Power distribution system for electric vehicles

Abstract

To provide a power distribution device for an electric vehicle that is able to distribute power, larger than power of a front wheel, to a rear wheel and is able to obtain stable behavior of the vehicle during braking.SOLUTION: A power distribution device for an electric vehicle is mounted on the electric vehicle including front and rear wheels, an electric motor for outputting power for traveling, and a mechanical brake for applying brake force to at least the front wheels. The power distribution device includes: a power distribution mechanism that distributes power, output from the electric motor, to the front wheel and the rear wheel; and a controller that controls the power distribution mechanism. The power distribution mechanism includes: a first clutch capable of fixing a power distribution ratio during straight traveling to a first distribution ratio; and a second clutch capable of fixing the power distribution ratio during straight traveling to a second distribution ratio. The controller brings the second clutch into an engaged state and brings the first clutch into a semi-engaged state during regenerative braking of the electric vehicle.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power distribution device for an electric vehicle.

Background Art

[0002] Patent Document 1 describes performing regenerative braking in an electric vehicle having a power distribution mechanism that transmits power to the front wheels and the rear wheels.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By distributing power greater than the power of the front wheels to the rear wheels by a power distribution mechanism, good vehicle behavior can be obtained during driving. On the other hand, when performing regenerative braking in a vehicle having the above power distribution mechanism, the braking force of the rear wheels becomes greater than the braking force of the front wheels, and an ideal braking force distribution ratio cannot be obtained.

[0005] An object of the present invention is to provide a power distribution device for an electric vehicle that can distribute power greater than the power of the front wheels to the rear wheels and can obtain stable vehicle behavior during braking.

Means for Solving the Problems

[0006] (1) One aspect of the present invention Power distribution system for electric vehicles is a power distribution device for an electric vehicle mounted on an electric vehicle including front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies a braking force to at least the front wheels, a power distribution mechanism that distributes the power output from the electric motor to the front wheels and the rear wheels, A controller for controlling the power distribution mechanism, is provided, The power distribution mechanism includes a first clutch capable of fixing the power distribution ratio during straight travel to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight travel to a second distribution ratio, The second distribution ratio is a distribution ratio in which the power of the rear wheels > the power of the front wheels, The first distribution ratio is a distribution ratio closer to being equal than the second distribution ratio, The controller When the electric vehicle is performing regenerative braking, engages the second clutch and keeps the first clutch in a semi-engaged state death, For at least a portion of the period during which both the regenerative braking force from the electric motor and the mechanical braking force from the mechanical brake are applied, the second clutch is engaged and the first clutch is partially engaged. . (2) Another embodiment of the present invention is a power distribution device for an electric vehicle, A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. The second clutch is switched to an engaged state at the start of braking of the electric vehicle, and thereafter the first clutch is set to a semi-engaged state. (3) Another embodiment of the present invention is a power distribution device for an electric vehicle, A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. If the vehicle speed of the electric vehicle falls below a first threshold during the braking period, the first clutch is switched from a partially engaged state to a disengaged state. (4) Another embodiment of the present invention is a power distribution device for an electric vehicle, A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. The first braking force based on the internal circulating torque of the power distribution mechanism is calculated, Furthermore, based on the required braking force based on the driving operation, the regenerative braking force from the electric motor, and the first braking force, the second braking force required for the mechanical brake is calculated. The mechanical brake is operated according to the calculated second braking force. [Effects of the Invention]

[0007] According to the present invention, it is possible to distribute power with a distribution ratio in which the power to the rear wheels is greater than the power to the front wheels, and to obtain stable vehicle behavior during braking. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing a configuration of an electric vehicle equipped with a power distribution device according to an embodiment of the present invention. [Figure 2] This is a braking force distribution diagram showing the ratio of braking force to the front wheels and braking force to the rear wheels. [Figure 3] This is a flowchart showing the braking process performed by the controller. [Figure 4] This is a time chart showing an example of the operation of an electric vehicle during braking. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will now be described in detail with reference to the drawings. In these embodiments, the state in which the clutch transmits approximately 100% of the torque is referred to as the engaged state, and the state in which the clutch does not transmit approximately any torque is referred to as the disengaged state. Furthermore, the state in which the clutch transmits torque while slipping is referred to as the semi-engaged state.

