Method for manufacturing bearing components of a turbocharger bearing, turbocharger bearing, turbocharger

Abstract

A turbocharger bearing (1) comprises several bearing rings (4, 5, 6), namely at least one inner ring (4) and at least one outer ring (5, 6), and rolling elements (7) rolling between the bearing rings (4, 5, 6), wherein the bearing rings (4, 5, 6) as well as the rolling elements (7) constitute bearing components (4, 5, 6, 7), and wherein at least one of the said bearing components (4, 5, 6, 7) is made of the steel 100CrSiMn6-5-4 and has a carbonitrided surface zone (12) in which a gradient of nitrogen and carbon concentration is present.

Description

[0001] The invention relates to a bearing designed as a rolling bearing for a turbocharger of an internal combustion engine. The invention further relates to a turbocharger and a method for manufacturing bearing components of a turbocharger bearing.

[0002] A turbocharger for an internal combustion engine is known, for example, from DE 10 2018 104 881 A1. A shaft of the known turbocharger is supported by a rolling bearing, which is designed as a double-row angular contact ball bearing. The rolling elements, i.e., balls, of the rolling bearing roll between bearing rings, which have at least a partially carbonitrided surface zone. DE 10 2018 104 881 A1 mentions steel 100CrSiMn6-4 as a possible material for the bearing rings. The carbonitrided surface zone contains, for example, a retained austenite content of up to 15%.

[0003] Further turbocharger bearings, which are also designed as rolling bearings, namely double-row ball bearings, can be found, for example, in documents DE 20 2008 020 067 A1 and DE 10 2010 054 926.

[0004] The invention is based on the objective of further developing rolling bearings for turbochargers compared to the aforementioned prior art, whereby a particularly favorable ratio between equipment effort and product properties, especially durability, is sought.

[0005] This problem is solved according to the invention by a turbocharger bearing having the features of claim 1. The turbocharger bearing is suitable for use in a turbocharger according to claim 7. Furthermore, the problem is solved by a method designed according to claim 8 for manufacturing a bearing component of a turbocharger bearing.

[0006] The following embodiments and advantages of the invention, explained in connection with the manufacturing process, also apply to the devices according to the application, i.e. the bearing and the turbocharger equipped therewith, intended for charging an internal combustion engine, and vice versa.

[0007] The turbocharger bearing according to the application comprises several bearing rings, namely at least one inner ring and at least one outer ring, as well as numerous rolling elements, in particular balls, rolling between the bearing rings. The bearing rings, like the rolling elements, constitute bearing components by definition. At least one of the various bearing components is made of 100CrSiMn6-5-4 steel and has a carbonitrided surface zone in which a gradient of nitrogen and carbon concentration exists.

[0008] It has been shown that, in this application, the steel 100CrSiMn6-5-4, particularly as the material from which the bearing rings are manufactured, is significantly superior to the common rolling bearing steel 100Cr6 in terms of its technical properties, and does not entail the increased manufacturing effort that, for example, the use of steel M50 would entail. Regarding steel M50, reference is made, by way of example, to documents WO 2016 / 015728 A1 and WO 2016 / 026490 A1, which concern bearings for aircraft.

[0009] In this case, for example, a single bearing ring of the turbocharger bearing, multiple bearing rings, or every bearing ring of the turbocharger bearing is made of 100CrSiMn6-5-4. In cases where a subset of the bearing rings is made of 100CrSiMn6-5-4 steel, this refers in particular to the inner ring or rings of the bearing, i.e., the rolling bearing. 100CrSiMn6-5-4 steel is offered, for example, under the Endurasco brand.

[0010] It is also possible to manufacture the outer ring(s) of the turbocharger bearing from 100CrSiMn6-5-4 steel. In configurations where only the inner ring(s) of the turbocharger bearing are made of 100CrSiMn6-5-4, the outer ring(s) of the same bearing can be made, for example, of 100Cr6 (material number 1.3505). Manufacturing the outer ring from 100CrMn6 (material number 1.3520) is also an option.

[0011] The rolling elements of the turbocharger bearing can be made of a ceramic or metallic material. In the latter case, any of the aforementioned steels can be used, in particular 100CrSiMn6-5-4. Overall, the turbocharger bearing is designed as a double-row angular contact ball bearing in numerous embodiments incorporating various material combinations.

