Patent Publication Number: US-2022213835-A1

Title: Isolation device with two or more springs in series

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application no. 62/844,904, filed May 8, 2019, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The specification relates generally to isolation devices for use on accessory drives for engines, and in particular for use on accessory drives for hybrid engines that incorporate a motor-generator unit (MGU) or similar device. 
     BACKGROUND OF THE DISCLOSURE 
     For engines, and in particular vehicular engines, an isolator is typically provided on the accessory drive so as to reduce the natural frequency of the external torque load driven by the crankshaft of the engine to be below the peak input torque frequency over a selected range of operating conditions for the engine. In some isolators, in addition to providing one or more springs there is frictional damping that is provided, which inhibits the isolator from going into resonance. Damping can be effective for this purpose, however, it is important not to provide too much damping, since this can negatively affect the performance of the isolator is primary function of reducing the natural frequency of the external torque load. 
     However, in some situations, it would be advantageous for the isolator to have a greater amount of damping. It would therefore be advantageous to provide an isolator that has an increased amount of damping in certain situations, but without having to have the increased amount of damping at all times. 
     Separately, it is generally desirable for the isolator to have as much travel as possible, in some situations, while having a reduced or at least not needing a large amount of travel in other situations. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, there is provided an isolation device, which includes a hub, a pulley and at least one isolation spring arrangement. The hub is mountable to a shaft. The pulley is rotatably mounted to the hub. The at least one isolation spring arrangement includes a first isolation spring and a second isolation spring. Each of the first and second isolation springs is a helical compression spring having a length. The first isolation spring has a first spring rate. The second isolation has a second spring rate and is positioned in series with the first isolation spring. The first spring rate is higher than the second spring rate. The first and second isolation springs are arranged such that the first isolation spring transfers torque from the second isolation spring into a first one of the hub and the pulley and the second isolation spring transfers torque from the first isolation spring into a second one of the hub and the pulley. Initially during torque transfer from the first one of the hub and the pulley to the second one of the hub and the pulley, the entire first isolation spring is slid along a friction surface towards the second one of the hub and the pulley by the first one of the hub and the pulley during compression of the second isolation spring thereby generating a first frictional damping torque. Initially during torque transfer from the second one of the hub and the pulley to the first one of the hub and the pulley, at least a portion of the first isolation spring remains stationary relative to the friction surface and the entire second isolation spring is slid along the friction surface, during compression of the first isolation spring by the second one of the hub and the pulley, thereby generating a second frictional damping torque. The first and second spring rates and the lengths of the first and second isolation springs are selected such that the first frictional damping torque is greater than the second frictional damping torque. 
     In another aspect, there is provided an isolation device, which includes a hub, a pulley and at least one isolation spring arrangement. The hub is mountable to a shaft. The pulley is rotatably mounted to the hub. The at least one isolation spring arrangement includes a first isolation spring and a second isolation spring. Each of the first and second isolation springs is a helical compression spring having a first end, a second end, and a plurality of coils between the first and second ends. The first ends of the first and second isolation springs face away from one another, and the second ends of the first and second isolation springs face one another. The first and second isolation springs each have a diameter, and extend along an arcuate path inside the pulley about an isolation device axis. The first isolation spring has a first spring rate, and wherein the second isolation has a second spring rate and is positioned in series with the first isolation spring, wherein the first spring rate is higher than the second spring rate. The first and second isolation springs are arranged such that the first isolation spring transfers torque from the second isolation spring into a first one of the hub and the pulley and the second isolation spring transfers torque from the first isolation spring into a second one of the hub and the pulley. A first spring drive surface on the first one of the hub and the pulley engages the first end of the first isolation spring, and a second spring drive surface on the second one of the hub and the pulley engages the first end of the second isolation spring. The second spring drive surface extends across a first portion of the diameter of the second isolation spring such that there is a space adjacent the second spring drive surface towards the isolation device axis. The space extends across a second portion of the diameter of the second isolation spring, from a side edge of the second spring drive surface to a radially inner edge of the second isolator spring relative to the isolation device axis. During torque transfer from the first one of the hub and the pulley to the second one of the hub and the pulley, the at least one isolation spring arrangement permits relative movement between the hub and the pulley through a first range of angular movement, and wherein, during torque transfer from the second one of the hub and the pulley to the first one of the hub and the pulley, the at least one isolation spring arrangement permits relative movement between the hub and the pulley through a second range of angular movement. The second spring rate and a size of the space are selected such that, at a selected torque transfer level during torque transfer between the hub and the pulley through the first and second isolation springs, the selected torque transfer level drives the coils of the second isolation spring to contact one another on the radially inner side of the second isolation spring relative to the isolation device axis, which in turn drives at least one of the coils at the free end of the second isolation spring to tip into the space, which in turn permits the first range of angular movement to exceed the second range of angular movement. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       For a better understanding of the embodiment(s) described herein and to show more clearly how the embodiment(s) may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: 
         FIG. 1  is an elevation view of an engine with an isolation device in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a perspective view of the isolation device shown in  FIG. 1 . 
