Method for cleaning a filter of a vacuum cleaning apparatus and vacuum cleaning apparatus therefor

Abstract

The invention relates to a method for cleaning a filter of a vacuum cleaning apparatus, wherein in operation of the vacuum cleaning apparatus the filter has suction air flowing therethrough, said suction air being generated by a fan, the method including measuring a first pressure at an inflow section of the filter, measuring a second pressure at an outflow section of the filter, determining a pressure drop at the filter as a pressure difference between the first pressure and the second pressure, determining a quantity characterizing a volume flow of the suction air in the outflow section of the filter, determining, from the pressure difference and the quantity that characterizes the volume flow, a quantity characterizing a flow resistance of the filter, and initiating a filter cleaning operation in dependence upon the determined quantity that characterizes the flow resistance of the filter.

Claims

1. A method for cleaning a filter of a vacuum cleaning apparatus, wherein in operation of the vacuum cleaning apparatus the filter has suction air flowing therethrough, said suction air being generated by a fan, the method comprising: measuring a first pressure at an inflow section of the filter; measuring a second pressure at an outflow section of the filter; determining a pressure drop at the filter as a pressure difference between the first pressure and the second pressure; determining a quantity characterizing a volume flow of the suction air in the outflow section of the filter via a corresponding sensor or from a characteristic curve of the fan which indicates a dependence of the volume flow on a pressure in the outflow section of the filter; said pressure being measured as the second pressure and wherein the characteristic curve or a relationship approximating it was previously determined and is stored in a storage device; determining, from the pressure difference and the quantity that characterizes the volume flow, a quantity characterizing a flow resistance of the filter, wherein the quantity characterizing the flow resistance is determined as the quotient of the determined pressure difference and a function of the determined quantity that characterizes the volume flow; and initiating a filter cleaning operation in dependence upon the determined quantity that characterizes the flow resistance of the filter, wherein the determined quantity that characterizes the flow resistance is compared with a threshold value, and if said quantity is above the threshold value, a filter cleaning operation is initiated.

2. The method in accordance with claim 1, wherein the threshold value is or will be predetermined.

3. The method in accordance with claim 1, wherein the quantity characterizing the volume flow is determined from a characteristic curve of the fan which indicates a dependence of the volume flow on a pressure in the outflow section of the filter.

4. The method in accordance with claim 1, wherein the quotient is calculated from the determined pressure difference and a power of the determined quantity that characterizes the volume flow.

5. The method in accordance with claim 1, wherein a test is performed as to whether the threshold value is exceeded multiple times within a specified period of time.

6. The method in accordance with claim 1, wherein a test is performed to determine if, after the exceeding of a threshold value which is a first threshold value, a second threshold value is exceeded, said second threshold value being greater than the first threshold value.

7. The method in accordance with claim 6, wherein a warning signal is output if at least one of the following occurs: (i) the first threshold value is exceeded a minimum number of times within the specified time period and (ii) the second threshold value is exceeded.

8. The method in accordance with claim 1, wherein the filter has external air admitted thereto for carrying out a filter cleaning operation.

9. The method in accordance with claim 8, wherein an external air valve device is controlled and, for cleaning the filter, brought from a closed valve position to an open valve position.

10. The method in accordance with claim 1, wherein initiating a filter cleaning operation comprises at least one of mechanical shaking of the filter and directing external air towards the filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic sectional view of an exemplary embodiment of a vacuum cleaner constructed in accordance with the invention;

(2) FIG. 2 is an enlarged representation of an external air valve device of the vacuum cleaner in accordance with FIG. 1;

(3) FIG. 3 is a block diagram of an exemplary embodiment of a control device of the vacuum cleaner in accordance with FIG. 1;

(4) FIG. 4 is an enlarged view of the filter device in accordance with FIG. 1, showing the pressure conditions;

(5) FIG. 5 is a schematic representation of a characteristic curve of a fan of the vacuum cleaner of FIG. 1 and a characteristic curve of the vacuum cleaner of FIG. 1;

