A method of operating a laundry washing machine comprising a recirculation circuit

Abstract

A method for operating a laundry washing machine comprising a washing tub external to a washing drum, a recirculation system comprising a recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit such liquid into the washing tub, a liquid level sensor device configured to detect the liquid level inside the washing tub, and a variable speed recirculation pump connected to the recirculation circuit. The method comprises a recirculation phase comprising controlling the recirculation pump by varying the rotation speed of the recirculation pump depending on a difference between the detected liquid level and a prefixed liquid level value.

1 . A method for operating a laundry washing machine comprising:
 a washing drum configured to receive laundry to be washed;   a washing tub external to the washing drum;   a water supply system configured to convey water to the washing tub;   a recirculation system comprising a recirculation circuit configured to drain liquid from a bottom of the washing tub and to re-admit the liquid into a first region of the washing tub, the recirculation system comprising a variable speed recirculation pump having an outlet connected to the recirculation circuit and wherein the recirculation pump is operable at variable rotation speeds to circulate liquid through the recirculation circuit;   a liquid level sensor device configured to detect a liquid level inside the washing tub;   wherein the method comprises operating the recirculation system in a recirculation phase to drain the liquid from the bottom of the washing tub and to re-admit the liquid into the first region of the washing tub through the recirculation circuit, wherein the recirculation phase comprises:
 determining a detected liquid level using the liquid level sensor device; 
 determining a difference between the detected liquid level and a prefixed liquid level value; and 
 the step of controlling the recirculation pump by varying a rotation speed of the recirculation pump depending to the difference between the detected liquid level and the prefixed liquid level value. 
   
     
     
         2 . The method according to  claim 1 , wherein the recirculation phase further comprises activating the recirculation pump when the detected liquid level is above the prefixed liquid level value. 
     
     
         3 . The method according to  claim 1 , wherein the recirculation phase further comprises deactivating the recirculation pump when the detected liquid level is equal to, or below the prefixed liquid level value. 
     
     
         4 . The method according to  claim 1 , wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises operating the rotation speed of the recirculation pump to be directly proportional to the difference between the detected liquid level and the prefixed liquid level value. 
     
     
         5 . The method according to  claim 1 , wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises maintaining the rotation speed of the recirculation pump between a minimum threshold value and a maximum threshold value. 
     
     
         6 . The method according to  claim 5 , wherein the minimum threshold value is zero. 
     
     
         7 . The method according to  claim 5 , wherein the minimum threshold value is greater than zero. 
     
     
         8 . The method according to  claim 1 , wherein controlling the recirculation pump by varying the rotation speed of the recirculation pump comprises varying the rotation speed of the recirculation pump over the time according to a continuous function or a step function. 
     
     
         9 . The method according to  claim 1 , wherein the recirculation phase further comprises reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by conveying an amount of water into the washing tub. 
     
     
         10 . The method according to  claim 1 , wherein the recirculation phase further comprises reestablishing the prefixed liquid level value inside the washing tub when the liquid level goes below the prefixed liquid level value by extracting an amount of water from the laundry in a dewatering process carried out by rotating the washing drum at a dewatering speed. 
     
     
         11 . The method according to  claim 1 , wherein the recirculation system comprises a second recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit the liquid into a second region of the washing tub, wherein the variable speed recirculation pump is a bi-directional variable speed pump having a second outlet connected to the second recirculation circuit, and wherein varying the rotation speed of the recirculation pump during the recirculation phase comprises:
 activating the recirculation pump in a first direction of rotation to drain the liquid from the bottom of the washing tub and to re-admit the liquid into the first region of the washing tub through the recirculation circuit, and   activating the recirculation pump in a second direction of rotation opposite to the first direction of rotation to drain liquid from the bottom of the washing tub and to re-admit the liquid into the second region of the washing tub through the second recirculation circuit.   
     
     
         12 . The method according to  claim 11 , wherein the recirculation pump is operated in the second direction at a first fixed speed. 
     
     
         13 . The method according to  claim 11 , wherein the recirculation pump is operated in the second direction at a speed varying over the time. 
     
     
         14 . The method according to  claim 1 , wherein the recirculation system comprises a second recirculation circuit configured to drain liquid from the bottom of the washing tub and to re-admit such liquid into a second region of the washing tub, wherein the outlet conveys liquid to a bifurcation for the recirculation circuit and the second recirculation circuit, wherein the recirculation circuits are configured so that a liquid in the second recirculation circuit requires a first pressure to reach the washing tub which is lower than a second pressure required for a liquid in the recirculation circuit to reach the washing tub, and in that the recirculation pump is operated at a first speed below, or equal to, a speed threshold to circulate liquid only in the second recirculation circuit to reach the washing tub and the recirculation pump is operated at a second speed above the speed threshold to circulate liquid both in the first recirculation circuit and the second recirculation circuit to reach the washing tub, wherein the step of controlling the recirculation pump by varying the rotation speed of the recirculation pump depending to the difference between the detected liquid level and the prefixed liquid level value is carried out when the recirculation pump is operated above the speed threshold. 
     
     
         15 . The method according to  claim 14 , wherein the recirculation pump is operated at a first speed to circulate liquid only in the second recirculation circuit to reach a bottom region of the washing tub and is operated at the second speed to circulate liquid also in the first recirculation circuit to reach an upper region of the washing tub.