Fixed capacitor, cooling circuit, motor vehicle and use of a coolant

Abstract

Fixed capacitor (10) for an electronic device of a motor vehicle, in particular a power converter (12) for the electric drive of the motor vehicle, with a case (24), a first electrode (16) provided inside the housing (24), a second electrode (18) separated from the first electrode (16) by an intermediate space (20) and cooperating with the first electrode (16) to generate an electric field inside the housing (24) and a dielectric provided in the space (20), the housing (24) has an inlet (32) communicating with the space (20) and an outlet (34) communicating with the space (20), and the dielectric is a coolant (28) of the motor vehicle, wherein at least one electrically non-conductive spacer is arranged in the space (20) to define a distance between the first electrode (16) and the second electrode (18), wherein within the space (20) a flow path for the coolant (28) leading from the inlet (32) to the outlet (34) is kept clear and in the space (20) an electrically non-conductive porous body (22) is provided to form the spacer, wherein the porous body (22) has a sponge-like structure.

Description

[0001] The invention relates to a fixed capacitor with which electrical capacitance can be provided in a motor vehicle, in particular in a motor vehicle's power converter. The invention further relates to the use of a coolant with which such a fixed capacitor can be cooled within a cooling circuit of the motor vehicle.

[0002] It is known to construct a fixed capacitor, intended to provide a constant electrical capacitance, by means of two electrodes separated by a dielectric within a housing. Such a fixed capacitor is used, for example, in a power converter of an electrically powered vehicle to dampen interference currents.

[0003] From US 2020 / 0 373 123 A1, a plasma generator with an antenna conductor is known, wherein the antenna conductor is permeated by a cooling fluid which also permeates a variable capacitor and thereby acts as the dielectric of the capacitor in order to fill or avoid any resulting free spaces when a change in the capacitance of the capacitor causes a change in the relative position of the electrodes to each other.

[0004] From US 2010 / 0 134 947 A1 a fixed capacitor is known in which the electrodes are electrically separated from each other by a honeycomb structure acting as a dielectric, wherein a cooling liquid can flow through the honeycomb structure to cool the electrodes without coming into contact with the electrodes and can contribute to the dielectric effect.

[0005] From DE 10 2021 121 444 B3 it is known to cool power electronics within a housing of a pulse inverter for operating an electric machine of a motor vehicle using an electrically insulating fluid.

[0006] There is a constant need to be able to effectively cool the heat-generating electrical components of a motor vehicle.

[0007] The purpose of the invention is to demonstrate measures that enable good cooling of heat-generating electrical components.

[0008] The problem is solved according to the invention by a fixed capacitor with the features of claim 1, a cooling circuit with the features of claim 5, a motor vehicle with the features of claim 7, and a use with the features of claim 8. Preferred embodiments of the invention are specified in the dependent claims and the following description, each of which may individually or in combination represent an aspect of the invention.

[0009] One aspect of the invention relates to a fixed capacitor for an electronic device of a motor vehicle, in particular a power converter for the electric drive of the motor vehicle, comprising a housing, a first electrode provided within the housing, a second electrode separated from the first electrode by an intermediate space and cooperating with the first electrode to generate an electric field within the housing, and a dielectric provided in the intermediate space, wherein the housing has an inlet and an outlet communicating with the intermediate space, and the dielectric is a coolant of the motor vehicle, wherein at least one electrically non-conductive spacer is arranged in the intermediate space for defining a distance between the first electrode and the second electrode.wherein a flow path for the coolant leading from the inlet to the outlet is kept clear within the space, wherein an electrically non-conductive porous body is provided in the space to form the spacer, wherein the porous body has a sponge-like structure.

