JPH0516780A - Slip control device for vehicle - Google Patents

Abstract

PURPOSE:To restrain slip of a turning inner wheel at low vehicle speed steering with no sacrifice of vehicle acceleration by modifying a threshold value for beginning brake control lower than a threshold value for beginning engine control contrary to an ordinary case at low vehicle speed steering. CONSTITUTION:In a slip control device 70 which is provided with a slip detecting means 72, a slip judging means 75, a control quantity computing means 76, and the like, and engine control and brake control are performed so as to conform the slip quantity of a drive wheel to a target slip quantity, a threshold value setting means 73 to set a threshold value for beginning brake control higher than a slip quantity threshold value for engine control is provided. Further, a threshold value modification judging means 77 is provided, and when three conditions are satisfied, namely, a handle steering angle detected with a steering angle sensor 69 is over a decided value, vehicle speed detected with a vehicle speed sensor is under a decided value, and an accelerator step-in quantity detected with an accelerator sensor is over a decided value, the threshold value for beginning brake control is modified lower than the set threshold value for beginning engine control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle slip control device.

[0002]

2. Description of the Related Art A slip control device for a vehicle detects the slip amount of the drive wheel in order to prevent the drive wheel from slipping due to an excessive drive torque and deteriorating the acceleration performance during acceleration of the vehicle. It is generally known to perform engine control for reducing the engine output and brake control for increasing the braking force so that the slip amount of the driving wheels becomes the target slip amount corresponding to the friction coefficient of the road surface.

In the slip control device having both the engine control system and the brake control system as described above, only engine control is performed when the slip amount is below a predetermined value, and when the slip amount exceeds the predetermined value. There is a proposal to set the engine control start threshold value and the brake control start threshold value to different values so that the brake control is performed (see Japanese Patent Laid-Open No. 62-149545).

[0004]

By the way, when the vehicle is started with the steering wheel turned, a larger slip is likely to occur in the turning inner wheel than in the turning outer wheel. On the other hand, in the above-mentioned proposal, when the slip amount of the turning inner wheel reaches the threshold value for starting engine control, the engine control is started and the engine output is reduced even if the slip amount of the turning outer wheel does not reach the threshold value. Will be done. In that case, the slip of the turning inner wheel is certainly subsided, but the acceleration (startability) of the vehicle is not so high because the engine output is reduced.

That is, an object of the present invention is to provide a slip control at a low vehicle speed and at the time of steering without sacrificing the acceleration of the vehicle as in the case where the vehicle is started with the steering wheel turned. It is to suppress the slip of the turning inner wheel.

[0006]

According to the present invention, the brake control is usually independent for the left and right drive wheels, and basically, the threshold value for starting the brake control is set higher than the threshold value for starting the engine control. In this way, the above problem is solved by correcting the threshold value for starting the brake control to be lower than the threshold value for starting the engine control during steering at a low vehicle speed.

That is, the means for that purpose comprises an engine output adjusting means for adjusting the engine output, and a braking force adjusting means for separately providing the left and right driving wheels and adjusting the braking force applied to each of the driving wheels. In order that the slip amount of the drive wheel with respect to the road surface becomes the target slip amount,
In a slip control device for a vehicle configured to perform engine control by the engine output adjustment means and independent brake control for each drive wheel by each brake force adjustment means, a slip amount threshold value for starting the engine control, and A threshold value setting means for setting the slip amount threshold value for starting the brake control so that the brake control start threshold value is higher than the engine control start threshold value, and the vehicle speed is detected. Vehicle speed detecting means, steering angle detecting means for detecting the steering angle of the steering wheel of the vehicle, vehicle speed detected by the vehicle speed detecting means is a predetermined value or less, and steering angle detected by the steering angle detecting means is a predetermined value or more. When, the brake control start threshold set by the threshold setting means is set to the engine control start threshold set by the threshold setting means. It is slip control device for a vehicle according to claim that a threshold value correction means for correcting to be lower than the threshold value.

The second means is that the vehicle differential in the first means does not include a differential limiting mechanism.

The third means includes accelerator depression amount detecting means for detecting the depression amount of the accelerator pedal, and the threshold value correcting means has a condition that the vehicle speed detected by the vehicle speed detecting means is equal to or less than a predetermined value, When the condition that the steering angle detected by the angle detection means is a predetermined value or more and the condition that the accelerator depression amount detected by the accelerator depression amount detection means is a prescribed value or more are both satisfied, the threshold setting means sets the threshold value. The threshold value for starting the brake control is corrected to be lower than the threshold value for starting the engine control set by the threshold value setting means.

