JP2015067176A - Master cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve suction performance from an atmospheric pressure chamber to a pressure chamber of brake fluid by a master cylinder.SOLUTION: A master cylinder comprises: a cylinder body which has a bottomed-cylindrical cylinder inner hole; a piston 21 which is assembled to the cylinder inner hole, forms a pressure chamber Rp1 in the cylinder body, and forms an atmospheric pressure chamber Ra1; and a piston seal ring 31 which is assembled to a seal groove 11a of the cylinder inner hole, can slide, contact an outer periphery of the piston 21 at an inner periphery, and can shield between the atmospheric pressure chamber Ra1 and the pressure chamber Rp1 by seal force to be obtained by cooperation with the seal groove 11a when the pressure chamber Rp1 becomes a positive pressure state. Seal structure S1 which is constituted of the seal groove 11a and the piston seal ring 31 is provided with a seal force losing part S1a which loses the seal force when the pressure chamber Rp1 becomes a negative pressure state, and the piston seal ring 31 moves from an end on a side of the atmospheric pressure chamber to a side of the pressure chamber of the seal groove 11a.

Description

  The present invention relates to a master cylinder for supplying brake fluid to a brake device in a vehicle.

  As one of the master cylinders of this type, there is provided a brake fluid supply path and a supply path communicating with the reservoir, and an annular seal groove interposed between the supply path and the supply path. A cylinder body having a bottomed cylindrical cylinder bore communicating with the passage, and the cylinder bore of the cylinder body is movable and liquid-tightly assembled in the cylinder bore direction, and the supply passage in the cylinder body And a piston that forms a pressure chamber that communicates with the replenishment passage and an atmospheric pressure chamber that communicates with the replenishment passage, and the piston that is assembled to the seal groove formed in the cylinder bore of the cylinder body at the inner periphery. When the pressure chamber is in a positive pressure state, the seal between the atmospheric pressure chamber and the pressure chamber is blocked by a sealing force obtained by cooperation with the seal groove. Have their ability piston sealing ring, for example, described in Patent Document 1 below.

JP 2012-210905 A

  In the master cylinder described in Patent Document 1, as the piston seal ring, an inner lip portion that is slidably contacted with an outer periphery of the piston, an outer lip portion that is engageable / detachable with an outer peripheral wall of the seal groove, A cup-shaped piston seal ring that is connected to the inner lip portion and the outer lip portion and has a base portion that can be engaged and disengaged from an end wall on the atmospheric pressure chamber side of the seal groove, and is restricted from moving in the axial direction. It has been adopted.

  In such a master cylinder, when the pressure chamber is in a positive pressure state, a sealing force obtained by cooperation of the piston seal ring with the seal groove (specifically, an inner lip portion in the seal groove) Is joined to the outer periphery of the piston, the outer lip part is joined to the outer peripheral wall of the seal groove, and the base part is joined to the end wall on the atmospheric pressure chamber side of the seal groove) The communication between the pressure chambers is configured to be cut off.

  In the master cylinder described in Patent Document 1, when the pressure chamber is in a negative pressure state, the outer lip portion is elastically deformed so as to be separated from the outer peripheral wall of the seal groove, and the base portion is the seal groove. The pressure chamber and the atmospheric pressure chamber are elastically deformed away from the end wall on the atmospheric pressure chamber side, and the pressure chamber and the atmospheric pressure chamber communicate with each other through a gap between the seal groove and the piston seal ring. In the master cylinder described above, the shape of the piston seal ring is set so that the above-described sealing force can be obtained even when the pressure chamber is in the atmospheric pressure state.

