EP3583304B1

EP3583304B1 - Pump group comprising an electric drive and a mechanical drive with a clutch

Info

Publication number: EP3583304B1
Application number: EP18708747.3A
Authority: EP
Inventors: Alfonso SURACE; Marco Pedersoli
Original assignee: Industrie Saleri Italo SpA
Current assignee: Industrie Saleri Italo SpA
Priority date: 2017-02-16
Filing date: 2018-02-13
Publication date: 2020-11-04
Anticipated expiration: 2038-02-13
Also published as: CN110199095B; CN110199095A; EP3583304A1; HUE052244T2; IT201700017415A1; WO2018150322A1

Description

The present invention relates to a pump group for a cooling system of a vehicle, preferably for cooling an engine, for example an internal combustion engine. In particular, the present invention refers to a pump group having a dual drive, i.e. comprising both an electric drive and a mechanical drive.
As is known, during the normal use of an engine, the intensity of the cooling action should vary. For example, intense cooling is required when the engine is running at full speed or in towing conditions or on an uphill road or at high ambient temperatures. On the contrary, in other conditions of use, it is appropriate that the cooling is not accentuated, for example when the engine is being started or when it is being shut off.
In the state of the art, cooling pumps are known wherein such need has been met by providing a dual drive. In other words, cooling pumps are known wherein the rotational speed of the impeller comprised therein is regulated by specific command means comprising both an electric drive and a mechanical drive.
In such cooling pumps, the rotation speed of the impeller is rotated according to need, either by the mechanical drive, typically operatively connected to the engine of the vehicle, and therefore a function of the engine rpm, or by the electric drive, typically comprising an electric motor, the drive of which is controlled electrically.
Unfortunately, such pumps have a particularly complex management with the two drives, as well as an articulated and bulky structure. An example of said pumps is disclosed in document DE102011117374 .
The object of the present invention is to provide a pump group for a cooling system of a vehicle, for example for an internal combustion engine, of the dual-drive type, which has a simple management of the two drives, and also simplifies the structure and the geometry thereof.
This object is achieved by a pump group made according to claim 1. The claims dependent on this claim refer to preferred embodiments, having further advantageous aspects.
The object of the present invention is hereinafter described in detail, with the aid of the accompanying figures, wherein:

figure 1 shows a perspective view with separate parts of the pump group object of the present invention, according to a possible first embodiment;
figure 2 shows a perspective view with separate parts of a mechanical drive comprised in the pump unit of figure 1;
figure 3 shows a longitudinal sectional view of the pump group of figure 1;
figure 4 shows a perspective view with separate parts of the pump group object of the present invention, according to a possible second embodiment;
figure 5 shows a perspective view in separate parts of a mechanical drive comprised in the pump unit of figure 4;
figure 6 shows a longitudinal sectional view of the pump group of figure 4.

With reference to the aforementioned figures, a pump group for a cooling system of an engine, preferably an internal combustion engine, is indicated collectively at reference number 1. Said pump group 1 is of the dual or hybrid type, comprising, as described below, command means 4 comprising an electric drive 5 and a mechanical drive 6.
The pump group 1 object of the present invention further comprises an impeller 2, rotatable about an axis X-X in such a way that the rotation of the impeller 2 corresponds to the movement of a predetermined quantity of coolant in the circuit.
Preferably, the impeller 2 is of the radial type, i.e., it provides that the inlet flow of coolant has a substantially axial overall direction and the outlet flow of coolant has a radial direction.
The aforementioned command means 4 are operatively connected to the impeller 2 to command its rotation speed as needed. In other words, the impeller 2 is drivable both mechanically and electrically.
Preferably, the pump group 1 object of the present invention, in any of the embodiments thereof, has an electric drive 5 and a mechanical drive 6 provided with the specific characteristics described.
The electric drive 5 comprises an electric motor 50 and a first unidirectional clutch 58, such that the electric motor 50 is operatively connected to the impeller 2 via said first unidirectional clutch 58. Preferably, the electric motor 50 comprises a rotor 51 and a stator 52: the rotor 51 is moved in rotation by the electric excitation of the stator 52 and is mounted on said first unidirectional clutch 58 to transmit the rotary action to the impeller 2 therethrough.
