrated with MoS ₂ . Alternatively, the piston 16 may also be isostatically pressed and sintered.

Last but not least, at least part of the roller 8, in particular the flat sections 12, consists of a wear-resistant material, namely of hard metal, of a precision casting material, made of a cast carbide material, a sintered tool steel or an alloyed nitriding steel.

Analogous to the piston foot plate 18, this is preferably realized in that the flat portions 12 are each provided with an insert 32 made of the wear-resistant material, as shown in Fig.1. Such insert 32 is positively and / or cohesively received in each case in a complementary shaped recess 34 in the flat portion 12, for example by gluing or by soldering. Alternatively, the entire roller 8 may consist of the wear-resistant material.

When using hard metal for the inserts 32 or for the roller 8 itself comes a particularly wear-resistant carbide with a Vickers hardness of at least HV 1100 and a fracture toughness K _IC > = 10 MPa / m ^3/2 with binder contents of 12 to 20% in question, particularly preferably G20, GC37 or GC20. In particular hard metals are used here, which have low adhesion coefficients. For example, GX-210WCr13 H forms a suitable investment casting material. For the cast carbide material, locally remelted carbide SoGGH (gradient material) may be considered. The sintered tool steel is ASP23. A nitriding steel alloyed specifically by nitriding or gas nitriding with Cr and / or Mo and / or V and / or C is used for a variant with gradient material. The basic elements and the process parameters during nitriding lead to a deep diffusion with hardnesses of HV 750 to 850 with simultaneously higher strength of the base material. The connecting layer forming in this process is removed by grinding for functional reasons. The surfaces of Kolbenfußplatte 18 and the roller 8 have on the sliding surfaces preferably a roughness R _z between 0.15 microns and 2 microns, depending on the materials used. The lower limit for ceramics, in particular a range from 0.15 μm to 0.5 μm, applies upper limit for metals such as SoGGH or ASP23. For carbide, a roughness R _{z of} between 0.3 μm and 1 μm is provided.

In the table below, preferred material pairings of the piston foot plate 18 on the one hand and the roller 8 on the other hand are listed. If 18 inserts are used both in the roller 8 and in the Kolbenfußplatte, any combinations of material pairings in each case unchanged support bodies are possible. In particular, in the pairings in the table in which the roller 8 preferably consists entirely of the wear-resistant material ("solid material"), inserts 32 of the corresponding material in the region of the flat sections 12 can alternatively also be used, as already shown in FIG is. The roller 8 as a support body for the inserts 32 may then consist of a different material, for example 50Cr4, 42CrV4 or 16MnCr5. A special role comes to the embodiment in the 3rd line in the table. In this case, a carbide zone is formed in each case in the region of the flat sections 12 of the roller 8, which is made of a cast steel material and is shown separately in FIG. This carbidic zone is generated either by a targeted solidification rate during casting of the roller 8 or by remelting and then preferably forms the gradient material SoGGH. The result is consequently a roller 8, in which a carbide zone 33 is formed in the area of the flat sections 12, while the remaining zones and areas of the roller 8 consist of cast steel with unchanged properties. Table: Preferred material pairings caster plunger foot Carbide inserts, eg G20, GC37, GC20 Solid material or inserts made a) ceramic, eg Si ₃ N ₄ .- ceramic b) shell casting, eg SoGGH c) Cermet Solid material made of investment casting material, eg GX-210WCr13 H Solid material or inserts made a) ceramic, eg Si ₃ N ₄ - ceramic b) carbide, eg G20 c) Cermet Solid material made of cast carbide material, eg shell casting SoGGH Solid material or inserts made a) ceramic, eg Si ₃ N ₄ - ceramic b) carbide, eg G20 c) Cermet solid material Solid material or inserts made - made of sintered tool steel, eg ASP23, a) ceramic, eg Si ₃ N ₄ - ceramic b) carbide, eg G20 - made of C, Cr, Mo, V-alloyed nitriding steel c) Cermet d) cast carbide material, eg SoGGH

In the region of the flat portions 12 of the roller 8, one or more transverse grooves 36 may be formed, as best seen with reference to Figure 6. As can be seen from FIG. 7, the transverse groove 36 is arranged in the center of a depression 29 forming a groove outlet of the flat section 12. The depression 29 is formed by two planes arranged at an angle with respect to the flat section 12, in whose section line the transverse groove 36 lies. The sink angle γ of the sink 29 is, for example, less than 15 degrees. The transition from the depression 29 and the flat portion 12 is rounded with a radius R ₄ of preferably less than or equal to 1 mm. The radius R ₄ is generated, for example, by vibratory grinding. In this transverse groove 36 acting as a stowage gap or sink 29, fuel can accumulate, which due to the sliding speed between the Flat portions 12 of the roller 8 and the Kolbenfußplatte 18 promotes the formation of a hydrodynamic sliding film, whereby the wear on the sliding surfaces is reduced.

In the embodiments shown in FIGS. 2 to 4, the parts which are identical and function the same as those of the example of FIG. 1 are identified by the same reference numerals. In contrast to this, in the example according to FIG. 2, the piston foot plate 18 is held by a plate holder 38 on the associated piston 16. The Kolbenfußplatte 18 has on its the piston 16 facing surface on a circular recess 40 into which engages the spherical shaped end 42 of the piston 16 and the bottom of the recess 40 contacted. The plate holder 38 is countered on the piston 16 by means of a snap ring 46 engaging in a groove 44 of the piston 16. In a circular recess 48 in the Kolbenfußplatte 18 a complementarily shaped insert 30 is held from one of the wear-resistant materials described above, for example by material bond, in particular by soldering. As is apparent from Fig.2a, the insert 30 is provided on its side facing the roller 8 surface 31 at the edge with an angular outlet 35, wherein the outlet angle α is about 15 degrees. Furthermore, the transition between this surface 31 and the outlet 35 is rounded with a radius R ₂ of about 2 mm. By means of a radius R ₁ of less than or equal to 1 mm, the transition between the outlet 35 and the edge surface 37 of the insert 30 is rounded.