[0012] In the manufacture of a bearing component, in particular a bearing ring, of the turbocharger bearing, a blank is used which is made of a steel which contains the elements C, Si, Mn, Ni, Cr, Mo in the following proportions (specified in weight percent): - Carbon: 0.9% to 1.05% - Silicon: 1.0% to 1.5% - Manganese: 0.8% to 1.2% - Nickel: 0.0% to 0.3% - Chromium: 1.2% to 1.8% - Molybdenum: 0.0% to 0.1%

[0013] In particular, this is a steel with the following composition: - Carbon: 0.9% to 1.05% - Silicon: 1.0% to 1.5% - Manganese: 0.8% to 1.2% - Nickel: 0.0% to 0.3% - Chromium: 1.2% to 1.8% - Molybdenum: 0.0% to 0.1% - Copper: 0.13% ± 0.013% - Sulfur: 0.005% ± 0.001% - Phosphorus: 0.013% ± 0.0026% - Aluminum: 0.02% ± 0.004% - Arsenic: 0.01% ± 0.002% - Tin: 0.01% ± 0.002% - Antimony: 0.001% ± 0.0005% - Lead: 0.003% ± 0.0006% - Titanium: <0.001% - Calcium: <0.0005% - Remainder: Iron and smelting-related impurities

[0014] The blank, which already has the final shape of the bearing component, in particular the bearing ring, with only minimal deviations from the intended form, is treated by carbonitriding until a diffusion depth of 0.3 ± 0.1 mm is achieved. Optionally, the bearing component is then deep-frozen following the carbonitriding process.

[0015] The silicon content is specifically between 1.20 and 1.25 percent by weight. In any case, the material from which the bearing component is manufactured is a through-hardening steel. The carbonitriding process creates a surface zone in which both the nitrogen and carbon content exhibit gradients.

[0016] The carbonitriding heat treatment to which the bearing components of the turbocharger bearing are subjected is carried out according to a possible process at a temperature of up to 950 °C with simultaneous carburizing and nitrogen deposition, followed by austenitizing at a maximum temperature of 880 °C. The dimensional growth is of the same order of magnitude as with conventional martensitic hardening.

[0017] Tempering of the workpiece, specifically the bearing ring, takes place at a temperature determined based on the operating temperatures of the turbocharger. The workpiece's heat resistance can extend up to the tempering temperature. The parameters set during heat treatment result in a defined retained austenite content.

[0018] Grinding can follow heat treatment as a final manufacturing step. For example, a grinding allowance of no more than 0.1 mm is used, so that the carbitriding effect in the edge zone of the bearing component is only affected to an acceptable degree.

[0019] Overall, the rolling bearing component treated according to the patent application is characterized by very good rolling resistance, in particular resistance to damage from particle impact, high thermal stability, and low abrasive wear. The process is not limited to specific rolling bearing types. For example, the rolling bearing can be designed as a single- or multi-row ball or roller bearing. Regarding the lubrication of the rolling bearing, a wide variety of solutions known from the prior art, tailored to the bearing's design and operating conditions, can be implemented.

[0020] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1. Sectional view of a turbocharger including a rolling bearing designed as a double-row angular contact ball bearing (in the sectional view), Fig. 2 a bearing ring, namely inner ring, of the rolling bearing, that is, turbocharger bearing, in a schematic sectional view.

[0021] A turbocharger, designated by reference numeral 10, of an internal combustion engine (not shown in further detail) comprises a turbocharger bearing 1, which is designed as a double-row angular contact ball bearing. Regarding the basic design and function of the turbocharger 10, including the turbocharger bearing 1, i.e., the rolling bearing, reference is made to the prior art cited above.

[0022] The turbocharger bearing 1 serves to support a shaft 2 in a housing 3 of the turbocharger 10. A single inner ring 4 of the turbocharger bearing 1 is held on the shaft 2. Two corresponding outer rings 5 ​​and 6 are inserted into the housing 3. The rolling elements 7, which roll between the inner ring 4 and the outer rings 5 ​​and 6, are designated as such. In this case, the rolling elements 7 are ceramic balls. Alternatively, steel balls can be used as rolling elements 7.

[0023] Overall, the rolling bearing 1 of the turbocharger 10 is designed as a double-row ball bearing in an O-arrangement. An X-arrangement could also be used instead of an O-arrangement (not shown), where the letter "O" or "X" refers in the usual way to the pattern described by the pressure lines, i.e., lines which are laid down by the contact points between the rolling elements 7 and the bearing rings 4, 5, 6, and which is symmetrical to the axis of rotation of the bearing, in this case turbocharger bearing 1.

[0024] During operation of the turbocharger bearing 1, the inner ring 4 is subjected to higher thermal loads than the outer rings 5 ​​and 6. These differing requirements are addressed by the choice of material. In this case, a steel with the following composition (in wt.%) is used for the inner ring 4: - Carbon: 1.03% - Silicon: 1.2% - Manganese: 0.97% - Nickel: 0.12% - Chromium: 1.47% - Molybdenum: 0.04% - Copper: 0.13% - Sulfur: 0.005% - Phosphorus: 0.013% - Aluminum: 0.02% - Arsenic: 0.01% - Tin: 0.01% - Antimony: 0.001% - Lead: 0.003% - Titanium: <0.001% - Calcium: <0.0005% - Remainder: Iron and smelting-related impurities

[0025] This steel, which falls under the specification of material 100CrSiMn6-5-4, undergoes heat treatment by carbonitriding. The workpiece, i.e., the bearing ring 4 currently being manufactured, experiences dimensional growth similar to that which occurs during conventional martensitic hardening. In this case, carbonitriding is followed by deep-freezing of the workpiece 4.

