METHOD FOR DETECTING MALFUNCTION OF A RECIRCULATION PUMP IN A WASHING MACHINE, AND WASHING MACHINE USING SUCH METHOD

Abstract

 A method for detecting malfunction of a recirculation pump 16 in a washing machine 10 having a tub 12 and a rotating drum 14, comprising monitoring the water level in the tub 12 and issuing a malfunction signal when the variation of said water level is not according to a predetermined threshold.

Description

[0001] The present invention relates to a method for detecting malfunction of a recirculation pump in a washing machine having a tub and a rotating drum.

[0002] Clothes washing machines which recirculates wash or rinse water from a surrounding tub into a clothes holding basket are well known in the art. The main advantage of such washing machine is to reduce the quantity of water required for wash and rinse cycles. In such machines the fill level is controlled by a pressure sensor in order to control water fill levels at the beginning of each wash and rinse cycle. A washing machine of this type is disclosed by US 4168615.

[0003] US 2013/0081431 discloses a similar washing machine in which relatively short bursts of operation of a recirculation pump are coordinated with corresponding intervals of drum rotation during the initial fill periods. The aim is to thoroughly wet the clothes early in each wash/rinse phase to thus improve the wash/rinse effectiveness.

[0004] In the above known washing machines the performances of the washing cycle depends on the proper function of the recirculation pump. If the pump presents problems of cavitation, priming, blocking or the like, the entire washing process may be greatly affected without any alerting signal to the user. To provide the circulation pump with "ad hoc" sensors (for instance temperature sensors, speed sensors etc.) may unduly increase the overall cost of the appliance, rendering it less appealing to the potential buyer.

[0005] It is therefore an object of the present invention to provide a method as mentioned at the beginning of the description which is capable of assessing malfunction or failure of the recirculation pump without any additional cost, i.e. by using the components already used in a washing machine.

[0006] The above object is reached thanks to the features listed in the appended claims.

[0007] According to the invention, the control unit of the washing machine is provided with an algorithm which is configured to detect different failure cases of the recirculation pump. If for instance the pump runs in cavitation/priming issues, or if the recirculation pump is blocked, then the algorithm according to the invention is able to sense such malfunction and to adopt the proper remedies, for instance to switch off the pump and to repeat the assessment a second time or more.

[0008] An analog pressure sensor (APS) is preferably used to monitor re-circulation pump as well as needed water quantity for laundry during wash process. Another advantage of the present invention is that pump monitoring can be done promptly, without waiting for the pump running in time out issue, by detecting rising water columns also during wash process indicating system malfunction. The algorithm according to the invention may be used as well to detect/eliminate priming issue during main wash, and not only during the initial filling, soaking and tumbling phase. According to the invention, when the circulation pump is started or restarted, after a predetermined time the water level in the tub should decrease of a predetermined value depending mainly of the geometry of the tub/drum and of the features of the pump (usually few millimeters of water column), otherwise priming issue is present. If during water level monitoring while recirculation pump is running, water level column increases then pump cavitation is present and pump triggering needs to be executed. The above level detection runs in parallel with level detection during main wash Saturation of the laundry during wash process can be also monitored, particularly in the initial step of water filling, soaking and tumbling. If water level does not increase over a predetermined value, then water refill has to be executed to guaranty proper amount of water for good performance results in wash process.

[0009] According to a preferred embodiment of the invention, the assessment of recirculation pump malfunction is assessed by switching off such pump and measuring a first water level in the tub, waiting for a predetermined rest period, measuring a second water level in the tub after such predetermined rest period is elapsed, comparing said first and second water levels and issuing a malfunction signal when said difference is below a predetermined value.

[0010] Further advantages and features of a method and of a washing machine according to the invention will become clear from the following detailed description, with reference to the attached drawings in which:

• Figure 1 is a schematic view of a washing machine according to the invention;
• Figure 2 is a diagram showing how the algorithm according to the invention works for two different loads;
• Figure 3 is an enlarged view of a portion of the diagram of figure 2;
• Figure 4 is a flowchart showing an embodiment of the algorithm according to the present invention; and
• Figure 5 is a flowchart showing an auxiliary algorithm used in the water filling stage of the washing process.

[0011] With reference to the drawings, a washing machine 10 comprises a tub 12 and a rotating drum 14 for containing the laundry. A conduit system 20 allows a recirculation of water and washing liquor through the recirculation pump 16. A pressure sensor 18 monitors the water level in the tub and sends signals to a control unit 19. The washing machine 10 comprises also a water spray nozzle 22, a water filling conduit 24 and a discharge pump 26 (which can be also integrated with the recirculation pump).

[0012] In figure 2 it is shown how the water level changes during the filling, soaking and tumbling phase for two different loads, curve A being for a load of 1 kg, while curve B being for a load of 3 kg.

