Motor

Abstract

The invention relates to an electric machine (1), comprising: a plurality of conductive tracks (20) defining a power circuit (10a) configured to provide a supply current to a plurality of electronic power components (12); a printed circuit board (11) on which the conductive tracks are mounted; a housing (4) defining a receiving portion for the printed circuit board and having a heat dissipation wall (4a); a heat conductive filler (8) interposed between the printed circuit board and the housing; an elastic device (30) acting on the printed circuit board to press it against the heat dissipation wall; a conductive element (25) held in place by at least one thermal joint (26) and arranged to connect a first track (21) and a second track (22) to close the power circuit (10a), the elastic device (30) comprising an elastic element (31) pressed against the conductive element (25) to exert a force on the thermal joint, and the thermal joint being configured to break when subjected to a temperature above a predetermined threshold temperature to disconnect the power circuit.

Description

Technical Field

[0001] The present invention relates to an electric motor, and more particularly to a system for protecting the electric motor from high internal temperature and a method for manufacturing the electric motor. Background Art

[0002] Typically, the electric machine comprises a housing having inside it a stator rigidly connected to the housing and a rotor rotatably connected to the housing, the rotor for example having permanent magnets, the electric machine being for example a brushless electric motor, to which reference will be made explicitly hereinafter without limiting the scope of the invention.

[0003] An example of a prior art electric machine, which is used as a reference for this patent, is described in application WO2013008180 in the name of the present applicant.

[0004] The electronic module connected to the stator of the brushless electric motor comprises a printed circuit board and on the printed circuit board itself are arranged a plurality of active and passive electronic components defining the power section and a plurality of electronic signal components defining the control section.

[0005] Some of these electronic components are surface mount devices (SMDs), such as power MOSFETs, which have the advantage of being able to be attached to printed circuit boards in bulk using a furnace soldering process.

[0006] The housing is closed by a cover to form a sealed container, from which connection pins protrude to allow power and control of the electronic drive circuit. In a sealed motor, the cover is closed in an airtight manner to isolate the electronic components and moving parts from moisture, dust and atmospheric agents.

[0007] This type of motor is used in particular in the automotive industry and other industries subject to constantly changing and stringent safety regulations. In particular, overheating of these motors poses a real risk if they are installed near internal combustion engines or other heat sources.

[0008] Possible effects of overheating may include failure of the motor itself, interference with or damage to the power supply system associated therewith and possible adverse consequences for other equipment connected thereto, and in the worst case may include fire and explosion.

[0009] To prevent overheating and reduce its adverse effects, several solutions have been devised and implemented. Most of these solutions are based on the development and improvement of convective heat dissipation within the machine. Patent document WO2014125412, filed in the name of the present applicant, describes a solution designed to dissipate heat generated by the electronic components of a generator.

[0010] Unfortunately, these solutions are ineffective if the temperature of the environment in which the motor is operating, with which it is designed to exchange heat for heat removal, unexpectedly rises. Such a temperature rise may be caused, for example, by a failure of the cooling system external to the motor.

[0011] The above solutions may also be ineffective in the case of faults and unexpected events related to the motor that may cause an unexpected increase in temperature.

[0012] Demands from the market as well as regulatory and certification bodies for increasingly safer motors have created a need for intrinsic safety mechanisms that cut power to the machine in the event of overheating before temperatures can reach dangerous levels.

[0013] One possible solution known in the prior art consists in installing conventional thermal fuses along the power circuit of the electronic power components inside the motor so as to cut off the power supply in order to stop the motor in the event of overheating. However, this solution has several disadvantages.

[0014] Known thermal fuses consist of a fusible disc that depresses a preloaded conductive spring. When the temperature rises, the disc melts and releases the spring, breaking the circuit. Unfortunately, the structure of known thermal fuses precludes furnace soldering with other electronic components because the heat from the furnace would trigger the thermal fuse. Therefore, the thermal fuse must be installed after the printed circuit board has passed through the furnace, and it must be attached using a specialized, localized process, which increases motor assembly time and cost.

[0015] Another disadvantage of known thermal fuses is that, due to the flux they contain, they tend to gradually degrade when subjected to sustained high temperatures, even below their rated triggering temperature. This makes them unsuitable for use in high-temperature environments, such as those typical in automotive applications, typically the engine compartment of a vehicle.

[0016] Other disadvantages of known thermal fuses are: their relatively high unit cost; the technical limitations to which they are subject, which limit their operating currents and temperatures and which generally conflict with the specific market requirements of the type of motor in question; and the impossibility of integrating them with other machine components and systems to make them more efficient in terms of cost, weight and overall functionality.

[0017] In this context, the technical purpose underlying the present invention is to propose an electric machine and a method for manufacturing the same in order to overcome the above-mentioned drawbacks of the prior art. Summary of the Invention

[0018] The object of the present invention is to provide an electric machine equipped with a high temperature protection system and a method for manufacturing such an electric machine which are more efficient in terms of production costs and components.

