CN111731252A - Brake-by-wire system with backup brake system and control method thereof - Google Patents
Brake-by-wire system with backup brake system and control method thereof Download PDFInfo
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- CN111731252A CN111731252A CN202010483837.1A CN202010483837A CN111731252A CN 111731252 A CN111731252 A CN 111731252A CN 202010483837 A CN202010483837 A CN 202010483837A CN 111731252 A CN111731252 A CN 111731252A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
- B60T13/74—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
- B60T13/746—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 and mechanical transmission of the braking action
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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
- B60T7/06—Disposition of pedal
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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
- B60T2270/00—Further aspects of brake control systems not otherwise provided for
- B60T2270/40—Failsafe aspects of brake control systems
- B60T2270/402—Back-up
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- Regulating Braking Force (AREA)
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Abstract
The invention discloses a line control brake system with a backup brake system and a control method thereof, wherein the system comprises: the brake system comprises a brake pedal module, a control module, a wheel module and a brake module; the brake pedal module includes: the brake pedal, the pedal rotating shaft, the connecting rod, the push rod and the pedal simulator are arranged on the brake pedal; the wheel module includes: a left front wheel, a left rear wheel, a right front wheel vehicle and a right rear wheel; the brake module includes: the brake comprises a motor, a transmission device and brakes arranged on wheels; the control module includes: the device comprises an electronic control unit, a pedal displacement sensor, a pedal speed sensor and a current adjusting module; the invention improves the reliability of the brake and the response speed of the backup brake system; and the reliability is strong, the cost is low and the modification is convenient.
Description
Technical Field
The invention belongs to the technical field of vehicle brake-by-wire, and particularly relates to a brake-by-wire system with a backup brake system and a control method thereof.
Background
The brake-by-wire system replaces the original mechanical connection and hydraulic pipeline with an electronic circuit, and is different from the traditional hydraulic brake system, and the brake-by-wire system device can be used for all hybrid and electric vehicle types on the market at present. The brake-by-wire system can customize the feel of the maneuver, the vehicle response, and the vehicle settings according to the driver's preferences.
At present, a brake system is developed comprehensively towards a wire control direction, all hydraulic devices, including a master cylinder, a hydraulic pipeline, a power assisting device and the like, are replaced by an electromechanical system, great challenge is brought to the reliability of the electromechanical brake system, and a corresponding backup brake system is required to be equipped for ensuring the reliability of the wire control brake system. The research progress of the brake-by-wire system is as the Chinese invention patent application number is CN 201710885196.0 at present, the name 'brake-by-wire system and vehicle' comprises an electric brake and a hydraulic brake, and a hydraulic control unit is used for simulating pedal signals; the Chinese invention patent application number is 201811553147.8, the name "an electronic mechanical brake system with a backup brake system", which proposes an electronic brake system which generates pedal feeling by hydraulic pressure, takes electronic brake as a main brake mode and simultaneously keeps a hydraulic pipeline as backup; the former lacks a backup brake system, while the latter backup brake system is not sensitive enough and difficult to implement, so that the existing brake-by-wire system lacks an effective and reliable backup brake system.
Magnetostrictive materials are a new class of smart materials that can interconvert electromagnetic and mechanical energy. When the material is magnetized in a magnetic field, the material can expand and contract along the magnetization direction, and when an electrified coil is used as a magnetic field source, the deformation amount of the magnetostrictive material can be controlled when the current passing through the coil is changed or the distance between the magnetostrictive material and the magnet is changed. Meanwhile, the magnetostrictive material displaces under the action of a magnetic field to work, and generates huge thrust to provide enough braking force for the brake. The magnetostrictive material also has the advantages of quick response time, good frequency characteristic, high energy density, good controllability, no overheating failure and the like.
