CN114228683A - Electronic hydraulic brake system and control method thereof - Google Patents
Electronic hydraulic brake system and control method thereof Download PDFInfo
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- CN114228683A CN114228683A CN202111628277.5A CN202111628277A CN114228683A CN 114228683 A CN114228683 A CN 114228683A CN 202111628277 A CN202111628277 A CN 202111628277A CN 114228683 A CN114228683 A CN 114228683A
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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
- B60T13/14—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 using accumulators or reservoirs fed by pumps
- B60T13/142—Systems with master cylinder
- B60T13/147—In combination with distributor valve
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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
- B60T13/662—Electrical control in fluid-pressure brake systems characterised by specified functions of the control system components
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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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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
- G05B13/02—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric
- G05B13/04—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric involving the use of models or simulators
- G05B13/042—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric involving the use of models or simulators in which a parameter or coefficient is automatically adjusted to optimise the performance
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
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- Physics & Mathematics (AREA)
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Abstract
The invention discloses an electronic hydraulic brake system and a control method thereof, wherein the system comprises a brake pedal, a main cylinder, a hydraulic pump, a wheel brake, a liquid storage tank, a high-pressure energy accumulator, a pedal feel simulator, a hydraulic control unit and a driving motor; the driving motor drives the hydraulic pump to pump the brake fluid from the liquid storage tank into the high-pressure accumulator for storage, and the brake fluid is used as a pressure source of the system; the pedal feeling simulator is controlled by a solenoid valve, and provides brake foot feeling feedback for a driver. According to the invention, an accurate electronic hydraulic brake model is obtained, and the state of a brake system is accurately monitored; the pressure increasing valve and the pressure reducing valve are controlled according to the expected wheel cylinder pressure value and the brake system state through a nonlinear back-stepping control strategy, so that the wheel cylinder pressure is adjusted to follow the expected value, a proper parameter value is determined by adopting a phase track analysis and time domain analysis mode, the method has better robustness, the function of accurately and quickly adjusting the wheel cylinder pressure is realized, and the safety performance of a vehicle is enhanced.
Description
Technical Field
The invention belongs to the technical field of automobile brake systems, and particularly relates to an electronic hydraulic brake system and a control method thereof.
Background
The electro-hydraulic brake system has become a current research hotspot due to its high degree of modularization, compact structure, high braking efficiency and no need of vacuum devices. However, it is an electromechanical, electric and hydraulic hybrid system using electronic components to replace some mechanical components of the conventional hydraulic brake system, and therefore, the system has strong non-linear characteristics, including compressibility of brake fluid, hysteresis effect of brake pipe, damping effect of solenoid valve, etc., and it is very difficult to accurately and rapidly control the wheel cylinder pressure due to the non-linear characteristics. Therefore, how to accurately and rapidly control the pressure of the brake wheel cylinder is a hot issue of research.
Currently, in order to precisely adjust the brake cylinder pressure, many control strategies are applied in the control of automotive brake systems. For example, chinese patent application No. cn201810987791.x, entitled "a pressure control method for a decoupled electronic hydraulic brake system," adopts an integral slip film control and a PID control method to increase a brake response speed and reduce brake pressure fluctuation; the Chinese patent application No. CN201811620832.8, entitled electronic hydraulic brake system control module and pressure control method, adopts a logic gate line control method, and can effectively avoid the over-high pressure of a brake master cylinder.
However, the existing technologies are almost all control methods that are not based on models, some characteristics of the brake system are ignored in designing the control strategy and it is difficult to accurately monitor the state of the brake system. However, the requirement of accurate and rapid control of the brake cylinder pressure has high accuracy requirement on the acquired brake system state. The control strategy based on the model nonlinear back stepping method breaks through the problem, and the control performance of the system is further improved while the nonlinear characteristic of the system is considered.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, an object of the present invention is to provide an electronic hydraulic brake system and a control method thereof, which includes first performing a test on the characteristics of the electronic hydraulic brake system to establish an accurate system model, and then designing a nonlinear back-stepping control strategy that fully considers the characteristics of the system according to the system model to improve the accuracy of the control of the electronic hydraulic brake system of the vehicle and enhance the safety performance of the vehicle.
In order to achieve the above object, an electro-hydraulic brake system disclosed in a first aspect of the present invention includes a brake pedal, a master cylinder, a hydraulic pump, a wheel brake, a liquid reservoir, a high-pressure accumulator, a pedal feel simulator, a hydraulic control unit, and a driving motor;
the driving motor drives the hydraulic pump to pump brake fluid from the liquid storage tank into the high-pressure accumulator for storage, and the brake fluid is used as a pressure source of the system;
the pedal feeling simulator is controlled by a solenoid valve, and provides braking foot feeling feedback for a driver.
Further, the hydraulic control unit is composed of ten electromagnetic valves:
the two normally-open electromagnetic valves are used as isolation valves, and have the function of isolating the master cylinder from the wheel cylinder when the electronic hydraulic brake system works, so that the master cylinder and the wheel cylinder are decoupled;
four normally closed linear solenoid valves are used for the pressure increase valves of the four wheel cylinders;
two normally closed linear solenoid valves are used for reducing valves of front wheel cylinders;
two normally open linear solenoid valves are used for the pressure reducing valve of the rear wheel cylinder.
Further, the front wheel loop where the isolation valve is located is used as a failure backup loop: when the system is powered off, the isolating valve keeps a power-off opening state, a driver steps on a brake pedal to build pressure in a main cylinder, and brake fluid flows to two front wheels from the main cylinder through the isolating valve to realize braking; when the brake is released, the driver releases the pedal, and the brake fluid returns along the original path.
A control method of an electro-hydraulic brake system disclosed in a second aspect of the present invention includes the steps of:
step 1: the following tests were performed on the component characteristics of the electro-hydraulic brake system: response characteristic test of the hydraulic pump, characteristic test of all linear solenoid valves and characteristic test of the high-pressure accumulator;
step 2: according to the tested element characteristic parameters, an electronic hydraulic brake system model is established to improve the control precision of the electronic hydraulic brake system, and the model is simplified on the basis to establish a single-wheel brake system model;
and step 3: designing a nonlinear backstepping control strategy based on the single-wheel braking system model to ensure that the pressure of a wheel cylinder is quickly and accurately controlled when an electronic hydraulic system works;
and 4, step 4: and determining suitable parameter values in the nonlinear back-stepping control strategy by adopting a phase trajectory analysis and time domain analysis mode.
Further, the hydraulic pump response characteristic test includes: testing the response characteristic of the hydraulic pump under the no-load condition and testing the response characteristic of the hydraulic pump under the load condition;
the all linear solenoid valve characteristic tests comprise: testing the increasing and reducing characteristics of the linear solenoid valve under different duty ratios; and (3) solenoid valve delay time testing:
the high pressure accumulator characteristic test comprises: testing the liquid charging characteristic of the high-pressure accumulator; and (5) testing the liquid discharge characteristic of the high-pressure accumulator.
Further, the single-wheel brake system model in step 2 includes: the system comprises a pressure source, a booster valve, a pressure reducing valve, a brake pipeline, a brake caliper and wheels, and comprises the compressibility of brake fluid, the damping effect of an electromagnetic valve and the system nonlinear characteristics of the hydraulic resistance, the hydraulic capacity and the hydraulic induction effect of the brake pipeline.
Further, the modeling of the single-wheel brake system in the step 2 adopts a power bonding diagram method to establish a model, and bonding primitives include Se, Sf, I, C, R, MR, TF, 0 and 1, wherein Se and Sf represent a potential source and a flow source respectively, I, C, R and MR represent an inertia element, a capacitive element, a resistive element and a modulation resistive element respectively, TF represents a converter of conversion relation between different energies in the system, 0 represents a node with the same energy form and the same potential variable size in the system and is called a common potential node, and 1 is a node with the same energy form and the same flow variable size in the system and is called a common flow node; the concrete modeling comprises 4 steps:
1) determining the representation mode of each element in the bonding graphic element: a potential source Se is selected to represent a system pressure source (31), and a pressure increasing valve (32) and a pressure reducing valve (36) in the HCU use a resistive element R to describe the damping effect of the electromagnetic valve; the liquid resistance effect, the liquid capacity effect and the liquid induction effect of the brake pipeline (33) are respectively represented by a resistance element R, a capacity element C and an inertia element I; the liquid capacity effect of the brake liquid in the wheel cylinder is represented by a capacitive element C; the pad is regarded as an elastic damping system, the elastic and damping effects of which are represented by capacitive and resistive elements C and R, respectively; describing the movement of the pads and pistons with inertial element I; converting hydraulic energy into mechanical energy and expressing the mechanical energy by using a converter TF;
2) finding out points with the same potential energy in the system, marking the points as 0-junctions, finding out nodes with the same flow energy, marking the nodes as 1-junctions, connecting a capacitive element C simulating a capacitive effect to the 0-junctions, and connecting a resistive element R simulating a resistive effect and an inertial element I simulating an inertial effect to the 1-junctions;
3) labeling the correct power flow direction: the friction pad and the brake disc have the functions of converting pressure into braking torque on the brake disc, converting positive pressure acting on the brake disc into friction force by using a modulation resistive element MR, and converting the friction force into the braking torque by using a converter TF;
4) the bonding diagram is further simplified, and the causal relationship is marked as follows: firstly, taking the generalized momentum corresponding to the inertial element I and the generalized displacement corresponding to the capacitive element C as state variables; taking the potential of the Se element and the flow of the Sf element as input variables; calculating output variables of the energy storage element and the resistive element according to a characteristic equation of the energy storage element and the resistive element in the bonding diagram; column writing out potential equation and flow equation of expression sum; substituting output variables of the energy storage element and the resistive element in the bonding diagram into each potential equation and flow equation, correcting the wheel cylinder pressure by adopting a first-order inertia loop order, and obtaining a mathematical expression of a system model by simplifying and arranging as follows:
in the formula, P4Is the pressure at the outlet of the pressure increasing valve (32) and the inlet of the pressure reducing valve (36); cd2And Cd5The flow coefficients of the pressure increasing valve (32) and the pressure reducing valve (36), respectively; a. the2And A5The maximum flow areas of the pressure increase valve (32) and the pressure decrease valve (36), respectively; c4The liquid volume of the brake liquid in the wheel cylinder; ρ is the density of the brake fluid; p0Is the pressure of the pressure source; p15Is the pressure at the outlet of the booster valve (32); v8Is the speed of movement of the friction pad; a is the bottom area of the piston in the wheel cylinder; m is8Is the equivalent mass of the brake caliper (34); r12Is an equivalent damping coefficient of the brake caliper (34); k is a radical of13Is the equivalent spring constant of the brake caliper (34); x13Is the displacement of the friction pad; pWCIs the wheel cylinder pressure; t is the inertial time constant; u. of1And u2Is the duty cycle control signal of the pressure increasing valve (32) and the pressure reducing valve (36), namely the input of the system, and the value thereof is between 0 and 1;
standardizing state variables of different orders in the system to obtain a system model:
in the formula (I), the compound is shown in the specification,
g1=10,
is an input to the system.
