CN109572644B - Integrated line control hydraulic braking system and ABS control method thereof - Google Patents
Integrated line control hydraulic braking system and ABS control method thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/176—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS
- B60T8/1761—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS responsive to wheel or brake dynamics, e.g. wheel slip, wheel acceleration or rate of change of brake fluid pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
- B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
- B60T13/12—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being liquid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
- B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
- B60T13/66—Electrical control in fluid-pressure brake systems
- B60T13/68—Electrical control in fluid-pressure brake systems by electrically-controlled valves
- B60T13/686—Electrical control in fluid-pressure brake systems by electrically-controlled valves in hydraulic systems or parts thereof
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
- B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
- B60T8/40—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition comprising an additional fluid circuit including fluid pressurising means for modifying the pressure of the braking fluid, e.g. including wheel driven pumps for detecting a speed condition, or pumps which are controlled by means independent of the braking system
- B60T8/4072—Systems in which a driver input signal is used as a control signal for the additional fluid circuit which is normally used for braking
- B60T8/4081—Systems with stroke simulating devices for driver input
- B60T8/409—Systems with stroke simulating devices for driver input characterised by details of the stroke simulating device
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- Mechanical Engineering (AREA)
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- Regulating Braking Force (AREA)
Abstract
The invention discloses an integrated line control hydraulic braking system and an ABS control method thereof, wherein the method is based on a double closed loop formed by slip rate and braking torque, adopts a layered control framework comprising upper layer control, middle layer control and bottom layer control, and calculates the target pressure of a wheel cylinder by taking the deviation between the current slip rate and the expected slip rate of an automobile as a control variable, thereby realizing the pressure regulation of the brake wheel cylinder.
Description
Technical Field
The invention relates to the field of automobile control, in particular to an integrated line control hydraulic braking system and an ABS control method thereof.
Background
An Anti-lock Braking System (ABS) is the most widely used electronic control device for automobile dynamics, and aims to maintain the wheel slip rate near the optimal slip rate by adjusting the pressure of a brake wheel cylinder in real time so as to improve the Braking stability of the automobile and shorten the Braking distance. Foreign companies have more intensive research on ABS, grasp many mature technologies including control strategies and road surface identification, and are widely applied to various vehicles; while the national understanding and comprehension of the ABS key technology is not deep enough, relatively mature products are basically designed based on a logic threshold value control method of a wheel acceleration threshold and a wheel deceleration threshold, and a traditional vehicle brake system is difficult to take a tire slip rate as a direct control target.
Meanwhile, with the increasingly prominent problems of energy, environment, safety, traffic jam and the like, green intelligent automobiles gradually become hot topics, so higher requirements are also put forward on a chassis dynamics control system. The green intelligent automobile requires the brake system to reduce or cancel the dependence on the vacuum degree of the engine, the brake feeling is not influenced by the coordination control process of regenerative braking and friction braking, and the brake system can realize low-noise active conventional braking. The development of the active safety technology puts higher requirements on a complete vehicle dynamics control system. In a traditional vehicle braking system, a chassis structure mainly comprises mechanical parts and hydraulic parts, and the chassis and an electric control structure of the traditional vehicle braking system do not have an active control function, are lack of flexibility and are difficult to deal with complex and variable running conditions and different driving targets. These new requirements are difficult to implement in conventional automotive brake systems, and have prompted the emergence of a new generation of brake systems.
Disclosure of Invention
The invention aims to solve the problem that a traditional vehicle braking system is difficult to deal with complex and changeable running conditions and different driving targets, provides an ABS control method based on an integrated line control hydraulic braking system (IEHB), and designs a tire slip rate controller based on the IEHB system by combining a layered control framework and utilizing a double-closed-loop nonlinear control method formed by slip rate and braking torque, so that the slip rate of an automobile tire can be effectively regulated and controlled, and the active safety performance of an automobile is improved. .
