MOTORIZED LIQUID PUMP WITH IMPROVED HEATING

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the field of electric pumps intended to manage the flow of fluid. More particularly, it relates to motorized pumps which must operate at ambient temperatures which may fall below the melting point of the fluid to be pumped.

[0002] Preferably but not limitingly, the present invention relates more particularly to the field of urea-based pumps used in the context of selective catalytic reduction (SCR) and requiring operation at ambient temperatures below -20°C while the melting point of the mixture is of the order of -10°C to -15°C.

[0003] Selective catalytic reduction effectively reduces nitrogen oxide (NOx) emissions from motor vehicles using a redox mechanism that combines NOx with a urea or ammonia-based reducing agent to achieve decomposition that releases mainly nitrogen and water.

[0004] In order for this decomposition mechanism to be implemented as quickly as possible when the vehicle is started, even in cold ambient temperature conditions (typically below -15°C), it is necessary to be able to heat the reducing agent as quickly as possible, i.e. to bring it past its melting point, so that the fluid can be pumped from a reservoir and injected into the reduction chamber. STATE OF PRIOR ART

[0005] The possibility of heating the tank containing the reducing agent is already known. For example, document US9273584 proposes heating a urea tank using flexible resistive tracks which can, from a central position in the tank, be distributed throughout the tank to create a layer. Under the action of an electric current, by Joule effect, this layer will heat the urea and allow it to pass the melting point and promote faster pumping.

[0006] However, this type of device does not allow for rapid heating of the reducing mixture that is still in the pump body. If the reducing agent remains in a solid state in the pump body, even though it has become liquid in the tank, pumping cannot begin. The activation of the overall mechanism is therefore dependent on the heating of the reducing agent in the pump body.

[0007] An example of a typical motorized pump body for this application is presented in application US20130071268. This is a pump body performing pumping using a motorized gear reducer under the action of an electric motor, generally brushless. Since the urea mixture is very corrosive and can quickly degrade the physical properties of the motor, it is essential to isolate the pump body from the motor stator. This application presents, for example, the use of a wall or protective casing insulating the fluid from the wound stator of the motor.

[0008] From this document, it is possible to imagine heating the urea mixture using the heat dissipated by the Joule effect in the coils of the electric motor. However, the relatively large distance required between the stator and the pump body, due to the thickness of the container and the air gap between the wound teeth (or poles) of the stator, does not allow for rapid heating.

[0009] Another example of a motorized pump body is presented in patent EP2273121, similarly presenting a container or casing enclosing the gear pump on the one hand and also the magnetized rotor of an electric motor on the other hand. The rotor and pump body assembly is thus completely isolated from the stator of the electric motor.

[0010] The state-of-the-art documents cited above present the basic elements of SCR technology allowing satisfactory operation of the mechanism even when the ambient temperature is cold.

[0011] However, the problem of rapid heating of the reducing agent inside the pump body is not directly addressed, this heating being thus typically achieved by the joint action of the reservoir heating system as presented by patent US9273584 and by the low remote action of the wound stator.

[0012] Wealso knows from patent application GB2488210 a pump which comprises a suction inlet for sucking in a liquid and a discharge outlet for discharging the sucked liquid. The suction and discharge directions of the liquid are perpendicular. The pump comprises a shaft positioned downstream of the longitudinal suction inlet, a disc-shaped impeller which rotates about a rotation axis located in the shaft, and having a plurality of radial blades, causing the liquid to be sucked from the suction inlet and discharged. A bearing has a portion for guiding the sucked liquid from the suction inlet to the discharge outlet, and at least a portion of the bearing is formed of a material containing a magnetic material. A magnetized portion positioned in an upward direction of the bearing attracts, by magnetic force and in the upward direction, the bearing formed of a material containing a magnetic material.

[0013] Patent application JP2020106733 (EP2781758) describes another example of a pump secured to a reservoir by self-tapping screws in the stator legs. The pump and the molded stator can be securely fastened to each other, and the pump and the reservoir or the like can be securely fastened to each other.

[0014] Application WO2016 / 092035 electric actuator formed from a polyphase brushless motor comprising a rotor provided with permanent magnets and secured to an output shaft, and a stator carrying coils and ensuring the magnetic drive of the rotor, a first electrical connection assembly supplying the coils, said stator being integrated into a stator module formed from a material coating the wound stator as well as the first electrical connection assembly characterized in that the rotor is integrated into a rotor module constituted by a flange coating a guide element for the rotor shaft and in that the stator and rotor modules have indexing and fixing elements relative to each other. STATEMENT OF THE INVENTION

[0015] The present invention aims to overcome the disadvantages of the state of the art by allowing faster heating of the reducing agent or, more generally, of the solidified fluid inside the container inside which the pump mechanism is located. This is achieved by the clever production of an overmolding of the stator allowing more rapid diffusion of the heat produced by the coils of the stator of the electric motor towards the container enclosing the pumping elements and the rotor of the electric motor.

