Title of Invention

"TURBOCHARGER COMPRISING A TURBINE WHEEL AND A METHOD OF MANUFACTURING THE SAME"

Abstract

A turbocharger comprises a compressor wheel (7) assembled to one end of a turbocharger shaft (8). A nut (17) is threaded on to the end of the shaft (8) to clamp the wheel (7) on the shaft to prevent both axial movement of the wheel (7) along the shaft (8) and rotational slippage. The torque capacity of the coupling between the compressor wheel (7) and nut (17) is increased by treating contacting surfaces of the coupling to increase their co-efficient of friction. Fig. 1.

Full Text

COMPRESSOR WHEEL ASSEMBLY This invention relates to the assembly of a compressor wheel to a rotating shaft In particuiar, the invention relates to the compressor wheel assembly of a iurbocharger., . Turbochargers arc well known devices for suplting air to the intake of an internal combustion engine at pressures above atmospheric (boost pessures). A conventional turbocharger essecntially corrrpriscs snexhaust gas driven turbine wheel mounted on a rotatabls shaft within a turbine housing. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a ccnnpressor housing.The compressor wheel delivers compressed air to the intake manifold of the migine, thereeby increasing engine power. The shaft is supported on journal and tbiiist bearing located within a coitral bearing housing connected between the turbine and compressor wheel housings. . A cnventional compressor wheel comprises an array of blades extending from s central hub provided -with a here for receiving one end of the turbocharger shaft. The compressor wheel is secured to the shaft by a nut which threads onto the end of the shaft where it extends through the wheel bore, and bears against the nose end of the wheel to clamp the wheel gainst a shaft shoulder (or other radially extending abutment that rotates with the shaft). Tt is important that the clamping force is sufficiently great to prevent slippage of the wheel on the shaft which could threw the wheel out of balance. An unbalanced wheel will at at the very least experience increased vibration, which could shorten the woiking life of the wheel, and at worst could suffer catastrophic failure. Modem donands on turbocharger performance require increased airflow from a turbocharger of a given size, leading to increased rotational speeds, for instance in excess of 100,000 ipm. To accommodate such high rotational speeds the tuibochargcr bearings, and thus the tmbocharger shaft diameter, must be minimize. However, the use of a relatively small diameter shaft is probomatical with the conventional compressor wheel mounting assembly because the shaft must be able to withstatid the high clamping force required to prevent slippage of the wheel. Thus, the strength of the shaft, i.e. the clamping load it can withstand, may limit the mass of compressor wheel that may be mounted to the shaft. The above problem is exacerbated as continued turbocharger development requires the use of higher performance materials such as titanium which has a greater density than the aluminium alloys conventionally used. The increased inertia of such materials increasesthe slikelihod of compressor wheel slippage, particulariy as fte compressor wheel rapidly accelerates during transient operating conditions. The clamping force required from a convcntionsl compressor wheel mounting assembly may well exceed that which the shaft can withstand. One possible way of avoiding the above problem is to use a so-called 'bore-less' compressor wheel such as disclosed in US patent number 4,705,463. With this compressor wheel assembly only a relatively short threaded bore is provided in the compressor wheel to receive the threaded end of a shortened tuibocharger shaft. However, such assemblies can also experience balancing problems as the threaded conection between the compressor wheel and the shaft, and the clearance inherent in such a connsotioa, tnay make it difficult to maintain the required degree of connectricity. It is 30 object of the present invention to obviate or mitigate the above problems. Accordmg to a first aspect of the present invention there is provided a turboscharger cmprising a turbine wheel mounted to a first end of a shaft for rotation withng a turbine housing, and a compressor wheel mounted to a second end of the shaft for rotation within a compressor housing, the compressor wheel having an axial through bore extending between a first end of the wheel and a second end of the wheel, said second end being remote from said turbine, wherein the second end of the shaft extends through the bore and a short distance beyond the second end of the compressor wheel and a nut is threaded onto said second end of the shaft to apply a clamping force to the compressor wheel either directly, or indirectly through an intcnnediate clamping monber disposal around said shaft adjaceut the second end of the compressor wheel, such that the second end of the compressor wheel has a radial sur&ce contacting a radial surface of the nut or intermediate clarnping member, and wherein at least one of said radal surface is treated to increase its co-efficient of friction with respect to the other surface. Thepresent invention thus increases the torque capacity of the clamping coupling without significant modification of the components of the compressor wheel assembly. The sorface treatment may for instance simply increase the roughness of the respective surface, for example hy laser etching an appropriate pattern into the suraface. . The preset invention also provides a method of increasing the torque capacity of an axial clamping assembly of a compressor wheel. Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawing which is an axial cross-section through a conventional turbocharger illustrating the major components of a turbnocharger and a conventional compressor wheel assembly. The illustratedturbocharger comprises a turbine 1 joined to a compressor 2 via a central bearing housing 3. The turbine l comprises a turbine housing 4 which houses a turbine -wheel S. Similarly, thecompressor 2 comprises a compressor housing 6 which houses acompressor wheel 7. The turbine wheel 5 and compressor wheel 7 are mounted on opposite ends of a common shaft 8 which is supported on bearing assemblies 9 within the besting housing 3. The turbine housing 4 is provided with an exhaust gas inlet 10 and an exhaust gas outlet 11. The inlet 10 directs incomnig exhaust gas to an annular inlet chamber 12 surrounding the turbine wheel 5. The exhaust gas flows through the turbine and into the outlet 11 via a circular outlet opening which is co-axial with the turbine wheel 5. Rotation of the turbine wheel 5 rotates the compressor wheel 7 which draws in air through axial inlet 13 and delivers compressed air to the ragine intake via an aimular outlet volute 14. Referring in more detail to the compressor wheel assembly, the compressor wheel comprises a