Abstract:
An arrangement of a suspension and of a rail is provided, in particular for suspending a travel and/or carrier rail or a lifting gear on a chassis or frame, having a tension element supporting the rail at one end thereof in the region of a profile head by a mounting element, with the head being substantially C-shaped in cross section, and forming a gap running at the top along a longitudinal center plane of the rail. The mounting element comprises a pivotable part that can be pivoted with respect to the tension element, the profile head and the pivotable part being designed such that the pivotable part can be guided through the gap from outside into the profile head in a loading position, and can be pivoted into a mounting position in which the pivotable part contacts the profile head from the inside, bridging the gap.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the priority benefits of International Patent Application No. PCT/EP2011/065331, filed on Sep. 5, 2011, and also of German Patent Application No. DE 10 2010 037 521.7, filed on Sep. 14, 2010, which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an arrangement of a suspension and of a rail, in particular for suspending a travel and/or carrier rail of a suspension track, a suspended conveyor or a lifting gear on a travelling mechanism or frame, having a tension element which supports the rail at one end in the region of a profile head by means of a mounting element, said head being substantially c-shaped in cross-section and forming at the top a gap extending along a longitudinal centre plane of the rail. 
         [0003]    European patent document EP 1 928 777 B1 discloses a device for suspending a rail which is used in particular for suspending a travel rail of a suspended conveyor or a lifting gear on a travelling mechanism or a frame. The device comprises a tension element which supports the rail at one end by means of a mounting element. The mounting element has a support element which widens and extends at least partially in the longitudinal direction of the rail and engages around a Y-shaped profile head of the rail from the outside in a clamping manner. The support element can be easily mounted at any location of the rail. For this purpose, mounting parts of the support element are assembled and clamped to the Y-shaped profile head by means of screws. The tension element comprises a lower bore for a bolt which is attached by means of the mounting element. The bolt has the lower bore extending therethrough and is mounted on the tension element via a ball-like joint, in particular via a spherical plain bearing. In the exemplified embodiment of  FIGS. 11 to 13  a suspension is described in which the mounting element consists of a frame-shaped mounting part which is slid from one end into a T-shaped groove of the rail. Alternatively, provision is made that the mounting part is placed onto the rail head from the top and slot nuts attached to the mounting part then protrude from the top into the T-shaped groove and are then rotated by 90 degrees in order for the slot nuts to partially engage below the upper webs of the T-shaped groove. 
         [0004]    Suspensions from Demag Cranes &amp; Components GmbH are also known within the scope of their so-called KBK III system and can be inserted from the top into a longitudinal opening of a C-shaped profile head—which is open at the top—of a rail. For this purpose, a support plate of the suspension is rotated by 90 degrees, as it is inserted through the longitudinal opening, and is then rotated back by 90 degrees so that the ends of the support plate now engage, in the manner of a slot nut, behind web ends of the profile head which delimit the longitudinal opening. Then, the support plate is prevented from being rotated back and displaced in the longitudinal direction of the longitudinal opening by being screwed to an outwardly adjacent counter-plate. This type of suspension allows a free and retroactive attachment of the suspension to the rail without disassembling the rail. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention creates an arrangement of a suspension and of a rail, in particular for suspending a travel and/or carrier rail of a suspension track, a suspended conveyor or a lifting gear on a travelling mechanism or frame, which combines simple assembly with a high level of security and high load-bearing capacity and which simultaneously allows free and retroactive positioning on the rail without disassembling the rail. 
         [0006]    In accordance with an embodiment of the invention, in the case of an arrangement of a suspension and of a rail, in particular for suspending a travel and/or carrier rail of a suspension track, a suspended conveyor or a lifting gear on a travelling mechanism or frame, having a tension element which supports the rail at one end in the region of a profile head by means of a mounting element, said head being substantially c-shaped in cross-section and forming at the top a gap extending along a longitudinal centre plane of the rail, an arrangement which combines simple assembly with a high level of security and high load-bearing capacity and simultaneously allows free and retroactive positioning on the rail without disassembling the rail is achieved by virtue of the fact that the mounting element comprises a pivotable part which can be pivoted with respect to the tension element, the profile head and the pivotable part are dimensioned such that the pivotable part can be inserted through the gap from the outside into the profile head in a pivoting position and can be pivoted into a mounting position in which the pivotable part lies against the profile head from the inside, bridging the gap. It is hereby achieved that the suspension can be pivoted in a corresponding rail through the gap in the hollow profile head in order to receive the pivotable part of the suspension. When the profile head and the suspension or its pivotable part are correspondingly dimensioned in a mutually adapted manner, the profile head is kept in a simple manner in the transverse direction by a positive-locking connection with the largest possible contact surface. 
