JPH04356261A - Method for judging coefficient of friction of road surface and method for controlling anti-skid brake using this judging method - Google Patents

Abstract

PURPOSE:To enable the mu of a road surface to be surely judged during anti-skid brake control and also to perform the anti-skid brake control more properly at a control pattern corresponding to the mu judged. CONSTITUTION:If the time for pressure reduction during anti-skid brake control is more than a first set value, mu is judged to be low; if the time for pressure reduction is not more than the first set value, duty control is performed and, if a state in which the time for pressure reduction during which duty ratio is 100% is more than a second set value is continued for a predetermined time, the mu is also judged to be low; if the time for pressure reduction during which the duty ratio is 100% is not more than the second set value, the mu is judged to be middle. When the time for pressure buildup is more than a third set value, the mu is judged to be high. When a road surface is judged to have low mu, a control value for low-mu roads is set for the anti-skid brake control, while when the road surface is judged to have high mu or middle mu, a control value for high-mu roads is set.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an anti-skid brake control method that determines the coefficient of friction (μ: hereinafter simply referred to as μ) of the road surface during braking and performs anti-skid brake control based on the determined μ of the road surface. Regarding this, we have developed a method for determining the coefficient of friction of the road surface, which determines the μ of the road surface based on the behavior of the decompression mode in anti-skid brake control, and a method to perform anti-skid brake control more appropriately based on μ determined by this determination method. The present invention relates to an anti-skid brake control method.

0002

[Prior art] Generally, anti-skid brake control is
When it is detected that a wheel is in a skid state during braking, the brake force on that wheel is weakened to eliminate the skid state, and then the brake force is increased again to stabilize vehicle handling and shorten the braking distance. Brake control is performed to make the length as short as possible.

[0003] In this anti-skid brake control, the brake fluid pressure control value differs depending on the μ of the road surface on which the vehicle is running, and the behavior of the wheel speed changes in response to changes in fluid pressure, so the μ of the road surface is taken into account. Anti-skid brake control is required.

[0004] Therefore, in the past, anti-skid brake control was performed depending on either a low μ road or a high μ road, or
Or, by performing a compromise anti-skid brake control for both low μ and high μ roads,
The anti-skid brake control is common to both.

[0005]

[Problem to be Solved by the Invention] However, in conventional anti-skid brake control, anti-skid is performed in common for low μ and high μ.
Anti-skid brake control is not always performed appropriately on both low μ and high μ roads.
The control had some incompatibility for low μ roads and high μ roads.

The present invention has been made in view of these problems, and its purpose is to provide a method for determining the coefficient of friction of a road surface that can reliably determine μ of the road surface during anti-skid brake control. It is to be. Another object of the present invention is to provide an anti-skid brake control method capable of performing anti-skid brake control with a control pattern corresponding to the determined μ when μ is determined by the above-described determination method. It is.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the invention of claim 1 provides a method for reducing pressure and short pressure increase when the pressure reduction time in the pressure reduction mode in anti-skid brake control is smaller than a first set value. The pressure reduction mode is set so that pressure reduction is performed by duty control, and the pressure reduction time when the duty ratio of the duty control is 100% is
The feature is that if the friction coefficient continues to be equal to or higher than a set value for a predetermined period of time, it is determined that the friction coefficient is low.

[0008] Furthermore, the invention according to claim 2 is provided when the pressure reduction time at a duty ratio of 100% of the duty control is smaller than a second set value, or when the pressure reduction time at a duty ratio of 100% of the duty control is equal to or greater than the second set value. It is characterized in that when a certain time does not continue for a predetermined period of time, it is determined that the road has a medium friction coefficient.

Furthermore, the invention according to claim 3 is characterized in that it is determined that the road surface has a low coefficient of friction when the pressure reduction time in the pressure reduction mode in the anti-skid brake control is equal to or greater than a first set value. Furthermore, the invention according to claim 4 is characterized in that it is determined that the road surface has a high coefficient of friction when the pressure increase time in the pressure increase mode in the anti-skid brake control is equal to or greater than a third set value.

