JP2003212104A - Brake control device - Google Patents

Abstract

(57) [Summary] When the slip ratio of a wheel becomes a second slip ratio having a larger slip ratio than the first slip ratio, after performing a pressure reduction larger than the above, a gentle pressure increase is performed. In the brake control device, the efficient execution of the ABS control by reducing the number of pressure reductions and the prevention of insufficient deceleration when the slip rate becomes larger than the second slip rate are compatible. Plan. SOLUTION: In ABS control, a gradient at the time of a slow increase when the wheel slip rate exceeds a second slip rate is steeper than a slope at a time of a slow increase when the wheel slip exceeds the first slip rate. Set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake control device for executing anti-lock brake control (hereinafter referred to as ABS control) for preventing wheels from being locked during braking, and more particularly to a road surface friction coefficient (hereinafter referred to as ABS control) only for a moment. The present invention relates to control technology when traveling on a road surface having a low friction coefficient (μ).

[0002]

2. Description of the Related Art Conventionally, as a brake control device for executing ABS control,
The wheel speed is compared to the vehicle body speed to determine the slip ratio of the wheel, and when the wheel exceeds a predetermined slip ratio, that is, when the wheel speed falls below the decompression threshold value, decompression is performed, and thereafter, a slow pressure increase, That is, a technique of increasing the pressure a plurality of times at a constant cycle is well known.

In such a conventional technique, it is known that the hydraulic pressure of the wheel cylinder is maintained in the vicinity of the hydraulic pressure at which a high braking force is obtained, and the number of pressure reductions is reduced to execute efficient control. That is, as shown in FIG. 6, the first (close) shallower vehicle body speed Vi based on the vehicle body speed Vi.
A decompression threshold value λ1 and a second decompression threshold value λ2 lower (deeper) than the decompression threshold value λ1 are formed. By executing the above, it is possible to obtain a high braking force by keeping the slip ratio of the wheel near a value (first depressurization threshold value λ1) at which the braking force can be efficiently obtained. In addition, the wheel slip rate may change due to a momentary change in the road surface μ, such as when passing through a manhole cover or a groove cover that crosses the road during braking, or a calculation error in the amount of pressure increase / decrease. Becomes larger and the wheel speed Vw falls below the second pressure reduction threshold value λ2, the pressure reduction amount is increased.

However, in the prior art, since the gradient in the gradually increasing pressure after depressurization is constant, as shown by B in FIG. 6, it is large as in the case where it is below the second depressurization threshold value. When the decompression occurs, the amount of re-increase due to the subsequent gradual increase in pressure may be insufficient and the deceleration may decrease. As described above, in the conventional technique, although the number of pressure reductions can be reduced and efficient braking can be performed, when a large pressure reduction occurs such as a momentary road surface change, the amount of re-pressure increase is insufficient, There was a risk that deceleration would be insufficient.

In order to solve this, if the gradient at the time of slow pressure increase is set steeply, the insufficient amount of re-pressure increase at the time of large pressure reduction can be resolved as shown in the time chart of FIG. However, the frequency of wheel slip rate increases, the total number of times of pressure reduction increases, and efficient A
It becomes difficult to perform BS control.

Further, as a conventional technique, when the wheel speed Vw is reduced below the first pressure reduction threshold value to reduce the pressure again, the pressure is gradually increased, and below the second pressure reduction threshold value, a large pressure reduction is performed. There is also a technology to perform large pressure increase (rapid pressure increase) instead of slow pressure increase at the time of re-increase after performing, but in this case, it is difficult to control the rapid pressure increase amount accurately, resulting in overpressure increase. As a result, the wheels may slip again and control hunting may occur in which sudden pressure reduction and pressure increase are repeated, and even with this technique, it is difficult to perform efficient ABS control.

