Patent Description:
A vacuum cleaner comprises a vacuum generator, a filter arrangement and a mouthpiece. The mouthpiece is adapted to be moved over a surface that is to be cleaned. The filter arrangement is usually disposed upstream the generator and adapted to hold back particles like dust that travel with the air sucked in through the mouthpiece.

In order to disengage particles from the surface, a rotating brush or bristle roller may be provided close to the mouth piece. The roller is rotated around a predetermined axis of rotation, so that the bristles brush over the surface. For powering the roller, a turbine may be disposed in the stream of air through the mouthpiece and provide a rotating motion for the bristle roller. As air speed through the mouthpiece may vary considerably during use of the cleaner, rotating speed of the turbine must be controlled in order to prevent damage on the roller or the surface.

<CIT> proposes to monitor the rotational speed of a turbo-powered bristle roller and reduce a driving torque when the speed exceeds a predetermined threshold. The driving torque may be controlled by allowing a stream of atmospheric air into the turbine, thereby reducing a pressure difference between its sides. This may require user intervention or equipping the mouthpiece part with an air valve for the stream of control air. Operating the valve may require some logic and an electric power supply from the vacuum generator, which makes the cleaner more complex.

<CIT> proposes a centrifugal brake on the turbine that brakes the turbine when it exceeds a predetermined maximum rotational speed. The brake comprises a metal disc that rotates with the turbine and an electric magnet disposed at a housing. The electric magnet generates a magnetic field in the rotating disc, causing eddy currents inside the disc. A magnetic braking force is generated that is proportional to the rotational speed and the strength of the magnetic field. The electric magnet requires a power source and a control circuit.

It is an object of present invention to provide an improved technique for limiting the rotational speed of a turbine for powering a brush roller for a vacuum cleaner. The invention solves the object through the subject matter of the independent claims. Dependent claims describe preferred embodiments.

A turbo nozzle for a vacuum cleaner comprises a brush roller and a turbine for setting the roller in rotational motion. The turbine is adapted to be traversed by a stream of air travelling through the nozzle. The nozzle further comprises a magnetic brake for limiting rotational speed of the roller, wherein the magnetic brake comprises a permanent magnet affixed to a rotating part of the turbine or the roller, and a conductive element affixed to a stationary part of the nozzle. This way, the moving magnet may cause an eddy current in the conductive element which counteracts rising revolution speeds of the rotating part. The turbine may also comprise a centrifugal displacement mechanism that is adapted to move the magnet towards the conductive element in answer to centrifugal forces acting upon the magnet. In other words, the magnet may be moved closer to the magnet as the rotational speed of the turbine or the brush rises. Over decreasing distance, magnetic forces between the magnet and the conductive element may be increased so that the braking force is also increased. A cut-off rotational speed may therefore be more clearly defined. This may aid to increase reactivity of the magnetic brake to varying air speeds acting on the turbine.

The eddy current may cause a magnetic force between the magnet and the conductive element so that the moveable part may be effectively braked. Advantageously the braking force may be proportional to a rotational speed of the rotating part so that little or no braking takes place when rotational speeds are low. Braking forces may also be dependent on a distance between the magnet and the conductive element so that a desired braking force may be achieved through dimensioning and relative positioning of the elements. The magnetic brake may operate without mechanical friction so that wear may be very low, making possible reliable operation over extended periods of operation. The magnetic brake may be adapted to prevent exceeding revolution speeds of the turbine and/or brush. Damage caused by an overly fast spinning brush on a surface to be cleaned with the nozzle may be prevented. The magnetic brake may be self-contained and require no electric control means and no electric power supply.

Said displacement mechanism may comprise an elastic element counteracting the centrifugal forces on the magnet. The magnet may be moved back to an inner radial position as the rotational speed decreases so that the braking forces may also be decreased. Effectively, rotational speed of the turbine may be kept as high as possible without exceeding said predetermined threshold. The turbine may be kept at an advantageous operating point and the brush may operate effectively.

Said mechanism may be adapted to restrict movement of said magnet to a rotational plane with respect to said axis of rotation. By preventing axial movement, a required space for the moveable magnet may be reduced. It is to be noted that movement of the magnet is not necessarily restricted to a radial direction. Instead, magnet movement may be limited to any predetermined curve that lies in a rotational plane around the rotating part's axis of rotation.

