DE69507000T2 - Spin cycle in a laundry washing machine - Google Patents

Description

The present invention relates to a washing machine and in particular to a domestic washing machine equipped with an improved device for carrying out the spin phase of its washing program.

Washing machines are known in the art which are controlled in operation by a device which controls the sequence of the washing programme, which normally comprises, at the end of the washing and rinsing phases, a spin phase carried out at high speed of rotation of the rotary drum in order to remove as much moisture as possible from the laundry and thus reduce as much as possible the time required for subsequent drying of the laundry, regardless of how this drying is carried out, i.e. whether it is carried out in a tumble dryer or in a more traditional way by spreading the laundry out and hanging it on the line in a dry environment.

The spin phase is controlled by the programme sequence controller which sets the spin time which, as it is preset in the programme sequence controller, has a fixed length and therefore does not take into account the actual degree of moisture removal achieved by the laundry during the spin phase.

It has been found that under certain conditions, such as with fabrics that normally absorb only small amounts of moisture, with small loads of laundry or with the much higher spin speeds that can be achieved with the latest models of washing machines, the desired level of moisture removal is achieved well before the pre-set end of the spin cycle, so that the final part of the spin cycle is actually of no practical use. This obviously leads to a considerable waste of both time and energy. Furthermore, the machine is subjected to unnecessary mechanical stress and avoidable additional wear.

Document EP-A-0 553 645 discloses a washing machine provided with a spin phase in which the drain pump is switched off after a predetermined period of time and the period of time between the time at which the pump is switched off and the time at which the water level reaches a predetermined level is measured.

However, this type of solution has the disadvantage that, in order for the wringing to be completed at the end of the spin phase, the phase must last for a rather long period of time and is therefore not necessary for most cases/loads. On the other hand, if the set spin time is shortened and the laundry is very heavy and water-absorbent, the drain pump will be activated again for a fixed period of time which may be too long for complete wringing.

It would therefore be desirable, and is the main purpose of the present invention, to provide a washing machine capable of automatically determining the degree of removal of moisture from the laundry and interrupting the spin phase as soon as the desired degree of moisture removal is reached, using for this purpose highly simple and reliable methods, inexpensive components and readily available techniques.

The invention will be better understood from the following description, given as a non-limiting example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of the various components that are integrated into a washing machine according to the invention;

Fig. 2 shows a diagram illustrating an example of the sequence of the spin phase according to the present invention.

In the following description, the general term "water" is used to refer to both the washing and rinsing liquids without distinction. However, such a simplification should not affect the comprehensibility of the explanation. taking into account the context in which the term is used, as will be obvious to a person skilled in the art.

With specific reference to Fig. 1, which represents a preferred embodiment of the present invention, a solution according to the present invention is described together with the associated operating principle.

The washing machine described comprises a tub 1, a rotary drum 2 which is arranged in the tub and receives the laundry 3, an electric motor (not shown) which is connected to the rotary drum and rotates it at variable, preselectable rotational speeds.

In addition to these components, all other state-of-the-art elements of the washing machine which, even if not specifically shown in the drawing, contribute to creating the conditions necessary for the system to function properly must also be taken into account in this context.

Underneath the lye container there is a drain line 5 which is arranged essentially vertically and is connected at its upper end to the interior of the lye container, with a lye pump 6 also being attached at its lower end.

During the spinning phase of the laundry after the washing and rinsing phases, the drain pump is kept constantly running so that it continuously sucks away the water separated by the centrifugal force exerted by the rapid rotation of the drum, which water falls to the bottom of the drain tank and enters the connected drain pipe, which in turn conveys it to the pump.

In order to eliminate the above-described disadvantage that the spinning phase lasts far beyond the necessary moisture removal, the present invention is based on the practical observation that when a spinning process begins, there is a continuous flow of water downwards in the drain line 5, The water flow rate decreases as the amount of residual moisture in the spun laundry decreases.

However, the drain pump flow rate is normally greater than the actual flow of water caused by spinning and this is important, once the initial transient state of emptying the drain tank has ended, to prevent excess spin water from accumulating inside the pipe above the drain pump.

The invention consists in the fact that the operation of the drain pump is interrupted in a sequence of consecutive times t1, t2, ... tn over correspondingly preset time periods S1, S2, ... Sn, while the actual spinning process can, however, run uninterrupted as usual.

As a result, during the periods S1, S2, ... Sn, during which the drain pump is switched off, the centrifuge water continues to flow into the drain line, but is no longer pumped out by the pump, so that it begins to collect and forms the water column Z, the level of which increases as water flows into the line.

When the drain pump is then switched on again and put into operation, the water that has accumulated in the pipe is quickly pumped out and the drain pipe is thus emptied.

When this on-off cycle is carried out, thus interrupting and resuming the operation of the drain pump at a sequence of consecutive times t1, t2, ... tn and for correspondingly preselected time periods S1, S2, ... Sn, an alternating pattern in the behavior of the level of the water column Z in the drain line results, as best illustrated in Fig. 2.

Tests have shown that, as expected, under the operating conditions described above, the curve of the water column level as a function of time has a sawtooth-like profile.

Due to the amount of residual water in the laundry, which gradually decreases, the flow rate of the spin water also decreases in the same way, so that the highest water columns, which rise to levels H₁, H₂, ... Hn at the end of the corresponding periods during which the operation of the pump is interrupted, gradually decrease in height until only slight changes occur during equal periods S1, S2, ... Sn, as best shown in Fig. 2.

It can therefore be experimentally demonstrated in advance that, for a given quantity of laundry and a given washing machine, the spin phase can be considered to be completed when the flow rate of spin water from the laundry drops below a predetermined value, in which case the flow rate of spin water can be related to the quantity of water entering the outlet pipe and not being pumped out by the drain pump at the end of the predetermined intervals and therefore to the highest level reached by the water column each time during the intervals.

It is therefore possible, by means of an analogue level sensor, such as an analogue pressure switch, which is widely available on the market, connected to a point located in the lower section of the line via a bell cap 9, as well as processing, storage and control devices (not shown) suitably connected to the drive motor, the drain pump and the analogue level sensor 8, to define a whole group of operating conditions which, once checked and processed, can be considered as representing the desired "wringing" state of the laundry and can therefore be used to cause the motor driving the rotary drum at its highest spin speed to automatically stop functioning.

Thus, with a washing machine equipped as described above, the gradual application of the spinning action on the laundry and the resulting gradual reduction in the flow of water discharged from the laundry can be continuously monitored by means of a series of successive measurements of the quantity of water entering the drain line, and the spinning phase can be automatically interrupted as soon as the desired water removal from the laundry, thus preventing the spin phase from being extended unnecessarily long.

It is obvious that this basic solution to the problems allows a number of modifications and improvements which seem appropriate. For example, a first modification may consist in not detecting and processing the greatest absolute height reached by the water column at the end of the various intervals, i.e. during the periods when the operation of the water pump is interrupted, but the differences between the greatest absolute heights Z1, Z2 detected at the end of two consecutive intervals for a plurality of pairs of such consecutive intervals.

It is possible to determine experimentally and for different loads of laundry a value of the difference between the highest levels reached by successive columns of water in the drainage line, the value corresponding to the "spinning completed" condition, so that when the difference is detected the device can automatically intervene to terminate the spinning phase.

Such a modification has the advantage that the difference between successive highest levels reached by the water column in the discharge line excludes, by compensation, any factors which may adversely affect the highest level that can be reached by the water column and thus cause incorrect information to be detected by the system.

A second variant consists in choosing an arrangement in which the periods S1, S2, ... Sn are not equal to each other, as this would be considerably easier to achieve, but instead are of different lengths, the length preferably increasing progressively for the periods after the first period. In this way, adequately high levels of the water column can be achieved even during the last sections of the spin phase, as longer shutdown intervals of the drain pump compensate for a decreasing flow rate of spin water into the drain line and thus a more slowly rising level of the water column in this drain line, thus avoiding the risk that the highest level reached by the water column at the end of the shutdown interval remains below the value detected by the level sensor, As a result, the actual difference between the respective consecutive columns would not be recorded and processed accordingly by the control device.

It is understood that further technical solutions and improvements can be derived by the person skilled in the art from the teaching of the present description using methods and knowledge available in the art. Therefore, although the present invention has been described here using generally known terminology, it should in no way be considered limited by the examples described.

Claims (4)

1. Washing machine comprising a lye container (1), a drum (2) which is rotatably arranged in the container and receives the laundry (3), an electric motor which can drive the drum at different rotational speeds including the spin speed, a drain line (5) which is arranged under the lye container, an analog level measuring device (8) which measures the level of water present in the drain line (5), a lye pump (6) which pumps the liquid contained in the line outwards, control, storage and processing devices which interrupt the function of the washing machine during the spin phase, characterized in that during the spin phase the function of the lye pump (5) is interrupted at a plurality of successive times (t1, t2, ... tn) over predetermined periods of time (S1, S2, ... Sn), the spin phase further being ended when the level of the Water column (Z), which is recorded by the level measuring device (8) at the end of the time periods, falls below a predetermined value. 2. Washing machine comprising a lye container (1), a drum (2) which is rotatably arranged in the container and receives the laundry (3), an electric motor which can drive the drum at different rotational speeds including the spin speed, a drain line (5) which is arranged under the lye container, an analog level measuring device (8) which measures the level of water present in the discharge line (5), a lye pump (6) which pumps the liquid contained in the line outwards, control, storage and processing devices which interrupt the function of the washing machine during the spin phase, characterized in that during the spin phase the function of the lye pump (5) is interrupted at a plurality of successive times (t1, t2... tn) over predetermined time periods (S1, S2, ... Sn), the value of the level which is reached by the water column (Z2), is detected and stored by the level measuring device (8) at the end of each shutdown interval of the drain pump, the value of the level of the water column is then compared with the value of the level reached by the water column (Z1) in the previous shutdown interval, and the spin phase is terminated when the difference between the values of the level of the water columns (Z1, Z2) is smaller than a predetermined value. 3. Washing machine according to claim 1 or 2, characterized in that the time periods (S1, S2, ... Sn) have a length which becomes increasingly longer for the time periods after the first time period. 4. Washing machine according to one of the preceding claims, characterized in that the analog level measuring device (8) consists of analog pressure switches which are connected to a bell air seal (9) which is connected to a lower point of the drain line.