Patent Application
20180073520
This application claims priority to German Patent Application No. DE 10 2016 217 446.0, filed on Sep. 13, 2016, the contents of which are incorporated herein by reference in its entirety.
The present invention relates to a charging device with a compressor and a shaft which is rotatably mounted in a bearing housing, with a compressor wheel arranged thereon. In addition, the invention relates to an internal combustion engine with such a charging device.
From EP 0 386 743 A2 a generic charging device with a compressor and a shaft that is rotatably mounted in a bearing housing, with a compressor wheel arranged thereon, is known. The known charging device additionally has a diffuser, which radially extends from a diffuser inlet on the compressor wheel to a diffuser outlet on a spiral-shaped compressor housing. Here, the diffuser itself is tapered with respect to its radial length by way of which a pressure increase and thus an increased efficiency are to be achieved.
Disadvantageous with the charging device known from the prior art however is that at low circumferential speeds and mass flows, i.e. near a surge limit, the risk of a flow separation and a backflow in the diffuser near a bearing housing wall are increased. In particular at low circumferential speeds and mass flows, this leads to a reduction of the efficiency.
The present invention therefore deals with the problem of stating an improved or at least an alternative embodiment for a charging device of the generic type, which is characterized in particular by an increased efficiency in an operating range near the surge limit.
According to the invention, this problem is solved through the subject of the independent claims. Advantageous embodiments are subject of the dependent claims.
The present invention is based on the general idea of forming, for the first time, a bearing housing wall delimiting a diffuser in the direction of a bearing housing of a compressor not radially, but obliquely, as a result of which in particular in the operating range near the surge limit, i.e. at comparatively low circumferential speeds and mass flows, a flow separation and a back flow in the diffuser near the bearing housing wall can be reduced. Because of this, the efficiency can be substantially increased in particular in this operating range. The charging device according to the invention comprises, in the known manner, a compressor and a shaft that is rotatably mounted in a bearing housing and a compressor wheel arranged thereon. Likewise, the charging device comprises a diffuser which radially extends from a diffuser inlet on the compressor wheel towards a diffuser outlet on a spiral-shaped compressor housing. It is now according to the invention that the diffuser on the one hand is delimited by a diffuser wall and on the other hand by a bearing housing wall and at the same time the bearing housing wall, in a first section originating from the diffuser inlet, is orientated by an angle α of 2°≦α≦30° obliquely to a radial direction and because of this brings about a tapering of the diffuser cross section in radial direction to the outside. Through the reduced flow cross section, an increase of the flow velocity in the diffuser can be achieved and because of this an increase of the efficiency with low mass flows. With the oblique bearing housing wall, the flow in the diffuser is decelerated and thus pressure build-up, wherein however the special advantage and basic idea of the present invention is that the efficiency at low mass flows and low circumferential speeds, i.e. in particular in a range near the surge limit can be increased, which can be achieved with the bearing housing wall that is inclined in its first section according to the invention. Conventional geometries by contrast have the problem that in the operating points at low circumferential speeds and mass flows the area enlargement in the diffuser in radial direction and thus the deceleration is too great, which as a consequence results in flow separations. The increase of the efficiency in this case is based in particular on the fact that through the oblique first section of the bearing housing wall a flow separation and a back flow in the diffuser at low rotational speed and mass flows can be reduced.
With an advantageous further development of the solution according to the invention, a width a on the diffuser outlet corresponds to approximately 37.5 to 95% of the width B on the diffuser inlet. By way of such a cross-sectional tapering an increase of the flow velocity or a reduction of the deceleration that otherwise occurs in this range takes place in the radial profile of the diffuser, as a result of which the efficiency of the charging device according to the invention can also be increased in lower rotational speed ranges.
With a further advantageous embodiment of the solution according to the invention, a radially extending second section adjoins the first section of the bearing housing wall radially on the outside, which opens into a volute of the compressor housing. The radially extending second section in this case is dependent on the angle of the inclination and the width a on the diffuser outlet.
Practically, a radial length L2 of the second section corresponds to 100% to 250% of the radial length L1 of the first section, wherein the radial length L2 is obtained from the outer diameter of the diffuser.
With a further advantageous embodiment of the solution according to the invention, the first section is formed in one piece with the bearing housing wall. This offers the great advantage that through a simple change of the shape of the bearing housing the shape of the diffuser can also be changed at the same time without assembly steps being subsequently required for this. In particular, by changing the casting mould of the bearing housing, a diffuser can be created for example at the same time. Alternatively to this it is obviously also conceivable that the first and the second section of the bearing housing wall are formed as a separate insert and are connected to the bearing housing wall. This in turn offers the great advantage that the production of the bearing housing with initially radial bearing housing wall can be continued and merely optionally equipped with the additional first and second section. Because of this, a significantly greater flexibility with respect to the production is also conceivable in particular, since for example different first sections with wedge surfaces of varying inclination and second sections of varying thickness can be kept in stock and can be individually arranged in otherwise same bearing housings or on otherwise same bearing housing walls. Because of this, a modular system could also be realised in particular.
