A method for establishing mathematical model of air spring control system

Abstract

A method for establishing a mathematical model of an air spring control system comprises the following steps: 1) establishing an air path mass flow equation group for determining the gas mass flow state of the air spring control system; 2) establishing an air spring internal pressure change equation group for reflecting the air pressure change in the air spring inner cavity; 3) establishing a suspension-body dynamics equation group for accurately expressing the relationship between the lifting acceleration, lifting speed, lifting height of the current suspension and the sprung mass, the air spring vertical force, the suspension friction force, the shock absorber damping force, and the force generated by the parasitic stiffness of the suspension; 4) combining the air path mass flow equation group, the air spring internal pressure change equation group, and the suspension-body dynamics equation group to construct an air spring control system mathematical model for the design of the air spring control system and to control the operation of the air spring control system.

Description

Technical Field

[0001] The invention relates to the field of suspension control, and in particular to a method for establishing a mathematical model of an air spring control system. Background Art

[0002] The air spring suspension electronic control system consists of a continuous damping control system (CDC) and an electronic-controlled air suspension (ECAS). The air spring control system, also known as the electronically controlled air suspension system, consists of a pressure sensor, a temperature sensor, a height sensor, a gas distribution valve, an air compressor, an air tank, and an air spring. Its function is to control the height and stiffness of the vehicle by collecting sensor signals, vehicle CAN bus signals, HMI interaction signals, and the driver's driving status, thereby improving the smoothness of the vehicle's ride.

[0003] However, the parameters involved in the operation of the air spring control system are mainly divided into the following two categories:

[0004] ① Many parameters directly related to the air spring control system (hereinafter referred to as key parameters): air spring body parameters (for example, the inner cavity volume of the air spring, the air pressure of the inner cavity of the air spring), air tank volume, air tank pressure, equivalent air path flow resistance coefficient, equivalent air path pipeline diameter, air compressor flow, etc.;

[0005] ② Many parameters indirectly related to the air spring control system (hereinafter referred to as vehicle parameters): single wheel spring mass, suspension lever ratio, suspension parasitic stiffness, suspension dynamic / static friction, shock absorber damping, etc.;

[0006] Usually, the vehicle manufacturer must determine the "vehicle parameters", and then the air spring manufacturer will determine the "key parameters" of the air spring body and the air spring control system based on the "vehicle parameters" for design and manufacturing. During the entire design and manufacturing process, different design teams of the air spring manufacturer are responsible for the design of different parameter values. After the values ​​of all parameters are designed, the air spring control system is manufactured based on these parameter values. Due to the large number of parameters, each parameter will affect each other. Usually, the air spring control system manufactured according to the parameter values ​​designed in the early stage cannot meet the factory requirements of the system lifting performance in the vehicle lifting performance debugging test. This requires each design team to continue to communicate with each other based on the test results, constantly redesign the values ​​of each parameter, and debug repeatedly until the manufactured air spring control system achieves the required lifting performance. This way of designing and manufacturing air spring control systems is time-consuming and labor-intensive, and greatly affects work efficiency.

[0007] Moreover, in actual applications, as the air spring control system is used for a long time, some parameter values ​​will change (for example, the inner volume of the air spring due to the aging of the bladder skin, the output flow of the air compressor due to the wear of the air compressor piston, the parasitic stiffness of the suspension due to the aging of the rubber bushing, the damping of the shock absorber due to the aging of the shock absorber, etc.), which will affect the normal operation of the entire air spring control system, and the vehicle's lifting height cannot be accurately controlled during driving, which greatly reduces the smoothness of the vehicle's driving. Summary of the invention

[0008] The purpose of the present invention is to provide a method for establishing a mathematical model of an air spring control system in response to the corresponding deficiencies in the prior art. First, a group of gas path mass flow equations is established according to the flow characteristics of the gas pipeline system, and a group of air spring internal pressure change equations is established according to the first law of thermodynamics and the gas state equation. Then, a group of suspension-body dynamics equations is established according to the law of force balance and Newton's second law. Finally, a mathematical model of an air spring control system is constructed using the group of gas path mass flow equations, the group of air spring internal pressure change equations, and the group of suspension-body dynamics equations. The design values ​​of key parameters of the air spring control system are determined by substituting the vehicle parameters into the mathematical model of the air spring control system, which are used for the design of the air spring control system and the operation of the air spring control system is controlled.

[0009] The object of the present invention is achieved by adopting the following scheme: A method for establishing a mathematical model of an air spring control system comprises the following steps:

[0010] 1) According to the flow characteristics of the gas pipeline system, a gas path mass flow equation group is established to determine the gas mass flow state of the air spring control system;

[0011] 2) According to the first law of thermodynamics and the gas state equation, the air spring internal pressure change equation group is established to reflect the air pressure change in the air spring cavity;

[0012] 3) According to the law of force balance and Newton's second law, a group of suspension-body dynamic equations is established to accurately express the relationship between the current suspension lifting acceleration, lifting speed, lifting height and the sprung mass, air spring vertical force, suspension friction, shock absorber damping force, and the force generated by the suspension parasitic stiffness;

[0013] 4) Combine the gas path mass flow equations, the air spring internal pressure change equations, and the suspension-body dynamics equations to construct a mathematical model of the air spring control system. Substitute the vehicle parameters into the mathematical model of the air spring control system to determine the design values ​​of the key parameters of the air spring control system, which are used to design the air spring control system and control the operation of the air spring control system.

[0014] Preferably, the gas path mass flow equation group includes a gas path mass flow model during the air spring inflation phase and a gas path mass flow model during the air spring deflation phase:

[0015] 1-1) Air path mass flow model during air spring inflation

[0016] q e-1 =max(q a ,q b )

[0017]

[0018] In the formula, q e-1 is the gas path mass flow rate during the air spring inflation phase, q a The mass flow rate of the air path when the air tank directly inflates the inner cavity of the air spring, q b is the gas mass flow rate when the air compressor extracts gas from the air tank to inflate the air spring, μ is the equivalent gas path flow resistance coefficient, A is the equivalent gas resistance geometric cross-sectional area, P t is the absolute pressure inside the gas tank, P s is the absolute pressure of the air spring cavity at the current moment (i.e., this is a variable during the operation of the air spring and will change with the opening time of the ventilation valve), T t is the thermodynamic temperature of the gas in the gas tank, k is the gas adiabatic index, R is the gas constant, σ e is the critical gas pressure ratio, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, and η is the working efficiency of the air compressor;

[0019] 1-2) Air spring air path mass flow model during deflation phase

[0020]

[0021] In the formula, q e-2 is the air mass flow rate of the air spring during the deflation phase, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, R is the gas constant, P s is the absolute pressure of the air spring cavity at the current moment, T s is the thermodynamic temperature of the gas in the inner cavity of the air spring, and η is the working efficiency of the air compressor.

[0022] Preferably, the air spring internal pressure variation equation group includes an internal pressure variation model in a constant volume inflation stage, an internal pressure variation model in a variable volume inflation stage, an internal pressure variation model in a polyvariable balance stage of an inflation process, an internal pressure variation model in a constant volume deflation stage, an internal pressure variation model in a variable volume deflation stage, and an internal pressure variation model in a polyvariable balance stage of a deflation process:

[0023] 2-1) Internal pressure change model during constant volume inflation:

[0024]

[0025] In the formula, is the absolute pressure change rate inside the air spring during the constant volume inflation stage, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state;

[0026] 2-2) Model of internal pressure change during variable volume inflation stage:

[0027]

[0028] In the formula, is the absolute pressure change rate inside the air spring during the variable volume inflation stage, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state. is the rate of change of the air spring inner cavity volume, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, and v2 is the velocity of the sprung mass;

[0029] 2-3) Model of internal pressure change in the multivariable equilibrium stage of the inflation process:

[0030]

[0031] Where P s1 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the charging phase. s1 P is the volume of the air spring cavity before the solenoid valve is closed during the charging phase. s2 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the inflation phase. s2 is the volume of the air spring cavity after the solenoid valve is closed during the charging phase, and w is the polynomial index;

[0032] 2-4) Internal pressure change model during constant volume deflation stage:

[0033]

[0034] In the formula, is the absolute pressure change rate inside the air spring during the constant volume deflation stage, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 It is the inner cavity volume of the air spring when it is in the designed load state;

[0035] 2-5) Model of internal pressure change during variable volume deflation stage:

[0036]

[0037] In the formula, is the absolute pressure change rate inside the air spring during the variable volume deflation stage, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 It is the inner cavity volume of the air spring when it is in the designed load state. is the rate of change of the air spring inner cavity volume, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, and v2 is the velocity of the sprung mass;

[0038] 2-6) Model of internal pressure change in the multivariable equilibrium stage of the deflation process

[0039]

[0040] Where P s3 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the deflation phase. s3 P is the volume of the air spring cavity before the solenoid valve is closed during the deflation phase. s4 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. s4 It is the volume of the air spring cavity after the solenoid valve is closed during the deflation stage, and w is the polynomial index.

[0041] Preferably, the suspension-body dynamics equations include a constant volume filling / deflating stage dynamics model and a variable volume filling / deflating to multi-variable equilibrium stage dynamics model:

[0042] 3-1) Constant volume filling / deflating stage kinetic model:

[0043] F s1 λ-f1=0

[0044] F s1 =(P s -P s0 )A e0

[0045] Where λ is the air spring lever ratio, f1 is the static friction of the suspension, and F s1 is the restoring force of the air spring during the constant volume filling / deflating stage, P s is the absolute pressure of the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0046] 3-2) Kinetic model of variable volume filling / deflating to multi-variable equilibrium stage:

[0047] F s2 λ-K j (x2-x1)-C(v2-v1)-f2=m u a

[0048] Where λ is the air spring lever ratio, K j is the parasitic stiffness of the suspension, x1 is the displacement of the unsprung mass, x2 is the displacement of the sprung mass, C is the equivalent damping coefficient of the shock absorber, v1 is the velocity of the unsprung mass, v2 is the velocity of the sprung mass, f2 is the dynamic friction of the suspension, m u is the mass on the suspension spring, a is the acceleration of the mass on the spring, F s2 The restoring force of an air spring during variable volume filling / deflating to a variable balance stage.

[0049] Preferably, the calculation formula of the restoring force of the air spring from the variable volume charging / deflating to the multi-variable balance stage under different conditions is as follows:

[0050] ① Variable volume filling / deflating stage:

[0051] F s2 =P s A e -P s0 A e0

[0052] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s is the absolute pressure of the air spring cavity at the current moment, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0053] ②Multiple balance stages of inflation process:

[0054] F s2 =P s2 A e -P s0 A e0

[0055] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s2 is the absolute pressure in the air spring cavity after the solenoid valve is closed during the charging phase, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0056] ③Multiple equilibrium stages of deflation process:

[0057] F s2 =P s4 A e -P s0 A e0

[0058] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s4 A is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state.

[0059] The advantages of the present invention are as follows:

[0060] ① In the design stage of the air spring system, the mathematical model of the air spring control system established by the present invention can easily determine the final design value of the "key parameter" according to the "whole vehicle parameter" of the air spring system, which greatly improves the work efficiency of designing and manufacturing the "air spring body" and "air spring control system", saving time and effort;

[0061] ② In the application stage of the air spring system, the mathematical model of the air spring control system established by the present invention can dynamically adjust the control parameters of the air spring control system according to the numerical changes of the "whole vehicle parameters" and "key parameters", so that the entire air spring control system always maintains a normal operating state. In this way, the control accuracy of the vehicle (i.e., displacement accuracy and speed accuracy) can be accurately restored during the vehicle's driving process, so that the lifting and lowering accuracy of the automobile suspension can be guaranteed, and the smoothness and safety of the vehicle's driving can be guaranteed as much as possible.

[0062] Glossary

[0063] Gas path mass flow rate: The gas mass flow rate in the pipelines connected within the entire air spring control system.

[0064] Inflate / Deflate: Inflate or deflate.

[0065] Cylinder: A cylinder is a cylindrical metal part that guides the piston to perform linear reciprocating motion in the cylinder. In an air compressor, one cylinder is equipped with one piston.

[0066] Piston stroke: The distance the piston moves from the bottom dead center to the top dead center in the cylinder. It can also be understood as the maximum distance the piston can move in the cylinder.

[0067] Unsprung mass: The mass of the vehicle components that are not supported by the suspension system, such as wheels, tires, brake system, etc.

[0068] Sprung mass: The mass of the part of the vehicle supported by the suspension system, such as the body, engine, passengers and luggage.

[0069] Unsprung mass displacement: generally refers to the position change of the unsprung mass of the vehicle during movement. In the present invention, it refers to the vertical displacement of the unsprung mass at the wheel center when the suspension of the air spring system is performing lifting and lowering movements.

[0070] Sprung mass displacement: generally refers to the position change of the sprung mass of a car during movement. In the present invention, it refers to the vertical displacement of the sprung mass at the wheel arch when the suspension of the air spring system is performing lifting and lowering movements. The "wheel arch" referred to in the present invention refers to the intersection of a straight line passing through the wheel center and perpendicular to the ground and the lower edge of the car's wheel arch.

[0071] Unsprung mass speed: When the vehicle is running, the unsprung mass will change in speed with the movement of the wheels. In the present invention, the unsprung mass speed refers to the vertical speed of the unsprung mass at the wheel center when the suspension of the air spring system is performing lifting and lowering movements.

[0072] Sprung mass speed: When a vehicle is running, the unsprung mass will change speed with the movement of the wheels. In the present invention, the sprung mass speed refers to the vertical speed of the sprung mass at the wheel arch when the suspension of the air spring system is performing lifting and lowering movements. The "wheel arch" referred to in the present invention refers to the intersection of a straight line passing through the wheel center and perpendicular to the ground and the lower edge of the vehicle's wheel arch.

[0073] Sprung mass acceleration: A physical quantity that describes the change in acceleration of the sprung mass of a car during movement. In the present invention, sprung mass acceleration refers to the vertical acceleration of the sprung mass at the wheel arch when the suspension of the air spring system is performing lifting and lowering movements. The "wheel arch" referred to in the present invention refers to the intersection of a straight line passing through the wheel center and perpendicular to the ground and the lower edge of the car's wheel arch.

[0074] Variable balance stage: After the air spring is inflated or deflated, the solenoid valve in the air circuit will be closed. After the solenoid valve is closed, the mass on the spring still has a certain speed and will continue to rise or fall, and gradually stabilize under the action of the suspension system damping. From the time the solenoid valve is closed to the time when the mass on the spring stabilizes and stops, the air spring is in a variable balance stage.

[0075] Constant volume inflation stage: When the air spring is inflated, it first needs to overcome the static friction of the suspension before it can move. Therefore, the first stage of air spring inflation has a zero displacement and the internal pressure increases, which is the constant volume inflation stage.

[0076] Constant volume deflation stage: When the air spring is deflated, it first needs to overcome the static friction of the suspension before it can move. Therefore, the first stage of air spring deflation has a zero displacement and a reduced internal pressure, which is the constant volume deflation stage.

[0077] Variable volume inflation stage: During the air spring inflation process, after overcoming the maximum static friction of the suspension, it begins to enter the continuous rising stage. During this stage, the volume of the air spring increases with increasing height, which is the variable volume inflation stage.

[0078] Variable volume deflation stage: During the deflation process of the air spring, after overcoming the maximum static friction of the suspension, it begins to enter the continuous lowering stage. During this stage, the volume of the air spring decreases as the height decreases, which is the variable volume deflation stage.

[0079] Air spring lever ratio: generally refers to the ratio of the lever arm of the lever mechanism connected to the air spring in the air spring suspension system. In this invention, it refers to the ratio of the displacement of the air spring and the swing arm installation center to the displacement of the wheel center when the suspension moves vertically;

[0080] Suspension static friction: the static friction that needs to be overcome when the suspension moves vertically;

[0081] Suspension dynamic friction: the sliding friction that needs to be overcome when the suspension moves vertically;

[0082] Relative compression stroke: once the air spring is installed in the predetermined position, the piston will be subjected to a certain external pressure (this pressure is usually called the design load), so that the air spring is in the design load state. The position of the piston at this time is taken as the relative zero point. When the piston is subjected to additional pressure at the installation position, the displacement of the piston from the initial position (relative zero point) to the end position is the relative compression stroke (Note: the additional external pressure on the piston does not include the design load of the air spring). In other words, the air spring in the design load state in the present invention refers to when the relative compression stroke of the piston is zero, and the "current moment" refers to when the relative compression stroke of the piston is Z. At this time, Z can be zero or other values;

[0083] The effective cross-sectional area of ​​the air spring cavity: Figure 2 As shown, the effective cross-sectional area A of the air spring cavity e is the area of ​​the actual working plane of the main air chamber of the air spring, which is perpendicular to the force direction of the piston. The actual working plane of the main air chamber is actually a force plane inside a rubber airbag defined artificially. The pressure on the air spring is equal to the effective cross-sectional area A of the inner cavity of the air spring at the current moment. e Multiply by the relative pressure of the air spring cavity (i.e. the difference between the pressure inside the main air chamber of the air spring and the atmospheric pressure). BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 is a flow chart of the present invention;

[0085] Figure 2 It is a schematic diagram of the effective cross-sectional area of ​​the inner cavity of the air spring at the current moment of the present invention;

[0086] Figure 3 Schematic diagram of an air spring control system according to an embodiment of the present invention;

[0087] Figure 4 Schematic diagram of parameters related to the mathematical model of the air spring control system in an embodiment of the present invention. DETAILED DESCRIPTION

[0088] like Figure 1 As shown, a method for establishing a mathematical model of an air spring control system comprises the following steps:

[0089] 1) According to the flow characteristics of the gas pipeline system, a gas path mass flow equation group is established to determine the gas mass flow state of the air spring control system;

[0090] The gas path mass flow equation group includes a gas path mass flow model in the air spring inflation stage and a gas path mass flow model in the air spring deflation stage:

[0091] 1-1) Air path mass flow model during air spring inflation

[0092] q e-1 =max(q a ,q b )

[0093]

[0094] In the formula, q e-1 is the gas path mass flow rate during the air spring inflation phase, q a The mass flow rate of the air path when the air tank directly inflates the inner cavity of the air spring, q b is the gas mass flow rate when the air compressor extracts gas from the air tank to inflate the air spring, μ is the equivalent gas path flow resistance coefficient, A is the equivalent gas resistance geometric cross-sectional area, P t is the absolute pressure inside the gas tank, P s is the absolute pressure of the air spring cavity at the current moment, T t is the thermodynamic temperature of the gas in the gas tank, k is the gas adiabatic index, R is the gas constant, σ e is the critical gas pressure ratio, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, and η is the working efficiency of the air compressor;

[0095] 1-2) Air spring air path mass flow model during deflation phase

[0096]

[0097] In the formula, q e-2 is the air mass flow rate of the air spring during the deflation phase, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, R is the gas constant, P s is the absolute pressure of the air spring cavity at the current moment, T s is the thermodynamic temperature of the gas in the inner cavity of the air spring, and η is the working efficiency of the air compressor.

[0098] 2) According to the first law of thermodynamics and the gas state equation, the air spring internal pressure change equation group is established to reflect the air pressure change in the air spring cavity;

[0099] The air spring internal pressure variation equation group includes an internal pressure variation model in a constant volume inflation stage, an internal pressure variation model in a variable volume inflation stage, an internal pressure variation model in a multi-variable balance stage of the inflation process, an internal pressure variation model in a constant volume deflation stage, an internal pressure variation model in a variable volume deflation stage, and an internal pressure variation model in a multi-variable balance stage of the deflation process:

[0100] 2-1) Internal pressure change model during constant volume inflation:

[0101]

[0102] In the formula, is the absolute pressure change rate inside the air spring during the constant volume inflation stage. This change rate represents the absolute pressure p inside the air spring during the constant volume inflation stage. s-定容充气 The degree of change over time, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state;

[0103] 2-2) Model of internal pressure change during variable volume inflation stage:

[0104]

[0105] In the formula, is the absolute pressure change rate inside the air spring during the variable volume filling stage. This change rate represents the absolute pressure p inside the air spring during the variable volume filling stage. s-变容充气 The degree of change over time, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state. is the rate of change of the air spring inner cavity volume, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, and v2 is the velocity of the sprung mass;

[0106] 2-3) Model of internal pressure change in the multivariable equilibrium stage of the inflation process:

[0107]

