WO2015198224A1

WO2015198224A1 - Rotary fluid pump

Info

Publication number: WO2015198224A1
Application number: PCT/IB2015/054705
Authority: WO
Inventors: Leonardo Cadeddu
Original assignee: Vhit S.P.A.
Priority date: 2014-06-23
Filing date: 2015-06-23
Publication date: 2015-12-30
Also published as: EP3158196B1; EP3158196A1

Abstract

Fluid pump (10) comprising a hollow body (100) in which a stator (101) and an external rotor (106) of an electric motor are mounted. The external rotor (106) is rotatably mounted about a main axis (X-X) and has an internal cavity (25) connected to an inlet port (114) and an outlet port (115) arranged to allow the inflow of a fluid into said internal cavity (25) and the outflow of said fluid from said internal cavity (25), respectively, an internal rotor (111) rotatably mounted in the internal cavity (25) so as to be free to rotate about a secondary axis (Y-Y), a vane (109) slidably guided in a slot (110) which is formed in the internal rotor (111) so as to pass through said rotor in a through manner and has a first end and a second end, wherein the first end is provided at a pivot (108). The internal rotor (111) and the vane (109) cooperate in such a way as to divide in a cyclic and fluid-tight manner said internal cavity (25) at least into a first chamber with variable volume and a second chamber with variable volume, said chambers communicating with said inlet port (114) and said outlet port (115), respectively. The pivot (108) is oscillatably mounted in the external rotor (106) so that the external rotor (106), by rotating about its main axis (X-X), entrains in its movement said pivot (108) of the vane (109) and the internal rotor (111), which is brought into rotation by the vane (109) and rotates idly about its secondary axis (Y-Y).

Description

"Rotary fluid pump"

~k ~k ~k

DESCRIPTION

Technical Field

The present invention relates to a rotary fluid pump, and more specifically to a rotary vacuum pump applied to an electric motor.

Preferably, though not exclusively, the invention finds application in the so-called mono-vane pumps, i.e. pumps in which the rotor comprises a single vane, and the following description will preferably, though not exclusively, refer to this kind of application.

Prior Art

In the field of rotary pumps, it is known to use positive displacement pumps with electric motors, for instance with a DC electric motor of the type without brushes or brushless type.

An example of such pumps is described in the Applicant's Patent Application WO2011033426, which discloses a pump structure having a body defining a cavity having an inlet port and an outlet port arranged to allow the inflow of a fluid into the cavity and the outflow of said fluid from such cavity, respectively. The known pumps comprises a rotor mounted in the hollow body so as to be rotatable about a main axis or revolution axis, and an orbiting piston driven by the rotor.

The orbiting piston is positioned eccentrically relative to the main axis, is mounted on the outside of the rotor so as to be rotatable about a secondary axis or rotation axis. The pump further includes a vane which is located in the cavity, is slidable within the orbiting piston and is mounted in a fixed peripheral portion of the hollow body between the inlet and outlet ports so as to be able to oscillate. The orbiting piston and the vane attached to the body cooperate in such a way as to divide in a cyclic and fluid-tight manner said cylindrical cavity into a first chamber with variable volume and a second chamber with variable volume, which first and second chambers communicate with the inlet port and the outlet port, respectively, and the point of separation between the two chambers is the point of articulation of the vane, said articulation point being fixed, whereas the point of tangency between the orbiting piston and the rotor is variable because of the roto- translational motion of the piston relative to the rotor.

Yet, vacuum pumps of the kind described above have some drawbacks .

A drawback is that said known vacuum pump has large axial dimensions that do not allow the pump to be mounted on the heat engine of a vehicle in the same space as that required by a mechanical vacuum pump.

A further drawback is that said pump, due to the fact that, because of its large dimensions, it cannot be mounted on the heat engine of the vehicle, must be mounted on the chassis or on the bodywork, thus increasing the noise of the pump .

