Cup seal, and master cylinder in which it is used

A cup seal (21) of the invention includes an intermediate lip portion (21d), positioned between an inner lip portion (21b) and an outer lip portion (21c), provided in a base portion (21a). The intermediate lip portion (21d) is configured in such a way that first intermediate lip portions (21d1), communication passages (21d3), second intermediate lip portions (21d2), whose axial direction length is less than that of the first intermediate lip portions (21d1), and the communication passages (21d3), which have no lip portion, are cyclically disposed, in this order, in the peripheral direction. An easy elastic deformation portion of the base portion (21a) which elastically deforms easily is formed by the second intermediate lip portions (21d2) and communication passages (21d3) and, by the easy elastic deformation portion elastically deforming easily when supplying liquid, a flow passage with a larger passage area is formed.

BACKGROUND ART

The present invention relates to a technical field of a cup seal, and a plunger type master cylinder including the cup seal, used in a cylinder device configured of a cylinder, such as a master cylinder of a brake or clutch in a vehicle such as an automobile, and a sliding member disposed in such a way that it can move inside the cylinder relative to the axial direction thereof.

To date, in a hydraulic brake system or hydraulic clutch system of an automobile, a master cylinder which generates hydraulic pressure in accordance with a tread force of a brake pedal or clutch pedal has been used to operate a brake or clutch. As the master cylinder, a plunger type master cylinder including a cylinder main body which has a cylinder hole, a piston, slidably inserted into the cylinder hole, which demarcates a hydraulic chamber, a communication passage, provided in the cylinder main body, which communicates with a reservoir, a relief port, formed in the piston, which connects the communication passage and hydraulic chamber, and a seal member which, as well as being housed in a depressed portion of the inner peripheral surface of the cylinder hole of the cylinder main body, is slidably passed through by the piston, and seals a space between the inner peripheral surface of the cylinder hole and the outer peripheral surface of the piston, is known from JP-A-2006-123879.

With the plunger type master cylinder, at an inoperative time, the relief port of the piston and the communication passage not being blocked off by the seal member, the hydraulic chamber communicates with the reservoir via the relief port and communication passage. Consequently, at the inoperative time, the inside of the hydraulic chamber is at atmospheric pressure, and no hydraulic pressure is generated. On the piston advancing to the hydraulic chamber side due to a pressing down upon the brake pedal or clutch pedal, the relief port and communication passage are blocked off by the seal member, and the hydraulic chamber is blocked off from the reservoir. Because of this, hydraulic pressure is generated in the hydraulic chamber along with the advancing of the piston.

A sealing function for preventing the hydraulic pressure from leaking when the hydraulic pressure is generated by the advancing of the piston, and a pumping function, which is a liquid supply function supplying braking liquid of the reservoir to the hydraulic chamber in order to increase responsiveness when the piston withdraws, are required of the seal member used in the plunger type master cylinder. Therein, in order to cause the seal member to fulfill these two functions, a cup seal is employed as the seal member.

A master cylinder using a cup seal of which a radial direction cross-section is formed in an E shape as the cup seal is proposed by the previously described 2006-123879. The E-type cup seal described in 2006-123879 includes a circular base portion, an inner peripheral lip portion projecting from the inner peripheral side of the base portion, an outer peripheral lip portion projecting from the outer peripheral side of the base portion, and an intermediate lip portion projecting from the base portion between the inner peripheral lip portion and the outer peripheral lip portion.

The inner peripheral lip portion, outer peripheral lip portion, and intermediate lip portion are all formed in a continuous circular shape. Also, a plurality of cutout grooves are formed, leaving intervals in the peripheral direction, in the leading end side of the intermediate lip portion. Then, by causing the hydraulic fluid to flow through the plurality of cutout grooves when loading hydraulic fluid into the master cylinder when removing the air of the master cylinder, it is possible to supply sufficient hydraulic fluid.

However, with the cup seal described in JP-A-2006-123879, the intermediate lip portion is provided continuously over the whole periphery. For this reason, the intermediate lip portion exerts a rib effect, and the base portion of the cup seal is comparatively stiff. In this case, the plurality of cutout grooves are formed in the leading end portion of the intermediate lip portion but, even though the cutout grooves are formed, the stiffness of the base portion of the cup seal barely changes. When the base portion is stiff in this way, it is difficult for the base portion to elastically deform. Consequently, the base portion barely elastically deforming when supplying hydraulic fluid to the master cylinder, the base portion does not greatly separate from a side wall of a housing depressed portion housing the cup seal of the master cylinder. For this reason, no large gap being formed between the base portion of the cup seal and the housing depressed portion, it is difficult to form a liquid passage with a sufficiently large passage area. Consequently, even when forming the cutout grooves in the leading end portion of the intermediate lip portion, there is a problem in that there is a limit to the supply of the hydraulic fluid, and a certain amount of time is needed to supply a sufficient amount of hydraulic fluid.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a cup seal with which it is possible to make a base portion effectively elastically deformable, and form a liquid passage with a larger passage area between the base portion and a depressed portion in which it is housed.