In summary, the existing electromechanical braking system does not completely realize electric control, and is lack of a backup braking system, so that the reliability is insufficient, and when the electric brake fails, a major accident can occur; although hydraulic braking and the like are used as backup systems, hydraulic mechanical systems have the disadvantages of high implementation difficulty, limited response speed and insufficient sensitivity due to the characteristics of the hydraulic mechanical systems, and hydraulic backup requires more parts, so that the cost is increased, and more vehicle layout space is occupied.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, an object of the present invention is to provide a brake-by-wire system with a backup brake system and a control method thereof, so as to solve the problems of the existing brake-by-wire system, such as lack of other backup systems, low reliability, complex backup brake system structure, high cost, slow response of the backup system, and insufficient sensitivity.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention relates to a brake-by-wire system with a backup brake system, which comprises: the brake system comprises a brake pedal module, a control module, a wheel module and a brake module;
the brake pedal module includes: the brake pedal, the pedal rotating shaft, the connecting rod, the push rod and the pedal simulator are arranged on the brake pedal; the input end of the pedal rotating shaft is fixedly connected with the output end of the brake pedal, and the output end of the pedal rotating shaft is fixedly connected with the input end of the connecting rod; the input end of the push rod is hinged with the output end of the connecting rod, and the output end of the push rod is fixedly connected with the input end of the pedal simulator;
the pedal simulator includes: the pedal simulator comprises a pedal simulator base, a pedal simulator lower shell, a pedal simulator upper shell, a lower end cover, an upper end cover, a secondary spring, a primary spring, a secondary piston and a primary piston;
the simulator base is fixedly arranged at the lower end of the lower shell of the pedal simulator;
the upper end cover is screwed on the upper shell of the pedal simulator;
the lower end cover is fixedly connected with one end of the upper shell of the pedal simulator and is screwed on the upper end of the lower shell of the pedal simulator together;
the first-stage spring and the second-stage spring are arranged in the lower shell of the pedal simulator and the upper shell of the pedal simulator; the pedal simulator comprises a pedal simulator base, a first-stage spring, a second-stage spring, a first-stage piston and a second-stage piston, wherein the first-stage spring is sleeved on the pedal simulator base and the first-stage piston, the middle part of the first-stage spring is clamped on the second-stage piston, and the second-stage spring is sleeved on the pedal simulator base and the second-stage piston;
the wheel module includes: a left front wheel, a left rear wheel, a right front wheel vehicle and a right rear wheel;
the brake module includes: the brake comprises a motor, a transmission device and brakes arranged on wheels;
the motors are respectively and fixedly arranged on the outer sides of the brakes, and the axial direction of the output shaft is consistent with that of the wheel hub;
the transmission device is divided into two parts, wherein the first part is a planetary gear mechanism connected with a motor, and the second part is a connecting mechanism;
the planetary gear mechanism includes: the sun gear shaft, the planet carrier, the gear ring and three identical planet gears take the sun gear shaft as input and the planet carrier as output;
the three planet gears are uniformly distributed in the planet carrier and are meshed with the central gear shaft;
one end of the gear ring is fixedly connected with the motor through a bolt and is meshed with the three planetary gears;
the outer side of the planet carrier is fixedly supported on the brake module through a bearing and is connected with an output shaft of the motor;
the input end of the connecting mechanism is fixedly connected with the planet carrier; the tail end of the output shaft of the motor is fixedly supported in the planet carrier through a bearing;
the brake includes: the input shafts of the electronic brake device and the magnetostrictive backup brake device are fixedly connected with the output end of the planet carrier;
the electric brake device and the magnetostrictive backup brake device include: the brake caliper comprises a ball screw mechanism, a connecting screw, a brake caliper body, a brake disc, a left brake block back plate, a left brake block, a right brake block back plate and a right brake block;
the ball screw mechanism includes: the front end of the ball screw is fixedly connected with the planet carrier, the ball screw is connected with the nut assembly, and the rear end of the nut assembly is connected with a brake block back plate on the inner side of the brake through a connecting screw;
the left brake block is fixed on a left brake block back plate, the right brake block back plate is fixed on the brake caliper body, and the right brake block is fixed on a right brake block back plate;
one end of the brake caliper body is fixedly connected with the other end of the gear ring through a screw; the other end is fixed on a steering knuckle or a rear axle of a front axle of the vehicle;
the nut assembly includes: the magnetic isolation device comprises a nut shell, an excitation coil, a demagnetizing coil, a magnetic isolation liner and a magnetic isolation top cover;
the excitation coil and the demagnetizing coil are wound on the inner layer of the nut shell, the deformation of the ball screw is controlled by controlling the current in the excitation coil so as to push the brake block to eliminate the brake clearance, and the hysteresis is eliminated by controlling the current in the demagnetizing coil;
the magnetic isolation gasket is tightly attached to the inner side of the outer layer of the nut shell;
the magnetism isolating top covers are arranged at the left end and the right end of the nut shell in a rotating mode and isolate the influence of a magnetic field on the outside together with the magnetism isolating gaskets;
when being installed, the brake disc is fixed on a wheel hub of a vehicle and extends into a position between the left brake block and the right brake block;
the control module includes: the device comprises an electronic control unit, a pedal displacement sensor, a pedal speed sensor and a current adjusting module;
the pedal displacement sensor is arranged on the push rod, is electrically connected with the electronic control unit, and is used for acquiring a displacement signal of the brake pedal and transmitting the signal to the electronic control unit;
the pedal speed sensor is arranged on the push rod, is electrically connected with the electronic control unit, and is used for acquiring a speed signal of the brake pedal and transmitting the signal to the electronic control unit;
and the electronic control unit drives the electronic and magnetostrictive backup braking device to generate required braking force according to signals of the pedal displacement sensor and the pedal speed sensor and vehicle state signals.
