Abstract:
A vehicle pressure vessel and manufacturing method which uses a vessel main part, an arched base, an arched cover, and one or more cross-webs connecting opposite walls of the vessel main part. The vessel main part is open at its top and bottom over which the cover and base respectively fit to close the vessel main part in a pressure-tight manner. A groove is embossed in the cross-webs where they connect to the opposite walls of the vessel main part. The cover and base each have an attachment rim that fits into the grooves when the cover and base are connected to the vessel main part.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for producing a pressure vessel, in particular a pressure vessel for a vehicle. Further, the invention relates to a pressure vessel, in particular a pressure vessel for a vehicle. 
     More specifically, the invention relates to a pressure vessel for receiving and storing a medium under overpressure and a method for producing same. 
     A pressure vessel, in particular for a vehicle, is known from document DE 299 09 827 U1. This document discloses a pressure vessel for receiving and storing a medium under overpressure, comprising a vessel main part which is closed in a pressure-tight manner by an arched cover and an arched base. For this purpose, the cover at the cover end of the vessel main part and the base at the base end of the vessel main part are welded to the vessel main part. The vessel main part has a plurality of cross-webs which connect opposite wall segments of the wall of the vessel main part to one another in order to give the vessel main part the required pressure resistance. 
     In the case of the known pressure vessel, the vessel main part is finish-machined before mounting the cover and the base on the vessel main part. On the one hand, this process involves introducing grooves into the cross-webs in the respective transition regions thereof into the wall of the vessel main part. The grooves serve for the centred reception of the cover and of the base at the first and second openings of the vessel main part. Moreover, the vessel main part is adapted to the outer circumference of the cover attachment rim and of the base attachment rim in the region of the first opening and of the second opening in order to compensate for tolerances between the vessel main part and the cover and base. 
     The finish-machining processes on the vessel main part which have been described above are each accomplished by cutting, i.e. by the removal of material. 
     However, a finish-machining process on the vessel main part involving cutting is expensive and time-consuming, and this has a disadvantageous effect on the production process. 
     Moreover, a finish-machining process on the vessel main part involving the removal of material in order to introduce the grooves and for the above-described tolerance compensation to allow accurately fitting reception of the cover and base ele-ments is associated with a reduction in the wall thickness of the vessel main part. This reduction in wall thickness leads to weakening of the wall of the vessel main part, espe-cially in the cover and base attachment regions of the vessel main part, and this can result in a preferential breaking point or a possible lack of leaktightness in the vessel main part. 
     The above-described weakening of the wall of the vessel main part due to the finish-machining involving cutting must therefore be compensated by deliberate reinforcement of the wall, at least in the cover and base attachment regions. Here, the reinforcement of the wall should be provided either during the production of the vessel main part, by producing the vessel main part overall with a greater wall thickness, or introduced subsequently into the vessel main part, e.g. by deposition welding. Producing the vessel main part with a greater wall thickness disadvantageously leads to a higher weight of the pressure vessel and to higher costs for materials in the production of the pressure vessel. Subsequent reinforcement of the wall of the vessel main part is a time-consuming and expensive measure. 
     DE 102 12 801 C1 discloses a cooler for liquid media which is con-structed from a main profile and a plurality of webs arranged therein. In order to ensure a meandering flow of the liquid medium, the ends of the webs, which project beyond the longitudinal ends of the main profile, are pressed into the interior of the profile. The open ends of the main profile are then soldered to end plates and thus closed. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method for producing a pressure vessel, in particular for a vehicle, which can be carried out with high production accuracy and with a lower outlay in terms of materials, time and cost. 
     It is another object of the invention to provide a pressure vessel of the type stated at the outset which can be produced with high production accuracy and with a lower outlay in terms of materials, time and cost. 
