Patent Publication Number: US-2010116617-A1

Title: Isolator with one-way clutch

Description:
FIELD OF THE INVENTION 
     The invention relates to an isolator with a one-way clutch, and more particularly to an isolator with one-way clutch having a resilient member operationally engaged between the one-way clutch and a belt engaging member. 
     BACKGROUND OF THE INVENTION 
     Serpentine accessory drive systems are widely used on various vehicle engines including automotive, industrial, truck and bus. A typical serpentine drive system includes a driving pulley on the crankshaft of the vehicle engine. A belt is trained on a series of driven pulleys for the accessories. An advantage of the serpentine drive is that, by providing an automatic belt tensioner in the system, the accessories can be fixedly mounted instead of requiring a means of adjustment to properly tension the belt. 
     The engine crankshaft by its periodic pulse nature establishes a highly dynamic loading on the belt. This high dynamic loading is due to the variable torque output characteristics of internal combustion engines. The tensioner cannot accommodate all of the variable torque characteristics which causes fluctuations in the belt tension. The result can be noise and decreased belt life due to instantaneous belt slippage between the belt and the crankshaft pulley. 
     Engine crank shaft decouplers are used to deal with the high dynamic belt loading. Generally, the decoupler must have a capacity equal to the system capacity. 
     Representative of the art is U.S. Pat. No. 5,139,463 to Bytzek et al. which discloses a serpentine belt drive system for an automotive vehicle in which the sequence of driven assemblies includes an alternator assembly comprising a housing and an armature assembly mounted in the housing for rotation about an armature axis. A hub structure is carried by the armature assembly outwardly of the housing for rotation therewith about the armature axis. A coil spring is disposed in operative relation between the alternator pulley and the hub structure for transmitting the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the armature assembly is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient rotational movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof. 
     What is needed is an isolator with one-way clutch having a resilient member operationally engaged between the one-way clutch and a belt engaging member. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide an isolator with one-way clutch having a resilient member operationally engaged between the one-way clutch and a belt engaging member. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises an isolator comprising a one-way clutch engaged with a hub structure, a belt engaging member, a resilient member operationally engaged between the one-way clutch and the belt engaging member, the belt engaging member engaged with the hub structure through a first and second ball bearing where by a radial load is transmitted through the first and second ball bearings, and the one-way clutch disposed between the first and second ball bearings such that no radial load is transmitted through the one-way clutch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is an exploded view of the preferred embodiment. 
         FIG. 2  is a perspective cross-sectional view of the embodiment in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the embodiment in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of a one-way clutch. 
         FIG. 5(   a ) is a graph of the speed difference versus time between the alternator hub and the alternator pulley at low alternator load. 
         FIG. 5(   b ) is a graph of the speed of the alternator hub, alternator pulley and the crankshaft at low alternator load. 
         FIG. 5(   c ) is a graph of the alternator current at low alternator load. 
         FIG. 6(   a ) is a graph of the speed difference versus time between the alternator hub and the alternator pulley at high alternator load. 
         FIG. 6(   b ) is a graph of the speed of the alternator hub, alternator pulley and the crankshaft at high alternator load. 
         FIG. 6(   c ) is a graph of the alternator current at high alternator load. 
         FIG. 7(   a ) is a graph of the difference in oscillation of the alternator pulley and the alternator rotor with the alternator unloaded. 
         FIG. 7(   b ) is a graph of the difference in oscillation of the alternator pulley and the alternator rotor with the alternator loaded. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is an exploded view of the preferred embodiment. The inventive isolator comprises a hub structure  30 . A one-way clutch  50  is mounted to the hub structure  30 . The hub structure may comprise a shaft for connection to an engine crankshaft (not shown) or driven accessory (not shown). 
     Inner carrier  40  is mounted to an outer surface  51  of one-way clutch  50 . 
     Resilient member  60  has a first end  61  connected to the inner carrier  40 . A second end  62  is connected to outer carrier  90 . Resilient member  60  may comprise a torsional spring. The torsional spring may be the flat type having a substantially rectangular cross-section across each volute as shown. 