On the other hand, the mechanical drive 6 comprises a centrifugal clutch 60, such that the mechanical drive 6 is operatively connected to the impeller 2 by means of said centrifugal clutch 60.
Specifically, the mechanical drive 6 is connectable to the engine of the vehicle, for example to the camshaft of the engine, by means of a kinematic chain preferably comprising a belt or a chain; e.g., in fact, the mechanical drive 6 comprises a pulley 66 operatively connectable with said kinematic chain and which is operatively connected to the impeller 2 by means of the centrifugal clutch 60.
Specifically, in accordance with a preferred embodiment, the centrifugal clutch 60 comprises, concentrically arranged, a clutch disc 61 controllable in rotation by the engine of the vehicle, for example by the rotation of the pulley 66, and a clutch drum 62 operatively connected to the impeller 2. Preferably, in some preferred embodiments, said clutch disc 61 and/or said clutch drum 62 extend in length for a short distance having a substantially annular shape. In further embodiments, said clutch disc 61 and/or said clutch drum 62 extend in length for a greater length having substantially the shape of a hollow shaft. The present invention is likewise not limited to particular embodiments or dimensions of the clutch disc 61 and/or of the clutch drum 62.
Preferably, the clutch disc 61 is integrally connected to the pulley 66 such that the rotation of the clutch disc 61 corresponds to the rotation by the pulley 66.
In a preferred embodiment, the clutch disc 61 and the pulley 66 are two distinct components, mutually joined by screws (as shown by way of example in the accompanying figures). In further embodiments, the clutch disc 61 is formable directly on the pulley 66, for example, the pulley 66 integrally comprises the clutch disc 61 (embodiment not shown in the accompanying figures). In still further embodiments, the clutch disc 61 has dimensions (particularly length) such as to house thereon special support elements (for example bearings) and the pulley itself is assembled directly thereon.
According to a preferred embodiment, moreover, the centrifugal clutch 60 comprises engagement means 65 suitable to associate and connect, on the action of the centrifugal force, the clutch disc 61 to the clutch drum 62.
In fact, the centrifugal clutch 60 has a resting configuration, wherein the mechanical drive 6 is operatively disengaged from the impeller 2, and an engagement configuration, wherein the mechanical drive 6 is operatively connected to the impeller 2.
In other words, the engagement means 65 are suitable to be arranged in a resting configuration, wherein the clutch disc 61 is disengaged from the clutch drum 62 and is free to rotate on the action of the pulley 66, and an engagement configuration, wherein the clutch disc 61 is, instead, engaged to the clutch drum 62, which is then pulled in rotation. Preferably, the passage between the two configurations is a function of the rotation speed of the clutch drum 61, and therefore of the engine of the vehicle, i.e. of the pulley 66.
In further other words, increasing the rotation speed increases the action of the centrifugal force endured by the engagement means 65; for example, at low speeds, the engagement means 65 are maintained in a resting configuration, at high speeds they pass into an engagement configuration, thus executing the engagement between the shafts. That is to say, the engagement means 65 permit an engagement between the clutch disc 61 and the clutch drum 62, being arranged in the aforesaid engagement configuration when the clutch disc 61 is driven in rotation at an rpm greater than a threshold value. Conversely, if the clutch disc 61 is driven in rotation at a speed lower than the aforesaid threshold value, the engagement means 65 remain arranged in the aforementioned resting configuration, while the clutch disc 61 and the clutch drum 62 remain disengaged from each other.
Said threshold value is variable depending on the specific application of the pump group 1: for example, depending on the type of vehicle, depending on the size of the vehicle, depending on the engine of the vehicle, depending on the expected mode of use of the vehicle.
By way of example, in the automotive sector, with an application of the pump group 1 object of the present invention on an average-size vehicle with an average-size engine, the threshold value is approximately 3000 rpm.
According to a preferred embodiment, the engagement means 65 comprise at least one engagement device 650 comprising a radial element 651 movable radially by the centrifugal force and suitable to connect operatively the clutch disc 61 and the clutch drum 62, and an elastic member 655 suitable to exert on the radial element 651 an action opposite to that of the centrifugal force.