(6) FIG. 6 is an exemplary embodiment of a flow chart for performing a test as to whether or not a filter cleaning operation is to be performed; and

(7) FIG. 7 is a schematic representation of the pressure conditions along a flow path in the vacuum cleaner of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(8) An exemplary embodiment of a vacuum cleaner 10, which is shown schematically in a sectional view in FIG. 1, has a dirt collection container 12 on which a suction head 14 is mounted. The vacuum cleaner 10 is an example of a vacuum cleaning apparatus and is configured as a stand-alone (autonomous) device. The dirt collection container 12 has a suction inlet 16 to which a suction hose 18 can be connected in the usual manner. The suction head 14 seals off the dirt collection container 12 on the upper side thereof and forms a suction outlet 20 on which is held a filter device 21 having (at least) one filter 22. Adjoining the filter 22 is a suction conduit 24 via which the dirt collection container 12 is in flow communication with a suction unit 26. The suction unit 26 comprises an electric motor device 25 having (at least) one electric motor 27 and a fan 28 driven in rotation by the electric motor 27.

(9) In operation of the vacuum cleaner 10, the suction unit 26 applies a negative pressure to the dirt collection container 12 so that a suction flow represented by arrows 30 in FIG. 1 is formed. Under the action of the suction flow 30, dirt-laden suction air can be drawn in via the suction inlet 16 into the dirt collection container 12, from where it can be sucked off by the suction unit 26. The suction air can be expelled to the surroundings by the suction unit 26 via exhaust air openings (FIG. 7) in the suction head 14.

(10) The suction air flows through the filter 22 so that entrained solid particles are deposited on the dirty side 32 of the filter 22 facing towards the dirt collection container 12. Therefore, the filter 22 needs to be cleaned from time to time; otherwise, it develops increasing resistance to flow, whereby the suction effect of the vacuum cleaner 10 is adversely affected.

(11) For cleaning the filter 22, a filter cleaning device 33 which is configured as an external air valve device 33 having (at least) one external air valve 34 (shown enlarged in FIG. 2) is arranged above the filter 22 in the suction head 14. It comprises a valve holder 36 which is held stationary in the suction head 14 and forms a valve seat for a movable valve body in the form of a valve disk 38. The valve disk 38 is biased in a direction towards the valve holder 36 by a closing force provided by a closing spring 40. The closing spring 40 is clamped between a plate-like filter holder 42 which has a plurality of flow passages and is held stationary in the suction head 14, and the valve disk 38. In addition to the closing spring 40, the filter holder 42 carries a resilient stop element in the form of a stop spring 44. In particular (and preferably like the closing spring 40), the stop spring 44 has a linear characteristic. It is formed as a coil spring for example. Unlike the closing spring 40, the stop spring 44 is not biased in the closed position of the valve disk 38. Only when the valve disk 38 lifts off the valve seat of the valve holder 36 does the stop spring 44 come into contact with the underside of the valve disk 38, and continued movement of the valve disk 38 causes the stop spring 44 to be compressed somewhat. It thereby exerts an increasing restoring force on the valve disk 38 and accelerates the movement of the valve disk 38 from its closed valve position (shown in FIG. 2) via an open valve position and back to the closed valve position. In the open valve position, the valve disk 38 assumes a position at a distance from the valve holder 36, which forms the valve seat.

(12) The valve holder 36 has a plurality of through-openings, not shown in the drawing, the mouth regions of which are closed off by the valve disk 38 when the latter assumes its closed valve position. At a level of the valve holder 36, the suction head 14 has a lateral opening 46. External air can flow into the through-openings of the valve holder 36 via the lateral opening 46. When the valve disk 36 assumes its open valve position spaced relative to the valve holder 36, the lateral opening 46 is in flow communication with the suction conduit 24 via the through-openings of the valve holder 36 and external air can be applied to the clean side 48 of the filter 22 facing away from the dirt collection container 12. When the valve disk 38 assumes its closed valve position, the flow communication between the lateral opening 46 and the suction conduit 24 is interrupted.

(13) In a central region, the valve holder 36 carries an electromagnet 50. The electromagnet 50 is surrounded in a circumferential direction by an annular space 52 which has extending thereinto a guide sleeve 54 integrally formed on the valve disk 38 on the upper side thereof. The guide sleeve 54 receives a magnetizable element, for example in the form of an iron plate 56, which in the closed valve position of the valve disk 38 contacts a free end edge 58 of the electromagnet 50 and in combination with the electromagnet 50 forms a closed magnetic circuit.

(14) The electromagnet 50 is in electrical communication, via a current supply line 60 (FIG. 3), with a(n) (electronic) control device 62 arranged in the suction head 14. During normal suction operation of the vacuum cleaner 10, a supply current is applied to the electromagnet 50 by the control device 62. As a result of the magnetic field generated thereby, the valve disk 38 is reliably held in its closed position. The holding force of the electromagnet 50 is assisted by the spring force of the closing spring 40.

(15) If the supply of current to the electromagnet 50 from the control device 62 is interrupted, then the magnetic holding force acting on the valve disk 38 does not occur and the valve disk 38 is lifted off the valve seat against the action of the closing spring 40 due to the pressure difference acting on the valve disk 38, said pressure difference resulting from the difference between the outside pressure of the external air in the region of the valve holder 36 and the inside pressure within the suction conduit 24. A sudden burst of external air is then allowed to pass through the through-openings of the valve holder 36 and into the suction conduit 24, and the external air is applied to the clean side 48 of the filter 22 in a sudden burst. This causes a mechanical shock to be applied to the filter 22. Furthermore, external air passes through the filter 22 in counterflow direction, i.e. counter to the flow direction 30 during normal suction operation. As a result, effective cleaning of the filter 22 is achieved.

(16) In an exemplary embodiment, energy supply for the vacuum cleaner 10 is provided by a rechargeable battery device 63. This comprises for example two rechargeable batteries 64, 66. The battery device 63 comprises for example one or more lithium-ion accumulators. These are arranged laterally beside the suction unit 26 in a battery compartment 68 of the suction head 14. The battery compartment 68 is accessible to the user for exchange of the batteries 64, 66 via a swing-out door 70.

(17) The electronic control device 62 is arranged in the suction head 14 above the suction unit 26 and is in electrical communication with the batteries 64 and 66 via supply lines 72, 73, 74, 75. At the input side, the control device 62 has connected thereto a push button 82 that can be manually actuated by the user and is arranged on the upper side of the suction head 14. The user can (manually) initiate a filter cleaning process by actuating the push button 82.

(18) The battery device may also comprise a fan device for cooling the batteries 64, 66 (not shown in the drawing). When accumulators that need to be cooled are used as batteries, this then allows for operation of the battery device to be implemented in a manner that is gentle on the accumulators. The fan device in turn receives its electrical energy for operation preferably from the batteries 64, 66 when running on battery power.

(19) In one embodiment, the electronic control device 62 is arranged on a circuit board. Further, the circuit board has arranged thereon a receptacle for the battery device 63. In particular, the receptacle receives the batteries 64, 66. A fan device of the battery device 63 can also be arranged in the receptacle.

(20) The control device 62 further comprises electronics for controlling and/or monitoring the battery device 63. By virtue of the control device 62, which controls the electric motor device 25, it is for example possible to control the fan device in such a manner that the latter is operated corresponding to the control of the electric motor device 25. By way of example, turning off the electric motor 27, which is controlled by the control device 62, also turns off the fan device (optionally after a time delay). It is for example also possible for the fan device to be turned off when in filter cleaning mode.

