Patent Publication Number: US-2009235815-A1

Title: Piston with built-in seal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national stage of the International Application No. PCT/JP2007/066332 filed on Aug. 23, 2007 and published in Japanese language. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piston with built-in seal used for a hydraulic operation clutch in an automatic transmission for a vehicle. 
     2. Description of the Conventional Art 
     In a hydraulic operation clutch in an automatic transmission for a motor vehicle, a clutch piston axially moving in a clutch cylinder by hydraulic pressure makes a drive plate at the drive shaft side and a driven plate at the driven shaft side in a multiple disk clutch to be contacted with pressure. As for the clutch piston, a piston with built-in seal (also called as bonded piston seal) is known. Such the piston with built-in seal is formed by integrating of seal lips to an outer peripheral part and an inner peripheral part of a piston body through vulcanizing and bonding. 
       FIG. 4  is a half sectional view of a conceptual configuration of a hydraulic operation clutch having a conventional piston with built-in seal, which is shown by a section along a plane passing through an axis O of the drive shaft.  FIG. 5  is an expanded sectional view of a part of  FIG. 4 . In the hydraulic operation clutch illustrated in  FIG. 4 , a reference numeral  1  is an annular clutch cylinder rotated with a drive shaft which is not illustrated. A numeral  2  is a piston with built-in seal, which is disposed to be axially movable in the clutch cylinder  1 . A numeral  3  is a spring holder disposed axially facing the piston with built-in seal  2  and fixed at an inner peripheral tube part  1   a  of the clutch cylinder  1  through a retaining ring  31 . A numeral  4  is a multiple disc clutch in which a plurality of drive plates  41  and a plurality of driven plates  42  are axially alternately disposed. The drive plates  41  are locked to the clutch cylinder  1  in a circumference direction in the state of being axially movable and the driven plates  42  are locked to a clutch hub  43  provided at the not-illustrated driven shaft side in a circumference direction in the state of being axially movable. An outer peripheral skirt part  2   a  of the piston with built-in seal  2  axially faces the drive plate  41  of the multiple disc clutch  4 , and a return spring  5  is inserted between the piston with built-in seal  2  and the spring holder  3  in the state of being properly compressed. 
     A plurality of the return springs  5  are disposed at a predetermined interval in the circumference direction around the axis O. One end  5   a  of each of return springs  5  is fitted to and locked by a circular guide projection  23  formed by embossing on the piston with built-in seal  2 , and another end  5   b  is held by a projection edge  3   a  formed along the outer periphery of the spring holder  3 . 
     The piston with built-in seal  2  integrally has seal lips  21  and  22  made of a rubber like elastic material on the inner and outer peripheries thereof, and the seal lips  21  and  22  tightly and slidably contact to the inner peripheral tube part  1   a  and the outer peripheral tube part lb of the clutch cylinder  1  respectively. Further, the inner peripheral tube part  1   a  of the clutch cylinder  1  has an oil passage  11  for introducing hydraulic pressure by oil (ATF) into a pressurizing chamber  6  defined between the clutch cylinder  1  and the piston with a built-in seal  2 . 
     That is, when hydraulic pressure is applied to the pressurizing chamber  6  through the oil passage  11 , the piston with built-in seal  2  is axially displaced in the clutch cylinder  1  in the direction for compressing the return spring  5  and presses the drive plate  41  toward the driven plate  42  in the multiple disc clutch  4 . Therefore, the hydraulic operation clutch becomes in a connection state for transmitting drive power from the drive shaft to the driven shaft. 
     Then, when the hydraulic pressure in the pressurizing chamber  6  is released, the piston with built-in seal  2  is axially displaced in the clutch cylinder  1  in the direction to decrease the capacity of the pressurizing chamber  6  by pressing force of the compressed return spring  5  and cancels the pressure contact of the drive plate  41  to the driven plate  42  in the multiple disc clutch  4 . Therefore, the transmission of the drive power from the drive shaft to the driven shaft is disconnected (for example, refer to Unexamined Japanese Patent Publication Laid-Open No. 9-189336). 
     However, according to the aforementioned conventional technique, the guide projection  23  for locking the one end  5   a  of each return spring  5  is embossed to have a bottomed shape at the time of press forming of the piston with built-in seal  2 . Thus, as illustrated in  FIG. 5 , an embossing height h cannot be made so high, while a diameter φ of the guide projection  23  is hardly decreased because of the strength of a press type punch. Therefore, the return spring  5  is loosened, inclined, or relatively rotated due to centrifugal force generated by rotation, etc. Thus, there are pointed-out problems that the return force of the piston with built-in seal  2  by the return springs  5  is not stable at a time of releasing of hydraulic pressure in the pressurizing chamber  6 , and that the one end  5   a  of the return spring  5  is displaced as illustrated with broken lines in  FIG. 5  due to deflection of the return spring  5  so that the return spring is easily removed from the guide projection  23 . 