     The torsional stiffness of member  60  should be approximately 0.5-1.0 N-m/degree to provide a suitable safety factor for one-way clutch  50 . Resilient member  60  engagement to the first and second end should be one directional, meaning the resilient member  60  is loaded in the unwinding direction. In other words when resilient member  60  is loaded its diameter increases. The expansion of resilient member  60  is limited by contact with the inner bore of belt engaging member  70 . This ensures that the resilient member  60  is not overstressed and suffers fatigue failure. Since resilient member  60  is never operated in the winding direction because of the decoupling nature of the one way clutch, resilient member  60  does not contact the outer surface  41  of carrier  40 . 
     End cap  10  is engaged with belt engaging member  70 . Opposite end cap  10 , outer carrier  90  is engaged with belt engaging member  70 . End cap  10  and outer carrier  90  are rotationally engaged through bearing  20  and bearing  80 , respectively. Each bearing  20  and  80  is engaged with hub structure  30 . 
     One-way clutch  50  comprises those available in the industry, including but not limited to NTN HF type clutches, including part numbers HFO-612, 812, and HF1-012, 216, 416, 616, 816, and HF2-016, 520, and HF3-020, 520. These clutches have the desirable feature of having a thin radial thickness which in turn reduces the overall diameter and mass of the isolator. 
     There are two requirements that are known related to one-way clutches outside the isolator arts. The first requirement is that the one-way clutch inner race should be supported concentrically with respect to the outer race. In other words a separate set of bearings should be used to accept any radial load present in the system which might otherwise deform the one-way clutch. For example, a radial load is imposed on the isolator due to a belt tensile load, see RL  FIG. 3 . 
     The most common location of the bearings is between input and output members, for example end cap  10  and outer carrier  90 . The bearings are located in such a way that input and output members are concentric. This allows the one-way clutch installed between the input and output members to operate properly without a radial load being transmitted to the one-way clutch, in turn the inner and outer races will remain concentric as well. This arrangement is not taught in the isolator arts. 
     The second requirement is an excess of load carrying capacity that that is routinely designed into the one-way clutch. System applications with moderate to high torsional vibration (torque pulses) require a safety factor to be 15 to 20 for a one-way clutch to be suitably durable. The present design which incorporates a resilient member  60  reduces the safety factor which leads to a reduction in size, weight, and cost of the one-way clutch. The present isolator allows a one-way clutch safety factor in the range of approximately 5 to 10. 
       FIG. 2  is a perspective cross-sectional view of the embodiment in  FIG. 1 . One-way clutch is mounted to hub structure  30  between bearings  20  and  80 . Inner carrier  40  is mounted to an outer surface  51  of one-way clutch  50 . Surface  71  of belt engaging member  70  may have any suitable profile for engaging a belt, including multi-ribbed, single v-rib, or cogged. The multi-ribbed profile is shown. 
     End cap  10 , inner carrier  40  and outer carrier  90  each seal the interior of the device, thereby protecting the one-way clutch from debris which could cause premature failure. 
       FIG. 3  is a cross-sectional view of the embodiment in  FIG. 1 . Belt engaging member  70  is freely rotatable about hub structure  30  through bearings  20  and  80 . Of course, free rotation of belt engaging member  70  is subject to operation of one-way clutch  50  and resilient member  60 . When locked one-way clutch  50  causes hub structure  30  to rotate in unison with belt engaging member  70  thereby allowing torque to be transmitted from belt engaging member  70  to hub structure  30 , and thereby to an accessory (not shown) connected to hub structure  30 . 
     Resilient member  60  resiliently controls rotational movement of belt engaging member  70  about hub structure  30  in a predetermined direction. In operation, torque pulses caused by cylinder firing of the IC engine are absorbed by the resilient member  60 , which reduces or eliminates transmission of those pulses to the accessory attached to hub  30 . In other words, an accessory (not shown) connected to the hub  30  is not forced to instantaneously follow the movements of the belt engaging member  70 . 
