Vacuum brake booster

A vacuum brake force booster for a vehicle brake system, in particular, with a master brake cylinder that can be attached along with the brake force booster to a wall of an automotive vehicle, with a housing comprised of at least two wall elements attached to each other, and with at least one reinforcing element that extends through the interior of the housing and has a thin-walled tubular shape. The essence of the present invention is that the reinforcing element on at least one end passes over into a radially extending fastening portion which extends, at least in a partial zone, in parallel to the associated wall element and is supported on the wall element so that the interior of the brake force booster is separated pressure-tightly from the atmosphere. The present invention permits a simple and low-cost assembly of the brake force booster without the necessity of additional sealing elements which are difficult to mount.

TECHNICAL FIELD
 The present invention generally relates to brake systems and more
 particularly relates to a vacuum brake force booster for a vehicle brake
 system.
 BACKGROUND OF THE INVENTION
 A vacuum brake force booster of this type is generally disclosed in EP 119
 880 A1. Principally, it must be taken into consideration that the interior
 of a vacuum brake force booster houses two pneumatic chambers which are
 separated from each other by a movable wall and are evacuated in the
 non-actuated condition of the brake system. Beside mechanical stresses of
 most different types, the housing must transmit pressure forces due to the
 differential pressure between the residual pressure in the interior of the
 brake force booster and the external atmospheric pressure so that there is
 an imperative need for defined minimum wall thicknesses of the housing
 which is made up of two wall elements fastened to one another. In terms of
 weight reduction of all components installed in an automotive vehicle,
 there is the increasing trend of employing, as a material, materials with
 a low specific weight, such as aluminum or plastics, or of using steels of
 higher rates of strength. In addition, a permanent objective is to
 minimize the wall thickness of component parts. Therefore, it has been
 known in the art, see e.g. the above-mentioned patent application, to
 provide reinforcing elements which extend through the interior of a brake
 force booster housing and have a thin-walled tubular shape. On the one
 hand, this means ensures that the two wall elements remain at a defined
 distance from each other even with a small wall thickness and with high
 pressure forces, so that the housing of the brake force booster will not
 yield. On the other hand, a tubular reinforcing element permits passing a
 fixing anchor through the interior of the brake force booster and
 attaching the brake force booster along with a master brake cylinder to a
 wall of an automotive vehicle.
 An arrangement of this type suffers from the disadvantage that the slots
 and gaps which are produced by the use of the tubular reinforcing element
 must be sealed pressure-tightly. This applies, on the one hand, to slots
 in the wall elements which extend from the interior of the brake force
 booster in an outward direction and, on the other hand, also to slots
 between the two pneumatic chambers.
 In the above-mentioned patent application, the reinforcing element is
 arranged in a third chamber which is separated by the two pneumatic
 chambers by means of an additional sealing element. Such a measure
 produces a major cost increase in large-series production which is a
 significant disadvantage. Besides, the mentioned third chamber is quasi
 permanently subjected to atmospheric pressure so that its surface does not
 assist in the generation of the boosting force. This shortcoming is
 principally unacceptable in view of ever more reduced mounting spaces and
 the necessity of still more powerful automotive vehicle brake devices.
 An object of the present invention is to provide an optimally sealed vacuum
 brake force booster which does not only permit low-cost manufacture in
 large quantities but also satisfies the demands with respect to structural
 volume, weight, strength and capacity. One objective of special emphasis
 is to configure the assembly made up of brake force booster and master
 brake cylinder so that it can be installed easily into an automotive
 vehicle.
 This object is achieved by the present invention wherein the reinforcing
 element on at least one end passes over into a radially extending
 fastening portion which extends at least in a partial zone in parallel to
 the associated wall element and is supported on the wall element so that
 the interior of the brake force booster is separated pressure-tightly from
 the atmosphere.
