EP1633971A1

EP1633971A1 - Radial piston pump for generating high pressure for fuel in fuel injection systems of combustion engines

Info

Publication number: EP1633971A1
Application number: EP04736393A
Authority: EP
Inventors: Gerhard Breuer; Claudia Kohler; Franz Rückert; Karl-Heinz Thiemann
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2003-06-14
Filing date: 2004-06-09
Publication date: 2006-03-15
Anticipated expiration: 2024-06-09
Also published as: DE502004003060D1; DE10326880A1; US20060222517A1; EP1633971B1; JP2006527329A; KR20060021377A; WO2004111435A1

Abstract

The invention relates to a radial piston pump (1) for generating high pressure in fuel injection systems of combustion engines, particularly in a common rail injection system, comprising a drive shaft (4), which is mounted in a pump case (2), has an eccentric shaft section (6), on which a roller (8) is mounted, and which preferably has a number of pistons (16). These pistons are placed in a respective cylinder (14) while being arranged radial to the drive shaft (4), and a piston foot plate (18) is placed at the ends of the piston facing the roller (8) while being in contact with the peripheral surface (10, 12) of the roller (8). The invention provides that at least the surface (28) of the piston foot plate (18) that contacts the peripheral surface (10, 12) of the roller (8) is made of a wear-resistant material, namely of hard metal, a ceramic material, a cast carbidic material or of cermet, and/or that at least one portion of the roller (8), particularly at least one portion of the peripheral surface (10, 12) of the roller (8), is made of a wear-resistant material, namely of hard metal, a precision cast material, a cast carbidic material, a sintered tool steel or of an alloyed nitrided steel and/or that the piston (16) is made of a ceramic material.

Description

DaimlerChrysler AG

Radial piston piston for high-pressure fuel generation in fuel injection systems of internal combustion engines

The invention relates to a radial piston pump for generating high fuel pressure in fuel injection systems of internal combustion engines, in particular in a common rail injection system, with a drive shaft mounted in a pump housing with an eccentric shaft section on which a roller is mounted, and preferably with a plurality of radial ones with respect to the drive shaft Pistons arranged in a respective cylinder, at the ends of which are facing the roller, a piston footplate 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 Al. The piston base plate and the roller of the known radial piston pump are usually made of case hardening steel or also ^' of tempering 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.

The present invention is based on the object of further developing 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. In that for the first time at least the surface of the piston foot plate contacting the peripheral surface of the roller consists of a wear-resistant material, namely of hard metal, of a ceramic material, of a cast carbide material or of cermet, and / or at least part of the roller, in particular at least a part of it If the circumferential surface of the roller is made of a wear-resistant material, namely of hard metal, of an investment casting material, of a cast carbide material, of a sintered tool steel or of an alloyed nitriding steel and / or the piston is made of a ceramic material, the piston base plate rollers will tend to wear -Grid pairing and the piston-cylinder pairing significantly reduced. The materials mentioned have a significantly higher modulus of elasticity than the steel materials previously used, which results in less deformation under load and consequently also in a more uniform surface pressure without any significant stress peaks. When using ceramic materials, their lower weight plays a role, which results in a low mass inertia of the roller, the piston and the piston foot plate.

The roller and / or the piston footplate can be made entirely of the wear-resistant material or these parts consist, as previously, of case-hardening steel or tempering steel and carry at least one insert made of the wear-resistant material. The use of inserts has the advantage of a modular structure, ie that a standardized roller and a standardized piston footplate can each be provided with inserts made of different materials and a large number of pairing variants can thus be generated. Due to the material properties of the wear-resistant materials used, the following pairings are particularly preferred:

The roller consists of a hardened and tempered steel and has inserts made of hard metal such as G20, GC37 or GC20 and the piston foot disc consists of ceramic such as Si ₃ N ₄ ceramic, from hard cast iron such as SoGSH or from Cermet or it has inserts made from the materials mentioned.

The roller consists of an investment casting such as GX-210WCrl3 H and the piston base plate made of ceramic such as Si ₃ N ₄ ceramic, hard metal such as G20 or cermet or it has inserts made of the materials mentioned.

The roller consists of a cast carbide material such as hard cast SoGGH and the piston base plate made of ceramic such as Si ₃ N ₄ ceramic, hard metal such as G20 or cermet or it has inserts made of the materials mentioned.

