| In recent years, because of the rapid development of economic construction andthe sharp increase of New Countryside Construction projects, quality problems ofconcrete construction caused widespread concern in the society, and the higherrequirements have been put forward to small concrete construction equipments. As acombine of concrete truck and concrete mixing station, Automatic Loading MobileConcrete Mixer has broad market prospect. In order to improve transmissionefficiency and expand the vehicles speed area, solving the problem of significantdifferences between the speed under inactivity state and the speed under operatingstate, Hydrostatic-mechanic Transmission System became widely used in theequipment. Its performance directly determines the handling, reliability and securityof vehicles. How to implement reasonable matching control of the system, improveenergy efficiency and optimize the performance of hydraulic components become thekey issues of the system research.Based on the school-enterprise cooperation project "Automatic Loading MobileConcrete Mixer Development", combined with system dynamic matching controltheory and mathematical models, relied on AMESim simulation platform andexperimental results, this paper studied the system performance and the keyparameters of Hydrostatic-mechanic Transmission System the machine used. The fulltext can be included in following aspects:(1) Through the analysis of vehicles’ major driving conditions and workingcharacteristics, the paper elaborated the matching and control objectives ofHydrostatic-mechanic Transmission System. With the efficiency range of system keycomponents: engine, variable pump, motor as the starting point, it studied the systemdynamic matching control strategy: speed-sensitive control and its majorimplementations: DA control and NFPE control. Studies have shown that NFPEcontrol is more flexible and it can improve fuel economy and operator comfort of theequipment. The current signal in NFPE control curve is mainly determined by thecontrol target torque of NFPE pump and its load control line. (2) On the basis of analyzing the principle and body structure of the closedhydraulic circuit and the pump displacement control mechanism, this paper hasestablished the mathematical model and derive system transfer function blockdiagram using classical control theory, then analysis the structural parameters’ impacton the system dynamic response qualitatively. It can find out that: The F00A andF00B orifice size in proportional solenoid valves have significant impact on theresponse of pump displacement, the smaller orifice, the slower the displacementresponse is. Reducing the proportional solenoid valve springs stiffnessK vandcylinder springs stiffnessK Pwill help to reduce the natural frequency of systemoscillation, increase the damping, and the system will has better stability. The flowgainK qvand pressure-flow coefficientK cvof proportional solenoid valve ports havegreat influence on the slope and the starting variable current of variable pumpdisplacement control curve, which is mainly determined by the throttle opening areagradient.(3) Relying on AMESim simulation platform, it has built the HCD simulationmodel of pump displacement changing mechanism according to its actual structureand the overall simulation model of the system, then conduct simulation to study thesystem performance and the key parameters. Simulation results show that the NFPEvariable displacement pump which has used speed-sensitive control can adjust itsdisplacement along with the speed changes, to prevent the engine flameout when thevehicle load suddenly increases. Under different operating conditions, distinguishingworking condition control strategies can set different vehicle control curves. Relativeto a single control curve, this control method can make the use of engine power morerational, and improve system reliability. By carrying on batch simulation ofcomponent key parameters, it verified the correctness of the theoretical analysis onmathematical model. To improve sensitivity and stability of displacement controlmechanism, we should choose the variable cylinder spring stiffness reasonably,reduce the damping without causing the system oscillation, increase the two orificediameter and the mass of proportional solenoid valve spool should be reduced as well.(4) Combining theoretical analysis of Hydrostatic-mechanic TransmissionSystem, this paper developed experimental test program, and analyzed theexperimental results. Results showed that: AMESim simulation model can reflect theactual status of the system to a certain extent. Two tranches gearbox can expand speed domain of the vehicle, adapt to the two kinds of huge difference load condition:highway and off-road in different stalls. The NFPE control strategy the vehicle usedcan realize system dynamic match through the real-time adjustment of the pumpdisplacement when the pressure fluctuated. |
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