Drive device

Abstract

A drive device according to the present invention includes: a first electric motor; a first power transmission mechanism that transmits power from the first electric motor to at least one of a right-left pair of drive wheels; a second electric motor; a second power transmission mechanism that transmits power from the second electric motor to at least the other of the right-left pair of drive wheels; and an energy storage device that supplies power to the first electric motor and the second electric motor. The drive device constitutes a charging circuit that supplies a charging current supplied by an external power source to the energy storage device via the neutral point of the first electric motor. The reaction force received by the first electric motor from the first power transmission mechanism when the first electric motor rotationally drives the first power transmission mechanism at a prescribed acceleration is greater than the reaction force received by the second electric motor from the second power transmission mechanism when the second electric motor rotationally drives the second power transmission mechanism at the prescribed acceleration.

Description

Drive unit

[0001] The technology disclosed in this specification relates to a drive device.

[0002] Patent Document 1 discloses a drive unit including two electric motors that drive left and right drive wheels. Patent Document 2 discloses a technology in which the two electric motors that drive the drive wheels are used to charge an electricity storage device. In the technology of Patent Document 2, electric power from a charging device external to the vehicle is supplied to the electricity storage device via the neutral point of one of the two electric motors.

[0003] JP 2016-205444 A JP 2009-118659 A

[0004] In Patent Document 2, when power from an external charging device is supplied to a power storage device, the power is supplied via the neutral point of one of two electric motors. In this case, current flows through the one electric motor, which may cause vibrations in the one electric motor. This specification provides a technology that can reduce vibrations in one of two electric motors when power is supplied from an external charging device to a power storage device via the neutral point of the one electric motor.

[0005] The drive device disclosed in this specification drives a pair of left and right drive wheels. The drive device includes a first electric motor, a first power transmission mechanism that transmits power from the first electric motor to at least one of the pair of left and right drive wheels, a second electric motor, a second power transmission mechanism that transmits power from the second electric motor to at least the other of the pair of left and right drive wheels, and an electric storage device that supplies power to the first electric motor and the second electric motor. The drive device configures a charging circuit that supplies a charging current, supplied from an external power source, to the electric storage device via a neutral point of the first electric motor. When the first electric motor drives and rotates the first power transmission mechanism at a predetermined acceleration, the reaction force that the first electric motor receives from the first power transmission mechanism is greater than the reaction force that the second electric motor receives from the second power transmission mechanism when the second electric motor drives and rotates the second power transmission mechanism at the predetermined acceleration.

[0006] The drive device described above is configured so that the first electric motor receives a relatively larger reaction force from the first power transmission mechanism than the second electric motor. Therefore, when a current flows through the first electric motor due to charging of the power storage device, the first power transmission mechanism suppresses the rotational displacement of the first electric motor. Therefore, vibration is less likely to occur in the first electric motor. This allows vibration of the first electric motor to be reduced even when the power storage device is charged at a high voltage using the coil of the first electric motor.

[0007] This specification also discloses a drive device according to another embodiment. The drive device of this embodiment drives a pair of left and right drive wheels. The drive device includes a first electric motor, a first power transmission mechanism that transmits power from the first electric motor to one of the pair of left and right drive wheels, a second electric motor, a second power transmission mechanism that transmits power from the second electric motor to the other of the pair of left and right drive wheels, and an electric storage device that supplies power to the first electric motor and the second electric motor. The drive device forms a charging circuit that supplies a charging current, supplied from an external power source, to the electric storage device via a neutral point of the first electric motor. The number of first rotating components included in the first power transmission mechanism is greater than the number of second rotating components included in the second power transmission mechanism, and the first rotating components include all components that are symmetrical to each of the second rotating components.

[0008] In the drive device described above, the number of first rotating parts in the first power transmission mechanism is greater than the number of second rotating parts in the second power transmission mechanism. Furthermore, the first rotating parts include all parts that are bilaterally symmetrical to each other of the second rotating parts. Therefore, when a current flows through the first electric motor due to charging of the power storage device, the first power transmission mechanism suppresses the rotational displacement of the first electric motor. Therefore, vibration is less likely to occur in the first electric motor. This makes it possible to reduce vibration of the first electric motor even when charging the power storage device at high voltage using the coil of the first electric motor. The term "first rotating parts" includes not only parts located on a transmission path through which the first power transmission mechanism transmits power, but also parts that rotate without contributing to the transmission of the first power.

[0009] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention."

[0010] A block diagram of an electric vehicle equipped with a drive device 20 of a first embodiment is shown. A circuit diagram of the drive device 20 of the first embodiment is shown. A detailed plan view of the drive device 20 of the first embodiment is shown. A detailed plan view of a drive device 120 of a second embodiment is shown. A detailed plan view of a drive device 220 of a third embodiment is shown. A detailed plan view of a drive device 320 of a fourth embodiment is shown. A detailed plan view of a drive device 420 of a fifth embodiment is shown.

