CN112622851A

CN112622851A - Brake control method according to road surface friction characteristics

Info

Publication number: CN112622851A
Application number: CN201910953100.9A
Authority: CN
Inventors: 林信全; 魏嘉乐
Original assignee: Automotive Research and Testing Center
Current assignee: Automotive Research and Testing Center
Priority date: 2019-10-08
Filing date: 2019-10-08
Publication date: 2021-04-09
Anticipated expiration: 2039-10-08
Also published as: CN112622851B

Abstract

The invention relates to a brake control method according to road surface friction characteristics, which is executed in an anti-lock brake system module, is applied to a stage type pressure increasing period and a stage type pressure releasing period of an intermittent brake mode, and comprises the following steps: calculating an instant wheel speed value according to the wheel speed signal; storing an instant wheel speed value obtained at present during braking as a wheel speed initial value; judging a relative peak value of the wheel speed according to the instant wheel speed value; calculating an estimated deceleration value of the vehicle according to the relative peak value of the wheel speed and the initial value of the wheel speed; generating an adjusting parameter according to the vehicle estimated deceleration value and the slip threshold value, wherein the adjusting parameter reflects the road surface friction coefficient; and adjusting the pressurization time of the staged pressurization period according to the adjustment parameter, or adjusting the pressure relief time of the staged pressure relief period according to the adjustment parameter.

Description

Brake control method according to road surface friction characteristics

Technical Field

The invention relates to a brake control method, in particular to a brake control method according to road surface friction characteristics.

Background

The Advanced vehicle driving Assistance System (ADAS) is a key point of active development in various automobile factories, and the System is mainly used for assisting a Driver in driving and actively intervening in vehicle control before an accident occurs, so that the safety of the Driver and passengers is guaranteed, the personal safety of passers-by outside the automobile is considered, and the harm of road facilities is reduced.

For example, referring to fig. 8, an Electronic Stability Control (ESC) includes a Control module 30 and a plurality of detectors electrically connected to the Control module 30, the detectors may include a wheel tachometer 31, an accelerometer 32, a steering angle detector 33, and a yaw rate detector 34, and the Control module 30 is in signal connection with Control systems such as a power system 40, a steering system 41, and a braking system 42 of a vehicle. The control module 30 determines whether the vehicle dynamics enter an unstable state using the values obtained from the plurality of detectors; if so, the control module 30 actively intervenes in the control of the vehicle, such as modifying the tire steer, limiting the power output, and adjusting the brake pressure … of the hydraulic devices of the braking system 42, etc., thereby attempting to stabilize the vehicle to avoid vehicle runaway.

As another example, referring to fig. 9, the conventional Anti-lock Braking System (ABS) includes a control module 50 and a wheel tachometer 51 electrically connected to the control module 50, wherein the control module 50 is in signal connection with a brake System 60 of a vehicle to adjust a Braking state of a hydraulic device of the brake System 60. The control module 50 of the anti-lock braking system (ABS) determines whether to actively intervene in the operation of the braking system 60 using the instant wheel speed value obtained from the wheel tachometer 51 and a slip condition (slip differential) based on the vehicle speed and the wheel speed, wherein the slip condition is the difference between the vehicle speed and the wheel speed, and is expressed as follows:

in terms of the number of detectors, the hardware cost of the anti-lock brake system (ABS) is lower than that of the electronic body stabilization system (ESC) because the ABS only uses the wheel tachometer 51, compared to the ESC.

Briefly describing the existing control flow of an anti-lock braking system (ABS), the control module 50 first determines whether a braking event is present, i.e., whether the brake pedal is depressed; if a braking event is determined, the wheel speed is slowed down, and the control module 50 determines whether the vehicle dynamics reaches an early warning threshold according to the instant wheel speed value and the slip state, for example, whether the wheel acceleration is reduced to a lower threshold value, or whether the slip state reaches an upper slip limit; if the pre-warning threshold is reached, which indicates that the wheel speed is suddenly slowed but the vehicle speed is not as expected, the control module 50 actively engages the braking system 60 to adjust the wheel slowing and reduce the slip condition, since the wheel is locked and the vehicle slips on the road surface. On the contrary, when the control module 50 determines that the vehicle dynamics does not reach the pre-warning threshold, it represents that the vehicle is still in a controllable state, so the control module 50 does not intervene in the control of the braking system 60.

