Abstract:
In an exhaust turbocharger for an internal combustion engine including a turbine and a compressor, which is driven by the turbine, wherein the compressor comprises a compressor impeller in a flow duct, a transfer component with flow passages extends radially around the compressor impeller in the axial direction of the impeller and provides for communication with the flow duct. To provide for variable adjustment of the effective flow cross-section of the transfer duct, a transfer ring is provided which comprises two component rings, which are rotatable relative to one another.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to an exhaust turbocharger for an internal combustion engine with a turbine and a compressor driven by the turbine and including means for controlling the flow volume delivered by the compressor.  
           [0002]    The operating range of compressors in exhaust turbochargers is limited by a surge line and a choke line. These lines denote boundary lines in performance graphs that characterize the behavior of the compressor. When the compressor is operated close to the surge line, there are locally limited separation zones at the blades of the compressor impeller, and these can lead to pulsations of the flow with a periodic reversal of the direction of flow. The surge line of the compressor can be reached when relatively small volume flows are being delivered by the compressor.  
           [0003]    When the operating point of the compressor shifts towards large volume flows in the compressor&#39;s performance characteristics, however, the choke line may be reached. This is distinguished by blockage of the volume flow at the entrance to the impeller.  
           [0004]    In order to extend the operating range of compressors, measures can be taken to stabilize the performance characteristics. These measures shift both the surge line and the choke line towards an extended operating range. One such measure to stabilize the performance characteristics is known, for example, from the publication DE 42 13 047 A1, according to which a bypass is provided in the compressor housing parallel to the compressor inflow duct to bypass one section of the inflow duct. If the compressor is operated in the region of the surge line, the bypass allows controlled recirculation of a mass flow component, which is recirculated in the bypass counter to the delivery direction. The mass flow component is fed back to the main mass flow and returned to the compressor together with the latter.  
           [0005]    The choke line too can be shifted to give an extended operating range by stabilizing the performance characteristics. As the volume flows increase, intake air is fed into the compressor because of the additional bypass flow cross-section, thereby shifting the choke line in the direction of larger mass flows.  
           [0006]    The disadvantage of the arrangement as shown in DE 42 13 047 A1 is that the measure to stabilize the performance characteristic is integrated in a fixed and invariable manner into the housing of the compressor, without any possibility of adjustment. It is therefore impossible to adapt the flow in the bypass (individually) as a function of the operating point of the compressor.  
           [0007]    DE 198 23 274 C1 represents an improvement in this respect. In the compressor described in this publication, an adjustable closure element is provided for variable adjustment of the effective flow cross-section of the bypass. This element is an adjustable guide vane structure comprising two concentrically arranged rings.  
           [0008]    It is the object of the present invention to provide, by simple means, a compressor in an exhaust turbocharger for an internal combustion engine with extended performance characteristics.  
         SUMMARY OF THE INVENTION  
         [0009]    In an exhaust turbocharger for an internal combustion engine including a turbine and a compressor which is driven by the turbine, wherein the compressor comprises a compressor impeller in a flow duct, at least one transfer duct extends radially around the compressor impeller in the axial direction of the impeller and provides for communication with the flow duct. To provide for variable adjustment of the effective flow cross-section of the transfer duct, a transfer ring with transfer grooves is provided which comprises two component rings, which are rotatable relative to one another.  
           [0010]    Preferably, at least one of the two component rings can be angularly adjusted by means of an actuating element depending on the operating condition of the internal combustion engine. In the overlapping position, the free cross-section of the transfer slot becomes a maximum whereas, in the blocking position, the free flow cross-section is reduced to a minimum, if appropriate to zero. With the component rings being adjustable rotationally relative to one another, the free flow cross-section through the transfer slots at the interface between the two component rings can be adjusted.  
           [0011]    The two component rings are advantageously arranged concentrically and radially one within the other. The radially inner component ring is disposed adjacent to the compressor impeller and the radially outer component ring is disposed remote from the compressor impeller. In the overlapping position, the cross-sections of the transfer slots on the radially inner side of the outer component ring overlap with those of the inner ring. The blocking position is achieved by rotation of the two component rings relative to one another, with the two corresponding cross-sections of the associated transfer slots in the inner and outer component rings moving into a position out of radial alignment. In the blocking position, the transfer duct is thus formed solely by the remaining open transfer slot of the inner component ring, which preferably extends radially through the entire wall of the inner component ring.  
