Air suspension smoothness control method and system based on height control

Abstract

The invention belongs to the field of suspension control, and particularly relates to an air suspension smoothness control method and system based on height control. The method comprises the following steps: collecting a vehicle attitude signal; judging a height gear; the height change of the air spring is controlled based on chassis protection and wind resistance reduction, and the internal air pressure of the air spring is controlled through a switch solenoid valve, so that the height of a vehicle body is adjusted. Obtaining a mechanical characteristic curve of the magnetorheological damper according to the test; and when height control is completed, damping force output of the magnetorheological damper is controlled according to a PID algorithm, and optimization of vehicle smoothness is carried out. On the basis that height control is achieved by controlling an electromagnetic valve switch, damping force is controlled, and height control and smoothness optimization are completed at the same time; and a magneto-rheological mechanical characteristic curve is iteratively calculated by utilizing a genetic algorithm and an improved sigmoid model, so that the damping force is more accurately controlled.

Description

Technical Field

[0001] The invention belongs to the field of suspension control, and in particular relates to a method and system for controlling the smoothness of an air suspension based on height control. Background Art

[0002] Air springs are widely used in the vehicle field because of their variable and stable stiffness and good vibration reduction performance. However, using only air springs for vibration reduction will lead to frequent inflation and deflation of the air springs, which will not only reduce their service life, but also cause control lag due to the time difference between inflation and deflation, affecting ride comfort.

[0003] To address this problem, scholars from East China Jiaotong University and Southeast University have chosen to use an electronically controlled air suspension that combines air springs with magnetorheological dampers for optimization. Magnetorheological dampers can change the viscosity of magnetorheological fluid within milliseconds, thereby quickly adjusting the damping force of the suspension. Combined with air springs, they can provide a smoother and more comfortable ride. However, current research focuses on height control or smoothness control only, and has not completed the integrated control of the two. Summary of the invention

[0004] The purpose of the present invention is to provide an air suspension smoothness control method and system based on height control, which uses a control algorithm to control the inflation and deflation of the air spring to ensure the effect of height control; and on this basis, the control algorithm is used to obtain the optimal damping force, which is mapped to the magnetorheological damper mechanical curve obtained by fitting to obtain the corresponding current size, which is input into the magnetorheological damper to complete the smoothness control.

[0005] The technical solution for achieving the purpose of the present invention is: an air suspension smoothness control method based on height control, which is based on a magnetorheological damper and an air spring. The damping force of the magnetorheological damper is controlled on the basis of adjusting the vehicle body height by controlling the internal air pressure of the air spring through a switch solenoid valve, and height control and smoothness optimization are completed at the same time; the magnetorheological mechanical characteristic curve is iteratively calculated using a genetic algorithm and an improved sigmoid model, thereby completing the control of the damping force.

[0006] Further, the specific steps include:

[0007] Step (1): collecting vehicle posture signals;

[0008] Step (2): Determine the height gear;

[0009] Step (3): Control the height change of the air spring based on the principle of protecting the chassis and reducing wind resistance, and control the internal air pressure of the air spring by switching the solenoid valve to complete the adjustment of the vehicle body height;

[0010] Step (4): obtaining a mechanical characteristic curve of the magnetorheological damper according to the experiment;

[0011] Step (5): While completing the height control, the damping force output of the magnetorheological damper is controlled according to the PID algorithm to optimize the vehicle smoothness.

[0012] Furthermore, the posture signals collected in step (1) include: vehicle body speed signal, suspension lower end speed signal, vehicle body vertical acceleration signal, vehicle body height signal and suspension lower end height signal, as well as air tank pressure signal and air spring pressure signal.

[0013] Furthermore, the height gear in step (2) is divided into four gears: a low gear for high-speed driving on a good road, a middle gear for low-speed driving on a good road, a high gear for low-speed driving on a bad road, and a highest gear for high-speed driving on a bad road;

[0014] Class A and Class B roads are classified as good roads, and Class C and Class D roads are classified as poor roads. The speed dividing line between high and low speeds is 60km / h.

[0015] Furthermore, step (3) specifically includes the following steps: Step (31): Establishing a two-degree-of-freedom suspension dynamics model:

[0016]

[0017] Where: m s 、m u and unsprung mass respectively; z s 、z u are the vertical displacements of the sprung and unsprung masses, respectively; k t is the tire stiffness, c s is the suspension damping coefficient; z r For random road surface excitation;

[0018] Air force F as The kinetic equation is as follows:

[0019] F as =P f ·A e

[0020] P f is the internal pressure of the air spring, A e is the effective area of ​​the air spring; P f The size of is related to the gas flow rate flowing into the solenoid valve. The specific expression is as follows:

[0021]

[0022] P spis the internal pressure of the air spring, q in The solenoid valve controls the gas flow rate flowing into the air spring, q out V is the size of the gas flow rate controlled by the solenoid valve. sp is the effective volume of the air spring, is the derivative of the effective volume of the air spring with respect to the vertical displacement, R is the gas constant, T is the thermodynamic temperature of the air spring, and κ is the gas polytropic index;

[0023] Step (32): Establish q in and q out Gas flow model: The air spring uses a high-speed switch solenoid valve to control the inlet and outlet of the internal gas; the valve port area of ​​the high-speed switch solenoid valve is immutable, and the flow is controlled by opening and closing the valve port; the solenoid valve model is abstracted as a throttle hole, and the gas flow through the solenoid valve is represented by the upstream and downstream air pressures:

[0024]

[0025] P u is the absolute pressure upstream of the solenoid valve, P d is the absolute air pressure downstream of the solenoid valve, Tu is the gas temperature upstream of the solenoid valve, and S is the valve port area of ​​the solenoid valve;

[0026] Step (33): Use fuzzy PID to control inflation and deflation: Use fuzzy PID to control inflation and deflation, select the input as the difference between the ideal height and the actual height and its derivative, and the gas flow rate as the output.

[0027] Furthermore, step (4) obtains experimental data of the magnetorheological damper through bench experiments, and adopts reverse development and curve fitting to obtain the mechanical characteristic curve of the magnetorheological damper. The specific steps are as follows:

[0028] Step (41): obtaining data through bench experiment;

[0029] Step (42): Use the improved sigmoid model for fitting, the expression is as follows:

[0030]

[0031] The unknown parameters in the improved sigmoid model are identified by genetic algorithm, where F m The value range is -100—1000, the value range of a is -100—500, the value range of k is -100—300, the value range of C0 is -100—500, the value range of f0 is -100—600, the number of individuals is 300, the maximum genetic generation is 500, the generation gap is 0.95, the crossover probability is 0.8, and the mutation probability is 0.2.

[0032] Furthermore, the output of the PID controller in step (5) is expressed as:

[0033]

[0034] Where K P , K I , K D They are proportional, differential and integral coefficients respectively; e(t) is the difference between 0 and the actual acceleration.

[0035] A height-control-based air suspension smoothness control system includes a vehicle height sensor, a pressure sensor, a charging and discharging solenoid valve switch, a magnetorheological damper and a control unit, wherein the control unit controls the vehicle suspension system according to the above method.

[0036] Compared with the prior art, the present invention has the following significant advantages:

[0037] (1) The fuzzy PID controller controls the inflation and deflation of the air spring through feedback of speed signal, height signal and pressure signal, effectively improving the height control effect;

[0038] (2) A dead zone is set up to prevent the air spring from being frequently inflated and deflated, which affects the height adjustment and smoothness control effects, thereby increasing the service life of the air spring;

[0039] (3) The optimal damping force for optimizing smoothness is obtained based on the PID algorithm. The optimal current is input into the damper based on the mechanical characteristics obtained by the genetic algorithm and the vehicle height signal and vehicle speed signal, which effectively improves the vehicle's smoothness and handling stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the upper and lower layer control principle of the present invention;

[0041] Figure 2 It is the height control gear position determination diagram;

[0042] Figure 3 It is a schematic diagram of a two-degree-of-freedom suspension model;

[0043] Figure 4 is the displacement-damping force curve of the magnetorheological damper obtained after identification;

[0044] Figure 5 Velocity-damping force curve of the magnetorheological damper obtained after identification. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. 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.

[0046] The present invention first determines a vehicle height control algorithm: collects a vehicle height signal, a road spectrum signal, a vehicle speed signal, a vehicle vertical acceleration signal, a solenoid valve air pressure signal, and an air spring air pressure signal.

[0047] Based on the collected speed signal and road spectrum signal, it is determined whether the vehicle is currently in a low position, a middle position, a high position or a highest position.

[0048] According to the vehicle height adjustment signal obtained by the controller, the solenoid valve switch is controlled according to the control algorithm to complete the charging and deflation operations.