piuraliiy of blades 15 extending from a central hub 16 which is provided with a through bore to receive one end of the shaft 8. The shaft 8 extends slightly from the nose of the compressor wheel 7 and is threaded to receive a nut 17 which bears against the compr^sor wheel nose to clamp the compressor wheel 7 gainst a thrust bearing and oii seal assembly 18. Details of the thrust bearing/oil seal assembly may vary and are not important to understanding of the compressor wheel mounting arrangement, Essentially, the compressor wheel 7 is prevented from slipping on the shaft 8 by the clamping force applied by the nut 16. Problems associated with the conventional compressor wheel assembly described above are discussed in the introduction to this specification. in accordance within the present invention the rotational drive force transmitted to the compressor wheel I may be iJscreased without increasing the clamping force, or significantly modifying the clamping components. This is achieved by treating the clamping surface of components to increase the co-efficient of diction therebetween. Referring to the convcntiooal clamping assembly of Figure 1, the radial surface of the nose portion of die conn»essor wheel 7, against which the nut 17 bears, may be treated to increase its co-efficient of friction with respect to the nut, for instance by increasing the surface roughness. For examine, a laser may be used to etch an an appropriate pattern into the surface to increase the surface roughness. This has been found to increase the torque capacity of the clamping joint without compromising the component form tolerances. The contact surface of the nut may similarly be treated, in addition to or instead of, the treatment of the compressor wheel surface, again to increase the coefficient of friction between the contacting surfaces. In some clamping arrangements a washer or the like may be disposed between the nut and the compressor wheel in which case the washer surface contacting the compressor wheel may be treated to provide the increased co-efficient of friction. It may also be desirable to increase the co-efficient of friction between tide back surface of the compressor wheel and the thrust bearing assembly, or other radial surface against which the compressor wheel is clamped by the force supplied by the nut 16. With the iUustmed embodiment descnbed above, this would involve treating either the back surface of the compressor wheel or the radial surfece of the thrust bearing assenihly. On other embodtments, , the shaft may be provided with an annular shoulder which bears against the bade surface of the compressr wheel and which may similarly be treated. . It will be appreciated that surface treatments other than laser etching may be employed to implement the present invention, including mechanical and chemical treatments to increase the surface roughness of the respective materials. Appropriate surface treatment methods will be readilyapparent to the skilled person WE CLAIM: 1. A turbocharger comprising a turbine wheel mounted to a first end of a shaft for rotation within a turbine housing, and a compressor wheel mounted to a second end of the shaft for rotation within a compressor housing, the compressor wheel having an axial through bore extending between a first end of the wheel and a second end of the wheel, said second end being remote from said turbine, wherein the second end of the shaft extends through the bore and a short distance beyond the second end of the compressor wheel and a nut is threaded onto said second end of the shaft to apply a clamping force to the compressor wheel either directly, or indirectly through an intermediate clamping member disposed around said shaft adjacent the second end of the compressor wheel, such that the second end of the compressor wheel has a radial surface contacting a radial surface of the nut or intermediate clamping member, and characterized in that at least one of said radial surfaces is treated to increase its co-efficient of friction with respect to the other surface. 2. The turbocharger as claimed in claim 1, wherein both of said surfaces are treated. 3. The turbocharger as claimed in claim 1 or 2, wherein said surface treatment comprises laser etching. 4. The turbocharger as claimed in claim 1 or 2, wherein said surface treatment comprises mechanical abrasion of the or each surface. 5. The turbocharger as claimed in claim 1 or 2, wherein said surface treatment comprises chemical etching or abrasion process. 6. The turbocharger as claimed in any of the preceding claims, wherein said first end of the compressor wheel is a radial surface which abuts a radial surface defined by a shaft or a thrust bearing assembly mounted on the shaft, and wherein at least one of said surfaces is treated to increase its co-efficient of friction with respect to the other surface. 7. A method of manufacturing a turbocharger comprising a turbine wheel mounted to one end of a shaft for rotation within a turbine housing, and a compressor wheel mounted to the other end of the shaft for rotation within a compressor housing, the compressor wheel having an axial through bore extending between a first end of the wheel and a second end of the wheel, said second end being remote from said turbine, wherein the second end of the shaft extends through the bore and a short distance beyond the second end of the compressor wheel and a nut is threaded onto said second end of the shaft to apply a clamping force to the compressor wheel either directly or indirectly through an intermediate clamping member disposed around said shaft adjacent the second end of the compressor wheel, such that the second end of the compressor wheel has a radial surface contacting a radial surface of the nut or intermediate clamping member, characterized in that it comprises the step of treating at least one of said radial surfaces to increase its co-efficient of friction with respect to the other. 8. The method as claimed in claim 7, wherein said treatment increases the surface roughness of the respective radial surface. 9. The method as claimed in claim 7 or 8, wherein said surface treatment comprises laser etching a pattern into the respective surface. 10. The method as claimed in claim 7 or 8, wherein said surface treatment comprises mechanical abrasion of the or each surface. 11. The method as claimed in claim 7 or 8, wherein said surface treatment comprises chemical etching or abrasion of the or each surface. 12. The method as claimed in any one of claims 7 to 11, wherein said surface treatment is applied to both of said radial contact surfaces. 13. The method as claimed in any one of claims 7 to 12, wherein the first end of the compressor wheel has a radial surface contacting a radial surface defined by the shaft or a thrust bearing assembly mounted on the shaft, and at least one of said surfaces is treated to increase its co-efficient of friction with respect to the other.

