EP3759349A1

EP3759349A1 - Vibration pump with improved actuation

Info

Publication number: EP3759349A1
Application number: EP19711717.9A
Authority: EP
Inventors: Gabriele BELLATO; Paolo Da Pont; Giuseppe Marone; Alessandro Rovera
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 2018-02-27
Filing date: 2019-02-27
Publication date: 2021-01-06
Anticipated expiration: 2039-02-27
Also published as: IT201800003069A1; EP3759349B1; WO2019166956A1

Abstract

The pump comprises a hollow body (6) having an inlet ( 8 ) and an outlet (10), between which a fluid can flow. The hollow body (6) further comprises a work chamber (7) located between the inlet ( 8 ) and the outlet ( 9 ). There is a piston (2) at least partly made of ferromagnetic material and configured for sliding in the hollow body (6) within the work chamber (7), so as to push the fluid from the inlet ( 8 ) to the outlet (10). A generator device (4) is configured for generating a magnetic field capable of commanding the displacement of the piston (2) within the work chamber (7). There is an elastic member (11) co-operating with the piston (2). The elastic member (11) is connected to the piston (2) and is configured for acting bidirectionally upon the piston (2) during the displacement thereof in the work chamber (7).

Description

VIBRATION PUMP WITH IMPROVED ACTUATION

DESCRIPTION

Technical field

The present invention relates to a vibration pump with improved actuation, in particular for a household appliance.

Background art

Vibration pumps are known, in particular for use in household appliances. Such pump type generally comprises a hollow body having an inlet and an outlet, between which a fluid can flow. The hollow body further comprises a work chamber located between the inlet and the outlet. There is also a piston at least partly made of ferromagnetic material and configured for sliding in the hollow body within the work chamber, so as to push the fluid from the inlet to the outlet. There is also a generator device configured for generating a magnetic field capable of commanding the displacement of the piston within the work chamber, and an elastic assembly situated within the work chamber and co operating with the piston.

One example of such type of vibration pump is described in document US 2012/0230847. However, said pump suffers from a few drawbacks, for which it should be found a remedy.

One drawback is that in said document the elastic assembly includes a pair of elastic members, in particular coil springs, both of which abut on axially opposite faces of the piston. In brief, on one side there is a first coil spring exerting a greater elastic force to withdraw the piston in one direction of movement against the action of the generator device, and on the other side there is a second coil spring exerting a smaller elastic force to move the piston in an opposite direction of movement, so as to cause the piston to return into an initial position.

The above-mentioned drawback translates into the necessity of oversizing the first coil spring so that it can, in order to perform its return function, "overcome" the smaller elastic force exerted by the second coil spring, which implies the use of excessive elastic force for the operation of the system.

Summary of the invention

It is one object of the present invention to provide a vibration pump which can solve the problems of the prior art, in particular which has an improved structure and ensures reliable operation.

According to the present invention, this and other objects are achieved through a vibration pump made in accordance with the appended independent claim.

In particular, according to the present invention, the elastic assembly comprises an elastic member connected to the piston. The elastic member is configured for acting bidirectionally upon the piston during the displacement thereof in said work chamber.

Thanks to such features, the pump can operate in a reliable manner, allowing for effective control of the elastic force acting upon the piston by means of the bidirectional co-operation existing between the elastic member and the piston, permitted by the constraint effected through the connection between said elastic member and said piston .

It is to be understood that the appended claims are an integral part of the technical teachings provided in the following detailed description of the present invention. In particular, the appended dependent claims define some preferred embodiments of the present invention, which include some optional technical features.

Further features and advantages of the present invention will become apparent from the following detailed description, which is supplied by way of non-limiting example with reference to the annexed drawings, which will be summarized below.

Brief description of the drawings

Figure 1 is a longitudinal sectional view of a vibration pump made in accordance with an exemplary embodiment of the present invention.

Figure 2 is a partial longitudinal sectional view showing a piston of a vibration pump made in accordance with an exemplary embodiment of the present invention.

Figure 3 is a schematic graph representing the elastic force - displacement diagram of a piston of a vibration pump made in accordance with a further exemplary embodiment of the present invention.

