Electric machine with a heat transfer device for transferring heat from an electronic component to a heat sink

Abstract

A rotary electric machine includes an electronic module and a heat sink for dissipating heat produced by the module. The module includes a printed circuit, an electronic component having a base positioned on the printed circuit, a heat transfer device connected to the printed circuit and to the electronic component for transferring heat generated by the component to the heat sink. The heat transfer device includes an upper portion extending from the printed circuit towards the heat sink from the same side of the component and a base portion connected to the upper portion and positioned in the printed circuit at least partly under the component to form, at least partly, a preferential path for the heat, from the base of the electronic component to the heat sink. The electronic component is connected at least partly by its own base to the base portion of the heat transfer device.

Claims

1. A rotary electrical machine comprising: an electronic module, a heat sink for dissipating the heat generated by the electronic module; the electronic module comprising a printed circuit and an electronic component connected to the printed circuit and having a base, a heat transfer device connected to the printed circuit and at least to the electronic component for transferring heat generated by the electronic component to the heat sink, the heat transfer device comprising an upper portion extending from the printed circuit towards the heat sink at a same side of the printed circuit on which is mounted the electronic component, a layer of thermally conductive material interposed between the upper portion of the heat transfer device and the heat sink, the heat transfer device transferring the heat generated by the electronic component to the heat sink via the thermally conductive material, wherein the heat transfer device comprises a base portion connected to the upper portion by a connecting portion, the base portion positioned in the printed circuit at least partly under the base of the electronic component to form, at least partly, a preferential path for the heat generated by the electronic component from the base of the electronic component to the heat sink, the electronic component being connected at least partly by the base to the base portion of the heat transfer device, wherein the preferential heat path follows a U-shaped path, downward from the base of the electronic component to the base portion of the heat transfer device, laterally to the connecting portion, and then upward to the upper portion and the heat sink.

2. The machine according to claim 1, wherein the printed circuit comprises a seat for the base portion of the heat transfer device, the base portion being inserted in the seat.

3. The machine according to claim 2, wherein the seat is configured as a through hole in the printed circuit.

4. The machine according to claim 1, wherein the base portion of the heat transfer device is incorporated in the printed circuit.

5. The machine according to claim 1, wherein the base portion has an upper face coplanar with an upper face of the printed circuit, the electronic component being at least partly connected to the upper face of the base portion of the heat transfer device.

6. The machine according to claim 1, wherein the upper portion of the heat transfer device comprises a wing which projects in a cantilever manner from the base portion on a same side as the electronic component, the wing being thermally in contact with the heat sink.

7. The machine according to claim 1, wherein the upper portion has a lower face substantially coplanar with an upper face of the printed circuit.

8. The machine according to claim 1, wherein the upper portion is connected to the printed circuit by a relative lower face.

9. The machine according to claim 1, wherein the upper portion and the base portion of the heat transfer device are made as a single body, the heat transfer device being defined by a single element comprising the upper portion and the base portion.

10. The machine according to claim 1, wherein the base portion has overall plan dimensions greater than or equal to plan dimensions of the electronic component.

11. The machine according to claim 1, wherein the electronic component is soldered to the base portion of the heat transfer device.

12. The machine according to claim 1, wherein the electronic module comprises a plurality of electronic components, each having a respective base connected by the respective base portion of the heat transfer device.

13. The machine according to claim 1, wherein the base portion has a lower face coplanar with a lower face of the printed circuit or protruding from the lower face of the printed circuit, or recessed in the printed circuit, the printed circuit comprising a seat configured as a hole passing through the base portion of the heat transfer device, the base portion being inserted in the seat.

14. The machine according to claim 1, wherein the upper portion and the base portion of the heat transfer device are parallel to each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other features and advantages of the invention are more apparent in the detailed description below, with reference to a non-limiting and non-exclusive preferred embodiment of a rotary electric machine, as illustrated in the accompanying drawings, in which:

(2) FIG. 1 illustrates a schematic exploded perspective view of a rotary electric machine in accordance with the invention with some parts cut away for greater clarity;

(3) FIG. 2 illustrates a schematic perspective view of a detail of the electronic module for controlling an electric machine in accordance with an aspect of the invention;

(4) FIG. 3 illustrates a different schematic perspective view of the detail of FIG. 2;

(5) FIG. 4 illustrates a schematic cross section of a detail of an electric machine in accordance with an aspect of the invention;

(6) FIG. 5 illustrates a schematic cross section of a detail of an electric machine in accordance with an aspect of the invention;

(7) FIG. 6 illustrates a schematic perspective view of a component of a rotary electric machine in accordance with an aspect of the invention;

(8) FIG. 7 illustrates a schematic perspective view of a component of a rotary electric machine in accordance with an aspect of the invention;

(9) FIG. 8 illustrates a schematic perspective view of a component of a rotary electric machine in accordance with an aspect of the invention;

(10) FIG. 9 illustrates a schematic cross-section of a detail of a rotary electric machine of known type.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(11) With particular reference in particular to FIG. 1, the numeral 1 denotes a rotary electric machine according to at least one aspect of the invention.

(12) The machine 1, in one embodiment, is an electric motor of the sealed type, that is, without any openings for access to the inside, to which express reference will hereinafter be made but without thereby limiting the scope of the invention.

(13) The electric machine 1 will be described in detail solely for the parts necessary for the understanding of the invention.

(14) The machine 1 comprises a casing 2 and a cap 3 for closing the casing 2 to form, with the casing 2, a case or closed container.

(15) The electric machine 1 comprises a stator 4 fixed to the casing 2 and a rotor 5, inserted in the case, and attached to the case in a rotary manner.

(16) The machine 1 has its own axis of rotation R around which the rotor 5 rotates.

(17) An example of the stator 4 is described in the patent EP2215705 in the name of the same Applicant which is referred to herein in its entirety for the purposes of a complete description.

(18) The electric machine 1 comprises an electronic module 6, partly illustrated in FIGS. 2 to 5, inserted at least partly in the casing 2, for supplying the stator 4.

(19) The electric machine 1 also comprises a heat sink 7 for dissipating the heat generated inside the motor 1, in particular by the electronic module 6.

(20) In the embodiment illustrated, the heat sink 7 is formed by the cap 3 for closing the casing 2.

(21) The electronic module 6 comprises a plurality of electronic components, including, for example, surface-mount electronic components 8, also known as SMD electronic components, and pin-through-hole electronic components 9, also known as PTH electronic components.

(22) The electronic module 6 of the electric machine 1 comprises a printed circuit 10.

(23) The printed circuit 10 is substantially known as a PCB, that is, a Printed Circuit Board.

(24) In the embodiment described in the example, the electronic components 8, 9 are mounted on the same side 10a of the printed circuit 10, also defined as the component side of the printed circuit 10.

(25) The components side 10a of the printed circuit 10 defines a first side or upper face 10a of the electronic module 6.

(26) The electronic components 8, 9 are positioned on the first side 10a of the electronic module 8 so that they face towards the cap 3 and are opposite it.

(27) The electronic module 6 also comprises a plurality of conductor tracks 11, such as, for example, the electronic module described and illustrated in the document WO2013008180 by the same Applicant, which implement the direct connections between all the electronic components 8, 9.

(28) The conductor tracks 11 are positioned on a second side 10b, or soldering side or lower face, opposite the components side 10a of the printed circuit 6.

(29) The assembly consisting of the printed circuit 10, the electronic components 8, 9 and the conductor tracks 11, form the electronic module 6 comprising the control circuit of the machine 1 which controls the power supply.

(30) The electronic components “SMD” 8 comprise MOSFETs 12 which are “SMD” electronic power components.

(31) The MOSFETs 12, which are substantially of known type and are therefore not described in detail here, are electronic components having a case 13, with a substantially parallelepiped shape and comprising a plastic part, and a base 14 at least partly metallic by which the MOSFETs 12 are connected to the printed circuit 10.

