Abstract:
In order to improve the deformation behavior of a vacuum brake booster provided with force transmission pins that are used to transmit forces onto a body splashboard of a motor vehicle, the invention discloses that the force transmission pins are made up of two sections having different strength. To achieve a sufficiently low strength when a fastening screw is used for a first section, the first section is embodied as a hollow body, and the fastening screw extends only over the length of a second section of the pin. Because the first section is configured as a hollow body, the screw arranged in the second section can be actuated through the first section.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a vacuum brake booster for motor vehicles with a booster housing including two opposed housing shells, with at least one movable wall subdividing the interior of the booster housing, as well as with at least one force transmission pin that extends in parallel to the longitudinal axis of the vacuum brake booster from one housing shell to the housing shell arranged on the opposite side of the movable wall and is sealed in relation to the movable wall, and at the ends of which force transmission pin fastening elements for a vehicle body wall or a master brake cylinder connected downstream of the vacuum brake booster are designed.  
       BACKGROUND OF THE INVENTION  
       [0002]     A vacuum brake booster of this type is disclosed in German patent DE 28 45 794. A disadvantage of this prior art vacuum brake booster is its unfavorable deformation behavior in accidents, causing deformations of the front part of the motor vehicle. The cause for this are the force transmission pins that increase the rigidity of the booster housing, have a comparatively large diameter and, in an accident, exert an excessive resistance against deformation of the booster. Consequently, the splashboard of the vehicle is deformed, whereby the position of the bearing for the pedal will change so that the pedal can injure the driver in an accident. Details on this feature are described in DE 19524492.  
         [0003]     DE 19523021 A1 discloses a vacuum brake booster for motor vehicles with a force transmission pin, said force transmission pin changing its length when a predetermined longitudinal force is exceeded.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     In view of the above, an object of the present invention is to disclose novel measures for a vacuum brake booster for motor vehicles with a booster housing including two opposed housing shells, with at least one movable wall subdividing the interior of the booster housing into two chambers, as well as with at least one force transmission pin that extends in parallel to the longitudinal axis of the vacuum brake booster from a first housing shell to the second housing shell arranged on the opposite side of the movable wall and is sealed in relation to the movable wall, and at the end of which force transmission pin preferably fastening elements for a vehicle body wall or a master brake cylinder connected downstream of the vacuum brake booster are designed, with the force transmission pin including at least one first section and one second section enabling further improvement of the booster&#39;s deformation behavior in accidents.  
         [0005]     A first solution of this object involves that the force transmission pin includes at least one first section and one second section, and that the material cross-section of the first section is chosen to be small compared to the material cross-section of the second section to such an extent that it decreases its length extending in the longitudinal direction of the pin when a predetermined force is exceeded. A very simple construction is achieved thereby, and the separate provision of special predetermined breaking points is avoided. The first section is shortened alone by its reduced strength or its strength reduced compared to the second section. On the other hand, the position of the shortened length that results from bulging or buckling is fixed by the position of the first section.  
         [0006]     In a preferred aspect of the invention, it is advisable that the first section is configured as a hollow cylinder, whose wall thickness is chosen so be so thin that the first section will reduce its length extending in the longitudinal direction of the pin when a predetermined force is exceeded. This provides an option in particular for the case that it is desired to screw the booster from the tandem master cylinder to the splashboard by means of a screw that projects through the booster. In this case, the screw can be introduced through the hollow cylinder of the first section, the outside peripheral surface of which is sealed in relation to the interior of the housing.  
         [0007]     It is preferred according to a favorable aspect of the invention that the pin comprises a second section designed as a hollow cylinder, and in that a fastening screw extends through the second section and is supported with its screw head at least indirectly on the end surface of the section that forms the second cylinder and, with its threaded other end projects through the second housing shell close to the body wall. Thus, a sealed passage is achieved through which the screw can extend for attachment. The difficulty is that the screw shall be rigid enough to anchor the booster at the splashboard. On the other hand, a screw disposed in the first section would considerably reinforce the section&#39;s strength. Buckling or bulging of the first section when subjected to a sufficient amount of longitudinal force would therefore be no longer ensured. Further features of claim  3  provide a remedy in this respect. More specifically, the screw is lowered so deeply into the hollow cylinder of the first section that the screw can no longer contribute to reinforcement of the first section. Nevertheless, it is still possible to fasten the booster, coming from the master cylinder, by means of a screw that extends through the housing.  
