Drive system

Abstract

In the present invention, a drive system comprises: a shift operation device; an accelerator operation device; a booster device that boosts the voltage of a battery and outputs the boosted voltage as a DC boosted voltage; a multi-level inverter that includes a switching element and can output a pulse voltage of three or more levels, the multi-level inverter converting the boosted voltage of the booster device into an AC output voltage and outputting the AC output voltage; a motor generator driven by the output voltage of the multi-level inverter; and a control device that controls the booster device and the multi-level inverter. A processor of the control device executes processes including determining the boosted voltage of the booster device on the basis of a shift operation acquired through the shift operation device, determining the output voltage of the multi-level inverter on the basis of an accelerator operation acquired through the accelerator operation device, and determining the number of levels of the multi-level inverter on the basis of the boosted voltage of the booster device and the output voltage of the multi-level inverter.

Description

Drive system

[0001] The present invention relates to a drive system.

[0002] For example, Patent Document 1 discloses a technique for controlling the drive of a motor by supplying the output voltage of a multilevel inverter to a motor generator. The multilevel inverter in Patent Document 1 is, for example, a three-level inverter.

[0003] Japanese Patent Application Laid-Open No. 2022-2430

[0004] In electric vehicles that include a motor generator as a drive source, the vehicle can be driven by controlling the rotation speed of the motor generator, eliminating the need for a transmission. For this reason, the shift operation device that is provided in internal combustion engine vehicles to change the shift position can sometimes be omitted in electric vehicles.

[0005] In engine vehicles, the driver can intentionally change the engine torque by shifting gears, but in electric vehicles, if a shift operation device is omitted, the driver cannot get the same feeling of vehicle operation as in engine vehicles.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a drive system that allows the driver to obtain a sense of vehicle operation through shift operations.

[0007] In order to solve the above problem, a drive system according to one embodiment of the present invention includes: a shift operation device that accepts shift operations; an accelerator operation device that accepts accelerator operations; a boost device that boosts battery voltage and outputs it as a DC boosted voltage; a multilevel inverter that includes a switching element and is capable of outputting pulse voltages of three or more levels, the multilevel inverter converting the boosted voltage of the boost device into an AC output voltage and outputting it; a motor generator that is driven by the output voltage of the multilevel inverter; and a control device that controls the boost device and the multilevel inverter, wherein the control device has one or more processors and one or more memories connected to the processors, and the processor executes processing including: determining the boosted voltage of the boost device based on the shift operation acquired through the shift operation device; determining the output voltage of the multilevel inverter based on the accelerator operation acquired through the accelerator operation device; and determining the number of levels of the multilevel inverter based on the boosted voltage of the boost device and the output voltage of the multilevel inverter.

[0008] According to the present invention, the driver can obtain a sense of vehicle operation through a shift operation.

[0009] FIG. 1 is a block diagram showing the configuration of a vehicle to which a drive system according to this embodiment is applied. FIG. 2 is a circuit diagram showing an example of the configuration of a multilevel inverter. FIG. 3 is a diagram illustrating the relationship between the rotation speed and torque of a motor generator for each number of levels of a multilevel inverter. FIG. 4 shows an example of the frequency spectrum of a sound generated when the number of levels is two. FIG. 5 shows an example of the frequency spectrum of a sound generated when the number of levels is three. FIG. 6 shows an example of the frequency spectrum of a sound generated when the number of levels is five. FIG. 7 is a diagram illustrating the relationship between the shift position of a shift operation device, the boosted voltage of a voltage boosting device, the output voltage of a multilevel inverter, and the number of levels. FIG. 8 is a diagram illustrating a case where an upshift operation to increase the shift position is acquired through the shift operation device. FIG. 9 is a diagram illustrating a case where a downshift operation to decrease the shift position is acquired through the shift operation device. FIG. 10 is a diagram illustrating another example of a case where a downshift operation is acquired through the shift operation device. FIG. 11 is a flowchart illustrating the operation flow of the drive control unit.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in the embodiments are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0011] 1 is a block diagram showing the configuration of a vehicle 1 to which a drive system 10 according to this embodiment is applied. The vehicle 1 is an electric vehicle or a hybrid electric vehicle that includes a motor generator 20 as a drive source. The drive system 10 is applied to the vehicle 1 and controls the drive of the vehicle 1.

[0012] In addition to the motor generator 20, the drive system 10 includes a battery 22, a boost device 24, a multilevel inverter 26, wheels 28, a shift operation device 30, an accelerator operation device 32, and a control device 34.

[0013] The battery 22 is a secondary battery that can be charged and discharged. The battery 22 is, for example, a lithium ion battery, but is not limited to this example and may be any secondary battery.

[0014] The boost device 24 is, for example, a DC-DC converter. The boost device 24 is electrically connected to the battery 22. The boost device 24 boosts the DC voltage of the battery 22 and outputs the boosted DC voltage. The boost device 24 is capable of changing the boosted voltage under the control of the control device 34. For example, the boost device 24 includes a switching element, and the boosted voltage can be changed by controlling the switching frequency of the switching element.

[0015] The multilevel inverter 26 is electrically connected to the boost device 24. The multilevel inverter 26 includes a plurality of switching elements. The multilevel inverter 26 is configured to be able to output pulse voltages of three or more levels. The multilevel inverter 26 is also capable of outputting pulse voltages of two levels.

[0016] The multilevel inverter 26 is configured to be able to change the number of levels of the pulse voltage it outputs. For example, the multilevel inverter 26 can output a pulse voltage with any number of levels determined from 2 to 8 levels by controlling the operation of the switching elements under the control of the control device 34. In this example, the multilevel inverter 26 can change the number of levels in seven stages from 2 to 8 levels.

[0017] Note that one level corresponds to direct current and does not constitute a pulse voltage, and is therefore not included in the number of levels of the multilevel inverter 26. Furthermore, the range of selectable levels of the multilevel inverter 26 is not limited to two to eight levels. The multilevel inverter 26 may be configured to determine the number of levels from a plurality of levels including any number of levels at least equal to three or more.

[0018] Moreover, the multilevel inverter 26 is capable of changing the output voltage by controlling the operation of the switching elements under the control of the control device 34 .

[0019] The multilevel inverter 26 converts the DC boosted voltage of the boost device 24 into an AC voltage and outputs it. For example, the multilevel inverter 26 generates a pulse voltage with a determined number of levels by performing a predetermined modulation on the boosted voltage supplied from the boost device 24 using a switching element. The generated pulse voltage is substantially a sinusoidal AC voltage. By outputting the generated pulse voltage, the multilevel inverter 26 outputs a substantially AC output voltage.

[0020] The motor generator 20 is electrically connected to the multilevel inverter 26. The motor generator 20 is driven by the output voltage of the multilevel inverter 26, which is supplied from the multilevel inverter 26.

[0021] The wheels 28 are mechanically connected to the motor generator 20 via a shaft and a gear mechanism (not shown). The wheels 28 rotate as the motor generator 20 drives them.

[0022] 2 is a circuit diagram showing an example of the configuration of the multilevel inverter 26. The multilevel inverter 26 is configured, for example, using a flying capacitor circuit system as shown in FIG. 2. The circuit system of the multilevel inverter 26 is not limited to the flying capacitor system, and may be configured using any known circuit system, such as a cascade H-bridge system or a diode clamp system. The following description will be given taking the flying capacitor system as an example.

[0023] 2, the multilevel inverter 26 includes a plurality of switching elements 50, a plurality of diodes 52, and a plurality of capacitor elements 54. The switching elements 50 are, for example, semiconductor switches such as insulated gate bipolar transistors (IGBTs). The capacitor elements 54 are, for example, capacitors.

[0024] The diode 52 is connected in anti-parallel to the switching element 50. One diode 52 is connected to one switching element 50. Hereinafter, for convenience of explanation, one set consisting of one switching element 50 and one diode 52 connected in anti-parallel may be referred to as a switch element.

[0025] In the multilevel inverter 26, a plurality of switch elements are connected in series to form an arm. Both ends of the arm serve as an input terminal 56. The input terminal 56 is connected to the boost device 24. The center of the arm serves as an output terminal 58. The output terminal 58 is connected to the motor generator 20.

[0026] The number of switch elements on one input end 56 side with respect to the output end 58 is the same as the number of switch elements on the other input end 56 side with respect to the output end 58. In the multilevel inverter 26, as the number of switch elements between one input end 56 and the output end 58 increases, the maximum number of determinable levels can be increased.

[0027] The capacitor element 54 is connected in parallel to a portion of the arm. More specifically, the capacitor element 54 is provided between a node between the switch elements between one input terminal 56 and output terminal 58 and a node between the switch elements between the other input terminal 56 and output terminal 58. The capacitor element 54 is connected to the arm so that the number of switch elements between the output terminal 58 and the node at which the capacitor element 54 is connected to the arm on the side of one input terminal 56 is the same as the number of switch elements between the output terminal 58 and the node at which the capacitor element 54 is connected to the arm on the side of the other input terminal 56. The capacitor element 54 is floating in a flying capacitor type circuit.

[0028] When an input voltage E is input to the input terminal 56, each capacitor element 54 holds a voltage that is reduced by a predetermined amount that differs for each capacitor element 54 based on the input voltage E. The multilevel inverter 26 can output a pulse voltage with a set number of levels by adding and subtracting the voltage values ​​of each capacitor element 54.

[0029] The multilevel inverter 26 employs, for example, a carrier phase shift modulation method as a modulation method. The carrier phase shift modulation method is a method in which the phases of (m-1) carrier waves corresponding to m levels are uniformly shifted and compared with a modulated wave. By performing modulation using the carrier phase shift modulation method, the multilevel inverter 26 can control the on / off timing of each switching element 50 and generate a pulse voltage with a predetermined number of levels.

[0030] 3 is a diagram illustrating the relationship between the rotation speed and torque of the motor generator 20 for each number of levels of the multilevel inverter 26. As shown in FIG. 3, as the number of levels of the multilevel inverter 26 increases, the rotation speed and torque of the motor generator 20 increase.

