Patent Publication Number: US-2021190200-A1

Title: Driving force transmission device

Description:
TECHNICAL FIELD 
     The present invention relates to a driving force transmission device. 
     BACKGROUND ART 
     The patent document 1 discloses a configuration in which a chain sprocket, which is a rotating member, is surrounded by a pair of baffle plates. 
     The patent document 2 discloses a configuration in which a gear, which is a rotating member, is surrounded by a pair of baffle plates. 
     The baffle plate of the patent document 2 is provided to surround a final gear in a differential device. 
     In the driving force transmission device including the final gear, in order to improve the fuel consumption by reducing the stirring resistance of the rotating member (final gear), it is basically preferable to suppress the amount of oil entering the space surrounded by the pair of baffle plates. 
     On the other hand, when the oil temperature becomes extremely low, an exceptional situation occurs. Namely, oil return from various routes in the whole driving force transmission device to an oil reservoir (oil pan) from which an oil pump sucks oil occurs at first. Then, when the oil temperature decreases, the viscosity of the oil increases and the fluidity of the oil decreases. 
     Therefore, in the whole driving force transmission device, when the oil temperature becomes low, the oil return to the oil reservoir (oil pan) from which the oil pump sucks the oil becomes slow. 
     Therefore, when the oil temperature becomes low, it is required to promote the oil return to the oil reservoir. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     Patent Document 1: JP2012-102818A 
     Patent Document 2: JP5844019B 
     SUMMARY OF INVENTION 
     The present invention provides a driving force transmission device including: 
     a baffle plate portion including a pair of baffle plates and a seal member disposed in a region between the pair of baffle plates; 
     a rotating member disposed within a rotating member chamber that is a space surrounded by the baffle plate portion; 
     an oil pump that serves as a source of oil for lubrication supplied to the rotating member; and 
     an oil pan in which the oil is stored and from which the oil pump sucks the oil, wherein 
     at least one of, one of the pair baffle plates, the other one of the pair of baffle plates and the seal member is formed by including a material that shrinks as an oil temperature decreases, and 
     the baffle plate portion is dimensioned such that the region between the pair of baffle plates is sealed by the seal member when the oil temperature is equal to or higher than a predetermined oil temperature and an aperture is formed in the region between the pair of baffle plates when the oil temperature is less than the predetermined oil temperature. 
     According to the present invention, when the oil temperature becomes low, the oil return to the oil reservoir can be promoted. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  are diagrams for explaining a main part of a transmission case. 
         FIGS. 2A and 2B  are diagrams illustrating an arrangement of baffle plates in the transmission case. 
         FIG. 3  is a diagram illustrating the baffle plates. 
         FIGS. 4A-4C  are views for explaining a body portion of the baffle plates. 
         FIGS. 5A and 5B  are views for explaining a cover portion of the baffle plates. 
         FIGS. 6A and 6B  are views for explaining a cover portion of the baffle plates. 
         FIGS. 7A and 7B  are view illustrating an operation of the baffle plates. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described by taking a case where a driving force transmission device is an automatic transmission  1  for a vehicle as an example. 
       FIGS. 1A and 1B  are diagrams for explaining a main part of a transmission case  10  and it is a diagram for explaining surroundings of an accommodating portion  15  of a differential device in a transmission case  10  of the automatic transmission  1 . 
       FIG. 1A  is a view of the transmission case  10  seen from a torque converter (not shown).  FIG. 1B  is an enlarged view of an area B in  FIG. 1A . 
     In  FIGS. 1A and 1B , a joint surface between the transmission case  10  and the converter housing (not shown) is indicated by hatching on the end surface on the paper front side of the outer wall portion  62  of the baffle plate  4 . 
       FIGS. 2A and 2B  are diagrams illustrating an arrangement of the baffle plate  4  in the transmission case  10 .  FIG. 2A  is a view showing the baffle plate  4  cut along the line A-A in  FIG. 1A , and  FIG. 2B  is a view showing the baffle plate  4  cut along the line C-C in  FIG. 1B . 
     In the following, the positional relationship of the components in the arrangement of the transmission case  10  in  FIGS. 1A and 1B  will be described. 
     In the following description, “upper side (upper)” means the upper side in the vertical line VL direction based on the installation state of the automatic transmission, and “lower side (lower)” means the lower side in the vertical line direction based on the installation state of the automatic transmission. 
     As shown in  FIGS. 1A and 1B , at the lower portion of the transmission case  10 , the accommodating portion  15  for the differential device is provided. The torque converter side, not shown (paper front side) of the accommodating portion  15  is open. 
     In the central portion of the accommodating portion  15 , a differential case  20  is rotatably supported. A final gear  25  having a ring shape when viewed from the direction in the rotation axis X 1  of the differential case  20  is fixed on an outer periphery of the differential case  20 . 
     On an outer periphery of the final gear  25 , teeth portions  250  are formed over the entire circumference in the circumferential direction around the rotation axis X 1 . 
     The teeth portions  250  of the final gear  25  are inclined at a predetermined angle with respect to the rotation axis X 1  when viewed from the radial direction of the rotation axis X 1 . The final gear  25  is a helical gear with the teeth portions  250  slanted. 
     At the upper side of the final gear  25 , a reduction gear  35  is positioned. Teeth portions  35   a  on an outer periphery of the reduction gear  35  mesh with the teeth portions  250  of the final gear  25 . 
     In the transmission case  10 , the reduction gear  35  is rotatably provided about the rotation axis X 2 . The rotation axis X 2  of the reduction gear  35  is provided above the rotation axis X 1  of the final gear  25  and parallel to the rotation axis X 1 . 
     An output rotation of a transmission mechanism (not shown) is input to the reduction gear  35  and the reduction gear  35  rotates about the rotation axis X 2 . Therefore, the final gear  25 , the outer periphery of which engages with the reduction gear  35 , rotates about the rotation axis X 1  by the rotation driving force transmitted from the reduction gear  35 . 
     During forward running of the vehicle equipped with the automatic transmission  1 , the final gear  25  rotates in the clockwise direction CW (forward direction) in the figure. 
     When viewed from the direction of the rotation axis X 1 , a peripheral wall portion  11  of the transmission case  10  has an arc shape surrounding the outer periphery of the final gear  25  in the vicinity region of the final gear  25 . 
     At the peripheral wall portion  11 , a plurality of bolt holes  12  are provided at intervals in the circumferential direction. An end surface  11   a  of the peripheral wall portion  11 , which is at the paper front side, has a joining surface with a converter housing (not shown) surrounding the torque converter (not shown). 
     In the transmission case  10 , a wall portion  13  covering a side surface of the final gear  25  is provided inside of the peripheral wall portion  11 . As shown in  FIG. 2A , the wall portion  13  is provided at the left side of the final gear  25  in the drawing and extends along a side surface  25   a  of the final gear  25 . 
     In the transmission case  10 , a baffle plate  4  (body portion  5 , cover portion  8  and cover portion  9 ) is provided (see  FIGS. 1A, 1B, 2A, 2B and 3 ). 
     The baffle plate  4  is provided across a region where the final gear  25  is provided and a region where a driven sprocket DS is provided in the transmission case  10 . 
       FIG. 3  is a diagram for explaining the baffle plate  4  (body portion  5 , cover portion  8 , and cover portion  9 ). In  FIG. 3 , the final gear  25  is shown by a virtual line, and the position of each component of the baffle plate  4  (body portion  5 , cover portion  8  and cover portion  9 ) and the final gear  25  are displaced in the direction of the rotation axis X 1 . 
       FIGS. 4A-4C  are diagrams illustrating a body portion  5  of the baffle plate  4 .  FIG. 4A  is a view of the body portion  5  seen from the direction of the rotation axis X 1 .  FIG. 4B  is the A-A sectional view of  FIG. 4A .  FIG. 4C  is the B-B cross-sectional view of  FIG. 4A . 
