JPH058666A - Slip control device - Google Patents

Abstract

PURPOSE:To perform slip control more excellently by optimizing control gains for setting the controlled gain of slip control in response to the running condition of a vehicle. CONSTITUTION:Torque to be imparted to each driving wheel is controlled so that the actual slip value of each front driving wheel 1FR and 1FL coincides with a target value for an engine or the target value of brake control. In the case of engine control, a regulating means 9 for torque generated by the engine 2 is controlled by means of feed-back operations. In the case of brake control, braking fluid pressure is built up within a master cylinder 8 with a brake booster 11 forcibly operated, so that fluid pressure adjusting values 15R and 15L are thereby controlled by the aforesaid pressure. Control gains GV for setting the controlled variable of engine control or brake control are changed in response to the running condition of a vehicle. The control gains are used when the controlled variable for the present time are found, for example, by the following equation: controlled variable for the present time = (control variable at the previous time + basic value X GV)/100.

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 for preventing excessive slip of driving wheels on a road surface.

[0002]

2. Description of the Related Art Various slip control devices (traction control devices) have been proposed which prevent excessive slippage of driving wheels on a road surface during acceleration of a vehicle and thereby satisfy acceleration and vehicle stability. ing.

The slip control is performed by reducing the torque applied to the drive wheels, and therefore the brake control for applying a brake force to the drive wheels and the engine for reducing the torque (output) generated by the engine. Control is performed. In both the brake control and the engine control, the feedback control is generally performed so that the actual slip value of the driving wheels on the road surface becomes a predetermined target value.

JP-A-60-128 discloses that slip control is performed by both brake control and engine control.
No. 028 and Japanese Patent Laid-Open No. 63-166649. Japanese Unexamined Patent Publication No. 60-128028 discloses that engine control is started when the rotational speed difference between the left and right drive wheels exceeds a predetermined value. JP 63-1
Japanese Patent No. 66649 discloses that only the engine control is performed when the slip value of the drive wheel is small, and both the engine control and the brake control are performed when the slip value of the drive wheel becomes large. Has been done.

At the start of the slip control, the torque applied to the drive wheels is reduced at once by a temporary feedforward control, and the amount of torque reduction applied at this time is set according to the road surface μ. Is also being done. Further, the target value for slip control control is also changed when turning.

[0006]

The control amount for slip control basically depends on the target value, but at what response speed the control amount determined according to the target value is achieved. That is, what value the control gain is set to is important for good slip control. However, conventionally, this control gain remains fixed at a certain constant value, which causes a problem in appropriately responding to various running states of the vehicle.

Therefore, an object of the present invention is to provide a vehicle slip control device in which the control gain of the slip control is set more appropriately so that a better slip control corresponding to the running state of the vehicle can be achieved. The purpose is to

[0008]

To achieve the above object, the present invention has the following configuration. That is, torque adjusting means for adjusting the torque applied to the drive wheels, slip detecting means for detecting the slip value of the drive wheels with respect to the road surface,
The slip control means controls the torque adjusting means so that the slip value detected by the slip detection means becomes a predetermined target value, the running state detecting means for detecting the running state of the vehicle, and the running state detecting means. And a control gain changing unit that changes the control gain of the control amount by the slip control unit according to the detected traveling state.

[0009]

According to the present invention, the control gain is changed according to the running state of the vehicle, so that the slip control can be made more appropriate for the running state.

The running state of the vehicle can be, for example, the engine speed and the drive wheel speed change rate. In this case, it can be considered that the transmission is upshifting when the engine speed is decreasing and the rate of change of the driving wheel speed is equal to or greater than a predetermined value. It is possible to prevent the slippage of the driving wheels due to the up-convergence more quickly or in advance.

As another example of the running state of the vehicle, the vehicle speed can be set to the vehicle speed. In this case, the control gain is reduced as the vehicle speed increases. That is, when the vehicle speed increases, the vehicle body vibration increases under the brake control and the engine hunting (torque fluctuation) easily occurs under the engine control. However, by decreasing the control gain, this vibration or hunting occurs. Can be prevented or reduced.

