Patent Publication Number: US-2017363183-A1

Title: Attachment method for pulley device and drive shaft and assembly formed thereby

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/089,403 filed Dec. 9, 2014, and U.S. Provisional Patent Application No. 62/126,664 filed Mar. 1, 2015, the contents of both of which are incorporated herein in their entirety. 
    
    
     FIELD 
     This disclosure relates to pulley devices such as pulleys, isolators and TVDs (Torsional Vibration Dampers), and in particular to isolators that are used on a drive shaft such as an engine crankshaft or a motor-generator unit (MGU) shaft, in vehicles in which accessories can be driven by the MGU, and/or in which the engine can be started or boosted by the MGU through a belt (e.g. an engine equipped with a belt-alternator start (BAS) drive system). 
     BACKGROUND 
     Isolators are known devices that are installed in accessory drive systems, on engine crankshafts and/or on accessory drive shafts for reducing the transmission of torsional vibrations from the crankshaft to a belt driven by the crankshaft and/or from the belt to the accessory drive shaft. In some instances where the engine is a hybrid engine that incorporates an MGU, the accessory drive system is operated in a first mode where the accessory drive belt is driven by the engine crankshaft and in turn drives the accessories, and in a second mode where the MGU drives the belt, which in turn drives the accessories (referred to as ISAF—Idle/Stop Accessory Function) and/or drives the engine crankshaft (such as during a BAS (Belt-Alternator Start) event, or a boost event where the MGU supplies additional power to the engine via the belt). In such systems, the isolator operates to transfer torque from the belt to a shaft in one mode, and operates to transfer torque from the shaft to the belt in the other mode. In order to ensure that the isolator remains fixed to the shaft to which it is installed, it is sometimes simply welded to the shaft. Welding is problematic, however, as it is time consuming and it requires grinding or the like in order to remove the isolator from the shaft, which will likely damage both the shaft and the isolator, thereby making the process of replacing a worn or defective isolator time consuming and expensive. In other cases an isolator may be keyed to the shaft. While a key arrangement is releasable, thereby facilitating removal and replacement of the isolator as needed, keying can be troublesome since some play can develop or is present from the beginning between the key and the key-receiving slot in the shaft, and/or between the key and the key-receiving slot in the isolator&#39;s shaft adapter. 
     It would be advantageous to be able to provide a connection that avoids damage to at least one of the shaft and the isolator during removal of the isolator from a drive shaft, such as the engine&#39;s crankshaft or an accessory shaft. 
     SUMMARY 
     In an aspect, there is provided a A method of attaching a pulley device to a drive shaft, wherein the pulley device includes a pulley and has a shaft adapter that has a bore extending from a first axial end of the shaft adapter to a second axial end of the shaft adapter. The pulley device further includes a shaft adapter shoulder proximate the first axial end, a first shaft adapter connection structure which is threaded and is in the bore, and a second shaft adapter connection structure, the drive shaft including a shaft axial end, a shaft shoulder, a first shaft connection structure which is threaded, and a second shaft connection structure. The method includes: 
     a) inserting the shaft axial end into the bore and causing relative rotation between the shaft and the shaft adapter in a first direction to engage the first shaft adapter connection structure and the first shaft connection structure with one another to provide a first non-destructively releasable connection; 
     b) engaging the second shaft adapter connection structure and the second shaft connection structure with one another to provide a second connection; and 
     c) generating a selected amount of axial compression force between the shaft adapter shoulder and the shaft shoulder. Steps a), b) and c) together generate a selected amount of combined resistance in the first and second connections to relative rotation between the shaft and the shaft adapter in a second direction that is opposite the first direction. 
