Electromotive drive mechanism for a body of furniture

An electromotive drive mechanism for a body of furniture, includes a worm drive which is activated by a motor and includes a worm received in the casing and a worm wheel in engagement with the worm. Received in the casing is a support body which is closely fitted around the worm and includes a receiving opening for engagement by the worm wheel.

CROSS-REFERENCES TO RELATED APPLICATIONS
 This application claims the priority of German Patent Application Serial
 No. 298 18 204.1, filed Oct. 12, 1998, the subject matter of which is
 incorporated herein by reference.
 BACKGROUND OF THE INVENTION
 The present invention relates, in general, to an electromotive drive
 mechanism for a body of furniture, and in particular to a drive mechanism
 of a type having a worm gear activated by a motor and essentially
 including a gearbox casing for housing a worm and a worm wheel which is in
 mesh with the worm.
 The type of electromotive drive, involved here, is applicable for a wide
 variety of different articles of furniture, for example beds, slatted bed
 frames or the like and is considered a small power drive. Typical drive
 mechanisms of this type for operating a body of furniture include a worm
 which is either fitted in fixed rotative engagement onto the output
 journal of an electric motor, or forms the output journal itself to reduce
 the overall dimensions. As a consequence of the geometry of the worm and
 the worm wheel, relatively high gearing forces are encountered that may
 lead to a flexure of the output journal when subject to respectively high
 loads. Thus, the diminished contact ratio between the worm and the worm
 wheel results in increased wear. In particular, the flanks of the worm
 wheel wear off, leading to a fracture of the output journal, so that the
 drive must be repaired or replaced by a new drive.
 SUMMARY OF THE INVENTION
 It is thus an object of the present invention to provide an improved
 electromotive drive mechanism, obviating the afore-stated drawbacks.
 In particular, it is an object of the present invention to provide an
 improved electromotive drive mechanism which is simple in structure and
 yet at least significantly reduces a flexure of the output journal of the
 motor or of the wormshaft.
 These objects, and others which will become apparent hereinafter, are
 attained in accordance with the present invention by providing a support
 body which is so insertable in the gearbox casing as to closely fit around
 the worm and includes a receiving opening for engagement by the worm
 wheel.
 The support body is made of suitable material to keep friction to a
 minimum, e.g. from plastic material through an injection molding process.
 Through the provision of a support body according to the present
 invention, a sagging or flexure of the wormshaft or output journal can
 reliably be prevented. Thus, the worm is in optimum fit with the flanks of
 the worm wheel so that wear is significantly reduced. The provision of the
 receiving opening enables an engagement of the worm windings with the
 gears of the worm wheel.
 According to another aspect of the present invention, the support body has
 a basic form of cylindrical configuration and is inserted in positive
 and/or non-positive engagement in a bore of the gearbox casing. Drives for
 articles of furniture have to be designed for realizing a self-locking
 action so that the attached piece of furniture is able to remain in any
 position, once the drive is shut down. Normally, the drive includes a
 spindle for driving the worm wheel, with the spindle having mounted
 thereon a spindle nut. In the event, the spindle is not constructed for
 self-locking action, but such action is desired, it is proposed, in
 accordance with another feature of the present invention, to provide the
 motor-facing end portion of the support body with several slots to realize
 deformable tongues. This end portion is suitably formed with an outer
 groove for accommodation of an annular spring retainer, whereby the spring
 retainer applies a precisely defined, constant friction force on the
 output journal of the motor to thereby effect a self-locking action of the
 drive mechanism, when the drive per se is not designed to include a
 self-locking mechanism.
 The drive mechanism according to the present invention is especially
 suitable for articles of furniture, which require a relatively small
 torque for adjustment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Turning now to FIG. 1, there is shown a worm drive for a drive mechanism,
 useful for height adjustment of an article of furniture (not shown). For
 the sake of simplicity, the drive mechanism will be described hereinafter
 only in connection with those parts that are necessary for the
 understanding of the present invention. Thus, it will be appreciated by
 persons skilled in the art that the drive mechanism must contain much
 mechanical apparatus which does not appear in the foregoing Figures and
 will not be described in detail, as this apparatus does not form part of
 the present invention.
 The worm drive includes a worm 10 which is driven by a motor, for example a
 fan motor, via a worm wheel 11. In the non-limiting example of FIG. 1, the
 worm 10 forms the output journal of the motor 12; However, it is certainly
 conceivable to place the worm onto a separate output journal. The worm 10
 and the worm wheel 11 are destined for accommodation in a gearbox casing
 13 which is formed with a bore 17. Fitted in the bore 17 in positive
 and/or non-positive engagement is a cylindrical support body 14 which has
 a bore 18 for receiving the worm 10. The bore 18 is of such dimensions
 that the support body 14 closely fits around the worm 10. The support body
 14 is further formed with a slotted receiving opening 19 for passage of
 the worm wheel 11 and engagement with the worm 10.
 The support body 14 has a motor-distal end, which is formed with a recess
 20, and a motor-proximal end portion, which is formed with several, for
 example four, inwardly directed longitudinal slots 15 to form resilient
 tongues to impart the motor-proximal end portion of the support body 14
 with a certain flexibility. The slots 15 are suitably offset to one
 another at an angle of 90.degree.. At a slight distance to the end face of
 the motor-proximal end portion, the support body 14 is formed with an
 outer circumferential groove 21 for receiving an annular spring 16 which
 applies a constant friction force, determined by the spring 16, onto a
 confronting smooth area of the motor shaft or output journal, so as to
 effect a self-locking action of the drive mechanism.
 As further shown in FIG. 1, the support body 14 has an outer contour of
 conical configuration, with the greatest diameter of the cone facing the
 motor 12, so as to realize a particular tight fit of the support body 14
 in the gearbox casing 13.
 While the invention has been illustrated and described as embodied in an
 electromotive drive mechanism for a body of furniture, it is not intended
 to be limited to the details shown since various modifications and
 structural changes may be made without departing in any way from the
 spirit of the present invention.
 What is claimed as new and desired to be protected by letters patent is set
 forth in the appended claims: