Abstract:
A jointed flexible drive shaft assembly is provided. The drive shaft has at least one flexible joint comprising a yoke connecting two drive shaft components together in a flexible manner which permits angular offsetting of the axis of rotation of one shaft component relative to the axis of rotation of another shaft component while a pilot and pilot bore cooperate to maintain the axes of rotation fixed against relative lateral offset a predetermined amount. The drive shaft assembly may be used on a test stand to couple a driving element with a driven element thereby reducing the need for a precision alignment between the driving and driven elements.

Description:
BACKGROUND OF INVENTION 
     Drive shafts with flexible joints for non-linear shaft component orientation are well known in the art. It is not uncommon to find a drive shaft having one or more flexible joints often referred to as a universal joint, Cardon joint or a Hooke&#39;s joint. This allows for the drive shaft to move relative to a driving or a driven element and to permit shaft portions to be out of coaxial alignment, i.e., set at an angle relative to one another and still permit rotation of a driven element by a driving element. Such drive shafts can be found on automobiles and trucks to drive the differential, front wheel drives that have constant velocity (CV) joints, in machines, lawn mowers and the like. Some jointed drive shafts are used to connect a driving element, for example, an electric motor to a driven element for testing of the driven element for various factors such as vibration, torque requirements and the like. 
     During the testing of a driven element, it is oftentimes desirable to eliminate noise from the system in order to obtain more accurate sensor readings. Oftentimes this is done by subtracting the noise of the drive system out of the total noise to obtain the noise or other measurements from the driven element. Additionally, audible noise, i.e., noise that can be heard by humans or other animals, can also be generated which in some environments can, when added to other noise, lead to objectionable noise levels including noise levels in excess of those permitted by government regulation. Thus, noise can generate at least two types of problems, readings from sensors and the audible sound level in a given environment. 
     Many types of joints between drive shaft segments are known. For example, the standard universal joint used in automobile drive shafts (a double gimble construction), bellows joint, elastomeric joints, Oldham joints, Waldron couplings and the like. While these joints have been used successfully in many applications, there is a need for their improvement in flexible joints to reduce noise while still maintaining the flexibility of such joints. 
     Thus, there is a need for an improved flexible drive joint to connect drive shaft components together. 
     SUMMARY OF INVENTION 
     One aspect of the present invention involves the provision of a test stand utilizing a drive element, for example, an electric motor, a drive shaft arrangement with at least one flexible drive joint therein, and a driven element. The driving element may be mounted to an anchor bed having one or more hold downs for securing the driving element in place. The driven element may also be mounted to the bed with the drive shaft connecting the driving element to the driven element. The flexible joint connects two shaft portions together permitting the axis of rotation of one shaft portion to be non-coaxial with the axis of rotation of another portion of the drive shaft, i.e. an angular misalignment. The two shaft portions are connected in driving engagement with one another by a flexible joint with a flexible yoke so that rotation of one shaft portion will effect rotation of another shaft portion allowing angular misalignment between the centers or axes of rotation of the drive shaft portions. At least one pilot is provided on either the driven or the driving side of the flexible joint and is received in a pocket or bore in the other of the driving or driven element shaft portions to maintain the two drive shaft portions axes of rotation laterally fixed in position relative to one another while still permitting angular offset misalignment of the axes of rotation. 
     The present invention can utilize a test stand for mounting of the driving and driven elements and to permit their connection together by the drive shaft for permitting some degree of angular and lateral offset misalignment of the axes of rotation of a drive device in the driven element and the drive device in the driving element. The pilot may be a single pilot mounted to be coaxial with the rotation axis of either the driven or the driving element while the bore that receives the pilot is in coaxial alignment with the center rotation of the other of the driving element and driven element. The pilot and the bore are configured to permit the angular misalignment while maintaining any lateral offset of the driven and driving portions of the drive shaft a predetermined amount. The pilot may be centrally located or may be located radially outwardly from the center of rotation and radially outwardly of a yoke that connects the drive shaft components in driving relationship which yoke can be inside of a plurality of pilots or external of one or more pilots. 
     Another aspect of the present invention involves using the drive shaft assembly of the present invention in a wide variety of other applications. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a test stand incorporating a driving element, a driven element and a connecting drive shaft. 
         FIG. 2  is an enlarged perspective view of the drive shaft of  FIG. 1 . 
         FIG. 3  is an enlarged plan view of the drive shaft. 
         FIG. 4  is an enlarged perspective view of one form of coupling yoke. 
         FIG. 5  is an enlarged sectional view of the drive shaft showing a portion thereof further enlarged for detail. 
         FIG. 6  is an enlarged sectional view of an alternate embodiment of the present invention. 
         FIG. 7  is a schematic illustration of drive shaft component misalignments. 
     
    
    
     Like numbers throughout the various figures represent like or similar parts and/or construction. 
     DETAILED DESCRIPTION 
     The reference numeral  1  designates generally a test stand or apparatus having a driving element  2  and a driven element  3  that are connected in driving relationship by a drive shaft assembly  4 . The driving element  2  and driven element  3  may be secured to an anchor bed  5  adapted for mounting the driving element  2  and driven element  3  thereon and to secure them in a position where their respective input and output shafts can be closely axially aligned. The stand  1  can be a dedicated stand for a particular combination of items or attachments may be provided for making the stand  1  more universal. 
     In the illustrated structure, the driving element  2  is an electric motor having its output shaft  7  connected to the drive shaft assembly  4 . In the illustrated structure, the driven element  3  can be any suitable device, for example, an internal combustion engine having an input shaft  8  (for the purpose of testing). Numerous types of driven elements  3  may be provided as for example, car and truck differentials or axles, transaxles, machine elements, generators and the like. 
     The anchor bed  5  can be in the form of a bed having a plurality of elongate T slots  9  used for securing clamps in place to secure the driving element  2  and driven element  3  in position on the bed  5 . The bed  5  may be made of any suitable material, e.g., cast iron, preferably malleable cast iron. It is to be understood however though, that any suitable bed  5  may be used. The bed  5  may be a permanent installation or a temporary installation or may be part of a floor structure or an elevated structure. Depending upon the type of driven device  3  being tested, the size of the bed  5  may be suitably selected as well as the output torque and power of the driving element or device  2 . 
     The drive shaft assembly  4  has one or more flexible joints therein with each flexible joint being as described below. The drive shaft assembly  4  directly couples the driving element  2  to the driven element or device  3  preferably through only the drive shaft assembly  4  as described below. In the illustrated structure, the drive shaft assembly includes a pair of flexible joint assemblies designated generally  11  and  12 . In the illustrated structure, a sensor  14  may be associated with the drive shaft assembly  4  with the sensor  14  being, e.g., a torque sensor, a vibration sensor or the like. A suitable torque sensor is, e.g., a torque or torsional acceleration sensor manufactured by ATI, PCB, HBM, or Lebow. The sensor  14  may be suitably secured to the bed  5  in a manner consistent with the construction of the sensor  14  and its functional coupling to the drive shaft. In the illustrated structure, the drive shaft assembly  4  has three flexibly coupled sections  21 ,  22  and  23 . The section  21  is coupled to the driving element  2  and the section  23  is coupled to the driven element  3 . The intermediate component  22  couples the components  21  and  23  together in driving relationship. 
     In the illustrated structure, the input component  21  of the drive shaft assembly  4  is coupled to the output shaft  7  and includes a plate  26  having a keyed socket  27  for receipt of the shaft  7  therein to mount the drive shaft assembly  4  to the shaft  7  for positive rotation. The intermediate shaft component  22  is in turn coupled to the adapter  27  which is coupled in driving relation to a yoke  28 . In the illustrated structure, the yoke  28  is in the form of a ring made of an elastomeric material with molded in metal inserts to provide the bores  24 ,  25 ,  FIG. 4 . The yoke  28  is secured to a plate  29  as with bolts  30  extending through bores  24 . The yoke  28  is connected to the centering adapter  31  as with bolts (not shown) extending through bores  25 . The joint assembly  11  is preferably balanced along with the other connected components to help reduce vibrations from being induced by the rotation of the shaft components  21 ,  22  and joint assembly  11 . The centering adapter  31  is shown as being in the form of a generally tubular member having an end wall with a pilot receiving bore  35  which may be defined by a replaceable bearing  37 . 
     A pilot  36  is received within the bore  35  in a manner that will permit some angular misalignment of the two shaft portions  21  and  22 . As shown, the pilot  36  has a rounded end  38  mounted on a support shaft  32 . The end  38  may be generally spherical, while the bore  35  is shown as being generally cylindrical. Other shapes of pilots  36  and bores  35  may be provided so long as some degree of angular misalignment of the shaft portions  21 ,  22  may be achieved while maintaining the centers of rotation of the shaft portions  21 ,  22  substantially fixed from relative lateral movement at the pivot point of the pilot  36  in the bore  35 , which, in the illustrated structure will be on the end  38  during rotation of the drive shaft assembly  4 . The angle A of deviation or misalignment of the two shaft portions  21 ,  22  is at least about 0.05° and preferably up to about 3° and more preferably up to about 5° for use on a test stand or at least about 5° when used in other applications such as a machine component or vehicle component. The diameter of the rounded pilot portion  38 , the depth of its insertion into bore  35 , the transverse size of shaft  32  and any bore open end chamfering will control the amount of permitted angular misalignment. The shaft  32  has a transverse size smaller than that of the bore  35  and the end  38  to permit angular misalignment. The pilot  36  and bore  35  cooperate to limit the shaft portions  21 ,  22  from relative lateral movement ( FIG. 7 ) a predetermined amount at their junction, even though there can be some misalignment at the angle A as best seen in  FIG. 7 . Preferably, the relative lateral movement is limited to less than about 0.001 inches, more preferably less than about 0.0005 inches and most preferably less than about 0.0002 inches as will be determined by the gap between the end  38  and bearing  37  sidewall surface  39 . 
