Electric vehicle

Abstract

To suppress sound in a vehicle interior from becoming louder.SOLUTION: An electric vehicle is provided with: a first motor and a second motor which drive left and right driving wheels, respectively and are housed in a first housing and a second housing, respectively; a first inverter and a second inverter which drive the first motor and the second motor, respectively by switching by a plurality of switching elements; and a control device that controls the first inverter and the second inverter, respectively by pulse-width modulation control using first and second carrier frequencies, respectively. The control device sets the first carrier frequency so that a frequency of carrier noise of the first motor can avoid resonant frequency bands of the first motor and of the first housing on the basis of the fact that the frequency of the carrier noise of the first motor is generated when the vehicle runs straight, or when the vehicle turns left or when the vehicle turns right, and also sets the second carrier frequency so that a frequency of carrier noise of the second motor can avoid resonant frequency bands of the second motor and of the second housing on the basis of the fact that the frequency of the carrier noise of the second motor is generated when the vehicle runs straight, or when the vehicle turns left or when the vehicle turns right.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to electric vehicles. [Background technology]

[0002] A conventional electric vehicle of this type includes a motor and an inverter that drives the motor, and generates PWM signals for multiple switching elements of the inverter based on a voltage modulation rate and voltage phase based on a torque command for the motor and the number of pulses per unit period of the motor's electrical angle to control the switching of the multiple switching elements (see, for example, Patent Document 1). In this electric vehicle, the number of pulses is set so that the frequency of the torque ripple generated by the switching of the multiple switching elements is outside a predetermined resonance region, thereby suppressing the amplification of motor vibration and noise caused by the torque ripple. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-68493 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of an electric vehicle having a first and second motor that drive the left and right drive wheels and are housed in a first and second housing, respectively, and a first and second inverter that drives the motor and the first and second motors, respectively, the resonant frequency band (a frequency band that is likely to increase the sound inside the vehicle cabin when it overlaps with the frequency of the motor's carrier noise (including sideband components) based on the motor's current fluctuation accompanying inverter switching) differs for each surface of the first and second housing, depending on the shape of the first and second housing, etc. When the vehicle turns, the orientation of the left and right drive wheels and the first and second housings changes compared to when traveling straight, so if PWM control of the first and second inverters is performed without taking this into consideration, the overlap between the frequency of the carrier noise and the resonant frequency band may increase the sound inside the vehicle cabin. The electric vehicle disclosed herein has as its main objective the suppression of increased sound inside the vehicle cabin. [Means for solving the problem]

[0005] The electric vehicle of the present disclosure employs the following means to achieve the above-mentioned main object. The electric vehicle of the present disclosure is an electric vehicle including first and second motors that drive left and right drive wheels and are housed in first and second housings, respectively, first and second inverters that drive the first and second motors by switching a plurality of switching elements, and a control device that controls the first and second inverters by pulse width modulation control using first and second carrier frequencies, respectively, in which the control device sets the first carrier frequency so as to avoid a resonance frequency band of the first motor and the first housing based on whether the frequency of the carrier noise of the first motor is when the vehicle is traveling straight, turning left, or turning right, and sets the second carrier frequency so as to avoid a resonance frequency band of the second motor and the second housing based on whether the frequency of the carrier noise of the second motor is when the vehicle is traveling straight, turning left, or turning right. In the electric vehicle of the present disclosure, this processing makes it possible to suppress an increase in noise inside the vehicle cabin depending on whether the vehicle is traveling straight, turning left, or turning right. [Brief description of the drawings]

[0006] [Figure 1] 1 is a schematic configuration diagram of an electric vehicle 20 according to an embodiment of the present disclosure. [Diagram 2] 13 is a flowchart illustrating an example of a carrier frequency setting process. [Diagram 3] 1 is an explanatory diagram showing the state of a vehicle when traveling straight and when turning left. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic diagram of an electric vehicle 20 according to an embodiment of the present disclosure. The electric vehicle 20 according to the embodiment is configured as a right-hand drive vehicle, and as shown in the figure, includes two motors 32, 42, two inverters 34, 44, a battery 50 as an electricity storage device, and an electronic control unit 70 as a control device.

[0008] The motors 32, 42 are in-wheel motors attached to the left and right front wheels 22a, 22b, and are both configured as synchronous generator motors. The motors 32, 42 are configured to the same specifications. The motors 32, 42 are accommodated in housings 33, 43. The inverters 34, 44 have a plurality of switching elements. The motors 32, 42 are rotationally driven by the electronic control unit 70 controlling the switching of the plurality of switching elements of the inverters 34, 44. The inverters 34, 44 and the battery 50 are connected to a power line 54. The battery 50 is configured as a lithium ion secondary battery, a nickel-metal hydride secondary battery, or the like.

