Patent Publication Number: US-2012032405-A1

Title: Sealing structure for continuously variable transmission

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2010-177178 filed on Aug. 6, 2010 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a sealing structure for a continuously variable transmission that seals a clearance between a movable sheave and a cylinder of the continuously variable transmission including: two pulleys connected to an input shaft and an output shaft, respectively, with the pulleys each including the movable sheave and a fixed sheave that are disposed facing each other; a belt that bridges the pulleys; and the cylinder that forms a hydraulic pressure chamber on a rear side of the movable sheave, wherein the continuously variable transmission is capable of changing a groove width of each of the pulleys by moving the corresponding movable sheave though supply and discharge of a hydraulic pressure to and from the cylinder. 
     DESCRIPTION OF THE RELATED ART 
     As a sealing structure for a continuously variable transmission of this type, related art proposes a belt-type continuously variable transmission in which a clearance between a movable sheave of a primary pulley and a housing portion is provided with a seal member structured to tightly seal the clearance (for example, see Japanese Patent Application Publication No. JP-A-2009-275718). In this continuously variable transmission, the housing portion is disposed on a rear side of the movable sheave to serve as a cylinder, and a clearance between the movable sheave and the housing portion is sealed. This forms a hydraulic pressure chamber for pressing the movable sheave from the rear side by a hydraulic pressure. 
     SUMMARY OF THE INVENTION 
     In a belt-type continuously variable transmission, a belt is sandwiched in a pulley in a semi-circular range. Therefore, a bending force in accordance with the product of a force that opens the pulley by the belt and a radius of a portion at which the belt contacts the pulley is produced within a range of an angle that indicates the meshing of the belt. The bending force acts once every full rotation of the pulley, and deforms the movable sheave and the housing portion (cylinder) to periodically crush the seal member provided in the clearance between the movable sheave and the housing portion. This may cause wear of the seal member. As a countermeasure, in order to suppress deformation of the sheave and the housing portion, the rigidity of these components may be increased, but the size and weight of the transmission may increase as a consequence. 
     It is a main object of a sealing structure for a continuously variable transmission according to the present invention to improve sealing performance while suppressing wear of the seal member, without using an excessively rigid sheave and cylinder. 
     In order to achieve the foregoing main object, the sealing structure for a continuously variable transmission according to the present invention employs the following means. 
     A first aspect of the present invention provides a sealing structure for a continuously variable transmission that seals a clearance between a movable sheave and a cylinder of the continuously variable transmission including: two pulleys connected to an input shaft and an output shaft, respectively, with the pulleys each including the movable sheave and a fixed sheave that are disposed facing each other; a belt that bridges the pulleys; and the cylinder that forms a hydraulic pressure chamber on a rear side of the movable sheave, wherein the continuously variable transmission is capable of changing a groove width of each of the pulleys by moving the corresponding movable sheave though supply and discharge of a hydraulic pressure to and from the cylinder. The sealing structure includes: an outer peripheral side seal member that is ring-shaped and disposed in a ring-shaped groove formed in one of the movable sheave and the cylinder; and an inner peripheral side seal member that is more elastic than the outer peripheral side seal member, ring-shaped, and disposed in a layered manner in the ring-shaped groove on an inner peripheral side with respect to the outer peripheral side seal member. Further, a side of the outer peripheral side seal member where the outer peripheral side seal member contacts the inner peripheral side seal member is chamfered. 
