Patent Publication Number: US-2022235852-A1

Title: Tooth jump protection device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority pursuant to 35 U.S.C. 119(e) to U.S. Provisional Patent Application Nos. 63/140,448, filed Jan. 22, 2021, and 63/218,129, filed Jul. 2, 2021, which applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     The present invention relates to chain slack buildup, and more specifically to devices which control the location of chain slack buildup. 
       FIGS. 1 a  and 1 b    shows an approximate location of the slack accumulation relative to a driven sprocket  6  and a drive sprocket  2  of a conventional chain system  1 , respectively. The drive sprocket  2  is connected to the driven sprocket  6  via a toothed chain  8 . The chain  8  meshes with the sprockets  2 ,  6 , transmitting rotary motion between the sprockets  2 ,  6 . A chain  8  can jump on either the driven sprocket  6  or the drive sprocket  2  of a chain system  1 . Jumping of the chain  8  near the driven sprocket  6  results in a chain  8  with a lower jump torque and jumping of the chain  8  near the drive sprocket  2  results in a higher jump torque of the chain  8 . Therefore, forcing jumps to only occur on the drive sprocket  2  allows a chain&#39;s jump torque performance to be higher. There are specific locations in which chain slack collects relative to the driven or drive sprocket  6 ,  2 , determining which sprocket the chain  8  will mostly likely jump.  FIG. 1 a    shows the slack accumulation occurring at the driven sprocket  6 , indicated by reference number  30  and  FIG. 1 b    shows the slack accumulation occurring at the drive sprocket  2 , indicated by reference number  32 . 
     SUMMARY 
     According to one embodiment of the present invention, a tooth jump protection device is used to control chain slack and delay the torque at which chain jump occurs, thus increasing jump torque performance 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 a    shows a schematic of an approximate location of slack accumulation relative to the driven sprocket in a conventional chain system. 
         FIG. 1 b    shows a schematic of an approximate location of slack accumulation relative to the drive sprocket in a conventional chain system. 
         FIG. 2  shows a schematic of a vertically mounted drive system. 
         FIG. 3  shows a schematic of an embodiment of a tooth jump protection device (TJPD). 
         FIG. 4  shows a schematic of another embodiment of a TJPD. 
         FIG. 5  shows a detailed view of the TJPD of  FIG. 4 . 
         FIG. 6  shows a sectional view of a TJPD as a fixed position compliant roller within a transfer case. 
         FIG. 7  shows a detailed view of a TJPD with a compliant roller. 
         FIG. 8 a    shows a schematic of a TJPD of a ramped snubber engaged with a chain within a transfer case. 
         FIG. 8 b    shows a schematic of the TJPD of the ramped snubber when tension is applied to the opposite chain strand. 
         FIG. 9  shows a prior art snubber engaged with a chain. 
         FIG. 10  shows another embodiment of a TJPD. 
         FIG. 11 a    shows a schematic of snubber placed at a specific distance relative to the driven sprocket and a specific gap relative to the chain. 
         FIG. 11 b    shows slack accumulation relative to the snubber of  FIG. 11   a.    
         FIG. 12  shows a view of a TJPD with a snubber mounted within a transfer case. 
         FIG. 13  shows a schematic of a TJPD of a compliant roller which is spring biased toward engagement with a chain. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment of the present invention, a tooth jump protection device (TJPD), can be used to control chain slack within a transfer case, such that the chain slack only builds on the drive sprocket resulting in a higher jump torque. A higher jump torque capability allows for reduced chain width. 
     In the system layout of  FIG. 2 , the drive and driven shafts  103 ,  104  associated with the drive and driven shafts  2 ,  6 , respectively, are shown in a vertical orientation with the driven sprocket  6  on the bottom and the drive sprocket  2  on the top within a transfer case  107 . A chain  8  connects the drive sprocket  2  to the driven sprocket  6 . Between the drive sprocket  2  and the driven sprocket  8 , the chain has a slack strand  8   b  and a tight strand  8   a.  As the transfer case approaches a vertical orientation, gravity encourages slack to build on the interface between the driven sprocket  6  and the chain  8  within the transfer case  107 . Studies of the tooth jump and the slack of the chain in this system layout were conducted using a rigid guide or tooth jump protection device (TJPD)  120  placed at the entrance of the slack strand  8   b  meshing with the driven sprocket  6  at various radial offsets. Through the studies conducted, it was determined that the TJPD device  120  preferably needs to be positioned a distance radially away from the sprocket center to avoid interference with the chain&#39;s natural engagement with the sprocket. This positioning increases as the chain wears. The distance will vary depending on the system layout, chain design and point of life of the chain. 