The present invention has been made in view of the above-mentioned problems of the prior art. When the slip ratio of the wheel becomes the second slip ratio which is larger than the first slip ratio, In a brake control device configured to perform a gradually increased pressure after performing a large pressure reduction, the number of pressure reductions is reduced to perform an efficient ABS control,
The purpose is to prevent the deceleration from becoming insufficient when the slip ratio becomes larger than the second slip ratio.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 is to provide a braking device for producing a braking force by a braking operation of a driver, and a generation state of the braking force in the braking device. And a braking control means for controlling the operation of the braking force adjustment means and for executing the ABS control for weakening the braking force generated at the time of braking and preventing the wheels from being locked. , The braking control means,
During the ABS control, the slip ratio of the wheel is compared with the reference slip ratio, and when the slip ratio is lower than the reference slip ratio, the braking force is reduced by a predetermined amount, and then the braking force is gradually increased, and the reference slip ratio is increased. The slip ratio has a first slip ratio and a second slip ratio that is larger than the first slip ratio, and when the wheel slip ratio exceeds the second slip ratio, the slip ratio exceeds the first slip ratio. In the brake control device in which the amount of decrease in the institutional force is relatively large compared to the above, the control means controls the gradient at the time of a gradual increase when the slip ratio of the wheel exceeds the second slip ratio during ABS control,
The method is characterized in that it is set to be steeper than the slope of the slow increase when the first slip ratio is exceeded.

According to a second aspect of the present invention, in the brake control device according to the first aspect, the braking device generates a braking pressure according to a braking operation of a driver, and a braking pressure generating means for generating the braking pressure. A wheel cylinder that operates by braking pressure to generate a braking force is provided, and as the braking force adjusting means, a pressure control valve that can increase / hold / decrease the braking pressure of the wheel cylinder is provided, and the braking control means is When the braking force is gradually increased, the gradual pressure increase control for increasing the pressure a plurality of times in a constant cycle is executed.

According to a third aspect of the present invention, in the brake control device according to the first or second aspect, the braking control means compares the slip ratio of the wheel with the first slip ratio and the second slip ratio. It is performed by comparing the wheel speed with a first threshold value and a second threshold value that are set based on the vehicle body speed, and the first threshold value is 95% of the vehicle body speed.
%, Or a value obtained by subtracting a predetermined value in the range of 3 to 4 km / h from the vehicle speed, and the second threshold value is 95% of the vehicle speed and a value in the range of 4 to 6 km / h. The value is set as a value.

[0011]

In the brake control device of the present invention, the ABS control is performed in the shallow slip state in which the slip ratio of the wheels exceeds the first slip ratio but does not exceed the second slip ratio. The amount by which the power is reduced (in the invention according to claim 2, the reduced pressure amount) is made relatively small. Further, the gradual increase of the braking force after the depressurization (the gradual increase in pressure in the invention described in claim 2) also relatively suppresses the gradient, that is, the rate of increase. As a result, the wheel speed is controlled so as not to decrease significantly, and the number of times the braking force is reduced (the number of times of pressure reduction in the invention according to claim 2) is suppressed, and the braking force can be efficiently obtained.

During ABS control, when a wheel passes through a place where the road surface μ is partially changed, such as a manhole or a lid of a groove, and the slip ratio of the wheel increases and exceeds the second slip ratio, Compared with the above, the amount of reduction of the braking force is made relatively large, and the wheel speed is quickly returned. Further, when the braking force is gradually increased thereafter (when the pressure is increased in the invention according to claim 2), the ascending slope (slow pressure increasing slope) is made relatively steeper than the above, and the braking force is insufficient. In addition, it prevents the occurrence of control hunting due to overshoot due to a rapid rise. As described above, according to the present invention, it is possible to reduce the number of times the braking force is reduced in the ABS control to perform efficient control and to prevent the deceleration from becoming insufficient due to an instantaneous change in the road surface μ. Can be achieved.

According to the third aspect of the invention, the ABS
At the time of control, the wheel speed can be kept at a value of about 95% of the vehicle body speed at which the friction coefficient between the tire and the road surface becomes large, and an efficient braking state can be maintained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A brake control device according to an embodiment of the present invention will be described below with reference to the drawings. First, the configuration will be described. FIG. 1 is an overall view showing a brake control device according to an embodiment of the present invention. The brake control device of this embodiment corresponds to the invention described in claims 1 to 3. In the figure, MC is a master cylinder as a braking pressure generating means, and when the brake pedal BP is depressed, a well-known tandem type which supplies brake fluid as fluid toward the wheel cylinder WC through the two brake circuits 1 and 2 belongs to. The master cylinder MC
Is provided with a reservoir RES that stores the brake fluid. These master cylinder MC, wheel cylinder W
A braking device is configured by C, the brake circuits 1 and 2.