     In  FIG. 4A , a part of the driven sprocket DS is shown by a virtual line. In  FIG. 4B , the final gear  25  is shown by a virtual line. In  FIG. 4C , a part of the driven sprocket DS and a part of a drive shaft SH are shown by a virtual line. 
     As shown in  FIG. 3 , the baffle plate  4  has the body portion  5  fixed to the transmission case  10 , the cover portion  8  fixed to the converter housing (not shown), and the cover portion  9  fixed to the body portion  5 . In this embodiment, the baffle plate  4  is formed of a polymer material having a large linear expansion coefficient at low temperatures. 
     When the cover portion  8  is assembled to the body portion  5 , an accommodating chamber Sa (rotating member accommodating chamber) for the final gear  25  is formed between the body portion  5  and the cover portion  8  (see  FIG. 2A ). 
     When the cover portion  9  is assembled to the body portion  5 , an accommodating chamber Sb (rotating member accommodating chamber) for the driven sprocket DS is formed between the body portion  5  and the cover portion  9  (see  FIG. 2B ). 
     As shown in  FIG. 4A , the body portion  5  of the baffle plate  4  has a first cover portion  6  covering the side surface of the final gear  25 , and a second cover portion  7  covering the side surface of the driven sprocket DS. 
     The first cover portion  6  and the second cover portion  7  are integrally formed by resin molding. 
     When viewed from the direction of the rotation axis X 1 , the first cover portion  6  has a plate shape base portion  60 . 
     The base portion  60  extends in the circumferential direction around the rotation axis X 1 . When viewed from the direction of the rotation axis X 1 , the base portion  60  has an arc shape. 
     The outer diameter R to the outer periphery of the base portion  60  is set to a diameter larger than the radius r to the outer periphery of the final gear  25 . 
     As shown in  FIG. 2A , in the transmission case  10 , the side surface  25   a  of the final gear  25  at the wall portion  13  side is covered by the base portion  60  of the first cover portion  6 . 
     As shown in  FIG. 4A , the base portion  60  is provided with a plurality of through holes  68 . Each of the through holes  68  penetrates the base portion  60  in the direction of the rotation axis X 1 . 
     When viewed from the direction of the rotation axis X 1 , the through holes  68  are provided at intervals in the circumferential direction around the rotation axis X 1  on an imaginary circle Im 1  centered on the rotation axis X 1 . 
     The first cover portion  6  of the baffle plate  4  is fixed to the transmission case  10  by bolts (not shown) inserted into the through holes  68 . 
     The base portion  60  further includes concave portions  66  surrounding the through holes  68  respectively and a concave groove  67 . 
     When viewed from the direction of the rotation axis X 1 , each of the concave portions  66  has a circle shape surrounding the through hole  68  and each of the concave portions  66  is formed to be recessed toward the paper back side. 
     As shown in  FIGS. 4A and 4B , when viewed from the direction of the rotation axis X 1 , the concave groove  67  is formed recessed toward the paper back side. 
     The concave groove  67  connects the concave portions  66  and  66  adjacent to each other in the circumferential direction around the rotation axis X 1 . 
     When viewed from the direction of the rotation axis X 1 , the concave groove  67  is formed in an arc shape along the imaginary circle Im 1  described above. 
     When viewed from the direction of the rotation axis X 1 , one end  601  of the base portion  60  is formed in an arc shape surrounding the through hole  68  provided at the one end  601  side while keeping a predetermined distance. 
     The other end  602  of the base portion  60  is formed in a straight line along a line segment La extending in the radial direction of the rotation axis X 1 . Here, when viewed from the direction of the rotation axis X 1 , the line segment La is a straight line orthogonal to the rotation axis X 1  and extending in the radial direction of the rotation axis X 1 . 
     An inner wall portion  61  protruding toward the paper front side is provided at the inner circumference edge of the base portion  60 . 
     In a plan view, the inner wall portion  61  has an arc shape, and the inner wall portion  61  is provided to have substantially the same protruding height over the entire length in the circumferential direction around the rotation axis X 1 . 
     An outer wall portion  62  protruding toward the paper front side is provided at the outer circumference edge of the base portion  60 . 
     The outer wall portion  62  is provided in a range extending from one longitudinal end  601  of the base portion  60  to the other longitudinal end  602  of the base portion  60 . 
     When viewed from the direction of the rotation axis X 1 , the outer wall portion  62  has an arc shape along the outer periphery of the final gear  25 . 
     As shown in  FIG. 1A , in the transmission case  10 , the oil OL is stored in the lower area in the vertical line VL direction in the installation state of the automatic transmission. 
     The baffle plate  4  is arranged such that one end  62   a  and the other end  62   b  of the outer wall portion  62  in the circumferential direction around the rotation axis X 1  are positioned above the oil level OL_level of the oil OL. 
     At the outer wall portion  62 , an oil hole  65  is provided at a position lower than the oil level OL_level of the oil OL (see  FIG. 3 ). 
     The oil hole  65  is provided to penetrate the outer wall portion  62  in the thickness direction (radial direction of the rotation axis X 1 ). 
     As shown in  FIG. 3 , the outer wall portion  62  is provided to have a predetermined height h 1  in the direction of the rotation axis X 1 . 
     The height h 1  of the outer wall portion  62  is set to be a height larger than the width W 1  of the final gear  25  in the direction of the rotation axis X 1  (h 1 &gt;W 1 ). 
     Therefore, as shown in  FIG. 4B , when viewed from the radial direction of the rotation axis X 1 , at the lower side of the transmission case  10 , the outer periphery of the final gear  25  is covered by the outer wall portion  62  surrounding the final gear  25  while keeping a predetermined distance (for example, 2 mm). 
     In the present embodiment, the oil hole  65  is provided at a substantially intermediate position of the outer wall portion  62  in the direction of the rotation axis X 1 . 
     As shown in  FIG. 4B , a belt shape rib  69  is provided on the outer periphery of the outer wall portion  62 . 
     The belt shape rib  69  is formed of a material having a large linear expansion coefficient at low temperatures like the material constituting the body portion  5  (outer wall portion  62 , base portion  60 ). 
     The belt shape rib  69  may be formed of a material having a larger linear expansion coefficient at low temperatures than the material constituting the body portion  5  (outer wall portion  62 , base portion  60 ). 
     The belt shape rib  69  is provided in a predetermined range in the circumferential direction around the rotation axis X 1 , the predetermined range being a range extending in a direction away from the second cover portion  7  (left direction in  FIG. 4A ) from the vicinity of the oil hole  65 . 
     The region provided with the belt shape rib  69  is a region at the downstream side of the oil hole  65  in the rotation direction of the final gear  25  during forward running of the vehicle and in the moving direction of the oil OL scraped by the rotating final gear  25 . 
     The belt shape rib  69  is provided across the outer wall portion  62  and the base portion  60  at the boundary portion between the outer wall portion  62  and the base portion  60 . 
     As shown in  FIG. 4B , the belt shape rib  69  includes a deformation promoting portion  691  integrally formed on the outer periphery of the outer wall portion  62 , and a bottom portion  692  integrally formed on the back surface of the base portion  60 . 
     The deformation promoting portion  691  protrudes outwardly from the outer periphery of the outer wall portion  62  by a predetermined width Wa (for example, 4 mm). The deformation promoting portion  691  is provided in a predetermined angle range in the circumferential direction around the rotation axis X 1 , the predetermined angle range is an angle range from the vicinity of the oil hole  65  to the vicinity of the other end  62   b  of the outer wall portion  62 . 
     The height h 2  of the deformation promoting portion  691  in the direction of the rotation axis X 1  is approximately half of the height h 1  of the outer wall portion  62 . The deformation promoting portion  691  is provided at a position away from the end portion  62   c  (free end) of the outer wall portion  62  and close to the base portion  60  (left side in  FIG. 4B ). 
     As shown in  FIG. 3 , at the deformation promoting portion  691 , a plurality of concave portions  693  (slits) are provided at intervals in the circumferential direction. When viewed from the radial direction of the rotation axis X 1 , each of the concave portions  693  has a rectangular shape and the outer periphery of the outer wall portion  62  is exposed through the concave portions  693 . 
     The bottom portion  692  extend inward in the radial direction on the outer surface of the base portion  60 , and extends to the region of the concave groove  67  described above (see  FIG. 4B ). Since the concave groove  67  is formed by recessing the base portion  60  as described above, the region provided with the concave groove  67  and the bottom portion  692  are positioned at the same level at the outer surface of the base portion  60 . 
     As shown in  FIG. 4A , a base portion  70  of the second cover portion  7  extends in the radial direction of the rotation axis X 1  from the outer periphery of the outer wall portion  62  of the first cover portion  6 . 
     The base portion  70  has a tapered shape in which the width in the circumferential direction around the rotation axis X 1  becomes narrower as the distance from the first cover portion  6  increases. 
     The base portion  70  of the second cover portion  7  and the base portion  60  of the first cover portion  6  are arranged by displacing in the direction of the rotation axis X 1 . In  FIG. 4A , the base portion of the second cover portion  7  is positioned at the paper front side with respect to the base portion  60  of the first cover portion  6 . 
     At the distal end portion in the extending direction of the base portion  70 , a mounting portion  73  of the cover portion  9  described later is provided. The mounting portion  73  is provided integrally with the base portion  70 . The mounting portion  73  extends in a direction away from the base portion  70 , and a bolt hole  73   a  opens at the distal end side of the mounting portion  73 . 
     An outer wall portion  72  is provided at the boundary portion between the mounting portion  73  and the base portion  70 . In  FIG. 4A , the outer wall portion  72  extends toward the paper front side, and the outer wall portion  72  extends along the side edge of the base portion  70  from the boundary portion between the mounting portion  73  and the base portion  70  to the outer wall portion  62  of the first cover portion  6 . 
     In the vicinity of the connecting portion between the outer wall portion  72  of the second cover portion  7  and the outer wall portion  62  of the first cover portion  6 , a mounting portion  74  of the cover portion  9  described later is provided. The mounting portion  74  is provided in the region between the outer wall portion  62  and the outer wall portion  72  and a bolt hole  74   a  opens at the center of the mounting portion  74 . 
     The mounting portion  74  and the mounting portion  73  described above are provided to have the same height in the direction of the rotation axis X 1 . 
     In the vicinity of the connecting portion between the outer wall portion  72  of the second cover portion  7  and the outer wall portion  62  of the first cover portion  6 , plate shape ribs  75  are provided. 
     The plate shape ribs  75  are provided across the outer wall portion  72  and the outer wall portion  62 . A plurality of plate shape ribs  75  are provided at predetermined intervals in the direction of the rotation axis X 1  (see  FIG. 3 ). 
     A plurality of ribs  79  are provided at intervals in the longitudinal direction on the outer periphery of the outer wall portion  72 . 
     The ribs  79  are also formed of a material having a large linear expansion coefficient at low temperatures like the material constituting the second cover portion  7  (outer wall portion  72 , base portion  70 ). 
     The ribs  79  may be formed of a material having a larger linear expansion coefficient at low temperatures than the material constituting the second cover portion  7  (outer wall portion  72 , base portion  70 ). 
     As shown in  FIG. 4A , when viewed from the direction of the rotation axis, the shape of each of the ribs  79  is a semicircular shape having the radius ra, and each of the ribs  79  protrudes outward from the outer periphery of the outer wall portion  72  while directing the apex P outward. 
     As shown in  FIG. 4C , the height h 4  of the ribs  79  in the direction of the rotation axis X 3  is lower than the height h 3  of the outer wall portion  72  in the direction of the rotation axis X 1  (h 3 &gt;h 4 ). The ribs  79  are provided at a position closer to the base portion  70  on the outer wall portion  72 . The ribs  79  are provided at a position away from the end portion  72   c  (free and) of the outer wall portion  72  and close to the base portion  70  (left side in  FIG. 4C ). 
     As shown in  FIG. 4A , a through hole  71  is provided in the center portion of the base portion  70 . The drive shaft SH (see  FIG. 4C ) of the oil pump OP (see  FIGS. 1A and 1B ) penetrates the through hole  71 . 
     As shown in  FIGS. 1A and 1B , in the transmission case  10 , the oil pump OP is disposed at the paper back side of the second cover portion  7  and the driven sprocket DS is disposed at the paper front side of the second cover portion  7 . 
     At the second cover portion  7 , the driven sprocket DS is connected to the drive shaft SH in the region between the outer wall portion  72  and the outer wall portion  62  of the first cover portion  6 , and the driven sprocket DS and the drive shaft SH are adapted to rotate integrally. 
     In the automatic transmission, the rotational driving force input from the engine is transmitted to the driven sprocket DS via the chain CH. 
     Then, the driven sprocket DS and the drive shaft SH rotate about the rotation axis X 3  to drive the oil pump OP. As a result, the oil OL in the oil pan  16  is sucked by the oil pump OP through an oil strainer  17  (see  FIG. 1A ). Then, the oil OL pressurized by the oil pump OP is supplied to the hydraulic control circuit provided in the automatic transmission. 
       FIGS. 5A and 5B  are views for explaining the cover portion  8  of the baffle plate  4 .  FIG. 5A  is a view of the cover portion  8  seen from the direction of the rotation axis X 1 .  FIG. 5B  is the A-A cross-sectional view in  FIG. 5A . In  FIG. 5B , a part of the final gear  25  in  FIG. 5B  is shown by a virtual line. 
     As shown in  FIGS. 5A and 5B , the cover portion  8  has a plate shape base portion  80 . 
     When viewed from the direction of the rotation axis X 1 , the base portion  80  extends in the circumferential direction around the rotation axis X 1 , and when viewed from the direction of the rotation axis X 1 , the base portion  80  has an arc shape. 
     As shown in  FIGS. 5A and 5B , the outer diameter R 1  to the outer periphery of the base portion  80  is smaller than the outer diameter R to the outer wall portion  62  of the body portion  5  (see  FIG. 4A ) and larger than the radius r to the outer periphery of the final gear  25  (see  FIG. 4A ). 
     Therefore, a gap CL 1  is formed between the outer peripheral portion  80   a  of the base portion  80  and the outer wall portion  62  (see  FIG. 5B ). 
     As shown in  FIG. 5B , in the automatic transmission  1 , the side surface  25   b  of the final gear  25  at the converter housing (not shown) side is covered by the base portion  80  of the cover portion  8 . 
     The base portion  80  is provided with a plurality of through holes  85 . Each of the through holes  85  penetrates the base portion  80  in the direction of the rotation axis X 1 . 
     When viewed from the direction of the rotation axis X 1 , each of the through holes  85  is located on a virtual circle Im 1  centered on the rotation axis X 1 . The through holes  85  are provided at intervals in the circumferential direction around the rotation axis X 1 . 
     The cover portion  8  of the baffle plate  4  is fixed to the converter housing (not shown) by bolts (not shown) inserted into the through holes  85 . 
     The base portion  80  is further provided with concave portions  86  surrounding the through holes  85  respectively. 
     As shown in  FIG. 5A , when viewed from the direction of the rotation axis X 1 , each of the concave portions  86  is formed to be recessed toward the paper front side. 
     When viewed from the direction of the rotation axis X 1 , one end  801  and the other end  802  of the base portion  80  are formed in a straight line along the line segments Lb and Lc extending in the radial direction of the rotation axis X 1 , respectively. 
     Here, when viewed from the direction of the rotation axis X 1 , the line segments Lb and Lc are straight lines orthogonal to the rotation axis X 1  and extending in the radial direction of the rotation axis X 1 . 
     As shown in  FIG. 5A , the line segment Lc is positioned above the line segment La. Therefore, when the cover portion  8  and the body portion  5  are assembled, the other end  802  of the cover portion  8  is positioned higher than the other end  602  the body portion  5 . 
     An inner wall portion  81  protruding toward the paper front side is provided at the inner circumference edge of the base portion  80 . 
     When viewed from the direction of the rotation axis X 1 , the inner wall portion  81  has an arc shape and has substantially the same protruding height h 5  over the entire length in the circumferential direction around the rotation axis X 1  (see  FIG. 5B ). 
     As shown in  FIG. 5B , the inner wall portion  81  has a first cylindrical portion  811  substantially parallel to the rotation axis X 1 , and a second cylindrical portion  812  inclined such that it approaches the rotation axis X 1  as the distance from the first cylindrical portion  811  increases. 
     Such that the inner wall portion  81  surrounds the outer periphery of the differential case  20  while keeping a predetermined distance, the inclinations with respect to the rotation axis X 1  are different between the first cylindrical portion  811  and the second cylindrical portion  812 . 
     As shown in  FIG. 5B , when viewed in the cross-sectional view of the cover portion  8 , the base portion  80 , the first cylindrical portion  811 , and the second cylindrical portion  812  are aligned in this order from the final gear  25  side in the direction of the rotation axis X 1 . 
     A belt shape seal member  88  is fit from the outside on the outer peripheral portion  80   a  of the base portion  80 . 
     The seal member  88  is member having a predetermined width W 3  formed of a material having a large linear expansion coefficient (for example, rubber), and has an arc shape when viewed from the direction of the rotation axis X 1  (see  FIG. 5A ). 
     The outer diameter R 2  of the seal member  88  is set slightly larger than the outer diameter R to the outer wall portion  62  of the body portion  5  (see  FIG. 4A ). 
     As shown in  FIG. 2A , when the cover portion  8  is assembled to the body portion  5 , the outer peripheral edge of the seal member  88  is pressed against the inner periphery of the outer wall portion  62 , and the gap CL 1  between the outer wall portion  62  of the body portion  5  and base portion of the cover portion  8  is sealed by the seal member  88 . In this state, the accommodating chamber Sa for the final gear  25  (rotating member accommodating chamber) is formed outside the final gear  25 . 
     A plurality of ribs  89  are provided at intervals in the longitudinal direction on the outer periphery of the first cylindrical portion  811 . 
     The ribs  89  are formed of a material having a large linear expansion coefficient at low temperatures like the material constituting the cover portion  8  (inner wall portion  81 , base portion  80 ), 
     The ribs  89  may be formed of a material having a higher linear expansion at low temperatures than the material constituting the cover portion  8  (inner wall portion  81 , base portion  80 ). 
     As shown in  FIG. 5A , when viewed from the direction of the rotational axis, the shape of each of the ribs  89  is a semicircular shape having the radius rb and each of the ribs  89  protrudes outward from the outer periphery of the first cylindrical portion  811  while directing the apex P outward. 
     The ribs  89  are provided across the base portion  80  and the first cylindrical portion  811 , and the height h 6  of the ribs  89  in the direction of the rotation axis X 1  is lower than the height h 7  of the first cylindrical portion  811  in the direction of the rotation axis X 1  (h 7 &gt;h 6 ). The ribs  89  are provide on the first cylindrical portion  811  while keeping a distance from the second cylindrical portion  812 . 
     The ribs  89  have a larger contact area with the first cylindrical portion  811  than with the base portion  80 . 
     The ribs  89  are provided at a position away from the outer peripheral portion  80   a  (free end) of the base portion  80  and close to the inner wall portion  81  (upper side in  FIG. 5B ). 
     When the cover portion  8  is assembled to the body portion  5 , the distal end of the seal member  88  is elastically pressed against the inner periphery of the outer wall portion  62  of the body portion  5 , and the gap CL 1  between the outer wall portion  62  of the body portion  5  and the outer periphery of the base portion  80  of the cover portion  8  is sealed by the seal member  88 . 
     As shown in  FIG. 2A , in a state where the cover portion  8  is assembled to the body portion  5 , as for the lower region of the final gear  25 , one side face  25   a  and the other side face  25   b  in the direction of the rotation axis X are covered by the base portion  60  of the body portion  5  and the base portion  80  of the cover portion  8  respectively, and the outer periphery of the final gear  25  is covered by the outer wall portion  62 . 
     Therefore, the lower region of the final gear  25  is disposed in a state in which the lower region of the final gear  25  is surrounded by the baffle plate  4  (baffle plate portion) disposed close to the final gear  25 . 
     As shown in  FIG. 5A , in the present embodiment, one longitudinal end  88   a  of the seal member  88  is located in the vicinity of one end  801  (line segment Lb) of the base portion  80 , and the other end  88   b  extends to the line segment La. 
     The other end  88   b  of the seal member  88  located at the side toward which the oil OL scraped by the final gear  25  moves (left side in  FIG. 5A ) is positioned higher than the one end  88   a  of the seal member  88 . 
       FIGS. 6A and 6B  is a view for explaining the cover portion  9  of the baffle plate  4 .  FIG. 6A  is a view of the cover portion  9  seen from the direction of the rotation axis X 3 .  FIG. 6B  is the A-A cross-sectional view in  FIG. 6A . 
     In  FIG. 6B , a part of the outer wall portion  72  of the body portion  5  and a part of the driven sprocket DS and a part of the drive shaft SH are shown in a virtual line. 
     As shown in  FIGS. 6A and 6B , the cover portion  9  has a plate shape base portion  90 . The base portion  90  is formed in a shape capable of overlapping with the base portion  70  of the second cover portion  7  when viewed in the direction of the rotation axis X 3  (see  FIG. 3 ). 
     When viewed from the direction of the rotation axis X 1 , the base portion  90  has a first side edge  901  having a shape along the outer periphery of the outer wall portion  62  of the first cover portion  6  and a second side edge  902  having a shape along the inner periphery of the outer wall portion  72  of the second cover portion  7 . 
     One end portions in the longitudinal direction of the first side edge  901  and the second side edge  902  are connected with each other. At the other end portion of the second side edge  902 , a mounting portion  91  having a bolt hole  91   a  is provided. 
     A third side edge  903  connected to the other end portion of the first side edge  901  is connected to the mounting portion  91  by passing the outside of the rotation axis X 3  of the driven sprocket DS and the opposite side of the second side edge  902  with respect to the rotation axis X 3 . 
     At the base portion  90 , the bolt hole  90   c  is provided in the vicinity of the connecting portion between the first side edge  901  and the second side edge  902 . 
     The bolt hole  91   a  and the bolt hole  90   c  of the cover portion  9  are provided at positions corresponding to the bolt holes  73   a ,  74   a  (see  FIG. 4A ) of the second cover portion  7  described above, respectively. 
     When the base portion  90  is placed on the mounting portions  73 ,  74  of the second cover portion  7 , the second side edge  902  is held while keeping the gap CL 2  from the outer wall portion  72  of the second cover portion  7 . 
     With the mounting portion  74  and the mounting portion  73 , the cover portion  9  is held substantially parallel to the base portion  70  of the second cover portion  7  and fixed to the second cover portion  7  by bolts B (see  FIG. 3 ). 
     A belt shape seal member  98  is fit to the outer periphery of the second side edge  902  from the outside. 