Preferably, the ball screw is made of a hysteresis material.
Preferably, the ball screw is made of a rare earth giant magnetostrictive material, the magnetostrictive coefficient of the ball screw is 2000ppm, and the length of the ball screw is 20 cm.
Preferably, the nut shell is a hollow structure, in particular a double-layer barrel-shaped structure, wherein the inner layer is provided with a thread structure.
Preferably, the primary spring and the secondary spring are in a natural state when not in work.
Preferably, the central gear shaft and the output shaft of the motor are the same shaft, the gear teeth of the central gear shaft are positioned at a distance from the inner part of the tail end of the output shaft, and the edge of the gear teeth is 25 mm away from the tail end of the output shaft.
Preferably, the vehicle state signal includes: vehicle speed signals and wheel speed signals.
The invention discloses a control method of a brake-by-wire system with a backup brake system, which comprises two working conditions, and comprises the following steps:
the first working condition is as follows: under the normal braking working condition, namely the braking process under the state that the motor is electrified and does not fail is as follows:
the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal, a pedal displacement signal acquired by the pedal displacement sensor is sent to the electronic control unit to calculate the torque which should be generated by the motors of the four wheels, and the motors transmit power to the ball screw through the planetary gear and the planet carrier to drive the axial movement of the nut assembly to push the brake block to clamp the brake disc backwards so as to realize braking;
the second working condition is as follows: when the conventional brake system fails, namely the motor is powered off or fails, the backup system is started:
(1) the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, and the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal;
(2) the electronic control unit calculates the current required target braking force according to the pedal displacement sensor, the pedal speed sensor and the vehicle state signal, distributes the braking force of each wheel according to the current required braking force, calculates the displacement required by the ball screw in the electronic braking device and the magnetostrictive backup braking device of each wheel, further calculates the required target current and controls the current regulation module to output corresponding current;
(3) the current is input into an excitation coil in the ball screw mechanism, the magnetic field intensity in the excitation coil changes, the ball screw deforms, and the nut assembly is driven to press against the brake block, so that the brake block clamps the brake disc, and braking is finished;
(4) when the brake pedal is released, the electronic control unit adjusts the current in the excitation coil according to the real-time pedal displacement, and controls the current adjusting module to introduce current in the direction opposite to that of the excitation coil into the demagnetizing coil, so that hysteresis is eliminated, and the system response is improved;
(5) and (4) completely loosening the brake pedal, recovering the initial length of the ball screw in the ball screw mechanism, and releasing the brake.
Preferably, the step (2) specifically comprises:
assuming that the magnetostrictive material is equivalent to an elastomer, hooke's law is satisfied:
F＝K· (1)
the deformation of the ball screw pair is as follows:
B＝μ0NI (3)
in the formula, K is a ball screw pairThe elastic coefficient of (a); the deformation of the ball screw pair; s is the effective end surface area of the ball screw pair; mu.s0Is a vacuum magnetic conductivity; n is the number of turns of the excitation coil; and B is magnetic induction intensity.
Preferably, the control method in step (2) adopts a series PID double closed loop control method, and is formed by connecting a displacement loop and a magnetic induction loop in series, and the specific steps are as follows:
(21) amount of magnetostrictive deformation required for target braking forceneedAnd the actual amount of deformationrealComparing to obtain a difference value delta:
Δ＝need-real(4)
(22) the difference value delta is used as the input of a displacement ring, and the required magnetic induction intensity value B is calculated by a PID methodneed(t)：
In the formula, Kp1Is the displacement ring scale factor; t is1Is a displacement loop integral coefficient; t isd1Is a differential coefficient of the displacement ring;
(23) the required magnetic induction intensity value and the actual magnetic induction intensity value B are comparedrealComparing to obtain a difference value delta B:
ΔB＝Bneed-Breal(6)
(24) the difference value delta B is used as the input of a magnetic induction intensity ring, and a required control current value u is calculated by a PID methodI(t)：
In the formula uI(t) is the output control current value; kp2Is the magnetic induction ring scale factor; t is2Is the magnetic induction loop integral coefficient; t isd2Is the differential coefficient of the magnetic induction ring;
(25) and (5) repeating the steps (22) to (24), and continuously adjusting the control current until the braking force is converged and the error requirement is met.
