Method for distributing braking torque of vehicle composite brake
阅读说明：本技术 一种车辆复合制动器制动力矩的分配方法 (Method for distributing braking torque of vehicle composite brake ) 是由 何仁 苑磊 于 2019-10-24 设计创作，主要内容包括：本发明公开了一种车辆复合制动器制动力矩的分配方法,车辆复合制动器包括车轮上同时设置的电子液压制动系统和电涡流制动系统,所述电子液压制动系统和电涡流制动系统同时由复合制动系统控制器控制,所述复合制动系统控制器根据电子液压制动系统温度、电涡流制动系统温度、电涡流制动系统能够提供的最大制动力矩、电涡流制动系统功率和电子液压制动系统功率实现对电子液压制动系统和电涡流制动系统制动力矩的分配；有益效果：本发明相互替换电子液压制动和电涡流制动实现制动效率最高或能耗最低,电子液压制动反馈补偿电涡流制动减少制动性能衰减和电子液压制动系统磨损,电涡流制动前馈补偿电子液压制动迟滞特性改善制动系统的响应特性。(The invention discloses a method for distributing braking torque of a vehicle composite brake, wherein the vehicle composite brake comprises an electronic hydraulic braking system and an eddy current braking system which are arranged on a wheel at the same time, the electronic hydraulic braking system and the eddy current braking system are controlled by a composite braking system controller at the same time, and the composite braking system controller realizes the distribution of the braking torque of the electronic hydraulic braking system and the eddy current braking system according to the temperature of the electronic hydraulic braking system, the temperature of the eddy current braking system, the maximum braking torque which can be provided by the eddy current braking system, the power of the eddy current braking system and the power of the electronic hydraulic braking system; has the advantages that: the invention realizes the highest braking efficiency or the lowest energy consumption by mutually replacing the electronic hydraulic braking and the electric eddy current braking, the electronic hydraulic braking feedback compensation electric eddy current braking reduces the braking performance attenuation and the electronic hydraulic braking system abrasion, and the electric eddy current braking feedforward compensation electronic hydraulic braking hysteresis characteristic improves the response characteristic of the braking system.)
1. A method for distributing braking torque of a vehicle composite brake is characterized in that: the vehicle composite brake comprises an electronic hydraulic braking system and an eddy current braking system which are arranged on a wheel, wherein the electronic hydraulic braking system and the eddy current braking system are simultaneously controlled by a composite braking system controller, and the composite braking system controller realizes the distribution of the braking torque of the electronic hydraulic braking system and the eddy current braking system according to the temperature of the electronic hydraulic braking system, the temperature of the eddy current braking system, the maximum braking torque which can be provided by the eddy current braking system, the power of the eddy current braking system and the power of the electronic hydraulic braking system; the distribution method of the braking torque comprises the following steps:
based on the electro-hydraulic brake system temperature and the eddy current brake system temperature being compared to respective maximum safety thresholds,
a) when both are greater than respective thresholds, the braking system is at risk of failure;
b) when the temperature of the electronic hydraulic braking system is smaller than the threshold value of the electronic hydraulic braking system and the temperature of the eddy current braking system is larger than the threshold value of the electronic hydraulic braking system, the electronic hydraulic braking system does not have failure risk, the eddy current braking system has failure risk, and the electronic hydraulic braking system is adopted for braking;
c) when the temperature of the electronic hydraulic braking system is greater than the threshold value of the electronic hydraulic braking system and the temperature of the eddy current braking system is less than the threshold value of the electronic hydraulic braking system, the electronic hydraulic braking system has failure risk, the eddy current braking system does not have failure risk, and the eddy current braking system is preferentially adopted for braking;
d) when the temperature of the electronic hydraulic braking system and the temperature of the electric eddy current braking system are both smaller than the threshold values, the working states of the electric eddy current braking system and the electronic hydraulic braking system are normal, and the electric eddy current braking system can meet the braking requirements, the power consumed by the two braking systems for providing the required braking torque is respectively calculated, and when the power value of the electric eddy current braking system is lower than the power of the electronic hydraulic braking system, the independent electric eddy current braking system is adopted for braking; when the power value of the eddy current braking system is higher than the power of the electronic hydraulic braking system, the electronic hydraulic braking system is adopted to brake independently;
e) when the temperature of the electronic hydraulic braking system and the temperature of the eddy current braking system are both smaller than the threshold values, the eddy current braking system and the electronic hydraulic braking system are in normal working states, and when the maximum braking torque provided by the eddy current braking system is smaller than the braking requirement, the eddy current braking system performs compensation braking of the feedforward compensation electronic hydraulic braking system.
2. The method of distributing vehicle compound brake braking torque according to claim 1, characterized in that: calculating the maximum braking torque which can be provided by the eddy current braking system in the step c; when the required braking torque is lower than the maximum braking torque which can be provided by the eddy current braking system, the eddy current braking system is independently adopted for braking; when the required braking torque is higher than the maximum braking torque which can be provided by the eddy current braking system, the eddy current braking system provides the maximum braking torque, and the electronic hydraulic braking system provides the residual braking torque.
3. The method of distributing vehicle compound brake braking torque according to claim 1 or 2, characterized in that: and d, when the power value of the eddy current braking system is higher than the power of the electronic hydraulic braking system in the step d, the eddy current braking system carries out compensation braking of the feedforward compensation electronic hydraulic braking system.
4. The method of distributing vehicle compound brake braking torque according to claim 2, characterized in that: the maximum braking torque which can be provided by the eddy current braking system is TemaxThe maximum braking torque applied to the brake disc by the eddy current braking system is as follows:
wherein B is the magnetic induction intensity passing through the brake disc, a is the width of the cross section of the magnetic pole, B is the length of the magnetic pole surface, L is the distance from the center of the brake disc to the center of the magnetic pole, and IeEffective value of the eddy current generated on the brake disk, i instantaneous value of the eddy current generated on the brake disk, ρ' specific resistance of the brake disk, ΔhFor the skin depth of the vortex on the brake disk, murFor relative permeability, ω is the angular speed of rotation of the brake disc, μ0For vacuum permeability, N is the number of turns of the coil on the core, ImaxFor maximum current intensity of electromagnetic brake, /)gIs the air gap spacing, keIs a conversion factor.
5. The method of distributing vehicle compound brake braking torque according to claim 1, characterized in that: the power P of the eddy current brake systemBeIs calculated according to the braking torque T of the eddy current braking systemeDetermining the current
Calculating power according to the electrified current of the eddy current braking system
PBe＝I2R
Wherein R is the total resistance of the coil of the eddy current braking system.
6. Vehicle compound brake actuation according to claim 1The torque distribution method is characterized in that: the electro-hydraulic brake system includes: the brake system comprises a motor, a transmission mechanism, a hydraulic brake cylinder, an electromagnetic valve and a brake wheel cylinder; establishing an electronic hydraulic braking system model according to mathematical models of all components of the system to perform power P of the electronic hydraulic braking systemBfAnd (4) calculating.
7. The method of distributing vehicle compound brake braking torque according to claim 6, characterized in that: the motor mathematical model is
In the formula of UsTo the terminal voltage of the machine, KeFor equivalent back EMF coefficient, RmIs the equivalent internal resistance of the motor, LmIs an equivalent inductance, KtIs an equivalent motor moment coefficient, imIs an equivalent current, TmeIn order to obtain the torque of the motor,the motor rotating speed;
according to the external characteristics of the motor, the output torque of the motor is limited:
in the formula, TmIn order to actually output the torque of the motor,
thus, the power of the motor can be expressed as:
the mathematical model of the transmission mechanism is
Input torque TinAnd output torque ToutInput rotation angle thetamAnd output a displacement SoutHas a transmission relationship of
The dynamic balance equation of the motor and the transmission mechanism is expressed as
In the formula, PmFor hydraulic brake cylinder pressure, AmArea of the hydraulic brake cylinder, JsysIs the system moment of inertia, CsysFor system damping, KsFor system stiffness, TfIn order to achieve the friction torque of the system,
the mathematical model of the hydraulic brake cylinder and the electromagnetic valve is
The adopted single-cavity hydraulic brake cylinder continuous flow dynamics expression is as follows
Wherein E is the bulk modulus of elasticity of the brake fluid, QmFlow of fluid from the hydraulic brake cylinder, ViniIs the initial volume of brake fluid in the cylinder, Qv(i) The flow rate of brake fluid flowing through each electromagnetic valve;
the flow equation of the brake fluid flowing through the solenoid valve can be expressed as
In the formula, i is 1 for the high-speed solenoid valve oil inlet, i is 2 for the high-speed solenoid valve oil outlet, Cd(i) For each solenoid valve flow coefficient, Av(i) For equivalent interception of each solenoid valveArea, Pw(i) Is the wheel cylinder pressure, ρ is the brake fluid density;
the mathematical model of the brake wheel cylinder is
The relationship between the wheel cylinder pressure and the brake fluid volume is represented by the relationship curve between the brake circuit pressure and the brake fluid volume
Pw(i)＝f(Vw(i)),Vw(i)＝∫Qv(i)dt
In the formula, Vw(i) I-1 is the high pressure brake fluid volume, i-2 is the low pressure brake fluid volume, Q is the brake fluid volumev(i) The flow rate of brake fluid flowing through the electromagnetic valve;
output braking torque of disc brake
The output braking torque of the disc brake can be obtained by calculating according to the pressure of the brake wheel cylinder
Tf＝2ηcRdPw(i)Ac
In the formula, ηcCoefficient of friction between brake lining and brake disc, RdEffective radius of brake disc, AcThe area of the brake wheel cylinder piston;
the power of the electro-hydraulic brake system is a function of the output braking torque of the disc brake according to the related mathematical equations of the motor, the transmission mechanism, the hydraulic brake cylinder, the electromagnetic valve and the brake wheel cylinder
PBf＝f(Tf)。
Technical Field
The invention relates to a method for distributing braking torque of a vehicle composite brake, in particular to a method for controlling the braking torque distribution of the composite brake based on eddy current braking and electronic hydraulic braking, and belongs to the field of automobile braking systems.
