Travel control method and travel control device for electric vehicle

Abstract

According to the present invention, a travel control method for an electric vehicle that comprises a disconnect mechanism (13) for putting a front wheel (11) and a front motor (15) or a rear wheel (13) and a rear motor (24) into a connected state or a disconnected state involves setting one of the front motor (15), which is for driving the front wheel (11), and the rear motor (24), which is for driving the rear wheel (13), as a first motor and setting the other of the front motor and the rear motor as a second motor and, when the first motor is in the connected state, the second motor is in the disconnected state, and the second motor is transitioned to the connected state, adjusting the rate of increase in the output torque of the first motor such that the torque transmitted from the first motor to the front wheel or the rear wheel reaches a required torque at timing at which the torque transmitted from the second motor to the front wheel or the rear wheel begins to increase.

Description

Travel control method and travel control device for electric vehicle

[0001] The present invention relates to a travel control method and a travel control device for an electric vehicle.

[0002] Patent Document 1 discloses an electric vehicle including a front motor for front wheels and a rear motor for rear wheels. Further, this electric vehicle is provided with a disconnect mechanism capable of switching the front wheels and the front motor between a connected state and a disconnected state in order to switch between two-wheel drive and four-wheel drive.

[0003] Japanese Unexamined Patent Application Publication No. 2022-2463

[0004] Incidentally, it is known that when the disconnect mechanism is constituted by a one-way clutch, an abrupt transmission torque is generated when the one-way clutch is engaged, which causes an impact. In order to suppress the generation of such abrupt transmission torque, control is performed that suppresses the rate of increase of the rotation speed of the motor. However, this approach has a problem that the switching from the disconnected state to the connected state is delayed.

[0005] The present invention has been made to solve the above problem. An object of the present invention is to provide a travel control method and a travel control device for an electric vehicle that drives front and rear wheels with independent motors and switches between two-wheel drive and four-wheel drive via a disconnect mechanism having a one-way clutch, which can quickly switch from two-wheel drive to four-wheel drive and suppress the generation of impact during the switching.

[0006] The travel control method according to the present invention is a travel control method for an electric vehicle comprising: front wheels; rear wheels; a front motor for driving the front wheels; a rear motor for driving the rear wheels; a battery that supplies electric power to the front motor and the rear motor; and a disconnect mechanism having a one-way clutch for switching between a connected state and a disconnected state between the front wheels and the front motor or between the rear wheels and the rear motor.

[0007] In this driving control method, one of the front motor or the rear motor is designated as the first motor, and the other of the front motor or the rear motor is designated as the second motor. When the first motor is in a connected state and the second motor is in a disconnected state, the output torque of the first motor is adjusted when switching the second motor to the connected state, so as to absorb the increase in the transmission torque of the second motor caused by the engagement of the one-way clutch by the decrease in the transmission torque of the first motor.

[0008] According to the present invention, in an electric vehicle in which the front and rear wheels are driven by independent motors and the two-wheel drive and four-wheel drive are switched by a disconnect mechanism having a one-way clutch, it is possible to quickly switch from two-wheel drive to four-wheel drive and suppress the occurrence of shocks during the switching process.

[0009] This is a schematic diagram of a battery residual value notification system according to one embodiment of the present invention. This is a schematic diagram showing an example of a disconnect mechanism. This is a block diagram showing the configuration of an electric vehicle controller. This is an example of a map showing the relationship between vehicle speed, target driving force, and accelerator opening. This is an example of a map showing the relationship between vehicle speed, target driving force, and the connected and disconnected states of the disconnect mechanism. This is a timing chart showing the behavior of the conventional front motor and rear motor when switching from two-wheel drive to four-wheel drive. This is a timing chart showing an example of the behavior of the front motor and rear motor in the present invention when switching from two-wheel drive to four-wheel drive. This is a flowchart showing an example of a specific control flow of a driving control method according to one embodiment of the present invention. This is a flowchart showing an example of a specific control flow of a driving control method according to one embodiment of the present invention.

[0010] Hereinafter, an embodiment of the electric vehicle driving control method and driving control device according to the present invention will be described with reference to the drawings. First, the drive structure of the electric vehicle will be described, and then the driving control method will be described.

