19.
A torquemeter system is shown in fig. 12-4. In this system, the axial thrust produced by the helical gears is opposed by oil pressure acting on a number of pistons; the pressure required to resist the axial thrust is transmitted to the indicator.
20.
In addition to providing an indication of engine power; the torquemeter system may also be used to automatically operate the propeller feathering system if the torquemeter oil pressure falls due to a power failure. It is also used, on some installations, to assist in the automatic operation of the water injection system to restore or boost the take-off power at high ambient temperatures or at high altitude airports (Part 17).
Engine speed
21. All engines have their rotational speed (r.p.m.) indicated. On a twin or triple-spool engine, the high pressure assembly speed is always indicated; in most instances, additional indicators show the speed of the low pressure and intermediate pressure assemblies.
22. Engine speed indication is electrically transmitted from a small generator, driven by the engine, to an indicator that shows the actual revolutions per minute (r.p.m.), or a percentage of the maximum engine speed (fig. 12-5). The engine speed is often used to assess engine thrust, but it
圖12-5 發(fā)動(dòng)機(jī)轉(zhuǎn)速指示器及發(fā)電機(jī)
26．除了提供轉(zhuǎn)子轉(zhuǎn)速的指示之外，轉(zhuǎn)速探頭中感應(yīng)的電流可以用來(lái)電亮儀表板上的警告燈，向駕駛員指示轉(zhuǎn)子組件正在轉(zhuǎn)動(dòng)。這在發(fā)動(dòng)機(jī)起動(dòng)時(shí)特別重要，因?yàn)樗ㄖ{駛員何時(shí)打開燃油開關(guān)，來(lái)向發(fā)動(dòng)機(jī)供油。該燈與起動(dòng)電路相連，因而僅僅在起動(dòng)過(guò)程中才亮。
25.轉(zhuǎn)速探頭位于壓氣機(jī)機(jī)匣上，與音輪對(duì)齊。音輪是壓氣機(jī)軸上經(jīng)機(jī)械加工的部分。每轉(zhuǎn)一圈音輪外圓上的齒通過(guò)探頭一次，通過(guò)改變探頭中線圈的磁通量而誘導(dǎo)出一股電流。電流的大小由磁通量的變化率控制，因而與發(fā)動(dòng)機(jī)轉(zhuǎn)速直接相關(guān)。
23.發(fā)動(dòng)機(jī)轉(zhuǎn)速發(fā)電機(jī)供應(yīng)三相交流電，其頻率取決于發(fā)動(dòng)機(jī)轉(zhuǎn)速。發(fā)電機(jī)的輸出頻率控制指示器中的同步馬達(dá)的轉(zhuǎn)速，位于鼓筒或阻力杯中的磁鐵組件的旋轉(zhuǎn)導(dǎo)致鼓筒的運(yùn)動(dòng)，進(jìn)而轉(zhuǎn)動(dòng)指示器的指針。
24.在沒(méi)有其它設(shè)備來(lái)驅(qū)動(dòng)發(fā)電機(jī)的場(chǎng)合，可以采用可變磁阻式轉(zhuǎn)速探頭，它與一個(gè)音輪相接，產(chǎn)生感應(yīng)電流，經(jīng)放大后送入指示器(圖12-6)。本方法可以用于提供發(fā)動(dòng)機(jī)的轉(zhuǎn)速指示，而不需有單獨(dú)驅(qū)動(dòng)的發(fā)電機(jī)以及其相應(yīng)的傳動(dòng)機(jī)構(gòu)，因而減少了發(fā)動(dòng)機(jī)的部件和運(yùn)動(dòng)零件的數(shù)量。
渦輪燃?xì)鉁囟?br />
27.始終要指示排氣溫度，以保證在任一特定的工作狀態(tài)下，能夠檢查渦輪組件的溫度。而且，通常還備有一個(gè)自動(dòng)燃?xì)鉁囟瓤刂葡到y(tǒng)，保證最大燃?xì)鉁囟炔恢卤怀^(guò)(第10章)。
Controls and instrumentation
28．渦輪燃?xì)鉁囟?T.G.T.)有時(shí)用排氣燃?xì)鉁囟龋‥.G.T.)或噴管溫度(J.P.T)來(lái)表示。它是發(fā)動(dòng)機(jī)工作中的關(guān)鍵參數(shù)，因而提供該溫度的指示極為重要。按照理想，應(yīng)當(dāng)測(cè)定渦輪進(jìn)口溫度(T.E.T.)。但是涉及到高溫，這是不現(xiàn)實(shí)的。但是渦輪中的溫度降是按已知的方式變化的，所以渦輪出口溫度通常由適當(dāng)安排的熱電偶測(cè)量。作為代替方式，也可以測(cè)量渦輪組件中間級(jí)的溫度，如圖12-7所示。
29.用于將溫度信號(hào)傳到指示器的熱電偶探頭由兩種不同的金屬絲構(gòu)成，在一個(gè)金屬套管內(nèi)部連接在一起。套管上的一些傳導(dǎo)孔允許排氣流流過(guò)接點(diǎn)。用于制造熱電偶絲的材料通常是鎳鉻和鎳鋁合金。
30.這些探頭在燃?xì)饬髦械呐渲靡ＷC能獲得良好的平均溫度讀數(shù)，通常將探頭連在一起構(gòu)成一個(gè)并聯(lián)電路。在電路(圖12-8)上連接一個(gè)指示器，它基本上是一個(gè)毫伏計(jì)，其讀數(shù)按攝氏度作了標(biāo)定。
Fig. 12-6 Variable-reluctance speed probe圖12-6 可變磁阻式轉(zhuǎn)速探頭和音輪
and phonic wheel.
does not give an absolute indication of the thrust being produced because inlet temperature and pressure conditions affect the thrust at a given engine speed.
23.
The engine speed generator supplies a three-phase alternating current, the frequency of which is dependent upon engine speed. The generator output frequency controls the speed of a synchronous motor in the indicator, and rotation of a magnet assembly housed in a drum or drag cup induces movement of the drum and consequent movement of the indicator pointer,
24.
Where there is no provision for driving a generator, a variable-reluctance speed probe, in conjunction with a phonic wheel, may be used to induce an electric current that is amplified and then transmitted to an indicator (fig. 12-6). This method can be used to provide an indication of r.p.m. without the need for a separately driven generator, with its associated drives, thus reducing the number of components and moving parts in the engine.
25. 中國(guó)航空網(wǎng) www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：勞斯萊斯噴氣引擎－中英(71)
