DE102018104881A1 - Turbocharger for an internal combustion engine - Google Patents

Abstract

The invention relates to a turbocharger (9) for an internal combustion engine, comprising a shaft (8) and a roller bearing (1) for supporting the shaft (8) with at least one inner ring (2), an outer ring (3) and spatially between the at least an inner ring (2) and the outer ring (3) arranged rolling elements (4), wherein the at least one inner ring (2) and / or the outer ring (3) are formed of a bearing steel, wherein the at least one inner ring (2) and / or the outer ring (3) at least partially has a carbonitrided edge zone (5). Furthermore, the invention relates to a method for producing a rolling bearing (1) for such a turbocharger (9).

Description

The invention relates to a turbocharger for an internal combustion engine or a turbo-compound engine. The turbocharger comprises at least one shaft and a rolling bearing for supporting the shaft with an inner ring, an outer ring and spatially arranged between the inner ring and the outer ring rolling elements, wherein the inner ring and / or the outer ring is formed of a bearing steel or are. Furthermore, the invention relates to a method for producing a rolling bearing for such a turbocharger.

Commonly known combustion engines are also called turbo-compound engines, in which the energy content of exhaust gases is utilized by a downstream turbine power to further relax the exhaust gases from the combustion. The energy recovered by the power turbine is then transferred to the crankshaft via a mechanical or hydraulic transmission, thus optimizing the efficiency and performance of the turbo-compound engine. The exhaust gases of the turbo-compound engine have a higher pressure than the ambient air when opening the exhaust valves, wherein at least part of this pressure gradient is used to drive the turbocharger to compress the air in the intake tract of the turbo compound engine.

From the DE 43 27 815 A1 is a ball bearing for a turbocharger with a housing and a rotating shaft for connecting a compressor wheel with a turbine known. The ball bearing is arranged in the radial direction between the housing and the rotary shaft and arranged in the axial direction between the compressor wheel and the turbine wheel. The ball bearing has an outer bearing ring supported by the housing, which in turn is provided with an inner peripheral surface in which an outer rolling track is formed, the ball bearing further having an inner ring fitted on the rotary shaft in a center portion with respect to the axial extent thereof is. The inner bearing ring has an outer circumferential surface in which an inner Wälzbahn is formed, wherein the inner bearing ring is made of a heat-resistant metal.

The object of the present invention is to further develop a turbocharger, and in particular to make the rolling bearing of waves of the turbocharger more resistant and durable. The object is solved by the subject matter of claims 1 and 9. Preferred embodiments are given in the dependent claims, the description and the figures.

An inventive turbocharger for a motor vehicle comprises a shaft and a roller bearing for supporting the shaft with at least one inner ring, an outer ring and spatially arranged between the at least one inner ring and the outer ring rolling elements, wherein the at least one inner ring and / or the outer ring formed from a roller bearing steel are, wherein the at least one inner ring and / or the outer ring at least partially has a carbonitrided edge zone. The rolling bearing is preferably designed for supporting the shaft as a double-row angular contact ball bearing, whereby alternative rolling bearing shapes, such as cylindrical roller bearings can be provided. Furthermore, one or more rolling bearings of the turbocharger may comprise carbonitrided components, the rolling bearings in turn comprising one or more carbonitrided inner rings and / or an integrally formed or multi-part Au βenring, wherein preferably only a part of the multi-part outer ring is carbonitrided.

According to the solution according to the invention, only the outer ring can have a carbonitrided edge zone. But it may also have only the inner ring a carbonitrierte edge zone. Further alternatively, the inner ring and the outer ring may have a respective carbonitrided edge zone. If the roller bearing has two or more inner rings and / or two or more outer rings, all inner rings and all outer rings can be carbonitrided. However, it is also conceivable that only one of the inner rings and / or only one of the outer rings have a carbonitrided edge zone. The choice of carbonitriding components is essentially dependent on the mechanical and thermal requirements that are placed on the turbocharger and in particular on the rolling bearing.

The at least one inner ring and / or the outer ring are at least partially subjected to a carbonitriding, that is, a combined carburizing and nitriding. Carbonitriding is a hardening process in which the edge zone of the inner ring and / or the outer ring is treated thermochemically. In the process, the boundary zone to be treated is enriched with carbon and nitrogen under high temperatures so that carbon and nitrogen atoms diffuse into the boundary zone. The nitrogen is preferably present during the carbonitriding in conjunction with hydrogen as ammonia and serves in particular as an alloying element in the edge zone of the inner ring and / or the outer ring. The carbon forms in particular carbides in the edge zone. After carbonitriding, the edge zone in the region of the component surface has a carbon content of 0.8 to 1.5% by weight and a nitrogen content of 0.05 to 0.5% by weight.

Depending on the selected carbonitriding parameters, such as process duration (diffusion duration) and temperature, the edge zone is in particular designed to improve the mechanical and thermal properties of the rolling bearing. The carbonitriding is advantageously used to give the edge zone of the inner ring and / or the outer ring a comparatively high hardness. The mechanical properties, which are significantly improved by the carbonitriding, are, for example, the rollover resistance of the rolling bearing, in particular the surface of the carbonitrided edge zone and the resistance to abrasive and adhesive wear. The rollover resistance describes the resistance of the carbonitrided inner ring and / or outer ring to damage caused by overrolled particles. The edge zone thus has a comparatively high wear resistance. Furthermore, the heat-treated carbonitrided components of the rolling bearing have a comparatively high heat resistance. In other words, the inner ring and / or the outer ring to a comparatively high thermal stability, is resistant to contamination and is therefore characterized by its increased fatigue strength.

The shaft of the turbocharger is preferably designed to rotate in a speed range of 10,000 to 300,000 revolutions per minute. Preferably, the shaft of the turbocharger is adapted to rotate in a speed range of 50,000 to 300,000 revolutions per minute, in particular 100,000 to 300,000 revolutions per minute.

Preferably, the edge zone has a thickness of 0.05 to 1.5 mm. Preferably, the edge zone has a thickness of 0.3 mm. The edge zone is designed, in particular, as a gradient edge zone with a carbonitriding hardening depth which, starting from the surface of the edge zone, has a carbon relationship or nitrogen concentration which changes in the form of a function. The carbonitriding depth depends on the process temperature during carbonitriding. Thus, the carbonitrided inner ring and / or outer ring has a comparatively low required diffusion depth (carbonitriding hardening depth) which provide the desired mechanical and thermal properties. It is advantageous that the process times of the heat treatment can be reduced by the carbonitriding, which has a positive effect on the process and manufacturing costs of the turbocharger. Furthermore, due to carbonitriding, the dimensional and shape deviations of the inner ring and / or outer ring that occur occur. The process-related dimensional and form deviations are essentially in the context of a martensitic hardening.
The thickness and the structure of the edge zone can be determined and examined, for example, on a transverse section of the inner ring and / or the outer ring. In particular, light microscopy and scanning electron microscopy are suitable for measuring and investigating the edge zone.

According to a preferred embodiment, the at least one inner ring and / or the outer ring are formed of 100Cr6. Alternatively, the at least one inner ring and / or the outer ring are formed of 100CrSiMn6-4. In other words, the at least one inner ring and / or the outer ring are formed in particular from a low-alloy and thermosetting bearing steel as the base material, wherein the at least one inner ring and / or the outer ring can also be formed from another low-alloy steel. As a result, a cost-effective carrier material is provided, wherein the desired mechanical and thermal properties are set by the thermochemical treatment and the edge zone formed therewith.

Preferably, the edge zone has a Vickers hardness of greater than 650 HV10. Thus, the Vickers hardness decreases DIN EN ISO 6507-1: 2005 to -4: 2005 determined on the surface of the carbonitrided edge zone by an equilateral diamond pyramid is pressed under a specified test force in the edge zone of the inner ring and / or the outer ring and then from the ratio of test force and impression surface including a conversion factor, the Vickers hardness can be determined.

Preferably, the edge zone is formed in the region of a raceway of the at least one inner ring and / or the outer ring. Consequently, the edge zone is formed in the region of maximum Hertzian pressure on the inner ring and / or on the outer ring.

Further preferably, the edge zone has a retained austenite content of at most 15%. During the hardening process following the carbonitriding, a residual austenite content remains in the microstructure of the edge zone due to the incomplete martensite formation, which influences in particular the mechanical properties of the carbonitrided edge zone as a function of the content. To determine the residual austenite content in the carbonitrided edge zone, for example, light microscopy, X-ray structure analysis or magnetic-inductive measuring methods are suitable.

According to a method of manufacturing a rolling bearing for a turbocharger according to the invention, at least one inner race and / or outer race of the rolling bearing is carbonitrided, carbon and nitrogen diffusing into a surface of the at least one inner race and / or outer race to form a rim the at least one inner ring and / or the outer ring hardened and then tempered. The carbonitriding is preferably carried out at temperatures between 850 and 950 ° C, wherein in addition to carbon small amounts of nitrogen diffuse into a surface of the at least one inner ring and / or the outer ring to form the edge zone. Since the at least one inner ring and / or the outer ring are exposed to relatively lower temperatures in this method and the process duration is generally shorter than, for example, during carburizing, the heat-treated inner ring and / or outer ring are less susceptible to warpage. The diffused nitrogen serves as an alloying element due to the comparatively small diffusion amount and reduces the hardening temperature and the critical quenching speed, which in turn improves the hardenability of the rolling bearing steel. Due to the resulting shorter process time, the production of the rolling bearing can be made more economical.

Immediately after the expiration of the diffusion time during the carbonitriding, the inner ring and / or the outer ring are quenched. This is preferably done in oil to prevent a delay. The edge zone has a thickness between 0.05 and 1.5 mm, the thickness being referred to as carbonitriding hardening depth (CHD). The carbonitriding hardening depth is dependent on the hardening temperature, the quenching rate, the hardenability of the rolling bearing steel and the dimensions of the at least one inner ring and / or the outer ring or the region of the at least one inner ring and / or the outer ring on which the carbonitriding takes place. The carbonitriding (thermal treatment) ends with tempering at comparatively low temperatures of 150 to 350 C in order to reduce brittleness generated as a function of the carbonitriding hardening depth and to set a desired surface hardness. The tempering temperature depends on the temperature in use of the turbocharger.

Preferably, deep cooling of the at least one inner ring and / or the outer ring takes place between hardening and tempering. Freezing causes additional conversion of retained austenite to martensite and an improvement in tempering and dimensional stability.

• 1 eine schematische Längsschnittdarstellung eines erfindungsgemäßen Turboladers gemäß einer bevorzugten Ausführungsform, und
• 2 eine schematische Schnittdarstellung eines teilweise gezeigten Wälzlagers des Turboladers gemäß 1.

Further measures improving the invention will be described in more detail below together with the description of a preferred embodiment of the invention with reference to the figures, wherein the same or similar elements are provided with the same reference numerals. It shows

• 1 a schematic longitudinal sectional view of a turbocharger according to the invention according to a preferred embodiment, and
• 2 a schematic sectional view of a partially shown rolling bearing of the turbocharger according to 1 ,

According to 1 includes a turbocharger 9 for a - not shown here - internal combustion engine a shaft 8th as well as a rolling bearing 1 for storage of the shaft 8th , The wave 8th is designed to rotate in a speed range of 10,000 to 300,000 revolutions per minute. The rolling bearing 1 is presently designed as a double-row angular contact ball bearings and has a two-part inner ring 2 and a one-piece outer ring 3 on, with the outer ring 3 radially and axially against a housing 10 of the turbocharger 9 supported. Spatially between the inner ring 2 and the outer ring 3 are rolling elements 4 arranged and roll on a particular track 6 of the inner ring 2 or the outer ring 3 from. The inner ring 2 and the outer ring 3 are made of 100Cr6 (bearing steel). Alternatively, the inner ring 2 and the outer ring 3 be formed of 100CrSiMn6-4. Further alternatively, the inner ring 2 made of 100Cr6 and the outer ring 3 be formed of 100CrSiMn6-4, or vice versa. In this sense, the materials and heat treatments for the individual components can be selected according to a modular principle.

In 2 is a detail sectional view of the rolling bearing 1 shown. In the present case, both the inner ring 2 as well as the outer ring 3 in the field of the respective career 6 a carbonitrided edge zone 5 on. The border zone 5 of the inner ring 2 and the outer ring 3 is ever made by carbonitriding, with carbon and nitrogen in a particular surface 7 of the inner ring 2 or the outer ring 3 diffuse. Subsequently, the inner ring 2 and the outer ring 3 hardened and tempered. The carbonitriding takes place at a temperature of 850-950 ° C and thereby generates a thickness (Carbonitrierhärteiefe) of the respective edge zone 5 of up to 1.5 mm, as well as a Vickers hardness of up to 1000 HV1. Furthermore, the edge zone 5 a retained austenite content of less than 15%. The thickness, the surface hardness and the retained austenite content of the edge zone 5 depend on the process parameters, such as diffusion duration and quenching rate as well as the dimensions of the surface to be carbonitrided. The border zone 5 improves mechanical and thermal properties of the rolling bearing 1 In particular, the rollover resistance and the resistance to abrasive and adhesive wear are optimized. Furthermore, the edge zone causes 5 a better thermal stability of the rolling bearing 1 with simultaneously improved fatigue strength.

LIST OF REFERENCE NUMBERS

1

roller bearing

2

inner ring

3

outer ring

4

rolling elements

5

border zone

6

career

7

surface

8th

wave

9

turbocharger

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4327815 A1 [0003]

Cited non-patent literature

• DIN EN ISO 6507-1: 2005 [0012]

Claims (10)

Turbocharger (9) for an internal combustion engine, comprising a shaft (8) and a roller bearing (1) for supporting the shaft (8) with at least one inner ring (2), an outer ring (3) and spatially between the at least one inner ring (2) and the outer ring (3) arranged rolling elements (4), wherein the at least one inner ring (2) and / or the outer ring (3) are formed of a bearing steel, characterized in that the at least one inner ring (2) and / or the Au having at least partially a carbonitrided edge zone (5). Turbocharger (9) after Claim 1 , characterized in that the shaft (8) is adapted to rotate in a speed range of 10,000 to 300,000 revolutions per minute. Turbocharger (9) according to one of the preceding claims, characterized in that the edge zone (5) has a thickness of 0.05 to 1.5 mm. Turbocharger (9) after one of Claims 1 to 3 , characterized in that the at least one inner ring (2) and / or the Au-βenring (3) made of 100Cr6 is formed. Turbocharger (9) after one of Claims 1 to 3 , characterized in that the at least one inner ring (2) and / or the Au-βenring (3) from 100CrSiMn6-4 is formed. Turbocharger (9) according to one of the preceding claims, characterized in that the edge zone (5) has a Vickers hardness of more than 650 HV10. Turbocharger (9) according to one of the preceding claims, characterized in that the edge zone (5) in the region of a raceway (6) of the at least one inner ring (2) and / or the outer ring (3) is formed. Turbocharger (9) according to one of the preceding claims, characterized in that the edge zone (5) has a retained austenite content of at most 15%. Method for producing a rolling bearing (1) for a turbocharger (9), wherein the rolling bearing (1) at least one inner ring (2), an outer ring (3) and spatially between the at least one inner ring (2) and the outer ring (3) arranged Rolling element (4), wherein the at least one inner ring (2) and / or the outer ring (3) are formed from a rolling bearing steel, comprising the following method steps: Carbonitriding the at least one inner ring (2) and / or the outer ring (3), carbon and nitrogen diffusing into a surface (7) of the at least one inner ring (2) and / or outer ring (3) to form a peripheral zone (5 ) to train; - Hardening of the at least one inner ring (2) and / or the outer ring (3); and - Starting the at least one inner ring (2) and / or the outer ring (3). Method according to Claim 9 , characterized in that deep cooling of the at least one inner ring (2) and / or the outer ring (3) takes place between hardening and tempering.

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