JP7581928B2 - Four-wheel drive vehicle control device - Google Patents

Description

The technology disclosed herein relates to a control device for a four-wheel drive vehicle.

Patent Document 1 describes a four-wheel drive vehicle based on a front-engine, rear-wheel drive vehicle. When traveling forward at a constant speed in four-wheel drive mode, this four-wheel drive vehicle transmits engine torque only to the rear wheels, and not to the front wheels. Also, when decelerating due to engine braking, if the rotation speed of the rear wheels directly connected to the engine decreases and falls below the rotation speed of the front wheels, deceleration torque is transmitted to the front wheels to prevent the rear wheels from slipping.

Japanese Patent Application Publication No. 10-71872

In a hybrid vehicle equipped with an engine and a traction motor, the motor may perform regenerative braking when the engine brake is applied. In a hybrid vehicle in which the motor is disposed on the engine output shaft and the engine torque and motor torque are distributed to the front and rear wheels by a transfer and electromagnetic coupling mechanism, the fastening torque of the electromagnetic coupling mechanism is adjusted so that the engine torque and motor torque are distributed to the front and rear wheels in the same distribution ratio.

In a hybrid vehicle having the above configuration, when braking is performed using both engine braking and regenerative braking of the motor, even if the distribution ratio between the torque of the front wheels and the torque of the rear wheels is set so that the distribution ratio of the torque of the front wheels is greater than the distribution ratio during driving, as in the control during deceleration using engine braking described in Patent Document 1, the load moves further forward of the vehicle due to the regenerative braking of the motor being applied to the vehicle, and the vehicle behavior may become unstable.

The technology disclosed here further stabilizes vehicle behavior in four-wheel drive vehicles based on front-engine, rear-wheel drive vehicles.

The technology disclosed herein relates to a control device for a four-wheel drive vehicle based on a front-engine, rear-drive vehicle.
The engine,
a motor disposed on an output shaft of the engine and performing power running and regenerative braking;
a transfer connected to the engine and the motor and distributing torque of the engine and the motor to front wheels and rear wheels;
an adjustment mechanism that changes a distribution ratio of the torque of the front wheels and the torque of the rear wheels;
a control unit that adjusts the distribution ratio through the adjustment mechanism in accordance with a running state of the four-wheel drive vehicle,
the control unit sets the distribution ratio to a first distribution ratio in which the torque of the rear wheels is greater than the torque of the front wheels in a running state in which the engine is generating a drive torque,
the control unit sets the distribution ratio to a second distribution ratio in a braking state in which engine braking is occurring, such that a distribution ratio of the torque to the front wheels is greater than the first distribution ratio;
The control unit sets the distribution ratio to a third distribution ratio in which the distribution ratio of the torque to the front wheels is greater than the second distribution ratio in a braking state in which engine braking is occurring and regenerative braking of the motor is being performed.

With this configuration, when the engine is generating drive torque while the vehicle is running, the distribution mechanism distributes the torque between the front and rear wheels so that the torque at the rear wheels is greater than the torque at the front wheels. This makes the four-wheel drive vehicle run more stably.

In a braking state where engine braking is occurring, the distribution mechanism sets the torque distribution ratio of the front wheels to a second distribution ratio. The second distribution ratio is a larger distribution ratio of torque to the front wheels compared to the first distribution ratio in a driving state where the engine is generating drive torque. Because the engine brake torque is distributed to the front wheels, the behavior of the four-wheel drive vehicle during braking is stabilized.

In a braking state where both engine braking and regenerative braking of the motor are occurring, the distribution mechanism sets the distribution ratio of torque to the front wheels to a third distribution ratio. The third distribution ratio is a larger distribution ratio of torque to the front wheels compared to the second distribution ratio in a braking state where engine braking is occurring. Because the braking torque distributed to the front wheels is even larger, the behavior of the four-wheel drive vehicle is stable in a braking state where both engine braking and regenerative braking of the motor are occurring.

The control device for a four-wheel drive vehicle includes:
The vehicle further includes a hydraulic brake device that applies a braking force to the front wheels and the rear wheels.
The control unit performs cooperative regeneration by causing the hydraulic brake device to generate a braking force and the motor to perform regenerative braking in response to a braking request operation by a driver,
The control unit may set the distribution ratio to a fourth distribution ratio in which the distribution ratio of the torque to the front wheels is greater than the third distribution ratio during the coordinated regeneration.

