Abstract:
An isolator is provided for use with an engine and in particular an engine that is assisted or started by MGU (Motor-Generator Unit) or a motor through an endless drive member. It comprises a double acting spring system for isolating crankshaft pulley from torsion vibration at the crankshaft, and in extreme conditions, such as during engine startup and accelerations or decelerations of the engine crankshaft relative to the pulley and when isolator operates in an “engine-driven” mode with the engine crank shaft is driven by the belt.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/826,492, filed May 23, 2013, the contents of which are incorporated by reference as if fully set forth in detail herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to isolators and in particular isolators that are used between the engine crankshaft and endless drive member in vehicles in which the engine can be started or assisted by the endless drive member (e.g. an engine equipped with a belt-alternator start (BAS) drive system). 
       BACKGROUND OF THE INVENTION 
       [0003]    Isolators are usually used for isolating crankshaft pulley from torsion vibration at the crankshaft that is a result of vibration in torque that occurs in internal combustion engines and in particular those with certain cylinder counts such as four- or- three cylinder engines, and diesel engines, and they are also used in extreme conditions, such as during the engine startup and accelerations or decelerations of the engine crankshaft relative to the pulley. In addition isolators can operate in an “engine-driven” mode with the engine crankshaft is driven by the belt. 
       SUMMARY 
       [0004]    In an aspect, the present disclosure provides an improved isolator for isolating of the torque vibration between crankshaft and an endless drive member in vehicles in which the engine can be started or assisted by the endless drive member. This isolator comprises a double acting spring system. The spring system is mounted in the spring tray, built from low friction material, and fixed to a pulley. The pulley has a bearing and is mounted on the hub and is thus centered on the crankshaft. The spring tray has two travel stops that are located in the diametrical opposite sides. The double acting spring system includes two arc compression springs that are located between two stops of the spring tray without preload. The ends of the springs are fixed on the pins mounted on the plastic guides. They have ability to move and compress the arc springs using symmetrical arms of the pivotable driver. The pivotable driver is coaxially fixed to the crankshaft. In spring balancing position the symmetrical arms of the driver remain balanced between the guides and the travel stops. The section width of the arms of the pivotable driver is greater than the corresponding width of the travel stops, which allows the driver passing through a neutral position without impact of the guides on the travel stops and changing of the springs compression direction. 
         [0005]    In another aspect, an isolator is provided, comprising a spring, a shaft adapter and a pulley. The spring has a first spring end and a second spring end. The shaft adapter is mountable to a crankshaft for rotation about an axis. The shaft adapter has a first adapter drive surface that is engageable with the first spring end and a second adapter drive surface that is angularly spaced from the first adapter drive surface by an adapter drive surface spacing and that is engageable with the second spring end. The pulley is engageable with an endless drive member and is rotatable relative to the shaft adapter. The pulley has a first pulley drive surface that is engageable with the first spring end and a second pulley drive surface that is angularly spaced from the first pulley drive surface by a pulley drive surface spacing and that is engageable with the second spring end. Torque is transferrable from the shaft adapter to the spring through the first spring end, and from the spring to the pulley through the second spring end. Torque is transferrable from the pulley to the spring through the first spring end, and from the spring to the shaft adapter through the second spring end. One of the adapter and pulley drive surface spacings is larger than the other of the adapter and pulley drive surface spacings. When transitioning from torque transfer from the shaft adapter to the pulley to torque transfer from the pulley to the shaft adapter, the second adapter drive surface engages the second spring end at a different time than the first adapter drive surface disengages from the first spring end, and the second pulley drive surface disengages from the second spring end at a different time than the first pulley drive surface engages the first spring end. Wherein when transitioning from torque transfer from the pulley to the shaft adapter to torque transfer from the shaft adapter to the pulley the first adapter drive surface engages the first spring end at a different time than the second adapter drive surface disengages from the second spring end, and the first pulley drive surface disengages from the first spring end at a different time than the second pulley drive surface engages the second spring end. 
