Abstract:
A torque dampening compensator for a vehicle including an isolator member disposed between an input member and an output member. The isolator member includes isolator elements disposed between corresponding lugs of the respective input and output members. The lugs of the output member have a draft angle, and the isolator elements have contact faces corresponding to the respective lugs with unequal axial depths to induce a moment on each isolator element that counteracts a thrust load between the input and output members initiated by the draft angle. One isolator element of the isolator member is formed to have a size corresponding to the space provided between adjacent lugs of the input and output members and a shape that is dissimilar from the space. The one isolator element is resiliently deformable into the space.

Description:
BACKGROUND 
     The present invention relates to torque dampening compensators for vehicles. Existing compensators suffer from several common drawbacks. First, compensators generally rely on the compression of elastic material enclosed between input and output members to dampen torque pulsations, resulting in thrust loading of the compensator when the elastic material expands parallel to the axis of rotation, perpendicular to the direction of compression. Expensive thrust bearings have commonly been employed to handle the thrust load. Additionally, the elastic material provided in existing compensators provides a relatively fixed damping rate. Such compensators must sacrifice performance in either low-torque/vibration compensation or high-torque compensation capacity in favor of the other. If a balance is desired between low-torque performance and high-torque capacity, the compensator can achieve only mediocre performance in both areas. Furthermore, compression set introduces driveline lash after repeated use. Existing compensators have addressed compression set by oversizing and preloading the elastic material, complicating assembly. 
     SUMMARY 
     In one embodiment, the present invention provides a torque dampening compensator for a vehicle. The compensator includes an input member operable to receive an input torque. The input member includes a first lug portion operable to transmit the input torque. An output member is operable to transmit an output torque that is less than or equal to the input torque. The output member includes a second lug portion operable to receive the output torque. An isolator member is disposed between the input member and the output member. The isolator member is operable to receive the input torque from the input member, to selectively absorb a portion of the input torque, and to transmit the output torque to the output member. The isolator member includes a first portion positioned in a space between the first lug portion and the second lug portion. The first portion of the isolator member has a size corresponding to the space and a shape that is dissimilar to the space. The first portion of the isolator member is resiliently deformable into the space. 
     In another embodiment, the invention provides a torque dampening compensator for a vehicle. An input member is rotatable about an axis and operable to receive an input torque. The input member includes a first radially-extending lug operable to transmit the input torque. The first radially-extending lug has a first radially-extending contact face. An output member is rotatable about the axis and operable to transmit an output torque that is less than or equal to the input torque. The output member includes a second radially-extending lug operable to receive the output torque. The second radially-extending lug has a second radially-extending contact face. An isolator member is disposed between the input member and the output member. The isolator member is operable to receive the input torque from the input member, to selectively absorb a portion of the input torque, and to transmit the output torque to the output member. The isolator member includes a first portion having a first surface in contact with the first contact face and a second surface in contact with the second contact face. At least one of the first and second contact faces being non-parallel with the axis and having a draft angle promoting a thrust load between the input member and the output member when the isolator member is compressed between the first and second lugs. The first and second surfaces of the isolator member are asymmetrical, counteracting the thrust load. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a motorcycle including a rear wheel compensator. 
         FIG. 2  is a side view of a rear wheel assembly of the motorcycle of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the rear wheel assembly taken along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is a detail cross-sectional view of the rear wheel compensator as shown in  FIG. 3 . 
         FIG. 5  is a perspective view of a sprocket of the rear wheel compensator of  FIG. 3 . 
         FIG. 6  is a side view of the sprocket of  FIG. 5 . 
         FIG. 7  is a perspective view of a wheel hub of the rear wheel compensator of  FIG. 3 . 
         FIG. 8  is a side view of the wheel hub of  FIG. 7 . 
         FIG. 9  is a perspective view of an isolator member of the rear wheel compensator of  FIG. 3 . 
         FIG. 10  is an alternate perspective view of the isolator member of  FIG. 9 . 
         FIG. 11A  is a side view of the isolator member of  FIG. 9 . 
         FIG. 11B  is a top view of the isolator member of  FIG. 9 . 
         FIG. 12  is a cross-sectional view of the rear wheel compensator taken along line  12 - 12  of  FIG. 3 . 
         FIG. 13  is a detail cross-sectional view of a portion of the rear wheel compensator taken along line  13 - 13  of  FIG. 12 . 
         FIG. 14  is a free body diagram of one isolator element of the isolator member of  FIGS. 9-11B . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a motorcycle  20  including a frame  22 , an engine/transmission assembly  24  (including an engine  24 A and a transmission  24 B), and a rear wheel assembly  26  that is coupled to the engine/transmission assembly  24  to propel the motorcycle  20 . The rear wheel assembly  26  receives rotational driving force from the engine/transmission assembly  24  through a drive member  27 . The drive member  27  is driven by a sprocket or output gear of the engine/transmission assembly  24  and may take the form of an endless member such as a belt or chain, or alternately a drive shaft. The rear wheel assembly  26  includes, among other things, a wheel  28  and a tire  30  coupled to a rim  28 A ( FIG. 2 ) of the wheel  28  to rotate with the wheel  28 . The tire  30  contacts a road surface to propel the motorcycle  20 . 
     During operation of the motorcycle  20  and transmission of power and torque from the engine/transmission assembly  24  to the rear wheel assembly  26 , torque spikes may occur (e.g., due to road conditions and/or abrupt throttle, clutch, or gear shift input from the rider, etc.). Such torque spikes occur in both the power-transmission direction (“positive”) and the anti-power-transmission (“negative”) direction. For example, a torque spike may occur in the positive direction when the engine  24 A is running and the clutch is abruptly engaged with the transmission  24 B in gear, and a torque spike may occur in the negative direction when the motorcycle  20  is traveling and the throttle position is abruptly reduced. 
     A torque dampening compensator assembly  34  (i.e., “compensator”) of the rear wheel assembly  26  is configured to attenuate the positive and negative torque peaks between the engine/transmission assembly  24  and the rear wheel assembly  26 . With reference to  FIGS. 2 and 3 , the compensator  34  includes an input member in the form of a belt-driven sprocket  38 , an isolator member  40 , and an output member in the form of a rear wheel hub  42 . The rear wheel hub  42  is part of the wheel  28  and is coupled to the rim  28 A and the tire  30  to rotate directly therewith. The sprocket  38  includes a plurality of spaced-apart teeth  38 A ( FIG. 5 ) and is rotated directly by the drive member  27  and is coupled to the rear wheel  28 , including the rear wheel hub  42 , to allow limited relative rotation therebetween. As described in further detail below, the isolator member  40  is disposed between the sprocket  38  and the rear wheel hub  42  to dampen the torque pulsations therebetween. 
     The sprocket  38  receives an input torque from the engine/transmission assembly  24  via the drive member  27 . As shown in  FIGS. 5 and 6 , the sprocket  38  includes a plurality of spaced-apart, radially-extending lugs  46  operable to transmit the input torque. The isolator member  40  is operable to receive the input torque from the lugs  46  of the sprocket  38  and transmit an output torque to the rear wheel hub  42  via a plurality of spaced-apart, radially-extending lugs  50  thereof ( FIGS. 7 and 8 ). The isolator member  40  selectively absorbs a portion of the input torque as described below. 
     The isolator member  40  is operable to transmit an output torque that is less than or equal to the input torque received from the sprocket lugs  46 . Torque is output from the engine  24 A according to a torque signature (related to the spaced-apart power strokes of the respective pistons). Thus, even at steady-state throttle and engine speed, the actual torque from the engine  24 A varies significantly. Commonly, an engine&#39;s output is measured and referred to by taking the average or mean of the peaks and valleys in the torque signature. When mean torque from the engine/transmission assembly  24  changes abruptly a non-steady-state torque condition is introduced (e.g., from an abrupt throttle input), the isolator member absorbs a portion of the input torque, so that only a fraction of the input torque from the sprocket  38  is initially transmitted to the rear wheel hub  42 . In addition to being responsive to changes in mean torque output, the compensator assembly  34  is operable to selectively absorb energy in order to smooth out the torque peaks in the engine&#39;s torque signature (that occur even during steady-state engine conditions), keeping the peak torque values closer to the mean torque output of the engine  24 A. The isolator member  40  also buffers the sprocket  38  from any abrupt change in rotation originating at the rear wheel  28  and tire  30 . 
     As shown in  FIGS. 3 and 4 , the rear wheel assembly  26  is rotatably coupled to a rear axle  54  with a pair of bearings  56 . The rear axle defines an axis of rotation A of the rear wheel assembly  26 . The sprocket  38  is supported at its center by additional bearings  58  (e.g., two single-row standard deep-groove ball bearings) for rotational movement relative to the axle  54  and, to a lesser degree, relative to the rear wheel hub  42 . As described in further detail below, the bearings  58  supporting the sprocket  38  need not include an angular contact ball bearing to withstand thrust loads, as the compensator  34  is designed to reduce or eliminate thrust loads between the sprocket  38  and the rear wheel hub  42 . 
     As shown in at least  FIGS. 5 and 6 , each of the lugs  46  includes a first contact face  60  and a second contact face  62 . The contact faces  60 ,  62  extend generally radially from a hub portion  64  of the sprocket  38 , perpendicular to the axis A. The five lugs  46  are arranged in a star-shaped pattern about the axis A. The rear wheel hub  42  is at least partially nested with the sprocket  38  such that the lugs  50  of the hub  42  overlap axially with the sprocket lugs  46 . As shown in at least  FIGS. 7 and 8 , each of the hub lugs  50  includes a pair of contact faces  66 ,  68 , each of which extends generally radially toward and perpendicular to the axis A from a rim portion  70  of the hub  42 . The lugs  46  of the sprocket  38  are intermeshed, although not contacting, with the lugs  50  of the hub  42  so that the respective lugs  46 ,  50  alternate circumferentially. The respective sets of lugs  46 ,  50  are circumferentially spaced from one another to create a plurality of spaces therebetween. In the illustrated embodiment, ten such spaces are present, each being occupied by a portion of the isolator member  40  ( FIG. 12 ). 
     The isolator member  40  is shown in  FIGS. 9-11B  and includes five pairs of isolator portions or elements  74 . The isolator member  40  includes five large isolator elements  74 A and five small isolator elements  74 B, each large isolator element  74 A being paired with a small isolator element  74 B such that the large and small isolator elements  74 A,  74 B alternate circumferentially. The large isolator elements  74 A are positioned between the respective first contact faces  60 ,  66  of the sprocket and hub lugs  46 ,  50  to absorb/transmit positive loads (e.g., upon acceleration). The small isolator elements  74 B are positioned between the respective second contact faces  62 ,  68  of the sprocket and hub lugs  46 ,  50  to absorb/transmit negative loads (e.g., upon deceleration). The large isolator elements  74 A have a higher energy absorption capacity necessary for the large amounts of power and torque that can potentially be transmitted abruptly from the engine/transmission assembly  24 . 
     Each pair of large and small isolator elements  74 A,  74 B are coupled by a strap  78  that is positioned across the isolator elements  74 A,  74 B (at a radially central location thereof). The straps  78  are positioned at the outboard or sprocket-facing side of the isolator member  40  and engage corresponding notches  80  in the hub lugs  50  ( FIGS. 7 and 8 ). The isolator member  40  further includes a central ring  82  to which each pair of isolator elements  74 A,  74 B is coupled. The central ring  82  is positioned at the inboard or hub-facing side of the isolator member  40 . Each paired set of isolator elements  74 A,  74 B straddles one of the hub lugs  50 , and the isolator member  40  as a whole is axially and radially positioned by the straps  78  contacting the respective hub lugs  50 . 
     Recesses  86  are formed in the sprocket  38  between adjacent lugs  46  as shown in  FIGS. 5 and 6 . The recesses  86  provide space in the axial direction to prevent rubbing between the sprocket  38  and outboard surfaces  88  of the isolator elements  74 A,  74 B that otherwise occurs in conventional compensators that are tightly packaged in the axial direction. The outboard surfaces  88  ( FIGS. 9 ,  11 B, and  13 ) are also truncated and/or concave to limit the amount of axial expansion that occurs under compression between sprocket and hub lugs  46 ,  50 . Thus, the likelihood of stretching and cracking of the material is reduced and durability is increased. Recesses  90  are also formed in the hub  42  between adjacent lugs  50  as shown in  FIGS. 7 and 8 . The recesses  90  provide space in the axial direction to prevent rubbing between the hub  42  and inboard surfaces  92  of the isolator elements  74 A,  74 B. The inboard surfaces  92  ( FIGS. 10 ,  11 A, and  13 ) are also truncated and/or concave to limit the amount of axial expansion that occurs under compression between sprocket and hub lugs  46 ,  50 . Ample axial clearance is provided on both sides of the isolator member  40  to prevent abrasion of the isolator elements  74 A,  74 B and thrust loading of the bearings (discussed in further detail below) during relative rotation between the sprocket  38  and the hub  42 . 
     As shown in  FIG. 12 , each of the large isolator elements  74 A includes a truncated portion  96  at a radially outward part thereof, creating a gap where the large isolator elements  74 A do not contact the sprocket  38  or the hub  42 . The gap exists as shown in  FIG. 12  when the compensator is in its neutral state and the isolator elements  74 A,  74 B are not compressed between respective sprocket and hub lugs  46 ,  50 . During compression of the large isolator elements  74 A, the gap size is decreased as increasing contact is established between the truncated portion  96  and both the sprocket lugs  46  and the rim portion  70  of the hub  42 . This gives the compensator a progressive damping rate that allows substantial absorption at high torque low engine speed (i.e., preventing audible rattling of transmission gears that may otherwise occur) while being stiff enough to offer acceptable drivability with little or no lag in power delivery. The available stiffness also eliminates resonances from occuring within the normal operating range of the engine. The torsional hysteresis curve of the isolator member  40  as it dissipates torsional vibration and shock loading is non-linear. 
     As shown in  FIG. 13 , each of the wheel lugs  50  is formed with a slight draft angle α such that the contact faces  66 ,  68  are not parallel with the compensator axis A. The contact faces  66 ,  68  lie at an angle α of about 3 degrees offset from being parallel with the axis A in the illustrated construction. The draft angle α is present for manufacturability to cast the hub  42 . When either the large or small isolator elements  74 A,  74 B are compressed between sprocket and hub lugs  46 ,  50 , the draft angle α on the hub lugs  50  tends to initiate or promote a thrust load between the sprocket  38  and the hub  42  through the compressed isolator elements  74 A or  74 B. Although the recesses  86 ,  90  in the sprocket  38  and hub  42  prevent substantial thrust loading of the bearings  58  caused by axial expansion of the isolator elements  74 A,  74 B, the draft angle α of the hub lugs  50  encourages the isolator elements  74 A,  74 B to slide axially relative to the sprocket  38  and the hub  42 . To counteract the thrust load from propogating through the isolator elements  74 A,  74 B and acting to push the sprocket  38  and the hub  42  apart, a moment is induced on each of the isolator elements  74 A,  74 B by a feature designed into the isolator elements  74 A,  74 B. The effect is illustrated and described below with particular reference to one of the large isolator elements  74 A for exemplary purposes. 
     As shown in  FIG. 13 , the large isolator element  74 A includes opposing surfaces  100 ,  102  in contact with the respective first contact faces  60 ,  66  of the sprocket and hub lugs  46 ,  50 . The surface  100  of the large isolator element  74 A that contacts the first contact face  60  of the sprocket lug  46  defines a first axial contact length L 1 . The surface  102  of the large isolator element  74 A that contacts the first contact face  66  of the hub lug  50  defines a second axial contact length L 2  that is larger than the first axial contact length L 1 . The effective contact between the hub lug  50  and the isolator element  74 A extends further outboard than the contact between the isolator element  74 A and the sprocket lug  46 . Therefore, the surfaces  100 ,  102  are asymmetrical and a moment is imparted to the large isolator element  74 A when it is compressed between the sprocket and hub lugs  46 ,  50 . The moment counteracts the thrust-load-inducing effect of the hub lug draft angle α by effectively “pulling” the sprocket  38  in towards the hub  42  through static friction between the isolator member  40  and the sprocket lugs  46 . 
       FIG. 14  is a simplified free body diagram of one large isolator element  74 A to illustrate how the asymmetry designed into the isolator member  40  counteracts thrust load from being propagated between the sprocket  38  and the hub  42 . Counteracting forces FX 1  and FX 2  are incident on the isolator element  74 A from the hub lug  50  and the sprocket lug  46 , respectively. The x-direction forces FX 1 , FX 2  are resolved from distributed surface forces to centralized point loads in  FIG. 14 . Because the x-direction forces FX 1 , FX 2  are offset in the y-direction by an axial offset distance Y 1 , a moment is necessarily generated. A reactant moment M (clockwise in  FIG. 14 ) about the point of application of the force FX 2  balances the initial moment (counterclockwise in  FIG. 14 ) to maintain static equilibrium. The static friction force (not shown in  FIG. 14 ) on the isolator element  74 A from the sprocket lug  46  on the corresponding surface  100  of the isolator element  74 A is responsible for the reactant moment M. The equal and opposite static friction force applied by the isolator element  74 A on the sprocket  38  creates the effect of “pulling” of the sprocket  38  axially inboard towards the hub  42  in order to counteract the natural tendency for the sprocket  38  and the hub  42  to experience a separation type thrust load due to the draft angle α. 
     It will be appreciated that the above-described phenomenon occurs at each of the isolator elements  74 A,  74 B, and the overall effect is counteraction of the thrust load on the bearings  58  as the sprocket  38  and the hub  42  are inhibited from being urged axially apart from each other by the isolator member  40 . Because substantial thrust loading between the sprocket  38  and the hub  42  is avoided, the bearings  58  that support the sprocket  38  on the hub  42  need not be configured to accommodate thrust loads. For example, a compensator that is not particularly configured to avoid thrust loading is typically provided with an angular contact ball bearing to properly bear the thrust load. In the compensator  34 , the bearings  58  are provided as two single-row standard deep-groove ball bearings that are widely available and relatively inexpensive compared to angular contact ball bearings or other means that may be provided to accommodating thrust loading. The illustrated compensator  34  eliminates the need for any such means. 
     As shown in  FIGS. 9-12 , one of the small isolator elements  74 B is formed differently from the rest and includes a lug-facing concave side  108 . Opposite the concave side  108 , a second side of the small isolator element  74 B includes a projection or protuberance  112  having a generally convex shape.  FIGS. 9-11B  illustrate the isolator member  40  in a natural, unstressed state. As shown in  FIG. 12 , the concave side  108  faces a hub lug  50  and the protuberance  112  faces an adjacent sprocket lug  46  when the isolator member is positioned in the compensator  34 .  FIG. 12  illustrates the compensator  34  in a neutral state in which the isolator member  40  is not being compressed to actively absorb rotational energy during transmission between the sprocket  38  and the hub  42 . In the neutral state of the compensator  34 , the one differently-formed small isolator element  74 B is deformed from its natural shape to fit into the space between the corresponding sprocket and hub lugs  46 ,  50 . Particularly, the concave side  108  is put into tension to assume a relatively flat shape to lie against the second contact face  68  of the corresponding hub lug  50 , and the protuberance  112  is compressed to assume a relatively flat shape to lie against the second contact face  62  of the corresponding sprocket lug  46 .  FIG. 12  shows the natural shape of the concave side  108  and the protuberance  112  in dashed lines. 
     As shown in  FIG. 12 , the differently-shaped small isolator element  74 B is not oversized for the space between the corresponding sprocket and hub lugs  46 ,  50 . Rather, the shape of the isolator element  74 B is different from the shape of the corresponding space. Accordingly, the differently-shaped isolator element  74 B must be deformed to assemble the compensator  34 , but the deformation is not in the form of overall compression of the isolator element  74 B into a smaller space (i.e., the allotted volume of space between the corresponding sprocket and hub lugs  46 ,  50  is not substantially smaller than the volume of the isolator element  74 B in its natural state). Thus, the bending of the isolator element  74 B (from the dashed line shape to the solid line shape in  FIG. 12 ) during assembly of the compensator  34  imparts a spring-biasing force or preload into the compensator  34 . The presence of this deformation and spring-bias reduces the effect of compression set in the compensator  34 , which commonly results in substantial lash or “play” in the driveline after repeated use in existing compensators. 
     Rather than making one or more of the isolator elements  74 A,  74 B oversized and requiring that they be compressed into place during assembly to achieve a preload in the compensator, the compensator  34  is assembled by deflecting or deforming only the one differently-shaped small isolator element  74 B. Thus, assembly of the compensator  34  is not complicated and requires low effort. Further easing assembly effort, the protuberance  112  does not extend the full axial depth of the small isolator element  74 B. As illustrated in  FIGS. 9 and 10 , the protuberance  112  extends only about three fourths of the overall axial depth of the small isolator element  74 B from the inboard side. 
     Thus, the invention provides, among other things, a compensator  34  that is easy to assemble, resistant to compression set, and inexpensive to manufacture due to the exclusion of a thrust bearing. The compensator  34  has progressive response and features that enhance durability and avoid excessive stretching of the isolator member  40  during compression. Various features and advantages of the invention are set forth in the following claims.