SELF-CLEANING FILTER ELEMENT FOR A VACUUM CLEANING

DEVICE

This invention relates, on the one hand, to a self-cleaning filter element for a vacuum cleaning device, comprising a filter medium provided on a fixing section, which filter medium is movable between a first and second position, and comprising return means which are provided in order to return the filter medium from the second position to the first position. On the other hand, this invention relates to a vacuum cleaning device provided with such a filter element.

This invention relates in particular to a self-cleaning filter element for a central vacuum cleaning system.

In a central vacuum cleaning system a central vacuum cleaning unit (the vacuum cleaner without the hose) is placed in the garage, in the loft or in the cellar, while PVC tubes connect the connection points fitted in the rooms to the central vacuum cleaning unit. The system is started automatically by inserting a flexible suction hose into a vacuum socket or by operating a switch on the handle of the flexible hose.

The sucked-up dust particles are centrifuged and collected in the waste bin of the central vacuum cleaning unit. A filter element provides secondary filtering (fine filtering) and will ensure that dust is not sucked towards the motor. The known filter elements comprise, on the one hand, a filter medium fixed on a metal ring and, on the other hand, a cloth bag sewn on the underside (which is the side where the dust collected in the waste bin comes into contact with the filter medium) of the filter medium, in which cloth bag a number of metal discs are assembled. In the idle state the filter bulges downwards through the force of gravity.

When the vacuum cleaning unit is switched on, air is sucked in through the pores of the filter medium and a partial vacuum is created above the filter element. When the pores are sufficiently soiled/blocked, the partial vacuum will ensure that the filter element bulges in the opposite direction (i.e. that the filter now bulges upwards). When the vacuum cleaning unit is switched off, the motor will slow down and come to a standstill after a few seconds. The partial vacuum will also decrease in direct

proportion to this motor movement. The result of this is that, under the influence of the weight of the cloth bag, the filter medium will return to its original position (bulging downwards).

Such known filter elements have a self-cleaning characteristic, owing to the fact that each time the vacuum cleaning unit is switched on and off the filter medium is partially cleaned. When the motor is switched on, the filter medium abruptly changes shape, and this movement causes a vibration, so that a large part of the collected dusts falls off the filter medium. A second cleaning occurs when the motor is switched off, when the filter medium will change shape again, so that the filter medium will again release dust particles, albeit to a lesser extent.

This method of cleaning has the great disadvantage that the greatest cleaning of the filter medium occurs at the time when the vacuum cleaning unit is started up. The dust is knocked off and begins a falling movement, but since the motor is running, the falling dust particles will immediately be sucked in again up against the filter medium. The second cleaning, when the motor is switched off, is then just not powerful enough to clean the filter sufficiently.

In order to achieve better cleaning, BE 570 906 and WO 95/34238, inter alia, disclose providing the filter element with a resilient element on its external surface.

The object of this invention is to provide a self-cleaning filter element, which filter element can be cleaned in a more efficient manner.

The object of the invention is achieved by providing a self-cleaning filter element for a vacuum cleaning device, comprising a filter medium provided on a fixing section, which filter medium is movable between a first and second position, and comprising return means which are provided to return the filter medium from the second position to the first position, the abovementioned return means being resiliently connected to the filter medium and/or fixing section, and the abovementioned filter element comprising at least one resilient element which can assume at least two stable positions. Connecting the return means resiliently to the filter medium and/or fixing section means that when the vacuum cleaning device is switched off, additional

vibrations will be generated, so that the greatest cleaning of the filter medium now occurs at the time when the vacuum cleaning device is switched off, with the result that the falling dust particles are no longer sucked in. This has the advantage that the transition from the one stable position to the other stable position results in a stroke movement leading to a swelling vibration in the resilient element and the filter medium. In this way even more dust will be released during both the switching on and the switching off of the vacuum cleaning device.

In a more preferred self-cleaning filter element according to this invention, the abovementioned resilient element can assume a first and second stable position, the first and second stable positions corresponding to the first and second positions of the filter medium respectively.

In a particular embodiment of the self-cleaning filter element according to this invention, the abovementioned filter element comprises two resilient elements disposed in the shape of a cross.

In a most particular embodiment of the self-cleaning filter element according to this invention, the abovementioned resilient element is a flexible lamella. The flexible lamella is preferably made of spring steel. In particular, the resilient element is of a stepped design.

In a particularly advantageous embodiment of the self-cleaning filter element according to this invention the abovementioned filter medium is a filter cloth.

In a more particularly advantageous embodiment of the self-cleaning filter element according to this invention the abovementioned return means comprise one or more elements with a total weight of at least 400 grams. The total weight preferably lies between 400 and 600 grams.

Another subject of this patent application relates to a vacuum cleaning device provided with a self-cleaning filter element comprising a filter medium provided on a fixing section, which filter medium is movable between a first and second position, and comprising return means which are provided to return the filter medium from the

second position to the first position, the abovementioned return means being resiliency connected to the filter medium and/or fixing section, and the abovementioned filter element comprising at least one resilient element which can assume at least two stable positions. Such a device has the great advantage that the filter element will be cleaned much more efficiently, with the result that the service life of the filter element will be extended. Moreover, the vacuum cleaning device will perform better, and the system also has an energy-saving effect.

In a preferred embodiment the vacuum cleaning device according to this invention comprises a self-cleaning filter element of the type described above.

The invention will now be explained in greater detail by means of the detailed description below of a number of preferred embodiments of a self-cleaning filter element according to this invention. This description is intended purely to give clarifying examples and to pinpoint further advantages and details of possible embodiments, and can therefore in no way be interpreted as a limitation of the field of application of the invention or of the patent rights applied for in the claims.

In this detailed description reference numerals are used to refer to the appended drawings, in which:

Figure 1 is a view of a self-cleaning filter element according to this invention;

- Figure 2 is a view of a lamella which is provided in the self-cleaning filter element according to this invention; - Figure 3 shows a graph of the theoretical functioning of the filter element;

- Figure 4 is a view of a vacuum cleaner unit provided with a self-cleaning filter element according to this invention.

The self-cleaning filter element (1) for a vacuum cleaning device, and as shown in Figure 1, comprises a filter medium (3) provided on a fixing section (2), which filter medium is movable between a first and second position, and comprises return means (4) which are provided to return the filter medium (3) from the second position to the first position.

The fixing section (2) is preferably of an annular design, but depending on the design of the vacuum cleaning device, it can also be, for example, of a square design. A possible fixing section (2) is a metal ring with a thickness of 3 mm (for strength) and a diameter of 320 mm. Of course, these values can vary depending on the dimensions of the vacuum cleaning device.

The filter medium (3) is preferably a filter cloth made of a fabric (e.g. TG 190 - "tissu de filtration densite 190" - filter fabric density 190). The filter cloth is sewn around the metal ring by means of an overlap and forms, as it were, a convex surface with a depth (in the first position)/height (in the second position) of, for example, 60 mm. The filter cloth is furthermore provided with a loop-shaped element (not shown in the figures), usually also made of a fabric, so as to enable the filter element to be removed easily.

The return means (4) are preferably designed as a dead weight, for example in the form of one or more disc-shaped elements. The dead weight has a total weight lying between 400 and 600 grams, and is preferably 580 grams. It is important for the functioning of the system for the dead weight to be situated on the top side of the filter cloth (3). It should be pointed out here that the underside of the filter cloth (3) is the side facing the waste bin (10) of the vacuum cleaning device.

In order to obtain efficient self-cleaning of the filter element (1), the disc-shaped element (4) is resiliently connected by means of a lamella system to the filter medium (3) and/or fixing section (2). The lamella system preferably comprises two flexible lamellae (5) which are disposed in the form of a cross and are connected at their ends to the filter cloth (3) and/or the metal ring (2) by means of, for example, plastic or metal rivets. The lamellae (5) used are in fact bistable lamellae and for this purpose, as shown in Figure 2, are of a stepped design in two places (A, B). This enables them to assume a first and second stable position. The lamellae (5) are connected to each other at their centre point (6) by means of, for example, a bolt (7) and nut connection. The same bolt (7) can be used for fixing the dead weight (4) to them. The lamellae (5) used are made of spring steel and have, for example, a thickness of 0.4 mm and a width of 12 mm.

The filter element (1) is in principle placed in a vacuum cleaning unit (11) in a similar way to that of the currently known filter elements. The filter element (1) is placed (see Figure 4) so that the loop-shaped element is situated on the underside and the lamella system together with the disc-shaped element (4) is situated above the filter cloth (3). In the idle position the lamellae (5) of the lamella system are situated in their first stable position.

When the vacuum cleaning unit is switched on, the filter element (1) according to the invention behaves largely in the same way as the known filter elements. The partial vacuum above the filter element (1) sucks in air through the pores of the filter until said pores are sufficiently saturated/blocked and the filter cloth (3) passes from its first position to its second position, in which the filter cloth (3) bulges upwards. This results in the lamellae (5) of the lamella system also passing from their first stable state to their second stable state.

When the vacuum cleaning unit is switched off, the motor will slow down and the partial vacuum created will decrease accordingly. Although the filter cloth (3) is no longer under pressure, the filter cloth (3) will initially retain its shape through the fact that for the most part the sucked-in dust particles remain adhering to the underside of the filter cloth and ensure that the filter cloth becomes slightly harder and retains its second position. However, under the influence of the weight of the disc-shaped element (4), the filter cloth (3) will return to its original position (first position), and at the same time the lamellae (5) of the lamella system change to their first stable position. All this happens in a few seconds and results in one great stroke movement and a swelling vibration in the lamellae (5) and filter cloth (3).

This stroke movement can be seen clearly in Figure 3, which is a graph with the vertical axis being the distance travelled by the lamellae (test carried out on filter element provided with two lamellae made of spring steel, 0.2 mm x 10 mm) and the horizontal axis being the time axis. The solid line (8) shows the position of the centre point (6) of the lamellae (5). The dashed line (9) shows the relative speed. It is clear from this graph that the lamellae (5) in each case still continue to vibrate for a time after the first stroke and therefore ensure that the filter cloth (3) is effectively cleaned at the time of switching off of the appliance.

The self-cleaning characteristic of the filter element (1) according to this invention is to be found at two times, namely when the motor (12) is switched on cleaning occurs through the sudden occurrence of a partial vacuum. The second cleaning occurs just after the motor (12) is switched off, after the lamellae (5) have become deformed again to their original shape and with an abrupt movement deform the filter cloth (3) again.

The great advantage of this new self-cleaning filter element (1) is in the moment of cleaning. The filter cloth (3) has to process an abrupt stroke when the motor (12) is started up, with the result that fine dust particles are released. However, this occurs at the very moment when the motor (12) is going into operation again and will suck up the floating particles again. The actual cleaning in the case of the filter element (1) according to this invention occurs after the motor is switched off, i.e. when no suction is any longer present and the released dust particles therefore cannot be sucked up again.

The self-cleaning filter elements (1) can be placed in the existing vacuum cleaning device to replace the known filter elements. It is, however, also possible to adapt the known filter elements by providing them with a lamella system and weight such as described above.