         [0006]    In another aspect, an isolator is provided, comprising a spring, a shaft adapter and a pulley. The spring has a first spring end and a second spring end. The shaft adapter is mountable to a crankshaft for rotation about an axis, wherein the shaft adapter has a first adapter drive surface that is engageable with the first spring end and a second adapter drive surface that is angularly spaced from the first adapter drive surface and that is engageable with the second spring end. The pulley is engageable with an endless drive member and that is rotatable relative to the shaft adapter. The pulley has a first pulley drive surface that is engageable with the first spring end and a second pulley drive surface that is angularly spaced from the first pulley drive surface and that is engageable with the second spring end. Torque is transferrable from the shaft adapter to the spring through the first spring end, and from the spring to the pulley through the second spring end. Torque is transferrable from the pulley to the spring through the first spring end, and from the spring to the shaft adapter through the second spring end. When the isolator is at rest, the adapter and pulley drive surfaces are configured have positions relative to one another that are selected based on a moment of inertia of the pulley and a moment of inertia of the shaft adapter, based on a maximum torque to be transferred therebetween, and based on a material of the adapter drive surfaces and a material of the pulley drive surfaces, such that when transitioning from torque transfer from the shaft adapter to the pulley to torque transfer from the pulley to the shaft adapter, the second adapter drive surface engages the second spring end with a first kinetic energy and at a different time than the first adapter drive surface disengages from the first spring end, and the second pulley drive surface disengages from the second spring end with a second kinetic energy and at a different time than the first pulley drive surface engages the first spring end, and such that when transitioning from torque transfer from the pulley to the shaft adapter to torque transfer from the shaft adapter to the pulley the first adapter drive surface engages the first spring end with a third kinetic energy and at a different time than the second adapter drive surface disengages from the second spring end, and the first pulley drive surface disengages from the first spring end with a fourth kinetic energy and at a different time than the second pulley drive surface engages the second spring end. The first, second, third and fourth kinetic energies are less than a selected value. 
         [0007]    Other features and advantages will be apparent by following the description with references to the drawings. 
     
    
     
       BRIEF DESCRIPTION ON THE DRAWINGS 
         [0008]      FIG. 1  is an elevation view of an engine with a crankshaft, a driven belt and an isolator in accordance with an embodiment of the present invention. 
           [0009]      FIG. 1 a    is a perspective right-side view of the isolator shown in  FIG. 1  with a double acting spring system with two springs. 
           [0010]      FIG. 2  is a perspective of longitudinal cross-section view of isolator in the springs balancing position. 
           [0011]      FIG. 3  is a perspective of longitudinal cross-section view of isolator with double acting spring system. 
           [0012]      FIG. 4  is a front view of isolator with double acting spring system excluding the pivotable driver and left spring. 
           [0013]      FIG. 5  is a perspective right-side view of isolator with double acting spring system excluding the driver and left spring. 
           [0014]      FIG. 6  is a detail perspective right-side view of isolator with double acting spring system. 
           [0015]      FIG. 7 a    is a perspective left-side view of isolator with double acting spring system with the pivotable driver in the position when the engine is started. 
           [0016]      FIGS. 7 b  and 7 c    are elevation side views of the isolator shown in  FIG. 1  during transition in torque transfer. 
           [0017]      FIG. 7 d    is a perspective left-side view of isolator with double acting spring system with the pivotable driver in the position when the engine crankshaft is driven by the belt. 
           [0018]      FIG. 8  is an edge view of a portion of the isolator to show elements that engage the springs of the spring system. 
           [0019]      FIG. 9  is a perspective left-side view of the pulley with spring tray of isolator with double acting spring system. 
           [0020]      FIG. 10  is a perspective left-side view of the pulley with spring tray and the support ring of isolator with double acting spring system. 
           [0021]      FIG. 11  is an exploded view of isolator with double acting spring system. 
           [0022]      FIG. 12  is a perspective right-side view of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0023]      FIG. 13  is a perspective of longitudinal cross-section view of isolator with double acting spring system in the springs balancing position, as a variant of embodiment of the invention. 
           [0024]      FIG. 14  is a perspective of longitudinal cross-section view of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0025]      FIG. 15  is a front view of isolator with double acting spring system excluding the driver, cover ring, and left spring, as a variant of embodiment of the invention. 
           [0026]      FIG. 16  is a perspective right-side view of isolator with double acting spring system excluding the driver, cover ring and left spring, as a variant of embodiment of the invention. 
           [0027]      FIG. 17  is a detail perspective right-side view of isolator with double acting spring system excluding the left spring and cover ring, as a variant of embodiment of the invention. 
           [0028]      FIG. 18  is a detail perspective right-side view of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0029]      FIG. 19  is a perspective left-side view of isolator with double acting spring system excluding the cover ring in the position of the pivotable driver, when the engine is started, as a variant of embodiment of the invention. 
           [0030]      FIG. 20  is a perspective left-side view of isolator with double acting spring system excluding the cover ring in the position of the pivotable driver, when the engine crankshaft is driven by the belt, as a variant of embodiment of the invention. 
