JP2021100834A - Vehicular traction control device - Google Patents

Abstract

To provide a vehicular traction control device that can improve acceleration performance of a vehicle while suppressing increase in acceleration slip of a drive wheel.SOLUTION: A vehicular traction control device 100 includes a brake control unit 72 that, when acceleration slip occurs on a first drive wheel which is one of the right drive wheel and left drive wheel, executes brake force imparting processing of suppressing the acceleration slip on the first drive wheel by imparting brake force to the first drive wheel. The brake control unit 72 reduces the brake force to be imparted to the first drive wheel in the brake force imparting processing when a slip rate on a second drive wheel which is the other of the right drive wheel and left drive wheel increases.SELECTED DRAWING: Figure 1

Description

The present invention relates to a vehicle traction control device.

In Patent Document 1, when acceleration slip occurs in at least one of the right drive wheel and the left drive wheel, the acceleration slip of the drive wheel is caused by applying a braking force to the drive wheel in which the acceleration slip occurs. A vehicle traction control device that implements suppression traction control is described.

Japanese Unexamined Patent Publication No. 8-133504

Depending on the traveling conditions of the vehicle, there is a situation in which acceleration slip occurs on one of the right drive wheels and the left drive wheel, and acceleration slip does not occur on the other drive wheel. In this situation, when the traction control as described above is implemented, a braking force is applied to one drive wheel in which the acceleration slip is generated, and a braking force is applied to the other drive wheel in which the acceleration slip is not generated. Not done. Then, in this case, if the driving force transmitted to the other driving wheel increases, the slip amount of the other driving wheel may start to increase.

Hereinafter, means for solving the above problems and their actions and effects will be described.
The vehicle traction control device for solving the above problems includes a power source, left drive wheels and right drive wheels driven by a driving force output from the power source, and the driving force is applied to the left drive wheels and the right drive. It is applied to a vehicle provided with a differential distributed to the wheels and a braking device for adjusting the braking force applied to the left drive wheel and the right drive wheel. The vehicle traction control device applies a braking force to the first drive wheel when an acceleration slip occurs in the first drive wheel, which is one of the left drive wheel and the right drive wheel. A braking control unit that performs a braking force applying process that suppresses the acceleration slip of the first driving wheel is provided. When the acceleration slip state amount of the left drive wheel and the second drive wheel, which is the other drive wheel of the right drive wheel, increases during the execution of the braking force applying process, the braking control unit performs the first drive. Reduce the braking force applied to the wheels.

In the traction control device of the vehicle, when the amount of acceleration slip state of the second drive wheel increases in the braking force applying process, the frictional force acting on the second drive wheel may exceed the friction circle of the second drive wheel. Therefore, the braking force applied to the first driving wheel is reduced. Then, due to the characteristics of the differential, the distribution ratio of the driving force transmitted to the differential to the first driving wheel increases, and the distribution ratio of the driving force to the second driving wheel decreases. As a result, it is possible to prevent the frictional force acting on the second drive wheels from exceeding the friction circle of the second drive wheels, so that it is possible to suppress the occurrence of acceleration slip on the second drive wheels. Therefore, according to the traction control device of the vehicle, the generation of acceleration slip of the drive wheel having the larger friction circle among the two drive wheels connected via the differential increases the braking force with respect to the drive wheel. Can be suppressed without.

The block diagram which shows the outline of the vehicle which comprises the traction control device of the vehicle which concerns on one Embodiment. The block diagram which shows the outline of the braking device to which the said traction control device is applied. The flowchart which shows the flow of the process which the said traction control apparatus carries out for traction control. The flowchart which shows the flow of the process which the traction control device performs in order to correct a braking force and a driving force during traction control. (A), (b), and (c) are timing charts showing changes in wheel speed, braking force, and driving force during traction control.

Hereinafter, the vehicle traction control device according to the embodiment will be described with reference to the drawings.
FIG. 1 shows a vehicle equipped with the traction control device 100 of the present embodiment. As shown in FIG. 1, the vehicle is provided with a right front wheel FR, a left front wheel FL, a right rear wheel RR, and a left rear wheel RL. This vehicle is a so-called four-wheel drive vehicle configured so that the driving force DP can be transmitted to all the wheels FR, FL, RR, and RL.

In this vehicle, the driving force DP output from the power source 11 such as the internal combustion engine is input to the transfer device 13 via the transmission 12. The transfer device 13 has a center differential 14 and a lock mechanism 15. Further, the transfer device 13 is connected to the front differential 17 via the front propeller shaft 16 and the rear differential 19 is connected to the transfer device 13 via the rear propeller shaft 18.

The driving force DP input to the transfer device 13 is distributed to the front differential 17 and the rear differential 19 by the center differential 14. Then, the driving force DP input to the front differential 17 is distributed to the right front wheel FR and the left front wheel FL by the front differential 17. Similarly, the driving force DP input to the rear differential 19 is distributed to the right rear wheel RR and the left rear wheel RL by the rear differential 19.

That is, the right front wheel FR and the left rear wheel RL correspond to an example of the "right drive wheel" and the "left drive wheel" in which the driving force DP is distributed via the front differential 17, and the right rear wheel RR and the left rear wheel. The RL corresponds to an example of a "right drive wheel" and a "left drive wheel" in which the driving force DP is distributed via the rear differential 19.

When the center differential 14 is locked by the lock mechanism 15 in the transfer device 13, the driving force DP distributed from the transfer device 13 to the front differential 17 side and the drive distributed from the transfer device 13 to the rear differential 19 side. The ratio to the force DP is held at a value determined from the specifications of the vehicle.

The vehicle is individually provided with braking mechanisms 30a, 30b, 30c, 30d for the wheels FR, FL, RR, and RL. These braking mechanisms 30a to 30d press the friction material 33 against the rotating body 32 that rotates integrally with the wheels FR, FL, RR, and RL as the WC pressure Pwc, which is the hydraulic pressure in the wheel cylinders 31a, 31b, 31c, and 31d, increases. It is configured to increase the force. The greater the force that presses the friction material 33 against the rotating body 32, the greater the braking force BP applied to the wheels FR, FL, RR, and RL.

The hydraulic pressure generating device 41 of the braking device 40 is provided with a master cylinder 42 that internally generates a hydraulic pressure according to the amount of operation of a braking operation member 43 such as a brake pedal. The hydraulic pressure in the master cylinder 42 is also referred to as "MC pressure Pmc".

The braking actuator 50 of the braking device 40 is provided with a first hydraulic circuit 511 and a second hydraulic circuit 512. A wheel cylinder 31a for the right front wheel FR and a wheel cylinder 31d for the left rear wheel RL are connected to the first hydraulic circuit 511. Further, a wheel cylinder 31b for the left front wheel FL and a wheel cylinder 31c for the right rear wheel RR are connected to the second hydraulic circuit 512.

As shown in FIG. 2, the first hydraulic circuit 511 includes a differential pressure adjusting valve 521 arranged between the master cylinder 42 and the wheel cylinders 31a and 31d, and the differential pressure adjusting valve 521 and the wheel cylinder 31a. A pump 531 for discharging the brake fluid is provided in the liquid passage between the and 31d. The pump 531 operates based on the drive of the electric motor 55, and pumps the brake fluid from the inside of the master cylinder 42 and the reservoir 591 described later. Then, by operating the pump 531 and the differential pressure adjusting valve 521, the differential pressure between the master cylinder 42 side of the differential pressure adjusting valve 521 and the wheel cylinders 31a and 31d of the differential pressure adjusting valve 521 is adjusted.

The first hydraulic circuit 511 is provided with a plurality of wheel-side adjusting mechanisms 56a and 56d individually corresponding to the plurality of wheel cylinders 31a and 31d. The wheel side adjustment mechanism 56a corresponds to the wheel cylinder 31a for the right front wheel FR, and the wheel side adjustment mechanism 56d corresponds to the wheel cylinder 31d for the left rear wheel RL. The wheel-side adjusting mechanisms 56a and 56d include holding valves 57a and 57d that are closed when the increase in the WC pressure Pwc is regulated, and pressure reducing valves 58a and 58d that are opened when the WC pressure Pwc is reduced. Each has. The holding valves 57a and 57d are arranged in the liquid passages between the differential pressure adjusting valve 521 and the wheel cylinders 31a and 31d, respectively. Brake fluid is discharged from the pump 531 into the liquid passage between the differential pressure adjusting valve 521 and the holding valves 57a and 57d. Therefore, by adjusting the opening degree of the holding valves 57a and 57d while generating the differential pressure by the operation of the common adjustment mechanism 541, the WC pressure Pwc in the wheel cylinders 31a and 31d is changed to the MC pressure Pmc in the master cylinder 42. It is possible to make it smaller than the sum of the above differential pressure and the above differential pressure.

Further, the pressure reducing valves 58a and 58d are arranged in the liquid passages connecting the wheel cylinders 31a and 31d and the reservoir 591, respectively. When the pressure reducing valves 58a and 58d are opened, the brake fluid in the wheel cylinders 31a and 31d flows out to the reservoir 591 side, so that the WC pressure Pwc in the wheel cylinders 31a and 31d can be reduced.

The structure of the second hydraulic circuit 512 is almost the same as the structure of the first hydraulic circuit 511. That is, the second hydraulic circuit 512 is provided with a common adjustment mechanism 542, the same number of wheel side adjustment mechanisms 56b and 56c as the wheel cylinders 31b and 31c, and a reservoir 592. The common adjustment mechanism 542 has a differential pressure adjusting valve 522 and a pump 532 powered by an electric motor 55. The wheel side adjustment mechanism 56b corresponds to the wheel cylinder 31b for the left front wheel FL, and the wheel side adjustment mechanism 56c corresponds to the wheel cylinder 31c for the right rear wheel RR. The wheel-side adjusting mechanisms 56b and 56c have holding valves 57b and 57c and pressure reducing valves 58b and 58c, respectively.

As shown in FIG. 1, the traction control device 100 includes a braking control device 70 and a drive control device 80 capable of transmitting and receiving various types of information to each other.
As shown in FIG. 1, signals are input to the braking control device 70 from various sensors such as the same number of wheel speed sensors 91a, 91b, 91c, 91d and steering angle sensor 92 as the wheels FR, FL, RR, and RL. To. The wheel speed sensors 91a to 91d detect the wheel speed VW of the corresponding wheels FR, FL, RR, RL. The steering angle sensor 92 detects the steering angle STR of the steering wheel 61 of the vehicle. Then, the braking control device 70 controls the braking actuator 50 based on input signals from various sensors 91a to 91d, 92, information received from the drive control device 80, and the like.

A signal is input to the drive control device 80 from the accelerator opening sensor 93 that detects the amount of operation of the accelerator operating member 62 such as the accelerator pedal. The drive control device 80 calculates the required driving force DPR required by the driver for the vehicle based on the amount of operation of the accelerator operating member 62 of the driver. If the vehicle is an autonomous driving vehicle, the required driving force DPR is calculated based on preset driving conditions and the like. Then, the drive control device 80 controls the power source 11, the transmission 12, and the transfer device 13. For example, the drive control device 80 controls the power source 11 so that the driving force DP output from the power source 11 becomes the required driving force DPR.

Subsequently, the contents of the traction control performed by the braking control device 70 will be described.
As shown in FIG. 1, the braking control device 70 calculates the slip amount Slp as a functional unit for suppressing the acceleration slip of the wheels FR, FL, RR, and RL while ensuring the acceleration property when the vehicle is running. It has a slip calculation unit 71 for performing traction control, and a braking control unit 72 for performing traction control by adjusting the braking force BP.

The slip calculation unit 71 calculates the slip amount Slp of the wheels FR, FL, RR, and RL. The slip amount Slp is a value representing the degree of acceleration slip of the wheels FR, FL, RR, and RL, and the larger the degree of acceleration slip, the larger the value. In the present embodiment, the slip amount Slp is an example of the “accelerated slip state amount”.

When an acceleration slip occurs in one of the left drive wheel and the right drive wheel, the braking control unit 72 applies a braking force BP to the drive wheel in which the acceleration slip occurs, thereby causing the acceleration slip of the drive wheel. Performing braking force applying processing to suppress. Specifically, the braking control unit 72 executes the braking force applying process when the slip amount Slp of the drive wheels becomes the first slip determination value SlpTh1 or more. The braking force BP applied to the drive wheels in which the acceleration slip occurs, that is, the target value of the WC pressure is calculated so as to increase as the slip amount Slp of the drive wheels in which the acceleration slip occurs increases. Then, the braking control unit 72 controls the braking actuator 50 according to the target value of the WC pressure.

Here, if the friction circle of one of the two drive wheels connected via the differential is smaller than the friction circle of the other drive wheel, acceleration slip may occur only in one drive wheel. is there. When the size of the friction circle between the right drive wheel and the left drive wheel is different, for example, when there is a difference between the friction coefficient between the right drive wheel and the road surface and the friction coefficient between the left drive wheel and the road surface. In some cases, there is a difference between the ground contact load of the right drive wheel on the road surface and the ground contact load of the left drive wheel on the road surface.

In the following description, among the right drive wheel and the left drive wheel, the drive wheel having a relatively small friction circle is referred to as a "first drive wheel", and the drive wheel having a relatively large friction circle is referred to as a "second drive wheel". To do. For example, when the friction circle of the right drive wheel is larger than the friction circle of the left drive wheel, the left drive wheel becomes the "first drive wheel" and the right drive wheel becomes the "second drive wheel". On the contrary, when the friction circle of the left drive wheel is larger than the friction circle of the right drive wheel, the right drive wheel becomes the "first drive wheel" and the left drive wheel becomes the "second drive wheel".

In the braking force applying process described above, when the braking force BP is applied to the first driving wheel in which the acceleration slip occurs, the distribution ratio of the driving force DP to the first driving wheel becomes smaller due to the differential characteristics, and the second driving wheel The distribution ratio of the driving force DP to is increased. Further, when the driving force DP transmitted differentially from the power source 11 increases due to the increase in the required driving force DPR, the driving force DP transmitted to the second driving wheel increases. When the driving force DP transmitted to the second driving wheel increases in this way, the frictional force acting on the second driving wheel may exceed the friction circle of the second driving wheel. That is, there is a possibility that the slip amount Slp2 of the second drive wheel increases during the braking force applying process for suppressing the acceleration slip of the first drive wheel.

Therefore, the braking control unit 72 can determine that a slight acceleration slip has occurred in the second drive wheel when the slip amount Slp2 of the second drive wheel increases in the braking force applying process. The braking force BP applied to the drive wheels is reduced. Specifically, when the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more as an example of the "slip determination value" in the braking force applying process, the braking control unit 72 sets the first drive wheel. The braking force BP to be applied is reduced. In this way, the braking control unit 72 reduces the distribution ratio of the driving force DP to the second driving wheel and suppresses the acceleration slip of the second driving wheel.

Further, when the braking force BP applied to the first driving wheel is reduced due to an increase in the slip amount Slp2 of the second driving wheel during the braking force applying process, the braking control unit 72 reduces the braking force BP applied to the first driving wheel. The amount of decrease in the braking force BP applied to the second drive wheel increases as the slip amount Slp2 of the second drive wheel increases. For example, in the braking force applying process, the braking force BP corresponding to the slip amount Slp1 of the first driving wheel applied to the first driving wheel is set as the "reference braking force", and the slip amount Slp2 of the second driving wheel and the second slip determination are determined. The value obtained by multiplying the difference from the value SlpTh2 by the correction coefficient K is defined as the "corrected braking force". In this case, the braking force BP applied to the first driving wheel is preferably a value obtained by subtracting the corrected braking force from the reference braking force. That is, in a situation where the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more during the execution of the braking force applying process, the first drive wheel becomes the first drive wheel as the slip amount Slp2 of the second drive wheel increases. The braking force BP applied to the first driving wheel decreases, and the braking force BP applied to the first driving wheel increases as the slip amount Slp2 of the second driving wheel decreases. The corrected braking force may be a value obtained by multiplying the slip amount Slp2 of the second driving wheel by the correction coefficient K. Further, the correction coefficient K may be a different value based on the state quantity of the vehicle such as the vehicle body speed VB.

When the braking force BP applied to the first driving wheel is reduced during the braking force applying process, the braking force BP applied to the first driving wheel is increased, as opposed to increasing the braking force BP applied to the first driving wheel. The distribution rate of the driving force DP becomes large. Therefore, when the braking force BP applied to the first driving wheel is reduced, the slip amount Slp1 of the first driving wheel can be increased. However, the first drive wheel is a drive wheel having a smaller friction circle and less influence on the behavior of the vehicle during traveling as compared with the second drive wheel. Therefore, even if the slip amount Slp1 of the first drive wheel increases, suppressing the acceleration slip of the second drive wheel leads to improvement in vehicle stability.

Therefore, during the braking force applying process, the slip amount Slp1 of the first driving wheel is increased under the condition that the braking force BP applied to the first driving wheel is reduced based on the increase of the slip amount Slp2 of the second driving wheel. Even if the first slip determination value is increased to SlpTh1 or more, the braking control unit 72 does not increase the braking force BP applied to the first drive wheels. For example, the braking control unit 72 is in a period from when the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more until the slip amount Slp2 of the second drive wheel becomes less than the second slip determination value SlpTh2. The reference braking force may be maintained at the reference braking force when the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more.

Further, in consideration of the stability of the vehicle, it is preferable that the slip amount Slp generated in the second drive wheel during the braking force applying process is small. Therefore, the braking control unit 72 sets the second slip determination value SlpTh2 for determining the occurrence of the acceleration slip of the second drive wheel to be smaller than the first slip determination value SlpTh1 for determining the occurrence of the acceleration slip of the first drive wheel. .. That is, it can be said that the first slip determination value SlpTh1 is a determination value for determining the occurrence of a normal acceleration slip, and the second slip determination value SlpTh2 is a determination value for determining the occurrence of a minute acceleration slip.

Further, when the vehicle is turning, the effect of the acceleration slip of the second driving wheel on the stability of the vehicle is likely to be larger than when the vehicle is traveling straight. Therefore, the braking control unit 72 makes the second slip determination value SlpTh2 smaller when the vehicle is turning than when the vehicle is traveling straight. Whether the vehicle is turning or going straight may be determined based on the steering angle STR of the steering wheel 61. Further, it may be determined whether or not the vehicle is turning based on the yaw rate and the lateral acceleration of the vehicle.

The first drive wheel and the second drive wheel in the present embodiment are a pair of drive wheels to which the driving force DP is distributed via the front differential 17 or the rear differential 19. For example, when traction control is performed due to the acceleration slip of the right front wheel FR, the right front wheel FR becomes the first drive wheel and the left front wheel FL becomes the second drive wheel. Further, when traction control is performed due to the acceleration slip of the right front wheel FR and the right rear wheel RR, the second drive wheel paired with the right front wheel FR as the first drive wheel becomes the left front wheel FL and becomes the first drive wheel. The second drive wheel paired with the right rear wheel RR is the left rear wheel RL.

Subsequently, the contents of the traction control performed by the drive control device 80 will be described.
As shown in FIG. 1, the drive control device 80 adjusts the driving force DP as a functional unit for suppressing acceleration slip of the wheels FR, FL, RR, and RL while ensuring acceleration when the vehicle is running. It has a drive control unit 81 that performs traction control by means of.

The drive control unit 81 performs a drive force adjustment process for adjusting the drive force DP output by the power source 11 when an acceleration slip occurs in the first drive wheel. The driving force adjustment process includes a first driving force adjustment process for reducing the driving force DP to less than the required driving force DPR, and a first driving force DP for increasing the driving force DP toward the required driving force DPR after the first driving force adjustment process is performed. 2 Includes driving force adjustment processing.

The first driving force adjusting process is performed, for example, during a period in which the slip amount Slp1 of the first driving wheel is increasing. By implementing the first driving force adjustment process, both the driving force DP transmitted to the first driving wheel and the second driving wheel is reduced, and the acceleration slip of the first driving wheel is alleviated.

The second driving force adjusting process is started when the slip amount Slp1 of the first driving wheel is reduced by the execution of the first driving force adjusting process and the braking force applying process described above. The second driving force adjusting process is a process performed following the first driving force adjusting process, and is not a process performed at the same time as the first driving force adjusting process. By executing the second driving force adjustment process, both the driving force DP transmitted to the first driving wheel and the second driving wheel increases, and the vehicle accelerates according to the required driving force DPR.

However, the drive control unit 81 limits the increase in the driving force DP when the slip amount Slp2 of the second driving wheel increases during the execution of the second driving force adjusting process. Specifically, the drive control unit 81 limits the increase in the driving force DP when the slip amount Slp2 of the second driving wheel becomes the second slip determination value SlpTh2 or more during the execution of the braking force applying process. As a method of limiting the increase in the driving force DP, for example, the rate of increase in the driving force DP after the slip amount Slp2 of the second driving wheel becomes the second slip determination value SlpTh2 or more is set to "0". Be done. Further, when the slip amount Slp2 of the second drive wheel is less than the second slip determination value SlpTh2, the speed of increase of the driving force DP after the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more. It is mentioned that the driving force DP of the driving force is less than the increasing speed of DP. When a control that gradually increases the driving force DP is adopted as a limitation of the increase in the driving force DP, the drive control unit 81 determines that the larger the slip amount Slp2 of the second drive wheel is, or the slip amount Slp2 of the second drive wheel is larger. The faster the rate of increase, the slower the rate of increase of the driving force DP may be. When the restriction on the increase in the slip amount Slp2 of the second drive wheel is lifted, that is, when the slip amount Slp2 of the second drive wheel becomes less than the second slip determination value SlpTh2, the drive control unit 81 sets the driving force DP. Remove the growth limit.

Next, with reference to FIG. 3, a flow of processing performed by the traction control device 100 for performing traction control will be described. This process is a process that is repeatedly executed in a predetermined control cycle while the vehicle is running.

As shown in FIG. 3, the traction control device 100 determines whether or not the start condition of the traction control for the first drive wheel is satisfied (S11). The start condition of traction control is that when the first drive wheel, which is one of the right drive wheel and the left drive wheel, has accelerated slip, the slip amount Slp1 of the first drive wheel is the first slip determination value SlpTh1 or more. It is established when becomes. If the traction control start condition is not satisfied (S11: NO), the traction control device 100 ends this process. On the other hand, when the traction control start condition is satisfied (S11: YES), the traction control device 100 executes a braking force applying process for applying the braking force BP to the first drive wheel (S12). .. Subsequently, the traction control device 100 carries out a driving force adjusting process for adjusting the driving force DP output by the power source 11 (S13). After that, the traction control device 100 determines whether or not the traction control end condition is satisfied (S14). The end condition of the traction control is satisfied, for example, when the driving force DP output by the power source 11 becomes the required driving force DPR and the acceleration slip of the first driving wheel is eliminated. When the traction control end condition is not satisfied (S14: NO), the traction control device 100 shifts the process to step S12. On the other hand, when the traction control end condition is satisfied (S14: YES), the traction control device 100 ends this process.

