Patent Publication Number: US-2005120819-A1

Title: Oscillating actuator

Description:
TECHNICAL FIELD  
      The present invention relates to a selecting actuator, which is incorporated into, for example, an electric drive apparatus for a transmission, for displacing a shift shaft for a gear unit in an axial direction.  
     BACKGROUND ART  
      A manual transmission is used as an automotive transmission. However, in recent years, there have been proposed various kinds of automotive transmissions each for automatically switching a gear unit and for automatically disconnection of a clutch. International Publication No. WO01/31234A1 discloses an electric drive apparatus for changing gears constituting a gear unit in such an automotive transmission. Hereinafter, the electric drive apparatus for a transmission according to the International Publication is described by referring to FIGS.  6  to  8 .  
      A mission case  1  is a case that incorporates a gear unit similar to a manual transmission. A tip end portion  3  of a shift shaft  2  for changing a gear ratio of this gear unit projects from a side surface of the mission case  1 . A male spline portion  4  is formed in a middle part of this tip end portion  3 . The male spline portion  4  is spline-engaged with a spline tube  5 , on the inner surface of which a female spline is formed. An engagement piece  7 , in the outer peripheral surface of which an engagement groove  11  is formed, is connected to a part that is closer to the tip of the tip end portion  3  protruding from the spline tube  5 .  
      The operation shift shaft  2  is displaced in an axial direction (a front-rear direction of the sheet of  FIG. 6 , an up-down direction of the sheet of  FIG. 7 ) in a selecting operation, and rotates in a shift operation. Incidentally, the selecting operation is an operation of displacing a shift lever in a direction of width of a vehicle in an ordinary manual floor shift car to thereby select a gear for changing a speed. On the other hand, the shifting operation is another operation of displacing the shift lever in a front-back direction of the vehicle to thereby connect a synchromesh mechanism corresponding to the selected gear.  
      Hereinafter, the selecting operation and the shifting operation are described in detail. A gear unit realizing six kinds of transmission states, which are five forward ones (first to fifth speed levels) and a rearward one (R), as shown in  FIG. 9 , are considered herein.  
      In the selecting operation, one of three kinds of positions, which are both lateral end positions and a laterally central position shown in  FIG. 9 , is selected. In this selecting operation, the synchromesh mechanisms are maintained in a free state. Thus, a neutral state is maintained, so that no speed change state occurs. In the shifting operation, the shift lever is displaced from one of the three kinds of positions in the neutral state in one direction (an upward or downward direction shown in  FIG. 9 ). Consequently, one of the synchromesh mechanisms is brought into a connected state, so that one of speed change states occurs. Incidentally, according to the International Publication No. WO01/31234A1, a selecting actuator  8 , which is a swinging actuator, is provided between an outer surface of the mission case  1  and the engagement piece  7  so as to displace the shift shaft  2  in the axial direction in the selecting operation.  
      As shown in  FIG. 8 , the selecting actuator  8  has a selecting electric motor  9 , and a multiple thread worm gear  10  rotate-driven by an output shaft of the selecting electric motor  9 . The multiple thread worm gear  10  meshes with a worm wheel  11 . An output shaft  12  serving as the center of rotation of the worm wheel  11  is connected and fixed to a base end portion of a swinging arm  13 . The swinging arm  13  rotates together with the worm wheel  11 . An engagement convex portion  14  formed on one side surface of the tip end portion (the top surface of the left end portion, as viewed in  FIG. 6 ) of the swinging arm  13  engages with the engagement groove  6  to thereby allow the shift shaft  2  to be displaceable.  
      On the other hand, a shifting actuator  16  serving as a direct acting actuator for rotating the shift shaft  2  is provided between an outer surface of the mission case  1  and a tip end portion of a driving arm  15  fixedly provided on an outer peripheral surface of the spline tube  5 . The shifting actuator  16  has a casing  17  supported in such a way as to be swingably displaceable with respect to the mission case  1 . A shifting motor, which is supported by and fixed to the casing  17  and can rotate forwardly and reversely, pushes and pulls the output shaft  18  in an axial direction through a ball screw mechanism provided in the casing  17 .  
