Abstract:
An accessory drive tuning device with a torsion spring for angular vibration isolation and having a spring pocket that frictionally engages the end of the torsion spring. The engagement may be with a wedge-shape on either the spring end or the pocket or both, adapted so that the spring end wedges into the pocket. The engagement may be by interference fit. One or both ends of the spring may be engaged in respective pockets.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to accessory drive tuning devices with torsion springs for isolation, and in particular, devices with a self-engaging torsion spring locking feature. 
         [0002]    This invention relates to accessory drive tuning devices with torsion springs for isolation of vibrations. These devices as commonly known in the art are alternator tuning pulleys and crankshaft tuning devices. Examples of such devices are the alternator isolator decoupler (“AID”) as described for example in U.S. Pat. No. 8,678,157, the alternator isolator pulley (“AIP”) as described for example in U.S. Pat. No. 7,207,910, a crankshaft isolator decoupler (“CID”), the overrunning alternator decoupler (“OAD”) as described for example in U.S. Pat. Appl. Pub. No. 2013/0098727, and the crankshaft isolator pulley sold under the trade name Torqfiltr by Litens. These devices may or may not have a one-way clutch. In either case the spring may exhibit spring rattle. Spring rattle occurs when the spring is allowed to slide in and out of its pocket or away from its stop. The speed fluctuation resulting from the torsional vibration of a firing engine can cause the spring to slide out in the same or opposite direction relative to the rotating direction of the pulley. The re-engagement of the spring in the pocket or against the stop can create a noise that would be unacceptable to the customer. 
       SUMMARY 
       [0003]    The present invention is directed to systems and methods which provide a solution to the problem of torsional spring rattle in accessory drive tuning devices such as decouplers or isolator pulleys. The solution is designated a “spring lock” and utilizes frictional engagement. One method of achieving a “spring lock” comprises a spring pocket adapted to wedgingly engage with a spring end. The pocket may have a wedge-shape adapted so that the spring end wedges into the pocket when biased into the pocket. 
         [0004]    In other embodiments, the spring end may be tapered for wedging into the pocket. Both the pocket and spring end may be wedge shaped. 
         [0005]    Another method of achieving a “spring lock” is to use an interference fit between at least a portion of the spring inner or outer diameter and a corresponding pocket surface as means of holding the spring in place. 
         [0006]    One or both ends of the torsional spring may engage with associated pockets. When both spring ends engage with their respective pockets, the same embodiment or two different embodiments of frictionally engaging spring locks may be utilized. 
         [0007]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings, which are incorporated in and form part of the specification in which like numerals designate like parts, illustrate embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
           [0009]      FIG. 1  is sectional view of a device according to an embodiment of the invention; 
           [0010]      FIG. 2  is a blow-up perspective view of the device of  FIG. 1 ; 
           [0011]      FIG. 3  is a plan view of a spring carrier with a wedge-shaped pocket; 
           [0012]      FIG. 4  is a perspective view of a spring in the spring carrier of  FIG. 3 ; 
           [0013]      FIG. 5  illustrates mathematically how a wedge may be set; 
           [0014]      FIG. 6  illustrates how a set wedge may resist release; 
           [0015]      FIG. 7  illustrates mechanical and noise measurements on a device without a spring lock feature; 
           [0016]      FIG. 8  illustrates mechanical and noise measurements on a device with a wedge-shaped spring lock feature according to an embodiment of the invention; 
           [0017]      FIG. 9  is a section view of a device that uses an interference fit to the spring inner diameter to hold the spring in place according to an embodiment of the invention; 
           [0018]      FIG. 10  is an exploded view of the device of  FIG. 9 ; 
           [0019]      FIG. 11  shows a more detailed view of the pulley for the embodiment of  FIG. 9 ; 
           [0020]      FIG. 12  shows a sectional view of the pulley of  FIG. 11 ; 
