JPH08230647A - Driving state detector of four-wheel driven vehicle - Google Patents

Abstract

PURPOSE: To secure reliability and reduce the cost of a driving state detector by judging presence of a two-wheel driven state when the detected results of No.1 and No.2 wheel speed difference detection means simultaneously satisfy respective detection conditions and judging presence of a four-wheel driven state in other cases. CONSTITUTION: An anti-skid control circuit 53 controls actuators 33FL to 33R for controlling the pressure supplied to the wheel cylinder provided to each wheel on the basis of wheel speeds VWFL to VWR and an estimated vehicle body speed VX. When such a state continues for more than specific hours as a rear wheel speed VWR under the reverse phase of the front two wheels is larger than front two wheel speeds VWFL, VWFR and the rear wheel speed VWR under the synchronized state of the front two wheels is not smaller than the front two wheel speeds VWFL, VWFR, the presence of two-wheel driven state is determined. Also when the front left wheel speed VWFL in negative value is known from the rear wheel speed VWR, presence of four-wheel driven state is judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a wheel speed detecting means for detecting the wheel speed of at least the front two wheels and the wheels to be controlled on the side of the rear wheels while having a transfer capable of selecting a two-wheel drive state and a four-wheel drive state. The present invention relates to a four-wheel drive vehicle equipped with an anti-skid control device having a braking pressure control means for individually controlling the braking pressure of a braking cylinder provided on the control target wheel based on a detected wheel speed value, and particularly to a two-wheel drive vehicle. The present invention relates to a drive state detection device for a four-wheel drive vehicle that can determine the state and the four-wheel drive state without using a separate detection element.

[0002]

2. Description of the Related Art As a four-wheel drive vehicle having a conventional anti-skid control device, for example, Japanese Patent Laid-Open No. 4-163264 is known.
Some are described in Japanese Patent Publication. In this conventional example,
In the two-wheel drive state (2WD) in which the driving force of the engine is transmitted to the front wheels or the rear wheels, the driving force of the engine is transmitted to the left and right front wheels via the transmission, the front differential and the front wheel drive shaft, and the left and right rear wheels. To the rigid four-wheel drive state (4W, which is transmitted through the transmission, the center differential, the propeller shaft, the rear differential, and the rear wheel drive shaft).
D) and 4WD select switches are selectable, and when the 2WD state is detected, the brake pressures of the left and right front wheels and both rear wheels are independently controlled when the anti-skid control is started. However, when the 4WD state is detected, if the anti-skid control is started, the front wheel side drive system and the rear wheel side drive system are connected, and the braking force on the front wheel side and the rear wheel side are controlled independently. If so, the torsional torque in the drive system may increase, and the wheel speeds of the front and rear wheels may oscillate.For example, the right rear wheel may tend to lock and the left and right wheels may move in accordance with the so-called select low principle. When the brake pressure of the rear wheels is also reduced, the brake pressure of the right front wheel on the same side as the right rear wheel is also reduced by a predetermined pressure at the same time, so that the brake pressure reduction control is performed on the front wheel side and the rear wheel side. Substantially in phase Anti-skid control apparatus is disclosed which is adapted to effectively suppress the vibration of the wheel speeds.

[0003]

However, in the four-wheel drive vehicle having the above-described conventional anti-skid control device, different anti-skid control is performed in the two-wheel drive state and the four-wheel drive state. Therefore, it is necessary to determine whether the drive system is in the two-wheel drive state or the four-wheel drive state during the anti-skid control. For this purpose, it is conceivable to use the switch signal of the 4WD select switch described above. In this case, the 4WD select switch only commands switching between 2WD and 4WD, and does not detect the actual driving state, so the transfer actually switches from 2WD to 4WD or vice versa. To detect this, it is necessary to separately detect the engaged state of the free running wheel and the state of the switching mechanism in the transfer. In addition to the need for a switch capable of detecting such a driving state and the detection signal thereof, the reliability of the component is not only ensured but also hardware such as addition of an element for detecting a defect of the component is required. It is necessary to add fail-safe logic after changing the software or detecting a failure,
There is an unsolved problem that the reliability decreases as the number of parts increases and the cost increases.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and accurately detects the two-wheel drive state and the four-wheel drive state without providing a separate detection switch to improve reliability. It is an object of the present invention to provide a drive state detection device for a four-wheel drive vehicle, which can secure the above-mentioned characteristics and reduce the cost.

[0005]

In order to achieve the above object, a drive state detecting device for a four-wheel drive vehicle according to a first aspect of the present invention comprises:
As shown in the basic configuration diagram of FIG. 1, a wheel speed detection unit that has a transfer that can select a two-wheel drive state and a four-wheel drive state and that detects the wheel speeds of at least the front two wheels and the wheels to be controlled on the rear wheel side. A four-wheel drive vehicle having an anti-skid control device having a braking pressure control means for individually controlling the braking pressure of the braking cylinders provided on the control target wheels based on the detected wheel speed value of the rear wheel side. First wheel speed difference detecting means for detecting that the wheel speed detection value of the front wheel exceeds the wheel speed detection value of the front two wheels, and the wheel speed detection value of the rear wheel side is the wheel speed detection value of the front two wheels. When the detection results of the second wheel speed difference detecting means and the first and second wheel speed difference detecting means for detecting that the state in which the temperature does not fall below a predetermined time continues for a predetermined time or more, simultaneously satisfy the respective detection conditions. It is judged that it is in a two-wheel drive state It is characterized in that a driving state determining means for determining that the four-wheel drive state when the other.

According to a second aspect of the present invention, there is provided a drive state detecting device for a four-wheel drive vehicle according to the first aspect, wherein the anti-skid control device is arranged to relax the rear wheels when the four-wheel drive state is detected. A feature is that the pressure increase suppression process is performed, and when the two-wheel drive state is detected, the slow pressure increase suppression process is canceled.

[0007]

In the invention according to claim 1, when the vehicle is in the four-wheel drive state, particularly in the direct-coupled four-wheel drive state, the front and rear wheels are in a dependent relationship, and the left and right phases are opposite phases on the front wheel side. Is symmetrical, but on the rear wheel side, the front wheels are in a reverse phase state, which is the average value of the front wheels, or due to backlash of the transfer, the two front wheels vibrate synchronously around the rear wheel speed when the wheel rotation direction resonates. The front wheels are in a synchronized state, or the left and right phases are opposite phases on the front wheel side and the acceleration / deceleration state is symmetrical, but on the rear wheels side, the front wheels are in a reverse phase state that is an average value of the front wheels. Therefore, during the anti-skid control, when the first wheel speed difference detection means detects that the wheel speed detection value of the rear wheels exceeds the wheel speed detection value of the two front wheels, the front wheel reverse operation in the four-wheel drive state is performed. When the second wheel speed difference detection means indicates that the wheel speed detection value of the rear wheel is not lower than the wheel detection value of the front two wheels for a predetermined time or more, the four wheels are not in phase. This indicates that the vehicle is not in the front wheel synchronization state in the drive state, and as a result, it can be determined that the vehicle is in the two-wheel drive state, and in other states it can be determined that it is the four-wheel drive state.

According to the second aspect of the present invention, when the anti-skid control device detects the four-wheel drive condition, the rear wheel slow pressure increase suppression processing is executed so that the braking force on the rear wheel side is applied to the front wheel side. In addition to preventing the influence, in the two-wheel drive state, the opportunity of gradually increasing the pressure of the rear wheels is increased to reduce the braking distance.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an engine as a rotary drive source, 2FL, 2
FR is a front wheel, 2RL, 2RR is a rear wheel, 3 is a drive force transmission system capable of changing the drive force distribution ratio to the wheels 2FL to 2RR, and 4FL to 4RR are braking cylinders mounted on the wheels 2FL to 2RR. It is a wheel cylinder.