Another object of the invention is to provide a master cylinder with which a hydraulic pressure generation is reliable, and moreover, it is possible to further increase responsiveness when a piston withdraws.

In order to achieve the objects, a cup seal according to the invention, is characterized by including at least a circular base portion housed in a depressed portion and extending in a radial direction, a circular inner lip portion disposed in the base portion extending in an axial direction from the inner peripheral side end portion thereof, a circular outer lip portion disposed in the base portion extending in the axial direction from the outer peripheral side end portion thereof, and separably making contact with a bottom wall of the depressed portion, and an intermediate lip portion disposed in the base portion, positioned between the inner lip portion and outer lip portion, extending in the axial direction, wherein the base portion includes an easy elastic deformation portion, which elastically deforms in the axial direction comparatively easily, and a difficult elastic deformation portion, which does not elastically deform in the axial direction as easily as the easy elastic deformation portion.

Also, the cup seal according to the invention is characterized in that in the intermediate lip portion, a plurality of lip portions being disposed in a circular form, and intermittently, either side of portions with no lip portion which set predetermined intervals in a peripheral direction, at least one of an axial direction length and thickness of intermediate lip portions, of the plurality of lip portions, disposed in the easy elastic deformation portion of the base portion is set to be less than that of intermediate lip portions disposed in the difficult elastic deformation portion of the base portion.

Furthermore, the cup seal according to the invention is characterized in that the intermediate lip portions disposed in the easy elastic deformation portion of the base portion, and the intermediate lip portions disposed in the difficult elastic deformation portion of the base portion, are disposed alternately, either side of the portions with no lip portion.

Furthermore, a master cylinder according to the invention is characterized by including a cylinder main body which has a cylinder hole, a piston, slidably inserted into the cylinder hole, which demarcates a hydraulic chamber, a communication passage, provided in the cylinder main body, which communicates with a reservoir in which is stored a hydraulic fluid, a relief port, formed in the piston, which constantly communicates with the hydraulic chamber, and connects the communication passage and hydraulic chamber, and a seal member which is housed in a depressed portion of the inner peripheral surface of the cylinder hole of the cylinder main body, is slidably passed through by the piston, and seals a space between the inner peripheral surface of the cylinder hole and the outer peripheral surface of the piston, wherein the communication passage and relief port communicate at an inoperative time, and at an operative time, the piston moves, and the communication passage and relief port are blocked off by the seal member, wherein the seal member is configured of the cup seal of the invention as described above.

According to the cup seal according to the invention configured in this way, as the base portion has an easy elastic deformation portion which elastically deforms in the axial direction comparatively easily, when causing the hydraulic fluid to flow from the back surface side of the base portion of the cup seal housed in the depressed portion, past the outer peripheral surface of the outer lip portion of the cup seal, to the front surface side of the cup seal, it is easily possible to cause the base portion to elastically deform in the axial direction due to a difference in pressure in front of and behind the cup seal.

Consequently, when causing the hydraulic fluid to flow from the back surface side of the cup seal to the front surface side in this way, the easy elastic deformation portion of the base portion elastically deforms, easily separating from a side wall of the depressed portion and, as well as it being possible to prevent a sticking of the base portion to the side wall, it is possible to reliably open a valve in a check valve function included in the cup seal. Then, as it is possible to prevent a sticking of the base portion to the side wall, it is possible to form a flow passage with a larger passage area between the base portion and the depressed portion in which it is housed.

Also, according to the master cylinder of the invention, as the easy elastic deformation portion of the base portion of the cup seal elastically deforms easily when supplying the hydraulic fluid to the hydraulic chamber, it is possible to form a hydraulic fluid flow passage with a large passage area. Because of this, it being possible to supply a large amount of hydraulic fluid to the hydraulic chamber when supplying the hydraulic fluid, it is possible to increase liquid suppliability.

Furthermore, as a large amount of hydraulic fluid can be supplied to the hydraulic chamber due to the cup seal, it is possible to carryout the withdrawal of the piston smoothly and swiftly when the operation is stopped. Consequently, it is possible to increase responsiveness when the piston withdraws.

In this way, according to the master cylinder according to the invention, it is possible to increase the responsiveness when the operation is stopped, while maintaining the pressure in the hydraulic chamber at a high level at an operative time, and moreover, it is possible to obtain a good liquid suppliability.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, using the drawings, a description will be given of a best mode for carrying out the invention.