           [0012]    The free flow cross-section of the transfer slot is substantially determined by the depth of the transfer slot measured in the radial direction. The depth of the transfer slot of the inner component ring is preferably between 10% and 50% of the total depth of both transfer slots, formed by addition of the individual slot depths of the inner component ring and the outer component ring. The maximum possible volume flow through the transfer slot in the blocking position can accordingly be reduced to 10% to 50% of the amount in the overlapping position. Reduction of the free flow cross-section may be considered especially in the operating range between the surge line and the choke line of the compressor performance graph since little or no air recirculation should take place in this stable region of the performance graph so as to avoid impairing optimum air delivery via the compressor impeller.  
           [0013]    A plurality of flow slots is advantageously distributed uniformly over the circumference of the two component rings in order for the air flow through the flow slots to be uniform over the circumference. The flow slots may not arranged radially in the component rings but at a particular angle relative to the circumferential direction; they preferably extend tangentially in the component rings. This imparts a desired rotational component to the airflow.  
           [0014]    As an alternative or in addition to component rings situated radially one above the other, it may also be appropriate to provide two or more component rings axially one adjacent the other. The flow slot also can be adjusted by rotation of one or more component rings into an overlapping position or into a blocking position. In this embodiment, it is possible, in particular, to manipulate the axial extent of the flow slots. The axially successive component rings can also be combined, if appropriate, with component rings that lie radially one above the other. Finally, it is also possible to arrange more than two component rings radially one above the other and/or axially one behind the other.  
           [0015]    Advantages embodiments of the invention will be described below on the basis of the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]    [0016]FIG. 1 is a cross-sectional view of a compressor with an adjustable transfer ring in an exhaust turbocharger of an internal combustion engine,  
         [0017]    [0017]FIG. 2 shows, in side view, the transfer ring comprising two concentric component rings lying radially one above the other,  
         [0018]    [0018]FIG. 3 is a side view of the compressor with the two component rings of the transfer ring in the overlapping position,  
         [0019]    [0019]FIG. 4 is a view corresponding to that of FIG. 3, with the outer component ring of the transfer ring rotated into the blocking position. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    In the descriptions that follow, identical components are provided with identical reference numerals.  
         [0021]    The compressor  1  illustrated in FIG. 1 forms part of an exhaust turbocharger for an internal combustion engine, e.g. an Otto engine or a Diesel engine. The compressor  1  is designed as a radial compressor and, in a housing  2 , has a compressor impeller  3 , which is arranged rotatably in a compressor flow duct  4  of the housing  2 . Rotation of the compressor impeller draws fresh air into the compressor flow duct  4  axially in the direction of arrows  5  and compresses it to an increased boost air pressure. After compression, the boost air is passed via a diffuser  6  into a spiral duct  7  in the housing  2  of the compressor  1 . The boost air emerging from the spiral duct is fed to the internal combustion engine.  
         [0022]    Arranged in the compressor flow duct  4  concentrically with the compressor impeller  3 , is a transfer ring  8  surrounding the compressor impeller  3  radially. Provided in the transfer ring  8  are transfer slots, via which air can be carried essentially co-axially to the compressor flow duct  4 . The transfer slots in the transfer ring  8  form a bypass to the compressor flow duct  4 , by means of which it is possible to extend the operating range of the compressor between the surge line and the choke line of the compressor performance graph. The effective flow cross-section of the transfer slots can be adjusted to ensure that the behavior of the flow through the transfer slots in the transfer ring  8  matches the various operating conditions of the compressor.  