     In another aspect, an assembly is provided and includes a pulley device and a drive shaft. The pulley device includes a pulley and has a shaft adapter that has a bore extending from a first axial end of the shaft adapter to a second axial end of the shaft adapter. The pulley device further includes a shaft adapter shoulder proximate the first axial end, a first shaft adapter connection structure which is threaded and is in the bore, and a second shaft adapter connection structure. The drive shaft includes a shaft axial end, a shaft shoulder, a first shaft connection structure which is threaded and a second shaft connection structure. The first shaft adapter connection structure and the first shaft connection structure are engaged with one another to provide a first non-destructively releasable connection such that relative rotation of the shaft and the shaft adapter in a first direction tightens the first connection and relative rotation of the shaft and the shaft adapter in a second direction loosens the first connection. The second shaft adapter connection structure and the second shaft connection structure are engaged with one another to provide a second connection. The shaft adapter shoulder and the shaft shoulder are engaged with one another to generate a selected compression force therebetween. A selected amount of combined resistance in the first and second connections to relative rotation in the second direction is generated by the first and second connections and the compression force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects will now be described by way of example only with reference to the attached drawings, in which: 
         FIG. 1  is a side view of an engine in a vehicle containing a pulley device on a shaft of an MGU (motor-generator unit), according to non-limiting embodiments; 
         FIG. 2  is a perspective view of an example of the pulley device shown in  FIG. 1 ; 
         FIG. 3  is a perspective exploded view of the pulley device shown in  FIG. 2 , including a shaft adapter and connected to a shaft of the MGU, with a portion cut away; 
         FIGS. 4-15  are perspective cutaway views that illustrate the assembling of the pulley device to the shaft of the MGU; 
         FIG. 15 a    is a sectional side view of a portion of the assembly formed by the pulley device and the shaft, showing forces and torques along the length of the shaft adapter; 
         FIG. 16  is a perspective cutaway view showing another embodiment of the pulley device and the assembly of the pulley device and the shaft of the MGU; 
         FIG. 17  is a sectional side view of another embodiment that is similar to the embodiment shown in  FIG. 16  but with a solid pulley as the pulley device; 
         FIG. 18  is a perspective cutaway view showing yet another embodiment of the pulley device and the assembly of the pulley device and the shaft of the MGU; 
         FIG. 19  is a sectional side view of another embodiment that is similar to the embodiment shown in  FIG. 18  but with a solid pulley as the pulley device; 
         FIG. 20  is a perspective cutaway view showing yet another embodiment of the pulley device and the assembly of the pulley device and the shaft of the MGU; 
         FIGS. 20-21  are perspective cutaway views that illustrate the assembling of another assembly of a pulley device and the shaft of the MGU; 
         FIG. 22  is a sectional side view of a variant of the assembly shown in  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Reference is made to  FIG. 1 , which shows an example pulley device  10  for transferring power in an accessory drive system  11  between an endless drive member  52 , such as an accessory drive belt, and a drive shaft. The endless drive member  52  is used to transfer power between a crankshaft pulley  50  mounted on a crankshaft  51   a  of an engine  51 , and a plurality of accessory drive shafts including, for example, the drive shaft  54   a  of an MGU  54  and a drive shaft  56   a  of an air conditioning compressor  56 . The pulley device  10  is shown as being mounted on the drive shaft  54   a  of the MGU  54 . However, it will be understood that the pulley device  10  could additionally or alternatively be mounted on any other suitable drive shaft, such as the crankshaft  51   a.    
     The endless drive member  52  may be referred to herein as the belt  52 , for readability. However, it will be understood that it may be any other suitable endless drive member  52  may be used. 
     The engine  51  may be a hybrid engine. The accessory drive system  11  may be operated in a first mode where the belt  52  is driven by the engine crankshaft  51   a  and in turn drives the accessories, and in a second mode where the MGU  54  drives the belt  52 , which in turn drives the accessories (referred to as ISAF—Idle/Stop Accessory Function) and/or drives the engine crankshaft  51   a  (such as during a BAS (Belt-Alternator Start) event, or a boost event where the MGU  54  supplies additional power to the engine  51  via the belt  52 ). Thus, torque is sometimes transferred from the belt  52  to the drive shaft  51   a  through the pulley device  10 , and is sometimes transferred to the belt  52  from the drive shaft  51   a  through the pulley device  10 . 
     The pulley device  10  may be an isolator as shown at  100  in  FIGS. 2 and 3 , or it may be some other suitable type of pulley device  10  such as a solid pulley shown at  99  in  FIG. 5 . 
     In the embodiment shown in  FIG. 3 , the pulley device  10  includes a shaft adapter  102 , a rotary drive member  104 , and a spring arrangement  106 . The shaft adapter  102  is used to mount the pulley device  10  to the drive shaft  51   a,  so as to form an assembly between pulley device  10  and the drive shaft  51   a.  Several embodiments of the shaft adapter  102  are described further below. The rotary drive member  104  may be any suitable type of rotary drive member such as a pulley. The rotary drive member  104  may be referred to as a pulley  104  for readability, in much the same way that the endless drive member  52  may be referred to as a belt  52 , however it will be understood that any other suitable rotary drive member may be used. 
     The spring arrangement  106  includes at least one spring. In the example shown, the spring arrangement includes two primary, outer, arcuate, helical compression springs  108  and two secondary, inner, arcuate, helical compression springs  110  that are nested in the two outer springs  108  and operate in parallel with the springs  108 . The springs  108  and  110  may generally be arranged to exhibit polar symmetry about the axis of rotation of the pulley device  10 , shown at A. Other types of spring may alternatively or additionally be used in the spring arrangement  106 . 
     The springs  108  and  110  may sit inside a spring shell  111  that is formed from a spring shell portions  111   a,    111   b,    111   c  and  111   d.  In the example shown, the spring shell  111  forms part of the pulley  104 . The outer springs  108  each have a first spring end  108   a  and a second spring end  108   b,  while the inner springs  110  each have a first spring end shown at  110   a  and a second spring end  110   b.    
     In the example shown, the shaft adapter  102  has a spring driver member  112  that has a plurality of first adapter spring drive surfaces  114  and second adapter drive surfaces  115  thereon for engagement with the springs  108  and  110 . The pulley  104  includes a plurality of first pulley spring drive surfaces  116  and second pulley spring drive surfaces  117 , for engagement with the ends  108   a  and  110  of the springs  108  and  110 . 
     In the first mode described above for the accessory drive system  11 , torque is applied to the pulley  104  from the belt  52  and may then be transferred from the pulley  104  through the spring arrangement  106  into the shaft adapter  102 , and finally from the shaft adapter  102  into the drive shaft  54   a.  In the second mode described above, torque is applied to the shaft adapter  102  from the drive shaft  54   a  of the MGU  54  ( FIG. 1 ) and is applied from the shaft adapter  102  through the spring arrangement  106  to the pulley  104 , and from the pulley  104  to the belt  52 . In the first mode, torque is transmitted from the first pulley spring drive surfaces  116  to the first spring ends  108   a  (and  110   a  if the torque is sufficiently high), and from the second spring ends  108   b  (and  110   b  if the torque is high enough) to the first adapter spring drive surfaces  114 . In the second mode, torque is transmitted from the second adapter spring drive surfaces  117  to the first spring ends  108   a  (and  110   a  if the torque is sufficiently high), and from the second spring ends  108   b  (and  110   b  if the torque is high enough) to the second pulley spring drive surfaces  115 . 
     The pulley  104  moves rotationally relative to the shaft adapter  10  in one direction or the other based on which way torque is being transferred. A bushing  118  may be provided between a pulley rotation surface  120  and a shaft adapter rotation surface  122 . 
     Other components such as a dust cover, thrust washers, damping members, bushings and the like, are shown and may be provided as necessary for the operation of the pulley device  10 . Apart from the description below relating to the structure of the shaft adapter  102  and its mounting to the drive shaft  54   a,  a suitable pulley device may, for example be as shown and described in PCT publication WO201206193A1 (which shows a helical torsion spring), or as shown and described in PCT publication WO2015027325A1 (which shows arcuate helical compression springs), the contents of both of which are incorporated fully herein by reference. 
     The shaft adapter  102  and the drive shaft  54   a  are described below in further detail. 
     Reference is made to  FIGS. 4-15 . The drive shaft  54   a  is shown in  FIG. 4  in section and the completed assembly of the drive shaft  54   a  and the pulley device  10  is shown in section in  FIG. 15 . The drive shaft  54   a  has a shaft axial end  150 , a shaft shoulder  152 , a first shaft connection structure  154  and a second shaft connection structure  156 . The first shaft connection structure  154  may include an outside surface of the shaft  54   a  and may be threaded with, for example, a right hand thread (as is typical for threaded elements). The thread itself is not shown in  FIG. 4 , but is shown in  FIG. 5 . The second shaft connection structure  156  may be the face at the axial end  150  of the drive shaft  54   a.  The drive shaft  54   a  may further include a shaft tool receiving structure  158 , which may, for example, be a hex-shaped aperture at the axial end  150 , which receives a shaft tool  159  ( FIG. 8 ). 
     For simplicity the pulley  10  is shown as a single solid item in  FIGS. 5-15 . As a result, it includes a pulley  160  and a shaft adapter  162  that are integral with one another. It will be understood however, that the pulley device  10  could be as shown in  FIGS. 2 and 3 , for example (or as in the aforementioned PCT publications) and could therefore include a pulley and a shaft adapter that are separate from one another and that transfer torque to one another through a spring arrangement. 
     The shaft adapter  162  has a bore  166  extending from a first axial end  168  of the shaft adapter  162  to a second axial end  170  of the shaft adapter  162 . The pulley device  10  further includes a shaft adapter shoulder  172  proximate the first axial end  168 , a first shaft adapter connection structure  174  that is in the bore  166 , and a second shaft adapter connection structure  176 . The first shaft adapter connection structure  174  is threaded and is configured to mate with the first shaft connection structure  154  (and which may therefore also have a right hand thread), so as to form a first, non-destructively releasable connection between the shaft adapter  162  and the shaft  54   a  as shown in  FIG. 5 . With their thread, relative rotation of the shaft  54  and the shaft adapter  162  in a first rotational direction (e.g. turning the shaft adapter  162  clockwise relative to the shaft  54   a  in the view shown in  FIG. 5 ) tightens the first connection therebetween, while relative rotation of the shaft  54  and the shaft adapter  162  in a second rotational direction (e.g. turning the shaft  54   a  clockwise relative to the shaft adapter  162  in the view shown in  FIG. 5 ), loosens the connection therebetween. 
     The second shaft adapter connection structure  176  may be threaded also, and may be an extension of the first shaft adapter connection structure  174 , which facilitates manufacture of the shaft adapter  162 . As shown in  FIG. 15 , the second shaft adapter connection structure  174  and the second shaft connection structure  154  are engaged with one another (indirectly, through a jam nut  180 ) to provide a second connection between the shaft adapter  162  and the shaft  54   a.  In the embodiment shown in  FIGS. 4-15 , the second connection is, like the first connection, non-destructively releasable. 
     In the example shown in  FIGS. 4-15 , the jam nut  180  has a first jam nut connection structure  182  (e.g. a threaded portion) that engages the second shaft adapter connection structure  174 , and a second jam nut connection structure  184  (e.g. an axial end face  186 ) that engages the second shaft connection structure  154 . 
     The shaft adapter  162  may further include a shaft tool receiving structure  178 , which may, for example, include a toothed portion that engages a shaft adapter tool  179  ( FIG. 7 ) that has a mating toothed portion. The use of the shaft and shaft adapter tool receiving portions  158  and  178  permit elements to be tightened or loosened relative to one another as needed during assembling or disassembling of the assembly. In the embodiment shown in  FIGS. 4-15 , the jam nut  180  further includes a jam nut tool receiving structure  188  (e.g. a hex-shaped aperture) that is shaped to receive a jam nut tool  189  ( FIG. 12 ). 
     Reference is made to  FIG. 15 a   , which shows the shaft adapter  162  and the shaft  54   a.  Shown in  FIG. 15 a    are some torque values that can be used in some embodiments at different stages of assembling, and some forces that exist in the assembly at different stages of assembling. As can be seen, after the assembly has been completed, the shaft adapter shoulder and the shaft shoulder are engaged with one another to generate a selected compression force therebetween. There is a selected amount of combined resistance in the first and second connections to relative rotation in the second direction (i.e. the direction that would loosen the first connection). This combined resistance, which is shown at  200 , is generated by the first and second connections and the compression force. In the example shown, the combined resistance is about 100 Nm. It will be noted that, while some resistance to rotation in the second direction is provided by the second connection formed via the jam nut  180 , the jam nut  180  also helps the resistance to rotation in the second direction because it is less prone to movement vibration relative to the shaft adapter  162 , due to the large discrepancy in size between them. Thus, it is less likely to unthread itself during any vibration or the like. As a result, it helps to keep an axial force between the shaft  54   a  and the shaft adapter  162 , which in turn inhibits elimination of the axial forces (resulting from the compression force between the shoulders  152  and  172  that keeps the threaded connection portions  154  and  174  well engaged and therefore resistant to relative rotation in the loosening direction. 
     It will be observed that the compression force the shoulders  152  and  172  directly generates a first amount of resistance in the first connection to relative rotation in the second direction, and a second amount of resistance to relative rotation in the second direction at the second connection, since the compression force is distributed through the engagement of the threads in the first and second connections, which provides a normal force to generate frictional resistance to turning in the circumferential directions (both the first and second directions). 
     As can be seen for the compression force curve shown at  230  in  FIG. 15 a   , the compression force at the shoulders  152  and  172  is high, and is distributed partially along the length of the first connection (see curve portion  232 ) and is distributed further along the length of the second connection (see curve portion  234 ). 
     As can be seen in the torque curve shown at  220 , there is some frictional resistance to relative rotation in the second direction (shown at  222 ) at the surfaces  152  and  172 , some further resistance to relative rotation in the second direction (shown at  224 ) along the length of the first connection, and some further resistance to relative rotation in the second direction (shown at  226 ) along the length of the second connection, which are all the direct result of the amount of compression force in the shaft adapter  162 . Thus, the combined resistance to relative rotation in the second direction includes the first and second amounts of resistance (at the first and second connections). As can be see, the combined resistance to relative rotation in the second direction also includes the frictional resistance at the shoulders  152  and  172 . 
       FIGS. 4-15  illustrate a method of assembling the assembly formed by the shaft  54   a  and the shaft adapter  162  and therefore of the assembly formed by the shaft  54   a  and the pulley device  10 . With reference to  FIG. 4 , the shaft  54   a  is shown in isolation. In a step shown  FIG. 5 , the shaft adapter  162  is mounted to the shaft  54   a  by inserting the shaft axial end  150  into the bore  166  and causing relative rotation between the shaft  54   a  and the shaft adapter  162  in the first direction to engage the first shaft adapter connection structure  154  and the first shaft connection structure  174  with one another to provide the first connection. Another step includes engaging the second shaft adapter connection structure  176  and the second shaft connection structure  156  with one another to provide the second connection. Another step includes generating a selected amount of axial compression force (i.e. compression force shown in curve  230 ) between the shaft adapter shoulder  172  and the shaft shoulder  152 . As noted above, although worded differently, the aforementioned three steps together generate a selected amount of combined resistance in the first and second connections to relative rotation between the shaft  54   a  and the shaft adapter  162  in the second direction. In relation to  FIGS. 4-15 , the second step noted above may include engaging the second shaft adapter connection structure  154  with the jam nut  180 . 
     It will be noted that the step noted above relating to generating of the compression force occurs during the steps where the first and second connection structures are engaged to form the first and second connections. 
     In the particular embodiment shown in  FIGS. 4-15 , in order to tighten the first connection sufficiently, the shaft tool  159  and the shaft adapter tool  179  are inserted through the bore  166  and are used to rotate the shaft  54   a  and the shaft adapter  162  as needed in the first direction. At this point, the jam nut  180  is still loose.  FIG. 7  illustrates the insertion of the shaft adapter tool  179  so as to engage the shaft adapter  162 .  FIG. 8  illustrates the insertion of the shaft tool  159  through an aperture in the shaft adapter tool  179 .  FIG. 9  illustrates the relative rotation carried out on the tools  159  and  179 . The torque applied to the shaft adapter  162  along its length in  FIG. 9 , is represented by a torque curve  240  in  FIG. 15 a   . The total applied torque may be, for example about  120  to about 130 Nm. This results in a compression curve  241  shown in  FIG. 15 a   . As can be seen the compression force at the shoulders  152  and  172  is high and is distributed only over the first connection as shown by curve portion  242 . The compression force results in a torque resistance curve  250  that shows a combined torque resistance  251  that includes a first torque resistance  252  that is analogous to the torque resistance shown at  222  in the curve  200 , and a first torque resistance  254  that is analogous to the torque resistance  224  in the curve  200 . In other words, when the jam nut  180  is loose, only the frictional resistance at the shoulders  152  and  172 , and the frictional resistance along the threads of the first connection contribute to the total torque resistance. For greater clarity, the term torque resistance means the same thing as the resistance to relative rotation in the second direction. As can be seen, the torque resistance may be about 100 Nm. 
       FIG. 10  illustrates removal of the tool  159 .  FIG. 11  illustrates insertion of the jam nut tool  189 . The jam nut  180  may be alternatively referred to as a fastener and the tool  189  may be referred to as a fastener tool.  FIG. 12  illustrates relative rotation (in the first direction) of the jam nut  180  and the shaft adapter  162  so as to drive the jam nut  180  tightly against the second shaft connection structure  154  and therefore against the second shaft adapter connection structure  174 . The torque applied to the shaft adapter  162  as a result of using the tools  179  and  189  is shown at torque curve  260 . The torque applied by the tools  179  and  189  may be about 60 to about 70 Nm. Once the tools  189  and  179  are removed ( FIGS. 13 and 14  respectively), an end plug  190  ( FIG. 15 ) may be inserted in the bore  166  to inhibit entry of dust or other contaminants. The compression force curve and the torque resistance curves at this stage are shown at  230  and  200  respectively. The assembly is completed as shown in  FIG. 15 . If no end plug  190  is used, the assembly is completed as shown in  FIG. 14 . 
     The disassembling of the assembly formed in  FIG. 15  is carried out easily by reversing the actions carried to create the assembly. Thus the end plug  190  is removed, the tools  179  and  189  are used to rotate the jam nut  180  and the shaft adapter  162  in the second direction, and finally the tools  179  and  159  are used to rotate the shaft  54   a  and the shaft adapter  162  in the second direction until the shaft adapter  162  is removed from the shaft  54   a.    
       FIGS. 16 and 17  illustrate another embodiment of the present disclosure.  FIG. 16  shows the isolator  100  in an assembled state as opposed to the exploded view shown in  FIG. 3 , but in cutaway so that the positional relationship between the elements making up the isolator  100  can be seen, whereas they are hidden in  FIG. 2 . 
     Also,  FIG. 16  shows different second connection structures  154  and  174  for providing the second connection. In the embodiment shown in  FIG. 16 , the fastener shown at  300  is not a jam nut but is instead a different type of fastener. The fastener includes a first fastener connection structure  302  (shown more clearly in  FIG. 17 ) that is a soft metallic layer, and a second fastener connection structure  304  that is a hex-shaped projection. The fastener  300  is pressed into the bore  166  such that the first connection structure  302  deforms and forms around the teeth that make up the shaft adapter tool receiving structure  178  and such that the hex-shaped projection snugly engages the shaft tool receiving structure  158 . As a result, the second connection formed via the fastener  300  prevents any relative rotation in the second direction. However, it will be noted that the second connection shown in  FIG. 16  is not a non-destructively releasable connection. To release such a connection, the fastener  300  may have to be drilled out. 
     As can be seen, the second connection structures  154  and  174  are also the tool receiving structures  158  and  178 . 
       FIG. 17  shows the second connection as a side view, and shows the pulley device  10  as a solid pulley  99  instead of the isolator  100  shown in  FIG. 16 . 
       FIGS. 18 and 19  illustrate another embodiment of the present disclosure.  FIG. 18  shows the isolator  100 , whereas  FIG. 19  shows the solid pulley  99 . As shown in  FIGS. 18 and 19 , the second shaft connection structure  154  has a left handed thread (i.e. a thread having the opposite orientation to the thread in the first shaft connection structure  152  (which is also the shaft tool receiving structure  158 ). A transfer member  350  is slid into place axially in abutment with the axial shaft end  150 . The transfer member  350  has a first transfer member connection structure  351  that is toothed and mates with the toothed shaft adapter tool receiving structure  178 . Thus the shaft adapter tool receiving structure  178  is also the second shaft adapter connection structure  174 . The fastener shown at  352  has a first fastener connection structure  354  that engages a second transfer member connection structure  356 . The fastener further includes a second fastener connection structure  358  that is a left handed thread (i.e. the same thread orientation as the connection structure  152 ) and engages with the connection structure  152 . The transfer member  350  has a third transfer member connection structure  360  that engages the axial end  150  of the shaft  54   a.  This arrangement forms the second connection between the shaft  54   a  and the shaft adapter  162 . The second connection in this embodiment is a non-destructively releasable connection. 
     Reference is made to  FIGS. 20-21  which show another embodiment. In this embodiment, the second shaft connection structure  154  includes a shaft press-fit surface  155  that is a portion of an outer surface of the shaft  54   a,  and the second shaft adapter connection structure  174  includes a shaft adapter press-fit surface  175  that is an inner surface in the bore  166 . In this embodiment, the second method step described above includes inserting the shaft press-fit surface  155  into the bore  166  to mate with the shaft adapter press-fit surface  175 . 
     In this embodiment, the second connection formed by the second connection structures  154  and  174  is non-destructively releasable. Furthermore, the second connection is not dependent on the axial compression force generated at the shoulders  152  and  172 . 
     In this embodiment, the method of assembling the assembly is illustrated in  FIGS. 20-21 . More specifically, the first two steps described above occur at the same time, however, during these two steps, but prior to the third step where the axial compression force is generated (i.e. prior to engagement between the shoulders  152  and  172 , the following steps are carried out. As a selected point during insertion of the axial shaft end  150  into the bore  166  such that partial engagement of the first connection structures  152  and partial engagement of the second engagement structures  154  and  174  has taken place, the method entails measuring a torque needed to continue carrying out the first two steps described above. In other words the torque required to continue rotating the shaft  54   a  and shaft adapter  162  in the first direction is measured. The method further includes only continuing to carry out the first two steps (i.e. continuing to rotate the shaft  54   a  and shaft adapter  162  in the first direction to further engage them) when the torque measured is within a selected range. The selected range may be, for example, between about 10 Nm and about 60 Nm. The selected point referred to above, may be when about three threads of the first shaft adapter connection structure  172  engage about three threads of the first shaft connection structure  152 . If the torque measured is in the selected range, the connection structures may be fully engaged and the shoulders  152  and  172  may be engaged ( FIG. 21 ). Thus, the compression force is generated and the combined torque resistance is provided by the first torque resistance at the first connection, the second torque resistance at the second connection and the third torque resistance at the engaged shoulders  152  and  172 . 
       FIG. 22  shows a variant in which the second connection structure  154  on the shaft  54   a  is proximally located relative to the shoulder  152 . The distal end of the shaft is the axial shaft end  150 . 
     While the above description constitutes a plurality of embodiments of the present invention, it will be appreciated that the present invention is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.