The conventional control flow of an Antilock Brake System (ABS) is described below by way of example. Please refer to fig. 10A to 10C, which respectively show a graph including a vehicle speed and a wheel speed, a wheel acceleration graph, and a brake pressure graph. As shown in FIG. 10C, when the brake pedal is at t₀When the vehicle is stepped on, the control module 50 determines that there is a braking event, and at this time, the braking pressure gradually increases with time, so that the vehicle speed and the wheel speed shown in fig. 10A decrease, the slip state increases gradually, the wheel acceleration shown in fig. 10B also decreases gradually, and the control module 50 determines whether the vehicle dynamics reaches the threshold of the warning.

When the wheel acceleration decreases to the lower threshold value (-a)_th) Or the slip condition reaches the slip upper limit, i.e. at t₁If the control module 50 determines that the vehicle dynamics has reached the pre-warning threshold, which represents that the wheel is about to be locked due to too fast deceleration and too large slip, the control module 50 intervenes in controlling the operation of the braking system 60, wherein the control module 50 determines that the vehicle dynamics has reached the pre-warning threshold at t₁When the acceleration of the wheel is detected to be too low and lower than the lower threshold value (-a)_th) And entering a pressure holding state. At t₂When the sliding difference is detected to be overlarge, the pressure relief state is entered. At t₃The acceleration of the wheel is detected to rise back to the lower threshold value (-a) because of the pressure relief state_th) And entering a pressure holding state. Therefore, after the wheel enters a pressure maintaining state under lower brake pressure, the wheel can slowly recover to rotate, so that the acceleration of the wheel gradually rises and is straightTo t₄Exceeding the wheel acceleration threshold a_limitThen enters a supercharging state. The brake pressure is continuously increased due to the pressurization state, so the wheel acceleration is gradually reduced, and the wheel acceleration is lower than the wheel acceleration threshold value a_limitAfter t₅Entering a pressure maintaining state, and continuously reducing the acceleration of the wheel in the pressure maintaining state until t₆Lower than an upper threshold (+ a)_th) And then entering a stage pressurization mode. And the pressurization and pressure relief processes are continuously executed in the same way. The step-boosting mode makes the brake pressure rise step by step until t₇The acceleration of the wheel is lower than the lower threshold value (-a)_th) Then enters a pressure relief state. As shown in FIG. 10C, the step-boosting mode consists of boosting and holding states, each boosting and holding state forms a boosting control period, and the total period length is T_increase。

In summary, the braking pressure variation of the intermittent braking mode substantially sequentially includes t₂To t₃Period of pressure release t₃To t₄Duration and t of₆To t₇Wherein the staged boosting period comprises one or more consecutive boosting control periods T_increaseFIG. 10C is a diagram showing a plurality of supercharging control periods T_increaseFor example, each boosting control period T_increaseIncluding pressurization and the pressure holding after pressurization, wherein the pressurization speed (the pressure increase amplitude in unit time) can be a preset control parameter.

As shown in fig. 10B, in the stepwise pressure-increasing period, the wheel acceleration decreases with time, and the wheel in the brake can be kept rotating to some extent to maintain the friction with the road surface, so that the increase in the speed of the slip state can be suppressed. When the control module 50 is at t₇If the vehicle dynamic reaches the threshold of the warning, which represents that the wheel is decelerated too fast and the slip is too large under the braking pressure, the next pressure relief period is entered, or the subsequent pressure holding period and the stage-type pressure increasing period … are entered, and so on, until the control module 50 determines that there is no braking action or meets other suspension conditions.