The invention has the beneficial effects that:
the backup brake system based on magnetostriction is added on the basis of an electronic brake system by utilizing the characteristics of the magnetostriction material, and the current in the excitation coil is controlled by the ECU in the linear control system, so that the backup brake system has the advantages of short response time, high precision, light weight and the like, and the reliability of the brake and the response speed of the backup brake system are improved; and the reliability is strong, the cost is low and the modification is convenient.
Drawings
FIG. 1 is a schematic diagram of a brake-by-wire system of the present invention;
FIG. 2 is a schematic view of an electric brake and magnetostrictive backup brake apparatus according to the present invention;
FIG. 3 is a schematic view of the internal structure of the nut assembly;
FIG. 4 is a schematic view of a pedal simulator in accordance with the present invention;
FIG. 5 is a view of the planetary gear structure of the present invention;
FIG. 6 is a schematic diagram of a series PID dual closed loop control method according to the invention;
in the figure, 1-pedal displacement sensor, 2-pedal speed sensor, 3-pedal simulator, 4-pedal rotating shaft, 5-connecting rod, 6-brake pedal, 7-push rod, 8-right rear brake, 9-right rear wheel, 10-left rear brake, 11-left rear wheel, 12-right front brake, 13-right front wheel, 14-left front brake, 15-left front wheel, 16-motor, 17-transmission device, 18-electronic and magnetostrictive backup brake device, 19-planetary gear mechanism, 20-connecting mechanism, 21-bearing, 22-ball screw mechanism, 23-connecting screw, 24-brake caliper body, 25-brake disc, 26-left brake block back plate, 27-left brake block, 28-right brake shoe backing plate, 29-right brake shoe, 30-ball screw, 31-nut assembly, 32-nut shell, 33-excitation coil, 34-degaussing coil, 35-magnetism isolating gasket, 36-magnetism isolating top cover, 37-nut internal thread, 38-pedal simulator base, 39(a) -pedal simulator lower shell, 39(b) -pedal simulator upper shell, 40-secondary spring, 41-primary spring, 42(a) -lower end cover, 42(b) -secondary piston, 43(a) -primary piston, 43(b) -upper end cover, 44-current regulation module; 45-sun gear shaft, 46-planet carrier, 47-ring gear, 48-planet gear.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.
Referring to fig. 1, a brake-by-wire system with a backup brake system according to the present invention includes: the brake system comprises a brake pedal module, a control module, a wheel module and a brake module;
the brake pedal module includes: the brake pedal 6, the pedal rotating shaft 4, the connecting rod 5, the push rod 7 and the pedal simulator 3; the input end of the pedal rotating shaft 4 is fixedly connected with the output end of the brake pedal 6, and the output end of the pedal rotating shaft is fixedly connected with the input end of the connecting rod 5; the input end of the push rod 7 is hinged with the output end of the connecting rod 5, and the output end of the push rod is fixedly connected with the input end of the pedal simulator 3;
the pedal simulator 3 includes: a pedal simulator base 38, a pedal simulator lower shell 39(a), a pedal simulator upper shell 39(b), a lower end cover 42(a), an upper end cover 43(b), a secondary spring 40, a primary spring 41, a secondary piston 42(b), and a primary piston 43 (a);
the simulator base 38 is fixedly mounted to the lower end of the pedal simulator lower housing 39 (a);
the upper end cover 43(b) is screwed on the upper shell 39(b) of the pedal simulator;
the lower end cover 42(a) is fixedly connected with one end of the upper pedal simulator shell 39(b) and is screwed on the upper end of the lower pedal simulator shell 39 (a);
the primary spring 41 and the secondary spring 40 are arranged inside the lower pedal simulator shell 39(a) and the upper pedal simulator shell 39 (b); the pedal simulator comprises a pedal simulator base 38, a first-stage piston 43(a), a second-stage piston 42(b), a first-stage spring 41, a second-stage spring 40 and a third-stage piston 43(b), wherein the first-stage spring 41 is sleeved on the pedal simulator base 38 and the first-stage piston 43(a), the middle part of the first-stage spring is clamped on the second-stage piston 42(b), and the second-stage spring 40 is sleeved on the; the primary spring and the secondary spring are in a natural state when not working;
the wheel module includes: a left front wheel 15, a left rear wheel 11, a right front wheel 13 and a right rear wheel 9;
the brake module includes: a motor 16, a transmission device 17 and brakes 14, 10, 12 and 8 arranged on each wheel;
the motors 16 are respectively and fixedly arranged on the outer sides of the brakes, and the axial direction of the output shaft is consistent with the axial direction of the wheel hub;
