Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2000-11-13
2002-08-13
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S588000
Reexamination Certificate
active
06430926
ABSTRACT:
This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Application No. 11(1999)-320228 filed on Nov. 10, 1999, Japanese Application No. 11(1999)-320631 filed on Nov. 11, 1999, Japanese Application No. 11(1999)-322394 filed on Nov. 12, 1999 and Japanese Application No. 11(1999)-322396 filed on Nov. 12, 1999, the entire content of all of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to vehicle brake systems. More particularly, the present invention pertains to a brake master cylinder for a vehicle brake system.
BACKGROUND OF THE INVENTION
Japanese Utility Model Publication No. 8(1996)-1997 describes a brake master cylinder that includes a body having an internal bore opening at a rear end, a cylinder cap assembled at an internal bore opening portion of the body and forming a cylinder housing with the body, a first piston positioned in the cylinder housing through the cylinder cap and slidably supported in the axial direction by a first cylindrical guide assembled in the cylinder cap, a second piston positioned coaxially with the first piston at the front of the first piston and axially slidable in the cylinder housing, and a cup seal sealing in a liquid-tight manner a first pressure chamber formed between the first piston and the second piston at the front of the guide (tandem type master cylinder).
The first guide slidably supporting the first piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap, a sleeve slidably supporting the first piston and the second piston in the axial direction at the front of the first guide is coaxially engaged with the internal bore of the cylinder cap, and the cup seal liquid-tightly sealing the first pressure chamber formed between the first piston and the second piston at the front of the guide is coaxially engaged with an internal bore provided at a rear end of the sleeve. The sleeve is disposed in the cylinder cap via the first guide at the rear end, and is disposed in the body via a second guide slidably supporting the second piston in the axial direction at the front end. The sleeve is supported along with both guides by the body and the cylinder cap, and the cylinder cap is fixed to the body by a screw connection.
Japanese Patent Laid-Open Publication No. H11-198794 discloses a brake master cylinder in which a guide (piston guide portion) slidably supporting a first piston in the axial direction at the rear of a cup seal is provided in one unit with an inner peripheral portion of a cylinder cap, and a first communication conduit (a conduit communicating with a piston part at a retracted position of the first piston) is provided on an inner peripheral portion of the guide. The first communication conduit is structured with a straight internal bore formed at the front inner periphery of the guide and a tapered internal bore wherein a diameter thereof is gradually enlarged from the rear end of the straight bore in the rear direction of the straight internal bore.
A second communication conduit (a conduit communicating the first communication conduit and an annular conduit formed on the body and the cylinder cap) provided on the cylinder cap is constructed with a first communication bore opening to the outer periphery surface of the cylinder cap, communicating with the annular conduit, and extending straight towards the inner periphery at a predetermined tilt angle relative to the central axis of a first piston and a second communication bore communicating by opening to the middle of the tapered internal bore of the first communication conduit. The second communication bore communicates with the first communication bore by extending straight towards the outer periphery with a tilt angle larger than that of the first communication bore.
In this brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H06-298072, a first seal member (O-ring) blocking the communication between an annular conduit and the atmosphere at the rear of the annular conduit is assembled at a first annular groove provided on the outer periphery of the cylinder cap. A second seal member (an O-ring whose diameter is smaller than that of the first seal member) is positioned at a second annular groove provided on the outer periphery of the cylinder cap.
The Japanese Utility Model Application published as Jitsu-kai-hei 5(1993)-80945 discloses a brake master cylinder in which an annular seal member is assembled at an annular recess portion provided on a cylinder cap at the rear of a guide. The seal member provides an air-tight and liquid-tight seal between the cylinder cap and a first piston. The recess portion of the cylinder cap is open to the front (open to both the front and rear), is in communication with an accommodation bore accommodating the guide, and is in communication with a second communication conduit provided with the cylinder cap via a communication groove formed on the rear end face of the guide with a fluid chamber formed with the seal member at the rear of the guide.
In the brake master cylinder described in the Japanese Utility Model Publication published as Jitsu-kai-hei 8(1996)-1997, the guide slidably supporting the first piston in the axial direction is coaxially engaged with the internal bore of the cylinder cap and the cup seal liquid-tightly sealing the first pressure chamber formed between the first piston and the second piston at the front of the guide is coaxially engaged with the internal bore of the sleeve coaxially engaged with the internal bore of the cylinder cap. Accordingly, it is difficult to improve the assembling precision of the guide and the cup seal and the cocentricity of the cup seal and the first piston supported by the guide.
Because the sleeve is inserted into and supported by the body, and the cylinder cap is connected to the body with screws along with both guides, the axial length of the sleeve and both guides should be designed to have sufficient length. Accordingly, the expanding and contracting amount of the sleeve and both guides that is generated due to the change of the surrounding temperature becomes large, and a looseness at the screw connecting portion of the body and the cylinder cap may be generated. When the cylinder cap is excessively tightened to prevent the generation of the looseness of the screw connecting portion, excessive load is added to the entire sleeve and both guides. As a result, a material possessing high durability is required to be adopted for the sleeve and both guides. This increases the manufacturing cost and may interfere with the assembling precision of the cup seal by deformation of the internal bore provided at the rear end of the sleeve in which the cup seal is disposed.
In the brake master cylinder described in Japanese Patent Laid-Open Publication No. H11-198794, because the second communication conduit is structured with the first communication bore and the second communication bore, and the second communication bore opens in the middle of the tapered internal bore, brake fluid flow from the reservoir to the first communication conduit via the reservoir connecting point and the annular conduit flows into this first pressure chamber through the first communication bore and the second communication bore of the second communication conduit and the small diameter portion of the tapered internal bore and the straight internal bore of the first communication conduit. Accordingly, brake fluid does not flow appropriately into a large diameter portion of the tapered internal bore wherein the air left in the large diameter portion of the tapered internal bore cannot be appropriately relieved and so air remains in the large diameter portion.
In the brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H11-198794 in which a bypass conduit opens to the large diameter portion of the tapered internal bore at the rear end and opens to a back face of the cup seal at the front end, when negative pressure is generated in the first press
Nakano Toshihiro
Okada Akimoto
Tsubouchi Kaoru
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Leslie Michael
Look Edward K.
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