The roller consists of sintered tool steel such as ASP23 or an alloyed nitriding steel and the piston base plate made of ceramic such as SI ₃ N ₄ ceramic, hard metal such as G20, cermet or a cast carbide material such as SoGGH or it has inserts made of the materials mentioned , The alloyed nitriding steel can contain C and / or Cr and / or V and / or Mo, is gas nitrided and in the contact area with the piston footplate there is no connection layer.

Another measure provides that the surface of the piston footplate and / or the roller has a roughness depth R _z between 0.15 μm and 2 μm. More precisely, the ceramic material has a roughness depth R _z between 0.15 μm and 0.5 μm, the hard metal has a roughness depth R _z between 0.3 μm and 1.0 μm and the cast carbide material has a roughness depth R _z between 0.5 μm and 2.0 µm. Particularly preferably, the roller has at least one transverse groove extending transversely to the direction of movement on its circumferential surface. In addition, the piston footplate can also have at least two intersecting grooves on its surface facing the roller. Fuel can accumulate in these grooves, each of which acts as a storage gap, which, due to the sliding movement between the circumferential surface of the roller and the piston foot plate, promotes the formation of a hydrodynamic sliding film, which further reduces wear on the sliding surfaces.

Last but not least, the flask preferably consists of an Si ₃ N ₄ or a ZrO ₂ ceramic, is produced by extrusion and has a porosity of less than 5%, the surface being infiltrated with MoS ₂ . In particular, the piston is extruded and sintered isostatically. This results in a very smooth surface with a low coefficient of friction, which also has a favorable effect on wear behavior.

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

Fig.l is a cross-sectional view of a radial piston pump with a piston foot plate and a drive shaft according to a first embodiment of the invention;

2 shows an enlarged cross-sectional view of a piston and a piston base plate according to a further embodiment;

2a shows an enlarged detail from FIG. 2;

2b shows a further enlarged detail from FIG. 2;

3 shows a view from below of the piston footplate of FIG. 2; 4 shows a cross-sectional view of a piston

Piston base plate and a drive shaft according to a further embodiment;

5 shows a cross-sectional view of a drive shaft according to a further embodiment;

Figure 6 is a view along the line VI-VI of Figure 5;

7 is a view along the line VII-VII of Fig.6.

The radial piston pump 1 shown in Fig.l is preferably used to generate 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 which is mounted in a pump housing 2 and has an eccentric shaft section 6, on which a polygonal roller 8 which is rotatable relative to the shaft section 6 is received. The polygonal roller 8 has flat flat sections 12 arranged along its circumferential surface 10 with circumferential spacing from one another.

A piston 16, which is guided radially in a cylinder 14 to the drive shaft 4 with its piston foot plate 18, is supported on the flat sections 12 of the roller 8. The piston base plate 18 is preferably pivotally connected to the end of the piston 16 facing the drive shaft 4 by means of a spherical bearing 20. The spherical bearing 20 is realized, for example, in that the piston end is designed as a partial ball 22 which engages in a complementarily designed spherical recess 24 in the piston foot plate 18. In addition, the piston base plate 18 is biased together with the piston 16 by a spring 26 against the associated flat portion 12 of the roller 8. The functioning of such a radial piston pump 1 is described, for example, in DE 198 02 475 A1 described, therefore we will not go into this here.

At least the surface 28 of the piston foot plate 18 contacting the peripheral surface 10 of the roller 8 is made of a wear-resistant material, namely of hard metal, of a ceramic material, of a cast carbide material or of cermet. This is preferably achieved in that the piston foot plate 18 has at least one, for example, disk-shaped insert 30 made of the wear-resistant material on its surface 28 facing the roller 8. The insert 30 can be connected to the remaining piston foot plate 18 in a form-fitting and / or cohesive manner, for example by gluing or by soldering. The insert 30 can, as shown in Fig.l, extend over the entire contact surface 28 of the piston foot plate 18 with the roller 8 or only over a part of it. Alternatively, the entire piston foot plate 18 can also be made of the wear-resistant material, so that no additional insert 30 is necessary.

When using a ceramic material for the piston base plate 18, this preferably contains silicon nitride Si ₃ N ₄ . Hard metals can consist of G20, GC37 or GC20, for example, while the cast carbide material can contain a hard cast material, in particular GGH or SoGGH.

Furthermore, the piston 16 itself can be made of wear-resistant material, for example of an Si ₃ N ₄ or a ZrO ₂ ceramic. The piston 16 can be produced by extrusion and have a porosity less than 5%, the surface being infiltrated with MoS ₂ . Alternatively, the piston 16 can 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 an investment casting material, from a cast carbide material, from a sintered tool steel or from an alloyed nitriding steel.

Analogous to the piston foot plate 18, this is preferably achieved in that the flat sections 12 are each provided with an insert 32 made of the wear-resistant material, as shown in FIG. Such an insert 32 is in each case received in a complementarily shaped recess 34 in the flat section 12 in a form-fitting and / or cohesive manner, for example by gluing or by soldering. Alternatively, the entire roller 8 can consist of the wear-resistant material.

When using hard metal for the inserts 32 or for the roller 8 itself, a particularly wear-resistant hard metal with a Vickers hardness of at least HV 1100 and a fracture toughness Ki _C > = 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. A suitable investment casting material is, for example, GX-210WCrl3 H, for the cast carbide material locally remelted, carbide SoGGH (gradient material) can be used. ASP23 is suitable for sintered tool steel. A nitriding steel specially alloyed 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 for nitriding lead to a deep diffusion with hardnesses of HV 750 to 850 and at the same time higher strength of the base material. The connection layer that forms is removed for functional reasons by grinding. The surfaces of the piston foot plate 18 and the roller 8 preferably have a roughness depth R _z between 0.15 μm and 2 μm on the sliding surfaces, depending on the materials used. The lower limit applies to ceramics, in particular a range from 0.15 μm to 0.5 μm upper limit for metals like SoGGH or ASP23. A roughness depth R _z between 0.3 μm and 1 μm is provided for hard metal.

In the table below, preferred material combinations of the piston foot plate 18 on the one hand and the roller 8 on the other hand are listed. If inserts are used both in the roller 8 and in the piston footplate 18, any combinations of material pairings are possible with the support bodies unchanged. In particular, in the pairings in the table, in which the roller 8 preferably consists ^entirely of the wear-resistant material (“solid material ^ΛΛ ), inserts 32 made 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 carrier body for the inserts 32 can then consist of another material, for example 50Cr4, 42CrV4 or 16MnCr5. The exemplary embodiment on the third line in the table plays a special role. In this case, a carbide zone is formed in the area of the flat sections 12 of the castor 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 when casting the roller 8 or by remelting and then preferably forms the gradient material SoGGH. The result is a roller 8, in which a carbide zone 33 is formed in the region of the flat sections 12, while the remaining zones and regions of the roller 8 consist of cast steel with unchanged properties.

Table: Preferred material pairings

One or more transverse grooves 36 can be formed in each case in the area of the flat sections 12 of the roller 8, as can best be seen from FIG. As can be seen from FIG. 7, the transverse groove 36 is arranged in the center of a depression 29 of the flat section 12 forming a groove outlet. The depression 29 is formed by two planes arranged at an angle with respect to the flat section 12, in the section line of which 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 section 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 or depression 29, which acts as a storage gap, fuel can accumulate which, due to the sliding speed, between the Flat sections 12 of the roller 8 and the piston foot plate 18 promote 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 that remain the same and have the same effect as in the example of FIG. 1 are identified by the same reference numerals. In contrast to this, the piston base plate 18 is held by a plate holder 38 on the associated piston 16 in the example according to FIG. The piston foot plate 18 has a circular recess 40 on its surface facing the piston 16, into which the crowned end 42 of the piston 16 engages and contacts the bottom of the recess 40. The plate holder 38 is countered on the piston 16 by means of a snap ring 46 which engages in a groove 44 of the piston 16. A complementarily shaped insert 30 made of one of the wear-resistant materials described above is held in a circular recess 48 in the piston foot plate 18, for example by material closure, in particular by soldering. As can be seen from FIG. 2a, the insert 30 is provided on the edge 31 on its surface 31 facing the roller 8 with an angular outlet 35, the outlet angle α being approximately 15 degrees. Furthermore, the transition between this surface 31 and the outlet 35 is rounded with a radius R ₂ of approximately 2 mm. The transition between the outlet 35 and the edge surface 37 of the insert 30 is also rounded by means of a radius Ri of less than or equal to 1 mm.

Analogous to the flat sections 12 of the roller 8, the inserts 30 of the piston foot plate 18 preferably have at least two intersecting grooves 50, as best shown in FIG. Due to the intersecting arrangement of the grooves 50, there is a high probability that one of the grooves 50 is oriented transversely to the direction of movement with regard to the piston foot plate 18, which is rotatable with respect to the plate holder 38, in order to promote the formation of a hydrodynamic lubricating film. The grooves 50 are preferably created by pressing. Thereby This results in a lower notch effect compared to cutting processes, since the material fibers are not cut. As can be seen from FIG. 2b, the grooves 50 are each arranged in the center of a depression 39 of the surface 31 forming a groove outlet. The depression is formed by two planes arranged at an angle with respect to the surface 31, in the intersecting line of which the respective groove 50 lies. The sink angle β of the sink 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 exemplary embodiment of FIG. 4, the piston foot plate 18 consists entirely of one of the abrasion-resistant materials mentioned above and is inserted into the through hole 52 of an annular sleeve 54 which is made of steel. The connection between the ring sleeve 54 and the piston foot plate 18 is preferably made by soldering. Of course, other possibilities are also conceivable for attaching wear-resistant material to the mutually associated sliding surfaces 12, 28 of the roller 8 and piston foot plate 18.

Claims

DaimlerChrysler AG patent claims

1. Radial piston pump (1) for generating high fuel pressure in fuel injection systems of internal combustion engines, in particular in a common rail injection system, with a drive shaft (4) mounted in a pump housing (2) with an eccentric shaft section (6) on which a roller (8) is mounted, and preferably with a plurality of pistons (16) arranged radially with respect to the drive shaft (4) in a respective cylinder (14), on the piston of which the roller

(8) facing ends a piston foot plate (18) is arranged, which the peripheral surface (10, 12) of the roller

(8) contacted, characterized in that at least the surface (28, 31) of the piston foot plate (18) contacting the peripheral surface (10, 12) of the roller (8) is made of a wear-resistant material, namely of hard metal, of a ceramic material a cast carbide material or cermet, and / or that at least a part of the roller (8), in particular at least a part of the peripheral surface (10, 12) of the roller (8) made of a wear-resistant material, namely hard metal, made of an investment casting material , consists of a cast carbide material, a sintered tool steel or an alloyed nitriding steel, and / or that the piston (16) consists of a ceramic material.

2. Radial piston pump according to claim 1, characterized in that the roller (8) on its peripheral surface (10, 12) and / or the piston base plate (18) on its surface (31) facing the roller (8) at least one insert (30, 32) made of the respective wear-resistant material.

3. Radial piston pump according to claim 1 or 2, characterized in that the roller (8) consists of a tempering steel and inserts (32) made of hard metal such as G20, GC37 or GC20 and that the piston base plate (18) made of ceramic such as Si ₃ N _4th - Ceramics, from hard cast iron such as SoGGH or from cermet or inserts (30) made of the materials mentioned.

4. Radial piston pump according to claim 1 or 2, characterized in that the roller (8) consists of an investment casting material such as GX-210WCrl3 H and that the piston base plate (18) made of ceramic such as Si ₃ N ₄ ceramic, hard metal such as G20 or Cermet consists or inserts (30) made of the materials mentioned.

5. Radial piston pump according to claim 1 or 2, characterized in that the roller (8) consists of a cast carbide material such as hard cast SoGGH and that the piston base plate (18) made of ceramic such as Si ₃ N _4th -Ceramic, consists of hard metal such as G20 or cermet or has inserts (30) made of the materials mentioned.

6. Radial piston pump according to claim 1 or 2, characterized in that the roller (8) consists of sintered tool steel such as ASP23 or an alloyed nitriding steel and that the piston base plate (18) made of ceramic such as Si ₃ N ₄ ceramic, hard metal such as G20 , consists of cermet or a cast carbide material such as SoGGH or inserts (30) made of the materials mentioned.

7. Radial piston pump according to claim 6, characterized in that the alloyed nitriding steel contains C and / or Cr and / or V and / or Mo, gas nitrided and in the contact area with the piston base plate (18) is free of a connection layer.

8. Radial piston pump according to at least one of the preceding claims, characterized in that the roller (8) on its peripheral surface (10, 12) has at least one transverse groove (36) extending transversely to the direction of movement.

9. Radial piston pump according to at least one of the preceding claims, characterized in that the piston foot plate (18) has at least two intersecting grooves (50) on its surface (31) facing the roller (8).

10. Radial piston pump according to at least one of the preceding claims, characterized in that the surface of the piston base plate (18) and / or the roller (8) has a roughness depth R _z between 0.15 μm and 2 μm.

11. Radial piston pump according to at least one of the preceding claims, characterized in that the piston consists of an Si ₃ N ₄ - or a ZrO ₂ ceramic.

12. Radial piston pump according to claim 11, characterized in that the piston (16) is made by extrusion and has a porosity less than 5%, the surface being infiltrated with MoS ₂ .

13. Radial piston pump according to claim 12, characterized in that the piston (16) is isostatically extruded and sintered.