     According to the invention, a method for producing a pressure vessel is provided, comprising the steps: 
     a) providing a vessel main part, which has a wall, a first opening at a first end, a second opening at a second end and at least one cross-web, which connects opposite wall segments of the wall of the vessel main part to one another, 
     b) providing an arched cover and an arched base, wherein the arched cover has a cover attachment rim and the arched base has a base attachment rim, 
     c) embossing, without cutting, a first and a second groove into the at least one cross-web at the first opening and introducing a third and fourth groove into the at least one cross-web at the second opening, wherein the grooves are embossed in respective regions of connection of the at least one cross-web to the opposite wall segments of the vessel main part, 
     d) inserting the cover attachment rim into the grooves at the first opening and inserting the base attachment rim into the grooves at the second opening, 
     e) securing the cover and the base on the vessel main part in the region of the first and second ends in order to close the vessel main part in a pressure-tight manner. 
     Further according to the invention, a pressure vessel for receiving and storing a medium under overpressure is provided, comprising a vessel main part having a wall and at least one cross-web connecting opposite wall segments of the wall to one another, and further comprising a first opening and a second opening, an arched cover closing the vessel main part at the first opening and having a cover attachment rim, an arched base closing the vessel main part at the second opening and having a base attachment rim, a first and a second groove in the at least one cross-web at the first opening in the vessel main part, the cover attachment rim being received in the first and second grooves, a third and a fourth groove in the at least one cross-web at the second opening in the vessel main part, the base attachment rim being received in the third and fourth grooves, the grooves being embossed, without cutting, in respective regions of connection of the at least one cross-web to the opposite wall segments. 
     In the case of the method according to the invention and of the pressure vessel according to the invention, the grooves for the centred reception of the cover and of the base are introduced into the at least one cross-web without cutting, more specifically by embossing. Embossing the grooves has the advantage that no material is removed during embossing, and therefore weakening of the material of the vessel main part is avoided. 
     In the context of the present invention, the term “groove” should be taken to mean a recess, the length of which can also be shorter than the width thereof. 
     As a result, it is possible to dispense with the additional use of reinforcing regions, at least in the region of the region of connection of the at least one cross-web to the opposite wall segments of the vessel main part, which is preferably produced as an extruded aluminium profile, thereby enabling the pressure vessel to be produced with a lower weight, at lower cost and with a reduced outlay on processing. 
     The grooves are preferably embossed into the at least one cross-web in such a way that centred reception of the cover attachment rim on the vessel main part at the first opening and of the base attachment rim on the vessel main part at the second opening is ensured. 
     This facilitates correctly positioned placement of the cover and of the base on the vessel main part. 
     In a preferred embodiment of the method according to the invention and of the pressure vessel according to the invention, the wall of the vessel main part is finish-sized by forming, without cutting, in the region of the first opening and of the second opening in order to adapt an inside of the wall to an outer circumference of the cover attachment rim and of the base attachment rim. 
     By means of this measure, any manufacturing tolerances of the vessel main part, of the cover and of the base are advantageously compensated, likewise without cutting, i.e. without removing material. Finish-sizing the vessel main part by forming without cutting has the advantage that weakening of the material of the wall of the vessel main part is avoided, thus eliminating the need for the vessel main part either to be produced with a greater wall thickness from the outset or for the wall thickness to be increased afterwards by the application of material. In combination with the embossed grooves, the pressure vessel according to the invention in this embodiment is particularly sparing of materials and can be produced at reasonable cost and with less expenditure of time. 
     Finish-sizing of the vessel main part by forming without cutting is preferably carried out by pressing the wall of the vessel main part, e.g. by pressing it from the outside in order to displace a wall segment inwards, and/or by pressing it from the inside in order to displace a wall segment outwards. 
     Finish-sizing ensures that the cover attachment rim and the base attachment rim can be received with an accurate fit into the attachment regions of the vessel main part which are predefined by the introduced grooves, on the one hand, and the inside of the wall, on the other hand, and this has an advantageous effect on the quality of attachment of the cover and of the base to the vessel main part. 
     In another preferred embodiment of the method and of the pressure vessel, the wall of the vessel main part is configured with a uniform wall thickness all the way round the perimeter. 
     It is advantageous here that the vessel main part can be produced at particularly low cost, in particular as an extruded aluminium profile. Moreover, it is ensured that the stresses acting on the wall of the vessel main part are distributed uniformly. 
     In another preferred embodiment of the method and of the pressure vessel, the cover and the base are joined to the vessel main part by a material joint, in particular a welded joint or an adhesive joint. 
     This measure has the advantage that the base and the cover can be joined to the vessel main part at low cost and in a pressure-tight manner by means of a welded or an adhesive joint. 
     In another preferred embodiment of the method, the grooves are formed with a bevelled shoulder in the form of a chamfer during embossing. 
     In the case of the pressure vessel, the grooves preferably have a bevelled shoulder in the form of a chamfer. 
     This measure advantageously facilitates the insertion of the cover attachment rim and the base attachment rim into the respective attachment regions formed by the grooves and the inside of the wall of the vessel main part. The chamfer is produced during the embossing of the grooves, thus advantageously eliminating an additional processing operation. 
     By means of the method according to the invention, the pressure vessel according to the invention can be produced at low cost, with a low weight and with a low reject rate in a series production process. 
     Further advantages and features will emerge from the following description and the attached drawing. 
     It is obvious that the features mentioned above and those which remain to be explained below can be used not only in the respectively indicated combination but also in other combinations or in isolation without exceeding the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An illustrative embodiment of the invention is shown in the drawing and is described in greater detail with reference to the latter. In the drawing: 
         FIG. 1  shows a pressure vessel in an exploded perspective view; 
         FIG. 2  shows, in perspective, a vessel main part of the pressure vessel in  FIG. 1  in an intermediate stage of the production of the pressure vessel in  FIG. 1 ; 
         FIG. 3  shows, in perspective, the vessel main part in  FIG. 2  in a further intermediate stage of the production of the pressure vessel; 
         FIG. 3   a  shows a detail A in  FIG. 3  on a larger scale than  FIG. 3 ; 
         FIG. 3   b  shows a detail B in  FIG. 3  on a larger scale than  FIG. 3 ; and 
         FIG. 4  shows, in perspective, the pressure vessel in  FIG. 1  in partially sectioned view in the finished condition. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A pressure vessel provided with the general reference sign  10  is shown in an exploded view in  FIG. 1 . Further details of the pressure vessel  10  and of the production thereof are shown in  FIGS. 2 to 4 . 
     The pressure vessel  10  is used in a vehicle (not shown). The pressure vessel  10  is used in general to receive and store a medium under overpressure, which can be a gas, a liquid or steam. The pressure vessel  10  can be used as a storage and compensation tank for pneumatic control systems in motor vehicles, for example. One specific application is, for example, the use of the pressure vessel  10  as a compensation and storage tank for compressed air in a pneumatic chassis suspension system of a vehicle. 
     The pressure vessel  10  has a vessel main part  12  which, overall, is formed integrally of metal, in particular steel or aluminium sheet. The vessel main part  12  can have been produced, for example, by a cold forming method, in particular by extrusion. 
     The pressure vessel  10  furthermore has a cover  14  and a base  16 , wherein both the cover  14  and the base  16  are of arched design. The shaping of the vessel main part  12 , of the cover  14  and of the base  16  can fundamentally be matched in terms of the geometry and configuration thereof to the installation location at which the pressure vessel  10  is to be positioned. The arching of the cover  14  and the arching of the base  16  fundamentally ensure uniform pressure distribution at the surface of the cover and the surface of the base. 
     On the side facing the vessel main part  12 , the cover  14  has a cover attachment rim  18 , which extends along the entire circumference of a cover rim  20 . On the side facing the vessel main part  12 , the base  16  has a base attachment rim  22 , which is formed along the entire circumference of a base rim  24 . 
     The vessel main part  12  has a substantially box-shaped form, wherein the vessel main part  12  furthermore has arched ends  26 ,  28 . Fundamentally, however, the vessel main part  12  can be configured in any desired box-shaped form which is matched to an installation location of the pressure vessel  10 . 
