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Bus electronically controlled air suspension system and its development trend

    With the increasing demand for vehicle ride comfort and technological development of passenger car suspension, air suspension on the bus is used widely.booster cables The traditional model is the air suspension with mechanical height control valve, the valve through the valve opening height adjustment of the charge air suspension air bags deflated, thereby maintaining a constant vehicle ride height.

    With the application of the promotion system and vehicle control technology, battery clip electronic control gradually replaced the traditional mechanical control of electronic control systems, not only improves the operation of comfort and response sensitivity, and can add a lot of auxiliary functions.

    In order to ensure that the suspension of the main features of the anti-vibration (vibration damping force), elastic constants, damper travel,tow rope continue the successful development of a variety of driving conditions can adapt to the optimal control mechanism.

    Electronically controlled active suspension system bus.

    Study on Active Suspension now focus two aspects: one is the control strategy; the other actuators. The first active suspension control strategy is the ceiling principle,ratchet tie dowm assuming a fixed body above the inertial reference, between the body and inertial reference there is a damper, the damper actuator force simulation to attenuate the vibration of the body. This control algorithm is simple, in some foreign models have been applied.

    With the development of modern control theory, put forward the optimal active suspension control method, which considered more than the ceiling principle variables, control is better, the current optimal control law in three ways: the linear optimal control, HQ optimal control and optimal preview control.

    As the actual suspension system there are many non-linear, time-varying, high-power system, the optimal control becomes unstable, and to this end the development of adaptive control methods. Adaptive control method has a parameter identification functions, to adapt to suspension loads and changes in device characteristics, automatically adjust the control parameters to maintain optimal performance. Adaptive control method also has gain scheduling, model reference adaptive control and self-tuning control of three categories.

    Volkswagen in Germany, the application of the adaptive chassis control law. The current development control policy is the most rapidly intelligent control (fuzzy control and neural network control). Fuzzy control method is a combination of brake adjustment input variables, membership function parameters and the number of fuzzy rules and other learning functions, computer simulation results show that the method is more effective.

    Neural network is a processing unit consisting of a large number of highly parallel nonlinear dynamic system, it can carry out data fusion, adaptive learning and parallel processing, studies show that it is better than the traditional control performance.

    Actuators to achieve control objectives is an important part, so go against the drive of the study is an important part of active suspension. To ensure the good performance of active suspension, the actuator must have a sensitive, stable condition, reliable, low energy consumption, low cost and total. At present the application of active suspension on the main hydraulic actuator structure.

    Nissan is developing a storage-type shock absorber, it will pressure control valve with a small accumulator and the hydraulic cylinder combine to make the road vibration is caused by uneven absorption of the accumulator, the body by the active damping and passive vibration isolation damping together to complete, thus energy consumption is reduced. However, there are a lot of hydraulic power system deficiencies, such as certain requirements of the work environment; high precision component manufacturers, the cost is difficult to decline; deal with small signal digital operation, error detection and amplification, testing and compensation, automation and achieve much from other functions such as electrical system is flexible and accurate. So now the main focus of the actuator in the linear servo motor, the direction of magnetic storage devices.

    Electrical power system for linear servo motor has more advantages, permanent magnet DC linear servo motor, driven by better performance than the hydraulic system, the future will replace the hydraulic actuator. Principle of using electromagnetic energy storage, combined with parameter estimation self-tuning controller, is expected to design a high performance and low power electromagnetic energy storage-type adaptive active suspension.

    Bus ECAS system functions and advantages.

    Automobile frame (or body) if directly installed in the axle (or wheel), due to uneven roads, the impact of the ground so that goods and people will feel very uncomfortable, this is because there is no reason for suspension device. Vehicle suspension is frame (or body) and the axle (or wheel) between the elastic coupling collectively. Its role is to connect the axle and the frame elastic (or body) to ease the moving vehicle by the impact. Goods and personnel to ensure good comfort;

    Attenuation of the vibration of the elastic system was introduced, making the car driving to maintain a stable posture, improved handling and stability; while passing the vertical suspension system bear the reaction force, vertical reaction force (traction and braking) and lateral reaction force, and these forces caused by the torque applied to the frame (or body), and to ensure the car ride;

    And when the wheels relative to the frame beats, especially in the steering, the wheel trajectory to meet certain requirements, so that the wheel suspension but also for a certain path relative to the body by beating the guide. Electronically controlled air suspension system bus (ECAS) system, often the following functions and advantages.

    (1) vehicle lift capabilities. Vehicle is in motion, ECAS maintain normal ride height, special road and driving conditions can be reduced by controlling the switch to enhance the vehicle's ride height or to facilitate vehicle ferry or through the tunnel. ECAS also allows the electronic control unit to set vehicle speed, vehicle speed control by a high degree, such as when the speed reaches 20km / h, the vehicle can automatically travel back to normal height.

    (2) roll function. This feature is dedicated for the function of city buses. When the vehicle arrival, the door side airbags deflated, as only the top side of the front door is about the same time two air balloon deflated, if before and after the two doors, the lateral side of the door air balloon deflated The stepping height can be automatically reduced to facilitate baby carriages, wheelchairs up and down, to facilitate the old, young and disabled passengers to travel.

