JPH11189148A - Travel control device for four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a travel control device that can perform appropriate braking operation to a vehicle even in the case of at least one wheel being put in a nongrounded state during engine braking in a four-wheel drive vehicle provided with a center differential gear. SOLUTION: A travel control device for a four-wheel drive vehicle has a braking force control means BC for imparting braking force independently to each wheel connected through a center differential gear DC, a nongrounded state judging means NC for judging whether or not at least one of the wheels is in a nongrounded state on the basis of wheel speed detected by a wheel speed detecting means WS, and an engine brake judging means EB for judging the engine brake state of a vehicle. At the time of judging the wheel to be in the nongrounded state in the engine braking state, the braking force control means BC imparts braking force to at least one wheel. A downward slope judging means GD can be further provided to add a condition that the travel road surface of the vehicle is a downward slope.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a travel control for controlling a four-wheel drive vehicle in which all wheels of the vehicle are drive wheels and provided with a center differential so that a stable traveling state can be maintained during engine braking. Related to the device.

[0002]

2. Description of the Related Art A general passenger vehicle has two front and rear wheels. In a front-wheel drive vehicle or a rear-wheel drive vehicle, either the front wheel or the rear wheel is a drive wheel that is connected to an internal combustion engine and directly driven. And the other is a driven wheel that is not connected to the internal combustion engine. On the other hand, a vehicle in which all of the front and rear wheels are drive wheels is referred to as a four-wheel drive vehicle (4WD). There are various types of four-wheel drive vehicles such as part-time and full-time systems. In the full-time system, all of the front and rear wheels are front differential (front differential) and rear differential (rear differential). Device) and a center differential (center differential device).

Also, in order to prevent the wheels from spinning due to excessive driving force during starting acceleration and so-called acceleration slip, an acceleration slip control device for limiting the driving force to the driving wheels to provide an appropriate rotational force, so-called traction Control devices have become widespread, and are disclosed, for example, in Japanese Patent Application Laid-Open No. 8-133504.

In the above-mentioned four-wheel drive vehicle of the part-time system, when a vehicle running with four-wheel drive turns,
Due to the rotation difference between the front and rear wheels, cornering traveling becomes difficult. This phenomenon is called a tight corner breaking phenomenon. On the other hand, in a full-time four-wheel drive vehicle, the center differential efficiently distributes the driving force transmitted through the transmission to the front and rear wheels, and the rotational difference between the front and rear wheels when the vehicle turns. Is absorbed, so that smooth cornering is possible. However, the presence of the center differential also raises new problems. That is, when one of the front and rear wheels idles, the other wheels do not generate any driving force. As a countermeasure, a center differential lock mechanism for locking the center differential by manual operation or the like is provided.

[0005]

However, in a full-time four-wheel drive vehicle, when the center differential is locked by the center differential lock mechanism, a tight corner braking phenomenon is caused.
Naturally, the turning motion of the vehicle becomes difficult. Therefore, when turning the vehicle, the driver of the vehicle needs to sufficiently decelerate. On the other hand, simply removing the center differential lock mechanism makes it difficult to cope with any one of the front and rear wheels running idle, as described above. For this reason, when the center differential lock mechanism is eliminated, a countermeasure for wheel idling is required.

If a traction control device is provided as a countermeasure, escape from mud becomes possible. However, when one of the wheels leaves the road surface while the vehicle is running on an unpaved steep downhill road with an engine brake applied, for example, the wheels operate in the braking direction with respect to each wheel due to the differential function of the center differential. The engine torque to be applied is not a wheel in contact with the ground (hereinafter referred to as a contact wheel) but a wheel that is idling in a contactless state (hereinafter referred to as a contactless wheel.
This non-ground wheel is not necessarily limited to a wheel completely separated from the road surface, but refers to a wheel in a state in which the load of the vehicle body is not substantially transmitted to the road surface).
The engine torque is used in the direction in which the non-ground wheel rotates in the reverse direction. Further, even when the vehicle is not on a downhill road, the engine brake may operate. In any case, some countermeasures are required at the time of engine braking, but if attention is paid to the movement of the load of the vehicle at the time of engine braking, a braking force corresponding to the engine brake may be applied to the wheels in front of the vehicle. Alternatively, a braking force may be applied to the non-ground wheels, and control may be performed so that the engine brake is appropriately applied to the other wheels.

In the case where such measures are taken, the non-contact wheels rotate in the reverse direction as described above, so that if the wheel speed in the vehicle traveling direction is positive, the wheel speed of the non-contact wheels becomes a negative value. However, since a wheel speed sensor, which is a wheel speed detecting means, cannot generally identify the direction of rotation and cannot distinguish between normal rotation and reverse rotation, its output signal is output as a positive value even when the wheel rotates in reverse. As a result, the non-grounded wheel is erroneously determined to be in the ground contact state, and as a result, there is a possibility that the desired braking force cannot be applied to the non-grounded wheel or the wheel in front of the vehicle. In order to cope with this, it is possible to take measures for enabling the identification of the rotation direction, but the device or control becomes complicated.

Accordingly, the present invention is directed to a four-wheel drive vehicle in which all wheels are drive wheels and provided with a center differential, even if at least one of the wheels is in a non-ground state during engine braking. It is an object to provide a travel control device capable of performing a braking operation on a vehicle.

Further, the present invention relates to a four-wheel drive vehicle in which all wheels of the vehicle are drive wheels and provided with a center differential. It is an object to be able to make a determination.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a front differential connected to each wheel in front of a vehicle, and a front differential connected to each wheel behind. A rear differential, a center differential connected to the rear differential and the front differential, and braking force control means for independently controlling braking forces applied to front and rear wheels of the vehicle. In a traveling control device for a wheel drive vehicle, a wheel speed detecting means for detecting a wheel speed of each wheel of the vehicle, and at least one of the wheels of the vehicle based on the detected wheel speed of the wheel speed detecting means A non-ground state determining means for determining whether or not the vehicle is in a non-ground state; and an engine for determining an engine brake state of the vehicle. Brake determining means, wherein the engine brake determining means determines that the vehicle is in an engine brake state, and the non-ground contact state determining means determines that the at least one wheel is in a non-ground state. The control means is configured to apply a braking force to at least one of all the wheels including the non-grounded wheel.

According to a second aspect of the present invention, there is provided a front differential connected to front wheels of a vehicle, a rear differential connected to rear wheels, the rear differential and the front differential. A traveling control device for a four-wheel drive vehicle, comprising: a center differential to be coupled; and braking force control means for independently controlling braking forces applied to front and rear wheels of the vehicle. Wheel speed detecting means for detecting a wheel speed of each wheel;
A non-ground state determining means for determining whether at least one of the wheels of the vehicle is in a non-ground state based on a wheel speed detected by the wheel speed detecting means; Downhill determination means for determining whether the road is a slope,
An engine brake determining unit for determining an engine brake state of the vehicle, wherein the downhill road determining unit determines that the vehicle is on a downhill road, the engine brake determining unit determines that the vehicle is in an engine brake state, and the non-ground contact state determining unit includes: When it is determined that the at least one wheel is in a non-contact state, the braking force control means applies a braking force to at least one of all the wheels including the non-contact state wheel. May be configured to be provided.

Preferably, the non-contact state determining means includes a slip detecting means for detecting a slip of each of the wheels based on a wheel speed detected by the wheel speed detecting means. When the detecting means detects the slip of the at least one wheel, it may be configured to determine that the at least one wheel is in a non-ground state.

Further, as set forth in claim 4, there is provided an estimated vehicle speed calculating means for calculating an estimated vehicle speed based on the detected wheel speed of the wheel speed detecting means, and the slip detecting means is provided with the wheel detecting means. A slip rate calculating means for calculating a slip rate based on the wheel speed detected by the speed detecting means and the estimated vehicle speed calculated by the estimated vehicle speed calculating means, wherein the slip rate is calculated based on the slip rate calculated by the slip rate calculating means. It can be configured to detect slip of one wheel.

According to a fifth aspect of the present invention, in addition to the configuration of the first or second aspect, an estimated vehicle speed calculating means for calculating an estimated vehicle speed of the vehicle based on the wheel speed detected by the wheel speed detecting means. The non-contact state determining means determines that the wheel speed of the at least one wheel falls below a first threshold value obtained by subtracting a first predetermined value from the estimated vehicle body speed of the vehicle. In addition, it may be configured to determine that the at least one wheel is in a non-ground state. .

Further, as set forth in claim 6, a state where the wheel speed of the at least one wheel exceeds a second threshold value obtained by subtracting a second predetermined value from the estimated vehicle body speed of the vehicle. When a predetermined time has elapsed, the contact state determination means for determining that the at least one wheel is in the contact state is provided, and the contact state determination means is such that the at least one wheel is in the contact state. When the determination is made, the braking force control means may cancel the application of the braking force to the at least one wheel.