  For this reason, in the master cylinder described in Patent Document 1, when the negative pressure obtained in the pressure chamber is not sufficient, the outer lip portion and the base portion of the piston seal ring are not sufficiently elastically deformed, The pressure chamber and the atmospheric pressure chamber may not communicate with each other through the gap between the seal groove and the piston seal ring (brake fluid is not sucked into the pressure chamber). Further, in the master cylinder described in Patent Document 1, there is a case where the thickness of the connecting portion between the inner lip portion and the base portion cannot be sufficiently secured due to the configuration of the piston seal ring (because it is cup-shaped). The strength and durability of the same part may not be sufficiently secured.

The present invention has been made in view of the above-described actual situation,
A bottomed cylindrical cylinder having a brake fluid supply path and a supply path communicating with the reservoir, and having an annular seal groove interposed between the supply path and the supply path, and communicating with the supply path and the supply path A cylinder body having an inner hole;
An atmospheric pressure chamber that is movable and fluid-tightly assembled in the cylinder bore of the cylinder body to form a pressure chamber that communicates with the supply passage and communicates with the supply passage. A piston to form a
The seal groove is assembled with the seal groove formed in the cylinder inner hole of the cylinder body and can be slidably contacted with the outer periphery of the piston at the inner periphery. A piston seal ring capable of blocking between the atmospheric pressure chamber and the pressure chamber with a sealing force obtained by the cooperation of
In the seal structure constituted by the seal groove and the piston seal ring, when the pressure chamber is in a negative pressure state and the piston seal ring moves from the atmospheric chamber side end of the seal groove to the pressure chamber side. There is a feature in the master cylinder provided with a sealing force loss part for losing the sealing force.

In carrying out the present invention, the seal structure includes:
A diameter-enlarged portion that is formed in a pressure chamber side portion of the seal groove and allows separation from the outer periphery of the piston due to an increase in diameter of the piston seal ring, and is formed in an atmospheric pressure chamber side portion of the seal groove. While having a reduced diameter portion for reducing the diameter of the piston seal ring and joining the outer periphery of the piston,
It is assembled in the seal groove so as to be movable in the axial direction, the diameter is reduced in the reduced diameter portion, the sealing force is exerted, the diameter is increased in the enlarged diameter portion, and the sealing force is lost. It has a piston seal ring with a rectangular cross section,
It is also possible that the sealing force loss part is constituted by the enlarged diameter part and the piston seal ring.
In this case, a protrusion for assisting the diameter expansion of the piston seal ring may be provided in the diameter expansion portion of the seal groove.

In carrying out the present invention, the sealing force loss portion is
A communication groove formed in the end portion of the pressure chamber from the axial intermediate portion of the outer peripheral wall in the seal groove and extending in the axial direction, and a pressure chamber of the piston seal ring formed in the end wall of the pressure chamber in the seal groove With a protrusion that prevents contact with the side end wall,
It is assembled in the seal groove so as to be movable in the axial direction, exhibits the sealing force in the state accommodated in the atmospheric pressure chamber side, and in the state accommodated in the pressure chamber side It is also possible to provide a piston seal ring with a rectangular cross section that loses the sealing force.
In this case, in place of the protrusion, a communication groove that is formed on the pressure chamber side end wall of the seal groove and extends in the radial direction and connects the pressure chamber side end of the communication groove and the pressure chamber is employed. It is also possible.

In carrying out the present invention, the seal structure is
A seal groove for accommodating the piston seal ring movably in the axial direction;
A first communication groove formed at an end portion of the piston seal ring on the pressure chamber side, and a second communication groove formed on an outer peripheral portion of the piston seal ring and communicating with the first communication groove; Piston seal with a rectangular cross section that exhibits the sealing force in a state accommodated in the atmospheric pressure chamber side portion of the seal groove and loses the sealing force in a state accommodated in the pressure chamber side portion of the seal groove It is also possible to have a ring.

