JP7552228B2 - Hybrid Vehicles - Google Patents

Description

This invention relates to hybrid vehicles.

Hybrid vehicles equipped with a so-called mild hybrid system that uses both the driving forces of an engine and a motor may employ a configuration in which one of the front and rear drive shafts (wheels) is driven by the engine and the other drive shaft (wheels) is driven by a motor (referred to here as a rear motor), each via a differential, as shown in Patent Document 1 and Patent Document 2 below. In this configuration, as shown in Patent Document 1, a motor (referred to here as a front motor) is often provided alongside the engine (see Figure 1 of Patent Document 1 and Figure 2 of Patent Document 2).

The front motor is primarily responsible for starting the engine and generating electricity, while the rear motor is responsible for power regeneration, driving assistance, and motor driving, but depending on the state of the vehicle (for example, when the vehicle speed exceeds the rear motor's maximum allowable RPMs or when the rear motor's temperature is high), the front motor may also regenerate power or assist driving. However, the front motor is prone to co-rotation losses from the engine and continuously variable transmission. For this reason, it is preferable to regenerate power as much as possible using the rear motor, which has a higher regenerative efficiency than the front motor.

JP 2008-126869 A JP 2006-50767 A

The rear motor has a relatively high regenerative efficiency compared to the front motor, but when the rear motor is not being used for drive, it rotates together with the drive shaft, placing a load on the drive shaft. The load on the drive shaft can be eliminated by passing a correction current of the opposite phase to the rear motor, which corresponds to the load, but the power consumption associated with passing the current becomes an issue. This power consumption increases in proportion to the increase in motor rotation speed (vehicle speed), so this problem is particularly noticeable at high vehicle speeds.

The clutch between the rear motor and the drive shaft can be disconnected to prevent the rear motor from rotating, but in this disconnected state, the rear motor cannot regenerate power, and power must be regenerated by the front motor, which has a relatively low regenerative efficiency.

Therefore, the objective of this invention is to reduce the motor's drag loss and regenerate power efficiently.

In order to solve the above problems, the present invention provides:
a first motor that drives a first drive shaft connected to one of the front and rear wheels and recovers regenerative power from a rotational force of the first drive shaft;
a first clutch that is switchable between a connected state in which a rotational force between the first drive shaft and the first motor can be transmitted and a disconnected state in which the rotational force cannot be transmitted;
a second motor provided on a second drive shaft connected to the other of the front and rear wheels and driven by the engine, for recovering regenerative electric power from the rotational force of the second drive shaft;
a second clutch that is switchable between a connected state in which a rotational force between the second drive shaft and the second motor can be transmitted and a disconnected state in which the rotational force cannot be transmitted;
a control unit that controls a switching operation between an engaged state and a disengaged state of the first clutch and the second clutch, and a synchronization operation that synchronizes the rotational speed of the first drive shaft side of the first clutch with the rotational speed of the first motor side;
Equipped with
The hybrid vehicle is configured to control the first clutch and the second clutch so that, when the control unit detects deceleration while traveling with the first clutch disengaged, it starts the synchronizing operation and connects the second clutch to perform regeneration with the second motor, and after completion of the synchronizing operation, it disconnects the second clutch, connects the first clutch, and performs regeneration with the first motor.

In the above configuration,
the second clutch is disposed between the engine and the second drive shaft,
The control unit can be configured to, when starting, connect the first clutch while disconnecting the second clutch, and drive the first drive shaft with the driving force of the first motor, and when the vehicle speed reaches a predetermined vehicle speed, switch the first clutch to the disconnected state and the second clutch to the connected state, and control the driving of the second drive shaft with the driving force of the engine.

In a configuration in which the first clutch is connected at the time of starting,
The control unit can be configured to control the first clutch and the second clutch so that, when the charge amount of the battery is less than a predetermined reference charge amount, the first clutch is disengaged and the second clutch is engaged at a vehicle speed lower than the specified vehicle speed, and the second drive shaft is driven by the driving force of the engine.

In each of the above configurations,
The control unit can be configured to control the first clutch and the second clutch so that, when it detects deceleration during driving with the first clutch disengaged, if the deceleration is smaller than a predetermined reference deceleration, it maintains the first clutch disengaged while switching the second clutch to a connected state and performs regeneration with the second motor, and when the deceleration is equal to or greater than the reference deceleration, it switches the first clutch to a connected state and the second clutch to a disconnected state and performs regeneration with the first motor.

In the configuration in which the reference deceleration is determined in advance,
The control unit may have a map indicating a relationship between vehicle speed and the reference deceleration, and in the map, the reference deceleration may be smaller as the vehicle speed increases.

In each of the above configurations,
The control unit may be configured to control the first clutch so as to disengage the first clutch when the vehicle speed reaches an upper limit rotation speed allowed for the first motor.

In this invention, by controlling the switching between the connected and disconnected states of the first clutch using a control unit, it is possible to suppress co-rotation of the drive shaft and the first motor while the vehicle is traveling, and to efficiently regenerate power using the first motor.

1 is a schematic diagram showing an example of a hybrid vehicle according to the present invention; FIG. 2 is a diagram illustrating a first example of control of the hybrid vehicle shown in FIG. 1 . FIG. 4 is a diagram illustrating a second example of control of the hybrid vehicle shown in FIG. FIG. 13 is a diagram illustrating a third example of control of the hybrid vehicle shown in FIG. FIG. 13 is a diagram illustrating a fourth example of control of the hybrid vehicle shown in FIG.

An example of a hybrid vehicle 1 according to the present invention is shown in FIG. 1. This hybrid vehicle 1 is a four-wheel drive mild hybrid vehicle in which the front wheels 2a are driven by the driving force of an engine 3, and the rear wheels 2b are driven by the driving force of a rear motor 4 (first motor). This hybrid vehicle is equipped with a rear motor 4, a rear clutch 5 (first clutch), a front motor 6 (second motor), a front clutch 7 (second clutch), and a control unit 8.

The rear motor 4 is provided on the rear wheel 2b side. This rear motor 4 drives the rear drive shaft 10 (first drive shaft) connected to the rear wheel 2b by power supply from the battery 9, while also recovering regenerative power from the rotational force of the rear drive shaft 10 to charge the battery 9. This rear motor 4 also has a driving assist function that assists the driving force when driving with the driving force of the engine 3, and a motor driving function that drives only with the driving force of the rear motor 4 when there is no driving force from the engine 3.

The rear clutch 5 is provided between the rear differential 11 attached to the rear drive shaft 10 and the rear motor 4. The rear clutch 5 can be switched between a connected state in which rotational force can be transmitted between the rear drive shaft 10 and the rear motor 4, and a disconnected state in which such transmission is not possible.

The front motor 6 is provided on the side of the front drive shaft 12 (second drive shaft) that is connected to the front wheels 2a and driven by the engine 3. This front motor 6 starts the engine 3 by power supply from the battery 9 and generates electricity by rotating the engine 3, and also has the function of regenerating power and assisting driving in place of the rear motor 4 when the rear motor 4 cannot regenerate power or assist driving, such as when the vehicle speed exceeds the allowable upper limit rotation speed of the rear motor 4 or when the temperature of the rear motor 4 is high.

The front clutch 7 is provided between a front differential 13 attached to the front drive shaft 12 and a continuously variable transmission 15 connected to the engine 3 via a torque converter 14. This front clutch 7 can be switched between a connected state in which rotational force can be transmitted between the front drive shaft 12 and the front motor 6, and a disconnected state in which such transmission is not possible.

The control unit 8 controls the switching operation between the connected and disconnected states of the rear clutch 5 and the front clutch 7, and the synchronization operation that synchronizes the rotation speed of the rear drive shaft 10 side of the rear clutch 5 and the rear motor 4 side to suppress connection shock when switching to the connected state. The basic control of this control unit 8 is to start the synchronization operation when deceleration is detected while driving with the rear clutch 5 in the disconnected state, and to connect the front clutch 7 and regenerate power with the front motor 6. Then, after the synchronization operation is completed, the rear clutch 5 and the front clutch 7 are respectively controlled so that the front clutch 7 is disconnected and the rear clutch 5 is connected to regenerate power with the rear motor 4.

In this hybrid vehicle 1, power can be regenerated by either the rear motor 4 or the front motor 6, but it is preferable to prioritize regeneration by the rear motor 4. This is because the rear motor 4 is connected to the rear drive shaft 10 via the rear differential 11, so there is little loss in rotational force transmission, whereas the front motor 6 has an engine 3, torque converter 14, and continuously variable transmission 15 between it and the front differential 13, so there is a certain amount of transmission loss due to the drag losses of these.

The hybrid vehicle 1 is further provided with a vehicle speed sensor 16 that detects the vehicle speed, a brake sensor 17 that detects the force applied to the brake pedal, and an accelerator sensor 18 that detects the force applied to the accelerator pedal. The vehicle speed sensor 16, the brake sensor 17, and the accelerator sensor 18 are each connected to the control unit 8.

A first example of the control of the hybrid vehicle 1 shown in FIG. 1 is shown in FIG. 2. This first example corresponds to the basic control of the hybrid vehicle 1 according to the present invention. In this figure (as well as in FIGS. 3 to 5 described below), the horizontal axis indicates time, and the vertical axis indicates the vehicle speed (revolutions per minute of the rear motor 4) or the state of the rear clutch 5. The solid line in this figure indicates when the vehicle speed is equal to or lower than the vehicle speed corresponding to the allowable upper limit rotation speed of the rear motor 4, and the dashed line indicates when the vehicle speed exceeds the allowable upper limit rotation speed of the rear motor 4.

In this series of controls, the control unit 8 monitors signals from the vehicle speed sensor 16, the brake sensor 17, and the accelerator sensor 18. When the vehicle speed sensor 16 detects a stopped state (the range of circled number 1 in FIG. 2), the control unit 8 disengages the rear clutch 5. This disengagement state is maintained during acceleration and constant speed driving (the range of circled number 2 in FIG. 2).

When deceleration is detected by the brake sensor 17, the vehicle speed detected by the vehicle speed sensor 16 is compared with the upper limit rotational speed of the rear motor 4. If the vehicle speed is below the upper limit rotational speed, the control unit 8 starts a synchronization operation to synchronize the rotational speed of the rear drive shaft 10 side of the rear clutch 5 with the rear motor 4 side (range of circled number 3 in Figure 2). During this synchronization operation, the front clutch 7 is kept connected and the front motor 6 regenerates electricity.

When the synchronization operation of the rear clutch 5 is completed (A1 in FIG. 2), the control unit 8 switches the rear clutch 5 to the connected state and the front clutch 7 to the disconnected state, and power is regenerated by the rear motor 4 (range of circled number 4 in FIG. 2). Then, when the vehicle speed sensor 16 detects a stopped state, the control unit 8 switches the rear clutch 5 to the disconnected state (range of circled number 5 in FIG. 2). In this way, by controlling the switching between the rear clutch 5 and the front clutch 7, it is possible to reduce the co-rotation loss of the rear drive shaft 10 and the rear motor 4 while the hybrid vehicle 1 is traveling.

On the other hand, when the vehicle speed exceeds the upper limit of the allowable rotation speed of the rear motor 4, the start of the synchronization operation is put on hold (the range of circled numbers 3'-1 in Figure 2). Then, when the vehicle speed falls below this upper limit of the allowable rotation speed (P in Figure 2), the synchronization operation is started (the range of circled numbers 3'-2 in Figure 2). During this synchronization operation (including the time when it is put on hold), the front clutch 7 remains connected, and power is regenerated by the front motor 6.

When the synchronizing operation of the rear clutch 5 is completed (A2 in FIG. 2), the control unit 8 switches the rear clutch 5 to an engaged state and the front clutch 7 to a disengaged state, and power is regenerated by the rear motor 4 (area indicated by circled number 4' in FIG. 2). The control after the vehicle comes to a halt is the same as the control when the vehicle speed is below the allowable upper limit rotation speed. In this way, by controlling to suspend the synchronizing operation when the vehicle speed exceeds the allowable upper limit rotation speed of the rear motor 4, over-rotation of the rear motor 4 can be prevented.

A second example of the control of the hybrid vehicle 1 shown in FIG. 1 is shown in FIG. 3. This second example corresponds to the control when the hybrid vehicle 1 is driven only by the driving force of the rear motor 4 when starting. In this series of controls, the control unit 8 monitors the charging state of the battery 9 along with signals from the vehicle speed sensor 16, the brake sensor 17, and the accelerator sensor 18. Then, first, it is determined whether the charging state is sufficient to start the vehicle using only the rear motor 4 (hereinafter referred to as the assist-enabled charging state). The assist-enabled charging state is evaluated based on whether the remaining charge of the battery 9 exceeds a predetermined reference charge amount, whether the temperature of the battery 9 is equal to or lower than a predetermined reference temperature, etc.

When the charge state of the battery 9 satisfies the assist-enabling charge state, the rear clutch 5 is switched from a disconnected state to a connected state by the control unit 8 (range of circled number 1 in FIG. 3) and the front clutch 7 is disconnected when the vehicle speed sensor 16 detects a stopped state. Then, by depressing the accelerator pedal, the rear drive shaft 10 is driven only by the driving force of the rear motor 4 (range of circled number 2 in FIG. 3). In this way, fuel efficiency can be improved by running the motor from a standstill in a low vehicle speed range where engine efficiency is low.

When the charge state of the battery 9 does not satisfy the assist-enabling charge state, it is difficult to obtain the driving force for starting using only the rear motor 4, so as explained in the first example above, the rear clutch 5 is disengaged and the front clutch 7 is engaged, and driving force is obtained from the engine 3.

When the vehicle reaches a predetermined upper battery speed limit during acceleration using the rear motor 4 (P in FIG. 3), the control unit 8 switches the rear clutch 5 to a disconnected state and the front clutch 7 to a connected state, transitioning from driving using the rear motor 4 to driving using the engine 3, and the rear clutch 5 is maintained in a disconnected state during this driving (range of circled number 3 in FIG. 3). In addition, when the charge state of the battery 9 no longer satisfies the assistable charge state, the vehicle will transition from driving using the rear motor 4 to driving using the engine 3 even before the vehicle speed reaches the upper battery speed limit.

When deceleration is detected by the brake sensor 17, the vehicle speed detected by the vehicle speed sensor 16 is compared with the maximum allowable rotation speed of the rear motor 4. If the vehicle speed is below the maximum allowable rotation speed, the control unit 8 starts a synchronization operation to synchronize the rotation speed of the rear drive shaft 10 side of the rear clutch 5 with the rear motor 4 side (range of circled number 4 in Figure 3). During this synchronization operation, the front clutch 7 is kept connected and the front motor 6 regenerates electricity.

When the rear clutch 5 synchronization operation is completed (A in FIG. 3), the control unit 8 switches the rear clutch 5 to the connected state and the front clutch 7 to the disconnected state, and power is regenerated by the rear motor 4 (range of circled number 5 in FIG. 2). Then, when the vehicle speed sensor 16 detects a stopped state, it is determined whether the charge state of the battery 9 is in an assistable charge state. If it is determined that assistance is possible, the rear clutch 5 is maintained in the connected state in preparation for starting off using the rear motor 4 (range of circled number 6 in FIG. 3). On the other hand, if it is determined that assistance is not possible, the control unit 8 switches the rear clutch 5 to the disconnected state and the front clutch 7 to the connected state in preparation for starting off using the engine 3.

Figure 4 shows a third example of the control of the hybrid vehicle 1 shown in Figure 1. This third example corresponds to the control when the hybrid vehicle 1 is repeatedly accelerated and decelerated while traveling. In this series of controls, the control unit 8 monitors the charging state of the battery 9, along with signals from the vehicle speed sensor 16, the brake sensor 17, and the accelerator sensor 18.

When deceleration is detected by the brake sensor 17 while driving (range of circled number 1 in FIG. 4), the vehicle speed detected by the vehicle speed sensor 16 is compared with the allowable upper limit rotation speed of the rear motor 4. If the vehicle speed is below the allowable upper limit rotation speed, the control unit 8 starts a synchronization operation to synchronize the rotation speed of the rear drive shaft 10 side of the rear clutch 5 with the rear motor 4 side (range of circled number 2 in FIG. 4). During this synchronization operation, the front clutch 7 is maintained in an engaged state, and power is regenerated by the front motor 6.

When the rear clutch 5 synchronization operation is completed (A1 in FIG. 4), the control unit 8 switches the rear clutch 5 to the connected state and the front clutch 7 to the disconnected state, and power is regenerated by the rear motor 4 (the range of the circled number 3 in FIG. 4). If the accelerator sensor 18 detects re-acceleration during this deceleration (A2 in FIG. 4), it determines three points: (a) whether assistance by the rear motor 4 is requested (determined from the amount of depression of the accelerator pedal, etc.), (b) whether the vehicle speed is below the allowable upper limit rotation speed of the rear motor 4 (or below the upper limit vehicle speed for driving using only the rear motor 4), and (c) whether the battery 9 is in an assistable charged state.

When all of the above (a) to (c) are met, the rear clutch 5 remains connected and acceleration assistance by the rear motor 4 (or driving by the rear motor 4 alone) is performed (range of circled number 4 in Figure 4). If any of the above conditions (a) to (c) are no longer met during this acceleration, the rear clutch 5 is switched to a disconnected state (A3 in Figure 4) and acceleration is transitioned to using the driving force of the engine 3 (range of circled number 5 in Figure 4). Furthermore, if deceleration is detected by the brake sensor 17 during acceleration by the rear motor 4, the rear clutch 5 remains connected and power regeneration is performed by the rear motor 4 (range of circled number 5' in Figure 4).

By controlling the rear clutch 5 in this way, it is possible to smoothly perform acceleration assistance by the rear motor 4 when re-accelerating (or running using only the driving force of the rear motor 4), and power regeneration by the rear motor 4 when decelerating again.

A fourth example of the control of the hybrid vehicle 1 shown in FIG. 1 is shown in FIG. 5. This fourth example corresponds to the control when the deceleration fluctuates during deceleration in this hybrid vehicle 1. In this series of controls, the control unit 8 monitors signals from the vehicle speed sensor 16 and the brake sensor 17.

When the brake sensor 17 detects depression of the brake pedal while driving (the range of circled number 1 in FIG. 5), the vehicle speed detected by the vehicle speed sensor 16 is compared with the maximum allowable rotation speed of the rear motor 4. When the vehicle speed is equal to or lower than the maximum allowable rotation speed, the amount of depression of the brake pedal detected by the brake sensor 17 is compared with a predetermined depression threshold. When the amount of depression is less than the depression threshold (deceleration less than a predetermined reference deceleration), the rear clutch 5 is maintained in a disengaged state and power is regenerated by the front motor 6 (the range of circled number 2 in FIG. 5).

When the depression of the brake pedal is small and the deceleration is small, the amount of power consumed for the synchronous operation of the rear clutch 5 may be greater than the amount of power regenerated by the rear motor 4. Therefore, by maintaining the rear clutch 5 in a disengaged state when the depression of the brake pedal is smaller than the depression threshold, it is possible to suppress the power consumption associated with the synchronous operation.

If the brake pedal is pressed harder during gentle deceleration, causing a sudden deceleration that exceeds the depression threshold (A1 in FIG. 5), the control unit 8 starts a synchronization operation to synchronize the rotation speed of the rear drive shaft 10 side of the rear clutch 5 with the rear motor 4 side (range of circled number 3 in FIG. 5). During this synchronization operation, the front clutch 7 remains connected, and power regeneration by the front motor 6 continues.

When the rear clutch 5 synchronization operation is completed (A2 in FIG. 5), the control unit 8 switches the rear clutch 5 to the connected state and the front clutch 7 to the disconnected state, and the rear motor 4 regenerates power (range of circled number 4 in FIG. 5). Even if the amount of brake pedal depression decreases during this sudden deceleration and the deceleration becomes slower with the depression amount falling below the depression threshold (A3 in FIG. 5), the rear clutch 5 remains connected and the rear motor 4 continues to regenerate power (range of circled number 5 in FIG. 5). Then, when the vehicle speed sensor 16 detects a stopped state, the control unit 8 switches the rear clutch 5 to the disconnected state.