     In the sealing structure for a continuously variable transmission according to the first aspect, the ring-shaped outer peripheral side seal member having a rectangular cross section and the ring-shaped inner peripheral side seal member that is more elastic than the outer peripheral side seal member are respectively disposed, in a layered manner, in the ring-shaped groove formed in one of the movable sheave and the cylinder that forms the hydraulic pressure chamber on the rear side of the movable sheave. In the sealing structure, the side of the outer peripheral side seal member where the outer peripheral side seal member contacts the inner peripheral side seal member is chamfered. This chamfering forms a space (relief space) between a side wall of the ring-shaped groove and the outer peripheral side seal member. Thus, even when the clearance between the sheave and the cylinder varies due to deformation of the sheave and the cylinder caused by meshing of the belt, and the inner peripheral side seal member is thus periodically deformed, the inner peripheral side seal member can move into the space, whereby the occurrence of drag wear of the inner peripheral side seal member can be suppressed. Consequently, sealing performance can be ensured without using an excessively rigid sheave and cylinder. Here, according to a second aspect of the present invention, the “outer peripheral side seal member” may be chamfered by plane chamfering. 
     In the thus configured sealing structure for a continuously variable transmission according to a third aspect of the present invention, the outer peripheral side seal member may be a rectangular cross-sectioned seal ring, and the inner peripheral side seal member may be a circular cross-sectioned O-ring. 
     Further, in the sealing structure for a continuously variable transmission according to a fourth aspect of the present invention, the movable sheave may be formed with a cylindrical portion that extends in an axial direction from an outer peripheral portion of the movable sheave, the cylinder may include an outer peripheral portion that extends in a radial direction to near an inner peripheral surface of the cylindrical portion of the movable sheave, and the seal member may be attached to a groove formed along an entire circumference of an outer peripheral edge of the cylinder. In this type of the continuously variable transmission, because deformation of the clearance between the movable sheave and the cylinder is relatively large, and thus an amplitude of the deformation of the seal member is also relatively large, the effect of the present invention is more pronounced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram that shows an overall configuration of a power transmission apparatus  20 ; 
         FIG. 2  is an explanatory diagram that shows a meshing angle of a belt  40  for a primary pulley  34 ; 
         FIG. 3  is an explanatory diagram that illustrates how the primary pulley  34  and a primary cylinder  38  deform in a CVT  30  according to an embodiment; 
         FIG. 4  is an explanatory diagram that illustrates how an O-ring  52  deforms when a seal ring  50  of the embodiment is used; 
         FIG. 5  is an explanatory diagram that illustrates how the O-ring  52  deforms when a seal ring  150  of a comparative example is used; 
         FIG. 6  is an explanatory diagram that illustrates how a primary pulley  134  and a primary cylinder  138  deform in a CVT of the comparative example; 
         FIG. 7  is an explanatory diagram that shows a relationship between a rotational angle of the primary pulley  34  and a margin for crushing the O-ring  52 ; 
         FIG. 8  is an explanatory diagram that illustrates a relationship between a speed ratio, engine torque, and an amplitude of the margin for crushing the O-ring  52  in the CVT  30  of the embodiment; 
         FIG. 9  is an explanatory diagram that illustrates the relationship between the speed ratio, the engine torque, and the amplitude of the margin for crushing the O-ring  52  in the CVT of the comparative example; 
         FIG. 10  is a cross-sectional view of a seal ring  50 B of a modification example; and 
         FIG. 11  is a cross-sectional view of a seal ring  50 C of another modification example. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Next, an embodiment of the present invention will be described. 
       FIG. 1  is a structural diagram that shows an overall configuration of a power transmission apparatus  20 . As shown in  FIG. 1 , the power transmission apparatus  20  is configured as a transaxle apparatus that transmits to axles  64   a ,  64   b  power from a transversely mounted engine (not shown) in which a crankshaft is disposed generally parallel to the axles  64   a ,  64   b . The power transmission apparatus  20  includes a torque converter  22  with a lock-up clutch, a forward/reverse travel switching unit  24 , and a continuously variable transmission (hereinafter abbreviated to “CVT”)  30 . The torque converter  22  includes a pump impeller  22   a  on an input side connected to the crankshaft of the engine, and a turbine runner  22   b  on an output side. The forward/reverse travel switching unit  24  is connected to the turbine runner  22   b  of the torque converter  22  and outputs power input from the turbine runner  22   b  with such power converted into a positive rotation or a negative rotation. The CVT  30  includes a primary shaft  32  connected to the forward/reverse travel switching unit  24 , and a secondary shaft  42  disposed parallel to the primary shaft  32 . The CVT  30  steplessly changes a speed of power input to the primary shaft  32  and outputs power at the changed speed to the secondary shaft  42 . 
     The CVT  30  includes a primary pulley  34 , a secondary pulley  44 , a belt  40 , a primary cylinder  38 , and a secondary cylinder  48 . The primary pulley  34  is attached to the primary shaft  32 , and the secondary pulley  44  is attached to the secondary shaft  42  disposed parallel to the primary shaft  32 . The belt  40  is disposed in respective grooves of the primary pulley  34  and the secondary pulley  44  so as to bridge the primary pulley  34  and the secondary pulley  44 . The primary cylinder  38  serves as a hydraulic actuator for changing a groove width in the primary pulley  34 , and the secondary cylinder  48  serves as a hydraulic actuator for changing a groove width in the secondary pulley  44 . The CVT  30  steplessly changes a speed of power input to the primary shaft  32  by changing the groove widths in the primary pulley  34  and the secondary pulley  44 , and then outputs power at the changed speed to the secondary shaft  42 . A hydraulic circuit, although not shown, supplies and discharges a hydraulic pressure to and from the primary cylinder  38  and to and from the secondary cylinder  48 . The hydraulic circuit includes: an oil pump; a regulator valve that regulates a hydraulic pressure from the oil pump; a control valve that controls connection and disconnection of an oil passage for supplying and discharging the hydraulic pressure to and from the primary cylinder  38  and to and from the secondary cylinder  48 , using the hydraulic pressure regulated by the regulator valve; and a solenoid valve that drives the control valve. The secondary shaft  42  is connected to the left and right axles  64   a ,  64   b  through a gear mechanism  60  and a differential gear  62 , and therefore power from the engine is transmitted to the axles  64   a ,  64   b , through the torque converter  22 , the forward/reverse travel switching unit  24 , the CVT  30 , the gear mechanism  60 , and the differential gear  62  in that order. 
     The primary pulley  34  is configured by a fixed sheave  35  that is formed integrally with the primary shaft  32 , and a movable sheave  36  that is slidably supported by the primary shaft  32  in an axial direction through a ball spline. The secondary pulley  44  is configured by a fixed sheave  45  that is formed integrally with the secondary shaft  42 , and a movable sheave  46  that is slidably supported by the secondary shaft  42  in the axial direction through a ball spline. It should be noted that the movable sheave  46  of the secondary pulley  44  is urged by a return spring  47  in a direction that reduces the groove width in the secondary pulley  44 . 
     The movable sheave  36  of the primary pulley  34  is integrated with a piston and also formed with a cylindrical portion  36   a  that extends in the axial direction from an outer peripheral portion of the movable sheave  36  toward the primary cylinder  38  side. Further, the primary cylinder  38  includes an outer peripheral portion that extends in a radial direction to the vicinity of an inner peripheral surface of the cylindrical portion  36   a  of the movable sheave  36 . A clearance between an outer peripheral edge of the primary cylinder  38  and the inner peripheral surface of the cylindrical portion  36   a  of the movable sheave  36  (piston) is sealed. This forms a hydraulic pressure chamber  39 . In addition, the movable sheave  46  of the secondary pulley  44  is integrated with a piston and also formed with a cylindrical portion that extends in the axial direction from an outer peripheral portion of the movable sheave  46  toward the secondary cylinder  48  side. Further, the secondary cylinder  48  includes an outer peripheral portion that extends in the radial direction to the vicinity of an inner peripheral surface of the cylindrical portion of the movable sheave  46 . A clearance between an outer peripheral edge of the secondary cylinder  48  and the inner peripheral surface of the cylindrical portion of the movable sheave  46  (piston) is sealed. This forms a hydraulic pressure chamber  49 . 
