Device for Preventing the Rotation of an Actuator Applied to a Ventilation Duct

Abstract

Various embodiments include a device for securing an actuator on an exterior of an HVAC duct against twisting during operation. The actuator includes a member for driving a flap in the duct for setting a volume flow. The actuator includes a housing with an underside facing the exterior of the ventilation duct. On the underside of the housing and spaced from an actuating axis of the connection is a receptacle for a fixing element against twisting of the actuator. The device may include: a flexible band for mounting on the exterior of the duct; and a fixing element on the upper side of the band. The fixing element is geometrically adapted to the receptacle so the fixing element can be inserted together with the band into the receptacle. The actuator is fixed about the actuating axis. The band comprises an adhesive and/or a magnetic layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. National Stage Application of International Application No. PCT/EP2018/062949 filed May 17, 2018, which designates the United States of America, and claims priority to DE Application No. 10 2017 209 075.8 filed May 30, 2017, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to HVAC systems. Various embodiments may include devices for securing an actuator mounted on an exterior of a ventilation duct against twisting during operation. The actuator has an actuating member for driving an actuating connection which cooperates with a flap arranged in the ventilation duct for setting a gaseous volume flow, in particular for the heating, ventilation or climate-control of a building.

BACKGROUND

[0003] Devices of this type are described, for example, from WO 2007/098620 A1, from CH 707 031 A1 and from CH 695 358 A5. The actuator typically has an electric motor, a reduction gearbox typically connected downstream of the electric motor and a gearbox-side actuating connection for attachment of the flap. In order to set the desired volume flow or airflow, the actuator displaces the actuating connection by a corresponding actuation angle. The ventilation duct usually has a round or rectangular cross-section. It can also be termed a ventilation duct or ventilation channel.

[0004] Such an actuator is to be secured against twisting so that the torque transmitted from the actuator to the actuating connection can be further transmitted to the flap connected thereto in the interior of the ventilation duct. For this purpose, a torque bracket is required. Conventionally, a protection against twisting includes additional connecting elements, for example, screws, nuts, rivets and with perforated rails and welded metal sheets. Thereby, the perforated rails and metal sheets were firmly attached to the ventilation duct and the actuator was then made secure to the perforated rails or to the metal sheets by means of the connecting elements. The actuator was thereby secured against twisting. The aforementioned measures are complex and time-consuming.

SUMMARY

[0005] Proceeding therefrom, teachings of the present disclosure describe an improved device for securing an actuator against twisting. Some embodiments include a device for securing an actuator against twisting which can take place without tools.

[0006] For example, some embodiments include a device (VS) for securing an actuator (1) mounted on an exterior (RA) of a ventilation duct (R) against twisting during operation, wherein the actuator (1) has an actuating member for driving an actuating connection (2) which cooperates with a flap arranged in the ventilation duct (R) for setting a gaseous volume flow, in particular, for the heating, ventilation or climate-control of a building, wherein the actuator (1) has a housing (3) with an underside (US), which faces the exterior (RA) of the ventilation duct (R), wherein provided on the underside (US) of the housing (3) and spaced from an actuating axis (SA) of the actuating connection (2) is a receptacle (A) for a fixing element (FE) against twisting of the actuator (1), characterized in that the device (VS) has a flexible band (FB) with an upper side (OV) and with an opposing underside (UV) provided for mounting on the exterior (RA) of the ventilation duct (R), wherein a fixing element (FE) is mounted or formed on the upper side (OV) of the flexible band (FB), the fixing element (FE) being geometrically adapted to the receptacle (A) on the underside (US) of the housing (3) such that said fixing element (FE) can be inserted together with the flexible band (FB), in particular, with low play into the receptacle (A), so that the actuator (1) is fixed against movements about the actuating axis (SA), and in that the flexible band (FB) comprises on its underside (UV) an adhesive layer (KL) and/or a magnetic layer (MAG) made of a magnetized ferromagnetic material.

[0007] In some embodiments, the receptacle (A) is formed in a transition region between the underside (US) of the housing (3) and an adjoining end face (ST) of the housing (3), typically extending perpendicularly to the underside (US), wherein the end face (ST) is spaced as far as possible from the actuating axis (SA) of the actuator (1).