The foregoing examples mainly illustrate that the conventional intermittent braking mode may include a staged boosting period, andin one aspect, the intermittent braking mode may also include a staged pressure relief period, as another example shown in FIGS. 11A and 11B, where the control module 50 is at t₁When the intermittent braking mode is executed by controlling the braking system 60, the pressure relief period may be a staged pressure relief period comprising one or more continuous pressure relief control periods T_decreaseAnd t is shown in FIG. 11B₁To t₂One pressure release control period T_decreaseEach pressure relief control period T_decreaseIncluding pressure relief and pressure holding after pressure relief, wherein the speed of pressure relief (pressure reduction amplitude in unit time) can be a preset control parameter, so as to perform staged pressure relief instead of continuous pressure relief as in the previous example. As shown in FIG. 11B, the staged pressure relief period is followed by a pressure holding period of t 3-t 4 and a staged pressure increasing period of t 4-t 5.

Although the conventional anti-lock braking system (ABS) performs the intermittent braking mode to help stabilize the vehicle in sudden braking, the boost control period T of the staged boost period_increasePressure release control period T corresponding to staged pressure release period_decreaseIs preset as a control parameter of the control module 50, i.e., each boost control period T in the staged boost period_increaseThe pressure boost time is a fixed value, and each pressure relief control period T in the staged pressure relief period_decreaseThe pressure relief time is also a fixed value, and the fixed values are unlikely to be incapable of coping with different road conditions.

For example, vehicular road environments tend to vary with weather or human factors, such as clear weather may result in dry roads, rainy weather may result in wet roads, and construction environments may result in muddy roads. Boost control period T_increaseAnd a pressure release control period T_decreaseIf the friction characteristic of the dry road surface is set, the braking stability of the wet road surface is poor; in contrast, the boost control period T_increaseAnd a pressure release control period T_decreaseIf the friction characteristics of the wet road surface are set, the distance from braking to stopping on the dry road surface is longer. Therefore, the existing brake control method of the anti-lock brake system (ABS) is still improvedIt is a good space.

Disclosure of Invention

The main objective of the present invention is to provide a brake control method according to road friction characteristics, which can adjust the braking means according to the friction characteristics of different roads, in order to overcome the disadvantage that the fixed stage pressure increasing period or stage pressure releasing period of the prior art cannot cope with the friction characteristics of different roads.

The invention is a brake control method according to road surface friction characteristic, which is executed in an anti-lock brake system module electrically connected with a wheel tachometer, the anti-lock brake system module starts an intermittent brake mode and receives a wheel rotating speed signal from the wheel tachometer, wherein the intermittent brake mode comprises a stage type pressure increasing period or a stage type pressure releasing period, the control method is applied to the stage type pressure increasing period and the stage type pressure releasing period and comprises the following steps:

calculating an instant wheel speed value according to the wheel speed signal;

storing an instant wheel speed value obtained at present during braking as a wheel speed initial value;

judging a relative peak value of the wheel speed according to the instant wheel speed value;

calculating an estimated deceleration value of the vehicle according to the relative peak value of the wheel speed and the initial value of the wheel speed;

generating an adjusting parameter according to the vehicle estimated deceleration value and a slip threshold value, wherein the adjusting parameter reflects the road surface friction coefficient; and

and adjusting the time length of the pressurization time of the stage type pressurization period according to the adjustment parameter, or adjusting the time length of the pressure relief time of the stage type pressure relief period according to the adjustment parameter.

According to the brake control method based on the road surface friction characteristics, when the road surface friction coefficient reflected by the adjusting parameter is higher, the supercharging time of the supercharging control period is longer; the lower the road surface friction coefficient reflected by the adjustment parameter is, the shorter the supercharging time of the supercharging control period is.

According to the brake control method based on the road surface friction characteristics, when the road surface friction coefficient reflected by the adjusting parameters is higher, the pressure relief time of the pressure relief control period is shorter; and when the road surface friction coefficient reflected by the adjusting parameter is lower, the pressure relief time of the pressure relief control period is longer.

In the brake control method according to the road friction characteristics, the staged boosting period includes a plurality of consecutive boosting control cycles with the same time length, including the boosting time adjusted according to the adjustment parameter and the holding time subsequent to the boosting time; the stage type pressure relief period comprises a plurality of continuous pressure relief control periods with the same time length, the pressure relief control periods comprise the pressure relief time adjusted according to the adjustment parameter and the pressure holding time continuing to the pressure relief time.