In one preferred embodiment, said mechanism comprises a lever with a first end and a second end. The first end is affixed to said magnet and the second end is hinged to the rotating part. An axis of the hinge is preferred to lie parallel to the turbine's axis of rotation, especially in some predetermined distance. Said lever may restrict movement of the magnet to a circle shaped curve in a rotational plane with respect to the rotating part. A length and hinge point of the lever may be chosen such that a predetermined cut-off speed is realized. A radial distance between the hinge and the axis of rotation may be varied to adapt the brake to a desired cut-off speed. The lever arrangement may be compact in size and sturdy to firmly hold said magnet. By using the lever, the magnet may be kept in the second position by means of centrifugal forces, making an end stop to the lever or magnet unnecessary. Longevity of the mechanism may be increased.

Said conductive element may be annulus shaped and disposed on an axial side of the magnet, with respect to said axis of rotation. In mathematics, an annulus is a ring-shaped object, a region bounded by two concentric circles. Practically, the conductive element will also have a predetermined axial thickness. The magnet may lie in an inner, open section of the annulus when in a radially inner position, and adjacent to the conductive element when in a radially outer position. A contrast between acting forces between the conductive element and the magnet may be greater than in an arrangement where the conductive element lies radially outwards the magnet.

It is especially preferred that a magnetic orientation of the magnet is parallel to said axis of rotation. The magnetic orientation may be understood as a line going through a magnetic north pole and a magnetic south pole of the magnet. In a pole section of the magnet, magnetic forces may be maximal, so that the conductive element may be most effective when placed close to a pole. In combination with the annulus-shaped conductive element in an axial position from the magnet, maximum magnetic engagement may be achieved when the magnet is in an outer radial position, and maximum magnetic disengagement (or minimum magnetic engagement) when the magnet is in an inner radial position.

Said mechanism may be adapted to move said magnet between a first position in which the magnet is substantially disengaged from the conductive element and a second position in which the magnet is engaged with the conductive element. The first position may correspond to an inner radial position and the second to an outer radial position. The magnet may assume the second position if its rotational speed around the rotating part's axis of rotation exceeds a predetermined threshold. The magnet may be pulled back into the first position when the rotational speed drops under a second predetermined threshold.

It is furthermore preferred that the magnetic brake comprises several magnets which are evenly distributed on a circumference around the axis of rotation and that said mechanism is adapted to synchronize movements of the magnets. By using more than one magnet, effective braking forces may be increased. The mechanism may especially synchronize radial distances of the magnets from the axis of rotation, respectively. Circumferential distances between neighbouring magnets may be kept the same. A heavy spot on the rotating part may be prevented. The rotating part may be balanced, independent of the radial positions the magnets assume. The centre of mass of the constellation may be kept aligned with the axis of rotation.

The mechanism may especially be adapted to keep the magnets on identical radial distances to the axis of rotation. The magnets are preferred to have identical effective masses. The mechanism may also keep relative distances of neighbouring magnets along the circumference identical.

In one preferred embodiment, said mechanism comprises a set of gearwheels that intermesh with one gearwheel coaxial to the axis of rotation. A magnet may be affixed to each of the outer gearwheels so that the magnets' radial positions and their relative positions along a circumference to said axis of rotation are synchronized. The magnets may additionally be guided in motion links that extend along circumferences of outer gearwheels' axis of rotation.

According to another aspect of present invention, a vacuum cleaner comprises a turbo nozzle described herein. The vacuum cleaner may show increased cleaning performance as the brush roller is kept closer to an optimal turning speed.

The invention will now be described in more detail making reference to the enclosed figures in which:.

<FIG> shows a nozzle <NUM> for a vacuum cleaner <NUM>. The nozzle <NUM> is adapted to be connected to an air duct leading to the vacuum cleaner <NUM>. The air duct typically comprises a tube or a flexible hollow tube. A brush roller <NUM> is provided to mechanically operate on a surface the nozzle <NUM> is placed upon. A turbine <NUM> is provided to set the brush roller <NUM> in motion. The turbine <NUM> lies in an air duct inside the nozzle <NUM>, the duct opening to the environment on one end and leading to the vacuum cleaner on another end. Air flowing through the nozzle <NUM> may pass through the turbine <NUM> on its way to the cleaner <NUM>.

