Motor unit

Abstract

A motor unit according to the present invention comprises a power supply unit that supplies power supplied from a power source to a motor. The power supply unit includes: a circuit board having a power line electrically connected to the power source and the motor, and a grounded ground line; a first wiring line with one end connected to the power line and the other end being an open end; a second wiring line with one end connected to the ground line and the other end being an open end; and a noise filter connected to the first and second wiring lines. The noise filter converts each of noise induced from the power line to the first wiring line and noise induced from the ground line to the second wiring line into thermal energy.

Description

Motor Unit

[0001] This application claims priority to Japanese Patent Application No. 2024-135631, filed on August 15, 2024, the contents of which are incorporated herein by reference.

[0002] A printed wiring board is known that includes a resonant filter having a first resonant pattern that has one end connected to a main wiring that is electrically connected to a power source and the other end being an open end, and a second resonant pattern that has one end connected to ground and the other end being an open end, with the first resonant pattern and the second resonant pattern being arranged in parallel (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2006-314046

[0004] In the above-mentioned printed wiring board, noise propagating through the main wiring is dissipated to the ground via a resonant filter, which makes it difficult to reduce common mode noise that returns to the power supply via the ground.

[0005] An object of one aspect of the present invention is to provide a motor unit that can prevent the intensity of noise propagating to a power supply from becoming too high.

[0006] One aspect of the motor unit of the present invention includes a power supply unit that supplies power from a power source to a motor. The power supply unit includes a circuit board having a power line electrically connected to the power source and the motor and a ground line, a first wiring having one end connected to the power line and the other end open, a second wiring having one end connected to the ground line and the other end open, and a noise filter connected to the first wiring and the second wiring. The noise filter converts noise induced from the power line to the first wiring and noise induced from the ground line to the second wiring into thermal energy.

[0007] According to one aspect of the present invention, in a motor unit, it is possible to prevent the intensity of noise propagating to a power supply from becoming too high.

[0008] Fig. 1 is a schematic diagram showing a motor unit of a first embodiment. Fig. 2 is a schematic diagram showing noise in the motor unit of the first embodiment. Fig. 3 is a first diagram showing radiated noise in the motor unit of the first embodiment. Fig. 4 is a second diagram showing radiated noise in the motor unit of the first embodiment. Fig. 5 is a diagram showing the average value of conducted noise in the motor unit of the first embodiment. Fig. 6 is a diagram showing the quasi-peak value of conducted noise in the motor unit of the first embodiment. Fig. 7 is a schematic diagram showing a motor unit of a second embodiment. Fig. 8 is a schematic diagram showing noise in the motor unit of the second embodiment.

[0009] <First embodiment> Fig. 1 is a schematic diagram showing a motor unit 10 of this embodiment. The motor unit 10 is a unit that operates a motor 13. In this embodiment, the motor unit 10 is mounted on a vehicle such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHV), or an electric vehicle (EV) to drive the vehicle. The motor unit 10 includes a housing 11, a motor 13, and a power supply unit 20.

[0010] The housing 11 is box-shaped and houses the motor 13 and the power supply unit 20. In this embodiment, the housing 11 is made of metal. The housing 11 is conductive. The housing 11 is grounded.

[0011] The motor 13 is housed inside the housing 11. In this embodiment, the motor 13 is a three-phase AC motor. The motor 13 may be a DC motor. The motor 13 is grounded via a first ground line 46 and the housing 11. A capacitor 46a is provided on the first ground line 46. The motor 13 has a rotor (not shown), a stator (not shown), and an inverter 14.

[0012] The inverter 14 is electrically connected to the power supply 50 via the power supply unit 20. The inverter 14 supplies power received from the power supply 50 via the power supply unit 20 to a stator (not shown). More specifically, the inverter 14 generates an AC current from the DC current received from the power supply 50 and supplies the AC current to a stator (not shown). When the inverter 14 supplies the AC current to the stator, the rotor is driven to rotate. Although not shown, the rotational torque of the rotor is transmitted to an axle of the vehicle. As a result, the motor 13 rotates the axle and drives the vehicle. The inverter 14 is grounded via a first ground line 46 and the housing 11. The inverter 14 has a switching element 14a.

[0013] The switching elements 14a generate AC current to be supplied to a stator (not shown). In this embodiment, the switching elements 14a are power semiconductor elements such as insulated gate bipolar transistors (IGBTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). The inverter 14 includes a plurality of switching elements 14a. This allows the inverter 14 to generate three-phase AC current.

