Patent Publication Number: US-2022235851-A1

Title: Method(s) to apply tension to increase drivetrain jump torque capacity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority pursuant to 35 U.S.C. 119(e) to U.S. Patent Application No. 63/140,457, filed Jan. 22, 2021, which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention relates to chain tensioner, and more specifically to a chain tensioner for a drive system which increases jump torques. 
     A tensioning device, such as a hydraulic tensioner, is used as a control device for a power transmission chain, or similar power transmission devices in the engine timing system, as the chain travels between a plurality of sprockets. In this device, the chain transmits power from a driving shaft to a driven shaft, so that part of the chain is slack and part of the chain is tight. Generally, it is important to impart and maintain a certain degree of tension in the chain to prevent noise, slippage, or the unmeshing of teeth (tooth jump) in the case of a toothed chain. Prevention of such slippage is particularly important in the case of a chain driven camshaft in an internal combustion engine because jumping of teeth will throw off the camshaft timing, possibly causing damage or rendering the engine inoperative. 
     In the harsh environment of an internal combustion engine, various factors can cause fluctuations in the chain tension. For instance, wide variations in temperature and thermal expansion coefficients among the various parts of the engine can cause the chain tension to vary between excessively high or low levels. During prolonged use, wear to the components of the power transmission system can cause a decrease in chain tension. In addition, camshaft and crankshaft induced torsional vibrations cause considerable variations in chain tensions. Reverse rotation of an engine, occurring for example during stopping of the engine or in failed attempts at starting, can also cause fluctuations in chain tension. For these reasons, a mechanism is desired to remove excessive tensioning forces on the tight side of the chain and to ensure the necessary tension on the slack side of the chain. 
     Currently in engine timing systems, a snubber, guide or tensioner is used to tension at least one strand of the chain to improve noise, vibration and harshness (NVH), by controlling strand resonance. Such chain strand management is not however seen in the drivetrain transfer cases. 
     Tensioning devices have not been used in drivetrain transfer cases for a number of reasons. The prior art has taught that tensioning the slack strand to take up chain slack can delay tooth jump, which equates to high tensioning forces and result in a greater jump torque, however, a tensioning device constantly applying a load to at least one strand of the chain reduces the system efficiency, such that high tensioning force results in greater jump torque, but worsens system efficiency significantly. The benefits associated with the improved jump torque performance does not outweigh the sacrifice in efficiency as shown in prior art  FIG. 1  of jump torque (Nm) versus tensioning device spring load (N). As the tensioning device spring load increases, the jump torque improvement increases. The jump torque improvement is seen when the tensioning device spring load is greater than 65N and up through 220N. However, with an increase in the tensioning device spring load comes a decrease in system efficiency as shown in prior art graph  FIG. 2 . In  FIG. 2 , a system with no tensioner results in approximately a 99.3% system efficiency, whereas a 215 N spring, which has the greater jump torque results in approximately a 96.8% system efficiency, which is drastic. 
     SUMMARY 
     According to an embodiment of the present invention, a chain tensioning device combats natural build-up of chain slack. In controlling the chain slack, the torque at which a chain jumps occurs is delayed resulting in a higher jump torque performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a graph of a conventional tensioning device used in an engine timing system of jump torque (Nm) versus tensioning device spring load (N). 
         FIG. 2  shows a graph of a conventional drivetrain transfer case and associated efficiency depending on the spring load used. 
         FIG. 3 a    shows a schematic of an approximate location of slack accumulation relative to the driven sprocket. 
         FIG. 3 b    shows a schematic of an approximate location of slack accumulation relative to the drive sprocket. 
         FIG. 4  shows a schematic of a chain system with tensioning devices applied asymmetrically toward the driven sprocket. 
         FIG. 5 a    is a schematic of a chain system within a drivetrain transfer case including a first and a second multi-pivot torsion spring tensioners of a first embodiment. 
         FIG. 5 b    is a detailed view of a first multi-pivot torsion spring tensioner of  FIG. 5   a.    