[0010] Figure 1 is a diagram showing an electric vehicle equipped with a power distribution device according to an embodiment of the present invention. The electric vehicle 1 of the embodiment includes front wheels 2, rear wheels 3, an electric motor 6, a battery 4 for storing power for driving, an inverter 5 for driving the electric motor 6, a power distribution mechanism 10 for distributing the power of the electric motor 6 to the front wheels 2 and the rear wheels 3, and a mechanical brake 7 for applying braking force to the front wheels 2 and the rear wheels 3.

[0011] The inverter 5 operates the electric motor 6 by transmitting power between the electric motor 6 and the battery 4. Power is output from the electric motor 6 when the inverter 5 operates the electric motor 6 in a powered manner. When the inverter 5 operates the electric motor 6 in a regenerative manner, the electric motor 6 generates electricity, and regenerative braking torque is generated on the motor shaft of the electric motor 6. Power and regenerative braking torque are transmitted to the front wheels 2 and rear wheels 3 via the power distribution mechanism 10. In this invention, "during regenerative braking" corresponds to when the braking force due to the regenerative braking torque (regenerative braking force) is acting. Even when the braking force due to the mechanical brake 7 (mechanical braking force) is acting, if the regenerative braking force is also acting at the same time, it corresponds to when regenerative braking is in operation.

[0012] The mechanical brake 7 generates frictional force to apply braking force to the front wheels 2 and the rear wheels 3. Specifically, the mechanical brake 7 is configured to generate frictional force between a mechanism (disc rotor, etc.) connected to the front wheels 2 and a mechanism (disc rotor, etc.) connected to the rear wheels 3. Alternatively, the frictional force may be generated between the front wheels 2 and the rear wheels 3 on the power transmission path, relative to the power distribution mechanism 10. The frictional force may be generated using hydraulic pressure or by other power sources.

[0013] The electric vehicle 1 further includes a controller 21 that controls the power distribution mechanism 10, an operation unit 22, a battery management unit 23, a driving control unit 24 that controls the inverter 5 and the mechanical brake 7, and a sensor 9 that detects the vehicle state, including vehicle speed. The power distribution mechanism 10 and the controller 21 correspond to the power distribution device 50 according to this embodiment.

[0014] The driving control unit 22 includes an accelerator control unit 22a, a brake control unit 22b, and a steering unit 22c, which are operated by the driver. As driving operation signals, signals indicating the amount of operation of the accelerator control unit 22a and signals indicating the amount of operation of the brake control unit 22b are sent to the driving control unit 24 and the controller 21. Note that the driving operation signals may also be sent to the driving control unit 24 and the controller 21 from the automatic driving system. The controller 21 may receive the driving operation signal values ​​from the driving control unit 24. The vehicle state values ​​detected by the sensor 9 are also sent to the driving control unit 24 and the controller 21 in the same way as the driving operation signals.

[0015] The driving control unit 24 can output power to the front wheels 2 and rear wheels 3 by operating the inverter 5 in a powered mode. The driving control unit 24 can also operate the inverter 5 in a regenerative mode and apply braking force to the front wheels 2 and rear wheels 3 by operating the mechanical brake 7. The driving control unit 24 controls the output of the above-mentioned power based on the driving operation and the vehicle status (vehicle speed, etc.). The driving control unit 24 controls the braking force based on the driving operation, the vehicle status (vehicle speed, etc.), the state of the battery 4, and the mechanical braking force instruction value from the controller 21.

[0016] The controller 21 can switch the first clutch 12 and the second clutch 14, described later, between engaged, semi-engaged, and disengaged states by operating a hydraulic circuit or electric actuator. The controller 21 can control the mechanical brake 7 by outputting a mechanical braking force instruction value to the travel control unit 24. The controller 21 can read the regenerative braking force value at that time from the travel control unit 24.

[0017] The controller 21 includes one ECU (Electronic Control Unit) or multiple ECUs that communicate with each other and operate in coordination. The controller 21 includes a storage unit 21a that stores control programs and control data, and executes the control programs stored in the storage unit 21a. The driving control unit 24 includes one ECU or multiple ECUs that communicate with each other and operate in coordination. The controller 21 and the driving control unit 24 communicate with each other and operate in coordination. The controller 21 and the driving control unit 24 may be integrated and provided in a common ECU.

[0018] <Power distribution mechanism> The power distribution mechanism 10 is provided between the drive shaft 30, which receives power from the electric motor 6, the front transmission shaft 32 which transmits power to the front wheels 2, and the rear transmission shaft 34 which transmits power to the rear wheels 3. The front transmission shaft 32 transmits power to the front wheels 2 via a gear mechanism 33 including a differential mechanism. The rear transmission shaft 34 transmits power to the rear wheels 3 via a gear mechanism 35 including a differential mechanism. A power transmission mechanism 31, which includes one or more of the following (not shown): a speed change mechanism, a gear mechanism, a clutch, etc., may be interposed between the electric motor 6 and the drive shaft 30.

[0019] The power distribution mechanism 10 includes a differential mechanism 11 capable of transmitting power without restricting the rotational speed difference between the front wheels 2 and the rear wheels 3, a first clutch 12 capable of fixing the power distribution ratio between the front wheels 2 and the rear wheels 3 to a first distribution ratio when driving straight, and a second clutch 14 capable of fixing the power distribution ratio between the front wheels 2 and the rear wheels 3 to a second distribution ratio when driving straight. The differential mechanism 11 includes three rotating elements, and the first clutch 12 and the second clutch 14 can achieve the above functions by connecting two of the three rotating elements via a linkage or gear mechanism.

[0020] For example, the differential mechanism 11 may be a planetary gear mechanism having a sun gear 11a connected to the rear transmission shaft 34, a planetary carrier 11d connected to the front transmission shaft 32 via a gear mechanism 16, an internal gear 11e connected to the drive shaft 30, and planetary gears 11b and 11c provided between the sun gear 11a and the internal gear 11e. The planetary gears 11b and 11c may be a two-stage configuration in which the planetary gear 11b located radially inward and the planetary gear 11c located radially outward mesh with each other.

[0021] In the configuration of the differential mechanism 11 described above, the first clutch 12 can be realized by a configuration that allows the sun gear 11a and the planetary carrier 11d to be connected. In the configuration of the differential mechanism 11 described above, the second clutch 14 can be realized by a configuration that allows the sun gear 11a and the planetary carrier 11d to be connected via the gear mechanism 13.

[0022] <Power distribution ratio> The power distribution mechanism 10 distributes power to the front wheels 2 and rear wheels 3 in the following distribution ratios, depending on the state of the first clutch 12 and the second clutch 14. Hereinafter, the power distribution ratio of the front wheels 2 to the rear wheels 3 will be referred to as the "front-to-rear power distribution ratio". A. When the first clutch 12 and the second clutch 14 are in the disengaged state. The power distribution ratio between the front and rear wheels is 50:50, and the rotational speed difference between the two front wheels and the three rear wheels is unconstrained. B. When the first clutch 12 is engaged and the second clutch 14 is disengaged. The power distribution ratio between the front and rear wheels is 50:50 (the first distribution ratio), and the difference in rotational speed between the front 2 wheels and the rear 3 wheels is constrained to a constant ratio. C. When the first clutch 12 is in the open state and the second clutch 14 is in the engaged state. The power distribution ratio between the front and rear wheels is 40:60 (the second distribution ratio), and the difference in rotational speed between the front 2 wheels and the rear 3 wheels is constrained to a constant ratio. However, the distribution ratio of B and C is limited to when traveling in a straight line.

[0023] Note that the first and second power distribution ratios are not limited to the examples above. The second power distribution ratio may be such that a larger proportion of power is distributed to the rear wheels. The first power distribution ratio may not be perfectly equal, but may be closer to equal than the second power distribution ratio.

[0024] The above power distribution ratios can be achieved by the following configuration. Specifically, distribution ratio A can be achieved by setting the gear ratios of each gear in the differential mechanism 11. Distribution ratio B (first distribution ratio) can be achieved by setting the gear ratio of the power transmission path so that the reduction ratio from the drive shaft 30 to the front wheel 2 and the reduction ratio from the drive shaft 30 to the rear wheel 3 are the same when the first clutch 12 is engaged. Distribution ratio C (second distribution ratio) can be achieved by setting the gear ratio of the power transmission path so that the reduction ratio from the drive shaft 30 to the front wheel 2 is slightly greater than the reduction ratio from the drive shaft 30 to the rear wheel 3 when the second clutch 14 is engaged.

[0025] The gear ratio settings described above can also be rephrased as follows: Reduction ratio from clutch 14 to front wheel 2 > Reduction ratio from clutch 14 to rear wheel 3 The reduction ratio from the first clutch 12 to the front wheel 2 is approximately equal to the reduction ratio from the first clutch 12 to the rear wheel 3.

[0026] With the gear ratio settings described above, if the first clutch 12 is engaged and the second clutch 14 is disengaged, and power is transmitted with the front wheels 2 and rear wheels 3 lifted off the ground, the front wheels 2 and rear wheels 3 will rotate at the same rotational speed, and power will be transmitted equally to both the front wheels 2 and rear wheels 3. However, it is assumed that the left and right front wheels 2 rotate at the same speed, and the left and right rear wheels 3 rotate at the same speed.

[0027] On the other hand, if the first clutch 12 is disengaged and the second clutch 14 is engaged, and power is transmitted with the front wheels 2 and rear wheels 3 lifted off the ground, the rotational speed of the rear wheels 3 will be slightly higher than that of the front wheels 2 (for example, +3%). Therefore, when moving in a straight line, more power is distributed to the rear wheels 3 than to the front wheels 2. However, it is assumed that the left and right front wheels 2 rotate at the same speed, and the left and right rear wheels 3 rotate at the same speed.

[0028] <Ratio of braking force between front and rear> Figure 2 is a braking force distribution diagram showing the ratio of braking force to the front wheels and braking force to the rear wheels.

[0029] In Figure 2, characteristic lines D and E represent the ideal braking force distribution line for constant volume, which provides stable braking behavior at the maximum vehicle weight, and the ideal braking force distribution line for light load, which provides stable braking behavior at the lightest vehicle weight (with only the driver on board), respectively. The ideal braking force distribution line for constant volume and the ideal braking force distribution line for light load are generally known ideal braking force distribution lines. By distributing braking force according to these braking force distribution lines, stable vehicle behavior during braking can be obtained.

[0030] Characteristic line A shows the braking force distribution line when the front-to-rear power distribution ratio is 40:60, regenerative braking occurs, and the mechanical brake 7 is released. Since the regenerative braking force is distributed in the same proportion as the front-to-rear power distribution ratio, in the above case, the ratio of braking force is 2:3 = 40:60 for the front wheels and rear wheels. The braking force distribution line of characteristic line A is far removed from the ideal braking force distribution line for constant load or the ideal braking force distribution line for light load. The braking force distribution line of characteristic line A corresponds to the braking force distribution line in the electric vehicle 1 of the embodiment when only regenerative braking occurs with the first clutch 12 in the open state and the second clutch 14 in the engaged state.

[0031] Characteristic line B shows the braking force distribution line when the power distribution ratio between the front and rear is 50:50, regenerative braking occurs, and the mechanical brake 7 is released. Since the regenerative braking force is distributed in the same proportion as the power distribution ratio between the front and rear, in the above case, the ratio of braking force is 2:3 = 50:50 for the front wheels and 3 for the rear wheels. The braking force distribution line of characteristic line B is far removed from the ideal braking force distribution line for constant load or the ideal braking force distribution line for light load. The braking force distribution line of characteristic line B corresponds to the braking force distribution line in the electric vehicle 1 of the embodiment when both the first clutch 12 and the second clutch 14 are in the disengaged state, or when the first clutch 12 is engaged and the second clutch 14 is disengaged, and only regenerative braking occurs.

[0032] Characteristic curve C shows the braking force distribution line in the electric vehicle 1 of the embodiment when the first clutch 12 is semi-engaged, the second clutch 14 is engaged, regenerative braking occurs, and the mechanical brake 7 is released. In the above case, an internal circulating torque is generated transmitted in the power transmission path between the first clutch 12 and the second clutch 14, and this internal circulating torque acts as a braking force. This internal circulating torque is a torque absorbed by the slippage of the first clutch 12. Furthermore, in the first clutch 12 where slippage is occurring, the braking torque is transmitted from the lower rotational speed to the higher rotational speed. That is, the braking torque is transmitted in the opposite direction to the direction in which the driving torque is transmitted. As a result, the braking force distribution line of characteristic curve C is such that the overall braking force of the front wheels 2 is appropriately greater than the braking force of the rear wheels 3. The braking force distribution line of characteristic curve C is close to the ideal braking force distribution line for constant volume and the ideal braking force distribution line for light volume.