         [0007]    A considerable advantage resides in the fact that the suspension can now be preassembled before it is inserted into the rail. It does not have to be assembled in the rail which is difficult or impossible owing to the small amount of space available and a special tool would possibly be required for this purpose. 
         [0008]    In addition, this type of suspension allows positioning at any location of the rail, even after assembly thereof. 
         [0009]    In a preferred embodiment, the pivotable part is aligned substantially horizontally in the mounting position and is aligned substantially vertically in the pivoting position. 
         [0010]    If the pivoting part is formed to be arc-shaped in cross-section, i.e., is bent upwards in a concave manner or like a banana, in particular upwards as seen in the suspension direction, it can securely engage behind the profile head in the mounting position. 
         [0011]    The pivoting process is thus facilitated since the pivotable part is disposed so as to be pivotable about a bolt mounted in the tension element in the longitudinal direction of the rail. 
         [0012]    A simple construction combined with angular mobility of the suspension is achieved by virtue of the fact that the bolt is attached to the tension element via a ball-like joint, in particular via a spherical plain bearing. The bolt can thus be connected directly with the mounting element and the installation height of the entire suspension is minimised. This direct connection increases the security of the suspension. The use of a spherical plain bearing allows long service lives to be achieved. The construction is simplified since spherical plain bearings which are produced in the industry, available on the market and are correspondingly low-wear can be used. 
         [0013]    The term “spherical plain bearing” is understood to mean standardised radial spherical plain bearings e.g., in accordance with DIN ISO 12240 which are produced in the industry, available on the market and ready to install, wherein these radial spherical plain bearings are articulated and allow spatial adjustments. Spherical plain bearings are structural units which comprise an outer ring in which an inner ring is mounted. The inner ring comprises a cylindrical bore for the rotationally-fixed reception of a bolt, and a spherical outer slide way for forming the spherical head. This outer slide way is engaged with a hollow-spherical inner slide way of the outer ring whose cylindrical peripheral surface is inserted into a bore in a rotationally-fixed manner. The outer slide way and the inner slide way can each be formed of steel and be in direct correlation with each other. A lubricant supply is then additionally provided in most cases. For the present application, spherical plain bearings are used which comprise a sliding layer or a sliding ring e.g., of synthetic material or Teflon, between the inner and outer ring. This sliding ring is then attached to the outer ring and the inner ring slides in the sliding ring. In another construction, the outer ring can be omitted as a separate component and its function assumed by the tension element. The inner ring is inserted transversely into the widened bore in the tension element and is rotated by 90° in the bore to its operating position. Then, the widened area of the bore and the gap between the inner ring and the bore is filled with a synthetic material which hardens to form the sliding ring. 
         [0014]    In a particular embodiment the suspension comprises a frame-like counter bearing which is formed to be arc-shaped in cross-section and is placed from the outside onto the profile head and is screwed with the pivotable part in the mounting position. The pivotable part is thus secured against displacement in the longitudinal direction of the rail and the pivotable part is also kept securely in the horizontal mounting position. 
         [0015]    Since the profile head delimits the gap on both sides with first web sections which extend outwardly and upwardly and in an inclined manner from the longitudinal centre plane, and the pivotable part engages into the crimps of the profile head thus formed by the first web sections, i.e., are disposed substantially in an approximate V-shaped manner and do not protrude back approximately horizontally in the direction of the vertical longitudinal centre plane like in the Prior Art, they prevent the rail profile itself from bending in the event of extreme overloading. In the case of an overloading, there is thus actually an increase in the clamping effect on the pivotable part of the suspension disposed in the gap since the first web sections are “pushed” towards one another in the case of an overloading. This effect is increased by the arc-shaped formation of the pivotable part. This is important since in the case of an overloading, there can also be no failure in the connection between the rail or its head profile and the suspension or its connecting element. The particular geometry of the profile head of the rail in accordance with the invention ensures that the rail is not the weakest link in the chain. 