[0049] The suspension dynamic deflection, vertical dynamic load and vertical acceleration are obtained according to the vehicle height signal, the vehicle speed signal, the suspension lower end speed signal and the suspension lower end height signal.

[0050] The ideal damping force is obtained according to the suspension dynamic deflection, vertical dynamic load and vertical acceleration according to the control algorithm.

[0051] The input current is obtained according to the fitted mechanical characteristic curve of the magnetorheological damper to achieve the control of smoothness and handling stability.

[0052] The present invention provides a vehicle body control device, comprising a vehicle body height sensor, a vehicle speed sensor, a pressure sensor, a charging and discharging solenoid valve, a magnetorheological damper and a control unit ECU, characterized in that the control unit ECU adjusts the vehicle body suspension system according to the vehicle body control method.

[0053] The present invention also provides an electronic device, comprising:

[0054] one or more processors;

[0055] A memory for storing one or more programs;

[0056] When the one or more programs are executed by the one or more processors, the one or more processors implement the vehicle body control method.

[0057] The present invention also provides a storage medium on which a computer program is stored, wherein the program is implemented by a processor to implement the vehicle body control method.

[0058] The hardware includes: height sensor, pressure sensor.

[0059] Vehicle height control methods include:

[0060] Step 1, collect the following vehicle posture signals: vehicle height, vehicle speed, vehicle vertical acceleration, suspension lower end speed, suspension lower end height, air spring pressure, air tank pressure, and road spectrum.

[0061] The vehicle body speed signal, the suspension lower end speed signal, the vehicle body vertical acceleration signal, the vehicle body height signal and the suspension lower end height signal are acquired through sensors, and the air tank pressure signal and the air spring pressure signal can be acquired through pressure sensors.

[0062] Step 2, determine the height gear: determine the height gear according to the road pattern, vehicle speed and vehicle height.

[0063] According to the classification of road surface roughness, Class A and Class B roads are classified as good roads, and Class C and Class D roads are classified as bad roads; according to urban and rural traffic regulations, the speed dividing line between high and low speeds is 60km / h. In order to protect the chassis and reduce wind resistance, the vehicle height is divided into four levels according to speed and road quality: low position for high speed driving on good roads, middle position for low speed driving on good roads, high position for low speed driving on bad roads, and highest position for high speed driving on bad roads. At the same time, the height control must also meet the function of lowering the vehicle body on one side.

[0064] Step 3, obtain data such as road spectrum input, vehicle height, vehicle speed, suspension bottom speed, suspension bottom height, etc. through sensors, control the height change of the air spring based on the principle of protecting the chassis and reducing wind resistance, and control the internal air pressure of the air spring by switching the solenoid valve, thereby completing the adjustment of the vehicle height;

[0065] Specific height control steps include:

[0066] Step (31): Figure 3 As shown, a two-degree-of-freedom suspension dynamics model is established:

[0067]

[0068] Where: m s 、m u and unsprung mass respectively; z s 、z u are the vertical displacements of the sprung and unsprung masses, respectively; k t is the tire stiffness, c s is the suspension damping coefficient; z r is a random road excitation.

[0069] Air force F as The kinetic equation is as follows:

[0070] F as =P f ·A e

[0071] P f is the internal pressure of the air spring, A e P is the effective area of ​​the air spring. f The size of is related to the gas flow rate flowing into the solenoid valve. The specific expression is as follows:

[0072]

[0073] P sp is the internal pressure of the air spring, q in The solenoid valve controls the gas flow rate flowing into the air spring, q out V is the size of the gas flow rate controlled by the solenoid valve. sp is the effective volume of the air spring, is the derivative of the effective volume of the air spring with respect to the vertical displacement, R is the gas constant, T is the thermodynamic temperature of the air spring, and κ is the gas polytropic index.

[0074] In order to protect the air spring and increase its service life, a dead zone needs to be set up to prevent the air spring from being inflated and deflated frequently. The inflation and deflation conditions of the air spring inflation and deflation model are the target height ±5mm.