     The TJPD  120  preferably provides a sufficient load to keep the chain  8  engaged on the driven sprocket  6 , with the sufficient load based on stiffness requirements. The stiffness requirements of the TJPD  120  are dependent on application peak torque, radial offset of the TJPD  120 , and chain type and design. As the applied torque increases, the required load from the TJPD  120  to maintain proper engagement also increases. As the chain  8  moves radially outward and deflects the TJPD  120 , the required force from the TJPD  120  to maintain driven sprocket engagement increases. In terms of the chain type and design, links of the chain that have steeper flank pressure angles will require less force from the TJPD  120 . It is noted that the TJPD  120  must be flexible enough to survive a catastrophic driven sprocket jump, in the event that the chain  8  was to wedge between the driven sprocket  6  and the TJPD  120 . 
       FIG. 2  shows the transfer case in a vertical position, but the system can be orientated in any angle within the application. The TJPD  120  is located at the entrance of the driven sprocket  6 . More specifically, the TJPD  120  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ). 
     In one embodiment, one-piece, fixed position TJPDs  130   a,    130   b  are placed at the driven sprocket  6 . The TJPD  130   a,    130   b  are at the entrance and/or exit of the driven sprocket  6  regardless of the transfer case orientation angle. More specifically, TJPD  130   a  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ) and the TJPD  130   b  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
     The one-piece fixed position TJPD  130   a,    130   b  has a body  131  which is produced from plastic, steel or aluminum and has a flat chain face  132  which interacts with the chain  8  that can include an elastomer coating. The one-piece fixed position TJPDs  130   a,    130   b  can be a snubber which is bolted to the transfer case  107  relative to the chain  8  and the driven sprocket  6 . The thickness of the elastomer coating can vary based on the chain and design layout. Furthermore, the body  131  and/or the thickness of the elastomer coating of the TJPDs  130   a,    130   b  on opposite sides of the driven sprocket  6  can be the same or different. 
       FIGS. 4-5  show another embodiment of a TJPD  175  mounted to the transfer case  107  and adjacent the chain  8  and the driven sprocket  6 . In this embodiment, the TJPD  175  is a an “L-shaped” one-piece multi-faceted ramp  140  with a mounting bracket  141 . The mounting bracket  141  may be integrally formed with the multi-faceted ramp  140 . In one embodiment, the mounting bracket  141  and the one-piece multi-faceted ramp  140  are formed from a single sheet of steel. The mounting bracket  141  is at approximately a 90 degree angle relative to a first flat face  142  of the multi-faceted ramp  140 . In other words, the mounting bracket is the vertical portion of an “L” and the multi-faceted ramp  140  is the horizontal portion of the “L”. The multi-faceted ramp  140  is preferably flexible and has a smooth contour. 
     The multi-faceted ramp  140  is comprised of a first flat surface  142  at approximately 90 degrees to the mounting bracket  141 , a first transition ramp  143 , an angled ramp  144 , a second transition ramp  145  and a second flat surface  146 . The second flat surface  146  has a face  146   a  which is offset from the chain  8  by a small gap  147  when installed. As the chain  8  wears or elongates, the gap  147  decreases and contact between the chain  8  and the face  146   a  is possible during normal operation of the chain  8 . As the chain  8  rotates, and a tooth jump occurs, the face  146   a  of the second flat surface  146  TJPD  175  applies a reaction force on the chain  8  to keep the chain  8  engaged with the driven sprocket  6  and to prevent chain slack buildup on the driven sprocket  6 . 