According to a seventh aspect of the present invention, the contact state determining means determines that a wheel speed of the at least one wheel is a second threshold value obtained by subtracting a second predetermined value from an estimated vehicle body speed of the vehicle. When at least one of the wheels is in a ground contact state when a state exceeding a third threshold value obtained by adding a third predetermined value to the estimated vehicle body speed of the vehicle continues for a predetermined time. It can be configured to determine.

Also, as described in claim 8, claim 1 is
Or the braking force control when the engine brake determining means determines that the engine is in the brake state and the non-ground contact state determining means determines that at least one wheel is in the non-ground state. The means may be configured to apply a braking force to both wheels in front of the vehicle.

Alternatively, according to a ninth aspect of the present invention, in the configuration of the first or second aspect, the engine brake determining means determines that the engine is in the brake state, and the non-ground contact state determining means determines that at least one of the at least one ground contact state is present. When it is determined that the wheel is in the non-ground state, the braking force control means may apply a braking force to the wheel in the non-ground state as a wheel to be controlled.

[0019] The downhill road determination means may include an inclination detection means for detecting an inclination angle of the vehicle, and at least the inclination detection means may determine whether the vehicle travels for a predetermined time. The vehicle may be configured to determine that the traveling road surface of the vehicle is a downhill road when detecting an inclination angle that is equal to or more than a predetermined angle with the direction side as the down direction.

Further, the engine brake determining means includes:
12. The vehicle according to claim 11, further comprising a shift position detecting means for detecting a shift position of the transmission of the vehicle, wherein at least the shift position detecting means detects a predetermined low-speed side shift position, and the downhill road When the determination means determines that the road is downhill,
The vehicle may be configured to determine that the vehicle is in an engine brake state.

[0021]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an outline of an embodiment of the present invention, in which a front differential DF connected to front wheels FR and FL of a vehicle, and a rear differential D connected to rear wheels RR and RL.
R, a driving control device for a four-wheel drive vehicle including a center differential DC connected thereto and braking force control means BC for independently controlling a braking force applied to each wheel. The driving force of the EG is output from the transmission GS, and the center differential DC
, And further transmitted to each wheel via a front differential DF and a rear differential DR.

The traveling control device according to this embodiment includes a wheel speed detecting means WS for detecting the wheel speed of each wheel, and at least one of the wheels based on the wheel speed detected by the wheel speed detecting means WS. Non-ground contact state determining means NC for determining whether or not the vehicle is in a non-ground state, downhill road determining means GD for determining whether or not the traveling road surface of the vehicle is a downhill road, and engine brake determination for determining the engine braking state of the vehicle. Means EB. Then, the downhill determination means GD determines that the road is a downhill, and the engine brake determination means E
B determines that the engine is in the brake state and the non-ground contact state determining means NC determines that at least one of the wheels is in the non-contact state. It is configured to apply a braking force to one wheel. In order to cope with engine braking on a road other than a downhill road, the downhill road determination means GD may be omitted.

The non-ground contact state determining means NC is provided with slip detecting means SR for detecting slip of each wheel based on the wheel speed detected by the wheel speed detecting means WS as shown by a broken line in FIG. When the slip detecting means SR detects slip of at least one wheel, it can be determined that at least one wheel is in a non-ground state. Further, an estimated vehicle speed calculating means ES for calculating an estimated vehicle speed based on the wheel speed detected by the wheel speed detecting means WS is provided.
R is provided with slip ratio calculating means (not shown) for calculating a slip ratio based on the wheel speed detected by the wheel speed detecting means WS and the estimated vehicle speed calculated by the estimated vehicle speed calculating means ES. The slip of at least one wheel may be detected based on the slip ratio calculated by the calculating means.

Further, the non-ground contact state determining means NC, when the wheel speed of at least one of the wheels falls below a first threshold value obtained by subtracting a first predetermined value from the estimated vehicle body speed of the vehicle, It may be configured to determine that the wheel is in a non-ground state. Further, as shown by a broken line in FIG. 1, a contact state determination means CS is provided, and the wheel speed of the at least one wheel is set to a second threshold value obtained by subtracting a second predetermined value from the estimated vehicle body speed of the vehicle. When the state of exceeding the wheel is determined to be in contact with the ground for a predetermined period of time, the wheel is determined to be in contact with the ground, and when the contact state determination means CS determines that the wheel is in contact with the ground, braking force control is performed. The means BC may be configured to release the application of the braking force to the wheels. As the contact state determination means CS, the wheel speed of the at least one wheel exceeds a second threshold value obtained by subtracting a second predetermined value from the estimated vehicle speed of the vehicle, and The configuration may be such that, when a state where the value falls below a third threshold value obtained by adding the predetermined value of 3 continues for a predetermined time, the wheel is determined to be in a ground contact state. Note that the first to third predetermined values may be equal.

In particular, in the traveling control device according to one embodiment described below, the downhill determination unit GD determines that the vehicle is on a downhill, the engine brake determination unit EB determines that the engine is in the brake state, and the non-ground contact state determination unit. When the NC determines that at least one of the wheels is in a non-ground state, the braking force control means BC sets the two wheels FR and F in front of the vehicle.
It is configured to apply a braking force to L. Specifically, when the slip detection means SR detects slip of at least one of the wheels RR and RL behind the vehicle in a state where the accelerator operation and the brake operation are not performed, the braking force control means The BC is configured to apply a braking force to both wheels FR and FL in front of the vehicle, and release the application of the braking force when the slip disappears.

In a traveling control device which will be described later as another embodiment, the downhill determination means GD determines a downhill road, the engine brake determination means EB determines an engine brake state, and the non-ground state determination means NC However, when it is determined that at least one of the wheels is in a non-ground state, the braking force control means BC applies the braking force to the wheel in the non-ground state as a wheel to be controlled. For example, slip detection means S for detecting slip of each wheel based on the wheel speed detected by wheel speed detection means WS
R, the downhill determination means GD
Is determined as a downhill road, when the engine brake determining means EB determines that the engine is in the brake state, and when the slip detecting means SR detects the slip of at least one of the wheels, this wheel is controlled as a wheel to be controlled. The power control means BC can be configured to apply a braking force.

Further, when the vehicle is provided with an estimated vehicle speed calculating means ES for calculating an estimated vehicle speed based on the detected wheel speed of the wheel speed detecting means WS, the slip detecting means SR is provided with a slip detecting means SR. Slip ratio calculating means (not shown) for calculating a slip rate based on the detected wheel speed and the estimated vehicle speed calculated by the estimated vehicle speed calculating means ES is provided, based on the slip rate calculated by the slip rate calculating means. It can be configured to detect slippage of at least one wheel. In this case, the braking force control means BC applies the braking force to the wheel to be controlled until the vehicle is substantially locked, and then stops applying the braking force at a predetermined time to reduce the braking force. If the slip ratio is lower than the predetermined value, the application of the braking force to the wheel to be controlled is terminated, and if the slip ratio is equal to or more than the predetermined value, the application of the braking force to the wheel to be controlled can be continued. . That is, after the braking force is applied to the wheel to be controlled once until the wheel is substantially locked, if the slip ratio of the wheel to be controlled when the braking force is reduced is equal to or greater than a predetermined value, the wheel idles. Can be determined that
Thereby, the state of the wheel to be controlled can be appropriately monitored.

The down-slope determining means GD is provided with a slope detecting means G for detecting the inclination angle of the vehicle as shown by a broken line in FIG.
R, and when at least the inclination detecting means GR detects an inclination angle that is inclined by a predetermined angle or more with the traveling direction side of the vehicle being a downward direction for a predetermined time, the traveling road surface of the vehicle is defined as a downhill road. It can be configured to determine. In addition, a condition that the estimated vehicle speed calculated by the above-described estimated vehicle speed calculating means ES is equal to or higher than a predetermined speed may be added to the determination condition. Further, a longitudinal acceleration detecting means (not shown) such as a so-called G sensor is provided, and an estimated vehicle acceleration is calculated based on the estimated vehicle speed calculated by the estimated vehicle speed calculating means ES. When the difference between the accelerations detected by the acceleration detecting means exceeds a predetermined threshold value, the traveling road surface of the vehicle may be determined to be a downhill road.

The engine brake determining means EB is provided with a shift position detecting means G for detecting a shift position of the transmission GS of the vehicle.
P, and the vehicle is determined to be in the engine brake state when at least the shift position detecting means GP detects a predetermined low speed side shift position and the downhill determination means GD determines that the vehicle is on a downhill. be able to. The engine brake determination means EB may add to the determination condition that the rate of increase in the acceleration of the vehicle is equal to or greater than a predetermined value. Furthermore, the fact that the accelerator operation of the vehicle has been released may be added to the determination condition. The release of the accelerator operation can be detected based on an idle switch signal of a throttle sensor described later. As will be described later, the braking force control means BC includes a wheel cylinder mounted on each wheel and a hydraulic pressure generator for supplying a brake fluid pressure to each of the wheel cylinders at least in accordance with an operation of a brake pedal. It can be constituted by a device and a brake fluid pressure control device interposed between the fluid pressure generating device and the wheel cylinder to control the brake fluid pressure of the wheel cylinder.

FIG. 2 shows the overall configuration of a vehicle control system according to an embodiment of the present invention. The brake hydraulic system is configured as shown in FIG. 3, for example. In FIG. 2, an engine EG is an internal combustion engine provided with a throttle control device TH and a fuel injection device FI.
In H, the main throttle opening of the main throttle valve MT is controlled according to the operation of the accelerator pedal AP. Further, the sub-throttle valve ST of the throttle control device TH is driven to control the sub-throttle opening in accordance with the output of the electronic control unit ECU, and the fuel injection device FI is driven to control the fuel injection amount. It is configured.

In FIG. 2, wheels FL indicate front left wheels as viewed from the driver's seat, wheel FR indicates front right wheels, wheel RL indicates rear left wheels, and wheel RR indicates rear right wheels. , RL, RR are mounted with wheel cylinders Wfl, Wfr, Wrl, Wrr, respectively. In the present embodiment, a four-wheel drive system is configured, and an engine EG is connected to wheels FL and FR in front of the vehicle via a front differential DF.
A rear wheel R via a transmission GS, a center differential DC, and a rear differential DR;
L, RR. Therefore, all the wheels FL,
FR, RL, and RR can be drive wheels.

The transmission GS is a shift lever (not shown)
Is changed to a plurality of shift positions, and among these, the shift position for selecting the low-range four-wheel drive gear is L4. The low-range shift position L4 is connected to the center differential lock mechanism in the conventional device. However, in the present invention, it is not necessary to provide a center differential lock mechanism. There is no connection to the mechanism.

Wheel speed sensors WS1 to WS4 are provided on the wheels FL, FR, RL, RR, and are connected to the electronic control unit ECU. The rotation speed of each wheel, that is, the number of pulses proportional to the wheel speed is determined. Is input to the electronic control unit ECU. Further, a brake switch BS that is turned on when the brake pedal BP makes a stroke, a G sensor (not shown) that detects the acceleration of the vehicle, and the like are connected to the electronic control unit ECU. Further, an electronic control unit ECU outputs an idle switch signal for outputting an idle area or an output area as an on / off signal from the throttle sensor TS, and a throttle opening signal of the main throttle valve MT and the sub throttle valve ST.
Is input to As described above, the operation and non-operation of the accelerator pedal AP can be detected based on the idle switch signal of the throttle sensor TS.

Further, an inclination sensor GX for detecting an inclination angle of the vehicle is provided, which is also connected to the electronic control unit ECU. The inclination sensor GX, which is an inclination detecting means,
A weight is provided that is swingably supported in the front-rear direction of the vehicle, and outputs a signal (Gx) representing a displacement that the weight has moved in accordance with the inclination of the vehicle in the front-rear direction. This signal G
Based on x, when the vehicle is stopped, the inclination angle (Gr) of the vehicle in the front-rear direction is obtained as Gr = K · Gx (K is a constant). On the other hand, when the vehicle moves, the signal Gx fluctuates according to the acceleration of the vehicle.
r is obtained based on the following equation.

That is, Gr (n) = kGr (n-1) + (1-
k) The present inclination angle G based on K · (Gx−Gw)
r (n) is required. Here, Gr (n-1) is a previously obtained inclination angle, and k represents a weight coefficient (where 0 <k <
1). Gw is the vehicle acceleration, which is substituted by the estimated vehicle acceleration DVso. Note that the inclination angle Gr in the present embodiment is set to a positive value when the traveling direction of the vehicle is an upward inclination, and is set to a negative value when the traveling direction is a downward direction.

The electronic control unit ECU has a microcomputer CMP, and as shown in FIG.
T, output port OPT, processing unit CPU,
The memory ROM and the memory RAM are interconnected via a bus. The wheel speed sensors WS1 to WS4,
Output signals from the brake switch BS, G sensor (not shown) and the like are configured to be input to the processing unit CPU from the input port IPT via an amplifier circuit (represented by AMP). Also, the output port OP
A control signal is output from T to a throttle control device TH and a brake fluid pressure control device PC via a drive circuit (typically represented by ACT). In the microcomputer CMP, the memory ROM stores a program corresponding to the flowchart shown in FIG. 4, etc., and the processing unit CPU executes the program while an ignition switch (not shown) is closed. Temporarily stores variable data necessary for executing the program.

FIG. 3 shows a brake hydraulic system according to an embodiment of the present invention. The front and rear piping type hydraulic system is divided into a front wheel hydraulic control system and a rear wheel hydraulic control system. Have been. The hydraulic pressure generator has a master cylinder MC and a regulator RG, which are driven in response to the operation of the brake pedal BP. Regulator RG
Are connected to an auxiliary hydraulic pressure source AS, which is connected to a low-pressure reservoir RS together with a master cylinder MC.

The auxiliary hydraulic pressure source AS has a hydraulic pump HP and an accumulator Acc. The hydraulic pump HP is driven by the electric motor M, boosts and outputs the brake fluid in the low-pressure reservoir RS, and the brake fluid is supplied to the accumulator Acc via the check valve CV6 and accumulated. The electric motor M is driven in response to the hydraulic pressure in the accumulator Acc falling below a predetermined lower limit, and stops in response to the hydraulic pressure in the accumulator Acc exceeding the predetermined upper limit. Thus, the so-called power hydraulic pressure is appropriately supplied from the accumulator Acc to the regulator RG. The regulator RG receives the output hydraulic pressure of the auxiliary hydraulic pressure source AS, and uses the output hydraulic pressure of the master cylinder MC as a pilot pressure to regulate the pilot hydraulic pressure to a regulator hydraulic pressure proportional to the pilot hydraulic pressure. The description is omitted. Note that a part of the regulator hydraulic pressure is used for driving the master cylinder MC at the double pressure.

Electromagnetic switching valves SA1 and SA2 are interposed in the front-wheel-side hydraulic pressure paths MF1 and MF2 connecting the master cylinder MC and the wheel cylinders Wfr and Wfl in front of the vehicle. Via AF1 and AF2, they are respectively connected to solenoid on-off valves PC1, PC5 and solenoid on-off valves PC2, PC6 for supply / discharge control. Hydraulic path M
F1 (or MF2) is provided with a pressure sensor PS that detects the output brake fluid pressure of the master cylinder MC. Also, the regulator RG and the wheel cylinder Wr
An electromagnetic opening / closing valve SA3 is interposed in the hydraulic passage MR for connecting each of r, Wrl, etc., and electromagnetic opening / closing valves for supply / discharge control are respectively provided in the hydraulic passages MR1 and MR2 branched from the hydraulic passage MR. P
C3, PC7 and solenoid on-off valves PC4, PC8 are interposed. The auxiliary hydraulic pressure source AS is connected to the downstream side of the electromagnetic on-off valve SA3 via the hydraulic pressure path AM, and the hydraulic pressure path AM is provided with an electromagnetic on-off valve STR. Solenoid on-off valve STR
Is a two-port, two-position solenoid on-off valve which is shut off when in the non-operating closed position and closed in the open position during operation.
1 to PC4 directly communicate with the accumulator Acc of the auxiliary hydraulic pressure source AS.

In the front-wheel-side hydraulic system, the electromagnetic switching valve SA1
And the electromagnetic switching valve SA2 is a three-port two-position electromagnetic switching valve. When not operated, it is at the first position shown in FIG. 3 and both the wheel cylinders Wfr and Wfl are connected to the master cylinder MC. When the solenoid coil is excited and switched to the second position, the wheel cylinders Wfr, Wf
In each of the drawings, communication with the master cylinder MC is interrupted, and the solenoid on-off valves PC1 and P1 are connected via hydraulic pressure paths AF1 and AF2, respectively.
It is connected between C5 and between the electromagnetic switching valves PC2 and PC6. The electromagnetic on-off valves PC1 and PC2 are connected to the electromagnetic on-off valve STR via a hydraulic passage AC. Further, the solenoid on-off valves PC5 and PC6 are connected to the reservoir RS via the hydraulic passage RC.

Check valves CV1 and CV2 are connected in parallel to the solenoid on-off valves PC1 and PC2. The inflow side of the check valve CV1 is a hydraulic passage AF1, and the inflow side of the check valve CV2 is a hydraulic passage AF2. Connected to each other. Check valve CV
When the brake pedal BP is released in a case where the electromagnetic switching valve SA1 is at the operating position (second position), the brake fluid pressure of the wheel cylinder Wfr quickly follows the decrease of the output fluid pressure of the regulator RG. The flow of the brake fluid in the direction of the regulator RG is allowed, but the flow in the reverse direction is restricted.
The same applies to the check valve CV2.

Next, in the rear-wheel-side hydraulic system, the solenoid on-off valve SA3 is a two-port, two-position solenoid on-off valve, and is in the open position shown in FIG.
Communicates with the regulator RG. At this time, the solenoid on-off valve STR is in the closed position, and the communication with the accumulator Acc is shut off. When the electromagnetic on-off valve SA3 is switched to the closed position at the time of operation, the electromagnetic on-off valves PC3 and PC4 are disconnected from the regulator RG, but when the electromagnetic on-off valve STR is activated, the electromagnetic on-off valves PC3 and PC4 (and PC1, PC2) are turned off.
PC2) is connected in communication with the accumulator Acc.

Further, check valves CV3 and CV4 are connected in parallel to the solenoid on-off valves PC3 and PC4. Connected to each other. These check valves CV3, CV4 are provided to make the brake fluid pressure of the wheel cylinders Wrr, Wrl quickly follow the decrease of the output fluid pressure of the regulator RG when the brake pedal BP is released. The flow of the brake fluid in the direction of the solenoid on-off valve SA3 is allowed, and the flow in the reverse direction is restricted. Further, the solenoid on-off valve SA
3, a check valve CV5 is provided in parallel with the brake pedal BP even when the electromagnetic on-off valve SA3 is closed.
Is operated, the brake fluid pressure from the regulator RG is supplied to the solenoid on-off valves PC1 to PC4 via the check valve CV5, and the brake pedal BP can be further depressed.

The electromagnetic switching valves SA1 and SA2 and the electromagnetic switching valves SA3 and STR, and the electromagnetic switching valves PC1 to PC
8 is driven and controlled by the electronic control unit ECU,
Various controls such as traction control are performed as described below. As described above, the hydraulic pump HP is driven by the electric motor M, and the power hydraulic pressure is accumulated in the accumulator Acc. During normal braking operation, each solenoid valve is in the normal position shown in FIG. When the brake pedal BP is depressed in this state, the master cylinder hydraulic pressure is output from the master cylinder MC and the regulator hydraulic pressure is output from the regulator RG, and the electromagnetic switching valves SA1 and SA2, the electromagnetic on-off valve SA3, and the electromagnetic on-off valve Wheel cylinders W via PC1 through PC4
fr to Wrl.

For example, when the control shifts to the traction control, for example, when the acceleration slip prevention control of the wheel FR is performed, the electromagnetic switching valve SA1 is switched to the second position, and the driven wheel side (rear wheel side) wheel cylinder is switched. Wrr,
The solenoid on-off valves PC3 and PC4 and the solenoid on-off valve SA3 connected to Wrl are in the closed position, and the solenoid on-off valves STR and PC1 are in the open position. As a result, the power hydraulic pressure accumulated in the accumulator Acc is supplied to the wheel cylinder Wfr via the electromagnetic opening / closing valve STR in the open position.

When the solenoid on-off valve PC1 is set to the closed position, the hydraulic pressure of the wheel cylinder Wfr is maintained. Therefore, if the solenoid on-off valve PC1 is intermittently controlled while the solenoid on-off valve PC5 is in the closed position, the brake fluid in the wheel cylinder Wfr is repeatedly increased in pressure and held, and increases in a pulsed manner, and is gradually increased. Further, when the solenoid on-off valve PC5 is set to the open position, the wheel cylinder Wfr communicates with the low-pressure reservoir RS via the hydraulic passage RC, and the wheel cylinder Wfr
Brake fluid flows out into the low-pressure reservoir RS and is decompressed.

Thus, by the intermittent control of the solenoid on-off valves PC1 and PC5 in accordance with the acceleration slip state of the wheel FR, any one of the hydraulic pressure modes of pressure increase, pressure decrease, and holding is set for the wheel cylinder Wfr. . As a result, the braking force is applied to the wheels FR, the rotational driving force is limited, the acceleration slip is prevented, and the traction control can be appropriately performed. Acceleration slip prevention control is similarly performed on wheel FL. Further, the brake control (hereinafter, simply referred to as brake control) for the wheels FR, FL to be controlled in the present embodiment can be performed by the intermittent control of the electromagnetic on-off valve PC1 and the like in the same manner as described above. The brake control will be described later in detail.

On the other hand, the mode shifts to the anti-skid control during the braking operation, for example, when it is determined that the wheel FR side is in a locking tendency, the electromagnetic switching valve SA1 is switched to the second position, and the electromagnetic switching valve PC1 is closed. At the same time, the electromagnetic on-off valve PC5 is set to the open position. Thus, the brake fluid in the wheel cylinder Wfr flows into the low-pressure reservoir RS and is reduced in pressure.

When the wheel cylinder Wfr enters the gradual pressure increase mode, the solenoid on-off valve PC5 is closed and the solenoid on-off valve PC1 is opened, and the solenoid on-off valves SA3 and SA3 whose regulator hydraulic pressure is in the open position from the regulator RG. The fluid is supplied to the wheel cylinder Wfr via the hydraulic pressure path AC, the electromagnetic switching valve PC1 at the open position, and the electromagnetic switching valve SA1 at the second position. Then, the electromagnetic on-off valve PC1 is intermittently controlled, and the brake fluid in the wheel cylinder Wfr is repeatedly increased in pressure and held, and increases in a pulsed manner, and is gradually increased. When the rapid pressure increase mode is set for the wheel cylinder Wfr, the solenoid on-off valves PC1 and PC5 are set to the normal positions shown in FIG. 3 and then the solenoid-operated switching valve SA1 is set to the first position. Cylinder hydraulic pressure is supplied. The brake hydraulic pressure of the wheel cylinder Wfl is similarly controlled. Rear wheels RR, RL
When the anti-skid control is performed, the solenoid on-off valves PC3 and PC
4 and the electromagnetic on-off valves PC7 and PC8 are controlled in the same manner as the front wheels.

In the control system configured as described above, a series of processes such as the traction control and the anti-skid control, as well as the brake control of the present invention, are performed by the electronic control unit ECU. The flowchart of FIG. 4 shows a brake control process when the engine is braked on a downhill road. When an ignition switch (not shown) is closed, the execution of the program starts. First, in step 101, the microcomputer CMP is initialized, and after various calculated values are cleared, in step 102, after the control timer is cleared, counting starts. Subsequently, at step 103, the detection signals of the wheel speed sensors WS1 to WS4, the shift position signal of the transmission GS, and the detection signal of the inclination sensor GX are read into the microcomputer CMP.

Next, the routine proceeds to step 104, where the wheel speed Vw is determined based on the detection signals of the wheel speed sensors WS1 to WS4.
** (** represents wheels FL, FR, RL, RR) is calculated, and the wheel speed Vw ** is differentiated to obtain the wheel acceleration DV.
w ** is calculated. Then, in step 105, the estimated vehicle speed Vso of the vehicle is calculated based on the wheel speed Vw **. Specifically, the previously calculated estimated vehicle speed is Vso (n
-1) and the estimated vehicle speed this time is Vso (n),
Vso (n) = MED [Vso (n-1) .alpha.up.t, MAX
(Vw **), Vso (n-1) .alpha.dw.t]. Here, MED is a function for obtaining an intermediate value, and MAX is a function for obtaining a maximum value. t represents a calculation cycle, and αup
Represents a constant acceleration and αdw represents a constant deceleration. Based on the previous estimated vehicle speed Vso (n-1), the maximum value MAX (Vw
**).

Vw ** is the wheel speed of each wheel **. MAX (Vw **) is calculated by calculating only the wheel speed of a wheel that is not a non-ground wheel (that is, a ground wheel) and is not controlled. Is used. Therefore, in the present embodiment, the wheel speed of the wheel (wheel RR or RL) that is not the non-grounded wheel among the wheels RR and RL behind the vehicle that is not the control target is the estimated vehicle body speed Vso.
It will be. Then, the current estimated vehicle speed Vs
o (n) and the previous estimated vehicle speed Vso (n-1) [Vso
(n) -Vso (n-1)], the estimated vehicle body acceleration DVso can be obtained.

Then, the routine proceeds to step 106, where the inclination angle Gr is a positive value based on the output signal of the inclination sensor GX as described above (a positive value when the traveling direction of the vehicle is an upward gradient, and a descending value when the traveling direction is a downward direction). Is a negative value). Then, in step 107, for example, the estimated vehicle speed V
Whether or not the vehicle is on a downhill road is determined based on so and the inclination angle Gr, which will be described later with reference to FIG. Further, the routine proceeds to step 108, where the slip state of the wheel is determined, and the presence or absence of the non-ground contact wheel is determined. This will be described later with reference to FIG.

In step 109, a determination is made as to whether or not the brake control can be performed on the control target wheels (the front wheels FR and FL in the present embodiment) at the time of engine braking, that is, a start determination is made. It is. The details will be described later with reference to FIG. Next, in step 110, a termination condition of the brake control is determined (the details will be described later with reference to FIG. 8). Subsequently, in step 111, the start condition of the start specifying control is determined, in step 112, the end condition of the start specifying control is determined, and in step 113, the start specifying control hydraulic mode is set (details are given respectively). 9, 10 and 11).

Then, in step 114, a hydraulic mode for normal control is set (details will be described later with reference to FIG. 12), and in step 115, a control mode will be set (details will be described with reference to FIG. 13). At step 116, a solenoid signal is output based on the hydraulic mode, and the wheel cylinder hydraulic pressure is controlled. Finally step 11
At 7, the control timer, which started counting at step 102, waits until a predetermined time Ts (for example, 10 ms) has elapsed, and then returns to step 102.

FIG. 5 shows a process of judging a downhill road executed in step 107 of FIG.
At 1, it is determined whether the estimated vehicle speed Vso is equal to or higher than a predetermined speed V1 (for example, 7 km / h). Estimated vehicle speed V
If so is determined to be equal to or higher than the predetermined speed V1, step 20
2 and the inclination angle Gr becomes a predetermined angle Kr (for example, −15).
Degree). When the inclination angle Gr is equal to or smaller than the predetermined angle Kr, that is, when the vehicle is on a downhill road inclined at a predetermined angle | Kr | ) Is determined. If the predetermined time T1 (for example, 1 second) has elapsed while the inclination angle Gr is equal to or smaller than the predetermined angle Kr, the process proceeds to step 204, where the downhill flag is set (1). If the predetermined time T1 has not elapsed, In step 205, the ON timer is incremented. Thereafter, at step 206, the OFF timer is cleared and the routine returns to the main routine.

When it is determined in step 202 that the inclination angle Gr exceeds the predetermined angle Kr, it is determined in step 207 whether the OFF timer has exceeded a predetermined time T1. If the predetermined time T1 has elapsed, the downhill flag is reset (0) at step 208, and if the predetermined time T1 has not elapsed, the OFF timer is incremented at step 209. Then, in step 210, the ON timer is cleared and the process returns to the main routine. On the other hand, if it is determined in step 201 that the estimated vehicle speed Vso is lower than the predetermined speed V1, the downhill flag is reset in step 211, and then the ON timer and the OFF
The timer is cleared and the process returns to the main routine.

That is, the inclination angle Gr equal to or smaller than the predetermined angle Kr.
(A state in which the vehicle is traveling on a slope inclined with the vehicle traveling direction as the down direction) for a predetermined time T1, the down slope flag is set, and conversely, the predetermined angle Kr
If the state of the inclination angle Gr exceeding the predetermined value continues for the predetermined time T1, the downhill flag is reset. At this time, since the delay timer is configured by the ON and OFF timers, the influence of the noise of the inclination sensor GX is avoided.

Next, FIG. 6 shows the non-ground wheel determination processing executed in step 108 of FIG. 4. Slip detecting means is configured to determine the slip state for each wheel. Is performed only for the rear wheels RR and RL. First, at step 301, it is determined whether or not the non-ground wheel flag is set for the wheel RR or RL. If the non-ground wheel flag is not set (0), the slip state of the wheel (RR or RL) is determined in steps 302 to 305. That is,
If the wheel speed is rapidly decreasing without the brake operation being performed, it is determined that the vehicle is slipping, but it is distinguished from anti-skid control or the like, and is determined to be a non-ground wheel that is idling. Specifically, first, at step 302, it is determined whether or not the brake switch BS is off. Brake pedal BP is not operated and brake switch BS
Is off, the routine proceeds to step 303, where it is determined whether or not the brake control has already been performed on the wheel to be controlled. If not, the routine proceeds to step 304.

In step 304, the wheel speed Vw ** is compared with the reference speed (Vso-KV1), and the reference speed (Vso-KV1) is compared.
If Kv1), the routine proceeds to step 305, where the wheel acceleration DVw ** is compared with the reference acceleration KG. When the wheel acceleration DVw ** is lower than the reference acceleration KG, it is determined that the wheel ** (the wheels RR and RL in the present embodiment) is slipping and is not in the ground contact state. The contact wheel flag is set (1). Then, after a timer counter described later is cleared (0) in step 307, the process returns to the main routine.
Note that Vso at the reference speed (Vso-KV1) is the estimated vehicle speed described above, and KV1 is a constant value. If any of the conditions in steps 302 to 305 is not satisfied, the process returns to the main routine.

On the other hand, if it is determined in step 301 that the non-ground wheel flag has already been set, step 3
In 08, it is determined whether or not the brake switch BS is off. When the brake pedal BP is operated and the brake switch BS is on, the routine jumps to step 313, and the non-ground wheel flag for the wheel is reset (0). If the brake pedal BP has not been operated yet and the brake switch BS is off, the process proceeds to steps 309 to 312 and the wheel (RR or R
It is determined whether or not L) is in contact with the ground and the wheel speed has been recovered. That is, the wheel speed Vw ** is equal to the reference speed (Vso-
KV2) and the reference speed (Vso + KV3), it is determined that the slip state has been released when it is determined that the state has been continued for the predetermined time T2, and the corresponding wheel (RR or R
The non-ground wheel flag of L) is reset (0). In addition, K
V2 is a constant value corresponding to the second predetermined value of the present invention, and the reference speed (Vso-KV2) corresponds to the second threshold value of the present invention. Similarly, KV3 is a constant value corresponding to the third predetermined value of the present invention, and the reference speed (Vso + KV3) corresponds to the third threshold value of the present invention.

Specifically, at step 309, the wheel speed Vw ** is changed to the reference speed (Vso-KV2) and the reference speed (Vso-KV2).
+ KV3), the timer counter is cleared (0) in step 311 and then in step 312
Proceed to. When the wheel speed Vw ** is between the reference speed (Vso-KV2) and the reference speed (Vso + KV3), at step 310, the timer counter is incremented (+
After 1), the process proceeds to step 312. Then, in step 312, when the timer counter becomes equal to or longer than the predetermined time T2, the non-ground wheel flag of the wheel (RR or RL) is reset (0). Thus, the wheel speed Vw **
Are the reference speed (Vso-KV2) and the reference speed (Vso + KV)
The reason that the condition for the recovery determination is that the state having the value between 3) and the predetermined time T2 has continued will be described later with reference to FIG.

FIG. 7 shows the brake control start determination process executed in step 109 of FIG. 4. First, in step 401, it is determined whether or not the idle switch signal of the throttle sensor TS is an ON signal. If it is determined that the idle switch signal is an ON signal (that is, if the accelerator pedal AP is in the non-operating state), step 40
The routine proceeds to 2, where it is determined whether or not the transmission GS is at the low-range shift position L4. If the transmission GS is in the low-range shift position L4, it is determined in step 403 whether the downhill flag is in the set (1) state. If the downhill road flag is set, step 404 is further executed.
Then, it is determined whether or not the above-mentioned non-ground wheel flag is set (1). If the non-ground wheel flag is set, the process proceeds to step 405.

Thus, in the present embodiment, step 4
01 to 404 are satisfied,
It is determined that the vehicle is in the engine braking state, and the routine proceeds to steps 405 and 406, where the brake control flag is set (1) for both the wheels FR and FL. In the determination of the engine brake, some of these conditions may be omitted as appropriate, or other conditions may be added. Steps 401 to 404 above
If any one of the conditions is not satisfied, the process returns to the main routine, and the brake control for the control target wheels (the wheels FR and FL in the present embodiment) at the time of engine braking is not performed.

FIG. 8 shows the brake control end determination process executed in step 110 of FIG. 4. In step 501, it is determined whether or not the idle switch signal of the throttle sensor TS is an ON signal. If the idle switch signal is an ON signal, the process proceeds to step 502, where it is determined whether or not the downhill flag is set. If the downhill flag is set, step 5
Proceeding to 03, it is determined whether or not the non-ground wheel flag is set for one of the wheels RR and RL behind the vehicle. Is continued. If any of the conditions in steps 501 to 503 is not satisfied, the brake control for both the wheels FR and FL is terminated, and the routine proceeds to steps 504 and 505, where the brake control flag for the wheels FR and FL is reset. After performing (0), the process returns to the main routine.

FIG. 9 shows the process of the start specific control start determination executed in step 111 of FIG. 4. In step 601, the previous state of the brake control flag of any one of the wheels ** is determined. . Note that the wheels to be controlled in FIGS. 9 to 13 are the wheels FR and FL in front of the vehicle in the present embodiment, but they are represented by the wheels ** without specifying them. In step 601, the previous time was wheels *
If it is determined that the * brake control flag is not set, the routine proceeds to step 602, where the current state of the brake control flag is determined. If it is determined that the brake control flag that has not been set previously is set this time (1), it means that the brake control has just started, and the process proceeds to step 603, where the wheel ** start specifying control flag is set. Is done. If it is determined in step 601 that the brake control flag has been set last time, or if it is determined in step 602 that it has not been set this time, the process returns to the main routine.

FIG. 10 shows the process of determining the end of the specific start control executed in step 112 of FIG. 4. In step 701, the state of the start specific control flag of any one of the wheels ** is determined. If the specific control in-progress flag is not set, the process returns to the main routine. If the start specific control in progress flag is set, step 70
Proceeding to 2, the start specific control counter CTF ** of the wheel ** is compared with a predetermined time KT. Start specific control counter CT
If F ** is determined to be equal to or longer than the predetermined time KT, step 70
At 3, the start specific control flag of the wheel ** is reset (0). In step 701, it is determined that the start specific control flag of wheel ** is in the reset state, or in step 702, start specific control counter CTF **.
If it is determined that the count value has not reached the count value corresponding to the predetermined time KT, the process returns to the main routine.

FIG. 11 shows the process of setting the start-specific control hydraulic pressure mode executed in step 113 of FIG. 4. In step 801, the state of the start-specifying control flag of any one of the wheels ** is determined. Is done. If the start specific control flag of the wheel ** is set, step 802 is executed.
** (In this embodiment, the wheels FR,
The hydraulic pressure mode of FL) is set to the rapid pressure increase mode. On the other hand, if the start-specific-control-in-progress flag is not set for the wheel **, the process returns to the main routine.

FIG. 12 shows the processing for setting the normal control hydraulic pressure mode executed in step 114 of FIG. 4. In step 901, the state of the brake control flag of any one of the wheels ** is determined, and If not, the process returns to the main routine of FIG. If the brake control flag is set for the wheel ** (the wheels FR and FL in front of the vehicle in the present embodiment), the process proceeds to step 902 and the subsequent steps, and the hydraulic pressure mode is set to one of the pulse pressure increasing, the pulse decreasing and the holding. Is done.

First, at step 902, the wheel speed V
w ** is compared with the estimated vehicle speed Vso, and if it exceeds, the pulse pressure increasing mode is set at step 903. If the wheel speed Vw ** is equal to or lower than the estimated vehicle body speed Vso, the wheel speed Vw ** is further compared with a reference speed (Vso-KV4) in step 904 (where KV4 is a constant speed). When the wheel speed Vw ** is also lower than the reference speed (Vso-KV4), the process further proceeds to step 905, where it is determined whether the wheel acceleration DVw ** is positive or negative. Is done. If the wheel acceleration DVw ** is 0 or a positive value, and if the wheel speed Vw ** is equal to or higher than the reference speed (Vso-KV4), the holding mode is set in step 907.

FIG. 13 shows the control mode setting process executed in step 115 of FIG.
At 01, the state of the start specific control flag of any one of the wheels ** is determined. If the start-specific-control-in-progress flag of the wheel ** has been set, the routine proceeds to step 1002, where the control mode is set to the start-specific control hydraulic mode. If the start-specific-control-in-progress flag of the wheel ** is not set in step 1001, the process proceeds to step 1003, and the state of the brake-control-in-progress flag of the wheel ** is determined. If the brake control flag of the wheel ** is set in step 1003, the process proceeds to step 1004, the control mode is set to the normal control hydraulic pressure mode, and if the brake control flag of the wheel ** is not set, the process proceeds to step 1004. Proceeding to 1005, the control mode is set to the pressure increase mode (normal braking operation state). Although FIG. 13 shows the relationship between the brake control and the start specifying control during engine braking in the present embodiment, control modes such as traction control and anti-skid control can be incorporated into this.

Next, the above control situation will be described with reference to FIG. In the upper part of FIG. 14, the wheel speeds VwF * of the front wheels FR and FL to be controlled are indicated by solid lines, and the wheel speeds VwR * of the rear wheels RR and RL which are non-ground wheels are indicated by broken lines. With respect to the wheel RR or RL, a slip state is determined in steps 302 to 305 in FIG. 6, the wheel speed VwR * falls below the reference speed (Vso−KV1), and the wheel acceleration DVwR * (omitted in FIG. K
G, the non-ground wheel flag is set and the wheel F
The brake control for R and FL starts. That is, FIG.
According to the processing of FIG. 7 and the wheels FR, FL at the point a in FIG.
Brake control is started, and the wheel cylinder hydraulic pressure is increased as shown in the lower part of FIG. From the point a to the point b in FIG. 14, the start specifying control is performed in accordance with the processing of FIGS. After the point b, the control shifts to the normal control of FIG. 12, and the pulse pressure increasing mode is set until the wheel speed VwF * falls below the estimated vehicle speed Vso, and the holding mode is set until the point d falls below the reference speed (Vso-KV4). It is said.

Then, the wheel speed VwF * becomes equal to the reference speed (Vs
If o-KV4) is exceeded, the mode is set to the pulse pressure reduction mode. If the wheel acceleration DVwF * turns to a positive value, the mode is set to the holding mode until point e. At point e, the wheel speed VwF * is the estimated vehicle speed Vs
When the vehicle speed exceeds o, a pulse pressure increase mode is set, and thereafter, similarly, the wheel cylinder fluid pressure of the wheels FR and FL is controlled, and the wheel speed VwR * of the wheel RR or RL is set to the reference speed (Vso-K
V2) and the reference speed (Vso + KV3), the brake control ends at the point f where the predetermined time T2 has elapsed, and the pressure is reduced.

By the way, the four-wheel drive vehicle provided with the center differential as in the present embodiment is put into an engine braking state while traveling on a downhill road, and the wheels RR behind the vehicle are driven.
Or, when RL is a non-ground wheel, the wheel rotates in the opposite direction, so the wheel speed VwR * falls below the speed 0,
Becomes a negative value. On the other hand, since the wheel speed sensors WS1 to WS4 cannot generally distinguish between normal rotation and reverse rotation, their output signals are as shown by two-dot chain lines in FIG. That is, the output signal of the wheel speed sensor WS2 or WS4, which indicates the wheel speed VwR *, has a positive value even during reverse rotation. As a result, the wheel speed VwR * is different from the actual wheel speed, as indicated by hatching in FIG.
−KV4), and it may be determined that the wheel speed has recovered.

Therefore, in this embodiment, as shown in steps 309 to 312 of the flowchart of FIG. 6, the wheel speed Vw ** (the wheel speed VwR * in FIG. 14) is set to the reference speed (Vso-KV2). The condition for the recovery determination is that the state having the value between the speed (Vso + KV3) and the predetermined time T2 has been continued, and is set so as to be able to be distinguished from the error caused when the wheel rotates in reverse. Note that the reference speed (Vso +
KV3) or less, and remove the reference speed (Vso-KV).
2) Only the above condition may be satisfied.

According to the traveling control device of the present embodiment, the four-wheel drive vehicle having the center differential is
For example, when at least one of the wheels RR and RL behind the vehicle is in a non-ground state in a state where the engine is braked while traveling on an unpaved steep downhill road, the wheel speed Vw
When R * falls below the reference speed (Vso-KV1), which is the first threshold, and the wheel acceleration DVwR * falls below the reference acceleration KG, the wheel RR or RL is determined to be a non-ground wheel. Then, when the wheel speed VwR * is equal to the reference speed (V
(so-KV2) and falls below the third threshold value of the reference speed (Vso + KV3) for a predetermined time T2, it is determined that the wheel RR or RL is in the ground contact state. The non-ground state and the ground state of the RL can be easily and reliably determined. Therefore, in this case, an appropriate braking operation can be performed by applying a braking force to the wheels FR and FL in front of the vehicle.
Although the downhill determination (step 107 and the like) is provided in the above-described embodiment, if this is omitted, the same can be applied to engine braking other than downhill.

Next, another embodiment of the present invention will be described with reference to FIG.
The description will be made with reference to the drawings after 5. Since the basic configuration of the present embodiment is the same as that of FIGS. 2 and 3 described above, the description thereof is omitted. The flowchart of the traveling control in the present embodiment is substantially the same as that described in the flowchart of FIG. 4 except for step 108, and thus the description thereof will be omitted. However, the wheel speed sensors WS1 to WS4 of the present embodiment are not described. Unlike the form (however, the sign is the same), the function of identifying the direction of rotation, namely, forward rotation (represented by +) in which the wheel rotates in the vehicle traveling direction and reverse rotation (represented by-) in the reverse direction ) Is identified. Although illustration of the structure is omitted, for example, by combining output signals of a pair of detection elements, it is possible to identify the rotation direction based on a phase difference or the like.

In the present embodiment, step 1 in FIG.
In step 108, the slip ratio Sa ** of each wheel is calculated as Sa ** = [(Vso-Vw) / Vs based on the wheel speed Vw ** calculated in steps 04 and 105 and the estimated vehicle speed Vso.
o] × 100 (%). At this time, assuming that the rotation direction of the wheels in the traveling direction of the vehicle is positive and the reverse direction is negative, the slip ratio Sa ** becomes a negative value during acceleration slip of the vehicle, and the slip ratio Sa ** becomes positive during deceleration slip. As a value, a value of 100% or more can be adopted. By setting the slip ratio Sa ** in this way, it can be effectively used in later calculations. In this embodiment,
4. Downhill determination corresponding to step 107 in FIG. 4, start identification control start determination corresponding to step 111, step 1
Start specific control end determination corresponding to step 12, and step 1
The control mode setting corresponding to No. 15 is the same as the processing described in FIGS. 5, 9, 10, and 13, respectively, and thus will not be described.

