CN112706727A - Brake system with variable pedal displacement-brake force characteristics and control method thereof - Google Patents

Brake system with variable pedal displacement-brake force characteristics and control method thereof Download PDF

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Publication number
CN112706727A
CN112706727A CN202110030984.8A CN202110030984A CN112706727A CN 112706727 A CN112706727 A CN 112706727A CN 202110030984 A CN202110030984 A CN 202110030984A CN 112706727 A CN112706727 A CN 112706727A
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China
Prior art keywords
pedal
power
brake
force
flat
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CN202110030984.8A
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CN112706727B (en
Inventor
吴刚
王春燕
周青华
赵万忠
刘利峰
刘晓强
孟琦康
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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Priority to CN202110030984.8A priority Critical patent/CN112706727B/en
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Publication of CN112706727B publication Critical patent/CN112706727B/en
Priority to PCT/CN2021/138519 priority patent/WO2022148220A1/en
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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
    • B60T7/00—Brake-action initiating means
    • B60T7/02—Brake-action initiating means for personal initiation
    • B60T7/04—Brake-action initiating means for personal initiation foot actuated
    • B60T7/042—Brake-action initiating means for personal initiation foot actuated by electrical means, e.g. using travel or force sensors
    • 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
    • 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
    • B60T13/74—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 electrical assistance or drive
    • B60T13/745—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 electrical assistance or drive acting on a hydraulic system, e.g. a master cylinder
    • 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
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/18—Safety devices; Monitoring
    • B60T17/22—Devices for monitoring or checking brake systems; Signal devices
    • 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
    • B60T7/00—Brake-action initiating means
    • B60T7/02—Brake-action initiating means for personal initiation
    • B60T7/04—Brake-action initiating means for personal initiation foot actuated
    • B60T7/06—Disposition of pedal

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Regulating Braking Force (AREA)
  • Braking Systems And Boosters (AREA)

Abstract

The invention discloses a brake system with variable pedal displacement-brake force characteristics and a control method thereof. The invention can freely design the feeling of the brake pedal aiming at various braking working conditions; the system has an active braking function, and can integrate active control technologies such as regenerative energy recovery, Electronic Stability Program (ESP), Adaptive Cruise Control (ACC) and the like to realize intelligent control of the vehicle; in addition, the redundancy of the failure backup mode is increased, and the braking safety is improved.

Description

Brake system with variable pedal displacement-brake force characteristics and control method thereof
Technical Field
The invention relates to the technical field of automobile braking, in particular to a braking system with variable pedal displacement-braking force characteristics and a control method thereof.
Background
The hydraulic braking system has the characteristics of high reliability and wide application, but the traditional hydraulic braking system has the defects of strong lag, slow pressure build-up, direct interaction with pedal force and the like due to the adoption of vacuum boosting, and is not beneficial to the design in the field of intelligent driving active control, such as incapability of being compatible with regenerative braking and brake pedal feeling, incapability of meeting the safety requirement of automatic emergency braking for quickly building brake hydraulic pressure and the like. With the trend that electronization and electromotion are gradually becoming the leading trends in the field of industrial machinery, more and more electric brake systems begin to appear, and more factors are considered in the design of the brake systems: basically, the characteristics of pedal force and displacement are kept unchanged after the conventional braking function is integrated; hydraulic pressure can be quickly and actively established under the condition of emergency braking; since the frequency of electrical and electronic failures is relatively high, in order to reduce the risk of accidents, a fail-back is also one of the functions that must be considered, and so on.
The braking systems proposed at present basically aim at achieving the above-mentioned functions, and they mostly start with the decoupling of the pedal from the master cylinder pressure. The brake-by-wire mode realizes decoupling by means of a pedal feeling simulator, but the pedal feeling is different from the real brake state; some brake systems select pedal force of a driver and motor assistance to be coupled through a feedback disc, a displacement difference sensor is used for collecting inner and outer ring shape variation of the feedback disc to control the assistance, and a control algorithm is complex; other boosting systems only adopting a spring, a hydraulic cavity compensation mode and the like to control pedal force are not ideal in practical application, because when a main cylinder is directly communicated to a feedback compensation cavity through an oil way, the pedal feeling and the hydraulic pressure cannot be coordinated along with regenerative braking. In addition, under the working modes of failure backup such as motor failure and the like, the pedal needs to directly push the master cylinder for braking, the built hydraulic pressure is very limited, and some systems with assistance only utilize the assistance ratio formed by the diameter difference of the wheel cylinder and the master cylinder.
Disclosure of Invention
The invention aims to solve the technical problem of providing a brake system with variable pedal displacement-brake force characteristics and a control method thereof, aiming at the defects related in the background technology, the control rate of various pedal force curves can be designed, the individual driving requirements can be met, when the motor has problems, the failure backup can be provided through a redundancy system, and the requirements of a driver can be met on the premise of ensuring the brake safety.
