Patent Publication Number: US-8123501-B2

Title: Turbocharger housing, turbocharger and a multi-turbocharger boosting system

Description:
The invention relates to a turbocharger housing, a turbocharger and a multi-turbocharger boosting system. 
     Generally, a turbocharger is used for compressing air which is supplied to an internal combustion engine. A conventional turbocharger comprises a main body which supports a common shaft, one end thereof being equipped with a compressor wheel, whereas the other end thereof is equipped with a turbine wheel. The main body and the shaft having the turbine wheel as well as the compressor wheel are housed in a turbocharger housing. An exhaust gas from the internal combustion engine is supplied through a first inlet opening formed in the turbocharger housing to the turbine wheel, while fresh air is supplied through a second inlet opening formed in the turbocharger housing to the compressor wheel. The exhaust gas supplied to the turbine wheel rotates the common shaft, so that the fresh air is compressed by the compressor wheel. 
     U.S. Pat. No. 4,480,440 discloses a generic turbocharger housing of a turbocharger, the turbocharger comprises a main body for bearing a shaft for carrying a turbine wheel and a compressor wheel, and a seal portion to seal a clearance between the shaft and the turbocharger housing. A lubricant is supplied to the shaft bearing by means of a passage in the main body. 
     According to document U.S. Pat. No. 4,157,834, another turbocharger is known which comprises one or more conventional sealing portions each comprising a circumferential groove accommodating a sealing ring. Further sealing arrangements are disclosed in the prior art documents EP-A1-1245793, EP-A2-1130220 and WO-A2-02083593. 
     The object of the invention is to provide a turbocharger housing, a turbocharger and a multi-turbocharger boosting system, in which the sealing arrangement is improved with respect to the function and the manufacturing thereof. 
     According to the invention, the object is achieved by a turbocharger housing having the features of claim  1 , by a turbocharger having the features of claim  9 , and by a multi-turbocharger boosting system having the features of claim  13 . Preferable embodiments of the invention are set forth in the dependent claims. 
     According to one aspect of the invention, the turbocharger housing comprises a main body for bearing a shaft for carrying a turbine wheel and a compressor wheel, and a seal portion for sealing a clearance between the shaft and the turbocharger housing, the seal portion being formed by an insert being fitted to the main body, wherein the insert comprises a passage for supplying a fluid to the seal portion. Advantageously, the passage within the insert is easy to manufacture, since the insert is a separate member which is attachable to and removable from the main body. It is to be noted that the main body generally is a die cast part, but it is not necessary to take complicated manufacturing steps for providing the passage within the main body, since the passage is not a part of the main body. 
     According to one embodiment according to this aspect of the invention, the seal portion of the insert is opposed to a seal bushing provided on the shaft, wherein the seal bushing supports a first piston ring, and the passage supplies the fluid to one side of the first piston ring. Advantageously, a pressure acting on this one side of the first piston ring is adjusted by the supplied fluid so that a predetermined pressure difference between this one side of the first piston ring and another side of the first piston ring can be decreased. Preferably, the fluid is supplied to a compressor wheel side of the first piston ring, thereby increasing the pressure on the compressor wheel side of the first piston ring so that there is no oil leakage from a main body side of the first piston ring toward the compressor wheel side. 
     According to the embodiment of this aspect of the present invention, the seal bushing preferably supports a second piston ring and the passage supplies the fluid in a space formed between first and second piston rings. Thereby, the same advantages as in the preceding embodiment are obtained. 
     According to another aspect of the present invention, the above-mentioned turbocharger housing is used in a first turbocharger of a multi-turbocharger boosting system. The multi-turbocharger boosting system furthermore comprises a second turbocharger, wherein the passage of the first turbocharger communicates with a compressor output and/or a turbine input of said second turbocharger. Preferably, the first turbocharger and the second turbocharger are connected in parallel. Advantageously, the second turbocharger can be used as a fluid source for supplying the fluid to the passage of the first turbocharger. 
    
    
     
       In the following, the invention with its function, effects and advantages will be explained by embodiments as non-restrictive examples with reference to the enclosed drawings in which 
         FIG. 1  shows a cross-sectional view of main parts of a turbocharger according to a first embodiment of the present invention; 
         FIG. 2  shows an enlarged view of a cross-sectional view of the main parts of the turbocharger according to the first embodiment of the present invention; 
         FIG. 3  shows a cross-sectional view of main parts of a turbocharger according to a second embodiment of the present invention; 
         FIG. 4  shows a cross-sectional view of an insert and a main body of the turbocharger according to the second embodiment of the present invention; 
         FIG. 5  shows a detail of the insert of the turbocharger according to the second embodiment of the present invention; 
         FIG. 6  shows a front view of the insert of the turbocharger according to the second embodiment of the present invention; and 
         FIG. 7  shows a concept of a multi-turbocharger boosting system according to a third embodiment of the present invention. 