[0014] In this embodiment, noise N is generated when the switching element 14a generates an AC current. In this embodiment, the noise N is common-mode noise that returns to the power supply 50 via the ground. The noise N includes noise that has a fundamental frequency, the switching frequency Fs of the switching element 14a, and is the sum of noises at frequencies that are integer multiples of the switching frequency Fs. In this embodiment, the switching frequency Fs of each switching element 14a is 0.01 MHz or higher and 0.2 MHz or lower. As described below, in this embodiment, the frequency band of the noise N to be reduced is assumed to be 10 MHz or higher and 300 MHz or lower. The noise N propagates from the inverter 14 to the power supply 50 via a path described below. If the intensity of the noise N propagated to the power supply 50 becomes too high, there is a risk of malfunction in the power supply 50. In this case, the power supplied to the inverter 14 becomes unstable, thereby impairing the stability of the operation of the motor 13.

[0015] The power supply 50 supplies power to the power supply unit 20. In this embodiment, the power supply 50 supplies direct current to the power supply unit 20. The current supplied by the power supply 50 to the power supply unit 20 may be alternating current. The power supply 50 is, for example, a battery provided in the vehicle. The power supply 50 is disposed outside the housing 11. The power supply 50 is grounded via a third ground line 48 and the housing 11. A capacitor 48a is provided on the third ground line 48.

[0016] The power supply unit 20 supplies the electric power received from the power supply 50 to the motor 13. More specifically, the power supply unit 20 supplies the electric power received from the power supply 50 to the inverter 14. The power supply unit 20 is disposed inside the housing 11. The power supply unit 20 has a circuit board 21, a first wiring 31, a second wiring 32, and a noise filter 35.

[0017] In this embodiment, the circuit board 21 is an insulating, plate-shaped printed circuit board. The circuit board 21 may be a flexible printed circuit board that is flexible in the thickness direction. The circuit board 21 has a power supply line 23 and a ground line 25.

[0018] The power supply line 23 is a wiring pattern provided on the circuit board 21. The power supply line 23 is made of, for example, copper foil. One end of the power supply line 23 is electrically connected to the power supply 50 via a first connection line 41. The other end of the power supply line 23 is electrically connected to the motor 13 via a third connection line 43. In this way, the power supply line 23 is electrically connected to the power supply 50 and the motor 13. As a result, power is supplied to the inverter 14 from the power supply 50 via the power supply line 23.

[0019] The ground line 25 is a wiring pattern provided on the circuit board 21. The power supply line 23 is made of, for example, copper foil. One end of the ground line 25 is electrically connected to the power supply 50 via a second connection line 42. The other end of the ground line 25 is electrically connected to the motor 13 via a fourth connection line 44. In this way, the ground line 25 is electrically connected to the power supply 50 and the motor 13. A capacitor 44a is provided on the fourth connection line 44. The ground line 25 is grounded via a second ground line 47 and the housing 11.

[0020] Here, the capacitors 44a, 46a, and 48a include, for example, Y capacitors connected via conductive members such as cables or bus bars, and stray capacitances generated by arranging components close to each other. In this embodiment, the capacitors 44a, 46a, and 48a are all assumed to be stray capacitances. As a result, between the motor 13 and the power supply 50, there is a circuit that passes through the power supply line 23 and a circuit that passes through the housing 11 or the ground line 25. Noise N propagates from the inverter 14 of the motor 13 to the power supply 50 via this circuit. In other words, the noise N includes common-mode noise that returns to the power supply 50 via the ground through the capacitors 44a, 46a, and 48a.

[0021] Each of the fourth connection line 44, the first ground line 46, and the third ground line 48 is a conductive member such as a cable or bus bar for connecting a Y capacitor, or a virtual conductive path for connecting stray capacitance.

[0022] The first wiring 31 is a wiring through which noise N generated in the inverter 14 is induced. One end 31 a of the first wiring 31 is connected to the power supply line 23. The other end 31 c of the first wiring 31 is an open end. In this embodiment, the first wiring 31 is a cable.

[0023] The second wiring 32 is a wiring through which noise N generated in the inverter 14 is induced. One end 32a of the second wiring 32 is connected to the ground line 25. The other end 32c of the second wiring 32 is an open end. In this embodiment, the second wiring 32 is a cable.

[0024] The first wiring 31 and the second wiring 32 function as antennas because the other ends 31c and 32c are open, respectively, and therefore induce noise N in a specific frequency band in each of the first wiring 31 and the second wiring 32.

[0025] In this embodiment, the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are approximately the same. In this embodiment, approximately the same length means that the ratio of the difference between the length L1 of the first wiring 31 and the length L2 of the second wiring 32 to the length L1 of the first wiring 31 is 10% or less. This makes it possible to reduce the difference between the length L1 of the first wiring 31 and the length L2 of the second wiring 32. In this embodiment, the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are the same. The length L1 of the first wiring 31 and the length L2 of the second wiring 32 may be different from each other.