Next, with reference to FIG. 4, a flow of processing executed by the traction control device 100 for correcting the braking force and the driving force during the traction control will be described.
As shown in FIG. 4, the traction control device 100 calculates the wheel speed VW of the wheels FR, FL, RR, and RL based on the detection signals from the wheel speed sensors 91a to 91d (S21). Subsequently, the traction control device 100 calculates the vehicle body speed VB based on the wheel speed VW of the wheels FR, FL, RR, and RL (S22). For example, the vehicle body speed VB is calculated based on the slowest wheel speed VW among the wheel speeds VW of the wheels FR, FL, RR, and RL.

Then, the traction control device 100 calculates the slip amount Slp of the wheels FR, FL, RR, and RL (S23). For example, the value obtained by subtracting the vehicle body speed VB from the wheel speed VW of the right front wheel FR is calculated as the slip amount Slp of the right front wheel FR. The slip amount Slp of the wheels FL, RR, and RL other than the right front wheel FR is calculated by the same method as the slip amount Slp of the right front wheel FR.

Subsequently, the traction control device 100 determines whether or not the slip amount Slp2 of the second drive wheel is increasing (S24). Specifically, it is determined whether or not the slip amount Slp2 of the second drive wheel is equal to or greater than the second slip determination value SlpTh2. When the vehicle is traveling straight, that is, when the absolute value | STR | of the steering angle of the steering wheel 61 is less than the turning determination value STRTh, the value for straight travel is set as the second slip determination value SlpTh2. On the other hand, when the vehicle is turning, that is, when the absolute value | STR | of the steering angle of the steering wheel 61 is equal to or greater than the turning determination value STRTh, the value for turning is set as the second slip determination value SlpTh2. Will be done.

When the slip amount Slp2 of the second drive wheel is not increased (S24: NO), that is, when the slip amount Slp2 of the second drive wheel is less than the second slip determination value SlpTh2, the traction control device 100 performs this process. finish. In this case, the braking force BP applied to the first driving wheel becomes the reference braking force based on the slip amount Slp1 of the first driving wheel. On the other hand, when the slip amount Slp2 of the second drive wheel is increasing (S24: YES), that is, when the slip amount Slp2 of the second drive wheel is the second slip determination value SlpTh2 or more, the traction control device 100 is the third. 1 The braking force BP applied to the drive wheels is reduced (S25). In this case, the braking force BP applied to the first drive wheel is a braking force obtained by subtracting the corrected braking force corresponding to the slip amount Slp2 of the second drive wheel from the reference braking force.

Subsequently, the traction control device 100 determines whether or not the second driving force adjustment process is being executed (S26). When the second driving force adjustment process is not being executed (S26: NO), that is, when the first driving force adjustment process is being executed, the traction control device 100 ends this process. On the other hand, when the second driving force adjustment process is being carried out (S26: YES), the traction control device 100 limits the increase in the driving force DP output by the power source 11. After that, the traction control device 100 ends this process.

The operation and effect of this embodiment will be described.
Specifically, with reference to the timing chart shown in FIG. 5, changes in wheel speeds VW1, VW2, braking forces BP1, BP2, and driving force DP when traction control is started while the vehicle is traveling on a split μ road will be described. To do. When the vehicle travels on the split μ road, the wheels touching the low μ road are the first drive wheels, and the wheels touching the high μ road are the second drive wheels.

As shown in FIGS. 5A, 5B, and 5C, in the period up to the first timing t11, the wheel speeds of the first driving wheels VW1 and the second driving wheels are increased as the required driving force DPR increases. Wheel speed VW2 increases. That is, the vehicle accelerates as the required driving force DPR increases. At the first timing t11, a frictional force exceeding the friction circle of the first driving wheel begins to act on the first driving wheel. That is, acceleration slip starts to occur in the first drive wheel. However, in the period from the first timing t11 to the second timing t12, the traction control is not started because the slip amount Slp1 of the first drive wheel is less than the first slip determination value SlpTh1.

At the second timing t12, when the slip amount Slp1 of the first drive wheel becomes the first slip determination value SlpTh1 or more, the traction control is started. That is, after the second timing t12, the braking force BP1 is applied to the first driving wheel, and the driving force DP output by the power source 11 is limited. Specifically, in the period from the second timing t12 to the next third timing t13, the braking force BP1 applied to the first driving wheel increases as the slip amount Slp1 of the first driving wheel increases, and the power source increases. The driving force DP output by 11 decreases with the passage of time. In this respect, the period after the second timing t12 is the period in which the braking force applying process is executed, and the period from the second timing t12 to the third timing t13 is the period in which the first driving force adjusting process is executed. It will be a period of time.

At the third timing t13, the slip amount Slp1 of the first drive wheel changes from an increasing tendency to a decreasing tendency. Therefore, after the third timing t13, the braking force BP1 applied to the first driving wheel begins to decrease, and the driving force DP of the power source 11 begins to increase toward the required driving force DPR. In this respect, the period after the third timing t13 is the period in which the second driving force adjustment process is performed.

At the fourth timing t14, as the driving force DP transmitted to the second driving wheels increases, a frictional force exceeding the friction circle of the second driving wheels begins to act on the second driving wheels. That is, a minute acceleration slip starts to occur in the second drive wheel.

At the fifth timing t15, when the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more, the braking force BP1 applied to the first drive wheel is reduced according to the slip amount Slp2 of the second drive wheel. Slip. Then, due to the differential characteristics, the distribution ratio of the driving force DP to the second driving wheels becomes smaller and the distribution ratio of the driving force DP to the first driving wheels becomes larger after the fifth timing t15. As a result, the excessive driving force DP is not transmitted to the second driving wheel, and the minute acceleration slip of the second driving wheel can be eliminated. That is, it is possible to eliminate the minute acceleration slip of the second drive wheel without applying the braking force BP2 to the second drive wheel. As a result, the stability of vehicle behavior can be maintained.

Further, at the fifth timing t15, when the slip amount Slp2 of the second drive wheel becomes the second slip determination value SlpTh2 or more, the increase in the driving force DP output by the power source 11 is limited. Specifically, at the fifth timing t15, the increasing speed of the driving force DP becomes “0”, and the driving force DP output by the power source 11 does not change from the driving force DP at the fifth timing t15. As a result, regardless of whether the components are distributed to the first drive wheels or the second drive wheels, an excessive driving force DP that can cause an acceleration slip in at least one of the first drive wheels and the second drive wheels is generated. It will not be transmitted to the differential. That is, even if the slip amount Slp1 of the first drive wheel temporarily increases as the distribution ratio of the driving force DP with respect to the first drive wheel increases, the slip amount Slp1 of the first drive wheel can be gradually reduced. ..

At the sixth timing t16 when the slip amount Slp2 of the second drive wheel becomes less than the second slip determination value SlpTh2, the braking force BP1 applied to the first drive wheel is assumed to be eliminated, assuming that the acceleration slip of the second drive wheel is eliminated. The reference braking force is obtained according to the slip amount Slp1 of the first drive wheel. Further, after the sixth timing t16, the restriction on the increase in the driving force DP output by the power source 11 is lifted. Specifically, the increasing speed of the driving force DP output by the power source 11 is the increasing speed in the period from the third timing t13 to the fifth timing t15. In this way, after the acceleration slip of the second driving wheel is eliminated, the driving force DP is immediately increased, so that the acceleration property of the vehicle is improved.

Even after the sixth timing t16, if acceleration slip occurs in the second drive wheel in response to the increase in the drive force DP transmitted to the second drive wheel, the braking force applied to the first drive wheel again is applied. BP1 is reduced and the increase in driving force DP is limited. In this way, the driving force DP is distributed to the second driving wheels so that the frictional force acts on the second driving wheels up to the vicinity of the limit of the friction circle of the second driving wheels.

As described above, in the traction control, the slip amount Slp1 of the first drive wheel is set to less than the first slip determination value SlpTh1 and the slip amount Slp2 of the second drive wheel is set to less than the second slip determination value SlpTh2. The stability of the vehicle can be improved. Further, the acceleration of the vehicle can be enhanced in that the frictional force is applied to the second drive wheels up to the vicinity of the limit of the friction circle of the second drive wheels.

This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
-The traction control device 100 does not have to limit the increase in the driving force DP when the slip amount Slp2 of the second driving wheel increases during the execution of the second driving force adjusting process. In this case, the traction control device 100 eliminates the increase in the slip amount Slp2 of the second drive wheel during the execution of the second drive force adjustment process only by the decrease in the braking force BP applied to the first drive wheel. ..

The traction control device 100 may set the corrected braking force to a constant value regardless of the slip amount Slp2 of the second drive wheel. Even in this case, since the braking force BP applied to the first driving wheel is reduced during the execution of the second driving force adjusting process, the slip amount Slp2 of the second driving wheel can be reduced.

-The second slip determination value SlpTh2 when the vehicle is turning may be smaller when it can be predicted that the lateral force generated in the drive wheels is large than when it can be predicted that the lateral force is small. That is, the larger the absolute value of the steering angle | STR |, the absolute value of the yaw rate of the vehicle, and the absolute value of the lateral acceleration, the smaller the second slip determination value SlpTh2 may be.

The traction control device 100 may set the second slip determination value SlpTh2 to be the same value when the vehicle is traveling straight and when the vehicle is turning.
When the slip amount Slp2 of the second driving wheel increases during the execution of the second driving force adjusting process, the traction control device 100 starts decreasing the braking force BP applied to the first driving wheel, and the power. The timing at which the limitation on the increase in the driving force DP output from the source 11 is started may be shifted.

-The traction control device 100 may use a state amount other than the slip amount Slp as the "acceleration slip state amount" indicating the degree of acceleration slip. For example, the traction control device 100 may use a differential value (rate of change) of the slip amount or an integrated value (addition value) of the slip amount as the “accelerated slip state amount”. In this case, the traction control device 100 reduces the braking force BP applied to the first driving wheel during the execution of the braking force applying process, or reduces the braking force BP applied to the first driving wheel according to the increase in the differential value of the slip amount or the integrated value of the slip amount. 2 The increase in the driving force DP is restricted during the execution of the driving force adjustment process.

In the braking actuator 50, the wheel cylinder 31a for the right front wheel FR and the wheel cylinder 31b for the left front wheel FL are connected to the first hydraulic circuit 511, and the left rear wheel RL is connected to the second hydraulic circuit 512. The wheel cylinder 31d and the wheel cylinder 31c for the right rear wheel RR may be connected to each other.

The braking device may have a configuration different from that of the braking device 40 described in the above embodiment as long as the braking force applied to each wheel FL, FR, RL, and RR can be individually adjusted.
The traction control device 100 is one of one or more processors that operate according to a computer program (software), dedicated hardware that executes at least a part of various processes (integrated circuit for specific applications: ASIC), and the like. It can be configured as the above dedicated hardware circuit or a circuit including a combination thereof. The processor includes a CPU and a memory such as a RAM and a ROM, and the memory stores a program code or a command configured to cause the CPU to execute a process. Memory, or storage medium, includes any available medium accessible by a general purpose or dedicated computer.

11 ... Power source 17 ... Front differential 19 ... Rear differential 40 ... Braking device 72 ... Braking control unit 81 ... Drive control unit BP, BP1, BP2 ... Braking force DP ... Driving force DPR ... Required driving force FR ... Right front wheel (right drive) Example of a ring)
FL ... Left front wheel (an example of left drive wheel)
RR ... Right rear wheel (an example of right drive wheel)
RL ... Left rear wheel (an example of left drive wheel)
Slp, Slp1, Slp2 ... Slip amount SlpTh1 ... First slip judgment value SlpTh2 ... Second slip judgment value (an example of slip judgment value)

Claims (4)

A power source, a left drive wheel and a right drive wheel driven by a drive force output from the power source, a differential that distributes the drive force to the left drive wheel and the right drive wheel, the left drive wheel, and the left drive wheel. It is applied to a vehicle provided with a braking device for adjusting the braking force applied to the right drive wheel.
When an acceleration slip occurs in the first drive wheel, which is one of the left drive wheel and the right drive wheel, the first drive wheel is accelerated by applying a braking force to the first drive wheel. Equipped with a braking control unit that performs braking force application processing to suppress slippage
When the acceleration slip state amount of the left drive wheel and the second drive wheel, which is the other drive wheel of the right drive wheel, increases during the execution of the braking force applying process, the braking control unit performs the first drive. A vehicle traction control device that reduces the braking force applied to the wheels. When the braking control unit reduces the braking force applied to the first driving wheel due to an increase in the acceleration slip state amount of the second driving wheel during the braking force applying process, the braking force is applied. The vehicle traction control device according to claim 1, wherein the reduction amount is increased as the acceleration slip state amount of the second drive wheel is larger. A drive control unit for performing a driving force adjusting process for adjusting the driving force when an acceleration slip occurs in at least one of the left driving wheel and the right driving wheel is provided.
The driving force adjusting process is a first driving force adjusting process for reducing the driving force to less than the required driving force for the power source, and after the first driving force adjusting process is performed, the driving force is converted to the required driving force. Including a second driving force adjustment process to increase toward
The drive control unit according to claim 1 or 2, which limits the increase in the driving force when the acceleration slip state amount of the second driving wheel increases during the execution of the second driving force adjusting process. Vehicle traction control device. The braking control unit
When the acceleration slip state amount of the second drive wheel becomes equal to or more than the slip determination value during the execution of the braking force applying process, it is determined that the acceleration slip state amount of the second drive wheel increases, and the first 1 Reduce the braking force applied to the drive wheels,
The vehicle traction control device according to any one of claims 1 to 3, wherein the slip determination value is made smaller when the vehicle is turning than when the vehicle is traveling straight.

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