[0019] Another object of the present invention is to provide a motor equipped with a high temperature protection system and a method of manufacturing such a motor, wherein the high temperature protection system can withstand long-term use at high temperatures close to a threshold temperature at which protection is triggered.

[0020] It is a further object of the present invention to provide an electric machine which may support a wider range of operating currents and temperatures than allowed by prior art devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features and advantages of the present disclosure will become more apparent from the following non-limiting description with reference to a preferred but non-exclusive embodiment of an electric machine shown in the accompanying drawings, in which:

[0022] - Figure 1 is an exploded perspective view of a motor according to the present invention, with some components removed for simplicity;

[0023] - Figure 2 yes Figure 1 A top view of the motor's electronic module, with some components removed for simplicity.

[0024] - Figure 3 yes Figure 2 A top view of a detailed electronic module;

[0025] - Figure 4 yes Figure 2 A perspective view of details of the electronic module;

[0026] - Figure 5 Shown Figure 1 Cross section of the motor;

[0027] - Figure 6 yes Figure 2 A top view of a detail of an electronic module, with some parts removed to better show other parts and certain items shown as hidden parts. DETAILED DESCRIPTION

[0028] Reference numeral 1 generally designates an electric machine according to the invention, which will be described in detail hereinafter only to the extent necessary for understanding the present disclosure.

[0029] The electric machine 1 is preferably a rotary electric machine and, in its preferred embodiment, is an electric motor of the sealed type, that is to say it has no openings to its interior, except for a possible pressure relief valve, which is in any case sealed. Explicit reference is made to this embodiment, without thereby losing generality.

[0030] In the embodiment shown, the electric machine 1 comprises a housing 2 and a cover 3 closing the housing 2 so as to define together with the housing 2 a housing 4 or container which is closed and preferably sealed.

[0031] The cover 3 has a heat dissipation wall 4 a configured to promote heat dissipation from components inside the housing 4 , and is preferably provided with a plurality of heat dissipation fins provided at the heat dissipation wall 4 a and facing outside the housing 4 .

[0032] Preferably, the electric machine 1 comprises a stator 5 fixedly mounted in the housing 2 and a rotor 6 associated with the stator 5 and rotatably connected to the casing 4 about an axis of rotation “R”.

[0033] Schematically, the stator 5 includes: a ferromagnetic core 5a; a plurality of conductive windings 5b wound around the ferromagnetic core; and a separator between the ferromagnetic core and the windings.

[0034] At least the ferromagnetic core 5a and the spacers define a stator mounting for the electrically conductive windings 5b.

[0035] In general, the term "stator mounting portion" as used in this disclosure refers to a collection of components of the electric machine 1 that maintain the windings 5b in proper shape and position, prevent them from accidental movement, and promote heat dissipation.

[0036] The spacers in the stator 5 (often called "front sheets") are insulating material, preferably made of a polymeric material.

[0037] The first front piece 40 of the stator front pieces is provided with a plurality of holes 40a extending parallel to the rotation axis "R".

[0038] The hole 40 a allows the stator 5 to be keyed into the housing 2 using a machine that uses a plurality of jaws that press directly onto the ferromagnetic core through the hole 40 a , thereby preventing damage to the front sheet 40 .

[0039] The motor 1 further includes power pins 7 a and 7 b , which, in the illustrated embodiment, pass through the housing 4 and are configured to be electrically connected to a DC power source external to the motor 1 .

[0040] The electric machine 1 comprises an electronic module 10 , which in turn comprises a printed circuit board 11 or PCB and a plurality of electronic power components 12 .

[0041] In a preferred embodiment, the electronic power components 12 include a plurality of power transistors (eg, MOSFETs 12 a ) electrically connected to the windings 5 ​​b to regulate their voltage and current, thereby driving and controlling the rotation of the rotor 6 .

[0042] Preferably, the electronic module 10 , in particular the printed circuit board 11 , is mounted on a support element 13 which is arranged on the underside of the printed circuit board 11 .

[0043] The support element 13 is interposed between the electronic module and the stator 5 and the rotor 6. The support element 13 is preferably made of a self-extinguishing, electrically insulating plastic and has a receptacle for the electronic module 10.

[0044] The support element 13 has side surfaces that are shaped to match the housing 2 or the cover 3 so as to reduce in practice the likelihood of movement of the electronic module 10 within the casing 4 .

[0045] The electronic module 10 includes a plurality of conductive tracks 20 arranged between the power pins 7a and 7b on the printed circuit board 11 and the electronic power component 12 to form a power supply circuit 10a for supplying power to the electronic power component 12. The conductive tracks 20 preferably protrude from the printed circuit board 11. In the embodiment shown, the conductive tracks 20 protrude from the printed circuit board 11 by 1.8 mm.