[0031] That is, when the number of levels is increased, the motor generator 20 is able to output a relatively high torque. In other words, when the number of levels is decreased, the motor generator 20 is only able to output a relatively low torque, and the torque can be limited.

[0032] Incidentally, in the multilevel inverter 26, a sound associated with the switching operation is generated in accordance with the switching operation of the switching element 50. The driver of the vehicle 1 can hear the sound generated from the multilevel inverter 26.

[0033] In the multilevel inverter 26, the pitch of the generated sound varies depending on the number of levels. In the multilevel inverter 26, when the number of levels is changed, the pitch of the generated sound changes in accordance with the change in the number of levels.

[0034] Fig. 4 shows an example of the frequency spectrum of a sound generated when the number of levels is two. Fig. 5 shows an example of the frequency spectrum of a sound generated when the number of levels is three. Fig. 6 shows an example of the frequency spectrum of a sound generated when the number of levels is five. In Figs. 4 to 6, the horizontal axis represents the frequency of the sound, and the vertical axis represents the normalized amplitude. In Figs. 4 to 6, peaks, which are portions where the amplitude increases sharply, appear at multiple frequencies.

[0035] In Fig. 4, amplitude peaks appear at relatively low frequencies (e.g., 2 kHz), and the intervals between the peaks are relatively narrow. In Fig. 5, the amplitude peaks are shifted to higher frequencies (e.g., 4 kHz) than in Fig. 4, and the intervals between the peaks are wider than in Fig. 4. In Fig. 6, the amplitude peaks are shifted to higher frequencies (e.g., 8 kHz) than in Fig. 5, and the intervals between the peaks are wider than in Fig. 5.

[0036] That is, in the multilevel inverter 26, the lower the number of levels, the lower the pitch of the generated sound, and the higher the number of levels, the higher the pitch of the generated sound.

[0037] For this reason, for example, when the number of levels changes from a relatively low state to a relatively high state, the pitch of the generated sound changes to a higher pitch, and when the number of levels changes from a relatively high state to a relatively low state, the pitch of the generated sound changes to a lower pitch.

[0038] Returning to FIG. 1 , the shift operation device 30 is configured to be able to receive a shift operation that instructs a change or specification of a shift position. The shift operation device 30 may be a paddle shift device or a shift lever device. The shift operation device 30 includes a sensor that can detect the received shift operation.

[0039] The accelerator operation device 32 is configured to be able to receive an accelerator operation command to accelerate the vehicle 1. The accelerator operation device 32 is, for example, an accelerator pedal. The accelerator operation device 32 includes a sensor that can detect the accelerator operation amount of the received accelerator operation.

[0040] The control device 34 includes one or more processors 70 and one or more memories 72 connected to the processors 70. The memories 72 include a ROM in which programs and the like are stored, and a RAM as a work area. The processors 70 of the control device 34 cooperate with the programs stored in the memories to control the entire vehicle 1.

[0041] The processor 70 of the control device 34 also functions as a drive control unit 74 that controls the drive of the motor generator 20. The drive control unit 74 controls the boost device 24 and the multilevel inverter 26, thereby substantially controlling the drive of the motor generator 20.

[0042] The drive control unit 74 can obtain the shift operation of the driver through the shift operation device 30. The drive control unit 74 determines the boost voltage of the boost device 24 based on the shift operation obtained through the shift operation device 30.

[0043] The drive control unit 74 can obtain the accelerator operation of the driver through the accelerator operation device 32. The drive control unit 74 determines the output voltage of the multilevel inverter 26 based on the accelerator operation obtained through the accelerator operation device 32.

[0044] The drive control unit 74 determines the number of levels of the multilevel inverter 26 based on the boosted voltage of the boost device 24 and the output voltage of the multilevel inverter 26. The determination of the number of levels will be described in detail later.

[0045] The drive control unit 74 transmits a boost voltage command instructing the determined boost voltage to the boost device 24. Upon receiving the boost voltage command, the boost device 24 operates the switching elements at a switching frequency corresponding to the boost voltage indicated by the received boost voltage command, and outputs the boost voltage to the multilevel inverter 26.

[0046] Furthermore, the drive control unit 74 transmits to the multilevel inverter 26 a level number command instructing the determined number of levels of the multilevel inverter 26 and an output voltage command instructing the determined output voltage of the multilevel inverter 26. Upon receiving the level number command and the output voltage command, the multilevel inverter 26 operates each switching element 50 so as to achieve the number of levels indicated by the received level number command and the output voltage indicated by the received output voltage command. As a result, the multilevel inverter 26 outputs to the motor generator 20 a pulse voltage that is the instructed number of levels and that is substantially the instructed output voltage.

[0047] 7 is a diagram illustrating the relationship among the shift position of the shift operating device 30, the boosted voltage of the voltage boosting device 24, the output voltage of the multilevel inverter 26, and the number of levels. Setting map information corresponding to the relationship diagram of FIG. 7 is pre-stored in the memory 72 of the control device 34.