[0013] In the initial phase, from 0 seconds to about 180 seconds, water is filled through pipe 24, then drum is rotated for soaking laundry, so that water level decreases. Then, around 850 seconds after the beginning of the filling phase, the recirculation pump 16 is switched on and at the same time water is filled again while the laundry is tumbling in the rotating drum 14. After around 1500 seconds, soaking, fill and heating phase is finished. Re-Circ Pump is switched on and water level decreases. At time indicated by reference M on figure 2, the recirculation pump is stopped, such idle condition being maintained for a time indicated in figure 2 with the reference L. Such period may be comprised between 10 and 500 seconds, more preferably between 30 and 100 seconds. At a time indicated by reference P in figure 2, i.e. after a period of time K after the recirculation pump 16 has been switched off, a first water level WL1 is detected. Then, at time indicated with reference Q in figure 2, circulation pump 16 and motor (not shown) driving the drum 14 are both switched on again and run for a predetermined period of time Z, comprised between 5 and 200 seconds, preferably between 10 and 60 seconds. At the end of such period (time indicated with reference R in figure 2), a second water level WL2 is measured by the sensor 18. If the difference between first water level WL1 and second water level WL2 is higher than a predetermined threshold value, this means that the recirculation pump does work properly and that the washing cycle can be initiated. If the above difference is below said threshold, then this means that the recirculation system, and particularly the recirculation pumps 16 is not working properly and that such pump is blocked or subject to cavitation. In this case the algorithm carries out pump triggering, and then it repeats the pump assessment cycle starting from point M, for one or more times

[0014] (two in the example shown in figure 4). If despite such further attempt the above level difference WL1 - WL2 is still below the threshold, then additional water is filled until a water level is reached where load can be washed without using recirculation functionality. At the end of the cycle on the display of the washing machine the user is alerted that the filter (not shown in figure 1 but usually placed upstream pump 16) has to be cleaned or that the pump 16 is not working. In figure 1 water levels WL1 and WL2 are only indicative; as a matter of fact the upper level WL1 does not contact the drum 14 during the normal washing cycle, a part from the filling step where, for a small load of clothes (curve A in figure 2), the water level can reach the level of the drum, which is indicated with reference D in figure 2. The algorithm according to the invention can be carried out properly only when water level WL1 or WL2 are underneath the drum 14. In case the water level is above le drum (i.e. inside the drum) there is no actual need for recirculation since a wash liquor exchange is already guaranteed.

[0015] Even if the example above is focused on the assessment of proper working of the recirculation pump 16 before the main wash cycle step, the same algorithm can be carried out at predetermined intervals also during the main wash phase or the rinsing phase, in order to promptly alert the control unit of any problem of the circulation pump 16.

[0016] Figure 5 describes an auxiliary algorithm which exploits the analog pressure sensor 18 and it is used during the water refilling step. According to such algorithm, after the recirculation pump 16 and the rotation of the drum 14 are stopped, the control unit 19 waits for a predetermined period time Z' and then water pressure (i.e. water level) is detected. If such pressure is above a predetermined value X', this means that a sufficient amount of water has been loaded in the tub 12. If not, a predetermined amount of water is fed into the tub and the algorithm is repeated.

[0017] Even if the above description is focused on a horizontal axis washer, the same method can be applied to a vertical axis washer or to a washer-dryer as well.

Claims

1. Method for detecting malfunction of a recirculation pump (16) in a washing machine (10) having a tub (12) and a rotating drum (14), characterized in that it comprises monitoring water level (WL1, WL2) and issuing a malfunction signal when variation of said water level is not according to a predetermined threshold.

2. Method according to claim 1, wherein the recirculation pump (16) is switched off, a first water level (WL1) is assessed after a first predetermined period (K), and a second water level (WL2) is assessed after the recirculation pump (16) has been switched on for a second predetermined period (Z), said threshold being compared with the difference of said water levels (WL1, WL2).

3. Method according to claim 2, wherein the recirculation pump (16) is switched on and off together with the motor driving rotation of the drum (14).

4. Method according to claim 2 or 3, wherein it comprises the following steps:

switching off the recirculation pump (16) and determining a first water level (WL1) in the tub (12), waiting for a predetermined rest period, switching on the recirculation pump (16) for a predetermined running period, determining a second water level (WL2) in the tub (12) after such running period is elapsed, comparing said first and second water levels (WL1, WL2) and issuing a malfunction signal when said difference is below the threshold value.

5. Washing machine (10) comprising a tub (12), a drum (14) rotatably mounted in the tub (12), a water level sensor (18) and a recirculation pump (16), characterized in that it comprises a control unit (19) configured to monitor water level (WL1, WL2) and issue a malfunction signal when variation of said water level is not according to a predetermined threshold.

6. Washing machine according to claim 5, wherein the control unit (19) is configured to asses a first water level (WL1) after the recirculation pump (16) is switched off for a first predetermined period (K), and to asses a second water level (WL2) after the recirculation pump (16) has been switched on for a second predetermined period (Z).

7. Washing machine according to claim 6, wherein the control unit (19) is configured to switch on and off the recirculation pump (16) together with the motor driving rotation of the drum (14).

8. Washing machine according to claim 6 or 7, wherein the control unit is configured to perform the following steps: switching off the recirculation pump (16) and determining a first water level (WL1) in the tub (12), waiting for a predetermined rest period, switching on the recirculation pump (16) for a predetermined running period, determining a second water level (WL2) in the tub (12) after such running period is elapsed, comparing said first and second water levels (WL1, WL2) and issuing a malfunction signal when said difference is below a predetermined value.

Drawing