[0026] The noise filter 35 converts the noise N induced from the power supply line 23 to the first wiring 31 and the noise N induced from the ground line 25 to the second wiring 32 into thermal energy. The noise filter 35 is connected to both the first wiring 31 and the second wiring 32. In this embodiment, the noise filter 35 is a common mode filter. As described above, in this embodiment, the noise N is common mode noise. Therefore, when the noise N is induced in each of the first wiring 31 and the second wiring 32, the noise filter 35 functions as an inductor, converting the noise N into thermal energy and dissipating it. This reduces the intensity of the noise N propagating to the power supply 50.

[0027] In this embodiment, the noise filter 35 is connected to a portion of the first wiring 31 on the one end 31a side. That is, the ratio of the length of the portion of the first wiring 31 between the one end 31a and the noise filter 35 to the length L1 of the first wiring 31 is 50% or less. Also, in this embodiment, the noise filter 35 is connected to a portion of the second wiring 32 on the one end 32a side. That is, the ratio of the length of the portion of the second wiring 32 between the one end 32a and the noise filter 35 to the length L2 of the second wiring 32 is 50% or less.

[0028] In this embodiment, if the speed of radio waves is C and the center frequency of the noise N converted into thermal energy by the noise filter 35 is Fc, the length L1 of the first wiring 31 and the length L2 of the second wiring satisfy the relationship L1 = L2 = C / (4 × Fc). In other words, the length L1 of the first wiring 31 and the length L2 of the second wiring are each ¼ the center wavelength λc of the noise N converted into thermal energy by the noise filter 35. By setting the length L1 of the first wiring 31 and the length L2 of the second wiring to satisfy the above formula, it is possible to induce noise N in a frequency band near the center frequency Fc in each of the first wiring 31 and the second wiring 32. Note that in the following description, the center frequency Fc of the noise N converted into thermal energy by the noise filter 35 may sometimes be simply referred to as the center frequency Fc of the noise N.

[0029] As described above, in this embodiment, the frequency band of the noise N to be reduced is assumed to be 10 MHz or more and 300 MHz or less. In this embodiment, the center frequency Fc of the noise N is 30 MHz. The center frequency Fc of the noise N may be less than 30 MHz or may be greater than 30 MHz. The speed C of the radio wave is 3.0×10 ８ m / s. Therefore, in this embodiment, the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are each 2.5 m. If the frequency band of the noise N generated in the inverter 14 is different from the frequency band of the noise N in this embodiment, the length L1 of the first wiring 31 and the length L2 of the second wiring can be adjusted appropriately based on the above formula. This makes it possible to suitably induce noise N in a frequency band near the center frequency Fc in each of the first wiring 31 and the second wiring 32. Note that the length L1 of the first wiring 31 and the length L2 of the second wiring 32 may be lengths that do not satisfy the above formula. Even in this case, noise N can be induced in the first wiring 31 and the second wiring 32.

[0030] As described above, in this embodiment, the noise N generated in the inverter 14 is common-mode noise that returns to the inverter 14 via the ground. Therefore, the noise N generated in the inverter 14 propagates to the ground line 25 via the fourth connection line 44, and then propagates to the power supply 50 via the second connection line 42. The noise N propagated to the power supply 50 propagates to the power supply line 23 via the first connection line 41, and then returns to the inverter 14 via the third connection line 43. In this case, if the intensity of the noise N propagating to the power supply 50 becomes too large, there is a risk that malfunction will occur in the operation of the power supply 50, as described above. This will cause the power supplied to the inverter 14 to become unstable, which will impair the stability of the operation of the motor 13.

[0031] In contrast, in the present embodiment, as shown in FIG. 2 , a portion of the noise N propagated from the inverter 14 to the ground line 25 via the fourth connection line 44 is induced to the second wiring 32. Furthermore, a portion of the noise N propagated from the power supply 50 to the power supply line 23 via the first connection line 41 is induced to the first wiring 31. The noise N induced to each of the first wiring 31 and the second wiring 32 is converted into thermal energy in the noise filter 35 and dissipated. This allows the noise filter 35 to remove the noise N. Therefore, in the present embodiment, the intensity of the noise N propagating to the power supply 50 can be reduced compared to a case in which the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35.

[0032] Furthermore, the ground line 25 connected to the second wiring 32 is connected to the housing 11 via the second ground line 47. Therefore, noise N propagating to the power supply 50 via the first ground line 46 and the third ground line 48 is also guided to the second wiring 32 via the second ground line 47. This allows the intensity of the noise N propagating to the power supply 50 to be suitably reduced.

[0033] FIG. 3 is a first diagram showing radiated noise from the motor unit 10 of this embodiment. The horizontal axis of FIG. 3 represents frequency F. The vertical axis of FIG. 3 represents the intensity Ah of the horizontally polarized radiated noise emitted from the motor unit 10. The solid line represents the radiated noise intensity Ah in this embodiment, while the dashed line represents the radiated noise intensity Ah when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35. Note that in FIG. 3, the dashed line represents the radiated noise standard S specified in CISPR25 by the Comite international Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC).