[0048] 7, the shift position is associated with the boost voltage in the drive system 10. More specifically, the boost voltage is set to increase as the shift position moves toward a higher speed.

[0049] In the example of Fig. 7, the shift positions are set from 1st to 8th speeds, with 1st speed being the lowest speed shift position and 8th speed being the highest speed shift position.

[0050] In the example of Figure 7, when the shift position is in first gear, the boosted voltage is 200V. When the shift position is in second gear, the boosted voltage is 300V. When the shift position is in third gear, the boosted voltage is 400V. When the shift position is in fourth gear, the boosted voltage is 500V. When the shift position is in fifth gear, the boosted voltage is 600V. When the shift position is in sixth gear, the boosted voltage is 700V. When the shift position is in seventh gear, the boosted voltage is 800V. When the shift position is in eighth gear, the boosted voltage is 900V.

[0051] The drive control unit 74 determines the boost voltage of the boost device 24 so that the boost voltage of the boost device 24 increases as the shift position moves toward a higher speed position and decreases as the shift position moves toward a lower speed position.

[0052] Furthermore, the upper limit of the voltage range that the multilevel inverter 26 can output is related to the input voltage of the multilevel inverter 26. In the drive system 10, the boost voltage is the input voltage to the multilevel inverter 26, so if the boost voltage varies, the upper limit of the output voltage of the multilevel inverter 26 will vary. As described above, the shift position and the boost voltage are associated with each other, so the upper limit of the output voltage of the multilevel inverter 26 will vary depending on the shift position.

[0053] In the example of Figure 7, output voltage Vup1 is the upper limit of the output voltage when in first gear. Output voltage Vup2 is the upper limit of the output voltage when in second gear. Output voltage Vup3 is the upper limit of the output voltage when in third gear. Output voltage Vup4 is the upper limit of the output voltage when in fourth gear. Output voltage Vup5 is the upper limit of the output voltage when in fifth gear. Output voltage Vup6 is the upper limit of the output voltage when in sixth gear. Output voltage Vup7 is the upper limit of the output voltage when in seventh gear. Output voltage Vup8 is the upper limit of the output voltage when in eighth gear.

[0054] The upper limit of the output voltage of the multilevel inverter 26 increases as the boost voltage increases, i.e., as the shift position moves toward a relatively higher speed. The upper limit of the output voltage of the multilevel inverter 26 decreases as the boost voltage decreases, i.e., as the shift position moves toward a relatively lower speed.

[0055] In this way, in the drive system 10, an upper limit value of the output voltage of the multilevel inverter 26 corresponding to the boosted voltage of the boost device 24 is set for each shift position.

[0056] Furthermore, in the drive system 10, the number of levels of the multilevel inverter 26 is associated with the output voltage of the multilevel inverter 26 within the voltage range that can be output by the multilevel inverter 26. More specifically, the number of levels of the multilevel inverter 26 is set to increase as the output voltage of the multilevel inverter 26 increases.

[0057] 7, the voltage range that can be output by the multilevel inverter 26 is divided into levels of 2 to 8. The number of levels of the multilevel inverter 26 is set to change by one level in order from 2 to 8 as it moves from the lower limit value to the upper limit value of the voltage range that can be output by the multilevel inverter 26. Furthermore, the number of levels is set at approximately equal intervals in the voltage range that can be output by the multilevel inverter 26 so that the width of the output voltage at each of the levels from 2 to 8 is approximately equal.

[0058] The correspondence between the number of levels and the output voltage is set for each shift position, in other words, for each boost voltage. For any of the first to eighth shift positions, the voltage range that can be output by the multilevel inverter 26 corresponding to each shift position is divided into approximately equal intervals by the number of levels from 2 to 8.

[0059] As described above, the upper limit value of the output voltage of the multilevel inverter 26 decreases as the shift position moves toward the lower speed side, and therefore the range of the output voltage corresponding to each of the levels divided into 2 to 8 levels narrows as the shift position moves toward the lower speed side.

[0060] For example, assume that the sixth-speed shift position is currently specified. In this case, the drive control unit 74 determines 700 V as the boost voltage. Furthermore, for example, assume that the drive control unit 74 determines the output voltage Va in FIG. 7 as the current output voltage of the multilevel inverter 26 based on the current accelerator depression amount. Then, the drive control unit 74 determines six levels as the number of levels of the multilevel inverter 26 based on the boost voltage of 700 V, the output voltage Va, and the setting map information. In this manner, the boost voltage of the boost device 24, the output voltage of the multilevel inverter 26, and the number of levels are determined.

[0061] Furthermore, for example, if six levels are determined as the number of levels of the multilevel inverter 26, the multilevel inverter 26 operates at six levels, generating sounds with pitches corresponding to the six levels. The driver of the vehicle 1 can hear sounds with pitches corresponding to the six levels.

