WO2004101836A2

WO2004101836A2 - Oil pump

Info

Publication number: WO2004101836A2
Application number: PCT/EP2004/004702
Authority: WO
Inventors: Volker Arnhold; Klaus Dollmeier; Harald Balzer; Vladislav Kruzhanov
Original assignee: Gkn Sinter Metals Holding Gmbh
Priority date: 2003-05-14
Filing date: 2004-05-04
Publication date: 2004-11-25
Also published as: CN1788098A; EP1623051A2; US20070259199A1; CN100400694C; WO2004101836A3; JP2007511692A; DE10321521B3

Abstract

The aim of the invention is to provide an oil pump that is both light and compact. To this end, the inventive oil pump comprises a housing consisting of a material containing aluminium, and mobile moulded parts are arranged in said housing. Said mobile moulded parts are at least partially produced from a sinterable material comprising at least one austenitic iron-base alloy, and the mobile moulded parts produced from the sinterable material have a heat coefficient corresponding to at least 60 % of that of the housing.

Description

oil pump

The present invention relates to an oil pump with a housing and movable molded parts arranged in this housing, such molded parts and methods for producing such molded parts.

Oil pumps of the type mentioned at the outset are used in particular in internal combustion engines in which higher temperatures prevail. Usual oil pumps known in the prior art have a housing made of cast iron and movable molded parts arranged in this housing, for example a gear rotor set in the case of an internal gear pump. The movable molded parts are made of ferrous alloys, usually in a sintered metallurgical manufacturing process. Iron copper alloys are used. The use of cast iron and iron copper alloys has the consequence that such oil pumps are relatively heavy. In view of the general tendency in automobile construction to reduce the weight of motor vehicles, it is therefore desirable to provide oil pumps which are lighter in weight.

For this purpose, it is known from the prior art to produce the housing of oil pumps not from a cast iron, but from an aluminum alloy using the casting process. Here, too, iron copper alloys are used as movable molded parts, for example as a toothed rotor set, arranged in the interior of the oil pump housing. The problem with such oil pumps, however, is that, owing to the temperature fluctuations and higher temperatures to which the oil pumps are exposed, particularly when an internal combustion engine is operating, there are gap losses which are usually compensated for by a larger dimensioning of the oil pump itself. However, the larger dimensioning of the oil pump means that the desired weight savings partially canceled.

There is therefore a need for oil pumps which on the one hand have a low weight but on the other hand have no or only slight gap losses.

The object of the present invention is therefore to provide oil pumps which do not have the aforementioned disadvantages.

To achieve this object, an oil pump is proposed with a housing made of a material comprising aluminum and movable molded parts arranged in the housing, the oil pump being characterized in that the movable molded parts are at least partially made of a sinterable material comprising have at least one austenitic iron-based alloy, and have a coefficient of thermal expansion which is at least 60% of that of the housing of the oil pump. The coefficient of thermal expansion is preferably at least 70%, more preferably at least 74%, of that of the housing of the oil pump. The oil pump can be designed, for example, as an external gear pump with involute teeth, an internal gear pump with trochoid teeth and a crescent moon, a G-rotor with cycloid teeth, a P-rotor or a vane pump.

Sintered molded parts in the sense of the present invention are understood to mean molded parts which have been produced entirely from a sinterable material, on the other hand also composite molded parts, whereby the base body of such a composite molded part can be made, for example, from an aluminum-containing powder mixture and the base body bonded body made of a further sinterable material, comprising at least one austenitic iron-based alloy. The main body from an aluminum-containing powder mixture could also be replaced by one made of solid cast aluminum. Conversely, the composite molded part can also have, for example, only a sintered layer of a sinterable material, comprising at least one austenitic iron-based alloy, only on the end faces or its surface, whereas the base body is made of, for example, steel or cast iron, sintered or solid.

The oil pump according to the invention has low gap losses, particularly when it is operated in an internal combustion engine. Therefore, a larger dimensioning is not necessary, and the weight of the oil pump is significantly reduced through the use of aluminum for the oil pump housing. The housing of the oil pump can either be produced using the casting process or via sintered metallurgical production processes. The housing is advantageously cast from an aluminum alloy.

The sinterable material from which the movable molded parts arranged in the housing of the oil pump are made is advantageously made from only one austenitic iron-based alloy. However, mixtures of different austenitic iron-based alloys are also possible. Furthermore, the sinterable material can comprise customary lubricants, pressing aids, lubricants or the like. Self-lubricating agents such as MoS _2f WS _{2 #} BN, MnS and graphite and / or others can be used as lubricants, which are added in an amount of about 0.2 to about 5% by weight, based on the total amount of the sinterable material Carbon modifications such as coke, polarized graphite or the like are used, which impart self-lubricating properties to the movable molded parts. As binders and / or lubricants, materials can be selected from a group comprising polyvinyl acetates, waxes, in particular amide waxes such as ethylene bissteamyl amide, shellac, polyalkylene oxides and / or polyglycols. Polyalkylene oxides and / or Glycols are preferably used as polymers and / or copolymers with an average molecular weight in a range from about 100 to 50,000 g / mol, preferably about 1,000 to 6,500 g / mol. Binding agents and / or lubricants are preferably used in an amount in a range from approximately 0.01 to 12% by weight, preferably in a range from approximately 0.5 to 5% by weight, based on the total amount of the sinterable material used.