     One-way clutch  50  provides an over-running feature. During engine deceleration belt engaging member  70  will proportionally decelerate because of the connection to a crankshaft pulley (not shown). However, the inertia of the accessories, for example an alternator, will tend to continue to rotate at its pre-deceleration speed (Newton&#39;s first law). The presence of the one-way clutch  50  will allow hub  30  to disengage and overrun the rest of the isolator structure since the isolator structure which will tend to rotate at the same speed as the decelerating crankshaft. The overrunning feature is vital since it eliminates the potential for belt slip and noise. 
       FIG. 4  is a cross-sectional view of a one-way clutch. One-way clutch  50  is mounted to a hub structure  30 . Inner carrier  400  is mounted to an outer surface of one-way clutch  50 . One-way clutch  50  comprises those available in the industry, including but not limited to NTN HF type clutches, including part numbers HFO-612, 812, and HF1-012, 216, 416, 616, 816, and HF2-016, 520, and HF3-020, 520. These clutches have the desirable feature of having a thin radial thickness. 
     Resilient member  60  is operationally engaged between inner carrier  400  and outer carrier  900 . Resilient member may comprise a torsion spring, for example, comprising a round wire or flat wire. 
     A portion  901  of outer carrier  900  slidingly engages an outer surface  401  of inner carrier  400 . A surface  902  engages a surface  402 . The sliding engagement between the inner carrier and the outer carrier enables the over-ride feature during engine deceleration, for example. Before overrunning can occur, a minimal amount of torque must exist between the belt engaging member  70  and hub  30 . Once the torque threshold is reached overrunning will occur. At this point the belt engaging member  70 , outer carrier  90 , resilient member  60  (displaced enough to cover the minimal torque) and inner carrier  40  rotate in unison as a single part at the same speed. 
     The one-way clutch described in  FIG. 4  can be used in any suitable application, besides in an alternator isolator. The resilient member  60  attributes a soft landing feature to the device. Normally, lock up of the clutch can cause a shock to be transmitted through the system. This can in turn decrease the operational life of the system and its components. The resilient member soft landing feature affords protection to components that are operationally connected to the one-way clutch by significantly reducing the magnitude of shocks that might otherwise be transmitted. 
     The one-way clutch used in the isolator comprises one-way clutch  50 , carrier  40 , resilient member  60 , and carrier  90 . 
       FIG. 5(   a ) is a graph of the speed difference versus time between the alternator hub and the alternator pulley at low alternator load. At low alternator loads the overrun speed is approximately 3000 RPM. The inventive one-way clutch is effective in decoupling alternator inertia during high engine decelerations and low alternator loads. 
       FIG. 5(   b ) is a graph of the speed of the alternator hub, alternator pulley and the crankshaft at low alternator load. 
       FIG. 5(   c ) is a graph of the alternator current at low alternator load. 
       FIG. 6(   a ) is a graph of the speed difference versus time between the alternator hub and the alternator pulley at high alternator load. At high alternator loads the overrun speed is approximately 1400 RPM. The inventive one-way clutch is effective in decoupling alternator inertia during high engine decelerations and high alternator loads. 
       FIG. 6(   b ) is a graph of the speed of the alternator hub, alternator pulley and the crankshaft at high alternator load. 
       FIG. 6(   c ) is a graph of the alternator current at high alternator load. 
       FIG. 7(   a ) is a graph of the difference in oscillation of the alternator pulley and the alternator rotor with the alternator unloaded. 
       FIG. 7(   b ) is a graph of the difference in oscillation of the alternator pulley and the alternator rotor with the alternator loaded. The inventive device is effective in reducing alternator rotor vibration compared to the alternator pulley vibration. Further, the plots demonstrate that the effectiveness and function of the isolator is not hindered by alternator load. This is a distinct advantage over prior art devices with only one-way clutches and no isolators, i.e., spring  60 . 
     The information shown in  FIGS. 5 and 6  was taken on the inventive device including the one-way clutch  50  while the data for the vibration attenuation shown in  FIG. 7  was taken with an isolator only device without the one-way clutch  50 . However, the behavior of the inventive device with a one-way clutch  50  is expected to be the same as shown in  FIG. 7 . 
     Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.