[0034] 3, when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35, the radiated noise intensity Ah is approximately the same as that of Standard S when the frequency F is around 130 MHz. In contrast, the motor unit 10 of this embodiment can reduce the radiated noise intensity Ah, particularly when the frequency F is in the range of 100 MHz or more and 200 MHz or less. This is because, as described above, in this embodiment, the noise N induced in each of the first wiring 31 and the second wiring 32 can be removed by the noise filter 35, thereby reducing the radiated noise emitted from the motor unit 10.

[0035] As described above, each of the first wiring 31 and the second wiring 32 functions as an antenna. Typically, an antenna radiates an induced AC signal into space as an electromagnetic wave, which can cause the radiated noise to worsen. In contrast, in this embodiment, the noise filter 35 converts the noise N into thermal energy, thereby reducing the energy of the radiated noise. Therefore, even when the first wiring 31 and the second wiring 32 functioning as antennas are provided, the radiated noise can be reduced.

[0036] Figure 4 is a second diagram showing the radiated noise in the motor unit 10 of this embodiment. The horizontal axis of Figure 4 represents frequency F. The vertical axis of Figure 4 represents the intensity Av of the vertically polarized waves of the radiated noise radiated from the motor unit 10. The solid line represents the radiated noise intensity Av in this embodiment, and the dashed line represents the radiated noise intensity Av when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35. Note that in Figure 4, the radiated noise standard S is shown by a dashed line.

[0037] 4, the motor unit 10 of this embodiment can reduce the intensity Av of radiated noise over almost the entire frequency band of 30 MHz or more and 200 MHz or less, compared to a motor unit 10 that does not include the first wiring 31, the second wiring 32, and the noise filter 35. This is because, similar to the intensity Ah of the horizontally polarized radiated noise shown in FIG. 3, in this embodiment, the noise N induced in each of the first wiring 31 and the second wiring 32 can be removed by the noise filter 35, thereby reducing the radiated noise emitted from the motor unit 10.

[0038] FIG. 5 is a diagram showing the average value of the conducted noise in the motor unit 10 of this embodiment. The horizontal axis of FIG. 5 represents frequency F. The vertical axis of FIG. 5 represents the average value Aa of the conducted noise intensity in the power supply line 23. The solid line represents the average value Aa of the conducted noise intensity in this embodiment, and the dashed line represents the average value Aa of the conducted noise intensity in the case where the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35. Note that in FIG. 5, the dashed line represents the standard S for the average value Aa of the conducted noise intensity specified in CISPR25 by the Comite international Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC).

[0039] 5, when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35, the average value Aa of the intensity of the conducted noise exceeds standard S in the frequency band where the frequency F is equal to or higher than 10 MHz and equal to or lower than 20 MHz. In contrast, in the motor unit 10 of the present embodiment, the intensity of the conducted noise in the frequency band where the frequency F is equal to or higher than 10 MHz and equal to or lower than 20 MHz can be reduced, and the average value Aa of the intensity of the conducted noise can be made smaller than standard S. This is because, as described above, in the present embodiment, the noise N induced in each of the first wiring 31 and the second wiring 32 can be removed by the noise filter 35, thereby reducing the conducted noise propagating to the power supply 50.

[0040] FIG. 6 is a diagram showing the quasi-peak value of the conducted noise in the motor unit 10 of this embodiment. The horizontal axis of FIG. 6 represents frequency F. The vertical axis of FIG. 6 represents the quasi-peak value Aq of the conducted noise intensity in the power supply line 23. The solid line indicates the quasi-peak value Aq of the conducted noise intensity in this embodiment, while the dashed line indicates the quasi-peak value Aq of the conducted noise intensity when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35. In FIG. 6, the dashed line indicates the standard S for the quasi-peak value Aq of the conducted noise intensity specified in CISPR25 by the Comite international Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC).

[0041] As shown in Fig. 6, when the motor unit 10 does not include the first wiring 31, the second wiring 32, and the noise filter 35, the quasi-peak value Aq of the intensity of the conducted noise exceeds the standard S in the frequency band where the frequency F is equal to or higher than 10 MHz and equal to or lower than 20 MHz. In contrast, in the motor unit 10 of the present embodiment, as described above, the intensity of the conducted noise can be reduced in the frequency band where the frequency F is equal to or higher than 10 MHz and equal to or lower than 20 MHz, and therefore the quasi-peak value Aq of the intensity of the conducted noise can be made smaller than the standard S. This is because, similar to the average value Aa of the intensity of the conducted noise shown in Fig. 5, in the present embodiment, the noise N induced in each of the first wiring 31 and the second wiring 32 can be removed by the noise filter 35, thereby reducing the conducted noise propagating to the power supply 50.