The invention adopts the following technical scheme for solving the technical problems:
a brake system with variable pedal displacement-brake force characteristics comprises a base, a first power-assisted adjusting device, a second power-assisted adjusting device, a pedal mechanism, a brake master cylinder, an oil tank, a pedal displacement sensor, a pressure sensor, a hydraulic control unit and an electronic control unit;
the base, the brake master cylinder and the oil tank are all fixed on the frame, wherein the brake master cylinder is used for outputting hydraulic pressure to the hydraulic control unit, and the oil tank is used for storing and supplying hydraulic oil to the brake master cylinder;
the first power-assisted adjusting device comprises a first power-assisted motor, a driving gear, a driven gear, a bearing bush, a flat-headed nut and a flat-headed screw;
the base is provided with a first sliding chute and a second sliding chute, and sliding blocks are arranged in the first sliding chute and the second sliding chute;
the outer wall of the bearing bush is fixedly connected with the sliding block in the first sliding groove, and the axis of the bearing bush is parallel to the first sliding groove;
the outer ring of the bearing is fixedly connected with the inner wall of the bearing outer sleeve, and the inner ring of the bearing is coaxially and fixedly connected with the column body of the flat-head nut;
a flat key/spline is further arranged on the outer wall of the column body of the flat-head nut, and the working surface of the flat key/spline is parallel to the axis of the flat-head nut;
the driven gear is a hollow gear sleeved outside the flat key/spline of the flat head nut, and the inner wall of the hollow gear is matched with the flat key/spline of the flat head nut, so that the driven gear cannot rotate around the axis of the hollow gear relative to the flat head nut but can freely slide along the working surface of the flat key/spline of the flat head nut;
the first power-assisted motor is fixed on the frame, and an output shaft of the first power-assisted motor is coaxially and fixedly connected with the driving gear; the driving gear is meshed with the driven gear;
the flat head end of the flat head screw is fixedly connected with the sliding block in the second sliding groove, the axis of the flat head screw is parallel to the second sliding groove, the flat head nut is in threaded fit with the flat head screw, and the equivalent friction angle between the flat head nut and the flat head screw is larger than the thread lead angle, namely, the flat head screw has self-locking property;
the head end of the flat-head screw rod is coaxially abutted against the push rod of the brake master cylinder;
the second power-assisted adjusting device comprises a second power-assisted motor, a worm gear, a first transmission gear, a second transmission gear, a sleeve and a rack;
the sleeve is sleeved outside the rod body of the flat-head screw rod, and one end of the sleeve is coaxially and fixedly connected with the flat-head end of the flat-head screw rod; the rack is arranged on the outer wall of the sleeve and is parallel to the axis of the sleeve; the second power-assisted motor is fixed on the frame, and an output shaft of the second power-assisted motor is coaxially and fixedly connected with the worm wheel and the worm; the first transmission gear and the second transmission gear are coaxially and fixedly connected, the first transmission gear is meshed with the worm gear, and the second transmission gear is meshed with the rack;
the pedal mechanism comprises a pedal, a pedal force simulation hydraulic cylinder, an electromagnetic valve and a simulator;
the pedal force simulation hydraulic cylinder is used for feeding back pedal force, a sliding groove parallel to the axis of the cylinder body is arranged on the outer wall of the cylinder body, and a sliding block is arranged in the sliding groove; a sliding block in a sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder is fixed on the base, so that the cylinder body of the pedal force simulation hydraulic cylinder can freely slide relative to the base along the sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder; the bottom of the pedal force simulation hydraulic cylinder body is abutted against the head end of the flat-head nut and is coaxial with the flat-head nut; the pedal is connected with a push rod of the pedal force simulation hydraulic cylinder through a force arm and used for pushing the push rod of the pedal force simulation hydraulic cylinder so as to enable a cylinder body of the pedal force simulation hydraulic cylinder to push the translation nut to move; the simulator is connected with the pedal force simulation hydraulic cylinder through an electromagnetic valve and is used for controlling the pedal force simulation hydraulic cylinder to provide feedback force when the electromagnetic valve is closed;
the pedal displacement sensor is arranged at the input end of a push rod of the pedal force simulation hydraulic cylinder and used for measuring a pedal displacement signal;
the pressure sensor is arranged at the output end of the hydraulic oil pipeline of the brake master cylinder and is used for measuring the pressure of the brake master cylinder;
the hydraulic control unit is connected with the brake master cylinder through a pipeline and is used for regulating and controlling the hydraulic pressure of four wheel cylinders of the automobile;
the electronic control unit is electrically connected with the pedal displacement sensor, the electromagnetic valve, the pressure sensor, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit respectively and used for controlling the electromagnetic valve, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit to work according to sensing signals of the pedal displacement sensor and the pressure sensor.
The invention also discloses a conventional braking method of the braking system based on the variable-length brake master cylinder push rod, which comprises the following specific steps:
step A.1), a driver steps on a pedal, an electronic control unit controls an electromagnetic valve to be switched off, a pedal force simulation hydraulic cylinder is switched on with a simulator, at the moment, the body of the pedal force simulation hydraulic cylinder is not moved, and pedal feeling is completely provided by the simulator;
step A.2), the electronic control unit obtains a target total braking force F according to a pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step A.2.1), and then calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμ0/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step A.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step A.3), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: in order to ensure that the pedal force simulation hydraulic cylinder does not move forwards, the effective thrust provided by the first power-assisted motor is greater than the thrust F generated by the pedalpcI.e. F1>Fpc(ii) a The thrust generated by the pedal is equal to the pedal force F output by the simulatorpc(x)＝Fsc(x) The pedal force can be easily obtained according to the output characteristic curve of the simulator; and presetting a margin threshold value delta F for the obtained pedal force, so that the electronic control unit decides the distribution mode of the effective thrust of the first booster motor to the second booster motor as follows:
F1＝Fpc(x)+ΔF
F2＝Fmc0-Fpc(x)-ΔF
step A.4), the electronic control unit performs target thrust control of the first to second power-assisted motors:
step A.4.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step A.4.2), and meanwhile, the electronic control unit takes the measured deviation value between the output hydraulic pressure of the brake master cylinder and the target pressure as the output of a PID control algorithmCalculating the residual effective thrust F of the demand in real time1aAnd the output thrust control is carried out on the first boosting adjusting device.