[0011] In one embodiment of the present technology, the inertia of the first power transmission mechanism may be greater than the inertia of the second power transmission mechanism. However, in another embodiment, the frictional resistance of the first power transmission mechanism may be greater than the frictional resistance of the second power transmission mechanism.

[0012] In one embodiment of the present technology, the number of first rotating components included in the first power transmission mechanism may be greater than the number of second rotating components included in the second power transmission mechanism. Here, the first rotating components included in the first power transmission mechanism broadly refer to components that rotate when the first power transmission mechanism transmits the power, and include components that do not directly contribute to the transmission of the first power, such as a parking brake gear or an oil pump. The same applies to the second rotating components.

[0013] In this configuration, the first power transmission mechanism, which includes more first rotating parts than the second power transmission mechanism, can suppress rotational displacement of the first electric motor when a current flows through the first electric motor due to charging of the power storage device, thereby making it less likely that vibration will occur in the first electric motor.

[0014] In one embodiment of the present technology, the first rotating component may include a parking brake gear of a vehicle including the pair of left and right drive wheels.

[0015] With this configuration, the reaction force that the first electric motor receives from the first power transmission mechanism can be easily increased by utilizing the parking brake gear.

[0016] In one embodiment of the present technology, the first rotating part may include an oil pump that supplies oil to the first power transmission mechanism.

[0017] With this configuration, the reaction force that the first electric motor receives from the first power transmission mechanism can be easily increased by utilizing the oil pump.

[0018] In an embodiment of the present technology, a first rotating shaft included in the first power transmission mechanism may have a first outer diameter. In this case, a second rotating shaft included in the second power transmission mechanism, which is disposed symmetrically with the first rotating shaft in a vehicle including the pair of left and right drive wheels, may have a second outer diameter smaller than the first outer diameter.

[0019] With this configuration, the inertia of the first power transmission mechanism can be easily increased by changing the outer diameter of the rotary shaft.

[0020] In one embodiment of the present technology, the frictional resistance of the first power transmission mechanism may be greater than the frictional resistance of the second power transmission mechanism. However, in another embodiment, the inertia of the first power transmission mechanism may be greater than the inertia of the second power transmission mechanism.

[0021] In one embodiment of the present technology, in a first bearing included in the first power transmission mechanism, a first rolling element of the first bearing may be pressed with a first preload. In this case, in a second bearing included in the second power transmission mechanism and disposed symmetrically to the first bearing in a vehicle including the pair of left and right drive wheels, a second rolling element of the second bearing may be pressed with a second preload smaller than the first preload.

[0022] With this configuration, the frictional resistance of the first power transmission mechanism can be easily increased by changing the preload setting of the corresponding bearing.

[0023] In one embodiment of the present technology, in a vehicle having the pair of left and right drive wheels, the first electric motor may be arranged symmetrically with the second electric motor, and in the vehicle, the first power transmission mechanism may be arranged symmetrically with the second power transmission mechanism.

[0024] With this configuration, the power of each electric motor is transmitted symmetrically to the drive wheels arranged symmetrically. This makes it easier to share the output of each electric motor. Therefore, each electric motor can be controlled more easily than in a configuration in which the power of each electric motor is transmitted asymmetrically. However, vibrations occurring only in the first electric motor arranged symmetrically with the second electric motor are likely to cause discomfort to the user. For this reason, the technology disclosed in this specification is particularly useful in a configuration in which the first and second electric motors and the first and second power transmission mechanisms are arranged symmetrically.

[0025] In one embodiment of the present technology, the drive device may further include a first inverter located between the first electric motor and the power storage device, and a second inverter located between the second electric motor and the power storage device. However, in another embodiment, the drive device does not need to include the first inverter and the second inverter.

[0026] In one embodiment of the present technology, the drive device may further include a casing that houses at least the first electric motor and the second electric motor. However, in another embodiment, the drive device may include a first casing that houses the first electric motor and a second casing that houses the second electric motor.

[0027] In one embodiment of the present technology, the first power transmission mechanism may transmit power from the first electric motor to one of the pair of left and right drive wheels, and the second power transmission mechanism may transmit power from the second electric motor to the other of the pair of left and right drive wheels. As a result, power from the electric motor corresponding to the drive wheel is transmitted to each of the pair of left and right drive wheels via the corresponding power transmission mechanism. Therefore, in the drive device of this embodiment, each of the pair of left and right drive wheels can be easily driven independently, compared to a configuration in which power is transmitted to both of the pair of left and right drive wheels via the first power transmission mechanism and the second power transmission mechanism. However, in another embodiment, the first power transmission mechanism may transmit power from the first electric motor to both of the pair of left and right drive wheels. In that case, the second power transmission mechanism may transmit power from the second electric motor to both of the pair of left and right drive wheels.

[0028] First Embodiment Fig. 1 shows a block diagram of an electric vehicle 10 equipped with a drive device 20 of this embodiment, as seen from above. In this specification, the front of the electric vehicle 10 (i.e., the upper side of the paper in Fig. 1) may be simply referred to as the "front," and the opposite side may be simply referred to as the "rear." Furthermore, the left side of the electric vehicle 10 (i.e., the left side of the paper in Fig. 1) may be simply referred to as the "left," and the opposite side may be simply referred to as the "right."

