Abstract:
A blade with first and second blade tabs extending outwardly from an edge of the blade; and a shell with a first indent and a first slot. The first blade tab is arranged to engage the first indent and the second blade tab is arranged to engage the first slot. In one embodiment, the first indent is arranged radially inward on the shell relative to the first slot. In one embodiment, the first blade tab is affixed to the first indent. In one embodiment, the second blade tab is bent over an outside surface of the turbine shell. In one embodiment, the shell includes a second indent and the blade includes a third blade tab extending outwardly from the edge and at least partially disposed in the second indent. A method of manufacturing a pump or turbine shell for a torque converter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/876,215, filed Dec. 21, 2006. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to torque converters, and more specifically, to components for torque converters, namely turbine and pump shells having blades attached by means of blade tabs, and to methods of manufacturing. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  illustrates a general block diagram showing the relationship of the engine  7 , torque converter  10 , transmission  8 , and differential/axle assembly  9  in a typical vehicle. It is well known that a torque converter is used to transmit torque from an engine to a transmission of a motor vehicle. 
     The three main components of the torque converter are the pump  37 , turbine  38 , and stator  39 . The torque converter becomes a sealed chamber when the pump is welded to cover  11 . The cover is connected to flexplate  41  which is, in turn, bolted to crankshaft  42  of engine  7 . The cover can be connected to the flexplate using lugs or studs welded to the cover. The welded connection between the pump and cover transmits engine torque to the pump. Therefore, the pump always rotates at engine speed. The function of the pump is to use this rotational motion to propel the fluid radially outward and axially towards the turbine. Therefore, the pump is a centrifugal pump propelling fluid from a small radial inlet to a large radial outlet, increasing the energy in the fluid. Pressure to engage transmission clutches and the torque converter clutch is supplied by an additional pump in the transmission that is driven by the pump hub. 
     In torque converter  10  a fluid circuit is created by the pump (sometimes called an impeller), the turbine, and the stator (sometimes called a reactor). The fluid circuit allows the engine to continue rotating when the vehicle is stopped, and accelerate the vehicle when desired by a driver. The torque converter supplements engine torque through torque ratio, similar to a gear reduction. Torque ratio is the ratio of output torque to input torque. Torque ratio is highest at low or no turbine rotational speed (also called stall). Stall torque ratios are typically within a range of 1.8-2.2. This means that the output torque of the torque converter is 1.8-2.2 times greater than the input torque. Output speed, however, is much lower than input speed, because the turbine is connected to the output and it is not rotating, but the input is rotating at engine speed. 
     Turbine  38  uses the fluid energy it receives from pump  37  to propel the vehicle. Turbine shell  22  is connected to turbine hub  19 . Turbine hub  19  uses a spline connection to transmit turbine torque to transmission input shaft  43 . The input shaft is connected to the wheels of the vehicle through gears and shafts in transmission  8  and axle differential  9 . The force of the fluid impacting the turbine blades is output from the turbine as torque. Axial thrust bearings  31  support the components from axial forces imparted by the fluid. When output torque is sufficient to overcome the inertia of the vehicle at rest, the vehicle begins to move. 
     After the fluid energy is converted to torque by the turbine, there is still some energy left in the fluid. The fluid exiting from small radial outlet  44  would ordinarily enter the pump in such a manner as to oppose the rotation of the pump. Stator  39  is used to redirect the fluid to help accelerate the pump, thereby increasing torque ratio. Stator  39  is connected to stator shaft  45  through one-way clutch  46 . The stator shaft is connected to transmission housing  47  and does not rotate. One-way clutch  46  prevents stator  39  from rotating at low speed ratios (where the pump is spinning faster than the turbine). Fluid entering stator  39  from turbine outlet  44  is turned by stator blades  48  to enter pump  37  in the direction of rotation. 