The invention also discloses a method for adjusting the linear relation between the hydraulic pressure of the brake master cylinder and the pedal displacement of the brake system with variable pedal displacement-braking force characteristics, which comprises the following specific steps:
step B.1), a driver steps on a pedal, the electronic control unit controls the electromagnetic valve to be electrified, and the pedal force simulation hydraulic cylinder is disconnected from the simulator; the pedal pushes the simulation hydraulic cylinder to prop against the flat head end of the flat head nut to enable the simulation hydraulic cylinder to integrally slide along the guide rail, and force is transmitted to the flat head screw through threads;
step B.2), the electronic control unit obtains the target total braking force F according to the pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step B.2.1), and then calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμ0/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step B.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step B.3), then the electronic control unit performs assistance control on the second assistance adjusting device, and the method specifically comprises the following substeps:
step B.3.1), the controller refers to a preset pedal force characteristic curve according to the measured pedal push rod displacement signal x to obtain a reserved pedal force Fp2(x2) In order to keep the pedal force characteristics consistent, the output characteristics of the simulator are used as the reference of the pedal force characteristics during control;
step B.3.2), the electronic control unit adopts a PI control algorithm to calculate the boosting value F of the second boosting adjusting device according to the target master cylinder pressure and the master cylinder output pressure difference delta measured by the pressure sensor22＝(Kp×Δ+Ki×∫Δ)-Fp2(x)，KpIs a proportionality coefficient; kiIs an integral coefficient;
and B.4), the electronic control unit performs speed regulation control on the first power-assisted adjusting device, and the target rotating speed is determined by a preset pedal displacement-braking force characteristic curve, and the specific steps are as follows:
step B.4.1), making the integral pushing speed of the pedal push rod be vpThread lead D, gear ratio i1The first booster motor has a rotation speed of omegam1Then velocity v of the master cylinder push rodmc＝vp+ωm1×D/i1；
Step B.4.2), displacing the brake master cylinder by xmcAnd brake master cylinder pressure P0Has a functional relationship of P0＝Gm(xmc) Master cylinder displacement xmcAnd pedal displacement xpIs xmc＝Kmp xpThe characteristic curve of pedal displacement-braking force is P0＝Gm(Kmp xp)；
When K ismpThe total action length of the flat-head nut and the flat-head screw is fixed as 1, i.e. omegam1When the pedal displacement-braking force characteristic curve is equal to 0, the characteristic curve shows a conventional characteristic; when K ismp>When 1, the characteristic curve of pedal displacement-braking force shows sensitive characteristic; when K ismp<When 1, the characteristic curve of pedal displacement-braking force shows a relieving characteristic; i.e. the proportionality coefficient KmpDetermining a pedal displacement-braking force characteristic of the braking system;
step B.4.3), further calculating a rotating speed control target of the first power assisting device:
Kmp＝xmc/xp＝dxmc/dxp＝vmc/vp＝1+D×ωm1/(i1×vp)
ωm1＝(Kmp-1)(i1×vp)/D
wherein dx ismcIs the brake master cylinder push rod displacement; dx (x)pIs the pedal push rod displacement;
step B.4.5), determining a coefficient K according to the sensitivity degree of a preset pedal displacement-braking force sensitivity characteristic curvemp；
Step B.5), the electronic control unit controls the target omega according to the rotating speedm1Controlling the first booster motor to work and providing reserved booster Fp2(x2) The brake master cylinder push rod is pushed together with a sleeve at the output end of the second boosting adjusting device so as to establish hydraulic pressure, and the function of changing the pedal displacement-braking force characteristic is realized;
and B.6) while the first power-assisted adjusting device provides power assistance, forces with equal magnitude and opposite directions are generated at the two ends of the flat-head nut, the force at the end of the flat-head screw is used for helping to establish the hydraulic pressure of the master cylinder, and the pedal force fed back to the driver is generated at one end of the pedal simulation cylinder.
The invention also discloses an active braking method of the braking system with variable pedal displacement-braking force characteristics, which comprises the following specific steps:
step C.1), the electronic control unit controls the electromagnetic valve to be switched on, and the pedal force simulation hydraulic cylinder and the simulator are switched off;
step C.2), the electronic control unit calculates the target total braking force according to the emergency degree of the current working condition and gives the maximum braking force demand F of the braking systemμmax；
Step C.3), calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμmax/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step C.4), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμmax
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step C.5), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: in order to ensure that a driver can strongly press the brake pedal to push the pedal force simulation hydraulic cylinder to assist braking in an emergency, the effective thrust provided by the first power-assisted motor does not exceed the maximum pedal force F output by the simulatorsc_maxHowever, if the output force of the first power motor is too small, the driver can easily step on the pedal and the brake pedal is mistakenly considered to be invalid, so that the lower limit value of 0.5F is set for the power motorsc_maxThen, the electronic control unit decides the distribution mode of the effective thrust of the first to second booster motors as follows:
F1＝αFsc_max(0.5<α<1)
F2＝Fmc0-F1
step C.6), the electronic control unit performs target thrust control on the first power-assisted motor, the second power-assisted motor and the third power-assisted motor:
step C.6.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step C.6.2), meanwhile, the electronic control unit takes the measured deviation value between the output hydraulic pressure of the brake master cylinder and the target pressure as the input of a PID control algorithm, and calculates the required residual effective thrust F in real time1aAnd the output thrust control is carried out on the first boosting adjusting device.
The system may provide two backups for any single failure. There are three ways of establishing hydraulic pressure in the system: the pedal establishes hydraulic pressure through a nut, a screw and a brake main cylinder push rod, the first power-assisted motor establishes hydraulic pressure through a gear reduction mechanism, the nut and the screw brake main cylinder push rod, and the second power-assisted motor establishes hydraulic pressure through a worm turbine, a sleeve, the screw and the brake main cylinder push rod. Any fault of the second power-assisted motor and the first power-assisted motor can utilize the rest normal motors to complete normal work, and braking is not affected (at the moment, the function of a high-speed electromagnetic valve needs to be played, and the characteristic of a conventional brake pedal is realized); if all the problems occur, the main cylinder is directly pushed by the pedal to establish hydraulic pressure.
