Drive device

Abstract

To provide a technology that is able to prevent occurrence of vibration of an electric motor.SOLUTION: A 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 a pair of drive wheels, left and right; 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 drive wheels, left and right; and a power storage device that supplies electric power to the first electric motor and the second electric motor. The drive device constitutes a charging circuit by which a charging current supplied from an external power supply is supplied to the power storage device via a neutral point of the first electric motor. A reaction force that the first electric motor receives from the first power transmission mechanism when the first electric motor rotationally drives the first power transmission mechanism at a predetermined acceleration, is larger than a reaction force that the second electric motor receives from the second power transmission mechanism when the second electric motor rotationally drives the second power transmission mechanism at a predetermined acceleration.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a drive device including two electric motors that drive left and right drive wheels. Further, Patent Document 2 discloses a technology that uses two electric motors that drive drive wheels for charging a power storage device. In the technology of Patent Document 2, power from a charging device outside the vehicle is supplied to the power storage device via the neutral point of one of the two electric motors.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 2, when supplying power from an external charging device to the power storage device, the power is supplied via the neutral point of one of the two electric motors. In this case, since current is flowing through the one electric motor, vibration may occur in the one electric motor. In this specification, a technology is provided that can reduce the vibration of one of the two electric motors when supplying an external charging device to the power storage device via the neutral point of one of the two electric motors.

Means for Solving the Problems

[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 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. 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.

[0006] The above-described drive device is configured such that the reaction force received by the first electric motor from the first power transmission mechanism is relatively large compared to the second electric motor. Therefore, when a current flows through the first electric motor due to charging of the power storage device, the rotational displacement of the first electric motor is suppressed by the first power transmission mechanism. Accordingly, vibration is less likely to occur in the first electric motor. Thereby, even when the power storage device is charged at a high voltage using the coil of the first electric motor, vibration of the first electric motor can be reduced.

[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 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 components included in the first power transmission mechanism is larger 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 with respect to left and right.

[0008] In the drive device described above, the number of first rotating components of the first power transmission mechanism is larger than the number of second rotating components of the second power transmission mechanism. Furthermore, the first rotating components include all components that are symmetrical to each of the second rotating components with respect to left and right. Therefore, when a current flows through the first electric motor due to charging of the power storage device, the rotational displacement of the first electric motor is suppressed by the first power transmission mechanism. Accordingly, vibration is less likely to occur in the first electric motor. Thereby, even when the power storage device is charged at a high voltage using the coil of the first electric motor, vibration of the first electric motor can be reduced. Note that the "first rotating components" include not only components located on the transmission path through which the first power transmission mechanism transmits power, but also components that rotate without contributing to the transmission of the first power.

[0009] Details and further improvements of the technology disclosed in this specification will be described in the following "Mode for Carrying Out the Invention".

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying out the Invention

[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 made greater than the frictional resistance of the second power transmission mechanism.

[0012] In one embodiment of the present technology, the number of the first rotating parts included in the first power transmission mechanism may be greater than the number of the second rotating parts included in the second power transmission mechanism. Here, the first rotating parts included in the first power transmission mechanism broadly mean the parts that rotate when the first power transmission mechanism transmits the power, and include, for example, gears for a parking brake and an oil pump, which do not directly contribute to the transmission of the first power. The same applies to the second rotating parts.

[0013] In such a configuration, the first power transmission mechanism including more first rotating parts than the second power transmission mechanism can suppress the rotational displacement of the first electric motor when a current flows through the first electric motor due to the charging of the power storage device. Therefore, vibration is less likely to occur in the first electric motor.

[0014] In one embodiment of the present technology, the first rotating parts may include gears for a parking brake of a vehicle provided with the pair of left and right drive wheels.

[0015] With such a configuration, by using the gear for the parking brake, the reaction force received by the first electric motor from the first power transmission mechanism can be easily increased significantly.

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

[0017] With such a configuration, by using the oil pump, the reaction force received by the first electric motor from the first power transmission mechanism can be easily increased significantly.

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

[0019] With such a configuration, by changing the outer diameter of the rotating shaft, the inertia of the first power transmission mechanism can be easily increased significantly.

[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 made greater than the inertia of the second power transmission mechanism.