     The seal member  98  is a member formed of an elastic material having a large liner expansion coefficient (for example, rubber) and having a predetermined width W 4 . The seal member  98  is formed in a curved shape corresponding to the shape of the second side edge  902 . 
     As shown in  FIG. 2B , when the cover portion  9  is assembled to the second cover portion  7  of the body portion  5 , the outer peripheral edge of the seal member  98  is pressed against the inner periphery of the outer wall portion  72  of the second cover portion  7 , and the gap CL 2  between the outer wall portion  72  of the body portion  5  and the base portion  90  of the cover portion  9  is sealed by the seal member  98 . 
     In this state, an accommodating chamber Sb for the driven sprocket DS (rotating member accommodating chamber) is formed outside of the driven sprocket DS. 
     As shown in  FIG. 2B , in a state where the cover portion  9  is assembled to the second cover portion  7 , as for the lower region of the driven sprocket DS, one side surface DSa and the other side surface DSb in the direction of the rotation axis X 3  are covered by the base portion  70  of the second cover portion  7  and the base portion  90  of the cover portion  9 , respectively, and the outer periphery of the driven sprocket DS is covered by the outer wall portion  72  of the second cover portion  7 . 
     The lower region of the driven sprocket DS is disposed in a state where the lower region of the driven sprocket DS is surrounded by the second cover portion  7  of the baffle plate  4  and the cover portion  9 . 
     As described above, the body portion  5  of the baffle plate  4 , the oil hole  65  (see  FIG. 3 ) is provided at the outer wall portion  62  surrounding the outer periphery of the final gear  25  while keeping the predetermined distance. 
     At the outer wall portion  62 , the oil hole  65  is provided in the vertical line direction in the installation state of the automatic transmission  1  and at a position below the oil level OL_level of the oil OL. 
     In the present embodiment, the negative pressure generated when the final gear  25  rotates causes the oil between the outer periphery of the outer wall portion  62  and the inner periphery of the peripheral wall portion  11  of the transmission case  10  to flow to the final gear  25  through the oil hole  65 . 
     That is, the oil OL outside the outer wall portion  62  can flow into the inside of the outer wall portion  62 . 
     Here, when the amount of oil OL flowing into the inside of the outer wall portion  62  increases, the oil OL flowed into becomes friction against the rotation of the final gear  25 . 
     Further, if the amount of oil OL flowing into the inside of the outer wall portion  62  becomes too small, not only the lubrication of the final gear  25  but also the lubrication around the reduction gear  35  becomes insufficient. This is because the amount of oil scraped up by the final gear  25  and supplied to the reduction gear  35  is reduced. 
     The baffle plate  4  is provided for the following purposes. 
     (a) to guide the oil OL scraped up by the final gear  25  to the reduction gear  35  (other gear). 
     (b) to reduce the resistance (stirring resistance) when the final gear  25  rotates. 
     Therefore, the opening diameter of the oil hole  65  is set to the minimum diameter that can achieve the above purposes (a), (b) through experimental results and simulations. 
     In the automatic transmission, when the oil pump OP is driven, the oil in the oil pan  16  is sucked into the oil pump OP through the oil strainer  17  (see  FIG. 1A ) attached to a control valve body (not shown). 
     Then, the oil OL, the pressure of which is regulated by the oil pump OP, is used for the operation of the transmission mechanism portion and the lubrication of rotating elements, and then returns to the oil pan  16  by its own weight. 
     In the oil pan  16  fixed to the lower portion of the transmission case  10 , the oil of a amount necessary for the operation of the transmission mechanism portion and the lubrication of the rotation elements is stored. 
     Here, immediately after the start of the engine in a low temperature environment such as winter, since the temperature of the oil in the automatic transmission  1  is low, the fluidity of the oil OL becomes low. 
     In such a case, since the return of the oil OL to the oil pan  16  delays, if the oil OL in the oil pan  16  is insufficient, air may be sucked in from the suction port of the oil strainer  17 . 
     In this case, the oil containing air is used for the operation of the transmission mechanism portion, and a shock or the like may occur. 
     In the present embodiment, in order to improve the return of the oil in the baffle plate  4  to the oil pan  16  when the temperature of the oil OL is low, the belt shape rib  69  and the ribs  79  are provided on the baffle plate  4 , and the ribs  89  are provided on the cover portion  8 . 
     These belt shape rib  69  and the ribs  79 ,  89  are formed of the material having a large linear expansion coefficient at low temperatures like the material constituting the components of the baffle plate  4 . 
     Therefore, in the present embodiment, the belt shape rib  69  and the ribs  79 ,  89  shrink greater than other portions at low temperatures, and thus the other portions adjacent to the belt shape rib  69  and the ribs  79 ,  89  are deformed greatly. 
     Hereinafter, a concrete description will be given. 
       FIGS. 7A and 7B  are diagrams illustrating an operation of the baffle plate  4  and illustrating an operation of the belt shape rib  69  and ribs  79 ,  89 . 
       FIG. 7A  is a view for explaining deformation of the outer wall portion  62  and the base portion  80  caused by the belt shape rib  69  and the rib  89 .  FIG. 7B  is a diagram for explaining the deformation of the outer wall portion  72  caused by the ribs  79 . 
     As shown in  FIG. 7A , at low temperatures, the ribs  89  on the cover portion  8  shrink greatly than other regions (base portion  80 , inner wall portion  81 ) adjacent to the ribs  89 . 
     Here, among the regions adjacent to the ribs  89  (base portion  80 , inner wall portion  81 ), since the inner wall portion  81  is formed in a bent shape at the boundary portion between the first cylindrical portion  811  and the second cylindrical portion  812 , the inner wall portion  81  is harder to bend than the base portion  80 . 
     On the other hand, the rigidity and strength of the base portion  80  is increased at the inner wall portion  81  side (inner side in the radial direction: the rotation axis X 1  side) and the outer side in the radial direction (outer peripheral portion  80   a : free end) can displace in the direction of the rotation axis X 1 . 
     Therefore, as the ribs  89  shrink, the base portion  80  is pulled toward the ribs  89  side, and the outer peripheral portion  80   a  side of the base portion  80  is curved in a direction away from the final gear  25 . 
     At low temperatures, the belt shape rib  69  of the first cover portion  6  shrinks greatly than other regions (base portion  60 , outer wall portion  62 ) adjacent to the belt shape rib  69  (see arrows in the drawing). 
     Here, among the regions adjacent to the belt shape rib  69  (base portion  60 , outer wall portion  62 ), the base portion  60  is harder to bend than the outer wall portion  62 , since a step formed by the concave groove  67  is provided at the base portion  60  and this portion also functions as a reinforce rib. 
     On the other hand, in the outer wall portion  62 , the strength of the base portion  60  side is higher than that of the end portion  62   c  on the cover portion  8  side, and the end portion  62   c  (free end) of the outer wall portion  62  is displaceable in the radial direction of the rotation axis X 1 . 
     Therefore, in the baffle plate  4 , when the belt shape rib  69  and the ribs  89  shrink at low temperatures, the end portion  62   c  side of the outer wall portion  62  and the outer peripheral portion  80   a  side of the base portion  80  are displaced in the direction away from each other, and the seal member  88  provided on the outer peripheral portion  80   a  is displaced in the direction away from the outer wall portion  62  (see  FIG. 7A ). 
     As a result, 
     (I) sealing of the gap between the inner periphery of the outer wall portion  62  of the body portion  5  and the base portion  80  of the cover portion  8  by the seal member  88  is cancelled when the temperature of the oil OL is low, and an aperture CL′ is formed. 
     Then, since the outer wall portion  62  is positioned on the lower side in the vertical line direction in the installation state of the automatic transmission, low fluidity oil OL accumulated inside the outer wall portion  62  is discharged downward toward the oil pan  16 . 
