Summary:

Since the invention of automobiles, people have never stopped pursuing the smooth running of automobiles. The invention of pneumatic tires allowed vehicles to run more smoothly and comfortably, and the load-bearing body and thickened chassis further improved the comfort of the car. With the development of science and technology and the improvement of living standards, people's requirements for the comfort, maneuverability and safety of cars are gradually increasing. Suspension system is one of the important systems of the vehicle, which directly affects the smoothness, handling stability, comfort and other performances of the vehicle during driving, and plays a vital role in the smoothness and handling stability of the vehicle. The driving conditions of the vehicle are complex and changeable, and the requirements for the suspension system are getting higher and higher. The traditional passive suspension has been difficult to achieve satisfactory vehicle performance. In order to improve the ride comfort and comfort of the vehicle, people continue to study the suspension structure. The new type of suspension has been developed rapidly. From the early non-independent suspension to the later independent suspension, from the integral suspension to the emergence of active suspension, the driving stability of the car has undergone a qualitative leap. Compared with the uncontrollable passive/semi-active suspension, which is difficult to adapt to various road conditions and changes in the driving environment, the active suspension generates active control force according to the movement state of the car and changes in road conditions, ensuring that the suspension system is always at its optimum. The best damping state. The development of active suspension technology is at the forefront of the times, from the initial air variable damping suspension to the world-leading MRC active electromagnetic suspension technology.

I. Introduction

In recent years, the application of electromagnetic suspension in the automotive industry has become more and more widespread, especially for sports cars that focus on handling. After solving the cost problem, the market application range of electromagnetic suspension will be significantly expanded, and it will gradually move from being only used in the high-end brand market to the low-end market, and it will be seen on more models. With the increasing intensity of market competition, it is believed that electromagnetic suspension can be widely used at a low market price in the near future, so that car owners can enjoy more comfortable and safe cars at an affordable price.

Now that science and technology is on the fast track of development, the suspension can also provide sufficient protection for the safety of the driver and passengers. The pace of human pursuit of stability, safety and comfort has not stopped here. Today, how to make the car become To be more intelligent, how to actively improve the comfort performance of cars has become a new direction for future development.

Two overview

1. Reviewed the research and application status of automotive electromagnetic suspension technology, based on the research on electromagnetic active suspension at home and abroad in recent years, analyzed and summarized the structure of electromagnetic active suspension for various vehicles, and analyzed the current status of electromagnetic active suspension The key issues are summarized, and its application prospects and possible future development trends are analyzed. This paper summarizes and analyzes the current research status of the suspension system's energy feedback and the research on the energy consumption and energy recovery of the electromagnetic active suspension, and discusses the development status and trend of the suspension energy feedback.

2. With the rapid development of automotive electronic technology and the development of new energy vehicles, electronic control systems and suspension vibration reduction technology, active suspension actuators (electromagnetic actuators) based on electromagnetic principles are used in automotive suspension systems The application of electromagnetic active suspension actuators began to attract attention, so the research status of electromagnetic active suspension actuators for various vehicles was analyzed and reviewed.

three definitions

Electromagnetic Active Suspension Electromagnetic Active Suspension/Electromagnetic oil variable damping shock absorber suspension system Magnetorheological Damper/Magneto-rheoloicaldamper, MRD/Active electromagnetic induction suspension MRC (Magnetic Ride Control )/Electromagnetic adjustable suspension/Magnetorheological Fluid (MR Fluid), referred to as electromagnetic suspension, belongs to variable damping shock absorber suspension. Electromagnetic suspension has a very technological nickname, That is magnetorheological suspension, which is derived from the core technology used in electromagnetic suspension, magnetorheological fluid (Magneto-Rheological Fluid), so it is also called MR suspension.

MRC/MR active electromagnetic suspension has become one of the representatives of variable damping suspension technology for mass-produced vehicles. It is a suspension method that uses electromagnetic response to change damping. It is a new type of independent suspension system. The control only needs to change the current to achieve the purpose of controlling the damping coefficient, and the strength of the electromagnetic field can be controlled only by changing the current. It can respond to road conditions in a very short time (1 millisecond) to suppress vibration and keep the body stable, especially in some relatively extreme environments, such as sudden bumps in high-speed driving, electromagnetic suspension The advantage will be very obvious, its response speed can be 5 times faster than the traditional suspension, far exceeding the traditional suspension. It can maximize its own advantages when the vehicle speed is high and suddenly encounters obstacles, and it can also keep the body running smoothly on bumpy roads.

The successfully developed power-generation shock absorber is an electromagnetic shock absorber completely composed of a linear motor electromagnetic system. It not only further simplifies the structure of the system, but also has the function of generating electricity under normal driving conditions. Each shock absorber can generate at least 25W of power to charge the lithium battery of the electric vehicle, which is very important for electric vehicles driven entirely by electricity. It is very advantageous, and can greatly increase the power of the lithium battery and prolong the driving range of the electric vehicle. Its unique feature is that it can not only provide current to the motor, but also generate current from the motor, which forms a set of power compensation mechanism.

And its most important shock absorption effect can be said to be even better than the magic carpet suspension shock absorption system!

"Magic Carpet" Suspension

With the rapid development of permanent magnet motor electromagnetic materials and electronic control technology, and under the influence of the development trend of smart cars, vehicle electromagnetic active suspension technology has attracted the attention of academia and industry, and has become a research hotspot at home and abroad. Theoretical research on automotive electromagnetic active suspension technology has gradually deepened, and some commercial applications have been obtained, and market products equipped with high-end passenger cars have appeared. However, the biggest disadvantage of high technology is that it is expensive. Such a shock absorber suspension is too heavy and expensive, so many car manufacturers will not consider using it for the time being.

four components

The electromagnetic suspension is an active suspension, which is relatively complicated. The electromagnetic suspension system is composed of an on-board control unit system, a wheel displacement sensor, and an MRC shock absorber (electromagnetic hydraulic rod and straight shock absorber).

There is a wheel displacement sensor at the connection between each wheel and the body, and the sensor is connected to the on-board control unit, which is connected to the electromagnetic hydraulic rod and the straight shock absorber. It is composed of magneto-rheological shock absorbers, ball screws, EHA electrohydrostatic pressure, and air springs, while the damping of the electromagnetic suspension is provided by electromagnetic actuators. The secrets of the electromagnetic suspension are mainly concentrated in the shock absorber. Although the shock absorber on the front axle is slightly different from the rear axle shock absorber in details, there are electronic control devices and corresponding cables in the middle of the piston.

The four shock absorbers work separately and independently. Even though they appear to be in the same state sometimes, each of them will be adjusted according to real-time road surface information, so that the vehicle can maintain a good performance when driving on any road surface. ride comfort. Coupled with acceleration sensors, controllers and accessories, etc., it constitutes a complete set of proprietary MRC (Magnetic Ride Control) system, a semi/full active suspension system.

Electromagnetic suspension includes wheel connectors, transmission mechanisms, motors, body connectors and control devices. The body connector is connected to the motor; the control device is electrically connected to the motor to obtain the current rotation parameter of the motor, and the target rotation parameter is obtained according to the current rotation parameter, and the motor is controlled to run at the target rotation parameter; the wheel connector is connected to the motor through a transmission mechanism , to convert the force on the wheel connector into the rotational driving force for the motor, and convert the force when the motor operates at the target rotation parameters into a damping force for the wheel connector.

1. A construction method for an intelligent controller of an active suspension electromagnetic actuator, including a dq-axis current decoupling control module, a current limiting control module, a field-oriented control module, a voltage 2/3 conversion module, a PWM adjustment module, and a voltage source The inverter and the AC linear motor are connected in series in sequence, together with the current 3/2 standard conversion module and the disturbance detection module as a whole to form an active suspension electromagnetic actuator, the parameter optimization module of the support vector machine controller, the support vector machine controller , optimization controller, robust controller and robust controller parameter optimization module are connected in parallel together with the speed given module and filter tracking error model to form an anti-interference intelligent controller, which integrates the external disturbance and the time-varying characteristics of the parameters of the electromagnetic actuator It is equivalent to the disturbance variable of the electromagnetic actuator, and the nonlinear model of the controller is regressed by the support vector machine, which effectively improves the robustness and real-time performance of the intelligent controller.

2. Unlike the traditional damping system, there is no small valve structure in the magnetorheological damper, and the damping effect is not achieved through the flow resistance of the liquid. In fact, magnetorheological fluid is used instead of ordinary shock absorber fluid, and the ordinary hydraulic oil of traditional shock absorbers is replaced with shock absorber oil with weak magnetic force. The electromagnetic suspension retains the traditional spring device in structure, still uses the spring to provide support, and fills the shock absorber with magnetorheological fluid.

Compared with other electronic shock absorption systems, the automobile electromagnetic suspension system is more unique. The core component of the electromagnetic suspension is the electromagnetic suspension shock-absorbing cylinder filled with magnetorheological fluid. The electromagnetic suspension shock absorber is similar to the traditional hydraulic single-tube shock absorber in appearance, and its general structure is similar to the traditional suspension shock-absorbing cylinder. , but the inside is quite different. The electromagnetic shock absorber consists of a simple electromagnet assembly and a special fluid, also known as magnetorheological fluid, instead of traditional hydraulic oil. An electromagnet (magnet coil) group is installed in the shock absorber core, and a precisely designed electromagnetic coil is used as a piston, that is, a coil is provided on the piston inside the shock absorber. When the piston rod moves downward, the magneto-rheological fluid in the cavity flows from the compression cavity to the stretch cavity through the annular damping channel, the normal through hole and the annular gap of the piston after being squeezed, and vice versa.

Electromagnetic suspension is also the most widely used damping adjustable shock absorber in high-performance cars by many car companies.

The device has the advantages of simple structure, extremely low power consumption, large control stress range, and instantaneous and precise control of damping force. And it is not sensitive to impurities, and has a wide working temperature range, and can work within -50°C~140°C. The advantages are smoother and more consistent damping forces, less internal complexity, less wear on internal moving parts over time, and less noise. Electromagnetic suspension can be directly powered by ordinary low-voltage power supply (general storage battery), avoiding the danger and inconvenience caused by high-voltage voltage. The biggest advantage is that it can monitor at a speed of thousands of times per second, and adapt to the road conditions at any time, especially when walking on gravel roads, the fine vibrations can basically be isolated. The damping force can be adjusted in real time, taking into account the handling and comfort of the car.

Compared with the traditional spool damping system, the electromagnetic suspension

The advantages and disadvantages of racks coexist:

Compared with traditional automobile shock absorbers, its moving parts are greatly reduced, and there is almost no collision, so the noise is low. One of the main features of electromagnetic suspension shock absorbers is the ability to adjust quickly in all situations. Since the adjustment of the damping force is controlled by magnetized fluid, it can be adjusted instantaneously without any disturbance due to the opening and closing of the valve. Delay. In addition, it should be noted that the adjustment speed of the damping force has nothing to do with the fluid flow rate, which is unique to magneto-rheological shock absorbers.

Its disadvantages are mostly related to magnetorheological fluid: magnetorheological fluid is very expensive due to its complexity; in addition, magnetorheological fluid is very abrasive due to the iron particles contained, which requires the internal parts of the shock absorber Expensive, high-quality surface coatings are applied; in addition, magnetorheological fluids require rather complex sealing systems, resulting in additional costs. The abrasive nature of magnetorheological fluids can also negatively affect the suspension system, so electromagnetic suspension shock absorbers have slightly higher internal friction than conventional adjustable shock absorbers, and slightly higher friction can cause the vehicle to The ride comfort is slightly worse when driving on smooth roads. Early magneto-rheological shock absorber designs had a higher potential for poor ride due to possible residual magnetism in the fluid. Over time, however, both issues were largely resolved through design improvements. Finally, electromagnetic suspension shock absorbers are more prone to base oil leakage due to the abrasive nature of the fluid. The absence of base oil makes the remaining MR fluid more viscous, resulting in stiffer shocks and a poorer ride.

(1) Magnetorheological Fluid (MR Fluid for short) is a new type of intelligent material. It can be used in intelligent dampers (that is, magnetorheological fluid shock absorbers) to make a new generation of high-performance, intelligent shock absorbers with continuously adjustable damping force. Magneto-rheological fluid shock absorbers can be directly powered by ordinary low-voltage power sources (ordinary storage batteries), avoiding the danger and inconvenience caused by high-voltage voltage.

1) The magnetorheological fluid is mainly composed of magnetic particle suspension (tiny magnetic particles with high magnetic permeability and low coercive force), mother liquid (carrier for magnetic particle suspension, low viscosity, high boiling point, low freezing point and high density), Surfactants consist of three parts. The magnetorheological fluid is composed of three parts. The first one is carrier liquid, such as mineral oil, silicone oil, etc.; the second one is magnetizable dispersed suspended particles, which are usually composed of elemental Fe and Fe3O4 powders with a definite particle size distribution. After chemical treatment to improve the durability of work; the third is the dispersant, which can structure the suspended particles and the carrier liquid to solve the problem of dispersion stability of the suspended particles in the carrier liquid. Magnetorheological fluid has a remarkable characteristic, that is, under an external magnetic field, it can change from a low-viscosity Newtonian fluid to a high-viscosity Bingham semi-solid in a short period of time (10ms), which is called the magnetorheological effect.

The magnetorheological fluid used in electromagnetic suspension shock absorbers is composed of base oil, iron particles, and several other components that can suspend iron particles. Magnetorheological fluid is a liquid containing very small (3-10 micron) magnetic particles. It is a special liquid called electromagnetic fluid. It is composed of synthetic hydrocarbons and fine magnetic iron with a size of 3-10 microns. grain composition. This hydraulic oil is not simple. It is not ordinary oil. It is a special liquid material called electromagnetic fluid. It is a hydraulic mixture of special damping fluid and magnetic parts. It is composed of synthetic hydrocarbons and fine iron particles. When When this liquid is magnetized, it changes from a liquid to a sticky substance like marl.

2) Electromagnetic suspension MRC is actually well understood. The secret of electromagnetic shock absorbers is that electromagnetic oil (magneto-rheological fluid) is added to the oil of the shock absorber, which acts as a damping medium, and its technical core is It is a new material that replaces traditional oils - "Magneto-rheological Fluids". The term "Magneto-rheological Fluids" refers to a fluid whose properties change when exposed to a magnetic field. The oil inside the magneto-rheological shock absorber is magnetized, and each shock absorber is filled with a magnetic polymer polymer liquid, which has achieved a breakthrough in the material level, and no longer uses traditional oil, that is, in The damping medium used in the shock absorber is electromagnetic oil. This controllable fluid can undergo instantaneous and reversible rheology under the action of a magnetic field; it is a special "particle" that changes the " Particles" arrangement, so as to control the internal liquid state. Magnetorheological fluid can also be understood as a kind of "liquid iron", which will be magnetized under the action of an external magnetic field, and rearranged and combined into various structures, changing from "liquid" to "solid". . Of course, once the effect of the magnetic field is lost, these "liquid iron" will return to the "liquid state" and return to the flowing state.

The core of MRC is a controllable fluid called "magnetorheological fluid" in the shock absorber. The rheology of this material under the action of a magnetic field is instantaneous and reversible, and it will appear liquid at zero magnetic field. , and will appear solid in a strong magnetic field, so as long as the magnetic field is changed, the state of the magnetorheological fluid can be changed, and then the resistance of the piston in the shock absorber can be changed.

Simulated magnetorheological fluid test: the closer the magnet is, the greater the resistance to pushing the needle tube

↑The working principle of magnetorheological effect

The shock absorber rod of the car is supported by oil (except air suspension), so the viscosity (fluidity) of the oil directly affects the softness and hardness of the shock absorber. The density of the polymeric liquid in the shock absorber can change instantly, and at its hardest it is like plastic or rubber. Of course, when the density is reduced, it feels like stepping on a blanket. The electromagnet assembly described above allows magnetorheological fluid to flow through the core when the shock absorber is compressed and stretched. The shock absorber has a solenoid in the piston rod that creates a variable magnetic current through the magnet. When not powered, fluid flows easily through the magnet assembly. If the electric control device is energized and a magnetic field is applied, when the magnetorheological fluid flows through the electric control device in the piston, the magnetic particles in the magnetorheological fluid will be magnetized and arranged regularly, and the viscosity will increase at this time.

MR material rheological simulation

↑Magnetorheological working principle of electromagnetic suspension

3) In the normal state, when the coil current is turned off or there is no magnetic field in the environment without electromagnetic field, these metal particles will be distributed in the liquid randomly, the magnetorheological liquid is not magnetized, and the soft iron particles are randomly dispersed in the liquid , its original unmagnetized state is a free dissociated state, the suspended phase particles are suspended in the mother liquid and are randomly distributed, and the magnetic particles in the oil are randomly distributed, which is a linear viscous Newtonian fluid with a low viscosity. At this time, the damping of the shock absorber The strength is constant, the performance of the suspension is the same as that of ordinary shock absorber fluid, and there is no difference from ordinary hydraulic suspension with ordinary shock absorbers.

Once the control unit sends out a pulse signal, the current is connected to the coil to generate a voltage. With the electrification, a magnetic field and a change in the magnetic flux are formed to form a magnetic field, which generates a magnetic force between the iron particles in the fluid and changes the arrangement of the metal particles. The iron particles form a fiber structure arrangement along the fluid direction, and the dispersed particles inside the magnetorheological fluid will rearrange into an orderly matrix, arrange and combine along a specific direction, and immediately arrange in a formation perpendicular to the pressure direction to form a certain structure. The magnetic particles arranged in order will make the viscosity of the magnetorheological fluid thicker, thicken the fluid into marl, and increase its flow resistance. The viscosity coefficient will also change accordingly, and the fluidity of the suspension will change accordingly. Thereby increasing the damping coefficient, resulting in increased damping, these magnetic particles will form resistance to reduce the flow capacity of the oil, hinder the flow of oil in the piston channel, increase the flow resistance, increase the damping strength of the shock absorber, and let the suspension The resistance of the suspension increases, and the damping force of the shock absorber is adjusted instantaneously to adjust the shock absorption effect of the suspension.

In the energized working state, after the external magnetic field is applied through the current, the polarization phenomenon appears on the surface of the particles, forming magnetic dipoles, and the magnetic bodies in the dispersed state are rearranged by the influence of electromagnetic induction, and the magnetic dipoles are along the outer surface. The direction of the magnetic field forms a chain and cluster structure, which has a certain shear yield stress. The shear yield stress between adjacent particles in the same polarization chain will increase with the increase of the applied magnetic field strength. When the magnetic field increases to a certain level, the interaction between the magnetic dipoles is enhanced, and the magnetorheological fluid presents a solid-like characteristic, which in turn affects the change of the liquid form inside the shock absorber, thereby increasing the damping of the shock absorber, and also That is, the damping is greatly increased, so that the overall elasticity of the suspension becomes "harder", and correspondingly, when the current becomes weaker, the shock absorber becomes "softer".

4) Energizing the coil can generate a magnetic field to change the properties of the magneto-rheological fluid located in the orifice, that is, to control the viscosity of the liquid in the shock absorber with the current. The viscosity of the oil is proportional to the strength of the magnetic field. The current on the electromagnet The larger the magnetic particles, the tighter the arrangement of the magnetic particles, the more viscous the fluid, the greater the flow resistance, and the higher the damping force will be, so changing the current will change the damping performance; when the magnetorheological fluid flows in the damping channel in the piston, by allowing The flow rate of the shock absorber oil is controlled by turning on or off the magnet group. The strength of the electromagnetic field can be controlled only by changing the current. By changing the magnetic field of the piston electromagnetic coil, its flow characteristics can be controlled to achieve the control of changing the damping force. Effect, that is to say, by controlling the magnitude of the current, the damping of this system can be steplessly changed with the strength of the magnetic field, and the range of variation is very wide. Only by changing the current can the purpose of controlling the damping coefficient be achieved, and the resistance can be adjusted. Precise adjustment and control.

By changing the charge of the liquid in the shock absorber and changing the magnetic field, the position and density of the magnetic polymer can be changed. By changing the density of the liquid in the shock absorber, the hardness of the shock absorber can be changed, so that it can be adjusted according to different driving conditions. Vary the speed and amount of shock rebound. The viscosity of the magnetorheological fluid is adjusted through the current, and the viscosity of the magnetorheological fluid is flexibly adjusted through the electronically controlled magnetic field, so as to achieve real-time changes to control the damping of the shock absorber, that is, to change the hardness of the suspension. The more current passed through the coil, the "stiffer" the suspension will be. The characteristics of the electromagnetic suspension are exactly: it should be soft when it should be soft, and it should be hard when it should be hard.

Due to the existence of these magnetic particles, changing the damping strength of the shock absorber only needs to control the current strength (magnetic field strength). This feature enables the damping control frequency of the electromagnetic suspension to be calculated in milliseconds. At the moment of tire jumping, the electromagnetic suspension can quickly judge the degree of vibration, and control the beating and rebounding strength of the wheel with the most appropriate damping strength. The electromagnetic suspension shock absorber uses this characteristic of magnetorheological fluid to adjust the damping force. It is precisely because of the current control that the biggest feature of the electromagnetic suspension is its rapid response. Some electromagnetic suspensions can respond thousands of times per second. The characteristic of magnetorheological fluid controlled by the magnetic field is the biggest feature of the electromagnetic suspension—quick response, so that the models equipped with the electromagnetic suspension can flexibly switch between travel, sports and track driving modes. Electromagnetic suspension systems are better at controlling body and wheel movements caused by large road disturbances. The electromagnetic suspension adjusts the damping of the shock absorber based on the magnetorheological effect, so as to achieve the purpose of controlling the response of the active suspension. Therefore, the damping force can be adjusted to any desired level only by changing the amount of current passing through the magnet.

↑The electromagnetic suspension adjusts the damping based on the magneto-rheological effect

4) Electrorheology has reached a certain mature stage, but magnetorheology is still developing, and the depth of its research will increase. Magnetorheological fluid is a specific non-colloidal suspension liquid formed by dispersing and dissolving micron-sized magnetically excited particles in an insulating carrier liquid, so its rheological properties change with an external magnetic field, and the magnetic flow becomes a Newtonian fluid when there is no magnetic field , when subjected to a strong magnetic field, the suspended particles are inductively polarized, interact with each other to form particle chains, and interact in a very short time, changing from a fluid to a viscoplastic body with a certain shear yield stress. The strengthening of the shear yield stress will also increase accordingly, which is the magnetorheological effect. A large number of experimental studies have shown that the shear stress of magnetorheological fluid under the action of a magnetic field has a certain relationship with the shear velocity.

There are mainly three working modes of magnetorheology:

Flow mode, shear mode and squeeze mode: the flow mode is filled with magnetorheological fluid between two stationary plates, and the shear mode is filled with magnetorheological fluid between two relatively moving plates. Both of them are magnetorheological liquids that are vertically acted on between the two polar plates by an external magnetic field through the pole plates, so that the flow properties of the magnetorheological fluid change, and the purpose of controlling the damping force by the external magnetic field is achieved. The magnetorheological body is filled between the upper and lower pole plates, the upper pole plate is a movable plate, and the lower pole plate is a fixed plate. The external magnetic field acts on the magnetorheological body between the two pole plates perpendicularly through the pole plate. When the upper pole plate moves along the magnetic field When the direction moves downward, the magnetorheological body flows around, and the damping force on the polar plate can be controlled by controlling the external magnetic field. Squeeze mode shock absorbers have the characteristics of small displacement and large damping, and are mainly used for vibration reduction of precision instruments. Automotive magneto-rheological shock absorbers are generally designed based on the flow mode or the mixed mode based on the flow mode and the shear mode.

In the description of the mathematical model of the damping force of the magnetorheological shock absorber, although the description of the mechanical properties of the magnetorheological shock absorber is relatively mature, the application range has its own limitations. Among them, Bouc. The Wen model is widely used in engineering practice. For practical engineering applications, a mathematical model of the damping force of the magneto-rheological shock absorber based on bench test data is established.

Detailed Explanation of Automotive Electromagnetic Suspension (Part 1)