JP2014148233A - Master cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a master cylinder capable of preventing the increase of invalid strokes.SOLUTION: A piston seal 45 is provided in a peripheral groove 32 formed in a bottomed cylindrical body 15 and the inner periphery thereof slidingly contacts a piston 18 to seal between a replenishing path 48 and a pressure chamber 85. The piston seal has a toric base 101, an inner peripheral lip 102 protruding from the inner peripheral side of the base 101 and slidingly contacting an outer peripheral face 18a of the piston 18, and an outer peripheral lip 103 protruding from the outer peripheral side of the base 101 and contacting the peripheral groove 32 of the cylindrical body 15. Further, a recess 110 is provided over the whole periphery on the top of the inner peripheral lip 102.

Description

  The present invention relates to a master cylinder that supplies hydraulic pressure to a brake cylinder of a vehicle.

  Some master cylinders have piston seals arranged in a circumferential groove of a cylinder main body to seal a pressure chamber while being in sliding contact with a moving piston (see, for example, Patent Document 1).

JP 2006-264689 A

  In the master cylinder, due to environmental conditions, when the piston moves, the piston seal does not slide smoothly with respect to the piston, and the piston is moved by the piston and the inner and outer sides move in opposite directions within the circumferential groove. There is a possibility that it will rotate. Then, the seal position of the piston seal with respect to the piston may shift, and the invalid stroke of the piston may increase.

  Therefore, an object of the present invention is to provide a master cylinder capable of suppressing an increase in invalid stroke.

  In order to achieve the above-mentioned object, the master cylinder of the present invention has a piston seal provided in a circumferential groove formed in a cylinder main body, an annular base portion, and an outer peripheral surface of the piston protruding from the inner peripheral side of the base portion. An inner peripheral lip portion that slidably contacts the outer peripheral lip portion that protrudes from the outer peripheral side of the base portion and abuts against the peripheral groove of the cylinder body, and a recess is provided at the tip of the inner peripheral lip portion over the entire circumference. The configuration.

  According to the master cylinder of the present invention, an increase in invalid stroke can be suppressed.

It is sectional drawing which shows the master cylinder of one Embodiment which concerns on this invention. It is a partial expanded sectional view which shows the principal part of the master cylinder of embodiment, Comprising: The state which has a piston in a basic position is shown. The piston seal of the master cylinder of embodiment is shown, (a) is a front view, (b) is a rear view. It is AA sectional drawing of (a) which shows the piston seal of the master cylinder of embodiment. It is a partial expanded sectional view which shows the principal part of the master cylinder of embodiment, Comprising: The state at the time of contact | abutting to the surrounding wall of an inner peripheral lip part is shown. It is a partial expanded sectional view which shows the principal part of the master cylinder of embodiment, Comprising: The deformation | transformation state of an inner peripheral lip | rip part is shown.

  An embodiment according to the present invention will be described with reference to the drawings. In the master cylinder 11 of the present embodiment shown in FIG. 1, a force corresponding to an operation amount of a brake pedal (not shown) is introduced via an output shaft of a brake booster (not shown). The brake fluid pressure is generated. A reservoir 12 (only a part of which is shown in FIG. 1) for supplying and discharging brake fluid is attached to the master cylinder 11 on the upper side in the vertical direction. In this embodiment, the reservoir 12 is directly attached to the master cylinder 11, but the reservoir may be arranged at a position separated from the master cylinder 11, and the reservoir and the master cylinder 11 may be connected by piping. .

  The master cylinder 11 is formed of a bottomed cylinder having a bottom portion 13 and a cylindrical portion 14 and is formed from a single material, and is disposed on the vehicle in a posture in which the axial direction is along the vehicle longitudinal direction. 15. A metal primary piston (piston) 18 is movably disposed on the opening 16 side of the cylinder body 15. Similarly, a metal secondary piston (piston) 19 is movably disposed on the bottom 13 side of the cylinder body 15 with respect to the primary piston 18. The primary piston 18 is formed with an inner peripheral hole 21 having a bottom surface, and the secondary piston 19 is formed with an inner peripheral hole 22 having a bottom surface, and the master cylinder 11 is of a so-called plunger type. The master cylinder 11 is a tandem type master cylinder having the two pistons 18 and 19 as described above. The present invention is not limited to the application to the tandem type master cylinder, and if it is a plunger type master cylinder, a single type master cylinder in which one piston is arranged in the cylinder body, or three or more types. The present invention can be applied to any plunger type master cylinder such as a master cylinder having a plurality of pistons.

  The cylinder body 15 has a mounting base portion 23 protruding outward in the radial direction of the cylindrical portion 14 (hereinafter referred to as the cylinder radial direction) at a predetermined position in the circumferential direction of the cylindrical portion 14 (hereinafter referred to as the cylinder circumferential direction). Are integrally formed. Mounting holes 24 and 25 for mounting the reservoir 12 are formed in the mounting base portion 23. In the present embodiment, the mounting holes 24 and 25 are shifted in position in the axial direction (hereinafter referred to as the cylinder axis) of the cylindrical portion 14 of the cylinder body 15 in a state where the positions in the cylinder circumferential direction coincide with each other. Is formed at the top.

  On the mounting base 23 side of the cylinder portion 14 of the cylinder body 15, there is a secondary discharge path (discharge path) 26 in the vicinity of the bottom portion 13, and a primary discharge path (discharge path) 27 on the opening 16 side than this, respectively. Is formed. Although not shown, the secondary discharge path 26 and the primary discharge path 27 communicate with a brake cylinder such as a disc brake or a drum brake via a brake pipe, and discharge brake fluid toward the brake cylinder. In the present embodiment, the secondary discharge passage 26 and the primary discharge passage 27 are formed by shifting the positions in the cylinder axial direction in a state where the positions in the cylinder circumferential direction coincide with each other.

  The secondary piston 19 is slidably guided to a sliding inner diameter portion 28 having an annular inner surface centered on the cylinder axis, which is formed on the inner peripheral portion on the bottom 13 side of the cylindrical portion 14 of the cylinder body 15. The primary piston 18 is slidably guided to a sliding inner diameter portion 29 having an annular inner surface centering on the cylinder axis, which is formed on the inner peripheral portion of the cylinder portion 14 of the cylinder body 15 on the opening 16 side.