     SUMMARY OF THE INVENTION 
     Problems to Be Solved by the Invention 
     The present invention is to solve the aforementioned problems, and an object of the present invention is to provide a piston with built-in seal capable of effectively preventing the occurrences of looseness, inclination, and relative rotation of return springs. 
     Means for Solving the Problem 
     In order to attain the aforementioned object, a piston with built-in seal according to a first aspect of the present invention includes a piton body made of a metal press-formed part and disposed to be axially movable in a clutch cylinder, and seal lips formed integrally on the piston body, wherein through tubular guide projections are formed on the piston body at positions at the outer side from a pressurizing chamber defined between the clutch cylinder and the piston body by the seal lips, and return springs for pressing the piston body toward the pressurizing chamber side are held on the guide projections. 
     According to the aforementioned configuration, since the guide projections of the piston body have a through tubular shape, the projection height of the press-formed guide projections, that is, the length of the parts for holding the return springs, can be enlarged than that of the guide projections press-formed to have a bottomed tubular shape. 
     A piston with built-in seal according to a second aspect of the present invention has the guide projections recited in the first aspect at the outer side from the pressurizing chamber defined between the clutch cylinder and the piston body by the seal lips. Accordingly, the through tubular guide projections prevent opening of the pressurizing chamber. 
     A piston with built-in seal according to a third aspect of the present invention has the guide projections described in the first aspect at a pressure receiving part of the piston body which faces to the pressurizing chamber defined between the clutch cylinder and the piston body by the seal lips, and inner peripheries of the guide projections are tightly plugged with plugging parts made of a rubber like elastic material. Accordingly, the through tubular guide projections prevent opening of the pressurizing chamber. 
     Effectiveness of the Invention 
     According to the piston with built-in seal according to the first to third aspects, since the guide projections formed on the piston body have a through tubular shape, the length of the parts for holding the return springs held on the guide projections can be made longer. As a result, looseness, inclination, and relative rotation of the return springs due to centrifugal force, etc. generated by rotation can be effectively prevented, and the return force toward the pressurizing chamber side by the pressing force of the return spring can be stabilized. 
    
    
     
       BRIEF EXPLANATION OF DRAWINGS 
         FIG. 1  is a half sectional view of a first embodiment of a piston with built-in seal according to the present invention, which is shown by a section along a plane passing through an axis O of the drive shaft together with a part of a hydraulic operation clutch, 
         FIG. 2  is a expanded sectional view of a part of  FIG. 1 , 
         FIG. 3  is a half sectional view of a second embodiment of a piston with built-in seal according to the present invention, which is shown by a section along a plane passing through an axis O of the drive shaft together with a part of a hydraulic operation clutch, 
         FIG. 4  is a half sectional view of a conceptual configuration of a hydraulic operation clutch having a conventional piston with built-in seal, which is shown by a section along a plane passing through an axis O of the drive shaft, and 
         FIG. 5  is an expanded sectional view of a part of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of a piston with built-in seal according to the present invention will be described below with reference to the drawings.  FIG. 1  is a half sectional view of a first embodiment of a piston with built-in seal according to the present invention, which is shown by a section along a plane passing through an axis O of the drive shaft with a part of a hydraulic operation clutch.  FIG. 2  is an expanded sectional view of a part of  FIG. 1 . 
     In a hydraulic actuator for an automatic transmission illustrated in  FIG. 1 , a reference numeral  110  is a clutch cylinder rotated around an axis O with a not-illustrated drive shaft. The clutch cylinder  110  is formed in an annular shape. The clutch cylinder  110  includes an inner peripheral tube part  111 , an inner peripheral disk part  112  extending from an axial one end of the inner peripheral tube part, an intermediate tube part  113  formed backwardly from an outer peripheral end part of the inner peripheral disc part  112 , and coaxially with the inner peripheral tube part  111 , an outer peripheral disk part  114  expanding to the outer peripheral side from an end part of the intermediate tube part  113 , and an outer peripheral tube part  115  extending coaxially with the inner peripheral tube part  111 , from an outer peripheral end part of the outer peripheral disc part  114 . 