(21) Furthermore, a control process can then be performed via the control device 62 which allows operating the battery device 63 in a gentle manner while optimizing for maximizing battery capacity. For example, a process of charging the battery device 63 can then also be appropriately controlled or monitored via the control device 62. Furthermore, the ageing process of the battery device 63 can be monitored via the control device 62.

(22) In an alternative embodiment, the vacuum cleaner 10 is supplied with mains current for its energy supply. Another embodiment implements adjustment options for adjusting whether the energy comes from the mains grid or from a battery device (see below).

(23) A first pressure sensor 84 is arranged upstream (in an inflow section) of the filter 22, and a second pressure sensor 86 is arranged downstream (in an outflow section) of the filter 22, these being signally and operatively connected to the control device 62 and each providing a pressure-dependent control signal. The first pressure sensor 84 measures a pressure p.sub.1 upstream of the filter 22 against atmosphere. The second pressure sensor 86 measures a pressure p.sub.2 downstream of the filter 22 against atmosphere. The pressure p.sub.2 is also a negative pressure which is created by the fan 28. By way of the two pressure sensors 84 and 86, the pressure difference p=p.sub.1p.sub.2 between an inflow section and an outflow section of the filter 22, occurring at the filter 22, can be determined.

(24) As has already been mentioned, filter cleaning is effected by momentarily interrupting the supply of current to the electromagnet 50 by the control device 62.

(25) The time-related course of the supply current that is provided to the electromagnet 50 by the control device 62 is described in PCT/EP2011/052039, or US 2013/0312792, filed on Feb. 11, 2011, which is incorporated herein and made a part hereof by reference in its entirety and for all purposes: At a point in time t.sub.2 (see FIG. 4 in PCT/EP2011/052039 or US 2013/0312792), the supply of current to the electromagnet 50 is interrupted so that the external air valve 34, starting from its closed valve position, transitions to its open valve position, and at a subsequent point in time t.sub.3 the supply of current to the electromagnet 50 is re-established so that the external air valve 34 resumes its closed valve position. In the illustrated exemplary embodiment, the supply of current is interrupted three times in rapid succession so that a sudden burst of external air is applied to the clean side 48 of the filter 22 three times in succession and a substantial portion of said external air is passed through the filter 22 in counterflow direction. This causes solid particles adhering to the dirty side 32 to be dislodged therefrom. The filter cleaning process is completed at the end of the third current interruption, i.e. at the point in time T.sub.E.

(26) In such an exemplary embodiment, a complete cleaning process therefore comprises three opening and closing movements of the external air valve in rapid succession. The length of the time interval between the points in time t.sub.2 and t.sub.3 may for example be 90 milliseconds. Following a filter cleaning process, normal suction operation resumes by supply current being applied to the electromagnet 50 by the control device 62 and by the external air valve 34 maintaining its closed valve position. During normal suction operation, the suction power of the suction unit 26 is kept constant. In time-controlled filter cleaning, a period of suction operation of for example 15 seconds is followed by another filter cleaning process in which external air is supplied three times in sudden bursts, as explained above. Preferably, the length of the time interval between two filter cleaning processes is capable of being adjusted manually. Alternatively or additionally, a filter cleaning process can be initiated manually by the push button 82 and/or in a sensor-controlled manner by the pressure sensors 84, 86.

(27) The vacuum cleaner 10 comprises a mains voltage supply device 88 (FIG. 3) by which the vacuum cleaner 10 can optionally or adjustably be supplied with mains current for its energy supply. FIG. 3 indicates an associated mains cable, designated by the reference numeral 90. It is then possible for a user to select whether energy is supplied via the mains voltage supply device 88 or the battery device 63.

(28) The mains voltage supply device 88 comprises a rectifier 92 which provides direct current or direct voltage at an output thereof.

(29) The control device 62 has a supply subunit 94 via which the components of the vacuum cleaner 10 are supplied with electrical energy. The supply subunit 94 provides the required electrical energy to the electromagnet 50 via the current supply line 60. It provides the electrical energy for powering the control device 62. It provides the electrical energy for controlling and actuating the electric motor 27. The corresponding electrical energy is delivered at an output (indicated at 96 in FIG. 3).

