Electric motor, air conditioning and control board

Abstract

An electric motor (1) comprises a stator, a rotor, and a circuit board (11) including an inverter (81) that supplies power to the stator. The inverter (81) comprises power transistors (81A to 81C) of an upper arm and power transistors (81D to 81F) of a lower arm. The power transistors of the upper arm and the lower arm that are more frequently affected by switching are arranged on a first surface and a second surface of the circuit board (11), the second surface being opposite the first surface.

Description

Field of InterestThe present disclosure relates to an electric motor including an inverter, an air conditioner, and a control board.BackgroundIn recent years, there has been a demand for increasing a power of a blower motor (an electric motor for a blower) of an air conditioner to save energy and improve heating capability of the air conditioner. There has also been a need to miniaturize the blower motor to ensure an air path. The incorporation of a downsized high-power motor results in a simple temperature rise of a control board including an inverter. Accordingly, it is desirable to limit a temperature rise of the control board including the inverter.An electric motor described in Patent Literature 1 is integrally formed with a control board to which an inverter is mounted. In the electric motor, in order to improve heat dissipation, a plurality of power supply relays and a plurality of switching elements are partially fixed to one surface of the control board, whereas the rest is fixed to the other surface.Citing listPatent LiteraturePatent Literature 1: Japanese Patent Application Laid-Open No. 2020-195236Overview of the InventionTechnical ProblemHowever, the technique of Patent Literature 1 has a problem in that a restriction amount of temperature rise of the control board is reduced in a case where the components each having a larger temperature rise amount are concentratedly arranged on a surface of the control board because the components are arranged on the control board without considering an operation of the components.The present disclosure has been made in view of these circumstances, and it is an object of the present disclosure to provide an electric motor that can greatly restrict a temperature rise of a control board.Solution of the ProblemIn order to solve the above-described problem and achieve the object, an electric motor according to the present disclosure includes a stator, a rotor, and a control board including an inverter circuit that supplies power to the stator. The inverter circuit includes a plurality of upper arm power transistors and a plurality of lower arm power transistors. The power transistors of the one of the upper arm and the lower arm which is more frequently involved in switching are arranged dividedly on a first surface and a second surface of the control board, the second surface being opposed to the first surface.Advantageous Effects of the InventionThe electric motor according to the present disclosure has an effect of being able to greatly restrict the temperature rise of the control board.Brief Description of the DrawingsFIG. 1 is a diagram showing an exemplary configuration of an electric motor according to a first embodiment. FIG. 2 is a diagram showing a circuit configuration of a built-in board included in the electric motor according to the first embodiment. FIG. 3 is a diagram for explaining an example of switching performed by the electric motor according to the first embodiment. FIG. 4 is a diagram showing arrangement positions of the power transistors arranged on the mounting board of the electric motor according to the first embodiment. FIG. 5 is a cross-sectional view schematically showing a first exemplary internal configuration of the electric motor according to the first embodiment. FIG. 6 is a cross-sectional view schematically showing a second exemplary internal configuration of the electric motor according to the first embodiment. FIG. 7 is a diagram schematically showing a first exemplary arrangement of the power transistors on the built-in board according to the first embodiment. FIG. 8 is a diagram schematically showing a second exemplary arrangement of the power transistors on the built-in board according to the first embodiment. FIG. 9 is a cross-sectional view schematically showing an internal configuration of an electric motor according to a comparative example. FIG. 10 is a schematic diagram of an air conditioner according to a second embodiment.DESCRIPTION OF EMBODIMENTSHereinafter, an electric motor, an air conditioner, and a control board according to embodiments of the present disclosure will be described in detail with reference to the drawings.First Embodiment.FIG. 1 is a diagram showing an exemplary configuration of an electric motor according to a first embodiment. Note that although the first embodiment describes a case where an electric motor 1 is a three-phase electric motor, the electric motor 1 according to the first embodiment is not limited to the three-phase electric motor.The electric motor 1 is a brushless DC motor. FIG. 1 shows a part of the electric motor 1 in a cross-sectional structure to describe the configuration of the electric motor 1. Note that although FIG. 1 shows a radial flux type brushless DC motor, the electric motor 1 according to the first embodiment is not limited to the radial flux type brushless DC motor.The electric motor 1 includes a rotor 30, a stator 20, a mounting board 11, and a mold resin 12. A rotary shaft 31 is inserted into the rotor 30. The stator 20 is provided on an outer periphery of the rotor 30. The built-in board 11 includes a substrate circuit that is a circuit that controls the drive of the rotor 30.The stator 20, the mounting board 11, and the mold resin 12 are fixedly joined as a molded stator 10. The stator 20 and the installation board 11 are integrally molded (inserted and molded to be one piece) as the molded stator 10. That is, the stator 20 and the mounting board 11 are fixedly connected as the molded stator 10 to be one piece. In addition, a recess is provided in the cast stator 10. The recess is shaped such that the rotor 30 can be received in the recess. Note that the stator 20 and the mounting board 11 may be individually insert molded. In this case, the molded stator 20 and the molded board 11 are connected to each other.The stator 20 includes a plurality of stator cores 21, an insulator 23, and a winding group 22. The stator cores 21 each include magnetic steel sheets that are joined together in a planar manner. The insulator 23 