The invention relates to a turbocharger, in particular a VTG exhaust-gas turbocharger, according to the preamble of claim 1.
Such a turbocharger is disclosed by U.S. Pat. No. 6,709,232 B1 (equivalent to EP 1 534 933 A1).
The advantages and the success of diesel engines with direct fuel injection in terms of drivability and low fuel consumption have been greatly assisted by the use of turbochargers having a turbine with adjustable guide vanes. This makes it possible to substantially increase the feasible operating range of the turbine, affording a higher level of efficiency compared to wastegate turbines.
In using a turbocharger with a variable turbine geometry (VTG), it is known that with straight blades (i.e. blades having a straight skeleton or profile center line and a symmetrical thickness distribution) efficiency limits are encountered at high levels of supercharging. This applies, in particular, to the engine starting range (low engine speed at full load). However, the straight blades can be said to have good characteristics in terms of their adjustability.
In order to compensate for said thermodynamic deficiencies of the straight blades, the aforementioned U.S. Pat. No. 6,709,232 B1 proposes to use curved and/or profiled blades. When these blades are in a closed state, that is to say when the blades are in very close proximity to one another, the arrangement of generic type disclosed by the publication of prior art results in incorrect incident flows, which lead to variable moments acting either in the opening direction or in the closing direction of the blades. The speed distribution and the resulting static pressure distribution in the channel formed by two adjacent blades furthermore has an influence on the moment acting on the blades. This effect can also lead to an increase in the control hysteresis, which may lead to the loss of adjusting capacity, if the forces occurring exceed the forces of the adjustment facility.
The object of the present invention, therefore, is to create a turbocharger of the type specified in the preamble to claim 1, which will afford good thermodynamic characteristics for the blades of its variable turbine geometry with an improved control characteristic.
This object is achieved by the features of claim 1.
By using a turbocharger having the blade shape according to the invention, it is possible, in addition to an improvement in the thermodynamics, to significantly reduce the closing moment by reducing the overall pressure losses in the distributor ring. It is therefore possible to improve the control action whilst maintaining the axis of rotation of the blade.
In order to obtain opening moments, the axis of rotation must be shifted towards the blade leading edge. The blade geometry according to the invention here affords the advantage that the axis of rotation only has to be shifted by a smaller amount compared to the blades disclosed by the state of the art. A smaller overall radial space is therefore required than in known solutions.
The dependent claims contain advantageous developments of the invention.
The undulating profile center line of the blade according to the invention comprises two opposing antinodes. If this profile center line shape is plotted on an X-Y system of coordinates having a horizontal X-axis and vertical Y-axis, negative Y-values are first generated adjacent to the blade leading edge, these values changing to positive Y-values after passing through the X-axis, and the profile center line having a point of inflexion.
The result with regard to the thermodynamic characteristics is a modified orientation of the blade leading edge, which reduces the loss of energy due to impact, owing to the flatter incident flow against the blade leading edge.
This also results in lower velocities in the channels between the blades, which produces smaller flow losses, it being nevertheless possible to maintain an approximately constant deflection in a peripheral direction.
There is also a variation in the moments occurring in the “opening” direction, which is achieved due to lower velocities in the channel, the static pressure rising and thereby in conjunction with the point of inflexion producing a moment in the “opening” direction. This applies to the leading area of the blade underside and the trailing area of the blade top side.
If the trailing area 13′ of the blade top side is of rectilinear shape, this results in an increase in the effective channel cross section.
This in turn results in smaller losses due to low velocities in the channel whilst maintaining the deflection in a peripheral direction.
This embodiment also results in a change in the moments occurring in the “opening” direction due to lower velocities in the channel, which in turn allows the static pressure to rise, which in conjunction with the point of inflexion produces a moment in the “opening” direction.
In claim 5 a blade according to the invention is defined as an independently marketable entity.
Further details, advantages and features of the present invention are set forth in the following description of exemplary embodiments, with reference to the drawing, in which:
The turbocharger 1 has a turbine housing 2, which comprises an exhaust gas intake opening 3 and an exhaust gas outlet opening 4.
Also arranged in the turbine housing 2 is a turbine rotor 5, which is fixed on a shaft 6.
A plurality of blades, of which only the blade 7 can be seen in
The turbocharger 1 according to the invention naturally also comprises all the other usual components of a turbocharger such as a compressor wheel, which is fixed on the shaft 6 and is arranged in a compressor housing, and the entire bearing unit, which are not described below, however, since they are not essential in order to explain the principles of the present invention.
The blade 7 has a blade underside 8, which in the fitted state is the blade side facing the turbine rotor 5.
The blade 7 furthermore has a blade top side 9, which together with the blade underside 8 defines the thickness of the blade 7.
In the position of the blade 7 represented in
The blade underside 8 and the blade top side 9 define a profile center line 12; which is situated between them and is also referred to as the skeletal line. As
In
The graph of the profile center line 12 shows the area 12B beginning at the blade leading edge 10, which has negative Y values between the blade leading edge 10 (X=0, Y=0) and the zero passage (X≈0.27; Y=0). The zero passage preferably lies in a range between X=0.10 and X=0.40.
From said zero passage onwards the second area 12A always has positive values up to the blade trailing edge 11 (X=1, Y=0). The point of inflexion WP occurs at a value of approximately X=0.4; Y=0.02).
In addition to the verbal description, explicit reference is also made to the drawing for disclosure of the features of the present invention.
Number | Date | Country | Kind |
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05025829.2 | Nov 2005 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/011298 | 11/24/2006 | WO | 00 | 5/23/2008 |