This application claims priority to European Patent Application No. EP11305761.6 filed on Jun. 17, 2011.
FIELD OF THE INVENTION
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The present invention relates to the field of turbochargers, and in particular those used in combustion engines for automotive vehicles.
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OF THE INVENTION
In such application, a turbocharger is used to enhance the combustion engine performance by blowing compressed air into the cylinders of said engine.
A turbocharger generally comprises a housing, a shaft extending through an opening formed on the housing, a turbine wheel mounted on a first end portion of the shaft and located in an exhaust gases passage of the combustion engine, a compressor wheel mounted on an opposite second end portion of said shaft and located in an admission gases passage of the engine, and rolling bearings disposed between the shaft and the housing. When the turbine wheel is rotated by the flow of the exhaust gases, the shaft and the compressor wheel are rotated which leads to a compression of the admission gases introduced into the cylinders of the combustion engine.
The engine oil may be used for the lubrication of the rolling bearings. However, when the combustion engine stops, the delivery of engine oil is shut off. This causes a strong temperature increase of the residual oil located between the shaft and the rolling bearing near to the turbine wheel. The cooling of said rolling bearing is thus not satisfactory. Otherwise, the engine oil may contain foreign matter, for example small metal particles, thereby causing a premature wear of the rolling bearings.
To overcome these drawbacks, European patent application EP-A2-2 042 758 discloses a turbocharger comprising a tank for storing a specific lubricating oil for the rolling bearings, said tank being formed within the housing. A tube is provided between the storage tank and the space where are housed the rolling bearings to supply by capillary action the lubricating oil. In the disclosed turbocharger, an intermediate bearing casing is also mounted between the rolling bearings and the housing, said casing being equipped with damper rings to reduce the transmission of vibrations emitted by the turbine and compression wheels.
This leads to a complex structure of the turbocharger as well as an increase of the mounting cost.
One aim of the present invention is therefore to overcome the aforementioned drawbacks.
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OF THE INVENTION
It is a particular object of the present invention to provide a turbocharger which is simple to manufacture and economic, while guaranteeing good sealing and damping properties.
In one embodiment, the turbocharger comprises a shaft, a housing, a turbine wheel and a compressor wheel mounted onto the shaft, and at least a rolling bearing disposed between the shaft and the housing and comprising an inner ring, an outer ring and at least one row of rolling elements disposed into a rolling space defined between the rings. A damping space is defined between an outer surface of the outer ring and a bore of the housing inside which a lubricant is located.
In one embodiment, the turbocharger further comprises at least two sealing means closing at least the rolling space.
In one embodiment, the turbocharger further comprises at least two sealing means closing the damping space and the rolling space.
In one embodiment, the turbocharger further comprises passage means for the lubricant putting the damping space and the rolling space into communication.
In one embodiment, the sealing means are axially offset outwards with respect to the passage means.
The passage means may comprise a gap between the outer ring and the housing. Alternatively or in combination, the passage means comprise holes made in the thickness of the outer ring. The lubricant located inside the damping space may be grease.
In one embodiment, the sealing means are disposed radially between the shaft and the housing.
In another embodiment, the sealing means are disposed radially between the inner and outer rings. The sealing means may only close the rolling space. The rolling space may be filled with a lubricant distinct from the lubricant located in the damping space.
In one embodiment, the axial length of the rolling bearing ranges between 30% and 95% of the axial dimension of the housing, and preferably ranges between 70% and 80%.
BRIEF DESCRIPTIONS OF THE DRAWINGS
The present invention and its advantages will be better understood by studying the detailed description of specific embodiments given by way of non-limiting examples and illustrated by the appended drawings on which:
FIG. 1 is an axial section of a turbocharger according to a first example of the invention, and
FIG. 2 is an axial section of a turbocharger according to a second example of the invention.
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OF THE INVENTION
As illustrated on the FIG. 1, which illustrates an embodiment of a turbocharger 10 according to an example of the invention, the turbocharger comprises a housing 12, a shaft 14 extending along a longitudinal axis 14a through a cylindrical bore or opening 16 of the housing, a rolling bearing 18 mounted onto the shaft 14 and disposed into the bore 16, a turbine wheel 20 fixed at one end of the shaft 14 and a compressor wheel 22 fixed at an opposite end of said shaft. The housing 12 comprises a cap 24 fixed at one axial end. In the disclosed embodiment, the axial length of the rolling bearing 18 ranges between 60% and 90% of the axial dimension of the bore 16 of the housing, and more precisely between 70% and 80%.
The rolling bearing 18 comprises an inner ring 26 and an outer ring 28 between which are housed two rows of rolling elements 30 and 32, which in this case are balls, and two annular cages 34, 36 respectively maintaining the circumferential spacing of the rolling elements 30, 32. The axis 18a of the rolling bearing is coaxial with the axis 14a of the shaft of the turbocharger.
The inner and outer rings 26, 28 are concentric and symmetric with respect to a transverse radial plane passing through the centre of the rolling bearing. The rings 26, 28 are of the solid type. A “solid ring” is to be understood as a ring obtained by machining with removal of material (by machining, grinding) from metal tube stock, bar stock, rough forgings and/or rolled blanks.
The outer ring 28 comprises an outer cylindrical surface 28a delimited by opposite radial lateral surfaces 28b and 28c, the radial surface 28c axially come into contact with a radial shoulder of the housing 12. The outer ring 28 also comprises a bore 28d of cylindrical shape from which are formed toroidal raceways (not referenced) having in cross-section a concave internal profile adapted to the rolling elements 30, 32. The raceways are symmetrical with respect to the transverse radial plane passing through the centre of the rolling bearing.
An annular radial gap or space 38 exists between the outer surface 28a of the outer ring and the bore 16 of the housing. The annular space 38 is delimited radially by the outer ring 28 and the bore 16 of the housing, and axially by the radial shoulder of said housing and the cap 24. An annular axial space or gap 39 is defined between the radial surface 28b of the outer ring and the cap 24.