Compared with the prior art, the invention adopting the technical scheme has the following technical effects:
1. the braking system of the variable-length brake master cylinder push rod can realize an active braking function and multiple failure backups to ensure the braking safety of intelligent driving through the coordinated work among all parts of the system in an intelligent driving scene, and can also realize the free design of pedal feeling by utilizing the push rod length adjusting device and the braking assistance adjusting device;
2. the brake pedal feeling can be freely designed according to various brake working conditions;
3. the system has an active braking function, and can integrate active control technologies such as regenerative energy recovery, Electronic Stability Program (ESP), Adaptive Cruise Control (ACC) and the like to realize intelligent control of the vehicle;
4. the redundancy of the failure backup mode is increased, and the braking safety is improved.
Drawings
FIG. 1 is a schematic illustration of the construction of the braking system of the present invention;
FIG. 2 is a graphical comparison of three different pedal displacement versus braking force characteristics for agility, normal and comfort in accordance with the present invention;
fig. 3 is a flow chart illustrating a conventional braking method according to the present invention.
1.1-a pedal of a pedal mechanism, 1.2-a push rod of a pedal force simulation hydraulic cylinder, 2-a pedal displacement sensor, 3.1-a cylinder body of the pedal force simulation hydraulic cylinder, 4-a base, 5-an electronic control unit, 6-a bearing bush, 7.1-a driven gear, 7.2-a driving gear, 8-a second booster motor, 9.1-a worm, 9.2-a first transmission gear, 10.1-a flat-head screw, 10.2-a flat-head nut, 11-a master cylinder pressure sensor, 12-a hydraulic control unit, 13-a master cylinder, 14-an oil tank, 15-an input shaft of the master cylinder, 16-a sleeve, 17-a first booster motor, 18-a bearing, 19-a simulator and 20-an electromagnetic valve.
Detailed Description
The technical scheme of the invention is further explained in detail by combining the attached drawings:
the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, components are exaggerated for clarity.
As shown in fig. 1, the invention discloses a brake system with variable pedal displacement-braking force characteristics, which comprises a base, a first power-assisted adjusting device, a second power-assisted adjusting device, a pedal mechanism, a brake main cylinder, an oil tank, a pedal displacement sensor, a pressure sensor, a hydraulic control unit and an electronic control unit, wherein the base is provided with a first power-assisted adjusting device and a second power-assisted adjusting device;
the base, the brake master cylinder and the oil tank are all fixed on the frame, wherein the brake master cylinder is used for outputting hydraulic pressure to the hydraulic control unit, and the oil tank is used for storing and supplying hydraulic oil to the brake master cylinder;
the first power-assisted adjusting device comprises a first power-assisted motor, a driving gear, a driven gear, a bearing bush, a flat-headed nut and a flat-headed screw;
the base is provided with a first sliding chute and a second sliding chute, and sliding blocks are arranged in the first sliding chute and the second sliding chute;
the outer wall of the bearing bush is fixedly connected with the sliding block in the first sliding groove, and the axis of the bearing bush is parallel to the first sliding groove;
the outer ring of the bearing is fixedly connected with the inner wall of the bearing outer sleeve, and the inner ring of the bearing is coaxially and fixedly connected with the column body of the flat-head nut;
a flat key/spline is further arranged on the outer wall of the column body of the flat-head nut, and the working surface of the flat key/spline is parallel to the axis of the flat-head nut;
the driven gear is a hollow gear sleeved outside the flat key/spline of the flat head nut, and the inner wall of the hollow gear is matched with the flat key/spline of the flat head nut, so that the driven gear cannot rotate around the axis of the hollow gear relative to the flat head nut but can freely slide along the working surface of the flat key/spline of the flat head nut;
the first power-assisted motor is fixed on the frame, and an output shaft of the first power-assisted motor is coaxially and fixedly connected with the driving gear; the driving gear is meshed with the driven gear;
the flat head end of the flat head screw is fixedly connected with the sliding block in the second sliding groove, the axis of the flat head screw is parallel to the second sliding groove, the flat head nut is in threaded fit with the flat head screw, and the equivalent friction angle between the flat head nut and the flat head screw is larger than the thread lead angle, namely, the flat head screw has self-locking property;
the head end of the flat-head screw rod is coaxially abutted against the push rod of the brake master cylinder;
the second power-assisted adjusting device comprises a second power-assisted motor, a worm gear, a first transmission gear, a second transmission gear, a sleeve and a rack;
the sleeve is sleeved outside the rod body of the flat-head screw rod, and one end of the sleeve is coaxially and fixedly connected with the flat-head end of the flat-head screw rod; the rack is arranged on the outer wall of the sleeve and is parallel to the axis of the sleeve; the second power-assisted motor is fixed on the frame, and an output shaft of the second power-assisted motor is coaxially and fixedly connected with the worm wheel and the worm; the first transmission gear and the second transmission gear are coaxially and fixedly connected, the first transmission gear is meshed with the worm gear, and the second transmission gear is meshed with the rack;
the pedal mechanism comprises a pedal, a pedal force simulation hydraulic cylinder, an electromagnetic valve and a simulator;
the pedal force simulation hydraulic cylinder is used for feeding back pedal force, a sliding groove parallel to the axis of the cylinder body is arranged on the outer wall of the cylinder body, and a sliding block is arranged in the sliding groove; a sliding block in a sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder is fixed on the base, so that the cylinder body of the pedal force simulation hydraulic cylinder can freely slide relative to the base along the sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder; the bottom of the pedal force simulation hydraulic cylinder body is abutted against the head end of the flat-head nut and is coaxial with the flat-head nut; the pedal is connected with a push rod of the pedal force simulation hydraulic cylinder through a force arm and used for pushing the push rod of the pedal force simulation hydraulic cylinder so as to enable a cylinder body of the pedal force simulation hydraulic cylinder to push the translation nut to move; the simulator is connected with the pedal force simulation hydraulic cylinder through an electromagnetic valve and is used for controlling the pedal force simulation hydraulic cylinder to provide feedback force when the electromagnetic valve is closed;
the pedal displacement sensor is arranged at the input end of a push rod of the pedal force simulation hydraulic cylinder and used for measuring a pedal displacement signal;
the pressure sensor is arranged at the output end of the hydraulic oil pipeline of the brake master cylinder and is used for measuring the pressure of the brake master cylinder;
the hydraulic control unit is connected with the brake master cylinder through a pipeline and is used for regulating and controlling the hydraulic pressure of four wheel cylinders of the automobile;
the electronic control unit is electrically connected with the pedal displacement sensor, the electromagnetic valve, the pressure sensor, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit respectively and used for controlling the electromagnetic valve, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit to work according to sensing signals of the pedal displacement sensor and the pressure sensor.