Figure 4 is a partial longitudinal sectional view wherein a comparison is made between the operating positions taken by a piston of a vibration pump made in accordance with a further exemplary embodiment of the present invention, according to the graph shown in Figure 3.

Figure 5 is a perspective view of a pump made in accordance with another exemplary embodiment of the present invention .

Figure 6 is an axial or longitudinal sectional view of the pump of Figure 5.

Detailed description of the invention

With reference to Figure 1, numeral 1 designates as a whole a vibration pump made in accordance with an exemplary embodiment of the present invention.

In particular, said pump substantially extends along a longitudinal axis x-x. Therefore, the terms "axial", "longitudinal", "transversal" and "radial" as used in the following description should be considered to refer to said longitudinal axis x-x.

By way of non-limiting example, said pump 1 can be used for pushing a fluid, in particular a liquid, e.g. water, in machines for making beverages, such as coffee, tea or the like. More in general, pump 1 can be used in household appliances .

In particular, as visible in Figure 1, pump 1 comprises a hollow body 6 having an inlet 8 and an outlet 10. Between inlet 8 and outlet 10 a fluid, in particular a liquid, e.g. water, can flow. Hollow body 6 comprises also a work chamber 7 located between inlet 8 and outlet 9.

Pump 1 further comprises a piston 2 at least partly made of ferromagnetic material and configured for sliding in the hollow body within work chamber 7, so as to push the fluid from said inlet 8 towards outlet 10.

In addition, pump 1 comprises a generator device, in particular a solenoid 4, configured for generating a magnetic field capable of commanding the displacement of piston 2 within work chamber 7.

Still with particular reference to Figure 1, pump 1 comprises an elastic member, particularly a spring 11 (e.g. a coil spring) co-operating with piston 2. Said elastic member, which in the illustrated embodiment comprises spring 11, is connected to piston 2 and is configured for acting bidirectionally upon piston 2 during the displacement thereof in work chamber 7.

Such technical features prevent any resonance from occurring between spring 11 and the reciprocating movements of piston 2, and prevent, in operation, any separation between spring 11 and piston 2, which might cause malfunctioning and noise when the pump is in use. With particular reference to Figures 3 and 4, there is schematically shown a part of a pump 1 made in accordance with a further embodiment of the present invention. In such further embodiment spring 11 is still connected to piston 2 and is configured for acting bidirectionally upon piston 2 during the displacement thereof in work chamber 7.

With reference to Figures 3 and 4, the following will describe, by way of example, the co-operation between spring 11 and piston 2. In the structure illustrated in Figure 4, spring 11 is mounted differently than in the embodiment shown in Figure 1; however, as will be apparent to a person skilled in the art, in the embodiment shown in Figure 4 it would be possible to adopt the same mounting arrangement of spring 11 as shown in Figure 1.

When solenoid 4 exerts a magnetic attraction force, piston 2 moves from an initial or idle position PO (corresponding to a null elastic force acting upon piston 2) to a first operating position PI (corresponding to the maximum elastic force acting upon piston 2), with a displacement si.

Subsequently, when solenoid 4 stops exerting the magnetic attraction force, piston 2 is pushed, under the withdrawing action of spring 11, from the first operating position PI to a second operating position P2 (corresponding to a negative elastic force acting upon piston 2) beyond initial or idle position PO . The displacement of piston 2 is designated as s2.

Therefore, when piston 2 is in the second operating position P2, it is pulled (as opposed to pushed) by spring 11 towards final position P3 corresponding to initial or idle position PO . In this case, the displacement of piston 2 is designated as s3.

In this way, total bidirectional control of the return of piston 2 from operating positions PI and P2 to initial position PO is accomplished by means of an elastic member, such as spring 11, connected to piston 2.

In particular, spring 11 is connected to the piston at an axial end 11a thereof.

In the illustrated embodiment, spring 11 is configured for working in both sliding directions of piston 2, and can therefore act upon piston 2 both by traction and by compression .

The connection between the elastic member and piston 2 can be effected in different ways. In the embodiment shown in Figure 1, as will be described in detail hereinafter, spring 11 and piston 2 are connected by mechanical coupling. According to an alternative embodiment, spring 11 and piston 2 are connected by welding.

