Housing assembly to enclose and ground an electrical subassembly

A housing assembly to enclose an electrical subassembly includes a housing formed from a conductive polymer. The housing has a cavity sized to receive an electronic sub-assembly therein. A conductive boss is insert-molded into the housing in conductive contact with the housing. A conductive bracket is fastened to the boss in conductive connection with the boss and the housing to support and electrically ground the housing.

TECHNICAL FIELD

Various embodiments relate to a housing assembly to enclose and ground an electrical subassembly.

BACKGROUND

In the advent of electric vehicles, hybrid electric vehicles, and any battery-powered vehicle, charger assemblies have been incorporated for charging the battery or batteries. Such charger assemblies often experience high voltages and are often utilized for converting alternating current to direct current. This conversion results in a high heat output and transmission of electromagnetic interference.

DETAILED DESCRIPTION

Referring now toFIG. 1, a charger assembly is illustrated and referenced generally by numeral20. The charger assembly20, according to an embodiment, is an onboard charger, which is mounted to a vehicle body for charging a battery or batteries of the vehicle. Therefore, the size, shape, weight, rate of heat transfer, electromagnetic interference, durability and cost are all factors for the charger assembly20and the associated vehicle.

In the depicted embodiment, the charger assembly20has a housing22. The housing22is generally hollow with a cavity therein for receiving components of the assembly20. The housing22may be formed from any suitable material, such as aluminum, or a polymer. For the depicted embodiment, the housing22is formed from a conductive polymeric material. The housing22has an opening24for receiving components of the assembly20within the cavity. A mounting surface26is provided about the opening24for receiving a faceplate28fastened to the mounting surface26.

Referring now toFIG. 3, the charger assembly20includes a substrate30. The substrate30may be formed of any suitable material such as plastic, aluminum, or the like. The substrate30is mounted to the cover28for being disposed within the cavity of the housing22.

A heat transfer duct32is provided by a continuous bent piece of round tubing32for conveying fluid such as water or a coolant through the charger assembly20. The tubing32has a pair of ends34,36that extends through the cover28to provide an inlet and an outlet for the heat transfer duct32. The tubing32extends straight in a depth direction from each of the ends34,36for providing a pair of straight regions38,40as inlet and outlet regions38,40. An intermediate region42extends between the straight regions38,40. The tubing32is formed from a continuous piece to avoid any fittings or connections within the charger assembly20. The tubing32is placed upon the substrate30. Of course, any pattern of the tubing32is contemplated.

The substrate30has a plurality of recesses44formed therein. The recesses44are aligned with high heat zones of associated circuit board assemblies. The recesses44are sized to receive a plurality of thermally conductive heat sinks46. The heat sinks46may be formed from a thermally conductive material, such as copper, aluminum, heat pipe, or the like. Each heat sink46has a generally planar contact portion48for contact with the associated circuit board assembly. Each heat sink46also includes an arcuate, or curved, contact portion50that is contoured to the shape of the tubing32for an area contact with the tubing32. The heat sinks46are not fastened to the substrate30. The heat sinks46are placed within the recesses44upon the substrate30as illustrated inFIG. 3. Since the tubing32is displaced along one side of the substrate30, the heat sinks46on the opposed side extend through apertures52so that the curved contact portions50engage the tubing32.

Referring now toFIG. 4, the cover28is assembled to the substrate30and the tubing32. Also, a plurality of circuit board assemblies54,56,58,60is assembled to both sides of the substrate30. The circuit board assemblies54,56,58,60each include an aperture pattern62that collectively corresponds with an aperture pattern64of the substrate30for receipt of fasteners66for assembling the circuit board assemblies54,56,58,60to the substrate30. By fastening the circuit board assemblies54,56,58,60to the substrate30, the heat sinks46are retained between each corresponding circuit board assembly54,56,58,60and the substrate30. The heat sinks46are aligned with high heat zones of the associated circuit board assemblies54,56,58,60to transfer the heat from the circuit board assemblies54,56,58,60to the tubing32. By conveying a fluid through the tubing32, the heat is transferred from the heat sinks46to the tubing32, and consequently to the fluid within the tubing32for transferring the heat out of the charger assembly20.

Although various circuit board assemblies54,56,58,60are contemplated, the circuit board assemblies (PCBs)54,56,58,60may each be provided on a printed circuit board. The circuit board assemblies54,56,58,60may include power PCB, control PCB, and power factor correction PCB. Of course, various circuit board assemblies are contemplated.

With reference now toFIG. 5, all of the components of the charger assembly20are assembled prior to being inserted into the housing22. Thus, assembly of the components can occur at a location that is external of the housing22. Therefore, accessibility to the various components is enhanced. Likewise, assembly does not occur within the housing22itself. In the depicted embodiment, the housing22has only one opening. The simplification is an enhancement over prior art charger assemblies that have various access openings and therefore various covers for access, assembly, and enclosing various components of the prior art charger assembly.

FIG. 5also illustrates a pair of mounting brackets68that are fastened to the cover28for supporting and fastening the charger assembly20to an underlying support structure, such as the vehicle body. The assembled cover28, mounting brackets68and housing22are illustrated inFIG. 6.FIG. 7illustrates a cross section of the charger assembly20. The housing22includes a cavity70for receiving the components assembled to the cover28. A channel72is formed within a bottom surface of the housing22for receiving a proximal end of the substrate30.

Referring again toFIG. 1, a plurality of connectors is assembled to the cover28in electrical connection with the circuit board assemblies54,56,58,60. For example, two power connectors74,76and one signal connectors78may be fastened to the cover28. Additionally, fittings80may be provided on the tubing ends34,36external of the housing22.

As discussed above, the housing22may be provided from a conductive plastic material. The conductive plastic material may be utilized for shielding electromagnetic interference (EMI) and/or grounding of the charger assembly20. Likewise, the relative flexibility of the housing22provides a sealed connection with the cover28so that an additional seal is not required in order to seal the components of the charger assembly20from external contaminants.

The packaging of the housing22permits simplified alignment and structure with all connections oriented in a common direction for accessibility, ease in assembly, and minimizing wiring, and permitting utilization of the housing22with only one opening24.

Prior art charger assemblies often utilize a cast aluminum housing with multiple openings requiring multiple covers. Due to the inflexibility of cast aluminum, seals are required, which are less reliable than the connection provided by fastening the cover28to the mounting surface26of the housing22. Therefore, leakage is reduced with the plastic housing22, while weight is also reduced. For example, the depicted charger assembly20weighs generally 5 kilograms wherein the prior art charger assembly weighs approximately 7 kilograms. Additionally, a molded conductive plastic housing is cheaper due to materials' cost and manufacturing cost than a comparable cast aluminum housing, that requires machining afterword.

By utilization of the heat sinks46, the heat can be conducted directly from the heat source to the tubing32thereby avoiding complicated tubing paths and geometries. By retaining the heat sinks46between the circuit board assemblies54,56,58,60and the substrate30, additional fasteners can be avoided.

FIGS. 8 and 9illustrate an EMI shield assembly82which can be utilized as the housing22according to at least one embodiment. The EMI shield assembly82includes a first housing84having a cavity86for receiving an electronic sub-assembly, such as the charger assembly20, therein. The first housing84provides the mounting surface26for the cover28. The first housing84is also illustrated inFIG. 10. The first housing84is formed from a conductive polymer, such as a polyamide66with ten percent Nickel Coated Carbon fiber, for example. The first housing84has a wall thickness of approximately one millimeter according to at least one embodiment.

A metallic layer88is provided about the first housing84. According to one embodiment, the first housing is coated with the metallic layer88. The metallic layer88may be provided by aluminum foil according to at least one embodiment, or by a steel box according to at least another embodiment. The first housing84shields against high frequency EMI, such as a range of 20 Hertz to 1.73 MHertz.

The EMI shield assembly82also includes a second housing90with a cavity92for receiving the first housing84and the metallic layer88within the second housing cavity92. The second housing is also illustrated inFIG. 11. Alternatively, the metallic layer88could be provided in the cavity92of the second housing90instead of being provided about the first housing84.

The second housing90is formed from a conductive polymer, such as a polyamide66with thirty percent Stainless Steel fiber according to at least one embodiment. The second housing90shields against low frequency EMI within a range of twenty-five to one hundred Hertz. The second housing90has a wall thickness of approximately two millimeters according to at least one embodiment.

The EMI shield assembly82utilizes conductive polymers for enclosing high voltage electronic sub-assemblies, instead of aluminum, as in the prior art. The conductive polymers permit grounding of the housings84,90while shielding a wide range of EMI from exiting, or entering the housings84,90. The EMI shield assembly82utilizes the housings84,90with materials having different shielding properties over defined frequency ranges to meet full range shielding efficiency requirements for a given application. The metallic layer88further enhances the shielding effectiveness of the first housing84for preventing EMI of the charger assembly20from interfering with other components located near the charger assembly20while preventing EMI from other components from interfering with the charger assembly20.

The housings84,90collectively provide a high structural strength to meet applicable crush test stresses and stiffness requirements. The multiple polymer layers provided by the housings84,90provide insulation of the charger assembly20from high temperatures that may be present in an environment under a hood of the vehicle. Additional thermal insulation may be provided between the housings84,90according to at least one embodiment. The EMI shielding assembly82provides the housing22for the charger at a compact size, such as approximately 313 millimeters by 122 millimeters by 199 millimeters.

Of course, the EMI shielding assembly82may be utilized for various electronic subassemblies.FIGS. 12 and 13illustrate another EMI shielding assembly94with a dual conductive plastic housing assembly96similar to the prior embodiment. The housings96provide a cavity98at an opening100with a mounting surface102. A 3D card104with a printed circuit board106connected at a back plane with heat pipes108is disposed within the cavity98and enclosed by a cover110fastened to the mounting surface102. A control fitting112and power fittings114are subsequently added to the cover110. This assembly82permits a compact 3D PCB assembly116that is compact and optimizes strength, insulation, EMI shielding, and heat transfer. For example the EMI shield assembly94may be approximately 180 millimeters by 125 millimeters by 193 millimeters.

Referring again toFIG. 1, it is common to ground electrical components within a vehicle. Therefore, the brackets68are conductive for electrical grounding of the charger assembly20to the vehicle. The brackets68contact a vehicle body and therefore ground any short circuiting that may occur in the charger assembly20. Referring now toFIGS. 1,5and6, the brackets68are fastened directly to the cover28by fasteners118. The cover28may be formed of a conductive material, such as aluminum, and provides a grounding plate for the components of the charger assembly20. Accordingly, the cover28has interfaces120for providing a surface area contact with the brackets68.

The cover28includes a plurality of grounding interfaces122for the circuit board assemblies54,56,58,60. Therefore, each of the circuit board assemblies54,56,58,60is grounded to the cover28. The cover28also includes a plurality of grounding interfaces124and126for connection and electrical grounding of the connectors74,76,78. Of course, any arrangement of grounding interfaces is contemplated. For ease in assembly, each of the described grounding interfaces120,122,124,126is provided on the cover28for access external of the housing22.

The cover28includes a plurality of enlarged tabs128formed around its periphery. Each tab128is provided with an aperture130for securing the cover28to the housing22. The housing22, likewise includes a plurality of tabs132formed along the mounting surface26, aligned with the tabs128of the cover28. Each housing tab132has an aperture134for receiving a fastener.

With reference toFIGS. 8-11and in the context of an embodiment wherein the housing22is a housing assembly22provided collectively by the first and second housings84,90, each of the housing tabs132may be provided collectively by both housings84,90. In another embodiment, the housing tabs132are provided on only one of the housings84,90.

In the depicted embodiment ofFIGS. 8-11, the first housing84provides the mounting surface26for the cover. The first housing84includes a plurality of tabs136formed around the mounting surface26. Each of the tabs136of the first housing84includes the aperture134formed therethrough. Likewise, the second housing90has a mounting surface137formed around the cavity92for receiving the tabs136of the first housing84. The second housing90includes a plurality of tabs138formed around the mounting surface137. Each tab138of the second housing90includes an aperture140formed therethrough. The tabs136and138of the first and second housings84,90collectively provide the tabs132of the housing assembly22.

FIG. 14illustrates a section view of the cover tab128and the housing tabs136,138taken across section line14-14inFIG. 6. The first housing84includes a plurality of conductive bosses142that are each insert-molded into one of the tabs136. The bosses142provide an electrical connection with conductive fibers within the conductive polymer material of the first housing84. Molded conductive plastics often have a resistant or non-conductive surface or skin due to the flow of the fibers during a molding operation. By overmolding the first housing84to the bosses142, the surface is penetrated by the bosses142thereby providing electrical contact between the fibers and the bosses142. This contact can be enhanced by serrations, splines, or the like formed on an external surface of the bosses. In the depicted embodiment, copper strand wires144are connected externally to the bosses142for extending into the material of the first housing84and further enhancing electrical contact with the fibers within the material.

According to at least one embodiment, the second housing90also includes a plurality of conductive bosses146that are each insert-molded into one of the tabs138. Likewise, the bosses146provide electrical contact with the fibers in the conductive plastic material of the second housing90. The bosses146may also include copper strand wires148for enhancing the electrical contact of the bosses146and the fibers within the material.

A plurality of conductive fasteners, such as screws150, is provided for securing the cover28to the housings84,80. Each screw150extends through the aperture130in the cover28and engages the corresponding bosses142,146of the first and second housings84,90. Additionally, the screws150provide an electrical connection between the cover28and the bosses142,146for providing an electrical connection between the housings84,90and the cover28. Therefore, the housings84,90are also grounded to the cover28, and consequently to the brackets68.

The metallic layer88between the first and second housings84,90is in direct electrical contact with one or both of the bosses142,146for an electrical grounding connection with the screws150and consequently the cover28and brackets68. Alternatively, the screws150may directly contact the metallic layer88.

According to at least one embodiment, seals may be provided between the cover28and the first housing84and/or between the first housing84and the second housing90to limit exposure of the bosses142,146to external contaminants and to avoid contact degradation from environmental exposure.

The grounding interfaces between the housings84,90and the brackets68provide maximum ground current capability through the shield assembly94with low resistance contact between the housings84,90and the cover28. The grounding system depicted is adequate for ground10Amps continuously and20Amp surges through the cover plate28.

For utilization of multiple charger assemblies20within a vehicle, grounding resistance of a wire shield from one cover28to another cover28is less than 1 milliohm. One milliohm ground circuit resistance for wiring shielding is achieved by utilization of parallel circuits (increased effective surface for transfer of ground circuit currents that are high frequency and are using only conductor surface for transfer—skin effect) and by enhanced interfaces between connectors74,76,78, wire shields and cover plates28. In case of bundle shielding, a bundle shield is engineered using right materials and conducting cross sections and lengths to meet maximum 1 milliohm ground circuit resistance.

A surface of engaged fibers within the conductive plastics may be controlled by turbulence induced in molding process by shape and construction of the bosses142,146. Distribution of the conductive fibers in the molded wall is effected by turbulence introduced in mold flow via gate design and by reduced back pressure which allows faster mold flow through the gate and higher turbulence. Contact resistance between the bosses142,146and conductive fibers is effected by conductive fibers concentration as well as with distribution.