[0033] Characteristic curve F is the braking force distribution curve when the mechanical brake 7 is applied without regenerative braking. In the above case, the load is transferred to the front wheels 2 during braking, resulting in a greater braking force being generated on the front wheels 2 than on the rear wheels 3. Characteristic curve F shows a greater distribution of braking force to the front wheels 2 than the ideal braking force distribution curve for constant volume and the ideal braking force distribution curve for light volume.

[0034] <Braking process> Figure 3 is a flowchart showing the braking process performed by the controller. The controller 21 continuously and repeatedly executes the control process at predetermined control cycles while the electric vehicle 1 is operating.

[0035] When braking is initiated, the controller 21 determines whether braking is in progress (step S1). If the answer is NO, the controller 21 terminates the braking process. If the answer is YES, the controller 21 proceeds to the next step.

[0036] Next, the controller 21 calculates the required braking force F1 (step S2). The required braking force F1 refers to the braking force required by the driving operation. The required braking force F1 should be calculated using a predetermined method based on the amount of braking operation and the vehicle condition (vehicle speed, etc.).

[0037] Next, the controller 21 determines whether it is time to start braking (step S3). If it is time to start braking, it switches the first clutch 12 to the open state and the second clutch 14 to the engaged state (step S4), and then proceeds to step S5. If, at this timing, the first clutch 12 is already in the open state and the second clutch 14 is already engaged, the controller 21 maintains that state. Through the processing in steps S3 and S4, even if the second clutch 14 was in the open state immediately before the braking process, the second clutch 14 will be switched to the engaged state.

[0038] On the other hand, if the braking start timing has passed in step S3, the controller 21 proceeds to the next step S5.

[0039] As the process progresses, the controller 21 then controls the first clutch 12 to a semi-engaged state (step S5). Step S5 is a process that is executed in the braking process of each control cycle if braking is in progress. When the controller 21 repeatedly executes the process of step S5 in multiple braking processes, it may perform control to adjust the engagement degree of the first clutch 12 so that the first clutch 12 gradually approaches a predetermined semi-engaged engagement degree.

[0040] The processes in step S4 and step S5 result in a braking force distribution that follows the characteristic curve C in Figure 2, excluding the braking force from the mechanical brake 7.

[0041] Next, the controller 21 calculates the braking force F2 based on the internal circulating torque generated by partially engaging the first clutch 12 (step S6). The controller 21 has a data table that shows the relationship between vehicle conditions such as vehicle speed and vehicle weight, the degree of engagement of the first clutch 12, and the braking force F2 based on the internal circulating torque, and can calculate the braking force F2 using this data table. The data table can be formed by testing or simulation and provided to the controller 21 in advance.

[0042] Next, the controller 21 reads the current regenerative braking force F3 from the driving control unit 24 (step S7). In a control process separate from the braking process shown in Figure 3, the driving control unit 24 works in cooperation with the battery management unit 23 to determine the regenerative braking force F3 according to the required braking force and the state of the battery 4, and operates the electric motor 6 in regenerative mode to obtain that regenerative braking force F3.

[0043] Next, the controller 21 calculates the mechanical braking force F4 to be generated in the mechanical brake 7 as shown in the following equation (1) (step S8). F4 = F1 - F2 - F3 ... (1) Note that the calculation in step S8 may be performed using map data.

[0044] Next, the controller 21 determines whether the vehicle speed has fallen below a first threshold vth, which indicates the vehicle is about to stop (step S9). The first threshold vth should be set to a value that determines the extremely low speed before stopping, and the first threshold vth may be a fixed value or a value that changes depending on the vehicle condition, etc. The extremely low speed value may be any value within the range of 1 to 10 [km / h], for example.

[0045] If the determination result in step S9 is NO, the controller 21 outputs an instruction value to the travel control unit 24 so that the mechanical braking force F4 calculated in step S8 is generated (step S11). As a result of this output, the mechanical brake 7 is activated and the mechanical braking force F4 is generated.

[0046] Then, the controller 21 finishes one braking process and repeats the process from step S1 again in the next control cycle.

[0047] On the other hand, if the determination result in step S9 is YES, the controller 21 controls the first clutch 12 in the direction of releasing it from the semi-engaged state (step S10). Step S10 is a process that is executed in the braking process of each control cycle until the vehicle speed becomes extremely low before stopping and the braking operation is released. When the controller 21 repeatedly executes the process of step S10 in multiple braking processes, it may perform control to adjust the engagement degree of the first clutch 12 so that the engagement degree of the first clutch 12 is gradually weakened until it is finally released.

[0048] Subsequently, the controller 21 executes the process described in step S11, completing one braking process. Then, in the next control cycle, the process from step S1 is repeated.

[0049] The braking process program described above is stored in a non-transient storage medium (non-transient computer-readable medium), such as the storage unit 21a of the controller 21. The controller 21 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium described above may store the braking process program described above.

[0050] <Example of operation> Figure 4 is a time chart showing an example of the operation of an electric vehicle during braking. In this time chart, the initial T1 corresponds to the period in which the first clutch 12 gradually increases its engagement degree toward a predetermined semi-engaged state due to the process of step S5 in Figure 3. The later T3 corresponds to the period in which the first clutch 12 gradually decreases its engagement degree toward the disengaged state due to the process of step S10 in Figure 3.

[0051] According to the braking process described above, based on the braking operation, a regenerative braking force F3, a mechanical braking force F4, and a braking force F2 based on internal circulating torque are generated so that the total braking force matches the required braking force F1.

[0052] Furthermore, during the mid-stage T2 of the braking period, the first clutch 12 is in a semi-engaged state and the second clutch 14 is in an engaged state, resulting in a regenerative braking force F3 and a braking force F2 based on the internal circulating torque. This braking force "F2 + F3" is allocated to the front wheels 2 and rear wheels 3 in a distribution close to the ideal braking force distribution line for constant volume or light volume, as shown by characteristic curve C in Figure 2. Therefore, even when the regenerative braking force F3 accounts for a large proportion of the required braking force F1, an ideal front-to-rear distribution of braking force can be obtained, enabling stable vehicle behavior during braking.

[0053] The ratio of regenerative braking force F3 to mechanical braking force F4 changes due to factors other than braking operation, such as the remaining charge of battery 4. For example, in the first half of the braking period, if battery 4 was able to be charged, the ratio of regenerative braking force F3 may be large and the ratio of mechanical braking force F4 may be small. Subsequently, in the second half of the braking period, if the remaining charge of battery 4 increases, the ratio of regenerative braking force F3 may decrease and the ratio of mechanical braking force F4 may increase.

[0054] Here, unlike in the case of Figure 4, we consider a case where, hypothetically, regenerative braking force F3 accounts for a large proportion in the first half of the braking period, and then mechanical braking force F4 accounts for a large proportion thereafter. In this case, unlike the embodiment, let's assume that the front-to-rear distribution of regenerative braking is 2:3 = 40:60 for the front wheels and that the front-to-rear distribution of mechanical braking is larger for the front wheels. In this configuration, the front-to-rear distribution of braking force changes abruptly from larger for the rear wheels to larger for the front wheels before and after the change in the proportion of regenerative braking force. Such abrupt changes in front-to-rear distribution can easily affect the behavior of the vehicle on low-friction road surfaces. However, in this embodiment, for at least a portion of the period during which both regenerative braking force and mechanical braking force are applied, the controller 21 controls the first clutch 12 to be semi-engaged and the second clutch 14 to be engaged. Therefore, even if there is a change during this control from a period in which regenerative braking force accounts for a large proportion to a period in which mechanical braking force accounts for a large proportion, the front-to-rear distribution of braking force does not change abruptly. Thus, stable vehicle behavior can be achieved.

[0055] Furthermore, according to the braking process described above, at the initial T1 of the braking period, the second clutch 14 is initially switched to an engaged state and the first clutch 12 to an open state at the start timing t1, and then the first clutch 12 is switched to a semi-engaged state. At the start timing t1 of braking, with the second clutch 14 engaged and the first clutch 12 open, the ratio of regenerative braking force F3 between the front and rear wheels is 3 > 2 for a short time. In this way, a relatively large braking force is distributed to the rear wheels 3 for only a short time at the beginning of braking, causing the entire vehicle, including the rear, to sink, and enabling more stable vehicle behavior during subsequent braking.

[0056] Furthermore, according to the braking process described above, during the initial T1 of the braking period, the first clutch gradually increases its engagement level until it reaches a predetermined semi-engaged state. In this way, by controlling the engagement level to change gradually, sudden changes in the front-to-rear distribution of braking force are reduced, and stable vehicle behavior can be achieved during this period.

[0057] Furthermore, according to the control process described above, the first clutch 12 is released in the later part of the braking period T3, that is, after timing t2 when the vehicle speed falls below the first threshold vth. When the first clutch 12 is in a semi-engaged state, a braking force F2 based on the internal circulating torque acts, making it easy for a shock to occur just before the electric vehicle 1 comes to a stop. In this embodiment, the occurrence of the above shock can be reduced.

[0058] Furthermore, according to the control process described above, during the later part of the braking period T3, the engagement degree of the first clutch 12 is gradually reduced until it is disengaged. In this way, by controlling the engagement degree to be changed gradually, sudden changes in the front-to-rear distribution of braking force are reduced, and stable vehicle behavior can be achieved during this period.

[0059] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, an electric vehicle having an electric motor as a power source for driving was described. However, the electric vehicle may include other power sources such as an internal combustion engine in addition to the electric motor as a power source for driving. Furthermore, in the above embodiments, an example of a power distribution mechanism was shown in detail, but other configurations may be applied as long as a similar power distribution is possible. In addition, in the above embodiments, the controller 21 was described as performing the following controls: engaging the second clutch 14 and nearly disengaging the first clutch 12 during the short braking start timing t1 to generate regenerative braking; gradually disengaging the first clutch 12 during the initial braking period T1; disengaging the first clutch 12 during the later braking period T3; and gradually disengaging the first clutch 12 during the later braking period T3. However, each of the above controls is optional and may be omitted. Other details shown in the embodiments can be modified as appropriate without departing from the spirit of the invention. [Explanation of Symbols]

[0060] 1. Electric Vehicle 2 Front wheels 3 Rear wheels 4 Batteries 5 Inverter 6 Electric motor 7 Mechanical brakes 9 sensors 10 Power distribution mechanism 11 Differential mechanism 12 First clutch 14. Second clutch 21 Controllers 21a Storage section 22. Operation Unit 24. Driving control unit 50 Power distribution device F1 required braking force F2 Braking force based on internal circulation torque (first braking force) F3 Regenerative braking force F4 Mechanical braking force (second braking force)

Claims

1. A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. A power distribution device for an electric vehicle, characterized in that the second clutch is engaged and the first clutch is partially engaged for at least a portion of the period during which both the regenerative braking force from the electric motor and the mechanical braking force from the mechanical brake are applied.

2. A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. A power distribution device for an electric vehicle, characterized in that the second clutch is switched to an engaged state at the timing of the start of braking of the electric vehicle, and thereafter the first clutch is set to a semi-engaged state.

3. A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. A power distribution device for an electric vehicle, characterized in that when the vehicle speed falls below a first threshold during the braking period of the electric vehicle, the first clutch is switched from a semi-engaged state to an open state.

4. A power distribution device for an electric vehicle, which is mounted on an electric vehicle comprising front wheels, rear wheels, an electric motor that outputs power for driving, and a mechanical brake that applies braking force to at least the front wheels, A power distribution mechanism that distributes the power output from the electric motor to the front wheel and the rear wheel, A controller for controlling the power distribution mechanism, Equipped with, The aforementioned power distribution mechanism is It includes a first clutch capable of fixing the power distribution ratio during straight-line driving to a first distribution ratio, and a second clutch capable of fixing the power distribution ratio during straight-line driving to a second distribution ratio, The second distribution ratio is such that the power of the rear wheels > the power of the front wheels. The first distribution ratio is a distribution ratio that is closer to equality than the second distribution ratio. The aforementioned controller, During regenerative braking of the electric vehicle, the second clutch is engaged and the first clutch is partially engaged. The first braking force based on the internal circulation torque of the power distribution mechanism is calculated, Furthermore, based on the required braking force based on the driving operation, the regenerative braking force from the electric motor, and the first braking force, the second braking force required for the mechanical brake is calculated. A power distribution device for an electric vehicle, characterized by operating the mechanical brake in accordance with the calculated second braking force.

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