         [0008]     In an improvement of the invention, the first and the second section are integrally formed or non-detachably interconnected. The non-detachable connection may e.g. be made by means of welding, soldering, cementing, form-lock or similar connection methods.  
         [0009]     A simple possibility of supporting forces that act on the second section can be achieved because the first section is provided with a projection preferably made by deformation, with pressure forces that act on the first housing shell or, as the case may be, tension forces being supported on said projection.  
         [0010]     A second solution of the object underlying the invention involves that the force transmission pin includes at least one first section and one second section, that the first section and the second section are configured as hollow cylinders, that the first and the second section are fixed in relation to each other by a holding connection in the longitudinal direction of the pin, that the holding connection is disengaged and the two sections are telescoped into each other when a predetermined force that acts in the longitudinal direction of the pin is exceeded, and that a fastening screw extends through the second section and is supported with its screw head on the end face of the cylinder forming the second section and with its other, threaded end projects through the second housing shell close to the body wall. This obviates the need for different strength or material thickness of the two sections. The second section is rather reinforced by the screw that extends only through it, yet does not contribute to reinforcing the first section. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  for better comprehension of the state of the art, is a view of a vacuum brake booster including a pin disclosed in DE 19523021 of the species of a brake booster to be taken from the preamble of claim  1 .  
         [0012]      FIG. 2  is a first embodiment of the invention.  
         [0013]      FIG. 3  is a second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The vacuum brake booster  1  shown in  FIG. 1  shows a booster housing  2  formed of two interconnected housing shells  20 ,  21 , of which especially housing shell  20  illustrated on the left in  FIGS. 1 and 2  carries a master brake cylinder (not shown), while the housing shell  21  illustrated on the right is attached to a motor vehicle body wall (likewise not shown). In a cylindrically designed extension (not shown) of the right housing shell  21 , a control housing  8  is slidably guided in a sliding sealing ring  3  and houses a control valve  9  that is operable by means of an input member  4  coupled to a brake pedal (not shown). At its end remote from the input member  4 , the control housing  8  carries a movable wall  5  formed of a diaphragm plate  22  and a rolling diaphragm  23  abutting thereon, said movable wall subdividing the interior of the brake booster housing  2  into a vacuum chamber  6  that can be evacuated and a working chamber  7 , with control valve  9  permitting a connection between the working chamber  7  and the vacuum chamber  6  or the atmosphere. The control valve  9  is preferably formed by two coaxially arranged annular sealing seats  10 ,  11  which cooperate with a rotationally symmetrical elastic valve member  12 , e.g. a poppet valve, or abut thereon in the release position of the vacuum brake booster  1 . The first sealing seat  10 , opening of which allows a connection between the two chambers  6 ,  7 , is designed in the control housing  8 . The second sealing seat  11 , opening of which allows ventilation of the working chamber  7 , is designed on a valve piston  15  that is guided in the control housing  8  and is in a force-transmitting connection with input member  4 . The valve piston  15  is in a force-transmitting connection with a rubber-elastic reaction plate  13  arranged in a cylindrical recess  16  of the control housing  8 , said reaction plate permitting a transmission of both the actuating force introduced at the input member  4  and the boosting force generated by the movable wall  5  onto an output member  14  that cooperates with a master brake cylinder piston (not shown).  
         [0015]     Preferably two rod-shaped force transmission pins are provided within the booster housing  2 , arranged in parallel to the longitudinal axis of the brake booster, with one of them designated by reference numeral  17  being shown. The control housing  8  carrying the movable wall  5  is displaceably guided on this connecting pin  17  and, therefore, is able to move uninhibited in an axial direction during operation. The sealing of the force transmission pins  17  in apertures  19  designed in the control housing  8  is preferably done by sliding seals integral with the rolling diaphragm  23 , with the sliding seal associated with the force transmission pin  17  being shown and designated by reference numeral  24 .  