     Here, in the present embodiment, the belt shape rib  69  is provided so as to extend from the outer wall portion  62  to the base portion  60 . Therefore, when the belt shape rib  69  shrinks, the belt shape rib  69  is pulled toward the base portion  60  side having high rigidity (left side in  FIG. 7A ). Therefore, by increasing the amount of displacement of the end portion  62   c  side of the outer wall portion  62 , the aperture CL′ from the outer peripheral portion  80   a  of the base portion  80  of the cover portion  8  can be widened. 
     Furthermore, at the deformation promoting portion  691  of the belt shape rib  69 , a plurality of concave portions  693  (slits) are provided at intervals in the circumferential direction around the rotation axis X 1 . 
     Therefore, the amount of deformation in the circumferential direction around the rotation axis X 1  becomes smaller in the region where the concave portions  693  are provided than in the region where the deformation promoting portion  691  are provided. 
     Therefore, when viewed from the direction of the rotation axis X 1 , it is possible to deform the end portion  62   c  side of the outer wall portion  62  having an arc shape in an undulating shape. 
     As a result, the aperture CL′ from the outer peripheral portion  80   a  of the base portion  80  of the cover portion  8  can be partially widened, so the oil OL having low fluidity accumulated inside the outer wall portion  62  can be appropriately discharged downward toward the oil pan  16 . 
     Furthermore, as shown in  FIG. 7B , at the outer wall portion  72  of the second cover portion  7 , the ribs  79  are provided on the outer periphery of the base portion  70 . 
     Therefore, in the outer wall portion  72 , the strength of the base portion  70  side is higher than that of the end portion  72   c  on the cover portion  9  side, and thus among the regions adjacent to the ribs  79  (base portion  70 , the outer wall portion  72 ), the outer wall portion  72  is easily displaced. 
     Therefore, in the baffle plate  4 , when the ribs  79  shrink at low temperatures, the end portion  72   c  (free end) side of the outer wall portion  72  is displaced in the radial direction of the rotation axis X 3  and in the direction away from the base portion  90 , and the seal member  98  provided on the outer peripheral portion  90   a  of the base portion  90  separates from the outer wall portion  72  (see  FIG. 7B ). 
     As a result, 
     (II) sealing of the gap between the inner periphery of the outer wall portion  72  of the body portion  5  and the base portion  90  of the cover portion  9  is cancelled when the temperature of the oil OL is low, and the aperture CL′ is formed. 
     Then, since the outer wall portion  72  is positioned on the lower side in the vertical direction in the installation state of the automatic transmission, low fluidity oil OL accumulated inside the outer wall portion  72  is discharged downward toward the oil pan  16 . 
     As described above, in the present embodiment, in order to improve the return of the oil in the baffle plate  4  to the oil pan  16  when the temperature of the oil OL is low, the belt shape rib  69  and the ribs  79  are provided on the body portion  5  and the ribs  89  are provided on the cover portion  8 . 
     These belt shape rib  69  and ribs  79 ,  89  are formed of a material having a large linear expansion coefficient at low temperatures (material that shrinks at low temperatures), and the portions of the belt shape rib  69  and the ribs  79 ,  89  shrink larger than the other portions at low temperatures. 
     Thus, the sealing of the gap CL 1  (gap between the outer wall portion  62  and the base portion  80 ) by the seal member  88  and the sealing of the gap CL 2  (gap between the outer wall portion  72  and the base portion  90 ) by the seal member  98  are cancelled, and the aperture CL′ through which the oil OL can be discharged is formed. 
     There are materials that expand at low temperatures and materials that shrink at low temperatures. 
     First, by selecting the latter material, the displacement of the components of the baffle plate portion (outer wall portions  62 ,  72  of the body portion  5 , base portion  80  of the cover portion  8 ) is urged at low oil temperatures, and thus the sealing by the seal members  88 ,  98  is cancelled. 
     Here, the sealing by the seal members may not be cancelled by simply replacing the components (belt shape rib  69 , ribs  78 ,  89 ) of the baffle plate  4  (baffle plate portion) with the material that shrinks at a low temperature. 
     This is because, for example, if the shrinkage amount at low temperatures so small that the seal members  88 ,  98  cannot be displaced by the shrinkage away from the outer wall portions  62 ,  72  of the baffle plate  4 , the sealing cannot be cancelled. 
     Therefore, in the present embodiment, considering the shrinkage amount, the dimensions of the seal members  88 ,  98  (widths W 3 , W 4 ) and/or the dimensions of the respective portions of the baffle plate  4  are set. 
     For example, in consideration of the shrinkage amount when the temperature decreases from the reference temperature to a predetermined temperature, the following dimensions are set so that the seal members  88 ,  98  separate from the outer wall portions  62 ,  72  of the baffle plate  4  when shrinkage of such a shrinkage amount occurs. 
     The dimensions of the seal members  88 ,  98  (widths W 3 , W 4 ) and/or the dimensions of the baffle plate  4  (the heights h 1 , h 3  of the outer wall portions  62 ,  72 , the width W 1  of the base portion  80  of the cover portion  8 , the gap CL 1  (see  FIG. 5B ) between the outer peripheral portion  80   a  of the base portion  80  of the cover portion  8  and the outer wall portion  62 , the gap CL 2  (see  FIG. 6B ) between the outer peripheral portion  90   a  of the base portion  90  of the cover portion  9  and the outer wall portion  72 ). 
     Here, as the reference temperature, an arbitrary temperature higher than a predetermined temperature may be set. For example, the reference temperature may be set to a normal temperature (25° C.), or may be set to an arbitrary temperature in a normal use temperature region (several ten degrees Celsius to one hundred and several ten degrees Celsius). 
     That is, for example, the smaller the pressing force of the seal members  88 ,  98  against the baffle plate (outer wall portions  62 ,  72 ) at the reference temperature, the smaller the shrinkage amount required when the temperature decreases below the predetermined temperature from the reference temperature. 
     Since the pressing forces of the seal members  88 ,  98  against the baffle plate  4  (outer wall portions  62 ,  72 ) depend on the dimensions of the seal members  88 ,  98  and/or the dimensions of the baffle plate  4 , these dimensions may be set such that the pressing force against the baffle plate  4  becomes small at the normal temperature. 
     By setting dimensions in this way, the aperture is formed at low temperatures, and the return of the oil from the inside of the baffle plate  4  (baffle plate portion) to the oil pan  16  can be promoted. 
     The dimensions can be appropriately set by a person skilled in the art by conducting experiments and/or calculations beforehand in accordance with the characteristics of the materials used, such as a linear expansion coefficient. 
     For example, the dimensions may be predetermined in various manners as follows.
         Measure changes in the dimensions by changing the temperature of the baffle plate  4  (baffle plate portion).   Measure changes in the dimensions by making a sample using the material used for the baffle plate  4  (baffle plate portion) and changing the temperature of the sample.   Calculate the theoretical shrinkage amount from the linear expansion coefficient of the material used for the baffle plate  4  (baffle plate portion) and the design dimensions of the baffle plate portion.       

     Further, in this embodiment, as the material constituting the belt shape rib  69  and the ribs  79 ,  89 , a polymer material is employed as an example. 
     Since the linear expansion coefficient of the material is not limited, any material such as a metal (including a pure metal and an alloy), a ceramic, polymer (in particular, an organic polymer (a polymer composed of an organic compound), or the like may be used. 
     However, when using a material having a small linear expansion coefficient (such as a metal), the pressing force of the seal members  88 ,  98  against the baffle plate need to be set extremely small at the reference temperature, and thus the sealing by the seal members  88 ,  98  will be lowered. 
     The linear expansion coefficient is preferably in the following range. 
