Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1999-09-15
2001-08-14
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
Reexamination Certificate
active
06272858
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a master cylinder which generates a fluid pressure for operating a brake apparatus.
As a conventional master cylinder, there can be mentioned a master cylinder disclosed in Unexamined Japanese Patent Application Public Disclosure No. 2-136363. This master cylinder comprises a cylinder, a piston slidably provided in the cylinder, an annular cup seal held on an inner circumferential surface of the cylinder, and a relief port formed in the piston. The piston and the cylinder define a pressure chamber for generating a fluid pressure on a side to which the piston advances. The cylinder and an outer circumferential surface of the piston define a fluid supply chamber which communicates with a reservoir. The cup seal is adapted to be slid against by the straight outer circumferential surface of the piston to separate the fluid supply chamber from the pressure chamber. The relief port has two openings. One of the two openings is open on the outer circumferential surface of the piston, while the other opening is always open to the pressure chamber. Thus, the relief port is capable of providing communication between the pressure chamber and the fluid supply chamber.
In this master cylinder, the piston needs to move (or advance) a large distance (invalid stroke) from its initial position to the position where the relief port is closed by the cup seal. Due to limitation on the magnitude of the invalid stroke, the relief port of the piston at the initial position cannot be displaced sufficiently rearwardly from a rear end portion of the cup seal, making it difficult to communicate the relief port with the fluid supply chamber to a satisfactorily large degree.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a master cylinder which is advantageously used in combination with a brake control apparatus, without increasing the invalid stroke of a piston.
According to the present invention, there is provided a master cylinder comprising a cylinder, a piston slidably provided in the cylinder, an annular cup seal held on an inner circumferential surface of the cylinder, and a relief port formed in the piston. The piston and the cylinder define a pressure chamber for generating a fluid pressure in front of the piston, and the cylinder and an outer circumferential surface of the piston define a fluid supply chamber which communicates with a reservoir. The cup seal is adapted to slide against the outer circumferential surface of the piston to separate the fluid supply chamber from the pressure chamber. The relief port has two openings, one of the two openings being open on the outer circumferential surface of the piston and the other opening being always open to the pressure chamber, so as to be capable of providing communication between the pressure chamber and the fluid supply chamber. A control taper surface is formed on the outer circumferential surface of the piston rearwardly from the opening of the relief port on the outer circumferential surface of the piston. The control taper surface is tapered toward the front of the piston and is capable of abutting against an inner circumferential surface of the cup seal.
As mentioned above, in the master cylinder of the present invention, a control taper surface tapered toward the front of the piston is formed on the outer circumferential surface of the piston rearwardly from the opening of the relief port, so as to be capable of abutting against the inner circumferential surface of the cup seal. By this arrangement, when the piston advances, the control taper surface abuts against the inner circumferential surface of a rear end portion of the cup seal, so as to compress the cup seal along the control taper surface to increase an inner diameter of the cup seal. When the cup seal is compressed along the control taper surface, a surface pressure between the cup seal and the piston becomes locally high. Therefore, it has become possible to seal off the pressure chamber from the fluid supply chamber by generating a sufficiently high surface pressure on the rear end portion of the cup seal and pressurize, by means of the piston, a brake fluid in the pressure chamber to thereby generate a fluid pressure.
Since the sufficiently high pressure for sealing off the pressure chamber from the fluid supply chamber can be generated by the control taper surface on the rear end portion of the cup seal, it is sufficient only if the opening of the relief port on the outer circumferential surface of the piston is positioned in front of the control taper surface. Consequently, the relief port of the piston at its initial position can be positioned rearwardly from the cup seal without increasing the invalid stroke, so that a sufficient degree of opening of the relief port relative to the fluid supply chamber (or the amount of communication therebetween) can be satisfactorily secured.
In the above-mentioned master cylinder, a recess may be formed on the outer circumferential surface of the piston so that the opening of the relief port on the outer circumferential surface of the piston is formed in the recess and the control taper surface is formed in the recess rearwardly from the opening of the relief port.
When the control taper surface is formed in the recess rearwardly from the opening of the relief port, the cross-sectional area of a flow path in the fluid supply chamber on a side of the relief port becomes large.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.
REFERENCES:
patent: 5878575 (1999-03-01), Kreh et al.
patent: 5953916 (1999-09-01), Wurl et al.
patent: 34 31 115 (1986-03-01), None
patent: 195 20 682 (1996-08-01), None
patent: 195 23 217 (1997-01-01), None
patent: 2645992 (1997-04-01), None
patent: 96/23683 (1996-08-01), None
Ando Hiromi
Ogiwara Takato
Takano Eiichi
Lopez F. Daniel
Tokico Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Master cylinder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Master cylinder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Master cylinder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2464911