The depression threshold (or reference deceleration) may be a constant value, but can also be set to a smaller value as the vehicle speed increases. In this way, regeneration by the rear motor 4 can be started quickly with a small brake depression amount in the high vehicle speed range where regeneration efficiency is high, which may further improve regeneration efficiency. The correspondence relationship between this depression threshold and vehicle speed can be stored in advance in the control unit 8 as a map.

In the above, the magnitude of deceleration is determined based on the amount of depression of the brake pedal, but it may also be possible to determine the magnitude of deceleration based on the accelerator pedal being released, or based on the detection value from a separately provided acceleration sensor.

The configuration of the hybrid vehicle 1 described in FIG. 1 and the control patterns described in FIG. 2 to FIG. 5 are merely examples for explaining the present invention, and the vehicle configuration, control patterns, etc. can be modified as appropriate as long as the problem of the present invention, which is to reduce the co-rotation loss of the motor and efficiently regenerate power, can be solved.

Reference Signs List 1 Hybrid vehicle 2a Front wheel 2b Rear wheel 3 Engine 4 Rear motor 5 Rear clutch 6 Front motor 7 Front clutch 8 Control unit 9 Battery 10 Rear drive shaft 11 Rear differential 12 Front drive shaft 13 Front differential 14 Torque converter 15 Continuously variable transmission 16 Vehicle speed sensor 17 Brake sensor 18 Accelerator sensor

Claims (4)

a first motor that drives a first drive shaft connected to one of the front and rear wheels and recovers regenerative power from a rotational force of the first drive shaft;
a first clutch that is switchable between a connected state in which a rotational force between the first drive shaft and the first motor can be transmitted and a disconnected state in which the rotational force cannot be transmitted;
a second motor provided on a second drive shaft connected to the other of the front and rear wheels and driven by the engine, for recovering regenerative electric power from the rotational force of the second drive shaft;
a second clutch that is switchable between a connected state in which a rotational force between the second drive shaft and the second motor can be transmitted and a disconnected state in which the rotational force cannot be transmitted;
a control unit that controls a switching operation between an engaged state and a disengaged state of the first clutch and the second clutch, and a synchronization operation that synchronizes the rotational speed of the first drive shaft side of the first clutch with the rotational speed of the first motor side;
Equipped with
When the control unit detects deceleration during traveling with the first clutch in a disengaged state, the control unit controls the first clutch and the second clutch so as to start the synchronous operation, connect the second clutch, and perform regeneration with the second motor, and after completion of the synchronous operation, disconnect the second clutch, connect the first clutch, and perform regeneration with the first motor ,
the second clutch is disposed between the engine and the second drive shaft,
the control unit, when starting, puts the first clutch in an engaged state while putting the second clutch in a disengaged state, and drives the first drive shaft with the driving force of the first motor, and when the vehicle speed reaches a predetermined vehicle speed, switches the first clutch to a disengaged state and the second clutch to a connected state, and controls the second drive shaft to be driven with the driving force of the engine;
A hybrid vehicle in which, when the charge amount of the battery is less than a predetermined reference charge amount, the control unit controls the first clutch and the second clutch to disengage the first clutch and connect the second clutch at a vehicle speed lower than the specified vehicle speed, so as to drive the second drive shaft with the driving force of the engine . 2. The hybrid vehicle according to claim 1, wherein the control unit controls the first clutch and the second clutch so that, when deceleration is detected during traveling with the first clutch disengaged, if the deceleration upon detection of the deceleration is smaller than a predetermined reference deceleration, the control unit maintains the first clutch in a disengaged state while switching the second clutch to a connected state and performs regeneration using the second motor, and when the deceleration upon detection of the deceleration is equal to or greater than the reference deceleration, the control unit switches the first clutch to a connected state and the second clutch to a disengaged state and performs regeneration using the first motor. 3. The hybrid vehicle according to claim 2 , wherein the control unit has a map indicating a relationship between a vehicle speed and the reference deceleration, and in the map, the reference deceleration decreases as the vehicle speed increases. 4. The hybrid vehicle according to claim 1, wherein the control unit controls the first clutch to disengage the first clutch when the vehicle speed reaches an upper limit rotation speed allowable for the first motor.

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