Further, in step 3, the design process of the nonlinear back-stepping control strategy comprises the following steps:
first, an error variable of a first state variable is defined:
e1=x1-x1d
in the formula, x1dIs a state variable x1The expected value of (d);
then a first Lyapunov function V is selected1:
For the first Lyapunov function V1Obtaining the components:
in the formula, x2Is a virtual control variable, x2The expected values of (c) are:
in the formula, k1>0;
When x is2Take the above formula expected value x2dWhen it is, then there areAccording to the Lyapunov progressive stability theorem, the error variable e1Is known;
second step, in order to guarantee the state variable x2Can be stabilized to a desired value x2dDefining a second error variable:
e2=x2-x2d
selecting a second Lyapunov function V2:
For the second Lyapunov function V2Obtaining the components:
x3is a virtual variable at this time, and x is known from the above expression3Is expected value x3dComprises the following steps:
in the formula, k2>0;
If x3Can be stabilized to its desired value x3dThen can be calculatedThus obtaining an error variable e1And e2Is progressively stable;
third, to further ensure the state variable x3Can reach its desired value x3dDefining a third error variable:
e3=x3-x3d
selecting a third Lyapunov function V3:
Calculating said third Lyapunov function V3Differentiation:
if a suitable value can be found that satisfies the above formula, thenI.e. the error variable e1、e2And e3Is progressively stable;
in the formula, k3>0;
For a system of differential state equations, the control input is U and the output is x3And the design combined with the control strategy can obtain:
x3dis the desired value, x, of the control strategy1And x2Is expected to pass through x3dTo obtain x3dCalculated from the mathematical expression of the system model:
in the formula, PWCdIs a desired value of the wheel cylinder pressure;
and fourthly, obtaining a system electromagnetic valve control law:
the true control input to the braking system is u1And u2Duty cycles of the PWM control signals representing the pressure increasing valve (32) and the pressure reducing valve (36), respectively; in a brake system, a pressure increasing valve (32) and a pressure reducing valve (36) are not always open at the same time: when the brake system is pressurized, the pressure increasing valve (32) is opened, and the pressure reducing valve (36) is closed, namely u20; when the system is depressurized, the pressure increasing valve (32) is closed, and the pressure reducing valve (36) is opened, i.e. u10; when the system maintains pressure, the pressure increasing valve (32) and the pressure reducing valve (36) are both closed, i.e. u10 and u20; the control law of the solenoid valve is therefore:
in the formula, e4Is the actual wheel cylinder pressure PWCWith the desired wheel cylinder pressure PWCdIs expressed as: e.g. of the type4=PWC-PWCd: at this time, the pressure increasing valve (32) and the pressure reducing valve (36) are controlled according to the expected wheel cylinder pressure value and the state of the brake system, so that the wheel cylinder pressure is adjusted to follow the expected value.
Further, in step 4, phase trajectory analysis and time domain analysis are used for determining a parameter k in the nonlinear back stepping control strategy1,k2And k3(ii) a The method comprises the following specific steps: carrying out simulation experiments by adopting a Matlab/Simulink simulation platform, setting the pressure of a pressure source of a brake system and the target pressure of an ideal wheel cylinder, and selecting proper k according to simulation results1,k2And k3And the following speed of the brake system is ensured, and the control precision of the system is ensured.
The invention has the following beneficial effects:
1) the electronic hydraulic brake system tests the element characteristics of the system, establishes an accurate electronic hydraulic brake system model, identifies parameters of the brake system model which are difficult to directly acquire, acquires the accurate electronic hydraulic brake model and realizes accurate monitoring of the state of the brake system.
2) The nonlinear back-stepping control strategy controls the pressure increasing valve and the pressure reducing valve according to the expected wheel cylinder pressure value and the state of the brake system, so that the wheel cylinder pressure is adjusted to follow the expected value, and a proper parameter value is determined by adopting a phase track analysis and time domain analysis mode. The method has better robustness, can realize the function of accurately and quickly adjusting the pressure of the wheel cylinder, and enhances the safety performance of the vehicle.
Drawings
FIG. 1 is a schematic diagram of the electro-hydraulic brake system of the present invention;
FIG. 2 is a simplified model diagram of a single-wheel brake system of the present invention;
FIG. 3 is a schematic diagram of a single wheel brake system in accordance with the present invention;
in FIG. 1, 1-pedal feel simulator; 2-pedal feel simulator solenoid control valve; 3-a brake pedal; 4-a master cylinder; 5-a liquid storage tank; 6-pressure sensor a; 7-left side wheel normally open type electromagnetic isolation valve; 8-pressure sensor b; 9-a high pressure accumulator; 10-a drive motor; 11-a hydraulic pump; 12-a left front wheel normally closed linear electromagnetic booster valve; 13-left rear wheel normally open type linear electromagnetic pressure reducing valve; 14-left front wheel normally closed linear electromagnetic pressure reducing valve; 15-left front wheel brake; 16-pressure sensor c; 17-left rear wheel brake; 18-pressure sensor d; 19-a normally closed linear electromagnetic pressure increasing valve for the left rear wheel; 20-right front wheel normally closed linear electromagnetic pressure reducing valve; 21-pressure sensor e; 22-right front wheel brake; 23-pressure sensor f; 24-right rear wheel brake; 25-right rear wheel normally open type linear electromagnetic pressure reducing valve; 26-right rear wheel normally closed linear electromagnetic pressure increasing valve; 27-a hydraulic control unit; 28-right front wheel normally closed linear electromagnetic booster valve; 29-right wheel normally open type electromagnetic isolation valve; 30-pressure sensor g.