     The vessel main part  12  has opposite lateral wall segments  30 ,  32 , which are connected to one another by cross-webs  34 . There are four cross-webs  34  in the embodiment shown. The vessel main part  12  thus has a wall  36  all around the circumference, being formed by the opposite wall segments  30 ,  32  and the wall segments of the arched ends  26 ,  28 . It is self-evident that the number of cross-webs  34  can be less than four or indeed greater than four, depending on the size of the pressure vessel  10 . 
     The cross-webs  34  which connect the opposite wall segments  30 ,  32  to one another extend in the vessel main part  12  from a cover-side first opening  38  at a first end  39  of the vessel main part  12 , to a base-side second opening  40  at a second end  41  of the vessel main part  12 . 
     In the embodiment shown, the individual cross-webs  34  are aligned so as to be straight and flat and parallel to one another. However, it is self-evident that the cross-webs  34  can also be arranged so as not to be parallel to one another. 
     Wall segments  30 ,  32  are formed integrally with the wall segments of the arched ends  26 ,  28  and the cross-webs  34 . This can be achieved by producing the vessel main part  12  as an extruded profile made of metal, e.g. aluminium. The direction of extrusion is in the direction of the longitudinal extent of the cross-webs  34 , i.e. in the direction of the connection between the cover-side first opening  38  and the base-side second opening  40 . In this case, the vessel main part  12  can be produced as a meter-length extruded profile and then cut to length as required from this meter-length material. 
     At wall segments  30 ,  32 , the cross-webs  34  each have regions  42  of connection to the wall  36 , said regions widening towards the walls  36  in a section plane orthogonal to the surface of the cross-webs  34  (cf. also  FIG. 3   a ,  FIG. 3   b ). 
     At the first opening  38 , the cross-webs  34  each have a first groove  44   a  and a second groove  44   b , which are introduced without cutting, by embossing (stamping), into the cross-webs  34  in the region of the respective regions  42  of connection of the cross-webs  34  to wall segments  30 ,  32 . Moreover, the cross-webs  34  each have, at the second opening  40 , further, third and fourth grooves  45   a ,  45   b  (see  FIG. 4 ), which are introduced without cutting, by embossing, into the cross-webs  34  in the region of the regions  42  of connection of the cross-webs  34  to wall segments  30 ,  32 . In this case, grooves  44   a  and  45   a  are situated opposite one another, as are grooves  44   b  and  45   b . The embossed grooves  44   a ,  44   b ,  45   a ,  45   b , on the one hand, and an inside  46  of the wall  36  of the vessel main part  12 , on the other hand, result in first and second attachment regions  48 ,  50  at the cover-side first opening  38  and at the base-side second opening  40 , said attachment regions receiving the cover attachment rim  18  of the cover  14  and the base attachment rim  22  of the base  16 , respectively. 
     In  FIG. 2 , the vessel main part  12  of the pressure vessel  10  is shown in an intermediate stage of production. In the intermediate stage show in  FIG. 2 , the vessel main part  12  is provided as an extruded profile, wherein the grooves  44   a ,  44   b  and  45   a ,  45   b  have not yet been introduced into the cross-webs  34 . 
     Starting from the stage in  FIG. 2 , the vessel main part  12  is shown in a subsequent stage of production in  FIG. 3 . At this stage, as explained above, the grooves  44   a ,  44   b ,  45   a ,  45   b  have been introduced into the cross-webs  34  of the extruded blank of the vessel main part  12  in the region of the cover-side first opening  38  and of the base-side second opening  40 . The grooves  44   a ,  44   b ,  45   a ,  45   b  are embossed into the cross-webs  34  in respective regions  42  of connection of the cross-webs  34  to wall segments  30 ,  32 . The grooves  44   a ,  44   b ,  45   a ,  45   b  are designed in such a way that they, on the one hand, and the inside  46  of the wall  36  of the vessel main part  12 , on the other hand, form the first attachment region  48  for the cover attachment rim  18  at the cover-side first opening  38  and the second attachment region  50  for the base attachment rim  22  at the base-side second opening  40  of the vessel main part  12 . In this case, the grooves  44   a ,  44   b ,  45   a ,  45   b  are designed in such a way that they can receive the cover attachment rim  18  and the base attachment rim  20  in a centred manner. 
