NL2014397A

NL2014397A - Safety gearbox for a pleated blind system.

Info

Publication number: NL2014397A
Application number: NL2014397A
Authority: NL
Inventors: Gloeckner Ulrich
Original assignee: Blocker Zweigniederlassung Der Hunter Douglas Holding Gmbh & Co Kg
Priority date: 2014-03-04
Filing date: 2015-03-04
Publication date: 2016-01-20
Also published as: PL226951B1; PL411470A1; NL2014397B1; DE102014003134A1; DE102014003134B4

Description

Safety gearbox for a pleated blind system

The present invention relates to a safety gearbox for operating e.g. opening or closing a pleated blind system.

Prior art gearboxes to open and/or close pleated blind systems comprise a drive wheel, for instance a drive sprocket, which is embraced by an endless pulling means, such as a chain. The problem here is that a pulling means embracing the drive wheel and hanging down in the form of a loop can pose a risk to infants. For example an infant can get entangled in and even strangulated by the pulling means. Trip forces for safety devices on pleated blind systems are standardized particularly in European Standard EN13120.

In order to exclude such risks, it is for example known from EP 2 574 717 A1 to use a safety gearbox having a drive wheel, which with a predetermined pulling force of the drive means separates from a housing and together with a housing element falls to the floor.

This solution it is disadvantageous in that the parts falling to the floor have corners and edges, which can injure humans or damage the floor. Also again there is a risk to infants, for instance from smaller parts. This is relevant particularly if the chain is easily accessible for children and can entice these to wilfully separate the drive sprocket and the housing element.

The object of the invention is to create a safety gearbox for a pleated blind system with which the aforesaid problems do not arise.

This object is achieved by a safety gearbox for a pleated blind system with drive wheel which is embraced by an endless pulling means hooked on hanging down in two strands, with a bearing for the drive wheel, which as a first degree of freedom comprises an axis of rotation, about which the drive wheel can be rotated by tug on the pulling means, and which, as further degree of freedom, permits a shift of the drive wheel from a first position - in which the drive wheel is embraced by the pulling means, is in driving connection with the pleated blind system and the pleated blind system can be operated by tug on the pulling means - to a second position held by the bearing, as reaction to a predetermined pulling force of the pulling means being exceeded, with a safety device firmly disposed on the safety gearbox for preventing the pulling means hooked on the drive wheel against self-acting separation from the drive wheel currently in the first position, wherein the safety device permits a separation of the pulling means from the drive wheel currently in the second position, as reaction to a pulling force, which does not exceed the predetermined pulling force. As pulling force, which results in the pulling means being separated from the drive wheel currently in the second position, the dead weight of the chain can be sufficient, or a stronger pulling force may be necessary but which is no greater than the predetermined pulling force, which causes the drive wheel to shift to the second position. Preferably the safety gearbox and the predetermined pulling force meet the requirements of EN 13120.

The further degree of freedom can be formed by straight-line mobility of the drive wheel, for example by a shift of the drive wheel along the axis of rotation or together with or transverse to the axis of rotation.

The further degree of freedom can be formed by rotatability of the axis of rotation of the drive wheel about a tilting axis, whereby the tilting axis can intersect the axis of rotation perpendicularly. By rotation about the tilting axis the drive wheel moves from the first position to the second position.

It may be contemplated that the safety device is formed by a housing element, which partly encloses the drive wheel, wherein an inner surface, turned towards the drive wheel, of the housing element has a distance to the drive wheel, which in the first position of the drive wheel is less than a cross-sectional dimension of the pulling means.

It may also be contemplated that the bearing is formed by a carrying element, on which a drive shaft supporting the drive wheel is mounted about the axis of rotation and which is rotatably held about the tilting axis by a housing between a first position and a second position.

The bearings can be configured as plain bearings, wherein the carrying element is mounted so as to slide in cylindrical slots of the housing.

In a refinement of the invention it may be contemplated that the carrying element is provided with at least one first snap-in element and the housing with at least one second snap-in element, wherein the carrying element or housing is provided with two first or second snap-in elements, which, seen in the circumferential direction, are arranged offset about the tilting axis at a predetermined angle, whereby in the first position of the carrying element, in which the drive wheel is currently in its first position, a first snap-in element is caught with a second snap-in element, and in the second position of the carrying element, in which the drive wheel is currently in its second position, another first snap-in element is caught with the second snap-in element or the first snap-in element is caught with another second snap-in element.

Alternatively a stop which limits the tilting movement can be provided for the snap-in elements working in the second position.

It may be contemplated that the at least one first snap-in element is formed by at least one sprung locking cam and the at least one second snap-in element is formed by at least one locking recess on the housing.