    ECAS can be achieved on a high setting and control of roll, roll, or single-axis tilting of unilateral choice of a variety of ways, but under the system monitor installed in the door contact switch to reduce the process to ensure the security, if the contact switch in reducing in the process of reaction, buses will automatically revert to the normal ride height.

    (3) vehicle height limit function. ECAS can set minimum and maximum vehicle chassis height. Once you reach the set minimum and maximum position, electronic control unit will automatically end height adjustment.

    (4) highly integrated system. System, fewer parts, easy installation reduces assembly costs.

    (5) rapid adjustment process. As a result of large cross section into (a) the solenoid valve air intake process of leaving all down very quickly.

    (6) to reduce air consumption. Avoid vibration of the vehicle during normal driving the air consumption. Example of low floor city bus with a high degree of mechanical valves compared with the control of the air suspension system, ECAS can save about 25% of the air consumption.

    (7) pressure monitoring. ECU test gas pressure, is considered safe if the air pressure falls below a certain value, down and roll function will be limited.

    (8) security control. ECU door switches based on the current information, to determine whether to increase / decrease vehicle.

    (9) maintenance inspection. Special diagnostic software and testing equipment, can be done off-line rapid detection and adjustment; convenient flash code function, easy to detect after-sales service.

    In China, ECAS has entered the luxury bus and coach market, its functionality and convenience more and more accepted by the market. Public transportation market in China, has begun with the ECAS scale use of city buses, city buses in China believe that with the performance improvements and product generation, the body can "roll" function of the ECAS system, the emergence of more and more In the city bus market, adding to public transport human color.
    Bus ECAS system architecture principles.

    ECAS system consists of electronic control unit (ECU), solenoid valves, height sensors, air bag and other components. Its basic principle is responsible for detecting the vehicle height sensor height (distance between the frame and axle) changes, and to pass this information to the electronic control unit, in addition to a high degree of information, the electronic control unit also accepts other input , such as speed information, braking information, the doors of information and information supply pressure, and then synthesize all of the electronic control unit input information to determine the current vehicle state in accordance with its internal control logic, to stimulate the work of the solenoid valve, air solenoid valve to achieve the various air conditioning air bag charge and discharge.

    One of the main advantages of ECAS can quickly achieve the required high degree of control, this is due to ECAS solenoid valve and out using a large air intake cross-section, but no matter how fast response solenoid valve may be too much air is still filled with air bag, and lead to higher than expected following the high standard height, the "overshoot." When the vehicle is unloaded state, because the system pressure and cylinder load, the air bag caused by air pressure difference between the large very fast, leading to this "overshoot" more frequently. Sometimes "overshoot" can lead to a high standard height around the long-term oscillations, the control process is not what we expected, but also reduces the life of the solenoid valve. Therefore, in order to achieve a high degree of accuracy standards, the control process must be conducted in accordance with the following: In the front is about to reach the standard height, reducing air flow and reduce the rate of increase. If the system is adjusted properly, will not be any "overshoot." Because the solenoid valve can control flow off, can not reduce the volume of gas, if the pulse current control solenoid valve, solenoid valve so the gas can interrupt the flow of short-term played a throttling effect.

    ECAS electronic control unit control the electromagnetic pulse valve opening, according to the current actual height and the deviation of the expected height adjustment, electronic control unit calculates the pulse length of the solenoid valve adjustment, if necessary adjust the height of volume, because there is no "overshoot" in dangerous, electronic control unit will give a long pulse, while the increase rate will decrease faster pulse length, so precise control of the vehicle height can adjust the speed, greatly to avoid a high degree of "overshoot", and oscillation adjustment .

    (1) electronic control unit. Electronic control unit (ECU) is usually installed in the cab or the electrical box, the value of different heights to achieve the management and storage, control, including more than one vehicle, including a high normal height, electronic control unit is responsible for the exchange of data and diagnostic tools while monitoring the operation of all system components, testing and storage of system failure.

    (2) solenoid valve. Solenoid valve is usually installed in the chassis or frame beams. ECAS solenoid valve is a highly integrated and modular design. Depending on configuration, the general layout of the external shell can be a different number of solenoid valve components. ECAS solenoid valve combination can greatly save the amount of parts and assembly costs and installation space. In order to reduce exhaust noise, exhaust valve with a silencer. For example, with the roll feature ECAS solenoid valve, which is contained inside a small solenoid valve 6, which are combined in a shell, front and rear axles to achieve individual control of all air balloon and roll control. 4 × 2 bus approached the bridge installed a height sensor, two height sensors mounted rear axle.

    (3) height sensor. Height sensor height of the shape and mechanical valves look similar, they are exactly the same installation and the installation location, usually arranged in the frame. Included within the sensor coil and pivot, when the distance between the axle and the body changes, a high degree of yaw rotation pole and the corresponding armature driven up and down linear motion in the coil, causing the coil inductance changes, electronic control unit detects This change in inductance and convert it into a high digital signal.