[0108] Where P s1 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the charging phase. s1 P is the volume of the air spring cavity before the solenoid valve is closed during the charging phase. s2 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the inflation phase. s2 is the volume of the air spring cavity after the solenoid valve is closed during the charging phase, and w is the polynomial index;

[0109] 2-4) Internal pressure change model during constant volume deflation stage:

[0110]

[0111] In the formula, is the absolute pressure change rate inside the air spring during the constant volume deflation stage. This change rate represents the absolute pressure p inside the air spring during the constant volume deflation stage. s-定容放气 The degree of change over time, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 It is the inner cavity volume of the air spring when it is in the designed load state;

[0112] 2-5) Model of internal pressure change during variable volume deflation stage:

[0113]

[0114] In the formula, is the absolute pressure change rate inside the air spring during the variable volume deflation stage. This change rate represents the absolute pressure p inside the air spring during the variable volume deflation stage. s-变容放气 The degree of change over time, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 is the inner volume of the air spring when it is under the design load state, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, v2 is the velocity of the sprung mass, is the rate of change of the inner volume of the air spring, which represents the inner volume V of the air spring s The degree of change caused by the change of suspension lifting height x, suspension lifting height x = x2-x1;

[0115] 2-6) Model of internal pressure change in the multivariable equilibrium stage of the deflation process

[0116]

[0117] Where P s3 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the deflation phase. s3 P is the volume of the air spring cavity before the solenoid valve is closed during the deflation phase. s4 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. s4It is the volume of the air spring cavity after the solenoid valve is closed during the deflation stage, and w is the polynomial index.

[0118] 3) According to the law of force balance and Newton's second law, a group of suspension-body dynamic equations is established to accurately express the relationship between the current suspension lifting acceleration, lifting speed, lifting height and the sprung mass, air spring vertical force, suspension friction, shock absorber damping force, and the force generated by the suspension parasitic stiffness;

[0119] The suspension-body dynamics equations include a constant volume filling / deflating stage dynamics model and a variable volume filling / deflating to multi-variable equilibrium stage dynamics model:

[0120] 3-1) Constant volume filling / deflating stage kinetic model:

[0121] F s1 λ-f1=0

[0122] F s1 =(P s -P s0 )A e0

[0123] Where λ is the air spring lever ratio, f1 is the static friction of the suspension, and F s1 is the restoring force of the air spring during the constant volume filling / deflating stage, P s is the absolute pressure of the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0124] 3-2) Kinetic model of variable volume filling / deflating to multi-variable equilibrium stage:

[0125] F s2 λ-K j (x2-x1)-C(v2-v1)-f2=m u a

[0126] Where λ is the air spring lever ratio, K j is the parasitic stiffness of the suspension, x1 is the displacement of the unsprung mass, x2 is the displacement of the sprung mass, C is the equivalent damping coefficient of the shock absorber, v1 is the velocity of the unsprung mass, v2 is the velocity of the sprung mass, f2 is the dynamic friction of the suspension, m u is the mass on the suspension spring, a is the acceleration of the mass on the spring, F s2 is the restoring force of the air spring from variable volume filling / deflating to multi-variable balance stage, and the calculation formula of the restoring force of the air spring from variable volume filling / deflating to multi-variable balance stage under different conditions is as follows:

[0127] ① Variable volume filling / deflating stage:

[0128] F s2 =P s A e -P s0 A e0

[0129] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s is the absolute pressure of the air spring cavity at the current moment, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0130] ②Multiple balance stages of inflation process:

[0131] F s2 =P s2 A e -P s0 A e0

[0132] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s2 is the absolute pressure in the air spring cavity after the solenoid valve is closed during the charging phase, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state;

[0133] ③Multiple equilibrium stages of deflation process:

[0134] F s2 =P s4 A e -P s0 A e0

[0135] In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s4 A is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state.

[0136] 4) Combine the gas path mass flow equations, the air spring internal pressure change equations, and the suspension-body dynamics equations to construct a mathematical model of the air spring control system. Substitute the vehicle parameters into the mathematical model of the air spring control system to determine the design values ​​of the key parameters of the air spring control system, which are used to design the air spring control system and control the operation of the air spring control system.

[0137] According to the above method, a mathematical model of the air spring control system is established, and an example is given as follows:

[0138] Example 1

[0139] The mathematical model of the air spring control system is established by using MATLAB of a computer according to the method of the present invention, and the final design value of the "key parameters" of the air spring control system is determined according to the "whole vehicle parameters", and an air spring control system that meets the factory requirements is designed, such as Figure 3 As shown:

[0140] In this embodiment, the air spring control system to be designed is a closed-loop system. The gas that makes the suspension move up and down is stored in the gas tank. The vehicle parameters of the air spring control system include suspension parameters, namely, air spring lever ratio λ, suspension static friction f1, suspension dynamic friction f2, suspension parasitic stiffness K j , shock absorber equivalent damping coefficient C, suspension spring mass m u .

