EP2194832B1

EP2194832B1 - Improved hydraulic pump

Info

Publication number: EP2194832B1
Application number: EP08786999A
Authority: EP
Inventors: Sergio Bonacina; Elvio Tonus
Original assignee: Nidec Sole Motor Corp SRL
Current assignee: Nidec Sole Motor Corp SRL
Priority date: 2007-09-25
Filing date: 2008-08-07
Publication date: 2012-11-28
Anticipated expiration: 2028-08-07
Also published as: EP2194832A1; ITPN20070068A1; WO2009040176A1

Description

The present invention refers to a pump, in particular a circulation pump of the kind driven by an electric motor and used in such household appliances as dishwashing machines, or the like, as defined in the preamble of claim 1 appended hereto.
Pumps of the above-indicated kind are widely known in the so-called white-goods industry, where they are largely used in washing appliances of various kinds, and are generally described in such publications as EP 1148 248 A2 and EP 1 369 977 A2 , to which reference shall therefore be made for the sake of brevity.
The pressure that is continuously being put on manufacturers from both a technical and a marketing point of view to find out ways for the cost, and hence the price, of electric household appliances to be cut, has induced appliance manufacturers to also look for cost-reduction opportunities and solutions also as far as the above-mentioned pumps are concerned. In this particular case, a viable way to obtain a desired reduction in costs would consist in a general reduction in the size of the electric motor, and therefore of the stator/rotor assembly thereof, used to drive such pumps.
At this point, however, the need arises for a technical introductory remark to be made in this connection, i.e. the power rating and the torque, in particular the starting torque, available at the shaft of the electric motors that are generally used to drive pumps of the above-cited kind shall be such as to ensure that the motor is able to start even under rather difficult conditions, which practically means that, if the machine where the pump is used is left inoperative for a certain extended period of time, i.e. for some weeks or even months, the same machine shall be able to be started and operate regularly as soon as it is switched on, at the lowest allowable voltage ensured by the power supply line to which the machine is connected.
However, during such extended period of time, in which the machine is kept inoperative, the same pump may undesirably run into a locked state, in that some of its parts that are in contact and interact with each other may "stick" together due to the presence of small particles or debris of foreign matters remaining and settling there from the last cycle of operation performed by the machine; in general such foreign matters or debris consist of minute particles of food, bread, etc., the effect of which - as all those skilled in the art are well aware of - is exactly such "sticking" problem arising between mutually interacting parts of the pump, so as to cause the drive motor to ultimately run into locked conditions.
For such "sticking" risk to be prevented, the related motors are generally oversized by design, so as to be able to provide a starting torque that is well in excess to the one that is normally required under ideal conditions. Now, owing to such oversizing, these motors tend to also provide a maximum torque that may be even far higher than the operating torque needed by the related pump for it to be able to operate correctly.
The idea, on which the present invention is based, is therefore the possibility for the size and, hence, the costs of the pump driving motor to be reduced to a significant extent, while overcoming the afore-described drawback of the same motor being likely to lock due to pump parts possibly sticking together under particular conditions.
In this connection, reference should now be made to Figures 1, 2 and 3, which illustrate a pump according to the prior art; in particular, Figures 1 and 2 are a perspective cross-sectional view and an axial sectional view, respectively, of the pump, which comprises a chamber 1, in which there is accommodated the impeller 2, an electric motor 3, a rotation shaft 4 of the motor transmitting the rotary motion thereof to said impeller, a centrifugal splash-guard member 5, of a kind as generally known as such in the art, which is mounted on said shaft 4, a rear wall 6 closing said chamber 1 at a position located between said impeller and the motor, said motor shaft 4 being obviously provided so as to extend through said rear wall.
A tightly sealing effect between said rear wall 6 and the motor shaft 4 is ensured by a pressure-induced contact between a suitable ring 7 provided concentrically to said rear wall 6 - and therefore stationary and usually made of a ceramic material - and a corresponding hollow cylindrical member 8 firmly joined to said impeller - and therefore rotating and usually made of a material such as Teflon^® - and capable of sliding in tightly sealing manner against said ring 7.
Such cylindrical member 8 is preferably connected to and supported on the impeller by means of appropriate cylindrical fittings or supports 9, which are in turn firmly joined to the same impeller.
The afore-described "sticking" problem occurs between the parts that slide against each other, i.e. in the plane annular region that is comprised in the area indicated at A between said ring 7, which is firmly joined to the structure of the chamber 1, and said rotating cylindrical member 8.
In view of reducing the motor locking effect brought about by such sticking together of pump parts, the most obvious solution would consist in reducing the diameters of both members 7 and 8 in a proportional manner, so as to reduce the overall sliding area.
In addition, the average distance from the axis of rotation of said cylindrical member 8 to said plane annular region A is also reduced as a logical result of said diameters being reduced as indicated above, and since such average distance corresponds to the lever arm, whose resisting force is given by the friction opposed - due to sticking - by said region A, it ensues that reducing said diameters will also cause said lever arm to be reduced; the ultimate result is that the resisting torque generated by said annular region A becomes markedly smaller, just as desired.
A reduction in the area of said annular region A, which necessarily implies a reduction of the mutually mating diameters, refers in particular to the reduction of the inside diameter D1 of the ring 7 extending around the tail piece 9 that is firmly joined with the impeller; said tail piece 9 is in fact an internally threaded hollow extension that is capable of being screwed on a corresponding threading 10 provided on the exterior of the shaft 4.
In practical words, the impeller is attached to the shaft by simply screwing said tail piece 9 thereof on to said outer threading 10 of the shaft.
The decrease in said diameter D1 shall therefore be matched by a corresponding decrease in the outside diameter D2 of the tail piece 9 and the outer threading 10 of the shaft 4.
Such decrease in the diameter D2, however, gives rise to a number of further drawbacks, i.e.:

