Patent Abstract:
The present invention relates to a brake booster device for a vehicle brake system comprising a force input element, a control valve arrangement actuable via the force input element, a chamber arrangement disposed in a housing and comprising a vacuum chamber and a working chamber, which is separated from the vacuum chamber by a movable wall and connectable selectively to a vacuum source or the atmosphere, and a force output element, wherein the movable wall is biased into a normal position by a resetting spring accommodated at least partially in the housing and wherein the housing is penetrated by at least one fastening bolt. In this case, it is provided that at least one damping element acts for the purpose of vibration damping on the resetting spring, wherein the at least one damping element is mounted on the at least one fastening bolt.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to International Patent Application No. PCT/EP2007/002719 filed Mar. 27, 2007, the disclosures of which are incorporated herein by reference in entirety, and which claimed priority to German Patent Application No. 10 2006 016 545.4 filed Apr. 7, 2006, the disclosures of which are incorporated herein by reference in entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a brake booster device for a vehicle brake system comprising a force input element, a control valve arrangement actuable via the force input element, a chamber arrangement disposed in a housing and comprising a vacuum chamber and a working chamber, which is separated from the vacuum chamber by a movable wall and connectable selectively to a vacuum source or the atmosphere, and a force output element, wherein the movable wall is biased into a normal position by means of a resetting spring accommodated at least partially in the housing and wherein the housing is penetrated by at least one fastening bolt. 
     Such a brake booster device is sufficiently known from the background art. There is also often mention of a pneumatic brake booster, in which where necessary by means of the control valve arrangement a pressure difference at the movable wall is built up, which then boosts the brake force applied to the brake pedal by the driver and therefore assists the braking operation. As a result, the driver need expend less force for a braking operation, so that even drivers with weak leg musculature may achieve an adequate braking effect in every driving situation. 
     It has however emerged that, particularly in the course of progressive weight reductions in automotive engineering that have led to the installation of increasingly lighter parts, there has been a disadvantageous change in the vibration response of individual components. Because of the use of low-mass parts, in particular as a result of the use of lightweight materials such as for example aluminium or magnesium or alloys containing these elements, these parts have an increasing tendency to vibrate. It has for example emerged that, if for example the brake mechanism, in particular the brake pedal and the pedal bracket are formed from such lightweight materials, the resulting low inertia may lead to the actuating mechanism having a specific tendency to vibrate, which then leads to undesirable noises. 
     From FR 2 817 219 an arrangement that is to counteract this problem is known. For this purpose, a pot-like damping element is slipped onto the end of the resetting spring of the brake booster device. 
     With this solution it has however in turn emerged that the fixing of the damping element to the resetting spring may cause problems both with regard to assembly and during operation, which may ultimately lead to malfunctioning of the brake booster. 
     BRIEF SUMMARY OF THE INVENTION 
     Against this background, a feature of the present invention is to provide a brake booster device of the initially described type, in which the tendency to vibrate is considerably reduced and easier, fault-free assembly combined with increased operational reliability is guaranteed. 
     This feature is achieved by a brake booster device having at least one damping element, which acts for the purpose of vibration damping on the resetting spring, wherein the at least one damping element is mounted on the at least one fastening bolt. 
     By acting directly on the resetting spring the damping element according to the invention is able to suppress the generation of vibrations, thereby also preventing corresponding vibrations from being transmitted to the actuating mechanism. Thus, the problem of the undesirable occurrence of vibrations is tackled right at the source, i.e. upon the development of such vibrations. The mounting according to the invention of the damping element on the at least one fastening bolt ensures fault-free assembly and stable positioning of the damping element throughout the life of the brake booster device without any risk of accidental separation or inappropriate positioning. It is moreover guaranteed that an unwanted displacement of the damping element inside the housing of the brake booster device does not occur, say, as a result of function-related movements of the resetting spring. 
     A development of the invention provides that the at least one damping element acts in a vibration-damping manner on a peripheral region, preferably on an outer peripheral region, of the resetting spring. The mounting on the outer peripheral region of the resetting spring offers the advantage of particularly effective vibration damping. It is however equally possible to act on the inner peripheral region of the resetting spring, for example by means of a damping tubular piece, which is introduced into the inner peripheral region and mounted by means of a fastening plate on the at least one fastening bolt. 