[0062] Figure 8 is a diagram illustrating a case where an upshift operation to raise the shift position is acquired through the shift operation device 30. In the example of Figure 8, it is assumed that when the shift position is in sixth gear, an upshift operation to raise the shift position to seventh gear is acquired. Figure 8 only shows the shift position of interest in Figure 7, and omits other shift positions.

[0063] As shown in FIG. 8, when the shift position is in sixth gear and an upshift operation to shift the shift position up to seventh gear is detected, the drive control unit 74 determines 800 V as the boost voltage corresponding to seventh gear.

[0064] That is, in response to acquiring an upshifting operation, the drive control unit 74 increases the boost voltage of the voltage boosting device 24 compared to before acquiring the upshifting operation.

[0065] 8, the current output voltage of the multilevel inverter 26 is assumed to be the output voltage Vb. In this example, when the shift position is the sixth speed, the number of levels of the multilevel inverter 26 is six.

[0066] When an upshift operation to shift the shift position up to seventh speed is acquired, the boost voltage and the shift position change while maintaining the current output voltage Vb of the multilevel inverter 26, as indicated by the thick arrow in Fig. 8. Then, the drive control unit 74 determines five levels as the number of levels of the multilevel inverter 26 based on the boost voltage of 800 V corresponding to seventh speed, the output voltage Vb, and the setting map information.

[0067] That is, the drive control unit 74 decreases the number of levels of the multilevel inverter 26 in response to an increase in the boosted voltage of the boost device 24 compared to before the upshift operation was acquired.

[0068] As the level number decreases, the torque of the motor generator 20 decreases. Therefore, when an upshift operation is performed, the torque of the motor generator 20 may decrease at the timing of the upshift operation compared to before the upshift operation. In other words, in the drive system 10, when the driver performs an upshift operation, the torque of the motor generator 20 can be freely reduced to a torque that meets the driver's intention.

[0069] Furthermore, when the number of levels of the multilevel inverter 26 is decreased in response to acquisition of an upshift operation, the pitch of the sound of the multilevel inverter 26 changes to a lower pitch compared to before acquisition of the upshift operation. In other words, the drive system 10 can convey that the shift position has been increased in response to an upshift operation by changing the pitch of the sound generated from the multilevel inverter 26.

[0070] When the driver of the vehicle 1 performs an upshift operation, the driver can hear a sound whose pitch changes to a lower pitch, thereby enabling the driver of the vehicle 1 to recognize that an upshift operation has been performed by the sound.

[0071] Even if the number of levels drops to level 5 by shifting up to 7th gear, by subsequently increasing the accelerator operation amount, the number of levels can be raised back to level 6 while still in 7th gear. In this way, the driver can freely control torque by changing the shift position and accelerator operation amount, just like in an internal combustion engine vehicle.

[0072] Furthermore, depending on the current output power of the multilevel inverter 26 and the relationship between the shift positions before and after the upshift operation, the number of levels may not be changed.

[0073] 9 is a diagram illustrating a case where a downshift operation to downshift the shift position is acquired through the shift operation device 30. In the example of FIG. 9, it is assumed that the shift position is in sixth gear and a downshift operation to downshift the shift position to fifth gear is acquired. In FIG. 9, only the shift position of interest in FIG. 7 is shown, and other shift positions are omitted.

[0074] As shown in FIG. 9, when the shift position is in sixth gear and a downshift operation to downshift to fifth gear is detected, the drive control unit 74 determines 600 V as the boost voltage corresponding to fifth gear.

[0075] That is, in response to acquiring a downshifting operation, the drive control unit 74 decreases the boost voltage of the voltage boosting device 24 compared to before acquiring the downshifting operation.

[0076] 9, the current output voltage of the multilevel inverter 26 is assumed to be the output voltage Vc. In this example, when the shift position is the sixth speed, the number of levels of the multilevel inverter 26 is four.

[0077] When a downshift operation to downshift the shift position to fifth gear is acquired, the boost voltage and the shift position change while maintaining the current output voltage Vc of the multilevel inverter 26, as indicated by the thick arrow in Fig. 9. Then, the drive control unit 74 determines five as the number of levels of the multilevel inverter 26 based on the boost voltage of 600 V corresponding to fifth gear, the output voltage Vc, and the setting map information.

[0078] That is, the drive control unit 74 increases the number of levels of the multilevel inverter 26 in response to the decrease in the boosted voltage of the boost device 24 compared to before the downshift operation was acquired.

[0079] As the level number increases, the torque of the motor generator 20 increases. Therefore, when a downshift operation is performed, the torque of the motor generator 20 may increase at the timing of the downshift operation compared to before the downshift operation. In other words, in the drive system 10, when the driver performs a downshift operation, the torque of the motor generator 20 can be freely increased to a torque that meets the driver's intention.

[0080] Furthermore, when the number of levels of the multilevel inverter 26 is increased in response to the acquisition of a downshift operation, the pitch of the sound of the multilevel inverter 26 changes to a higher pitch compared to before the downshift operation was acquired. In other words, the drive system 10 can convey that the shift position has been lowered in response to a downshift operation by changing the pitch of the sound generated from the multilevel inverter 26.

