Floor cleaning machine with a device for determining the level in a dirty water tank

Abstract

A floor cleaning machine (1) for cleaning a floor surface is shown and described, comprising a cleaning device (11) for engaging with the floor surface (9) to be cleaned, a receiving device (15) for receiving liquid from the floor surface (9) to be cleaned, a wastewater tank (25) for receiving liquid received by the receiving device (15), a vacuum device (29) configured to generate a vacuum in the wastewater tank (25) above the maximum level, so that liquid is conveyed from the receiving device (15) to the inlet (27) and into the wastewater tank (25), a first pressure sensing device (31) arranged to detect the pressure in the wastewater tank (25) above the maximum level, and a second pressure sensing device (33) connected to the interior of the wastewater tank (25) via a line (35).with a device (41) for determining the pressure difference between the pressures detected by the first and second devices, wherein the line (35) has an opening (37) directed towards the wastewater tank (25), wherein the line (35) has a first section (39) which, when the floor surface (9) to be cleaned is horizontal and the floor cleaning machine (1) is arranged on this floor surface (9), extends vertically, and wherein the line (35) has a second section (43) between the first section (39) and the opening (37), which is designed such that, when the floor surface (9) to be cleaned is horizontal and the floor cleaning machine (1) is arranged on this floor surface (9), the second section (43) extends horizontally or rises from the opening (37),wherein the tangents to the second section (43) between a starting point (43') and an end point (43") of the second section (43) are inclined at less than 25° to the horizontal.

Description

[0001] The present invention relates to a floor cleaning machine for cleaning a floor surface, wherein the floor cleaning machine is designed to be moved over a floor surface to be cleaned and preferably has a chassis, with a cleaning device for engaging with the floor surface to be cleaned, with a receiving device for receiving liquid from the floor surface to be cleaned, with a dirty water tank for receiving liquid received by the receiving device, wherein the dirty water tank is connected to the receiving device via a connecting line and wherein the connecting line opens into the dirty water tank at an inlet which is arranged above a maximum level for liquid in the dirty water tank, with a vacuum device which is designed to generate a vacuum in the dirty water tank above the maximum level,so that liquid is pumped from the receiving device to the inlet and into the waste water tank.

[0002] For example, EP 3 335 611 A1 discloses floor cleaning machines comprising a dirty water tank, a suction device connected to a dirty water tank via a suction line, and a measuring device that detects a differential pressure between the dirty water tank and the suction line.

[0003] Such floor cleaning machines are well known from the prior art, such as EP 3 335 611 A1. With the help of the cleaning device, which may, for example, be a brush head with driven brushes, dirt is removed from the floor surface to be cleaned, with cleaning fluid being applied to the floor surface to be cleaned in the area of ​​the brush head or cleaning device. The receiving device, which is arranged behind the cleaning device as seen in the normal direction of travel of the floor cleaning machine, then serves to collect the fluid applied in the area of ​​the cleaning device, which then also contains the previously removed dirt, with this dirt-laden fluid then being pumped into the dirty water tank.

[0004] Due to the dirt contained in the liquid that is collected by the receiving device and pumped into the recovery tank, it is not possible to incorporate complex mechanical devices for determining the fill level in the recovery tank, as such devices would quickly become inoperable due to the dirt. On the other hand, in order to inform the user of the fill level in the recovery tank during machine operation, it is still desirable to be able to perform a fill level measurement. This allows the fill level to be determined based on the gravity pressure of the liquid in the recovery tank and a measurement of this.However, since in such a floor cleaning machine dirty liquid is drawn into the dirty water tank with the help of a suction device or suction turbine, which creates a negative pressure above the liquid level in the dirty water tank, it is necessary to correct the recorded gravitational pressure accordingly by the negative pressure. In order to determine the correct fill level from the recorded gravitational pressure of the dirty water liquid, the pressure above the liquid level in the dirty water tank that is created by the suction device or the suction turbine must also be recorded at the same time, although this negative pressure fluctuates. In particular, the negative pressure above the liquid level depends on how closely the suction device lies against the floor surface to be cleaned, i.e. whether the volume surrounded by the suction device is more or less well sealed off from the environment.If the floor surface to be cleaned is uneven and the sealing lips provided on the receiving device, for example, cannot seal the volume surrounded by them well, the vacuum device or the suction turbine can only generate a comparatively low negative pressure within the dirty water tank, whereas in the case where there is a smooth surface that is also comparatively flat, a better seal can be achieved and thus a greater negative pressure is generated within the dirty water tank.