In particular, spring 11, on the side opposite to that whereon it is connected to piston 2, is locked relative to hollow body 6. Preferably, pump 11 comprises a locking element 26 mounted on hollow body 16, wherein spring 11 is retained axially between locking element 26 and hollow body 6. Particularly, locking element 26 defines an annular housing 26a in which the other axial end lib of spring 11 is inserted, which is opposite to axial end 11a connected to piston 2.

Preferably, locking element 26 comprises a centering portion 26b situated in a position radially internal to annular housing 26a and surrounded by spring 11.

In the illustrated embodiment, spring 11 is thus retained, at its axial end lib, by hollow body 6 and, at its opposite axial end 11a, by piston 2 to which it is connected.

In particular, spring 11 is compression-loaded and tends to move piston 2 away from inlet 8 towards outlet 10, contrary to the magnetic action that solenoid 4 is configured to exert on piston 2.

As known in the art, in the embodiment illustrated herein by way of example piston 2 also has a through cavity 2a adapted to be selectively crossed by the fluid, through co-operation with a normally closed valve device 12 that can be opened by the pressure of the fluid in work chamber 7, so as to allow the fluid to flow from inlet 8 towards outlet 10.

With reference to the embodiment shown by way of example in Figure 1, the following will describe in detail the structure of piston 2 and that of work chamber 7 in which piston 2 is slidably mounted.

More in detail, as known in the art, piston 2 divides work chamber 7 into:

- a suction compartment 36 situated upstream of piston 2 and operationally intended to receive the fluid coming from inlet 8;

- a delivery compartment 9 situated downstream of piston 2 and selectively communicating with suction compartment 36 via through cavity 2a by means of valve device 12; and

- a compensation compartment 38 communicating with suction compartment 36 and fluidically separate from delivery compartment 9, so as to allow the reciprocating motion of piston 2.

Communication between suction compartment 36 and compensation compartment 38 may occur through a communication duct formed between them. In one embodiment, said communication duct may be obtained by means of one or more recesses formed along the radially internal lateral surface of hollow body 6 and/or along the radially external lateral surface of piston 2.

In the illustrated embodiment, piston 2 comprises a radially external annular portion 17 and a radially internal tubular portion 16 protruding axially from annular portion 17. Tubular portion 16 internally defines through cavity 2a.

Preferably, annular portion 17 and tubular portion 16 are made as two separate components, which are then mutually connected during assembly to form a single piston. In the illustrated embodiment, annular portion 17 and tubular portion 16 are both made of steel, in particular each one of them being made of a different steel type; as an alternative, tubular portion 16 may also be made of plastic material (e.g. by injection moulding) .

As aforementioned, tubular portion 16 may be made of steel. For example, tubular portion 16 may be manufactured by extrusion. Such extrusion process avoids the use of numerical control machines, e.g. a lathe, for manufacturing tubular portion 16. This aspect is advantageous because such a process generates, on the outer surface of the tubular portion, machining lines oriented substantially in the longitudinal direction, which, for this very reason, do not substantially affect the life of the annular gasket (e.g. an 0-ring) . On the contrary, machining by machine tool (i.e. by removal of material, as in a lathe) generates transversal machining lines that cause significant wear of said annular gasket 19 during the use of the pump.

In particular, annular portion 17 and tubular portion 16 are slidably supported by hollow body 6 within work chamber 7.

In the illustrated embodiment, annular portion 17 is slidably supported between suction compartment 36 and compensation compartment 38, thus creating a mobile division between them. Moreover, tubular portion 16 is slidably supported in delivery compartment 9. Conveniently, suction compartment 36 and compensation compartment 38 have substantially the same cross-section.

In the illustrated embodiment, tubular portion 16 is inserted into annular portion 17 and crosses it in the axial direction. Also, tubular portion 16 comprises a protruding tract 16a that extends axially beyond annular portion 17.

In particular, protruding tract 16a is slidably supported by delivery compartment 9. Conveniently, delivery compartment 9 has a smaller cross-section than that of the rest of work chamber 7, i.e. that of suction compartment 36 and of compensation compartment 38.