The alloys 316L, 305, 308, 317 L and 321 or mixtures thereof are particularly suitable as austenitic iron-based alloys. The austenitic iron-based alloys used preferably comprise 0.005 to 0.04% by weight of carbon, 0.1 to 1.5% by weight of silicon, 8 to 18% by weight of nickel, 0 to 25% by weight of chromium, 1 to 4% by weight of molybdenum and 0.05 up to 1% by weight manganese in addition to iron.

The movable molded parts of the oil pump produced from the sinterable material advantageously have a Brinell hardness according to DIN EN 24498-1 of at least 100 HB, preferably 120 HB, more preferably at least 130 HB, more preferably at least 140 HB. The Brinell hardness is determined using a hardened steel ball as an indenter with a diameter of 2.5 cm and a load of 62.5 kg. Such long, movable molded parts can achieve long lifetimes for the oil pumps according to the invention. Because it must be taken into account that the thermal expansion coefficients of conventional cast aluminum alloys are in a range of about 20 to 24 ppm, but that of the austenitic iron-based alloys used as sinterable material are below this.

The coefficient of thermal expansion of the movable molded parts produced from the sinterable material is preferably in a range from approximately 12-21 ppm, preferably 16-19 ppm. Movable molded parts of this type ensure that the oil pump according to the invention is able to withstand the meets the Chinese tribological requirements, especially when used in an internal combustion engine. The movable molded parts of the oil pump preferably comprise a rotor set, the axial play between at least one rotor of the rotor set arranged on a shaft and the wall of the housing of the oil pump, against which the rotor works, being less than 50 μm, preferably less than 40 μm. The oil pump according to the invention can thus advantageously be made very compact. Furthermore, a high performance of the oil pump according to the invention is achieved by the axial play as defined above.

The invention further relates to molded parts, which are arranged in the housing of the oil pump, and a method for producing these molded parts, wherein

- In a first step, a sinterable material, comprising at least one austenitic iron-based alloy, is filled into a mold;

- In a second step, a green compact is pressed at a pressure of at least 500 MPa with a density according to DIN ISO 2738 of at least 6.5 g / cm ³ ; and

- In a third step, the green compact is sintered at a temperature of at least 1,000 ° C in a gas atmosphere, comprising nitrogen and / or hydrogen. If a mixed gas atmosphere of hydrogen and nitrogen is provided, the ratio of the proportions of nitrogen and hydrogen is at least 66:33, preferably more than 95: 5.

The process according to the invention produces nitridic phases in the movable molded parts produced from at least one austenitic iron-based alloy, by means of which these meet the requirements for hardness and strength necessary for the operation of an oil pump according to the invention, in particular in internal combustion engines. len. An alternative to introducing nitridic phases via a mixed gas atmosphere according to the method according to the invention is so-called plasma nitriding, which can also be combined in a further step with the method according to the invention.

Advantageously, in the method according to the invention, in one

fourth step, the sintered molded part is calibrated at a pressure of at least 600 MPa, preferably at least 750 MPa, to a density in accordance with DIN ISO 2738 of at least 6.7 g / cm ³ .

These and other advantages of the invention are explained with the aid of the following example and the figure. It shows:

Fig. 1 shows a cross section through a schematic representation of an oil pump according to the invention (detail).

1 shows an oil pump 1 of the type P-rotor (as disclosed for example in DE 196 46 39 C2) according to the invention, generally designated by the reference numeral 1, with a housing 2, which is formed here in two parts (2 ¹ , 2 "). In this housing 2, a toothed rotor set 4 is arranged with an inner rotor 6 arranged on a shaft 5 in the direction of the Z axis and surrounding planet gears 8. The toothed rotor set 4 further comprises a rotatable bearing ring 9 with bearing pockets, not shown here, in which the rotatably mounted bearings Planetary rotors 8. The inner rotor 6 is mounted eccentrically to the bearing ring 9 and has an approximately star-shaped outer contour, which is provided with external teeth, as usual, the toothed rotor set 4 has a suction area, not shown here, a pressure area and a displacement chamber A drive torque is applied to the toothed inner rotor 6 via the drive shaft 5 transmitted as ¹ movable 1, the bearing ring 9, the inner rotor 6, the planetary rotors 8 and the shaft 5 including the entrainment (not shown) arranged on them are to be addressed in accordance with the present invention.