In the brake control method according to the road friction characteristics as described above, the adjustment parameters are expressed as follows:

wherein u is an adjustment parameter which reflects the road surface friction coefficient; a is an estimated deceleration value of the vehicle; ABSout is a slip threshold value that is greater than zero and less than 1.

In the braking control method according to the road surface friction characteristic as described above, the vehicle estimated deceleration value is expressed as follows:

wherein: x: the number of times; a is_x: estimating a deceleration value of the vehicle; v. of_x: relative peak wheel speed; t is t_x: relative peak value v of wheel speed_xThe occurrence time point of (c); v. of₀: the initial value of the wheel speed; t is t₀: initial value v of wheel speed₀The occurrence time point of (c).

In the brake control method according to the road surface friction characteristics as described above, the instant wheel speed value is expressed as follows:

wherein: v. of_wheel: an instant wheel speed value; v. of_rpm: the number of revolutions of the wheel in each minute; r: radius of the wheel (unit: meter).

In the brake control method according to the road surface friction characteristic, the control module determines the relative peak value of the wheel speed according to the slope of the curve of the instant wheel speed value from positive to negative.

The invention utilizes the characteristic that the vehicle estimated deceleration value has relevance with the road surface friction characteristic, for example, compared with the road surface friction coefficient with different heights, when the vehicle runs on the road surface with higher road surface friction coefficient for sudden braking, the wheels are not easy to be locked, the braking effect is better, the vehicle speed is reduced faster, so the vehicle estimated deceleration value is higher; on the other hand, when the vehicle runs on a road with a low road surface friction coefficient and performs sudden braking, wheels are easy to lock and slip, the braking effect is poor, the vehicle speed is reduced slowly, and therefore the estimated deceleration value of the vehicle is low.

It can be seen that the vehicle estimated deceleration value has a correlation with the road surface friction characteristic. The invention carries out brake control according to the road surface friction characteristics, can adaptively adjust the brake means according to different road surface friction characteristics, and overcomes the problems in the prior art.

The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.

Drawings

FIG. 1: schematic block diagram of the circuit of the anti-lock braking system (ABS);

FIG. 2: the invention discloses a flow schematic diagram of an embodiment of a brake control method according to road surface friction characteristics;

FIG. 3A: a graph of the instant wheel speed value;

FIG. 3B: the invention is a schematic diagram of adjustment parameters obtained at different time points;

FIG. 4A: a waveform schematic of brake pressure during a staged boost period;

FIG. 4B: a timing diagram of a boost control cycle;

FIG. 5A: a timing diagram of a boost control cycle;

FIG. 5B: a timing diagram of a boost control cycle;

FIG. 6A: a waveform schematic diagram of brake pressure during a staged pressure release period;

FIG. 6B: a timing diagram of a pressure relief control cycle;

FIG. 7A: a timing diagram of a pressure relief control cycle;

FIG. 7B: a timing diagram of a pressure relief control cycle;

FIG. 8: a schematic block diagram of a circuit of an existing electronic body stabilization system (ESC);

FIG. 9: a schematic block diagram of a circuit of an existing anti-lock braking system (ABS);

FIG. 10A: a waveform diagram of the speed and the wheel speed after braking;

FIG. 10B: a waveform schematic diagram of wheel acceleration after braking;

FIG. 10C: a waveform schematic diagram of the braking pressure after braking;

FIG. 11A: a waveform diagram of the vehicle speed after braking;

FIG. 11B: and a waveform diagram of the braking pressure after braking.

Wherein the reference numerals

10 control module 11 wheel tachometer

20 braking system 30 control module

31-wheel tachometer 32 accelerometer

33 steering angle detector 34 yaw rate detector

40 power system 41 steering system

42 braking system 50 control module

51-wheel tachometer 60 braking system

v_rpmWheel speed signal

P_increaseStaged ramp-up period

T_increaseBoost control period

P_decreaseStaged pressure relief period

T_decreasePeriod of pressure relief control

Detailed Description

The technical means adopted by the invention to achieve the preset purpose are further described below by combining the accompanying drawings and the preferred embodiments of the invention.

Referring to fig. 1, an Anti-lock Braking System (ABS) mainly includes a control module 10 and a wheel tachometer 11 electrically connected to the control module 10, the control module 10 is in signal connection with a Braking System 20 of a vehicle, and the control module 10 receives a wheel speed signal v from the wheel tachometer 11_rpmSaid wheel speed signal v_rpmReflecting the number of revolutions of the wheel per unit time (per minute). The control module 10 may provide a wheel speed signal v_rpmConverted into an instantaneous wheel speed value v_wheelFor example, it can be expressed as follows:

in the above formula, r is the radius (unit: meter) of the wheel.

Generally, after the vehicle is started, the control module 10 records the instant wheel speed v_wheelReferring to fig. 2, a control module 10 of an Anti-lock Braking System (ABS) first determines whether a Braking event occurs (step S01); if so, the control module 10 further determines whether the vehicle dynamics reaches a threshold (step S02), and 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 an instant wheel speed value v_wheelWhen the wheel speed value v is on_wheelThe amount of change in the decrease per unit time reaches a threshold value representing a sharp decrease in the wheel speed, which may lead to the wheel being locked. On the contrary, in step S02, when the control module 10 determines that the vehicle dynamics does not reach the threshold, which indicates that the slowing speed of the wheels is within the allowable range, the vehicle is still in a controllable state, so the control module 10 does not intervene in the control of the braking system 20, and the vehicle brakes normally. When the control module 10 determines no in step S02, an estimated vehicle speed value is generated (step S04), which is derived from the instantaneous wheel speed v_wheelThe process returns to step S01 as the vehicle speed estimation value.

After the control module 10 actively intervenes in the operation of the braking system 20 (step S03), an intermittent braking mode may be performed, in which the braking pressure variation mode of the intermittent braking mode substantially sequentially includes a pressure relief period, a pressure holding period and a pressure boost period, wherein the pressure relief period may be a staged pressure relief period, and the pressure boost period may be a staged pressure boost period, so that the intermittent braking mode may include the staged pressure boost period, the staged pressure relief period or both the staged pressure boost period and the staged pressure relief period. It should be noted that the intermittent braking mode executed by the anti-lock braking system (ABS), the conditions for entering the staged pressure-increasing period and the staged pressure-releasing period, the pressure-increasing speed of the staged pressure-increasing period and the pressure-releasing speed … of the staged pressure-releasing period, etc. are well known to those skilled in the art, and as described in the prior art, they are not described in detail herein.

When the control module 10 intervenes in the operation of the braking system 20, in the embodiment of the invention, the pressurization time of the staged pressurization period can be adaptively adjusted according to the road friction characteristics, and the pressure relief time of the staged pressure relief period can be adaptively adjusted according to the road friction characteristics, as described later.

1. Initial value of wheel speed

As previously mentioned, the control module 10 may record the instantaneous wheel speed v when the vehicle is started_wheelIn one embodiment of the present invention, the control module 10 will generate an instant wheel speed v obtained when a braking event occurs (e.g. when the brake pedal is taken down)_wheelStored as an initial value v of wheel speed₀. Such asAs shown in FIG. 3A, the control module 10 is at t₀When a braking event occurs, the current instant wheel speed value v is measured_wheelStored as an initial value v of wheel speed₀I.e. t₀Is an initial value v of wheel speed₀The occurrence time point of (c).

2. Relative peak value of instant wheel speed value

In the intermittent braking mode, the instant wheel speed v_wheelFollowing the fluctuation, the control module 10 may adjust the wheel speed v according to the real-time wheel speed value_wheelDetermining a relative peak value of wheel speed, for example, referring to FIG. 3A, when the slope of the curve of the instant wheel speed value is at t₁When the signal is positive or negative, the control module 10 will control t₁Instant wheel speed value v_wheelIs judged as the relative peak value v of the first wheel speed₁. By analogy, with the time advance, a plurality of wheel speed relative peak values v can be judged₂、v₃…, etc.