         [0016]    Provision is advantageously made that the web sections extend at an angle of approximately 15 to 35 degrees relative to the longitudinal centre plane. The pivotable part is held in this angular range in a particularly secure manner. 
         [0017]    If the profile head comprises two opposing second web sections which extend downwardly and outwardly, as seen in cross-section, and which are attached to the first web sections, and also subsequently comprises third web sections protruding back inwardly in the direction of the vertical longitudinal centre plane, which are attached to the second web sections, i.e., the profile head is wider at the base and narrows in the direction away from the profile body, a suspension can be used for the rail which can “pivot” through the gap into the hollow profile head since the diagonal extension (as seen in cross-section) is thus large enough in order to accommodate a pivotable part of a suspension which is then pivoted approximately horizontally and engages in a positive-locking manner into the crimps of the profile head formed by the first web sections. When the profile head and the suspension or its pivotable part are correspondingly dimensioned in a mutually adapted manner, the profile head is thus kept in a simple manner in the transverse direction by a positive-locking connection. 
         [0018]    The arrangement in accordance with the invention consisting of a suspension and rail can be used in a variety of ways, and in particular as a running rail and/or carrier rail for single-beam or double-beam suspension cranes. 
         [0019]    Further details, features and advantages of the invention will become apparent from the following description of an exemplified embodiment with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a perspective and schematic view of a single-beam suspension crane in accordance with the Prior Art for illustrating the possible applications of corresponding rails; 
           [0021]      FIG. 2  shows a perspective view of a rail in accordance with the invention; 
           [0022]      FIG. 3  shows a cross-section through the rail of  FIG. 2 ; and 
           [0023]      FIG. 4  shows a cross-section through the rail of  FIG. 2  in the region of the suspension of the profile head; and also 
           [0024]      FIG. 5  shows the cross-section of  FIG. 4  with the suspension being inserted; and 
           [0025]      FIG. 6  shows a perspective exploded view of an alternative configuration of the suspension on a rail corresponding to  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    In order to illustrate the very different ways of using connected rail sections to form rails, a single-beam suspension crane is illustrated in  FIG. 1 . 
         [0027]    By means of suspension devices  1 , rails  2 , which extend substantially horizontally and are profiled in a c-shaped manner open at the bottom, are suspended on support elements  3  or further rails  2 . The support elements  2  are formed as double-T beams. Since the present exemplified embodiment relates to a single-beam suspension crane, two first rails  2   a  are provided which extend substantially horizontally and in parallel with and at a spaced disposition with respect to each other and are used as travel rails of the single-beam suspension crane, and a second rail  2   b  is provided which forms a crane rail which is aligned substantially transversely with respect to the first rails  2   a  and can be displaced along the first rails  2   a.  In this respect, the second rail  2   b  is suspended via two suspension devices  1  in each case on a travelling mechanism which is not illustrated and can be displaced along the first rails  2   a . Suspended on the second rail  2   b  in a conventional manner is a lifting gear  4  such as a chain or cable hoist, which can be displaced along the second rail  2   b  by means of a further travelling mechanism, not shown. The lifting gear  4  can be controlled via a suspended switch  5  which is suspended on a lifting gear  4 . 
         [0028]    The rails  2   a,    2   b  can thus be used selectively as crane track rails or carrier rails. 
         [0029]    A rail  2  in accordance with the invention or a first suspension will now be described with reference to  FIGS. 2 to 5 . 
         [0030]    The rails  2   a  and  2   b  each consist of two or more rail sections  2   aa  and  2   ab  or  2   ba  and  2   bb  respectively depending upon the length requirement. 
         [0031]    The rail sections  2   aa  and  2   ab  or  2   ba  and  2   bb  are connected together via end-side butt joints  6 . 
         [0032]    By way of example, only the butt joint  6  of the rail sections  2   aa  and  2   ab  will be explained hereinafter with reference to  FIGS. 2 and 3  since the butt joint of the rail sections  2   ba  and  2   bb  is formed in a corresponding manner. The profile of the rail sections of  FIGS. 2 and 3  is merely similar, but not identical, to that of  FIG. 1 . 
