Abstract:
A method for evaluating energy transmission from an axle through a vehicle suspension system. The methodology employs a torsional actuator to apply input energy to the vehicle in a manner that mimics the energy that is generated by the axle during the operation of the vehicle so that both the driving load and the vibration induced by gearset motion variation are simulated. Since the energy input can be quantified and monitored, the same amount of torque can be applied during each test to permit the technician to fully comprehend differences in the designs of several axles on the transmission of noise and vibration.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a method for the evaluation of noise from an axle into a vehicle and more particularly to a method for experimentally evaluating the transfer functions that dictate the amount and type of axle energy that is transferred through a vehicle suspension system into the vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    Scientific evaluation of complex noise sources in automobiles, such as axles, has long been desired, particularly in view of recent advancements in the sound-proofing of modern automobiles. One problem that is encountered in this evaluation concerns the various paths through which noise may be transferred from its source into the vehicle. More specifically, the amount and type of energy that is transmitted from a noise source into the vehicle is a function of the interactions between the noise source and each item, component and/or assembly that couples the noise source to the vehicle. Without a thorough understanding and quantification of these transfer functions, the task of noise attenuation may be at least partially based upon improvements that are discovered through trial-and-error testing. Accordingly, the task of noise attenuation usually cannot be accomplished in the most expedient and efficient manner without a thorough understanding and quantification of the transfer functions that link a noise source to the vehicle.  
           [0003]    In the context of an axle assembly, the amount and type of energy that is transmitted into the vehicle is a function of the interactions between the axle assembly and the vehicle suspension system (since the axle assembly is coupled to the vehicle suspension system) and the interactions between the vehicle suspension system and the vehicle body (since the vehicle suspension system is coupled to the vehicle body).  
           [0004]    Mathematical (i.e., calculation-based) modeling of these transfer functions can be extremely complex and time consuming. Further complicating matters is the fact that a set of transfer functions is usually unique to a particular vehicle configuration. Changes in the suspension system, the vehicle body or the coupling of the suspension system to the vehicle body may therefore affect a vehicle&#39;s set of transfer functions to the extent that a new mathematical model would be desired.  
           [0005]    Accordingly, there remains a need in the art for a method which improves the speed and accuracy with which a set of transfer functions that quantify the amount and type of energy that is transmitted from an axle through a vehicle suspension system are fashioned.  
         SUMMARY OF THE INVENTION  
         [0006]    In one preferred form, the present invention provides a method for evaluating energy transmission into a vehicle over at least one transfer path between an axle and a vehicle suspension system. The method includes the steps of: applying a torsional input to a gearset in the axle to torsionally excite the axle in a manner that mimics the gearset&#39;s excitation of the axle during operation of the vehicle; and monitoring the energy that is transmitted through the vehicle suspension system into the vehicle via the at least one transfer path.  
           [0007]    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  
       [0008]    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:  
         [0009]    [0009]FIG. 1 is a schematic view of an exemplary vehicle that is being tested in accordance with the teachings of the present invention;  
         [0010]    [0010]FIG. 2 is a schematic view of a portion of the vehicle of FIG. 1; and  
         [0011]    [0011]FIG. 3 is a partially broken away view of a portion of the vehicle of FIG. 1 illustrating the gearset of the axle in greater detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    With reference to FIGS. 1 through 3 of the drawings, an exemplary vehicle tested in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . The vehicle  10  is illustrated to include a vehicle body  12 , a chassis  14 , a suspension system  16 , a motor  18 , a transmission  20 , a propshaft  22  and an axle assembly  24 . As these components are well known to those skilled in the art, a detailed discussion of their construction and operation need not be provided herein.  
         [0013]    Briefly, the suspension system  16  resiliently couples the axle assembly  24  to the chassis  14  via conventional components such as shock absorbers  26  and struts  28 . The motor  18  and the transmission  20  are conventionally operable for supplying a rotary input to the axle assembly  24  via the propshaft  22 .  
         [0014]    With specific reference to FIGS. 2 and 3, the axle assembly  24  is illustrated to include a differential assembly  30 , a left axle shaft assembly  32 , and a right axle shaft assembly  34 . The differential assembly includes a housing  36 , a differential unit  38  and an input shaft assembly  40 . The housing  36  supports the differential unit  38  for rotation about a first axis  42  and further supports the input shaft assembly  40  for rotation about a second axis  44  that is generally perpendicular to the first axis  42 .  
         [0015]    The housing  36  is typically formed in a suitable casting process and is thereafter machined as required. The housing  36  includes a wall member  48  that defines a central cavity  50  having a left axle aperture  52  and a right axle aperture  54 .  
         [0016]    The left axle shaft assembly  32  includes a first axle tube  60 , which extends into the left axle aperture  52  and is fixedly coupled to the housing  36 , as well as a first axle half-shaft  62  that is supported for rotation in the first axle tube  60  about the first axis  42 . Similarly, the right axle shaft assembly  34  includes a second axle tube  64 , which extends into the right axle aperture  54  and is fixedly coupled to the housing  36 , as well as a second axle half-shaft  66  that is supported for rotation in the second axle tube  64  about the first axis  42 .  