3. Estimated deceleration value of vehicle

The invention calculates a vehicle estimated deceleration value according to the wheel speed relative peak value and the wheel speed initial value, and the vehicle estimated deceleration value can be expressed as follows:

in the above formula, x represents the number of times, a_xEstimating a deceleration value, v, for the x-th vehicle_xIs the x-th relative peak of wheel speed, t_xIs the x-th relative peak value v of the wheel speed_xPoint of occurrence of v₀As an initial value of wheel speed, t₀Is an initial value v of wheel speed₀The occurrence time point of (c). Therefore, in the embodiment of the present invention, as shown in FIG. 3A, when the control module 10 is at t₁Obtaining a first wheel speed relative peak value v₁According to the relative peak value v of the first wheel speed₁And the initial value v of the wheel speed₀Calculating a first estimated vehicle deceleration value a₁The following are:

further, a deceleration value a is estimated from the first vehicle₁Can be used for calculating a first estimated vehicle speed value v_vehicle,1It is expressed as follows:

V_vehicle，1＝V₀-a₁×t

in the above equation, t is the time elapsed after the occurrence of the braking event.

As time progresses, when the control module 10 is at t₂Obtaining a second wheel speed relative peak value v₂Then, the control module 10 can determine the relative peak value v of the second wheel speed according to the relative peak value v of the second wheel speed₂And the initial value v of the wheel speed₀Calculating a second estimated deceleration value a of the vehicle₂It is expressed as follows:

likewise, the deceleration value a is estimated from the second vehicle₂For calculating a second estimated vehicle speed value v_vehicle,2It is expressed as follows:

V_vehicle，2＝V₀-a₂×t

And so on, as time goes forward after the braking event occurs, the control module 10 can sequentially obtain a plurality of estimated deceleration values of the pen vehicle 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 values a of the vehicles can be respectively associated with the initial values v of the wheel speeds₀Calculating an estimated value v of vehicle speed_vehicleExpressed as follows:

V_vehicle＝V₀-a×t

In other words, the vehicle estimated deceleration value a and the vehicle speed estimated value v calculated according to the embodiment of the present invention_vehicleIs dependent on the instant wheel speed value v_wheelIs continuously updated.

On the other hand, to estimate the relative peak value v of wheel speed up to the first wheel speed after a braking event has occurred₁Before occurrence (i.e. t)₀To t₁Period), as shown in fig. 3A, the embodiment of the present invention is based on a preset deceleration value a_presetCalculating a vehicle speed reference value v_ref(step S03A), which is represented as follows:

V_ref＝V₀-a_preset×t

in the above formula, t is the time elapsed after the occurrence of the braking event, and t is₁Before. The control module 10 then compares the vehicle speed reference v_refAnd the instant wheel speed v_vehicleWhen the vehicle speed reference value v is_refGreater than the instant wheel speed value v_vehicleIs the vehicle speed reference value v_refAs an estimated value of vehicle speed; in contrast, when the vehicle speed reference value v is_refBelow the instant wheel speed value v_vehicleIs the instant wheel speed value v_vehicleAs an estimated value of the vehicle speed (step S03B). The preset deceleration a_presetIs greater than zero and less than 1g, wherein g is 9.8 (meters per second)²)。

4. Adjustment parameter reflecting road surface friction coefficient

In the embodiment of the present invention, after the control module 10 intervenes in the operation of the braking system 20, an adjustment parameter is generated according to the estimated deceleration values 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 an adjustment parameter which can reflect the road surface friction coefficient; a is an estimated deceleration value of the vehicle; ABSout is the slip threshold. It should be noted that the slip threshold ABSout is a preset constant, and the value thereof is greater than zero and less than 1, that is, 0< ABSout <1, and as long as the anti-lock braking system (ABS) determines that the slip value of the vehicle reaches the slip threshold ABSout, the anti-lock braking system (ABS) controls the braking system 20 to suspend the pressure relief state and turn into the pressure boost state, which is the existing function of the anti-lock braking system (ABS), and will not be described in detail herein, but this function will affect the wheel deceleration performance, so that the estimated deceleration value a of the vehicle obtained through calculation is slightly lower than the actual vehicle deceleration, so (1-ABSout) is used as a constant for correction, and the obtained adjustment parameter u of the present invention can better meet the actual condition. In the field of vehicle technology, the slip equation can be generally expressed as follows:

on the other hand, compared with a wet road surface, the friction force performance of the wheels on the dry road surface is better than that of the wheels on the wet road surface, so that when the vehicle brakes, the deceleration of the wheels on the dry road surface is slower than that of the wheels on the wet road surface, and the adjusting parameter u is calculated by the vehicle estimated deceleration value, so that the adjusting parameter u can reflect the road surface friction coefficient; in other words, the smaller the adjustment parameter u, the smaller the estimated deceleration value of the vehicle, which may reflect a road surface with a lower coefficient of friction; on the contrary, when the adjustment parameter u is higher, the estimated deceleration value of the vehicle is larger, and the road surface with higher friction coefficient can be reflected.

It can be seen that, referring to fig. 3B, as time goes on, different adjustment parameters u can be calculated respectively at different estimated deceleration values a of the vehicle, for example, the estimated deceleration value a of the first vehicle₁Corresponding to a first adjustment parameter u₁Expressed as follows:

second vehicle estimated deceleration value a₂Corresponding to a second adjustment parameter u₂Expressed as follows:

the next adjustment parameters can be analogized.

5. Controlling and adjusting the brake according to the adjustment parameter

Referring to fig. 4A and 4B, the control module 10 enters any one of the staged boosting periods P_increaseAfter the period of time (P), there is a corresponding adjustment parameter u, wherein the stage-type boosting period P_increaseComprising one or more boost control periods T of consecutive and mutually equal duration_increaseEach boost control period T_increaseInvolving a boost time T₁And is continued for a supercharging time T₁After holding pressure time T₂The control module 10 controls the cycle T according to the respective boost pressures_increaseAdjusting the boost time T by the current adjustment parameter u₁And a holding pressure time T₂So that the control module 10 adjusts boost control according to the adjustment parameter (step S07), wherein the boost control period T is set to be longer as the road friction coefficient reflected by the adjustment parameter u is higher_increaseBoost time T₁The longer; when the road surface friction coefficient reflected by the adjusting parameter u is lower, the supercharging control period T is_increaseBoost time T₁The shorter.

For example, comparing 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 can be extended₁Because of the boost control period T_increaseIs fixed, so that the holding pressure time T is relatively reduced₂(ii) a In contrast, as shown in FIG. 5B, when the adjustment parameter u reflects a low road friction coefficient, the supercharging time T can be shortened₁Relatively extending the holding pressure time T₂. Wherein the boost control period T_increaseMay be, for example, 20 milliseconds (ms), the boost time T of fig. 5A₁May be, for example, 15 milliseconds (ms), the boost time T of fig. 5B₁For example, but not limited to, 5 milliseconds (ms).

Similarly, referring to fig. 6A and 6B, the control module 10 enters any one of the staged pressure relief periods P_decreaseAfter the period (c), there is a corresponding adjustment parameter u, wherein the stage-type pressure-relief period P_decreaseComprising one or more pressure relief control periods T of consecutive and mutually equal duration_decreaseEach pressure relief control period T_decreaseIncluding time T of pressure relief₃And is continued for a pressure relief time T₃After holding pressure time T₄The control module 10 controls the period T according to the pressure relief_decreaseAdjusting the current adjustment parameter u to adjust the pressure relief time T₃And a holding pressure time T₄So that the control module 10 adjusts the pressure relief control according to the adjustment parameter (step S07), wherein when the adjustment parameter u reflects a higher road friction coefficient, the pressure relief control period T is longer_decreasePressure relief time T₃The shorter; when the road surface friction coefficient reflected by the adjusting parameter u is lower, the pressure relief control period T is shorter_decreasePressure relief time T₃The longer.