[0005] In this context, the term "negative pressure" refers to the pressure by which the pressure inside the wastewater tank is below the ambient pressure. Therefore, the greater the negative pressure in the wastewater tank, the lower the absolute pressure in the wastewater tank compared to the ambient pressure.

[0006] It is now known from the prior art that the gravitational pressure of the liquid is measured by providing a measuring line which extends into the wastewater tank and has a first section which extends essentially vertically from the opening of the line towards the internal volume of the wastewater tank. This measures the gravitational pressure of the liquid in the wastewater tank in the region of the inlet opening in the line. At the same time, the pressure above the liquid level in the wastewater tank is measured in order to determine the negative pressure exerted on the wastewater due to the suction device. Using a differential pressure measuring device, the difference between the two measured pressures is determined, so that only the gravitational pressure of the wastewater can be determined. From this, the level in the wastewater tank and thus the fill level can be determined.

[0007] This has now become apparent that significant measurement inaccuracies occur. In particular, it has been discovered that the previously described system incorrectly determines the actual fill level in the wastewater tank. This can lead to the actual fill level in the wastewater tank being continuously overestimated or underestimated due to the pressure measurement.

[0008] Therefore, the object of the present invention is to provide a floor cleaning machine with an improved device for determining the fill level in the dirty water tank.

[0009] This object is achieved by a floor cleaning machine for cleaning a floor surface, wherein the floor cleaning machine is designed to be moved over a floor surface to be cleaned and preferably has a chassis, with a cleaning device for engaging with the floor surface to be cleaned, with a receiving device for receiving liquid from the floor surface to be cleaned, with a dirty water tank for receiving liquid received by the receiving device, wherein the dirty water tank is connected to the receiving device via a connecting line and wherein the connecting line opens into the dirty water tank at an inlet which is arranged above a maximum level for liquid in the dirty water tank, with a vacuum device which is designed to generate a vacuum in the dirty water tank above the maximum level,so that liquid is pumped from the receiving device to the inlet and into the waste water tank.

[0010] Furthermore, the floor cleaning machine according to the invention comprises a first pressure detection device arranged such that it is suitable for detecting the pressure in the dirty water tank above the maximum level, a second pressure detection device connected via a line to the interior of the dirty water tank, and a device for determining the pressure difference between the pressures detected by the first and second devices, wherein the line has an opening directed towards the dirty water tank, wherein the line has a first section which, when the floor surface to be cleaned is horizontal and the floor cleaning machine is arranged on this floor surface, runs vertically, and wherein the line has a second section between the first section and the opening which is designed such that, when the floor surface to be cleaned is horizontal and the floor cleaning machine is arranged on this floor surface,the second section is horizontal or rises from the opening, with the tangents to the second section between a starting point and an end point of the second section being inclined by less than 25° to the horizontal.

[0011] According to the last characteristic, if the second section extends along a straight line, it is inclined by less than 25° to the horizontal. However, if the second section is curved, the last characteristic results in the tangents to the second section between its start and end points being inclined by less than 25°. In any case, this ensures that between the opening of the pipe and the vertical section provided therein there is a second section, which can be straight or curved and which has a slight inclination to the horizontal. The start point of the second section is the point of this section closest to the opening of the pipe leading into the interior of the waste water tank, while the end point is the point of the second section furthest from the opening.

[0012] The structure according to the invention solves the following problem which occurs in the prior art with a vertical first section provided near the inlet opening in the line from the waste water tank to the first pressure measuring device.

[0013] As the dirty water tank progressively fills during operation of the floor cleaning machine, a level is eventually reached in the dirty water tank at which the water reaches the opening to the line, and the opening is sealed off by the dirty water, preventing the air in the dirty water tank from entering. At this point, the pressure in the line to the second pressure sensing device is equal to the pressure generated by the vacuum device just above the liquid level. However, as already explained, this pressure depends on how well the receiving device is in contact with the floor surface to be cleaned.

[0014] For example, it is conceivable that at the time the dirty water in the dirty water tank closes the opening in the line, the receiving device has poor contact with the floor surface to be cleaned. In this case, the negative pressure in the line is comparatively low. If the dirty water tank continues to fill during operation with the contact between the receiving device and the floor surface to be cleaned remaining the same, the pressure in the line and also the level in it rises. The differential pressure is then determined using the two pressure measuring devices, whereby the negative pressure above the liquid level is added to the pressure measured in the line (the negative pressure is calculated as a negative). This differential pressure determined in this way is proportional to the height of the liquid column between the level in the line on the one hand and the liquid level in the dirty water tank on the other.This differential pressure can therefore be used to determine the fill level in the wastewater tank.

[0015] However, if during further operation the contact between the receiving device and the floor surface to be cleaned improves so that the negative pressure above the liquid level in the dirty water tank increases and thus changes compared to the initial situation, dirty water is pushed out of the line and the level in the line changes without the level or fill level in the dirty water tank necessarily changing. If the differential pressure between the pressure in the line and that above the liquid level is then determined, the resultant pressure is proportional to the changed height of the liquid column between the level in the line and the level in the dirty water tank. This in turn leads to the supposed fill level in the dirty water tank calculated from the differential pressure changing without this actually having changed.In the case described here, a higher level would suddenly be determined without there actually being any change.

[0016] A very similar situation arises if, at the time the level in the wastewater tank reaches the opening of the pipe, there is very good contact between the receiving device and the floor surface to be cleaned, and the negative pressure above the liquid level in the wastewater tank is very high, and later the contact deteriorates. Then, the wastewater is pushed further into the pipe and upwards thanks to the vertical section, which ultimately leads to a decrease in the apparent level resulting from the differential pressure measurement.

[0017] The invention has thus initially recognized this problem, and as a solution according to the invention it is proposed that in the area between the opening of the line and the first section of the line which runs vertically during normal operation, a further section is provided which, during normal operation, when the floor surface to be cleaned runs horizontally, is also aligned horizontally or runs at an angle of maximum 20° thereto.

[0018] This means that if, after the level in the dirty water tank has been reached at which the dirty water has risen above the opening in the line, there is a change in this negative pressure above the liquid level, this does not result in the level in the line changing. Rather, the liquid shifts along the essentially horizontal second section, but this does not result in the height of the water column between the level in the line and the total level in the dirty water tank changing significantly. As a result, the design according to the invention ensures that the fill level resulting from the differential pressure between the pressure in the line and the negative pressure above the level in the dirty water tank does not change when the negative pressure in the dirty water tank changes after the level in the dirty water tank has risen above the opening in the line to the interior of the dirty water tank.

[0019] As a result, the reliability of the level determination in the waste water tank is significantly improved according to the invention, and the fluctuations in the determined level that occur in the prior art are significantly reduced.

[0020] In general, therefore, according to the present invention, the problem existing in the prior art is solved, in which the fill level in the waste water tank, determined from the pressure difference, changes solely because the negative pressure above the liquid level changes.

[0021] The pressure detection devices used within the scope of the present invention can be conventional pressure sensors that detect the pressure present at a measuring surface, such as sensors that operate using a capacitive or inductive measuring principle or that utilize the piezoelectric effect. In particular, silicon pressure sensors can be used. These can then be connected to a device that determines the difference between the pressures detected by the pressure detection devices. However, it is also possible for the first pressure detection device and the second pressure detection device to be combined in a pressure difference sensor, which additionally has or is designed to directly output a signal that is at least proportional to the difference between the two detected pressures, on the one hand in the line and on the other hand above the liquid level in the wastewater tank.The pressure sensing devices alone do not need to be designed to output a signal that is solely a measure of the pressure they sense. They simply need to be capable, when used in conjunction with the pressure differential determination device, of delivering a signal to the latter so that the latter can determine the differential pressure.

[0022] Furthermore, a "vertically extending" first section of the conduit is understood to mean a section that does not run horizontally, but rather, in the case where the floor cleaning machine is standing on a horizontal floor surface, extends away from this floor surface. It is not necessary for the first section to also run in a straight line. Nevertheless, in a preferred embodiment of the present invention, the first section can run in a straight line.