<FIG> shows an explosion view of a turbine <NUM> for a nozzle <NUM> of a vacuum cleaner <NUM>. The turbine <NUM> comprises an axis of rotation <NUM> around which a part <NUM> is rotatable. In present embodiment, said part <NUM> comprises air blades or vanes that are adapted to catch a stream of air passing through a housing <NUM>. The part <NUM> may be affixed to a shaft <NUM> that may be coupled to said brush roller <NUM> to provide a driving torque to set the brush roller <NUM> in motion. The brush roller <NUM> may be coupled rotatable, directly or by means of gears or similar, to the shaft <NUM>.

A magnetic brake <NUM> is affixed to said rotating part <NUM>. In a different embodiment, the brake <NUM> may also be affixed to a rotating part of the brush roller <NUM> or a rotating part of gears or wheels coupling the turbine <NUM> with the brush roller <NUM>. For the purposes of explaining present invention, reference will be made to the axis of rotation <NUM>, which may correspond to any rotating part <NUM> coupled to the brush roller <NUM> or the turbine <NUM>.

The magnetic brake <NUM> comprises two permanent magnets <NUM> mounted to the rotating part <NUM> and a conductive element <NUM> mounted to a fixed part, especially the housing <NUM>. A mechanism <NUM> may be provided for moving the magnets <NUM> between first and second positions. In the first position, a magnet <NUM> lies close to the axis of rotation <NUM> and is magnetically disengaged from the conductive element <NUM>, while in the second position, said magnet <NUM> lies further out in a radial direction with respect to the axis of rotation <NUM> and is magnetically engaged with the conductive element.

The conductive element <NUM> is preferred to be of the non-magnetic type and may comprise non-magnetic material like aluminium or brass. A ferrous material may also be used. Magnetic engagement occurs when a magnet <NUM> is moved with respect to the element <NUM>, so that eddy currents are caused in the element <NUM> through magnetic induction. Such electric currents will be transposed into heat almost instantaneously. The energy required to form the eddy currents is taken from the movement of the magnet <NUM> in close vicinity to the element <NUM> so that a braking force between the two elements is generated. The braking force may be dependent on the relative speed between the magnet <NUM> and the conductive element <NUM>, on the strength of the magnetic field of the magnet <NUM> and the distance between magnet <NUM> and element <NUM>.

It is preferred that the conductive element <NUM> is annulus shaped and lies in an axial direction from the magnets <NUM>. Dimensions of the annulus are preferred to be chosen such that the magnets <NUM> lie in the centre opening of the annulus when resting in the first position and adjacent to the body of the annulus when they are in the second position. A magnet <NUM> may have a magnetic orientation <NUM> that is defined as a line going through North and South poles of a magnet. The orientation <NUM> is preferred to lie parallel to the axis of rotation <NUM>, so that a pole of the magnet <NUM> is as close as possible to conductive material of the element <NUM> when the magnet <NUM> is in the second position.

The mechanism <NUM> guiding the magnets <NUM> between the first and second positions may comprise a lever <NUM> for each magnet <NUM>. The lever <NUM> has a first end that is connected to the magnet <NUM> and a second end that is hinged to the rotatable part <NUM>. For hinging, an axis <NUM> may be provided on the rotatable part <NUM>. The axis <NUM> is preferred to extend parallel to the axis of rotation <NUM>. In present embodiment, a radial distance of the axis <NUM> from the axis of rotation <NUM> may be roughly half the distance between first and second positions of a magnet <NUM>. The axis <NUM> may be spaced evenly on a circumference around the axis of rotation <NUM>. Lengths of the levers <NUM> and radial distances of the axis <NUM> from the axis of rotation <NUM> are preferred to be equal. Likewise, the magnets <NUM> are preferred to be equal in size, shape and mass. Magnetic strengths of the magnets <NUM> may also be comparable. The magnets <NUM> may comprise a metal or rare earth, like neodymium, so that magnetic forces may be high.

