JPH0516686A - Vehicle running state determination device and vehicle power transmission control device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the running stability of a four-wheel drive vehicle equipped with a center differential according to various running conditions. A center differential 3, differential limiting means for limiting a differential function of the center differential 3, rotational speed difference detecting means for detecting a rotational speed difference between front and rear wheels, and rotational speed difference detecting means for detecting the rotational speed difference. A differential limiting amount controller 20 for controlling the differential limiting amount by the differential limiting means according to the rotational speed difference.
And to prevent the wheels from being locked during braking with the brake A
In a four-wheel drive vehicle equipped with the BS controller 24,
During braking, when the rotational speed difference detecting means detects that the rear wheel rotational speed is higher than the front wheel rotational speed, it is determined that the vehicle is in a sudden braking state, and the differential limiting means performs the differential limiting operation. If the front wheel rotation speed is higher than the rear wheel rotation speed by the rotation speed difference detection means when the vehicle speed is reduced, the vehicle is determined to be in a rapid acceleration state, and the differential The amount of differential limitation by the limiting means is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle running condition judging device and a vehicle power transmission control device, and more particularly to a running condition judging device for a four-wheel drive vehicle equipped with a center differential device for differentiating front wheels and rear wheels. And a power transmission control device.

[0002]

2. Description of the Related Art A four-wheel drive vehicle in which output torque of a power train composed of an engine, a transmission and the like is transmitted to front wheels and rear wheels so that the vehicle is driven by all wheels has been conventionally known. .

By the way, when the vehicle is turning, the turning radius of the rear wheels is generally smaller than the turning radius of the front wheels. Therefore, in order to make the vehicle travel smoothly during turning, the rotation speed of the rear wheels is made smaller than the rotation speed of the front wheels. However, in a four-wheel drive vehicle, if the output torque of the power train is directly transmitted to the front wheel side and the rear wheel side, the front wheel rotation speed becomes equal to the rear wheel rotation speed. Receives a braking force from the road surface, a so-called tight corner braking phenomenon occurs.

Therefore, in order to transmit the output torque of the power train to the front wheels and the rear wheels, and to enable the differential between the front wheels and the rear wheels, a center differential device () is provided between the power train and the front and rear wheels. Hereinafter, abbreviated as “center differential” is provided.

However, when such a center differential is provided, when the front wheels or the rear wheels slip, most of the torque is distributed to the slipping wheels, so that the driving force of the vehicle is substantially lost. There is such a problem.

On the other hand, the difference in the number of rotations between the front and rear wheels is detected, and when the difference in the number of rotations is large, it is determined that the wheels are in a slip state, and the front wheel side and the rear wheel side are geared. A differential limiting device has been proposed in which the differential function of the center differential is stopped by mechanically connecting the differential limiting device. Also,
When the longitudinal acceleration and deceleration of the vehicle exceed the set values,
A four-wheel drive vehicle in which the center differential is locked to stop the differential function has also been proposed (actually developed 62-31531).
(See the official gazette).

However, in these conventional differential limiting devices, either the center differential is freely differentiated or the direct differential state is established. Therefore, the differential limiting amount depends on the degree of wheel slip. It was not possible to perform appropriate differential limiting amount control according to the running state of the vehicle, such as adjusting.

Therefore, the front wheel side axle and the rear wheel side axle are engaged with each other with an arbitrary degree of engagement, or the input shaft of the center differential is engaged with any one of the wheel side axles with an arbitrary degree of wetness. A differential limiting device such as a clutch is provided, and the degree of engagement of the differential limiting device is adjusted according to the rotational speed difference between the front and rear wheels, that is, the degree of slip, to limit the differential between the front and rear wheels. A differential limiting device designed to do so has been proposed.
63-96938).

[0009]

[Problems to be Solved by the Invention]
In the conventional differential limiting device disclosed in Japanese Patent Laid-Open No. 63-96938, since the differential limiting amount of the center differential is simply changed according to the rotational speed difference between the front and rear wheels,
There is a problem in that the drivability of the vehicle cannot be stabilized according to various running conditions of the vehicle.

The present invention has been made in view of the above-mentioned conventional problems, and in a four-wheel drive vehicle equipped with a center differential, it is intended to stabilize the running performance of the vehicle according to various running conditions. An object of the present invention is to provide a vehicle traveling state determination device and a vehicle power transmission control device.

