CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority from Italian patent application no. 102019000015386 filed on September 2, 2019, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD The invention relates to an axial flowmeter, in particular for household appliances.

In particular, the invention relates to an axial flowmeter to measure the flow rate of a fluid in a duct, which is used in hydraulic circuits of coffee machines and water dispensers, without for this reason limiting the wide range of possible applications of the invention.

BACKGROUND ART

Different types of flowmeters are currently known and exploit different operating principles. Among them, axial flowmeters are known, in which the fluid flowing along the axis of the flowmeter causes the rotation of an impeller around said axis and a sensor detects the rotary motion of the impeller and provides signals concerning the fluid flow rate.

The correct measurement of the flow rate depends on design parameters and on the correct installation of the different components.

Known axial flowmeters do not allow users to check whether the different components were mounted correctly. DISCLOSURE OF INVENTION

The object of the invention is obviate the drawbacks of the prior art.

According to the invention, there is provided an axial flowmeter to measure the flow rate of a flow of fluid in a duct, the flowmeter comprising:

- a tubular body extending along a longitudinal axis and configured to convey the fluid;

- a shaft located inside the tubular body and configured to rotate around the longitudinal axis; - a first and a second support, each mounted in the tubular body and coupled to a respective end of the shaft in a rotary manner so as to allow the shaft to rotate around the longitudinal axis;

- an impeller fixed to the shaft and configured to rotate clockwise or counterclockwise around the longitudinal axis depending on the direction of the flow of fluid; and

- a sensor coupled to the tubular body and configured to detect the rotation speed of the impeller; wherein the impeller has only two vanes, which are arranged on opposite sides of the shaft, extend in a direction parallel to the longitudinal axis and have two respective coplanar central portions and two respective end portions inclined relative to the central portions. In this way, it is possible to measure the flow rates of a fluid whose flow is variable depending on the direction.

In other words, it is possible to measure flow rate values inside ducts where the fluid alternatively flows in both directions. Thanks to the two vanes, the fluid flow determines the rotation of the impeller around the longitudinal axis.

Furthermore, thanks to the two sole vanes, the fluid flow is subjected to small pressure drops when it flows through the flowmeter. The two vanes extend along the same plane and the inclined end portions form an angle of attack with the direction of the flow so as to facilitate the rotation of the impeller around the longitudinal rotation axis clockwise or counterclockwise depending on the direction of the fluid flow.

In particular, the flowmeter comprises an identification member, which is fixed to the shaft or to the impeller and is correlated with the shape of the impeller; the tubular body being made of a transparent material.

Thanks to the invention, users can visually check whether the components of the flowmeter are correctly fitted in the tubular body and install the flowmeter without having to worry about the direction of insertion into the duct, with a consequent ease of installation and saving of time.

Indeed, the flowmeter is fitted with impellers with different geometries depending on the ranges of flow rate values to be measured for which it is used, whereas the geometry of the remaining components of the flowmeter remains unchanged. Therefore, the identification member allows users to identify the flowmeter suited for a given use, even when the geometric differences between the impellers are not easily perceivable. More in detail, thanks to the identification member, it is possible to visually identify, from the outside of the tubular body, the different type of impeller present in the tubular body of the flowmeter.

In this way, the installation of the flowmeter is further simplified.

In particular, the identification member is a coloured ring.

In this way, the type of impeller present inside the flowmeter can be visually identified even when the flowmeter is being used and the impeller is rotating.

In particular, the impeller is at least partially made of sintered magnetic material, in particular by moulding sintered magnetic material on the shaft.

In this way, the fluid flow rate can be measured by detecting magnetic field changes caused by the rotation of the impeller around the longitudinal axis.

Furthermore, the impeller can be manufactured in a simple, quick and economic fashion.

In particular, the end portions of each vane substantially have the same inclinations relative to the respective central portion, in particular the angle between each central portion and the respective end portions ranges from 10° to 30°.

In this way, the rotation speed of the impeller around the longitudinal axis is within a given speed range.