[0046] Conductive tracks 20 are positioned facing heat sink wall 4 a and are preferably made of a copper alloy, which is a good conductor of electricity and heat. Furthermore, conductive tracks 20 are dimensioned to define heat pipes between electronic power components 12 and heat sink wall 4 a. In particular, the thermal dimensioning of conductive tracks 20 involves oversizing them for electrical conductivity without undesirable effects and minimizing electrical resistance.

[0047] A thermally conductive filler 8 (eg, comprising thermally conductive paste) is placed between the conductive track 20 and the heat dissipation wall 4a to fill the gap between the two components and promote heat conduction therebetween. Figure 2 、 Figure 3 and Figure 6 As shown, the thermally conductive filler 8b is indicated by cross-hatching.

[0048] A heat-conducting filler 8 is also placed between at least some of the electronic power components 12 and the heat dissipation wall 4 a to promote direct dissipation of the heat generated by them.

[0049] The conductive track 20 has surfaces for contacting the MOSFET 12a and the heat sink 4a (via the thermally conductive filler 8), the dimensions of which are designed to form a preferential path for dissipating the heat generated by the MOSFET 12a in combination with the dimensions of the conductive track 20 itself.

[0050] This path is preferably configured to keep the temperature of MOSFET 12a below 160°C, preferably at 150°C, when motor 1 operates in an atmosphere of 120°C, such as an engine room of a vehicle.

[0051] The electric machine 1 comprises a plurality of elastic means 30 acting on the electronic module 10 to press the electronic module 10 against the cover 3 .

[0052] In the example shown, the elastic device 30 includes a metal spring 30 a , which may be replaced by, for example, an elastomer.

[0053] The at least partially compressed thermally conductive filler 8 promotes heat conduction at least between the conductive tracks 20 and the heat dissipation wall 4a and between the electronic components and the heat dissipation wall 4a, thereby allowing the heat generated by the motor 1 to be regularly dissipated over time.

[0054] In a preferred embodiment, at least some of the springs 30a are inserted into the holes 40a of the front plate 40, and one end of the springs rests on the ferromagnetic core and the other end rests on the support element 13 to press the entire module 10 toward the heat sink 4a and away from the stator 5. In this way, the conductive rails 20 and the thermally conductive filler 8 thereon are particularly pressed against the heat sink 4a.

[0055] The plurality of conductive tracks 20 preferably comprises a first conductive track 21 and a second conductive track 22 which form an integral component of the power supply circuit 10 a such that the supply current of the electronic power component 12 flows through them.

[0056] In the embodiment shown by way of example, the first rail 21 and the second rail 22 are provided on top of the printed circuit board 11, near the power pins 7a and 7b, preferably protruding therefrom. More specifically, the first rail 21 includes one of the power pins 7a and 7b, while the second rail 22 is connected to the rest of the electronic module 10.

[0057] The electronic module 10 comprises a conductive element 25 , such as a metal plate or a bridge, electrically connected to the first rail 21 and the second rail 22 to close the power supply circuit 10 a .

[0058] In the example shown, the conductive element 25 allows current flow between the power pins 7 a and 7 b to power the plurality of electronic power components 12 and drive the rotor 6 to rotate.

[0059] The thickness of the conductive element 25 is preferably greater than or equal to 1.8 mm; that is, the same size as the track so as not to form a resistance element that significantly affects the power supply circuit 10a.

[0060] The conductive element 25 is fixed to the first and second rails 21 , 22 by respective thermal joints 26 which, in the embodiment shown, are welds comprising a brazing alloy, preferably an alloy of tin and silver.

[0061] In a preferred embodiment, the conductive element 25 is arranged to partially overlap the first track 21 and the second track 22 to form a bridge therebetween.

[0062] Advantageously, the elastic means 30 comprise an elastic element 31 acting on the conductive element 25 to exert thereon a thrust away from the first and second conductive tracks 21 , 22 , the elastic element 31 preferably being a metal spring, to which reference is made explicitly without loss of generality.

[0063] The thrust is transmitted to the electronic module 10 through the thermal connector 26 to help push the electronic module 10 toward the heat dissipation wall 4 a.

[0064] Preferably, the first end of the elastic element 31 is arranged to abut against the ferromagnetic core 5 a of the stator 5 .

[0065] The elastic element 31 passes through a hole 40a with a specific cup-shaped receiving portion in the front plate to directly abut against the ferromagnetic core 5a.

[0066] On the other hand, the second end of the spring 31 is operatively arranged to abut against the conductive element 25 .

[0067] Indeed, in the embodiment shown by way of example, the spring 31 has a line of action which is parallel to the axis of rotation of the electric motor 1 .

[0068] A cover or spacer 32 made of an electrically insulating material is provided between the end of the spring 31 and the conductive element 25 to prevent a short circuit between the spring and the ferromagnetic core 5a.