In FIG. 2, 31-pressure source; 32, a first step of removing the first layer; a pressure increasing valve; 33-brake line; 34-a brake caliper; 35-pressure reducing valve.
In FIG. 3, Se at S00Is the pressure source 31, 1 at S1 is the node of equal flow at the pressurization valve 32, R at S22Is the damping effect of the pressure increasing valve 32, 0 at S3 is the same pressure junction at the outlet of the pressure increasing valve 32 and the inlet of the pressure reducing valve 36,c at S44Is the liquid volume effect of the brake fluid in the wheel cylinder, R at S55Is the damping effect of the pressure reducing valve 36, TF at S6 is the converter converting hydraulic energy into mechanical energy, 1 at S7 is the junction point of the same speed as the brake caliper 34 is moving, I at S88Is the inertia effect of the brake caliper 34, 0 at S9 is the node of the brake caliper 34 with the same acting force, 1 at S10 is the node of the brake caliper 34 with the same moving speed of the equivalent spring damping system, and Se at S1111Is the positive pressure of the brake caliper acting on the brake disc, R at S1212Is the damping effect of the equivalent spring damping system of the brake caliper 34, C at S1313Is the spring effect of the equivalent spring damping system of the brake caliper 34, 1 at S14 is the same flow node at the relief valve 36, Se at S1515Is the pressure at the outlet of the pressure reducing valve 36.
Detailed Description
The invention is further described with reference to the accompanying drawings, but the invention is not limited in any way, and any alterations or substitutions based on the teaching of the invention are within the scope of the invention.
Aiming at the defects of the prior art, the electronic hydraulic brake system and the control method thereof firstly establish an accurate system model by performing test on the characteristics of the electronic hydraulic brake system, and then design a nonlinear back stepping control strategy fully considering the characteristics of the system according to the system model so as to improve the control accuracy of the automobile electronic hydraulic brake system and enhance the safety performance of a vehicle.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention relates to an electronic hydraulic brake system, which comprises a brake pedal 3, a master cylinder 4, a driving motor 10, a hydraulic pump 11, a liquid storage tank 5, a high-pressure energy accumulator 9, a pedal feeling simulator 1, a hydraulic control unit 27, a left front wheel brake 15, a left rear wheel brake 17, a right front wheel brake 22, a right rear wheel brake 24 and the like, wherein a vacuum booster in the traditional hydraulic brake system is omitted, electric power is used as a power source, and the driving motor 10 drives the hydraulic pump 11 to pump brake liquid from the liquid storage tank 5 into the high-pressure energy accumulator 9 for storage, so that the brake liquid is used as the pressure source of the system.
The pedal feel simulator 1 is controlled by the electromagnetic control valve 2 of the pedal feel simulator, and provides more comfortable brake foot feel feedback for a driver.
The hydraulic control unit 27 is composed of ten solenoid valves: wherein the two normally open solenoid valves serving as the isolation valve include: the left-side wheel normally-open type electromagnetic isolation valve 7 and the right-side wheel normally-open type electromagnetic isolation valve 29 have the function of isolating the master cylinder from the wheel cylinder when the electronic hydraulic brake system works, so that the master cylinder and the wheel cylinder are decoupled; the pressure increase valves of the four normally closed type linear solenoid valves for the four wheel cylinders include: a left front wheel normally closed linear electromagnetic booster valve 12, a left rear wheel normally closed linear electromagnetic booster valve 19, a right rear wheel normally closed linear electromagnetic booster valve 26, and a right front wheel normally closed linear electromagnetic booster valve 28; the pressure reducing valve for the front wheel cylinder using two normally closed linear solenoid valves includes: a left front wheel normally closed type linear solenoid pressure reducing valve 14 and a right front wheel normally closed type linear solenoid pressure reducing valve 20; the pressure reducing valve for a rear wheel cylinder using two normally open linear solenoid valves includes: a left rear wheel normally open type linear electromagnetic pressure reducing valve 13, and a right rear wheel normally open type linear electromagnetic pressure reducing valve 25. The front wheel loop where the left-side wheel normally-open type electromagnetic isolation valve 7 and the right-side wheel normally-open type electromagnetic isolation valve 29 are located is used as a failure backup loop: when the system is powered off, the left wheel normally-open type electromagnetic isolation valve 7 and the right wheel normally-open type electromagnetic isolation valve 29 are kept in a power-off opening state, a driver steps on the brake pedal 3 to build pressure in the master cylinder 4, and brake fluid flows to the two front wheels from the master cylinder 4 through the left wheel normally-open type electromagnetic isolation valve 7 and the right wheel normally-open type electromagnetic isolation valve 29 to realize braking; when the brake is released, the driver releases the brake pedal 3, and the brake fluid returns along the original path.