There is an axial play A between the inner wall 3 of the housing part 2 'of the oil pump 1 and the end face 10 of the inner rotor 6, which is 40 μm.

The gear rotor set 4 shown in FIG. 1 was produced from a mixture containing 1% by weight of the lubricant Licowax C, from Clariant GmbH, Frankfurt, which is a polyamide wax, and 99% by weight of the austenitic iron-based alloy 316L, containing 0.02% by weight of 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, the remaining constituent being formed by iron. The 316L austenitic iron base alloy was obtained from Hoeganaes AB, Stockholm, Sweden.

The mixture defined above was first pressed at a pressure of 600 MPa and room temperature into a green compact with a density in a range from 6.6 to 6.7 g / cm ³ , which was then in a second step in a walking beam furnace for 15 minutes was sintered at a temperature of 1,280 ° C under a mixed gas atmosphere of 70% nitrogen and 30% hydrogen. Then, in a further step, the rotor set sintered in this way was calibrated under a pressure of 800 MPa to a density of 6.8 to 7.0 g / cm ³ . The hardness of the movable molded parts of the gear rotor set produced in this way was 141 HB, 62.5 / 2.5 according to DIN EN 24498-1 (Brinell hardness). The coefficient of thermal expansion, determined according to the DIN 51045 standard (temperature range 25 ° C - 200 ° C), was determined to be 17 ppm.

The gear rotor set produced in this way was placed in a cast aluminum housing made of GD-AlSi ₉ Cu ₃ (material number 3.2163.05), which had a thermal expansion coefficient of 23 ppm according to DIN 51405 (temperature range 25 ° C - 200 ° C).

The oil pump produced in this way showed only slight gap losses even after longer running times under load and elevated temperatures, as are common in internal combustion engines. In contrast to oil pumps customary in the prior art, it is considerably lighter.

According to the present invention, it is also possible not only to produce a complete set of toothed rotor assemblies, as described above, from a material comprising at least one austenitic iron-based alloy, but within the meaning of the invention, only the inner rotor can also be produced entirely from a material comprising an austenitic iron-based alloy. However, the individual components of a rotor set, in particular the inner wheel, can also be produced as a composite molded part, in which case either the toothing of the inner rotor, for example, and / or the end face 10 of the inner rotor, for example facing the wall 3, with a coating of a material comprising an austenitic iron-based alloy is made. Furthermore, conversely, only the toothing of rotor parts of a rotor set can be made of another material, for example an aluminum-based alloy, whereas the base body of the rotors in question can be made of an austenitic iron-based alloy. Furthermore, it is also possible to produce only the entrainment of the inner rotor of a gear rotor set from austenitic iron-based alloy material. However, the subject matter of the present invention is in no way limited to the combinations mentioned, but extends to any other possible combinations of the movable molded parts arranged in an oil pump. With the present invention, it is thus possible, on the one hand, to provide both compactly built and light oil pumps which have run times which are comparable to those of an iron cast housing with oil pumps.

Claims

claims

1. Oil pump (1) with a housing (2), made of a material comprising aluminum, and in the housing (2) arranged movable molded parts, characterized in that the movable molded parts are at least partially made of a sinterable material, comprising have at least one austenitic iron-based alloy, and have a coefficient of thermal expansion which is at least 60% of that of the housing (2).

2. Oil pump (1) according to claim 1, characterized in that the molded parts made of the sinterable material have a Brinell hardness according to DIN EN 24 498-1 of at least 100 HB.

3. Oil pump (1) according to one of the preceding claims, characterized in that the coefficient of thermal expansion of the molded parts made from the sinterable material is in a range from about 15 to about 21 ppm.

4. Oil pump (1) according to one of the preceding claims, characterized in that the movable molded parts comprise a rotor set (4), the axial play between at least one rotor (6) arranged on a shaft (5) of the rotor set (4). and the wall (3) of the housing (2) is less than 50 μm.

5. Molded parts according to one of claims 1 to 4.

6. A method for producing molded parts according to claim 5, characterized in that

- In a first step, sinterable material comprising at least one austenitic iron-based alloy is filled into a mold; il

- In a second step, a green compact is pressed at a pressure of at least 500 MPa with a density according to DIN ISO 2738 of at least 6.5 g / m ³ ; and

- In a third step, the green body is sintered at a temperature of at least 1,000 ° C in a gas atmosphere comprising nitrogen and / or hydrogen.

7. The method according to claim 6, characterized in that

- In a fourth step, the sintered molded part is calibrated at a pressure of at least 600 MPa to a density according to DIN ISO 2738 of at least 6.7 g / cm ³ .