Abstract:
A device ( 100 ) for assembling a pneumatic booster ( 200 ) wherein a cover ( 203 ) of the booster is housed in a support ( 101 ) and a cylindrical cap ( 104 ) whose internal volume ( 107 ) is greater than a volume of a cylinder ( 206 ) of the booster, covers the cylinder placed on the cover. A gearing element ( 110 ) of the device rotates two sets of rollers ( 109 A and  109 B) about the booster and an eccentric ( 118 ) controlled by the gearing element allows an oscillating movement of the rollers against a wall of the booster. The swaging is achieved by alternately applying the rollers ( 109 A) and ( 109 B) and an angle of attack ( 114 A) of the first rollers is greater than an angle of attack ( 114 B) of the second rollers.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for assembling a pneumatic booster of a motor vehicle braking device. More precisely, the invention relates to a device making it possible to fixedly attach a cover and a cylinder of a pneumatic booster. The invention also relates to a method making it possible to assemble the cylinder and the cover by using the device of the invention. The invention finally relates to a pneumatic booster. 
     One object of the invention is to provide a booster that can be used safely in a braking device. Another object of the invention is to prevent a disassembly of the booster during its use, irrespective of the thickness of a metal sheet forming the booster. An additional object of the invention is to provide a booster that is lightweight, without its strength being affected. 
     In a motor vehicle braking device, a booster may be mounted between a brake control and a master cylinder. The pneumatic booster has the role of amplifying a force at the brake control, so that a hydraulic pressure in the master cylinder is greater. 
     A booster may be furnished with a generally cylindrical-shaped casing. The casing is formed of a cylinder and a cover. The cylinder and the cover are fixedly attached to one another. A front chamber and a rear chamber are arranged in an internal volume of the casing. The front chamber is directed toward the master cylinder, and has a variable volume. The rear chamber, equally with a variable volume, is directed toward the brake control. The front chamber is separated from the rear chamber by a movable partition. The movable partition is formed by a sealed and flexible membrane and by a rigid skirt plate. The front chamber is connected pneumatically to a vacuum source. The rear chamber is connected pneumatically, in a manner controlled by a valve, to a source of propelling fluid. A brake control actuates a control rod of the booster. The actuation of the rod controls the opening of the valve and an inflow of fluid into the rear chamber. The change of pressure that results therefrom causes a movement of the rigid skirt plate. 
     During braking, wrenching forces exerted at the location of the booster are extremely great. Specifically, the chambers of the booster are subjected to sudden changes of pressure. In particular, during braking, air is allowed into the rear chamber. This inlet of air propels the movable partition toward the front chamber. Since the casing of the booster is made of two originally independent parts, it is essential that these two parts are firmly fixed together. It is therefore necessary that the contact between the cover and the cylinder is sufficient so that, during braking and more precisely during the propulsion of the skirt plate, the cylinder is not wrenched away from the cover. 
     In order to ensure that the cover is properly attached to the cylinder, spot swaging is currently carried out on an external periphery of the walls of the cover and the cylinder. “Spot swaging” means swaging at localized points. In order to hold the cylinder firmly onto the cover, these swaging points are evenly distributed over the whole external periphery of the casing. Hitherto, such an assembly has been sufficient. 
     However, for some time, the search has been on to reduce the weight of the booster. Specifically, the booster and more precisely the booster casing is formed of metal sheet walls. A thickness of the metal sheet and a shape of the booster therefore have an effect on its weight. The search in particular is to reduce the weight of the booster by reducing the thickness of the metal sheet forming the casing. The thickness and the shape of the booster have been modified in order to obtain a minimum weight. “Minimum weight” means the lowest weight of the booster at which the same rigidity and the same resistance to wrenching as a conventional booster is obtained. 
     However, the breaking strength at the location of the join between the cover and the cylinder is reduced. A spot swaging of the cover with the cylinder therefore does not provide full satisfaction when the thickness of the metal sheet is greatly reduced. 
     SUMMARY OF THE INVENTION 
     The invention seeks in particular to solve this problem by providing a booster whose thickness and shape may be modified in order to obtain a minimum weight. The booster obtained is such that it has a great resistance to wrenching, including at the location of the join between the cover and the cylinder of the casing. 
     For this, the invention proposes a device for assembling a booster and more precisely a cover and a cylinder of a casing of the booster. The assembly device of the invention allows a continuous swaging, over the whole external periphery of the casing, of the cylinder and of the cover. Continuous swaging makes it possible to obtain a strong hold of the two parts, one on the other. The zone of contact offers a better resistance to the wrenching forces. 
