DE69618563T2 - Dishwasher with rotating spray arm with selectively powered spray nozzles and processes - Google Patents

Description

The present invention relates to a dishwasher with at least one and preferably two rotating spray devices provided with selectively fed spray nozzles, and to an associated cleaning method.

It is known that dishwashers essentially consist of a washing chamber which is closed at the bottom by a tank for collecting liquid and into which washing water, descaled if necessary, is introduced and, at appropriate stages of the cleaning process, is suitably heated and mixed with detergent.

The cleaning liquid is sucked in during the cleaning process by a pump and fed into spray devices which are generally of the type with rotating arms arranged symmetrically relative to an axis of rotation and spraying by their movement, if possible with a uniform distribution of the spray jets in the chamber, the dishes being placed in suitable baskets in the washing chamber.

The use of rotating arms makes it possible to obtain good cleaning with a minimum volume of liquid, which is made to circulate from the collection tank back into the spray arms by a low power pump with a small flow rate and a sufficient pressure to give the spray jets a speed and therefore kinetic energy adequate for cleaning effectiveness.

The reason for this is obvious: the power used by the pump is in first approximation for the same pressure H, which determines the discharge velocity of the jets, proportional to the cumulative flow rate of the jets, and the smaller the latter, the lower the power used.

Furthermore, the smaller the flow rate, the more it is possible to reduce the dimensions of the pump and the recirculation pipes and therefore the capacity of the recirculation system, without causing appreciable pressure losses, with an obvious reduction in the amount of cleaning fluid used.

With this dual aim, a common means in dishwashers is to feed each of the two rotating spray devices, an upper one and a lower one, alternately in a mutually exclusive manner and, if necessary, to feed the two devices simultaneously, dividing the flow between the two arms, which is varied as a function of time.

Recently, dishwashers have also been proposed in which the pump is driven by variable speed motors, for example by asynchronous three-phase motors powered by a converter whose frequency can be controlled.

Since the flow rate of a turbopump is, to a first approximation, proportional to its rotational speed and the pressure is proportional to the square of the rotational speed, it is possible to reduce the rotational speed and the power consumed in order to reduce the kinetic energy of the jets when they are not required by slightly reducing the flow rate and to increase it when the cleaning operation requires a higher energy of the spray jets.

This solution leads to a certain saving in consumption, but is cost-intensive and does not solve the problem of reconciling cleaning effectiveness with short operating times and reduced consumption.

The cleaning process or cycle generally includes various phases of pre-cleaning, cleaning and rinsing, in which the cleaning liquid that is sprayed onto the dishes should have different properties.

In the pre-cleaning and rinsing phases it is necessary to remove the dirt particles loosely attached to the surface of the dishes, ideally with a high flow rate of liquid (to make the operation faster) and a high speed (hence kinetic energy) of the spray jets is not required.

However, during the cleaning phase(s) it is necessary to apply a local mechanical action of considerable pressure in order to cause the dirt particles to detach, which can only be achieved by means of a particularly high speed of the spray jets, which must hit all points of the surfaces to be washed during the cleaning phase.

From this point of view, the use of variable speed pumps does not give an optimal result, since a reduction in speed entails a reduction in pressure but also in flow rate, whereas an increase in the latter is desirable.

Another disadvantage of known dishwashers is that the rotating spray arms of the hydraulic vortex type are set in rotation by the torque of at least one spray jet and always rotate in the same direction: the arrangement of the dishes in the baskets therefore leads, depending on the shape of the dishes, to the formation of shadow areas, i.e. surface areas of the dishes which cannot be directly reached by the spray jets.

A further limitation of known dishwashers is that the rotating spray arms are provided with a fair number of spray nozzles which, during the rotation of the arms, travel along predetermined spray perimeters or "paths" which produce discontinuous spray cones such that the direct effect of the jets on the surface of the dishes is not complete even in the absence of shadow areas.

To avoid this limitation, it would be necessary to increase the number of nozzles, while their dimensions and therefore the required flow rate cannot fall below certain limits, with a consequent increase in the power of the pumps and their dimensions and those of the recirculation pipes and finally the capacity of the recirculation circuit.

DE-A-38 16 408 and DE-A-38 13 510 disclose dishwashers with spray elements divided into two channels and a transition device to connect the channels to a circulation pump.

These disadvantages are overcome by the dishwasher which is the subject of the present invention and is defined in claim 1.

According to a further feature of the present invention, the spray nozzles opening into one manifold are arranged at a radial distance from the axis of rotation of the device between those of the spray nozzles opening into the other manifold, so as to double the number of spray paths.

According to a further feature of the present invention, the thrust nozzles opening into the two distributors are oriented so as to apply torques in the same direction to the spray device.

According to another feature of the present invention, the thrust nozzles opening into the two distributors are oriented so as to apply opposite torques to the spray element so as to rotate the spray device in one or the other of the two directions of rotation depending on whether one or the other of the two distributors is fed.

Advantageously, in this case, the thrust nozzles are dimensioned and/or arranged at a distance from the axis of rotation of the device and/or are fed with a fluid at different pressure in such a way that the opposing torques generated in the case of a combined feeding of the two tubes do not neutralize each other and the resulting torque causes the spray device to rotate.

According to a further feature of the present invention, the dishwasher is equipped with programming means for arranging the combined feeding of the two distributors during the pre-wash and wash phases of a wash cycle and the intermittent, mutually exclusive feeding of one or the other distributor during the wash phase of a wash cycle.

The characteristics and advantages of the invention will become clearer from the following description of a preferred embodiment and its variants, set out with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic overall view of a dishwasher with two spray devices in vertical section, each of which includes two separate and distinct distributors, with means for feeding one distributor independently of the other.

Fig. 2 is a plan view of a preferred embodiment of a spray device for the machine shown in Fig. 1.

Fig. 3 is a sectional view of the spray device along the section line A-A in Fig. 1.

Fig. 4 is a sectional view of a second embodiment of the spray device also along the section line A-A in Fig. 1.

Fig. 5 shows in a qualitative diagram a number of curves describing the functional characteristics of a pump for a dishwasher and the load curves of a spray device such as that shown in Figs. 2, 3 and 4.

Fig. 6 shows diagrammatically the effect of the spray jets on the dishes in a machine equipped with a spray element such as that shown in Fig. 4.

With reference to Fig. 1, a dishwasher according to the invention essentially comprises a washing chamber 1 which terminates at the bottom in a tank 2 for collecting liquid and in a basin 3 for holding a filter (not shown) and for directing liquid to at least one recirculation or drain pump 4.

The pump 4 is actuated by a motor 5, generally a synchronous motor, and its outlet is connected to the inlet of a diverter unit 6, for example of the rotating cylinder type, actuated by a motor element 7.

A filling solenoid valve 8, when open, with an inlet connected to the main water line, supplies the tank 2 with liquid, if required via a softening cell (not shown).

A level detector 9, for example of the pressure switch type, sends a level signal to a programming unit 10 which orders the activation of the solenoid valve 8, the motor 5 and the motor element 7 according to the various phases of a cleaning cycle.

In the prior art, the diverter 6 selectively directs the flow generated by the pump 4 in a mutually exclusive manner towards a first rotating spray device 11 or lower rotor, a second rotating spray device 12 or upper rotor arranged in the rinsing chamber 1, or towards a drain 13.

Here, instead, the diverter 6 is modified to operate in a completely different manner, which will be considered below after the basic feature of the present invention has been explained.

According to the basic feature of the present invention, at least one of the spray devices and preferably the lower rotor 11 consists of two spray distributors which are separate and different and can be fed individually.

The structure of the rotor 11 is shown in Figs. 1, 2 and 3, in which it is shown in a composite vertical section (Fig. 1) along the section line B-B in Fig. 3, in a plan view (Fig. 2) and in a horizontal section along the section line marked A-A in Fig. 1 (Fig. 3).

The rotor consists of two rotating arms 14, 15 arranged symmetrically with respect to a rotation axis 16 and forming two flow chambers or distributors 17, 18 suitably separated by internal partitions 19, 20.

A plurality of N spray openings or nozzles 21, 22, 23, 24, 25, 26 open into the upper wall of the two arms, which cause the distributor 17 to communicate with the outside space.

Due to the effect of the rotation of the arms around the rotation axis 11, the nozzles move along N concentric paths, which are preferably, but not necessarily, equidistant.

The distance between the paths is essentially equal to (D-d)/(N-1), where D is the diameter of the outermost path, d is the diameter of the innermost path, and N is the number of nozzles.

At the ends of the arms 14, 15, the distributor 17 is provided with thrust nozzles 27, 28 for ejecting two jets of liquid with a velocity component that imparts a torque to the arms, for example in a clockwise direction with reference to Figs. 2 and 3, represented by the arrows 29, 30.

In the upper wall of the rotating arms 14, 15 there also open a second plurality of spray openings or nozzles 31, 32, 33, 34, 35, 36 (in a number M preferably, but not necessarily equal to N) which cause the distributor 18 to communicate with the outside space and which are arranged in such a way that these nozzles, by the effect of the rotation of the arms, travel along paths lying between those along which the nozzles of the first plurality travel.

In this way, the distance between the different spray paths is halved and the sprayed area is covered by the spray jets with a greater resolution.

The distributor 18 is also preferably provided at the ends of the arms with thrust nozzles 37, 38 for the ejection of two jets of liquid with a velocity component which imparts a torque to the arms, for example in the same direction as that caused by the jets emanating from the nozzles 27, 28.

Alternatively, as shown in Fig. 4, the two manifolds 17 and 18 may be provided with thrust nozzles 39, 40 and 41, 42 respectively for ejecting jets of liquid imparting opposing torques to the arms, shown by arrows 43, 44 respectively, preferably of different sizes which can be easily achieved by different diameters of the thrust nozzles, by different pressures of the liquid allowed to flow from the nozzles, by different distances of the nozzles from the axis of rotation, by different orientations of the nozzles to achieve different usable thrust components, or by a combination of these factors.

As can be clearly seen from Fig. 1 and in the sections in Figs. 3 and 4, the rotor 11, which is formed by the arms 14, 15, is provided with a hub 45, in which a screw is inserted for fixing the rotor with the function of an axle on a support in which two coaxial pipes 47, 48 are formed, which open on the upper side of the support and are connected to the distributor 18 through two openings 49, 50 in the shape of a circular segment, each, and to the distributor 17 through an opening 51 in the shape of a circular ring surrounding the hub 45, the openings opening in the lower wall of the rotor and facing the coaxial pipes 47, 48.

The pipes 47, 48 of the support 46 are selectively caused to communicate with the outlet of the pump 4 by means of the diverter unit 6.

Conveniently, the diverter unit 6 can be designed to operate according to 4 angular positions of its rotating cylinder as follows:

1. Position: Pump outlet is only connected to pipe 47.

2nd position: The pump outlet is connected to pipe 47 and at the same time also to pipe 48.

3. Position: Pump outlet is only connected to pipe 48.

4th position: The pump outlet is only connected to the drain pipe 13.

The diverter unit 6 is a possible means for feeding one of the manifolds 17, 18 independently of the other manifold and can of course be replaced by other equivalent means, for example independent valve devices for closing/opening each flow path. However, for use as means for feeding at least one of the manifolds 17, 18 with a flow of spray liquid independently of the other manifold, the present invention, as set out in claim 1, provides a first pump (e.g. pump 4) and a second pump which can be activated individually for feeding each flow path.

Before describing the various possible operating methods of a dishwasher such as the one described, it is appropriate to consider, with reference to Fig. 5, the characteristic curves of a pump used in the dishwasher shown in Fig. 1 under various working conditions.

For reasons of cost and simplicity of construction, the pumps used in dishwashers have a characteristic speed or characteristic number of revolutions n9 = n Q/H3/4 (where n = rotational speed in revolutions/minute, Q = flow rate in m³/s and H = head in meters), which is medium/high, greater than 100.

For this type of pump with a constant rotation speed, the generated pressure gradient decreases considerably with an increase in the supplied flow rate and is shown by the curve H(Q).

The power consumed by the pump is shown by curve P and initially increases for low flow rates before rapidly decreasing with increasing flow rate.

The supply is represented by the curve η.

The operating point of the pump is defined by the intersection of the characteristic curve H(Q) with a load curve.

As a first approximation, the total pressure head of the pump is converted into kinetic energy and hence the discharge velocity from the nozzles, since the function of the pump is to generate spray jets and therefore the pressure losses of the hydraulic circuit and the static pressure head between the liquid level in the basin 3 and the level of the spray nozzles can be neglected.

The loading curve is therefore represented to a good approximation by the equation Q = S 2gH, where S is the discharge cross-section corrected to account for the contraction of the fluid flow.

The curve QL1 represents, as an indication, the load curve for a cross-section S1 equal to the cumulative discharge opening of the nozzles opening to the outside space in the distributor 17 and corresponds qualitatively to an optimal state of use of the pump, corresponding to the maximum supply and the maximum power consumed.

It is clear that if the nozzles opening into the distributor 18 have the same usable cross-section, the curve QL1 also represents the load curve for this group of nozzles.

The cumulative load curve of the two groups of nozzles opening into the manifolds 17 and 18 is clearly given by the sum of the two load curves with respect to the flow rate axis and is represented by the curve Q(L1 + L2) in Fig. 5.

It is therefore clear that when the nozzles of only the distributor 17 or only the distributor 18 are fed, the conditions for an outgoing flow from the working nozzles of the pump are defined by the point 149, while the outgoing flow and the working conditions are defined by the point 60 when the nozzles of both distributors are fed together.

In practice, the resulting cumulative outgoing flow is much larger (up to 50%) and the velocity of the outgoing flow from the nozzles is lower (roughly 25%), which consequently halves the power of the spray jets and significantly reduces the power consumed by the pump.

It is therefore possible to obtain a relatively high flow rate of the spray jets at a reduced jet power, which is particularly effective for carrying out pre-cleaning and rinsing operations, without modifying the characteristics of the pump, for example by increasing the number of its revolutions, which would produce an increase in the flow rate, but would also entail a more than proportional increase in the pressure and therefore in the power consumed.

If desired, the common supply of the two distributors 17, 18 can be combined with a slight increase in the rotation speed of the pump.

Consequently, the characteristic curve of the pump is represented by the curve Q1(H), the consumed power by the curve P1 and the supply by the curve η1.

The working conditions in this case are represented by point 150 and include a power consumption approximately equal to that which occurs at a lower speed when only one of the distributors 17, 18 is fed.

Consideration will now be given to various possible modes of operation of a dishwasher according to the present invention, that is to say a dishwasher equipped with a rotating spray element with two spray distributors that can be fed selectively.

During a pre-cleaning phase, the programming unit 10 (Fig. 1) requests the supply from both distributors 17 and 18 (Fig. 3).

These processes therefore take place with an increased flow rate Q2 (Fig. 5) and with a spray jet power that is lower and correlated with the pressure head H2 (Fig. 5).

The spray jets are distributed along spray paths that are very close to each other and the operations are particularly effective without overloading the motor that activates the pump (even in a case where the flow rate is further increased to the value Q3 as the rotation speed increases).

It is easy to verify that the rotation speed of the spray element when the thrust nozzles work together is higher than that given to the spray element when only one distributor is fed.

If the thrust nozzles are antagonistic but the torques generated do not cancel each other out, the rotation speed of the spray element is lower.

The flow rate of liquid hitting the sprayed surface is the same in both cases and the effectiveness of pre-cleaning and rinsing is the same, with some advantage in the second case since each point on the sprayed surface received pulses of spray liquid of longer duration, albeit at a lower frequency.

After the pre-cleaning phase has been completed, a cleaning phase is requested during which only one of the rotor’s distributors is fed.

The cleaning phase is then carried out with a reduced flow rate Q1 (Fig. 5) but the power of the jets is correlated with a high pressure head H1, which is therefore suitable for removing deposits of stubborn dirt with an effective mechanical action.

As a possible and preferred alternative, the cleaning phase can be divided into two or more sub-phases, during which one or the other of the distributors 17, 18 is alternately fed in a mutually exclusive manner.

In this way, the spray jets from the two distributors, which travel along different spray paths, hit the surface to be cleaned with twice the resolution.

Two cases can be distinguished:

In a case where the thrust nozzles of the two distributors exert a torque in the same direction on the rotating spray element, it will always rotate in the same direction in the different sub-phases and possibly at different speeds.

The combination of the rotational speed of the spray element with the outflow velocity of the jets from the nozzles, which generally points in the same direction as the axis of rotation, gives the jets a transverse component (which increases with the distance of the jets from the axis of rotation).

If the rotation speed is different in the different sub-phases, as can easily be achieved by dimensioning, positioning and orientation of the thrusters, the transverse component is different in the different sub-phases and, in addition to an increased resolution in the cleaning process, it is possible to exert mechanical stresses acting in different directions and it is it is made possible for the jets to penetrate between adjacent walls of objects to be cleaned, whereby in one of the partial phases they directly hit surface points which in another partial phase are sprayed indirectly by reflection of the jets, since they are hidden from direct action by the presence of other dishes.

This effect, which is diagrammatically illustrated in Fig. 6, is intensified in a case where the thrust nozzles exert opposite torques on the spray element: In Fig. 6, two plates to be cleaned 51, 52, arranged vertically in a washing basket (not shown), are sprayed by jets G1 during a first cleaning sub-phase and by jets G2 during a second sub-phase.

The G1 rays act effectively on the inside of the plates, and the G2 rays act effectively in a direct manner on the outside.

The number of usable reflections is also increased.

For example, the reflected beam G1R makes it possible to spray a zone of the plate that cannot be sprayed directly by the beams G1 and G2, and the reflected beam G2R makes it possible to spray a zone of the plate 52 that cannot be sprayed by the beams G1, G2 directly or by the reflection of the beam G1.

After the cleaning phase has been completed, the cleaning liquid in the basin 3 is emptied and replaced with rinse water in response to a command from the programming unit 10 (Fig. 1).

The rinsing phase can then be carried out with a high spray flow rate achieved by feeding the two manifolds simultaneously as in the pre-cleaning case.

The process is therefore carried out effectively in a very short time with a clear saving in consumption.

In the above description, reference has been made to a single spray device 11 formed by two separate distributors, which are individually and selectively fed by a liquid flow.

However, it is clear that the same concepts can also be applied in the case of dishwashers provided with two spray devices for spraying dishes placed in a lower basket and dishes placed in an upper basket respectively.

In Fig. 1, for example, an upper spray device 12 is shown, which can have a structure identical to that of the spray element 11.

In order to feed them with two liquid flows which are selectively fed into the distributors, the support 46 is provided with two connections 53, 54 which connect the liquid supply lines 47 and 48, respectively, to the spray element 12 by means of pipes 55, 56 and an upper support (not shown) for the rotating spray element.

In this way, the upper spray element 12 is connected in parallel to the lower spray element 11 in the various phases of the cleaning cycle.

It is clear, however, that the upper spray element 12 can be provided with an independent feed circuit fed by its own pump, as well as with a feed circuit comprising a pump for a common supply for the two spray elements, but equipped with valve devices which shut off and pass the flow for its feed independently of that of the lower spray element in such a way that, for example, the operations of pre-cleaning and rinsing by feeding both distributors of the two spray elements together and the operation of cleaning by selectively feeding one of the different distributors of the two spray elements are carried out at a given time or in a suitable combination according to the degree of contamination.

The above description relates only to a preferred embodiment of a dishwasher with rotating spray elements with a number of liquid distributors.

It will be understood, however, that various modifications may be made without departing from the scope of the invention as defined in the appended claims.

For example, instead of being formed by a pair of rotating arms in which the two distributors are formed, the spray elements can also consist of more than two rotating arms in any number N.

Furthermore, if the number N of arms is even and preferably greater than or equal to 4 (for reasons of balancing the thrust of the nozzles), the two distributors can be formed in one half and in the other half of the number of arms respectively.

The number of distributors can also be greater than two to achieve even greater operational versatility.

Claims (8)

1. Dishwasher comprising at least a first rotatable spray element (11) which is set in rotation by the hydrodynamic thrust of the jet leaving at least one nozzle (29, 30), the spray element (11) comprising at least two separate and different distributors (17, 18) each provided with a plurality of spray nozzles (21, ..., 26, 31, ..., 36), the dishwasher comprising means (4, 6) for supplying a flow of spray liquid to at least one of the distributors (17, 18) independently of the other distributor, characterized in that the supply means (4, 6) comprise a first pump (4) and a second pump, the pumps being independently operable to feed the first distributor and the second distributor respectively. 2. A dishwasher according to claim 1, including means (4, 6) for supplying a flow of spray liquid to each of the pipe connections (17, 18) in a mutually exclusive manner. 3. Dishwasher according to claim 1 or 2, comprising means (4, 6, 5, 7, 10) for feeding the distributors (17, 18) together during a cleaning and/or pre-cleaning phase of a cleaning cycle. 4. A dishwasher according to claim 1, 2 or 3, wherein nozzles (22, 23, 24, 25) of one (17) of the distributors in the distributor (17) are open at distances from the axis of rotation of the rotatable spray element which are between the distances from the axis of rotation at which the nozzles (31, 32, 33, 34, 35, 36) of the other (18) of the distributors are open. 5. Dishwasher according to claim 1, 2, 3 or 4, in which the flow of spray liquid feeding one or the other of the distributors (17, 18) causes the spray element to rotate in the same direction. 6. A dishwasher according to claim 1, 2, 3 or 4, wherein the flow of spray liquid feeding one of the distributors (17, 18) rotates the spray element in a first direction at a first rotational speed and the flow of spray liquid feeding the other of the distributors rotates the spray element in the direction opposite to the first direction at a second rotational speed different from the first speed, in such a way that the flow of spray liquid feeding the distributors together rotates the spray element at a third speed. 7. Dishwasher according to the preceding claims, which includes a second rotatable spray element (12) having at least two separate and different distributors, each provided with a plurality of spray nozzles and means (4, 6) for jointly supplying a flow of spray liquid to a distributor of the first spray element (11) and to a distributor of the second spray element (12). 8. Dishwasher according to one of claims 1 to 6, comprising a second rotatable spray element (12) having at least two separate and different distributors, each provided with a plurality of spray nozzles and means for supplying the distributors of the second spray element (12) independently of the supply of the distributors (17, 18) of the first spray element (11) to selectively supply a stream of a spray liquid.