[0029] The electric vehicle 10 includes a vehicle body 2, a pair of left and right front wheels 4R, 4L, a pair of left and right rear wheels 5R, 5L, a charging inlet 6, a parking brake 9, and a drive unit 20. The drive unit 20 includes a pair of left and right electric motors 30R, 30L, a pair of left and right inverters 40R, 40L, a pair of left and right power transmission mechanisms 50R, 50L, and a battery pack 3. Hereinafter, the term "left and right pair" may be simply referred to as "a pair."

[0030] The drive unit 20 supplies electric power from the battery pack 3 to the pair of electric motors 30R, 30L to drive the pair of front wheels 4R, 4L. This drives the electric vehicle 10. In other words, the pair of front wheels 4R, 4L are the drive wheels of the electric vehicle 10. In a modified example, the pair of rear wheels 5R, 5L may be the drive wheels of the electric vehicle 10, or the pair of front wheels 4R, 4L and the pair of rear wheels 5R, 5L may be the drive wheels of the electric vehicle 10. Note that the term "electric vehicle" in this specification includes, for example, a rechargeable electric vehicle that is charged by an external power source, a fuel cell vehicle that uses a fuel cell as a power source, and a hybrid vehicle that also has an engine.

[0031] The charging inlet 6 is disposed on the right side of the vehicle body 2. The charging inlet 6 is configured to be connected to an external DC power source 7 (for example, a charging stand) via a power cable 8.

[0032] The drive unit 20 of this embodiment has a substantially symmetrical shape with respect to the center line CL1 in the left-right direction of the electric vehicle 10. Therefore, in this embodiment, the configuration located to the right of the center line CL1 of the drive unit 20 will be mainly described. A right inverter 40R is disposed above the right electric motor 30R (i.e., toward the front of the paper in FIG. 1 ). A right power transmission mechanism 50R is disposed to the left of the right electric motor 30R. A left power transmission mechanism 50L is disposed between the right power transmission mechanism 50R and the left electric motor 30L.

[0033] The right power transmission mechanism 50R drives the right front wheel 4R at a rotational speed that is reduced from the rotational speed of the right electric motor 30R, for example. That is, the right power transmission mechanism 50R transmits the power of the right electric motor 30R to the right front wheel 4R. The right power transmission mechanism 50R includes a right drive shaft 14R. The right electric motor 30R drives the right front wheel 4R via the right drive shaft 14R. Similarly, the left electric motor 30L drives the left front wheel 4L via the left drive shaft 14L. In this embodiment, the right drive shaft 14R and the left drive shaft 14L are separated at the center of the electric vehicle 10 in the left-right direction. The pair of front wheels 4R, 4L are independently driven by the pair of electric motors 30R, 30L.

[0034] As shown in FIG. 2 , the drive unit 20 constitutes part of a circuit connecting the external DC power supply 7 and the battery pack 3. The drive unit 20 constitutes a charging circuit 11 for supplying a charging current supplied from the external DC power supply 7 to the battery pack 3. The right electric motor 30R is a three-phase motor including a U-phase coil 35U, a V-phase coil 35V, and a W-phase coil 35W. One ends of the U-phase coil 35U, the V-phase coil 35V, and the W-phase coil 35W are connected to a neutral point NP. The other end of the U-phase coil 35U is connected to a U-phase arm 42U, the other end of the V-phase coil 35V is connected to a V-phase arm 42V, and the other end of the W-phase coil 35W is connected to a W-phase arm 42W.

[0035] In the charging circuit 11 of this embodiment, one terminal of the charging inlet 6 is connected to the positive electrode of the battery pack 3 via the neutral point NP of the right electric motor 30R and the right inverter 40R. The other terminal of the charging inlet 6 is connected to the negative electrode of the battery pack 3 via the right inverter 40R. The charging circuit 11 supplies charging current to the battery pack 3 via the neutral point NP of the right electric motor 30R. This allows the right electric motor 30R and the right inverter 40R to function as three boost circuits connected in parallel between the charging inlet 6 and the battery pack 3. This allows the drive unit 20 to boost the output voltage of the external DC power supply 7 using the right electric motor 30R and the right inverter 40R. This allows rapid charging to be performed even if the output voltage of the external DC power supply 7 is lower than the voltage of the battery pack 3. Furthermore, one terminal of the charging inlet 6 is directly connected to the positive electrode of the battery pack 3 via the switch 13. When the output voltage of the external DC power supply 7 is equal to the voltage of the battery pack 3, the charging circuit 11 turns on the switch 13 to allow the output voltage of the external DC power supply 7 to bypass the neutral point NP of the right electric motor 30R. Although not shown, the charging circuit 11 further includes a charging unit including a relay, a capacitor, etc. The charging unit is connected to the neutral point NP and the right inverter 40.

[0036] The detailed structure of the drive unit 20 will be described with reference to FIG. 3 . The right electric motor 30R of the drive unit 20 includes a right motor case 32R, a right motor bearing 33R, a right rotor 34R, and a right stator 35R. The right motor case 32R houses the right rotor 34R and the right stator 35R. The right rotor 34R has a permanent magnet 36R. The right stator 35R faces the right rotor 34R from the radially outer side. The outer periphery of the right stator 35R is covered by a U-phase coil 35U, a V-phase coil 35V, and a W-phase coil 35W (see FIG. 2 ). The coils 35U, 35V, and 35W of each phase are arranged along the circumferential direction of the right stator 35R. The right motor bearing 33R is, for example, a ball bearing, and includes a cylindrical inner raceway ring fixed to the rotating shaft, an outer raceway ring positioned radially outward of the inner raceway ring, and balls disposed between the inner and outer raceways. The right motor bearing 33R rotates the first shaft 51R by rolling balls along an inner raceway. The other bearings are also ball bearings. In a modified example, each bearing may be a roller bearing instead of a ball bearing.

[0037] In addition to the right drive shaft 14R, the right power transmission mechanism 50R includes a first shaft 51R, a right transmission case 52R, a first bearing 53R, a first gear 54R, a second shaft 55R, a pair of second bearings 56R, a second gear 57R, a third shaft 59R, a pair of third bearings 58R, a third gear 60R, a fourth gear 61R, a fifth gear 62R, and a fourth shaft 63R. These components, excluding the right transmission case 52R, are rotating components included in the right power transmission mechanism 50R and rotate when the right power transmission mechanism 50R transmits power. The fourth shaft 63R is connected to the right drive shaft 14R.

[0038] The first shaft 51R is inserted into the right rotor 34R of the right electric motor 30R and rotates together with the right rotor 34R. The first shaft 51R is rotatably fixed to the left and right ends of the motor case 32R via a pair of motor bearings 33R. The first shaft 51R passes through the left side wall of the motor case 32R and extends into the right transmission case 52R. The left end of the first shaft 51R is rotatably held in the right transmission case 52R by the first bearing 53R.

[0039] The first gear 54R is disposed adjacent to the right of the first bearing 53R. The first gear 54R is fixed to the first shaft 51R and rotates together with the first shaft 51R. The first gear 54R meshes with the second gear 57R. The second gear 57R is fixed to the second shaft 55R and rotates the second shaft 55R. Both left and right ends of the second shaft 55R are rotatably held in the right transmission case 52R by a pair of second bearings 56R. The second gear 57R meshes with a third gear 60R fixed to the third shaft 59R. The third gear 60R rotates the third shaft 59R. Both left and right ends of the third shaft 59R are rotatably held in the right transmission case 52R by a pair of third bearings 58R. A fourth gear 61R is disposed adjacent to the right of the third gear 60R. The fourth gear 61R is fixed to the third shaft 59R and rotates together with the third shaft 59R.

[0040] The fourth gear 61R meshes with the fifth gear 62R. The fifth gear 62R is fixed to the fourth shaft 63R and rotates the fourth shaft 63R. As described above, the fourth shaft 63R is connected to the right drive shaft 14R and rotates the right drive shaft 14R. In this way, the right power transmission mechanism 50R transmits the power of the right electric motor 30R to the right front wheel 4R via multiple shafts, bearings, and gears.

[0041] Similarly, the left power transmission mechanism 50L includes a left motor bearing 33L, a left rotor 34L, a first shaft 51L, a left transmission case 52L, a first bearing 53L, a first gear 54L, a second shaft 55L, a pair of second bearings 56L, a second gear 57L, a third shaft 59L, a pair of third bearings 58L, a third gear 60L, a fourth gear 61L, a fifth gear 62L, and a fourth shaft 63L. These components, excluding the left transmission case 52L, are rotating components included in the left power transmission mechanism 50L and rotate when the left power transmission mechanism 50L transmits power. The rotation of the rotating components included in the left power transmission mechanism 50L transmits power from the left electric motor 30L to the left front wheel 4L. As described above, the left power transmission mechanism 50L has a configuration that is approximately bilaterally symmetrical to the right power transmission mechanism 50R. In other words, the rotating parts of the right power transmission mechanism 50R include all of the rotating parts of the left power transmission mechanism 50L that are symmetrical to each other, and these rotating parts are arranged symmetrically with respect to the center line CL.

[0042] As described above, the drive device 20 of this embodiment configures the charging circuit 11 that supplies charging current from the external DC power supply 7 to the battery pack 3 via the neutral point NP of the right electric motor 30R. Therefore, while current flows through the charging circuit 11 (i.e., while the charging inlet 6 is connected to the external DC power supply 7 via the power cable 8), current flows through the coils 35U, 35V, and 35W of each phase of the right electric motor 30R. As a result, for example, a d-axis current may be generated in the right electric motor 30R, causing the right electric motor 30R to vibrate.