     
    
    
     In the following, the currently preferred embodiments are explained on the basis of the drawings. 
     First Embodiment 
     The essential parts of a turbocharger according to a first embodiment of the invention are illustrated in  FIGS. 1 and 2 . Some parts of the turbocharger housing and the particular construction of the turbocharger parts are not shown in detail. The turbocharger comprises a compressor wheel  3  and a turbine wheel  17  mounted on the opposite ends of a common shaft  2 . The shaft  2  is freely rotatable in a bearing provided in a main body  1  of the turbocharger housing. The bearing  11  is lubricated with a lubricant. In this embodiment, the lubricant is an engine oil which is supplied from an oil circuit (not shown) of a combustion engine, to which the turbocharger is assembled. The oil is supplied to the middle of the main body  1  and flows to a space  12  at the end of the main body  11  before it is discharged to the oil circuit of the combustion engine. 
     The oil must not enter a clearance between the shaft  2  and the main body  1  and leak out to the compressor wheel  3 , which would contaminate the intake air of the combustion engine. To avoid such a leaking, a sealing arrangement is provided for. The sealing arrangement according to the present invention comprises an insert  5 , a shaft bushing  22 , and at least two piston rings, namely a first piston ring  18  and a second piston ring  19 . The insert  5  is a substantially ring-shaped member fitted to the main body  1  at the compressor wheel side, thereby closing the main body  1 . An inner circumference of the insert  5  forms a seal portion  4  for sealing a clearance between the shaft  2  and the turbocharger housing. The shaft  2  is passed through the seal portion  4  of the insert  5 . The shaft bushing  22  is directly fitted to the shaft  2  at a predetermined position so that the shaft bushing  22  faces the seal portion  4  of the insert  5 . The shaft bushing  22  has at least two grooves on its outer circumference for supporting the mating piston rings  18 ,  19 . The piston rings  18 ,  19  are positioned on the outer circumference thereof in a sealing contact with the seal portion  4  of the insert  5 . The sealing arrangement prevents the oil supplied to the main body  11  from leaking out to the compressor wheel  3  which otherwise would contaminate the intake air of the combustion engine. 
     A critical situation occurs at low compressor wheel speeds and mostly during operation modes in which there is almost no rotation of the compressor wheel  3 . In this case, the pressure generated by the compressor wheel  3  is quite low, while the oil pressure within the space  12  is maintained on a high level. Thereby, a pressure difference exists between both sides of the piston rings  18 ,  19 , i.e. between the compressor wheel side of the piston rings  18 ,  19  and their side opposed thereto, respectively. The pressure difference acts on the piston rings  18 ,  19  and tends to cause an oil leakage from the space  12  to the compressor wheel  3 . 
     As a counter-measure, the insert  5  provides at least one passage  6 ,  7  which opens in a space between the two piston rings  18 ,  19  in order to communicate the space between the piston rings  18 ,  19  with the air outside the turbocharger, i.e. the passage supplies air outside the turbocharger to the space between the piston rings  18 ,  19 . Thereby, the pressure within the space between the piston rings  18 ,  19  is increased so that the respective pressure differences acting on the piston rings  18 ,  19  are decreased. As a result, there is no oil leakage from the space  12  toward the compressor wheel  3 . 
     The details of the passage are shown in  FIG. 2 . The passage is formed by a radial bore  6  and an axial bore  7  through the insert  5 . As shown in  FIG. 2 , the radial bore  6  at the outer circumference is closed by a male thread  13 . The radial bore  6  intersects the axial bore  7  which opens at the plane surface at the main body side of the insert  5  to form an inlet opening. The axial bore  7  in the insert  5  is aligned to a corresponding outlet opening  8  in the main body  1 . Into the outlet opening  8  of the main body  1 , a fluid feeding passage or a pipe  9  is fitted which leads to the outside of the turbocharger. The interface between the axial bore  7  of the insert  5  and the fluid feeding passage  9  is sealed by an O-ring  24 . 