     To achieve such a continuous swaging, the device of the invention is furnished with at least one set of rollers. The rollers are rotated about the booster. The rollers come into contact with the booster at the location of the join between the cover and the cylinder of the casing. The rollers, when they pass, fold one end of a metal sheet forming the wall of the cylinder around an end of a metal sheet forming the wall of the cover. 
     In a particular exemplary embodiment of the invention, the device is furnished with two different sets of rollers. The first set of rollers makes it possible to bend the end of the metal sheet forming the wall of the cylinder around the end of the metal sheet forming the wall of the cover, at a first angle. The second set of rollers, for its part, makes it possible to bend the metal sheet of the cylinder at a second, more acute angle than the first. A roller of the second set of rollers is not pressed against the external wall of the casing until a roller of the first set of rollers has first passed. 
     Thus, the rollers of the first set of rollers begin to bend the metal sheet of the cylinder. The first bending action makes it possible to bend, from an initial position parallel to an axis of rotation of the device, the metal sheet by thirty to sixty degrees. The metal sheet is thus partially pushed inward in the direction of the center of the booster. An initial position of the end of the wall of the cover is perpendicular to the end of the wall of the cylinder. “Initial position” means the position in which the cover and the cylinder are placed one on the other, but not attached to one another. After the pass of at least one roller of the first set of rollers, the metal sheet of the cylinder is folded back in the direction of the metal sheet of the cover, which it swages lightly. A roller of the second set of rollers is then pressed against the metal sheet of the casing, where the first roller passed, in order to further fold the metal sheet of the cylinder against the metal sheet of the cover. Ideally, the metal sheet of the cylinder is folded ninety degrees after the rollers of the second set of rollers have passed. 
     The sets of rollers of the device of the invention are, for example, furnished with three rollers each. The rollers of the first set are alternated with the rollers of the second set. For an assembly device of generally circular cylindrical shape, the rollers are distributed evenly over a complete perimeter of the device. Thus, for example, a roller of the first set is separated by 120° from another roller of the first set. A roller of the first set is separated by 60° from a roller of the second set. 
     So that the swaging is carried out in two successive steps, the rollers of the second set must be pressed against the wall of the casing only at the locations where the rollers of the first set have already passed. For this, in addition to a rotary movement of the rollers about the booster, each of the rollers is forced to make an alternating radial movement relative to the booster. Such an oscillating movement is made possible by an eccentric mechanism of the assembly device. The rollers of the two sets are angularly out of phase with one another. The rollers of one and the same set are however angularly in phase. Thus, the rollers of the first set and then the rollers of the second set are alternately brought toward the center of the booster. This is how to obtain a continuous swaging of the casing of the booster in one or more complete rotations of the rollers about the booster. 
     The invention also proposes a method of assembling the casing of the booster. The method of the invention makes it possible to swage the cover and the cylinder of the casing in a continuous manner over the whole external perimeter of the casing. 
     The subject of the invention is therefore a pneumatic booster for a motor vehicle braking device, characterized in that a cover and a cylinder of said booster are attached to one another over a complete external contour. 
     A further subject of the invention is a device for assembling a pneumatic booster, characterized in that it comprises
         a fixed cylindrical support whose internal volume is greater than the volume of a cover of the booster, the cover being housed in the support,   a cylindrical cap whose internal volume is greater than the volume of a cylinder of the booster, said cap imposing an axial load on the cylinder,   at least one set of rollers, rotated by a motor, the rollers rotating at least partially about the support.       

     An additional subject of the invention is a method of swaging a booster, characterized in that it comprises the steps
         a cover of a booster is inserted into a support of a swaging device, a top end of a wall of the cover resting on a top end of an internal wall of the support,   a cylinder of the booster is placed on the cover, a bottom end of a wall of the cylinder resting on the top end of the wall of the cover,   a cap of the swaging device is placed on the support, a bottom end of the cap compressing the bottom end of the wall of the cylinder onto the top end of the wall of the cover,   a motor is actuated,   the swaging rollers are made to rotate about the booster, by means of the motor,   the bottom end of the wall of the cylinder is swaged continuously onto the top end of the wall of the cover.       

     The invention will be better understood on reading the following description and on examining the figures that accompany it. The latter are given as an indication and in no way limit the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section of a booster housed in an assembly device of the invention; 
         FIG. 2   a  and  FIG. 2   b  are enlarged views of  FIG. 1  at the location of a connection between a cover and a cylinder of the booster, and of a roller of the invention; and 
         FIG. 3  is a cross section of an assembly device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an exemplary embodiment of a device  100  for assembling a booster  200 . The device  100  is furnished with a fixed support  101 . In the example represented in  FIG. 1 , the support  101  has a generally cylindrical shape. An internal volume  102  of the support  101  is such that it is possible to insert therein a rear portion  201  of the booster  200 . “Rear portion  201  of the booster  200 ” means a control rod  202  and cover  203  of the booster  200 . The cover  203  also has a generally cylindrical shape. 
     One end  2004  of a wall  205  forming the cover  203  rests on a top end  105  of a center positioner  106 . The center positioner  106  is, for example, generally ring-shaped. A diameter of the ring  106  is approximately equal to an internal diameter of the support  101  in the location of a top end  103  of the support  101 . Thus, the center positioner  106  is placed in an internal perimeter of the support  101  in the location of a top end  103 . The center positioner  106  makes it possible to ensure a good position for the cover  203 . “Good position of the cover  203  in the support  101 ” means a position allowing the device  100  to successfully assemble the booster  200 . 
     In another exemplary embodiment, the center positioner  106  consists of at least two distinct parts. Thus, the center positioner  106  does not fully follow the internal contour of the support  101 . It may be placed evenly, at different points on the internal diameter of the support  101 . The various elements forming the center positioner  106  thus make it possible to support the cover  203  at certain points and to center it. In another embodiment, it is also possible to use no center positioner  106 . The cover  203  then rests directly on the support  101 , at the location of the top end  103  of said support  101 . 
     Once the cover  203  has been placed in the interior  102  of the support  101 , a cylinder  206  of the booster  200  is positioned. The cylinder  206  forms a front portion of the booster  200 . The cylinder  206  has a generally cylindrical shape. The cylinder  206  is placed on the cover  203  so that an end  208  of a wall  209  forming the cylinder  206  rests on the end  204  of the cover  203 . In the example shown in  FIG. 1 , an end  211  of a sealing membrane  210  of the booster  200  forms a fold  211 . The fold  211  is trapped between the ends  204  and  208  respectively of the cover  203  of the cylinder  206 . The fold  211  particularly provides a seal at the location of contact between the cover  203  and the cylinder  206 . 
     A cap  104  of the assembly device  100  is then placed on the support  101 . The cap  104  is generally cylindrical in shape. An internal volume  107  of the cap  104  is such that the cylinder  206  can be housed therein. A first end  108  of the cap  104  rests against the end  208  of the wall  209  of the cylinder  206 . “First end” means in the description the end directed toward the left in the figure. Conversely, “second end” means in the description the end directed toward the right in the figure. The end  108  of the cap  104  is then pressed in a direction D onto the end  208  of the cylinder  102 . This imposes an axial load at the location of the connection between the cover  203  and the cylinder  206 . The fold  211  is compressed between the two walls  205  and  209  at the location of their ends, respectively  204  and  208 . 
     Rollers  109  (two rollers visible in  FIG. 1 ) are placed on an outer periphery of the support  101 .  FIG. 3  shows more precisely the disposition of the rollers  109  of the device  100 . The rollers  109  are six in number. Rollers  109 A of a first set are interspaced with rollers  109 B of a second set. The rollers  109  are placed evenly over the whole periphery of the support  101 . 
       FIG. 1  shows that the rollers are in contact with the booster  200  at the location of the connection between the cover  203  and the cylinder  206 . 
       FIGS. 2   a  and  2   b  show two enlargements, respectively an enlargement of  FIG. 1  at the location of contact between a roller  109 A and the booster  200 , and at the location of contact between a roller  109 B and the booster  200 . In both cases, it can be seen that the end  204  of the cover  203  rests on the top end  105  of the center positioner  106 . Similarly, the fold  211  of the sealing membrane  210 , compressed between the end  204  of the cover  203  and the end  208  of the cylinder  206  can be seen. The end  208  of the cylinder  206  is compressed by the end  108  of the cap  104 . The end  208  of the cylinder  206  is approximately parallel to an axis of rotation of the center positioner  106 . The end  204  of the cover  203 , for its part, is perpendicular to the end  208 . The end  208  extends toward the right in  FIG. 2   a  beyond a point of contact with the end  204 . 
     In the invention, the end  208  can be bent around the end  204  and the fold  211  so that the end  208  is ideally perpendicular to the axis of the center positioner  106 . The desire is to achieve such a bend on the whole periphery of the booster  200 . 