Background
In the face of increasingly severe pressure on energy conservation, environmental protection, safety, traffic jam and the like, new energy automobiles and intelligent automobiles become the key points of the development of the modern automobile industry, and the trend also promotes the development of automobile braking systems to the aspects of integration, wire control, high efficiency, safety and the like.
In order to cooperate with the recovery of the braking energy of the new energy automobile and meet the requirement of intelligent auxiliary braking of the automobile, the decoupling of man-machine braking must be realized, and the electronic hydraulic braking system can realize the braking decoupling and the accurate adjustment of the wheel cylinder pressure, so the electronic hydraulic braking system has wide application prospect. Compared with electronic hydraulic braking, the eddy current braking has the advantages of good low-speed braking effect, high response speed, non-contact braking and the like, and is not restricted by the charging condition of an energy storage device and the like compared with motor feedback braking. Both electro-hydraulic braking and eddy current braking have problems with reduced, or even failure, brake overheating efficiency.
The brake force distribution optimization method of the integrated brake system of the commercial vehicle in China patent CN105292092B under different working conditions provides a brake torque distribution optimization method of a front axle friction brake, a rear axle friction brake and an eddy current brake, but does not consider the energy consumption problem of the two brake systems and the difference of the response characteristics of the two brake systems.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects in the prior art, the invention provides a method for distributing the braking torque of a vehicle composite brake. The invention can provide braking torque distribution strategies with different control targets according to different braking conditions, and achieves the purposes of considering the different requirements of different braking conditions on various braking performances and improving the braking efficiency, stability, safety and economy of the vehicle under the braking conditions.
The technical scheme is as follows: a distribution method of braking torque of a vehicle composite brake comprises an electronic hydraulic braking system and an electric eddy current braking system which are arranged on wheels, wherein the electronic hydraulic braking system and the electric eddy current braking system are simultaneously controlled by a composite braking system controller; the distribution method of the braking torque comprises the following steps:
based on the electro-hydraulic brake system temperature and the eddy current brake system temperature being compared to respective maximum safety thresholds,
based on a brake inertia bench test, a heat fading test under the continuous braking condition of a long downhill section of an automobile is simulated, a two-dimensional relation model of the braking times and the temperature is solved through least square approximation according to a test data relation graph, the temperature rising trend is further predicted, and the hydraulic braking failure temperature threshold is found out.
According to the eddy current braking torque heat fading test, obtaining an eddy current braking torque-time relation curve at a certain constant rotating speed through the test, carrying out a drag grinding test, and recording the temperature of the eddy current braking system as the highest temperature threshold of the eddy current braking system when the eddy current braking torque is smaller than 15% of the braking torque at the initial moment.
a) When both are greater than respective thresholds, the braking system is at risk of failure;
b) when the temperature of the electronic hydraulic braking system is smaller than the threshold value of the electronic hydraulic braking system and the temperature of the eddy current braking system is larger than the threshold value of the electronic hydraulic braking system, the electronic hydraulic braking system does not have failure risk, the eddy current braking system has failure risk, and the electronic hydraulic braking system is adopted for braking;
c) when the temperature of the electronic hydraulic braking system is greater than the threshold value of the electronic hydraulic braking system and the temperature of the eddy current braking system is less than the threshold value of the electronic hydraulic braking system, the electronic hydraulic braking system has failure risk, the eddy current braking system does not have failure risk, and the eddy current braking system is preferentially adopted for braking;
d) when the temperature of the electronic hydraulic braking system and the temperature of the electric eddy current braking system are both smaller than the threshold values, the working states of the electric eddy current braking system and the electronic hydraulic braking system are normal, and the electric eddy current braking system can meet the braking requirements, the power consumed by the two braking systems for providing the required braking torque is respectively calculated, and when the power value of the electric eddy current braking system is lower than the power of the electronic hydraulic braking system, the independent electric eddy current braking system is adopted for braking; when the power value of the eddy current braking system is higher than the power of the electronic hydraulic braking system, the electronic hydraulic braking system is adopted to brake independently;
e) when the temperature of the electronic hydraulic braking system and the temperature of the eddy current braking system are both smaller than the threshold values, the eddy current braking system and the electronic hydraulic braking system are in normal working states, and when the maximum braking torque provided by the eddy current braking system is smaller than the braking requirement, the eddy current braking system performs compensation braking of the feedforward compensation electronic hydraulic braking system.
Preferably, in order to avoid the use of an inefficient electro-hydraulic brake system, the maximum braking torque that can be provided by the eddy current brake system is calculated in step c; when the required braking torque is lower than the maximum braking torque which can be provided by the eddy current braking system, the eddy current braking system is independently adopted for braking; when the required braking torque is higher than the maximum braking torque which can be provided by the eddy current braking system, the eddy current braking system provides the maximum braking torque, and the electronic hydraulic braking system provides the residual braking torque.
Preferably, in order to utilize the eddy current brake to feed forward compensate the hysteresis characteristic of the electronic hydraulic brake system and improve the response characteristic of the brake system, in step d, when the power value of the eddy current brake system is higher than the power of the electronic hydraulic brake system, the eddy current brake system performs compensation braking of the feed forward compensation electronic hydraulic brake system.
Preferably, the maximum braking torque which can be provided by the eddy current braking system is TemaxThe maximum braking torque applied to the brake disc by the eddy current braking system is as follows:
wherein B is the magnetic induction intensity passing through the brake disc, a is the width of the cross section of the magnetic pole, B is the length of the magnetic pole surface, L is the distance from the center of the brake disc to the center of the magnetic pole, and IeEffective value of the eddy current generated on the brake disk, i instantaneous value of the eddy current generated on the brake disk, ρ' specific resistance of the brake disk, ΔhFor the skin depth of the vortex on the brake disk, murFor relative permeability, ω is the angular speed of rotation of the brake disc, μ0For vacuum permeability, N is the turns of the coil disturbed by the coreNumber, ImaxFor maximum current intensity of electromagnetic brake, /)gIs the air gap spacing, keIs a conversion factor.
Preferably, the eddy current braking system power PBeIs calculated according to the braking torque T of the eddy current braking systemeDetermining the current
Calculating power P according to the electrified current of the eddy current braking systemBe＝I2R
Wherein R is the total resistance of the coil of the eddy current braking system.
The electro-hydraulic brake system includes: the brake system comprises a motor, a transmission mechanism, a hydraulic brake cylinder, an electromagnetic valve and a brake wheel cylinder; establishing an electronic hydraulic braking system model according to mathematical models of all components of the system to perform power P of the electronic hydraulic braking systemBfAnd (4) calculating.