         FIG. 5 c    is a detailed view of a second multi-pivot torsion spring tensioner of  FIG. 5   a.    
         FIG. 6  is a partial view of a drivetrain transfer case including a torsion spring tensioner of a second embodiment. 
         FIG. 7  shows a schematic of a chain system within a drivetrain transfer case including a blade spring tensioner of a third embodiment. 
         FIG. 8  shows a schematic of a chain system with a dual strand tensioner. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 3 a  and 3 b    shows an approximate location of the slack accumulation  30 ,  32  relative to a driven sprocket  6  and a drive sprocket  2  of a 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. Through testing, it was discovered that 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. Through testing it was determined that 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 jump.  FIG. 3 a    shows the slack accumulation occurring at the driven sprocket  6 , indicated by reference number  30  and  FIG. 3 b    shows the slack accumulation occurring at the drive sprocket  2 , indicated by reference number  32 . 
     Placement of at least one conventional tensioning device at specific places on the chain strands of the chain between the driven and drive sprockets in a transfer case can be used to force drive sprocket jumps, increasing the chain&#39;s jump torque rating, thus allowing narrower chains to be applied while maintaining the system&#39;s jump torque requirement. Therefore, forcing drive sprocket jumps for narrow chain and sprockets provides the advantages of reducing mass and reducing cost. For example, by forcing jumps to occur closer to the drive sprocket, the chain can be reduced in width by ¼ inch (6.35 mm). Therefore, in a conventional chain system with a chain requiring 1.5 inch wide chain (38.10 mm), application of a tensioning device of the current invention allows for narrower chain to be used, for example 1.25 inches (31.75 mm) in width. Differing application designs and requirements may allow for greater or less than the ¼ inch (6.35 mm) width reduction. Embodiments of the present invention can apply to chains which are between ½ inch (12.70 mm) to 2 inches (50.8 mm) in diameter. 
     Through additional studies it was determined that low force springs can force drive sprocket jumps when the tensioning device is applied asymmetrically towards the driven sprocket as shown in  FIG. 4 . In  FIG. 4 , a first tensioner device  40  with a single pivot point has a chain sliding surface  44  which can engage with a first strand  8   a  of the chain  8  and is mounted relative to the chain  8  at a first mounting position. In one embodiment, the first tensioner device  40  can be triangular in shape with the single pivot pin  42  being received at a pivot pin hole  54  at a central point opposite the chain sliding surface  44 . Opposite the first tensioner device  40  is a second tensioner device  48  with a single pivot point and a chain sliding surface  52  which can engage with the second strand  8   b  of the chain  8  and is mounted at a second mounting position. In one embodiment, the second tensioner device  48  can be triangular in shape with the single pivot pin  50  being received at a pivot pin hole  55  at a central point opposite the chain sliding surface  52 . The pivot pins  42 ,  50  are preferably mounted to the drivetrain transfer case. It is noted that the placement or mounting positions of the first and second tensioner devices  40 ,  48  is closer to the driven sprocket  6  than the drive sprocket  2 , such that the tension to either strand  8   a ,  8   b  of the chain  8  is being applied asymmetrically toward the driven sprocket  6 , thus allowing slack of the chain  8  to instead accumulate near the drive sprocket  2  at location  32  as in  FIG. 3   b.    
     Furthermore, with the tensioning force applied at the driven sprocket  6 , forcing the tooth jump to occur at the drive sprocket  2 , a low force spring, as applied to the tensioner devices is required, for example such that a 25 N torsion spring could be used resulting in approximately 98.9% efficiency, reducing the negative impact on system efficiency as shown in  FIG. 6 . Additionally, as conventionally known, tensioning a chain strand can improve NVH by controlling strand resonance. 