In order to realize the purpose, the invention adopts the following technical scheme:
an ABS control method of an integrated line control hydraulic braking system is based on a double closed loop formed by a slip rate and a braking torque, adopts a layered control framework, and calculates a wheel cylinder target pressure by using a tire slip rate to realize pressure regulation of a brake wheel cylinder.
Preferably, the layered control framework comprises three layers, namely an upper layer control layer, a middle layer control layer and a bottom layer control layer; the upper-layer control takes the slip rate of the tire as a control variable, calculates the target braking torque of the wheel cylinder by adopting a linear proportion term and a nonlinear compensation term, and transmits the target braking torque to the middle-layer control; the middle-layer control estimates the longitudinal slip rate of the brake wheel, corrects the target brake torque according to different longitudinal slip rates to obtain the actual brake torque, and transmits the actual brake torque to the lower-layer control; and the bottom layer control is used for calculating the target pressure of each wheel cylinder by adopting a corresponding control scheme according to the actual control moment and transmitting the target pressure to the executing mechanism so as to realize the control of the brake wheel cylinder.
Preferably, the upper-layer control adopts a deviation between the current slip rate and the expected slip rate of the automobile as a control variable, and adopts a proportional term and a nonlinear compensation control algorithm to determine the target braking torque of the wheel cylinder;
the wheel cylinder target braking torque is represented by the following formula:
wherein: k1Is the coefficient of the proportional term, K2Is a nonlinear term coefficient and is determined by experiments. sijIs the actual slip ratio, s0_ijTo target slip ratio, Td_ijFor the wheel cylinder target control torque, i, j refer to a specific wheel cylinder.
A1, prepared from
Estimating the longitudinal slip rate of the brake wheel;
where u is the vehicle speed and ω is the angular velocity of the wheel as measured by the wheel speed sensor
A2, correcting the target wheel cylinder braking torque according to the longitudinal slip rate of the braking wheel, and determining the actual wheel cylinder braking torque, wherein the actual wheel cylinder braking torque is respectively as follows:
when the estimated longitudinal slip value of the brake wheel is less than s0_ij(1+xm) While taking the actual braking torque Tr_ij＝0；
When the estimated longitudinal slip value of the brake wheel is larger than s0_ij(1-xm) While taking the actual braking torque Tr_ij＝Td_ij
When the estimated longitudinal slip value of the brake wheel is larger than s0_ij(1+xm) And is less than s0_ij(1-xm) While taking the actual braking torque
Wherein x ismThe slip ratio control margin is provided.
Preferably, the bottom layer control determines the ABS control pressure according to the actual braking torque of the wheel cylinder, compares the ABS control pressure with the acquired actual pressure, calculates the target pressure of each wheel cylinder by adopting different control strategies according to the comparison result, and controls the braking wheel;
the ABS control pressure is calculated as follows:
PABS_ij＝|Tr_ij|/Ksys
wherein, PABS_ijIs the ABS control pressure of the brake wheel cylinder, KsysIs the equivalent area of action, the value of which depends on the brake disc size; i. j denotes a specific wheel cylinder.
Preferably, the control strategies are respectively:
s1, determining the average pressure (P) of four wheel cylinders11+P12+P21+P22) And 4, the ABS control pressure of the left rear wheel and the right rear wheel of the automobile is smaller than the average value of the ABS control pressures of the left rear wheel and the right rear wheel of the automobile, and the target pressures of the wheel cylinders of the four wheels of the automobile are the average value of the ABS control pressures of the left front wheel and the right front wheel, namely:
Pd_11＝Pd_12＝Pd_21＝Pd_22＝(PABS_11+PABS_12)/2
s2, determining the average pressure (P) of four wheel cylinders11+P12+P21+P22) The/4 is larger than the average value of the ABS control pressure of the left rear wheel and the right rear wheel of the automobile, and the rear wheel is easy to be locked in consideration of the axle load transfer during braking, so the target pressure of only controlling the left front wheel and the right front wheel is the average value of the ABS control pressure of the left front wheel and the right front wheel, and the rear wheel is not controlled, namely:
Pd_11＝(PABS_11+PABS_12)/2，
Pd_12＝(PABS_11+PABS_12)/2，
Pd_21＝P21， Pd_22＝P22；
wherein, Pd_ijIndicating target pressure of brake cylinder, i, j indicating specific wheel cylinder, PijIndicating the actual pressure of the brake wheel cylinder.
