Cleaning device for cleaning a surface

1. A nozzle arrangement for a cleaning device, the nozzle arrangement comprising:

a nozzle housing,

a brush rotatable about a brush axis, the brush being provided with flexible brush elements having tip portions for contacting the surface to be cleaned and picking up dirt and/or liquid particles from the surface during the rotation of the brush, wherein the brush is at least partly surrounded by the nozzle housing and protrudes at least partly from a bottom side of the nozzle housing,

a drive unit for rotating the brush,

a squeegee element which is spaced apart from the brush and attached to the bottom side of the nozzle housing on a first side of the brush where the brush elements enter the nozzle housing during the rotation of the brush, wherein the squeegee element is configured for wiping dirt and/or liquid particles across or off the surface to be cleaned during a movement of the cleaning device

a deflector for contacting the brush and deflecting the brush elements during the rotation of the brush, and

a restriction element for at least partly restricting air from getting sucked into the nozzle housing at a second side of the brush where the brush elements leave the nozzle housing,

wherein the restriction element is, seen in a rotation direction of the brush, arranged behind the deflector, such that the brush elements, during the rotation of the brush, contact the deflector before passing the restriction element and then leaving the nozzle housing at the bottom side,

characterized in that the restriction element comprises a mechanically flexible element that is, due to its flexibility, configured to follow an outer surface of the brush and to contact the tip portions during the rotation of the brush.

2. The nozzle arrangement as claimed in claim 1 , wherein the mechanically flexible element is made of a sheet of fabric material, rubber or plastic.

3. The nozzle arrangement as claimed in claim 1 , wherein the deflector is made of a mechanically flexible material.

4. The nozzle arrangement as claimed in claim 1 , wherein the restriction element comprises a plurality of slits that are arranged parallel to each other and perpendicular to the brush axis.

5. The nozzle arrangement as claimed in claim 1 , wherein the restriction element and the deflector are arranged on the second side of the brush where the brush elements leave the nozzle housing during the rotation of the brush, wherein the second side is opposite to the first side with respect to the brush axis.

6. The nozzle arrangement as claimed in claim 1 , wherein the squeegee element comprises a switching unit for switching the squeegee element to a closed position, in which the squeegee element is configured to push or wipe dirt and/or liquid particles across or off the surface to be cleaned, when the cleaning device is moved on the surface in a forward direction, in which the squeegee element is, seen in the direction of movement of the cleaning device, located behind the brush, and for switching the squeegee element to an open position, in which dirt and/or liquid particles from the surface to be cleaned can enter the suction area through an opening between the squeegee element and the surface, when the cleaning device is moved on the surface in a backward direction, in which the squeegee element is, seen in the direction of movement of the cleaning device, located in front of the brush.

7. The nozzle arrangement as claimed in claim 1 , wherein a linear mass density of a plurality of the brush elements is, at least at the tip portions, lower than 150 g per 10 km, preferably lower than 20 g per 10 km.

8. The nozzle arrangement as claimed in claim 1 , wherein the drive unit is adapted to realize a centrifugal acceleration at the tip portions of the brush elements which is, in particular during a dirt release period when the brush elements are free from contact to the surface during rotation of the brush, at least 3,000 m/s 2 , more preferably at least 7,000 m/s 2 , and most preferably 12,000 m/s 2 .

9. The nozzle arrangement as claimed in claim 1 , wherein the drive unit is adapted to realize an angular velocity of the brush which is in a range of 3,000 to 15,000 revolutions per minute, more preferably in a range of 5,000 to 8,000 revolutions per minute, during operation of the device.

10. The nozzle arrangement as claimed in claim 1 , wherein the brush has a diameter which is in a range of 10 to 100 mm, more preferably in a range of 20 to 80 mm, most preferably in a range of 35 to 50 mm, when the brush elements are in a fully outstretched condition during the rotation of the brush, and wherein the length of the brush elements is in a range of 1 to 20 mm, preferably in a range of 8 to 12 mm, when the brush elements are in a fully outstretched condition during the rotation of the brush.

11. The nozzle arrangement as claimed in claim 1 , wherein a packing density of the brush elements is at least 30 tufts of brush elements per cm 2 , and wherein a number of brush elements per tuft is at least 500.

12. A cleaning device for cleaning a surface, the cleaning device comprising:

the nozzle arrangement as claimed in claim 1 ; and

a vacuum aggregate for generating an under-pressure in a suction area between the nozzle housing and the brush.

13. The cleaning device as claimed in claim 12 , wherein the vacuum aggregate is configured to generate an under-pressure in a range of 3 to 70 mbar, preferably in a range of 4 to 50 mbar, most preferably in a range of 5 to 30 mbar.