The invention also discloses a conventional braking method of the braking system based on the variable pedal displacement-braking force characteristic, which comprises the following specific steps:
step A.1), a driver steps on a pedal, an electronic control unit controls an electromagnetic valve to be switched off, a pedal force simulation hydraulic cylinder is switched on with a simulator, at the moment, the body of the pedal force simulation hydraulic cylinder is not moved, and pedal feeling is completely provided by the simulator;
step A.2), the electronic control unit obtains a target total braking force F according to a pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step A.2.1), depending on the brake energy efficiencyFactor C calculates the target pressure P of the master cylinder0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then: p0＝rFμ0/(2(1+β)×D2/4 XnxnXCXR), R is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step A.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step A.3), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: in order to ensure that the pedal force simulation hydraulic cylinder does not move forwards, the effective thrust provided by the first power-assisted motor is greater than the thrust F generated by the pedalpcI.e. F1>Fpc(ii) a The thrust generated by the pedal is equal to the pedal force F output by the simulatorpc(x)＝Fsc(x) The pedal force can be easily obtained according to the output characteristic curve of the simulator; and presetting a margin threshold value delta F for the obtained pedal force, so that the electronic control unit decides the distribution mode of the effective thrust of the first booster motor to the second booster motor as follows:
F1＝Fpc(x)+ΔF
F2＝Fmc0-Fpc(x)-ΔF
step A.4), the electronic control unit performs target thrust control of the first to second power-assisted motors:
step A.4.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step A.4.2), and meanwhile, the electronic control unit outputs the measured hydraulic pressure of the brake master cylinderThe deviation value of the target pressure is used as the input of a PID control algorithm, and the required residual effective thrust F is calculated in real time1aAnd the output thrust of the first boosting adjusting device is controlled, and the control block diagram is shown in figure 3.
The invention also discloses a method for adjusting the linear relation between the hydraulic pressure of the brake master cylinder and the pedal displacement of the brake system based on the variable pedal displacement-braking force characteristic, which comprises the following specific steps:
step B.1), a driver steps on a pedal, the electronic control unit controls the electromagnetic valve to be electrified, and the pedal force simulation hydraulic cylinder is disconnected from the simulator; the pedal pushes the simulation hydraulic cylinder to prop against the flat head end of the flat head nut to enable the simulation hydraulic cylinder to integrally slide along the guide rail, and force is transmitted to the flat head screw through threads;
step B.2), the electronic control unit obtains the target total braking force F according to the pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step B.2.1), and then calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμ0/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step B.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step B.3), then the electronic control unit performs assistance control on the second assistance adjusting device, and the method specifically comprises the following substeps:
step B.3.1), the controller refers to a preset pedal force characteristic curve according to the measured pedal push rod displacement signal x to obtain a reserved pedal force Fp2(x2) In order to keep the pedal force characteristics consistent, the output characteristics of the simulator are used as the reference of the pedal force characteristics during control;
step B.3.2), the electronic control unit adopts a PI control algorithm to calculate the boosting value F of the second boosting adjusting device according to the target master cylinder pressure and the master cylinder output pressure difference delta measured by the pressure sensor22＝(Kp×Δ+Ki×∫Δ)-Fp2(x)，KpIs a proportionality coefficient; kiIs an integral coefficient;
and B.4), the electronic control unit performs speed regulation control on the first power-assisted adjusting device, and the target rotating speed is determined by a preset pedal displacement-braking force characteristic curve, and the specific steps are as follows:
step B.4.1), making the integral pushing speed of the pedal push rod be vpThread lead D, gear ratio i1The first booster motor has a rotation speed of omegam1Then velocity v of the master cylinder push rodmc＝vp+ωm1×D/i1；
Step B.4.2), displacing the brake master cylinder by xmcAnd brake master cylinder pressure P0Has a functional relationship of P0＝Gm(xmc) Master cylinder displacement xmcAnd pedal displacement xpIs xmc＝Kmp xpThe characteristic curve of pedal displacement-braking force is P0＝Gm(Kmp xp)；
When K ismpThe total action length of the flat-head nut and the flat-head screw is fixed as 1, i.e. omegam1When the pedal displacement-braking force characteristic curve is equal to 0, the characteristic curve represents a conventional characteristic, such as the characteristic curve (r) in fig. 2; when K ismp>1, a characteristic curve of pedal displacement-braking force shows sensitive characteristics, such as a characteristic curve II in a graph 2; when K ismp<1 hour, pedal displacementThe braking force characteristic exhibits a soothing characteristic, such as characteristic (c) in fig. 2; i.e. the proportionality coefficient KmpDetermining a pedal displacement-braking force characteristic of the braking system;
step B.4.3), further calculating a rotating speed control target of the first power assisting device:
Kmp＝xmc/xp＝dxmc/dxp＝vmc/vp＝1+D×ωm1/(i1×vp)
ωm1＝(Kmp-1)(i1×vp)/D
wherein dx ismcIs the brake master cylinder push rod displacement; dx (x)pIs the pedal push rod displacement;
step B.4.5), determining a coefficient K according to the sensitivity degree of a preset pedal displacement-braking force sensitivity characteristic curvemp；
Step B.5), the electronic control unit controls the target omega according to the rotating speedm1Controlling the first booster motor to work and providing reserved booster Fp2(x2) The brake master cylinder push rod is pushed together with a sleeve at the output end of the second boosting adjusting device so as to establish hydraulic pressure, and the function of changing the pedal displacement-braking force characteristic is realized;
and B.6) while the first power-assisted adjusting device provides power assistance, forces with equal magnitude and opposite directions are generated at the two ends of the flat-head nut, the force at the end of the flat-head screw is used for helping to establish the hydraulic pressure of the master cylinder, and the pedal force fed back to the driver is generated at one end of the pedal simulation cylinder.
