US20070259199A1

US20070259199A1 - Oil pump

Info

Publication number: US20070259199A1
Application number: US11/274,458
Authority: US
Inventors: Volker Arnhold; Klaus Dollmeier; Harald Balzer; Vladislav Kruzhanov
Original assignee: Individual
Current assignee: GKN Sinter Metals Holding GmbH
Priority date: 2003-05-14
Filing date: 2005-11-14
Publication date: 2007-11-08
Also published as: CN100400694C; DE10321521B3; WO2004101836A2; JP2007511692A; EP1623051A2; WO2004101836A3; CN1788098A

Abstract

Certain preferred embodiments of the present invention provide an oil pump which is both light as well as compact. Accordingly, certain presently preferred embodiments disclose an oil pump having a housing comprising aluminum, and at least one mobile molded part therein. The mobile molded part being at least partially made from a sinterable composition comprising at least one austenitic iron-based alloy powder. The mobile molded part also has a heat expansion coefficient, which amounts to at least 60% of the heat expansion coefficient for the oil pump housing.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP2004/004702 filed May 4, 2004, which claims priority to German Application Number 103 21 521.2 filed May 14, 2003, each of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to molded parts, methods for producing such molded parts, and oil pumps having a housing and at least one such molded part, movably arranged in said housing.

BACKGROUND OF THE INVENTION

Oil pumps of the type mentioned at the outset are particularly used in internal combustion engines, in which higher temperatures are dominant. Conventional oil pumps according to prior art are provided with a housing made from cast iron and mobile molded parts arranged therein, for example a toothed set of rotors in the case of an internal gear pump.
Conventional mobile molded parts are usually made from a ferriferous alloy via a sintered metallurgical production method. These mobile molded parts are typically made from an iron-copper alloy. The use of cast iron and iron-copper alloys results in such pumps having a relatively high weight. Considering the general trend in automobile construction to reduce the weight of motor vehicles it is therefore desirable to provide oil pumps which have a lesser weight.
For this purpose, it is known from prior art to produce the oil pump housing from cast aluminum alloy rather than from cast iron. Yet even in these circumstances, iron-copper alloys are used for mobile molded parts such as, for example, a set of toothed rotors arranged inside the housing of the oil pump. However gap leakage is problematic in such oil pumps, particularly during operation in an internal combustion engine because of environmental temperature variations and generally high temperatures. This problem is usually addressed by increasing the dimensions of the oil pump itself. However, increasing the pump dimension is counterproductive since the desired weight savings are offset by the increased size of the oil pump.
Therefore, there is a need in the art for oil pumps having both lower weight and minimal gap leakage.