[0011]

In order to achieve the above object, the invention of claim 1 compares a center differential for differentiating a front wheel and a rear wheel with a front wheel rotational speed and a rear wheel rotational speed. 4 equipped with a rotational speed difference detection means for detecting the rotational speed difference between the wheels
In a wheel drive vehicle, when the rotational speed difference detecting means detects that the rear wheel rotational speed is higher than the front wheel rotational speed during braking by a brake, it is determined that the vehicle is in a sudden braking state. There is provided a traveling state determination device for a vehicle.

According to a second aspect of the present invention, in the four-wheel drive vehicle, when the rotational speed difference detecting means detects that the front wheel rotational speed is higher than the rear wheel rotational speed during non-braking,
Provided is a running state determination device for a vehicle, which determines that the vehicle is in a rapid acceleration state.

Further, the invention of claim 3 includes a center differential,
Differential limiting means for limiting the differential function of this center differential,
Rotational speed difference detecting means for detecting a rotational speed difference between the front and rear wheels, and a differential limiting amount for controlling the differential limiting amount by the differential limiting means according to the rotational speed difference detected by the rotational speed difference detecting means. In a four-wheel drive vehicle including control means and anti-lock control means for preventing wheel lock during braking by a brake, during brake braking, the rotational speed difference detection means causes the rear wheel rotational speed to be higher than the front wheel rotational speed. If it is detected to be high, it is determined that the vehicle is in a sudden braking state, the differential limiting amount by the differential limiting means is reduced, and when the braking is not applied, the front wheel rotational speed is determined by the rotational speed difference detecting means. When it is detected that the rotational speed is higher than the rear wheel rotational speed, it is determined that the vehicle is in a rapid acceleration state, and the differential limiting amount by the differential limiting means is increased to increase the differential limiting amount. I will provide a.

According to the invention of claim 4, claim 3
In addition to the constituent features of the invention of claim 1, a rear differential device (hereinafter abbreviated as "rear differential") for differentially adjusting the left and right rear wheels, and second differential limiting means for limiting the differential function of the rear differential are further provided. In response to the determination that the vehicle is in the sudden braking state, the differential limiting amount by the second differential limiting means is reduced, and in response to the determination that the vehicle is in the sudden acceleration state, the second There is provided a power transmission control device for a vehicle, wherein the differential limiting amount of the differential limiting means is increased.

Further, according to the invention of claim 5, in addition to the configuration of the invention of claim 4, a front differential device (hereinafter abbreviated as "front differential") for differentially adjusting the left and right front wheels, and this front differential. Third differential limiting means for limiting the differential function is further provided, and the differential limiting amount by the third differential limiting means is reduced in response to the determination that the vehicle is in the sudden braking state, and A power transmission control device for a vehicle, which controls the third differential limiting means so that the front differential is in a half-locked state in response to the determination that the vehicle is in the rapid acceleration state. .

[0016]

Generally, in a vehicle, the center of gravity of the vehicle moves rearward and a large load is applied to the rear wheels during acceleration, and the center of gravity of the vehicle moves forward and a large load is applied to the front wheels during braking by a brake. Therefore, in a four-wheel drive vehicle, the front wheels rotate faster than the rear wheels during sudden acceleration, and the rear wheels rotate higher than the front wheels during sudden braking.

According to the present invention, the differential differential limiting amount is changed according to the rotation difference between the front and rear wheels. Therefore, slip prevention during acceleration and ABS control during braking due to differential differential limiting are performed. It is possible to eliminate adverse effects, which can stabilize drivability and improve fuel efficiency.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a four-wheel drive vehicle has a power train P including an engine 1 and a transmission 2, and a transfer device 4 including a center differential 3 having an electromagnetic clutch type differential limiting mechanism (EMCD). The torque input to the center differential 3 is distributed and output to the front wheel side propeller shaft 5 and the rear wheel side propeller shaft 6.

The torque of the front wheel side propeller shaft 5 is input to a front differential 7 provided with an electromagnetic clutch type differential limiting mechanism (EMCD), further transmitted to a left front wheel 9 via a left front axle shaft 8, and It is adapted to be transmitted to the right front wheel 11 via the right front axle shaft 10. On the other hand, the torque of the rear wheel side propeller shaft 6 is the electromagnetic clutch type differential limiting mechanism (EMC
D) is input to the rear differential 12, and further transmitted to the left rear wheel 14 via the left rear axle shaft 13 and to the right rear wheel 16 via the right rear axle shaft 15. Center differential 3,
The electromagnetic clutch differential limiting mechanism (EMCD) provided in each of the front differential 7 and the rear differential 12 is configured to control each differential limiting amount by a current output from the differential limiting amount controller 20. .

The differential limiting amount controller 20 is a digital controller composed of a microcomputer, and is detected by a throttle sensor 21 provided for a throttle valve (not shown) in the intake passage of the engine 1. Brake switch 22 provided for a throttle opening signal TVO and a brake pedal (not shown)
Brake ON / OFF signal generated by the transmission 2
A neutral signal output from a neutral switch 23 provided in the vehicle, an ABS operation signal output from an ABS controller 24 for controlling an antilock braking system (ABS), and the like are input to the differential limiting amount controller 20.

Further, the left front axle shaft 8
The front left wheel speed (rotation speed) NfL detected by the first rotation speed sensor 25 provided for the right front wheel speed (detected by the second rotation speed sensor 26 provided for the right front axle shaft 10 ( Rotation speed) NfR,
Third provided on the left rear axle shaft 13
The left rear wheel speed (rotation speed) NrL detected by the rotation speed sensor 27 and the right rear wheel speed (rotation speed) NrR detected by the fourth rotation speed sensor 28 provided for the right rear axle shaft 15 are respectively represented. The signal is AB
Differential limiting amount controller 2 via S controller 24
It is designed to be input to 0. The differential limiting amount controller 20 uses these signals as input information by the method described later, and uses the center differential 3, the front differential 7, and the rear differential 12.
The current limiting of each differential limiting mechanism is performed to enhance the running stability, fuel efficiency, etc. of the four-wheel drive vehicle. The differential limiting force controller 20 is provided with an operation knob 29 capable of selecting four control modes of an auto mode Auto, a center differential lock mode C, a rear differential lock mode R, and a front differential lock mode F.

The control method of the differential limiting force control by the differential limiting amount controller 20 will be described below with reference to the flowcharts shown in FIG.

FIG. 2 shows a routine for calculating the vehicle body speed Vsp. In step S1, four wheel speeds (rotation speeds) Nf are shown.
L, NfR, NrL and NrR are input. Then, in step S2, the minimum value of the four wheel speeds is defined as the vehicle body speed Vsp.

Next, FIG. 3 shows a calculation routine for the center differential differential rotation speed (the rotation speed difference between the front and rear wheels) ΔNc. In step S3, four wheel speeds NfL, NfR, NrL, Nr are shown.
R is input, and in step S4 the center differential differential rotation speed Δ
Nc is calculated by the following formula. ΔNc = (NfL + NfR) / 2- (NrL + NrR) / 2

FIG. 4 shows a routine for calculating the rear differential differential rotation speed (the rotation speed difference between the left and right rear wheels) ΔNr, and step S5.
Then, the rear wheel speeds NrL and NrR are input, and in the next step S26, the rear differential differential rotation speed ΔNr is calculated by the following equation. ΔNr = | NrL-NrR |

FIG. 5 shows a map control current value setting routine for the center differential 3. First, in step S7, the control current value Ic of the center differential 3 is set as a function of the center differential differential rotation speed ΔNc and the throttle opening TVO. Next, in step S8, it is determined whether or not the control current value Ic is greater than or equal to the maximum current value Imax (lock current value, Imax = 2.2 amperes). If the determination is "YES", the timer Tc is set in step S9. After resetting, the map control current value Ica = Imax is set in the next step S10. And step S1
The timer is incremented in 1 and it is determined in step S12 whether or not the timer time is equal to or longer than the predetermined hold time Ta. If Tc <Ta, the process returns to step S11 to increment the timer time. And step S1
When the determination of 2 is "YES", the process returns to step S7. A map showing the relationship between the control current value Ica and the center differential rotation speed ΔNc is shown in FIG.

Next, FIG. 6 shows a map control current value setting routine for the rear differential 12. Similar to the case of FIG. 5, first in step S13, the control current value Ir of the rear differential 12 is set as a function of the rear differential differential rotation speed ΔNr and the throttle opening TVO. Next, in step S14, it is determined whether or not the control current value Ir is the maximum current value Imax (lock current value, Imax = 4.1 ampere) or more, and this determination is "YES".
If so, the timer Tr is reset in step S15,
In the next step S16, the map control current value Ira = Imax is set. Then, in step S17, the timer is incremented, and in step S18, it is determined whether or not the timer time is equal to or longer than a predetermined hold time Ta, and Tr <Ta.
If so, the process returns to step S17 to increment the timer. When the determination in step S18 is "YES", the process returns to step S13. A map showing the relationship between the control current value Ira and the rear differential rotation speed ΔNr is shown in FIG. 11.

7 to 9 are flowcharts of a control current value determination routine for the front differential 7, the center differential 3, and the rear differential 12. First, in step S21, the map control current values Ica, Ira, AB set in FIGS. 5 and 6 are set.
The S signal, the brake signal, the control mode signal, and the vehicle speed Vsp calculated in FIG. 2 are input. And step S
At 22, it is determined whether the control mode is the auto mode. If it is the automatic mode, the process proceeds to step S23, and the control routine is executed in the automatic mode shown in FIG. 12 described later.

If the determination in step S22 is "NO", it is determined in the next step S24 whether the control mode is the center lock mode. Then, in the center lock mode, the center differential lock mode control routine shown in FIG. 8 is executed. In addition, the determination in step S24 is
If "O", the process proceeds to step S25, it is determined whether or not the control mode is the rear differential lock mode, and if it is the rear lock mode, the rear lock mode control routine shown in FIG. 9 is executed. If the determination in step S25 is also “NO”, it means the front lock mode, and thus step S2
The control current value is determined according to the vehicle body speed Vsp.

In steps S26, S27 and S28, the vehicle body speed Vsp is 100 km / h or more, less than 100 km / h 50 km / h or more, less than 50 km / h 30 km / h or more, 30 km / h It is determined whether or not each is less than. When the vehicle body speed Vsp is 100 km / h, the control current value If of the front differential is set to 0 in step S29, and the control current values Ic of the center differential 3 and the rear differential 7 are set to
Ir is the map control values Ica and Ira set in FIGS. 5 and 6, respectively. If the vehicle body speed Vsp is less than 100 km / h and 50 km / h or more, in Step S30, If
= 0, Ic = 2.2 amperes (Imax), and Ir = Ira. If the vehicle speed Vsp is less than 50 km / h and 30 km / h or more, then in step S31, If = 0, Ic = 2.2 amperes (Imax), and Ir = 4.1 amperes (Imax) are set.
Furthermore, when the vehicle body speed Vsp is 30 km / h or less, I
f = 2.1 amps (Imax), Ic = 2.2 amps (Ima
x), lock all diffs with Ir = 4.1 amps (Imax).

In the center differential lock mode of FIG. 8, it is first determined in step S33 whether or not the brake switch 22 is on, and if it is not braking, in step S34 it is determined whether or not the vehicle body speed Vsp is 100 km / h or more. Is determined. If it is 100 km / h or more, if = 0, Ic = Ica, and Ir = Ira are set at step S35. Again 10
If less than 0 km / h, If = 0, Ic = 2.2 amps
(Imax) and Ir = Ira.

On the other hand, if the brake switch 22 is on, the routine proceeds to step S37, where it is judged if the ABS is operating or not, and if the ABS is not operating, the step S3 is performed.
At 8, If = 0, Ic = 0.8 amperes, and Ir = 0. When the ABS is operating, If = 0, Ic = 0, and Ir = 0 are set in step S39 so as not to hinder the ABS control.

Next, in the rear differential lock mode of FIG. 9, it is first determined in step S40 whether or not the brake switch 22 is on, and if it is not braking, step S41,
Whether the vehicle speed Vsp is 100 km / h or more in S42, 1
Less than 00km / h 50km / h or more, or 50km
/ H is determined. If the vehicle body speed Vsp is 100 km / h or more, If = 0 in step S43,
Ic = Ica and Ir = Ira. If the vehicle speed Vsp is less than 100 km / h and 50 km / h or more, step S44.
At If = 0, Ic = 2.2 Amps (Imax), Ir = Ira
It is said that Further, if the vehicle body speed Vsp is less than 50 km / h, If = 0, Ic = 2.2 amps (Im
ax) and Ir = 4.1 ampere (Imax), and the center differential 3 and the rear differential 12 are locked.

On the other hand, if the brake switch 22 is on, the routine proceeds to step S46, where it is judged if the ABS is operating or not. If the ABS is not operating, the step S4 is performed.
At 7, If = 0, Ic = 0.8 amps and Ir = 1.2 amps. At the time of ABS operation, if = 0, Ic = 0, If = 0 in step S48 so as not to hinder the ABS control.
Ir = 0 is set.

FIG. 10 is a diagram showing the relationship between the center differential differential rotation speed (= front wheel rotation speed-rear wheel rotation speed) ΔNc and the map control current value Ica of the center differential 3, which is the front wheel rotation speed (Nf).
L + NfR) / 2 is the rear wheel speed (NrL + NrR) / 2
Higher front wheel rotation speed range (ΔNc> 0) and rear wheel rotation speed (NrL + NrR) / 2 are front wheel rotation speed (NfL + N).
The differential limiting force target value, that is, the map control current value Ica is set individually for the rear wheel high rotation region higher than fR) / 2.

In the high front wheel rotation speed range (ΔNc> 0), Ica = 0 is set in a region where the center differential differential rotation speed ΔNc is equal to or less than α to provide a dead zone on the front wheel high rotation speed side and the center differential differential rotation speed ΔNc. In the region between α and A, Ica linearly increases with an increase in ΔNc to reach the upper limit value Imax. When Ica reaches Imax (2.2 amps), center differential 3
Is locked and the differential between the front and rear wheels is completely stopped.

On the other hand, in the rear wheel high rotation speed region (ΔNc <0), in the region where the center differential differential rotation speed ΔNc is β or more, Ica is set to zero to provide a dead zone on the rear wheel high rotation speed side and the center differential difference. In the region where the dynamic rotational speed ΔNc is between α and β, I increases as the absolute value of ΔNc increases.
Ca increases linearly to reach the upper limit value Imax.

Next, FIG. 11 is a diagram showing the relationship between the rear differential differential rotation speed (rotational speed difference between the left and right rear wheels) ΔNr and the map control current value Ira of the rear differential 12, where the rear differential differential rotation speed ΔNr is γ. In the region below, Ira = 0 is set to provide a dead zone, and in the region where the rear differential differential rotation speed ΔNr is between γ and C, Ira is increased with respect to ΔNr.
Is linearly increased to reach the upper limit value Imax (4.1 amperes). When Ira reaches Imax, the differential between the left and right rear wheels is completely stopped.

FIG. 12 is a flow chart showing the auto mode control routine shown in step S23 of FIG. First, in step S51, the center differential differential rotation speed ΔN
c, the rear differential differential rotation speed ΔNr and the brake signal are input. Then, in the next step S52, it is determined whether or not the brake switch 22 is on, and if it is during non-braking, the process proceeds to step S53 and it is determined whether or not ΔNc is larger than A. If ΔNc> A, it is determined that the vehicle is accelerating suddenly, and If = 1.05 amperes (1/2) in step S54.
Imax), Ic = 2.2 amps (Imax), and Ir = 4.1 amps (Imax). That is, the center differential 3
The rear differential 12 is completely locked, but the locking of the front differential 7 greatly affects the turning performance of the vehicle. Therefore, in step S54, If = 1/2 Imax is set to set the front differential 7 in the half-locked state. , So that the turning performance is not extremely deteriorated. Then step S5
5, the timer T is reset, the timer is incremented in step S56, it is determined in step S57 whether or not the timer time is equal to or longer than the predetermined hold time Ta, and T <
While Ta, the process returns to step S56 to increment the timer. Then, the determination in step S57 is "YE
When "S" is reached, the process returns to step S51.

On the other hand, if it is determined in step S52 that the brake switch 22 is on, the process proceeds to step S58, and it is determined whether ΔNc is smaller than B or not. . If ΔNc <B, it is determined that the wheel slip has occurred due to sudden braking, and if If is determined in step S59 in order to cope with the ABS control.
= 0, Ic = 0, Ir = 0, all differentials 3,
7 and 12 are free. Furthermore, if ΔNc ≦ A is determined in the determination in step S53, or
When ΔNc ≧ B is determined in the determination of 58, it is determined that the wheel slips due to a partial low μ road surface, and Ic =
Control according to the maps shown in FIGS. 10 and 11 is performed with Ica and Ir = Ira.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a power transmission system of a four-wheel drive vehicle including a traveling state determination device and a power transmission control device according to the present invention.