Preferably, in fact, the radial element 651 comprises a disc portion 651' integrally connected to the clutch disc 61 and a drum portion 651" adapted to engage the clutch drum 62, preferably by friction. According to a preferred embodiment, the drum portion 651" is made of a material, or is coated with a material, with a high friction coefficient.
Preferably, the elastic member 655 is suitable to act in particular on said drum portion 651".
In other words, the threshold value is defined according to the features and the action executed by the elastic member 655: the threshold value corresponds to the number of revolutions per minute necessary to achieve an action of centrifugal force on the radial element 651 and in particular on the drum portion 651" thereof, such as to overcome the action of the elastic member 655.
Preferably, the radial element 651 has a first end connected to the clutch disc 61 or the pulley 66 and a second end connected to the drum portion 651".
Preferably, moreover, the radial element 651 is hinged to the clutch disc 61 with its disc portion 651', having the other end, its drum portion 651", free to move in the radial direction, exclusive of the action of the elastic member.
According to a preferred embodiment, the elastic member 655 is a tension spring. For example, in a preferred embodiment, the tension spring is a helical spring.
Preferably, primarily, the threshold value is directly a function of the physical characteristics of the elastic member 655. In addition, preferably, the threshold value is also directly a function of the physical characteristics of the radial element 651.
According to a preferred embodiment, the engagement means 65 comprise a plurality of engagement devices 650 arranged angularly equidistant from each other. For example, in the preferred embodiment, shown by way of example in the accompanying figures, the engagement means 65 comprise three engagement devices 650.
According to the object of the present invention, the command means 4 described above are suitable to command in rotation the impeller 2 according to the operating conditions and the needs of the vehicle, either with the electric drive 5 or with the mechanical drive 6.
Preferably, in fact, at low engine rotation speeds or in a configuration wherein the engine is switched off, the mechanical drive 6 has the centrifugal clutch 60 in the resting configuration; in such situations, therefore, the impeller 2 is drivable in rotation by means of the electric drive 5 as needed.
For example, when the vehicle is started, when the engine is still cold (so-called "warm-up" configuration), and therefore the driver of the vehicle is driving the vehicle at low engine speeds, the electric drive 5 is left deactivated. In this situation, therefore, the impeller 2 remains stationary, the liquid does not circulate in the circuit and the engine heats up faster.
Or again, in an opposite situation in which one finds oneself completing the use of the vehicle and the engine is very hot, the electric drive 5 is activated in such a way as to maintain the rotation of the impeller 2 and the coolant (such stage is therefore called "post run"). Thus, although the mechanical drive 6 is completely inactive as the engine of the vehicle is stationary, the impeller 2 rotates at a predetermined rotational speed resulting in a circulation of the coolant.
Other situations occur in the presence of high loads, for example when the vehicle tows a load or faces an uphill road, typically going at low speed (therefore, with low engine rpm); in such situations, the centrifugal clutch 60 is in a resting configuration and therefore cooling is fully managed by the electric drive 5.
On the other hand, at high engine revolutions (in which a greater cooling of the engine is therefore necessary), the mechanical drive 6 has the centrifugal clutch 60 in the engagement configuration; in such situations, therefore, the impeller 2 is drivable in rotation, preferably by the mechanical drive 6. In such situations, the first unidirectional clutch 58 is therefore suitable to release the electric motor 50 from the impeller 2; even if not required, it is preferably possible, in such situations, to even provide for the electrical deactivation of the electric motor 50.
In accordance with the present invention, several structural configurations of the pump group 1 having the above described operating features are foreseeable.
First, the pump group 1 comprises a pump body 100 suitable to rotationally support the electric drive 5, housing it inside a housing chamber 100' and suitable to support rotationally the mechanical drive 6, preferably cantilevered. In other words, the electric drive 5 is housed inside the pump body 100 while the mechanical drive 6 is for the most part placed externally thereto, as shown in the attached drawings.
Preferably, the pump body 100 comprises an impeller chamber 120 (shown only schematically in the accompanying figures) wherein the impeller 2 is housed and wherein, upon the action of the impeller 2, the coolant flows, entering through an inlet duct and exiting through an outlet duct.