[0008] In some embodiments, the flexible band (FB) has an elastic bending radius of at least 50 cm, in particular of at least 10 cm.

[0009] In some embodiments, the flexible band (FB) has a metal band, in particular a steel band or a sheet metal strip, or a plastics band or a plastics strip.

[0010] In some embodiments, the fixing element (FE) is a headed stud (KB) with one narrow end piece (SE) and with one broad end piece (BE), wherein the longitudinal axis of the headed stud (KB) extends perpendicularly to the upper side (OV) of the flexible band (FB) and wherein the broad end piece (BE) is spaced further from this upper side (OV) than the narrow end piece (SE).

[0011] In some embodiments, the headed stud (KB) is geometrically matched to a receptacle (A) formed as a T-groove (TN) on the underside (US) of the actuator housing (3), wherein the T-groove (TN) extends in the direction toward the actuating axis (SA) and in the opposite direction toward the end face (ST) of the housing (3), and wherein, after the insertion of the headed stud (KB) into the T-groove (TN), the actuator (1) is fixed against movements about the actuating axis (SA) and against movements parallel to the actuating axis (SA).

[0012] In some embodiments, the fixing element (FE) is a fold (FZ) formed in the flexible band (FB), wherein the fold (FZ) has one broad end piece (BE) and one narrow end piece (SE), wherein the fold (FZ) extends perpendicularly away from the upper side (OV) of the flexible band (FB) and wherein the broad end piece (BE) of the fold (FZ) is spaced further from this upper side (OV) than the narrow end piece (SE) of the fold (FZ).

[0013] In some embodiments, the fold (FZ) is geometrically matched to a receptacle (A) formed as a T-groove (TN) on the underside (US) of the actuator housing (3), the T-groove (TN) extending in the direction toward the actuating axis (SA) and in the opposite direction toward the end face (ST) of the housing (3), and wherein, after the insertion of the fold (FZ) into the T-groove (TN), the actuator (1) is fixed against movements about the actuating axis (SA) and against movements parallel to the actuating axis (SA).

[0014] In some embodiments, the fixing element (FE) is a protrusion (BU) formed in the flexible band (FB) and extending parallel away from the upper side (OV) and wherein the protrusion (BU) is preferably a half-open cut-out (AS) extending transversely to the longitudinal extent (LE) of the flexible band (FB) as a lateral stop.

[0015] In some embodiments, the protrusion (BU) is geometrically matched to a receptacle (A) formed as a T-bar (TT) on the underside (US) of the actuator housing (3), wherein the T-bar (TT) extends in the direction toward the actuating axis (SA) and in the opposite direction toward the end face (ST) of the housing (3), and wherein, after the insertion of the protrusion (BU) into the T-bar (TT), the actuator (1) is fixed against movements about the actuating axis (SA) and against movements parallel to the actuating axis (SA).

[0016] In some embodiments, after the insertion of the protrusion (BU) into the T-bar (TT), the cut-out (AS) introduced into the protrusion abuts against a narrow end piece (SE) of the T-bar (TT) as a stop (AN), and wherein the actuator (1) is thereby fixed against movements in directions toward the actuating axis (SA).

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The teachings herein and various embodiments of the present disclosure are described by reference to the accompanying drawings, in which:

[0018] FIG. 1 is an exemplary ventilation duct with a round cross-section and with an actuator mounted thereon incorporating teachings of the present disclosure;

[0019] FIG. 2 is an example of a device with a headed stud as the fixing element incorporating teachings of the present disclosure;

[0020] FIG. 3 is the example according to FIG. 2 in a plan view according to the viewing direction III indicated there,

[0021] FIG. 4 is an example of a device with a fold as the fixing element, incorporating teachings of the present disclosure;

[0022] FIG. 5 is the example according to FIG. 4 in a plan view according to the viewing direction V indicated there,

[0023] FIG. 6 is an exemplary actuator which is secured by means of a device incorporating teachings of the present disclosure; and

[0024] FIG. 7 is an example of an inventive device with a protrusion and with a lateral cut-out as a stop for the actuator shown in FIG. 6 with a T-bar as the receptacle.