[0026] Unlike the inner ring 4, the outer rings 5 ​​and 6 are made of a common bearing steel, namely 100Cr6. Alternatively, outer rings 5 ​​and 6 can be made of 100CrMn6. Compared to the inner ring 4, which sits directly on the shaft 2 connected to the compressor wheel and the turbine wheel of the turbocharger 10, the outer rings 5 ​​and 6 are exposed to lower temperatures during normal operation of the turbocharger 10.

[0027] In the illustrated embodiment, ceramic balls are used as rolling elements 7. Depending on the conditions prevailing during the operation of the turbocharger 10, rolling elements 7 designed as balls and made of 100Cr6, 100CrMn6 or 100CrSiMn6-5-4 are also suitable for use in the turbocharger bearing 1.

[0028] The carbonitriding process, which is carried out in the case of the inner ring 4, creates a surface zone 12 of the bearing ring 4, as shown in Fig.Figure 2 shows a gradient in the concentration of atoms, specifically carbon and nitrogen atoms, that have diffused into the bearing component, in this case, the bearing ring 4. In contrast, the concentration of carbon and nitrogen atoms is not increased in the core zone of bearing component 4, designated 11. The diffusion depth, i.e., the thickness of the outer zone 12, is 0.3 ± 0.1 mm. Grinding after the heat treatment results in a significant, but tolerable, reduction in the thickness of the outer zone 12 produced by carbonitriding. Reference symbol list 1 turbocharger bearing, roller bearing 2nd wave 3 cases 4 inner ring 5 outer ring 6 outer ring 7 rolling elements, ball 8 first row of rolling elements 9 second row of rolling elements 10 turbochargers 11 Core zone 12 Edge zone QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2018 104 881 A1

[0002] DE 20 2008 020 067 A1

[0003] DE 10 2010 054 926

[0003] WO 2016 / 015728 A1

[0008] WO 2016 / 026490 A1

[0008]

Claims

[1] Turbocharger bearing (1), comprising a plurality of bearing rings (4, 5, 6), namely at least one inner ring (4) and at least one outer ring (5, 6), and rolling elements (7) rolling between the bearing rings (4, 5, 6), wherein the bearing rings (4, 5, 6) as well as the rolling elements (7) represent bearing components (4, 5, 6, 7), and wherein at least one of the various bearing components (4, 5, 6, 7) is made of the steel 100CrSiMn6-5-4 and has a carbonitrided edge zone (12) in which a gradient of the nitrogen and carbon concentration is present. [2] Turbocharger bearing (1) according to claim 1, characterized by that all bearing rings (4, 5, 6) are made of steel 100CrSiMn6-5-4. [3] Turbocharger bearing (1) according to claim 1, characterized by that exclusively the at least one inner ring (4) is made of the steel 100CrSiMn6-5-4, wherein the at least one outer ring (5, 6) is made of the steel 100Cr6. [4] Turbocharger bearing (1) according to claim 1, characterized by that exclusively the at least one inner ring (4) is made of the steel 100CrSiMn6-5-4, wherein the at least one outer ring (5, 6) is made of the steel 100CrMn6. [5] Turbocharger bearing (1) according to one of claims 1 to 4, characterized by that the rolling elements are made of steel, in particular 100CrSiMn6-5-4. [6] Turbocharger bearing (1) according to one of claims 1 to 4, characterized by that ceramic balls are provided as rolling elements. [7] Turbocharger of an internal combustion engine, comprising a turbocharger bearing (1) designed as a double-row angular contact ball bearing according to claim 1. [8] Method for producing a bearing component of a turbocharger bearing (1), comprising the following steps: - Providing a blank of a bearing component made of a steel containing 0.9% to 1.05% carbon, 1.0% to 1.5% silicon, 0.8% to 1.2% manganese, a maximum of 0.3% nickel, 1.2% to 1.8% chromium, and a maximum of 0.1% molybdenum, each expressed as a percentage by weight, - Treatment of the bearing component by carbonitriding until a diffusion depth of 0.3 ± 0.1 mm is reached. [9] Method according to claim 8, characterized by that the bearing component treated by carbonitriding has the following composition: • Carbon: 0.9% to 1.05% • Silicon: 1.0% to 1.5% • Manganese: 0.8% to 1.2% • Nickel: 0.0% to 0.3% • Chromium: 1.2% to 1.8% • Molybdenum: 0.0% to 0.1% • Copper: 0.13% ± 0.013% • Sulphur: 0.005% ± 0.001% • Phosphorus: 0.013% ± 0.0026% • Aluminum: 0.02% ± 0.004% • Arsenic: 0.01% ± 0.002% • Tin: 0.01% ± 0.002% • Antimony: 0.001% ± 0.0005% • Lead: 0.003% ± 0.0006% • Titanium: <0.001% • Calcium: <0.0005% • Rest: iron and smelting-related impurities [10] Method according to claim 9, characterized by that the bearing component is deep-frozen after carbonitriding

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