67．可调节流孔面积的控制是压力比控制装置的一种功能，它位于燃油流量调节器中。压力比控制活门感受P4和P1压力，调节燃油流量调节器膜盘的移动，进而控制可调节流孔的面积。以产生油门或功率操纵杆所给定的压力比。
68．在任何一个稳定的运转状态，燃油泵的供油输出总是大于发动机的需求。压力降溢流活门的打开，可使过剩的燃油返回到油泵的进口侧。这个动作接燃油流量调节器所要求的值控制供油量。
pressure drop control piston. It therefore gives a sat-triangular orifice, known as the variable metering
isfactory idling fuel flow at all altitudes.
64. On engines featuring water injection (Part 17), a reset device (fig. 10-11), operated by a piston and reset cam, increases the loading on the throttle control spring and stirrup arm, thus selecting a higher engine speed during water injection. To prevent the power limiter (fig, 10-9) cancelling the effect of water injection, a capsule in the limiter is subjected to water pressure to raise the compressor delivery pressure at which the power limiter operates.
Pressure ratio control
65. The pressure ratio control (fig. 10-12) is a mechanical system similar to the combined acceler-ation and speed control system, but uses the ratio of
H.P. compressor delivery pressure to air intake pressure (P4/P1) as the main controlling parameter. It needs no separate governor unit for controlling the maximum r.p.m. The controlling mechanism is contained in one unit, which is usually referred to as a fuel flow regulator (F.F.R.). A gear-type pump is used, as described in para. 88, and the pump output to the F.F.R. is controlled by a pressure drop spill valve.
66. The F.F.R. is driven by the engine through a gear train and has two rotating valves. One valve, orifice (V.M.O.), and this sleeve is given axial movement by a capsule assembly. The other valve, known as the pressure drop control valve, is provided with axial movement by a centrifugal governor, known as a pressure drop control governor, Both valves form variable restrictors which control the fuel flow to the spray nozzles.
67.
Control of the V.M.O. area is a function of a pressure ratio control unit housed in the F.F.R. A pressure ratio control valve, subjected to P4 and P1, pressures, regulates the movement of the F.F.R. capsule and thus controls the V.M.O. area to produce the pressure ratio dictated by the throttle or power lever.
68.
At any steady running condition, the output of the fuel pump is greater than the engine requirement. The pressure drop spill valve is open to allow surplus fuel to return to the inlet side of the pump. This action controls the fuel delivery to that demanded by the
F.F.R.
69. When the throttle is slowly opened, the throttle-controlled orifice is increased and the control pressure falls, thus allowing the pressure ratio control valve to move towards the closed position (acceleration stop). F.F.R. capsule chamber pressure 水
高压
空气
图10-11 喷水调整对转速控制调节器的影响
Fig. 10-11 Effect of water reset on speed control governor.
低压燃油
油泵供油(高压燃油)
高压燃油去燃油
流量调节器进口
初级燃油
主燃油
Fuel system
降低高压压气机
出口压力(部分P4)
燃油流量调节器
膜盒腔内压力
控制压力
去低压系统 来自低压系统 减压活门 作动筒 放大器
燃油流量调节器膜盒
69．当油门缓慢打开时，被油门控制的孔增大，控制压力下降，因而允许压力比控制活门向关闭位置移动(停止加速)。燃油流量调节器膜盒腔的压力增加，膜盒带动节流套筒，来增大可调节流孔的面积。打开可调节流孔的效果是减小压力差。压力差由压力降调节器感测，它打开压力降控制孔。降低了的系统压力差直接由压力降溢流活门感测，它向关闭位置移动，由此增加燃油输出。增加的燃油流量使发动机加速，随之增大压力比(P4／P1)。当达到要求的压力比之后，压力比控制活门打开，燃油流量调节器膜盘腔的压力降低。膜盒组件发生膨胀，移动可调节流孔套筒，以减小孔的面积。由此增加的压力差由压力降控制调节器感测，它将压力降控制孔调节到某一点上，在这一点时能使压力降溢流活门给出的燃油供油量符台稳态运转的要求。
控制膜盒
压降控制调节器
减速止动钉
压比控制器
喷嘴
加速止动钉
压比控制活门
真空膜盒
油门控制孔
高压燃油
停车活门
慢车调节器
油门杆
压降控制孔
通气口
地面慢车电磁阀
P1控制孔
微调活门
可调节流套筒
真空膜盒
燃油量调节器
可调节流孔
进气道(P1)
高压压气机进口(P3)
高压压气机出口(P4)
燃气温度热电偶
辅助油门开关
空气压力控制
低压轴转速
压力降
溢流活门
燃油压力
可调限流器
燃油泵及
活门组件
图10-12 一种压力比控制装置
110
而活门碰到加速止动销。燃油流量调节器膜盒腔内压力增加，膜盒移动，将可调节流孔的面积增加。这个动作一直继续进行到达到要求的压力比P4／P1时为止。增加的P4压力使压力比控制膜盒重新膨胀，活门返回到稳定运转位置。
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