(30) The supply subunit 94 can be formed by the battery device 63 or by the mains voltage supply device 88. It may also comprise a switch or the like which is used to manually or automatically adjust whether the vacuum cleaner 10 is supplied with energy from the rechargeable battery device 63 or from the mains voltage supply device 88.

(31) The control device 62 comprises an external air valve control subunit 98. This is signally and operatively connected to the push button 82, the first pressure sensor 84 and the second pressure sensor 86. These provide corresponding signals to the external air valve control subunit 98, which then correspondingly controls the electromagnet 50 via a signal line 100. The external air valve control subunit 98 controls the electromagnet 50 in such a manner that the magnetic holding force acting on the valve disk 38 is released and hence a filter cleaning process is performed when a manual initiation process by the push button 82 is detected.

(32) In an embodiment, the electric motor 27 is a permanent magnet-excited synchronous motor. In a permanent magnet-excited synchronous motor, the rotor has a plurality of permanent magnets. A stator is provided with coils which are controlled by the control device 62. The control is such that an electronic commutation process takes place. To this end, the control device 62 has (at least) one controller 102 which correspondingly controls the electric motor 27 and in particular the coils in the stator of the electric motor 27.

(33) Control of the electric motor 27 by the controller 102 is in particular by pulse width modulated signals. The electric motor 27 is thereby supplied with the corresponding energy by control signals.

(34) The electric motor 27 is in particular a brushless permanent magnet motor (EC motor). Using such a motor can achieve rotational speeds of for example 20,000 rpm or more with high efficiency and low noise. (Lower rotational speeds can also be achieved.)

(35) In an exemplary embodiment, the electric motor is a three-phase motor and in particular a permanent magnet-excited three-phase synchronous motor. Provision may also be made for the permanent magnet-excited synchronous motor as the electric motor 27 to be only single-phase or two-phase.

(36) In an embodiment, the control device 62 comprises a motor control subunit 104 which is in particular part of the controller 102 and is signally and operatively connected to the external air valve control subunit 98. In principle, a unidirectional connection may be provided in which either the external air valve control subunit 98 provides the motor control subunit 104 with corresponding signals which characterize whether or not a filter cleaning process is performed, or the motor control subunit 104 provides the external air valve control subunit 98 with signals regarding the motor control of the electric motor 27. A bidirectional data connection may also exist in which motor control data and external air valve control data are exchanged between the external air valve control subunit 98 and the motor control subunit 104.

(37) It is thereby possible for a corresponding external air valve control to be taken into account directly in the motor control. Alternatively or additionally, it is possible for motor control data to be taken into account in the external air valve control.

(38) The vacuum cleaner 10 further comprises a determination device 106 which determines a quantity Q characterizing a volume flow of suction air, said quantity Q characterizing the volume flow being determined in the outflow section of the filter 22.

(39) In principle, provision may be made for a volume flow sensor to be arranged in the outflow section of the filter 22 and, in particular, for the volume flow Q to be then measured directly.

(40) In an exemplary embodiment, the determination device 106 is integrated in the control device 98. It determines the quantity Q characterizing the volume flow from a characteristic curve of the fan 28 or from a relationship approximating said characteristic curve. This will be explained in greater detail below.

(41) The control device 98 further comprises a storage device 108 which stores data for the characteristic curve or the relationship approximating said characteristic curve.

(42) Furthermore, the control device 98 comprises an evaluation device 110. The evaluation device determines, from the data from the first pressure sensor 84 and the second pressure sensor 86, transmitted to the control device, and further from the data provided by the determination device 106, a quantity that is characteristic of the flow resistance of the filter 22.