During coordinated regeneration when both hydraulic braking and regenerative braking of the motor are occurring, the distribution mechanism sets the distribution ratio of the torque to the front wheels to a fourth distribution ratio. The fourth distribution ratio is a larger distribution ratio of the torque to the front wheels than the third distribution ratio during a braking state when engine braking and regenerative braking of the motor are occurring. Here, hydraulic brakes generally have a larger braking torque to the front wheels than to the rear wheels. By further increasing the braking torque distributed to the front wheels during coordinated regeneration, the distribution ratio of the torque to the front wheels and the torque to the rear wheels for regenerative braking corresponds to the distribution ratio of the torque to the front wheels and the torque to the rear wheels for the hydraulic brake. During coordinated regeneration, the behavior of the four-wheel drive vehicle becomes stable.

The control unit may set the distribution ratio so that the torque distribution ratio to the front wheels is greater when the ratio of the regenerative braking force of the motor to the braking force of the hydraulic brake device is high than when the ratio is low.

When the ratio of regenerative braking force of the motor is high, a large amount of regenerative power can be secured, improving the fuel economy of the hybrid vehicle. With the above configuration, when the ratio of regenerative braking force is high, the regenerative braking torque to the front wheels becomes large, so the behavior of the four-wheel drive vehicle during coordinated regeneration becomes stable.

The control unit may set the distribution ratio so that the torque distribution ratio to the front wheels increases as the regenerative braking force of the motor increases.

With this configuration, when the regenerative braking force is large and the braking force applied to the four-wheel drive vehicle is large, the regenerative braking torque to the front wheels becomes large, so the behavior of the four-wheel drive vehicle during braking becomes stable.

The control unit may set the distribution ratio so that the torque distribution ratio to the front wheels is greater when the vehicle speed during braking is high than when the vehicle speed is low.

When braking at high vehicle speeds, the braking torque to the front wheels becomes larger, stabilizing the behavior of four-wheel drive vehicles.

The control unit may set the distribution ratio so that when the steering angle of the vehicle during braking is large, the torque distribution ratio to the front wheels is greater than when the steering angle is small.

When braking while turning, the braking torque applied to the steered front wheels is large, stabilizing the behavior of a four-wheel drive vehicle.

The above-mentioned control device for a four-wheel drive vehicle can further stabilize the vehicle's behavior.

FIG. 1 shows an example of the configuration of a four-wheel drive vehicle. FIG. 2 shows an example of the configuration of a control device for a four-wheel drive vehicle. FIG. 3 is a flowchart relating to the vehicle control executed by the control device. FIG. 4 is a diagram illustrating the characteristics of each parameter. FIG. 5 is a time chart relating to vehicle control.

Below, an embodiment of a control device for a four-wheel drive vehicle will be described with reference to the drawings. The four-wheel drive vehicle and its control device described here are examples.

Figure 1 illustrates an example of the configuration of a four-wheel drive vehicle 1. The four-wheel drive vehicle 1 is based on a front-engine, rear-wheel drive vehicle. The four-wheel drive vehicle 1 is equipped with an engine 2, a motor system 3, a transmission 4, a transfer 54, a rear propeller shaft 51, and a front propeller shaft 55.

Engine 2 is a gasoline engine that is supplied with fuel containing at least gasoline, or a diesel engine that is supplied with diesel fuel. The engine is of the spark ignition or compression ignition type. There are no particular limitations on the type of engine 2. Engine 2 is installed in an engine room located at the front of the vehicle in a so-called vertical orientation.

The motor system 3 includes an electric motor 30, an inverter 31, and a battery 32. The electric motor 30 is disposed on the output shaft of the engine 2. As illustrated in FIG. 1, the electric motor 30 is disposed between the engine 2 and a transmission 4 described later. The electric motor 30 outputs a drive torque for driving the vehicle during power running, and also performs regeneration to apply a braking force to the vehicle. The battery 32 is connected to the electric motor 30 via the inverter 31. The battery 32 supplies driving power to the electric motor 30, and is charged during regeneration of the electric motor 30. The inverter 31 receives a control signal from the control unit 10 described later, and supplies power from the battery 32 to the electric motor 30 during power running, and sends the generated power of the electric motor 30 to the battery 32 during regeneration.