         [0033]    In order to form the butt joints  6  of the rail sections  2   aa  and  2   ab , the rail sections  2   aa  and  2   ab  comprise in each case at their outer sides mounting elements formed as sleeves  7  which are disposed on the rail section ends  8  in longitudinally extending angular spaces or grooves  9  of the rail sections  2   aa  and  2   ab.    
         [0034]    In the illustrated example, four sleeves  7  are used for each rail section and are disposed in each case in corresponding longitudinal grooves  9 . Two sleeves  7  are thus provided in each case for each rail section longitudinal side. 
         [0035]    Stud bolts engage through the sleeves  7  as connection elements and the sleeves form for the heads or nuts thereof a bearing surface  16  extending transversely with respect to the longitudinal direction of the rail sections as a counter bearing surface. 
         [0036]    The sleeves  7  are attached to the rail sections  2   aa  and  2   ab  in each case by a weld seam  12 , extending in the longitudinal direction of the rail section  2   aa  and  2   ab , on each of the two longitudinal sides of the sleeves  7 . The weld seams  12  do not have to extend over the entire length of the sleeves  7  and can be formed differently from one another. 
         [0037]    The end  13  of the weld seam  12  remote from the end-side deviates form the longitudinal direction. The end  13  thus forms an angle  14  with respect to the rest of the weld seam  12  and extends from the groove  9  to the lateral surface  15  of the rail profile or the continued profile wall. 
         [0038]    In cross-section, the rail  2  consists of two identical profiles  20   a,    20   b  disposed symmetrically with respect to the vertical longitudinal centre plane L. 
         [0039]    The rail comprises a profile head  22  which is disposed relatively along the longitudinal centre plane L at the top, and a profile body  23  which is located beneath the profile head and is connected thereto. 
         [0040]    As seen in cross-section, the profile head  22  is a substantially C-shaped profile head open at the top, whose opening forms a gap  24  extending along the longitudinal centre plane L, said gap being delimited on both sides by first web sections  25   a,    25   b  which extend outwardly and simultaneously upwardly in an inclined manner from the longitudinal centre plane L. 
         [0041]    The angle  21  of the web sections  25   a,    25   b  is approximately  25  degrees relative to the longitudinal centre plane L. 
         [0042]    In cross-section, the profile head  22  further comprises two opposing second web sections  26   a ,  26   b  Which extend downwardly and outwardly and are attached to the first web sections  25   a ,  25   b,  and the profile head also finally comprises third web sections  27   a,    27   b  which protrude back inwardly in the direction of the vertical longitudinal centre plane L and are attached to the second web sections  26   a,    26   b.    
         [0043]    In other words, the profile head  22  is wider at its base and narrows in the directions away from the profile body  23 . Therefore, a suspension  34  can be used for the rail  2  which can “pivot” through the gap  24  into the hollow profile head  22  (cf.  FIGS. 4 and 5 ) since the diagonal extension (as seen in cross-section) is thus large enough in order to accommodate a pivotable part  35  of the suspension  34  which is then pivoted approximately horizontally and engages in a positive-locking manner into the crimps  36   a,    36   b  of the profile head  22  formed by the first web sections  25   a,    25   b.  When the profile head  22  and the suspension  23  or its pivotable part  25  are correspondingly dimensioned in a mutually adapted manner, the profile head  22  is thus kept in a simple manner in the transverse direction by a positive-locking connection. 
         [0044]    Alternatively, the height of the profile head  22  would have to turn out to be considerably greater and the rail  2  could be formed as a whole in a less compact and rigid manner. 
         [0045]    In order to attach and fix the suspension  34  on the profile head  22 , initially the mentioned pivotable part  35  is pivoted to lie on one side approximately perpendicularly on the suspension so that it can be inserted with the other side into the gap  24 . 
         [0046]    Then the suspension  34  is slid with the pivotable part  35  in an inclined manner into one of the lower corners of the profile head  22  which are formed by the web sections  26   a,    27   a  or  26   b ,  27   b.    