[0011] <1. Drive Structure of Electric Vehicle> Figure 1 is a diagram showing the system configuration of an electric vehicle 100 to which the driving control device of this embodiment is applied. As shown in Figure 1, this electric vehicle 100 is a so-called four-wheel drive vehicle and is equipped with a front drive system 1, a rear drive system 2, a battery 3, and controllers 4 to 7. That is, although this electric vehicle is a four-wheel drive vehicle, it is possible to switch between four-wheel drive and two-wheel drive by a disconnect mechanism described later.

[0012] The front drive system 1 comprises a pair of front wheels 11, a front drive shaft 12, a disconnect mechanism 13, a front reduction gear 14, a front motor 15, a front inverter 16, etc., and the front wheels 11 are driven by the front motor 15.

[0013] The front motor 15 is, for example, a three-phase AC synchronous motor and is driven by AC power input from the front inverter 16. The output torque of the front motor 15 generates torque in the front wheels 11. In addition, the front motor 15 generates so-called regenerative torque when its drive shaft is rotated along with the front wheels 11. As a result, the front motor 15 can recover the kinetic energy of the electric vehicle 100 as electrical energy.

[0014] The front inverter 16 includes, for example, two pairs of switching elements for each phase of the front motor 15. The front inverter 16 opens and closes these switching elements in response to a PWM (Pulse Width Modulation) signal input from the motor controller 6.

[0015] The front reduction gear 14 transmits the braking and driving force of the front motor 15 to the front wheels 11 via the front drive shaft 27. At that time, the front reduction gear 26 controls the rotational speed of the front motor 15 to a predetermined gear ratio (N f The front drive shaft 27 and front wheels 11 are rotated at a reduced rotational speed. In addition, although not shown in Figure 1, a differential gear device is provided on the front drive shaft, and the rotational speed reduced by the front reduction gear 14 is transmitted to the front wheels 11 via the differential gear device.

[0016] The rear drive system 2 comprises a pair of rear wheels 21, a rear drive shaft 22, a rear reduction gear 23, a rear motor 24, a rear inverter 25, etc., and the rear motor 24 drives the rear wheels 21. Each of these components constituting the rear drive system 2 functions in the same way as each component of the front drive system 1.

[0017] Battery 3 is provided in common to both the front drive system 1 and the rear drive system 2, and supplies power to drive the front motor 15 and the rear motor 24. In addition, during regenerative control, battery 3 is charged by the regenerative power generated by the front motor 15 and the rear motor 24.

[0018] As described above, the front drive system 1 is provided with a disconnect mechanism 13. The disconnect mechanism 13 is provided on the front drive shaft 12 that extends from the differential gear device to one of the front wheels 11.

[0019] Figure 2 shows an example of a disconnect mechanism. As shown in Figure 2, the front drive shaft 12 consists of an inner shaft 121 on the differential gear device 17 side and an outer shaft 122 on the front wheel 11 side, and a disconnect mechanism 13 is provided between these inner shaft 121 and outer shaft 122. This disconnect mechanism 13 has a one-way clutch (OWC). Therefore, when the one-way clutch is engaged, the front motor 15 and the front wheel 11 are connected, and when it is disengaged, they are disconnected. When connected, it is a four-wheel drive system where the front wheel 11 and rear wheel 21 are driven, and when disconnected, it is a two-wheel drive system where only the rear wheel 21 is driven.

[0020] <2. Controller> Figure 3 is a block diagram showing the configuration of the controller, and Figure 4 is a block diagram of control by the controller. As shown in Figure 3, in this embodiment, a disconnect controller 4, a powertrain controller 5, a front motor controller 6, and a rear motor controller 7 are provided, and these are able to communicate with each other. Furthermore, these controllers 4 to 7 are composed of a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input / output interface (I / O interface). It is also possible to configure each controller with multiple microcomputers.

[0021] <2-1. Disconnect Controller> The disconnect controller 4 switches the disconnect mechanism 13 to a connected state or a disconnected state based on a command from the powertrain controller 5.

[0022] At this time, whether the disconnect mechanism 13 is in a connected or disconnected state can be detected by a sensor provided on the disconnect mechanism 13. For example, the disconnect controller 4 can determine that the vehicle is in a connected state if it determines that there is no difference in rotational speed between the inner shaft 121 and the outer shaft 122 of the front drive shaft 12, and in a disconnected state if it determines that there is a difference in rotational speed.

[0023] <2-2. Powertrain Controller> The powertrain controller 5 receives detection signals from various sensors, such as the remaining charge (SOC) of the battery 3, the accelerator pedal position, and the wheel speed sensor. Based on these detection signals, the powertrain controller 5 determines the target operation of the front motor 15 and the rear motor 24 and transmits it as a command to the front motor controller 6 and the rear motor controller 7.

[0024] Furthermore, the powertrain controller 5 calculates the target driving force of the electric vehicle 100 based on the accelerator opening and wheel speed sensors. The target driving force is, for example, the torque required to perform the target operation of the electric vehicle 100, and is calculated, for example, according to the map in Figure 4. As shown in Figure 4, the target driving force increases as the accelerator opening increases. Note that, due to the characteristics of the motor, torque output becomes less efficient at higher rotational speeds, so the target driving force decreases as the vehicle speed increases.

[0025] The powertrain controller 5 then switches between four-wheel drive and two-wheel drive based on the target driving force and vehicle speed. Figure 5 is a map that determines whether the disconnect mechanism 13 is connected or disconnected, and the disconnect mechanism 13 is controlled according to this map. As shown in Figure 5, whether the disconnect mechanism is connected or disconnected is based on the vehicle speed and target driving force. If the vehicle speed and target driving force are in the disconnected region of Figure 5, the powertrain controller 5 sends a command to the disconnect controller 4 to connect the disconnect mechanism 13. On the other hand, if the vehicle speed and target driving force are in the connected region, the powertrain controller 5 sends a command to the disconnect controller 4 to connect the disconnect mechanism 13. In addition, the vehicle's driving mode switch can also be used to switch between connected and disconnected states.

[0026] <2-3. Motor Controller> When the front motor controller 6 receives a command from the powertrain controller 5 (for example, a target torque (required torque)), it controls the current of the front motor 15, controls the output torque, etc., based on the motor rotation speed detected by the rotation sensor of the front motor 15. Similarly, the rear motor controller 7 also controls the rear motor 24.

[0027] <3. Control by Controllers> Next, we will explain the control of each motor 15, 24 by the controllers 4 to 7 described above. First, we will explain the problems of the conventional method, and then we will explain the control method of this embodiment.

[0028] <3-1. Overview of Control Method> Figure 6 is a timing chart showing the control of both motors before and after driving a conventional disconnect mechanism. In the following explanation, the target transmission torques Tr1 and Tr2 are the transmission torques required to rotate the wheels. Therefore, rather than the torque directly output from each motor 15 and 24, the output torques from each motor 15 and 24 are adjusted so that transmission torques are actually generated.

[0029] The initial state is two-wheel drive. That is, as shown in Figure 6, the electric vehicle 100 is driven by the rear motor 24, and the front motor 15 is disconnected from the drive system and stopped by the disconnect mechanism 13. In this state, when the accelerator is pressed at time t1 and the map in Figure 4 transitions from the disconnected region to the connected region, the powertrain controller 5 transmits a target torque (requested torque) to the front motor controller 6. As a result, the front motor 15 increases its rotational speed in accordance with the vehicle speed.

[0030] The disconnect mechanism 13 waits for a time tm (rotation synchronization time) while the rotational speed of the front motor 15 is increasing to correspond to the vehicle speed before switching to the connected state. After that, the one-way clutch is engaged in the disconnect mechanism 13, and the system switches to the connected state at time t2. As a result, the transmission torque of the front motor 15 increases, but the impact when the one-way clutch engages becomes larger if the difference in rotational speed between the inner shaft 121 and the outer shaft 122 is large. Therefore, when increasing the transmission torque of the front motor 15 in a short time, a sudden increase in transmission torque occurs at the time of engagement, which causes an impact (see D1 at time t2).

[0031] Furthermore, the powertrain controller 5 transmits a target torque (requested torque) Tr1 corresponding to the accelerator opening to the rear motor controller 7. As a result, the rear motor 24 increases the torque transmitted to the rear wheels 21 until time t2, and thereafter drives with torque Tr2.

[0032] When the disconnect mechanism 13 is disconnected, the electric vehicle 100 runs on only the rear wheels 21, but when the disconnect mechanism 13 is connected, the front wheels 11 are also driven. In other words, the torque transmitted by the front motor 15 is added to the torque transmitted by the rear motor 24, and the electric vehicle 100 runs. Therefore, as described above, if there is a sudden increase in the torque transmitted by the front motor 15, a point (see D1) will occur in the process of increasing the vehicle driving force, and the occupants may feel an impact.

[0033] To suppress such shocks, one option is to reduce the rate of increase in the transmitted torque of the rear motor 24 and the front motor 15, as shown by the dotted line in Figure 6. However, doing so would introduce the problem of the disconnect mechanism 13 taking time to switch over.

[0034] Therefore, in this embodiment, the control shown in Figure 7 is performed. First, as shown by the solid line in Figure 6, the rate of increase of the transmission torque of the rear motor 24 and the front motor 15 is increased. Here, as an example, the rate of increase of the transmission torque of both motors 15 and 24 is made the same. When the one-way clutch is engaged at time t2, the transmission torque of the front motor 15 increases rapidly (see D1), but in synchronization with this, the transmission torque of the rear motor 24 is rapidly reduced to Tr1a (see D2), and the reduced transmission torque is maintained until time t3. As a result, the rapid increase in the transmission torque of the front motor 15 is absorbed by the rapid decrease in the transmission torque of the rear motor 24, so that there is no rapid increase in vehicle driving force at time t2.

[0035] Subsequently, the transmission torque of the front motor 15 reaches the target transmission torque Tr2 at time t3, but the transmission torque of the rear motor 24 remains at the reduced Tr1a. Therefore, at time t3, the transmission torque of the rear motor 24 is increased at the aforementioned rate of increase, and controlled to reach the original target transmission torque Tr1 at time t4 (see D3). Through this control, vehicle driving force is generated with the transmission torques of both the rear motor 24 and the front motor 15 reaching their targets.

[0036] <3-2. Specific Flowchart of Control Method> The control of each motor as described above will be explained with reference to the flowcharts shown in Figures 8 and 9.

[0037] First, as the accelerator opening increases, the target driving force and vehicle speed increase, as shown in Figure 4. Then, when the vehicle speed and target driving force transition from the disconnected region to the connected region in the map of Figure 5 (YES in step S11), the powertrain controller 5 sends a command to the disconnect controller 4 to switch the disconnect mechanism 13 to the connected state.

[0038] Furthermore, the powertrain controller 5 calculates the output torque (rotational synchronization torque) required to synchronize the rotational speed of the front motor 15 with the rotational speed of the rear motor, corresponding to the current vehicle speed (step S12). At this time, the State of Control (SOC) is taken into consideration. For example, a higher SOC allows for a higher rotational synchronization torque. If the torque used to drive the rear motor 24 is large, the rotational synchronization torque of the front motor 15 will relatively decrease.

[0039] The powertrain controller 5 calculates the transmission torque of the front motor when the one-way clutch is engaged (step S13). That is, it calculates the rapidly changing transmission torque Tr2a at D1 in Figure 6. This transmission torque Tr2a can be calculated, for example, using the following formula: Transmission torque Tr2a of the front motor 15 when the one-way clutch is engaged = (Inertia of front motor 15 + Inertia of front reduction gear 14) × Rotational angular acceleration

[0040] This transmitted torque Tr2a increases as the rate of increase of the rotational synchronous torque of the front motor 15 increases.

