JPH1148938A - Antiskid controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize antiskid control with high responsiveness, in which the influence upon both vehicle behavior and deceleration is considered, taking advantage of enhancement in brake deceleration, and to enhance the performance of antiskid control by estimating the car-body speed with high accuracy. SOLUTION: This antiskid controller is provided with an antiskid controlling part (g) which regulates each wheel pressure to a target wheel speed; a wheel speed convergent state judging means (c) which judges the convergent state of each wheel to the target wheel speed; and a target slip ratio changing means (d) which changes the target slip ratio of at least one wheel into a lower value, according to the judgment of the wheel speed convergent state judging means (c). The controller is also provided with a coefficient of friction on a road estimating means (a) and a car-body-speed estimating means (b) which estimates the car-body-speed by using the coefficient of friction on a road thus estimated of each wheel. In addition, the changing means (d) changes the slip ratio of the wheel selected by a wheel selecting means (e) which selects the wheel exerting least influence upon the behavior of the vehicle, when the slip state of the wheel is changed, based on the detection value of a vehicle traveling state detecting means (f).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An anti-skid system of a vehicle avoids wheel lock during braking, stabilizes the vehicle behavior, and shortens the braking distance. Proposals have been made (for example, JP-A-6-298065 (Document 1)).
JP-A-7-237537 (Document 2) and the like.

In the anti-skid control device, when estimating the vehicle speed, which is a basic signal for anti-skid control, it is customary to select the wheel speed of each wheel and use the selected wheel speed after filtering. (For example, the above-mentioned document 1). When the change amount of the selected wheel speed is equal to or larger than the set vehicle body change amount, it is general to estimate the vehicle body speed so as to follow the selected wheel speed within the set value (FIG. 14).

[0004]

However, according to the following considerations, there is room (problem) to be improved in the following points. (B) In the conventional vehicle speed estimation using the above-mentioned select wheel speed, the wheel speed of each wheel is selected as the vehicle speed, and the filtered wheel speed is used, and all the wheels are slipping. In this state, accurate vehicle speed cannot be estimated. For this reason, as shown in FIG. 14 which will be referred to in comparison with the embodiment of the present invention, the vehicle speed (Vi) is generally
Is calculated to be smaller than it actually is, resulting in the phenomenon that the wheel slips deeper. Further, in order to prevent the vehicle speed from being calculated extremely low and the wheels from locking early, control is inevitably made to hunt the wheels to some extent, and as a result, the braking force decreases and the braking distance increases. Problems and problems that can be improved in terms of anti-skid control performance, such as the occurrence of such problems, remain.

(B) If the brake fluid pressure is controlled so that the wheel speed converges to the target wheel speed, the braking deceleration is improved and the braking distance is shortened, but it becomes more difficult to accurately estimate the vehicle speed. However, there is a high possibility that the estimated vehicle speed decreases. Therefore, as in the case of (a), since the accurate vehicle speed cannot be estimated, as shown in the upper part of FIG. However, this also tends to be a factor of earlier locking.

On the other hand, as a countermeasure, a technique for avoiding a decrease in the estimated vehicle body speed is proposed in the above-mentioned document 2. These aims are higher than the first target wheel speed for actually converging the wheel speed and the estimated vehicle speed for correcting the estimated vehicle speed ("pseudo vehicle speed" in the literature 2). It has a large second target vehicle speed, and thereby switches between the two target vehicle speeds in a predetermined cycle, thereby achieving both convergence of wheels and prevention of slippage of the estimated vehicle speed.

Here, in the above-mentioned document 2, the target wheel speed is switched at a predetermined cycle, and the wheels for changing the target alternate between the front wheels and the rear wheels.

(C) Although the above-described effects can be expected from the change of the target wheel speed, the effect of changing the target wheel speed on the vehicle behavior and deceleration is considered. The following can be said. Generally speaking, anti-skid controlled wheels are usually at the tire limit. Therefore, in such a limit state of the tire, suddenly reducing the slip of the wheel has a considerable effect on the vehicle behavior, and therefore, it is not possible to change the target of the front and rear wheels alternately to a predetermined cycle uniformly in the vehicle. In some cases, the behavior may be adversely affected. FIG.
This is also referred to in comparison with the embodiment of the present invention in the following description. However, when the target change of the wheel speed is performed alternately between the front and rear wheels (switching of the target change flag), the wheel cylinders of the front and rear wheels are simply changed. The (W / C) pressure (brake pressure) is controlled in a transition as shown in the figure, and as a result, the yaw rate may be disturbed as shown in the figure.

(D) Focusing on a braking control scene in an actual vehicle equipped with an anti-skid system, there are always fine irregularities on the actual road surface, and all wheels always converge on the target for a long time. In some cases, one of the wheels may deviate from the target, resulting in a state of shallow slip. Even in such a state, when the wheel slip determined at a predetermined cycle is recovered (the timing of switching the target change flag in FIG. 12), the deceleration may be affected, and, for example, the target is sufficiently converged to the target. In some cases, the deceleration may be reduced by reducing the brake pressure to recover the slippage of the wheels, and such considerations should still be improved. There is a problem and a problem that there is room.

It is desirable that, even when the brake pressure of each wheel is controlled so that the wheel speed converges to the target value, the advantage such as improvement of the braking deceleration is utilized as much as possible.
It is to be able to realize anti-skid control performance with high responsiveness in consideration of the above-described effects on vehicle behavior and deceleration. More desirably, while improving the braking deceleration and the like by similarly converging the wheel speed to the target wheel speed, and also improving the anti-skid control performance by estimating the vehicle speed with high accuracy. The above can be realized.

The present invention is based on the above considerations and the following considerations, and seeks to make improvements and improvements from these points. In particular, each of the wheels is adjusted to a target value of the wheel speed. Anti-skid control that is suitable for performing anti-skid control to control the brake pressure of the vehicle, taking full advantage of the improvement of braking deceleration, etc., as well as highly responsive anti-skid control taking into account the effect on vehicle behavior and deceleration It makes it possible to get performance. Similarly, by converging the wheel speed to the target wheel speed to improve braking deceleration and the like, and by estimating the vehicle speed with high accuracy, the anti-skid control performance is improved, and The aim is to provide an improved anti-skid control device that can be realized.

[0012]

According to the present invention, the following anti-skid control device is provided. That is, the anti-skid control device of the present invention is an anti-skid control device including an anti-skid control unit that controls the brake pressure of each wheel so that the wheel speed becomes the target wheel speed. A wheel speed convergence state determining unit that determines a convergence state; and a target slip ratio changing unit that changes a target slip ratio of at least one wheel to a shallower one according to the determination of the wheel speed convergence state determining unit. (FIG. 1).

Further, there is provided a road surface μ estimating means for estimating a road surface friction coefficient (road surface μ), and a vehicle body speed estimating means for estimating a vehicle body speed using the road surface μ of each wheel estimated by the road surface μ estimating means. An anti-skid control device for setting a target wheel speed of each wheel based on the vehicle speed estimated by the vehicle speed estimating means, and controlling a brake pressure of each wheel so that each wheel speed converges to the target value. A wheel speed convergence state determining means for determining a convergence state of each wheel to a target wheel speed, and changing a target slip ratio of at least one wheel to a shallower one according to the determination by the wheel speed convergence state determining means. And a target slip ratio changing means.

In the above, the target slip ratio changing means selects the wheel having the least effect on the vehicle behavior when the slip state of the wheel is changed based on the detection value of the vehicle running state detecting means. And changing the slip ratio of the wheel selected by the following.

Further, the target slip ratio changing means changes the slip ratio of the wheel on the lower side of the slip ratio when synchronous control of the left and right wheels or the front and rear wheels of the anti-skid control is performed. It is a feature.

Further, the wheel speed convergence state judging means judges the convergence state according to the time during which the deviation between the wheel speed and the target wheel speed exists within a set value. Further, the wheel speed convergence state determination means determines the convergence state according to a time when all wheel speeds are in a state smaller than a convergence determination wheel speed threshold different from the target wheel speed. Things.

The road surface μ estimating means includes: a wheel acceleration calculated from a wheel speed detected by the wheel speed detecting means of each wheel; a wheel load detected by the wheel load detecting means of each wheel; Of the brake fluid pressure estimated by the brake fluid pressure estimating means, and for the drive wheels,
Further, the road surface μ is calculated from the driving torque estimated by the driving torque estimating means.

Further, the vehicle speed estimating means calculates the selected wheel speed calculated from the wheel speed detected by the wheel speed detecting means of each wheel with the road surface μ of each wheel estimated by the road surface μ estimating means. And estimating the vehicle speed so as to follow a vehicle speed change amount calculated by a lateral speed detected by the lateral speed detecting means of the vehicle and a yaw rate detected by the yaw rate detecting means. Things.

