Abstract:
A sunshade for a motor vehicle roof ( 2 ) with a shade screen ( 5 ) which can be wound onto a winding rod ( 6 ) and which is located underneath the roof, the opposing side edges of the shade screen are movably guided in the direction of shade motion on guide rails ( 7 ) and are held in the transverse direction with pre-tensioning of the shade screen ( 5 ). To produce pretension in the transverse direction without tensioning elements or bars which are permanently attached to the shade screen and which would hinder rewinding, it is provided that the engagement elements, which are guided on the guide rails ( 7 ), can be coupled to the side edges of the length ( 5 ) of shade when it is unwound to keep the length ( 5 ) of shade pre-tensioned in the transverse direction, so that the sunshade ( 4 ) located under an arched vehicle roof ( 2 ) can follow the arch of the roof, but can be disengaged for the shade screen ( 5 ) as it is wound onto the winding rod so as to enable the shade screen to be wound more compactly.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a sunshade for a motor vehicle roof with a shade screen which can be wound onto a winding rod and which is located underneath the roof; the opposing side edges of the shade being movably guided in the direction of shade motion on guide rails and being held in the transverse direction with pre-tensioning of the shade.  
           [0003]    2. Description of the Related Art  
           [0004]    Published German Patent Application DE 197 39 919 A1 discloses one such sunshade in which edge stiffening is formed on the side edges of the shade, for example, in the form of a U-shaped, injected-on plastic edge which is movably held in a bent guide area of the guide rail and due to its stiffness and greater thickness in the transverse direction cannot slide out of the guide rail. When the shade screen is wound onto the winding shaft, however, the thickened edge is disadvantageous, since a nonuniform winding diameter is formed over the length of the winding shaft.  
           [0005]    U.S. Pat. No. 6,161,893 discloses a sunshade for motor vehicle roofs which has a shade with several bars which are guided in lateral guide rails. When the shade is unwound from the winding shaft, the bars are arched by the two guide rails in the vertical direction, so that the shade is held in tension. However, when the shade is wound up, the bars greatly increase the winding diameter and the bars cause a nonuniform winding process.  
         SUMMARY OF THE INVENTION  
         [0006]    The primary object of the present invention is to devise a sunshade of the initially mentioned type which is improved as compared to the known constructions and which, in particular, does not require excess winding volume.  
           [0007]    This object is achieved by a sunshade having a shade screen in which engagement elements are guided on the guide rails and are coupleable to the shade screen, the shade being pre-tensioned in the transverse direction when coupled to the engagement elements. Since the engagement elements are coupled to the shade screen only when the shade screen is being unrolled and pulled out from the winding shaft, and thus, when the shade screen is rolled up, there are no edge-side tensioning and holding elements, the thickness of the shade screen and thus also the winding diameter are uniform and also comparatively small over the entire width of the shade screen, so that the sunshade or winding shaft requires only a small installation space. The shade screen is formed of a length conventional shade material which is opaque or semi-transparent and contains for example a network structure. The sunshade, due to the transverse tension of the shade screen, is suitable not only for flat sunshades, but also for those curved in the lengthwise direction, which follow the curvature or arch of the motor vehicle roof.  
           [0008]    Preferably, in the area of the front pull-out edge of the shade screen which is formed, for example, by a drawbar, the main engagement element engages on the respective side edge via which the shade screen is coupled to the engagement elements in the direction of motion of the shade. The engagement of the main engagement element is thus intended primarily for transfer of lengthwise forces, but in addition can also transfer transverse forces to produce the transverse tension.  
           [0009]    Preferably, the engagement elements are located spaced apart on a carrier element that is strong in tension, especially a cable. The engagement elements which are formed, for example, as spheres, cubes, disks or plates, and especially have an outer side that is flat or planar as the engagement side. The engagement elements are, for example, formed from plastic or metal and, are pressed securely on the cable or a cord. In one preferred embodiment, the engagement elements form a endless drive chain which is guided over a drive wheel which is coupled to the winding shaft. However, there can also be engagement elements on fixed, movable carrier parts, such as rails, pieces of rail, or racks.  
           [0010]    Because, according to one preferred embodiment, the engagement elements fit into recesses on the side edges and are held in the recesses with play in the direction of motion of the shade, the lengthwise tension in the shade screen can be set without bracing relative to individual engagement elements.  