FIG. 1(a) is a vertical sectional view showing one example of an embodiment of a master cylinder including a cup seal according to the invention,FIG. 1(b) is a partial enlargement of a first cup seal portion inFIG. 1(a), and FIGS.2(a) and (b) are diagrams showing the cup seal used in the master cylinder. The “front” and “rear” of the master cylinder in the following description refer respectively to “left” and “right” in the drawings.

As shown inFIG. 1(a), a plunger type master cylinder1, being used as a master cylinder of a brake system, includes a cylinder main body2. A cylinder hole3is formed inside the cylinder main body2.

A primary piston4and secondary piston5are slidably inserted into the cylinder hole3. The primary piston4is configured so that it moves to the left due to an unshown brake pedal, or brake booster which boosts and outputs a tread force of the brake pedal. Because of the primary piston4and secondary piston5, a first hydraulic chamber6is formed demarcatedly between the primary piston4and secondary piston5, and a second hydraulic chamber7is formed demarcatedly between the secondary piston5and a bottom portion3aof the cylinder hole3, in the cylinder hole3.

A first axle member8being provided in the first hydraulic chamber6, a left-and-right pair of first and second retainers9and10are provided for the first axle member8. The first retainer9is fixed to the first axle member8, but the second retainer10can slide along the first axle member8. In this case, by the second retainer10coming into contact with a flange8aformed at the right end of the first axle member8, the first and second retainers9and10are set in a condition with a maximum distance apart from each other shown inFIG. 1(a). A first return spring11is provided contractedly between the first and second retainers9and10. The first retainer9being constantly in contact with the secondary piston5, and the second retainer10being constantly in contact with the primary piston4, at the inoperative time of the master cylinder1shown inFIG. 1(a), the primary piston4and secondary piston5are set in a condition with a maximum distance apart.

Also, a second axle member12being disposed in the second hydraulic chamber7, a third retainer13is fitted slidably onto the second axle member12. In this case, by the third retainer13coming into contact with a flange formed at the right end of the second axle member12, the third retainer13are set in a condition with a maximum distance apart from each other shown inFIG. 1(a). A second return spring14is provided contractedly between a flange formed at the left end of the second axle member12and the third retainer13. The third retainer13being constantly in contact with the secondary piston5, and the second axle member12being constantly in contact with the bottom portion3aof the cylinder hole3, at the inoperative time of the master cylinder1shown inFIG. 1(a), the secondary piston5is set in a condition with a maximum distance apart from the bottom portion3a.

A reservoir15storing a braking liquid, which is a hydraulic fluid, is provided in the cylinder main body2. The reservoir15can communicate with the first hydraulic chamber6via a first communication passage16, and a first relief port17, formed in the primary piston4, which is in constant communication with the first hydraulic chamber6. The first relief port17is configured of a radial direction communication hole, provided boredly through a left end side tubular portion4aof the primary piston4, which connects the first hydraulic chamber6on the inner peripheral side of the primary piston4and the first communication passage16on the outer peripheral side. Also, the reservoir15can communicate with the second hydraulic chamber7via a second communication passage18, and a second relief port19formed in the secondary piston5. In the same way as the first relief port17, the second relief port19is also configured of a radial direction communication hole, provided boredly through a tubular portion5aof the secondary piston5, which connects the second hydraulic chamber7on the inner peripheral side of the secondary piston5and the second communication passage18on the outer peripheral side.

A depressed portion20is formed in the inner peripheral surface of the cylinder hole3in which the primary piston4is disposed. As shown inFIG. 1(b), as well as a circular first cup seal21being housed in the depressed portion20, the primary piston4passes through the first cup seal21liquid-tightly and slidably.

As shown inFIGS. 2(a) to (d), the circular first cup seal21includes a circular base portion21a, which is provided extendingly in a radial direction, and which the primary piston4slidably passes through, a circular inner lip portion21b, which is provided extendingly in an axial direction from an inner peripheral side end portion of the base portion21a, and which the primary piston4slidably passes through, a circular outer lip portion21c, which is provided extendingly in the axial direction from an outer peripheral side end portion of the base portion21a, and which comes into contact with a bottom wall20aof the depressed portion20in such a way that they can be moved apart, and an intermediate lip portion21d, which is positioned in a radial direction midpoint of the inner lip portion21band outer lip portion21c, and which is provided extendingly from a left surface side of the base portion21ain a leftward axial direction.

In this case, a leading end portion of the outer lip portion21copposes a first side wall20con a forward side of the depressed portion20. Also, the outer lip portion21cbeing elastically flexible, it easily draws in the braking liquid from the reservoir15. Furthermore, an axial direction length of the outer lip portion21cis formed to be approximately equivalent to a length of the inner lip portion21b. By a leading end portion outer peripheral surface of the outer lip portion21ccoming into contact with the bottom wall20aof the depressed portion20, a seal portion21c1, which seals a space between itself and the bottom wall20a, is formed.

