機(jī)械外文翻譯--被困-容積泵的設(shè)計-其他專業(yè)(參考版)
2025-01-23 06:13本頁面
【正文】 and, as a result, energy was added to the pistonchamber volume. At top dead center, the valveplate slot is used to depress the fluid that was pressed at bottom dead center. This depression or expansion of the fluid results in a flow through the slot which releases the stored energy in the fluid. Piston Kinematics The threedimensional trajectory of the nth piston within the pump may be determined from geometry. Using Fig. 1, it may be shown that the kinematic behavior of the nth piston in the xdirection is given by （ 1） where, r is the piston pitch radius, a is the swashplate angle, and u n is the angular position of the nth piston chamber about the centerline of the pump shaft. Piston Pressure and Flow General. Figure 2 shows a piston as it operates within its bore where the volume of fluid within the bore is taken as the control volume of study. The pressure outside the piston bore, Pb , is not shown but must vary with time to simulate the fact that as the cylinder block rotates about the xaxis, this pressure repeatedly changes from the discharge pressure, Pd , to the intake pressure, Pi . The discharge area of the piston bore, An , also varies with time which models the transition regions on the valve plate where the slots provide a variable opening into each port. The fluid pressure within the nth piston chamber is governed by the standard pressureriserate equation which is given by （ 2） where Qn is the volumetric flow rate of fluid exiting the piston chamber, Vn is the instantaneous volume of the piston chamber itself, and b is the fluid bulkmodulus. If it is assumed that the flow in and out of the piston bore occurs at a high velocity and thus a high Reynoldsnumber!, the flow rate Qn may be modeled using the classical orifice equation which is based upon Bernoulli principles. This equation may be adapted to the current situation shown in Fig. 2 and written as （ 3） Journal of Dynamic Systems, Measurement, and Control where the ‘‘sign’’ function takes on the value 61 depending upon the sign of its argument, Cd is the orifice dischargecoefficient, and Pb is the boundary pressure outside the control volume ~either Pi or Pd!. The instantaneous volume of the nth pistonbore may be determined using the kinematic results of Eq. ~1!, the area on the face of a single piston, Ap , and the nominal piston volume, Vo . This quantity is expressed （ 4） By definition, dt5(1/v)du n . Using this definition with Eqs. ~2!, ~3!, and ~4!, the pressure riserate within a single piston chamber may be rewritten as （ 5） Equation ~5! is a nonlinear, first order, differential equation that does not have an analytical solution. In the following sections, Eqs. ~3! and ~5! will be investigated using closedform approximations for the pressure, Pn . Standard Pump Design. Shows a schematic of a standard valveplate design that is typically used within pumps. In this figure, a kidneyshaped flow passage from a single piston chamber is shown to match the arcuate porting geometry of the valve plate. As this flow passage moves toward topdeadcenter ~., toward u n5p/2! the actual flow passage is gradually cut off due to the terminating portgeometry of the valve plate in this region. When the piston chamber is located exactly at topdeadcenter, the piston chamber is plet
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