[0010] Instead of filling the space between the electrodes of the fixed capacitor with a solid dielectric, a liquid dielectric is used, which can be a non-conductive fluid. This allows the capacitance of the fixed capacitor to be changed by replacing the liquid dielectric with another liquid dielectric with a different dielectric constant, resulting in a different constant electrical capacitance. This can be achieved by draining one liquid dielectric through the outlet and introducing the other through the inlet, even simultaneously. This allows an otherwise identical fixed capacitor to be configured for different constant electrical capacitances depending on the liquid dielectric used, thus enabling cost savings in mass production using a large number of identical parts.Furthermore, it is possible to replace an already aged liquid dielectric with a fresh liquid dielectric in order to compensate for aging effects of the fixed capacitor and to increase the lifespan of the fixed capacitor.

[0011] Since the housing has both an inlet and an outlet, it is possible to allow the liquid dielectric to flow through the space between them, for example, to cool the liquid dielectric in a heat exchanger, so that warm liquid dielectric can be replaced by cold liquid dielectric. This can increase the lifespan of the solid capacitor.

[0012] Furthermore, it was recognized that electrically non-conductive coolants already exist that can be used to directly cool electrically conductive components. In particular, anhydrous liquids, such as those described in WO 95 / 07 323 A1, the contents of which are hereby incorporated as part of the invention, can be used for this purpose. Instead of using a separate liquid dielectric for the fixed capacitor, the coolant already intended for direct cooling of electrical components in motor vehicles can be used as the dielectric for the fixed capacitor. It was recognized that, due to the non-conductive nature of the coolant, a sufficiently high dielectric constant can generally be provided by the coolant itself.The coolant can cool the solid capacitor not only from the outside but also from the inside via the inlet and outlet of the housing, by flowing through the space between the electrodes as a liquid dielectric, absorbing heat generated in the electrodes and dissipating it as part of the heat flow to be carried away by the coolant.

[0013] This approach also leverages the understanding that electric vehicles designed as sports cars or racing cars often exhibit a very high-performance driving style, resulting in high power density and significant heat generation in the electronic components, particularly the power converter. For providing sufficient cooling capacity, even for extreme performance ranges of the vehicle, the pressure losses occurring during the flow through the fixed capacitor would be negligible and likely insignificant compared to the improved cooling of the capacitor achieved.By allowing the coolant, which acts as a dielectric and is already used in the motor vehicle, to flow through the space between the solid capacitors, internal cooling of the solid capacitor can be achieved, thus enabling good cooling of heat-generating electrical components in a motor vehicle.

[0014] A fixed capacitor is a type of capacitor with a defined, constant capacitance value, subject to tolerances. It differs from a variable capacitor in that its electrical capacitance is fixed and cannot be intentionally altered. While the constant capacitance may change due to aging, damage, or similar factors, a deliberate change in capacitance, as is possible with variable capacitors, is inherently impossible. Fixed capacitors are available in numerous different technology families, designs, and packages, depending on technical requirements such as voltage rating, current carrying capacity, capacitance stability, temperature coefficient, operating frequency range, temperature range, or mounting type (SMD design), as well as economic considerations.Preferably, the fixed capacitor is designed as a film capacitor. Particularly preferably, the fixed capacitor is dimensioned for use in a power converter, especially a pulse inverter, of an electrically powered vehicle, for example as an X-capacitor and / or Y-capacitor for damping interference currents.

[0015] The housing forms the outer surface of the solid capacitor, which can also be exposed to the coolant, which also flows through the space inside the housing. The housing can be made of an electrically non-conductive plastic material. Preferably, the housing is designed as a rigid body into which the electrodes can be inserted. Compared to a potting compound, the inlet and outlet can easily be provided in the rigid body, and blockage of the coolant flow path through the space by cooled potting compound can be avoided.For example, the electrodes are rolled into a cylinder which can be inserted axially into the correspondingly shaped housing with a defined insertion depth, so that the electrodes are securely blocked from rolling up through the housing and the inlet and outlet can be positioned at precisely predefined relative positions to the space between.

[0016] The first and second electrodes can each be connected to an electrical potential. The first and second electrodes can generate an electric field across the gap between them, in which electrical energy can be (temporarily) stored. Preferably, the first and / or the second electrode is coated with an electrically insulating layer, which preferably also provides protection, particularly corrosion protection, against the coolant used as a liquid dielectric.