The invention also discloses an active braking method of the braking system with variable pedal displacement-braking force characteristics, which comprises the following specific steps:
step C.1), the electronic control unit controls the electromagnetic valve to be switched on, and the pedal force simulation hydraulic cylinder and the simulator are switched off;
step C.2), the electronic control unit calculates the target total braking force according to the emergency degree of the current working condition and gives the maximum braking force demand F of the braking systemμmax；
Step C.3), calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμmax/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step C.4), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμmax
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step C.5), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: in order to ensure that a driver can strongly press the brake pedal to push the pedal force simulation hydraulic cylinder to assist braking in an emergency, the effective thrust provided by the first power-assisted motor does not exceed the maximum pedal force F output by the simulatorsc_maxHowever, if the output force of the first power motor is too small, the driver can easily step on the pedal and the brake pedal is mistakenly considered to be invalid, so that the lower limit value of 0.5F is set for the power motorsc_maxThen, the electronic control unit decides the distribution mode of the effective thrust of the first to second booster motors as follows:
F1＝αFsc_max(0.5<α<1)
F2＝Fmc0-F1
step C.6), the electronic control unit performs target thrust control on the first power-assisted motor, the second power-assisted motor and the third power-assisted motor:
step C.6.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step C.6.2), and simultaneously, the electronic control unit measures the deviation value between the output hydraulic pressure of the brake master cylinder and the target pressureCalculating the required residual effective thrust F in real time as input to the PID control algorithm1aAnd the output thrust control is carried out on the first boosting adjusting device.
The system may provide two backups for any single failure. There are three ways of establishing hydraulic pressure in the system: the pedal establishes hydraulic pressure through a nut, a screw and a brake main cylinder push rod, the first power-assisted motor establishes hydraulic pressure through a gear reduction mechanism, the nut and the screw brake main cylinder push rod, and the second power-assisted motor establishes hydraulic pressure through a worm turbine, a sleeve, the screw and the brake main cylinder push rod. Any fault of the second power-assisted motor and the first power-assisted motor can utilize the rest normal motors to complete normal work, and braking is not affected (at the moment, the function of a high-speed electromagnetic valve needs to be played, and the characteristic of a conventional brake pedal is realized); if all the problems occur, the main cylinder is directly pushed by the pedal to establish hydraulic pressure.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A brake system with variable pedal displacement-brake force characteristics is characterized by comprising a base, a first power-assisted adjusting device, a second power-assisted adjusting device, a pedal mechanism, a brake main cylinder, an oil tank, a pedal displacement sensor, a pressure sensor, a hydraulic control unit and an electronic control unit;
the base, the brake master cylinder and the oil tank are all fixed on the frame, wherein the brake master cylinder is used for outputting hydraulic pressure to the hydraulic control unit, and the oil tank is used for storing and supplying hydraulic oil to the brake master cylinder;
the first power-assisted adjusting device comprises a first power-assisted motor, a driving gear, a driven gear, a bearing bush, a flat-headed nut and a flat-headed screw;
the base is provided with a first sliding chute and a second sliding chute, and sliding blocks are arranged in the first sliding chute and the second sliding chute;
the outer wall of the bearing bush is fixedly connected with the sliding block in the first sliding groove, and the axis of the bearing bush is parallel to the first sliding groove;
the outer ring of the bearing is fixedly connected with the inner wall of the bearing outer sleeve, and the inner ring of the bearing is coaxially and fixedly connected with the column body of the flat-head nut;
a flat key/spline is further arranged on the outer wall of the column body of the flat-head nut, and the working surface of the flat key/spline is parallel to the axis of the flat-head nut;
the driven gear is a hollow gear sleeved outside the flat key/spline of the flat head nut, and the inner wall of the hollow gear is matched with the flat key/spline of the flat head nut, so that the driven gear cannot rotate around the axis of the hollow gear relative to the flat head nut but can freely slide along the working surface of the flat key/spline of the flat head nut;
the first power-assisted motor is fixed on the frame, and an output shaft of the first power-assisted motor is coaxially and fixedly connected with the driving gear; the driving gear is meshed with the driven gear;
the flat head end of the flat head screw is fixedly connected with the sliding block in the second sliding groove, the axis of the flat head screw is parallel to the second sliding groove, the flat head nut is in threaded fit with the flat head screw, and the equivalent friction angle between the flat head nut and the flat head screw is larger than the thread lead angle, namely, the flat head screw has self-locking property;
the head end of the flat-head screw rod is coaxially abutted against the push rod of the brake master cylinder;
the second power-assisted adjusting device comprises a second power-assisted motor, a worm gear, a first transmission gear, a second transmission gear, a sleeve and a rack;
the sleeve is sleeved outside the rod body of the flat-head screw rod, and one end of the sleeve is coaxially and fixedly connected with the flat-head end of the flat-head screw rod; the rack is arranged on the outer wall of the sleeve and is parallel to the axis of the sleeve; the second power-assisted motor is fixed on the frame, and an output shaft of the second power-assisted motor is coaxially and fixedly connected with the worm wheel and the worm; the first transmission gear and the second transmission gear are coaxially and fixedly connected, the first transmission gear is meshed with the worm gear, and the second transmission gear is meshed with the rack;
the pedal mechanism comprises a pedal, a pedal force simulation hydraulic cylinder, an electromagnetic valve and a simulator;
the pedal force simulation hydraulic cylinder is used for feeding back pedal force, a sliding groove parallel to the axis of the cylinder body is arranged on the outer wall of the cylinder body, and a sliding block is arranged in the sliding groove; a sliding block in a sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder is fixed on the base, so that the cylinder body of the pedal force simulation hydraulic cylinder can freely slide relative to the base along the sliding groove in the outer wall of the cylinder body of the pedal force simulation hydraulic cylinder; the bottom of the pedal force simulation hydraulic cylinder body is abutted against the head end of the flat-head nut and is coaxial with the flat-head nut; the pedal is connected with a push rod of the pedal force simulation hydraulic cylinder through a force arm and used for pushing the push rod of the pedal force simulation hydraulic cylinder so as to enable a cylinder body of the pedal force simulation hydraulic cylinder to push the translation nut to move; the simulator is connected with the pedal force simulation hydraulic cylinder through an electromagnetic valve and is used for controlling the pedal force simulation hydraulic cylinder to provide feedback force when the electromagnetic valve is closed;
the pedal displacement sensor is arranged at the input end of a push rod of the pedal force simulation hydraulic cylinder and used for measuring a pedal displacement signal;
the pressure sensor is arranged at the output end of the hydraulic oil pipeline of the brake master cylinder and is used for measuring the pressure of the brake master cylinder;
the hydraulic control unit is connected with the brake master cylinder through a pipeline and is used for regulating and controlling the hydraulic pressure of four wheel cylinders of the automobile;
the electronic control unit is electrically connected with the pedal displacement sensor, the electromagnetic valve, the pressure sensor, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit respectively and used for controlling the electromagnetic valve, the first power-assisted motor, the second power-assisted motor and the hydraulic control unit to work according to sensing signals of the pedal displacement sensor and the pressure sensor.
2. The conventional braking method of the braking system based on the variable pedal displacement-braking force characteristic as claimed in claim 1, is characterized by comprising the following specific steps:
step A.1), a driver steps on a pedal, an electronic control unit controls an electromagnetic valve to be switched off, a pedal force simulation hydraulic cylinder is switched on with a simulator, at the moment, the body of the pedal force simulation hydraulic cylinder is not moved, and pedal feeling is completely provided by the simulator;
step A.2), the electronic control unit obtains a target total braking force F according to a pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step A.2.1), and then calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμ0/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step A.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step A.3), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: to ensure pedal forceThe simulation hydraulic cylinder does not move forwards, and the effective thrust provided by the first power-assisted motor is greater than the thrust F generated by the pedalpcI.e. F1>Fpc(ii) a The thrust generated by the pedal is equal to the pedal force F output by the simulatorpc(x)＝Fsc(x) The pedal force can be easily obtained according to the output characteristic curve of the simulator; and presetting a margin threshold value delta F for the obtained pedal force, so that the electronic control unit decides the distribution mode of the effective thrust of the first booster motor to the second booster motor as follows:
F1＝Fpc(x)+ΔF
F2＝Fmc0-Fpc(x)-ΔF
step A.4), the electronic control unit performs target thrust control of the first to second power-assisted motors:
step A.4.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step A.4.2), meanwhile, the electronic control unit takes the measured deviation value of the output hydraulic pressure of the brake master cylinder and the target pressure as the input of a PID control algorithm, and calculates the required residual effective thrust F in real time1aAnd the output thrust control is carried out on the first boosting adjusting device.
3. The method for adjusting the linear relation between the hydraulic pressure of the brake master cylinder and the pedal displacement of the brake system based on the variable pedal displacement-braking force characteristic as claimed in claim 1 is characterized by comprising the following specific steps:
step B.1), a driver steps on a pedal, the electronic control unit controls the electromagnetic valve to be electrified, and the pedal force simulation hydraulic cylinder is disconnected from the simulator; the pedal pushes the simulation hydraulic cylinder to prop against the flat head end of the flat head nut to enable the simulation hydraulic cylinder to integrally slide along the guide rail, and force is transmitted to the flat head screw through threads;
step B.2), the electronic control unit obtains the target total braking force F according to the pedal displacement signal of the first displacement sensor and a preset pedal displacement-braking force characteristic curveμ0M is the whole vehicle mass; a is the braking deceleration;
step B.2.1), and then calculating the target pressure of the master cylinder according to the brake energy efficiency factor CP0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμ0/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step B.2.2), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμ0
Fmc0＝F1+F2
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step B.3), then the electronic control unit performs assistance control on the second assistance adjusting device, and the method specifically comprises the following substeps:
step B.3.1), the controller refers to a preset pedal force characteristic curve according to the measured pedal push rod displacement signal x to obtain a reserved pedal force Fp2(x2) In order to keep the pedal force characteristics consistent, the output characteristics of the simulator are used as the reference of the pedal force characteristics during control;
step B.3.2), the electronic control unit adopts a PI control algorithm to calculate the boosting value F of the second boosting adjusting device according to the target master cylinder pressure and the master cylinder output pressure difference delta measured by the pressure sensor22＝(Kp×Δ+Ki×∫Δ)-Fp2(x)，KpIs a proportionality coefficient; kiIs an integral coefficient;
and B.4), the electronic control unit performs speed regulation control on the first power-assisted adjusting device, and the target rotating speed is determined by a preset pedal displacement-braking force characteristic curve, and the specific steps are as follows:
step B.4.1), making the integral pushing speed of the pedal push rod be vpThread guideRange D, gear ratio i1The first booster motor has a rotation speed of omegam1Then velocity v of the master cylinder push rodmc＝vp+ωm1×D/i1；
Step B.4.2), displacing the brake master cylinder by xmcAnd brake master cylinder pressure P0Has a functional relationship of P0＝Gm(xmc) Master cylinder displacement xmcAnd pedal displacement xpIs xmc＝Kmp xpThe characteristic curve of pedal displacement-braking force is P0＝Gm(Kmp xp)；
When K ismpThe total action length of the flat-head nut and the flat-head screw is fixed as 1, i.e. omegam1When the pedal displacement-braking force characteristic curve is equal to 0, the characteristic curve shows a conventional characteristic; when K ismp>When 1, the characteristic curve of pedal displacement-braking force shows sensitive characteristic; when K ismp<When 1, the characteristic curve of pedal displacement-braking force shows a relieving characteristic; i.e. the proportionality coefficient KmpDetermining a pedal displacement-braking force characteristic of the braking system;
step B.4.3), further calculating a rotating speed control target of the first power assisting device:
Kmp＝xmc/xp＝dxmc/dxp＝vmc/vp＝1+D×ωm1/(i1×vp)
ωm1＝(Kmp-1)(i1×vp)/D
wherein dx ismcIs the brake master cylinder push rod displacement; dx (x)pIs the pedal push rod displacement;
step B.4.5), determining a coefficient K according to the sensitivity degree of a preset pedal displacement-braking force sensitivity characteristic curvemp；
Step B.5), the electronic control unit controls the target omega according to the rotating speedm1Controlling the first booster motor to work and providing reserved booster Fp2(x2) The brake master cylinder push rod is pushed together with a sleeve at the output end of the second boosting adjusting device so as to establish hydraulic pressure, and the work of changing the pedal displacement-braking force characteristic is realizedEnergy is saved;
and B.6) while the first power-assisted adjusting device provides power assistance, forces with equal magnitude and opposite directions are generated at the two ends of the flat-head nut, the force at the end of the flat-head screw is used for helping to establish the hydraulic pressure of the master cylinder, and the pedal force fed back to the driver is generated at one end of the pedal simulation cylinder.
4. The active braking method of a braking system based on variable pedal displacement-braking force characteristics of claim 1, characterized by comprising the following specific steps:
step C.1), the electronic control unit controls the electromagnetic valve to be switched on, and the pedal force simulation hydraulic cylinder and the simulator are switched off;
step C.2), the electronic control unit calculates the target total braking force according to the emergency degree of the current working condition and gives the maximum braking force demand F of the braking systemμmax；
Step C.3), calculating the target pressure P of the master cylinder according to the brake energy efficiency factor C0And if the energy efficiency factors of the front wheel brake and the rear wheel brake are the same, then:
P0＝rFμmax/(2(1+β)×D2/4×n×C×R)
wherein r is the tire rolling radius; β is the front and rear axle brake force distribution coefficient; d is the diameter of the oil cylinder; n is the number of single-side oil cylinders; r is the brake caliper working radius;
step C.4), calculating the total thrust F to be provided by the first booster motor and the second booster motormc0I.e. by
Fmc0＝Amc×P0＝K0×Fμmax
Wherein A ismcIs the cross section area of the inner diameter of the main cylinder; k0Theoretical coefficients of thrust required for total braking force to build master cylinder pressure; f1Effective thrust provided for the first power assist device; f2Effective thrust is provided for the second power assisting device;
step C.5), the electronic control unit distributes effective thrust of the first power assisting motor to the second power assisting motor: in order to ensure that the driver can strongly press the brake pedal to drive the pedal force simulation hydraulic cylinder to assist braking in an emergency, the first booster motorThe effective thrust provided does not exceed the maximum pedal force F output by the simulatorsc_maxHowever, if the output force of the first power motor is too small, the driver can easily step on the pedal and the brake pedal is mistakenly considered to be invalid, so that the lower limit value of 0.5F is set for the power motorsc_maxThen, the electronic control unit decides the distribution mode of the effective thrust of the first to second booster motors as follows:
F1＝αFsc_max(0.5<α<1)
F2＝Fmc0-F1
step C.6), the electronic control unit performs target thrust control on the first power-assisted motor, the second power-assisted motor and the third power-assisted motor:
step C.6.1), the electronic control unit controls the second power-assisted adjusting device to firstly follow F2Outputting thrust;
step C.6.2), meanwhile, the electronic control unit takes the measured deviation value between the output hydraulic pressure of the brake master cylinder and the target pressure as the input of a PID control algorithm, and calculates the required residual effective thrust F in real time1aAnd the output thrust control is carried out on the first boosting adjusting device.
CN202110030984.8A 2021-01-11 2021-01-11 Brake system with variable pedal displacement-brake force characteristics and control method thereof Active CN112706727B (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022148220A1 (en) * 2021-01-11 2022-07-14 南京航空航天大学 Brake system having variable pedal displacement - brake force characteristic, and control method therefor
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