[0141] At the beginning of the design, in addition to the above vehicle parameters, it is also necessary to temporarily set the initial design values ​​of the following parameters, and substitute them into the mathematical model of the air spring control system together with the design values ​​of the vehicle parameters, and then determine the final design values ​​of the key parameters of the air spring control system according to the design requirements:

[0142] (1) Gas tank related parameters:

[0143] 1.1 Gas tank cavity volume: the initial design value of the gas tank cavity volume;

[0144] 1.2 Initial air pressure of the gas tank: This is the initial design value of the absolute pressure in the inner cavity of the gas tank, which is directly substituted into P when participating in the calculation. t ;

[0145] 1.3 Initial temperature of gas tank: the initial design value of the thermodynamic temperature of the gas in the inner cavity of the gas tank, which is directly substituted into T when participating in the calculation t ;

[0146] (2) Pipeline equivalent parameters:

[0147] 2.1 Equivalent gas path flow resistance coefficient: that is, the initial design value of the equivalent gas path flow resistance coefficient, which is directly substituted into μ when participating in the calculation;

[0148] 2.2 Equivalent air resistance geometric cross-sectional area: that is, the initial design value of the equivalent air resistance geometric cross-sectional area, which is directly substituted into A when participating in the calculation;

[0149] (3) Air spring related parameters:

[0150] 3.1 Initial cross-sectional area of ​​the air spring cavity: The effective cross-sectional area of ​​the air spring cavity when it is under the design load state, which is directly substituted into A when participating in the calculation e0 ;

[0151] 3.2 Initial air pressure in the air spring cavity: the absolute pressure in the cavity of the air spring when it is in the design load state, which is directly substituted into P when participating in the calculation s0 ;

[0152] 3.3 The initial design value of the thermodynamic temperature of the gas in the air spring cavity is directly substituted into T when participating in the calculation. s ;

[0153] 3.4 Initial volume of the air spring cavity: that is, the volume of the air spring cavity when it is in the design load state, which is directly substituted into V when participating in the calculation s0 ;

[0154] 3.5 Air spring volume change rate: the initial design value of the air spring inner cavity volume change rate, which is directly substituted into the calculation This rate of change represents the degree to which the volume of the air spring cavity changes as the suspension lift height changes;

[0155] (4) Air compressor related parameters:

[0156] 4.1 Diameter of a single piston of an air compressor: An air compressor generally has multiple identical cylinders, each with a piston. When participating in the calculation, the diameter of a single piston is directly substituted into D;

[0157] 4.2 Piston stroke of a single cylinder of an air compressor: Generally speaking, it refers to the distance between the upper and lower dead points of the piston (i.e., the upper dead point and the lower dead point), which can be directly substituted into l when participating in the calculation;

[0158] 4.3 Air compressor efficiency: that is, the working efficiency of the air compressor, which is directly substituted into η when participating in the calculation;

[0159] 4.4 Motor rated speed: the speed of the air compressor drive motor, which is directly substituted into n when participating in the calculation;

[0160] In this embodiment, the key parameters of the air spring control system include:

[0161] (1) Gas tank related parameters:

[0162] 1.1 Gas tank inner volume V t The final design value of the gas tank is actually based on the initial gas pressure P of the gas tank. t The final design value and the gas quality of the entire system are determined;

[0163] 1.2 Initial air pressure of gas tank P t The final design value of

[0164] (2) Pipeline equivalent parameters:

[0165] 2.1 Final design value of equivalent gas path flow resistance coefficient μ;

[0166] 2.2 Final design value of equivalent air resistance geometric cross-sectional area A;

[0167] (3) Air spring related parameters:

[0168] 3.1 The final design value of the change rate of the effective cross-sectional area of ​​the air spring cavity. This change rate represents the effective cross-sectional area A of the air spring cavity. e The degree of change caused by the relative compression stroke of the piston;

[0169] 3.2 Initial effective cross-sectional area of ​​the air spring cavity: The effective cross-sectional area A of the air spring cavity when it is under the design load state e0 The final design value of

[0170] 3.3 Initial air pressure in the air spring cavity: the absolute pressure P in the cavity when the air spring is in the designed load state s0 The final design value of

[0171] 3.4 Initial volume of the air spring cavity: that is, the cavity volume V of the air spring when it is under the design load state s0 The final design value of

[0172] (4) The final design value of the rated speed n of the air compressor drive motor.

[0173] According to the degree of mutual influence of the above key parameters in the design stage and the degree of influence on the suspension lifting performance, the design difficulty of each parameter is determined and the design sequence is judged:

[0174] Usually, the first thing that needs to be determined is the final design value of the initial air pressure of the air tank and the volume of the inner cavity of the air tank, and then the final design value of the initial air pressure of the inner cavity of the air spring, the initial volume of the inner cavity of the air spring, the initial effective cross-sectional area of ​​the inner cavity of the air spring, and the rate of change of the effective cross-sectional area of ​​the inner cavity of the air spring are determined, and finally the final design value of the rated speed of the motor of the compressor and the equivalent parameters of the pipeline are determined.

[0175] For example, in a closed air suspension developed in a certain project, the closed air suspension system (i.e., the air spring control system excluding the air spring) and the air spring body were provided by two suppliers respectively. Through simulation calculations using MATLAB, it was found that the suspension raising speed was 2 mm / s away from the design target (8 mm / s), and the lowering speed was 3 mm / s away from the target (12 mm / s). In order to achieve the design target, various key parameters were determined within the allowable range of each parameter through continuous simulation tests:

[0176] First, the design value of the initial air pressure of the air tank can be adjusted in MATLAB from 15bar to 17bar, and it is found that the lifting performance of the entire system is still not up to standard; only by continuing to increase the design value of the inner cavity volume of the air tank from 5L to 6L, it is found that the design target cannot be achieved. Then the entire system can only meet the performance target by adjusting the relevant parameters of the air spring and the equivalent parameters of the pipeline. In other words, if the design target can be achieved only by adjusting the initial air pressure of the air tank and the design value of the initial air pressure of the air tank, there is no need to adjust the design values ​​of other subsequent parameters. If the system still does not achieve the design target after adjusting the relevant parameters of the air spring and the equivalent parameters of the pipeline, the system can also achieve the design target by adjusting the rated speed of the motor of the air compressor. When the closed air suspension system reaches the design target, the final design values ​​corresponding to all key parameters are recorded, and the air spring control system is manufactured according to the recorded data.

[0177] Example 2

[0178] The established mathematical model of the air spring system is stored in the main control chip of the air spring control system. In this way, the control parameters of the air spring control system can be dynamically adjusted according to the value changes of "vehicle parameters" and "key parameters" during the application stage of the air spring system, such as the opening and closing time of the charging / discharging solenoid valve, or the opening degree of the solenoid valve. Figure 4 The closed loop air spring control system shown is controlled. Figure 4 The reference numerals in the figures are as follows:

[0179] 1. Air filter; 2, 4, 7. Check valve; 3. Air compressor; 5, 10, 12-18. Two-position two-way solenoid valve; 6. Dryer; 8. Throttle hole; 9. Pressure-limiting safety valve; 11. Air storage tank; 19-22. Air spring.

[0180] The changes in key parameters of the closed-loop air spring control system during operation are shown in the following table:

[0181]

[0182] Table 1

[0183] After the closed-loop air spring system is installed on the vehicle, as the vehicle is used for a longer time, the main control chip detects the following deviations in the parameters of the closed-loop air spring system:

[0184] ① The actual height of the suspension when it is raised (i.e. the displacement of the sprung mass) deviates by 3mm from the target height;

[0185] ② The actual speed of the suspension when it is raised (i.e. the speed of the sprung mass) deviates by 1 mm / s from the target raising speed of 8 mm / s;

[0186] ③ There is a 2mm deviation between the actual height of the suspension when it is lowered and the target height;

[0187] ④ The actual speed when the suspension is lowered deviates from the target lowering speed of 12 mm / s by 1 mm / s.

[0188] ⑤The inner cavity volume of the air spring increases by 0.1L;

[0189] ⑥The working efficiency of the air compressor decreases by 5%.

[0190] The main control chip uses the mathematical model of the air spring system to perform calculations and adaptively adjust the control parameters as follows:

[0191] ⑴ Extend the opening time of the solenoid valve during the suspension lifting stage by 0.45s;

[0192] (2) Extend the opening time of the solenoid valve during the suspension lowering stage by 0.42s;

[0193] After adaptive adjustment, the suspension lifting displacement accuracy and lifting speed of the air spring system are restored to the factory state, so that the entire air spring control system can continue to maintain normal operation, accurately control the vehicle height and stiffness during driving, and ensure the smoothness and safety of the vehicle.

[0194] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for establishing a mathematical model of an air spring control system, characterized in that: The following steps are involved: 1) According to the flow characteristics of the gas pipeline system, a gas path mass flow equation group is established to determine the gas mass flow state of the air spring control system. The gas path mass flow equation group includes a gas path mass flow model in the air spring inflation stage and a gas path mass flow model in the air spring deflation stage: 1-1) Air path mass flow model during air spring inflation q e-1 =max(q a ,q b ) In the formula, q e-1 is the gas path mass flow rate during the air spring inflation phase, q a The mass flow rate of the air path when the air tank directly inflates the inner cavity of the air spring, q b is the gas mass flow rate when the air compressor extracts gas from the air tank to inflate the air spring, μ is the equivalent gas path flow resistance coefficient, A is the equivalent gas resistance geometric cross-sectional area, P t is the absolute pressure inside the gas tank, P s is the absolute pressure of the air spring cavity at the current moment, T t is the thermodynamic temperature of the gas in the gas tank, k is the gas adiabatic index, R is the gas constant, σ e is the critical gas pressure ratio, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, and η is the working efficiency of the air compressor; 1-2) Air spring air path mass flow model during the deflation phase In the formula, q e-2 is the air mass flow rate of the air spring during the deflation phase, a is the number of cylinders of the air compressor, D is the diameter of a single piston of the air compressor, l is the piston stroke of a single cylinder of the air compressor, n is the real-time speed of the air compressor drive motor, R is the gas constant, P s is the absolute pressure of the air spring cavity at the current moment, T s is the thermodynamic temperature of the gas in the inner cavity of the air spring, and η is the working efficiency of the air compressor; 2) According to the first law of thermodynamics and the gas state equation, an air spring internal pressure change equation group is established to reflect the air pressure change in the air spring cavity. The air spring internal pressure change equation group includes an internal pressure change model in a constant volume inflation stage, an internal pressure change model in a variable volume inflation stage, an internal pressure change model in a polyvariable equilibrium stage of an inflation process, an internal pressure change model in a constant volume deflation stage, an internal pressure change model in a variable volume deflation stage, and an internal pressure change model in a polyvariable equilibrium stage of a deflation process: 2-1) Internal pressure change model during constant volume inflation: In the formula, is the absolute pressure change rate inside the air spring during the constant volume inflation stage, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state; 2-2) Model of internal pressure change during variable volume inflation stage: In the formula, is the absolute pressure change rate inside the air spring during the variable volume inflation stage, k is the gas adiabatic index, R is the gas constant, T t is the thermodynamic temperature of the gas in the gas tank, q e-1 is the gas path mass flow rate during the air spring charging stage, V s0 It is the inner cavity volume of the air spring when it is in the designed load state. is the rate of change of the air spring inner cavity volume, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, and v2 is the velocity of the sprung mass; 2-3) Model of internal pressure change in the multivariable equilibrium stage of the inflation process: Where P s1 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the charging phase. s1 P is the volume of the air spring cavity before the solenoid valve is closed during the charging phase. s2 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the charging phase. s2 is the volume of the air spring cavity after the solenoid valve is closed during the charging phase, and w is the polynomial index; 2-4) Internal pressure change model during constant volume deflation stage: In the formula, is the absolute pressure change rate inside the air spring during the constant volume deflation stage, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 It is the inner cavity volume of the air spring when it is in the designed load state; 2-5) Model of internal pressure change during variable volume deflation stage: In the formula, is the absolute pressure change rate inside the air spring during the variable volume deflation stage, k is the gas adiabatic index, R is the gas constant, T s is the thermodynamic temperature of the gas in the air spring cavity, q e-2 is the gas path mass flow rate during the deflation phase of the air spring, V s0 It is the inner cavity volume of the air spring when it is in the designed load state. is the rate of change of the air spring inner cavity volume, x1 is the unsprung mass displacement, x2 is the sprung mass displacement, P s is the absolute pressure of the air spring cavity at the current moment, v1 is the velocity of the unsprung mass, and v2 is the velocity of the sprung mass; 2-6) Model of internal pressure change in the multivariable equilibrium stage of the deflation process Where P s3 V is the absolute pressure in the air spring cavity before the solenoid valve is closed during the deflation phase. s3 P is the volume of the air spring cavity before the solenoid valve is closed during the deflation phase. s4 V is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. s4 is the volume of the air spring cavity after the solenoid valve is closed during the deflation phase, and w is the polynomial index; 3) According to the law of force balance and Newton's second law, a suspension-body dynamics equation group is established to accurately express the relationship between the current suspension lifting acceleration, lifting speed, lifting height and the sprung mass, air spring vertical force, suspension friction, shock absorber damping force, and the force generated by the suspension parasitic stiffness. The suspension-body dynamics equation group includes a constant volume filling / deflating stage dynamics model and a variable volume filling / deflating to multi-variable balance stage dynamics model: 3-1) Constant volume filling / deflating stage kinetic model: F s1 λ-f1=0 F s1 =(P s -P s0 )A e0 Where λ is the air spring lever ratio, f1 is the static friction of the suspension, and F s1 is the restoring force of the air spring during the constant volume filling / deflating stage, P s is the absolute pressure of the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state; 3-2) Kinetic model of variable volume filling / degassing to multi-variable equilibrium stage: F s2 λ-K j (x2-x1)-C(v2-v1)-f2=m u a Where λ is the air spring lever ratio, K j is the parasitic stiffness of the suspension, x1 is the displacement of the unsprung mass, x2 is the displacement of the sprung mass, C is the equivalent damping coefficient of the shock absorber, v1 is the velocity of the unsprung mass, v2 is the velocity of the sprung mass, f2 is the dynamic friction of the suspension, m u is the mass on the suspension spring, a is the acceleration of the mass on the spring, F s2 The restoring force of the air spring from the variable volume filling / deflating to the variable balance stage; 4) Combine the gas path mass flow equations, the air spring internal pressure change equations, and the suspension-body dynamics equations to construct a mathematical model of the air spring control system. Substitute the vehicle parameters into the mathematical model of the air spring control system to determine the design values ​​of the key parameters of the air spring control system, which are used to design the air spring control system and control the operation of the air spring control system.

2. The method for establishing a mathematical model of an air spring control system according to claim 1, characterized in that: The calculation formula of the restoring force of the air spring in the variable volume filling / deflating to multi-variable balance stage under different conditions is as follows: ① Variable volume filling / deflating stage: F s2 =P s A e -P s0 A e0 In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s is the absolute pressure of the air spring cavity at the current moment, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state; ②Multiple balance stages of inflation process: F s2 =P s2 A e -P s0 A e0 In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s2 is the absolute pressure in the air spring cavity after the solenoid valve is closed during the charging phase, A e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state; ③Multiple equilibrium stages of deflation process: F s2 =P s4 A e -P s0 A e0 In the formula, F s2 P is the restoring force of the air spring from variable volume filling / deflating to variable balance stage. s4 A is the absolute pressure in the air spring cavity after the solenoid valve is closed during the deflation phase. e is the effective cross-sectional area of ​​the air spring cavity at the current moment, P s0 A is the absolute pressure of the inner cavity of the air spring when it is in the design load state. e0 It is the effective cross-sectional area of ​​the inner cavity when the air spring is in the designed load state.

Images