[0069] Advantageously, the thrust exerted by the elastic element 31 on the conductive element 25 generates a strain in the thermosensitive joint 26, which is configured to mechanically resist the strain when its temperature is below a predetermined threshold temperature, in particular the temperature at which the brazing alloy melts, preferably between 180°C and 250°C, more preferably between 200°C and 230°C.

[0070] If the temperature of the thermally sensitive joint 26 is greater than a predetermined threshold temperature, for example due to melting of the brazing alloy, the joint mechanically yields to the strain and breaks, causing the conductive element 25 to move away from the first conductive track 21 and / or the second conductive track 22 to break the electrical connection therebetween.

[0071] This event disconnects the power supply circuit of the power circuit 10a and instantly cuts off the power supply to the electronic power components 12, thereby stopping the motor 1. Advantageously, these features constitute a high-temperature protection for the motor 1.

[0072] Preferably, the conductive element 25 is configured to allow a current greater than 80 amperes, and preferably greater than 100 amperes, to pass between the first rail 21 and the second rail 22. More specifically, the dimensions of the interface surfaces between the conductive element 25 and the first rail 21 and the second rail 22 are designed to allow such a current to pass without causing damage to the thermal joint 26 or creating a resistance at the end of the conductive element 25 that is approximately comparable to the resistance of the heat dissipating components of the motor 1.

[0073] In an alternative embodiment not shown, the conductive element 25 is fixed to only one of the first rail 21 and the second rail 22 via the thermal joint 26 and is permanently electrically connected to the other rail, so that when the temperature rises above a threshold temperature, only the thermal joint 26 breaks under the pressure of the elastic element 31, thereby causing the power supply circuit 10a to be disconnected.

[0074] The printed circuit board 11 and the support element 13 are shaped so as to allow the spring 31 to be positioned between the ferromagnetic core 5 a and the conductive element 25 .

[0075] Preferably, the printed circuit board 11 has a recess, ie, missing material, at the spring 31 .

[0076] In the embodiment shown, the material absence or recess of the printed circuit board 11 is defined by a portion formed on its outer periphery delimited by the concave end edge 14 .

[0077] Preferably, the support member 13 has a through hole 13 a below and substantially at the concave portion.

[0078] Preferably, the first track 21 and the second track 22 have a first end portion 21 a and a second end portion 22 a respectively, which face each other and protrude toward each other from the end edge 14 to form a cantilevered conductive portion extending above the recess of the printed circuit board 11.

[0079] Preferably, the conductive element 25 is welded to the first end portion 21a and the second end portion 22a in respective areas where the first and second tracks are thinner than in the rest of their structure. These thin areas are preferably shaped to match the outer contour of the conductive element 25 to define a receptacle for receiving or positioning the conductive element.

[0080] In other words, the end portion 21 a of the rail 21 and the end portion 22 a of the rail 22 are shaped so as to define a receiving portion that receives the conductive element 25 .

[0081] More specifically, also due to the accommodation portion for configuration, the conductive element 25 is soldered on the first end portion 21 a and the second end portion 22 a so as to be suspended above the recess of the printed circuit board 11 .

[0082] Preferably, the printed circuit board 11 and the conductive element 25 are constructed and positioned relative to each other in such a way that a vertical projection of the conductive element on the positioning plane of the printed circuit board 11 is completely located in the recess and at least 1 mm, preferably 2 mm, from the end edge 14 .

[0083] Advantageously, this feature prevents melting and other accidental damage to the printed circuit board 11 from causing a short circuit to the conductive element 25 by sealing the power circuit 10a after it is opened upon failure of the thermal contact 26.

[0084] Preferably, the first end portion 21a and the second end portion 22a are spaced apart from each other by a distance D of 5 mm to 10 mm, preferably 6.5 mm to 8.5 mm, more preferably 7 mm to 8 mm. In the embodiment shown, the distance D is 7.5 mm and determines the maximum voltage between the first rail 21 and the second rail 22 within which the described components ensure that the power circuit 10a remains disconnected after the conductive element 25 is triggered, thereby preventing the generation of an arc between the first rail 21 and the second rail 22.

[0085] With particular reference Figure 5 The portion of the housing 4 above the conductive element 25 defines an accommodation space “V”, which is suitable for enabling the conductive element 25 to move away from the first track 21 and the second track 22 .

[0086] The motor 1 further includes a stopper element 35 disposed near the conductive element 25 along the thrust direction of the elastic element 31 , so as to determine a stop position of the conductive element 25 driven by the elastic element 31 when the thermal joint 26 is broken.

[0087] The stop element 35 is preferably at least partially coupled to the support element 13 .

[0088] More specifically, the stop element 35 is arranged in the accommodation space "V" and is preferably fastened to the printed circuit board 11 and / or the support element 13 by a reversible clip so that the stop position of the conductive element 25 is a position in which the elastic element 31 is still loaded and presses the conductive element 25 against the stop element 35 to prevent further movement, which further movement could produce a short circuit between one conductive track 20 and the grounded housing 4 or between other components of the electronic module 10 and the power supply circuit 10a.

