IN PARTICULAR OF THE HOOD MOVABLE TYPE

TECHNICAL FIELD

The present invention relates to a professional dishwashing machine, in particular of the type in which the washing chamber is defined by a tank and by a hood, vertically movable with respect to the tank, in which the tank has such a shape as to improve the machine performance in use. The invention further relates to such a tank.

BACKGROUND ART

A dishwashing machine of the above type is known, for example, from US-A-4536043. In this type of machines, the tank is usually made as shown in figure 5; it is obtained in one piece by deep-drawing a flat metal sheet panel, typically stainless steel, so that the tank is peripherally delimited by a lateral wall B, obtained by plastic deformation of the above panel, on which a first step C is obtained, all around the tank, which forms along at least three sides of the tank (having a generally quadrangular shape) , in particular the front side and the two opposite sides immediately adjacent and perpendicular to the front side, a generally concave upper edge D of the tank, which edge delimits in use a maximum filling level of the tank and is adapted to cooperate in use with a support shelf for a dish-holder basket (not shown); towards the fourth side of the tank, i.e. the rear side, step C has a larger extension and generally forms a shelf E which carries a seat F for the lower sprinkler arm(s) of the dishwashing machine. Moreover, the tank is delimited at the bottom by a bottom wall provided with an outlet opening G for the recirculation of the washing liquid; the bottom wall is arranged at a predetermined distance from step C, which distance determines the filling depth of the tank and thus the maximum head of washing liquid present in use above opening G and, accordingly, the pressure present at the inlet of the recirculation pump of the dishwashing machine, contained within the machine casing, which feeds in use the lower sprinkler arm(s) and a corresponding upper sprinkler arm housed in the washing chamber.

Although the above-described type of tank is satisfactory, it has the drawback of not ensuring the presence of a constant pressure at the inlet of the recirculation pump; in fact, as the washing liquid collected in the tank is drawn by the pump, the liquid head on the outlet opening G lowers, thus dropping the pressure at the inlet of the pump, because the amount of liquid drawn is instantly larger, at least in the pump start-up step, than that returned into the tank through the feeding by the sprinkler arms of the pump.

This pressure change results in a difficult operation with a low efficiency of the pump, thus increasing the energy consumptions. On the other hand, there are design constraints to the maximum volume of the tank and to the minimum liquid head height to be constantly ensured above opening G, which apparently do not allow such a problem to be solved; in fact, a large depth of the tank is required in order to ensure good operation of the tank, which enhances the above-mentioned problem; on the other hand, making large plan sized tanks so that the change in the liquid head height is minimum when the volume of liquid drawn by the pump is the same, besides resulting in unacceptable increases in the overall dimensions, with the total volume of the tank being equal, also results in the maximum liquid head being reduced, with consequent non optimal operation of the pump.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a dishwashing machine for professional use of the above- described type which overcomes the above-mentioned drawbacks, being also reliable, easy to be implemented and assembled, and small in size.

A dishwashing machine for professional use is thus provided according to the invention, as defined in claim 1.

A tank for collecting the washing liquid for a dishwashing machine is also provided according to claim 9.

In particular, the dishwashing machine according to the invention comprises a support casing and a washing chamber formed in use within the casing and defined at a lower part thereof by a washing liquid collection tank carried by the casing and peripherally delimited by a lateral wall, on which a first step is obtained, which step forms a generally concave upper edge along at least three sides of the tank, which edge delimits in use a maximum filling level of the tank and is adapted to cooperate in use with a support shelf for a dish-holder basket; moreover, the tank is delimited at the bottom by a bottom wall provided with an outlet opening for the recirculation of the washing liquid and arranged at a predetermined distance from the first step, which distance determines a filling depth of the tank.

According to a feature of the invention, the tank has a second step, which is formed in the bottom wall of the tank and which divides the bottom wall into a first and a second portion arranged at two different distances from said first step, so that the second step divides the tank into a first section, delimited at the bottom by the first bottom wall portion, and a second section, delimited at the bottom by the second bottom wall portion, wherein the first section has a greater depth than that of the second section; moreover, the outlet opening is obtained at the first tank section, through the first bottom wall portion.

Moreover, according to a further aspect of the invention, the first step has, on a horizontal plane and all around the tank, the same horizontal extension, which is relatively small as compared to the size of the tank, so that the generally concave edge extends all about the tank and defines only a resting frame about the same, which determines a plan size of the tank substantially equal to that of the washing chamber.

Herein and hereinafter, "horizontal extension of the step which is relatively small as compared to the size of the tank" is intended to mean that the horizontal extension of the step is about one order of magnitude smaller than that of the tank. In the practice, according to a preferred embodiment of the invention, shelf E usually provided in known tanks is eliminated.

Thereby, the drawbacks of the prior art are overcome since a large depth of the tank is obtained at the outlet opening from which the pump draws the washing liquid to be recirculated, but at the same time the quantity of liquid drawn only negligibly decreases the height of the liquid head above the outlet opening, which is determined not only by the plan extension of the first tank section but by the plan extension of the whole bottom wall of the tank, and thus also by the liquid volume present in the second section of the tank .

To this end, the size of the first and second sections is such that a first partial inner volume of the tank delimited over the whole horizontal extension of the bottom wall, and thus at both the first and second bottom wall portions, and over the whole height of the second section only, is greater than a second partial inner volume of the tank delimited on the horizontal extension of the first bottom wall portion only and over the whole height of the first section, and therefore equal to the total inner volume of the first section only.

In the practice, with the liquid head above the outlet opening being equal, there is a smaller water volume.

Moreover, thanks to the elimination of the usual shelf, a larger volume available for the liquid to be collected is obtained, with the overall plan dimensions of the tank being equal .