The transmission 4 is, for example, an automatic transmission including at least one planetary gear mechanism. However, the transmission 4 is not limited to an automatic transmission. The transmission 4 is coupled to the output shafts of the engine 2 and the electric motor 30. The transmission 4 changes the torque of the engine 2 and/or the electric motor 30 and outputs it.

The transfer 54 is connected to the output shaft of the transmission 4. The rear propeller shaft 51 and the front propeller shaft 55 are each connected to the transfer 54. The transfer 54 distributes the torque of the engine 2 and/or the electric motor 30 to the front wheels 61 and the rear wheels 62.

The rear propeller shaft 51 extends from the transfer 54 toward the rear of the vehicle. The rear propeller shaft 51 is connected to the rear drive shaft 53 via the rear differential gear 52. The rear drive shaft 53 is connected to the left and right rear wheels 62. The rear differential gear 52 adjusts the difference in rotation speed between the left and right rear wheels 62.

The front propeller shaft 55 extends from the transfer 54 toward the front of the vehicle. The front propeller shaft 55 is connected to a front drive shaft 57 via a front differential gear 56. The front drive shaft 57 is connected to the left and right front wheels 61. The front differential gear 56 adjusts the difference in rotation speed between the left and right front wheels 61.

The front propeller shaft 55 is connected to the transfer 54 via an electromagnetic coupling mechanism 58. The electromagnetic coupling mechanism 58 changes the distribution ratio between the torque of the front wheels 61 and the torque of the rear wheels 62 by adjusting the fastening torque. Assuming that the input torque of the transfer 54 is constant, the higher the fastening torque, the greater the torque distribution ratio of the front wheels 61. Also, assuming that the fastening torque is constant, the higher the input torque of the transfer 54, the greater the torque distribution ratio of the front wheels 61. The electromagnetic coupling mechanism 58 receives a control signal from the control unit 10 and changes the distribution ratio to a distribution ratio that corresponds to the driving state of the four-wheel drive vehicle 1.

Figure 2 illustrates an example of the configuration of a control device for a four-wheel drive vehicle 1. The control device includes a control unit 10, an accelerator opening sensor 71, a brake depression amount sensor 72, a steering angle sensor 73, and a vehicle speed sensor 74. The accelerator opening sensor 71, the brake depression amount sensor 72, the steering angle sensor 73, and the vehicle speed sensor 74 are each connected to the control unit 10.

The accelerator opening sensor 71 is attached to the accelerator pedal and outputs a signal corresponding to the accelerator opening corresponding to the amount of depression of the accelerator pedal by the driver to the control unit 10. The brake depression amount sensor 72 is attached to the brake pedal and outputs a signal corresponding to the amount of depression of the brake pedal by the driver to the control unit 10. The steering angle sensor 73 is attached to the steering shaft and outputs a signal corresponding to the amount of steering of the steering wheel by the driver to the control unit 10. The vehicle speed sensor 74 is mounted on the vehicle and outputs a signal corresponding to the vehicle speed to the control unit 10.

The control unit 10 is a controller based on a known microcomputer, and includes a central processing unit (CPU) that executes a program, a memory that is configured, for example, by a RAM (Random Access Memory) or a ROM (Read Only Memory) to store the program and data, and an I/F circuit that inputs and outputs electrical signals. The control unit 10 judges the running state of the four-wheel drive vehicle 1 based on signals from an accelerator opening sensor 71, a brake depression amount sensor 72, a steering angle sensor 73, and a vehicle speed sensor 74. The control unit 10 outputs control signals to the engine 2, the motor system 3, and the electromagnetic coupling mechanism 58. The engine 2 receives the control signal and operates to output a predetermined torque. The motor system 3 receives the control signal and performs power running or regenerative braking. The electromagnetic coupling mechanism 58 receives the control signal and changes the fastening torque. The torque of the engine 2, or the torque of the engine 2 and the electric motor 30, is transmitted to the front wheels 61 and the rear wheels 62, and the four-wheel drive vehicle 1 runs. The torque distribution ratio between the front wheels 61 and the rear wheels 62 is changed according to the driving state of the four-wheel drive vehicle 1 by changing the fastening torque of the electromagnetic coupling mechanism 58.