(43) The control device 98 further comprises a threshold value test device 112. Said threshold value test device 112 receives data from the evaluation device 110 and tests whether or not a determined quantity that is characteristic of the flow resistance of the filter 22 exceeds a threshold value, and if the threshold value is exceeded, a filter cleaning operation is initiated by a corresponding control signal being sent to the electromagnet 50.

(44) The filter cleaning control scheme works as follows:

(45) FIG. 7 is a schematic representation of the pressure conditions existing along a suction air flow path of the vacuum cleaner 10. The pressures are related to atmospheric pressure, and in FIG. 7 negative pressures with respect to atmosphere (which create a suction flow) are shown with positive sign. The purpose of FIG. 7 is to qualitatively explain the pressure conditions.

(46) FIG. 7 shows an exemplary case of a heavily soiled filter 22 represented in broken lines (reference numeral 114) and an exemplary case of a less-than-heavily-soiled (clogged) filter 22 represented as solid lines (reference numeral 116).

(47) Driven by the electric motor 27, the fan 28 of the suction unit 26 generates a suction flow. A negative pressure 118 relative to atmospheric pressure is generated. This negative pressure 118 is present in the suction conduit 24.

(48) Between the fan 28 and the exhaust air openings 29, the pressure rises to atmospheric pressure.

(49) The above-mentioned negative pressure 118 in the suction conduit 24 is present between the fan 28 and the filter 22 and may experience a drop (in the sense that it drops to a lower value) due to the flow path.

(50) The pressure downstream of the filter 22, i.e. in the outflow section of the filter 22, is the pressure p.sub.2, which is measured by the second pressure sensor 86. The pressure p.sub.2 is a good measure of the negative pressure 118 in the suction conduit 24.

(51) The pressure upstream of the filter 22, i.e. at the inflow section of the filter 22, is the pressure p.sub.1, which is measured by the first pressure sensor 84. The filter has a pressure drop thereacross of p=p.sub.1p.sub.2. The more clogged the filter becomes, the greater this pressure drop p becomes.

(52) Further pressure drop is experienced along the path between the inflow section of the filter 22 and the suction inlet 16. A pressure drop also occurs in the suction hose 18. A pressure drop also occurs inside a nozzle 120 connected to the suction hose 18. The pressure existing outside the nozzle 120 is again atmospheric.

(53) The pressure drop occurring in the filter 22 depends on how clogged the filter is, as is apparent from the comparison of the curves 114 and 116 of FIG. 7. The pressure course in the further flow path also depends on how dirty the filter 22 is.

(54) In principle the pressure drop p across the filter 22 also depends, aside from the dirtiness of the filter 22, on the remaining flow path inside the vacuum cleaner 10.

(55) The solution in accordance with the invention takes into account, with respect to filter cleaning control, a volume flow Q of the suction air in the suction conduit 24.

(56) As mentioned above, this volume flow can in principle be measured directly by a corresponding sensor. In an exemplary embodiment of simple design, the volume flow is determined by calculation:

(57) The fan 28 has a characteristic curve with respect to the (negative) pressure 118 in the suction conduit 24.

(58) As mentioned above, the pressure p.sub.2 measured by the second pressure sensor 86 is a suitable measure of the pressure 118 in the suction conduit 24.

(59) An exemplary embodiment of a characteristic curve of the fan 28 in dependence on the pressure p.sub.2 is shown in FIG. 5 and indicated therein by reference character 122. For small pressures p.sub.2 (small pressures 118), the volume flow is high, and the higher the pressure p.sub.2 becomes, i.e. the more it approximates atmospheric pressure, the smaller the volume flow becomes.

(60) For (at least some) commercially available fans 28, the characteristic curve 122 is at least approximately linear.

(61) It has been shown that even when the characteristic curve is not linear, a linear approximation is usually sufficient in carrying out the method in accordance with the invention.

(62) The vacuum cleaner itself has a characteristic curve 124 with respect to the dependence of the volume flow on the pressure 118. Said characteristic curve 124 depends on the entire flow path in the vacuum cleaner 10, including the suction hose 18 and the nozzle 120. At small pressures p.sub.2, the volume flow is low, while pressure increase increases the volume flow.

