GB2081751A

GB2081751A - Water Level Regulation in an Automatic Washing Machine

Info

Publication number: GB2081751A
Application number: GB8123312A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-12
Filing date: 1981-07-30
Publication date: 1982-02-24
Also published as: FR2488624A1; IT1137813B; GB2081751B; IT8123394A0; DE3030501C2; DE3030501A1; FR2488624B1

Abstract

An automatic washing machine is provided with regulating means for regulating the water-level in a drum of the machine, the regulating means comprising at least one electrically controllable valve for the feed water and at least one device recognizing the level of the entered water and having a switching range (SB), the lower limit (NU) of which determines a minimum wash level and controls the opening of the valve and the upper limit (NO) of which controls the closing of the valve. The switching range (SB), for a given size of drum and valve, makes possible the feed of approximately 1 litre of water and the drum is rotated during the feed process. <IMAGE>

Description

SPECIFICATION Water Level Regulation in an Automatic Washing Machine The present invention relates to an automatic washing machine provided with regulating means for regulating the water level in a rotatable drum of the machine.

It is known that in an automatic washing machine the feed water valve is controlled from the water level reached in the wash liquid tank via a device which recognizes this level. It is known to use a pressure measuring cell as such a device (for example, DE-GM 19 91 525).

For recognizing different levels, a number of pressure measuring cell systems have been provided in automatic washing machines, which intentionally have a wide switching interval. This means that the upper switching point, at which the feed water valve closes, is associated with a level higher by approximately 40 mm water gauge than the lower switching point, at which the feed water valve is again opened. In general, there is a trend towards further increasing the switching interval. The cause of this lies on the one hand in the lower cost of a pressure measuring cell having a wider switching interval compared with one having a smaller switching interval, and on the other hand in the fact that there is a view among specialists that it is the upper switching point only which determines the desired level.The feed operation is carried out with the drum stationary, as otherwise the pressure surges that would occur with a moving drum could cause premature switching of the pressure measuring cell.

However, this has the effect that the feed operation must be terminated provisionally by the upper switching point of the pressure measuring cell, so that too high a level does not result. The laundry which hitherto has not been in movement then absorbs a considerable quantity of the entered water and thereby reduces the value for the measured level.

The corresponding conditions are illustrated in Fig. 1. In Fig 1 the full line indicates the filling operation for a drum content with a high absorption capability. As soon as the level NU corresponding to the lower switching point has again been reached, the feed water valve is again opened and water is again supplied to the wash liquid tank, until the level NO corresponding to the upper switching point is again reached. On the assumption that the drum is loaded with laundry having a high absorption capability, a negative control deviation from a taget level NS would become established at the end of the filling operation, known as the recovery phase.The absorption capability of the laundry decreases, however, during the recovery phase, so that the ratios of the switched-on times tE to the oscillation times T always continue to decreaSe, namely from tEh to Th, through tEm to Tm; to tEs to Ts. If the absorption capacity of the materials contained in the drum is poor, the level falls from the upper value NO only slowly towards the lower value NU, and on the average of a number of filling operations usually reaches a positive control deviation (+RA) from the target level NS.

In the pressure measuring cell according to Fig. 1, one half of the switching interval SB represents, for instance, a level difference of 20 mm.

From this brief explanation it will be clear that the widely differing absorption capabilities of the laundry to be washed represents an imponderable, which has hitherto caused washing machine manufacturers to set optimum conditions for a full laundry loading in the standard programme. These conditions are indeed specified by standard regulations. This, however, leads to the result that, in the case of underloading, washing is frequently carried out with too much water, due to the above-described circumstances.

If the absorption capability of the laundry is low (for example synthetics, or in the case of a very small loading with other articles), then with approximately 2.5 litres, so much further water will be drawn in that the average wash level is displaced towards the upper switching point. If, for example, there is less than 1 kg of laundry in the drum, then the water level will be filled up to the upper switching point, and therefore by much more extra water than the laundry is capable of absorbing. The dependence of the entered volume of water upon the quantity of the introduced laundry, for a constant absorption capability, is represented by the S-shaped curve in Fig. 2 shown as a dashed line.

A further cause for the pronounced upwards scatter of the average wash level in the case of the conventional control lies in the fact that, when upward pressure surges occur in the wash liquid tank, the laundry loading present exerts a certain damping action, so that the upper switching point more seldomly responds unintentionally. By contrast, negative pressure surges frequently influence the pressure measuring cell, so that in spite of a large switching range the control device draws in too much water, because the lower switching point frequently responds prematurely.

There is accordingly a need for a washing machine in which the average wash level of the entered water can be set more accurately than hitherto and in which, in addition, the feed operation, which with the known control systems takes a comparatively long time when the drum is fully loaded, can be decisively shortened.

According to the present invention there is provided an automatic washing machine provided with regulating means for regulating the water level in a rotatable washing drum of the machine, the regulating means comprising at least one electrically controllable valve for controlling the flow of water into the drum, switching control means responsive to the level of water in the drum and operable to open the valve at a lower limit of a switching range of the control means and to close the valve at an upper limit of the range, the lower limit determining a minimum wash level and the switching range being so related to the flow cross-section of the valve and the volume of the drum as to allow substantially one litre of water to flow into the drum between opening and closing of the valve, and means to cause the drum to rotate during water flow into the drum.

Expediantly,-therefore, for a given drum size and valve size, the switching range is such as to make possible the entry of approximately 1 litre of water, and the drum is rotated during the feed operation. The rotation of the drum during the feed operation has the effect of reducing disturbing influences on the regulating means due to absorption processes. Furthermore, by contrast to the past practice of providing as wide as possible a switching interval, in a machine embodying the present invention the swtiching range is kept so small that in each recovery cycle only 1 litre of water flows in. This makes possible, even for an error of the same relative magnitude, a smaller absolute control deviation of the average wash level from the target level.

In a preferred automatically controlled washing machine for carrying out the above-described water feed control, the control means comprises a damped pressure measuring cell with a switching point at the lower limit. The pressure surges which occur in the measuring line as the drum revolves with the laundry tumbling over are largely balanced out by the damping of the pressure measuring cell. Since the lower limit of the switching range determines the minimum level for the associated washing programme, this pressure measuring cell can also bring the average wash level of the switching range closer to the required minimum water quantity.

If, in an advantageous embodiment of the invention, the pressure measuring cell also has a switching point at the upper limit, the switching range can be maintained in a simple manner.

In another advantageous embodiment of the invention, the control means comprises a timer which limits the upper end of the switching range, which timer can be switched on by the pressure measuring cell when the switching point is reached. After the timer has run through, the feed water valve, which was switched on when the switching point was reached, can again be switched off, so that the timer determines the switching interval.

Preferably, the pressure measuring cell comprises an electronic circuit, which serves for preparing a continuously pressure-proportional output signal for the switching functions. In a washing machine equipped in this manner, the problems of the design-imposed switching interval is very small, because on each pressure change, however small, a proportional output signal change occurs. The selection of the desired switching ranges is therefore no more difficult than the choice of their lower limits.

In a particularly advantageous embodiment of the washing machine according to the invention, one or more nozzles are disposed in the measuring line for fluid damping, it has been found that condensation does not take place inside the measuring line, so that there is no barrier to the use of small nozzles in washing appliances. Expediently, the measuring line comprises a hose approximately 350 mm long having an internal diameter of approximately 4.5 mm, and the nozzle has an internal diameter of approximately 0.3 mm. With these dimensions, it has been found easy to set the desired conditions.

For preference, the output line from the electronic circuit includes a resistor-capacitor damping element, the time constant of which is of approximately the same magnitude as that of the' fluid damping.

An embodiment of the present invention will now be more particularly described, by way of i? example, with reference to the accompanying drawings, in which: Fig. 1 is a diagram showing the behaviour of the water level in the wash liquid tank, for three different laundry properties, in a known control system, Fig. 2 is a diagram showing the average results for the set water level with a known control system and with a method exemplifying the present invention, Fig. 3 is a diagram showing the level behaviour of entered water in a method examplifying the present invention, Fig. 4 is a diagram of part of a circuit for electrical damping of a pressure measuring cell in regulating means of a washing machine embodying the invention, and Fig. 5 is a sectional view of part of a measuring line, with fluid damping, of such a measuring cell.

The diagram of Fig. 1 has already been explained with reference to the evaluation of the state of the art. This diagram shows a full line for laundry having high absorption capacity, a dotand-dash line for laundry of medium absorbtion capacity, and a dotted line for laundry with low absorption capacity.

It has been explained that in the state of the art, average wash levels are obtained which are regularly higher with each loading, sometimes much higher, than the necessary filled level shown by the full line in Fig. 2. The necessary filled level below the range of 1 kg laundry is shown only in broken line, because such small """ loadings hardly ever occur.

A method exemplifying this invention, in particular a method of operating a washing machine embodying the invention, is explained in more detail with reference to Fig. 3, which shows a curve achieved by use of the method and which comes extremely close to the curve illustrated in Fig. 2 for the necessary filled level along the full line, even if not identical with that curve. The smaller switching interval for a pressure measuring cell of water level regulating means of washing machine embodying this invention leads to a flatter form of the descrinding parts of the curve, which characterize the absorption process. Since the absolute switching interval is considerably smaller, relative errors have a correspondingly smaller effect.Thus, with a loading of the drum with highly absorbent laundry, hardly any control deviation occurs; the control deviation RA tends towards zero. For a drum loading with laundry having low absorption capacity (dotted line), the comparatively still too large, switching range-dependent water quantity can lead to a small positive control deviation (+RA). Since, however, this control deviation in the most unfavourable case is of approximately the same size as the control deviation of the state of the art, but the absolute switching interval is smaller, the excess quantity of water is considerably smaller.On the other hand, however, the revolving drum and the damping of the pressure measuring cell are factors which almost always bring this control deviation to zero, so that when a method exemplifying the present invention is used the average wash level almost always agrees with the set-point level NS.

Since the switching range in the pressure measuring cell is considerably smaller than in the state of the art, the target level NS (approximately mid-way between the upper level NO and lower level NU) lies in the same ratio nearer to the minimum wash level; the excess quantity of water is at most a little more than 0.5 litre.

This results in the advantage that, with a knowledge of this accurate level regulation, the lower level can be set to be lower by the amount of one half of the switching range, without having to accept the disadvantage that a highly absorbent batch of laundry has to be washed with a lower water level than the minimum washing level.

For the realization of electrical damping of the pressure measuring cell, Fig. 4 shows a part of a circuit 30 of the pressure measuring cell, illustrated inside the dotted outline, which comprises an output amplifier 31, the output line 32 of which contains a resistor-capacitor damping element consisting of a capacitor 33 and resistor 34. The effect of such a damping element is generally known and therefore does not need to be explained in more detail. The damped output signal can be tapped from a point 35 of the output line 32.

Fig. 5 shows diagrammatically an arrangement of a pair of nozzles 51 and 52 in a hose-like measuring line 50 coupled to a pressure measuring cell 53, of which only the lower plate is shown in part, by a hose connection 54. Suddenly occurring pressure fluctuations in the measuring line 50 require, for their detection in the pressure measuring cell 53, a gas stream which is highly braked through the fine nozzles 51 and 52 and therefore causes damping of the pressure fluctuations.

Claims

1. An automatic washing machine provided with regulating means for regulating the water level in a rotatable washing drum of the machine, the regulating means comprising at least one electrically controllable valve for controlling the flow of water into the drum, switching control means responsive to the level of water in the drum and operable to open the valve at a lower limit of a switching range of the control means and to close the valve at an upper limit of the range, the lower limit determining a minimum wash level and the switching range being so relatied to the flow cross-section of the valve and the volume of the drum as to allow substantially one litre of water to flow into the drum between opening and closing of the valve, and means to cause the drum to rotate during water flow into the drum.

2. A washing machine as claimed in claim 1, the control means comprising a damped pressure measuring cell with a switching point at said lower limit.

3. A washing machine as claimed in claim 2, wherein the pressure measuring cell additionally has a switching point at said upper limit.

4. A washing machine as claimed in claim 2, the control means further comprising a timer limiting the upper end of the switching range, the timer being adapted to be switched on by the pressure measuring cell at said switching point thereof.

5. A washing machine as claimed in any one of claims 2 to 4, wherein the pressure measuring cell includes electrical circuit means for providing a switching output signal having a value proportion to the instantaneous pressure in the drum.

6. A washing machine as claimed in any one of claims 2 to 5, comprising at least one flow damping nozzle arranged in a measuring line of the pressure measuring cell to damp the rate of fluid flow thereto.

7. A washing machine as claimed in claim 6, wherein the measuring line comprises a hose of substantially 350 millmetres length and 4.5 millimetres internal diameter, the or each nozzle having an internal diameter of substantially 0.3 millimetres.

8. A washing machine as claimed in either claim 6 or claim 7 when appended to claim 5, wherein the circuit means is provided in an output signal path thereof with resistor-capacitor damping means having a time constant substantially equal to the amount of flow damping provided by the nozzle or nozzles.

9. An automatic mashing machine provided with water level regulating means substantially as hereinbefore described with reference to Figs. 3 to 5 of the accompanying drawings.