SUMMARY OF THE INVENTION

The present invention relates to molded parts, methods for producing such molded parts, and oil pumps having a housing and at least one such molded part, movably arranged in said housing. Certain preferred embodiments of the present invention include an oil pump having a housing, made from a material comprising aluminum, and mobile molded parts arranged inside the housing. For example, the oil pump may be an external gear pump with involute toothing, an interior gear pump with trochoidal toothing and crescent, G-rotors with cycloidal gear, P-rotors, or a vane cell pump. The oil pump mobile molded parts are at least partially made from a material that can be sintered, comprising at least one austenitic iron-based alloy powder. Molded parts, according to certain aspects of the present invention, also have a heat expansion coefficient which amounts to at least 60% of the oil pump housing heat expansion coefficient. Preferably, the molded part heat expansion coefficient amounts to at least 70%, more preferably at least 74%, in reference to that of the oil pump housing.
Sintered molded parts, according to certain aspects of the present invention, may be made entirely from a material that can be sintered. Sintered molded parts may also include compound molded parts in which the body portion of such compound molded parts, for example, are made from an aluminum-containing powder mixture. Still further, such a body portion, further connected to another body portion, may be made from another sinterable material comprising at least one austenitic iron-based alloy. The body portion made of an aluminum-containing powder mixture may also be replaced by one made from solid cast aluminum. Conversely, the sinterable material molded part can comprise, for example, body portions having a sintered layer, comprising at least one sinterable austenitic iron-based alloy powder, at the facial sides or its surface. The body portion, for example, may be made from sintered steel, cast steel, sintered cast iron, cast iron, or combinations thereof.
The oil pump, according to the certain preferred aspects of the present invention, provides minimal gap leakage during operation in an internal combustion engine. Therefore, larger dimensions are not necessary and, by the use of aluminum, the oil pump housing weight is considerably reduced. The housing of the oil pump can either be made in a casting process or via sinter-metallurgical production methods. The housing is preferably cast from an aluminum alloy.
The material that can be sintered, from which the mobile molded parts arranged inside the housing of the oil pump are made, are preferably produced from a single austenitic iron-based alloy powder. However, mixtures of several austenitic iron-based alloy powders may also be used. Furthermore, the material that can be sintered can also comprise common lubricants, compression agents, gliding agents, and the like. Lubricants, which are added in an amount of approximately 0.2% to approximately 5% by weight in reference to the total amount of the material that can be sintered, can be self-lubricating agents, such as MoS₂, WS₂, BN, MnS, as well as graphite and/or other carbon modifications such as coke, polarized graphite, and the like, which provide the mobile formed parts with self-lubricating characteristics. Binders and/or lubricants can be selected from materials of a group comprising polyvinyl acetate, wax, in particular amide wax such as ethylene-bisstearoylamide, shellac, polyalkylene oxide and/or polyglycol. Polyalkylene oxide and/or polyglycol is preferably used in the form of polymer and/or copolymer with a medium molar weight in a range from approximately 100 to 50,000 g/mol, preferably approximately 1,000 to 6,500 g/mol. Binders and/or lubricants are preferably used in an amount ranging from approximately 0.01 to 12% by weight, preferably ranging from approximately 0.5 to 5% by weight in reference to the total amount of the used material that can be sintered.
Particularly suitable as austenitic iron-based alloys powders are the alloys 316L, 305, 308, 317 L and 321 or mixtures thereof. Preferred austenitic iron-based alloy powders comprise iron and 0.005 to 0.04% by weight carbon; 0.1 to 1.5% by weight silicon; 8 to 18% by weight nickel; 0 to 25% by weight chromium; 1 to 4% by weight molybdenum; and 0.05 to 1% by weight manganese, in reference to the total amount of austenitic iron-based alloy.
The oil pump mobile molded parts of the present invention exhibit a Brinell-hardenss, according to DIN EN 24498-1, of at least 100 HB, preferably 120 HB, more preferred at least 130 HB, still more preferred at least 140 HB. Here, the Brinell-hardness is determined via a hardened steel ball used as an inserted body having a diameter of 2.5 cm and a weight of 62.5 kg. Using such hard mobile molded parts can achieve a long life for the oil pumps according to the present invention. It must be considered that the heat expansion coefficient of conventional aluminum cast alloys range from approximately 20 to 24 ppm, while the heat expansion coefficient of preferred sinterable austenitic iron-based alloys used can be below that of conventional aluminum cast alloys.
Preferably, the heat expansion coefficient of the mobile molded parts, produced from the material that can be sintered ranges from approximately 12 to approximately 21 ppm, preferably from 16-19 ppm. Using such mobile molded parts it is ensured that the oil pump according to the invention fulfills the mechanical tribological requirements, in particular for use in an internal combustion engine. Preferably, the mobile molded parts of the oil pump comprise a set of rotors, with the axial play (i.e., distance) between at least one rotor of the set of rotors arranged on a shaft and the wall of the oil pump housing, against which the rotors operates, preferably amounting to less than 50 μm, preferably less than 40 μm. Therefore, the oil pump, as a presently preferred embodiment of the invention, can advantageously be constructed in a very compact manner. Furthermore, the axial play defined in the above-described manner achieves high performance of the oil pump in accordance with certain preferred aspects of the present invention.
Certain embodiments of the invention further relate to molded parts, which are arranged inside the housing of the oil pump, and to a methods for producing such molded parts. In a presently preferred embodiment:

- a material that can be sintered and comprising at least one austenitic iron-based alloy, being filled into a pressed mold;
- in a second step, a green body being pressed with a pressure of at least 500 MPa, having a density according to DIN ISO 2738 amounting to at least 6.5 g/cm³; and
- in a third step, the green body being sintered at a temperature of at least 1,000° C. in a gaseous atmosphere, comprising nitrogen and/or hydrogen.
  When a gaseous atmosphere mixed from hydrogen and nitrogen is used, the ratio of the portions of nitrogen and hydrogen is at least 66:33, preferably more than 95:5.

