DE102008060849A1 - Rotating machine i.e. exhaust gas turbo-charger, for use in internal combustion engine compartment of motor vehicle, has socket whose expansion co-efficient coincides to that of rotor and stator so that bearing tolerances are constant - Google Patents

Abstract

The machine has a rotor rotatably supported in a stator around a rotation axis via a hydrodynamic radial sliding bearing. The bearing has a bearing socket i.e. floating socket, whose thermal expansion co-efficient coincides to that of the rotor and stator such that inner and external bearing tolerances remain constant or decreases or increases with increasing operating temperature, respectively. The inner tolerance is radially formed between the bearing socket and the rotor regarding to the axis. The external tolerance is formed between the socket and the stator regarding to the axis.

Description

The The present invention relates to a rotary machine for an internal combustion engine, in particular a motor vehicle. Prefers the invention relates to an exhaust gas turbocharger for an internal combustion engine, in particular a motor vehicle.

rotating Machines, such. Eg electric motors, generators, pumps, compressors and charging devices, in particular turbochargers, have a rotor, the at least one radial bearing about an axis of rotation is rotatably mounted in a stator. For high speeds have radial plain bearings, especially hydrodynamic Radial plain bearings proved to be particularly advantageous. Such radial plain bearings have a bearing bush in the installed state coaxial with the axis of rotation is arranged. In a hydrodynamic radial plain bearing is formed radially between the bearing bush and the rotor an annular gap, which can also be referred to as an internal bearing clearance. In this inner Bearing clearance may be in operation a lubricating oil film between Rotor and bearing bush form, which is an extremely low-friction bearing allows. For the realization of emergency running properties it is common practice to make the bushing from a material which is softer than the material of the rotor. Usually is used for the bearing bushes brass while the rotor is preferably made of steel. For certain applications z. For example, with turbochargers, the operating temperature changes. Different coefficients of thermal expansion of brass and steel cause the inner bearing clearance increased with increasing operating temperature. As the operating temperature increases, however, the Viscosity of the lubricating oil, so that in itself a smaller inner bearing clearance would be required.

at The bushings are rigid bushes and floating bushes from each other distinguished. While a rigid bushing rotatably in the stator is arranged, a floating bushing can rotate with the rotor, So it is rotatably mounted in the stator about the axis of rotation. For this is radially between the bearing bush and the stator another annular gap trained, which also referred to as external bearing clearance can be. while on the inner bearing game The rotary bearing of the rotor is done over the outer Bearing clearance achieved in the first place damping of storage, as well can be about the outer radial play compensate for certain positional tolerances. The speed of such a floating bush results from a difference in the inner and outer Annular gap or prevailing in the respective oil film shear forces. Since usually also the stator made of steel is, the outer radial play increases with increasing Operating temperature. That means the damping effect in operation on the one hand by the decreasing outer Radial play and on the other hand in addition by the decreasing Viscosity of the lubricating oil decreases.

From the JP 01-073127 For example, an exhaust-gas turbocharger is known whose rotor shaft is provided with an amorphous layer, wherein a bearing bush made of a ceramic material is used to support the shaft.

From the DE 103 36 407 A1 and from the JP 02-178395 Alloys are known which are used for the production of bearing parts in exhaust gas turbochargers.

The The present invention addresses the problem of for a rotating machine of the type mentioned, in particular for an exhaust gas turbocharger, an advantageous or at least to provide another embodiment which is characterized in particular in that the bearing of the rotor over the entire operating temperature range is improved.

This Problem is inventively by the subject of the independent claim. advantageous Embodiments are the subject of the dependent Claims.

The invention is based on a first solution based on the general idea to match the materials of bearing bush and rotor to each other so that set for the bearing bush and the rotor thermal expansion coefficients, which provide a constant or a decreasing internal bearing clearance with increasing operating temperature. In other words, the material selection for the bearing bush according to the invention should be made so that the coefficient of thermal expansion of the bearing bush is equal to or smaller than the thermal expansion coefficient of the rotor or the rotor material. Of particular interest are embodiments in which the inner bearing clearance decreases with increasing operating temperature. By decreasing the operating temperature inner bearing clearance can be more or less compensated for a viscosity decrease associated with increasing operating temperature of the lubricating oil. With specific design or with a specific selection of the bearing bush material thus the inner bearing clearance can be optimized with regard to the temperature-dependent viscosity of the lubricating oil, in particular over the entire operating temperature range of the respective rotating machine. For example, at low operating temperatures, this can provide a relatively large internal radial clearance that, in conjunction with the relatively high viscosity of the lubricating oil at low operating temperatures, provides low friction bearing for the rotor. At high temperatures, the viscosity of the lubricating oil decreases. At the same time, the internal bearing clearance then decreases, so that optimum storage for the rotor can be achieved even at high operating temperatures.

Corresponding a second solution, analogous to the above The basic idea is based on a swimming bush configured bearing bush, the material selection for the bearing bush also be tuned so that the coefficients of thermal expansion from bushing and stator cause the outer Bearing clearance with increasing operating temperature remains constant or increases. Also preferred here is the variant in which the thermal expansion coefficient the bearing bush or the bearing bush material is smaller than the one of the stator or the stator material. As a result, the outer takes Radial play with increasing operating temperature too. For the damping effect of the lubricating oil in the outer Radial play this means that the viscosity decrease of the lubricating oil with increasing operating temperature Enlargement of the outer radial play can be counteracted, so that the attenuation-reducing Effect of decreasing viscosity more or less compensated can be. Such a floating bushing is due to frictional forces taken by the rotation of the rotor, so that they are opposite Rotates the rotor reduced speed in the stator. For example The floating bushing turns about at half the speed as the rotor.