     The blade inlet and exit angles, the pump and turbine shell shapes, and the overall diameter of the torque converter influence its performance. Design parameters include the torque ratio, efficiency, and ability of the torque converter to absorb engine torque without allowing the engine to “run away.” This occurs if the torque converter is too small and the pump can&#39;t slow the engine. 
     At low speed ratios, the torque converter works well to allow the engine to rotate while the vehicle is stationary, and to supplement engine torque for increased performance. At speed ratios less than 1, the torque converter is less than 100% efficient. The torque ratio of the torque converter gradually reduces from a high of about 1.8 to 2.2, to a torque ratio of about 1 as the turbine rotational speed approaches the pump rotational speed. The speed ratio when the torque ratio reaches 1 is called the coupling point. At this point, the fluid entering the stator no longer needs redirected, and the one way clutch in the stator allows it to rotate in the same direction as the pump and turbine. Because the stator is not redirecting the fluid, torque output from the torque converter is the same as torque input. The entire fluid circuit will rotate as a unit. 
     Peak torque converter efficiency is limited to 92-93% based on losses in the fluid. Therefore torque converter clutch  49  is employed to mechanically connect the torque converter input to the output, improving efficiency to 100%. Clutch piston plate  17  is hydraulically applied when commanded by the transmission controller. Piston plate  17  is sealed to turbine hub  19  at its inner diameter by o-ring  18  and to cover  11  at its outer diameter by friction material ring  51 . These seals create a pressure chamber and force piston plate  17  into engagement with cover  11 . This mechanical connection bypasses the torque converter fluid circuit. 
     The mechanical connection of torque converter clutch  49  transmits many more engine torsional fluctuations to the drivetrain. As the drivetrain is basically a spring-mass system, torsional fluctuations from the engine can excite natural frequencies of the system. A damper is employed to shift the drivetrain natural frequencies out of the driving range. The damper includes springs  15  in series with engine  7  and transmission  8  to lower the effective spring rate of the system, thereby lowering the natural frequency. 
     Torque converter clutch  49  generally comprises four components: piston plate  17 , cover plates  12  and  16 , springs  15 , and flange  13 . Cover plates  12  and  16  transmit torque from piston plate  17  to compression springs  15 . Cover plate wings  52  are formed around springs  15  for axial retention. Torque from piston plate  17  is transmitted to cover plates  12  and  16  through a riveted connection. Cover plates  12  and  16  impart torque to compression springs  15  by contact with an edge of a spring window. Both cover plates work in combination to support the spring on both sides of the spring center axis. Spring force is transmitted to flange  13  by contact with a flange spring window edge. Sometimes the flange also has a rotational tab or slot which engages a portion of the cover plate to prevent over-compression of the springs during high torque events. Torque from flange  13  is transmitted to turbine hub  19  and into transmission input shaft  43 . 
     Energy absorption can be accomplished through friction, sometimes called hysteresis, if desired. Hysteresis includes friction from windup and unwinding of the damper plates, so it is twice the actual friction torque. The hysteresis package generally consists of diaphragm (or Belleville) spring  14  which is placed between flange  13  and one of cover plates  16  to urge flange  13  into contact with the other cover plate  12 . By controlling the amount of force exerted by diaphragm spring  14 , the amount of friction torque can also be controlled. Typical hysteresis values are in the range of 10-30 Nm. 
     Turbine shell  22  and pump shell  34  comprise a plurality of slots arranged to engage with turbine blades  23  and pump blades  33 , respectively. Each turbine blade and pump blade comprises a blade tab arranged to engage each slot in the turbine or pump shell. The blades are then secured to the shells by an attachment means. Conventionally, the blade tabs are bent once they protrude through the shell. The blades are then usually brazed to strengthen the connection. 
