A clamping force estimation method for electromechanical brake system based on improved super-helical sliding mode observer

Abstract

The present invention belongs to the field of automobile technology, specifically, a method for estimating the clamping force of an electronic mechanical brake system based on an improved super-helical sliding mode observer. Step one, establish an electronic mechanical brake system model, including a drive motor model, a friction model, and a transmission mechanism model; Step two, use direct testing method, least squares method, and linear regression method to accurately identify the internal parameters of the system friction model, namely, static friction torque, viscous friction coefficient, Coulomb friction torque under no-load, and Coulomb friction coefficient; Step three, based on the above-established accurate electronic mechanical brake system model, design a method for estimating the clamping force of an electronic mechanical brake system based on an improved super-helical sliding mode observer to achieve accurate estimation of the clamping force. The present invention accurately estimates the clamping force of the electronic mechanical brake system, providing a basic basis for the design of future intelligent automobile brake pressure control algorithms.

Description

Technical Field

[0001] The invention belongs to the field of automobile technology, and in particular is a method for estimating the clamping force of an electronic mechanical brake system based on an improved super-helical sliding mode observer. Background Art

[0002] The rapid development of electrification and intelligent vehicles has necessitated new features such as brake energy recovery and active braking in chassis braking systems. Traditional hydraulic brake systems are unable to actively adjust braking force for extended periods, making it difficult to achieve high levels of brake energy recovery. In contrast, electromechanical brake systems eliminate all hydraulic piping and instead utilize a servo motor and transmission mechanism to directly drive the caliper to clamp the wheel for braking. These systems offer advantages such as a simple and compact structure, rapid response, and independent decoupling, making them considered a key development direction for future automotive brake systems. Given the strong coupling, multivariable, and nonlinear characteristics of electromechanical brake systems, pressure sensors are required in practical applications to provide pressure feedback and achieve precise control of clamping force. However, pressure sensors are expensive, and their placement and calibration are challenging within the highly integrated structure of electromechanical brake actuators. Consequently, companies and researchers are currently adopting stiffness characteristic curve and state observer methods to estimate the clamping force of electromechanical brake systems, eliminating pressure sensors and effectively addressing cost and reliability issues. The stiffness characteristic curve method estimates the clamping force based on the relationship between the clamping force and the motor angular displacement, but it cannot overcome the inherent hysteresis problem of the system, and its estimation accuracy decreases with the wear between the brake pad and the brake disc; the state observer method is based on the torque balance equation of the electronic mechanical braking system, and estimates the clamping force according to the input and output of the system, but its anti-interference ability is weak. At the same time, in order to improve the estimation accuracy of the clamping force, it is often necessary to accurately identify the friction model of the system. Summary of the Invention

[0003] To solve the above problems, the present invention provides an electronic mechanical brake system clamping force estimation method based on an improved super-helical sliding mode observer, which accurately estimates the electronic mechanical brake system clamping force and provides a basic basis for the design of future intelligent automobile brake pressure control algorithms.

[0004] The technical solution of the present invention is described as follows in conjunction with the accompanying drawings:

[0005] A method for estimating the clamping force of an electromechanical brake system based on an improved super-helical sliding mode observer comprises the following steps:

[0006] Step 1: Establish an electromechanical brake system model, including a drive motor model, a friction model, and a transmission mechanism model;

[0007] Step 2: Use direct testing method, least square method and linear regression method to calculate the internal parameter of the system friction model, static friction torque T s , viscous friction coefficient D, Coulomb friction torque C and Coulomb friction coefficient G under no load for accurate identification;

[0008] Step 3: Based on the accurate electro-mechanical brake system model established above, a clamping force estimation method for the electro-mechanical brake system based on an improved super-helical sliding mode observer is designed to achieve accurate estimation of the clamping force.

