Electrical system and electric drive unit

Abstract

An electrical system with optimized heat dissipation, the electrical system comprising: a busbar (1), a machine element (20), and a heat-conducting element (40) which thermally contacts the busbar (1), wherein the machine element (20) has, at least in some areas, a shaped element (30) projecting from an outer extension plane (21) on a side facing the busbar (1), which forms a contact surface (31), and the heat-conducting element (40) thermally contacts the contact surface (31) with a bottom-side contact element (41) and encases the projecting shaped element (30) with a sheathing element (42), characterized in that the electrical system has several projecting shaped elements (30), and the heat-conducting element (40) has several sheathing elements (42) and several bottom-side contact elements (41), each of which encases and covers a projecting shaped element (30).and the sheathing elements (42) and the bottom-side system elements (41) are mechanically connected to each other by respective transition areas (43).

Description

The invention relates to an electrical system with optimized heat dissipation and an electrical drive unit comprising the electrical system. In electrical systems, especially those operated at high voltage, busbars are often used as conductors. Due to the high currents involved, resistance-induced heating, including of the busbars, frequently occurs. To reduce resistance-related losses and / or to protect the busbar itself or other adjacent components, it is often necessary or advisable for safety reasons to dissipate heat from the busbar. However, particularly in configurations where the busbar is electrically coupled to a module that itself has a plastic housing or casing, heat transfer to such a module is limited and also carries the risk of damaging the module's plastic. For heat dissipation, there are, for example, so-called gap pads, which are essentially two-dimensional bodies made of thermally conductive material to create thermal interfaces between electronic components and heat sinks in air gaps. Such gap pads must, however, meet the electrical requirements regarding sufficient clearance and creepage distance. With two-dimensionally shaped gap pads, this is only possible if the gap pad has extended areas that project beyond the contact surface to which the gap pad is thermally conductive. This design, however, requires a considerable amount of installation space, since the edge of the gap pad must be positioned sufficiently far from an adjacent current-carrying component to maintain a sufficient clearance. However, particularly with adjacent busbars of different polarities, there is often insufficient installation space to position gap pads with extended edges on both busbars, as they are often located relatively close together. Furthermore, with such a gap pad design, there is a risk that such a large edge area will vibrate and thereby generate acoustic emissions and / or strike adjacent components. To overcome the aforementioned disadvantages, the contact surfaces on machine elements into which heat from the respective busbar is to be conducted could be made smaller, in order to extend the projecting areas of a respective gap pad sufficiently far beyond these surfaces. This, in turn, results in a reduced surface area over which heat can be transferred, thus correspondingly reducing the heat dissipation effect. From DE 10 2009 042 270 A1 an electrical system according to the preamble of claim 1 is known. Regarding further state of the art, reference is made to DE 10 2019 101 973 A1 and DE 10 2018 118 525 A1. Based on this, the present invention aims to provide an electrical system and an electrical drive unit equipped with it, which ensure optimized heat dissipation with a small installation space requirement. This problem is solved by the electrical system according to claim 1 and by the electrical drive unit according to claim 9. Advantageous embodiments of the electrical system are specified in dependent claims 2 to 8. The features of the claims can be combined in any technically meaningful way, taking into account the explanations from the following description as well as features from the figures, which include supplementary embodiments of the invention. The invention relates to an electrical system with optimized heat dissipation, comprising a busbar, a machine element, and a thermally conductive element that makes thermally conductive contact with the busbar. The machine element includes, at least partially, a shaped element projecting from an outer plane on one side facing the busbar, forming a contact surface. The thermally conductive element makes thermal contact with the contact surface via a bottom-side contact element and encases the projecting shaped element with a sheathing element. The outer extension plane of the machine element is a plane in which the outside of a boundary wall facing the conductor rail runs outside the respective protruding form element. In one embodiment, the busbar is designed to electrically connect a power module and a capacitor. The power module and the capacitor can be components of a power electronics system that forms a high-voltage intermediate circuit between a battery or electrical energy storage device and an electric drive motor, particularly in an electric vehicle. The capacitor can be a component of an inverter designed to quickly supply the DC voltage or current provided by the battery to the power module via the busbar, which then converts it into AC voltage. Heat from the busbar is transferred from the busbar to the machine element via the thermal interface material (TIM). Such a thermal interface material is also known as a gap pad or thermal interface material. Because the machine element is a large-volume component of considerable mass, especially if it is a housing element or enclosure, its specific heat capacity is high and its surface area exposed to the ambient air is large. This allows the machine element to absorb a significant amount of heat and / or dissipate it to the environment via convection. This effect is further enhanced when the machine element is thermally connected to other components. According to the invention, the heat from the busbar does not have to remain within the busbar or be dissipated via a poorly thermally conductive plastic housing. This results in a structurally optimized