Preferably, the housing chamber 100' and the rotating chamber 120 are respectively sealingly divided, comprising a dynamic seal 190 fitted on a subsequently described impeller shaft 3. In accordance with this embodiment, the housing chamber 100' is dry and the electric motor 50 has a dry-type rotor 51.
Preferably, the pump group 1 comprises an impeller shaft 3 extending along the axis X-X, such that the electric drive 5 and the mechanical drive 6 are operatively connected to said impeller shaft 3 to control the rotation speed thereof and therefore to control the rotation speed of the impeller 2.
According to a preferred embodiment, the impeller shaft 3 comprises an impeller end 32 to which the impeller 2 is integrally connected.
Moreover, the rotating shaft 3 comprises a command portion 34 on which the command means 4 act, being operatively connected respectively to the electric drive 5 and the mechanical drive 6.
In a preferred embodiment, the command portion 34 comprises a mechanical end 36 operatively connected to the mechanical drive 6; preferably, the mechanical end 36 is opposite the impeller end 32.
In addition, the command portion 34 comprises an electric zone 35 operatively connected to the electric drive 5. Preferably, in the embodiment wherein the mechanical end 36 is opposite the impeller end 32, the electric zone 35 is arranged between the two.
Preferably, the electric drive 5 and the mechanical drive 6 are on the same side with respect to the impeller 2, for example rearward thereto, as in the embodiments shown in the accompanying drawings. However, according to the same inventive concept, solutions of pump groups 1, not shown in the accompanying figures, are foreseeable wherein the electric drive 5 and the mechanical drive 6 are arranged in front of the impeller 2 or are arranged on opposite sides of the impeller 2.
According to a preferred embodiment, the aforesaid mechanical end 36 is engaged with the centrifugal clutch 60, in particular with the clutch drum 62. In other words, the centrifugal clutch 60 is operatively connected to the pulley 66, comprised in the mechanical drive 6, so that the pulley 66 and the clutch 60 are inserted on the impeller shaft 3. In other words, the pulley 66 and the clutch 60 are penetrated by the impeller shaft 3. Preferably, the induced rotation of the clutch drum 62 corresponds to a rotation of the impeller shaft 3. Preferably, in such embodiment, the engagement of the centrifugal clutch 60 is directed onto the impeller shaft 3: a rotation of the impeller shaft 3 corresponds to the rotation of the centrifugal clutch 60 in the engagement configuration.
In accordance with such preferred embodiment, the electric drive 4 and the mechanical drive 5 are rotationally supported by the impeller shaft 3. Preferably, the pump body 100 comprises a first bearing 161 and a second bearing 162, housed inside the housing chamber 100', suitable to rotationally support the impeller shaft 3. Preferably, in this embodiment, the first bearing 161 is of the sliding type, e.g., a bushing.
Preferably, in the aforesaid embodiment, it is foreseeable that the activation of the electric drive 5 is managed in such a way as to deactivate it over certain rpms, and therefore it is not in constant rotation when the mechanical drive 6 moves the impeller shaft 3 in rotation.
By way of example, this embodiment is shown in figures 1 to 3.
In an alternative embodiment, on the other hand, the mechanical end 36 is engaged with the centrifugal clutch 60, in particular, with the clutch drum 62, by means of a second unidirectional clutch 68.
Preferably, in fact, the mechanical drive 6 comprises a mechanical shaft 600 which extends in length, preferably along the axis X-X, which rotationally supports the mechanical drive 6. In other words, the centrifugal clutch 60 is operatively connected to the pulley 66, comprised in the mechanical drive 6, so that the pulley 66 and the clutch 60 are fitted on the mechanical shaft 600. In other words, the pulley 66 and the clutch 60 are penetrated by the mechanical shaft. Preferably, a rotation of the mechanical shaft 600 corresponds to the induced rotation of the clutch drum 62 and through the second unidirectional clutch 68 eventually correspond to a rotation of the impeller shaft 3.