           [0011]    Advantageously, each guide rail for the engagement elements contains a channel which is formed in a guide slot for the side edge of the shade screen. In the channel, the engagement elements can be moved in the lengthwise directions together with the shade screen, while they are supported in the transverse direction, especially towards the center of the shade screen, and thus, can apply the tension force for the shade screen in the transverse direction. Furthermore, the guide rail can have a return channel for the engagement elements in which the endless drive chain is guided back again. However, the engagement elements can also return outside the guide rail.  
           [0012]    When the drive wheel is coupled via a spring to the winding shaft and a closed flow of force is formed via the drive chain, the side edge of the shade screen, the winding shaft and the drive wheel, the shade screen can be pulled out into any position and can be located in it without an additional blocking means by the longitudinal tension of the spring. Furthermore, if the spring is a torsion-loaded helical spring which undergoes a change of tensioning when the shade screen is unwound as a result of the varying winding diameter relative to the constant diameter of the drive wheel, when the shade screen is pulled out the tension can be increased so that, for example, with the roof opened, fluttering of the pulled-out shade screen is counteracted.  
           [0013]    The drawbar of the sunshade can be actuated manually or via a drive. Furthermore, a drive means can be provided with a drive motor, by which a respective drive cable is provided at each guide rail and is coupled or connected to the sunshade which can be unwound by the winding shaft which is pre-tensioned by spring force. In this case, the drive cable can be connected, for example, to the drawbar of the shade screen or to a drive chain which bears the engagement elements and which are coupled onto the shade screen.  
           [0014]    Advantageously, the engagement elements, in an inlet section, are caused to engage the side edge of the shade screen which is not tensioned in the transverse direction and the shade screen is tensioned in or then on this inlet section in the transverse direction.  
           [0015]    Instead of a endless drive chain, the drive chain which contains the engagement elements can have a free trailing end which is pushed into a return channel of the guide rail or into an outlet tube. The drive chain is formed to be relatively compressively stiff and/or guided against lateral deflection.  
           [0016]    According to another preferred embodiment, it can be provided that the shade screen has teeth on its side edges, that a chain wheel which guides the drive chain is attached torsionally strong with the winding shaft to each of the two ends of the winding shaft and the chain wheel has teeth for respective engagement with the engagement elements of the drive chain, that the teeth of the chain wheel in joint rotation of the chain wheel with the winding shaft are positioned over the assigned teeth on the side edge of the wound shade screen and then pass through gaps between the teeth of the shade screen, the drive chain during unwinding of the shade screen from the winding shaft engaging the recesses on the teeth on the shade screen and continuing to be moved with of shade screen. The drive chain is thus placed in the plane of its lengthwise motion on the side edge of the shade screen, while the teeth of the chain wheel swivel away downward through the respective gaps on the edge of the shade screen. The transverse tension is then produced in the obliquely running guide section of the guide rail.  
           [0017]    According to another preferred embodiment, the engagement elements are sections of a helical or screw-shaped drive part which fit into recesses on the side edge of the shade screen, are moved by rotation of the drive part around its lengthwise axis in the lengthwise direction, and in doing so, entrain the shade screen which is guided between two guide parts. The drive motion thus takes place in sliding engagement between the sections of the helical or screw-shaped drive part which continue to move apparently in the lengthwise direction, and the recesses of the shade screen. Since the drive part does not execute actual lengthwise motion, return for a endless drive chain or for the trailing end of the drive chain is not necessary, by which less space is required on the guide rail.  
           [0018]    Basically, it can be provided that the guide rails are adjustable in the transverse direction or that they are supported spring-elastically. Thus, position tolerances which form during installation or in operation can be equalized later.  
           [0019]    The motor vehicle roof can generally have a fixed transparent roof section or a roof opening with a movable, especially transparent cover, under which the sunshade is located.  
           [0020]    The sunshade is explained in detail below using embodiments with reference to the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is schematic top view of a motor vehicle roof with a fixed glass cover and a sunshade located under it;  
         [0022]    [0022]FIG. 2 shows one side of the sunshade in an exploded perspective view;  
         [0023]    [0023]FIG. 3 is a top view of a portion of one side edge of a shade screen engaged with the drive chain;  
         [0024]    [0024]FIG. 4 is a perspective view of a section of a guide rail of the sunshade with a drive chain guided in it;  
         [0025]    [0025]FIG. 5 is a view similar to that of FIG. 4, but showing another embodiment of the guide rail with a modified drive chain;  
         [0026]    [0026]FIG. 6 is a perspective view of a section a front end piece of the guide rail;  
         [0027]    [0027]FIG. 7 is a schematic side view of the sunshade;  
         [0028]    [0028]FIG. 8 is a partial schematic side view a modification of the FIG. 7 sunshade;  
         [0029]    [0029]FIG. 9 is an exploded sectional view of a winding shaft and an end bearing part therefor;  
         [0030]    [0030]FIG. 10 is a plan view of a portion of the sunshade in the area of the winding shaft and feed of the drive chain to the shade screen;  
         [0031]    [0031]FIG. 11 is a plan view of another embodiment of a sunshade;  
         [0032]    [0032]FIG. 12 is a side view of the area of the winding shaft of the embodiment of FIG. 11;  
         [0033]    [0033]FIG. 13 is a sectional view of the attachment of the guide rail to the roof frame part;  
         [0034]    [0034]FIG. 14 is a sectional view of another embodiment of the attachment of the guide rail to the roof frame part;  
         [0035]    [0035]FIG. 15 is a plan view of the attachment of the guide rail to the roof frame part as shown in FIG. 14;  
         [0036]    [0036]FIG. 16 is a perspective exploded view of another embodiment of a sunshade with a chain wheel attached to the end of the winding shaft;  
         [0037]    [0037]FIG. 17 is a perspective view yet another embodiment of a sunshade with a screw drive for moving the length of shade; and  
         [0038]    [0038]FIG. 18 is a sectional view taken along line A-A in FIG. 17 showing a guide for the screw drive. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    A motor vehicle  1  has a motor vehicle roof  2  with a transparent roof section which, in the embodiment shown, is a fixed glass cover  3  (see FIG. 1). The transparent roof section can also be a movable cover for closing and at least partially clearing the roof opening of a motor vehicle roof which is to be opened, for example, a sliding roof, a sliding and lifting roof, a spoiler roof or the like. Underneath the motor vehicle roof  2  or the glass cover  3 , there is a sunshade  4  which has a shade screen  5  and a winding shaft  6  for rolling and unrolling the shade screen  5 , and two lateral guide rails  7  which run in the lengthwise direction of the vehicle, which are located opposite one another with respect to the glass cover  3  and follow the arch of the roof or of the glass cover  3  in the lengthwise direction. The winding shaft  6  has a hollow cylindrical winding body  8  (see FIG. 2 in which only the right side of the sunshade is shown), each end of which receives a respective bearing part  9  which is pivotally mounted on the motor vehicle roof via an axially projecting bearing journal  10 . A helical leg spring  11  is attached coaxially to the bearing journal  10  (see also FIG. 9) and fixed with one leg  12  on it, while the other leg  13  is connected to the winding body  8  which extends over the leg spring  11 , for example, by fitting into an axial groove  14  on the winding body  8  so that the leg  13  cannot rotate relative to the winding body  8 . The winding body  8  can thus be rotated relative to the bearing journal  10  by an angle of rotation with respect to the axis  15  of rotation against the spring force of the leg spring  11 .  
         [0040]    The shade screen, which can be unwound from the winding shaft  6 , is guided on the respective lateral guide rail  7  via a front drawbar  16  with a sliding element  17  on each end of the drawbar  16  being movably held between the top leg  18  and the lower leg  19  of the respective guide rail  7 . The shade screen  5  has side edges  20 , each of which projects laterally beyond the drawbar  16  or the slide element  17  and is held and guided in a guide slot  21  of the guide rail  7  (see FIGS. 2 &amp; 4). The guide slot  21  adjoins the inside  22  of the lower leg  19  which forms a slide surface for the slide element  17  and the side edge  20  of the shade screen in the plane of the shade screen to the outside. A plurality of rectangular perforations or recesses  23  which are spaced uniformly apart are formed along side edge  20  of the shade screen  5 . The rectangular perforations or recesses  23  are located in a widened area, which is formed as the transport or guide channel  24 , when the side edge  20  of the shade screen is held in the guide gap  21 .  
         [0041]    In the transport channel  24 , a continuous, i.e., endless, drive chain  25  is guided and contains a cable  26  that is strong in tension and a plurality of engagement elements in the form of, for example, balls  27  which are attached to the cable  24  mutually spaced from each other at distance which corresponds to the spacing that separates the recesses  23  in the shade screen from one another. The drive chain  25  runs from a drive wheel  30  which is attached to the bearing part  10  so as to rotate with it, in a closed circuit, forward through the transport channel  24  of the guide rail  7 , into a termination part or deflection part  28  which is attached to the front end of the guide rail  7  and in which it is redirected by in the opposite direction into an idle channel or return channel  29  of the guide rail  7  and finally back into the transport channel  24 .  
         [0042]    The first recess  23   a  which borders the drawbar  16  is matched to the shape of the balls  27  such that the ball  27  which is assigned to the first recess  23   a  is permanently located as the main engagement element in it in interlocking engagement without play both in the lengthwise direction and also in the transverse direction. The, for example, rectangular (see FIG. 2) or also round first recess  23   a  is surrounded by a reinforcement  31  on the shade screen  5  so that when the shade screen is being rolled or unrolled, force can be reliably transferred to the drive chain  25  via the ball  23   a  in the lengthwise direction.  
         [0043]    On the section of the side edge  20  which is held according to the respective pull-out position of the shade screen  5  in the guide rail  7  or in the guide slot  21 , thus a ball  27  of the drive chain  25  engages in each recess  23  (see FIG. 3), each ball  27  adjoining the outside edge  32  of the recess  23  with a tensioning force which is directed outward (shown schematically by the arrow F) so that the shade screen is held tensioned in the transverse direction, while it can be moved in the lengthwise direction jointly with the drive chain  25 . Within the rectangular recess  23 , the ball  27  is held in the lengthwise direction roughly in the middle with bilateral play towards the front edge and rear edge of the recess  23 . Instead of balls  27 , engagement elements can also be, for example, elements flattened on the outer engagement side, for example, disks or plates  33  (see FIGS. 3 &amp; 5) which enable more uniform transfer of force to the shade screen  5  in the transverse direction due to line contact of its flat side surface  34  (in contrast to point contact of balls) with the outside edge  32  of the recess  23 .  
         [0044]    Thus, there is a closed flow of force from the drive wheel  30 , via which the balls  27  of the drive chain  25  run without slipping in the peripheral direction, via the drive chain  25  in the idle channel  29  and the first ball  27  in the first recess  23   a  to the shade screen  5  which in turn is rolled up on the winding body  8  which is coupled to the drive wheel  30 . The tension of the shade screen in the lengthwise direction is achieved by the pre-tensioning of the winding body  8  as a result of the pre-tensioning of the leg spring  11  relative to the bearing part  9 . The lengthwise tensioning of the shade screen can always be maintained uniformly over the entire pull-out length since only the first ball  27  is fixed in the first recess  23   a  in the lengthwise direction and the other balls  27  are held in their recesses  23  with play in the lengthwise direction. The transverse stress and lengthwise stress make it possible for the shade screen to follow the arch of the motor vehicle roof in the lengthwise direction without additional intermediate bars.  
         [0045]    The lengthwise tensioning in the shade screen  5  can be set when the winding body  8  is mounted on the bearing part  9  by the winding body  8  being coupled to the leg spring  11  which is accordingly pre-tensioned rotationally, and for different coupling points, for example, on the end face of the winding body  8  several axial grooves  14  can be formed which are distributed around the periphery.  
         [0046]    When the shade screen  5  is pulled out and unrolled from the winding shaft  6  or the winding body  8 , either by manual actuation or a drive which acts, for example, on the drawbar, the winding diameter on the winding body  8  decreases, while the diameter of the drive wheel  30  which is relevant to the drive chain  25  is constant. The resulting path difference between the moving drive chain  25  and the shade screen in the lengthwise direction is equalized by relative twisting of the winding body  8  which bears the shade screen relative to the drive wheel  30  with increasing pre-tensioning by the leg spring  11 .  