           [0031]      FIG. 21  is a perspective left-side view of the pulley and spring tray of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0032]      FIG. 22  is a perspective left-side view of the pulley with spring tray and the support ring of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0033]      FIG. 23  is an exploded view of isolator with double acting spring system, as a variant of embodiment of the invention. 
           [0034]      FIG. 24  is rotary speed profile of isolator with double acting spring system. 
           [0035]      FIG. 25  is a front view of double acting spring system in the neutral balanced position, as a reference to the double acting functionality. 
           [0036]      FIG. 26  is a front view of double acting spring system in the balanced position excluding the pivotable driver, as a reference to the double acting functionality. 
           [0037]      FIG. 27  is a front view of double acting spring system in the position when the pivotable driver is transferred a load an arrow direction, as a reference to the double acting functionality. 
           [0038]      FIG. 28  is a front view of double acting spring system in the position when the pivotable driver transfers a load in the arrow direction opposite to  FIG. 27 , as a reference to the double acting functionality. 
           [0039]      FIG. 29  is a perspective view of the support ring, as a variant with friction inserts. 
           [0040]      FIG. 30  is a perspective view of the pulley, as a variant where the travel stops of the spring support with friction inserts. 
           [0041]      FIG. 31  is a perspective view of the guide, as a variant with the damping material insert. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    Reference is made to  FIG. 1 , which shows an isolator  1  for transferring power between a crankshaft  50  on an engine  51  and an endless drive member  52 , such as an accessory drive belt, in accordance with an embodiment of the present invention. The isolator  1  isolates the endless drive member  52  from vibrations or other sudden changes in torque in the crankshaft  50 , and vice versa. 
         [0043]    The isolator  1  is useful in any engine, but is particularly useful in an engine that incorporates a BAS (belt-alternator start) system, in which the engine  51  is initially started normally (e.g. using a starter motor) but is shut down for brief periods (e.g. while the vehicle is at a stoplight) and then restarted by driving the crankshaft via the belt  52 . The belt  52  would be driven by a separate motor (e.g. an electric motor) that is engaged with the belt  52  via a pulley, or by using an MGU (shown at  53 ) that would replace the alternator. Such systems are becoming increasingly common in an effort to increase fuel economy of vehicles and reduce emissions. 
         [0044]    As seen in  FIG. 1 a   , the isolator  1  includes a pulley  2 , a shaft adapter  54  and two springs  5 . The two springs  5  are shown individually at  5   a  and  5   b.  Each spring  5  has a first end  40  and a second end  42 . The springs  5  elastically deform to isolate the endless drive member  52  and the crankshaft  50  from vibrations or other sudden changes in torque in one another. The springs  5  in the examples shown are arcuate, helical coil compression springs. However, any other suitable type of springs could be used, such as, for example, arcuate closed cell foam springs. 
         [0045]    Referring to  FIGS. 2, 3 and 11 , the shaft adapter  54  is fixedly mountable in any suitable way to the crankshaft  50  for rotation about an axis A. For example, the crankshaft  50  may include a crankshaft end  13  that mounts to the rest of the crankshaft  50  via of a threaded fastener  20  such as a spline socket head cap screw. The shaft adapter  54  may include a hub  9  that abuts a shoulder on the crankshaft end  13  in surrounding relationship to an axial projection  55  so as to align the hub  9  about the axis A, and a driver  8  that abuts an axial end face of the hub  9 . A plurality of splined socket head cap screws (in this example, there are four)  17  pass through apertures  44  in the driver  8 , and apertures  46  in the hub  9 , and pass into aperture  48  in the crankshaft end  13  to hold the driver  8  and the hub  9  to the crankshaft  50 . A dowel pin  56  is pressed through an aperture  58  in the driver and into a corresponding aperture  60  ( FIG. 11 ) in the hub  9  to cause alignment of the driver  8  with the axis A. 
         [0046]    Referring to  FIG. 4 , the driver  8  has a central body  62 , a first arm  12   a  and a second arm  12   b.  The driver  8  has a first adapter drive surface  64  on one side of the first arm  12   a,  which is engageable with the first spring end  40  of the first spring  5   a  and a second adapter drive surface  66  on one side of the second arm  12   b,  which is angularly spaced from the first adapter drive surface  64  by an adapter drive surface spacing S 1 , and which is engageable with the second spring end  42  of the first spring  5   a.  The driver  8  has another first adapter drive surface  68  on another side of the second arm  12   b , which is engageable with the first spring end  40  of the second spring  5   b  and a second adapter drive surface  70  on another side of the first arm  12   a,  which is angularly spaced from the first adapter drive surface  68  (also by the spacing S 1 ) and which is engageable with the second spring end  42  of the second spring  5   b.    
