Electric vehicle drive unit

Abstract

To reduce a response delay until a large torque corresponding to a sudden acceleration request is generated when the sudden acceleration request is made.SOLUTION: The rotation speed of first and second electric motors at a given vehicle speed is set to a rotation speed in a range in which an upper limit value TM1_u of the torque of a first electric motor and an upper limit value TM2_u of the torque of a second electric motor at that speed are the maximum values. When there is a sudden acceleration request, the output torque of the driving device can be set to the maximum value at that speed without changing the rotation speed of the first and second electric motors.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a drive device for an electric vehicle, and more particularly to a device equipped with two electric motors. [Background technology]

[0002] The following Patent Documents 1 and 2 disclose a drive device for an electric vehicle that includes two electric motors and combines the outputs of the two motors using a planetary gear mechanism to output the combined power. By providing a planetary gear mechanism, it is possible to change the speed of each electric motor even when the vehicle speed is the same. The following Patent Document 1 describes that when a vehicle is driven by two electric motors, the two electric motors are operated at rotational speeds that are efficient for each motor (see paragraph 0027). The following Patent Document 2 describes that by determining the planetary gear ratio based on the maximum power or maximum torque of the two electric motors, even when the two electric motors are controlled so that the planetary gear mechanism does not cause differential motion, it is possible to obtain torque characteristics that are approximately equivalent to those obtained when differential motion is allowed over a wide operating range of the drive device (see paragraph 0027). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-100709 [Patent Document 2] Japanese Patent Application Publication No. 2018-117409 Summary of the Invention [Problem to be solved by the invention]

[0004] In a drive system for an electric vehicle equipped with two electric motors and a planetary gear mechanism connecting them, the rotational speeds of the two electric motors can be selected relatively freely, although there are restrictions on the planetary gear ratio. However, when the output of the drive system is set to maximum torque or torque close to maximum torque, the rotational speeds of the two electric motors may be limited.

[0005] When a sudden acceleration request is made to this drive device, the rotational speed of the two electric motors at that time is not necessarily a rotational speed that can generate a large torque that corresponds to the sudden acceleration request. Therefore, in order to generate a large torque that corresponds to the sudden acceleration request, it may be necessary to change the rotational speed of the two rotating electric machines, and there may be a delay before the large torque is actually generated.

[0006] An object of the present invention is to reduce the delay until a corresponding torque is generated when a sudden acceleration request is made. [Means for solving the problem]

[0007] The drive device for an electric vehicle of the present invention includes a first electric motor and a second electric motor, and further includes a planetary gear mechanism having a first input element connected to the first electric motor, a second input element connected to the second electric motor, and an output element connected to a drive wheel. The rotational speeds of the first input element and the second input element are Within the speed range used by the electric vehicle For each vehicle speed, the rotation speed is set to a value that can generate the maximum torque of the output element at that vehicle speed.

[0008] By setting the rotational speeds as described above, when a request for increased torque is made, the output torque of the drive unit at that vehicle speed can be maximized without changing the rotational speeds of the first electric motor and the second electric motor.

[0009] Furthermore, the rotational speeds of the first input element and the second input element can be set so that the absolute value of the input speed difference, which is the difference between the rotational speeds of the first input element and the second input element, is minimized. By minimizing the input speed difference, it is possible to reduce differential loss in the planetary gear mechanism.

[0010] Furthermore, when at least one of the first and second electric motors operates in the upper limit constant torque region, the input speed difference, which is the difference in rotational speed between the first input element and the second input element, can be set to have the same mathematical relationship as the input speed difference and the speed of the output element when both the first and second electric motors operate in the upper limit constant power region and at less than their maximum rotational speed. By setting the input speed difference as described above, the method for calculating the speeds of the first and second electric motors when they operate below their maximum rotational speeds is unified. [Effects of the Invention]

[0011] By being able to set the output torque of the drive device to its maximum value at that time without changing the rotation speeds of the first and second motors, it is possible to reduce the response delay when a request for an increase in torque is made. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating a schematic configuration of a drive device according to an embodiment. [Figure 2] FIG. 3 is an explanatory diagram showing the output characteristics of an electric motor. [Figure 3] FIG. 10 is a diagram showing upper torque limits of the first and second electric motors when the vehicle speed is 20 km / h. [Figure 4] FIG. 4 is a diagram showing the speed difference between the first sun gear and the second sun gear when the vehicle speed is 20 km / h. [Figure 5] FIG. 10 is a diagram showing upper torque limits of the first and second electric motors when the vehicle speed is 37 km / h. [Figure 6] FIG. 10 is a diagram showing the speed difference between the first sun gear and the second sun gear when the vehicle speed is 37 km / h. [Figure 7] FIG. 10 is a diagram showing upper torque limits of the first and second electric motors when the vehicle speed is 50 km / h. [Figure 8] FIG. 4 is a diagram showing the speed difference between the first sun gear and the second sun gear when the vehicle speed is 50 km / h. [Figure 9] FIG. 10 is a diagram illustrating an example of the relationship between the vehicle speed and a set speed difference. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a drive system 10 for an electric vehicle according to this embodiment. The drive system 10 includes a first electric motor M1 and a second electric motor M2, each of which is connected to a separate input element of a planetary gear mechanism 12. The output element of the planetary gear mechanism 12 is connected to left and right drive wheels 16 via a final reduction gear 14 including a differential.

[0014] The planetary gear mechanism 12 has two input elements: a first sun gear 18 to which a first electric motor M1 is connected, and a second sun gear 20 to which a second electric motor M2 is connected. The second sun gear 20 meshes with a plurality of outer planetary pinions 24 (hereinafter referred to as outer pinions 24) rotatably supported on a planetary carrier 22 (hereinafter referred to as carrier 22). The first sun gear 18 meshes with a plurality of inner planetary pinions 26 (hereinafter referred to as inner pinions 26) rotatably supported on the carrier 22. Each inner pinion 26 also meshes with one outer pinion 24. The first sun gear 18, the second sun gear 20, and the carrier 22 are rotatable around a common axis. The carrier 22 is an output element of the planetary gear mechanism 12, and includes an output gear 28 integral with the carrier 22. This output gear 28 constitutes a final reduction gear pair 32 together with a driven gear 30 which rotates integrally with the differential.

[0015] Planetary gear mechanism 12 is a compound planetary gear mechanism including a first planetary gear train 34 consisting of a first sun gear 18, an outer pinion 24, and an inner pinion 26, and a second planetary gear train 36 consisting of a second sun gear 20 and an outer pinion 24. First planetary gear train 34 is a double-pinion type planetary gear train, and second planetary gear train 36 is a single-pinion type planetary gear train.

[0016] The first sun gear 18 is fixed to a first input shaft 38, which is further connected to a first electric motor shaft 42, which is the output shaft of the first electric motor M1, via a first input gear pair 40. Alternatively, the first electric motor shaft 42 itself may serve as the first input shaft 38. The second sun gear 20 is fixed to a second input shaft 44, which is further connected to a second electric motor shaft 48, which is the output shaft of the second electric motor M2, via a second input gear pair 46. Alternatively, the second electric motor shaft 48 itself may serve as the second input shaft 44. The first and second input gear pairs 40, 46 represent a transmission mechanism between the first and second electric motor shafts 42, 48 and the first and second input shafts 38, 44. However, other configurations, such as a gear train consisting of three or more gears, may be used. Alternatively, the first and second input gear pairs 40, 46 may be replaced by other speed conversion mechanisms, such as a transmission mechanism including a chain and sprockets.

[0017] Planetary gear mechanism 12 is a three-element, two-degree-of-freedom mechanism, and once the rotational speeds of two of the three elements are determined, the rotational speed of the remaining element is uniquely determined. For example, once the rotational speeds of first sun gear 18 and second sun gear 20 are determined, the rotational speed of carrier 22 is determined accordingly.

[0018] A clutch element is provided in the transmission system from second electric motor M2 to second sun gear 20. This clutch element allows rotation of second sun gear 20 in the rotational direction when the vehicle moves forward and prevents rotation in the reverse direction. The clutch element is, for example, a one-way clutch 50 provided on second input shaft 44.

[0019] The driving device 10 further includes a control unit 52 that controls the first electric motor M1 and the second electric motor M2. The control unit 52 controls the output torque and rotation speed of the first electric motor M1 and the second electric motor M2.

[0020] The drive unit 10 can run in two modes: a first mode in which the vehicle is driven only by the output of the first electric motor M1, and a second mode in which the vehicle is driven by the outputs of both the first electric motor M1 and the second electric motor M2. The first mode is used under low-speed, low-load conditions, and the second mode is used under high-speed, high-load conditions.

[0021] Figure 2 shows the output characteristics of a typical electric motor. The output characteristics of an electric motor are such that the upper limit of torque is constant relative to the rotation speed below a base rotation speed, and the upper limit of power is constant relative to the rotation speed above the base rotation speed. A constant upper limit of power means that the upper limit of torque decreases in inverse proportion to the rotation speed. Hereinafter, the region where the upper limit of torque is constant will be referred to as the upper limit constant torque region, and the region where the upper limit of power is constant will be referred to as the upper limit constant power region. The first electric motor M1 and second electric motor M2 described above also have similar output characteristics.

[0022] As in the drive unit 10, when two electric motors are connected to two of the three elements of a planetary gear mechanism and the remaining element is an output element, there are multiple selectable rotational speeds for the two electric motors for a given rotational speed of the output element, provided there is a margin from the upper torque limit. When both electric motors are operating in a region with sufficient margin from the maximum rotational speed in the upper torque limit constant region and at a torque lower than the upper torque limit, the torque of the output element can be maximized for that rotational speed by maintaining the current rotational speed of both motors and increasing the torque to the upper torque limit for that rotational speed, regardless of the rotational speed of the two motors. On the other hand, when two electric motors are operating in the upper power limit constant region, even if the torque of both motors is increased to the upper torque limit for that rotational speed while maintaining the current rotational speed of the two motors, it is not necessarily possible to maximize the torque of the output element for that rotational speed. In order to maximize the torque of the output element, it may be necessary to change the rotational speed of the two electric motors. In this case, it takes time to change the rotational speed of the electric motors, and therefore it takes time to reach the upper torque limit. As a result, when the driver of the vehicle requests sudden acceleration, there may be a time delay before the output torque increases accordingly, and even when the torque corresponding to the driver's request is close to the upper torque limit, there may be a similar time delay.

[0023] Even if the required torque of the output element is low, if the two electric motors are operated at a rotational speed that can generate the maximum torque of the output element at that rotational speed, there is no need to change the rotational speed of the electric motors when sudden acceleration is required, and the time delay until the torque corresponding to the requested sudden acceleration is reached can be reduced. Below, setting the rotational speeds of the two electric motors will be explained with specific examples.

[0024] The parameters of the driving device 10 and the specific values ​​of the parameters are determined as follows.

[0025] [Table 1]

[0026] [Table 2]

[0027] The planetary gear ratio ρ is the relative speed ΔN of the first sun gear 18 (first input element) with respect to the carrier 22 (output element). sd (=N sd -N c ) and the relative speed ΔN of the second sun gear 20 (second input element) ss (=N ss -N c ) and have opposite signs, it is defined as the absolute value of the ratio of these relative velocities (ρ = |ΔN sd / ΔN ss In the case of the planetary gear mechanism 12 shown in the driving device 10, the planetary gear ratio ρ is the number of teeth Z of the first sun gear 18. sd and number of teeth Z of second sun gear 20 ss The ratio of (ρ=Z sd / Z ss ).

[0028] Torque T of carrier 22 C and the torque T of the first sun gear 18. sd and the torque T of the second sun gear 20 ss It is balanced (T C =T sd +T ss The rotation speed of each element is constrained by the relationship shown in the following equation (1). ρN sd +N ss =(1+ρ)N c ···(1)

[0029] Rotational speed N of the first sun gear 18 sd and the rotation speed N of the second sun gear 20 ss Difference ΔN s (ΔN s =N sd -N ss ), the rotational speed N of the first and second sun gears 18, 20 is calculated as follows: sd ,N ss can be expressed as the following equations (2) and (3). N sd =Nc +ΔN s / (1+ρ) (2) N ss =N c -ρΔN s / (1+ρ) (3) In addition, the torque T of the first sun gear 18 sd and torque T of second sun gear 20 ss has the relationship of the following equation (4). T sd =ρT ss ···(4)

[0030] FIG. 3 shows the torque upper limit values ​​T of the first and second electric motors M1, M2 when both the first and second electric motors M1, M2 are operating in the upper limit constant torque region and in a region away from the maximum rotation speed of the upper limit constant torque region. M1_u ,T M2_u 3 is a diagram showing the torque of the first and second electric motors M1 and M2 when the vehicle speed is 20 km / h, in the case where each parameter of the drive device 10 is the specific value shown in Table 1. The torque upper limit value T of the second electric motor M2 M2_u The part indicated by the solid line is the maximum torque T of the second electric motor M2. M2_max and the upper torque limit T M1_u The part indicated by the solid line in the figure is where the second electric motor M2 generates the maximum torque T M2_max In this drive system 10, due to the limitation of the formula (4), when the vehicle is driven by the outputs of both the first electric motor M1 and the second electric motor M2, the first electric motor M1 generates a maximum torque T M1_max The torque T of the first electric motor M1 is M1 is the reduction ratio γ of the first and second input gear pairs 40, 46 M1 ,γ M2 And from the relationship of equation (4), the torque T of the second electric motor M2 is M2 The thin lines show the torque characteristics of the first and second electric motors M1 and M2 alone.

[0031] Rotation speed N of the first electric motor M1 M1 and the rotation speed N of the second electric motor M2M2 As can be seen from equation (1), when one is high, the other is low. M1_u The dashed line on the right side of the figure slopes downward to the right in accordance with the output characteristics of the electric motor alone, shown by the thin line. M2_u The torque upper limit T of the first electric motor M1 is set to a value higher than the left-sloping portion of the output characteristic of the single motor, as shown by the dashed line, so as to satisfy the formula (4). M1_u The downward-sloping portion indicated by the dashed line in the figure is also the torque upper limit T M2_u The driving device 10 is configured such that the first and second electric motors M1 and M2 are driven at a torque upper limit T M1_u ,T M2_u The output torque is maximum when the first and second electric motors M1, M2 are operating within the range indicated by the solid line. Therefore, if the first and second electric motors M1, M2 are operating within the range indicated by the solid line, when a request is made to increase the output torque, the drive unit 10 can make the output torque the maximum value that can be generated at that time without changing the rotation speeds of the first and second electric motors M1, M2.

[0032] In a specific example, when the vehicle is traveling at a speed of 20 km / h, the rotational speed of the drive wheels 16 is 126.01 rpm, and the carrier rotational speed N c is 541.86 rpm. In this case, when the first electric motor M1 operates at 153.67 to 4055.64 rpm and the second electric motor M2 operates at 2850.54 to 108.01 rpm, the output torque of the drive device 10 can be maximized. Therefore, if the rotational speeds of the first and second electric motors M1, M2 are kept within the above ranges while the vehicle is traveling at a speed of 20 km / h, when a request to increase the output torque is made, the output torque can be increased to the maximum value at that time (for a vehicle speed of 20 km / h) while maintaining the rotational speeds of the two electric motors.

[0033] FIG. 4 shows the speed difference ΔN between the first sun gear 18 and the second sun gear 20 under the same conditions as in FIG. sand the torque of the drive wheels 16. The part indicated by the solid line is the range of the maximum value of the output torque of the drive unit 10 at this vehicle speed, that is, the torque upper limit value T M1_u ,T M2_u 4, in the range where the output torque of the drive unit 10 is at its maximum value, the speed difference ΔN s The minimum speed difference ΔN s_min In this case, the minimum speed difference ΔN s_min is 0. This minimum speed difference ΔN s_min The operating point D of the first and second electric motors M1 and M2 is M1 (ΔN s_min ),D M2 (ΔN s_min ) is shown in FIG. 3. In a specific example, ΔN s_min When = 0, the rotation speed of the first electric motor M1 is 1896.50 rpm, and the rotation speed of the second electric motor M2 is 1625.57 rpm.

[0034] Speed ​​difference ΔN s If is 0, then the differential of the planetary gear mechanism 12, that is, the loss due to the speed difference between the two input elements, becomes 0.

[0035] FIG. 5 shows the torque upper limit values ​​T of the first and second electric motors M1, M2 when both the first and second electric motors M1, M2 are operating near the maximum rotation speed in the upper limit torque constant region. M1_u ,T M2_u In particular, FIG. 5 illustrates the torque upper limit values ​​of the first and second electric motors M1 and M2 when the vehicle speed is 37 km / h, in the case where each parameter of the drive device 10 is the specific value shown in Table 1. As in FIG. 3, the torque upper limit value T M1_u ,T M2_u The part indicated by the solid line is where the second motor M2 generates the maximum torque T M2_max The thin lines indicate the torque characteristics of the first and second electric motors M1 and M2 alone.