Disclosure of the Invention

It is an object of the present invention to provide a fluid rotary pump that is integrated in an electric motor, has small axial dimensions and is suitable for being mounted on the heat engine of a vehicle and is preferably lubricated with the engine oil that is self-sucked by the pump itself, and has the same space requirements as those of a mechanical pump .

It is another object of the present invention to provide a rotary pump that is integrated in an electric motor and is suitable for being mounted on the heat engine of a vehicle so as to reduce the noise of the pump.

It is a further object of the present invention to provide a rotary pump of the "stand-alone" type that is integrated with an electric motor of the type without brushes or brushless type and has extremely reduced axial dimensions .

These and other objects are achieved by the present invention by providing a rotary pump integrated in an electric motor according to the appended claims.

It is understood that the appended claims are an integral part of the technical teachings provided herein in the present description of the invention.

Brief Description of the Drawings

Further features and advantages of the present invention will become apparent from the following detailed description, given only by way of non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 is a radial sectional view of a first embodiment of a fluid rotary pump according to the present invention;

Figure 1A is an axial sectional view of the first embodiment of the fluid rotary pump according to the present invention;

- Figure 2 is a radial sectional view of the first embodiment of the fluid rotary pump according to the present invention;

Figure 3 is an axial sectional view of the first embodiment of the fluid rotary pump according to the present invention;

Figure 4 is a view of an enlarged detail of the radial section of the first embodiment of the fluid rotary pump according to the present invention;

Figure 5 is a radial sectional view of a second embodiment of a fluid rotary pump according to the present invention;

Figures 6-8 show a third embodiment of the fluid rotary pump according to the present invention and an operating sequence thereof;

Figures 9-11 show a fourth embodiment of the fluid rotary pump according to the present invention and an operating sequence thereof. Description of a Preferred Embodiment

Referring to the Figures, there is illustrated an exemplary embodiment of a fluid rotary pump or enclosed positive displacement mechanism 10, for example a vacuum pump, to which reference is made hereinafter, integrated in an electric motor according to the present invention.

The vacuum pump 10 (Fig. 1) comprises a hollow body 100, a stator 101, an external rotor 106, an internal rotor 111, and a vane 109.

The body 100 is a housing defining a substantially cylindrical cavity 20 in which the stator 101 and the external rotor 106, which is rotatably mounted in said stator 101 and has a cylindrical internal cavity 25 enclosing the internal rotor 111 and the vane 109, are mounted. Said body 100 has an inlet port 114 and an outlet port 115, shown in Figure 2. The inlet port 114 is connected to a suction duct and allows the inflow of a fluid into the internal cavity 25, whereas the outlet port 115 is connected to a discharge duct and allow the outflow of the fluid from said internal cavity 25. The body 100 is preferably made of a non-magnetic material, such as a thermoplastic or thermosetting material, or of an aluminium alloy. Polyphenylene sulphide (PPS) is preferred for use as a thermoplastic material, whereas phenolic plastics or resins (PF) , charged with glass fibres, carbon fibres or aramidic fibres, are preferred as thermosetting materials. Advantageously, the body 100 is made by moulding.

In particular, the body 100 is sealed in a fluid-tight manner, for example by means of a gasket, by a cover so as to define the cavity 20.

Referring to Figure 1, the stator 101 constitutes, with the external rotor 106, an electric motor, for example a DC motor of the brushless type. The stator 111 is housed, for instance fitted, in the body 100 of the pump and is preferably formed by a pack of lamellae 102 made for example of a ferromagnetic material, for instance a silicon plate, including a plurality of windings 103 and corresponding polar expansions 104.

Preferably, the stator 101 houses a guiding ring 105 having a small thickness and a cylindrical shape and made of a non-magnetic material of a plastic or metal type, for instance bronze, which has the function of guiding the external rotor 106. The guiding ring 105 forms the gap between the windings 103, with their corresponding polar expansions 104, and a plurality of permanent magnets 107 that are arranged on the outer periphery of the external rotor 106.

The electromagnetic stator 101 and the permanent magnets 107 are arranged for mutually interacting electromagnetically and rotating the external rotor 106 rotatable about a main axis X-X. Preferably, said main axis X-X coincides with the axis of the cylindrical cavity 20.

