Patent Publication Number: US-2019178751-A1

Title: Testing apparatus for gears

Description:
TECHNICAL FIELD 
     The present invention relates to a test apparatus for testing gears, in particular a test apparatus for fatigue testing of gears. 
     BACKGROUND OF THE DISCLOSURE 
     Gears have applications within transmission systems in different fields, as the automotive, the naval or the aeronautic fields. 
     The gears applied in aeronautical transmission systems have to satisfy extremely demanding reliability and durability requirements. 
     A common parameter for evaluating the reliability and durability of gears is the fatigue strength, which is estimated by means of fatigue tests performed on specific test rigs. 
     In the commonly known test rigs, the tested gear is clamped in a fixed position on a test apparatus and a force is applied onto the flank of one or more teeth of the gear by means of an actuator and a force application column which transfers the force from the actuator onto the above mentioned flank along a force application direction. 
     In some of the test rigs, the force application column typically is provided in the form of a rigid anvil and acts by means of an interaction element simultaneously on the flanks of two adjacent teeth. 
     In other test rigs the interaction element of the force application column applies the force on the flank of a single tooth. However, during the application of the force such tooth is deformed, so that the interaction element can slide over the flank. In these cases, the interaction element contacts the flank at a position that can slightly vary during the test. 
     This limits the possibility to obtain precise results from the test measurements because of the uncertainty associated to the friction at the tooth flank surface. 
     A test rig applying the force onto the flank of a single tooth along a force application direction is disclosed in CN-U-202083601. The test rig comprises a clamping device for clamping the gear in such a manner that the central axis of the gear is coaxial with a clamping axis, the clamping axis being orthogonal to the force application direction. The test rig also has a force application column provided with two elastically deformable plate portions, which are aligned with each other and are arranged between respective rigid portions of the force application column. Each of the plate portions is deformable and give a certain freedom of movement to the end of the column along a deformation direction parallel to the clamping axis. 
     However, this freedom of movement cannot compensate for the deformation of the tooth and obtain a stable contact point between the column and the flank of such tooth. 
     Overall, a drawback of the known test rigs is that they permit comparative tests between different gears, but they are limited in their possibility and reliability of obtaining absolute results in terms of gears fatigue strength data. 
     BRIEF DESCRIPTION 
     It is therefore an object of the present invention to provide a test apparatus to overcome, in a straightforward and low-cost manner, the aforementioned drawbacks. 
     According to the present invention, there is provided a test apparatus as claimed in claim  1 . 
     There is furthermore provided a test rig as claimed in claim  13 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of a test rig having an embodiment of the test apparatus according to the present invention, with parts removed for clarity; 
         FIG. 2  shows a perspective view of another side of the test apparatus of  FIG. 1 , with parts removed for clarity; 
         FIGS. 3A and 3B  shows a detail of the test apparatus of  FIGS. 1 and 2 , being in two different configurations; and 
         FIG. 4  is a sectioned view along plane IV of  FIG. 2  and shows another detail of the test apparatus of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Number  1  in  FIG. 1  indicates, as a whole, a test rig for testing a gear  2  having a plurality of teeth  3 , in particular for fatigue testing of gear  2 . 
     Rig  1  comprises: 
     an actuator  4  for generating a force along a force application axis F, in particular force application axis F having a vertical orientation; and a test apparatus  5  securing and clamping gear  2 , coupled to actuator  4  and configured to transfer the force generated by actuator  4  onto the flank of a single tooth  3  of gear  2 . 
     Rig  1  furthermore has a support structure  6  for carrying actuator  4  and test apparatus  5 . 
     In particular, support structure  6  comprises an upper transversal bar  7  carrying actuator  4  and a base  8  supporting test apparatus  5 . 
     With reference to  FIGS. 1 to 4 , apparatus  5  comprises: 
     a clamping device  12  clamping and securing gear  2  in a fixed position within apparatus  5 ; and 
     a force application frame  13  configured to transfer the force generated by actuator  4  towards the flank of the tooth  3  of gear  2 . 
     In more detail, clamping device  12  comprises: 
     a single support block  14  having one through passage  15  extending along a central axis A, with an orientation that is transversal, in particular orthogonal, to axis F; and a shoulder  16  transversal to axis A and, in particular orthogonal to axis A and parallel to axis F; and a securing bolt  17  axially extending through passage  15 , having a shoulder  18  and comprising a pin  19  and a tightening member  20  screwed on pin  19  so as to axially clamp gear  2  in fixed position between shoulders  16  and  18 . 
     More specifically, pin  19  has a threaded portion  19   a  axially protruding from passage  15 , and tightening member  20  is defined by a nut element secured on threaded portion  19   a.    
     Furthermore, support block  14  comprises a fixed protrusion  24 , in particular having a cylindrical outer surface  24   a,  axially projecting with respect to shoulder  16  and defining an axial end portion  15   a  of passage  15 . Gear  2  is directly fitted onto outer surface  24   a.  Additionally, shoulder  18  is axially spaced apart from protrusion  24  so as to leave a gap allowing for transferring the axial clamping force only onto gear  2 , and not onto protrusion  24 . 
     With particular reference to  FIGS. 3 and 4 , clamping device  12  further comprises a first and a second spacer element  25 ,  26 , directly fitted onto outer surface  24   a  of protrusion  24  and arranged between shoulders  16  and  18 . Spacer elements  25 ,  26  are arranged on the opposite sides of gear  2 , so as to sandwich in between gear  2 . 
     Furthermore, the axial thickness of spacer element  25  is identical to the axial thickness of spacer element  26 , so as to avoid errors in positioning the spacer elements  25 , 26  during the operations carried out to mount gear  2  in clamping device  12 . The axial thickness of spacer elements  25  and  26  depend on the axial thickness of gear  2  to be tested and is chosen during the mounting stage so as to align the tooth to be tested and center the axial position of such tooth with force application axis F. 
     In more detail, support block  14  comprises: 
     a single support plate  27 , which projects in a fixed position transversally to axis A and substantially parallel to force application axis F, defines shoulder  16  and has a cylindrical seat  28 , coaxial with passage  15  along axis A; and a positioning pin  29  defining the whole passage  15  and comprising a hollow cylindrical portion  29   b  that engages seat  28  with an interference fit, so as to be fixed with respect to support plate  27 . 
     In other words, the outer diameter of the portion  29   b  is equal to the diameter of seat  28 , apart from the manufacturing tolerances that have to ensure the interference coupling. 
     Additionally, an end portion  29   a  of positioning pin  29  defines protrusion  24 . 
     Positioning pin  29  further comprises a flange  29   c.  Flange  29   c  axially rests onto a contact surface  30  of support block  14  axially opposite of shoulder  16  and provided on support plate  27 . 
     In particular, positioning pin  29  is mounted into seat  28  by means of a press fit, so as to axially insert cylindrical portion  29   b  into seat  28  until flange  29   c  comes into axial contact with surface  30 . 
     In particular, tightening member  20  axially and directly rests onto flange  29   c.  In the meantime, pin  19  comprises a head  19   b  axially and directly resting onto spacer element  26  and defining shoulder  18 . 
     According to a variant (not shown), the positions of head  19   b  and tightening member  20  is inverted, so that shoulder  18  is defined by tightening member  20 . According to another variant, shoulder  18  is defined by a further tightening member, in particular a further nut element which is tightened on a threaded portion of pin  19 , at the axial end opposite to tightening member  20 . 
     In the an embodiment that is shown in the attached drawings, it is clear that protrusion  24  and shoulder  16  are defined by two distinct work pieces, i.e. pin  29  and support plate  27 , so as to simplify the manufacturing operations for obtaining support block  14 . 
     As an alternative (not shown), support plate  27  and protrusion  24  are provided as a single work piece, without the need of press coupling operations. 
     Overall, shoulder  18  is in contact with spacer element  26 , spacer element  26  is in contact with gear  2  from a first side of gear  2 , spacer element  25  is in contact from a second side of gear  2  opposite of the first side, spacer element  25  is also in contact with shoulder  16 : friction between these contact areas defines the transversal and angular retention of the gear  2 . Such friction is a function of the axial load exerted by tightening member  20 , which in turn is a function of the driving torque of tightening member  20 . 
     Further on, with particular reference to  FIGS. 1 and 2 , support block  14  defines part of a support frame  31 , which, in more detail, is fixed on base  8 . 
     Furthermore, force application frame  13  comprises a single force application column  35 , which is aligned with actuator  4  and is elongated along force application axis F. Column  35  is adapted to interact with the flank of the tooth  3  of gear  2  for applying the force exerted by actuator  4  on the flank of the tooth  3 . 
     More specifically, column  35  is moveable along force application axis F with respect to clamping device  12  under the action of actuator  4  and exerts the force onto the flank of tooth  3 . Furthermore, column  35  is orthogonal and radially spaced apart with respect to axis A. 