(32) The MOSFETS 12 embody, in this description, electronic power components which are equipped with a base or tab 14.

(33) The aspects of the invention referred to the MOSFETs are fully valid for any electronic power component having a base 14.

(34) Generally speaking, the base 14 is a packaging for supporting a chip of the electronic component and has both a mechanical function and a thermal and electrical function.

(35) Each MOSFET 12 has a defined height h1 which in the solution shown in the example extends in a direction parallel to the axis of rotation R.

(36) More in general, the height h1 extends in a direction which is substantially perpendicular to the printed circuit 10.

(37) Each MOSFET 12 has its own power connection terminals 15.

(38) In the example illustrated, the terminals 15 of each MOSFET 12 are on opposite sides of the case 13.

(39) According to an aspect of the invention, the electronic module 6 comprises a plurality of elements for transferring heat or “heat transfer devices” 17 each connected to at least one respective electronic component 8, such as the MOSFETs 12, and illustrated in more detail, for example, in FIG. 6.

(40) In an embodiment, illustrated for example in FIGS. 7 and 8, the heat transfer device 17 may be sized to receive more than one electronic component 12.

(41) As illustrated, for example, in FIGS. 1 and 2, each MOSFET 12 may be connected to a respective heat transfer device 17 as described in more detail below.

(42) The heat transfer device 17 is preferably an element with a high thermal and electrical conductivity of the “SMD” type, that is, “Surface Mount Device”.

(43) According to an embodiment, the heat transfer devices 17 are associated with one or more electronic power components, in particular with a respective MOSFET 12, to increase the surface area for heat exchange and favour the transmission of the heat generated inside the component towards the heat sink 7.

(44) In particular each heat transfer device 17 is soldered to the components side 10a of the printed circuit 10, so that it also is facing, at least partly, the cap 3; for simplicity of description, reference is made below to a single heat transfer device 17 the heat transfer devices 17 preferably being all equal to each other.

(45) According to an aspect of the invention, the heat transfer device 17 comprises an upper portion 18 and a base portion 19 connected to the upper portion 18.

(46) In accordance with an aspect of the invention, when the heat transfer device 17 is mounted in the printed circuit 10, the upper portion 18 extends or projects from the printed circuit board 10 towards the heat sink 7, that is, towards the cap 3.

(47) The upper portion 18 projects from the printed circuit 10 on the same side 10a of the respective MOSFET 12, more specifically on the same side 10a of the case 13 of the MOSFET 12.

(48) According to an aspect of the invention, when the heat transfer device 17 is mounted in the printed circuit 10, the base portion 19 is positioned in the printed circuit 10 at least partly underneath the respective electronic component, in particular a MOSFET 12.

(49) According to an aspect of the invention, the base portion 19 has plan dimensions which are greater than or equal to the plan dimensions of the MOSFET 12, in such a way as to maximize the contact surface between MOSFET and heat transfer device.

(50) As illustrated in FIGS. 7 and 8, the base portion 19 is sized to receive a number of MOSFETs 12 greater than one, that is, three in the example illustrated.

(51) In other words, the base portion is divided into as many pads as there are electronic components to be coupled to the heat transfer device 17 and the upper portion 18 is shaped in such a way as to be maximised compatibly with the limits of the size of the electronic module.

(52) The base portion 19 forms, at least partly, a preferential path for the heat generated by the electronic component 12 from the base 14 of the electronic component 12 to the heat sink 7.

(53) With particular reference to FIGS. 4 and 5, it can be seen how, in use, the heat generated by the MOSFET 12 flows mostly from the base 14 of the MOSFET to the base portion 19 of the heat transfer device 17 and from there to the upper portion 18.

(54) The upper portion 18 is located in thermal contact with the heat sink 7, that is to say, with the cap 3, in such a way that the heat can be dissipated outside the motor 1.

(55) According to an aspect of the invention, the heat transfer device 17 comprises the base portion 19 from which the upper portion 18 projects in a cantilever fashion.

(56) As illustrated for example in FIG. 6, the upper portion 18 surrounds at least partly the lower portion 19, leaving free a side at the connection terminals of the electronic component 12.

(57) The portion 19 is substantially flat and is designed to receive the MOSFET 12 or several MOSFETs 12; for convenience of description reference is also made to a single MOSFET 12.

(58) The portion 19 has a flat upper face 19a, on which may be positioned the MOSFET 12 with the base 14 resting on the face 19a, and a lower face 19b.

(59) The upper portion 18 extends preferably as a flap, to which explicit reference will be made without thereby limiting the scope of the invention, from the base portion 19.

(60) The upper portion 18 or flap of the heat transfer device 17 has an upper face 18a and a lower face 18b.

(61) The flap 18 extends parallel to the base portion 19 and, according to an aspect of the invention, its shape depends on the free space in the electronic module 6.

(62) Generally speaking, an attempt is made to maximise the surface of the flap 18 since it is designed to exchange heat with the cap 3.

(63) In the example of FIG. 6, the flap 18 surrounds the MOSFET 12 on three sides and in the example of FIGS. 7 and 8 each MOSFET 12 is surrounded on three sides by the upper portion 18.

(64) In embodiments not illustrated, the MOSFETs 12 may be close to each other on the base portion 16 with the upper portion 18 which surrounds only externally the electronic components.

(65) It should be noted that preferably, a solution with several electronic components 12 soldered on a same heat transfer device can be actuated when an electrical connection between the bases of the separate electronic components is desired.

(66) In general, the lower face 18b of the upper portion 18 of the heat transfer device is substantially coplanar with the upper face 19a of the base portion 19.

(67) Since, as described in more detail below, the upper face 19a of the base portion 19 of the heat transfer device 17 is preferably coplanar with the upper face 10a of the printed circuit 10, the relative positioning of the lower face 18b of the upper portion 18 and the upper face 19a of the base portion, that is, the shape of the heat transfer device 17, takes into account the thickness of a solder paste, not illustrated, normally provided under the upper portion 18 for fixing the heat transfer device 17 to the printed circuit 10.

(68) The paste usually has a thickness of approximately 2 tenths of a millimetre.

(69) In that way, when the heat transfer device 17 is soldered to the printed circuit 10, in particular to the first edge 10a, by the lower face 18b of the flap 18, the upper face 19a of the base portion 19 is substantially coplanar with the side 10a of the printed circuit 10.

(70) According to an aspect of the invention, the heat transfer device 17 has a portion 20 for connecting the base portion 19 with the flap 18a.

(71) In an embodiment not illustrated, the upper portion 18 and the base portion 19 of the heat transfer device 17 are soldered to each other and a soldering defines, in practice, the connecting portion 20 between the two portions 18 and 19.

(72) In a preferred embodiment illustrated in the accompanying drawings, the upper portion 18 and the base portion 20 are made in a single body.

(73) The heat transfer device 17 is defined by a single element comprising the upper portion 18 and the base portion 19 of the for example joining the portion 20.

(74) If the heat transfer device 17 is made as a single body it may be made by drawing and/or pressing and cutting from a tinned sheet of thermally conductive material.

(75) The printed circuit 10 comprises a seat 21 for the base portion 19 of the heat transfer device whilst, as mentioned above, the upper portion 18 is above of the printed circuit 10, from the side of the components 12.

(76) As illustrated, for example in FIG. 3, the base portion 19 of the heat transfer device 17 is inserted in the respective seat 21.

(77) In an embodiment, such as the one illustrated for example, the seat 21 is in the form of a through hole in the printed circuit 10.

(78) In an alternative embodiment, the seat 21 is in the form of a blind hole in the printed circuit 10.

(79) With particular reference to FIGS. 4 and 5, when the heat transfer device is mounted in the printed circuit 10 it should be noted that the flap 18 has the lower face 18b substantially coplanar to the upper face 10a of the printed circuit 10, except for the thickness of the solder paste, not illustrated, between heat transfer device and PCB.

(80) The flap 18 is connected to the printed circuit 10 through its lower face 18b and the heat transfer device 17 is connected to the printed circuit through the flap 18.

(81) In a preferred embodiment, the base portion 19 has the lower face 19b coplanar with the side 10b of the printed circuit 10 or, in alternative embodiments, not illustrated, projecting from it or recessed in it.

(82) In that way, the face 19b may also be used, if necessary, to remove heat from the MOSFET 12.

(83) In an embodiment not illustrated, the base portion 19 of the heat transfer device can be incorporated in the printed circuit 10.

(84) The printed circuit 10 can be produced with a thermally conductive insert substantially at a pad for positioning and fixing the MOSFET.

(85) In this case, during the assembly of the electronic module, the upper portion 18 of the heat transfer device 17 and the MOSFET 12 are soldered to the lower portion 19 incorporated in the printed circuit 10.

(86) Each heat transfer device 17 has a height h2 above the printed circuit 10, defined, in the solution shown in the example, in a direction parallel to the axis of rotation R.

(87) In general, the height h2 extends in a substantially perpendicular direction to the printed circuit 10.

(88) The value h2 also identifies the thickness of the flap 18 which, in the embodiment illustrated by way of example, corresponds to the thickness of the base portion 19 of the heat transfer device 17.

(89) Since the MOSFETs 12 may be brought into direct contact with the cap 3 through the above-mentioned plastic part of their case 13 (therefore without any electrical short-circuit problems), the machine 1 comprises a layer of thermally conductive and electrically isolating filler material 22 interposed between the heat transfer device 17 and the heat sink 7.

(90) The material 22 may be for example in the form of a paste interposed at least between the heat transfer device 17 and the heat sink 7.

(91) Since between the MOSFET 12 and the heat transfer device 17 there is direct contact at the base 14, the interposing of a layer of material 22, for example the so-called “thermally conductive gap filler”, with a thickness between the values of the heights h1-h2, between the heat transfer device 17 and cap 3 creates a preferential path for the transfer of the heat dissipated by the MOSFET 12.

(92) The heat transfer device 17 acts as a “thermal joint”, that is, a means favouring the transfer of the heat generated by the MOSFET 12 towards the cap 3.

(93) Each heat transfer device 17 has the upper face 18a of the flap 18 facing towards the cap 3; the upper face 18a defines the heat exchange surface by which the heat transfer device 17 transfers most of the heat generated by the MOSFET 12 to the cap 3 which, as already mentioned, acts in turn as a heat sink.

(94) The area of the surface 18a is made as large as possible, as mentioned, within the design constraints for size, so as to minimise the resistance to the passage of heat.

(95) A part of the heat generated by each MOSFET 12 is transferred to the cap 3 also by the case 13 facing it which is preferably in mechanical contact with the cap 3.

(96) However, most of the heat generated by each MOSFET 12 is transferred to the cap 3 by the corresponding heat transfer device 17.

(97) According to an aspect of the invention, the height h2 of each heat transfer device 17, in particular of the upper portion 18, is less than the height h1 of the case 13 of the corresponding MOSFET 12, so that the MOSFETs 12 act as spacer elements separating the cap 3 from the heat transfer devices 17, thus preventing any short circuits which could occur following direct contact between the heat transfer devices 17 and the cap 3 of the machine 1.

(98) Alternatively, if the height h2 of the heat transfer device 17, in particular of the portion 18 on the components side 10a, is greater than the height h1 of the case 13 of the MOSFET 12, an alternative arrangement for preventing the short circuits resulting from direct mechanical contact between the heat transfer device 17 and the cap 3 would be to insert a thermally and electrically conductive material, such as “Sil-Pad”, between the cap 3 and the upper face 18a of the heat transfer device 17.