DETAILED DESCRIPTION

[0025] In some embodiments, the device has a flexible band with an upper side and with an opposing underside provided for mounting on the exterior of the ventilation duct. A fixing element is mounted or formed on the upper side of the flexible band. The fixing element is geometrically adapted to the receptacle on the underside of the housing such that said fixing element can be inserted together with the flexible band, in particular, with low play into the receptacle, so that the actuator is fixed against movements about the actuating axis. The flexible band comprises on its underside an adhesive layer and/or a magnetic layer made of a magnetized ferromagnetic material. Regardless thereof, dependent upon the pre-defined form of the ventilation duct and, in particular, dependent upon the stability of the flexible band, a positive locking is possible. For this purpose, the flexible band can be tensioned or wrapped round the pre-defined ventilation duct in the manner of a belt.

[0026] In some embodiments, the twist prevention can be applied to the ventilation duct directly without any preparation, by means of an adhesive band which is already applied onto one side on the sheet metal strip. Therein, no further materials or tools are needed. Since the adhesive is applied in the form of an adhesive strip on a thin mobile sheet metal strip as an exemplary flexible band, the possibility exists of applying the fastening to ventilation ducts with the most varied of cross-sectional geometries. The adhesive strip or adhesive layer can be provided with a removable protective foil in order to prevent adhesion to itself or to other objects, and with dirt and dust.

[0027] In some embodiments, a magnetized, ferromagnetic layer can be applied on the underside of the flexible band. By means of the magnetized layer, the flexible band adheres magnetically on the iron metal sheet from which the ventilation duct is typically made.

[0028] The ventilation duct is not damaged thereby. In addition, the ventilation duct is not changed in its shape nor in its material. In particular, no holes have to be bored into the ventilation duct. By this means, the inside of the ventilation duct is also free from screws, rivets, assembly debris, such as for example, metal swarf and suchlike.

[0029] In some embodiments, the receptacle is formed in a transition region between the underside and an adjoining end face of the housing, typically extending perpendicularly to the underside. The end face is spaced as far as possible from the actuating axis of the actuator. By this means, a lateral insertion of the fixing element from the end face is easily possible. By means of a greatest possible spacing of the then positioned fixing element from the actuating axis, the greatest possible leverage to the torque brackets is possible. The bracing force from the receptacle acting upon the fixing element is then correspondingly small. This relatively small force can be conducted easily and reliably into the flexible band and then further via the adhesive or magnetic layer into the exterior of the ventilation duct.

[0030] In some embodiments, the flexible band has an elastic bending radius of at least 50 cm, in particular of at least 10 cm. Elastic is taken to mean that no irreversible damage occurs in the material of the flexible band at the minimum radius. In some embodiments, the flexible band has a band thickness in the range of 0.1 mm to 2 mm, e.g. in the range of 0.25 mm to 1 mm. The width of the flexible band is, in particular, in the range of 1 cm to 5 cm, e.g. in the range of 2.5 cm to 3.5 cm. The length of the flexible band is, in particular, in the range of 15 cm to 100 cm, e.g. in the range of 25 to 50 cm.

[0031] In some embodiments, the flexible band has a metal band, in particular a steel band or a sheet metal strip, or a plastics band or a plastics strip. The flexible band can also be a link belt made, for example, of metal.

[0032] In some embodiments, the fixing element is a headed stud with one narrow end piece and with one broad end piece. The longitudinal axis of the headed stud extends perpendicularly to the upper side of the flexible band. The broad end piece is spaced further from the upper side of the flexible band than the narrow end piece. Typically, the headed stud is configured cylindrical and is thus a rotationally symmetrical component. The headed stud can be, for example, riveted, glued, welded, press-fitted or soldered onto the flexible band. The diameter of the broad end piece of the headed stud, i.e. the diameter of the stud head is in the range of 3 mm to 20 mm, e.g. in the range of 7.5 mm to 10 mm.

[0033] In some embodiments, the headed stud is geometrically matched to a receptacle formed as a T-groove on the underside of the actuator housing. The T-groove extends in the direction toward the actuating axis and in the opposite direction toward the end face of the housing. Furthermore, the T-groove extends parallel to the underside of the housing. The T-groove can be produced from the same material as the housing, for example, from a metal such as aluminum or from a plastics material. The T-groove can alternatively be produced from a metal such as aluminum or iron and can be jointly cast or injection molded into a housing made of a plastics material. After the insertion of the headed stud into the T-groove, the actuator is fixed against movements about the actuating axis and against movements parallel to the actuating axis, i.e. along the actuating axis.