Then, at the inoperative time of the master cylinder1, in the condition in which the first cup seal21is housed in the depressed portion20as shown inFIGS. 1(a) and (b), the seal portion21c1, comes into contact with the bottom surface20a.

The intermediate lip portion21dis such that a predetermined number (12in the example shown) of intermediate lip portions, including first intermediate lip portions21d1and second intermediate lip portions21d2, are disposed in a circular form, leaving predetermined intervals, in a peripheral direction. In this case, the first and second intermediate lip portions21d1and21d2are disposed alternately and intermittently in the peripheral direction. Communication passages21d3, which connect the inner and outer peripheral sides of the intermediate lip portion21d, are formed by peripheral direction intervals (portions with no lip) between mutually adjacent first and second intermediate lip portions21d1and21d2. Consequently, the first intermediate lip portions21d1, communication passages21d3, second intermediate lip portions21d2, and communication passages21d3, are cyclically disposed, in this order, in the peripheral direction.

Consequently, as shown inFIG. 2(b), the first cup seal21is such that a radial direction cross-section in the communication passages21d3is formed in an approximate inverse U shape (an approximate left-opening U shape). Also, as shown inFIGS. 2(c) and (d), the first cup seal21is such that a radial direction cross-section of the first and second intermediate lip portions21d1and21d2is formed in an approximate inverse E shape. In this case, a length (height) L2of the second intermediate lip portions21d2is set to be a predetermined amount less than a length (height) L1in the axial direction of the first intermediate lip portions21d1(L2<L1) in a condition in which the first cup seal21is free. The thicknesses of the first and second intermediate lip portions21d1and21d2are set to be mutually equivalent, or approximately equivalent.

As shown inFIG. 3(b), in a condition in which the first cup seal21is embedded in the depressed portion20, the leading ends of the first intermediate lip portions21d1are disposed slightly away from the first side wall20cof the depressed portion20. Then, in this condition, when a predetermined pressure or more is applied to the right surface side (back surface side) of the base portion21aof the first cup seal21, the first cup seal21moves in a forward axial direction, and the leading ends of the first intermediate lip portions21d1are brought into contact with the first side wall20cof the depressed portion20. By the leading ends coming into contact with the first side wall20c, a further movement of the first cup seal21in the forward axial direction is prevented.

Also, in a condition in which the first cup seal21is embedded in the depressed portion20, and no pressure is applied to the right surface (back surface) of its base portion21a, the leading ends of the second intermediate lip portions21d2are disposed farther apart from the first side wall20cof the depressed portion20than the leading ends of the first intermediate lip portions21d1.

An axial direction passage22, positioned in a vicinity behind the first cup seal21, which connects the first relief port17and first communication passage16, is provided in the cylinder main body2. The axial direction passage22is in constant communication with the right surface of the base portion21aof the first cup seal21.

A depressed portion (reference numeral omitted) which is the same as the previously described depressed portion20is also formed in the inner peripheral surface of the cylinder hole3in which the secondary piston5is disposed. As well as a circular second cup seal23being housed in the depressed portion, the secondary piston5passes through the second cup seal23liquid-tightly and slidably. The second cup seal23is formed in exactly the same way as the first cup seal21. Consequently, a detailed description thereof will be omitted.

Furthermore, although not clearly shown inFIG. 1(a), an axial direction passage, exactly the same as the axial direction passage22, which connects the second communication passage18and second relief port19is also formed in a vicinity behind the second cup seal23. Then, this axial direction passage too is in constant communication with the right surface of a base portion of the second cup seal23(the same as the right surface of the base portion21aof the first cup seal21).

The first hydraulic chamber6, as well as being communicated with a first output port24, is connected to a wheel cylinder of a wheel of one brake system, of two unshown brake systems, via the first output port24. Also, the second hydraulic chamber7, as well as being communicated with a second output port25, is connected to a wheel cylinder of a wheel of the other brake system, of the two unshown brake systems, via the second output port25.

A cup seal26being provided in a rear end portion inner periphery of the cylinder hole3of the cylinder main body2, the primary piston4passes slidably through the cup seal26. The cup seal26, being formed of a heretofore known cup seal differing from the previously described first and second cup seals21and23, maintains liquid-tightness between the inner peripheral surface of the cylinder hole3of the cylinder main body2and the outer peripheral surface of the primary piston4. Because of this, the braking liquid of the first communication passage16is prevented from leaking into the exterior from the cylinder main body2.

In the same way, a cup seal27being provided in a portion of the cylinder hole3of the cylinder main body2in a vicinity behind the second communication passage18, the secondary piston5passes slidably through the cup seal27. The cup seal27, also being formed of a heretofore known cup seal differing from the previously described first and second cup seals21and23, maintains liquid-tightness between the inner peripheral surface of the cylinder hole3of the cylinder main body2and the outer peripheral surface of the secondary piston4. Because of this, the hydraulic pressure of the first hydraulic chamber6is maintained.