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

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

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

[0024] With such a configuration, with respect to the drive wheels arranged symmetrically left and right, the power of each electric motor is transmitted by a symmetric configuration. As a result, it becomes easier to make the outputs of the electric motors common. For this reason, compared with a configuration in which the power of each electric motor is transmitted by an asymmetric configuration left and right, each electric motor can be easily controlled. However, the vibration generated only in the first electric motor arranged symmetrically with respect to the second electric motor is likely to make the user uncomfortable. For this reason, the technology disclosed in this specification is particularly beneficial in a configuration in which each of the first and second electric motors and the first and second power transmission mechanisms is arranged symmetrically left and right.

[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 may not 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. Thereby, the power of the electric motor corresponding to each of the pair of left and right drive wheels is transmitted to the corresponding drive wheel via the corresponding power transmission mechanism. For this reason, in the drive device of the present embodiment, compared with the 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, each of the pair of left and right drive wheels can be easily driven independently. However, in another embodiment, the first power transmission mechanism may transmit the power of 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 the power of 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 the drive device 20 of the present embodiment as viewed 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 "front", and the opposite side may be simply referred to as "rear". Further, 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 "left", and the opposite side may be simply referred to as "right".

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

[0030] The drive device 20 drives a pair of front wheels 4R and 4L by supplying the power of the battery pack 3 to a pair of electric motors 30R and 30L. Thereby, the electric vehicle 10 is driven. That is, the pair of front wheels 4R and 4L are the drive wheels of the electric vehicle 10. In a modified example, a pair of rear wheels 5R and 5L may be the drive wheels of the electric vehicle 10, or a pair of front wheels 4R and 4L and a pair of rear wheels 5R and 5L may be the drive wheels of the electric vehicle 10. Note that the "electric vehicle" in this specification includes, for example, a rechargeable electric vehicle charged by an external power source, a fuel cell vehicle using a fuel cell as a power source, and a hybrid vehicle having an engine.

[0031] The charging inlet 6 is arranged on the right side surface 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 device 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, mainly, the configuration located on the right side of the center line CL1 of the drive device 20 will be described. Above the right electric motor 30R (that is, in the direction in front of the paper surface of FIG. 1), a right inverter 40R is arranged. On the left side of the right electric motor 30R, a right power transmission mechanism 50R is arranged. Between the right power transmission mechanism 50R and the left electric motor 30L, a left power transmission mechanism 50L is arranged.

[0033] The right power transmission mechanism 50R drives the right front wheel 4R at a reduced rotational speed of, for example, the rotational speed of the right electric motor 30R. 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 in the left-right direction of the electric vehicle 10. The pair of front wheels 4R and 4L are independently driven by the pair of electric motors 30R and 30L.

[0034] As shown in FIG. 2, the drive device 20 constitutes a part of a circuit that connects the external DC power supply 7 and the battery pack 3. The drive device 20 constitutes a charging circuit 11 for supplying the 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 end of each of the U-phase coil 35U, the V-phase coil 35V, and the W-phase coil 35W is connected to the neutral point NP. The other end of the U-phase coil 35U is connected to the U-phase arm 42U, the other end of the V-phase coil 35V is connected to the V-phase arm 42V, and the other end of the W-phase coil 35W is connected to the 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. Also, 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 a charging current to the battery pack 3 via the neutral point NP of the right electric motor 30R. Thereby, the right electric motor 30R and the right inverter 40R can function as three boost circuits connected in parallel between the charging inlet 6 and the battery pack 3. Thereby, the drive device 20 can boost the output voltage of the external DC power supply 7 by using the right electric motor 30R and the right inverter 40R. Thereby, even if the output voltage of the external DC power supply 7 is lower than the voltage of the battery pack 3, rapid charging can be executed. Also, one terminal of the charging inlet 6 is directly connected to the positive electrode of the battery pack 3 via the switch 13. The charging circuit 11 can bypass the neutral point NP of the right electric motor 30R to the output voltage of the external DC power supply 7 by turning on the switch 13 when the output voltage of the external DC power supply 7 is equal to the voltage of the battery pack 3. Also, 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] Referring to FIG. 3, the detailed structure of the drive device 20 will be described. The right electric motor 30R of the drive device 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 permanent magnets 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 race ring fixed to the rotating shaft, an outer race ring located radially outside the inner race ring, and balls disposed between the two. The right motor bearing 33R rotates the first shaft 51R by rolling the balls along the inner race ring. 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, except for 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 in the lateral direction of the motor case 32R via a pair of motor bearings 33R. The first shaft 51R penetrates 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 by 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 in the lateral direction of the second shaft 55R are rotatably held by the right transmission case 52R by a pair of second bearings 56R. The second gear 57R meshes with the third gear 60R fixed to the third shaft 59R. The third gear 60R rotates the third shaft 59R. Both left and right ends in the lateral direction of the third shaft 59R are rotatably held by the right transmission case 52R by a pair of third bearings 58R. To the right of the third gear 60R, a fourth gear 61R is disposed adjacent thereto. The fourth gear 61R is fixed to the third shaft 59R. The fourth gear 61R 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 a plurality of 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. When the rotating components included in the left power transmission mechanism 50L rotate, the power of the left electric motor 30L is transmitted to the left front wheel 4L. As described above, the left power transmission mechanism 50L has a substantially left-right symmetric configuration with the right power transmission mechanism 50R. That is, the rotating components of the right power transmission mechanism 50R include all the components obtained by making each of the rotating components of the left power transmission mechanism 50L left-right symmetric, and these rotating components are symmetrically arranged with respect to the center line CL.

[0042] As described above, the drive device 20 of the present embodiment constitutes a charging circuit 11 that supplies a charging current supplied from an external DC power source 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 (that is, while the charging inlet 6 is connected to the external DC power source 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 is generated in the right electric motor 30R, and the right electric motor 30R may vibrate.

[0043] Here, 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 components 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. The parking gear 70 meshes with a parking lock (not shown) in response to the operation of the parking brake 9 (see FIG. 1) to fix the first shaft 51R. Further, an oil pump 72 is fixed to the right end of the third shaft 59R. The oil pump 72 is one of the rotating components 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 and circulates the oil in the drive device 20. Although it is an example, the oil pump 72 of the present embodiment is configured to pump oil to an oil pipe 74 passing through the third shaft 59R. The oil pipe 74 extends through the third shaft 59R to the left transmission case 52L of the left power transmission mechanism 50L. Thereby, the oil pump 72 supplies oil to the right power transmission mechanism 50R and the left power transmission mechanism 50L.

[0044] As shown in FIG. 3, the parking gear 70 is not disposed on the first shaft 51L of the left power transmission mechanism 50L. For this reason, the inertia of the first shaft 51R of the right power transmission mechanism 50R is larger than the inertia of the first shaft 51L of the left power transmission mechanism 50L.

[0045] Similarly, the oil pump 72 is not fixed to the third shaft 59L of the left power transmission mechanism 50L. For this reason, the inertia of the third shaft 59R of the right power transmission mechanism 50R is larger than the inertia of the third shaft 59L of the left power transmission mechanism 50L.

[0046] Therefore, the right power transmission mechanism 50R has a lower power transmission efficiency to the right front wheel 4R than the left power transmission mechanism 50L. In other words, in the drive device 20, when the right electric motor 30R rotationally drives the right power transmission mechanism 50R at a predetermined acceleration, the reaction force received by the right electric motor 30R from the right power transmission mechanism 50R is greater than the reaction force received by the left electric motor 30L from the left power transmission mechanism 50L when the left electric motor 30L rotationally drives the left power transmission mechanism 50L at a predetermined acceleration. For this reason, for example, even if a d-axis current is generated in the right electric motor 30R due to the 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. That is, the right electric motor 30R is less likely to vibrate. Therefore, when charging the battery pack 3, the drive device 20 can reduce the vibration of the right electric motor 30R. As a result, the state of the right electric motor 30R through which current flows during charging of the battery pack 3 approaches the state of the left electric motor 30L through which no current flows. Thereby, it is possible to prevent the vibration generated only in one of the pair of left and right electric motors 30R and 30L, i.e., the right electric motor 30R, from making the user uncomfortable.

[0047] Furthermore, by increasing the inertia of the right power transmission mechanism 50R using the parking gear 70 and the oil pump 72 required for the electric vehicle 10, for example, compared to a configuration provided with a separate mechanism for increasing the inertia of the right power transmission mechanism 50R, the vibration of the right electric motor 30R can be reduced with higher mass efficiency.

[0048] There may be a minute gap between the rotating bodies (for example, the first gear 54R and the second gear 57R) of the right power transmission mechanism 50R that mesh with each other. For this reason, in other conventional structures, for example, when the inertia of the second gear 57R is large, although the vibration after the second gear 57R can be suppressed, the first gear 54R can vibrate by the amount of the gap. Therefore, the parking gear 70 of the present embodiment is attached to the first shaft 51R directly connected to the right electric motor 30R. For this reason, the parking gear 70 can surely reduce the vibration of the right electric motor 30R as compared with a configuration that increases the inertia of a rotating body (for example, the second gear 57R) indirectly connected to the right electric motor 30R via other rotating bodies.

[0049] In the drive device 20 of the present embodiment, the right power transmission mechanism 50R and the left power transmission mechanism 50L basically have a bilaterally symmetric configuration. However, the right power transmission mechanism 50R is provided with a parking gear 70 and an oil pump 72 that do not exist in the left power transmission mechanism 50L. As a result, the number of rotating parts included in the right power transmission mechanism 50R is larger 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 larger than the inertia of the left power transmission mechanism 50L. For this reason, when current flows through the right electric motor 30R due to charging of the battery pack 3, the rotational displacement of the right electric motor 30R is suppressed by the right power transmission mechanism 50R. Therefore, vibration hardly occurs in the right electric motor 30R. Thereby, 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, the vibration of the right electric motor 30R can be reduced.

[0050] When the electric vehicle 10 travels, the ECU (not shown) of the electric vehicle 10 controls each electric motor 30R and 30L in consideration of 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 and 50L does not affect the running of the electric vehicle 10. Further, when the electric vehicle 10 stops running, each electric motor 30R and 30L functions as a generator and supplies regenerative power to the battery pack 3. At this time, since the right electric motor 30R drives the right power transmission mechanism 50R having a larger inertia than the left power transmission mechanism 50L, the right electric motor 30R can supply a larger amount of regenerative power to the battery pack 3 than the left electric motor 30L. Therefore, it is possible to suppress the deterioration of the energy efficiency of the drive device 20 due to the large inertia of the right power transmission mechanism 50R.

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

[0052] (Second Embodiment) Referring to FIG. 4, the structure of the drive device 120 of the second embodiment will be described. Compared with the drive device 20 of the first embodiment described above, in the drive device 120 of this embodiment, the arrangement of each electric motor 130R, 130L, each power transmission mechanism 150R, 150L, and the inverter 140 is different. Further, in the drive device 120 of this embodiment, the right drive shaft 114R and the left drive shaft 114L are connected via a connection shaft 163. That is, the drive device 120 of this embodiment drives a single drive shaft by the power of each electric motor 30R, 30L. However, the drive device 120 of this embodiment has substantially the same configuration as the drive device 20 of the first embodiment.

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

[0054] In this embodiment, each electric motor 130R, 130L is housed in a common motor case 131, which is different from the electric motors 30R, 30L of the first embodiment. The motor case 131 may be constituted by one case, or a plurality of cases may be fixed and integrally formed. Further, in this embodiment, a pair of power transmission mechanisms 150R, 150L are arranged outside the vehicle of the motor case 131. In other words, the motor case 131 that houses the pair of electric motors 130R, 130L is arranged between the pair of power transmission mechanisms 150R, 150L. Further, the inverter 140 is also arranged between the pair of power transmission mechanisms 150R, 150L. The inverter 140 is arranged behind the motor case 131. The inverter 140 has the functions of the above-described inverters 40R, 40L.

[0055] The drive device 120 of this embodiment does not have the parking gear 70 described above. In the drive device 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 arranged symmetrically with respect to the first shaft 151R of the right power transmission mechanism 150R has an outer diameter D2 smaller than the outer diameter D1. Each of the shafts 151R and 151L has a cylindrical shape and is made of the same material. Therefore, the inertia of the first shaft 151R having the large outer diameter D1 is larger than the inertia of the first shaft 151L having the small outer diameter D2. Thus, in the drive device 120 of this embodiment, since the inertia of the first shaft 151R of the right power transmission mechanism 150R connected to the right electric motor 130R that is energized during charging of the battery pack 3 is larger than the inertia of the left power transmission mechanism 150L, the vibration of the right electric motor 130R during charging of the battery pack 3 can be reduced. In this embodiment, the motor case 131 is an example of a "casing".

[0056] (Third Embodiment) Referring to FIG. 5, the structure of the drive device 220 of the third embodiment will be described. When compared with the drive device 120 of the second embodiment described above, in the drive device 220 of this embodiment, similar to the drive device 20 of the first embodiment, the right drive shaft 214R and the left drive shaft 214L are separated. Further, in the drive device 220 of this embodiment, the first shafts 251R, 251L of the respective power transmission mechanisms 250R, 250L have the same outer diameter. However, in the drive device 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 for the first bearing 253R of the right power transmission mechanism 250R, and a second preload smaller than the first preload is set for the first bearing 253L of the left power transmission mechanism 250L. For this reason, in the first bearing 253R of the power transmission mechanism 250R, the balls 282R of the first bearing 253R are pressed by the inner race ring 281R and the outer race ring 283R with the first preload. On the other hand, in the first bearing 253L of the left power transmission mechanism 250L, the balls 282L of the first bearing 253L are pressed by the inner race ring 281L and the outer race ring 283L with a second preload smaller than the first preload. That is, 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, when the first shaft 251R of the right power transmission mechanism 250R rotates, the frictional resistance generated in the first bearing 253R 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 rotationally drives the right power transmission mechanism 250R at a predetermined acceleration, the reaction force received by the right electric motor 230R from the right power transmission mechanism 250R is greater than the reaction force received by the left electric motor 30L from the left power transmission mechanism 250L when the left electric motor 230L rotationally drives the left power transmission mechanism 250L at a predetermined acceleration. For this reason, during charging of the battery pack 3, the vibration of the right electric motor 230R can be reduced. In the present embodiment, the ball 282R is an example of the "first rolling element", and the ball 282L is an example of the "second rolling element".

[0058] (Fourth Embodiment) Referring to FIG. 6, the drive device 320 of the fourth embodiment will be described. In the first to third embodiments described above, each of the drive devices 20, 120, 220 has a substantially bilaterally symmetric shape with respect to the center line CL1 in the left-right direction of the electric vehicle 10. However, the drive device 320 of the present embodiment does not have a bilaterally symmetric shape with respect to the center line CL1. Each of the electric motors 330R, 330L of the present embodiment is arranged along the vehicle front-rear direction. In the present 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. Further, each of the electric motors 330R, 330L is disposed between a pair of power transmission mechanisms 350R, 350L.

[0059] As a result, as shown in FIG. 6, the distance in the front-rear direction between the right electric motor 330R and the right drive shaft 314R becomes 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, 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, 363L and gears arranged on each shaft. The right electric motor 330R rotates five shafts 351R, 356R, 359R, 376R, 363R and five gears attached thereto, and the left electric motor 330L rotates four shafts 351L, 356L, 359L, 363L and four gears attached thereto. For this reason, when the right electric motor 330R rotationally drives the right power transmission mechanism 350R at a predetermined acceleration, the reaction force received by the right electric motor 330R from the right power transmission mechanism 350R is greater than the reaction force received by the left electric motor 330L from the left power transmission mechanism 350L when the left electric motor 330L rotationally drives the left power transmission mechanism 350L at a predetermined acceleration. For this reason, vibration of the right electric motor 330R can be reduced during charging of the battery pack 3. In the present 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) Referring to FIG. 7, the drive device 420 of the fifth embodiment will be described. Similar to the drive device 320 of the fourth embodiment described above, in the drive device 420 of the present embodiment, the electric motors 430L and 430R are arranged along the vehicle front-rear direction. That is, the drive device 420 has an asymmetrical shape in the left-right direction. However, in the drive device 420 of the present embodiment, the left power transmission mechanism 450L is arranged on the right side of each of the electric motors 430L and 430R, and the right power transmission mechanism 450R is arranged on the right side of the left power transmission mechanism 450L.

[0061] Also in the drive device 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, 463R and the gears arranged on each shaft. Further, 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, 463L and the gears arranged on each shaft. Furthermore, 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 rotationally drives the right power transmission mechanism 450R at a predetermined acceleration, the reaction force received by the right electric motor 430R from the right power transmission mechanism 450R is greater than the reaction force received by the left electric motor 430L from the left power transmission mechanism 450L when the left electric motor 430L rotationally drives the left power transmission mechanism 450L at a predetermined acceleration. For this reason, vibration of the right electric motor 430R can be reduced during charging of the battery pack 3.

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

[0063] (Modification 1) In the drive device 20 of the first embodiment described above, by arranging the parking gear 70 and the oil pump 72 in the right power transmission mechanism 50R, the inertia of the right power transmission mechanism 50R is increased. In this modification, instead, for example, by forming an opening for reducing the mass in the first gear 54L of the left power transmission mechanism 50L, the inertia of the first gear 54L may be made 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 may not include the inverters 40R and 40L.

[0065] (Modification 3) In addition to each electric motor 130R and 130L, the motor case 131 of the drive device 120 according to the third embodiment may further accommodate each power transmission mechanism 150R and 150L.

[0066] The technical elements described in this specification or the drawings 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. Further, the technologies exemplified in this specification or the drawings can achieve a plurality of objectives simultaneously, and achieving one of those objectives itself has technical utility.

Description of Reference Numerals

[0067] 3: Battery pack, 4L: Left front wheel, 4R: Right front wheel, 5L, 5R: Rear wheels, 6: Charging inlet, 7: External DC power supply, 8: Power cable, 9: Parking brake, 10: Electric vehicle, 11: Charging circuit, 13: Switch, 14L, 114L, 214L, 314L, 414L: Left drive shaft, 14R, 114R, 214R, 314R, 414R: Right drive shaft, 20, 120, 220, 320, 420: Drive device, 30L, 230L, 330L, 430L: Left electric motor, 30R, 130R, 230R, 330R, 430R: Right electric motor, 32R: Right motor case, 33R: Right motor bearing, 34R: Right rotor, 35R: Right stator, 35U: U-phase coil, 35V: V-phase coil, 35W: W-phase coil, 36R: Permanent magnet, 40L: Left inverter, 40R: Right inverter, 42U: U-phase arm, 42V: V-phase arm, 42W: W-phase arm, 50L, 150L, 250L, 350L: Left power transmission mechanism, 50R, 150R, 250R, 350R: Right power transmission mechanism, 51L, 51R, 151L, 151R, 251L, 251R, 451R: First shaft, 52L: Left transmission case, 52R: Right transmission case, 53R, 253L, 253R: First bearing, 54L, 54R: First gear, 55R: Second shaft, 56R: Second bearing, 57R: Second gear, 58R: Third bearing, 59L, 59R: Third shaft, 60R: Third gear, 61R: Fourth gear, 62R: Fifth gear, 63R: Fourth shaft, 70, 470: Parking gear, 72: Oil pump, 74: Oil pipe, 140: Inverter, 131: Motor case, 163: Connection shaft, 281L, 281R: Inner track wheel, 282L, 282R: Ball, 283L, 283R: Outer track wheel, CL1: Center line, D1, D2: Outer diameter, NP: Neutral point

Claims

1. A drive 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; a power storage device for supplying power to the first electric motor and the second electric motor; The drive device is provided with: 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; 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; Drive device.

2. The drive 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 drive 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 drive 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 drive 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, The second rotating shaft included in the second power transmission mechanism, and the second rotating shaft arranged symmetrically 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 drive device according to claim 2.

7. The drive 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, and the second bearing arranged symmetrically with the first bearing in a vehicle including 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 with respect to the left and right. In the vehicle, the first power transmission mechanism is arranged symmetrically with respect to the left and right 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, a second inverter located between the second electric motor and the power storage device, and includes The drive device according to claim 1.

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

12. The first power transmission mechanism transmits power from the first electric motor to one of the pair of left and right drive wheels. 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 that drives 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, and includes 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 components included in the first power transmission mechanism is larger than the number of second rotating components included in the second power transmission mechanism. The first rotating components include all components that are symmetric with respect to the left and right of each of the second rotating components. Drive device.

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