[0089] The stop position determines that the distance between the conductive element 25 and each of the first track 21 and the second track 22 is at least 2 mm, preferably at least 3 mm.

[0090] Preferably, the elastic element 31 is configured to exert a residual pressure on the conductive element 25 in the rest position so as to lock the conductive element in this position in the presence of accelerations of up to 20 g, preferably up to 50 g, on the conductive element, which may occur on the electric machine 1 in situations resulting from high shocks or resonances in the engine compartment of a vehicle, where it is crucial that the power supply circuit 10 a remain disconnected.

[0091] In a preferred embodiment, the stop element 35 has a concave shape and is configured to completely surround the conductive element 25 in the stopped position. Furthermore, the stop element 35 and the support element 13 are configured to define a protective shield around the conductive element 25 to prevent the ingress of particles or foreign matter large enough to close the power circuit 10 a when the conductive element 25 is in the stopped position.

[0092] More specifically, the stopper member 35 defines an upper portion of the cover, and a portion of the support member 13 around the through-hole 13 a through which the elastic member 31 passes is configured to close the upper portion at the bottom.

[0093] Preferably, both the stop element 35 and the support element 13 are made of a self-extinguishing electrically insulating material having a melting point at least 80°C higher than a predetermined threshold temperature, so as to keep the power circuit 10a in a disconnected state in the event of abnormally high temperatures inside the housing 4 and other faults or abnormal events.

[0094] In a preferred embodiment, the electronic module 10 includes a protection circuit 50 arranged along the power circuit 10a. The protection circuit 50 includes at least one MOSFET 12a (preferably two) and has a dual function.

[0095] One function of the protection circuit 50 is to provide active protection against polarity reversal on the terminals of the power supply circuit 10 a ; if this occurs, the protection circuit 50 disconnects the power supply circuit 10 a to prevent damage to the electronic module 10 .

[0096] In order to minimize the possibility that a short circuit still exists in the electronic module 10 after the power circuit 10a is disconnected by the conductive element 25, the conductive element 25 is arranged at a position close to the power pin 7a.

[0097] In the embodiment described by way of example, the two components (conductive element / power pins) are separated by approximately 30 mm.

[0098] The power pin 7a is preferably one end 21b of the first track 21. To allow the aforementioned soldering to take place, the mass of the first track 21 must be able to provide a heat capacity greater than 2.5 J / K, preferably greater than 3 J / K, which represents approximately 7.5 grams of copper-based alloy. Advantageously, this heat capacity allows the first track 21 to absorb the transient heat associated with the aforementioned soldering before the material of the thermally sensitive joint 26 melts.

[0099] In another embodiment, not shown, components similar to those described are located along the power circuit 10a and are repeated both near the power pin 7a and near the power pin 7b. Advantageously, such a system can protect the motor 1 not only from problems involving short circuits between the negative pin and other components of the motor 1 (e.g., the cover 3) in the event that the power circuit 10a is disconnected at the positive pin and may be rendered useless, but also from problems involving short circuits between the positive pin and other components.

[0100] The invention also aims at a method for manufacturing an electric machine 1 of the type described above, comprising a step of preparing an electronic module 10 of the type described above.

[0101] The description of the method is limited to the steps necessary for understanding the present invention. The method comprises the following steps: fastening the conductive element 25 to the power supply circuit 10a by means of at least one thermal joint 26, preferably one thermal joint 26 for fastening the conductive element 25 to the first rail 21 and one thermal joint 26 for fastening the conductive element 25 to the second rail 22, so as to close the power supply circuit 10a.

[0102] Preferably, the fastening step includes furnace brazing, which is performed while the printed circuit board 11 is passing through a furnace, wherein the plurality of electronic power components 12, including the aforementioned MOSFET 12a, are attached to the conductive tracks 20 by brazing. More specifically, the thermally sensitive joints 26 are formed by placing the aforementioned brazing alloy between the conductive element 25 and the first track 21 and / or the second track 22 and melting it during furnace brazing. Preferably, the first track 21 and the second track 22 are pre-tinned to facilitate brazing, and before being brazed in the furnace, cuts are made in the tin layer to prevent capillary diffusion of the brazing alloy on the surface.

[0103] The electronic module 10 is then preferably placed in the support element 13 .

[0104] In this embodiment of the method, the method comprises the step described above with reference to the electric machine 1 of fastening the stop element 35 on the conductive element 25 in its thrust direction.

[0105] The stop element 35 is preferably at least partially coupled to the support element 13 .

[0106] Once the stator 5 and rotor 6 are placed in the housing 2 , the springs 30 a , 31 are inserted into corresponding holes 40 a in the front piece 40 and the support element 13 / electronic module 10 assembly is also placed in the housing and over the stator 5 .