     A reference numeral  120  is a piston with built-in seal disposed so as to be axially movable in the clutch cylinder  110 . A reference numeral  130  is a spring holder disposed axially facing the piston with built-in seal  120  and fixed at the inner peripheral tube part  111  of the clutch cylinder  110  through a retaining ring  131 . A reference numeral  140  is a multiple disc clutch in which a plurality of drive plates  141  and a plurality of driven plates  142  are axially alternately disposed. The drive plates  141  are locked to the outer peripheral tube part  115  of the clutch cylinder  110  in a circumference direction in the state of being axially movable, and the driven plates  142  are locked to a clutch hub  143  provided at the not-illustrated driven shaft side in a circumference direction in the state of being axially movable. A reference numeral  150  is a return spring inserted between the piston with built-in seal  120  and the spring holder  130  in the state of being properly compressed. 
     The piston with built-in seal  120  includes an annular piston body  121  around an axis O, and seal lips  122  and  123  formed integrally with the piston body  121 . 
     The piston body  121  in the piston with built-in seal  120  is made of a metal by press-forming. The piston body  121  includes a pressure receiving part  121   a  at the inner peripheral side which axially faces the inner peripheral disc part  112  of the clutch cylinder  110 , a flange part  121   c  expanding to have a disk shape from the outer peripheral side of the pressure receiving part  121   a  through an outer tube part  121   b  and axially facing the outer peripheral disk part  114  of the clutch cylinder  110 , and a clutch pressing part  121   d  formed at an outer peripheral end part of the flange part  121   c  and axially facing the drive plate  141  of the multiple disc clutch  140  closely. 
     The seal lips  122  and  123  in the piston with built-in seal  120  are formed integrally on an inner peripheral part and an outer peripheral part of the pressure receiving part  121   a  in the piston body  121  with a rubber like elastic material. Among these seal lips, the seal lip  122  on the inner peripheral side is slidably brought in close contact with an inner peripheral face of the inner peripheral tube part  111  of the clutch cylinder  110 , and the seal lip  123  on the outer peripheral side is slidably brought in close contact with an inner peripheral face of the intermediate tube part  113  of the clutch cylinder  110 . Further, a pressurizing chamber A is defined between the clutch cylinder  110  and the pressure receiving part  121   a  of the piston body  121  by the seal lips  122  and  123 , and an oil passage  111   a  for introducing hydraulic pressure by oil (ATF) into the pressurizing chamber A is provided in the inner peripheral tube part  111  of the clutch cylinder  110 . 
     The flange part  121   c  of the piston body  121  in the piston with built-in seal  120  has guide projections  124  which project in the reverse direction to the facing direction to the outer peripheral disk part  114  of the clutch cylinder  110 , that is, toward the spring holder  130  side. The guide projections  124  are formed to project in a through tubular shape by deep drawing at the flange part  121   c  at the time of press-forming of the piston body  121 , and a plurality of the guide projections  124  are provided at a predetermined interval in the circumference direction around the axis O. 
     The return spring  150  is a metallic coil spring. A plurality of the return springs  150  are disposed at a predetermined interval in the circumference direction around the axis O, and are provided between the flange part  121   c  of the piston body  121  and the spring holder  130  in the state of being properly compressed. As illustrated in  FIG. 2 , one end  151  of each of the return springs  150  is fitted on the guide projection  124  to be thereby held in the state of contacting to the flange part  121   c.  Another end  152  is contacted with the spring holder  130 , and displacement toward the outer peripheral side of the other end  152  is regulated by a projection edge  130   a  formed along the outer periphery thereof. 
     Further, a facing distance L between the guide projections  124  and the spring holder  130  at the time when the piston with built-in seal  120  is placed at an upper side stroke end position for making the capacity of the pressurizing chamber A to be the minimum, is set to be properly larger than a stroke length of the piston with built-in seal  120 . That is, even when the piston with built-in seal  120  is moved to a lower side stroke end position where the clutch pressing part  121   d  presses the multiple disc clutch  140 , the guide projections  124  do not contact to the spring holder  130 . 
     According to the aforementioned configuration, when operational hydraulic pressure is applied to the pressurizing chamber A through the oil passage  111   a  or the hydraulic pressure is released, the piston with built-in seal  120  is displaced axially in the clutch cylinder  110  so as to make the multiple disc clutch  140  to carry out a connecting operation or a disconnecting operation, like the aforementioned configuration in  FIG. 4 . 
     That is, when the pressurizing chamber A is pressurized by supplying of oil, the piston with built-in seal  120  is displaced downward in  FIG. 1  while compressing the return springs  150 , and the clutch pressing part  121   d  of the piston with built-in seal  120  frictionally engages the drive plates  141  and the driven plates  142  of the multiple disc clutch  140 . Consequently, the multiple disc clutch  140  becomes in the connection state, and a drive torque from a not-illustrated drive shaft side is transmitted to a not-illustrated driven shaft through the clutch cylinder  110 , the drive plate  141  and the driven plate  142  of the multiple disc clutch  140 , and the clutch hub  143 . 