isolates the stator cores 21 from the winding group 22.In the electric motor 1, the windings of the winding group 22 are wound around the stator cores 21 integrally molded with the insulator 23 through each space of the stator cores 21 to form the stator 20. The windings of the winding group 22 are made of copper, aluminum, or the like.An output-side bearing 33 rotatably supporting the rotation shaft 31 is provided at one end of the rotation shaft 31. An output-side opposite bearing 34 rotatably supporting the rotation shaft 31 is provided at another end of the rotation shaft 31.The output side bearing 34 is covered with an electrically conductive bracket 60. The bracket 60 is formed such that a press-fitted portion 61 of the bracket 60 is fitted into an inner peripheral portion of the molded stator 10 so as to cover an opening of the recess provided in the molded stator 10. In addition, an outer ring of the output-side-opposite bearing 34 is fitted into the bracket 60.The mounting board 11 includes a circuit included in a control unit 70 described later and a magnetic sensor 50. the magnetic sensor 50 detects the position of the rotor 30.The mounting board 11 is disposed between the output-side bearing 33 and the stator 20 perpendicular to a direction of an axis of the rotation shaft 31, and is fixed to the insulator 23. A cable output portion 14 is disposed on the mounting board 11. A cable 13 leads out of the cable outlet section 14. The cable 13 is connected to a host system (e.g., a board on a unit side of an air conditioning device). The host system is a system in which the electric motor 1 is mounted. For example, the cable 13 is connected to a unit-side board (such as an indoor unit board 211 described later) of an air conditioning device. In addition, passive components are disposed on the mounting board 11. The passive components are, for example, an operational amplifier, a comparator, a regulator, a diode, a resistor, a capacitor, an inductor, and a fuse.For example, the mounting board 11 is in the form of a disk having a through hole at the center thereof. Note that the mounting board 11 may have a shape other than the shape of the disk, such as a semicircular shape. The rotation shaft 31 penetrates through the through hole provided in the mounting board 11. The mounting board 11 is disposed inside the electric motor 1 such that an upper surface and a lower surface are perpendicular to the direction of the axis of the rotation shaft 31.A rotor insulation portion 32 is disposed at an outer peripheral portion of the rotating shaft 31. The rotor insulation portion 32 is an annular member. The rotor 30 includes a magnet 40 disposed within the cast stator 10. The magnet 40 is positioned on an outer circumferential side of the rotating shaft so as to face the stator cores 21. The magnet 40 is formed of a cylindrical permanent magnet. The magnet 40 is fixed to the rotating shaft 31.The magnet 40 is formed by injection molding a ferrite magnet or a bonded magnet formed by a mixture of rare earth magnets (a samarium-iron-nitrogen magnet, a neodymium magnet, or the like) with a thermoplastic resin material. For injection molding the magnet 40, a magnet is installed in a metal mold and poured while being aligned. Note that the magnet 40 may be a sintered magnet.The magnet 40 includes a sensor magnet portion and a main magnet portion in the direction of the axis of the rotation shaft 31. The remaining part other than the sensor magnetic portion serves as the main magnetic portion. The sensor magnetic portion causes the magnetic sensor 50 to detect the position of the rotor 30. The main magnet portion causes the rotor 30 to generate a rotational force in accordance with the magnetic flux generated from the winding group 22.The magnet 40 has a smaller outer diameter in the part closer to the magnetic sensor 50 of the mounting board 11 than in the remaining part. That is, in the magnet 40, the outer diameter of the sensor magnet portion is smaller than the outer diameter of the main magnet portion. This shape of the magnet 40 allows the magnetic flux to easily enter the magnetic sensor 50 mounted on the mounting board 11. In order to minimize the effect of the magnetic flux generated from the winding group 22 of the stator 20, the magnetic sensor 50 is positioned away from the winding group 22, that is, positioned closer to the rotation shaft 31.Note that although FIG. 1 shows a case where the main magnet portion and the sensor magnet portion are included in the single magnet 40, the main magnet portion and the sensor magnet portion may be provided as separate magnets.For configuring the magnetic sensor 50, a Hall integrated circuit (Hall IC) that outputs digital signals may be used. Alternatively, a Hall element that outputs analog signals may be used for configuring the magnetic sensor 50. That is, the magnetic sensor 50 may detect the position of the rotor 30 using a Hall IC, or may detect the position of the rotor 30 using a Hall element.In addition, the Hall IC may be one (a Hall IC of a first method) that detects the position of the rotor 30 by the first method, or one (a Hall IC of a second method) that detects the position of the rotor 30 by the second method. The first method and the second method will be described later.In the Hall IC of the first method, a sensor section and an amplifier section are formed of separate semiconductor chips. In the Hall IC of the first method, the sensor portion is made of a semiconductor different from silicon, and the amplifier portion is made of silicon. Hereinafter, the Hall IC of the first method will be referred to as a non-silicon Hall IC. In the Hall integrated circuit of the second method, a sensor portion and an amplifier portion are included in a single silicon semiconductor chip.Since two chips are mounted in the non-silicon Hall IC, the sensor portion is disposed such that the center of the sensor portion does not coincide with the center of a body of the integrated circuit. For the sensor portion, a non-silicon semiconductor such as indium antimonide (InSb) is used. Non-silicon semiconductors are advantageous in that they have better sensitivity than silicon semiconductors and a deviation due to stress strain in non-silicon semiconductors is less than that in silicon semiconductors.Next, a circuit configuration of the built-in board 11 shown in FIG. 1 will be described. FIG. 2 is a diagram showing a circuit configuration of a built-in board included in the electric motor according to the first embodiment. FIG. 2 shows the mounting board 11, the winding group 22, and the magnetic sensors 50.The built-in board 11 includes an overcurrent detection resistor 75 and the control unit 70.The control unit 70 is connected to the host system, a gate drive circuit 82, a ground 79A, and the magnetic sensors 50. Furthermore, the control unit 70 is connected to a low-voltage supply 78 via a connection point 48. In addition, the control unit 70 is connected to a ground 79C via a connection point 41, a connection point 42, and the overcurrent detection resistor 75.The gate driver circuit 82 is connected via the junction 48 to the low voltage supply 78 and via a junction 47 to a high voltage supply 77. The low voltage power supply 78 outputs a voltage lower than a voltage of the high voltage power supply 77. the high voltage power supply 77 is a bus power supply.Further, the gate drive circuit 82 is connected to the inverter 81. In addition, the gate drive circuit 82 is connected to a protection circuit 83 and a ground 79B via a connection point 43.The protection circuit 83 is connected to the connection point 41 and the connection point 43. That is, the protection circuit 83 is connected to the ground 79C via the connection point 41, the connection point 42, and the overcurrent detection resistor 75. In addition, protection circuit 83 is connected to ground 79B via connection point 43.The inverter 81 is connected to the winding group 22 of the stator 20 and supplies current to the winding group 22 of the stator 20. In addition, the inverter 81 is connected to the ground 79C via the connection point 42 and the overcurrent detection resistor 75. The masses 79A to 79C are common masses having the same potential.The inverter 81 includes six power transistors 81A to 81F. In the inverter 81, the six power transistors 81A to 81F are separately provided. That is, the six power transistors 81A to 81F are provided as separate components (chips).The gate drive circuit 82 may include a single integrated circuit or three integrated circuits provided separately for three phases. In addition, the gate drive circuit 82 and the control unit 70 may be provided as a single integrated circuit. Further, the control unit 70 may include a single dedicated integrated circuit (control IC), or may include a microcomputer or the like.The power transistors 81A to 81F each include a superjunction metal oxide semiconductor field effect transistor (MOSFET), a planar MOSFET, an insulated bipolar transistor (IGBT), or the like. Large currents flow into the power transistors 81A to 81F. Consequently, a lot of heat is generated therein, which is thus to be dissipated.The first embodiment will describe a case where the magnetic sensor 50 detects magnetic flux corresponding positions of the magnetic poles of the rotor 30, and the mounting board 11 controls the electric motor based on the magnetic pole positions. Note that the built-in board 11 can perform sensorless control of the electric motor 1 with estimation of the positions of the magnetic poles from a current flowing through the winding group 22 and from voltages applied to and generated by the winding group 22. Further, the built-in board 11 for detecting a current may amplify a current signal obtained using a shunt resistor and a current sensor by an operational amplifier or the like. In addition, the built-in board 11 may use a comparator to generate, from the current signal, a signal for overcurrent protection to be provided to the control unit 70.On the built-in board 11, a voltage (e.g., 15 V) for driving the gates of the power transistors 81A to 81F may be different from a microcomputer supply voltage (e.g., 5 V) which is a voltage for operating the control unit 70 such as a microcomputer. In this case, the electric motor 1 uses a regulator for generating another supply from a supply provided from the outside. For example, the built-in board 11 is supplied with a power of 15 V from the outside, and the regulator generates a power of 5 V and supplies the power to the built-in board 11. The regulator may be incorporated in the gate driver circuit 82.The inverter 81 converts an input DC voltage into an AC voltage for three phases including a U phase, a V phase, and a W phase, and supplies the AC voltage to the winding group 22 of the stator 20. The power transistor 81A is a U-phase upper arm power transistor. The power transistor 81B is a V-phase upper arm power transistor. The power transistor 81C is a W-phase upper arm power transistor. The power transistor 81D is a U-phase forearm power transistor. The power transistor 81E is a V-phase forearm power transistor. The power transistor 81F is a W-phase forearm power transistor.That is, the power transistor 81A is a U-phase upper arm power transistor, the power transistor 81B is a V-phase upper arm power transistor, and the power transistor 81C is a W-phase upper arm power transistor. In addition, the power transistor 81D is a U-phase lower arm power transistor, the power transistor 81E is a V-phase lower arm power transistor, and the power transistor 81F is a W-phase lower arm power transistor.As described above, the inverter 81 includes the plurality of upper arm power transistors and the plurality of lower arm power transistors. In the first embodiment, the power transistors of the one of the upper arm and the lower arm which is more frequently involved in switching are arranged dividedly on an upper surface (first surface) and a lower surface (second surface) of the mounting board 11, the lower surface being opposed to the first surface. In addition, in the first embodiment, the power transistors of the other of the upper arm and the lower arm less subject to switching are disposed on the upper surface of the mounting board 11.The electric motor 1 includes, as the windings included in the winding group 22, a U-phase winding 22U, a V-phase winding 22V, and a W-phase winding 22W. The U-phase winding 22U is connected to the power transistors 81A and 81D. The V-phase winding 22V is connected to the power transistors 81B and 81E. The W-phase winding 22W is connected to the power transistors 81C and 81F.The gate drive circuit 82 controls the turn-on and turn-off of the power transistors 81A to 81F in accordance with switching signals received from the control unit 70.Three magnetic sensors 50 are arranged around the winding group 22. Each of the three magnetic sensors 50 outputs a magnetic pole position signal corresponding to the position of the rotor 30 to the control unit 70. The electric motor 1, which is a brushless DC motor, obtains a rotational power by switching the six (in this case, the three phases) power transistors 81A to 81F at appropriate times in accordance with the positions of the magnetic poles of the rotor 30.In addition, in a case where the temperature of the inverter 81 and / or the gate drive circuit 82 rises to a high temperature, the protection circuit 83 turns off all of the power transistors 81A to 81F of the inverter 81 to prevent destruction of elements due to the high temperature.The overcurrent detection resistor 75 is connected to lower arm switches included in the power transistors 81D to 81F. The protection circuit 83 prevents an overcurrent from flowing through the winding group 22, and achieves overcurrent protection by monitoring the voltage of the overcurrent detection resistor 75 to turn off the power transistors 81A to 81F when the voltage of the overcurrent detection resistor 75 reaches or exceeds a specific voltage value. Note that the overcurrent detection unit may be incorporated in the control unit 70 or incorporated in the gate drive circuit 82.Note that a temperature sensitive element (not shown) may be provided on the mounting board 11 or the like. In this case, upon receiving a signal indicating an abnormal temperature from the temperature sensitive element, the control unit 70 forces the power transistors 81A to 81F to be turned off to achieve the overheat protection.The control unit 70 generates switching signals for controlling the turning on and off of the power transistors 81A to 81F at a specific frequency (carrier frequency) in accordance with a speed command signal received from the host system.The control unit 70 performs pulse width modulation (PWM) control on the power transistors 81A to 81F by outputting the switching signals to the gate drive circuit 82. The control unit 70 estimates positions of the magnetic poles of the rotor 30 based on the magnetic pole position signal received from the magnetic sensor 50, and calculates a rotational speed of the rotor 30 from the estimated positions of the magnetic poles. The control unit 70 outputs a rotation speed signal indicating the calculated rotation speed to the host system.In the case of the three phases, the electric motor 1, which is a brushless DC motor, obtains a rotational power by switching the six power transistors 81A to 81F at appropriate times in accordance with the positions of the magnetic poles of the magnet 40 of the rotor 30. The operating principle of the electric motor 1 will be described.In the electric motor 1, the control unit 70 estimates the positions of the magnetic poles of the rotor 30 based on the magnetic pole position signal of the magnetic sensor 50 or a current value of the current flowing through the winding group 22. The control unit 70 generates switching signals for switching the power transistors 81A to 81F in accordance with the positions of the magnetic poles of the rotor 30 and the speed command signal output from the host system. The gate drive circuit 82 performs switching between the turn-on and the turn-off of the power transistors 81A to 81F in accordance with the switching signals generated by the controller 70.Examples of a power conduction method used by the electric motor 1 include a 120-degree power conduction control, a 150-degree power conduction control, and a sine wave power conduction control.For example, in the 120-degree current conduction control, timings for switching between the turn-on and the turn-off of the six power transistors 81A to 81F coincide with the leading edge and the trailing edge of each of the detection signals of the three Hall ICs. Thus, in the 120-degree power line control, the control unit 70 may be implemented by a combination circuit that does not require a clock.On the other hand, in the case of controlling requiring estimation of the positions of the magnetic poles, such as the 150-degree current conduction control, the sine wave current conduction control, a phase control, or a sensorless control, the controller 70 includes a complicated digital circuit including a clock. For example, the time period between the leading edge and the trailing edge of each of the detection signals of the three Hall ICs is finely estimated in the estimation of the positions of the magnetic poles.The sensorless control is a control that does not use the magnetic sensor 50. In the sensorless control, positions of the magnetic poles are estimated from a current value detected by a current detection resistor, a current detection transformer, or the like to perform the control. In the sensorless control, a signal appropriately detected by a current detection resistor, a current detection transformer, or the like is amplified with an operational amplifier or the like in some cases.As described above, the control unit 70 adjusts the voltages applied to the winding group 22 by performing the PWM control on the power transistors 81A to 81F. In order to reduce loss due to switching of the inverter 81, the electric motor 1 switches only one of the upper and lower arms in some cases.The switching performed by the electric motor 1 will now be described. FIG. 3 is a diagram for explaining an example of switching performed by the electric motor according to the first embodiment. FIG. 3 shows gate signals (switching signals) for the power transistors 81A to 81F. The inverter 81 according to the first embodiment performs control in which the number of times of switching between the upper arm and the lower arm is different.The gate signal for the power transistor 81A, which is the U-phase upper arm power transistor, is an upper U-phase gate signal 93A. The gate signal for the power transistor 81B, which is the V-phase upper arm power transistor, is an upper V-phase gate signal 93B. The gate signal for the power transistor 81C, which is the W-phase upper arm power transistor, is an upper W-phase gate signal 93C.In addition, the gate signal for the power transistor 81D, which is the U-phase forearm power transistor, is a lower U-phase gate signal 93D. The gate signal for the power transistor 81E, which is the V-phase forearm power transistor, is a lower V-phase gate signal 93E. The gate signal for the power transistor 81F, which is the W-phase forearm power transistor, is a lower W-phase gate signal 93F.FIG. 3 shows flowcharts of the gate signals for the power transistors 81A to 81F in a case where the upper arm is more frequently involved in switching than the lower arm (in a case of switching the upper arm) in a specific period T 1.When the gate signal is high, the power transistor is turned on, and when the gate signal is low, the power transistor is turned off. In the case of the flowcharts shown in FIG. 3, the upper arm performs the switching in a shorter cycle than the lower arm. The control unit 70 controls the electric motor 1 by changing the voltage applied to the winding group 22 by changing the upper arm switching operation.The configuration of the electric motor 1 will be described below using, as an example, a case where the upper arm is more frequently involved in switching than the lower arm (in the case of switching the upper arm) in the specific period T 1. Note that the electric motor 1 according to the first embodiment can be transmitted to a case where the lower arm is switched similarly to the switching of the upper arm in the present case.FIG. 4 is a diagram showing arrangement positions of the power transistors arranged on the mounting board of the electric motor according to the first embodiment. FIG. 4 schematically shows a stator-side opposite surface of the mounting board 11 (an upper surface that is a surface on a side not facing the stator 20). Here, FIG. 4 omits illustration of a through hole (a hole penetrated by the rotation shaft 31) provided in the mounting board 11.On the mounting board 11, one of the six power transistors 81A to 81F is disposed on a stator side surface (a lower surface) of the mounting board 11, and the remaining five power transistors are disposed on a stator side opposite surface (upper surface). FIG. 4 shows a case where the upper arm power transistor 81B is disposed on the stator side surface of the mounting board 11 and the remaining power transistors 81A and 81C to 81F are disposed on the stator side opposite surface.As described above, the power transistors (the power transistors whose temperature slightly rises) of the arm, which is more frequently involved in switching, are arranged dividedly on the stator-side surface and the stator-side-opposing surface of the mounting board 11. Consequently, the built-in board 11 can avoid heat concentration on the built-in board 11 and limit the temperature rise of the power transistors 81A to 81F. Accordingly, the built-in board 11 can greatly limit the temperature rise of the built-in board 11.When three upper arm power transistors are arranged side by side on the mounting board 11 in a specific direction, the effect of limiting the heat concentration on the mounting board 11 is enhanced when the power transistor to be arranged at the center is arranged on the stator side surface among the three upper arm power transistors.With respect to the mounting board 11, in a plan view of the upper surface of the mounting board 11, the upper and lower arms of each phase are arranged as a pair in a radial direction (in a direction from the center toward the outer periphery). That is, with respect to the mounting board 11, in a plan view of the upper surface of the mounting board 11, the upper and lower arms of the U phase are arranged as a pair in the radial direction (a first radial direction), the upper and lower arms of the V phase are arranged as a pair in the radial direction (a second radial direction), and the upper and lower arms of the W phase are arranged as a pair in the radial direction (a third radial direction).In addition, with respect to the mounting board 11, in a plan view of the upper surface of the mounting board 11, the upper arms of the three phases are arranged in a circumferential direction (a first circumferential direction) with respect to an axis direction of the rotation shaft 31, and the lower arms of the three phases are arranged side by side in a circumferential direction (a second circumferential direction). Consequently, on the upper surface of the mounting board 11, the upper arm power transistors and the lower arm power transistors are arranged in two rows in the circumferential direction. The circumferential direction (the first circumferential direction and the second circumferential direction) of the installation board 11 is a direction along the outer periphery of the installation board 11.FIG. 4 shows a case where the power transistors 81A to 81C are arranged in the circumferential direction in a plan view of the upper surface of the mounting board 11. FIG. 4 also shows a case where the power transistors 81D to 81F are arranged in the circumferential direction in a plan view of the upper surface of the mounting board 11.In the first embodiment, for example, the power transistors 81A and 81C are disposed on the upper surface of the mounting board 11, and the power transistor 81B is disposed on the lower surface of the mounting board 11. In addition, the power transistors 81D to 81F are disposed on the upper surface of the mounting board 11.Such arrangement of the power transistors 81A to 81F facilitates pattern wiring for the power transistors 81A to 81F. In this case, the upper arm power transistors, which is more frequently affected by switching, are arranged on an outer circumferential side, and the lower arm power transistors, which is less rarely affected by switching, are arranged on an inner circumferential side.That is, in the mounting board 11, the power transistors of the arm that is more frequently affected by switching are disposed closer to the outer peripheral side than the power transistors of the arm that is less rarely affected by switching. Then, at least one of the power transistors of the arm more frequently affected by switching is disposed on the lower surface of the built-in board 11.As described above, the power transistors of the arm (here, the upper arm power transistors) more frequently involved in switching are arranged on the outer peripheral side, and one (here, the power transistor 81B) of the upper arm power transistors is arranged on the stator side surface of the mounting board 11.The temperature of the power transistor 81B disposed on the stator side surface slightly increases due to the influence of the winding group 22. However, since the power transistor 81B is disposed closer to the outer circumferential side than the lower arm power transistors, heat from the power transistor 81B is also easily dissipated from a side surface of the electric motor 1. As described above, heat dissipation of the built-in board 11 is improved because the heat from the power transistor 81B disposed on the stator-side surface is also easily dissipated from the side surface of the electric motor 1. That is, due to the arrangement of the power transistors of the arm more frequently affected by switching on the outer peripheral side, the power transistors of the arm more frequently affected by switching are easily discharged from the side surface of the electric motor 1, thus increasing the effect of limiting the temperature rise.Note that in a case where an arm more frequently involved in switching is the lower arm, the power transistors of the lower arm are arranged in the circumferential direction at a position closer to the outer circumferential side than the power transistors of the upper arm. Then, at least one (e.g., the power transistor 81E) of the power transistors 81D to 81F is disposed on the lower surface of the mounting board 11.FIG. 5 is a cross-sectional view schematically showing a first exemplary internal configuration of the electric motor according to the first embodiment. Here, FIG. 5 omits the illustration of the power transistors 81D to 81F that are the lower arm power transistors. FIG. 5 shows a case where the power transistor 81A and the power transistor 81B are positioned to face each other with the built-in board 11 interposed therebetween. However, as shown in FIG. 4, the power transistor 81B may be positioned not to face the power transistors 81A and 81C.For example, of the power transistors 81A to 81C which are the upper arm power transistors, the power transistors 81A and 81C are disposed on the surface of the mounting board 11 located on a side opposite to the winding group 22. That is, the power transistors 81A and 81C are disposed on the stator opposite side of the mounting board 11. In other words, in a case where the stator core 21 and the winding group 22 are positioned to face the lower surface of the mounting board 11, the power transistors 81A and 81C are disposed on the upper surface opposite to the lower surface of the mounting board 11. Consequently, the power transistors 81A and 81C will be less susceptible to the action of heat transferred from the winding group 22. Thus, the built-in board 11 can limit the temperature rise of the power transistors 81A and 81C.In addition, of the power transistors 81A to 81C which are the upper arm power transistors, the power transistor 81B is disposed on the stator side of the mounting board 11. In other words, the power transistor 81B is disposed on the lower surface of the mounting board 11. Consequently, power transistor 81B will be less susceptible to the action of heat transferred from power transistors 81A and 81C. Thus, the built-in board 11 can limit the temperature rise of the power transistor 81B.Note that the power transistor 81A may be disposed on the stator side of the mounting board 11, and the power transistors 81B and 81C may be disposed on the stator opposite side of the mounting board 11. In addition, the power transistor 81C may be disposed on the stator side of the mounting board 11, and the power transistors 81A and 81B may be disposed on the stator opposite side of the mounting board.In addition, of the power transistors 81A to 81C, two power transistors may be disposed on the stator side of the built-in board 11.The power transistors 81D to 81F are disposed on the stator opposite side of the mounting board 11. As described above, the number of power transistors disposed on the stator opposite side is larger than the number of power transistors disposed on the stator side. In the built-in board 11, heat dissipation on the stator opposite side is better than on the stator side, and thus heat dissipation is improved when a large number of power transistors are disposed on the stator opposite side.FIG. 6 is a cross-sectional view schematically showing a second exemplary internal configuration of the electric motor according to the first embodiment. Here, FIG. 6 omits the illustration of the power transistors 81D to 81F that are the lower arm power transistors. FIG. 6 shows a case where the power transistor 81A and the power transistor 81B are positioned to face each other with the built-in board 11 interposed therebetween. However, as shown in FIG. 4, the power transistor 81B may be positioned not to face the power transistors 81A and 81C.FIG. 6 shows a case where the electric motor 1 includes a heat sink 5. The heat sink 5 dissipates heat generated by the electric motor 1. Other configurations of the electric motor 1 including the heat sink 5 are the same as those of the electric motor 1 shown in FIG. 5. for example, in the electric motor 1, in some cases, the heat sink 5 is disposed on the opposite side to the stator with respect to the mounting board 11 by the mold resin 12. The heat sink 5 is integrally molded with the mounting board 11 by the mold resin 12, or the mounting board 11 is molded with the mold resin 12 and then attached to the heat sink 5. In this case, in order to reduce the thermal contact resistance between the heat sink 5 and the mold resin 12, a heat dissipation means is disposed between the heat sink and the mold resin 12. For example, the heat dissipation means is a heat conducting layer, a heat conducting grease or a heat conducting pad.Although the heat dissipation patterns (heat dissipation board patterns 2A described later) of the power transistors 81A and 81C disposed on the stator opposite side and the axial heights of the bodies or the heat dissipation protrusions of the power transistors 81A and 81C disposed on the stator opposite side are not uniform, a space on the stator opposite side of the built-in board 11 is filled with the mold resin 12 without gaps. Consequently, the stator-opposite-side power transistors 81A and 81C and the heat sink 5 can be connected to each other by filling the mold resin 12 without gaps. Accordingly, it is possible to prevent remarkably less heat conduction of the heat sink 5 due to a gap or the like.When the built-in board 11 is not molded with the mold resin 12, a heat conductive pad is disposed between the heat sink 5 and the power transistors 81A and 81C or the heat dissipation patterns. In this case, the alignments of the heights of the bodies of the power transistors 81A and 81C and the heights of the heat dissipation patterns make it difficult to fill a space between the heat sink 5 and the mounting board 11 with the heat conduction pad without gaps. On the other hand, in the first embodiment, since the built-in board 11 is molded with the mold resin 12, the mold resin 12 can fill the space between the heat sink 5 and the built-in board 11 without gaps.Note that a heat dissipation pattern (a heat dissipation board pattern 2B described later) of the power transistor disposed on the stator side is connected to a heat dissipation extension (heat dissipation extension 85T described later) of the power transistor. Then, the mold resin 12 is disposed so as to cover the power transistor together with the heat dissipation extension 85T.As described above, in the electric motor 1, at each of the two surfaces of the mounting board 11, at least one of the power transistors of the one of the upper arm and the lower arm that is more frequently involved in switching is disposed. That is, in the electric motor 1, the power transistors of the arm more frequently involved in switching are arranged dividedly on the upper surface and the lower surface of the built-in board 11.In the electric motor 1, the arm more frequently affected by switching has a higher temperature rise than the arm less rarely affected by switching. Consequently, the effect of limiting the temperature rise is increased when the power transistors of the arm more frequently involved in switching are arranged divided at the upper surface and the lower surface of the built-in board.Note that a through hole may be provided in the built-in board 11 to improve heat dissipation of the power transistor mounted on the stator side. Now, the configuration of the mounting board 11 for a case where a through hole is provided will be described.FIG. 7 is a diagram schematically showing a first exemplary arrangement of the power transistor on the built-in board according to the first embodiment. FIG. 7 is a cross-sectional view of the mounting board 11 in a case where the through holes 4 are provided.The heat dissipation board pattern 2A is disposed on the upper surface (the surface opposite to the stator side) of the built-in board 11, and the heat dissipation board pattern 2B is disposed on the lower side (the stator side surface) of the built-in board 11. The heat dissipation board patterns 2A and 2B are patterns that dissipate heat generated by the built-in board 11. The heat dissipation board pattern 2A is a first heat dissipation board pattern, and the heat dissipation board pattern 2B is a second heat dissipation board pattern.Further, the power transistor 81B disposed on a lower surface side of the mounting board 11 includes the heat dissipation extension 85T for improving heat dissipation. The heat dissipation extension 85T dissipates heat generated by the power transistor 81B.The heat dissipation board pattern 2B is connected to the heat dissipation extension 85T. The heat dissipation board pattern 2B connected to the heat dissipation extension 85T is connected to the heat dissipation board pattern 2A on the opposite side to the stator through the through holes 4. The through holes 4 are each a hole penetrating through the mounting board 11. In the through holes 4, a agent having a thermal conductivity higher than a specific thermal conductivity value may be embedded. For example, a medium having a thermal conductivity higher than the thermal conductivity of the mounting board 11 may be embedded in the through holes 4.With such a configuration of the built-in board 11, heat is released from the power transistor 81B via the heat dissipation extension 85T, the heat dissipation board pattern 2B, the through holes 4, and the heat dissipation board pattern 2A.Note that the power transistors 81A, 81C, and 81D to 81F disposed on the upper surface side of the built-in board may include the heat dissipation extension 85T. In addition, the heat dissipation extension 85T may not be disposed on the mounting board 11. In this case, the power transistor 81B is not connected to the heat dissipation extension 85T.FIG. 8 is a diagram showing a second exemplary arrangement of the power transistor on the built-in board according to the first embodiment. FIG. 8 is a cross-sectional view of the mounting board 11 in the case where the through holes 4 are provided.Even when the heat dissipation extension 85T is not disposed on the mounting board 11, the heat dissipation board pattern 2A is disposed on the upper surface (the stator-side opposing surface) of the mounting board 11 and the heat dissipation board pattern 2B is disposed on the lower surface (the stator-side surface) of the mounting board 11.When the heat dissipation extension 85T is not disposed on the built-in board 11, a lower portion of the case of the power transistor 81B whose temperature is to be raised to a high temperature is connected to the heat dissipation board pattern 2B. Then, the heat dissipation board pattern 2B connected to the lower portion of the housing of the power transistor 81B is connected to the heat dissipation board pattern 2A on the opposite side to the stator through the through holes 4. With such a configuration, heat is released from the power transistor 81B through the heat dissipation board pattern 2B, the through holes 4, and the heat dissipation board pattern 2A.A configuration of an electric motor of a comparative example will now be described. FIG. 9 is a cross-sectional view schematically showing an internal configuration of the electric motor according to the comparative example. In an electric motor 1X according to the comparative example, all the power transistors 81A to 81F are disposed on the same surface (the upper surface) on the mounting board 11X. That is, in the electric motor 1X according to the comparative example, the power transistors 81A to 81C are disposed on the surface of the built-in board 11X that is on an opposite side to the winding group 22. Here, FIG. 9 omits the illustration of the power transistors 81D to 81F.In the electric motor 1 according to the first embodiment, of the power transistors 81A to 81C, the power transistors 81A and 81C are disposed on the surface of the built-in board 11 that is on the opposite side to the winding group 22. Thus, the built-in board 11 included in the electric motor 1 according to the first embodiment can more limit the temperature rise than the built-in board 11X included in the electric motor 1X according to the comparative example. More specifically, in the built-in board 11 included in the electric motor 1 according to the first embodiment, the components each having the larger temperature increase amount are not disposed only on one surface of the built-in board 11. Thus, the limitation amount of the temperature rise of the built-in board 11 increases.As described above, in the electric motor 1 according to the first embodiment, the power transistors of the one of the upper arm and the lower arm which is more frequently involved in switching are arranged dividedly on the upper surface and the lower surface of the mounting board 11. Consequently, the electric motor 1 can greatly limit the temperature rise of the built-in board 11 which is the control board.Second Embodiment.Next, a second embodiment will be described with reference to FIG. 10. In the second embodiment, the electric motor 1 described in the first embodiment is used in an air conditioner.FIG. 10 is a schematic diagram of an air conditioner according to the second embodiment. An air conditioner 200, which is the air conditioner device, includes an indoor unit 210 and an outdoor unit 220 connected to the indoor unit 210. The indoor unit 210 includes the electric motor 1, an indoor unit board 211, and an indoor unit blower (not shown). The outdoor unit 220 includes an outdoor unit blower 223.The outdoor unit blower 223 and the indoor unit blower each include, as a drive source, the electric motor 1 described in the first embodiment. Particularly, in the air conditioner 200 for business use, there is a need for high heat dissipation capability, and thus the heat dissipation effect is enhanced by using the electric motor 1 described in the first embodiment.Note that the electric motor 1 can be installed and used in addition to the air conditioner 200, for example, in a fan, a home appliance, a machine tool, or the like.As described above, since the electric motor 1 according to the second embodiment described in the first embodiment is used in the air conditioner 200, it is possible to greatly limit the temperature rise of the built-in board 11.The configurations described in the above embodiments are for illustrative purposes only and may be combined with the other known techniques, the embodiments may be combined with each other, and a part of each of the configurations may be omitted or modified without departing from the spirit.List of reference characters1, 1X electric motor; 2A, 2B heat dissipation board pattern; 4 through hole; 5 heat sink; 10 molded stator; 11, 11X installation board; 12 molding resin; 13 cable; 14 cable output portion; 20 stator; 21 stator core; 22 winding group; 22U U-phase winding; 22V V-phase winding; 22W W-phase winding; 23 insulator; 30 rotor; 31 rotating shaft; 32 rotor insulation portion; 33 output-side bearing; 34 output-side opposing bearing; 40 magnet; 41 to 43, 47, 48 connection point; 50 magnetic sensor; 60 bracket; 61 press-fitted portion; 70 control unit; 75 overcurrent detection resistor; 77 high voltage supply; 78 low voltage supply; 79A to 79C ground; 81 Inverter; 81A to 81F Power Transistor; 82 Gate Driving Circuit; 83 Protection Circuit; 85T Heat Dissipation Extension; 93A Upper U-phase Gate Signal; 93B Upper V-phase Gate Signal; 93C Upper W-phase Gate Signal; 93D Lower U-phase Gate Signal; 93E Lower V-phase Gate Signal; 93F Lower W-phase Gate Signal; 200 Air Conditioner; 210 Indoor Unit; 211 Indoor Unit Board; 220 Outdoor Unit; 223 Outdoor Unit Blower.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2020-195236

[0004]

Claims

An electric motor, comprising: a stator; a rotor; and a control board having an inverter circuit for supplying current to the stator, wherein the inverter circuit comprises a plurality of upper arm power transistors and a plurality of lower arm power transistors, and wherein the power transistors of the one of the upper arm and the lower arm that is more frequently involved in switching are arranged divided at a first surface and a second surface of the control board, the second surface being opposite to the first surface.The electric motor according to claim 1, wherein the second surface is a surface on a side where the stator is disposed, and more power transistors are disposed on the first surface than on the second surface.The electric motor according to claim 1 or 2, wherein in the control board, the plurality of upper arm power transistors are arranged in a first circumferential direction in a plan view of the first surface of the control board, and the plurality of lower arm power transistors are arranged in a second circumferential direction in a plan view of the first surface of the control board, such that the plurality of upper arm power transistors and the plurality of lower arm power transistors are arranged in two rows in a circumferential direction in a plan view of the first surface of the control board, and the power transistors of an arm more frequently affected by switching are arranged on the first surface of the control board closer to an outer circumferential side than the power transistors of an arm less frequently affected by switching.The electric motor according to any one of claims 1 to 3, wherein the power transistor disposed on the second surface includes a heat dissipation extension for dissipating heat generated by the power transistor, wherein a first heat dissipation board pattern, which is a pattern for dissipating heat generated by the control board, is disposed on the first surface of the control board, wherein a second heat dissipation board pattern, which is a pattern for dissipating heat generated by the control board, is disposed on the second surface of the control board, and wherein the heat dissipation extension is connected to the second heat dissipation board pattern, and the first heat dissipation board pattern and the second heat dissipation board pattern are connected to each other via a through hole penetrating through the control board.The electric motor according to any one of claims 1 to 3, wherein a first heat dissipation board pattern that is a pattern for dissipating heat generated by the control board is disposed on the first surface of the control board, wherein a second heat dissipation board pattern that is a pattern for dissipating heat generated by the control board is disposed on the second surface of the control board, and wherein the first heat dissipation board pattern and the second heat dissipation board pattern are connected to each other via a through hole penetrating through the control board.The electric motor according to any one of claims 1 to 5, further comprising a heat sink for dissipating heat, wherein the control board is provided by insert molding using a resin, and wherein the heat sink is disposed on the first surface of the control board, wherein the resin is disposed between the heat sink and the control board.An air conditioner comprising the electric motor according to any one of claims 1 to 6.A control board comprising an inverter circuit for supplying current to a stator of an electric motor comprising the stator and a rotor, wherein the inverter circuit comprises a plurality of power transistors of an upper arm and a plurality of power transistors of a lower arm, and wherein the power transistors of that one of the upper arm and the lower arm which is more frequently involved in switching are arranged divided at a first surface and a second surface of a board, the second surface being opposite to the first surface.

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