    Electronically controlled air suspension market prospects and development trends.

    Not long ago, commercial auto show in Beijing, Xiamen Golden Dragon, the Yellow Sea and other passenger car manufacturers display Dandong large articulated BRT buses are the city adopted a new configuration - electronically controlled air suspension (ECAS system). The system can achieve a high degree of automatic vehicle movements, also has a roll function to facilitate the mobility problems on and off, greatly improving the comfort of the vehicle, the design embodies the concept of human nature.
    Electronically controlled air suspension, air suspension on behalf of the current direction of development. It is understood that the development of the international experience of automotive suspension of the "composite leaf spring suspension air bag → → → passive full air suspension, air suspension, all active (ie the ECAS system)," the change process. ECAS part of the current bus system in Europe, has already begun on the application. As the vehicle control technology, electronic control gradually replace the traditional mechanical control, ECAS air suspension system, this advanced system will be a development direction of vehicle suspension.

    Electronically controlled air suspension is currently in the country has already begun on the application of passenger cars, particularly in urban buses, such as Beijing and other cities of the BRT buses have adopted this advanced suspension system to facilitate the elderly or the disabled on and off.

    Although the electronic controlled air suspension is considered one of the development trend of passenger cars, but from the large area of marketing is still a long way. Now electronically controlled air suspension is also very narrow application areas. Only a few high-end buses and special purpose vehicles, to meet the requirements reduce the ride height air suspension with electronic control. Currently on air suspension bus usage in the country only about 10%, electronic controlled air suspension is less than 1%, the market capacity is very small. For a long period of time, electronically controlled air suspension on a large number of applications in the passenger car is not realistic. After all, this high-end products, higher prices than ordinary air suspension 2 to 3 times, and vehicle factories in controlling costs, for the suspension, as long as the height adjustable airbags to basically meet the requirements, the need for expensive electronic control systems to automatically adjust. The promotion of an advanced product guide mainly by government regulations, and market demand, electronic controlled air suspension is no exception. The market demand has not significantly improved, there is no legislation to force the installation of the situation, electronically controlled air suspension of the market prospects are good.

    Electronic Control Suspension bus need to be addressed in future technologies.

    Passive suspension will remain in a certain period of time is the most extensive suspension system, suspension by further optimizing the structure and parameters can continue to improve suspension performance. Active suspension, superior performance, for cost reasons but also can be advanced racing cars and equipment. Its research focuses on high-performance actuators and control based on neural network strategy. Semi-active suspension than passive suspension performance, cost, much lower than the active suspension, suspension system should be the main future direction of development. Of reliable performance, easy adjustment of the adjustable damper and the algorithm is simple and effective control strategy will be the semi-active suspension to the public to pass.

    Bus suspension need to be addressed in future technologies are: pneumatic suspension technology: parts and spring systems by the oil and gas joint support body, changes in carrying capacity based on the vehicle, adjust the suspension by the oil and gas components horizontal position, the spring to maintain the normal use position ; damping adjustable shock absorber: perceived by the sensor when the vehicle driving conditions, including load size, uneven pavement, is turning, whether accelerating or braking, the electronic control unit analysis to determine, by a solenoid valve hydraulic system, regulation shock absorber damping. This technology has become a semi-active suspension technology; full active suspension technology: electro-hydraulic system not only by adjusting the damping and elastic adjustment, level location.

    Nonlinear characteristics of suspension system for the study of appropriate technology is the electronically controlled suspension system of automobile suspension system vibration performance improvement direction. Between the suspension and tires in the body, the movement of the vehicle performance, ride comfort has a significant impact. Road driving conditions in accordance with optimal control, suspension performance to ensure performance and comfort of vehicles, electronic control suspension will further develop in the direction to the performance. As the suspension to achieve optimal control of this one way is to use "predict sensor" to predict the control of the "predict the control suspension." Has made a variety of programs, and look forward to the emergence of this new sensor. On the other hand, from the Earth's environment to consider, to further save energy, suspension control to high pressure, high-voltage technology, small lightweight development. In the control theory is working on fuzzy logic control, neural network control used in the research suspension.

    From the appearance of seemingly simple suspension, contains a variety of power cooperation is crucial parts of modern passenger one. As the bus structure and function of continuous improvement and perfection of passenger vibration, designing new electronically controlled suspension system, vibration control to the lowest level is to improve the quality of the important measures of modern passenger cars. Currently, the bus suspension system has entered into the controller to control the use of electronic era. The optimum control method used to obtain high-damping effect, and the energy consumption as low as possible is the development of passenger car suspension system, the main direction.

    With the people's living standards improve, more and more to consider the design of city bus people-oriented ideas. Electronically controlled air suspension system (ECAS) not only improves comfort, and its height adjustment feature to achieve the passengers get on and off more convenient, and because the dynamic movement of air spring control process, compared with the conventional air suspension, less of its gas consumption. ECAS system through the application of low-floor city bus, reliability test and the actual use situation is very successful. ECAS city bus system installed will become the future trend of development.

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