         [0047]    The guide rail  7  has an inlet section  24 ′ (see FIG. 10) in which the balls  27  of the drive chain  25  are guided at an acute angle to the plane  36  of motion of the recesses  23  which are moved in the lengthwise or pull-out direction with the unwinding shade screen which is not tensioned in the lengthwise direction and are inserted into the recess. After the balls  27  have been caused to fit into the recesses  23 , they are guided outwardly in the transverse direction by a small path length  37  in the following short tensioning section  24 ″ of the guide channel  24  so that they tension the shade screen in the transverse direction.  
         [0048]    In the open position of the sunshade, the drawbar  16  remains on the back end of the guide rail  7 , the shade screen with the reinforced first recess  23   a  also remaining in the guide rail  7  and the continuous engagement of the ball  27  or of the engagement element and thus the closed flow of force are preserved.  
         [0049]    The drive chain  25  can be guided (see FIGS. 2 &amp; 7) originating from the upper return channel  29  in one simple deflection via the drive wheel  30  and in the lower guide channel  24 . The shade screen  5  slides, for example, on the inside  22  of the lower leg  19  of the guide rail  7 . In an alternative embodiment, the drive chain  25  can run crossing between the guide rail  7  and the drive wheel  30  (see FIG. 8), and the shade screen  5  can be rolled up and unrolled in the opposite winding direction and is guided to slide on the inside of the upper leg  18  of the guide rail  7 .  
         [0050]    The termination or deflection part  28  (see FIGS. 1 &amp; 6) which is mounted on the front end of the guide rail  7  contains a guideway  35  which forms a deflection connection for the engagement elements or the balls  27  of the drive chain  25  between the return channel  29  and the guide channel  24 . The guideway  35  can be formed within the deflection part  28  or also in front of it. Instead of the guideway, there can also be a deflection wheel or a comparable deflection means.  
         [0051]    The sunshade  4  can also be used in the pulled-out position with the sliding roof opened while driving since as a result of the pre-tensioning in the transverse direction and the laterally fixed side edges of the shade screen fluttering of the shade screen  5  can be largely prevented.  
         [0052]    In one modified embodiment (see FIGS. 11 &amp; 12), the sunshade  4  contains a drive means with a drive motor  40 , by which each drive cable  42 , guided in a respective tube  41 , runs to each guide rail  7  and is guided through the guide channel  24  as far as the shade screen  5 . The connection of the drive cable  42  to the shade screen takes place, for example, by attachment to the drawbar  16  or by a connection to the drive chain  25  which, in this example, begins with the first ball  27  in the first recess  23   a  (see FIG. 2) via which the drive wheel  30  is guided and extends into the return channel  29 . The winding shaft  6  or the winding body  8  is pre-tensioned by means of a winding spring (not shown) which is supported on the vehicle counter to the pull-out direction (closed direction of the sunshade). When the sunshade  4  is closed, by actuating the drive motor  40 , the shade screen  5  is unwound from the winding body  8 , the pull-out force increasing by the tensioning winding spring.  
         [0053]    When the shade screen is pulled out, in the already described manner, on each side of the shade screen  5 , the engagement elements or balls  27  of the drive chain  25  are caused to fit into the recesses  23  on the side edge  20  of the shade screen  5  and by transverse motion pointed toward the outside, they apply transverse tension to the shade screen  5 . The free end of the drive chain  25  is pulled out of the return channel  29  when the sunshade  4  is closed. When the partially or completely closed sunshade  4  is being opened, the shade screen  5  is retracted by the corresponding actuation of the drive motor  40  and by supporting the winding springs and is rewound again. In doing so, the drive chain  25  is decoupled from the shade screen and retracted via the drive wheel  30  into the return channel  29 . The drive chain  25 , for this purpose, is formed with a relatively compressively stiff cable  26 , or instead of the cable  26 , with partially flexible connection elements between the balls  27 . In addition, there can be a guide rail  43  (FIG. 12) which surrounds the drive wheel  30  and prevents lateral deflection of the pushed drive chain  25  by the drive wheel  30 .  
         [0054]    Alternatively, the free end of each drive chain  25  can be held in an additional outlet tube  44  (shown in FIG. 11 with interrupted lines), and when the sunshade  4  is closed, it can be pulled out of the tube  44  and when the sunshade  4  is opened can be pushed back into it.  
