Patent Publication Number: US-10329948-B2

Title: Stamped variable geometry turbocharger lever using retention collar

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to turbochargers with variable geometry, and more particularly, to pivot shaft assemblies and methods of manufacturing same. 
     BACKGROUND 
     Turbochargers are a type of forced induction system which deliver air to the engine intake at greater density than would be possible in the normally aspirated configuration. In general, turbochargers include a turbine housing having a turbine inlet and a turbine wheel for receiving exhaust flow from the engine exhaust manifold, as well as a compressor housing having a compressor inlet and a compressor wheel for receiving filtered air. More specifically, the flow of exhaust gases through the turbine housing drives the turbine wheel, which in turn drives the compressor wheel to draw filtered air into the compressor housing. Spent exhaust gases are extracted from an exducer of the turbine housing and through the downpipe of the vehicle exhaust system, while compressed inlet air is released through a compressor discharge and delivered to the engine intake usually via an intercooler. 
     The power developed by the turbine stage is a function of the expansion ratio across the turbine stage, which is the expansion ratio from the turbine inlet to the turbine exducer. The range of the turbine power is a function of, among other parameters, the flow through the turbine stage. The power generated by the turbine stage to the shaft and wheel drives the compressor wheel to produce a combination of static pressure with some residual kinetic energy and heat. By allowing more fuel to be combusted, the power that is output from a given engine can be increased without significantly increasing engine weight. Moreover, because a smaller turbocharged engine can replace larger normally aspirated engines, turbochargers also enable notable reduction in the mass and aerodynamic frontal area of the vehicle. Due to these and other advantages, turbocharger systems are repeatedly chosen over naturally aspirated arrangements, and incremental improvements for turbochargers continue to be developed. 
     In its most basic form, a turbocharger employs a fixed turbine housing, where the shape and volume of the turbine housing volute is determined at the design stage and cast in place. The fixed turbine housing is the most cost-effective option simply because it has the fewest parts. In one improvement, the volute is cast in place, but the volute is fluidly connected to the exducer by a duct and flow through the duct is controlled by a wastegate valve. Because the outlet of the wastegate duct is on the exducer side of the volute, which is downstream of the turbine wheel, flow through the wastegate duct is able to bypass the turbine wheel without contributing to the power delivered to the turbine wheel. In further improvements, rotating vanes, sliding sections or rings, or adjusting guide vanes are used to adjust the geometry of the turbine. Some conventional turbochargers with adjustable geometries include variable geometry turbines or turbochargers (VGTs), variable nozzle turbines (VNTs), and other turbochargers having variable geometry (VG) or variable turbine geometry (VTG). 
     In general, a VTG turbocharger employs adjustable guide vanes mounted to rotate between a pair of vane rings and/or one vane ring and a nozzle wall. The vanes are adjusted to control the exhaust gas backpressure and the turbocharger speed by modulating the exhaust gas flow to the turbine wheel. In many configurations, the vanes are rotated through vane lever assemblies, which are coupled to an adjustment ring, which is further rotated via a pivot shaft assembly that is linked to an actuator. As shown for example in  FIG. 1 , a conventional pivot shaft assembly  100  may include a pivot shaft  102 , a pivot fork  104 , a VTG lever  106  pivotally extending from the pivot shaft  102 , and one or more bushings  108 . The pivot shaft assembly shown in  FIG. 1  and the lever thereof is typically required to maintain friction or press fitments that are sufficient to translate torque through the adjustment ring and to the corresponding vanes. In order to satisfy these criteria, the lever and the geometry thereof may need to be carefully formed using more costly and time-consuming processes such as metal injection molding (MIM), powder metallurgy (PM), or the like, and cannot be formed by stamping or other more cost-efficient and simple processes. 
     Accordingly, there is a need to provide a turbocharger with all of the benefits associated with variable geometries, but at even less cost and delay in manufacturing same. The present disclosure is directed at addressing one or more of the deficiencies and disadvantages of the prior art set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent express noted. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a pivot shaft assembly for a turbocharger with variable turbine geometry (VTG) is provided. The pivot shaft assembly may include a pivot shaft, a pivot fork extending from the pivot shaft, a VTG lever disposed on the pivot shaft, and a retention collar axially coupled to the pivot shaft such that the VTG lever is axially aligned with the retention collar and the pivot shaft. 
     In another aspect of the present disclosure, a pivot shaft assembly for a VTG turbocharger with is provided. The pivot shaft assembly may include a pivot shaft, a pivot fork extending from the pivot shaft, a VTG lever disposed on the pivot shaft, a retention collar axially coupled to the pivot shaft such that the VTG lever is axially aligned with the retention collar and the pivot shaft, and a support collar axially coupled to the mounting shaft such that the vane lever is disposed between the retention collar and the support collar. 
     In yet another aspect of the present disclosure, a method of manufacturing a pivot shaft assembly for a VTG turbocharger is provided. The method may include providing a pivot shaft, stamping a VTG lever sized to axially receive the pivot shaft, providing a retention collar sized to axially receive the pivot shaft, and coupling the VTG lever onto the pivot shaft using the retention collar. 
     These and other aspects and features will be more readily understood when reading the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial perspective view of a pivot shaft assembly of the prior art; 
         FIG. 2  is a partial cross-sectional perspective view of a turbocharger having variable geometry and employing one exemplary pivot shaft assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 3  is a partial perspective view of another exemplary pivot shaft assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 4  is a partial cross-sectional view of the exemplary pivot shaft assembly of  FIG. 3 ; 
         FIG. 5  is a partial cross-sectional view of another exemplary pivot shaft assembly constructed in accordance with the teachings of the present disclosure; and 
         FIG. 6  is a flowchart depicting an exemplary disclosed method that may be used to manufacture a pivot shaft assembly in accordance with the teachings of the present disclosure. 
     
    
    
     While the following detailed description will be given with respect to certain illustrative embodiments, it should be understood that the drawings are not necessarily to scale and the disclosed embodiments are sometimes illustrated diagrammatically and in partial view. In addition, in certain instances, details which are not necessary for an understanding of the disclosed subject matter or which render other details too difficult to perceive may have been omitted. It should therefore be understood that this disclosure is not limited to the particular embodiments disclosed and illustrated herein, but rather to a fair reading of the entire disclosure and claims, as well as equivalents thereto. 
     DETAILED DESCRIPTION 
     Referring first to  FIG. 2 , an example embodiment of a prior art pivot shaft assembly  200  as implemented into a turbocharger having variable geometry, or variable turbine geometry (VTG)  202  is provided. As shown, the turbocharger  202  may include an adjustment ring  204 , a vane ring  206 , and a plurality of vane lever assemblies  208 . More specifically, the adjustment ring  204  may be rotatable about the turbocharger centerline  210  relative to the associated vane ring  206 , such as via a circumferential motion of one or more adjustment pins  212 , or the like. Furthermore, rotation of the adjustment ring  204  may be configured to cause a plurality of pivot blocks  214  to circumferentially rotate about the turbocharger centerline  210 , thereby also causing each of the vane lever  216  coupled thereto to rotate about the respective vane shaft centerline  218 . Moreover, rotating the vane levers  216  about the vane shaft centerlines  218  may cause the corresponding vane shafts  220  and vanes  222  to rotate, pivot or otherwise change position relative to the turbocharger  202 . 
     As shown in  FIG. 2 , the prior art pivot shaft assembly  200  may be used to circumferentially rotate the adjustment pin  212  and thus the adjustment ring  204  about the turbocharger centerline  210 , so as to ultimately cause the vanes  222  to rotate, pivot, or adjust position relative to the turbocharger  202 . The pivot shaft assembly  200  may generally include a pivot shaft  224 , a pivot fork  226 , a VTG lever  228  and one or more bushings  230 . The pivot shaft  224  may axially extend from the adjustment ring  204  and attach to the VTG lever  228 . The pivot fork  226  may extend radially outwardly from the end of the pivot shaft  224  most proximate to the adjustment ring  204 , and configured to couple to the adjustment pin  212  of the adjustment ring  204 . The VTG lever  228  may be configured with a support end  232  and a linkage end  234 , where the support end  232  is disposed on or coupled to the pivot shaft  224 , and where the linkage end  234  of the pivot shaft  224  is coupled to a linkage  236  that is actuatable by an actuator not depicted. The bushings  230  may be axially and rotatably coupled to the pivot shaft  224  and configured to at least partially support and axially align the VTG lever  228  relative to the pivot shaft  224 . 
     Turning now to  FIG. 3 , one exemplary embodiment of an improved pivot shaft assembly  300  that is constructed in accordance with the present disclosure and that may be used in conjunction with a modified or a conventional turbocharger  202  is provided. As shown, the pivot shaft assembly  300  may generally include at least a pivot shaft  302 , a pivot fork  304 , a VTG lever  306 , one or more bushings  308  and a retention collar  310 . The pivot shaft  302  may axially extend from the adjustment ring  204  and attach to the VTG lever  306 . The pivot fork  304  may extend radially outwardly from the end of the pivot shaft  302  most proximate to the adjustment ring  204 , and may be configured to couple to or otherwise engage the adjustment pin  212  of the adjustment ring  204 . The VTG lever  306  may be configured with a support end  312  and a linkage end  314 , where the support end  312  is disposed on or coupled to the pivot shaft  302 , and where the linkage end  314  of the pivot shaft  302  is coupled to an actuator via a linkage  236 . The bushings  308  may be axially coupled to the pivot shaft  302  and configured to at least partially support and axially align the VTG lever  306  relative to the pivot shaft  302 . 