         FIG. 3  is a perspective exploded view of the isolation device shown in  FIG. 2 . 
         FIG. 4  is an isolation spring arrangement from a prior art isolation device. 
         FIG. 5  is isolation spring arrangement from the isolation device shown in  FIG. 2 . 
         FIG. 6  is a perspective view of a portion of the isolation device shown in  FIG. 1 , showing torque transfer from a hub of the isolation device to a pulley of the isolation device. 
         FIG. 7  is a perspective view of a portion of the isolation device shown in  FIG. 1 , showing torque transfer from a pulley of the isolation device to a hub of the isolation device. 
         FIG. 8  is a graph illustrating torque output from the isolation device shown in  FIG. 1  on a test machine simulating an engine. 
         FIG. 9  is a graph illustrating torque output from an isolation device of the prior art. 
         FIG. 10A  is a plan view of the portion of the isolation device shown in  FIG. 6 , showing a first range of movement available during torque transfer from the hub to the pulley. 
         FIG. 10B  is a plan view of the portion of the isolation device shown in  FIG. 7 , showing a second range of movement available during torque transfer from the pulley to the hub. 
         FIG. 11A  is a magnified plan view of the isolation spring arrangement immediately prior to tipping of coils from one of the isolation springs in the isolation spring arrangement. 
         FIG. 11B  is a magnified plan view of the isolation spring arrangement immediately after tipping of coils from one of the isolation springs in the isolation spring arrangement. 
         FIG. 12  is a sectional view of a portion of the isolation device shown in  FIG. 2 . 
         FIG. 13  is a magnified view of one of the isolation springs in the isolation spring arrangement of the isolation device shown in  FIG. 2 , with an optional flattening of certain surfaces thereof. 
         FIG. 14  is a perspective view of a variant of the isolation device shown in  FIG. 2 , where each isolation spring arrangement includes first, second and third isolation springs all in series with one another. 
         FIG. 15  is a perspective view of another variant of the isolation device shown in  FIG. 2 , where each isolation spring arrangement includes first, second and third isolation springs where two of the springs are in series and a third spring is in parallel with the two springs in series. 
         FIG. 16  is a perspective view of yet another variant of the isolation device shown in  FIG. 2 , including a connector that connects the isolation springs that make up the isolation spring arrangement. 
     
    
    
     Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale. 
     DETAILED DESCRIPTION 
     For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. 
     Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: “or” as used throughout is inclusive, as though written “and/or”; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; “exemplary” should be understood as “illustrative” or “exemplifying” and not necessarily as “preferred” over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description. It will also be noted that the use of the term “a” will be understood to denote “at least one” in all instances unless explicitly stated otherwise or unless it would be understood to be obvious that it must mean “one”. 
     Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     Reference is made to  FIG. 1 , which shows an engine  10  for a vehicle. The engine  10  includes a crankshaft  12  which drives an endless drive element, which may be, for example, a belt  14 . Via the belt  14 , the engine  10  drives a plurality of accessories  16  (shown in dashed outlines), such as a motor/generator unit (MGU) and an air conditioning compressor. Each accessory  16  includes an accessory shaft  15  with a pulley  13  thereon, which is driven by the belt  14 . Additionally, shown in the present embodiment is an idler pulley shown at  17   a  on an idler shaft  17   b,  and a tensioner pulley  19   a  rotatably mounted on a tensioner arm  19   b,  which form part of a belt tensioner  19 . The functions of the idler pulley  17   a  and the belt tensioner  19  are well known to one of skill in the art. 
     An isolation device  20  may be provided instead of a pulley, in one or more places to control torque transfer between the crankshaft  12  and the accessory shafts  15 . In  FIG. 1 , the isolation device  20  is provided on the crankshaft  12 . The isolation device  20  transfers torque between the crankshaft  12  and the belt  14 , but attenuates torsional vibrations from the crankshaft  12  from being transmitted to the belt  14 . Such torsional vibrations, oscillations in the speed of the crankshaft  12 , are inherent to internal combustion piston engines. These oscillations are isolated from the belt  14  by the isolation device  20 , and as a result, the stresses that would otherwise be incurred by the belt  14  and by the accessory shafts  15  are reduced. 