The invention discloses a control method of an electronic hydraulic brake system, which is based on the system and comprises the following steps:
step 1: testing the element characteristics of the automotive electronic hydraulic brake system: a hydraulic pump 11 response characteristic test, an all-linear solenoid valve characteristic test and a high pressure accumulator 9 characteristic test.
Step 2: and establishing an accurate electronic hydraulic brake system model according to the tested element characteristic parameters so as to improve the control accuracy of the electronic hydraulic brake system. On the basis, the model is simplified, and a single-wheel braking system model is established to facilitate analysis and operation.
And step 3: based on the established single-wheel braking system model, a nonlinear backstepping control strategy is designed, and the pressure of a wheel cylinder is rapidly and accurately controlled when the electronic hydraulic system works.
And 4, step 4: and determining appropriate parameter values in the nonlinear back-stepping control strategy by adopting a phase trajectory analysis and time domain analysis mode.
Preferably, the hydraulic pump 11 response characteristic test in step 1 includes: testing the response characteristic of the hydraulic pump 11 under the no-load condition; the response characteristic of the hydraulic pump 11 under load is tested.
Preferably, all the linear solenoid valve characteristic tests in step 1 include: testing the increasing and reducing characteristics of the linear solenoid valve under different duty ratios; and (5) testing the delay time of the solenoid valve.
Preferably, the characteristic test of the high-pressure accumulator 9 in the step 1 includes: testing the charging characteristic of the high-pressure accumulator 9; and (5) testing the liquid discharging characteristic of the high-pressure accumulator 9.
Preferably, the single-wheel brake system model in step 2 includes: the pressure source 31, the pressure increasing valve 32, the pressure reducing valve 36, the brake pipe 33, the brake caliper 34, the wheel 35 and other elements, and the system nonlinear characteristics such as compressibility of brake fluid, damping effect of the electromagnetic valve, and fluid resistance, fluid capacity, fluid sensing effect of the brake pipe are considered.
Preferably, the modeling of the single-wheel brake system in the step 2 adopts a power bonding diagram method to establish a model, and the bonding primitives used include Se, Sf, I, C, R, MR, TF, 0 and 1. Wherein Se and Sf represent a potential source and a flow source respectively, I, C, R and MR represent an inertia element, a capacitive element, a resistive element and a modulation resistive element respectively, TF represents a converter for converting relations among different energies in the system, 0 represents a node with the same energy form and the same potential variable size in the system and is called a common potential node, and 1 is a node with the same energy form and the same flow variable size in the system and is called a common flow node. The concrete modeling comprises 4 steps:
1) determining the representation mode of each element in the bonding graphic element: the potential source Se is selected to represent the system pressure source 31, and the pressure increasing valve 32 and the pressure reducing valve 36 in the HCU use a resistive element R to describe the damping effect of the electromagnetic valve; the liquid resistance effect, the liquid capacity effect and the liquid induction effect of the brake pipeline 33 are respectively represented by a resistance element R, a capacity element C and an inertia element I; the brake caliper 34 is a relatively complex part, and the fluid capacity effect of the brake fluid in the wheel cylinder is represented by a capacitive element C; the pad is regarded as an elastic damping system, the elastic and damping effects of which are represented by capacitive and resistive elements C and R, respectively; the inertia element I is used for describing the movement of moving parts such as a friction pad, a piston and the like; the conversion of hydraulic energy into mechanical energy is represented using the converter TF.
2) And finding out points with the same potential energy in the system, marking as 0-junctions, finding out nodes with the same flow energy, marking as 1-junctions, connecting a capacitive element C simulating a capacitive effect to the 0-junctions, and connecting a resistive element R simulating a resistive effect and an inertial element I simulating an inertial effect to the 1-junctions.
3) Labeling the correct power flow direction: the pad acts on the brake disc to convert the pressure into a braking torque on the brake disc, the positive pressure acting on the brake disc can be converted into a friction force with the modulated resistive element MR, and the friction force can then be converted into a braking torque with the converter TF.
4) The bonding diagram is further simplified, and appropriate causal relationships are labeled: firstly, taking the generalized momentum corresponding to the inertial element I and the generalized displacement corresponding to the capacitive element C as state variables; taking the potential of the Se element and the flow of the Sf element as input variables; calculating output variables of the energy storage element and the resistive element according to a characteristic equation of the energy storage element and the resistive element in the bonding diagram; column writing out potential equation and flow equation of expression sum; substituting output variables of the energy storage element and the resistive element in the bonding diagram into each potential equation and flow equation, correcting the wheel cylinder pressure by adopting a first-order inertia loop order, and simplifying and arranging to obtain a mathematical expression of the system model:
in the formula, P4Is the outlet of the pressure increasing valve 32 and the pressure decreasing valveThe pressure at the inlet of the pressure valve 36; cd2And Cd5The flow coefficients of the pressure increasing valve 32 and the pressure reducing valve 36, respectively; a. the2And A5The maximum flow areas of the pressure increasing valve 32 and the pressure reducing valve 36, respectively; c4The liquid volume of the brake liquid in the wheel cylinder; ρ is the density of the brake fluid; p0Is the pressure of the pressure source; p15Is the pressure at the outlet of the booster valve 32; v8Is the speed of movement of the friction pad; a is the bottom area of the piston in the wheel cylinder; m is8Is the equivalent mass of the brake caliper 34; r12Is the equivalent damping coefficient of the brake caliper 34; k is a radical of13Is the equivalent spring constant of the brake caliper 34; x13Is the displacement of the friction pad; pWCIs the wheel cylinder pressure; t is the inertial time constant; u. of1And u2Is the duty cycle control signal for the pressure increasing valve 32 and the pressure reducing valve 36, i.e. the input to the system, which has a value between 0 and 1.