 Thus, according to the present invention, the reinforcing element
 independently ensures the necessary sealing without requiring a separate
 structural element or sealing element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A master brake cylinder 2 for the actuation of a vehicle brake system is
 arranged on a lefthand end face of a vacuum brake force booster 1
 according to FIG. 1. The assembly composed of a vacuum brake force booster
 and a master brake cylinder (the so-called brake device) is intended for
 attachment to a (non-illustrated) wall of an automotive vehicle, and the
 brake force booster has a housing 3 made up of at least two wall elements
 4, 5 secured to one another. The interior of the housing 3 houses, among
 others, a first pneumatic chamber 6, i.e., a working chamber, and a second
 pneumatic chamber 7, i.e., a vacuum chamber. The two pneumatic chambers 6,
 7 are separated from one another by a movable wall 8 and, in dependence on
 the respective actuating condition, pressure prevails in the first
 pneumatic chamber 6 which corresponds to the pressure in the second
 pneumatic chamber 7, to the atmospheric air pressure, or a pressure
 between these two extreme values. There is no need for a more detailed
 explanation of the exact functioning of the vacuum brake force booster 1
 in this respect.
 The interior of the brake force booster 1, this means also the two chambers
 6, 7, is penetrated by a thin-walled tubular reinforcing element 9.
 Further, the reinforcing element 9 serves as a support of the two wall
 elements 4, 5 with respect to each other in the direction of the axis 10.
 At a first end 11, the reinforcing element 9 passes over into a radially
 extending fastening portion 12 which, as becomes obvious from FIG. 3,
 extends in a partial area in parallel to the wall element 5 associated
 with it and is supported on the wall element 5 in such a way that the
 interior of the brake force booster 1 is pressure-tightly isolated from
 the atmosphere.
 On a second end 13, the reinforcing element 9 engages into a fastening
 member 14 rigidly connected to the wall element 4, as can be seen in
 detail in FIG. 2. The fastening member 14 extends with a bushing 15
 through a bore in the wall element 4 and a bore in a flange 16 of the
 master brake cylinder 2. The bushing 15 has an external thread and
 projects through the flange 16 so that the attachment between the wall
 element 4 and the master brake cylinder 2 can be effected by means of a
 nut 17. For fastening the assembly made up of vacuum brake force booster 1
 and master brake cylinder 2 to the wall of an automotive vehicle (not
 shown) a threaded pin 18 is used which is slipped through the assembly
 made up of master brake cylinder 2 and brake force booster 1 in such a
 fashion that a screw coupling on the wall (not shown) can be performed by
 means of a threaded portion 19 on an end opposite to the head.
 FIG. 2 shows a section A on an enlarged scale so that details of the
 present invention can be described with greater precision. The reinforcing
 element 9 which, moreover, has a precisely defined length engages with its
 second end 13 into a bore 20 of the hollow fastening member 14. To seal
 the reinforcing element 9, a sealing element, for example an O-ring 21, is
 arranged in a groove of the bore 20 and acts upon an outside periphery of
 the reinforcing element 9, thereby sealing the second pneumatic chamber 7
 with respect to the environment.
 Further, it can be taken clearly from FIG. 2 that the fastening member 14
 has a collar 22 with in the second pneumatic chamber 7 and backgrips with
 it the bore in the wall element 4.
 Also, the fastening member 14 is connected to the wall element 4 in a
 positive and operative engagement as well as in particular in a
 rotationally secured and vacuum-tight fashion because a rim 23 of the bore
 provided in the wall element 4 is embossed into a circumferential groove
 24 of the fastening member 14 which extends in a transverse radial
 direction. Further, a bore step is arranged within the bore in the
 fastening member 14, on which bore step an end piece of the reinforcing
 element 9 abuts by the intermediary of a spacer 30. In a particularly
 favorable embodiment of the present invention, one single component
 combines the function of the force-transmitting distance washer and the
 function of the sealing element 21 so that the number of necessary
 components is reduced. This aim is principally achieved in that the spacer
 30 is made of an elastically and/or plastically deformable material and,
 in the unmounted condition, has a small oversize at least in an axial
 direction (with respect to its thickness). When the brake force booster is
 mounted, with the reinforcing element 9 with its end piece exerting force
 on the spacer 30, the spacer undergoes adaption, the result of which is
 complete sealing. This consequently obviates the need for a separate
 sealing element 21 which abuts on the periphery of the reinforcing element
 9. Or, element 21 may be optionally provided in addition for sophisticated
 applications, as the requirement may be.