In the illustrated embodiment, protruding tract 16a of tubular portion 16 is slidably and sealingly housed in delivery compartment 9. The example shows an annular gasket 19 situated in delivery compartment 9 and operationally arranged around protruding tract 16a.

In the illustrated embodiment, with particular reference to Figure 1, pump 1 comprises a retaining bushing 21 that retains annular gasket 19 axially in abutment against a seat formed in hollow body 6.

Preferably, retaining bushing 21 is coupled to hollow body 6, in particular by ultrasonic welding in an annular housing of the hollow body, located upstream of annular gasket 19. As an alternative, retaining bushing 21 may be connected to the hollow body by mechanical coupling, e.g. by interference fit.

In the illustrated embodiment, with particular reference to Figure 1, retaining bushing 20 consists of a teflon disk having an axial through cavity.

In the illustrated embodiment, tubular portion 16 has no apertures in its side walls, but the fluid flowing through tubular portion 16 is intended to exit only through the axial end of protruding tract 16a.

In the illustrated embodiment, tubular portion 16 has a flange 16b in an opposite position of protruding tract 16a. When piston 2 is mounted, said head portion or flange 16b is axially in abutment against annular portion 17.

Preferably, when piston 2 is mounted, spring 11 is retained axially between tubular portion 16 and annular portion 17. In particular, end 11a of spring 11 is retained between flange 16b and axial end 17a of annular portion 17. This provides an exemplary mechanical coupling between spring 11 and piston 2.

As an alternative to the above, spring 11 may be coupled or secured to piston 2 in a different manner. For example, said spring 11 may be directly coupled to annular portion 17, without it being axially retained between said annular portion 17 and tubular portion 16. In addition, tubular portion 16 may even lack flange 16b, being however still coupled to annular portion 17.

In the illustrated embodiment, when piston 2 is mounted, tubular portion 16, after having been inserted into annular portion 17, is locked on annular portion 17.

Optionally, locking occurs by plastic deformation of protruding tract 16a against the walls of annular portion 17, e.g. by caulking and/or squashing.

With reference to Figure 2, there is shown a piston 2 designed in a manner that is alternative to the one of Figure 1. In particular, it can be noticed that tubular portion 16 - in this case preferably made of plastic material - is connected to annular portion 17 by interference fit. In particular, tubular portion 16 comprises a plurality of lateral fins 16c, preferably having an inclined profile, situated in an intermediate tract and tending to expand elastically outwards in a radial direction. When tubular portion 16 is inserted into annular portion 17 and lateral fins 16c enter annular portion 17, they are pushed in such a way that they will withdraw radially inwards (in particular, due to co-operation between the inclined profile and the shoulder of annular portion 17) . When tubular portion 16 is afterwards pushed and protruding tract 16a goes completely past annular portion 17, lateral fins 16c are again free to expand radially outwards. Should tubular portion 16 be then pushed backwards, lateral fins 16c are configured to abut axially against annular portion 17 and prevent extraction or removal of the tubular portion from annular portion 17.

In the illustrated embodiment, spring 11 is housed in suction compartment 36 and operates by compression to withdraw piston 2 from the first operating position Pi (into which it is attracted by the magnetic force generated by solenoid 4 ) .

Preferably, without however any limitation, there are no elastic means in abutment between hollow body 6 and piston 2 within compensation compartment 38. In particular, in compensation compartment 38 there are no elastic means in abutment between hollow body 6 and annular portion 17. This feature is advantageous in that it fully exploits the bidirectionality of spring 11 connected to piston 2, thus reducing the number of necessary components. In less preferred variants, however, it is possible to envisage the use of additional elastic means in abutment between the hollow body and the piston within the compensation chamber.

According to an alternative embodiment (not shown), spring 11 may be situated in compensation compartment 38 and be still connected to piston 2 (to the face thereof located in compensation compartment 38) . For example, in such an alternative embodiment spring 11 is arranged to work by traction, so as to be capable of withdrawing piston 2, in particular from the first operating position Pi (into which it is attracted by the magnetic force generated by solenoid 4) . In this case as well, as aforementioned, spring 11 is connected to piston 2 (and possibly also to hollow body 6) . Such connection may be effected by welding and/or mechanical coupling .

With reference to the exemplary embodiment shown in Figure 1, the following will describe in detail valve device 12 housed in piston 2 and the principle of operation thereof.

Valve device 12 is normally closed and can be opened by the fluid in suction device 36, under the action of the reciprocating motion of piston 2.

When electric current flows through solenoid 4, the magnetic field thus generated pushes piston 2 towards inlet 8, thereby reducing the volume of suction compartment 36 and pressurizing the fluid contained therein. In this way, the fluid reaches a pressure that is sufficient to open valve device 12, so that it can flow through through cavity 2a.

Vice versa, when solenoid 4 is electrically de energized, spring 11 pushes piston 2 back towards outlet 10, thereby increasing the volume of suction compartment 36 and reducing the pressure acting upon the fluid contained therein. In this way, valve device 12 returns into the closed position, thus stopping the flow of fluid through through cavity 2a. Preferably, valve device 12 includes a mobile shutter 12a within through cavity 2a, a seat 12b formed in through cavity 2a, and an elastic element, e.g. a return spring 18, acting upon mobile shutter 12a and tending to hold it against seat 12b.

In particular, seat 12b is formed in an axially intermediate position of through cavity 2a, which, in the illustrated embodiment, is defined in tubular portion 16.

Preferably, mobile shutter 12a comprises a ball shutter .

Preferably, seat 12b consists of a narrower portion defined in an intermediate portion of through cavity 2a. In particular, said narrower portion is defined by tubular portion 16, e.g. by a radially inward deformation of the latter .

In the illustrated embodiment, return spring 18 is housed in through cavity 2a and is connected to one end of piston 2. Return spring 18 acts upon mobile shutter 12a to hold it against seat 12b.

In particular, return spring 18 is connected to the downstream end of piston 2 and, being compression preloaded, presses against mobile shutter 12a.

As known in the industry, in the exemplary embodiment shown herein pump 1 comprises a non-return valve 14 situated in hollow body 6 downstream of work chamber 7, in particular of delivery compartment 9, and upstream of outlet 10. Said non-return valve 14, including a respective spring 15, is designed to prevent the fluid from returning from outlet 10 towards work chamber 7, in particular towards delivery compartment 9.

The following will describe in detail some optional implementation aspects related to the embodiment shown in Figure 1.

Solenoid 4 is in a position radially external to piston

2.

Preferably, pump 1 comprises a ferromagnetic assembly arranged around hollow body 6 and comprising, at least partly, ferromagnetic material. The ferromagnetic assembly is positioned transversally between solenoid 4 and hollow body 6.

Conveniently, said ferromagnetic assembly comprises a pair of blocks 5 of ferromagnetic material interposed between solenoid 4 and hollow body 6 in which piston 2 slides. Such blocks 5 preferably have a "C" shape. Each block 5 is arranged circumferentially around core 2. Solenoid 4 is conveniently housed in a respective housing 40 mounted around hollow body 6.

The solution of making tubular portion 16 and annular portion 17 as two separate pieces is simple and economical to implement. In particular, tubular portion 16 is configured in a manner such that the fluid will flow from suction compartment 36 to delivery compartment 9 through cavity 2a. Therefore, the fluid cannot flow from compensation compartment 38 to delivery compartment 9 through the side walls of tubular portions 16.

In fact, as aforementioned, the side walls of tubular portion 16 have no such apertures as to allow the fluid to flow directly from compensation compartment 38 to the inside of tubular portion 16 and then back into suction compartment 36.

With reference to the illustrated embodiment, pump 1 further comprises an integrated flow-rate measuring device. Such device is intended to measure the flow rate of the fluid being delivered by the pump. In particular, the flow-rate measuring device is situated upstream of piston 2, in particular upstream of work chamber 7, with reference to the fluid flow. In particular, the flow-rate measuring device comprises:

- an impeller 20 situated between piston 2 and inlet 8, and configured for being turned by a flow of fluid entering through inlet 8 and directed towards work chamber 7, and

- a sensing device 24 configured for sensing the rotation of impeller 20, for the purpose of measuring the fluid flow rate .