Next, a description will be given of an operation of the master cylinder1of the example configured in this way.

In the brake inoperative condition shown inFIG. 1(a), the primary piston4and secondary piston5are both set in the inoperative positions shown inFIG. 1(a). The inoperative position is a withdrawal limit position of the two pistons4and5. In the withdrawal limit position of the primary piston4, one portion of the rear end side of the first relief port17is positioned behind the rear end of the base portion21aof the first cup seal21, and a predetermined gap α (shown inFIG. 1(b)) is formed. Then, by means of the gap α, the first relief port17and first communication passage16communicate via the axial direction passage22. Consequently, the first hydraulic chamber6communicates with the reservoir15, and the inside of the first hydraulic chamber6, no hydraulic pressure being generated, is at atmospheric pressure. In the same way, in the withdrawal limit position of the secondary piston5, the second hydraulic chamber7communicates with the reservoir15, and the inside of the second hydraulic chamber7, no hydraulic pressure being generated, is at atmospheric pressure.

On the brake pedal being pressed down upon, and the primary piston4advancing, the whole of the first relief port17is closed off by the base portion21aand inner lip portion21bof the first cup seal21. For this reason, the first relief port17and first communication passage16being blocked off, the first hydraulic chamber6is blocked off from the reservoir15, and a hydraulic pressure according to the pedal tread force is generated in the first hydraulic chamber6. Also, the secondary piston5advances in accordance with the tread force transmitted, via the first return spring11, due to the advancing of the primary piston4, and in the same way, the second hydraulic chamber7is blocked off from the reservoir15, and a hydraulic pressure is generated in the second hydraulic chamber7.

Then, as shown inFIGS. 3(a) and (b), the first cup seal21is pressed backward in the depressed portion20in accordance with the hydraulic pressure in the first hydraulic chamber6, and the rear end surface of the base portion21ais brought into close contact with a second side wall20bof the depressed portion20. Then, the base portion21aseals a space between itself and the second side wall20bof the depressed portion20. Also, as well as the inner lip portion21bof the first cup seal21being brought into close contact with the outer peripheral surface of the primary piston4, the seal portion21c1of the outer lip portion21cof the first cup seal21is brought into close contact with the bottom wall20aof the depressed portion20. Then, the seal portion21c1seals a space between itself and the bottom wall20aof the depressed portion20. That is, the base portion21aand seal portion21c1, being disposed in series, configure a double seal portion against the flow of the braking liquid from the first hydraulic chamber6toward the reservoir15, passing between the outer peripheral surface of the outer lip portion21cand bottom wall20aof the depressed portion20, and between the rear end surface of the base portion21aand second side wall20bof the depressed portion20.

Because of this, the first hydraulic chamber6being sealed off from the reservoir15, the braking liquid of the first hydraulic chamber6does not leak into the reservoir15, and the hydraulic pressure of the first hydraulic chamber6is maintained. At this time, it is hypothesized that the seal surface pressure of the seal portion21c1is weak in part, and the braking liquid of the first hydraulic chamber6leaks from, of the sealed portion between the seal portion21c1and bottom wall20aof the depressed portion20, the portion with the weak seal surface pressure. However, the braking liquid which leaks from the seal portion21c1is blocked off by the sealed portion between the base portion21aand second side wall20bof the depressed portion20, and does not leak toward the axial direction passage22.

In this way, the leaking of the braking liquid of the first hydraulic chamber6is reliably prevented by the double seal configured of the seal portion21c1and base portion21adisposed in series in the direction of flow of the braking liquid, and the hydraulic pressure of the first hydraulic chamber6is highly-maintained.

On the primary piston4advancing further, the hydraulic pressure of the first hydraulic chamber6rises. The hydraulic pressure of the first hydraulic chamber6is fed from the first output port24to the wheel cylinder of one of the brake systems, and the brake of the one brake system operates.

On the secondary piston5advancing, a hydraulic pressure is generated in the second hydraulic chamber7. In the same way, a leaking of the braking liquid of the second hydraulic chamber7is reliably prevented by a double seal configured of the base portion and a seal portion of the second cup seal23, and the hydraulic pressure of the second hydraulic chamber7is highly-maintained.

On the secondary piston5advancing further, the hydraulic pressure of the second hydraulic chamber7rises. The hydraulic pressure of the second hydraulic chamber7is fed from the second output port25to the wheel cylinder of the other brake system, and the brake of the other brake system operates.

