A design method for an electronically controlled air suspension controller without air pressure sensor

Abstract

The present invention provides a design method of an electronically controlled air suspension controller without an air pressure sensor, which relates to the technical field of vehicle suspension control, and includes the following steps: S1: establishing a two-degree-of-freedom electronically controlled air suspension model; S2: determining the main control target; S3: designing a sliding mode observer to estimate the internal air pressure of the air spring; S4: designing a suspension controller using the Backstepping method for system errors; S5: building an area-normalized fluid mass model of the air spring, and calculating the area-normalized mass flow between the high-pressure source and the low-pressure source of the air spring; S6: taking the ratio of the expected air flow calculated by the controller to the area-normalized mass flow between the high-pressure source and the low-pressure source of the air spring as the duty cycle, and converting the controller output into a PWM signal for controlling the solenoid valve of the air spring. The present invention aims to control the height of the sprung mass of the vehicle, establishes a performance function constraint error, and uses the Backstepping algorithm to design a controller to calculate the expected output, and finally converts it into a PWM signal to control the solenoid valve of the electronically controlled air suspension to charge and discharge air to achieve height control, so as to improve the ride comfort and smoothness of the vehicle.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle suspension control, and in particular to a design method of an electronically controlled air suspension controller. Background Art

[0002] As a key assembly of the vehicle chassis, the suspension system is an important factor that determines the ride comfort and handling stability of the vehicle. The electronically controlled air suspension has the advantages of intelligent control, which is of great significance to improving the ride comfort and handling stability of the vehicle. Nowadays, the electronically controlled air suspension is recognized as the most promising and core high-end suspension technology in the domestic and foreign markets.

[0003] In order to control the height of the vehicle's sprung mass, the air spring pressure value is often required as a parameter when designing the controller. However, the actual air spring may lack an air pressure sensor, which brings difficulties to the design of the electronic air suspension controller.

[0004] In summary, there is an urgent need to invent a design method for an electronically controlled air suspension controller without an air pressure sensor. Summary of the invention

[0005] The invention provides a design method of an electronically controlled air suspension controller without an air pressure sensor, which solves the height adjustment problem of the electronically controlled air suspension controller lacking an air pressure sensor.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A method for designing an electronically controlled air suspension controller without an air pressure sensor, the method comprising the following steps:

[0008] S1. The established dynamic model of the electronically controlled air suspension is:

[0009]

[0010] where x 1 =z s represents the vertical displacement of the sprung mass, is the vertical velocity of the sprung mass, x 3 =p e Indicates the internal air pressure of the air spring, A e represents the effective area of ​​the air spring, θ represents the inverse of the sprung mass, and b s represents the damping coefficient of the air spring, z u represents the unsprung mass displacement, g represents the acceleration due to gravity, Q m =krT(q in -q out ) / V asCalculate the required output for the controller, k is the gas polytropic index, r is the ratio of the gas constant to the molar mass of air, T is the gas temperature in the air spring, q in and q out Respectively represent the gas flow into and out of the air spring, V as =V 0 +A e (z s -z u ) represents the volume of the air spring, z u is the unsprung mass displacement, V 0 is the volume of the air spring in its initial state, p atm is the atmospheric pressure.

[0011] S2. The main control target is to make the height of the electronically controlled air suspension within the specified height range so that the actual height of the electronically controlled air suspension sprung mass is consistent with the expected height x 1d The error between the two is within the set range, and the sprung mass height error is defined as:

[0012] e 1 (t) = x 1 (t)-x 1d (t).

[0013] S3. Design a sliding mode observer to estimate the internal air pressure of the air spring. The constructed sliding mode observer is:

[0014]

[0015] The sliding mode error is:

[0016]

[0017] The sliding surface is:

[0018]

[0019] S4. The suspension controller is designed using the Backstepping method for system errors, and the intermediate virtual control quantity is obtained as follows:

[0020]

[0021]

[0022] The controller output is:

[0023]

[0024] The expected air flow rate is:

[0025]

[0026] S5. Build an area-normalized fluid mass model for the air spring and calculate the area-normalized mass flow rate between the high-pressure source and the low-pressure source of the air spring; the area-normalized fluid mass model used is:

[0027]

[0028] where q is the area-normalized mass flow rate between the high-pressure source and the low-pressure source, C q is the flow coefficient, p d and p u are the downstream pressure and the upstream pressure, γ is the specific heat of air, and r is the specific gas constant; the flow type depends on p d / p u and critical pressure ratio P cr .