     Advantageously, the passage  6 ,  7  within the insert  5  is easy to manufacture, because the insert  5  is a separate member which is attachable to and removable from the main body  1 . It is to be noted that the main body  1  generally is a die cast part, but it is not necessary to take complicated manufacturing steps for providing the passage  6 ,  7  within the main body  1 , since the passage is not a part of the main body  1 . Preferably, the insert  5  is made of aluminum. As a further advantage, the insert  5  additionally has the function of a backplate at the compressor side of the turbocharger, so that no additional part is necessary for forming the passage  6 ,  7 . 
     In  FIG. 1 , the attachment of the insert  5  to the main body  1  is shown in more detail. The insert  5  is fixed to the main body  1  by means of screws  14  which are circumferentially arranged at a plane face of the insert  5 . The plane face of the insert  5  at the main body side is provided with a portion for supporting an O-ring  15 . The O-ring  15  seals the interface between the insert  5  and the main body  1  to avoid oil leakage from the space  12  to the outside. 
     Second Embodiment 
     A turbocharger according to a second embodiment is described below on the basis of  FIGS. 3 through 6 . Mainly, the differences between the turbocharger according to the first embodiment and the turbocharger according to the second embodiment are described below. 
     Some details of a main body  101  and an insert  105  of the turbocharger according to the second embodiment are shown in  FIGS. 4 and 5 . The radial bore  106  of the insert  105  is communicated via an axial bore  107  with a corresponding outlet opening  108  in the main body  101  which leads to a fluid feeding port  109 . The radial bore  106  opens at its other end in a space between piston rings  118  and  119 . 
     Advantageously, the fluid feeding port  109  is universally connectable with various fluid sources. For instance, the fluid feeding port  109  is connectable to a compressor output and/or a turbine input of the turbocharger. Alternatively, the fluid feeding port  109  is connectable with a space where the turbine wheel  117  or the compressor wheel  103  of the turbocharger is located. Unlike in the first embodiment, the passage  106 ,  107  within the insert  105  is not necessarily communicated with the air outside the turbocharger, but the passage  106 ,  107  is communicatable with various fluid sources from the turbocharger and the engine environment. 
     A further detail of the attachment of the insert  105  to the main body  101  is shown in  FIGS. 3 ,  4  and  6 . Preferably, the insert  105  is attached to the main body  101  by means of screws  114 . As can be gathered from the plane view in.  FIG. 6  in combination with the sectional view in  FIG. 3  of the insert  105 , the plane surface of the insert  105  at the main body side has protrusions  120  protruding from the plane surface. The screws  114  are arranged within the protrusions  120 . Thereby, the insert  105  can reliable be fitted to the main body  101  without deforming the insert  105  by the attachment of the screws  114 . 
     As further shown in  FIG. 4  and in particular in the detailed view of  FIG. 5 , the interface between the insert  105  and the main body  101  is a sealed O-ring  115  which is accommodated into a groove  116  along the outer circumference of the insert  105 . At the same time, the radial  106  bore of the insert  105  is sealed by this O-ring  115 , and the number of O-rings is reduced compared to the first embodiment. 
     Third Embodiment 
     The turbocharger according to the second embodiment is preferably used in a multi-turbocharger boosting system shown in  FIG. 7 . The multi-turbocharger boosting system comprises a turbocharger A according to the second embodiment as a first turbocharger, and furthermore a second turbocharger B, wherein the two turbochargers A and B are generally connected in parallel in relation to an internal combustion engine. Advantageously, the second turbocharger is used as a fluid source for supplying the fluid to the passage of the first turbocharger. 
     The second turbocharger B preferably comprises a free floating turbine  317   b  at its turbine side, whereas the first turbocharger A is equipped with a variable geometry turbine  317   a . The turbines  317   a  and  317   b  and respective compressors  303   a  and  303   b  are connected in parallel. According to the layout, fresh air is fed in parallel to each of the compressors by means of a first fresh air conduit  334  and second fresh air conduit  336  and the air discharged from the compressors is guided through an intercooler  342  to the intake side of the internal combustion engine  333 . At the turbine side of the layout, the exhaust gas from the engine  333  is fed through a first exhaust conduit  338  and a second exhaust conduit  340  branching from a conduit or piping  353  to the first and second turbine  303   a  and  303   b , respectively, and the exhaust discharged from the parallel turbines is guided to a catalyst  344 . 
