Abstract
Keywords - passenger car, active suspension, air spring, anti-roll, air suspension
An active anti-roll air suspension system is developed on the basis of the original passive air springs. The key points of this active system focus on the actuator and the control strategy. In the actuator, two additional air volumes and a hydraulic or pneumatic supply element is integrated as a moveable element, which works to keep down the roll movement of car body. For the concept development, three concept models of the actuator are simulated. The hydropneumatic actuator is chosen because of its high velocity of movement, high precision of displacement und low impulse force on the actuator. For controlling the movement of the actuator, four discrete control strategies are compared. The Pulse Width Modulation (PWM) and PID controller is the best choice because of its small control error, high control speed and simple control loop. For the simulation of the whole car, a cosimulation model between DSH-plus and Matlab/Simulink is built. The simulation results show that the roll angle of the car is reduced from 3.5° with the passive suspension to 0° with the active suspension. In a simple validation test, a pneumatic cylinder is driven by a hydraulic cylinder. The test result shows that the roll angle of the car is reduced ca. 1.5° with the active actuator only on the front axle. So the active volume change of the air springs is an effective way to reduce the roll movement of the car. By car turning, this active anti-roll system acts to the better safety, stability and comfort for the car.
With the high speed development of economy and technology, many requirements on the ride comfort, handling stability and safety are consequently taken into account by the automobile engineers while developing a passenger car. Due to many advantages, which are described in (1), such as high comfort, clean operation and convenient adjustment, air spring systems are installed more and more in passenger cars. As an important developing tendency of enviromental protection technology in car, air spring system will be used more frequently than other traditional suspension systems.
In (2), it is noted that the usage of air spring system in vehicle can be traced back to the early 20th century. With the development of electronics and control technology, in the 60s of 20th century the active suspension technology became gradually a new research direction. The hydropneumatic suspension system (3) of Citroën Company was one of typical representatives in that time. Hereafter many automobile engineers paid more and more attention to the active air suspension systems. For example, in 1985 a German engineer Gall designed a concept model (4) for an active control air spring. He divided the volume of air spring into two parts: additional volume and air spring volume. They are connected by a valve. While the car turning, the air pressure difference between left and right air springs works on the valve and the valve shuts off. The additional volume of air spring is separated to the air spring. So the air spring rate is increased to reduce the roll movement of car. The automobile engineers from Aachen institute of Automotive Engineering in Aachen University changed the concept more practical. They installed a valve between the left and right air springs, which is controlled by the air pressure difference between the left and right air springs in (5). A special designed actuator is controlled by the valve to push the additional volume of air spring with low pressure to the air spring with high pressure so that the volume of air spring with high pressure will be continuously increased. Therefore the roll angle of car body by turning is reduced. Furthermore some similar researches are taken also in some other automobile producers and components suppliers such as Daimler Chrysler, BMW, VW, Continental, Vibracoustic and so on.