[0016] The container heating process consists of installing, for a time necessary for the liquefaction of the fluid to be pumped, a constant or variable current in the stator coils in order to promote the thermal diffusion of the power dissipated by the coils by Joule effect towards the container by means of the overmolding. The use of a container casing made of an electrically conductive and non-magnetic material (for example stainless steel) will allow, in the case of use of a variable heating current, to complete this heating by heating the casing thanks to the currents induced by inductive effect (eddy currents).

[0017] To do this, the present invention proposes to produce an overmolding of the stator having a conductivity higher than that of air, this overmolding advantageously making it possible to fill the space between the teeth of the stator to form a thermal diffusion body near or in contact with the container. This improved diffusion makes it possible to heat the fluid contained in the container more quickly. Surprisingly, gains in heating time of up to a factor of 2 have been observed when compared with a motor not having such overmolding.

[0018] More particularly, the invention refers to a motorized pump for pumping a fluid comprising an electric motor and consisting of a container and a stator assembly, said stator assembly having a set of ferromagnetic sheets forming teeth extending radially and defining inter-dental spaces and an interior volume, said teeth carrying, each or in part, electric coils, said container being housed in said interior volume, hermetically insulated from said stator assembly, and comprising a rotor formed of alternating magnetized poles, the container being formed of a casing enclosing said rotor, a pumping element actuated by said rotor, and channels for circulating said fluid allowing the circulation of said fluid to and from the pumping element,characterized in that the stator assembly has an overmolding in a plastic material having a thermal conduction coefficient greater than that of air, in that said overmolding encompasses the assembly of sheets and the electric coils and in that it fills the interdental spaces.,

[0019] In a first embodiment, the stator assembly is overmolded before the container is placed in place and said overmolding leaves the ends of the teeth of the stator assembly flush; but it may be envisaged that the stator assembly is overmolded before the container is placed in place and that the overmolding covers the ends of the teeth of the stator assembly. It may also be envisaged that the stator assembly is overmolded with the container in place so that the overmolding is in contact with said container.

[0020] Generally, the overmolding defines a cavity with a section complementary to the external section of said container.

[0021] When the container is placed after overmolding, the radial distance between the overmolded stator assembly and the container is less than 0.5 mm.

[0022] Preferably, the thermal conductivity of said plastic material is greater than 0.2 W / m / K.

[0023] Preferably again, the pumping element is a gear pump and the pump is a urea pump intended for a motor vehicle or a truck.

[0024] Generically, the overmolded stator comprises a set of conductive tracks supplying the electrical coils, said tracks exiting at one of their ends through a connector formed by said overmolding.

[0025] These tracks can be located behind the rotor or between the rotor and the inlets / outlets of the pumping element or the overmolded stator assembly has fixing ears and said tracks are positioned at the fixing ears.

[0026] The object of the invention is also to propose a method for mounting a motorized pump as defined above, characterized in that the container is positioned and held in place on the stator assembly thanks to the magnetic force exerted between the rotor and the stator assembly and in that the assembly formed by the container and the overmolded stator assembly is placed and fixed in a housing of the application without additional mounting part.

[0027] Another object of the invention is to propose a method of manufacturing a motorized pump characterized in that it comprises a step of inserting the container inside the interior volume defined by the teeth of the stator assembly and a step of injecting an overmolding resin having a thermal conduction coefficient greater than that of air. BRIEF DESCRIPTION OF THE FIGURES

[0028] Other characteristics and advantages of the invention will emerge from the following reading of detailed embodiment examples, with reference to the appended figures which represent respectively: there figure 1 , a general side view of an exemplary embodiment of a pump according to the invention, the figure 2 , an axial sectional view of an exemplary embodiment of a pump according to the invention, the figure 3, an axial sectional view of a particular embodiment of the stator assembly whose poles are flush with the overmolding, whose connector is arranged parallel to the axis of the stator assembly and whose electrical connection tracks are arranged on the side opposite the fixing points, the figure 4 , an axial sectional view of a particular embodiment of the stator assembly whose poles are flush with the overmolding, whose connector is arranged parallel to the axis of the stator assembly and whose electrical connection tracks are arranged on the same side as the fixing points, the Figure 5 , a view of the pumping mechanism and more precisely of the two gears from which it is formed, the figure 6 , a side view of the subassembly containing the pumping element, the Figures 7a and 7b , respectively an exploded view of the pump with its mounting bracket, and an assembled view of the pump on the mounting bracket, the figure 8, an alternative embodiment where the pump is secured to the stator assembly by overmolding, the figure 9 an axial sectional view of a particular embodiment of the stator assembly whose poles are covered by the overmolding, whose connector is arranged perpendicular to the axis of the stator assembly and whose electrical connection tracks are arranged on the side opposite the fixing points, the figure 10 a cross-sectional view of the figure 4 , THE Figures 11a and 11b respectively a perspective view of the stator assembly and a sectional view of a pump according to a particular embodiment using Hall probes used for commutation of the motor. DETAILED DESCRIPTION OF AN EMBODIMENT

[0029] THE Figures 1 and 2 represent an external view of the pump according to a first example embodiment.