[0009] The electronic control unit 70 includes a microcomputer having a CPU, a ROM, a RAM, a flash memory, an input / output port, and a communication port, various driving circuits, and various logic ICs. The electronic control unit 70 receives signals from various sensors via the input ports. For example, the electronic control unit 70 receives rotational positions θma and θmb from rotational position sensors 32a and 42a that detect the rotational positions of the rotors of the motors 32 and 42, and phase currents Iua, Iva, Iub, and Ivb from current sensors 32u, 32v, 42u, and 42v that detect the phase currents of the U phase and V phase of the motors 32 and 42. The electronic control unit 70 also receives a voltage Vb from a voltage sensor attached between the terminals of the battery 50, and a current Ib from a current sensor attached to the output terminal of the battery 50. The electronic control unit 70 also receives inputs of a start signal from a start switch 80, a shift position SP from a shift position sensor 82 that detects the operation position of a shift lever 81, an accelerator opening Acc from an accelerator pedal position sensor 84 that detects the depression amount of an accelerator pedal 83, and a brake pedal position BP from a brake pedal position sensor 86 that detects the depression amount of a brake pedal 85. The electronic control unit 70 also receives inputs of a vehicle speed V from a vehicle speed sensor 87 and a steering angle θw (negative value when turning left, positive value when turning right) from a steering angle sensor 88. The electronic control unit 70 outputs various control signals via output ports. For example, the electronic control unit 70 outputs switching control signals to multiple switching elements of the inverters 34 and 44. The electronic control unit 70 calculates electrical angles θea and θeb and rotation speeds Nma and Nmb of the motors 32 and 42 based on rotation positions θma and θmb of the rotors of the motors 32 and 42 from the rotation position sensors 32a and 42a.

[0010] In the electric vehicle 20 of the embodiment thus configured, the electronic control unit 70 first sets a required torque Td* required for traveling based on the accelerator opening Acc and the vehicle speed V. Next, it sets the torque distribution ratios Da, Db (Da+Db=1) of the motors 32, 42 based on the steering angle θw and the like. Then, it multiplies the required torque Td* by the torque distribution ratios Da, Db to set torque commands Tma*, Tmb* for the motors 32, 42, and performs switching control of the multiple transistors of the inverters 34, 44 so that the motors 32, 42 are driven by the torque commands Tma*, Tmb*.

[0011] Here, the control of the inverters 34, 44 by the electronic control unit 70 will be described. The inverters 34, 44 are basically controlled by pulse width modulation control (PWM control). In the control of the inverters 34, 44, first, the sum of the phase currents of the motors 32, 42 is set to zero, and the U-phase phase currents Iua, Iub and the V-phase phase currents Iva, Ivb are coordinate-converted (3-phase-2-phase conversion) into d-axis currents Ida, Idb and q-axis currents Iqa, Iqb using the electrical angles θea, θeb of the motors 32, 42. Next, the d-axis current commands Ida*, Idb* and the q-axis current commands Iqa*, Iqb* are set based on the torque commands Tma*, Tmb* of the motors 32, 42. Then, the d-axis voltage commands Vda*, Vdb* and the q-axis voltage commands Vqa*, Vqb* are set so that the differences between the d-axis current commands Ida*, Idb* and the q-axis current commands Iqa*, Iqb* and the d-axis currents Ida, Idb and the q-axis currents Iqa, Iqb are cancelled out. Furthermore, using the electrical angles θea, θeb of the motors 32, 42, the d-axis voltage commands Vda*, Vdb* and the q-axis voltage commands Vqa*, Vqb* are coordinate-transformed (2-phase to 3-phase transformation) into U-phase voltage commands Vua*, Vub*, V-phase voltage commands Vva*, Vvb*, and W-phase voltage commands Vwa*, Vwb*. Then, by comparing the U-phase voltage commands Vua*, Vub*, the V-phase voltage commands Vva*, Vvb*, and the W-phase voltage commands Vwa*, Vwb* with carrier voltages (triangular wave voltages) Vca, Vcb of carrier frequencies fca, fcb, PWM signals are generated for the multiple transistors of inverters 34, 44, and switching control is performed.

[0012] Next, the operation of the electric vehicle 20 of the embodiment, in particular the process of setting the carrier frequencies fca, fcb used in the PWM control of the inverters 34, 44, will be described. Fig. 2 is a flowchart showing an example of the carrier frequency setting process repeatedly executed by the electronic control unit 70. Note that the case where the control mode of the inverters 34, 44 is the asynchronous PWM mode will be described. The asynchronous PWM mode is a control mode in which the carrier frequencies fca, fcb are not synchronized with the rotation speeds Nma, Nmb of the motors 32, 42.

