Expansible chamber devices – Plural flexible wall working members
Patent
1995-11-13
1997-10-28
Denion, Thomas E.
Expansible chamber devices
Plural flexible wall working members
91533, F01B 1900
Patent
active
056808070
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP94/03556 filed Oct. 28, 1994.
BACKGROUND OF THE INVENTION
The present invention pertains to a vacuum brake booster for motor vehicles, with a first and a second booster space, which are separated from one another by a partition. A first and a second movable wall respectively divide the first booster space into a first vacuum chamber and a first working chamber and the second booster space into a second vacuum chamber and a second working chamber. Each movable wall is formed by a diaphragm disk and a rolling diaphragm in contact with the diaphragm disk. The first movable wall is arranged on a control housing accommodating the control valve, and the second movable wall is arranged on a connection tube extending through the partition. The connection tube is provided with a radial collar axially supported on the control housing. The radially inner edge area of the first diaphragm disk surrounds the control housing, is axially in contact with the collar, and is held by the first rolling diaphragm. The first rolling diaphragm has a bead which is clamped in an annular groove, which is provided in the control housing outside of the area of the control housing which is encompassed by the connection tube and proximate the fastening area of the connection tube and the first diaphragm disk to the control housing.
Such a vacuum brake booster and such a manner of fastening its movable walls to the control housing and to the connection tube are described in German Patent DE-OS 39 04 641. The first rolling diaphragm, which forms part of the first movable wall, is bound to the edge of the annular bead located adjacent to the first diaphragm disk. The bead of the second rolling diaphragm, sealing the second movable wall against the connection tube. is held between the second diaphragm disk supported by a second radial collar of the connection tube and a claw ring pushed over the connection tube. The second diaphragm disk is firmly connected, for example welded, to the collar of the connection tube.
However, such prior art vacuum brake boosters involve the risk that the rolling diaphragms could become detached under certain operating conditions, which considerably impairs the reliability of operation of such brake devices.
This risk occurs especially as a consequence of dynamic pressure in the brake device due to it being actuated without vacuum or with the check valve outlets closed, because force components acting in the radial direction are generated due to the pressure occurring in the brake booster housing. These force components tend to pull the annular bead of the first rolling diaphragm out of the circumferential groove of the control housing or to displace the first diaphragm disk against the actuating pressure, so that the annular bead is pushed out of the groove. This leads to failure of the brake device, whose boosting force cannot be built up any more.
The relatively high manufacturing costs associated with the use of the above-mentioned claw ring, as well as the difficulties occurring during its mounting, are also disadvantageous.
SUMMARY OF THE INVENTION
A vacuum brake booster according to the present invention minimizes the above-described disadvantages, maintains the design and the ratings of the device, and maintains a reliable operation by using the parts already present. In particular, according to the present invention, an additional part for fastening and sealing the second movable wall is not needed, mounting is simple, and a pressure difference which exists between the second vacuum chamber and the second working chamber and acts in the reverse (i.e., "wrong") direction can be eliminated with certainty.
According to the present invention, the first rolling diaphragm is bound to the edge of the bead located away from the first diaphragm disk or from the collar of the connection tube such that with the first diaphragm disk, the first rolling diaphragm defines a pneumatic space to which pressure occur
REFERENCES:
patent: 3146679 (1964-09-01), Ayers, Jr.
patent: 5014597 (1991-05-01), Rueffer et al.
patent: 5040450 (1991-08-01), Jakobi
patent: 5062348 (1991-11-01), Gotoh et al.
patent: 5158004 (1992-10-01), Bauer
patent: 5214996 (1993-06-01), Gautier et al.
Graichen Kai-Michael
Jakobi Ralf
Wagner Wilfried
Denion Thomas E.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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