The vehicle running state detecting means detects a running state of the vehicle based on at least one of a vehicle speed, a longitudinal acceleration, a lateral acceleration, a yaw rate, a steering angle, a wheel load, a wheel slip ratio, a vehicle body and a wheel side slip angle. To be performed.

The target slip ratio changing means monitors a change in the hydraulic pressure of a wheel selected when the target slip ratio is changed for a set time, and changes the target slip ratio when the depressurization mode is entered. It is a feature. Further, the target slip ratio changing means holds the target slip ratio in a shallow state until the wheel speed of the wheel having changed the target slip ratio follows the target, and returns to the original target slip ratio after following. It is assumed that.

[0021]

According to the present invention, with the above configuration, anti-skid control for controlling the brake pressure of each wheel so that the wheel speed becomes the target wheel speed is performed, while the target wheel speed of each wheel is controlled. At the same time, the target slip ratio of at least one wheel can be changed to a shallower one according to the wheel speed convergence state determination judgment, and therefore, the wheel speed of each wheel is converged to the target value. Even when controlling the brake pressure, it is possible to realize anti-skid control performance with high responsiveness taking into account the effects on vehicle behavior and deceleration, while taking advantage of the benefits such as improved braking deceleration as much as possible. Becomes Therefore, the above-described problem to be improved can be satisfactorily achieved, and an improved anti-skid control device can be provided.

Further, the present invention provides,
Estimating the road surface μ, estimating the vehicle speed using the estimated road surface μ of each wheel, and setting the target wheel speed of each wheel based on the estimated vehicle speed in this way, While performing anti-skid control for controlling the brake pressure of each wheel so as to converge to the target value, as described above,
The state of convergence of each wheel to the target wheel speed is determined, and at least one
The present invention can be suitably implemented as a configuration in which the target slip ratio of the wheel is changed to a shallower one. Similarly, in this case, even in the case of the anti-skid control in which the brake pressure of each wheel is controlled so that the wheel speed converges to the target value, the vehicle behavior and the deceleration are improved while taking advantage of the improvement of the braking deceleration as much as possible. To achieve a highly responsive anti-skid control performance that takes into account the effect on vehicle speed, and to converge the wheel speed to the target wheel speed to improve braking deceleration, etc., and estimate the vehicle speed with high accuracy This can improve the anti-skid control performance and realize the above.

In this case, preferably, claim 3
As described above, the target slip ratio changing means, by changing the slip state of the wheels based on the detection value of the vehicle running state detecting means, by the wheel selecting means to select the wheel that has the least effect on the vehicle behavior. The present invention can be suitably implemented as a configuration for changing the slip ratio of the selected wheel.
In this way, in addition to the above-described effects, the effect on the vehicle behavior that is not taken into account by the above-mentioned document 2 and the like can be sufficiently considered, and the adverse effect on the vehicle behavior can be avoided. It is possible to further enhance the effectiveness of a certain anti-skid control, to achieve a balance in this respect, and to appropriately realize the above.

According to the aspect of the present invention, when the synchronous control of the left and right wheels or the front and rear wheels of the anti-skid control is performed, the slip of the wheel having a smaller slip ratio is performed. By changing the rate, for example, when select-low control or the like of the rear wheels is performed, the slip rate of the wheel having a smaller slip rate is changed by the select-row control in accordance with the select-row control. Therefore, it is possible to further obtain an effect that this type of synchronization control is effective when the synchronization control is performed.

Further, the wheel speed convergence state determining means determines the convergence state according to the time during which the deviation between the wheel speed and the target wheel speed exists within a set value. The present invention can be suitably implemented, and similarly, the above can be realized. Further, in this case, by looking at the time, if the time is long, the time during which the anti-skid control for converging the wheel speed is performed very well is long, so that there is a possibility that the estimation deviation of the vehicle body speed may occur. It is possible to appropriately determine that there is such a convergence state. Similarly, based on the result of the wheel speed convergence state determination, the target slip ratio can be changed to correct the deviation of the estimated vehicle speed so that the vehicle speed can be estimated with high accuracy. Further, the determination of the wheel speed convergence state is not limited to the case of the configuration according to claim 5, but may be performed as described in claim 6. Even if the convergence state is determined in this manner, it is possible to determine that there is a possibility that the estimated vehicle body speed may fall.

In the case of estimating the road surface μ and estimating the vehicle speed using the estimated road surface μ of each wheel, the road surface μ estimating means estimates the road surface μ by: The wheel acceleration calculated from the wheel speed detected by the wheel speed detecting means of each wheel, the wheel load detected by the wheel load detecting means of each wheel, and the brake fluid estimated by the brake fluid pressure estimating means of each wheel The present invention has a configuration in which the road surface μ is calculated from the wheel acceleration, the wheel load, the estimated brake fluid pressure, and the drive torque estimated by the drive torque estimating means for the drive wheels. Can be suitably implemented, and the same can be realized in the same manner. In this case, it is possible to more appropriately calculate the road surface μ of each wheel as a basis for estimating the vehicle body speed, and as a result, it is effective to estimate the vehicle body speed more accurately.

The vehicle speed estimating means may calculate the selected wheel speed calculated from the wheel speeds detected by the wheel speed detecting means for each wheel by using the estimated road surface μ of each wheel. As a configuration for estimating the vehicle speed so as to follow the vehicle speed change amount calculated by the lateral speed of the vehicle and the yaw rate, the present invention can be suitably implemented.
The above can be realized. Further, in the case of this aspect of the vehicle body speed estimation, in estimating the vehicle body speed applied to the setting of the target wheel speed of each wheel, the influence on the vehicle body speed due to the lateral force of the tire is more accurately considered. As a result, the accuracy can be further improved, and the anti-skid control performance can be improved.

Further, the detection of the vehicle running state applied to the selection of the target slip ratio changing wheel can be suitably carried out by the vehicle running state detecting means having the structure according to the ninth aspect. The above can be realized. Then, in this case, it is possible to optimally select and determine the wheel for which the target slip ratio is changed according to the running state of the vehicle. In the case of claim 4, for example, when the anti-skid control is a select low control of the left and right wheels or the front and rear wheels, a wheel having a lower slip ratio of the wheel subjected to the select low control changes the slip ratio. The target target slip ratio changing wheel is selected as a wheel that has little effect on the vehicle behavior, while in the case of claim 9, the wheel is adjusted according to one or more states of various quantities obtained as the running state of the vehicle. In addition, the target slip ratio changing wheel can be determined appropriately, and is optimally determined as the target wheel, for example, an inner wheel after turning, or an outer wheel after turning or an inner wheel before turning.

Further, according to the present invention, when the target slip ratio is changed, the change of the target slip ratio is monitored by changing the hydraulic pressure of the wheel selected for a set time. In consideration of the processing for changing the target slip ratio, the processing can be suitably performed. Thus, in this case, the effect on the deceleration when the brake fluid pressure is reduced to correct the estimation of the vehicle body speed can be further reduced.

In the case of the eleventh aspect, the target slip ratio is maintained in a shallow state until the wheel speed of the wheel having changed the target slip ratio follows the target, and after following the target slip ratio, the target slip ratio is returned to the original target slip ratio. The present invention can be embodied as a more effective configuration in consideration of the processing. In this case, once the target slip ratio is changed to be shallow, the wheel is held until it follows the changed slip ratio, and after being followed, the wheel returns to the normal target value. The original target slip ratio can be returned.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing the configuration of one embodiment of the present invention. In this embodiment, a vehicle (automobile) to which the present invention is applied
Denotes a rear-wheel drive vehicle (AT vehicle, vehicle equipped with a conveyor differential), and anti-skid control (ABS control) assumes a braking device that can independently control the left and right braking forces (braking fluid pressure) for both front and rear wheels. .

In the figure, 1 is a brake pedal, 2 is a booster, 3 is a reservoir, and 4 is a master cylinder. 10 and 20 are left and right front wheels (driven wheels), and 30 and 4
0 indicates left and right rear wheels (drive wheels), respectively. Each wheel is provided with a brake disk 11, 21, 31, 41, and a wheel cylinder (W) that applies a hydraulic pressure to apply frictional force to the brake disk to apply a braking force (braking force) to each wheel.
/ C) 12, 22, 32, 42, and the pressure control unit 5
Each wheel is individually braked when supplied with hydraulic pressure from the vehicle.

The pressure control unit 5 constitutes an anti-skid control device together with a controller to be described later including the pressure control unit 5. The pressure control unit 5 adjusts the hydraulic pressure from the master cylinder 4 according to an input signal, and controls the wheel cylinders 12, 22, 3 of each wheel.
The brake fluid pressure to be supplied to 2, 42 is controlled. The pressure control unit 5 is provided for each hydraulic pressure supply system (each channel) for the front and rear wheels
It is configured to include an actuator individually. As the actuator, an actuator having a pressure-intensifying valve and a pressure-reducing valve as control valves so that pressure-reducing, holding, and pressure-increasing control can be used. Pressure control unit 5 (pressure servo unit)
FIG. 3 shows an example.

In this embodiment, as shown in the figure, the master cylinder 4 and the wheel cylinders 11, 21, 3
Between 1 and 41, an anti-skid device is provided, the control device is therefore a 4ch anti-skid system, thereby avoiding wheel lock when the anti-skid control is activated.

Here, pressure increasing valves 14, 24, 34, 44 as inlet valves and pressure reducing valves 15, 25, 35, as outlet valves are provided in channels for each wheel.
45, and the reservoirs 16 and 17 and the motor 36
Driving pumps 26 and 27 are included as elements, and these are connected and connected by a brake hose or the like as shown in the figure to form a hydraulic circuit.

In the brake fluid pressure system from the master cylinder 4 to the wheel cylinders 11 to 41, in the front wheel (front) brake system, the master cylinder fluid passage connects the pressure boost valves 14 and 24 individually to each other. From the front wheel 10,
20 wheel cylinders 11 and 21. Similarly, in the rear wheel (rear) brake system, the master cylinder fluid path is connected to each of the pressure boosting valves 33 and 44, and from the pressure boosting valves, the rear wheel 3 is passed through the fluid path on each wheel cylinder side.
0 and 40 wheel cylinders 31 and 41, respectively.

Each of the wheel cylinder fluid paths connected to each of the front wheel wheel cylinders 11 and 21 is branched from the middle thereof, and these branch fluid paths are connected to the front wheel reservoir 16 via the pressure reducing valves 15 and 25, and the front wheel is also connected. Through the master pump 26 to the master cylinder fluid path on the upstream side. Similarly, the wheel cylinder fluid passages connected to the wheel cylinders 31 and 41 of the rear wheels are also branched from the middle, respectively, and the branched fluid passages are connected to the rear wheel reservoir 17 via the pressure reducing valves 35 and 45, respectively. Through the rear wheel pump 27, it is connected to the master cylinder fluid path on the upstream side.

The pressure-intensifying valves 14, 24, 34, and 44 are at the positions shown in the figure during normal braking. Pressure reducing valve 1
3, 23, 33, and 43 are normally in the positions shown in the figure, and the connection between the valve input / output ports, and hence the connection with the corresponding reservoirs 16 and 17, is cut off. And thus the position at which the wheel cylinders are connected to the corresponding reservoirs 16,17.
Thus, during anti-skid control, this valve guides the brake fluid of the corresponding wheel cylinder to the reservoir to reduce the wheel cylinder pressure.

In the normal braking state, when the hydraulic pressure from the master cylinder 4 is supplied to each wheel cylinder by the driver's depressing operation of the brake pedal 1 at the illustrated position of each pressure increasing valve and pressure reducing valve, The master cylinder pressure is the master cylinder fluid path, each booster valve,
And through the wheel cylinder fluid path,
Therefore, the brake hydraulic pressure (braking hydraulic pressure P) can be increased toward the master cylinder hydraulic pressure, which is the original pressure, and each wheel is individually braked to perform normal braking.

At the time of such braking, when the pressure reducing valves 15, 25, 35, and 45 of each channel are operated to open and close, the branch fluid paths to the corresponding reservoirs 16 and 17 are opened at the valve open positions. Open during the period of operation, the brake fluid of the corresponding wheel cylinder is guided to the reservoir and drained. In addition, during the period in which the valve is closed, the communication with the reservoir is cut off to cut off the above-mentioned brake fluid pressure. Thus, by such valve opening / closing drive control, a reduced pressure state is established in which the brake fluid pressure is released to the corresponding reservoir and reduced.

The brake fluid accumulated in the reservoirs 16 and 17 due to the pressure reduction is returned to the upstream of the pressure increasing valves 14, 24, 34 and 44 by pumps 26 and 27 driven by a motor 36. Then, the returned brake fluid is used for pressure increase.

Returning to FIG. 2, signals to the control valves of the respective channels of the pressure control unit 5 are supplied from a controller 50. The controller 50 has an acceleration sensor for detecting the front and rear and lateral accelerations Xg and Yg of the vehicle. Signal from 6,
Signals from the yaw rate sensor 7 for detecting the yaw rate φ, and signals Vw1 (front wheel left side) and Vw2 from the wheel speed sensors 13, 23, 33, 43 for detecting the wheel speeds arranged on the respective wheels 10, 20, 30, 40. (Front wheel right side), Vw3 (rear wheel left side), Vw4 (rear wheel right side) and the like are input. Further, in this embodiment, the controller 50 is connected to an engine controller 51 for controlling the engine and an AT controller 52 for controlling the transmission, and the controller 51, 52 controls the engine drive torque Te, Automatic transmission (not shown)
Is also input. Here, the driving torque Te and the gear position GR information are stored in the driving wheels 30, 40.
Can be used as information for estimating the driving torque for

The controller 50 includes a microcomputer, and includes an input detection circuit, an arithmetic processing circuit (CPU), a control program for anti-skid control executed by the arithmetic processing circuit and other control programs, And a storage circuit (RA
M, ROM), and an output circuit that outputs control signals such as pressure increase, pressure decrease, and hold command signals for each channel to the pressure control unit 5.

In the present embodiment, the controller 50 controls the pressure increasing valve and the pressure reducing valve of each channel to prevent the wheel from being locked by braking based on the input information in the braking situation where the anti-skid control is activated during braking. A drive pulse is output to control the brake fluid pressure of each wheel to control the wheel braking force. In this case, in the case of the ABS control of the four-channel four-sensor system as in this example, basically, the wheel speed information Vwi (i = 1 to 4) for each of the four front, rear, right and left wheels is obtained, and the vehicle speed (the vehicle body speed) is obtained. Speed), and in the case of using the wheel acceleration, the wheel acceleration is also calculated from the wheel speed for each wheel, and the target pressure increase / decrease amount is obtained from the wheel speed, the wheel acceleration, and the body speed. By controlling the wheel cylinder hydraulic pressure, it is possible to perform control for avoiding wheel lock during braking.

In the above control, the controller 50 controls the brake pressure of each wheel so that the wheel speed becomes the target wheel speed, and performs anti-skid control in this case, thereby improving the braking deceleration. While utilizing as much as possible, and in order to make it highly responsive considering the effect on vehicle behavior and deceleration, a wheel speed convergence state judgment is performed to determine the convergence state of each wheel to the target wheel speed. Target slip ratio change control is also executed to change the target slip ratio of at least one wheel to a shallower one in accordance with the determination of the wheel speed convergence state. In this case, preferably, the road surface μ is estimated, the vehicle speed is estimated using the estimated road surface μ of each wheel, and the target wheel speed of each wheel is set based on the estimated vehicle speed. Then, while controlling the brake pressure of each wheel so that each wheel speed converges to its target value, the wheel speed convergence state determination for determining the convergence state of each wheel to the target wheel speed is performed as described above. The target slip ratio is changed to change the target slip ratio of at least one wheel to a shallower one in accordance with the determination of the wheel speed convergence state.

FIG. 4 is a block diagram showing an example of functions in the embodiment system shown in FIG. 2 for such wheel speed convergence state determination and anti-skid control including target slip ratio change control. It is a representation. FIG.
Among them, a is road surface μ estimating means (estimating section), b is vehicle speed estimating means (estimating section), c is wheel speed convergence state judging means (judging section), d is target slip ratio changing means (changing section), e Is a wheel selection means (selection unit), f is a vehicle traveling state detection means (detection), and g is an anti-skid control unit. In this case, the pressure control unit 5 and elements of these functions can be included.

Road surface μ estimating means a is a means for estimating u road surface μ of each wheel, and vehicle speed estimating means b is road surface μ estimating means a.
The anti-skid control unit g sets the target wheel speed of each wheel based on the vehicle speed estimated by the vehicle speed estimation means b. Then, the control method is such that the brake pressure of each wheel is controlled so that each wheel speed converges to its target value. In such anti-skid control, the wheel speed convergence state determining means c for determining the convergence state of each wheel to the target wheel speed, and the target slip ratio of at least one wheel are determined in accordance with the determination of the wheel speed convergence state determining means c. The target slip ratio is changed by the target slip ratio changing means d for changing the target slip ratio to a shallower one.

In addition to these means, when the vehicle further includes a wheel selecting means e and a vehicle running state detecting means f as shown in the drawing, the change of the target slip ratio is determined by the wheel speed convergence state determining means c. In addition, vehicle running state detecting means f
This can be done by changing the slip ratio of the wheel selected by the wheel selecting means e that selects the wheel that has the least effect on the vehicle behavior when the slip state of the wheel is changed based on the detected value of .

Further, the determination by the wheel speed convergence state determining means c may be performed in a mode in which the convergence state is determined in accordance with the time during which the deviation between the wheel speed and the target wheel speed is within a set value, or when all the wheel speeds are equal to the target wheel speed. A mode in which the convergence state is determined according to a certain time in a state in which the wheel speed is smaller than a wheel speed threshold value for convergence determination different from the wheel speed may be adopted. In a preferred embodiment, the road surface μ estimating means a has a wheel acceleration calculated from a wheel speed detected by the wheel speed detecting means of each wheel, a wheel load detected by the wheel load detecting means of each wheel,
The road surface μ can be calculated from the brake fluid pressure estimated by the brake fluid pressure estimating means of each wheel, and for the driving wheels, from them and the driving torque further estimated by the driving torque estimating means. In a preferred embodiment, the vehicle speed estimating means b calculates the selected wheel speed calculated from the wheel speed detected by the wheel speed detecting means of each wheel to the road surface of each wheel calculated by the road surface μ calculating detecting means. The vehicle speed can be estimated so as to follow the vehicle speed change amount calculated by μ, the lateral speed detected by the lateral speed detecting means of the vehicle, and the yaw rate detected by the yaw rate detecting means. In the present embodiment, each of the units a to h can include a corresponding sensor or the like in FIG. 2 and a part of the controller 50.

FIG. 5 is a flowchart of an example of a control program including the above-described wheel speed convergence state determination, the target slip ratio changing process, and other processes executed by the controller 50. This process is executed by a non-illustrated operating system at regular time intervals. First, in step S101, each of the sensors 6, 7, 1
Various data from 3, 23, 33, 43, controllers 51, 52 and the like are read. That is, the longitudinal acceleration Xg,
Lateral acceleration Yg, yaw rate φ, each wheel speed Vwi (i = 1
4), the engine drive torque Te and the gear position GR are read.

In the following step S102, the wheel speed Vwi
Is calculated based on the wheel acceleration Vwdi (i = 1 to 4). In this embodiment, it is calculated according to the following equation.

Vwdi = ((Vwi1 + Vwi0) − (Vwi4 + Vwi3)) / 2ΔT (1) Here, the subscripts 0 to 4 indicate the number of cycles before the control cycle the wheel speed. ΔT is a control cycle. If the wheel speed Vwi value in the earlier control cycle period is larger, the wheel is in a state of being decelerated.

In the following step S103, select wheel speed Vfs is calculated. In the present embodiment, the wheel speed Vw of each wheel
A filter is applied to i according to acceleration / deceleration, etc., and Vwfi (i = 1 to 4) closer to the vehicle speed is calculated for each wheel. Depending on conditions such as when the anti-skid control is activated / deactivated, By selecting the largest one from each Vwfi / selecting the average value of the non-driven wheels, the selected wheel speed Vfs closest to the vehicle body speed is calculated.

In the following step S104, the wheel load Wi of each wheel is calculated. In the present embodiment, each wheel load Wfr (front wheel right), the values Xg and Yg of the front and rear G and side G sensors are used.
Wfl (front wheel left), Wrr (rear wheel right), and Wrl (rear wheel left) are calculated according to the following equations. Before and after G and lateral G are used after applying a first-order lag filter.

Wfr = Wfr0 + kx × Xg + kyf × Yg 2a Wfl = Wfl0 + kx × Xg + kyf × Yg 2b Wrr = Wrr0 + kx × Xg + kyr × Yg 2c Wrl = x kx, kyf, and kyr are constants determined by the distribution of the wheel base, the height of the center of gravity, the tread, and the roll rigidity. Wfr0, Wfl0, Wrr0, Wrl0 are initial loads (static loads).

In this embodiment, the front and rear G and side G sensors are used. However, instead of the front and rear G sensor values, the change amount of the vehicle body speed calculated up to the previous time or the estimated value of the road surface μ may be used. Good. Instead of the lateral G, the lateral G may be estimated from the vehicle speed and the steering angle, the vehicle speed and the yaw rate, or the vehicle speed and the difference between the left and right wheel speeds.

In the following step S105, an estimated brake fluid pressure Pwsi is calculated. In this embodiment, the brake pressure of each wheel is estimated from the history of the brake fluid pressure increase / decrease pulse output to the pressure control unit 5 for controlling the brake fluid pressure. By performing the reverse of the process of calculating the valve drive time Ti from the pressure increase / decrease amount ΔP ^* (target value) described later,
The actual pressure increase / decrease amount ΔP (change in pressure increase / decrease according to the valve driving time) is calculated, and the current brake fluid pressure P is calculated according to the following equation.
Estimate wsi.

Pwsi = Pwsi (previous value) + ΔP (3)

In the following step S106, the slip ratio Si of each wheel is calculated. In the present embodiment, the wheel speed Vw of each wheel
The slip ratio is calculated by the following equation from i and the vehicle speed Vi calculated last time (the Vi value calculated in step S110 in the previous loop).

## EQU4 ## Si = (Vi-Vwi) / Vi ... 4

In the following step 107, each wheel is set on the road surface μ.
It is determined whether or not the peak value is reached. In this embodiment, it is determined whether or not a peak is obtained from the wheel acceleration Vwdi and the slip ratio Si calculated in the above steps S102 and S106. In other words, when the wheel state is in the set area (shaded area) in the characteristic diagram of the slip ratio and the wheel acceleration (deceleration) shown in FIG. 6, it is determined that the wheel is at the peak value of the road surface μ. . Here, the threshold value for this determination is the same as the control start determination for the anti-skid control. In addition, as an example of each of the values S ₁ , S ₂ , α ₁ , α ₂ applied for setting the determination area in FIG.
₁ = 0.05, S ₂ = 0.15, α ₁ = 3.0, α ₂ =
1.0.

Here, in the anti-skid control, the control is usually performed by the wheel deceleration and the wheel slip ratio. For example, in a typical ABS, the control is performed by a deceleration-slip ratio map as shown in the upper part of FIG. The mode can be determined and the anti-skid control can be executed. That is, in the illustrated example, the pressure is reduced and the anti-skid control is started only when the slip ratio becomes equal to or less than the predetermined value Sx (threshold value). FIG. 6 is the same as changing the threshold value Sx by deceleration. That is, the start timing of the anti-skid control and the determination of the road μ peak are made the same (FIG. 6, FIG. 7, lower part). Conversely, basically, when the anti-skid control operates, it is assumed that the road surface μ is at the peak.

In this way, in the road surface μ peak determination in step S107, this is performed by determining that the road surface μ has the peak value according to the acceleration of each wheel and the slip ratio of the wheel. Then, once the anti-skid control has been activated, if the exceptional control described later is not performed, it is determined that the wheel state is at the peak value of the road surface μ for a while even if the wheel state is out of the above-mentioned region. continue. Here, as means for this, for example, when the wheels are under anti-skid control, once it is determined that the road surface μ is at the peak, the determination threshold values of the wheel acceleration and the slip ratio are changed. Alternatively, a method may be employed in which the determination that the user is at the peak is maintained to some extent by providing a certain set time. When such a method is taken into consideration, for example, the start timing of the anti-skid control and the road surface μ peak determination for obtaining the calculated value for the road surface μ on which the vehicle speed is estimated are made the same, Once the control has been activated,
By continuing the determination that the wheel is at the peak value of, immediately after the relevant wheel is determined to be at the peak of the road surface μ, immediately, a determination result that the wheel is not at the road surface μ peak occurs,
It is properly avoided that the road surface μ on the wheel side becomes inapplicable to the above-mentioned vehicle body speed estimation, there is no undesirable control hunting, and the vehicle body speed is well estimated during anti-skid control. It is possible to make it.

Further, even when the wheels are in the anti-skid control state, the left and right or front and rear wheels are synchronously controlled, ie, so-called select-low control, and the initial pressure is gradually increased, ie, so-called yaw moment control. When exceptional controls are being performed, the slip rate is not sufficiently large due to those controls, and it is meaningless to calculate the road surface μ, so that it is determined that the road surface μ is not at the peak. In the determination of the road surface μ peak in step S107, this processing is also taken into consideration, and therefore, even when the wheels are under the anti-skid control, the slip when the above-described exceptional control is performed is performed. It is determined that the wheel on the side with a lower rate is not on the road surface μ peak.

In the following step S108, the value μi (i = 1 to 4) of the road surface μ is calculated for the wheels for which the road surface μ is determined to be at the peak according to the determination in the above step S107 (therefore, in step S107). If it is determined that all wheels are at the peak of the road surface μ, then all wheels are μi
The corresponding wheel is excluded when it is determined that the road surface μ is not at the peak in the determination processing.) In the present embodiment, each of the above steps S102, S104, S1
Using the wheel acceleration Vwdi, the wheel load Wi, and the estimated brake fluid pressure Pwsi calculated in step S05, and for the drive wheels (30 and 40 in the present embodiment), the above-described step S10 is further performed.
Engine drive torque Te and gear position GR read in
, The road surface μ is calculated for each of the non-driven wheels (10, 20 in this embodiment) and the driven wheels according to the following equation.