[0023] In a preferred embodiment of the present invention, the tangents have a uniform angle to the horizontal when the floor surface to be cleaned is horizontal and the floor cleaning machine is arranged on this floor surface. If, as in this embodiment, the second section is designed to be straight such that the gradient is constant, it has been found that the fluctuations in the determined pressure difference that occur when the negative pressure above the liquid level in the dirty water tank changes are particularly small.

[0024] Furthermore, it is preferred that, when the floor surface to be cleaned is horizontal and the floor cleaning machine is arranged on this floor surface, the tangents to the second section between a starting point and an end point of the second section run at an angle of less than 20°, preferably less than 15°, to the horizontal. Even with such a configuration, it has been found that the fill level in the dirty water tank can then be determined particularly accurately.

[0025] Finally, it is preferred if the length and cross-section of the second section are selected such that it can accommodate dirty water with a volume that is at least 15%, preferably at least 20%, of the volume of the entire line. Such a design of the second section ensures that, during the fluctuations in the negative pressure above the liquid level in the dirty water tank that normally occur during operation of a floor cleaning machine according to the invention, the level in the line always remains within the substantially horizontally extending second section.

[0026] The present invention is explained below with reference to a drawing which shows only a preferred embodiment, wherein Figure 1 shows a floor cleaning machine according to the prior art and the pressure conditions occurring at the pressure detection devices, and Figure 2 shows a floor cleaning machine according to an embodiment of the present invention and the pressure conditions occurring there.

[0027] Figure 1aFirst, it shows a floor cleaning machine 1 according to the prior art, wherein the floor cleaning machine 1 has a chassis 3 comprising front and rear wheels 5, 7. By means of the chassis 3, the floor cleaning machine 1 can be moved over a floor surface 9 to be cleaned. The floor cleaning machine 1 shown here is designed as a so-called ride-on machine, in which the user sits on the machine and can steer it. However, the present invention is not limited to use with ride-on machines, but can also be used in the same way with hand-held machines in which a user walks behind or away from the machine.

[0028] Furthermore, the floor cleaning machine 1 comprises a cleaning device 11, which, in the illustrated embodiment, has rotating brushes 13 that can engage the floor surface 9 to be cleaned in order to loosen dirt therefrom. Cleaning fluid, preferably in the form of water, is also introduced into the area of ​​the cleaning device 11, which absorbs the dirt loosened by the cleaning device 11 and the brushes 13.

[0029] Furthermore, a receiving device 15 is provided on the floor cleaning machine 1, which in the exemplary embodiment shown here comprises a suction foot 17, in which an inner volume 19 is surrounded by sealing lips 21, such that the inner volume 19 is open to the floor surface 9 to be cleaned. When the inner volume 19 is subjected to a negative pressure, the sealing lips 21 rest against the floor surface 9 to be cleaned and essentially seal the inner volume 19 from the environment, wherein dirty water located on the floor surface 9 to be cleaned is sucked away. For this purpose, the receiving device 15 is connected via a connecting line 23 to a dirty water tank 25 provided on the floor cleaning machine, wherein the dirty water tank 25 is intended to receive dirty water.

[0030] For this purpose, the dirty water tank 25 has an inlet 27, which is provided above a maximum level in the wall of the dirty water tank 25, up to which dirty water can stand in the dirty water tank 25. Furthermore, the dirty water tank 25 is provided with a vacuum device, which in the present embodiment is designed as a suction turbine 29, with which the area of ​​the dirty water tank 25 above the maximum level can be subjected to a negative pressure. This allows dirty liquid to be pumped from the interior volume 19 of the suction foot 17 into the dirty water tank 25.

[0031] Furthermore, Figure 1a It can be seen that the waste water tank 25 is provided with a first pressure detecting device 31 which is arranged such that it detects the pressure in the waste water tank 25 above the maximum level for the waste water therein.

[0032] Furthermore, the floor cleaning machine 1 has a second pressure sensing device 33 on the dirty water tank 25, which is connected to the interior of the dirty water tank 25 via a line 35, wherein the line 35 has an opening 37 facing the interior of the dirty water tank 25. Finally, between the opening 37 and the second pressure sensing device 33 in the line 35, a first, substantially vertically extending section 39 is provided, into which the dirty water of the dirty water tank 25 can rise due to the pressure of gravity. At this point, it should be noted that here and also in a construction according to the invention, the line 35 can run completely or only partially through the interior of the dirty water tank 25.

