Abstract:
A winding mechanism for controlling the retraction and deployment of an architectural covering, such as a window blind or shade having a winding element  12 , about which the covering, or its lift cord or tapes are wound and unwound with rotation of the winding element about a first axis of rotation, and a fluid brake  40  for retarding the rotation of the winding element in at least one direction about the first vaxis. The fluid brake comprises a fluid tight compartment  42  containing a liquid and an impeller  46 . The compartment and the impeller are adapted for relative rotation about a second axis, which can be the same as or coaxial with the first axis. Either the compartment or the impeller is operatively connected to the winding element. In operation the liquid rotates with the rotation of the compartment or the impeller about the second axis. Rotation of the liquid relative to the impeller or to the compartment in at least a first direction about the second axis is effective to retard the rotation of the winding element in at least a second direction about the first axis. The impeller  46 , or a peripheral wall surface  43  of the compartment  42  has a first surface  49 B that extends generally radially and substantially parallel with respect to the second axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of prior U.S. patent application Ser. No. 09/208,891, filed Dec. 10, 1998, U.S. Pat. No 6,155,328, entitled WINDING MECHANISM. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a winding mechanism for controlling the retraction and deployment of an architectural covering, especially a covering for an architectural opening, such as a window blind or shade. This invention particularly relates to a spring-assisted winding mechanism useful for controlling the winding and unwinding of the covering, itself, about a tubular roller or for controlling the winding and unwinding of lift cords and/or tapes of the covering about a spool or the like. This invention quite particularly relates to a fluid brake which can be used in such a winding mechanism to control the retraction or winding up of the covering or the lift cords or tapes. 
     Winding mechanisms for retracting or raising window shades and blinds have often used a spring retraction mechanism to bias the shades and blinds towards their retracted position. To hold a shade or blind in its deployed or lowered position, these mechanisms have also been provided with a locking mechanism. Conventionally, the locking mechanism has involved an arrangement in which, when the shade or blind has been pulled down or unwound and then released, the shade or blind has been locked in the lowered position. If the shade or blind has been pulled down again, the locking mechanism has been released, and a spring retraction mechanism has caused the shade or blind to be retracted or rolled up again. Such roller mechanisms have been used, for example, for winding and unwinding roller blinds and lift cords of pleated blinds and roman shades. See EP 0 087 146. 
     Recently, there has been an increased demand for a device for retarding or braking the rotational speed of retraction of spring-assisted winding mechanisms of shades and blinds. Such rotational speed of retraction, if not smoothed or controlled, can cause shades and blinds to fly up and can easily damage their components when they are retracted. To avoid such damage, it has been proposed to use mechanical braking or retarding devices to obtain a continuous, smooth and controlled retraction of the blinds. One such retarding device, described in EP 0 093 289, has used a pair of centrifugally-acting brake shoes inside a brake drum. To achieve the required centrifugal speed, an epicyclic gear train has been provided to speed up rotation of the assembly, upon which the brake shoes are mounted. However, because it is essentially a mechanical retarding device, the retarding device of EP 0 093 289 has been subject to friction and wear and thus has tended to become less effective over time. 
     An additional demand has been for a retarding device which is effective in only the direction of rotation for retracting the shades and blinds, in order not to interfere with unwinding or lowering them. This has also been achieved to some extent by means of the one-way helically-wound spring clutch used in the retarding device described in EP 0 093 289. 
     It has also been proposed, in DE-G-92 03 450, to use a fluid brake containing a liquid, the viscosity of which increases when it is subjected to increasing shear stresses, for retarding the rotational speed of retraction of spring-assisted winding mechanisms of shades and blinds. In this regard, such a liquid (e.g., a silicon oil) has been provided in a fluid-tight cylindrical compartment within a roller, and a fixed centre shaft of the roller has been positioned axially within the compartment. Upon rapid rotation of the roller and compartment about the shaft when retracting a shade, the liquid is subjected to increased shear stress, causing its viscosity to increase and causing it to retard such rotation. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with this invention, a winding mechanism for controlling the retraction and deployment of an architectural covering, such as a window blind or shade, is provided having a winding element, about which the covering or its lift cord or tapes are wound and unwound with rotation of the winding element about a first axis of rotation, and a fluid brake for retarding the rotation of the winding element in at least one direction about the first axis; the fluid brake comprising a fluid-tight compartment containing a liquid and an impeller and wherein: the compartment and the impeller are adapted for relative rotation about a second axis of rotation; the compartment or the impeller is operatively connected to the winding element; the liquid rotates with rotation of the compartment or the impeller about the second axis; rotation of the liquid relative to the impeller or to the compartment in at least a first direction about the second axis is effective to retard the rotation of the winding element in at least a second direction about the first axis; and the impeller or an inner peripheral wall surface of the compartment has a first surface that extends generally radially and substantially parallel with respect to the second axis. 
