Research Into Dynamic Performance And Digital Valve For Hydraulic Free Piston Engine

This doctoral thesis comes from the project "Free Piston Engine Hydraulic Reciprocating Pump" supported by the National High Technology Research and Development Program ("863" Program, the project serial number is 2001 AA423150) and the project "Study on the Mechanism of Hydraulic Free Piston Internal Combustion Engine" (the project serial number 50075077) supported by National Science Foundation of china (NSFC).A hydraulic free piston engine (abbreviated as HFPE) integrates internal combustion engine and a hydraulic pump into one compact unit. In practical view, there is only one linearly moving part, i.e. the piston assemble in the HFPE. Comparing with crankshaft internal combustion engine , the piston assemble within HFPE is not restricted by any mechanical linkages, so its forth between left and right extremes by means of the fuel energy, simultaneously its hydraulic piston directly produce hydraulic energy.Comparing with the single piston or opposed piston HFPE, the dual piston HFPE (abbreviated as DHFPE) has its own special features such as the highest power density, so the aim of this thesis is to study the mechanism of DHFPE and its key component. The main content of this thesis could fall into five chapters as the followings.Chapter 1 the history and current research status of HFPE are introduced based on a lot of the publications and conference papers. The key techniques of HFPE are also described. Consequently, the goal of research and project are brought forward.Chapter 2 study on the mechanism of the DHFPE. The mathematical models of every subsystem included in the DHFPE have been built up and verified by experiment data. Based on simulation result of DHFPE, DHFPE structure parameters optimization were developed. Then the performance and stability of DHFPE was analyzed. The motion of DHFPE is self-sustained oscillation with variable rigidity and variable damp. According to DHFPE amplitude frequency characteristics, the necessary condition of DHFPE stable operation was presented.Chapter 3 discusses the design of digital valve spool. A new slid valve has been developed. The valve, named "slot valve" because of its slop-spool shape, make it possible to keep flow force in low level. A new method was presented to reduce flow force of diverged flow cone valve, the damping ring method. First an experiment device was designed that used for measuring flow force without friction influence. Then spool flow force with various design parameters was measured by the experiment device. Final the relationship between cone valve design parameter and flow force is presented. At the end of this chapter, a new k-...