         [0017]    The differential unit  38  is disposed within the central cavity  50  of the housing  36  and includes a case  70 , a ring gear  72  that is fixed for rotation with the case  70 , and a differential gearset  74  that is disposed within the case  70 . The differential gearset  74  includes first and second side gears  76  and  78 , respectively, and a plurality of differential pinions  80  that are rotatably supported on pinion shafts  82  that are mounted to the case  70 . The case  70  includes a pair of trunnions  84  and  86  and a gear cavity  88 . A pair of bearing assemblies  90  are shown to support the trunnions  84  and  86  for rotation about the first axis  42 . The first axle half-shaft  62  and the second axle half-shaft  66  extend through the left and right axle apertures  52  and  54 , respectively, and are coupled for rotation with the first and second side gears  76  and  78 , respectively. The case  70  is operable for supporting the plurality of differential pinions  80  for rotation within the gear cavity  88  about one or more axes that are perpendicular to the first axis  42 . The first and second side gears  76  and  78  each include a plurality of teeth  94  that meshingly engage teeth  96  that are formed on the differential pinions  80 .  
         [0018]    The input shaft assembly  40  extends through the input shaft aperture  98  and includes an input pinion shaft  100 , a conventional propshaft coupling flange  102  and a pair of conventional bearing assemblies  104 . Each of the bearing assemblies  104  is coupled to the housing  36  and supports the input pinion shaft  100  for rotation about the second axis  44 . The input pinion shaft  100  includes a plurality of pinion teeth  106  that meshingly engage the ring gear  72 . Accordingly, rotary power transmitted to the input pinion shaft  100  (via the propshaft  22 ) is communicated to the ring gear  72  which serves to rotate the case  70  to thereby transmit the rotary power through the differential gearset  74  and to the first and second axle half-shafts  62  and  66  in a predetermined manner.  
         [0019]    As the vehicle body  12  is coupled to the chassis  14 , noise generated by the axle assembly  24  during the operation of the vehicle  10  is able to migrate into the vehicle passenger compartment  12   a  where it would be felt or heard by the vehicle passengers. One component of the noise that is generated by the axle assembly  24  is induced by subtle variances in the formation of each tooth in the axle gearset  110  (i.e., the input pinion teeth  106 , the ring gear  72 , and the differential gearset  74 ), as well as subtle variances in the location of each tooth relative to the pitch diameter of its associated gear and in the mounting of the gear relative to the other gears in the axle gearset  110 . Another component of the noise that is generated by the axle assembly is gearset motion variation, which may be described as an acceleration (positive or negative) that migrates through the axle gearset  110  in response to variances in the magnitude of the rotary input (i.e., torque or speed) that is transmitted to the axle gearset  110  via the propshaft  22 .  
         [0020]    With additional reference to FIG. 1, the methodology of the present invention will now be discussed in detail. The vehicle  10  is prepared for testing by uncoupling the propshaft  22  from the propshaft coupling flange  102  and locking the drive wheels  120  so as to prevent the axle assembly  24  from rotating the drive wheels  120  during the test. An appropriate sensor array having a plurality of vibration sensors  130 , such as accelerometers, is employed to generate a sensor signal in response to the sensed vibrations that are being transmitted into the vehicle passenger compartment  12   a . As is discussed in detail in commonly assigned copending U.S. patent application Ser. No. 09/796,205 entitled “Active Vibration Control”, the disclosure of which is hereby incorporated by reference as if fully set forth herein, vibrations are transmitted into the vehicle passenger compartment  12   a  through a plurality of transfer paths  136 , wherein each transfer path  136  includes a component or assembly of the suspension system  16  that links or couples the axle assembly  24  to the chassis  14 . Accordingly, the suspension system  16  and/or vehicle body  12  may be instrumented with one or more vibration sensors  130  to generate a sensor signal in response to the vibrations that are produced by the axle assembly  24 .  
         [0021]    An actuator  140 , which is coupled to the input shaft assembly  40  (e.g., to the propshaft coupling flange  102 , is configured to apply a torsional input to the axle assembly  24 . In the particular embodiment illustrated, the actuator  140  includes a servo-control system  142  having a controller  144 , a hydraulic pump  146  and a linear actuator  148  that is coupled in fluid connection to the hydraulic pump  146 .  
         [0022]    Preferably, the torsional input excites the axle gearset  110  in a manner that mimics the excitation of the axle gearset  110  as it would ordinarily be during the normal operation of the vehicle  10 . Accordingly, the controller  144  is employed to regulate and control the magnitude of the torsional input. More specifically, the controller  144  controls the actuator  140  (i.e., the hydraulic pump  146 ) in a manner such that a fist portion of the torsional input simulates a powertrain input torque (i.e., a torque that is delivered to the axle assembly  24  from the propshaft  22  for propelling the vehicle  10 ) and a second portion of the torsional input simulates a torsional vibration induced by gearset motion variation. Preferably, the first portion is static and approximately constant over a predetermined time increment, while the second portion is dynamic and oscillates over the same time increment.  
         [0023]    Vibrations transmitted through the suspension system  16  and into the vehicle body  12  are sensed by the vibration sensors  130 , which produces an associated array of sensor signals in response thereto. The sensor signals permit the technician to evaluate the relative degree to which noise induced by gearset motion variation is transmitted into the vehicle passenger compartment  12   a . As will be apparent to those skilled in the art, the energy that is input by the actuator to the axle assembly  24  may be readily quantified and monitored and as such, noise dampening efforts may be tailored to meet a given noise threshold in a manner that is both convenient and cost effective.  
         [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.