[0033] Finally, the first pressure sensing device 31 and the second pressure sensing device 33 are connected to a device 41 with which the differential pressure between the pressures sensed by the pressure sensing devices can be determined. Thus, the fill level of the wastewater in the wastewater tank 25 can be determined by means of the device 41.

[0034] The previously described structure according to the prior art now gives rise to the following problem, which has already been generally described.

[0035] As the dirty water tank 25 progressively fills during cleaning operation, starting from an empty state, a level is eventually reached at which the opening 37 to the line 35 is reached and the opening 37 is closed off by the dirty water from the air contained in the dirty water tank 25. Thus, the pressure initially prevailing in the line 35 to the second pressure sensing device 33 is that generated in the dirty water tank 25 just above the liquid level by the suction turbine 29. However, as already explained in the introduction to the description, this pressure depends on how well the receiving device 15, and in particular the sealing lips 21 of the squeegee 21, are in contact with the floor surface 9 to be cleaned.

[0036] For example, at the time when the dirty water in the dirty water tank 25 closes the opening 37 of the line 35, the sealing lips 21 may have poor contact with the floor surface 9 to be cleaned. Then, the negative pressure x prevailing in the line 35 is comparatively low. If, during further operation, the dirty water tank 25 continues to fill with constant contact between the receiving device 15 or the sealing lips 21 and the floor surface 9 to be cleaned, as shown in Figure 1bAs shown, the pressure in line 35 rises and the level therein also rises because the air in line 35 is compressed. Using the two pressure sensing devices 31, 33, the differential pressure is now determined, whereby the negative pressure x above the liquid level is added to the pressure sensed in line 35 (the negative pressure is calculated as negative). This differential pressure Δp so determined in this way is proportional to the height of the liquid column between the level in line 35 on the one hand and the liquid level in the waste water tank 25 on the other. From this differential pressure Δp so, a fill level in the waste water tank 25 can be determined.

[0037] However, if during further operation the contact between the receiving device 15 or the sealing lips 21 provided thereon and the floor surface 9 to be cleaned improves, so that the negative pressure p above the liquid level in the dirty water tank 25 increases from the original value x (see Figure 1d) and thus changes compared to the initial situation, dirty water is forced out of the pipe 35 solely due to this change. This changes the level in the pipe 35 without the level or the actual fill level in the dirty water tank 25 changing. If the differential pressure Δp s2 between the pressure in the pipe 35 and the pressure above the liquid level is determined, a differential pressure results which is proportional to the changed height of the liquid column between the level in the pipe 35 and the level in the dirty water tank 25. This in turn leads to the supposed fill level in the dirty water tank 25 calculated from the differential pressure Δp s2 changing without this actually having changed. In the case of Figure 1d In the case described, a higher fill level would suddenly be determined without there actually being any change.

[0038] A very similar picture arises if, at the time when the level in the dirty water tank 25 reaches the opening 37 of the line 35 and closes it, there is very good contact between the sealing lips 21 of the suction foot 17 of the receiving device 15 and the floor surface 9 to be cleaned and the negative pressure x above the liquid level in the dirty water tank 25 is very high and later the contact deteriorates so that the negative pressure p decreases (see Figure 1c ).

[0039] Then, dirty water is pushed further into the pipe 25 and upwards thanks to the vertical first section 39, which results in the apparent filling level resulting from the differential pressure measurement decreasing because the differential pressure Δp s1 is lower.