         [0023]    [0023]FIG. 1 illustrates recirculation of a mass flow component of the fresh air that flows counter to the main direction of flow  5  and subsequently is reintroduced into the main flow. The axial transfer slots in the transfer ring  8  can be used to divert, recirculate and reintroduce the mass flow component. The operating range illustrated with a mass flow component guided counter to the main direction of flow is implemented when operating the compressor in the region of the surge line. When the compressor operates in the region of the choke line, a mass flow component is likewise passed axially through the transfer slots of the transfer ring  8  but in the same direction as the main direction of flow  5  of the flow of fresh air flowing into the compressor flow duct  4 . In the large operating range between the surge line and the choke line, flow through the transfer slots is prevented or reduced to a minimum. This is advantageously achieved by limiting the cross-section of the transfer slots.  
         [0024]    [0024]FIG. 2 is a side view of a transfer ring  8 . The transfer ring  8  is of two-part construction and has a radially outer component ring  11 , which surrounds the inner component ring  10 . The inner component ring  10  is preferably fixed in relation to the housing, while the outer component ring  11  is preferably rotatably supported on the inner component ring  10  and can be rotated in the direction of arrow  13  relative to the inner component ring  10 . Connected to the outer component ring  11  is an actuating element  12  by which the outer component ring  11  can be adjusted as a function of the operating conditions of the internal combustion engine or compressor and/or the turbine of the exhaust turbocharger.  
         [0025]    In Both, the inner component ring  10  and the outer component ring  11  of the transfer ring  8 , there is a plurality of transfer slots  9 , which are distributed uniformly over th circumference. They are disposed at a defined angle to the circumferential direction in the transfer ring  8  and, in particular, extend over the entire axial length of the transfer ring  8 . Each transfer slot  9  comprises an inner portion  9   a , which advantageously completely penetrates the inner component ring  10  radially, and an outer portion  9   b  in the outer component ring  11 . The inner portion  9   a  and the outer portion  9   b  of each flow slot  9  are matched to one another in such a way that there is at least one radial position of the outer component ring  11  in which in each case one inner portion  9   a  and one outer portion  9   b  of the transfer slots are in alignment. This position is referred to as the overlapping position of the two component rings  10  and  11 . If, on the other hand, the outer component ring  11  is turned in the direction of arrow  13  out of the overlapping position shown in FIG. 2, the associated portions  9   a  and  9   b  of the transfer slots  9  move out of alignment. This position is referred to as the blocking position of the component rings  10  and  11 . In the overlapping position, each transfer slot  9  has a maximum cross-section, which is formed by a combination of the individual cross-sections of the inner portion  9   a  and the outer portion  9   b . In the blocking position, on the other hand, only the inner portions  9   a  of the transfer slots are effective and only this inner portion  9   a  takes part in the bypass flow parallel to the compressor flow duct.  
         [0026]    Preferably, the transfer slots  9  in the transfer ring  8  are sloped relative to the circumferential direction. This has the advantage that the transfer slots can have a larger cross-sectional area for a given wall thickness of the two component rings  10  and  11  than would be the case if the transfer slots were to extend only radially.  
         [0027]    [0027]FIGS. 3 and 4 each is a side view of the compressor  1  with a transfer ring  8 , which surrounds the compressor impeller. The component rings  10  and  11  of the transfer rings  8  are in the overlapping position in FIG. 3 and in the blocking position in FIG. 4. The inner portions  9   a  of the flow slots in the inner component ring  10  are open radially inwards towards the compressor impeller&#39;s flow duct  4  over the entire axial length of the component ring  10 . According to FIG. 3, the slot depth  1   ges , measured in the tangential direction, is effective in the overlapping position. In the blocking position, shown in FIG. 4, only the inner portions  9   a  of the transfer slots are effective with a slot depth  1   1 , measured in the tangential direction. The outer portions  9   b  of the transfer slots remain inoperative owing to the position out of engagement or blocking position. The slot depth  1   i  of the inner portions  9   a  of the flow slots is advantageously between 10% and 50% of the total slot depth  1   ges , which is formed by addition of the component slot depths of the inner portion  9   a  and outer portion  9   b  of the flow slots.  
         [0028]    A preferably automatic adjustment of the degree of overlap between the component rings  10  and  11  as a function of the operating condition of the internal combustion engine or of the charger is possible by means of the actuating element  12 .