           [0021]      FIG. 13  shows a more detailed view of the clutch carrier for the embodiment of  FIG. 9 ; 
           [0022]      FIG. 14  shows a sectional view of the clutch carrier of  FIG. 13 ; 
           [0023]      FIG. 15  is a section view of a device that uses an interference fit to the spring outer diameter to hold the spring in place according to an embodiment of the invention; 
           [0024]      FIG. 16  shows a more detailed view of the pulley for the device of  FIG. 15 ; 
           [0025]      FIG. 17  shows a sectional view of the pulley of  FIG. 16 ; 
           [0026]      FIG. 18  shows a more detailed view of the clutch carrier for the device of 
           [0027]      FIG. 15 ; and 
           [0028]      FIG. 19  shows a sectional view of the clutch carrier of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    This invention relates to accessory drive tuning devices with torsion springs for isolation angular vibrations. The device may or may not have a one-way clutch, but in either case the torsional spring must be kept in position to prevent spring rattle. Spring rattle occurs when the spring is allowed to slide in and out of its pocket. The speed fluctuation resulting from the torsional vibration of a firing engine can cause the spring to slide out in a clockwise and counter-clockwise direction relative to the rotating direction of the pulley. The re-engagement of the spring can create a noise that would be unacceptable to the customer. What is needed is a locking method to retain the end of the torsional spring in its pocket. To make retaining of the spring end feasible for manufacturing the locking method needs to be self engaging. 
         [0030]    Generally, herein “isolator” is the spring function which provides relative displacement, while being still connected, and “decoupler” is the clutch function which provides an on or off connection. Also, generally “torsional vibration” refers to the twisting of the crankshaft—which is generally controlled by a crank damper, and angular vibration is the rigid body motion of the crank nose which effects the accessory belt drive system (“ABDS”). An isolator decoupler preferably works on the crank angular vibration input to the ABDS, for example, protecting the alternator, but generally not affecting the crank torsional vibration. 
         [0031]      FIG. 1  is a section view of one example of an accessory drive tuning device  100  according to an embodiment of the invention.  FIG. 2  is an exploded view of the device  100  of  FIG. 1 . In  FIGS. 1 and 2 , the torsional spring  4  is housed in pulley  5  and spring carrier  6 .  FIG. 3  is a plan view of spring carrier  6  showing the spring pocket  610  with wedge taper  612 .  FIG. 4  is a perspective view of the spring  4  in the wedge in spring carrier  6 . A similar wedge-shaped pocket for the opposite end of spring  4  may be included in pulley  5 .  FIG. 5  illustrates how the wedge is set in terms of the setting force P, which biases the spring into the pocket, and the resulting wedging force F y .  FIG. 6  illustrates the resistance force R after it is set with the setting force P. The resistance force will hold the spring from moving out of the wedge. If R is less than or equal to F y , then the spring will not pull free from the wedge. This condition results in Equation 1. If Equation 1 is met then the wedge will be self locking and hold the spring in place. 
         [0000]      μ/tan θ≧1  Equation 1
 
         [0032]    θ=Wedge angle 
         [0033]    μ=Coefficient of friction 
         [0034]    The other parts of the exemplary device  100  of  FIGS. 1 and 2  may be described in more detail. Pulley  5  engages a belt (not shown) to drive a device such as an alternator. Pulley  5  houses ball bearing  8  and needle bearing  3  which allow relative motion between shaft  1  and pulley  5  while transferring the radial load to shaft  1 . Pulley  5  is the input to the device and power flows from pulley  5  to one end of coil spring  4 , then from the other end of spring  4  to spring carrier  6 . Pulley  5  and spring carrier  6  each have a recess or pocket  610  machined therein with circular arc  611  to receive Spring  4 . The start of circular arc  611  has radial taper  612  to retain the spring. The angle of radial taper  612  is such that it is a self locking wedge. The end  614  of the pocket would be the stop but for the wedge effect of taper  612 . The device may include various covers, caps, seals, spacers, reinforcing rings or the like, such as covers  9  and  2  and ring  7  in  FIGS. 1 and 2 . Other optional device features include one-way clutch  10 . 
         [0035]    To illustrate how the design works as shown in  FIG. 3  the wedge angle as shown is 5°. If we assume that pulley  5  and spring carrier  6  and spring  4  are made of steel and assume that the steel surfaces are lubricated such that the coefficient of friction is 0.15 then these conditions satisfy Equation 1 and the spring will stay in place unless it is pulled out by some other greater force. 
         [0036]    A prototype isolator decoupler with a torsional spring and with a spring carrier with a wedge-shaped pocket machined therein to function as a stop and catch for the spring end was constructed. The device included a one-way clutch device and was constructed to test the invention. The spring rattling problem was solved in the prototype.  FIGS. 7 and 8  show the noise, pulley speed, and rotor speed with and without the wedge-shaped pocket.  FIG. 7  is without the wedge-shaped pocket and  FIG. 8  is with the wedge-shaped pocket. Comparing the measured noise level (sound pressure in Pa) from both  FIGS. 7 and 8  it is clear that there is less noise with the wedge-shaped pocket. Further proof that the spring is not sliding out is the speed of the rotor. Both  FIGS. 7 and 8  have the same input at the pulley and the rotor speed represents the output. The device with the wedge-shaped pocket has a higher rotor speed in comparison to the device without the wedge shaped pocket. The difference in speed is due to the spring sliding in and out of the pocket only in the device without the wedge shaped pocket. 
         [0037]    Either or both sides of the pocket could be angled to form the wedge. The spring end could be tapered as well, but that is not necessary. The spring end could be tapered or wedge-shaped instead of the pocket. An advantage of the invention is that it is self-engaging and self-locking, so that if the forces increase so that a spring end disengages, the engagement force will generally increase also to engage the spring end in the wedge-shaped pocket even tighter than before it slipped out, thereby locking it in or stabilizing it for the higher force level. 
         [0038]      FIG. 9  is a section view of accessory drive tuning device  200  that illustrates a second embodiment in which an interference fit to the spring inner diameter is used as a means to hold the spring in place.  FIG. 10  is an exploded view of device  200 . In  FIGS. 9-10 , parts numbered 1-3 and 7-10 are as described above for the first embodiment. As shown in  FIGS. 9 ,  11  and  12 , at least a portion of outer cylindrical surface  151  of pulley  15  is larger in diameter than inner diameter  141  of spring  14 . This frictionally restrains spring  14  from sliding out of spring pocket  152  of pulley  15  which is shown in  FIG. 11 . The other end of spring  14  may be retained in a similar fashion. As shown in  FIGS. 9 ,  13  and  14 , at least a portion of outer cylindrical surface  161  of clutch carrier  16  is larger in diameter than spring inner diameter  142  of spring  14 . This frictionally restrains spring  14  from sliding out of spring pocket  162  which is shown in  FIG. 13 . 
         [0039]      FIG. 15  is a section view of accessory drive tuning device  300  that illustrates a third embodiment where an interference fit to the spring outer diameter is used as a means to hold the spring in place. As shown in  FIGS. 15-17 , at least a portion of inner cylindrical surface  251  of pulley  25  is smaller in diameter than outer diameter  241  of spring  24 . This holds spring  24  from sliding out of spring pocket  252  of pulley  25  which is shown in  FIG. 16 . The other end of spring  24  may be retained in a similar fashion or via one of the other embodiments described herein. As shown in  FIGS. 15 ,  18  and  19 , at least a portion of inner cylindrical surface  261  of clutch carrier  26  is smaller in diameter than spring outer diameter  242  of spring  24 . This frictionally restrains spring  24  from sliding out of spring pocket  262  which is shown in  FIG. 18 . 
         [0040]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. The invention disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein.