Patent Publication Number: US-7905002-B2

Title: Method of manufacturing a steel housing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Application No. PCT/EP2005/013606, filed on Dec. 16, 2005, which claims priority under 35 U.S.C. § 119 to German Application Nos. 10 2004 060 862.8, filed Dec. 17, 2004 and 10 2005 053 674.3, filed Nov. 10, 2005, the entire disclosures of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention is based on a method for manufacturing steel housings, composed of at least two housing components, for assemblies installed in vehicles, in particular in utility vehicles. 
     In order to activate brakes in utility vehicles, use is made, inter alia, of combined pneumatic service brake cylinders and spring brake cylinders. Such a combination cylinder is, connected in series, a combination of a service brake cylinder for activating the service brake and a spring brake cylinder for activating the auxiliary (parking) and spring brake. 
     A method is known from EP 1 136 337 B1, which discloses a combined service brake cylinder and spring brake cylinder of a utility vehicle, in which the housing of the service brake cylinder and the housing of the spring brake cylinder are connected to one another by the edge of the spring brake cylinder overlapping the edge of the service brake cylinder in a positively locking fashion, which is also referred to as beading. 
     Such beading is frequently produced by rolling, i.e. the edge of at least one housing component is shaped plastically by a circulating rolling tool. However, at least the outwardly pointing surface of the housing components must firstly be provided with a corrosion prevention means since assemblies of vehicles, such as, for example, combined service brake cylinders and spring brake cylinders of utility vehicles which are arranged near to the wheel, are subjected to moisture which is permeated by de-icing salt. Corrosion prevention layers which are used in this context are composed, for example, of a sprayed-on epoxy plastic layer or of a simple zinc layer. However, it has become apparent that the corrosion prevention layer can be damaged by the beading fabrication step and therefore the necessary resistance to corrosion is not achieved, the resistance being, for example, that the housing has to withstand over 400 hours of uninterrupted wetting with salt water without corroding. 
     The invention is based on the object of developing a method for manufacturing housings, composed of at least two housing components, for assemblies installed in vehicles, in particular in utility vehicles, in such a way that it permits beading which shapes the housing components to be fabricated without adversely affecting the corrosion prevention means of such housing components. 
     This object is achieved according to the invention by application of a corrosion prevention layer comprising zinc or an alloy containing zinc to at least one outwardly pointing surface of at least one housing component with subsequent passivation, and manufacture of a positively locking overlap by the edge of one housing component over the edge of the other housing component by way of relative movement of the housing components which have previously been oriented with respect to one another and in relation to a die which plastically shapes the edge of one housing component and/or the edge of the other housing component. 
     The invention is based on an advantageous combination of two method steps, specifically on the one hand the fabrication of beading by use of a die and, on the other hand, the coating of the surface with a corrosion prevention layer comprising zinc or an alloy containing zinc, and subsequent passivation. It has become apparent that such a corrosion prevention layer is not damaged if the beading is manufactured with a die. 
     The protection against corrosion which is provided by the zinc or the other metal alloys is due to the fact that it is even more stainless than the basic metal steel and therefore functions as the sacrificial anode. As long as the covering zinc layer is present, the basic metal is protected against corrosion. Other metals can influence the corrosion protection provided by the zinc layer. Iron, nickel or cobalt are therefore used selectively as alloy components for the purpose of bringing about improvement. The zinc is itself protected against corrosive attack by the passivation, generally by chromatization. The thicker, denser and more chemically resistant the layer of chromate, the better the barrier effect. 
     As a result of this, a high degree of resistance to corrosion is provided for a housing which is manufactured according to the inventive method, and a high degree of operational reliability is provided, which is essential in particular if the component is a brake cylinder. 
     Advantageous developments and improvements of the invention are described herein. 
     The assembly whose housing is fabricated by the method according to the invention is preferably a brake cylinder, in particular a combined service brake and spring brake cylinder, an air dryer or a brake booster of a utility vehicle, therefore assemblies with sheet metal housings which have at least two components and are, for example, deep drawn. 
     The relative movement between the die and the housing components particularly preferably occurs in an axial direction with respect to a central axis of the assembly. Alternatively, the relative movement can occur in a radial direction with respect to the central axis of the assembly. 
     The die can be embodied as a single-component or multi-component ring with a radially inner recess which exerts pressure against the edge of the one housing component and/or the edge of the other housing component. In the case of an axial relative movement between the die and the housing halves, the die can be embodied as a single component or multiple components, and in the case of a radial relative movement it can only be in multiple components, for example if the housing components have regions which project radially beyond their end edges and would therefore collide with a single-component ring which is guided in the axial direction and surrounds the housing components. 
     Before the application of the die, for example one housing component is clamped in through a clamping device and the other housing component is fitted onto the latter in such a way that the edges of the housing components overlap. The reaction forces which arise during the deformation are held then by the housing components themselves or by structures which are located in the interior, and are conducted away via the clamping device. In cases in which this is possible, a die plate which is assigned to the die can be dispensed with, otherwise, if the housing components are not sufficiently rigid, there has to be a fixed die plate which absorbs the reaction forces and can additionally serve to shape the beading by being provided with corresponding recesses itself. 