 In detail, the first end 11 with the radially extending fastening portion
 12 can be seen in FIG. 3. The fastening portion 12 extends quasi like a
 flange radially outwardly and is in parallel to the associated wall
 element 5, at least in a radially external partial area, it being
 supported on the wall element 5 so that the interior of the brake force
 booster, especially the first pneumatic chamber 6, is pressure-tightly
 isolated from the atmosphere. In this connection, the flange-shaped end
 provides a good force transmission in an axial direction, and it can be
 seen that the fastening portion 12 with its bottom side 25 abuts on an
 inner side 26 of the associated wall element 5. Besides, an additional
 supporting plate 27 bears against a top side 28 of the fastening portion
 12. According to the preferred embodiment as shown in this Figure, the
 reinforcing element 9 is molecularly interfaced with the wall element 5 by
 means of an annularly circumferential welding seam 29. Manufacture and
 assembly are especially simplified when the reinforcing element 9 along
 with the supporting plate 27 is pressure-tightly connected and molecularly
 interfaced with the wall element 5.
 It applies to all embodiments of the present invention that it is
 principally also possible for both ends of the reinforcing element 9, 42,
 50 to have an identical construction, without departing from the spirit of
 the present invention. This standardization achieves an additional
 reduction in the necessary effort and structure and is preferred under
 cost aspects.
 In another embodiment of the present invention (FIG. 4) which corresponds
 in some points to the embodiment according to FIG. 2, a sealing element 40
 embraces an annular spacer 41 and sealingly abuts on the periphery of the
 reinforcing element 42 and on the fastening member 43. As can be seen in
 this Figure, the fastening member 43 has an annular slot 44 which is
 produced between a first socket 45, that extends from the body of the
 fastening member 43 axially into the housing interior, and a second socket
 46 that projects in an axial direction. The annular slot 44 permits a very
 simple and, so-to-speak, self-centering pressing in of the sealing element
 40, without the risk of damage. Both the sockets 45, 46 and the annular
 slot 44 extend concentrically to the reinforcing element 42, and the
 radially external socket 46 has a greater axial length than the radially
 internal socket 45 so that it overlaps the sealing element 40 in full and
 the reinforcing element 42 at least in part.
 The sealing element 40 permits special ease of manipulation during the
 assembly when its elastic material is cast or injection-moulded integrally
 to the spacer 41 made of a rigid material so that the spacer 41 is
 additionally used as a carrier member. This provision reduces the risk of
 faulty positioning of the sealing element in addition and, besides,
 achieves the benefit of reducing the logistics. For example, when the
 sealing element 40 is preassembled with the spacer 41 in the annular slot
 44, there is only need of slipping in the reinforcing element 42. It
 should be noted further that, with this assembly, the circumferential area
 of the reinforcing element 42 slipped into the bore may generally be left
 in the condition it is supplied, i.e., without finishing operations.
 In the embodiments according to FIGS. 5 and 6, reinforcing element 50 has a
 step 51 at its periphery, and reinforcing element 53 is supported on the
 radial abutment surface 52 of step 51. With its other side, spacer 53 is
 abutted on a front surface 54 of a socket 55 which overlaps the
 reinforcing element 50 at least in part. Consequently, pressure forces
 which are applied to the housing are transmitted to step 51 rather than
 via the front surface of the end 13 as is the case in the embodiments
 according to FIGS. 2 and 4. This permits very simply determining the
 distances between the abutment surface 52 and the front surface 54 so that
 the selection of fitting spacers with the necessary thickness is
 facilitated. With respect to the measuring operation and the selection and
 tolerances of the spacers 30, 41, 53, German patent application, serial
 No. DE 19 904 430.9, which is not prior published, is referred to and its
 disclosure is included in this respect.
 It can be taken from FIG. 6 that the spacer 56 between reinforcing element
 50 and fastening member 57 defines an annular chamber 58 in which the
 sealing element 59 is provided. An inclined surface 60 as in the drawing
 is advantageous because the sealing element 59 abuts on three surfaces in
 total, of which one sealing surface 61 on the end surface of a socket and
 one sealing surface at the periphery of the reinforcing element form a
 right angle. More specifically, in contrast to right-angled recesses or
 grooves, the risk of damage is reduced because due to the three-cornered
 annular chamber 58 no sharp edges or rims will get into contact with the
 sealing element 59. Instead, there are plane abutments exclusively, even
 during the assembly.