The external rotor 106 is preferably made of a ferromagnetic material, or for example of a thermoplastic, thermosetting, metallic material, for instance of an aluminium alloy. Advantageously, the external rotor 106 is manufactured by moulding/sintering.

In further variants it is conceivable that the external rotor 106 is made of a ferromagnetic material. The permanent magnets 107 can be co-moulded with the rotor or mounted in the rotor, for example they can be made of materials belonging to the family of "rare earths", or of ferromagnetic materials.

The rotary vacuum pump 10 integrated, in accordance with the present invention, in an electric motor preferably comprises an electronic control unit which controls, in a known manner by means of a dedicated software entirely or partially mounted on the control unit of the pump, the passage of electric current through the windings 103 that work as electromagnets. For example, the electronic control unit is a printed circuit board of a type known per se. Advantageously, the electronic control unit can command in an electronically controlled manner the rotational speed of the external rotor 106.

The internal rotor 111 is mounted so as to be rotatable in the internal cavity 25, on a guide 112 provided in the body 100 so that said internal rotor is free to rotate about a secondary axis or rotation axis Y-Y of its own that is eccentrically positioned relative to the main axis X-X.

As is further visible from the Figures, the vane 109 is slidably guided in a slot 110 which is radially provided in the internal rotor 111 and passes through said rotor in a through manner. In addition, the vane 109 has a first end with a pivot 108 having a center or articulation axis C and is mounted in the external rotor 106 so as to be able to oscillate about the center C.

The external rotor 106, rotating about its main axis X- X and preferably guided by the guiding ring 105, entrains in its movement the pivot 108 of the vane 109 which is guided by the radial slot 110 of the internal rotor 111; said internal rotor 111, idly rotating about its secondary axis Y-Y, is brought into rotation by the vane 109 with a rotational period or rotational frequency equal to the one of the external rotor 106.

The internal rotor 111 and the vane 109 mounted on the external rotor 106 cooperate in such a way as to divide in a cyclic and fluid-tight manner the cylindrical cavity 25 into a first chamber with variable volume and a second chamber with variable volume. The first and second chambers are mutually complementary and communicate with the inlet port 114 and the outlet port 115, respectively.

The vane 109 preferably is a mono-vane with a first end having a pivot 108 hinged inside the external rotor 106 and a second end terminating with a tip 123 that is guided in the body of the vane 109 and is axially slidable, for example pushed by an elastic element 124 or by the centrifugal force or by both.

The vane 109 is mounted hinged to the external rotor

106 in such a way that the vane, during its oscillation, passes through the internal rotor 111 in a through manner and is in contact with the internal side surface of the internal cylindrical cavity 25 at the tip 123 of its second end, thus separating the first chamber from the second chamber in a fluid-tight manner.

In the first embodiment, the external rotor 106 preferably comprises undercuts 106c that are suitably shaped so that the center C of the pivot 108 of the vane 109 remains, when in use, at a fixed distance R from the main axis X-X of the external rotor 106, i.e. so as to allow the pivot 108 to have solely a rotational motion about the center C and to prevent a translational motion thereof directed towards the inside of the cavity 25.

Further embodiments are illustrated below that differ from the first preferred embodiment in the kind of vane that is used, in the number of vanes or in the geometry of the internal cavity. The stator 101 and the various magnetic elements 103, 104, 107 arranged to operate the stator and the external rotor 106 as an electric motor remain unchanged, whereby what has already been described in respect of the first embodiment still applies.

In a second embodiment, shown in Figure 5, the internal surface of the external rotor 106 comprises a first portion 106a, to which the pivot 108 of the vane 109 is hinged, and a second portion 106b, which is distal relative to the pivot 108. The vane 109 is made without movable compensating tip 123 and thus has a fixed vane length 1, intended as the distance between the second end of the vane and the center C of the pivot 108.

The first portion 106a of the internal surface of the rotor 106 has a section having a circular profile in order to guarantee a point of tangency between the surface portion 106a and the internal rotor 111 during rotation of the rotors; said first portion 106a corresponds to the portion of the internal surface of the rotor 106 over which the second end of the vane 109 does not move during rotation. The second portion 106b of the internal surface of the rotor 106, substantially corresponding to the surface portion over which the second end of the vane 109 moves, has a section with such a profile that each point P thereof that, during rotation of the rotors, is in a position opposite to the center C of the pivot 108 relative to the secondary axis Y-Y of the internal rotor 111, has the same distance from the center C of the pivot 108. Said distance is preferably equal to the length 1 of the vane 109, so that the second end of the vane 109, during the whole rotation of the pump rotors, is preferably always in contact with the second portion 106b of the internal surface of the rotor 106, in contact points that are the points P of the second portion 106b as defined above .

In particular, the profile of the second portion 106b of the internal surface of the external rotor 106 is geometrically describable by means of a distance D, defined as the distance between the main axis X-X of the external rotor 106 and the contact point P between the second end of the vane 109 and the second portion 106b, and by means of an angle β, defined as the angle between a direction passing through the point P and through the axis X-X of the rotor 106 and a direction passing through the center C of the pivot 108 and through the axis X-X.

These two values are described by the following relations:

D = r + J(I - r)² + R² - 2R l - r) cos(i9 - φ),

_ (R cos ϋ— (e— r) cos φ

β = 2π— ϋ— cos — I per φ < π,

where :

r is the radius of the second end of the vane 109,

1 is the length of the vane (i.e. the distance between the center C of the pivot 108 of the vane and the second end of the vane) ,

R is the distance between the main axis X-X of the external rotor 106 and the center C of the pivot 108,

^■& is the angle between a reference direction passing through the main axis X-X of the external rotor 106 (for example, as shown in Figure 5, the direction passing through the axis X- X and the axis Y-Y of the internal rotor 111) and a direction passing through the center C of the pivot 108 of the vane 109 and through the axis X-X (or, in other words, is the angle of rotation of the external rotor 106) ,

φ is the angle between the reference direction passing through the axis X-X and a direction passing through the center C of the pivot 108 and through the axis Y-Y of the internal rotor 111, and e is the eccentricity between the external rotor 106 and the internal rotor 111 (interaxis between the axes X-X and Y-Y) . The arrangement of the second embodiment allows to have a displacement substantially identical to the one of the first embodiment, though using a vane with a fixed length and without movable compensating tip 123.

Preferably, in accordance with this embodiment, the pivot 108 at the first end of the vane does not require optional undercuts 106c at the region where the vane is hinged in the rotor 106, because the profile of the portion 106b is such that it keeps the clearance between the vane 109 and the portion 106b constant.

Advantageously, this makes the structure of the rotor at the hinge stronger, easier to manufacture and therefore more reliable.

In accordance with a third embodiment, shown in Figure 6, it is provided that the vane 109 has a fixed length and does not have the movable compensating tip 123 and that the internal cavity 25 is cylindrical, whereby the displacement, as will be easily understood by the person skilled in the art, will be approximately 1/2 of the displacement of the first and second embodiments.

In this embodiment, as the second end of the vane 109 is not always in contact with the internal wall of the external rotor 106, the external rotor 106 comprises undercuts 106c that are suitably shaped so that the center C of the pivot 108 of the vane 109 remains, when in use, at a fixed distance R from the main axis X-X of the external rotor 106, said distance R being greater than the radius of the internal cavity 25 by a quantity λ. In other words, the presence of the undercuts allows the pivot 108 to have solely a rotational motion about the center C and prevents a translational motion thereof directed towards the inside of the cavity 25. The operation of the third embodiment is represented in the Figures 6, 7 and 8.

In a preferred way, the internal rotor 111 (Fig. 1 - Fig. 8) has an external cylindrical surface that is tangentially almost in contact, as is usual, with the internal cylindrical surface of the external rotor 106 in their point of tangency 113 lying on the axis passing through the centers of the axes X-X and Y-Y.

Preferably, the vacuum pump 10 includes, in the embodiments described so far, an inlet non-return or unidirectional valve 116 and an outlet lamellar non-return or "reed" valve 117 associated to the inlet port 114 and the outlet port 115, respectively.

Through a hole 118 provided in the hollow body 100 and appropriate lubrication channels, not shown, the lubricating oil is sucked from the inside of the heat engine and said oil, after having lubricated the pump, will become mixed with the sucked air and form a mixture that will be discharged into the engine through the outlet lamellar non- return or "reed" valve 117.

Operation of the rotary vacuum pump integrated in an electric motor 10 of the invention is as follows.

The external rotor 106, rotating about its main axis X-X and preferably guided by the guiding ring 105, entrains in its movement the pivot 108 of the vane 109 which is guided by the radial slot 110 of the internal rotor 111. Said internal rotor 111, idly rotating about its secondary axis Y-Y, is brought into rotation by the vane 109 with a rotational period or rotational frequency equal to the one of the external rotor 106, with a an angular speed that is variable (and symmetrical to each half-period: indeed, the enclosed positive displacement mechanism is symmetrical with respect to the axis passing through the centers of the axes X-X and Y-Y) . As can be easily understood by the person skilled in the art, the profile of the angular speed of the internal rotor depends on the dimensions of the enclosed positive displacement mechanism that is being described.

During this rotation of the external rotor 106 and the internal rotor 111, their point of tangency 113 remains substantially fixed.

The rotational speed is governed by the following mathematical law: φ= , '-—3 where :

φ is the rotational speed of the vane guide,

3 and 3 are the rotational angle and the (constant) rotational speed of the outer ring, respectively,

R is the distance between the center of the external rotor 106 and the center C of the pivot or hinge 108 between the blade and the outer ring,

e is the eccentricity between the external ring and the vane guide (interaxis between the axes X-X and Y-Y) .

The displacement of this kind of pump is equivalent to the volume subtended between the two ends of the vane when this is positioned orthogonally relative to the axis passing through the centers of the axes X-X and Y-Y, multiplied by two, this condition being created at each round angle of rotation of the external rotor 106 and internal rotor 111.

The Figures 6, 7 and 8 show the positions of rotation that are significant for understanding the operation of the third embodiment of the pump 10 of the invention, wherein the vane 109 is made without movable compensating tip 123 and therefore, as is clear to the person skilled in the art, the displacement of this solution is the volume obtained by subtracting, from the internal volume of the external rotor for each round angle of rotation of the external rotor 106 and internal rotor 111, the volume of the internal rotor and of the part of vane projecting from said rotor; therefore in this arrangement the displacement is half that of the first embodiment, thus providing less variation of the resistive torque both at start and upon maintaining of depression; the emptying performance will in any case depend on the displacement .

The enclosed positive displacement mechanisms illustrated have been further integrated, in the preferred embodiment, in a brushless type electric motor. This provides in an advantageous manner the fluid-tight sealing of the hollow body with its movable component arranged inside it. Indeed, in this way the hollow body does not require any further openings for a mechanical connection to further outer movable elements adapted to impart motion to the rotor.

In accordance with other embodiments, the electric motor can also be a motor provided with brushes, even if this solution involves more maintenance than a brushless motor.

In a fourth embodiment, shown in Figure 9, the vacuum pump is a multi-vane pump 200.

The pump comprises the stator 101 and the various magnetic elements 103, 104, 107 as described in connection with the first embodiment, to which reference is made for a detailed description .

The pump 200 further includes an external rotor 106 having an internal cylindrical cavity 25 in which an internal rotor 211 enclosed.

The internal rotor 211 has a first slot 210a and a second slot 210b provided radially relative to the rotor and so as to pass through the rotor in a through manner. The first slot 210a and the second slot 210b are preferably arranged perpendicularly to each other. A first vane 209a is slidably guided in the first slot 210a and has a first end with a pivot 108 that is mounted in the external rotor 106 so as to be able to oscillate; this rotor, similarly to what is provided for the preceding embodiments, rotates on its main axis X-X and entrains in its movement the pivot 108 of the vane 209a, which, being guided by the slot 210a, brings into rotation the internal rotor 211.

The pump 200 further comprises a second vane 209b, this too being slidably guided in the first slot 210a, and two further vanes 219a, 219b that are slidably guided in the second slot 210b.

Preferably, the vanes 209b, 219a and 219b are mutually equal .

In accordance with this embodiment, two walls 226, 227 are provided arranged along the longitudinal edges of the first slot 210a at the second slot 210b.

These walls 226, 227 allow to prevent the vanes 219a, 219b from engaging the first slot 210a and hitting against the vanes 209a, 209b guided by the first slot 210a, especially at low rotational speed, where the centrifugal force may not keep them in contact with the wall of the cavity 25, thus avoiding frictions between the vanes.

In other embodiments said walls are not necessary.

This solution, in particular, is preferably applicable in the case where the length of the vane 209a is such as to at least partially engage, in all the arrangements, the intersection between the slot 210a and the slot 210b.

The operation of the rotary vacuum pump 200 integrated in an electric motor according to the fourth embodiment is described below with reference to Figures 9, 10, 11 showing three positions of rotation that are significant for its understanding .

As in the previous embodiments, the external rotor 106 rotates, guided by the ring 105, and entrains in its movement the vane 209a slidably guided by the radial slot 210a of the inner rotor 211. The rotor 211, idly rotating on its axis Y-Y, is then brought into rotation by the vane 209a, with as rotational period equal to the rotational period of the external rotor 106 and with an angular speed that is variable over the period with a profile depending on the dimensions of the enclosed positive displacement mechanism as described, according to a relation equal to the one illustrated above for the mono-vane embodiments.

The vanes 209b, 219a and 219b, when the internal rotor 211 is rotating, are subjected to a centrifugal force such that it brings them far from the secondary axis Y-Y of the internal rotor 211, making them partially come out of their corresponding slots until they encounter the internal side surface of the cavity 25. The internal rotor 211 and the vanes 209a, 209b, 219a and 219b cooperate in such a way as to divide in a cyclic and fluid-tight manner the internal cylindrical cavity 25 into four chambers with variable volume, so as to suck, in a known manner, air from the inlet port 114 and to discharge the same from the outlet port 115, thanks to the fact that the internal rotor rotates counter^¬ clockwise, as shown in Fig. 10.

This arrangement allows to eliminate the outlet valve provided in the mono-vane embodiments, because the stages of inflow of the fluid into the cavity 25 and of outflow of the fluid from the cavity 25 take place in chambers that are separated by the additional vanes provided.

The multi-vane arrangement further provides the advantage of obtaining a more regular flow rate of the pump.

Obviously, the embodiments and the constructive particulars can be widely varied with respect to what has been described and illustrated merely by way of non-limiting example, without departing from the scope of the present invention as defined in the appended claims.

Claims

1. Fluid pump (10) comprising:

a hollow body (100) in which a stator (101) and an external rotor (106) of an electric motor are mounted, said external rotor (106) being rotatably mounted about a main axis (X-X) and having an internal cavity (25) connected to an inlet port (114) and an outlet port (115) arranged to allow the inflow of a fluid into said internal cavity (25) and the outflow of said fluid from said internal cavity (25) , respectively;

an internal rotor (111, 211) rotatably mounted in the internal cavity (25) so as to be free to rotate about a secondary axis (Y-Y) ;

a vane (109, 209a) having a first end and a second end, wherein said first end is provided at a pivot (108);

slidingly guided in a slot (110) formed in the internal rotor (111), said vane (109) having a pivot (108) at its first end;

said internal rotor (111, 211) and said vane (109, 209a) cooperating in such a way as to divide in a cyclic and fluid-tight manner said internal cavity (25) at least into a first chamber with variable volume and a second chamber with variable volume, said first and second chambers communicating with said inlet port (114) and said outlet port (115), respectively;

characterized in that

- said pivot (108) is oscillatably mounted in the external rotor (106) so that the external rotor (106), by rotating about its main axis (X-X) , entrains in its movement said pivot (108) of the vane (109, 209a) and the internal rotor (111, 211), which is brought into rotation by the vane (109, 209a) and rotates idly about its secondary axis (Y-Y) , and in that

- said vane (109, 209a) is slidably guided in a first slot (110, 210a) provided in the internal rotor (111, 211) and passing through the internal rotor in a through manner.

2. Fluid pump (10) according to claim 1, characterized in that the second end of said vane (109) terminates in a tip (123) which is guided in the body of the vane (109) and is axially slidable.

3. Fluid pump (10) according to claim 2, characterized in that said tip (123) slides axially pushed by an elastic element ( 124 ) .

4. Fluid pump (10) according to claim 1, characterized in that

the internal cavity (25) is defined by an internal surface having a first portion (106a) with substantially round section and a second portion (106b) with a section having a profile such that each point (P) of said second portion (106b) has the same distance from the center (C) of the pivot (108), and in that

the vane (109) has a distance (1) between the first and second ends such that the second end of the vane (109) is, when in use, in contact with the second portion (106b) of the internal surface of the external rotor (106) .

5. Fluid pump (10) according to claim 1, further comprising a second vane (209b) , a third vane (219a) and a fourth vane (219b) and wherein a second slot (210b) is provided in said internal rotor (211),

said second vane (209b) being slidably mounted in said first slot (210a) and said third vane (219a) and fourth vane (219b) being slidably mounted in said second slot (210b) , said internal rotor (211) and said vanes (209a, 209b, 219a, 219b) cooperating in such a way as to divide in a cyclic and fluid-tight manner said internal cavity (25) into said first chamber with variable volume and said second chamber with variable volume, which first and second chambers communicate with said inlet port (114) and said outlet port (115), respectively, and into two further chambers with variable volume .

6. Fluid pump (10) according to claim 5, wherein said first slot (210a) and said second slot (210b) are arranged perpendicularly to each other.

7. Fluid pump (10) according to any one of the claims 4 to 5, wherein the first slot (210a) comprises two walls (226, 227) arranged along its longitudinal edges at the second slot (210b) .

8. Fluid pump (10) according to any one of the preceding claims, characterized in that said electric motor is a DC motor of the type without brushes or brushless type.

9. Fluid pump (10) according to claim 8, characterized in that said external rotor (106) comprises a plurality of permanent magnets (107) located on its outer periphery.

10. Fluid pump (10) according to any one of the preceding claims, characterized in that said pump (10) is a vacuum pump .

11. Fluid pump (10) according to any one of the preceding claims, characterized in that a guide ring (105) adapted to guide the external rotor (106) is housed inside the stator (101) .

12. Fluid pump (10) according to any one of the preceding claims, characterized in that it further comprises a hole (118), which is formed in the hollow body (100), and lubrication channels, which suck from the inside of the heat engine the lubricating oil that, after having lubricated the pump and having become mixed with the sucked air, is adapted to form a mixture to be discharged into the engine through an outlet valve (117) .

13. Method of making a fluid pump (10) driven by an electric motor, said pump (10) comprising an external rotor (106) rotatably mounted about a main axis (X-X) of the electric motor; characterized by the steps of:

- rotatably mounting, in an internal cavity (25) of said external rotor (106), an internal rotor (111, 211) adapted to rotate about a secondary axis (Y-Y) different from said main axis (X-X) ;

- mounting a first vane (109, 209a) slidably guided in a first slot (110, 210a) which is provided in the internal rotor (111, 211) so as to pass through said internal rotor (111, 211) in a through manner;

attaching one end of said vane (109) to said external rotor (106) .

14. Method according to claim 13, further comprising the steps of:

- mounting a second vane (209b) slidably guided in said first slot (210a) ;

- mounting a third vane (219a) and a fourth vane (219b) in a second slot (210b) provided in the internal rotor (211) .