Analogous to the flat portions 12 of the roller 8, the inserts 30 of the Kolbenfußplatte 18 preferably at least two intersecting grooves 50, as best Fig.3 shows. Due to the intersecting arrangement of the grooves 50, the likelihood is high that with respect to the piston foot plate 18 rotatable with respect to the plate holder 38, one of the grooves 50 is oriented transversely to the direction of motion to promote formation of a hydrodynamic lubricating film. The grooves 50 are preferably produced by press-fitting. Thereby results in a lower notch effect compared to cutting processes, since the material fibers are not severed. As is apparent from Fig.2b, the grooves 50 are each arranged in the center of a groove forming a drain 39 of the surface 31. The depression is formed by two planes arranged at an angle with respect to the surface 31, in whose section line the respective groove 50 lies. The sink angle β of the depression 39 is, for example, 5 degrees. The transition from the depression 39 and the surface 31 is rounded with a radius R ₃ of preferably less than or equal to 1 mm.

In the embodiment of Fig. 4, the piston foot plate 18 is made entirely of one of the above-mentioned wear-resistant materials and is inserted into the through-hole 52 of a ring bushing 54 made of steel. The connection between the annular bushing 54 and the Kolbenfußplatte 18 is preferably made by soldering. Of course, further possibilities are conceivable to attach wear-resistant material to the mutually associated sliding surfaces 12, 28 of the roller 8 and piston foot plate 18.

Claims (14)

1. A radial piston pump (1) for high-pressure fuel generation in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a drive shaft (4) which is mounted in a pump casing (2) and has an eccentric shaft section (6) on which a running roller (8) is mounted, and having preferably a plurality of pistons (16), which are arranged in a respective cylinder (14) radially with respect to the drive shaft (4) and each have a piston footplate (18), which makes contact with the circumferential surface (10, 12) of the running roller (8), at their ends facing the running roller (8), characterized in that that surface (28, 31) of the piston footplate (18) which is in contact with the circumferential surface (10, 12) of the running roller (8) has at least one insert (30) made from a wear-resistant material, namely of hard metal, a ceramic material, a cast carbide material or cermet, and/or in that at least part of the running roller (8), in particular at least part of the circumferential surface (10, 12) of the running roller (8), consists of a wear-resistant material, namely of hard metal, a sintered tool steel or an alloyed nitriding steel.
2. The radial piston pump as claimed in claim 1, characterized in that the piston (16) consists of a ceramic material.
3. The radial piston pump as claimed in at least one of the preceding claims, characterized in that the running roller (8) consists of a heat-treated steel and has inserts (32) made from hard metal, such as G20, GC37 or GC20, and in that the piston footplate (18) has inserts (30) made from ceramic, such as Si₃N₄ ceramic, from chilled cast iron, such as SoGGH, or from cermet.
4. The radial piston pump as claimed in claim 1 or 2, characterized in that the running roller (8) consists of a precision-cast material, such as GX-210WCr13 H, and in that the piston footplate (18) has inserts (30) made from ceramic, such as Si₃N₄ ceramic, from hard metal, such as G20, or from cermet.
5. The radial piston pump as claimed in claim 1 or 2, characterized in that the running roller (8) consists of a cast carbide material, such as chilled cast iron SoGGH, and in that the piston footplate (18) has inserts (30) made from ceramic, such as Si₃N₄ ceramic, from hard metal, such as G20, or from cermet.
6. The radial piston pump as claimed in claim 1 or 2, characterized in that the running roller (8) consists of sintered tool steel, such as ASP23, or of an alloyed nitriding steel, and in that the piston footplate (18) has inserts (30) made from ceramic, such as Si₃N₄ ceramic, from hard metal, such as G20, from cermet or from a cast carbide material, such as SoGGH.
7. The radial piston pump as claimed in claim 6, characterized in that the alloyed nitriding steel contains C and/or Cr and/or V and/or Mo, is gas-nitrided and does not have a compound layer in the region of contact with the piston footplate (18).
8. The radial piston pump as claimed in at least one of the preceding claims, characterized in that the running roller (8), on its circumferential surface (10, 12), has at least one insert (32) made from the respective wear-resistant material.
9. The radial piston pump as claimed in at least one of the preceding claims, characterized in that the running roller (8), on its circumferential surface (12), has at least one transverse groove (36) extending transversely to the direction of movement.
10. The radial piston pump as claimed in at least one of the preceding claims, characterized in that the piston footplate (18) has at least two grooves (50) which cross one another on its surface (31) facing the running roller (8).
11. The radial piston pump as claimed in at least one of the preceding claims, characterized in that the surface of the piston footplate (18) and/or of the running roller (8) has a surface roughness R_z of between 0.15 µm and 2 µm.
12. The radial piston pump as claimed in claim 2, characterized in that the piston consists of an Si₃N₄ ceramic or a ZrO₂ ceramic.
13. The radial piston pump as claimed in claim 11, characterized in that the piston (16) is produced by extrusion and has a porosity of less than 5%, the surface being infiltrated with MoS₂.
14. The radial piston pump as claimed in claim 12, characterized in that the piston (16) is isostatically extruded and sintered.

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