The brake circuits 1 and 2 have a so-called X pipe connection structure. That is, the brake circuit 1 is branched at the branch point 1b, and the wheel cylinder WC (FL) of the left front wheel and the wheel cylinder WC of the right rear wheel are branched.
The brake circuit 2 is configured to branch at a branch point 2b to connect the wheel cylinder WC (FR) for the right front wheel and the wheel cylinder WC (RL) for the left rear wheel.

Branch point 1 in the brake circuits 1 and 2
A brake unit BU as a braking force adjusting means is provided in the downstream of b and 2b (on the wheel cylinder WC side). For this brake unit BU,
In the middle of the drain circuit 10 that connects the reservoir 7 and the inflow valves 5 and 5 that are provided in the middle of the brake circuits 1 and 2 and are solenoid-driven normally open ON / OFF valves. Is normally closed ON / OFF of solenoid drive
And an outflow valve 6 formed of a valve. These inflow valves 5
The outflow valve 6 and the outflow valve 6 correspond to the pressure control valve according to claim 2, and when the inflow valve 5 is opened and the outflow valve 6 is closed, the upstream and downstream of the brake circuits 1 and 2 are detected. When the pressure is increased to allow the flow to the downstream side and both valves 5 and 6 are closed, the wheel cylinder WC is held in a state where the brake hydraulic pressure is contained, and the inflow valve 5 is closed and the outflow valve 6 is opened. If the valve is opened, the brake pressure in the wheel cylinder WC is released to the reservoir 7 in a reduced pressure state. A bypass circuit 51 is provided in parallel with the inflow valve 5, and the bypass circuit 51 is provided with a one-way valve 52 that allows only the fluid to return from the wheel cylinder WC to the master cylinder MC.

Further, the brake unit BU is provided with a pump 4 connected to the brake circuits 1 and 2. The pump 4 sucks the brake fluid released to the reservoir 7 by the ABS control from the suction circuit 41 and returns the brake fluid to the brake circuits 1 and 2 via the discharge circuit 43. In the present embodiment, the motor 8 is used. It uses a driven plunger pump.

Therefore, in the present embodiment, when wheel locking is likely to occur during braking, the inflow valve 5 and the outflow valve 6 are actuated as necessary to increase and maintain the pressure of the wheel cylinder WC. It is possible to execute the ABS control in which the brake fluid pressure is optimally controlled by reducing the pressure and the brake fluid released to the reservoir 7 is returned to the brake circuits 1 and 2 at any time.

The motor 8 in such ABS control
The drive of the (pump 4) and the drive of each of the inflow valve 5 and the outflow valve 6 are controlled by the control unit CU.
The control unit CU has, as input means, a wheel speed sensor 21 that detects a wheel speed, which is a rotation speed of each wheel (not shown), and a brake switch 22 that is turned on in response to an operation of a driver depressing a brake pedal BP. Are connected.

Next, the basic control flow of the ABS control executed in the control unit CU will be described with reference to the flowchart of FIG. Step 201
Then, the signal is read from each wheel speed sensor 21, the wheel speed Vw of each wheel is calculated, and each wheel speed V is calculated.
The rate of change of w, that is, the wheel acceleration ΔVw is calculated. In step 202, the pseudo vehicle body speed Vi, which is the estimated vehicle body speed, is obtained based on the wheel speed Vw. The pseudo vehicle body speed Vi is formed based on the largest value among the wheel speeds Vw. In step 203, a process for obtaining the pressure reduction threshold value is performed. In the present embodiment, two thresholds, a first pressure reduction threshold λ1 and a second pressure reduction threshold λ2, are obtained as pressure reduction thresholds. The second decompression threshold value λ2
Can be obtained, for example, by the calculation of λ2 = Vi × 0.95-K. Note that K is a constant, and for example, a value of about 6 km / h is used for the high μ road, and a value of about 4 km / h is used for the low μ road. Further, the first pressure reduction threshold value λ1 is a value shallower than the second pressure reduction threshold value λ2 (the difference from the pseudo vehicle body speed Vi is small), and for example, λ1 =
The smaller value of the vehicle speed x 0.95 and the vehicle speed -Lkm / h is used. The L is a constant, for example 3 to 4
The value of degree is used. The slip rate is 95% of the vehicle speed.
The value of about% is a region in the vicinity indicated by SG in the tire μ characteristic diagram of FIG. 5, and is a region where the largest friction coefficient is obtained. Therefore, if the slip ratio of the wheels is kept near 95% of the vehicle body speed during braking, a large braking force can be obtained. The first pressure reduction threshold λ1 and the second pressure reduction threshold λ2 correspond to the first slip ratio and the second slip ratio in the claims.

At step 204, ABS control judgment is performed. In this ABS control judgment, the slip judgment of each wheel is made based on the wheel speed Vw of each wheel and both pressure reduction threshold values λ1 and λ2, and the ABS control judgment is made according to the judgment result. In the present embodiment, the ABS control is started when the wheel speed Vw becomes less than the first pressure reduction threshold value λ1. In step 205, the PI control target wheel speed is calculated for the ABS control target wheel. The PI control target wheel speed is a wheel speed at which a braking force can be efficiently obtained, and is calculated based on the pseudo vehicle body speed Vi and the like. In step 206, the pressure increase / decrease gain is calculated. The pressure increase / decrease gain is a gain used in ABS control, and can be determined by a road surface friction coefficient (deceleration during braking. If the deceleration is equal to or higher than a predetermined value, high μ and deceleration are It can be determined to be low μ if it is less than a predetermined value). Further, in the present embodiment, there are two values as the gradual pressure increase gain at the time of gradual pressure increase after depressurization, but the details will be described later. In step 207, the pressure increase / decrease pulse is calculated based on the PI control target wheel speed and the pressure increase / decrease gain. In step 208, the pressure increasing / decreasing pulse calculated in step 207 is output.

Next, the control flow for determining the pressure-increasing gain at the time of slow pressure increase, which is a characteristic control of the present embodiment, is shown in FIG.
The flowchart will be described. In addition, as the pressure increasing gain, an initial value is set to a preset normal gain. In step 301, it is determined whether the wheel speed Vw is less than the first pressure reduction threshold value λ1,
When Vw <λ1, the process proceeds to step 302 and Vw ≧ λ1
In the case of, the process proceeds to step 306. When the process proceeds to step 302, the pressure reduction FLAG0 is set to 1, and in the subsequent step 303, the wheel speed Vw is set to the second pressure reduction threshold value λ2.
If Vw>, then step 3
Go to 09. If the wheel speed Vw ≦ the second depressurization threshold value λ2 in step 303, step 30
4, the pressure reduction FLAG0 is reset to 0, and further, the pressure reduction FLAG1 is set to 1 in step 305, and then the process proceeds to step 309.

In step 301, the wheel speed Vw ≧
When the process proceeds to step 306 with λ1, in this step 306, it is determined whether the wheel acceleration ΔVw is 0 m / s2 or less, and if ΔVw ≦ 0 m / s2, step 30
In step 7, the pressure reduction FLAG0 is reset to 0, and in step 308, the pressure reduction FLAG1 is reset to 0, and then the process proceeds to step 309. If the wheel acceleration ΔVw is 0 m / s2 or more in step 306, NO
If it is determined to be, the process proceeds directly to step 309.

Next, in step 309, the reduced pressure FLAG is used.
It is determined whether or not 1 = 1, and if the pressure reduction FLAG ≠ 1, the process proceeds to step 310, and the pressure reduction gain adjustment FLAG is performed.
After setting = 0, the process proceeds to step 313. On the other hand, in step 309, when the pressure reduction FLAG = 1, the flow proceeds to step 311, and it is determined whether or not the previous value of the pressure reduction FLAG0 = 1 and the current value of the pressure reduction FLAG0 = 0, and the previous time of the pressure reduction FLAG0. Value = 1 and reduced pressure FLAG
0 If the current value = 0, the process proceeds to step 312, sets the pressure increase gain adjustment flag = 1, and then proceeds to step 313.
Proceed to. If NO is determined in step 311, the process directly proceeds to step 313.

In step 313, the pressure increase gain adjustment FL
It is determined whether or not AG = 1, and the pressure increase gain adjustment FLAG
When = 1, the routine proceeds to step 314, where the pressure increase gain is processed by the normal pressure increase gain × α to make the pressure increase gradient steeper than the normal gain. Incidentally, α is a numerical value larger than 1.

Next, an example of operation when the wheel speed Vw changes as shown in the time chart of FIG. 4 will be described. First, when the wheel speed Vw falls below the first pressure reduction threshold value λ1 (at time t1), the ABS control is started and pressure reduction is performed. At this time, in the control for determining the pressure increase gain in FIG. 3, steps 301 → 302 → 303 → 309 → 310
→ 313 → END, and the boosting gain is set to the normal gain. Therefore, in the slow pressure increase after the pressure reduction of t1, the pressure is normally increased by the gain. In addition,
The gradual pressure increase is a constant cycle in which a pressure increase state in which only the inflow valve 5 is opened and a hold state in which the inflow valve 5 and the outflow valve 6 are closed are repeated. Further, in the section described as the control cycle after t1 in the figure, the wheel speed Vw becomes equal to or higher than the first pressure reduction threshold value λ1 due to the pressure reduction, and when the vehicle body speed is restored, the flow of steps 301 → 306 → 307 → 308 follows. , Pressure reduction FLAG0 and pressure reduction FLAG1 are reset to 0, and further steps 309 → 310 → 313 → END
As a result, the pressure increase gain is kept set to the normal pressure increase gain, and the normal pressure increase gain is gradually increased during the control period. After that, at time t2, the wheel speed Vw again becomes less than the first pressure reduction threshold value λ1, so that the above-described pressure reduction and slow pressure increase are performed again.

Next, at time t3, the road surface μ is momentarily decreased due to riding on the manhole cover or the gutter cover, the slip ratio is rapidly increased, and the wheel speed Vw becomes the first pressure reduction threshold value. below λ1, and the second decompression threshold λ2
It shows the case where it is lower than. In this case, when the wheel speed Vw becomes lower than the second pressure reduction threshold value λ2, the pressure reduction FLAG0 is reset from 1 to 0 based on the processing of steps 301 → 302 → 303 → 304 → 305, while the pressure reduction FLAG1 is changed. = 1 is set. As a result, the flow of steps 309 → 311 → 312 becomes
Boosting gain adjustment FLAG = 1 is set, step 3
13 → 314, and the pressure increase gain is changed to a steeper slope than the normal gain. Therefore, as shown in the time chart of FIG. 4, at the time of t3, deep decompression is performed and the subsequent gentle pressure increase is performed with a steeper gradient than usual.

As described above, when the wheel speed Vw is momentarily deeply reduced (when the slip ratio is momentarily large), a large amount of pressure reduction is performed and the subsequent slow increase is performed. Since it is formed with a steep gradient, it is possible to obtain a large braking force as compared with the case of performing a normal slow pressure increase.

Further, if the pressure is rapidly increased after the large pressure reduction, there is a risk of overshooting and control hunting in which the large pressure reduction and the large pressure increase are repeated. By performing the above-described slow pressure increase, it is possible to prevent the control hunting due to the overshoot, to execute the efficient ABS control, and to be less susceptible to the influence of disturbance.

As described above, in this embodiment, the ABS
At the time of control, the wheel speed Vw is kept near the first decompression threshold value λ1, that is, near 95% of the pseudo vehicle body speed Vi at which a large braking force can be obtained, and the braking force is efficiently obtained. Further, when the slip ratio is deep due to the instantaneous change of the road surface μ, that is, the wheel speed Vw is deeply decreased, the wheel speed Vw is increased by increasing the pressure reduction amount and the subsequent gentle pressure increase gradient. Can be quickly restored, and insufficient braking force and control hunting can be prevented.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention. Even if it exists, it is included in the present invention. For example, in the embodiment, the wheel cylinder operated by the fluid pressure is shown as the braking device, but the invention is not limited to this, and a motor is used as the braking force adjusting means, and the rotor on the wheel side is driven by driving the motor. You may use the braking device of the structure which the pad by the side of a vehicle body contacts. Further, the first slip ratio and the second slip ratio (the first pressure reduction threshold value and the second pressure reduction threshold value) are based on the wheel speed at which the braking force is efficiently obtained, and are shown in the embodiment. The value is not limited. In the embodiment, the ABS unit B that performs only ABS control as the brake unit is used.
Although U is shown, the present invention is not limited to this, and a hydraulic pressure source is provided in addition to the master cylinder to automatically generate a braking force when necessary to control the vehicle speed, or to control the vehicle. It can also be applied to a brake unit configured to generate a braking force on a desired wheel in order to generate a yaw moment in a vehicle in a stabilizing direction. Further, as the pressure control valve, a valve composed of two sets of solenoid valves of the inflow valve 5 and the outflow valve 6 is shown, but one solenoid of 3 port type capable of forming a pressure increasing state, a pressure reducing state and a holding state. It can also consist of a valve.

[Brief description of drawings]

FIG. 1 is an overall view showing a brake control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a basic control flow in ABS control according to the embodiment.

FIG. 3 is a flowchart showing a flow of pressure increase gain control in the embodiment.

FIG. 4 is a time chart showing an operation example of the embodiment.

FIG. 5 is a tire μ characteristic diagram.

FIG. 6 is a time chart illustrating a conventional technique.

[Explanation of symbols]

BU brake unit (braking force adjustment means) CU control unit (braking control means) MC master cylinder (braking device) WC Wheel cylinder (braking device) 1 Brake circuit (braking device) 2 Brake circuit (braking device) 4 pumps 5 Inflow valve (pressure control valve) 6 Outflow valve (pressure control valve) 7 Reservoir 10 drain circuit 21 Wheel speed sensor 22 Brake sensor

Claims (3)

[Claims] 1. A braking device that generates a braking force by a driver's braking operation, a braking force adjusting means that can adjust the generation state of the braking force in the braking device, and an operation of the braking force adjusting means. And a braking control means for executing ABS control for weakening the braking force generated during braking to prevent wheel locking, wherein the braking control means compares the wheel slip ratio with a reference slip ratio during ABS control. Then, when the value falls below the reference slip rate, a predetermined amount of braking force is reduced, and then a slow increase is performed to gently increase the braking force, and the reference slip rate is the first slip rate and the first slip rate. The second slip rate is larger than the second rate, and the wheel slip rate is the second
When the slip ratio is exceeded, the brake control device is such that the amount of decrease in the institutional force is relatively large as compared with the case where the first slip ratio is exceeded, wherein the control means controls the slip ratio of the wheels during ABS control. The slope at the time of slow increase when the second slip ratio is exceeded,
The brake control device is characterized in that it is set to be steeper than the slope of slow increase when the slip ratio is exceeded. 2. The brake control device according to claim 1, wherein the braking device is a braking pressure generating unit that forms a braking pressure according to a braking operation of a driver, and a braking pressure that is generated by the braking pressure. A wheel cylinder for generating power, and a pressure control valve capable of increasing / holding / decreasing the braking pressure of the wheel cylinder as the braking force adjusting means, wherein the braking control means slowly increases the braking force. Sometimes
A brake control device, characterized in that a gradual pressure increase control for increasing the pressure a plurality of times in a fixed cycle is executed. 3. The brake control device according to claim 1, wherein the braking control means compares the wheel speed with the vehicle body speed when comparing the wheel slip ratio with the first slip ratio and the second slip ratio. First threshold value and second threshold value
The first threshold value is calculated by comparing with a threshold value.
95% of vehicle speed or 3 to 4 km from vehicle speed
/ H is a value obtained by subtracting a predetermined value in the range, and the second threshold is a value obtained by subtracting a value in the range of 4 to 6 km / h from 95% of the vehicle body speed. apparatus.