[0034] In some embodiments, the fixing element is a fold formed into the flexible band. The fold has a broad end piece and a narrow end piece. The fold extends perpendicularly away from the upper side of the flexible band. The broad end piece of the fold is spaced further from the upper side of the flexible band than the narrow end piece of the fold. The fold is introducible into the flexible band by means of a folding, bending or press-fitting tool. In some embodiments, no separate component such as a headed stud according to the preceding embodiment, is required.

[0035] In some embodiments, the fold is geometrically matched to a receptacle formed as a T-groove on the underside of the actuator housing. The T-groove extends in the direction toward the actuating axis and in the opposite direction toward the end face of the housing. Furthermore, the T-groove extends parallel to the underside of the housing. The T-groove can be produced from the same material as the housing, for example, from a metal such as aluminum or from a plastics material. The T-groove can alternatively be produced from a metal such as aluminum or iron and can be jointly cast or injection molded into a housing made of a plastics material. After the insertion of the fold into the T-groove, the actuator is fixed against movements about the actuating axis and against movements along the actuating axis.

[0036] In some embodiments, the fixing element is a protrusion formed into the flexible band and extending parallel away from the upper side. The protrusion preferably has a half-open cut-out extending transversely to the longitudinal extent of the flexible band as a lateral stop. The protrusion is introducible into the flexible band by means of a bending/stamping tool. In some embodiments, no separate component such as a headed stud according to the first embodiment is required.

[0037] In some embodiments, the protrusion is geometrically matched to a receptacle formed as a T-bar on the underside of the actuator housing. The T-bar extends in the direction toward the actuating axis and in the opposite direction toward the end face of the housing. Furthermore, the T-bar extends parallel to the underside of the housing. The T-bar can be produced from the same material as the housing, for example, from a metal such as aluminum or from a plastics material. The T-bar can alternatively be produced from a metal such as aluminum or iron and can be jointly cast or injection molded into a housing made of a plastics material. After the insertion of the protrusion into the T-bar, the actuator is fixed against movements about the actuating axis and against movements parallel to the actuating axis.

[0038] In some embodiments, after the insertion of the protrusion into the T-bar, the cut-out introduced into the protrusion abuts against a narrow end piece of the T-bar as a stop. The actuator is thereby also fixed against movements in directions toward the actuating axis.

[0039] FIG. 1 shows an exemplary ventilation duct R with a round cross-section and with an actuator 1 mounted thereon and with an inventive device VS. RA denotes the duct exterior and HR denotes a hollow space formed in the ventilation duct R for the transport, in particular, of air. The actuator 1 shown has an actuating connection 2 which cooperates with a flap arranged in the ventilation duct R (not shown in this drawing) for setting an air flow. The actuator 1 further comprises a housing 3 with an underside US which lies opposite the duct exterior RA. Provided on the housing underside US and also spaced from an actuating axis SA of the actuating connection 2 is a receptacle A for a fixing element FE in order to prevent a co-rotation of the actuator 1 with the actuating connection 2. The fixing element FE therefore secures the actuator 1 against twisting, as a torque bracket.

[0040] VS denotes an device for securing the actuator 1 mounted on the ventilation duct R against twisting during operation. The device VS comprises a flexible band FB which possesses mechanical properties such that it can be applied and/or conform to the duct exterior RA. In the present example, the flexible band FB is a sheet metal strip that is flexible to a certain extent. The band FB has an upper side OV and an opposing underside UV, provided for mounting on the duct exterior RA (see also FIG. 2). Mounted on the upper side OV is a fixing element FE, indicated as a headed stud KB. The fixing element is herein geometrically adapted to the receptacle A such that said FE can be inserted together with the flexible band FB into the receptacle A. By this means, the actuator 1 is fixed against movements about the actuating axis SA.

[0041] The receptacle A is formed, for example, in the transition region between the underside US of the housing 3 and an adjoining end face ST of the housing 3 extending perpendicularly to the underside US. The end face ST is herein that housing side which is spaced the furthest from the actuating axis SA of the actuator 1, specifically at a spacing H which with regard to the function of the fixing element FE as the torque bracket can also be termed the lever or the lever distance.

