The invention relates to a viscoelastic transmission device which, inside a winding tube for a blind, for a roller shutter or for a roll-up screen, provides the mechanical connection between the shaft of an actuator and a driving wheel that drives the winding tube.
Winding tubes are not standardized. They have a wide variety of cross sections (circular, pentagonal, hexagonal, octagonal, etc.) and dimensions in an orthogonal cross section.
A driving wheel according to the prior art comprises a housing able to accept an output shaft of the actuator and comprises an exterior profile able to fit inside the winding tube, with a limited clearance between the exterior profile of the wheel and the interior profile of the winding tube.
For one same type of actuator, there are therefore a great many driving wheels, differing only in terms of their exterior profile, each wheel being able to collaborate with one specific winding tube.
In order to prevent actuator vibrations (caused by an electric motor and by reduction gearing) from spreading to the winding tube, or at least to limit this spread, it is known practice to use a driving wheel equipped with a viscoelastic material as a replacement for a driving wheel made of one single material, for example of plastic.
Patent application WO 2006/032761 describes a driving wheel that allows the use of several viscoelastic tiles working in compression and positioned between elastic beam elements.
U.S. Pat. No. 4,159,162 describes a driving wheel with vibration-damping effect that can be fitted into a tube made of rolled sheet, of circular profile, with bend channel.
Patent DE 197 36 770 likewise describes such a driving wheel, with vibration-damping effect. An exterior component has a cross section tailored to that of the winding tube. An interior component of this driving wheel acts as a housing for a splined shaft of the actuator. Torque is transmitted between the shaft and the wheel by direct collaboration of complementary shapes between the splined shaft and the internal profile. The elastic material is firmly attached to the interior component and to the exterior component.
However, this driving wheel is specific to one particular winding tube, for example an octagonal tube made of bent sheet, with bend channel, the wheel having a recess to accommodate the bend channel.
What this means is that there are as many driving wheels with damper to be designed as there are driving wheels without damper, which means an increase in different stock items that is all the more troublesome given that it is difficult to predict which applications will require a damped driving wheel because of special installation requirements.
The driving wheels of the prior art have damping elements that work essentially in compression. A viscoelastic material working in compression is able to transmit a higher load, and therefore a higher actuator torque.
However, the ability of the material to dissipate vibrational energy is much poorer than when the material is working in shear. Conversely, the transmission of shear load is limited by the risks of the material failing (by tearing).
Also known, from document DE 196 18 635, is an elastic transmission coupling for a sewing machine comprising an elastic element equipped with a cylindrical exterior profile with a groove for collaborating with a first shaft and an exterior profile shaped to collaborate with a second shaft that has a bore with internal teeth. Hence, mechanical power can be transferred from the first shaft to the second.
Also known, from document U.S. Pat. No. 1,780,727, is a power transmission device for a motor vehicle. The transmission device is of the type involving obstacles consisting of teeth between which an elastic material designed to damp out jerkiness is located.
Document U.S. Pat. No. 6,979,962 discloses an actuator comprising a motor suspended internally both by an attachment of the viscoelastic type and by a viscoelastic transmission device interposed between the shaft of the motor and the output shaft of the actuator.
It is an object of the invention to provide a device for transmitting mechanical power that overcomes the above disadvantages and improves the mechanical power-transmission devices known from the prior art. In particular, the invention makes it possible to produce a transmission device that is able to limit the diversity of driving wheels that have to be produced for a range of home automation installations.