# Semi-Active System of Vehicle Vibration Damping
## 1 Introduction  
This article discusses the vehicle vibration induced by uneven road surfaces and also by the inertial forces affecting the body. As a result of such a vibration, the driving comfort deteriorates and the dynamic load on the vehicle structure increases. Moreover, wheel pressure on the road surface changes (change in the dynamic loads in the suspension), which can contribute to slippage during acceleration, braking, or driving on a curve. In order to reduce vehicle body vibration, various kinds of devices are commonly used, dispersing the energy, known as vibration dampers.  
The problem area related to applying the semi-active dampers to reduce the vibration of vehicles, machines or buildings has long been considered. However, in recent years, technical conditions have emerged that enable practical implementation of such a way of reducing vehicle vibration [1, 2]. There has been development in the field of controlled structures based on smart materials. These materials include magnetorheological fluids [3, 4], electrorheological fluids [5, 6] and vacuum-packed particles [7].  
At the end of the 20 th century, magnetorheological fluid technology was developed. That laid the groundwork for the development of magnetorheological dampers (MR dampers). In the beginning, the technology was developed by the LORD Corporation, Cary, North Carolina, USA. MR dampers have been used in human prostheses and vehicle seats [8, 9]. In the following years, further research related to the development of MR dampers began, which resulted in new solutions presented in publications [10, 11, 12]. Currently, controlled MR dampers are used in different fields: damping vibrations of buildings [13, 14], reducing vibrations of washing machines [15, 16], in suspensions of high-speed trains [17, 18] and in automotive suspensions [19, 20, 21]. These conditions were created due to the possibility of using on-board computers with high computing power and semi-active dampers.  
An important problem is the determination of the control signal for semi-active dampers. For this purpose, different methods were developed where the control signal is determined on the basis of the measurement signals. In multi-body systems, Zero Residual Vibration-Derivative methods [22; 23] are used to determine the control signal. Another solution to the problem is to use Hybrid Prediction Control [24; 25]. Sky-hook and ground-hook methods [26; 27] are common in semi-active suppression of vehicle vibration. The authors of the work developed original methods of minimizing acceleration in a selected point of the car body [11].  
In the presented system, the vibration control of the vehicle is carried out by means of semi-active dampers based on the control signals from the LVDT displacement sensors. The original mechatronic system, based on a dedicated algorithm for determining the control signals, was developed for control. Controlling the frictional force in vibration dampers was adopted to reduce the vertical accelerations affecting the vehicle passengers. In the discussed solution, a controlled magnetorheological damper (MR) was used.