Preferably, sensing device 24 comprises a magnetic sensor. In particular, impeller 20 comprises one or more magnets 22, and sensing device 24 is adapted to sense the rotation of magnet 22 for the purpose of measuring the fluid flow rate.

Sensing device 24 is configured for sensing magnetic field variations caused by the rotation of impeller 20 and of magnet 22 integral with said impeller 20. For example, sensing device 24 may be a sensor of the electric, electronic or magnetic type, such as, for example, a magnetic sensor. Impeller 20 is adapted to turn about an axis of rotation x- x, which, in particular, is coaxial to piston 2. Impeller 20 is conveniently supported in rotation by a support.

In the illustrated embodiment, said impeller support is, advantageously, the previously mentioned locking element 26. However, in further implementation variants said support may be a separate component .

The support, which in the illustrated embodiment is provided by locking element 2, has a pin 28 inserted into a matching recess in impeller 20, so as to allow rotation thereof. As can be noticed, the pump is very compact, and there is no need for a long tube connecting outlet 10 or inlet 8 to an external flowmeter, in which the liquid, e.g. water, may stagnate. This aspect is particularly advantageous in beverage dispensers, wherein it is advantageous to prevent the liquid from remaining in contact with the outside environment for long periods of time; also, this prevents undesired dripping. According to possible variants, sensing device 24 is of the optical type, e.g. for reading reading portions (e.g. differently coloured stripes or other distinctive marks) on impeller 20.

In particular, pump 1 includes a cover 32 removably mounted (e.g. by means of screws 33) to hollow body 6, between which a gasket 34 is conveniently interposed. In cover 32 housing chamber 30 is formed. Housing chamber 30 is defined between cover 32 and hollow body 6. Moreover, cover 32 comprises inlet 8. Conveniently, the sensing device is associated with cover 32. Conveniently, inlet 8 is configured to direct a flow of fluid tangentially onto impeller 20, particularly onto blades of impeller 20.

In accordance with one possible alternative embodiment, the pump is comprised in an apparatus, such as a beverage dispensing machine or a coffee-making machine, and, when said apparatus is resting on a horizontal surface, hollow body 6, and in particular work chamber 7, is tilted relative to a horizontal plane, e.g. by an angle of 10° to 80°, preferably 10° to 60°, more preferably 10° to 30°. In this way, it is advantageously possible to facilitate the elimination of the air from housing chamber 30 of impeller 20, thus making the measurement more accurate. In particular, work chamber 7 as a whole is situated in a higher position than impeller 20 or housing chamber 30. For example, the tilted position corresponds to the position taken by the pump of Figure 1 when it is turned counterclockwise by a few degrees. Thus, impeller 20 can rotate while staying immersed in the liquid. Cylinder 6, and in particular work chamber 7, is arranged on a longitudinal axis, which in particular coincides with axis x-x. Therefore, axis x-x can be tilted relative to the horizontal.

According to a further exemplary embodiment (not shown) , locking element 26 is movably and adjustably mounted in hollow body 6 in abutment against spring 11. This permits calibrating the compression exerted on piston 2 by elastic member 11 in a customized manner dependent on the specific operating conditions in which the pump will have to work. By way of example, in this embodiment locking element 26 is mounted in hollow body 6, and these are threadedly coupled together .

Preferably, locking element 26 is at least partly made of ferromagnetic material.

Preferably, annular portion 17 of core 2 has a substantially circular cross-section. More preferably, the inner cavity of annular portion 17 of core 2 also has a substantially circular cross-section.

With reference to Figures 5 and 6, there is shown a pump made in accordance with a further embodiment of the present invention.

In such an embodiment, pump 1 comprises also a connection element coupled around hollow body 6 and configured to allow the pump to be installed in a household appliance. In particular, the connection element is a yoke 42 having a pair of lateral jaws or appendices 44 which seize hollow body 6 and which extend transversally beyond the latter, so as to allow the pump to be installed in a household appliance .

In the illustrated embodiment, yoke 42 is in axial abutment against the assembly of ferromagnetic material, which preferably includes blocks 5, and retains it within hollow body 6.