         [0055]    [0055]FIG. 13 shows the attachment of the guide rail  7  by means of a screw  45  which passes through the oblong hole  46  which is formed in the transverse direction of the guide rail  7  on the roof frame part  47 . In this way, the guide rail  7  can be adjusted on the roof frame part  47  during installation or subsequently to the required distance to produce the desired transverse tensioning of the shade screen  5 . The guide rail  7  is attached to the roof frame part  47  with several screws  45  along their length. The adjustment play can also be produced by a round hole with a diameter which is much larger than the screw shaft instead of by means of an oblong hole  46 .  
         [0056]    In the mounting shown in FIGS. 14 &amp; 15, the guide rail  7  contains two lateral lengthwise grooves  48 ,  49  on its top which open in opposite directions and fit movably in the holding legs  50 ,  51  of a roof frame part  52  which are pointed opposite one another so that the holding legs  50 ,  51  hold the guide rail  7  in the vertical direction without play. A leaf spring  53  which is bent in a corrugated shape is inserted between the stop  54  on the guide rail  7  and the stop  55  on the roof frame part  52  and pretensions the guide rail  7  outwardly in the transverse direction. In this way, with the spring force set accordingly, transverse pre-tensioning of the shade screen  5  can also be maintained even at installation tolerances.  
         [0057]    Another modified embodiment of the sunshade  4  contains a winding shaft  6 ′ (see FIG. 16), on the respective end of which a chain wheel  56  is attached to rotate with the winding shaft  6 ′. The chain wheel  56  has, on its periphery in the direction of the axis  15 , rotation teeth  57  which project laterally toward the shade screen  5 ′ and which each contain an opening  58  for holding a ball  27  of the drive chain  25 . The teeth  57  of the chain wheel  56 , which is attached to the winding shaft  6 ′ (FIG. 16 shows the chain wheel  56  before attachment to the end face of the winding shaft  6 ′, spaced away from the latter) extend beyond the edge  59  of the shade screen  5 ′, which has teeth  60  which project laterally in the direction of the axis  15  of rotation, the teeth  60  each having a recess  23  for the balls  27 . The recesses  58  on the teeth  57  of the chain wheel  56  and the recesses  23  on the teeth  60  on the edge  59  of the shade screen are located in the same plane perpendicular to the axis  15  of rotation of the winding shaft  6 ′.  
         [0058]    The width of each tooth  60  on the edge  58  of the shade screen is smaller than the gaps  61  between the teeth  57  of the chain wheel  56  so that when the shade screen  5 ′ is unrolled from the winding shaft  6 ′, a tooth  60  of the shade screen  5 ′ can always pass through the gap  61  on the chain wheel  56 .  
         [0059]    Since the winding diameter on the winding shaft  6 ′ changes when rolling and unrolling the shade screen  5 ′, the distance of two adjacent teeth  60  along the length of the shade screen  5  is matched to this change so that unhindered passage of the teeth  60  of the shade screen through the gaps  61  between the teeth  57  of the chain wheel  56  is always ensured. The drive chain  25  can be caused to engage the recesses  23  on the unrolling shade screen  5 ′ in this way without acutely-angled feed.  
         [0060]    Another embodiment of the sunshade (see FIGS. 17 &amp; 18) contains a screw drive for moving the shade screen along a guide rail  62 . The screw drive has a drive cable  63  as is used in the drive shown in FIG. 11 or in a sliding roof drive. The drive cable  63  which contains a continuous screw coil  64  is held in an trough-shaped or roughly semi-cylindrical lengthwise recess  65  in the guide rail  62  such that its core  66  is located underneath the top  67  of the guide rail  62  and only the screw coil  64  projects upward. The shade screen  5 , which can be wound and unwound on the winding shaft  6 , contains on its side edge a perforation with a plurality of recesses  68  which have a size and shape such that when the shade screen rests on the guide rail  62 , the recesses hold the individual sections  69  of the screw coil  64  which project upward.  
         [0061]    A second guide rail  70  (see FIG. 18, not shown in FIG. 17) is located above the first lower guide rail  62  with a defined distance in which the shade screen is movably held in the lengthwise direction. The drive cable  63  is turned around its lengthwise axis so that the screw coil  64  “migrates” in the lengthwise direction for displacing the shade screen  5  along the guide rails  62 ,  70  by the coil sections  69  fitting into the recesses  68  of the shade screen  5 . In the transverse direction, the shade screen is held tensioned between the screw coils  64  of the two opposing drive cables  63 .