[0036] As can be seen from Figure 5, the range in which the second electric motor M2 can generate maximum torque is very narrow. In this specific example, the rotation speed of the drive wheels 16 is 233.12 rpm, and the carrier rotation speed N c is 1002.44 rpm. In this case, when the first electric motor M1 operates at 3731.58 to 4055.64 rpm and the second electric motor M2 operates at 2850.54 to 2622.77 rpm, the output torque of the drive unit 10 can be maximized. Therefore, if the rotational speeds of the first and second electric motors M1 and M2 are within the above range, when a request to increase the output torque is made, the output torque can be maximized without changing the rotational speeds of the first and second electric motors M1 and M2. Conversely, if the rotational speeds of the first and second electric motors M1 and M2 are outside the above range, maintaining the rotational speeds will only produce the output torque indicated by the dashed line, and the output torque of the drive unit 10 cannot be maximized at the current speed. Therefore, in order to maximize the output torque, it is necessary to change the rotational speeds of the first and second electric motors M1 and M2.

[0037] FIG. 6 shows the speed difference ΔN between the first sun gear 18 and the second sun gear 20 under the same conditions as in FIG. s 6 is a diagram showing the relationship between the speed difference ΔN and the torque of the drive wheels 16. The part shown by the solid line corresponds to the range of the maximum value of the output torque of the drive unit 10 at this vehicle speed. In FIG. 6, in the range where the output torque of the drive unit 10 is at the maximum value, s The minimum speed difference ΔN s_min This minimum speed difference ΔN s_min is 115.99 rpm, which is not 0. At this time, the operating point D of the first and second electric motors M1 and M2 is M1 (ΔN s_min ),D M2 (ΔN s_min ) is shown in Figure 5. Also, in Figure 5, the speed difference ΔN s Operating point D when =0 M1 (ΔN s =0),D M2 (ΔN s As can be seen from FIG. 5, the drive unit 10 is driven by a speed difference ΔNs When a torque increase request is made while the vehicle is operating at 0, it is necessary to change the rotation speeds of the first and second electric motors M1, M2 in order to obtain the maximum value of the output torque at that time (vehicle speed 37 km / h). Therefore, when the vehicle is traveling at a speed of 37 km / h, the speed difference ΔN s It is preferable to control the first and second electric motors M1, M2 so that the rotational speed is 115.99 rpm.

[0038] FIG. 7 shows the state where both the first and second electric motors M1 and M2 are in the upper limit power constant region and the maximum rotation speed N M1_max ,N M2_max The upper torque limit T of the first and second electric motors M1 and M2 when they are operating at less than M1_u ,T M2_u 7 is a diagram showing the torque of the first and second electric motors M1, M2 when the vehicle speed is 50 km / h, in the case where each parameter of the drive unit 10 is the specific value shown in Table 1. At this time, there is only one set of operating points of the first and second electric motors M1, M2 that gives the maximum value of the output torque of the drive unit 10. The rotation speed of the drive wheels 16 and the carrier rotation speed N c In this specific example, the rotation speeds of the first electric motor M1 and the second electric motor M2 are 315.03 rpm and 1354.64 rpm, respectively. At this time, the rotation speed of the first electric motor M1 is 5261.62 rpm, and the rotation speed of the second electric motor M2 is 3698.16 rpm.

[0039] FIG. 8 shows the speed difference ΔN between the first sun gear 18 and the second sun gear 20 under the same conditions as in FIG. s and the torque of the drive wheels 16. The speed difference ΔN that gives the maximum value of the output torque of the drive unit 10 at this time is s When the rotation speeds of the first and second electric motors M1 and M2 are both lower than the maximum rotation speed, the speed difference ΔN s From equation (4), P sd / N sd =ρ(P ss / N ss) ···(5) Substituting equations (2) and (3) into this, the speed difference ΔN s If we rearrange it to find the answer, we get the following equation (6).

[0040]

number

[0041] The rotation speed N of the carrier 22 at that time c , that is, the speed difference ΔN in equation (6) depending on the vehicle speed s The rotation speed N of the first and second electric motors M1 and M2 is set to be minimum. M1 ,N M2 and operating at this rotation speed, when there is a sudden demand for an increase in output torque, the output torque can be set to the maximum value at that vehicle speed without changing the rotation speed.

[0042] When one of the first and second electric motors M1, M2 reaches its maximum rotation speed and the vehicle speed is increased further, one of the electric motors cannot output maximum power in order to balance the torque of the three elements, and therefore, Equation (6) cannot be applied. In this case, based on the above-mentioned Equation (1), , the speed difference ΔN s Determine.

[0043] In the drive device 10, the first electric motor M1 reaches the maximum rotation speed first, so the rotation speed N of the first sun gear 18 corresponding to the maximum rotation speed of the first electric motor M1 is sd_max Substituting this into equation (1), the rotational speed N of the second sun gear 20 is ss Ask for. N ss =(1+ρ)N c -ρN sd_max Speed ​​difference ΔN s is expressed by the following formula: ΔN s =(1+ρ)(N sd_max -N c ) ···(7)

[0044] FIG. 9 shows the relationship between the vehicle speed and the speed difference ΔN between the first sun gear and the second sun gear when the first and second electric motors M1, M2 are operating at speeds lower than the maximum rotation speed. s The solid line represents the speed difference ΔN at which the output torque of the drive unit 10 can be maximized for each speed. s The smallest speed difference ΔN s_min In the range where the vehicle speed exceeds approximately 39 km / h, the speed difference ΔN that can maximize the output torque is s is uniquely determined as shown in Figures 7 and 8. The speed difference ΔN s is expressed by equation (6). is about At speeds below 39km / h, the speed difference ΔN that maximizes the output torque s is not uniquely determined, but can be selected within a certain range. The solid line in Figure 9 shows the minimum speed difference ΔN s_min In particular, at speeds below approximately 35 km / h, the speed difference ΔN s can be set to 0. This minimum speed difference ΔN s_min By controlling the rotational speeds of the first and second electric motors M1, M2 so as to satisfy the above equation, it is possible to reduce the loss due to the differential of the planetary gear mechanism 12 and also to reduce the response delay when there is a sudden request to increase the output torque.

[0045] The dashed line in Fig. 9 shows the speed difference ΔN when the vehicle speed exceeds approximately 39 km / h. s This figure shows the case where equation (6) is applied to the range where the vehicle speed is about 39 km / h or less. That is, the speed difference ΔN that gives the maximum output torque when the first and second electric motors M1 and M2 are operating in the upper limit constant power range is s This shows the case where the two motors are not operating in the upper limit power constant region. In this case, when the first and second motors M1 and M2 are operating at less than the maximum rotation speed, the speed difference ΔN s can be determined by one equation, which simplifies the control of the first and second electric motors M1 and M2. sSince the value of the rotational speed of the planetary gear mechanism 12 does not become 0, the meshing position of the gears of the planetary gear mechanism 12 moves, and it is possible to prevent wear of the gears from concentrating in one place.

[0046] The control unit 52 calculates the minimum speed difference ΔN shown by the solid line in FIG. 9 from the vehicle speed. s_min The rotation speeds of the first and second electric motors M1 and M2 are determined based on the vehicle speed and the carrier rotation speed N c Since there is a one-to-one relationship between the vehicle speed and the vehicle speed, the minimum speed difference ΔN s_min For example, the vehicle speed and the minimum speed difference ΔN s_min The relationship between the speeds of the vehicles is determined in advance, and the minimum speed difference ΔN s_min This minimum speed difference ΔN s_min Applying these to equations (2) and (3), the rotational speed of the first sun gear N sd and the rotation speed of the second sun gear N ss The rotation speed N of the first and second sun gears can be calculated. sd ,N ss are the rotation speeds N of the first and second motors, respectively. M1 ,N M2 Since there is a one-to-one relationship between the rotation speed of the first and second sun gears, sd ,N ss to the rotation speed N of the first and second motors M1 ,N M2 can be calculated.

[0047] Alternatively, the control unit 52 may calculate the rotation speeds of the first and second electric motors M1, M2 based on the following equation (6): Carrier rotation speed N calculated from vehicle speed c Applying this to equation (6) gives the velocity difference ΔN s By calculating this and applying it to equations (2) and (3), the rotational speeds N of the first and second sun gears are calculated. sd ,N ss Then, the rotation speeds N of the first and second sun gears can be calculated. sd ,N ss to the rotation speed N of the first and second motorsM1 ,N M2 can be calculated.

[0048] The planetary gear mechanism 12 of the drive unit 10 shown in FIG. 1 is a mechanism in which two sun gears 18, 20 are used as input elements and a carrier 22 is used as an output element, but planetary gear mechanisms of other structures can be used. For example, the most common planetary gear mechanism having a sun gear, a ring gear, and a planetary carrier that supports planetary pinions that mesh with the sun gear and ring gear can be used. In this case, electric motors are connected to the sun gear and ring gear, respectively, and driving wheels are connected to the planetary carrier. The planetary gear ratio ρ is determined by the ratio Z of the number of teeth of the sun gear and ring gear to the number of teeth of the ring gear. s ,Z r Then, ρ=Z s / Z r and the rotation speeds of the two electric motors can be determined in the same manner as in the driving device 10 shown in FIG.

[0049] As a planetary gear mechanism of yet another structure, a so-called double-pinion type planetary gear mechanism can be adopted, which has a sun gear, a ring gear, an inner planetary pinion that meshes with the sun gear, and a planetary carrier that supports an outer planetary pinion that meshes with the ring gear and the inner planetary pinion. In this case, electric motors are connected to the sun gear and the carrier, respectively, and the ring gear is connected to the drive wheels. The planetary gear ratio ρ is calculated by multiplying the number of teeth of the sun gear and the ring gear by Z. s ,Z r Then, ρ=Z s / (Z r -Z s ) and the rotational speeds of the two motors can be determined in the same manner as in the drive device 10 shown in FIG.

[0050] Other aspects of the invention are set forth below. [1] a first electric motor; A second electric motor; a planetary gear mechanism having a first input element connected to the first electric motor, a second input element connected to the second electric motor, and an output element connected to a drive wheel; a control device that controls the first electric motor and the second electric motor so that the rotational speeds of the first input element and the second input element are rotational speeds that can generate a maximum value of torque of the output element at each vehicle speed; A drive device for an electric vehicle comprising: [2] The drive device for the electric vehicle described in [1] above, the control device controls the first electric motor and the second electric motor so that an absolute value of an input speed difference, which is a difference in rotation speed between the first input element and the second input element, is minimized. Drive unit for electric vehicles. [3] The drive device for the electric vehicle described in [1] above, the control device controls the first electric motor and the second electric motor so that, when at least one of the first electric motor and the second electric motor operates in an upper limit constant torque region, an input speed difference, which is a difference in rotation speed between the first input element and the second input element, has a mathematical relationship similar to a mathematical relationship between the speed of the output element and the input speed difference when both the first electric motor and the second electric motor operate in an upper limit constant power region and at a speed lower than a maximum rotation speed. Electric vehicle drive unit [Explanation of symbols]

[0051] 10 Drive unit, 12 Planetary gear mechanism, 14 Final reduction gear, 16 Drive wheel, 18 First sun gear, 20 Second sun gear, 22 Planetary carrier, 24 Outer planetary pinion, 26 Inner planetary pinion, 28 Output gear, 30 Driven gear, 32 Final reduction gear pair, 34 First planetary gear train, 36 Second planetary gear train, 38 First input shaft, 40 First input gear pair, 42 First electric motor shaft, 44 Second input shaft, 46 Second input gear pair, 48 Second electric motor shaft, 50 One-way clutch, 52 Control unit, M1 First electric motor, M2 Second electric motor, N sd First sun gear rotation speed, N ss Second sun gear rotation speed, N c Carrier rotation speed, ΔN s Difference in rotational speed between the first and second sun gears, ΔN s_minThe minimum rotational speed difference that allows the output torque to reach its maximum value is T sd No. 1 sun gear torque, T ss No. 2 sun gear torque, T C Carrier torque, T M1_u Upper limit of torque of the first electric motor, T M2_u Upper limit of torque for the second electric motor.

Claims

1. A first electric motor; A second electric motor; a planetary gear mechanism including a first input element connected to the first electric motor, a second input element connected to the second electric motor, and an output element connected to a drive wheel; A drive device for an electric vehicle comprising: the rotational speeds of the first input element and the second input element are set to rotational speeds that can generate a maximum value of torque of the output element at each vehicle speed within a speed range used by the electric vehicle; Drive unit for electric vehicles.

2. The drive device for an electric vehicle according to claim 1, the rotational speeds of the first input element and the second input element are set so that an absolute value of an input speed difference, which is a difference between the rotational speeds of the first input element and the second input element, is minimized; Drive unit for electric vehicles.

3. The drive device for an electric vehicle according to claim 1, When at least one of the first electric motor and the second electric motor operates in an upper limit constant torque region, an input speed difference, which is a difference in rotation speed between the first input element and the second input element, is set to have a mathematical relationship similar to a mathematical relationship between the speed of the output element and the input speed difference when both the first electric motor and the second electric motor operate in an upper limit constant power region and at a speed lower than a maximum rotation speed. Drive unit for electric vehicles.

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