[0030] The pump (1) consists, seen from the outside, of an electric motor formed by an overmolded stator assembly (2) inside which a container (20) is inserted. This container (20) comprises in particular a casing (21) surrounding a pumping element (3), a rotor (6) of the electric motor as well as channels (16, 17) for circulating the fluid to be pumped. The overmolded stator assembly (2) comprises fixing lugs (4) as well as an electrical connector (5). This connector (5) is here oriented perpendicular to the axis of the pump (1) but it is also possible to envisage an outlet of the connector in the direction parallel to the axis of the pump (1), as shown in figure 3 for example. The overmolded stator assembly (2) is formed by a pack of ferromagnetic sheets (14).

[0031] As shown in the figure 2, the overmolded stator assembly (2) also comprises connection tracks (9) also overmolded. The connection tracks (9) make it possible to electrically connect the coils (13) of the overmolded stator assembly (2) to the connector (5).

[0032] These connection tracks (9) can be located either on the side opposite the opening of the overmolded stator assembly (2), as shown in figure 3 , either on the same side as the opening of the stator assembly (2) overmolded as shown in figure 4 . On these Figures 3 and 4 , we see the interior volume (23) defined by the stator assembly (2) and in which the container (20) is housed.

[0033] There figure 10 is a sectional view of the figure 4where the interdental spaces (24) are pointed out. These are the volumes located between the teeth (19) of the overmolded stator assembly (2). The overmolding produced fills these interdental spaces (24). Here the ends of the teeth (19) are flush with the overmolding but it can be considered to completely cover the teeth (19) as illustrated in figure 9 .

[0034] In this first embodiment, the overmolding surrounding the ferromagnetic sheets (14) covers the outer surface but leaves the inner surface visible in order to promote heat exchange between the stator sheets (14) and the container (20). To this end, the overmolding fills the interdental space formed by the ferromagnetic sheets (14) to leave the ends of the teeth (19) flush. By the judicious choice of the overmolding material, the heat exchange between the overmolded stator assembly (2) and the container (20) will thus be promoted.

[0035] In figure 2, representing a sectional view of the pump (1), the components of the pump (1) can be seen, in particular the rotor (6) of the electric motor. This rotor (6) is guided by an axis (7) fixed in the upper element (8) of the pump (1) in which the inlet (16) and outlet (17) channels of the fluid are integrated, as visible in figure 1 . This same rotor (6) drives by mechanical contact the first gear (10) of the pumping element (3). The second gear (11) is driven by the first (10) and the two gears (10, 11) rotate in the central element (12) of the container (20) in which the pumping cavities (18) of the fluid are created, as visible in Figure 5 .

[0036] The assembly comprising the electric coils (13), the sheets (14) of the stator magnetic circuit, the electrical connection tracks (9) as well as the connectors form a single body: the overmolded stator assembly (2).

[0037] The container (20), of which an isolated view can be seen in figure 6 and a sectional view at the figure 2 , and comprising the rotor (6), formed by a permanent magnet, is an assembly independent of the overmolded stator assembly (2). It is assembled by simple insertion into the overmolded stator assembly (2). The attractive force between the stator laminations (14) and the rotor magnet (6) makes it possible to temporarily hold the container (20) in the overmolded stator assembly (2). The mechanical fixing of the container (20) is then carried out when the pump (1) is fixed to its support (15) making it possible to trap the container (20) between the overmolded stator assembly (2) and its support (15). The different subassemblies formed by the overmolded stator assembly (2), the container (20) and the support (15) are shown in exploded view and assembled respectively in Figures 7a and 7b .

[0038] In an alternative embodiment shown in figure 8, it is possible to envisage a connection of the container (20) to the overmolded stator assembly (2) directly by the overmolding. In this case, the overmolding operation is carried out after insertion of the container (20) into the stator. In this way, mechanical contact is achieved between the overmolding and the container (20), optimizing the heat exchange by conduction.

[0039] In another embodiment shown in figure 9 , it is possible to carry out a complete overmolding of the stator, not leaving the teeth (19) of the stator flush, that is to say completely covering these teeth (19), by forming a skin (22) on the inner surface of the latter, protecting the coils (13) and the sheets (14) of the stator. This alternative embodiment also makes it possible to promote an efficient heat exchange between the overmolded stator assembly (2) and the container (20).