     In a preferred embodiment, a chain system in a drivetrain transfer case includes at least a chain with a drive sprocket, a driven sprocket, and at least one tensioning device. The chain, the drive sprocket, and driven sprocket have a ¼ in (6.35 mm) reduction on width compared to conventional chain systems in drivetrain transfer cases. The mass of the at least one tensioning device is less than the mass saved in the reduction to the chain, drive sprocket and driven sprocket. For example, if a conventional application requires a 1.5″ (38.10 mm) wide chain, the present invention uses a narrower 1.25″ (31.75 mm) width chain with the same efficiency. Differing application designs and requirements may allow for greater or less than a ¼″ (6.35 mm) width reduction. It is noted that the ¼ inch width reduction is related to generic chain size naming. Actual dimensions vary slightly. Furthermore, as the chain is narrowed, the sprockets can also be narrowed. 
       FIGS. 5 a   - 8  show chains systems within a drivetrain transfer case that include at least one tensioning device that reduced the size and mass of the chain system, while maintaining system efficiency, and without increasing cost. 
       FIGS. 5 a -5 c    shows schematics of a chain system within a drivetrain transfer case including first and second multi-pivot torsion spring tensioners of a second embodiment. The drivetrain transfer case  60  receives a drive sprocket  2 , a driven sprocket  6 , a chain  8 , a first multi-pivot torsion spring tensioner  61  and a second multi-pivot torsion spring tensioner  63 . The drive sprocket  2  is connected to the driven sprocket  6  via the toothed chain  8 . The chain  8  meshes with the sprockets  2 ,  6 , transmitting rotary motion between the two sprockets. 
     The first and second multi-pivot torsion spring tensioners  61 ,  63  each have a mounting bracket  62   a ,  62   b  with a pivot axle  64   a ,  64   b  extending perpendicular therefrom. 
     Each tensioner  61 ,  63  also includes an arm  68   a ,  68   b  that has a body  75   a ,  75   b  which includes a first plate  81   a ,  81   b  a second plate  82   a ,  82   b , and a pivot pin  70   a ,  70   b . The first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  of each arm  68   a ,  68   b  each have a first end  67   a ,  67   b  and a second end  69   a ,  69   b . The first plate  81   a ,  81   b  has a first hole  83   a ,  83   b  at the first end  67   a ,  67   b , and a second hole  84   a ,  84   b  at the second end  69   a ,  69   b . The second plate  82   a ,  82   b  has a first hole  85   a ,  85   b  at the first end  67   a ,  67   b  and a second hole  86   a ,  86   b  at the second end  69   a ,  69   b . The first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  are connected together and aligned by the pivot axle  64   a ,  64   b  of the mounting bracket  62   a ,  62   b  and a pivot pin  70   a ,  70   b  received within the second holes  84   a ,  84   b ,  86   a ,  86   b  of the first plate  81   a ,  81   b  and the second plate  82   a ,  82   b . The distance between the first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  is equivalent to at least a portion of the length of the pivot axle  64   a ,  64   b  and the pivot pin  70   a ,  70   b . The first hole  83   a ,  83   b ,  85   a ,  85   b  of the first end  67   a ,  67   b  of the first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  receive the pivot axle  64   a ,  64   b  and the torsion spring  66   a ,  66   b . The pivot axle  64   a ,  64   b  is surrounded by a torsion spring  66   a ,  66   b , with a first end of the torsion spring  66   a ,  66   b  biasing the arm  68   a ,  68   b  towards the chain  8  and a second end of the torsion spring  66   a ,  66   b  is mounted to the mounting bracket  62   a ,  62   b.    
     Mounted to the pivot pin  70   a ,  70   b  at the second end  69   a ,  69   b  of the first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  and between the first plate  81   a ,  81   b  and the second plate  82   a ,  82   b  is a tensioning foot  72   a ,  72   b . The tensioning foot  72   a ,  72   b  has a body  87   a ,  87   b  with a pivot point hole  88   a ,  88   b  and a chain sliding surface  74   a ,  74   b . The tensioning foot  72   a ,  72   b  receives the pivot pin  70   a ,  70   b  within the pivot point hole  88   a ,  88   b  of the body  87   a ,  87   b , with the associated pivot point being opposite the chain sliding surface  74   a ,  74   b . In one embodiment, the pivot point hole  88   a ,  88   b  is centrally located opposite chain sliding surface  74   a ,  74   b  which interacts with the chain  8 . 