[0040] The invention has recognized this problem described above, and as will be apparent from the following description of the Figure 2As can be seen from the exemplary embodiment of the inventive solution shown, a second section 43 is provided in the area between the opening 37 of the line 35 and the first section 39 of the line 35, which in normal operation runs vertically upwards, which section 43 is also horizontally aligned or runs at an angle of less than 25° to the floor surface to be cleaned in normal operation. Figure 2a which shows an embodiment of a floor cleaning machine 1 according to the invention, this also has, just like the one in Figure 1aThe floor cleaning machine 1 shown has a chassis 3 with front and rear wheels 5, 7, wherein the floor cleaning machine 1 also has a cleaning device 11 which has driven brushes 13 that can engage with the floor surface 9 to be cleaned. This exemplary embodiment also has a receiving device 15 which is designed as a suction foot 17 with an internal volume 19 that is delimited by sealing lips 21. The receiving device 15 is connected to a dirty water tank 25 via a connecting line 23, wherein the connecting line 23 opens into the dirty water tank 25 at an inlet 27. The inlet 27 is located above a maximum level up to which the dirty water tank 25 can be filled with dirty water.In this case, too, the dirty water tank 25 can be subjected to a negative pressure by a vacuum device designed as a suction turbine 29, so that dirty water can be pumped from the inner volume 19 into the dirty water tank 25.

[0041] In addition, in the embodiment of the invention of a floor cleaning machine 1 according to Figure 2a a first pressure detection device 31 and a second pressure detection device 33 are provided, the latter being connected to the bottom region of the waste water tank 25 via a line 35 which has an opening 37 pointing towards the waste water tank 25.

[0042] In contrast to the state-of-the-art floor cleaning machine as described in Figure 1 is indicated, the embodiment according to the present invention has Figure 2a modified line 35 between the second pressure detection device 33 and the opening 37 of the line 35. In the embodiment according to the invention, a substantially horizontally extending second section 43 is provided between the first section 39, which runs vertically during normal operation when the floor cleaning machine 1 is arranged on a horizontally extending floor surface 9 to be cleaned, and the opening 37. According to the invention, the second section 43 is designed such that when the floor surface 9 to be cleaned runs horizontally and the floor cleaning machine 1 is arranged on this floor surface 9, the second section 43 runs horizontally or rises from the opening 37, wherein the tangents to the second section 43 between a starting point 43' and an end point 43" of the second section 43 are inclined by less than 25° to the horizontal.Preferably, the tangents run at an angle of less than 20° and particularly preferably less than 15° to the horizontal.

[0043] Accordingly, the second section 43, when it extends along a straight line, is inclined by less than 25° to the horizontal. However, when the second section is curved, the tangents to the second section 43 between its starting and end points 43', 43" are inclined by less than 25°. In any case, this ensures that between the opening 37 of the line 35 and the first vertical section 39 provided therein, there is a second section 43, which can be straight or curved and which has a slight inclination relative to the horizontal.

[0044] Furthermore, the second section 43 may extend straight in a vertical plane, as shown in Figure 2a shown. However, it is also conceivable that the second section 43 is curved.

[0045] The length and cross-section of the second section 43 are selected such that it can accommodate dirty water with a volume that is at least 15%, preferably at least 20%, of the volume of the entire line 35. This ensures that the level of the dirty water in the line 35 does not rise from the second section 43 into the vertical first section 39 during normal operation.

[0046] This inventive design of the line 35 with the second section 43 configured as described results in a change in this negative pressure above the liquid level after reaching the level in the wastewater tank 25 at which the opening 37 in the line 35 lies below the level, this does not result in a significant change in the level in the line 35. Rather, the liquid shifts along the essentially horizontal second section 43, which, however, does not result in a change in the height of the water column between the level in the line 35 and the level in the wastewater tank 25.

[0047] As a result, the inventive design ensures that the fill level determined from the differential pressure between the pressure in the line 35 and the negative pressure p above the level in the waste water tank 25 does not change when the negative pressure in the waste water tank 25 changes after the level has risen above the opening 37 of the line 35. This can be seen below using the Figures 2b and 2c be explained.

[0048] In the case of Figure 2bThe case is shown in which the negative pressure p in the dirty water tank 25 is reduced compared to the original value x due to a deteriorated contact between the sealing lips 21 of the receiving device 15 and the floor surface 9 to be cleaned. This has the effect that dirty water is drawn into the line 35. However, this does not also have the effect that the height of the water column between the level of the dirty water in the line 35 and the level in the dirty water tank 25 changes significantly. At most, a negligible change occurs. Rather, the level of the dirty water only shifts in the region of the second section 43 of the line 35, and thus in the essentially horizontal region of the line 35, which does not lead to a change in the height of the water column and therefore also not to a significant change in the differential pressure Δp s1.The filling level determined from this differential pressure Δp s1 therefore does not change or only changes insignificantly.