the transmission device 17 is divided into two parts, wherein the first part is a planetary gear mechanism 19 connected with the motor 16, and the second part is a connecting mechanism 20;
the planetary gear mechanism 19 includes: a sun gear shaft 45, a planet carrier 46, a ring gear 47 and three identical planet gears 48, with the sun gear shaft 45 as input and the planet carrier 46 as output;
the three planet gears 48 are uniformly distributed in the planet carrier 46 and are meshed with the central gear shaft 45;
one end of the gear ring 47 is fixedly connected with the motor 16 through a bolt and is meshed with the three planetary gears 48;
the outer side of the planet carrier 46 is fixedly supported on the brake module framework through a bearing and is connected with an output shaft of the motor 16;
the input end of the connecting mechanism 20 is fixedly connected with the planet carrier 46; the tail end of the output shaft of the motor 16 is fixedly supported in the planet carrier 46 through a bearing 21;
the central gear shaft and the output shaft of the motor 16 are the same shaft, the gear teeth of the central gear shaft are positioned at a distance close to the inner part of the tail end of the output shaft, and the edge of the gear teeth is 25 mm away from the tail end of the output shaft;
the brake includes: the input shafts of the electronic brake device and the magnetostrictive backup brake device 18 are fixedly connected with the output end of the planet carrier 46;
the electric and magnetostrictive backup brake device 18 comprises: a ball screw mechanism 22, a connecting screw 23, a caliper body 24, a brake disc 25, a left brake pad backing plate 26, a left brake pad 27, a right brake pad backing plate 28, and a right brake pad 29;
the ball screw mechanism 22 includes: the front end of the ball screw 30 is fixedly connected with the planet carrier, the ball screw 30 is connected with the nut assembly 31, and the rear end of the nut assembly 31 is connected with the brake block back plate 26 on the inner side of the brake through the connecting screw 23; the ball screw 22 is made of a hysteresis material.
The ball screw is made of a rare earth giant magnetostrictive material, the magnetostrictive coefficient of the ball screw is 2000ppm, and the length of the ball screw is 20 cm.
The left brake block 27 is fixed on the left brake block back plate 26, the right brake block back plate 28 is fixed on the caliper body 24, and the right brake block 29 is fixed on the right brake block back plate 28;
one end of the brake caliper body 24 is fixedly connected with the other end of the gear ring 47 through a screw; the other end is fixed on a steering knuckle or a rear axle of a front axle of the vehicle;
the nut assembly 31 includes: a nut shell 32, an excitation coil 33, a demagnetizing coil 34, a magnetic isolation liner 35 and a magnetic isolation top cover 36; the nut shell is of a hollow structure, particularly of a double-layer barrel-shaped structure, wherein the inner layer is provided with a thread structure;
the exciting coil 33 and the demagnetizing coil 34 are wound on the inner layer of the nut shell 32, the deformation amount of the ball screw 30 is controlled by controlling the current in the exciting coil 33 to push the brake block to eliminate the brake clearance, and the hysteresis phenomenon is eliminated by controlling the current in the demagnetizing coil 34;
the magnetic isolation gasket 35 is tightly attached to the inner side of the outer layer of the nut shell 32;
the magnetic isolation top cover 36 is screwed at the left end and the right end of the nut shell 32 and isolates the influence of a magnetic field on the outside together with the magnetic isolation liner 35;
when being installed, the brake disc 25 is fixed on a hub of a vehicle and extends between the left brake block 27 and the right brake block 29;
the control module includes: an Electronic Control Unit (ECU), a pedal displacement sensor 1, a pedal speed sensor 2, a current regulation module 44;
the pedal displacement sensor 1 is arranged on the push rod 7, is electrically connected with the electronic control unit, and is used for obtaining a displacement signal of the brake pedal 6 and transmitting the signal to the electronic control unit;
the pedal speed sensor 2 is arranged on the push rod 7, is electrically connected with the electronic control unit, and is used for acquiring a speed signal of the brake pedal 6 and transmitting the signal to the electronic control unit;
the electronic control unit drives the electronic and magnetostrictive backup brake device 18 to generate the required braking force according to the signals of the pedal displacement sensor 1 and the pedal speed sensor 2 and the vehicle state signal.