[0075] Step (32): Establish q in and q out Gas flow model: The air spring uses a high-speed switch solenoid valve to control the inlet and outlet of the internal gas. The valve port area of ​​the high-speed switch solenoid valve is immutable, and the flow is controlled by opening and closing the valve port. The solenoid valve model is abstracted as a throttle hole, and the gas flow through the solenoid valve can be expressed by the upstream and downstream air pressures:

[0076]

[0077] P u is the absolute pressure upstream of the solenoid valve, P d is the absolute pressure downstream of the solenoid valve, T u is the gas temperature upstream of the solenoid valve, and S is the valve port area of ​​the solenoid valve.

[0078] Step (33): Use fuzzy PID to control the charging and discharging: To prevent overcharging and overdischarging, use fuzzy PID to control the charging and discharging. The input is the difference between the ideal height and the actual height and its derivative, and the gas flow rate is used as the output. The PID control parameters are manually adjusted to the following values: K p =0.5, K i =1, Kd =0.25. After combining with the fuzzy controller, each PID parameter is adaptively changed according to the fuzzy rules, and the specific fuzzy rules are as follows:

[0079] Table 1 Fuzzy rules table

[0080]

[0081] Step 4, obtaining a mechanical characteristic curve of the magnetorheological damper according to the experiment;

[0082] The experimental data of the magnetorheological damper is obtained through bench experiments, and the mechanical characteristic curve of the magnetorheological damper is obtained by reverse development and curve fitting. The specific steps are as follows:

[0083] Step (41): obtaining data through bench experiment;

[0084] Step (42): Select a suitable mathematical model to fit the curve. The traditional sigmoid model has the advantages of few parameters and easy programming. However, it cannot reflect the hysteresis loop of the magnetorheological damper at low speed, and the accuracy is not high. The improved sigmoid model can reflect the mechanical characteristics of the magnetorheological damper in multiple dimensions. The fitting requires few parameters and high accuracy. The improved sigmoid model is fitted, and the expression is as follows:

[0085]

[0086] The unknown parameters in the improved sigmoid model are identified through genetic algorithm, as follows: the algorithm parameters are set, including subgroup size, evolutionary generations, crossover probability, mutation probability, etc.

[0087] In the present invention, the genetic algorithm parameter settings are shown in Table 1:

[0088] Table 2 Parameters of genetic algorithm

[0089]

[0090]

[0091] The mechanical characteristic curve of magnetorheological damping force obtained after identification is as follows: Figure 4 , Figure 5 shown.

[0092] Step 5: While completing the height control, the damping force output of the magnetorheological damper is controlled according to the PID algorithm to optimize the vehicle ride comfort. The output of the PID controller can be expressed as:

[0093]

[0094] Where K P , KI , K D are proportional, differential and integral coefficients respectively. e(t) is the difference between 0 and the actual acceleration.

[0095] After completing the modeling and simulation according to the design ideas of this example, the root mean square value of the height during the inflation and deflation process was reduced by 19.3%, the maximum value was reduced by 20.4%, and the minimum value was optimized by 27%; in the process of controlling smoothness, the root mean square value of the vertical acceleration was reduced by 33%, the vertical dynamic load was reduced by 34%, and the dynamic deflection of the suspension did not change much, which would not cause the limit block to be penetrated.

[0096] Table 3 RMS values ​​of performance indicators

[0097]

[0098] The present invention provides a vehicle body control device, comprising a vehicle body height sensor, a pressure sensor, a charging and discharging electromagnetic valve, a magnetorheological damper and a control unit ECU. The control unit ECU adjusts a vehicle body suspension system according to the vehicle body control method.

[0099] The method of the present invention may be implemented in hardware, firmware, or as software or computer code that may be stored in a recording medium (such as a CDROM, RAM, floppy disk, hard disk, or magneto-optical disk), or as computer code that is originally stored in a remote recording medium or a non-temporary machine-readable medium downloaded over a network and will be stored in a local recording medium, so that the method described herein may be stored in such software processing on a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It is understood that a computer, processor, microprocessor controller, or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code, and when the software or computer code is accessed and executed by a computer, processor, or hardware, the method described herein is implemented. In addition, when a general-purpose computer accesses the code for implementing the method shown herein, the execution of the code converts the general-purpose computer into a dedicated computer for executing the method shown herein.

Claims

1. A height-controlled air suspension ride comfort control method based on a magnetorheological damper and an air spring, characterized in that: The vehicle height is adjusted by controlling the internal air pressure of the air spring through the switch solenoid valve, and the damping force of the magnetorheological damper is controlled to achieve height control and smoothness optimization at the same time; the magnetorheological mechanical characteristic curve is iteratively calculated using a genetic algorithm and an improved sigmoid model to achieve damping force control.