Preferably, the actuator adjusts the wheel cylinder pressure by the electric master cylinder and the hydraulic pressure adjusting unit in accordance with the wheel cylinder target pressure.
Preferably, the actuator adjusts the pressure of the brake cylinder in three modes, namely a pressure maintaining state, a pressure increasing state and a pressure reducing state:
e1, when in a pressurization state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is TmThe control instruction of the liquid inlet valve is 0, the control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0;
e2, when in pressure maintaining state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is 0, and the control instruction of the liquid inlet valve is UpcThe control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0;
e3, when in decompression state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is TmThe control instruction of the liquid inlet valve is UpcThe control instruction of the liquid outlet valve is UpcThe control instruction of the oil return pump is Upc。
Further, the invention also adopts the following technical scheme:
an ABS control system based on an integrated line control hydraulic brake system comprises a pedal stroke simulator, an electric brake master cylinder, a hydraulic adjusting unit, a sensor and a controller; the pedal stroke simulator identifies the braking intention of a driver through a pedal displacement sensor signal and simulates the feeling of a brake pedal; the electric brake master cylinder is responsible for realizing fine adjustment of the output pressure of the brake hydraulic source; the hydraulic adjusting unit tracks a target value by adjusting the actual brake torque of the pressure of the brake wheel cylinder; the sensor is used for collecting the displacement of the brake pedal and the output pressure of the brake master cylinder; the controller controls a brake system by using a double closed loop formed by a slip rate and a brake torque and adopting a layered control mode according to the operation requirements of a driver and the motion requirements of the whole vehicle; the controller is used for realizing the control method; the actuating mechanism is used for executing the control method.
Preferably, the controller is divided into an upper controller, a middle controller and a lower controller, and the upper controller obtains the target braking torque of the wheel cylinder by using the tire slip rate; the middle-layer controller determines an actual braking torque according to the target braking torque; the bottom layer controller determines the target pressure of the wheel cylinder by adopting a corresponding strategy according to the actual braking torque, and transmits the target pressure to the execution layer, so that the execution layer can adjust the pressure of the brake wheel cylinder through the electric brake master cylinder and the hydraulic pressure adjusting unit; the actuating mechanism comprises an electric brake master cylinder, a hydraulic pressure adjusting unit, a pressure sensor, a motor, a low-pressure liquid storage tank, a solenoid valve and an oil return pump.
Compared with the prior art, the invention has the beneficial effects that:
the invention adopts a layered control structure to design the ABS system control strategy, which is not only convenient for the expansion and verification of each layer of control function, but also convenient for the integration of the whole system control strategy software.
Furthermore, a double closed loop formed by the slip rate and the braking torque is utilized, the robustness is good, the interference generated by the change of the wheel speed caused by the sudden change of the road surface condition can be resisted, and the change characteristics of the acceleration and the slip rate when the wheel has the unstable motion trend can be quickly captured, so that the control is accurate and quick.
Furthermore, a target braking torque is determined by adopting a proportional term and a nonlinear compensation control algorithm, so that the accuracy of torque calculation is improved, and the robustness of the system is ensured; and a hyperbolic tangent continuous function tanh (x) is selected in the nonlinear compensation term, so that buffeting in sliding mode control is effectively reduced.
Furthermore, the electromechanical-hydraulic integrated component replaces the traditional hydraulic or pneumatic brake actuating mechanism, has the characteristics of high control precision, high response speed, easy integration with other control functions and the like, and greatly improves the safety performance of the vehicle during braking.