a first drawback derives from the reduction in the wall thickness of the tail piece, which is connected with a resulting weakening in the radial direction thereof; practically, when such tail piece is ultimately screwed and tightened on, the same tail piece tends to deform into a stepped configuration, i.e. to form into steps around said outer threading 10, thereby preventing a firm and reliable grip from being ensured between the impeller and the shaft;
a second drawback is brought about by the fact that reducing the diameter D2 of the tail piece 9 enables the same tail piece to move further forwards against a side of the splash-guard member 5; this of course determines an increase of the load between the ring 7 and the cylinder 8, thereby causing the same cylinder 8 to be exposed to early wear-out;
a third drawback lies in the fact that, when the impeller is screwed fully and tightly on the shaft 4, the head of the latter ends up by abutting against the bottom of the inner cavity of said tail piece, and this implies that a locking of the impeller on the same shaft becomes Insecure owing to its depending practically on two mutually opposing abutments, none of which can become secure, actually, as anyone skilled in the art is well aware of.

Such effect gives rise to a loss of tightness between the tail piece and said splash-guard member 5; now, such tightness is of paramount importance, since any small amount of liquid that is possibly able to leak or seep through the seal provided between the ring 7 and the cylinder 8 would then tend to seep further on towards the shaft 4 through the abutment between the head of the tail piece and said splash-guard member 5, with the result that, in order to prevent the same shaft from oxidizing and ultimately breaking down, it should be made of a suitable oxidation-resistant material, such as stainless steel, thereby affecting costs in quite unfavourable a manner.
From EP 1 279 936 A it is divulged a kind of pump for dish-washers provided with a tail-piece which is firmly joined to the impeller and protrudes towards the motor shaft, to which it is engaged by suitable screwing.
However said embodiment cannot prevent a deformation of said tall-piece, consisting in forming steps around the shaft outer threading, thereby preventing a firm and reliable grip between the impeller and the shaft.
Moreover the sealing itself between the shaft and the impeller is made less secure, due to the possibility that the locking between impeller and shaft be based on two mutually opposing abutments.
It would therefore be desirable, and it is actually a main object of the present invention, to provide a pump, in particular of the kind adapted to circulate liquids in electric household appliances, such as dishwashing machines or the like, in which the casing of the pump is attached to the casing of a drive motor, and is provided with an inner hollow pump chamber adapted to accommodate an impeller provided with vanes, and comprising:

a rotor connected to as respective shaft that is externally threaded along the terminal portion thereof;
a centrifuging flange that is firmly joined to said shaft;
a back wall of said inner hollow pump chamber, which is provided with a sealing ring - generally of a ceramic material - in the middle portion thereof;
a hollow cylindrical member - usually made of a material such as Teflon^® - that rotates on a support firmly joined to or mounted integrally with an impeller that is shrink-fitted on to said shaft, said member being adapted to ensure the tightness of the inner space of the cavity of the impeller withy respect to said back wall owing to its being slidably coupled in a tightly sealing manner with said sealing ring of said back wall;
a hollow, internally threaded tube provided coaxially to and firmly joined with said impeller, which is screwed on the outer threads provided on the terminal portion of said shaft, said hollow cylindrical member 8 being shrink-fitted on to said tube;

According to the present invention, these aims, along with further ones that will become apparent from the following disclosure, are reached in a particular kind of pump provided with a particular coupling between the impeller and the rotor shaft incorporating the features and characteristics as defined and recited in the appended claims.
Advantages and features of the present invention will anyway be more readily understood from the description that is given below by way of non-limiting example with reference to the accompanying drawings, in which:

Figure 4 is a median cross-sectional view, across the common axis of the pump and the motor and the related mechanical connections, of a pump according to the present invention;
Figure 5 is an exploded view of the most significant parts making up the pump shown in Figure 4;
Figure 6 is a perspective cross-sectional view of the representation in Figure 5;
Figure 7 is an exploded axial sectional view of the pump generally shown in Figure 4, as suitably enlarged to better illustrate a possible water-tightness problem;
Figure 7A shows the same view as Figure 7, wherein the related component parts are shown in the assembled state thereof;
Figure 8 is an axial sectional view of the pump shown in Figure 4, as provided with a first improved embodiment aimed at solving the water-tightness problem illustrated in Figures 7 and 7A;
Figure 9 is a further axial sectional view of the pump shown in Figure 4, as provided with a second improved embodiment.

With reference to Figures 4, 5 and 6, which are cross-sectional, exploded axial sectional and perspective axial sectional views, respectively, of a pump according to the present invention, such pump can be noticed to comprise (wherever possible, when details and parts of the pump shown in Figure 1 are the same as and similar to the ones used in the pump illustrated in the subsequent Figures, the same reference numerals will of course be used to indicate them):

a pump chamber 1 accommodating
the impeller 2,
an electric rotor 3,
a rotation shaft 4 of the motor transmitting the rotary motion thereof to said impeller,
a centrifugal splash-guard member 5, of a kind generally known as such in the art, mounted to said shaft 4,
a back wall 6 closing said pump chamber 1 at a position located between said impeller and said motor, wherein such wall is of course adapted to enable the rotor shaft 4 to extend therethrough,
an appropriate ring 7 provided concentrically to said back wall 6, as generally made of a ceramic material,
a corresponding cylindrical member 8 coaxial to and firmly joined, and therefore rotating, with said impeller, as generally made of a material such as Teflon^® and capable of sliding in a tightly sealing manner on said ring 7, as duly pressed by a spring of a kind as generally known as such in the art thereagainst, wherein such cylindrical member 8 is connected to and supported on the impeller by means of appropriate cylindrical fittings or supports 11, which are in turn firmly and sealingly joined to the same impeller.

Said fittings 11 are in turn coaxial and tightly applied on to the tail piece 9, which is firmly joined with the impeller.
Moreover, said tail piece 9 is in turn tightly screwed on to the rotation shaft 4.
As a result, owing to:

said ring 7 engaging said cylindrical member 8,
said cylindrical member 8 in turn engaging said cylindrical supports 11,
said cylindrical supports 11 in turn engaging the tail piece 9, and
the tail piece 9 in turn engaging the rotation shaft 4