The vehicle state signal includes: vehicle speed signals and wheel speed signals.
The invention discloses a control method of a brake-by-wire system with a backup brake system, which comprises two working conditions, and comprises the following steps:
the first working condition is as follows: under the normal braking working condition, namely the braking process under the state that the motor is electrified and does not fail is as follows:
the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal, a pedal displacement signal acquired by the pedal displacement sensor is sent to the electronic control unit to calculate the torque which should be generated by the motors of the four wheels, and the motors transmit power to the ball screw through the planetary gear and the planet carrier to drive the axial movement of the nut assembly to push the brake block to clamp the brake disc backwards so as to realize braking;
the second working condition is as follows: when the conventional brake system fails, namely the motor is powered off or fails, the backup system is started:
(1) the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, and the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal;
(2) the electronic control unit calculates the current required target braking force according to the pedal displacement sensor, the pedal speed sensor and the vehicle state signal, distributes the braking force of each wheel according to the current required braking force, calculates the displacement required by the ball screw in the electronic braking device and the magnetostrictive backup braking device of each wheel, further calculates the required target current and controls the current regulation module to output corresponding current;
(3) the current is input into an excitation coil in the ball screw mechanism, the magnetic field intensity in the excitation coil changes, the ball screw deforms, and the nut assembly is driven to press against the brake block, so that the brake block clamps the brake disc, and braking is finished;
(4) when the brake pedal is released, the electronic control unit adjusts the current in the excitation coil according to the real-time pedal displacement, and controls the current adjusting module to introduce current in the direction opposite to that of the excitation coil into the demagnetizing coil, so that hysteresis is eliminated, and the system response is improved;
(5) and (4) completely loosening the brake pedal, recovering the initial length of the ball screw in the ball screw mechanism, and releasing the brake.
Preferably, the step (2) specifically comprises:
assuming that a magnetostrictive material is approximately macroscopically equivalent to an elastomer, hooke's law is satisfied:
F＝K· (1)
the deformation of the ball screw pair is as follows:
B＝μ0NI (3)
in the formula, K is the elastic coefficient of the ball screw pair; the deformation of the ball screw pair; s is the effective end surface area of the ball screw pair; mu.s0Is a vacuum magnetic conductivity; n is the number of turns of the excitation coil; and B is magnetic induction intensity.
Preferably, the control method in step (2) adopts a series PID double closed loop control method, and is formed by connecting a displacement loop and a magnetic induction loop in series, and the specific steps are as follows:
(2.1) amount of magnetostrictive deformation required for target braking forceneedAnd the actual amount of deformationrealComparing to obtain a difference value delta:
Δ＝need-real(4)
(2.2) inputting the difference value delta as a displacement ring, and calculating by a PID method to obtain a required magnetic induction intensity value:
in the formula, Kp1Is the displacement ring scale factor; t is1Is a displacement loop integral coefficient; t isd1Is a differential coefficient of the displacement ring;
(2.3) comparing the required magnetic induction intensity value with the actual magnetic induction intensity value BrealComparing to obtain a difference value delta B:
ΔB＝Bneed-Breal(6)
(2.4) inputting the difference value delta B as a magnetic induction intensity ring, and calculating by a PID method to obtain a required control current value uI(t)：
In the formula uI(t) is the output control current value; kp2Is the magnetic induction ring scale factor; t is2Is the magnetic induction loop integral coefficient; t isd2Is the differential coefficient of the magnetic induction ring;
and (2.5) repeating the steps (2.2) to (2.4), and continuously adjusting the control current until the braking force is converged and the error requirement is met.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (10)
1. A brake-by-wire system having a backup brake system, comprising: the brake system comprises a brake pedal module, a control module, a wheel module and a brake module;
the brake pedal module includes: the brake pedal, the pedal rotating shaft, the connecting rod, the push rod and the pedal simulator are arranged on the brake pedal; the input end of the pedal rotating shaft is fixedly connected with the output end of the brake pedal, and the output end of the pedal rotating shaft is fixedly connected with the input end of the connecting rod; the input end of the push rod is hinged with the output end of the connecting rod, and the output end of the push rod is fixedly connected with the input end of the pedal simulator;
the pedal simulator includes: the pedal simulator comprises a pedal simulator base, a pedal simulator lower shell, a pedal simulator upper shell, a lower end cover, an upper end cover, a secondary spring, a primary spring, a secondary piston and a primary piston;