  The sliding inner diameter portion 28 is formed with a circumferential groove 30 and a circumferential groove 31 that are formed in this order from the bottom portion 13 side in a plurality of positions, in the cylinder axis direction, in a plurality of shapes, specifically in any two places. Also, the sliding inner diameter portion 29 is formed with a circumferential groove 32 and a circumferential groove 33 that are formed in this order from the bottom 13 side in a plurality of positions, in the cylinder axis direction, in a plurality of positions, specifically in any two places. . These circumferential grooves 30 to 33 have an annular shape in the cylinder circumferential direction and have a shape that is recessed outward in the cylinder radial direction, and all are formed by cutting.

  The circumferential groove 30 closest to the bottom portion 13 is formed in the vicinity of the mounting hole 24 on the bottom portion 13 side of the mounting holes 24 and 25, and is held in the circumferential groove 30 in the circumferential groove 30. Further, an annular piston seal 35 is disposed.

  The cylinder diameter is such that a communication hole 36 formed from the mounting hole 24 on the bottom portion 13 side is opened in the cylindrical portion 14 on the opening portion 16 side of the sliding inner diameter portion 28 of the cylinder body 15 on the opening portion 16 side. An annular opening groove 37 that is recessed outward in the direction is formed. Here, the opening groove 37 and the communication hole 36 mainly constitute a secondary supply path (supply path) 38 provided in the cylinder body 15 and always communicating with the reservoir 12.

  The sliding inner diameter portion 28 of the cylinder body 15 is formed with the circumferential groove 31 on the side opposite to the circumferential groove 30 of the opening groove 37 in the cylinder axis direction, that is, on the opening portion 16 side. The annular partition seal 42 is disposed so as to be held in the circumferential groove 31.

  The above-mentioned circumferential groove 32 is formed in the sliding inner diameter portion 29 of the cylinder body 15 in the vicinity of the mounting hole 25 on the opening 16 side. An annular piston seal 45 is disposed in the circumferential groove 32 so as to be held in the circumferential groove 32.

  In the sliding inner diameter portion 29 of the cylinder body 15, on the opening portion 16 side of the circumferential groove 32, a communication hole 46 drilled from the mounting hole 25 on the opening portion 16 side is opened in the cylinder portion 14. An annular opening groove 47 that is recessed outward in the radial direction is formed. Here, the opening groove 47 and the communication hole 46 mainly constitute a primary supply path (supply path) 48 provided in the cylinder body 15 and always communicating with the reservoir 12.

  A circumferential groove 33 is formed on the sliding inner diameter portion 29 of the cylinder body 15 on the side opposite to the circumferential groove 32 of the opening groove 47, that is, on the opening 16 side. The circumferential groove 33 is held in the circumferential groove 33. As shown, an annular partition seal 52 is disposed.

  The secondary piston 19 fitted to the bottom 13 side of the cylinder body 15 has a bottomed cylindrical shape having a cylindrical portion 55 and a bottom portion 56 formed on one side in the axial direction of the cylindrical portion 55. . The inner peripheral hole 22 is formed by the cylindrical portion 55 and the bottom portion 56. The secondary piston 19 is slid on the inner periphery of each of the piston seal 35 and the partition seal 42 provided on the sliding inner diameter portion 28 of the cylinder body 15 with the cylindrical portion 55 disposed on the bottom 13 side of the cylinder body 15. It is movably fitted.

  An annular step portion 59 having a step shape so as to be located radially inward of the outermost surface 58 having the largest diameter in the secondary piston 19 is disposed on the outer peripheral portion on the end opposite to the bottom portion 56 of the cylindrical portion 55. Is formed. In the stepped portion 59, a plurality of ports 60 penetrating in the cylinder radial direction are formed on the bottom 56 side so as to be radially formed at equal intervals in the cylinder circumferential direction.

  An interval adjustment unit including a secondary piston spring 62 between the secondary piston 19 and the bottom portion 13 of the cylinder body 15 for determining these intervals in a non-braking state without input from a brake pedal (not shown) (right side in FIG. 1). 63 is provided. The interval adjusting portion 63 is connected to the locking member 64 that contacts the bottom portion 13 of the cylinder body 15 and the locking member 64 so as to slide only within a predetermined range, and contacts the bottom portion 56 of the secondary piston 19. And a locking member 65. The secondary piston spring 62 is interposed between the locking members 64 and 65 on both sides.

  Here, a portion formed by being surrounded by the bottom portion 13 of the cylinder body 15 and the bottom portion 13 side of the cylinder portion 14 and the secondary piston 19 generates a brake fluid pressure and supplies the brake fluid pressure to the secondary discharge passage 26. A secondary pressure chamber (pressure chamber) 68 is formed. In other words, the secondary piston 19 forms a secondary pressure chamber 68 that supplies hydraulic pressure to the secondary discharge passage 26 between the secondary piston 19 and the cylinder body 15. The secondary pressure chamber 68 communicates with the secondary supply path 38, that is, the reservoir 12 when the secondary piston 19 is in a position for opening the port 60 into the opening groove 37.

  The partition seal 42 held in the circumferential groove 31 of the cylinder body 15 is an integrally molded product made of synthetic rubber such as EPDM, and one side shape of the radial cross section including the center line thereof is C-shaped. The partition seal 42 is in sliding contact with the outer periphery of the secondary piston 19 that moves in the cylinder axial direction, and the outer periphery abuts against the circumferential groove 31 of the cylinder body 15 so that the partition seal 42 of the secondary piston 19 and the cylinder body 15 Always seal position gaps.

  The piston seal 35 held in the circumferential groove 30 of the cylinder body 15 is an integrally molded product made of synthetic rubber such as EPDM, and the one-side shape of the radial cross section including the center line thereof is C-shaped. The piston seal 35 has an inner periphery that is in sliding contact with the outer periphery of the secondary piston 19 that moves in the cylinder axial direction, and the outer periphery is in contact with the circumferential groove 30 of the cylinder body 15. The piston seal 35 can seal between the secondary supply passage 38 and the secondary pressure chamber 68 in a state in which the secondary piston 19 positions the port 60 on the bottom 13 side of the piston seal 35, that is, the secondary pressure chamber 68. The communication with the secondary supply path 38 and the reservoir 12 can be blocked. In this sealed state, the secondary piston 19 slides on the sliding inner diameter portion 28 of the cylinder body 15 and the inner periphery of the piston seal 35 and the partition seal 42 held by the cylinder body 15 and moves to the bottom 13 side. The brake fluid in the secondary pressure chamber 68 is pressurized and supplied from the secondary discharge passage 26 to the brake cylinder on the wheel side.

  When there is no input from a brake pedal (not shown) and the secondary piston 19 is in a basic position (non-braking position) where the port 60 is opened in the opening groove 37 as shown in FIG. In the stepped portion 59 of the secondary piston 19, a part thereof overlaps with the port 60. When the secondary piston 19 moves to the bottom 13 side of the cylinder body 15 and the inner peripheral portion of the piston seal 35 is entirely overlapped with the port 60, the communication between the secondary pressure chamber 68 and the reservoir 12 is blocked. Yes.

  The primary piston 18 fitted to the opening 16 side of the cylinder body 15 includes a first cylindrical portion 71, a bottom portion 72 formed on one side in the axial direction of the first cylindrical portion 71, and a first portion of the bottom portion 72. It has a shape having a second cylindrical portion 73 formed on the opposite side to the first cylindrical portion 71. The inner peripheral hole 21 is formed by the first cylindrical portion 71 and the bottom portion 72 among them. The primary piston 18 has the first cylindrical portion 71 disposed on the secondary piston 19 side in the cylinder body 15 and each of the piston seal 45 and the partition seal 52 provided on the sliding inner diameter portion 29 of the cylinder body 15. The inner periphery is slidably fitted. Here, the output shaft of the brake booster is inserted inside the second cylindrical portion 73, and the bottom portion 72 is pressed by this output shaft.

  On the outer peripheral portion on the end side opposite to the bottom portion 72 of the first cylindrical portion 71, an annular step having a step shape so as to be located radially inward from the outermost surface 74 having the largest diameter in the primary piston 18. A portion 75 is formed. The step portion 75 is formed with a plurality of ports 76 penetrating in the radial direction on the bottom portion 72 side so as to be radially arranged at equal intervals in the cylinder circumferential direction.

  Between the secondary piston 19 and the primary piston 18, there is provided a distance adjusting portion 79 including a primary piston spring 78 that determines these distances in a non-braking state without input from a brake pedal side (right side in FIG. 1). It has been. The gap adjusting portion 79 includes a locking member 81 that contacts the bottom 72 of the primary piston 18, a locking member 82 that contacts the bottom 56 of the secondary piston 19, and one end fixed to the locking member 81. And a shaft member 83 that slidably supports the stop member 82 only within a predetermined range. The primary piston spring 78 is interposed between the locking members 81 and 82 on both sides.

  Here, a portion surrounded by the cylinder portion 14 of the cylinder body 15, the primary piston 18 and the secondary piston 19 generates a brake fluid pressure and supplies a brake fluid to the primary discharge passage 27 (primary pressure chamber ( Pressure chamber) 85. In other words, the primary piston 18 forms a primary pressure chamber 85 that supplies hydraulic pressure to the primary discharge passage 27 between the secondary piston 19 and the cylinder body 15. The primary pressure chamber 85 communicates with the primary replenishment path 48, that is, the reservoir 12 when the primary piston 18 is in a position where the port 76 is opened to the opening groove 47.

  The partition seal 52 held in the circumferential groove 33 of the cylinder body 15 is the same component as the partition seal 42, and is an integrally molded product made of synthetic rubber such as EPDM, and has a one-side shape with a radial cross section including the center line thereof. Is C-shaped. The partition seal 52 is in sliding contact with the outer periphery of the primary piston 18 that moves in the cylinder axis direction, and the outer periphery abuts on the circumferential groove 33 of the cylinder body 15 so that the partition seal 52 of the primary piston 18 and the cylinder body 15 Always seal position gaps.

  The piston seal 45 held in the circumferential groove 32 of the cylinder body 15 is the same component as the piston seal 35, and is an integrally molded product made of synthetic rubber such as EPDM, and has a one-side shape in a radial direction including its center line. Is C-shaped. The piston seal 45 is configured such that the inner periphery is in sliding contact with the outer periphery of the primary piston 18 moving in the cylinder axis direction, and the outer periphery is in contact with the circumferential groove 32 of the cylinder body 15. The piston seal 45 can seal between the primary supply passage 48 and the primary pressure chamber 85 when the primary piston 18 has the port 76 positioned on the bottom 13 side of the piston seal 45, that is, the primary pressure chamber 85. And communication with the primary supply path 48 and the reservoir 12 can be blocked. In this sealed state, the primary piston 18 slides on the sliding inner diameter portion 29 of the cylinder body 15 and the inner periphery of the piston seal 45 and the partition seal 52 held on the cylinder body 15 and moves to the bottom 13 side. The brake fluid in the primary pressure chamber 85 is pressurized and supplied from the primary discharge passage 27 to the wheel-side braking cylinder.

  When there is no input from the brake pedal (not shown) and the primary piston 18 is in the basic position (non-braking position) where the port 76 is opened in the opening groove 47 as shown in FIG. A part of the port 76 overlaps the port 76 in the step 75 of the primary piston 18. When the primary piston 18 moves to the bottom 13 side of the cylinder body 15 and the inner peripheral portion of the piston seal 45 overlaps with the port 76, the communication between the primary pressure chamber 85 and the reservoir 12 is blocked. Yes.

  Here, the structure part which consists of the circumferential groove 30 of the cylinder main body 15 and its vicinity part, the piston seal 35, and the sliding contact part of the piston seal 35 of the secondary piston 19 is called secondary side seal structure part SS. Further, a structure portion including the circumferential groove 32 of the cylinder body 15 and the vicinity thereof, the piston seal 45, and the sliding contact portion of the piston seal 45 of the primary piston 18 is referred to as a primary-side seal structure portion SP. The secondary-side seal structure SS and the primary-side seal structure SP have the same structure. Therefore, in the following, these details will be described with reference to FIGS. 2 to 6 mainly using the seal structure portion SP on the primary side as an example.

  As shown in FIG. 2, the circumferential groove 32 includes a groove bottom portion 88 on the outermost side in the cylinder radial direction (upper side in FIG. 2) and the opening 16 side of the cylinder body 15 in the groove bottom portion 88 (right side in FIG. 2. , Referred to as the cylinder opening side) and the peripheral wall 89 extending inwardly in the cylinder radial direction from the edge of the cylinder, and the bottom 13 side of the cylinder body 15 at the groove bottom 88 (left side in FIG. 2; hereinafter referred to as the cylinder bottom side). A peripheral wall 90 extending inwardly in the cylinder radial direction from the end edge portion of the cylinder. The groove bottom portion 88, the peripheral wall 89, and the peripheral wall 90 are formed integrally with the cylinder body 15, and are formed by cutting the cylinder body 15.

  The groove bottom portion 88 has a groove bottom surface 88a. The groove bottom surface 88a is an annular inner surface with the cylinder axis as the center, and the length in the cylinder axis direction is constant over the entire circumference.

  The peripheral wall 89 has a wall surface 89a. The wall surface 89a is a flat surface parallel to a plane orthogonal to the cylinder axis, and has a constant inner diameter, a constant outer diameter, and a constant width in the cylinder radial direction. The wall surface 89a has an annular shape centered on the cylinder axis. The boundary position between the large diameter side of the wall surface 89a and the cylinder opening side of the groove bottom surface 88a, and the boundary position between the small diameter side of the wall surface 89a and the cylinder opening side of the peripheral groove 32 of the sliding inner diameter portion 29 are respectively R Chamfered.

  The peripheral wall 90 facing the peripheral wall 89 has a wall surface 90a and a tapered surface 90b. The wall surface 90a is a flat surface on the side of the groove bottom 88 in the cylinder radial direction on the peripheral wall 90 and parallel to the orthogonal surface of the cylinder axis. The wall surface 90a has a constant inner diameter and a constant outer diameter, a constant width in the cylinder radial direction, and has an annular shape centering on the cylinder axis. The tapered surface 90b is located on the inner side in the cylinder radial direction with respect to the wall surface 90a of the peripheral wall 90, and extends from the inner end edge of the wall surface 90a in the cylinder radial direction to the cylinder bottom side so as to reduce in diameter toward the cylinder bottom side. Yes. The tapered surface 90b has a constant inner diameter and a constant outer diameter, a constant width in the cylinder axial direction and a cylinder radial direction, and is arranged in an annular shape centering on the cylinder axis. The boundary portion 91 with the wall surface 90a which is the base point of the tapered surface 90b has an annular shape centering on the cylinder axis, and the diameter of the boundary portion 91, that is, the maximum diameter of the tapered surface 90b is the flat wall surface of the peripheral wall 89. The diameter is larger than the minimum diameter of 89a. The vicinity including the boundary portion 91 has a shape protruding obliquely inward in the cylinder radial direction and in the cylinder opening direction, and the angle formed by the tapered surface 90b and the wall surface 90a in the cross section passing through the cylinder axis is an obtuse angle. It has become. As described above, the tapered surface 90b is formed on the opening side (radially inward) of the circumferential groove 32 in the circumferential wall 90 on the cylinder bottom side of the circumferential groove 32, and on the groove bottom portion 88 side of the tapered surface 90b in the cylinder radial direction. Wall surfaces 90a are formed adjacent to each other. R chamfering is applied to the boundary position between the large diameter side of the wall surface 90a and the cylinder bottom side of the groove bottom surface 88a.

  The step portion 75 formed in the primary piston 18 has a cylindrical surface 75a, a tapered surface 75b, and a tapered surface 75c. The cylindrical surface 75a has a smaller diameter than the outermost cylindrical surface 74 having the largest diameter in the primary piston 18, and has a constant width in the axial direction. The tapered surface 75b extends so as to increase in diameter from the end of the cylinder surface 75a on the cylinder opening side toward the cylinder opening side, and is connected to a portion on the cylinder opening side of the stepped portion 75 of the outer diameter surface 74. ing. The tapered surface 75c extends so as to increase in diameter from the edge of the cylindrical surface 75a on the cylinder bottom side toward the cylinder bottom side, and is connected to a portion on the cylinder bottom side of the stepped portion 75 of the outer diameter surface 74. ing.

  The cylindrical surface 75 a, the tapered surface 75 b, and the tapered surface 75 c are formed around the central axis of the primary piston 18 like the outer diameter surface 74. The port 76 that always communicates with the primary pressure chamber 85 is formed at a position that spans both the cylindrical surface 75a and the tapered surface 75b. In other words, the end of the cylinder bottom side is connected to the cylindrical surface 75a and the cylinder opening side. Are located on the tapered surface 75b.

  The piston seal 45 disposed in the circumferential groove 32 has a base portion 101, an inner peripheral lip portion 102, and an outer peripheral lip portion 103. The base 101 is disposed on the cylinder opening side (right side in FIG. 2) of the piston seal 45, and has an annular plate shape parallel to the axis orthogonal plane of the piston seal 45. The inner peripheral lip portion 102 has an annular cylindrical shape protruding from the inner peripheral end of the base portion 101 toward the cylinder bottom side (left side in FIG. 2) along the cylinder axial direction. The outer peripheral lip 103 has an annular cylindrical shape that protrudes from the outer peripheral end of the base 101 toward the cylinder bottom along the cylinder axial direction. The inner peripheral lip portion 102 has an annular cylindrical shape that projects from the base portion 101 toward the bottom of the cylinder along the cylinder axial direction beyond the outer peripheral lip portion 103.

  In the piston seal 45, the inner peripheral lip portion 102 is in sliding contact with the outer peripheral surface 18a including the cylindrical surface 75a, the tapered surface 75b, the tapered surface 75c, and the outer diameter surface 74 of the primary piston 18 moving in the cylinder axial direction. Thus, the outer peripheral lip 103 comes into contact with the groove bottom 88 of the peripheral groove 32 of the cylinder body 15.

  The piston seal 45 in a natural state before being incorporated in the master cylinder 11 will be described with reference to FIGS. 3 and 4. The base 101, the inner peripheral lip 102, and the outer peripheral lip 103 have the same central axis, and this central axis is the central axis of the piston seal 45. In the following description, the base 101 side in the axial direction is the back side, and the protruding sides of the inner peripheral lip portion 102 and the outer peripheral lip portion 103 in the axial direction are front sides.

  As shown in FIG. 4, the base 101 has a back surface 101 a and a curved surface 101 b in order from the radially inner side on the back side, and an intermediate surface 101 c between the front-side inner peripheral lip portion 102 and the outer peripheral lip portion 103. have. The back surface 101 a is located at the end on the most back side in the axial direction of the piston seal 45, and forms a plane parallel to the axial orthogonal surface of the piston seal 45. The back surface 101 a has a constant inner diameter, a constant outer diameter, and a constant width in the radial direction, and has an annular shape centering on the central axis of the piston seal 45.

  The curved surface 101b is inclined so that the outer side in the radial direction is located on the front side. The curved surface 101 b has an arc shape in which the cross-sectional shape including the central axis of the piston seal 45 has a center on the inner side of the base 101. The curved surface 101 b has a constant inner diameter and a constant outer diameter, a constant width in the axial direction and the radial direction, and has an annular shape centering on the central axis of the piston seal 45.

  The intermediate surface 101 c is a plane parallel to the axis orthogonal surface of the piston seal 45. The intermediate surface 101 c has a constant inner diameter, a constant outer diameter, and a constant width in the radial direction, and has an annular shape centering on the central axis of the piston seal 45.

  The inner peripheral lip portion 102 has a tapered cylindrical shape that has a slightly smaller diameter as it moves away from the base portion 101 in the axial direction. On the inner peripheral side of the base 101 and the inner peripheral lip portion 102, a reduced diameter inner peripheral surface 102a and an enlarged inner peripheral surface 102b are formed in this order from the back side in the axial direction. The reduced diameter inner peripheral surface 102a is formed across the base 101 and the inner peripheral lip 102, and is centered on the central axis of the piston seal 45 so as to become smaller (that is, reduce in diameter) as it is positioned on the front side. It extends in a tapered shape. The enlarged inner peripheral surface 102b is formed in the inner peripheral lip portion 102, and becomes larger in diameter from the front end edge in the axial direction of the reduced inner peripheral surface 102a (that is, the diameter is increased). ) And extending in a tapered shape with the central axis of the piston seal 45 as the center. R chamfering is applied to the boundary position between the reduced diameter inner peripheral surface 102 a of the inner peripheral lip 102 and the back surface 101 a of the base 101.

  Here, in the inner peripheral lip portion 102, a boundary portion between the reduced diameter inner peripheral surface 102a and the enlarged inner peripheral surface 102b is a minimum diameter portion 108 having the smallest inner diameter, and the minimum diameter portion 108 is a piston. The seal 45 has an annular shape around the central axis. The smallest diameter portion 108 is a portion having the smallest inner diameter in the piston seal 45 as well. Therefore, the minimum diameter portion 108 is a maximum tightening allowance that maximizes the allowance for the primary piston 18 in the piston seal 45.

  A reduced-diameter outer peripheral surface 102 c is formed on the outer peripheral side of the inner peripheral lip portion 102. The reduced diameter outer peripheral surface 102c extends in a tapered cylindrical shape centering on the central axis of the piston seal 45 so that the diameter is smaller (that is, the diameter is reduced) toward the front side in the axial direction. R chamfering is applied to the boundary position between the reduced diameter outer peripheral surface 102 c of the inner peripheral lip 102 and the intermediate surface 101 c of the base 101.

  A tip surface 102d, a tip curved surface 102e, an outer peripheral surface 102f, a concave curved surface 102g, a tapered surface 102h, and a convex curved surface 102i are formed in order from the radially inner side at the most front end of the inner peripheral lip portion 102. ing.

  The front end surface 102d extends outward in the radial direction from the edge on the surface side of the enlarged inner peripheral surface 102b in parallel with the axis orthogonal to the piston seal 45. The distal end surface 102 d has a constant inner diameter and a constant outer diameter, a constant width in the radial direction of the piston seal 45, and an annular shape centering on the central axis of the piston seal 45.

  The distal curved surface 102e extends so as to incline so that the radially outer side is located on the back side from the radially outer edge of the distal surface 102d. The distal curved surface 102 e has an arc shape in which the cross-sectional shape including the central axis of the piston seal 45 has a center on the inner side of the inner peripheral lip portion 102. The distal curved surface 102 e has a constant inner diameter and a constant outer diameter, a constant width in the axial direction and the radial direction, and has an annular shape centering on the central axis of the piston seal 45.

  The outer peripheral surface 102f extends from the edge on the back side of the tip curved surface 102e to the back side so that the diameter is slightly increased toward the back side. The outer peripheral surface 102 f has a constant inner diameter and a constant outer diameter, a constant width in the axial direction and the radial direction, and has a tapered shape centering on the central axis of the piston seal 45.

  The concave curved surface 102g has a shape that extends obliquely from the back edge of the outer peripheral surface 102f to the back side and radially outward, and then obliquely extends to the front side and radially outward. The concave curved surface 102g has an arc shape in which a cross-sectional shape including the central axis of the piston seal 45 has a center on the outer side of the inner peripheral lip portion 102, and an annular shape centering on the central axis of the piston seal 45. There is no.

  The tapered surface 102h extends from the radially outer edge of the concave curved surface 102g to the front side so as to increase in diameter toward the front side. The tapered surface 102 h has a constant inner diameter and a constant outer diameter, a constant width in the radial direction and the axial direction of the piston seal 45, and has a taper shape centered on the central axis of the piston seal 45.

  The convex curved surface 102i extends obliquely outward and radially outward from the front edge of the tapered surface 102h, and then obliquely extends outward and radially outward to the front end of the reduced diameter outer peripheral surface 102c. The shape is connected to the edge. The convex curved surface 102 i has an arc shape in which a cross-sectional shape including the central axis of the piston seal 45 has a center on the inner side of the inner peripheral lip portion 102, and an annular shape centering on the central axis of the piston seal 45. I am doing.

  In the axial direction of the piston seal 45, the position of the tip surface 102d serving as the tip of the inner peripheral lip 102 is the position of the front end of the convex curved surface 102i serving as the tip of the outer periphery. Rather than the front side, that is, the side opposite to the base 101.

  By forming the outer peripheral surface 102f, the concave curved surface 102g, and the tapered surface 102h, the piston seal 45 is provided with a concave portion 110 that is recessed on the back side in the axial direction over the entire circumference at the tip of the inner peripheral lip portion 102. Yes. The recess 110 has an annular shape centering on the central axis of the piston seal 45, and is opposite to the axial base portion 101 with respect to the minimum diameter portion 108 that is the maximum fastening margin of the inner peripheral lip portion 102. The whole is arranged within the range. In other words, the most concave position of the concave curved surface 102g on the most base 101 side in the axial direction of the recess 110 is opposite to the base 101 in the axial direction with respect to the minimum diameter portion 108, that is, on the inner peripheral lip 102. Located on the tip side.

  Further, the enlarged inner peripheral surface 102b, the front end surface 102d, the front end curved surface 102e, the outer peripheral surface 102f, and the concave curved surface 102g are formed, so that the piston seal 45 has the front end of the inner peripheral lip portion 102 over the entire circumference. An inner convex portion 111 protruding to the front side in the axial direction is provided. The inner convex portion 111 also has an annular shape centering on the central axis of the piston seal 45, and is within a range on the opposite side of the base portion 101 in the axial direction from the minimum diameter portion 108 of the inner peripheral lip portion 102. The whole is arranged.

  Further, by forming the concave curved surface 102g, the tapered surface 102h, the convex curved surface 102i and the reduced diameter outer peripheral surface 102c, the piston seal 45 has a front side in the axial direction over the entire circumference at the tip of the inner peripheral lip portion 102. The outer convex part 112 which protrudes in is provided. The outer convex portion 112 also has an annular shape centering on the central axis of the piston seal 45 and is within a range on the opposite side of the base portion 101 in the axial direction from the minimum diameter portion 108 of the inner peripheral lip portion 102. The whole is arranged. The inner convex portion 111 and the outer convex portion 112 are radially separated from each other at the tip of the inner peripheral lip portion 102, and the inner convex portion 111 protrudes larger in the axial direction than the outer convex portion 112.

  The outer peripheral lip 103 extends in a tapered cylindrical shape centering on the central axis of the piston seal 45 so that the outer diameter of the outer peripheral lip 103 becomes larger as a whole on the front side in the axial direction. On the inner peripheral side of the outer peripheral lip 103, an enlarged inner peripheral surface 103a is formed. The expanded inner peripheral surface 103a extends in a taper shape with the central axis of the piston seal 45 as the center so that the diameter increases toward the front side in the axial direction (that is, the diameter increases). An R chamfer is applied to the boundary position between the enlarged inner peripheral surface 103 a of the outer peripheral lip 103 and the intermediate surface 101 c of the base 101.

  On the outer peripheral side of the outer peripheral lip 103 and the base 101, the curved surface 101b, the enlarged outer peripheral surface 103b, and the enlarged outer peripheral surface 103c are formed in this order from the back side in the axial direction. The diameter-enlarged outer peripheral surface 103b is formed across the base 101 and the outer peripheral lip 103, and increases from the front edge of the curved surface 101b of the base 101 toward the front side in the axial direction (that is, the diameter increases). The piston seal 45 extends in a tapered shape with the central axis as the center.

  The diameter-enlarged outer peripheral surface 103c is formed on the outer peripheral lip 103, and the piston seal 45 is configured such that the diameter increases from the front edge of the diameter-enlarged outer peripheral surface 103b toward the front side in the axial direction (that is, the diameter increases). It extends in a taper shape centered on the central axis. The enlarged outer peripheral surface 103c has a smaller taper than the enlarged outer peripheral surface 103b. The front end surface 103d of the outer peripheral lip 103 is parallel to the axial orthogonal surface of the piston seal 45, has a constant inner diameter and a constant outer diameter, and a constant width in the radial direction of the piston seal 45. It has an annular shape centered on the center axis.

  Next, the piston seal 45 in a state of being incorporated in the circumferential groove 32 of the cylinder body 15 will be described with reference to FIGS. 2 and 5. As shown in FIG. 2, the piston seal 45 appropriately contacts the axial intermediate position of the cylindrical surface 75a of the step 75 of the primary piston 18, and the peripheral wall 89 on the cylinder opening side (right side in FIG. 2) of the peripheral groove 32. Is a non-braking state before the brake pedal is operated, and is a basic state, in which the circumferential groove 32 is separated from the circumferential wall 90 on the cylinder bottom side (left side in FIG. 2) of the circumferential groove 32.

  When in this basic state, the piston seal 45 is such that the base portion 101 is positioned closest to the cylinder opening side, and the back surface 101a of the base portion 101 abuts against the wall surface 89a of the peripheral wall 89. Further movement to the side will be restricted.

  Further, when the piston seal 45 is in the basic state, the inner peripheral lip 102 on the innermost peripheral side of the piston seal 45 contacts the cylindrical surface 75a of the stepped portion 75 of the outer peripheral surface 18a of the primary piston 18 at the inner peripheral portion. To do. At this time, the piston seal 45 has the reduced diameter inner peripheral surface 102a of the base 101 and the inner peripheral lip 102 shown in FIG. 4 and the reduced inner peripheral surface 102a side of the enlarged inner peripheral surface 102b shown in FIG. It contacts the cylindrical surface 75a and deforms into a cylindrical surface with a larger diameter than before the deformation following the cylindrical surface 75a. Therefore, the base 101 and the inner peripheral lip portion 102 come into contact with the cylindrical surface 75a with a tightening margin. At this time, the minimum diameter portion 108 shown in FIG. This is the maximum tightening allowance. Therefore, the most recessed position of the recessed portion 110 is located on the tip side of the inner peripheral lip portion 102 with respect to the maximum fastening allowance portion.

  Further, when in the basic state, the distal end surface 102d, the distal end curved surface 102e, the outer peripheral surface 102f, the concave curved surface 102g, the tapered surface 102h and the convex curved surface 102i on the distal end side of the inner peripheral lip portion 102, There is a gap in the cylinder axis direction between the peripheral walls 90 facing each other in the cylinder axis direction. In this state, the tip surface 102d, the tip curved surface 102e, and the outer peripheral surface 102f are aligned with the tapered surface 90b of the peripheral wall 90 in the cylinder radial direction, and the tapered surface 102h and the convex curved surface 102i are aligned with the wall surface 90a of the peripheral wall 90. The cylinder radial position matches. Therefore, the position of the tip of the inner convex portion 111 and the tapered surface 90b of the peripheral wall 90 in the cylinder radial direction match, and the position of the tip of the outer convex portion 112 and the wall surface 90a of the peripheral wall 90 match in the cylinder radial direction. In other words, the concave portion 110 of the inner peripheral lip portion 102 is aligned with the boundary portion 91 between the wall surface 90a and the tapered surface 90b in the cylinder radial direction. Specifically, the concave curved surface 102g of the concave portion 110 is aligned with the boundary portion 91 and the cylinder diameter. The direction is correct. In other words, the recess 110 is disposed so as to face the boundary portion 91 that is the starting point of the tapered surface 90b formed on the opening side of the circumferential groove 32 in the circumferential wall 90 on the cylinder bottom side of the circumferential groove 32.

  Further, when in the basic state, the piston seal 45 has a groove bottom portion of the circumferential groove 32 in which the outer peripheral lip 103 on the outermost peripheral side is on the side of the enlarged outer peripheral surface 103c and the enlarged outer peripheral surface 103c of the enlarged outer peripheral surface 103b. 88 abuts against the groove bottom surface 88a and is bent radially inward.

  When there is no input from the brake pedal (not shown) and the primary piston 18 is in a basic position (non-braking position) for opening the port 76 into the opening groove 47 as shown in FIG. The inner peripheral portion of the lip portion 102 and the base portion 101 is at the position of the cylindrical surface 75 a of the step portion 75 of the primary piston 18, and the inner peripheral portion of the base portion 101 overlaps a part of the port 76 with the position in the cylinder axial direction. It is like that.

  Then, when there is an input from the brake pedal side and the primary piston 18 moves to the cylinder bottom side (left side in FIG. 2), the primary piston 18 moves on the taper surface 75b of the stepped portion 75 on the cylinder opening side of the piston seal 45. The piston seal 45 is pressed against the cylinder bottom side in contact with the inner peripheral side of the base 101. Then, the piston seal 45 moves integrally with the primary piston 18. As a result, the piston seal 45 moves toward the peripheral wall 90 in the peripheral groove 32, and as shown in FIG. 5, after the back surface 101a of the base 101 is separated from the wall surface 89a of the peripheral wall 89 in the cylinder axial direction, The lip portion 102 contacts the peripheral wall 90. At this time, in the inner peripheral lip portion 102, the tip curved surface 102e of the inner convex portion 111 abuts on the tapered surface 90b of the peripheral wall 90, and the convex curved surface 102i of the outer convex portion 112 abuts on the wall surface 90a of the peripheral wall 90. In addition, they abut almost simultaneously. When the tip curved surface 102e contacts the tapered surface 90b and the convex curved surface 102i contacts the wall surface 90a in this way, the boundary portion 91 of the peripheral wall 90 enters the concave portion 110 of the inner peripheral lip portion 102.

  When the primary piston 18 further moves to the cylinder bottom side, as shown in FIG. 6, in the piston seal 45, the inner convex portion 111 is crushed by the tapered surface 90b, and the outer convex portion 112 is crushed by the wall surface 90a. It will be. At this time, the inner convex portion 111 is deformed while sliding on the tapered surface 90b inwardly in the cylinder radial direction due to the inclination of the tapered surface 90b. Further, since the outer convex portion 112 has a tapered surface 102h on the inner side and has a shape that is easily deformed radially outward, the outer convex portion 112 is deformed while sliding on the wall surface 90a outward in the cylinder radial direction. Then, in the inner peripheral lip portion 102, a force directed inward in the cylinder radial direction is generated by the inner convex portion 111, and a force directed outward in the cylinder radial direction is generated by the outer convex portion 112. The power will be balanced. Further, the inner peripheral lip portion 102 is crushed by the inner convex portion 111 and the outer convex portion 112, so that the frictional resistance against the peripheral wall 90 increases. In addition, the boundary portion 91 of the peripheral wall 90 enters between the inner convex portion 111 and the outer convex portion 112, and in order for the crushed inner convex portion 111 or the outer convex portion 112 to get over the boundary portion 91, a cylinder A large force is required in the radial direction, and thus overcoming of these is restricted. As described above, the posture of the inner peripheral lip portion 102 of the piston seal 45 is stabilized.

  When the elastic deformation of the inner convex portion 111 and the outer convex portion 112 of the inner peripheral lip portion 102 is finished, the piston seal 45 is stopped. In this state, when the primary piston 18 further moves to the cylinder bottom side, the piston seal 45 The 45 base portions 101 ride on the tapered surface 75 b of the primary piston 18 to a position beyond the port 76 and close the port 76. Then, the communication between the primary replenishment path 48 and the primary pressure chamber 85 is interrupted, and when the primary piston 18 moves further to the cylinder bottom side, the primary replenishment path 48 is basically at a pressure higher than the hydraulic pressure of the primary replenishment path 48 that is atmospheric pressure. The hydraulic pressure in the pressure chamber 85 becomes higher, and the brake fluid in the primary pressure chamber 85 is supplied from the primary discharge path 27 shown in FIG. 1 to the brake cylinder on the wheel side.

  Here, when the base 101 of the piston seal 45 rides on the tapered surface 75b of the primary piston 18 as described above, a force directed from the tapered surface 75b to the cylinder bottom side is applied to the inner peripheral side of the base 101 of the piston seal 45. As a result, the inner peripheral lip portion 102 moves to the piston seal 45 while moving upward in the cylinder radial direction with respect to the primary piston 18 and moves to the cylinder bottom side, and the outer peripheral lip portion 103 moves to the cylinder opening side. Rotational moment in the direction may occur. Further, depending on environmental conditions such as low temperature, even when the cylindrical surface 75a of the primary piston 18 moves relative to the base 101 of the piston seal 45, a similar rotational moment may occur.

  In contrast, in the present embodiment, as described above, the inner peripheral lip portion 102 is deformed by the inner convex portion 111 being in contact with the tapered surface 90b and the outer convex portion 112 is deformed by being in contact with the wall surface 90a. Since the boundary portion 91 is inserted between them, the tip end portion of the inner peripheral lip portion 102 struggles against the outward movement in the cylinder radial direction, and the rotation of the piston seal 45 is restricted. To do. As a result, the inner peripheral side of the base 101 of the piston seal 45 is prevented from moving to the cylinder bottom side. Therefore, the seal position of the piston seal 45 that closes the port 76 of the primary piston 18 is suppressed from shifting to the cylinder bottom side, and an increase in invalid stroke can be suppressed.

  In addition to the above, there is a possibility that the leading end of the inner peripheral lip portion 102 enters the gap between the cylinder body 15 and the primary piston 18, so-called entrainment may occur. Since the distal end portion of the portion 102 strides and resists movement inward in the cylinder radial direction, the occurrence of such entrainment can be suppressed.

  As described above, it is possible to minimize the opposite posture changes in both directions such as lifting and taking-in that may occur in the piston seal 45 when the primary piston 18 is pushed into the cylinder body 15. Moreover, since it is possible to cope with the shape of the piston seal 45 without increasing the number of parts, the performance can be improved at low cost.

  After the port 76 is closed, when the primary piston 18 moves further to the cylinder bottom side, the piston seal 45 rides on the outer diameter surface 74 with the base 101 getting over the tapered surface 75b. At the same time, the inner peripheral lip portion 102 rides on the tapered surface 75 b, and then the inner peripheral lip portion 102 rides on the outer diameter surface 74.

  In the master cylinder described in the above-mentioned Patent Document 1, the direction in which the inner circumference side moves to the cylinder bottom side and the outer circumference side moves to the cylinder opening side by connecting to the piston without sliding smoothly with respect to the piston. Rotational moment may occur. Then, the piston seal rotates in the direction in which the distal end side of the inner peripheral lip part moves away from the piston, the base part moves to the cylinder bottom side more than necessary, and the seal position where the piston seal closes the piston port shifts to the cylinder bottom side. There is a possibility that the invalid stroke which is the movement amount of the piston until the brake fluid pressure is generated increases.

  On the other hand, according to the master cylinder of the first embodiment, the movement of the primary piston 18 causes a rotational moment in the direction in which the inner peripheral side moves to the cylinder bottom side and the outer peripheral side moves to the cylinder opening side. Even so, as described above, the inner convex portion 111 inside the concave portion 110 of the inner peripheral lip portion 102 of the piston seal 45 contacts the tapered surface 90b, and the outer convex portion 112 outside the concave portion 110 contacts the wall surface 90a. Since the boundary portion 91 is inserted between the inner peripheral lip portion 102 and the inner peripheral lip portion 102, the inner peripheral lip portion 102 resists the movement outward in the cylinder radial direction. Movement to the cylinder bottom side is suppressed. As a result, the seal position of the piston seal 45 that closes the port 76 of the primary piston 18 is prevented from shifting to the bottom 13 side of the cylinder body 15, and the increase in invalid stroke can be suppressed.

  Further, in the master cylinder described in Patent Document 1 described above, for example, a tapered surface is formed on the opening side of the circumferential groove, and the tip of the inner circumferential lip portion is brought into contact with the tapered surface, whereby the piston seal 45 It is also possible to suppress the increase in invalid strokes by regulating the rotation. However, simply contacting the tip of the inner circumferential lip portion with the tapered surface will guide the inner circumferential lip portion into the gap between the inner circumferential portion of the cylinder body and the piston. There is a possibility of causing so-called biting.

  In contrast, according to the master cylinder of the first embodiment, as described above, the inner convex portion 111 of the inner peripheral lip portion 102 of the piston seal 45 abuts on the tapered surface 90b, and the outer convex portion 112 on the wall surface 90a. Since the abutting portion 91 is brought into contact with each other, the inner peripheral lip portion 102 resists against the inward movement of the cylinder in the radial direction of the cylinder. 15 is prevented from being guided in the gap between the inner peripheral portion of 15 and the primary piston 18. Therefore, the occurrence of biting can be suppressed.

  Further, since the concave portion 110 is disposed so as to face the boundary portion 91 that is the starting point of the tapered surface 90b of the peripheral wall 90 on the cylinder bottom side of the peripheral groove 32, the concave portion 110 of the inner peripheral lip portion 102 of the piston seal 45 is arranged. The inner convex portion 111 on the inner side can be brought into contact with the tapered surface 90b, the outer convex portion 112 on the outer side of the concave portion 110 can be brought into contact with the wall surface 90a, and the boundary portion 91 can be inserted therebetween. Therefore, the inner peripheral lip portion 102 is surely strung and resists movement in both the inner and outer directions in the cylinder radial direction.

  Moreover, since the recessed part 110 is formed in the range on the opposite side to the base part 101 rather than the minimum diameter part 108 which is the maximum fastening margin part of the inner peripheral lip part 102, the rigidity reduction of the inner peripheral lip part 102 is suppressed. can do.

  In the above embodiment, the primary-side seal structure portion SP has been described in detail as an example, but the secondary-side seal structure portion SS has the same structure, and thus the same effect can be achieved. Similar changes are possible.

  The above embodiment is provided with a bottomed cylindrical cylinder body having a brake fluid discharge path and a replenishment path communicating with the reservoir, and is movably disposed in the cylinder body. A piston that forms a pressure chamber that supplies hydraulic pressure to the discharge path, and an inner circumference that is provided in a circumferential groove formed in the cylinder body and that is in sliding contact with the piston to seal between the supply path and the pressure chamber A piston seal that protrudes from the outer peripheral side of the base, and an annular base, an inner peripheral lip that protrudes from the inner peripheral side of the base and slidably contacts the outer peripheral surface of the piston, A master cylinder comprising an outer peripheral lip portion that abuts on the circumferential groove of the cylinder body, wherein a concave portion is provided over the entire circumference at the tip of the inner peripheral lip portion. Thereby, both sides of the concave portion abut against the peripheral wall of the peripheral groove on the bottom side of the cylinder body, so that a resistance force can be generated against the movement of the tip end portion of the inner peripheral lip portion in the radial direction of the cylinder body. Therefore, an increase in invalid stroke can be suppressed.

  In addition, a tapered surface is formed on the opening side of the circumferential groove on the circumferential wall on the bottom side of the cylinder body of the circumferential groove, and the recessed portion is disposed so as to face the starting point of the tapered surface. Also, the inner portion can be brought into contact with the tapered surface. Therefore, it is possible to generate a resistance force against the radially outward movement of the cylinder main body at the tip end portion of the inner peripheral lip portion. Therefore, an increase in invalid stroke can be further suppressed.

  Moreover, since the said recessed part is formed in the range on the opposite side to the said base part rather than the largest fastening allowance part of the said inner peripheral lip part, the rigidity fall of an inner peripheral lip part can be suppressed.

11 Master cylinder 12 Reservoir 13 Bottom 15 Cylinder body 16 Opening 18 Primary piston (piston)
18a Outer peripheral surface 19 Secondary piston (piston)
26 Secondary discharge path (discharge path)
27 Primary discharge path (discharge path)
30, 32 Circumferential groove 35, 45 Piston seal 38 Secondary supply path (supply path)
48 Primary supply path (supply path)
68 Secondary pressure chamber (pressure chamber)
85 Primary pressure chamber (pressure chamber)
90 Perimeter wall (perimeter wall on the bottom side of the cylinder body)
90b Tapered surface 91 Boundary (starting point)
101 Base part 102 Inner peripheral lip part 103 Outer peripheral lip part 108 Minimum diameter part (maximum fastening allowance part)
110 recess

Claims (3)

A bottomed cylindrical cylinder body having a brake fluid discharge path and a supply path communicating with the reservoir;
A piston that is movably disposed within the cylinder body, and that forms a pressure chamber between which the fluid pressure is supplied to the discharge passage;
A piston seal provided in a circumferential groove formed in the cylinder body and having an inner circumference slidingly contact the piston and sealing between the supply path and the pressure chamber;
The piston seal is
An annular base,
An inner peripheral lip projecting from the inner peripheral side of the base and slidingly contacting the outer peripheral surface of the piston;
An outer peripheral lip that protrudes from the outer peripheral side of the base and contacts the peripheral groove of the cylinder body;
In a master cylinder comprising
A master cylinder characterized in that a concave portion is provided at the tip of the inner peripheral lip portion over the entire circumference. A tapered surface is formed on the opening side of the circumferential groove in the circumferential wall of the circumferential side of the cylinder body on the bottom side of the circumferential groove,
The master cylinder according to claim 1, wherein the concave portion is disposed so as to face a starting point of the tapered surface.   3. The master cylinder according to claim 1, wherein the concave portion is formed within a range opposite to the base portion with respect to a maximum fastening allowance portion of the inner peripheral lip portion.

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