[0107] Next, after placing the thermally conductive compound 8 at least on the conductive tracks 20 and the electronic power components 12 , the method comprises the following step: closing the housing 2 with the cover 3 .

[0108] The closing step includes the step of compressing the elastic means 30 to press the electronic module 10 against the heat dissipation wall 4 a of the cover 3 and also compressing the thermally conductive filler 8 .

[0109] In this pressing step, the elastic element 31 is pressed between the ferromagnetic core 5 a and the conductive element 25 to generate a force on the heat-sensitive joint 26 and obtain the above-described embodiment.

[0110] Preferably, the step of compressing the elastic means 30 is achieved by moving the housing 2 and the cover 3 towards each other so that the elastic element 31 abuts against the stator 5 , in particular the ferromagnetic core 5 a of the stator 5 and the conductive element 25 and is compressed therebetween.

[0111] After the housing 2 and the cover 3 have been moved towards each other, they are connected to each other to define and close an inner sealed housing 4 .

[0112] The method of the present invention further comprises the steps of electrically connecting a power cable (not shown) to the power pins 7a and 7b and then sealing the connection area.

[0113] This step is performed by heating the end portion 21b for a welding time that is less than the time required for the heat-sensitive junction 26 to reach a predetermined threshold temperature.

[0114] In some embodiments constructed to provide protection to the motor 1 against faults involving a short circuit between the power pin 7a and other components of the motor 1 and against faults involving a short circuit between the power pin 7b and other components, some steps of the method for manufacturing the motor 1 are specifically adapted to repeatedly disconnect components of the power circuit 10a near the power pin 7b.

[0115] More specifically, when the printed circuit board 11 passes through the furnace, two conductive elements 25 similar to the conductive elements described above are soldered to conductive tracks facing each other and spaced apart from each other, similar to the first track 21 and the second track 22 described above, repeated at the power pins 7a and 7b. The subsequent step of compressing the two elastic elements 31 between the conductive elements 25 and the stator mounting portion 5a is performed similarly to the above description.

[0116] The present invention achieves the objectives set forth by overcoming the drawbacks of the prior art. In fact, the use of a layer of thermosensitive material subjected to the force of an elastic element to connect the conductive element to the conductive track constitutes an effective protection system against high temperatures and currents, capable of cutting off the power supply to the electronic components of the motor.

[0117] Advantageously, in the above-described method for manufacturing an electric motor, the conductive element is attached to the conductive track before being subjected to the force of the elastic element, whose force is applied at a later stage. This allows the elastic element to be attached to the conductive track while the track is passing through the furnace where other SMD components are soldered, thereby enabling the implementation of a high-temperature protection system without the need for an additional, time-consuming operation dedicated to attaching the elastic element. Another advantage of the above-described method is that the only step that distinguishes the described motor from a motor without high-temperature protection is the step of placing the elastic element. This means that both motors can be manufactured on the same production line; if the motor being manufactured does not have high-temperature protection, simply omitting the step of placing the elastic element is sufficient.

[0118] A further advantage of the described machine and production method is that it can withstand prolonged use at high temperatures below the protection triggering temperature. This resistance is due to the absence of the flux commonly used in most prior art thermal fuses.

[0119] The system described herein also has the advantage of being scalable in size as needed, and thus can be designed to withstand much higher currents than prior art thermal fuses can withstand.

[0120] Finally, in the motor described herein, the elastic element that pushes the conductive element serves a dual purpose: providing the aforementioned protection from high temperatures and currents, and pressing the electronic module against the heat sink wall to promote heat dissipation. Advantageously, this results in high production efficiency and low production costs.

Claims

1. A motor (1), comprising: - an electronic module (10) comprising a printed circuit board (11), a plurality of electronic power components (12) and a plurality of conductive tracks (20) arranged on the printed circuit board (11) and defining a power supply circuit (10a) between respective power pins of the motor (1) to provide a supply current for the electronic power components (12); - a housing (4) which defines a receptacle for the electronic module (10) and has at least one heat dissipation wall (4a); - a heat-conductive filler (8) placed between the electronic module (10) and the housing (4) to promote heat conduction from the electronic module (10) to the heat dissipation wall (4a); - an elastic device (30) acting on the electronic module (10) to press the electronic module (10) against the heat dissipation wall (4a) of the housing (4), thereby compressing the thermal conductive filler (8); -characterized in that, the motor comprises: - a conductive element (25) arranged to connect a first track (21) and a second track (22) of the plurality of conductive tracks (20) to close the power supply circuit (10a), the conductive element (25) being held in place by at least one thermally sensitive joint (26); The elastic device (30) comprises an elastic element (31) which presses against the conductive element (25) to exert a force on the at least one thermal junction (26), and the at least one thermal junction (26) is configured to be broken by the force when subjected to a temperature above a predetermined threshold temperature to disconnect the power circuit (10a).