Drawings
FIG. 1 is a schematic diagram of a brake system configuration of an ABS control method according to the present invention;
FIG. 2 is a schematic diagram of the overall control framework structure of the ABS control method of the present invention;
FIG. 3 is a schematic diagram of a hierarchical control architecture of the ABS control method of the present invention;
FIG. 4 is a flow chart of middle layer control of the ABS control method of the present invention;
FIG. 5 is a bottom control flow chart of the ABS control method of the present invention.
Detailed Description
An integrated hydraulic brake-by-wire system (IEHB) is shown in fig. 1, and comprises a pedal stroke simulator 9, an actuating mechanism and an IEHB controller, wherein the actuating mechanism comprises an electric brake master cylinder 7, a hydraulic adjusting unit (1, 4, 5, 10), a sensor 6, a motor 8, a wheel cylinder pressure sensor 2 and a low-pressure liquid storage tank 3, the pedal stroke simulator 9 is used for recognizing the brake intention of a driver through a pedal displacement sensor signal, and the brake pedal feeling is simulated through the pedal simulator; the electric brake master cylinder 7 is responsible for realizing fine adjustment of the output pressure of the hydraulic source; the hydraulic adjusting units (1, 4, 5 and 10) are responsible for monitoring the brake fluid pressure of each wheel cylinder and tracking a target value by adjusting the actual brake torque of the wheel cylinder pressure; the sensor 6 is responsible for collecting the displacement of the brake pedal and the pressure of the main cylinder; the IEHB controller is responsible for controlling a brake system by utilizing a double closed loop formed by a slip rate and a brake torque and adopting a layered control mode according to the operation requirements of a driver and the motion requirements of the whole vehicle.
The IEHB controller has a structure as shown in fig. 3, and comprises an upper controller, a middle controller and a lower controller, wherein the upper controller calculates a target wheel cylinder braking torque by using a linear proportional term and a nonlinear compensation term and taking a slip rate of a tire as a control variable, and transmits the target wheel cylinder braking torque to the middle controller; the target braking torque of the wheel cylinder output by the sliding mode controller has a certain degree of chattering, so that control overshoot is caused, and further, a braking wheel is locked, and therefore the target braking control torque of the wheel cylinder needs to be corrected by the middle-layer controller. The middle-layer controller firstly estimates the longitudinal slip rate of the brake wheel, corrects the target brake torque of the brake wheel cylinder according to different longitudinal slip rates to obtain the actual brake torque of the brake wheel cylinder, and transmits the actual brake torque to the lower-layer controller; and the bottom layer controller calculates the wheel cylinder target pressure of each wheel cylinder by adopting a corresponding control scheme according to the actual control moment and transmits the wheel cylinder target pressure to the execution mechanism, so that the execution mechanism can adjust the pressure of the brake wheel cylinders through the electric brake master cylinder and the hydraulic pressure adjusting unit to control the four brake wheel cylinders of the automobile.
The integrated hydraulic brake-by-wire system adopts a layered control architecture, as shown in fig. 2, and accordingly, the IEHB control includes an upper control layer, a middle control layer, and a bottom control layer. The working process is as follows:
aiming at the nonlinear problem of a controlled vehicle and a braking system in the braking process, an upper control layer takes the deviation between the current slip rate and the expected slip rate of the vehicle as a control variable, adopts a proportional term and a nonlinear compensation control algorithm to determine the target braking torque of a wheel cylinder, and selects a hyperbolic tangent continuous function tanh (x) to replace a traditional discontinuous function sgn (x) in a nonlinear compensation term in order to reduce buffeting in sliding mode control.
The target wheel cylinder braking torque is calculated by the following formula:
wherein: k1Is the coefficient of the proportional term, K2Is a nonlinear term coefficient and is determined by experiments. sijIs the actual slip ratio, s0_ijTo target slip ratio, Td_ijFor the wheel cylinder target control torque, i, j refer to a specific wheel cylinder.
The target braking torque of the wheel cylinder can be calculated by the formula, wherein the first term
Is a linear term, a second term
As the nonlinear compensation, since the hyperbolic tangent function tanh (x) is a continuous function, the unstable jitter in the control process can be effectively reduced.
