PUMP UNIT, PARTICULARLY FOR DISHWASHERS

Abstract: Pump unit for dishwashers having a reversible motor whose shaft (3) drives the impellers (4,5) of a pe­ ripheral outflow discharge pump (6) and a centrifu­ gal circulating pump (7). The impeller (5) of the centrifugal pump is of the kind having blades (12) which are oriented forwards with respect to the di­ rection of rotation (13) of the shaft (3) in which the centrifugal pump is pumping and the discharge pump is rotating in a reverse direction. The overall energy consumption, hydraulic noise and vibrations of the whole pump unit are reduced.

Description: The present invention relates to a pump unit, particularly to be used in dishwashers, of the kind including a couple of pumps which are operable by a common drive shaft. A pump unit of this type is disclosed, for instance, by GB-A-1.257.101, wherein the impellers of two separate pumps are keyed on a common drive shaft which is rotatable in both directions, so that one of the impellers rotates in a reverse direction when the other is driven in the forward direction, and vice-versa. In particular, one pump is a centrifugal pump of the radial type having backward-oriented blades and the other pump is of the so-called peripheral outflow kind; when applied in a dishwasher, the centrifugal pump is capable of circulating water within the wash tub of the machine and the peripheral outflow pump is capable of discharging the water therefrom. According to such a solution, the pump unit is of sufficiently integrated construction, but suffers from the drawback that during the water discharge phases a high energy consumption, which substantially is wasted, occurs in the centrifugal pump, which is rotating in the reverse direction. In particular, the energy consumption of a centrifugal pump of the radial type having backward-oriented blades is higher when its impeller rotates in the reverse direction than in the operative forward direction. It was experimentally found that during the water discharge phases the energy consumption of the centrifugal pump amounts to about 80% of the overall pump unit consumption. As a consequence, the electric drive motor of the pump unit considerably must be oversized compared with the actual operative requirements. Furthermore, the circulating pump, during the phases in which its impeller rotates in the reverse direction, is a source of hydraulic noise and vibrations which is desirable to reduce at a minimum. It was suggested, for instance in IT-A-860.156, to provide the side wall of the pressure chamber of the centrifugal pump with a bended buffle extending inwards. The buffle, or the like, is such that, when the impeller of the centrifugal pump rotates in the reverse direction, the water ring which is formed in the pressure chamber is diverted so as to partially cross the suction mouth of the pump. As a consequence, possible incoming water is ejected through the suction mouth of the pump, whereas the water column at the delivery side only reaches a low level. It was experienced that with such a solution the shortcomings mentioned above are only slightly reduced, mainly because of the braking action which is produced on the impeller of the centrifugal pump by the water ring in the pressure chamber. On the other hand, the centrifugal pump is of relatively complicated construction and shows a limited yield during the regular pumping phases. It is a scope of the present invention to provide a pump unit, particularly applicable in dishwashing machines, which is of simple and integrated construction and in which the energy wasting, hydraulic noise and vibrations are reduced to a minimum extent. According to the invention, this scope is obtained in a pump unit, particularly for dishwashers, comprising a reversible electric motor the shaft of which drives the impellers of a first and a second pump which are alternatively capable of delivering a liquid when the drive shaft rotates in a first and a second direction, respectively, the impeller of the first pump being of the peripheral ouflow kind, whereas the second pump is a centrifugal pump and its impeller is provided with blades, characterized in that the blades are oriented forwards with respect to said second direction of rotation. The characteristics and advantages of the invention will become apparent from the following description, which is only given as a non-limiting example, with reference to the accompanying drawings, wherein: Fig. 1 shows a longitudinal section of the main elements of the pump unit according to a preferred embodiment of the invention; Fig. 2 diagrammatically shows a front view of a particular of Fig. 1. With reference to Fig. 1, the pump unit according to the present invention includes a reversible electric motor (not shown for simplicity sake) on the drive shaft 3 of which the relevant impellers 4 and 5 of a first and a second pump 6,7 are keyed. Preferably, but not exclusively, the pump 6 can be used for discharging water from the sump of a dishwasher (not shown), while the pump 7 is utilized for circulating water to proper spray means in order to sprinkle crockery to be cleaned. Pumps 6 and 7 are made in a single-piece structure and are mutually separated by means of a partition 8. In particular, the impeller 4 of the discharge pump 6 is of the peripheral outflow kind, known per sè, and is capable of pumping at its delivery side (represented by arrow 10) the fluid from its suction side (which is represented by arrow 9 and connected with the collecting sump of the dishwasher) when the drive shaft 3 is rotating in the first direction indicated by arrow 11. The circulating pump 7 is a centrifugal pump and its impeller 5 is shaped as shown in Figures 1 and 2, i.e. provided with a plurality of blades 12 which are oriented forwards with respect to a direction of rotation of the shaft which in Fig. 2 is indicated by arrow 13 and is opposite to the first direction 11. Centrifugal pumps provided with an impeller having forward-oriented blades, i.e. pumps of the so-called "action" type instead of the traditional "reaction" type, have till now been used only separately and for special applications, i.e. for pressurizing water jets of fire extinguishing equipments, where high-speed water jets are requested. It is to be noted, in particular, that such "action" centrifugal pumps have never been operated for a rotation of their impeller in the reverse direction. On the contrary, in the pump unit according to the present invention the surprising effect was experimented that the energy consumption of the centrifugal pump 7 is particularly reduced when its impeller 5 rotates in the direction 11, opposite to the pumping direction 13. It was, in fact, experimentally found that when the drive shaft 3 is rotating in the direction indicated by arrow 11, i.e. when, in practice, only the discharge pump 6 is in operation, the energy consumption of the centrifugal pump 7 is lower than 30% of the overall energy consumption of the whole pump unit; such overall energy consumption is also particularly reduced thanks to the per sè known characteristics of the peripheral outflow pump 6. On the other hand, the centrifugal pump of the action type 7 maintains a high yield even when it is pumping, that is when the drive shaft 3 is rotating in the direction shown by arrow 13. In the specific application in a dishwasher, during this phase the discharge pump 6 practically intakes air only, so that its energy consumption is particularly low. Thus, even during the water circulating phases the overall energy consumption of the pump unit according to the invention advantageously is reduced and is substantially equal to the energy consumption occurring during the water discharge phases. As a consequence, thanks to the particular combination of pump 6 and 7 it is possible to correspondingly downsize the reversible electric motor, which can also have reduced overall dimensions. In this connection, it is to be noted that the overall dimensions of the pump unit further can be reduced, compared with the traditional solutions, thanks to the intrinsic characteristics of the centrifugal pump 7 having an impeller of the action type. It is known, in fact, that - under the same conditions with regard to revolving speed and hydraulic head - the diameter of the impeller, and therefore the overall dimensions of the revelant scroll, of a pump of this kind is shorter in comparison with a centrifugal pump of the radial type having backward-oriented blades. Moreover, the hydraulic noise and vibrations occurring in the pump unit according to the invention are reduced to the same extent as the energy wasting. Of course, the pump unit described above may undergo many modifications without departing from the scope of the invention. For instance, the partition 8 between the two pumps 6 and 7 may be provided with a calibrated opening 14, which preferably is an annular opening, in correspondence of the common hub 15 of impellers 4 and 5. Thanks to the combined action of pumps 6 and 7, the flux of liquid through the opening 14 always occurs in a single direction, i.e. from pump 7 towards pump 6. In fact, when the impellers of the pumps are rotating in the direction indicated by arrow 13 such a flux of fluid is caused by a strong hydraulic head at the centrifugal pump 7, and when the impellers are rotating in the opposite direction 11 the flux of liquid through the opening 14 is produced by the suction effect of the peripheral outflow pump 6, a low hydraulic head occurring in the meanwhile at the centrifugal pump 7. As a consequence, particularly when the pump unit is applied in a dishwasher, no soiled water can flow, through opening 14, from the water discharge circuit (connected with pump 6) to the water circulating circuit (connected with pump 7). On the contrary, the slight flow of clean water from the circulating circuit to the discharge circuit prevents the opening 14 from being clogged and in the meanwhile enables both discharge and circulating circuits to be completely emptied during the discharge phases. This is particularly important when, as it is preferable, the above two circuits are substantially separated from one another, since even in this case there is no need to provide special arrangements for evacuating water from both hydraulic circuits. Obviously, the pump unit according to the invention also is simple and reliable because the opening 14 replaces the traditional sealing gasket, which suffers from well known wearing problems. It is taken for granted that the pump unit according to the invention may effectively be used in appliances other than dishwashers; for instance, it may be applied in a clothes washing machine of the kind providing a recirculation of the operative liquid.