     In manufacturing the turbine shell and pump shell, manufacturers commonly start with a flat piece of material that is cut in a circular shape. The slots are then punched or cut into the shells in any arrangement suited to engage the blade tabs. The shells are then stamped (or similarly formed) into the semi-toroidal shapes seen most clearly in  FIGS. 5 and 6 . Such a forming process is disclosed in U.S. Pat. No. 5,868,025 (Fukuda et al.). This forming process deforms the slots and can result in misaligned blades and blade tabs. Thus, the prior art is not able to form a slot shape and width such that their dimensions after the final stamping/forming process are within acceptable tolerance limits to engage with the blades and blade tabs. The largest amount of deformation of the slots occurs in the slots most radially centered. That is, the slots closest to the axis of rotation are most affected by slot deformation during the final stamping process. 
     Misaligned blade tabs result in poor attachment of a blade to a shell. Poorly attached blades can easily break away from the shell when the torque converter is in use. Thus, misaligned structures are usually scrapped. 
     To overcome the extent of deformation and scrapped structures, some manufacturers have simultaneously cut slits into the shell and punched the shell into the semi-toroidal shape such as described in U.S. Pat. No. 5,946,962 (Fokuda et al.). However, this process requires a very precise level of control in order to assure slot deformation is within acceptable limits to produce the desired slot widths and shapes. 
     The brazing process that conventionally follows the above processes includes adding a brazing paste to the blade tabs prior to inserting the blade tabs into the shell slots, and then passing the assembly of shell and blades through a furnace. This is most commonly done using a furnace conveyor belt. The position and level of deformation of the slots can lead to brazing paste leaking through the slots and depositing atop the furnace belt. The deposition of brazing paste leads to delays in factory processes and can result in furnace malfunction. 
     A method of drastically reducing blade tab attachment deformation is to form indentations arranged to engage blade tabs in lieu of slots. Indents deform much less than slots, especially in the inner radial sections of the shells. A method of forming these indentations by means of stamping or pressing is disclosed in commonly owned U.S. Patent Application No. 2004/0250594 (Schwenk), which is incorporated by reference herein. However, blade tabs for indents are usually smaller in overall dimensions than blade tabs for slots to accommodate the smaller size of the indents. Because the blade tabs for indents do not structurally hold the blades in place against the shell, it is often difficult and not cost effective to only use indents to arrange a plurality of blades against a shell and braze or weld the blades into place. Conventionally, a separate structure is introduced to the blade and shell assembly that is opposite the shell and holds the blade tabs in their respective indents in the shell, so that the blade tabs can be brazed to their respective indentations. However, this process is prone to failure inadequate alignment between blade tabs and indentations. 
     Accordingly, there is a need for an improved blade attachment means that greatly reduces the blade tab misalignment and increases manufacturability. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention broadly comprises a shell assembly for a torque converter including: a blade with first and second blade tabs extending outwardly from an edge of the blade; and a shell with a first indent and a first slot. The first blade tab is arranged to engage the first indent and the second blade tab is arranged to engage the first slot. In one embodiment, the first indent is arranged radially inward on the shell relative to the first slot. In one embodiment, the first blade tab is affixed to the first indent. In one embodiment, the second blade tab is bent over an outside surface of the turbine shell. In one embodiment, the shell includes a second indent and the blade includes a third blade tab extending outwardly from the edge and at least partially disposed in the second indent. 
     In one embodiment, the shell includes a second slot and the blade includes a third blade tab extending outwardly from the edge and at least partially disposed in the second slot. In one embodiment, the shell assembly includes a plurality of blades, each blade includes the first and second blade tabs, the shell includes respective pluralities of indents and slots in respective concentric rows, and for each blade, the first and second blade tabs are engaged with the respective pluralities of indents and slots, respectively. In one embodiment, the shell is a turbine shell or a pump shell. 
