Patent ID: 12224129

DESCRIPTION OF EMBODIMENTS

A stacked film capacitor that forms the basis of a stacked film capacitor according to one or more embodiments of the present disclosure typically includes a body cut from an elongated stack and thus is to have cut surfaces with improved insulation. Patent Literature 1 describes a stacked polypropylene film capacitor including polypropylene films as dielectric films and including cover films containing a polyolefin hot-melt resin melted and bonded externally to exposed two side surfaces that are adjacent to two side surfaces with metal-sprayed electrodes. The cover films reduce discharge from the two externally exposed side surfaces under a voltage being applied.

FIG.1is a perspective view of an example stacked film capacitor according to an embodiment of the present disclosure.FIG.2is a cross-sectional view taken along line II-II inFIG.1.FIG.3is a cross-sectional view taken along line inFIG.1. As illustrated inFIGS.1to3, a stacked film capacitor A includes a film capacitor body3and a pair of a first metal-sprayed electrode4aand a second metal-sprayed electrode4b. The film capacitor body3may also be simply referred to as the body3. The body3includes a stack of first dielectric films1a, first metal films2a, second dielectric films1b, and second metal films2b. The body3is rectangular and includes a pair of first surfaces3aand3bopposite to each other in the stacking direction in which the dielectric films and the metal films are stacked, a pair of first side surfaces3cand3d, and a pair of second side surfaces3eand3f. The pairs are both located between the first surfaces3aand3bto connect the first surfaces3aand3b. In the figures referred to below, the dimensions of the components of the body3are exaggerated for ease of explanation. The thicknesses of the actual components are much smaller than the thicknesses of the illustrated components of the body3. The metal films2aand2bare deposited on each of the at least one dielectric film1aand1bby vapor deposition.

The first metal-sprayed electrode4ais formed on the first side surface3cof the body3, and the second metal-sprayed electrode4bis formed on the first side surface3dof the body3both through metal spraying. Cover films16aand16bthat are electrically insulating are located on the second side surfaces3eand3fof the body3.

As illustrated inFIG.2, the body3in the stacked film capacitor A includes first metalized films6aand second metalized films6bthat are alternately stacked on each other. Each first metalized film6aincludes the first metal film2aon a surface1acof the first dielectric film1a. Each second metalized film6bincludes the second metal film2bon a surface1bcof the second dielectric film1b. Each first metal film2ais electrically connected to the first metal-sprayed electrode4aon the first side surface3cof the body3. Each second metal film2bis electrically connected to the second metal-sprayed electrode4bon the first side surface3dof the body3. As illustrated inFIG.1, a first direction x refers to the direction in which the first metal-sprayed electrode4aand the second metal-sprayed electrode4bare located, and a second direction y refers to the direction in which the cover films16aand16bare located. A third direction z refers to the thickness direction of the first dielectric films1aand the second dielectric films1b, or more specifically, the stacking direction.

Each first metalized film6aincludes the first dielectric film1aand the first metal film2aon the surface1ac. Each first metalized film6aincludes, on the surface1acadjacent to a side surface1afwithout the first metal film2abeing formed, or in other words, in an area on which the first dielectric film1ais exposed, an insulating margin7aextending continuously in the second direction y.

Each second metalized film6bincludes the second metal film2bon the surface1bcof the second dielectric film1b. Each second metalized film6bincludes, on the surface1bcadjacent to a side surface1bfwithout the second metal film2bbeing formed, or in other words, in an area on which the second dielectric film1bis exposed, an insulating margin7bextending continuously in the second direction y.

As illustrated inFIG.2, the metalized films6aand6bare stacked on each other with a slight deviation from each other in the first direction x, which is also referred to as the width direction.

Any potential difference between the first metal film2aand the second metal film2bgenerates capacitance in an active area8in the first metal film2aand the second metal film2boverlapping each other across the first dielectric film1aor the second dielectric film1b.

The stacked film capacitor A described above is obtained in the manner described below. The first metalized film6aand the second metalized film6bthat are both elongated are stacked on each other with a slight deviation from each other in the first direction x or the width direction, thus forming a stack. The first metal-sprayed electrode4ais formed on the first side surface3cin the first direction x of the resultant stack, and the second metal-sprayed electrode4bis formed on the first side surface3d. The stack including the metal-sprayed electrodes4, or specifically the first metal-sprayed electrode4aand the second metal-sprayed electrode4b, is cut in the first direction x into individual elements. The metal-sprayed electrodes4may be formed on the individual bodies3cut from the stack. The cut surfaces resulting from the stack being cut are the second side surfaces3eand3fof the bodies3.

The features common to the first metalized film6aand the second metalized film6bin the stacked film capacitor A according to the present embodiment will be described below. InFIG.3, the components may be simply referred to as dielectric films1, metal films2, the metal-sprayed electrodes4, or metalized films6without the reference signs a and b.

As illustrated inFIGS.1to3, in the present embodiment, the film capacitor A includes, among the four side surfaces3c,3d,3e, and3fof a film capacitor device12including the stack of the metalized film6aand6b, the two side surfaces3eand3fadjacent to the other two side surfaces3cand3dwith the metal-sprayed electrodes4aand4b. The side surfaces3eand3fare located on the two ends of the film capacitor device12in the length direction (lateral direction inFIG.3) and are entirely covered with cover films16aand16bfor separation from outside. The two cover films16aand16bare melted and bonded (bonded by melting) to the side surfaces of the dielectric films1aand1bin the metalized films6aand6bexposed on the side surfaces3eand3f.

In the present embodiment, the film capacitor A is thus less likely to have a leakage current from the two side surfaces3eand3f, and can have a longer creepage distance between the metal films2aand2bin the metalized films6aand6bto reduce short-circuiting resulting from discharge between the metal films2aand2band to have an improved withstand voltage. The side surfaces of the dielectric films1aand1bin the metalized films6aand6bexposed on the side surfaces3eand3fare fully in close contact with the cover films16aand16bto prevent entry of moisture and air between the side surfaces of the dielectric films1aand1b(and thus the side surfaces of the metalized films6aand6b) and the cover films16aand16b.

The two cover films16aand16binclude polyester hot-melt films containing a polyester hot-melt resin similar to polyarylate in the dielectric films1aand1bin the metalized films6aand6band having high performance in thermal melting and bonding (melting and bonding performance) to polyarylate. Using the two cover films16aand16bcontaining the resin material, the cover films16aand16bare melted and bonded reliably and firmly to the side surfaces of the dielectric films1aand1bin the metalized films6aand6bexposed on the two side surfaces3eand3fof the film capacitor device12.

FIG.4is a schematic diagram of a test piece for examining the bonding state. A polyethylene terephthalate plate B containing a resin similar to polyarylate was bonded to a rectangular plate A with a vertical width a of 25 mm, a horizontal width b of 33 mm, and a thickness t of 2 to 5 mm including a polyarylate plate by heat treatment at 100° C. A polycarbonate plate B was also bonded to a rectangular plate A by heat treatment at 180° C. The bonding state of each test piece was examined to reveal that the polyethylene terephthalate plate and the polycarbonate plate were both bonded firmly to the polyarylate plates.

The two cover films16aand16bare to contain a polyester hot-melt resin, although the two cover films16aand16bmay contain a polyester hot-melt resin of any type or with any structure. More specifically, various known polyester hot-melt resins can be used as a material for the two cover films16aand16b.

The two cover films16aand16bincluding such a polyester hot-melt resin are formed to cover the entire surfaces of the side surfaces3eand3fof the film capacitor device12using, for example, the methods described below.

The first method is, for example, to form a film of polyester hot-melt resin with a predetermined thickness by spraying the polyester hot-melt resin in a melted state with heat onto the entire side surfaces3eand3fof the film capacitor device12using a nozzle or by applying the resin using a roller. The ends of the metalized films6aand6bincluding the side surfaces of the dielectric films1aand1bexposed on the side surfaces3eand3fof the film capacitor device12are then melted with the heat of the polyester hot-melt resin in a melted state. These components are then cooled to solidify. This allows the two cover films16aand16beach containing the polyester hot-melt film to cover the entire side surfaces3eand3fof the film capacitor device12and to be melted and bonded to the side surfaces of the dielectric films1aand1b.

The second method is, for example, to form a polyester hot-melt film on the entire side surfaces3eand3fof the film capacitor device12, and heat and melt the polyester hot-melt film. The ends including the side surfaces of the dielectric films1aand1bin the metalized films6aand6bexposed on the side surfaces3eand3fof the film capacitor device12may be melt These components are then cooled to solidify. This also allows the two cover films16aand16bto cover the entire side surfaces3eand3fof the film capacitor device12and to be melted and bonded to the side surfaces of the dielectric films1aand1b. The polyester hot-melt film to be formed on the side surfaces3eand3fof the film capacitor device12may be, for example, an extruded product in a semi-melted state formed with a predetermined die, in addition to a common film.

The cover films16aand16bon the side surfaces3eand3fof the film capacitor device12may have any thickness that may be, for example, about 0.1 to 1000 μm. The cover films16aand16bwith a thickness of less than 0.1 μm may be too thin to achieve a sufficiently long creepage distance of the metal films2aand2bin the metalized films6aand6band to have a sufficiently improved withstand voltage. The cover films16aand16bhaving a thickness exceeding 1000 μm may not achieve an improved effect and may have, for example, an increased cost of the cover films16aand16b. The cover films16aand16bmay thus have a thickness of less than or equal to 1000 μm.

The polyester hot-melt resin in the two cover films16aand16bmay have a lower melting point than polyarylate in the dielectric films1aand1band have high wettability with the polyarylate to heat and melt the side surfaces of the dielectric films1aand1bin the metalized films6aand6bto which the cover films16aand16bare melted and bonded. A material with high wettability maintains the bonding strength with the polyarylate.

In manufacturing the film capacitor device12, elongated protective films are formed on the two end faces of an elongated stack including multiple elongated metalized films6aand6bthat are stacked alternately with a deviation between them in the width direction to form an elongated film capacitor device base material. This base material is then cut in the width direction using a cutting blade such as a rotary saw blade at, for example, multiple positions at a predetermined distance between them in the length direction. This produces multiple film capacitor devices12at a time. The two side surfaces3cand3dof the film capacitor device12in the width direction are the surfaces to receive the two metal-sprayed electrodes4aand4b, whereas the two side surfaces3eand3fof the film capacitor device12in the length direction, including the cut surfaces of the film capacitor base material, are the surfaces to receive the two cover films16aand16b.

When the cover films16aand16bare applied at temperatures greatly exceeding 220° C., which is the glass transition point (Tg) of polyarylate, the film capacitor device12can soften and deform or cause self-healing failure. Thus, the cover films16aand16bcontain a polyester resin with a melting point of 150 to 250° C. that is less than or similar to the glass transition point Tg of 220° C. with high wettability and with a glass transition point Tg of 50 to 160° C.

The polyester hot-melt resin in the cover films16aand16bhas a lower melting point than polyarylate as a resin material in the dielectric films1aand1b. The polyester hot-melt resin as the material in the cover films16aand16bthus reduces deformation of the dielectric films1aand1b, and reduces self-healing failure resulting from the heat of the polyester hot-melt resin in a melted state in the cover films16aand16bwhen the cover films16aand16bare melted and bonded to the side surfaces3eand3fof the dielectric films1aand1b(when the cover films16aand16bare formed on the side surfaces3eand3fof the film capacitor device12). The polyester hot-melt resin with a low glass transition point Tg has high wettability with polyarylate and maintains the bonding strength with polyarylate, thus reducing the likelihood that the cover films16aand16bmelted and bonded to the dielectric films1aand1bare separate from the dielectric films1aand1b. This structure can satisfy the operating temperatures of 125 to 150° C. for high-temperature resistant film capacitors.

The polyester hot-melt resin in the cover films16aand16bhas a melt viscosity in the range of 500 to 50000 mPa·s at 150 to 250° C.

As described above, in the present embodiment, the film capacitor A includes the two cover films16aand16bcovering the entire surfaces of the remaining two side surfaces3eand3fother than the side surfaces3cand3dto receive the metal-sprayed electrodes4aand4bto reduce a leakage current from the two side surfaces3eand3fand provide a longer creepage distance between the metal films2aand2bof the metalized films6aand6b. The two cover films16aand16bcontaining the polyester hot-melt resin are melted and bonded to the side surfaces of the dielectric films1aand1bincluding polyester of the metalized films6aand6bexposed on the two side surfaces3eand3f. The side surfaces of the dielectric films1aand1bare thus fully in close contact with the cover films16aand16bwithout small gaps between them. This effectively and reliably reduces the entry of water vapor or air between the side surfaces of the dielectric films1aand1band the cover films16aand16b. This is combined with an increase in the creepage distance between the metal films2aand2bto reduce degradation of the dielectric films1aand1band the metal films2aand2bdue to contact with water vapor. This also reduces discharge between the metal films2aand2bto effectively improve the withstand voltage.

The surfaces of the metal films2aand2band the metal-sprayed electrodes4aand4bare oxidized to contain Al—O—Al, a hydroxyl group, or a carboxyl group. A polyolefin resin used for known cover films is a low polar resin and contains no carboxyl group or no hydroxyl group. The polyolefin resin thus interacts less with a metal oxide (with low van der Waals force and without a hydrogen bond). A polyester resin used for the cover films16aand16bis a polar resin, and contains an ether bond, a carbonyl group, a carboxyl group, or a hydroxyl group, which interacts highly with a metal oxide (with high van der Waals force and including a hydrogen bond). The cover films16aand16bin the present embodiment interact with the metal films2aand2band with the metal-sprayed electrodes4aand4bmore than known cover films. This effectively reduces the likelihood that the cover films16aand16bmelted and bonded to the side surfaces3eand3fare separated.

The film capacitor A simply including the thin cover films16aand16b, each including a resin film, on the two side surfaces3eand3fmay produce the advantageous features described above. The above features can be achieved without the entire film capacitor A becoming larger or the costs becoming higher.

Thus, the film capacitor according to the present embodiment can substantially reduce a leakage current, maintain the expected capacitor performance stably for a longer period, and improve the withstand voltage without increasing the size or the production cost of the film capacitor.

FIG.5is a schematic perspective view of a connected capacitor in an example. InFIG.5, a case and an external resin covering the capacitor surface are not illustrated for ease of explanation. A connected capacitor C includes multiple stacked film capacitors connected in parallel with a pair of busbars21and23. The busbars21and23include terminals21aand23afor external connection and lead terminals21band23b. The lead terminals21band23bare connected to the corresponding metal-sprayed electrodes4aand4bin the film capacitor.

The film capacitor in the connected capacitor C may include the film capacitor A with the cover films16aand16b. The resultant connected capacitor C may have insulation resistance less likely to decrease.

The connected capacitor C may include at least one film capacitor A, and may include two or more film capacitors A. The connected capacitor C includes multiple film capacitors, for example, four capacitors aligned with one another as illustrated inFIG.4, and includes the busbars21and23attached to the metal-sprayed electrodes at the two ends of the body3with a bond.

The connected capacitor C may include the film capacitors arranged horizontally as illustrated inFIG.5or stacked vertically. The film capacitors may be arranged in the direction perpendicular to the first direction x in which the metal-sprayed electrodes4are located.

FIG.6is a schematic diagram describing an example inverter.FIG.6illustrates an inverter D that converts direct current (DC) to alternating current (AC). As illustrated inFIG.6, the inverter D includes a bridge circuit31and a capacitance portion33. The bridge circuit31includes switching elements such as insulated-gate bipolar transistors (IGBTs) and diodes. The capacitance portion33is across the input terminals of the bridge circuit31to stabilize the voltage. The inverter D includes the film capacitor A as the capacitance portion33.

The inverter D is connected to a booster circuit35that raises the voltage of a DC power supply. The bridge circuit31is connected to a motor generator M as a drive source.

FIG.7is a schematic diagram of an electric vehicle.FIG.7illustrates a hybrid electric vehicle (HEV) as an example of the electric vehicle.

The electric vehicle E includes a motor41, an engine43, a transmission45, an inverter47, a power supply (battery)49, front wheels51a, and rear wheels51b.

The electric vehicle E includes an output unit, such as the motor41, the engine43, or both, as the drive source. The output from the drive source is transmitted to the pair of left and right front wheels51athrough the transmission45. The power supply49is connected to the inverter47, which is connected to the motor41.

The electric vehicle E illustrated inFIG.7also includes a vehicle electronic control unit (ECU)53and an engine ECU57. The vehicle ECU53centrally controls the entire electric vehicle E. The engine ECU57controls the rotational speed of the engine43and drives the electric vehicle E. The electric vehicle E further includes an ignition key55operable by, for example, a driver, and driving components such as an accelerator pedal and a brake (not illustrated). The vehicle ECU53receives an input drive signal in response to an operation on a driving component performed by, for example, the driver. The vehicle ECU53outputs, based on the drive signal, an instruction signal to the engine ECU57, the power supply49, and the inverter47as a load. In response to the instruction signal, the engine ECU57controls the rotational speed of the engine43and drives the electric vehicle E.

The inverter47in the electric vehicle E includes the inverter D, which includes the film capacitor A as the capacitance portion33. The electric vehicle E includes the film capacitor A that has insulation resistance less likely to decrease. In a harsh environment such as in an engine part of the electric vehicle E, the film capacitor A may have insulation resistance less likely to decrease over a long period. The electric vehicle E thus allows more stable current control performed by controllers such as ECUs.

In addition to HEVs, the inverter D in the embodiment is also applicable to various power converting products such as electric vehicles (EVs), fuel cell vehicles, electric bicycles, power generators, and solar cells.

The present disclosure may be implemented in the following forms.

In one or more embodiments of the present disclosure, a film capacitor includes a stack including at least one dielectric film including a polyarylate film and a plurality of metal films being alternate to each other, cover films containing a polyester hot-melt resin and located on two first side surfaces of the stack opposite to each other in a first direction orthogonal to a stacking direction of the stack, and metal-sprayed electrodes on two second side surfaces of the stack opposite to each other in a second direction perpendicular to the first direction and orthogonal to the stacking direction.

In one or more embodiments of the present disclosure, a connected capacitor includes a plurality of film capacitors including the above film capacitor, and a busbar connecting the plurality of film capacitors.

In one or more embodiments of the present disclosure, an inverter includes a bridge circuit including a switching element, and a capacitance portion connected to the bridge circuit. The capacitance portion includes the above film capacitor.

In one or more embodiments of the present disclosure, an electric vehicle includes a power supply, an inverter connected to the power supply and being the above inverter, a motor connected to the inverter, and wheels drivable by the motor.

In one or more embodiments of the present disclosure, the film capacitor can reduce discharge from the metal films due to gaps between the cover films and the metal films.

In one or more embodiments of the present disclosure, the connected capacitor can have insulation resistance less likely to decrease.

In one or more embodiments of the present disclosure, the inverter includes the film capacitor that can have insulation resistance less likely to decrease.

In one or more embodiments of the present disclosure, the electric vehicle allows more stable current control performed by the controllers such as the ECUs.

Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the embodiments described above, and may be changed or varied in various manners without departing from the spirit and scope of the present disclosure. The components described in the above embodiments may be entirely or partially combined as appropriate unless any contradiction arises.

REFERENCE SIGNS

A film capacitorC connected capacitorD inverterE electric vehicle1,1a,1bdielectric film2,2a,2bmetal film3body3a,3bfirst surface3c,3dfirst side surface3e,3fsecond side surface4,4a,4bmetal-sprayed electrode6,6a,6bmetalized film7,7a,7binsulating margin12film capacitor device16a,16bcover film21,23busbar31bridge circuit33capacitance portion35booster circuit41motor43engine45transmission47inverter49power supply51afront wheel51brear wheel53vehicle electronic control unit (ECU)55ignition key57engine electronic control unit (ECU)