[0042] Next, a procedure for determining the length L1 of the first wiring 31 and the length L2 of the second wiring 32 in the motor unit 10 of this embodiment will be described. In this specification, "developers, etc." includes developers who perform each task and measuring devices, etc. Each task may be performed by developers alone, by assembly devices alone, or by both developers and assembly devices.

[0043] First, the developers measure the noise N in the motor unit 10 that does not include the first wiring 31, the second wiring 32, and the noise filter 35. Next, the developers perform a frequency analysis of the measured noise N and determine the center frequency Fc. The developers may set the frequency at which the intensity of the noise N is at its maximum as the center frequency Fc. Furthermore, as described above, the noise N in this embodiment includes noise that is the sum of noises at frequencies that are integer multiples of the switching frequency Fs, and therefore the center frequency Fc may be determined taking this into consideration.

[0044] After determining the center frequency Fc, the developers calculate the length L1 of the first wiring 31 and the length L2 of the second wiring 32 based on the above-mentioned formula L1 = L2 = C / (4 × Fc), connect the first wiring 31 of these lengths to the power supply line 23, and connect the second wiring 32 to the ground line 25. Next, the developers connect the noise filter 35 to the first wiring 31 and the second wiring 32, and then measure the noise N again. If the intensity of the re-measured noise N is smaller than standard S or a desired target value that is smaller than standard S, the developers determine the length L1 of the first wiring 31 and the length L2 of the second wiring 32. If the intensity of the re-measured noise N is greater than standard S or the desired target value, the developers perform a frequency analysis of the re-measured noise N and again determine the center frequency Fc, the length L1 of the first wiring 31, and the length L2 of the second wiring 32. Thereafter, these operations are repeated until the intensity of the noise N becomes smaller than the standard S or a desired target value, and the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are determined.

[0045] In this embodiment, noise countermeasures can be implemented by appropriately adjusting the length L1 of the first wiring 31 and the length L2 of the second wiring 32 according to the procedure described above. Therefore, even if developers or the like recognize the occurrence of noise N in the latter stages of development of the motor unit 10, noise countermeasures can be implemented without making design changes to the inverter 14 of the motor 13, the circuit board 21, or the like.

[0046] According to this embodiment, the power supply unit 20 includes a circuit board 21 having a power supply line 23 electrically connected to a power supply 50 and the motor 13 and a grounded ground line 25, a first wiring 31 having one end 31 a connected to the power supply line 23 and the other end 31 c being an open end, a second wiring 32 having one end 32 a connected to the ground line 25 and the other end 32 c being an open end, and a noise filter 35 connected to the first wiring 31 and the second wiring 32, and the noise filter 35 converts into thermal energy each of the noise N induced from the power supply line 23 to the first wiring 31 and the noise N induced from the ground line 25 to the second wiring 32. Therefore, as described above, the noise N, which is common mode noise generated in the inverter 14 of the motor 13, can be guided from each of the power supply line 23 and the ground line 25 provided on the circuit board 21 to each of the first wiring 31 and the second wiring 32 and removed by the noise filter 35. This prevents the intensity of noise N propagating to the power supply 50 from becoming too large, stabilizing the operation of the power supply 50. This stabilizes the power supplied to the inverter 14, stabilizing the operation of the motor 13. Furthermore, as described above, the intensities Ah and Av of the radiated noise emitted from the motor unit 10 can be reduced.

[0047] According to this embodiment, the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are substantially the same, and the noise filter 35 is a common mode filter. Therefore, the difference between the length L1 of the first wiring 31 and the length L2 of the second wiring 32 can be reduced, making it easier to induce noise N of the same frequency band in each of the first wiring 31 and the second wiring 32. Furthermore, if the noise N is common mode noise, the noise N passing through the first wiring 31 and the noise passing through the second wiring 32 are in the same direction. Furthermore, the common mode filter has a high impedance for noise N in the same direction. As a result, the noise filter 35 can effectively convert the noise N induced in each of the first wiring 31 and the second wiring 32 into thermal energy. Therefore, the intensity of the noise N propagating to the power supply 50 can be more effectively prevented from becoming too large, thereby more effectively stabilizing the operation of the power supply 50. This more effectively stabilizes the operation of the motor 13.

[0048] According to this embodiment, the first wiring 31 and the second wiring 32 are each a cable. Therefore, the first wiring 31 and the second wiring 32 can be easily connected to the circuit board. Therefore, as described above, developers can implement noise countermeasures by measuring the noise N generated in the motor unit 10, determining the center frequency Fc, and then appropriately adjusting the length L1 of the first wiring 31 and the length L2 of the second wiring 32 based on the determined center frequency Fc. Therefore, even if developers recognize the generation of noise N in the latter stages of development of the motor unit 10, they can implement noise countermeasures without making design changes to the inverter 14, the circuit board 21, etc. This prevents an increase in the number of steps required to implement noise countermeasures, thereby shortening the development period for the motor unit 10.

