Motor-driven compressor

Abstract

Motor-driven compressor (11) with: a compression section (18) which compresses fluid, an electric motor (19) which drives the compression section (18), an inverter device (30) which drives the electric motor (19), and a metal housing (14) accommodating the inverter device (30), wherein the inverter device (30) an inverter circuit (31) which converts direct current power into alternating current power, and a noise reduction device (32) arranged on an input side of the inverter circuit (31), the noise reduction device (32) reducing common-mode noise and differential-mode noise contained in the DC power before supply to the inverter circuit, the interference reduction device (32) a common mode choke coil (34), and a smoothing capacitor (35) which forms a low-pass filter circuit (36) together with the common-mode choke coil (34), the common mode choke coil (34) a loop-shaped core (50), a first winding (60) wound around the core (50), a second winding (61) wound around the core (50), the second winding (61) being located away from the first winding (60) and opposite the first winding (60), and a loop-shaped conductor (70) covering the core (50) while extending over the first winding (60) and the second winding (61), where the conductor (70) has sections which are opposite to each other and are located away from each other, with the first winding (60) and the second winding (61) therebetween, the conductor (70) has a heat radiation section (71) which is thermally coupled to the housing (14), and an average value of the electrical resistance value per unit length in a circumferential direction of the heat radiation portion (71) of the conductor (70) is greater than an average value of the electrical resistance value per unit length of locations other than the heat radiation portion (71).

Description

BACKGROUND1. Field of InterestThe following description relates to a motor driven compressor.2. Description of the Prior ArtDE 10 2018 100 048 A1 discloses an on-board fluid machine including a housing configured to allow fluid to flow into the housing, an electric motor accommodated in the housing, and a driver supplied by a DC power supply and driving the electric motor. The driver includes a low pass filter circuit and an inverter circuit. The low pass filter circuit includes a common mode choke coil and a capacitor. The driver further includes an attenuation unit located at a position where magnetic field lines produced by the common mode choke coil generate an eddy current.International Patent Publication No. WO 2017 / 170 817 A1 describes a motor driven compressor with a common mode choke coil used for an inverter device driving an electric motor. The common mode choke coil described in the publication is covered with a conductor to achieve a damping effect by which a common mode current through the conductor generates an induced current in the conductor, which is converted into thermal energy.When the reactor is covered with the conductor, heat is likely to be trapped inside. This requires a structure against heating. However, the conductor must have a certain electric resistance value in order to have the damping effect. In this case, the conductor generates heat. This requires measures to efficiently transfer the heat of the conductor to a heat radiating member.SummaryIt is an object of the present invention to provide a motor-driven compressor having an improved heat radiation capability.This object is achieved by a motor driven compressor as set out in claim 1.Advantageous embodiments are specified in the dependent patent claims.According to a general aspect, an engine driven compressor is provided. The motor-driven compressor includes a compression portion that compresses fluid, an electric motor that drives the compression portion, an inverter device that drives the electric motor, and a metal case in which the inverter device is accommodated. The inverter apparatus includes an inverter circuit that converts DC power into AC power, and noise reducer disposed on an input side of the inverter circuit, in which the noise reducer reduces common mode noise and differential mode noise included in the DC power before being supplied to the inverter circuit. The interference reducer includes a common mode choke coil and a smoothing capacitor that forms a low-bass filter circuit together with the common mode choke coil. The common mode choke coil includes a loop-shaped core, a first winding wound around the core, a second winding wound around the core, in which the second winding is located away from the first winding and opposite to the first winding, and a loop-shaped conductor covering the core while extending over the first winding and the second winding. The conductor has portions that are opposed to each other and are located away from each other between the first winding and the second winding, the conductor has a heat radiation portion that is thermally coupled to the housing, and an average value of the electric resistance value per unit length in a circumferential direction of a heat radiation portion of the conductor is larger than an average value of the electric resistance value per unit length from locations other than the heat radiation portion.Other features and embodiments will become apparent from the following detailed description, drawings and claims.Brief Description of the DrawingsFIG. 1 is a schematic diagram illustrating an overall structure of an in-vehicle motor-driven compressor. FIG. 2 is a circuit diagram of a driving device and an electric motor. FIG. 3A is a plan view of the driving device. FIG. 3B is a front view of the driving device as viewed from a direction A in FIG. 3A. FIG. 4A is a bottom view of the driving device as viewed from the direction C in FIG. 3B. FIG. 4B is a side view of the driving device as viewed from a direction B in FIG. 3A. FIG. 5 is a cross-sectional view taken along line 5- 5 in FIG. 3A. FIG. 6 is a perspective view of a core and windings. FIG. 7 shows a perspective illustration of a common mode choke coil. FIG. 8 is a perspective view illustrating a metal film. FIG. 9 is a perspective view illustrating a metal film in a modification. FIG. 10 is a perspective view illustrating a metal film in another modification. FIG. 11 is a perspective view illustrating a metal film for comparison.In the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and representation of elements in the drawings may be exaggerated for clarity, illustration, and ease of representation.DETAILED DESCRIPTIONThis description provides a thorough understanding of the described methods, apparatus, and / or systems. Modifications and equivalents of the described methods, apparatus, and / or systems will be apparent to those skilled in the art. Operation procedures are exemplary and may be changed as apparent to those skilled in the art, except for procedures that necessarily occur in a certain order. Descriptions of functions and constructions known to those skilled in the art may be omitted.Example embodiments have different shapes, and are not limited to the described examples. However, the examples described are exhaustive and will provide those skilled in the art with the full scope of the disclosure.An embodiment of the present invention will be described below with reference to the drawings. An in-vehicle motor-driven compressor 11 according to the present embodiment includes a compression portion that compresses fluid, which is a refrigerant, and is used in an in-vehicle air conditioning apparatus 10. That is, the fluid compressed in the in-vehicle motor-driven compressor 11 is a refrigerant.As shown in FIG. 1, the in-vehicle air conditioner 10 includes the in-vehicle motor-driven compressor 11 and an external refrigerant circuit 12 that supplies a refrigerant to the in-vehicle motor-driven compressor 11. The external refrigerant circuit 12 includes a heat exchanger, an expansion valve, and the like. The in-vehicle motor-driven compressor 11 compresses refrigerant, and the external refrigerant circuit 12 performs heat exchange and expansion of the refrigerant. This cools or warms the passenger compartment.The in-vehicle air conditioner 10 includes an air conditioner ECU 13 that controls the entire in-vehicle air conditioner 10. The air conditioner ECU 13 is configured to acquire parameters such as the temperature of the passenger compartment and a target temperature of the in-vehicle air conditioner 10. The air conditioner ECU 13 sends various kinds of commands such as an on-off command to the in-vehicle motor-driven compressor 11 based on the parameters.The in-vehicle motor-driven compressor 11 includes a housing 14 having a suction port 14 athrough which refrigerant is drawn in from the external refrigerant circuit 12. The housing 14 is made of a thermally conductive material such as aluminum. The housing 14 is grounded to the body of the vehicle.The housing 14 has a suction housing member 15, an exhaust housing member 16, and a cover member 25 which are integrally assembled with each other. The suction housing member 15 has a tubular shape having a closed end and an open end. The suction housing member 15 has a plate-shaped bottom wall 15a and an annular side wall 15b extending from the periphery of the bottom wall 15a toward the exhaust housing member 16. The exhaust case member 16 is attached to the intake case member 15 while closing the opening of the intake case member 15. Accordingly, an internal space is defined in the housing 14.The suction port 14 ais provided in the side wall 15 bof the suction housing member 15. Specifically, the suction port 14 ais formed in a portion of the side wall 15 bthat is closer to the bottom wall 15 athan to the exhaust case member 16.The housing 14 has an ejection port 14 bthrough which coolant is ejected. The ejection port 14 bis provided in a portion of the ejection housing member 16 that is opposed to the bottom wall 15 a.The in-vehicle motor-driven compressor 11 includes a rotation shaft 17, a compression portion 18, and an electric motor 19 accommodated in the housing 14. The rotary shaft 17 is rotatably supported by the housing 14. The axial direction of the rotating shaft 17 corresponds to the thickness direction of the bottom pan 15 a, that is, the axial direction of the side wall 15 b. The rotary shaft 17 is coupled to the compressing portion 18.The compressing portion 18 is located at a portion of the housing 14 that is closer to the discharge port 14 bthan to the suction port 14 a(the bottom wall 15 a). When the rotary shaft 17 rotates, the compressing portion 18 compresses refrigerant drawn into the housing 14 through the suction port 14 aand discharges the compressed refrigerant through the discharge port 14 b. The compression portion 18 may be any of a scroll type, a piston type, and a vane type.The electric motor 19 is disposed in the housing 14 between the compressing portion 18 and the bottom wall 15 a. The electric motor 19 drives the compressing portion 18 by rotating the rotating shaft 17. The electric motor 19 includes a cylindrical rotor 20 fixed to the rotating shaft 17 and a starter 21 fixed to the housing 14. The stator 21 includes a cylindrical stator core 22 and coils 23 wound around the teeth of the stator core 22. The rotor 20 faces the stator 21 in the radial direction of the rotary shaft 17. When currents are supplied to the coils 23, the rotor 20 and the rotating shaft 17 rotate, and accordingly, the compressing portion 18 compresses refrigerant.The in-vehicle motor-driven compressor 11 also includes a driving device 24 that drives the electric motor 19 and receives DC power, and a cover member 25 that defines an accommodation chamber S 0 for accommodating the driving device 24.The cover member 25 has a tubular shape having a closed end and an end opened to the bottom wall 15 aof the intake housing member 15. The cover member 25 is attached to the bottom wall 15a by bolts 26 with the open end abutting the bottom wall 15a. The opening of the cover member 25 is closed by the bottom wall 15 a. The accommodation chamber S 0 is contained in the housing 14.The accommodation chamber S 0 is located on the side of the bottom wall 15 aopposing the electric motor 19. The compression portion 18, the electric motor 19, and the drive device 24 are arranged in this order in the axial direction of the rotary shaft 17.The cover member 25 has a connector 27. The connector 27 is electrically connected to the driving device 24. DC power is supplied from an in-vehicle electric storage device 28 mounted on the vehicle via the connector 27 of the driving device 24. The air conditioner ECU 13 and the driving device 24 are electrically connected to each other via the connector 27. The in-vehicle electric storage device 28 is a vehicle-mounted DC power supply that is a rechargeable battery, a capacitor, or the like.The driving device 24 includes a circuit board 29, an inverter device 30 disposed on the circuit board 29, and two connection lines EL 1 and EL 2. The connection lines EL 1 and EL 2 are used for electrically connecting the connector 27 to the inverter device 30.The circuit board 29 is flat. The circuit board 29 is located at a predetermined distance from the bottom wall 15 ain the axial direction of the rotation shaft 17. As shown in FIG. 2, the inverter device 30 includes an inverter circuit 31 and a noise reducer 32. The inverter circuit 31 converts DC power into AC power. The noise reducer 32 is disposed at the input side of the inverter circuit 31, and reduces the common mode noise and the differential mode noise included in the DC power before being supplied to the inverter circuit 31.The electrical configuration of the electric motor 19 and the driving device 24 will be described below.As shown in FIG. 2, the coils 23 of the electric motor 19 are of a three-phase structure including a U-phase coil 23 u, a V-phase coil 23 v, and a W-phase coil W. The coils 23 uto 23 bare connected in a star connection.The inverter circuit 31 includes U-phase switching elements Qu 1, Qu 2 corresponding to the U-phase coil 23 u, V-phase switching elements Qv 1, Qv 2 corresponding to the V-phase coil 23 v, and W-phase switching elements Qw 1, Qw 2 corresponding to the W-phase coil 23 w. Each of the switching elements Qu 1 to Qw 2 is a power switching element such as an insulated gate bipolar transistor (IGBT). The switching elements Qu 1 to Quw 2 include free wheeling diodes (body diodes) Du 1 to Db 2.The U-phase switching elements Qu 1, Qu 2 are connected in series to each other through a connection wire connected to the U-phase coil 23 u. The series circuit body of the U-phase switching elements Qu 1 and Qu 2 is electrically connected to the connection lines EL 1, EL 2. The series connection body receives DC power from the in-vehicle electric storage device 28.Except for the connected coil, the other switching elements Qv 1, Qv 2, Qw 1, Qw 2 have the same connection structure as the U-phase switching elements Qu 1, Qu 2.The driving device 24 includes a controller 33 that controls the operation of the switching elements Qu 1 to Qw 2. The control device 33 is constructed, for example, by at least one special hardware circuit and / or at least one processor(s) which operates in accordance with a computer program (software). The processor includes a CPU memory such as a RAM and a ROM. The memories store program code or instructions configured to cause the processor to execute various types of processes. The memory or computer readable medium includes any type of medium accessible by general purpose computers and special purpose computers.The controller 33 is electrically connected to the air conditioner ECU 13 via the connector 27. Based on commands from the air conditioner ECU 13, the controller 33 periodically turns on and off the switching elements Qu 1 to Qw 2. Specifically, the controller 33 performs pulse width modulation (PWM) control on the switching elements Qu 1 to Qw 2 based on commands from the air conditioner ECU 13. More specifically, the controller 33 uses a carrier signal and a command voltage value signal (comparison signal) to generate control signals. The controller 33 performs ON-OFF control on the switching elements Qu 1 to Qw 2 by using the generated control signals, thereby converting the DC power into AC power.The noise reducer 32 includes a common mode choke coil 34 and an X capacitor 35. The X capacitor 35, which is a smoothing capacitor, and the common mode choke coil 34 form a low pass filter circuit 36. The low-pass filter circuit 36 is disposed between the connector 27 and the inverter circuit 31 in terms of the circuit arrangement.The common mode choke coil 34 is arranged on the connecting lines EL 1 and EL 2. The X capacitor 35 is disposed at an output stage of the common mode choke coil 34 (closer to the inverter circuit 31). The X capacitor 35 is electrically connected to the connection lines EL 1 and EL 2. The common mode choke coil 34 and the X capacitor 35 form an LC resonant circuit. The low-pass filter circuit 36 according to the present embodiment is an LC resonant circuit having the common mode choke coil 34.Y capacitors 37, 38 are connected in series. Specifically, the driving device 24 includes a bypass line EL 3 that connects a first end of the first Y capacitor 37 and a first end of the second Y capacitor 38 to each other. The bypass line EL 3 is grounded to the body of the vehicle.The series circuit body of the Y capacitors 37, 38 is disposed between the common mode choke coil 34 and the X capacitor 35, and is electrically connected to the common mode choke coil 34. A second end of the first Y capacitor 37 is connected to a portion of the first connection line EL 1 that connects the first winding of the common mode choke coil 34 and the inverter circuit 31 to each other. A second end of the second Y capacitor 38 is connected to a portion of the second connection line EL 2 that connects the second winding of the common mode choke coil 34 and the inverter circuit 31 to each other. The vehicle includes, as an in-vehicle device, for example, a power control unit (PCU) 39 that is separate from the drive device 24. The PCU 39 uses DC power from the in-vehicle electric storage device 28 to drive a travel motor mounted in the vehicle. According to the present embodiment, the PCU 39 and the drive device 24 are connected in parallel with the in-vehicle electric storage device 28. The in-vehicle electric storage device 28 is shared by the PCU 39 and the drive device 24.The PCU 39 includes a boost converter 40 and a power supply capacitor 41. The boost converter 40 includes a boost switching element, and periodically switches the boost switching element on and off to boost the DC power from the in-vehicle electric storage device 28. The power supply capacitor 41 is connected in parallel to the in-vehicle electric storage device 28. Although not illustrated, the PCU 39 includes a vehicle drive inverter that converts the DC power boosted by the boost converter 40 into drive power capable of driving the traction motor.In the above-described configuration, a disturbance generated by switching operations of the boost switching element flows into the driving device 24 as a push-pull disturbance. In other words, the push-pull noise includes a noise component corresponding to the switching frequency of the boost switching element.The configuration of the common mode choke coil 34 at an arrangement location serving as a part of the driving device will be described below with reference to FIGS. 3A, 3B, 4A, 4B, and 5. In the drawings, a triaxial orthogonal coordinate system is defined in which the axial direction of the rotary shaft 17 in FIG. 1 is defined as the Z direction, and the directions perpendicular to the Z direction are defined as the X and Y directions.The common mode choke coil 34 is mounted on the printed circuit board 29. The common mode choke coil 34 is thermally connected to the bottom wall 15A. Thus, as shown in FIG. 5, heat Q generated in the common mode choke coil 34 is transferred to the bottom wall 15A. Specifically, heat generated in a metal film 70 is transferred to the bottom wall 15A via a heat paste 90.The common mode choke coil 34 is configured to limit transmission of high frequency noise generated in the vehicle-side PCU 39 to the compressor-side inverter circuit 31. Specifically, a differential-mode inductance of leakage magnetic fluxes is used as the L component in the low-pass filter circuit (LC filter) 36 that eliminates the differential-mode noise (differential mode noise). That is, the common mode choke coil 34 is configured to reduce the common mode noise and the differential mode noise (differential mode noise). According to the present embodiment, a single choke coil reduces the two kinds of noise without using a common mode choke coil and a differential mode (differential mode) choke coil, respectively.As shown in FIGS. 3A, 3B, 4A, 4B, and 5, the common mode choke coil 34 includes a loop-shaped core 50, a first winding 60, a second winding 61, and a metal film 70 that is a loop-shaped conductor.The core 50 has a square cross section as shown in FIG. 5, and has a rectangular shape in its entirety in the X-Y plane. As shown in FIGS. 3A and 5, the core 50 has an inner space Sp 1.The first winding 60 and the second winding 61 are wound around the core 50. The core 50 is rectangular and has two long side portions. One long side portion forms a first linear part 51, and the other long side portion forms a second linear part 52. That is, the core 50 includes a first linear part 51 and a second linear part 52 that are arranged in parallel to each other and extend linearly. At least a part of the first winding 60 is wound around the first linear part 51, and at least a part of the second winding 61 is wound around the second linear part 52. The winding directions of the two windings 60, 61 are reversed from each other. Further, the first winding 60 and the second winding 61 are located away from each other while being opposed to each other on the opposite sides from the central axis LC of the core 50.A plastic container (not shown) is provided between the core 50 and the coils 60 and 61. A protrusion (not shown) extends from the plastic container. The protrusion abuts against the metal film 70 to restrict the movement of the metal film 70. The metal film 70 is made of a copper foil. That is, the metal film 70 is a loop-shaped conductor. The thickness of the metal film 70 is 10 μm to 100 μm. For example, the thickness of the metal film 70 may be 35 μm. The reason for thinning the metal film 70 is to increase the resistance value when an induced current flows and convert the current into heat. However, when the metal film 70 is thinned, it is difficult to maintain its strength and original shape.The metal film 70 is band-shaped and endless. The width of the metal film 70 is constant, and the thickness of the metal film 70 is constant. The metal film 70 having a rectangular loop shape includes a set of a first linear part 71 and a second linear part 72 opposing each other and a set of a third linear part 73 and a fourth linear part 74 opposing each other, as shown in FIG. 4B. The first linear part 71 is opposed to the bottom wall 15A of the suction housing member 15. The first linear part 71 is a heat radiation portion in contact with the heat radiation surface SR, which is the surface of the bottom wall 15A. The first linear part 71 is thermally coupled to the housing 14. The third linear part 73 and the fourth linear part 74 extend from the bottom wall 15A.As shown in FIGS. 3A and 5, the metal film 70 covers the core 50 while extending over the first coil 60 and the second coil 61. Specifically, the metal film 70 is configured to completely cover the first coil 60 and the second coil 61 and partially cover the inner space Sp 1 of the core 50. Generally, the metal film 70 is configured to cover at least a part of the first coil 60, the second coil 61, and the inner space Sp 1 of the core 50. The inner space Sp 1 is defined between the first coil 60 and the second coil 61. The metal film 70 has portions that are opposite to each other and are located away from each other between the first coil 60 and the second coil 61, that is, on opposite sides of the internal space Sp 1.As shown in FIGS. 4B and 5, the metal film 70 includes a plastic layer 80 formed between the inner surface of the metal film 70 and the outer surfaces of the first coil 60 and the second coil 61. The plastic layer 80 provides insulation between the two windings 60, 61 and the metal film 70, as well as the strength and high rigidity of the metal film 70. The plastic layer 80 maintains the strength and shape of the thin metal film 70. The thickness of the plastic layer 80 is, for example, 10 μm. This is because it is desirable that the two windings 60 and 61 and the metal film 70 be as close to each other as possible, and an induced current easily flows by receiving a magnetic field generated by the windings 60 and 61 on the metal film 70 when the two windings 60 and 61 are close to each other.The metal film 70 and the plastic layer 80 are bonded to each other by an adhesive (not shown). The adhesive may be a thermosetting adhesive, a thermoplastic adhesive (hot melt adhesive), or a pressure sensitive adhesive.The metal film 70 may be formed as described below. First, a tape-shaped metal film integrated with a plastic layer by the same manufacturing method as a method for manufacturing a general flexible substrate is prepared. Then, the metal film is bent together with the plastic layer, and the opposite ends of the metal film are welded together to form the loop-shaped metal film 70. In this way, it is easy to form the metal film 70 into a loop shape, which improves productivity.As shown in FIG. 3A, the core 50 has exposed portions 53 and 54 not covered with the metal film 70. As shown in FIGS. 3B and 5, the thermal paste 90 is applied to the surface of the metal film 70 that is opposite to the bottom wall 15A of the suction housing member 15. Thus, the metal film 70 is thermally coupled to the suction housing member 50, namely, the housing 14, via the thermal paste 90.The push-pull mode (differential mode) will be described below with reference to FIGS. 6 and 7. As shown in FIG. 6, currents i 1 and i 2 flow by energization in the first winding 60 and the second winding 61, which generates magnetic fluxes φ 1, φ 2 in the core 50, and leakage magnetic fluxes φ 3, φ 4. The magnetic fluxes φ1, φ2are mutually opposite magnetic fluxes. As shown in FIG. 7, an induced current i 10 flows in the circumferential direction inside the metal film 70, so that magnetic fluxes are generated in the direction that resists the leakage magnetic fluxes φ 3, φ 4.In this way, an induced current (eddy current) i 10 flows in the circumferential direction of the metal film 70, so that a magnetic flux is generated in the direction resisting the leakage magnetic flux generated by the energization of the first coil 60 and the second coil 61. The induced current flowing in the circumferential direction refers to a current flow around the core 50.In the common mode, currents flow in the same direction in the first winding 60 and the second winding 61 when energized. This generates magnetic fluxes in the same direction into the core 50. during feeding in the common mode, magnetic flux is generated inside the core 50, while almost no leakage magnetic flux is generated. This maintains a common impedance.When the common mode choke coil 34 does not include the metal film 70, the Q factor of the low pass filter circuit 36, particularly, the Q factor of the LC resonant circuit including the common mode choke coil 34 and the X capacitor 35, is high. Therefore, the differential mode noise of frequencies close to the resonance frequency of the low pass filter circuit 36 cannot be easily reduced. In contrast, according to the present embodiment, the common mode choke coil 34 includes the metal film 70 at a location where eddy current is generated by magnetic fluxes (leakage magnetic fluxes φ3, φ4) generated in the common mode choke coil 34. The metal film 70 is disposed at the position passing through the loops of the leakage magnetic fluxes φ3, φ4. That is, the metal film 70 is configured to generate an induced current that generates magnetic fluxes in a direction that cancels out the leakage magnetic fluxes 43, 44. As a result, the metal film 70 acts to lower the Q factor of the low pass filter circuit 36, and thus the differential mode noise having the frequencies close to the resonance frequency of the low pass filter circuit 36 is also reduced by the low pass filter circuit 36.In this way, the present embodiment adopts a metal shield structure with the band-shaped and endless metal film 70 in the common mode choke coil. The common mode choke coil is used in the low pass filter circuit, so that the common mode noise is reduced. In addition, leakage magnetic fluxes which are utilized with respect to a differential mode current (differential mode current) are utilized to obtain a filtering capability suitable for reducing the differential mode disturbance (differential mode disturbance). That is, the use of the band-shaped and endless metal film 70 generates magnetic fluxes that resist the leakage magnetic fluxes generated during the feeding of the push-pull current (differential mode current), and flows a current and is consumed as heat in the metal film 70 by electromagnetic induction.Since the metal film 70 serves as a magnetic resistor, a damping effect is provided. This suppresses a resonance peak caused by the low pass filter circuit. During feeding in the common mode, magnetic flux is generated inside the core, while almost no leakage magnetic flux is generated. This maintains the common impedance. Further, by providing the plastic layer (polyimide layer) 80 on the inner circumferential side of the metal film (metal foil) 70, the shape of the metal film 70 is maintained, and insulation between the metal film 70 and the windings 60, 61 is ensured.When the circuit board 29 is disposed close to the common mode choke coil 34, an insulating spacer 200 may be disposed between the common mode choke coil 34 and the circuit board 29 as shown by imaginary lines in FIG. 3B. As shown in FIG. 8, the first linear part 71, which is a portion of the metal film 70 that is in contact with the heat radiation surface Sr, has a rectangular slit 75. The rectangular slit (through hole) 75 is located at the center portion of the metal film 70 in the width direction. Two long sides of the slot 75 extend in parallel to each other in the longitudinal direction of the metal film 70, and two short sides of the slot 75 extend in parallel to each other in the width direction of the metal film 70.As shown in FIG. 8, the width of the metal film 70 is W 1, the thickness of the metal film 70 is t 1, and the width of the slit 75 is W 2. The width of a portion of the metal film 70 extending along one of the long sides of the slit 75 is W3, and the width of a portion of the metal film 70 extending along the other of the long sides of the slit 75 is W4. In the metal film 70, the location of the first linear part 71 where the slit 75 is formed has a total cross-sectional area of W3×t1+W4×t1 in the longitudinal direction in which current flows. Locations other than the first linear part 71 have a total cross-sectional area of W 1×t 1 in the longitudinal direction in which current flows. Thus, the location of the first linear part 71 where the slit 75 is formed has a cross-sectional area smaller than a cross-sectional area of locations other than the first linear part 71. An electric resistance value (resistance value Ω) increases as the cross-sectional area decreases. As a result, the average value of the electric resistance value per unit length in the circumferential direction of the first linear part 71 that is in contact with the heat radiation surface Sr is larger than the average value of the electric resistance value per unit length in the circumferential direction at locations other than the first linear part 71. in this way, the slit 75 formed in the metal film 70 narrows the path of current flowing in the circumferential direction of the metal film 70, and the temperature is more likely to be raised higher than when a metal film 100 shown in FIG. 11 is used without the slit.As shown in FIG. 5, the thermal paste 90 functioning as a heat radiation resin material is coated inside the slit 75 extending through the metal film 70 in the thickness direction. Thus, the surfaces of the coils 60, 61 associated with the bottom wall 15 aare thermally coupled to the bottom wall 15 avia the thermal paste 90. In other words, the thermal paste 90 is applied within the slot 75 such that the first coil 60, the second coil 61, and the first linear part 71 are thermally coupled to the suction housing member 15, that is, the housing 14, via the thermal paste 90.The operation will be described belowCurrent flows inside the band-shaped and endless metal film 70, so that magnetic fluxes are generated in the direction that resists the stray magnetic fluxes, and heat is generated when power is consumed.As shown in FIG. 5, the metal film 70 is thermally connected to the bottom wall 15 a, so that heat Q generated in the common mode choke coil 34 is transferred to the bottom wall 15 a. Since heat generated in the metal film 70 is transferred via the thermal paste 90, the heat radiation performance for the heat radiation surface is improved.A more specific description will be given below.The common mode choke coil 34 is used for the inverter device 30 that drives the electric motor 13 in the in-vehicle motor-driven compressor 11. The windings 60, 61 of the common mode choke coil 34 are covered with the metal film 70 to achieve the attenuation effect by which a differential-mode current through the metal film 70 generates an induced current in the metal film 70, which is converted into thermal energy. The metal film 70 must have a certain electric resistance value in order to have the damping effect. In this case, the metal film 70 generates heat.As shown in FIG. 7, when an induced current i 10 flows into the metal film 70, the metal film 70 generates heat that raises the temperatures of the plastic layer 80 and the periphery of the metal film 70. This may cause the temperature to exceed the thermal resistance limit of the plastic layer 80. This may also cause the temperature to exceed the limits of the thermal resistance value of a joining material for joining portions at the ends of the metal film 70 and solder joining the first coil 60 and the second coil 61 to the circuit board 29.Usually, a structure that transfers the heat of the metal film 70 to the heat radiation surface Sr is effective. However, the layout of the circuit board 29 restricts portions where the metal film 70 and the heat radiation surface Sr are in contact with each other. Thus, portions of the metal film 70 that are farther away from the heat radiation surface Sr, such as the second linear part 72 that is farther away from the bottom wall 15 aof the suction housing member 15 as shown in FIG. 4B, have a high temperature, making it difficult to reduce the temperature of the entire metal film 70.According to the present embodiment, as shown in FIG. 8, the slit 75 is formed in the portion of the metal film 70 that is close to the heat radiation surface Sr. This provides a portion having a small cross-sectional area in the circumferential direction. Thus, the portion where the slit 75 is formed has a small cross-sectional area for the path of the current, so that the electric resistance value in the current path increases and more heat is generated. By increasing heat generation in the first linear part 71 having excellent heat radiation performance in this manner, the portion of the metal film 70 that is close to the heat radiation surface Sr has a high temperature. Further, the amount of heat transfer from the common mode choke coil 34 to the heat radiation surface Sr depends on the temperature difference of the boundary at which the common mode choke coil 34 and the heat radiation surface Sr are thermally in contact with each other. Thus, the amount of heat transfer increases as the temperature of the first linear part 71 rises, which efficiently transfers the heat of the metal film 70 to the heat radiation surface Sr and reduces temperatures of the entire metal film 70.When a push-pull current flows, the temperatures of the windings 60, 61 increase, so that the temperatures of the core 50 and the like in contact with the windings 60, 61 also increase. In an attempt to apply heat paste 90 to the coils 60, 61 to transfer heat to the heat radiation surface Sr, the heat paste 90 cannot be applied to the coils 60, 61 because the metal film 70 covers the coils 60, 61. Thickening the windings 60, 61 to reduce the electric resistance value will increase the size of the windings 60, 61 so that the windings 60, 61 cannot be applied to an in-vehicle motor-driven compressor.According to the present embodiment, as shown in FIG. 5, the slit 75 is formed in the portion of the metal film 70 that is close to the heat radiation surface Sr, and the heat paste 90 is applied to the coils 60, 61 to improve the heat radiation performance. This transfers heat Q to the heat radiating surface Sr via the thermal paste 90 applied within the slot 75. the amount of heat transfer from the common mode choke coil 34 to the heat radiating surface Sr depends on the thermal conductivity of a material, so that the thermal paste 90 having good thermal conductivity increases the amount of heat transfer. The heat radiation performance and the damping effect are provided without requiring a large space.The above-described embodiment has the following advantages. (1) The in-vehicle motor-driven compressor 11 includes a compression portion 18, the electric motor 19, the inverter 30, and the housing 14. The inverter device 30 includes the inverter circuit 31 and the noise reducer 32. The noise reducer 32 includes the common mode choke coil 34 and the X capacitor 35. The common mode choke coil 34 includes the loop-shaped core 50, the first winding 60, the second winding 61, and the metal film 70. The metal film 70 has portions that are opposed to each other and are located away from each other between the first winding 60 and the second winding 61. The metal film 70 includes the first linear part 71 thermally coupled to the suction housing member 15, namely, the housing 14. The average value of the electric resistance value per unit length in the circumferential direction of the first linear part 71 is larger than the average value of the electric resistance value per unit length in the circumferential direction from locations other than the first linear part 71.The metal film 70 is loop-shaped to cover the core 50 while extending over the first winding 60 and the second winding 61. This results in an excellent damping effect, whereby a push-pull current through the metal film 70 generates an induced current in the metal film 70, which is converted into thermal energy. The directions of the leakage magnetic fluxes φ 3, φ 4 generated from the first winding 60 and the second winding 61 intersect with the circumferential cross section of the loop-shaped metal film 70. As a result, a push-pull choke coil can be omitted.The metal film 70 is thermally coupled to the suction housing member 15, namely, the housing 14. Further, the average value of the electric resistance value per unit length in the circumferential direction of the first linear part 71 that is in contact with the heat radiation surface Sr is larger than the average value of the electric resistance value per unit length in the circumferential direction from locations other than the first linear part 71. The heat of the metal film 70 is efficiently transferred to the heat radiation surface Sr corresponding to the large temperature difference from the suction housing member 15. This improves the heat radiation performance for the heat radiation surface. This reduces the temperature of the entire metal film 70. (2) The slit 75 formed in the first linear part 71 of the metal film 70 increases the average value of the electric resistance value per unit length in the circumferential direction. Thus, the portion of the metal film 70 that is close to the heat radiation surface Sr easily has a high temperature. Forming the slit 75 in the metal film 70 having the same width and thickness is easy and practical in manufacturing. (3) The heat paste 90 is coated within the slot 75 so that the first coil 60, the second coil 61, and the first linear part 71 are thermally coupled to the housing 14 via the heat paste 90. This transfers heat Q generated in the coils 60, 61 to the heat radiation surface Sr via the thermal paste 90 applied within the slot 75 in addition to the heat generated in the metal film 70. (4) The plastic layer 80 insulating the first coil 60 and the second coil 61 is formed on the inner surface of the metal film 70. That is, the plastic layer 80 is formed between the inner surface of the metal film 70 and the outer surfaces of the first coil 60 and the second coil 61. This maintains strength, improves rigidity, and ensures insulation, even when the thickness of a conductor is reduced to increase resistance characteristics in the filter circuit, with excellent heat radiation performance and damping effect.The present embodiment may be modified as described below.As shown in FIG. 9, the metal film 70 may have two slits 76 a, 76 bextending in parallel to each other. As shown in FIG. 10, the metal film 70 may have two slits 77 a, 77 band two slits 77 c, 77 dextending parallel to each other. The slits 77 a, 77 band the slits 77 c, 77 dmay be arranged in the longitudinal direction of the metal film 70.The slit 75 is formed in the heat radiation portion of the metal film 70 that is in contact with the heat radiation surface Sr. Instead, the heat radiation portion may be thinned. In other words, the cross-sectional area of the heat radiation portion can be reduced without forming the slit 75 in the metal film 70 having the same width and thickness.The heat radiation portion of the metal film 70 that is in contact with the heat radiation surface Sr may be made of a material having an electric resistance value that is larger than portions other than the heat radiation portion.The heat paste 90 may be replaced with a heat radiating sheet. In other words, a heat radiation resin material having high or superior thermal conductivity may be used.In addition to a copper foil, the metal film 70 may be made of an aluminum foil, a brass foil, a stainless steel foil, or the like. These non-magnetic metals are easy to handle without magnetization or magnetic saturation. Further, the material is not limited to a non-magnetic material such as copper, but may be a magnetic material such as iron.The conductor covering the core 50 is not limited to a film as long as it is looped. The conductor may be a relatively thick plate.In addition to polyimide, the plastic layer 80 may be made of polyester, PET, PEN, or the like.Instead of the plastic layer 80, the thickness of the insulating coatings of the first winding 60 and the second winding 61 may be increased to improve insulation.In place of the plastic layer 80, another member may be used to support the metal film 70 without contacting the first coil 60 or the second coil 61. The core 50 may be covered with, for example, a plastic container having the same shape as the core 50. In this case, two arm members may be formed on the container so that the metal film 70 does not contact the first coil 60 or the second coil 61.A metal base member serving as a part of the housing may be located between the bottom wall 15 aand the first linear part 71.The present invention can be applied to a motor-driven compressor that is not installed in a vehicle.As described above, a metal film (70) has portions that are opposed to and away from each other between a first coil (60) and a second coil (61). The metal film ( 70) includes the first linear part ( 51) thermally coupled to a case. The average value of an electric resistance value per unit length in the circumferential direction of the first linear part ( 51) of the metal film ( 70) is larger than an average value of the electric resistance value per unit length from locations other than the first linear part.

Claims

A motor-driven compressor (11) comprising: a compressing portion (18) that compresses fluid; an electric motor (19) that drives the compressing portion (18); an inverter device (30) that drives the electric motor (19); and a metal case (14) that houses the inverter device (30), wherein the inverter device (30) includes an inverter circuit (31) that converts DC power into AC power and a noise reducer (32) disposed at an input side of the inverter circuit (31), wherein the noise reducer (32) reduces a common mode noise and a differential mode noise included in the DC power before being supplied to the inverter circuit, the noise reducer (32) includes a common mode choke coil (34), and a smoothing capacitor (35) that forms a low pass filter circuit (36) together with the common mode choke coil (34), the common mode choke coil (34) includes a loop-shaped core (50), a first winding (60) wound around the core (50), a second winding (61) wound around the core (50), the second winding (61) being away from the first winding (60) and opposing the first winding (60), and a loop-shaped conductor (70) covering the core (50) while extending over the first winding (60) and the second winding (61), the conductor (70) having portions opposing each other and, with the first winding (60) and the second winding (61) therebetween, being away from each other, the conductor (70) having a heat radiation portion (71) thermally coupled to the housing (14), and an average value of the electric resistance value per unit length in a circumferential direction of the heat radiation portion ( 71) of the conductor ( 70) is larger than an average value of the electric resistance value per unit length of sites other than the heat radiation portion ( 71).The motor-driven compressor (11) according to claim 1, comprising a slit (75) formed in the heat radiation portion (71) such that the average value of the electric resistance value per unit length in the circumferential direction is increased.The motor-driven compressor (11) according to claim 2, comprising a heat radiation resin material (90) provided within the slot (75), wherein the first coil (60), the second coil (61), and the heat radiation portion (71) are thermally coupled to the housing (14) via the heat radiation resin material (90).The motor driven compressor (11) according to any one of claims 1 to 3, comprising a plastic layer (80) formed on an inner surface of the conductor (70), the plastic layer (80) providing insulation between the first winding (60) and the second winding (61) and the conductor (70).

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