Abstract:
The present invention provides a damping apparatus and/or method for a rotatable shaft. The damping apparatus includes a damper housing disposed about a portion of the rotatable shaft. A variable viscosity fluid, such as a magneto-rheological fluid, is disposed within the damper housing and in contact with the rotatable shaft. A control device is operatively connected with respect to the variable viscosity fluid. The control device is configured or operable to control the viscosity of the variable viscosity fluid and correspondingly control the amount of rotational resistance applied to the rotatable shaft.

Description:
TECHNICAL FIELD  
       [0001]     The present invention pertains generally to an improved damping apparatus and a method for damping a rotatable shaft.  
       BACKGROUND OF THE INVENTION  
       [0002]     Intermeshing gears may sometimes produce a noise or gear rattle during transient relative rotational speed changes between a drive and a driven gear. One example where this may occur is within a manual shift or countershaft transmission. A countershaft transmission has an input shaft, a countershaft, and an output shaft. The input shaft and the countershaft are interconnected by meshing gears (head gear set). The countershaft and the output shaft are interconnected by a plurality of meshing gears (speed gears) that are selectively connectible to one of the shafts through synchronizer clutch arrangements. Thus, a plurality of gear meshes are present between the input shaft and the output shaft. The speed ratio between the input shaft and the output shaft is controlled by the meshing speed gears. The speed ratio between the input shaft and the output shaft is changed by interchanging the synchronizers that control the connection of the speed gears to their respective shafts. The head gear set and the active speed gear set have a lash condition. Under some operating conditions, the lash condition of the head gear set and the active speed gear set can reverse possibly resulting in a gear rattle caused by the lash reversal.  
         [0003]     Gear rattle may occur as a transient lash condition during transient drive events such as throttle “tip in”, throttle “tip out”, and rapid clutch disengagement. As is well known, the clutch is disengaged and re-engaged for each ratio interchange and during stopping and launching of the vehicle. Additionally, a countershaft transmission may exhibit gear rattle under steady state drive events, such as when the vehicle is traversing a hill in gear. The gear rattle, in this case, is caused by engine generated torque oscillations within the driveline.  
         [0004]     Modern vehicular drivelines may have a number of additional components that may also include meshing gear sets that may be subject to gear rattle. These may include transaxles, transfer cases, and differentials.  
         [0005]     Attempts have been made to attenuate gear rattle. These include various bearing designs, component designs, and gear designs to name a few. Each of these attempts may result in increased drag on the shafts to which the gear is mounted, which may be continuously present. This inherent drag may reduce the mechanical efficiency of the system.  
       SUMMARY OF THE INVENTION  
       [0006]     The damping apparatus of the present invention includes a damper housing disposed about a portion of a rotatable shaft. A variable viscosity fluid, such as a magneto-rheological fluid, is disposed within the damper housing and is operatively associated with the rotatable shaft. A control device is operatively connected to the variable viscosity fluid. The control device is configured or controllable to control the viscosity of the variable viscosity fluid and correspondingly control the amount of rotational resistance applied to the rotatable shaft.  
         [0007]     A preferred method for damping a rotatable shaft includes providing a variable viscosity fluid, such as a magneto-rheological fluid, disposed in contact with the rotatable shaft. Thereafter, a variable strength magnet field is preferably generated within the variable viscosity fluid to alter the viscosity thereof. The strength of the magnetic field is controlled to selectively alter the viscosity of the variable viscosity fluid such that the amount of rotational resistance applied to the rotatable shaft is variable.  
         [0008]     According to one aspect of the invention, the damping apparatus includes a magnetic device operatively connected to the control device, wherein the magnetic device is configured or controllable to produce a variable strength magnetic fluid within the variable viscosity fluid and thereby selectively alter the viscosity thereof.  
         [0009]     According to another aspect of the invention, the damping apparatus includes a fin mounted to the rotatable shaft configured to increase the drag transferred to the rotatable shaft when engaged by the variable viscosity fluid.  
         [0010]     According to yet another aspect of the invention, the damping apparatus includes a seal disposed within a seal groove defined by the damper housing.  
         [0011]     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic cross-sectional view of a powertrain including a damper assembly in accordance with the present invention; and  
         [0013]      FIG. 2  is a schematic cross-sectional view of a damper assembly of the powertrain of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a powertrain  10  including an engine  12 , a countershaft transmission  14 , and a manually operated clutch assembly  16  operatively connected therebetween. The countershaft transmission  14  is shown for illustrative purposes, and it should be appreciated that the present invention may also be applied to alternate applications that incorporate a rotatable shaft. The transmission  14  includes a transmission housing  24  having a front cover  27  mounted thereto. The transmission  14  also includes an input shaft  18 , a countershaft  20 , and an output shaft  22  that are at least partially disposed within the housing  24 . The input shaft  18  is coaxially aligned with the output shaft  22 , and the countershaft  20  is in parallel relation with both the input shaft  18  and the output shaft  22 . The engine  12  has a throttle control  26  and the clutch assembly  16  has a clutch control  28 . Both of the controls  26  and  28  are manually operated by the operator. When the clutch  16  is engaged, the engine  12  will rotate the input shaft  18 .  