The driving force transmission system 3 changes the driving force from the engine 1 at a selected gear ratio, and the driving force from the transmission 5 to the front wheels 2FL, 2FR and the rear wheels (normal drive). The wheel 6 has a transfer 6 that is divided into 2RL and 2RR sides. Then, in the driving force transmission system 3, the front wheel driving force divided by the transfer 6 is transmitted to the front wheels 2FL and 2FR via the front wheel side output shaft 7, the front differential gear 8 and the front wheel side drive shaft 9, while the rear wheels are The side driving force is transmitted through the propeller shaft 10, the rear differential gear 11 and the rear wheel side drive shaft 12 to the rear wheel 2R.
It is transmitted to L and 2RR.

The transfer 6 is connected to an input shaft 15 connected to the output shaft of the transmission 5, a main gear 16 connected to the input shaft 15, and a propeller shaft 10, as shown in the schematic structure of FIG. A rear wheel output shaft 17, a low gear 20 connected to the main gear 16 via a counter gear 18 and rotatably arranged around the rear wheel output shaft 17 via a bearing 19, and a rear wheel output shaft. L- for selectively connecting the input shaft 15 and the low gear 20 with respect to 17
The H coupling sleeve 21, a front wheel drive sprocket 23 rotatably arranged around the rear wheel output shaft 17 via a bearing 22, and a sprocket 25 formed on the front wheel output shaft 24 are stretched. The drive chain 26 is provided, and the 2-4 coupling sleeve 27 that connects and disconnects the front wheel side drive sprocket 23 and the rear wheel side output shaft 17 is provided.

Then, the L-H coupling sleeve 21
And the 2-4 coupling sleeve 27 are shifted by shifting a transfer shift lever 28 (see FIG. 1) provided near the driver's seat. That is, by selecting the 2H position with the transfer shift lever 28, the L-H coupling sleeve 21 directly connects the input shaft 15 and the rear wheel side output shaft 17, and
-4 The coupling sleeve 27 comes to a position where it is separated from the front wheel side drive sprocket 23, and only the rear wheels are driven into a two-wheel drive state. By selecting the 4H position, the L-H coupling sleeve 21 remains as it is.
Only the 4-coupling sleeve 27 is connected to the front-wheel-side drive sprocket 23 for high-speed four-wheel drive, and N
By selecting the position, the 2-4 coupling sleeve 27 is left as it is, the L-H coupling sleeve 21 is in a neutral state in which it is separated from both the input shaft 15 and the low gear 20, and by selecting the 4L position,
With the 2-4 coupling sleeve 27 as it is, the rear wheel side output shaft 17 and the low gear 20 are connected by the LH coupling sleeve 21 to establish a low-speed four-wheel drive state.

On the other hand, front wheel cylinders 4FL, 4FR
The master cylinder pressure from the master cylinder 32 that generates the master cylinder pressure of the two systems on the front wheel side and the rear wheel side in response to the depression of the brake pedal 31 is individually supplied to the front wheel actuators 33FL and 33FR. With
The master cylinder pressure from the master cylinder 32 is supplied to the rear wheel side wheel cylinders 4RL and 4RR through a common rear wheel side actuator 33R, and as a whole, three sensors 3 are provided.
Configured into a channel system.

As shown in FIG. 4, each of the actuators 33FL to 33R includes a hydraulic pipe 34 connected to the master cylinder 32, and an electromagnetic inflow valve 35 interposed between the wheel cylinders 4FL to 4RR, and an electromagnetic inflow valve 35. A series circuit of an electromagnetic outflow valve 36, a hydraulic pump 37 and a check valve 38 connected in parallel with the electromagnetic inflow valve 35, and an accumulator 39 connected to a hydraulic pipe between the electromagnetic outflow valve 36 and the hydraulic pump 37. The electromagnetic inflow valve 35, the electromagnetic outflow valve 36, and the hydraulic pump 37 of each actuator 33FL to 33R are
It is controlled by the braking pressure control signals EV, AV and MR from the controller 40.

The controller 40 includes wheel speed pulse signals P _FL and P _FR corresponding to the wheel speeds of the front wheels 2FL and 2FR.
Front wheel side wheel speed sensors 41FL and 41FR, rear wheel side wheel speed sensors 41R that output the wheel speeds of the rear wheels 2RL and 2RR as a wheel speed pulse signal P _R according to the rotation speed of the propeller shaft 10, and the vehicle body. Longitudinal acceleration sensor 42 for detecting the longitudinal acceleration of the vehicle and wheel speed sensors 41FL, 41
Braking pressure control signals EV, AV and MR are output to the actuators 33FL to 33R based on the detection signals of the FR and 41R and the longitudinal acceleration sensor 42.

That is, the controller 40 is shown in FIG.
The wheel speed sensors 41FL to 41R.
Loose signal P_FL~ P_RIs input, and these and each wheel 2FL ~
2w radius of gyration and wheel peripheral speed (wheel speed) Vw_FL
~ Vw_RWheel speed calculation circuits 44FL to 44R for calculating
Wheel speed Vw of wheel speed calculation circuits 44FL to 44R_FL~ Vw _R
And the longitudinal acceleration X of the longitudinal acceleration sensor 42_GOn the basis of
Anti-skip for controlling actuators 33FL-33R
The control unit 46 is provided.

The anti-skid control unit 46 selects the highest wheel speed (select high wheel speed) Vw _H of the wheel speeds Vw _{FL to} Vw _R of the wheel speed calculation circuits 44FL to 44R, and the select high switch 51. The select high wheel speed Vw _H selected by the select high switch 51 and the longitudinal acceleration detection value X _{G of the} longitudinal acceleration sensor 42 are input, and the estimated vehicle body speed V _X corresponding to the actual vehicle body speed is calculated based on these. Estimated vehicle speed calculation circuit 52, estimated vehicle speed V _X output from this estimated vehicle speed calculation circuit 52, and wheel speed Vw of wheel speed calculation circuits 44FL to 44R.
Actuators 33FL to 33R based on _{FL to} Vw _R
And an anti-skid control circuit 53 as a braking pressure control means for controlling.

The estimated vehicle speed calculation circuit 52 is shown in FIG.
As shown in 6, selected by the select high switch 51
Select high wheel speed Vw_HWheel speed sampling value V
_SSample hold circuit 52a for holding
The longitudinal acceleration detection value X of the acceleration sensor 42_GAbsolute value circuit
52b converts it to an absolute value, and the offset value output circuit 52
Add an offset value corresponding to, for example, 0.3 G from c
The longitudinal acceleration correction value X is added by the calculation circuit 52d._GCOutput
Sensor output correction circuit 52e and an operational amplifier
An integrating circuit 52f that integrates the input voltage E, and this integrating circuit
52f integral output V_eOf the sample and hold circuit 52a
Wheel speed sampling value V_SEstimated vehicle speed V by adding and
_X52g for calculating V and the select high wheel speed V
w_HIs the estimated vehicle speed V_XThe preset
Within the band width, that is, V_X-1km / h <Vw _H<V_X+ 1km / h
Whether or not_X-1km / h <Vw_H<V_X+ 1km
Output C when / h₁And C₂Are both low level,
Vw_H≧ V_XOutput C when + 1km / h₁High level
And then Vw_H≤V_XOutput C when -1km / h ₂To
The dead zone detection circuit 52h for setting the high level and the dead zone detection
Select high wheel speed Vw at output circuit 52h_HIn the dead zone
And the ON signal IG of the ignition switch
Is input to the sample and hold circuit 52a.
Select high wheel speed Vw_HHold and integrate
A reset circuit 52i for resetting the circuit 52f and a selector
Kutohai wheel speed Vw_HAnd within the dead band width
Set with the off-delay timer 52j after the band is out of band
Predetermined time T₃Product of zero voltage as integrated input voltage E
Vw is supplied to the branch circuit 52f._H> V_X+ 1km / h
From the predetermined time T₃+ During non-anti-skid control after
Negative voltage corresponding to 0.4G is under anti-skid control
Is the negative input voltage corresponding to + 10G
It is supplied to the integrating circuit 52f as E, and further Vw_H<V_X
Predetermined time T after reaching -1km / h₃Sensor output after elapse
Longitudinal acceleration correction value X of the correction circuit 52e_GCIntegrated input voltage
The selection circuit 52k supplied to the integration circuit 52f as E is
Have.

The anti-skid control circuit 53 controls the wheel speed V
Each wheel 2F based on w _{FL to} Vw _R and estimated vehicle speed V _X
The actuators 33FL to 33R for controlling the supply pressure to the wheel cylinders 4FL to 4RR provided in L to 2RR are controlled, and are configured by, for example, a microcomputer, and execute the braking force control process shown in FIGS. 7 and 8. . As shown in FIG. 7, the braking force control process is executed as a timer interrupt process for a predetermined time, for example, every 10 msec. First, in step S1, an anti-skid control process for the actuator 33FL of the front left wheel 2FL is executed, and then in step S
2, the anti-skid control process for the actuator 33FR of the front right wheel 2FR is executed, and then step S
3, the rear wheel wheel speed Vw _{R (N)} is read, then the process proceeds to step S4, and whether the anti-skid control flag AS is set to "1" in the rear wheel side braking pressure control process described later. If AS = 0, it is determined that the anti-skid control is not started, the process proceeds to step S5, the drive state flag F _2WD is set to "1", and the drive state determination process described later is performed. After resetting the timekeeping state flag F1 to "0", step S described later
The process proceeds to the rear wheel side braking pressure control process 10 and when AS = 1, the process proceeds to step S6.

In step S6, the wheel speed V of the rear wheels is
w _R and the two front wheels of the wheel speed Vw _FL, Vw is compared with the _FR, the rear wheels of the wheel speed Vw _R is the wheel speed Vw _FL of the two front wheels, Vw _FR
And the wheel speed Vw _R of the rear wheels is not lower than the wheel speeds Vw _FL, Vw _FR of the front two wheels for a predetermined time (for example, 350 msec) or more. It is determined whether the vehicle is in the four-wheel drive state.

Here, the reason why the four-wheel drive state and the two-wheel drive state can be discriminated by the fluctuation of the rear wheel acceleration / deceleration Vw _R ′ is as follows. That is, in the two-wheel drive state, as will be described later, when the condition for slowly increasing the pressure on the rear wheel side is limited when both the front wheels 2FL and 2RR are in the pressure increasing state, a frozen road, a snow road, a rain road, etc. As shown in FIG. 11, the front wheels 2FL and 2FR are in a state of being out of phase on the left and right sides due to the friction of the front differential gear 8 while traveling on the low friction coefficient road of
Both are less likely to be in a pressure-increased state, and as a result, the pressure increase state on the rear wheel side cannot be obtained and wheel slip does not occur.Therefore, the rear wheel acceleration / deceleration does not exceed the vehicle deceleration. Instead, the movement is slow with little fluctuation.

On the other hand, in the direct drive four-wheel drive state, the front and rear wheels are both
Are free to move freely in a subordinate relationship
Instead, as shown in FIG.
Degree Vw _FL, Vw_FROf the rear wheel
Wheel speed Vw_RIs the wheel speed Vw of the front wheels_FL, Vw_FRAverage value of
The front two wheels will be in the reverse phase state, as shown in Fig. 12 (b).
As the backlash of the transfer causes resonance in the wheel rotation direction,
Rear wheel speed Vw when it occurs_RFront two wheels centering on
Speed Vw_FLAnd Vw_FRFront two-wheel synchronous condition
It becomes a state.

Therefore, the rear wheel speed Vw _{R under the} condition that cannot be the four-wheel drive condition, that is, the front two-wheel reverse phase condition is larger than the front two wheel speeds Vw _FL, Vw _FR , and in the front two-wheel synchronous condition. The rear wheel speed Vw _R is the front two wheel speed Vw
It is possible to determine that the vehicle is in the two-wheel drive state when the state of not falling below _FL, Vw _FR continues for a predetermined time or longer.

That is, in the drive state determination process of step S6, as shown in FIG. 8, first, in step S6a, the speed difference obtained by subtracting the wheel speed Vw _FL of the front left wheel 2FL from the rear wheel wheel speed Vw _R includes a positive value. , Vw _R −VW
_{When FL} <0, it is determined that the vehicle is in the four-wheel drive state, the process proceeds to step S6b, and the control flag F1 described later is used.
And F2 are reset to "0", and then step S6c
Then, the drive state flag F _2WD is reset to "0" indicating the four-wheel drive state, and then the process proceeds to step S6d.

In step S6d, it is determined whether or not the drive state flag F _2WD is the two-wheel drive state in which the drive state flag F _2WD is set to "1". If F _2WD = 1, the process proceeds to step S7 described above. When F _2WD = 0, the process proceeds to step S6 described above. On the other hand, step S6a
If Vw _R −VW _FL ≧ 0, the process proceeds to step S6e, and the speed difference obtained by subtracting the wheel speed Vw _FR of the front right wheel 2FR from the rear wheel speed Vw _R is positive including zero. If Vw _R −VW _FR <0, it is determined that the vehicle is in the four-wheel drive state, and the step S6 is performed.
If bw _R −VW _FR ≧ 0, the process proceeds to step S6f.

In this step S6f, the rear wheel speed Vw
_RTo front left wheel 2FL wheel speed Vw_FLThe speed difference obtained by subtracting is negative
Vw_R-VW_FLWhen ≧ 0
In step S6g, it is determined that the vehicle is in the four-wheel drive state.
And the flag F1 representing the initial state is set to "0".
After resetting, the process proceeds to step S6d, and Vw _R
-VW_FLWhen <0, the process proceeds to step S6h
It

In step S6h, the rear wheel speed Vw is set.
_RTo front right wheel 2FR wheel speed Vw_FRThe speed difference obtained by subtracting is negative
Vw_R-VW_FRWhen ≧ 0
It is determined that the vehicle is in the four-wheel drive state, and the step S
Moved to 6g, Vw_R-VW _FLIf <0, then
Move to step S6i. In this step S6i,
The timekeeping status flag F1 indicating the time status is set to "1".
If F1 = 1, the timekeeping
And jump to step S6m, and F1
When = 0, it is determined that it is time to start timing, and step
After shifting to S6j, the clock timer T is set to, for example, 350 mse.
a predetermined value T corresponding to c₀Preset, then step
Go to step S6k and set the timekeeping status flag F1 to "1".
Then, the process proceeds to step S6m.

In step S6m, the clock timer T is decremented, and then the process proceeds to step S6n to determine whether or not the count value of the clock timer T is "0".
This determination is to determine whether or not the wheel speeds Vw _FL and Vw _{FR of the} two front wheels are lower than the wheel speed Vw _{R of the} rear wheels for a predetermined time or longer, and when T> 0. In some cases, it is determined that the predetermined time has not elapsed, and the process directly proceeds to step S6d. When T = 0, the predetermined time has elapsed, it is determined that the two-wheel drive state is reached, and the process proceeds to step S6o. Then, the drive state flag F _2WD is set to "1" and then the process proceeds to step S6d.

When the determination result of the drive state determination processing in step 6 is the four-wheel drive state, the process proceeds to step S7, in which the front two wheels are both in a slow pressure increasing mode and a high pressure side holding mode which will be described later. In either mode, it is determined whether or not both are in a pressure increasing state. This determination is made by determining whether or not the mode determination flags F _MFL and F _MFR are set to “2” or “3” in step S24 or step S26 in the anti-skid control process of FIG. 8 described later, When the two front wheels are both in a pressure boosted state,
When the process proceeds to step S8, the slow pressure increase permitting flag F _S for permitting the slow pressure increase of the rear wheels 2RL and 2RR is set to "1", and then the process proceeds to step S10. , The process proceeds to step S9, and the slow pressure increase permission flag F
_{After S} is reset to "0", the process proceeds to step S10.

In step S10, the anti-skid control process for the rear wheels 2RL, 2RR is executed, the timer interrupt process is terminated, and the process returns to the predetermined main program. On the other hand, when the determination result of step S6 is the two-wheel drive state, the process directly proceeds to step S8 so that the rear wheel side slow pressure increase suppression processing is omitted, and the slow pressure increase permission flag F _S is always set to “1”. After setting, the process proceeds to step S10.

In addition, the front wheel side unwinding in steps S1 and S2
The chiskid control process is the same as the subroutine process shown in FIG.
Run. In this subroutine processing, first, step S1
1 outputs from the wheel speed calculation circuit 34j (j = FL, FR).
Present detected wheel speed value Vw_{j (N)}Read, then step
Go to step S12 and read the wheel speed read in the previous processing.
Detection value Vw_{j (N-1)}From the wheel speed read in step S11
Detection value Vw_{j (N)}Is subtracted, and the subtracted value is the timer interrupt cycle
By dividing by
Chi wheel acceleration / deceleration Vw _j′ Is calculated and stored in the storage device.
Stored in the constant storage area, then move to step S13
And the estimated vehicle body speed V from the estimated vehicle body speed calculation circuit 52._X
Is read, and then step S14 follows and the following (1)
The slip ratio S of each wheel is calculated by the formula_jTo calculate.

S_j= {(V_X-Vw_j) / V_X} × 100 (1) Then, the process proceeds to step S15, and in step S14.
Calculated slip ratio S _jPreset target slip
Rate S₀(For example, 20%) or more is determined, S
_j<S₀If so, the process proceeds to step S16.
In step S16, the value of the decompression timer L is set to the current value.
Value obtained by decrementing "1" from the current decompression timer L value
And “0” are compared, and whichever is larger, select
Go to step S17.

In step S17, it is determined whether or not a preset control end condition is satisfied. This judgment is
For example, it is performed by determining whether the switch signal of the brake switch is in the off state, whether the vehicle speed is zero, and the like, and if the control end condition is satisfied, step S
Go to 18. In step S18, the depressurization timer L is cleared to "0" and the anti-skid control flag AS is reset to "0". Then, the process proceeds to step S19, in which the pressure of the actuator 33j is adjusted according to the pressure of the master cylinder 32. After setting the rapid pressure increase mode in which the pressure is increased, the process returns to the process of FIG. 7. In this rapid pressure increase mode, the control signals EV _j and AV _j for the actuator 33j are generated.
Are both set to the logical value "0" to control the inflow valve 35 of the actuator 33j to the open state and the outflow valve 36 to the closed state, and set the mode determination flag F _Mj to "0".

On the other hand, when the result of the determination in step S17 does not satisfy the control end condition, the routine proceeds to step S20, where it is determined whether or not the depressurization timer L is a positive value, and L
When it is> 0, the process proceeds to step S21, the depressurization mode for depressurizing the wheel cylinder 4j is set, and then the process of FIG. 7 is returned to. In this pressure reduction mode, the control signals EV _j , AV _j and MR _j for the actuator 33j are generated.
Are both set to a logical value "1", the inflow valve 35 of the actuator 33j is closed, the outflow valve 36 is opened, and the pressure retained in the wheel cylinder 4j is set to the outflow valve 36, the hydraulic pump 37, and the check valve 38. Through master cylinder 3
Then, the internal pressure of the wheel cylinder 4j is reduced, and "1" is set as the mode determination flag F _Mj .

If the result of the determination in step S20 indicates that the decompression timer L is cleared to "0", step S20 is executed.
In step 22, it is determined whether the wheel acceleration / deceleration Vw _j ′ calculated in step S12 is equal to or greater than a preset acceleration threshold value + α ₁ and when Vw _j ′ <+ α ₁ ,
In step S23, it is determined whether or not the wheel acceleration / deceleration Vw _j ′ is less than or equal to a preset deceleration threshold −α ₂ and when Vw _j ′ ≦ −α ₂ , the process proceeds to step S24. , The actuator 33j is set to the high pressure side holding mode in which the inner pressure of the wheel cylinder 4j is held at a constant value, and then the process returns to the process of FIG. In the high-pressure side holding mode, the control signal EV _j for the actuator 33j is set to the logical value "1" and the control signal AV _j is set to the logical value "0" to close the inflow valve 35 of the actuator 33j and the outflow valve 36. Are controlled to be in a closed state, and the internal pressure of the wheel cylinder 4j is maintained at the pressure immediately before that.
"2" is set as the mode determination flag F _Mj .

On the other hand, the determination result of step S23 is V
When w _j ′> −α ₂ , the process proceeds to step S25, and it is determined whether or not the antiskid control flag AS is reset to “0”. If it is reset to “0”, the above step is performed. Move to S19,
If it is set to "1", the process proceeds to step S26.

In step S26, the actuator 23j is set in the slow pressure increasing mode in which the pressure of the wheel cylinder 4j is gradually increased, and then the process of FIG. 7 is returned to. In the slow pressure increasing mode, the control signal EV _j for the actuator 23j is kept at the logic value "0" for a predetermined time, for example, 8 msec, and then switched to the logic value "1", and the control signal AV _R is repeated every predetermined time. Is set to a logical value "0", the inflow valve 35 of the actuator 33j is intermittently opened, and the outflow valve 36 is closed to gradually increase the internal pressure of the wheel cylinder 4j in a stepwise manner and determine the mode. "3" is set as the flag F _Mj .

On the other hand, the judgment result of the step S22 is V
When w _j ′ ≧ + α ₁ , the process proceeds to step S27, it is determined whether or not the antiskid control flag AS is reset to “0”, and the control flag AS is “0”.
When the control flag AS is set to "1", the process proceeds to step S28 and the actuator 33i
Is set to the low pressure side holding mode in which the pressure of the wheel cylinder 4j is held at the value immediately before it on the low pressure side, and then the processing returns to the processing of FIG. In this low pressure side holding mode, the control signal EV _j for the actuator 33j is set to the logical value “1” and the control signal AV _j is set to the logical value “0” in the same manner as in the high pressure side holding mode in step S24 described above. 33i, the inflow valve 35 is closed, and the outflow valve 36
Is controlled to a closed state, the internal pressure of the wheel cylinder 4j is maintained at the pressure immediately before, and "4" is set as the mode determination flag F _Mj .

Further, the judgment result of the step S15 is
When S _j ≧ S ₀ , the process proceeds to step S29,
Wheel acceleration / deceleration Vw _j ′ is preset acceleration threshold value + α
It is determined whether or not it is ₁ or more, and when Vw _j ′ ≧ + α ₁ , the process proceeds to step S30 to clear the decompression timer L to “0”, and then proceeds to step S17.
When Vw _j ′ <+ α ₁ , the process proceeds to step S21, the anti-skid control flag AS is set to “1”, the depressurization timer L is set to a positive predetermined value L ₀ , and then the process proceeds to step S17. To do.

On the other hand, in the rear wheel side anti-skid control process of step S10, as shown in FIG. 10, in the process of FIG. 9, the slow pressure increase permission flag F _S is set to "1" between steps S25 and S26. Step S32 for determining whether or not the pressure increase has been performed
Step S26 only when _S is set to "1"
And the slow pressure increase mode is set, and the slow pressure increase permission flag F is set.
_{When S} is reset to "0", step S2
8, the low pressure holding mode is set, and steps S19, S21, S24, S26, S of each mode setting process are performed.
9 except that there is no need to set a flag at 28.
The same processing is performed, the same steps as those in FIG. 9 are given the same step numbers, and detailed description thereof will be omitted.

The processes of FIGS. 7, 9 and 10 correspond to the braking pressure control means, and the processes of steps S6a and S6e in the process of FIG. 8 showing the process of step S6 of FIG. 7 are the first wheel speed. Corresponding to the difference detecting means, steps S6f to S6
The processing of o corresponds to the second wheel speed difference detecting means, and the processing of step S6d corresponds to the driving state determining means. Next, the operation of the above embodiment will be described with reference to the time chart shown in FIG.