back wall

rotation shaft

Anyway, a pump basically made according to the prior art has been described hitherto.
According to the present invention, said splash-guard member 5, which is shrink-fitted on to the shaft 4 externally with respect to said back wall 6, is so shaped as to feature an inner cavity 5A opening towards the impeller and provided with an inner step-like configuration 12 situated at a certain distance from the outer edge 14 thereof, and having an inside fit-in diameter M1 that is larger than the diameter M2 thereof after said step-like configuration 12.
The outer terminal portion of the tail piece 9 is so sized as to ensure that the outside diameter thereof is substantially equal to said inside fit-in diameter M1, so that it is able to exactly fit into said cavity 5A of said splash-guard member 5, while however stopping with the cylindrical annular border 18 thereof abutting against said step-like configuration 12.
As a result, the terminal portion of the tail piece 9 is accommodated within the outermost portion of the splash-guard member 5, in which it is shut-in and locked-up, actually.
This fact, therefore, prevents the tail piece from deforming into a stepped configuration against and around the threading therebelow, when the same tail piece 9 is being screwed onto the outer threading 10 provided on the shaft 4 and, in particular, during the final tightening phase of such screwing process, since the terminal portion of such tail piece is in fact designed to fit into the internally hollow portion of the splash-guard member 5 that envelops it to thereby positively oppose it from possibly deform radially outwards.
This practically enables the primary object of the present invention to be reached, since the wall thickness of the tail piece 9, and therefore also the outside diameter M1 thereof, can in this case be reduced even sensibly.
With reference to Figures 7 and 7A, it is however possible for small amounts of water, which usually seep through the seal between the ring 7 and the cylindrical member 8, to be able to ooze (arrow F) into and through the very narrow interstice 14 between said centrifugal splash-guard member 5 and the outer surface of the terminal portion of the tail piece 9.
Such liquid would then be able to reach the body of the shaft 4, thereby exposing the latter to oxidation and - as a result - to gradual embrittlement up to ultimate breakdown in the long run.
In view of doing away with such problem, said shaft 4 may of course be made of an oxidation-resistant material such as stainless steel, but this would mean a definite increase in costs that is inconsistent with the actual purpose of the present invention.
As a result, in order to prevent water from being able to seep through said interstice 14 in the afore-described manner at all, with reference to Figure 8 use is made of a suitable, adequately sized elastic seal means, such as a O-ring 16, to be applied on to the inner surface of the cavity 5A of the centrifugal splash-guard member 5.
All those skilled in the art will at this point be fully able to appreciate that - owing to its working by radial compression - such O-ring is effective in opposing and fully stopping any seepage of liquid into said interstice 14, thereby positively protecting the shaft 4 against the afore-described risk of oxidation.
With reference to Figure 9, the above-described effect may also be reached with an alternative embodiment of the preceding solution, i.e. by providing an annular planar sealing gasket 17 against and along said step-like configuration 12 in the cavity of said centrifugal splash-guard member 5, so that - when the tail piece 9 is finally tightly screwed on at the end of the screwing process - said annular cylindrical border 18 is pressed into firmly abutting against said annular gasket 17, thereby blocking any seepage of liquid therethrough.
Other solutions may of course be embodied in view of positively preventing liquid from seeping through said interstice 14 and towards said shaft 4. These solutions, however, are not only generally known as such in the art, but also easy to implement, so that they shall not be explained any further.
A further drawback may still arise, however, in that there is a possibility that, when the tail piece 9 is fully and tightly screwed on to the shaft 4, the terminal planar side 20 of the same shaft enters into contact with and abuts against the corresponding bottom 21 of a cavity inside the tail piece 9.
In this case, even if the shaft is fully tightened into the tail piece 9, it may occur that the above-cited abutting contact practically acts so as to prevent the annular cylindrical border 18 from correctly positioning itself against said step-like configuration 12.
This possible occurrence may lead to an insecure engagement of the parts involved with each other, i.e. may cause the parts involved to engage each other in an uncertain manner, since it is not established which engagement is working, actually. Moreover, it may also make the solution shown in Figure 5 ineffective, since said annular planar gasket might in fact remain at least partly unaffected, i.e. loose between said annular cylindrical border 18 and said step-like configuration 12 due to abut thereagainst, and this would most obviously fail to effectively prevent liquid from seeping therethrough.
In order to do away with such drawback, the length of the shaft 4 and the inner cavity of the tail piece 9 is defined so that, even after the tail piece is fully tightened on to the shaft, between the terminal planar side 20 of the same shaft and said bottom 21 inside the tail piece 9 there still remains a small empty chamber 23, as this is schematically illustrated in Figures 6 and 9, thereby ensuring a permanent separation of said terminal planar side 20 from said bottom 21.

Claims

Pump, in particular of the kind adapted to circulate liquids in electric household appliances, such as dishwashing machines or the like, In which the casing of the pump is attached to the casing of a drive motor, and is provided with an inner hollow pump chamber adapted to accommodate an impeller provided with vanes, and comprising:
- a pump chamber (1) accommodating

- an impeller (2);

- an electric rotor (3),

- a rotation shaft (4) of said rotor, adapted to rotatably drive said impeller, and threaded externally along the terminal portion thereof,

- a centrifugal splash-guard member (5) mounted to said shaft (4),

- a back wall (6) closing said pump chamber (1) at a position between said impeller and said rotor,

- a ring (7) provided concentrically to said back wall (6) and located at the portion thereof lying adjacent to the rotation shaft,

- a corresponding cylindrical member (8) coaxial to and firmly joined, and therefore rotating, with said impeller, and capable of sliding in a tightly sealing manner on said ring (7), as elastically pressed thereagainst,

- connecting means (11) connecting said cylindrical member (8) with said impeller,

- a hollow, internally threaded tail piece (9), which is firmly joined to said impeller, and extends to protrude towards said shaft (4) so as to be able to be screwed on to it,
characterized In that

- said splash-guard member (5) is provided with a cavity (5A) that is open towards said tail piece (9) and has a step-like configuration (12) provided thereinside, the diameter (M2) of which is smaller than the inside fit-in diameter (M1) of said cavity (5A) of said splash-guard member (5),

- and said tail piece (9) has an outside diameter that is substantially similar to said inside fit-in diameter (M1) of said cavity (5A) so as to be able to be inserted and fit into said inside fit-in diameter (M1) of said cavity (5A).
Pump according to claim 1, characterized in that there are provided sealing means adapted to ensure water-tightness between said tail piece (9) and said shaft (4).
Pump according to claim 2, characterized in that said sealing means comprise a O-ring (16) placed between the outer surface of said tail piece (9) and the inner surface of said cavity (5A) of said splash-guard member (5).
Pump according to claim 2, characterized in that said sealing means comprise an annular, preferably planar gasket (17) placed between the outermost cylindrical annular border (18) of said tail piece (9) and said step-like configuration (12).
Pump according to any of the preceding claims, characterized in that the terminal planar side (20) of said shaft (4) is separated from the bottom (21) inside of said tail piece (9).