Documents:

1295-DEL-2003-Abstract-(17-03-2010).pdf

1295-DEL-2003-Abstract-(28-06-2010).pdf

1295-del-2003-abstract.pdf

1295-DEL-2003-Claims-(17-03-2010).pdf

1295-DEL-2003-Claims-(28-06-2010).pdf

1295-del-2003-claims.pdf

1295-del-2003-Correspondence Others-(10-07-2014).pdf

1295-del-2003-Correspondence Others-(15-07-2014).pdf

1295-DEL-2003-Correspondence-Others-(17-03-2010).pdf

1295-DEL-2003-Correspondence-Others-(28-06-2010).pdf

1295-del-2003-correspondence-others.pdf

1295-del-2003-correspondence-po.pdf

1295-del-2003-description (complete).pdf

1295-del-2003-drawings.pdf

1295-DEL-2003-Form-1-(28-06-2010).pdf

1295-del-2003-form-1.pdf

1295-del-2003-form-18.pdf

1295-DEL-2003-Form-2-(28-06-2010).pdf

1295-del-2003-form-2.pdf

1295-del-2003-form-26.pdf

1295-del-2003-Form-3-(10-07-2014).pdf

1295-DEL-2003-Form-3-(17-03-2010).pdf

1295-del-2003-form-3.pdf

1295-del-2003-form-5.pdf

1295-del-2003-GPA-(10-07-2014).pdf

1295-del-2003-GPA-(15-07-2014).pdf

1295-DEL-2003-Petition 137-(17-03-2010).pdf