# A Hydraulic Semi-Active Suspension Based on Road Statistical Properties and Its Road Identification  
[PERSON]  
1 School of Automation, Beijing University of Posts and Telecommunications, 10 Xitucheng Road Haidian District, Beijing 100876, China; [EMAIL_ADDRESS] (L.Z. ); [EMAIL_ADDRESS] (F.Y. ); [EMAIL_ADDRESS] (S.W.) [PERSON]  
2 School of Transportation and Vehicle Engineering, Shandong University of Technology, 12 Zhangzhou Road, Zibo 255049, China  
it is difficult to achieve mass production for vehicles with MR dampers. The wide application of ER dampers depends on the research and breakthrough of ER fluid materials [18; 19]. Compared with MR dampers, the application of ER dampers is even less in the vehicle market. Vehicles with ER dampers are still in the testing phase [20; 21]. It can be seen that the existing semi-active suspensions with MR or ER dampers are very expensive and difficult to be popularized. The hydraulic damper has become the most widely used in suspension systems of various vehicles [22]. It has simple structure, reliable performance, and relatively low price. Thus, it is very popular with vehicle manufacturers. In recent years, scholars have paid more attention to it. Moreover, a broad variety of controllable hydraulic dampers were developed based on the traditional hydraulic damper. For all controllable hydraulic dampers, a fatal shortcoming exists. Their dynamic response is slower than that of MR dampers and ER dampers [23]. Because of this shortcoming, the vibration isolation effect of the vehicle suspension with controllable hydraulic dampers is not ideal. The existing real-time control strategy, i.e., the skyhook control [24], is not very applicable to controllable hydraulic dampers. Thus, in the previous work [25], we developed an optimal damping ratio control method based on road statistical properties. Moreover, we validated its effectiveness. Because this method is essentially based on statistical theory, it does not need the rapid response characteristics of controllable hydraulic dampers. However, it needs the road condition information. The existing road condition identification methods are hard to realize and the cost is relatively high, which has a certain effect on the application of semi-active suspensions. At present, related vehicle experts and scholars have carried out many works on the model and method of road identification. The existing identification methods of road conditions are mainly based on video cameras, acoustic sensing devices, and so on. Usually, they also need certain complex control algorithms. Their reliability, real-time, and implementation cost have some limits in application. The representative research works are as follows: [PERSON] et al. used stereo cameras to monitor road conditions [26]; [PERSON] et al. used acoustic equipment to measure the tire noise and identified the road condition by a neural network [27]; [PERSON] et al. proposed an identification method based on a noise sensor and the support vector machine technology [28]; [PERSON] et al. comprehensively used probability statistics and neural network to identify road types [29]; [PERSON] et al. identified the unpaved roads by remote sensing technologies [30]; and [PERSON] et al. monitored the road levels through the engine speed [31]. These works play a role in promoting the realization of road identification technologies. However, at present, there are few studies focusing on road condition identification methods that are simple and reliable, and easy to implement at low cost. To reduce the product cost of semi-active suspensions, this paper proposes a new hydraulic semi-active suspension system based on road statistical properties and creates a feasible identification method of road conditions. To verify the effectiveness of the identification method, a road test was carried out. The main contributions are as follows:  
(1) A new hydraulic semi-active suspension based on road statistical properties was proposed and its working process was given in details.