In the illustrated embodiment, yoke 42 is axially retained between solenoid 4 and a stopping member mounted on hollow body 6. In particular, the stopping member is a hydraulic connector or union 46 mounted to one end, e.g. the outlet end, of hollow body 6.

Preferably, yoke 42 is made of elastomeric material.

In the illustrated embodiment, the ferromagnetic assembly further comprises a spacer 48 located between two blocks 5. Thus, blocks 5 and spacer 48 are stackable in the axial direction and axially retained within hollow body 6 by the connection element, in particular yoke 42.

In particular, on one side the ferromagnetic assembly is in axial abutment with a flange or perimetrical extension 50 of hollow body 6. On the other side, said ferromagnetic assembly is in axial abutment with the connection element, in particular yoke 42.

As will be apparent to a person skilled in the art, according to another aspect of the present invention, the pump illustrated in Figures 5 and 6 may not employ an elastic member, such as spring 11, connected to piston 2 and configured for acting bidirectionally upon piston 2 during the displacement thereof in work chamber 7. In particular, said pump may be modified in such a way as to incorporate a pair of springs acting upon piston 2, as in the above- mentioned prior-art examples.

Of course, without prejudice to the principle of the invention, the forms of embodiment and the implementation details may be extensively varied from those described and illustrated herein by way of non-limiting example, without however departing from the scope of the invention as set out in the appended claims.

For example, as the present description has made clear, solenoid 4 shown in the illustrated embodiment may be replaced with any other generator device capable of creating a magnetic field.

For example, as the present description has made clear, spring 11 shown in the illustrated embodiment may be replaced with any other elastic member.

For example, as the present description has made clear, counter-spring 18 shown in the illustrated embodiment may be replaced with any other elastic member.

In the illustrated embodiment, seat 12b is formed in an intermediate portion of piston 2. In this regards, it will be apparent to a person skilled in the art that the term "intermediate position" does not mean that said seat 12b should be equidistant from the axial ends of piston 2, but rather that said seat is in a position generally spaced out from both axial ends of the piston.

In the illustrated embodiments, piston 2 comprises a tubular portion 16 and an annular portion 17 crossed by tubular portion 16. However, as will be apparent to a person skilled in the art, the piston may also be constructed differently. For example, one may conceive a structure made up of two pieces assembled together, wherein the tubular portion is situated at the end of the annular portion without going through it as shown in Figures 1 to 4.

A further advantage is given by the fact that element 16 can have a small diameter, e.g. as small as 3 mm, and a thin tube, e.g. as thin as 0.2 mm. In other words, manufacturing element 16 requires less material.

Claims

1. Vibration pump (1), in particular for a household appliance; said pump comprising:

- a hollow body (6) having an inlet (8) and an outlet

(10), between which a fluid can flow; said hollow body (6) further comprising a work chamber (7) located between said inlet (8) and said outlet (9);

- a piston (2) at least partly made of ferromagnetic material and configured for sliding in the hollow body (6) within said work chamber (7), so as to push said fluid from said inlet (8) to said outlet (10);

- a generator device (4) configured for generating a magnetic field capable of commanding the displacement of said piston (2) within said work chamber (7);

- elastic means (11) located in said work chamber (7) and co-operating with said piston (2);

said pump being characterized in that said elastic means comprise an elastic member (11) connected to said piston (2) and configured for acting bidirectionally upon said piston (2) during the displacement thereof in said work chamber (7) .

2. Pump according to claim 1, wherein said elastic member

(11) and said piston (2) are connected by welding.

3. Pump according to claim 1, wherein said elastic member (11) and said piston (2) are connected by means of a mechanical coupling.

4. Pump according to claim 3, wherein said piston (2) comprises a radially external annular portion (17) and a radially internal tubular portion (16) .

5. Pump according to claim 4, wherein said annular portion (17) and said tubular portion (16) are made separately and connected to each other.

6. Pump according to claim 5, wherein said annular portion (17) is made of ferromagnetic material.

7. Pump according to claim 5 or 6, wherein said tubular portion is made of plastic material.

8. Pump according to claim 5 or 6, wherein the tubular portion (16) is made of steel.

9. Pump according to claim 8, wherein the tubular portion is manufactured by extrusion.

10. Pump according to claim 8 or 9, wherein the annular portion (17) and the tubular portion (16) are made of different steel types from one another.