The motor mathematical model is
In the formula of UsTo the terminal voltage of the machine, KeFor equivalent back EMF coefficient, RmIs the equivalent internal resistance of the motor, LmIs an equivalent inductance, KtIs an equivalent motor moment coefficient, imIs an equivalent current, TmeIn order to obtain the torque of the motor,the motor rotating speed;
according to the external characteristics of the motor, the output torque of the motor is limited:
in the formula, TmIn order to actually output the torque of the motor,
thus, the power of the motor can be expressed as:
the mathematical model of the transmission mechanism is
Input torque TinAnd output torque ToutInput rotation angle thetamAnd output a displacement SoutHas a transmission relationship of
The dynamic balance equation of the motor and the transmission mechanism is expressed as
In the formula, PmFor hydraulic brake cylinder pressure, AmArea of the hydraulic brake cylinder, JsysIs the system moment of inertia, CsysFor system damping, KsFor system stiffness, TfIn order to achieve the friction torque of the system,
the mathematical model of the hydraulic brake cylinder and the electromagnetic valve is
The adopted single-cavity hydraulic brake cylinder continuous flow dynamics expression is as follows
Wherein E is the bulk modulus of elasticity of the brake fluid, QmFlow of fluid from the hydraulic brake cylinder, ViniIs the initial volume of brake fluid in the cylinder, Qv(i) The flow rate of brake fluid flowing through each electromagnetic valve;
the flow equation of the brake fluid flowing through the solenoid valve can be expressed as
In the formula, i is 1 for the high-speed solenoid valve oil inlet, i is 2 for the high-speed solenoid valve oil outlet, Cd(i) For each solenoid valve flow coefficient, Av(i) For equivalent shut-off area, P, of each solenoid valvew(i) Is the wheel cylinder pressure, ρ is the brake fluid density;
the mathematical model of the brake wheel cylinder is
The relationship between the wheel cylinder pressure and the brake fluid volume is represented by the relationship curve between the brake circuit pressure and the brake fluid volume
Pw(i)＝f(Vw(i)),Vw(i)＝∫Qv(i)dt
In the formula, Vw(i) I-1 is the high pressure brake fluid volume, i-2 is the low pressure brake fluid volume, Q is the brake fluid volumev(i) The flow rate of brake fluid flowing through the electromagnetic valve;
output braking torque of disc brake
The output braking torque of the disc brake can be obtained by calculating according to the pressure of the brake wheel cylinder
Tf＝2ηcRdPw(i)Ac
In the formula, ηcCoefficient of friction between brake lining and brake disc, RdEffective radius of brake disc, AcThe area of the brake wheel cylinder piston;
the power of the electro-hydraulic brake system is a function of the output braking torque of the disc brake according to the related mathematical equations of the motor, the transmission mechanism, the hydraulic brake cylinder, the electromagnetic valve and the brake wheel cylinder
PBf＝f(Tf)。
Has the advantages that: according to the invention, the braking torque is distributed according to the braking torque of the maximum eddy current braking system, the braking power of the eddy current braking system and the braking power of the electronic hydraulic braking system, the electronic hydraulic braking and the eddy current braking are mutually replaced to realize the highest braking efficiency or the lowest energy consumption, the electronic hydraulic braking feedback compensation eddy current braking reduces the braking performance attenuation and the abrasion of the electronic hydraulic braking system, the response characteristic of the braking system is improved by the eddy current braking feedforward compensation electronic hydraulic braking hysteresis characteristic, the working efficiency of the brake is improved, the energy consumption problem of the braking system is considered at the same time, and the braking stability is enhanced.
Drawings
FIG. 1 is a schematic diagram of the operation of the compound brake system of the present invention;
FIG. 2 is a flow chart of the brake torque distribution of the present invention;
fig. 3 is a flowchart of calculating the braking power of the electro-hydraulic brake system of the present invention.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.
Fig. 1 is a composite braking system based on eddy current braking and electro-hydraulic braking: the composite braking system based on the eddy current braking and the electronic hydraulic braking is composed of an eddy current braking system, an electronic hydraulic braking system, a composite braking system controller and wheels. Wherein, a wheel speed sensor is arranged on the wheel, and a brake disc in the eddy current braking system and a friction disc in the electronic hydraulic braking system are respectively provided with a temperature sensor. The basic idea is as follows: the method comprises the steps of dividing the braking working conditions into four working conditions of eddy current braking, electronic hydraulic braking feedback compensation eddy current braking and electronic eddy current braking feedforward compensation electronic hydraulic braking hysteresis, calculating the maximum braking torque, the power of an eddy current brake and the power of an electronic hydraulic brake on line through a target braking torque and a wheel speed signal according to the temperature signal of the electronic hydraulic brake, the temperature signal of the eddy current brake and the like, and dynamically distributing and optimizing the electronic hydraulic braking and the eddy current braking by adopting different braking modes according to different working conditions. The electronic hydraulic brake and the eddy current brake are mutually replaced by the distribution of the braking torque to realize the highest braking performance or the lowest energy consumption; the electronic hydraulic brake feedback compensates the eddy current brake to reduce the brake performance attenuation and the electronic hydraulic brake system abrasion; the eddy current brake feedforward compensation electro-hydraulic brake hysteresis characteristic improves the response characteristic of the brake system.
Calculation of composite brake distribution strategy conditions
During the distribution of the composite braking torque, the maximum braking torque of the eddy current brake, the power of the eddy current brake and the power of the electronic hydraulic brake need to be calculated.
(1) Maximum braking torque T of eddy current brakeemaxComputing
The braking torque applied to the brake disc by the electromagnetic brake is Te＝2BIebL (1)
Wherein the content of the first and second substances,S＝ab，
therefore, the temperature of the molten metal is controlled,
in the formula, TeFor eddy current braking torque, TemaxFor maximum eddy current braking torque, B is the magnetic induction intensity across the brake disc, a is the width of the cross section of the magnetic pole, B is the length of the magnetic pole face, L is the distance from the center of the brake disc to the center of the magnetic pole, and IeEffective value of the eddy current generated on the brake disk, i instantaneous value of the eddy current generated on the brake disk, ρ' specific resistance of the brake disk, ΔhFor the skin depth of the vortex on the brake disk, murFor relative permeability, ω is the angular speed of rotation of the brake disc, μ0For vacuum permeability, N is the number of turns of the coil on the core, ImaxFor maximum current intensity of electromagnetic brake, /)gIs the air gap spacing, keFor the conversion factor, 1.5 is usually taken.
(2) Power P of electric eddy current brakeBeComputing
According to the braking torque T of the eddy current brakeeDetermining the current of the electromagnetic brake
Calculating the power P of the eddy current brake according to the electrifying current of the electromagnetic brakeBe＝I2R (4)
Wherein R is the total resistance of the eddy current brake coil.
(3) Electro-hydraulic brake power PBfComputing
The electronic hydraulic brake system mainly includes: the brake system comprises a motor, a transmission mechanism, a hydraulic brake cylinder, an electromagnetic valve and a brake wheel cylinder. And (3) establishing an electronic hydraulic brake system model (the influence of a brake pipeline on the system pressure is not considered for the moment) according to mathematical equations of all parts of the system, and calculating the power of the electronic hydraulic brake system.
1) Equation of the motor
In order to ensure the reliability of the driving motor in the braking system, a brushless motor is generally adopted, and a permanent magnet synchronous motor can also be simplified into a direct current motor mode, and the motor equation can be expressed as
In the formula of UsTo the terminal voltage of the machine, KeFor equivalent back EMF coefficient, RmIs the equivalent internal resistance of the motor, LmIs an equivalent inductance, KtIs an equivalent motor moment coefficient, imIs an equivalent current, TmeIn order to obtain the torque of the motor,
And limiting the output torque of the motor according to the external characteristics of the motor.
In the formula, TmIn order to actually output the torque of the motor,
Thus, the power of the motor may be expressed as
2) Equation of dynamics of transmission mechanism
At present, a transmission mechanism mainly adopts two forms of gear reduction, ball screw, worm and gear and rack, and the input torque T of the transmission mechanism is not limited by any transmission forminAnd output torque ToutInput rotation angle thetamAnd output a displacement SoutAll can be expressed as
The dynamic balance equation of the motor and the transmission mechanism can be expressed as
In the formula, PmFor hydraulic brake cylinder pressure, AmArea of the hydraulic brake cylinder, JsysIs the system moment of inertia, CsysFor system damping, KsFor system stiffness, TfIn order to achieve the friction torque of the system,is the angular acceleration of the motor.
3) Hydraulic brake cylinder and electromagnetic equation
According to the definition of the volume elastic modulus of the brake fluid, the dynamic expression of the continuous flow of the single-cavity hydraulic brake cylinder adopted by the invention is
Wherein E is the bulk modulus of elasticity of the brake fluid, QmFlow of fluid from the hydraulic brake cylinder, ViniIs the initial volume of brake fluid in the cylinder, Qv(i) The flow rate of the brake fluid flowing through each solenoid valve.
The flow equation of the brake fluid flowing through the solenoid valve can be expressed as
In the formula, i is 1 for the high-speed solenoid valve oil inlet, i is 2 for the high-speed solenoid valve oil outlet, Cd(i) For each solenoid valve flow coefficient, Av(i) For equivalent shut-off area, P, of each solenoid valvew(i) The wheel cylinder pressure ρ is the brake fluid density.
4) Brake wheel cylinder
For a specific brake system, the relationship between the wheel cylinder pressure and the brake fluid volume can be represented by a relationship curve (P-V characteristic curve) between the circuit pressure including the brake pipe, hose, wheel cylinder and the brake fluid volume thereof, i.e. the relationship curve is represented by
Pw(i)＝f(Vw(i)),Vw(i)＝∫Qv(i)dt (12)
In the formula, Vw(i) I-1 is the high pressure brake fluid volume, i-2 is the low pressure brake fluid volume, Q is the brake fluid volumev(i) The flow rate of the brake fluid flowing through the solenoid valve.
