Clamping force control method for EMB executing mechanism of electric vehicle

Abstract

The invention provides a clamping force control method for an EMB executing mechanism of an electric vehicle. The clamping force control method comprises the following steps that a backstepping controller is used for controlling a motor used for driving the EMB executing mechanism; observing the load torque of the motor through a load observer, and obtaining the current position of a motor rotor through a sensor after the load torque of the motor is obtained; obtaining an expected motor rotation angle corresponding to the current expected brake clamping force according to the brake clamping force and motor rotation angle characteristic curve; and finally, according to the obtained deviation between the expected motor rotation angle value and the actual value, a backstepping controller is designed in combination with the motor load torque, and accurate output control over the brake clamping force is achieved. According to the invention, the EMB actuating mechanism is controlled in a manner of accurately controlling the permanent magnet synchronous motor by using the backstepping controller, so that the accurate output of the braking clamping force is realized, and the accurate control of the braking clamping force of the EMB actuating mechanism is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicle brake clamping force control, and in particular relates to a clamping force control method of an electric vehicle EMB actuator. Background Art

[0002] The rapid development of new energy vehicles has led to higher demands for technological breakthroughs and innovative upgrades in intelligent automotive technology. As a key technology in intelligent technology, chassis-by-wire technology offers high control precision, excellent road adaptability, and rapid response. It can better integrate with upper-level controllers to implement functions such as energy recovery and active braking. Compared to traditional chassis, it is more adaptable to the executive layer requirements of intelligent vehicles and more in line with the manufacturing philosophy of a separate chassis. As one of the core technologies of a chassis-by-wire system, the brake-by-wire system decouples the brake pedal from the brake, realizing the driver's braking needs through electrical signals. Combined with vehicle dynamics control technology, it can improve the response speed, stability, and safety of vehicle braking during driving.

[0003] When the vehicle brakes, precisely driving the permanent magnet synchronous motor in the electronic mechanical brake (EMB) actuator enables the EMB actuator to quickly and accurately output the brake clamping force, which is a prerequisite for achieving safe vehicle braking.

[0004] In order to solve the problem of brake clamping force output accuracy of the EMB actuator, the present invention proposes a clamping force control method for the EMB actuator of an electric vehicle, which controls the EMB actuator by precisely controlling the permanent magnet synchronous motor to achieve accurate output of the brake clamping force. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a clamping force control method of an EMB actuator of an electric vehicle in view of the above-mentioned deficiencies in the prior art, so as to solve the problems raised in the above-mentioned background technology.

[0006] To solve the above technical problems, the present invention adopts a technical solution: a method for controlling the clamping force of an EMB actuator of an electric vehicle, comprising the following steps: A backstepping controller is used to control the motor used to drive the EMB actuator; the motor load torque is then observed through a load observer. After obtaining the motor load torque, the current position of the motor rotor is obtained through a sensor; the expected motor angle corresponding to the current expected brake clamping force is then obtained based on the brake clamping force and motor angle characteristic curve; finally, based on the deviation between the obtained expected motor angle value and the actual value, combined with the motor load torque, a backstepping controller is designed to achieve precise output control of the brake clamping force.

[0007] As a further explanation of the present invention, the sensor is specifically a Hall sensor capable of calculating the motor rotor speed, motor position and current.

[0008] As a further illustration of the present invention, the load observer completes the observation of the motor load torque and uses it as the input of the backstepping controller. The steps of the load observer are as follows: Set load torque The value of remains unchanged, and the mechanical motion equation of the permanent magnet synchronous motor is determined as follows:

[0009]

[0010] in, is the motor rotor moment of inertia; is the mechanical angular velocity of the motor rotor; is the motor load torque;

[0011] is the electromagnetic torque acting on the motor rotor; is the number of motor pole pairs; is the motor damping coefficient; is the permanent magnet flux; is the q-axis current; Then rewrite the above simulation into the state equation:

[0012] Set the state matrix:

[0013]

[0014]

[0015] Write the observer observability discriminant matrix as

[0016] After the discriminant matrix is ​​obtained to be full rank, the state observation equation is established and the observation error is defined. At the same time, the exponential reaching law is introduced as the sliding mode control rate:

[0017] Where, is the mechanical angular velocity observation value; is the observed value of load torque; is the sliding mode reaching law; is the feedback gain of the sliding mode observer;

[0018] in, is the mechanical angular velocity observation error; is the load torque observation error;

[0019] in, is the switching gain, is the exponential coefficient, , .

[0020] As a further illustration of the present invention, the three-phase currents A, B, and C obtained by the sensor are transformed using Park transformation and Clark transformation to obtain the currents of the direct axis and quadrature axis. The SVPWM algorithm is then used to output PWM modulation waves to achieve motor drive.

[0021] As a further illustration of the present invention, the brake clamping force is generated by the compression of the components of the EMB actuator. The brake clamping force depends on the amount of compression. The brake clamping force and the deformation of the brake friction pad conform to the following cubic polynomial:

[0022] in,

[0023] is the deformation of the brake friction pad, 、 are the coefficients of the cubic polynomial to be fitted; The brake clamping force vs. motor angle characteristic curve was fitted using measured experimental data using a cubic polynomial. The drive motor was controlled starting from 0 rad and rotating in steps of 1 rad, while the corresponding brake clamping force data was recorded. Each experiment was repeated three times and the average value was taken. To eliminate the effects of nonlinear parameters such as motor temperature and mechanical friction in the transmission mechanism on the fitting results, a five-minute interval was maintained between each test.

[0024] As a further illustration of the present invention, the basic steps of the backstepping controller are as follows: First write the permanent magnet synchronous motor system state space equation and define the system error

[0025]

[0026] Where: is the desired motor angle; is the current motor rotor angle; are the virtual control variables to be designed, representing the expected angular velocity, expected quadrature-axis current, and expected direct-axis current of the current system respectively; Represents the motor d-axis current; are the control errors of the subsystems respectively; is the stator resistance of the motor; Then define the Lyapunov functions and virtual control quantities of the three subsystems as

[0027]

[0028]

[0029] Design system control functions

[0030] in, 、 are the voltages of the motor d and q axes respectively.

[0031] Compared with the prior art, the present invention has the following advantages: In the present invention, a backstepping controller is used to precisely control the permanent magnet synchronous motor to control the EMB actuator, thereby achieving precise output of the brake clamping force. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 1 is a control system block diagram of a backstepping brake clamping force control method according to an embodiment of the present invention; Figure 2 2 is a characteristic curve diagram of motor rotation angle and clamping force in an embodiment of the present invention; Figure 3 Schematic diagram of the braking condition simulation results in the experimental example of the present invention.

[0033] (a) Brake clamping force curve under normal braking conditions; (b) Motor speed curve under normal braking conditions; (c) Brake clamping force curve under emergency braking conditions; (d) Motor speed curve under emergency braking condition; (e) Brake clamping force curve when ABS is triggered during emergency braking; (f) Motor speed curve when ABS is triggered during emergency braking. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] like Figure 1 As shown, the present invention provides a technical solution: a method for controlling the clamping force of an EMB actuator of an electric vehicle, characterized in that it includes the following steps: The backstepping controller is used to control the motor used to drive the EMB actuator; the motor is a permanent magnet synchronous motor, and the load torque of the motor is observed through the load observer; The load observer completes the observation of the motor load torque and uses it as the input of the backstepping controller. The steps of the load observer are as follows: Since the control cycle is very short, it is approximately assumed that the load torque value remains unchanged within the control cycle. The value of remains unchanged, and the mechanical motion equation of the permanent magnet synchronous motor is determined as follows:

[0036]

[0037] in, is the motor rotor moment of inertia; is the mechanical angular velocity of the motor rotor; is the motor load torque; is the electromagnetic torque acting on the motor rotor; is the number of motor pole pairs; is the motor damping coefficient; is the permanent magnet flux; is the q-axis current; Then rewrite the above simulation into the state equation:

[0038] Set the state matrix:

[0039]

[0040]

[0041] Write the observer observability discriminant matrix as

[0042] After the discriminant matrix is ​​obtained to be full rank, the state observation equation is established and the observation error is defined. At the same time, the exponential reaching law is introduced as the sliding mode control rate:

[0043] Where, is the mechanical angular velocity observation value; is the observed value of load torque; is the sliding mode reaching law; is the feedback gain of the sliding mode observer;

[0044] in, is the mechanical angular velocity observation error; is the load torque observation error;

[0045] in, is the switching gain, is the exponential coefficient, , .

[0046] The basic steps of the backstepping controller are as follows: First write the permanent magnet synchronous motor system state space equation and define the system error

[0047]

[0048] Where: is the desired motor angle; is the current motor rotor angle; are the virtual control variables to be designed, representing the expected angular velocity, expected quadrature-axis current, and expected direct-axis current of the current system respectively; Represents the motor d-axis current; respectively are control errors of the subsystems; is the motor stator resistance; Lyapunov functions and virtual control variables of the three subsystems are defined respectively as

[0049]

[0050]

[0051] Design system control function

[0052] wherein, , are voltages of the motor d, q axes respectively.