     In order to keep the forces occurring during deformation low, before the application of the die, the edge of one housing component can be preshaped to form a shoulder which projects radially outward. This may have already taken place within the scope of a preceding deep drawing process. Particularly good rigidity of the beading connection is obtained if this shoulder has an undercut cross section. 
     Particularly good protection against corrosion is obtained if the corrosion prevention layer has pure zinc, a zinc/iron alloy, or an alkaline zinc/nickel alloy, and the passivation includes chromatization. In order to meet the EU guideline 2000/53/CE, solutions containing chromium (VI) (chromium in the hexavalent state) should be avoided. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a half-sectional illustration of a combined service brake and spring brake device, which has been fabricated in accordance with a preferred embodiment of the method of the invention; 
         FIG. 2  is a schematic cross-sectional illustration of the combined service brake and spring brake device from  FIG. 1  during a fabrication step; 
         FIG. 3  is a schematic cross-sectional illustration of the combined service brake and spring brake device from  FIG. 1  during a further fabrication step; and 
         FIG. 4  is a schematic cross-sectional illustration of the combined service brake and spring brake device from  FIG. 1  during a still further fabrication step. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an already completed, combined service brake and spring brake device  1  according to a preferred embodiment of the invention. The latter includes a service brake device  2  with a steel service brake cylinder  4  in which a service brake piston  6 , which is acted on pneumatically, is guided and which activates, via a service brake piston rod  8 , for example a disk brake (not illustrated for reasons of scale) of a utility vehicle. Furthermore, there is a spring brake device  10  with a steel spring brake cylinder  12  in which a spring brake piston  18 , which can be clamped by pneumatic pressure in a spring brake chamber  14  counter to the spring force of a storage spring  16 , and by which the service brake piston  6  can be acted upon in the brake-applying direction. The service brake cylinder  4  and the spring brake cylinder  12  form, in their coaxial arrangement one behind the other, a combination brake cylinder  20 . Furthermore, steel attachment bolts  22  project away from the service brake cylinder  4  at the head end in order to be able to attach the combination brake cylinder  20  to the vehicle. 
     A spring brake piston rod  24  of the spring brake piston  18  projects in a seal-forming fashion through an opening  26  in a dividing wall  28  between the spring brake cylinder  12  and the service brake cylinder  4  and can bear with its end face against the service brake piston  6 . The latter can contain an axially movable diaphragm  32  which is clamped in at the outer edge between the dividing wall  28  and a radially outer shoulder  30  on the edge of the service brake cylinder  4 , as well as a central piston plate  34  which is connected to the diaphragm  32 . 
     The shoulder  30  is bent over preferably through more than 90 degrees so that an oblique contact face with respect to the diaphragm  32  is produced. On the other hand, the dividing wall  28  is also provided at its radially outer edge with an oblique contact face so that a cross section which extends radially outward in wedge shape is produced between them, in which cross section the outer edge  36 , which is recessed in a complementary fashion, of the diaphragm  32  is held in a positively locking fashion. 
     Furthermore, the spring brake piston  18  can be moved in a known fashion into the release position counter to the effect of the storage spring  16  by venting the spring brake chamber  14 . Furthermore, by venting a service brake chamber  38 , which extends between the dividing wall  28  and the service brake piston  6 , it is possible to move the latter into a brake-application position counter to the effect of a return spring  40  which is supported at one end on the service brake piston  6  and at the other end on an end wall of the service brake cylinder  4 . Last but not least, a mechanical release device  46  with which emergency release of the spring brake can be carried out if there is a drop in pressure is integrated within the spring brake piston rod  24 . 
     Against this background, the method of functioning of the combined service brake and spring brake device  1  is as follows. 
     Taking the situation shown in  FIG. 1  as a basis, in which both the spring brake and the service brake are released, the service brake chamber  38  is vented in order to apply the service brake, after which, on the one hand, the service brake piston  6  is moved to the left away from the dividing wall  28 . The displacement of the service brake piston  6  causes, for example, a disk brake to be applied. 
     On the other hand, venting the service brake chamber  38  ensures that the service brake piston  6  is moved into the release position, i.e. to the right in  FIG. 1 , by the return spring  40 , and bears against the end face of the spring brake piston rod  24  or the dividing wall  28 . 
     In order to hold the service brake in the brake application position for longer, i.e. if the pneumatic pressure in the service brake chamber  38  has dropped after a certain time or the service brake chamber  38  has been selectively vented, the spring brake should now be applied. For this purpose, the spring brake chamber  14  is vented, after which the storage spring  16  forces the spring brake piston  18 , together with the spring brake piston rod  24 , to the left in  FIG. 1 , said spring brake piston rod  24  being in contact at the end with the service brake piston  6 . This movement is followed by the service brake piston  6  and the service brake piston rod  8  which is coupled to it and which moves or keeps the disk brake in the applied position. 
     Within the scope of the method for manufacturing the combination brake cylinder  20  before the service brake cylinder  4  and the spring brake cylinder  12  are equipped with the components and assemblies described above, at least the outward pointing surfaces of the two cylinders  4 ,  12  and the attachment bolts  22  which are essential for secure attachment of the combination brake cylinder  20  are firstly coated with a corrosion prevention layer comprising zinc or an alloy containing zinc. 
     The protection of the zinc and of the further metal alloys against corrosion is due to the fact that it is even more stainless than the basic metal steel and therefore functions as a sacrificial anode. As long as the covering zinc layer is present, the basic metal remains protected against corrosion. Other metals can influence the protection of the zinc layer against corrosion. Iron, nickel or cobalt can therefore be selectively used as alloy components for the purpose of improvement. The zinc is itself protected against corrosive attack by the passivation, preferably by chromatization. 
     Particularly good protection against corrosion is obtained if the corrosion prevention layer has pure zinc, a zinc/iron alloy or an alkaline zinc/nickel alloy and the passivation includes chromatization. In order to meet the EU European guideline 2000/53/CE, solutions containing chromium (VI) (hexavalent chromium) should be avoided. 
     The service brake cylinder  4  and the spring brake cylinder  12  are then equipped with the components and assemblies described above. For this purpose, for example the dividing wall  28  is pushed into the spring brake cylinder  12  axially from above until it makes contact, with a shoulder  48  which is formed on its radially outer circumferential face, with a complementary shoulder  50  in the outer casing wall of the spring brake cylinder  12 , as a result of which an axial stop is formed. 
     Referring to  FIGS. 2-4 , the connection between the two cylinders  4 ,  12  is produced by beading  54  by firstly clamping, for example, the spring brake cylinder  12  with its outer casing surface radially into a clamping device  56  and fitting the service brake cylinder  4  onto the spring brake cylinder  12  in such a way that its edges  30 ,  52  overlap, i.e. on the one hand the straight end edge  52  of the spring brake cylinder  12  radially encloses the edge of the service brake cylinder  4  which is shaped as a radially outer shoulder  30 , and on the other hand an axial overlap occurs because the straight edge  52  of the spring brake cylinder  12  projects axially a certain distance beyond the shoulder  30  of the service brake cylinder  4 . The service brake cylinder  4  is, on the one hand, secured and centered in this position by, for example, its attachment bolts  22 , which are plugged through openings in a fixed head plate  58  as part of the clamping device  56 . On the other hand, the edge  36  of the diaphragm  32  of the service brake piston  6  is already positioned between the dividing wall  28  and the shoulder  30 . This initial position is illustrated in  FIG. 2 . 
     The beading  54  is produced by a relative movement of a die  60  with respect to the service brake and spring brake cylinders  4 ,  12  which have previously been oriented with respect to one another and which plastically shaped, for example, only the initially still straight edge  52  of the spring brake cylinder  12 . For this purpose, the die  60  is preferably embodied as a single-component ring with a central opening  62 , which is just large enough that it can enclose the service brake cylinder  4  without collision and can be moved axially along it. Furthermore, the die  60  has at its end face pointing toward the combination brake cylinder  20  a radially inner, preferably rounded recess  64 , which can exert pressure against the edge  52  of the spring brake cylinder  12  in order to press it, with plastic deformation, against the shoulder  30  of the service brake cylinder  4  and shape it against the shoulder. For this purpose, the die  60  moves in the axial direction with respect to a central axis  66  of the combination brake cylinder  20 . This situation is shown by  FIG. 3  in which the die  60  in its end position makes contact, with its end face, with a stopper ring  68  which rests on the opposite end face of the clamping device  56  and whose height depends on the desired degree of deformation and can be adapted on a case by case basis. 
     In  FIG. 4 , the die  60  is again disengaged from the combination brake cylinder  20 , with the edge  52  of the spring brake cylinder  14  engaging in positively locking fashion over the shoulder  30  of the service brake cylinder  4  and at the same time exerting pressure on the radially outer edge  36  of the diaphragm  32 , which is thus likewise secured in a positively locking fashion. Since the shoulders  48 ,  50  make axial contact with the radially outer circumferential face of the dividing wall  28  and with the outer casing wall of the spring brake cylinder  14  which also absorb the reaction forces, the dividing wall  28  is thus also held in a positively locking fashion in the spring brake cylinder  12 . With a single movement of the die  60 , four separate components are consequently connected to one another in a positively locking fashion: the service brake cylinder  4 , the diaphragm  32 , the spring brake cylinder  12  and the dividing wall  28 . 
     In the case of an axial die movement, the die  60  can be constructed as a single component or multiple components. Furthermore, cases in which the housing components have regions which project radially beyond their end edges, and would therefore collide with an annular die guided in the axial direction, are also contemplated. In these cases, the die  60  must be divided at least once in its circumferential extent, with the die arcs then carrying out a radial movement with respect to the central axis  66  of the combination brake cylinder  20 . Last but not least, the die  60  could also shape the edge  30  of the service brake cylinder  4  or else both edges  30 ,  52 . Furthermore, the shoulder  30  of the service brake cylinder  4  could be fabricated with the edge  52  of the spring brake cylinder  12  by way of the beading  54  without the intermediate arrangement of a dividing wall  28 . The spring brake cylinder  12  could be closed off, for example at its end face pointing to the service brake cylinder, by a wall which is connected to it or embodied integrally with it. 
     The method described above is not restricted to the manufacture of combination brake cylinders  20 . Instead, it can be used to fabricate housings of any assemblies in vehicles, and utility vehicles such as brake cylinders, air dryers or brake boosters. 
     
       
         
           
               
             
               
                   
               
               
                 Table of Reference Numerals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Service brake and spring brake device 
               
               
                 2 
                 Service brake device 
               
               
                 4 
                 Service brake cylinder 
               
               
                 6 
                 Service brake piston 
               
               
                 8 
                 Service brake piston rod 
               
               
                 10 
                 Spring brake device 
               
               
                 12 
                 Sprin brake cylinder 
               
               
                 14 
                 Spring brake chamber 
               
               
                 16 
                 Storage spring 
               
               
                 18 
                 Spring brake piston 
               
               
                 20 
                 Combination brake cylinder 
               
               
                 22 
                 Attachment bolt 
               
               
                 24 
                 Spring brake piston rod 
               
               
                 26 
                 Opening 
               
               
                 28 
                 Dividing wall 
               
               
                 30 
                 Shoulder 
               
               
                 32 
                 Diaphragm 
               
               
                 34 
                 Piston plate 
               
               
                 36 
                 Edge 
               
               
                 38 
                 Service brake chamber 
               
               
                 40 
                 Return spring 
               
               
                 46 
                 Release device 
               
               
                 48 
                 Shoulder 
               
               
                 50 
                 Shoulder 
               
               
                 52 
                 Edge 
               
               
                 54 
                 Beading 
               
               
                 56 
                 Clamping device 
               
               
                 58 
                 Head plate 
               
               
                 60 
                 Die 
               
               
                 62 
                 Opening 
               
               
                 64 
                 Recess 
               
               
                 66 
                 Central axis 
               
               
                 68 
                 Stopper ring 
               
               
                   
               
            
           
         
       
     
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.