EP2009165A1

EP2009165A1 - Operating cycle for the drain pump of a household washing appliance

Info

Publication number: EP2009165A1
Application number: EP07425397A
Authority: EP
Inventors: Lucio Gastaldelli; Marco Molinari; Mauro Tosi
Original assignee: Bonferraro SpA
Current assignee: Bonferraro SpA
Priority date: 2007-06-28
Filing date: 2007-06-28
Publication date: 2008-12-31

Abstract

An operating cycle for the drain pump (DP) of a household washing appliance, such as a dishwasher or a washing machine, is controlled not only on the basis of the time calculated to drain the water from the sump (MS) but also on the basis of the level of the water to be drained actually detected by a pressure switch (PS) and possibly provides an intermittent activation to prevent the air that sets in the pump body and therefore between the impeller blades from causing the cavitation problem.

Description

The present invention relates to household washing appliances, such as dishwashers and washing machines, and in particular to a household appliance in which the drain pump operates according to a particular cycle.
It is known that water drain pumps used in household washing appliances are conventionally operated with a cycle that provides the operation of the pump for a preset time calculated on the basis of the amount of water to be drained and of the pump flow rate.
However, pumps are not seldom subject to cavitation problems, i.e. they stop operating properly when inside the pump impeller there are air bubbles that trigger a phenomenon due to which the pump, though electrically operating, can no longer mechanically evacuate the water.
In practice, a discontinuity occurs in the liquid passing through the impeller because the air trapped within the pump body prevents the passage of the residual liquid to be drained. In order to overcome this drawback, where possible, the pipings are arranged so as to guarantee that the impeller is never invaded by substantial air flows, rather it is always able to draw liquid. As an alternative, vents are made at strategic positions along the hydraulic circuit to prevent air from reaching the pump.
It is clear that said cavitation problem therefore poses some constraints to the arrangement of the pipings and of the pump itself, and possibly requires also the addition of additional components such as the vents, resulting in an increase in manufacturing costs.
Therefore the obj ect of the present invention is to provide an operating cycle for the drain pump which overcomes said drawbacks. This object is achieved by means of a cycle in which the pump operation is controlled not only on the basis of the calculated drain time but also on the basis of the level of the water to be drained actually detected, and possibly provides an intermittent activation to prevent the air that sets in the pump body and therefore between the impeller blades from causing the cavitation problem.
The main advantage of the cycle according to the present invention is that it offers the possibility of locating the pump at positions within the appliance that are apparently unsuitable for the correct operation of the pump, so as to achieve the maximum flexibility in the arrangement of the pipings and to reduce the manufacturing costs.
A further advantage of this cycle stems from the fact that its implementation does not require any additional component with respect to those already usually present in the appliance.
These and other advantages and characteristics of the cycle according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:

Fig.1 is a diagram of the household appliance components that cooperate in implementing the cycle according to the invention; and
Fig.2 is a flow chart of said cycle.

With reference to Fig.1, there is seen that in a household washing appliance, such as a dishwasher, the water to be drained is collected in a machine sump MS connected through a pipe to the drain pump DP, from which a further pipe branches out to the drain. The water level in sump MS is detected by a pressure switch PS, that is conventionally employed to check the amount of water introduced in the machine during the loading phase, which is connected to a control unit CU which in turn controls the drain pump DP.
The simple and effective operation of the cycle according to the present invention is described in the flow chart illustrated in Fig. 2.
At the cycle start, the drain pump is activated by the control unit that detects the water level in the sump through the pressure switch, and it is operated for a preset period of time which in the absence of cavitation problems is sufficient to empty the sump down to the required minimum level. At the end of the preset period of time, a check is performed whether said level has been reached and in the affirmative the drain pump is stopped and the cycle ends.
On the contrary, if the pressure switch indicates that the level has not been reached that means that the drain pump is in a state of mechanical stall in which an air bubble does not allow the water to be properly drained. In such an instance, the control unit temporarily interrupts the operation of the drain pump, indicatively for a duration between 1 and 15 seconds, to allow the liquid to oscillate within the pump and thus move the air bubble into a position where it can be evacuated.
It has been found that this generally occurs upon the first try, but were it not the case the cycle is repeated until the object is achieved. The exact durations of the operating time and of the temporary interruption time are defined according to the size and type of the hydraulic circuit.
The novel cycle according to the present invention can therefore be summarized in the following steps:

a) activating the drain pump;
b) operating the drain pump for a preset time;
c) checking that the minimum level in the sump has been reached;
d) in case of negative outcome of the check, returning to cycle start after some seconds of temporary stop of the drain pump, and in case of positive outcome of the check, finally stopping the drain pump and ending the cycle.

It is clear that the above-described and illustrated embodiment of the cycle according to the invention is just an example susceptible of various modifications. In particular, the duration of the step of temporary stop of the drain pump may be increased and possibly divided into two or more steps, i.e. there may be provided two or more steps of stopping/restarting the pump prior to returning to cycle start in order to further facilitate the evacuation of the air bubble.

Claims

Operating cycle for the drain pump (DP) of a household washing appliance, said household appliance including a sump (MS) for collecting the water to be drained that is connected through a pipe to said drain pump (DP) whose operation is controlled by a control unit (CU), said cycle including the steps of:
a) activating the drain pump (DP);

b) operating the drain pump (DP) for a preset time;
and being characterized in that it further includes the steps of:
c) checking that the minimum level in said sump (MS) has been reached;

d) temporarily or finally stopping the drain pump (DP) according to the outcome of said check.
Operating cycle according to claim 1, characterized in that if the check of step c) has a negative outcome step d) provides the temporary stop of the drain pump (DP) followed by the return to cycle start.
Operating cycle according to claim 1, characterized in that if the check of step c) has a positive outcome step d) provides the final stop of the drain pump (DP) followed by the cycle end.
Operating cycle according to one of the preceding claims, characterized in that the check of step c) is performed by means of a pressure switch (PS) operatively connected to the sump (MS) and to the control unit (CU).
Operating cycle according to one of the preceding claims, characterized in that the duration of the step of temporary stop of the drain pump (DP) ranges from 1 to 15 seconds.
Operating cycle according to one of the preceding claims, characterized in that the duration of the step of temporary stop of the drain pump (DP) is divided into two or more steps separated by one or more restarts of the drain pump (DP).