     In this embodiment, the multi-pivot torsion spring tensioners  61 ,  63  have two pivot points, the pivot axle  64   a ,  64   b  and the pivot pin  70   a ,  70   b  connecting the arm  68   a ,  68   b  to the tensioning foot  72   a ,  72   b . The arms  68   a ,  68   b  preferably have rigid bodies. 
     The first and second torsion spring tensioners  61 ,  63  are each fixed via the mounting brackets  62   a ,  62   b  to the transfer case  60  closer to the driven sprocket  6  than the drive sprocket  2 , such that the tension to either strand  8   a ,  8   b  of the chain  8  is being applied asymmetrically toward the driven sprocket  6 , thus allowing slack of the chain  8  to instead accumulate near the drive sprocket  2  at slack location  32 . 
     The first and second multi-pivot torsion spring tensioners  61 ,  63  provide:
         minimum slack strand mechanical preload or force to the chain to prevent or force tooth jump to the drive sprocket;   minimized tight strand mechanical preload or force;   tensioner chain sliding surface travel to manage dynamic chain slack for forward and reverse drive and static chain wear; and   limiting chain sliding surface and chain motion during chain tooth jump events.       

     A stop feature  95  can be added to prevent tensioner device damage from a tooth jump event. During a tooth jump event, the tensioning device can rotate away from the chain strands  8   a ,  8   b , with the rotation being limited by the interface between the stop feature  95  and the drivetrain transfer case  60 . A stop feature  95 , is shown as being applied to the tensioner foot  72   a ,  72   b  in  FIG. 5 a -5 b   , however the stop feature  95  can also be applied to the tensioner arm or tensioner face. The stop feature  95  creates a “low stress” contact so as not to damage the tensioner or reduce the tensioner&#39;s ability to control chain slack. 
     The torsion spring  66   a ,  66   b  can be designed with low spring rates, applying lower force to the strands  8   a ,  8   b  of the chain  8  in order to achieve a balance between tensioner position with the application to minimize spring force and rates for optimized chain slack  8   a ,  8   b  control and efficiency. 
     In this embodiment, the arm  68   a ,  68   b  of the first and second multi-pivot torsion spring tensioners  61 ,  63  acts as a constant moment arm with the tensioner foot  72   a ,  72   b  during articulation and results in a constant force through the range of motion, optimizing control and system efficiency. Additionally, the package can be reduced, as the tensioners  61 ,  63  cover a large articulation angle. 
       FIG. 6  is a partial view of a drivetrain transfer case including a torsion spring tensioner of a third embodiment. The drivetrain transfer case  60  receives a drive sprocket  2 , a driven sprocket  6 , a chain  8 , and a single pivot torsion spring tensioner  261 . The drive sprocket  2  is connected to the driven sprocket  6  via the toothed chain  8 . The chain  8  meshes with the sprockets  2 ,  6 , transmitting rotary motion between the two. 
     The single pivot torsion spring tensioner  261  has a mounting bracket  262  with a pivot axle  264  extending perpendicular therefrom. The pivot axle  264  receives an arm  268 . The arm  268  preferably has a single piece body  278 , but can be manufactured from multiple pieces. The arm  268  has a body  278  with a first end  268   a , a second end  268   b , and a chain sliding surface  274  which interacts with a single chain strand  8   a  close to the driven sprocket  6 . At the first end  268   a  of the body  278  is a hole  279  for receiving the pivot axle  264 . 
     A torsion spring  266  is present between the mounting bracket  262  and acts upon the first end  267  of the one-piece arm  268  on the pivot axle  264 . One end  266   a  of the spring  266  is grounded relative to the mounting bracket  262  and the second end  266   b  contacts the arm  268 . 