FIG. 15 shows a brake control start determination executed in this embodiment (corresponding to step 109 in FIG. 4).
First, in step 1401, it is determined whether or not the idle switch signal of the throttle sensor TS is an ON signal. When the idle switch signal is determined to be an ON signal (accelerator pedal AP is not operated)
In step 1402, it is determined whether the transmission GS is at the low-range shift position L4. If the transmission GS is at the low-range shift position L4, then step 1
At 403, it is determined whether the downhill flag is in the set (1) state. If the downhill flag has been set, the routine proceeds to step 1404, where the acceleration state of the vehicle is determined.

That is, the current estimated vehicle acceleration DVso (n)
It is determined whether or not the difference between the previous estimated vehicle acceleration DVso (n-1) and the previous estimated vehicle acceleration DVso (n-1) exceeds a predetermined acceleration D1 (for example, 0.05 G, where G is the gravitational acceleration). When it is determined that the difference exceeds the predetermined acceleration D1, the vehicle is being driven in the acceleration direction, and the condition for starting the anti-skid control is sharply distinguished. Thus, in the present embodiment, when all of the conditions of steps 1401 to 1404 are satisfied, it is determined that the vehicle is in the engine braking state, and the process proceeds to step 1405. In the determination of the engine brake, some of these conditions may be omitted as appropriate, or other conditions may be added.

Then, in step 1405, the slip ratio Sa ** of any one of the wheels ** is set to the predetermined slip ratio S1.
If it is not less than (for example, 30%), it is determined that the wheel ** is idling without contact with the ground, and the routine proceeds to step 1406, where the brake control flag of the wheel ** is set (1). When the slip ratio Sa ** of the wheel ** is equal to or higher than the predetermined slip ratio S1, the start condition of the anti-skid control for the wheel ** may be satisfied. Thus, it is clear that the vehicle is being driven in the acceleration direction, so that there is no confusion with the start condition of the anti-skid control. If any of the conditions in steps 1401 to 1405 is not satisfied, the process returns to the main routine without performing the brake control.

FIG. 16 shows the brake control end determination process (corresponding to step 110 in FIG. 4) executed in this embodiment. In step 1501, the estimated vehicle speed Vso is reduced to the predetermined speed V2 (for example, 15 km / sec. h) It is determined whether or not: When the estimated vehicle speed Vso is the predetermined speed V
If it is determined that the value is 2 or less, the process proceeds to step 1502, and it is determined whether or not the hydraulic mode at that time is the pressure reduction mode. * Is compared with a predetermined slip ratio S2 (for example, 20%). If it is determined in step 1503 that the slip ratio Sa ** is equal to or smaller than the predetermined slip ratio S2, the process proceeds to step 1504, where it is determined whether the estimated value of the brake fluid pressure at that time is zero. If the estimated value of the brake fluid pressure is 0 (point f in FIG. 19) and it is determined that the brake operation has not been performed, step 150
At 5, the brake control flag for the wheel ** is reset (0) and the process returns to the main routine. Step 1 above
If any of the conditions from 501 to 1504 is not satisfied, the process returns to the main routine and brake control is continued.

FIG. 17 shows the setting of the start-specific control hydraulic pressure mode executed in the present embodiment (step 113 in FIG. 4).
In step 1801, the state of the start-specific-control flag of any one of the wheels ** is determined. If the start specific control flag of the wheel ** is set, the routine proceeds to step 1802, where the start specific control counter CTF ** of the wheel ** is incremented (+1).
00%. When it is determined in step 1803 that the slip ratio Sa ** is less than 100%,
Since the wheel ** is in the normal rotation state, the flow proceeds to step 1804, and the hydraulic mode for the wheel ** is set to the rapid pressure increase mode (point a in FIG. 19). On the other hand, when it is determined that the slip ratio Sa ** is 100% or more, it means that the wheel ** is in a stopped or reverse rotation state. Mode is set (b in FIG. 19).
point). If the start-specific-control-in-progress flag of the wheel ** is not set, in step 1806, the start specific control counter CTF ** is cleared (0) and the process returns to the main routine.

FIG. 18 shows the process of setting the normal control hydraulic pressure mode (corresponding to step 114 in FIG. 4) executed in this embodiment. Is determined, and if not set, the process returns to the main routine of FIG. If the brake control flag of the wheel ** is set, the process proceeds to step 1902, and according to the value of the slip ratio Sa ** of the wheel **, step 19 in FIG.
According to the map in 02, any one of the hydraulic modes of rapid pressure increase, pulse pressure increase, pulse pressure reduction, and rapid pressure reduction is set. still,
Since the pulse pressure increase (or pulse pressure reduction) is a repetition of the pressure increase (or pressure reduction) and the holding, the holding mode is included in these in the present embodiment. Slip ratio Sa ** is 100
% Is the area when the wheel ** rotates forward and the slip ratio Sa
The region where ** is 100% or more indicates that the wheel ** is in an engine braking state when the wheel rotates in reverse.

The situation during this period will be described with reference to FIG. 19. At point a, it is determined that the brake control has started, and the rapid pressure increase mode is set. The period of the predetermined time from the point a to the point c is processed as the above-described flowchart shown in FIG. 11 as the start specifying control. Slip ratio S at point b
When a ** becomes 100% (that is, when Vw ** = 0 km / h,
When the wheel is stopped or when the rotation is switched from normal rotation to reverse rotation or vice versa), the brake fluid pressure of the wheel cylinder is held. Can be switched. When it is determined that the wheels have returned to the normal rotation at the point e, the pulse pressure reduction mode is set. Thereafter, the pulse pressure reduction mode is maintained at the point f until the brake control is terminated, and the wheel speed Vw is reduced to the estimated vehicle speed Vso. Is controlled to asymptotically.

As described above, according to the present embodiment, in the start specific control, the wheel ** to be controlled is pressurized in the rapid pressure increase mode until the wheel ** to be controlled is once locked (slip ratio Sa ** = 100%). Thereafter, when pulse decompression is performed, the wheel ** starts either forward rotation or reverse rotation. When the wheel ** starts normal rotation, it is in contact with the ground, so it is set to the pulse depressurization mode. When it starts reverse rotation, it is idling, so the pressure increase mode is maintained and the lock state is established. Is maintained. Thus, the slip ratio Sa ** is 100% (V
w ** = 0 km / h) By controlling the brake fluid pressure of the wheel cylinder of the wheel to be controlled in the vicinity, the engine brake can be properly applied to the other wheels even when traveling on unpaved steep downhill roads. Can be. It should be noted that, if the downhill determination is omitted in the above-described embodiment, the same can be applied to engine braking other than downhill.

[0087]

The present invention has the following effects because it is configured as described above. That is, in the travel control device for a four-wheel drive vehicle provided with the center differential according to the first aspect, the engine brake determining means determines that the engine is in the brake state, and at least one of the wheels of the vehicle has at least one wheel. Since the braking force control means is configured to apply the braking force to at least one of all the wheels including the non-grounded wheel when the vehicle is in the non-grounded state, Even if at least one of the wheels is in a non-ground state in a state where the brake is applied, an appropriate braking operation can be performed. Furthermore, even if the center differential lock mechanism is eliminated, for example, smooth cornering can be performed without causing a tight corner braking phenomenon.

In particular, the traveling control device according to the second aspect of the present invention is further provided with downhill road determination means, which is also required to be traveling on a downhill road. When at least one of the wheels is in a non-ground state while the engine is being braked while traveling on a slope, a reliable and appropriate braking operation can be performed.

[0089] In the traveling control device, the determination as to whether or not the at least one wheel is in a non-contact state is made based on a wheel speed based on a wheel speed of the at least one wheel. If the vehicle is configured to determine that the wheel is in a non-ground state when it is detected, the non-ground state can be easily determined. Further, the detection of the slip of the wheel may be such that the slip ratio is calculated based on the wheel speed and the estimated vehicle speed, and the slip of the wheel is detected based on the slip ratio. The slip can be detected easily and reliably.

In the running control apparatus for a four-wheel drive vehicle according to the fifth aspect, the first threshold value obtained by subtracting the first predetermined value from the estimated vehicle body speed is set to one of the wheels. When the speed falls, it is configured to determine that the wheel is in a non-ground contact state. The non-ground state can be easily and reliably determined.

In the cruise control device according to the sixth aspect, in addition to the above, it is possible to easily and reliably determine that the at least one wheel has come into contact with the ground by the contact state determining means. When the determination is made, the application of the braking force to the wheels is released, so that the vehicle can be appropriately braked.
Further, in the travel control device according to the seventh aspect, it is possible to more reliably determine that the at least one wheel has come into contact with the ground.

The down-slope determination means may include an inclination detection means for detecting an inclination angle of the vehicle, and at least the inclination detection means may detect the inclination direction of the vehicle for a predetermined time. When the vehicle detects a slope angle that is equal to or more than a predetermined angle with the side as the downward direction, the traveling road surface of the vehicle can be determined to be a downward slope, and it is possible to appropriately determine the downward slope with a simple configuration. it can.

The engine brake judging means may include a shift position detecting means for detecting a shift position of the transmission of the vehicle, wherein at least the shift position detecting means is provided with a predetermined low speed. The vehicle can be configured to determine that the vehicle is in an engine braking state when the side shift position is detected and the downhill determination unit determines that the vehicle is on a downhill. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of an embodiment of a travel control device for a four-wheel drive vehicle of the present invention.

FIG. 2 is an overall configuration diagram of an embodiment of a traveling control device according to the present invention.

FIG. 3 is a configuration diagram illustrating an example of a brake hydraulic system according to an embodiment of the present invention.

FIG. 4 is a flowchart showing the entire running control of the four-wheel drive vehicle in one embodiment of the present invention.

FIG. 5 is a flowchart showing downhill determination of traveling control in one embodiment of the present invention.

FIG. 6 is a flowchart showing a non-ground wheel determination of traveling control in one embodiment of the present invention.

FIG. 7 is a flowchart illustrating a start determination of traveling control according to the embodiment of the present invention.

FIG. 8 is a flowchart showing a determination of the end of traveling control in one embodiment of the present invention.

FIG. 9 is a flow chart showing a start of a traveling control according to an embodiment of the present invention.

FIG. 10 is a flowchart illustrating determination of the start of the traveling control and the termination of the control according to the embodiment of the present invention.

FIG. 11 is a flowchart showing a hydraulic control mode setting for starting control of traveling control according to the embodiment of the present invention.

FIG. 12 is a flowchart illustrating a normal control hydraulic mode setting of the traveling control according to the embodiment of the present invention.

FIG. 13 is a flowchart showing a control mode setting of traveling control according to the embodiment of the present invention.

FIG. 14 is a graph showing an example of a traveling control state of a four-wheel drive vehicle according to one embodiment of the present invention.

FIG. 15 is a flowchart illustrating a start determination of traveling control according to another embodiment of the present invention.

FIG. 16 is a flowchart illustrating a determination of the end of traveling control according to another embodiment of the present invention.

FIG. 17 is a flowchart showing a hydraulic control mode setting for starting control of traveling control according to another embodiment of the present invention.

FIG. 18 is a flowchart showing a hydraulic mode setting for traveling control according to another embodiment of the present invention.

FIG. 19 is a graph showing an example of a traveling control state of a four-wheel drive vehicle according to another embodiment of the present invention.

[Explanation of symbols]

 BP Brake pedal MC Master cylinder AS Auxiliary hydraulic pressure source PC Brake hydraulic pressure control device SA1, SA2 Solenoid switching valve SA3, STR Solenoid on-off valve PC1 to PC8 Solenoid on-off valve FL, FR, RL, RR Wheels Wfl, Wfr, Wrl, Wrr Wheel cylinder WS1 to WS4 Wheel speed sensor EG engine GS transmission DF Front differential RF Rear differential CF Center differential GX Tilt sensor ECU Electronic control unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tosumi Ishikawa 2-1-1 Asahi-machi, Kariya-shi, Aichi Aisin Seiki Co., Ltd. (72) Inventor Yosuke Takahira 1-Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Corporation Inside

Claims (11)

[Claims] A front differential connected to each wheel in front of the vehicle, a rear differential connected to each rear wheel, a center differential connected to the rear differential and the front differential, and a front differential and a front differential connected to the vehicle. A traveling control device for a four-wheel drive vehicle including: a braking force control unit that independently controls a braking force applied to each rear wheel; a wheel speed detection unit that detects a wheel speed of each wheel of the vehicle; A non-ground state determining means for determining whether at least one of the wheels of the vehicle is in a non-ground state based on the wheel speed detected by the wheel speed detecting means; and an engine braking state of the vehicle. Engine brake determining means for determining whether the engine brake When the at least one wheel is in the non-contact state, and the braking force control means determines that the at least one wheel is in the non-contact state. A travel control device for a four-wheel drive vehicle, characterized in that a braking force is applied to at least one of the wheels. A front differential connected to each wheel in front of the vehicle, a rear differential connected to each wheel in the rear, a center differential connected to the rear differential and the front differential, and a front differential connected to the front and rear of the vehicle. A traveling control device for a four-wheel drive vehicle including: a braking force control unit that independently controls a braking force applied to each rear wheel; a wheel speed detection unit that detects a wheel speed of each wheel of the vehicle; A non-ground state determining means for determining whether at least one of the wheels of the vehicle is in a non-ground state based on a wheel speed detected by the wheel speed detecting means; Downhill determination means for determining whether or not the vehicle is on a downhill; and engine brake determination for determining the engine braking state of the vehicle. The downhill road determination unit determines that the vehicle is on a downhill road, the engine brake determination unit determines that the vehicle is in an engine brake state, and the non-ground contact state determination unit determines that the at least one wheel is in a non-ground state. Wherein the braking force control means is configured to apply a braking force to at least one of all the wheels including the non-grounded wheel. Control device for a four-wheel drive vehicle. 3. The non-ground contact state judging means includes slip detecting means for detecting a slip of each wheel based on a wheel speed detected by the wheel speed detecting means, wherein the slip detecting means detects a slip of the at least one wheel. 3. The system according to claim 1, wherein when the slip is detected, the at least one wheel is determined to be in a non-ground state.
A travel control device for a four-wheel drive vehicle as described in the above. 4. An estimated vehicle speed calculating means for calculating an estimated vehicle speed based on the detected wheel speed of said wheel speed detecting device, wherein said slip detecting device includes a wheel speed detected by said wheel speed detecting device and said estimated vehicle speed. A slip rate calculating means for calculating a slip rate based on the estimated vehicle speed calculated by the calculating means, wherein the slip of the at least one wheel is detected based on the slip rate calculated by the slip rate calculating means. The travel control device for a four-wheel drive vehicle according to claim 3, wherein: 5. An estimated vehicle speed calculating means for calculating an estimated vehicle speed of the vehicle based on the wheel speed detected by the wheel speed detecting device, wherein the non-contact state determining means determines a vehicle speed based on the estimated vehicle speed of the vehicle. A first threshold value obtained by subtracting a predetermined value of 1 from the first threshold value, when the wheel speed of the at least one wheel is lower, it is determined that the at least one wheel is in a non-contact state. The travel control device for a four-wheel drive vehicle according to claim 1 or 2, wherein: 6. The wheel speed of said at least one wheel is:
When a state exceeding a second threshold value obtained by subtracting a second predetermined value from the estimated vehicle body speed of the vehicle continues for a predetermined time,
Ground contact state determining means for determining that at least one wheel is in contact with the ground; when the contact state determining means determines that the at least one wheel is in contact with the ground, the braking force control means 6. The four-wheel drive vehicle travel control device according to claim 5, wherein the application of the braking force to the at least one wheel is released. 7. The ground contact state determining means, wherein a wheel speed of the at least one wheel exceeds a second threshold value obtained by subtracting a second predetermined value from an estimated vehicle speed of the vehicle, and And determining that at least one of the wheels is in contact with the ground when a state that is less than a third threshold value obtained by adding a third predetermined value to the estimated vehicle body speed has continued for a predetermined time. The travel control device for a four-wheel drive vehicle according to claim 6, wherein: 8. The braking force control means when the engine brake determination means determines that the engine is in a brake state and the non-ground state determination means determines that at least one wheel is in a non-ground state. 3. The travel control device for a four-wheel drive vehicle according to claim 1, wherein the vehicle is configured to apply a braking force to both wheels in front of the vehicle. 9. The braking force control means when the engine brake determining means determines that the engine is in the brake state and the non-ground state determining means determines that the at least one wheel is in the non-ground state. 3. The travel control device for a four-wheel drive vehicle according to claim 1 or 2, wherein the vehicle is configured to apply a braking force using the wheel in the non-ground state as a wheel to be controlled. 10. The downhill road judging means includes an inclination detecting means for detecting an inclination angle of the vehicle, and at least the inclination detecting means determines that the traveling direction of the vehicle is a downward direction for a predetermined time. The travel control device for a four-wheel drive vehicle according to claim 2, wherein when a tilt angle that is more than an angle is detected, the travel road surface of the vehicle is determined to be a downhill road. 11. The engine brake determining means includes shift position detecting means for detecting a shift position of a transmission of the vehicle, at least the shift position detecting means detects a predetermined low-speed shift position, and 3. The vehicle according to claim 2, wherein the vehicle is determined to be in an engine braking state when the downhill determination unit determines that the vehicle is on a downhill.
A travel control device for a four-wheel drive vehicle as described in the above.