[0009] Furthermore, the specific method of step one is as follows:

[0010] 11) Assuming that the drive motor of the electronic mechanical brake system adopts an ideal permanent magnet synchronous motor and ignoring eddy current and hysteresis losses, the stator voltage equation on the excitation axis-torque axis is established as follows:

[0011]

[0012] Where u d is the motor excitation shaft voltage; u q is the motor torque shaft voltage; R is the motor stator resistance; i d is the motor excitation shaft current; i q is the motor excitation torque shaft current; L d is the motor excitation shaft inductance; L q is the motor torque shaft inductance; ψ f is the motor rotor flux; ω e is the motor electrical angular velocity;

[0013] The electromagnetic torque equation of the surface-mounted permanent magnet synchronous motor is:

[0014] T m =K T i q (2)

[0015] K T =1.5P n ψ f (3)

[0016] Where, T m is the motor torque; K T is the motor torque coefficient; P n is the number of motor pole pairs; i q is the actual motor excitation torque shaft current; f is the motor rotor flux;

[0017] According to the balance relationship of the output shaft of the drive motor, the kinematic equation of the drive motor is established as follows:

[0018]

[0019] Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque;

[0020] 12) The friction model of the electronic mechanical brake system is established as:

[0021]

[0022] Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force; ε is the critical speed, which is close to 0; T m is the driving motor torque; T L is the load torque; T s is the static friction torque;

[0023] 13) The transmission mechanism of the electronic mechanical brake system consists of a planetary gear reducer and a ball screw pair. The planetary gear reducer amplifies the motor torque, and the ball screw pair converts the torque into axial thrust, thereby pushing the brake caliper to clamp the brake disc, generating a clamping force F cl At the same time, the clamping force generated will also react on the motor through the transmission mechanism to form a load torque T L for:

[0024] T L =NF cl (6)

[0025]

[0026] Where, T L is the load torque; N is the torque amplification factor; F cl is the clamping force; L is the ball screw lead; η s is the transmission efficiency of the ball screw pair; i is the transmission ratio of the planetary gear reducer; η p is the transmission efficiency of the planetary gear reducer.

[0027] Furthermore, the specific method of step 2 is as follows:

[0028] 21) For static friction torque T s According to the motor torque balance equation (4), under the condition of no load and zero mechanical angular acceleration of the motor, the friction torque is equal to the motor torque, that is, T f =Tm Keep the piston in the electronic mechanical brake system in the gap stage, that is, the no-load state, and control the motor current to gradually increase until the ball screw displacement changes, and record the corresponding motor torque at this time; measure the motor torque corresponding to different positions within the brake gap range multiple times, and take the average value as the static friction torque T of the system. s ;

[0029] 22) For the viscous friction coefficient D and the Coulomb friction torque C without load, according to the friction model (5), when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the formula for the friction torque is:

[0030] T f =Dω m +C (8)

[0031] Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load;

[0032] The drive motor is controlled to rotate at a constant speed during the gap elimination process of the electronic mechanical brake system. The motor torque corresponding to different motor mechanical angular velocities is recorded. The relationship curve between the friction torque and the motor mechanical angular velocity is fitted using the least squares method. The slope of the curve is the viscous friction coefficient D, and the offset is the Coulomb friction torque C under no-load conditions.

[0033] 23) For the Coulomb friction coefficient G, when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the friction model (5) is rewritten into a matrix form:

[0034]

[0035] Where, T f is the friction torque; D is the viscous friction coefficient; ω is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force;

[0036] Let X = [ωsign(ω)F cl sign(ω)],Y=T f , but

[0037] Y=XZ (11)

[0038] Then, through linear regression method, we get:

[0039] Z=(X T X) -1 X TY (12)

[0040] The friction torque is obtained from the motor torque balance equation (4):

[0041]

[0042] Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque;

[0043] Given the step current of the driving motor of the electronic mechanical brake system, the motor mechanical angular velocity, motor torque and load torque in the dynamic process are collected, and the corresponding friction torque under different loads is calculated according to formula (13). Then, the linear regression equation (11) is applied to obtain the Coulomb friction coefficient G.