     Preferably the first and second axes are coaxial, and advantageously the first and second directions are the same. 
     Advantageously the compartment is operatively connected to, and rotates with, the winding element and rotation of the liquid with the compartment, relative to the impeller, in at least the first direction about the second axis is effective to retard the rotation of the winding element in at least the second direction about the first axis. Advantageously, the fluid brake is within the winding element. 
     The liquid preferably has a viscosity that increases with increasing agitation of the liquid in the compartment. 
     In accordance with one embodiment of the invention, the first surface is on a vane eccentrically mounted on, and protruding axially from, a radially-extending disk of the impeller or is on a vane mounted on, and protruding radially from, a hub of the impeller, especially where: i) the inner peripheral wall surface of the compartment is generally cylindrical; ii) the impeller has a plurality of the vanes which are movable and can be flexible and resilient but are advantageously hingedly connected to the impeller; and iii) each vane also has a second surface that can be moved towards the inner peripheral wall surface when pressure is exerted by the liquid against the first surface of the vane. In this regard, it is particularly advantageous that the second surface of each vane can frictionally engage the inner peripheral wall surface of the compartment when pressure is exerted by the liquid against the first surface of the vane, especially where each vane has a curvilinear cross-section that is concave towards the first surface. 
     In accordance with another embodiment of the invention, the impeller does not rotate or rotates in the opposite direction from the rotation of the compartment about the second axis. In this regard, it is particularly advantageous that a one-way clutch be interposed between the winding element and the compartment or the impeller, especially where an inverting gear assembly, particularly a speed-up gear assembly, is interposed between the clutch and the compartment or the impeller. The speed-up gear assembly may comprise an epicyclic gear train having a sun gear, planet gear wheels and a ring gear; and wherein the impeller is connected to the sun gear, the planet gear wheels are rotatably carried by the one-way clutch, and the ring gear is connected to the winding element for rotation therewith. 
     It is also contemplated that the winding mechanism should further comprise: an elongate longitudinally-extending hollow roller extending along the first axis, having its opposite ends rotatably connected to a pair of bearing journals and having an end of the covering attached to it; a fixed element within the roller, connected to one of the bearing journals; and a spring-urged winding mechanism operatively connected to the fixed element and the roller and adapted to urge the roller to rotate in a first direction about the first axis to retract the covering; and wherein the fluid brake is within the roller, is operatively connected to the roller and the fixed element, and retards substantially only rotation of the roller in the first direction of rotation. In this regard, it is particularly advantageous that the compartment of the fluid brake be connected to the roller for rotation therewith. 
