TWI718672B - Brake control method based on the friction characteristics of the road - Google Patents

Abstract

A braking control method based on the friction characteristics of the road surface is implemented in the anti-lock braking system module. The control method is applied to the staged pressure increase period and staged pressure release period of the intermittent braking mode, and includes: according to wheel speed signal Calculate the real-time wheel speed value; store the real-time wheel speed value obtained at the moment of braking as an initial wheel speed value; determine the relative peak wheel speed according to the real-time wheel speed value; calculate the vehicle estimate based on the relative peak wheel speed and the initial wheel speed value Deceleration value; generate an adjustment parameter based on the estimated deceleration value of the vehicle and the slip threshold value, and the adjustment parameter reflects the friction coefficient of the road surface; and adjust the boost time of the staged boost period according to the adjustment parameter, or adjust according to the adjustment parameter The pressure relief time of the staged pressure relief period.

Description

Braking control method based on the friction characteristics of the road

The present invention relates to a braking control method, in particular to a braking control method based on the friction characteristics of the road surface.

Equipping the vehicle with Advanced Driver Assistance System (ADAS) is the focus of the active development of various car manufacturers. Its main purpose is to help the driver to drive the vehicle. It can actively intervene in the control of the vehicle before the accident, so as to protect the driver and The safety of passengers, in turn, takes into account the personal safety of passersby outside the vehicle and reduces the hazards of road facilities.

For example, please refer to FIG. 8. The Electronic Stability Control (ESC) system includes a control module 30 and a plurality of detectors electrically connected to the control module 30. The detectors may include wheel speeds. A meter 31, an accelerometer 32, a steering angle detector 33, and a yaw rate detector 34. The control module 30 is connected to the vehicle's power system 40, steering system 41, brake system 42 and other control system signals. The control module 30 uses the values obtained from the detectors to determine whether the vehicle dynamics has entered an unstable state; if so, the control module 30 actively intervenes in the control of the vehicle, such as correcting tire steering, limiting power output, and adjusting the brake The brake pressure of the hydraulic device of the system 42... etc., so as to try to stabilize the vehicle to avoid loss of control of the vehicle.

For another example, please refer to FIG. 9. The conventional Anti-lock Braking System (ABS) includes a control module 50 and a tachometer 51 electrically connected to the control module 50. The control The module 50 is signal-connected with the braking system 60 of the vehicle to adjust the braking state of the hydraulic device of the braking system 60. The anti-lock braking system (ABS) control module 50 uses the real-time wheel speed value obtained from the wheel tachometer 51 and determines whether to actively intervene in the operation of the brake system 60 according to the slip differential between the vehicle speed and the wheel speed. The slip state refers to the speed difference between vehicle speed and wheel speed, expressed as follows:

In terms of the number of detectors, compared with the electronic body stabilization system (ESC), because the anti-lock braking system (ABS) only uses the wheel tachometer 51, the hardware cost of the anti-lock braking system (ABS) It is lower than the electronic body stability system (ESC).

The following briefly describes the conventional control flow of the anti-lock braking system (ABS). The control module 50 first determines whether there is a braking event, that is, whether the brake pedal is depressed; if it is determined that there is a braking event, the wheel speed is reduced at this time Slow, the control module 50 judges whether the vehicle dynamics reaches the early warning threshold according to the real-time wheel speed value and the slip state, for example, whether the wheel acceleration drops to a lower threshold, or whether the slip state reaches an upper slip limit; If the warning threshold is reached, it means that the wheel speed has slowed down rapidly but the vehicle speed has not slowed down as expected, which may cause the wheels to be locked and the vehicle will slip on the road. Therefore, the control module 50 actively intervenes in the braking system 60 to adjust the wheel reduction Slow speed and reduce slip state. Conversely, when the control module 50 determines that the vehicle dynamics has not reached the early warning threshold, it means that the vehicle is still in a controllable state, so the control module 50 does not intervene in the control of the brake system 60.

The following examples illustrate the conventional control flow of the anti-lock braking system (ABS). Please refer to FIGS. 10A to 10C, which are graphs including vehicle speed and wheel speed, wheel acceleration graph, and braking pressure graph, respectively. As shown in Figure 10C, when the brake pedal _{is depressed at t 0} , the control module 50 determines that there is a braking event. At this time, the braking pressure gradually increases with time, so the vehicle speed and wheel speed shown in Figure 10A decrease with time. Slow, the slip state is an increasing trend, and the wheel acceleration shown in FIG. 10B is also a decreasing trend. At the same time, the control module 50 determines whether the vehicle dynamics reaches the early warning threshold.

When the wheel acceleration drops to the lower threshold (-a _th ) or the slip state reaches the upper limit of slip, that is, at t ₁ , the control module 50 determines that the vehicle dynamics has reached the threshold for early warning, which means that the wheels decelerate too fast and slip If it is too large, it may cause the wheels to be locked up, so it intervenes to control the operation of the brake system 60. The control module 50 _{detects that the wheel acceleration is too low at t 1} and is lower than the lower threshold (-a _th ), Enter the state of holding pressure. Excessive slip is detected at t _{2 and the pressure is released.} To t ₃ because the wheel acceleration detected state back up to the pressure release threshold (-a _th), the state enters the holding pressure. Therefore, after entering the holding pressure state under a lower braking pressure, the wheels will slowly resume rotation, so the wheel acceleration gradually rises until t ₄ , which exceeds the wheel acceleration threshold a _limit and enters the supercharged state. The pressurization state causes the braking pressure to continue to rise, so the wheel acceleration gradually decreases. After the wheel acceleration is below the wheel acceleration threshold a _limit , it _{enters the holding pressure state at t 5} , and the wheel acceleration continues to decrease under the holding pressure state until t _{6 is} lower than the upper limit. After the threshold (+a _th ), it enters the phase boost mode. The process of pressurization and depressurization is continuously executed by analogy. The stage boost mode makes the brake pressure rise in stages until the _{acceleration of wheel t 7} is lower than the lower threshold value (-a _th ) and enters the pressure relief state. As shown in Fig. 10C, the stage boost mode is composed of boost and pressure holding states. Each boost plus the pressure holding state forms a boost control cycle, and the total cycle length is T _increase .

In summary, the brake pressure change of the intermittent braking mode generally includes the pressure relief period _{from t 2} to t _{3 , the pressure holding period from t 3} to t ₄ , and the stepwise boost period from t _{6 to t 7 in sequence.} , Where the staged boosting period includes one or a plurality of continuous boosting control periods T _increase . Figure 10C takes the plural boosting control period T _increase as an example. Each boosting control period T _increase includes boosting and continuing in The holding pressure after pressurization, where the speed of pressurization (pressure increase in unit time) can be a preset control parameter, as shown in Figure 10B, during the staged pressurization period, the wheel acceleration decreases with time, allowing the brakes The wheels in the middle still keep a certain degree of rotation to maintain friction with the road surface, so the increase in the slip state can be suppressed. When the control module 50 determines that the vehicle dynamics t ₇ reaches the warning threshold, this represents the brake pressure in the wheel deceleration and the slip too large, the process proceeds to the next relief of, or re-enter the subsequent pressure holding period and The staged supercharging period... etc., and so on, until the control module 50 determines that there is no braking behavior or other suspension conditions are met.

The foregoing example mainly illustrates that the conventional intermittent braking mode can include a staged pressure increase period. On the other hand, the intermittent braking mode can also include a staged pressure relief period. Another example is shown in FIGS. 11A and 11B. When the module 50 _{intervenes to control the control of the braking system 60 and executes the intermittent braking mode at t 1} , the pressure relief period entered may be a staged pressure relief period, which includes one or more continuous pressure relief control periods T _decrease , Figure 11B shows a pressure relief control cycle T _{decrease from t 1} to t _2. Each pressure relief control cycle T _decrease includes pressure relief and the holding pressure following the pressure relief. The pressure relief speed (pressure per unit time) The reduction range) can be a preset control parameter to perform stepwise pressure relief instead of continuous pressure relief as in the previous example. As shown in FIG. 11B, after the staged pressure relief period, there are successively a pressure holding period from t3 to t4 and a staged pressure increase period from t4 to t5.

Although the conventional anti-lock braking system (ABS) implements the intermittent braking mode to help stabilize the vehicle in sudden braking, its boost control cycle T _increase in the staged boost period and pressure relief control in the staged pressure relief period The period T _decrease is a control parameter preset in the control module 50, that is, the pressure _increase time of each pressure increase control period T increase in the stage pressure increase period is a fixed value, and each pressure relief control period T during the stage pressure relief period T increase _{The decompression} time of decrease is also a fixed value, and these fixed values may not be able to cope with different road conditions.

For example, the road environment for vehicles often changes with climate or human factors. For example, sunny weather can lead to dry roads, rainy days can lead to wet roads, and the construction environment can lead to muddy roads. If the boost control cycle T _increase and the pressure relief control cycle T _decrease are set based on the friction characteristics of dry roads, the braking stability on wet roads will be poor; on the contrary, the boost control cycle T _increase and the pressure relief control cycle If T _decrease is set based on the friction characteristics of wet roads, the distance from braking to stopping on dry roads is longer. Therefore, the conventional anti-lock braking system (ABS) brake control method still has room for improvement and improvement.

The main purpose of the present invention is to provide a braking control method based on the friction characteristics of the road surface, which can adapt the braking means according to the friction characteristics of different road surfaces, in order to overcome the inability of the fixed stage boosting period or staged pressure relief period described in the prior art. Cope with the shortcomings of different road friction characteristics.

The braking control method according to the friction characteristic of the road surface of the present invention is implemented by an anti-lock braking system module electrically connected to a wheel tachometer, and the anti-lock braking system module activates an intermittent brake Mode and receive a round speed signal from the wheel tachometer, wherein the intermittent braking mode includes a one-stage boosting period or a one-stage pressure relief period, and the control method is applied to the staged boosting period and the staged pressure relief period And includes: calculating the real-time wheel speed value according to the wheel speed signal; storing the real-time wheel speed value obtained at the moment of braking as an initial wheel speed value; judging a wheel speed relative peak value according to the real-time wheel speed value; Calculate an estimated vehicle deceleration value based on the relative peak wheel speed and the initial value of the wheel speed; generate an adjustment parameter based on the estimated vehicle deceleration value and a slip threshold value, and the adjustment parameter reflects the road friction coefficient; and adjust according to the adjustment parameter The time length of the pressurization time of the staged pressurization period, or the time length of the pressure release time of the staged pressurization period is adjusted according to the adjustment parameter.

The present invention utilizes the characteristics of the correlation between the deceleration value of the vehicle and the friction characteristics of the road surface. For example, comparing the friction coefficient of the road surface with different heights, when the vehicle is driving on a road with a higher friction coefficient, the wheels will be more severely braked. It is not easy to be locked, the braking effect is better, and the vehicle speed drops faster, so the estimated deceleration value of the vehicle is higher; relatively, when the vehicle is driving on a road with a lower friction coefficient and a higher friction coefficient, the wheels are more likely to be locked While skidding, the braking effect is poor, and the vehicle speed drops slowly, so the estimated deceleration value of the vehicle is low.

It can be seen that the estimated deceleration value of the vehicle is related to the friction characteristics of the road surface. With the braking control method according to the road friction characteristics of the present invention, the adjustment parameter is used to adjust the staged pressure increase period and the staged pressure release period, wherein the adjustment parameter is a value calculated based on the estimated deceleration value of the vehicle In addition, the estimated deceleration value of the vehicle is related to the friction coefficient of the road surface. Therefore, the present invention performs braking control according to the friction characteristics of the road surface, and can adapt the braking means according to the friction characteristics of the road surface to overcome the problems described in the prior art.

10: Control module

11: Wheel tachometer

20: Brake system

30: control module

31: Wheel tachometer

32: accelerometer

33: steering angle detector

34: Yaw rate detector

40: Power System

41: Steering system

42: Brake system

50: control module

51: Wheel tachometer

60: Brake system

v _rpm : wheel speed signal

P _increase : staged boost period

T _increase : boost control cycle

P _decrease : staged pressure relief period

T _decrease : pressure relief control cycle

Figure 1: The circuit block diagram of the anti-lock braking system (ABS).

Fig. 2: A schematic flowchart of an embodiment of the braking control method according to the road friction characteristic of the present invention.

Figure 3A: Schematic diagram of the real-time wheel speed curve.

Fig. 3B: A schematic diagram of the adjustment parameters obtained by the present invention at different time points.

Figure 4A: A schematic diagram of the waveform of the braking pressure during the staged supercharging period.

Figure 4B: The timing diagram of the boost control cycle.

Figure 5A: The timing diagram of the boost control cycle.

Figure 5B: The timing diagram of the boost control cycle.

Figure 6A: A schematic diagram of the waveform of the braking pressure during the staged pressure relief period.

Figure 6B: The timing diagram of the pressure relief control cycle.

Figure 7A: The timing diagram of the pressure relief control cycle.

Figure 7B: The timing diagram of the pressure relief control cycle.

Figure 8: The circuit block diagram of the conventional electronic body stabilization system (ESC).

Figure 9: The circuit block diagram of the conventional anti-lock braking system (ABS).

Figure 10A: Waveform diagram of vehicle speed and wheel speed after braking.

Figure 10B: Waveform diagram of wheel acceleration after braking.

Figure 10C: Waveform diagram of braking pressure after braking.

Figure 11A: Waveform diagram of vehicle speed after braking.

Figure 11B: Waveform diagram of braking pressure after braking.

Please refer to Figure 1, the anti-lock braking system (Anti-lock Braking System, ABS) mainly includes a control module 10 and a tachometer 11 electrically connected to the control module 10, the control module 10 and the braking system of the vehicle 20 signal connection, the control module 10 receives a wheel speed signal v _rpm from the wheel tachometer 11, and the wheel speed signal v _rpm reflects the number of rotations of the wheel in a unit time (per minute). The control module 10 can convert the wheel speed signal v _rpm into a real-time wheel speed value v _wheel , which can be expressed as follows:

In the above formula, r is the radius of the wheel (unit: meters).

Generally speaking, after the vehicle is started, the control module 10 can record the real-time wheel speed value v _wheel . Please refer to Figure 2. The control module 10 of the Anti-lock Braking System (ABS) first determines whether there is Braking event (step S01); if yes, the control module 10 further determines whether the vehicle dynamics reaches the threshold (step S02). When the vehicle dynamics reaches the threshold, the control module 10 actively intervenes in the operation of the braking system 20 (step S03). Wherein, for example, the vehicle dynamics may refer to the real-time wheel speed value v _wheel . When the decrease in the real-time wheel speed value v _wheel per unit time reaches a threshold value, it means that the wheel speed is drastically slowed down, which may cause the wheel to be damaged. Locked up. On the contrary, in step S02, when the control module 10 determines that the vehicle dynamics has not reached the threshold, it means that the speed of the wheels slowing down is within the allowable range and the vehicle is still in a controllable state, so the control module 10 does not intervene in the braking system 20 control, the vehicle brakes normally. Wherein, when the control module 10 judges no in step S02, it can generate an estimated vehicle speed (step S04), use the real-time wheel speed value v _wheel as the estimated vehicle speed, and then return to step S01.

After the control module 10 actively intervenes in the operation of the braking system 20 (step S03), an intermittent braking mode can be performed. The braking pressure change mode of the intermittent braking mode generally includes a pressure relief period and a holding period in sequence. Pressure period and a pressure increase period, where the pressure relief period can be a step pressure relief period, and the pressure pressure period can be a step pressure pressure period. Therefore, the intermittent braking mode can include the step pressure pressure period, the The staged pressure relief period may include both a staged pressurization period and the staged pressure relief period. It should be noted that the intermittent braking mode implemented by the anti-lock braking system (ABS), the conditions for entering the staged boosting period and the staged pressure relief period, the boosting speed and the staged boosting period The pressure relief rate during the staged pressure relief period... etc., The technical field of the present invention is well known to those with ordinary knowledge, and it has been described in the prior art, and will not be detailed here.

When the control module 10 intervenes in the operation of the braking system 20, in the embodiment of the present invention, the boosting time of the staged boosting period can be adaptively adjusted according to the road friction characteristics, and the stage can be adaptively adjusted according to the road friction characteristics The pressure relief time of the type pressure relief period is explained as follows.

1. Initial value of wheel speed

As mentioned above, when the vehicle is started, the control module 10 can record the real-time wheel speed value v _wheel . In the embodiment of the present invention, the control module 10 will cause the braking event to occur at the moment (for example, the moment when the brake pedal is taken). The obtained real-time wheel speed value v _{wheel is} stored as an initial _{wheel speed value v 0} . As shown in FIG. 3A, the control module 10 _{has a braking event at t 0 and} stores the current real-time wheel speed value v _wheel as the initial wheel speed value v ₀ , that is, t ₀ is the occurrence time of the initial wheel speed value v ₀ point.

2. The relative peak value of the real-time wheel speed value

In the intermittent braking mode, the real-time wheel speed value v _wheel fluctuates accordingly. The control module 10 can determine a relative peak value of the wheel speed according to the real-time wheel speed value v _wheel . For example, please refer to Figure 3A. When the slope of the curve of the wheel speed value changes _{from positive to negative at t 1} , the control module 10 judges the real-time wheel speed value v _{wheel of t 1} as the first wheel speed relative peak value v ₁ . By analogy, as time progresses, several relative peak values of wheel speed v ₂ , v ₃ ... etc. can be judged.

3. Estimated vehicle deceleration value

The present invention calculates an estimated vehicle deceleration value based on the relative peak value of the wheel speed and the initial value of the wheel speed. The estimated vehicle deceleration value can be expressed as follows:

In the above formula, x represents the number of times, a _x is the estimated deceleration value of the x-th vehicle, v _x is the relative peak value of the x-th wheel speed, t _x is the occurrence time of the x-th wheel speed relative peak v _{x , v 0} Is the initial value of wheel speed, t ₀ is the time point when the initial value of wheel speed v _{0 occurs.} Therefore, in the embodiment of the present invention, as shown in FIG. 3A, when the control module 10 obtains the first wheel speed relative peak value v _{1 at t 1} , it can be based on the first wheel speed relative peak value v ₁ and the initial wheel speed The value v ₀ calculates a first vehicle estimated deceleration value a ₁ as follows:

Furthermore, according to the first vehicle estimated deceleration value a _1, a first vehicle speed estimated value v _vehicle,1 can be calculated, which is expressed as follows: v _vehicle,1 =v ₀ -a ₁ ×t

In the above formula, t is the elapsed time after the occurrence of the braking event.

As time progresses, when the control module 10 obtains the second wheel speed relative peak value v _{2 at t 2} , the control module 10 can calculate according to the second wheel speed relative peak value v ₂ and the initial wheel speed value v ₀ A second vehicle estimated deceleration value a ₂ , which is expressed as follows:

Similarly, according to the second vehicle estimated deceleration value a _2, a second vehicle speed estimated value v _vehicle,2 can be calculated, which is expressed as follows: v _vehicle,2 =v ₀ -a ₂ ×t

In the above formula, t is the elapsed time after the occurrence of the braking event.

It can be deduced by analogy. Therefore, after a braking event occurs, as time progresses, the control module 10 can sequentially obtain a plurality of vehicle estimated deceleration values according to the relative peak value of the wheel speed and the initial value of the wheel speed (step S05). Furthermore, as mentioned above, the estimated deceleration value a of these vehicles can be _{calculated with the initial wheel speed v 0 to} calculate the estimated vehicle speed v _vehicle , which is expressed as follows: v _vehicle = v ₀ -a×t

In the above formula, t is the elapsed time after the occurrence of the braking event.

In other words, the estimated vehicle deceleration value a and the estimated vehicle speed value v _vehicle calculated by the embodiment of the present invention are continuously updated as the instantaneous wheel speed value v _{wheel changes.}

On the other hand, in order to estimate the vehicle speed from the occurrence of the braking event to the occurrence of the first wheel speed relative peak v ₁ (that is, the period from t _{0 to t 1} ), as shown in FIG. 3A, the embodiment of the present invention is based on a preset deceleration The value a _preset calculates a vehicle speed reference value v _ref (step S03A), which is expressed as follows: v _ref = v ₀ -a _preset ×t

In the above formula, t is the elapsed time event brake and before t _1. Then the control module 10 compares the vehicle speed reference value v _ref with the real-time wheel speed value v _vehicle . When the vehicle speed reference value v _{ref is} greater than the real wheel speed value v _vehicle , the vehicle speed reference value v _{ref is} used as the vehicle speed estimate Measured value; relatively, when the vehicle speed reference value v _{ref is} lower than the instant wheel speed value v _vehicle , the instant wheel speed value v _{vehicle is} used as the vehicle speed estimation value (step S03B). The value of the preset deceleration a _preset is greater than zero and less than 1 g, where g=9.8 ( meters/second ² ).

4. Reflect the adjustment parameters of the road friction coefficient

In the embodiment of the present invention, after the control module 10 intervenes in the operation of the braking system 20, it generates an adjustment parameter based on the estimated deceleration value of each vehicle obtained in step S05 and a slip threshold value (step S06), which is expressed as follows:

In the above formula, u is the adjustment parameter, which can reflect the friction coefficient of the road surface; a is the estimated deceleration value of the vehicle; ABSout is the slip threshold value. It should be noted that the slip threshold value ABSout is a preset constant, and its value is greater than zero and less than 1, that is, 0<ABSout<1, as long as the anti-lock braking system (ABS) determines the slip value of the vehicle When the slip threshold value ABSout is reached, the anti-lock braking system (ABS) will control the brake system 20 to stop the pressure relief state and switch to a pressurized state, which is an existing function of the anti-lock braking system (ABS). I will not go into details here, but this function will affect the performance of wheel deceleration, resulting in the calculated vehicle deceleration value a being slightly lower than the actual vehicle deceleration, so (1-ABSout) is used as the constant for correction. The adjustment parameter u obtained by the present invention can be more in line with actual conditions. In the field of vehicle technology, the slip formula can generally be expressed as follows:

On the other hand, comparing dry roads with wet roads, the friction performance of wheels on dry roads is better than that of wheels on wet roads. Therefore, when braking, the deceleration of wheels on dry roads is slower than that of wheels on wet roads. The deceleration of, and the adjustment parameter u is calculated based on the estimated deceleration value of the vehicle, so the adjustment parameter u can be used to reflect the friction coefficient of the road surface; in other words, when the adjustment parameter u is smaller, the estimated deceleration value of the vehicle is smaller. It can reflect a road with a lower friction coefficient; on the contrary, when the adjustment parameter u is higher, it means that the estimated deceleration value of the vehicle is larger, which can reflect a road with a higher friction coefficient.

It can be seen that, referring to Figure 3B, as time progresses, different vehicle estimated deceleration values a can be calculated to obtain different adjustment parameters u. For example, the first vehicle estimated deceleration value a ₁ corresponds to a first The adjustment parameter u _{1 is} expressed as follows:

The estimated deceleration value a _{2 of the} second vehicle corresponds to a second adjustment parameter u ₂ , which is expressed as follows:

The following adjustment parameters can be deduced by analogy.

5. Control and adjust the brakes according to the adjustment parameters

Please refer to FIGS. 4A and 4B. When the control module 10 enters any staged boosting period P _increase , there is a corresponding adjustment parameter u at that time, where the staged boosting period P _increase includes one or more _{Continuous boost control periods T increase} with the same length of time each other, each boost control period T _increase includes a boost time T ₁ and a pressure holding time T _{2 following the boost time T 1} , the control module 10 is based on The current adjustment parameter u of each boost control period T _{increase adjusts the time length of the boost time T 1} and the holding time T ₂ , so the control module 10 adjusts the boost control according to the adjustment parameter (step S07 ), wherein, the higher the road surface friction coefficient u reflect the adjustment parameter, the supercharger boost control period _T increase the longer the time T _1; the lower the road surface friction coefficient when the adjustment parameter u reflected, the pressure increase control The boosting time T _{1 of} the period T _increase is shorter.

For example, please compare FIG. 5A with FIG. 5B. As shown in FIG. 5A, when the adjustment parameter u reflects a higher road friction coefficient, the boosting time T ₁ can be extended because the time of the boosting control period T _increase The length is fixed, so the holding time T ₂ is relatively reduced; relatively, as shown in Fig. 5B, when the adjustment parameter u reflects a lower road friction coefficient, the pressurizing time T ₁ can be shortened, and the holding pressure can be relatively extended Time T ₂ . Wherein, the time length of the boost control period T _increase may be, for example, 20 milliseconds (ms), the boost time T _{1 in} FIG. 5A may be, for example, 15 milliseconds (ms), and the boost time T _{1 in} FIG. 5B may be, for example, 5 milliseconds. (ms), but not limited to this.

For the same reason, please refer to Figures 6A and 6B. After the control module 10 enters any staged pressure relief period P _decrease , there is a corresponding adjustment parameter u at that time. Among them, the staged pressure relief period P _decrease includes One or a plurality of continuous pressure relief control periods T _decrease with the same time length. Each pressure relief control period T _decrease includes a pressure relief time T ₃ and a pressure holding time T ₄ following the pressure relief time T _3. The control mode The group 10 adjusts the time length of the pressure relief time T ₃ and the pressure holding time T ₄ according to the current adjustment parameter u of each pressure relief control period T _decrease , so the control module 10 adjusts the pressure relief control according to the adjustment parameter (step S07) wherein, when the road surface friction coefficient higher u reflect the adjustment parameter, the control period _T decrease the pressure relief relief shorter time T _3; the lower the road surface friction coefficient when the adjustment parameter u reflect the The longer the pressure relief time T _{3 of} the pressure relief control period T _{decrease is.}

Please compare Figure 7A and Figure 7B. As shown in Figure 7A, when the adjustment parameter u reflects a higher road friction coefficient, the pressure holding time T ₄ can be extended and the pressure relief time T ₃ can be reduced; on the contrary, as shown in Figure 7B As shown, when the adjustment parameter u reflects a lower road friction coefficient, the pressure relief time T ₃ can be extended and the pressure holding time T ₄ can be reduced. The time length of the pressure relief control period T _decrease may be, for example, 20 milliseconds (ms), the pressure relief time T _{3 in} FIG. 7A may be, for example, 5 milliseconds (ms), and the pressure relief time T _{3 in} FIG. 7B may be, for example, 15 milliseconds. (ms), but not limited to this.

In summary, the present invention controls and adjusts the brakes according to the adjustment parameters. Because the adjustment parameters reflect the coefficient of friction of the road surface, the present invention can adjust the time length of the pressure relief time of the staged pressure relief period adaptively according to different road conditions, or adjust The length of the boosting time of the staged boosting period, which effectively keeps the wheels in the brakes rotating to a certain degree to maintain friction with the road surface and prevent the wheels from being locked.

Claims (10)

A braking control method based on road friction characteristics is executed by an anti-lock braking system module electrically connected to a wheel tachometer. The anti-lock braking system module activates an intermittent braking mode and receives it from the wheel tachometer. A speed signal, wherein the intermittent braking mode includes a one-stage boost period or a one-stage pressure relief period, the control method is applied to the stage boost period and the stage pressure relief period, and includes: according to the The wheel speed signal calculates the real-time wheel speed value; stores the real-time wheel speed value obtained at the moment of braking as an initial wheel speed value; judges a wheel speed relative peak value according to the real-time wheel speed value; according to the wheel speed relative peak value and the wheel speed The initial value calculates an estimated deceleration value of the vehicle; generates an adjustment parameter based on the estimated deceleration value of the vehicle and a slip threshold value, and the adjustment parameter reflects the friction coefficient of the road surface; and adjusts the increase of the staged boost period according to the adjustment parameter The time length of the pressure relief time, or the time length of the pressure relief time of the staged pressure relief period adjusted according to the adjustment parameter. The braking control method according to the friction characteristics of the road surface as described in claim 1, wherein, when the road friction coefficient reflected by the adjustment parameter is higher, the pressure increase time of the boost control period is longer; when the adjustment parameter reflects The lower the friction coefficient of the road surface, the shorter the boost time of the boost control cycle. The braking control method according to the friction characteristics of the road surface according to claim 1 or 2, wherein, when the road friction coefficient reflected by the adjustment parameter is higher, the pressure relief time of the pressure relief control period is shorter; when the adjustment parameter The lower the friction coefficient of the road surface reflected by the parameter, the longer the pressure relief time of the pressure relief control period. According to the braking control method according to the friction characteristic of the road surface as described in claim 3, the staged supercharging period includes a plurality of consecutive supercharging control periods with the same time length, which includes the supercharging time adjusted according to the adjustment parameter , And the pressure-holding time following the boosting time; this staged pressure-releasing period includes a plurality of continuous pressure-releasing control periods with the same time length, which includes the pressure-releasing time adjusted according to the adjustment parameter, And the holding time following the pressure relief time. For the braking control method according to the friction characteristics of the road surface as described in claim 1 or 2, the adjustment parameters are expressed as follows:

Among them, u is the adjustment parameter, which reflects the friction coefficient of the road surface; a is the estimated deceleration value of the vehicle; ABSout is the slip threshold value, and its value is greater than zero and less than 1. According to the braking control method according to the friction characteristics of the road surface as described in claim 3, the adjustment parameters are expressed as follows:

Among them, u is the adjustment parameter, which reflects the friction coefficient of the road surface; a is the estimated deceleration value of the vehicle; ABSout is the slip threshold value, and its value is greater than zero and less than 1. According to the braking control method according to the friction characteristics of the road surface as described in claim 4, the adjustment parameters are expressed as follows:

Among them, u is the adjustment parameter, which reflects the friction coefficient of the road surface; a is the estimated deceleration value of the vehicle; ABSout is the slip threshold value, and its value is greater than zero and less than 1. According to the braking control method according to the friction characteristics of the road surface as described in claim 7, the estimated deceleration value of the vehicle is expressed as follows:

Among them: x: times; a _x : estimated vehicle deceleration value; v _x : relative peak value of wheel speed; t _x : time point of occurrence of relative peak value of wheel speed v _{x ; v 0} : initial value of wheel speed; t ₀ : wheel speed The time point when the initial value v _{0 occurs.} The braking control method according to the friction characteristic of the road surface as described in claim 7, wherein the real-time wheel speed value is expressed as follows:

Among them: v _wheel : real-time wheel speed value; v _rpm : the number of turns of the wheel per minute; r: the radius of the wheel (unit: meters). The braking control method according to the friction characteristic of the road surface according to claim 7, wherein the control module determines the relative peak value of the wheel speed when the slope of the curve of the real-time wheel speed value changes from positive to negative.

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