         [0047]    In the embodiment shown, the driver  8  is generally planar but for a raised center portion  72  that is thicker than the remaining portion so as to impart strength and resistance to elongation of the apertures  44  and  58 . 
         [0048]    The driver  8  may be made from any suitable material such as a suitable steel. 
         [0049]    The pulley  2  is engageable with the endless drive member  52  and is rotatably mounted to the shaft adapter  54  so that the pulley  2  is rotatable relative to the shaft adapter  54 . The rotatable mounting of the pulley  2  to the shaft adapter  54  may be by any suitable means. For example, the pulley  2  may be mounted to one or more bearings  10  (in this example there are two bearings  10 ) which are themselves mounted to the outer surface of the hub  9 . 
         [0050]    The pulley  2  has an inner pulley portion  74  that is rotatably mounted to the shaft adapter  54  via the bearings  10 , an outer pulley portion  76  that is engageable with the endless drive member  52 , and a web  78  that connects the inner and outer portions  74  and  76 . The web  78  and the outer portion  76 , (and, in this example, the inner portion  74 ) together in part define a spring chamber  80  in which each spring  5  is held. In the example shown there are two spring chambers  80 , each one holding one of the springs  5 . The pulley  2  may be made from steel or some other suitable material. 
         [0051]    A spring engagement lining  3  is provided on at least the surfaces of the web  78  and outer portion  76  that define the spring chamber  80  and is configured to support the springs  5  and to permit sliding of the springs  5  thereon with relatively little friction. The spring engagement lining  3  may be polymeric and may, for example, be made from nylon impregnated with PTFE, or from some other suitable material. In embodiments wherein the spring engagement lining  3  is a coating on the associated surfaces of the web  78  and outer portion  76 , it may alternatively be referred to as a spring engagement coating. In embodiments wherein the spring engagement lining  3  is a separate element that is self-supporting and that is pressed into place into the outer portion  76 , it may alternatively be referred to as a spring tray. In either case, the web  78  and the outer portion  76  may be considered structural portions of the pulley  2 , while the lining  3  may be provided so as to provide a selected amount of friction during sliding movement with the springs  5 . 
         [0052]    With reference to  FIG. 4 , the pulley  2  has a first pulley drive surface  82  that is engageable with the first spring end  40  of the first spring  5   a,  and a second pulley drive surface  84  that is angularly spaced from the first pulley drive surface  82  by a pulley drive surface spacing S 2 , and that is engageable with the second spring end  42  of the first spring  5   a.  The pulley  2  has another first pulley drive surface  86  that is engageable with the first spring end  40  of the second spring  5   b,  and a second pulley drive surface  88  that is angularly spaced from the first pulley drive surface  86  (also by the spacing S 2 ), and that is engageable with the second spring end  42  of the second spring  5   b.    
         [0053]    A first end member  6   a  is provided at the first end  40  of each spring  5 . The first end member  6   a  is engaged with the first spring end  40 . A second end member  6   b  is provided at the second end  42  of each spring  5 . The second end member  6   b  is engaged with the second spring end  42 . Each spring  5  has an opening  90  at each of the first and second ends  40  and  42 . The first and second end members  6   a  and  6   b  each have a coil retaining projection  7  thereon which is snugly captured in the opening  90  so as to hold the first and second spring ends  40  and  42 . 
         [0054]    The first pulley drive surface  82  and first adapter drive surface  64  are proximate each other axially, as can be seen in  FIG. 8 , and are both engageable with the first spring end  40  on the first spring  5   a  through the first end member  6   a.  Similarly, the first pulley drive surface  86  and first adapter drive surface  68  are proximate each other axially and are both engageable with the first spring end  40  on the second spring  5   b  through the other first end member  6   a  (as shown in  FIGS. 7 a  and 7 d    respectively). With continued reference to  FIGS. 7 a  and 7 d   , the second pulley drive surface  84  and second adapter drive surface  66  are both engageable with the second spring end  42  of the first spring  5   a  through the second end member  42 . As shown in  FIG. 8 , the second pulley drive surface  88  and second adapter drive surface  70  are both engageable with the second spring end  42  of the second spring  5   b  through the other second end member  42 . 