[0081] When the driver of the vehicle 1 performs a downshift operation, the driver can hear a sound whose pitch changes to a higher pitch, thereby enabling the driver of the vehicle 1 to recognize that a downshift operation has been performed by the sound.

[0082] Even if the number of levels increases to level 5 by shifting down to fifth gear, by subsequently decreasing the accelerator operation amount, the number of levels can be decreased back to level 4 while still in fifth gear. In this way, the driver can freely control torque by changing the shift position and accelerator operation amount, just like in an internal combustion engine vehicle.

[0083] Furthermore, depending on the current output power of the multilevel inverter 26 and the relationship between the shift positions before and after the downshift operation, the number of levels may not be changed.

[0084] In this way, the drive system 10 can improve the operational feel of the vehicle 1 that is experienced by the driver of the vehicle 1. For example, the drive system 10 can provide the driver of the vehicle 1 with an operational feel that is similar to that of an engine vehicle.

[0085] Figure 10 is a diagram illustrating another example of a case where a downshift operation is acquired through the shift operation device 30. In the example of Figure 10, it is assumed that a downshift operation to downshift the shift position to fifth gear is acquired when the shift position is sixth gear. Figure 10 only shows the shift position of interest in Figure 7, and omits other shift positions.

[0086] As shown in FIG. 10, when the shift position is in sixth gear and a downshift operation to downshift to fifth gear is detected, the drive control unit 74 determines 600 V as the boost voltage corresponding to fifth gear.

[0087] 10, the current output voltage of the multilevel inverter 26 is assumed to be the output voltage Vd. In this example, when the shift position is the sixth speed, the number of levels of the multilevel inverter 26 is eight.

[0088] In this example, when a downshift operation to downshift the shift position to fifth gear is detected, the output voltage Vd of the multilevel inverter 26 exceeds the upper limit output voltage Vup5 of fifth gear after the downshift operation.

[0089] In such a case, the drive control unit 74 limits the output voltage of the multilevel inverter 26 to an upper limit value, that is, an output voltage Vup5, in the fifth gear after the downshift operation, as shown by the thick arrow in FIG.

[0090] That is, when a limiting condition regarding the output voltage of the multilevel inverter 26 is satisfied, the drive control unit 74 limits the output voltage to an upper limit value after downshifting due to a downshift operation. The limiting condition is that both of the following first and second conditions are satisfied. The first condition is that a downshift operation is detected. The second condition is that the output voltage of the multilevel inverter 26 exceeds the upper limit value of the output voltage of the multilevel inverter 26 at the shift position after downshifting due to a downshift operation.

[0091] This allows the drive control unit 74 to cause the multilevel inverter 26 to output an appropriate output voltage corresponding to the shift position.

[0092] In addition, since the output voltage is limited when the above-mentioned limiting conditions are met, the driver can, for example, perform a downshift operation to intentionally limit the output voltage and intentionally reduce the torque of the motor generator 20.

[0093] Fig. 11 is a flowchart illustrating the flow of operations of the drive control unit 74. The drive control unit 74 repeatedly executes the series of processes in Fig. 11 every time a predetermined interrupt timing occurs at a predetermined cycle.

[0094] When a predetermined interrupt timing arrives, the drive control unit 74 determines whether or not a shift operation that changes the shift position from the current shift position has been acquired through the shift operation device 30 (S10). The shift operation may specify an absolute shift position, or may specify a shift position relative to the current shift position.

[0095] If a shift operation that changes the shift position from the current shift position is acquired (YES in S10), the drive control unit 74 updates the shift position in accordance with the acquired shift operation (S11). Note that the drive control unit 74 may store the updated shift position in the memory 72.

[0096] After updating the shift position, the drive control unit 74 updates the boost voltage of the boost device 24 based on the updated shift position (S12), and proceeds to the processing of step S15. The drive control unit 74 may store the updated boost voltage in memory.

[0097] If the shift operation acquired in step S10 is an upshift operation, the drive control unit 74 increases the boost voltage in step S12. If the shift operation acquired in step S10 is a downshift operation, the drive control unit 74 decreases the boost voltage in step S12.

[0098] Furthermore, if a shift operation that changes the shift position from the current shift position is not acquired in step S10 (NO in S10), the drive control unit 74 maintains the current shift position (S13). Since the shift position is maintained, the drive control unit 74 also maintains the boosted voltage of the voltage booster 24 (S14), and proceeds to the process of step S15.

[0099] In step S15, the drive control unit 74 generates a boost voltage command based on the boost voltage updated in step S12 or the boost voltage maintained in step S14 (S15).

[0100] Next, the drive control unit 74 acquires the current accelerator operation amount via the accelerator operation device 32 (S16). The drive control unit 74 determines the output voltage of the multilevel inverter 26 based on the acquired current accelerator operation amount (S17).