         [0015]     The input shaft  18  has a head gear  38  drivingly connected thereto and meshing with a head gear  40  that is drivingly connected with the countershaft  20  such that the countershaft  20  will rotate whenever the input shaft  18  is rotating. The countershaft  20  has a plurality of speed or ratio gears  42 ,  44 ,  46 , and  48  drivingly connected therewith and meshing with respective speed or ratio gears  50 ,  52 ,  54  and  56  that are disposed on the output shaft  22 . A reverse idler  58  is rotatably mounted on an idler shaft (not shown), and is meshing with a ratio gear  60  on the countershaft  20  and a ratio gear  62  on the output shaft  22 . Each of the ratio gears  50 ,  52 ,  54 ,  56 , and  62  are selectively individually connectable with the output shaft  22  by respective synchronizers, not shown, of conventional design. A selectively actuatable damper assembly  64  is mounted to the front cover  27  as will be described in detail hereinafter.  
         [0016]     When the operator wishes to change the speed ratio between the input shaft  18  and the output shaft  22 , the throttle control  26  is released and clutch mechanism is  28  is actuated by the operator. The operator then manually, through a conventional shift control linkage (not shown), manipulates the synchronizers to release one ratio and engage the other. This operation is well-known. Also during vehicle deceleration, the operator releases the throttle control  26  to permit the engine to reduce in speed thereby slowing the vehicle. The throttle release is also known as “tip out”.  
         [0017]     It is well known to apply drag to one or more of the input shaft  18 , the countershaft  20 , and/or the output shaft  22  in an attempt to slow the relative speed of meshing gears and thereby reduce gear noise. These attempts include various bearing designs, component designs, and gear designs. It has been observed, however, that this additional drag may reduce the mechanical efficiency of the system. Advantageously and in accord with this invention, the damper assembly  64  is selectively actuatable or operable such that it may be implemented when there is an increased likelihood of gear noise, such as, for example, during transient drive events including throttle “tip in”, throttle “tip out”, or rapid clutch disengagement; and thereafter the damper assembly  64  may be deactivated to improve the mechanical efficiency of the system.  
         [0018]     Referring to  FIG. 2 , the damper assembly  64  is shown in more detail. To facilitate engagement with the damper assembly  64 , an end portion  66  of the countershaft  20  is extended through the front cover  27  and out of the transmission housing  24 . The damper assembly  64  includes a damper housing  70  circumscribing the end portion  66  of the countershaft  20  and is mounted to the front cover  27  such as with the threaded fasteners  72 . When mounted to the front cover  27 , the damper housing  70  defines a reservoir or cavity  74  that is filled with a controlled volume of variable viscosity fluid  76 . The damper housing  70  preferably also defines a seal groove  78  adapted to accommodate an O-ring seal  79  and thereby seal the interface between the front cover  27  and the damper housing  70  such that the variable viscosity fluid  76  does not leak out of the reservoir  74 . Similarly, the front cover  27  preferably defines a seal groove  90  adapted to accommodate a seal  92  and thereby seal the interface between the front cover  27  and the countershaft  20  such that the variable viscosity fluid  76  does not leak out of the reservoir  74 .  
         [0019]     In the preferred embodiment, the variable viscosity fluid  76  is a magneto-rheological (MR) fluid  80 ; however alternate fluids such as, for example, electro-rheological fluid may also be envisioned. The MR fluid  80  has a dense suspension of micrometer-sized particles in a liquid that will cause the MR fluid  80  to solidify into a pasty consistency of high viscosity in the presence of a magnetic field, and re-liquefy upon removal of the field. Accordingly, the damper assembly  64  preferably includes a magnetic device or source  82  retained by the damper housing  70 . The magnetic device  82  is configured to selectively produce a magnetic field within the MR fluid  80  to control the viscosity thereof. The magnetic device  82  is connected electrically with a control device such as an electronic control unit (ECU)  84  (shown in  FIG. 1 ) that controls engine performance and has a plurality of sensors that include a throttle position sensor, a clutch actuator sensor, and input and output speed sensors. The ECU  84  preferably includes a programmable digital computer that issues commands to the powertrain  10  (shown in  FIG. 1 ).  
         [0020]     The ECU  84  (shown in  FIG. 1 ) is selectively programmable to command the magnetic device  82  to produce a variable strength magnetic field. By varying the strength of the magnetic field, the viscosity of the MR fluid  80  is correspondingly variable. As the viscosity of the MR fluid  80  is increased, the end portion  66  of the countershaft  20  encounters greater rotational resistance such that drag is applied to the countershaft  20 . The drag applied to the countershaft  20  resists relative motion between the input shaft  18 , the countershaft  20  and the output shaft  22  such that gear noise is minimized. The ECU  84  preferably activates or energizes the magnetic device  82  only when there is an increased likelihood of gear noise, such as, for example, during transient drive events including throttle “tip in”, throttle “tip out”, or rapid clutch disengagement; and thereafter the magnetic device  82  is deactivated reduce countershaft  20  resistance and improve the mechanical efficiency of the system. The normal state of the magnetic device  82  is preferably “off” or “low” so that vehicle performance and fuel economy are not unnecessarily diminished.  
         [0021]     According to a preferred embodiment, the end portion  66  of the countershaft  20  includes a plurality of fins  68  configured to increase drag transferred to the countershaft  20  when engaged by the MR fluid  80 . In some applications; however, the MR fluid  80  can transfer enough drag directly to the end portion  66  of the countershaft  20  so that the fins  68  are not required. According to alternate embodiments, the fins  68  may be formed onto a separate attachment or extension (not shown) that is mounted to a conventional countershaft.  
         [0022]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.