      The electric drive apparatus for a transmission changes the gears of the gear unit incorporated in the mission case  1  in the following manner. First, the selecting electric motor  9  is rotated in a predetermined direction to thereby swing and displace the swinging arm  13  in an up-down direction as viewed in  FIG. 7 . Then, the shift shaft  2  is axially displaced in a predetermined direction through the engagement piece  7  by the engagement convex portion  14  formed on the tip end portion of the swinging arm  13  to thereby perform a selecting operation. After the selecting operation is performed, the shift shaft  2  is rotated in a predetermined direction through the driving arm  15  by elongating and contracting the shifting actuator  16  so as to perform a shifting operation.  
      In the case of the aforementioned structure, the base end portion of the swinging arm  13  is connected to an end portion of the output shaft  12  through a connecting screw. However, the connecting screw, which connects the base end portion of the swinging arm  13  to the end portion of the output shaft  12 , may be loosened by prolonged use thereof. When the this swinging arm  13  displaces the shift shaft  2  in an axial direction, relative displacement of the base end portion of this swinging arm  13  with respect to the end portion of the output shaft  12  occurs in a direction that is slightly opposite to the direction of rotation of this output shaft  12 . This displacement is based on a reaction to the operation of displacing the shift shaft  2  in the axial direction, and caused by the minute gap between inner surfaces of a concave portion  23 , which is formed in the end surface of the output shaft  12 , and both side edges of the base end portion of the swinging arm  13 , or by elastic deformation of both side parts of this concave portion  23 .  
      In either case, when the base end portion of the swinging arm  13  displaces with respect to the end portion of the output shaft  12 , the connecting screw, whose head portion abuts against the outer surface of this swinging arm  13 , tends to displace in the same direction as that in which this swinging arm  13  displaces. In the case of the aforementioned structure, a screw hole, into which the connecting screw is screwed, is present in the central portion of the output shaft  12 . Thus, the connecting screw tends to rotate with respect to the screw hole with the progress of the displacement. This tendency therein to rotate occurs in both directions as the swinging arm  13  performs reciprocating swinging motions. However, a force needed for rotating the connecting screw with respect to the screw hole in a loosening direction is smaller in magnitude than a force needed for rotating the connecting screw in a tightening direction. Therefore, there is the possibility that the connecting screw is gradually loosened with repetition of the reciprocating swinging motions of the swinging arm  13 .  
      To prevent the connecting screw from being loosened due to the aforementioned causes, it is considered that an engagement portion for preventing the connecting screw from being loosened is provided between the head portion of this connecting screw and the swinging arm  13 . Incidentally, the provision of the engagement portion specifically used for preventing the connecting screw from being loosened complicates processing and assembling operations and causes a cost rise.  
     DISCLOSURE OF THE INVENTION  
      In view of such circumstances, a swinging actuator of the invention realizes a configuration enabled to prevent a screw, which is used for connecting and fixing the swinging actuator to an output shaft, from being loosened.  
      A swinging actuator of the invention has an output shaft rotatably supported by a support member, a driving source for rotate-driving the output shaft, and an output arm, whose base end portion is connected and fixed to an end surface of the output shaft. A portion to be driven is driven by the end portion of the output arm. This swinging actuator comprises a screw hole provided in a portion, which is positioned off the center of rotation of the output shaft, a through hole formed in the base end portion of the output arm, a connecting screw screwed into the screw hole in a state in which the connecting screw is inserted into the through hole, and an engagement portion provided between a part, which is positioned off the through hole and in the end portion of the output arm, and a part, which is off the screw hole and in the end surface of the output shaft.  