Further important features and advantageous of the invention are obtained from the subclaims, from the drawing and from the associated FIGURE description by way of the drawing.
It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.
A preferred exemplary embodiment of the invention is shown in the drawing and is explained in more detail in the following description.
The only FIGURE shows a sectional representation through a charging device according to the invention.
According to the FIGURE, a charging device 1 according to the invention, which can be designed in particular as exhaust gas turbocharger 2 in a motor vehicle, comprises a compressor 3 and a shaft 5 that is rotatably mounted in a bearing housing 4 with a compressor wheel 6 arranged thereon. Likewise, the charging device 1 according to the invention comprises a diffuser 7, which radially extends from a diffuser inlet 8 on the compressor wheel 6 towards a diffuser outlet 9 on a spiral-shaped compressor housing 10. According to the invention, the diffuser 7 is now delimited on the one hand by a diffuser wall 11 and on the other hand by a bearing housing wall 12. According to the invention, the bearing housing wall 12 is orientated on a first section originating from the diffuser inlet 8 obliquely to a radial direction 14 by an angle α between 2 and 30° and brings about a tapering of the diffuser cross section in radial direction 14 towards the outside. A bearing housing wall which a compressor known from the prior art and designed as usual would have is drawn with dashed line and marked with the reference number 15. This previous bearing wall 15 usually runs parallel to the diffuser wall 11.
Thus looking at the FIGURE it is evident that the first section 13 of the bearing housing wall 12 formed obliquely according to the invention runs significantly inclined to the radial direction 14, as a result of which in particular the risk of a flow separation and of an undesirable back flow in the diffuser 7 near the bearing housing wall 12 at low circumferential speeds and thus also low mass flows, i.e. in the range of a surge limit, can be substantially reduced, as a result of which in this operating range a significantly increased efficiency can be achieved.
A width a on the diffuser outlet 9 corresponds to approximately 0.375 B≦a≦0.95 B of the width B on the diffuser inlet 8. Looking at the FIGURE it is evident that the width B corresponds to the sum of b and c, wherein b corresponds to a diffuser width of a compressor known from the prior art.
In addition to this, a ratio of a diffuser width a to b amounts to approximately 0.6 to 0.95, wherein a corresponds to a diffuser width of the charging device 1 according to the invention, while b marks the diffuser width of a diffuser known from the prior art.
At the same time it is evident that an axial shift of the bearing housing wall 12 in the region of the diffuser inlet 8 compared with a bearing housing wall 15 of a charging device known from the prior art takes place, namely by a value c between 0.2 mm and 1 mm.
According to the FIGURE it is additionally evident that the compressor wheel 6 engages with a wheel back 16 into a recess 17 on the bearing housing 4.
The first section 13 radially on the outside is adjoined by a radially extending second section 18 of the bearing housing wall 12, which opens into a volute 19 of the compressor housing 10. The second section 16 in this case runs preferentially parallel to the diffuser wall 11. A radial length L2 of the second section 18 amounts to approximately 100% to 250% of the radial length L1 of the first section 13. The length L2 follows the length L1 and goes as far as to the outer diameter of the diffuser 7 or of the compressor 3.
In addition it can be provided that the first section 13 is formed in one piece with the bearing housing wall 12 or that the first section 13 and the second section 18 of the bearing housing wall 12 are formed as a separate insert and connected to the bearing housing wall 12. The first case offers the great advantage that a comparatively cost-efficient production is made possible since the first section 13 and the second section 18 can be produced in one piece and thus in a common production step with the bearing housing 4. With the second mentioned embodiment there is the advantage that the first and second section 13, 18 formed as a separate insert makes possible a flexible assembly as a result of which the bearing housing previously used could be continued to be used. The previous bearing housing wall 15, which is shown drawn with dashed line, constitutes an outer limit of the bearing housing produced up to now.
In the region of the diffuser 7, the bearing housing wall 12 can comprise a cooling duct or an air gap insulation. The charging device 1 according to the invention can be employed for example in an internal combustion engine 20.
With the charging device 1 according to the invention, in particular a significantly increased efficiency in the lower rotational speed range, i.e. near a surge limit, can be achieved since a flow separation or a back flow in the diffuser 7 can be reduced here.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 217 446.0 | Sep 2016 | DE | national |