     According to a constructional variant of the invention, it may be provided that the at least one damping element is of a cylindrical, preferably hollow-cylindrical, in particular cup-shaped design. It is therefore possible to provide a single cylindrical damping element that surrounds the resetting spring. It is however equally possible to provide individual damping elements, wherein a damping element is associated with each fastening bolt. This damping element then acts only in sections on the resetting spring that is to be damped. For example, the individual damping elements in this constructional variant may each have a location opening, by which they are mounted onto the respective fastening bolt and fixed thereon. The invention therefore provides that a plurality of damping elements are disposed around the outer periphery of the resetting spring on a corresponding plurality of fastening bolts. As an alternative to this, it may be provided that the at least one damping element surrounds the resetting spring over the entire periphery thereof, as already outlined above. 
     As regards the axial extent, it may be provided that the at least one damping element extends at least along part of the axial length of the resetting spring. Naturally, it is also possible for the damping element to extend along the entire axial length of the resetting spring, but in this case the damping element has to be of an axially compressible design. 
     In order to achieve a particularly good damping effect, a development of the invention provides that in the region of the ends of the resetting spring in each case at least one damping element is disposed. 
     As regards the choice of material of the damping element, according to the invention it may be provided that the damping element is manufactured from an elastically deformable material, in particular a rubber- or foam material. 
     An alternative constructional variant of the invention provides that the at least one damping element is of a disk-shaped design and extends in between turns of the resetting spring. Instead of acting on the outer peripheral region of the resetting spring, the damping element prevents vibrations by engaging between individual spring turns of the resetting spring and hence acting in a vibration-damping manner thereon. Particularly with this form of construction, a plurality of such disk-shaped damping elements may be used. 
     An advantageous constructional variant, which is notable in particular for its low weight, provides that the at least one damping element comprises a cylindrical damping body and at least one fastening disk connected thereto. The damping body may therefore be of a relatively thin-walled design, which as a rule offers adequate damping. The fastening to the fastening bolt is then effected by means of the likewise thin-walled fastening disk. To save weight, a construction of the one or more damping elements from solid material may therefore be avoided. In this connection, it may be provided that the at least one damping element—viewed in an axis-containing section—comprises a U-section. Given a construction of the damping element from a U-section, this provides for example a tubular damping body as well as two fastening disks, which extend orthogonally relative to the longitudinal direction of the tubular damping body and are used for the fastening to the fastening bolt. If only one fastening disk per damping element is used, it may be provided that the at least one damping element—viewed in an axis-containing section—comprises a T-section. This means that the damping disk is then disposed approximately in the centre of the tubular body and extends orthogonally relative to the longitudinal direction thereof. Damping element and fastening disk may be formed integrally with one another, but may equally be glued or vulcanized to one another. It should moreover be stressed that L-sections or asymmetrical sections may also be used. 
     The invention further relates to a damping element having the previously described features for use in a brake booster device of the previously described type. To avoid repetition, the damping element features described in detail above are not mentioned again here. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an axis-containing section of a brake booster device according to the invention with the damping elements in a first form of construction of the invention; 
         FIG. 2  is a front view of a damping element of a cup-shaped design; 
         FIG. 3  is a front view of a cylindrical damping element made of solid material; 
         FIG. 4  is a view corresponding to  FIG. 1  of a second form of construction of the invention; 
         FIG. 5  is a front view of the damping element used in  FIG. 4 ; 
         FIG. 6  is a sectional view corresponding to  FIGS. 1 and 4  of a third constructional variant of the invention; 
         FIG. 7  is a front view of the damping element used in the form of construction according to  FIG. 6 ; 
         FIG. 8  is a sectional view corresponding to  FIGS. 1 ,  4  and  6  of a fourth form of construction of the invention and 
         FIG. 9  is a front view of the damping element used in the fourth form of construction according to  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  a brake booster according to the invention is generally denoted by  10 . It comprises a force input element  12 , a control valve arrangement  14  connected to the force input element, and a housing  16 . Disposed in the housing  16  is a movable wall  18  that separates a vacuum chamber  20  in a sealing manner from a working chamber  22 . The two chambers  20  and  22  form a chamber arrangement  24 . The control valve  14  contains two valve seats  26  and  28 , which are associated with a control valve housing  30  and a control valve element  32 . Associated with the control valve  14  is a force output element  34 , which is connected by a rubber-elastic reaction element  36  to the control valve housing. 