the simulator base is fixedly arranged at the lower end of the lower shell of the pedal simulator;
the upper end cover is screwed on the upper shell of the pedal simulator;
the lower end cover is fixedly connected with one end of the upper shell of the pedal simulator and is screwed on the upper end of the lower shell of the pedal simulator together;
the first-stage spring and the second-stage spring are arranged in the lower shell of the pedal simulator and the upper shell of the pedal simulator; the pedal simulator comprises a pedal simulator base, a first-stage spring, a second-stage spring, a first-stage piston and a second-stage piston, wherein the first-stage spring is sleeved on the pedal simulator base and the first-stage piston, the middle part of the first-stage spring is clamped on the second-stage piston, and the second-stage spring is sleeved on the pedal simulator base and the second-stage piston;
the wheel module includes: a left front wheel, a left rear wheel, a right front wheel vehicle and a right rear wheel;
the brake module includes: the brake comprises a motor, a transmission device and brakes arranged on wheels;
the motors are respectively and fixedly arranged on the outer sides of the brakes, and the axial direction of the output shaft is consistent with that of the wheel hub;
the transmission device is divided into two parts, wherein the first part is a planetary gear mechanism connected with a motor, and the second part is a connecting mechanism;
the planetary gear mechanism includes: the sun gear shaft, the planet carrier, the gear ring and three identical planet gears take the sun gear shaft as input and the planet carrier as output;
the three planet gears are uniformly distributed in the planet carrier and are meshed with the central gear shaft;
one end of the gear ring is fixedly connected with the motor through a bolt and is meshed with the three planetary gears;
the outer side of the planet carrier is fixedly supported on the brake module through a bearing and is connected with an output shaft of the motor;
the input end of the connecting mechanism is fixedly connected with the planet carrier; the tail end of the output shaft of the motor is fixedly supported in the planet carrier through a bearing;
the brake includes: the input shafts of the electronic brake device and the magnetostrictive backup brake device are fixedly connected with the output end of the planet carrier;
the electric brake device and the magnetostrictive backup brake device include: the brake caliper comprises a ball screw mechanism, a connecting screw, a brake caliper body, a brake disc, a left brake block back plate, a left brake block, a right brake block back plate and a right brake block;
the ball screw mechanism includes: the front end of the ball screw is fixedly connected with the planet carrier, the ball screw is connected with the nut assembly, and the rear end of the nut assembly is connected with a brake block back plate on the inner side of the brake through a connecting screw;
the left brake block is fixed on a left brake block back plate, the right brake block back plate is fixed on the brake caliper body, and the right brake block is fixed on a right brake block back plate;
one end of the brake caliper body is fixedly connected with the other end of the gear ring through a screw; the other end is fixed on a steering knuckle or a rear axle of a front axle of the vehicle;
the nut assembly includes: the magnetic isolation device comprises a nut shell, an excitation coil, a demagnetizing coil, a magnetic isolation liner and a magnetic isolation top cover;
the excitation coil and the demagnetizing coil are wound on the inner layer of the nut shell, the deformation of the ball screw is controlled by controlling the current in the excitation coil so as to push the brake block to eliminate the brake clearance, and the hysteresis is eliminated by controlling the current in the demagnetizing coil;
the magnetic isolation gasket is tightly attached to the inner side of the outer layer of the nut shell;
the magnetism isolating top covers are arranged at the left end and the right end of the nut shell in a rotating mode and isolate the influence of a magnetic field on the outside together with the magnetism isolating gaskets;
when being installed, the brake disc is fixed on a wheel hub of a vehicle and extends into a position between the left brake block and the right brake block;
the control module includes: the device comprises an electronic control unit, a pedal displacement sensor, a pedal speed sensor and a current adjusting module;
the pedal displacement sensor is arranged on the push rod, is electrically connected with the electronic control unit, and is used for acquiring a displacement signal of the brake pedal and transmitting the signal to the electronic control unit;
the pedal speed sensor is arranged on the push rod, is electrically connected with the electronic control unit, and is used for acquiring a speed signal of the brake pedal and transmitting the signal to the electronic control unit;
and the electronic control unit drives the electronic and magnetostrictive backup braking device to generate required braking force according to signals of the pedal displacement sensor and the pedal speed sensor and vehicle state signals.
2. The brake-by-wire system with backup brake system of claim 1, wherein said ball screw is made of hysteresis material.
3. The brake-by-wire system with backup brake system according to claim 2, wherein said ball screw is made of rare earth giant magnetostrictive material, its magnetostrictive coefficient is 2000ppm, and the length of ball screw is 20 cm.
