Key Technology And Optimization Of Pneumatic Cabin Pressure Regulating System

New combat aircrafts with features of high-altitude,high-velocity,and high-mobility bring new challenges to performance of cabin pressure regulating systems.In the flight practice,there are two main problems with the presently used pneumatic cabin pressure regulating system(pneumatic CPRS).Firstly,the dynamic characteristics are undesirable.In high-speed dives,the pressurization process is very slow at higher altitudes.However exssive cabin pressure change rate happens at lower altitudes.Secondly,the system is not sufficiently stable,which lead to continuous cabin pressure oscillation at certain flight altitudes.The problems may cause serious ear discomfort on pilots,the symptoms including affected hearing,annoying feeling of fullness,tinnitus,or even vertigo,and pain.The existing of these symptoms seriouly affects the comfort of pilots and poses a significant threat to the flight safety.In the paper,mathematical models of components constituting the pneumatic cabin pressure regulating system are built,applying theory of fluid dynamics,mechanical dynamics and automatic control.By means of theoretical analysis,numerical simulation and experimental study,some innovative outcomes are obtained in pressure change-rate control,stability analysis and system optimization.(1)The control strategy and characteristics of the present system are fully studied.The generating mechamism of pressure schedule and its control logic are revealed.The effects of main components' structural parameters on performance of the system are investigated.The outcomes build theoretical foundations for the solution of the existing problems,at the same time it provides theoretical basis and technical support for development and optimization of the new systems.(2)To solve the problem of excessive cabin pressure change rate in diving process,faced by new generation of aircrafts characterized by high-altitude,high-mobility and high-speed,a differential pressure compensating method is put forward to improve dynamic performance of pneumatic CPRS.By optimizing flow parameter of the capillary restriction,dynamic performance of the system is greatly promoted.A differential pressure compensator is designed.It dynamically adjusts,according to flying altitude,pressure difference applied to flow restriction element.By this way,high altitude performace of the system is raised more than 25%.Experimental results show that in process of high speed diving,the scope,where cabinpressure change rate varies within limitation,is extended more than 2000 m downward.The result provides an efficient scheme for improving comfortability of cabin pressure environment,especially for aircraft under extreme flight condition of high-altitude,high-velocity and high-mobility.(3)The time constants of transfer functions of pneumatic elements vary with working condion(pressure and signal amplitudes).Accordingly,a frequency characteristics analysis method based on grid linearization is proposed,to obtain magnitude-phase characteristics of pneumatic system under all working condition(set-member magnitude-phase curves).The research results build theoretical basis for stability analysis of pneumatic CPRS.The grid linearization method has reference significance to linearization of nonlinear parameter varing system.(4)Taking into consideration complex parameter-varing nonlinear characteristics of pneumatic CPRS,set-member describing function method is proposed to analyze stability of the system.The cabin pressure oscillation,presented in high altitude aircrafts at certain flight altitude,is eliminated.The intersection point(or points)of-1 / N(x)curve of constant nonlinearity and set-mumbership amplitude-phase curves are used as criteria of system instability.By optimizing structural parameters of a pressure schedule generating component,the open loop magnification of the system is reduced and stability of the system is achieved.The set-member describing function method has instructive significance for stability analysis of pneumatic systems and other nonlinear systems.To testify feasibility and validity of the optimization methods proposed in the present paper,a series of simulated flight experiments were done on a testing platform for pneumatic CPRS of XX type aircraft.The test program includes takeoff and landing at airports of different elevations,climbing,diving,and air supply surge.The experimental result shows that after optimization the dynamic performance of the system is greatly improved.The problem of excessive cabin pressure change rate is well settled,and the stability of the system under all working conditions is achieved.The optimized CPRS can satisfy practical needs of the new generation of aircrafts.