[0044] 24) Determine whether the friction model simulation curve after identification is consistent with the actual friction torque curve; if it meets the requirements, output the accurate friction model T f ; If the requirements are not met, the friction model parameter identification is performed again until the requirements are met.

[0045] Furthermore, the specific method of step three is as follows:

[0046] 31) In the electronic mechanical braking system, the state variable is selected as the motor mechanical angular velocity ω m , Substitute the transmission mechanism model (6) into the motor torque balance equation (4), and the state equation is obtained:

[0047]

[0048] Where, ω m is the mechanical angular velocity of the motor; J is the equivalent moment of inertia converted to the motor shaft; T m is the electromagnetic torque of the motor; T f is the friction torque; N is the amplification factor; F cl is the clamping force;

[0049] 32) Two linear terms of observation errors are added to the traditional super-helical sliding mode observer. The basic structure is as follows:

[0050]

[0051] Where, is the estimated value of the motor mechanical angular velocity; is the motor mechanical angular velocity error value; J is the equivalent moment of inertia converted to the motor shaft; k1, k2, k3 and k4 are the observer gain parameters; is the disturbance term; T m is the motor torque; T f is the friction torque;

[0052] 33) The observer parameters k1, k2, k3 and k4 should be selected to meet the following range:

[0053]

[0054] Where k1, k2, k3 and k4 are observer gain parameters; δ1, δ2, δ3 and δ4 are constants greater than 0;

[0055] And the disturbance term The upper bound is satisfied:

[0056]

[0057] Where, is the disturbance term; ω m is the motor mechanical angular velocity; δ1 and δ2 are constants greater than 0, which can ensure the stability of the system and converge to the sliding surface in a finite time;

[0058] When the system is stable on the sliding surface, the estimated clamping force is calculated as follows:

[0059]

[0060] Where, is the estimated clamping force; k1, k2, k3 and k4 are the observer gain parameters; is the motor mechanical angular velocity error.

[0061] The beneficial effects of the present invention are:

[0062] 1) The present invention establishes an electromechanical brake system model including the drive motor, transmission mechanism, and mechanical friction, which fully reflects the key behavioral characteristics exhibited during the operation of the electromechanical brake system;

[0063] 2) The present invention designs a typical experimental friction model identification process method, and identifies the internal parameters of the friction model based on direct testing method, least square method and linear regression method to obtain an accurate friction model;

[0064] 3) A clamping force estimation strategy for an electromechanical brake system based on a super-helical sliding mode observer is adopted to achieve accurate estimation of the clamping force;

[0065] 4) The present invention improves the clamping force estimation effect by adding two observation error linear terms on the basis of the traditional observer, which can not only suppress the chattering phenomenon of the observer, but also enhance the dynamic performance and anti-interference ability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0067] Figure 1 It is a framed schematic diagram of the present invention;

[0068] Figure 2 Schematic diagram of the structure of the electronic mechanical brake;

[0069] Figure 3 Schematic diagram of the process for accurate identification of internal parameters of the friction model;

[0070] Figure 4 is the static friction torque T s Schematic diagram of identification experiment curve;

[0071] Figure 5 Schematic diagram of the fitting curve of friction torque and motor mechanical angular velocity;

[0072] Figure 6 Schematic diagram of friction torque data points corresponding to different clamping forces;

[0073] Figure 7 Schematic diagram of the estimation method effect. DETAILED DESCRIPTION

[0074] 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0075] Example 1

[0076] This embodiment provides a method for estimating the clamping force of an electromechanical brake system based on an improved super-helical sliding mode observer. Figure 1 The figure shows the architecture of the clamping force estimation method for an electronic mechanical brake system based on an improved super-helical sliding mode observer designed in this invention. First, a model including the drive motor, transmission mechanism, and mechanical friction is established based on the working principle of the electronic mechanical brake system. Then, according to the typical experimental friction model identification process, the static friction torque T of the friction model internal parameter is determined by direct testing, least squares method, and linear regression method. s, viscous friction coefficient D, Coulomb friction torque C under no-load conditions, and Coulomb friction coefficient G are identified to obtain an accurate friction model. Finally, a clamping force estimation strategy for an electromechanical brake system based on an improved super-helical sliding mode observer is designed to achieve accurate clamping force estimation and enhance the system's dynamic performance and anti-interference capabilities. The details are as follows:

[0077] Step 1: Establish an electromechanical brake system model as follows:

[0078] The schematic diagram of the electromechanical brake system is as follows: Figure 2 As shown, it consists of a drive motor, transmission mechanism, brake caliper, brake disc and other components. Its specific working principle is described as follows:

[0079] (1) According to the top-level braking requirements, the internal drive motor of the electronic mechanical brake system operates to output torque; (2) The transmission mechanism consists of two parts: a planetary gear reducer and a ball screw pair. The motor torque is amplified by the planetary gear and transmitted to the ball screw. The ball screw mechanism converts the output torque of the planetary gear into axial force and outputs it through the screw nut; (3) The screw nut pushes the brake pad, driving the brake caliper to clamp the brake disc to generate braking force.

[0080] 11) Assuming that the drive motor of the electronic mechanical brake system adopts an ideal permanent magnet synchronous motor and ignoring eddy current and hysteresis losses, the stator voltage equation on the excitation axis-torque axis is established as follows:

[0081]

[0082] Where u d is the motor excitation shaft voltage; u q is the motor torque shaft voltage; R is the motor stator resistance; i d is the motor excitation shaft current; i q is the motor excitation torque shaft current; L d is the motor excitation shaft inductance; L q is the motor torque shaft inductance; ψ f is the motor rotor flux; ω e is the motor electrical angular velocity;

[0083] The electromagnetic torque equation of the surface-mounted permanent magnet synchronous motor is:

[0084] T m =K T i q (2)

[0085] K T =1.5P n ψ f (3)

[0086] Where, Tm is the motor torque; K T is the motor torque coefficient; P n is the number of motor pole pairs; i q is the actual motor excitation torque shaft current; f is the motor rotor flux;

[0087] According to the balance relationship of the output shaft of the drive motor, the kinematic equation of the drive motor is established as follows:

[0088]

[0089] Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque;

[0090] 12) Considering factors such as static friction, viscous friction and Coulomb friction, the friction model of the electronic mechanical brake system is established as follows:

[0091]

[0092] Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force; ε is the critical speed, which is close to 0; T m is the driving motor torque; T L is the load torque; T s is the static friction torque;

[0093] 13) The transmission mechanism of the electronic mechanical brake system consists of a planetary gear reducer and a ball screw pair. The planetary gear reducer amplifies the motor torque, and the ball screw pair converts the torque into axial thrust, thereby pushing the brake caliper to clamp the brake disc, generating a clamping force F cl At the same time, the clamping force generated will also react on the motor through the transmission mechanism to form a load torque T L for:

[0094] T L =NF cl (6)

[0095]

[0096] Where, T L is the load torque; N is the torque amplification factor; F cl is the clamping force; L is the ball screw lead; ηs is the transmission efficiency of the ball screw pair; i is the transmission ratio of the planetary gear reducer; η p is the transmission efficiency of the planetary gear reducer.

[0097] Step 2: Use direct testing method, least square method and linear regression method to calculate the internal parameter of the system friction model, static friction torque T s , viscous friction coefficient D, Coulomb friction torque C and Coulomb friction coefficient G under no load are accurately identified as follows:

[0098] 21) According to Figure 3 The typical experimental identification friction model process method designed first conducts the static friction torque T s According to the motor torque balance equation (4), under the condition of no load and zero mechanical angular acceleration of the motor, the friction torque is equal to the motor torque, that is, T f =T m Keep the piston in the electronic mechanical brake system in the gap stage, that is, the no-load state, and control the motor current to gradually increase until the ball screw displacement changes, and record the corresponding motor torque at this time; measure the motor torque corresponding to different positions within the brake gap range multiple times, and take the average value as the static friction torque T of the system. s ,like Figure 4 As shown;

[0099] 22) For the viscous friction coefficient D and the Coulomb friction torque C without load, according to the friction model (5), when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the formula for the friction torque is:

[0100] T f =Dω m +C (8)

[0101] Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load;

[0102] The drive motor is controlled to rotate at a constant speed during the gap elimination process of the electronic mechanical brake system, and the motor torque corresponding to different motor mechanical angular velocities is recorded. The relationship curve between the friction torque and the motor mechanical angular velocity is fitted by the least squares method. The slope of the curve is the viscous friction coefficient D, and the offset is the Coulomb friction torque C when there is no load, as shown in the figure. Figure 5 As shown;

[0103] 23) For the Coulomb friction coefficient G, when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the friction model (5) is rewritten into a matrix form:

[0104]

[0105] Where, T f is the friction torque; D is the viscous friction coefficient; ω is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force;

[0106] Let X = [ωsign(ω)F cl sign(ω)],Y=T f ,

[0107] but

[0108] Y=XZ (11)

[0109] Then, through linear regression method, we get:

[0110] Z=(X T X) -1 X T Y (12)

[0111] The friction torque is obtained from the motor torque balance equation (4):

[0112]

[0113] Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque;

[0114] Given the step current of the driving motor of the electronic mechanical brake system, the motor mechanical angular velocity, motor torque and load torque in the dynamic process are collected, and the corresponding friction torque under different loads is calculated according to formula (13). Then, the linear regression equation (11) is applied to obtain the Coulomb friction coefficient G, as shown in the following example: Figure 6 As shown;

[0115] 24) Determine whether the friction model simulation curve after identification is consistent with the actual friction torque curve; if it meets the requirements, output the accurate friction model T f ; If the requirements are not met, the friction model parameter identification is performed again until the requirements are met.

[0116] Step 3: Based on the accurate electromechanical brake system model established above, a clamping force estimation method for the electromechanical brake system based on an improved super-helical sliding mode observer is designed to achieve accurate estimation of the clamping force, as follows:

[0117] 31) In the electronic mechanical braking system, the state variable is selected as the motor mechanical angular velocity ω m , Substitute the transmission mechanism model (6) into the motor torque balance equation (4), and the state equation is obtained:

[0118]

[0119] Where, ω m is the mechanical angular velocity of the motor; J is the equivalent moment of inertia converted to the motor shaft; T m is the electromagnetic torque of the motor; T f is the friction torque; N is the amplification factor; F cl is the clamping force;

[0120] 32) Two linear terms of observation errors are added to the traditional super-helical sliding mode observer. The basic structure is as follows:

[0121]

[0122]

[0123] Where, is the estimated value of the motor mechanical angular velocity; is the motor mechanical angular velocity error value; J is the equivalent moment of inertia converted to the motor shaft; k1, k2, k3 and k4 are the observer gain parameters; is the disturbance term; T m is the motor torque; T f is the friction torque;

[0124] 33) The observer parameters k1, k2, k3 and k4 should be selected to meet the following range:

[0125]

[0126] Where k1, k2, k3 and k4 are observer gain parameters; δ1, δ2, δ3 and δ4 are constants greater than 0;

[0127] And the disturbance term The upper bound is satisfied:

[0128]

[0129] Where, is the disturbance term; ω m is the motor mechanical angular velocity; δ1 and δ2 are constants greater than 0, which can ensure the stability of the system and converge to the sliding surface in a finite time;

[0130] When the system is stable on the sliding surface, the estimated clamping force is calculated as follows:

[0131]

[0132] Where, is the estimated clamping force; k1, k2, k3 and k4 are the observer gain parameters; is the motor mechanical angular velocity error.