The control unit 10 is also connected to a hydraulic brake device 8. The hydraulic brake device 8 applies braking force to each of the left and right front wheels 61 and the left and right rear wheels 62 by supplying brake hydraulic pressure to each of the left and right front wheels 61 and the left and right rear wheels 62. When braking the four-wheel drive vehicle 1, the control unit 10 performs coordinated regeneration by applying both the braking force of the hydraulic brake device 8 and the regenerative braking force of the electric motor 30 to each of the left and right front wheels 61 and the left and right rear wheels 62. The control unit 10 adjusts the ratio between the braking force of the hydraulic brake device 8 and the regenerative braking force of the electric motor 30 according to the driving state of the four-wheel drive vehicle 1.

(Braking control of four-wheel drive vehicles)
As described above, the control unit 10 changes the distribution ratio between the torque of the front wheels 61 and the torque of the rear wheels 62 according to the driving state of the four-wheel drive vehicle 1 through control of the electromagnetic coupling mechanism 58. Specifically, in a normal driving state in which the driver depresses the accelerator pedal and the engine 2 generates a driving torque, the control unit 10 sets the distribution ratio so that the torque of the rear wheels 62 is greater than the torque of the front wheels 61 (i.e., the first distribution ratio). Note that even in a driving state in which both the engine 2 and the electric motor 30 generate driving torque, the distribution ratio is set to the first distribution ratio in which the torque of the rear wheels 62 is greater than the torque of the front wheels 61. Driving stability is ensured in the four-wheel drive vehicle 1 based on a front-engine, rear-drive vehicle.

When the driver stops depressing the accelerator pedal (i.e., the accelerator opening is zero), and engine braking is occurring, the control unit 10 sets the distribution ratio so that the torque of the front wheels 61 is greater than the first distribution ratio (i.e., the second distribution ratio). When the load moves forward due to the application of braking force to the four-wheel drive vehicle 1, the engine brake torque applied to the rear wheels 62 decreases and the engine brake torque applied to the front wheels 61 increases, thereby improving the stability of the four-wheel drive vehicle 1 with engine braking acting.

When the target deceleration is even higher and engine braking is occurring, the control unit 10 sets the distribution ratio so that the torque of the front wheels 61 is even greater than the second distribution ratio (i.e., the third distribution ratio) when regenerative braking of the electric motor 30 is performed. When the load moves further forward on the vehicle as a result of regenerative braking of the electric motor 30, the engine brake torque applied to the rear wheels 62 decreases and the engine brake torque applied to the front wheels 61 increases, thereby improving the stability of the four-wheel drive vehicle 1 during regenerative braking of the electric motor 30.

As described above, when braking the four-wheel drive vehicle 1, the control unit 10 performs cooperative regeneration by using both the braking force of the hydraulic brake of the hydraulic brake device 8 and the regenerative braking of the electric motor 30. When performing cooperative regeneration, the control unit 10 sets the distribution ratio so that the torque of the front wheels 61 is even greater than the third distribution ratio (i.e., the fourth distribution ratio).

The hydraulic brake device 8 sets the braking force applied to the front wheels 61 higher than the braking force applied to the rear wheels 62, taking into account the load shift of the four-wheel drive vehicle 1 when braking force is applied. During coordinated regeneration, the regenerative braking torque of the electric motor 30 is distributed to the front wheels 61 and the rear wheels 62 according to the distribution ratio of the torque of the front wheels 61 and the torque of the rear wheels 62, which is a ratio adjusted by the fastening torque of the electromagnetic coupling mechanism 58. By increasing the regenerative braking torque distributed to the front wheels 61, the distribution ratio of the regenerative braking torque to the front wheels 61 and the rear wheels 62 corresponds to the distribution ratio of the braking force of the hydraulic brake. As a result, the stability of the four-wheel drive vehicle 1 during coordinated regeneration is improved.

Next, the braking control by the control unit 10 will be described with reference to the flowchart in FIG. 3. This flow starts when the driver stops depressing the accelerator pedal. The control unit 10 determines that the accelerator pedal is no longer being depressed based on the signal from the accelerator opening sensor 71. In step S31 after the start, the control unit 10 reads the brake depression amount, steering angle, and vehicle speed. In the following step S32, the control unit 10 sets a target deceleration for the four-wheel drive vehicle 1. The target deceleration is set according to the brake depression amount, steering angle, and vehicle speed.

In step S33, the control unit 10 sets the amount of regenerative braking and/or hydraulic braking to achieve the target deceleration.

The amount of regenerative braking is set by multiplying the base value of the amount of regenerative braking by regenerative coefficient a and regenerative coefficient b.

Graph 401 in FIG. 4 illustrates the relationship between the target deceleration and the basic value of the regenerative braking amount. The basic value of the regenerative braking amount is zero until the target deceleration exceeds a predetermined value e. Until the target deceleration exceeds the predetermined value e, the target deceleration is achieved by engine braking. When the target deceleration exceeds the predetermined value e, the basic value of the regenerative braking amount is set to a larger value as the target deceleration increases. Furthermore, when the basic value of the regenerative braking amount reaches an upper limit value, the basic value of the regenerative braking amount remains at the upper limit value even if the target deceleration becomes large. The upper limit value is set according to the characteristics of the electric motor 30.

Graph 402 in FIG. 4 illustrates the relationship between vehicle speed and regeneration coefficient a. When the vehicle speed is low, the regeneration coefficient a is set to be greater than 1. Due to the characteristics of the electric motor 30, when the rotation speed is low, the regenerative braking torque of the electric motor 30 is large and the power generation efficiency is also high. When the vehicle speed is low and the rotation speed of the electric motor 30 is low, the regeneration coefficient a is set to be greater than 1 in order to increase the regenerative braking force of the electric motor 30. This is advantageous for improving the power consumption performance of the four-wheel drive vehicle 1. As the vehicle speed increases, the regeneration coefficient a gradually decreases with respect to the vehicle speed. When the vehicle speed of the four-wheel drive vehicle 1 reaches or exceeds a predetermined vehicle speed, the regeneration coefficient a becomes 1.

Graph 403 in FIG. 4 illustrates the relationship between the steering angle and the regeneration coefficient b. When the steering angle is small, the regeneration coefficient b is set to 1. When the steering angle is large, the regeneration coefficient b is set to a value smaller than 1. The larger the steering angle, the smaller the regeneration coefficient b is set to. When the steering angle is large, the regenerative braking force is reduced to ensure vehicle stability during cornering. The lower limit of the regeneration coefficient b is greater than 0. By not setting the regenerative braking amount to zero, the power consumption performance of the four-wheel drive vehicle 1 is improved.

In step S33, once the regenerative braking amount is set, the control unit 10 sets the hydraulic braking amount. The hydraulic braking amount is set by subtracting the braking force due to the engine brake and the regenerative braking amount from the target deceleration.

In step S34, the control unit 10 sets the basic distribution of the braking torque of the front wheels 61 based on the ratio of the regenerative braking amount/hydraulic braking amount. Graph 404 in FIG. 4 illustrates an example of the relationship between the ratio of the regenerative braking amount/hydraulic braking amount and the basic distribution of the braking torque of the front wheels 61. As the ratio of the regenerative braking amount to the hydraulic braking amount increases, the braking torque distributed to the front wheels 61 increases. In this way, the distribution characteristics of the regenerative braking force to the front wheels 61 and the rear wheels 62 correspond to the distribution characteristics of the hydraulic brake (i.e., the characteristic in which the braking force to the front wheels 61 is higher than the braking force to the rear wheels 62). In the cooperative regeneration in which the braking force of the hydraulic brake and the regenerative braking force of the motor 30 are applied, the stability of the four-wheel drive vehicle 1 is improved. An upper limit value max is set for the distribution ratio to the front wheels 61.

If the driver is not depressing the brake pedal and the hydraulic braking force is zero, the control unit 10 sets the basic distribution of the braking torque of the front wheels 61 to a predetermined value in step S34 without relying on the graph 404.

In step S35, the control unit 10 sets the torque distribution of the front wheels 61. The torque distribution of the front wheels 61 is set by multiplying the basic distribution of the braking torque of the front wheels 61 by the torque distribution coefficient c and the torque distribution coefficient d.

Graph 405 in Figure 4 illustrates the relationship between the vehicle speed of the four-wheel drive vehicle 1 and the torque distribution coefficient c. When the vehicle speed is high, the torque distribution coefficient c is larger than when the vehicle speed is low. As a result, when the vehicle speed is high, the distribution of the braking torque to the front wheels 61 is large. During braking at high vehicle speeds, the braking torque applied to the front wheels 61 is large, improving the stability of the four-wheel drive vehicle 1.

Graph 406 in Figure 4 illustrates the relationship between the steering angle of the four-wheel drive vehicle 1 and the torque distribution coefficient d. When the steering angle is large, the torque distribution coefficient d is larger than when the steering angle is small. As a result, when the steering angle is large, the distribution of the braking torque to the front wheels 61 is large. During braking in a turning state, the braking torque applied to the front wheels 61, which are the steered wheels, is large, and the stability of the four-wheel drive vehicle 1 is improved.

After setting the torque distribution for the front wheels 61 in step S35, the control unit 10 calculates the fastening torque of the electromagnetic coupling mechanism 58 in step S36 so as to realize the set torque distribution ratio for the front wheels 61. Assuming that the input torque of the transfer 54 is constant, the fastening torque of the electromagnetic coupling mechanism 58 and the torque distribution ratio for the front wheels 61 are proportional, and the greater the fastening torque, the greater the torque distribution ratio for the front wheels 61.

In step S37, the control unit 10 instructs the motor system 3 to perform regenerative braking, and if hydraulic braking is required, instructs the hydraulic brake device 8 to perform hydraulic braking. The control unit 10 instructs the electromagnetic coupling mechanism 58 to perform a fastening operation with the fastening torque set in step S36.

In the next step S38, the control unit 10 determines whether the target deceleration has become zero, and if the target deceleration is not zero, the process returns to step S31 to repeat the above-mentioned steps. If the target deceleration is zero, the process proceeds to step S39. To end braking of the four-wheel drive vehicle 1, the control unit 10 instructs the motor system 3 to end regenerative braking and instructs the hydraulic brake device 8 to end hydraulic braking. The control unit 10 also instructs the electromagnetic coupling mechanism 58 to change the fastening operation so as to change the distribution ratio between the torque of the front wheels 61 and the torque of the rear wheels 62.

Next, the front/rear braking force distribution in a four-wheel drive vehicle 1 will be described with reference to the time chart in FIG. 5. Graph 501 in FIG. 5 illustrates an example of changes in the amount of depression of the accelerator pedal. The driver stops depressing the accelerator pedal at time t1.

Before time t1, the four-wheel drive vehicle 1 is in a driving state in which the engine 2 generates drive torque (see graph 506). As illustrated in graphs 507 and 508, the torque distribution ratio of the front wheels 61 is relatively small (i.e., the first distribution ratio). The torque distributed to the rear wheels 62 is greater than the torque distributed to the front wheels 61. The four-wheel drive vehicle 1 is essentially driven by rear-wheel drive. The driving stability of the four-wheel drive vehicle 1 based on a front-engine, rear-drive vehicle is improved. Note that, as illustrated in graphs 503 and 505, before time t1, regenerative braking of the motor 30 is not performed, and the regenerative braking torque of the motor 30 is zero.

After time t1, engine braking is applied to the four-wheel drive vehicle 1 (see graph 506). In the example of FIG. 5, the drive torque of the engine 2, i.e., the positive torque, and the braking torque of the engine 2, i.e., the negative torque, have the same absolute value. Therefore, the change in the fastening torque of the electromagnetic coupling mechanism 58, which will be described later, does not include the influence of torque fluctuations of the engine 2.

In an operating state where engine braking is occurring, the fastening torque of the electromagnetic coupling mechanism 58 increases relatively (see graph 508). Due to the increase in fastening torque, the torque distribution ratio of the front wheels 61 becomes greater than the first distribution ratio (i.e., the second distribution ratio), as shown in graph 507. As described above, since there is no change in the magnitude of the torque of the engine 2 input to the transfer 54 between before time t1 and after time t1, the increase in fastening torque corresponds to an increase in the torque distribution ratio of the front wheels 61.

In order to achieve the target deceleration, regenerative braking of the motor 30 is initiated at time t2 (see graph 503). As shown in graph 505, regenerative braking torque of the motor 30, i.e., negative torque, is generated. When engine braking is occurring and regenerative braking torque of the motor 30 is being generated, the fastening torque of the electromagnetic coupling mechanism 58 is further increased (see graph 508). Due to the increase in fastening torque, as shown in graph 507, the torque distribution ratio of the front wheels 61 becomes greater than the second distribution ratio (i.e., the third distribution ratio, see the upward arrow in graph 507).