Without being limited by theory, it is believed that nitride phases are created in the mobile molded parts made in accordance with the present invention using at least one austenitic iron-based alloy. It is further believed that these nitride phases fulfill the requirements necessary for the operation of the oil pump, made in accordance with certain preferred aspects of the current invention, regarding hardness and structural integrity. These properties are particular useful in internal combustion engines. Alternative to facilitating nitride phase formation via a mixed gaseous atmosphere according to the preferred embodiments of the present invention, plasma-nitration may also be performed in combination with other steps of the present method to provide for nitride phase formation.

- The process according to the present invention, may further preferably including:
- in a fourth step, the sintered molded part is re-pressed at a pressure of at least 600 MPa, preferably at least 750 MPa, to a density of at least 6.7 g/cm³, according to DIN ISO 2738.

BRIEF DESCRIPTION OF THE DRAWINGS

These and additional advantages of the invention will be explained using the following example and the FIGURE. It shows:
FIG. 1 is a cross-section of the schematic representation of an oil pump according to the invention (section).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows an oil pump of the type P-rotor according to the invention, in its entirety indicated with the reference number 1, (as it is disclosed in DE 196 46 359 C2, for example, having a housing 2, which is embodied in two parts (2′, 2″) here. In this housing 2, a set of toothed rotors 4 is arranged, having an interior rotor 6 arranged on a shaft 5 in the direction of the axis Z, and the planet wheels 8 encircling it. It will be appreciated by one skilled in the art that the description given herein with respect to those FIG. 1 is for exemplary purposes only and is not intended in any way to limit the scope of the present invention.
Furthermore, the set of toothed rotors 4 comprises a rotating circular bearing 9 with bearing pockets, not shown here, in which the pivotally supported planet wheels 8 are arranged. The interior rotor 6 is supported eccentrically in reference to the circular bearing 9, and is provided with an approximately star-shaped exterior contour, which is provided with external teeth. The set of toothed gears 4 comprises, as it is common, a suction area not shown in greater detail, a pressure area, and a displacement chamber. Via the drive shaft 5, a drive moment is transferred to the toothed interior rotor 6. The mobile molded parts in the sense of the present invention, according to FIG. 1, include the circular bearing 9, the interior rotor 6, the planet rotors 8, as well as the shaft 5 including the catch (not shown) arranged on it.
Between the interior wall 3 of the housing part 2′ of the oil pump 1 and the face 10 of the interior rotor 6 an axial play A is present, which amounts to 40 μm.
The set of toothed rotors, shown in FIG. 1, is made from a sinterable composition comprising 1% by weight of the lubricant Licowax C, Company Clariant GmbH, Frankfurt, which represents a polyamide wax, and 99% by weight of the austenitic iron-based alloy 316 L, comprising 0.02% by weight carbon, 0.8% by weight silicon, 13% by weight nickel, 17% by weight chromium, 2.2% by weight molybdenum, and 0.2% by weight manganese, with the remaining portion formed by iron. The austenitic iron-based alloy 316L has been supplied by the company Hoeganaes AB, Stockholm, Sweden.
In an embodiment of the present invention, the above-defined mixture was first pressed into a green body at a pressure of 600 MPa and room temperature, to a density in a range from 6.6 to 6.7 g/cm³, which subsequently in a second step was sintered in a walking beam furnace for 15 minutes at a temperature of 1,280° C. under a mixed gaseous atmosphere comprising 70% nitrogen and 30% hydrogen. Subsequently, in another step, the such sintered set of rotors was re-pressed under a pressure of 800 MPa to a density of 6.8 to 7.0 g/cm3. The hardness of mobile molded parts of the set of toothed rotors made in such manner was 141 HB, 62.5/2.5 according to DIN EN 24498-1 (Brinell-hardness). The heat expansion coefficient, determined according to DIN 51045 (temperature range 25° C.-200° C.), was determined to be 17 ppm.
The set of toothed rotors made in such manner was used in a cast aluminum housing made from GD-AlSi₃Cu₃(material code 3.2163.05), which is provided with a heat expansion coefficient of 23 ppm according to DIN 51405 (temperature range 25° C.-200° C.)
The oil pump made in this fashion showed minimal gap leakage, even after extended operation under load and increased temperatures, as common in internal combustion engines. In reference to oil pumps according to prior art, it is considerably lighter.
According to the present invention it is also possible to produce not only a complete set of toothed rotors, as described above, from a material comprising at least one austenitic iron-based alloy powder, but according to certain aspects of the present invention, it is also possible to produce the interior rotor in its entirety from a material comprising such austenitic iron-based alloy powder. Individual rotor components may also be produced as a compound material, in particular the interior wheel, with either the gears, for example of the interior rotor, and/or the face 10 of the interior rotor facing the wall 3, being produced with a coating made from a material comprising an austenitic iron-based alloy. Furthermore, inversely, only the toothing of rotor parts of a set of rotors can be made from a different material, for example an aluminum-based alloy, while the body material of the respective rotors being made from an austenitic iron-based alloy. Furthermore, it is also possible to merely produce the catch of the interior rotors of a set of geared rotors from an austenitic iron-based alloy powder material. However, the object of the present invention is not limited to the combinations mentioned, but includes any possible other combination of the mobile molded parts arranged in an oil pump.
Thus, certain embodiments of the present invention provide both compactly constructed as well as light oil pumps, which achieve an operational life comparable to oil pumps provided with cast iron housings. Certain preferred aspects of the present invention having been disclosed in connection with the foregoing variations and examples, additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations and examples specifically mentioned, and accordingly reference should be made to the appended claims to assess the spirit and scope of the invention in which exclusive rights are claimed.