     Accommodated in the housing  16  is a resetting spring  38 , which is supported by its, in  FIG. 1 , left end against the left housing wall and acts with its, in  FIG. 1 , right end on the control valve housing  30 . As may be seen in  FIG. 1 , the control valve housing  30  is connected in a fixed manner to the movable wall  18  for joint movement along the longitudinal axis A. In the course of such a movement the movable wall ( 18 ), sealed by sealing elements  44  and  46 , slides along the fastening bolts  40  and  42 . 
     Mounted on the fastening bolts  40 ,  42  are damping elements  48  and  50  respectively, which are of a substantially cylindrical design. The damping elements  48  and  50  are dimensioned in such a way that they act with their outer periphery on a longitudinal portion a of the resetting spring  38  at the outer periphery thereof. 
     The brake booster  10  according to the invention operates as follows: 
     As a result of an actuation of the brake pedal by an actuating force F, as indicated in  FIG. 1 , the force input element  12  is displaced in  FIG. 1  to the left along the longitudinal axis A. This leads in an as such known manner to opening of the control valve arrangement so that the working chamber  22  is temporarily connected to the ambient atmosphere. The vacuum chamber  20  is held constantly sub vacuo, in that it remains connected for example to a vacuum source or to the intake tract of the vehicle. As a result of the pressure difference that builds up at the movable wall  18 , the movable wall  18  is pressed in  FIG. 1  to the left, with the result that the control valve housing  30  is pulled along until the control valve arrangement  14  closes again. A quasi-stationary state is then reached, in which a specific braking effect is maintained. 
     When the driver eases off the pedal and reduces the pedal force to zero, the sealing seat  26  is opened, with the result that a pressure equalization may occur at the movable wall  18  in that the working chamber  22  is connected to the vacuum chamber  20 . As a result of this, upon release of the brake pedal the arrangement is moved by means of the resetting spring  38  back into the normal state shown in  FIG. 1 . 
     During this operation but also during starting of the vehicle, after which a vacuum builds up in the vacuum chamber  20 , the spring  38  may be excited into vibrations, which may then be transmitted via the control valve housing  30  and the force input element  12  to the brake pedal (not shown). In conventional brake systems, these vibrations would as a rule be rapidly reduced because of the inertia of the brake pedal and further components. In the course of the progressive use of components manufactured in a lightweight style of construction, such as for example a brake pedal manufactured from magnesium, such vibrations however occur to a greater extent and occasionally lead to unpleasant noises. 
     In this connection, the invention provides that the vibrations arising at the resetting spring  38  are, immediately upon their development, damped by means of the damping elements  48  and  50 . The damping elements  48  and  50  for this purpose are manufactured from a rubber-elastic material, for example from an elastomeric foam material, and ensure an effective damping of vibrations by acting directly on the outer periphery of the resetting spring  38 . 
       FIG. 2  shows by way of example a damping element  48  in a cup shape. It comprises a base  52 , onto which a hollow-cylindrical portion  54  is integrally moulded. In the centre, the base  52  is designed with a fastening opening  56 . During assembly, the damping element  48  may simply be mounted onto a fastening bolt  42  and is held in a stable position on the fastening bolt  42  by means of an interference fit between the fastening bolt  42  and the fastening hole  56  or by means of additional clamping or screw-connection means. The mutual abutment of the outer peripheral regions of resetting spring  38  and damping elements  48  and  50  ensures a reliable damping of the vibrations at the resetting spring  38 , even when the abutment extends only over the longitudinal portion a. 
       FIG. 3  shows an alternative constructional variant of a damping element  48 ′, which is formed cylindrically from a solid foam material body and has a central fastening opening  56 ′. The mode of operation of this damping element is identical to that of  FIG. 2 . The damping element  48 ′ according to  FIG. 3  exhibits an increased damping response compared to the damping element of  FIG. 2  because the entire peripheral region is deformed to a lesser extent than the region of the tubular portion  54  remote from the base  52  in the form of construction according to  FIG. 2 . 