2. The method according to claim 1, characterized in that The specific steps include: Step (1): collecting vehicle posture signals; Step (2): Determine the height gear; Step (3): Control the height change of the air spring based on the principle of protecting the chassis and reducing wind resistance, and control the internal air pressure of the air spring by switching the solenoid valve to complete the adjustment of the vehicle body height; Step (4): obtaining a mechanical characteristic curve of the magnetorheological damper according to the experiment; Step (5): While completing the height control, the damping force output of the magnetorheological damper is controlled according to the PID algorithm to optimize the vehicle smoothness.

3. The method according to claim 2, characterized in that The posture signals collected in step (1) include: vehicle body speed signal, suspension lower end speed signal, vehicle body vertical acceleration signal, vehicle body height signal and suspension lower end height signal, as well as air tank pressure signal and air spring pressure signal.

4. The method according to claim 3, characterized in that: Step (2) The height gear is divided into four gears: a low gear for high-speed driving on a good road, a middle gear for low-speed driving on a good road, a high gear for low-speed driving on a bad road, and a highest gear for high-speed driving on a bad road; Class A and Class B roads are classified as good roads, and Class C and Class D roads are classified as poor roads. The speed dividing line between high and low speeds is 60km / h.

5. The method according to claim 4, characterized in that Step (3) specifically includes the following steps: Step (31): Establish a two-degree-of-freedom suspension dynamics model: Where: m s 、m u and unsprung mass respectively; z s 、z u are the vertical displacements of the sprung and unsprung masses, respectively; k t is the tire stiffness, c s is the suspension damping coefficient; z r For random road surface excitation; Air force F as The kinetic equation is as follows: F as =P f ·A e P f is the internal pressure of the air spring, A e is the effective area of ​​the air spring; P f The size of is related to the gas flow rate flowing into the solenoid valve. The specific expression is as follows: P sp is the internal pressure of the air spring, q in The solenoid valve controls the gas flow rate flowing into the air spring, q out V is the size of the gas flow rate controlled by the solenoid valve. sp is the effective volume of the air spring, is the derivative of the effective volume of the air spring with respect to the vertical displacement, R is the gas constant, T is the thermodynamic temperature of the air spring, and κ is the gas polytropic index; Step (32): Establish q in and q out Gas flow model: The air spring uses a high-speed switch solenoid valve to control the inlet and outlet of the internal gas; the valve port area of ​​the high-speed switch solenoid valve is immutable, and the flow is controlled by opening and closing the valve port; the solenoid valve model is abstracted as a throttle hole, and the gas flow through the solenoid valve is represented by the upstream and downstream air pressures: P u is the absolute pressure upstream of the solenoid valve, P d is the absolute air pressure downstream of the solenoid valve, Tu is the gas temperature upstream of the solenoid valve, and S is the valve port area of ​​the solenoid valve; Step (33): Use fuzzy PID to control inflation and deflation: Use fuzzy PID to control inflation and deflation, select the input as the difference between the ideal height and the actual height and its derivative, and the gas flow rate as the output.

6. The method according to claim 5, characterized in that Step (4) obtains the experimental data of the magnetorheological damper through bench experiments, and obtains the mechanical characteristic curve of the magnetorheological damper by reverse development and curve fitting. The specific steps are as follows: Step (41): obtaining data through bench experiment; Step (42): Use the improved sigmoid model for fitting, the expression is as follows: The unknown parameters in the improved sigmoid model are identified by genetic algorithm, where F m The value range is -100—1000, the value range of a is -100—500, the value range of k is -100—300, the value range of C0 is -100—500, the value range of f0 is -100—600, the number of individuals is 300, the maximum genetic generation is 500, the generation gap is 0.95, the crossover probability is 0.8, and the mutation probability is 0.

2.

7. The method according to claim 6, characterized in that The output of the PID controller in step (5) is expressed as: Where K P , K I , K D They are proportional, differential and integral coefficients respectively; e(t) is the difference between 0 and the actual acceleration.

8. An air suspension ride comfort control system based on height control, characterized in that: The vehicle comprises a vehicle height sensor, a pressure sensor, a charging and discharging solenoid valve switch, a magnetorheological damper and a control unit, wherein the control unit controls the vehicle body suspension system according to the method described in any one of claims 1 to 7.

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