On releasing the pressing down of the brake pedal in the condition in which the brake is operating, the primary piston4withdraws under the spring force of the first return spring11, and attempts to return to the inoperative position, meaning that the hydraulic pressure of the first hydraulic chamber6falls, momentarily becoming slightly negative. Also, the rear end side of the outer lip portion21c, communicating with the reservoir15, is at atmospheric pressure. Consequently, a difference in pressure occurs between the front surface side and rear surface side of the base portion21a, and the base portion21ais pressed forward by the difference in pressure For this reason, as shown inFIGS. 3(c) and (d), the base portion21aelastically flexes forward and, as well as a gap occurring between the rear end surface of the base portion21aand second side wall20bof the depressed portion20, the leading ends of the second intermediate lip portions21d2make contact with the first side wall20c. Also, as well as the leading end side of the outer lip portion21celastically flexing inward, the first and second intermediate lip portions21d1and21d2elastically flex inward, meaning that the whole of the base portion21amoves slightly forward, and the gap between the rear end surface of the base portion21aand second side wall20bof the depressed portion20becomes larger.

Because of this, the braking liquid of the reservoir15flows into the front side of the first cup seal21through the first communication passage16, the axial direction passage22, the gap between the rear end surface of the base portion21aand second side wall20bof the depressed portion20, and the gap between the bottom wall20aand outer lip portion21c.

In this case, with the first cup seal21of the example, as the length L2of the second intermediate lip portions21d2is set to be shorter than the length L1of the first intermediate lip portions21d1, and the communication passages21d3, in which there is no lip portion, are formed on either end side of the second intermediate lip portions21d2, a rib effect of the second intermediate lip portions21d2is effectively small. That is, the portion of the base portion21ain which the second intermediate lip portions21d2, and the communication passages21d3on either end side thereof in which there is no lip portion, are disposed is more pliant than the portion of the base portion21ain which the first intermediate lip portions21d1are disposed. In particular, by the communication passages21d3, in which there is no lip portion, being formed on either end side of the second intermediate lip portions21d2, the portion of the base portion21ain which the second intermediate lip portions21d2and communication passages21d3are disposed is effectively pliant in comparison with the cup seal described in the previously described JP-A-2006-123879. For this reason, the portion of the base portion21awith the second intermediate lip portions21d2and communication passages21d3can elastically deform easily and effectively. That is, as well as the portion of the base portion21awith the second intermediate lip portions21d2and communication passages21d3being an easy elastic deformation portion, the portion of the base portion21awith the first intermediate lip portions21d1is a difficult elastic deformation portion.

Consequently, as shown inFIGS. 3(c) and (d), the portion of the base portion21awith the second intermediate lip portions21d2flexes forward considerably, and the gap between the rear end surface of the base portion21aand second side wall20bof the depressed portion20becomes its largest. Consequently, a braking liquid flow passage with a large passage area is formed between the rear end surface of the base portion21aand second side wall20bof the depressed portion20. Because of this, a large amount of braking liquid can flow.

Furthermore, the braking liquid, as well as causing the first intermediate lip portions21d1to flex inward, and flowing into the first hydraulic chamber6, flows into the first hydraulic chamber6through the gap between the leading ends of the second intermediate lip portions21d2and first side wall20cof the depressed portion20, and through the communication passages21d3.

In this way, the base portion and seal portion21c1, in response to the flow of the hydraulic fluid from the reservoir15to the first hydraulic chamber6, separate from the bottom wall20aof the depressed portion20and second side wall20brespectively, and configure a sealed portion which forms a gap between themselves and the bottom wall20aand second side wall20b. By this means, the braking liquid is reliably supplied from the reservoir15to the first hydraulic chamber6, the hydraulic pressure of the first hydraulic chamber6falls, and the primary piston4withdraws smoothly and swiftly under a bias force of the first return spring11.

Due to the withdrawal of the primary piston4and fall in hydraulic pressure of the first hydraulic chamber6, the secondary piston5attempts to withdraw under a bias force of the second return spring14. At this time, in the same way as with the previously described first hydraulic chamber6, a large amount of the braking liquid of the reservoir15is supplied to the second hydraulic chamber7. Consequently, the secondary piston5also withdraws smoothly and swiftly, and the hydraulic pressure of the second hydraulic chamber7falls.

On the primary piston4withdrawing, and one portion of the rear end side of the first relief port17being positioned behind the rear end of the base portion21aof the first cup seal21, as shown inFIGS. 1(a) and (b), the first relief port17and first communication passage16communicate via the axial direction passage22. Because of this, the braking liquid of the first hydraulic chamber6is exhausted to the reservoir15through the first relief port17and first communication passage16, and the hydraulic pressure of the first hydraulic chamber6falls further.

In the same way, by the secondary piston5withdrawing, the second relief port19and second communication passage18communicate, the braking liquid of the second hydraulic chamber7is exhausted to the reservoir15through the second relief port19and second communication passage18, and the hydraulic pressure of the second hydraulic chamber7falls further.