2. The motor (1) according to claim 1, comprising a stator (5) arranged inside the housing (4) and a rotor (6) associated with the stator (5), the stator (5) comprising a stator mounting portion and a plurality of windings (5b) wound on the stator mounting portion, the elastic element (31) being arranged against the stator mounting portion to apply a force between the stator mounting portion and the conductive element (25).

3. The electric machine (1) according to claim 2, characterized in that The stator mounting portion comprises a core made of ferromagnetic material, and one end of the elastic element (31) is arranged against the core made of ferromagnetic material.

4. The electric machine (1) according to claim 3, characterized in that The elastic element (25) comprises a metal spring and a cover (32) made of an electrically insulating material, the cover being arranged to prevent a short circuit between the core made of a ferromagnetic material and the conductive element through the spring.

5. The electric machine (1) according to any one of claims 1 to 4, characterized in that: The conductive element (25) is welded to the first track (21) and / or the second track (22), and the at least one heat-sensitive joint (26) is made of a welding alloy.

6. The electric machine (1) according to claim 5, characterized in that The conductive element (25) is welded to the first track (21) and the second track (22) through two corresponding thermal joints (26), and is arranged to overlap the first track (21) and the second track (22) to form a bridge spanning the first track (21) and the second track (22).

7. The electric machine (1) according to any one of claims 1 to 4, characterized in that: The first rail (21) and the second rail (22) respectively have a first end portion (21a) and a second end portion (22a), and the first end portion (21a) and the second end portion (22a) are spaced apart from each other by a distance of 5 mm to 10 mm, and the distance defines a maximum voltage between the first rail (21) and the second rail (22), within which the power circuit (10a) can be ensured to be disconnected.

8. The electric machine (1) according to claim 7, characterized in that The printed circuit board (11) is provided with a recess defined by an end edge (14) between the first track (21) and the second track (22), the first track (21) and the second track (22) each having a respective end portion protruding from the end edge (14) toward the other of the first track (21) or the second track (22), the conductive element (25) being fastened to the first end portion (21a) and the second end portion (22a) at a hanging position above the recess.

9. The electric machine (1) according to claim 8, characterized in that The conductive element (25) and the printed circuit board (11) are positioned and / or constructed relative to each other in such a way that a projection of the conductive element (25) onto a positioning plane of the printed circuit board (11) is at least 1 mm from the end edge (14).

10. The electric machine (1) according to any one of claims 1 to 4, characterized in that The conductive element (25) has a corresponding docking surface for docking with the first track (21) and / or the second track (22), and the docking surface is configured to allow a current greater than 80 amperes to flow through the conductive element (25) without causing damage to the at least one thermally sensitive joint (26).

11. The motor (1) according to any one of claims 2 to 4, comprising a stop element (35) arranged along the thrust direction of the elastic element (31), the elastic element (31) being configured to move the conductive element (25) toward the stop element (35) after the at least one thermal joint (26) is broken, and the stop element (35) is configured to stop the conductive element (25) at a stop position so that the elastic element (31) maintains a residual pressure on the conductive element (25) sufficient to keep the conductive element (25) against the stop element (35).

12. The electric machine (1) according to claim 11, characterized in that The elastic element (31) is configured to exert the residual pressure so that the conductive element (25) remains in the stop position when an acceleration of up to 20 g is applied to the electric machine (1).

13. The electric machine (1) according to claim 11, characterized in that The stop element (35) is configured to determine the stop position of the conductive element (25) in such a manner as to ensure that the distance between the conductive element (25) and any component of the power circuit (10a) is at least 2 mm.

14. The electric machine (1) according to claim 11, characterized in that The stop element (35) is made of an electrically insulating, self-extinguishing material having a melting point above the threshold temperature.

15. The motor (1) according to claim 11, comprising a supporting element (13), which is interposed between the electronic module (10) and the stator (5) to support the electronic module (10), the supporting element (13) being provided with a through hole for the passage of the elastic element (31) between the stator mounting portion and the conductive element (25), and the supporting element (13) being made of an electrically insulating, self-extinguishing material having a melting point higher than the threshold temperature.

16. The electric machine (1) according to claim 15, characterized in that The stop element (35) and the support element (13) define a protective cover which is placed around the conductive element (25) and is configured to prevent foreign matter large enough to enter and close the power circuit (10a) when the conductive element (25) is in the stop position.

17. The electric machine (1) according to any one of claims 1 to 4, characterized in that The conductive element (25) is arranged close to a power pin of the motor (1), the first track (21) connects the power pin to the conductive element (25), and the heat capacity of the first track (21) is greater than 2.5 J / K.

18. The electric machine (1) according to any one of claims 1 to 4, characterized in that The plurality of conductive tracks (20) are protrudingly disposed on the printed circuit board (11), and a portion of the thermal conductive filler (8) is interposed between the conductive tracks (20) and the housing (4) to transfer heat from the conductive tracks (20) to the housing (4).