5) Output braking torque of disc brake
The output braking torque of the disc brake is T which can be obtained by calculation according to the pressure of the brake wheel cylinderf＝2ηcRdPw(i)Ac(13)
In the formula, ηcCoefficient of friction between brake lining and brake disc, RdEffective radius of brake disc, AcThe area of the brake wheel cylinder piston.
According to the related mathematical equations of the motor, the transmission mechanism, the hydraulic brake cylinder, the electromagnetic valve and the brake wheel cylinder, the power of the electronic hydraulic brake system is mainly the motor power, and the energy consumption of the electromagnetic valve is small and can be ignored. By way of analysis, the output of the electrohydraulic brake system is a function of the output braking torque of the disc brake, and can be determined, as shown. The solving process can refer to fig. 3.
PBf＝f(Tf) (14)
Second, the distribution of the optimal braking torque of the composite braking system
The eddy current brake has high response speed and controllability, but provides limited braking torque, and has higher energy consumption when the braking torque is larger. The electronic hydraulic brake has strong stability, can provide larger braking torque, and has higher response speed than an eddy current brake. At the same time, neither is suitable for continuous operation at high temperatures. Therefore, according to the difference and the sameness of the eddy current brake and the electronic hydraulic brake, the invention considers two aspects of braking efficiency and energy consumption, and realizes the distribution strategy of the electronic hydraulic brake composite braking torque of the eddy current brake and the electronic hydraulic brake system.
Fig. 2 is a flow chart of the method of the present invention for distributing the braking torque of the hybrid braking system. The electro-hydraulic brake system temperature and the eddy current brake system temperature are compared to respective maximum safety thresholds.
The temperature of the electronic hydraulic brake is based on a brake inertia bench test, a heat fading test under the continuous braking working condition of a long downhill section of an automobile is simulated, a two-dimensional relation model of the braking times and the temperature is solved through least square approximation according to a test data relation graph, then the temperature rising trend is predicted, and the failure temperature threshold of the hydraulic brake is found out.
The temperature of the eddy current brake is tested according to the heat fading of the eddy current braking torque, an eddy current braking torque-time relation curve under a certain constant rotating speed is obtained through the test, a drag-grinding test is carried out, and when the eddy current braking torque is smaller than 15% of the braking torque at the initial moment, the temperature of the eddy current braking system is recorded and is used as the highest temperature threshold of the eddy current braking system. When the temperature of the eddy current brake disc is high, the failure possibility of the eddy current brake is reduced.
The braking conditions can be divided into electric eddy current braking, electronic hydraulic braking feedback compensation electric eddy current braking and electric eddy current braking feedforward compensation electronic hydraulic braking retardation.
(1) Electric eddy current brake
When the temperature of the friction disk is greater than a given temperature threshold T1And the eddy current brake temperature is less than a given temperature threshold T2When the electric eddy current brake is used, the use of the electric eddy current brake is not limited, the electronic hydraulic brake efficiency is reduced, and the electronic hydraulic brake is avoided as much as possible in the brake process. At the moment, the maximum eddy current braking torque T which can be provided by the eddy current brake under the current working condition is calculatedemax. If maximum eddy current braking torque TemaxGreater than target braking torque TBBy controlling the eddy current braking torque TeProviding braking torque TB. Under the working condition, the brake system has better response characteristic, and the low efficiency of the electronic hydraulic brake system is avoided.
When the temperature of the friction disk is less than a given temperature threshold T1At the same time, the temperature of the eddy-current brake is less than a given temperature threshold value T2Then (c) is performed. At the moment, the maximum eddy current braking torque T which can be provided by the eddy current brake under the current working condition is calculatedemax. If maximum eddy current braking torque TemaxGreater than target braking torque TBCalculating the electro-hydraulic braking power P satisfying the target braking torqueBfAnd eddy current braking power PBeWhen P isBeLess than PBfBy controlling the eddy-current braking torque TeProviding braking torque TB. Under the working condition, the brake requirement is met, the response characteristic is good, and the energy consumption is reduced.