  In the master cylinder of the present invention described above, since the sealing force loss portion is provided in the sealing structure described above, the pressure chamber is in a negative pressure state, and the piston seal ring extends from the end portion on the atmosphere chamber side of the seal groove. When moved to the pressure chamber side, the sealing force can be lost. By the way, the force for moving the piston seal ring from the atmospheric chamber side end of the seal groove to the pressure chamber side can be reduced by reducing the sliding resistance acting on the piston seal ring. For this reason, even when the negative pressure obtained in the pressure chamber is not sufficient, the sealing force can be lost, and the pressure chamber and the atmospheric pressure chamber can be accurately communicated with each other. It is possible to accurately inhale the pressure chamber (improving the suction performance of the brake fluid from the atmospheric pressure chamber to the pressure chamber).

  Further, when a piston seal ring having a rectangular cross section is used as the piston seal ring in the practice of the present invention, the piston seal ring can be sufficiently thick, and the strength and durability of the piston seal ring can be ensured. It is possible to ensure enough.

It is principal part sectional drawing which shows one Embodiment of the master cylinder by this invention. It is the enlarged view which showed the relationship between the piston (primary piston) and the piston seal ring of the right side in embodiment (1st Embodiment) shown in FIG. It is operation | movement explanatory drawing when a pressure chamber becomes a negative pressure in FIG. It is the enlarged view which showed the relationship between the piston (primary piston) and piston seal ring of the right side in 2nd Embodiment. FIG. 5 is an operation explanatory diagram when the pressure chamber becomes negative in FIG. 4. It is the enlarged view which showed the relationship between the piston (primary piston) and piston seal ring of the right side in 3rd Embodiment. FIG. 7 is an operation explanatory diagram when the pressure chamber becomes negative in FIG. 6.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of a master cylinder MC according to the present invention. The master cylinder MC includes a cylinder body 10 assembled to a brake booster (not shown) and a piston assembled to the cylinder body 10. 21 and 22, piston seal rings 31, 32 and 41, 42, and return mechanisms 50, 60.

  The cylinder body 10 has a bottomed cylindrical cylinder inner hole 11 extending in the axial direction from the closed front end (left end in FIG. 1) to the open rear end (right end in FIG. 1), and accommodates brake fluid. It has a pair of front and rear connection ports 12 and 13 connected to the reservoir R. The cylinder body 10 has communication holes 14 and 15 that allow the cylinder inner hole 11 and the connection ports 12 and 13 to communicate with each other, and four wheel cylinders (not shown) via a hydraulic pressure control device (not shown). A pair of front and rear outlet ports 16 and 17 connected to each other. The communication holes 14 and 15 are part of the supply path of the present invention, and the outlet ports 16 and 17 are part of the supply path of the present invention.

  The rear piston (primary piston) 21 is pushed forward by a brake operation by the driver, and is fluid-tight and axially connected to the rear portion of the cylinder bore 11 via piston seal rings 31 and 41. The primary hydraulic pressure chamber Rp1 is defined on the front side (closed end side), and the atmospheric pressure liquid chamber (atmospheric pressure chamber) Ra1 is formed between the piston seal rings 31 and 41. The rear end protrudes out of the cylinder body 10. A plurality of piston ports 21 a that open to the outer peripheral wall surface of the piston 21 and communicate with the primary hydraulic chamber Rp <b> 1 at the inner end are formed at the front end of the piston 21. Plural piston ports 21a are formed at equal intervals in the circumferential direction. The primary hydraulic pressure chamber Rp1 communicates with the rear outlet port 17 and is the pressure chamber of the present invention.

  The primary hydraulic chamber Rp1 is always in communication with the rear outlet port 17 and is at atmospheric pressure through a piston port 21a provided in the rear piston 21 in the state shown in FIG. 1 (the non-operating state in which the piston 21 is in the initial position). 1 is a hydraulic chamber communicating with the liquid chamber Ra1, the rear piston 21 is moved forward by a required amount from the non-actuated position of FIG. 1, and the communication between the piston port 21a and the atmospheric pressure liquid chamber Ra1 is caused by By blocking, the communication with the atmospheric pressure liquid chamber Ra1 is blocked and sealed. The atmospheric pressure liquid chamber Ra <b> 1 is a hydraulic pressure chamber that always communicates with the rear connection port 13 through the rear communication hole 15, and always communicates with the reservoir R. For this reason, the atmospheric pressure liquid chamber Ra1, the rear communication hole 15, the rear connection port 13 and the like constitute the supply path of the present invention.