[0017] The inlet and outlet can be designed as a through-opening in the housing material, allowing communication between the space inside the housing and a volume outside the housing via the inlet and / or outlet. The inlet and outlet are, in particular, separate from and distinct from each other. The inlet can be located at the beginning of a flow path through the space, and the outlet at the end of the flow path, wherein the flow path covers, in particular, nearly the entire space, at least 90%, preferably at least 95%, of the length of the space along the flow path.

[0018] The coolant is an electrically non-conductive fluid, which allows it to additionally fulfill the function of the dielectric in the fixed capacitor. The coolant is specifically part of a closed cooling circuit in which it is circulated. Upstream and / or downstream of the fixed capacitor, the coolant is in contact with another heat-generating component of the vehicle to dissipate the heat generated there. This heat-generating component can be part of the same vehicle component and / or the same electronic device in which the fixed capacitor is located, so that the coolant can cool both the heat-generating component and the fixed capacitor within a common component housing.However, it is also possible that the fixed capacitor cooled by the coolant is arranged downstream and / or upstream of a heat-generating component cooled by the same coolant.

[0019] Within the space between the electrodes, at least one electrically non-conductive spacer is arranged to define a distance between the first and second electrodes, while the flow path for the coolant leading from the inlet to the outlet remains unobstructed within this space. The spacer, preferably a plurality of spacers, provides mechanical support for the first and second electrodes across the space, thus preventing any displacement of the first electrode relative to the second electrode that could alter the distance between them.In contrast to a solid that completely fills the space, the sum of the provided spacers is only located in a partial volume of the space, so that a flow cross-section for the coolant, which is as large as possible, remains free, through which the coolant can flow from the inlet to the outlet.

[0020] The space between the two surfaces contains an electrically non-conductive porous body that serves as a spacer. This porous body can be processed similarly to a solid dielectric, such as a sintered one, during the manufacture of the solid capacitor. However, due to its porous structure, the body has a sufficient number of pores to allow the coolant to flow through it from the inlet to the outlet. The porosity of the body can be large enough to avoid unnecessarily obstructing the flow cross-section in the coolant's flow path. The porous body exhibits a sponge-like structure. This allows it to simultaneously offer good mechanical stability and integrity while providing a large flow cross-section.

[0021] Particularly preferably, the porous body is at least partially configured as a filter element for retaining impurities in the cooling fluid. The porous body can provide a comparatively large flow cross-section, for example, over 75%, and particularly over 90%, of the cross-section of the cavity through which the cooling fluid flows. This flow cross-section is formed not by a few large pores, but by many small pores. The pores of the porous body can thus be so small that the porous body can additionally function as a solids filter. This allows suspended solids, solid particles, or other impurities to be retained and, particularly preferably, prevented from entering the cavity in the first place.This can eliminate or at least reduce the risk of electrically conductive contaminants in the coolant, which may have been carried into the coolant by abrasion particles washed out during the cooling of other vehicle components.

[0022] Preferably, the porous body is formed as a solidified foam and / or sintered body. This makes the production of the porous body easy and cost-effective.

[0023] A filter for retaining impurities in the coolant is particularly preferred in the inlet and / or the intermediate space. The filter can comprise one or more filter elements. The filter element can, for example, be a nonwoven fabric, knitted fabric, perforated material, grid, or similar material capable of retaining solid particles down to a certain minimum size while allowing liquids to pass through. The pressure drop across the filter can be low enough to allow the coolant to flow through the filter element at a velocity sufficient for cooling within the intermediate space. This allows electrically conductive solid particles to be retained by the filter cost-effectively and with minimal effort.The filter preferably includes an electrical filter element for generating an electric and / or magnetic field to deflect and retain electrically and / or magnetically reactive components of the coolant. This utilizes the fact that electrically conductive contaminants interact with an electric and / or magnetic field. For example, metal particles can be deflected and retained in an electric and / or magnetic field. The electrical filter element therefore also enables the filtration of particularly small electrically conductive particles that, due to their small size, might otherwise pass through a mechanical filter. This can improve the filter's performance with regard to electrically conductive contaminants.

[0024] Another aspect concerns a cooling circuit for cooling a motor vehicle component, comprising an electrically non-conductive coolant, a motor vehicle component through which the coolant flows to cool a heat-generating element within the motor vehicle component, and an additional fixed capacitor through which the coolant flows, which can be designed and further developed as described above, wherein the fixed capacitor is provided inside or outside the motor vehicle component, and in particular, the fixed capacitor is part of a power converter for the electric drive of the motor vehicle.By circulating the coolant, which acts as a dielectric and is already provided in the motor vehicle, through the space between the solid capacitors, internal cooling of the solid capacitor can be achieved, so that good cooling of heat-generating electrical components in a motor vehicle is made possible with the help of the cooling circuit.

[0025] Another aspect concerns a motor vehicle with an electric machine for its electric propulsion, a traction battery for operating the electric machine, and a power converter connected between the traction battery and the electric machine. A cooling circuit, which can be configured and further developed as described above, is provided for cooling the traction battery and the power converter and / or the electric machine. The power converter includes a fixed capacitor, which can be configured and further developed as described above. The flow of the coolant, which acts as a dielectric and is already present in the motor vehicle, through the space between the fixed capacitor allows for internal cooling of the capacitor, thus enabling effective cooling of heat-generating electrical components in the motor vehicle.

[0026] One aspect of the invention relates to the use of an electrically non-conductive coolant for cooling both a heat-generating element within a motor vehicle component and, additionally, a fixed capacitor installed in the motor vehicle, which can be designed and further developed as described above, wherein the coolant flows through the fixed capacitor as a dielectric. By allowing the coolant, which already acts as a dielectric, to flow through the space between the fixed capacitor and the capacitor, internal cooling of the fixed capacitor can be achieved, thus enabling effective cooling of heat-generating electrical components in a motor vehicle.

[0027] The invention is explained below by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention, either individually or in combination. The drawings show: Fig. 1 a schematic cutaway representation of a fixed capacitor and Fig. 2 a schematic diagram of a cooling circuit for the fixed capacitor made of Fig. 1.

[0028] The in Fig. The fixed capacitor 10 shown in Figure 1 can be installed, in particular, in a power converter 12, preferably a pulse inverter, of an electrically powered motor vehicle, which is cooled by a cooling circuit 14. For the sake of simplicity, the fixed capacitor is shown in Figure 1. Fig. Figure 1 is simplified and shown only in principle. The fixed capacitor 10 can actually have different configurations. The fixed capacitor 10 has a first electrode 16 and a second electrode 18, which are spaced apart from each other by a gap 20. The gap 20 is filled with a sponge-like, foamed porous body 22, which provides sufficient mechanical stability to keep the electrodes 16 and 18 at a constant distance from each other. The electrodes 16 and 18 are provided in a housing 24, with the aid of which the fixed capacitor 10 can be attached to a printed circuit board 26, also referred to as a "PCB". The printed circuit board 26, together with the fixed capacitor 10, is provided in a component housing 30 of a motor vehicle component, in particular the power converter 12, through which a coolant 28 flows.

[0029] The housing 24 has an inlet 32 ​​and an outlet 34, through which the space 20 can communicate with the volume inside the component housing 30 and outside the housing 24 through which the coolant 28 flows. The coolant 28 can flow into the interior of the fixed capacitor 10 via the inlet 32 ​​and essentially flow through the entire space 20 up to the outlet. The sponge-like foamed porous body 22 provides a sufficiently large flow cross-section for the coolant 28. Since an electrically non-conductive dielectric fluid is used as the coolant 28, it can not only cool the fixed capacitor 10 from the inside, but also simultaneously form a dielectric with a previously known dielectric constant for the fixed capacitor 10.In particular, a filter 36 is provided in the inlet 32, which can filter out electrically conductive impurities in the coolant 28.

[0030] The in Fig. The cooling circuit 14 shown in Figure 2 includes, in particular, the power converter 12 as a vehicle component to be cooled. The power converter 12 can include at least one fixed capacitor 10, which, for example, is configured as shown in Figure 2. Fig. The cooling circuit 14 can be configured as shown in Figure 1. In particular, the power converter 12 and / or another vehicle component not shown has a heat-generating element 38 within the cooling circuit 14 that requires cooling. This element is surrounded, especially on its outer surface, by the coolant 28, which is also used for cooling inside the fixed capacitor 10. The heated coolant 28 can be cooled downstream of the power converter in a heat exchanger 40, in particular an air-cooled front radiator of the vehicle. The coolant 28 can be circulated through the cooling circuit 14 by means of a pump 42.

[0031] A motor vehicle (not shown in the figures) can use the converter 12 to convert direct current supplied by a traction battery into alternating current in order to operate an electric motor for the electric propulsion of the motor vehicle. Heat generated in the converter 12 can be dissipated using the [missing information - likely a specific heat sink or heat sink]. Fig. The heat is dissipated via the cooling circuit 14 shown in section 2. In particular, the cooling circuit 14 can also be suitablely connected to the traction battery and / or the electric motor in order to dissipate heat generated there as well.

Claims

[1] Fixed capacitor (10) for an electronic device of a motor vehicle, in particular a power converter (12) for the electric drive of the motor vehicle, with a case (24), a first electrode (16) provided inside the housing (24), a second electrode (18) separated from the first electrode (16) by an intermediate space (20) and cooperating with the first electrode (16) to generate an electric field inside the housing (24) and a dielectric provided in the space (20), the housing (24) has an inlet (32) communicating with the space (20) and an outlet (34) communicating with the space (20), and the dielectric is a coolant (28) of the motor vehicle, wherein at least one electrically non-conductive spacer is arranged in the space (20) to define a distance between the first electrode (16) and the second electrode (18), wherein within the space (20) a flow path for the coolant (28) leading from the inlet (32) to the outlet (34) is kept clear and in the space (20) an electrically non-conductive porous body (22) is provided to form the spacer, wherein the porous body (22) has a sponge-like structure. [2] Fixed capacitor (10) according to claim 1, wherein the porous body (22) is at least partially designed as a filter element for retaining impurities in the cooling liquid (28). [3] Solid capacitor (10) according to claim 1 or 2, wherein the porous body (22) is designed as a solidified foam and / or sintered body. [4] Fixed capacitor (10) according to one of claims 1 to 3, wherein a filter (36) for retaining impurities in the coolant (28) is provided in the inlet (32) and / or in the space (20). [5] Cooling circuit (14) for cooling a motor vehicle component of a motor vehicle, comprising an electrically non-conductive coolant (28), a motor vehicle component through which the coolant (28) flows for cooling a heat-generating element (38) within the motor vehicle component and an additional fixed capacitor (10) through which the coolant (28) flows according to one of claims 1 to 4, wherein the fixed capacitor (10) is provided inside or outside the motor vehicle component. [6] Cooling circuit (14) according to claim 5, wherein the fixed capacitor (10) is part of a power converter (12) for the electric drive of the motor vehicle. [7] Motor vehicle comprising an electric machine for the electric propulsion of the motor vehicle, a traction battery for operating the electric machine and a power converter (12) connected between the traction battery and the electric machine, wherein a cooling circuit (14) according to claim 5 or 6 is provided for cooling the traction battery and / or for cooling the electric machine and for cooling the power converter (12) and the power converter (12) comprises a fixed capacitor (10) according to any one of claims 1 to 4. [8] Use of an electrically non-conductive coolant (28) for cooling both a heat-generating element (38) within a motor vehicle component of a motor vehicle and additionally a fixed capacitor (10) installed in the motor vehicle according to one of claims 1 to 4, wherein the coolant (28) flows through the fixed capacitor (10) as a dielectric.

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