Preferably, in such embodiment, the engagement of the centrifugal clutch 60 is indirect on the impeller shaft 3: rotating the centrifugal clutch 60 in an engagement configuration corresponds to a rotation of the mechanical shaft 600 and only possibly through the second unidirectional clutch 68 is the impeller shaft 3 commanded in rotation. In this embodiment, in fact, because the mechanical drive 5 commands the impeller shaft 3 in rotation, the rotation speed of the mechanical shaft 600 must be greater than the rotation speed of the electric drive 4.
Due to the presence of the two unidirectional clutches, only the drive which controls the higher rotational speed is operatively connected to the rotating shaft 3 to command it in rotation. Preferably, therefore, in such embodiment, the rotation of the impeller shaft 3 does not influence the rotation of the slower unidirectional clutch, i.e. the unidirectional clutch which is not transmitting the rotary motion to the shaft.
Preferably, also in the aforesaid embodiment, it is foreseeable that the activation of the electric drive 5 is managed in such a way as to deactivate it over certain rpms, and therefore it is not in constant rotation when the mechanical drive 6 is moving the impeller shaft 3 in rotation, but, additionally, it is also foreseeable that the electric drive 5 is activated whenever it is necessary to increase the cooling capacity, independently of the mechanical drive 6, bound to the engine speed.
Preferably, furthermore, in the aforesaid embodiment, the pump body 100 comprises a first bearing 161 and a second bearing 162, housed inside the housing chamber 100', suitable to rotationally support the impeller shaft 3, wherein the second bearing 162 is suitable to support rotationally the mechanical shaft 600. In other words, the second bearing 162 is suitable to absorb the actions due to the mechanical drive 6 to discharge them onto the pump body 100.
Preferably, in this embodiment, both the first bearing 161 and the second bearing 162 are of the rolling type.
By way of example, such further embodiment is the one shown in figures 4 to 6.
In other words, as evident in the accompanying figures, the mechanical drive 6 is mounted cantilevered on the pump body 100, having, in the first embodiment, the mechanical end 36 of the impeller shaft 3 outside the chamber housing 100', while in the second embodiment having a portion of the mechanical shaft 600, outside of the housing chamber 100'.
According to the present invention, the first unidirectional clutch 58 comprises a rolling bearing preferably of the needle type. For example, the rolling bearing is of the roller or needle type, having rolling elements located between the driven ring and the driving ring. Preferably, the first unidirectional clutch 68 is integrally connected to the rotor 51 of the electric motor 50.
According to the present invention, moreover, the second unidirectional clutch 52 comprises a rolling bearing preferably of the needle type. For example, the rolling bearing is of the roller or needle type, having rolling elements located between the driven ring and the driving ring. Preferably, the second unidirectional clutch 68 is integral with, or an integral part of, the mechanical shaft 600.
In accordance with the foregoing, in a preferred embodiment, the pump group 1 comprises an electronic control unit for controlling the electric drive 5. In a further preferred embodiment, the pump group 1 is connectable to a control unit of the vehicle on which it is mounted.
Innovatively, the pump group object of the present invention satisfies the engine cooling requirements and overcomes the drawbacks mentioned above.
Advantageously, the pump group according to the invention is very flexible, since it responds to the cooling needs of the vehicle according to the actual demand and not according to the engine speed or the availability of electrical power of the system. That is to say that, advantageously, the pump group is particularly suitable to manage in its entirety the quantity of coolant in the cooling system, for example managing the cooling of further components of the vehicle in addition to the engine, such as the turbo group, remedying the need to have specific electric pumps that move the predefined quantity of coolant in these components, allowing more space to be gained in the engine compartment.
Moreover, advantageously, the pump group is particularly compact and of compact size, being particularly suitable to be housed in the engine compartment of a motor vehicle.
For example, advantageously, the impeller (and the impeller chamber with the volute) is more compact and not oversized and operates always in conditions of optimum efficiency with respect to the known pump groups, where the impeller is often oversized to compensate for the poor flexibility of mechanical pumps and the limited power of electric pumps.
Another advantageous aspect is that the pump unit requires a limited number of dynamic seals: specifically, only one dynamic seal is required, which is necessary to divide only the impeller chamber from the housing chamber. Advantageously, the electric motor of the pump group object of the present invention is foreseeably of the dry rotor type, provided with a reduced air gap suitable to achieve a high electrical efficiency (with respect to electric motors with wet rotors). Advantageously, therefore, the electric motor has no friction due to the presence of coolant and therefore its operation is not affected by the hydrodynamic braking effect of the coolant.
Advantageously, the dynamic seal comprised in the pump body has compact dimensions as it must confront low intensity action due to friction.
Advantageously, the presence of the centrifugal clutch allows a further simplified management of the mechanical drive.
Advantageously, the presence of both the first unidirectional clutch and the centrifugal clutch guarantees an even more simplified management of the two drives on the impeller. In fact, advantageously, the transition from the electric drive to the mechanical drive and vice versa is mechanically managed by the synergic presence of the centrifugal clutch and the first unidirectional clutch. Therefore, advantageously, the electronic management of the pump group is very simple. In still other words, advantageously, in the pump group of the present invention, it is not necessary to have an electrical synchronization of the activation of the two drives, as, for example, is necessary in some dual drive pumps comprising an electromagnetic pulley in the mechanical drive: the electric drive alone must be managed electrically only in rotation speeds lower than those ensured by the mechanical drive following activation of the centrifugal clutch.
Advantageously, the pump group is able to avoid the action of cooling, even if the engine is running, when, for example in "warm-up" conditions, it is appropriate to heat the engine. In a further advantageous aspect, the pump group has the "fail-safe" feature; in fact, in the event of an electric drive failure, the pump group, due to the mechanical drive and the first unidirectional clutch, continues to ensure the movement of the impeller. According to a further advantageous aspect, the pump group is operative in "post-run" conditions, i.e. with the engine turned off.
Moreover, the kinematic chain between mechanical drive, electric drive and impeller is extremely simplified.
Advantageously, the presence of the centrifugal clutch (and even more in the configuration of the pump group with also the second unidirectional clutch) allows, in a configuration wherein the impeller is rotated by the electric drive, the friction due to the mechanical part to be reduced to zero, there is therefore no energy absorption, for example, of the pulley and/or any provided bearings. Likewise, advantageously, the first unidirectional clutch allows, in a configuration wherein the impeller is rotated by the mechanical drive, that the rotor is not driven in rotation by the shaft; therefore, magnetic friction is not produced (nor does the rotor-stator assembly work as an electric generator).
A further advantageous aspect lies in the fact that, in the configuration wherein it is envisaged, the mechanical shaft is supported by the pump body in such a way that all the loads, for example due to elevated belt loads associated with the belt action or the tension of the belt, are absorbed by the pump body and do not discharge onto the impeller shaft. Advantageously, the designer is free to design the impeller shaft in the dimensions, measurements and diameters as required depending on the loads it must support for the most part associated with the action of the impeller and not the mechanical drive. Advantageously, therefore, the impeller shaft is designable with compact size, length and diameter; similarly, therefore, also the bearings that support it and the dynamic seal fitted thereon are designed with compact dimensions. The presence of bearings and of compact (and not oversized) dimensions therefore involves achieving better energy efficiency of the pump group with respect to the solutions currently known in the state of the art.
Advantageously, the dual pump group is suitable to operate in the described operating situations in the most effective manner possible, solving the need for an electromagnetically controllable pulley. The mechanical drive of the dual pump object of the present invention is therefore of a more compact size, lower weight, and does not require electrical energy to operate.
Advantageously, the pump group is efficient, controllable and flexible, and for most of the life of the vehicle presents a mechanical operation only when the cooling (and therefore hydraulic power) demand is greater than that which may be electrically managed by the electric drive.
Advantageously, the pump group is particularly advantageous also in the situations of starting the engine, and of "Start & Stop", which typically involves a heavy load on the components dedicated to starting (for example on the starter motor) which undergo accelerated wear; in fact, due to the presence of the centrifugal clutch, in such situations, the pump group does not contribute to generating unfavorable loads on said members dedicated to starting.
It is clear that one skilled in the art, in order to meet contingent needs, may make changes to the pump group, all contained within the scope of protection defined by the following claims. Furthermore, each variant described as belonging to a possible embodiment may be achieved independently of the other variants described.

Claims

Pump group (1) for a cooling system of an engine of a vehicle, comprising:
- an impeller (2) rotatable around an axis (X-X);

- command means (4) operatively connected to the impeller (2) to command its rotation speed, comprising:
i) an electric drive (5) comprising an electric motor (50) and a first unidirectional clutch (58), wherein the electric motor (50) is operatively connected to the impeller (2) via the unidirectional clutch (58);

ii) a mechanical drive (6) comprising a centrifugal clutch (60), wherein the mechanical drive is operatively connected to the impeller (2) via the centrifugal clutch (60) .
Pump group (1) according to claim 1, wherein the centrifugal clutch (60) comprises, concentrically arranged, a clutch disc (61) operated in rotation by the engine of the vehicle and a clutch drum (62) operatively connected to the impeller (2), and comprises engagement means (65) suitable to connect upon action of the centrifugal force, the clutch drum (61) and clutch disc (62) .
Pump group (1) according to claim 2, wherein the engagement means (65) comprise at least one engagement device (650) comprising:
i) a radial element (651) movable radially by the centrifugal force comprising a disc portion (651') integrally connected to the clutch disc (61), a drum portion (651") suitable to engage the clutch drum (62), preferably by friction;

ii) an elastic member (655) suitable for exerting on the radial element (651), in particular on the drum portion (651"), an action opposite to that of the centrifugal force.
Pump group (1) according to claim 3, wherein the engagement means (65) comprise a plurality of engagement devices (650) angularly equidistant to each other.
Pump group (1) according to any of the claims from 2 to 4, wherein the engagement means (65) allow an engagement between the clutch disc (61) and the impeller shaft (62) when the clutch disc (61) is commanded in rotation at a speed higher than a predetermined threshold value, preferably roughly 3000 rpm.
Pump group (1) according to any of the preceding claims, further comprising an impeller shaft (3) which extends along the axis (X-X), comprising an impeller end (32) to which the impeller (2) is integrally constrained, and a command portion (34) operatively connected to the electric drive (5) and the mechanical drive (6).
Pump group (1) according to claim 6, wherein the command portion (34) comprises a mechanical end (36) operatively connected to the mechanical drive (6) and an electric zone (35) operatively connected to the electric drive (5), wherein the mechanical end (36) is opposite the impeller end (32) and the electric zone (35) is placed between the two.
Pump group (1) according to claim 7, wherein the mechanical end (36) is engaged with the centrifugal clutch (60), in particular, with the clutch drum (62).
Pump group (1) according to claim 8, wherein the electric drive (4) and the mechanical drive (5) are rotationally supported by the impeller shaft (3).
Pump group (1) according to claim 7, wherein the mechanical end (36) is operatively connected to the centrifugal clutch (60), in particular to the clutch drum (62), via a second unidirectional clutch (68).
Pump group (1) according to claim 10, wherein the mechanical drive (6) comprises a mechanical shaft (600) which extends in length, preferably along the axis (X-X), which rotationally supports the mechanical drive (6), wherein the centrifugal clutch (60) is fitted on said mechanical shaft (600).
Pump group (1) according to any of the claims from 6 to 11, further comprising a pump body (100) suitable to rotationally support the electric drive (5), housing it inside a housing chamber (100') and to rotationally support the mechanical drive (6) cantilevered.
Pump group (1) according to claim 12, wherein the housing chamber (100) is sealed tight by means of a dynamic seal (190) fitted on the impeller shaft (3).
Pump group (1) according to any of the preceding claims, wherein the electric motor (50) comprises a rotor (51) and a stator (52), wherein said rotor (51) is of the dry type.
Pump group (1) according to claims from 12 to 14, wherein the pump body (100) comprises a first bearing (161) and a second bearing (162), housed inside the housing chamber (100'), suitable to rotationally support the impeller shaft (3).
Pump group (1) according to claims from 12 to 14, in conjunction with claims 10 and 11, wherein the pump body (100) comprises a first bearing (161) and a second bearing (162), housed inside the housing chamber (100'), suitable to rotationally support the impeller shaft (3), wherein the second bearing (162) is suitable to rotationally support the mechanical drive (600).