At time t3, the driver depresses the brake pedal. This applies the braking force of the hydraulic brake to the front wheels 61 and rear wheels 62. Coordinated regeneration is performed between the braking force of the hydraulic brake and the regenerative braking force of the motor 30. As shown in graph 508, the fastening torque of the electromagnetic coupling mechanism 58 further increases. As a result of the increase in fastening torque, the torque distribution ratio of the front wheels 61 becomes greater than the third distribution ratio (i.e., the fourth distribution ratio), as shown in graph 507.

In the example of FIG. 5, during coordinated regeneration, the regenerative braking torque of the motor 30 gradually increases in response to a gradual decrease in vehicle speed (graph 505, see graph 402 in FIG. 4). The fastening torque of the electromagnetic coupling mechanism 58 increases in accordance with the increase in the regenerative braking torque of the motor 30, thereby keeping the torque distribution ratio of the front wheels 61 constant.

In addition, instead of keeping the torque distribution ratio of the front wheels 61 constant, the fastening torque of the electromagnetic coupling mechanism 58 may be changed in accordance with the increase in the regenerative braking torque of the motor 30 so that the torque distribution ratio of the front wheels 61 increases in accordance with the increase in the regenerative braking torque of the motor 30 (see the dashed line in graph 507). When the regenerative braking force is large and the braking force applied to the four-wheel drive vehicle 1 is large, the regenerative braking torque to the front wheels 61 becomes large, so the behavior of the four-wheel drive vehicle 1 in the braking state becomes stable.

In the example shown in Figure 5, a trigger to end regenerative braking is entered, and regenerative braking ends.

1 Four-wheel drive vehicle 10 Control unit 2 Engine 30 Electric motor 54 Transfer 58 Electromagnetic coupling mechanism (adjustment mechanism)
8. Hydraulic brake device

Claims (6)

A control device for a four-wheel drive vehicle based on a front-engine, rear-drive vehicle, comprising:
The engine,
a motor disposed on an output shaft of the engine and performing power running and regenerative braking;
a transfer connected to the engine and the motor and distributing torque of the engine and the motor to front wheels and rear wheels;
an adjustment mechanism that changes a distribution ratio of the torque of the front wheels and the torque of the rear wheels;
a control unit that adjusts the distribution ratio through the adjustment mechanism in accordance with a running state of the four-wheel drive vehicle,
the control unit sets the distribution ratio to a first distribution ratio in which the torque of the rear wheels is greater than the torque of the front wheels in a running state in which the engine is generating a drive torque,
the control unit sets the distribution ratio to a second distribution ratio in a braking state in which engine braking is occurring, such that a distribution ratio of the torque to the front wheels is greater than the first distribution ratio,
the control unit sets the distribution ratio to a third distribution ratio in which the distribution ratio of the torque to the front wheels is greater than the second distribution ratio in a braking state in which engine braking is occurring and regenerative braking of the motor is being performed.
A control device for a four-wheel drive vehicle. 2. The control device for a four-wheel drive vehicle according to claim 1,
The vehicle further includes a hydraulic brake device that applies a braking force to the front wheels and the rear wheels.
The control unit performs cooperative regeneration by causing the hydraulic brake device to generate a braking force and the motor to perform regenerative braking in response to a braking request operation by a driver,
the control unit sets the distribution ratio to a fourth distribution ratio in which the distribution ratio of the torque to the front wheels is greater than the third distribution ratio during the coordinated regeneration.
A control device for a four-wheel drive vehicle. 3. The control device for a four-wheel drive vehicle according to claim 2,
the control unit sets the distribution ratio so that the torque distribution ratio to the front wheels is greater when a ratio of the regenerative braking force of the motor to the braking force of the hydraulic brake device is high than when the ratio is low.
A control device for a four-wheel drive vehicle. The control device for a four-wheel drive vehicle according to any one of claims 1 to 3,
the control unit sets the distribution ratio such that the torque distribution ratio of the front wheels increases as the regenerative braking force of the motor increases.
A control device for a four-wheel drive vehicle. The control device for a four-wheel drive vehicle according to any one of claims 1 to 4,
the control unit sets the distribution ratio so that the torque distribution ratio to the front wheels is greater when the vehicle speed during braking is high than when the vehicle speed is low.
A control device for a four-wheel drive vehicle. The control device for a four-wheel drive vehicle according to any one of claims 1 to 5,
the control unit sets the distribution ratio so that the torque distribution ratio to the front wheels is greater when the steering angle of the vehicle during braking is large than when the steering angle is small.
A control device for a four-wheel drive vehicle.

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