And transmitting the target braking torque obtained by the above formula to the middle-layer controller.
And the middle control layer corrects the target braking torque calculated by the upper control layer, so that the overshoot of the control quantity caused by the jitter of the target braking torque output by the upper control layer is avoided, and the locking phenomenon of the wheel caused by the overshoot is also avoided.
Firstly, by
Estimating the longitudinal slip ratio Sij of the brake wheel; secondly, correcting the target braking torque according to the longitudinal slip rate of the braking wheel, and determining the actual braking torque Tr_ij。
The control strategy is carried out in a segmented mode:
2.1) when the estimated longitudinal slip ratio Sij value of the brake wheel is less than s0_ij(1+xm) When the brake torque is set to T, the actual brake torque of the wheel cylinder is set to Tr_ij0; in the formula, xmAdjusting and controlling the margin for the slip ratio;
2.2) when the estimated longitudinal slip ratio Sij of the brake wheel is larger than s0_ij(1-xm) When the slip ratio is relatively large, the actual braking torque of the wheel cylinder is set as the target wheel cylinder braking torque Tr_ij＝Td_ij；
2.3) when the estimated longitudinal slip ratio Sij value of the brake wheel is larger than s0_ij(1+xm) And is less than s0_ij(1-xm) When the actual braking torque of the wheel cylinder is set to be
The actual braking torque of the wheel cylinder corrected by the middle control layer can well eliminate the chattering, the braking torque is relatively gentle, and the control of an actuating mechanism is facilitated. The middle control layer transmits the corrected actual braking torque of the wheel cylinder to the bottom control layer.
The flow chart is shown in fig. 4, and comprises the following steps:
b1, start
B2, input sij, s0_ijA value of (d);
b3, judgment sijWhether the brake pressure is less than or equal to 0 is established, if the brake pressure is not established, the brake pressure is a non-braking working condition, and ABS control is not executed; if yes, executing the next step;
b4, judgment sij≤s0_ij(1+xm) If yes, executing the next step; if not, executing B6;
b5, output Tr_ij0, turn B9;
b6, judgment sij≤s0_ij(1-xm) If yes, executing the next step; if not, executing B8;
b7, output
Turning to B9;
b8, output Tr_ij＝Td_ij；
B9, end
Thirdly, the bottom control layer firstly determines ABS control pressure P according to the following formula according to the actual braking torque of the wheel cylinderABS_ij＝|Tr_ij|/Ksys，
In the formula PABS_ijIs the ABS control pressure of the brake wheel cylinder, KsysIs the equivalent area of action, the value of which depends on the brake disc size;
and secondly, comparing the actual wheel cylinder pressure acquired by the sensor with the ABS control pressure, calculating the specific wheel cylinder pressure of the four wheel cylinders by adopting different control strategies according to the comparison result, and controlling the corresponding brake wheel. The specific strategy is as follows:
3.1), average pressure (P) of the four-wheel cylinder if wheel11+P12+P21+P22) And 4, the ABS control pressure of the left rear wheel and the right rear wheel of the automobile is smaller than the average value of the ABS control pressures of the left rear wheel and the right rear wheel of the automobile, and the target pressures of the wheel cylinders of the four wheels of the automobile are the ABS control pressures of the left front wheel and the right front wheelControlling the mean value of the pressure, i.e.
Pd_11＝Pd_12＝Pd_21＝Pd_22＝(PABS_11+PABS_12)/2
3.2) average pressure (P) of the four-wheel cylinder if wheel11+P12+P21+P22) The/4 is larger than the average value of the ABS control pressure of the left rear wheel and the right rear wheel of the automobile, and the rear wheel is easy to be locked in consideration of the axle load transfer during braking, so the target pressure of the wheel cylinder only controlling the left front wheel and the right front wheel is the average value of the ABS control pressure of the left front wheel and the right front wheel, and the rear wheel is not controlled, namely:
Pd_11＝(PABS_11+PABS_12)/2，
Pd_12＝(PABS_11+PABS_12)/2，
Pd_21＝P21，Pd_22＝P22。
as described above, the actual target pressures of the respective wheel cylinders of the automobile are calculated and transmitted to the actuator.
The flow chart is shown in fig. 5, and comprises the following steps:
c1, start
C2, input Tr_ijValue of (A)
C3、PABS_ij＝|Tr_ij|/Ksys
C4, judging whether (P11+ P12+ P13+ P14)/4 ≦ (PABS _21+ PABS _22)/2 is true, if true, executing the next step; if not, executing C6;
c5, output Pd_11＝Pd_12＝Pd_21＝Pd_22＝(PABS_11+PABS_12) 2; to C7
C6, output Pd_11＝(PABS_11+PABS_12)/2；Pd_12＝(PABS_11+PABS_12)/2； Pd_21＝P21，Pd_22＝P22；
And C7, ending.
Referring to fig. 2, the actuator adjusts the wheel cylinder pressure through the electric brake master cylinder and the hydraulic pressure adjusting unit according to the wheel cylinder target pressure calculated by the bottom control layer.
The system has three working states, namely a pressurization state, a pressure maintaining state and a pressure reducing state.
In a pressurization state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is TmThe control instruction of the liquid inlet valve is 0, the control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0. Brake fluid directly enters each wheel cylinder through the master cylinder and the pressure increasing valve. At this stage, since the power source comes from the driver, the brake fluid circuit is: master cylinder-pressure increasing valve-wheel cylinder. It is necessary to design the throttle bore diameter of the pressure increase valve so as to limit the pressure increase rate of the wheel cylinder.
In the pressure maintaining state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is 0, and the control instruction of the liquid inlet valve is UpcAnd the control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0. At this time, the hydraulic circuit between the wheel cylinder and the master cylinder is completely blocked, and the tightness of the solenoid valve is an important index for realizing a strict pressure maintaining function.
When the wheel pressure is too high, there is a tendency of locking, and at this time, the pressure of the wheel needs to be reduced, and the decompression state is started.
In the decompression state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is TmThe control instruction of the liquid inlet valve is UpcThe control instruction of the liquid outlet valve is UpcThe control instruction of the oil return pump is Upc. The brake fluid flows back from the wheel cylinder to the low-pressure accumulator which basically does not store the pressure through the pressure reducing valve, and the plunger pump pumps the brake fluid in the accumulator back to the brake master cylinder with higher pressure through reciprocating motion. In this process, the hydraulic circuit is: wheel cylinder-pressure reducing valve-accumulator-plunger pump-damper-brake master cylinder. When reducing pressure, rapid pressure reduction needs to be realized, and residual pressure cannot exist, so that the capacity of the energy accumulator needs to be ensured to store all brakes in the two wheel cylindersAnd meanwhile, the plunger pump is ensured to pump all brake fluid in the energy accumulator back to the brake master cylinder.
The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and such substitutions and modifications are to be considered as within the scope of the invention.
Claims (10)
1. An ABS control method of an integrated hydraulic brake-by-wire system is characterized in that: based on a double closed loop formed by slip rate and braking torque, a layered control framework is adopted, one layer of control comprises the steps of calculating the target braking torque of a wheel cylinder by using the deviation between the slip rate of a tire and an expected slip rate as a control variable and adopting a linear proportion term and a nonlinear compensation term, the other layer of control comprises the steps of estimating the longitudinal slip rate of the braking wheel, correcting the target braking torque according to different longitudinal slip rates, calculating the target pressure of each wheel cylinder by combining actual pressure, and realizing the pressure regulation of the braking wheel cylinder.