     Placement of the single pivot torsion spring tensioner  261  mounted closer to the driven sprocket  6  than the drive sprocket  2  results in asymmetric tension being applied to the strand  8   a , such that the slack of the chain accumulates near the drive sprocket  2 . 
       FIG. 7  shows a schematic of a chain system within a drivetrain transfer case including a blade spring tensioner of a fourth embodiment. 
     The drivetrain transfer case  60  receives a drive sprocket  2 , a driven sprocket  6 , a chain  8 , a first blade spring tensioner  361  and a second blade spring tensioner  363 . The drive sprocket  2  is connected to the driven sprocket  6  via the toothed chain  8 . The chain  8  meshes with the sprockets  2 ,  6 , transmitting rotary motion between the two. 
     The first and second blade spring tensioners  361 ,  363  each have a mounting bracket  362   a ,  362   b  with a pivot axle  364   a ,  364   b  extending perpendicular therefrom and a mounting surface  375   a ,  375   b . The pivot axle  364   a ,  364   b  pivotably receives a first end  367   a ,  367   b  of the resilient blade tensioner arm body  368   a ,  368   b  via a pivot hole  381   a ,  381   b . The second end  369   a ,  369   b  of the resilient blade tensioner arm body  368   a ,  368   b  is adjacent to and interacts with the mounting surface  375   a ,  375   b . The resilient blade tensioner arm body  368   a ,  368   b  has a chain sliding surface  374   a ,  374   b  with a profile of a path of a new chain that interacts with a chain strand  8   a ,  8   b  of the chain  8 . Opposite the chain sliding surface  374   a ,  374   b  is a means for receiving and containing at least the ends of a blade spring  366   a ,  366   b . The blade spring  366   a ,  366   b  can be contained by pockets formed by the tensioner arm body  368   a ,  368   b  of the tensioner, tabs or other means of securing at least the ends of the blade spring  366   a ,  366   b  to the tensioner body  368   a .  368   b  such that the blade spring  366   a ,  366   b  can bow. The resilient blade tensioner arm body  368   a ,  368   b  and the blade spring  366   a ,  366   b  can flex and bow outwards and away from the mounting surface  375   a ,  375   b.    
     The first and second blade spring tensioners  361 ,  363  are each fixed via the mounting brackets  362   a ,  362   b  to the transfer case  160  closer to the driven sprocket  6  than the drive sprocket  2 , such that the tension to either strand  8   a ,  8   b  of the chain  8  is being applied asymmetrically toward the driven sprocket  6 , thus allowing slack of the chain  8  to instead accumulate near the drive sprocket  2 . 
       FIG. 8  shows a schematic of a chain system with a dual strand tensioner. 
     A drivetrain transfer case receives a drive sprocket  2 , a driven sprocket  6 , a chain  8 , a first tensioner  461  and a second tensioner  463 . The drive sprocket  2  is connected to the driven sprocket  6  via the toothed chain  8 . The chain  8  meshes with the sprockets  2 ,  6 , transmitting rotary motion between the two. 
     In this embodiment, a first tensioner  461  and a second tensioner  463  act on chain strands  8   a ,  8   b  adjacent the driven sprocket  6 . The first tensioner  461  and the second tensioner  463  are mechanically connected  480  together, such that rotation towards a strand  8   a  of the chain  8  by the first tensioner  461  causes the second blade spring tensioner  463  to pivot away from the opposite chain strand  8   b.    
     The first and second tensioners  461 ,  463  are each mounted closer to the driven sprocket  6  than the drive sprocket  2 , such that the tension to either strand  8   a ,  8   b  of the chain  8  is being applied asymmetrically toward the driven sprocket  6 , thus allowing slack of the chain  8  to instead accumulate near the drive sprocket  2 . 
     While not shown, in an alternate embodiment, the first tensioning device can be a different device than the second tensioning device. In an example, the first tensioning device is first multi-pivot torsion spring  61  and the second tensioning device is a second blade spring tensioner  363 . This example is not limiting, and other combinations are possible. 
     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.