圖10-7 一種比例式流量控制系統(tǒng)
Fig. 10-7 A proportional flow control system.
24．在低的高壓軸轉(zhuǎn)速下，旋轉(zhuǎn)溢流活門保持打開，但是當發(fā)動機轉(zhuǎn)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(cè)的回油，直到在調(diào)節(jié)轉(zhuǎn)速下，調(diào)節(jié)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(zhuǎn)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(jié)流柱塞
慢車活門
燃油噴嘴
電磁線圈
壓降控制
低壓軸轉(zhuǎn)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(zhuǎn)速調(diào)節(jié)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(diào)節(jié)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(diào)節(jié)器
壓力分布
25．如果發(fā)動機燃氣溫度要超過最大極限值，在低壓轉(zhuǎn)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(zhuǎn)，通常在多轉(zhuǎn)子發(fā)動機上裝有一個低壓壓氣機軸轉(zhuǎn)速調(diào)節(jié)器。低壓軸轉(zhuǎn)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(tǒng)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(nèi)裝有2個起動噴嘴，每個噴嘴都位于點火電嘴之前。當發(fā)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(tǒng)工作順利。
流量控制
29．燃油流量控制系統(tǒng)通常比壓力控制系統(tǒng)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(fā)動機轉(zhuǎn)速相關；因此，在發(fā)動機低轉(zhuǎn)速下，供油壓力相當?shù)汀？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(jù)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(diào)節(jié)燃油流量。
Fuel system
30．比例式流量控制系統(tǒng)(圖10-7)是流量控制系統(tǒng)的一種，它更適合用于發(fā)動機要求大燃油流量的場合，它還使燃油微調(diào)裝置能更精確地調(diào)節(jié)燃油流量。這種系統(tǒng)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(diào)節(jié)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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