       FIGS. 4 and 5  show a second embodiment of the brake booster device according to the invention. To avoid repetition, only the differences from the first embodiment are described, wherein for components of an identical type or of an identical effect the same reference characters as for the first embodiment are used, only with the lower case letter “a” as a suffix. 
     In contrast to the first embodiment according to  FIGS. 1 to 3 , in the second embodiment according to  FIGS. 4 and 5  only one damping element  58   a  is provided, the base of which is designed in the shape of a diamond with rounded corners, as  FIG. 5  reveals. It is further evident from  FIG. 5  that the damping element  58   a  has two fastening openings  60   a  and  62   a , as well as a central hole  64   a . The fastening openings  60   a  and  62   a  are used for mounting onto the fastening bolts  40   a  and  42   a . The diameter d of the central hole  64   a  is smaller than the inside diameter D of the resetting spring  38   a . The inside diameter d is however large enough to receive without contact the force output element  34   a  and a piston end of a master cylinder arrangement, which is connected to the force output element  34   a  but is not shown in the figures. 
     Because of such a dimensioning of the inside diameter d of the central hole  64   a , the damping element  58   a  extends in between two turns of the resetting spring  38   a  and acts at least in sections also on these turns. A vibrational movement of the resetting spring  38   a  is therefore damped in the region of these turns by friction as a result of the contact between damping element  58   a  and resetting spring  38   a . The damping element  58   a , as already explained, has been slipped onto the fastening bolts  40   a  and  42   a  and fixed thereon by means of an interference fit or additional clamping elements. It should further be mentioned that the damping element  58   a  is formed from elastically deformable material so that it may, on the one hand, adapt to the shape of the turns and, on the other hand, provide adequate damping. 
     In a development of the embodiment according to  FIG. 4 , it may also be provided that a plurality of damping elements  58   a  are slipped in axial direction onto the fastening bolts  40   a  and  42   a  and engage in each case between axially successive turns. 
       FIGS. 6 and 7  show a third constructional variant of the invention. Once more, only the differences from the first and second constructional variants of the invention are described and for components of an identical type and an identical effect the same reference characters are used, only with the lower case letter “b” as a suffix. 
     The form of construction according to  FIGS. 6 and 7  shows a damping element  66   b , which comprises a tubular damping body  68   b  and two fastening disks  70   b  and  72   b . The two fastening disks  70   b  and  72   b  are mounted on the respective axial ends of the damping body  68   b . As is evident from  FIG. 7 , the fastening disks  70   b  are designed likewise in the shape of a diamond with rounded edges. They do however have a relatively large central hole  74   b , which corresponds approximately to the outside diameter of the resetting spring  38   b . More precisely, the damping body  68   b  lies against the outer periphery of the resetting spring  38   b.    
     The form of construction according to  FIGS. 6 and 7  is notable for the fact that it lies over a relatively long axial region of the resetting spring  38   b  against the outer periphery thereof and may effectively dampen the vibrations thereof. By virtue of providing two fastening disks  70   b  and  72   b , the damped vibrations may be diverted more efficiently to the fastening bolts  40   b  and  42   b . What is more, by virtue of providing two fastening disks  70   b  and  72   b , a stable mounting of the damping element  66   b  in the housing  16   b  is guaranteed. The sectional representation according to  FIG. 6  reveals a cross section of the sealing element  66   b  in the shape of a U-section. 
     Finally,  FIGS. 8 and 9  show a further embodiment of the invention, wherein once more the same reference characters as before are used for components of an identical effect or of an identical type, only with the lower case letter “c” as a suffix. 
     This form of construction differs from the last-mentioned form of construction according to  FIGS. 6 and 7  in that the damping element  74   c  in cross section is designed like a T-section, i.e. with a tubular damping body  68   c  in the style of the form of construction according to  FIG. 6  but with only one fastening disk  70   c , which is disposed approximately in the centre of the tubular damping body  68   c  and extends from there radially outwards for the purpose of mounting on the fastening bolts  40   c  and  42   c.    
     A common feature of all of the forms of construction is however that the respective damping element is mounted on the fastening bolts and is therefore easier to assemble and more stable, in terms of positioning, throughout the life of the brake booster. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Technology Classification (CPC): 5