4. Brake-by-wire system with backup brake system according to claim 1, characterized in that the nut housing is of hollow construction, in particular of double barrel construction, with an inner layer with a threaded construction.
5. The brake-by-wire system with backup brake system of claim 1, wherein said primary and secondary springs are in a natural state when not in operation.
6. The brake-by-wire system with backup brake system of claim 1, wherein said sun gear shaft is the same shaft as the output shaft of the motor, with the gear teeth portion located a distance inward of the output shaft end and the gear teeth edge located 25 mm from the output shaft end.
7. The brake-by-wire system with backup braking system of claim 1, wherein said vehicle status signal comprises: vehicle speed signals and wheel speed signals.
8. A control method of a brake-by-wire system with a backup brake system is characterized by comprising two working conditions, and the steps are as follows:
the first working condition is as follows: under the normal braking working condition, namely the braking process under the state that the motor is electrified and does not fail is as follows:
the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal, a pedal displacement signal acquired by the pedal displacement sensor is sent to the electronic control unit to calculate the torque which should be generated by the motors of the four wheels, and the motors transmit power to the ball screw through the planetary gear and the planet carrier to drive the axial movement of the nut assembly to push the brake block to clamp the brake disc backwards so as to realize braking;
the second working condition is as follows: when the conventional brake system fails, namely the motor is powered off or fails, the backup system is started:
(1) the brake pedal is stepped on, the pedal simulator generates a certain feedback force through the deformation of the primary spring and the secondary spring, and the simulated pedal force is fed back to a driver through the push rod, the connecting rod and the brake pedal;
(2) the electronic control unit calculates the current required target braking force according to the pedal displacement sensor, the pedal speed sensor and the vehicle state signal, distributes the braking force of each wheel according to the current required braking force, calculates the displacement required by the ball screw in the electronic braking device and the magnetostrictive backup braking device of each wheel, further calculates the required target current and controls the current regulation module to output corresponding current;
(3) the current is input into an excitation coil in the ball screw mechanism, the magnetic field intensity in the excitation coil changes, the ball screw deforms, and the nut assembly is driven to press against the brake block, so that the brake block clamps the brake disc, and braking is finished;
(4) when the brake pedal is released, the electronic control unit adjusts the current in the excitation coil according to the real-time pedal displacement, and controls the current adjusting module to introduce current in the direction opposite to that of the excitation coil into the demagnetizing coil, so that hysteresis is eliminated, and the system response is improved;
(5) and (4) completely loosening the brake pedal, recovering the initial length of the ball screw in the ball screw mechanism, and releasing the brake.
9. The control method of a brake-by-wire system having a backup brake system according to claim 8, wherein the step (2) specifically includes:
assuming that the magnetostrictive material is equivalent to an elastomer, hooke's law is satisfied:
F＝K· (1)
the deformation of the ball screw pair is as follows:
B＝μ0NI (3)
in the formula, K is the elastic coefficient of the ball screw pair; the deformation of the ball screw pair; s is the effective end surface area of the ball screw pair; mu.s0Is a vacuum magnetic conductivity; n is the number of turns of the excitation coil; and B is magnetic induction intensity.
10. The method for controlling a brake-by-wire system having a backup brake system according to claim 8, wherein the control method in step (2) adopts a series PID double closed loop control method, and is formed by connecting a displacement loop and a magnetic induction loop in series, and comprises the following steps:
(21) amount of magnetostrictive deformation required for target braking forceneedAnd the actual amount of deformationrealComparing to obtain a difference value delta:
Δ＝need-real(4)
(22) the difference value delta is used as the input of a displacement ring, and the required magnetic induction intensity value B is calculated by a PID methodneed(t)：
In the formula, Kp1Is the displacement ring scale factor; t is1Is a displacement loop integral coefficient; t isd1Is a differential coefficient of the displacement ring;
(23) the required magnetic induction intensity value and the actual magnetic induction intensity value B are comparedrealComparing to obtain a difference value delta B:
ΔB＝Bneed-Breal(6)
(24) the difference value delta B is used as the input of a magnetic induction intensity ring, and a required control current value u is calculated by a PID methodI(t)：
In the formula uI(t) is the output control current value; kp2Is the magnetic induction ring scale factor; t is2Is the magnetic induction loop integral coefficient; t isd2Is the differential coefficient of the magnetic induction ring;
(25) and (5) repeating the steps (22) to (24), and continuously adjusting the control current until the braking force is converged and the error requirement is met.
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