In particular, the first and second supports are substantially equal to one another and face one another. In this way, the first and the second support are mounted in a symmetrical manner relative to a plane going through the centre of the flowmeter and transverse relative to the longitudinal axis. In particular, each one of the first and second support comprises a respective annular body; and a respective cylindrical body configured to be coupled to the respective end of the shaft. In this way, the first and the second support can be coupled to the tubular body and the shaft can be coupled to the respective cylindrical body so as to allow the shaft to rotate around the longitudinal axis.

In particular, each end of the shaft is tapered; each cylindrical body having a recess so as to house a respective end of the shaft.

In this way, the shaft can be supported and, at the same time, the shaft can rotate around the longitudinal axis with no need for bearings. In particular, the flowmeter comprises a seat fixed to the tubular body and configured to house the sensor.

In this way, the sensor can be fixed to the tubular body.

In particular, the sensor is configured to detect the magnetic field variations caused by the rotation of the impeller around the longitudinal axis; in particular, the sensor is a Hall effect sensor.

In this way, the sensor emits electrical signals depending on the rotation speed of the impeller.

A further object of the invention is to provide a method to manufacture a flowmeter, which reduces at least one of the drawbacks of the prior art.

According to the invention, there is provided a method to manufacture an axial flowmeter to measure the flow rate of a fluid, the method comprising:

- providing a shaft extending along a longitudinal axis;

- moulding an impeller of sintered magnetic material on the shaft;

- inserting one between the first and the second support inside a transparent tubular body; inserting the shaft and the impeller inside the tubular body;

- inserting the other one between the first and the second support inside the tubular body, so as to couple the ends of the shaft to the first and the second support inside the tubular body; and

- placing a sensor on the outside of the tubular body to detect the rotation speed of the impeller.

In this way, a flowmeter can be manufactured and assembled in a simple, quick and cost-effective fashion.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be best understood upon perusal of the following description of a non-limiting embodiment thereof, with reference to the accompanying Figures, wherein: Figure 1 is a perspective view, with parts removed for greater clarity, of a flowmeter according to the invention;

- Figure 2 is a side elevation view, with parts removed for greater clarity, of the flowmeter of Figure 1;

- Figure 3 is a cross-section view, with parts removed for greater clarity, of the flowmeter of Figure 1 along cross-section lines III-III; and

- Figure 4 is a perspective view, with parts removed for greater clarity, of a detail of the flowmeter of Figure

1.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to Figures 1, 2 and 3, number 1 indicates, as a whole, an axial flowmeter to measure the flow rate of a fluid inside a duct, which finds particular application in the field of household appliances.

In particular, the flowmeter 1 is used to measure the flow rate of a fluid in hydraulic circuits of coffee machines and water dispensers, without for this reason limiting the wide range of possible applications of the invention.

The flowmeter 1 comprises a tubular body 2 extending along a longitudinal axis A, where the fluid flow flows; a seat 3, which is fixed on the outside of the central portion of the tubular body 2; a sensor 4, which is housed in the seat 3; and two manifolds 5 and 6, which are fixed to a respective end of the tubular body 2 and are configured to connect the tubular body 2 to a respective duct.

With reference to Figure 3, the flowmeter 1 comprises a shaft 7, which is arranged inside the tubular body 2 and is configured to rotate around the longitudinal axis A; two supports 8 and 9, each fixed inside the tubular body 2 and coupled to a respective end of the shaft 7; an impeller 10, which is fixed to the shaft 7; and an identification member 11, which preferably is a coloured ring and is fixed to the shaft 7.

The tubular body 2 is made of a transparent material. In particular, the tubular body 2 is made of a plastic material, preferably PC or PPSU. The tubular body 2 has a seat in the area of each end for housing a respective manifold 5 or 6.

The manifolds 5 and 6 are substantially equal and are arranged in the respective seat in a symmetrical manner relative a plane going through the centre of the flowmeter 1 and transverse to the longitudinal axis A.

The supports 8 and 9 are substantially equal and face one another in a symmetrical manner relative a plane going through the centre of the flowmeter 1 and transverse to the longitudinal axis A.

Each support 8 and 9 comprises a respective annular body 12, which is arranged around the longitudinal axis A and is configured to be fixed inside the tubular body 2; a respective cylindrical body 13, which is configured to be coupled to the respective end of the shaft 7; and four respective supports 14, which connect each annular body 12 to the respective cylindrical body 13.

Each annular body 12 is housed in a respective annular seat obtained in the tubular body 2.

The number of supports 14 can be different and does not limit the invention.

Each cylindrical body 13 has a recess with a conical shape so as to be coupled to the respective end of the shaft

7.

Each end of the shaft 7 is tapered so as to be inserted into the recess of the respective cylindrical body 13.

In other words, the ends of the shaft 7 have a conical shape and are coupled to the recess of the respective cylindrical body 13 in order to allow the shaft 7 to rotate around the longitudinal axis A. The impeller 10 is made of a sintered magnetic material and is configured to rotate clockwise or counterclockwise around the longitudinal axis A depending on the direction of the fluid flow.

In other words, the impeller 10 is configured to alternatively change its direction of rotation depending on the direction of the fluid flow.

The sensor 4 is configured to detect the rotation speed of the impeller 10.

More in detail, the sensor 4 is a Hall effect sensor, which is configured to measure the rotation speed of the impeller 10 by detecting the magnetic field variations caused by the rotation of the impeller 10 around the longitudinal axis A.

According to an alternative embodiment, the sensor 4 is an optical sensor, which is configured to detect the rotation speed of the impeller 10 by means of photosensors or photodetectors

According to a further embodiment, the sensor 4 is an ultrasound sensor or an accelerometer, which is configured to detect the vibrations caused by the rotation of the impeller 10 around the longitudinal axis A.

With reference to Figures 3 and 4, the impeller 10 is manufactured by overmoulding sintered magnetic material on the shaft 7. The impeller 10 comprises two vanes 15 and 16, which are arranged on opposite sides relative to the shaft 7 and each extend in a direction parallel to the longitudinal axis

A.

With reference to Figure 4, the vanes 15 and 16 have two respective coplanar central portions 17 and two respective end portions 18 and 19, which are inclined relative to the central portions 17.

In other words, in the vanes 15 and 16, the central portions 17 extend along a plane P, on which the longitudinal axis A lies, and the end portions 18 and 19 are inclined relative to the plane P.

The end portions 18 and 19 substantially have the same inclination relative to the respective central portion 17, in particular the angle between each central portion 17 and the respective end portions 18 and 19 ranges from 10° to 30°.

In other words, the end portions 18 and 19 substantially have the same inclination relative to the plane P.

Furthermore, the end portion 18 of the vane 15 is adjacent to the end portion 19 of the vane 16.

The identification member 11 is fixed in the area of an end of the impeller 10 and is configured to visually stand out from the shaft 7 and the impeller 10.

In use and with reference to Figure 3, the fluid flow flows inside the tubular body 2 and, by interacting with the vanes 15 and 16, causes the rotation of the impeller 10 around the longitudinal axis A.

When each vane 15 and 16 gets close to the sensor 4 there is a change in the magnetic field in the proximity of the sensor 4, which detects the magnetic field variation and emits an electrical signal.

In other words, the rotation of the impeller 10 causes the sensor 4 to emit an electrical impulse when a vane 15 or 16 passes close to the sensor 4. By calculating the number of electrical impulses emitted per unit of time it is possible to determine the rotation speed of the impeller 10, thus obtaining the value of the flow rate of the fluid flowing through the flowmeter 1. When, depending on the specific circumstances, the fluid flow changes direction, the impeller 10 changes rotation direction.

The identification member 11 allows for an immediate visual identification of the particular geometry of the impeller 10 even when the flowmeter 1 is being used.

Finally, the invention can evidently be subjected to variants to the embodiments described herein, though without going beyond the scope of protection set forth in the appended claims.