[0010]

In each of the above means, when the vehicle speed is high or the steering angle is less than the predetermined value, the threshold value setting means sets the threshold value for starting the brake control to a value higher than the threshold value for starting the engine control. Therefore, when the slip of the drive wheels becomes large, the engine control is started first,
When slip cannot be converged by this engine control,
Brake control is executed. Therefore, frequent brake control does not cause early wear of the brake pad, and the load on the brake system is reduced.

On the other hand, as in the case where the vehicle is started with the steering wheel turned, at low vehicle speed and steering,
The slip of the turning inner wheel becomes larger than that of the turning outer wheel, but the threshold value for control start at that time is corrected by the threshold value correction means so that the threshold value for brake control start becomes lower than the threshold value for engine control start. Has been done. Therefore, when the slip amount of the turning inner wheel increases, first, the brake control of only the inner wheel is started, and the engine control is not started at that time. Therefore, the engine output does not decrease and the brake control of the turning outer wheel is performed. Does not even start.

Therefore, while suppressing the slip of the turning inner wheel by the above-mentioned brake control, the unreduced engine output is given to the turning outer wheel that can obtain the gripping force on the road surface, and the turning outer wheel with this margin is maximized to accelerate the vehicle. (Startability) can be obtained.

Further, in this case, in the differential device with the differential limiting mechanism (limited slip differential), since the left and right driving wheels rotate integrally, use a differential device without the differential limiting mechanism. Is desirable.

Further, when the accelerator pedal depression amount is small, the slip amount of the turning inner wheel is small and the large acceleration is not required. Therefore, it is preferable not to modify the threshold value. It is preferable to set the accelerator depression amount as a condition for making the starting threshold value lower than the engine control starting threshold value.

[0015]

Therefore, according to the present invention, the engine control and the independent brake control for the left and right driving wheels are performed, and the threshold value for starting the brake control is higher than the threshold value for starting the engine control. In the vehicle slip control device set to, when the vehicle speed is equal to or less than a predetermined value and the steering angle is equal to or more than a predetermined value, the brake control start threshold value is corrected to be lower than the engine control start threshold value. Since the threshold correction means is provided, the engine control is mainly performed when a normal slip occurs to prevent frequent brake control to reduce the load on the brake system, and it is possible to start the vehicle with the steering wheel turned. In addition, at low vehicle speed and during steering, the slip of the turning inner wheel is suppressed by the brake control without reducing the engine output, and Given a comparatively large engine output turning outer lip force can be obtained, the turning outer with this margin can be enhanced accelerating performance by making the most.

Further, according to the vehicle using the differential device without the differential limiting mechanism, while the slip of the turning inner wheel is suppressed by the brake control, a relatively large driving force is applied to the turning outer wheel to obtain acceleration. Effective use of the means can be achieved.

If the accelerator depression amount is set as a condition for lowering the brake control start threshold value to be lower than the engine control start threshold value, the driver's request can be reflected to improve the acceleration performance. it can.

[0018]

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

FIG. 1 shows the overall structure of a vehicle slip control device. In this vehicle, the left and right front wheels 2FL and 2FR are driven wheels, and the left and right rear wheels 2RL and 2RR are driven wheels. A slip control means 70 is provided for performing brake control, engine control, and lockup control via the AT controller 60 for gear shift control in order to control the drive amount of the 2RL and 2RR to control the slip amount.

In the above vehicle, an engine 1 is mounted on the front part of the vehicle body, and the torque generated by the engine 1 includes a hydraulic automatic transmission 3, a propeller shaft 4, and a differential gear 5 not equipped with a differential limiting mechanism. After that, it is transmitted to the left rear wheel 2RL via the left drive shaft 6L and to the right rear wheel 2RR via the right drive shaft 6R.

The automatic transmission 3 comprises a fluid torque converter 11 and a multi-stage transmission gear mechanism 12.
The speed change gear mechanism 12 is of a hydraulically operated type as is known, and in the embodiment, it is for four forward gears and one reverse gear.
That is, shifting is performed by changing the combination of excitation and demagnetization of the plurality of solenoids 13a incorporated in the hydraulic circuit. Further, the torque converter 11 has a hydraulically operated lock-up clutch 11a, and engagement and disengagement are performed by switching excitation and demagnetization of a solenoid 13b incorporated in the hydraulic circuit.

