Ren Haoling

Boom energy recovery system with auxiliary throttle based on hybrid excavator

To obtain good performance in the conventional energy regeneration system which has worse dynamic actuator performance than traditional orifice control systems, an energy regeneration system that employs a proportional throttle valve and a proportional directional valve to avail a hydraulic motor controlling the boom is proposed. The control model is constructed and the control properties are analyzed. Based on the proposed energy regeneration system, the new operation mode of the boom system with an energy regeneration system is characterized by the status of the joystick and the pressure of the boom cylinder. Considering the performance under the bad control in the low rotational speed, the total power loss of the hydraulic motor and the generator, a dynamic-working-points control strategy of the generator is discussed. Then, as the displacement and velocity sensors cannot be easily assembled in a hydraulic excavator, a compound control that consists of throttle control and volume control is presented. Finally, a test rig is constructed, the recovery efficiency of the proposed energy regeneration system is approximately 35% and it is also shown that the proposed energy regeneration system had better control performance than the conventional energy regeneration system.

Stability research of the compression process of two-cylinder four-stroke single-piston hydraulic free piston engine

An invariable compression ratio in certain conditions must be achieved to ensure a steady and efficient performance of the single-piston hydraulic free piston engine. The compression ratio is determined by the characteristics of the compression stroke. The mathematical models of the key components during the compression process are established. The kinematic characteristics of the free piston assembly are analyzed under two conditions. One condition is that free piston assembly is driven by the compression accumulator only and the other one is that free piston assembly is driven by the compression accumulator and the pump station. Pressures in compression accumulator and compression chamber are analyzed and compared in both conditions. According to the experimental results, pressures in the compression chamber and compression accumulator are not constant in both conditions during the compression process. The compression stroke and compression time vary with the changing of the pressure in the compression accumulator, which adds the complexity and changeability to the compression ratio control. An improved configuration is put forward to solve the pressure variation. The results show that the improved configuration can make the pressure invariable at the inlet of the compression chamber and the compression process keeps almost the same regardless of the pressure changing in the compression accumulator. With this new structure, there is about 2.5% energy loss, which is acceptable considering the stable compression stroke.