     A ring groove  38   a  is formed along the entire circumference of the outer peripheral edge of the primary cylinder  38 . A seal ring  50  and an O-ring  52  are attached on an outer peripheral side and an inner peripheral side of the ring groove  38   a , respectively, in a layered manner. The seal ring  50  is made of a resin material (for example, fluorine resin) and has a rectangular cross section, and the O-ring  52  is made of a rubber material with higher elasticity than that of the seal ring  50  (for example, fluorine rubber) and has a circular cross section. Among four corners of the seal ring  50 , two corners on a side where the seal ring  50  contacts the O-ring  52  are chamfered. In the embodiment, the two corners are chamfered by plane chamfering at a chamfering angle of generally 45 degrees. The reason for chamfering the seal ring  50  will be described later. 
       FIG. 2  is an explanatory diagram that shows how the belt  40  meshes in the primary pulley  34 . As shown in  FIG. 2 , because the belt  40  is sandwiched in the primary pulley  34  in a semi-circular range, a bending force in accordance with the product of a force that opens the pulleys toward one side by the belt  40  and a radius of a portion at which the belt  40  contacts the primary pulley  34  acts on the primary pulley  34  within a range of a meshing angle θ that indicates the meshing of the belt  40 . This bending force acts once every full rotation of the primary pulley  34 . Therefore, the primary pulley  34  and the primary cylinder  38  periodically deform once every full rotation thereof.  FIG. 3  shows how the primary pulley  34  and the primary cylinder  38  deform in the CVT  30  according to the embodiment. It should be noted that dotted lines in  FIG. 3  indicate a state before deformation, and solid lines indicate the state after deformation. As illustrated, the primary pulley  34  (movable sheave  36 ) deforms in a direction that causes the cylindrical portion  36   a  to approach an axial center in a section where the belt  40  meshes, and deforms in a direction that causes the cylindrical portion  36   a  to separate from the axial center in a section where the belt  40  does not mesh. On the other hand, the primary cylinder  38  deforms in the axial direction opposite from the primary pulley  34  along the entire circumference. Such deformation of the primary pulley  34  and the primary cylinder  38  periodically changes a distance between a bottom surface of the ring groove  38   a  of the primary cylinder  38  and the inner peripheral surface (sliding surface) of the movable sheave  36  once every full rotation. Therefore, the O-ring  52  whose elasticity is higher than that of the seal ring  50  is crushed in the radial direction. In consideration of the hydraulic pressure generated in the hydraulic pressure chamber  39 , the O-ring  52  is crushed in the radial direction in the state where the O-ring  52  and the seal ring  50  are together pressed in the axial direction against a side wall of the ring groove  38   a  of the primary cylinder  38  due to the hydraulic pressure in the hydraulic pressure chamber  39 . 
       FIG. 4  shows how the O-ring  52  deforms when the seal ring  50  of the embodiment is used, and  FIG. 5  shows how the O-ring  52  deforms when a seal ring  150  of a comparative example is used. Here, in  FIG. 4 , the seal ring  50  of the embodiment in which, among four corners in the rectangular cross section, two corners on the side where the seal ring  50  contacts the O-ring  52  are chamfered is used. Further, in  FIG. 5 , the seal ring  150  that has no chamfering is used. In the embodiment, as shown in  FIG. 4 , the two corners of the seal ring  50  on the side where the seal ring  50  contacts the O-ring  52  are chamfered. Therefore, a V-shaped groove is formed between the side wall of the ring groove  38   a  and a side surface of the seal ring  50  (see portion A in  FIG. 4 ), and the O-ring  52  moves into the V-shaped groove when crushed. On the other hand, in the comparative example, the seal ring  150  is not chamfered. Accordingly, even when the O-ring  52  is crushed, there is no relief space into which the O-ring  52  can move (see portion B in  FIG. 5 ), and drag wear occurs due to periodic crushing of the O-ring  52  occurring once every full rotation. Among four corners of the seal ring  50  in the rectangular cross section, two corners on the side where the seal ring  50  contacts the O-ring  52  are chamfered in order to suppress the occurrence of drag wear of the O-ring  52  by providing a relief space into which the O-ring  52  can move when the O-ring  52  is periodically crushed as the primary pulley  34  and the primary cylinder  38  deform. 
