The present invention relates to the field of washing machines, that is to say machines for washing clothing and textile articles in general. The invention lies entirely outside the field of dishwashers such as those described for example in the prior art documents US-2006/157 086 and DE-199 40 162.

Washing machines are typically provided with a pump for metering the cleansing agent to be fed into the washing chamber. In particular, in top-range models, this pump is controlled by a programming device as a function of the load and the type of wash to be performed, in such a way that the consumption of cleansing agent is optimized.

An object of the present invention is to provide a washing machine in which the possibility of adapting the metering of the cleansing agent to specific operating conditions is further improved.

This object is achieved by means of a washing machine which includes the features of claim 1.

The washing machine according to the invention therefore overcomes the problems caused by a metered feed of the cleansing agent which is not matched to the hardness of the water used. In fact, if the water is very hard, the effectiveness of the cleansing agent is reduced, and an adequate washing action can be achieved by increasing the metered amount above the standard level. On the other hand, if the water hardness is low, the quantity of cleansing agent used can be reduced, with evident advantages in financial terms. At the same time, the washing action is improved because the presence of excess cleansing agent can lead to undesired effects such as the formation of light-coloured stains on dark garments.

Furthermore, because of the adaptation of the operating conditions of the machine to the water hardness conditions, the addition of water-softening additive to the cleansing agent becomes unnecessary.

The aforementioned advantageous effects are also found if the washing machine has a water-softener which reduces the hardness of the mains water. This is because the effectiveness of the water-softening process varies over time, since the ion exchange resins typically used for this purpose tend to become depleted and their effectiveness therefore falls from an initial maximum value to a predetermined threshold level, and must be regenerated by exposure to brine when this threshold level is reached.

In the case of the washing machine according to the invention, these variations of effectiveness of the water-softening process, and the consequent variations of the hardness of the water treated and fed to the washing chamber, have no effect, since the amount of cleansing agent fed in is adapted automatically to the degree of hardness sensed.

A further object of the present invention is a washing process performed in a washing machine of the aforementioned type.

Further advantages and characteristics of the present invention will be made clear by the following detailed description, which refers to the attached drawings provided by way of non-limiting example, in which:

• Figure 1 is a schematic representation of the principal components of a washing machine according to the invention, and
• Figure 2 is a schematic representation of a variant embodiment of a washing machine according to the invention.

A washing machine comprises, in a conventional way, a fixed support structure in which a washing chamber 10 is located (Fig. 1), which the user can access by opening a door hinged on the support structure. The chamber 10 is typically a rotating drum. A water feed conduit 12, in which a shut-off valve 14 and a water hardness sensor 16 are positioned, opens into the washing chamber 10. The machine further comprises a cleansing agent container 20 having a pump 22 for the metered feed of the cleansing agent into the chamber 10, and a programming device 24 which controls its operation.

Among its various functions, the programming device 24 receives the value of water hardness sensed by the sensor 16, and controls the operation of the cleansing agent metering pump 22 as a function of this value. In particular, as the hardness of the water decreases, the amount of cleansing agent needed is reduced, and vice versa.

Figure 2 shows a washing machine which comprises an auxiliary feed conduit 26 having its own shut-off valve 28, and on which it is placed a known water-softener 30, which comprises hardness sensors 16 for the water softened within it, and which is housed in the fixed support structure of the washing machine. The auxiliary conduit 26 opens into the first conduit 12 at a point 32 upstream of the washing chamber 10.

The water fed into the washing chamber 10 is therefore a mixture of softened water, taken from the conduit 26, and water with its original hardness, taken from the conduit 12. The overall hardness of the mixture depends on the different hardnesses of the two flows and on their relative amounts, which in turn are determined by the times for which the corresponding valves 14, 28 are open, and this overall hardness is calculated by the programming device 24. The programming device can then control the cleansing agent metering pump 22 in such a way that it supplies the optimal amount, according to the degree of hardness of the water fed into the washing chamber 10.

Clearly, provided that the principle of the invention is retained, the details of construction and the embodiments can be varied widely from what has been described purely by way of example, without departure from the scope of the invention, as defined by the claims.