     Reference is made to  FIGS. 2 and 3 , which show a perspective assembled view, and a perspective exploded view of the isolation device  20 , respectively. The isolation device  20  includes a hub  22 , a pulley  24 , first and isolation spring arrangements, each shown at  28 . In the example shown in  FIGS. 2 and 3 , the isolation device  20  further includes optional elements including a bushing  29 , seals  30  and a thrust plate  35 . 
     The hub  22  includes a shaft adapter  22   a  and a driver  22   b  in the embodiment shown. The shaft adapter  22   a  is adapted to mount to the crankshaft  12  in any suitable way. For example, the shaft adapter  22  may have a shaft-mounting aperture  36  therethrough that defines a rotational axis A for the isolation device  20 . The shaft mounting aperture  36  may be configured to snugly receive the end of the crankshaft  12 . A plurality of shaft-mounting fasteners  37 , such as bolts, ( FIG. 1 ) may be inserted through a distal end  38  shaft adapter  22   a  and driver  22   b  to fixedly mount them to the crankshaft  12  so that the hub  22  and the crankshaft  12  co-rotate together about the axis A. 
     The driver  22   b  includes first and second drive arms  100 , individually shown at  100   a  and  100   b.  Each drive arm  100  has a first hub/spring interface surface  102  and a second hub/spring interface surface  104 . The first and second hub/spring interface surfaces  102  and  104  are positioned to engage ends of the isolation spring arrangements  28  as described further below. 
     The pulley  24  is rotatably coupled to the shaft adapter  22 . The pulley  24  has an outer surface which includes a belt engagement surface  40  that is configured to engage the belt  14  ( FIG. 1 ). The belt  14  may thus be a multiple-V belt. 
     The pulley  24  may be formed from a main pulley portion  24   a  that includes the belt engagement surface  40  thereon, and a pulley cover  24   b  that cooperates with the main pulley portion  24   a  to define a spring shell  42 , for holding the first and second isolation spring arrangements  28 . 
     The pulley  24  further includes an inner surface  43 . The bushing  27  engages the inner surface  43  of the pulley  24  and rotatably supports the pulley  24  on the shaft adapter  22   a.  The bushing  27  may be a polymeric member that has a selected, low friction coefficient. Suitable materials for the bushing  27  include, for example, certain forms of nylon. 
     The pulley  24  includes two pairs of lugs that are formed by pressing in the material of the main pulley portion  24   a  and the pulley cover  24   b  inwardly. A first pair of lugs  109   a  is shown in  FIG. 3 . The second pair of lugs  109   b  is shown in  FIG. 12 . The first pair of lugs  109   a  face one another, and the second pair of lugs  109   b  face one another. The pulley  24  includes first and second pulley/spring interface surfaces  106  and  108 , which are positioned to engage ends of the isolation spring arrangements  28 , as described further below. In the embodiment shown, the first pulley/spring interface surfaces  106  are provided on a first side of the lugs  109   a  and  109   b,  and the second pulley/spring interface surfaces  108  are provided on a second side of the lugs  109   a  and  109   b.    
     The isolation spring arrangements  28  are provided to accommodate oscillations in the speed of the crankshaft  12  in relation to the belt  14 , as noted above. The isolation spring arrangements  28  may each include a first isolation spring  110  and a second isolation spring  112 . Each of the first and second isolation springs  110  and  112  ( FIG. 5 ) is a helical compression spring, and preferably extends along an arcuate path inside the pulley  24 . Each of the first and second isolation springs  110  and  112  has a first end  114 , a second end  116 , and a plurality of coils  118  between the first and second ends  114  and  116 . The first ends  114  of the first and second isolation springs  110  and  112  face away from one another, and the second ends  116  of the first and second isolation springs  110  and  112  face one another. The first and second isolation springs  110  and  112  a length L 1  and L 2  ( FIG. 5 ), respectively, and a diameter D 1  and D 2  ( FIG. 5 ), respectively. The first and second isolation springs  110  and  112  have respective first and second spring rates K1 and K2. In the embodiment shown, the diameters D 1  and D 2  are approximately equal, though they do not need to be strictly equal. In the embodiment shown, the length L 1  is greater than the length L 2 , though this need not be true in all embodiments. In the embodiment shown, the first spring rate K1 is greater than the second spring rate K2, though this need not be true in all embodiments. 
     The first and second isolation springs  110  and  112  are arranged in series with one another, such that the first isolation spring  110  transfers torque from the second isolation spring  112  into a first one of the hub  22  and the pulley  24  and the second isolation spring  112  transfers torque from the first isolation spring  110  into a second one of the hub  22  and the pulley  24 . In the example shown in  FIG. 6 , the first one of the hub  22  and the pulley  24  is the hub  22  and the second one of the hub  22  and the pulley  24  is the pulley  24 . As can be seen in this example, the first end  114  of the second isolation spring  112  remains fixed rotationally relative to the pulley  24 , while the driver  22   b  engages the first end  114  of the first isolation spring  110 . 
     Because the first spring rate K1 is higher than the second spring rate K2, what occurs initially during torque transfer from the first one of the hub  22  and the pulley  24  to the second one of the hub  22  and the pulley  24 , is that the entire first isolation spring  110  is slid along a friction surface  120  (which in this instance is a surface of the pulley cover  24   b ) towards the second one of the hub  22  and the pulley  24  by the first one of the hub  22  and the pulley  24  during compression of the second isolation spring  112  thereby generating a first frictional damping torque TF 1 . This damping torque can be seen in the torque/displacement curve shown at  200  in  FIG. 8 . This damping torque TF 1  arises from friction generated by the movement of the first isolation spring  110  along the friction surface  120 , and by the movement of a portion of the second isolation spring  112  along the friction surface  120 . Only a portion of the second isolation spring  112  moves, or moves significantly, along the friction surface  120  in this example, since the first end  114  of the second isolation spring  112  is engaged with the second pulley/spring interface surface  108 . 
     During this initial range of torque transfer (shown at  202  in  FIG. 8 ), the effective spring rate of the isolation spring arrangement  28  is equal to 1/(1/K1+1/K2). Once the torque transfer through the first and second isolation springs  110  and  112  reaches a first selected torque transfer level TS 1  ( FIG. 8 ), the first isolation spring  110  is fully compressed, at which point only the second isolation spring  112  continues to be compressed, which defines a second range of torque transfer. In this second period of torque transfer, the effective spring rate of the isolation spring arrangement  28  is only the spring rate K2, since the first spring is effectively a solid member, having been compressed fully. This second range of torque transfer is shown at  204  in  FIG. 8 . 
     By contrast,  FIG. 7  (and the torque curve  250  in  FIG. 8 ) illustrate torque transfer from the second one of the hub  22  and the pulley  24  to the first one of the hub  22  and the pulley  24 . As can be seen, the first end  114  of the second isolation spring  112  is engaged with the first pulley/spring interface surface  106 . As a result, initially a portion of the second isolation spring  112  remains stationary relative to the friction surface  120  and the entire second isolation spring  112  is slid along the friction surface  120  during compression of the first isolation spring  110  by the second one of the hub  22  and the pulley  24 , thereby generating a second frictional damping torque TF 2  ( FIG. 8 ). 
     The first and second spring rates K1 and K2 and the lengths L 1  and L 2  of the first and second isolation springs  110  and  112  impact the first and second frictional damping torques TF 1  and TF 2 , and may be selected such that the first frictional damping torque TF 1  is greater than the second frictional damping torque TF 2 . The size of the difference between the first and second frictional damping torques TF 1  and TF 2  depends at least in part on such factors as the particular lengths selected for L 1  and L 2  and the particular spring rates selected for K1 and K2. 
     Also, in the example shown in  FIG. 7 , relating to curve  250  in  FIG. 8 , once the torque transfer through the first and second isolation springs  110  and  112  reaches a second selected torque transfer level TS 2  ( FIG. 8 ), the first isolation spring  110  is again fully compressed, at which point only the second isolation spring  112  continues to be further compressed, which defines a second range of torque transfer. As can be seen, because of the increased amount of damping torque that is present initially during torque transfer from the first one of the hub  22  and the pulley  24  to the second one of the hub  22  and the pulley  24  relative to initially during transfer from the second one of the hub  22  and the pulley  24  to the first one of the hub  22  and the pulley  24 , the first selected torque transfer level TS 1  at which the first isolation spring  110  is fully compressed and the isolation spring arrangement  28  enters the second range of torque transfer is higher than the second selected torque transfer level TS 2  at which the first isolation spring  110  is fully compressed and the isolation spring arrangement  28  enters the second range of torque transfer. 
     By contrast, an isolation spring arrangement of the prior art is shown at  280  in  FIG. 4  and has a torque curve that is shown at  300  in  FIG. 9 . The torque curve  300  shown in  FIG. 9  is mathematically derived, and thus appears much cleaner than the torque curves shown in  FIG. 8 , which were derived from a simulated engine. The isolation spring arrangement  280  shown in  FIG. 4  includes first and second isolation springs  282  and  284  which are nested (i.e. such that the second isolation spring  284  is nested within and is shorter than, the first isolation spring  282 ). With springs that are nested, the amount of frictional damping that is provided is more or less solely dependent on friction between the outer spring (i.e. the first isolation spring  282 ), and the friction surface (not shown) against which it rubs. Accordingly, there is essentially no difference in the amount of damping torque regardless of whether the hub of such an isolator would transfer torque to the pulley, or whether the pulley would transfer torque to the hub. Thus the curve  300  is representative of the torque transfer both ways, (i.e. regardless of which end of the isolation spring assembly  280  is being moving relative to the friction surface against which the isolation spring arrangement  280  slides). 
     These properties of the isolation device  20  described herein, may be advantageous in a number of situations or applications. For example, in a situation in which the engine  10  is equipped with the MGU  16   a,  the engine  10  may have two modes of starting, including a first start mode (referred to as a key start) in which the engine  10  is started via a starter motor engaged with the flywheel until combustion takes over, and a second start mode (referred to as an MGU start) in which the MGU drives the crankshaft  12  via the belt  14  until combustion takes over. During a key start, it may be desirable to have a relatively high amount of friction in the initial range of torque transfer through the isolation device  20 , and it may be desirable to move the torque at which the isolation spring arrangement  28  enters the second range of torque transfer to be as late as possible. This inhibits the isolation device  20  from cycling between the first ranges and second ranges of torque transfer. During an MGU start, however, there may be less need for frictional damping for certain reasons. For example, during an MGU start there is a lower likelihood of resonance from occurring. 
     Another feature of the isolation device  20  is illustrated in  FIGS. 11 and 12 , and relates to the hub/spring interface surfaces  102  and  104  and in particular the pulley/spring interface surfaces  106  and  108 . For the purposes of discussing this feature, whichever of the hub/spring interface surfaces  102  and  104  or the pulley/spring interface surfaces  106  and  108  is engaged with the first end  114  of the first isolation spring  110  will be referred to as a first spring drive surface  140 , and whichever of the hub/spring interface surfaces  102  and  104  or the pulley/spring interface surfaces  106  and  108  is engaged with the first end  114  of the second isolation spring  112  will be referred to as a second spring drive surface  142 . In the example situation shown in  FIG. 6 , the first spring drive surfaces  140  are the first hub/spring interface surfaces  104 , and the second spring drive surfaces  142  are the first pulley/spring interface surfaces  106 . 
     As can be seen based on  FIGS. 6 and 12 , the second spring drive surface  142  extends across a first portion  144  of the diameter D 2  of the second isolation spring  112  such that there is a space  146  adjacent the second spring drive surface  142  towards the isolation device axis A. The space  146  extends across a second portion  148  of the diameter D 2  of the second isolation spring  112 , from a side edge of the second spring drive surface  142  to a radially inner side  150  of the second isolator spring  112  relative to the isolation device axis A. 
     As can be seen from  FIGS. 10A and 10B , during torque transfer from the first one of the hub  22  and the pulley  24  to the second one of the hub  22  and the pulley  24 , the isolation spring arrangements  28  permit relative movement between the hub  22  and the pulley  24  through a first range of angular movement (R 1  shown in  FIG. 10A ), and wherein, during torque transfer from the second one of the hub  22  and the pulley  24  to the first one of the hub  22  and the pulley  24 , the isolation spring arrangements permit relative movement between the hub  22  and the pulley  24  through a second range of angular movement R 2  shown in  FIG. 10B . 
     The second spring rate K2 and the size of the space  146  are selected such that, at a selected torque transfer level TS 3  during torque transfer between the hub  22  and the pulley  24  through the first and second isolation springs  110  and  112 , the selected torque transfer level TS 3  drives the coils  118  of the second isolation spring  112  to contact one another on the radially inner side  150  of the second isolation spring  112  relative to the isolation device axis A, and to drive at least one of the coils  118  at the first end  114  of the second isolation spring  112  to tip into the space  146 , which in turn permits the first range of angular movement to exceed the second range of angular movement. 
     The reason for this is that the first spring rate K1 of the first isolation spring  110  is relatively high. As a result, there is no tendency for the first isolation spring  110  to tip into the space  146  in order to extend the range of movement available, when the first spring drive surface  140  is one of the pulley/spring interface surfaces  106  and  108 . This extension of the first range of movement relative to the second range of movement is advantageous in certain scenarios. For example, when the engine undergoes a key start, it is beneficial to provide as much range of movement as possible in order to prevent lock up of the isolation device  20 . However, by contrast, during an MGU start, it is sometimes considered advantageous to have a shorter range of movement prior to lock up of the isolation device, in order to provide high torque to the crankshaft  12  relatively quickly. 
     The space  146  may extend across any suitable amount of the diameter of the second isolation spring  112 . In an embodiment, the space  146  may extend across at least 30% of the diameter of the second isolation spring  112 . In an embodiment, the space  146  may extend across at least one third of the diameter of the second isolation spring  112 . 
     It will be noted that the first and second isolation springs shown in the embodiment shown in  FIGS. 3-12  are coiled oppositely to one another. As a result, when torque is transferred through their respective second ends  116  to one another, there is no likelihood of the first and second isolation springs  110  and  112  entangling. By contrast, this would be possible if the first and second isolation springs  110  and  112  were coiled the same way (e.g. both right handed, or left handed coiling). 
     Reference is made to  FIG. 13 , which shows an optional feature on the second isolation spring  112 . In order to reduce stresses on the coils  118  and slippage between the coils  118  of the isolation spring  112  when the torque applied through the isolation spring arrangement  28  is such that the coils  118  of the second isolation spring  112  contact one another, the mating surfaces shown at  180  of the coils  118  (i.e. also referred to as the intra-coil surfaces  180 , are flattened prior to formation of the stock wire into the second isolation spring  112 . 
     Reference is made to  FIG. 14 , which shows a variant of the isolation device  20 , in which each isolation spring arrangement  28  includes the first isolation spring  110 , the second isolation spring  112  and a third isolation spring  182  that is in series with the first and second isolation springs  110  and  112 . In the embodiment shown, the third isolation spring  182  has a third spring rate K3 that is higher than the second spring rate K2, and which may be higher or lower than the first spring rate K1. The advantages above regarding the increased amount of damping torque, the shift in the torque at which the isolation device enters into the second range of torque transfer and the increased range of movement during torque transfer are all present in this variant. 
     Reference is made to  FIG. 15 , which shows another variant of the isolation device  20 , in which each isolation spring arrangement  28  includes the first isolation spring  110 , the second isolation spring  112  and a third isolation spring  186  that is in parallel with the first and second isolation springs  110  and  112 . In the embodiment shown, the third isolation spring  182  has a third spring rate K3 that is higher than the second spring rate K2, and which may be higher or lower than the first spring rate K1. The advantages above regarding the increased amount of damping torque, the shift in the torque at which the isolation device enters into the second range of torque transfer and the increased range of movement during torque transfer are all present in this variant. 
     A variant of the isolation device  20  is shown in  FIG. 16 . As can be seen, a connector  190  is provided, which holds the second ends  116  of the first and second isolation springs  110  and  112 . The connector includes a plate  192  that engages the second ends  116  of the first and second isolation springs  110  and  112 , a first projection  194  extending from the plate  192  into the first isolation spring  110  (i.e. into a hollow  195  in the first isolation spring  110 ), and a second projection  196  extending from the plate  192  into the second isolation spring  112  (i.e. into a hollow  197  in the second isolation spring  112 . The plate  192  and projections  194  and  196  maintain the second ends  116  of the first and second isolation springs  110  and  112  parallel with one another, so as to maintain torque transfer across an entirety of the second ends  116  between the first and second isolation springs  110  and  112 . 
     It will be noted that, while the embodiments herein show the isolation device  20  on the crankshaft  12  it is alternatively possible to provide the isolation device  20  on the shaft of the MGU  16   a  or any other suitable accessory. In such embodiments, the arrangement of the first and second isolation springs  110  and  112  may need to be reversed, depending on when the application calls for higher friction, longer travel and any of the other features described herein. 
     Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible, and that the above examples are only illustrations of one or more implementations. The scope, therefore, is only to be limited by the claims appended hereto and any amendments made thereto.