Now, by selecting the two-wheel drive state by the transfer shift lever 28, the 2-4 coupling sleeve 27 disconnects the rear wheel side output shaft 17 and the front drive sprocket 23, and L- It is assumed that the H coupling sleeve 21 connects the main gear 16 and the rear wheel side output shaft 17 and is in a high speed position. In this state, the driving force from the transmission 5 is transmitted to the rear wheel side output shaft 17 via the input shaft 15 and the L-H coupling sleeve 21, so that the driving force is transmitted.
It is transmitted to the rear wheels 2RL and 2RR via 0, and only the rear wheels are in a two-wheel drive state.

In this two-wheel drive state, as shown in FIG. 13, if it is assumed that the vehicle is traveling at a constant speed on a good road at a time point t ₀ in a non-braking state, the antiskid control section 46 estimates the estimated vehicle speed V _X and the wheels. Since the speeds Vw _i (i = FL, FR, R) match, the slip ratio S calculated in step S14 of the front wheel side braking force control process and the rear wheel side braking force control process of FIGS. 9 and 10. _{Since i} becomes "0" and it is in the non-braking state,
After shifting from step S15 to step S16, the decompression timer L is cleared to "0" at the previous processing during constant speed running, so that "0" is selected as the timer value and then the processing shifts to step S17. .

In this step S17, it is judged that the control is not completed and the control end condition is satisfied, and it is determined in step S1.
8, the depressurization timer L and the anti-skid control flag AS are cleared to "0", and then the process proceeds to step S19 to set the rapid pressure increase mode. In this rapid pressure increase mode, the master cylinder 3 is driven by the actuator 33i.
2 and each wheel cylinder 4i are in communication with each other, but since the brake cylinder 31 is not depressed and the pressure in the master cylinder 32 is substantially zero, the pressure in the wheel cylinder 4i is also substantially zero. Maintain zero and maintain non-braking state.

In this constant speed traveling state, the estimated vehicle body speed V _X of the estimated vehicle body speed calculation circuit 52 and the select high wheel speed V
w _H is substantially the same, and the integration circuit 5k selects the zero-voltage integration input voltage E, so that the integration circuit 5k
The output of 2f is zero, and the estimated vehicle body speed V _X does not fluctuate and substantially matches the actual vehicle body speed. When the brake pedal 31 is stepped on at the time t ₁ from the non-braking constant-speed running state to bring it into the braking state, the master cylinder pressure of the master cylinder 32 rapidly increases. In this state, since the rapid pressure increase mode is set as described above, the wheel cylinder 4 for the front wheels 2FL, 2FR is set.
The cylinder pressures P _{WCFL and} P _{WCFR of} FL and 4FR are also shown in FIG.
As shown in (b) and (c), the wheel cylinder pressure P _WCR that is rapidly increased to a pressure equal to the master cylinder pressure and is controlled by the actuator 23R for the rear wheels 2RL and 2RR is also as shown in FIG. 13 (d). The pressure is rapidly increased to a pressure equal to the master cylinder pressure.

In this way, each wheel cylinder 4FL-
The cylinder pressure of 4RR is suddenly increased so that it is not driven.
Wheel speed Vw of front wheels 2FL and 2FR_FL, Vw_FRIs a figure
As shown in 13 (a), it decreases relatively sharply, but
Wheel speed Vw on the rear wheel side that is the driving wheel_RIs engine inertia
Wheel and engine brake
Speed Vw_RThe decrease will be slow. In addition, in FIG.
For the sake of clarity, the front wheel side is
Wheel speed Vw_FL, Vw_FRAnd rear wheel speed Vw _RAnd minutes
However, they are described as different wheel speeds.

In this way, when the vehicle is in the braking state, the estimated vehicle body speed calculation circuit 52, as shown in FIG. 13A, selects the rear wheel speed Vw _R as the select high wheel speed Vw _H until time t _3. Is selected, which is the wheel speed sampling value V of the sample hold circuit 52a before the time point t _1.
When the predetermined time T ₃ set by the off-delay timer 52j elapses after the estimated vehicle speed V _{X of S} is reduced by 1 km / h, the selection circuit 17k offsets the longitudinal acceleration X _G output from the output correction circuit 52e. The longitudinal acceleration correction value X _GC corrected by adding the values is selected as the integrated input voltage E, which is integrated by the integration circuit 52f and supplied to the addition circuit 52g as a negative speed correction value.
Since it is subtracted from the wheel speed sampling value V _S at 2 g,
The estimated vehicle body speed V _X decreases in accordance with the decrease in the vehicle body speed, and then substantially coincides with the right front wheel speed Vw _FR selected as the select high wheel speed Vw _H at time t ₆ , so that the right front wheel speed at this time is Vw _FR is held as the wheel speed sampling value V _S , and after that, when the select high wheel speed Vw _H exceeds the dead zone and the predetermined time T ₃ set by the off-delay timer 52 j elapses, the anti-skid control is started and the control signal is given. Since MR is "1", the negative voltage corresponding to +10 g is input to the integrating circuit 52f as the integrated input voltage E in the selecting circuit 52k, so that the estimated vehicle body speed V _X sharply increases and the selection is made. High wheel speed Vw
_{Following H} , when the select high wheel speed Vw _H decreases by more than 1 km / h from the estimated vehicle speed V _{X, the} speed decreases with a gradient according to the longitudinal acceleration X _G. Note that, in FIG. 13A, the estimated vehicle body speed V _X is shown to decrease linearly for simplification of description. However, in reality, as described above, the selected high wheel speed V _{W H} It changes like a polygonal line based on the longitudinal acceleration X _G.

On the other hand, when the wheel acceleration / deceleration Vw _FL ′, Vw _FR ′ of the left and right front wheels falls below the deceleration threshold −α ₂ at time t ₂ ,
When the processing of FIG. 9 is executed, steps S11 to S1
After 7, S20, S22 and S23, the process proceeds to step S24 and the high pressure side holding mode is set.
Both the inflow valve 35 and the outflow valve 36 of the actuators 33FL and 33FR are closed, and the cylinder pressures of the wheel cylinders 4FL and 4FR on the front wheels are held as shown in FIGS. 13 (b) and 13 (c).

Then, at time t₃So the front wheel 2FR wheel pickpocket
Up rate S_FRIs the target slip ratio S₀Below is the right front wheel
Wheel speed Vw_FRIs the estimated vehicle speed V_XOn target wheel slip
Rate S _FR13A calculated by multiplying by
Target wheel speed Vw^*In the following cases, the processing of FIG.
When executed, the process goes from step S15 to step S29.
Shift, acceleration / deceleration Vw of the right front wheel_FR′ Is the acceleration threshold + α
₁Since it is less than, it moves to step S31,
While the kid control flag AS is set to "1",
Decompression timer L is a predetermined value L₀Is preset to. But
Therefore, when the process proceeds to step S20, L> 0.
Then, move to step S21 and set the decompression mode.
This causes the cylinder pressure P of the right front wheel 2FR to rise._WCFRIs Figure 1
As shown in Fig. 3 (c), the low pressure holding mode is set after the sudden decrease.
It

[0050] Then, since at time t ₄ is the wheel speed Vw _FL of the left front wheel 2FL the target wheel speed Vw ^* and the same becomes a decompression mode, cylinder pressure P _WCfl of the left front wheel 2FL Figure 1
As shown in FIG. 3 (c), the pressure is rapidly reduced and then the low pressure holding mode is set. In this way, the wheel cylinder pressure P _WCFR,
When P _WCFL is depressurized, the braking force on the front wheels 2FL, 2FR becomes smaller, so the front wheel speeds Vw _FR, Vw _{FL change} from a decreasing tendency to an increasing tendency.

From time t ₁ to time t ₄ , the rear wheel wheel acceleration / deceleration Vw _R ′ is as shown in FIG. 13 (e).
This represents the deceleration in the negative direction. Since the anti-skid control flag AS has been reset to "0" in the rear wheel braking force control process in FIG. 10, the process directly proceeds from step S5 to step S9, and the rear wheel side braking control is performed. Power control processing is executed. And
At time t ₃ , the rear wheel acceleration / deceleration Vw _R ′ is equal to the deceleration threshold −
When it becomes α ₂ or less, when the rear wheel braking force control process in FIG. 10 is executed, the process proceeds from step S23 to step S24, and the high pressure side holding mode is set, whereby the wheel cylinder pressure P on the rear wheel side is set. _WCR is held at a high value as shown in FIG.

Therefore, the wheel speed Vw _R of the rear wheels 2RL, 2RR
Gradually decreases as shown in FIG. 13 (a), and time t ₅
When the rear wheel slip ratio S _R is equal to or higher than the target slip ratio S ₀ and the rear wheel wheel speed Vw _R is equal to or lower than the target wheel speed Vw ^* ,
When the process of FIG. 10 is executed, the process proceeds from step S15 to step S29 to step S31 to set the anti-skid control flag AS to "1", and
Decompression timer L is preset in the setting value L _0, then the process proceeds to step S21 through steps S17, S20 are set vacuum mode, this wheel cylinder pressure P _{WC R} of the rear wheel side by the in FIG. 13 (d) It is sharply reduced as shown.

Thus, at time t_FiveThen, the rear wheel side in FIG.
In the braking pressure control process, the anti-skid control flag A
S_RIs set to “1”, the braking force of FIG.
When the control process is executed, the steps from step S4 are started.
The process proceeds to step S6, and the drive state determination process is executed. This
At time t_FiveThen, the rear wheel speed Vw_RHowever, in Fig. 13 (a)
As shown, the wheel speed Vw of the two front wheels_FL, Vw_FRAbove
Therefore, steps S6a to S6e, S6f, S6h
After that, the process proceeds to step S6i, and the anti-skid control flow
Rug AS_RTime is displayed when is reset to "0"
Since the status flag F1 has been reset to "0",
Go to step S6j, where the count value of the clock timer T is
Fixed value T ₀Preset, then measure the time in step S6k
Step S6 after setting the status flag F1 to "1"
m, and decrement the count value of the clock timer T.
However, at this point, the clock counter T is preset.
Since it has just been completed, T> 0 and step S6d.
After step S8 in FIG. 7 and then step S10 rear wheel
The side braking pressure control process is executed. However, this condition
Then, the rear wheel deceleration Vw_R’Is negative and accelerates
Degree threshold α₁Because it is smaller, the rear wheels are 2RL and 2RR
Cylinder pressure P_WCRContinues the depressurized state.

Thereafter, at the time point t ₆ , the front wheel speed Vw _FR exceeds the rear wheel speed Vw _R , so when the processing of FIG. 8 is executed, the steps S6e to S6b are executed.
The process proceeds to, step S6 is reset to reset the clocking state flag F1 to "0", and the drive state flag F _2WD in step S6c representing the four-wheel drive state "0"
The process shifts to d, and the decrement of the clock timer T is stopped.

[0055] Therefore, the process proceeds to step S7 in the process of FIG. 7, but the wheel cylinder pressure P _WCFR Only in this time t ₆ before right wheel 2FR is a slow increase mode is increased stepwise, before Since the left wheel 2FL is still in the pressure reducing mode, the process proceeds to step S9, the slow pressure increase permission flag F _S is reset to "0", and then the rear wheel side braking pressure control process of step S10 is performed.

At this time t ₆ , the wheel acceleration / deceleration Vw of the rear wheels is
_{Since R} ′ is greater than or equal to the acceleration threshold α ₁ , step S29
To step S30 to preset the depressurization timer L again, step S20 to step S21
And the depressurization mode is continued. After that, time t ₇
When the rear wheel acceleration / deceleration Vw _R ′ becomes equal to or greater than the acceleration threshold α ₁ as shown in FIG. 13 (e), when the process of FIG. 10 is executed, the process proceeds from step S22 to step S28 and the rear wheel The side actuator 33R is set to the low pressure holding mode, and the wheel cylinder pressure P _WCR of the rear wheels 2RL and 2RR is set.
Are held on the low voltage side as shown in FIG. 13 (d).

[0057] Then, in front wheels 2FL time t _8, the actuator 2FR 33FL, 33FR both become slow increase mode, when the processing of FIG. 7 is executed, gradual pressure increase shifts from step S7 to step S8 Set the permission flag F _S to “1”
After being set to, the rear wheel side braking pressure control process of step S10 is executed. At this time point t ₈ , the rear wheel acceleration / deceleration Vw _R ′ becomes less than the acceleration threshold value α ₁ as shown in FIG. 13 (e), so when the braking pressure control process of FIG. 10 is executed, from step S22. After steps S23 and S25, the process proceeds to step S32, and since the slow pressure increase permission flag F _S is set to "1", the process proceeds to step S26 and the rear wheel side actuator 33R is set to the slow pressure increasing mode. It Therefore, the wheel cylinder pressure P _WCR of the rear wheels 2RL, 2RR is increased stepwise as shown in FIG. 13 (e), but at time t ₉ , the actuator 3 of the front right wheel 2FR is operated.
Since the 3FR shifts to the depressurization mode, when the process of FIG. 7 is executed, the process shifts from step S7 to step S9,
The gradual pressure increase permission flag F _S is reset to “0”. Therefore, when the rear wheel side braking pressure control process in FIG. 10 is manually executed, the process proceeds from step S32 to step S28.
By setting the holding mode, the wheel cylinder pressure P _WCR of the rear wheels 2RL, 2RR is held at a somewhat high pressure increased by the previous slow pressure increasing mode, as shown in FIG. 13 (e).

After that, at time t ₁₀ , the rear wheel wheel speed Vw _R returns to a state in which it exceeds the wheel speeds Vw _FL and Vw _FR of the two front wheels, so when the drive state determination processing of FIG. 8 is executed, step S6a. , S6e, S6f, S6h, and S6i, the process proceeds to step S6j, and the clock timer T is again set to the state shown in FIG.
As shown in (f), preset to a predetermined value T ₀ ,
Transition to decrement state.

In this state, since the count value of the clock timer T does not become "0", the drive state flag F _2WD indicates the four-wheel drive state set in the previous processing by directly shifting to step S6d. Since the state of "0" is continued, the mode for suppressing the slow increase in pressure on the rear wheel side is continued, as shown in FIG.
The rear wheel side as shown in (d) the wheel cylinder pressure P _{WC R}
Is held.

However, after time t _{10, the} rear wheel speed V
Since w _R continues to exceed the front two wheel speeds Vw _FL and Vw _FR , the count value of the clock timer T is as shown in FIG.
When the count value is sequentially decreased as shown in (f) and the count value becomes “0” at time t ₁₁ , steps S6n to S6o.
Then, the drive state flag F _2WD is set to “1” indicating the two-wheel drive state, and thus the process directly proceeds to step S8 in FIG. 7 to set the slow pressure increase permission flag F _S to “1”. Then, after the rear wheel side slow pressure increase suppression mode is released, the process proceeds to the rear wheel side braking pressure control processing in step S10.

Therefore, at time t ₁₁ , the wheel acceleration / deceleration Vw _R ′ of the rear wheel becomes an intermediate value between the acceleration threshold α ₁ and the deceleration threshold −α ₂ , so that the rear wheel side braking pressure control process of FIG. When it is executed, since the slow pressure increase permission flag F _S is set to “1”, the steps S32 to S2 are executed.
6, the anti-skid 33R on the rear wheel side is set to the mode for gradually increasing pressure, whereby the wheel cylinder pressure P _WCR of the rear wheels 2RL, 2RR is increased stepwise as shown in FIG. 13 (d). .

After that, at time t ₁₂ , the wheel speed V of the front left wheel 2FL
Since w _FL exceeds the rear wheel speed Vw _R , FIG.
When the processing has been executed, the process proceeds from step S6a in step S6b, with counting state flag F1 is reset to "0", the transition to the drive state flag F _2WD four-wheel drive state in step S6c Since the value is reset to "0" as shown, the state in which the rear wheel is gradually increased is suppressed.

After that, at time t ₁₃ , when the wheel speed Vw _R of the rear wheels 2RL and 2RR again exceeds the wheel speeds Vw _FL and Vw _FR of the front two wheels 2FL and 2FR, the clock timer T is set to the predetermined value T.
_It is preset to ₀ and becomes decremented, and at time t
_{At 14} , the count value of the clock timer T becomes "0". Therefore, in the process of FIG. 8, the process proceeds from step S6n to step S6o, and the drive state flag F _2WD is set to "1" indicating the two-wheel drive state. The slow pressure increase suppression process on the wheel side is canceled. Therefore, immediately the rear wheels 2RL, is set slow increase mode of 2RR, the rear wheel 2RL, as shown in FIG. 13 (d), the wheel cylinder pressure P _WCR of 2RR is increased stepwise, thereafter time t ₁₅ Front right wheel 2FR wheel speed Vw _FR is rear wheel speed V
Since it exceeds w _R , the four-wheel drive state is determined again, and the rear wheel side gradually increased pressure suppression processing state is set.

As described above, when it is determined in step S6 in FIG. 7 that the vehicle is in the two-wheel drive state, the mode for setting the pressure reduction mode for the rear wheels is increased by canceling the mode for suppressing the slow pressure increase on the rear wheels. Therefore, the braking distance during the anti-skid control can be shortened. By the way, even in the two-wheel drive state, when the setting of the rear wheel side slow pressure increasing mode is allowed only when the front two wheels are both in the slow pressure increasing mode, the two wheel driving state is set. Then, as shown in FIG. 13 (a), since the wheel speeds Vw _{FL and} Vw _FR of the front two wheels fluctuate in an antiphase relationship, it is unlikely that both of them are in the slow pressure increasing mode. The wheel cylinder pressure P _WCR of the wheels 2RL and 2RR is maintained in a low pressure state as shown by the alternate long and short dash line in FIG. 13 (d), and the wheel speed Vw _R changes substantially to the vehicle body speed. The distance will increase.

Next, when the 2-4 coupling sleeve 27 is connected to the front drive sprocket 23 by shifting the transfer shift lever 28 to the 4H position from the above two-wheel drive state and the four-wheel drive state is reached, the input shaft 15 The drive torque transmitted from the transmission 5 to the rear wheel side output shaft 17 is transmitted to the front wheel side output shaft 24 via the drive chain 26, and the four wheel drive state is established.

Even in the four-wheel drive state, when the braking state is reached, the same braking pressure control processing as in the two-wheel drive state is executed as shown in FIG. That is, in the four-wheel drive state, the wheel speeds Vw _R of the rear wheels 2RL and 2RR detect the rotational speed of the propeller shaft 10 as shown in FIG.
As shown in (a), wheel speeds Vw _FL and Vw on the front wheel side
_{At the same time as} the average value of _FR , the front wheel side tends to alternate between the left and right wheel speeds Vw _FL and Vw _FR due to the influence of the front differential gear 11.

[0067] Therefore, now, the actuator 33FL for the left front wheel 2FL is at high pressure holding mode when t ₂₀ in FIG. 14, the wheel cylinder pressure P _WCfl is relatively high pressure as shown in FIG. 14 (b), right Anti-skid 33FR of front wheel 2FR is in low pressure holding mode, and its wheel cylinder pressure P
_Assuming that the _WCFR is maintained at the low pressure side as shown in FIG. 14C, and the anti-skid control is being performed, the anti-skid control flag AS on the rear wheel side is set to "1", and the driving state is further set. It is assumed that the flag F _{2WD is} also reset to "0".

At this time t ₂₀ , since the rear wheel speed Vw _R is lower than the front left wheel 2FL wheel speed Vw _FL as shown in FIG. 14A, when the processing of FIG. 8 is executed. , Step S6a to Step S6b, reset the timekeeping state flag F1 to "0", and
Since the drive state flag F _2WD is reset to "0" indicating the four-wheel drive state by shifting to 6c, the decrement process of the clock timer T is not executed, and the determination of the four-wheel drive state is continued. Therefore, the process proceeds from step S6 to step S7 in FIG. 7 and the slow pressure increase permission flag F _S is set to "1" only when both the front two wheels 2FL and 2FR are in the slow pressure increase mode.

At this time t ₂₀ , since the front two wheels 2FL and 2FR are not in the mode for slowly increasing pressure, the routine proceeds to step S9, where the modest pressure increasing permission flag F _S is reset to "0", and therefore the rear Even if the wheel acceleration / deceleration Vw _R of the wheel is in a state where the pressure can be increased below the acceleration threshold α ₁ as shown in FIG. 14E, the process proceeds from step S32 to step S28 in the process of FIG. The shift to the mode is suppressed and the low pressure side holding mode is continued, and the wheel cylinder pressure P _WCR of the rear wheels 2RL and 2RR is held in the low pressure state as shown in FIG. 14 (d).

After that, up to time t ₂₅ , the wheel speed Vw of either front wheel 2FL or 2FR with respect to the rear wheel speed Vw.
_{Since FL} or Vw _FR becomes higher, when the process of FIG. 8 is executed, the same process as at the time point t ₂₀ is repeated and the drive condition flag F _2WD is reset to “0” to set the rear wheel side. The gradual pressure increase suppression process is continued, but at time t ₂₅ , the previous 2
Since both wheels 2FL and 2FR are in the slow pressure increasing mode, the process proceeds from step S7 to step S8 in the process of FIG. 7 and the slow pressure increasing permission flag F _S is set to “1”, so that the rear wheels of FIG. When the side braking pressure control process is executed, step S3
After shifting from 2 to step S26, the rear wheel side actuator 33R is set to the gradually increasing pressure mode, and the wheel cylinder pressure P _WCR of the rear wheels 2RL, 2RR increases stepwise as shown in FIG. 14 (d).

Thereafter, at time t ₂₆ , the wheel speed Vw _{R of the} rear wheels and the wheel speeds Vw _FL and Vw _{FR of the} two front wheels 2FL and 2FR coincide with each other. Therefore, when the processing of FIG. 8 is executed, step S6 is executed.
At time t ₂₆ ′ immediately after that, the wheel speed Vw _FL of the front left wheel 2FL is changed to the rear wheel speed Vw _R by shifting to j and presetting the clock timer T to a predetermined value T _0. Drive status flag F
_{The 2WD} continues to be reset to "0", and when the two front wheels are in the mode for gradually increasing pressure at time t ₂₉ thereafter, the moderate increase permission flag F _S is set to "1" again. At this time, since the rear wheel acceleration / deceleration Vw _R ′ is less than the acceleration threshold value α ₁ , the rear wheel side actuator 33R is set to the slow pressure increasing mode.

Thereafter, at the time point t ₃₀ , the rear wheel speed Vw _R and the wheel speeds Vw _FL and Vw _{FR of the} front two wheels 2FL and 2FR match at the time point t ₂₆ as at the time point t _26.
Although it is preset to ₀ , immediately after that, the wheel speed Vw _FL of the front left wheel 2FL exceeds the rear wheel speed Vw _R ,
The drive state flag F _2WD continues to be reset to "0".

Therefore, in the four-wheel drive state, when the front two wheels are in the depressurized state and are in the process of spin-up, if the rear wheel side is set to the slowly increasing pressure state and the braking force is applied to the rear wheels 2RL and 2RR, This braking force is applied to the propeller shaft 10, 2-4.
It is transmitted to the left and right front wheels 2FL and 2FR through the coupling sleeve 27, the chain 26, the front wheel side output shaft 24, etc., and the recovery of the wheel speeds Vw _FL and Vw _FR of the left and right front wheels 2FL and 2FR and the vehicle speed are suppressed. Although it causes a downward movement, it is impossible to effectively exert the anti-skid control effect.However, in the present embodiment, except when both the front two wheels are in the slow boosting mode state in the four-wheel drive state, Since it is prohibited to set the actuator 33R of the wheels 2RL and 2RR to the slow pressure increasing mode, the left and right front wheels 2FL and 2FR
It is possible to effectively recover the wheel speed, and surely prevent the vehicle from moving down with respect to the vehicle speed, thereby exerting an excellent actuator control effect.

As described above, according to the above embodiment, by monitoring the front and rear wheel speeds Vw _FL , Vw _FR and Vw _R , it is possible to provide a special sensor, switch, etc.
It is possible to reliably discriminate between the two-wheel drive state and the four-wheel drive state, and it is possible to execute the optimum braking pressure control processing according to the discriminated drive state. Further, in the two-wheel drive state, the rear wheel side slow pressure increase suppression mode in the four-wheel drive state is canceled, so the chances of demagnetizing the rear wheel side slow pressure increase mode in the two-wheel drive state are increased. Thus, the braking distance during the anti-skid control can be shortened.

When the transfer shift lever 28 is shifted to the 4L position, the LH coupling sleeve 21 connects the low gear 20 and the rear wheel side output shaft 17, and the front wheels 2FL, 2FR and the rear wheels 2RL. , 2RR can be driven to rotate at a low speed in the four-wheel drive state, and even in this state, good braking pressure control processing can be performed as in the above case.

In the above embodiment, the case where the rear wheels are driven during two-wheel driving has been described, but the present invention is not limited to this, and the front wheels may be driven during two-wheel driving, and the transfer 6 However, the present invention is not limited to the configuration of the above-described embodiment, and a hydraulic clutch may be used to switch between a two-wheel drive state and a four-wheel drive state. It is also possible to control the clutch engagement force based on the control based on this, and in short, any transfer can be applied as long as it is a configuration in which the two-wheel drive state and the four-wheel drive state can be arbitrarily selected.

Further, in the above embodiment, when it is determined that the vehicle is in the four-wheel drive state, the rear wheels are set to the slow pressure increasing mode only when the front two wheels are both in the slow pressure increasing mode. Although the case where the pressure suppression process is performed and the rear wheel side slow pressure increase suppression process is canceled when it is determined that the vehicle is in the two-wheel drive state has been described, the present invention is not limited to this, and the rear wheel side slow increase is performed during the two-wheel drive. It is also possible to perform pressure processing and stop the braking pressure control processing for the rear wheels during four-wheel drive so that the brake torque transmitted from the front wheels is applied to the rear wheels. An arbitrary control mode that differs depending on the state can be adopted.

Further, in the above embodiment, the case where the estimated vehicle body speed calculation circuit 52 is composed of an electronic circuit has been described, but the present invention is not limited to this, and the calculation processing may be performed by a microcomputer. Furthermore, in the above embodiment, the case where the present invention is applied to the anti-skid control device of the three-sensor three-channel system has been described, but the present invention is not limited to this, and the left and right wheels on the rear wheel side are also individually The present invention can be applied to a four-sensor four-channel anti-skid control device provided with a wheel speed sensor, and other types of anti-skid control devices.

Furthermore, in the above embodiment, the case where the microcomputer is applied as the anti-skid control circuit 53 has been described, but the invention is not limited to this, and electronic circuits such as comparison circuits, arithmetic circuits, logic circuits, etc. It can also be configured by combining. Further, in the above-described embodiment, the case where the rear wheel slow pressure increase suppression process is performed in the four-wheel drive state and the release is canceled in the two-wheel drive state has been described, but the present invention is not limited to this and other control is performed. The method can also be applied.

[0080]

As described above, according to the first aspect of the present invention, it is detected that the wheel speed detection value on the rear wheel side exceeds the wheel speed detection value on the front two wheels. Wheel speed difference detection means, and second wheel speed difference detection means for detecting that the state in which the wheel speed detection value on the rear wheel side does not fall below the wheel speed detection value for the two front wheels continues for a predetermined time or more. A drive that determines that the two-wheel drive state is in effect when the detection results of the first and second wheel speed difference detection means simultaneously satisfy the respective detection conditions, and otherwise determines that the four-wheel drive state is in effect. Since it is configured to include the state determination means, it is not necessary to provide a special sensor or switch for detecting the drive state, the drive state can be accurately detected, and reliability is ensured and cost is reduced. The effect that it can be obtained is obtained.

According to the second aspect of the present invention, the braking force on the rear wheel side is reduced by executing the rear wheel slow pressure increase suppressing process when the four-wheel drive state is detected by the anti-skid control device. It is possible to prevent the influence on the front wheels and to increase the chances of gradually increasing the pressure of the rear wheels to reduce the braking distance in the two-wheel drive state.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing a schematic configuration of an anti-skid control device according to the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 3 is a skeleton diagram showing an example of a transfer applicable to FIG.

FIG. 4 is a schematic configuration diagram showing an actuator applicable to FIG.

5 is a block diagram showing an example of a controller applicable to FIG. 2. FIG.

FIG. 6 is a block diagram showing an example of an applied estimated vehicle speed calculation circuit in FIG. 2;

FIG. 7 is a flowchart showing an example of control processing executed by an anti-skid control circuit of the controller.

FIG. 8 is a flowchart showing drive state determination processing.

FIG. 9 is a flowchart showing a front wheel side braking pressure control process.

FIG. 10 is a flowchart showing a rear wheel side braking pressure control process.

FIG. 11 is an explanatory diagram showing a wheel speed fluctuation state of front and rear wheels in a two-wheel drive state.

FIG. 12 is an explanatory diagram showing a wheel speed fluctuation state of front and rear wheels in a four-wheel drive state.

FIG. 13 is a time chart for explaining the operation in the two-wheel drive state.

FIG. 14 is a time chart for explaining the operation in the four-wheel drive state.

[Explanation of symbols]

 1 Engine 2FL, 2FR Front Wheel 2RL, 2RR Rear Wheel 3 Driving Force Transmission System 4FL-4RR Wheel Cylinder 5 Transmission 6 Transfer 10 Propeller Shaft 28 Transfer Shift Lever 31 Brake Pedal 32 Master Cylinder 33FL-33R Actuator 40 Controller 41FL-41R Wheel Speed sensor 42 Front-rear acceleration sensor 46 Anti-skid control unit 52 Estimated vehicle speed calculation circuit 53 Anti-skid control circuit

Claims (2)

[Claims] 1. A wheel speed detection value of a wheel speed detection means for detecting a wheel speed of at least front two wheels and control target wheels of a rear wheel, the transfer having selectable two-wheel drive state and four-wheel drive state. Based on a four-wheel drive vehicle having an anti-skid control device having a braking pressure control means for individually controlling the braking pressure of the braking cylinders provided on the control target wheels, the wheel speed detection value on the rear wheel side is First wheel speed difference detecting means for detecting that the front two wheels have exceeded the wheel speed detection value, and a state in which the rear wheel side wheel speed detection value does not fall below the front two wheel speed detection values is predetermined. It is in the two-wheel drive state when the detection results of the second wheel speed difference detecting means for detecting the continuation of time or more and the detection results of the first and second wheel speed difference detecting means simultaneously satisfy the respective detection conditions. At other times A drive state detection device for a four-wheel drive vehicle, comprising: drive state determination means for determining that the vehicle is in a four-wheel drive state. 2. The anti-skid control device performs a slow pressure increase suppression process on the rear wheels when a four-wheel drive condition is detected, and cancels the slow pressure increase suppression process when a two-wheel drive condition is detected. The drive state detection device for a four-wheel drive vehicle according to claim 1, wherein