         [0016]     To attach the above-mentioned master brake cylinder to the housing shell  20  shown on the left in  FIG. 1  or the vacuum brake booster  1  to the body splashboard, fastening elements  25 ,  26  provided on the ends of the force transmission pins  17  are associated with the two housing shells  20 ,  21 . To ensure that a defined deformation of the booster housing  2  occurs in an accident that has deformations of the vehicle front part as a result, the force transmission pins  17  include three radial grooves or notches  18 ,  27 ,  28 . While the grooves or notches  18  and  28  are designed in the area of the fastening elements  25 ,  26 , the third groove or notch  27  is disposed in the area of the apertures  19  through which the force transmission pin  17  extends and receives the above-mentioned sliding seal  24 . The grooves or notches  18 ,  27 ,  28 , the influence of which in the transmission of forces is well known to the one skilled in the art, may preferably have a triangular, square or semicircular design in cross-section. However, other cross-sectional shapes are of course feasible as well. Favorably, the force transmission pins  17  may also be seal-tightly coated with a plastic layer  56  that has gliding qualities.  
         [0017]     It is particularly disadvantageous in the prior art solution that the booster cannot be screwed to the splashboard directly by a screw projecting through the housing without minimizing the collision protection of the booster. Figure z shows how this is possible with the invention nevertheless. Only those components that differ from  FIG. 1  are described.  
         [0018]      FIG. 2  shows a pin  101  for force transmission, which is formed of a first section  102  and a second section  103 . A fastening screw  112  extends through the housing wall  120  of a first housing shell  121 . The fastening screw  112  has a bore  122 . Bore  122  receives the end of the first section  102  being thus sealedly held in housing  121 . A circumferential edge  123  takes up the tensile forces that act on the first section  102 . The first section  102  is sealed by means of a seal  114 . Externally acting longitudinal forces at the first section  102  are conducted by way of a circumferential projection  105  at the first section  102  to the housing  121  by way of a spacer  106 . The second section  103  is sealed and connected to the first section  102 . In the area of the connection, a step  108  is provided through which longitudinal forces can be transmitted to the right in  FIG. 2  by way of a screw  117 . The setup of the connection between the first section  102  and the second section  103  as shown in  FIG. 2  is not imperative for the invention. The two sections can also be integrally connected to each other. It is only significant that there is a projection allowing a screw  117  to make catch at pin  101  with its two sections so that the screw in  FIG. 2  can apply longitudinal forces to the right, by which the booster can be drawn against the splashboard. The section  103  is sealingly applied to a wall (not shown) of the second housing shell in such a fashion that the screw  117  is able to exert longitudinal forces beyond its edge  110  on the second housing shell (not shown). To this end, there is an opening (not shown in the drawing) in the second housing shell through which the end of the screw extends through the second housing shell and can be connected to the splashboard. The function of the illustrated notch of screw  117  has already been described with regard to  FIG. 1 , it is, however, not absolutely necessary in the present embodiment. Screw  117  may include a hexagon socket  118  by way of which it can be tightened from the outside by means of a tool reaching through the first section  102 .  
         [0019]     It is especially important for the invention that the rigidity of the first section  102  vis-à-vis longitudinal forces, especially pressure forces, is significantly lower than that of the second section  103  having not only a larger wall thickness but, in addition, being also reinforced vis-à-vis lateral forces by the screw  117 . Thus, screw  117  has two functions: it is not only used to fasten the booster to the splashboard but additionally reinforces the strength of the second section  103 . Also, it is this way possible to define the place of the deformation of the pin in a crash more precisely.  
         [0020]     The following features are important for dimensioning pin  101 . The pin must be apt to take up the longitudinal forces and pressure forces necessary for the mode of operation of the booster without becoming deformed. On the other hand, the pin shall be shortened compared to the normal distance of its two ends for the case that the pressure forces that act on it exceed a defined value. The second section  103  of the pin now as before must be able to take up the additional longitudinal forces required to hold the booster on the splashboard. Another requirement is that the first section now as before makes catch at the second housing section  121  by a simple measure, which is satisfied by the circumferential projection  105  in the present case.  
         [0021]     The solution of  FIG. 3  differs from the solution of  FIG. 2  as follows. On the one hand, the wall thickness of the first section  102  is as strong as the wall thickness of the second section  103 . The connection  119  between the first section  102  and the second section  103  is chosen such that it can be disrupted by a sufficient amount of force in the longitudinal direction of pin  101 . The force necessary for disrupting the connection is higher than the forces that normally develop in the mode of operation of the booster. This force occurs in a crash. When the connection is disengaged in a crash, longitudinal forces can no longer be transmitted by way of pin  101 , and the first section  102  is displaced telescopically over the second section  103 , thereby reducing the length of the pin  101 .