[0040] The fact that the electric motor used consists of a rotor hermetically insulated from the stator is not in itself a problem for control when using a brushless motor. It is indeed well known to control this motor using so-called "sensorless" techniques, for example by measuring the voltage induced in the non-powered phases of the motor during operation.

[0041] However, if it is useful, for better control of the motor, to install magnetic field detection probes to enable the motor to be controlled, it is entirely possible to place, on the bottom of the stator assembly, a printed circuit (26) having at least one magnetosensitive probe (25) intended to detect the magnetic field of the rotor (6) to enable the electric motor to be controlled. This is illustrated in Figures 11a and 11b .

Claims

1. Motorized pump (1) suitable for pumping a fluid at ambient temperatures which may fall below the melting point of said fluid to be pumped, by heating the fluid, comprising an electric motor formed by a rotor (6) having alternating magnetized poles, which drives pumping elements (3, 10, 11), and by a stator assembly (2) having: - a set of ferromagnetic metal sheets (14) forming teeth (19) extending radially and defining inter-tooth spaces (24) and an interior volume (23), - said teeth (19) supporting, each or in part, electrical coils (13), characterized in that: - it comprises a container (20) formed by a shell (21) enclosing said rotor (6), pumping elements (3, 10, 11) actuated by said rotor (6), and circulation channels (16, 17) for said fluid allowing the circulation of said fluid to and from the pumping element (3), - said container (20) being housed in said interior volume (23) of said stator assembly (2), hermetically sealed from said stator assembly (2), - the stator assembly (2) having an overmolding made of a plastics material with a thermal conductivity coefficient greater than that of air, encompassing the set of metal sheets (14) and the electrical coils (13) and filling the inter-tooth spaces (24).

2. Motorized pump according to claim 1, characterized in that said overmolding of said stator assembly (2) leaves the ends of the teeth (19) of the stator assembly (2) flush.

3. Motorized pump according to claim 1, characterized in that said overmolding of said stator assembly (2) covers the ends of the teeth (19) of the stator assembly (2).

4. Motorized pump according to claim 1, characterized in that the stator assembly (2) and the container (20) are overmolded with the container (20) in place so that the overmolding is in contact with said container (20).

5. Motorized pump according to claim 1, characterized in that the overmolding defines a cavity having a cross-section complementary to the external cross-section of said container (20).

6. Motorized pump according to claims 1 or 2, characterized in that the radial distance between the overmolded stator assembly (2) and the container (20) is less than 0.5 mm.

7. Motorized pump according to claim 1, characterized in that the thermal conductivity of said plastics material is greater than 0.2 W / m / K.

8. Motorized pump according to claim 1, characterized in that the pumping element (3) is a gear pump.

9. Motorized pump according to claim 1, characterized in that the pump (1) is a urea pump for a motor vehicle.

10. Motorized pump according to claim 1, characterized in that the pump (1) is a urea pump for a truck.

11. Motorized pump according to claim 1, characterized in that the overmolded stator assembly (2) comprises a set of conductive connection tracks (9) supplying the electrical coils (13), said tracks (9) exiting at one of their ends via a connector (5) formed by said overmolding.

12. Motorized pump according to claim 11, characterized in that the conductive tracks (9) are positioned behind the rotor (6).

13. Motorized pump according to claim 11, characterized in that the conductive tracks (9) are positioned between the rotor (6) and the inlets / outlets (16, 17) of the pumping element (3).

14. Motorized pump according to claim 11, characterized in that the overmolded stator assembly (2) has fastening lugs (4) and in that said tracks (9) are positioned at the fastening lugs (4).

15. Motorized pump according to claim 1, characterized in that the shell (21) of the container (20) is made of an electrically conductive and non-magnetic material.

16. Motorized pump according to claim 1, characterized in that the bottom of the stator assembly accommodates a printed circuit (26) having at least one magneto-sensitive probe (25) designed to detect the magnetic field of the rotor (6) in order to allow the electric motor to be controlled.

17. Method for mounting a motorized pump as defined by claim 1, characterized in that the container (20) is positioned and held in place on the stator assembly (2) by the magnetic force exerted between the rotor (6) and the stator assembly (2) and in that the assembly formed by the container (20) and the overmolded stator assembly (2) is placed and fixed in a housing of the application without additional mounting parts.

18. Method for producing a motorized pump according to claim 1, characterized in that it comprises a step of inserting the container (20) inside the internal volume (23) defined by the teeth (19) of the stator assembly (2) and a step of injecting an overmolding resin having a thermal conductivity coefficient greater than that of air.

19. Method for heating a motorized pump according to claim 1, characterized in that an electric current is introduced into the coils (13) for a time required to liquefy the fluid to be pumped.

20. Method for heating a motorized pump according to claim 19, characterized in that the current is constant.

21. Method for heating a motorized pump according to claim 19, characterized in that the current is variable over time.