[0101] Next, the drive control unit 74 determines whether or not a limiting condition related to limiting the output voltage of the multilevel inverter 26 is satisfied in the shift position after the update in step S11 or the shift position maintained in step S13 (S18). The drive control unit 74 may determine that the limiting condition is satisfied if the output voltage of the multilevel inverter 26 in step S17 exceeds the upper limit value in the shift position after the update in step S11 or the shift position maintained in step S13.

[0102] If the limiting condition is satisfied (YES in S18), the drive control unit 74 limits the output voltage of the multilevel inverter 26 to the upper limit value of the output voltage of the multilevel inverter 26 at the shift position after the downshift operation (S19). Thereafter, the drive control unit 74 proceeds to the process of step S20.

[0103] If the restriction condition is not met (NO in S18), the drive control unit 74 proceeds to the process of step S20.

[0104] In step S20, the drive control unit 74 determines the number of levels of the multilevel inverter 26. More specifically, if the limitation in step S19 is performed, the drive control unit 74 determines the number of levels based on the output voltage of the multilevel inverter 26 after the limitation, the boost voltage determined in step S12 or step S14, and the setting map information. If the limitation in step S19 is not performed, the drive control unit 74 determines the number of levels based on the output voltage of the multilevel inverter 26 determined in step S17, the boost voltage determined in step S12 or step S14, and the setting map information.

[0105] If the shift operation acquired in step S10 is an upshift operation, the drive control unit 74 may decrease the level number in step S20 compared to before the upshift operation was acquired. Also, if the shift operation acquired in step S10 is a downshift operation, the drive control unit 74 may increase the level number in step S20 compared to before the downshift operation was acquired.

[0106] The drive control unit 74 generates a level number command based on the number of levels determined in step S20 (S21).

[0107] The drive control unit 74 generates an output voltage command (S22). More specifically, if the limitation of step S19 has been performed, the drive control unit 74 generates the output voltage command based on the output voltage of the multilevel inverter 26 after the limitation. If the limitation of step S19 has not been performed, the drive control unit 74 generates the output voltage command based on the output voltage of the multilevel inverter 26 determined in step S17.

[0108] Then, the drive control unit 74 transmits the generated boost voltage command to the boost device 24, and transmits the generated level number command and output voltage command to the multilevel inverter 26 (S23), and ends the series of processes.

[0109] As described above, the drive control unit 74 of the drive system 10 of this embodiment determines the boost voltage of the boost device 24 based on the shift operation acquired through the shift operation device 30. The drive control unit 74 determines the output voltage of the multilevel inverter 26 based on the accelerator operation acquired through the accelerator operation device 32. The drive control unit 74 determines the number of levels of the multilevel inverter 26 based on the boost voltage of the boost device 24 and the output voltage of the multilevel inverter 26.

[0110] In the drive system 10 of this embodiment, when the shift position is changed by a shift operation, the number of levels of the multilevel inverter 26 may change. When the number of levels changes, the torque characteristics of the motor generator 20 change. More specifically, when the number of levels increases, the torque of the motor generator 20 increases, and when the number of levels decreases, the torque of the motor generator 20 decreases.

[0111] Therefore, in the drive system 10 of this embodiment, the driver can freely increase and decrease the torque of the motor generator 20 to a torque that meets the driver's intention by performing a shift operation.

[0112] For example, when merging onto a highway, the driver can intentionally downshift to increase the torque of the motor generator 20 and rapidly accelerate the vehicle 1, allowing the vehicle to merge onto the highway appropriately.

[0113] Therefore, in the drive system 10 of this embodiment, the driver can obtain the same operational feeling of the vehicle 1 by shifting the gears as in an engine vehicle.

[0114] Furthermore, in the drive system 10 of this embodiment, when the number of levels changes, the pitch of the sound associated with the switching operation of the switching elements 50 of the multilevel inverter 26 changes. Therefore, in the drive system 10 of this embodiment, the shift operation can be indicated by a change in the sound of the multilevel inverter 26. In other words, in the drive system 10 of this embodiment, the change in the sound of the multilevel inverter 26 can evoke the change in engine sound that occurs when a shift operation is performed in an internal combustion engine vehicle.

[0115] Therefore, in terms of such noise, the drive system 10 of this embodiment allows the driver to obtain the same operating feel of the vehicle 1 by shifting gears as in an engine vehicle. As a result, the drive system 10 of this embodiment can provide the driver with the same driving pleasure as when operating an engine vehicle.

[0116] Furthermore, when the number of levels of the multilevel inverter 26 changes, the efficiency of the multilevel inverter 26 changes. Of the 2 to 8 levels, for example, the efficiency of level 5 and levels therearound may be relatively high, and the efficiency of levels 2 to 3 may be relatively low. The efficiency of the multilevel inverter 26 affects the electricity consumption of the vehicle 1. For this reason, in the drive system 10 of this embodiment, the driver can shift gears to drive the vehicle 1 at the electricity consumption intended by the driver.

[0117] Furthermore, for example, when the shift position is eighth gear and the number of levels is three, the efficiency of the multilevel inverter 26 is relatively low, and the power consumption is relatively low. However, in this case, since the shift position is eighth gear, the multilevel inverter 26 can tolerate a relatively high output voltage.