     In accordance with other aspects of the invention, an architectural covering, such as a window blind or shade, is provided comprising the winding mechanism just described, and a fluid brake is provided as just described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may more readily be understood, the following is given, merely by way of example, reference being made to the accompanying drawings in which: 
     FIG. 1 is a schematic perspective view of a blind with a first embodiment of a winding mechanism of this invention; 
     FIGS. 2 and 3 are longitudinal cross-sections through a portion of the winding mechanism of FIG. 1, with a first embodiment of its fluid brake shown with the vanes of its impeller in two different working positions—unflexed and flexed, respectively; 
     FIGS. 2A and 3A are cross-sections along the lines II—II and III—III of FIGS. 2 and 3 respectively; 
     FIG. 4 is a view similar to FIG. 2 of the winding mechanism of FIG. 1 with a second embodiment of its fluid brake; 
     FIG. 4A is a cross-section along the line IV—IV of FIG. 4; 
     FIG. 5 is a longitudinal cross-section of a winding mechanism of this invention (with a portion shown broken away); 
     FIG. 6 is a fragmentary cross-section of a modified winding mechanism; 
     FIG. 7 is an end elevation of the epicyclic gear train mechanism shown in FIG. 6; 
     FIG. 8 is an end elevation of the one-way clutch shown in FIG. 6; 
     FIG. 9 is a view similar to FIG. 4A of a third embodiment of fluid brake; 
     FIG. 9A is a cross-section along the line IX—IX of FIG. 9; 
     FIG. 10 is a view similar to FIG. 4A of a fourth embodiment of fluid brake; 
     FIG. 10A is a cross-section along the line X—X of FIG. 10; 
     FIG. 11 is a view similar to FIG. 4A of a fifth embodiment of fluid brake; 
     FIG. 11A is a cross-section along the line XI—XI of FIG. 11; 
     FIG. 12 is an exploded view of an impeller of a sixth embodiment of a fluid brake; 
     FIG. 13 is a perspective view of the impeller of FIG. 12 with its vanes unextended; 
     FIG. 14 is an end view of the impeller of FIG. 13; 
     FIG. 15 is a perspective view of the impeller of FIG. 12 with its vanes extended; and 
     FIG. 16 is an end view of the impeller of FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a roller blind  1 , the ends of which are attached to a pair of conventional brackets  10 A and  10 B for mounting the roller blind  1  on a wall, adjacent to a window. The roller blind  1  has an elongate hollow tubular roller  12  which cannot be seen in FIG. 1 because a top portion  14  of a shade  16  is wound about the roller  12 . The top end of the shade  16  is attached to the roller  12  in a conventional manner. A conventional pull-tab  18  is provided at the bottom end of the shade  16 . 
     FIG. 5 shows the interior of the longitudinally-extending hollow tubular roller  12  of the roller blind  1  in longitudinal cross-section. Within the left end portion of the roller  12  is a coaxially-extending journal end member  20 , which is fixed to the roller  12  and is therefore rotatable therewith. A longitudinally-extending journal spigot  21  on the left end of the end member  20  rotatably engages the adjacent left bracket  10 A, so that the end member  20  and roller  12  are rotatably journalled relative to the left bracket  10 A. 
     Within the right end portion of the roller  12 , as shown in FIG. 5, is an end cap  22 , non-rotatably mounted on the right end of a longitudinally-extending centre rod  24 . Roller  12  will rotate relative to the end cap  22 . A flattened right end portion  26 , preferably of rectangular cross-section, of the centre rod  24  engages a corresponding, preferably rectangular, opening in the adjacent right bracket  10 B, so that the centre rod  24  is non-rotatably connected to the right bracket  10 B, with the roller  12  journalled relative to the centre rod  24 . 
     FIG. 5 also shows the end cap  22  engaging a longitudinally-extending sleeve  28  which serves as a bearing for the roller  12 . The sleeve  28  has an end wall  29  at its left end and accommodates a conventional lock  30 , such as is described in EP 0 087 146 and commonly used in spring-loaded blinds, such as roller blinds. The lock  30  serves to releasably restrain the end cap  22 , the sleeve  28  and roller  12  from rotating about the fixed centre rod  24 . In use, one pulls downwardly on the tab  18  to lower or unwind the shade  16 , and the lock  30  holds the roller  12  and thereby the shade in that position. In order to raise or wind up the shade  16 , one pulls down again on the tab  18  to unlock the lock  30 , and a spring mechanism, described below, causes the roller  12  to rotate and the shade  16  to be raised. The roller  12  can be arrested in any desired position of either retracting or unwinding the shade  16 , using the lock  30 . 
     Within the roller  12  and to the left of the end wall  29  of the sleeve  28  is a coaxially-extending first spring retainer  32 . The first spring retainer  32  is rotatably mounted on the centre rod  24 , which is fixed to the right bracket  10 B, and engages, preferably frictionally, the inside surface of the roller  12  so that the first retainer rotates with the roller about the centre rod. In this regard, the first spring retainer  32  is retained axially in place by a first circlip  34 , fixed on the centre rod. Further to the left of the end wall  29 , a coaxially-extending second spring retainer  36  is non-rotatably secured to the fixed centre rod  24  and retained axially in place by a second circlip  38 . 
