EP0782833B1 - Drawing device for a curtain - Google Patents

Description

The invention relates to a so-called curtain pull, that is to say a drive arrangement for an electrically operated curtain, according to the preamble of claim 1, as is known from US-A-4 683 935 is known.

Such electric curtain trains are used in particular in hotels used to a greater extent to make the guests more comfortable to use to offer, which has been shown to be often relative heavy curtains of motorized curtains in comparison for manual operation when opening and closing considerably be spared. However, you can also find them in public and semi-public buildings and especially with larger windows also used in private households.

A disadvantage of the known electric curtain pulls is that In the event of a power failure, the curtain does not move or only moves extremely difficult to open and close by hand over the Curtain (or an operating rod connected to the towing vehicle) exerted a tensile force on the towing carriage in the direction of the running rail is because this is firmly connected to a run of the drive belt and, accordingly, the resistors for moving the towing vehicle of the drive (including its gearbox) should be what due to the existing translation ratios is generally not possible. Since the train car at a drive that has come to a standstill due to a power failure is blocked, attempts are made to get one to open such a curtain by hand, therefore often to tear of the curtain or other damage. That being said it is also highly desirable to have one with an electric curtain equipped curtain in case of power failure by hand to be able to open because then the lighting will also fail, so it is particularly in the unfamiliar environment panic in a hotel room. In particular in the event of a fire or other dangerous conditions it may be necessary to keep people as free as possible to be able to save from outside through windows. But also under less critical circumstances, it is highly desirable to get one to be able to open such a curtain by hand in the event of a power failure, because i.a. not only in daylight with the curtain open so much light falls into the room in question that one Orientation of the person in the room in question is possible.

Furthermore, it can also be quite desirable to get one curtain that can be driven by means of an electric curtain pull to be able to close by hand in the event of a power failure, namely for example, when you have to rest during the day wants to issue.

In the curtain pull known from US-A-4 683 935, the drive belt is designed as a so-called ball chain, the coupling bolt, which is arranged and guided vertically in the towing vehicle, engages positively between two balls of the ball chain in the coupled state with its free end section facing away from the spring acting on it , and the slipping clutch created in this way must (and only) be uncoupled if a force (in the longitudinal direction of the ball chain) acts between the towing vehicle and the ball chain that is greater than a certain (lower) limit value. If no pulling force is exerted on the ball chain, or only a pulling force that is less than this limit value, the curtain pull is always in the coupled state.

The present invention has for its object a curtain to improve the genus described at the beginning that the curtain in question is in the event of a power failure can also be effortlessly opened and closed by hand, if the towing vehicle is uncoupled from the drive belt for so long by a force exerted on it in the direction of the running rail, which can be generated manually via the curtain (and thus can be moved freely in the running rail like the other running carriages) is until the drive belt is to be driven by the electric motor again, whereby it should also be possible to close the curtain again by motor press when the power failure is over without it any installation measures are required.

The solution to this problem is inventively by the kummorichundem feature of claim 1 solved. The necessary for this Winkelund Spring selection is empirically possible without further ado.

Such a mode of operation, in which the coupling bolt at normal motor drive coupled into the locking opening remains (and not via the decoupling ramp from the locking opening slides out) while moving towards the curtain at one the track on the train hand force exerted by the The locking opening is uncoupled (and does not remain in the locking opening), is surprisingly in relatively wide ranges of Ramp helix angles and spring stiffness possible. This is based on the knowledge that the motor drive of the Towing vehicle on the drive belt required by the clutch The force to be transmitted is relatively small because of the force on the carriage effective resistance forces are very small, if the carriages are equipped with rollers, while the at stationary drive on the drive belt and thus on the second coupling part effective resistances already because of the drive belt related gear are relatively large, so that the second coupling part having the latching opening is practical is blocked or locked when the drive is at a standstill a force is exerted on the towing vehicle by hand.

