JP4729891B2 - Differential limiting control device for vehicle - Google Patents

Description

  The present invention relates to a differential limiting control device for a vehicle that performs differential limitation between wheels subject to differential limitation, such as left and right wheels or front and rear wheels.

2. Description of the Related Art Conventionally, as a method for controlling vehicle behavior or driving force during traveling of an automobile or the like, a method in which braking force is controlled is known. Also, for example, when the turning limit of the vehicle is detected, the braking force is forcibly controlled to prevent the vehicle from deviating from the lane, and when it is in the 4WD state at this time, it is driven by switching to the 2WD state. An apparatus that reduces the inertia of the system and stabilizes the turning behavior of the vehicle has also been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 09-20217

By the way, in general, in the differential restriction control device that realizes the differential restriction by controlling the braking force, the braking force control by the differential restriction control interferes with the braking force by the driver's brake operation. When the driver performs a brake operation, the differential limiting control is prohibited.
Here, in a situation where the driver releases the brake operation on the so-called split μ road surface where the friction coefficient with the road surface differs between the left and right wheels, the return gradient of the left and right wheel speeds after the brake operation is released is a low friction coefficient. Compared to the road surface side, the high friction coefficient road surface side becomes larger.

  At this time, for example, in the case of a differential limiting control device that performs differential limiting of the left and right wheels when the wheel speed difference between the left and right wheels is greater than a preset threshold value, the difference occurs when the brake operation is released. As described above, the return gradient of the left and right wheel speeds after release of the brake operation is higher on the high friction coefficient road surface side than on the low friction coefficient road surface side. If the wheel speed difference between the left and right wheels is larger than the threshold value, it is determined that it is necessary to limit the differential between the left and right wheels. There is a possibility that a braking force for limiting the differential is unnecessarily added to the wheels on the road surface side.

In other words, there is a difference in rotational speed between the left and right wheels, but this is because the wheel speed on the low friction coefficient road surface side is smaller than the wheel speed on the high friction coefficient road surface side. The wheel on the side is not in an accelerated slip state. Therefore, although it is not necessary to limit the differential, it is erroneously determined that a difference in rotational speed has occurred between the left and right wheels due to acceleration, and a braking force is unnecessarily applied to the high friction coefficient road surface side. There is a problem of fear.
Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and even when the differential restriction target wheels are located on road surfaces having different friction coefficients, the differential restriction is accurately performed. An object of the present invention is to provide a vehicle differential limiting control device capable of performing control.

In order to achieve the above object, a differential limiting control device for a vehicle according to the present invention includes a wheel speed detecting means for detecting a wheel speed of a differential limiting target wheel , and a differential limiting detected by the wheel speed detecting means. Differential limiting control means for limiting the differential between the differential limiting target wheels when the difference in wheel speeds of the target wheels is greater than a preset threshold, and differential in the differential limiting control means during braking A differential limiting prohibiting device for a vehicle, comprising: a differential limiting prohibiting unit that prohibits limiting control; the differential limiting prohibiting unit includes: a vehicle body speed detecting unit that detects a vehicle body speed; and at least a differential control target wheel. Vehicle body speed estimating means for estimating the pseudo vehicle speed based on the wheel speed including the vehicle speed, and the vehicle speed detected by the vehicle speed detecting means after the brake is released. Subtract the differential control limit until Following are characterized by the ban.

The differential limiting control device for a vehicle according to the present invention prohibits differential limiting control during braking by the differential limiting prohibiting means, but even after releasing the brake, based on at least the wheel speed including the differential control target wheels. Since the differential limit control is continuously prohibited until the estimated pseudo vehicle speed becomes equal to or higher than the vehicle speed , the difference after the brake is released due to the difference in the coefficient of friction with the road surface of the differential limit target wheel. Even if there is a difference between the wheel speeds of the wheels subject to differential restriction because the return gradients of the wheel speeds of the restricted wheels are different, unnecessary differential restriction is avoided and differential restriction is performed. Control can be performed accurately.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic configuration diagram showing a four-wheel drive vehicle equipped with a vehicle differential limiting control device according to the present invention.
In FIG. 1, 1FL and 1FR are front left and right wheels, 1RL and 1RR are rear left and right wheels, and a rotational driving force from an engine (not shown) is branched to the front and rear propeller shafts 5 via a transmission or the like. It is transmitted equally to the rear left and right wheels 1RL and 1RR via the wheel-side rear differential gear RDG and to the front left and right wheels 1FL and 1FR via the front wheel-side front differential gear FDG. Each wheel 1FL to 1RR is provided with a wheel cylinder 2FL to 2RR as a brake cylinder, and each wheel 1FL to 1RR is a wheel for outputting a sine wave signal corresponding to the number of wheel rotations. Speed sensors 3FL to 3RR are provided.

  Further, a center differential lock mechanism CDF that mechanically or electrically controls the driving force distribution state between the front and rear wheels is inserted in the front and rear propeller shafts 5 described above. The center differential lock mechanism CDF is operated so that the driving force is equally distributed to the front left and right wheels 1FL and 1FR and the rear left and right wheels 1RL and 1RR, or the front wheel side or the rear wheel side. The two-wheel drive state in which the driving force is distributed to only one of the two is switched to one. Here, it is assumed that only a direct-coupled four-wheel drive state in which the driving force is equally distributed to the front left and right wheels and the rear left and right wheels is assumed.

  Further, the rear differential gear RDG includes a lock mechanism that couples the rear left and right wheels 1RL and 1RR to each other at a constant speed, and can cancel the function of the differential gear and limit the differential to a so-called differential lock state. It has become. The rear differential gear RDG is controlled by a braking control device 22 (to be described later) in accordance with the difference between the left and right rotational speeds.

On the other hand, the wheel cylinders 2FL to 2RR are controlled by controlling a braking pressure to the wheel cylinders 2FL to 2RR by a hydraulic circuit 21. The hydraulic circuit 21 is configured in the same manner as a known TCS control hydraulic circuit or the like, and is configured to generate a braking force independently of the operation of the brake pedal 31.
The hydraulic circuit 21 is controlled by the brake control device 22, and when the brake pedal 31 is operated, the fluid pressure from the master cylinder 32 corresponding to the operation amount of the brake pedal 31 is braked to the wheel cylinders 2FL to 2RR. When the brake pedal 31 is not operated, a motor (not shown) is driven to operate the oil pump to generate a designated braking pressure.

  As shown in FIG. 1, the brake control device 22 includes a brake LSD control unit 22a that performs a known brake LSD control, and a differential restriction prohibiting unit 22b that prohibits the brake LSD control in the brake LSD control unit 22a. Has been. The brake LSD control unit 22a reads each wheel speed from the wheel speed sensors 3FL to 3RR and a detection signal of the hydraulic pressure sensor 25 for detecting the fluid pressure of the master cylinder 32, and based on these, a known brake LSD is read. Control is executed in a predetermined cycle set in advance. That is, based on the wheel speeds from the wheel speed sensors 3RL and 3RR, the rotational speed difference between the rear left and right wheels 1RL and 1RR is detected, and when the rotational speed difference is greater than a preset threshold value, the rear left and right wheels The hydraulic circuit 21 is driven so as to apply braking force to the wheels on the high-speed rotation side so that the rotational speeds of the rear left and right wheels 1RL and 1RR are equal to each other. To do.

The differential restriction prohibiting unit 22b monitors whether the brake pedal 31 is operated, and prohibits the brake LSD control when the brake pedal 31 is operated. Further, when the brake pedal 31 is operated, a virtual pseudo vehicle speed Vref ^* described later is sequentially calculated, and when the depression of the brake pedal 31 is released, the brake LSD control is prohibited for a predetermined period from this point.

  Further, the brake LSD control unit 22a calculates the pseudo vehicle speed Vref based on each wheel speed, and when the brake pedal 31 is depressed, the wheel speed having the highest wheel speed (select high) is selected. When the brake pedal 31 is not depressed, the wheel speed with the smallest wheel speed (select low) is selected from the wheel speeds, and a first-order lag filtering process is performed on the selected wheel speed. It is set as the vehicle speed Vref (pseudo vehicle speed estimation means).

Here, the case where the pseudo vehicle speed Vref is calculated by performing filter processing on select low or select high of each wheel speed has been described. However, the present invention is not limited to this. It is possible to apply other calculation methods such as using the average value of.
FIG. 2 is a flowchart showing an example of a processing procedure of a brake LSD control prohibition process for prohibiting the brake LSD control, which is executed by the differential restriction prohibiting unit 22b. The brake LSD control prohibition process is executed at a predetermined cycle set in advance.

In the brake LSD control prohibition process, first, in step S1, it is determined whether or not a flag Fs indicating whether or not the brake LSD control is prohibited is set to “1”. This flag Fs is set to “0” at the time of activation.
When the flag Fs is not set to “1”, that is, when the brake LSD control is not prohibited, the process proceeds to step S2 to determine whether the vehicle is decelerating. This determination is made by, for example, calculating a deceleration based on the previous value and the current value of the pseudo vehicle body speed Vref.

  If the vehicle is decelerating, the process proceeds to step S3, and then it is determined whether the rear differential gear RDG is in a locked state, that is, in a state where differential limitation is performed. This determination is made based on, for example, a locked state acquired by a monitor function for monitoring whether or not the rear differential gear RDG is in a locked state. In addition, when the on / off switching of the lock of the rear differential gear RDG can be executed also by the driver's switch operation, the determination may be made using the operation state of this switch.

  When the rear differential gear RDG is in the locked state, the process proceeds to step S4, and it is determined whether or not the brake pedal 31 is operated. This determination is made based on the detection signal of the hydraulic sensor 25. Here, the case where it is determined whether or not the brake pedal 31 is operated based on the detection signal of the hydraulic sensor 25 has been described. However, the present invention is not limited to this. For example, the depression amount of the brake pedal 31 or Brake operation detection means for detecting whether or not the brake pedal 31 has been operated may be provided, and determination may be made based on the detection signal of the brake operation detection means.

When it is determined in step S4 that the brake pedal 31 is being operated, the process proceeds to step S5, and the flag Fr indicating whether the virtual pseudo vehicle speed Vref ^* is being calculated is “1”. Determine if there is. The flag Fr is set to “0” at the time of activation.
When the flag Fr is “0” and the calculation process of the virtual pseudo vehicle speed Vref ^* is not performed, the process proceeds to step S11, and the calculation process of the virtual pseudo vehicle speed Vref ^* is started. The virtual pseudo vehicle speed Vref ^* is set to an initial value Vref ^* (0), which is the virtual vehicle speed Vref immediately before the brake pedal 31 is operated, and is decelerated at a preset deceleration G ^* from the initial value Vref ^* (0). A value to be calculated is calculated as a virtual pseudo withdrawal speed Vref ^* .

The deceleration G ^* is set to a value corresponding to the deceleration obtained when the brake pedal 31 is operated while traveling on a low friction coefficient road surface, for example, about 0.08 [G].
Then, if the calculation of the virtual pseudo vehicle speed Vref ^* is started, the process proceeds to step S12, the flag Fr is set to “1”, and the process ends.
On the other hand, when the flag Fr is “1” in step S5, the process proceeds to step S6, where the vehicle is decelerating, the rear differential gear RDG is locked, and the brake pedal 31 is depressed in advance. It is determined whether or not it has continued for a predetermined time. In addition, this predetermined time is set to a value that can ensure the accuracy of a signal by communication between the brake control device 22 and various sensors and the hydraulic circuit 21 connected thereto, for example.

  When the vehicle is decelerating and the rear differential gear RDG is locked and the brake pedal 31 is depressed for a predetermined time or longer, that is, the vehicle is decelerating and the rear differential gear RDG. Is determined to be in a locked state and the brake pedal 31 is depressed, the process proceeds to step S7, where the vehicle body speed of the host vehicle, that is, the pseudo vehicle body speed Vref is set to a preset threshold value, for example, 15 [km / h! And when it determines with the own vehicle driving | running | working 15 km / h or more, it transfers to step S8 and the said brake LSD control is prohibited.

  Note that the determination in step S7 is performed in order to avoid unnecessary prohibition of the brake LSD control. In other words, when the host vehicle is traveling at a relatively low vehicle speed, it is assumed that the differential gradient is erroneously caused by the difference in the return gradient between the high friction coefficient road surface side and the low friction coefficient road surface side as described above. Even if the restriction is made, it does not affect the vehicle behavior. Therefore, when traveling at a vehicle speed that does not affect the vehicle behavior in this way, the brake LSD control, that is, unnecessary. It avoids prohibiting differential limiting.