     A conventional, longitudinally-extending torsion or coil spring  39  is helically wound about the centre rod  24  between the spring retainers  32 ,  36 . The ends of the spring  39  are held by the spring retainers  32 ,  36 , whereby the spring can thereby function as a spring motor or retraction mechanism between the roller  12  and the centre rod. The spring  39 , which is tensioned as a result of lowering the shade  16 , relaxes when the shade is fully retracted by being rolled up about the roller  12 . 
     The arrangement of the shade  16  and roller  12 , described so far, is generally conventional. However in accordance with this invention, the shade-winding mechanism of the roller blind  1  further includes a fluid brake or speed retarding mechanism  40 , which is operative between the roller  12  and the fixed centre rod  24  only when rewinding or retracting the shade  16 . In this regard, the roller  12  has, to the left of the second spring retainer  36 , a coaxially-extending, preferably generally cylindrical, fluid-tight compartment  42  with a closure lid  44  mounted on its right end as shown in FIG.  5 . The left end portion of the centre rod  24  is located axially within the fluid-tight compartment  42  and has as an impeller  46  mounted on it. The impeller  46  is positioned concentrically within the compartment  42  with the hub  47  of the impeller on the longitudinally-extending axis of rotation of the compartment. Mounted on the circumference of the impeller hub  47  within the compartment  42  are a plurality, preferably 2 or 3, vanes  48 , extending generally radially from, and substantially parallel to, the axis of rotation of the compartment. As seen from FIGS. 2,  2 A,  3  and  3 A, the vanes  48  are flexible and preferably inherently resilient. The radial ends of the vanes are close to, but spaced away from, the cylindrical inner peripheral wall surface  43  of the compartment  42 , and the longitudinal ends of the vanes are close to, but spaced away from, the longitudinal ends of the compartment  42 . In this regard, each vane  48  has a first surface  49 A, the radial end of which can be moved towards and away from the inner surface  43  of the compartment  42  when pressure is exerted against a second surface  49 B of the vane, on the opposite side of the vane. Preferably, each vane  48  has a curvilinear cross-section that is concave towards its second surface  49 B, and is convex towards its first surface  49 A. 
     The fluid-tight compartment  42  of the fluid brake  40  of FIGS. 2 and 3 is filled with a liquid, preferably a viscous liquid, which is somewhat sticky and therefore will readily rotate within the compartment with rotation of the inner surface  43  of the compartment. The viscosity of the liquid can be constant or variable. In certain embodiments of the fluid brake of this invention, the viscosity of its liquid is preferably variable and increases with increasing agitation and turbulence of the liquid caused by its relative movement around the impeller  46  and vanes  48  but decreases to its initial value when it is no longer agitated and turbulent. Examples of such a liquid include conventional silicone oils, such as are available from Drawin Vertriebs GmbH, Postfach 110, D-85509 Ottobrunn. In this regard, the use of a liquid, the chain length of the molecules of which effectively becomes longer with increasing agitation and turbulence, whereby the liquid thickens, is especially preferred in the fluid brakes  40  of FIGS. 9 to  11  (discussed below) but can also be used in the fluid brakes of FIGS. 2,  3  and  4  (discussed below). Examples of such a liquid include conventional aqueous starch solutions. When additionally a planetary gear is coupled to the hub  47  of the impeller  46 , as described below with reference to FIG. 6, a liquid that is relatively less viscous can be used in the fluid brake  40 . 
     FIGS. 2A and 3A show that the inner surface of the roller  12  has a longitudinally-extending key  19  which engages a corresponding longitudinally-extending slot in the outer surface of the compartment  42  of the fluid brake  40 . As a result, the compartment  42  and roller  12  rotate together, and any braking of the rotation of the compartment  42  will brake rotation of the roller  12 . 
     In use, when the shade  16  is to be raised or retracted, the spring  39  loosens or unwinds, which causes the roller  12  to rotate clockwise in FIGS. 2A and 3A. When the roller  12  rotates clockwise, the compartment  42  of the fluid brake  40  rotates clockwise with it, and the liquid in the compartment  42  rotates clockwise with the inner surface  43  of the compartment. However, the vanes  48  of the impeller  46 , mounted on the fixed centre rod  24 , do not rotate. As a result, the clockwise rotation of the liquid is hindered by the second surface  49 B of each of the vanes  48 , and the liquid can only flow between the ends of the vanes and the inner wall surface  43  of the compartment. This causes the differential pressure of the liquid on the concave second surfaces  49 B of the vanes  48 , relative to their first surfaces  49 A, to be positive during clockwise acceleration and rotation of the roller  12  and compartment  42 , whereby the vanes flex, from the position shown in FIG. 2A, radially outwardly in a clockwise direction and their first surfaces  49 A move towards the cylindrical inner surface  43  of the compartment  42  and finally to the position shown in FIG.  3 A. This flexing of the vanes  48 , in turn, causes their second surfaces  49 B to block even more the clockwise flow of the liquid between the ends of the vanes and the inner wall surface  43  of the compartment  42 , thereby further increasing the liquid pressure and friction on the rotating inner wall surface  43  of the compartment, which tends to brake the clockwise acceleration and the rotation of the compartment and thereby tends to brake the clockwise acceleration and the rotation of the roller  12  in accordance with this invention when retracting the shade  16 . In addition, this flexing of the vanes  48  causes the ends of their first surfaces  49 A (when the vanes are fully flexed) to be pushed against, and frictionally restrain rotation of, the inner surface  43  of the compartment  42 , thereby still further braking the clockwise rotation of the compartment  42  and the roller  12  in accordance with this invention. 
     If desired, a liquid can be used in the compartment  42  of the fluid brake  40 , the viscosity of which increases with increased agitation as a result of the radial flexing of the vanes  48 . This will tend to brake further the clockwise acceleration and the rotation of the compartment  42  and the roller  12  caused by the flexing of the vanes in accordance with this invention when retracting the shade  16 . 
     By comparison, when the shade  16  is lowered or unwound and the spring  39  becomes tighter or wound up, the roller  12  and the roller-retarding compartment  42  of the fluid brake  40  rotate counter-clockwise in FIGS. 2A and 3A, and the liquid in the compartment  42  rotates counter-clockwise with the inner surface  43  of the compartment, but the vanes  48  of the impeller  46 , mounted on the fixed centre rod  24 , do not rotate. However, the ends of the first vane surfaces  49 A of the vanes  48 , because of their flexibility and resilience, move away from the inner surface  43  of the compartment  42  when the positive differential pressure between the second surface  49 B and first surface  49 A of each of the vanes is removed by the counter-clockwise rotation of the viscous liquid in the compartment. Moreover, the ends of the first vane surfaces  49 A, because of their convex shape, are urged away from the inner surface  43  of the compartment  42  by the negative differential pressures between the second surfaces  49 B and first surfaces  49 A of the vanes caused by any acceleration of the counter-clockwise rotation of the liquid in the compartment. As a result, the vanes  48  do not block significantly the counter-clockwise flow of the liquid in the compartment  42  between the ends of the vanes and the inner surface  43 , and in addition, the viscosity of the liquid, if variable, does not increase. Thus when unwinding the shade  16 , there is not significant pressure on the inner surface  43  of the compartment  42  from either the liquid in the compartment or from the vanes  48  which retards or brakes significantly the counter-clockwise acceleration of the rotation of the compartment and the roller  12  in accordance with this invention 
     A modified version of the fluid brake  40  of FIGS. 2,  2 A,  3  and  3 A is shown in FIGS. 4 and 4A, and like parts are indicated by like reference numerals. Secured to the left end portion of the fixed centre rod  24 , within the fluid-tight compartment  42  of the fluid brake  40 , is an impeller  46 . The impeller  46  is positioned concentrically within the compartment  42  on the longitudinally-extending axis of rotation of the compartment. The impeller  46  has a hub  47 , on which is a radially-extending disk  50 , preferably integral with the hub, carrying a plurality of flexible and preferably inherently resilient vanes  52 . The vanes  52 , which are eccentrically positioned on the left side of the disk  50 , are of triangular cross-section and extend longitudinally to the left, so that they are close to, but spaced away from, the left end of the compartment  42 . Each vane  52  has a first curvilinear surface  54  corresponding to the inner peripheral wall surface  43  of the compartment  42 , a second angled surface  56  that extends substantially parallel to the axis of rotation of the compartment, and a third surface  58  extending radially of the axis of rotation of the compartment  42 . The first surface  54  of each vane  52  is adjacent to the inner wall surface  43  and can be flexibly moved towards the inner surface  43  when there is a radially outwardly directed pressure on the second surface  56  of the vane, relative to its first surface  54 . When such radial pressure is removed, each vane  52  can return to its relaxed state with its first surface  54  spaced slightly away from the inner surface  43 . During acceleration of clockwise rotation of the roller  12  when unwinding the shade  16 , the compartment  42  and the liquid in the compartment (in FIG. 4 a ) also rotate clockwise with the roller, and the differential pressure of the liquid on the second surfaces  56  of the vanes  52 , relative to their first surfaces  54 , is nil or negative. Therefore, the vanes remain at rest so that their first surfaces  54  are spaced away from the inner wall surface  43  of the compartment  42 . This allows the inner wall surface  43  to rotate freely in the clockwise direction. 
     During acceleration of the counter-clockwise rotation of the roller  12  when retracting the shade  16 , the compartment  42  and the liquid (in FIG. 4 a ) also rotate counter-clockwise with the roller, and the differential pressure of the liquid on the second surfaces  56  of the vanes  52 , relative to their first surfaces  54 , is positive. Therefore, the vanes flex so that their first surfaces  54  are pushed against, and frictionally restrain rotation of, the inner surface  43  of the compartment. Thereby, the impeller  46  and its fixed disk  50  and vanes  52  provide braking of the counter-clockwise acceleration of the rotation of the compartment  42  of the fluid brake  40  and the roller  12  when retracting the shade  16  in accordance with this invention. If desired, this effect can be enhanced by using a liquid in the compartment  42  whose viscosity increases with increasing agitation of the liquid caused by increases in the rotational speed of the liquid about the vanes  52 . 
     FIG. 6 shows another modified roller  12 , in which like parts are indicated by like reference numerals. The shade-winding mechanism in accordance with the invention includes a fluid brake  40 , as shown in FIGS. 2,  2 A,  3  and  3 A, with a hub  47  of an impeller  46  that is coupled to a one-way clutch  60 , preferably via an epicyclic gear train  70 , so that the fluid brake is operative between the roller  12  and the fixed centre rod  24  only when rewinding or retracting the shade  16 . In this regard, the one-way clutch  60 , shown in more detail in FIG. 8, has an outer longitudinally-extending tubular bushing  62  surrounding an inner, radially-extending ramp wheel  64  that is fixed to the left end of the fixed centre rod  24 . Curvilinear notches  66  are provided at the periphery of the ramp wheel  64 , and within the notches  66  are longitudinally-extending rollers or needles  68 . On the left end of the bushing  62  (remote from the centre rod  24 ) are mounted longitudinally-extending pins  71  (shown in FIG. 6) that form the axes of the planet gear wheels  72  of the epicyclic gear train  70  shown in FIGS. 6 and 7 and discussed below. 
     When the roller  12  rotates in a clockwise direction (in FIGS. 6-8) when retracting the shade  16 , the compartment  42  of the fluid brake  40  also rotates clockwise, causing the liquid in the compartment to tend to rotate clockwise. However, the clockwise rotation of the liquid within the compartment is hindered by the surfaces of the vanes  48  of the impeller  46 , which extend radially of the axis of rotation of the compartment  42  as discussed above. As a result, the liquid hinders the clockwise rotation of the compartment which in turn retards the clockwise rotation of the roller  12 . This retarding effect on the clockwise rotation of the roller is increased by the use of a one-way clutch  60  of FIG.  8  and an epicyclic gear train  70  of FIG. 7 to rotate the impeller  46  in a counter-clockwise direction as described below. 
     As best shown in FIGS. 6 and 7, the epicyclic gear train  70  has an outer ring gear  74  connected to the inner surface of the roller  12 . When the roller  12  rotates clockwise, so does the outer ring  74  of the gear train  70 . This causes the planet gear wheels  72 , engaged by the outer ring gear  74 , to rotate clockwise about their own axes and the axis of the gear train  70 . As a result, the planet gear wheels  72 , rotatably mounted on the bushing  62  of the one-way clutch  60 , cause the bushing  62  to also rotate clockwise. This causes the inner surface of the bushing  62  to frictionally urge the needles  68  of the one-way clutch  60  to also move in a clockwise direction, which causes the needles  68  to move up ramp-like surfaces  67  of the notches  66  of the ramp wheel  64  where the needles  68  become wedged between the inner surface of the bushing  62  and the notches  66 . Because the ramp wheel  64  is fixed to the centre rod  24 , the bushing  62  and its pins  71  can no longer rotate clockwise once the needles  68  become so-wedged, and as a result, the planet gear wheels  72  no longer rotate clockwise about the axis of the gear train  70  but rotate only clockwise about their own axes with clockwise rotation of the roller  12  and the outer ring gear  74 . Such clockwise rotation of the planet gear wheels  72  about their own axes causes a sun gear  76  of the gear train  70  to rotate in a counter-clockwise direction at a speed higher than that of the roller  12 . 
     The sun gear  76  is mounted on the right end of a longitudinally-extending shaft  78  which extends through the cover  44  of the compartment  42  of the fluid brake  40 . The left end of the shaft  78 , within the compartment  42 , is affixed to the impeller hub  47 , with the vanes  48  on it as shown in FIGS. 2 and 3. As a result, clockwise rotation of the roller  12 , which causes counter-clockwise rotation of the sun gear  76 , also causes counter-clockwise rotation of the impeller  46  in the compartment  42  while the compartment and its liquid are rotating clockwise. Thereby, the retarding effect of the radial surfaces of the vanes  48  of the impeller  46  of the fluid brake  40  on the rotation of the liquid, the compartment  42  and the roller  12  of FIG. 6, connected to the compartment, is increased as compared to the effect achieved within the roller  12  of FIG.  5 . Thus, a less viscous liquid can be used for certain shades and blinds. 
     When the roller  12  rotates in a counter-clockwise direction (in FIGS. 6-8) when unwinding the shade  16 , the outer ring gear  74  of the gear train  70  also rotates counter-clockwise. As a result, the planet gear wheels  72  also rotate counter-clockwise about their own axes and the axis of the gear train, which causes the bushing  62  of the one-way gear  60  also to rotate counter-clockwise. Counter-clockwise rotation of the bushing  62  causes its inner surface to frictionally urge the needles  68  of the clutch also to move counter-clockwise, which causes the needles  68  to move away from the ramp-like surfaces  67  of the notches  66  of the ramp wheel  64 , away from the inner surface of the bushing  62  and against radially-extending curved surfaces  69  of the notches  66  as shown in FIG.  8 . As a result, the inner surface of the bushing  62  and its pins  71  can continue to rotate counter-clockwise, without hindrance from the needles  68  or the ramp wheel  64 , fixed to the centre rod  24 . Thereby, the planet gear wheels  72  also can continue to rotate counter-clockwise about the axis of the gear train  70 , and this causes the counter-clockwise rotation of the outer ring gear  74  with the roller  12  to be transmitted to the sun gear  76  so that the sun gear, together with the shaft  78  and impeller  46  also rotate counter-clockwise. Thus, the impeller  46  with its vanes  48  will rotate counter-clockwise with the liquid in the fluid brake, so as not to retard the rotation of the liquid or the compartment  42  or the roller  18 . 
     This arrangement of FIGS. 6-8 provides an improved braking effect on the spring-assisted clockwise rotation of the roller  12  when winding up the shade  16 , but it allows relatively free counter-clockwise rotation of the roller  12  when unwinding the shade and tensioning the spring  39 . This is because the one-way clutch  60  of FIG. 8 is disengaged when the roller shade  12  is pulled downwardly to unroll it but is engaged when the shade is retracted, and unnecessary resistance from the fluid brake  40  and the gear train  70  on rotation of the roller  12  is eliminated when unwinding the shade. Alternatively, an impeller  46  with the disk  50  of FIGS. 4 and 4A can be fixed to the left end of the shaft  78  in this arrangement, provided that the other elements of the roller blind  1  are reversed to have spring-assisted counter-clockwise rotation of the roller  12  when winding up the shade  16  and clockwise rotation of the roller when unwinding the shade. 
     It will be appreciated that in any architectural covering of this invention, such as the roller blind  1  shown in the Figures, the fluid brake  40 , instead of being within the roller  12 , could be mounted externally of the roller and be, for example, on one of the mounting brackets  10 A or  10 B. Likewise, the fluid brake  40  could be provided within a spool or other winding element, about which a lift cord or tape of an architectural covering, such as a pleated blind, is wound and unwound with rotation of the winding element about its axis of rotation. Also, the impeller  46 , instead of being mounted so as to be stationary within the compartment  42  of the fluid brake  40  shown in FIG. 5, could be designed to rotate with the roller  12  in order to brake its rotation in accordance with this invention, with the compartment  42  then being designed to remain stationary with the centre rod  24  or to rotate in a direction opposite to the direction of rotation of the vanes and disk. 
     Furthermore when a viscous liquid is used in the compartment  42  of the fluid brake  40 , the viscosity of which increases with increasing agitation and turbulence thereof, the vanes  48  protruding radially from the hub  47  of the impeller  46  of FIGS. 2,  2 A,  3  and  3 A and the vanes  52  eccentrically mounted on, and protruding axially from, the radially-extending disk  50  of the impeller  46  of FIGS. 4 and 4A can be replaced by other structures for agitating and creating turbulence in the viscous liquid. For example, the elliptical vanes  48 A of FIGS. 9 and 9A, the cylindrical finger  52 A of FIGS. 10 and 10A or the helical stirring element  52 B of FIGS. 11 and 11A can be part of the impeller  46  mounted on the fixed centre rod  24  of FIG. 5 or on the rotatable shaft  78  of FIG. 6 within the compartment  42 . Likewise, the vanes  48  of the impeller  46  of FIGS. 2,  2 A,  3  and  3 A could be replaced by radially extending vanes on the inner surface  43  of the fluid-tight compartment  42 . 
     An especially preferred impeller  46  for a fluid brake  40  of this invention is shown in FIGS. 12-16. The impeller comprises a plurality of vanes  48 B that protrude radially from, and are hingedly connected to, the hub  47  of the impeller  46 . Preferably, each vane  48 B is connected to the impeller hub  47  by means of a longitudinally-extending rounded bead  80  on the bottom of the vane which is slidingly inserted into a mating longitudinally-extending, rounded groove  82  on the circumference of the impeller hub  47 . Each vane  48 B is relatively rigid and preferably has a curvilinear cross-section that is concave towards its second surface  49 B. It is particularly preferred that the impeller  46  and its vanes  48 B be longitudinally elongate, particularly when a less viscous liquid is to be used in the fluid brake  40 . 
     The vanes  48 B can move radially outwardly, in a counter-clockwise direction in FIGS. 14 and 16, between an unextended position as shown in FIGS. 13-14 and an extended position as shown in FIGS. 15-16. The vanes  48 B can move in this way when pressure is exerted against their second surfaces  49 B by counter-clockwise rotation in FIGS. 14 and 16 of the viscous liquid in the fluid-tight compartment  42  of the fluid brake, in response to counter-clockwise rotation of the roller  12  when raising the shade  12 . The vanes  48 B can also move radially inwardly, in a clockwise direction in FIGS. 14 and 16, between an extended position as shown in FIGS. 15-16 and an unextended position as shown in FIGS. 13-14. The vanes can move in this manner when pressure is exerted against their first surfaces  49 A by clockwise rotation in FIGS. 14 and 16 of the viscous liquid in the fluid-tight compartment  42  (not shown in FIGS. 12-16) of the fluid brake, in response to clockwise rotation of the roller  12  when lowering the shade  16 . 
     Preferably, the hub  47  of the impeller  46  of FIGS. 12-16 is provided with a stop member  84  for each vane  48 B. It is preferred that each stop  84  be integrally formed on the impeller hub  47 , adjacent to one of its grooves  82  and adapted to abut against the vane  48 B in the groove when the vane moves to its fully extended position as shown in FIGS. 15 and 16. In this regard, it is especially preferred that the stops  84  limit the travel of the radial ends of the vanes  48 B, particularly to a travel of about 1.5-3 mm, quite particularly about 2 mm. 
     This invention is, of course, not limited to the above-described embodiments which may be modified without departing from the scope of the invention or sacrificing all of its advantages. In this regard, the terms in the foregoing description and the following claims, such as “left”, “right”, “longitudinal”, “bottom”, “top”, “axial”, “radial”, “clockwise”, “counter-clockwise”, “inner”, “outer” and “end”, have been used only as relative terms to describe the relationships of the various elements of the winding mechanism of the invention for architectural coverings.