2. The ABS control method according to claim 1, characterized in that: the layered control framework comprises three layers, namely an upper layer control layer, a middle layer control layer and a bottom layer control layer;
the upper-layer control takes the deviation between the slip rate of the tire and the expected slip rate as a control variable, calculates the target braking torque of the wheel cylinder by adopting a linear proportion term and a nonlinear compensation term, and transmits the target braking torque to the middle-layer control;
the middle-layer control estimates the longitudinal slip rate of the brake wheel, corrects the target brake torque according to different longitudinal slip rates to obtain the actual brake torque, and transmits the actual brake torque to the lower-layer control;
and the bottom layer control is used for determining ABS control pressure according to the actual control torque, comparing the ABS control pressure with the acquired actual pressure, calculating target pressure of each wheel cylinder by adopting different control strategies according to a comparison result, and transmitting the target pressure to an execution mechanism to realize control of the brake wheel cylinder.
3. The ABS control method according to claim 2, characterized in that: the upper-layer control is to determine the target braking torque of the wheel cylinder by taking the deviation between the current slip rate and the expected slip rate of the automobile as a control variable and adopting a proportional term and a nonlinear compensation control algorithm;
the wheel cylinder target braking torque is represented by the following formula:
Td_ij＝K1×(sij-s0_ij)+K2×tanh(sij-s0_ij+K1∫(sij-s0_ij)dt)
wherein: k1Is the coefficient of the proportional term, K2Is a nonlinear term coefficient and is determined by experiments; sijIs the actual slip ratio, s0_ijTo target slip ratio, Td_ijFor the wheel cylinder target control torque, i, j refer to a specific wheel cylinder.
4. The ABS control method according to claim 3, characterized in that: the middle layer control comprises the following steps:
a1, prepared from
Estimating the longitudinal slip rate of the brake wheel;
wherein u is a vehicle speed and ω is an angular velocity of the wheel measured by the wheel speed sensor; r represents a tire radius;
a2, correcting the target wheel cylinder braking torque according to the longitudinal slip rate of the braking wheel, and determining the actual wheel cylinder braking torque, wherein the actual wheel cylinder braking torque is respectively as follows:
when the estimated longitudinal slip value of the brake wheel is less than s0_ij(1+xm) While taking the actual braking torque Tr_ij＝0；
When the estimated longitudinal slip value of the brake wheel is larger than s0_ij(1-xm) When it is true, get the fruitInter braking torque Tr_ij＝Td_ij
When the estimated longitudinal slip value of the brake wheel is larger than s0_ij(1+xm) And is less than s0_ij(1-xm) While taking the actual braking torque
Wherein x ismFor slip ratio control margin, xijThe slip ratio of each tire is shown, and i and j are tire positions.
5. The ABS control method according to claim 4, characterized in that: the bottom layer control determines ABS control pressure according to the actual braking torque of the wheel cylinder, compares the ABS control pressure with the acquired actual pressure, calculates the target pressure of each wheel cylinder by adopting different control strategies according to the comparison result, and controls the braking wheel;
the ABS control pressure is calculated as follows:
in the formula PABS_ijIs the ABS control pressure of the brake wheel cylinder, KsysIs the equivalent area of action, the value of which depends on the brake disc size; i. j denotes a specific wheel cylinder.
6. The ABS control method according to claim 5, characterized in that: the control strategies are respectively as follows:
s1, determining the average pressure (P) of four wheel cylinders11+P12+P21+P22) And 4, the ABS control pressure of the left rear wheel and the right rear wheel of the automobile is smaller than the average value of the ABS control pressures of the left rear wheel and the right rear wheel of the automobile, and the target pressures of the wheel cylinders of the four wheels of the automobile are the average value of the ABS control pressures of the left front wheel and the right front wheel, namely:
Pd_11＝Pd_12＝Pd_21＝Pd_22＝(PABS_11+PABS_12)/2
s2, determining the average pressure (P) of four wheel cylinders11+P12+P21+P22) The/4 is larger than the average value of the ABS control pressure of the left rear wheel and the right rear wheel of the automobile, and the rear wheel is easy to be locked in consideration of the axle load transfer during braking, so the target pressure of only controlling the left front wheel and the right front wheel is the average value of the ABS control pressure of the left front wheel and the right front wheel, and the rear wheel is not controlled, namely:
Pd_11＝(PABS_11+PABS_12)/2，
Pd_12＝(PABS_11+PABS_12)/2，
Pd_21＝P21，Pd_22＝P22；
wherein, Pd_ijIndicates the target pressure of the brake wheel cylinder, i and j refer to specific wheel cylinders, specifically, i-1 indicates the left tire, i-2 indicates the right tire, j-1 indicates the front tire, j-2 indicates the rear tire, PijIndicating the actual pressure of the brake wheel cylinder.
7. The ABS control method according to claim 6, characterized in that: and adjusting the wheel cylinder pressure through the electric brake master cylinder and the hydraulic adjusting unit according to the wheel cylinder target pressure executing mechanism.
8. The ABS control method according to claim 7, characterized in that: the executing mechanism adopts three modes to adjust the pressure of the brake wheel cylinder, namely a pressure maintaining state, a pressure increasing state and a pressure reducing state:
e1, when in a pressurization state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is TmThe control instruction of the liquid inlet valve is 0, the control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0;
e2, when in pressure maintaining state, the input control torque of a Permanent Magnet Synchronous Motor (PMSM) of the electric brake master cylinder is 0, and the control instruction of the liquid inlet valve is UpcThe control instruction of the liquid outlet valve is 0, and the control instruction of the oil return pump is 0;
e3 Permanent Magnet Synchronous Motor (PMSM) output of electric brake master cylinder in decompression stateThe input control moment is TmThe control instruction of the liquid inlet valve is UpcThe control instruction of the liquid outlet valve is UpcThe control instruction of the oil return pump is Upc。
9. The utility model provides a ABS control system based on integrated form drive-by-wire hydraulic braking system which characterized in that: the device comprises a pedal stroke simulator, an electric brake master cylinder, a hydraulic adjusting unit, a pedal displacement sensor, a wheel cylinder pressure sensor and a controller; the pedal stroke simulator identifies the braking intention of a driver through a pedal displacement sensor signal and simulates the feeling of a brake pedal; the electric brake master cylinder is responsible for realizing fine adjustment of the output pressure of the brake hydraulic source; the hydraulic adjusting unit tracks a target value by adjusting the actual brake torque of the pressure of the brake wheel cylinder; the pedal displacement sensor and the wheel cylinder pressure sensor are respectively responsible for collecting the brake pedal displacement and the output pressure of the brake master cylinder; the controller controls a brake system by using a double closed loop formed by a slip rate and a brake torque and adopting a layered control mode according to the operation requirements of a driver and the motion requirements of the whole vehicle; the controller is used for realizing the control method of claims 1-8; the actuator is used for implementing the control method of claim 8.
10. The ABS control system according to claim 9, wherein: the controller is divided into an upper layer controller, a middle layer controller and a bottom layer controller, and the upper layer controller calculates to obtain a target braking torque of the wheel cylinder by using the tire slip rate; the middle-layer controller determines an actual braking torque according to the target braking torque; the bottom layer controller determines the target pressure of the wheel cylinder by adopting a corresponding strategy according to the actual braking torque, and transmits the target pressure to the execution layer, so that the execution layer can adjust the pressure of the brake wheel cylinder through the electric brake master cylinder and the hydraulic pressure adjusting unit; the actuating mechanism comprises an electric brake master cylinder, a hydraulic pressure adjusting unit, a pedal displacement sensor, a wheel cylinder pressure sensor, an electromagnetic valve and an oil return pump.
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| CN111775914A (en) * | 2020-07-21 | 2020-10-16 | 西南石油大学 | Braking control method for rail electric engineering vehicle |
| CN112172531B (en) * | 2020-11-10 | 2022-04-08 | 上海拿森汽车电子有限公司 | Braking energy recovery control method and control device |
| CN114194158A (en) * | 2021-12-16 | 2022-03-18 | 吉林大学 | Active brake wheel cylinder pressure control method based on integrated electro-hydraulic brake system |
| CN116985767B (en) * | 2023-09-27 | 2023-12-19 | 万向钱潮股份公司 | Pressure adjusting method and device for electric automobile wheel cylinder |
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