CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2018/056296, filed Mar. 13, 2018, which designated the United States and has been published as International Publication No. WO 2018/167094 A1 and which claims the priority of German Patent Application, Serial No. 20 2017 101 480.0, filed Mar. 14, 2017, pursuant to 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to an electromotive furniture drive having a drive motor, wherein the drive motor has a drive shaft mechanically coupled to a brake device, wherein the brake device has a looping wrap spring.

An electromotive furniture drive with a drive motor and a brake device can be found, for example, in publication DE 20 2015 107 053, wherein the brake device comprises a brake element which acts directly on the drive shaft of the drive motor and generates a uniform braking torque in both directions of rotation. This allows the same braking torques to be generated regardless of the direction of rotation so that the electromotive furniture drive experiences its mechanical self-locking at standstill and an already lifted load can be safely held. A disadvantage is that the braking torque is generated in both directions of rotation of the drive shaft.

An electromotive furniture drive of the type mentioned above is known from the publication U.S. Pat. No. 9,431,871, wherein three brake elements in segment form surround the drive shaft and are encased directly by a wrap spring so that a braking torque is generated in only one direction of rotation of the drive shaft. A disadvantage here is the increased installation effort and that in addition to the pretensioning force of the wrap spring, a relatively poorly controllable additional tensioning force results from the Eytelwein wrap, which means a high tolerance in the application of the brake torques.

The present invention is based on the object of creating an electromotive furniture drive with a drive motor and a brake device, which no longer has the above-mentioned disadvantages, is also easy to install and in which the braking torques lie within a small tolerance range.

SUMMARY OF THE INVENTION

The solution to this object is provided in accordance with the invention by an electromotive furniture drive having a drive motor, wherein the drive motor has a drive shaft which is mechanically coupled to a brake device, wherein the brake device has a looping wrap spring, wherein the brake device includes a brake element which is designed to apply a braking torque to the drive shaft in one direction of rotation, wherein the brake element is in mechanical operative connection with a coupling element, and wherein the wrap spring is placed on an outer jacket surface of the coupling element.

Further advantageous embodiments are the subject matter of the dependent claims.

In an advantageous embodiment, the electromotive furniture drive has a transmission drivetrain which is driven by the drive motor and which reduces a high speed of the drive motor either to a lower angular speed or to a low linear speed. A typical transmission drivetrain has a worm gear, the teeth of which mesh with the teeth of the drive motor, and also has a worm nut lifting gear, which is supplied with rotational energy by the worm gear and transforms the rotational movement into a linear output movement.

According to a typical embodiment, the threaded spindle is fixed in a housing of the electromotive furniture drive, but rotatably mounted relative to it, and is driven in rotation by the drive motor, while a spindle nut is mounted on the threads of the spindle, which in turn executes the output linear movement when the threaded spindle rotates, and is further connected indirectly or directly to other elements such as lifting tubes, adjusting elements and/or fork heads and finally to a furniture component. When the electromotive furniture drive is operated in one piece of furniture, at least two furniture components are adjusted relative to each other. It is also possible to arrange several drive motors and/or worm nut lifting gear units in one housing.

The transmission drivetrain of the present electromotive furniture drive is not self-locking so that the connected furniture component would move in the direction of gravity when the drive motor is switched off. The brake device generates a braking torque that counteracts the gravity-induced lowering of the connected furniture component. Prior art brake devices have a brake element which generates a constant braking torque independent of the direction of rotation of the drive motor. The brake element has spring-elastic sections, for example, and directly or indirectly provides brake surfaces which are directly connected to the drive shaft of the drive motor. A braking torque that can always be generated uniformly is thus given.

The brake torque that can be generated is relatively small compared to the drive torque of the drive motor and the brake torque can be adjusted in advance by dimensioning the brake element and the pressure forces. The level of this preset braking torque is selected to provide self-locking of the transmission drivetrain, including a safety margin for the normal operating condition.

According to the invention, the brake element is mechanically connected to a coupling element. The simplest mechanical operative connection is provided by a kind of claw coupling, wherein at least one claw, preferably three claws arranged uniformly in the circumference, are provided with the corresponding recesses in each case so that sections of the brake element and coupling element intermesh in a claw-like manner. The claw-like connection is provided with a small play and is positive-locking. The brake element can be arranged completely or alternatively at least in sections in a concentric recess of the coupling element. Other forces, such as radial forces exerted by the wrap spring on the coupling element, are therefore not transmitted to the brake element so that they do not affect the brake element.

The coupling element has a jacket surface which is preferably designed as an outer jacket surface and alternatively as an inner jacket surface. For example, the jacket surface is cylindrical. A looping wrap spring with preferably more than one wrap winding is frictionally connected to the jacket surface. The free end of the wrap spring is designed as a retaining element, for example in the form of a hook, and is intended for fastening in a housing. Such housings are formed by the housing of the drive motor or may alternatively be attached to the housing of the drive motor or further such housings may be formed by the housing of the electromotive furniture drive or one of its components itself. The retaining element is arranged in such a way that it cannot rotate about the axis of the drive shaft and is stationary relative to the drive motor when the drive motor is in operation.

When the wrap spring is not mounted, it has a diameter which is an oversize compared to the diameter of the jacket surface and after mounting. If the wrap spring is placed on an outer jacket surface after assembly, the inner diameter of the unassembled wrap spring is slightly smaller than the outer diameter of the jacket surface of the coupling element. Because the wrap spring is placed on the coupling element with more than one wrap winding and with an oversize, according to Eytelwein's wrap a slippage or a transmission of a torque of the coupling element occurs in a first direction of rotation with a very low height, which is due to the spring pretension providing the oversize after assembly has been completed. In the second direction of rotation of the coupling element, however, very high torques are transmitted between the coupling element and the wrap spring, so that if a predetermined number of wraps is exceeded, a frictionally tight connection is practically achieved. The brake device is configured so that the second direction of rotation corresponds to the direction of rotation of the drive motor, which is intended to move the connected furniture component in the direction of gravity.

In an inventive manner, a brake device for an electromotive furniture drive has thus been created which, when the connected furniture component moves against the force of gravity, is practically designed as a freewheel and the brake element has no or only a small braking extension due to the above-mentioned oversize. In the second direction of rotation of the drive shaft, however, the brake element forms with the coupling element a rotationally fixed frictional connection or a connection subject to rotational braking with the wrap spring, with the result that the spindle drivetrain appears to be self-locking when the drive motor is switched off and the load connected to the electromotive furniture drive is held securely in position.

A further inventive aspect is the above-mentioned decoupling in the form of a claw coupling between brake element and coupling element, because neither the spring pretension of the looping wrap spring forming the oversize nor the high braking forces exerted by the wrap spring itself during the second direction of rotation and producing this by the wrap spring itself have any effect on the brake quality of the brake element, because no forces of the wrap spring can be exerted on the brake element by the play-related connection between the brake element and the coupling element, but only forces in the circumferential direction can be transmitted to the brake element in the form of torques, so that the brake element is always in the same frictional torque entrainment connection with the drive shaft, irrespective of the direction of rotation and the force generated by the wrap spring.

In another advantageous embodiment of the electromotive furniture drive, an axial bearing is arranged centrally on the coupling element. The axial bearing, for example in the form of a plain bearing, can be essentially disc-shaped and held by webs running radially outwards. The axial bearing with a first bearing surface is preferably in contact with an end face of the drive shaft. Alternatively or additionally, the axial bearing with a second bearing surface can rest against a cover of a housing of the brake device. The axial bearing prevents axial movement of the coupling element. Such a movement could lead to an axial oscillation of the coupling element on the drive shaft, which is accompanied by undesirable vibrations and noise development of the drive motor.