Claims: Pump unit, particularly for dishwashers, comprising a reversible electric motor the shaft of which drives the impellers (4,5) of a first (6) and a second (7) pump which are alternatively capable of delivering a liquid when the drive shaft rotates in a first and a second direction, respectively, the impeller (4) of the first pump (6) being of the peripheral outflow kind, whereas the second pump (7) is a centrifugal pump and its impeller (5) is provided with blades (12), characterized in that the blades are oriented forwards with respect to said second direction of rotation (13). Pump unit according to claim 1, wherein said pumps are separated from one another by means of a partition, characterized in that the partition (8) is provided with at least one calibrated opening (14) capable of interconnecting said pumps (6,7). Pump unit according to claim 2, characterized in that said calibrated opening (14) is a substantially annular opening and is provided in correspondance of a hub (15) which is common to the impellers (4,5) of said pumps (6,7). Dishwashing machine having a water circulating circuit and a water discharge circuit, characterized in that it comprises a pump unit according to the preceding claims, the intake of the centrifugal pump (7) and that of the peripheral outflow pump (6) being connected with said water circulating circuit and water discharge circuit, respectively.

Inventors: FAVRET, UGO, MARTEGANI, ANTONIO, MILOCCO, CLAUDIO
Applicants: INDUSTRIE ZANUSSI S.P.A.
Application year: 1987
Main classification: A47L15
IPC codes: A47L15