heat dissipation of the busbar. The heat-conducting element not only covers the protruding component at its contact surface, in particular completely, but also covers the protruding component at its lateral boundary surfaces if the protruding component has a polygonal cross-section, or at one lateral boundary surface if it has a circular cross-section. Only the area or side of the protruding component where it is connected to the machine element is not covered by the heat-conducting element. A lateral boundary surface of the protruding form element is a surface that, in the machine element, realizes the connection between the plane in which the outside of a boundary wall facing the busbar runs and the contact surface of the machine element against which the heat-conducting element rests. Accordingly, the heat-conducting element is designed to be three-dimensionally shaped, essentially like a pot or bowl, with a base-facing contact element forming the bottom of the pot and the casing element forming the pot wall. The casing element can also be thermally conductive and in contact with one or more lateral boundary surfaces of the protruding element. In an alternative embodiment, a minimal gap is maintained between the casing element and the one or more lateral boundary surfaces. The machine element can be, in particular, a housing element or even the complete housing of a component. The protruding element can also be described as a cooling plateau, which is enclosed by the casing element of the heat-conducting element. The heat-conducting element forms a base element adjacent to the mounting surface, which is firmly and thermally connected to the casing element. In particular, the base element and the casing element are integral components of the heat-conducting element. The three-dimensionality of the heat-conducting element serves to increase the surface area for heat dissipation to the environment via convection, to improve heat transfer to the machine element, and to extend the creepage distance without significantly utilizing installation space. The heat-conducting element can be manufactured in a simple embodiment using injection molding, but manufacturing using additive manufacturing processes, such as 3D printing, is also possible. In one embodiment of the electrical system, it is provided that at least one lateral boundary surface of the protruding form element is arranged at an angle of 60° to 120° in relation to the contact surface. In an advantageous embodiment, the contact surface is flat. Accordingly, the projecting element essentially forms the shape of a projection with an end-face contact surface and a polygonal or circular cross-section, wherein the sheathing element of the heat-conducting element is formed around the projecting element about a longitudinal axis of the projecting element, which runs essentially perpendicular to the contact surface. The machine element can be made of a material with a thermal conductivity of at least 40 W / mK. In particular, the machine element can be made of a metallic material, such as cast steel or cast iron. The heat-conducting element can consist of a material that has a thermal conductivity of at least 1.6 W / mK. In particular, a silicone with ceramic and / or glass fiber additives is suitable as a material for the heat conducting element. Simultaneously, the material of the heat-conducting element should exhibit electrical insulation due to a dielectric strength of at least 12 kV / mm. In one embodiment of the electrical system, the distance As between the busbar and the contact surface of the protruding element is a maximum of 3 mm. The intermediate, bottom-side contact element of the heat-conducting element is correspondingly thick, and this bottom-side contact element can be arranged with a slight press fit between the busbar and the contact surface. In an advantageous embodiment, the distance is no more than 2 mm, or optionally no more than 1 mm. This means that each protruding element, which forms a so-called plateau as its contact surface, extends to within a minimal distance of the busbar. In an advantageous embodiment, the ratio of the distance aE of the outer extension plane of the machine element to the busbar to the distance aS between the busbar and the contact surface of the protruding form element is aE / aS > 4. This means that a protruding feature extends relatively far from the outer plane of extension towards the busbar. In this embodiment, it can be provided that a protruding feature is formed by the machine element only at those points where a heat-conducting element is to be arranged. The protruding design element can be designed with a cavity open on the side facing the busbar. The open cavity in the protruding mold element offers technological advantages, particularly during the demolding process, especially when manufacturing the machine element using casting technology. Furthermore, inclusions in the casting, such as pores or cavities, can be reduced by using wall thicknesses optimized for casting. Although a protruding mold element with a cavity has a reduced contact area compared to a protruding mold element made of solid material, and consequently causes increased thermal resistance when heat is conducted into the protruding mold element, the increased contact area can be achieved by means of the sheathing element of the heat-conducting element, so that ultimately a respective protruding mold element can be optimized from a casting technology perspective and still ensure sufficient heat conduction into the protruding mold element or into the machine element. The electrical system can be designed such that the heat-conducting element, with at least one internal cantilever element, rests against an inner side surface of the protruding form element that defines the cavity. The electrical system can include a converter, wherein the machine element is the housing or part of a housing of the converter. Furthermore, the electrical system has several protruding shaped elements, and the heat-conducting element has several sheathing elements as well as several bottom-side contact elements, each of which encases and covers a protruding shaped element, the sheathing elements and bottom-side contact elements being mechanically connected to each other by respective transition areas. This means that each of the cladding elements is mechanically connected to every other