[0049] According to this embodiment, the noise filter 35 is connected to a portion of the first wiring 31 on one end 31 a side and a portion of the second wiring 32 on one end 32 a side. When the length L1 of the first wiring 31 and the length L2 of the second wiring 32 are each ¼ of the center wavelength λc of the noise N, the current value of the noise N induced in the first wiring 31 is maximized at the one end 31 a, and the current value of the noise N induced in the second wiring 32 is maximized at the one end 32 a. Therefore, by connecting the noise filter 35 to each of the one end 31 a of the first wiring 31 and the one end 32 a of the second wiring 32, it is possible to maximize the current value of the noise N converted into thermal energy in the noise filter 35. On the other hand, if the noise filter 35 is too close to the one end 31 a of the first wiring 31 and the one end 32 a of the second wiring 32, radiation noise generated in the inverter 14, which is a noise source, is likely to be excited in the portion of the first wiring 31 between the noise filter 35 and the other end 31 c and in the portion of the second wiring 32 between the noise filter 35 and the other end 32 c. Therefore, the noise filter 35 is preferably connected at a position some distance away from the one end 31 a and the one end 32 a. In this embodiment, as described above, the noise filter 35 is connected to the portion of the first wiring 31 on the one end 31 a side and the portion of the second wiring 32 on the one end 32 a side. Therefore, the noise filter 35 can be connected at a position close to the one end 31 a and the one end 32 a and at a position some distance away from the one end 31 a and the one end 32 a. This increases the current value of the noise N converted into thermal energy in the noise filter 35 and reduces the radiation noise excited in each of the first wiring 31 and the second wiring 32.

[0050] According to this embodiment, when the length of the first wiring is L1, the length of the second wiring is L2, the speed of radio waves is C, and the center frequency of the noise N converted into thermal energy by the noise filter 35 is Fc, the relationship L1 = L2 = C / (4 × Fc) is satisfied. Therefore, of the noise N propagated through the power supply line 23 and the ground line 25, the noise N having a frequency close to the center frequency Fc can be more effectively guided to the first wiring 31 and the second wiring 32, respectively. This more effectively reduces the intensity of the noise N propagating through the power supply line 23 and the ground line 25. Therefore, the intensity of the noise N propagating to the power supply 50 can be more effectively prevented from becoming too high, thereby more effectively stabilizing the operation of the power supply 50. This more effectively stabilizes the operation of the motor 13.

[0051] 7 , in a motor unit 210 of this embodiment, first wiring 231 and second wiring 232 are each a wiring pattern provided on a circuit board 221. In the following description, components that are the same as those in the first embodiment described above are given the same reference numerals, and description thereof will be omitted. The motor unit 210 includes a housing 11, a motor 13, and a power supply unit 220.

[0052] The power supply unit 220 supplies the power supplied from the power supply to the inverter 14 of the motor 13. The power supply unit 220 has a circuit board 221, a first wiring 231, a second wiring 232, and a noise filter 235.

[0053] In this embodiment, the circuit board 221 is an insulating, plate-shaped printed circuit board. The circuit board 221 has a power supply line 23, a ground line 25, a first wiring 231, and a second wiring 232. The configurations of the power supply line 23 and the ground line 25 of this embodiment are similar to those of the power supply line 23 and the ground line 25 of the first embodiment described above.

[0054] The first wiring 231 is a wiring through which noise N generated in the inverter 14 is induced. In this embodiment, the first wiring 231 is a wiring pattern provided on the circuit board 221. The first wiring 231 is made of, for example, copper foil. One end 231a of the first wiring 231 is connected to the power supply line 23. The other end 231c of the first wiring 231 is an open end.

[0055] The second wiring 232 is a wiring through which noise N generated in the inverter 14 is induced. In this embodiment, the second wiring 232 is a wiring pattern provided on the circuit board 221. The second wiring 232 is made of, for example, copper foil. One end 232a of the second wiring 232 is connected to the ground line 25. The other end 232c of the second wiring 232 is an open end.

[0056] The first wiring 231 and the second wiring 232 function as antennas because the other ends 231c and 232c are open, respectively, and therefore noise N in a specific frequency band is induced in each of the first wiring 231 and the second wiring 232.

[0057] The length L1 of the first wiring 231 and the length L2 of the second wiring 232 are substantially the same. In this embodiment, the length L1 of the first wiring 231 and the length L2 of the second wiring 232 are the same. The length L1 of the first wiring 231 and the length L2 of the second wiring 232 may be different from each other. As in the first embodiment described above, in this embodiment, the frequency band of the noise N to be reduced is assumed to be 10 MHz or higher and 300 MHz or lower. In this embodiment, the center frequency Fc of the noise N is 30 MHz. The length L1 of the first wiring 231 and the length L2 of the second wiring satisfy the relationship L1 = L2 = C / (4 × Fc). In this embodiment, the length L1 of the first wiring 231 and the length L2 of the second wiring 232 are each 2.5 m. Therefore, the noise N in the frequency band near the center frequency Fc can be suitably induced in each of the first wiring 231 and the second wiring 232. Other configurations of the circuit board 221 of this embodiment are similar to other configurations of the circuit board 21 of the first embodiment described above.

[0058] The noise filter 235 converts the noise N induced from the power supply line 23 to the first wiring 231 and the noise N induced from the ground line 25 to the second wiring 232 into thermal energy. The noise filter 235 is connected to both the first wiring 231 and the second wiring 232. In this embodiment, the noise filter 235 is a common mode filter. In this embodiment, the noise N is common mode noise. Therefore, when the noise N is induced in each of the first wiring 231 and the second wiring 232, the noise filter 235 functions as an inductor, converting the noise N into thermal energy and dissipating it. This reduces the intensity of the noise N propagating to the power supply 50.

[0059] 8 , in this embodiment, a portion of the noise N propagating from the inverter 14 to the ground line 25 via the fourth connection line 44 is induced to the second wiring 232. Furthermore, a portion of the noise N propagating from the power supply 50 to the power supply line 23 via the first connection line 41 is induced to the first wiring 231. The noise N induced to each of the first wiring 231 and the second wiring 232 is converted into thermal energy in the noise filter 235 and dissipated. This allows the noise filter 235 to remove the noise N. Therefore, in this embodiment, the intensity of the noise N propagating to the power supply 50 can be reduced compared to a case in which the motor unit 10 does not include the first wiring 231, the second wiring 232, and the noise filter 235.

[0060] Furthermore, the ground line 25 connected to the second wiring 232 is connected to the housing 11 via the second ground line 47. Therefore, noise N propagating to the power supply 50 via the first ground line 46 and the third ground line 48 is also guided to the second wiring 232 via the second ground line 47. This allows the intensity of the noise N propagating to the power supply 50 to be suitably reduced.

[0061] In this embodiment, the noise filter 235 is connected to a portion of the first wiring 231 on the one end 231a side. Furthermore, in this embodiment, the noise filter 235 is connected to a portion of the second wiring 232 on the one end 232a side. Therefore, similar to the first embodiment described above, in this embodiment, the noise filter 235 can be connected to a position close to the one end 231a and the one end 232a, and at a position somewhat distant from the one end 231a and the one end 232a. This increases the current value of the noise N converted into thermal energy in the noise filter 235, and reduces the radiated noise excited in each of the first wiring 231 and the second wiring 232. Other configurations of the power supply unit 220 of this embodiment are similar to those of the power supply unit 20 of the first embodiment described above. Other configurations of the motor unit 210 of this embodiment are similar to those of the motor unit 10 of the first embodiment described above.

[0062] Next, a procedure for determining the length L1 of the first wiring 231 and the length L2 of the second wiring 232 in the motor unit 210 of this embodiment will be described. First, as in the first embodiment described above, the developers measure the noise N in the motor unit 210 that does not include the first wiring 231, the second wiring 232, and the noise filter 35. Next, the developers perform a frequency analysis of the measured noise N to determine the center frequency Fc.

[0063] Once the developers have determined the center frequency Fc, they calculate the length L1 of the first wiring 231 and the length L2 of the second wiring 232 based on the above-described relational expression L1 = L2 = C / (4 × Fc). Next, they mount the first wiring 231 and the second wiring 232 having these lengths on the circuit board 221. Next, they connect the noise filter 235 to the first wiring 231 and the second wiring 232, and then measure the noise N again. Thereafter, they determine the length L1 of the first wiring 231 and the length L2 of the second wiring 232 according to the same procedure as in the first embodiment described above.

[0064] In this embodiment, noise countermeasures can be implemented by appropriately adjusting the length L1 of the first wiring 231 and the length L2 of the second wiring 232 according to the above-described procedure. Therefore, even if developers or the like recognize the generation of noise N in the latter stages of development of the motor unit 210, noise countermeasures can be implemented by adjusting only the length L1 of the first wiring 231 and the length L2 of the second wiring 232 provided on the circuit board 221. Therefore, noise countermeasures can be implemented without changing the design of the inverter 14 or the like of the motor 13.

[0065] According to this embodiment, the first wiring 231 and the second wiring 232 are each a wiring pattern provided on the circuit board 221. Therefore, as described above, even if a developer or the like recognizes the occurrence of noise N in the latter stages of development of the motor unit, noise countermeasures can be implemented without changing the design of the inverter 14 or the like of the motor 13. This prevents an increase in the number of steps required to implement noise countermeasures, thereby shortening the development period of the motor unit 210.

[0066] In this embodiment, the power supply unit 220 includes a first wiring 231 having one end 231a connected to the power supply line 23 and an open end at the other end 231c, a second wiring 232 having one end 232a connected to the ground line 25 and an open end at the other end 232c, and a noise filter 235 connected to the first wiring 231 and the second wiring 232. Therefore, common-mode noise N generated in the inverter 14 of the motor 13 can be guided from the power supply line 23 and the ground line 25 to the first wiring 231 and the second wiring 232, respectively, and removed by the noise filter 235. This prevents the intensity of the noise N propagating to the power supply 50 from becoming too large, thereby stabilizing the operation of the power supply 50. This, in turn, stabilizes the operation of the motor 13.

[0067] The present invention is not limited to the above-described embodiment, and other configurations and methods may be adopted within the scope of the technical concept of the present invention. For example, the noise filter may be connected to the other end of the first wiring and the other end of the second wiring. In this case, the noise filter can also remove noise induced in each of the first wiring and the second wiring, thereby preventing the intensity of noise propagating to the power supply from becoming too high.

[0068] Furthermore, the configuration of the noise filter is not limited to that of this embodiment and may be, for example, a plurality of resistors provided on each of the first wiring and the second wiring. Even in this case, the noise induced in each of the first wiring and the second wiring can be converted into thermal energy by the noise filter. Therefore, since the noise can be removed by the noise filter, the intensity of the noise propagating to the power supply can be prevented from becoming too large.

[0069] The power supply unit may also include a plurality of noise filters, in which case the plurality of noise filters are connected in parallel to the first wiring and the second wiring.

[0070] Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the embodiments.

[0071] The present technology may be configured as follows: (1) A motor unit including a power supply unit that supplies power supplied from a power source to a motor, the power supply unit including: a circuit board having a power line electrically connected to the power source and the motor and a ground line; a first wiring having one end connected to the power line and the other end open; a second wiring having one end connected to the ground line and the other end open; and a noise filter connected to the first wiring and the second wiring, the noise filter converting noise induced from the power line to the first wiring and noise induced from the ground line to the second wiring into thermal energy. (2) The motor unit described in (1), in which the first wiring and the second wiring have approximately the same length, and the noise filter is a common mode filter. (3) The motor unit described in (1) or (2), in which each of the first wiring and the second wiring is a cable. (4) The motor unit according to (1) or (2), wherein the first wiring and the second wiring are each a wiring pattern provided on the circuit board. (5) The motor unit according to any one of (1) to (4), wherein the noise filter is connected to a portion on the one end side of the first wiring and a portion on the one end side of the second wiring. (6) The motor unit according to any one of (1) to (5), wherein the relationship L1 = L2 = C / (4 × Fc) is satisfied, where L1 is the length of the first wiring, L2 is the length of the second wiring, C is the speed of radio waves, and Fc is the center frequency of noise converted into thermal energy by the noise filter.

[0072] 10, 210...motor unit, 13...motor, 20, 220...power supply unit, 21, 221...circuit board, 23...power supply line, 25...ground line, 31, 231...first wiring, 31a, 231a...one end, 31c, 231c...other end, 32, 232...second wiring, 32a, 232a...one end, 32c, 232c...other end, 35, 235...noise filter, 50...power supply, C...speed of radio wave, Fc...center frequency of noise, L1...length of first wiring, L2...length of second wiring, N...noise

Claims

1. A motor unit comprising a power supply unit that supplies power supplied from a power source to a motor, the power supply unit having: a circuit board having a power supply line electrically connected to the power supply and the motor, and a ground line that is grounded; a first wiring having one end connected to the power supply line and the other end being an open end; a second wiring having one end connected to the ground line and the other end being an open end; and a noise filter connected to the first wiring and the second wiring, wherein the noise filter converts each of noise induced from the power supply line to the first wiring and noise induced from the ground line to the second wiring into thermal energy.

2. The motor unit according to claim 1, wherein the first wiring and the second wiring are substantially the same length, and the noise filter is a common mode filter.

3. The motor unit according to claim 1 or 2, wherein the first wiring and the second wiring are each a cable.

4. The motor unit according to claim 1 or 2, wherein the first wiring and the second wiring are each a wiring pattern provided on the circuit board.

5. The motor unit according to claim 1 or 2, wherein the noise filter is connected to a portion of the first wiring on the one end side and a portion of the second wiring on the one end side.

6. A motor unit as described in claim 1 or 2, which satisfies the relationship L1 = L2 = C / (4 x Fc), where L1 is the length of the first wiring, L2 is the length of the second wiring, C is the speed of radio waves, and Fc is the center frequency of the noise converted into thermal energy by the noise filter.

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