The hydraulic system.

The relief valve set the oil pressure of the hydraulic system to ensure the oil pressure constant after running. When the electro-hydraulic proportional of the relief valve receives the electrical signal, by changing the position of the valve, thereby changing the output pressure of the relief valve to adjust the inlet pressure of the solenoid directional valve, by controlling the output force of the hydraulic cylinder, so as to control the output size of the force to the car by the hydraulic cylinder. Using the pressure-flow gain of the solenoid directional valve to increase the damping ratio of the system and improve the stability of the hydraulic system. The throttle valve is mainly used to control the traffic of the reflux way to ensure the smooth operation of the hydraulic cylinder[2].

The electro-hydraulic control system.

The position sensor detects the displacement of the capsule, the electrical signal inputs the amplifier after through the controller. After amplified by the power amplifier to drive the proportional solenoid，so as to control the valve opening of the relief valve.

The improved hydraulic system of the hydraulic elevator For the deficiency of the hydraulic system, this paper presents a new hydraulic system. It can real-time monitor the upstream and downstream speed deviation of the compensation capsule, so that the speed change of the hydraulic rod is more slowly and steadily and the capsule run more smoothly, safe and reliable. The improved hydraulic system of the hydraulic elevator is as following:

Fig.2 The improved hydraulic system of the hydraulic elevator

This system is consists of the oil circuit system, the control system and the electro-hydraulic proportional valve system. The hydraulic oil in the oil tank is driven by the hydraulic pump station, flowing into the solenoid directional valve and the electro-hydraulic proportional valve system, then into the bottom of the hydraulic cylinder to drive the hydraulic rod extended, and the lift up. Above the process, the speed detection system real-time monitoring, when the velocity changes is not reliable, the speed monitoring system transmits signals to the amplifier, and the amplifier transmits signals to the electro-hydraulic proportional valve system, then the electro-hydraulic proportional valve spool action to adjust the size of the opening and the flow of the hydraulic oil, compensating the operation deviation of the speed，so that the speed change is small and the car run smoothly[3].

The solenoid directional valve connects the upstream and downstream oil pressure detector to monitor of upstream and downstream oil pressure condition in real time, then feedback the monitoring values to the control system and the control system to make feedback, then real-time adjusts the speed of the hydraulic pump, by adjusting the displacement of the hydraulic pump to adjust the speed, so as to compensate for the speed deviation and make the car speed run more smoothly[4].

Dynamic response characteristics of the system

The mathematical models of two kinds of hydraulic systems are established respectively, to obtain the transfer function of the two systems. Substitution of the relevant data, then getting two transfer function value of the two systems. The step dynamic response curves of the two system by computer simulation are seen in Fig 3 (A) and (B).  

Fig 3 The step dynamic response curves of the two system

Summary

The simulation results show that the improved hydraulic system can be more stable. With the speed bidirectional detection function of the hydraulic system runs more smoothly and rides more comfortable and secure.

References

[1]. Yongxiang Lu. Electro-hydraulic proportional control technology (1 Edition)[J]. Beijing Machinery Industry Press, 1988.

[2]. Lizhen Zhang. Research on speed feedback hydraulic elevator operating characteristics[C], 1999.

[3]. Guojun Zhao, Huayong Yang. The hydraulic elevator system with car speed feedback control. Zhejiang University of Technology, Hangzhou, 1996.