     The invention also broadly comprises a shell for a torque converter including: a first indent arranged to receive a first blade tab for a blade; and a first slot arranged to receive a second blade tab for the blade. In one embodiment, said first indent is arranged radially inward on said shell relative to said first slot. In one embodiment, said first blade tab is arranged to be affixed to said first indent. In one embodiment, said second blade tab is arranged to be bent over an outside surface of the shell. In one embodiment, the shell includes a second indent and the blade includes a third blade tab arranged to be at least partially disposed in the second indent. In one embodiment, the shell includes a second slot and the blade includes a third blade tab arranged to be at least partially disposed in the second slot. In one embodiment, the shell includes respective pluralities of indents and slots in respective concentric rows arranged to engage respective first and second tabs from a plurality of blades. The shell can be a turbine shell or a pump shell. 
     The invention broadly comprises a method of manufacturing a pump or turbine shell for a torque converter including the steps of: forming a circular row of indents into a circular disk; forming a first circular row of slots into the circular disk; forming the circular disk into a shell with a semi-toroidal shape; for each blade in a plurality of blades, inserting a first blade tab into a respective indent in the plurality of indents and inserting a second blade tab into a respective slot in the first row of slots; bending the second blade tab onto the shell, and affixing the first blade tab to the shell. In one embodiment, the steps of forming a circular row of indents into a circular disk and forming a first circular row of slots into the circular disk are performed substantially simultaneously. 
     In one embodiment, the steps of forming a circular row of indents into a circular disk and forming a first circular row of slots into the circular disk and the step of forming the circular disk into a shell with a semi-toroidal shape are performed sequentially. In one embodiment, the steps of forming a circular row of indents into a circular disk, forming a first circular row of slots into the circular disk, and forming the circular disk into a shell with a semi-toroidal shape are performed substantially simultaneously. In one embodiment, the row of radial indents is displaced radially inwards with respect to the first row of radial slots. In one embodiment, the method includes: forming a second circular row of slots into the circular disk; for each blade in the plurality of blades, inserting a third blade tab into a respective slot in the second row of slots; and bending the third blade tab onto the shell. 
     It is a general object of the present invention to provide a means for attaching a blade to a shell of a torque converter, by affixing a blade to the shell by both a bent tab and a tab resting in an indent in the shell that is brazed, welded or similarly affixed. 
     It is also a general object of the present invention to provide a method of manufacturing a pump or turbine shell for a torque converter by forming at least one row of radial indents into a circular disk, forming at least one row of radial slots into the circular disk, and forming the circular disk into a shell with a semi-toroidal shape. 
     It is a further objective of the present invention to improve manufacturability and limit waste in the manufacturing of turbine and pump shell and blade assemblies, by reducing blade tab misalignment and leakage during brazing. 
     Other objects, features, and advantages of the invention will be apparent from the drawings, specification and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIG. 1  is a general block diagram illustration of power flow in a motor vehicle, intended to help explain the relationship and function of a torque converter in the drive train thereof; 
         FIG. 2  is a cross-sectional view of a prior art torque converter, shown secured to an engine of a motor vehicle; 
         FIG. 3  is a left view of the torque converter shown in  FIG. 2 , taken generally along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the torque converter shown in  FIGS. 2 and 3 , taken generally along line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a first exploded view of the torque converter shown in  FIG. 2 , as shown from the perspective of one viewing the exploded torque converter from the left; 
         FIG. 6  is a second exploded view of the torque converter shown in  FIG. 2 , as shown from the perspective of one viewing the exploded torque converter from the right; 
         FIG. 7A  is a perspective view of a cylindrical coordinate system demonstrating spatial terminology used in the present application; 
         FIG. 7B  is a perspective view of an object in the cylindrical coordinate system of  FIG. 7A  demonstrating spatial terminology used in the present application; 
         FIG. 8  is a top view of an unprocessed circular shell to be formed into a shell for a torque converter; 
         FIG. 9  is a partial cross-sectional view of the shell shown in  FIG. 8 , taken generally along line  9 - 9  in  FIG. 8  during the slot and indent forming process; 