As another example of the traveling state of the vehicle, the engine speed and the vehicle speed can be used. In this case, when the vehicle speed shows a deceleration while the engine speed is increasing, it can be considered that this deceleration is due to noise. In this case, the torque applied to the drive wheels is adjusted so as not to deteriorate the acceleration performance. Only the control gain in the decreasing direction is reduced.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 1FL is a left front wheel, 1FR is a right front wheel, 1RL is a left rear wheel, and 1RR is a right rear wheel. The engine 2 is horizontally mounted on the front of the vehicle body.
The torque generated by the clutch 3 is the clutch 3, the transmission 4, the differential gear 5
Is transmitted to the left front wheel 1FL via the left drive shaft 6L and to the right front wheel 1FR via the right drive shaft 6R. In this way, the vehicle has front wheels 1F.
L and 1FR are driving wheels, and rear wheels 1RL and 1RR are driven wheels.

Brake 7FR to 7R mounted on each wheel
R is a hydraulic disc brake.
Further, the master cylinder 8 as a source of the brake fluid pressure is generated.
Is a tandem type having two discharge ports 8a and 8b. The break pipe 13 extending from one discharge port 8a of the master cylinder 8 is branched into two in the middle,
The branch pipe 13F is connected to the left front wheel brake 7FL (the wheel cylinder mounted in the caliper), and the branch pipe 13R is connected to the right rear wheel brake 7RR.
The branch pipe 14 extending from the other discharge port 8b of the master cylinder 8 is also branched into two, the branch pipe 14F is connected to the right front wheel brake 7FR, and the branch pipe 14R is connected to the left rear wheel brake 7RL. It is connected.

Branch pipe 13 for front wheels, that is, for drive wheels
Electromagnetic hydraulic pressure adjusting valve 15L or 1 is provided on F and 14F.
5R is connected, and an electromagnetic opening / closing valve 16L or 16R is connected to the branch pipes 13R and 14R for the rear wheels. The hydraulic pressure adjusting valves 15L and 15R are the brake 7FL,
The brake fluid pressure supply from the master cylinder 8 to the 7FR and the brake fluid pressures of the brakes 7FL and 7FR are provided in the pipe 2
The mode of switching to the reservoir tanks 22L and 22R via 1L and 21R is switched. The brake liquid in the reservoir tank 21L is returned by the pump 23L to the pipe 13 via the pipe 25L to which the check valve 24L is connected. Similarly, the brake liquid in the reservoir tank 22R is pumped by the pump 23L.
By R, the check valve 24R is returned to the pipe 14 via the pipe 25R to which the check valve 24R is connected.

The stepping force on the brake pedal 12 is
It is transmitted to the master cylinder 8 via a booster or brake booster 11. This booster 11 is basically the same as a known vacuum booster, but during slip control, as will be described later, even if the brake pedal is not stepped on, a boosting operation is performed. Is configured to do.

The booster 11 has a case 31 fixed to the vehicle body and the master cylinder 8, and the inside of the case 31 is composed of a diaphragm 32 and a valve body 33 fixed thereto. A chamber 34 and a second chamber 35 are defined. Negative pressure (for example, intake negative pressure of the engine 2) is constantly supplied to the first chamber 34, and when the brake pedal is not depressed, the second chamber 35 is communicated with the first chamber 34 and -The operation of the star 11 is stopped. When the brake pedal 12 is depressed,
Atmospheric pressure is supplied to the second chamber 35, whereby the diaphragm 32 is displaced forward together with the valve body 33 to perform a boosting function.

The switching between the negative pressure supply and the atmospheric pressure supply to the second chamber 35 is basically performed by a valve device mounted inside the valve body 33. This valve body 33
The part will be described with reference to FIG.

First, the valve body 33 has a power piston 41 fixed to the diaphragm 32, and a recess 41a formed in the power piston 41 has a recess 41a formed therein. And are fitted. The output shaft 43 serves as an input shaft of the master cylinder 8. A valve plunger 45 is attached in the valve body 33 at the tip of the input shaft 44 connected to the brake pedal 12. A vacuum valve 46 is arranged behind the valve plunger 45.

The power piston 41 has a pressure introducing passage 50.
The pressure introducing passage 50 is always communicated with the space X formed around the valve plunger 45. This space X is always communicated with the second chamber 35. A valve seat 47, on which the vacuum valve 46 is seated, is formed at the end of the pressure introducing passage 50 that opens toward the space X. In addition, the vacuum valve 46 is a valve plunger 45.
The valve seat 45a formed at the rear end is also seated on and off.

In the above structure, it is assumed that a negative pressure is being introduced into the pressure introducing passage 50. In this state, when the brake pedal 12 is not depressed, the vacuum valve 46 is seated on the valve seat 45a by the urging force of the springs 48 and 49 in the state of FIG. 2, but is separated from the valve seat 47. ing. Therefore, the pressure introducing passage 5
The negative pressure from 0 is introduced into the second chamber 35 through the space X, and the boosting action is not performed.

When the brake pedal 12 is depressed,
The input shaft 44 and therefore the valve plunger 45 are moved forward (moved leftward in the figure). During this forward movement, the vacuum valve 46
Is first seated on the valve seat 47, and the space X and the pressure introducing passage 50 are
Communication with the vacuum valve 46 and then the valve seat 45
a is separated. By separating the vacuum valve 46 and the valve seat 45a, the atmospheric pressure from the rear of the valve body 33 is introduced into the space X, and the second chamber 35 becomes the atmospheric pressure. As a result, the diaphragm 32 is displaced forward together with the valve body 33, and as a result, the output shaft 43 moves forward and a boosting action is performed. The brake reaction force from the master cylinder 8 is transmitted to the valve plunger 45 and thus the brake pedal 12 via the reaction disc 42.
When the stepping operation force of the brake pedal 12 is released, the return spring 36 (see FIG. 1) returns to the state of FIG. 2 to prepare for the next boosting action.

The part described above is the same as the known vacuum booster, but in this embodiment, the negative pressure of the first chamber 34 is introduced into the pressure introducing passage 50 for slip control. The state is switched to the state where the atmospheric pressure is introduced. That is, the first chamber 34 and the pressure introducing passage 5
0 is connected via a pipe 37, and a three-way electromagnetic switching valve 38 (see FIG. 1) is connected to the pipe 37. The switching valve 38 communicates the pressure introducing passage 50 with the first chamber 34 during demagnetization, and introduces atmospheric pressure into the pressure introducing passage 50 during excitation. When the switching valve 38 is excited and atmospheric pressure is introduced into the pressure introducing passage 50, the space X, and thus the second chamber 35.
Becomes atmospheric pressure even when the brake pedal 12 is not depressed, and as a result, a boosting action is performed to generate a brake hydraulic pressure in the master cylinder 8.

FIG. 3 schematically shows a control system, in which U is a control unit constructed by using a microcomputer.
Signals from the sensors or switches S1 to S8 are input. The sensors S1 to S4 detect the rotation speeds of the wheels 1FL to 1RR. The switch S5 is an accelerator switch that is turned on when the accelerator pedal 10 is fully closed. Switches S6 and S7 are not
It is operated when the key pedal 12 is depressed, and for example, one switch is a normally open type and the other is a normally closed type. The sensor S8 detects the engine speed. Further, although the control unit U outputs to each device shown in FIG. 3, reference numeral 9 is a torque adjusting means for adjusting the torque generated by the engine 2. The torque adjusting means 9 adjusts the generated torque, for example, by adjusting the intake air amount or by combining the number of fuel cut cylinders and the ignition timing adjustment.

Next, an outline of slip control is shown in FIG.
The explanation will be made by also referring to. In FIG. 4, the left drive wheel 1
An example is shown in which the right drive wheel 1FR is not slipped and the right drive wheel 1FR is largely slipped.

Engine Control First, engine control starts with the left and right front wheels 1FL, 1FR.
Of the respective slip values, the larger slip value becomes greater than or equal to a predetermined start threshold value (t in FIG. 4).
1 time point). The engine control is performed by feedback controlling the torque adjusting means 9 so that the actual slip value becomes the engine target value (first target value) STE. The engine control is stopped when the accelerator is fully closed or when the actual slip value reaches the control continuation threshold value SC (smaller than the first target value) for a predetermined time or longer (Fig. 4 from t6 to t7).

Break Control The start of the brake control is when all of the following conditions are satisfied. The first start condition is that the engine is being controlled. The second start condition is the left and right drive wheels 1FL, 1F.
This means that the difference between the actual slip values of R has become equal to or greater than the predetermined value (t2 in FIG. 4). The third start condition is that the vehicle speed is equal to or lower than the predetermined first vehicle speed V1. The fourth start condition is that a predetermined delay time described below has elapsed.

Prior to the start of the brake control, a response delay is expected, and at the same time when the engine control is started, the switching valve 38 is started.
Is boosted, the booster 11 is put into the boosting action state, the hydraulic pressure adjusting valves 15L and 15R are in the relief position, and the opening / closing valves 16L and 16R are closed. Then, after exciting the switching valve 38, when the actual slip value shows a predetermined deceleration (the time until the predetermined deceleration is shown is the delay time, between t2 and t3 in FIG. 4). , Blur
Control is started.

For the brake control, the left and right driving wheels 1FL, 1F are used.
By independently controlling the feedback of the hydraulic pressure adjusting valves 15L and 15R so that the actual slip value becomes the brake target value (second target value) STB (> STE). Is performed (duty control).

The break control is stopped when any one of the following conditions is satisfied. The first stop condition is when the engine control is stopped. The second stop condition is when the vehicle speed becomes a high vehicle speed equal to or higher than a predetermined second vehicle speed V2 (V2> V1). The third stop condition is that the control signals for the left and right hydraulic pressure adjustment valves 15L and 15R both indicate a reduced pressure and for a predetermined time (500 mse in the embodiment).
c) It is when it continues (t4 to t5 in FIG. 4).

The fourth stop condition is the left and right brakes 7F.
This is when the brake fluid pressures of L and 7FR both become zero. The fifth stop condition is when the depression of the brake pedal 12 is detected by one of the switches S6 and S7 (the brake pedal 12 is depressed by the switches S6 and S7). If that is detected, the start of the brake control is prohibited).

When the brake control is stopped, the switching valve 38 is operated as long as the engine control is performed, the hydraulic pressure adjusting valves 15L and 15R are in the relief position, and the opening / closing valve 1 is opened.
6L and 16R are closed (the same state as the standby state until the start of the brake control). The switching valve 38 is demagnetized when the engine control is stopped or when the brake pedal 12 is depressed.

Next, a control example of the present invention will be described with reference to the flow charts of FIG. 5 and subsequent figures. In the following description, P indicates a step. FIG. 5 shows the overall flow. First, at P1, signals from respective sensors are input, and then at P2, the rotational speeds WSRL and WSRR of the left and right drive wheels 1FL, 1FR are averaged, The vehicle speed VS is calculated.

At P3, the first target value STE for engine control and the second target value STB for brake control are determined in a known manner (STB> STE). In P4,
The slip value SFL of the left driving wheel 1FL is the rotational speed W
It is calculated by subtracting the vehicle speed VS from SFL, and similarly, the slip value SFR of the right drive wheel 1FR is calculated by subtracting the vehicle speed VS from its rotation speed WSFR.

In the processes of P5 to P7, the larger slip value of the slip values SFL and SFR of the left and right drive wheels is set as the slip value SA for engine control. In P8, it is determined whether or not the slip flag is currently 1, and when the slip flag is 1, it means that the slip control is being performed (at least the engine control is being performed). When the determination in P8 is NO, after the start determination of engine control, which will be described later, is made in P9,
At 0, the end determination described later is made.

When the determination in P8 is YES, the engine control is performed in P11, and then in P12.
It is determined whether or not the break flag is 1, and when the break flag is 1, it means that the break control is in progress. When the determination in P12 is NO, after the brake start determination described below is performed in P13, the determination in P10 is performed.
Move to. If the determination in P12 is YES, P
After the brake control is performed at 14, the process proceeds to P10.

FIG. 6 shows the contents of P9 in FIG. First,
At P21, the actual slip value SA for the engine
Is greater than or equal to a predetermined value indicating a predetermined start threshold value. If the determination in P21 is NO, it means that the slip control is unnecessary, and therefore the routine is returned to P1 as it is. When the determination in P21 is YES, the slip flag is set to 1 in P22, the engine control is started in P23, and the brake control start is prepared in P24. Specifically, in the preparation at P24, the switching valve 38 is excited to move the master cylinder 8 to the brake.
To generate hydraulic pressure, and to adjust the hydraulic pressure adjustment valves 15L, 1
Setting 5R to the relief position and opening / closing valves 16L and 16
To close R.

FIG. 7 shows the contents of P13 in FIG. First, at P31, it is judged if the vehicle speed VS is equal to or lower than the first vehicle speed V1. If YES in the determination in P31, the rotational speed difference DNL between the left and right drive wheels 1FL and 1FR is calculated in P32, and then in P33.
It is determined whether this difference DNL is greater than or equal to a predetermined value.
If YES in the determination in P33, in P34,
It is determined whether or not a predetermined delay time has elapsed since the above difference occurred (t2 to t3 in FIG. 4). If the determination in P34 is YES, the brake flag is set to 1 in P35, and then in P36, the hydraulic pressure adjusting valve 15L,
The brake control is started by controlling 15R. NO if the name is P31, P33, or P34
In case of, it ends as it is.

FIG. 8 shows the contents of P10 in FIG. First, in P41, it is determined whether or not the accelerator is fully closed. When the determination in P41 is YES, P42
At S43, after the slip control, that is, the engine control and the brake control are both stopped, each flag is reset to 0 at P43.

If NO in P41, it is determined in P45 whether the actual engine control slip value SA is less than or equal to the end threshold SC. This P45
If the determination is YES, it is determined in P46 whether or not the state in which SA is equal to or less than the termination threshold SC continues for 1000 msec. YES in the determination of P46
In the case of, it shifts to P42 and the slip control is stopped.

When the determination in P45 or P46 is NO, it is determined in P47 whether the vehicle speed VS is equal to or higher than the second vehicle speed V2. When the determination in P47 is YES, it is determined again in P48. The brake control is stopped while gradually reducing the brake fluid pressure to prevent slippage, and then the brake flag is reset to 0 at P49. The break control is gradually stopped by reducing the pressure reducing signal to the hydraulic pressure adjusting valves 15L and 15R at predetermined time intervals, but the degree of pressure reduction at each time becomes large. Restrictions are added to prevent it from passing.

When the determination in P47 is NO, it is determined in P50 whether or not the brake hydraulic pressures of the left and right drive wheel brakes 7FL and 7FR have both become zero. This P50
If the determination is YES, the brake control is stopped in P51 and then the process proceeds to P49. The estimation of the brake fluid pressure can be indirectly obtained by various methods already proposed, but a sensor for directly detecting the brake fluid pressure can be used.

When the determination in P50 is NO, it is determined in P52 whether or not the control signals to the hydraulic pressure adjusting valves 15L and 15R both indicate a reduction in pressure.
If the determination is YES, it is determined whether or not the state where both the pressure reduction signals are 0 continues for 500 msec. If the determination in P53 is YES, the brake control is stopped in P51. When the determination in P52 or P53 is NO, the process ends as it is (continuation of engine control and brake control).

Here, the break switch S6 or S
On the other hand, when it is detected that the brake pedal 12 is depressed, the brake control is forcibly stopped by the interrupt process for the flow chart.

FIG. 9 shows a flow chart for changing the control gain. In the present embodiment, the basic value determined by the feedback control formula so as to be the target value SBT or SET for the brake control or the engine control is controlled by using the following formula (1). The quantity is calculated, and GV in the equation (1) represents a control gain. Current control amount = {previous control amount + basic value x GV} / 100 (1)

As is apparent from the equation (1), the larger the control gain GV, the more the target value SBT or SET.
The response speed until the controlled variable corresponds to is increased. However, the control gain GV has a positive value when decreasing the torque applied to the drive wheels and a negative value when increasing the torque applied to the drive wheels. Of course, the control gain itself in the feedback control formula may be changed (for example, the response speed becomes faster as the proportional coefficient or the differential coefficient as the control gain is increased).

Based on the above, first, at P61, the correction coefficient K1 according to the vehicle speed is determined with reference to the map shown in FIG. The correction coefficient K1 is set to decrease as the vehicle speed increases. P2
Then, the control gain GV is calculated by multiplying the basic control gain GVB by the correction coefficient K1. In this way, the control gain GV is basically set to decrease as the vehicle speed increases.

At P64, it is judged if the engine speed has decreased. If the determination in P65 is YES, in P65, the dVWD of the drive wheel speed is the predetermined value α.
It is determined whether or not it is larger. Y is determined by P66.
In the case of ES, the control gain GV determined in P62 is changed to a large value, and then the process proceeds to P67. Also, P6
If NO in 4 or P65, the process proceeds to P67 without passing through P66. The process of P64 to P66 is a process of promptly converging the slip of the drive wheels that is likely to occur at the time of upshifting. The degree of increasing the control gain GV in P66 is set to be larger, for example, as the dVWD is larger or the degree of decrease in the engine speed is larger, or is larger than the control gain GV determined in P62 by a predetermined ratio. It can also be set as an increased certain value.

At P67, it is judged if the engine speed is increasing. When the determination in P67 is YES, it is determined in P68 whether the vehicle speed, that is, the driven wheel speed, is decreasing. YES in P68
In this case, at P69, it is judged if the control gain is negative, that is, if the torque applied to the drive wheels is increased. If YES in the determination in P69,
At P70, the negative control gain GV is reduced. The processing of P67 to P70 is processing for ensuring sufficient acceleration of the vehicle without unnecessarily reducing the torque applied to the drive wheels due to noise or the like. P
The degree of decreasing the control gain GV at 70 is, for example, P
It may be set to be smaller as the degree of decrease in vehicle speed at P68 with respect to the degree of increase in engine speed at 67 is smaller, or may be set as a constant value that is smaller than the control gain GV determined at P62 by a predetermined ratio. P
If NO in any of 67, P68 and P69, the routine returns without passing through P70.

Although the embodiments have been described above, the slip value is calculated not as the difference between the driving wheel and the driven wheel but as a ratio, for example, as the driving wheel speed / driven wheel speed, or (driving wheel speed-driven wheel speed). ) / Driven wheel speed can also be shown.
In addition, the brake hydraulic pressure for controlling the brake is the booster 11
Alternatively, the pump may be separately generated by using a dedicated pump. Further, the running state of the vehicle as a parameter for changing the control gain can be set in various ways other than that shown in the embodiment. Furthermore, the slip control may be performed only by the engine control or only the brake control.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an example of a vehicle to which the present invention is applied.

FIG. 2 is a cross-sectional view showing a main part of a brake booster.

FIG. 3 is a diagram showing a relationship between inputs and outputs to a control unit.

FIG. 4 is a time chart schematically showing a control example of the present invention.

FIG. 5 is a flowchart showing a control example of the present invention.

FIG. 6 is a flow chart showing a control example of the present invention.

FIG. 7 is a flowchart showing a control example of the present invention.

FIG. 8 is a flowchart showing a control example of the present invention.

FIG. 9 is a flowchart showing a control example of the present invention.

FIG. 10 is a diagram showing a correction coefficient of a control gain according to a vehicle speed.

[Explanation of symbols]

1FL, 1FR Front wheels (driving wheels) 1RL, 1RR Rear wheel (driven wheel) 2 engine 7FL-7RR Break 8 master cylinder 9 Torque adjusting means 11 Break Buster (Booster) 12 brake pedal 15L, 15R Liquid pressure adjusting valve 16L, 16R open / close valve 38 Switching valve (negative pressure supply, atmospheric pressure supply switching) U control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location F02D 45/00 330 8109-3G 345 G 8109-3G (72) Inventor Hiroaki Sakamoto Fuchu, Aki-gun, Hiroshima Prefecture No. 3 Shinmachi, Mazda Co., Ltd.

Claims (4)

[Claims] 1. A torque adjusting means for adjusting a torque applied to a driving wheel, a slip detecting means for detecting a slip value of a driving wheel with respect to a road surface, and a slip value detected by the slip detecting means is a predetermined target value. According to the traveling state detected by the traveling state detecting means for detecting the traveling state of the vehicle, the slip control means for controlling the torque adjusting means,
A slip control device for a vehicle, comprising: a control gain changing unit that changes a control gain of a control amount by the slip control unit. 2. The driving state detecting means according to claim 1, wherein the running state detecting means detects an engine speed and a drive wheel speed change rate, and the control gain changing means drives the engine when the engine speed is lowered. A control gain is increased when the rate of change in wheel speed is equal to or greater than a predetermined value. 3. The driving state detecting means according to claim 1, wherein the traveling state detecting means detects the vehicle speed, and the control gain changing means reduces the control gain when the vehicle speed is high compared to when the vehicle speed is low. 4. The driving state detecting means according to claim 1, wherein the engine speed and the vehicle speed are detected, and the control gain changing means indicates that the engine speed is increasing and the vehicle speed is decelerating. At times, only the control gain in the direction of reducing the torque applied to the drive wheels is reduced.