[0043] A parking gear 70 is disposed on the first shaft 51R of the right power transmission mechanism 50R. The parking gear 70 is one of the rotating parts included in the right power transmission mechanism 50R and rotates together with the first shaft 51R when the right power transmission mechanism 50R transmits power. The parking gear 70 is disposed between the first gear 54R and the motor case 32R. When the parking brake 9 (see FIG. 1) is operated, the parking gear 70 engages with a parking lock (not shown) to lock the first shaft 51R. Furthermore, an oil pump 72 is fixed to the right end of the third shaft 59R. The oil pump 72 is one of the rotating parts included in the right power transmission mechanism 50R and rotates together with the third shaft 59R when the right power transmission mechanism 50R transmits power. The oil pump 72 is a so-called impeller that circulates oil within the drive unit 20. As an example, the oil pump 72 in this embodiment is configured to pump oil to an oil pipe 74 that passes through the third shaft 59R. The oil pipe 74 passes through the third shaft 59R and extends to the left transmission case 52L of the left power transmission mechanism 50L. This allows the oil pump 72 to supply oil to the right power transmission mechanism 50R and the left power transmission mechanism 50L.

[0044] 3, the first shaft 51L of the left power transmission mechanism 50L is not provided with the parking gear 70. Therefore, the inertia of the first shaft 51R of the right power transmission mechanism 50R is greater than the inertia of the first shaft 51L of the left power transmission mechanism 50L.

[0045] Similarly, the third shaft 59L of the left power transmission mechanism 50L does not have the oil pump 72 fixed thereto. Therefore, the inertia of the third shaft 59R of the right power transmission mechanism 50R is greater than the inertia of the third shaft 59L of the left power transmission mechanism 50L.

[0046] For this reason, the right power transmission mechanism 50R is less likely to transmit power to the right front wheel 4R than the left power transmission mechanism 50L. In other words, in the drive unit 20, when the right electric motor 30R drives the right power transmission mechanism 50R to rotate at a predetermined acceleration, the reaction force that the right electric motor 30R receives from the right power transmission mechanism 50R is greater than the reaction force that the left electric motor 30L receives from the left power transmission mechanism 50L when the left electric motor 30L drives the left power transmission mechanism 50L to rotate at a predetermined acceleration. For this reason, even if a d-axis current is generated in the right electric motor 30R due to charging of the battery pack 3 via the neutral point NP of the right electric motor 30R, the rotational displacement of the right electric motor 30R is suppressed by the right power transmission mechanism 50R. In other words, the right electric motor 30R is less likely to vibrate. Therefore, the drive unit 20 can reduce vibration of the right electric motor 30R when charging the battery pack 3. As a result, the state of the right electric motor 30R, in which current flows while the battery pack 3 is being charged, approaches the state of the left electric motor 30L, in which no current flows. This makes it possible to prevent vibrations occurring only in the right electric motor 30R, one of the pair of left and right electric motors 30R, 30L, from causing discomfort to the user.

[0047] Furthermore, by increasing the inertia of the right power transmission mechanism 50R by utilizing the parking gear 70 and oil pump 72 required for the electric vehicle 10, it is possible to reduce the vibration of the right electric motor 30R in a mass-efficient manner compared to, for example, a configuration that includes a separate mechanism for increasing the inertia of the right power transmission mechanism 50R.

[0048] There is a possibility that a small gap may occur between the meshing rotating bodies (e.g., the first gear 54R and the second gear 57R) of the right power transmission mechanism 50R. Therefore, in other conventional structures, if the inertia of the second gear 57R is large, for example, vibrations from the second gear 57R onward can be suppressed, but the first gear 54R may vibrate by the amount of the gap. Therefore, the parking gear 70 of this embodiment is attached to the first shaft 51R, which is directly connected to the right electric motor 30R. Therefore, the parking gear 70 can reliably reduce vibrations of the right electric motor 30R compared to a structure that increases the inertia of a rotating body (e.g., the second gear 57R) that is indirectly connected to the right electric motor 30R via another rotating body.

[0049] In the drive system 20 of this embodiment, the right power transmission mechanism 50R and the left power transmission mechanism 50L are basically symmetrical. However, the right power transmission mechanism 50R is provided with a parking gear 70 and an oil pump 72, which are not provided in the left power transmission mechanism 50L. As a result, the number of rotating parts included in the right power transmission mechanism 50R is greater than the number of rotating parts included in the left power transmission mechanism 50L. As a result, the total weight of the rotating parts included in the right power transmission mechanism 50R is heavier than the total weight of the rotating parts included in the left power transmission mechanism 50L, and the inertia of the right power transmission mechanism 50R is greater than the inertia of the left power transmission mechanism 50L. Therefore, when current flows through the right electric motor 30R due to charging of the battery pack 3, the right power transmission mechanism 50R suppresses the rotational displacement of the right electric motor 30R. Therefore, vibration is less likely to occur in the right electric motor 30R. This makes it possible to reduce vibrations of the right electric motor 30R even when the battery pack 3 is charged at a high voltage using the coils 35U, 35V, and 35W of the right electric motor 30R.

[0050] When the electric vehicle 10 is traveling, the ECU (not shown) of the electric vehicle 10 controls the electric motors 30R, 30L taking into account the difference in inertia between the right power transmission mechanism 50R and the left power transmission mechanism 50L. Therefore, the difference in inertia between the power transmission mechanisms 50R, 50L does not affect the traveling of the electric vehicle 10. Furthermore, when the electric vehicle 10 stops traveling, the electric motors 30R, 30L function as generators and supply regenerative power to the battery pack 3. At this time, the right electric motor 30R drives the right power transmission mechanism 50R, which has a greater inertia than the left power transmission mechanism 50L, and therefore the right electric motor 30R can supply greater regenerative power to the battery pack 3 than the left electric motor 30L. Therefore, it is possible to prevent a deterioration in the energy efficiency of the drive unit 20 due to the greater inertia of the right power transmission mechanism 50R.

[0051] (Correspondence) The right electric motor 30R is an example of a "first electric motor." The left electric motor 30L is an example of a "second electric motor." In a modified example, the right electric motor 30R may be a "second electric motor," or the left electric motor 30L may be a "first electric motor." The battery pack 3 is an example of an "electricity storage device." The outer diameter D1 is an example of a "first outer diameter." The outer diameter D2 is an example of a "second outer diameter." The right inverter 40R is an example of a "first inverter." The left inverter 40L is an example of a "second inverter."

[0052] Second Embodiment The structure of a drive unit 120 of a second embodiment will be described with reference to FIG. 4 . Compared to the drive unit 20 of the first embodiment described above, the drive unit 120 of this embodiment differs in the arrangement of the electric motors 130R, 130L, the power transmission mechanisms 150R, 150L, ​​and the inverter 140. Furthermore, in the drive unit 120 of this embodiment, the right drive shaft 114R and the left drive shaft 114L are connected via a connecting shaft 163. That is, the drive unit 120 of this embodiment drives a single drive shaft using the power of the electric motors 30R, 30L. However, the drive unit 120 of this embodiment has a configuration substantially similar to that of the drive unit 20 of the first embodiment.

[0053] Although the arrangement of the right power transmission mechanism 150R in this embodiment is different from the arrangement of the right power transmission mechanism 50R in the first embodiment, the two have substantially the same configuration, and therefore, a detailed description of the structure by which the right power transmission mechanism 150R drives the right front wheel 4R will be omitted.

[0054] In this embodiment, unlike the electric motors 30R and 30L in the first embodiment, the electric motors 130R and 130L are housed in a common motor case 131. The motor case 131 may be formed as a single case, or may be formed by fixing multiple cases together to form an integrated unit. Furthermore, in this embodiment, a pair of power transmission mechanisms 150R and 150L are disposed on the vehicle outer side of the motor case 131. In other words, the motor case 131 housing the pair of electric motors 130R and 130L is disposed between the pair of power transmission mechanisms 150R and 150L. Furthermore, the inverter 140 is also disposed between the pair of power transmission mechanisms 150R and 150L. The inverter 140 is disposed behind the motor case 131. The inverter 140 has the functions of the inverters 40R and 40L described above.

[0055] The drive unit 120 of this embodiment does not include the parking gear 70 described above. In the drive unit 120, the first shaft 151R of the right power transmission mechanism 150R has an outer diameter D1. On the other hand, the first shaft 151L of the left power transmission mechanism 150L, ​​which is disposed symmetrically to the first shaft 151R of the right power transmission mechanism 150R, has an outer diameter D2 that is smaller than the outer diameter D1. Both shafts 151R and 151L have a cylindrical shape and are made of the same material. Therefore, the inertia of the first shaft 151R, which has a larger outer diameter D1, is greater than the inertia of the first shaft 151L, which has a smaller outer diameter D2. As described above, in the drive device 120 of this embodiment, the inertia of the first shaft 151R of the right power transmission mechanism 150R connected to the right electric motor 130R, which is energized when the battery pack 3 is being charged, is greater than the inertia of the left power transmission mechanism 150L, ​​so that it is possible to reduce vibration of the right electric motor 130R when the battery pack 3 is being charged. In this embodiment, the motor case 131 is an example of a "casing."

[0056] Third Embodiment The structure of a drive unit 220 of a third embodiment will be described with reference to FIG. 5 . Compared to the drive unit 120 of the second embodiment described above, the drive unit 220 of this embodiment has separate right and left drive shafts 214R and 214L, similar to the drive unit 20 of the first embodiment. Furthermore, in the drive unit 220 of this embodiment, the first shafts 251R and 251L of the power transmission mechanisms 250R and 250L have the same outer diameter. However, in the drive unit 220 of this embodiment, the preload setting of the first bearing 253R disposed at the right end of the first shaft 251R of the right power transmission mechanism 250R is different from the preload setting of the first bearing 253L disposed at the right end of the first shaft 251L of the left power transmission mechanism 250L. Specifically, a first preload is set on the first bearing 253R of the right power transmission mechanism 250R, and a second preload smaller than the first preload is set on the first bearing 253L of the left power transmission mechanism 250L. Therefore, in the first bearing 253R of the power transmission mechanism 250R, the ball 282R of the first bearing 253R is pressed with the first preload by the inner raceway 281R and the outer raceway 283R. In contrast, in the first bearing 253L of the left power transmission mechanism 250L, the ball 282L of the first bearing 253L is pressed with the second preload smaller than the first preload by the inner raceway 281L and the outer raceway 283L. In other words, the first bearing 253R of the right power transmission mechanism 250R is more difficult to rotate than the first bearing 253L of the left power transmission mechanism 250L.

[0057] Therefore, the frictional resistance generated in the first bearing 253R when the first shaft 251R of the right power transmission mechanism 250R rotates is greater than the frictional resistance generated in the first bearing 253L when the first shaft 251L of the left power transmission mechanism 250L rotates. As a result, when the right electric motor 230R drives the right power transmission mechanism 250R to rotate at a predetermined acceleration, the reaction force that the right electric motor 230R receives from the right power transmission mechanism 250R is greater than the reaction force that the left electric motor 230L receives from the left power transmission mechanism 250L when the left electric motor 230L drives the left power transmission mechanism 250L to rotate at a predetermined acceleration. This makes it possible to reduce vibration of the right electric motor 230R when charging the battery pack 3. In this embodiment, the ball 282R is an example of a "first rolling element," and the ball 282L is an example of a "second rolling element."

[0058] Fourth Embodiment A drive unit 320 of a fourth embodiment will be described with reference to FIG. 6 . In the first to third embodiments described above, the drive units 20, 120, and 220 have a substantially symmetrical shape with respect to the center line CL1 in the left-right direction of the electric vehicle 10. However, the drive unit 320 of this embodiment does not have a symmetrical shape with respect to the center line CL1. The electric motors 330R and 330L of this embodiment are arranged along the longitudinal direction of the vehicle. In this embodiment, the right electric motor 330R that drives the right front wheel 4R is disposed in front of the left electric motor 330L that drives the left front wheel 4L. Furthermore, the electric motors 330R and 330L are disposed between a pair of power transmission mechanisms 350R and 350L.

[0059] As a result, as shown in Figure 6, the distance in the front-rear direction between the right electric motor 330R and the right drive shaft 314R is longer than the distance in the front-rear direction between the left electric motor 330L and the right drive shaft 314R. The right power transmission mechanism 350R transmits the power of the right electric motor 330R to the right drive shaft 314R via five shafts 351R, 356R, 359R, 376R, and 363R and gears arranged on each shaft. On the other hand, the left power transmission mechanism 350L transmits the power of the left electric motor 330L to the left drive shaft 314L via four shafts 351L, 356L, 359L, and 363L and gears arranged on each shaft. The right electric motor 330R rotates five shafts 351R, 356R, 359R, 376R, and 363R and five gears attached thereto, while the left electric motor 330L rotates four shafts 351L, 356L, 359L, and 363L and four gears attached thereto. Therefore, when the right electric motor 330R drives and rotates the right power transmission mechanism 350R at a predetermined acceleration, the reaction force that the right electric motor 330R receives from the right power transmission mechanism 350R is greater than the reaction force that the left electric motor 330L receives from the left power transmission mechanism 350L when the left electric motor 330L drives and rotates the left power transmission mechanism 350L at a predetermined acceleration. This reduces vibration of the right electric motor 330R when the battery pack 3 is being charged. In this embodiment, the right electric motor 30R located in the front is an example of the “first electric motor,” and the left electric motor 30L located in the rear is an example of the “second electric motor.” In a modified example, the “first electric motor” may be located behind the “second electric motor.”

[0060] Fifth Embodiment A drive unit 420 of a fifth embodiment will be described with reference to FIG. 7 . Similar to the drive unit 320 of the fourth embodiment described above, in the drive unit 420 of this embodiment, the electric motors 430L, 430R are arranged along the longitudinal direction of the vehicle. That is, the drive unit 420 has an asymmetrical shape. However, in the drive unit 420 of this embodiment, the left power transmission mechanism 450L is disposed to the right of the electric motors 430L, 430R, and the right power transmission mechanism 450R is disposed to the right of the left power transmission mechanism 450L.

[0061] In the drive unit 420 of this embodiment, the right power transmission mechanism 450R transmits the power of the right electric motor 430R to the right drive shaft 414R via five shafts 451R, 456R, 459R, 476R, and 463R and gears arranged on each shaft. The left power transmission mechanism 450L transmits the power of the left electric motor 430L to the right drive shaft 414L via four shafts 451L, 456L, 459L, and 463L and gears arranged on each shaft. A parking gear 470 is attached to the first shaft 451R of the right power transmission mechanism 450R. Therefore, when the right electric motor 430R drives and rotates the right power transmission mechanism 450R at a predetermined acceleration, the reaction force that the right electric motor 430R receives from the right power transmission mechanism 450R is greater than the reaction force that the left electric motor 430L receives from the left power transmission mechanism 450L when the left electric motor 430L drives and rotates the left power transmission mechanism 450L at a predetermined acceleration. This makes it possible to reduce vibration of the right electric motor 430R when charging the battery pack 3.

[0062] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Modifications of the above examples are listed below.

[0063] (Variation 1) In the drive unit 20 of the first embodiment described above, the inertia of the right power transmission mechanism 50R is increased by arranging the parking gear 70 and the oil pump 72 in the right power transmission mechanism 50R. In this variation, instead of this, for example, an opening for reducing mass may be formed in the first gear 54L of the left power transmission mechanism 50L, thereby making the inertia of the first gear 54L smaller than the inertia of the first gear 54R of the right power transmission mechanism 50R.

[0064] (Modification 2) The drive device 20 of the first embodiment does not need to include the inverters 40R and 40L.

[0065] (Modification 3) The motor case 131 of the drive unit 120 of the third embodiment may house the power transmission mechanisms 150R and 150L in addition to the electric motors 130R and 130L.

[0066] The technical elements described in this specification or drawings may exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings may achieve multiple objectives simultaneously, and achieving one of those objectives alone is technically useful.

Claims

1. A driving device for driving a pair of left and right drive wheels, comprising: a first electric motor; a first power transmission mechanism for transmitting power from the first electric motor to at least one of the pair of left and right drive wheels; a second electric motor; a second power transmission mechanism for transmitting power from the second electric motor to at least the other of the pair of left and right drive wheels; and a power storage device for supplying power to the first electric motor and the second electric motor. The driving device constitutes a charging circuit for supplying a charging current supplied from an external power source to the power storage device via the neutral point of the first electric motor. When the first electric motor rotationally drives the first power transmission mechanism at a predetermined acceleration, the reaction force received by the first electric motor from the first power transmission mechanism is greater than the reaction force received by the second electric motor from the second power transmission mechanism when the second electric motor rotationally drives the second power transmission mechanism at the predetermined acceleration.

2. The driving device according to claim 1, wherein the inertia of the first power transmission mechanism is greater than the inertia of the second power transmission mechanism.

3. The driving device according to claim 1, wherein the number of first rotating parts included in the first power transmission mechanism is greater than the number of second rotating parts included in the second power transmission mechanism.

4. The driving device according to claim 3, wherein the first rotating parts include a gear for a parking brake of a vehicle including the pair of left and right drive wheels.

5. The driving device according to claim 3, wherein the first rotating parts include an oil pump for supplying oil to the first power transmission mechanism.

6. The first rotating shaft included in the first power transmission mechanism has a first outer diameter, and the second rotating shaft included in the second power transmission mechanism, which is symmetrically arranged with the first rotating shaft in a vehicle including the pair of left and right drive wheels, has a second outer diameter smaller than the first outer diameter. The driving device according to claim 2.

7. The driving device according to claim 1, wherein the frictional resistance of the first power transmission mechanism is greater than the frictional resistance of the second power transmission mechanism.

8. In the first bearing included in the first power transmission mechanism, the first rolling element of the first bearing is pressed with a first preload. In the second bearing included in the second power transmission mechanism, which is arranged symmetrically with the first bearing in a vehicle provided with the pair of left and right drive wheels, the second rolling element of the second bearing is pressed with a second preload smaller than the first preload. The drive device according to claim 7.

9. In a vehicle including the second electric motor and the pair of left and right drive wheels, the first electric motor is arranged symmetrically. In the vehicle, the first power transmission mechanism is arranged symmetrically with the second power transmission mechanism. The drive device according to claim 1.

10. The drive device further includes a first inverter located between the first electric motor and the power storage device, and a second inverter located between the second electric motor and the power storage device. The drive device according to claim 1.

11. The drive device further includes a casing that houses at least the first electric motor and the second electric motor. The drive device according to claim 1.

12. The first power transmission mechanism transmits power from the first electric motor to one of the pair of left and right drive wheels, and the second power transmission mechanism transmits power from the second electric motor to the other of the pair of left and right drive wheels. The drive device according to claim 1.

13. A drive device for driving a pair of left and right drive wheels, including a first electric motor, a first power transmission mechanism that transmits power from the first electric motor to one of the pair of left and right drive wheels, a second electric motor, a second power transmission mechanism that transmits power from the second electric motor to the other of the pair of left and right drive wheels, and a power storage device that supplies power to the first electric motor and the second electric motor. The drive device constitutes a charging circuit that supplies a charging current supplied from an external power source to the power storage device via the neutral point of the first electric motor. The number of first rotating parts included in the first power transmission mechanism is larger than the number of second rotating parts included in the second power transmission mechanism. The first rotating parts include all parts that are symmetrical to each of the second rotating parts. Drive device.

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