         [0055]    The end members  6   a  and  6   b  are constrained to move along a circumferential path about the axis A. For example, in the embodiment shown in  FIGS. 1 a   - 11  the end members  6   a  and  6   b  are constrained axially by a flange  16  on a support ring  4 , which may also be referred to as a bushing  4 . The flange  16  is received in a groove  15  in each of the end members  6   a  and  6   b,  and the end members  6   a  and  6   b  are constrained radially by the outer portion  76  of the pulley  2  (specifically the portion of the lining  3  that is on the outer portion  76 ) and by the outer surface of the bushing  4 . 
         [0056]      FIG. 7 a    shows torque transfer (see arrows  91 ) from the shaft adapter  54  to the pulley  2 , as would occur during normal operation of the engine  51 . This torque transfer drives the belt  52  ( FIG. 1 ) which in turn drives one or more accessories such as the MGU  53 . As can be seen, torque is transferrable from the shaft adapter  54  to the springs  5  through the first spring ends  40 , and from the springs  5  to the pulley  2  through the second spring ends  42 .  FIG. 7 d    shows torque transfer from (see arrows  92 ) the pulley  2  to the shaft adapter  54 , as would occur during a BAS start event (i.e. when the MGU  53  ( FIG. 1 ) is used to drive the belt  52 , in order to start the engine by transferring torque from the belt  52  to the crankshaft). As can be seen, torque is transferrable from the pulley  2  to the springs  5  through the first spring ends  40 , and from the springs  5  to the shaft adapter  54  through the second spring ends  42 . 
         [0057]    As can be seen in  FIG. 4 , one of the adapter and pulley drive surface spacings S 1  and S 2  is larger than the other of the adapter and pulley drive surface spacings S 1  and S 2 . In the example embodiment shown in  FIG. 1 a   - 11 , the spacing S 2  is larger than the spacing S 1 . However, it is alternatively possible for the spacing S 1  between the adapter drive surfaces  64  and  66  (and between surfaces  68  and  70 ) to be larger than the spacing S 2  between the pulley drive surfaces  82  and  84  (and between surfaces  86  and  88 ). 
         [0058]    As a result of having one spacing S 1  or S 2  be larger than the other, when transitioning from torque transfer from the shaft adapter  54  to the pulley  2  to torque transfer from the pulley  2  to the shaft adapter  54 , the second adapter drive surfaces  66  and  70  engage the second spring ends  42  (via the end members  6   b ) at a different time than the first adapter drive surfaces  64  and  68  disengage from the first spring ends  40 , and the second pulley drive surfaces  84  and  88  disengage from the second spring ends  42  at a different time than the first pulley drive surfaces  82  and  86  engage the first spring ends  40  (via the end members  6   a ). Analogously, when transitioning from torque transfer from the pulley  2  to the shaft adapter  54  to torque transfer from the shaft adapter  54  to the pulley  2  the first adapter drive surfaces  64  and  68  engage the first spring ends  40  at a different time than the second adapter drive surfaces  66  and  70  disengage from the second spring ends  42 , and the first pulley drive surfaces  82  and  86  disengage from the first spring ends  40  at a different time than the second pulley drive surfaces  84  and  88  engage the second spring ends  42 . 
         [0059]    The transition from torque transfer from the shaft adapter  54  to the pulley  2  to torque transfer from the pulley  2  to the shaft adapter  54  is illustrated in the progression of figures from  FIG. 7 a    to  FIG. 7 d   . As shown in  FIG. 7 a   , when torque is being transferred from the shaft adapter  54  to the pulley  2 , the first adapter drive surfaces  64  and  68  are engaged with the first spring ends  40  through the first end members  6   a,  and the second spring ends  42  are engaged with the second pulley drive surfaces  84  and  88  via the second end members  6   b.  In the example shown, the shaft adapter  54  and the pulley  2  rotate clockwise, however, in other examples, it will be understood that they could rotate counterclockwise. As the torque transferred from the shaft adapter  54  to the pulley  2  decreases, the restoring force in the springs  5  drives the pulley  2  clockwise relative to the shaft adapter  54 .  FIG. 7 b    illustrates the moment when the springs  5  have driven the pulley  2  sufficiently clockwise that the second adapter drive surfaces  66  and  70  have engaged the second spring ends  5   b  via the second end members  6   b,  and the second pulley drive surfaces  84  and  88  are just about to disengage from the second end members  6   b  and therefore from the second spring ends  5   b.    FIG. 7 b    illustrates the moment that the torque transfer from the shaft adapter  54  to the pulley  2  drops to zero. If the torque on the pulley  2  is greater than the torque on the shaft adapter  54 , the pulley  2  will proceed to overrun the shaft adapter  54 . Shortly thereafter, the first pulley drive surfaces  82  and  86  will engage the first spring ends  40  via the first end members  6   a.    FIG. 7 c    shows the moment when the first pulley drive surfaces  82  and  86  engage the first end members  6   a  (and therefore the first spring ends  40 ) and when the relative movement of the pulley  2  with respect to the shaft adapter  54  is about to cause disengagement of the first adapter drive surfaces  64  and  68  from the first end members  6   a  (and therefore from the first spring ends  40 ).  FIG. 7 d    illustrates the state, as noted above, where torque is transferred from the pulley  2  to the shaft adapter  54 . 
         [0060]    The transition from torque transfer from the pulley  2  to the shaft adapter  54  to torque transfer from the shaft adapter  54  to the pulley  2  is illustrated in the progression of figures from  FIG. 7 d    to  FIG. 7 a   .  FIG. 7 c    shows the moment when the first adapter drive surfaces  64  and  68  engage the first end members  6   a  (and therefore the first spring ends  40 ) and when the relative movement of the shaft adapter  54  with respect to the pulley  2  is about to cause disengagement of the first pulley drive surfaces  64  and  68  from the first end members  6   a  (and therefore from the first spring ends  40 ). Shortly thereafter, continued relative movement of the shaft adapter  54  compared to the pulley  2 , will cause the second pulley drive surfaces  84  and  88  to engage the second spring ends  42  via the first end members  6   b.    FIG. 7 b    shows the moment that the second pulley drive surfaces  84  and  88  to engage the second spring ends  42  via the first end members  6   b  and are about to cause disengagement of the second adapter drive surfaces  66  and  70  from the second end members  6   b  and therefore from the second spring ends  42 .  FIG. 7 a    illustrates the state, as noted above, where torque is transferred from the shaft adapter  54  to the pulley  2 . 
         [0061]    It can be seen from  FIGS. 7 b  and 7 c    that there is a small amount of lost motion provided between the pulley drive surfaces and the adapter drive surfaces. This lost motion is provided because of the spacing difference between the spacings S 1  and S 2 . This lost motion is generally small and would, under many circumstances, not be sufficient to prevent torque transfer from taking place between the shaft adapter  54  and pulley  2  during startup of a typical engine. By contrast, the spacing difference between spacings S 1  and S 2  is not selected to prevent torque transfer during engine startup; it is instead selected to keep the kinetic energies of impacts during engagement of the various drive surfaces with the spring ends below a selected level so that the noise associated with these impacts is less than a selected threshold level. The selected threshold level may differ for different applications. For example, when configuring the isolator  1  on a luxury car, a relatively low threshold may be used, and when configuring the isolator  1  on a luxury car, a relatively higher threshold may be used. However, in each case, the size of the spacing difference used is based on keeping the kinetic energies of the aforementioned impacts is below a selected threshold. There are four impacts that take place, each having an associated kinetic energy. A first kinetic energy is associated with the impact during engagement between the second adapter drive surfaces  66  and  70  and the second spring ends  42  (via the end members  6   b ). A second kinetic energy is associated with the impact during engagement between the first pulley drive surfaces  82  and  86  and the first spring ends  40  (via the end members  6   a ). A third kinetic energy is associated with the impact during engagement between the first adapter drive surfaces  64  and  68  and the first spring ends  40  (via the end members  6   a ). A fourth kinetic energy is associated with the impact during engagement between the second pulley drive surfaces  84  and  88  and the second spring ends  42  (via the end members  6   b ). 
         [0062]    In order to keep the kinetic energies of the impacts sufficiently low, the spacing difference is selected, based on one or more of several parameters (and preferably all of these parameters). The parameters include the moment of inertia of the pulley, the moment of inertia of the shaft adapter, the maximum amount of torque that the isolator  1  will be designed to transfer, the materials that make up the adapter drive surfaces  64 ,  66 ,  68  and  70  and the materials that make up the pulley drive surfaces  82 ,  84 ,  86  and  88 . In particular, the spacing difference may be reduced as the moment of inertia of either the pulley  2  or the shaft adapter  54  increases. The spacing difference may be reduced as the maximum torque to be transferred increases. The spacing difference may be reduced as the hardness of the materials of the pulley and adapter drive surfaces increases. By reducing the spacing difference, the amount of energy buildup that takes place between the first impact and the second impact that occur during a transition in torque transfer from the shaft adapter  54  to the pulley  2  to torque transfer from the pulley  2  to the shaft adapter  54 , or during a transition in torque transfer from the pulley  2  to the shaft adapter  54  to torque transfer from the shaft adapter  54  to the pulley  2 . 
         [0063]    In general, throughout this disclosure, the term ‘impact’ refers to when engagement occurs between one of the pulley or adapter drive surfaces and an associated surface of the end members  6 . 
         [0064]    Put another way, when the isolator  1  is at rest, the adapter and pulley drive surfaces are configured have positions relative to one another that are selected based on a moment of inertia of the pulley  2  and a moment of inertia of the shaft adapter  54 , based on a maximum torque to be transferred therebetween, and based on a material of the adapter drive surfaces  64 ,  66 ,  68  and  70  and a material of the pulley drive surfaces  82 ,  84 ,  86 , and  88 , such that when transitioning from torque transfer from the shaft adapter  54  to the pulley  2  to torque transfer from the pulley  2  to the shaft adapter  54 , the second adapter drive surfaces  66  and  70  engage the second spring ends  42  with a first kinetic energy and at a different time than the first adapter drive surfaces  64  and  68  disengage from the first spring ends  40 , and the second pulley drive surfaces  66  and  70  disengage from the second spring ends  42  with a second kinetic energy and at a different time than the first pulley drive surfaces  82  and  86  engage the first spring ends  40 , and such that when transitioning from torque transfer from the pulley  2  to the shaft adapter  54  to torque transfer from the shaft adapter  54  to the pulley  2  the first adapter drive surfaces  64  and  68  engage the first spring ends  40  with a third kinetic energy and at a different time than the second adapter drive surfaces  66  and  70  disengage from the second spring ends  42 , and the first pulley drive surfaces  82  and  86  disengage from the first spring ends  40  with a fourth kinetic energy and at a different time than the second pulley drive surfaces  84  and  88  engage the second spring ends  42 . 
         [0065]    In many instances, it has been found that the spacing difference that was found to be acceptable is less than about 5 degrees. In many instances, it has been found that the spacing difference that was found to be acceptable is more than about 0.5 degrees. 
         [0066]    It will be noted that the arrangement shown in  FIGS. 1 a   - 11  is particularly suited for use on a European engine. In Europe, it is typical to provide a relatively larger crankshaft end  13  and to use four fasteners  17  to mount the shaft adapter  54  to it. A variant of the isolator  1  is shown in  FIGS. 12-23  that is particularly suited for use on a North American engine, which typically employs a relatively smaller crankshaft end  24  and a single centrally located fastener  23  and washer  19  ( FIG. 23 ). A key  25  engages a slot in the crankshaft end  24  and corresponding slots in the hub  9 , the driver  8 , and a cap shown at  21 . Some other differences between the isolator  1  shown in  FIGS. 1 a   - 11  and the isolator  1  shown in  FIGS. 12-23  are described below. 
         [0067]    As can be seen in  FIG. 23  and the sectional views shown in  FIGS. 13 and 14 , the driver  8  has a different construction than the driver  8  shown in  FIGS. 1 a   - 11 . The driver  8  in  FIGS. 12-23  is made from a material having a uniform thickness. The driver  8  in  FIGS. 12-23  further includes skirts  102  that extend axially out of the plane of the remainder of the driver  8 . These skirts  102  impart some rigidity to the driver  8 . As can be seen in  FIGS. 20-23  there is a circumferential gap G between each pair of mutually facing ends of the skirts  102 . Thus there are two gaps G in the embodiment shown in  FIGS. 12-23 . This circumferential gap G is filled with a projection  104  on a support ring  18  (which also may be referred to as a bushing  18 ). The bushing  18  shown in  FIGS. 12-23  has two projections  104  to fill the two gaps G. The outer surface of the projections  104  and the outer surface of the skirts  102  combine to form a radial constraining and slide surface  106  for the end members  6   a  and  6   b.  As can be seen in  FIGS. 19 and 20  in particular, the end members  6   a  and  6   b  slide along surface  106  during operation of the isolator  1 . 
         [0068]    It will be noted that the surface  106  does not include a flange that engages a groove in the end members  6 . Instead, a cover member  22  is provided that forms part of the pulley  2  and partially encloses the spring chamber  80  that is defined in part by the web  78  and the outer portion  76 . The end members  6  are constrained axially by the cover member  22  and by the web  78 , and radially by the bushing (and optionally, as shown, by the outer surface of the skirts  102 ), and by the outer portion of the pulley, so as to permit travel along a circumferential path. The constraining of the end members  6  can be seen in  FIG. 18 . 