[0010] Furthermore, the invention of claim 5 is based on claims 1 to 4.
When the friction coefficient of the road surface is determined to be a low friction coefficient by the method for determining the friction coefficient of the road surface described in any one of the above, the control value regarding the anti-skid brake control is set to a preset low friction coefficient control value. When the friction coefficient of the road surface is determined to be a high friction coefficient or a medium friction coefficient, the control value for anti-skid brake control is set to a preset high friction coefficient control value, and the control value is It features anti-skid brake control based on

[0011]

[Operation] In the method for determining the friction coefficient of a road surface according to the present invention configured as described above, when the pressure reduction time in the pressure reduction mode is smaller than the first set value, pressure reduction is performed by duty control using pressure reduction and short pressure increase. be exposed. Then, the pressure reduction time with a duty ratio of 100% in this duty control is
When the coefficient of friction of the road surface continues to be equal to or greater than the set value for a predetermined period of time, it is determined that the coefficient of friction of the road surface is low μ, such as μ on an icy road.

Further, in the invention of claim 2, when the pressure reduction time with a duty ratio of 100% in the duty control is smaller than the second set value, or when the pressure reduction time with a duty ratio of 100% in the duty control is greater than or equal to the second set value. When a certain moment does not continue for a predetermined period of time, it is determined that the friction coefficient of the road surface is larger than low μ, for example, medium μ, such as μ on a snowy road.

Furthermore, in the third aspect of the invention, when the pressure reduction time in the pressure reduction mode is equal to or greater than the first set value, it is determined that the coefficient of friction of the road surface is low μ. Furthermore, in the invention of claim 4, when the pressure increase time in the pressure increase mode is equal to or greater than the third set value, the friction coefficient of the road surface is higher than medium μ, for example, high μ such as μ on a normal road surface such as an asphalt road surface. It is determined that In this way, the μ of the road surface can be easily and reliably determined during anti-skid brake control.

Further, in the anti-skid brake control method according to the present invention, the μ of the road surface is determined during the anti-skid brake control, and the anti-skid brake control is performed based on the determined μ. Therefore, anti-skid brake control can be performed more appropriately in accordance with the μ of the road surface.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. 1 to 4 show the behavior of the brake fluid pressure increase/decrease mode used in the method of determining the coefficient of friction of a road surface according to the present invention, and FIG. 1 is a diagram illustrating brake fluid pressure control on a high μ road surface. Figure 2 is a diagram explaining brake fluid pressure control when the master cylinder pressure is high on a low μ road surface, Figure 3 is a diagram explaining brake fluid pressure control when the master cylinder pressure is low on a low μ road surface, and Figure 4 FIG. 2 is a diagram illustrating brake fluid pressure control on a medium-μ road surface. In this embodiment, the high μ road surface is assumed to be a normal road surface such as asphalt, the medium μ road surface is assumed to be a snowy road surface, and the low μ road surface is assumed to be an icy road surface.

Anti-skid brake control is performed when the wheels of a running vehicle tend to skid when the brakes are applied. In this case, if the vehicle is running on a high μ road as shown in FIG. The anti-skid brake control has a control pattern in which the pressure increase time in the pressure increase mode is relatively long and the pressure decrease time in the pressure decrease mode is short. In anti-skid brake control on this high μ road surface,
The control pattern is almost the same whether the master cylinder pressure is high or low.

Furthermore, as shown in FIG. 2, when the vehicle is traveling on a low μ road and the master cylinder pressure is high, the anti-skid brake control is effective as the pressure reduction time in the pressure reduction mode becomes longer and the pressure increase in the pressure increase mode increases. This is a control pattern that takes less time. In that case, in the pressure reduction mode, continuous pressure reduction without short pressure increases is performed.

Furthermore, as shown in FIG. 3, when the vehicle is traveling on a low μ road and the master cylinder pressure is low, such as when the driver lightly depresses the brake pedal, the anti-skid brake control will increase the pressure. The control pattern is such that the pressure increase time in the mode is slightly longer than the pressure reduction time in the pressure reduction mode. In this case, the pressure is reduced by duty control that includes a short pressure increase in the pressure reduction mode. Further, as is clear from FIG. 3, the pressure reduction time with a duty ratio of 100% is relatively long.

Furthermore, as shown in FIG. 4, when the vehicle is traveling on a medium μ road, the anti-skid brake control is performed at an approximately intermediate level where the pressure reduction time in the pressure reduction mode and the pressure increase time in the pressure increase mode are approximately equal. This is the control pattern. In this case, the pressure is reduced by duty control that includes a short pressure increase in the pressure reduction mode. Also, as is clear from Figure 4,
The depressurization time with a duty ratio of 100% is relatively short compared to that with a low μ. Anti-skid brake control on medium μ road surfaces uses almost the same control pattern whether the master cylinder pressure is high or low.

As described above, different phenomena appear in the control pattern of anti-skid brake control on high-μ roads, medium-μ roads, and low-μ roads, and the control pattern of anti-skid brake control also changes depending on the master cylinder pressure. Since different phenomena appear, by utilizing these phenomena, it becomes possible to determine whether the road surface on which the vehicle is traveling is a high μ road, a medium μ road, or a low μ road.

In this embodiment, this phenomenon is utilized to determine the μ of the road surface. That is, when the continuous pressure reduction time is equal to or greater than a preset first set value, it is determined that the road is low μ. When the pressure reduction time is smaller than the first set value, pressure reduction is performed by duty control, but this pressure reduction by duty control is either pressure reduction when the master cylinder pressure is low on a low μ road or pressure reduction on a medium μ road. Since μ of the road surface cannot be determined due to either of the above, the length of the decompression time with a duty ratio of 100% is determined.

[0022] When the pressure reduction time with a duty ratio of 100% is equal to or greater than a preset second set value for a predetermined period of time, it is determined that the road is low μ. Further, if the pressure reduction time with a duty ratio of 100% is smaller than the second set value, or if the pressure reduction time with a duty ratio of 100% does not continue for a predetermined time, it is determined that the road is a medium μ road.

On the other hand, if the pressure increase time is equal to or greater than a preset third set value, it is determined that the road is high μ. In this way, μ of the road surface can be easily determined.

In the anti-skid brake control method of this embodiment, control values related to anti-skid brake control are set to a high μ control value and a low μ control value, and the high μ control value is set to a high μ control value and a low μ control value.
When it is determined that the road is a road or a medium μ road, a high μ control value is set, and when it is determined that the road is a low μ road, a low μ control value is set.

FIG. 5 shows how μ is determined by utilizing the different phenomena of control patterns that appear on high μ roads, medium μ roads, and low μ roads, and the control value related to anti-skid brake control is increased based on the determined μ. FIG. 7 is a diagram illustrating a flow for switching and setting the μ road control value or the low μ road control value.

As shown in FIG. 5, in step 1, it is first determined whether anti-skid brake control is currently being performed. When it is determined that anti-skid brake control is being performed, it is determined in step 2 whether or not pressure is currently being reduced. If it is determined that the pressure is being reduced, it is determined in step 3 whether the pressure reduction time is longer than the first set value. If it is determined that the decompression time is equal to or greater than the first set value, the high μ flag is cleared and the low μ flag is set in step 4, and then the road surface μ determination process is completed.

If it is determined in step 3 that the decompression time is not equal to or greater than the first set value, then in step 5 the duty ratio is set to 1.
It is determined whether the 00% depressurization time is equal to or greater than a second set value. When it is determined that the decompression time with a duty ratio of 100% is equal to or greater than the second set value, the counter value whose initial value is set in advance is incremented by a predetermined value in step 6.

Next, in step 7, it is determined whether this counter value is greater than or equal to a fourth preset value. When it is determined that the counter value is equal to or higher than the fourth set value,
The process moves to step 4, where the high μ flag is cleared and the low μ flag is set in the same manner as described above, and then the road surface μ determination process is completed. When it is determined in step 5 that the decompression time with a duty ratio of 100% is not equal to or greater than the second set value, and when it is determined in step 7 that the counter value is not equal to or greater than the fourth set value, the road surface μ is determined. is terminated.

If it is determined in step 2 that the pressure is not being reduced, then in step 8 it is determined whether the pressure increase time is equal to or greater than a third set value. When it is determined that the pressure increase time is equal to or greater than the third set value, the counter value is cleared in step 9, and then the low μ flag is cleared in step 10 to indicate a high μ
The flag is set, and then the road surface μ determination process is completed. If it is determined in step 8 that the pressure increase time is not equal to or greater than the third set value, the road surface μ determination process is terminated. When it is determined in step 1 that anti-skid brake control is not being performed, the process moves to step 9, and after the processes of step 9 and step 10 are performed in the same manner as described above,
The road surface μ determination process is completed.

In this way, when the road surface is determined to be low μ and the low μ flag is set, or when the road surface is determined to be a high μ or medium μ road and the high μ flag is set, the anti-skid brake control control is performed. The values are set to preset low μ road control values or high μ road control values, respectively.

[0031] The control value related to anti-skid brake control is set in accordance with low μ or high μ.
Filter value for determining upper and lower limit values when calculating estimated vehicle speed, adjustment of duty ratio of pressure increase/decrease according to μ, μ
There are settings for the duty ratio of pressure increase/decrease to match the pressure increase/decrease, the slope of pressure increase/decrease of the wheel cylinder, the threshold value for starting pressure increase/decrease, the threshold value for starting pressure increase/decrease, etc.

In this way, the anti-skid brake control is set to a control pattern corresponding to μ determined during this control. As a result, when the wheels are locked and anti-skid brake control is performed, anti-skid brake control can be performed more appropriately using a control pattern that corresponds to the μ of the road surface determined during the control. For example, on low-μ roads, low-μ anti-skid brake control is performed, but in this case it is possible to create a more appropriate estimated vehicle speed, prevent the vehicle from spinning, and reduce the amount of brake pedal travel. becomes smaller. In addition, the threshold for starting the pressure increase/depressurization mode can be quickly switched between the threshold for high μ roads and the threshold for low μ roads, so the pressure increase time can be compared on high μ roads. The pressure reduction time is set relatively long to improve the braking force, and on low μ roads, the pressure reduction time is set relatively long to further suppress wheel locking.

In the above-mentioned embodiment, the medium-μ road is controlled by high-μ control, but the medium-μ road may be controlled by low-μ control, or the control related to anti-skid brake control may be performed. Values are set in advance to three control values for high μ roads, medium μ roads, and low μ roads, and high μ control, medium μ control, and low μ control are performed based on these control values. You can also do it.

[0034]

As is clear from the above description, according to the method for determining the coefficient of friction of a road surface according to the present invention, μ of the road surface can be reliably and easily determined during anti-skid brake control. Further, since there is no need to provide a device such as a G sensor for determining μ, the number of parts can be reduced and costs can be reduced.

Further, according to the anti-skid brake control method according to the present invention, since the control is performed based on the friction coefficient of the road surface determined during the anti-skid brake control, the anti-skid brake control is performed based on the friction coefficient of the road surface. You will be able to respond and do better.

For example, on a low μ road, the estimated vehicle speed can be created more appropriately, so that spin of the vehicle body can be prevented and the amount of movement of the brake pedal can be reduced. In addition, the threshold for starting the pressure increase/depressurization mode can be quickly switched between the threshold for high μ roads and the threshold for low μ roads, so the braking force can be reduced on high μ roads. In addition to this, it also makes it possible to further suppress wheel locking on low μ roads.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating brake fluid pressure control on a high-μ road surface in a brake fluid pressure increase/decrease mode used in the method for determining the coefficient of friction of a road surface according to the present invention.

FIG. 2 is a diagram illustrating brake fluid pressure control when the master cylinder pressure is high on a low μ road surface.

FIG. 3 is a diagram illustrating brake fluid pressure control when the master cylinder pressure is low on a low μ road surface.

FIG. 4 is a diagram illustrating brake fluid pressure control on a medium-μ road surface.

FIG. 5 is a diagram illustrating an embodiment of the present invention and a flowchart of a process for determining μ.

Claims (5)

[Claims] 1. The pressure reduction mode is set so that when the pressure reduction time in the pressure reduction mode in anti-skid brake control is smaller than a first set value, the pressure reduction is performed by duty control using pressure reduction and short pressure increase, and the duty A method for determining a coefficient of friction of a road surface, characterized in that the coefficient of friction of a road surface is determined to be low when the depressurization time with a control duty ratio of 100% is equal to or greater than a second set value for a predetermined period of time. [Claim 2] The duty ratio of the duty control is 1.
When the pressure reduction time of 00% is smaller than the second set value, or when the pressure reduction time of 100% duty ratio of the duty control does not continue for a predetermined time, it is determined that the road is a medium friction coefficient road. Claim 1 characterized in that
How to judge the coefficient of friction of the road surface described. 3. The friction of the road surface according to claim 1 or 2, wherein the road surface is determined to have a low friction coefficient when the pressure reduction time in the pressure reduction mode in the anti-skid brake control is equal to or greater than a first set value. How to determine the coefficient. 4. A method for determining the coefficient of friction of a road surface, comprising determining that the road surface has a high coefficient of friction when the pressure increase time in the pressure increase mode in anti-skid brake control is equal to or greater than a third set value. 5. When the friction coefficient of the road surface is determined to be a low friction coefficient by the method for determining the friction coefficient of the road surface according to any one of claims 1 to 4, the control value regarding the anti-skid brake control is determined in advance. When the friction coefficient of the road surface is determined to be a high friction coefficient or a medium friction coefficient, the control value for anti-skid brake control is set to the preset high friction coefficient. An anti-skid brake control method characterized in that the anti-skid brake control method is characterized in that the anti-skid brake control is performed based on the control value.