Patent Publication Number: US-7588259-B2

Title: Reduction gear and vehicular active stabilizer system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present claims priority from Japanese patent application 2006-346612, filed 22 Dec. 2006. The entire disclosure of each of the referenced priority documents is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a reduction gear which outputs rotation of a carrier as relative rotation of first and second sun gears, and a vehicular active stabilizer system using the reduction gear. 
   2. Description of the Background Art 
   Japanese Patent Publication No. 2002-518245 discloses a device including a stabilizer whose opposite ends are connected to left and right suspension devices, and an actuator provided at an intermediate portion of the stabilizer. Left and right halves of the stabilizer are relatively twisted in opposite directions to control yaw moment of a vehicle. In this device, the actuator comprises three in-line-connected planetary gear mechanisms and a motor for inputting a driving force thereto. 
   Because the above conventional stabilizer is a type using a planetary gear mechanism as a reduction gear of an actuator, three planetary gear mechanisms are required to obtain a sufficient reduction ratio, leading to a problem that the number of components and cost are increased and the actuator becomes large. Also, in order to change the reduction ratio of the reduction gear of the actuator, a design change of the entire planetary gear mechanisms is required, leading to a problem of a further increased cost. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above situation, and has an object to provide a small reduction gear which provides a large reduction ratio and facilitates a change of the reduction ratio. 
   To achieve the above object, according to a first aspect of the present invention, there is provided a reduction gear comprising: a carrier which is rotatable about a first axis and has a circular supporting hole defined about a second axis offset from the first axis; a ring gear which is rotatably fitted in the supporting hole of the carrier and has inner teeth on an inner peripheral surface thereof; a first sun gear which is rotatably supported about the first axis and has first outer teeth meshed with the inner teeth of the ring gear; and a second sun gear which is rotatably supported about the first axis and has second outer teeth meshed with the inner teeth of the ring gear, the number of the second outer teeth being different from that of the first outer teeth, wherein rotation of the carrier is outputted as relative rotation of the first and second sun gears. 
   With the first aspect of the present invention, the reduction gear includes: the rotatable carrier; the ring gear rotatably fitted in the offset supporting hole in the carrier; and the first and second sun gears having the first and second outer teeth meshed with the inner teeth of the ring gear, respectively. The rotation of the carrier is reduced in speed and outputted as relative rotation of the first and second sun gears. Thus, it is possible to secure a large reduction ratio although in a small structure having a small number of components. Also, it is possible to change the reduction ratio by a slight design change, e.g., changing the number of teeth in one of the outer teeth of the first and second sun gears, thereby improving the versatility. 
   According to a second aspect of the present invention, in addition to the first aspect, the reduction gear further comprises a bearing which is interposed between the carrier and the ring gear. 
   With the second aspect of the present invention, the bearing interposed between the carrier and the ring gear enables a smooth relative rotation therebetween. 
   According to a third aspect of the present invention, there is provided a vehicular active stabilizer system using the reduction gear according to the first or second aspect, and comprising: a left stabilizer half having an outer end adapted to be connected to a left suspension device and an inner end connected to the first sun gear; a right stabilizer half having an outer end adapted to be connected to a right suspension device and an inner end connected to the second sun gear; and a driving source for driving the carrier. 
   With the third aspect of the present invention, the reduction gear of the present invention is used in a vehicular active stabilizer system, wherein the outer ends of the left and right stabilizer halves are adapted to be connected to the suspension devices, and the inner ends thereof are connected to the first and second sun gears; the carrier is driven by the driving source to generate relative rotation having a reduced speed between the first and second sun gears; and the left and right stabilizer halves are relatively twisted and deformed to generate a roll moment. 
   A knuckle  11  of an embodiment corresponds to the suspension device of the present invention, an actuator  15  of the embodiment corresponds to the reduction gear of the present invention, a motor  16  of the embodiment corresponds to the driving source of the present invention, and a needle bearing  32  of the embodiment corresponds to the bearing of the present invention. 
   The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from a present exemplary embodiment, which will be described in detail below with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view showing an active stabilizer system according an embodiment of the present invention. 
       FIG. 2  is an enlarged sectional view taken along line  2 - 2  of  FIG. 1 . 
       FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 2 . 
       FIG. 4  is an exploded perspective view of an actuator of the embodiment of  FIG. 1 . 
       FIG. 5  is a view for explaining the operation of the actuator. 
       FIG. 6  is a view for explaining the relationship between reduction ratio and the number of teeth of each gear in the actuator. 
   

   DESCRIPTION OF THE PRESENT EMBODIMENT 
   As shown in  FIG. 1 , a vehicular active stabilizer system S is divided into two halves along at its center in the vehicle width direction, and includes: left and right stabilizer halves  12 ,  13  having outer ends which are respectively connected to knuckles  11  for rotatably supporting right and left wheels; left and right supporting brackets  14  for supporting the stabilizer halves  12 ,  13  on a vehicle body; and an actuator  15  for connecting the inner ends of the left and right stabilizer halves  12 ,  13  to each other, the inner ends being opposed to each other in the vehicle width direction. A motor  16  may be integrally provided with the actuator  15  so as to serve as a driving source for the actuator  15 . 
   As shown in  FIGS. 2 to 4 , the actuator  15  includes a left housing  22  and a right housing  23  which are integrally coupled by a bolt  21 . The left stabilizer half  12  is rotatably supported in the left housing  22  by a ball bearing  24 . The right stabilizer half  13  is relatively non-rotatably coupled to the right housing  23  via a serration coupling  25 . A small diameter portion  12   a  formed at a tip end of the left stabilizer half  12  is relatively rotatably fitted in an axial hole  13   a  formed at a tip end of the right stabilizer half  13 , with two needle bearings  26  therebetween. 
   An annular carrier  29  is rotatably supported within the left and right housings  22  and  23  via a pair of needle bearings  27  and a pair of thrust sliding bearings  28 . Assuming that the stabilizer halves  12  and  13  supported by the left and right housings  22  and  23  have a first axis L 1  as a central axis of rotation, the carrier  29  has outer teeth  29   a  on its outer periphery around the first axis L 1 , and a pinion  30  has outer teeth  30   a  which are meshed with the outer teeth  29   a  and is rotatably supported in the left and right housings  22  and  23  via two ball bearings  31 . The pinion  30  is coaxially connected to a rotation shaft for rotation of the motor  16  supported in the right housing  23 . 
   The carrier  29  has an inner periphery forming a circular supporting hole  29   b  about a second axis L 2  that is offset from the first axis L 1 . Thus, the carrier  29  includes a thick portion  29   c  having the maximum thickness in the radial direction and a thin portion  29   d  having the minimum thickness in the radial direction, with a phase difference of 180° therebetween. A ring gear  33  is rotatably provided on the inner periphery of the supporting hole  29   b  of the carrier  29  via two needle bearings  32 . The needle bearings  32  allow the carrier  29  and the ring gear  33  to smoothly rotate relative to each other. Provided on the inner peripheral surface of ring gear  33  are first inner teeth  33   a  on the left side and second inner teeth  33   b  on the right side, which have different numbers of teeth. The ring gear  33  has a uniform thickness in the radial direction, and thus the first and second inner teeth  33   a  and  33   b  share a center on the second axis L 2 . 
   A first sun gear  34  is fixed to the left stabilizer half  12  in the left housing  22 , and has first outer teeth  34   a  formed on its outer periphery so as to be meshed with the first inner teeth  33   a  of the ring gear  33 . A second sun gear  35  is fixed to the right stabilizer half  13  in the right housing  23 , and has second outer teeth  35   a  formed on its outer periphery so as to be meshed with the second inner teeth  33   b  of the ring gear  33 . The number of the first outer teeth  34   a  of the first sun gear  34  is different from that of the second outer teeth  35   a  of the second sun gear  35 . 
   The operation of the embodiment of the present invention having the above-described arrangement will now be described. 
     FIG. 5  shows views illustrating the operation of the embodiment where the motor  16  is driven in one direction while the first sun gear  34  is fixed (see the Δ mark), and the pinion  30  connected to the motor  16  rotates the carrier  29  clockwise by 270°. 
   First, reference is made on the behavior of the first sun gear  34  shown on the upper row in  FIG. 5 . When the rotational angle of the carrier  29  is zero, the thick portion  29   c  is positioned on the upper side in  FIG. 5 , and the outer teeth  34   a  of the first sun gear  34  are meshed with the first inner teeth  33   a  of the ring gear  33  on the upper side in  FIG. 5 . When the carrier  29  is rotated clockwise by 90°, the thick portion  29   c  is moved to rightward in  FIG. 5 , and the ring gear  33  is slightly rotated counterclockwise (see the ▾ mark) due to the difference between the number of the outer teeth  34   a  of the first sun gear  34  and the number of the first inner teeth  33   a  of the ring gear  33 . When the carrier  29  is further rotated clockwise from 180° to 270°, the thick portion  29   c  is moved from the lower side to the left side in  FIG. 5 , so that correspondingly the ring gear  33  is further rotated counterclockwise (see the ▾ mark). 
   In the meantime, corresponding to the above-described clockwise rotation of the carrier  29 , the second sun gear  35  having the outer teeth  35   a  meshed with the second inner teeth  33   b  of the carrier  29  is slightly rotated counterclockwise (see the ⋄ mark) due to the difference between the number of the outer teeth  35   a  of the second sun gear  35  and the number of the second inner teeth  33   b  of the ring gear  33 . Thus, the rotation of the carrier  29  by 270° generates a phase difference of an angle θ between the first sun gear  34  and the second sun gear  35 . 
   The above description is based on the assumption for the sake of convenience that the first sun gear  34  is fixed, but even if the sun gear  34  is not fixed, the first sun gear  34  and the second sun gear  35  can be relatively rotated by an angle θ while the carrier  29  is rotated by 270°. Therefore, the left stabilizer half  12  and the right stabilizer half  13  can be relatively twisted in one or the other direction by a normal or reverse rotation of the carrier  29  by the motor  16 , thereby vertically moving the left and right wheels in opposite phases to generate a roll moment. Conversely, if the motor  16  is electrically locked to prevent rotation, the left stabilizer half  12  and the right stabilizer half  13  become substantially integral to each other to function as a normal stabilizer, thereby vertically moving the left and right wheels in the same phase to control the rolling of the vehicle. 
   As shown in  FIG. 6 , when each of the gears is provided so as to have the following number of teeth:
         number Z 1  of the outer teeth  34   a  of the first sun gear  34 =36;   number Z 2  of the outer teeth  35   a  of the second sun gear  35 =39;   number Z 3  of the first inner teeth  33   a  of the ring gear  33 =40;   number Z 4  of the second inner teeth  33   b  of the ring gear  33 =44;   number Z 5  of the outer teeth  29   a  of the carrier  29 =80; and   number Z 6  of the outer teeth  30   a  of the pinion  30 =20,
 
a reduction ratio R 1  of a first stage which is determined based on the number of teeth of the outer teeth  29   a  of the carrier  29  and the number of teeth of the outer teeth  30   a  of the pinion  30  is calculated as follows:
 
 R 1 =Z 5 /Z 6=80/20=4
       

   Also, a reduction ratio R 2  of a second stage which is determined based on the number of teeth of the outer teeth  34   a  of the first sun gear  34 , that of the outer teeth  35   a  of the second sun gear  35 , that of the first inner teeth  33   a  of the ring gear  33 , and that of the second inner teeth  33   b  of the ring gear  33  is calculated as follows: 
   
     
       
         
           
             
               
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 = 
                 
                   1 
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                     { 
                     
                       1 
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                           ( 
                           
                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               3 
                               / 
                               Z 
                             
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                             1 
                           
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                             Z 
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                     } 
                   
                 
               
             
           
           
             
               
                 = 
                 
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                       1 
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                             40 
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                             39 
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                 = 
                 66 
               
             
           
         
       
     
   
   Thus, a reduction ratio R 3  which is a total of the reduction ratios R 1  and R 2  in the first and second stages is obtained as follows:
 
 R 3= R 1 ×R 2=4×66=264
 
   When the number Z 2  of the outer teeth  35   a  of the second sun gear  35  is changed from  39  to  40 , the reduction ratio R 2  is calculated as follows: 
   
     
       
         
           
             
               
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 = 
                 
                   1 
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                     { 
                     
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                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
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                             Z 
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                               Z 
                             
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                             4 
                           
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                     } 
                   
                 
               
             
           
           
             
               
                 = 
                 
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                       1 
                       - 
                       
                         
                           ( 
                           
                             40 
                             / 
                             36 
                           
                           ) 
                         
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                             40 
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                           ) 
                         
                       
                     
                     } 
                   
                 
               
             
           
           
             
               
                 = 
                 99 
               
             
           
         
       
     
   
   Thus, the reduction ratio R 3  which is a total of the reduction ratios R 1  and R 2  in the first and second stages is obtained as follows:
 
 R 3 =R 1 ×R 2=4×99=396
 
   That is, a mere change of the number of the outer teeth  35   a  of the second gear  35 , among the first and second sun gears  34  and  35 , increases the reduction ratio R 2  of the second stage from 66 to 99, and increases the total reduction ratio R 3  from 264 to 396, without changing the number of other gears or the number of their teeth. Thus, it is possible to change the reduction ratio at an remarkably low cost without a major design change of the actuator  15 . Also, because the second sun gear  35  having the changed number of teeth is housed inside the supporting hole  29   b  of the carrier  29 , the change in the number of teeth does not increase the outer dimensions of the actuator  15 . 
   As described above, because the actuator  15  of the present embodiment has a small diameter but provides a large reduction ratio, it is possible to easily secure a space in an intermediate portion of the active stabilizer system S for mounting the actuator  15  therein. Also, even when the active stabilizer systems S are applied to both the front and rear wheels, or applied to different types of vehicles, change of reduction ratio is possible by a slight design change of the actuator  15 , thereby improving the versatility and contributing to cost reduction. 
   The exemplary embodiment of the present invention has been described above, but various changes in design may be made without departing from the subject matter of the present invention. 
   For example, in the above embodiment, the actuator  15  is applied to the vehicular active stabilizer system S, but may be used as a reduction gear for any other application. That is, not only the rotation of the carrier  29  is reduced in speed and outputted as relative rotation of the first and second sun gears  34  and  35  as described in the above embodiment, but also other situations may be envisioned which can use a reduction gear according to the present invention in which the rotation of the carrier  29  is reduced in speed and outputted to one of the first and second sun gears  34  and  35  while the other sun gear being fixed. 
   Also, in the above embodiment, the first and second inner teeth  33   a  and  33   b  of the ring gear  33  have different numbers of teeth, but they may have the same number of teeth. 
   Further, in the above embodiment, the number of the outer teeth  34   a  of the first sun gear  34  is changed in order to change a reduction ratio, but the number of the outer teeth  35   a  of the second sun gear  35  or the numbers of both the outer teeth  34   a  and  35   a  of the first and second sun gears  34  and  35  may be changed instead. 
   Furthermore, in the above embodiment, the actuator  15  is provided in the intermediate portion of the stabilizer in the lateral direction, but may be provided at a position offset from the center to the left or right side of the vehicle.