The levers <NUM> may be coupled mechanically through gears. In present embodiment, each lever <NUM> comprises teeth around a circumference of the associated axis <NUM>. One gearwheel <NUM> is centred on the axis or rotation <NUM> and its teeth intermesh with the teeth of each lever <NUM>. The centre gearwheel <NUM> may rotate freely around said axis of rotation <NUM> and may be held on the shaft <NUM>. By means of the intermeshing gears, all magnets <NUM> are coupled mechanically in such a way that their radial distances to the axis of rotation <NUM> will be kept identical and their spacing in a circumferential direction with be equal. Especially, angles between neighbouring magnets <NUM> with respect to the axis of rotation <NUM> may be kept at a predetermined value. An elastic element <NUM> may be provided to push, pull or swivel the magnets <NUM> radially inwards to the first position. A pin <NUM> may be provided on the rotating element <NUM> for the elastic element <NUM> to hook into. The elastic element <NUM> may act upon a lever <NUM> or on the centre gearwheel <NUM>. In present embodiment, one elastic element <NUM> is associated to each lever <NUM>.

An optional disc <NUM> may be placed axially between the magnets <NUM> and the conductive element <NUM>. The disc <NUM> may have cut-outs <NUM> in which the magnets <NUM> may lie. The cut-outs <NUM> may be shaped such that the magnets may move between first and second positions. In one embodiment, a cut-out <NUM> may guide an associated magnet <NUM> in its movement in a plane perpendicular to said axis of rotation <NUM>, thus forming a motion link for the magnet <NUM>.

A lid <NUM> may be provided to close the housing <NUM> on one axial end so that the rotating element <NUM> and the mechanism <NUM> are accommodated inside the housing <NUM>.

<FIG> shows a partly mounted turbine <NUM> with magnetic brake <NUM> elements in a first position. Pushed inward by the elastic elements, <NUM>, the magnets <NUM> lie in first positions radially close to the shaft <NUM> and close to the axis of rotation <NUM>. The centre gearwheel <NUM> may have cut-outs to allow the magnets <NUM> to move radially further in. The cut-outs may be in places that do not get in contact with teeth of the levers <NUM> if the magnets <NUM> are moved from first to second positions. This may be especially easily done if the number of magnets is two and a radius of the centre gearwheel <NUM> approximately matches a length of a lever <NUM>.

<FIG> shows an axial view (to the left) and a longitudinal section (to the right) of a turbine <NUM> with magnetic brake <NUM> elements in the first position.

In the axial view, the lid <NUM> is removed so that the magnets <NUM> can be seen through a centre opening of the annulus shaped element <NUM>. The magnets <NUM> lie in the above-mentioned cut-outs in the gearwheel <NUM>. The longitudinal section goes through a plane denoted A-A in the axial view.

<FIG> shows a partly mounted turbine <NUM> with magnetic brake <NUM> elements in a second position. <FIG> corresponds to <FIG> apart from the position of the magnetic brake <NUM> elements. Here, magnets <NUM> lie in larger radial distances to the axis of rotation <NUM> than in the first position. If the conductive element <NUM> is mounted, poles of the magnets <NUM> lie in close axial proximity to the conductive material of the element <NUM>.

It can be seen that cut-outs in the centre gearwheel <NUM>, in which the magnets <NUM> may be disposed when resting in the first position, do not limit movability of the levers <NUM> and allow their teeth to keep intermeshing with the gearwheel <NUM>.

Claim 1:
A turbo nozzle (<NUM>) for a vacuum cleaner (<NUM>), the nozzle (<NUM>) comprising a brush roller and a turbine (<NUM>) for setting the roller in rotational motion; wherein the turbine (<NUM>) is adapted to be traversed by a stream of air travelling through the nozzle (<NUM>); the nozzle (<NUM>) further comprising a magnetic (<NUM>) brake for limiting rotational speed of the roller; wherein the magnetic (<NUM>) brake comprises a permanent magnet (<NUM>) affixed to a rotating part of the turbine (<NUM>) or the roller and a conductive element (<NUM>) affixed to a stationary part of the nozzle (<NUM>); such that the moving magnet (<NUM>) causes an eddy current in the conductive element (<NUM>) wherein said turbo nozzle (<NUM>) comprises a centrifugal displacement mechanism (<NUM>) that is adapted to move the magnet (<NUM>) towards the conductive element (<NUM>) in answer to centrifugal forces acting upon the magnet (<NUM>) .