Claims

1-7. (canceled)

8. An oil pump comprising:

a housing comprising aluminum, said housing having a first heat expansion coefficient; and

at least one molded part comprising at least one sinterable composition,

said sinterable composition comprising at least one austenitic iron-based alloy powder, and said molded part further having a second heat expansion coefficient at least 60% of said first heat expansion coefficient.

9. The oil pump according to claim 8, wherein said second heat expansion coefficient is at least 70% of said first heat expansion coefficient.

10. The oil pump according to claim 8, wherein said second heat expansion coefficient is at least 74% of said first heat expansion coefficient.

11. The oil pump according to claim 8, wherein said at least one molded part further comprises aluminum-containing alloy powder.

12. The oil pump according to claim 8, wherein said austenitic iron-based alloy powder comprises:

iron; and

0.005 to 0.04 weight percent carbon, 0.1 to 1.5 weight percent silicon, 8 to 18 weight percent nickel, 0 to 25 weight percent chromium, 1 to 4 weight percent molybdenum, and 0.05 to 1 weight percent manganese, based on the weight of the austenitic iron-based alloy powder.

13. The oil pump according to claim 8, wherein said at least one molded part further comprises cast aluminum, cast iron, sintered cast iron, steel, or combinations thereof.

14. The sinterable composition of claim 8, further comprising from 0.2 to 5 weight percent of at least one lubricant, based on the weight of said sinterable composition.

15. The sinterable composition of claim 14, wherein said at least one lubricant is MoS₂, WS₂, BN, MnS, or carbon.

16. The sinterable composition of claim 8, further comprising polyvinyl acetate, an amide wax, or combinations thereof.

17. The sinterable composition of claim 16, wherein the amide wax comprises ethylene-bisstearoylamide, shellac, polyalkylene oxide, polyglycol, or combinations thereof.

18. The oil pump according to claim 8, wherein said at least one molded part has a hardness of at least 100 HB, according to DIN EN 24 498-1.

19. The oil pump according to claim 8, wherein said at least one molded part has a hardness of at least 120 HB, according to DIN EN 24 498-1.

20. The oil pump according to claim 8, wherein said at least one molded part has a hardness of at least 130 HB, according to DIN EN 24 498-1.

21. The oil pump according to claim 8, wherein said at least one molded part has a hardness of at least 140 HB, according to DIN EN 24 498-1.

22. The oil pump according to claim 8, wherein said second heat expansion coefficient is from about 15 to about 21 ppm.

23. The oil pump according to claim 8, wherein said second heat expansion coefficient is from about 16 to about 19 ppm.

24. The oil pump according to claim 8, wherein said at least one molded part comprises at least one rotor arranged on a shaft, and the axial distance between said rotor and said housing is less than 50 μm.