(63) In operation of the vacuum cleaner 10, a pressure p.sub.2* occurs at a volume flow Q* at which the characteristic curve 124 intersects the characteristic curve 122. The corresponding point 126 may vary during operation. The point 126 depends in principle on the configuration of the flow path and also, for example, on how long and what diameter the suction hose 18 is and how the nozzle 120 is configured. It may further vary depending on the nature of the surface upon which the nozzle 120 acts.

(64) FIG. 5 shows that with the pressure 118 known, it is possible to determine from the characteristic curve 122 the volume flow at least as the quantity Q that characterizes the volume flow (as an approximation to the volume flow). The pressure p.sub.2 is determined by the second pressure sensor 86.

(65) The characteristic curve 122 or the relationship that approximates it is stored for example as a table of values in the storage device 108. To this end, the characteristic curve was previously measured and stored in the storage device 108.

(66) The pressure drop p=p.sub.1p.sub.2 at the filter 22 can be determined from the measured values p.sub.1 and p.sub.2. Furthermore, the volume flow Q in the suction conduit 24, i.e. in the outflow section of the filter 22, is at least approximately known from the pressure p.sub.2 and the characteristic curve 122. From this, the evaluation device 110 in turn then determines a quantity characterizing the flow resistance of the filter 22. Said quantity characterizing the flow resistance is determined in particular as the quotient of the pressure difference p and a function of the determined volume flow.

(67) In an exemplary embodiment, a loss coefficient of the filter 22 is calculated as

(68) $\begin{array}{cc}{c}_W=\frac{p}{Q^2}& \left(1\right)\end{array}$

(69) The determined volume flow (or the quantity Q characterizing the volume flow) enters into this loss coefficient of the filter 22 as a power to two.

(70) Equation (1) lacks a proportionality factor. The threshold value test device 112 performs a test as to whether or not the quantity determined according to equation (1) exceeds a predetermined threshold value. Since a proportionality factor does not matter for this threshold value test (as it would be included in the threshold value), it was omitted from equation (1).

(71) One or more threshold values against which the test is made were previously determined and are in particular stored in the storage device 108.

(72) If the quantity c.sub.w, calculated in accordance with equation (1) and characterizing the flow resistance, is found to exceed the predetermined threshold value in the test, a filter cleaning operation is initiated by the control device 98 sending a corresponding control signal to the electromagnet 50.

(73) FIG. 6 is a schematic representation of the sequence:

(74) First, in a computation step 128, the evaluation device 110 of the control device 98 calculates the quantity c.sub.w that characterizes the flow resistance of the filter 22.

(75) Next, at a threshold value test step 130, a check is made as to whether or not the predetermined threshold value (and in particular a predetermined first threshold value) is exceeded. If the threshold value is not exceeded, normal suction operation is carried on or continued (reference numeral 132 in FIG. 6).

(76) If the threshold value is found to be exceeded in the test, a filter cleaning operation is performed (reference numeral 134 in FIG. 6).

(77) Provision may be made for an additional test procedure to be performed, checking for a filter problem and, for example, checking as to whether the filter 22 needs replacement.

(78) To this end, a test is performed as to whether the first threshold value is exceeded multiple times within a specified time period or whether for example a second threshold value above the first threshold value is exceeded.

(79) For example, after the result that the threshold value has been exceeded, this result is stored at a storing step 136.

(80) In a further test step 138, a test is performed as to whether the threshold value has been exceeded a specified number of times within a specified period of time. If not, the filter cleaning operation 134 is performed.

(81) If, at test step 138, the threshold value is determined to have been exceeded a specified number of times within the specified period of time, then this is an indication of a filter problem and, for example, a corresponding warning indication 140 is output.