  The piston seal ring 31 is assembled to the annular seal groove 11a formed in the cylinder inner hole 11 of the cylinder body 10 on the outer periphery of the piston 21 so as to be movable in the axial direction, as shown in FIGS. In the closed state (in the atmosphere chamber side end portion of the seal groove 11a), the inner periphery is in sliding contact with the outer periphery of the piston 21, the outer periphery is in sliding contact with the outer peripheral wall of the seal groove 11a, and the right end in the drawing is the seal groove 11a. The primary hydraulic pressure chamber Rp1 and the atmospheric pressure liquid chamber Ra1 can be shut off at the outer periphery of the piston 21. The primary hydraulic chamber Rp1 is always in communication with the inner periphery of the front end of the seal groove 11a. The atmospheric pressure liquid chamber Ra1 is always in communication with the inner periphery of the rear end of the seal groove 11a.

  The piston seal ring 41 is assembled in an annular seal groove 11b formed in the cylinder inner hole 11 of the cylinder body 10 on the outer periphery of the piston 21 (a portion on the opening side of the seal groove 11a). The piston 21 is slidably in contact with the outer periphery of the piston 21, and the atmospheric pressure liquid chamber Ra <b> 1 and the atmosphere can be shut off on the outer periphery of the piston 21. As is well known, the piston seal ring 41 has a lip that prevents liquid leakage from the atmospheric pressure liquid chamber Ra1 to the atmosphere.

  The front piston (secondary piston) 22 is pushed forward in accordance with the forward movement of the rear piston 21, and liquid is passed through the piston seal rings 32, 42 to the front portion of the cylinder inner hole 11. It is assembled densely and movably in the axial direction of the cylinder. A secondary hydraulic pressure chamber Rp2 is defined forward (closed end side), and an atmospheric pressure liquid chamber Ra2 is formed between the piston seal rings 32 and 42. ing. A plurality of piston ports 22 a that open to the outer peripheral wall surface of the piston 22 and communicate with the secondary hydraulic pressure chamber Rp <b> 2 at the inner end are formed at the front end portion of the piston 22. Plural piston ports 22a are formed at equal intervals in the circumferential direction.

  The secondary hydraulic pressure chamber Rp2 is always in communication with the front outlet port 16 and is at atmospheric pressure through a piston port 22a provided in the front piston 22 in the state shown in FIG. 1 (the non-operating state in which the piston 22 is in the initial position). The fluid pressure chamber communicates with the fluid chamber Ra2, and the piston 22 on the front side moves forward by a required amount from the non-operating position in FIG. By being cut off, the communication with the atmospheric pressure liquid chamber Ra2 is cut off and sealed. The atmospheric pressure liquid chamber Ra <b> 2 is a hydraulic pressure chamber that always communicates with the front connection port 12 through the front communication hole 14, and always communicates with the reservoir R. For this reason, the atmospheric pressure liquid chamber Ra2, the front communication hole 14, the front connection port 12 and the like constitute the supply path of the present invention.

  The piston seal ring 32 is assembled to the annular seal groove 11c formed in the cylinder inner hole 11 of the cylinder body 10 on the outer periphery of the piston 22 so as to be movable in the axial direction. The outer periphery of the piston 22 is in sliding contact with the outer peripheral wall of the seal groove 11c, and is joined to the end wall of the seal groove 11c at the atmospheric pressure chamber side at the right end of the figure. It is possible to shut off from the atmospheric pressure liquid chamber Ra2. The secondary hydraulic pressure chamber Rp2 is always in communication with the inner periphery of the front end of the seal groove 11c. The atmospheric pressure liquid chamber Ra2 is always in communication with the inner periphery of the rear end of the seal groove 11c.

