圖10-7 一種比例式流量控制系統
Fig. 10-7 A proportional flow control system.
24．在低的高壓軸轉速下，旋轉溢流活門保持打開，但是當發動機轉速增加時，離心載荷使活門向關閉方向移動，抵消膜片載荷。這樣便限制了向活門低壓側的回油，直到在調節轉速下，調節器壓力使伺服控制膜片撓曲，并打開伺服溢流活門，由此來控制燃油流量，進而控制高壓軸轉速。
102
燃油控制裝置
空氣開關
加速控制裝置
油門及增壓活門裝置
功率限制器
油門開關及停車開關
最小油量活門
分布配重
燃油節流柱塞
慢車活門
燃油噴嘴
電磁線圈
壓降控制
低壓軸轉速信號
限制器
溫度控制
信號放大器
燃氣溫度
熱電偶
進氣道空氣
壓氣機供氣
慢車轉速調節器
高度傳感器
比例活門
敏感活門
比例活門裝置
減少壓氣機供氣
空氣開關
控制空氣壓力
伺服活塞
燃油泵
加速控制裝置伺服
調節器
比例流量
伺服控制
控制燃油壓力
低壓燃油
油泵供油(高壓油)
油門進口
油門出口
初級燃油
主燃油
液壓機械調節器
壓力分布
25．如果發動機燃氣溫度要超過最大極限值，在低壓轉速限制器及溫度控制器的線圈中的電流減小，使溢流活門打開，以減小作用在壓力降控制膜片上的壓力。然后，流量控制溢流活門打開，使油泵伺服壓力和燃油泵輸出減小。
26．為防止低壓壓氣機超轉，通常在多轉子發動機上裝有一個低壓壓氣機軸轉速調節器。低壓軸轉速及進氣口溫度信號被輸入放大器和電磁活門，該活門以控制燃氣溫度(第25段)的同樣方法來限制燃油流量。
27．在上述的系統中采用了由高壓截止活門控制的主噴嘴和起動噴嘴。在燃燒室內裝有2個起動噴嘴，每個噴嘴都位于點火電嘴之前。當發動機起動之后，向這些噴嘴供應的燃油由高壓截止活門切斷。
28．為了在高空條件下保證能維持供應噴嘴的燃油壓力適當，位于油門活門下游的反壓活門將壓力提高，足以保證燃油泵伺服系統工作順利。
流量控制
29．燃油流量控制系統通常比壓力控制系統更為緊湊，它對于油門下游流量變化的影響反應不敏感。燃油泵供油壓力與發動機轉速相關；因此，在發動機低轉速下，供油壓力相當低�？刂迫加捅玫妮敵鍪菫榱嗽诤愣ǖ倪M氣道條件下保持油門活門前后的壓力差恒定。還采用其他各種裝置，依據進氣道空氣
壓力變化、慢車和加速控制，燃氣溫度和壓氣機出口壓力控制來調節燃油流量。
Fuel system
30．比例式流量控制系統(圖10-7)是流量控制系統的一種，它更適合用于發動機要求大燃油流量的場合，它還使燃油微調裝置能更精確地調節燃油流量。這種系統能形成一股小的控制流量，它與主流量具有相同的特性，該控制流量(即比例流量)被用來調節主流量。
until the fuel flow matches the airflow. Conversely, an increase in air intake pressure closes the spill valve to increase the fuel flow.
23.
H.P. compressor shaft r.p.m. is governed by a hydro-mechanical governor which uses hydraulic pressure proportional to engine speed as its controlling parameter. A rotating spill valve senses the engine speed and the controlling pressure is used to limit the pump stroke and so prevent over-speeding of the H.P. shaft rotating assembly. The controlling pressure is unaffected by changes in fuel specific gravity.
24.
At low H.P. shaft speeds, the rotating spill valve is held open, but as engine speed increases, centrifugal loading moves the valve towards the closed position against the diaphragm loads. This restricts the bleed of fuel to the L.P. side of the valve until, at governed speed, the governor pressure deflects the servo control diaphragm and opens the servo spill valve to control the fuel flow and thereby the H.P. shaft speed.
25.
If the engine gas temperature attempts to exceed the maximum limitation, the current in the
L.P. speed limiter and temperature control solenoid is reduced. This opens the spill valve to reduce the pressure on the pressure drop control diaphragm. The flow control spill valve then opens to reduce the pump servo pressure and fuel pump output.
26.
To prevent the L.P. compressor from over-speeding, multi-spool engines usually have an L.P. compressor shaft speed governor. A signal of L.P. shaft speed and intake temperature is fed to an amplifier and solenoid valve, the valve limiting the fuel flow in the same way as the gas temperature control (para. 25).
27.
The system described uses main and starting spray nozzles under the control of an H.P. shut-off valve. Two starting nozzles are fitted in the combustion chamber, each being forward of an igniter plug. When the engine has started, the fuel flow to these nozzles is cut off by the H.P. shut-off valve.
28.
To ensure that a satisfactory fuel pressure to the spray nozzles is maintained at high altitudes, a back pressure valve, located downstream of the throttle valve, raises the pressure levels sufficiently to ensure satisfactory operation of the fuel pump servo system.
Flow control
29.
A flow control fuel system is generally more compact than a pressure control system and is not sensitive to flow effect of variations downstream of the throttle. The fuel pump delivery pressure is related to engine speed; thus, at low engine speeds pump delivery pressure is quite low. The fuel pump output is controlled to give a constant pressure difference across the throttle valve at a constant air intake condition. Various devices are also used to adjust the fuel flow for air intake pressure variations, idling and acceleration control, gas temperature and compressor delivery pressure control.
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