[0133] Example 2

[0134] This embodiment uses a simulation platform based on MATLAB / Simulink to test the clamping force estimation method of the electromechanical brake system designed by the present invention. A simulation experiment is carried out with a sinusoidal clamping force of 10000N offset, 8000N amplitude and 1Hz frequency as the control target of the electromechanical brake system. The test results are shown in Figure 2. Figure 7 As shown. Figure 7 It can be seen that the clamping force estimation value output by the caliper braking force estimation method of the electro-mechanical brake system established in the present invention closely follows the actual clamping force value.

[0135] In summary, the present invention accurately estimates the clamping force of the electromechanical brake system, providing a basic basis for the design of brake pressure control algorithms for future intelligent vehicles.

[0136] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the scope of protection of the present invention is not limited to the specific details of the above embodiments. Within the technical concept of the present invention, any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and inventive concept of the present invention within the technical scope disclosed by the present invention. These simple variations all fall within the scope of protection of the present invention.

[0137] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0138] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for estimating the clamping force of an electromechanical brake system based on an improved super-helical sliding mode observer, characterized in that: The following steps are involved: Step 1: Establish an electromechanical brake system model, including a drive motor model, a friction model, and a transmission mechanism model; Step 2: Use direct testing method, least square method and linear regression method to calculate the internal parameter of the system friction model, static friction torque T s , viscous friction coefficient D, Coulomb friction torque C and Coulomb friction coefficient G under no load for accurate identification; Step 3: Based on the accurate electro-mechanical brake system model established above, a clamping force estimation method for the electro-mechanical brake system based on an improved super-helical sliding mode observer is designed to achieve accurate estimation of the clamping force; The specific method of step three is as follows: 31) In the electronic mechanical braking system, the state variable is selected as the motor mechanical angular velocity ω m , Substitute the transmission mechanism model (6) into the motor torque balance equation (4), and the state equation is obtained: Where, ω m is the mechanical angular velocity of the motor; J is the equivalent moment of inertia converted to the motor shaft; T m is the electromagnetic torque of the motor; T f is the friction torque; N is the amplification factor; F cl is the clamping force; 32) Two linear terms of observation errors are added to the traditional super-helical sliding mode observer. The basic structure is as follows: Where, is the estimated value of the motor mechanical angular velocity; is the motor mechanical angular velocity error value; J is the equivalent moment of inertia converted to the motor shaft; k1, k2, k3 and k4 are the observer gain parameters; is the disturbance term; T m is the motor torque; T f is the friction torque; 33) The observer parameters k1, k2, k3 and k4 should be selected to meet the following range: Where k1, k2, k3 and k4 are observer gain parameters; δ1, δ2, δ3 and δ4 are constants greater than 0; And the disturbance term The upper bound is satisfied: Where, is the disturbance term; ω m is the motor mechanical angular velocity; δ1 and δ2 are constants greater than 0, which can ensure the stability of the system and converge to the sliding surface in a finite time; When the system is stable on the sliding surface, the estimated clamping force is calculated as follows: Where, is the estimated clamping force; k1, k2, k3 and k4 are the observer gain parameters; is the motor mechanical angular velocity error.