     In the illustrated structure, the coupler  12  includes a bellows form of yoke  50  which permits the axial misalignment of shaft portions  22 ,  23  at an angle similar to that described above for shaft portions  21 ,  22 . The yoke  50  may be of a metallic material. The use of the couplers  11  and  12 , permit angular misalignment and/or lateral offset, as described above, of the axis of rotation of the driving element  2  and the axis of rotation of the driven element  3 . The drive shaft assembly  4  does not need to be supported by other than the driving and driven elements  2 ,  3 , respectively, but could be supported as with support  53 . The coupler  12  has a centering device similar to that shown and described for the coupler  11  including a pilot  51  and bore  52  similar to pilot  36  and bore  35  as described above. The bellows  50  acts as a yoke as does the elastomeric ring of the yoke  28 . By utilization of the pilot  51  and bore  52 , and by controlling the clearance therebetween, the amount of noise generated or produced as compared to a standard drive shaft, can be greatly reduced. For example, a typical drive shaft has been known to generate about 100 dB&#39;s of audible noise whereas, the present invention provides a similarly sized drive shaft which generates less than about 60 dB&#39;s of audible noise thus making the machine more comfortable to be around. The inventive drive shaft assembly  4  can also reduce signal noise generated by operation of the drive shaft as it would be picked up by measuring sensors such as microphones, accelerometers, torque transducers, and laser vibrometers. 
     The above-described yoke and pilot arrangements are endo arrangements, i.e., the pilot or pilots are on the respective axes of rotation and/or inside of the yoke.  FIG. 6  shows an alternative embodiment of the present invention where the pilot is not on the centerline of rotation of the drive shaft assembly  4  but rather spaced outwardly therefrom. In this alternate embodiment, the flexible joint assembly  59  has at least one pilot  60  and at least one pilot receiving bore  61 . The yoke  63  is mounted radially inwardly of a surface  64  defining the bore  61 . The yoke  63  can be similar in construction to the yoke  28  and can be secured to an adapter plate  66  as with bolts  67 . A keyed shaft pocket  68  can be provided on the plate  66  for the mounting of the plate  66  to a drive shaft on either a driving or driven element  2 ,  3  respectively. The surfaces  64 ,  65  may be appropriately contoured to provide for axial misalignment as described above. The surface  65  will preferably have a radius approximately equal to the radial distance of the surface  65  from the axes of rotation  69  of the pilot  60 . The surface  64  may be transversely radiused or generally cylindrical as desired. The gap between the surfaces  64 ,  65  will fix the pilot against lateral movement, as seen schematically in  FIG. 7 , by the amount of the gap. The difference between the flexible joint assembly  59  and the flexible joint assemblies  11  and  12  is that the pilot is not mounted on the centerline of the axes of rotation of either of the shaft portions  21 ,  22  or  23 . 
     Surprisingly, by maintaining a centered relationship between the various segments of the drive shafts, through the use of the pilot and bore arrangement, the noise reduction of a draft shaft is between about 25 dB&#39;s and about 40 dB&#39;s. Additionally, sensor pickup noise has been reduced by about 50% for a linear sensor. The present invention provides for a drive shaft arrangement that allows for angular misalignment of two shaft components from parallel (0°) (coaxial) to an angle A as described above. The use of the drive shaft of the present invention permits quicker setup of a test apparatus to test a driven element  3  by a driving element  2  because their axes of rotation being in substantially perfect alignment is no longer necessary to achieve reduced noise operation. 
     The sensor  14  and/or a sensor  69  operably associated with the driven element  3  provides a respective output signal indicative of an operating parameter of the driven element. 
     While the present invention is illustrated as being used in a test stand, a drive shaft  4  of the present invention can also be used in a wide variety of other applications and environments such as a substitute for a standard drive shaft, for example, those found in an automobile drive train, as a substitute for a constant velocity or CV joint, as machine drive elements such as those found in manufacturing machines, lawn mowers, heavy duty mowers and the like. 
     Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “having” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required”. Many changes, modifications, variations and other uses and applications of the present invention will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.