       FIG. 6  is an explanatory diagram that illustrates how a primary pulley  134  and a primary cylinder  138  deform in a CVT of the comparative example. It should be noted that dotted lines in  FIG. 6  indicate a state before deformation, and solid lines indicate a state after deformation. In this comparative example, as illustrated, the primary cylinder  138  is formed with a cylindrical outer peripheral portion  138   a . A movable sheave  136  includes an outer peripheral portion that extends in the radial direction to the vicinity of an inner peripheral surface of the outer peripheral portion  138   a  of the primary cylinder  138 . A ring groove  136   a  is formed along the entire circumference of an outer peripheral edge of the movable sheave  136 , and the seal ring  50  and the O-ring  52  are attached to an outer peripheral side and an inner peripheral side of the ring groove  136   a , respectively, in a layered manner. This forms a hydraulic pressure chamber  139 . In the CVT of the comparative example thus configured, the primary pulley  134  (movable sheave  136 ) deforms in the axial direction toward the primary cylinder  138  side in a section where the belt  40  meshes in the primary cylinder  138 , and deforms in a direction that causes the outer peripheral portion to separate from the axial center in a section where the belt  40  does not mesh in the primary cylinder  138 . Further, the primary cylinder  138  deforms in the direction that causes the cylindrical portion  138   a  to separate from the axial center along the entire circumference.  FIG. 7  shows a relationship between a rotational angle of the primary pulley  34  and a margin for crushing the O-ring  52 .  FIG. 8  shows a relationship between a speed ratio, an engine torque, and an amplitude of the margin for crushing the O-ring  52  in the CVT  30  of the embodiment.  FIG. 9  shows the relationship between the speed ratio, the engine torque, and the amplitude of the margin for crushing the O-ring  52  in the continuously variable transmission of the comparative example. It should be noted that a solid line in  FIG. 7  indicates the margin for crushing the O-ring  52  in the embodiment, and a chain line indicates the margin for crushing the O-ring  52  in the comparative example. As shown in  FIGS. 7 to 9 , the amplitude of the margin for crushing the O-ring  52  due to the deformation of the primary pulley  34  and the primary cylinder  38  tends to be larger in the embodiment compared to the comparative example. That is, in the embodiment, drag wear of the O-ring  52  is more likely to occur compared to the comparative example, and thus it is more meaningful to apply the present invention. 
     According to the sealing structure for a continuously variable transmission of the embodiment described above, the clearance between the movable sheave  36  and the primary cylinder  38  that forms the hydraulic pressure chamber  39  on the rear side of the movable sheave  36  is sealed by attaching the rectangular cross-sectioned seal ring  50  and the circular cross-sectioned O-ring  52  on the outer peripheral side and the inner peripheral side, respectively, in a layered manner, and two corners of the seal ring  50  on the side where the seal ring  50  contacts the O-ring  52  among the four corners are chamfered. This chamfering forms the V-shaped groove between the side wall of the ring groove  38   a  and the side surface of the seal ring  50 , and the O-ring  52  can move into the V-shaped groove even when the O-ring  52  is periodically crushed due to deformation of the primary pulley  34  (the movable sheave  36 ) and the primary cylinder  38  caused by the belt  40 , whereby the occurrence of drag wear of the O-ring  52  can be suppressed. Consequently, sealing performance can be ensured without using an excessively rigid movable sheave  36  and primary cylinder  38 . 