     Alternatively, the multifaceted ramp  140  can include offset flat planes with a cantilever between the offset flat planes. More specifically, the multifaceted ramp  140  can include a first flat face  142 , a second flat face  146  and an angled ramp  144 , without transition ramps  143 ,  145 . The angled ramp  144  is preferably flexible and has a smooth contour. 
     The face  146   a  can contain plastic or an elastomer face to minimize noise, vibration, and harshness (NVH) concerns and improve wear resistance of the TJPD  140 . The TJPD  140  is preferably mounted such that the face  146   a  of the second flat surface  146  is placed at the driven sprocket  6  and/or the drive sprocket  2  along a diameter and located at the entrance and/or exit of the driven sprocket  6  or the driving sprocket  2  regardless of orientation angle of the transfer case. More specifically, at least a first TJPD  140  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ). A second TJPD  140  can be located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
     Alternatively, the TJPD  140  can include a stop  180  as shown in  FIG. 10 . In this embodiment, a stop  180  is mounted to the mounting bracket  141 . The stop  180  is preferably placed adjacent the first transition ramp  143  of the multi-faceted ramp  140 . The stop  180  may be a tab or other such protrusion. The stop  180  may be integrally formed with the mounting bracket  141 . 
     The addition of the stop  180  reduces bending of the entire multi-faceted ramp  140  at the point of connection  191  between the multi-faced ramp  140  and the bracket  141 . Additionally, the stop  180  reduces bending at the first transition ramp  143  so that stress on the multi-faceted ramp  140  is more evenly distributed. 
       FIG. 6  shows an embodiment in which the TJPD  190   a,    190   b  is a fixed position roller. Each TJPD  190   a,    190   b  includes a bolt  195  fixedly mounted to the transfer case  107 . Surrounding and freely spinning on the bolt  195  is a rolling element  196 . The rolling element  196  preferably has an elastomer coating. 
     The TJPDs  190   a,    190   b  are placed at the driven sprocket  6 . The TJPD  190   a,    190   b  are at the entrance and/or exit of the driven sprocket regardless of the transfer case orientation angle. More specifically, TJPD  190   a  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ) and the TJPD  190   b  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
       FIG. 7  shows an embodiment in which the TJPD  180  is a ramped roller TJPD. The TJPD  180  is mounted within a transfer case  107  and adjacent the chain  8  and the driven sprocket  6 . 
     The mounting brackets  151  are at approximately a 90 degree angle relative to a first flat face  152  which transitions to a first transition ramp  153 , an angled ramp  154  and to a compliant roller holder  155  which receives a compliant roller  156 . In other words, the mounting bracket is the vertical portion of an “L” and the first transition ramp  153  is the horizontal portion of the “L”. The angle of the mounting of the bracket  151  relative to the compliant roller  156  may be any angle which both mounts the TJPD  150   a,    150   b  to the transfer case  107  and allows the compliant roller  156  to engage with the chain  8 . 
     The TJPD  180  is preferably mounted such that the face compliant rollers  156  are placed at the driven sprocket  6  and/or the drive sprocket  2  along a diameter and located at the entrance and/or exit of the driven sprocket  6  or the driving sprocket  2  regardless of orientation angle of the transfer case. More specifically, at least a first TJPD  180  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ). A second TJPD  180  can be located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
     The face compliant roller  156  may be made of plastic. Alternatively, the face compliant roller  156  may be made of plastic or other material and coated with an elastomer to reduce wear. The face compliant roller  156  can be a single roller mounted to the compliant roller holder  155  or multiple different rollers mounted on either side of the compliant roller holder  155  as shown in  FIGS. 7 and 13 . 
     In an alternate embodiment, shown in  FIG. 13 , the TJPD  170  with face compliant roller  156  is spring  157  biased towards engagement with the chain  8  to further focus the accumulation of system slack at specific locations of the drive or driven sprocket  2 ,  6  to lower contact forces. The face compliant roller  156  is received on a compliant roller holder  155  which is integral with an arm  159 . The face compliant roller  156  has a reduced amount of friction relative to the chain  8  in comparison to the chain sliding across a conventional tensioner arm. 
     The arm  159  is pivotably attached to the mounting bracket  151  via pivot pin  158  received within a pivot hole  168  of the arm  159  at a second end  159   b  of the arm  159  opposite of the compliant roller holder  155  at the first end  159   a.  The pivot pin  158  is mounted to the mounting bracket at a 90 degree angle. The arm  159  is preferably rigid. 
     A spring  157  is present between the first end  159   a  of the arm  159  and the bracket  151  to bias the arm  159  and thus the face compliant roller  156 . The spring forces for each sprocket  2 ,  6  or the entrance and exit of the chain  8  from either of the driven sprocket  6  or the drive sprocket  2  may be different or the same. The spring  157  may be a torsional spring, a blade spring or other type of spring. The use of the spring  157  increases the compliance allowing for reduced contact forces. Furthermore, the spring  157  used can have a limited stroke range, such that in a first position, the spring  157  biases the face compliant roller  156  such that the face compliant roller  156  does not engage with the chain  8  and a clearance is present between the face compliant roller  156  and the chain  8 . When the chain  8  contacts the face compliant roller  156  with enough force to overcome the preload of the spring, the face compliant roller  156  moves to a second position by rotating the arm  159  connected to compliant roller holder  155 , such that the arm  159  pivots via pivot pin  158  relative to the mounting brocket  151 . The spring preload is used to prevent tooth jump of the chain. The spring load is preferably tuned to the required force to prevent tooth jump and therefore reduce or prevent chain slack from building at the driven sprocket  6 . 
     The TJPD  170  is preferably mounted such that the face compliant roller  156  is placed at the driven sprocket  6  and/or the drive sprocket  2  along a diameter and located at the entrance and/or exit of the driven sprocket  6  or the driving sprocket  2  regardless of orientation angle of the transfer case. More specifically, at least a first TJPD  170  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ). A second TJPD  170  can be located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
       FIGS. 8 a -8 b    shows another embodiment of TJPD. In this embodiment, the TJPD is a biased snubber  160 . The biased snubber  160  is mounted to the drivetrain transfer case  107 . The biased snubber  160  has a body  161  with a first end  162 , a second end  163  opposite the first end  162  with a length L between the first end  162  and the second end  163 , a snubber face  164 , and a second face  165 , opposite the snubber face  164 . Along the snubber face  164  an intended angle α (alpha) is present between the first end  162  and the second end  163  relative to a straight line  193  extending from the first end  162  to the second end  163  and parallel to the snubber face  164 . The intended angle α is between 0-5 degrees and more preferably, greater than 0 degrees. 
     The biased snubber  160  creates an intended angle α between the path of the chain  8  and snubber face  164 , such that an intended angle α is present between the chain path and the snubber face  164 . The snubber face  164  is shaped such that the snubber face  164  is closer to the chain  8  near the driven sprocket  6  as compared to the driving sprocket  2 . The intended a angle forces the chain slack to accumulate near the chain exit of the driving sprocket  2  as indicated by reference number  32 . The biased snubber  160  is fully outside of the chain path when the tension is applied to the adjacent chain strand as shown in  FIG. 8   a.    
     When tension is applied to the opposite chain strand, slack will accumulate on the chain strand adjacent to the biased snubber  160  and the intended angle α (alpha) of the biased snubber  160  forces the excess chain to accumulate in a known location that improves tooth jump as shown in  FIG. 8   b.  Therefore, slack accumulation is present only near the drive sprocket  2  and can be used to control chain slack within a transfer case, such that the chain slack only builds on the drive sprocket  2  resulting in a higher jump torque. A higher jump torque capability allows for reduced chain width. 
     It is noted that the biased snubber  160  can also be mounted a targeted distance relative to the driven sprocket and within a targeted or specific chain-to-snubber gap to prevent slack accumulation relative to the driven sprocket  6  and force slack accumulation near the drive sprocket  2  as described below relative to  FIGS. 11 a   - 11   b.    