     With particular reference to  FIGS. 1, 2, 3A and 3B , column  35  comprises: 
     a first end  36  coupled to a moveable section  4   a  of actuator  4 ; a second end  37 , axially opposite to end  36  and configured to contact the flank of the tooth  3  at a contact area; and at least one intermediate portion  38 , which is axially arranged between ends  36  and  37  and which is elastically deformable so as to allow for a displacement of end  37  in relation to end  36  along a displacement direction D 1  orthogonal to force application axis F and to axis A. 
     In particular, end  36  has a recess  39  receiving the axially moveable section  4   a.  In further detail, column  35  comprises a first and a second rigid portion  40 ,  41  and the intermediate portion  38  being arranged between portions  40  and  41 . In particular, end  36  defines a part of portion  40 , while portion  41  carries end  37 . In the shown embodiment, end  37  is defined by a separate piece mounted to portion  41  in a fixed position. However, it must be understood that end  37  and portion  41  could be defined by one single work piece. 
     According to an aspect of the present invention, intermediate portion  38  comprises at least one deflectable member, in particular two bendable plate elements  42 , connecting portions  40  and  41  with each other. In an un-deformed condition, the plate elements  42  are substantially parallel to force application axis F and are elastically bendable about rotation axes that are parallel to axis A, so as to allow a movement of portion  41  along a direction D 2 , parallel to the above identified direction D 1 , with respect to portion  40 . 
     In more detail, bendable plate elements  42  are spaced apart from each other along direction D 2  and are arranged parallel to each other.  FIG. 3A  shows intermediate portion  38 , and in particular plate elements  42 , prior to the application of a force on the flank of the tooth  3 .  FIG. 3B  shows intermediate portion  38 , and in particular plate elements  42 , during the application of a force on the flank of the tooth  3 , when such tooth  3  deforms and this deformation causes a displacement of the contact area with the end  37 . Please note that  FIG. 3B  shows a deformation that is enlarged and does not represent the real condition, so as to highlight the displacement along direction D 2  for sake of clarity. 
     It should be noted that intermediate portion  38  behaves just like a four-bar linkage (see  FIG. 3B ). Therefore, portion  41  and end  37  translate along direction D 2 , D 1  without rotations. 
     Additionally, with reference to  FIG. 2 , force application frame  13  comprises a carrier structure  43  moveably carrying column  35 . 
     Carrier structure  43  comprises: 
     two lateral rigid support pillars  44 ; and four flexible connecting members, in particular connecting plate arms  45 , which are fixed to portion  40  at two opposite sides of column  35  and each one being fixed to a respective rigid support pillar  44 . 
     Each one of connecting plate arms  45  is bendable about rotation axes that are parallel to axis A, so as to allow for the displacement of portion  40  and, therefore, for guiding the movement of column  35  along force application axis F. 
     In even more detail, in an un-deformed condition, connecting plate arms  45  are parallel to each other and orthogonal to force application axis F. Furthermore, connecting plate arms  45  are symmetric with respect to a symmetry plane in which force application axis F lies. 
     In the specific embodiment, the pillars  44 , the connecting plate arms  45 , the intermediate portion  38  and portions  40  and  41  of column  35  are formed as one single work piece. As mentioned above, end  37  is provided as a separate piece mounted to portion  41 . 
     With particular reference to  FIGS. 1 and 2 , apparatus  5  further comprises height adjusting means  46  configured to adjust the height of pillars  44 , in particular to define the distance of end  37  from the flank of tooth  3 , prior to the exertion of the force. In this way, apparatus  5  can be setup to test gears  2  having the same base diameter, but different numbers of teeth and/or to load the same tooth at different radii of the involute profile. 
     In more detail, height adjusting means  46  comprise at least two distancing elements  47 , each one interposed between one respective rigid support pillar  44  and one respective support beam  31   a  of clamping device  12 . In particular, by replacing distancing elements  47  of one thickness with distancing elements  47  of another thickness it is possible to define the distance of end  37  from the flank of tooth  3 . 
     Apparatus  5  also comprises a sensor device (not shown) configured to determine the stress applied by column  35  on the flank of tooth  3 . In particular, the sensor device comprises a plurality of strain gauges positioned onto plate arms  45  and onto plate elements  42 , so as to detect the deformation of such parts and therefore to determine the above mentioned stress on the basis of such deformation. Additionally, actuator  4  is configured to provide for displaying the force generated by actuator  4  itself. 
     In use, prior to the testing, gear  2  is clamped and secured by clamping device  12 . 
     More specifically, gear  2  is fitted onto outer surface  24   a  of protrusion  24 . Radial clearance between protrusion  24  and gear  2  is avoided because the diameter of surface  24   a  is set during the design stage so as to be substantially equal to the inner diameter of the gear  2 , in particular with a very tight clearance to enable manual assembly and disassembly without introducing significant uncertainties in the location of the loaded point on the tooth flank. 
     Gear  2  is angularly and axially secured by tightening member  20  onto the pin  19 , so as to sandwich and clamp gear  2  between shoulders  16  and  18 . 
     Prior, but possibly also after, the clamping of gear  2 , height adjusting means  46  are, in case of need, selected to set the height of pillars  44  in order to prepare apparatus  4  to the specific gear  2  to be tested. Therefore, the distance of end  37  to the flank of tooth  3  is set by height adjusting means  46 . More specifically, pillars  44  are moved away from support beams  31   a  and the distancing elements  47  present are removed and are replaced with distancing elements  47  having the desired thickness. Then the pillars  44  are placed again on distancing elements  47  and pillars  44  and support beams  31   a  are fixed to each other. 
     Once the gear  2  is secured within clamping device  12  and the desired distance between end  37  and the flank of the tooth  3  is set, the actual test of gear  2  is initiated. 
     Actuator  4  is activated to drive column  35  along force application axis F and column  35  transfers the force on the flank of the tooth  3 . Therefore, activation of actuator  4  leads to movement of column  35  along force application axis F. 
     During the application of the force by actuator  4  movement of column  35  along force application axis F is guided by deflection of connecting plate arms  45 . 
     During movement of column  35 , end  37  permanently contacts the flank of tooth  3 . During force application, the tooth  3  elastically deforms, so that the position of the contact area can slightly change under load. 
     Thanks to the flexibility of intermediate portion  38 , end  37  can move along direction D 1 , together with the deformation of the tooth  3 , so as to adapt its position as a function of the deformation and to avoid a sliding along the flank of the tooth  3 . In other words, end  37  automatically follows the deformation of the tooth  3  by displacing with respect to end  36 . As a final consequence, end  37  continues to contact the flank of tooth  3  at the same and only contact area, notwithstanding the possible movement of such contact area. 
     More specifically, the relative movement of end  37  with respect to end  36  is provided for by the bending of plate elements  42  along the deformation direction D 2  (see  FIG. 3B ) upon the application of the force on the flank of tooth  3 . 
     This compensation or adaptation carried out by the intermediate portion  38  is reached by a single piece, i.e. the ensemble of portions  40 ,  41  and  38 , so that no clearance is provided between portions  40  and  38  and between portions  38  and  41 . 
     In particular, the opposite roots of the plate elements  42  define respective virtual hinges that allow for deflection of portion  38  as a four-bar linkage and, therefore, for a pure translation of portion  41 . 
     The advantages of test apparatus  5  according to the present invention are clear from the foregoing description. 
     Overall, test apparatus  5  allows to exert the force onto an unchangeable contact area of the flank of tooth  3  upon the test. In other words, the elasticity of the intermediate portion  38  provides for the contact area staying the same throughout the complete test. This result contributes to a more accurate evaluation of the gear fatigue properties because it prevents the detrimental effects of micro-sliding on the contacting surfaces. 
     Furthermore, connecting plate arms  45  allow to precisely define and guide movement of force application column  35  along force application axis F. Just as for the plate elements  42 , plate arms  45  are not pieces separate from pillars  44  and portion  40 , so that clearance is completely avoided. 
     In particular, the opposite roots of plate arms  45  define respective virtual hinges that allow for deflection of the plate arms  45 , as a four-bar linkage at each side of the column  35 , and allow, therefore, for a pure translation of the column  35  along direction D 1 . In the meantime, the symmetry of the plate arms  45  allows for maintaining axis F always in the same position. 
     In particular, the pillars  44 , the connecting plate arms  45 , the intermediate portion  38  and portions  40  and  41  of column  35  are formed as one single work piece. The complexity of test apparatus  5  is reduced with respect to the known test apparatuses, and clearances are completely avoided, as mentioned above, while movements of the end  37  along axis F and along direction D 1  are allowed. 
     Overall, test apparatus  5  allows for obtaining absolute fatigue strength data, thanks to the very accurate loading system and the absence of friction at the loaded tooth contact point. 
     A further advantage is seen in height adjusting means  46  of test apparatus  5  providing for a simple setup of the test apparatus  5 , in particular by choosing the correct thickness of distancing elements  47 . 
     Clearly, changes may be made to test apparatus  5  as described herein without, however, departing from the scope of protection as defined in the accompanying claims.