     In the sealing structure for a continuously variable transmission according to the embodiment, the cylindrical portion  36   a  that extends in the axial direction from the outer peripheral portion of the movable sheave  36  is formed, and the outer peripheral portion of the primary cylinder  38  extends in the radial direction to the vicinity of the cylinder portion  36   a . In addition, the ring groove  38   a  is formed along the entire circumference of the outer peripheral edge of the primary cylinder  38 , and the seal ring  50  and the O-ring  52  are attached to the outer peripheral side and the inner peripheral side of the ring groove  38   a , respectively, in a layered manner. This forms the hydraulic pressure chamber  39 . However, as shown in  FIG. 6 , the hydraulic pressure chamber  139  may be formed by: cylindrically forming the outer peripheral portion  138   a  of the primary cylinder  138 , extending the outer peripheral portion of the movable sheave  136  in the radial direction to the vicinity of the inner peripheral surface of the outer peripheral portion  138   a  of the primary cylinder  138 , forming the ring groove  136   a  along the entire circumference of the outer peripheral edge of the movable sheave  136 , and attaching the seal ring  50  and the O-ring  52  to the outer peripheral side and the inner peripheral side of the ring groove  136   a , respectively, in a layered manner. In this case, as described above, the amplitude of the margin for crushing the O-ring  52  in accordance with the rotation of the pulley  134  is smaller than that in the embodiment. It is thus slightly less meaningful, compared to the embodiment, to apply the present invention. 
     In the sealing structure for a continuously variable transmission according to the embodiment, the rectangular cross-sectioned seal ring  50  is chamfered by plane chamfering at a chamfering angle of generally 45 degrees. However, as long as a clearance (relief space) is formed between the side wall of the ring groove  38   a  of the primary cylinder  38  and the side surface of the seal ring  50  into which the O-ring  52  can move when the O-ring  52  is crushed due to a change in the clearance between the primary pulley  34  (movable sheave  36 ) and the primary cylinder  38 , the chamfering angle for plane chamfering is not limited to 45 degrees, and may be other chamfering angles, such as 30 degrees, 40 degrees, 50 degrees, or 60 degrees. Moreover, the chamfering shape is not limited to plane chamfering, and may be any chamfering shapes, such as round chamfering (R chamfering) as shown by a seal ring  50 B of a modification example in  FIG. 10 , and L-shaped chamfering as shown by a seal ring  50 C of another modification example in  FIG. 11 . 
     In the sealing structure for a continuously variable transmission according to the embodiment, among four corners of the rectangular cross-sectioned seal ring  50 , two corners on the side where the seal ring  50  contacts the O-ring  52  are chamfered. However, the present invention is not limited to this, and only one corner of two corners may be chamfered on the side where the seal ring  50  contacts the O-ring  52 , which is located on a side opposite to the hydraulic pressure chamber  39  (a side where the seal ring  50  and the O-ring  52  are pressed against the side wall of the ring groove  38   a  of the primary cylinder  38  by the hydraulic pressure of the hydraulic pressure chamber  39 ). 
     Here, the correspondence relation will be explained between main elements of the embodiment and main elements of the invention as described in the Summary of the Invention. In the embodiment, the seal ring  50  corresponds to an “outer peripheral side seal member”, and the O-ring  52  corresponds to an “inner peripheral side seal member”. Note that with regard to the correspondence relation between the main elements of the embodiment and the main elements of the invention as described in the Summary of the Invention, the embodiment is only an example for giving a specific description of the invention explained in the Summary of the Invention. This correspondence relation does not limit the elements of the invention as described in the Summary of the Invention. In other words, any interpretation of the invention described in the Summary of the Invention shall be based on the description therein; the embodiment is merely one specific example of the invention described in the Summary of the Invention. 
     The above embodiment was used to describe the present invention. However, the present invention is not particularly limited to such an example, and may obviously be carried out using various embodiments without departing from the scope of the present invention. 
     The present invention may be used in a manufacturing industry of a continuously variable transmission.