cladding element, possibly indirectly. The same applies to the ground-level system components. A heat-conducting element thus forms several pot-like structures, each of which has a sheathing element and a bottom-side mounting element. The multiple sheathing elements and the base-side mounting elements associated with these sheathing elements can be arranged in series, with the electrical system comprising several busbars that are essentially parallel to each other. A longitudinal axis of the series arrangement can run transversely to the longitudinal direction of the busbars, so that a base-side mounting element of the heat-conducting element rests against at least two of the busbars. The busbars can be polarized differently. The transverse direction can, for example, be in an angle range of 30°-150° between the longitudinal axis of the row arrangement in relation to the longitudinal direction of the busbars. By encasing or enclosing at least one protruding form element with a sheathing element, the heat-conducting element is further fixed in relation to the machine element in at least two translational degrees of freedom and two rotational degrees of freedom. The length of each sheathing element, measured essentially perpendicular to the floor-side installation element, can be adapted to the respective electrical system, ensuring a necessary long creepage distance through the sheathing element. Another aspect of the present invention is an electric drive unit comprising at least one electric rotary machine and power electronics for controlling and / or supplying power to the electric rotary machine, as well as an electrical system according to the invention as a component of the power electronics. The invention described above is explained in detail below in the context of the relevant technical background, with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, and it should be noted that the embodiments shown in the drawings are not limited to the dimensions depicted. Figure 1 shows the electrical system in a sectional view, Figure 2 shows the heat-conducting element 40 in a first perspective view, and Figure 3 shows the heat-conducting element 40 in a second perspective view. The electrical system according to the invention, shown in Fig. 1, comprises a busbar 1, which is composed of a first part 11 of the busbar 1 and a second part 12 of the busbar 1. In particular, these two parts 11, 12 of the busbar 1 are welded together. The busbar 1 connects a capacitor 70, which may, for example, have a plastic casing, to a power module 60. Below the busbar 1 is a machine element 20, which forms a housing or part of a housing of a converter 80 of the electrical system. The machine element 20 comprises a shaped element 30 projecting from an outer extension plane 21, which generally forms an outer surface of the machine element 20. The projecting shaped element 30 forms a contact surface 31 with which the projecting shaped element 30 thermally contacts a heat-conducting element 40. The heat-conducting element 40, in turn, thermally contacts the first part 11 of the busbar 1. Accordingly, heat can be transferred from the busbar 1 via the heat conducting element 40 into the protruding form element 30 or into the machine element 20, essentially along the sketched heat flow 90. To improve the heat conduction from the busbar 1 to the machine element 20 and to extend the creepage distance, the heat conducting element 40 comprises a sheathing element 42, which extends from a bottom-side mounting element 41 located between busbar 1 and machine element 20. The cladding element 42 rests against an outer lateral boundary surface 34 of the projecting shaped element 30. The bottom-side contact element 41 rests against the contact surface 31 of the projecting shaped element 30. Heat can be transferred from the busbar 1 to the heat-conducting element 40, and from there to the machine element 20, via both the cladding element 42 and the bottom-side contact element 41. The casing element 42 extends from the plane of the mounting surface 31 towards the outer extension plane 21 of the machine element 20. The protruding form element 30 is designed with a cavity 32 which forms an opening 33 in the mounting surface 31. Alternatively or additionally, at least one cantilever element could be present, which extends along the inner side surface 35 of the projecting form element 30 and rests against it in order to introduce heat into the projecting form element 30. It is evident that the distance aS between the busbar 1 and the mounting surface 31 is much smaller than the distance aE between the busbar 1 and the outer extension plane 21 of the machine element 20. This means that the protruding form element 30 makes a significantly greater contribution to bridging the distance between the outer extension plane 21 of the machine element 20 than the heat-conducting element 40. The elements described here are components of a power electronics system, in particular a power electronics system for an electrically powered motor vehicle. Figures 2 and 3 each show a heat-conducting element 40 with three sheathing elements 42 and three bottom-side mounting elements 41 in a row arrangement. A transition area 43 is located between adjacent sheathing elements 42. It can be seen that each bottom-side attachment element 41 together with each casing element 42 essentially forms a pot shape, wherein the bottom-side attachment element 41 forms the pot bottom, and the casing element 42 forms the pot wall. Furthermore, it is evident that the bottom-side system elements 41 and the casing elements 42 are integral components of the same component, or are made of the same material. The proposed electrical system and the electric drive unit equipped with it provide facilities that ensure optimized heat dissipation with minimal installation space requirements. Reference symbol list 1 Busbar 11 First part of the busbar 12 Second part of the busbar 20 Machine element 21 Outer extension plane 30 Protruding shaped element 31 Contact surface 32 Cavity 33 Opening 34 Lateral boundary surface Outer side surface of the protruding shaped element 40 Heat conducting element 41 Bottom-side contact element 42 Sheathing element 43 Transition area 60 Power module 70 Capacitor 80 Converter 90 Heat flow aS Distance between the busbar and the contact surface aE Distance between the busbar and the outer extension plane