25. The oil pump according to claim 8, wherein said at least one molded part comprises at least one rotor arranged on a shaft, and the axial distance between said rotor and said housing is less than 40 μm.

26. A method for producing at least one molded part, comprising:

providing a sinterable composition, having at least one austenitic iron-based alloy powder, to a mold;

pressing said sinterable composition under a pressure of at least 500 MPa to obtain a density of at least 6.5 g/cm³, according to DIN ISO 2738; and

sintering said sinterable composition at a temperature of at least 1,000° C. in a gaseous atmosphere comprising at least one of nitrogen and hydrogen.

27. The method of claim 26, wherein the ratio of said nitrogen to said hydrogen is at least 66:33.

28. The method of claim 26, wherein the ratio of said nitrogen to said hydrogen is at least 95:5.

29. The method according to claim 26, further comprising:

pressing said sinterable composition at a pressure of at least 600 MPa to a density of at least 6.7 g/cm³, said density being in accordance with DIN ISO 2738.

30. The method according to claim 26, further comprising:

pressing said sinterable composition at a pressure of at least 750 MPa to a density of at least 6.7 g/cm³, said density being in accordance with DIN ISO 2738.

31. The method of claim 26, wherein said sinterable composition further comprises aluminum-containing alloy powder.

32. The method of claim 26, wherein said austenitic iron-based alloy powder comprises:

iron; and

0.005 to 0.04 weight percent carbon, 0.1 to 1. weight percent silicon, 8 to 18 weight percent nickel, 0 to 25 weight percent chromium, 1 to 4 weight percent molybdenum, and 0.05 to 1 weight percent manganese, based on the weight of the austenitic iron-based alloy powder.

33. The method of claim 26, wherein said sinterable composition further comprises from 0.2 to 5 weight percent of at least one lubricant, based on the weight of said sinterable composition.

34. The method of claim 33, wherein said at least one lubricant is MoS₂, WS₂, BN, MnS, or carbon.

35. The method of claim 26, wherein said sinterable composition further comprises polyvinyl acetate, an amide wax, or combinations thereof.

36. The method of claim 35, wherein the amide wax comprises ethylene-bisstearoylamide, shellac, polyalkylene oxide, polyglycol, or combinations thereof.

37. A molded part made by the method of claim 26.

38. A molded part made by the method of claim 29.

39. An oil pump comprising:

at least one molded part comprising at least one sinterable austenitic iron-based alloy, said alloy having a second heat expansion coefficient at least 60% of said first heat expansion coefficient; and

said at least one molded part being made by the method comprising providing a sinterable composition, comprising at least one austenitic iron-based alloy, to a mold;

pressing said sinterable composition under a pressure of at least 500 MPa with a density, according to DIN ISO 2738, amounts to at least 6.5 g/cm³, and

40. The oil pump according to claim 39, wherein said at least one molded part has a hardness of at least 100 HB, according to DIN EN 24 498-1.

41. The oil pump according to claim 39, wherein said at least one molded part has a hardness of at least 120 HB, according to 3 EN 24 498-1.

42. The oil pump according to claim 39, wherein said at least one molded part has a hardness of at least 130 HB, according to DIN EN 24 498-1.

43. The oil pump according to claim 39, wherein said at least one molded part has a hardness of at least 140 HB, according to DIN EN 24 498-1.

44. The oil pump according to claim 39, wherein said second heat expansion coefficient is at least 70% of said first heat expansion coefficient.

45. The oil pump according to claim 39, wherein said second heat expansion coefficient is at least 74% of said first heat expansion coefficient.

46. The oil pump according to claim 39, wherein said second heat expansion coefficient is from about 15 to about 21 ppm.

47. The oil pump according to claim 39, wherein said at least one molded part comprises at least one rotor arranged on a shaft, and the axial distance between said rotor and said housing is less than 40 μm.

48. The oil pump according to claim 39, wherein said at least one molded part comprises at least one rotor arranged on a shaft, and the axial distance between said rotor and said housing is less than 50 μm.

49. The method according to claim 39, further comprising:

50. The method according to claim 39, further comprising:

51. The method of claim 39, wherein the ratio of said nitrogen to said hydrogen is at least 66:33.

52. The method of claim 39, wherein the ratio of said nitrogen to said hydrogen is at least 95:5.