[0049] The situation is quite analogous in the embodiment according to the invention in the Figure 2c shown case. Here, the negative pressure p increases compared to the original negative pressure x, which prevailed when the level in the wastewater tank 25 had risen so much that the opening 37 was closed. Due to the subsequent increase in the negative pressure p, wastewater is drawn out of the line 35. However, this does not lead to a change in the height of the water column between the level of the wastewater in the line 35 and the level in the wastewater tank 25, so that the differential pressure Δp s2 also changes only insignificantly or not at all. Here, too, this does not lead to a change in the fill level determined from the differential pressure Δp s1.

[0050] From the above description of the embodiment according to the invention it follows that with the solution according to the invention a reliable determination of the fill level of the dirty water in the dirty water tank 25 is possible, even if the negative pressure above the dirty water changes due to a different degree of engagement between the receiving device 15 and the floor surface 9 to be cleaned. List of reference symbols:

[0051] 1 Floor cleaning machine 3 Chassis 5 Front wheels 7 Rear wheels 9 Floor area to be cleaned 11 Cleaning device 13 Brushes 15 Pick-up device 17 Squeegee 19 Internal volume 21 Sealing lips 23 Connecting line 25 Dirty water tank 27 Inlet 29 Suction turbine 31 First pressure sensing device 33 Second pressure sensing device 35 Line 37 Opening 39 First section 41 Device for determining the pressure difference 43 Second section 43 Starting point - second section 43 End point - second section

Claims

1. A floor cleaning machine (1) for cleaning a floor surface, wherein the floor cleaning machine (1) is designed to be moved over a floor surface (9) to be cleaned and preferably has a chassis (3), having a cleaning device (11) for engaging with the floor surface (9) to be cleaned, having a receiving device (15) for receiving liquid from the floor surface (9) to be cleaned, having with a dirty water tank (25) for receiving liquid collected by the receiving device (15), wherein the dirty water tank (25) is connected to the receiving device (15) via a connecting line (23) and wherein the connecting line (23) opens at an inlet (27) into the dirty water tank (25), which is arranged above a maximum level for liquid in the dirty water tank (25), having a negative pressure device (29), which is designed to generate a negative pressure in the dirty water tank (25) above the maximum level, so that liquid is conveyed from the receiving device (15) to the inlet (27) and into the dirty water tank (25), having a first pressure detection device (31), which is arranged in such a way that it is suitable for detecting the pressure in the dirty water tank (25) above the maximum level, having a second pressure detection device (33), which is connected to the interior of the dirty water tank (25) via a conduit (35), having a device (41) for determining the pressure difference between the pressures detected by the first device and the second device, wherein the conduit (35) has an opening (37) directed towards the dirty water tank (25), characterized in that the conduit (35) has a first portion (39) which, when the floor surface (9) to be cleaned extends horizontally and the floor cleaning machine (1) is arranged on this floor surface (9), extends vertically, and wherein the conduit (35) has a second portion (43) between the first portion (39) and the opening (37), which second portion is designed in such a way that when the floor surface (9) to be cleaned extends horizontally and the floor cleaning machine (1) is arranged on said floor surface (9), the second portion (43) extends horizontally or rises as viewed from the opening (37), wherein the tangents to the second portion (43) between a starting point (43') and an end point (43") of the second portion (43) are inclined by less than 25° to the horizontal.

2. The floor cleaning machine according to claim 1, wherein, when the floor surface (9) to be cleaned extends horizontally and the floor cleaning machine (1) is arranged on said floor surface (9), the tangents to the second portion (43) have a uniform angle to the horizontal.

3. The floor cleaning machine according to claim 1 or 2, wherein, when the floor surface (9) to be cleaned extends horizontally and the floor cleaning machine (1) is arranged on said floor surface (9), the tangents to the second portion (43) between a starting point (43') and an end point (43") of the second portion (43) extend at an angle of less than 20°, preferably less than 15°, to the horizontal.

4. The floor cleaning machine according to one or more of claims 1 to 3, wherein the length and the cross-section of the second portion (43) are selected such that dirty water can be accommodated therein with a volume which is at least 15%, preferably at least 20%, of the volume of the entire conduit (35).

Images