     For this, as shown in  FIG. 1 , the assembly device  100  is furnished with a gearing element  110  rotating the rollers  109  all about the booster  200 . The gearing element is itself rotated by a motor (not shown). The gearing element  110  is furnished with two gear wheels  111  and  112 . The wheels  111  and  112  have a different number of teeth. 
     By means of the first wheel  111 , the gearing element  110  rotates the whole set of rollers  109 A and  109 B about the booster  200 . The second gear wheel  112  rotates an eccentric  118  imposing a periodic sinusoidal movement on the rollers  109 . Thus, by means of this eccentric  118 , the rollers  109  are not pressed continuously against the walls  205  and  209  of the booster  200 . 
     When the assembly device  100  is placed in motion, the rollers  109  rotate continuously all about the booster  200  and are pressed radially against the walls  205  and  209  of the booster  200  in a periodic intermittent manner. The sets of rollers  109 A and  109 B are angularly out of phase. The angular-out-of-phase arrangement is such that it allows a pressure of the rollers  109 A against the wall of the booster  200  to alternate with a pressure of the rollers  109 B. 
     In order to achieve a good swage, the desire is to press the rollers  109 A radially against the booster  200  before the rollers  109 B. Specifically, the rollers  109 A and  109 B differ from one another in their angles of attack.  FIGS. 2   a  and  2   b  show that the rollers  109 A and  109 B are all furnished respectively with a bevel  113 A and  113 B. A beveled cut forming the bevels  113 A and  113 B is made on a top face of the rollers  109 A and  109 B. The shape of the bevels  113 A and  113 B is different. Specifically, an angle of attack  114 A of the bevel  113 A is greater than the angle of attack  114 B of the bevel  113 B. “Angle of attack” means the angle formed by the beveled cut of the bevels  113 . 
     A first contact between the roller  109 A and the end  208  of the wall  209  of the cylinder  206  makes it possible to slightly bend the end  208  in the direction of an axis C of the support  101 . The roller  109 B is then pressed against the end  208  that is already partially bent. Since the angle of attack  114 B is less than the angle of attack  114 A, it is possible to bend the end  208  slightly more in the direction of the axis C. 
     For example, the angle of attack  114 A lies between 115° and 135°. The angle of attack  114 B, for its part, lies between 80° and 90°. In a preferred example, the angle of attack  114 A is 120°. Thus, the end  208  is folded 60° during the pass of the roller  109 A. Then, during the pass of the roller  109 B, the end  208  is bent an additional 25°. Finally, the end  208  is virtually perpendicular to the axis of the center positioner  106 . The end  208  swages the end  104  while trapping the fold  211 . 
     In the invention, such a swaging operation is performed over the whole periphery of the booster  200 . The device  100  makes as many rotations around the booster  200  as necessary for the cylinder  206  to be attached to the cover  203 . 
       FIG. 1  shows a particular exemplary embodiment of the device making it possible to rotate the rollers  109  and impart thereto a radially oscillating movement relative to an axis C of the support  101 . 
     The gear wheel  111  of the gearing element  110  rotates a pinion  115 . A body  116  is attached to the pinion  115 . The body  116  is therefore rotated by the rotation of the wheel  111 . The body  116  is thus rotated all around the support  101 . The wheel  112  of the gearing element  110  rotates a pinion  117 . The pinion  117  is attached free in rotation to the body  116 . Thus, the pinion  117  rotates independently of the body  116 . The rotations of the body  116  and of the pinion  117  depend respectively on the rotation of the wheel  111  and the wheel  112  of the gearing element  110 . The number of teeth of the wheel  111  is different from the number of teeth of the wheel  112 . The body  116  and the pinion  117  therefore do not rotate at the same speed. The pinion  117  rotates the eccentric  118  by means of a pinion  119 . The eccentric  118  follows at least partially an internal periphery of the body  116 . 
     The rollers  109  are mounted on a top end of the eccentric  118 . The eccentric  118  is attached to the body  116 . The rollers  109  are therefore rotated all about the booster  200 . But since the eccentric  118  is also in contact with the pinion  117 , the pinion  117  imposes a radial oscillating movement relative to the axis C of the support  101  on the eccentric  118  and the rollers  109 . 
     This gives, in addition to a rotary movement of all the rollers  109  about the booster  200 , a radial oscillating movement of each of the rollers  109  relative to the axis C of the support  101 . The rollers  109  are therefore periodically pressed against the wall of the booster  200  and then separated therefrom. The angular-out-of-phase arrangement between the rollers  109 A and the rollers  109 B makes it possible to press the rollers  109 A first against the wall of the booster  200 . The rollers  109 B are pressed only after the rollers  109 B have passed.