         [0047]    It is then possible to insert the other end of the pivotable part  35  past the web section  25   a  or  25   b  into the gap  24  and finally to pivot the pivotable part horizontally and insert it into the crimps  36   a,    36   b.  In order for the pivotable part  35  to engage with its ends  35   a,    35   b  into the crimps  36   a,    36   b,  or to lie against them, in a positive-locking manner it is formed in an arc-shaped manner as seen in cross-section ( FIGS. 4 and 5 ). 
         [0048]    The suspension  34  thus already supports the rail  2  via the pivotable part  35  without the need for a screw-connection etc. Therefore, the entire loading can be absorbed by the pivot bolt  37  of the suspension which can be dimensioned to be substantially more capable of absorbing loads than a normal stud bolt of a clamping connection from the Prior Art. 
         [0049]    In addition to the pivotable part  35 , the mounting element  38  consists of a frame-like counter bearing  39  which is also arc-shaped. In order to fix the pivotable part  35  at a desired location in the longitudinal direction of the rail  2 , the pivotable part  35  is pushed upwards via screws  40  and is thus supported on the lower side of the web sections  25   a,    25   b  or crimps  36   a,    36   b.  The screws  40  are supported on the upper side of the web sections  25   a,    25   b  on the counter bearing  39 . Therefore, the mounting element  38  is fixedly clamped on the web sections  25   a,    25   b.  If the screws  40  become defective, the rail  2  is still retained via the pivotable part  35 . 
         [0050]    The pivotable part  35  can be divided into a mounting region  41  and a suspension region  42  attached thereto. The suspension region  42  consists substantially of two bores for receiving the bolt  37  which are spaced apart via an intermediate space into which a spherical plain bearing  43  with the tension element  44  is received. The intermediate space also comprises inwardly protruding protrusions in order to centre the spherical plain bearing. The bolt  37  extending through the two bores and the spherical plain bearing  43  comprises at its end a head which is prevented from rotating via a cut-out in the counter bearing  39  and is kept in the bore. In the region of the bores, the pivotable part  35  is formed to be thicker towards the top in the manner of bearing blocks  45 . This bearing blocks  45  protrude upwardly from the gap  24  and form the actual receptacles for the bolt  37 . 
         [0051]    The tension element  44  is formed as a flat bracket in the manner of a connecting rod or in a strip-like manner and is aligned approximately perpendicularly with respect to the longitudinal direction of the rail  2 . This tension element  44  comprises an upper bore  46  and a lower bore  47 . The tension element  44  is suspended on a travelling mechanism or beam via a hook, grommet, etc. The upper bore  46  comprises a knife edge bearing, i.e., the bore  46  is formed in a spherical manner and the bolt is guided in an angularly mobile and punctiform manner on the knife edge formed by the sphericity. Alternatively, a spherical plain bearing can be disposed in the upper bore. 
         [0052]    The lower bore  47  is used for the suspension of the rail  2  on the tension element  44 . For this purpose, the spherical plain bearing  43  is inserted in the lower bore  47  and the bolt  37  is guided through the bore of the spherical plain bearing. The ends of the bolt  37  protruding in the respective longitudinal direction of the rail  2  beyond the tension element  44  or the spherical plain bearing  43  engage into the bearing blocks  45  and are held so as to be rotationally-fixed in bores therein. 
         [0053]    The tension element  44  comprises on both sides of the upper bore  46  a lug  48  so that the tension element  44  on the travelling mechanism, beam etc. does not dangle in the hook, grommet, etc. in spite of the slim construction. 
         [0054]    In addition, fourth web sections  28   a,    28   b  extending approximately along the longitudinal centre plane L are provided on the profile head  22  and are attached to the third web sections  27   a,    27   b  and connect the profile head  22  to the profile body  23  via its upper profile walls  29   a,    29   b.    
         [0055]    The fourth web sections  28   a,    28   b  of the profile head  22  lie against one another and are welded together at that location. The profiles  20   a,    20   b  are thus connected to form the rail  2 . 