Standardizing state variables of different orders in the system to obtain a system model:
Preferably, in step 3, the design process of the nonlinear back-stepping control strategy specifically includes 4 steps:
1) first, an error variable of a first state variable is defined:
e1=x1-x1d
in the formula, x1dIs a state variable x1Is calculated from the expected value of (c).
Then a first Lyapunov function V is selected1:
To lyapunov function V1Obtaining the components:
in the above formula, x2Is a virtual control variable. It can be seen that x2The expected values of (c) are:
in the formula, k1>0。
Obviously, when x2Take the above formula expected value x2dWhen it is, then there areAccording to the Lyapunov progressive stability theorem, the error variable e1Is known.
2) Second step, in order to guarantee the state variable x2Can be stabilized to a desired value x2dDefining a second error variable:
e2=x2-x2d
similarly, a second Lyapunov function V is selected2:
To lyapunov function V2Obtaining the components:
obviously, x3Is the virtual variable at this time. From the above formula, x3Is expected value x3dComprises the following steps:
in the formula, k2>0。
Also, if x3Can be stabilized to its desired value x3dThen can be calculatedThus obtaining an error variable e1And e2Is progressively stable.
3) Third, to further ensure the state variable x3Can reach its desired value x3dDefining a third error variable:
e3=x3-x3d
selecting a third Lyapunov function V3:
Lyapunov function V3Differentiation:
if a suitable value can be found that satisfies the above formula, thenI.e. the error variable e1、e2And e3Is progressively stable.
In the formula, k3>0。
For a system of differential state equations, the control input is U and the output is x3And the design combined with the control strategy can obtain:
x3dis a desired value of the control strategy, therefore, x1And x2Can be calculated by x3dThus obtaining the product. x is the number of3dCan be calculated from the mathematical expression of the system model:
in the formula, PWCdIs the expected value of the wheel cylinder pressure.
4) And fourthly, obtaining a system electromagnetic valve control law:
the true control input to the braking system is u1And u2Which represent the duty cycles of the PWM control signals for the pressure increasing valve 32 and the pressure decreasing valve 36, respectively. In a braking system, the pressure increasing valve 32 and the pressure reducing valve 36 are not always opened at the same time: when the brake system is pressurized, the pressure increasing valve 32 is opened and the pressure reducing valve 36 is closed, i.e. u20; when the system is depressurized, the pressure increasing valve 32 is closed and the pressure reducing valve 36 is opened, i.e. u10; while maintaining the pressure in the system, the pressure increasing valve 32 and the pressure reducing valve 36 are both closed, i.e. u10 and u20; the control law of the solenoid valve is therefore:
in the formula, e4Is the actual wheel cylinder pressure PWCWith the desired wheel cylinder pressure PWCdIs expressed as: e.g. of the type4=PWC-PWCd. At this time, according to the expected wheel cylinder pressure value and the brake system state,the pressure increasing valve 32 and the pressure reducing valve 36 are controlled to adjust the wheel cylinder pressure to follow a desired value.
Preferably, the phase trajectory analysis and the time domain analysis in step 4 are used for determining the parameter k in the nonlinear back-stepping control strategy1,k2And k3. A Matlab/Simulink simulation platform can be adopted to carry out simulation experiments, the pressure of a pressure source of a brake system and the target pressure of an ideal wheel cylinder are set, and a proper k is selected according to a simulation result1,k2And k3And the following speed of the brake system is ensured, and the control precision of the system is ensured.
The invention has the following beneficial effects:
1) the electronic hydraulic brake system tests the element characteristics of the system, establishes an accurate electronic hydraulic brake system model, identifies parameters of the brake system model which are difficult to directly acquire, acquires the accurate electronic hydraulic brake model and realizes accurate monitoring of the state of the brake system.
2) The nonlinear back-stepping control strategy controls the pressure increasing valve and the pressure reducing valve according to the expected wheel cylinder pressure value and the state of the brake system, so that the wheel cylinder pressure is adjusted to follow the expected value, and a proper parameter value is determined by adopting a phase track analysis and time domain analysis mode. The method has better robustness, can realize the function of accurately and quickly adjusting the pressure of the wheel cylinder, and enhances the safety performance of the vehicle.
The word "preferred" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "preferred" is not necessarily to be construed as advantageous over other aspects or designs. Rather, use of the word "preferred" is intended to present concepts in a concrete fashion. The term "or" as used in this application is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless specified otherwise or clear from context, "X employs A or B" is intended to include either of the permutations as a matter of course. That is, if X employs A; b is used as X; or X employs both A and B, then "X employs A or B" is satisfied in any of the foregoing examples.
Also, although the disclosure has been shown and described with respect to one or an implementation, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The present disclosure includes all such modifications and alterations, and is limited only by the scope of the appended claims. In particular regard to the various functions performed by the above described components (e.g., elements, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or other features of the other implementations as may be desired and advantageous for a given or particular application. Furthermore, to the extent that the terms "includes," has, "" contains, "or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term" comprising.
Each functional unit in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or a plurality of or more than one unit are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium. The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc. Each apparatus or system described above may execute the storage method in the corresponding method embodiment.
In summary, the above-mentioned embodiment is an implementation manner of the present invention, but the implementation manner of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent replacements within the protection scope of the present invention.
Claims (9)
1. An electronic hydraulic brake system comprises a brake pedal, a master cylinder, a hydraulic pump and a wheel brake, and is characterized by also comprising a liquid storage tank, a high-pressure energy accumulator, a pedal feel simulator, a hydraulic control unit and a driving motor;
the driving motor drives the hydraulic pump to pump brake fluid from the liquid storage tank into the high-pressure accumulator for storage, and the brake fluid is used as a pressure source of the system;
the pedal feeling simulator is controlled by a solenoid valve, and provides braking foot feeling feedback for a driver.
2. The electro-hydraulic brake system of claim 1, wherein the hydraulic control unit is comprised of ten solenoid valves:
the two normally-open electromagnetic valves are used as isolation valves, and have the function of isolating the master cylinder from the wheel cylinder when the electronic hydraulic brake system works, so that the master cylinder and the wheel cylinder are decoupled;
four normally closed linear solenoid valves are used for the pressure increase valves of the four wheel cylinders;
two normally closed linear solenoid valves are used for reducing valves of front wheel cylinders;
two normally open linear solenoid valves are used for the pressure reducing valve of the rear wheel cylinder.
3. The electro-hydraulic brake system of claim 2, wherein the front wheel circuit in which the isolation valve is located functions as a fail-back circuit: when the system is powered off, the isolating valve keeps a power-off opening state, a driver steps on a brake pedal to build pressure in a main cylinder, and brake fluid flows to two front wheels from the main cylinder through the isolating valve to realize braking; when the brake is released, the driver releases the pedal, and the brake fluid returns along the original path.
4. A control method of an electro-hydraulic brake system according to any one of claims 1 to 3, characterized by comprising the steps of:
step 1: the following tests were performed on the component characteristics of the electro-hydraulic brake system: response characteristic test of the hydraulic pump, characteristic test of all linear solenoid valves and characteristic test of the high-pressure accumulator;
step 2: according to the tested element characteristic parameters, an electronic hydraulic brake system model is established to improve the control precision of the electronic hydraulic brake system, and the model is simplified on the basis to establish a single-wheel brake system model;
and step 3: designing a nonlinear backstepping control strategy based on the single-wheel braking system model to ensure that the pressure of a wheel cylinder is quickly and accurately controlled when an electronic hydraulic system works;
and 4, step 4: and determining suitable parameter values in the nonlinear back-stepping control strategy by adopting a phase trajectory analysis and time domain analysis mode.
5. The control method of an electro-hydraulic brake system according to claim 4, wherein the hydraulic pump response characteristic test includes: testing the response characteristic of the hydraulic pump under the no-load condition and testing the response characteristic of the hydraulic pump under the load condition;
the all linear solenoid valve characteristic tests comprise: testing the increasing and reducing characteristics of the linear solenoid valve under different duty ratios; and (3) solenoid valve delay time testing:
the high pressure accumulator characteristic test comprises: testing the liquid charging characteristic of the high-pressure accumulator; and (5) testing the liquid discharge characteristic of the high-pressure accumulator.
6. The control method of an electro-hydraulic brake system according to claim 4, wherein the single wheel brake system model in step 2 includes: the system comprises a pressure source, a booster valve, a pressure reducing valve, a brake pipeline, a brake caliper and wheels, and comprises the compressibility of brake fluid, the damping effect of an electromagnetic valve and the system nonlinear characteristics of the hydraulic resistance, the hydraulic capacity and the hydraulic induction effect of the brake pipeline.
7. The method for controlling the electronic hydraulic brake system according to claim 6, wherein the modeling of the single-wheel brake system in step 2 is modeled by a power bonding diagram method, and the bonding primitives include Se, Sf, I, C, R, MR, TF, 0 and 1, wherein Se and Sf represent a potential source and a flow source respectively, I, C, R and MR represent an inertial element, a capacitive element, a resistive element and a modulation resistive element respectively, TF represents a converter for conversion relationship among different energies in the system, 0 represents a node with the same energy form and the same potential variable size in the system, and is called a common potential node, and 1 represents a node with the same energy form and the same flow variable size in the system, and is called a common current node; the concrete modeling comprises 4 steps:
1) determining the representation mode of each element in the bonding graphic element: a potential source Se is selected to represent a system pressure source (31), and a pressure increasing valve (32) and a pressure reducing valve (36) in the HCU use a resistive element R to describe the damping effect of the electromagnetic valve; the liquid resistance effect, the liquid capacity effect and the liquid induction effect of the brake pipeline (33) are respectively represented by a resistance element R, a capacity element C and an inertia element I; the liquid capacity effect of the brake liquid in the wheel cylinder is represented by a capacitive element C; the pad is regarded as an elastic damping system, the elastic and damping effects of which are represented by capacitive and resistive elements C and R, respectively; describing the movement of the pads and pistons with inertial element I; converting hydraulic energy into mechanical energy and expressing the mechanical energy by using a converter TF;
2) finding out points with the same potential energy in the system, marking the points as 0-junctions, finding out nodes with the same flow energy, marking the nodes as 1-junctions, connecting a capacitive element C simulating a capacitive effect to the 0-junctions, and connecting a resistive element R simulating a resistive effect and an inertial element I simulating an inertial effect to the 1-junctions;
3) labeling the correct power flow direction: the friction pad and the brake disc have the functions of converting pressure into braking torque on the brake disc, converting positive pressure acting on the brake disc into friction force by using a modulation resistive element MR, and converting the friction force into the braking torque by using a converter TF;
4) the bonding diagram is further simplified, and the causal relationship is marked as follows: firstly, taking the generalized momentum corresponding to the inertial element I and the generalized displacement corresponding to the capacitive element C as state variables; taking the potential of the Se element and the flow of the Sf element as input variables; calculating output variables of the energy storage element and the resistive element according to a characteristic equation of the energy storage element and the resistive element in the bonding diagram; column writing out potential equation and flow equation of expression sum; substituting output variables of the energy storage element and the resistive element in the bonding diagram into each potential equation and flow equation, correcting the wheel cylinder pressure by adopting a first-order inertia loop order, and obtaining a mathematical expression of a system model by simplifying and arranging as follows:
in the formula, P4Is the pressure at the outlet of the pressure increasing valve (32) and the inlet of the pressure reducing valve (36); cd2And Cd5The flow coefficients of the pressure increasing valve (32) and the pressure reducing valve (36), respectively; a. the2And A5The maximum flow areas of the pressure increase valve (32) and the pressure decrease valve (36), respectively; c4The liquid volume of the brake liquid in the wheel cylinder; ρ is the density of the brake fluid; p0Is the pressure of the pressure source; p15Is the pressure at the outlet of the booster valve (32); v8Is the speed of movement of the friction pad; a is the bottom area of the piston in the wheel cylinder; m is8Is the equivalent mass of the brake caliper (34); r12Is an equivalent damping coefficient of the brake caliper (34); k is a radical of13Is the equivalent spring constant of the brake caliper (34); x13Is the displacement of the friction pad; pWCIs the wheel cylinder pressure; t is the inertial time constant; u. of1And u2Is the duty cycle control signal of the pressure increasing valve (32) and the pressure reducing valve (36), namely the input of the system, and the value thereof is between 0 and 1;
standardizing state variables of different orders in the system to obtain a system model:
in the formula (I), the compound is shown in the specification,
g1=10,
is an input to the system.
8. The control method of an electro-hydraulic brake system according to claim 7, wherein in step 3, the design process of the non-linear step-back control strategy includes the steps of:
first, an error variable of a first state variable is defined:
e1=x1-x1d
in the formula, x1dIs a state variable x1The expected value of (d);
then a first Lyapunov function V is selected1:
For the first Lyapunov function V1Obtaining the components:
in the formula, x2Is a virtual control variable, x2The expected values of (c) are:
in the formula, k1>0;
When x is2Take the above formula expected value x2dWhen it is, then there areAccording to the Lyapunov progressive stability theorem, the error variable e1Is known;
second step, in order to guarantee the state variable x2Can be stabilized to a desired value x2dDefining a second error variable:
e2=x2-x2d
selecting a second Lyapunov function V2:
For the second Lyapunov function V2Obtaining the components:
x3 is a virtual variable at this time, and x is shown by the above formula3Is expected value x3dComprises the following steps:
in the formula, k2>0;
If x3Can be stabilized to its desired value x3dThen can be calculatedThus obtaining an error variable e1And e2Is progressively stable;
third, to further ensure the state variable x3Can reach its desired value x3dDefining a third error variable:
e3=x3-x3d
selecting a third Lyapunov function V3:
Calculating said third Lyapunov function V3Differentiation:
if a suitable value can be found that satisfies the above formula, thenI.e. the error variable e1、e2And e3Is progressively stable;
in the formula, k3>0;
For a system of differential state equations, the control input is U and the output is x3And the design combined with the control strategy can obtain:
x3dis the desired value, x, of the control strategy1And x2Is expected to pass through x3dTo obtain x3dCalculated from the mathematical expression of the system model:
in the formula, PWCdIs a desired value of the wheel cylinder pressure;
and fourthly, obtaining a system electromagnetic valve control law:
the true control input to the braking system is u1And u2Duty cycles of the PWM control signals representing the pressure increasing valve (32) and the pressure reducing valve (36), respectively; in a brake system, a pressure increasing valve (32) and a pressure reducing valve (36) are not always open at the same time: when the brake system is pressurized, the pressure increasing valve (32) is opened, and the pressure reducing valve (36) is closed, namely u20; when the system is depressurized, the pressure increasing valve (32) is closed, and the pressure reducing valve (36) is opened, i.e. u10; when the system maintains pressure, the pressure increasing valve (32) and the pressure reducing valve (36) are both closed, i.e. u10 and u20; the control law of the solenoid valve is therefore:
in the formula, e4Is the actual wheel cylinder pressure PWCWith the desired wheel cylinder pressure PWCdIs expressed as: e.g. of the type4=PWC-PWCd(ii) a At this time, the pressure increasing valve (32) and the pressure reducing valve (36) are controlled according to the expected wheel cylinder pressure value and the state of the brake system, so that the wheel cylinder pressure is adjusted to follow the expected value.
9. The method of controlling an electro-hydraulic brake system of claim 8, wherein the parameter k in the non-linear step-back control strategy is determined in step 4 using phase trajectory analysis and time domain analysis1,k2And k3(ii) a The method comprises the following specific steps: carrying out simulation experiment by adopting Matlab/Simulink simulation platform, and setting pressure of pressure source of brake systemAnd the target pressure of an ideal wheel cylinder, and selecting proper k according to the simulation result1,k2And k3And the following speed of the brake system is ensured, and the control precision of the system is ensured.
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