Referring to FIG. 7A and FIG. 7B, as shown in FIG. 7A, when the adjustment parameter u reflects a higher road friction coefficient, the holding pressure time T can be extended₄Thereby reducing the pressure relief time T₃(ii) a In contrast, as shown in FIG. 7B, when the adjustment parameter u reflects a low road friction coefficient, the pressure relief time T can be prolonged₃While reducing the holding pressure time T₄. Wherein, the pressure relief control period T_decreaseMay be, for example, 20 milliseconds (ms), the pressure relief time T of fig. 7A₃Which may be, for example, 5 milliseconds (ms), the pressure relief time T of fig. 7B₃For example, but not limited to, 15 milliseconds (ms).

In summary, the present invention controls and adjusts the brake according to the adjustment parameter, and since the adjustment parameter reflects the friction coefficient of the road surface, the present invention can adaptively adjust the time length of the pressure relief time of the staged pressure relief period or adjust the time length of the pressure boost time of the staged pressure boost period according to different road conditions, so as to effectively keep the wheels in the brake rotating to a certain degree to maintain the friction with the road surface, thereby preventing the wheels from being locked.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A brake control method according to road surface friction characteristics is characterized in that the brake control method is executed by an anti-lock brake system module electrically connected with a wheel tachometer, the anti-lock brake system module starts an intermittent brake mode and receives a wheel rotating speed signal from the wheel tachometer, wherein the intermittent brake mode comprises a stage type pressure increasing period or a stage type pressure releasing period, and the control method is applied to the stage type pressure increasing period and the stage type pressure releasing period and comprises the following steps:

calculating an instant wheel speed value according to the wheel speed signal;

2. The brake control method according to the road surface friction characteristics according to claim 1, characterized in that the supercharging time of the supercharging control period is longer as the road surface friction coefficient reflected by the adjustment parameter is higher; the lower the road surface friction coefficient reflected by the adjustment parameter is, the shorter the supercharging time of the supercharging control period is.

3. The brake control method according to the road surface friction characteristics according to claim 1 or 2, wherein when the road surface friction coefficient reflected by the adjustment parameter is higher, the pressure relief time of the pressure relief control period is shorter; and when the road surface friction coefficient reflected by the adjusting parameter is lower, the pressure relief time of the pressure relief control period is longer.

4. The brake control method according to the road surface friction characteristics, as recited in claim 3, wherein the staged boosting period includes a plurality of consecutive boosting control cycles having the same time length, including the boosting time adjusted according to the adjustment parameter and a holding pressure time following the boosting time;

the stage type pressure relief period comprises a plurality of continuous pressure relief control periods with the same time length, the pressure relief control periods comprise the pressure relief time adjusted according to the adjustment parameter and the pressure holding time continuing to the pressure relief time.

5. The brake control method according to the road surface friction characteristics according to claim 1 or 2, characterized in that the adjustment parameters are expressed as follows:

6. A brake control method according to road surface friction characteristics, according to claim 3, characterized in that the adjustment parameters are expressed as follows:

7. The brake control method according to the road surface friction characteristics as claimed in claim 4, wherein the adjustment parameter is expressed as follows:

8. A brake control method according to road surface friction characteristics, according to claim 7, wherein the vehicle estimated deceleration value represents:

wherein:

x: the number of times;

a_x: estimating a deceleration value of the vehicle;

v_x: relative peak wheel speed;

t_x: relative peak value v of wheel speed_xThe occurrence time point of (c);

v₀: the initial value of the wheel speed;

t₀: initial value v of wheel speed₀The occurrence time point of (c).

9. The brake control method according to the road surface friction characteristics, according to claim 7, characterized in that the instant wheel speed values are expressed as follows:

wherein:

v_wheel: an instant wheel speed value;

v_rpm: the number of revolutions of the wheel in each minute;

r: the radius of the wheel.

10. The brake control method according to the road surface friction characteristics as claimed in claim 7, wherein the control module determines the relative peak value of the wheel speed when the slope of the curve of the instant wheel speed value is positive or negative.