FIG. 2 is a flowchart of a vehicle body speed calculation routine.

FIG. 3 is a flowchart of a center differential differential rotation speed calculation routine.

FIG. 4 is a flowchart of a rear differential differential rotation speed calculation routine.

FIG. 5 is a flowchart of a center differential map control current value setting routine.

FIG. 6 is a flowchart of a rear differential map control current value setting routine.

FIG. 7 is a flowchart of a control current value determination routine.

8 is a flowchart of a control current value determination routine connected to FIG.

9 is a flowchart of a control current value determination routine connected to FIG.

FIG. 10 is a diagram showing a relationship between a center differential differential rotation speed and a center differential map control current value.

FIG. 11 is a diagram showing a relationship between a rear differential differential rotation speed and a rear differential map control current value.

FIG. 12 is a flowchart of a control current value determination routine in auto mode control.

[Explanation of symbols]

1 engine 2 transmission 3 Center differential 4 Transfer device 7 front differential 9 left front wheel 11 right front wheel 12 Rear differential 14 left rear wheel 16 right rear wheel 20 Differential limit controller 21 Throttle sensor 22 Brake switch 23 Neutral switch 24 ABS controller 25-28 RPM sensor

Continued front page    (72) Inventor Yu Shiraishi             3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda             Within the corporation

Claims (5)

[Claims] 1. A center differential device for differentiating front and rear wheels, and a rotational speed difference detecting means for comparing a rotational speed of front wheels and a rotational speed of rear wheels to detect a rotational speed difference between front and rear wheels. In a four-wheel drive vehicle, when the rotation speed difference detection means detects that the rear wheel rotation speed is higher than the front wheel rotation speed during braking by the brake, it is determined that the vehicle is in the sudden braking state. A traveling state determination device for a vehicle. 2. A center differential device for differentiating front and rear wheels, and a rotational speed difference detecting means for comparing the rotational speeds of the front and rear wheels to detect the rotational speed difference between the front and rear wheels. In a four-wheel drive vehicle, when the rotation speed difference detection means detects that the front wheel rotation speed is higher than the rear wheel rotation speed during non-braking, it is determined that the vehicle is in the rapid acceleration state. A device for determining a running state of a vehicle. 3. A center differential device for differentiating front and rear wheels, differential limiting means for limiting the differential function of this center differential device, and front and rear wheel speeds by comparing front and rear wheel speeds. Rotational speed difference detecting means for detecting the rotational speed difference between the wheels, and differential limiting amount control for controlling the differential limiting amount by the differential limiting means according to the rotational speed difference detected by the rotational speed difference detecting means. In a four-wheel drive vehicle equipped with means and an anti-lock control means for preventing wheel lock during braking by a brake, during braking by a brake, the rotational speed difference detection means causes the rear wheel rotational speed to be higher than the front wheel rotational speed. When it is detected that it is high, it is determined that the vehicle is in a sudden braking state and the differential limiting amount by the differential limiting means is reduced, and when the vehicle is not braking, the front wheel rotational speed is reduced by the rotational speed difference detecting means. A power transmission control device for a vehicle, wherein when it is detected that the rotational speed is higher than the wheel rotational speed, it is determined that the vehicle is in a rapid acceleration state and the differential limiting amount by the differential limiting means is increased. 4. A rear differential device for differentially adjusting the left and right rear wheels, and a second differential limiting device for limiting the differential function of the rear differential device are provided, and it is possible to determine that the vehicle is in the sudden braking state. In response, the differential limiting amount by the second differential limiting means is reduced, and the differential limiting amount by the second differential limiting means is set in response to the determination that the rapid acceleration state is established. The power transmission control device for a vehicle according to claim 3, wherein the power transmission control device is increased. 5. A front differential device for differentially adjusting the front left and right wheels, and a third differential limiting means for limiting the differential function of the front differential device are provided, and respond to the determination that the vehicle is in the sudden braking state. Then, the differential limiting amount by the third differential limiting means is reduced, and in response to the determination that the vehicle is in the rapid acceleration state, the front differential device is set to the half lock state. The power transmission control device for a vehicle according to claim 4, wherein the differential limiting means is controlled.