     One of the grooves  44   a  is shown on an enlarged scale in  FIG. 3   a . One of the grooves  44   b  is shown on an enlarged scale in  FIG. 3   b . Grooves  44   a ,  44   b  and grooves  45   a ,  45   b  are introduced by embossing material of the cross-webs  34 . During the embossing of grooves  44   a ,  44   b , material of the cross-webs  34  is displaced in a direction from the first opening  38  towards the second opening  40 . The embossing of grooves  45   a ,  45   b  takes place in the opposite direction, i.e. in a direction from the second opening  40  towards the first opening  38 . As is evident from  FIGS. 3   a  and  3   b , grooves  44   a ,  44   b  have a substantially rectangular profile (and the same applies to grooves  45   a ,  45   b ). On the side thereof facing away from the wall  36 , the grooves  44   a ,  44   b ,  45   a ,  45   b  have a bevelled shoulder  52  in the form of a chamfer, which makes it easier to insert the cover attachment rim  18  and the base attachment rim  22  into the grooves  44   a ,  44   b ,  45   a ,  45   b.    
     It is self-evident that the profiles of grooves  44   a ,  44   b  and  45   a ,  45   b  can also have profile shapes which deviate from the profile shape shown. Thus, grooves  44   a ,  44   b  and  45   a ,  45   b  can also be of round or stepped design. 
     Embossing the grooves  44   a ,  44   b ,  45   a ,  45   b  ensures that the wall thickness  54  of the wall  36  is not reduced in the attachment regions  48 ,  50 . 
     In order to adapt the inside  46  of the wall  36  to the outer circumference of the cover attachment rim  18  and to the outer circumference of the base attachment rim  22 , the wall  36  of the vessel main part  12  is finish-sized by forming, without cutting, in the region of the first opening  38  and of the second opening  40 , if such adaptation is required due to manufacturing tolerances during the production of the vessel main part  12 , of the cover  14  and/or of the base  16 . 
     Finish-sizing the vessel main part  12  by forming without cutting in the region of the first opening  38  and of the second opening  40  is accomplished by pressing the wall  36  of the vessel main part  12  in sections, namely inwards (e.g. arrows  53  in  FIG. 3 ) and/or outwards (e.g. arrows  55  in  FIG. 3 ), depending on whether the outer circumference of the vessel main part  12  has to be reduced or increased completely or in sections at the first opening  38  and at the second opening  40 . By virtue of the finish-sizing by forming without cutting, the vessel main part  12  has a uniform wall thickness  54  over the entire circumference (see  FIGS. 3   a  and  3   b ). 
       FIG. 4  shows the pressure vessel  10  in the finished stage. In contrast to  FIG. 1 , the pressure vessel  10  in  FIG. 4  is shown with a view of the base  16 , whereas  FIG. 1  shows the pressure vessel  10  with a view of the cover  14 . Moreover, in  FIG. 4  the base  16  is shown cut away. 
     During the transition from  FIG. 3  to  FIG. 4 , the cover  14  has been placed on the first opening  38  of the vessel main part  12 , or, to be more specific, the cover attachment rim  18  has been inserted into grooves  44   a ,  44   b  of the cross-webs  34 . During this process, grooves  44   a ,  44   b  bring about centring of the cover  14  on the vessel main part  12 . 
     In the same way, the base  16  has been placed on the second opening  40  of the vessel main part  12 , i.e. the base attachment rim  22  is inserted into grooves  45   a ,  45   b  of the cross-webs  34 . Here too, grooves  45   a ,  45   b  bring about centring of the base  16  on the vessel main part  12 . 
     The cover  14  and the base  16  are then welded to the vessel main part  12  in order to close the pressure vessel  10  in a pressure-tight manner.  FIG. 4  shows the welding by means of weld seams  56 , which extend around the entire circumference of the vessel main part  12 . 
     It is also possible for the cover  14  and/or the base  16  to be connected to the vessel main part  12  by adhesive bonding instead of by welding.