2. According to the method for estimating the clamping force of an electromechanical brake system based on an improved super-helical sliding mode observer of claim 1, the specific method of step 1 is as follows: 11) Assuming that the drive motor of the electronic mechanical brake system adopts an ideal permanent magnet synchronous motor and ignoring eddy current and hysteresis losses, the stator voltage equation on the excitation axis-torque axis is established as follows: Where u d is the motor excitation shaft voltage; u q is the motor torque shaft voltage; R is the motor stator resistance; i d is the motor excitation shaft current; i q is the motor excitation torque shaft current; L d is the motor excitation shaft inductance; L q is the motor torque shaft inductance; f is the motor rotor flux; ω e is the motor electrical angular velocity; The electromagnetic torque equation of the surface-mounted permanent magnet synchronous motor is: T m =K T i q (2) K T =1.5P n ψ f (3) Where, T m is the motor torque; K T is the motor torque coefficient; P n is the number of motor pole pairs; i q is the actual motor excitation torque shaft current; f is the motor rotor flux; According to the balance relationship of the output shaft of the drive motor, the kinematic equation of the drive motor is established as follows: Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque; 12) The friction model of the electronic mechanical brake system is established as: Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force; ε is the critical speed, which is close to 0; T m is the driving motor torque; T L is the load torque; T s is the static friction torque; 13) The transmission mechanism of the electronic mechanical brake system consists of a planetary gear reducer and a ball screw pair. The planetary gear reducer amplifies the motor torque, and the ball screw pair converts the torque into axial thrust, thereby pushing the brake caliper to clamp the brake disc, generating a clamping force F cl At the same time, the clamping force generated will also react on the motor through the transmission mechanism to form a load torque T L for: Where, T L is the load torque; N is the torque amplification factor; F cl is the clamping force; L is the ball screw lead; η s is the transmission efficiency of the ball screw pair; i is the transmission ratio of the planetary gear reducer; η p is the transmission efficiency of the planetary gear reducer.

3. According to the method for estimating the clamping force of an electromechanical brake system based on an improved super-helical sliding mode observer of claim 2, the specific method of step 2 is as follows: 21) For static friction torque T s According to the motor torque balance equation (4), under the condition of no load and zero mechanical angular acceleration of the motor, the friction torque is equal to the motor torque, that is, T f =T m Keep the piston in the electronic mechanical brake system in the gap stage, that is, the no-load state, and control the motor current to gradually increase until the ball screw displacement changes, and record the corresponding motor torque at this time; measure the motor torque corresponding to different positions within the brake gap range multiple times, and take the average value as the static friction torque T of the system. s ; 22) For the viscous friction coefficient D and the Coulomb friction torque C without load, according to the friction model (5), when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the formula for the friction torque is: T f =Dω m +C (8) Where, T f is the friction torque; D is the viscous friction coefficient; ω m is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; The drive motor is controlled to rotate at a constant speed during the gap elimination process of the electronic mechanical brake system. The motor torque corresponding to different motor mechanical angular velocities is recorded. The relationship curve between the friction torque and the motor mechanical angular velocity is fitted using the least squares method. The slope of the curve is the viscous friction coefficient D, and the offset is the Coulomb friction torque C under no-load conditions. 23) For the Coulomb friction coefficient G, when the motor mechanical angular velocity ω m When the speed is greater than the critical speed ε, the friction model (5) is rewritten into a matrix form: Where, T f is the friction torque; D is the viscous friction coefficient; ω is the motor mechanical angular velocity; C is the Coulomb friction torque when there is no load; G is the Coulomb friction coefficient; F cl is the clamping force; Let X = [ω sign(ω) F cl sign(ω)], Y = T f , but Y=XZ (11) Then, through linear regression method, we get: Z=(X T X) -1 X T Y (12) The friction torque is obtained from the motor torque balance equation (4): Where, J is the equivalent moment of inertia converted to the motor shaft; ω m is the motor mechanical angular velocity; T m is the motor torque; T f is the friction torque; T L is the load torque; Given the step current of the driving motor of the electronic mechanical brake system, the motor mechanical angular velocity, motor torque and load torque in the dynamic process are collected, and the corresponding friction torque under different loads is calculated according to formula (13). Then, the linear regression equation (11) is applied to obtain the Coulomb friction coefficient G. 24) Determine whether the friction model simulation curve after identification is consistent with the actual friction torque curve; if it meets the requirements, output the accurate friction model T f ; If the requirements are not met, the friction model parameter identification is performed again until the requirements are met.

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