[0013] 2, the electronic control unit 70 first compares the absolute value of the steering angle θw with a threshold value θWref to determine whether the vehicle is traveling straight or turning (turning left or right) (step S100). If it is determined that the vehicle is traveling straight, the electronic control unit 70 sets the carrier frequency fca using the first map for traveling straight (step S110) and sets the carrier frequency fcb using the second map for traveling straight (step S120), and then ends this process.

[0014] If it is determined in step S100 that the vehicle is turning, the sign of the steering angle θw is checked to determine whether the vehicle is turning left or right (step S130). If it is determined that the vehicle is turning left, the carrier frequency fca is set using the first map for turning left (step S140), and the carrier frequency fcb is set using the second map for turning left (step S150), and the process ends. On the other hand, if it is determined that the vehicle is turning right, the carrier frequency fca is set using the first map for turning right (step S160), and the carrier frequency fcb is set using the second map for turning left (step S170), and the process ends.

[0015] FIG. 3 is an explanatory diagram of the state of the vehicle when going straight and when turning left. FIG. 3(A) shows the state of the vehicle when going straight, and FIG. 3(B) shows the state of the vehicle when turning left. In FIG. 3(A), (i) shows the state of the vehicle when going straight, (ii) shows an example of the first map when going straight, and (iii) shows an example of the second map when going straight. In FIG. 3(B), (i) shows the state of the vehicle when turning left, (ii) shows an example of the first map when turning left, and (iii) shows an example of the second map when turning left. The motors 32, 42 and the housings 33, 43 have different resonant frequency bands (frequency bands that tend to increase the sound inside the vehicle cabin when overlapping with the frequency of the carrier noise (including sideband components) of the motors 32, 42 based on the current fluctuation of the motors 32, 42 accompanying the switching of the multiple switching elements of the inverters 34, 44) for each surface of the housings 33, 43 due to the shape of the housings 33, 43, etc. In FIG. 3, the motors 32, 42 and the housings 33, 43 have a resonant frequency band f1 toward the rear of the vehicle and a resonant frequency band f2 toward the inside in the left-right direction of the vehicle in the direction of the housings 33, 43 when traveling straight.

[0016] When traveling straight, as shown in FIG. 3(A)(i), the resonance frequency band f1 of the motors 32, 42 and the housings 33, 43 becomes a problem in the vehicle interior. For this reason, in the embodiment, as shown in FIG. 3(A)(ii) and (iii), the first and second maps for traveling straight are used to set the carrier frequencies fca, fcb based on the rotation speeds Nma, Nmb of the motor 32 so that the frequency of the carrier noise of the motors 32, 42 does not overlap with the resonance frequency band f1. When turning left, as shown in FIG. 3(B)(i), the resonance frequency band f1 of the motor 32 and the housing 33 becomes a problem in the vehicle interior, and the resonance frequency bands f1, f2 of the motor 42 and the housing 43 become a problem in the vehicle interior. For this reason, in the embodiment, as shown in FIG. 3(B)(ii), the first map for turning left is used to set the carrier frequency fca based on the rotation speed Nma of the motor 32 so that the frequency of the carrier noise of the motor 32 does not overlap with the resonance frequency band f1. 3B(iii), the second map for turning left sets the carrier frequency fcb based on the rotation speed Nmb of the motor 42 so that the frequency of the carrier noise of the motor 42 does not overlap with the resonance frequency bands f1 and f2. Turning right can be considered similar to turning left. By setting the carrier frequencies fca and fcb in this manner, it is possible to suppress the sound inside the vehicle from increasing depending on whether the vehicle is traveling straight, turning left, or turning right.

[0017] In the electric vehicle 20 of the present embodiment described above, the carrier frequency fca is set so as to avoid the resonant frequency band of the motor 32 and the housing 33 based on whether the frequency of the carrier noise of the motor 32 is when the vehicle is traveling straight, turning left, or turning right, and the carrier frequency fcb is set so as to avoid the resonant frequency band of the motor 42 and the housing 43 based on whether the frequency of the carrier noise of the motor 42 is when traveling straight, turning left, or turning right. This makes it possible to suppress the sound inside the vehicle from becoming louder depending on whether the vehicle is traveling straight, turning left, or turning right.

