The present invention relates to an automatic filter cleaning system. The cleaning system may be used with a vacuum cleaner. The filter cleaning system cleans the filter by blowing air backwards through the filter ("back flow filter cleaning").

Background of the Invention

Filter cleaning is becoming more important as the requirements regarding filtration levels are increased. Thus, the importance of cleaning the filter becomes important in order to maintain a high air flow through the filter (i.e. to avoid that the filter is getting clogged).

Today, several systems are available. WO 2008/014794 Al discloses a system with a large solenoid opening a valve positioned aboye the filter. When opening the yalve, the air flows into the tank due to the effect of under pressure. Thus, the filter is thereby cleaned by "blowing" the dust into the tank. Generally, this system has proven to be effective, but complex and expensive control electronics are required.

W 2010/028787 Al discloses another system, said system being effective, but highly com- plex and expensive as it requires 2 filters, an electrical actuated direction valve and a solenoid valve to open for the "back flow" in order to clean the filter. Furthermore, complex and expensive control electronics are needed to render the system operational.

GB 1 259 557 A discloses an air filtering installation comprising a motor, which rotates a hammer, said hammer being fastened to a leaf-spring. During the rotation, the hammer slides along the guide surface and edge, thus, resulting in the conversion of the rotational movemen of the hammer into an axial movement of said hammer. The hammer controls the tension of the leaf-spring, and thereby the opening of the plate valve. However, leaf-springs possess some disadvantages, i.a. proper adjustment is difficult, and, thus, alternatives are needed. As apparent from the above, simple, effective and less expensive filter cleaning systems are needed. By the present invention, such is provided.

Object of the Invention

It is an object for the present invention to provide a back flow automatic filter cleaning system being simple, durable and cost-effective. Furthermore, the system of the present invention neither does incorporate nor require any control electronics. Description of the Invention

In a first aspect, the present invention relates to automatic filter cleaning systems, said system comprising an electrical motor configured to drive or rotate, directly or indirectly, a piston which is configured to control the compression of one or more compression spring(s) and one or more filter cleaning vaive(s) configured to open for one more filter cleaning back flow air stream(s) to flow into one or more filter(s), where said one or more filter cleaning valves are configured to be activated, directly or indirectly, by the piston and a piston guide, whereby the piston guide and the one or more compression spring(s) are arranged to convert the rotary movement of the piston into an axial movement of the piston. According to the invention, the piston is spring-loaded by one or more compression spring(s). The axial movement of the piston determines the compression level of the one ore more spring(s). The one or more filter cleaning valve(s) may be configured to open for a filter cleaning back flow air stream in order to clean the filter. The filter cleaning valve(s) may suitably be configured to be activated by the piston. A piston guide ensures the conversion of the rotary movement of the spring-loaded piston into an axial movement. When the piston hits the filter cleaning valve, it opens for a short period of time, thus creating a "hammer effect" that will overcome the flow forces acting on the filter cleaning valve.

In another embodiment according to the invention, the piston comprises a piston slide feature that is configured to only slide on the piston guide sliding surface during a spring compression phase of one rotation of the piston. Accordingly, the piston is provided with a piston slide feature adapted to slide on the piston guide sliding surface provided at the piston guide.

In one preferred embodiment according to the invention, the piston comprises a piston slide feature that is configured to only slide on the piston guide sliding surface during a spring compression phase of one rotation of the piston.

Accordingly, the piston guide is provided with a piston guide non-sliding surface. When the piston slide feature, during rotation, has reached the piston guide non-sliding surface, the en- ergy accumulated in the compression spring and piston is released. Accordingly, the piston moves down and hits the filter cleaning valve causing the filter cleaning valve to open shortly. Depending on the rotation speed of the electrical motor and the number of slide/non sliding surfaces on the piston guide, the time interval between each filter cleaning can be controlled by simple mechanical means.

By way of example the time interval between each filter cleaning may be 20-30 seconds. Moreover, if customers do not want to use the automatic filter cleaning system a simple inexpensive switch can be worked in to stop the electrical motor.

The piston guide non- sliding surface may be a steep surface onto which the piston cannot slide on.

In another embodiment according to the invention, the outer part of the piston is made of a plastic material and has a piston core made of a material with higher density e.g. a metal.

The plastic material is suitably selected from any conventional plastic material suited for the purpose of this invention. Representative, but non-limiting, examples include PET (polyethylene terephthalate), PE (polyethylene), HDPE (high-density polyethylene), PVC (polyvinyl chloride), LDPE (low-density polyethylene), PP (polypropylene), PS (polystyrene), PE/ABS (polyethyiene/acrylonitrile butadiene styrene), and PC/ABS (poiycarbonate/acryionitrile butadiene styrene), The metal may suitably be selected from iron or titanium and various alloys thereof. The weight of the piston shall be sufficient to generate a desired and suitable "hammer effect" of the piston. The electrical motor is preferably an alternating current (AC) synchronous motor, Furthermore, said motor may preferably be connected directly to the main power supply. Even more preferred, said motor is such which does not require any control electronics to be operational for the purpose of the present invention.

The electrical motor to be used in accordance with this invention may be equipped with an inbuilt gearbox configured to reduce speed and increase torque. One well-known example of an AC motor is the one provided by a conventional vacuum cleaner. In another embodiment according to the invention, the filter cleaning valve is made of a plastic material. Suitable plastic materials are mentioned above. The plastic material selected should have sufficient sealing properties.

The weight of the piston may be larger than 150g, depending on the application. Test has shown that this weight in most applications creates sufficient weight to obtain the necessary "hammer effect", by which the piston is able to open the filter cleaning valve shortly and effectively.

In yet another embodiment according to the invention, the compression spring(s) have a com- bined spring constant larger than 3 N/mm. Hereby, sufficient energy can be accumulated in the spring to be released to open the filter cleaning valve.

It may be an advantage that a return spring is arranged to facilitate the piston to be returned the return to its initial position (Position 1) by pushing toward the distal end of the piston. Hereby, return of the piston can be achieved by using simple mechanical means.

It may be beneficial that the return spring is arranged at the bottom portion of the piston guide. Hereby, a simple and reliable construction can be provided. It may be advantageous that the piston slide feature protrudes from the piston and extends radially with respect to the longitudinal axis of the piston. The invention is not limited to the above-described, but may be modified in various ways,

Description of the Drawing

Preferred embodiments of the present invention are described with reference to the accompanying drawings, wherein:

Figure 1 shows a vacuum cleaner in ISO view;

Figure 2 shows a vacuum cleaner in side view with and without tank;

Figure 3 shows a vacuum cleaner top view with indication for cross sectional view;

Figure 4 shows the cross sectional view defined in Figure 3;

Figure 5 shows internal parts of the vacuum cleaner and the filter cleaning valve

actuator;

Figure 6 shows the filter cleaning system in Position 1;

Figure 7 shows the filter cleaning system in Position 2;

Figure 8 shows the filter cleaning system in Position 3;

Figure 9 shows the piston guide and piston slide and

Figure 10 shows the movement of the piston and filter cleaning valve during use Detailed Description of the Invention

Figure 1 illustrates a vacuum cleaner 1 in an ISO view consisting of a head 2 and a tank 4 with a suction hose 3.

Figure 2 illustrates the vacuum cleaner 1 without the tank 4, thereby showing the filter 21, which during suction of dust will become clogged, and thus, may need to be cleaned in order restore sufficient air flow/suction of the vacuum cleaner 1. The finer the dust is, the faster the filter 21 gets clogged, resulting in a decrease of suction.

In Figure 3, shows a top view of the vacuum cleaner I showing a section cutting plane A- A indicated in Figure 4. In Figure 4, the cross sectional view A-A of Figure 3 is shown. The vacuum cleaner motor 41 creating the air suction in the vacuum cleaner 1 is illustrated. The filter 21 filtering the air, before exhausted, flowing into the vacuum cleaner 1 is also shown. The filter cleaning valve 42 is also shown. When the filter cleaning valve 42 opens, the filter cleaning back flow air stream flows into the filter and backwards through the filter due to under pressure inside the tank. Thus, the filter 21 is cleaned. A filter cleaning actuator 43 is also visualised.

In Figure 5, the head 2)is shown. Several parts have been omitted to better illustrate the filter cleaning actuator 43. The filter cleaning actuator 43 is composed of an electrical motor 53, a piston 52 and a piston guide 51. The shaft of the electrical motor 53 rotates the piston 52 in the direction shown by the piston rotation direction arrow 54.