The Both alternative solutions described above can can also be realized cumulatively.

By the targeted design of the bearing bush in terms of their thermal expansion coefficient It is thus in a designed as a floating bush bearing bush possible, radially inside the bearing of the shaft by a Defined to improve temperature-dependent bearing clearance and on the other hand radially outward by a defined temperature-dependent To improve bearing clearance.

Especially advantageous is a development in which the material selection for the designed as a rigid socket or as a floating bush Bearing bush is taken so that the thermal expansion coefficient of bearing bush and rotor are coordinated so that the inner bearing clearance within a predetermined temperature range at least 30% or more preferably at least 40% or preferred decreases by at least 50%. Additionally or alternatively the thermal expansion coefficients of bearing bush and rotor also be coordinated so that the inner bearing clearance decreases within the predetermined temperature range by a maximum of 60%. This means that the gap of the inner bearing clearance on upper end of the operating temperature range at least 30% or at least 40% or at least 50% and / or 60% less than at the bottom End of the operating temperature range. It will not only be here generates a random decrease of the inner bearing clearance, but generates a targeted, significant change that the viscosity decrease of the lubricating oil acts.

at a swimming bush can also according to a preferred embodiment be provided that the material the bearing bush is chosen with regard to the material of the stator, that the thermal expansion coefficient of bearing bush and stator are coordinated so that the outer Bearing clearance within a predetermined operating temperature range increases by at least 30% or in particular by at least 50% and / or increases by a maximum of 60%. In other words, a gap of the outer Bearing clearance is at the upper end of the operating temperature range at least 30% or at least 50% and / or up to 60% larger as at the lower end of the operating temperature range.

Consequently This is also a targeted enlargement the outer radial clearance to improve the Damping effect depending on the operating temperature.

Of the The aforementioned predetermined operating temperature range may be at preferred use of including -30 ° C up to and including + 150 ° C. Such a Operating temperature range may be especially in vehicle applications occur. For example, rotating machines are in one Engine compartment of a motor vehicle are arranged, such a temperature range exposed. In particular, it may be in the rotating machine For example, to act a charging device with relatively high speeds is working. In particular, it is thus an exhaust gas turbocharger. The rotor of an exhaust gas turbocharger usually comprises a shaft, on the one hand a compressor wheel and on the other hand Turbine wheel rotatably bears. A housing of the exhaust gas turbocharger, in the compressor wheel, turbine wheel and shaft are arranged forms while the stator.

For the production of the bearing bush different materials are suitable. Here are plastics, metal alloys and ceramic materials in question. It is important in all variants, the realization of a desired coefficient of thermal expansion of the bearing bush in coordination with the coefficient of thermal expansion of the rotor and / or the thermal expansion coefficient of the stator. For example, the bushing may be made of at least one of the following materials: silicon, graphite, carbon fiber reinforced carbon (CFC), pyrolyzed carbon fiber reinforced plastic (CFRP), and SSiC with a graphite layer, where SSiC stands for silicon carbide ceramic.

in the The difference is the rotor and the housing usually made of the same materials, eg. Example of steel or out Gray cast iron. Suitably have rotor and stator same thermal expansion coefficient.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 01-073127 [0004]
• - DE 10336407 A1 [0005]
• - JP 02-178395 [0005]

Claims (8)

Rotating machine for an internal combustion engine, in particular a motor vehicle, With a rotor, the at least one hydrodynamic radial plain bearing is rotatably mounted about a rotation axis in a stator, - in which the respective radial plain bearing has a bearing bush whose Thermal expansion coefficient so on the thermal expansion coefficient the rotor is tuned to that one with respect to the axis of rotation radially formed between the bearing bush and the rotor inner Bearing clearance with increasing operating temperature remains constant or decreases, and / or - where the coefficient of thermal expansion the bearing bush so on the thermal expansion coefficient the stator is tuned to that with respect to the axis of rotation radially formed between the bearing bush and the stator outer Bearing clearance with increasing operating temperature remains constant or increases. Machine according to claim 1, characterized in that that the thermal expansion coefficient of the bearing bush so matched to the thermal expansion coefficient of the rotor is that the inner bearing clearance within a predetermined operating temperature range at least 30% or at least 40% or at least 50% decreases. Machine according to claim 1 or 2, characterized that the thermal expansion coefficient of the bearing bush so matched to the thermal expansion coefficient of the rotor is that the inner bearing clearance within a predetermined operating temperature range decreases by a maximum of 60%. Machine according to one of claims 1 to 3, characterized in that the thermal expansion coefficient the bearing bush so on the thermal expansion coefficient The stator is matched to that of the outer bearing clearance within a predetermined operating temperature range by at least 30% or at least 50% increases. Machine according to one of claims 1 to 4, characterized in that the thermal expansion coefficient the bearing bush so on the thermal expansion coefficient The stator is matched to that of the outer bearing clearance within a predetermined operating temperature range by a maximum 60% increases. Machine according to one of claims 2 to 5, characterized in that the operating temperature range of including -30 ° C up to and including + 150 ° C enough. Machine according to one of claims 1 to 6, characterized in that the respective bearing bush from at least one of the following materials: silicon, graphite, carbon fiber reinforced carbon (CFC), pyrolyzed carbon fiber reinforced plastic (CFRP), silicon carbide (SSiC) with graphite layer. Machine according to one of claims 1 to 7, characterized in that the rotating machine is an exhaust gas turbocharger is.