         [0056]    A hollow space H for travelling mechanisms is formed by the profile body  23  with upper profile walls  29   a,    29   b  which extend in a substantially horizontal manner and profile sidewalls  30   a,    30   b  extending downwardly in a slightly inclined manner with respect to the longitudinal centre plane L as well as two lower profile walls  32   a, b  located on both sides of a lower slot  31  and being slightly inclined downwards with respect thereto, wherein lower profile walls  32   a ,  32   b  form a running surface for the corresponding wheels. In addition, a contact line can be disposed in the region of the upper profile walls  29   a,    29   b.    
         [0057]    The lower profile wall  32   a,    32   b  on the slot  31  continues substantially downwards and then inclined outwards and finally inclined downwards. The thus produced end sections  33   a,    33   b  of the lower profile wall  32   a,    32   b  allow the passage of the weld seam  12 , as discussed above. 
         [0058]    The angle of the end sections  33   a,    33   b  of the lower profile wall  32   a,    32   b  is approximately 110 degrees relative to the horizontal. 
         [0059]      FIG. 6  illustrates a perspective exploded view of an alternative configuration of the suspension on a rail corresponding to  FIG. 2 , which means that there is no need to again describe the rail  2 . Only the particular features of the alternative suspension  49  will be described hereinafter. 
         [0060]    In the illustrated alternative, the suspension  49  is attached by means of a ball and socket joint  50  on the rail  2  or the frame  3 . 
         [0061]    In order to receive the spherical head  50 , the pivotable part  51  forms a ball socket having a central opening for the passage of the tension element  52 . The pivotable part  51  can be pivoted about the spherical head  50  instead of the bolt  37  of the above embodiment. 
         [0062]    The tension element  52  is formed in a rod-like manner and includes three parts, namely a threaded rod  53  disposed in the centre and at the top and bottom a threaded sleeve  54  having an integrally connected spherical head  50 . In order to improve pivotability, the threaded sleeve  54  comprises a cylindrical region  56  having a smaller diameter between the actual sleeve part  55  and the spherical head  50 . 
         [0063]    The pivotable part  51  is pivoted or inserted into the profile head  22  in a similar manner to the above embodiment. Then, the suspension  49  is fixed to a counter bearing  57 , which is correspondingly frame-like and is likewise arc-shaped, in the longitudinal direction of the rail  2  at the gap  24 . 
         [0064]    Thereafter, the threaded rod  53  can be rotated in the threaded sleeve  54  and be prevented from rotating and secured against loss by means of a securing pin  58 . 
         [0065]    For this purpose, the threaded rod  53  comprises in each case in the upper and lower regions a through-going bore  59  and the threaded sleeves  54  comprise corresponding elongate holes  60 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Suspension device 
           2  Rail 
           2   aa , 2   ab ,  2   ba ,  2   bb  Rail section 
           3  Support elements 
           4  Lifting gear 
           5  Suspended switch 
           6  Butt joint 
           7  Sleeve 
           8  Rail section end 
           9  Groove 
           12  Weld seam 
           13  End of the weld seam 
           14  Angle 
           15  Lateral surface 
           16  Bearing surface 
           20   a,    20   b  Profile 
           21  Angle 
           22  Profile head 
           23  Profile body 
           24  Gap 
           25   a,    25   b  First web section 
           26   a,    26   b  Second web section 
           27   a,    27   b  Third web section 
           28   a,    28   b  Fourth web section 
           29   a,    29   b  Upper profile wall 
           30   a,    30   b  Profile sidewall 
           31  Slot 
           32   a,    32   b  Lower profile wall 
           33   a,    33   b  End section 
           34  Suspension 
           36   a,    36   b  Crimp 
           35  Pivotable part 
           37  Pivot bolt 
           38  Mounting element 
           39  Counter bearing 
           40  Screws 
           41  Mounting region 
           42  Suspension region 
           43  Spherical plain bearing 
           44  Tension element 
           45  Bearing block 
           46  Bore 
           47  Bore 
           48  Lug 
           49  Suspension 
           50  Spherical head 
           51  Pivotable part 
           52  Tension element 
           53  Threaded rod 
           54  Threaded sleeve 
           55  Sleeve part 
           56  Region having a smaller diameter 
           57  Counter bearing 
           58  Securing pin 
           59  Bore 
           60  Elongate hole 
         A Suspension direction 
         H Hollow space 
         L Longitudinal centre plane