The ramp angle (s) to be selected depends, among other things. from the friction conditions between coupling pin and the one with it in Engaging side wall of the locking opening, since the at Applying manual force to the towing vehicle and thus to the coupling bolt generated frictional force between the coupling pin and Side wall of the locking opening must be overcome to the coupling bolt to allow sliding out of the locking opening. This would obviously not be possible if both the peripheral surface of the end section of the coupling bolt which engages in the latching opening as well as the side wall of the locking opening in parallel run to the longitudinal axis of the coupling pin, their angle to Longitudinal axis of the coupling pin is zero, and is not possible if the angle is only a few degrees. On the other hand But this ramp angle must not be too large either, because then there is a risk that the coupling pin even then from the Detent opening slides when the drive from the electric motor over the Drive belt takes place because then in the direction of the running rail directional driving force to be transmitted from the clutch is greater can be than that required to disengage the clutch Force. However, it has been shown that the ramp angle is not can be empirically determined individually for each application must, but that under normal conditions a ramp angle between 30 and 60 ° is suitable to ensure the desired result, namely that the coupling pin in normal engine operation remains in the latching opening while it is at a standstill Drive slides out of the locking opening when the towing vehicle passes over the Manual force applied to the curtain in the longitudinal direction of the running rail becomes.

Furthermore, it is preferably provided that the coupling pin in supported its uncoupled state with a stop on the towing vehicle which is its axial movement generated by the spring limited so that the free end of the coupling pin in the uncoupled Condition is arranged at a distance from the drive belt, that is cannot come into contact with it so the curtain after the uncoupling is free to move.

To automatically re-engage after a power failure to allow when the drive belt from the electric motor to drive again and thereby relative to the drive belt uncoupled train carriage is to be moved is preferably provided that the attached to the inside of the drive belt, the Second coupling part having a detent opening on the coupling bolt facing inside with at least one guide ramp is provided for guiding the coupling bolt, which is in Longitudinal direction of the running rail from the edge of the locking opening up to an end of the second coupling part, the height this guide ramp from the locking opening to the end of the second Coupling part decreases and there is so high that the free end portion of the coupling pin on the guide ramp runs up when the two coupling parts relative to each other be moved. To allow the coupling pin thereby from one or the other side of the locking opening can be engaged again, is the second coupling part preferably with two guide ramps running counter to the latching opening Mistake.

The drive belt is preferably included in a manner known per se Provide through openings with the same mutual distance are provided so that trained in the manner of sprockets Deflection disks with their teeth in these through openings can grip, the second coupling part, which is preferred is designed as a tab on the drive belt facing it Is provided on the outside with form-fitting in the through openings of the drive belt grip around the second Connect the coupling part to the drive belt. Such an arrangement can expediently be used at the same time around the mutually facing end sections of the drive belt to connect, to make the drive belt endless, if the second coupling part is substantially centered on the connection point the drive belt is arranged so that a separate Connection becomes unnecessary.

Further preferred configurations of the present connection are described in the subclaims.

Fig. 1:

eine vereinfachte perspektivische Darstellung eines erfindungsgemäßen Elektro-Vorhangzuges, die insbesondere die zwischen dem Zugwagen und dem Antriebsband vorgesehene Kupplung zeigt, wobei diverse übrige Teile weggelassen bzw. gebrochen dargestellt sind, um die im entkuppelten Zustand dargestellte Kupplung verdeutlichen zu können;

Fig. la:

eine Darstellung gemäß Fig. 1, bei welcher ein Abschnitt des Behangs dargestellt ist, und außerdem Befestigungsmittel, mit denen die Laufschiene zu befestigen ist;

Fig. 2:

eine Darstellung gemäß Fig. 1 in verkleinertem Maßstab, welche die Kupplung während des Einkuppelvorgangs zeigt;

Fig. 3:

eine Darstellung gemäß Fig. 2, welche die Kupplung in eingekuppeltem Zustand zeigt;

Fig. 4:

eine schematisierte Schnittdarstellung durch den Zugwagen des Vorhangzuges gemäß den Figuren 1 - 3;

Fig. 5:

einen Schnitt durch die Darstellung gemäß Fig. 4 in Richtung der Schnittlinie V-V in Fig. 4 gese

Fig. 6:

einen Schnitt durch die Darstellung gemäß Fig. 4 in Richtung der Schnittlinie VI-VI in Fig. 4 gesehen;

Fig. 7:

einen Schnitt durch die Darstellung gemäß Fig. 4 in Richtung der Schnittlinie VII-VII in Fig. 4 gesehen;

Fig. 8:

einen Schnitt durch die Darstellung gemäß Fig. 4 in Richtung der Schnittlinie VIII-VIII in Fig. 4 gesehen;

Fig. 9:

einen gegenüber den Figuren 1 - 8 vergrößerten, noch weiter vereinfachten Längsschnitt durch die Laufschiene und das Antriebsband im Bereich der Kupplung in deren ausgekuppelten Zustand;

Fig.10:

eine Darstellung gemäß Fig. 9 in eingekuppelten Zustand; und

Fig. 11:

eine schematische Teildarstellung der Kupplung.

The invention is explained below using an exemplary embodiment with reference to a drawing. It shows:

Fig. 1:

a simplified perspective view of an electric curtain train according to the invention, which shows in particular the coupling provided between the towing vehicle and the drive belt, various other parts being omitted or broken in order to illustrate the coupling shown in the uncoupled state;

Fig la:

a representation of Figure 1, in which a portion of the curtain is shown, and also fasteners with which the rail is to be fastened.

Fig. 2:

a representation of Figure 1 on a smaller scale, showing the clutch during the coupling process.

Fig. 3:

a representation of Figure 2, showing the clutch in the engaged state.

Fig. 4:

a schematic sectional view through the towing vehicle of the curtain train according to Figures 1-3;

Fig. 5:

4 in the direction of the section line VV in FIG

Fig. 6:

a section through the representation of Figure 4 seen in the direction of section line VI-VI in Fig. 4.

Fig. 7:

seen a section through the representation of Figure 4 in the direction of section line VII-VII in Fig. 4.

Fig. 8:

seen a section through the representation of Figure 4 in the direction of section line VIII-VIII in Fig. 4.

Fig. 9:

an enlarged compared to Figures 1 - 8, further simplified longitudinal section through the running rail and the drive belt in the region of the clutch in its disengaged state;

Fig. 10:

a representation of FIG 9 in the engaged state. and

Fig. 11:

a schematic partial representation of the clutch.

Fig. 1 shows the explanation of the present invention essential parts of a curtain train designated as a whole, with various parts omitted or shown broken away are to better illustrate the present invention to be able to. The curtain pull 1 is an essential part a curtain, the curtain 2 also omitted in Fig. 1 is, but indicated in the figures la, 2 and 3 in the detail is. Fig. La also shows fasteners 26, with which the curtain pull 1 e.g. on a lintel or to fix the ceiling of a room.

The curtain 2 has a plurality at its upper edge 2 ' attached by carriage 3, with locking hooks 4, each are to be snapped into an eyelet 5 (see FIG. 6). The carriages 3 are provided with rollers 6, which are on a horizontal, stationary running rail 7 are supported (see FIG. 6). she are freely movable along the running rail 7.

The one arranged in the area of a vertical curtain edge 8 first carriage is designed as a train carriage 3 'and differentiates differs from the other carriages 3 essentially by that it is powered by the drive described below is, while the remaining carriage 3 with this directly but only connected via the curtain 2 are.

The drive consists of a dash-dotted in Fig. 1 Lines indicated electric motor 9 with a gear 10 connected is. The gear 10 acts on one in FIG. 1 on the right End of the running rail 7 arranged in the gear housing, as Sprocket-designed drive disc with a vertical axis of rotation, whose teeth in recesses 11 of a self-contained, grab flexible drive belt 12, which at the other end of the Track 7 from a sprocket also formed Deflection pulley with a vertical axis of rotation is deflected.

Since the construction of the curtain 1 described so far the expert is known, is based on a graphic representation of the drive or deflection disks, the gearbox etc. have been dispensed with. In this regard, it should only be noted that the mode of operation in normal operating condition is such that the reversible electric motor 9 when actuated by a switch, not shown is driven in its one direction of rotation and the drive belt 12 drives via the transmission and the drive pulley, so that its two dreams 12 'and 12 "are in opposite directions Move direction in the running rail 7, the train carriage 3 'with the strand 12 'of the drive belt 12 is connected (see FIG. 3), so that the curtain 2, for example, from its open position in its closed position is moved by first with the Drive belt 12 in related towing cars 3 'is moved and takes the carriage 3 following it with him when the Curtain 2 is stretched between this and the towing vehicle 3 'and the like. The curtain 2 is closed by actuating the electric motor 9 in the opposite direction of rotation, again the sole with the drive belt 12 connected towing vehicle 3 'driven until he drives against the carriage 3 next to him and take it with you and so on expressly pointed out that the neighboring 3 ' further carriages 3 are omitted in the drawing.

In contrast to known generic curtain trains, in which the towing vehicle 3 'is suspended in recesses 11 of the drive belt 12 or otherwise permanently fixed to the drive belt 12 is connected, in the present curtain 1 between the train carriage 3 'and the drive belt 12 (more precisely its Run 12 ') one of two coupling parts or halves 13 and 14 existing clutch provided in the normal operating condition is engaged (see Figures 3, 8, 10) and is designed so that it remains engaged when the drive belt 12 from the electric motor 9 is driven, but can be disengaged when on the Train carriage 3 'over the curtain 2 in the direction of the running rail 7 from Hand a force is exerted on the train carriage 3 ', this Coupling 13, 14 shown in Fig. 1 in the uncoupled state is.

For this purpose, the first coupling part arranged on the towing vehicle 3 'has 13 one in the direction of the run 12 'of the drive belt 12 laterally on the towing car 3 'projecting coupling pin 15, the one in the engaged, normal operating state with its free End portion 15 'in a locking opening 16 of the inside of the Drive belt 12 attached second coupling part 14 engages, namely, the coupling pin 15 becomes concentric by means of it surrounding compression spring 17 pressed into the locking opening 16. The coupling pin 15 is against in the direction of its longitudinal axis 19 the restoring force of the spring 17 is movably mounted on the towing vehicle 3 '.

As can be seen in particular from FIGS. 9-11, runs the peripheral surface 18 of the free end portion 15 'of the coupling pin 15 at an acute angle α to the longitudinal axis 19 of the Coupling bolt 15, which in the illustrated embodiment Is 40 °. The side wall also extends at this angle α 16 'of the locking opening to the longitudinal axis 19. However, it could also at a different angle and possibly even parallel to the longitudinal axis 19, as this with in Fig. 11 dash-dotted lines is indicated.

As can be seen from FIGS. 1 and 9, the coupling pin lies 15 in its uncoupled state with a stop 20 a side wall of the towing vehicle 3 ', the stop 20 the axial movement of the coupling pin while the Spring 17 limited so that the free end 15 'of the coupling pin 15 in the uncoupled state at a distance from the run 12 'of the drive belt 12 is arranged, so no connection between the train car 3 'and the drive belt 12 there. The stop 20 is as Flange formed, on the opposite side of the stop Side the pre-tensioned as a coil spring Spring 17 is supported, which with its other end on the opposite side wall of the train carriage 3 'is supported.

That attached to the inside of the run 12 'of the drive belt 12 second coupling part 14 is a tab-shaped plastic molded part trained and has at its the coupling pin 15 facing inside two opposite to the locking opening 16 extending guide ramps 21 and 21 'for guiding the coupling bolt 15, which run in the longitudinal direction of the running rail 7 and each from the edge of the locking opening 16 to the end of extend second coupling part 14, the height of the guide ramps 21, 21 'of locking opening 16 to the respective end of the second coupling part 14 decreases and formed there so high is that the free end portion 15 'of the coupling pin 15th runs onto the relevant guide ramp 21 or 21 'if the two coupling halves 13 and 14 are relatively moved towards each other as explained below.

The second coupling part 14 is on the drive belt 12 facing the outside with lugs 22, which form-fitting in through openings 11 of the drive belt 12 to grab. Since the second coupling part 14 is centered on the two arranged end portions of the drive belt 12 facing each other is, this can be done by means of the second coupling part 14 can be made endless without taking further measures requirement.

The diameter D of the coupling pin is 3 mm. He attacks only slightly into the locking opening when engaged 16 a.

For a better understanding of what is shown in the drawing Embodiment should be noted that the Train carriages 3 'of two carriages 3 each similar Blocks exist, which are fixed to one another via a bracket 23 are connected. This measure, in particular 4 shows, is provided to the acting as an overflow bracket 23 in a simple and stable To be able to attach, which bends away from the running rail is to create a vertical edge section when closing the curtain to be able to run over a second curtain.

The sectional view seen in the direction of the section line V-V 5 shows the profile of the running rail 7 and recognize that the strands 12 'and 12' 'of the drive belt 12 on the side walls the track 7 run.

The sectional view of FIG. 6 shows that the carriage 3rd between the two runs 12 ', 12' 'of the drive belt 12 in the Track 7 are guided, the carriage recognizable in Fig. 6 3 is omitted in FIG. 4, however.

7 shows a sectional view in the area of the train carriage 3, and Fig. 8 is a sectional view in Area of the first coupling part 13 or the coupling bolt 15.

In the normal operating state (see Figures 3, 8, 10) the free one is End section 15 'of the coupling bolt 15 into the latch opening 16 of the second coupling part 14 locked, so that the two coupling parts 13,14 are engaged. The electric motor 9 actuated, it drives the curtain 2 via the gear 10, the Drive pulley, the run 12 'of the drive belt 12, the clutch 13, 14 and the train carriage 3 'either in the opening or in the closing direction on. There is no decoupling because the coupling bolt 15 axially into the latching opening by means of a force F (see FIG. 11) 16 is pressed and the driving force A thereby generated, the between the side wall 16 'of the locking opening 16 and Circumferential surface 18 of the conical free end portion 15 'of the coupling pin 15 is transmitted, is not sufficient to the coupling pin 15 slide out of the locking opening 16. This is based on the fact that the curtain 2 or the carriage 3 generated resistance forces to be overcome during their movement due to the rolling friction between the carriage 3 and the running rail 7 are extremely low.

But if there is a power failure, the electric motor 9 can not be operated, and is on the train car 3 'and so that the coupling pin 15 against the then practically blocked second coupling part 14 in the direction of the running rail 7 a manual force H exercised by - in one direction or another - in Direction of the track 7 is pulled on the curtain, so it comes in this case for pressing the peripheral surface 18 of the free end section 15 'of the coupling pin 15 to the side wall 16' the locking opening 16, the coupling pin 15 in the direction of Arrow 24 (see FIG. 11) slides out of the latching opening 16, if that caused by the hand force H in this direction Force component is greater than that of the mutual pressure generated effective against the direction of arrow 24 friction force. Since this is not only due to the coefficient of friction and thus from the materials and the surface quality of each other adjacent surfaces 18, 16 'of the coupling bolt 15 and the second coupling part 14 depends, but also proportional to the normal force acting between these two surfaces 18, 16 ' and this is determined by the spring force F of the spring 17 is visible when the curtain is installed the possibility of the friction between coupling bolts 15 and detent opening 16 by choosing a weaker or stronger To influence spring 17 or change the spring preload. However, it has been shown that this occurs under normal conditions is not necessary, since that of an easily generated Hand force H achievable decoupling force at ramp angles α by 45 ° is sufficient to overcome the friction, and to still cause the clutch 13, 14 to remain engaged, when the drive from the electric motor 9 via the drive belt 12 he follows. As already mentioned, this is based, among other things, on thereon, that one by hand over the curtain 2 on the train carriage 3 'in its longitudinal direction applicable force advantageously significantly is greater than that generated by or on the carriages effective resistance forces (even in the final phase the opening or closing process when all carriages are moving ) and that during normal engine operation of the force to be transmitted to the clutch 13, 14 these resistance forces yes does not exceed, so that - expediently by appropriate Attempts - an empirical way of proportioning can be easily found, in which the to Uncouple the required manual force between the maximum that can be applied Hand force and the maximum required with such curtains Driving force is so that the curtain 1 or his Coupling 13,14 for a variety of applications or even is suitable for all possible applications.

As soon as the coupling bolt 15 slid out of the locking opening 16 its free end reaches the guide ramp 21 (see Fig. 2) or 21 'and slides on pulling the curtain 2 under the action of the spring 17 along this until it is free from the second coupling part 14. This position is in the Figures 1 and 9 shown. The curtain can then effortlessly move from Hand completely opened or closed, since now the Zugwagen 3 'has become a "normal" carriage 3, the no longer has a connection to the drive belt 12.

If the electric motor 9 is switched on after the power failure has ended, that the second coupling part fastened to the drive belt 12 14 moved towards the train carriage 3 ', so the clutch 13,14 automatically engaged again. That’s what happens second coupling part 14 in the direction of arrow 25 (see FIG. 9) to the train carriage 3 ', the guide ramp 21 runs on the free end portion 15 'of the coupling pin 15 and presses progressively countering this in the direction of its longitudinal axis 19 the spring 17 in the train carriage 3 'until the locking opening 16 is reached and the coupling pin 15 engages in the locking opening 16. The same happens automatically when the towing vehicle 3 'on the other side of the second coupling part 14 and this via the drive belt 12 in the opposite Direction is driven.

Because of the configuration according to the invention, it is now possible to hang the curtain with an electric curtain pull Curtains effortlessly and without a power failure Risk of damage to open or close, whereby the Curtain after the end of the power outage in turn in the intended way to be operated via its electric drive can, since the clutch is still uncoupled automatically engaged again and so long during further operation remains engaged until a new power failure a force is exerted on the towing vehicle by hand, which leads to uncoupling the clutch 13,14 leads.

Claims (11)

1. A means (1) for drawing an electrically driven curtain, the hanging part (2) of which is fastened at its upper edge (2') to carriages (3, 3') which abut a horizontal stationary rail (7) and are freely movable along the rail (7), wherein a carriage (3') disposed in the region of a vertical edge (8) of the hanging operates as a tractor (3') driven by a run (12') of an endless flexible driving belt (12) guided around two pulleys or the like having a vertical axis of rotation, disposed at respective ends of the rail (7) and engaging the driving belt (12), one pulley being drivable by an electric motor (9) via a gear mechanism (10), wherein the carriages (3, 3') are guided between the two runs (12', 12") of the driving belt (12) in the rail (7), wherein the carriage (3') is connected to the driving belt (12) via a coupling (13, 14) which is in engagement in normal operation and can be disengaged by a manual force on the hanging exerted on the carriage (3') in the direction of the rail (7), the disengaged coupling automatically re-engaging when the driving belt (12) is driven by the electric motor (9), wherein the first coupling part (13) disposed on the tractor carriage (3') has a coupling pin (15) which is pressed by a spring (17) into a catch opening (16) and is mounted on the tractor carriage (3') so as to be movable in the direction of its longitudinal axis (19) against the restoring force of the spring (17) and wherein the coupling pin (15) remains in the catch opening (16) when the driving belt (12) is driven by the electric motor (9), characterised in that in the normal operating state an end portion (15') of the coupling pin (15) projecting freely sideways over the tractor carriage (3') engages in a catch opening (16) in the second coupling part (14) fastened to the inside of the driving belt (12), and in that the peripheral surface (18) of the end portion (15') of the coupling pin (15) engaging in the catch opening (16) and/or the side wall (16') of the catch opening (16) extends at an acute angle (α) to the longitudinal axis (19) of the coupling pin (15) and forms an uncoupling slope, wherein the angle or angles (α) and the elasticity of the spring (17) are so chosen that the coupling pin (15) slides out of the catch opening (16) against the restoring force of the spring (17) when the tractor carriage (3') is moved by hand in the longitudinal direction of the rail (7).
2. A curtain-drawing means according to claim 1, characterised in that the angle (α) between the peripheral surface (18) of the free end portion (15') of the coupling pin (15) and its longitudinal axis (19) is about 30 - 60°.
3. A curtain-drawing means according to claim 1 or 2, characterised in that the coupling pin (15) when disengaged abuts a stop (20) on the tractor carriage (3') which limits its axial motion so that the free end of the coupling pin (15) is disposed at a distance from the driving belt (12).
4. A curtain-drawing means according to one or more of claims 1 to 3, characterised in that the second coupling part (14) fastened to the inside of the driving belt (12), on its inside facing the coupling pin (15), is provided with at least one guide slope (21, 21') for guiding the coupling pin (15), the slope extending in the longitudinal direction of the rail (7) from the edge of the catch opening (16) to one end of the second coupling part (14), wherein the height of the guide slope (21, 21') decreases from the catch opening (16) to the end of the second coupling part (14) where the height is such that the free end portion (15') of the coupling pin (15) runs on to the guide slope (21 or 21') when the two coupling parts (13, 14) are moved relative to one another and towards one another.
5. A curtain-drawing means according to claim 4, characterised in that the second coupling part (14) has two guide slopes (21, 21') extending in opposite directions towards the catch opening (16).
6. A curtain-drawing means according to claim 4 or 5, characterised in that the second coupling part (14) is in the form of a plate.
7. A curtain-drawing means according to one or more of the preceding claims comprising a driving belt (12) formed with passage openings (11) for engagement of guide pulleys after the style of chain wheels, characterised in that the second coupling part (14), at its outer side facing the driving belt (12), has extensions (22) which positively engage in passage openings (11) in the driving belt (12).
8. A curtain-drawing means according to claim 7, characterised in that the second coupling part (14) is disposed substantially centrally relative to the place where the driving belt (12) is connected, and joins the facing end portions of the driving belt (12).
9. A curtain-drawing means according to claim 3, characterised in that the stop (20) is in the form of a flange and the spring (17), in the form of a prestressed coil spring, abuts the side of the flange opposite the stop side, the spring being disposed concentrically with the coupling pin (15) and its other end abutting the tractor carriage (3').
10. A curtain-drawing means according to one or more of the preceding claims, characterised in that the coupling pin (15) has a diameter of about 2 mm.
11. A curtain-drawing means according to claim 10, characterised in that the coupling pin (15) in the coupled state extends about 1 - 2 mm into the catch opening (16).

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