         [0069]      FIGS. 19 and 20  illustrate torque transfer from the shaft adapter  54  to the pulley  2  and from the pulley  2  to the shaft adapter  54  respectively. The transition between these two torque transfers is unchanged as compared to  FIGS. 7 a -7 d   . Additionally, the spacings S 1  and S 2  and the spacing differences are the same for the isolator  1  shown in  FIGS. 12-23  as they are for the isolator  1  shown in  FIGS. 1 a   - 11 .  FIG. 15  shows the spacings S 1  and S 2 . 
         [0070]      FIGS. 16 and 17  show that the adapter drive surfaces  64 ,  66 ,  68  and  70  are axially adjacent the pulley drive surfaces that are on the projections  11 . 
         [0071]      FIGS. 21 and 22  show the relationship between the projections  104  on the bushing  18  and the projections  11  that hold the pulley drive surfaces  82 ,  84 ,  86  and  88 . 
         [0072]    Due to the smaller size of the crankshaft end  24 , a single larger bearing  10  may be used between the pulley  2  and the hub  9  in the embodiment shown in  FIGS. 12-23  instead of the two smaller bearings  10  shown in  FIG. 11 . 
         [0073]    Referring to  FIG. 24 , a graph is provided which shows the amplitudes of oscillation of the shaft adapter  54  (curve  200 ) and the corresponding amplitudes of oscillation of the pulley  2  (curve  202 ), while running a test engine at different speeds. As can be seen, there is a significant reduction in the amplitudes of oscillation at the pulley  2  as compared to the shaft adapter  54 .  FIG. 24  is illustrative of the performance of the isolator  1  in both  FIGS. 1 a   - 11  and  12 - 23 . 
         [0074]      FIGS. 25-28  illustrate yet another variant of the isolator  1 , but with a single spring  5  instead of two springs  5   a  and  5   b  as shown in  FIGS. 1-23 . In this embodiment, there is a only one first adapter drive surface (surface  64 ), one second adapter drive surface (surface  66 ) spaced from the surface  64  by spacing S 1 , one first pulley drive surface (surface  82 ) and one second pulley drive surface (surface  84 ), spaced from the surface  82  by spacing S 2 . The connection to the crankshaft is not shown (no fasteners are illustrated). Any suitable connection may be provided. 
         [0075]      FIG. 25  shows the isolator  1  with the driver  8  thereon and with spacing S 1 .  FIG. 26  shows the isolator  1  with the driver  8  removed so as to show the pulley drive surfaces and the spacing S 2 .  FIG. 27  shows torque transfer from the shaft adapter  54  to the pulley  2 .  FIG. 28  shows torque transfer from the pulley  2  to the shaft adapter  54 . The spacings S 1  and S 2  may have the same relationships as the spacings S 1  and S 2  in  FIGS. 1 a   - 11  and in  FIGS. 12-23 . 
         [0076]      FIGS. 29 and 30  illustrate friction members  31  and  32  that could be used to provide damping of the movement of the pulley  2  relative to the shaft adapter  54 , particularly during movement that is proximate the rest positions of the pulley  2  and shaft adapter  54  (e.g. as shown in  FIGS. 4 and 15 ). The amount of damping provided would depend on the coefficient of friction between the friction members  31  and the associated surfaces of the projections  11  and on the force therebetween, or on the coefficient of friction between the friction members  32  and the associated surfaces of the arms  12  of the driver  8 , and on the force therebetween. In the embodiment shown in  FIG. 29 , the friction member  31  is fixedly connected to the shaft adapter  54  (by virtue of being on the projections  102  which engage the gaps G between the skirts  102  of the driver  8 ), and is frictionally engageable with the pulley  2 . In the embodiment shown in  FIG. 30 , the friction member  31  is fixedly connected to the pulley  2  (by virtue of being on the projections  11 ), and is frictionally engageable with the shaft adapter  54 . 
         [0077]      FIG. 31  shows another optional element, which is a bumper shown at  33  that would be mounted in each of the end members  6 . A first bumper  33  on the first end members  6   a  would be engaged with the first adapter drive surfaces  64  and  68  during torque transfer therewith, and would be engaged with the first pulley drive surfaces  82  and  86  during torque transfer therewith. A second bumper  33  on the second end members  6   b  would be engaged with the second adapter drive surfaces  66  and  70  during torque transfer therewith and that is engaged with the second pulley drive surfaces  84  and  88  during torque transfer therewith. 
         [0078]    Throughout the figures, components are sometimes removed to better show components that would otherwise be obscured. For example, in  FIGS. 4, 5 and 6  one of the springs  5  is removed to illustrate certain components more clearly. 
         [0079]    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.