Preferably it is contemplated that a first bevel gear, which engages with a second bevel gear mounted on the carrying element about the tilting axis is non-rotatably held on the drive shaft, wherein the second bevel gear is in drive connection with the pleated blind system.

Alternatively a flexible shaft can be provided to transmit force via bevel gears.

Preferably the invention proposes that the housing has a first housing segment and a second housing segment, wherein the drive wheel is mounted in the housing segments and the second housing segment comprises at least one spring element, which has a spring arm, extending outwards from an outer side of the second housing segment, whereby the pleated blind system comprises an upper rail in the form of a profile, having at least one longitudinal slot, into which the spring arm engages and which secures the housing and the profile to one another.

The inventive safety gearbox comprises a drive wheel, a housing, in which the drive wheel is rotatably mounted about an axis of rotation, as the result of which a first degree of freedom is formed, and a pulling means, which embraces the drive wheel. The drive wheel possesses at least a further degree of freedom. For example the drive wheel can be tiltably mounted about a further axis and/or be adjustable along a further axis or orbit. For the sake of simplicity below the description drive sprocket includes any design of drive wheel and the description chain includes any strand-type pulling means such as cord, chain, ball chain, belt, loop and the like.

The drive sprocket by exploiting at least a further degree of freedom can be changed over from a first position to a second position. The changeover is tripped as the result of a pulling force transmitted from the chain to the drive sprocket exceeding a predetermined value. In other words the pulling force transmitted from the chain to the drive sprocket can twist or push the drive sprocket relative to the housing, in which the drive sprocket is mounted, against retention- or friction forces acting between a bearing of the drive sprocket and the housing.

In this case the second position can be configured so that the chain separates from the drive sprocket by the drive sprocket changing over from the first position to the second position induced by the pulling force of the drive sprocket and can fall to the floor. For example the second position can be such that the chain slips from the drive sprocket, for example by the axis of rotation of the drive sprocket in the first position being horizontally aligned and in the second position being inclined to this at a predetermined angle or by being aligned so as to tilt about a horizontal axis. This horizontal axis is known below as tilting axis. The tilting axis and the drive axis can lie in a plane and run perpendicularly to each other.

Alternatively the changeover of the drive sprocket to the second position can be configured so that the drive sprocket is led past a housing element, which separates the chain from the chain wheel, for example by a distance between the chain wheel and the housing element being less than a cross-sectional dimension of the chain, so that the housing element strips the chain off the drive sprocket, whenever the drive sprocket is led past the housing element. In other words the housing element can be configured so that the drive sprocket can be moved past it without colliding, while in the second position a part of the chain collides with the housing element and, as consequence of the collision, slips or slides off the drive sprocket.

If the drive sprocket has recesses or hollows and the chain has balls, the balls of the chain engaging into the recesses or hollows in operation, the predetermined tilting angle between the first and the second position can be selected so that the recesses or hollows are aligned in the second position, such that the chain undergoes a horizontal movement or additionally a vertical movement directed downwards while sliding over an edge of the drive sprocket. The drive sprocket can have slots distributed over its periphery for ball elements of a ball chain, whereby the slots can have a grooved base which has a curvilinear cross-section and can be parallel to the axis of rotation.

This offers the advantage that, whenever a pulling force tugging on the chain exceeds a predetermined value, only the chain as such separates and falls to the floor, as the result of which injuries or damage by parts falling on the floor can be avoided, since the weight of the chain is only light and whenever configured as ball chain has no corners and edges.

The safety gearbox can have a housing element as safety device, which at least partly encloses the drive sprocket. The surface, turned towards the drive sprocket, or at least a part of the surface, turned towards the drive sprocket, of the housing element can be arranged and configured so that the chain cannot separate from the drive sprocket, whenever the drive sprocket is currently in the first position. For example a distance between at least a part of the surface, turned towards the drive sprocket, of the housing element can have a distance to the drive sprocket, which is less than a cross-sectional dimension of the chain, or less than a maximum chain cross-section. Also during the changeover of the chain wheel from the first position to the second position, the distance between at least a part of the surface, turned towards the drive sprocket, of the housing element can be less than the cross-sectional dimension or the maximum chain cross-section.

The housing element at least partly enclosing the drive sprocket can comprise an area lying opposite a front of the drive sprocket pointing away from the housing which, seen towards the axis of rotation, has the shape of a semi-circle, circular section or annular ring, and encloses at least a circular-section or part annular area of the drive sprocket, which is turned away from the pulling direction of the chain, whenever the drive sprocket is in the first position. The circular side of the semi-circle, circular section or annular ring can be turned towards the side of the drive sprocket, which in operation is turned away from the pulling direction of the chain.

The surface, turned towards the drive sprocket, of the housing element at least partly enclosing the drive sprocket can have an inner contour, which on the one hand during a changeover from the first position to the second position allows the drive sprocket to rotate about a tilting axis, without colliding with the housing element enclosing the drive sprocket. For example the housing element enclosing the drive sprocket can have a concave surface, seen towards the drive sprocket, lying opposite the drive sprocket. The distance between the concave surface and the chain wheel can be dimensioned just as the distance described above, so that the chain in the second position can slide off. On the other hand the distance in the first position is so small that the chain cannot pass between drive wheel and surface and slide off from the drive wheel.

The inner contour can be formed so that the chain cannot yet separate from the drive sprocket while changing over from the first position to the second position. For example the surface, turned towards the drive sprocket, of the housing element enclosing the drive sprocket can have an inner contour, which is curvilinear in at least a vertical sectional plane, running parallel to the axis of rotation of the drive sprocket, with a tilting axis point of the drive sprocket as centre. The run of the curvilinear contour can extend over an angle, which is less than the angle of rotation about the tilting axis of the drive sprocket between the first and the second position. The surface, turned towards the drive sprocket, of the housing element enclosing the drive sprocket can have a convex shape.

As a result it is ensured that when the drive sprocket changes over from the first position to the second position, the chain cannot separate from the drive sprocket and does not jam with the housing element enclosing the drive sprocket. The chain can only separate from the drive sprocket on reaching the second position.

The drive sprocket enclosing the housing element can be configured to be detachable from the housing, so that the drive sprocket can be exposed by removing the housing element enclosing the drive sprocket. For example the housing element enclosing the drive sprocket can be connected to the housing by means of at least one connecting member for instance screws or clamp- or snap-in elements.

In the case of such an embodiment the chain in a particularly simple way can be again looped around the drive sprocket, whenever the drive sprocket is currently in the second position and the chain has separated from the drive sprocket. Furthermore a conversion of the safety gearbox to wand- or crank drive operation is possible by means of an adapter, which will be explained in detail below.

The drive sprocket can be pivotally mounted about the tilting axis and by pivoting about the tilting axis can be changed over from the first position to the second position. The tilting axis can be aligned so that it intersects the axis of rotation of the drive sprocket and with this includes an angle of 90°. The tilting axis can be horizontally aligned in operation, so that during a changeover from the first position to the second position the drive sprocket performs a tilting movement directed downwards. The tilting movement can extend over a predetermined angle, e.g. 10° to 90°, for instance 20°, 30°, 45° or 60°. The drive sprocket at the end of the tilting movement can lock into the second position.

The tilting movement in operation allows the drive sprocket to give way vertically relative to the pulling force, acting on the drive sprocket by means of the chain or the pulling force transmitted to the drive sprocket by means of the chain results in an evasive movement of the drive sprocket about the tilting axis, which diverts a part of the periphery of the drive sprocket from the housing element partly enclosing the drive sprocket and allows the chain to slip and/or slide over the edge of the drive sprocket.

The drive sprocket may sit on a drive shaft, which can be mounted about the axis of rotation on two bearings. The bearings may be attached to a carrying element, which can be cylindrical or substantially annular. The cylindrical and/or substantially annular carrying element can be penetrated transversely to its longitudinal axis by the drive shaft in the radial direction. A first bearing adjacent to the drive sprocket can be provided in a recess of the carrying element, so that the drive shaft penetrates the carrying element at one place. A second bearing remote from the drive sprocket can likewise be provided in a recess of the carrying element, or the second bearing can be arranged on an inner side of the carrying element. The first or the second bearing can be configured to define the position of the drive shaft in the axial direction. The bearings can be roller bearings or plain bearings. The carrying element can be made from metal or plastic, e.g. aluminium or polyamide. The bearings can comprise sliding elements made from metal, plastic, glass or ceramic.

The carrying element may be cylindrical and have a flattened section, or have the shape of a an annular ring with an even peripheral area . The second bearing can be provided on the even peripheral area or in a recess therein.

The carrying element can be pivotally mounted about the tilting axis in or on the housing. For example the carrying element can be mounted so as to slide in a correspondingly shaped bearing recess of the housing. The bearing recess can be shaped to fit the cylindrical and/or substantially circular carrying element, i.e. cylindrically or annularly. The carrying element or its surface and the cylindrical and/or circular bearing recess or its surface can be made from plastic i.e. polyamide.

The carrying element can have at least one locking cam, which cooperates in the first position with a locking recess of the housing. If a locking cam engages into a corresponding locking recess of the housing, the carrying element is detachably locked or fixed in the first position, depending on the configuration of the locking cam.

In a first variant the locking cam can be flexible or resilient and/or biased by a spring.

The spring is arranged in such a way that a spring force acts on the at least one locking cam in a locking direction, so that engagement of the locking cam into a locking recess is only broken whenever a torque produced on the carrying element by the chain exceeds a predetermined value. As long as the pulling force of the chain or the torque about the tilting axis does not exceed a predetermined value, the engagement of the locking cam into the corresponding locking recess is not broken and the carrying element and thus the drive sprocket remain in the first position.

Alternatively the locking cam can be rigidly formed, for instance by means of a pin, which supports at least one locking cam in a locking direction against the carrying element, so that the engagement of the locking cam into the corresponding locking recess is not broken even if there is a high pulling force on the chain. This is expedient when a crank- or an electrical wand drive is used, since no safety trip is needed here.

The carrying element and the housing can have several locking cams and/or locking recesses, which are arranged so that several alignments of the carrying element exist as pivoting positions about the tilting axis, in which locking cams engage into locking recesses.

Thus locking cams of the carrying element can engage in different alignments of the carrying element respectively into locking recesses of the housing and lock or fix the carrying element in different alignments or tilting positions. A first bevel gear can be non-rotatably arranged on the drive shaft. A second bevel gear on an output shaft, which is in engagement with the first bevel gear attached to the drive shaft, can be mounted on the carrying element. The output shaft can be rotated about an axis of rotation, which corresponds to the tilting axis of the carrying element.

As a result it is ensured that the second bevel gear is in engagement with the first bevel gear both in the first and in the second position of the carrying element.

The second bevel gear can be in driving connection with an intermediate gear. The intermediate gear can be connected to an output shaft, which can be turned by rotating the drive sprocket via a tug on the chain. The output shaft can be a control- or an actuation shaft of the pleated blind system, through rotating which the blind can be opened or closed. The intermediate gear can be a planetary gear. The translation of the intermediate gear can range between 1:2 and 1:5 and amount in particular to 1:3. Instead of a planetary carrier of the planetary gear, a rigid connecting member can be provided in the planetary gear, so that a translation of 1: 1 translation results.

The drive shaft can have an adapter, by which the drive sprocket is detachably connected to the drive shaft. The adapter can be formed so as to be connected to a crank or a transportable rod-type electric drive, also described as an electrical wand. The crank, electrical wand or adapter can have a slip clutch, limiting the torque which can be transmitted to the drive shaft by the crank or the electrical wand. The coupling or the electrical wand can have a universal joint, so that if the position of the crank is vertical operation is possible or as electrical wand.

For using a crank or an electrical wand, the carrying element in operation can be currently in a tilting position pivoted about the tilting axis, in which the drive shaft includes a predetermined angle to the horizontal. In other words the axis of rotation of the drive shaft is not horizontally aligned in operation, but bent and/or tilted downwards. This is particularly rendered possible if the carrying element and the housing have the locking cams and corresponding locking recesses described above, which enables the carrying element to be fixed in various tilting positions.

As a result it is ensured that the safety gearbox can be easily converted from chain drive to crank-or electrical wand drive. If a crank or an electrical wand is used, in the case of the locking cams the springs described are replaced by the aforesaid pins, so that the carrying element is fixed in a predetermined bent alignment or tilting position.

Furthermore the housing can have a first housing segment and a second housing segment. The drive sprocket can be mounted in the first housing segment. At least one spring element can be attached to the second housing segment, which extends outwards by an outer surface of the second housing segment. The pleated blind system can comprise a profile, which has at least one recess on an inner side, into which the spring element can engage, in order to secure the housing on the profile.

Preferred embodiments of the present invention are described below by way of example with the aid of the figures wherein : FIG. 1 is a perspective view according to the invention of a pleated blind system equipped with a safety gearbox; FIG. 2 is a view of the safety gearbox of Fig. 1 in an operational condition, FIG. 3 shows the safety gearbox of Fig. 2 in a tripping condition, FIG. 4 is a view according to Fig. 3 with partly removed housing, FIG. 5 is a cutaway view of the safety gearbox in accordance with Fig. 4, FIG. 6 is an exploded illustration similar to Fig. 4, FIG. 7 is an exploded illustration of the safety gearbox with a planetary gear, FIG. 8 is a view similar to Fig. 6 as variant for crank drive, FIG. 9 shows the variant of Fig. 8 in the assembled condition, FIG. 10 is an illustration similar to Fig. 9 with attached crank, FIG. 11 is a rear view of a carrying element and a second bevel gear, FIG. 12 shows the safety gearbox before being installed into a blind rail, FIG. 13 shows the safety gearbox in the condition partly installed into a blind rail, FIG. 14 is an enlarged cutaway view of the safety gearbox in operating position, FIG. 15 is an illustration according to FIG. 14 in a tilted position, FIG. 16 is a lateral view of the safety gearbox in operating position, and FIG. 17 is a lateral view of the safety gearbox in tripping position. FIG. 1 shows pleated blind system 20, which is provided with an upper rail 22, a lower rail 24 and a shade 26 disposed between the rails 22, 24. An inventive safety gearbox 1 is attached to an end of the upper rail 22 and permits the pleated blind system 20 to be adjusted, for example by raising or lowering the lower rail 24, while the upper rail 22 can be firmly attached to an architectural opening such as for instance a window frame. The safety gearbox 1 is operated with an endless ball chain 4 as pulling means. FIGS. 2 to 6 show a schematic view of a preferred embodiment of the inventive safety gearbox 1, which comprises a drive sprocket 2 and a housing 3, in which the drive sprocket 2 is rotatably mounted about an axis of rotation 2a. The ball chain 4 embraces the drive sprocket 2 in a semicircular way. The housing 3 has a housing element 5, which encloses a part of the drive sprocket 2 entirely or partly embraced by the chain 4. The housing element 5 with the housing 3 forms a gap, in which the part of the drive sprocket 2 embraced by the chain 4 is accommodated. A usual pulling direction 4a of the chain 4 runs vertically and is directed transversely to the axis of rotation 2a.

The safety gearbox 1 is connected to the upper rail 22 in the form of a profile, for example an extruded profile. The profile 22 is secured to the housing 3 by means of at least one spring element 13. The profile 22 can be made from metal or plastic, for example aluminium or polyamide. The profile 22 has at least one longitudinal slot 12 on an inner side, into which a spring arm 13a of the at least one spring element 13 engages, whenever the housing 3 holding the spring element 13 is pushed into the profile 22 (FIGS. 12, 13). If the housing 3 is pushed into the profile 22, the spring arm 13a flexibly presses against the longitudinal slot 12 of the profile. If the profile is completely pushed onto the housing 3, the spring arm 13a and particularly its sharp-edged end, due to the resetting force of the spring element 13, lie firmly against the longitudinal slot 12 on the profile 22, so that the housing 3 is secured to the profile 22 and cannot easily be pulled from it. The profile 22 can have a recess, through which the spring arm 13a is accessible from the outside, in order to release it relative to the longitudinal slot 12 and so as to be able to separate the profile 22 from the housing 3. FIG. 7 shows further elements of the safety gearbox 1. The safety gearbox 1 comprises a carrying element 6, in which a drive shaft 14 supporting the drive sprocket 2 is mounted. The carrying element 6 also has at least one flexible snap-in or locking cam 7 in a longitudinal direction 6b of the safety gearbox (see also FIG. 11). The at least one locking cam 7 can be biased in the longitudinal direction by a spring 8, which has a predetermined spring action. The spring 8 is held in an oblong spring slot 8a running in the longitudinal direction 6b in the carrying element 6. The carrying element 6 is rotatably or tiltably mounted about a tilting axis 6a in the housing 3, which is formed of two segments 3a, 3b, in a respective cylindrical bearing slot 3c. The tilting axis 6a runs parallel to the longitudinal axis 6b of the housing 3. The housing 3 also has at least one snap-in or locking recess 7c, into which in operation at least one locking cam 7 engages in a first position of the drive sprocket 2.

Preferably two locking cams 7 in the longitudinal direction 6b respectively lie opposite one another. The carrying element 6 adjacent to the locking cams 7 has recesses 7a running in the circumferential direction, as a result of which flexible bars 7b are formed, the locking cams 7 being arranged on a bar 7b of the carrying element 6 in each case. As a result flexibility in the longitudinal direction 6b is lent to the locking cams 7. If the locking cams 7 engage into the locking recesses 7c, the force exerted by the spring 8 on the locking cams 7 additionally impedes rotation of the carrying element 6 about the tilting axis 6a relative to the cylindrical slots 3c of the housing 3, in which the carrying element 6 is mounted so as to be able to slide. FIGS. 3 to 6 show a tripping condition of the safety gearbox 1, in which the drive sprocket 2 is brought from its first position in accordance with FIGS. 1 and 2 to a second position, in which the chain 4 can separate from it.

If a pulling force which exceeds a predetermined value is transmitted to the drive sprocket 2 by means of the chain 4, the at least one locking cam 7 is pressed against the spring action of the bar 7b and the spring 8 out of the at least one locking recess 7c and the carrying element 6 is pivoted about the tilting axis 6a. The housing 3 can have further locking recesses 7c, which have a predetermined distance or circumferential angle in respect to the tilting axis 6a from the locking recesses 7c, into which the locking cams 7 engage, whenever in operation the carrying element is currently in the first position. If the carrying element 6 is rotated by the pulling force transmitted by the chain 4 about a predetermined angle to the second position, the locking cams 7 engage into the further locking recesses, as a result of which the carrying element 6 in the second position is locked against a further turn. The predetermined angle or tipping angle between the first and the second position can range between 10° and 90°, for instance 20°, 30°, 45° or 60°.

The safety gearbox 1 has a housing element 5, which at least partly covers the drive sprocket 2. The housing element 5 in the chain pulling direction 4a has a recess and is formed so as to be closed on the opposite side. The housing element 5 can be formed so that it is detachable from the remaining housing 3, that is to say from the housing segments 3a, 3b. The housing element 5 prevents the chain 4 from sliding off the drive sprocket 2, whenever this with the carrying element 6 is currently in the first position. The inner surface, turned towards the drive sprocket 2, of the housing element 5 has a distance from the drive sprocket 2 currently in the first position, which is less than a cross-section of the chain 4, so that the chain is secured against separation.

As FIG. 7 shows, the drive sprocket 2 is connected to a drive shaft 14, supporting a first bevel gear 15, which in operation drives a second bevel gear 16, mounted on the carrying element 6. As evident from FIG. 11, the carrying element 6 has a cylindrical bearing journal 16c oriented in the longitudinal direction 6b, on which the second bevel gear 16 is mounted about an axis of rotation, which corresponds to the tilting axis 6a. The second bevel gear 16 is connected to an output shaft 16a, which is joined to an intermediate gear 10. The intermediate gear 10 can be a planetary gear. The intermediate gear 10 can be connected to a control shaft 9 (FIG. 7) of the pleated blind system 20. By rotating the control shaft 9 the shade 26 can be opened or closed. The output shaft 16a, which can be formed integrally with the second bevel wheel 16, is connected to the intermediate gear 10 either by a rigid connecting member 16b, then the output shaft 16a being directly connected to the control shaft 9, or however via a planetary carrier 10a, then the intermediate gear 10 acting as planetary gearbox and a reduction of 1:3 for example is achieved between output shaft 16a and control shaft 9, so that even large and heavy pleated blinds can be operated by means of the chain 4, without excessive pulling force having to be applied and without the safety gearbox 1 being tripped undesirably.

Due to the concentric configuration of the second bevel gear 16, the output shaft 16a and the control shaft 9 with the tilting axis 6a of the carrying element 6, it is ensured that the output shaft 16a always aligns with the intermediate gear and the control shaft 9, irrespective of whether the carrying element 6 is in the first or second position. FIG. 5 shows a schematic view of a section transverse to the tilting axis 6a or longitudinal direction 6b of the safety gearbox in a tripped condition, in which the drive sprocket 2 depending on the pulling force has changed over from the first position to the second position. In the second position the distance between the inner surface 5a, turned towards the drive sprocket 2, of the housing element 5 at least partly covering the drive sprocket 2 in the first position, is greater than the chain cross-section, or anyhow only so great that the chain separates from the drive sprocket when impinged with no more than the predetermined pulling force, which leads to a changeover to the second position. In addition the configuration can be such that the direction of the pulling force is no longer perpendicular to the contact surface between drive sprocket 2 and chain 4. As a result the chain 4 can slip or slide off the drive sprocket 2 more easily.

The inner surface 5 a, turned towards the drive sprocket 2, of the housing element 5 enclosing the drive sprocket 2 as described has a contour, which secures the drive sprocket 2 in the first position on the drive sprocket 2, and when the drive sprocket changes over from the first position to the second position does not collide with this. Preferably the housing element 5 enclosing the drive sprocket 2 for this reason has a concave surface lying opposite the front of the drive sprocket 2, the distance of which to a movement orbit of the chain wheel 2 is less than the chain cross-section. In other words the shortest connecting lines in each case or the distance between a surface of the volume swept over by the drive sprocket 2 with overlying chain 4 and the inner surface 5a of the housing element 5 are shorter and/or less than a relevant cross-sectional dimension of the chain 4 during the changeover from the first to the second alignment.

With reference to FIGS. 5, 14 and 15 the shape of the inner surface 5a of the housing element 5, which partly covers the drive sprocket 2, is once again discussed in detail. FIG. 5 shows the second position of the drive sprocket 2 in a position pivoted about the tilting axis 6a relative to the first position, while FIG. 14 shows the first position, in which the axis of rotation 2a of the drive sprocket 2 is horizontally aligned. FIG. 15 illustrates a somewhat smaller tipping angle than in FIG. 5. The presentation- and sectional plane of FIGS. 4, 14 and 15 runs perpendicularly to the tipping axis 6a and the longitudinal direction 6b of the housing 3 and contains the axis of rotation 2a of the drive sprocket 2. In this plane the inner surface 5a adjoining a first part area 5a', which extends radially around the drive sprocket 2, is cylindrical and in cutaway view appears as straight horizontal contour line, in a second part area 5a " has a curvilinear contour, the centre of curvature of which lies on the tilting axis 6a. The radius of curvature of the contour 5 a " is slightly greater than a maximum distance of an outer contour of the chain 4 from the tilting axis 6a, so that if the chain is moved a slight gap between the chain and the inner contour still remains in the area 5a ", therefore the chain does not touch the housing element 5 either in the first position according to FIG. 14 or during the changeover of the drive sprocket to the second position according to FIGS. 15 and/or 5.

In sectional planes not shown, which are parallel to the sectional plane illustrated in FIGS. 5, 14 and 15, the contour of the inner surface 5a is formed accordingly, running as a straight-line in the cylindrical area 5a' around the drive sprocket 2 and a curvilinear section, the centre of curvature of which lies on the tilting axis 6a and has a radius, which corresponds to a distance from the tilting axis 6a of a point remote from the tilting axis 6a of the contour of the chain 4, in the respective plane. The inner surface 5a of the housing element 5 between the cylindrical part area 5a' and the part area 5a ", containing the said curvilinear contours, has a transient area 5a "\ which roughly follows the contour of the chain 4.

As a result of this shaping of the inner surface 5a it is ensured that the chain 4 does not touch the housing element 5 in the first position of the drive sprocket (FIG. 14), when it is in full contact with the drive sprocket, and cannot slide off the drive sprocket 2. On the other hand the chain 4 in the second position (FIGS. 5, 15) of the drive sprocket 2 is free, under its own dead weight or induced by the pulling force to simply slide off the drive sprocket 2, either with or without light contact of the housing element 5. FIGS. 8 to 10 illustrate a second embodiment of the safety gearbox, which in this case works without the safety function described above by releasing the chain and can be operated with a manually turned crank 18 or by means of an electrical wand 19 containing an electric drive. In a variant, which is illustrated in FIGS. 8 and 9, the drive shaft 14, on which the first bevel gear 15 sits, instead of the drive sprocket 2, carries an adapter 18a, onto which an output end of an electrical wand 19 can be placed with positive locking, in order to operate the blind system. Another variant is illustrated in FIG. 10, wherein the drive shaft 14 comprises a universal joint 18b, which is connected to a crank 18 instead of the drive sprocket 2. In both cases a slip clutch 17 is provided in order to protect the safety gearbox from overload.

When the crank 18 or the electrical wand 18 is used, the cylindrical and/or circular element 6 can be aligned in operation so that the axis of rotation 2a of the drive shaft 14 connected to the adapter 18a, which is mounted in the cylindrical element 6, in operation includes a predetermined angle to the horizontal. This angle can correspond to the angle between the first and the second position of the carrying element in the case of the first embodiment and can be 40° for example. Expressed differently the cylindrical element 6 can be tilted relative to the first position at an angle of 40° about the tilting axis 6a, or can be currently in the second position described above. For this purpose the housing 3 can have locking recesses 7c, into which the at least one locking cam 7 of the cylindrical element 6 engages, whenever it is arranged so as to be tilted at the predetermined angle. Instead of a spring 8 in this case it is expedient to provide a rigid pin or bolt, which is inserted in the spring slot 8a and which limits the elasticity of the bars 7b, carrying the locking cams 7, of the cylindrical element 6 or locks these and as a result fixes the cylindrical element 6 in the tilted alignment or second position as the only functional position. FIGS. 16 and 17 illustrate a segment 5b of the housing element 5, which can be configured approximately in the shape of a circular section or semi-circle and is positioned so that the housing element 5 with a boundary area of the segment 5b or an area adjacent to the segment 5b acts as safety device in the way described. The axis of rotation 2a of the drive wheel 2 lies in the first position (FIG. 16) within the segment 5b, while an edge- or peripheral area of the drive wheel 2 is covered by the housing element 5, in each case seen towards the axis of rotation 2a, and prevents the chain 4 from sliding off the drive sprocket 2 in the first position. In the second position of the drive sprocket 2 (FIG. 17 ) the drive chain 4 can enter the segment 5b in its entire area lying on the drive sprocket 2 or expressed differently pass through a gap between the housing element and the tilted drive wheel 2 and thus slide off the drive sprocket 2, either without touching the housing element 5 or with slight deformation of the housing element 5, a specific pulling force on the chain 4 possibly being necessary for sliding off the drive sprocket 2.

Reference numbers drawings 1 Safety gearbox 2 Drive sprocket (drive wheel) 2a Axis of rotation 3 Housing 3a First housing segment 3b Second housing segment 3c Bearing slot 4 Chain (pulling means) 4a Pulling direction 5 Housing element (safety device) 5 a Inner surface 5a ' First part area 5a '' Second part area 5a ''' Transient area 5b Segment 6 Carrying element 6a Tilting axis 6b Longitudinal direction 7 Snap-in/locking cam (first snap-in element) 7a Recess 7b Bar 7c Snap-in/locking recess (second snap-in element) 8 Spring 8 a Spring slot 9 Control shaft 10 Intermediate gear 10a Planetary carrier 12 Recess (longitudinal slot) 13 Spring element 13a Spring arm 14 Drive shaft 15 First bevel gear 16 Second bevel gear 16a Output shaft 16b Connecting member 16c B earing j ournal 17 Slip clutch 18 Crank 18a Adapter 18b Universal joint 19 Electrical wand 20 Pleated blind system 22 Upper rail (profile) 24 Lower rail 26 Shade

Claims

A safety transmission mechanism (1) for a curtain device (20) with a drive wheel (2), which is embraced by an imposed endless pulling means (4) suspended in two strands, with a bearing for the drive wheel (2), which is the first degree of freedom comprises a pivot axis (2a), about which the drive wheel (2) can be rotated by pulling a pulling means (4), and that, as a further degree of freedom, a displacement of the drive wheel (2) from a first position in which the drive wheel is moved by the pulling means (4) is embraced, is in drive communication with the curtain device (20) and the curtain device (20) is operable by pulling on the pulling means (4), permitting a second position held by the bearing, in response to an advance being exceeded determined pulling force of the traction means (4), with a safety means (5) fixedly arranged on the safety transmission mechanism (1) to prevent the traction means (4) superimposed on the drive wheel (2) against automatically loosening securing the driving wheel (2) located in the first position, the safety means (5) disengaging the pulling means (4) from the driving wheel (2) located in the second position in response to a pulling force which does not exceed the predetermined pulling force , permits.

Safety transmission mechanism according to claim 1, characterized in that the further degree of freedom is formed by the linear mobility of the drive wheel (2).

Safety transmission mechanism according to claim 1, characterized in that the further degree of freedom is formed by a rotatability of the axis of rotation (2a) of the drive wheel (2) about a tilt axis (6a).

Safety transmission mechanism according to claim 3, characterized in that the tilt axis (6a) intersects the axis of rotation (2a) perpendicularly.

Safety transmission mechanism according to one of the preceding claims, characterized in that the safety means is formed by a housing element (5) which partially encloses the drive wheel (2), an inner surface (5a) of the drive wheel (2) facing the drive wheel (2) housing element (5) has a distance to the drive wheel (2) which in the first position of the drive wheel (2) is smaller than a cross-sectional dimension of the traction means (4).

Safety transmission mechanism according to claim 3, characterized in that the bearing is formed by a bearing element (6) on which a drive shaft (14) carrying the drive wheel (2) is mounted around the axis of rotation (2a) and which is supported by a housing (3) ) is rotatably held between a first position and a second position about the tilt axis (6a).

A safety transmission mechanism according to claim 6, characterized in that the bearing is designed as a slide bearing, the bearing element (6) being mounted in cylindrical bearing slots (3c) of the housing (3).

A safety transmission mechanism according to claim 6 or 7, characterized in that the support element (6) is provided with at least a first locking element (7) and the housing (3) with at least one second locking element (7c), the support element (6) 6) on the housing (3) is provided with two first or second locking elements (7, 7c) which, viewed in the circumferential direction about the tilt axis (6a), are arranged at a predetermined angle, wherein in the first position of the supporting element ( 6), in which the drive wheel (2) is in its first position, a first locking element (7) is locked with a second locking element (7c), and in the second position of the carrier element (6), in which the drive wheel (2) is in its second position, another first locking element (7) is locked with the second locking element (7c) or the first locking element (7) with another second locking element (7c).

Safety transmission mechanism according to claim 8, characterized in that the at least one first locking element is formed by at least one spring-elastic locking cam (7) and the at least one second locking element by at least one locking recess (7c) on the housing (3) .

Safety transmission mechanism according to one of claims 6 to 9, characterized in that a first cone-shaped gear (15) is mounted non-rotatably on the drive shaft (14) which engages a bearing on the support element (6) tilting shaft (6a) mounted second cone-shaped gear (16), the second cone-shaped gear (16) being in drive communication with the curtain device.

11.

Safety transmission mechanism (1) according to claim 1, characterized in that the housing (3) comprises a first housing segment (3a) and a second housing segment (3b), the drive wheel (2) being mounted in the housing segments (3a, 3b) and the second housing segment (3b) comprises at least one spring element (13), which has a spring arm (13a) which extends outwards from the outside of the second housing segment (3b), the curtain device (20) having an upper rail (22) in the form of a profile, which has at least one longitudinal slot (12), into which the spring arm (13a) engages and the housing (3) and the profile (12) lock together.