11. Pump according to any one of claims 5 to 10, wherein said tubular portion (16) and said annular portion (17) are connected by interference fit.

12. Pump according to any one of claims 5 to 11, wherein said elastic member (11) is retained between said annular portion (17) and said tubular portion (16) .

13. Pump according to claim 12, wherein said tubular portion (16) crosses said annular portion (17) and comprises a protruding tract (16a) axially going past said annular portion (17).

14. Pump according to claim 13, wherein said tubular portion (16) has a flange (16b) located in a position axially opposite to said protruding tract (16a) and axially facing towards said annular portion (17) .

15. Pump according to claim 14, wherein said elastic member (11) is axially retained between said flange (16a) and said annular portion (17) .

16. Pump according to any one of the preceding claims, wherein said elastic member (11) is locked relative to the hollow body ( 6 ) .

17. Pump according to claim 16, further comprising a locking element (26) axially mounted to said hollow body (16) and configured for retaining said locking element (26) .

18. Pump according to claim 17, wherein said locking element (26) has an annular housing (26a) that receives one end (lib) of said elastic member (11) .

19. Pump according to any one of the preceding claims, wherein said locking element (26) is adjustably movable in said hollow body (6) and abuts against said elastic member

(11), so as to calibrate the compression exerted on the piston (2) by said elastic member (11) .

20. Pump according to claim 17, wherein said locking element (26) and said hollow body (6) are threadedly coupled together .

21. Pump according to any one of the preceding claims, further comprising a valve device (12) located in a through cavity (2a) of said piston (2) and configured for selectively allowing said fluid to flow through said through cavity (2a) as a function of the pressure of said fluid in said work chamber ( 7 ) .

22. Pump according to claim 21, wherein said valve device

(12) has a mobile shutter (12a) which is movable in said through cavity (2a), a seat (12b) formed in said through cavity (12a), and an elastic element (18) tending to push said mobile shutter (12a) against said seat (12b) .

23. Pump according to claim 22, wherein said seat (12b) is created by a narrower portion defined in said through cavity (2a) .

24. Pump according to claim 23, wherein said narrower portion is a deformation obtained radially inwards on said piston ( 2 ) .

25. Pump according to any one of claims 22 to 24, wherein said seat (12b) is formed in an intermediate position between the axial ends of said piston (2) .

26. Pump according to claim 4, further comprising an annular gasket (19) retained in said hollow body (6), through which an end tract (16a) of the tubular portion (16) slides.

27. Pump according to claim 26, further comprising a retaining bushing (21) coupled to said hollow body (6), which axially retains said annular gasket (19) in abutment against a seat formed in said hollow body (6) .

28. Pump according to any one of the preceding claims, further comprising a ferromagnetic assembly (5, 48, 5) comprising, at least partly, ferromagnetic material, surrounding said hollow body (6) and arranged transversally between said generator device (4) and said hollow body (6) .

29. Pump according to any one of the preceding claims, further comprising a connection element (42) coupled around said hollow body (6) and having at least one appendix (44) extending transversally and configured for allowing said pump to be installed in a household appliance.

30. Pump according to claims 28 and 29, wherein said connection element (42) is in axial abutment against said ferromagnetic assembly (5, 48, 5) .

31. Pump according to claim 30, wherein said ferromagnetic assembly includes stackable components (5, 48, 5) retained in the hollow body by said connection element (42) .

32. Pump according to claim 30 or 31, wherein said connection element (42) is axially retained between said generator device (4) and a stopping member (46) mounted on said hollow body (6) .

33. Pump according to claim 32, wherein said stopping member is a hydraulic connector or union (46) mounted to one end of said hollow body (6) .

34. Pump according to any one of claims 29 to 33, wherein said connection element is a yoke (42) having two lateral appendices (44) which laterally seize said hollow body (6) and which are configured to be coupled to a part of the household appliance.

35. Pump according to any one of claims 29 to 34, wherein said connection element (42) is made of elastomeric material.

36. Household appliance comprising a pump according to any one of the preceding claims.