[0118] In contrast, for example, when the shift position is second gear and the number of levels is five, the efficiency of the multilevel inverter 26 is relatively high and the power consumption is relatively high. However, in this case, since the shift position is second gear, the output voltage of the multilevel inverter 26 can only be allowed up to a relatively low upper limit value.

[0119] In this way, the driver can freely change the shift position by shifting, thereby intentionally prioritizing ensuring driving performance by expanding the voltage range of the output voltage, or intentionally prioritizing electricity efficiency.

[0120] Furthermore, in the drive system 10 of this embodiment, the boosted voltage decreases as the shift position moves toward a lower speed side. As a result, in the drive system 10 of this embodiment, the upper limit value of the output voltage of the multilevel inverter 26 decreases as the shift position moves toward a lower speed side.

[0121] For example, when driving at high speeds on a highway or the like, the driver may shift the gear so that the shift position is on the relatively high-speed side, and when driving at low speeds on an ordinary road or the like, the driver may shift the gear so that the shift position is on the relatively low-speed side. In this case, the drive system 10 of this embodiment can stably perform high-speed driving by supplying a relatively high output voltage to the motor generator 20 during high-speed driving. Furthermore, the drive system 10 of this embodiment prevents the output voltage from becoming excessively high during low-speed driving, thereby improving safety.

[0122] While the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present invention.

[0123] For example, in the above embodiment, when the limiting condition is satisfied, the output voltage of the multilevel inverter 26 is limited to an upper limit value. However, when the limiting condition is satisfied, the drive control unit 74 may not permit the shift position to be lowered and may maintain the current shift position.

[0124] REFERENCE SIGNS LIST 10 Drive system 20 Motor generator 22 Battery 24 Boost device 26 Multilevel inverter 30 Shift operation device 32 Accelerator operation device 34 Control device 50 Switching element 70 Processor 72 Memory 74 Drive control unit

Claims

1. A drive system comprising: a shift operation device that accepts a shift operation; an accelerator operation device that accepts an accelerator operation; a boost device that boosts a battery voltage and outputs it as a DC boosted voltage; a multilevel inverter including a switching element and capable of outputting a pulse voltage of three or more levels, the multilevel inverter converting the boosted voltage of the boost device into an AC output voltage and outputting it; a motor generator that is driven by the output voltage of the multilevel inverter; and a control device that controls the boost device and the multilevel inverter, wherein the control device has one or more processors and one or more memories connected to the processors, and the processor executes processes including: determining the boosted voltage of the boost device based on the shift operation obtained through the shift operation device; determining the output voltage of the multilevel inverter based on the accelerator operation obtained through the accelerator operation device; and determining the number of levels of the multilevel inverter based on the boosted voltage of the boost device and the output voltage of the multilevel inverter.

2. The drive system according to claim 1, wherein the multilevel inverter generates a sound associated with the switching operation of the switching elements, and the pitch of the sound changes according to a change in the number of levels.

3. The drive system of claim 1, wherein the processor executes processing including determining the boost voltage of the boost device so that the boost voltage of the boost device increases as the shift position progresses toward a higher speed position and decreases as the shift position progresses toward a lower speed position.

4. The drive system of claim 1, wherein the processor executes processing including: increasing the boost voltage of the boost device in response to a shift-up operation that raises a shift position being obtained through the shift operation device, compared to before the shift-up operation was obtained; and decreasing the number of levels of the multilevel inverter in response to the increase in the boost voltage of the boost device, compared to before the shift-up operation was obtained.

5. The drive system according to claim 4, wherein the multilevel inverter generates a sound associated with the switching operation of the switching elements, the pitch of the sound changes in accordance with a change in the number of levels, and when the number of levels of the multilevel inverter is lowered in response to the acquisition of the shift-up operation, the pitch of the sound of the multilevel inverter changes to a lower pitch compared to before the shift-up operation was acquired.

6. The drive system of claim 1, wherein the processor executes processing including: in response to a downshift operation to lower a shift position being acquired through the shift operation device, decreasing the boost voltage of the boost device compared to before the downshift operation was acquired; and in response to the decrease in the boost voltage of the boost device, increasing the number of levels of the multilevel inverter compared to before the downshift operation was acquired.

7. The drive system according to claim 6, wherein the multilevel inverter generates a sound associated with the switching operation of the switching elements, the pitch of the sound changes in response to a change in the number of levels, and when the number of levels of the multilevel inverter is increased in response to the acquisition of the downshift operation, the pitch of the sound of the multilevel inverter changes to a higher pitch compared to before the downshift operation was acquired.

8. The drive system of claim 1, wherein an upper limit value of the output voltage of the multilevel inverter corresponding to the boosted voltage of the boost device is set for each shift position, and the processor executes processing including limiting the output voltage of the multilevel inverter to the upper limit value when a downshift operation for downshifting a shift position is acquired through the shift operation device and the output voltage of the multilevel inverter exceeds the upper limit value of the output voltage of the multilevel inverter at the shift position after downshifting by the downshift operation.

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