         FIG. 10  is a top view of the shell shown in  FIG. 8  after the slot and indent forming process has been completed; 
         FIG. 11  is a partial cross-sectional view of the shell shown in shown in  FIG. 9  during a first forming process to create a semi-toroidal shape; 
         FIG. 12  is a partial cross-sectional view of the shell shown in shown in  FIG. 11  during a second forming process to create a semi-toroidal shape; 
         FIG. 13  is a perspective view from the front of the finished shell for a torque converter after the second forming process is completed; 
         FIG. 14  is a top view of the shell shown in  FIG. 13  having blades attached to the shell; 
         FIG. 15  is a partial cross-sectional view of the shell shown in  FIG. 14  taken generally along line  15 - 15  in  FIG. 14 ; 
         FIG. 16  is a top view of a shell having two pluralities of indents; and,  FIG. 17  is a partial cross-sectional view of the shell shown in  FIG. 16  taken generally along line  17 - 17  in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred embodiments, it is understood that the invention is not limited to the disclosed embodiments. In the description below, the terms “top”, “bottom”, “upper”, “lower”, “front”, “back”, “rear”, “left”, “right”, and their derivatives, should be interpreted from the perspective of one viewing the invention shown in  FIG. 1 . 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
       FIG. 7A  is a perspective view of cylindrical coordinate system  80  demonstrating spatial terminology used in the present application. The present invention is at least partially described within the context of a cylindrical coordinate system. System  80  has a longitudinal axis  81 , used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis  81 , radius  82  (which is orthogonal to axis  81 ), and circumference  83 , respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects  84 ,  85 , and  86  are used. Surface  87  of object  84  forms an axial plane. That is, axis  81  forms a line along the surface. Surface  88  of object  85  forms a radial plane. That is, radius  82  forms a line along the surface. Surface  89  of object  86  forms a circumferential plane. That is, circumference  83  forms a line along the surface. As a further example, axial movement or disposition is parallel to axis  81 , radial movement or disposition is parallel to radius  82 , and circumferential movement or disposition is parallel to circumference  83 . Rotation is with respect to axis  81 . 
     The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis  81 , radius  82 , or circumference  83 , respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes. 
       FIG. 7B  is a perspective view of object  90  in cylindrical coordinate system  80  of  FIG. 7A  demonstrating spatial terminology used in the present application. Cylindrical object  90  is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention in any manner. Object  90  includes axial surface  91 , radial surface  92 , and circumferential surface  93 . Surface  91  is part of an axial plane, surface  92  is part of a radial plane, and surface  93  is part of a circumferential plane. 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
       FIG. 8  is a top view of shell  100  prior to any forming or processing. Shell  100  is essentially a disk of circular shape having a hole in the center. The structures and forming process recited below will form shell  100  into a shell having a blade attachment means according to the present invention. 
       FIG. 9  is a partial cross-sectional view of shell  100  taken generally along line  9 - 9  in  FIG. 8  during the slot and indent forming process. In this forming process, at least first indent  102  and at least first slot  104  are formed into shell  100 . Preferably, indent  102  is formed radially inwards, closer to the center of shell  100 , in shell  100  respective to first slot  104 . In this preferred embodiment comprising first indent  102  and first slot  104 , shell  100  further includes second slot  106 . It should be appreciated, however, that second slot  106  could be replaced by a second indent. It should also be appreciated that any number, combination, or configuration of slots and indents is included in the spirit and scope of the claimed invention. The invention is in no way limited to only the configuration of first indent slot  102  and first shell slot  104 . 
     First shell indent  102  is formed by holding shell  100  between upper punch plate  108  and lower punch plate  110 , and forming indent  102  with indent stamp  112 . Upper punch plate  108  includes indent guide  114  to allow shell  100  to deform and create indent  102 , and lower punch plate  110  includes indent stamp guide  116  which enable indent stamp  112  to move up and down. First shell slot  104  is formed by punching slot punch  118  through shell  100  and removing blank  120  through first slot opening  122  of lower punch plate  110 . Slot punch  118  travels through upper punch plate  108  through first slot punch guide  124 . Second shell slot  106  is formed through means similar to that of first shell slot  104 . 
     In one embodiment, the process shown in  FIG. 9  is simultaneously completed, across the entirety of shell  100 , producing a plurality of rows of concentric, circumferentially spaced slots and indents. This is shown in  FIG. 10 , which is a top view of the shell shown in  FIG. 8  after the slot and indent forming process has been completed. Shell  100 , as shown in  FIG. 10 , shows three concentric rows of circumferentially spaced indents and slots, namely indent row  130  and slots rows  132  and  134 . In one embodiment, row  134  can be a row of indents instead of a row of slots as shown in  FIGS. 16 and 17 . 
     Shells in torque converters have a semi-toroidal shape as seen in shells in  22  and  34  of  FIG. 5  for example. Care must be taken in forming shell  100  into a semi-toroidal shape in order to maintain the structure of indent  102 . As shown in  FIG. 11 , a partial cross-sectional view of shell  100  shown in  FIG. 9  during a first forming process to create a semi-toroidal shape, shell  100  can be placed in forming apparatus  140 . Apparatus  140  includes forming block  142  which includes ridge  144  for maintaining the shape and alignment of indent  102  during the forming process when shell  100  is engaged between block  142  and block  146 . Block  146  includes indent guide  148  to accommodate the shape of indent  102  as well as curved surface  150  for engagement with curved surface  152  of block  142 . By engaging blocks  142 ,  144 ,  154  and  156  a partial semi-toroidal shape can be formed. 
     To complete the semi-toroidal shape, a second forming process is preferably completed as shown in  FIG. 12 , a partial cross-sectional view of shell  100  shown in  FIG. 11  during the second forming process. Shell  100  is further formed into a semi-toroidal shape in apparatus  160 , comprising blocks  162 ,  164 ,  166  and  168 . Block  164  includes indent guide  170  and block  168  includes ridge  172  to accommodate the shape of indent  102 . Surface  174  of block  166  and surface  176  of block  168  engage with shell  100  to complete the semi-toroidal shape. 
     It should be appreciated that the forming process recited above and shown in  FIGS. 11 and 12  can be accomplished in one simultaneous forming process. However, two separate processes are preferred due to deformation limitations in such forming processes. 
     After the second forming process shown in  FIG. 12  is completed, the shell has a semi-toroidal shape as shown in  FIG. 13 , which is a perspective view from the front of shell  100 .  FIG. 14  is a top view of a shell for a torque converter (not shown) having blades  200  attached to shell  100 , through bent tabs  204  and  206 . The attachment means between blades  200  and shell  100  is more clearly shown in  FIG. 15 , which is a partial cross-sectional view of shell  100  shown in  FIG. 14  taken generally along line  15 - 15  in  FIG. 14 . 
     Blade  200  include blade tab  202  extending outwardly from blade  200  and arranged to engage shell indent  102 , blade tab  204  extending outwardly from blade  200  and arranged to engage shell slot  104 , and blade tab  206  extending outwardly from blade  200  and arranged to engage shell slot  106 . It should be readily appreciated that shell blade tab  206  could also be arranged to engage a shell indent instead of shell slot  106 . Blade tab  202  and shell indent  102  are arranged radially inwards on shell  100  relative to second blade tab  204  and first shell slot  202 . 
     To further secure blades  200  to shell  100 , blade tabs  204  and  206  are preferably bent onto shell  100  as is most clearly shown in  FIG. 14 . Blades  200  can be fixed to the shell by any means known in the art, including, but not limited to, brazing, welding, embossing, soldering, pressure fitting, snap-fitting, ultra-sonic welding or laser welding. In a preferred embodiment, blades  200  are brazed to shell  100 . 
     Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention.