JPH05170085A - Slip control device for vehicle - Google Patents

Abstract

PURPOSE:To perform appropriate slip control corresponding to low mu by estimating the road surface mu to be used for braking force control on the basis of the rate-of-change of wheel speed detected by a rate-of-change detecting means when the specified time elapses after the start of braking force holding control. CONSTITUTION:After the road surface mu is initialized to 3 (high mu), signals from each sensor and the like for detecting the rotating speed of each wheel are inputted. In the case of the acceleration/deceleration of wheel speed being smaller than 0 upon the lapse of the specified time after a timer being set, the value obtained by deducting 1 from the preceding estimated road surface muis set as the present road surface mu. That is, if the preceding road surface muis 3 indicating high mu, the present road surface mu is made into 2 indicating medium mu. Since the lowest set value of the road surface is 1 (low mu), when the preceding estimated road surface mu is 1, 1 is set as it is. In the case of acceleration/deceleration being O, no change is made, and the preceding road surface mu is used as it is as the present road surface.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Recently, as is well known by the name of ABS device, many vehicles are equipped with an anti-skid brake device for preventing the wheels from being locked during a brake (for example, an ABS device). (See JP-A-58-194647). In the slip control, that is, the braking force control, there are at least two types of control modes of increasing the braking force and decreasing the braking force, and in addition to this, there is also a control mode of holding the braking force.

In order to make the braking force control more appropriate according to the road surface μ, the road surface μ is estimated and the content of the braking force control is changed according to the estimated road surface μ, for example, the braking force. For example, the switching threshold value for switching the control contents of the increase, the braking force decrease, and the braking force holding is changed.

[0004]

By the way, how to estimate the road surface μ with good responsiveness is extremely important for making the slip control appropriate for the road surface μ. On the other hand, in recent slip control, there is an extremely strong demand for shortening the braking distance, and from this viewpoint, the road surface μ is estimated as high as possible unless there is a strong need to estimate it as low μ. It would be desirable to be estimated. However, in the conventional road surface μ estimating method, it is difficult to reliably perform the determination of the low μ while accurately performing the estimation of the road surface μ, particularly the estimation of the low μ.

Therefore, an object of the present invention is to enable the estimation of the road surface μ, in particular, the estimation that the road surface μ is low, with good response, so that the slip control according to the road surface μ can be performed more appropriately. Another object of the present invention is to provide a slip control device for a vehicle.

[0006]

In order to achieve the above object, the present invention has the following first construction. That is, the braking force control including at least the braking force increase, the braking force decrease, and the braking force retention is performed so that the wheels are not locked during the braking, and the content of the braking force control is changed according to the road surface μ. In a slip control device for a vehicle, change rate detecting means for detecting a change rate of wheel speed, based on a change rate of wheel speed detected by the change rate detecting means when a predetermined time has elapsed from the start of control of holding braking force. Estimating means for estimating the road surface μ used for the braking force control.

In order to achieve the above object, the present invention has the following second construction. That is, the braking force control including at least the braking force increase, the braking force decrease, and the braking force retention is performed so that the wheels are not locked during the braking, and the content of the braking force control is changed according to the road surface μ. In the vehicle slip control device configured as described above, an estimating unit that estimates the road surface μ used for braking force control based on a preset condition, a change rate detecting unit that detects a change rate of wheel speed, and a braking force holding unit When a predetermined time has elapsed from the start of the control, a correction unit that corrects the road surface μ estimated by the estimation unit based on the change rate of the wheel speed detected by the change rate detection unit is provided.

The behavior of the wheel during the holding of the braking force, particularly the rate of change of the wheel speed (wheel acceleration / deceleration), reflects the road surface μ fairly accurately. Therefore, it is possible to estimate the road surface μ with good response and fairly accurately according to the rate of change in wheel speed after a lapse of a predetermined time in which the braking force holding state is considered to be stable. That is, since the magnitude of the wheel speed change rate after a predetermined time has elapsed from the start of holding the braking force indicates the degree of recovery of the wheel speed according to the reaction force from the road surface, that is, the road surface μ, for example, the change in wheel speed. When the rate shows deceleration, it can be reliably determined that the road surface μ is low μ.

Although it is possible to estimate the road surface μ depending on the magnitude of the holding time of the braking force, in this case, the time required for estimating the road surface μ is extremely long, such as from the start to the end of the holding of the braking force. It will take time,
It is not preferable in terms of responsiveness.

[0010]

According to the first configuration, the estimation of the road surface μ can be performed with good response, and the low μ can be surely determined. This means that, while slip control is usually performed assuming that the friction coefficient is relatively high, the braking distance is shortened, but when the friction coefficient μ becomes low, the braking force control corresponding to the low friction coefficient is promptly performed. It is possible to reliably prevent the wheels from being locked by shifting to.

According to the second configuration, the braking distance is shortened by the slip control which is usually presumed by the estimating means on the basis of the relatively high μ, and when the μ is low, the estimating is performed by the correcting means. Reliable and quickly low μ
It is possible to correct to the side and promptly shift to the slip control corresponding to this low μ to reliably prevent the wheels from being locked.

[0012]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 1FR is a right front wheel, 1FL is a left front wheel, 1RR is a right rear wheel, 1
RL is the left rear wheel. Reference numeral 2 denotes an engine, and the torque generated by the engine 2 is transmitted to the clutch 3, the transmission 4, the propeller shaft 5, and the differential device 6 and then to the right rear wheel 1RR via the drive shaft 6R. Drive shaft 6
It is transmitted to the left rear wheel 1RL via L. Each wheel 1FR ~
The break devices 7FR to 7RL are provided in the 1RL, respectively. Each of the breaking devices 7FR to 7RL includes a disk 8 that rotates integrally with a wheel, and a caliper 9 that incorporates a wheel cylinder.

Numeral 11 is a master cylinder as a brake fluid pressure generating means, and the driver's stepping force on the brake pedal 12 is inputted through a known booster 13 and a brake corresponding to the stepping force is inputted. Liquid pressure is generated. This master cylinder 11 is of a tandem type having two discharge ports. The brake pipe 14 extending from one discharge port of the master cylinder 11 is branched into two in the middle, and one branch pipe 14FR is connected to the brake device 7FR (wheel cylinder) for the right front wheel, The other branch pipe 14FL
Is connected to (the wheel cylinder of) the braking device 7FL for the left front wheel. The brake pipe 15 extending from the other discharge port of the master cylinder 11 is branched into two in the middle, and one branch pipe 15RR is connected to (the wheel cylinder of) the brake device 7RR for the right front wheel. The other branch pipe 15RL is a brake device 7RL (for the left rear wheel)
Connected to the cylinder).

A hydraulic pressure adjusting mechanism 21FR is provided in the branch pipe 14FR for the right front wheel, a hydraulic pressure adjusting mechanism 21FL is provided in the branch pipe 14FL for the left front wheel, and a hydraulic pressure adjusting mechanism 21R is provided in the pipe 15 common to the left and right rear wheels. Are connected. Each hydraulic pressure adjustment mechanism 2
1FR, 21FL and 21R are the first on-off valve 2 respectively.
2 and the second opening / closing valve 23. Each open / close valve 22, 2
3 are electromagnetic type, and the first opening / closing valve 22 is the pipe 1
Open and close 4FR, 14FL or 15 to open the second opening / closing valve 2
Reference numeral 3 connects and disconnects each pipe and the reservoir tank. As a result, when the brake fluid pressure is generated in the master cylinder 21, the brake device 7 is operated.
The pressure increase, the pressure retention, and the pressure reduction of the brake hydraulic pressure supplied to FR to 7RL are switched. That is, the pressure is reduced by closing the first opening / closing valve 22 and opening the second opening / closing valve 23, and held by closing both opening / closing valves 22 and 23,
The pressure is increased by opening the first opening / closing valve 22 and closing the second opening / closing valve 23. Then, in the embodiment, the pressure is initially increased rapidly, and then gradually increased.
This is performed by, for example, duty-controlling the opening speed (opening) of the first opening / closing valve 22.

In FIG. 1, U is a control unit constructed by using a microcomputer, and signals from the respective sensors or switches S1 to S5 are input to the control unit U. The sensors S1 to S4 are used for the wheels 1FR to 1R.
The rotation speed of L is detected. The switch S5 is
The brake switch is turned on when the brake pedal 12 is depressed.

The control unit U includes the hydraulic pressure adjusting mechanism 21.
Although FR, 21FL, and 21R are controlled, as is clear from the above description, slip control is individually performed for the left and right front wheels 1FR and 1FL, and the left and right rear wheels 1RR and 1RL are integrated. Slip control is performed. The slip control is performed by the brake switch S.
It may be performed on the assumption that 5 is ON, or may be performed without such an assumption.

Description of FIG . 2 The content of the slip control by the control unit U will be described with reference to FIG. In this slip control, Phase 0, Phase 1, Phase 2, Phase 3, Phase
No. 5 is used, and its meaning is as follows. Phase 0: Indicates that non-slip control is in progress. Phase 1: means increasing pressure (increasing braking force). Phase 2: means holding (holding braking force) after non-slip control or after pressure increase. Phase 3: means decompression (reduction of braking force). Phase 5: Retaining after depressurization.

The slip value, which indicates the tendency of the wheels to lock, is determined by, for example, the following equation. The estimation of the pseudo vehicle body speed will be described later. Slip value = (wheel speed / pseudo vehicle speed) × 100% As described above, in the embodiment, the slip value is set such that the smaller the slip value, the greater the tendency of the wheels to lock.

On the premise of the above, the slip control is not performed until the time point t1 and the blur control is performed.
As the hydraulic pressure increases, the wheel speed gradually decreases from the pseudo vehicle speed. Due to the decrease in the wheel speed, the deceleration of the wheel speed decreases to a predetermined value as the slip control start condition at time t1, that is, time A. The slip control is started from the time point A, but it is performed by first maintaining the brake hydraulic pressure. During this holding, the wheel speed decreases and B
When the slip value falls to a predetermined threshold value as shown at the time point, the pressure is reduced. Due to this pressure reduction, the degree of decrease of the wheel speed is weakened, and the deceleration becomes near 0 at the time C.

At the time C when the deceleration is close to 0, the wheel is held, whereby the wheel speed gradually increases and the slip value returns to the predetermined threshold value at the time D.
From the time point D, the pressure is increased, but the pressure is rapidly increased in the initial stage and then gradually increased. Due to the pressure increase, the deceleration of the wheel speed is reduced again to the predetermined value set as the slip control start condition at the time point E. This allows
After the brake fluid pressure is maintained, when the slip value decreases to a predetermined threshold value at time F, pressure reduction is performed. Then, from the time point G corresponding to the time point C, the blur
Liquid pressure is maintained.

The above is the outline of the slip control, and the period from the end of the phase 5 (retention after pressure reduction) (start of pressure increase) to the end of the next phase 5 is one control cycle. However, this one cycle is from the start of holding the phase 2 to the end of the phase 5 only when the slip control is started (since the slip control is started from the phase 2).
The threshold value when the phase is changed is changed according to the road surface μ (friction coefficient), and a specific setting example of the threshold value according to the road surface μ is shown in the following table.

[0022]

[Table 1]

Description of FIG. 3 FIG. 3 is a flow chart showing a control example of the present invention.
In the following description, P indicates a step. First, after signals from sensors S1 to S5 are input at P100, P110
At μ, the road surface μ is estimated. At P120, the pseudo vehicle speed is estimated, and at P130, the slip value for slip control described above is calculated. Then, at P140, the slip control as described with reference to FIG. 2 is performed.
The details of P110, P120, and P140 will be described later.

Description of FIG. 4 FIG. 4 is for estimating the road surface μ, and is indicated by P in FIG.
The contents of 110 are shown. The control of FIG. 4 is performed independently for each wheel. First, P4
1, the road surface μ is initialized to 3 (high μ) (this initialization is actually the initialization at the start point of FIG. 3), and then the signals from the respective sensors are input at P42. ..

At P43, it is judged if the slip control (ABS control) is currently being performed. When the determination in P43 is NO, the road surface μ is set to 3 in P51. As described above, by the initialization and the processing of P51, the estimated road surface μ is set to 3 indicating high μ unless the slip control is performed, so that the braking distance is shortened.

When the result of the determination in P43 is YES, it is determined whether or not the control for holding the braking force after the decrease of the braking force in Phase 5 has been started. YE in this P44 judgment
In case of S, after the timer is set in P45,
In P46, it is determined whether or not a predetermined time (for example, 100 msec) has elapsed from the start of the phase 5. If the determination in P46 is NO, it is determined in P47 whether or not it is still Phase 5, and if the determination in P47 is YES, the process returns to P46 again.

When the determination in P46 is YES, it is determined whether the rate of change of the wheel speed, that is, the acceleration / deceleration of the wheel speed is smaller than 0 (whether or not the deceleration is indicated).
When the determination in P48 is NO, in P49, the previously estimated road surface μ is set as it is as the current road surface μ. When the determination in P48 is YES, in P50, the value obtained by subtracting 1 from the previously estimated road surface μ is set as the current road surface μ. That is, the front circuit surface μ
Is 3 indicating high μ, it is set to 2 indicating medium μ. In addition,
Although the steps for processing are omitted in FIG. 4, the road surface μ
Since the minimum setting value of is 1 (low μ), when the road surface μ estimated last time is 1, 1 is set as it is in P50.

When the determination in P44 is NO, or when the determination in P47 is NO, the engine is returned as it is (without changing the estimated road surface μ, the front circuit surface μ is used as it is as the current road surface μ). ..

Instead of the processing of P48 to P50, the following processing may be performed. That is, the correspondence between the rate of change in wheel speed and the road surface μ is mapped and stored in advance, the road surface μ corresponding to the rate of change in wheel speed at the time of P48 is read from the map, and the read road surface μ
May be finally used as the road surface μ for slip control. In this case, the map is μ = 3 (high μ) when the wheel speed change rate indicates a predetermined value or more, and μ = 1 (low μ) when the wheel speed change rate indicates a deceleration of a predetermined value or more. In other cases, it may be set such that μ = 2 (medium μ).

Description of FIGS . 5 and 6 FIG. 5 is for estimating the pseudo vehicle body speed.
Corresponds to the contents of P120 of. In P21 of FIG.
Of the wheels 1FR to 1RL, the wheel with the highest wheel speed is W.
It is set as M. After that, in P22, the maximum wheel speed WM is differentiated to calculate the amount of change, that is, the acceleration / deceleration WM · G for the maximum wheel speed.

At P23, the reference deceleration-GO corresponding to the road surface μ is determined, and this reference deceleration-GO is
It is the maximum wheel deceleration that is expected to occur according to the road surface μ at the time of braking, and the corresponding relationship is shown in FIG. In this case, the smaller the road surface μ, the reference deceleration −G
O is set to be small (the absolute value of GO is larger as the road surface μ is larger). However, in the embodiment, since the road surface μ is determined in three stages, -GO is also determined in three stages.

In P24, WM · G is the reference deceleration-GO
Is less than or equal to. If the determination in P24 is YES, the pseudo vehicle body speed VR is set to a value based on the reference deceleration-GO in P25. That is, at this time, when the wheel speed suddenly decreases, the speed corresponding to the reference deceleration-GO from the previously determined pseudo vehicle speed is suppressed in order to suppress the sudden decrease in the pseudo vehicle speed. The value obtained by subtracting is set as the pseudo vehicle body speed VR this time.

When the result of the determination in P24 is NO, it is determined in P26 whether or not the value obtained by subtracting the maximum wheel speed WM from the previous pseudo vehicle speed VR is equal to or greater than a predetermined value. Even when the determination in P26 is YES, it means that the wheel speeds are decreasing sharply. Therefore, also in this case, the process shifts to P25 in order to suppress the rapid decrease in the pseudo vehicle body speed. If NO in P26, in P27, maximum wheel speed WM
Is set as the pseudo vehicle speed. Of course, P25
Alternatively, the pseudo vehicle body speed determined in P27 is used as the previous pseudo vehicle body speed in P26.

Description of FIG . 7 FIG . 7 shows another control example of the present invention. While the road surface μ is estimated based on the wheel acceleration / deceleration, the estimated road surface μ is shown in P44 to P50 of FIG. The case where correction is performed by processing is shown. In other words, FIG. 7 corresponds to the process performed before P44 of FIG.

On the premise of the above, in P1,
It is determined whether or not slip control is currently being performed. This P
When the determination result in 1 is NO, the road surface μ is set to 3 in P2 (high μ). When the determination in P1 is YES, the acceleration / deceleration WG of the wheel is calculated by differentiating the wheel speed in P3. When this WG is calculated, the maximum value within a predetermined time (which can be set as a long time corresponding to one control cycle in FIG. 2, for example) is stored as the acceleration, and the minimum value is stored as the deceleration. After P3, in P4, it is determined whether or not the deceleration of the WG is smaller than a predetermined threshold value of -20G. It should be noted that -20G as the threshold value means a value corresponding to -20G in a predetermined sampling period (the same applies hereinafter).

When the determination in P4 is YES, the road surface μ may be low. At this time, first, at P5, it is judged if the acceleration of the WG is greater than 10G. When the determination in P5 is NO, P = 1 is set (low μ) in P8. YES in P5
If, and if the determination in P4 is NO, it is determined in P6 whether or not the acceleration of the WG is greater than 20G. If YES in the determination in P6, μ = 3 is set in P9, and NO in the determination in P6.
In the case of, μ = 2 (medium μ) is set in P7.

After the above P7, P8 or P9, FIG.
The process of shifting to P44 is performed. However,
In this case, the last μ at P49 or P50 is P
The road surface μ is set at 7, P8 or P9.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing an example of slip control.
To.

FIG. 3 is a flowchart showing a control example of the present invention.

FIG. 4 is a flow chart showing a control example of the present invention.
To.

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

FIG. 6 is a diagram showing a relationship between a reference deceleration and a road surface μ.

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

[Explanation of symbols]

 1FR to 1RL: Wheels 7FR to 7RL: Breaking device 14, 15: Breaking piping 14FR, 14FL: Branch piping 15RR, 15RL: Branch piping 21FR, 21FL, 21R: Hydraulic pressure adjusting mechanism U: Control units S1 to S4 : Wheel speed sensor

Claims (7)

[Claims] 1. A braking force control including at least a braking force increase, a braking force decrease, and a braking force retention is performed so that the wheels are not locked during braking, and the content of the braking force control is changed according to the road surface μ. In the vehicle slip control device, the change rate detecting means for detecting the change rate of the wheel speed, the change of the wheel speed detected by the change rate detecting means after a predetermined time has elapsed from the start of the control of holding the braking force. A slip control device for a vehicle, comprising: an estimating unit that estimates a road surface μ used for braking force control based on a rate. 2. The method according to claim 1, wherein the estimating means is set to estimate only a low μ that is equal to or less than a road surface μ estimated last time. 3. The device according to claim 2, further comprising a returning means for setting the road surface μ used for the braking force control to the highest μ when the braking force control is not being performed. 4. The braking force control according to claim 1, wherein the braking force control includes at least a braking force increase, a braking force decrease, and a braking force retention so that the wheels are not locked at the time of braking, and the braking force control is performed according to the road surface μ. In the vehicle slip control device adapted to change the contents of the above, an estimating means for estimating the road surface μ used for the braking force control based on a preset condition, and a change rate for detecting the change rate of the wheel speed. Detecting means, and a correcting means for correcting the road surface μ estimated by the estimating means based on the rate of change of the wheel speed detected by the rate of change detecting means when a predetermined time has elapsed from the start of control of holding the braking force. A slip control device for a vehicle, comprising: 5. The correction device according to claim 4, wherein the correction unit is set to perform only correction to a low μ side of a road surface μ or less estimated by the estimation unit. 6. The method according to claim 5, wherein the estimating means estimates the road surface μ based on the maximum acceleration and the minimum acceleration of the wheels within a predetermined time. 7. The braking force holding control according to any one of claims 1 to 6, when the road surface μ is determined,
This is the control for holding the braking force that is performed after the control for reducing the braking force.