[0018] In the above-described embodiment, in the carrier frequency setting process of Fig. 2, if it is determined in step S100 that the vehicle is turning left or right, the process proceeds to step S130. However, when it is determined in step S100 that the vehicle is turning left or right, if the vehicle speed V is less than the threshold value Vref, the process proceeds to step S130, and if the vehicle speed V is equal to or greater than the threshold value Vref, the process proceeds to step S110. The threshold value Vref is determined as the upper limit vehicle speed at which the in-vehicle sound becomes a problem (is easily felt by the driver). This is because when the vehicle speed V is high, the sound is easily blended in with the traveling sound.

[0019] In the above embodiment, the case where the control mode of the inverters 34, 44 is the asynchronous PWM mode has been described, but the same can be considered for the case where the control mode is the synchronous PWM mode. The synchronous PWM mode is a control mode in which the carrier frequencies fca, fcb are synchronized with the rotational speeds Nma, Nmb of the motors 32, 42. When the control mode of the inverter 34 is the synchronous PWM mode, the carrier frequency fca is set by setting the number of synchronizations between the carrier voltage Vca and the voltage commands Vu*, Vv*, Vw* of each phase so as to avoid the resonance frequency band of the motor 32 and the housing 33 based on whether the frequency of the carrier noise of the motor 32 is traveling straight, turning left, or turning right, and the carrier frequency fcb is set in the same manner. This makes it possible to suppress the sound inside the vehicle from becoming louder depending on whether the vehicle is traveling straight, turning left, or turning right. For example, the asynchronous PWM mode is used when the rotation speeds Nma, Nmab of the motors 32, 42 are less than the threshold value Nmref, and the synchronous PWM mode is used when the rotation speeds Nma, Nmab of the motors 32, 42 are equal to or greater than the threshold value Nmref.

[0020] In the above embodiment, the carrier frequency fca is set so as to avoid the resonant frequency band for the motor 32 and the housing 33 in the vehicle cabin based on whether the frequency of the carrier noise of the motor 32 is when the vehicle is traveling straight, turning left, or turning right, but the carrier frequency fca may be set so as to avoid the resonant frequency band in the vehicle cabin and the resonant frequency band outside the vehicle cabin (outside the vehicle). The same applies to the setting of the carrier frequency fcb.

[0021] In the above-described embodiment, the motors 32, 42 of the electric vehicle 20 are in-wheel motors attached to the left and right front wheels 22a, 22b, but they may be attached to left and right axles connected to the left and right front wheels 22a, 22b. The electric vehicle 20 includes two motors 32, 42 that drive the left and right front wheels 22a, 22b, respectively, but in addition to or instead of this, two motors 32r, 42r that drive the left and right rear wheels 22c, 22d, respectively, may be provided. Furthermore, the electric vehicle 20 uses a battery 50 as an electricity storage device, but instead of or in addition to this, a capacitor or the like may be used.

[0022] The relationship between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problems will be described. In the embodiment, the motors 32 and 42 correspond to the "first and second motors", the inverters 34 and 44 correspond to the "first and second inverters", and the electronic control unit 70 corresponds to the "control device".

[0023] Note that the correspondence between the main elements of the embodiment and the main elements of the invention described in the Means for Solving the Problem column does not limit the elements of the invention described in the Means for Solving the Problem column, since the embodiment is an example for specifically explaining the form for implementing the invention described in the Means for Solving the Problem column. In other words, the interpretation of the invention described in the Means for Solving the Problem column should be made based on the description in that column, and the embodiment is merely a specific example of the invention described in the Means for Solving the Problem column.

[0024] The above describes embodiments for implementing the present disclosure, but the present disclosure is not limited to these embodiments, and it goes without saying that the present disclosure can be implemented in various forms without departing from the gist of the present disclosure. [Industrial Applicability]

[0025] The present disclosure can be used in the electric vehicle manufacturing industry and the like. [Explanation of symbols]

[0026] 20 electric vehicle, 22a, 22b front wheels, 32, 42 motor, 33, 43 housing, 34, 44 inverter, 70 electronic control unit.

Claims

[Claim 1] An electric vehicle including first and second motors that drive left and right drive wheels, respectively, and that are housed in first and second housings, first and second inverters that drive the first and second motors by switching a plurality of switching elements, respectively, and a control device that controls the first and second inverters by pulse width modulation control using first and second carrier frequencies, the control device sets the first carrier frequency so as to avoid a resonance frequency band of the first motor and the first housing based on whether a frequency of carrier noise of the first motor is when the vehicle is traveling straight, turning left, or turning right, and sets the second carrier frequency so as to avoid a resonance frequency band of the second motor and the second housing based on whether a frequency of carrier noise of the second motor is when the vehicle is traveling straight, turning left, or turning right. Electric car.

Images