     In the multi-turbocharger boosting system shown in  FIG. 7 , the first compressor A is provided with an air re-circulation system using air flow regulating means for adjusting the amount of the re-circulated air. The re-circulation system in this embodiment includes a by-pass conduit  343  with a butterfly valve  345  for adjusting the air mass-flow recirculated back into the second fresh air conduit  336  connecting the inlet of the first compressor  303   a  with an air filter  349 . 
     The multi-turbocharger boosting system further comprises an additional butterfly valve  369  arranged in the conduit  371  connecting the first compressor  303   a  with the intercooler  342  between the merging point of the by-pass conduit  343  downstream of the first compressor  303   a  and the merging point of the second compressor  303   b  in the conduit  371 . 
     At the turbine side of the multi-turbocharger boosting system, there is provided a bypass passage  355  with a corresponding waste gate valve  359 . A butterfly or throttle valve  363  is arranged in the second exhaust conduit  340 . 
     The multi-turbocharger boosting system according to  FIG. 7  allows a highly efficient function of the internal combustion engine at low, medium and high rotational speeds of the internal combustion engine. 
     At a low rotational speed of the internal combustion engine  333 , which means at about 1000-2000 rpm, the exhaust gas supplied through the exhaust conduit or piping  353  drives the free floating turbine  317   b  of the second turbocharger B. The butterfly valve  363  is closed or nearly closed so as to reduce the exhaust gas flowing into the first turbine  317   a , thereby ensuring an idling rotation of the first turbocharger A so as to merely avoid oil leakage from the bearing system thereof. Under this condition, the speed of the second turbocharger B is controlled by means of the waste gate valve  359 . At this stage, the second turbocharger B works normally to supercharge the engine  333 . 
     At the low rotational speed, the butterfly valve  345  is open so that a re-circulation at the first compressor  303   a  is achieved. Due to the particular design of the layout, during the re-circulation, the pressure in the first compressor  303   a  can be lowered so that the trust load becomes less important and the reliability is improved. 
     The additional butterfly valve  369  remains closed and the second compressor  303   b  works normally to supercharge the engine  303 . 
     In the range of a medium rotational speed of the internal combustion engine, which means at about 2000-2500 rpm, the butterfly or throttle valve  363  opens progressively so as to regulate the pressure before the first turbine  317   a  and the exhaust gas flow drives the first turbocharger A. At the same time, the butterfly valve  345  is progressively closed in order to balance the power between the first compressor  303   a  and the first turbine  317   a , so that by operation of the butterfly valve  345 , the speed of the first turbocharger A can be regulated. 
     In the range of a high rotational speed of the internal combustion engine, which means at about 2500-4000 rpm, the butterfly valve  363  is completely or almost completely open, wherein the speed of the first turbine  317   a  is regulated by means of the waste gate valve  359 . During this operation, the additional butterfly valve  396  is open and the butterfly valve  345  is totally closed. 
     In the above-mentioned mode of operation at a low rotational speed, the butterfly valve  363  can be closed or nearly closed without thereby causing an oil leakage. 
     The advantages of the third embodiment are apparent with respect to the structure of the first turbocharger which is similar to the turbocharger shown in  FIG. 3 . Although the pressure behind the first compressor  303   a  of the first turbocharger A becomes quite low, the pressure drop at the outer piston ring  119  is decreased by ventilating the space between the outer and inner piston rings  119  and  118  by air at normal atmospheric pressure. The inner piston ring  118  positioned between the radial bore  106  and the bearing  111  is also subject to a reduced pressure difference so that an oil leakage to the compressor side of the first turbocharger A can efficiently be avoided even if the rotation of the first turbocharger is stopped. 
     Modifications 
     According to the first and second embodiment shown in  FIGS. 1 and 3 , the outer piston rings  19  and  119 , respectively, and their corresponding grooves can be omitted, whereas the merging point of the radial bore  6  and  106 , respectively, is to be arranged close to a single piston ring  18 ,  118  at the corresponding groove. 
     According to the first and second embodiment shown in  FIGS. 1 and 3 , the passages  6 ,  7  and  106 ,  107  are completely formed inside the inserts  5  and  105 , respectively. It is possible that the passage is at least partially formed at an outer surface of the insert. For instance, the passage can be formed by a groove on the outer surface of the insert, wherein the. groove is closed by an opposed face of the main body when the insert is fitted to the main body. 
     It is obvious to the skilled person that the present invention is not restricted by the embodiments illustrated herein. The scope of the present invention is rather defined by the appended claims.