Abstract:
A damper mechanism for absorbing torsional vibrations in a rotating shaft. The damper mechanism includes a vibration absorbing mechanism and at least one actuator that is controllable to affect the torsional vibration absorbing characteristics of the vibration absorbing mechanism.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to devices for controlling noise, vibration and harshness (NVH) and more particularly to a device for actively reducing or canceling vibration in a rotating shaft.  
         BACKGROUND OF THE INVENTION  
         [0002]    Propshafts are commonly employed for transmitting power from a rotational power source, such as the output shaft of a vehicle transmission, to a rotatably driven mechanism, such as a differential assembly. As is well known in the art, the torsional loading of the propshaft is rarely uniform over an extended period of time even at relatively constant vehicle speeds and as such, the propshaft is typically subjected to a continually varying torsional load. These variances in the torsional load carried by the propshaft tend to create noise in the vehicle drivetrain that is undesirable to passengers riding in the vehicle. In especially severe instances, the vibration that is transmitted through the propshaft can generate fatigue in the propshaft and other drivetrain components to thereby shorten the life of the vehicle drivetrain. Thus, it is desirable and advantageous to attenuate vibrations within the propshaft in order to reduce noise and guard against undue fatigue.  
           [0003]    It is known in the art to provide tuned torsional vibrations dampers for attachment to shafts, such as crankshafts and propshafts, to attenuate torsional vibrations. This approach, however, has several drawbacks. One such drawback is that these devices are usually tuned to a specific frequency and consequently, will only damp vibrations within a relatively narrow frequency band. Accordingly, these devices are typically employed to effectively damp vibrations at a single critical frequency and offer little or no damping for vibrations which occur at other frequencies.  
           [0004]    Another drawback with conventional mechanical damping devices relates to their incorporation into an application, such as an automotive vehicle. Generally speaking, these devices tend to have a relatively large mass, rendering their incorporation into a vehicle difficult due to their weight and overall size. Another concern is that it is frequently not possible to mount these devices in the position at which they would be most effective, as the size of the device will often not permit it to be packaged into the vehicle at a particular location.  
         SUMMARY OF THE INVENTION  
         [0005]    In one preferred form, the present invention provides a dynamic damper mechanism for damping torsional vibration in a shaft. The mechanism includes a damper device having a mass member, an attachment member, a vibration absorbing mechanism and at least one actuator. The attachment member is coupled for rotation with the shaft and the mass member is disposed circumferentially about the attachment member. The vibration absorbing mechanism resiliently couples the mass member to the attachment member and has a torsional vibration absorbing characteristic. The actuator is coupled to the vibration absorbing mechanism and is operable in at least two conditions, with each condition affecting the torsional vibration absorbing characteristic of the vibration absorbing mechanism. The mechanism also includes a first sensor, which is configured to sense a rotational position of the shaft and to generate a position signal in response thereto, as well as a second sensor, which is configured to sense a magnitude of the torsional vibration in the shaft and to generate a vibration signal in response thereto. The controller receives the position signal and the vibration signal and controls the at least one actuator in response thereto to cause the at least one actuator to affect the torsional vibration absorbing characteristic of the vibration absorbing mechanism so as to damp the torsional vibration in the shaft.  
           [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a schematic view of an exemplary vehicle having a propshaft assembly constructed in accordance with the teachings of the present invention;  
         [0009]    [0009]FIG. 2 is a perspective view of the propshaft assembly of FIG. 1;  
         [0010]    [0010]FIG. 3 is an partially broken away front elevation view of the propshaft assembly of FIG. 1; and  
         [0011]    [0011]FIG. 4 is a partially broken away front elevation view of a propshaft assembly constructed in accordance with the teachings of an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    With reference to FIG. 1 of the drawings, a propshaft assembly constructed in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . The propshaft assembly  10  is illustrated in operative associate with an exemplary vehicle  12 . The vehicle  12  conventionally includes a vehicle body  14 , a chassis  16 , a suspension system  18 , a motor  20 , a transmission  22  and an axle assembly  24 . As the construction and operation of the vehicle body  14 , chassis  16 , suspension system  18 , motor  20 , transmission  22  and axle assembly  24  are well known to those skilled in the art, these components need not be discussed in significant detail.  
         [0013]    Briefly, the suspension system  18  resiliently couples the axle assembly  24  to the vehicle chassis  16 . The transmission  22 , which receives a rotary output from the motor  20 , includes a plurality of gear ratios (not specifically shown) that are employed to selectively change the speed ratio of a transmission output shaft  22   a . Rotary power is transmitted via the propshaft assembly  10  to the input pinion  24   a  of an axle assembly  24 . The axle assembly  24  operates to selectively direct the rotary power to a pair of drive wheels  26 .  
         [0014]    With additional reference to FIGS. 2 and 3, the propshaft assembly  10  includes a propshaft  40  and a dynamic damper mechanism  42 . The propshaft  40  includes a tubular body  44  and a pair of conventional spider assemblies  46 . The spider assemblies  46  are coupled the opposite ends of the tubular body  44  and permit the propshaft  40  to be coupled to the transmission output shaft  22   a  and the input pinion  24   a  in a conventional manner.  
         [0015]    The dynamic damper mechanism  42  includes an inner ring  50 , an outer ring  52 , a resilient coupling  54 , an actuator  56  and a controller  58 . The inner ring  50  is coupled for rotation with the tubular body  44  of the propshaft  40  by any conventional process, including fastening, welding, bonding and/or an interference fit (e.g. press fit or shrink fit). The outer diameter of the inner ring  50  includes a plurality of circumferentially-spaced lugs  60  that extend outwardly toward the outer ring  52 .  
         [0016]    The outer ring  52  is concentrically disposed around the inner ring  50  and includes a sufficient amount of mass to accomplish the cancellation of vibration as will be discussed in detail, below. The inner side of the outer ring  52  includes a plurality of circumferentially-extending lugs  62  that extend radially inwardly toward the inner ring  50 . Each of the lugs  62  is disposed between a pair of the lugs  60 . The lugs  60  and  62  do not extend in so far in a radial direction that they contact the outer or inner ring  52  or  50 , respectively.  
         [0017]    The resilient coupling  54  maintains the concentric positioning of the outer ring  52  relative to the inner ring  50 . The resilient coupling  54  may include a plurality of compression springs or may be an elastomeric material as is shown in the example provided.  
         [0018]    One or more actuators  56  are disposed between the inner and outer rings  50  and  52  and in contact with the mutually opposed faces  60   a  and  62   a  of the lugs  60  and  62 , respectively. The actuators  56  may use any appropriate means to extend and retract between the faces  60   a  and  62   a , but in the particular embodiment provided, the actuators includes a magnetostrictive member whose length may be changed by varying the magnitude of an electrical charge that is applied to it. The controller  58  is electrically coupled to the actuators  56  and is operable for selectively controlling the charge that is applied to the magnetostrictive member.  
         [0019]    During the operation of the propshaft assembly  10 , the spring rate of the resilient coupling permits the outer ring  52  to damp vibrations within a predetermined frequency band. The controller  58 , however, may be employed to extend or retract the actuators  56  to change the tangentially applied load on the resilient coupling  54  to thereby affect the spring rate of the resilient coupling  54 . Those skilled in the art will appreciate that the actuators  56  may be controlled so as to cancel-out torsional vibrations entering the axle assembly  24 . More preferably, however, the actuators  56  are controlled so as to cancel out vibration that is generated by the axle assembly  24 , including vibration that is generated by the meshing of the ring gear (not shown) and pinion axle gears (not shown). As this vibration is typically a function of the rotational speed of the propshaft  40 , the response of the controller  58  to a given propshaft rotational speed may be preprogrammed in a look-up table  70 . The controller  58  may utilize the existing vehicle sensors (not shown) and in-vehicle network (not shown) to determine the rotational speed of the propshaft  40  and thereafter control the actuators  56  according to the parameters found in the look-up table  70 .  
         [0020]    Alternatively, the controller  58  may include one or more vibration sensors  72  that are coupled to portions of the vehicle (e.g., the axle assembly  24 ). The vibration sensors  72  are operable for producing a vibration signal in response to sensed vibrations. The controller  58  responsively controls the actuators  56  so as to generate vibrations that are of sufficient amplitude and shifted in phase to cancel out the vibrations that are sensed by the vibration sensors  72 .  
         [0021]    While the propshaft assembly  10  has been described thus far as including a dynamic damper mechanism  42  that includes a resilient coupling that connects a pair of concentric rings, those skilled in the art will appreciate that the present invention, in its broader aspects, may be constructed somewhat differently. As illustrated in FIG. 4 for example, the dynamic damper mechanism  42 ′ may be constructed with a single ring  100  having a plurality of pockets  102  and a plurality of actuators  104 . The pockets  102 , which are circumferentially spaced apart from one another, include a pair of opposite faces  106 .  
         [0022]    Each actuator  104  is disposed in a pocket  102  between the faces  106  and is selectively controllable to expand or contract in a direction that is approximately tangential to the point at which it is mounted in the ring  100 . The actuators  104  may use any appropriate means to extend and retract between the faces  106 , but in the particular embodiment provided, the actuators  104  include a magnetostrictive member whose length may be changed by varying the magnitude of an electrical charge that is applied to the magnetostrictive member. The controller  58 ′ is electrically coupled to the actuators  104  and is operable for selectively controlling the charge that is applied to the magnetostrictive member.  
         [0023]    The controller  58 ′ controls the simultaneous actuation (i.e., expansion or retraction) of the actuators  104  to torsionally excite the ring  100 . Like the dynamic damper mechanism  42 , the actuators  104  of the dynamic damper mechanism  42 ′ may be controlled in a predetermined manner, such as based on the rotational speed of the propshaft  40 , for example, or in response to one or more vibration signals that are generated by an associated vibration sensor.  
         [0024]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.