[0042] For the possible insertion of a headed stud KB as a fixing element FE, the receptacle A is configured as a T-groove TN which extends on one side in the direction toward the actuating axis SA and on the other side in the opposite direction toward the end face ST of the housing 3. The T-shaped cross-section or the T-shaped profile of the T-groove TN is geometrically matched to the side profile of the headed stud KB that is to be inserted. The headed stud KB can thus be inserted form-fittingly into the T-groove TN, preferably with little to no play. After the insertion of the headed stud KB into the T-groove TN, the actuator 1 is fixed against movements about the actuating axis SA and also against movements parallel to the actuating axis SA.

[0043] The flexible band FB comprises on its underside UV an adhesive layer KL and/or a magnetic layer MAG made of a magnetized ferromagnetic material. The design of the device VS according to the invention is shown in more detail in the following drawings.

[0044] FIG. 2 shows an example of a device VA with a headed stud KB as the fixing element FE in a sectional view. The headed stud KB has one broad cylindrical end piece BE and one narrow cylindrical end piece SE. The former is further removed from the upper side OV of the flexible band FB. A headed stud KB is formed centrally on the upper side OV of the flexible band FB. The mounting takes place herein by means of a cylindrical rivet N which is formed on the headed stud KB opposite the broad end piece BE. The rivet N is riveted or press-fitted to a corresponding opening in the flexible band FB. A continuous adhesive layer KL or a magnetized layer MAG is provided on the underside UV. This serves for frictional connection between the underside UV of the flexible band FB with the exterior RA of the ventilation duct R. D denotes the thickness of the flexible band FB.

[0045] FIG. 3 shows the example according to FIG. 2 in a plan view according to the viewing direction III indicated there. B denotes the width of the flexible band FB and LE denotes the longitudinal extent of the flexible band FB.

[0046] FIG. 4 shows an example of a device VS with a fold FZ as the fixing element FE in a sectional view. Similarly to the side profile of the headed stud KB, the fold FZ also has a T-shaped cross-section and/or a T-shaped profile. As distinct from the preceding example, herein, adhesive pads KL or magnetic pads MAG are arranged on the underside UV of the flexible band FB.

[0047] FIG. 5 shows the example according to FIG. 4 in a plan view according to the viewing direction V indicated there. In this representation, the distribution of the adhesive pads KL and/or magnetic pads MAG on the underside UV and along the longitudinal extent LE of the flexible band FB is particularly clearly apparent.

[0048] FIG. 6 shows an actuator 1 which is secured by means of the device VS in an alternative embodiment against twisting. In the present case, the receptacle A is configured as a T-bar TT. This alternative is, in effect, the inverse solution as compared with the preceding solutions. BE denotes the broad end piece of the T-bar TT and SE denotes the narrow end piece of the T-bar TT. AN denotes a stop which is formed on the narrow end piece SE of the T-bar TT.

[0049] Finally, FIG. 7 shows an example of a device VS with a protrusion BU and with a lateral cut-out AS in the flexible band FB as a stop for the actuator 1 shown in FIG. 6 with a T-bar TT as the receptacle A. The protrusion BU is arranged offset parallel by a distance AB from the upper side OV of the remaining flexible band FB and is provided and/or formed in the flexible band FB. In some embodiments, the stamped out half-open cut-out AS provided laterally in the protrusion BU extends parallel to the upper side OV and transversely to the longitudinal extent LE of the flexible band FB. The contour of the half-open cut-out AS is hereby geometrically matched to the stop formed on the narrow end piece SE of the T-bar TT.

LIST OF REFERENCE SIGNS

[0050] 1 Actuator

[0051] 2 Actuating connection, drive, flap connection

[0052] 3 Housing

[0053] A Receptacle for fixing element

[0054] AB Distance

[0055] AN Stop

[0056] AS Cut-out, laterally half-open cut-out

[0057] B Width of flexible band

[0058] BE Broad end piece

[0059] BU Protrusion

[0060] D Thickness of flexible band

[0061] FB Flexible band, sheet metal strip, steel metal sheet

[0062] FE Fixing element

[0063] H Spacing, lever, lever distance

[0064] KB Headed stud

[0065] KL Adhesive layer

[0066] MAG Magnetic layer, magnet layer

[0067] LE Longitudinal extent

[0068] N Rivet

[0069] OV Upper side of the twist prevention

[0070] RA Exterior of the ventilation duct

[0071] SE Narrow end piece

[0072] ST End face

[0073] TN T-groove

[0074] TT T-bar

[0075] US Underside of the actuator

[0076] UV Underside of the twist prevention

[0077] VS Twist prevention, adhesive band

Claims

1. A device for securing an actuator mounted on an exterior of a ventilation duct against twisting during operation, wherein the actuator includes an actuating member for driving an actuating connection cooperating with a flap arranged in the ventilation duct for setting a gaseous volume flow, wherein the actuator includes a housing with an underside facing the exterior of the ventilation duct, wherein provided on the underside of the housing and spaced from an actuating axis of the actuating connection is a receptacle for a fixing element against twisting of the actuator, the device comprising: a flexible band with an upper side and an opposing underside provided for mounting on the exterior of the ventilation duct; and a fixing element mounted or formed on the upper side of the flexible band; wherein the fixing element is geometrically adapted to the receptacle on the underside of the housing such that said fixing element can be inserted together with the flexible band into the receptacle, so that the actuator is fixed against movements about the actuating axis; and the flexible band comprises an adhesive layer and/or a magnetic layer made of a magnetized ferromagnetic material.

2. The device as claimed in claim 1, wherein: the receptacle is disposed in a transition region between the underside of the housing and an adjoining end face of the housing; and the end face is spaced as far as possible from the actuating axis of the actuator.

3. The device as claimed in claim 1, wherein the flexible band has an elastic bending radius of at least 50 cm.

4. The device as claimed in claim 1, wherein the flexible band includes a metal band or a plastics band or a plastics strip.

5. The device as claimed in claim 1, wherein: the fixing element comprises a headed stud with one narrow end piece and with one broad end piece; the longitudinal axis of the headed stud extends perpendicularly to the upper side of the flexible band; and the broad end piece is spaced further from this upper side than the narrow end piece.

6. The device as claimed in claim 5, wherein: the receptacle is disposed in a transition region between the underside of the housing and an adjoining end face of the housing; the end face is spaced as far as possible from the actuating axis of the actuator; the headed stud is geometrically matched to a receptacle formed as a T-groove disposed on the underside of the actuator housing; the T-groove extends in the direction toward the actuating axis and in the opposite direction toward the end face of the housing; and after the insertion of the headed stud into the T-groove, the actuator is fixed against movements about the actuating axis and against movements parallel to the actuating axis.

7. The device as claimed in claim 1, wherein: the fixing element comprises a fold formed in the flexible band; the fold includes one broad end piece and one narrow end piece; the fold extends perpendicularly away from the upper side of the flexible band; and the broad end piece of the fold is spaced further from this upper side than the narrow end piece of the fold.

8. The device as claimed in claim 7, wherein: the receptacle is disposed in a transition region between the underside of the housing and an adjoining end face of the housing; the end face is spaced as far as possible from the actuating axis of the actuator; the fold is geometrically matched to a receptacle formed as a T-groove on the underside of the actuator housing, the T-groove extending in the direction toward the actuating axis and in the opposite direction toward the end face of the housing; and after the insertion of the fold into the T-groove, the actuator is fixed against movements about the actuating axis and against movements parallel to the actuating axis.

9. The device as claimed in claim 1, wherein: the fixing element comprises a protrusion formed in the flexible band and extending parallel away from the upper side; and the protrusion comprises a half-open cut-out extending transversely to the longitudinal extent of the flexible band as a lateral stop.

10. The device as claimed in claim 9, wherein: the receptacle is disposed in a transition region between the underside of the housing and an adjoining end face of the housing; the end face is spaced as far as possible from the actuating axis of the actuator; the protrusion is geometrically matched to a receptacle comprising a T-bar on the underside of the actuator housing; the T-bar extends in the direction toward the actuating axis and in the opposite direction toward the end face of the housing; and after the insertion of the protrusion into the T-bar, the actuator is fixed against movements about the actuating axis and against movements parallel to the actuating axis.

11. The device as claimed in claim 10, wherein: after the insertion of the protrusion into the T-bar, the cut-out introduced into the protrusion abuts against a narrow end piece of the T-bar as a stop; and the actuator is thereby fixed against movements in directions toward the actuating axis.