19. The electric machine (1) according to claim 18, characterized in that The plurality of conductive tracks (20) are configured and dimensioned to define a preferential path between the electronic power component (12) and a heat sink wall (4a) of the housing (4) for dissipating heat.

20. The electric machine (1) according to any one of claims 1 to 4, characterized in that The housing (4) comprises a shell (2) and a cover (3) for sealing, the shell (2) and the cover (3) being connected to each other to seal the housing (4), the cover (3) defining a plurality of heat sinks at the heat dissipation wall (4a), and the elastic device (30) being configured to press the electronic module (10) against the cover (3) so as to compress the thermal conductive filler (8).

21. The electric machine (1) according to any one of claims 1 to 4, characterized in that The threshold temperature is between 180°C and 250°C.

22. The electric machine (1) according to claim 5, characterized in that The solder alloy is a tin-based brazing alloy.

23. The electric machine (1) according to claim 5, characterized in that The solder alloy is an alloy of tin and silver.

24. The electric machine (1) according to claim 7, characterized in that The first end portion (21a) and the second end portion (22a) are spaced apart from each other by a distance of 6.5 mm to 8.5 mm.

25. The electric machine (1) according to claim 7, characterized in that The first end portion (21a) and the second end portion (22a) are spaced apart from each other by a distance of 7 mm to 8 mm.

26. The electric machine (1) according to claim 9, characterized in that The projection of the conductive element (25) onto the positioning plane of the printed circuit board (11) is 2 mm away from the end edge (14).

27. The electric machine (1) according to claim 10, characterized in that The abutment surface is configured to allow current greater than 100 amperes to flow through the conductive element (25) without causing damage to the at least one thermally sensitive joint (26).

28. The electric machine (1) according to claim 12, characterized in that The elastic element (31) is configured to exert the residual pressure so that the conductive element (25) remains in the stop position when an acceleration of up to 50 g is applied to the electric machine (1).

29. The electric machine (1) according to claim 13, characterized in that The stop element (35) is configured to determine the stop position of the conductive element (25) in such a manner as to ensure that the distance between the conductive element (25) and any component of the power circuit (10a) is 3 mm.

30. The electric machine (1) according to claim 14, characterized in that The locking element (35) is made of an electrically insulating, self-extinguishing material having a melting point at least 80° C. above the threshold temperature.

31. The electric machine (1) according to claim 17, characterized in that The heat capacity of the first track (21) is greater than 3 J / K.

32. The electric machine (1) according to claim 21, characterized in that The threshold temperature is between 200°C and 230°C.

33. A method for manufacturing an electric machine, comprising the steps of: - providing an electronic module (10) comprising a printed circuit board (11) mounted with a plurality of conductive tracks (20) defining a power supply circuit (10a), the power supply circuit (10a) being configured to provide a supply current to a plurality of electronic power components (12), the plurality of conductive tracks (20) comprising a first track (21) and a second track (22) which can be electrically connected to each other to close the power supply circuit (10a); - fastening a conductive element (25) to the power supply circuit (10a) via at least one thermal joint (26) to electrically connect the first track (21) and the second track (22); - providing a housing (2); - placing a stator (5) comprising a stator mounting portion and a plurality of windings (5b) surrounding the stator mounting portion in the housing (2); - placing a rotor (6) associated with said stator (5) in said housing; - placing the electronic module in the housing; - juxtaposing a cover including a heat dissipation wall with the housing to form a closed housing; arranging an elastic device (30) in the housing, the elastic device (30) being suitable for pressing the printed circuit board (11) and / or the plurality of conductive tracks (20) and / or the plurality of electronic power components (12) against the heat dissipation wall (4a), the step of juxtaposing the cover with the housing comprising the step of compressing the elastic device (30) to press the printed circuit board (11) and / or the plurality of conductive tracks (20) and / or the plurality of electronic power components (12) against the heat dissipation wall (4a); The step of compressing the elastic means (30) comprises the step of pressing the elastic element (31) against the conductive element (25) to exert a force on the at least one thermal contact (26), The at least one thermally sensitive junction (26) is configured to be broken by the force when the temperature is above a predetermined threshold temperature to disconnect the power circuit (10a).

34. The method according to claim 33, characterized in that The step of fastening the conductive element (25) comprises a step of furnace welding, wherein the conductive element (25) is welded to the first track (21) and the second track (22) to form the at least one thermal joint (26), and wherein in the same step of furnace welding, a plurality of electronic power components (12) are attached to the plurality of conductive tracks (20).

35. A method according to claim 33 or 34, comprising the step of electrically connecting a wiring harness to a power pin of the power circuit (10a), comprising the step of welding the wiring harness to one end (21b) of the first track (21), the welding step being performed by heating the end (21b) for a welding time which is less than the time required for the thermosensitive joint (26) to reach the threshold temperature, the thermal capacity of the first track (21) being configured to determine sufficient thermal inertia to keep the thermosensitive joint (26) at a temperature below the threshold temperature during welding.

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