  The piston seal ring 42 is assembled in an annular seal groove 11d formed in the cylinder inner hole 11 of the cylinder body 10 on the outer periphery of the piston 22, and is in sliding contact with the outer periphery of the piston 22 on the inner periphery. Between the atmospheric pressure liquid chamber Ra2 and the primary hydraulic pressure chamber Rp1 can be cut off at the outer periphery of the piston 22. As is well known, the piston seal ring 42 has a lip that prevents liquid leakage from the primary hydraulic chamber Rp1 to the atmospheric pressure liquid chamber Ra2.

  The rear return mechanism 50 is for returning the rear piston 21 to the non-operation position (initial position) shown in FIG. 1 and is provided in the primary hydraulic pressure chamber Rp1, and includes a retainer 51, a stopper 52, A rod 53 and a spring 54 are provided. The retainer 51 is assembled to the rear piston 21. The stopper 52 is engaged with the front piston 31. The rod 53 is fixed to the retainer 51 and is assembled so as to be movable a predetermined amount forward from the illustrated position with respect to the stopper 52. The spring 54 is interposed between the retainer 51 and the stopper 52, the set load in the state of FIG. 1 is set to f1, and the rear piston 21 is urged rearward.

  The front return mechanism 60 is for returning the front piston 22 to the inoperative position shown in FIG. 1, and is provided in the secondary hydraulic pressure chamber Rp2, and includes a retainer 61, a stopper 62, a rod 63, and a spring. 64. The retainer 61 is assembled to the front piston 22. The stopper 62 is engaged with the bottom of the cylinder body 10. The rod 63 is fixed to the retainer 61 and is assembled so as to be movable a predetermined amount forward from the illustrated position with respect to the stopper 62. The spring 64 is interposed between the retainer 61 and the stopper 62. The set load in the state of FIG. 1 is set to f2 (f2 <f1), and the front piston 22 is attached to the rear. It is fast.

  By the way, in this 1st Embodiment, seal force loss | disconnection part S1a, S2a is provided in each seal structure S1, S2 comprised by each seal groove 11a, 11c and each piston seal ring 31,32. Each of the seal structures S1 and S2 is formed in the same shape, and as shown in an enlarged manner in FIGS. 2 and 3 with the seal structure S1 at the rear as an example, the pressure chamber side portion (the left half in the figure) of the seal groove 11a. ) And a reduced diameter portion 11a2 formed in the atmosphere chamber side portion (the right half in the figure) of the seal groove 11a, and a piston seal ring 31 having a rectangular cross section, The enlarged-diameter portion 11a1 and the piston seal ring 31 constitute a sealing force loss portion S1a.

  The enlarged diameter portion 11a1 is formed by a taper shape in which the left half of the peripheral wall in the seal groove 11a is enlarged in the forward direction, and as shown in FIG. 3, the enlarged diameter of the piston seal ring 31 is increased. Is configured to allow separation from the outer periphery of the piston 21. The reduced diameter portion 11a2 is formed by making the right half of the peripheral wall of the seal groove 11a shown in the figure into a cylindrical shape, and reduces the piston seal ring 31 from the free state (for example, the shape shown in FIG. 3) by a predetermined amount. As shown in FIG. 2, the piston 21 is configured to be joined to the outer periphery.

  The piston seal ring 31 is assembled in the seal groove 11a so as to be movable in the axial direction. The piston seal ring 31 is reduced in diameter in the reduced diameter portion 11a2 of the seal groove 11a to exert a sealing force, and the seal groove 11a is expanded. The diameter is increased in the diameter portion 11a1 and the sealing force is lost. The axial movement of the piston seal ring 31 is mainly caused by the differential pressure between the primary hydraulic chamber (pressure chamber) Rp1 and the atmospheric pressure chamber Ra1, and for example, the primary hydraulic chamber (pressure chamber) Rp1 When a negative pressure state is reached, the piston seal ring 31 moves from the atmospheric chamber side end (position in FIG. 2) of the seal groove 11a to the pressure chamber side (position in FIG. 3), and the primary hydraulic chamber (pressure chamber). When Rp1 is in a positive pressure state, the piston seal ring 31 moves from the pressure chamber side (position in FIG. 3) of the seal groove 11a to the atmospheric chamber side end (position in FIG. 2).

  For this reason, in the first embodiment, the hydraulic chambers (pressure chambers) Rp1 and Rp2 are in a negative pressure state, and the piston seal rings 31 and 32 are connected to the end portions of the seal grooves 11a and 11c from the atmosphere chamber side. When moved to the pressure chamber side, each sealing force can be lost (set to zero). By the way, the force when moving the piston seal rings 31 and 32 from the atmospheric chamber side ends of the seal grooves 11a and 11c to the pressure chamber side reduces the sliding resistance acting on the piston seal rings 31 and 32. It is possible to make it small. For this reason, even when the negative pressure obtained in each of the hydraulic chambers (pressure chambers) Rp1 and Rp2 is not sufficient, each of the sealing chambers is lost, and each of the hydraulic chambers (pressure chambers) Rp1 and Rp2 and each of the atmospheric pressures. As illustrated in FIG. 3, the liquid chambers Ra1 and Ra2 can be accurately communicated with each other through a gap formed between the inner periphery of each piston seal ring 31 and 32 and the outer periphery of each piston 21 and 22. Can be accurately sucked from the atmospheric pressure liquid chambers Ra1 and Ra2 into the hydraulic pressure chambers (pressure chambers) Rp1 and Rp2 (improvement of the suction performance of the brake fluid from the atmospheric pressure chamber to the pressure chamber). .

  In the first embodiment, since the piston seal rings 31 and 32 having a rectangular cross section are used as the piston seal rings, the thickness of the piston seal rings 31 and 32 can be sufficiently secured. Thus, it is possible to sufficiently ensure the strength and durability of the piston seal rings 31 and 32.

  Further, in the first embodiment, as shown in FIGS. 2 and 3, a protrusion 11a3 for assisting the diameter expansion of the piston seal ring 31 is provided in the diameter expansion portion 11a1 of the seal groove 11a. Yes. The protrusions 11a3 are formed in a wedge shape, and a plurality of protrusions 11a3 are provided at equal intervals in the circumferential direction. For this reason, even when the piston seal ring 31 is attached to the outer periphery of the piston 21 (for example, when the diameter expansion due to the elastic return of the piston seal ring 31 is hindered), the piston seal ring 31 is accurately positioned by the protrusion 11a3. It is possible to increase the diameter. It is also possible to carry out without providing the protrusion 11a3.

  In the first embodiment described above, the entire left half of the peripheral wall in the seal groove 11a is tapered so that the diameter increases toward the front, thereby forming the enlarged diameter portion 11a2 of the sealing force loss portion S1a. However, the illustrated left half of the peripheral wall of the seal groove 11a is connected to the reduced diameter portion 11a2 at the rear end and has a tapered hole portion that expands toward the front, and is connected to the large diameter portion of the tapered hole portion and directed forward. It is also possible to form an enlarged diameter portion 11a2 of the sealing force loss portion S1a.

  Further, in the first embodiment described above, the seal structures S1 and S2 for sealing between the hydraulic chambers (pressure chambers) Rp1 and Rp2 and the atmospheric pressure liquid chambers Ra1 and Ra2 are illustrated in FIGS. 2 and 3. The seal structure S1 having the configuration is employed. Instead of the seal structure S1, the seal structure S1 of the second embodiment illustrated in FIGS. 4 and 5 or the seal structure of the third embodiment illustrated in FIGS. 6 and 7 is used. It is also possible to adopt S1.