(2) Feedback compensation electric eddy current brake of electronic hydraulic brake
When the temperature of the friction disc is greater than a given temperature T1And the temperature of the eddy current brake is less than the given temperature T2When the electric eddy current brake is used, the use of the electric eddy current brake is not limited, the electronic hydraulic brake efficiency is reduced, the electronic hydraulic brake is avoided as much as possible in the brake process, and the electric eddy current brake is preferentially carried out. At the moment, the current worker is calculatedUnder the condition of maximum eddy current braking torque T provided by the eddy current brakeemax. If the maximum eddy current braking torque is smaller than the target braking torque TB，TemaxAll provided with braking torque TBI.e. Te＝TemaxThe electronic hydraulic brake system is based on the target braking torque TfAnd maximum eddy current braking torque TemaxProviding a residual braking torque, i.e. Tf＝TB-Temax. Under the working condition, the unlimited eddy current brake can provide more braking torque as far as possible, the burden of electronic hydraulic braking of the electronic hydraulic braking system is reduced, the stability of the braking system is improved to the maximum extent, and the high efficiency of the braking system is realized.
(3) Electronic hydraulic brake
When the temperature of the friction disk is less than a given temperature threshold T1And the eddy current brake temperature is greater than the given temperature T2When the brake is applied, the electro-hydraulic brake is applied. By controlling the electrohydraulic braking torque T of the electrohydraulic braking systemfIndependently of TfProviding a target braking torque TBI.e. TB＝Tf. Under the working condition, the low efficiency of the eddy current brake system is avoided, and only the electronic hydraulic brake system works as the traditional electronic hydraulic brake system.
When the temperature of the friction disk is greater than a given temperature threshold T1The eddy current brake temperature is also greater than a given temperature threshold T2When the electronic hydraulic brake and the eddy current brake are both in the limit condition, the brake system gives an alarm to remind a driver that the brake system is possibly low in efficiency or even fails, and the electronic hydraulic brake system is used for stopping the electronic hydraulic brake.
(4) Eddy current brake feedforward compensation electronic hydraulic brake hysteresis
When the temperature of the friction disk is less than a given temperature threshold T1At the same time, the temperature of the eddy-current brake is less than a given temperature threshold value T2Then (c) is performed. At the moment, the maximum eddy current braking torque T which can be provided by the eddy current brake under the current working condition is calculatedemax. If maximum eddy current braking torque TemaxLess than target braking torque TBAt this time, the use of the electro-hydraulic brake and the eddy current brake is not limited, and the eddy current brake torque cannot meet the requirement of the target brake torque, but the response characteristic of the eddy current brake is obviously higher than that of the electro-hydraulic brake generated by the electro-hydraulic brake system, and the hysteresis characteristic of the electro-hydraulic brake feedforward compensation electro-hydraulic brake of the eddy current brake is provided. Under the working condition, the response characteristic of the brake system can be effectively improved.
When the temperature of the friction disk is less than a given temperature threshold T1At the same time, the temperature of the eddy-current brake is less than a given temperature threshold value T2Then (c) is performed. At the moment, the maximum eddy current braking torque T which can be provided by the eddy current brake under the current working condition is calculatedemax. If maximum eddy current braking torque TemaxGreater than target braking torque TBCalculating the electro-hydraulic braking power P satisfying the target braking torqueBfAnd eddy current braking power PBeWhen P isBeGreater than PBfWhen the electronic hydraulic brake is used preferentially, but the response characteristic of the electric eddy current brake is obviously higher than that of the electronic hydraulic brake generated by an electronic hydraulic brake system, and the hysteresis characteristic of the electric eddy current brake feedforward compensation electronic hydraulic brake is provided. Under the working condition, the response characteristic of the brake system can be effectively improved.
The specific process of the electric eddy current braking feedforward compensation electronic hydraulic braking is as follows: obtaining target braking torque T according to automobile working conditionbAnd apply a braking torque TbThe signal is sent to an electronic hydraulic brake system, and an electronic hydraulic controller realizes the braking torque TbThe tracking control of (2). However, the tracking control for tracking the high-frequency signal cannot be realized due to the obvious hysteresis characteristic of the electro-hydraulic brake system. The hysteresis compensation controller samples the braking torque TbThe signal is used for solving the change rate of the electronic hydraulic braking torque in the braking system, and the first-order Taylor series feedforward compensation control method is used for solving the hysteresis compensation braking torque T of the electronic hydraulic braking systeme. The hysteresis compensation controller will compensate the braking torque TcThe signal is sent to a composite braking system controller, and the eddy current brake realizes the braking torque TeThe tracking control of (2). Finally, the process is carried out in a batch,braking torque T generated by electronic hydraulic braking systemfAnd braking torque T generated by eddy current brakingeAdding to obtain the composite braking torque T after hysteresis compensationbAnd acts on the braking system.
TB＝Tf+Te(15)
The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.
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