[0029] S6. The ratio of the desired air flow calculated by the controller to the area normalized mass flow between the high-pressure source and the low-pressure source of the air spring is used as the duty cycle, and the controller output is converted into a PWM signal for controlling the air spring solenoid valve. The ratio of the desired air flow calculated by the controller to the flow per unit time of the solenoid valve is the required duty cycle of the PWM signal:

[0030]

[0031] The beneficial effects of the present invention are:

[0032] 1. The present invention adopts a sliding mode observer to estimate the internal air pressure of the air spring, so that the internal air pressure of the air spring can be obtained without an air pressure sensor, and the error is kept within a small range, which provides necessary parameters for the design of the subsequent height controller.

[0033] 2. The present invention adopts the Backstepping method to design a controller for an air suspension without an air pressure sensor. When designing the controller, the air pressure value estimated by the observer is used to replace the actual value of the air spring pressure, thereby achieving control of the air suspension height and ensuring that the vehicle's driving height converges to near the desired height.

[0034] 3. The present invention adopts an area normalized mass flow model to calculate the area normalized mass flow between the high-pressure source and the low-pressure source of the air spring, and converts the output calculated by the controller into a PWM control signal that can be actually used in the air suspension equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 A flow chart for designing the active suspension controller of the present invention.

[0037] Figure 2 It is a schematic diagram of a quarter vehicle with an air spring according to the present invention. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, the numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0042] The present invention provides a technical solution, a design method of an active suspension controller, and the method is as follows:

[0043] S1. First, according to Figure 2 The electronically controlled air suspension model is based on Newton's second law and the first law of thermodynamics, ignoring tire damping, and establishing a two-degree-of-freedom electronically controlled air suspension model:

[0044]

[0045] where x 1 =z s represents the vertical displacement of the sprung mass, is the vertical velocity of the sprung mass, x 3 =p e Indicates the internal air pressure of the air spring, A e represents the effective area of ​​the air spring, θ represents the inverse of the sprung mass, and b s represents the damping coefficient of the air spring, z u represents the unsprung mass displacement, g represents the acceleration due to gravity, Q m =krT(q in -q out ) / V as Calculate the required output for the controller, k is the gas polytropic index, r is the ratio of the gas constant to the molar mass of air, T is the gas temperature in the air spring, q in and q out Respectively represent the gas flow into and out of the air spring, V as =V 0 +A e (z s -z u ) represents the volume of the air spring, z u is the unsprung mass displacement, V 0is the volume of the air spring in its initial state, p atm is the atmospheric pressure.

[0046] S2. Determine the main control target as the height of the electronically controlled air suspension within the specified height range, so that the error between the actual height of the electronically controlled air suspension sprung mass and the expected height is within the set range. Define the sprung mass height error as:

[0047] e 1 (t) = x 1 (t)-x 1d (t)

[0048] S3. Design a sliding mode observer to estimate the internal air pressure of the air spring, and construct the following equation based on the electronically controlled air suspension model:

[0049]

[0050] where z as =z s -z u Represents the deformation of the air spring, and the sliding mode state observer is constructed as follows:

[0051]

[0052] The observer estimation error is:

[0053]

[0054] a in the formula 1 , a 2 The value needs to satisfy the requirement that the eigenvalue of the 2×2 matrix in which it is located is in the left half plane, defining the sliding surface:

[0055]

[0056] The sliding mode conditions are:

[0057]

[0058] Where η is a positive constant, assuming that the sprung mass acceleration error is bounded by a bounded function F

[0059]

[0060] When K 1 When ≥η+F, the sliding mode condition can be met and the sliding mode observer can estimate the air spring pressure.

[0061] S4. Design the suspension controller using the Backstepping method for system errors and construct the first Lyapunov function:

[0062]

[0063] Differentiate it to get:

[0064]

[0065] To ensure system stability, Negative definite, with dummy variable x 2d

[0066]

[0067] where k 1 is any positive constant. 2d The deviation is:

[0068]

[0069] Its differential with respect to time is:

[0070]

[0071] in The expression is:

[0072]

[0073] To make the system stable, ensure Negative definite, get dummy variable:

[0074]

[0075] The differential expression is:

[0076]

[0077] Construct the third Lyapunov function:

[0078]

[0079] Its differential is:

[0080]

[0081] The final output of the controller is:

[0082]

[0083] The expected air flow rate is:

[0084]

[0085] S5. Build an area-normalized fluid mass model for the air spring and calculate the area-normalized mass flow rate between the high-pressure source and the low-pressure source of the air spring. The area-normalized fluid mass model is:

[0086]

[0087] where q is the area-normalized mass flow rate between the high-pressure source and the low-pressure source, C q is the flow coefficient, p d and p u are the downstream pressure and the upstream pressure, γ is the specific heat of air, and r is the specific gas constant; the flow type depends on p d / p u and critical pressure ratio P cr .