     For metals, linear expansion coefficients between 5-25×10 −6 K −1 . For ceramics, linear expansion coefficients between 0.5-15×10 −6 K −1 . For polymers, linear expansion coefficients between 50-300×10 −6 K −1 . 
     As described above, the present embodiment exemplifies the case where all of the constituent elements of the baffle plate portion (baffle plate  4 ), that is, the body portion  5 , the cover portions  8 ,  9 , and the seal members  88 ,  98  are all formed of a material such as a polymer having a large linear expansion coefficient at low temperatures. 
     The present invention is not limited only to this embodiment. At least one of the body portion  5 , the cover portions  8 ,  9  and the seal members  88 ,  98  may be formed of a material such as a polymer having a large linear expansion coefficient at low temperatures. In this case, a combination of constituent elements formed of a material such as a polymer can be appropriately selected. 
     In addition, when the body portion  5  and the cover portions  8 ,  9  are formed of a material such as a polymer, all of the body portion  5  and the cover portions  8 ,  9  need not be formed of a material such as a polymer, and only a partial region of them may be formed of a material such as a polymer. 
     Similarly, when the seal members  88 ,  98  are formed of a material such as a polymer, all of the seal members  88 ,  98  need not be formed of a material such as a polymer, and only a partial region of them may be formed of a material such as a polymer. 
     As described above, the present embodiment has the following configuration. 
     (1) The driving force transmission (automatic transmission  1 ) includes: 
     the baffle plate portion (baffle plate  4 ) including the pair of baffle plates (body portions  5 , cover portions  8 ,  9 ) and the seal members  88 ,  98  disposed within the space between the pair of baffle plates; 
     the rotating member (final gear  25 , driven sprocket DS) disposed within the rotating member chamber (accommodating chambers Sa, Sb) that is the space surrounded by the baffle plate portion; 
     the oil pump OP that serves as the source of oil for lubrication (oil OL) supplied to the rotating member (final gear  25 , driven sprocket DS), and 
     the oil pan  16  in which oil (oil OL) is stored and from which the oil pump OP sucks the oil. 
     At least one of, one of the pair of baffle plates (body portion  5  and cover portions  8 ,  9 ), the other one of the pair of baffle plates (body portion  5  and cover portions  8 ,  9 ), and the seal members  88 ,  98  is formed by including a material that shrink as the oil temperature (temperature of the oil OL) decreases (a material having a large linear expansion coefficient at a low temperature). 
     The baffle plate portion (body portion  5 , the cover portions  8 ,  9 ) is dimensioned such that the region (gaps CL 1 , CL 2 ) between the pair of baffle plates (body portion  5 , the cover portions  8 ,  9 ) is sealed by the seal members  88 ,  98  when the oil temperature is equal to or higher than the predetermined oil temperature and the aperture CL′ is formed in the region between the pair of baffle plates (body portion  5 , the cover portions  8 ,  9 ) when the oil temperature is less than the predetermined oil temperature. 
     The gap CL 1  is the gap between the inner periphery of the outer wall portion  62  of the body portion  5  and the outer peripheral portion  80   a  of the base portion  80  of the cover portion  8 . 
     The gap CL 2  is the gap between the inner periphery of the outer wall portion  72  of the body portion  5  and the outer peripheral portion  90   a  of the base portion  90  of the cover portion  9 . 
     By configuring in this way, the sealing of the gaps CL 1 , CL 2  between the inner peripheries of the outer wall portions  62 ,  72  of the body portion  5  and the outer peripheral portions  80   a ,  90   a  of the base portions  80 ,  90  of the cover portions  8 ,  9  by the seal members  88 ,  98  are cancelled when the temperature of the oil OL is low and the apertures CL′, CL′ are formed. 
     Then, since the outer wall portions  62 ,  72  are positioned on the lower side in the vertical line direction in the installation state of the automatic transmission  1 , the oil OL having low fluidity accumulated inside the outer wall portions  62 ,  72  is discharged downward toward the oil pan  16 . 
     Thus, the aperture CL′ is formed at low temperatures, and it is possible to promote the oil return (return of the oil OL) from the inside of the baffle plate portion (body portion  5  and the cover portions  8 ,  9 ) to the oil pan  16 . 
     Further, by providing the seal members  88 ,  98 , the aperture CL′ is made to “0 (zero)” by the seal members  88 ,  98  until the temperature becomes less than the predetermined temperature, and therefore, the effect of suppressing the oil entering when the oil temperature becomes high can be enhanced. 
     The present embodiment has the following configuration. 
     (2) The material is a polymer material, and the polymer material is a resin material or a rubber material. 
     By using a polymer which is a material having a large linear expansion coefficient, the shrinkage amount can be increased. It is possible to increase the pressing force of the seal members  88 ,  98  against the baffle plate (outer wall portions  62 ,  72 ) at the reference temperature, and it is possible to improve the sealing by the seal members  88 ,  98 . 
     The present embodiment has the following configuration. 
     (3) The baffle plate portion (body portion  5 , cover portion  8 ) has the ribs (belt shape rib  69 , ribs  79 ,  89 ) formed of a polymer material. 
     When the ribs (belt shape rib  69 , ribs  79 ,  89 ) formed of a polymer material are formed at the baffle plate portion (body portion  5 , cover portion  8 ) or the polymer material forming the seal members, since the shrinkage amount and the expansion amount due to temperature change becomes large as the thickness of the polymer material increases, the aperture CL′ formed at low temperatures can be widened. 
     Therefore, the shrinkage amount and the expansion amount due to temperature change can be increased by locally forming thick portions by forming the ribs (belt shape rib  69 , ribs  79 ,  89 ). 
     Thus, even if the pressing force of the seal members  88 ,  98  against the outer wall portions  62 ,  72  at the reference temperature is increased, the seal members  88 ,  98  can displace away from the outer wall portions  62 ,  72  to form the aperture CL′. Therefore, the sealing of the accommodating chambers Sa, Sb can be improved at the baffle plate  4 . 
     Here, it is conceivable to thicken the entire baffle plate  4 , but instead, by forming ribs formed locally, the effect of weight reduction and cost reduction can be obtained. 
     Further, for example, since the baffle plate portion (body portion  5 , cover portions  8 ,  9 ) or the seal members  88 ,  98  formed of a polymer material are formed by cooling the melted raw material, the surface area of the thick portions can be increased, and the cooling efficiency can be relatively increased. 
     If the cooling efficiency is poor, distortion may occur and cracks may be developed. By increasing the cooling efficiency, occurrence of such a problem may be suitably prevented. 
     The present embodiment has the following configuration. 
     (4) The automatic transmission  1  (driving force transmission device) includes: 
     the baffle plate portion (baffle plate  4 ) including the pair of baffle plates (body portion  5 , cover portions  8 ,  9 ); 
     the rotating member (final gear  25 , driven sprocket DS) disposed within the rotating member chamber (accommodating chambers Sa, Sb) which is the space surrounded by the baffle plate portion (baffle plate  4 ); 
     the oil pump OP that serves as the source of the oil for lubrication (oil OL) supplied to the rotating member (final gear  25 , driven sprocket DS); and 
     the oil pan  16  in which the oil (oil OL) is stored and from which the oil pump OP sucks the oil. 
     At least one of the pair of baffle plates (body portion  5 , cover portions  8 ,  9 ) is formed by including a polymer material. 
     The baffle plate portion (baffle plate  4 ) has ribs (belt shape rib  69  and ribs  79 ,  89 ) formed of a polymer material. 
     As the thickness of the polymer material increases, the shrinkage amount and the expansion amount due to temperature change increase. Therefore, the shrinkage amount and the expansion amount due to temperature change can be increased by locally forming thick portions by forming the ribs (belt shape rib  69 , rib  79 ). 
     Therefore, in the case of the baffle plate without the seal member, since the change in the aperture due to temperature change can be increased, the aperture at the reference temperature can be made smaller and the effect of reducing the stirring resistance can be improved. 
     On the other hand, in the case of the baffle plate with the seal member, the change in the aperture due to temperature change can be increased. Thus, the pressing force of the seal member can be increased at the reference temperature, sealing can be improved, and the effect of reducing the stirring resistance can be improved. 
     The present embodiment has the following configuration. 
     (5) A plurality of ribs  79  and  89  are provided. 
     If ribs of the same volume are formed, since the surface area of a plurality of ribs can be made larger than that of a single rib, the cooling efficiency can be improved. 
     The present embodiment has the following configuration. 
     (6) The slits (concave portions  693 ) are formed at the rib  69 . 
     Since the surface area can be increased by providing the slits (concave portions  693 ), the cooling efficiency at the portion of the belt shape rib  69  can be enhanced. The surface area may be increased by providing slits at other ribs  79 , 879 . 
     The present embodiment has the following configuration. 
     (7) The ribs (belt shape rib  69 , ribs  89 ) are arranged at a position away from the gap CL 1  causing the aperture CL′. 
     The ribs  79  are arranged at a position away from the aperture (gap CL 2 ). 
     The belt shape rib  69  is arranged at a position away from the gap CL 1  in the direction of the rotation axis X 1 . 
     The ribs  89  are arranged at positions away from the gap CL 1  in the radial direction of the rotation axis X 1 . 
     The gap CL 1  is the gap between the outer wall portion  62  on which the belt shape rib  69  is provided and the base portion  80  of the cover portion  8  on which the ribs  89  are provided. 
     The gap CL 1  is the gap in the radial direction of the rotation axis X 1  between the end portion  62   c  of the outer wall portion  62  and the outer peripheral portion  80   a  of the base portion  80 . 
     The gap CL 2  is the gap between the outer wall portion  72  on which the ribs  79  are provided and the base portion  90  of the cover portion  9 . 
     The gap CL 2  is the gap in the radial direction of the rotation axis X 1  between the end portion  72   c  of the outer wall portion  72  and the outer peripheral portion  90   a  of the base portion  90 . 
     By placing the ribs (belt shape rib  69 , ribs  79 ,  89 ) at positions away from the gap CL 1  that causes the aperture CL′, the change in the aperture CL′ due to shrinkage and expansion can be increased. 
     That is, if the shrinkage amount and the expansion amount are constant, the change amount of the aperture CL′ due to the shrinkage and the expansion increases as the distances from the gaps CL 1 , CL 2  increases, and the change amount of the aperture CL′ increases as the shrinkage amount and the expansion amount increase. 
     Therefore, as the distances of the ribs (belt shape rib  69 , ribs  79 ,  89 ), the shrinkage amount and expansion amount of which is large, from the gaps CL 1 , CL 2  which cause the aperture CL′ increase, the change amount of the caused aperture CL′ increases. 
     The present embodiment has the following configuration. 
     (8) At least one of the pair of baffle plates has the plate portion (cover portion  8 ) which adjoins the gap CL 1  that causes the aperture. 
     when the plate portion (cover portion  8 ) is partitioned into two regions (base portion  80 , inner wall portion  81 ) in the axial direction (rotation axis X 1 ) of the rotating member (final gear  25 ), 
     the ribs  79  are arranged such that the area where the ribs  89  overlap with one of the two regions (inner wall portion  81 ) not adjacent to the aperture (gap CL 1 ) is larger than the area where the ribs  89  overlap with the other one of the two regions (base portion  80 ) adjacent to the aperture (gap CL 1 ). 
     The region (inner wall portion  81 ) not adjacent to the aperture extends in the direction of the rotation axis X 1  from a position away from the aperture (gap CL 1 ) in the region (base portion  80 ) adjacent to the aperture (gap CL 1 ). 
     By placing the ribs  89  in the region away from the aperture (gap CL 1 ), the ribs  89  can be positioned away from the gap CL 1  that causes the aperture and the change amount in the aperture can be increased. 
     The present embodiment has the following configuration. 
     (9) The body portion  5 , which is at least one of the pair of baffle plates, has the first plate portion (base portion  60 ) adjacent to the gap CL 1  causing the aperture, and the second plate portion (outer wall portion  62 ) which is adjacent to the first plate portion and projecting in the axial direction (direction of the rotation axis X 1 ) of the rotating member (final gear  25 ). 
     The rib (belt shape rib  69 ) is provided on the second plate portion (outer wall portion  62 ). 
     Since the rib  69  (belt shape rib  69 ) can be provided at a position away from the gap CL 1  which causes the aperture, the change amount of the aperture can be increased. 
     (10) The rib (belt shape rib  69 ) is disposed in contact with the boundary between the first plate portion (base portion  60 ) and the second plate portion (outer wall portion  62 ). 
     The rib (belt shape rib  69 ) is provided across the first plate portion (base  60 ) and the second plate portion (outer wall portion  62 ), and is disposed in contact with the first plate portion (base portion  60 ) and the second plate portion (outer wall portion  62 ). 
     Since the ribs  69  can be provided at a position away from the gap CL 1  which causes the aperture, the change amount of the aperture can be increased. 
     In addition, since the force can be directly applied to the first plate portion (base portion  60 ), the change amount of the aperture can be increased. 
     The present embodiment has the following configuration. 
     (11) The ribs (belt shape rib  69 , ribs  89 ) are provided on both of the pair of baffle plates (body portion  5 , cover portion  8 ). 
     Since the shrinkage force of the ribs (belt shape rib  69  and ribs  89 ) can be applied to both the body portion  5  and the cover portion  8 , the force for opening the aperture (gap CL 1 ) can be applied to both the outer wall portion  62  of the body portion  5  and the base portion  80  of the cover portion  8 . Therefore, the change amount of the aperture can be increased. 
     The present embodiment has the following configuration. 
     (12) The ribs (belt shape rib  69 , ribs  89 ) is disposed outside the rotating member chamber (accommodating chamber Sa) for the rotating member (final gear  25 ). 
     If the ribs (belt shape rib  69 , ribs  89 ) are disposed inside the rotating member chamber (accommodating chamber Sa), there is a possibility that the ribs interfere with the rotating member (final gear  25 ) and the limitation on the layout of the rotating member (final gear  25 ) may increase. Therefore, the ribs are disposed outside the rotating member chamber. 
     The present embodiment has the following configuration. 
     (13) The rotating member is the gear (final gear  25 ) or the chain sprocket (driven sprocket DS). 
     The final gear  25  and the driven sprocket DS are arranged at the lower part in the transmission case, and the baffle plate (body part  5 , cover part  8 ) is provided in a range across the final gear  25  and the driven sprocket DS. 
     Therefore, by providing the ribs so that the sealing of the gap CL 1  by the seal member is cancelled, the oil OL stored in the baffle plate at extremely low temperature can be returned to the oil pan  16  provided at the lower portion of the transmission case  10 . 
     Since the sealing by the seal member  88  can be cancelled at extremely low temperature only, it improves the fuel consumption. 
     In the embodiment described above, the case where the driving force transmission device is an automatic transmission for a vehicle has been exemplified. The driving force transmission device of the present invention is not limited to only an automatic transmission for a vehicle. 
     The present invention is also applicable to a gear train composed of a plurality of gears, wherein at least one gear is configured to scrape up oil in a housing case of the gear train. As such a device, a deceleration device for decelerating and outputting the input rotation is exemplified. 
     While the embodiments of the present invention have been described above, the present invention is not limited to aspects shown in these embodiments. Changes and modifications can be made appropriately within the scope of the technical ideas of the present invention. 
     The present application claims a priority of Japanese Patent Application No. 2018-095159 filed with the Japan Patent Office on May 17, 2018, all the contents of which are hereby incorporated by reference.