[0041] Next, the time (tm) until the one-way clutch engages is calculated (step S14). This time can be calculated, for example, using the following formula: • Time (tm) until the one-way clutch engages = (Desired front motor rotational speed - Initial front motor rotational speed) / Angular acceleration • Angular acceleration = Output torque of the front motor / Upstream inertia of the one-way clutch (Synertia of the front motor 15 and inertia of the front reduction gear 14)

[0042] Subsequently, the increase rate (gradient) of the transmission torque of the rear motor 24 is calculated from the time (tm) until the one-way clutch is engaged and the required transmission torque (Tr1) of the rear motor 24 (step S15). ・Increase rate of rear motor transmission torque (ΔT) = required transmission torque of rear motor (Tr1) / time (tm) until one-way clutch is engaged

[0043] Next, control of the front motor 15 will be described with reference to FIG. 9. The sections in which the processes of steps S22, S24, S26, and S27 shown below are performed are also illustrated in FIG. 7. First, it is determined whether the disconnect mechanism is in a connected state or a disconnected state (step S16). When the disconnect controller 4 is determined to be in the disconnected state (NO in step S21), the transmission torques of the rear motor 24 and the front motor 15 are set according to the following formula (step S22). This is a process performed between time t1 and t2 in FIG. 7. ・Transmission torque of rear motor 24 = increase rate (ΔT) × elapsed time since accelerator was turned ON ・Although the transmission torque of front motor 15 is 0, the rotation speed of front motor 15 is increased until it corresponds to the vehicle speed.

[0044] On the other hand, when the disconnect controller 4 is determined to be in the connected state (YES in step S21), if the transmission torque of the front motor 15 has not reached the required torque (NO in step S23), the transmission torques of the rear motor 24 and the front motor 15 are set according to the following formula (step S24). This is a process performed between time t2 and t3 in FIG. 7. ・Transmission torque of rear motor 24 (Tr1a) = (required rear motor transmission torque Tr1) − (front motor transmission torque Tr2a at the time of one-way clutch engagement) ・Transmission torque of front motor 15 = increase rate (ΔT) × elapsed time since one-way clutch engagement

[0045] As described above, the transmission torque Tr2a increases as the rate of increase in the rotational synchronous torque of the front motor 15 increases. Accordingly, the transmission torque of the rear motor 24 is adjusted. Further, if the acceleration of the electric vehicle driven by the rear motor 24 until the one-way clutch is engaged is large, the aforementioned impact tends to be less perceivable. Therefore, when the acceleration of the electric vehicle is large, the transmission torque Tr1a of the rear motor 24 can be increased (the reduction amount of the transmission torque can be decreased).

[0046] Further, when the transmission torque of the front motor 15 has reached the required torque (YES in step S23), but the transmission torque of the rear motor 24 has not reached the required torque (YES in step S25), the transmission torques of the rear motor 24 and the front motor 15 are set to comply with the following formulas (step S26). This is the processing performed between time t3 and time t4 in FIG. 7. ・Transmission torque of rear motor 24 = Transmission torque Tr1a + Increase rate (ΔT) × Elapsed time after time t3 in FIG. 7・Transmission torque of front motor 15 = Required torque Tr2

[0047] On the other hand, when the transmission torque of the rear motor 24 has reached the required torque (YES in step S25), the transmission torques of the rear motor 24 and the front motor 15 are set to comply with the following formulas (step S27). This is the processing performed after time t4 in FIG. 7. ・Transmission torque of rear motor 24 = Required transmission torque Tr1 ・Transmission torque of front motor 15 = Required torque Tr2

[0048] As described above, control is performed such that the front motor 15 and the rear motor 24 exhibit the behavior shown in FIG. 7.

[0049] <4. Features> As described above, the following control is performed according to this embodiment. (1) Control 1 The control shown in Figure 7 is performed. If the rotational synchronization time (tm) of the front motor 15 is shortened, the transmission torque of the front motor 15 increases rapidly when the one-way clutch is engaged at time t2 (see D1). If the transmission torque of the rear motor 24 is rapidly reduced to Tr1a in synchronization with this (see D2), the rapid increase in the transmission torque of the front motor 15 is absorbed, and a rapid increase in the vehicle driving force at time t2 can be suppressed. In other words, with this control, even if the time until the one-way clutch is engaged is shortened, the impact at the time of engagement can be suppressed.

[0050] (2) Control 2 At time t3, the transmission torque of the front motor 15 reaches the target transmission torque Tr2, but the transmission torque of the rear motor 24 remains at the reduced Tr1a. Therefore, at time t3, the transmission torque of the rear motor 24 is increased by the above-mentioned rate of increase (ΔT), and controlled to reach the original target transmission torque Tr1 at time t4 (see D3). As a result, vehicle driving force is generated with the transmission torques of both the rear motor 24 and the front motor 15 reaching their targets.

[0051] <5. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. For example, the following modifications are possible. Furthermore, the gist of the following modifications can be combined with each other as appropriate, and can also be combined with the above embodiment.

[0052] (1) In the above embodiment, as shown in Figure 7, the timing at which the transmission torque of the rear motor 24 reaches the target torque Tr1 (time t2) coincides with the timing at which the transmission torque of the front motor 15 begins to increase, but this timing may be shifted. For example, as shown in Figure 10, after the transmission torque of the rear motor 24 reaches the target torque Tr1 at time t2, the transmission torque of the front motor 15 may begin to increase at time t3, a predetermined time later. Also, the rate of increase of the transmission torque of the rear motor and the front motor do not have to be the same and may be different. In the example of Figure 10, the rate of increase (slope) of the transmission torque of the rear motor 24 from time t1 to t2 and the rate of increase (slope) of the transmission torque of the front motor 15 from time t3 to t4 are different.

[0053] (2) The disconnect mechanism 13 may be provided in the rear drive system 2. Also, the SOC does not necessarily have to be taken into consideration when calculating the rotational synchronization time of the front motor 15, and may be taken into consideration as needed. This is the same even if the disconnect mechanism 13 is provided in the rear drive system 2.

[0054] (3) The hardware and software configurations of the electric vehicle 100 shown in Figures 1 to 5 are examples, and these configurations can be changed as appropriate, as long as they are configured to at least enable the control 1 described above.

[0055] 3: Battery 11: Front wheel 13: Disconnect mechanism 15: Front motor 21: Rear wheel 24: Rear motor 100: Electric vehicle Tr1: Target torque Tr2: Target torque ΔT: Increase rate

Claims

1. A method for controlling the driving of an electric vehicle comprising: front wheels, rear wheels, a front motor for driving the front wheels, a rear motor for driving the front wheels, a battery for supplying power to the front motor and the rear motor, and a disconnect mechanism having a one-way clutch for connecting or disconnecting the front wheels and the front motor or the rear wheels and the rear motor, wherein one of the front motor or the rear motor is designated as a first motor, and the other of the front motor or the rear motor is designated as a second motor, and when the first motor is in the connected state and the second motor is in the disconnected state, the method for controlling the driving of an electric vehicle is characterized by adjusting the output torque of the first motor so as to absorb the increase in the transmission torque of the second motor caused by the engagement of the one-way clutch by a decrease in the transmission torque of the first motor when switching the second motor to the connected state.

2. The driving control method according to claim 1, wherein, after the transmission torque of the second motor reaches the required torque, the transmission torque of the first motor is increased by the amount by which it was reduced.

3. The driving control method according to claim 1, wherein the amount of reduction in the transmitted torque of the first motor is adjusted according to the rate of increase in the rotational speed of the second motor before the engagement of the one-way clutch.

4. The driving control method according to claim 1, wherein the amount of reduction in the transmission torque of the first motor is adjusted according to the acceleration of the electric vehicle up to the engagement of the one-way clutch.

5. The driving control method according to claim 1, wherein the rate of increase of the output torque of the first motor is adjusted so that the torque transmitted from the first motor to the front wheel or the rear wheel reaches a required torque at the timing when the torque transmitted from the second motor to the front wheel or the rear wheel begins to increase.

6. The driving control method according to claim 1, wherein the rate of increase of the transmission torque of the first motor is matched with the rate of increase of the transmission torque of the second motor.

7. A driving control device for an electric vehicle, comprising a battery, a first motor for driving either the front wheel or the rear wheel, a second motor for driving the other of the front wheel or the rear wheel, and a disconnect mechanism having a one-way clutch for connecting or disconnecting the front wheel and the first motor or the rear wheel and the second motor, wherein when the first motor is in the connected state and the second motor is in the disconnected state, the driving control device adjusts the output torque of the first motor so as to absorb the increase in the transmission torque of the second motor caused by the engagement of the one-way clutch by the decrease in the transmission torque of the first motor when switching the second motor to the connected state.

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