52.燃油流量调节器由发动机通过齿轮系驱动。它有2个离心调节器，即转速控制调节器和压力降控制调节器。齿轮系还带动2个滑阀旋转。一个阀是可调节流套筒，带有三角形孔，即可调节流孔，该套筒在膜盒组件作用下产生轴向移动。可调节流孔套筒在一个不旋转的调节器套筒中移动，后者靠转速控制调节器作轴向运动。另一个阀，即压力降控制阀，由压力降控制调节器轴向驱动。它也有一十三角形小孔，即压力降控制孔和一个固定面积的长方孔。转速控制调节器的位置南油门杆通过调节器内的一个凸轮、一根弹簧和一个托架臂设定。
54.当进气道空气压力为一恒定值时，膜盒载荷使旋转的可调节流孔套筒保持在一个固定的轴向位置。由于油门位置是固定的，它在转速控制调节器上保持一个固定的载荷，因而只要转速恒定，调节器套简便处于一个固定的位置。
53．在任何稳定运转状态，发动机转速由控制燃油流量的调节器控制。靠油泵伺服活塞上施加的系统压力差，使燃油泵的供油被固定在一个恒定值。该压力差用于平衡伺服活塞的弹簧力。
Fuel system
53.
At any steady running condition, the engine speed is governed by the regulator controlling the fuel flow. The fuel pump delivery is fixed at a constant value by applying the system pressure difference to the fuel pump servo piston. This is arranged to balance the servo piston spring forces.
54.
When the air intake pressure is at a constant value, the rotating V.M.O. sleeve is held in a fixed axial position by the capsule loading. The fixed throttle setting maintains a set load on the speed control governor and, as the r.p.m. is constant, the governor sleeve is held in a fixed position.
55.
The fuel pump delivery is passed to the annulus surrounding the V.M.O.; the annulus area is controlled by the governor sleeve, and the exposed area of the orifice is set by the axial position of the
V.M.O. sleeve. Consequently, fuel passes to the inside of the sleeve at a constant flow and therefore at a constant pressure difference.
56.
The pressure drop control valve, which also forms a piston, senses the pressure difference across the V.M.O. and maintains the fuel flow at a fixed value in relation to a function of engine speed, by controlling the exposed area of the pressure drop control orifice.
57.
When the throttle is slowly opened, the load on the speed control governor is increased, so moving the governor sleeve to increase the V.M.O. annulus area. The effect of opening the V.M.O. is to reduce the pressure difference and this is sensed by the pressure drop control governor, which opens the pressure drop valve. The reduced system pressure difference is immediately sensed by the fuel pump servo piston, which increases the pump stroke and consequently the fuel output. The increased compressor delivery pressure acts on the capsule assembly, which gradually opens the V.M.O. so that the fuel flow and engine speed continue to increase. At the speed selected, centrifugal forces acting on the speed control governor move the governor sleeve to reduce the V.M.O. annulus area. The resultant increased pressure difference is sensed by the pressure drop control governor, which adjusts the pressure drop valve to a point at which the pump servo system gives an output to match the engine requirements. The function of the governors and the control of the fuel flow is shown diagrammatically in fig. 10-10.
58.
During a rapid acceleration, the initial degree of overselling is mechanically controlled by a stop that limits the opening movement of the speed control
governor sleeve. A similar stop also prevents the fuel supply from being completely cut off by the governor sleeve during a rapid deceleration.
59.
Changes in altitude or forward speed of the aircraft vary the fuel flow required to maintain a constant engine speed. To provide this control, the capsule assembly senses changes in H.P. compressor inlet and delivery pressures and adjusts the V.M.O. accordingly. For instance, as the aircraft altitude increases, the compressor delivery pressure falls and the capsule assembly expands to reduce the V.M.O. The increased system pressure drop is sensed by the fuel pump servo piston, which adjusts the pump output to match the reduced airflow and so maintain a constant engine speed. Conversely, an increase in aircraft forward speed causes the capsule assembly to be compressed and increase the V.M.O. The reduced system pressure drop causes the fuel pump to increase its output to match the increased airflow.
60.
To prevent the maximum gas temperature from being exceeded, fuel flow is reduced in response to signals from thermocouples sensing the temperature (Part 12). When the maximum temperature is reached, the signals are amplified and passed to a rotary actuator which adjusts the throttle mechanism. This movement has the same effect on fuel flow as manual operation of the throttle.
61.
To ensure that the engine is not overstressed, the H.P. compressor delivery pressure is controlled to a predetermined value. At this value, a pressure limiting device, known as a power limiter, reduces the pressure in the capsule chamber, thus allowing the capsule assembly to expand and reduce the V.M.O. so preventing any further increase in fuel flow.
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