     In contrast to prior art pivot shaft assemblies  100 ,  200  as shown in  FIGS. 1 and 2 , the pivot shaft assembly  300  in  FIG. 3  may employ a retention collar  310  to further support the VTG lever  306  relative to the pivot shaft  302 . As shown in  FIG. 3 , the retention collar  310  may be axially coupled to one or more of the pivot shaft  302  and the VTG lever  306 , and designed to interface with the pivot shaft  302  and/or the bushings  308  in a manner configured to align the VTG lever  306  with each of the retention collar  310  and the pivot shaft  302 . As further shown in  FIG. 4  for example, the retention collar  310  may be configured to axially couple onto the pivot shaft  302 , while also rigidly abutting the VTG lever  306  onto the pivot shaft  302  or an enlarged section thereof. Alternatively, as shown for example in  FIG. 5 , the retention collar  310  may be configured to axially couple onto pivot shaft  302 , while the VTG lever  306  may be rigidly coupled onto the outer circumference of the retention collar  310 . 
     In either arrangement, the retention collar  310  may be rigidly coupled to one or more of the VTG lever  306  and the pivot shaft  302  via press-fitting, welding, clinching, or any other suitable technique sufficient to maintain rigid and proper alignment of the VTG lever  306  and to ensure effective torque transfer between the pivot shaft  302  and the VTG lever  306 . Also, while the bushings  308  may be omitted, if one is provided, the retention collar  310  may be configured to function in conjunction with the bushings  308  to further support and align the VTG lever  306 . As shown in the embodiment of  FIG. 4  for example, the retention collar  310  may be configured to abut the VTG lever  306  at least partially against the bushings  308 , or such that the VTG lever  306  is disposed and supported between the retention collar  310  and the bushings  308 . While only certain arrangements are provided, other comparable and suitable arrangements will be apparent to those of ordinary skill in the art. 
     Still referring to  FIGS. 3-5 , the added support and axial reinforcement provided by the retention collar  310  may further enable the design of the VTG lever  306  itself to be significantly more simple than in prior art assemblies without compromising structural integrity or exhibiting other adverse effects. As shown in each of the embodiments of  FIGS. 3-5 , and as compared to the prior art VTG lever  106  of  FIG. 1 , the overall thickness of the VTG lever  306  is substantially more thin, and the geometry or construction of the VTG lever  306  is relatively more simple. Moreover, because the VTG lever  306  encompasses a reduced thickness as well as a less complex design and geometry, the VTG lever  306  may be constructed using faster, easier and more cost efficient manufacturing techniques or processes, such as stamping, or the like. For example, the VTG lever  306  of the present disclosure may have approximate thicknesses of less than 4 mm, thicknesses achievable via stamping processes, and still enable sufficient torque transfer to the VTG lever  306 , whereas those of the prior art may need to be approximately 6-8 mm in thickness, thicknesses unachievable via typical stamping processes, in order to provide comparable torque transfer. Techniques or processes other than stamping, that are capable of manufacturing the overall reduced thickness of the VTG lever  306  disclosed herein at reduced cost, will be apparent to those of ordinary skill in the art and may also be used to achieve comparable results. 
     Turning now to  FIG. 6 , one exemplary method  400  of manufacturing a pivot shaft assembly  300  of the present disclosure is provided. As shown in block  402 , and in accordance with the embodiments disclosed in  FIGS. 3-5 , the method  400  may initially provide or form the pivot shaft  302  of the pivot shaft assembly  300 . For example, in the turbocharger  202  of  FIG. 2  or in other comparable VTGs, the pivot shaft  302  may be designed to extend from the adjustment ring  204  and attach to the corresponding VTG lever  306 . In block  404 , the method  400  may form the VTG lever  306  of the pivot shaft assembly  300  of  FIGS. 3-5  with an overall reduced thickness by a suitable stamping process. Moreover, the stamping process of block  404  may be configured to form the VTG lever  306  with a support end  312  and a linkage end  314 , such that the support end  312  is sized to receive the pivot shaft  302 , and such that the linkage end  314  is sized to receive a linkage  236  and thereby couple to an actuator, or the like. 
     According to block  406  of  FIG. 6 , the method  400  may be configured to provide or form a retention collar  310  sized to axially receive the pivot shaft  302  of the pivot shaft assembly  300 . Optionally or additionally, in block  408 , the method  400  may be configured to provide or form one or more bushings  308  sized to axially receive the pivot shaft  302  and support the VTG lever  306 , for instance, such that the VTG lever  306  is rigidly fit or held between the retention collar  310  and the one or more bushings  308 . Still further, in block  410 , the method  400  may include coupling the support end  312  of the VTG lever  306  onto the pivot shaft  302  using the retention collar  310 , such as in any of the arrangements shown in  FIGS. 3-5 . For example, the retention collar  310  may be coupled onto the pivot shaft  302  and configured to axially abut the VTG lever  306  onto the pivot shaft  302  as shown in  FIG. 4 . Alternatively, the retention collar  310  may be coupled onto the pivot shaft  302 , and the VTG lever  306  may be coupled onto the retention collar  310  as shown in  FIG. 5 . Moreover, the retention collar  310  may be coupled onto one or more of the VTG lever  306  and the pivot shaft  302  using press-fitting, welding, clinching, and/or any other suitable technique. 
     From the foregoing, it will be appreciated that while only certain embodiments have been set forth for the purposes of illustration, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.