Here, the brake LSD control is prohibited when the host vehicle is traveling at 15 km / h or more. However, the present invention is not limited to this. Even if the differential limitation is erroneously performed due to the difference in the return gradient to the speed, it may be set according to the upper limit value of the vehicle body speed that does not affect the vehicle behavior.
Next, the process proceeds to step S9, the flag Fs indicating that the brake LSD control is prohibited is set to “1”, and then the process ends.

On the other hand, when the vehicle is not decelerating at step S2, or when the rear differential gear RDG is not locked at step S3, or when the brake pedal 31 is not depressed at step S4, the process proceeds to step S10. A flag Fr indicating whether or not the calculation process of the vehicle body speed Vref ^* is being executed is set to “0” ^{. If} the calculation process of the virtual pseudo vehicle body speed Vref ^* is being executed at this time, this process is terminated. Then, the brake LSD control prohibition process is terminated.

In step S6, when the vehicle is decelerating, the rear differential gear RDG is in the locked state and the brake pedal 31 is not depressed for a predetermined time or more, step S7 is performed. When the vehicle body speed is lower than 15 [km / h], the brake LSD control prohibition process is terminated.
On the other hand, when the flag Fs is set to “1” in step S1 and the brake LSD control is prohibited, the process proceeds to step S21 and is calculated by the virtual pseudo vehicle speed calculation process started in the process of step S11. The virtual simulated vehicle body speed Vref ^* and the simulated vehicle body speed Vref are compared to determine whether the simulated vehicle body speed Vref is equal to or higher than the virtual simulated vehicle body speed Vref ^* .

Then, when the pseudo vehicle speed Vref is not equal to or higher than the virtual simulated vehicle speed Vref ^* , the process is terminated as it is. When the simulated vehicle speed Vref is equal to or higher than the virtual simulated vehicle speed Vref ^* , the process proceeds to step S22. The prohibition of the prohibited brake LSD control is released. That is, the brake LSD control is resumed. Then, the process proceeds to step S23, the flag Fs is set to “0”, and the process is terminated.

Next, the operation of the above embodiment will be described.
FIG. 3 shows the state before and after releasing the brake pedal 31 when the rear right wheel is traveling on the high friction coefficient road surface and the rear left wheel is traveling on the low friction coefficient road surface when the driver releases the depression of the brake pedal 31. FIG. 6 shows changes in the wheel speeds of the rear left and right wheels, the pseudo vehicle speed Vref, and the virtual pseudo vehicle speed Vref ^* . In FIG. 3, the solid line represents the wheel speeds of the rear left and right wheels, the broken line represents the virtual pseudo vehicle speed Vref ^* , the thin solid line represents the real vehicle speed, and the alternate long and short dash line represents the pseudo vehicle speed Vref.

Now, the host vehicle decelerates in a directly connected four-wheel drive state, and the driver operates the brake pedal at time t1 from the state where the rear differential gear RDG is in a locked state and differential restriction is applied to the rear left and right wheels. When step 31 is depressed, the rear differential gear RDG is in a locked state, so the process proceeds from step S1 in FIG. 2 to steps S2, S3, and S4 to step S5 to step S11. At this point, the broken line in FIG. As shown, a virtual simulated vehicle body speed Vref ^* that decreases at a predetermined deceleration G ^* from the simulated vehicle body speed Vref is calculated using the simulated vehicle body speed Vref at time t1 as an initial value Vref ^* (0).

Since the brake pedal 31 is depressed, a value obtained by filtering the largest of the wheel speeds of each wheel is set as the pseudo vehicle body speed Vref as indicated by a one-dot chain line in FIG.
Then, when it is recognized that the host vehicle is decelerating and the state where the rear differential gear RDG is locked and the brake pedal 31 is depressed for a predetermined time or longer, the process proceeds from step S6 to step S7 at time t2. If the vehicle body speed at this time is 15 [km / h] or more, the process proceeds from step S7 to step S8, and the brake LSD control is prohibited. Therefore, interference between the braking force caused by the depression of the brake pedal 31 and the braking force caused by the brake LSD control is avoided.

Since the brake LSD control is prohibited and the flag Fs is set to “1” (step S9), the process proceeds from step S1 to step S21, and the virtual simulated vehicle body speed Vref ^* and the simulated vehicle body speed Vref are compared. During braking, the brake LSD control is continuously prohibited while the pseudo vehicle speed Vref is smaller than the virtual pseudo vehicle speed Vref ^* .
Then, for example, when the driver releases the brake pedal 31 at time t3 because the left wheel on the low friction coefficient road surface side tends to lock due to the depression of the brake pedal 31, each wheel speed returns to the vehicle speed. However, at this time, as indicated by a solid line in FIG. 3, the return gradient of the right wheel on the high friction coefficient road surface side is larger than that on the left wheel on the low friction coefficient road surface side.

  Here, when the brake LSD control is restarted when the depression of the brake pedal 31 is released at time t3, the return gradient of the right wheel on the high friction coefficient road surface side is compared with the left wheel on the low friction road surface side. Therefore, a difference occurs in the wheel speed between the left wheel on the low friction coefficient road surface side and the right wheel on the high friction coefficient road surface side, and this wheel speed difference is used to determine the execution of the differential restriction in the brake LSD control. If this threshold is exceeded, differential limiting is performed. That is, as shown in FIG. 3, the threshold value indicated by a two-dot chain line in which the wheel speed of the right wheel on the high friction coefficient road surface side is obtained by adding the threshold value to the wheel speed of the left wheel on the low friction coefficient road surface side. Differential restriction is performed in a section larger than the equivalent value, but the state where this wheel speed difference is occurring is not the state where the wheel on the road surface side with high friction coefficient is slipping. Although it is not necessary to apply a braking force to the coefficient road surface side, an unnecessary braking force is erroneously applied to the high friction coefficient road surface side.

However, as described above, even if the depression of the brake pedal 31 is released at time t3, the pseudo vehicle speed Vref is smaller than the virtual pseudo vehicle speed Vref ^* , that is, the pseudo vehicle speed Vref is smaller than the actual vehicle speed. In other words, if the wheel on the low friction coefficient road surface side does not show a value corresponding to the actual vehicle speed and it is predicted that the judgment of the differential restriction cannot be performed accurately, the brake LSD control is prohibited. Therefore, it is possible to avoid erroneously applying braking force to the rear right wheel on the road surface side with a high coefficient of friction, and to avoid erroneous differential restriction on the rear left and right wheels. it can.

Even after the brake pedal 31 is released, the brake LSD control is continuously prohibited while the pseudo vehicle speed Vref is smaller than the virtual pseudo vehicle speed Vref ^* , and the pseudo vehicle speed Vref becomes the virtual pseudo vehicle speed Vref at time t4. ^{* When the} above is reached, the process proceeds from step S21 in FIG. 2 to step S22, the prohibition of the brake LSD control is released, and the brake LSD control is resumed.

At this time point t4, the pseudo vehicle speed Vref is equal to or higher than the virtual vehicle speed Vref ^* , and the pseudo vehicle speed Vref can be regarded as being equivalent to the actual vehicle speed, that is, the wheel speed on the low friction coefficient road surface side. Therefore, even if the brake LSD control is resumed at this time, the differential limitation is not erroneously performed.
Since the brake LSD control is resumed and the flag Fs is set to “0” (step S23), the process proceeds from step S1 to step S2 in FIG. 2 to step S10 to calculate the virtual pseudo vehicle speed Vref ^* . And the flag Fr is set to “0”. Therefore, thereafter, the brake LSD control is executed until the brake pedal 31 is depressed again.

On the other hand, when the host vehicle exists on the road surface with a high coefficient of friction, the state where the vehicle is decelerating, the rear differential gear RDG is in the locked state, and the brake pedal 31 is depressed is a predetermined time or longer as described above. When the vehicle speed of the host vehicle is 15 km / h or higher (time t2), the brake LSD control is prohibited, but when the depression of the brake pedal 31 is released at time t3, The wheel speed of each wheel recovers with a return gradient equivalent to that of the right wheel in FIG. 3, and the pseudo vehicle speed Vref quickly recovers to the virtual pseudo vehicle speed Vref ^* or higher, so that the vehicle exists on the split μ road surface. The brake LSD control is immediately restarted at a point earlier than the case.

  As described above, in the above embodiment, after the brake pedal 31 is operated, the brake LSD control is prohibited until the simulated vehicle speed Vref recovers to the same level as the actual vehicle speed, and the simulation calculated based on each wheel speed. The brake LSD control is resumed when it can be determined that the vehicle body speed Vref is equivalent to the actual vehicle body speed, that is, when each wheel speed can be regarded as having returned to the same as the actual vehicle body speed. Thus, it is possible to avoid accidentally applying an unnecessary braking force to the wheels on the road surface side with a high friction coefficient, and to perform the brake LSD control accurately.

The lower the friction coefficient of the road surface, the lower the return speed of the wheel on the low friction coefficient road surface side, and the difference in wheel speed between the right wheel on the high friction coefficient road surface side and the left wheel on the low friction coefficient road surface side increases. The wheel speed difference between the left and right wheels tends to exceed the threshold value, and the differential restriction on the wheels on the high friction coefficient road surface side is easily performed. However, the virtual pseudo vehicle speed Vref ^* is set to a value corresponding to the deceleration obtained when the normal braking operation is performed on the low friction coefficient road surface, and is calculated based on this value. The pseudo vehicle speed Vref ^* can be estimated. Furthermore, since the virtual vehicle speed Vref exceeds the virtual vehicle speed Vref ^* and the vehicle speed Vref can be regarded as equivalent to the actual vehicle speed, the prohibition of the brake LSD control is canceled. The brake LSD control prohibition can be canceled when it can be assumed that the differential limitation is not performed, and the brake LSD control can be resumed at an appropriate timing, and the brake LSD control is resumed. At this point, it is possible to avoid the differential restriction being erroneously performed on the wheel on the road surface side with the high friction coefficient.

In the above-described embodiment, the virtual pseudo vehicle speed Vref ^* is calculated based on the preset deceleration G ^* . However, the present invention is not limited to this. For example, the navigation device Alternatively, when a deceleration detecting means capable of detecting the deceleration of the vehicle such as an acceleration sensor is installed, the deceleration detected by the deceleration detecting means is applied as the deceleration G ^*. The virtual pseudo vehicle speed Vref ^* may be calculated based on the actual deceleration.

The virtual pseudo vehicle speed Vref ^* is calculated based on the deceleration G ^* . For example, a vehicle speed detection means capable of detecting the vehicle speed such as a vehicle speed sensor and a navigation device is installed. In this case, the vehicle speed detected by the vehicle speed detection means can be applied as the virtual pseudo vehicle speed Vref ^* , and can be regarded as having returned to the vehicle speed equivalent. It is also possible to apply the wheel speed of the rear right wheel RR located on the high friction coefficient side road surface as the virtual simulated vehicle body speed Vref ^* . In other words, it is only necessary to be able to determine whether the wheel speed on the high friction coefficient side road surface and the wheel speed on the low friction coefficient side road surface are equivalent to each other. The value corresponding to the wheel speed on the coefficient side road surface and the value corresponding to the wheel speed on the low friction coefficient side road surface may be detected.

In the above embodiment, the case where the pseudo vehicle speed Vref and the virtual vehicle speed Vref ^* are compared has been described. However, as described above, the wheel speed on the high friction coefficient side road surface and the low friction coefficient side road surface Since it is only necessary to be able to determine whether or not it is possible to determine that the wheel speed is equivalent to the wheel speed, the wheel speed of the rear left wheel RL on the low friction coefficient side road surface side is replaced with the pseudo vehicle body speed Vref. The virtual simulated vehicle body speed Vref ^* may be compared. That is, the pseudo vehicle speed Vref is calculated based on each wheel speed, and when any wheel speed is not a value corresponding to the actual vehicle speed, the influence appears on the pseudo vehicle speed Vref. Therefore, when the pseudo vehicle speed Vref and the virtual pseudo vehicle speed Vref ^* are equal to each other, it can be considered that each wheel speed represents a value equivalent to the actual vehicle speed, that is, on the high friction coefficient side. Since it can be determined that the wheel speed of the road surface wheel and the wheel surface of the low friction coefficient side road surface can be regarded as being equal, the wheel speed of the rear left wheel RL and the virtual pseudo vehicle speed Vref ^* Even if it is a case where it is made to compare, the effect equivalent to the above can be acquired.

In other words, it is determined whether the wheel speed, which is lower than the vehicle speed due to braking, has a difference in the respective wheel speeds of the differential target wheels due to the difference in the friction coefficient of each road surface of the differential target wheels. Can be prohibited.
In the above embodiment, when the pseudo vehicle body speed Vref is equal to or higher than the virtual pseudo vehicle body speed Vref ^* , that is, the wheel speed equivalent value on the low friction coefficient side road surface is equal to or higher than the wheel speed equivalent value on the high friction coefficient side road surface. However, the present invention is not limited to this. As described above, since the differential limitation is performed when the wheel speed difference between the wheel on the high friction coefficient side road surface and the wheel on the low friction coefficient side road surface exceeds the threshold value, the pseudo vehicle speed Vref When the sum of the offset value set in accordance with the threshold value is equal to or higher than the virtual pseudo vehicle speed Vref ^* , the prohibition of the brake LSD control may be canceled. An effect can be obtained. The offset value may be set equal to the threshold value or a value obtained by adding a margin to the threshold value. The wheel speed of the low friction coefficient side road surface may be set to the wheel speed of the high friction coefficient side road surface. And a value that can be considered to have returned until the difference between the wheel speed of the road surface on the low friction coefficient side road surface becomes smaller than the threshold value.

In the above embodiment, the virtual pseudo vehicle speed Vref is satisfied when the vehicle is decelerating in step S2 in FIG. 2 and the rear differential gear RDG is in the locked state in step S3. ^Although the case where calculation of ^* is started has been described, it is not always necessary to satisfy these conditions. Similarly, the state in which the vehicle is decelerating in step S6, the rear differential gear RDG is in the locked state, and the brake pedal 31 is depressed is continued for a predetermined time or more, and the vehicle speed in step S7. In the above description, the brake LSD control is prohibited when satisfying the condition of 15 [km / h] or more. However, it is not always necessary to satisfy these conditions.

In the above-described embodiment, the case where the brake LSD control is continuously prohibited after the operation of the brake pedal 31 is released until the pseudo vehicle speed Vref becomes equal to or higher than the virtual vehicle speed Vref ^* has been described. For example, when the operation of the brake pedal 31 is released, the prohibition of the brake LSD control is released, and thereafter, when the wheel speed difference between the left and right wheel speeds becomes larger than the threshold value, the pseudo vehicle body speed Vref is assumed to be virtual. The brake LSD control may be prohibited again until the vehicle speed becomes the pseudo vehicle speed Vref ^* or higher.

In the above embodiment, the case where the differential limitation is performed by controlling the braking force of the rear left and right wheels has been described. However, the present invention is not limited to this. For example, the rear differential gear RDG includes a clutch. It can be applied even when it is configured with a control type differential limiting device, etc., and it is a differential limiting device that detects the presence or absence of a difference in rotational speed between the left and right and limits the differential accordingly. Any format can be applied.
In the above embodiment, the case where the differential differential of the rear differential gear RDG of the direct-coupled four-wheel drive vehicle is differentially limited has been described. However, the present invention is not limited to this. Any device can be applied.

In the above embodiment, the differential limiting device for limiting the differential between the left and right wheels has been described. However, the present invention is not limited to this, and the differential limiting device is configured to limit the differential between the front and rear wheels. Even can be applied. In this case, of the front and rear wheels, the wheel with the smaller wheel speed is regarded as the wheel on the low friction coefficient side road surface, and the wheel with the larger wheel speed is regarded as the wheel on the high friction coefficient side road surface. When the wheel speed of the smaller one of the front and rear wheels is equal to or higher than the virtual pseudo vehicle speed Vref ^* , the prohibition of the front and rear wheel differential restriction (for example, engagement of the 4WD clutch) control may be canceled. . In this case, the wheel speed corresponding to the wheel on the low friction coefficient side road surface is not limited to the case of comparing the virtual pseudo vehicle speed Vref ^* , but the wheel on the low friction coefficient side road surface such as the pseudo vehicle speed Vref. The virtual pseudo vehicle body estimated based on the value corresponding to the speed and the vehicle speed detected by the vehicle speed detection means for detecting the vehicle speed as described above or the deceleration detected by the deceleration detection means for detecting the deceleration You may make it compare with the value equivalent to the wheel speed of the road surface of a high friction coefficient side, such as speed. Also in this case, the value corresponding to the wheel speed on the low friction coefficient side road surface is not limited to the value corresponding to the wheel speed on the high friction coefficient side road surface, but corresponds to the wheel speed on the low friction coefficient side road surface. When the difference between the value and the value corresponding to the wheel speed of the road surface on the high friction coefficient side is less than the threshold value for the differential restriction execution determination, the prohibition of the front and rear wheel differential restriction control is canceled. Also good.

  In the above embodiment, the wheel speed sensors 3RL and 3RR correspond to the wheel speed detection means, the brake LSD control unit 22a corresponds to the differential limit control means, and after steps S8 and S9, the steps S1 and S1 are performed. The process of repeating S21 corresponds to the differential restriction prohibiting means, and the process of step S11 corresponds to the vehicle body speed detecting means.

It is a schematic block diagram which shows an example of the vehicle to which the differential limiting control apparatus for vehicles by this invention was applied. It is a flowchart which shows an example of the process sequence of the arithmetic processing performed with the braking control apparatus of FIG. It is a time chart with which it uses for description of operation | movement of this invention.

Explanation of symbols

1FL to 1RR Wheel 2FL to 2RR Wheel cylinder 3FL to 3RR Wheel speed sensor 21 Hydraulic circuit 22 Brake control device 22a Brake LSD control unit 22b Differential restriction prohibition unit 25 Hydraulic pressure sensor 31 Brake pedal 33 Master cylinder CDF Center differential lock mechanism FDG Front differential Gear RDG Rear differential gear

Claims (7)

Wheel speed detection means for detecting the wheel speed of each of the differential restriction target wheels;
Differential limiting control means for limiting the differential between the differential limiting target wheels when the difference in wheel speed of the differential limiting target wheels detected by the wheel speed detecting means is greater than a preset threshold value;
A differential limiting control device for a vehicle comprising differential limiting prohibiting means for prohibiting differential limiting control by the differential limiting control means during braking,
The differential restriction prohibiting means includes:
Vehicle speed detection means for detecting the vehicle speed;
A pseudo vehicle body speed estimating means for estimating a pseudo vehicle body speed based on a wheel speed including at least a differential control target wheel;
After the braking is released, the differential control restriction for vehicles is continuously prohibited until the pseudo vehicle speed estimated by the pseudo vehicle speed estimation means becomes equal to or higher than the vehicle speed detected by the vehicle speed detection means. Control device. The vehicle body speed detection means uses the pseudo vehicle body speed estimated by the pseudo vehicle body speed estimation means when braking is started as an initial value, and estimates the vehicle body speed based on the initial value and a preset deceleration. The differential limiting control device for a vehicle according to claim 1 . 3. The vehicle differential limiting control device according to claim 2, wherein the deceleration is set to a deceleration according to a friction coefficient of a low friction coefficient road surface . The vehicle body speed detection means includes a deceleration detection means for detecting a deceleration of the vehicle, and detects the vehicle body speed based on the deceleration detected by the deceleration detection means. A differential limiting control device for a vehicle. The vehicle body speed detecting means detects the wheel speed on the high rotation side after the wheel speed on the high rotation side of the differential restriction target wheel returns to a wheel speed equivalent to the vehicle body speed as the vehicle body speed. The differential limiting control device for a vehicle according to claim 1 . 6. The vehicle according to claim 1, wherein the pseudo vehicle body speed estimation unit uses a wheel speed on a low rotation side of the differential restriction target wheel as the pseudo vehicle body speed . 6. Differential limiting control device. Wheel speed detection means for detecting the wheel speed of each of the differential restriction target wheels;
Differential limiting control means for limiting the differential between the differential limiting target wheels when the difference in wheel speed of the differential limiting target wheels detected by the wheel speed detecting means is greater than a preset threshold value;
A differential limiting control device for a vehicle comprising differential limiting prohibiting means for prohibiting differential limiting control by the differential limiting control means during braking,
The differential restriction prohibiting means includes:
Vehicle speed detection means for detecting the vehicle speed;
A pseudo vehicle body speed estimating means for estimating a pseudo vehicle body speed based on a wheel speed including at least a differential control target wheel;
After the braking is released, the difference is increased until the sum of the pseudo vehicle speed estimated by the pseudo vehicle speed estimation means and the offset value set according to the threshold becomes equal to or higher than the vehicle speed detected by the vehicle speed detection means. A differential limiting control device for a vehicle, wherein dynamic control limiting is continuously prohibited .

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