  The seal structure S1 of the second embodiment illustrated in FIGS. 4 and 5 includes a seal groove 11a and a piston seal ring 31 having a rectangular cross section. The seal groove 11a includes a communication groove 11a4 and a protrusion 11a5. The communication groove 11a4 is formed in a linear shape extending from the axial direction intermediate portion of the outer peripheral wall of the seal groove 11a to the pressure chamber side end portion and extending in the axial direction (it can be implemented in a shape other than a straight shape (for example, a curved shape)). A plurality of communication grooves are provided at equal intervals in the circumferential direction (the number can be set as appropriate, and at least one can be implemented). A plurality of protrusions 11a5 are formed at equal intervals in the circumferential direction on the pressure chamber side end wall in the seal groove 11a (the number can be set as appropriate, and at least one can be implemented), and the piston seal ring It functions to prevent the contact of 31 with the pressure chamber side end wall. The piston seal ring 31 having a rectangular cross section illustrated in FIGS. 4 and 5 is assembled in the seal groove 11a so as to be movable in the axial direction, and is accommodated on the atmospheric pressure chamber side as shown in FIG. In the state where the seal groove 11a cooperates with the seal groove 11a and exerts a sealing force, the communication groove 11a4 and the protrusion 11a5 provided in the seal groove 11a are accommodated on the pressure chamber side as shown in FIG. The sealing force is lost in cooperation with the above. In the seal structure S1 according to the second embodiment, the communication groove 11a4, the protrusion 11a5, and the like provided in the seal groove 11a and the piston seal ring 31 in the state accommodated in the pressure chamber side portion of the seal groove 11a are used. S1a is configured.

  In the seal structure S1 of the second embodiment illustrated in FIGS. 4 and 5, the communication groove 11a4 and the protrusion 11a5 are provided in the seal groove 11a. However, instead of the protrusion 11a5, the pressure groove side in the seal groove 11a is provided. A straight line formed on the end wall and extending in the radial direction to communicate the pressure chamber side end of the communication groove 11a4 and the hydraulic pressure chamber (pressure chamber) Rp1 (can be implemented in a shape other than a straight shape (for example, a curved shape)) It is also possible to employ the communication groove 11a6 (see phantom lines in FIGS. 4 and 5). Similar to the communication groove 11a4, a plurality of communication grooves 11a6 are provided at equal intervals in the circumferential direction (the number can be set as appropriate, and at least one can be implemented).

  The seal structure S1 of the third embodiment illustrated in FIGS. 6 and 7 includes a seal groove 11a and a piston seal ring 31 having a rectangular cross section. The seal groove 11a accommodates the piston seal ring 31 so as to be movable in the axial direction. The piston seal ring 31 is formed in a linear communication groove 31a formed at an end portion on the pressure chamber side (can also be implemented in a shape other than a straight shape (for example, a curved shape)) and an outer peripheral portion thereof. And a second communication groove 31b having a linear shape (can be implemented in a shape other than a straight shape (for example, a curved shape)) communicating with the first communication groove 31a. The sealing force is exerted in the accommodated state (the state of FIG. 6), and the sealing force is lost in the accommodated state (for example, the state of FIG. 7) in the pressure chamber side portion of the seal groove 11a. It is configured. Note that a plurality of first communication grooves 31a and second communication grooves 31b are provided at equal intervals in the circumferential direction (the number can be set as appropriate, and at least one can be implemented). In the seal structure S1 of the third embodiment, the first communication groove 31a, the second communication groove 31b, and the seal groove 11a provided in the piston seal ring 31 accommodated in the pressure chamber side portion of the seal groove 11a. A sealing force loss portion S1a is configured.

MC: Master cylinder, 10: Cylinder body, 11: Cylinder bore, 11a, 11c ... Seal groove, 16, 17 ... Outlet port (supply path), Ra1, 15, 13 ... Atmospheric pressure liquid chamber (atmospheric pressure chamber), Rear communication hole, rear connection port (supply path), Ra2, 14, 12 ... atmospheric pressure liquid chamber (atmospheric pressure chamber), front communication hole, front connection port (supply path), 21, 22 ... piston, 21a, 22a ... piston port, 31, 32 ... piston seal ring, Rp1, Rp2 ... hydraulic chamber (pressure chamber), R ... reservoir, S1, S2 ... seal structure, S1a, S2a ... seal power loss part

Claims (6)

A bottomed cylindrical cylinder having a brake fluid supply path and a supply path communicating with the reservoir, and having an annular seal groove interposed between the supply path and the supply path, and communicating with the supply path and the supply path A cylinder body having an inner hole;
An atmospheric pressure chamber that is movable and fluid-tightly assembled in the cylinder bore of the cylinder body to form a pressure chamber that communicates with the supply passage and communicates with the supply passage. A piston to form a
The seal groove is assembled with the seal groove formed in the cylinder inner hole of the cylinder body and can be slidably contacted with the outer periphery of the piston at the inner periphery. A piston seal ring capable of blocking between the atmospheric pressure chamber and the pressure chamber with a sealing force obtained by the cooperation of
In the seal structure constituted by the seal groove and the piston seal ring, when the pressure chamber is in a negative pressure state and the piston seal ring moves from the atmospheric chamber side end of the seal groove to the pressure chamber side. A master cylinder provided with a sealing force loss portion for losing the sealing force. The master cylinder according to claim 1, wherein the seal structure includes:
A diameter-enlarged portion that is formed in a pressure chamber side portion of the seal groove and allows separation from the outer periphery of the piston due to an increase in diameter of the piston seal ring, and is formed in an atmospheric pressure chamber side portion of the seal groove. While having a reduced diameter portion for reducing the diameter of the piston seal ring and joining the outer periphery of the piston,
It is assembled in the seal groove so as to be movable in the axial direction, the diameter is reduced in the reduced diameter portion, the sealing force is exerted, the diameter is increased in the enlarged diameter portion, and the sealing force is lost. It has a piston seal ring with a rectangular cross section,
The master cylinder, wherein the diameter-loss portion and the piston seal ring constitute the sealing force loss portion.   3. The master cylinder according to claim 2, wherein a protrusion for assisting the diameter expansion of the piston seal ring is provided in the diameter expansion portion of the seal groove. The master cylinder according to claim 1, wherein the sealing force loss portion is
A communication groove formed in the end portion of the pressure chamber from the axial intermediate portion of the outer peripheral wall in the seal groove and extending in the axial direction, and a pressure chamber of the piston seal ring formed in the end wall of the pressure chamber in the seal groove With a protrusion that prevents contact with the side end wall,
It is assembled in the seal groove so as to be movable in the axial direction, exhibits the sealing force in the state accommodated in the atmospheric pressure chamber side, and in the state accommodated in the pressure chamber side A master cylinder comprising a piston seal ring having a rectangular cross section that loses the sealing force.   5. The master cylinder according to claim 4, wherein, instead of the protrusions, communication is formed on a pressure chamber side end wall of the seal groove and extends in a radial direction so that the pressure chamber side end of the communication groove communicates with the pressure chamber. A master cylinder characterized by a groove. The master cylinder according to claim 1, wherein the seal structure includes:
A seal groove for accommodating the piston seal ring movably in the axial direction;
A first communication groove formed at an end portion of the piston seal ring on the pressure chamber side, and a second communication groove formed on an outer peripheral portion of the piston seal ring and communicating with the first communication groove; Piston seal with a rectangular cross section that exhibits the sealing force in a state accommodated in the atmospheric pressure chamber side portion of the seal groove and loses the sealing force in a state accommodated in the pressure chamber side portion of the seal groove A master cylinder comprising a ring.

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