[0062]

(5) Non-drive wheel side: μi = (I × Vwdi + K × Pwsi × R) / (Wi × R ² ) 5a Drive wheel side: μi = (I × Vwdi + K × Pwsi × R−k × Te) / (Wi × R ² ) ··· 5b where K is a constant determined by brake specifications (pat μ, wheel cylinder area, wheel cylinder effective diameter), k
Is a constant determined according to the transmission gear ratio corresponding to the gear position GR and the differential final gear ratio, I is the inertial mass of the tire, and R is the tire effective diameter. Here, the calculated road surface μ estimated value may be subjected to, for example, a first-order lag filter process.

In the following step S109, the road surface μ of each wheel
Is used to calculate the vehicle speed change amount Vid. In the present embodiment, the wheel whose road surface μ is determined to be at the peak (therefore, also in this case, the road surface μ is determined in the determination processing in step S107).
Wheel is determined to be not at the peak) is excluded)
Is used as the vehicle speed change amount.

Vid = (Σ (μi)) / n (6) where n is the number of wheels for which the road surface μ is determined to be at the peak.

Here, this value Vid is an acceleration that can be generated by the vehicle body, for example, a limit of a maximum value of 1.3 g as a predetermined upper limit, and 0 as a predetermined lower limit for preventing excessive release of brake pressure. A limit of .05g is imposed.
Further, in order to further prevent the brake pressure from being excessively released by estimating the vehicle speed Vi to be slightly smaller, for example, 0.1 g
May be offset by a predetermined value. Also,
If there is no wheel for which the road surface μ is determined to be the peak, all the wheels have not reached the limit yet, and the anti-skid control has not been activated.
For example, it is assumed that Vid = 1.3 g (predetermined upper limit value).

In the calculation of step S109, instead of the above, instead of the mere average value of the road surface μ of each wheel, the amount of change in the vehicle body speed may be calculated by multiplying the weight according to the wheel load distribution of each wheel. Good. That is, if it is determined in step S107 that all the wheels are at the peak of the road surface μ, the vehicle body speed change amount Vid is simply calculated using the wheel load Wi calculated in step S104, for example, by the following equation. It may be.

[Expression 7] Vid = Σ (μi × (Wi / W)) 7

However, W is the weight. If any of the wheels is not determined to be at the peak of the road surface μ, (A) μi of the left and right opposite wheels determined to be at the peak is substituted. B) After the processing of substituting μi calculated as the largest, the value Vid is calculated according to the above equation (7).

Here, this is based on the following viewpoints. That is, in the case of Equation 6, the average value of each road surface μ is used as the vehicle speed change amount in estimating the wheel speed. By the way, it is considered whether there is no problem even if the road μ estimated on each wheel is significantly different on the so-called right and left split roads when the road μ on the left and right of the vehicle is extremely different. Since the road surface μ of the wheel with the shallow slip of the wheel performing the select low control is ignored (step S107), there is no problem by calculating the vehicle body speed change amount Vid by the average value of the road surface μ of the other wheels. .

Although there are not many braking scenes to be encountered, if further consideration is given to the case where the road surfaces μ of the four wheels are largely different, it is more preferable to be able to cope with this. Therefore, in the mode according to the above equation 7, taking this into consideration, it is not a simple average value of the road surface μ of each wheel.
The vehicle body speed change amount is calculated by multiplying the weight according to the wheel load distribution of each wheel. When the control program is executed in this manner, the selected wheel speed Vfs calculated from the wheel speed Vwi is calculated in step S108 if there is a wheel whose road surface μ is determined to be at the peak. The vehicle body speed Vi can be estimated so that the road surface μ of each wheel is weighted according to the wheel load Wi by the above equation 7 and is followed by the vehicle body speed change amount Vid (step S112).
Considering the case where the road μ of the four wheels is greatly different,
It is possible to deal with this.
Therefore, in the vehicle speed change amount calculation processing in step S109, this may be performed.

In the following step S110, the lateral speed Vy of the vehicle is calculated. In this embodiment, the vehicle lateral speed V is integrated by using the lateral acceleration Yg, the yaw rate φ, and the vehicle speed Vi (previous value), which are the sensor signals, as in the following equations.
Calculate y.

ΔVy = Yg (n) −φ (n) · Vi (n−1) 8a Vy (n) = Vy (n−1) + ΔVy · ΔT 8b (ΔT is a control cycle, ((N) indicates the current value, (n-1) indicates the previous value)

In this embodiment, the vehicle lateral speed is calculated by integral calculation from each sensor signal. However, a vehicle model is provided in the controller 50, and the vehicle lateral slip is calculated based on the vehicle speed Vi and the steering angle δ. Estimate the angle β, β and Vi
Vy may be calculated by the following equation.

Vy = β × Vi (9)

In the following step S111, the turning correction amount Vh
Is calculated. In this embodiment, the turning correction amount Vh is calculated by the m-th order equation.

Vh = Vy × φ 10

In the following step S112, the vehicle speed Vi is calculated according to the vehicle body shift amount Vid and the turning correction amount Vh. In the present embodiment, when the anti-skid control is activated (when there is a wheel whose road surface μ is determined to be at a peak), the previous value of the vehicle body speed Vi and the selected wheel speed Vfs value in the above step S103 are used. (1) If Vi (previous value) ≧ Vfs, it is determined that the vehicle is decelerating, and the vehicle speed Vi is calculated according to the following equation.

## EQU11 ## Vi = Vi (previous value) -Vid-Vh (11) If Vi (previous value) <Vfs, it is determined that the vehicle body is accelerating, and the vehicle speed Vi is calculated according to the following equation. .

Vi = Vi (previous value) +5.0 g (12) In other words, in the case of the above equation 11, each time the execution of this step S112 is performed with respect to the previous value of the vehicle body speed Vi, The vehicle speed change amount Vid obtained by using the road surface μ is reduced, and the correction of the turning correction amount Vh = Vy × φ (the third term on the right-hand side of Equation 11) is also taken into account to determine the vehicle speed Vi. This time is the value. Then, in the case of the above equation 12, this step S112 is performed with respect to the previous value of the vehicle speed Vi.
Is executed, and a predetermined value (5.
0g) to obtain the current value of the vehicle speed Vi. In this manner, the vehicle speed Vi can be estimated using the road surface μ of each wheel, and in this way, when the program is executed, the selected wheel speed Vfs is determined and the road surface μ is at a peak. The vehicle speed V is controlled to follow the vehicle speed change amount corresponding to the average value of the road surface μ when there is a wheel to be determined.
i can be estimated. On the other hand, when the anti-skid control is not operating (when there is no wheel whose road surface μ is determined to be the peak), Vi = Vfs.

This makes it more effective in estimating the vehicle speed. That is, Vi = Vi (previous value) −Vid without applying the third term on the right side of calculation formula 11 when Vi (previous value) ≧ Vfs described above.
Although the present invention can be implemented by the method according to the above method, the influence on the vehicle speed due to the lateral force of the tire can be more accurately considered in comparison with the case of the method, and the accuracy can be further improved. The anti-skid control performance can be improved.

In the present embodiment, when the vehicle speed is estimated so that the selected wheel speed calculated from the wheel speed is followed by the vehicle speed change obtained by using the road surface μ, the road surface speed change is used as the vehicle speed change. When there is a wheel whose road surface μ is determined to be at the peak in the μ peak determination, the calculation is performed using the road surface μ of each wheel calculated by the road surface μ calculation, and this is further calculated by the lateral speed Vy of the vehicle. The vehicle speed Vi can be estimated as the corrected vehicle speed change amount corrected by the turning correction amount Vh calculated by the yaw rate φ and the yaw rate φ. On the other hand, in a mode in which the turning correction amount Vh is not applied, When the vehicle speed change amount Vid is calculated in accordance with the estimated road surface μ and the vehicle speed is estimated based on Vi = Vi (previous value) −Vid. The road surface μ is the road surface in the front-rear direction of the tire Only the reaction force is taken into account. Therefore, when further improvement in accuracy is desired, the influence on the vehicle speed due to the lateral force of the tire should be more accurately considered, and this embodiment is also considered. .

In a succeeding step S113, a convergence state of the wheel speed is determined. This is because, as described above, when the brake fluid pressure is controlled so that each wheel speed becomes the target wheel speed, the wheel speed converges to the target value (the actual value of the wheel speed follows the target value. The anti-skid control so that the deviation is small) is effective in terms of improving braking deceleration and the like, but on the other hand, there is a possibility that the estimated vehicle speed tends to "fall down". It is intended to check whether such a situation exists in a state where each wheel converges to the target wheel speed.

In this embodiment, a step S117 to be described later is performed.
Before and after the target wheel speed Vwsi calculated by
su, Vwsl (threshold for convergence determination) are set, and when the time Tw during which all the wheel speeds Vwi are within the threshold exceeds a set value Tss (in this embodiment, a predetermined value), the wheels are set. Since the time during which the anti-skid control for converging the speed is performed very well is long, it is determined that there is a possibility that the estimated vehicle speed Vi is largely deviated, and the slip ratio of one of the wheels is changed to be shallow. Decide that. Here, for example, the target slip ratio Si ^* of the anti-skid control
Is 0.15, the slip ratios corresponding to the threshold values Vwsu, Vwsl are Ssu = 0.1, Ssl = 0.25.
Is determined according to the following equation.

Vwsu = Vi × (1-Ssl) 13b Vwsu = Vi × (1-Ssl) 13b

In the present embodiment, the time discrimination value Tss relating to the time Tw used for the convergence judgment is set to a predetermined value. It may be smaller. In this embodiment, two thresholds Vwsu and Vwsl (thresholds for convergence determination) are used.
Since the main purpose of the processing in step 3 and the related steps is to avoid a decrease in the estimated vehicle speed Vi, the convergence state is determined using only the threshold value smaller than the target slip ratio. May be.

Here, the "downward movement" of the estimated vehicle speed Vi and the like will be supplementarily described with reference to FIGS.
FIG. 14 shows changes in the wheel speed and the actual vehicle speed in the case of the conventional example. In the case of FIG. 14, the estimated vehicle speed Vi is shown.
Is basically calculated from the select wheel speed Vfs, so that Vi is "downhill" and has a larger width than the actual vehicle speed.
This is because the wheel speed slips only for the brake. In the figure, in the change relationship between the front wheel speed (solid line) and the rear wheel speed (dotted line), the one obtained by simply selecting the larger one (upper side) is the simple select wheel speed (selection). However, if the filter processing is further performed on such a simple select wheel speed (selection), the select wheel speed Vf as indicated by a thick broken line in the figure is obtained.
s.

Here, with respect to the phenomenon of the estimated vehicle speed being “upward” and “downward”, the estimated vehicle speed Vi is calculated based on the actual vehicle speed (V
car), it is called “upshift” (the estimation is shifted upward (largely)), and the estimation that is shifted downward is “downshift” ( The lower side or the estimation is slightly smaller). One of the biggest problems of the ABS control is how to accurately estimate the vehicle speed. When ABS control is applied to all wheels, 4
Since the wheels are slipping, the vehicle speed is unknown only from the signal from the wheel speed sensor, and the vehicle must be estimated. Then, when the estimation is shifted, what will be concretely considered is as follows.

[Decrease of Vi] For example, as shown in the upper part of FIG. 15, when the estimated vehicle speed Vi decreases, the target value also decreases, so that the wheel speed Vw is controlled by a deep slip.
Locking may occur in the low-speed range (this is early locking).

[Case of Vi shift] On the other hand, as shown in the lower part of FIG. 15, when the estimated vehicle speed Vi increases, the target value also increases, so that the wheel speed Vw is controlled with a shallow slip. Then, when this state continues, the target value becomes larger than the actual vehicle speed Vcar as shown in the figure, and the slip state is established. At this time, the brake pressure continues to be reduced, resulting in an excessively reduced pressure state, resulting in insufficient deceleration (the brake fluid pressure reaches 0 if the pressure is reduced). Therefore, in this sense, "upward" has a greater effect than "downward".

In the above-described determination of the convergence state of the wheel speed Vwi, the above-mentioned 2 is basically based on avoiding the occurrence of a large “descent” of the estimated vehicle body speed Vi as shown in the upper part of FIG.
The convergence state is determined according to the time Tw existing within the threshold values Vwsu, Vwsl using the two convergence determination wheel speed thresholds Vwsu, Vwsl. If the time Tw continues over a period exceeding the predetermined value Tss according to the result of the determination, it is determined that there is a possibility that the estimated vehicle body speed Vi is deviated at that time, and the estimated vehicle speed Vi is greatly reduced. , The target slip ratio change processing is determined so as to change the target slip ratio of at least one wheel to a shallower one.

Returning to FIG. 5, in step S114 following step S113, the running state is determined. Here, the detection of the vehicle running state includes the vehicle speed, the longitudinal acceleration Xg, and the lateral acceleration Y
The running state of the vehicle can be detected from at least one of g, yaw rate φ, steering angle δ, wheel load, wheel slip ratio, vehicle body and wheel side slip angle. In the present embodiment, the turning direction is determined based on the output value Yg of the lateral G sensor,
At the same time, the slip state of each wheel is compared based on the slip ratio Si of each wheel. Here, the yaw rate φ, the difference between the left and right wheel speeds (Vw), the steering angle δ, and the side slip angle β may be used for the turning determination. Further, the wheel load Wi estimated above may be used.

In the following step S115, in response to the determination of the change in the slip ratio in the above-mentioned step S113, a wheel having a changed slip ratio is selected according to the running state of the vehicle. In this embodiment, the slip ratio of the inner wheel after turning is normally changed. This is because, after turning, the inner wheel has the smallest wheel load and the smallest tire friction circle, so that the change in the slip ratio has little effect on the vehicle behavior. Thus, when the present program is executed through the processing of step S116 and subsequent steps, the target slip ratio of only one of the inner wheels after the turning is changed to the shallower one, and the brake fluid pressure of the wheel is changed to the inner wheel after the turning. (See the right rear wheel speed, the target change flag, and the W / C pressures of the right rear wheel and the other three wheels in right turn braking in FIG. 11). ).

In the present embodiment, the inner wheel after turning is selected as the optimum wheel which has little effect on the vehicle behavior when the slip state of the wheel is changed according to the running state of the vehicle in this way. The slip ratio of the selected inner wheel after turning can be changed. However, in the slip state of each wheel, if the slip of the outer wheel after turning or the inner wheel before turning is within the above-mentioned convergence determination threshold but is the shallowest, the slip ratio of that wheel is changed. In this manner, when the convergence state is determined in accordance with the time during which the deviation between the wheel speed and the target wheel speed exists within the set value and the target slip ratio of at least one wheel is changed to a shallower one, the above-described viewpoint is used. Therefore, it is possible to change the target slip ratio of the wheel that has the least effect on the vehicle behavior. In this embodiment, the slip ratio of the inner wheel after turning is normally changed in the slip ratio changing wheel selection process in step S115. However, the present invention is not limited to this. It is natural to select the most suitable wheel as the rate change target wheel, and the selection criteria are those that can determine the wheel whose slip rate is changed according to vehicle characteristics such as drive system, weight distribution, roll rigidity distribution, etc. It is.

At the next step S116, a target slip ratio Si ^* is calculated. In the present embodiment, the target slip ratio Si ^* is usually set to a predetermined value (for example, 0.
15), and the target slip ratio of the wheel selected in step S115 is changed to be shallow (for example, 0). At this time, the target can be changed with a first-order delay, for example. Further, in the present embodiment, the predetermined value is normally set, but may be changed depending on a turning state or a road surface μ. Further, different values may be used for the front and rear wheels.

Further, regarding the slip ratio to be changed,
Instead of 0 as in the above example, it may be a small slip value such as 0.02 or a negative value, and the changing method may be such that no delay is added or a second-order delay is added. This is because these also depend on vehicle characteristics (including brake characteristics) and tire characteristics.

Further, once the target slip ratio is changed to be shallow, the wheel is held until it follows the changed slip ratio, and after the change, the wheel is returned to the normal target value.
Thus, in the process of changing the target slip ratio, the wheel speed of the wheel whose target slip ratio has been changed (in this embodiment, for example, the right rear wheel speed Vw4 which is usually the inner wheel after turning) follows the target. The target slip ratio (S4 ^* = 0) can be held in a shallow state, and a process of returning to the original target slip ratio after following can be added, so that the original target slip ratio can be returned at an optimal timing. (FIG. 11).

In the following step S117, the vehicle speed Vi is
Is used to calculate the target wheel Vwsi of each wheel. In this embodiment
Is the target slip ratio set in step S116.
Si ^*(The target slip rate has been changed to be shallower
The target wheel selected as the target slip rate change target wheel
Target wheel slip ratio (eg, 0 or 0.02)
) Is calculated according to the following equation.

Vwsi = Vi × (1-Si ^* ) 14

In the following step 118, the brake fluid pressure increase / decrease amount ΔP ^* is calculated. In this embodiment, the target wheel speed Vw
ΔP ^* is calculated by the following equation from si and the wheel speed Vwi.

ΔP ^* = k1 × ε + k2 × (dε / dt) 15a ε = Vwsi−Vwi 15b Note that dε / dt in the expression 10a is the actual wheel speed represented by the expression 10b. Means the derivative of the deviation ε between the value and the target value.
Further, k1 and k2 are feedback gains (proportional control gain and differential control gain, respectively), and are changed according to the road surface μ and the vehicle speed.

In the following step S119, as described above,
Target increase / decrease amount ΔP^*After calculating the
The process of outputting the drive signal to the control valve (step S120)
The pressure increase / decrease amount ΔP^*Calculate valve drive time Ti according to
Put out. In this embodiment, the upstream pressure Pu of the control valve (the pressure
The master cylinder pressure Pm / c,
Eel cylinder pressure Pw / c) and downstream pressure Pl (for booster valve
Wheel cylinder pressure Pw / c if pressure reduction valve
Pressure) and increase / decrease amount ΔP ^*And valve drive time Ti
formula,

## EQU16 ## The pulse drive time Ti is calculated from Ti = f1 (Pu, P1, ΔP ^* ) (16). Graphs of the above relational expressions are shown in FIGS. For example, at the time of pressure increase (FIG. 8), the pressure increase valves (14, 24, 34, 44) to be controlled
Master cylinder pressure Pm / c, which is the upstream pressure (Pu), and the corresponding wheel cylinder pressure Pw / c, which is the downstream pressure (Pl)
And the target pressure increasing amount ΔP ^* , the corresponding drive time T of the pressure increasing valve
i is calculated.

FIG. 8 shows the characteristics when Ti = Tu is constant, and the driving times other than Tu are obtained by proportionally complementing. Here, in obtaining the value Ti, for example, it can be obtained from a three-dimensional map of Ti = f (Pu, Pl, ΔP), but the following method can be adopted. As shown in FIG. 10, specifically, Ti = t
As u, ΔP is calculated, and is repeatedly calculated until it matches ΔP ^* . That is, Ti = tu
When ΔP = (Pu, Pl, Ti) is ΔP ^* > ΔP (the first calculated value of ΔP is still the target ΔP
^If it is less than ^* , recalculation is further performed with Ti = 2tu (the first and second black circle points from the left side of the figure). Then, until ΔP ^* ≦ ΔP is satisfied (that is, until ΔP becomes at least equal to or exceeds ΔP ^* ) (Ti = 3tu,
4tu (third and fourth black circle points from the left side of the figure)
...), for example, ΔP (Pu, Pl, 3tu) <ΔP
^* Ti ≦ 4tu when ≦ ΔP (Pu, Pl, 4tu)
(The case in the figure corresponds to this).
Ti may be obtained in this manner. FIG. 9 (at the time of depressurization) shows the characteristics when Ti = Tl is constant (in this case, the depressurizing valve (15, 25, 3
5, 45) corresponds to the downstream pressure Pl of the reservoir (16, 45).
Since the pressure is 17), Pl is always 0 (open to the atmosphere).

Here, the value of the master cylinder pressure Pm / c as the upstream pressure Pu applied to the calculation of the valve drive time Ti may be a sensor detection value using a master cylinder pressure sensor. It may be calculated by simply estimating the time until the anti-skid control is started. For the current wheel cylinder pressure as the downstream pressure Pl or the upstream pressure Pu,
From the previous valve drive time Ti,

## EQU17 ## The actual pressure increase / decrease amount is estimated using ΔP = f2 (Pu, Pl, Ti)... 12 and added to the previous estimated wheel cylinder pressure value in accordance with Equation 3 shown in step S105. Is calculated by

After calculating the valve drive time Ti, the brake fluid pressure control is executed by outputting a valve drive signal to the pressure control unit 5 in this step every time step S120 is executed based on the calculated valve drive time Ti. The brake fluid pressure of each wheel is controlled such that each wheel speed Vwi converges to a target value (target wheel speed Vwsi) of each wheel set based on the estimated vehicle body speed Vi. The pressure is controlled by controlling the corresponding control valve of each channel.

In this embodiment, the anti-skid control portion performs feedback control according to the deviation ε between the wheel speed Vi and the target wheel speed Vwsi. However, if the pressure control unit 5 has sufficient responsiveness, The wheel speed Vw is controlled so as to accurately follow the target. When all the wheel speeds converge with a certain deceleration slip in this way, the conventional vehicle speed estimation method uses the “upward shift” of the estimated vehicle speed (FIG. 15).
There is concern that insufficient deceleration due to the lower part and early locking due to "slipping down" (the upper part in FIG. 15), however, according to this method, the vehicle speed can be accurately determined even when all the wheels are decelerating and slipping. Vi can be estimated, and even if a deviation occurs in the vehicle body speed estimation, the deviation of the vehicle body speed estimated value can be corrected by restoring the slip of the wheel that has the least effect on the vehicle behavior and the deceleration. Good anti-skid performance without sacrificing.

FIG. 11 is an example of a time series graph showing the operation when this control is performed. Here, as in the case of FIG. 12 as a comparative example, a control scene from a right turn is compared as an example. That is, changes in various amounts such as the wheel speed and the vehicle speed in the case of following this program example are shown, and the actual vehicle speed (broken line) for the vehicle speed, the estimated vehicle speed (step S112) indicated by the solid line, and the wheel speed are shown. The transition of the front wheel right wheel speed (solid line) which is the inner wheel before turning and the rear wheel right wheel speed (dashed line and dashed line) which is the inner wheel after turning are shown. Further, a target slip ratio changing process (step S11) based on the determination of the wheel speed convergence state during the anti-skid control operation according to the present program example.
3 to S116), the target change flag applied, the change transition of the generated yaw rate φ during the control, and the change transition of the wheel cylinder pressure (W / C pressure) of each of the front, rear, left and right wheels are shown. In this control, the braking deceleration is improved by converging the wheel speed to the target wheel speed, and the anti-skid control performance is improved by estimating the vehicle speed with high accuracy.

When the vehicle speed is calculated from the selected wheel speeds as described above with reference to FIGS. 14 and 15, it is not possible to accurately estimate the vehicle speed when all the wheels are slipping. When the anti-skid control is performed so as to converge to the vehicle speed, it becomes more difficult to estimate the vehicle speed. According to the present logic, as shown in FIG. 11, the wheel speed Vw is controlled so as to accurately follow the target wheel speed Vws. During the process, even during anti-skid control where all the wheels are braking and slipping, the problem of "upward" and "downward" of the estimated vehicle speed, which causes such insufficient deceleration and early locking, is avoided. In particular, the difference between the estimated vehicle body speed and the actual vehicle speed is small (the downhill is also small), and the accuracy of the slip ratio control is greatly improved. In the case of FIG. 14, the estimated wheel speed is calculated from the selected wheel speed obtained by selecting and filtering the wheel speed of each wheel. However, as shown in the processing in steps S109 and S110, the estimated wheel speed is not calculated from the wheel speed ( That is, since the error is estimated from the road surface μ), an error of the braking slip included in the wheel speed is basically not included, and the accuracy is improved.

Therefore, in this respect, according to the present embodiment, even during the anti-skid control in which all the wheels are braking and slipping, it is possible to accurately estimate the vehicle speed and improve the anti-skid control performance. It is possible to solve the problems discussed in (a) and (b) at the beginning of the specification, to prevent the wheels from slipping deeply and to control the wheels to hunt to some extent to prevent early locking. Such a problem that the braking force is reduced and the braking distance is increased can be satisfactorily solved.

In addition to this, the matters discussed in (c) and (d) at the beginning of the specification can be satisfactorily eliminated at the same time. In the case of the comparative example of FIG. 12, even during braking from the same right turn, the target is switched periodically for a predetermined period of time, and the wheels for changing the target are located behind the front wheels as shown in the figure. 12, the front wheel right wheel speed (solid line) and the rear wheel right wheel speed (bold one-dot chain line) also change as shown in FIG. The turbulence is large, and the effect of the vehicle behavior is large. At the same time, the reduction in the W / C pressure of the front left and right wheels and the rear right and left wheels to be changed when the target is changed is also large. The decrease is also large.

On the other hand, in the case of the present embodiment shown in FIG.
Such a situation is also avoided, and in such a right turn braking, the wheel targeted for the change of the target slip ratio is selected based on the wheel speed convergence state determination as described above and as illustrated. The rear wheel is the right rear wheel which is the rear inner wheel, and the rear wheel is also the right wheel even when the next target slip ratio is changed (therefore, it is not a mode in which the front wheel and the rear wheel are alternately performed at a predetermined cycle). Thus, the correction of the estimated wheel speed is performed at each timing, and at this time, the disturbance of the yaw rate is not large, and at the same time, the estimation of the vehicle body speed at the right rear wheel, which is the inner wheel after turning, is corrected. It can be seen that the reduction in the W / C pressure is also small. Thus, according to this,
It is possible to further improve the braking deceleration by converging the wheel speeds to the target wheel speeds and to improve the anti-skid control performance by estimating the vehicle speed with high accuracy.

The present invention can be carried out in the following modes in addition to the above-mentioned embodiment (first embodiment). In the first embodiment, the wheel whose target slip ratio is changed according to the running state of the vehicle is determined (steps S114 and S115). However, the present embodiment (second embodiment).
Then, as mentioned above, when the anti-skid control performs a synchronous control of the left and right (or front and rear) wheels (a so-called select-low control or the like), a wheel having a lower slip ratio of the wheels subjected to the select-low control is used. Change the slip rate.

In this embodiment, regarding the system configuration,
This is the same as the case of the first embodiment shown in FIG. However, here, the rear wheels are subjected to select low control. FIG. 13 is a flowchart of an example of a control program executed by the controller 50 in the present embodiment. Hereinafter, the main part of the present embodiment will be described.

In FIG. 13, steps S201 to S213
Are the same as steps S101 to S113 in FIG. 5 of the first embodiment. Here, the first
It is not necessary to judge the running state in step S114 of the embodiment, and thereafter, each step is moved up one by one,
This corresponds to the processing of steps S214 to S219 of the present embodiment.

In the selection of the wheel to change the slip in step S214 in FIG. 13, the wheel whose slip ratio is shallow by the select-low control of the rear wheel is selected as the wheel to change the slip ratio. Then, the subsequent steps S215 to S2
The processing is executed up to 19, and the processing in the current loop of this program is ended. The contents are the same as those in steps S116 to S200 of the first embodiment. In this case, when the synchronous control of the left and right wheels or the front and rear wheels, that is, the select low control of the rear wheels as in this example, is performed,
In accordance with the select row control, the select side control can change the slip ratio on the wheel side where the slip ratio becomes shallower, and therefore, is effective when such kind of synchronous control is performed. Becomes

Further, another embodiment (third embodiment) of the present invention will be described. In the present embodiment, when the target slip ratio is changed, when the target slip ratio is changed, the hydraulic pressure fluctuation of the selected wheel is monitored for a set time, and the target slip ratio is changed when the pressure reduction mode is entered. is there. That is, in the first embodiment, the target slip ratio is immediately changed when it is determined that there is a possibility of the estimated deviation of the vehicle speed in the determination of the convergence state of the wheel speeds. When a wheel for changing the target slip ratio is selected after this determination, the change in the hydraulic pressure of the selected wheel is monitored during the set time Tsg, and the target slip ratio is changed when the pressure reduction mode is entered. . If the pressure reduction mode is not entered within the set time Tsg, the target slip ratio is changed at that time. This can further reduce the effect on deceleration when the brake fluid is depressurized to correct the estimation of the vehicle body speed. The invention may be implemented in this way.

The present invention is not limited to the above embodiment. For example, in the embodiment, the vehicle to be applied is a rear wheel drive vehicle (AT vehicle, vehicle equipped with a Convedev), but is not limited to this. In addition, the front and rear wheels are 4-channel ABS that can control the left and right brake pressures independently.
However, the present invention is not limited to the three-channel brake system in which the left and right front wheels are independently controlled and the rear two wheels are commonly controlled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic conceptual diagram of the present invention.

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

FIG. 3 is a view showing the configuration of the embodiment, and showing an example of an applicable pressure control unit.

FIG. 4 is a functional block diagram illustrating an example of a basic configuration of control contents.

FIG. 5 is a flowchart illustrating an example of a control program executed by a controller.

FIG. 6 is a diagram illustrating an example of a characteristic used for explaining road surface μ peak determination;

FIG. 7 is a diagram also provided for a similar description.

FIG. 8 is a diagram illustrating an example of a characteristic used for explaining a valve driving time calculation.

FIG. 9 is a characteristic diagram for the same explanation.

FIG. 10 is a diagram which is also used for the same description and shows an example of a calculation method.

FIG. 11 is an example of a time-series graph used for explaining control contents.

FIG. 12 is an example of a time-series graph in a comparative example shown in comparison with FIG. 11;

FIG. 13 shows another embodiment of the present invention, and is a flowchart showing an example of the control program.

FIG. 14 is a diagram showing changes in wheel speed, actual vehicle speed, and the like in general anti-skid control.

FIG. 15 is a diagram provided for describing an effect of a deviation in estimated vehicle body speed.

[Explanation of symbols]

Reference Signs List 1 brake pedal 2 booster 3 reservoir 4 master cylinder 5 pressure control unit (pressure servo unit) 6 longitudinal / lateral acceleration sensor 7 yaw rate sensor 10, 20, 30, 40 left front wheel, right front wheel, left rear wheel, right rear wheel 11, 21, 31, 41 Brake discs 12, 22, 32, 42 Wheel cylinders 13, 23, 33, 43 Wheel speed sensors 14, 24, 34, 44 Pressure increasing valves (control valves) 15, 25, 35, 45 Pressure reducing valves (control Valve) 16, 17 Reservoir 26, 27 Pump 36 Motor 50 Controller 51 Engine control controller 52 AT control controller

Claims (11)

[Claims] 1. An anti-skid control device including an anti-skid control unit for controlling a brake pressure of each wheel so that a wheel speed becomes a target wheel speed, and determines a convergence state of each wheel to a target wheel speed. A wheel speed convergence state determining means, and at least one
An anti-skid control device comprising: target slip ratio changing means for changing a target slip ratio of a wheel to a shallower one. 2. A road surface friction coefficient estimating means for estimating a road surface friction coefficient, and a vehicle speed estimating means for estimating a vehicle speed using a road surface friction coefficient of each wheel estimated by the road surface friction coefficient estimating means. An anti-skid control device that sets a target wheel speed for each wheel based on the vehicle speed estimated by the vehicle speed estimation means, and controls a brake pressure of each wheel so that each wheel speed converges to its target value. A wheel speed convergence state determining means for determining a convergence state of each wheel to a target wheel speed;
An anti-skid control device, comprising: a target slip ratio changing means for changing a target slip ratio of a wheel to a shallower one. 3. The target slip ratio changing unit is selected by a wheel selecting unit that selects a wheel that has the least effect on the vehicle behavior when the wheel slip state is changed based on a detection value of the vehicle running state detecting unit. The anti-skid control device according to claim 1 or 2, wherein a slip ratio of a wheel is changed. 4. The target slip ratio changing means, when synchronous control of the left and right wheels or the front and rear wheels of the anti-skid control is performed, changes a slip ratio of a wheel having a smaller slip ratio. The anti-skid control device according to claim 1 or 2, wherein 5. The convergence state determination unit according to claim 1, wherein the wheel speed convergence state determination unit determines the convergence state according to a time during which a deviation between the wheel speed and the target wheel speed exists within a set value. 5. The anti-skid control device according to any one of 4. 6. The convergence state judging means judges the convergence state according to a time when all wheel speeds are smaller than a convergence judgment wheel speed threshold value different from the target wheel speed. The anti-skid control device according to any one of claims 1 to 4, wherein: 7. The road surface friction coefficient estimating means includes: a wheel acceleration calculated from a wheel speed detected by a wheel speed detecting means of each wheel; a wheel load detected by a wheel load detecting means of each wheel; From the brake fluid pressure estimated by the wheel brake fluid pressure estimating means, and, for the drive wheels, from these, and from the driving torque further estimated by the driving torque estimating means,
The anti-skid control device according to any one of claims 2 to 6, wherein a road surface friction coefficient is calculated. 8. The vehicle body speed estimating means calculates a selected wheel speed calculated from a wheel speed detected by a wheel speed detecting means of each wheel by using a road surface friction coefficient estimated by the road surface friction coefficient estimating means. The vehicle speed is estimated so as to follow a vehicle speed change amount calculated by a coefficient, a lateral speed detected by the vehicle lateral speed detecting means, and a yaw rate detected by the yaw rate detecting means. The anti-skid control device according to any one of claims 2 to 7, wherein 9. The vehicle running state detecting means detects a running state of the vehicle based on at least one of a vehicle speed, a longitudinal acceleration, a lateral acceleration, a yaw rate, a steering angle, a wheel load, a wheel slip ratio, a vehicle body and a wheel side slip angle. The anti-skid control device according to claim 3, or any one of claims 5 to 8. 10. The target slip ratio changing means monitors a change in the hydraulic pressure of a wheel selected when the target slip ratio is changed for a set time, and changes the target slip ratio when entering a pressure reduction mode. The anti-skid control device according to any one of claims 1 to 10, wherein: 11. The target slip ratio changing means holds the target slip ratio in a shallow state until the wheel speed of a wheel having changed the target slip ratio follows the target, and returns to the original target slip ratio after following. The anti-skid control device according to any one of claims 1 to 10, wherein: