A method for washing laundry in a laundry washing machine and laundry washing machine implementing the method

Abstract

A method for washing laundry in a laundry washing machine comprising a washing tub external to a washing drum and an electrical conductivity detecting device. The method comprises the steps of comparing a first measured conductivity with a first threshold and comparing a second measured conductivity with a second threshold for performing one or more actions based on the result of said first comparison step and/or said second comparison step. The value of said second threshold is lower than the value of said first threshold.

1 . A method for washing laundry in a laundry washing machine comprising:
 a washing drum;   a washing tub external to said washing drum and configured to receive the laundry to be washed;   a water supply system configured to convey water to said washing tub;   a treating agents dispenser configured to supply at least one treating agent into said washing tub, one of said at least one treating agent comprising a detergent;   a liquid outlet circuit configured to withdraw liquid from a bottom region of said washing tub and draining said liquid to an outside of said washing tub;   an electrical conductivity detecting device configured to measure a conductivity of the liquid flowing therethrough;   wherein the method comprises:   performing one or more treating phases for treating said laundry and performing the washing of said laundry;   measuring a first conductivity of said liquid through said electrical conductivity detecting device during said one or more treating phases;   comparing said first conductivity with a first threshold;   measuring a second conductivity of said liquid through said electrical conductivity detecting device during said one or more treating phases after said first measurement;   comparing said second conductivity with a second threshold; and   performing one or more actions based on the result of said first comparison step and/or said second comparison step;   wherein a value of said second threshold is lower than a value of said first threshold.   
     
     
         2 . The method according to  claim 1 , wherein:
 measuring said first conductivity is performed after introducing water and detergent into said washing tub and before a draining liquid to the outside of said washing tub;   the method further comprises determining whether said detergent is a powder detergent or a liquid detergent by said step of comparing said first conductivity with said first threshold; and   measuring said second conductivity is performed during a further treating phase.   
     
     
         3 . The method according to  claim 2 , wherein:
 said further treating phase is a first rinsing phase; and   the method further comprises determining whether at least one additional rinsing phase is required by said step of comparing said second conductivity with said second threshold.   
     
     
         4 . The method according to  claim 2 , further comprising determining that said detergent is a powder detergent upon determining that said first measured conductivity is higher than said first threshold, or determining that said detergent is a liquid detergent upon determining that said first measured conductivity is not higher than said first threshold. 
     
     
         5 . The method according to  claim 3 , further comprising determining that at least one additional rinsing phase is required upon determining that the second conductivity is higher than said second threshold. 
     
     
         6 . The method according to  claim 2 , wherein said laundry washing machine further comprises a turbidity detecting device and the method further comprises, upon determining that said detergent is said liquid detergent:
 determining a soil level of said laundry by operating said turbidity device to measure a turbidity of said liquid; and   performing at least one soil removal phase before said first rinsing phase.   
     
     
         7 . The method according to  claim 6 , further comprising determining that said soil level is above a predetermined value upon determining that said turbidity is lower than a predetermined threshold. 
     
     
         8 . The method according to  claim 6 , wherein said at least one soil removal phase comprises introducing water into said washing tub, tumbling the laundry and draining liquid to the outside of the washing tub. 
     
     
         9 . The method according to  claim 1 , wherein:
 measuring said first conductivity and comparing said first conductivity with said first threshold is performed during a first rinsing phase to determine if at least one additional rinsing phase is required; and   comparing said second measured conductivity with said second threshold is performed to determine if at least one further additional rinsing phase is required.   
     
     
         10 . The method according to  claim 1 , further comprising introducing a waiting period before at least one of measuring said first conductivity and measuring said second conductivity, the waiting period being selected to allow said liquid to obtain a substantially steady state. 
     
     
         11 . The method according to  claim 1 , wherein:
 comparing said first conductivity with said first threshold comprises calculating a difference between a current measured value of conductivity of the liquid containing the detergent and a conductivity reference value which refers to the conductivity of clean water, or substantially clean water, and comparing said difference with said first threshold; or   comparing said second conductivity with said second threshold comprises calculating a difference between a current measured value of conductivity of the liquid containing the detergent and a conductivity reference value which refers to the conductivity of clean water, or substantially clean water, and comparing said difference with said second threshold.   
     
     
         12 . The method according to  claim 11 , it further comprising said conductivity reference value. 
     
     
         13 . The method according to  claim 1 , wherein:
 comparing said first conductivity with said first threshold comprises comparing directly a current measured value of conductivity with said first threshold; or   comparing said second conductivity with said second threshold comprises comparing directly a current measured value of conductivity with said second threshold.   
     
     
         14 . The method according to  claim 3 , wherein said rinsing phase comprises adding clean water to the laundry and draining said liquid to the outside of the washing tub. 
     
     
         15 . A laundry washing machine comprising
 a washing drum;   a washing tub external to said washing drum and configured to receive the laundry to be washed;   a water supply system configured to convey water to said washing tub;   a treating agents dispenser configured to supply at least one treating agent into said washing tub, one of said at least one treating agent comprising a detergent;   a liquid outlet circuit configured to withdraw liquid from a bottom region of said washing tub and draining said liquid to an outside of said washing tub;   an electrical conductivity detecting device configured to measure a conductivity of the liquid flowing therethrough; and   a control unit configured to:
 perform one or more treating phases for treating said laundry and performing the washing of said laundry; 
 measure a first conductivity of said liquid through said electrical conductivity detecting device during said one or more treating phases; 
 compare said first conductivity with a first threshold; 
 measure a second conductivity of said liquid through said electrical conductivity detecting device during said one or more treating phases after said first measurement; 
 compare said second conductivity with a second threshold; and 
 perform one or more actions based on the result of said first comparison step and/or said second comparison step; 
 wherein a value of said second threshold is lower than a value of said first threshold.