[0053] After the motor load torque is obtained, the current position of the motor rotor is obtained through a sensor, and the sensor is a Hall sensor capable of calculating the motor rotor speed, motor position and current; Then, the expected motor angle corresponding to the expected brake clamping force is obtained according to the brake clamping force and motor angle characteristic curve, and the brake clamping force and motor angle characteristic curve is fitted by actual test data, as shown in Figure 2 The brake clamping force is generated by the compression of the components of the EMB actuator, and the brake clamping force depends on the size of the compression amount. The brake clamping force and the deformation of the brake friction block conform to the following cubic polynomial:

[0054] wherein,

[0055] is the deformation of the brake friction block, , is the coefficient to be fitted of the cubic polynomial; The brake clamping force and motor angle characteristic curve is fitted by actual test data, and the fitting method adopts a cubic polynomial for fitting. The control driving motor starts from 0 rad, and the execution step is 1 rad of angle input. The corresponding brake clamping force data is recorded synchronously, and each group of experiments is repeated 3 times to take the average value. In order to eliminate the influence of nonlinear parameter changes such as motor temperature and transmission mechanism mechanical friction on the fitting results, each test is interval 5 minutes.

[0056] ​The fitting method uses a cubic polynomial for fitting. The specific steps are: finally, based on the deviation between the expected motor angle value and the actual value, combined with the motor load torque, a backstepping controller is designed to achieve precise output control of the brake clamping force; the three-phase currents A, B, and C obtained by the sensor are transformed using Park transformation and Clark transformation; after obtaining the currents of the direct axis and the quadrature axis, a PWM modulation wave is output through the SVPWM algorithm to achieve motor drive.

[0057] Experimental examples, such as Figure 3 As shown in FIG, for emergency braking conditions, three step signals of target brake clamping force are set to 6.5 kN, 13 kN, and 26 kN. The brake clamping force signal steps to the response target value in 0.2 s and maintains it.

[0058] According to experimental results, the brake clearance elimination time of the brake clamping force control method used is approximately 0.0695s, and the response target brake clamping force times under three working conditions are 0.129s, 0.162s, and 0.241s, respectively. In terms of brake clamping force, this control method quickly and accurately achieves the output of brake clamping force without overshoot. The brake clamping force control error can be controlled within 0.1%, and the speed curve is relatively smooth.

[0059] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0060] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the clamping force of an EMB actuator of an electric vehicle, characterized by: The following steps are involved: A backstepping controller is used to control the motor used to drive the EMB actuator; the motor load torque is then observed through a load observer. After obtaining the motor load torque, the current position of the motor rotor is obtained through a sensor; the expected motor angle corresponding to the current expected brake clamping force is then obtained based on the brake clamping force and motor angle characteristic curve; finally, based on the deviation between the obtained expected motor angle value and the actual value, combined with the motor load torque, a backstepping controller is designed to achieve precise output control of the brake clamping force.

2. The clamping force control method of an electric vehicle EMB actuator according to claim 1, characterized in that: The sensor is specifically a Hall sensor capable of calculating the motor rotor speed, motor position and current.

3. The clamping force control method of an electric vehicle EMB actuator according to claim 2, characterized in that: The load observer completes the observation of the motor load torque and uses it as the input of the backstepping controller. The steps of the load observer are as follows: Set load torque The value of remains unchanged, and the mechanical motion equation of the permanent magnet synchronous motor is determined as follows: ； ； in, is the motor rotor moment of inertia; is the mechanical angular velocity of the motor rotor; is the motor load torque; is the electromagnetic torque acting on the motor rotor; is the number of motor pole pairs; is the motor damping coefficient; is the permanent magnet flux; is the q-axis current; Then rewrite the above simulation into the state equation: ； Set the state matrix: ； ； ； Write the observer observability discriminant matrix as ； After the discriminant matrix is ​​obtained to be full rank, the state observation equation is established and the observation error is defined. At the same time, the exponential reaching law is introduced as the sliding mode control rate: ； Where, is the mechanical angular velocity observation value; is the observed value of load torque; is the sliding mode reaching law; is the feedback gain of the sliding mode observer; ； in, is the mechanical angular velocity observation error; is the load torque observation error; ； in, is the switching gain, is the exponential coefficient, ， 。 4. The method for controlling the clamping force of an EMB actuator of an electric vehicle according to claim 3, characterized in that: The three-phase currents A, B, and C obtained by the sensor are transformed using Park transform and Clark transform to obtain the direct-axis and quadrature-axis currents. The SVPWM algorithm is then used to output PWM modulation waves to achieve motor drive.

5. The method for controlling the clamping force of an EMB actuator of an electric vehicle according to claim 1, characterized in that: The basic steps of the backstepping controller are as follows: First write the permanent magnet synchronous motor system state space equation and define the system error ； ； Where: is the desired motor angle; is the current motor rotor angle; are the virtual control variables to be designed, representing the expected angular velocity, expected quadrature-axis current, and expected direct-axis current of the current system respectively; Represents the motor d-axis current; are the control errors of the subsystems respectively; is the stator resistance of the motor; Then define the Lyapunov functions and virtual control quantities of the three subsystems as ； ； ； Design system control functions ； in, 、 are the voltages of the motor d and q axes respectively.

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