On the two pistons4and5reaching the withdrawal limit positions shown inFIG. 1(a), the two pistons4and5stop, the first and second hydraulic chambers6and7are at atmospheric pressure, the master cylinder1is in the inoperative condition, and the brakes are released.

In this way, according to the first and second cup seals21and23of the example, as the intermediate lip portion21ddisposed in a circular form is configured of a cyclical disposition of the longer first intermediate lip portions21d1, the communication passages21d3, which are the portions with no lip, the shorter second intermediate lip portions21d2, and the communication passages21d3, which are the portions with no lip, the portion of the base portion21aof the first and second cup seals21and23in which the shorter second intermediate lip portions21d2are disposed, and the portion in which the communication passages21d3, the portions with no lip, positioned on either end side of this portion are disposed, can easily be made elastically deformable.

Consequently, with the portion in which the second intermediate lip portions21d2are disposed and the communication passages21d3, the portions with no lip, it is possible to form an easy elastic deformation portion, which can easily elastically deform, and a difficult elastic deformation portion, in which an elastic deformation is not as easy as in the easy elastic deformation portion. Because of this, when the braking liquid flows from the rear surface to the front surface of the first and second cup seals21and23, passing between the rear surface of the base portion21aand the front surface of the second side wall20bof the depressed portion20, and between the outer peripheral surface of the outer seal portion21cand the bottom wall20aof the depressed portion20, the easy elastic deformation portion of the base portion21aelastically deforms, easily separating from the second side wall20bof the depressed portion20and, as well as it being possible to prevent a sticking of the base portion21ato the second side wall20b, it is possible to reliably open a valve in a check valve function included in the first and second cup seals21and23. Then, as it is possible to prevent a sticking of the base portion21ato the second side wall20b, it is possible to form a flow passage with a larger passage area.

Also, according to the master cylinder1of this example, when supplying the braking liquid to the first and second hydraulic chambers6and7of the master cylinder1, as the portion of the base portion21aof the first and second cup seals21and23in which the second intermediate lip portions21d2are disposed easily elastically deforms, it is possible to form a braking liquid flow passage with a large passage area. Because of this, it being possible to supply a large amount of braking liquid to the first and second hydraulic chambers6and7when supplying the braking liquid, it is possible to increase liquid suppliability.

Furthermore, as a large amount of braking liquid can be supplied to the first and second hydraulic chambers6and7due to the first and second cup seals21and23, it is possible to carry out the withdrawal of the primary piston4and secondary piston5smoothly and swiftly when the operation is stopped. Consequently, it is possible to increase responsiveness when the two pistons4and5withdraw.

In this way, according to the master cylinder1of the example, it is possible to increase the responsiveness when the operation is stopped, while maintaining the pressure in the first and second hydraulic chambers6and7at a high level at an operative time, and moreover, it is possible to obtain a good liquid suppliability.

FIGS. 4(a) to (d) are the same kinds of drawing asFIGS. 2(a) to (d) respectively, and show another example of the cup seals used in the master cylinder of the previously described example. By giving the same reference numerals and characters to components which are the same as those of the previously described example, a detailed description thereof will be omitted.

With the first cup seal21of the example shown in the previously describedFIGS. 2(a) to (d), the length L2of the second intermediate lip portions21d2configuring the intermediate lip portion21dis less than the length L1of the first intermediate lip portions21d1, and the portion of the base portion21ain which the second intermediate lip portions21d2are formed can be easily elastically deformed. As opposed to this, as shown inFIGS. 4(a) to (d), with the first cup seal21of the example, a thickness t2of fourth intermediate lip portions21d5configuring the intermediate lip portion21dis set to be less than a thickness t1of third intermediate lip portions21d4(t2<t1), and a portion of the base portion21ain which the fourth intermediate lip portions21d5are formed can be easily elastically deformed. In this case, the lengths in the axial direction of each of the third and fourth intermediate lip portions21d4and21d5are set to be mutually equivalent, or approximately equivalent.

With the first cup seal21of the example too, the third intermediate lip portions21d4, communication passages21d3, fourth intermediate lip portions21d5, and communication passages21d3, are cyclically disposed, in this order, in the peripheral direction. The second cup seal23of the example too is configured in exactly the same way as the first cup seal21of the example. In this case, as well as the portion of the base portion21ain which the fourth intermediate lip portions21d5are disposed being an easy elastic deformation portion, which can easily elastically deform, the portion of the base portion21ain which the third intermediate lip portions21d4are disposed is a difficult elastic deformation portion, in which an elastic deformation is not as easy as in the easy elastic deformation portion.

In the first and second cup seals21and23of the example too, in the same way as in the first and second cup seals21and23of the previously described example, as shown inFIGS. 5(a) and (b), when the master cylinder1operates, the first and second cup seals21and23move backward and, as well as the rear surface of the base portion21amaking contact with the second side wall20bof the depressed portion20, the seal portion21c1of the outer lip21cmakes contact with the bottom wall20aof the depressed portion20. Also, as shown in FIGS.5(c) and (d), at the liquid supply time of the master cylinder1, the first and second cup seals21and23move forward and, as well as the rear surface of the base portion21aseparating from the second side wall20bof the depressed portion20, the portion of the base portion21ain which the fourth intermediate lip portions21d5are disposed elastically deforms considerably, and a braking liquid flow passage with a large passage area is formed.

Other configurations and other working effects of each of the first and second cup seals21and23, and master cylinder1, of the example are all the same as the first and second cup seals21and23, and master cylinder1, of the previously described example.

In the previously described examples, the first and second intermediate lip portions21d1and21d2, or the third and fourth intermediate lip portions21d4and21d5, are alternately disposed regularly one by one, and on either side of the communication passages21d3, but it is also possible to dispose the first and second intermediate lip portions21d1and21d2, or the third and fourth intermediate lip portions21d4and21d5, alternately irregularly, and on either side of the communication passages21d3. That is, it is possible to optionally set the numbers and disposition order of the first and second intermediate lip portions21d1and21d2, or the third and fourth intermediate lip portions21d4and21d5as, for example, mutually differing numbers, an irregular disposition order, or the like.

Also, with the example shown inFIG. 4, the axial direction length of the fourth intermediate lip portions21d5can also be made less than the axial direction length of the third intermediate lip portions21d4. That is, it is also possible to make both the axial direction lengths and thicknesses of the third and fourth intermediate lip portions21d4and21d5mutually different.

Furthermore, it is also possible to dispose the first intermediate lip portions21d1and second intermediate lip portions21d2of the example shown inFIG. 2, and the third intermediate lip portions21d4and fourth intermediate lip portions21d5of the example shown inFIG. 4, mixed in a circular form.

Furthermore, in each of the previously described examples, the peripheral direction length of each of the first intermediate lip portions21d1and second intermediate lip portions21d2, or the peripheral direction length of each of the third intermediate lip portions21d4and fourth intermediate lip portions21d5, are all set to be equivalent, but it is possible to make the peripheral direction length of the second intermediate lip portions21d2less than the peripheral direction length of the first intermediate lip portions21d1, or the peripheral direction length of the fourth intermediate lip portions21d5less than the peripheral direction length of the third intermediate lip portions21d4.

Furthermore, in the previously described examples, the first and second cup seals21and23are both taken to be double seals configured of the seal portion of the outer lip and the base portion, but it is also possible to arrange that the sealing, not being carried out by the base portion, is done only by the seal portion of the outer lip. In this case, for example, by forming a predetermined number of radial direction grooves, communicating from the inner lip side to the outer lip side, in the rear surface of the base portion, leaving predetermined intervals in the peripheral direction, it is possible to increase the braking liquid suppliability using the grooves.

Furthermore, in the previously described examples, the first side wall20cof the depressed portion20in which the first cup seal21is housed is taken to be a flat surface perpendicular to the axial direction of the cylinder3but, as shown by the two-dot chain line inFIG. 1(b), it is also possible to make it a tapered surface20c′ wherein an opening end portion of the first side wall20cof the depressed portion20slopes forward toward an opening end.

Furthermore, the cup seal of the invention, not being limited to the master cylinder of a brake device as in the previously described examples, can be used in any kind of cylinder device provided that it is a cylinder device which, being a cylinder device configured of a cylinder, and a sliding member disposed in such a way that it can move inside the cylinder relative to the axial direction thereof, prevents the flow of hydraulic fluid from one side of the axial direction of the cup seal to the other side of the axial direction, and allows the flow of the hydraulic fluid from the other side of the axial direction of the cup seal to the one side of the axial direction.

Furthermore, the master cylinder of the invention, not being limited to the master cylinder of a brake device as in the previously described examples, can be applied to any kind of hydraulic device, including the master cylinder of a clutch device, provided that it generates hydraulic pressure in a hydraulic chamber with the advancing of a piston. Also, in the previously described examples, a description has been given of a tandem master cylinder in which two pistons are disposed in series, but it is possible to apply the master cylinder of the invention to any kind of master cylinder, including a single master cylinder, provided that it is a plunger type master cylinder.

INDUSTRIAL APPLICABILITY

The cup seal and master cylinder according to the invention can preferably be used in a plunger type master cylinder which includes a cup seal, generates hydraulic pressure in a hydraulic chamber when a piston advances, and supplies a hydraulic braking liquid to the hydraulic chamber when the piston withdraws. In particular, it can preferably be used in a master cylinder of a brake or clutch in a vehicle, such as an automobile.