       FIGS. 11 a -11 b    show an embodiment of a TJPD of a snubber  200  that is placed at a specific or targeted distance relative to the driven sprocket  6  and within a targeted or specific chain-to-snubber gap to prevent slack accumulation relative to the driven sprocket  6  and force slack accumulation near the drive sprocket  2 . The snubber  200  has a body  201  with a first end  202  and a second end  203  and a first face  205  and a second face  204 . The second face  204  is adjacent the chain  8 . Optionally, the second face  204  can include a pad or elastomeric surface to reduce noise vibration harshness (NVH) concerns. The snubber&#39;s location is positioned a gap distance g 1  away from the chain and biased a distance d 1  away from the driven sprocket  6 . These distances g 1 , d 1  are determined by the mounting location of the chain  8  and the sprockets  2 ,  6  relative to the transfer case  107 . 
     The snubber  200  is placed between the driven sprocket  6  and the drive sprocket  2  at a specific distance d 1  from a centerline C 1  of the driven sprocket  6  and also at a specific gap distance g 1  between the second face  204  and the chain  8 . In one example, the gap distance g 1  between the chain  8  and the snubber  200  is in a range between 0-7 mm. In another embodiment, the range can be 0-1 mm. In another embodiment, the range can be 0-2 mm. In yet another example, the gap distance g 1  is 0.5 mm or less. By setting a gap distance between the chain  8  and the snubber  200 , the contact forces and wear of the snubber  200  decreases. Using chain pitch lengths, the distance d 1  could be approximately two chain pitch lengths. For example, a 9.525 mm pitch chain, d 1  would be approximately 19 mm. For a 11.039 mm pitch chain, the distance d 1  would be approximately 22 mm. 
     When tension is applied to the opposite chain strand from which the snubber  200  is adjacent, slack will accumulate on the chain strand adjacent to the snubber  200  due to the gap distance g 1  and the distance d 1  forcing the excess chain to accumulate in a known location near the drive sprocket  2  resulting in a higher jump torque. The higher jump torque capability allows for reduced chain width to be used. 
       FIG. 9  shows a conventional or traditional snubber. The traditional snubber  50  does not have an angle and instead is straight or approximately 180 degrees between the first end  51  and the second end  52  across the length, such that the entire snubber face  53  interacts with the chain strand  8  and a minor gap of approximately 0.1 mm is present between the traditional snubber  50  and the chain. Slack accumulates near the drive sprocket  2  at the position indicated by reference number  32  as well as near the driven sprocket  6  indicated by reference number  30 . Therefore, slack is permitted to accumulate near both the drive sprocket  2  and the driven sprocket  6 , and tooth jump may occur on either sprocket. 
       FIG. 12  shows a TJPD  300  mounted to the transfer case  107  and situated adjacent the chain  8  and the driven sprocket  6 . In this embodiment, the TJPD  300  is a one-piece multi-faceted ramp  310  with a mounting bracket  301  and snubber  302 . 
     The mounting bracket  301  may be integrally formed with the multi-faceted ramp  310 . Additionally, the mounting bracket  301  may be integrally formed with snubber  302 . 
     The snubber  302  has a first flat face  302   a  and a second, opposite flat face  302   b  adjacent the chain  8 . Attached to the second flat face  302   b  is a pad or elastomer pad  303 . The pad  303  contacts the chain  8 . 
     Also attached to the mounting bracket  301  is a multi-faceted ramp  310 . The multi-faceted ramp  310  has a first body portion  304  with a flat face connected to the mounting bracket  301  and a ramped second body portion  305 . The ramped second body portion  305  is connected to a first transition ramp  306 , which is connected to a first flat surface  307 . Attached to a face  307   a  of the second flat surface  307  is a pad or elastomer face  309 . 
     The pad  309  is offset from the chain  8  by a small gap when installed. For example, the gap between the pad  309  and the chain  8  is between 0.5-1.5 mm. As the chain  8  wears or elongates, the gap decreases and contact between the chain  8  and the pad  309  is possible during normal operation of the chain  8 . As the chain  8  rotates, and a tooth jump occurs, the pad  309  of the TJPD  300  applies a reaction force on the chain  8  to keep the chain  8  engaged with the driven sprocket  6  and to prevent chain slack buildup on the driven sprocket  6 . The pad  303  maintains contact with the chain  8  during normal operation of the chain. The pad  303  acts like a snubber to attenuate chain resonance and contacts the chain when the chain enters a resonance condition. 