To this end, the second step has, over its whole height, a projecting part which protrudes into the first section of the tank and which is vertically delimited by a cylindrical wall and which forms, flushed with the second bottom wall portion, an annular reception seat for a vertical supporting shaft of at least one lower sprinkle arm arranged in use above the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention will become apparent from the following description of a non- limiting embodiment thereof, provided by way of mere example and with reference to the figures of the accompanying drawings, in which:

figure 1 schematically shows a perspective three- quarter front view, and with parts removed for simplicity, of a professional dishwashing machine of the type with a vertically movable hood made according to the invention;

- figure 2 shows a perspective view on enlarged scale of the detail of the tank of the dishwashing machine in figure 1;

- figures 3 and 4 show an orthogonal elevation view and a plan top view of the tank in figure 2, respectively; and

- figure 5 shows a perspective top three-quarter view of a tank for dishwashing machines according to the prior art. BEST MODE FOR CARRYING OUT THE INVENTION

With particular reference to figures 1 to 4, reference numeral 1 indicates as a whole a dishwashing machine, to which reference will be made hereinafter simply as "dishwasher 1" for shortness, comprising a support casing 2, a tank 3 and a hood 5, known and only schematically shown with a broken line for simplicity, carried so as to vertically slide by casing 2 in a known manner, over tank 3, so as to define in use a washing chamber 4 within casing 2, formed in use by tank 3 and hood 5 and defined at a lower part thereof by tank 3, which serves for collecting a washing liquid which is fed within the washing chamber 4 by a pump, known and not shown for simplicity, through respective known sprinkler arms, an upper arm (not shown) and a lower arm 6 (figure 3), respectively. The non-limiting example in figure 3 shows only one arm 6 for simplicity, but normally the dishwashing machine 1 is provided with two lower arms 6, mounted coaxially and overlapping each other.

Tank 3 generally has a quadrangular shape in plan, with rounded vertexes (figure 4), is carried by casing 2 and is peripherally delimited by a lateral wall 7 on which a first step 8 is obtained, which forms a generally concave upper edge 9 along at least three sides of tank 3 and, according to the invention, along all the four sides of tank 3, which edge 9 forms an annular shallow recess 10 all around tank 3 and delimits in use a maximum filling level L of tank 3; in particular, edge 9 is adapted to cooperate in use with a support shelf 11 for a dish-holder basket 12.

Tank 3 is delimited at the bottom by a bottom wall 13 provided with an outlet opening 14 for the recirculation of the washing liquid, arranged at a predetermined distance from step 8, which distance determines the filling depth of tank 3.

According to the invention, tank 3 also has a second step 15, which is formed in the bottom wall 13 of tank 3 and divides the bottom wall 13 into a first portion 16 and a second portion 17 arranged at two different distances Dl and D2 (figure 3) , respectively, from the first step 8, so that the second step 15 divides tank 3 into a first section 18, delimited at the bottom by the first bottom wall portion 16, and a second section 19, delimited at the bottom by the second bottom wall portion 17; Dl is greater than D2, thus the first section 18 has a greater depth than that of the second section 19; in combination with such a structure of tank 3, the outlet opening 14 is obtained at the first tank section 18, through the first bottom wall portion 16.

According to the above-mentioned aspect of the invention, the usual shelf E of the prior art tanks (figure 5) is eliminated; to this end, the first step 8 has, on a horizontal plane and all around tank 3, the same horizontal extension, which is relatively small as compared to the size of tank 3 (about one tenth) , so that the generally concave edge 9 extends all about tank 3 and defines only a resting frame about the same, consisting of the annular shallow recess 10 having a substantially constant and small width (less than about one order of magnitude) with respect to the plan size of the casing 2 of dishwasher 1, which thus determines a plan size of tank 3 substantially equal to that of the washing chamber 4.

In order to ensure the support of the at least one arm 6 (or of the two arms 6, as mentioned above) , the second step 15 has, over the whole height thereof, a projecting part 20 which protrudes into the first section 18 of tank 3; the projecting part 20 is vertically delimited by a cylindrical wall 21 and forms, flushed with the second bottom wall portion 17, an annular reception seat 22 for a vertical supporting shaft (figure 3) for the lower sprinkler arm(s) 6 arranged in use above tank 3. Shaft 23 has such a height as to be substantially flushed with edge 9, starting from the bottom wall portion 17, and is a component normally absent, at least with such a height, in the prior art dishwashers; therefore, it is also part of the invention, in combination with the shape and structure of tank 3.

Moreover, the relative size of first section 18 and second section 19 of tank 3 are designed so that a first partial inner volume VI of tank 3 delimited over the whole horizontal extension of the bottom wall 13, and thus at both the first and second bottom wall portions 16 and 17, and over the whole height D2 of the second section 19 only, is greater than a second partial inner volume V2 of tank 3 delimited on the horizontal extension of the first portion 16 of bottom wall 13 only and over the whole height Dl of the first section 18, and therefore equal to the total inner volume of the first section 18.

In particular, the inner volume V2 of the first section 18 is equal to half, or preferably less than half, the first partial inner volume VI of tank 3, which first partial inner volume VI is defined by the total inner volume of the second section 19 plus a part of the same volume V2 of the first section 18 having height equal to D2.

The second section 19 of tank 3 is preferably provided with a second outlet opening 24 for the washing liquid obtained through the second bottom wall portion 17 in a position (figure 4) diametrically opposite, with respect to the annular seat 22, to the outlet opening 14 with which the first section 18 is provided.

Moreover, the second outlet opening 24 is smaller than the outlet opening 14 with which the first section 18 is provided .

As already described, tank 3 has a substantially quadrangular shape in plan, with rounded vertexes, and is obtained in one piece with the first and second steps 8 and 15 by deep-drawing an originally flat metal sheet panel 25.