(82) In an exemplary embodiment, the control device 98 then controls a warning indication which is in particular arranged at a housing of the vacuum cleaner 10. The warning indication 142 may for example be a visual and/or audible warning indication.

(83) If the test step 138 indicates that previous filter cleaning operations have failed to be successful, then this indicates filter problems; by way of the test at step 138, a determination can be made as to whether filter 22 recovery occurs, or no longer occurs, as a result of filter cleanings. If in performing this test it is determined that such recovery does not occur any longer, then for example a special cleaning procedure is required or the filter 22 must be exchanged.

(84) For example, it is also possible for the test step 138 to include, as a measure of whether or not recovery is achieved, a test as to whether after the first threshold limit has been reached the second threshold value is exceeded, said second threshold value being higher than the first threshold value.

(85) In the solution in accordance with the invention, filter cleaning is effected on an as-needed basis, depending on the conditions prevailing at the filter 22. The pressure loss p across the filter 22 is determined. In addition, the volume flow Q is determined, at least approximately, in order thus to be able to determine the conditions at the filter 22 independently of the remaining flow path inside the vacuum cleaner 10. To this end, in addition to the pressure loss p measured via the pressure values p.sub.1 and p.sub.2 from the first pressure sensor 84 and the second pressure sensor 86, the volume flow Q in the suction conduit 24 is determined, at least approximately. This in turn is determined from the characteristic curve 122 of the fan 28. The characteristic curve 122 is stored in the storage device 108, for example as a table of values, or a relationship approximating said characteristic curve 122 is stored in the storage device 108. A quantity Q that characterizes the volume flow is determined from the measured value p.sub.2, and this is used to determine, by equation (1), a quantity c.sub.w characterizing the flow resistance at the filter 22. The clogging conditions at the filter 22 can thereby be determined directly and with good accuracy.

(86) A loss coefficient c.sub.w of the filter 22 or a quantity proportional to the loss coefficient c.sub.w can be determined directly, and this quantity is capable of being determined with sufficient accuracy even under variations or fluctuations in operation of the vacuum cleaner 10.

(87) Any potential influences on the pressure difference p in the flow path that are not attributable to a dirty filter condition (but rather, for example, to blockage inside the suction hose 18, changing to another attachment such as a nozzle 120, etc.) are taken into account automatically in the solution in accordance with the invention because it takes into account the volume flow in the suction conduit 24 for carrying out filter cleanings.

(88) The method in accordance with the invention can be implemented using simple design.

(89) The vacuum cleaning apparatus may also be integrated in a surface cleaning machine, such as a self-propelled sweeping machine.

REFERENCE SYMBOL LIST

(90) 10 vacuum cleaner 12 dirt collection container 14 suction head 16 suction inlet 18 suction hose 20 suction outlet 21 filter device 22 filter 24 suction conduit 25 electric motor device 26 suction unit 27 electric motor 28 fan 29 exhaust air opening 30 suction flow 32 dirty side 33 external air valve device 34 external air valve 36 valve holder 38 valve disk 40 closing spring 42 filter holder 44 stop spring 46 lateral opening 48 clean side 50 electromagnet 52 annular space 54 guide sleeve 56 iron plate 58 end edge 60 current supply line 62 control device 63 battery device 64 battery 66 battery 68 battery compartment 70 door 72 supply line 73 supply line 74 supply line 75 supply line 82 push button 84 first pressure sensor 86 second pressure sensor 88 mains voltage supply device 90 mains cable 92 rectifier 94 supply subunit 96 output 98 external air valve control subunit 100 signal line 102 controller 104 motor control subunit 106 determination device 108 storage device 110 evaluation device 112 threshold value test device 114 heavy soiling 116 less-than-heavy soiling 118 negative pressure 120 nozzle 122 fan characteristic curve 124 vacuum cleaner characteristic curve 126 point 128 computation sensor 130 threshold value test sensor 132 suction operation 134 filter cleaning operation 136 stored value 138 test sensor 140 warning indication 142 warning indication