     The TJPD  300  is preferably mounted such that the pad  309  of the multi-faceted ramp  310  is placed at the driven sprocket  6  or the drive sprocket  2  along a diameter of the driven sprocket  6  or the drive sprocket  2  and located at the entrance and/or exit of the driven sprocket regardless of the transfer case orientation angle. 
     More specifically, at least a first TJPD  300  is located at a position in which the chain  8  is tangent to the driven sprocket  6  at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ). A second TJPD  300  can be located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
     In one embodiment, the mounting bracket  301  and the snubber  302  are formed from a single sheet of steel. The mounting bracket  301  is at approximately a 90 degree angle relative to a first flat face  302   a  of the snubber  302 . 
     The snubber  302  of the TJPD  300  provides an additional reduction of noise vibration and harshness (NVH) to reduce by controlling strand resonance associated with the chain system, while the multi-faceted ramp  310  of the TJPD  300  limits slack accumulation on the driven sprocket  6 . 
     While two TJPD  130 ,  140 ,  150 ,  160 ,  170 ,  180 ,  190   200 ,  300  are shown on either side of the driven sprocket  6 , a single TJPD may be placed a specific or targeted distance relative to the driven sprocket  6 . 
     In another embodiment, either a single TJPD or two TJPD can be shown on either side of a driving sprocket  2  to force slack accumulation to occur on the driven sprocket  6 . 
     While not shown, in an alternate embodiment, the two TJPD devices mounted along a diameter of the driven sprocket and/or driving sprocket can be different devices. Any combination of TJPDs disclosed within the application can be present on the entrance and exit of the chain from the driven sprocket  6 . Therefore, the first TJPD at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ) can be the same or different than a second TJPD located at a position in which the chain  8  is tangent to the driven sprocket  6  at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain (e.g. the exit of the chain  8  from the driven sprocket  6 ). 
     For example, one piece fixed position TJPD  130  may be mounted at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ) and a second TJPD may be a L-shaped one piece multi-faceted ramp TJPD  140  mounted at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain. In another example, the fixed position compliant roller TJPD  150  can be mounted at the first engagement of the driven sprocket  6  with the slack strand  8   b  of the chain  8  (e.g. the entrance of the chain  8  onto the driven sprocket  6 ) and a second TJPD may be a snubber TJPD  300 , mounted at the last engagement of the driven sprocket  6  with the tight strand  8   a  of the chain. The examples above are not limiting, and other combinations are possible. 
     Furthermore, along the chain spans between the driven and driving sprockets, the TJPDs which are mounted on opposite chain strands can also differ. For example, one the TJPD can be a biased snubber TJPD  160  and the opposite TJPD mounted relative to the opposite chain strand is snubber TJPD  200 . The examples above are not limiting, and other combinations are possible. 
     In yet another embodiment, a single TJPD  130 ,  140 ,  150 ,  160 ,  170 ,  180 ,  190 ,  300  can be placed at the entrance of the slack strand  8   b  meshing with the driven sprocket  6 . 
     In yet another embodiment, a single TJPD  160 ,  200  is placed relative to one of the strands  8   a,    8   b  of the chain  8 . 
     In another embodiment, when the transfer case is installed in a horizontal position, the opposite midpoints correspond to a 12 o&#39;clock and 6 o&#39;clock position along a central diameter of the driven sprocket  6  and/or the drive sprocket  2 . The TJPDs of the above embodiments are installed at the opposite midpoints of the driven sprocket  6  and/or the drive sprocket  2 . 
     In another embodiment, when the transfer case is installed in a vertical position, the opposite midpoints correspond to at the 3 o&#39;clock and the 9 o&#39;clock of the driven sprocket  6  and/or the drive sprocket  2 . The TJPDs of the above embodiments are installed at the opposite midpoints of the driven sprocket  6  and/or the drive sprocket  2 . 
     Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.