The solenoids 13a and 13b are controlled by an AT controller 60 for controlling the shift of the automatic transmission 3. The AT controller 60 stores the shift characteristic and the lockup characteristic in advance, and performs the shift control and the lockup control based on this. Therefore, the AT controller 60 receives the throttle opening signals from the main throttle opening sensor 61 that detects the opening of the main throttle valve 43 and the sub throttle opening sensor 62 that detects the opening of the sub throttle valve 45. A vehicle speed signal from the vehicle speed sensor 63 for detecting the vehicle speed (in the embodiment, a rotation speed signal of the propeller shaft 4) is input.

-Brake Force Adjusting Means- Each wheel 2FL, 2FR, 2RL, 2RR is provided with brakes 21FL to 21RR for the above-mentioned brake control. Brake fluid pressure is supplied to the calipers (wheel cylinders) 22FL to 22RR of the brakes 21FL to 21RR via pipes 23FL to 23RR, respectively. The configuration for supplying this brake fluid pressure is
It is as follows.

First, the depression force of the brake pedal 25 is boosted by a hydraulic booster 26 and transmitted to a tandem master cylinder 27. A brake pipe 23FL for the left front wheel is connected to the first discharge port 27a of the master cylinder 27, and a brake pipe 23FR for the right front wheel is connected to the second discharge port 27b of the master cylinder 27.

The booster 26 is supplied with hydraulic pressure from a pump 29 via a pipe 28, and excess liquid pressure is returned to a reservoir tank 31 via a return pipe 30. A branch pipe 28a branched from the pipe 28 is connected to a merging portion a which will be described later, and an electromagnetic opening / closing valve 32 is provided in the branch pipe 28a. The booster hydraulic pressure generated by the booster 26 is supplied to the merging portion a through a pipe 33, and an electromagnetic on-off valve 34 is also provided in the pipe 33. It is set up. And the pipe 3
A parallel valve 3 is provided with a one-way valve 35 that allows only the flow toward the merging portion a.

Brake pipes 23RL and 23RR for the left and right rear wheels are connected to the merging portion a. This piping 2
3RL and 23RR are electromagnetic on-off valves 36A or 3
7A is interposed and the on-off valves 36A, 37A
An electromagnetic opening / closing valve 36B or 37B is connected to the relief passage 38L or 38R connected to the downstream side of.

Each of the on-off valves 32, 34, 36A, 37
The slip control means 70 controls A, 36B, and 37B. That is, slip control (brake control)
If not performed, the on-off valve 32 is closed as shown in the figure,
The on-off valve 34 is opened, the on-off valves 36B and 37B are closed, and the on-off valves 36A and 37A are opened. As a result, when the brake pedal 25 is depressed, the front wheel brake 21
Brake fluid pressure is supplied to FL and 21FR via the master cylinder 27. In addition, the rear wheel brake 21
To RL and 21RR, a booster hydraulic pressure corresponding to the depression force of the brake pedal 25 from the hydraulic booster 26 is supplied as a brake hydraulic pressure via a pipe 33.

Further, as will be described later, when the slip amount of the rear wheels 2RL, 2RR as the driving wheels with respect to the road surface becomes large and slip control is performed, the open / close valve 34 is closed and the open / close valve 32 is opened. And the on-off valves 36A, 3
By the duty control of 6B (37A, 37B), the holding of the brake fluid pressure and the pressure increase and pressure decrease are performed. More specifically, assuming that the open / close valve 32 is open, the brake fluid pressure is maintained when the open / close valves 36A, 36B, 37A, 37B are closed, and the open / close valve 36A (37
When A) is opened and the on-off valve 36B (37B) is closed, the pressure is increased, and when the on-off valve 36A (37A) is closed and the on-off valve 36B (37B) is opened, the pressure is decreased. Then, the brake fluid pressure passing through the branch pipe 28a is applied to the one-way valve 35
The action of does not act as a reaction force to the brake pedal 25.

When the brake pedal 25 is depressed while the slip control is being performed, the brake fluid pressure from the booster 26 corresponding to the depression is changed to the one-way valve 35.
Is supplied to the rear wheel brakes 21RL and 21RR via.

-Engine Output Adjusting Means- The slip control means 70 performs brake control on the drive wheels 2RL, 2RR in order to reduce the drive torque of the drive wheels 2RL, 2RR, and at the same time, the drive wheels 2RL, 2R.
The driving force transmitted to R, that is, the output (generated torque) of the engine 1 is also reduced. Therefore, the intake passage 41 of the engine 1 is provided with the above-mentioned main throttle valve 43 connected to the accelerator pedal 42 and the above-mentioned sub-throttle valve 45 connected to the throttle opening adjustment actuator 44. The sub throttle valve 45 is controlled by the slip control means 70 via the actuator 44.

-Slip control means 70-The slip control means 70 includes a throttle opening sensor 6
1, 62 and signals from the vehicle speed sensor 63, the wheel speed signals from the wheel speed sensors 66FL to 66RR that detect the speeds of the wheels 2FL to 2RR, the accelerator sensor 67 that detects the amount of depression of the accelerator pedal, A steering angle sensor 69 for detecting the steering angle of the steering wheel, a mode signal from a manually operated switch 71, and the like are input.

Further, the slip control means 70 has an input interface for receiving signals from the respective sensors, a microcomputer including a CPU, a ROM and a RAM, an output interface, valves 32 and 36A,
37A, 36B, 37B and a drive circuit for driving the actuator 44, the ROM is provided with a control program necessary for slip control, various maps, and the RAM is provided with various kinds of control necessary for executing the control. Memory is provided.

<Specific Structure of Slip Control Means 70> As shown in FIG. 2, the slip control means 70 includes a slip detecting means 72, a threshold value (target slip amount) setting means 73, a road surface friction coefficient calculating means 74, and a slip determination. Means 75, control amount calculation means 76, and threshold value correction means 77 are provided.

(Regarding the slip detecting means 72) The slip amount of the driving wheels is determined by the wheel speed sensors 66FR, 66FL, 6FL.
It is detected based on the detection signals from 6RR and 66RL.
That is, the slip detection means 72 calculates the slip amount by subtracting the speed of the driven wheels from the speed of the driving wheels. In calculating the slip amount, in the case of engine control, the speed of the driving wheels is selected from the larger of the left and right driving wheels, and the average value of the left and right driven wheels is used as the speed of the driven wheels. In the case of brake control, the speeds of the driven wheels are the same as those for engine control, but the speeds of the driving wheels are different from those of the left and right driving wheels in order to control the braking force to the left and right driving wheels independently of each other. To be

(Threshold setting means 73 and threshold correcting means 77
FIG. 3 is a block diagram showing a circuit for determining the engine control start threshold value (target slip amount) SET and the brake control start threshold value (target slip amount) SBT. There are an accelerator depression amount, a steering wheel steering angle, an operation state of the mode switch 71, and a road surface friction coefficient μ.

That is, in the figure, the basic value STA0 of SET and the basic value STB0 of SBT are stored in the map 81 using the road surface friction coefficient μ as a parameter. In this case, the basic values STAO and STBO increase as the road surface friction coefficient μ increases (STB0
> STA0). Then, the basic values STB0, STA0
Is multiplied by the correction gain coefficient KD to obtain SET and SBT.

The correction gain coefficient KD is obtained by multiplying each gain coefficient VG, ACPG, STRG, and MODEG. The gain coefficient VG has a vehicle speed as a parameter and is stored as a map 82. The gain coefficient ACPG has the accelerator opening as a parameter and is stored as the map 83. The gain coefficient STRG uses the steering angle of the steering wheel as a parameter, and is stored as the map 84. The gain coefficient MODEG is manually selected by the driver and is stored in the table 85. This table 8
In 5, the sports mode, the normal mode, and the safety mode are provided.

Thus, the obtained brake control start threshold value SBT is corrected by the threshold value correction means 77 when the vehicle speed, the steering wheel steering angle and the accelerator depression amount are in predetermined states. That is, the threshold correction means 77 determines that the vehicle speed V is equal to or lower than the predetermined value Vo, the steering wheel angle θH is equal to or higher than the predetermined value θHo,
And when the accelerator depression amount Ac is equal to or greater than the predetermined value Aco, that is, when the operating state in which a relatively large slip is generated only in the turning inner wheel, the above S
The subtraction correction of the predetermined value α (value of 3 or more) is given to BT, and SB
This is to make T <SET. Further, the threshold correction means 77 receives the engine control flag ECFL = 1 described later and cancels the threshold correction after the engine control is started.

FIG. 4 shows the flow of the threshold value correction control. After the data is input, the engine control is not in progress (ECFL =
0), low vehicle speed (V ≦ Vo), large steering angle (θH ≧ θHo), and large accelerator depression amount (Ac ≧ Aco), the threshold value is corrected and the threshold value flag F = 1. (Steps S1 to S7). On the other hand, when any one of the above conditions is not satisfied, the threshold value is not corrected, and when any one of the above conditions is not satisfied after the threshold value is corrected, the threshold value correction is canceled (steps S8 to S10). .

A lower limit limit value SM, which will be described later, is stored as a map 91 using the vehicle speed and the road surface friction coefficient μ as parameters, as shown in FIG. In addition, in FIG.
μ = 1 is the minimum friction coefficient, and μ = 5 is the maximum friction coefficient.

(Regarding Road Surface Friction Coefficient Calculation Means 74) The road surface friction coefficient μ, which is the friction coefficient between the tire and the road surface, is
It is calculated based on the vehicle speed Vr and the vehicle acceleration VG.

That is, in calculating the vehicle body acceleration VG, the timer A (100 msec count) and the timer B (500 ms) are calculated.
ec count) and. That is, the vehicle body acceleration VG
Is 100ms every 100msec from the start of slip control until 500msec (the vehicle body acceleration is not large enough).
Calculated by the following formula (1) based on the change of the vehicle speed Vr between ec (in this example, the faster wheel speed of the front wheels 2FL and 2FR, unit: km / h), and 500 msec elapses. After that (the vehicle body acceleration is sufficiently developed), it is obtained by the following equation (2) based on the change of the vehicle body speed Vr for every 500 msec every 100 msec.

-(1) Formula-VG = Gk1 × {Vr (k) -Vr (k-100)}-(2) Formula-VG = Gk2 × {Vr (k) -Vr (k-500)} Gk1 and Gk2 are coefficients. Also, Vr (k) is present, Vr (k-100) is 100 msec ago, and Vr (k-500) is 50
Each vehicle speed is 0 msec before.

Then, from the vehicle body acceleration VG and the vehicle body speed Vr calculated as described above, the road surface friction coefficient μ is obtained by three-dimensional interpolation according to the following Table 1.

[0045]

[Table 1]

(Regarding Slip Judgment Means 75) The slip judgment by the slip judgment means 75 is performed by detecting the slip amount detected by the slip detection means 72 and the thresholds SET and SB.
It is performed by comparison with T. That is, when the detected slip amount is greater than SET, it is determined that engine control is required, the engine control flag ECFL is set to 1, and when the detected slip amount is greater than SBT, it is determined that brake control is required.

(Regarding the control amount calculation means 76) The control amount calculation means 76 calculates the control amount based on the difference between the detected slip amount and the threshold values SET and SBT. That is, the target throttle opening degree (opening degree of the sub-throttle valve 45) TH · S necessary for setting the threshold value SET is, for example, PI.
-The braking force Pn (valves 32, 34, 36A, 36B, which is determined by PD control and is required to achieve the threshold value SBT,
Alternatively, the operation amount of 37A and 37B = duty ratio) is determined by the I-PD control, for example.

-Details of Slip Control-SBT> SE during normal times when the above threshold value correction is not applied.
T. FIG. 6 shows the contents of the slip control by the slip control means 70 in that case, focusing on the engine control and the brake control.

[0049] Until time point t ₁ before, a large slip on the drive wheels has not occurred, the engine control is not performed, thus the sub-throttle valve 45 is a full open throttle opening Tn (both the throttle valve 43 , 45, which is the combined opening of the throttle valve, which corresponds to the opening of the throttle valve with the smaller opening) is the main throttle opening TH · M corresponding to the accelerator depression amount.

At time t ₁ , the slip amount of the driving wheels is S
It is when a large slip occurs that is ET. In this state, the accelerator pedal 42 is depressed, and slip control is started unless the depression is released or the brake pedal 25 is depressed. Then, at this time t ₁ , the throttle opening is reduced to the lower limit control value SM at once (feedforward control). And once SM
After that, the opening degree of the sub-throttle valve 45 is feedback-controlled so that the slip amount of the driving wheels becomes SET. At this time, the throttle opening Tn becomes the sub-throttle valve opening TH · S.