Claims

An electrical system with optimized heat dissipation, the electrical system comprising: a busbar (1), a machine element (20), and a heat-conducting element (40) which thermally contacts the busbar (1), wherein the machine element (20) has, at least in some areas, a shaped element (30) projecting from an outer extension plane (21) on a side facing the busbar (1), which forms a contact surface (31), and the heat-conducting element (40) thermally contacts the contact surface (31) with a bottom-side contact element (41) and encases the projecting shaped element (30) with a sheathing element (42), characterized in that the electrical system has several projecting shaped elements (30), and the heat-conducting element (40) has several sheathing elements (42) and several bottom-side contact elements (41), each of which encases and covers a projecting shaped element (30).and the casing elements (42) and bottom-side system elements (41) are mechanically connected to each other by respective transition areas (43). Electrical system according to claim 1, characterized in that at least one lateral boundary surface (34) of the projecting form element (30) is arranged at an angle of 60° to 120° in relation to the contact surface (31). Electrical system according to claim 1 or 2, characterized in that the machine element (20) consists of a material which has a thermal conductivity of at least 40 W / mK. Electrical system according to one of claims 1 to 3, characterized in that the heat conducting element (40) consists of a material which has a thermal conductivity of at least 1.6 W / mK. Electrical system according to one of claims 1 to 4, characterized in that the distance (aS) between the busbar (1) and the contact surface (31) of the protruding form element (30) is a maximum of 3 mm. Electrical system according to one of claims 1 to 5, characterized in that the protruding form element (30) is designed with a cavity (32) open on the side facing the busbar (1). Electrical system according to one of claims 1 to 6, characterized in that the electrical system has a converter (80), and the machine element (20) is the housing or part of a housing of the converter (80). Electrical system according to claim 7, characterized in that the sheathing elements (42) and the bottom-side contact elements (41) associated with these sheathing elements (42) are arranged in series, the electrical system has several busbars (1) which are oriented substantially parallel to each other, and a longitudinal axis of the series arrangement runs transversely in relation to the longitudinal direction of the busbars (1), so that a bottom-side contact element (41) of the heat conducting element (40) is in contact with at least two of the busbars (1). Electric drive unit comprising: at least one electric rotary machine, power electronics for controlling and / or supplying power to the electric rotary machine, and an electrical system according to one of claims 1 to 8 as part of the power electronics.

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