In Figure 6, Position 1 for the piston 52 in the filter cleaning actuator 43 is shown. In Position 1, the compression spring 61 is not compressed. A return spring 62 is also shown, facilitating the return to Position 1 of the piston 52 . The piston 52 may have an inner piston core 64 made of a higher density material to increase the weight of the piston, and thereby the impact of the piston 52 when hitting/opening the filter cleaning valve 42. A piston shaf 63 connected to the shaft of the electrical motor 53 drives the piston 52. In Position 1 of the piston 52, the filter cleaning valve 42 is closed.

In Figure 7, Position 2 for the piston 52 is shown. The compression spring 61 is now fully compressed, as the Piston 52 has moved up (shown by direction arrow 71 ) due to the axial rotation of the piston 52 and the shape of the piston guide 51. The filter cleaning valve 42 is closed.

In Figure 8, Position 3 for the piston 52 is shown. The energy accumulated during the spring compression phase is now released and the piston 52 moves down (shown by direction arrow

81) . Thereby, the filter cleaning valve 42 is activated and opened (show by direction arrow

82) . A "hammer effect" is created by the piston 52 on the filter cleaning valve 42, forcing it to open shortly. The filter cleaning air steam 83 enters the inside of the filter 21 shortly and cleans the filter 21 due to the under pressure inside the tank 4. This filter cleaning operation is accomplished in a very short lime and the piston 52 returns to Position 1, whereby the filter cleaning valve 42 closes.

In Figure 9, a more detailed view of the filter cleaning actuator 43 is shown. As can be seen, the piston 52 has a piston slide feature 92 enabling sliding on a piston guide sliding surface 91 on the piston guide 51. The piston guide 51 also has a piston guide non-sliding surface 93, e.g. a steep surface onto which the piston 5) canno slide on. When the piston slide feature 92, during rotation, has reached the piston guide non-sliding surface 93, the energy accumulated in the compression spring 61 and piston 52 is released, and the piston 52 moves down and hits the filter cleaning valve 42, thereby opening it shortly. Thus, depending on the rotation speed of the electrical motor 53 and the number of slide/non sliding surfaces 91, 92 on the piston guide 51, the time between each filter cleaning can be controlled. In general, the period could suitably be 20-30 seconds. In the shown system, no complex control electronics are needed to control the electrical motor 53 as it just runs continuously when the vacuum cleaner (1) is turned on. If customers do not want to use the automatic filter cleaning system, a simple inexpensive switch configured to stop the electrical motor 53 can be integrated.

Figure 10 illustrates the cycle if the piston 52 and the filter cleaning valve 42. In Figure 10, the piston 52 starts the cycle in Position I. The filter cleaning valve 42 is closed. Due to the rota- tion of the piston 52, the piston will gradually compress the compression spring 61 until the maximum compression is reached in Position 2. The filter cleaning valve 42 remains closed. Thus, Position 1 through Position 2 is denoted the spring compression phase 101 . The piston 52 is then released from the sliding surface on the piston guide 51 and moves down to Position 3, thereby also activating/opening the filter cleaning valve 42. Due to the return spring 62 and the flow forces on the filter cleaning valve 42, the piston 51 rapidly returns to Position 1. The filter cleaning valve 42 is thereby opened shortly and creates an impulse cleaning of the filter 21. The suction performance of the vacuum cleaner 1 is only reduced shortly. Thus, Position 2 through Position 1 via Position 3 is the spring decompression phase 102. NOMENCLATURE

1. Vacuum cleaner

2. Head

3. Hose

4. Tank

21. Filter

41. Vacuum cleaner motor

42. Filter cleaning valve

43. Filter cleaning actuator

51. Piston guide

52. Piston

53. Electrical motor

54. Piston rotation direction arrow

61. Compres sion spring

62. Return spring

63. Piston shaft

64. Piston core

71. Piston direction upwards movement 81. Piston direction downwards movement

82. Fi lter cleaning valve open movement

83. Filter cleaning back flow air stream

91. Piston guide sliding surface

92. Piston slide feature

93. Piston guide non sliding surface 101; Spring compression phase

102: Spring decompression phase