[0088] S6. The ratio of the desired air flow calculated by the controller to the area normalized mass flow between the high-pressure source and the low-pressure source of the air spring is used as the duty cycle, and the controller output is converted into a PWM signal for controlling the air spring solenoid valve. The ratio of the desired air flow calculated by the controller to the flow per unit time of the solenoid valve is the required duty cycle of the PWM signal.

[0089]

[0090] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for designing an electronically controlled air suspension controller without an air pressure sensor, characterized in that: The design method comprises the following steps: S1: Establish a two-degree-of-freedom electronically controlled air suspension model; the established electronically controlled air suspension dynamics model is: where x1 = z s represents the vertical displacement of the sprung mass, represents the vertical velocity of the sprung mass, x3=p e Indicates the internal air pressure of the air spring, A e represents the effective area of ​​the air spring, θ represents the inverse of the sprung mass, and b s represents the damping coefficient of the air spring, z u represents the unsprung mass displacement, g represents the acceleration due to gravity, Q m = krT(q in -q out ) / V as Calculate the required output for the controller, k is the gas polytropic index, r is the ratio of the gas constant to the molar mass of air, T is the gas temperature in the air spring, q in and q out Respectively represent the gas flow into and out of the air spring, V as =V0+A e (z s -z u ) represents the volume of the air spring, z u is the unsprung mass displacement, V0 is the volume of the air spring in its initial state, and p atm is the atmospheric pressure; S2: Based on S1, determine the main control objectives to achieve smooth and rapid height adjustment of the sprung mass while ensuring vehicle safety; S3: Based on S2, considering the lack of air pressure sensor in the air spring, a sliding mode observer is designed to estimate the internal air pressure of the air spring; the following equation is constructed according to the electronically controlled air suspension model: where z as =z s -z u Indicates the air spring deformation, m s represents the air suspension sprung mass, and the sliding mode state observer is constructed as follows: The observer estimation error is: The values ​​of a1 and a2 in the formula need to satisfy the requirement that the eigenvalues ​​of the 2×2 matrix in which they are located are in the left half plane, defining the sliding surface: The sliding mode conditions are: Where η is a positive constant, assuming that the sprung mass acceleration error is bounded by a bounding function F: When K1≥η+F, the sliding mode condition is satisfied, and the sliding mode observer can estimate the air spring pressure; S4: Based on S3, the estimated value of the air spring pressure is used as the controller parameter, and the suspension controller is designed using the Backstepping method for the system error; S5: Build an area-normalized fluid mass model for the air spring and calculate the area-normalized mass flow rate between the high-pressure source and the low-pressure source of the air spring; S6: Based on S4 and S5, the ratio of the desired air flow calculated by the controller and the area normalized mass flow between the high-pressure source and the low-pressure source of the air spring is used as the duty cycle, and the controller output is converted into a PWM signal for controlling the air spring solenoid valve.

2. The design method of an electronically controlled air suspension controller without an air pressure sensor according to claim 1, wherein in said S2, the main control target is the height of the electronically controlled air suspension within a specified height range, so that the actual height of the electronically controlled air suspension sprung mass is consistent with the desired height x 1d The error between the two is within the set range, and the sprung mass height error is defined as: e1(t)=x1(t)-x 1d (t)。 3. The method for designing an electronically controlled air suspension controller without an air pressure sensor according to claim 1, wherein in S4, a backstepping method is used to design the controller and a first Lyapunov function is constructed: Differentiate it to get: To ensure system stability, Negative definite, with dummy variable x 2d where k1 is any positive constant, for x 2d The deviation is: Its differential with respect to time is: in The expression is: To make the system stable, ensure Negative definite, get dummy variable: The differential expression is: Construct the third Lyapunov function: Its differential is: The final output of the controller is: The expected air flow rate is:

4. According to the method for designing an electronically controlled air suspension controller without an air pressure sensor in claim 3, in said S5, the area normalized fluid mass model used is: where q is the area-normalized mass flow rate between the high-pressure source and the low-pressure source, C q is the flow coefficient, p d and p u are the downstream pressure and the upstream pressure, γ is the specific heat of air, and r is the specific gas constant; the flow type depends on p d / p u and critical pressure ratio P cr .

5. The design method of an electronically controlled air suspension controller without an air pressure sensor according to claim 4, wherein in S6, the ratio of the desired air flow rate calculated by the controller to the flow rate per unit time of the solenoid valve is the required duty cycle of the PWM signal:

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