At time t ₂ , the slip amount of the drive wheels is equal to SB.
When it becomes equal to or more than T, at this time, the brake fluid pressure is supplied to the brakes 21RL and 21RR of the drive wheels, and the slip control is started by both the engine control and the brake control. The brake fluid pressure is feedback-controlled so that the slip amount of the drive wheels becomes SBT. t
_{At the 3rd} time point, the slip amount of the drive wheels becomes less than SBT, whereby the brake fluid pressure is gradually reduced, and eventually the brake fluid pressure becomes zero. However, engine control is still continued.

However, when the vehicle is started in the steered state, the threshold value is corrected and SBT> SET. FIG. 7 shows the content of the slip control by the control means 70 in that case.

That is, of the two drive wheels, the turning inner wheel has a larger slip amount than the turning outer wheel.
The turning inner wheel crosses the SBT modified to a value lower than SET (the turning outer wheel does not cross). At this point in time, no slip more than SET has occurred, and therefore the brake control is executed only for the turning inner wheel. As a result, the slip of the turning inner wheel is suppressed and the engine output is not reduced, so it is possible to apply the driving force by directly utilizing the engine output to the turning outer wheel, which has a large grip on the road surface, and has good startability. Become. Of course, even if the slip amount of the turning outer wheel becomes large and the brake control is executed for this outer wheel, the execution of the engine control is delayed, which is advantageous in terms of improving the startability.

The slip amount of the turning inner wheel is set to SET.
If the value exceeds a large value, the engine control is started, the correction of the threshold value is canceled, and the normal slip control is started.

The engine control may be executed by the retard control of the ignition timing or the fuel cut control instead of the sub-throttle valve.

[Brief description of drawings]

The drawings show embodiments of the invention.

FIG. 1 is an overall configuration diagram of a vehicle slip control device.

FIG. 2 is a block diagram of a control system

FIG. 3 is a circuit diagram for determining a control start threshold value.

FIG. 4 is a flowchart of threshold correction control.

FIG. 5 is a map diagram for setting a lower limit limit value SM.

FIG. 6 is a time chart diagram of slip control without threshold correction.

FIG. 7 is a time chart diagram of slip control when the threshold value is corrected.

[Explanation of symbols]

2RL, 2RR drive wheels 63 vehicle speed sensor 66FR-66RL Wheel speed sensor 67 Accelerator sensor 69 Rudder angle sensor 70 Slip control means 72 Slip detection means 73 Threshold (target slip amount) setting means 74 Road surface friction coefficient calculation means 75 Slip determination means 76 Control amount calculation means 77 Threshold correction means

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

Claims (3)

[Claims] 1. An engine output adjusting means for adjusting an engine output, and a braking force adjusting means for separately adjusting the braking force applied to each of the left and right driving wheels and adjusting the braking force applied to each of the driving wheels. In a vehicle slip control device configured to perform engine control by the engine output adjusting means and independent brake control by each driving wheel by each brake force adjusting means so that the slip amount for the target slip amount becomes A slip amount threshold value for starting the engine control,
A slip amount threshold value for starting the brake control, a threshold value setting means for setting the threshold value for the brake control to be higher than the threshold value for starting the engine control, and a vehicle speed for detecting the speed of the vehicle. A detection means, a steering angle detection means for detecting a steering angle of the steering wheel of the vehicle, a vehicle speed detected by the vehicle speed detection means is a predetermined value or less, and a steering angle detected by the steering angle detection means is a predetermined value or more. And a threshold correction means for correcting the brake control start threshold set by the threshold setting means to be lower than the engine control start threshold set by the threshold setting means. Slip control device for a vehicle. 2. The slip control device for a vehicle according to claim 1, wherein the differential device for the vehicle does not include a differential limiting mechanism. 3. An accelerator pedal depression amount detecting means for detecting the depression amount of an accelerator pedal, wherein the threshold value correcting means has a condition that the vehicle speed detected by the vehicle speed detecting means is a predetermined value or less, and the steering angle detecting means. When both the condition that the detected steering angle is equal to or greater than a predetermined value and the condition that the accelerator depression amount detected by the accelerator depression amount detection means are equal to or greater than a predetermined value are satisfied, the brake control set by the threshold setting means is performed. The vehicle slip control device according to claim 1, wherein the starting threshold value is modified to be lower than the engine control starting threshold value set by the threshold value setting means.