      In the case of the swinging actuator constituted as described above, the screw hole is provided in a portion that is off the center of rotation of the output shaft. Thus, a force in the direction of rotation thereof is hard to be applied to the connecting screw, which is screwed into the screw hole, as a swinging arm performs reciprocating swinging motions. Consequently, even in a case where an engagement portion specifically used for preventing the connecting screw from being loosened is not provided therein, the connecting screw is difficult to be loosened. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a front view shoring a selecting actuator according to an embodiment of the invention;  
       FIG. 2  is a plan view showing the selecting actuator according to the embodiment of the invention;  
       FIG. 3  is a rear view showing the selecting actuator according to the embodiment of the invention;  
       FIG. 4  is a side view showing the selecting actuator according to the embodiment of the invention;  
       FIG. 5  is a cross-sectional view taken along line A-A in  FIG. 1 ;  
       FIG. 6  is a plan view showing an example of an electric drive apparatus for a transmission, which incorporates a swinging actuator;  
       FIG. 7  is a is a cross-sectional view taken along line B-B in  FIG. 6 ;  
       FIG. 8  is a cross-sectional view taken along line C-C in  FIG. 6 ; and  
       FIG. 9  is a schematic plan view showing an example of a shift pattern of a transmission. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      An embodiment of a swinging actuator according to the invention is described in detail. Incidentally, the feature of this embodiment resides in that for the purpose of preventing the connecting screw, which is used for connecting the base end portion of the swinging arm to the end surface of the output shaft, from being loosened, a structure for connecting the base end portion of the swinging arm and the end surface of the output shaft is devised. Hereinafter, this is described in detail by referring to the accompanying drawings.  
       FIG. 1  is a front view showing a selecting actuator that is an embodiment of the swinging actuator according to the invention.  FIG. 2  is a plan view showing the selecting actuator.  FIG. 3  is a rear view showing the selecting actuator.  FIG. 4  is a side view showing the selecting actuator.  FIG. 5  is a cross-sectional view taken along line A-A in  FIG. 1 .  
      The selecting actuator according to this embodiment has a casing  19 , a selecting electric motor  9   a , which is a driving source assembled to the casing  19 , and an output shaft  12   a  assembled to the casing  19 . A transmission shaft  32  provided at an end of a rotation drive shaft  20  of the selecting electric motor  9   a  is fixedly provided on a pinion gear  21 , and rotate-drives the coaxially disposed pinion gear  21 . The pinion gear  21  meshes with a sector gear  22  fixedly provided on the outer peripheral surface of a middle portion of the output shaft  12   a , so that the output shaft  12   a  can freely be rotate-driven in both directions by a predetermined angle. The transmission shaft  32  and the output shaft  12   a  are rotatably supported by pairs of ball bearings, respectively, in the casing  19  in such a way as to be parallel to each other. With the aforementioned configuration, the rotation of the rotation drive shaft  20  of the selecting electric motor  9   a  is transmitted to the output shaft  12   a  through the transmission shaft  32 , the pinion gear  21 , and the sector gear  22 .  
      A screw hole  24  and a latch hole  33  are formed in the end surface (the right end surface as viewed in  FIG. 5 ) of the output shaft  12   a  along an axial direction thereof. The screw hole  24  is a portion, which is off the center of rotation of the output shaft  12   a , that is, a portion positioned closer to the outer peripheral surface of the output shaft  12   a . On the other hand, the latch hole  33  is formed in a portion, which is a part of the end surface of the output shaft  12   a  and shifted from the screw hole  24  in an opposite direction with respect to the center of the end surface thereof. In other words, the center of the end surface thereof (the shaft center of the output shaft  12   a ) is present in a middle portion (which is not necessarily a central portion) of a straight line connecting the centers of the screw hole  24  and the latch hole  33 .  
      On the other hand, a through hole  25  and a second through hole  34  are formed in the base end portion of the swinging arm  13   a . The pitch between the through hole  25  and the second through hole  34  is equal to that between the screw hole  24  and the latch hole  33 . Therefore, in a state in which the through hole  25  is aligned with the screw hole  24 , the latch hole  33  is aligned with the second through hole  34 . Further, the second through hole  34  is formed in a portion that is closer to the base end portion of the swinging arm  13   a  than the through hole  25 .  
      The base end portion of the swinging arm  13   a , in which the through hole  25  and the second through hole  34  are formed, is connected and fixed to the end surface of the output shaft  12   a , which has the screw hole  24  and the latch hole  33 . On connecting therebetween, first, in a state in which the latch hole  33  and the second through hole  34  are aligned with each other, a spring pin is put between both the holes  33  and  34 . In this state, the spring pin  35  frictionally engages with the inner peripheral surface of one or each of both the holes  33  and  34 . Subsequently, a connecting screw  26  inserted into the through hole  25  is screwed into the screw hole  24  and then tightened securely. In this state, a part of a separate washer  36 , which is integrally formed with a head portion  31  of the connecting screw  26  or fitted onto the connecting screw  26 , blocks a part of the second through hole  34 . Thus, the slip-off of the spring pin  35  from between both the holes  33  and  34  is surely prevented. An ordinary pin having no elasticity may be used as a member put between both the holes  33  and  34 .  
      An engagement convex portion  14   a  is fitted and fixed to the end portion of the swinging arm  13   a . The engagement convex portion  14   a  is constituted in such a manner as to be engageable with an engagement piece  7  (see  FIGS. 6 and 7 ) fixed to the shift shaft  2 .  
      In the casing  19 , a displacement sensor  27  is supported coaxially with the output shaft  12   a . An engagement projection  29 , which is provided on a detection portion  28  of this displacement sensor  27  in such a way as to protrude therefrom, engages with an engagement concave portion  30  formed in the base end part of the detection portion  28 . The displacement sensor  27  is constituted like a potentiometer, whose electric characteristics, such as values of resistance, change according to an angle of rotation of the detection portion  28 , and enabled to detect a swinging angle of the output shaft  12   a.    
      In a case where the shift shaft  2  shown in  FIG. 6  is displaced in the axial direction by the selecting actuator  8   a , the pinion gear  21  is rotated in a predetermined direction by driving the selecting electric motor  9   a . The output shaft  12   a  is turned by the rotation of the pinion gear  21  through the sector gear  22 . Thus, the swinging displacement of the swinging arm  13   a  is caused. Then, the engagement convex portion  14   a  provided at the end portion of this swinging arm  13   a  displaces the shift shaft  2  in the axial direction. Then, the displacement sensor  27  detects a displacement magnitude as an angle of rotation of the output shaft  12   a.    
      As described above, according to this embodiment, in a state in which the base end portion of the swinging arm  13   a  is connected and fixed to the end surface of the output shaft  12   a , torque is transmitted from the output shaft  12   a  to the swinging arm  13   a . Regardless of minute swinging displacement of he base end portion of the swinging arm  13   a  with respect to the end portion of the output shaft  12   a , which is caused by this transmission of torque, the connecting screw is prevented from being loosened.  
      That is, similarly, in this embodiment, the transmission of torque causes the minute relative displacement of the base end portion of the swinging arm  13   a  around the shaft center of the output shaft  12   a  with respect to the end portion of the output shaft  12   a  in a direction opposite to the direction of rotation of this output shaft  12   a . In the case of this embodiment, the screw hole  24 , into which the connecting screw  26  is screwed, is provided in the portion that is positioned off the shaft center of the output shaft  12   a . Thus, with the minute displacement, a force in a direction of rotation of the connecting screw  26  is hard to be applied to the connecting screw  26  screwed into the screw hole  24 . Consequently, even when an engagement portion specifically used for preventing the connecting screw from being loosened is not provided, the connecting screw  26  is hard to be loosened.  
      Incidentally, according to this embodiment, the position of the screw hole  24 , in which the connecting screw  26  is screwed, is devised. Consequently, the connecting screw  26  is prevented from being loosened. The structure for preventing an occurrence of the relative rotation of the swinging arm  13   a  around the connecting screw  26  with respect to the output shaft  12   a  is not limited to the spring pin  35 . Various structures, which have hither to be known, may be employed. Incidentally, in the case of the structure implemented by the engagement between a pin and a hole can reduce the cost, because of easiness of processing each of the parts.  
      Although the embodiment according to the invention has been described in the foregoing description, it is apparent to those skilled in the art that various alterations and modifications may be made without departing from the spirit and scope of the invention.  
      The present application is based on the Japanese Patent Application (No. 2002-031248), filed Feb. 7, 2000, the contents of which are incorporated by reference.  
     Industrial Applicability  
      A highly reliable and low cost swinging actuator can be obtained.