     Further, when the hydraulic pressure in the pressurizing chamber A is released in the connection state, the piston with built-in seal  120  is displaced upward in  FIG. 1  so as to decrease the volume of the pressurizing chamber A by returning force of the compressed return springs  150 , and then the pressing to the multiple disc clutch  140  is canceled. Thus, the frictional engaging of the drive plates  141  and the driven plates  142  of the multiple disc clutch  140  is canceled, and transmission of the drive torque from the drive shaft to the driven shaft is disconnected. 
     In those operations, the guide projections  124  in the piston with built-in seal  120  are formed to project in a through tubular shape by deep drawing. Thus, a projection height h illustrated in  FIG. 2 , that is, a length h of the parts for holding the return springs  150  fitted on the guide projections  124  to be thereby held, can be made sufficiently larger than that of the conventional one formed in a bottomed tubular shape by embossing. Therefore, looseness, inclination, and relative rotation of the return springs  150  due to centrifugal force etc. generated by rotation can be effectively suppressed, and thus returning force of the piston with built-in seal  120  toward the pressurizing chamber A side by pressing force of the return springs  150  can be stabilized. 
     Then,  FIG. 3  is a half sectional view of a second embodiment of a piston with built-in seal according to the present invention, which is shown by a section along a plane passing through an axis O of the drive shaft together with a part of a hydraulic operation clutch. In the aforementioned first embodiment illustrated in  FIG. 1 , in order to prevent that the piston with built-in seal  120  becomes inoperable because the pressurizing chamber A communicates with a space B at the spring holder  130  side by the through tubular guide projections  124 , the guide projections  124  are formed at the flange part  121   c  in the piston body  121 , that is, are formed at an outer position from the seal lip  123  for defining the pressurizing chamber A. In contrast, in the second embodiment, the guide projections  124  are formed at the pressure receiving part  121   a  of the piston body  121 , and inner peripheries thereof are filled with a rubber like elastic material to be thereby tightly plugged. 
     That is, as illustrated in  FIG. 3 , the flange part  121   c  of the piston body  121  in the piston with built-in seal  120  does not have guide projections, and the guide projections  124  are formed at the pressure receiving part  121   a  of the piston body  121  to project toward the reverse direction to the facing direction to the inner peripheral disk part  112  of the clutch cylinder  110 , that is, toward the spring holder  130  side. The guide projections  124  are formed to project in a through tubular shape by deep drawing at the pressure receiving part  121   a  at the time of press-forming of the piston body  121 , and a plurality of the guide projections  124  are provided at a predetermined interval in the circumference direction around the axis O. 
     An elastic layer  125  is formed so as to cover a face at the pressurizing chamber A side of the pressure receiving part  121  a of the piston body  121  and extends from a base of the seal lip  122  (or the seal lip  123 ). A plugging parts  126  extending from the elastic layer  125  plug the inner peripheries of the through tubular guide projections  124 . That is, when the seal lips  122  and  123  are formed integrally on the piston body  121  with a rubber like elastic material, the plugging parts  126  are formed by a part of the rubber material being filled in the inner peripheries of the guide projections  124 . 
     A plurality of the return springs  150  are disposed at a predetermined interval in the circumference direction around the axis O, and provided between the pressure receiving part  121   a  of the piston body  121  and the spring holder  130  in the state of being properly pre-compressed. Further, one end  151  of each of the return springs  150  is fitted on the guide projection  124  to be thereby held in the state of contacting to the pressure receiving part  121   a.  Another end  152  is contacted with the spring holder  130  and displacement toward the outer peripheral side of the other end  152  is regulated by a projection edge  130   a  formed along an outer periphery of the spring holder  130 . 
     In addition, other parts of the second embodiment are basically configured like  FIG. 1 . 
     That is, like the first embodiment, since the guide projections  124  of the piston with built-in seal  120  are formed to project in a through tubular shape by deep drawing and the return springs  150  are fitted on such the guide projections  124 , a length of the parts for holding the return springs  150  can be made sufficiently large. Therefore, looseness, inclination and relative rotation of the return springs  150  due to centrifugal force etc. generated by rotation can be effectively suppressed, and thus returning force of the piston with built-in seal toward the pressurizing chamber A side by pressing force of the return springs  150  can be stabilized. 
     Further, the inner peripheries of the through tubular guide projections  124  formed at the pressure receiving part  121   a  of the piston body  121  are tightly plugged with the plugging parts  126  made of a rubber like elastic material. Thus, it can be prevented that the piston with built-in seal  120  becomes inoperable because the pressurizing chamber A communicates with the space B on the spring holder  130  side.